JP2012202384A - Apparatus for detecting abnormality of inter-cylinder air-fuel ratio variation of multi-cylinder internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maximally prevent deterioration in exhaust emission caused by the execution of abnormality detection.SOLUTION: An apparatus for detecting an abnormality of an inter-cylinder air-fuel ratio variation of a multi-cylinder internal combustion engine increases the fuel injection quantity of a prescribed target cylinder and detects an abnormality of an inter-cylinder air-fuel ratio variation on the basis of at least a change in the rotation of the target cylinder after an increase in fuel injection quantity. The increase in the fuel injection quantity is executed during the execution of prescribed rich control. The increase in the fuel injection quantity is executed by utilizing the timing of the rich control. Therefore, it is possible to maximally prevent the deterioration in exhaust emission caused by the execution of abnormality detection.

Description

  The present invention relates to an apparatus for detecting an abnormal variation in the air-fuel ratio between cylinders of a multi-cylinder internal combustion engine, and more particularly to an apparatus for detecting that the air-fuel ratio between cylinders in a multi-cylinder internal combustion engine is relatively large. .

  In general, in an internal combustion engine equipped with an exhaust gas purification system using a catalyst, a mixture ratio of air and fuel in an air-fuel mixture burned in the internal combustion engine, that is, an air-fuel ratio, is used to efficiently remove harmful components in exhaust gas with a catalyst. Control is essential. In order to perform such air-fuel ratio control, an air-fuel ratio sensor is provided in the exhaust passage of the internal combustion engine, and feedback control is performed so that the air-fuel ratio detected thereby coincides with a predetermined target air-fuel ratio.

  On the other hand, in a multi-cylinder internal combustion engine, air-fuel ratio control is normally performed using the same control amount for all cylinders. Therefore, even if air-fuel ratio control is executed, the actual air-fuel ratio may vary between cylinders. If the degree of variation is small at this time, it can be absorbed by air-fuel ratio feedback control, and harmful components in the exhaust gas can be purified by the catalyst, so that exhaust emissions are not affected and there is no particular problem.

  However, for example, if the fuel injection system of some cylinders breaks down and the air-fuel ratio between the cylinders varies greatly, exhaust emission deteriorates, causing a problem. It is desirable to detect such a large air-fuel ratio variation that deteriorates the exhaust emission as an abnormality. In particular, in the case of an internal combustion engine for automobiles, it is required to detect an abnormal variation in air-fuel ratio between cylinders in an in-vehicle state in order to prevent the vehicle from running with deteriorated exhaust emissions (so-called OBD; On-Board Diagnostics). Recently, there is a movement to make it legally regulated.

  For example, in the apparatus described in Patent Document 1, when it is determined that an air-fuel ratio abnormality has occurred in any of the cylinders, the fuel injected into each cylinder until the cylinder in which the air-fuel ratio abnormality has occurred is misfired. The injection time is reduced by a predetermined time, thereby identifying the abnormal cylinder.

JP 2010-112244 A

  By the way, when an air-fuel ratio abnormality has occurred in any of the cylinders, if the fuel injection amount of the cylinder is forcibly increased or decreased, the rotational fluctuation of the cylinder becomes significantly large. Therefore, by detecting such an increase in rotational fluctuation, it is possible to detect an abnormality in air-fuel ratio variation.

  However, an increase or decrease in the fuel injection amount worsens the exhaust emission. Therefore, it is desirable to increase or decrease the fuel injection amount at a timing at which exhaust emission is not deteriorated as much as possible.

  Accordingly, the present invention has been made in view of the above circumstances, and an object of the present invention is to provide an inter-cylinder air-fuel ratio variation abnormality detection device for a multi-cylinder internal combustion engine that can prevent exhaust emission deterioration due to abnormality detection execution as much as possible. .

According to one aspect of the invention,
Rich control means for executing predetermined rich control for enriching the air-fuel ratio;
Detecting means for increasing a fuel injection amount of a predetermined target cylinder and detecting an abnormality in air-fuel ratio variation between cylinders based on at least the rotational fluctuation of the target cylinder after the increase;
With
The detection means performs an increase in the fuel injection amount during the execution of the rich control. An apparatus for detecting an abnormality in an air-fuel ratio variation among cylinders of a multi-cylinder internal combustion engine is provided.

  Preferably, the rich control includes a temperature rise suppression rich control that is executed to suppress a temperature increase of the catalyst provided in the exhaust passage.

Preferably, the abnormality detection device further includes temperature acquisition means for detecting or estimating the temperature of the catalyst,
The rich control means executes the temperature increase suppression rich control when the catalyst temperature detected or estimated by the temperature acquisition means becomes equal to or higher than a predetermined temperature.

  Alternatively, the rich control may comprise acceleration rich control that is executed during acceleration of the internal combustion engine.

In this case, preferably, the abnormality detection device further includes load detection means for detecting a load of the internal combustion engine,
The rich control means executes the acceleration rich control when the load detected by the load detection means becomes a predetermined value or more.

  Preferably, the detection means detects a rich shift abnormality of the target cylinder based on a difference in rotational fluctuation before and after the increase of the fuel injection amount in the target cylinder.

According to another aspect of the invention,
Air-fuel ratio detection means for detecting the air-fuel ratio of the exhaust gas;
Detecting means for reducing a fuel injection amount of a predetermined target cylinder, and detecting an abnormality in air-fuel ratio variation between cylinders based on at least the rotational fluctuation of the target cylinder after the reduction;
With
The detection means reduces the fuel injection amount when the air-fuel ratio detected by the air-fuel ratio detection means becomes a predetermined value that is leaner than a predetermined reference value. An apparatus for detecting an abnormality in air-fuel ratio variation between cylinders of an engine is provided.

Preferably, the abnormality detection device further includes air-fuel ratio control means for feedback-controlling the air-fuel ratio of the mixture so that the air-fuel ratio detected by the air-fuel ratio detection means becomes the reference value,
The detection means reduces the fuel injection amount when the air-fuel ratio detected by the air-fuel ratio detection means during the feedback control becomes equal to or greater than the predetermined value.

  Preferably, the reference value is stoichiometric.

  Preferably, the detection means detects a lean deviation abnormality of the target cylinder based on a difference in rotational fluctuation before and after the fuel injection amount is reduced in the target cylinder.

  According to the present invention, an excellent effect that exhaust gas emission deterioration due to abnormality detection can be prevented as much as possible is exhibited.

1 is a schematic view of an internal combustion engine according to an embodiment of the present invention. It is a graph which shows the output characteristic of a pre-catalyst sensor and a post-catalyst sensor. It is a time chart for demonstrating the value showing rotation fluctuation. It is a time chart for demonstrating another value showing rotation fluctuation. It is a graph which shows the change of rotation fluctuation when fuel injection quantity is increased or decreased. It is a figure which shows the mode of the increase in fuel injection quantity, and the change of the rotation fluctuation | variation before and behind the increase. It is a time chart which shows the mode of a state change in case rich control is temperature rising suppression rich control. It is a flowchart which shows the control routine of the example of FIG. It is a time chart which shows the mode of a state change in case rich control is acceleration rich control. 10 is a flowchart showing a control routine of the example of FIG. It is a time chart which shows the mode of the state change of other embodiment. It is a flowchart which shows the control routine of the example of FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 schematically shows an internal combustion engine according to this embodiment. An illustrated internal combustion engine (engine) 1 is a V-type 8-cylinder spark ignition internal combustion engine (gasoline engine) mounted on an automobile. The engine 1 has a first bank B1 and a second bank B2, and the first bank B1 is provided with odd-numbered cylinders, that is, # 1, # 3, # 5, and # 7 cylinders. B2 is provided with even-numbered cylinders, that is, # 2, # 4, # 6, and # 8 cylinders. The # 1, # 3, # 5, and # 7 cylinders form the first cylinder group, and the # 2, # 4, # 6, and # 8 cylinders form the second cylinder group.

  Each cylinder is provided with an injector (fuel injection valve) 2. The injector 2 injects fuel into the intake passage of the corresponding cylinder, particularly into an intake port (not shown). Each cylinder is provided with a spark plug 13 for igniting the air-fuel mixture in the cylinder.

  The intake passage 7 for introducing the intake air includes a surge tank 8 as a collective portion, a plurality of intake manifolds 9 connecting the intake ports of each cylinder and the surge tank 8, and the upstream side of the surge tank 8. Of the intake pipe 10. The intake pipe 10 is provided with an air flow meter 11 and an electronically controlled throttle valve 12 in order from the upstream side. The air flow meter 11 outputs a signal having a magnitude corresponding to the intake flow rate.

  A first exhaust passage 14A is provided for the first bank B1, and a second exhaust passage 14B is provided for the second bank B2. The first and second exhaust passages 14 </ b> A and 14 </ b> B are joined on the upstream side of the downstream catalyst 19. Since the structure of the exhaust system upstream of the merge position is the same in both banks, only the first bank B1 side will be described here, and the second bank B2 side will be given the same reference numeral in the drawing and description thereof will be omitted. To do.

  The first exhaust passage 14A includes exhaust ports (not shown) of the cylinders # 1, # 3, # 5, and # 7, an exhaust manifold 16 that collects exhaust gases of these exhaust ports, and an exhaust manifold 16 And an exhaust pipe 17 installed on the downstream side. The exhaust pipe 17 is provided with an upstream catalyst 18. A pre-catalyst sensor 20 and a post-catalyst sensor 21 that are air-fuel ratio sensors for detecting the air-fuel ratio of the exhaust gas are installed on the upstream side and the downstream side (immediately and immediately after) of the upstream catalyst 18, respectively. Thus, one upstream catalyst 18, one before catalyst 20 and one after catalyst 21 are provided for each of a plurality of cylinders (or cylinder groups) belonging to one bank.

  In addition, it is also possible to provide the downstream catalyst 19 separately in these, without making the 1st and 2nd exhaust passage 14A, 14B merge.

  The engine 1 is provided with an electronic control unit (hereinafter referred to as ECU) 100 as control means and detection means. The ECU 100 includes a CPU, a ROM, a RAM, an input / output port, a storage device, and the like, all not shown. In addition to the air flow meter 11, the pre-catalyst sensor 20 and the post-catalyst sensor 21, the ECU 100 includes a crank angle sensor 22 for detecting the crank angle of the engine 1 and an accelerator opening sensor 23 for detecting the accelerator opening. The water temperature sensor 24 for detecting the temperature of the engine cooling water and other various sensors are electrically connected via an A / D converter or the like (not shown). The ECU 100 controls the injector 2, spark plug 13, throttle valve 12, etc. so as to obtain a desired output based on detection values of various sensors and the like, and controls the fuel injection amount, fuel injection timing, ignition timing, throttle opening degree. Control etc.

  The throttle valve 12 is provided with a throttle opening sensor (not shown), and a signal from the throttle opening sensor is sent to the ECU 100. The ECU 100 normally feedback-controls the opening of the throttle valve 12 (throttle opening) to an opening determined according to the accelerator opening.

  Further, the ECU 100 detects the amount of intake air per unit time, that is, the amount of intake air based on the signal from the air flow meter 11. The ECU 100 detects the load of the engine 1 based on at least one of the detected accelerator opening, throttle opening, and intake air amount.

  The ECU 100 detects the crank angle itself and the rotational speed of the engine 1 based on the crank pulse signal from the crank angle sensor 22. Here, “the number of rotations” means the number of rotations per unit time and is synonymous with the rotation speed. In the present embodiment, it means rpm per minute.

  The pre-catalyst sensor 20 is a so-called wide-range air-fuel ratio sensor, and can continuously detect an air-fuel ratio over a relatively wide range. FIG. 2 shows the output characteristics of the pre-catalyst sensor 20. As shown in the figure, the pre-catalyst sensor 20 outputs a voltage signal Vf having a magnitude proportional to the detected exhaust air-fuel ratio (pre-catalyst air-fuel ratio A / Ff). The output voltage when the exhaust air-fuel ratio is stoichiometric (theoretical air-fuel ratio, for example, A / F = 14.5) is Vreff (for example, about 3.3 V).

  On the other hand, the post-catalyst sensor 21 is a so-called O2 sensor and has a characteristic that the output value changes suddenly at the stoichiometric boundary. FIG. 2 shows the output characteristics of the post-catalyst sensor 21. As shown in the figure, the output voltage when the exhaust air-fuel ratio (post-catalyst air-fuel ratio A / Fr) is stoichiometric, that is, the stoichiometric equivalent value is Vrefr (for example, 0.45 V). The output voltage of the post-catalyst sensor 21 changes within a predetermined range (for example, 0 to 1 V). Generally, when the exhaust air-fuel ratio is leaner than stoichiometric, the output voltage Vr of the post-catalyst sensor is lower than the stoichiometric equivalent value Vrefr. When the exhaust air-fuel ratio is richer than stoichiometric, the output voltage Vr of the post-catalyst sensor is higher than the stoichiometric equivalent value Vrefr. Get higher.

  The upstream catalyst 18 and the downstream catalyst 19 are made of a three-way catalyst, and simultaneously purify NOx, HC and CO, which are harmful components in the exhaust gas, when the air-fuel ratio A / F of the exhaust gas flowing into each of them is near the stoichiometric. The air-fuel ratio width (window) that can simultaneously purify these three with high efficiency is relatively narrow.

  Therefore, during normal operation of the engine, the ECU 100 executes air-fuel ratio control (stoichiometric control) for controlling the air-fuel ratio of the exhaust gas flowing into the upstream catalyst 18 in the vicinity of the stoichiometric. In this air-fuel ratio control, the air-fuel ratio of the air-fuel mixture (specifically, the fuel injection amount) is feedback-controlled so that the exhaust air-fuel ratio detected by the pre-catalyst sensor 20 becomes a stoichiometric value that is a predetermined target air-fuel ratio. Fuel ratio control (main air-fuel ratio feedback control) and auxiliary air-fuel ratio control that feedback-controls the air-fuel ratio (specifically, fuel injection amount) of the air-fuel mixture so that the exhaust air-fuel ratio detected by the post-catalyst sensor 21 becomes stoichiometric. (Auxiliary air-fuel ratio feedback control).

  Thus, in the present embodiment, the reference value of the air-fuel ratio is stoichiometric, and the fuel injection amount corresponding to this stoichiometric (referred to as stoichiometric equivalent amount) is the reference value of the fuel injection amount. However, the reference values for the air-fuel ratio and the fuel injection amount may be other values.

  The air-fuel ratio control is performed on a bank basis or on a bank basis. For example, the detection values of the pre-catalyst sensor 20 and the post-catalyst sensor 21 on the first bank B1 side are used only for air-fuel ratio feedback control of the # 1, # 3, # 5, and # 7 cylinders belonging to the first bank B1. This is not used for the air-fuel ratio feedback control of the # 2, # 4, # 6, and # 8 cylinders belonging to the second bank B2. The reverse is also true. Air-fuel ratio control is executed as if there were two independent in-line four-cylinder engines. In the air-fuel ratio control, the same control amount is uniformly used for each cylinder belonging to the same bank.

  For example, in some cylinders (particularly one cylinder) of all the cylinders, a failure of the injector 2 or the like may occur, and variations in air-fuel ratio (imbalance) may occur between the cylinders. For example, for the first bank B1, the fuel injection amount of the # 1 cylinder becomes larger than the fuel injection amounts of the other # 3, # 5, and # 7 cylinders due to poor closing of the injector 2, and the air-fuel ratio of the # 1 cylinder is This is a case where the air-fuel ratio of the other # 3, # 5, and # 7 cylinders is greatly shifted to the rich side.

  Even at this time, if a relatively large correction amount is given by the above-described air-fuel ratio feedback control, the air-fuel ratio of the total gas (exhaust gas after joining) supplied to the pre-catalyst sensor 20 may sometimes be stoichiometrically controlled. However, looking at each cylinder, # 1 cylinder is larger and richer than stoichiometric, and # 3, # 5, and # 7 cylinders are leaner than stoichiometric. Is clear. In view of this, the present embodiment is equipped with a device that detects such a variation in air-fuel ratio between cylinders.

  Here, a value that is an imbalance rate is used as an index value that represents the degree of variation in the air-fuel ratio between cylinders. The imbalance rate is the ratio of the fuel injection amount of the cylinder (imbalance cylinder) causing the fuel injection amount deviation when only one cylinder among the plurality of cylinders causes the fuel injection amount deviation. Thus, it is a value indicating whether or not there is a deviation from the fuel injection amount of the cylinder (balance cylinder) in which the fuel injection amount deviation has not occurred, that is, the reference injection amount. When the imbalance rate is IB (%), the fuel injection amount of the imbalance cylinder is Qib, and the fuel injection amount of the balance cylinder, that is, the reference injection amount is Qs, IB = (Qib−Qs) / Qs × 100. The greater the imbalance rate IB, the greater the fuel injection amount deviation between the imbalance cylinder and the balance cylinder, and the greater the air-fuel ratio variation.

  On the other hand, in this embodiment, the fuel injection amount of a predetermined target cylinder is actively or forcibly increased or decreased, and a variation abnormality is detected based on at least the rotation fluctuation of the target cylinder after the increase or decrease.

  First, rotational fluctuation will be described. The rotational fluctuation means a change in the engine rotational speed or the crankshaft rotational speed, and can be expressed by, for example, the following values. In this embodiment, the rotation fluctuation for each cylinder can be detected.

  FIG. 3 shows a time chart for explaining the rotation fluctuation. The illustrated example is an example of an in-line four-cylinder engine, but it will be understood that the present invention can also be applied to a V-type eight-cylinder engine as in this embodiment. The firing order is the order of # 1, # 3, # 4, and # 2 cylinders.

  In FIG. 3, (A) shows the crank angle (° CA) of the engine. One engine cycle is 720 (° CA), and the crank angle for a plurality of cycles detected sequentially is shown in a sawtooth shape in the figure.

  (B) shows the time required for the crankshaft to rotate by a predetermined angle, that is, the rotation time T (s). Here, the predetermined angle is 30 (° CA), but may be another value (for example, 10 (° CA)). The longer the rotation time T, the slower the engine rotation speed. Conversely, the shorter the rotation time T, the faster the engine rotation speed. The rotation time T is detected by the ECU 100 based on the output of the crank angle sensor 22.

  (C) shows a rotation time difference ΔT described later. In the drawing, “normal” indicates a normal case in which no air-fuel ratio shift occurs in any cylinder, and “lean shift abnormality” indicates an imbalance rate IB = −30 (%) for only the # 1 cylinder. This shows an abnormal case where the lean deviation of is occurring. The lean deviation abnormality can be caused by, for example, clogging of an injector nozzle hole or a poor valve opening.

  First, the rotation time T at the same timing of each cylinder is detected by the ECU. Here, the rotation time T at the timing of compression top dead center (TDC) of each cylinder is detected. The timing at which the rotation time T is detected is referred to as detection timing.

  Next, at each detection timing, the ECU calculates a difference (T2−T1) between the rotation time T2 at the detection timing and the rotation time T1 at the immediately preceding detection timing. This difference is a rotation time difference ΔT shown in (C), and ΔT = T2−T1.

  Usually, in the combustion stroke after the crank angle exceeds TDC, the rotational speed increases, so the rotational time T decreases. In the subsequent compression stroke, the rotational speed decreases, and the rotational time T increases.

However, as shown in (B), when the # 1 cylinder has an abnormal lean shift, even if the # 1 cylinder is ignited, a sufficient torque cannot be obtained and the rotational speed is difficult to increase. The rotation time T is increased. Therefore, the rotation time difference ΔT in the # 3 cylinder TDC is a large positive value as shown in (C). The rotation time and rotation time difference in the # 3 cylinder TDC are defined as the rotation time and rotation time difference of the # 1 cylinder, respectively, and are represented by T ₁ and ΔT ₁ , respectively. The same applies to the other cylinders.

Next, since the # 3 cylinder is normal, when the # 3 cylinder is ignited, the rotational speed increases sharply. As a result, at the timing of the next # 4 cylinder TDC, the rotation time T is only slightly reduced compared to that of the # 3 cylinder TDC. Therefore, the rotation time difference ΔT ₃ of the # 3 cylinder detected in the # 4 cylinder TDC is a small negative value as shown in (C). Thus, the rotation time difference ΔT of a certain cylinder is detected for each next ignition cylinder TDC.

In the subsequent # 2 cylinder TDC and # 1 cylinder TDC, the same tendency as in the case of the # 4 cylinder TDC is observed, and the rotation time difference ΔT ₄ of the # ₄ cylinder and the rotation time difference ΔT ₂ of the # 2 cylinder detected at both timings. Both are small negative values. The above characteristics are repeated every engine cycle.

  Thus, it can be seen that the rotation time difference ΔT of each cylinder is a value representing the rotation fluctuation of each cylinder, and is a value correlated with the air-fuel ratio deviation amount of each cylinder. Therefore, the rotation time difference ΔT of each cylinder can be used as an index value of the rotation fluctuation of each cylinder. As the air-fuel ratio deviation amount of each cylinder increases, the rotational fluctuation of each cylinder increases and the rotation time difference ΔT of each cylinder increases.

  On the other hand, as shown in FIG. 3C, in the normal case, the rotation time difference ΔT is always near zero.

  In the example of FIG. 3, the case of the lean deviation abnormality is shown. However, the reverse tendency of the rich deviation, that is, the case where a large rich deviation occurs in only one cylinder has the same tendency. This is because when a large rich shift occurs, combustion is insufficient due to excessive fuel even when ignited, and sufficient torque cannot be obtained, resulting in large rotational fluctuations.

  Next, another value representing the rotation variation will be described with reference to FIG. (A) shows the crank angle (° CA) of the engine as in FIG. 3 (A).

  (B) shows the angular velocity ω (rad / s) which is the reciprocal of the rotation time T. ω = 1 / T. As a matter of course, the larger the angular velocity ω, the faster the engine rotational speed, and the smaller the angular velocity ω, the slower the engine rotational speed. The waveform of the angular velocity ω has a shape obtained by vertically inverting the waveform of the rotation time T.

  (C) shows the angular velocity difference Δω, which is the difference in angular velocity ω, as with the rotation time difference ΔT. The waveform of the angular velocity difference Δω also has a shape obtained by vertically inverting the waveform of the rotation time difference ΔT. “Normal” and “lean deviation abnormality” in the figure are the same as those in FIG.

  First, the angular velocity ω at the same timing of each cylinder is detected by the ECU. Again, the angular velocity ω at the timing of compression top dead center (TDC) of each cylinder is detected. The angular velocity ω is calculated by dividing 1 by the rotation time T.

  Next, at each detection timing, the ECU calculates a difference (ω2−ω1) between the angular velocity ω2 at the detection timing and the angular velocity ω1 at the immediately preceding detection timing. This difference is the angular velocity difference Δω shown in (C), and Δω = ω2−ω1.

  Normally, the rotational speed increases in the combustion stroke after the crank angle exceeds TDC, so the angular speed ω increases. In the subsequent compression stroke, the rotational speed decreases, and the angular speed ω decreases.

However, as shown in (B), when the # 1 cylinder has an abnormal lean shift, even if the # 1 cylinder is ignited, a sufficient torque cannot be obtained and the rotational speed is difficult to increase. The angular velocity ω at is small. Therefore, the angular velocity difference Δω in the # 3 cylinder TDC is a large negative value as shown in (C). The angular velocity and the angular velocity difference in the # 3 cylinder TDC are the angular velocity and the angular velocity difference of the # 1 cylinder, respectively, and are represented by ω ₁ and Δω ₁ , respectively. The same applies to the other cylinders.

Next, since the # 3 cylinder is normal, when the # 3 cylinder is ignited, the rotational speed increases sharply. As a result, at the timing of the next # 4 cylinder TDC, the angular velocity ω is only slightly increased compared to that of the # 3 cylinder TDC. Therefore, the angular velocity difference Δω ₃ of the # 3 cylinder detected in the # 4 cylinder TDC is a small positive value as shown in (C). Thus, the angular velocity difference Δω of a certain cylinder is detected for each subsequent ignition cylinder TDC.

Subsequent # 2 cylinder TDC and # 1 cylinder also seen the same tendency as in the case of the fourth cylinder TDC at TDC, the angular velocity difference [Delta] [omega ₄ and # 2 cylinder of the detected # 4 cylinder in both timing angular difference [Delta] [omega ₂ Both are small positive values. The above characteristics are repeated every engine cycle.

  Thus, it can be seen that the angular velocity difference Δω of each cylinder is a value representing the rotational fluctuation of each cylinder and is a value correlated with the air-fuel ratio deviation amount of each cylinder. Therefore, the angular velocity difference Δω of each cylinder can be used as an index value of the rotation fluctuation of each cylinder. As the air-fuel ratio deviation amount of each cylinder increases, the rotational fluctuation of each cylinder increases, and the angular velocity difference Δω of each cylinder decreases (increases in the minus direction).

  On the other hand, as shown in FIG. 4C, in the normal case, the angular velocity difference Δω is always near zero.

  As described above, there is a similar tendency in the case of reverse rich shift abnormality.

  Next, changes in rotational fluctuation when the fuel injection amount of one cylinder is actively increased or decreased will be described with reference to FIG.

  In FIG. 5, the horizontal axis indicates the imbalance rate IB, and the vertical axis indicates the angular velocity difference Δω as an index value of rotational fluctuation. Here, the imbalance rate IB of only one cylinder among all eight cylinders is changed, and the relationship between the imbalance rate IB of the one cylinder and the angular velocity difference Δω of the one cylinder at this time is indicated by a line a. The one cylinder is referred to as an active target cylinder. All the other cylinders are balance cylinders, and the stoichiometric equivalent amount is injected as the reference injection amount Qs.

  On the horizontal axis, IB = 0 (%) means a normal case where the imbalance ratio IB of the active target cylinder is 0 (%) and the active target cylinder is injecting a stoichiometric amount. The data at this time is indicated by plot b on line a. When moving from the state of IB = 0 (%) to the left side in the figure, the imbalance rate IB increases in the positive direction, and the fuel injection amount becomes excessive, that is, a rich state. On the contrary, when moving from IB = 0 (%) to the right side in the figure, the imbalance rate IB increases in the minus direction, and the fuel injection amount becomes too small, that is, a lean state.

  As can be seen from the characteristic line a, even if the imbalance ratio IB of the active target cylinder increases in the positive direction from 0 (%) or increases in the negative direction, the rotation fluctuation of the active target cylinder increases, and the active target cylinder increases. The angular velocity difference Δω tends to increase in the minus direction from near zero. As the imbalance rate IB increases from 0 (%), the slope of the characteristic line a becomes steeper, and the change in the angular velocity difference Δω with respect to the change in the imbalance rate IB tends to increase.

  Here, as indicated by an arrow c, it is assumed that the fuel injection amount of the active target cylinder is forcibly increased from the stoichiometric amount (IB = 0 (%)) by a predetermined amount. In the illustrated example, the imbalance rate is increased by approximately 40 (%). At this time, since the slope of the characteristic line a is gentle in the vicinity of IB = 0 (%), the angular velocity difference Δω remains substantially unchanged even after the increase, and the difference between the angular velocity differences Δω before and after the increase is extremely small. .

  On the other hand, as shown by plot d, consider a case where a rich shift has already occurred in the active target cylinder and the imbalance rate IB has a relatively large positive value. In the illustrated example, a rich shift of about 50 (%) occurs in the imbalance rate. As indicated by an arrow e from this state, if the fuel injection amount of the active target cylinder is forcibly increased by the same amount, the slope of the characteristic line a is steep in this region, so the angular velocity difference Δω after the increase is increased. Changes to the minus side largely before the increase, and the difference in angular velocity difference Δω before and after the increase becomes larger. In other words, the rotational fluctuation of the active target cylinder increases as the fuel injection amount increases.

  Therefore, it is possible to detect a variation abnormality based on at least the angular velocity difference Δω of the active target cylinder after the increase when the fuel injection amount of the active target cylinder is forcibly increased by a predetermined amount.

  That is, when the angular velocity difference Δω after the increase is smaller than a predetermined negative abnormality determination value α as shown in the figure (Δω <α), it is determined that there is a variation abnormality and the active target cylinder is identified as an abnormal cylinder. Can do. Conversely, if the angular velocity difference Δω after the increase is not smaller than the abnormality determination value α (Δω ≧ α), at least the active target cylinder can be determined to be normal.

  Alternatively, as shown in the drawing, it is possible to detect a variation abnormality based on the difference dΔω of the angular velocity difference Δω before and after the increase. In this case, if the angular velocity difference before the increase is Δω1 and the angular velocity difference after the increase is Δω2, the difference dΔω can be defined as dΔω = Δω1−Δω2. When the difference dΔω exceeds a predetermined positive abnormality determination value β1 (dΔω ≧ β1), it can be determined that there is a variation abnormality and the active target cylinder can be identified as an abnormal cylinder. Conversely, when the difference dΔω does not exceed the abnormality determination value β1 (dΔω <β1), at least the active target cylinder can be determined to be normal.

  The same can be said when forced reduction is performed in a region where the imbalance rate is negative. As indicated by an arrow f, it is assumed that the fuel injection amount of the active target cylinder is forcibly reduced by a predetermined amount from the stoichiometric amount (IB = 0 (%)). In the illustrated example, the imbalance rate is reduced by about 10%. The reason why the amount of reduction is smaller than the amount of increase is that if too much weight reduction is performed on the lean deviation abnormal cylinder, a misfire will occur. At this time, since the slope of the characteristic line a is relatively gradual, the angular velocity difference Δω after the decrease is only slightly smaller than before the decrease, and the difference between the angular velocity differences Δω before and after the increase is small.

  On the other hand, as shown by the plot g, let us consider a case where a lean shift has already occurred in the active target cylinder and the imbalance rate IB has a relatively large negative value. In the illustrated example, a lean shift of about −20 (%) occurs in the imbalance rate. As indicated by the arrow h from this state, if the fuel injection amount of the active target cylinder is forcibly reduced by the same amount, the slope of the characteristic line a is relatively steep in this region. The difference Δω is greatly changed to the minus side before the weight reduction, and the difference between the angular velocity differences Δω before and after the weight reduction becomes large. That is, the rotational fluctuation of the active target cylinder increases due to the decrease in the fuel injection amount.

  Therefore, it is possible to detect a variation abnormality based on at least the angular velocity difference Δω of the active target cylinder after the reduction when the fuel injection amount of the active target cylinder is forcibly reduced by a predetermined amount.

  That is, if the angular velocity difference Δω after the reduction is smaller than a predetermined negative abnormality determination value α as shown in the figure (Δω <α), it is determined that there is a variation abnormality and the active target cylinder is identified as an abnormal cylinder. Can do. Conversely, if the angular velocity difference Δω after the reduction is not smaller than the abnormality determination value α (Δω ≧ α), at least the active target cylinder can be determined to be normal.

  Alternatively, as shown in the drawing, it is possible to detect a variation abnormality based on the difference dΔω of the angular velocity difference Δω before and after the weight reduction. Also in this case, the difference dΔω between them can be defined as dΔω = Δω1−Δω2. When the difference dΔω exceeds a predetermined positive abnormality determination value β2 (dΔω ≧ β2), it can be determined that there is a variation abnormality and the active target cylinder can be identified as an abnormal cylinder. Conversely, when the difference dΔω does not exceed the abnormality determination value β2 (dΔω <β2), at least the active target cylinder can be determined to be normal.

  Here, since the increase amount is significantly larger than the decrease amount, the abnormality determination value β1 at the time of increase is made larger than the abnormality determination value β2 at the time of decrease. However, both abnormality determination values can be arbitrarily determined in consideration of the characteristics of the characteristic line a and the balance between the increase amount and the decrease amount. Both abnormality determination values can be set to the same value.

  It will be understood that when the rotation time difference ΔT is used as an index value of the rotation fluctuation of each cylinder, it is possible to detect an abnormality and specify an abnormal cylinder by the same method. Further, other values than those described above can be used as the index value of the rotational fluctuation of each cylinder.

  FIG. 6 shows the increase in the fuel injection amount for all eight cylinders and the change in rotational fluctuation before and after the increase. The upper row is before the increase, and the lower row is after the increase. As shown in the left end column in the left-right direction, as a method of increasing, all cylinders are increased uniformly and simultaneously by the same amount. That is, here, the predetermined target cylinders are all cylinders. Before the increase, a valve opening command is issued to inject the stoichiometric amount of fuel to the injectors 2 of all the cylinders, and after the increase, a predetermined amount of fuel is injected into the injectors 2 of all the cylinders by a predetermined amount more than the stoichiometric amount. A valve opening command is issued.

  In addition to the method of increasing all the cylinders at the same time, there is a method of increasing the number of cylinders in order and alternately in an arbitrary number of cylinders. For example, there is a method of increasing the amount by one cylinder, increasing the amount by two cylinders, or increasing the amount by four cylinders. The number of cylinders to be increased and the cylinder number can be arbitrarily set.

  As the number of target cylinders increases, there is a merit that the total increase time can be shortened, and there is a demerit that exhaust emission deteriorates. Conversely, the smaller the number of target cylinders, there is a merit that deterioration of exhaust emission can be suppressed, but there is a demerit that the total increase time becomes longer.

  Similar to FIG. 5, the angular velocity difference Δω is used as an index value of the rotation fluctuation of each cylinder.

  For example, in the normal state shown in the center column in the left-right direction, that is, when there is no air-fuel ratio deviation abnormality in any cylinder, the angular velocity difference Δω of all the cylinders is almost equal to 0 before the increase, There is little rotation fluctuation of the cylinder. Further, even after the increase, the angular velocity difference Δω of all the cylinders is almost equal and slightly increases in the minus direction, and the rotational fluctuations of all the cylinders do not increase that much. Therefore, the difference dΔω in the angular velocity difference before and after the increase is small.

  However, when the abnormality is shown in the right end column in the left-right direction, the behavior is different from that in the normal state. At the time of this abnormality, a rich shift abnormality corresponding to an imbalance rate of 50% occurs only in the # 8 cylinder, and only the # 8 cylinder is an abnormal cylinder. In this case, the angular velocity difference Δω of the remaining cylinders other than the # 8 cylinder is approximately equal to 0 before the increase, but the angular velocity difference Δω of the # 8 cylinder is slightly larger in the minus direction than the angular velocity difference Δω of the remaining cylinder.

  Nevertheless, there is not much difference between the angular velocity difference Δω of the # 8 cylinder and the angular velocity difference Δω of the remaining cylinders. Therefore, depending on the angular velocity difference Δω before the increase, abnormality detection and abnormal cylinder identification cannot be performed with sufficient accuracy.

  On the other hand, after the increase, the angular velocity difference Δω of the remaining cylinders is almost equal and slightly changes in the minus direction compared to before the increase, but the angular velocity difference Δω of the # 8 cylinder greatly changes in the minus direction. Therefore, the difference dΔω in angular velocity difference before and after the increase in the # 8 cylinder is significantly larger than that in the remaining cylinders. Therefore, using this difference, abnormality detection and abnormal cylinder identification can be performed with sufficient accuracy.

  In this case, only the difference dΔω between the # 8 cylinders becomes larger than the abnormality determination value β1, so that it is possible to detect that there is a rich shift abnormality in the # 8 cylinder.

  It will be understood that the same method can be adopted when the fuel injection amount is forcibly reduced to detect a lean deviation abnormality of any cylinder.

  The above is the outline of variation abnormality detection in this embodiment. Hereinafter, unless otherwise specified, the angular velocity difference Δω is used as an index value of the rotation fluctuation of each cylinder.

  By the way, the forced increase of the fuel injection amount worsens the exhaust emission (especially HC, CO). This is because the fuel injection amount is shifted from the stoichiometric amount. For this reason, when detecting the rich shift abnormality of any cylinder by forcibly increasing the fuel injection amount, it is desirable to perform detection at a timing at which exhaust emission is not deteriorated as much as possible.

  Therefore, in the present embodiment, forced increase of the fuel injection amount is executed during execution of predetermined rich control for enriching the air-fuel ratio. That is, the fuel injection amount is forcibly increased by using the rich control timing in such a manner as to share or overlap with the rich control timing. Thereby, it is possible to avoid performing forced increase for abnormality detection alone, and to prevent exhaust emission deterioration due to abnormality detection execution as much as possible.

  Here, the rich control includes, for example, a temperature rise suppression rich control that is executed to suppress the temperature increase of the upstream catalyst 18. That is, when the engine is operated at a high load for a relatively long time, the temperature of the upstream catalyst 18 may rise to an excessive temperature. This excessive temperature rise may cause damage such as thermal damage to the upstream catalyst 18. Therefore, the temperature rise suppression rich control is performed to increase the fuel injection amount by a predetermined amount from the stoichiometric amount to prevent the upstream catalyst 18 from being overheated.

  When the temperature rise suppression rich control is executed, the in-cylinder air-fuel mixture becomes in a state of excessive fuel and insufficient oxygen, and as a result, the exhaust temperature decreases. Therefore, by supplying the exhaust gas whose temperature has decreased to the upstream catalyst 18, an increase in the temperature of the upstream catalyst 18 can be suppressed, or the temperature thereof can be decreased, and an excessive temperature increase can be prevented.

  The temperature increase suppression rich control is executed when the temperature of the upstream catalyst 18, that is, the catalyst temperature Tc becomes equal to or higher than a predetermined temperature. The catalyst temperature Tc may be directly detected by a temperature sensor, but in the present embodiment, the catalyst temperature Tc is estimated by the ECU 100 based on engine parameters (for example, the rotational speed and the load) representing the engine operating state.

  Alternatively, the rich control may comprise acceleration rich control that is executed when the engine is accelerated. That is, it is necessary to quickly accelerate the engine when there is a request for acceleration from the user. Therefore, at this time, in order to increase the engine output with a high response, acceleration rich control is executed in which the fuel injection amount is increased from the stoichiometric amount. The acceleration rich control is executed when the detected engine load becomes a predetermined value or more.

  Note that the air-fuel ratio feedback control is stopped during the execution of the rich control, and the fuel injection amount is controlled by the open control. At this time, the fuel injection amount is controlled to an amount corresponding to the air-fuel ratio, for example 14.0.

  In the temperature increase suppression rich control, for example, a value obtained by simply averaging the catalyst temperatures Tc of the two upstream catalysts 18 in both banks can be used as the catalyst temperature Tc. Alternatively, for safety, the catalyst temperature Tc of the one upstream catalyst 18 on the high temperature side may be used.

  FIG. 7 shows a state change when the rich control is the temperature rise suppression rich control.

  (A) is a catalyst temperature Tc (° C.) as an estimated value, (B) is an on / off state of temperature increase suppression rich control, and (C) is an on / off state of active rich control that is forced increase control for abnormality detection. . Here, “on” and “off” refer to states of execution and non-execution, respectively.

  When the catalyst temperature Tc rises and reaches the predetermined temperature T1 or higher, the temperature rise suppression rich control and the active rich control are executed and started (time t1).

  Here, the temperature rise suppression rich control and the active rich control are substantially the same. For convenience, in the latter case, during execution of the active rich control, as shown in FIG. 6, the fuel injection amounts of all the cylinders are simultaneously increased by a predetermined amount from the stoichiometric amount. The amount of increase may be the same as or different from the amount of increase in temperature increase suppression rich control alone, but if it is different, it is preferable to increase the amount of increase compared to the case of temperature increase suppression rich control alone.

  Further, the angular velocity difference Δω of all cylinders is detected immediately before the increase. Note that the angular velocity difference Δω of all cylinders may always be detected, and the angular velocity difference Δω of all cylinders at the timing immediately before the increase may be obtained.

  Next, when the catalyst temperature Tc decreases and becomes lower than the predetermined temperature T1, the temperature increase suppression rich control and the active rich control are ended (time t2). As a result, active rich control is executed only for a time TR from time t1 to time t2.

  During execution of active rich control, the angular velocity difference Δω of all cylinders after the increase is always detected for a plurality of samples. Simultaneously with or immediately after the end of the active rich control, the plurality of samples are simply averaged, and the angular velocity difference Δω of all the cylinders after the final increase is calculated. Then, the difference dΔω in angular velocity difference before and after the increase is calculated.

  When the difference dΔω among all the cylinders does not exceed the abnormality determination value β1, it is determined that no rich deviation abnormality has occurred in any of the cylinders. On the other hand, if the difference dΔω between the cylinders exceeds the abnormality determination value β1, it is determined that the rich deviation abnormality has occurred in the cylinder.

  Note that the active rich control does not necessarily have to be executed during the entire period of the temperature rise suppression rich control, and may be executed only during a partial period thereof. Similarly, at least one of the start timing and the end timing of the active rich control may not necessarily coincide with at least one of the start timing and the end timing of the temperature increase suppression rich control. For example, the active rich control may be started later than the start timing of the temperature rise suppression rich control. Further, the active rich control may be terminated when a predetermined time has elapsed from the start of the active rich control, or the active rich control is performed when a predetermined number of samples (for example, 100) are acquired from the start of the active rich control. May be terminated.

  In general, if the execution time TR of the active rich control is lengthened, it is advantageous for increasing the number of samples and improving detection accuracy. However, the total increase time is prolonged, which is disadvantageous in terms of exhaust emission. Conversely, shortening the execution time TR of the active rich control is advantageous in terms of exhaust emission by shortening the total increase time, but is disadvantageous in improving detection accuracy because the number of samples is reduced.

  FIG. 8 shows a control routine of the example of FIG. This routine can be repeatedly executed by the ECU 100 at every predetermined calculation cycle.

  In step S101, it is determined whether the temperature rise suppression rich control is being executed. If it is not being executed, the process is terminated. If it is being executed, the process proceeds to step S102 where active rich control is executed.

  Next, the case where the rich control is the acceleration rich control will be described with reference to FIG. (A) shows the detected engine load KL, (B) shows the on / off state of acceleration rich control, and (C) shows the on / off state of active rich control.

  When the load KL increases and reaches a predetermined value KL1 or more, acceleration rich control and active rich control are executed and started (time t1). The acceleration rich control and the active rich control are substantially the same. Then, when the load KL decreases and becomes less than the predetermined value KL1, the acceleration rich control and the active rich control are ended (time t2). Other points are the same as in the above example.

  FIG. 10 shows a control routine of the example of FIG. This routine can be repeatedly executed by the ECU 100 at every predetermined calculation cycle.

  In step S201, it is determined whether acceleration rich control is being executed. If it is not being executed, the process is terminated. If it is being executed, the process proceeds to step S202 where active rich control is executed.

  Next, another embodiment will be described. The description of the same parts as in the basic embodiment described above will be omitted, and the differences will be mainly described below.

  In this other embodiment, when the air-fuel ratio detected by the pre-catalyst sensor 20 constituting the air-fuel ratio detection means becomes a predetermined reference value that is leaner than a predetermined reference value, the fuel injection amount is forcibly reduced. It is something to execute.

  When air-fuel ratio feedback control (stoichiometric control) is performed with the stoichiometric target air-fuel ratio as described above, the exhaust air-fuel ratio detected by the pre-catalyst sensor 20, that is, the pre-catalyst air-fuel ratio A / Ff, is usually located in the vicinity of the stoichiometry. . However, during transient operation such as when the engine is accelerating or decelerating, the pre-catalyst air-fuel ratio A / Ff may temporarily deviate from stoichiometry and become leaner than stoichiometry.

  In the present embodiment, the pre-catalyst air-fuel ratio A / Ff is utilized leaner than the stoichiometry, and the forced reduction of the fuel injection amount is executed in a manner such as to ride on or overlap with this. Thereby, it is possible to avoid performing forced reduction for abnormality detection alone, and to prevent exhaust emission deterioration (particularly NOx deterioration) due to abnormality detection execution as much as possible.

  Note that the timing at which the pre-catalyst air-fuel ratio A / Ff becomes leaner than the stoichiometric is not limited to the temporary timing at the time of transient operation. For example, when performing lean burn control in which the target air-fuel ratio is set to a value leaner than the stoichiometric value for the purpose of improving fuel efficiency or the like, forced reduction for abnormality detection may be performed during the lean burn control.

  FIG. 11 shows a state change according to the present embodiment. (A) shows the pre-catalyst air-fuel ratio A / Ff detected by the pre-catalyst sensor 20, and (B) shows the on / off state of active lean control, which is forced reduction control for abnormality detection.

  For example, during the execution of stoichiometric control, when the pre-catalyst air-fuel ratio A / Ff reaches a predetermined value Z1 (for example, 14.7) that is leaner than stoichiometric due to the transient operation of the engine, active lean control is executed at that time. Start (time t1).

  That is, when the pre-catalyst air-fuel ratio A / Ff is equal to or greater than the predetermined value Z1, the fuel injection amounts of all the cylinders are simultaneously reduced by a predetermined amount from the stoichiometric equivalent amount. Therefore, this reduction is regarded as active lean control and is used for detecting rotational fluctuations after reduction. This means that forced reduction is executed when the pre-catalyst air-fuel ratio A / Ff becomes equal to or greater than the predetermined value Z1. The amount of reduction is a value corresponding to the difference between the pre-catalyst air-fuel ratio A / Ff and stoichiometry.

  Similar to the basic embodiment, the angular velocity difference Δω of all the cylinders is detected immediately before the pre-catalyst air-fuel ratio A / Ff becomes equal to or greater than the predetermined value Z1. Alternatively, the angular velocity difference Δω of all cylinders may be detected at all times, and the angular velocity difference Δω of all cylinders at the timing immediately before the pre-catalyst air-fuel ratio A / Ff becomes equal to or greater than the predetermined value Z1 may be obtained.

  Alternatively, the angular velocity difference Δω of all the cylinders at the timing when the pre-catalyst air-fuel ratio A / Ff is near the stoichiometric may be acquired. Here, the vicinity of stoichiometry means within a range of ± α with respect to stoichiometry. α is a minute predetermined value, for example, 0.1.

  Next, when the pre-catalyst air-fuel ratio A / Ff decreases (moves to the rich side) and becomes less than the predetermined value Z1, the active lean control is terminated (time t2). That is, this time is the end time of the rotation fluctuation detection after the reduction, which means the end of the active lean control. As a result, active lean control is executed for a time TL from time t1 to time t2.

  During the execution of active lean control, the angular velocity difference Δω of all the cylinders after reduction is always detected for a plurality of samples. Simultaneously with or immediately after the end of the active lean control, the plurality of samples are simply averaged, and the angular velocity difference Δω of all the cylinders after the final weight reduction is calculated. Then, the difference dΔω in the angular velocity difference before and after the reduction is calculated.

  When the difference dΔω among all the cylinders does not exceed the abnormality determination value β2, it is determined that no lean deviation abnormality has occurred in any cylinder. On the other hand, if the difference dΔω between the cylinders exceeds the abnormality determination value β2, it is determined that a lean deviation abnormality has occurred in the cylinder.

  Note that the active lean control does not necessarily have to be executed during the entire period (referred to as the lean period) in which the pre-catalyst air-fuel ratio A / Ff is equal to or greater than the predetermined value Z1, and is executed only during a partial period. Also good. Similarly, at least one of the start timing and the end timing of active lean control may not necessarily coincide with at least one of the start timing and end timing of the lean period. For example, the active lean control may be started after the start timing of the lean period. In this case, as the rotation fluctuation before the decrease, it is preferable to use the rotation fluctuation just before the start of the lean period or before that. Further, the active lean control may be terminated when a predetermined time has elapsed from the start of the active lean control during the lean period, or a predetermined number (for example, 100) of each cylinder during the lean period and from the start of the active lean control. The active lean control may be terminated when each sample is acquired.

  FIG. 12 shows a control routine of the example of FIG. This routine can be repeatedly executed by the ECU 100 at every predetermined calculation cycle.

  In step S301, it is determined whether the pre-catalyst air-fuel ratio A / Ff is equal to or greater than a predetermined value Z1. If not, the process is terminated. If so, the process proceeds to step S302, and active lean control is executed.

  The preferred embodiment of the present invention has been described in detail above, but various other embodiments of the present invention are conceivable. For example, instead of using the difference dΔω between the angular velocity difference Δω1 before the increase and the angular velocity difference Δω2 after the increase, the ratio between the two can be used. The same applies to the difference in angular velocity difference dΔω before and after the decrease, or the difference in rotation time difference ΔT before and after the increase or decrease. The present invention is not limited to a V-type 8-cylinder engine but can be applied to engines of various other types and the number of cylinders. As the post-catalyst sensor, a wide air-fuel ratio sensor similar to the pre-catalyst sensor may be used.

  The embodiment of the present invention is not limited to the above-described embodiment, and includes all modifications, applications, and equivalents included in the concept of the present invention defined by the claims. Therefore, the present invention should not be construed as being limited, and can be applied to any other technique belonging to the scope of the idea of the present invention.

1 Internal combustion engine
2 Injector 11 Air flow meter 12 Throttle valve 18 Upstream catalyst 20 Pre-catalyst sensor 22 Crank angle sensor 23 Accelerator opening sensor 100 Electronic control unit (ECU)

Claims (10)

Rich control means for executing predetermined rich control for enriching the air-fuel ratio;
Detecting means for increasing a fuel injection amount of a predetermined target cylinder and detecting an abnormality in air-fuel ratio variation between cylinders based on at least the rotational fluctuation of the target cylinder after the increase;
With
The detection means executes an increase in the fuel injection amount during execution of the rich control. An inter-cylinder air-fuel ratio variation abnormality detection device for a multi-cylinder internal combustion engine. 2. The inter-cylinder air-fuel ratio of the multi-cylinder internal combustion engine according to claim 1, wherein the rich control is a temperature increase suppression rich control that is executed to suppress a temperature increase of a catalyst provided in an exhaust passage. Variation abnormality detection device. A temperature acquisition means for detecting or estimating the temperature of the catalyst;
3. The multi-cylinder internal combustion engine according to claim 2, wherein the rich control unit performs the temperature increase suppression rich control when the catalyst temperature detected or estimated by the temperature acquisition unit becomes equal to or higher than a predetermined temperature. An abnormality detection device for variation in air-fuel ratio between cylinders of an engine. The said rich control consists of acceleration rich control performed at the time of the acceleration of the said internal combustion engine. The inter-cylinder air-fuel ratio variation abnormality detection apparatus of the multi-cylinder internal combustion engine according to claim 1. A load detecting means for detecting a load of the internal combustion engine;
5. The inter-cylinder space of the multi-cylinder internal combustion engine according to claim 4, wherein the rich control unit performs the acceleration rich control when a load detected by the load detection unit exceeds a predetermined value. Fuel ratio variation abnormality detection device. The detection means detects a rich shift abnormality of the target cylinder based on a difference in rotational fluctuation before and after the increase of the fuel injection amount in the target cylinder. The inter-cylinder air-fuel ratio variation abnormality detecting device for a multi-cylinder internal combustion engine as described. Air-fuel ratio detection means for detecting the air-fuel ratio of the exhaust gas;
Detecting means for reducing a fuel injection amount of a predetermined target cylinder, and detecting an abnormality in air-fuel ratio variation between cylinders based on at least the rotational fluctuation of the target cylinder after the reduction;
With
The detection means reduces the fuel injection amount when the air-fuel ratio detected by the air-fuel ratio detection means becomes a predetermined value that is leaner than a predetermined reference value. An abnormality detection device for variation in air-fuel ratio between cylinders of an engine. Air-fuel ratio control means for feedback-controlling the air-fuel ratio of the air-fuel mixture so that the air-fuel ratio detected by the air-fuel ratio detection means becomes the reference value;
The said detection means performs the reduction | decrease of the said fuel injection amount, when the air fuel ratio detected by the said air fuel ratio detection means becomes more than the said predetermined value during the said feedback control. The cylinder air-fuel ratio variation abnormality detection apparatus of the multi-cylinder internal combustion engine. 9. The inter-cylinder air-fuel ratio variation abnormality detection device for a multi-cylinder internal combustion engine according to claim 7 or 8, wherein the reference value is stoichiometric. 10. The lean detection apparatus according to claim 7, wherein the detection unit detects a lean deviation abnormality of the target cylinder based on a difference in rotational fluctuation before and after a decrease in the fuel injection amount in the target cylinder. The inter-cylinder air-fuel ratio variation abnormality detecting device for a multi-cylinder internal combustion engine as described.

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