JP2010007561A - Air-fuel ratio control device and air-fuel ratio control method - Google Patents

Abstract

An air-fuel ratio control apparatus and an air-fuel ratio control method capable of accurately determining an abnormality in exhaust gas purification are provided.
A feedback correction value for correcting a fuel injection amount is calculated so that an air-fuel ratio detected upstream of a catalyst provided in an exhaust passage becomes a target air-fuel ratio, and an oxygen concentration detected downstream. The sub-feedback correction value for correcting the air-fuel ratio is calculated based on the above, and the learning value for compensating for the steady deviation of the air-fuel ratio from the target air-fuel ratio is updated based on the oxygen concentration. Further, the updating of the learning value is stopped, the oxygen storage amount of the catalyst is calculated using the learning value calculated in advance, and abnormality determination control is performed for detecting an abnormal state in exhaust purification based on the oxygen storage amount, When the execution time of the abnormality determination control is longer than the reference time, and the oxygen storage amount calculated by the control is less than a predetermined determination value, the execution of the abnormality determination control is prohibited.
[Selection] Figure 1

Description

  The present invention relates to an air-fuel ratio control device and an air-fuel ratio control method.

  Conventionally, there is an apparatus in which an air-fuel ratio sensor is provided upstream of an exhaust purification catalyst in an exhaust passage, and an oxygen sensor is provided downstream of the catalyst. Since this catalyst can purify exhaust components most efficiently when the air-fuel ratio of the inflowing exhaust gas is within a predetermined range, the air-fuel ratio of the exhaust gas flowing into the catalyst becomes the target air-fuel ratio based on the output of the air-fuel ratio sensor. Thus, the fuel injection amount is feedback controlled (main feedback control).

  Further, in the above apparatus, for the purpose of improving emission, sub feedback control for correcting the feedback (F / B) correction value calculated in the main feedback control is also performed based on the output signal from the oxygen sensor. In the sub-feedback control, a sub-feedback (F / B) correction value is calculated based on the deviation between the output of the oxygen sensor and the reference output when the upstream air-fuel ratio becomes the target air-fuel ratio. The correction value is reflected in the F / B correction value.

  In addition to sub-feedback control, sub-feedback learning is used to learn steady-state deviations caused by variations in each cylinder, such as the characteristics of each injector, gas hits according to the mounting position of the air-fuel ratio sensor or oxygen sensor, and sensor characteristics. It is done together. The learning value calculated by this learning is reflected in the F / B correction value together with the sub F / B correction value.

On the other hand, based on the oxygen concentration detected downstream of the catalyst, active air-fuel ratio control for forcibly changing the air-fuel ratio upstream of the catalyst to the rich side and lean side is performed, and the oxygen storage amount calculated based on the changing air-fuel ratio An abnormality determination method for determining whether or not is within a predetermined range is generally performed (see, for example, Patent Document 1). In this method, for example, when the oxygen storage amount is less than the reference value, it is determined that the catalyst has deteriorated. When executing this active air-fuel ratio control, the sub-feedback learning described above is interrupted, and the air-fuel ratio control is performed based on the learning value calculated before the execution of the active air-fuel ratio control.
Japanese Patent Laid-Open No. 2006-090000

  However, when the active air-fuel ratio control is performed, the sub F / B learning value calculated before the active air-fuel ratio control is used, so that an error included in the learning value may increase. When the error included in the learning value increases, the abnormality determination control is adversely affected, and although the catalyst is not deteriorated, an erroneous abnormality determination that the catalyst has deteriorated is performed, or the abnormality determination control itself is performed. There is a risk that it will not complete normally.

  The present invention has been made in view of the above problems, and an object thereof is to provide an air-fuel ratio control apparatus and an air-fuel ratio control method capable of accurately determining an abnormality in exhaust gas purification.

Means and effects for solving the above problems will be described below.
The invention according to claim 1 calculates a feedback correction value for correcting the fuel injection amount so that the air-fuel ratio detected upstream of the catalyst provided in the exhaust passage becomes the target air-fuel ratio, and is detected downstream. In the air-fuel ratio control apparatus for an internal combustion engine, a sub-feedback correction value that corrects the air-fuel ratio based on the oxygen concentration is calculated, and a learning value that updates a steady deviation of the air-fuel ratio based on the oxygen concentration is updated. The update of the learning value is stopped, the oxygen storage amount of the catalyst is calculated using the learning value calculated in advance, and abnormality determination control is performed to detect an abnormal state in exhaust purification based on the oxygen storage amount, Execution of the abnormality determination control is prohibited when the execution time of the abnormality determination control is longer than a reference time and the oxygen storage amount calculated by the control is less than a predetermined determination value. To.

  According to the above configuration, when the abnormality determination control in which the learning value is not updated is executed, the execution time of the abnormality determination control is longer than the reference time, and the oxygen storage amount calculated by this control is determined in advance. When it is less than the value, the abnormality determination control is prohibited. For this reason, when the error included in the learning value calculated in advance increases, the learning value can be prevented from adversely affecting the abnormality determination control.

  The invention according to claim 2 calculates the feedback correction value for correcting the fuel injection amount so that the air-fuel ratio detected upstream of the catalyst provided in the exhaust passage becomes the target air-fuel ratio, and is detected downstream. In the air-fuel ratio control apparatus for an internal combustion engine, a sub-feedback correction value that corrects the air-fuel ratio based on the oxygen concentration is calculated, and a learning value that updates a steady deviation of the air-fuel ratio based on the oxygen concentration is updated. The update of the learning value is stopped, the oxygen storage amount of the catalyst is calculated using the learning value calculated in advance, and abnormality determination control is performed to detect an abnormal state in exhaust purification based on the oxygen storage amount, When the calculated oxygen storage amount is larger than a determination value calculated in advance, execution of the abnormality determination control is prohibited.

  According to the above configuration, when the abnormality determination control in which the learning value is not updated is executed, the abnormality determination control is prohibited when the calculated oxygen storage amount is larger than the determination value. For this reason, when the error included in the learning value calculated in advance increases, the learning value can be prevented from adversely affecting the abnormality determination control.

  The invention according to claim 3 calculates the feedback correction value for correcting the fuel injection amount so that the air-fuel ratio detected upstream of the catalyst provided in the exhaust passage becomes the target air-fuel ratio, and is detected downstream. In the air-fuel ratio control apparatus for an internal combustion engine, a sub-feedback correction value that corrects the air-fuel ratio based on the oxygen concentration is calculated, and a learning value that updates a steady deviation of the air-fuel ratio based on the oxygen concentration is updated. The update of the learning value is stopped, the oxygen storage amount of the catalyst is calculated using the learning value calculated in advance, and abnormality determination control is performed to detect an abnormal state in exhaust purification based on the oxygen storage amount, The execution time of the abnormality determination control is longer than a reference time, and the oxygen storage amount calculated by the control is less than the first determination value, or the calculated oxygen storage amount is If it exceeds the second determination value larger than the first determination value, it prohibits the execution of the abnormality determination control.

  According to the above configuration, in the abnormality determination control in which the learning value is not updated, when the execution time of the abnormality determination control is longer than the reference time and the oxygen storage amount calculated by this control is less than the first determination value, Alternatively, the abnormality determination control is stopped when the oxygen storage amount exceeds the second determination value. For this reason, when the error included in the learning value calculated in advance increases, the learning value can be prevented from adversely affecting the abnormality determination control in consideration of the magnitude of the error.

The invention according to claim 4 calculates a feedback correction value for correcting the fuel injection amount so that the air-fuel ratio detected upstream of the catalyst provided in the exhaust passage becomes the target air-fuel ratio, and is detected downstream. In the air-fuel ratio control method for an internal combustion engine, a sub-feedback correction value that corrects the air-fuel ratio based on the oxygen concentration is calculated, and a learning value that updates a steady deviation of the air-fuel ratio based on the oxygen concentration is updated. The update of the learning value is stopped, the oxygen storage amount of the catalyst is calculated using the learning value calculated in advance, and abnormality determination control is performed to detect an abnormal state in exhaust purification based on the oxygen storage amount, Execution of the abnormality determination control is prohibited when the execution time of the abnormality determination control is longer than a reference time and the oxygen storage amount calculated by the control is less than a predetermined determination value. To.

  According to the above method, when the abnormality determination control in which the learning value is not updated is executed, the execution time of the abnormality determination control is longer than the reference time, and the oxygen storage amount calculated by this control is determined in advance. When it is less than the value, the abnormality determination control is prohibited. For this reason, when the error included in the learning value calculated in advance increases, the learning value can be prevented from adversely affecting the abnormality determination control.

  The invention according to claim 5 calculates the feedback correction value for correcting the fuel injection amount so that the air-fuel ratio detected upstream of the catalyst provided in the exhaust passage becomes the target air-fuel ratio, and is detected downstream. In the air-fuel ratio control method for an internal combustion engine, a sub-feedback correction value that corrects the air-fuel ratio based on the oxygen concentration is calculated, and a learning value that updates a steady deviation of the air-fuel ratio based on the oxygen concentration is updated. The update of the learning value is stopped, the oxygen storage amount of the catalyst is calculated using the learning value calculated in advance, and abnormality determination control is performed to detect an abnormal state in exhaust purification based on the oxygen storage amount, When the calculated oxygen storage amount is larger than a determination value calculated in advance, execution of the abnormality determination control is prohibited.

  According to the above method, when the abnormality determination control in which the learning value is not updated is executed, the abnormality determination control is prohibited when the calculated oxygen storage amount is larger than the determination value. For this reason, when the error included in the learning value calculated in advance increases, the learning value can be prevented from adversely affecting the abnormality determination control.

  The invention according to claim 6 calculates the feedback correction value for correcting the fuel injection amount so that the air-fuel ratio detected upstream of the catalyst provided in the exhaust passage becomes the target air-fuel ratio, and is detected downstream. In the air-fuel ratio control method for an internal combustion engine, a sub-feedback correction value that corrects the air-fuel ratio based on the oxygen concentration is calculated, and a learning value that updates a steady deviation of the air-fuel ratio based on the oxygen concentration is updated. The update of the learning value is stopped, the oxygen storage amount of the catalyst is calculated using the learning value calculated in advance, and abnormality determination control is performed to detect an abnormal state in exhaust purification based on the oxygen storage amount, The execution time of the abnormality determination control is longer than a reference time, and the oxygen storage amount calculated by the control is less than the first determination value, or the calculated oxygen storage amount is If it exceeds the second determination value larger than the first determination value, it prohibits the execution of the abnormality determination control.

  According to the above method, in the abnormality determination control in which the learning value is not updated, when the execution time of the abnormality determination control is longer than the reference time and the oxygen storage amount calculated by this control is less than the first determination value, Alternatively, the abnormality determination control is stopped when the oxygen storage amount exceeds the second determination value. For this reason, when the error included in the learning value calculated in advance increases, the learning value can be prevented from adversely affecting the abnormality determination control in consideration of the magnitude of the error.

Hereinafter, an embodiment embodying the present invention will be described with reference to FIGS. FIG. 1 is a schematic diagram of an internal combustion engine on which the air-fuel ratio control apparatus of the present invention is mounted and the surrounding configuration.
The intake passage 11 of the internal combustion engine 10 is provided with a throttle valve 15 whose passage area is variable, and the amount of air taken in through the air cleaner 14 is adjusted by opening degree control. The amount of air sucked here (intake air amount) is detected by the air flow meter 16. The air drawn into the intake passage 11 is mixed with fuel injected by an injector 17 provided downstream of the throttle valve 15 and then sent to the combustion chamber 12.

  On the other hand, the exhaust passage 13 is provided with an exhaust purification system. The exhaust purification system includes a catalyst 18 that purifies components in the exhaust. The catalyst 18 has an effect of purifying the exhaust gas by oxidizing HC and CO in the exhaust gas and reducing NOx in the exhaust gas in a state where the combustion is performed in the vicinity of the theoretical air-fuel ratio. The catalyst 18 has a main component that decomposes main harmful components (HC, CO, NOx), and an oxygen storage component that accelerates the reaction and stores oxygen. The oxygen storage component stores oxygen in the exhaust when the air-fuel ratio of the exhaust gas passing through the catalyst 18 is leaner than the stoichiometric air-fuel ratio, and promotes the NOx reduction reaction. Further, the stored oxygen is released when the air-fuel ratio is richer than the stoichiometric air-fuel ratio, and the oxidation reaction of components such as HC and CO is promoted. The catalyst 18 is provided with a catalyst bed temperature sensor 21 for detecting the catalyst bed temperature.

The exhaust purification system also includes an air-fuel ratio sensor 19 provided on the upstream side of the catalyst 18 in the exhaust passage 13 and an oxygen sensor 20 provided on the downstream side of the catalyst 18.
The air-fuel ratio sensor 19 is a known limiting current oxygen sensor. The output of the air-fuel ratio sensor 19 becomes “0” when the air-fuel ratio is the stoichiometric air-fuel ratio, and the output current increases in the negative direction as the air-fuel ratio becomes rich. As the air-fuel ratio becomes leaner, the output current increases in the positive direction. Therefore, the lean degree or rich degree on the upstream side of the catalyst 18 can be detected based on the output of the air-fuel ratio sensor 19.

  The oxygen sensor 20 is a known concentration battery type sensor. In the oxygen sensor 20, an output of about 1V is obtained when the air-fuel ratio is richer than the stoichiometric air-fuel ratio, and an output of about 0V is obtained when the air-fuel ratio is leaner than the stoichiometric air-fuel ratio. In addition, the output voltage greatly changes in the vicinity of the theoretical air-fuel ratio.

  By comparing the air-fuel ratio upstream of the catalyst based on the air-fuel ratio sensor 19 and the air-fuel ratio downstream of the catalyst based on the oxygen sensor 20, the oxygen storage state of the catalyst 18 can be estimated. For example, when the output of the air-fuel ratio sensor 19 is rich and the output of the oxygen sensor 20 is lean, it can be estimated that the oxygen stored in the catalyst 18 is released and the oxidation reaction is promoted. When the output signal of the air-fuel ratio sensor 19 indicates lean and the output of the oxygen sensor 20 indicates rich, it can be estimated that oxygen in the exhaust is occluded in the catalyst 18 and the reduction reaction is promoted.

  As described above, since the catalyst 18 efficiently purifies the main harmful components in the exhaust gas by the oxygen reduction reaction only in a narrow range (window) in the vicinity of the stoichiometric air-fuel ratio, Strict air-fuel ratio control is required to adjust the air-fuel ratio of the gas to the center of the window.

  This air-fuel ratio control is performed by the electronic control unit 22. The electronic control device 22 detects the air flow meter 16, the air-fuel ratio sensor 19, the oxygen sensor 20, the catalyst bed temperature sensor 21, an accelerator sensor (not shown) that detects the amount of depression of the accelerator pedal, or an engine speed. Detection signals of various sensors such as a rotation speed sensor (not shown) are input. The air-fuel ratio control is performed by drivingly controlling the throttle valve 15 and the injector 17 in accordance with the operating conditions of the internal combustion engine 10 and the vehicle grasped by the detection signals of the sensors.

Next, an outline of air-fuel ratio control will be described. First, the electronic control unit 22 obtains a required amount of intake air amount that is acquired according to the amount of depression of the accelerator pedal and the detection result of the engine speed, and the throttle valve 15 is configured so that the intake air amount corresponding to the required amount is obtained. Adjust the opening. On the other hand, a fuel injection amount sufficient to obtain the stoichiometric air-fuel ratio is obtained from the actually measured value of the intake air amount detected by the air flow meter 16, and the injection amount from the injector 17 is adjusted based on this fuel injection amount. As a result, the air-fuel ratio of the air-fuel mixture burned in the combustion chamber 12 can be brought close to the stoichiometric air-fuel ratio, but this process alone is not sufficient as the required accuracy.

  Further, the electronic control unit 22 obtains an actual measurement value of the air-fuel ratio upstream of the catalyst 18 based on the detection result of the air-fuel ratio sensor 19 so that the actual measurement value approaches the target air-fuel ratio, that is, the stoichiometric air-fuel ratio. The main feedback control is performed to correct the fuel injection amount compensation based on the degree of deviation. Here, a main feedback (F / B) correction value is calculated, and the fuel injection amount is corrected using this correction value.

  Further, the main feedback (F / B) learning value is updated along with the calculation of the main F / B correction value. The main F / B learning value is a value that compensates for a steady deviation caused by the characteristics of the intake system and the fuel injection system in the internal combustion engine 10. The main F / B learning value is updated based on the main F / B correction value. The updated main F / B learning value is reflected in the fuel injection amount.

  Further, the electronic control unit 22 performs sub-feedback control for correcting the air-fuel ratio upstream of the catalyst based on the oxygen concentration of the oxygen sensor 20 detected downstream of the catalyst. In this sub feedback control, a sub feedback (F / B) correction value is calculated. Then, the fuel injection amount is corrected by reflecting the sub F / B correction value on the output of the air-fuel ratio sensor 19.

  In addition to the calculation of the sub F / B correction value, sub feedback learning for learning a stationary component included in the sub F / B correction value is also performed. In sub-feedback learning, a steady deviation of the air-fuel ratio with respect to the target air-fuel ratio is caused by variations in each cylinder, such as injector characteristics, gas hits according to the mounting position of the air-fuel ratio sensor or oxygen sensor, sensor characteristics, etc. Calculated as a sub F / B learning value. Then, the sub-F / B learning value is reflected in the output of the air-fuel ratio sensor 19 to indirectly correct the fuel injection amount.

  An example of the sub feedback control and the sub feedback learning control will be described. Here, the output Vaf of the air-fuel ratio sensor 19 is corrected by the sub F / B correction value VCSB and the sub feedback learning value LSB as shown in Expression (1), and main feedback control is performed using the corrected output Vaf. The main F / B correction value is corrected. That is, the output Vaf of the air-fuel ratio sensor 19 is used as a parameter when calculating the main F / B correction value.

Vaf = Vaf ′ + VCSB + LSB (1)
Note that “Vaf ′” on the right side is the output value of the air-fuel ratio sensor 19 before update, and “Vaf” on the left side is the output value after update.

  The sub F / B correction value VCSB is increased or decreased based on the output value of the oxygen sensor 20 downstream of the catalyst. This sub F / B correction value VCSB is calculated using the equation (2) based on the voltage deviation ΔV, the proportional gain Kp, the voltage deviation integrated value ΣΔV, the integral gain Ki, the voltage differential value dV, and the differential gain Kd. .

VCSB = ΔV · Kp + ΣΔV · Ki + dV · Kd (2)
In equation (2), the voltage deviation ΔV on the right side is a value obtained by subtracting the theoretical output (for example, 0.5 V) when the air-fuel mixture is burned at the stoichiometric air-fuel ratio from the output of the oxygen sensor 20. It is. The term “ΔV · Kp” on the right side is a proportional term that is proportional to the voltage deviation ΔV, and the main F / B correction value is increased or decreased by an amount corresponding to the deviation amount. Is a term for bringing the value closer to “0”.

  The proportional gain Kp is a constant obtained in advance by experiments or the like, and is set to a negative value here. The term “ΣΔV / Ki” is an integral term for eliminating a residual deviation that cannot be canceled only by the proportional term “ΔV / Kp”. Then, by increasing or decreasing the main F / B correction value by the integral term, the actual value for the oxygen concentration downstream of the catalyst is matched with the value when combustion at the stoichiometric air-fuel ratio is performed. It is like that. The integral gain Ki is a constant obtained in advance through experiments or the like, and is set as a negative value here.

  The voltage differential value dV used for “dV · Kd” on the right side is a value obtained by time-differentiating the output of the oxygen sensor 20, and indicates the amount of change per unit time of the output signal. The differential gain Kd is a constant obtained in advance by experiments or the like, and is set as a negative value here.

  Therefore, when the oxygen concentration in the exhaust gas downstream of the catalyst is lower than the value at the time of combustion at the stoichiometric air-fuel ratio (during rich combustion), the voltage deviation ΔV in the above equation (2) changes in the positive direction. Therefore, the sub F / B correction value VCSB decreases. Further, when the oxygen concentration in the exhaust gas downstream of the catalyst is higher than the value at the time of combustion of the stoichiometric air-fuel ratio (during lean combustion), the voltage deviation ΔV in the above equation (2) changes in the negative direction. Therefore, the sub F / B correction value VCSB increases.

  The sub F / B learning value LSB is updated, for example, every time fuel injection is performed a predetermined number of times during normal operation. At the time of update, the latest sub F / B correction value VCSB is subjected to a gradual change process to calculate an update amount QRN, and using this update amount QRN, the sub F / B learning value LSB is calculated based on the following equation (3). Update.

LSB = LSB '+ QRN (3)
When the sub F / B correction value VCSB is larger than “0”, the sub F / B learning value LSB is updated so as to increase, and through correction of the main F / B correction value by the sub F / B learning value LSB. The fuel injection amount is corrected. When the sub F / B correction value VCSB is smaller than “0”, the sub F / B learning value LSB is updated in a decreasing direction, and the main F / B correction value based on the sub F / B learning value LSB is updated. Through the correction, the fuel injection amount is corrected.

  By such sub feedback control and sub feedback learning control, the sub F / B correction value VCSB gradually converges to “0”. Further, when the sub F / B correction value VCSB approaches “0” to some extent and becomes stable, the sub F / B learning value LSB has less variation for each update, converges to a constant value, and stabilizes.

The sub-feedback learning calculates an oxygen storage amount OSC (Oxygen Storage Capacity) stored in the catalyst 18 and executes an abnormality determination process for diagnosing deterioration of the catalyst 18 and abnormality of the oxygen sensor 20. Execution is prohibited. That is, in such an abnormality determination process, for example, the gain or the like in the sub-feedback control may be changed, or a sub-feedback control different from the normal time may be performed. Is not updated. For this reason, the sub F / B learning value LSB calculated before the abnormality determination process is reflected in the output signal of the oxygen sensor 20.

  Next, an outline of the abnormality determination process will be described. In the abnormality determination process, the so-called Cmax method is used to forcibly change the air-fuel ratio on the upstream side of the catalyst and perform active air-fuel ratio control to reverse the rich side and the lean side, thereby causing deterioration of the catalyst 18 and abnormality of the oxygen sensor 20. Determine.

This determination process is executed when a preset execution condition is satisfied. For example, the execution condition is that the internal combustion engine is in a steady operation state, the catalyst bed temperature is in a predetermined temperature range, and the like, and is executed when the steady operation state and the catalyst bed temperature are in a predetermined temperature range. Normally, this determination process is performed once within a period from when the internal combustion engine is started to when it is stopped.

  This active air-fuel ratio control will be described with reference to FIG. As shown in FIG. 2A, the target air-fuel ratio is forced to the lean side (for example, target air-fuel ratio = 15.1) and the rich side (for example, target air-fuel ratio = 14.1) around the theoretical air-fuel ratio. Can be switched to. As shown in FIG. 2B, the air-fuel ratio upstream of the catalyst based on the air-fuel ratio sensor 19 also fluctuates with the change in the target air-fuel ratio, and based on the oxygen sensor 20 as shown in FIG. The air-fuel ratio downstream of the catalyst also varies.

  At time T1, when the execution of active air-fuel ratio control is permitted while the output of the oxygen sensor 20 is lean, the target air-fuel ratio is changed from the stoichiometric air-fuel ratio to the rich target value R. When the target air-fuel ratio is changed to rich, the fuel injection amount is gradually increased until the output of the air-fuel ratio sensor 19 indicates the target rich degree, and is delayed from the target air-fuel ratio change time (time T1). At the timing, the air-fuel ratio upstream of the catalyst becomes rich. When the air-fuel ratio upstream of the catalyst is rich, the stored oxygen is released from the catalyst 18. Thereby, the air-fuel ratio downstream of the catalyst becomes the lean air-fuel ratio.

  Then, when all of the oxygen stored in the catalyst 18 is released, oxygen is not released into the rich exhaust gas flowing into the catalyst 18, so that the air-fuel ratio downstream of the catalyst is reversed to the rich side (time T2). Using this inversion as a trigger, the target air-fuel ratio is switched to the lean target value L. Thus, the fuel injection amount is gradually reduced so that the air-fuel ratio on the upstream side of the catalyst approaches the lean target value L. Then, after a certain delay from time T2, the air-fuel ratio upstream of the catalyst becomes lean.

  When the air-fuel ratio upstream of the catalyst is lean, oxygen in the exhaust gas is occluded by the catalyst 18. Thereby, the air-fuel ratio downstream of the catalyst detected by the oxygen sensor 20 becomes the rich-side air-fuel ratio (time T2 to T3). When the oxygen storage function of the catalyst 18 reaches the limit and oxygen in the exhaust gas is no longer stored by the catalyst 18, the air-fuel ratio downstream of the catalyst is reversed to the lean side (time T3).

  Thereafter, the target air-fuel ratio is reversed every time the air-fuel ratio downstream of the catalyst is reversed from rich to lean and from lean to rich. Then, as shown in FIG. 2 (b), when the oxygen amount in the period from when the air-fuel ratio upstream of the catalyst becomes lean and until the air-fuel ratio downstream of the catalyst reverses from rich to lean is integrated, The value A1 is the oxygen storage amount OSC. The oxygen storage amount OSC is the maximum oxygen amount stored by the catalyst 18, and an abnormality determination method using the oxygen storage amount OSC is called a so-called Cmax method.

  Then, when the target air-fuel ratio is inverted a predetermined number of times and the oxygen storage amount OSC is calculated for each of the above-described periods, the calculated oxygen storage amounts OSC are averaged. When the oxygen storage amount OSC is less than the reference value VS1, it is determined that the catalyst 18 has deteriorated. That is, as the use period of the catalyst 18 increases, the oxygen storage component described above disappears, or the contact area with the exhaust gas gradually decreases due to sintering of the catalyst component. As a result, the oxygen storage amount OSC gradually decreases, but the lower limit value of the oxygen storage amount that can withstand use is determined in advance as the reference value VS1, and when it becomes less than the reference value VS1, it is determined that the catalyst 18 has deteriorated. .

Further, when the oxygen storage amount OSC is larger than the reference value VS2, it is determined that an abnormality has occurred in the oxygen sensor 20. That is, if an abnormality occurs in the oxygen sensor 20, the responsiveness corresponding to the reversal of the target air-fuel ratio deteriorates, the output of the oxygen sensor 20 sticks to a constant value, or the reversal timing is delayed. The oxygen storage amount OSC calculated on the basis of the output of is higher than that when the oxygen sensor 20 is normal. Therefore, the reference value VS2 is set based on the maximum value of the oxygen storage amount OSC using the oxygen storage amount OSC of the new catalyst 18, and the oxygen storage amount OSC calculated at each time exceeds the reference value VS2. In this case, it is determined that an abnormality has occurred in the oxygen sensor 20.

  In this abnormality determination process, since execution of sub F / B learning is prohibited as described above, the sub F / B learning value LSB calculated before execution of the abnormality determination process is used. Therefore, when the abnormality determination process is executed when the variation of each sub F / B learning value LSB calculated before execution is large, the sub F / B learning value LSB is included in the output Vaf of the air-fuel ratio sensor 19. It will be reflected. Since the oxygen storage amount OSC is based on the oxygen concentration detected by the air-fuel ratio sensor 19, if the error of the sub F / B learning value LSB is large, the oxygen storage amount OSC is not properly calculated and an erroneous determination is made. there is a possibility.

  Further, if the sub F / B learning value LSB having a large variation is reflected in the output Vaf of the air-fuel ratio sensor 19, the output inversion of the oxygen sensor 20 may not be normally performed in the active air-fuel ratio control. For example, if the output Vaf of the air-fuel ratio sensor 19 is corrected by the sub-F / B learning value LSB having a large error and a state in which the lean target value is not reached occurs, the degree of leanness of the exhaust gas flowing into the catalyst 18 is increased. Lower. If the lean degree upstream of the catalyst is low, the rich degree of the exhaust gas that hits the oxygen sensor 20 becomes low, so the timing of reversal from rich to lean is delayed. As described above, since the calculation of the oxygen storage amount OSC is continued until the air-fuel ratio downstream of the catalyst reverses from rich to lean, the value of the oxygen storage amount OSC exceeds the allowable range.

  For this reason, in the present embodiment, in the abnormality determination process, it is determined whether or not the sub F / B learning value LSB is stable, and this is used when the sub F / B learning value LSB is stable. In addition, when the sub F / B learning value LSB is not stable, execution of the abnormality determination process is prohibited, and sub feedback learning is performed until the sub F / B learning value LSB converges to a certain value and stabilizes. I do.

Next, the processing procedure of the abnormality determination process will be described with reference to FIGS. FIG. 3 shows a main flow of the abnormality determination process.
First, the electronic control unit 22 determines whether or not the abnormality determination process execution flag Flg1 is OFF (step S1). The execution flag Flg1 is a flag that indicates whether or not the abnormality determination process has been executed from the starting point of the internal combustion engine 10 to the starting point, and is set to OFF immediately after the internal combustion engine 10 is started.

  If it is determined that execution flag Flg1 is off (YES in step S1), it is determined whether or not the above-described execution condition is satisfied (step S2). If the above condition is not satisfied (eg, NO in step S2), such as immediately after the internal combustion engine 10 is started and the catalyst bed temperature has not reached the predetermined temperature range, the process returns to step S1.

If it is determined that the execution condition is satisfied (YES in step S2), a cancellation determination process described later is performed (step S3). In this interruption determination process, the stability of the sub F / B learning value LSB is determined by determining whether or not the sub F / B learning value LSB has an adverse effect on the calculation of the oxygen storage amount OSC. If not, a cancel request for prohibiting the execution of the abnormality determination process is made, and if stable, the abnormality determination process is executed. Then, it is determined whether or not there is a cancellation request for the abnormality determination process, which is output in the cancellation determination process (step S4). In the cancellation determination process, as described above, when it is determined that the sub F / B learning value LSB is not stable and a cancellation request is made (YES in step S4), execution of the abnormality determination process is prohibited in this process. (Step S5). Thereby, the sub feedback learning is continued, and the update of the sub F / B learning value LSB is continued. In the cancellation determination process, a cancellation request is made until the sub F / B learning value LSB is stabilized, and when the sub F / B learning value LSB is stabilized, the cancellation request is stopped. Thus, in the abnormality determination process, active air-fuel ratio control can be performed using the stabilized sub F / B learning value LSB.

  On the other hand, when the cancellation request is not made (NO in step S4), the abnormality determination process is started, and the active air-fuel ratio control is executed as described above (step S6). When the active air-fuel ratio control is started, the elapsed time from the start time is measured as the execution time ΔT. Further, it is determined whether or not there is a predetermined end trigger such that the target air-fuel ratio has been inverted a predetermined number of times, and the completion of the control is awaited (step S7).

  If active air-fuel ratio control is not completed (NO in step S7), the process returns to step S3, and a stop determination process is performed. Then, the active air-fuel ratio control and the stop determination process are repeated until the target air-fuel ratio is inverted a predetermined number of times. If a stop request is made during execution of active air-fuel ratio control (YES in step S4), the abnormality determination process is stopped (step S5), and the process returns to step S1 while the execution flag Flg1 remains off. Sub-feedback learning is sufficiently performed.For example, when active air-fuel ratio control is started again after a predetermined time has elapsed, no active stop request is issued during execution of active air-fuel ratio control, and active air-fuel ratio control is completed. To do.

  If it is determined that the active air-fuel ratio control has been completed (YES in step S7), an abnormality determination for catalyst 18 and oxygen sensor 20 is performed (step S8). For example, as described above, when the oxygen storage amount OSC is less than the reference value VS1, it is determined that the catalyst 18 has deteriorated, and when it is determined that the oxygen storage amount OSC is greater than the reference value VS2, the oxygen sensor 20 It is determined that an abnormality has occurred. If it is determined that the oxygen storage amount OSC is not less than the reference value VS1 and not more than the reference value VS2, it is determined that the oxygen sensor 20 is not in a deteriorated state and that the oxygen sensor 20 is not abnormal.

  When the abnormality determination is completed, the execution flag Flg1 is set to ON (step S9). When the execution flag Flg1 is set to ON, the abnormality determination process is not executed until the internal combustion engine 10 is stopped. Note that the execution flag Flg1 is initialized to OFF when the internal combustion engine 10 is stopped or after the internal combustion engine 10 is started again after the stop.

  Next, the cancellation determination process will be described with reference to FIG. First, it is determined whether or not the oxygen storage amount OSC calculated based on the output Vaf of the air-fuel ratio sensor 19 is larger than a determination value CQ1 (first determination value) (step S11).

  During execution of active air-fuel ratio control, for example, if the sub-F / B learning value LSB is reflected in the output Vaf of the air-fuel ratio sensor 19 in a state where the sub-feedback learning is insufficient, the corrected output Vaf becomes leaner. There is a case. In this case, when the air-fuel ratio downstream of the catalyst is reversed from rich to lean, the target air-fuel ratio is changed from lean to rich, but the output Vaf of the air-fuel ratio sensor 19 is corrected to lean, so the lean target value L It becomes difficult to reach. As a result, exhaust gas having a low richness flows into the catalyst 18, and the rate at which the catalyst 18 releases oxygen decreases. For this reason, the time until the release of the stored oxygen is completed and the air-fuel ratio downstream of the catalyst is reversed from lean to rich becomes longer. At this time, since the oxygen storage amount OSC is continuously calculated based on the output Vaf of the air-fuel ratio sensor 19, the oxygen storage amount OSC becomes excessive. Therefore, a value serving as a guide for the oxygen storage amount OSC calculated when the sub F / B learning value LSB is not stable is obtained, and this value is set as the determination value CQ1. The determination value CQ1 is a value smaller than the reference value VS1 for determining sensor abnormality.

  When the execution of the active air-fuel ratio control is not started, since the oxygen storage amount OSC is not calculated, it is determined that the oxygen storage amount OSC is equal to or less than the determination value CQ1 (NO in step S11), and step S12 Proceed to

  When it is determined that the oxygen storage amount OSC is larger than the determination value CQ1 (YES in step S11), a request for stopping the abnormality determination process is made (step S14). When a cancel request is made, it is determined that there is a cancel request in step S4 shown in FIG. 3 (YES in step S4), and execution of the abnormality determination process is prohibited.

  On the other hand, when it is determined that the oxygen storage amount OSC is equal to or smaller than the determination value CQ1 before or during execution of active air-fuel ratio control (NO in step S11), the execution time ΔT of active air-fuel ratio control described above is determined as the reference time. It is determined whether it is larger than TA (step S12). Further, it is determined whether or not the calculated oxygen storage amount OSC is less than a determination value CQ2 (second determination value) (step S13).

  Here, it is determined whether or not the output Vaf of the air-fuel ratio sensor 19 is approaching the stoichiometric air-fuel ratio by using the unstable sub F / B learning value LSB. That is, when active air-fuel ratio control is being executed, the output Vaf of the air-fuel ratio sensor 19 is close to the stoichiometric air-fuel ratio that deviates from the lean target value L or the rich target value R despite the change in the target air-fuel ratio. When the value is reached, the exhaust gas having a low lean or rich degree flows into the catalyst 18. For this reason, the oxygen storage speed or the oxygen release speed is remarkably reduced, and the time until the air-fuel ratio downstream of the catalyst is reversed becomes abnormally long. At this time, the calculation of the oxygen storage amount OSC is continuously performed based on the output Vaf of the air-fuel ratio sensor 19, but since the output Vaf is close to the theoretical air-fuel ratio, the calculated value of the oxygen storage amount OSC is stable. Compared to the case where the sub F / B learning value LSB is used, it does not become large. Accordingly, the oxygen storage amount calculated by optimizing the reference time TA and the determination value CQ2 of the oxygen storage amount OSC as a guide for determining the case where the unstabilized sub F / B learning value LSB is used by experiments or the like. It is determined whether the OSC exceeds the reference time TA and the oxygen storage amount OSC is less than the determination value CQ2.

  If execution time ΔT is greater than reference time TA (YES in step S12) and oxygen storage amount OSC is less than determination value CQ2 (YES in step S13), a request for stopping the abnormality determination process is made (step S14). ). Therefore, when correction is performed so that the output Vaf of the air-fuel ratio sensor 19 is close to the theoretical air-fuel ratio, it is determined that the sub F / B learning value LSB is not stable, the abnormality determination process is stopped, and the sub feedback is performed. Learning resumes.

  On the other hand, before execution of active air-fuel ratio control or during active air-fuel ratio control, it is determined that execution time ΔT is equal to or less than reference time TA (NO in step S12), and oxygen storage amount OSC is determined to be equal to or greater than determination value CQ2. Then (YES in step S13), the abnormality determination process is not stopped and the process returns to step S11. Even when the execution time ΔT exceeds the reference time TA, if the oxygen storage amount OSC is equal to or greater than the determination value CQ2 (NO in step S13), the oxygen storage capacity is simply large and the catalyst 18 is in the storage process. Therefore, the process returns to step S11 without stopping the abnormality determination process.

  For this reason, in this embodiment, when the sub F / B learning value LSB is not stable, the execution of the abnormality determination process is prohibited, so that an erroneous determination is made without adversely affecting the catalyst deterioration determination and the sensor abnormality determination. Can be prevented. Further, by using the sub-F / B learning value LSB that is not stabilized, the following two conditions were set in consideration of the degree of deviation from the target value of the air-fuel ratio.

-Oxygen storage amount OSC is larger than judgment value CQ1.
The active air-fuel ratio control execution time ΔT is longer than the reference time TA, and the oxygen storage amount OSC is less than the determination value CQ2.

  Then, when any one of the conditions is satisfied, the abnormality determination process is prohibited, so that the abnormality determination process can be accurately performed regardless of the magnitude of the error of the sub F / B learning value LSB. it can. In addition, instead of directly determining the magnitude of the sub F / B learning value LSB, the execution time ΔT and the oxygen storage amount OSC directly related to the abnormality determination of the catalyst 18 and the oxygen sensor 20 are used for the determination of cancellation. It is possible to efficiently perform the abnormality determination process by eliminating an unnecessary cancellation request that causes the abnormality determination process to be canceled despite no influence.

According to the above embodiment, the following effects can be obtained.
(1) In the above embodiment, the feedback correction value for correcting the fuel injection amount is calculated so that the air-fuel ratio detected upstream of the catalyst 18 provided in the exhaust passage 13 becomes the target air-fuel ratio, and detected downstream. A sub-feedback correction value for correcting the air-fuel ratio is calculated based on the oxygen concentration. Further, based on the oxygen concentration, the sub F / B learning value LSB for compensating for a steady deviation of the upstream air-fuel ratio from the target air-fuel ratio is updated. Further, when executing the abnormality determination control, the updating of the sub F / B learning value LSB is stopped, and the oxygen storage amount OSC of the catalyst 18 is calculated using the sub F / B learning value LSB calculated in advance. An abnormal state in exhaust purification is detected based on the oxygen storage amount OSC. The execution of the abnormality determination control is prohibited when the execution time ΔT of the active air-fuel ratio control is longer than the reference time TA and the oxygen storage amount OSC calculated by the control is less than a predetermined determination value CQ2. To do. Further, when the oxygen storage amount OSC calculated by the control exceeds a predetermined determination value CQ1, the execution of the abnormality determination control is prohibited. For this reason, when the error included in the pre-calculated sub F / B learning value LSB becomes large, the sub F / B learning value LSB is reflected in the output Vaf of the air-fuel ratio sensor 19, thereby deteriorating the catalyst. It is possible to prevent erroneous determination that it is determined that the catalyst 18 has deteriorated despite the fact that no oxygen has occurred, or that the sensor 18 is abnormal even though the oxygen sensor 20 is normal. That is, it is possible to prevent the abnormality determination control from being adversely affected by the sub F / B learning value LSB.

  (2) In the above embodiment, the oxygen storage amount OSC is greater than the determination value CQ1, or the active air-fuel ratio control execution time ΔT is greater than the reference time TA, and the oxygen storage amount OSC is less than the determination value CQ2. The execution of the abnormality determination process is prohibited when at least one of the two conditions is satisfied. For this reason, it is possible to make a cancellation determination in consideration of the magnitude of the error included in the sub F / B learning value LSB.

In addition, you may change the said embodiment as follows.
In the above embodiment, as one of the execution conditions of the abnormality determination process, it is determined whether or not the catalyst bed temperature is included in the predetermined range, but it is determined using other parameters indicating the operating state of the internal combustion engine 10. May be.

  In the above embodiment, the Cmax method is used as a method for diagnosing catalyst deterioration, but a method for determining based on the trajectory length of the air-fuel ratio may be used. That is, when the air-fuel ratio on the upstream side of the catalyst is forcibly vibrated around the theoretical air-fuel ratio, the air-fuel ratio on the downstream side of the catalyst vibrates following the vibration on the upstream side as the degree of deterioration of the catalyst increases. Therefore, by oscillating the upstream air-fuel ratio, calculating the ratio between the trajectory length of the output signal of the air-fuel ratio sensor 19 and the trajectory length of the output signal of the oxygen sensor 20, and comparing the trajectory length ratio with the determination value The deterioration of the catalyst 18 may be determined. Alternatively, the locus length of the output signal of the oxygen sensor 20 may be compared with a determination value.

1 is a schematic view of an internal combustion engine including an exhaust purification system. (A) is a target air-fuel ratio, (b) is an upstream air-fuel ratio, and (c) is a time chart in active air-fuel ratio control showing a downstream air-fuel ratio. The flowchart of the abnormality determination process of this embodiment. The flowchart of the cancellation determination process of this embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine, 13 ... Exhaust passage, 18 ... Catalyst, 22 ... Electronic control device as air-fuel ratio control device, CQ1, CQ2 ... Determination value, LSB ... Sub F / B learning value, OSC ... Oxygen storage amount, TA ... Reference time, ΔT: Execution time.

Claims (6)

A feedback correction value for correcting the fuel injection amount is calculated so that the air-fuel ratio detected upstream of the catalyst provided in the exhaust passage becomes the target air-fuel ratio, and the air-fuel ratio is calculated based on the oxygen concentration detected downstream. In an air-fuel ratio control apparatus for an internal combustion engine that calculates a sub-feedback correction value to be corrected and updates a learning value that compensates for a steady deviation of the air-fuel ratio based on the oxygen concentration,
The update of the learning value is stopped, the oxygen storage amount of the catalyst is calculated using the learning value calculated in advance, and abnormality determination control is performed to detect an abnormal state in exhaust purification based on the oxygen storage amount. ,
The execution of the abnormality determination control is prohibited when the execution time of the abnormality determination control is longer than a reference time and the oxygen storage amount calculated by the control is less than a predetermined determination value. An air-fuel ratio control device. A feedback correction value for correcting the fuel injection amount is calculated so that the air-fuel ratio detected upstream of the catalyst provided in the exhaust passage becomes the target air-fuel ratio, and the air-fuel ratio is calculated based on the oxygen concentration detected downstream. In an air-fuel ratio control apparatus for an internal combustion engine that calculates a sub-feedback correction value to be corrected and updates a learning value that compensates for a steady deviation of the air-fuel ratio based on the oxygen concentration,
The update of the learning value is stopped, the oxygen storage amount of the catalyst is calculated using the learning value calculated in advance, and abnormality determination control is performed to detect an abnormal state in exhaust purification based on the oxygen storage amount. ,
An air-fuel ratio control apparatus that prohibits execution of the abnormality determination control when the calculated oxygen storage amount is larger than a predetermined determination value. A feedback correction value for correcting the fuel injection amount is calculated so that the air-fuel ratio detected upstream of the catalyst provided in the exhaust passage becomes the target air-fuel ratio, and the air-fuel ratio is calculated based on the oxygen concentration detected downstream. In an air-fuel ratio control apparatus for an internal combustion engine that calculates a sub-feedback correction value to be corrected and updates a learning value that compensates for a steady deviation of the air-fuel ratio based on the oxygen concentration,
The update of the learning value is stopped, the oxygen storage amount of the catalyst is calculated using the learning value calculated in advance, and abnormality determination control is performed to detect an abnormal state in exhaust purification based on the oxygen storage amount. ,
The execution time of the abnormality determination control is longer than a reference time, and the oxygen storage amount calculated by the control is less than a first determination value, or the calculated oxygen storage amount is the first determination value. An air-fuel ratio control apparatus that prohibits execution of the abnormality determination control when a second determination value that is larger than the second determination value is exceeded. A feedback correction value for correcting the fuel injection amount is calculated so that the air-fuel ratio detected upstream of the catalyst provided in the exhaust passage becomes the target air-fuel ratio, and the air-fuel ratio is calculated based on the oxygen concentration detected downstream. In the air-fuel ratio control method for an internal combustion engine, which calculates a sub-feedback correction value to be corrected, and updates a learning value that compensates for a steady deviation of the air-fuel ratio based on the oxygen concentration.
The update of the learning value is stopped, the oxygen storage amount of the catalyst is calculated using the learning value calculated in advance, and abnormality determination control is performed to detect an abnormal state in exhaust purification based on the oxygen storage amount. ,
The execution of the abnormality determination control is prohibited when the execution time of the abnormality determination control is longer than a reference time and the oxygen storage amount calculated by the control is less than a predetermined determination value. An air-fuel ratio control method. A feedback correction value for correcting the fuel injection amount is calculated so that the air-fuel ratio detected upstream of the catalyst provided in the exhaust passage becomes the target air-fuel ratio, and the air-fuel ratio is calculated based on the oxygen concentration detected downstream. In the air-fuel ratio control method for an internal combustion engine, which calculates a sub-feedback correction value to be corrected, and updates a learning value that compensates for a steady deviation of the air-fuel ratio based on the oxygen concentration.
The update of the learning value is stopped, the oxygen storage amount of the catalyst is calculated using the learning value calculated in advance, and abnormality determination control is performed to detect an abnormal state in exhaust purification based on the oxygen storage amount. ,
An air-fuel ratio control method, wherein execution of the abnormality determination control is prohibited when the calculated oxygen storage amount is larger than a determination value calculated in advance. A feedback correction value for correcting the fuel injection amount is calculated so that the air-fuel ratio detected upstream of the catalyst provided in the exhaust passage becomes the target air-fuel ratio, and the air-fuel ratio is calculated based on the oxygen concentration detected downstream. In the air-fuel ratio control method for an internal combustion engine, a sub-feedback correction value to be corrected is calculated, and a learning value that updates a steady deviation of the air-fuel ratio based on the oxygen concentration is updated.
The update of the learning value is stopped, the oxygen storage amount of the catalyst is calculated using the learning value calculated in advance, and abnormality determination control is performed to detect an abnormal state in exhaust purification based on the oxygen storage amount. ,
The execution time of the abnormality determination control is longer than a reference time, and the oxygen storage amount calculated by the control is less than a first determination value, or the calculated oxygen storage amount is the first determination value. An air-fuel ratio control method that prohibits execution of the abnormality determination control when a second determination value that is larger than the second determination value is exceeded.

Images