JP2012077740A - Fuel injection amount control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel injection amount control device for an internal combustion engine hardly degrading its emission by bringing an average air-fuel ratio of the engine closer to an appropriate air-fuel ratio even when an alcohol containing fuel is used and a non-uniformity of the fuel-air ratio among cylinders is increased.SOLUTION: The fuel injection amount control device for the internal combustion engine (control device) includes an upstream air-fuel ratio sensor 56 arranged upstream from a three-way catalyst 43, a downstream air-fuel ratio sensor 57 arranged downstream from the three-way catalyst 43, and an alcohol concentration sensor 59. The control device performs a main feedback control so that the air-fuel ratio represented by an output value from the upstream air-fuel ratio sensor conforms to a target air-fuel ratio, and performs a sub-feedback so that an output value from the downstream air-fuel ratio sensor conforms to a downstream target value. The control device obtains an air-fuel ratio imbalance index value which increases as a difference in the air-fuel ratio of each cylinder among the cylinders increases, and increases a guard range of a sub FB learning value the larger the air-fuel ratio imbalance index value is and also the higher the detected alcohol concentration is.

Description

  The present invention relates to a fuel injection amount control device for a multi-cylinder internal combustion engine.

  Conventionally, as shown in FIG. 1, a three-way catalyst (43) disposed in an exhaust passage of an internal combustion engine and an upstream air-fuel ratio sensor (56) disposed upstream of the three-way catalyst (43). Are widely known.

  The air-fuel ratio control device outputs the output of the upstream air-fuel ratio sensor (56) so that the air-fuel ratio of the air-fuel mixture supplied to the engine (the air-fuel ratio of the engine, and hence the exhaust gas air-fuel ratio) matches the target air-fuel ratio. An air-fuel ratio feedback amount (main feedback amount) is calculated based on the value, and the air-fuel ratio of the engine is feedback controlled based on the main feedback amount. This feedback amount is a control amount common to all cylinders. The target air-fuel ratio is set to a predetermined reference air-fuel ratio in the window of the three-way catalyst (43). The reference air / fuel ratio is generally a stoichiometric air / fuel ratio. The reference air-fuel ratio can be changed to a value close to the theoretical air-fuel ratio according to the intake air amount of the engine, the degree of deterioration of the three-way catalyst (43), and the like.

  In general, such an air-fuel ratio control device is applied to an internal combustion engine that employs an electronically controlled fuel injection device. The internal combustion engine includes at least one fuel injection valve (33) in each cylinder or an intake port communicating with each cylinder. Therefore, when the characteristic of the fuel injection valve of a specific cylinder becomes “a characteristic of injecting an amount of fuel that is larger than the instructed fuel injection amount (indicated fuel injection amount)”, the mixture supplied to the specific cylinder Only the air air-fuel ratio (the air-fuel ratio of the specific cylinder) largely changes to the rich side. That is, the non-uniformity of air-fuel ratio among cylinders (air-fuel ratio variation among cylinders, air-fuel ratio imbalance among cylinders) increases. In other words, an imbalance occurs between the “cylinder air-fuel ratio” that is the air-fuel ratio of the air-fuel mixture supplied to each cylinder.

  In the following, a cylinder corresponding to a fuel injection valve having a characteristic of injecting an amount of fuel that is larger or smaller than the commanded fuel injection amount is also referred to as an imbalance cylinder, and the remaining cylinders (the fuel of the commanded fuel injection amount) The cylinder corresponding to the fuel injection valve to be injected) is also referred to as a non-imbalance cylinder (or normal cylinder).

  When the characteristic of the fuel injection valve of a specific cylinder becomes “a characteristic of injecting an amount of fuel that is larger than the indicated fuel injection amount”, the average of the air-fuel ratio of the air-fuel mixture supplied to the entire engine becomes the reference air-fuel ratio. The air-fuel ratio becomes richer than the set target air-fuel ratio. Accordingly, the air-fuel ratio of the specific cylinder is changed to the lean side so as to be close to the reference air-fuel ratio by the air-fuel ratio feedback amount common to all the cylinders, and at the same time, the air-fuel ratios of the other cylinders are It is changed to the lean side so as to be away from the air-fuel ratio. As a result, the average air-fuel ratio of the air-fuel mixture supplied to the entire engine (the average air-fuel ratio of exhaust gas) matches the air-fuel ratio in the vicinity of the reference air-fuel ratio.

  However, the air-fuel ratio of the specific cylinder is still richer than the reference air-fuel ratio, and the air-fuel ratio of the remaining cylinders is leaner than the reference air-fuel ratio. As a result, the amount of emissions discharged from each cylinder (the amount of unburned matter and / or the amount of nitrogen oxides) is increased as compared with the case where the air-fuel ratio of each cylinder is the reference air-fuel ratio. For this reason, even if the average of the air-fuel ratio of the air-fuel mixture supplied to the engine is the reference air-fuel ratio, the three-way catalyst cannot completely purify the increased emission, and as a result, the emission may be deteriorated.

  Therefore, the non-uniformity between cylinders in the air-fuel ratio for each cylinder is excessive (the non-uniformity in the air-fuel ratio among cylinders is excessive, that is, an air-fuel ratio imbalance state between cylinders occurs. It is important to prevent any worsening of emissions. The air-fuel ratio imbalance among cylinders also occurs when the characteristic of the fuel injection valve of a specific cylinder becomes “a characteristic for injecting an amount of fuel that is smaller than the commanded fuel injection amount”.

  One conventional fuel injection amount control device acquires the locus length of the output value (output signal) of the upstream air-fuel ratio sensor (56). Further, the control device compares the trajectory length with a “reference value that changes according to the engine speed” and determines whether or not an air-fuel ratio imbalance among cylinders has occurred based on the comparison result. (For example, see Patent Document 1).

  By the way, when non-uniformity of cylinder air-fuel ratio occurs between cylinders, the true average air-fuel ratio of the engine is obtained by changing the air-fuel ratio represented by the output value of the upstream air-fuel ratio sensor (56) to “theoretical air-fuel ratio or the like”. By the main feedback control for matching with the “target air-fuel ratio set to the reference air-fuel ratio”, the air-fuel ratio is controlled to be “an air-fuel ratio larger than the reference air-fuel ratio (an air-fuel ratio leaner than the reference air-fuel ratio)”. Hereinafter, this reason will be described.

The fuel supplied to the engine is a compound of carbon and hydrogen. Therefore, if the air-fuel ratio of the air-fuel mixture used for combustion is an air-fuel ratio richer than the stoichiometric air-fuel ratio, unburned substances such as “hydrocarbon HC, carbon monoxide CO and hydrogen H ₂ ” are intermediate products. Is generated as In this case, as the air-fuel ratio of the air-fuel mixture used for combustion is richer than the stoichiometric air-fuel ratio and farther from the stoichiometric air-fuel ratio, the probability that the intermediate product encounters oxygen and combines during the combustion period is increased. It decreases rapidly. As a result, as shown in FIG. 2, the amount of unburned matter (HC, CO, and H ₂ ) increases as the air-fuel ratio of the air-fuel mixture supplied to the cylinder becomes richer (for example, two It increases in terms of a function.

Now, it is assumed that “non-uniformity of air-fuel ratio by cylinder” occurs, in which only the air-fuel ratio of a specific cylinder is greatly shifted to the rich side. In this case, the air-fuel ratio of the air-fuel mixture supplied to the specific cylinder (the air-fuel ratio of the specific cylinder) is larger than the air-fuel ratio of the air-fuel mixture supplied to the remaining cylinders (the air-fuel ratio of the remaining cylinders). It changes to the rich side air-fuel ratio (small air-fuel ratio). At this time, an extremely large amount of unburned matter (HC, CO, H ₂ ) is discharged from the specific cylinder. Therefore, even if the average air-fuel ratio of the air-fuel mixture supplied to the engine is “a certain value”, the total amount of hydrogen discharged from the engine when the degree of non-uniformity of the air-fuel ratio by cylinder increases. Is much larger than the total amount of hydrogen generated when the non-uniformity of the air-fuel ratio by cylinder does not occur.

  On the other hand, the upstream air-fuel ratio sensor (56) is a porous layer (for example, for allowing a gas in a state where unburned matter and oxygen are in chemical equilibrium (gas after oxygen equilibrium) to reach the air-fuel ratio detection element (for example, A diffusion resistance layer or a protective layer). The upstream air-fuel ratio sensor (56) passes through the diffusion resistance layer and reaches the exhaust gas-side electrode layer (surface of the air-fuel ratio detection element) of the upstream air-fuel ratio sensor (56).・ Output values corresponding to “oxygen concentration” and the amount of unburned material (partial pressure of unburned material / unburned material concentration) ”.

On the other hand, hydrogen H ₂ is a small molecule compared to hydrocarbon HC and carbon monoxide CO. Therefore, hydrogen H ₂ diffuses more quickly in the porous layer of the upstream air-fuel ratio sensor (56) than other unburned substances (HC, CO). That is, selective diffusion (preferential diffusion) of hydrogen H ₂ occurs in the porous layer.

  Therefore, when the air-fuel ratio by cylinder becomes non-uniform among the cylinders (when non-uniformity of the air-fuel ratio occurs between the cylinders), the output of the upstream air-fuel ratio sensor (56) is caused by this selective diffusion of hydrogen. The value shifts to the rich value. That is, the air-fuel ratio represented by the output value of the upstream air-fuel ratio sensor (56) is “richer air-fuel ratio” than the true air-fuel ratio of the engine. As a result, the true average air-fuel ratio of the engine is controlled to “an air-fuel ratio larger than the reference air-fuel ratio (an air-fuel ratio leaner than the reference air-fuel ratio)” by the main feedback control.

  On the other hand, the exhaust gas that has passed through the three-way catalyst (43) reaches the downstream air-fuel ratio sensor (57) disposed downstream of the three-way catalyst (43). Hydrogen is purified to some extent in the three-way catalyst (43). Therefore, the output value of the downstream air-fuel ratio sensor outputs a value close to the true average air-fuel ratio of the engine even when the degree of non-uniformity of the cylinder-by-cylinder air-fuel ratio becomes large.

  Therefore, another conventional fuel injection amount control device includes an air-fuel ratio detected based on the upstream air-fuel ratio sensor (56) and an air-fuel ratio detected based on the downstream air-fuel ratio sensor (57). Whether or not the non-uniformity of the cylinder-by-cylinder air-fuel ratio has become large is determined based on a parameter representing the state of deviation (see Patent Document 2).

US Pat. No. 7,152,594 JP 2009-30455 A

  The above-mentioned “transition of the air-fuel ratio to the lean side caused by selective hydrogen diffusion and main feedback control” is also simply referred to as “lean miscontrol”. The “lean erroneous control” occurs in the same manner even when the air-fuel ratio of the imbalance cylinder shifts to the lean side from the air-fuel ratio of the non-imbalance cylinder.

  When the lean erroneous control occurs, the true average air-fuel ratio of the engine (and hence the average of the true air-fuel ratio of the exhaust gas) sometimes becomes leaner (larger) than the “three-way catalyst window”. Therefore, the NOx (nitrogen oxide) purification efficiency of the three-way catalyst (43) may decrease, and the NOx emission amount may increase.

  As described above, the output value of the downstream air-fuel ratio sensor (57) outputs a value close to the true average air-fuel ratio of the engine even when the degree of non-uniformity of the cylinder-by-cylinder air-fuel ratio increases. To do. Therefore, if “well-known sub-feedback control” for matching the output value of the downstream air-fuel ratio sensor with the “downstream target value corresponding to the air-fuel ratio in the vicinity of the theoretical air-fuel ratio” is executed, the lean erroneous control occurs. Can be avoided.

  Further, even when the sub feedback control condition is not satisfied and the sub feedback amount is not updated, the learning value of the sub feedback amount (hereinafter also referred to as “sub FB learning value”) becomes an appropriate value. If so, it is possible to avoid the occurrence of “lean erroneous control” by controlling the air-fuel ratio based on the sub-FB learning value. The sub FB learning value is a value corresponding to a stationary component (for example, an integral term) of the sub feedback amount. The sub FB learning value is stored in the backup RAM and the nonvolatile memory.

  On the other hand, recently, fuel containing alcohol such as ethanol (hereinafter also referred to as “alcohol-containing fuel”) may be used. When the alcohol-containing fuel burns, more hydrogen is generated than when the fuel not containing alcohol burns. The amount of hydrogen generated by the combustion of the alcohol-containing fuel increases as the alcohol concentration of the fuel increases.

  Therefore, when the alcohol-containing fuel is used, the output value of the upstream air-fuel ratio sensor (56) is caused by the selective diffusion of hydrogen, as in the case where the degree of non-uniformity of the air-fuel ratio by cylinder is increased. Shifts to the rich value. That is, the air-fuel ratio represented by the output value of the upstream air-fuel ratio sensor (56) is “richer air-fuel ratio” than the true air-fuel ratio of the engine. As a result, the true average air-fuel ratio of the engine is controlled to be leaner than the reference air-fuel ratio such as the stoichiometric air-fuel ratio by the main feedback control based on the output value of the upstream air-fuel ratio sensor (56). That is, even if the non-uniformity of the cylinder-by-cylinder air-fuel ratio does not occur, lean miscontrol occurs when alcohol-containing fuel is used. As a result, the NOx purification efficiency of the three-way catalyst (43) may decrease and the NOx emission amount may increase.

  On the other hand, the above-described sub FB learning value is regulated within a predetermined guard width range in order to avoid deterioration of emission when the sub FB learning value becomes an incorrect value.

  However, if the non-uniformity of the air-fuel ratio by cylinder and the use of alcohol-containing fuel occur at the same time, the sub FB learning value should be a value exceeding the guard width. Will be regulated. As a result, it becomes difficult to completely compensate for the lean erroneous control by the sub FB learning value, so that the NOx emission amount may increase.

  Therefore, one of the objects of the present invention is to set the true average air-fuel ratio of the engine to an appropriate air-fuel ratio even when the degree of non-uniformity of the cylinder-by-cylinder air-fuel ratio increases when alcohol-containing fuel is used. Accordingly, it is an object to provide a fuel injection amount control device (hereinafter also simply referred to as “the device of the present invention”) for an internal combustion engine in which the emission is unlikely to deteriorate.

  One aspect of the device of the present invention includes a three-way catalyst, an upstream air-fuel ratio sensor, a downstream air-fuel ratio sensor, a main feedback control means, a sub-feedback control means, a plurality of fuel injection valves, and an indicated fuel injection. A fuel injection amount control device for an internal combustion engine comprising an amount determination means and an injection instruction signal transmission means, further comprising an air-fuel ratio imbalance index value acquisition means, an alcohol concentration acquisition means, and a learned value guard width change means And comprising.

  The three-way catalyst is disposed at a position downstream of the “exhaust collecting portion of the exhaust passage of the engine” where exhaust gases discharged from a plurality of cylinders of the multi-cylinder internal combustion engine gather.

  The upstream air-fuel ratio sensor is disposed at a position between the exhaust collecting portion of the exhaust passage and the three-way catalyst. The upstream air-fuel ratio sensor may be a limit current type air-fuel ratio sensor or an electromotive force type (concentration cell type) oxygen concentration sensor.

  The downstream air-fuel ratio sensor is disposed at a position downstream of the three-way catalyst in the exhaust passage.

  The main feedback control means sets the “value corresponding to the detected air-fuel ratio acquired based on the output value of the upstream air-fuel ratio sensor (for example, the detected air-fuel ratio or the output value of the upstream air-fuel ratio sensor)” A value corresponding to the detected air-fuel ratio is set to a main feedback amount for matching with a value corresponding to a predetermined target air-fuel ratio (for example, a target air-fuel ratio or an output value of an upstream air-fuel ratio sensor corresponding to the target air-fuel ratio). And a value corresponding to the target air-fuel ratio.

  The sub-feedback control means sets at least the output value of the downstream air-fuel ratio sensor and the sub-feedback amount for making the “output value of the downstream air-fuel ratio sensor” coincide with the “predetermined downstream target value”. It is calculated based on an integration processing value obtained by integrating a value corresponding to “deviation from the downstream target value”. Further, the sub-feedback control means acquires (calculates) a learning value of the sub-feedback amount based on the integration processing value or the sub-feedback amount, and uses the acquired (calculated) learning value as a predetermined guard. Regulate within the width.

  Each of the plurality of fuel injection valves is configured to inject fuel contained in an air-fuel mixture supplied to each combustion chamber of the plurality of cylinders.

  The command fuel injection amount determining means is configured to “correct the amount of fuel injected from the fuel injection valve” based on the main feedback amount, the sub-feedback amount, and the learning value. An indicated fuel injection amount that is an “indicated value of the amount of fuel injected from each of the valves” is determined. The learning value may be used for determining the command fuel injection amount together with the sub feedback amount during a period in which the sub feedback amount is updated. Further, the learning value is not used during a period in which the sub feedback amount is updated (that is, the command fuel injection amount is determined by the main feedback amount and the sub feedback amount), and the sub feedback amount is not updated. It may be used in a period.

  The injection instruction signal sending means sends an injection instruction signal to the plurality of fuel injection valves so that an amount of fuel corresponding to the indicated fuel injection amount is injected from each of the plurality of fuel injection valves.

  The air-fuel ratio imbalance index value acquisition means is configured to determine the degree of non-uniformity among the plurality of cylinders of “a cylinder-specific air-fuel ratio that is an air-fuel ratio of an air-fuel mixture supplied to a combustion chamber of each of the plurality of cylinders”. An air-fuel ratio imbalance index value that increases as “” increases. As will be described later, the air-fuel ratio imbalance index value can be obtained by various methods.

  The alcohol concentration acquisition means acquires the alcohol concentration of the fuel.

  The learned value guard width changing means increases the guard width (guard width of the learned value of the sub feedback amount) as the acquired air-fuel ratio imbalance index value increases, and as the acquired alcohol concentration increases. Enlarge.

  According to this, the guard width of the learning value of the sub-feedback amount increases as the degree of non-uniformity of the air-fuel ratio by cylinder (air-fuel ratio imbalance index value) increases, and increases as the alcohol concentration increases. Therefore, the learning value of the sub feedback amount can reach an appropriate value (a value that can compensate for the lean erroneous control) regardless of the degree of non-uniformity of the alcohol concentration and the cylinder-by-cylinder air-fuel ratio. As a result, it is possible to avoid deterioration of emissions. Further, when the alcohol concentration is low and / or when the degree of non-uniformity of the air-fuel ratio for each cylinder is small, the guard width of the learning value is small. Therefore, it is possible to avoid the emission from deteriorating due to an erroneous learning value (mislearning).

  The learning value change rate (learning value update rate) is generally set relatively small for the purpose of preventing erroneous learning. However, when fuel with a high alcohol concentration is supplied and immediately after that, the degree of non-uniformity of the cylinder air-fuel ratio increases, the learning value must change greatly. Therefore, even if the guard width of the learning value is increased, it takes a long time for the learning value to reach the appropriate value, so that the learning value may not reach the appropriate value. For example, if the operation of the engine is terminated before the learned value reaches the appropriate value, the next time the engine is started, the learned value deviates from the appropriate value, so the emission deteriorates.

Therefore, in the aspect of the device of the present invention,
The sub feedback control means includes
The learning value change rate is set such that the greater the acquired air-fuel ratio imbalance index value, the greater the change rate of the learned value, and the higher the acquired alcohol concentration, the greater the change rate of the learned value. Configured to change.

  According to this, since the learning value can be brought close to the appropriate value quickly, it is possible to avoid the emission from deteriorating. Furthermore, when the alcohol concentration is low and / or when the degree of non-uniformity of the air-fuel ratio by cylinder is small, the learning value is not updated at an unnecessarily large speed, so that the possibility of erroneous learning occurring can be reduced. it can.

In this way, when changing the change rate of the learning value, the sub feedback control means,
As “a value according to the deviation between the output value of the downstream air-fuel ratio sensor and the downstream target value”, “a value obtained by multiplying the deviation by a predetermined gain” is adopted,
The learning is performed by setting the gain to a larger value as the acquired actual air-fuel ratio imbalance index value is larger, and setting the gain to a larger value as the acquired actual alcohol concentration is higher. It can be configured to change (increase) the rate of change of the value.

Alternatively, the sub-feedback control means is
The learning value is updated every elapse of a predetermined learning interval time, the learning interval time is set to a shorter time as the acquired air-fuel ratio imbalance index value is larger, and the acquired actual alcohol By setting the learning interval time to a shorter time as the concentration is higher, the change rate of the learning value can be changed (increased).

  The sub feedback control means may be configured to change (increase) the change rate of the learning value by changing the gain and changing the learning interval time.

  According to the above configuration, it is possible to avoid the lean erroneous control from occurring due to the sub feedback amount and / or the learning value. However, when the intake air amount of the engine increases, a large amount of hydrogen is generated, and the output value of the upstream air-fuel ratio sensor shifts to a richer value. The same applies to the case where the upstream air-fuel ratio sensor has a catalyst portion and detects the air-fuel ratio of the exhaust gas after hydrogen is processed (oxidized) in the catalyst portion. This is probably because when the amount of intake air is large, a large amount of generated hydrogen cannot be sufficiently processed in the catalyst section. Accordingly, when the intake air amount is large (in the high intake air amount region), the occurrence of lean erroneous control cannot be suppressed even by the sub feedback amount and / or the learning value, and the emission deteriorates. Furthermore, when the intake air amount suddenly increases, the “sub-feedback amount and / or the learned value is a value that deviates from their appropriate values” continues, so the emission may be greatly deteriorated. .

  In view of this, the aspect of the apparatus of the present invention is configured such that the larger the intake air amount of the engine, the greater the acquired air-fuel ratio imbalance index value, and the higher the acquired alcohol concentration, There is provided enriching means for setting the fuel ratio to a smaller air-fuel ratio or correcting the detected air-fuel ratio to a larger air-fuel ratio.

  Changing the target air-fuel ratio to a smaller air-fuel ratio and correcting the detected air-fuel ratio to a larger value can cause the air-fuel ratio of the engine to become larger when considering the main feedback control based on the main feedback amount. It is substantially synonymous in the sense of reducing (enriching).

  According to this, even when the intake air amount of the engine is large, it is possible to avoid the deterioration of the emission.

  In another aspect of the device of the present invention, the sub feedback amount itself is also regulated within the guard width of the sub feedback amount. In this case, it is preferable that the guard width of the sub feedback amount is increased as the acquired air-fuel ratio imbalance index value is increased and increased as the acquired alcohol concentration is increased.

  According to this, even when the sub-feedback amount itself is regulated within the guard width of the sub-feedback amount, the sub-feedback amount becomes “the degree of non-uniformity of the alcohol concentration and the air-fuel ratio by cylinder” The appropriate value can be reached. Therefore, it is possible to avoid the emission from deteriorating.

  As described above, the air-fuel ratio imbalance index value can be obtained by various methods. For example, the air-fuel ratio imbalance index value acquisition means sets a basic parameter that increases as the air-fuel ratio variation of “the exhaust gas passing through the position where the upstream air-fuel ratio sensor is disposed” increases as “the upstream air-fuel ratio index value”. The air-fuel ratio imbalance index value may be acquired based on the “basic parameter correlation value that is a value correlated with the basic parameter”.

Further, in this case, the air-fuel ratio imbalance index value acquisition means is
Differential value d (Vabyfs) / dt with respect to time of the output value Vabyfs of the upstream air-fuel ratio sensor (including a value obtained by performing high-pass filtering on the output value Vabyfs),
A differential value d (abyfs) / dt with respect to time of the detected air-fuel ratio abyfs (including a value obtained by subjecting the detected air-fuel ratio abyfs to high-pass filtering) acquired based on the output value of the upstream air-fuel ratio sensor,
Second-order differential value d ² (Vabyfs) / dt ^{2 with} respect to time of the output value Vabyfs of the upstream air-fuel ratio sensor, and
Second-order differential value d ² (abyfs) / dt ^{2 with} respect to the time of the detected air-fuel ratio abyfs obtained based on the output value of the upstream air-fuel ratio sensor,
A value corresponding to one of the values (for example, an average value of one of these values in one combustion cycle (720 degree crank angle)) may be obtained as a basic parameter.

  In this way, the value corresponding to the “differential value and second-order differential value” of “the output value Vabyfs of the upstream air-fuel ratio sensor or the detected air-fuel ratio abyfs” or the like is used as a basic parameter for obtaining the air-fuel ratio imbalance index value. In this case, even if the degree of non-uniformity of the cylinder-by-cylinder air-fuel ratio is “a certain value”, it has been found that the basic parameters fluctuate according to “the engine rotational speed and the intake air amount of the engine”. Further, it has been found that if the degree of non-uniformity of the cylinder-by-cylinder air-fuel ratio differs, the degree of influence of the “engine speed and engine intake air amount” on the air-fuel ratio imbalance index value also changes.

Therefore, in the aspect of the device of the present invention,
The air-fuel ratio imbalance index value acquisition means is
The basic parameter correlation value is corrected based on a value corresponding to the basic parameter, a value corresponding to the rotational speed of the engine, and a value corresponding to the intake air amount of the engine, and based on a corrected value obtained by the correction. Preferably, the air-fuel ratio imbalance index value is acquired.
The basic parameter correlation value is an average value of a plurality of basic parameters or the like, and is a value that varies with correlation with the basic parameters. The value corresponding to the basic parameter may be a basic parameter correlation value or a value obtained by calculation different from the basic parameter correlation value.

  According to this, since the influence of the “engine rotational speed and the intake air amount of the engine” on the air-fuel ratio imbalance index value can be reduced, the air-fuel ratio imbalance index that accurately represents the degree of non-uniformity of the cylinder-by-cylinder air-fuel ratio. The value can be obtained. As a result, the guard width of the learned value, the change rate of the learned value (the gain, the learning time interval), the degree of enrichment of the target air-fuel ratio, the guard width of the sub feedback amount, and the like are more appropriate values. Can be set to

  Furthermore, when using a value according to “differential value and second-order differential value” of “output value Vabyfs of upstream air-fuel ratio sensor or detected air-fuel ratio abyfs” or the like as a basic parameter for obtaining an air-fuel ratio imbalance index value, It has been found that even if the degree of non-uniformity of the cylinder-by-cylinder air-fuel ratio is “a certain value”, the basic parameter varies depending on the alcohol concentration. This is because the higher the alcohol concentration of the fuel, the more hydrogen is generated, and the change rate of the output value of the upstream air-fuel ratio sensor changes (becomes larger).

Therefore, the air-fuel ratio imbalance index value acquisition means is
Preferably, the basic parameter correlation value is corrected based on the acquired alcohol concentration, and the air-fuel ratio imbalance index value is acquired based on a corrected value obtained by the correction. In this case, the basic parameter correlation value is corrected according to the alcohol concentration so that the air-fuel ratio imbalance index value decreases as the alcohol concentration increases, and the air-fuel ratio imbalance is calculated based on the corrected value obtained by the correction. It is desirable to obtain an index value.

  According to this, since the influence of the “alcohol concentration” on the air-fuel ratio imbalance index value can be reduced, an air-fuel ratio imbalance index value that accurately represents the degree of non-uniformity of the cylinder-by-cylinder air-fuel ratio can be acquired. . As a result, the learning value guard width, the learning value change rate (the gain, the learning time interval), the degree of enrichment of the target air-fuel ratio, the guard width of the sub feedback amount, and the like are more appropriately set. Can be set to a value.

Another aspect of the apparatus of the present invention includes the three-way catalyst, the upstream air-fuel ratio sensor, the plurality of fuel injection valves, and the injection instruction signal sending means. Further, this aspect includes an indicated fuel injection amount determination unit and an air-fuel ratio imbalance index value acquisition unit described below.

The indicated fuel injection amount determining means includes
A main feedback amount for making a value corresponding to the detected air-fuel ratio acquired based on the output value of the upstream side air-fuel ratio sensor coincide with a value corresponding to a predetermined target air-fuel ratio is a value corresponding to the detected air-fuel ratio. Determined based on a value corresponding to the target air-fuel ratio,
By correcting the amount of fuel injected from the fuel injection valve based on the determined main feedback amount, an indication value of the amount of fuel injected from each of the plurality of fuel injection valves (ie, indicated fuel injection) Amount).

The air-fuel ratio imbalance index value acquisition means is
Based on the output value of the upstream air-fuel ratio sensor, obtaining a basic parameter that increases as the fluctuation of the air-fuel ratio of the exhaust gas that passes through the position where the upstream air-fuel ratio sensor is disposed,
An air-fuel ratio imbalance index that increases as “the degree of non-uniformity among the plurality of cylinders” of “the air-fuel ratio by cylinder that is the air-fuel ratio of the air-fuel mixture supplied to the respective combustion chambers of the plurality of cylinders” increases. A value is acquired based on “a basic parameter correlation value that is a value having a correlation with the basic parameter”.

In addition, the air-fuel ratio imbalance index value acquisition means includes
The alcohol concentration of the fuel is acquired, the basic parameter correlation value is corrected based on the acquired alcohol concentration, and the air-fuel ratio imbalance index value is acquired based on the corrected value obtained by the correction. Configured.

Further, the indicated fuel injection amount determining means includes
The commanded fuel injection amount is increased and corrected so that the commanded air / fuel ratio determined by the commanded fuel injection amount becomes smaller (in a region below the theoretical air / fuel ratio) as the acquired air / fuel ratio imbalance index value becomes larger (that is, The air-fuel ratio of the engine is enriched). The method for correcting the increase in the indicated fuel injection amount is not particularly limited, but the target air-fuel ratio is changed to a smaller air-fuel ratio, the detected air-fuel ratio is corrected to a larger value, and the sub-feedback amount is set to “fuel injection”. And so on, "correcting so that the amount increases." This point is common throughout this specification.

  According to this, the basic parameter correlation value is corrected based on the alcohol concentration, and the air-fuel ratio imbalance index value is acquired based on the corrected value obtained by the correction. Therefore, as described above, since the influence of the “alcohol concentration” on the air-fuel ratio imbalance index value can be reduced, an air-fuel ratio imbalance index value that accurately represents the degree of non-uniformity of the cylinder-by-cylinder air-fuel ratio is obtained. Can do. Note that correcting the basic parameter correlation value based on the alcohol concentration includes correcting the basic parameter itself based on the alcohol concentration and then determining the basic parameter correlation value based on the corrected basic parameter. . This point is also common throughout this specification.

  On the other hand, as the air-fuel ratio imbalance index value is larger, the indicated air-fuel ratio is changed to a smaller value (a richer value). Thereby, since the lean erroneous control can be compensated with high accuracy, the emission can be maintained at a good value.

In this case, the air-fuel ratio imbalance index value acquisition means
The basic parameter correlation value is corrected based on a value corresponding to the basic parameter, a value corresponding to the rotational speed of the engine, and a value corresponding to the intake air amount of the engine, and based on a corrected value obtained by the correction. Preferably, the air-fuel ratio imbalance index value is acquired. The correction of the basic parameter correlation value based on “a value according to the basic parameter, a value according to the rotational speed of the engine, and a value according to the intake air amount of the engine” Correction based on a value corresponding to the basic parameter, a value corresponding to the rotational speed of the engine, and a value corresponding to the intake air amount of the engine, and then determining a basic parameter correlation value based on the corrected basic parameter. . This point is also common throughout this specification.

  According to this, since the influence of the “engine rotational speed and the intake air amount of the engine” on the air-fuel ratio imbalance index value can be reduced, the air-fuel ratio imbalance index that accurately represents the degree of non-uniformity of the cylinder-by-cylinder air-fuel ratio. The value can be obtained. As a result, the lean erroneous control can be compensated more accurately, so that the emission can be maintained at a good value.

  In this aspect, more specifically, the commanded fuel injection amount determination means is configured such that the target air-fuel ratio becomes smaller (in a region below the theoretical air-fuel ratio) as the acquired air-fuel ratio imbalance index value increases. Further, the command fuel injection amount can be increased and corrected by changing the target air-fuel ratio. As a result, even if the degree of non-uniformity of the cylinder-by-cylinder air-fuel ratio is large, the target air-fuel ratio can be set to “appropriate value to compensate for lean lean control”, so that the emission can be maintained at a good value. Can do.

  Further, the commanded fuel injection amount determining means changes the target air-fuel ratio so that the target air-fuel ratio becomes smaller (in a region below the theoretical air-fuel ratio) as the intake air amount of the engine increases. As described above, as the intake air amount increases, the air-fuel ratio of the engine shifts to the lean side due to lean lean control. Therefore, if the target air-fuel ratio is changed as described above, the target air-fuel ratio can be set to an “appropriate value for compensating for lean lean control” even when the intake air amount is large. Can be maintained at a good value.

  By the way, when the alcohol concentration is increased, the combustion temperature is decreased, so that the amount of NOx generated is decreased. For this reason, when the alcohol concentration is high, the target air-fuel ratio is reduced when the degree of non-uniformity of the cylinder-by-cylinder air-fuel ratio is large as compared with the case where the alcohol concentration is low (that is, the NOx associated with lean miscontrol). The degree of enrichment required to suppress “occurrence”) may be small. In addition, HC and CO tend to increase as the alcohol concentration increases.

  Therefore, it is preferable that the commanded fuel injection amount determining means changes the target air-fuel ratio so that the target air-fuel ratio increases (in a region below the theoretical air-fuel ratio) as the alcohol concentration of the fuel increases. As a result, the target air-fuel ratio can be set to a more appropriate value regardless of the alcohol concentration, so that the emission can be maintained at a good value.

  Still another aspect of the apparatus of the present invention includes the three-way catalyst, the upstream air-fuel ratio sensor, the plurality of fuel injection valves, the indicated fuel injection amount determining means, the injection instruction signal sending means, Air-fuel ratio imbalance index value acquisition means.

  Furthermore, this other aspect estimates the catalyst temperature, which is the temperature of the three-way catalyst, based on the operating state of the engine (for example, the engine operating state parameters such as the intake air amount or load and the engine speed). A catalyst temperature estimating means is provided.

The catalyst temperature estimating means includes
The catalyst temperature is estimated so that the estimated catalyst temperature increases as the acquired air-fuel ratio imbalance index value increases.
The indicated fuel injection amount determining means includes
When the estimated catalyst temperature is higher than a predetermined threshold temperature, the indicated fuel injection amount is increased or corrected so that the indicated air-fuel ratio determined by the indicated fuel injection amount is smaller than the theoretical air-fuel ratio, or “predetermined The fuel injection stop control (fuel cut) executed when the fuel cut condition is satisfied is prohibited.

  When the degree of non-uniformity of the cylinder-by-cylinder air-fuel ratio is large, rich air-fuel ratio exhaust gas and lean air-fuel ratio exhaust gas alternately flow into the three-way catalyst in a short cycle. For this reason, since the oxidation-reduction reaction in the three-way catalyst is frequently repeated, the active state of the three-way catalyst is improved, and as a result, the temperature of the catalyst rises quickly. Therefore, as in the above configuration, the catalyst temperature estimated based on the operating state of the engine (for example, the intake air amount, the engine load, the engine speed, etc.) has a degree of non-uniformity of the air-fuel ratio for each cylinder. A larger temperature is estimated as a relatively low temperature. From this, the non-uniformity of the cylinder-by-cylinder air-fuel ratio is obtained by estimating the catalyst temperature so that the estimated catalyst temperature increases as the acquired air-fuel ratio imbalance index value increases as in the above configuration. The catalyst temperature can be accurately estimated even when the degree of performance is large. As a result, overheat prevention control of the catalyst based on “enrichment of the air-fuel ratio of exhaust gas by increasing the indicated fuel injection amount” or “a large amount of oxygen flows into the catalyst during fuel injection stop control (fuel cut)” Thus, it is possible to appropriately perform control (prohibition of execution of fuel injection stop control) that avoids the “temperature rise of the catalyst due to the operation”.

  In this case, the catalyst temperature estimating means is configured to acquire the alcohol concentration of the fuel and to estimate the catalyst temperature so that the estimated catalyst temperature is lower as the acquired alcohol concentration is higher. It is preferable. This is because the higher the alcohol concentration, the lower the combustion temperature, and the lower the exhaust gas temperature. As a result, the catalyst temperature also decreases.

  Further, in this aspect, the air-fuel ratio imbalance index value acquisition means sets the basic parameter correlation value as a value according to the basic parameter, a value according to the rotational speed of the engine, and a value according to the intake air amount of the engine. Preferably, the air-fuel ratio imbalance index value is acquired based on the corrected value obtained by the correction. According to this, since the influence of the “engine rotational speed and the intake air amount of the engine” on the air-fuel ratio imbalance index value can be reduced, the air-fuel ratio imbalance index that accurately represents the degree of non-uniformity of the cylinder-by-cylinder air-fuel ratio. The value can be obtained. As a result, since the temperature of the three-way catalyst is estimated with higher accuracy, it is possible to avoid unnecessary increase of fuel and unnecessary prohibition of fuel injection stop control to prevent overheating of the catalyst. Can do.

  In addition, also in this aspect, the air-fuel ratio imbalance index value acquisition unit acquires the alcohol concentration of the fuel and corrects the basic parameter correlation value based on the acquired alcohol concentration. It is preferable that the air-fuel ratio imbalance index value is acquired based on the obtained corrected value. As described above, the air-fuel ratio imbalance index value is affected by the alcohol concentration. Therefore, with this configuration, even when the alcohol concentration is high, an air-fuel ratio imbalance index value that accurately represents the degree of non-uniformity of the cylinder-by-cylinder air-fuel ratio can be acquired. As a result, since the temperature of the three-way catalyst is estimated with higher accuracy, it is possible to avoid unnecessary increase of fuel and unnecessary prohibition of fuel injection stop control to prevent overheating of the catalyst. Can do.

In the device of the present invention, the air-fuel ratio imbalance index value acquisition means is
A value correlated with the difference between the maximum value and the minimum value in a predetermined period of the output value Vabyfs of the upstream air-fuel ratio sensor, or
A value correlated with a difference between a maximum value and a minimum value in a predetermined period of the detected air-fuel ratio abyfs acquired based on an output value of the upstream air-fuel ratio sensor,
The air-fuel ratio imbalance index value may be acquired.

Further, the air-fuel ratio imbalance index value acquisition means, as described in Patent Document 1,
A value that correlates with the trajectory length of the upstream side air-fuel ratio sensor output value Vabyfs (including the value obtained by performing high-pass filter processing on the output value Vabyfs) or the detected air-fuel ratio abyfs (high-pass filter processing the detected air-fuel ratio abyfs) A value that correlates with the trajectory length in a predetermined period (including the measured value) may be acquired as the air-fuel ratio imbalance index value.

  In addition, as described in Patent Document 2, the air-fuel ratio imbalance index value acquisition unit acquires a value correlated with the sub-feedback amount or the learned value as the air-fuel ratio imbalance index value. Can be configured.

Further, the air-fuel ratio imbalance index value acquisition means includes:
A value that increases as a variation in the rotational speed of the engine increases can be obtained as the air-fuel ratio imbalance index value.

  Other objects, other features and attendant advantages of the inventive device will be readily understood from the description of each embodiment of the inventive device described with reference to the following drawings.

FIG. 1 is a schematic view of an internal combustion engine to which a fuel injection amount control device according to each embodiment of the present invention is applied. FIG. 2 is a graph showing the relationship between the air-fuel ratio of the air-fuel mixture supplied to the cylinder and the amount of unburned components discharged from the cylinder. 3A to 3C are schematic cross-sectional views of an air-fuel ratio detection unit provided in the air-fuel ratio sensor (upstream air-fuel ratio sensor) shown in FIG. FIG. 4 is a graph showing the relationship between the air-fuel ratio of exhaust gas and the limit current value of the air-fuel ratio sensor. FIG. 5 is a graph showing the relationship between the air-fuel ratio of exhaust gas and the output value of the air-fuel ratio sensor. FIG. 6 is a graph showing the relationship between the air-fuel ratio of exhaust gas and the output value of the downstream air-fuel ratio sensor shown in FIG. FIG. 7 is a graph showing the relationship between the alcohol concentration, the true air-fuel ratio of the exhaust gas, and the output value of the air-fuel ratio sensor. FIG. 8 shows a case where an air-fuel ratio imbalance state between cylinders occurs (when the degree of non-uniformity of the air-fuel ratio per cylinder is large) and a case where an air-fuel ratio imbalance state between cylinders does not occur (the air-fuel ratio per cylinder). 7 is a time chart showing “the behavior of each value related to the air-fuel ratio imbalance index value” in the case where non-uniformity does not occur. FIG. 9 is a graph showing the relationship between the actual imbalance ratio and the air-fuel ratio imbalance index value correlated with the detected air-fuel ratio change rate. FIG. 10 is a flowchart showing a routine executed by the CPU of the fuel injection amount control apparatus (first control apparatus) according to the first embodiment of the present invention. FIG. 11 is a flowchart showing a routine executed by the CPU of the first control device. FIG. 12 is a flowchart showing a routine executed by the CPU of the first control device. FIG. 13 is a flowchart showing a routine executed by the CPU of the first control device. FIG. 14 is a flowchart showing a routine executed by the CPU of the first control device. FIG. 15 is a flowchart showing a routine executed by the CPU of the first control device. FIG. 16 is a flowchart showing a routine executed by the CPU of the fuel injection amount control device (second control device) according to the second embodiment of the present invention. FIG. 17 is a flowchart showing a routine executed by the CPU of the fuel injection amount control device (third control device) according to the third embodiment of the present invention. FIG. 18 is a graph showing the relationship between the alcohol concentration, the true air-fuel ratio of the exhaust gas, and the output value of the air-fuel ratio sensor that is the “electromotive force type oxygen concentration sensor”. FIG. 19 is a graph showing the relationship between the degree of non-uniformity of the air-fuel ratio for each cylinder, the true air-fuel ratio of exhaust gas, and the output value of the air-fuel ratio sensor that is the “electromotive force type oxygen concentration sensor”. is there. FIG. 20 is a graph showing the relationship between the basic air-fuel ratio imbalance index value based on the detected air-fuel ratio change rate and the ethanol concentration. FIG. 21 is a flowchart showing a routine executed by the CPU of the fuel injection amount control apparatus (fifth control apparatus) according to the fifth embodiment of the present invention. FIG. 22 is a lookup table referred to by the CPU of the fifth control device. FIG. 23 is a look-up table referred to by the CPU of the fifth control apparatus. FIG. 24 is a look-up table referred to by the CPU of the fifth control device. FIG. 25 is a flowchart showing a routine executed by the CPU of the fuel injection amount control apparatus (sixth control apparatus) according to the sixth embodiment of the present invention. FIG. 26 is a flowchart showing a routine executed by the CPU of the fuel injection amount control device (seventh control device) according to the seventh embodiment of the present invention. FIG. 27 is a flowchart showing a routine executed by the CPU of the seventh control apparatus of the present invention. FIG. 28 is a flowchart showing a routine executed by the CPU of the seventh control apparatus of the present invention.

  Hereinafter, a fuel injection amount control device (hereinafter also simply referred to as “control device”) for an internal combustion engine according to each embodiment of the present invention will be described with reference to the drawings. This control device is a part of an air-fuel ratio control device that controls the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine (the air-fuel ratio of the engine), and is also a part of an air-fuel ratio imbalance among cylinders determination device. .

<First Embodiment>
(Constitution)
FIG. 1 shows a system in which a control device according to the first embodiment (hereinafter also referred to as “first control device”) is applied to a 4-cycle, spark ignition type, multi-cylinder (in-line 4-cylinder) internal combustion engine 10. The schematic structure of is shown.

  Internal combustion engine 10 includes an engine body 20, an intake system 30, and an exhaust system 40.

  The engine body portion 20 includes a cylinder block portion and a cylinder head portion. The engine body 20 includes a plurality of cylinders (combustion chambers) 21. Each cylinder communicates with an “intake port and exhaust port” (not shown). A communicating portion between the intake port and the combustion chamber 21 is opened and closed by an intake valve (not shown). A communicating portion between the exhaust port and the combustion chamber 21 is opened and closed by an exhaust valve (not shown). Each combustion chamber 21 is provided with a spark plug (not shown).

  The intake system 30 includes an intake manifold 31, an intake pipe 32, a plurality of fuel injection valves 33, and a throttle valve 34.

  The intake manifold 31 includes a plurality of branch portions 31a and a surge tank 31b. One end of each of the plurality of branch portions 31a is connected to each of the plurality of intake ports. The other ends of the plurality of branch portions 31a are connected to the surge tank 31b.

  One end of the intake pipe 32 is connected to the surge tank 31b. An air filter (not shown) is disposed at the other end of the intake pipe 32.

  One fuel injection valve 33 is provided for each cylinder (combustion chamber) 21. The fuel injection valve 33 is provided at the intake port. That is, each of the plurality of cylinders includes a fuel injection valve 33 that supplies fuel independently of the other cylinders. The fuel injection valve 33 responds to the injection instruction signal, and when it is normal, “the fuel of the indicated fuel injection amount included in the injection instruction signal” is input into the intake port (therefore, the cylinder corresponding to the fuel injection valve 33). It comes to inject.

  More specifically, the fuel injection valve 33 opens for a time corresponding to the commanded fuel injection amount. The pressure of the fuel supplied to the fuel injection valve 33 is kept constant. Therefore, if the fuel injection valve 33 is normal, the fuel injection valve 33 injects the indicated fuel injection amount of fuel. However, when an abnormality occurs in the fuel injection valve 33, the fuel injection valve 33 injects an amount of fuel different from the command fuel injection amount. As a result, non-uniformity among cylinders of the air-fuel ratio for each cylinder occurs.

  The throttle valve 34 is rotatably disposed in the intake pipe 32. The throttle valve 34 has a variable opening cross-sectional area of the intake passage. The throttle valve 34 is rotationally driven in the intake pipe 32 by a throttle valve actuator (not shown).

  The exhaust system 40 includes an exhaust manifold 41, an exhaust pipe 42, an upstream catalyst 43 disposed in the exhaust pipe 42, and a “downstream catalyst (not shown) disposed in the exhaust pipe 42 downstream of the upstream catalyst 43. Is provided.

  The exhaust manifold 41 includes a plurality of branch portions 41a and a collecting portion 41b. One end of each of the plurality of branch portions 41a is connected to each of the plurality of exhaust ports. The other ends of the plurality of branch portions 41a are gathered in the gathering portion 41b. The collecting portion 41b is also referred to as an exhaust collecting portion HK because exhaust gas discharged from a plurality of (two or more, four in this example) cylinders gathers.

  The exhaust pipe 42 is connected to the collecting portion 41b. The exhaust port, the exhaust manifold 41 and the exhaust pipe 42 constitute an exhaust passage.

Each of the upstream side catalyst 43 and the downstream side catalyst is a so-called three-way catalyst device (exhaust purification catalyst) carrying an active component made of a noble metal (catalyst substance) such as platinum, rhodium and palladium. Each catalyst oxidizes unburned components such as HC, CO, and H ₂ when the air-fuel ratio of the gas flowing into each catalyst is “the air-fuel ratio within the window of the three-way catalyst (for example, the theoretical air-fuel ratio)”. In addition, it has a function of reducing nitrogen oxides (NOx). This function is also called a catalyst function. Further, each catalyst has an oxygen storage function for storing (storing) oxygen. Each catalyst can purify unburned components and nitrogen oxides even if the air-fuel ratio shifts from the stoichiometric air-fuel ratio due to the oxygen storage function. That is, the window width is expanded by the oxygen storage function. The oxygen storage function is provided by an oxygen storage material such as ceria (CeO ₂ ) supported on the catalyst.

  This system includes a hot-wire air flow meter 51, a throttle position sensor 52, a water temperature sensor 53, a crank position sensor 54, an intake cam position sensor 55, an upstream air-fuel ratio sensor 56, a downstream air-fuel ratio sensor 57, an accelerator opening sensor 58, An alcohol concentration sensor 59 is provided.

  The air flow meter 51 outputs a signal corresponding to the mass flow rate (intake air flow rate) Ga of intake air flowing through the intake pipe 32. That is, the intake air amount Ga represents the intake air amount taken into the engine 10 per unit time.

  The throttle position sensor 52 detects the opening (throttle valve opening) of the throttle valve 34 and outputs a signal representing the throttle valve opening TA.

  The water temperature sensor 53 detects the temperature of the cooling water of the internal combustion engine 10 and outputs a signal representing the cooling water temperature THW. The coolant temperature THW is a parameter that represents the warm-up state of the engine 10 (temperature of the engine 10).

  The crank position sensor 54 outputs a signal having a narrow pulse every time the crankshaft rotates 10 ° and a wide pulse every time the crankshaft rotates 360 °. This signal is converted into an engine speed NE by an electric control device 70 described later.

  The intake cam position sensor 55 outputs one pulse every time the intake cam shaft rotates 90 degrees, 90 degrees, and 180 degrees from a predetermined angle. The electric control device 70 described later acquires an absolute crank angle CA based on the compression top dead center of the reference cylinder (for example, the first cylinder) based on signals from the crank position sensor 54 and the intake cam position sensor 55. It has become. This absolute crank angle CA is set to “0 ° crank angle” at the compression top dead center of the reference cylinder, and increases to a 720 ° crank angle according to the rotation angle of the crankshaft. Set to

  The upstream air-fuel ratio sensor 56 is disposed in “any one of the exhaust manifold 41 and the exhaust pipe 42” at a position between the collecting portion 41 b (exhaust collecting portion HK) of the exhaust manifold 41 and the upstream catalyst 43. . The upstream air-fuel ratio sensor 56 corresponds to the air-fuel ratio sensor in the present invention.

  The upstream air-fuel ratio sensor 56 is disclosed in, for example, “Limit current type wide area air-fuel ratio including diffusion resistance layer” disclosed in JP-A-11-72473, JP-A-2000-65782, JP-A-2004-69547, and the like. Sensor ".

  As shown in FIG. 3, the upstream air-fuel ratio sensor 56 has an air-fuel ratio detection unit 56a. The air-fuel ratio detection unit 56a is accommodated in a “hollow cylindrical protective cover made of metal” (not shown). A through hole is provided in the side surface and the lower surface of the protective cover. The exhaust gas flows into the protective cover through the through hole on the side surface, reaches the air-fuel ratio detection unit 56a, and then flows out of the protective cover through the through hole on the lower surface.

  That is, the exhaust gas that has reached the protective cover is sucked into the protective cover by the flow of the exhaust gas flowing in the vicinity of the through hole on the lower surface of the protective cover. For this reason, the flow rate of the exhaust gas inside the protective cover changes according to the flow rate of the exhaust gas flowing in the vicinity of the through hole on the lower surface of the protective cover (accordingly, the intake air amount Ga which is the intake air amount per unit time). Accordingly, the output responsiveness (responsiveness) of the upstream air-fuel ratio sensor 56 to “the air-fuel ratio of the exhaust gas flowing through the exhaust passage” increases as the intake air amount Ga increases.

  As shown in FIGS. 3A to 3C, the air-fuel ratio detection unit 56a includes a solid electrolyte layer 561, an exhaust gas side electrode layer 562, an atmosphere side electrode layer (reference gas side electrode layer) 563, A diffusion resistance layer 564, a first wall portion 565, a catalyst portion 566, a second wall portion 567, and a heater 568 are included.

The solid electrolyte layer 561 is an oxygen ion conductive oxide sintered body. In this example, the solid electrolyte layer 561 is a “stabilized zirconia element” in which CaO is dissolved in ZrO ₂ (zirconia) as a stabilizer. The solid electrolyte layer 561 exhibits well-known “oxygen battery characteristics” and “oxygen pump characteristics” when its temperature is equal to or higher than the activation temperature.

  The exhaust gas side electrode layer 562 is made of a noble metal having high catalytic activity such as platinum (Pt). The exhaust gas side electrode layer 562 is formed on one surface of the solid electrolyte layer 561. The exhaust gas side electrode layer 562 is formed to have sufficient permeability (that is, in a porous shape) by chemical plating or the like.

  The atmosphere-side electrode layer 563 is made of a noble metal having high catalytic activity such as platinum (Pt). The atmosphere-side electrode layer 563 is formed on the other surface of the solid electrolyte layer 561 so as to face the exhaust gas-side electrode layer 562 with the solid electrolyte layer 561 interposed therebetween. The atmosphere-side electrode layer 563 is formed to have sufficient permeability (that is, in a porous shape) by chemical plating or the like. The atmosphere side electrode layer 563 is also referred to as a reference gas side electrode layer.

  The diffusion resistance layer (diffusion limiting layer) 564 is a porous layer made of porous ceramic (heat-resistant inorganic substance). The diffusion resistance layer 564 is formed by, for example, a plasma spraying method so as to cover the outer surface of the exhaust gas side electrode layer 562.

  The first wall portion 565 is made of alumina ceramic that is dense and does not allow gas to pass therethrough. The first wall portion 565 is formed so as to cover the diffusion resistance layer 564 except for a corner (part) of the diffusion resistance layer 564. That is, the first wall portion 565 includes a penetration portion that exposes a part of the diffusion resistance layer 564 to the outside.

  The catalyst part 566 is formed in the penetration part so as to close the penetration part of the first wall part 565. Similar to the upstream catalyst 43, the catalyst unit 566 supports a catalyst material that promotes a redox reaction and an oxygen storage material that exhibits an oxygen storage function. The catalyst part 566 is a porous body. Therefore, as indicated by the white arrows in FIGS. 3B and 3C, the exhaust gas (exhaust gas that has flowed into the protective cover described above) passes through the catalyst portion 566 and diffuses resistance. The exhaust gas reaches the layer 564, and the exhaust gas further passes through the diffusion resistance layer 564 and reaches the exhaust gas side electrode layer 562.

  The second wall portion 567 is made of alumina ceramic that is dense and does not allow gas to pass therethrough. The second wall portion 567 is configured to form an “atmosphere chamber 56 </ b> A” that is a space for accommodating the atmosphere-side electrode layer 563. The atmosphere is introduced into the atmosphere chamber 56A.

  A power source 569 is connected to the upstream air-fuel ratio sensor 56. The power source 569 applies the voltage V (= Vp) so that the atmosphere-side electrode layer 563 side has a high potential and the exhaust gas-side electrode layer 562 has a low potential.

  The heater 568 is embedded in the second wall portion 567. The heater 568 generates heat when energized by an electric control device 70 described later, heats the solid electrolyte layer 561, the exhaust gas side electrode layer 562, and the atmosphere side electrode layer 563, and adjusts the temperatures thereof.

  As shown in FIG. 3B, the upstream air-fuel ratio sensor 56 having such a structure causes the diffusion resistance layer 564 to be formed when the air-fuel ratio of the exhaust gas is a leaner air-fuel ratio than the stoichiometric air-fuel ratio. The oxygen that passes through and reaches the exhaust gas side electrode layer 562 is ionized and passed to the atmosphere side electrode layer 563. As a result, the current I flows from the positive electrode to the negative electrode of the power supply 569. As shown in FIG. 4, when the voltage V is set to a predetermined voltage Vp, the magnitude of this current I is the amount of oxygen that reaches the exhaust gas side electrode layer 562 (oxygen partial pressure, oxygen concentration, and hence the exhaust gas empty space). It becomes a constant value proportional to (fuel ratio). The upstream air-fuel ratio sensor 56 outputs a value obtained by converting this current (that is, the limit current IL) into a voltage as an output value Vabyfs.

On the other hand, as shown in FIG. 3C, when the air-fuel ratio of the exhaust gas is a richer air-fuel ratio than the stoichiometric air-fuel ratio, the upstream air-fuel ratio sensor 56 detects oxygen present in the atmospheric chamber 56A. Is ionized to lead to the exhaust gas side electrode layer 562, and unburned substances (HC, CO, H _{2 and the} like) that reach the exhaust gas side electrode layer 562 through the diffusion resistance layer 564 are oxidized. As a result, a current I flows from the negative electrode of the power source 569 to the positive electrode. As shown in FIG. 4, when the voltage V is set to a predetermined voltage Vp, the magnitude of the current I is the amount of unburned matter that has reached the exhaust gas side electrode layer 562 (partial pressure of unburned matter, unburned matter It becomes a constant value proportional to the concentration, that is, the air-fuel ratio of the exhaust gas. The upstream air-fuel ratio sensor 56 outputs a value obtained by converting this current (that is, the limit current IL) into a voltage as an output value Vabyfs.

  That is, as shown by the solid line L1 in FIG. 5, the air-fuel ratio detector 56a flows through the position where the upstream air-fuel ratio sensor 56 is disposed, and reaches the air-fuel ratio detector 56a through the through hole of the protective cover. The output value Vabyfs corresponding to the air-fuel ratio of the gas being output is output as the “air-fuel ratio sensor output”. In other words, the upstream air-fuel ratio sensor 56 passes through the diffusion resistance layer 564 of the air-fuel ratio detection unit 56a and reaches the exhaust gas side electrode layer 562 with the “oxygen partial pressure (oxygen concentration, oxygen amount) and unburned matter” The output value Vabyfs that changes according to the "partial pressure (concentration of unburned material, amount of unburned material)" is output.

  The output value Vabyfs increases as the air-fuel ratio of the gas reaching the air-fuel ratio detection unit 56a increases (lean). That is, the output value Vabyfs has no non-uniformity in the air-fuel ratio for each cylinder (that is, the air-fuel ratio of each cylinder is the same between the cylinders), and the fuel used does not contain alcohol. (Ie, when the alcohol concentration of the fuel is “0”), it changes as indicated by the solid line in FIG. The output value Vabyfs matches the stoichiometric air-fuel ratio equivalent value Vstoich when the air-fuel ratio of the gas reaching the air-fuel ratio detection unit 56a is the stoichiometric air-fuel ratio.

  The electric control device 70 to be described later stores an air-fuel ratio conversion table (map) Mapabyfs (Vabyfs) shown in FIG. The electric control device 70 detects the actual upstream air-fuel ratio abyfs by applying the output value Vabyfs of the upstream air-fuel ratio sensor 56 to the air-fuel ratio conversion table Mapabyfs (that is, obtains the detected air-fuel ratio abyfs). Of course, the detected air-fuel ratio abyfs itself is a value corresponding to the detected air-fuel ratio abyfs.

  As described above, the upstream air-fuel ratio sensor 56 is “disposed in the exhaust passage of the engine 10 and between the exhaust collecting portion HK and the three-way catalyst 43, and the air-fuel ratio detection element (solid electrolyte layer). ) 561, an exhaust gas side electrode layer 562 and a reference gas side electrode layer 563 disposed so as to face each other with the air-fuel ratio detection element 561 interposed therebetween, and a porous layer (diffusion resistance layer) covering the exhaust gas side electrode layer 562 ) 564, which is included in the exhaust gas passing through the position where the air-fuel ratio sensor is disposed and reaching the exhaust gas side electrode layer 562 through the porous layer 564 It is an air-fuel ratio sensor that outputs an output value corresponding to the amount of oxygen and the amount of unburned matter.

  By the way, unburned matter containing hydrogen contained in the exhaust gas is purified to some extent in the catalyst unit 566. However, when the exhaust gas contains a large amount of unburned matter, the unburned matter cannot be completely purified by the catalyst unit 566. As a result, “oxygen and excessive unburned matter relative to the oxygen” may reach the outer surface of the diffusion resistance layer 564. Furthermore, as described above, since hydrogen has a smaller molecular diameter than other unburned materials, hydrogen diffuses preferentially in the diffusion resistance layer 564 as compared with other unburned materials.

  Referring to FIG. 1 again, the downstream air-fuel ratio sensor 57 is disposed in the exhaust pipe 42. The downstream air-fuel ratio sensor 57 is disposed downstream of the upstream catalyst 43 and upstream of the downstream catalyst (that is, the exhaust passage between the upstream catalyst 43 and the downstream catalyst). It is. The downstream air-fuel ratio sensor 57 is a known electromotive force type oxygen concentration sensor (a known concentration cell type oxygen concentration sensor using a solid electrolyte such as stabilized zirconia). The downstream air-fuel ratio sensor 57 generates an output value Voxs corresponding to the air-fuel ratio of the gas to be detected, which is a gas that passes through the exhaust passage and the portion where the downstream air-fuel ratio sensor 57 is disposed. ing. In other words, the output value Voxs is a value corresponding to the air-fuel ratio of the gas flowing out from the upstream catalyst 43 and flowing into the downstream catalyst.

  As shown in FIG. 6, the output value Voxs becomes a maximum output value max (for example, about 0.9 V to 1.0 V) when the air-fuel ratio of the detected gas is richer than the stoichiometric air-fuel ratio. The output value Vabyfs becomes the minimum output value min (for example, about 0.1 V to 0 V) when the air-fuel ratio of the gas to be detected is leaner than the stoichiometric air-fuel ratio. Further, when the air-fuel ratio of the gas to be detected is the stoichiometric air-fuel ratio, the output value Voxs is a voltage Vst (intermediate voltage Vst, stoichiometric air-fuel ratio equivalent voltage Vst, for example, approximately halfway between the maximum output value max and the minimum output value min. 0.5V). The output value Voxs suddenly changes from the maximum output value max to the minimum output value min when the air-fuel ratio of the gas to be detected changes from an air-fuel ratio richer than the stoichiometric air-fuel ratio to a lean air-fuel ratio. Similarly, the output value Voxs suddenly changes from the minimum output value min to the maximum output value max when the air-fuel ratio of the detected gas changes from an air-fuel ratio leaner than the stoichiometric air-fuel ratio to a rich air-fuel ratio.

  The downstream air-fuel ratio sensor 57 is also provided with an “exhaust gas side electrode layer and an atmosphere side (reference gas side) electrode layer disposed on both sides of the solid electrolyte layer so as to face each other with the solid electrolyte layer interposed therebetween. The exhaust gas side electrode layer is covered with a porous layer (protective layer). Therefore, when the gas to be detected passes through the porous layer, the gas to be detected changes to a gas after oxygen equilibration (a gas after oxygen and unburned substances are combined), and reaches the exhaust gas side electrode layer. Hydrogen passes through the porous layer more easily than other unburned materials. However, the “excess hydrogen generated when the non-uniformity of the cylinder-by-cylinder air-fuel ratio” is purified by the upstream catalyst 43 except in special cases. Therefore, the output value Voxs of the downstream side air-fuel ratio sensor 57 does not change depending on the degree of non-uniformity of the cylinder-by-cylinder air-fuel ratio except in special cases.

  The accelerator opening sensor 58 shown in FIG. 1 outputs a signal representing the operation amount Accp (accelerator pedal operation amount, accelerator pedal AP opening amount) of the accelerator pedal AP operated by the driver. The accelerator pedal operation amount Accp increases as the operation amount of the accelerator pedal AP increases.

  The alcohol concentration sensor 59 is disposed in a fuel supply pipe FP that connects a plurality of fuel injection valves 33 and a fuel tank (not shown). The alcohol concentration sensor 59 outputs a signal Et indicating the alcohol concentration (ethanol concentration) contained in the fuel. The alcohol concentration sensor 59 is well known (see, for example, JP-A-2005-201670 and JP-A-7-77507). The alcohol concentration sensor 59 may be a capacitance type sensor that detects the alcohol concentration based on the dielectric constant of the fuel, or may be an optical sensor that detects the alcohol concentration based on the refractive index of the fuel. Good.

  The electric control device 70 includes a “CPU, a program executed by the CPU, a ROM in which tables (maps, functions) and constants are stored in advance, a RAM in which the CPU temporarily stores data as necessary, a backup RAM, and It is a well-known microcomputer composed of an interface including an AD converter.

  The backup RAM is supplied with electric power from a battery mounted on the vehicle regardless of the position of an ignition key switch (not shown) of the vehicle on which the engine 10 is mounted (any one of an off position, a start position, an on position, etc.). It is like that. When receiving power from the battery, the backup RAM stores data according to an instruction from the CPU (data is written) and holds (stores) the data so that the data can be read. Therefore, the backup RAM can hold data even when the operation of the engine 10 is stopped.

  The backup RAM cannot retain data when the power supply from the battery is interrupted, for example, when the battery is removed from the vehicle. Therefore, when the power supply to the backup RAM is resumed, the CPU initializes (sets to the default value) data to be held in the backup RAM. The backup RAM may be a readable / writable nonvolatile memory such as an EEPROM.

  The electric control device 70 is connected to the above-described sensors and the like, and supplies signals from these sensors to the CPU. Further, the electric control device 70 is responsive to an instruction from the CPU to provide a spark plug (actually an igniter) provided for each cylinder, a fuel injection valve 33 provided for each cylinder, and a throttle. A drive signal (instruction signal) is sent to a valve actuator or the like.

  The electric control device 70 sends an instruction signal to the throttle valve actuator so that the throttle valve opening TA increases as the acquired accelerator pedal operation amount Accp increases. That is, the electric control device 70 changes the opening degree of the “throttle valve 34 disposed in the intake passage of the engine 10” according to the acceleration operation amount (accelerator pedal operation amount Accp) of the engine 10 changed by the driver. Throttle valve drive means is provided.

(Outline of fuel injection amount control by the first controller)
Next, an outline of fuel injection amount control (air-fuel ratio feedback control) by the first control device will be described.

1. Regarding the relationship between the output value of the upstream air-fuel ratio sensor 56 and the alcohol concentration The higher the alcohol concentration of the fuel (in this example, the ethanol ratio), the more hydrogen is generated by the combustion of the fuel. For this reason, the amount of hydrogen that reaches the outer surface of the diffusion resistance layer 564 of the upstream air-fuel ratio sensor 56 also increases. As a result, the hydrogen concentration (partial pressure) reaching the exhaust gas side electrode layer 562 when the alcohol concentration is high is higher than the hydrogen concentration (partial pressure) reaching the exhaust gas side electrode layer 562 when the alcohol concentration is low. It will be much higher.

  Therefore, as shown in FIG. 7, the output value Vabyfs of the upstream air-fuel ratio sensor 56 increases with respect to the true air-fuel ratio of the engine 10 (the true air-fuel ratio of exhaust gas) as the alcohol concentration increases. The value shifts to a value corresponding to the air-fuel ratio. In other words, even if the true air-fuel ratio of the exhaust gas is constant, the output value Vabyfs decreases as the alcohol concentration increases. In addition, each line shown in FIG. 7 is a case where non-uniformity of the cylinder-by-cylinder air-fuel ratio does not occur, and “relationship between the output value Vabyfs and the true air-fuel ratio of exhaust gas” in the following cases. Indicates.

Solid line C1: When the alcohol concentration is “0”. At this time, the alcohol concentration is expressed as “first concentration or reference alcohol concentration”. The solid line C1 matches the solid line L1 in FIG.
Broken line C2: When the alcohol concentration is “a second concentration higher than the first concentration”.
One-dot chain line C3: When the alcohol concentration is “a third concentration greater than the second concentration”.
Two-dot chain line C4: When the alcohol concentration is “fourth concentration higher than the third concentration”.

  Assume that the true air-fuel ratio of the exhaust gas is “value c shown in FIG. 7”. In this case, when the alcohol concentration is the first concentration, the second concentration, the third concentration, and the fourth concentration, the output values Vabyfs are V1, V2, V3, and V4 (V1> V2> V3> V4), respectively. That is, as described above, the output value Vabyfs decreases as the alcohol concentration increases even if the true air-fuel ratio of the exhaust gas is constant. Therefore, the air-fuel ratio converted by the air-fuel ratio conversion table Mapabyfs (Vabyfs) determined for the case where the non-uniformity of the air-fuel ratio by cylinder does not occur and the alcohol concentration is “0” is The higher the alcohol concentration, the richer the air-fuel ratio with respect to the true air-fuel ratio c.

  That is, for example, if the actual output value Vabyfs is “value V3 shown in FIG. 7”, the air-fuel ratio converted by the air-fuel ratio conversion table Mapabyfs (Vabyfs) is the air-fuel ratio a. In other words, the electric control device 70 recognizes that the air-fuel ratio of the exhaust gas is “a”.

  However, if the alcohol concentration is the second concentration, the true air-fuel ratio of the exhaust gas is the air-fuel ratio b (b> a), and if the alcohol concentration is the third concentration, the true air-fuel ratio of the exhaust gas is the air-fuel ratio c (c > B), and if the alcohol concentration is the fourth concentration, the true air-fuel ratio of the exhaust gas is the air-fuel ratio d (d> c). Thus, when the actual output value Vabyfs is `` a certain value '', as the alcohol concentration increases, the `` air-fuel ratio obtained by the air-fuel ratio conversion table Mapabyfs (Vabyfs) '' is greater than `` the true air-fuel ratio of exhaust gas '' Becomes the rich air-fuel ratio (small air-fuel ratio). This is the reason why “lean miscontrol due to alcohol concentration” occurs.

2. Regarding the relationship between the output value of the upstream air-fuel ratio sensor 56 and the degree of non-uniformity of the cylinder-by-cylinder air-fuel ratio On the other hand, even if the alcohol concentration of the fuel is constant, the degree of non-uniformity of the cylinder-by-cylinder air-fuel ratio is The larger it is, the more unburned material is generated. That is, when the average air-fuel ratio of the engine is, for example, the stoichiometric air-fuel ratio, when there is no non-uniformity in the air-fuel ratio by cylinder, relatively little hydrogen is generated from each cylinder (see FIG. 2), if the degree of non-uniformity of the cylinder-by-cylinder air-fuel ratio becomes large, a very large amount of hydrogen is generated from the cylinder to which the air-fuel mixture richer than the stoichiometric air-fuel ratio is supplied (FIG. 2). (See H2 and H3.) Therefore, as the degree of non-uniformity of the cylinder-by-cylinder air-fuel ratio increases, the amount of hydrogen that reaches the outer surface of the diffusion resistance layer 564 also increases.

  As a result, the hydrogen concentration (partial pressure) reaching the exhaust gas side electrode layer 562 when the degree of non-uniformity of the cylinder-by-cylinder air-fuel ratio is large is the exhaust gas side when the degree of non-uniformity of the cylinder-by-cylinder air-fuel ratio is small. This is much higher than the concentration (partial pressure) of hydrogen reaching the electrode layer 562. Therefore, as the degree of non-uniformity of the cylinder-by-cylinder air-fuel ratio increases, the output value of the upstream-side air-fuel ratio sensor 56 increases with respect to the richer air side than the true air-fuel ratio of the engine 10 (the true air-fuel ratio of exhaust gas). It shifts to a value corresponding to the fuel ratio.

  In other words, when the actual output value Vabyfs is `` a certain value '', as the degree of non-uniformity of the air-fuel ratio by cylinder increases, the `` air-fuel ratio obtained by the air-fuel ratio conversion table Mapabyfs (Vabyfs) '' becomes `` exhaust gas '' The air-fuel ratio on the rich side (smaller air-fuel ratio) than the “true air-fuel ratio”. This is the reason why “lean erroneous control due to non-uniformity of the air-fuel ratio by cylinder” occurs.

3. Compensation of Lean Miscontrol by Sub Feedback Amount and Sub FB Learning Value By the way, hydrogen contained in exhaust gas is purified (oxidized) by the three-way catalyst 43. The downstream air-fuel ratio sensor 57 is disposed downstream of the three-way catalyst 43. Therefore, the output value Voxs of the downstream air-fuel ratio sensor 57 is not easily affected by the amount of hydrogen that changes according to the alcohol concentration and / or the degree of non-uniformity of the cylinder-by-cylinder air-fuel ratio.

  Accordingly, the fuel injection is performed so that the output value Voxs of the downstream side air-fuel ratio sensor 57 coincides with “a value corresponding to a reference air-fuel ratio (for example, a theoretical air-fuel ratio) that is an air-fuel ratio in the window of the three-way catalyst 43”. If the amount is feedback controlled, the average of the true air-fuel ratio of the exhaust gas substantially coincides with the reference air-fuel ratio regardless of the alcohol concentration and / or the degree of non-uniformity of the air-fuel ratio for each cylinder. As a result, the emission can be maintained satisfactorily. This feedback control is referred to as sub-feedback control.

  A control amount used in the sub feedback control is referred to as a sub feedback amount. The sub-feedback amount is substantially equal to the target air-fuel ratio abyfr so that the output value Voxs of the downstream air-fuel ratio sensor 57 matches the “downstream target value Voxsref corresponding to the reference air-fuel ratio (for example, the theoretical air-fuel ratio)”. The amount to be changed. The sub feedback amount may be a value that directly changes the target air-fuel ratio abyfr, and the target air-fuel ratio abyfr is substantially (indirectly) corrected by correcting the output value Vabyfs of the upstream air-fuel ratio sensor 56 with the sub-feedback amount. It is also possible to change the value.

  The sub feedback amount is such that when the output value Voxs of the downstream air-fuel ratio sensor 57 is richer than the target value Voxsref, the target air-fuel ratio abyfr is substantially shifted to the lean side, and the output value Voxs becomes the target value Voxsref. When the value is on the lean side, the target air-fuel ratio abyfr is substantially shifted to the rich side.

  The learning value of the sub feedback amount (sub FB learning value) is a value that changes according to the stationary component of the sub feedback amount. For example, when the sub feedback amount is calculated in accordance with “PID control or PI control or the like” using the deviation D (output deviation amount DVoxs) between the output value Voxs and the downstream target value Voxsref, that is, the sub feedback When the amount includes at least a proportional term and an integral term with respect to the deviation D, a value corresponding to the integral term is a stationary component of the sub-feedback amount.

  The sub FB learning value is stored in the backup RAM. The sub FB learning value is used for fuel injection amount control even in a situation where the sub feedback control condition is not satisfied and the sub feedback amount is not updated. Therefore, for example, when the engine is started, by using the sub FB learning value, the air-fuel ratio of the exhaust gas (the air-fuel ratio of the engine 10) can be brought close to an appropriate value.

  On the other hand, the sub feedback amount and / or the sub FB learning value is provided with a guard so that they do not become excessive or small due to erroneous control. That is, the sub-feedback guard width (sub-feedback amount upper limit value to sub-feedback amount lower limit value) is set so that the sub-feedback amount does not become smaller than the sub-feedback amount lower limit value and does not become larger than the sub-feedback amount upper limit value. Value). Similarly, the guard width for the sub FB learning value (sub FB learning value) is set so that the sub FB learning value does not become smaller than the sub FB learning value lower limit and does not become larger than the sub FB learning value upper limit. Upper limit value to sub FB learning value lower limit value).

  However, such a guard width is set on the assumption that a fuel not containing alcohol is not used, for example. Therefore, if the degree of non-uniformity of the cylinder-by-cylinder air-fuel ratio is increased when alcohol-containing fuel is used, the sub feedback amount and / or the sub FB learning value is regulated within the guard width (that is, the guard width is reduced). It is not possible to reach an appropriate value (a value that can compensate for the lean erroneous correction) that should be originally reached. As a result, there is a risk that emissions will deteriorate.

  Therefore, the first control device determines the degree of non-uniformity of the alcohol concentration of the fuel and the air-fuel ratio for each cylinder (actually, for each cylinder so that the sub-feedback amount and / or the sub-FB learning value can reach an appropriate value. Based on the air-fuel ratio imbalance index value indicating the degree of air-fuel ratio non-uniformity), the guard width is changed. As a result, the sub feedback amount and / or the sub FB learning value can reach an appropriate value regardless of the degree of non-uniformity of the alcohol concentration and the cylinder-by-cylinder air-fuel ratio. Therefore, it is possible to avoid the emission from deteriorating. Furthermore, in the first control device, the guard width is not unnecessarily enlarged. Therefore, for example, when a fuel with a low alcohol concentration is used and the degree of non-uniformity of the air-fuel ratio for each cylinder is small, the sub feedback amount and / or the sub FB learning value may be excessively or too small due to erroneous control. Can be avoided. As a result, it is possible to avoid deterioration of emissions.

4). Outline of Acquisition of Air-fuel Ratio Imbalance Index Value and Determination of Imbalance Between Air-fuel Ratios Next, acquisition of the air-fuel ratio imbalance index value and determination of imbalance between air-fuel ratios adopted by the first controller will be described. The air-fuel ratio imbalance index value represents “the degree of non-uniformity of air-fuel ratios among cylinders (non-uniformity of air-fuel ratios between cylinders, imbalance)” caused by changes in characteristics of the fuel injection valve 33 or the like. It is a parameter.

The first control device acquires the air-fuel ratio imbalance index value as follows.
(1) When a predetermined parameter acquisition condition (air-fuel ratio imbalance index value acquisition condition) is satisfied, the first control device indicates that “the air-fuel ratio represented by the output value Vabyfs of the upstream air-fuel ratio sensor 56 (the above-mentioned "Detected air-fuel ratio abyfs)""change amount per unit time (constant sampling time ts)" is acquired.

  The “change amount per unit time of the detected air-fuel ratio abyfs” is a differential value (time differential value d (abyfs)) with respect to the time of the detected air-fuel ratio abyfs when the unit time is an extremely short time, for example, about 4 milliseconds. / dt, first-order differential value d (abyfs) / dt). Therefore, “the amount of change in the detected air-fuel ratio abyfs per unit time” is also referred to as “the detected air-fuel ratio change rate ΔAF”. Further, the detected air-fuel ratio change rate ΔAF is also referred to as “basic index amount or basic parameter”.

(2) The first control device obtains an average value AveΔAF of the absolute values | ΔAF | of the plurality of detected air-fuel ratio change rates ΔAF acquired in one unit combustion cycle period. The unit combustion cycle period is a period in which the crank angle required for each combustion stroke to end in all the cylinders that exhaust the exhaust gas that reaches one upstream air-fuel ratio sensor 56 elapses. The engine 10 of this example is an in-line 4-cylinder 4-cycle engine, and exhaust gas from the first to fourth cylinders reaches one upstream air-fuel ratio sensor 56. Therefore, the unit combustion cycle period is a period during which the 720 ° crank angle elapses.

(3) The first control device obtains an average value of the average values AveΔAF obtained for each of the plurality of unit combustion cycle periods, and adopts the value as an air-fuel ratio imbalance index value RIMB (parameter for imbalance determination). To do. The air-fuel ratio imbalance index value RIMB is also referred to as an air-fuel ratio imbalance ratio index value between cylinders or an imbalance ratio index value. The air-fuel ratio imbalance index value RIMB is not limited to the value obtained in this way, and can be obtained by various methods to be described later.

  The air-fuel ratio imbalance index value RIMB (a value correlated with the detected air-fuel ratio change rate ΔAF) obtained as described above has a large “degree of air-fuel ratio non-uniformity between cylinders, that is, air-fuel ratio difference by cylinder”. It is a value that becomes larger. That is, the air-fuel ratio imbalance index value RIMB is a value that increases as the difference between the air-fuel ratios of the air-fuel mixture supplied to the combustion chambers of the plurality of cylinders (cylinder-specific air-fuel ratio difference) increases. Hereinafter, this reason will be described.

  The exhaust gas from each cylinder reaches the upstream air-fuel ratio sensor 56 in the ignition order (hence, the exhaust order). When there is no cylinder-by-cylinder air-fuel ratio difference, the air-fuel ratios of exhaust gases that are exhausted from the cylinders and reach the upstream air-fuel ratio sensor 56 are substantially the same. Therefore, the detected air-fuel ratio abyfs when there is no cylinder-by-cylinder air-fuel ratio difference changes, for example, as shown by the broken line C1 in FIG. That is, when there is no air-fuel ratio non-uniformity between the cylinders, the waveform of the output value Vabyfs of the upstream air-fuel ratio sensor 56 is substantially flat. For this reason, as indicated by a broken line C3 in FIG. 8C, when there is no cylinder-by-cylinder air-fuel ratio difference, the absolute value of the detected air-fuel ratio change rate ΔAF is small.

  On the other hand, when the characteristic of the “fuel injection valve 33 that injects fuel into a specific cylinder (for example, the first cylinder)” becomes the “characteristic of injecting fuel larger than the indicated fuel injection amount”, the air-fuel ratio difference between cylinders becomes growing. That is, the air-fuel ratio of the exhaust gas of the specific cylinder (the air-fuel ratio of the imbalance cylinder) is greatly different from the air-fuel ratio of the exhaust gas of the cylinders other than the specific cylinder (the air-fuel ratio of the non-imbalance cylinder).

  Accordingly, the detected air-fuel ratio abyfs when the air-fuel ratio imbalance among cylinders is occurring varies greatly for each unit combustion cycle period, for example, as shown by the solid line C2 in FIG. For this reason, as shown by the solid line C4 in FIG. 8C, when the air-fuel ratio imbalance among cylinders is occurring, the absolute value of the detected air-fuel ratio change rate ΔAF becomes large.

  In addition, the absolute value | ΔAF | of the detected air-fuel ratio change rate ΔAF varies greatly as the air-fuel ratio of the imbalance cylinder deviates from the air-fuel ratio of the non-imbalance cylinder. For example, it is assumed that the detected air-fuel ratio abyfs when the magnitude of the difference between the air-fuel ratio of the imbalance cylinder and the air-fuel ratio of the non-imbalance cylinder is the first value changes as indicated by a solid line C2 in FIG. For example, the detected air-fuel ratio abyfs when the magnitude of the difference between the air-fuel ratio of the imbalance cylinder and the air-fuel ratio of the non-imbalance cylinder is “a second value larger than the first value” is shown in FIG. B) It changes like the one-dot chain line C2a.

  Therefore, as shown in FIG. 9, the average value AveΔAF (air-fuel ratio imbalance index value RIMB) in the “plurality of unit combustion cycle periods” of the absolute value | ΔAF | of the detected air-fuel ratio change rate ΔAF is As the air-fuel ratio deviates from the air-fuel ratio of the non-imbalance cylinder (the actual imbalance ratio increases), the air-fuel ratio increases. That is, the air-fuel ratio imbalance index value RIMB increases as the degree of non-uniformity among cylinders of the cylinder-by-cylinder air-fuel ratio increases.

  The first control device may be configured to compare the air-fuel ratio imbalance index value RIMB with the imbalance determination threshold value RIMBth when the air-fuel ratio imbalance index value RIMB is acquired. In this case, the first control apparatus may be configured to determine that the air-fuel ratio imbalance among cylinders has occurred when the air-fuel ratio imbalance index value RIMB is larger than the imbalance determination threshold value RIMBth. Further, the first control device may be configured to determine that the air-fuel ratio imbalance among cylinders has not occurred when the air-fuel ratio imbalance index value RIMB is smaller than the imbalance determination threshold value RIMBth. .

(Actual operation)
<Fuel injection amount control>
The CPU of the first control device repeatedly executes the fuel injection control routine shown in FIG. 10 for each cylinder every time the crank angle of any cylinder reaches a predetermined crank angle before the intake top dead center. It has become. The predetermined crank angle is, for example, BTDC 90 ° CA (90 ° crank angle before intake top dead center). A cylinder whose crank angle coincides with the predetermined crank angle is also referred to as a “fuel injection cylinder”. The CPU calculates the commanded fuel injection amount Fi and instructs fuel injection by this fuel injection control routine.

  When the crank angle of an arbitrary cylinder matches the predetermined crank angle before the intake top dead center, the CPU starts the process from step 1000, and in step 1010, determines whether or not the value of the fuel cut flag XFC is “0”. judge. The value of the fuel cut flag XFC is set to “1” when the fuel cut condition (hereinafter referred to as “FC condition”) is satisfied when the value of the fuel cut flag XFC is “0”. The value of the fuel cut flag XFC is set to “0” when the fuel cut end condition is satisfied when the value of the fuel cut flag XFC is “1”. Further, the value of the fuel cut flag XFC is set to “0” in the initial routine executed when the engine 10 is started.

  Assume that the value of the fuel cut flag XFC is “0”. In this case, the CPU sequentially performs the processing from step 1020 to step 1060 described below, proceeds to step 1095, and once ends this routine.

  Step 1020: The CPU is based on “the intake air amount Ga measured by the air flow meter 51, the engine speed NE acquired based on the signal of the crank position sensor 54, and the lookup table MapMc (Ga, NE)”. Then, “in-cylinder intake air amount Mc (k)” which is “the amount of air taken into the fuel injection cylinder in one intake stroke of the fuel injection cylinder” is acquired. The in-cylinder intake air amount Mc (k) is stored in the RAM while corresponding to each intake stroke. The in-cylinder intake air amount Mc (k) may be calculated by a well-known air model (a model constructed according to a physical law simulating the behavior of air in the intake passage).

  Step 1030: The CPU determines a target air-fuel ratio abyfr (upstream target air-fuel ratio abyfr). The target air-fuel ratio abyfr is set to a predetermined reference air-fuel ratio within the window of the upstream side catalyst 43. The reference air-fuel ratio can be changed to a value close to the theoretical air-fuel ratio according to the intake air amount Ga, the degree of deterioration of the upstream catalyst 43, and the like. In this example, the target air-fuel ratio abyfr is set to the stoichiometric air-fuel ratio stoich. The target air-fuel ratio abyfr is naturally a value corresponding to the target air-fuel ratio abyfr.

  Step 1040: The CPU obtains the basic fuel injection amount Fbase by dividing the in-cylinder intake air amount Mc (k) by the target air-fuel ratio abyfr. Therefore, the basic fuel injection amount Fbase is a feedforward amount of the fuel injection amount necessary for calculation in order to obtain the stoichiometric air-fuel ratio stoich. This step 1040 constitutes feedforward control means (basic fuel injection amount calculation means) for making the air-fuel ratio of the air-fuel mixture supplied to the engine coincide with the target air-fuel ratio abyfr.

  Step 1050: The CPU calculates the indicated fuel injection amount Fi by correcting the basic fuel injection amount Fbase with the main feedback amount DFi. More specifically, the CPU calculates the command fuel injection amount Fi by adding the main feedback amount DFi to the basic fuel injection amount Fbase. The command fuel injection amount Fi is a command value of the amount of fuel injected from each of the plurality of fuel injection valves 33. The main feedback amount DFi is an air-fuel ratio feedback amount for making the air-fuel ratio of the engine coincide with the target air-fuel ratio abyfr, and is obtained based on the detected air-fuel ratio abyfs obtained by converting the output value Vabyfs of the upstream air-fuel ratio sensor 56. This is the feedback amount of the fuel ratio. A method for calculating the main feedback amount DFi will be described later.

  Step 1060: The CPU sends to the fuel injection valve 33 an injection instruction signal for injecting “the fuel of the indicated fuel injection amount Fi” from the “fuel injection valve 33 provided corresponding to the fuel injection cylinder”. To do. That is, in step 1060, an injection instruction signal is transmitted to the plurality of fuel injection valves 33 so that an amount of fuel corresponding to the instruction fuel injection amount Fi is injected from each of the plurality of fuel injection valves 33. Means.

  As a result, an amount of fuel necessary for making the air-fuel ratio of the engine coincide with the target air-fuel ratio abyfr (an amount estimated to be necessary) is injected from the fuel injection valve 33 of the fuel injection cylinder. That is, Step 1020 to Step 1060 are “mixing supplied to the combustion chambers 21 of a plurality of cylinders (two or more cylinders, all cylinders in this example) that exhaust the exhaust gas reaching the air-fuel ratio sensor 56”. The commanded fuel injection amount control means is configured to control the commanded fuel injection amount Fi so that the “air fuel ratio of the air” becomes the target air-fuel ratio abyfr.

  On the other hand, if the value of the fuel cut flag XFC is “1” at the time when the CPU executes the process of step 1010 (if the FC condition is satisfied), the CPU makes a “No” determination at step 1010. Then, the routine directly proceeds to step 1095 to end the present routine tentatively. In this case, since fuel injection by the process of step 1060 is not executed, fuel cut control (fuel supply stop control) is executed.

<Calculation of main feedback amount>
The CPU repeatedly executes the “main feedback amount calculation routine” shown in the flowchart of FIG. 11 every elapse of a predetermined time. Accordingly, when the predetermined timing comes, the CPU starts the process from step 1100 and proceeds to step 1105 to determine whether or not the “main feedback control condition (upstream air-fuel ratio feedback control condition)” is satisfied.

The main feedback control condition is satisfied when all of the following conditions are satisfied.
(A1) The upstream air-fuel ratio sensor 56 is activated.
(A2) The engine load KL is equal to or less than the threshold KLth.
(A3) Fuel cut control is not being performed.

Here, the load KL is a load factor obtained by the following equation (1). Instead of the load KL, an accelerator pedal operation amount Accp may be used. In the equation (1), Mc is the in-cylinder intake air amount, ρ is the air density (unit is (g / l)), L is the exhaust amount of the engine 10 (unit is (l)), and “4” is the engine. The number of cylinders is 10.

KL = (Mc / (ρ · L / 4)) · 100% (1)

  The description will be continued assuming that the main feedback control condition is satisfied. In this case, the CPU makes a “Yes” determination at step 1105 to sequentially perform the processing from step 1110 to step 1140 described below, proceeds to step 1195, and once ends this routine.

Step 1110: The CPU acquires the feedback control output value Vabyfc according to the following equation (2). In the equation (2), Vabyfs is an output value of the upstream air-fuel ratio sensor 56, and Vafsfb is a sub-feedback amount calculated based on the output value Voxs of the downstream air-fuel ratio sensor 57. A method of calculating the sub feedback amount will be described later.

Vabyfc = Vabyfs + Vafsfb (2)

Step 1115: The CPU obtains the feedback control air-fuel ratio abyfsc by applying the feedback control output value Vabyfc to the table Mapabyfs shown in FIG. 5 as shown in the following equation (3).

abyfsc = Mapabyfs (Vabyfc) (3)

Step 1120: In accordance with the following equation (4), the CPU “in-cylinder fuel supply amount Fc (k−N)” that is “the amount of fuel actually supplied to the combustion chamber 21 at a time point N cycles before the current time point”. " In other words, the CPU divides “the in-cylinder intake air amount Mc (k−N) at a point N cycles before the current point (ie, N · 720 ° crank angle)” by “the feedback control air-fuel ratio abyfsc”. Thus, the in-cylinder fuel supply amount Fc (k−N) is obtained.

Fc (k−N) = Mc (k−N) / abyfsc (4)

  Thus, in order to obtain the in-cylinder fuel supply amount Fc (k−N), the in-cylinder intake air amount Mc (k−N) N cycles before the current time is divided by the feedback control air-fuel ratio abyfsc. This is because “a time corresponding to N cycles” is required until “the exhaust gas generated by the combustion of the air-fuel mixture in the combustion chamber 21” reaches the upstream air-fuel ratio sensor 56.

Step 1125: In accordance with the following equation (5), the CPU “target in-cylinder fuel supply amount Fcr (k) which is“ the amount of fuel that should have been supplied to the combustion chamber 21 at the time N cycles before the current time ”. -N) ". That is, the CPU obtains the target in-cylinder fuel supply amount Fcr (k−N) by dividing the in-cylinder intake air amount Mc (k−N) N cycles before the current by the target air-fuel ratio abyfr. Note that the target air-fuel ratio abyfr used in equation (5) is preferably the target air-fuel ratio abyfr (k−N) N cycles before the present time.

Fcr = Mc (k−N) / abyfr (5)

Step 1130: The CPU acquires the in-cylinder fuel supply amount deviation DFc according to the above equation (6). That is, the CPU obtains the in-cylinder fuel supply amount deviation DFc by subtracting the in-cylinder fuel supply amount Fc (k−N) from the target in-cylinder fuel supply amount Fcr (k−N). This in-cylinder fuel supply amount deviation DFc is an amount representing the excess or deficiency of the fuel supplied into the cylinder at the time point before the N stroke.

DFc = Fcr (k−N) −Fc (k−N) (6)

Step 1135: The CPU obtains the main feedback amount DFi according to the following equation (7). In this equation (7), Gp is a preset proportional gain, and Gi is a preset integral gain. Further, the “value SDFc” in the equation (7) is “an integral value of the in-cylinder fuel supply amount deviation DFc”. That is, the CPU calculates the “main feedback amount DFi” by proportional-integral control for making the feedback control air-fuel ratio abyfsc coincide with the target air-fuel ratio abyfr.

DFi = Gp · DFc + Gi · SDFc (7)

  Step 1140: The CPU adds the in-cylinder fuel supply amount deviation DFc obtained in the above step 1130 to the integral value SDFc of the in-cylinder fuel supply amount deviation DFc at that time, so that a new in-cylinder fuel supply amount deviation DFc is obtained. An integral value SDFc is obtained.

  As described above, the main feedback amount DFi is obtained by proportional integral control, and this main feedback amount DFi is reflected in the commanded fuel injection amount Fi by the processing of step 1050 in FIG.

  On the other hand, if the main feedback control condition is not satisfied at the time of determination in step 1105 of FIG. 11, the CPU determines “No” in step 1105 and proceeds to step 1145 to set the value of the main feedback amount DFi to “0”. To "". Next, in step 1150, the CPU stores “0” in the integral value SDFc of the in-cylinder fuel supply amount deviation. Thereafter, the CPU proceeds to step 1195 to end the present routine tentatively. Thus, when the main feedback control condition is not satisfied, the main feedback amount DFi is set to “0”. Accordingly, the basic fuel injection amount Fbase is not corrected by the main feedback amount DFi.

<Calculation of sub feedback amount and sub FB learning value>
The CPU executes the routine shown in FIG. 12 every elapse of a predetermined time in order to calculate the “sub feedback amount Vafsfb” and the “learning value (sub FB learning value) Vafsfbg of the sub feedback amount Vafsfb”. Therefore, when the predetermined timing comes, the CPU starts the process from step 1200 and proceeds to step 1205 to determine whether or not the sub feedback control condition is satisfied.

  The sub-feedback control condition is satisfied when all of the following conditions are satisfied. In this example, the sub feedback control condition and the sub feedback amount learning condition are the same. However, other conditions (conditions such as the load KL being within a predetermined range) may be added to the sub feedback control condition as the learning condition for the sub feedback amount.

(B1) The main feedback control condition is satisfied.
(B2) The downstream air-fuel ratio sensor 57 is activated.

  The description will be continued assuming that the sub-feedback control condition is satisfied. In this case, the CPU makes a “Yes” determination at step 1205 to sequentially perform the processing from step 1210 to step 1240 described below to calculate the sub feedback amount Vafsfb.

Step 1210: The CPU obtains “output deviation amount DVoxs” which is a difference between “downstream target value Voxsref” and “output value Voxs of downstream air-fuel ratio sensor 57” in accordance with the following equation (8). That is, the CPU obtains “output deviation amount DVoxs” by subtracting “current output value Voxs of downstream air-fuel ratio sensor 57” from “downstream target value Voxsref”. The downstream target value Voxsref is set to a reference air-fuel ratio (a value Vst (0.5 V) corresponding to the theoretical air-fuel ratio in this example).

DVoxs = Voxsref−Voxs (8)

  Step 1215: The CPU determines a gain K (predetermined adjustment value K, integral gain K). In the first control device, the gain K is set to a constant value.

Step 1220: The CPU updates the integration processing value SDVoxs (the output deviation amount integration processing value SDVoxs) based on the following equation (9). That is, the CPU adds a product (K · DVoxs) of the output deviation amount DVoxs obtained in step 1210 and the gain K (K · DVoxs) to the “integration processing value SDVoxs at the time of proceeding to step 1215”. The processing value SDVoxs is obtained (the integration processing value SDVoxs is updated.) That is, the integration processing value SDVoxs is a value (K corresponding to the deviation DVoxs between the output value Voxs of the downstream air-fuel ratio sensor 57 and the downstream target value Voxsref.・ DVoxs) is obtained by integrating

SDVoxs = SDVoxs + K · DVoxs (9)

  As understood from the above equation (9), the update amount per integration processing value SDVoxs is a value (K · DVoxs) obtained by multiplying the output deviation amount DVoxs by the gain K. In another embodiment, by changing the gain K, the update amount K · DVoxs per integration value SDVoxs is changed. When the gain K is changed, the changing speed of the “sub feedback amount and sub FB learning value” is changed.

Step 1225: The CPU follows the following equation (10) from “the output deviation amount DVoxs calculated in the above step 1210” to “the previous output deviation amount DVoxsold which is the output deviation amount calculated when this routine was executed last time”. By subtracting, a new differential value (time differential value) DDVoxs of the output deviation amount is obtained.

DDVoxs = DVoxs−DVoxsold (10)

Step 1230: The CPU obtains a sub feedback amount Vafsfb according to the following equation (11). In this equation (11), Kp is a preset proportionality constant, Ki is a preset integration constant, and Kd is a preset differential constant. In equation (11), Kp · DVoxs corresponds to a proportional term, Ki · SDVoxs corresponds to an integral term, and Kd · DDVoxs corresponds to a differential term. The differential term Kd · DDVoxs can be omitted.

Vafsfb = Kp · DVoxs + Ki · SDVoxs + Kd · DDVoxs (11)

  The sub feedback amount Vafsfb calculated in this way is determined so as to gradually increase when the output value Voxs is smaller than the downstream target value Voxsref (that is, when the output deviation amount DVoxs is positive). That is, when the air-fuel ratio indicated by the output value Voxs is an air-fuel ratio leaner than the air-fuel ratio indicated by the downstream target value Voxsref, the sub feedback amount Vafsfb increases. As the sub-feedback amount Vafsfb increases, the feedback control output value Vabyfc increases (see equation (2) and step 1110 in FIG. 11). That is, the feedback control output value Vabyfc is corrected to a “larger value (lean side value)”. As a result, the feedback control air-fuel ratio abyfsc increases (becomes a lean-side air-fuel ratio), so the engine air-fuel ratio is controlled to the rich side (smaller value) by main feedback control using the main feedback amount. The

  On the other hand, the sub feedback amount Vafsfb is determined so as to gradually decrease when the output value Voxs is larger than the downstream target value Voxsref. That is, when the air-fuel ratio indicated by the output value Voxs is richer than the air-fuel ratio indicated by the downstream target value Voxsref, the sub feedback amount Vafsfb decreases. When the sub feedback amount Vafsfb becomes smaller (becomes a negative value), the feedback control output value Vabyfc becomes smaller (see the above equation (2) and step 1110 in FIG. 11). That is, the feedback control output value Vabyfc is corrected to “a smaller value (a rich value)”. As a result, the air-fuel ratio for feedback control abyfsc becomes small (becomes the rich-side air-fuel ratio), so the main feedback control using the main feedback amount controls the engine air-fuel ratio to the lean side (a larger value). The

  Step 1235: The CPU stores “the output deviation amount DVoxs calculated in step 1210” as “the previous output deviation amount DVoxsold”.

  Step 1240: The CPU regulates the sub feedback amount Vafsfb within the guard width for sub feedback. That is, the CPU restricts the sub feedback amount Vafsfb to “a value between the upper limit value VlimitR of the sub feedback amount and the lower limit value VlimitL of the sub feedback amount” by executing the guard processing routine shown in FIG. The routine shown in FIG. 13 will be described later.

  Next, the CPU proceeds to step 1245 to determine the learning interval time Tth. In the first control device, the learning interval time Tth is set to a fixed time.

  Next, the CPU proceeds to step 1250 to determine whether or not the learning interval time Tth has elapsed since the last update time of the sub FB learning value Vafsfbg. At this time, if the learning interval time Tth has not elapsed since the last update of the sub FB learning value Vafsfbg, the CPU makes a “No” determination at step 1250 to directly proceed to step 1295 to end the present routine tentatively. .

  On the other hand, if the learning interval time Tth has elapsed since the last update of the sub FB learning value Vafsfbg at the time when the CPU executes the process of step 1250, the CPU determines “Yes” in step 1250. In step 1255, the product (Ki · SDVoxs) of the integration processing value SDVoxs and the integration constant Ki at that time is stored in the backup RAM as the sub FB learning value Vafsfbg.

  Thus, the CPU uses the steady component (integral term, steady term) Ki · SDVoxs of the sub feedback amount Vafsfb at the time when a period longer than the period in which the sub feedback amount Vafsfb is updated as the sub FB learning value Vafsfbg. take in.

  The integration processing value SDVoxs converges to a predetermined value (convergence value SDVoxs1) when the sub feedback control (that is, the update of the sub feedback amount Vafsfb) is stably performed over a sufficiently long period. In other words, the convergence value SDVoxs1 is a value corresponding to the stationary component of the sub feedback amount. The convergence value SDVoxs1 is, for example, a value reflecting an air amount measurement error of the air flow meter 51, an air-fuel ratio detection error of the upstream air-fuel ratio sensor 56, a degree of non-uniformity of the air-fuel ratio by cylinder, an alcohol concentration, and the like. .

  Next, the CPU proceeds to step 1260 to restrict the sub FB learning value Vafsfbg within the guard width for the sub FB learning value. That is, the CPU restricts the sub FB learning value Vafsfbg to “a value between the upper limit value VglimitR of the sub FB learning value and the lower limit value VglimitL of the sub FB learning value” by executing the guard processing routine shown in FIG. To do. The routine shown in FIG. 14 will be described later. Thereafter, the CPU proceeds to step 1295 to end the present routine tentatively.

  Through the above processing, the sub feedback amount Vafsfb and the sub FB learning value Vafsfbg are updated.

  On the other hand, if the sub feedback control condition is not satisfied, the CPU makes a “No” determination at step 1205 to proceed to step 1265 to set “the value of the sub FB learning value Vafsfbg” as the “sub feedback amount Vafsfb”. . As a result, when the sub feedback control condition is not satisfied, the sub feedback amount Vafsfb used in step 1110 of FIG. 11 matches the sub FB learning value Vafsfbg. Next, the CPU proceeds to step 1270 to set a value (Vafsfbg / Ki) obtained by dividing the sub feedback amount Vafsfb by the integration constant Ki as the integration processing value SDVoxs. Thereafter, the CPU proceeds to step 1295 to end the present routine tentatively. As described above, the main feedback control and the sub feedback control are executed.

<Guard processing of sub feedback amount>
As described above, when the CPU proceeds to step 1240 in FIG. 12, the CPU regulates the sub feedback amount Vafsfb within the “guard width for sub feedback” by executing the routine shown in FIG.

  That is, when the CPU proceeds to step 1240 in FIG. 12, the process starts from step 1300 in FIG. 13 and proceeds to step 1310. The upper limit value VlimitR of the sub feedback amount is calculated as “actual alcohol concentration Et and separately calculated. It is determined based on the “actual air-fuel ratio imbalance index value RIMB”. The upper limit value VlimitR of the sub feedback amount is also referred to as a rich correction side guard value VlimitR.

  More specifically, in step 1310, the CPU applies the actual alcohol concentration (ethanol concentration) Et and the actual air-fuel ratio imbalance index value RIMB to the look-up table described in step 1310. The upper limit value VlimitR is determined. According to this look-up table, the upper limit value VlimitR is determined such that it increases as the alcohol concentration (ethanol concentration in this example) Et increases, and increases as the air-fuel ratio imbalance index value RIMB increases. In addition, the numerical value described in the table in the block of step 1310 is an example.

  Next, the CPU proceeds to step 1320 to determine “whether the sub feedback amount Vafsfb is equal to or larger than the upper limit value VlimitR”. At this time, if the sub feedback amount Vafsfb is equal to or larger than the upper limit value VlimitR, the CPU proceeds to step 1330 to make the sub feedback amount Vafsfb coincide with the upper limit value VlimitR. As a result, the sub feedback amount Vafsfb is limited so as not to be larger than the upper limit value VlimitR.

  On the other hand, if the sub feedback amount Vafsfb is less than the upper limit value VlimitR at the time when the CPU executes the process of step 1320, the CPU proceeds to step 1340 and reads “the lower limit value VlimitL of the sub feedback amount is constant (in this example, -0.1) The lower limit value VlimitL is also referred to as a lean correction side guard value VlimitL.

  Next, the CPU proceeds to step 1350 to determine whether or not the sub feedback amount Vafsfb is less than or equal to the lower limit value VlimitL. At this time, if the sub feedback amount Vafsfb is less than or equal to the lower limit value VlimitL, the CPU proceeds to step 1360 to make the sub feedback amount Vafsfb coincide with the lower limit value VlimitL. As a result, the sub feedback amount Vafsfb is limited so as not to become smaller than the lower limit value VlimitL. Thereafter, the CPU proceeds to step 1395 to end the present routine tentatively.

  On the other hand, if the sub feedback amount Vafsfb is larger than the lower limit value VlimitL at the time when the CPU executes the process of step 1350, the CPU proceeds directly to step 1395 to end the present routine tentatively.

  As a result, the sub feedback amount Vafsfb is set to a value not less than the lower limit value VlimitL and not more than the upper limit value VlimitR.

<Guard processing of sub FB learning value>
As described above, when the CPU proceeds to step 1260 in FIG. 12, the CPU regulates the sub FB learning value Vafsfbg within the “guard width for the sub FB learning value” by executing the routine shown in FIG.

  That is, when the CPU proceeds to step 1260 in FIG. 12, the CPU starts the processing from step 1400 in FIG. 14 and proceeds to step 1410 to set the upper limit value VglimitR of the sub FB learning value as “actual alcohol concentration (ethanol concentration) Et and The actual air-fuel ratio imbalance index value RIMB calculated separately is determined.

  More specifically, in step 1410, the CPU applies the actual alcohol concentration Et and the actual air-fuel ratio imbalance index value RIMB to the lookup table described in step 1410, whereby the upper limit value VglimitR is applied. To decide. According to this lookup table, the upper limit value VglimitR is determined so as to increase as the alcohol concentration Et increases and to increase as the air-fuel ratio imbalance index value RIMB increases. It should be noted that the numerical values described in the table in the block in step 1410 are only examples, and further, “corresponding regions (alcohol concentration Et and air-fuel ratio imbalance index) described in the table in the block in step 1310 in FIG. (A region determined by the value RIMB) ”may be different (in general, each block of the table in step 1410 is set to a value smaller than the value in the corresponding block of the table in step 1310. .)

  Next, the CPU performs processing of a necessary step among steps 1420 to 1460 to limit the sub FB learning value Vafsfbg to “a value that is not less than the lower limit value VglimitL and not more than the upper limit value VglimitR”. That is, the sub FB learning value Vafsfbg is restricted within the guard width for the sub FB learning value. The upper limit value VglimitR is also called “rich correction side guard value VglimitR of the sub FB learning value”, and the lower limit value VglimitL is also called “lean correction side guard value VglimitL of the sub FB learning value”. The lower limit value VglimitL is a constant value (−0.1).

  Steps 1420 to 1460 are the same as steps 1320 to 1360 of FIG. Accordingly, a brief description will be given below.

  If the CPU determines in step 1420 that “the sub FB learning value Vafsfbg is equal to or higher than the upper limit value VglimitR”, the CPU proceeds to step 1430 to make the sub FB learning value Vafsfbg coincide with the upper limit value VglimitR. As a result, the sub FB learning value Vafsfbg is limited so as not to be larger than the upper limit value VglimitR.

  On the other hand, if the sub FB learning value Vafsfbg is less than the upper limit value VglimitR at the time when the CPU executes the process of step 1420, the CPU proceeds to step 1440 and “the lower limit value VglimitL of the sub FB learning value is constant (this example -0.1) is set.

  Next, the CPU proceeds to step 1450 and subsequent steps. If the sub FB learning value Vafsfbg is equal to or lower than the lower limit value VglimitL, the sub FB learning value Vafsfbg is matched with the lower limit value VglimitL in step 1460. As a result, the sub FB learning value Vafsfbg is limited so as not to become smaller than the lower limit value VglimitL.

<Acquisition of air-fuel ratio imbalance index value and air-fuel ratio imbalance determination between cylinders>
Next, a process for acquiring the air-fuel ratio imbalance index value will be described. The CPU executes the routine shown by the flowchart in FIG. 15 every time 4 ms (predetermined constant sampling time ts) elapses.

  Therefore, at a predetermined timing, the CPU starts the process from step 1500 and proceeds to step 1505 to determine whether or not the value of the parameter acquisition permission flag Xkyoka is “1”.

  The value of the parameter acquisition permission flag Xkyoka is “1” when a parameter acquisition condition (air-fuel ratio imbalance index acquisition permission condition) described later is satisfied when the absolute crank angle CA becomes 0 ° crank angle. And is immediately set to “0” when the parameter acquisition condition is not satisfied.

  The parameter acquisition condition is satisfied when all of the following conditions (conditions C1 to C5) are satisfied. Accordingly, the parameter acquisition condition is not satisfied when at least one of the following conditions (conditions C1 to C5) is not satisfied. Of course, the conditions constituting the parameter acquisition conditions are not limited to the following conditions C1 to C5.

(Condition C1) The intake air amount Ga acquired by the air flow meter 51 is within a predetermined range. That is, the intake air amount Ga is not less than the low threshold air flow rate GaLoth and not more than the high threshold air flow rate GaHith.
(Condition C2) The engine speed NE is within a predetermined range. That is, the engine rotational speed NE is equal to or higher than the low-side threshold rotational speed NELoth and equal to or lower than the high-side threshold rotational speed NEHith.
(Condition C3) Cooling water temperature THW is equal to or higher than threshold cooling water temperature THWth.
(Condition C4) The main feedback control condition is satisfied.
(Condition C5) Fuel cut control is not being performed.

  Assume that the value of the parameter acquisition permission flag Xkyoka is “1”. In this case, the CPU makes a “Yes” determination at step 1505 to proceed to step 1510 to acquire “the output value Vabyfs of the upstream air-fuel ratio sensor 56 at that time”.

  Next, the CPU proceeds to step 1520 to apply the output value Vabyfs acquired in step 1510 to the air-fuel ratio conversion table Mapabyfs shown in FIG. 5, thereby acquiring the current detected air-fuel ratio abyfs. Note that the CPU stores the detected air-fuel ratio abyfs acquired when this routine was executed last time as the previous detected air-fuel ratio abyfsold before the process of step 1515. That is, the previous detected air-fuel ratio abyfsold is the detected air-fuel ratio abyfs at a time point 4 ms (sampling time ts) before the current time. The initial value of the previous detected air-fuel ratio abyfsold is set to a value corresponding to the theoretical air-fuel ratio in the initial routine executed when the engine 10 is started.

Next, the CPU proceeds to step 1520, and
(A) Obtain the detected air-fuel ratio change rate ΔAF,
(B) updating the integrated value SAFD of the absolute value | ΔAF | of the detected air-fuel ratio change rate ΔAF;
(C) Update the integration number counter Cn of the absolute value | ΔAF | of the detected air-fuel ratio change rate ΔAF to the integrated value SAFD.
Hereinafter, these update methods will be described in detail.

(A) Acquisition of detected air-fuel ratio change rate ΔAF.
The detected air-fuel ratio change rate ΔAF (differential value d (abyfs) / dt) is data (basic index amount, basic parameter) that is the original data of the air-fuel ratio imbalance index value RIMB. The CPU obtains this detected air-fuel ratio change rate ΔAF by subtracting the previous detected air-fuel ratio abyfsold from the current detected air-fuel ratio abyfs. That is, if the detected air-fuel ratio abyfs this time is expressed as abyfs (n) and the previous detected air-fuel ratio abyfsold is expressed as abyfs (n-1), the CPU determines in step 1520 “current detected air-fuel ratio change rate ΔAF (n)”. Is obtained according to the following equation (12).

ΔAF (n) = abyfs (n) −abyfs (n−1) (12)

(B) Updating the integrated value SAFD of the absolute value | ΔAF | of the detected air-fuel ratio change rate ΔAF.
The CPU obtains the current integrated value SAFD (n) according to the following equation (13). That is, the CPU adds the absolute value | ΔAF (n) | of the detected air-fuel ratio change rate ΔAF (n) calculated this time to the previous integrated value SAFD (n−1) at the time of proceeding to Step 1520. Then, the integrated value SAFD is updated.

SAFD (n) = SAFD (n−1) + | ΔAF (n) | (13)

  The reason why “the absolute value of the detected air-fuel ratio change rate | ΔAF (n) |” is added to the integrated value SAFD is, as will be understood from FIGS. 8B and 8C, the detected air-fuel ratio change. This is because the rate ΔAF (n) can be a positive value or a negative value. The integrated value SAFD is also set to “0” in the above-described initial routine.

(C) Update of the integration number counter Cn to the integrated value SAFD of the absolute value | ΔAF | of the detected air-fuel ratio change rate ΔAF.
The CPU increases the value of the counter Cn by “1” according to the following equation (14). Cn (n) is the updated counter Cn, and Cn (n−1) is the updated counter Cn. The value of the counter Cn is set to “0” in the above-described initial routine, and is also set to “0” in step 1530 and step 1570 described later. Therefore, the value of the counter Cn indicates the number of data of the absolute value | ΔAF | of the detected air-fuel ratio change rate ΔAF integrated with the integrated value SAFD.

Cn (n) = Cn (n−1) +1 (14)

  Next, the CPU proceeds to step 1525 to determine whether or not the crank angle CA (absolute crank angle CA) based on the compression top dead center of the reference cylinder (first cylinder in this example) is a 720 ° crank angle. judge. At this time, if the absolute crank angle CA is less than the 720 ° crank angle, the CPU makes a “No” determination at step 1525 to directly proceed to step 1595 to end the present routine tentatively.

  Step 1525 is a step for determining a minimum unit period for obtaining the average value of the absolute values | ΔAF | of the detected air-fuel ratio change rate ΔAF. Here, “720 ° crank angle as a unit combustion cycle period” is set. This corresponds to the minimum period. Of course, this minimum period may be shorter than the 720 ° crank angle, but it is desirable that the minimum period be a period more than a multiple of the sampling time ts. Furthermore, it is desirable that the minimum period be a natural number times the unit combustion cycle period.

  On the other hand, if the absolute crank angle CA is 720 ° crank angle at the time when the CPU performs the process of step 1525, the CPU determines “Yes” in step 1525 and proceeds to step 1530.

At step 1530, the CPU
(D) calculating an average value AveΔAF of the absolute value | ΔAF | of the detected air-fuel ratio change rate ΔAF;
(E) update the integrated value Save of the average value AveΔAF, and
(F) Update the cumulative number counter Cs.
Hereinafter, these update methods will be described in detail.

(D) Calculation of the average value AveΔAF of the absolute value | ΔAF | of the detected air-fuel ratio change rate ΔAF.
The CPU calculates the average value AveΔAF of the absolute value | ΔAF | of the detected air-fuel ratio change rate ΔAF by dividing the integrated value SAFD by the value of the counter Cn, as shown in the following equation (15). Thereafter, the CPU sets the integrated value SAFD and the value of the counter Cn to “0”.

AveΔAF = SAFD / Cn (15)

(E) Update of the integrated value Save of the average value AveΔAF.
The CPU obtains the current integrated value Save (n) according to the following equation (16). That is, the CPU updates the integrated value Save by adding the calculated average value AveΔAF to the previous integrated value Save (n−1) at the time of proceeding to Step 1530. The value of the integrated value Save (n) is set to “0” in the above-described initial routine, and is also set to “0” in step 1565 described later.

Save (n) = Save (n−1) + AveΔAF (16)

(F) Update of the cumulative number counter Cs.
The CPU increases the value of the counter Cs by “1” according to the following equation (17). Cs (n) is the updated counter Cs, and Cs (n−1) is the updated counter Cs. The value of the counter Cs is set to “0” in the above-described initial routine, and is also set to “0” in step 1565 described later. Therefore, the value of the counter Cs indicates the number of data of the average value AveΔAF integrated with the integrated value Save.

Cs (n) = Cs (n−1) +1 (17)

  Next, the CPU proceeds to step 1535 to determine whether or not the value of the counter Cs is greater than or equal to the threshold value Csth. At this time, if the value of the counter Cs is less than the threshold value Csth, the CPU makes a “No” determination at step 1535 to directly proceed to step 1595 to end the present routine tentatively. Note that the threshold Csth is a natural number and is desirably 2 or more.

On the other hand, if the value of the counter Cs is equal to or greater than the threshold value Csth at the time when the CPU performs the process of step 1535, the CPU determines “Yes” in step 1535 and proceeds to step 1540. In step 1540, the CPU divides the integrated value Save by the value of the counter Cs (= Csth) according to the following equation (18) to obtain the air-fuel ratio imbalance index value RIMB (= air-fuel ratio fluctuation index amount AFD). get. The air-fuel ratio imbalance index value RIMB is a value obtained by averaging the average value AveΔAF in each unit combustion cycle period of the absolute value | ΔAF | of the detected air-fuel ratio change rate ΔAF for a plurality of (Csth) unit combustion cycle periods. The air-fuel ratio imbalance index value RIMB is also referred to as an imbalance determination parameter.

RIMB = AFD = Save / Csth (18)

Next, the CPU proceeds to step 1545, and stores (stores) the air-fuel ratio imbalance index value RIMB calculated in step 1540 in the backup RAM as a learned value RIMBgaku of the air-fuel ratio imbalance index value RIMB. The CPU calculates the weighted average of the learned value RIMBgaku (= RIMBgaku (n−1)) already stored in the backup RAM and the air-fuel ratio imbalance index value RIMB obtained this time according to the following equation (19). Then, the weighted average value RIMBgaku (n) may be stored in the backup RAM as a new learning value RIMBgaku. In the equation (19), β is a predetermined value greater than 0 and less than 1.

RIMBgaku (n) = β · RIMBgaku (n−1) + (1−β) · RIMB (19)

  Next, the CPU proceeds to step 1565 to set “each value used for calculating the air-fuel ratio imbalance index value RIMB (ΔAF, SAFD, Cn, AveΔAF, Save, Cs, etc.)” to “0”. (clear. Thereafter, the CPU proceeds to step 1595 to end the present routine tentatively.

  If the value of the parameter acquisition permission flag Xkyoka is not “1” when the CPU proceeds to step 1505, the CPU makes a “No” determination at step 1505 to proceed to step 1570. In step 1570, the CPU sets (clears) “each value used for calculating the average value AveΔAF (ΔAF, SAFD, Cn, etc.)” to “0”. Next, the CPU proceeds to step 1595 to end the present routine tentatively.

  The CPU may determine whether or not the air-fuel ratio imbalance among cylinders is occurring only once during one operation from when the engine 10 is started to when it is stopped. However, the CPU repeatedly updates the air-fuel ratio imbalance index value RIMB during one operation from when the engine 10 is started to when it is stopped.

As described above, the first control device
Detected air-fuel ratio abyfs acquired based on the output value Vabyfs of the upstream air-fuel ratio sensor 56 (the output value Vabyfs and the exhaust gas when the non-uniformity of the cylinder-by-cylinder air-fuel ratio does not occur and the alcohol concentration is “0”) The main feedback amount DFi for making the air / fuel ratio obtained by applying the actual output value Vabyfs in relation to the true air / fuel ratio equal to the predetermined target air / fuel ratio abyfr is “the detected air / fuel ratio abyfs and the target air / fuel ratio” main feedback control means (FIG. 11) determined based on “abyfr”,
The sub feedback amount Vafsfb for making the output value Voxs of the downstream air-fuel ratio sensor 57 coincide with the predetermined downstream target value Voxsref is integrated with at least “a value according to the deviation between the output value Voxs and the downstream target value Voxsref”. Is calculated based on the integration processing value SDVoxs obtained by the above (step 1220 in FIG. 12), and a learning value of the sub feedback amount (sub FB learning value Vafsfbg) is calculated based on the integration processing value SDVoxs (FIG. 12). And the calculated sub FB learning value Vafsfbg is restricted within a predetermined guard width (guard width of the sub FB learning value) (see step 1260 in FIG. 12 and FIG. 14). Sub-feedback control means (FIG. 12);
By correcting the amount of fuel injected from the fuel injection valve 33 based on the main feedback amount DFi, the sub feedback amount Vafsfb, and the sub FB learning value Vafsfbg, the indicated fuel injection amount Fi (each of the plurality of fuel injection valves 33) is corrected. Command fuel injection amount determination means (step 1050 in FIG. 10, step 1110 in FIG. 11, step 1230 and step 1265 in FIG. 12, etc.)
Injection instruction signal sending means for sending injection instruction signals to the plurality of fuel injection valves 33 so that an amount of fuel corresponding to the indicated fuel injection quantity Fi is injected from each of the plurality of fuel injection valves 33 (step of FIG. 10) 1060)
A fuel injection amount control device for an internal combustion engine comprising:
An air-fuel ratio imbalance index value RIMB that increases as the degree of non-uniformity among the plurality of cylinders of the air-fuel ratio by cylinder, which is the air-fuel ratio of the air-fuel mixture supplied to the respective combustion chambers of the plurality of cylinders, is acquired. Air-fuel ratio imbalance index value acquisition means (FIG. 15),
Alcohol concentration acquisition means (alcohol concentration sensor 59) for acquiring the alcohol concentration Et of the fuel;
Learning value guard width changing means for increasing the guard width (guard width of the sub FB learning value) as the acquired air-fuel ratio imbalance index value RIMB increases and increases as the acquired alcohol concentration Et increases. Step 1410) of FIG.
Is provided.

  Therefore, even when the alcohol concentration Et is high and the air-fuel ratio imbalance index value RIMB becomes large, the sub FB learning value Vafsfbg can reach a value that can compensate for the “lean miscorrection”. Deterioration can be avoided.

Note that the CPU may calculate the sub FB learning value Vafsfbg based on the sub feedback amount Vafsfb in step 1255 of FIG. In this case, for example, the CPU may obtain a weighted average of the sub feedback amount Vafsfb according to the following equation (20), and acquire the weighted average value as the sub FB learning value Vafsfbg. That is, the sub FB learning value Vafsfbg may be a value corresponding to the steady component of the sub feedback amount Vafsfb. In equation (20), the value γ (weighting coefficient γ) is a predetermined value greater than 0 and less than 1, Vafsfbg (n) is the updated sub FB learning value Vafsfbg, and Vafsfbg (n−1) is the sub FB learning before update. The values Vafsfbg and Vafsfb (n) are the sub-feedback amounts Vafsfb newly calculated in step 1230 of FIG.

Vafsfbg (n) = (1-γ) · Vafsfbg (n−1) + γ · Vafsfb (n) (20)

  Further, the first control device sets the “limit value for correcting the air-fuel ratio of the engine 10 to the rich side” of the sub-feedback amount Vafsfb and the sub-FB learning value Vafsfbg as the alcohol concentration Et becomes higher and the air-fuel ratio imbalance index. It can be said that the larger the value RIMB, the larger.

<Second Embodiment>
Next, a control device (hereinafter simply referred to as “second control device”) according to a second embodiment of the present invention will be described.

  The change rate of the sub FB learning value (sub FB learning value update rate) is generally set to be relatively small for the purpose of preventing erroneous learning. However, if fuel with a high alcohol concentration is supplied and immediately after that, the degree of non-uniformity of the cylinder-by-cylinder air-fuel ratio increases, the sub-FB learning value must change greatly. Accordingly, even if the guard width of the sub FB learning value is increased, it takes a long time for the sub FB learning value to reach the appropriate value, and thus the sub FB learning value may not reach the appropriate value. For example, if the operation of the engine 10 is terminated before the sub FB learning value reaches the appropriate value, the learning value when the engine 10 is started next deviates from the appropriate value, so that the emission deteriorates. .

  Therefore, the second control device increases the change rate of the sub FB learning value as the air-fuel ratio imbalance index value RIMB increases, and increases the change rate of the sub FB learning value as the alcohol concentration Et increases. The change rate of the sub FB learning value is changed.

(Actual operation)
The CPU of the second control device executes the routines shown in FIGS. Further, the CPU of the second control device executes an “integral gain determination routine” shown in FIG. 16 when the processing proceeds to step 1215 in FIG. The routines shown in FIGS. 10 to 15 have been described. Accordingly, the routine shown in FIG. 16 will be described below.

  When the CPU proceeds to step 1215 in FIG. 12, the CPU starts processing from step 1600 in FIG. 16, proceeds to step 1610, and determines a gain K (integral gain K). More specifically, the CPU applies the “actual alcohol concentration (ethanol concentration) Et and the actual air-fuel ratio imbalance index value RIMB” to the look-up table described in step 1610 to thereby obtain the gain K. decide.

  According to this look-up table, the gain K is calculated so that the gain K increases as the alcohol concentration Et increases, and the gain K increases as the air-fuel ratio imbalance index value RIMB increases. Thereafter, the CPU proceeds to step 1220 and subsequent steps in FIG.

  As described above, the update amount per integration processing value SDVoxs is a value (K · DVoxs) obtained by multiplying the output deviation amount DVoxs by the gain K (see step 1220 in FIG. 12). Therefore, when the gain K increases, the update amount K · DVoxs per integration value SDVoxs increases. On the other hand, the sub feedback amount Vafsfb includes an integral term that is a product of the integral processing value SDVoxs and the integral constant Ki. The sub FB learning value Vafsfbg is a product of the integration processing value SDVoxs and the integration constant Ki. Therefore, when the gain K is changed, the changing speed of the sub feedback amount Vafsfb and the changing speed of the sub FB learning value Vafsfbg are increased.

  As a result, the sub feedback amount Vafsfb and the sub FB learning value Vafsfbg can quickly approach appropriate values. Therefore, even when the alcohol concentration Et is high and the degree of non-uniformity of the cylinder-by-cylinder air-fuel ratio becomes large, the engine air-fuel ratio (exhaust gas air-fuel ratio) is determined by the sub feedback amount Vafsfb and / or the sub FB learning value Vafsfbg. Can be brought close to an appropriate value.

As described above, the sub feedback control means of the second control device is
The change rate of the sub FB learning value Vafsfbg increases as the acquired air-fuel ratio imbalance index value RIMB increases, and the change rate of the sub FB learning value Vafsfbg increases as the acquired alcohol concentration Et increases. The change rate of the sub FB learning value Vafsfbg is changed (see step 1215, step 1220 and FIG. 16 in FIG. 12).

Further, the sub-feedback control means
The deviation (output deviation) is used as a “value according to the deviation (output deviation amount DVoxs) between the output value Voxs of the downstream air-fuel ratio sensor 57 and the downstream target value Voxsref” used to calculate the sub feedback amount Vafsfb. Value (DVoxs) multiplied by a predetermined gain K (integrated value SDVoxs = K · DVoxs)
The gain K is set to a larger value as the actual air-fuel ratio imbalance index value RIMB is larger, and the gain K is set to a larger value as the acquired actual alcohol concentration Et is higher. The change rate of the learning value Vafsfbg is changed (FIG. 16).

  The second control device changes the change rate of the sub FB learning value Vafsfbg by changing the learning interval time Tth instead of changing the integral gain K or in addition to changing the integral gain K. May be.

  That is, in this case, when the CPU of the second controller proceeds to step 1245 in FIG. 12, the learning interval time Tth is set based on “the actual alcohol concentration Et and the actual air-fuel ratio imbalance index value RIMB”. More specifically, the CPU of the second control device sets the learning interval time Tth to be shorter as the actual alcohol concentration Et becomes higher, and the learning interval time Tth as the actual air-fuel ratio imbalance index value RIMB becomes larger. Set to short.

  As a result, the sub FB learning value Vafsfbg becomes closer (set) to the changing “output deviation amount DVoxs multiplied by the gain K (K · DVoxs)”, and the time interval becomes short, so the sub FB learning value Vafsfbg The rate of change of can be increased.

  Further, when the sub FB learning value Vafsfbg is calculated according to the above equation (20), the CPU sets the “weighting factor γ” to a larger value as the actual air-fuel ratio imbalance index value RIMB increases, and The change rate of the sub FB learning value Vafsfbg may be changed (increased) by setting the “weighting factor γ” to a larger value as the acquired actual alcohol concentration Et is higher.

<Third Embodiment>
Next, a control device (hereinafter simply referred to as “third control device”) according to a third embodiment of the present invention will be described.

  As described above, the guard width of the sub feedback amount Vafsfb is expanded, the guard width of the sub FB learning value Vafsfbg is expanded, and the change rate of the sub feedback amount Vafsfb and / or the sub FB learning value Vafsfbg is increased. Accordingly, the sub feedback amount Vafsfb and / or the sub FB learning value Vafsfbg approaches the appropriate values. Therefore, it is possible to avoid the occurrence of lean erroneous control.

  However, when the intake air amount Ga of the engine 10 increases, a large amount of hydrogen is generated, and the output value of the upstream air-fuel ratio sensor 56 shifts to a “richer value”. This is presumably because the catalyst unit 566 of the upstream air-fuel ratio sensor 56 cannot sufficiently process (oxidize) the hydrogen generated in a large amount when the intake air amount is large.

  Therefore, when the intake air amount is large (in the high intake air amount region), the lean feedback control may not be suppressed even with the sub feedback amount Vafsfb and / or the sub FB learning value Vafsfbg, and the emission may deteriorate. In particular, when the intake air amount Ga suddenly increases, the “state in which the sub feedback amount Vafsfb and / or the sub FB learning value Vafsfbg deviates from their appropriate values” continues, so the emission is large. Sometimes it gets worse.

  Therefore, the third control device determines that the higher the intake air amount Ga, the larger the air-fuel ratio imbalance index value RIMB, and the higher the alcohol concentration Et, the “upstream target air-fuel ratio used for main feedback control”. “Set abyfr to a small air-fuel ratio” or “correct the detected air-fuel ratio abyfs to a large air-fuel ratio (that is, increase the feedback control air-fuel ratio abyfsc)”. Thus, even when the intake air amount Ga is large, the true air-fuel ratio of the exhaust gas obtained as a result of the main feedback control becomes the air-fuel ratio in the “window of the upstream catalyst 43”. Can further reduce the possibility of worsening of emissions.

(Actual operation)
The CPU of the third control device executes the routines shown in FIGS. Further, the CPU of the third control device executes the “target air-fuel ratio determination routine” shown in FIG. 17 when the routine proceeds to step 1030 in FIG. The routines shown in FIGS. 10 to 16 have been described. Accordingly, the routine shown in FIG. 17 will be described below.

  When the CPU proceeds to step 1030 in FIG. 10, the CPU starts processing from step 1700 in FIG. 17 and proceeds to step 1710 to determine the target air-fuel ratio correction amount daf. More specifically, the CPU applies the “actual intake air amount Ga and the actual air-fuel ratio imbalance index value RIMB” to the look-up table described in step 1710, so that the target air-fuel ratio correction amount daf Is calculated.

According to this lookup table, the target air-fuel ratio correction amount daf is determined as follows.
The target air-fuel ratio correction amount daf increases as the intake air amount Ga increases.
The target air-fuel ratio correction amount daf increases as the air-fuel ratio imbalance index value RIMB increases.
The target air-fuel ratio correction amount daf is set to “0” in the low intake air amount region.
The target air-fuel ratio correction amount daf is set to “0” when the air-fuel ratio imbalance index value RIMB is substantially “0”.

  Next, the CPU proceeds to step 1720 to acquire the alcohol concentration correction value kET. More specifically, the CPU calculates the alcohol concentration correction value kET by applying “actual alcohol concentration Et (ethanol concentration in this example)” to the lookup table described in step 1720.

  According to this lookup table, the alcohol concentration correction value kET is calculated so as to increase as the alcohol concentration Et increases.

  Next, the CPU proceeds to step 1730, where a value obtained by subtracting the “product of the target air-fuel ratio correction amount daf and the alcohol concentration correction value kET (kET · daf)” from the “theoretical air-fuel ratio stoich which is the reference air-fuel ratio” Adopted as the target air-fuel ratio abyfr. When the sub feedback amount and the sub FB learning value are used to correct the target air-fuel ratio abyfr, the value obtained by subtracting the product (kET · daf) from the target air-fuel ratio corrected by them is Set as air-fuel ratio abyfr. Thereafter, the CPU proceeds to step 1030 in FIG. This target air-fuel ratio abyfr is also used in step 1125 of FIG. Therefore, step 1730 (FIG. 17) corresponds to the enrichment means.

As a result, the target air-fuel ratio abyfr is changed as follows.
The target air-fuel ratio abyfr decreases as the intake air amount Ga increases (the richer air-fuel ratio is set) so that the absolute value of the difference from the stoichiometric air-fuel ratio stoich increases.
The target air-fuel ratio abyfr decreases as the air-fuel ratio imbalance index value RIMB increases so that the absolute value of the difference from the stoichiometric air-fuel ratio stoich increases (set to a richer air-fuel ratio) .)
The target air-fuel ratio abyfr decreases as the alcohol concentration Et increases (the richer air-fuel ratio is set) so that the absolute value of the difference from the stoichiometric air-fuel ratio stoich increases.

  Therefore, the command fuel injection amount Fi is increased by the amount corresponding to the increase in the intake air amount Ga as the intake air amount Ga increases (the indicated fuel that increases based on the increase in the intake air amount Ga when the target air-fuel ratio abyfr is constant). It increases by an amount larger than the increase amount of the injection amount Fi) and increases as the air-fuel ratio imbalance index value RIMB and / or alcohol concentration Et increases. As a result, the commanded air-fuel ratio determined by the intake air amount Ga and the commanded fuel injection amount Fi increases as the intake air amount Ga increases, the air-fuel ratio imbalance index value RIMB increases, and the alcohol concentration Et increases. Modified to be smaller.

  Accordingly, since the command fuel injection amount Fi is appropriately controlled according to the intake air amount Ga, the degree of non-uniformity of the cylinder-by-cylinder air-fuel ratio, and the alcohol concentration, the lean erroneous correction is reliably avoided, and the nitrogen oxidation It is possible to avoid an increase in the amount of discharged materials.

  Note that the third control device uses the detected air-fuel ratio (feedback control output value Vabyfc) used for the main feedback control instead of correcting the target air-fuel ratio abyfr as “the intake air amount Ga, the air-fuel ratio imbalance index value RIMB”. The target air-fuel ratio may be substantially changed to a smaller value by performing correction so that the larger the “alcohol concentration Et” becomes, the larger the air-fuel ratio becomes.

<Fourth embodiment>
Next, a control device according to a fourth embodiment of the present invention (hereinafter simply referred to as “fourth control device”) will be described. The fourth control device uses the same electromotive force type oxygen concentration sensor as the upstream air-fuel ratio sensor 56 (a well-known concentration cell type oxygen concentration sensor using a solid electrolyte such as stabilized zirconia). Is different from the first control device in that it is used.

  As described above, the electromotive force type oxygen concentration sensor also includes a porous layer. Therefore, when the electromotive force type oxygen concentration sensor is disposed “between the exhaust collecting portion HK and the upstream side catalyst 43”, the output value Voxs of the electromotive force type oxygen concentration sensor is obtained by selectively diffusing hydrogen. to be influenced. For this reason, as shown in FIG. 18, the output value Voxs with respect to the true air-fuel ratio of the exhaust gas changes according to the alcohol concentration. Furthermore, as shown in FIG. 19, the output value Voxs with respect to the true air-fuel ratio of the exhaust gas changes according to the degree of non-uniformity of the cylinder-by-cylinder air-fuel ratio.

  In general, when an electromotive force type oxygen concentration sensor is used as an “upstream air-fuel ratio sensor for main feedback control”, an output value Voxs is “a value Vst corresponding to the reference air-fuel ratio (for example, theoretical air-fuel ratio)”. The air-fuel ratio feedback control is executed so as to coincide with the target value Vref set to “. That is, the main feedback amount DFi is calculated so that the value corresponding to the detected air-fuel ratio acquired based on the output value Voxs matches the value corresponding to the target air-fuel ratio.

  Therefore, as the degree of non-uniformity of the alcohol concentration and / or the air-fuel ratio by cylinder increases, the average of the true air-fuel ratio of the exhaust gas obtained as a result of the main feedback control becomes an air-fuel ratio leaner than the reference air-fuel ratio. It will move to. That is, lean miscontrol occurs.

  Therefore, the fourth control device increases the guard width of the sub feedback amount Vafsfb “as the alcohol concentration Et is higher and as the air-fuel ratio imbalance index value RIMB is larger”, as in the first control device. Further, as in the first control device, the fourth control device increases the guard width of the sub FB learning value “as the alcohol concentration Et is higher and as the air-fuel ratio imbalance index value RIMB is larger”. Further, the fourth control device changes the changing speed of the sub feedback amount Vafsfb and the changing speed of the sub FB learning value Vafsfbg, similarly to the second control device.

The CPU of the fourth control device executes main feedback control as follows. In other words, the fourth control device sets the target value Vref (for example, Vst = Vst = the output value Voxs of the electromotive force oxygen concentration sensor disposed at the position of the upstream air-fuel ratio sensor 56 to a value corresponding to the target air-fuel ratio abyfr. The main feedback amount DFi is obtained according to the following equation (21) so as to coincide with 0.5V). In the equation (21), Kpp is a preset proportional constant, Kii is a preset integral constant, and Kdd is a preset differential constant. The output deviation amount Ds is “a value obtained by subtracting the output value Voxs from the target value Vref”. SDs is an integral value of the output deviation amount Ds, and DDs is a differential value of the output deviation amount Ds.

DFi = Kpp / Ds + Kii / SDs + Kdd / DDs (21)

  As described above, the CPU performs proportional / integral / differential (PID) control for matching the output value Voxs of the electromotive force type oxygen concentration sensor disposed at the position of the upstream air-fuel ratio sensor 56 with the target value Vref. The “main feedback amount DFi” is obtained. This main feedback amount DFi is used in step 1050 of FIG. The CPU of the fourth control device determines the air-fuel ratio imbalance index based on the differential value d (Voxs) dt of the output value Voxs of the electromotive force type oxygen concentration sensor disposed at the position of the upstream air-fuel ratio sensor 56. Get the value RIMB.

<Fifth Embodiment>
Next, a control device according to a fifth embodiment of the present invention (hereinafter simply referred to as “fifth control device”) will be described. The fifth control device uses the learning value RIMBgaku of the air-fuel ratio imbalance index value (hereinafter also simply referred to as “index learning value RIMBgaku”) in place of the air-fuel ratio imbalance index value RIMB to “sub-feedback amount Vafsfb of It differs from the first control device in that the guard width (actually the upper limit value VlimitR of the sub feedback amount Vafsfb) and the guard width of the sub FB learning value (actually the upper limit value VglimitR of the sub FB learning value) are determined. .

  Further, the fifth control apparatus obtains the index learning value RIMBgaku as follows. The index learning value RIMBgaku is also referred to as a corrected air-fuel ratio imbalance index value RIMBgaku.

(1) The fifth control device uses the time differential value d (abyfs) / dt of the detected air-fuel ratio abyfs as a basic value (basic index value or basic parameter) for obtaining the corrected air-fuel ratio imbalance index value RIMBgaku. (That is, the detected air-fuel ratio change rate ΔAF) is obtained (see the above equation (12)). The basic parameters are the second-order differential value d ² (abyfs) / dt ² of the detected air-fuel ratio abyfs, the time differential value d (Vabyfs) / dt of the output value Vabyfs of the upstream air-fuel ratio sensor 56, and the output value Vabyfs. The second order differential value d ² (Vabyfs) / dt ² , etc. may be used, and the average value AveΔAF of these values in the unit combustion cycle period may be used.

(2) The fifth control device, like the first control device, sets the average value AveΔAF in each unit combustion cycle period of the absolute value | ΔAF | of the detected air-fuel ratio change rate ΔAF to a plurality (Csth) of unit combustion cycle periods. To obtain the basic air-fuel ratio imbalance index value RIMBb (see the above equation (18)). The basic air-fuel ratio imbalance index value RIMBb is a value having a correlation with the basic parameter, and is also referred to as “basic parameter correlation value RIMBb”. Furthermore, since the basic air-fuel ratio imbalance index value RIMBb is a value before correction described later, it is also referred to as “pre-correction air-fuel ratio imbalance index value RIMBb”.

(3) The fifth control device sets the basic air-fuel ratio imbalance index value RIMBb (basic parameter correlation value) to “the basic air-fuel ratio imbalance index value RIMBb (value corresponding to the basic parameter), engine speed NE (according to engine speed). The index learning value RIMBgaku is obtained by performing correction based on the value), the intake air amount Ga (value corresponding to the intake air amount Ga), and the alcohol concentration Et ”.

  As described above, the reason why the basic air-fuel ratio imbalance index value RIMBb is corrected based on the “basic air-fuel ratio imbalance index value RIMBb, engine speed NE and intake air amount Ga” is that the non-uniformity of the air-fuel ratio by cylinder is Even if the degree (imbalance ratio) is “a certain value”, the detected air-fuel ratio change rate ΔAF (and hence the basic air-fuel ratio imbalance index value RIMBb), which is a basic parameter, is “engine speed NE and intake air amount Ga”. It is because it fluctuates according to. Furthermore, if the degree of non-uniformity of the cylinder-by-cylinder air-fuel ratio differs, the degree of influence of the “engine speed NE and intake air amount Ga” on the basic air-fuel ratio imbalance index value RIMBb changes.

  The reason why the basic air-fuel ratio imbalance index value RIMBb is corrected based on the alcohol concentration Et is that, as the alcohol concentration Et is higher, the amount of hydrogen generated increases, and as shown in FIG. This is because even if the degree of uniformity is “a certain value”, the detected air-fuel ratio change rate ΔAF varies according to the alcohol concentration Et.

(Actual operation)
Hereinafter, the operation of the fifth control device will be described. The CPU of the fifth control device executes the routines shown in FIGS. 10 to 14 in the same manner as the CPU of the first control device. However, the CPU of the fifth control device replaces the air-fuel ratio imbalance index value RIMB with the index learning value RIMBgaku (that is, the corrected air-fuel ratio imbalance index value RIMBgaku in Step 1310 in FIG. 13 and Step 1410 in FIG. 14). ) Is applied to each lookup table to obtain each guard value (upper limit value VlimitR and upper limit value VglimitR).

  Further, the CPU of the fifth control device executes the routine shown in FIG. 21 instead of FIG. 15 every time 4 ms (predetermined constant sampling time ts) elapses. Of the steps shown in FIG. 21, steps for performing the same processing as those already described are denoted by the same reference numerals as those already described. Detailed description of these steps will be omitted as appropriate.

  When the CPU proceeds to step 1535 in FIG. 21 when the value of the counter Cs becomes equal to or greater than the threshold value Csth, the CPU makes a “Yes” determination at step 1535 and sequentially executes the processing from step 2110 to step 2150 described below. Do.

Step 2110: The CPU obtains a basic air-fuel ratio imbalance index value RIMBb (= basic parameter correlation value) by dividing the integrated value Save by the value of the counter Cs (= Csth) according to the following equation (22). The basic air-fuel ratio imbalance index value RIMBb is a value obtained by averaging the average value AveΔAF in each unit combustion cycle period of the absolute value | ΔAF | of the detected air-fuel ratio change rate ΔAF for a plurality of (Csth) unit combustion cycle periods. .

RIMBb = Save / Csth (22)

  Step 2120: The CPU applies the “engine speed NE, intake air amount Ga, and basic air-fuel ratio imbalance index value RIMBb” to the look-up table MapK1 (NE, Ga, RIMBb), thereby setting the first correction coefficient K1. get.

  22 and 23 show examples of the lookup table MapK1 (NE, Ga, RIMBb). The table shown in FIG. 22 defines the relationship between the intake air amount Ga, the basic air-fuel ratio imbalance index value RIMBb, and the first correction coefficient K1 when the engine speed NE is 1800 rpm. The table shown in FIG. 23 defines the relationship between the intake air amount Ga, the basic air-fuel ratio imbalance index value RIMBb, and the first correction coefficient K1 when the engine speed NE is 2000 rpm. As described above, the table MapK1 (NE, Ga, RIMBb) is a table that defines the “relationship between the intake air amount Ga and the basic air-fuel ratio imbalance index value RIMBb and the first correction coefficient K1”. It is prepared for each.

  According to the table MapK1 (NE, Ga, RIMBb), the first correction coefficient K1 increases as the engine speed NE increases, decreases as the intake air amount Ga increases, and the basic air-fuel ratio imbalance index value RIMBb increases. It is required to become smaller. As will be described later, the learned index value RIMBgaku is calculated by multiplying the basic air-fuel ratio imbalance index value RIMBb by “first correction coefficient K1 and second correction coefficient K2 described later” (see step 2140 in FIG. 21). .) Therefore, the CPU determines that the basic air-fuel ratio imbalance index value RIMBb is “higher as the engine speed NE is higher, and smaller as the intake air amount Ga is larger, and the basic air-fuel ratio imbalance index value RIMBb is the first correction coefficient K1. The index learning value RIMBgaku is calculated by correcting the basic air-fuel ratio imbalance index value RIMBb so that it decreases as the value increases.

  This is an example, and the relationship between the “first correction coefficient K1” and the “engine speed NE, intake air amount Ga, and basic air-fuel ratio imbalance index value RIMBb” is that the alcohol concentration Et is a predetermined constant value. If the degree of non-uniformity (imbalance ratio) of cylinder-by-cylinder air-fuel ratio is “a certain value” in some cases, “engine speed NE, intake air amount Ga, and basic air-fuel ratio imbalance index value RIMBb” change. Even so, the “basic air-fuel ratio imbalance index value RIMBb corrected by the first correction coefficient K1 (that is, the index learning value RIMBgaku)” is determined by experiments so that it is always substantially the same value. Of course, a function having NE, Ga, and RIMBb as variables may be obtained in advance, and the CPU may acquire the first correction coefficient K1 using the function.

  Step 2130: The CPU obtains the second correction coefficient K2 by applying the alcohol concentration Et to the lookup table MapK2 (Et) shown in FIG. According to this table MapK2 (Et), the second correction coefficient K2 is determined so as to decrease as the alcohol concentration Et increases.

  As described above, the learned index value RIMBgaku is calculated by multiplying the basic air-fuel ratio imbalance index value RIMBb by the first correction coefficient K1 and the second correction coefficient K2 (see step 2140). Therefore, the CPU calculates the index learning value RIMBgaku by correcting the basic air-fuel ratio imbalance index value RIMBb so that the higher the alcohol concentration Et is, the smaller the basic air-fuel ratio imbalance index value RIMBb is. To do.

  Note that the table shown in FIG. 24 is an example, and the relationship between the second correction coefficient K2 and the alcohol concentration Et is such that “the engine speed NE, the intake air amount Ga, and the basic air-fuel ratio imbalance index value RIMBb” are predetermined. If the degree of non-uniformity (imbalance ratio) of the cylinder-by-cylinder air-fuel ratio is “a certain value”, even if the alcohol concentration Et changes, “the basic sky corrected by the second correction coefficient K2”. The fuel ratio imbalance index value RIMBb (that is, the index learning value RIMBgaku) is determined by experiments so that it is always substantially the same value. In other words, the relationship between the second correction coefficient K2 and the alcohol concentration Et is that if the degree of non-uniformity (imbalance ratio) of the air-fuel ratio by cylinder is “a certain value”, the first correction coefficient K1 and the second correction coefficient K1. The basic air-fuel ratio imbalance index value RIMBb (that is, the index learning value RIMBgaku) corrected by the coefficient K2 is determined by experiments so that it is always substantially the same value. A function having the alcohol concentration Et as a variable may be obtained in advance, and the CPU may acquire the second correction coefficient K2 using the function.

Step 2140: The CPU corrects the basic air-fuel ratio imbalance index value RIMBb based on the first correction coefficient K1 and the second correction coefficient K2 according to the following equation (23) to obtain a corrected value RIMBc. That is, the CPU obtains the corrected value RIMBc by multiplying the basic air-fuel ratio imbalance index value RIMBb by the first correction coefficient K1 and the second correction coefficient K2.

RIMBc = K1, K2, RIMBb (23)

Step 2150: The CPU stores the corrected value RIMBc as the index learned value RIMBgaku. That is, the CPU acquires the index learning value RIMBgaku based on the corrected value RIMBc. The index learning value RIMBgaku is stored in the backup RAM. The CPU may calculate the index learning value RIMBgaku according to the following equation (24). The index learning value RIMBgaku (n) on the left side of the equation (24) is the updated index learning value RIMBgaku, and the index learning value RIMBgaku (n−1) on the right side of the equation (24) is the index learning value RIMBgaku before the update. is there. In the equation (24), δ is a constant larger than 0 and smaller than 1.

RIMBgaku (n) = (1-δ) · RIMBgaku (n−1) + δ · RIMBc (24)

  Thereafter, the CPU proceeds to step 2195 via step 1565. As described above, the index learning value RIMBgaku is acquired. As described above, this index learning value RIMBgaku is used in place of the air-fuel ratio imbalance index value RIMB in step 1310 in FIG. 13 and step 1410 in FIG.

  As described above, the fifth control apparatus acquires the differential value d (abyfs) / dt (detected air-fuel ratio change rate ΔAF) with respect to the time of the detected air-fuel ratio abyfs as a basic parameter (step 1520 in FIG. 21). reference.). This basic parameter is a value that increases as the fluctuation of the air-fuel ratio of the exhaust gas that passes through the position where the upstream air-fuel ratio sensor 56 is disposed increases. Then, the fifth control device sets the average value of the detected air-fuel ratio change rate ΔAF, which is a basic parameter (that is, a value correlated with the basic parameter) as a “basic air-fuel ratio imbalance index value RIMBb as a basic parameter correlation value”. (See Steps 1520 to 1535 and Step 2110 in FIG. 21).

  Further, the fifth control device sets a basic air-fuel ratio imbalance index value RIMBb (basic parameter when the counter threshold Csth is “1”), which is a basic parameter correlation value, to “a basic air-fuel ratio non-uniformity that is a value corresponding to the basic parameter”. Correction based on the equilibrium index value RIMBb, engine speed NE, and intake air amount Ga ”(refer to Step 2120 to Step 2140), and the corrected air-fuel ratio non-correction based on the corrected value RIMBc obtained by the correction. An equilibrium index value (= index learning value RIMBgaku) is acquired (see step 2150).

  Therefore, the corrected air-fuel ratio imbalance index value (index learning value RIMBgaku) is a value from which the influence of the intake air amount Ga, the engine speed NE, and the alcohol concentration Et is excluded, and therefore, a plurality of air-fuel ratios for each cylinder are set. Expresses the degree of non-uniformity (imbalance ratio) between cylinders with high accuracy. As a result, the “upper limit value VlimitR and upper limit value VglimitR” acquired based on the index learning value RIMBgaku becomes a value corresponding to the true imbalance ratio. As a result, the guard width of the sub feedback amount Vafsfb and the guard width of the sub FB learning value Vafsfbg become appropriate widths according to the true imbalance ratio. Therefore, even when the imbalance ratio increases, the sub feedback amount Vafsfb and the sub FB learning value Vafsfbg can be changed to appropriate values, so that the emission can be maintained well. Furthermore, it is possible to avoid the possibility that the sub feedback amount Vafsfb and the sub FB learning value Vafsfbg become inappropriate values when the imbalance ratio is small.

The first correction coefficient K1 and the second correction coefficient K2 can be obtained as one correction coefficient Kt (that is, a value corresponding to K1 · K2). In this case, the look-up table MapKt (NE, Ga, RIMBb, Et) may be used, and the correction coefficient Kt may be obtained by a function having NE, Ga, RIMBb, Et as variables. The simplest example of this function is shown in the following equation (25). In equation (25), a1, a2, a3, and a4 are coefficients, which may be constant values, and are obtained by a function having at least one of NE, Ga, RIMBb, and Et as a variable. It may be a value.

Kt = a1 · NE + a2 · Ga + a3 · RIMBb + a4 · Et (25)

<Sixth Embodiment>
Next, a control device according to a sixth embodiment of the present invention (hereinafter simply referred to as “sixth control device”) will be described. The sixth control device acquires the index learning value RIMBgaku in the same manner as the fifth control device. Then, the correction amount daf of the target air-fuel ratio abyfr is determined by regarding the index learning value RIMBgaku as the air-fuel ratio imbalance index value RIMB. Further, the correction amount daf is corrected based on the alcohol concentration Et, and the target air-fuel ratio abyfr is corrected (determined) based on the corrected correction amount K3 · daf.

(Actual operation)
The CPU of the sixth control device executes the routines shown in FIGS. 10 to 14 and FIG. Further, the CPU of the sixth control device executes a “target air-fuel ratio determination routine” shown in FIG. 25 when the routine proceeds to step 1030 in FIG. The routines shown in FIGS. 10 to 14 and FIG. 21 have been described. Therefore, the routine shown in FIG. 25 will be described below.

  When the CPU proceeds to step 1030 in FIG. 10, the CPU starts processing from step 2500 in FIG. 25 and proceeds to step 2510 to determine the target air-fuel ratio correction amount daf. More specifically, the CPU sets the “intake air amount Ga and the index learning value RIMBgaku obtained in step 2150 of FIG. 21 (that is, the corrected value RIMBc) in the lookup table described in step 2510. ) "Is applied to calculate the target air-fuel ratio correction amount daf. This lookup table is the same table as the lookup table shown in Step 1710 of FIG.

  Next, the CPU proceeds to step 2520 to acquire an alcohol concentration correction value (third correction coefficient) K3. More specifically, the CPU calculates the alcohol concentration correction value K3 by applying “actual alcohol concentration Et (ethanol concentration in this example)” to the lookup table described in step 2520.

  According to this lookup table, the alcohol concentration correction value K3 is calculated to be smaller as the alcohol concentration Et is higher.

  Next, the CPU proceeds to step 2530, in which the value obtained by subtracting the “product of the target air-fuel ratio correction amount daf and the alcohol concentration correction value K3 (K3 · daf)” from the “theoretical air-fuel ratio stoich that is the reference air-fuel ratio” Adopted as the target air-fuel ratio abyfr. When the sub feedback amount and the sub FB learning value are used so as to directly correct the target air-fuel ratio abyfr itself, a value obtained by subtracting the product (K3 · daf) from the target air-fuel ratio corrected by them is Is set as the target air-fuel ratio abyfr. Thereafter, the CPU proceeds to step 1030 in FIG. This target air-fuel ratio abyfr is also used in step 1125 of FIG. Therefore, step 2530 (FIG. 25) corresponds to the enrichment means, and the product (K3 · daf) can be said to be a rich correction amount.

  As described above, the lean erroneous control that occurs when the degree of non-uniformity (imbalance ratio) of the air-fuel ratio for each cylinder increases can be compensated by the sub feedback amount Vafsfb and / or the sub FB learning value Vafsfbg. . However, when the intake air amount Ga of the engine increases, a large amount of hydrogen is generated, and the output value Vabyfs of the upstream air-fuel ratio sensor 56 shifts to a richer value. This is considered to be because when the intake air amount Ga is large, a large amount of generated hydrogen cannot be sufficiently processed in the catalyst unit 566 of the upstream air-fuel ratio sensor 56. Accordingly, the sixth control device shifts the target air-fuel ratio abyfr to the rich side in the high intake air amount region, similarly to the third control device. At this time, the shift amount of the target air-fuel ratio abyfr (that is, the product (K3 · daf) which is the rich correction amount) is the index learning value RIMBgaku from which the influence of the intake air amount Ga, the engine speed NE, and the alcohol concentration Et is eliminated. To be determined. Therefore, according to the sixth control device, the target air-fuel ratio abyfr can be set to a more appropriate value according to the true imbalance ratio, and the amount of NOx generated when the air-fuel ratio of the engine becomes lean is reduced. can do.

  On the other hand, when the alcohol concentration (ethanol concentration) Et increases, the combustion temperature decreases, so the amount of NOx generated decreases. For this reason, when the alcohol concentration Et is high, it is necessary to reduce the amount of NOx generated when the degree of non-uniformity (imbalance ratio) of the air-fuel ratio by cylinder is larger than when the alcohol concentration Et is low. The “rich correction amount (K3 · daf)” is reduced. Furthermore, as the alcohol concentration Et increases, HC and CO tend to increase.

  From this point of view, the sixth control device decreases the rich correction amount (K3 · daf) as the alcohol concentration Et is higher by the processing in step 2520 and step 2530. As a result, even when the degree of non-uniformity (imbalance ratio) of the cylinder-by-cylinder air-fuel ratio including the high intake air amount region becomes large, more appropriate air-fuel ratio control is performed regardless of the alcohol concentration Et. Can be done. Therefore, the emission can be maintained at a good value.

As described above, the sixth control device
The alcohol concentration of the fuel is acquired, and the basic parameter correlation value is corrected based on the acquired alcohol concentration (see Step 2130 to Step 2150 in FIG. 21), and the corrected value obtained by the correction is obtained. Air-fuel ratio imbalance index value acquisition means for acquiring the air-fuel ratio imbalance index value (that is, the index learned value RIMBgaku which is the corrected air-fuel ratio imbalance index value) based on RIMBc (see the routine of FIG. 21). When,
Instructed fuel injection amount determining means (step 2510 in FIG. 25) for increasing and correcting the indicated fuel injection amount so that the indicated air-fuel ratio determined by the indicated fuel injection amount becomes smaller as the acquired air-fuel ratio imbalance index value becomes larger. And step 2530).

Further, the air-fuel ratio imbalance index value acquisition means includes:
The basic parameter correlation value (basic air-fuel ratio imbalance index value RIMBb) is corrected based on a value corresponding to the basic parameter, a value corresponding to the rotational speed of the engine, and a value corresponding to the intake air amount of the engine, and the correction The corrected air-fuel ratio imbalance index value (index learned value RIMBgaku) is acquired based on the corrected value (RIMBc) obtained by the above (see Step 2110 to Step 2150 in FIG. 21). ).

In addition, the indicated fuel injection amount determination means includes
The indicated fuel injection amount is increased and corrected by changing the target air-fuel ratio so that the target air-fuel ratio becomes smaller as the acquired air-fuel ratio imbalance index value (index learned value RIMBgaku) becomes larger. (See Step 2510 and Step 2530 in FIG. 25).

Further, the indicated fuel injection amount determining means includes
The higher the alcohol concentration of the fuel, the more the target air-fuel ratio is changed so that the target air-fuel ratio becomes larger in the range below the stoichiometric air-fuel ratio stoich (steps 2520 and 2530 in FIG. 25). See).

<Seventh embodiment>
Next, a control device according to a seventh embodiment of the present invention (hereinafter simply referred to as “seventh control device”) will be described. The seventh control device estimates the temperature of the upstream catalyst 43 (catalyst temperature TempCCRO) based on the engine operating state parameters such as the intake air amount or load and the engine speed, for example, and the estimated catalyst temperature TempCCRO Based on the above, "fuel increase control for catalyst overheating prevention and fuel cut inhibition control for catalyst heating prevention" is performed. Further, the seventh controller considers the alcohol concentration Et when estimating the catalyst temperature TempCCRO. Other points are the same as in the sixth control device.

(Actual operation)
The CPU of the seventh control device executes the routines shown in FIGS. 10 to 14 and FIG. 21 in the same manner as the CPU of the sixth control device. Further, the CPU of the seventh control device repeatedly executes each of the routines shown in FIGS. 26 to 28 every elapse of a predetermined time.

  Therefore, when the predetermined timing is reached, the CPU starts processing from step 2600 in FIG. 26, sequentially performs the processing from step 2610 to step 2650 described below, proceeds to step 2695, and once ends this routine.

  Step 2610: The CPU estimates the exhaust gas temperature Tex based on the engine operation state parameter of “intake air amount Ga (or load KL) and engine rotation speed NE” representing the engine operation state. That is, the CPU obtains the exhaust temperature Tex by applying the intake air amount Ga and the engine rotational speed NE to the look-up table MapTex (Ga, NE).

Step 2620: The CPU acquires a pre-correction catalyst temperature Tcb based on the exhaust gas temperature Tex. More specifically, the CPU calculates the pre-correction catalyst temperature Tcb based on the following equation (26). The pre-correction catalyst temperature Tcb is a value obtained by performing a first-order lag process on the exhaust gas temperature Tex. Tcb (n) on the left side of equation (26) is the pre-correction catalyst temperature Tcb after update, and Tcb (n-1) on the right side is the pre-correction catalyst temperature Tcb before update. “B” in the equation (26) is a constant larger than 0 and smaller than 1. The CPU may acquire the pre-correction catalyst temperature Tcb based on the exhaust gas temperature Tex according to another calculation formula (first-order lag filter processing).

Tcb (n) = b · Tex + (1−b) · Tcb (n−1) (26)

  Step 2630: The CPU obtains the first catalyst temperature correction coefficient Ktc1 by applying the index learning value RIMBgaku to the lookup table MapKtc1 (RIMBgaku). According to this table MapKtc1 (RIMBgaku), the first catalyst temperature correction coefficient Ktc1 is determined so as to gradually increase as the index learning value RIMBgaku increases (in the range of “1” or more). Of course, the CPU may calculate the first catalyst temperature correction coefficient Ktc1 by a function having the index learning value RIMBgaku as a variable.

  Step 2640: The CPU obtains the second catalyst temperature correction coefficient Ktc2 by applying the alcohol concentration (ethanol concentration) Et to the lookup table MapKtc2 (Et). According to this table MapKtc2 (Et), the second catalyst temperature correction coefficient Ktc2 is determined so as to gradually decrease as the alcohol concentration Et increases (in the range of “1” or less). Of course, the CPU may calculate the second catalyst temperature correction coefficient Ktc2 by a function having the alcohol concentration Et as a variable.

Step 2650: The CPU obtains the corrected catalyst temperature TempCCRO by correcting the pre-correction catalyst temperature Tcb based on the “first catalyst temperature correction coefficient Ktc1 and second catalyst temperature correction coefficient Ktc2”. More specifically, the CPU multiplies the catalyst temperature TempCCRO by multiplying the pre-correction catalyst temperature Tcb by the “product of the first catalyst temperature correction coefficient Ktc1 and the second catalyst temperature correction coefficient Ktc2” according to the following equation (27). Is calculated.

TempCCRO = Ktc1 / Ktc2 / Tcb (27)

  As described above, the pre-correction catalyst temperature Tcb is based on the first catalyst temperature correction coefficient Ktc1, and as the index learning value RIMBgaku increases, that is, the degree of non-uniformity of the air-fuel ratio by cylinder (imbalance ratio). As the value increases, the correction is made to increase. This is because when the degree of non-uniformity of the cylinder-by-cylinder air-fuel ratio is large, the rich air-fuel ratio and the lean air-fuel ratio alternately flow into the catalyst 43 in a short cycle, so that the oxidation-reduction reaction in the catalyst 43 frequently occurs. This is because, as a result, the temperature of the catalyst 43 rises quickly. As a result, the catalyst temperature TempCCRO is accurately estimated regardless of the degree of non-uniformity of the cylinder-by-cylinder air-fuel ratio.

  Further, the pre-correction catalyst temperature Tcb is corrected so as to decrease as the alcohol concentration Et increases, based on the second catalyst temperature correction coefficient Ktc2. This is because the higher the alcohol concentration Et, the lower the combustion temperature and the lower the exhaust gas temperature. As a result, the temperature of the catalyst 43 also decreases. As a result, the catalyst temperature TempCCRO is accurately estimated regardless of the alcohol concentration Et.

  Further, at a predetermined timing, the CPU starts the process from step 2700 in FIG. 27 and proceeds to step 2510 to acquire the target air-fuel ratio correction amount daf based on the index learned value RIMBgaku and the intake air amount Ga. This process is the same as the process of step 2510 in FIG.

  Next, the CPU proceeds to step 2520 to acquire an alcohol concentration correction value (third correction coefficient) K3 based on the alcohol concentration Et. This process is the same as the process of step 2520 in FIG.

  Next, the CPU proceeds to step 2710 to determine whether or not the corrected catalyst temperature TempCCRO estimated in step 2650 of FIG. 26 is equal to or lower than the overheat prevention threshold temperature TCth. At this time, if the catalyst temperature TempCCRO is equal to or lower than the overheat prevention threshold temperature TCth, the CPU makes a “Yes” determination at step 2710 to proceed to step 2530, from “the stoichiometric air-fuel ratio stoich that is the reference air-fuel ratio” to “target air A value obtained by subtracting the product of the fuel ratio correction amount daf and the alcohol concentration correction value K3 (K3 · daf) is adopted as the target air-fuel ratio abyfr. This process is the same as the process of step 2530 in FIG. Thereafter, the CPU proceeds to step 2795 to end the present routine tentatively.

  On the other hand, when the catalyst temperature TempCCRO is higher than the overheat prevention threshold temperature TCth, the CPU makes a “No” determination at step 2710 to proceed to step 2720 to set the target air-fuel ratio abyfr to a positive predetermined value from the stoichiometric air-fuel ratio stoich. A value obtained by subtracting the value C (stoich−C> 0) is set. The value stoich-C is smaller than the stoichiometric air-fuel ratio stoich, and is set to a value that can lower the temperature of the catalyst 43. Further, the value stoich-C is set to a value equal to or smaller than the minimum value of the value stoich-K3 · daf.

  The target air-fuel ratio abyfr is determined by the above processing. According to this processing, when the catalyst temperature TempCCRO estimated more accurately is higher than the overheat prevention threshold temperature TCth, the target air-fuel ratio abyfr is rich (the air-fuel ratio smaller than the stoichiometric air-fuel ratio stoich) stoich-C. Is set. Therefore, overheating of the catalyst 43 can be avoided reliably without consuming unnecessary fuel.

  Further, at a predetermined timing, the CPU starts the processing of the routine of FIG. By this routine, the value of the fuel cut flag XFC is set. When the CPU proceeds to step 2810, the CPU determines whether or not the value of the fuel cut flag XFC is “0”.

  Now, it is assumed that the value of the fuel cut flag XFC is “0” and the fuel cut control (fuel injection stop control) is not executed. In this case, the CPU makes a “Yes” determination at step 2810 to proceed to step 2820 to determine whether or not the throttle valve opening degree TA is “0”. If the throttle valve opening degree TA is not “0”, the CPU makes a “No” determination at step 2820 to directly proceed to step 2895 to end the present routine tentatively.

  If the throttle valve opening degree TA is “0”, the CPU makes a “Yes” determination at step 2820 to proceed to step 2830 to determine whether the engine speed NE is equal to or higher than the fuel cut start speed threshold value NEFC. judge. At this time, if the engine rotational speed NE is less than the fuel cut start rotational speed threshold value NEFC, the CPU makes a “No” determination at step 2830 to directly proceed to step 2895 to end the present routine tentatively.

  On the other hand, if the engine rotational speed NE is equal to or higher than the fuel cut start rotational speed threshold NEFC, the fuel cut condition is satisfied. Therefore, the CPU makes a “Yes” determination at step 2830 to proceed to step 2840 to determine whether or not the catalyst temperature TempCCRO estimated at step 2650 in FIG. 26 is equal to or lower than the fuel cut prohibition temperature TFCth. At this time, if the catalyst temperature TempCCRO is higher than the fuel cut prohibition temperature TFCth, the CPU makes a “No” determination at step 2840 to directly proceed to step 2895 to end the present routine tentatively. Accordingly, since the value of the fuel cut flag XFC is maintained at “0” (not changed to “1”), execution of the fuel cut control is prohibited.

  On the other hand, if the catalyst temperature TempCCRO is equal to or lower than the fuel cut prohibition temperature TFCth, the CPU makes a “Yes” determination at step 2840 to proceed to step 2850 to set the value of the fuel cut flag XFC to “1”. As a result, the CPU makes a “Yes” determination at step 1010 in FIG. 10 to directly proceed to step 1095. Therefore, since step 1060 is not executed, fuel injection is stopped (fuel cut is executed).

  When the CPU proceeds to step 2810 in a state where the value of the fuel cut flag XFC is set to “1”, the CPU makes a “No” determination at step 2810 to proceed to step 2860, and the throttle valve TA is set to “0”. It is determined whether it is larger than ". At this time, if the throttle valve TA is greater than “0”, the CPU makes a “Yes” determination at step 2860 to proceed to step 2870 to set the value of the fuel cut flag XFC to “0”. As a result, the fuel cut control ends and fuel injection starts again.

  On the other hand, if the throttle valve opening degree TA is “0”, the CPU makes a “No” determination at step 2860 to proceed to step 2880 to determine whether the engine rotational speed NE is lower than the fuel cut end rotational speed threshold NERTth. Determine whether. The fuel cut end rotational speed threshold value NERTth is smaller than the fuel cut start rotational speed threshold value NEFC.

  At this time, if the engine rotational speed NE is lower than the fuel cut end rotational speed threshold NERTth, the CPU makes a “Yes” determination at step 2880 to proceed to step 2870 to set the value of the fuel cut flag XFC to “0”. To do. As a result, the fuel cut control ends and fuel injection starts again.

  On the other hand, if the engine rotational speed NE is equal to or higher than the fuel cut end rotational speed threshold NERTth, the CPU makes a “No” determination at step 2880 to directly proceed to step 2895 to end the present routine tentatively. As a result, the value of the fuel cut flag XFC is maintained at “1”, so that the fuel cut control is continued.

As described above, the seventh control device
Fuel injection of an internal combustion engine comprising catalyst temperature estimation means (see FIG. 26) for estimating a catalyst temperature that is the temperature of the three-way catalyst 43 based on the operating state of the engine, and the indicated fuel injection amount determination means A quantity control device,
The catalyst temperature estimating means includes
The catalyst temperature TempCCRO is estimated so that the estimated catalyst temperature TempCCRO increases as the acquired air-fuel ratio imbalance index value (index learning value RIMBgaku) increases (steps 2630 and 2650 in FIG. 26 are performed). reference.),
The indicated fuel injection amount determining means includes
When the estimated catalyst temperature TempCCRO is higher than a predetermined threshold temperature (TCth, TFCth), the commanded fuel injection amount is increased and corrected so that the commanded air-fuel ratio determined by the commanded fuel injection amount becomes smaller than the theoretical air-fuel ratio. (Refer to step 2720 in FIG. 27, step 1040 in FIG. 10, etc.) or when a predetermined fuel cut condition is satisfied (determining “Yes” in both steps 2820 and 2830 in FIG. 28). (Refer to “No” in Step 2840 of FIG. 28).

  Therefore, it is possible to avoid wasteful consumption of fuel while avoiding overheating of the catalyst 43.

  As described above, the fuel injection amount control apparatus for an internal combustion engine according to each embodiment of the present invention is a lean engine that is generated when the “degree of alcohol concentration and / or the non-uniformity of the air-fuel ratio of each cylinder” increases. It is possible to prevent erroneous control as much as possible. Therefore, the air-fuel ratio of the exhaust gas can be brought close to the target air-fuel ratio, so that the amount of emissions such as NOx can be reduced.

  The present invention is not limited to the above embodiment, and various modifications can be employed within the scope of the present invention. For example, the air-fuel ratio imbalance index value acquisition unit of each embodiment may acquire the air-fuel ratio imbalance index value RIMB as described below. In the following, the value correlated with the value X is, for example, an average value of absolute values of a plurality of values X acquired in a predetermined period (for example, a unit combustion cycle period or a period that is a natural number times the unit combustion cycle period) , And a value that varies according to the value X, such as a difference between the maximum value and the minimum value of the value X during a predetermined period.

(A) The air-fuel ratio imbalance index value acquisition means has a large fluctuation (variation width) of the air-fuel ratio of the exhaust gas passing through the position where the upstream air-fuel ratio sensor 56 is disposed as the air-fuel ratio imbalance index value RIMB. It can be configured to obtain a value that increases.

More specifically, the air-fuel ratio imbalance index value acquisition means is
Differential value d (Vabyfs) / dt with respect to time of the output value Vabyfs of the upstream air-fuel ratio sensor (including a value obtained by performing high-pass filtering on the output value Vabyfs),
A differential value d (abyfs) / dt with respect to time of the detected air-fuel ratio abyfs (including a value obtained by subjecting the detected air-fuel ratio abyfs to high-pass filtering) acquired based on the output value of the upstream air-fuel ratio sensor,
Second-order differential value d ² (Vabyfs) / dt ^{2 with} respect to time of the output value Vabyfs of the upstream air-fuel ratio sensor, and
Second-order differential value d ² (abyfs) / dt ^{2 with} respect to the time of the detected air-fuel ratio abyfs obtained based on the output value of the upstream air-fuel ratio sensor,
A value corresponding to one of the basic parameters is acquired as a basic parameter, and the air-fuel ratio imbalance index value RIMB is acquired based on a value correlated with the acquired basic parameter.

Since the output value Vabyfs and the detected air-fuel ratio abyfs are substantially proportional to each other (see FIG. 5), the second-order differential value d ² (Vabyfs) / dt ² is the second order with respect to the time of the detected air-fuel ratio abyfs. The same tendency as the differential value d ² (abyfs) / dt ² is shown. Therefore, the second-order differential value d ² (Vabyfs) / dt ² becomes a relatively small value as shown by the broken line C5 in FIG. 8D when the cylinder-by-cylinder air-fuel ratio difference is small. When the difference is large, the value is relatively large as indicated by a solid line C6 in FIG.

The second-order differential value d ² (Vabyfs) / dt ² is obtained by subtracting the output value Vabyfs before a certain sampling time from the current output value Vabyfs to obtain a `` differential value d (Vabyfs) / dt at a certain sampling time '' Can be obtained by subtracting “differential value d (Vabyfs) / dt before a certain sampling time” from “newly obtained differential value d (Vabyfs) / dt”. Further, the second order differential value d ² (abyfs) / dt ² is obtained by subtracting the detected air-fuel ratio change rate ΔAF obtained before a certain sampling time from the detected air-fuel ratio change rate ΔAF obtained in step 1520 of FIG. It can ask for.

The air-fuel ratio imbalance index value acquisition means is
A value that correlates with a difference ΔX between a maximum value and a minimum value in a predetermined period (for example, a period that is a natural number times the unit combustion cycle period) of the output value Vabyfs (including a value obtained by performing high-pass filtering on the output value Vabyfs), or The value correlated with the difference ΔY between the maximum value and the minimum value in a predetermined period of the detected air-fuel ratio abyfs (including the value obtained by subjecting the detected air-fuel ratio abyfs to high-pass filtering) represented by the output value Vabyfs is an air-fuel ratio imbalance index value It may be configured to obtain as a RIMB. As is apparent from the solid line C2 and the broken line C1 shown in FIG. 8B, the difference ΔY (the absolute value of ΔY) increases as the cylinder-by-cylinder air-fuel ratio difference increases. Therefore, the difference ΔX (the absolute value of ΔX) increases as the cylinder-by-cylinder air-fuel ratio difference increases.

The air-fuel ratio imbalance index value acquisition means is
As the air-fuel ratio imbalance index value RIMB, a value correlated with a locus length in a predetermined period (for example, a unit combustion cycle period) of the output value Vabyfs (including a value obtained by subjecting the output value Vabyfs to high-pass filtering), or by the output value Vabyfs The detected air-fuel ratio abyfs (including a value obtained by subjecting the detected air-fuel ratio abyfs to high-pass filtering) may be configured to acquire a value that correlates with the trajectory length in the predetermined period. As is apparent from FIG. 8B, these trajectory lengths increase as the air-fuel ratio difference for each cylinder increases.

  Further, the greater the degree of non-uniformity of the air-fuel ratio for each cylinder, the greater the difference in torque generated by each cylinder. Therefore, the rotational fluctuation of the engine 10 becomes large. Therefore, the air-fuel ratio imbalance index value acquisition means may be configured to acquire a value that increases as the fluctuation in the rotational speed of the engine 10 increases as the air-fuel ratio imbalance index value.

  Further, each of the above control devices can be applied to a V-type engine. In this case, the V-type engine includes a right bank upstream side catalyst downstream of the exhaust collecting portion of two or more cylinders belonging to the right bank. Further, the V-type engine includes a left bank upstream side catalyst downstream of an exhaust collecting portion of two or more cylinders belonging to the left bank.

  In addition, the V-type engine includes an upstream air-fuel ratio sensor and a downstream air-fuel ratio sensor for the right bank upstream and downstream of the right bank upstream catalyst, respectively, and a left bank upstream and downstream of the left bank upstream catalyst. The upstream air-fuel ratio sensor and the downstream air-fuel ratio sensor can be provided.

  Each upstream air-fuel ratio sensor, like the air-fuel ratio sensor 56, is disposed between the exhaust collection portion of each bank and the upstream catalyst of each bank. In this case, the main feedback control and the sub feedback control for the right bank are executed, and the main feedback control and the sub feedback control for the left bank are executed independently.

  In this case, the control device obtains an air-fuel ratio imbalance index value RIMB for the right bank based on the output value of the upstream air-fuel ratio sensor for the right bank, and uses the air-fuel ratio imbalance index value RIMB and the alcohol concentration Et. Based on this, the “sub feedback amount guard width, sub FB learning value guard width, sub FB learning value change rate, and target air-fuel ratio abyfr” for the right bank are changed. Similarly, the control device obtains the air-fuel ratio imbalance index value RIMB for the left bank based on the output value of the upstream air-fuel ratio sensor for the left bank, and uses the air-fuel ratio imbalance index value RIMB and the alcohol concentration Et. Based on this, the “sub feedback amount guard width, sub FB learning value guard width, sub FB learning value change rate, and target air-fuel ratio abyfr” for the left bank are changed.

  DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine, 21 ... Combustion chamber, 33 ... Fuel injection valve, 41 ... Exhaust manifold, 41b ... Collecting part (exhaust collecting part HK), 42 ... Exhaust pipe, 43 ... Upstream catalyst (three-way catalyst), 56 ... Upstream air-fuel ratio sensor, 57... Downstream air-fuel ratio sensor, 70.

Claims (19)

A three-way catalyst disposed at a position downstream of the exhaust collecting portion of the exhaust passage of the engine in which exhaust gases discharged from a plurality of cylinders of the multi-cylinder internal combustion engine gather;
An upstream air-fuel ratio sensor disposed at a position between the exhaust collecting portion of the exhaust passage and the three-way catalyst;
A downstream air-fuel ratio sensor disposed at a position downstream of the three-way catalyst in the exhaust passage;
A main feedback amount for making a value corresponding to the detected air-fuel ratio acquired based on the output value of the upstream side air-fuel ratio sensor coincide with a value corresponding to a predetermined target air-fuel ratio is a value corresponding to the detected air-fuel ratio. Main feedback control means for determining based on a value corresponding to the target air-fuel ratio;
Integrates a sub-feedback amount for matching the output value of the downstream air-fuel ratio sensor with a predetermined downstream target value, at least according to the deviation between the output value of the downstream air-fuel ratio sensor and the downstream target value And calculating a learning value of the sub feedback amount based on the integration processing value or the sub feedback amount, and obtaining the acquired learning value within a predetermined guard width. Sub-feedback control means to regulate to,
A plurality of fuel injection valves, each of which is configured to inject fuel contained in an air-fuel mixture supplied to each combustion chamber of the plurality of cylinders;
An indication value of the amount of fuel injected from each of the plurality of fuel injection valves by correcting the amount of fuel injected from the fuel injection valve based on the main feedback amount, the sub feedback amount and the learning value Indicated fuel injection amount determining means for determining the indicated fuel injection amount,
Injection instruction signal sending means for sending an injection instruction signal to the plurality of fuel injection valves so that an amount of fuel corresponding to the indicated fuel injection amount is injected from each of the plurality of fuel injection valves;
A fuel injection amount control device for an internal combustion engine comprising:
An air-fuel ratio imbalance index value that increases as the degree of non-uniformity among the plurality of cylinders of the air-fuel ratio of each cylinder, which is the air-fuel ratio of the air-fuel mixture supplied to each combustion chamber of the plurality of cylinders, is acquired Air-fuel ratio imbalance index value acquisition means;
Alcohol concentration acquisition means for acquiring the alcohol concentration of the fuel;
Learning value guard width changing means for increasing the guard width as the acquired air-fuel ratio imbalance index value increases and increasing the acquired alcohol concentration;
A fuel injection amount control device. The fuel injection amount control device according to claim 1,
The sub feedback control means includes
The learning value change rate is set such that the greater the acquired air-fuel ratio imbalance index value, the greater the change rate of the learned value, and the higher the acquired alcohol concentration, the greater the change rate of the learned value. Configured to change,
Fuel injection amount control device. The fuel injection amount control device according to claim 2,
The sub feedback control means includes
A value obtained by multiplying the deviation by a predetermined gain as a value according to the deviation between the output value of the downstream air-fuel ratio sensor and the downstream target value,
The learning is performed by setting the gain to a larger value as the acquired actual air-fuel ratio imbalance index value is larger, and setting the gain to a larger value as the acquired actual alcohol concentration is higher. Configured to change the rate of change of the value,
Fuel injection amount control device. The fuel injection amount control device according to claim 2,
The sub feedback control means includes
The learning value is updated every elapse of a predetermined learning interval time, the learning interval time is set to a shorter time as the acquired air-fuel ratio imbalance index value is larger, and the acquired actual alcohol The learning interval time is set to a shorter time as the concentration is higher, thereby changing the change rate of the learning value.
Fuel injection amount control device. A fuel injection amount control device according to any one of claims 1 to 4,
The value corresponding to the detected air-fuel ratio is the value of the detected air-fuel ratio itself,
The value corresponding to the target air-fuel ratio is the value of the target air-fuel ratio itself,
Whether the target air-fuel ratio is set to a smaller air-fuel ratio as the intake air amount of the engine is larger, the acquired air-fuel ratio imbalance index value is larger, and the acquired alcohol concentration is higher. Alternatively, a fuel injection amount control device comprising a rich means for correcting the detected air-fuel ratio to a large air-fuel ratio. A three-way catalyst disposed at a position downstream of the exhaust collecting portion of the exhaust passage of the engine in which exhaust gases discharged from a plurality of cylinders of the multi-cylinder internal combustion engine gather;
An upstream air-fuel ratio sensor disposed at a position between the exhaust collecting portion of the exhaust passage and the three-way catalyst;
A downstream air-fuel ratio sensor disposed at a position downstream of the three-way catalyst in the exhaust passage;
A main feedback amount for making a value corresponding to the detected air-fuel ratio acquired based on the output value of the upstream side air-fuel ratio sensor coincide with a value corresponding to a predetermined target air-fuel ratio is a value corresponding to the detected air-fuel ratio. Main feedback control means for determining based on a value corresponding to the target air-fuel ratio;
A sub-feedback amount for making the output value of the downstream air-fuel ratio sensor coincide with a predetermined downstream target value is calculated based on the output value of the downstream air-fuel ratio sensor, and the calculated sub-feedback amount is predetermined. Sub-feedback control means for determining a sub-feedback amount by regulating within the guard width of
A plurality of fuel injection valves, each of which is configured to inject fuel contained in an air-fuel mixture supplied to each combustion chamber of the plurality of cylinders;
An indication fuel that is an indication value of the amount of fuel injected from each of the plurality of fuel injection valves by correcting the amount of fuel injected from the fuel injection valve based on the main feedback amount and the sub feedback amount Instructed fuel injection amount determining means for determining an injection amount;
Injection instruction signal sending means for sending an injection instruction signal to the plurality of fuel injection valves so that an amount of fuel corresponding to the indicated fuel injection amount is injected from each of the plurality of fuel injection valves;
A fuel injection amount control device for an internal combustion engine comprising:
An air-fuel ratio imbalance index value that increases as the degree of non-uniformity among the plurality of cylinders of the air-fuel ratio of each cylinder, which is the air-fuel ratio of the air-fuel mixture supplied to each combustion chamber of the plurality of cylinders, is acquired Air-fuel ratio imbalance index value acquisition means;
Alcohol concentration acquisition means for acquiring the alcohol concentration of the fuel;
Sub feedback amount guard width changing means for increasing the guard width as the acquired air-fuel ratio imbalance index value increases and increasing the acquired alcohol concentration;
A fuel injection amount control device. The fuel injection amount control device according to any one of claims 1 to 6,
The air-fuel ratio imbalance index value acquisition means is
Based on the output value of the upstream air-fuel ratio sensor, a basic parameter that increases as the fluctuation of the air-fuel ratio of the exhaust gas that passes through the position where the upstream air-fuel ratio sensor is disposed is acquired. A fuel injection amount control device configured to acquire the air-fuel ratio imbalance index value based on a basic parameter correlation value that is a value having a correlation. The fuel injection amount control device according to claim 7,
The air-fuel ratio imbalance index value acquisition means is
Differential value d (Vabyfs) / dt with respect to time of the output value Vabyfs of the upstream air-fuel ratio sensor,
Differential value d (abyfs) / dt with respect to time of the detected air-fuel ratio abyfs obtained based on the output value of the upstream air-fuel ratio sensor,
Second-order differential value d ² (Vabyfs) / dt ^{2 with} respect to time of the output value Vabyfs of the upstream air-fuel ratio sensor, and
Second-order differential value d ² (abyfs) / dt ^{2 with} respect to the time of the detected air-fuel ratio abyfs obtained based on the output value of the upstream air-fuel ratio sensor,
A fuel injection amount control device configured to acquire a value corresponding to one of the basic parameters as the basic parameter. In the fuel injection amount control device according to claim 7 or 8,
The air-fuel ratio imbalance index value acquisition means is
The basic parameter correlation value is corrected based on a value corresponding to the basic parameter, a value corresponding to the rotational speed of the engine, and a value corresponding to the intake air amount of the engine, and based on a corrected value obtained by the correction. A fuel injection amount control device configured to acquire the air-fuel ratio imbalance index value. The fuel injection amount control device according to any one of claims 7 to 9,
The air-fuel ratio imbalance index value acquisition means is
A fuel injection amount control device configured to correct the basic parameter correlation value based on the acquired alcohol concentration and to acquire the air-fuel ratio imbalance index value based on a corrected value obtained by the correction. . A three-way catalyst disposed at a position downstream of the exhaust collecting portion of the exhaust passage of the engine in which exhaust gases discharged from a plurality of cylinders of the multi-cylinder internal combustion engine gather;
An upstream air-fuel ratio sensor disposed at a position between the exhaust collecting portion of the exhaust passage and the three-way catalyst;
A plurality of fuel injection valves, each of which is configured to inject fuel contained in an air-fuel mixture supplied to each combustion chamber of the plurality of cylinders;
A main feedback amount for making a value corresponding to the detected air-fuel ratio acquired based on the output value of the upstream side air-fuel ratio sensor coincide with a value corresponding to a predetermined target air-fuel ratio is a value corresponding to the detected air-fuel ratio. Each of the plurality of fuel injection valves is determined based on a value corresponding to the target air-fuel ratio, and by correcting the amount of fuel injected from the fuel injection valve based on the determined main feedback amount. Commanded fuel injection amount determining means for determining a commanded fuel injection amount that is a command value of the amount of fuel injected from
Injection instruction signal sending means for sending an injection instruction signal to the plurality of fuel injection valves so that an amount of fuel corresponding to the indicated fuel injection amount is injected from each of the plurality of fuel injection valves;
Based on an output value of the upstream air-fuel ratio sensor, a basic parameter that increases as a variation in the air-fuel ratio of the exhaust gas that passes through the position where the upstream air-fuel ratio sensor is disposed is acquired, and the plurality of cylinders The air-fuel ratio imbalance index value that increases as the degree of non-uniformity among the plurality of cylinders of the air-fuel ratio of each cylinder, which is the air-fuel ratio of the air-fuel mixture supplied to each of the combustion chambers, is correlated with the basic parameter. An air-fuel ratio imbalance index value obtaining means for obtaining based on a basic parameter correlation value which is a value having;
A fuel injection amount control device for an internal combustion engine comprising:
The air-fuel ratio imbalance index value acquisition means is
The alcohol concentration of the fuel is acquired, the basic parameter correlation value is corrected based on the acquired alcohol concentration, and the air-fuel ratio imbalance index value is acquired based on the corrected value obtained by the correction. Configured as
The indicated fuel injection amount determining means includes
A fuel injection amount control device configured to increase and correct the indicated fuel injection amount so that the indicated air-fuel ratio determined by the indicated fuel injection amount becomes smaller as the acquired air-fuel ratio imbalance index value becomes larger. The fuel injection amount control device according to claim 11,
The air-fuel ratio imbalance index value acquisition means is
The basic parameter correlation value is corrected based on a value corresponding to the basic parameter, a value corresponding to the rotational speed of the engine, and a value corresponding to the intake air amount of the engine, and based on a corrected value obtained by this correction. A fuel injection amount control device configured to acquire the air-fuel ratio imbalance index value. The fuel injection amount control device according to claim 11 or 12,
The indicated fuel injection amount determining means includes
Fuel injection amount control configured to increase and correct the indicated fuel injection amount by changing the target air-fuel ratio so that the target air-fuel ratio becomes smaller as the acquired air-fuel ratio imbalance index value becomes larger apparatus. The fuel injection amount control device according to claim 13,
The indicated fuel injection amount determining means includes
A fuel injection amount control device configured to change the target air-fuel ratio so that the target air-fuel ratio becomes smaller as the intake air amount of the engine becomes larger. The fuel injection amount control device according to claim 13 or 14,
The indicated fuel injection amount determining means includes
A fuel injection amount control device configured to change the target air-fuel ratio so that the target air-fuel ratio increases as the alcohol concentration of the fuel increases. A three-way catalyst disposed at a position downstream of the exhaust collecting portion of the exhaust passage of the engine in which exhaust gases discharged from a plurality of cylinders of the multi-cylinder internal combustion engine gather;
An upstream air-fuel ratio sensor disposed at a position between the exhaust collecting portion of the exhaust passage and the three-way catalyst;
A plurality of fuel injection valves, each of which is configured to inject fuel contained in an air-fuel mixture supplied to each combustion chamber of the plurality of cylinders;
A main feedback amount for making the value corresponding to the detected air-fuel ratio acquired based on the output value of the upstream side air-fuel ratio sensor coincide with the value corresponding to the target air-fuel ratio set to the value corresponding to the theoretical air-fuel ratio. Determining based on a value corresponding to the detected air-fuel ratio and a value corresponding to the target air-fuel ratio, and correcting the amount of fuel injected from the fuel injection valve based on the determined main feedback amount; A command fuel injection amount determination means for determining a command fuel injection amount that is a command value of the amount of fuel injected from each of the plurality of fuel injection valves by
Injection instruction signal sending means for sending an injection instruction signal to the plurality of fuel injection valves so that an amount of fuel corresponding to the indicated fuel injection amount is injected from each of the plurality of fuel injection valves;
Based on an output value of the upstream air-fuel ratio sensor, a basic parameter that increases as a variation in the air-fuel ratio of the exhaust gas that passes through the position where the upstream air-fuel ratio sensor is disposed is acquired, and the plurality of cylinders The air-fuel ratio imbalance index value that increases as the degree of non-uniformity among the plurality of cylinders of the air-fuel ratio of each cylinder, which is the air-fuel ratio of the air-fuel mixture supplied to each of the combustion chambers, is correlated with the basic parameter. An air-fuel ratio imbalance index value obtaining means for obtaining based on a basic parameter correlation value which is a value having;
Catalyst temperature estimating means for estimating a catalyst temperature which is a temperature of the three-way catalyst based on an operating state of the engine;
A fuel injection amount control device for an internal combustion engine comprising:
The catalyst temperature estimating means includes
The catalyst temperature is estimated so that the estimated catalyst temperature increases as the acquired air-fuel ratio imbalance index value increases.
The indicated fuel injection amount determining means includes
When the estimated catalyst temperature is higher than a predetermined threshold temperature, the indicated fuel injection amount is increased and corrected so that the indicated air-fuel ratio determined by the indicated fuel injection amount is smaller than the theoretical air-fuel ratio, or A fuel injection amount control device configured to prohibit execution of fuel injection stop control that is executed when a fuel cut condition is satisfied. The fuel injection amount control device according to claim 16,
The catalyst temperature estimating means includes
A fuel injection amount control device configured to acquire an alcohol concentration of the fuel and to estimate the catalyst temperature such that the estimated catalyst temperature decreases as the acquired alcohol concentration increases. The fuel injection amount control device according to claim 16 or 17,
The air-fuel ratio imbalance index value acquisition means is
The basic parameter correlation value is corrected based on a value corresponding to the basic parameter, a value corresponding to the rotational speed of the engine, and a value corresponding to the intake air amount of the engine, and based on a corrected value obtained by the correction. A fuel injection amount control device configured to acquire the air-fuel ratio imbalance index value. The fuel injection amount control device according to any one of claims 16 to 18,
The air-fuel ratio imbalance index value acquisition means is
The alcohol concentration of the fuel is acquired, the basic parameter correlation value is corrected based on the acquired alcohol concentration, and the air-fuel ratio imbalance index value is acquired based on the corrected value obtained by the correction. A fuel injection amount control device configured as described above.

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