JP2008038785A - Cylinder-by-cylinder air-fuel ratio control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent an erroneous diagnosis of an abnormal diagnosis influenced by a cylinder-by-cylinder air-fuel ratio control, in a system for controlling the air-fuel ratio of respective cylinders based on a detecting value of one air-fuel ratio sensor arranged in an exhaust confluent part of an internal combustion engine. <P>SOLUTION: The air-fuel ratio of the respective cylinders is estimated based on the detecting value of the air-fuel ration sensor 37 arranged in the exhaust confluent part 36; a cylinder-by-cylinder air-fuel ratio correction quantity is calculated based on the estimated air-fuel ratio of the respective cylinder; the cylinder-by-cylinder air-fuel ratio correction quantity is learnt by dulling processing; the air-fuel ratio (a fuel injection quantity) of an air-fuel mixture supplied to the respective cylinders, is corrected every cylinder based on the cylinder-by-cylinder air-fuel ratio correction quantity and its learning value; and is controlled so as to reduce a variation in the air-fuel ratio between the cylinders. The erroneous diagnosis of the abnormal diagnosis is prevented by prohibiting the abnormal diagnosis influenced by the cylinder-by-cylinder air-fuel ratio control, when a state of falling wide from a predetermined range (an allowable range) in the cylinder-by-cylinder air-fuel ratio correction quantity of any cylinder, continues for a while, when controlling this cylinder-by-cylinder air-fuel ratio. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a cylinder of an internal combustion engine having a function of estimating an air-fuel ratio (cylinder-specific air-fuel ratio) of each cylinder based on a detection value of an air-fuel ratio sensor installed in an exhaust gas merging portion where exhaust gases of a plurality of cylinders merge. It is an invention related to another air-fuel ratio control device.

In recent years, as described in Patent Document 1 (Japanese Patent Application Laid-Open No. 2005-207405), a plurality of cylinders based on the output of one air-fuel ratio sensor installed at an exhaust merging portion where exhaust gases from a plurality of cylinders merge. The air-fuel ratio of each cylinder is estimated for each cylinder, and the air-fuel ratio correction amount (cylinder-by-cylinder correction amount) for each cylinder for correcting the variation in the air-fuel ratio for each cylinder is calculated. There is one that performs cylinder-by-cylinder air-fuel ratio control for controlling the air-fuel ratio (fuel injection amount) of a plurality of cylinders for each cylinder based on the correction amount. Further, in the cylinder-by-cylinder air-fuel ratio control system of Patent Document 1, the learning value of the cylinder-by-cylinder air-fuel ratio correction amount is obtained under operating conditions in which it is difficult to estimate the cylinder-by-cylinder air-fuel ratio (it is difficult to calculate the cylinder-by-cylinder air-fuel ratio correction amount). Is used to perform the air-fuel ratio control for each cylinder.
JP 2005-207405 A

  In engine control systems that have become increasingly electronically controlled in recent years, self-diagnosis that performs various abnormality diagnosis such as catalyst deterioration diagnosis, fuel system abnormality diagnosis, air-fuel ratio sensor abnormality diagnosis, combustion state diagnosis (misfire detection), and fuel property diagnosis The function is installed.

  All of these abnormality diagnoses are performed using the output of the air-fuel ratio sensor or a parameter that changes under the influence of the air-fuel ratio (for example, engine rotation fluctuation), so the control state of the cylinder-by-cylinder air-fuel ratio control is not stable. In some cases, the influence may cause misdiagnosis of the abnormality diagnosis.

  The present invention has been made in view of such circumstances. Accordingly, the object of the present invention is to provide a cylinder-by-cylinder air-fuel ratio control based on a detection value of one air-fuel ratio sensor installed in an exhaust gas merging section. An object of the present invention is to provide a cylinder-by-cylinder air-fuel ratio control apparatus for an internal combustion engine that can prevent an erroneous diagnosis of an abnormality diagnosis that is affected by another air-fuel ratio control.

  In order to achieve the above object, according to the first aspect of the present invention, an air-fuel ratio sensor for detecting an air-fuel ratio of the exhaust gas is installed at an exhaust merging portion where exhaust gases of a plurality of cylinders of the internal combustion engine merge, Cylinder air-fuel ratio estimating means for estimating the air-fuel ratio of each cylinder based on the detection value of the air-fuel ratio sensor, and air-fuel ratio correction of each cylinder for correcting the inter-cylinder variation of the air-fuel ratio for each of the plurality of cylinders A cylinder-by-cylinder air-fuel ratio correction amount calculating means for calculating the amount (hereinafter referred to as “cylinder-by-cylinder air-fuel ratio correction amount”), and correcting the fuel injection amount of each cylinder based on the cylinder-by-cylinder air-fuel ratio correction amount, In a cylinder-by-cylinder air-fuel ratio control device having a cylinder-by-cylinder air-fuel ratio control means for performing cylinder-by-cylinder air-fuel ratio control for reducing variation in fuel ratio, the output of the air-fuel ratio sensor and / or other exhaust gas sensor, or Effect of air-fuel ratio An abnormality diagnosis means for performing an abnormality diagnosis based on the received and changed parameters, and the abnormality diagnosis when the cylinder-by-cylinder air-fuel ratio correction amount or the learning value of one or more cylinders is out of a predetermined range; And a diagnosis prohibiting means for prohibiting at least one of the abnormality diagnosis by the means or invalidating the diagnosis result.

  In this way, when the cylinder-by-cylinder air-fuel ratio correction amount or the learned value of any one or more cylinders deviates from the predetermined range (allowable range), the control state of the cylinder-by-cylinder air-fuel ratio control is not good. Since it can be judged stable and the abnormality diagnosis can be prohibited or the diagnosis result can be invalidated, it is possible to prevent erroneous diagnosis of the abnormality diagnosis affected by the air-fuel ratio control for each cylinder, and the reliability of the abnormality diagnosis Can be improved.

  In this case, as in claim 2, at least the abnormality diagnosis by the abnormality diagnosing means is performed only for the operation region where the cylinder-by-cylinder air-fuel ratio correction amount or the learning value thereof is out of the predetermined range. One may be prohibited or the diagnosis result may be invalidated. In this way, the cylinder-by-cylinder air-fuel ratio correction amount or the cylinder-by-cylinder air-fuel ratio correction amount is prevented while prohibiting or invalidating the abnormality diagnosis only in the operation region where the learning value is outside the predetermined range. Alternatively, in other operating regions where the learned value falls within the predetermined range, the abnormality diagnosis can be continued, so that the abnormality can be detected early when an abnormality occurs.

  Further, as described in claim 3, whether or not the abnormality diagnosis by the abnormality diagnosing means is performed based on the comparison result of any one or two or more cylinder-by-cylinder air-fuel ratio correction amount or its learning value with a predetermined range. May be determined by the diagnosis execution condition determining means. Even if it does in this way, the effect similar to the said Claim 1 can be acquired.

  In this case, as described in claim 4, in an operation region different from the operation region in which the air-fuel ratio correction amount or the learning value for each cylinder of any one or two or more cylinders is out of the predetermined range, an abnormality is detected by the abnormality diagnosis means. The execution of diagnosis may be permitted. Even if it does in this way, the effect similar to the said Claim 2 can be acquired.

  Further, as described in claim 5, any one or two or more cylinder-by-cylinder air-fuel ratio correction amounts or learning values thereof are compared with a predetermined range, and determination of abnormality diagnosis by the abnormality diagnosis means based on the comparison result A condition (for example, a determination threshold value or a diagnostic parameter) may be changed by a determination condition changing unit. In this way, when the cylinder-by-cylinder air-fuel ratio correction amount of any one or two or more cylinders is out of the predetermined range, the abnormality diagnosis determination condition is changed to a severe determination condition in which abnormality is not easily detected. This makes it possible to prevent erroneous diagnosis of abnormality diagnosis that is affected by the cylinder-by-cylinder air-fuel ratio control.

  In this case, as in the sixth aspect, in the operating region where the air-fuel ratio correction amount for each cylinder of one or more cylinders or the learning value thereof is different from the operating region outside the predetermined range, the abnormality diagnosis determination condition Is preferably set to the same determination condition as the operation region when the cylinder-by-cylinder air-fuel ratio correction amount is within a predetermined range. In this way, the abnormality diagnosis judgment condition is changed to a strict judgment condition in which the abnormality is difficult to be detected only in the operation region where the cylinder-by-cylinder air-fuel ratio correction amount or the learning value thereof is out of the predetermined range, and the abnormality diagnosis misdiagnosis is performed. In other operating regions where the cylinder-by-cylinder air-fuel ratio correction amount or its learned value falls within a predetermined range, the same abnormality diagnosis as in normal times can be continued, and the abnormality is detected early when an abnormality occurs. be able to.

  In the invention according to claims 1 to 6 described above, as in claim 7, the catalyst deterioration diagnosis, the fuel system abnormality diagnosis, the air system abnormality diagnosis, the air-fuel ratio sensor abnormality diagnosis, the exhaust gas sensor abnormality diagnosis, It is preferable to perform at least one of a combustion state diagnosis and a fuel property diagnosis. Any of these abnormality diagnoses is an abnormality diagnosis performed based on an output of the air-fuel ratio sensor and / or other exhaust gas sensor or a parameter that changes under the influence of the air-fuel ratio.

  By the way, in the control (exhaust gas recirculation control, blow-by gas recirculation control, evaporation gas purge control, etc.) that affects the air-fuel ratio in cylinder distribution, the degree of influence on the air-fuel ratio of each cylinder may be different for each cylinder. This causes a large variation in air-fuel ratio between cylinders. Therefore, if the control that affects the air-fuel ratio in the cylinder distribution is performed in the same way as normal when the cylinder-by-cylinder air-fuel ratio correction amount or the learning value thereof deviates from the predetermined range (allowable range), the cylinder-by-cylinder air-fuel ratio correction amount Alternatively, there is a possibility that the learning value becomes an abnormal value and the control state of the cylinder-by-cylinder air-fuel ratio control gets worse.

  In consideration of such circumstances, as in the eighth aspect, in the system that executes the control that affects the air-fuel ratio in the cylinder distribution, the cylinder-by-cylinder air-fuel ratio correction amount of one or more cylinders or When the learning value is out of a predetermined range, a configuration may be provided that includes a limiting unit that reduces the control ratio of the control that affects the air-fuel ratio in cylinder distribution or prohibits the control. By so doing, it is possible to suppress the deterioration of the control state of the cylinder-by-cylinder air-fuel ratio control by the limiting means, and it is possible to prevent erroneous diagnosis of abnormality diagnosis that is affected by the cylinder-by-cylinder air-fuel ratio control.

  In this case, as in the ninth aspect, the air-fuel ratio is affected by the cylinder distribution only in the operation region where the cylinder-by-cylinder air-fuel ratio correction amount or the learning value thereof is out of the predetermined range. You may make it make the control ratio of the exerted control small, or prohibit the said control. In this way, even when the cylinder-by-cylinder air-fuel ratio correction amount or the learning value of any one or more cylinders is out of the predetermined range, depending on the operation region, the air-fuel ratio is affected by cylinder distribution. Control can be performed in the same way as normal.

  Several embodiments embodying the best mode for carrying out the present invention will be described below.

A first embodiment of the present invention will be described with reference to FIGS.
First, a schematic configuration of the entire engine control system will be described with reference to FIG.
An air cleaner 13 is provided at the most upstream portion of the intake pipe 12 of an in-line four-cylinder engine 11 that is an internal combustion engine, for example, and an air flow meter 14 that detects the intake air amount is provided downstream of the air cleaner 13. . On the downstream side of the air flow meter 14, a throttle valve 15 whose opening is adjusted by a motor or the like and a throttle opening sensor 16 for detecting the throttle opening are provided.

  Further, a surge tank 17 is provided on the downstream side of the throttle valve 15, and an intake pipe pressure sensor 18 for detecting the intake pipe pressure is provided in the surge tank 17. The surge tank 17 is provided with an intake manifold 19 for introducing air into each cylinder of the engine 11, and a fuel injection valve 20 for injecting fuel is attached in the vicinity of the intake port of the intake manifold 19 of each cylinder. Yes. During engine operation, the fuel in the fuel tank 21 is sent to the delivery pipe 23 by the fuel pump 22 and fuel is injected from the fuel injection valve 20 of each cylinder at each injection timing of each cylinder. A fuel pressure sensor 24 that detects fuel pressure (fuel pressure) is attached to the delivery pipe 23.

  Further, the engine 11 is provided with variable valve timing mechanisms 27 and 28 for changing the opening and closing timings of the intake valve 25 and the exhaust valve 26, respectively. Further, the engine 11 is provided with an intake cam angle sensor 31 and an exhaust cam angle sensor 32 that output a cam angle signal in synchronization with the rotation of the intake cam shaft 29 and the exhaust cam shaft 30, and the rotation of the crank shaft of the engine 11. Is provided with a crank angle sensor 33 for outputting a pulse of a crank angle signal at every predetermined crank angle (for example, every 30 ° C. A).

  On the other hand, an air-fuel ratio sensor 37 for detecting the air-fuel ratio of the exhaust gas is installed in the exhaust gas converging portion 36 where the exhaust manifold 35 of each cylinder of the engine 11 joins. A catalyst 38 such as a three-way catalyst for purifying CO, HC, NOx and the like is provided. Further, an oxygen sensor 41 (exhaust gas sensor) that detects rich / lean exhaust gas that has passed through the catalyst 38 is installed on the downstream side of the catalyst 38. The output of the oxygen sensor 41 is used for sub-feedback control for correcting the target air-fuel ratio upstream of the catalyst 38, or used for diagnosing deterioration of the catalyst 38.

  Although not shown, the engine 11 includes an exhaust gas recirculation device that recirculates part of the exhaust gas to the intake system, a blowby gas recirculation device that recirculates blowby gas leaking into the crankcase to the intake system, and fuel. An evaporative gas purge device that adsorbs evaporative gas (fuel evaporative gas) generated in the tank 21 into the canister and purges (releases) it into the intake system is mounted.

  Outputs of various sensors such as the air-fuel ratio sensor 37 described above are input to an engine control circuit (hereinafter referred to as “ECU”) 40. The ECU 40 is mainly composed of a microcomputer, and executes various engine control programs stored in a built-in ROM (storage medium), so that the fuel of the fuel injection valve 20 of each cylinder according to the engine operating state. Control injection quantity and ignition timing.

  Further, the ECU 40 diagnoses an abnormality based on the output of the air-fuel ratio sensor 37 upstream of the catalyst 38 and / or the oxygen sensor 41 downstream of the catalyst 38, or a parameter (engine speed fluctuation) that changes under the influence of the air-fuel ratio. For example, deterioration diagnosis of the catalyst 38, fuel system abnormality diagnosis, air system abnormality diagnosis, air-fuel ratio sensor 37 responsiveness abnormality diagnosis, oxygen sensor 41 abnormality diagnosis, combustion state diagnosis (misfire) Detection) and various abnormality diagnosis such as fuel property diagnosis.

  For example, the deterioration diagnosis of the catalyst 38 is diagnosed based on the ratio between the output change amount of the air-fuel ratio sensor 37 and the output change amount of the oxygen sensor 41. The fuel system abnormality diagnosis is made based on a cylinder-by-cylinder air-fuel ratio correction amount, which will be described later, and a learning value thereof. The responsiveness abnormality diagnosis of the air-fuel ratio sensor 37 is made based on the output change amount of the air-fuel ratio sensor 37. Misfire detection is diagnosed based on fluctuations in engine speed. The abnormality diagnosis of the oxygen sensor 41 is performed based on the relationship between the output behavior of the oxygen sensor 41 and the output behavior of the air-fuel ratio sensor 37. For example, if the air-fuel ratio on the upstream side of the catalyst 38 continues to be rich, the air-fuel ratio on the downstream side of the catalyst 38 changes to a rich state after a delay in which the rich component adsorption amount of the catalyst 38 becomes saturated. Therefore, at this time, whether or not the oxygen sensor 41 is abnormal may be determined based on whether or not the output of the oxygen sensor 41 has changed richly.

  In the first embodiment, the ECU 40 executes the routines for cylinder-by-cylinder air-fuel ratio control in FIGS. 2 to 4, thereby using the cylinder-by-cylinder air-fuel ratio estimation model to be described later during engine operation. Based on the detected value (the actual air-fuel ratio of the exhaust gas flowing through the exhaust gas merging portion 36), the air-fuel ratio of each cylinder (air-fuel ratio for each cylinder) is estimated, and the average value of the estimated air-fuel ratios of all cylinders is calculated. The value is set to the reference air-fuel ratio (target air-fuel ratio for all cylinders), and the deviation between the estimated air-fuel ratio of each cylinder (the estimated air-fuel ratio for each cylinder) and the reference air-fuel ratio is calculated for each cylinder. A fuel correction coefficient (cylinder-by-cylinder air-fuel ratio correction amount) for the fuel injection amount of each cylinder is calculated so as to decrease, and this cylinder-by-cylinder air-fuel ratio correction amount is learned by smoothing processing, etc. And the fuel injection amount of each cylinder based on the learned value It is, controlled so as to reduce the air-fuel ratio variation among the cylinders fuel ratio of a mixture supplied to each cylinder is corrected for each cylinder (hereinafter, this control of cylinder air-fuel ratio control). At this time, the cylinder-by-cylinder air-fuel ratio correction amount is learned by a smoothing process or the like, and the learned value is updated and stored for each cylinder in a rewritable nonvolatile memory (not shown) such as a backup RAM of the ECU 40. Note that, under operating conditions in which it is difficult to estimate the cylinder-by-cylinder air-fuel ratio (calculation of the cylinder-by-cylinder air-fuel ratio correction amount), the cylinder-by-cylinder air-fuel ratio control is performed using the learning value of the cylinder-by-cylinder air-fuel ratio correction amount. May be.

  Here, a specific example of a model (hereinafter referred to as “cylinder-specific air-fuel ratio estimation model”) that estimates the air-fuel ratio of each cylinder based on the detection value of the air-fuel ratio sensor 37 (the actual air-fuel ratio of the exhaust gas flowing through the exhaust gas merging portion 36). An example will be described.

  Paying attention to the gas exchange in the exhaust gas merging section 36, the detected value of the air-fuel ratio sensor 37 is given a predetermined weight to the estimated air-fuel ratio history of each cylinder and the detected value history of the air-fuel ratio sensor 37 in the exhaust gas merging section 36, respectively. The model is obtained by multiplying and adding, and the air-fuel ratio of each cylinder is estimated using the model. At this time, a Kalman filter is used as an observer.

More specifically, a gas exchange model in the exhaust merging portion 36 is approximated by the following equation (1).
ys (t) = k1 * u (t-1) + k2 * u (t-2) -k3 * ys (t-1) -k4 * ys (t-2)
...... (1)
Here, yS is a detected value of the air-fuel ratio sensor 37, u is an air-fuel ratio of the gas flowing into the exhaust gas merging portion 36, and k1 to k4 are constants.

  In the exhaust system, there are a primary delay element of gas inflow and mixing in the exhaust confluence 36 and a primary delay element due to a response delay of the air-fuel ratio sensor 37. Therefore, in the above equation (1), the history for the past two times is referred to in consideration of these first order lag elements.

When the above equation (1) is converted into a state space model, the following equations (2a) and (2b) are derived.
X (t + 1) = A.X (t) + B.u (t) + W (t) (2a)
Y (t) = C · X (t) + D · u (t) (2b)
Here, A, B, C, and D are model parameters, Y is a detected value of the air-fuel ratio sensor 37, X is an estimated air-fuel ratio of each cylinder as a state variable, and W is noise.

Further, when the Kalman filter is designed by the above equations (2a) and (2b), the following equation (3) is obtained.
X ^ (k + 1 | k) = A.X ^ (k | k-1) + K {Y (k) -C.A.X ^ (k | k-1)} (3) where X ^ (X hat) is the estimated air-fuel ratio of each cylinder, and K is the Kalman gain. The meaning of X ^ (k + 1 | k) represents that the estimated value of the next time (k + 1) is obtained from the estimated value of time (k).

  As described above, by configuring the cylinder-by-cylinder air-fuel ratio estimation model using the Kalman filter type observer, it is possible to sequentially estimate the air-fuel ratio of each cylinder as the combustion cycle progresses.

  By the way, during the engine operation, the ECU 40 performs deterioration diagnosis of the catalyst 38, fuel system abnormality diagnosis, air system abnormality diagnosis, air-fuel ratio sensor 37 abnormality diagnosis, oxygen sensor 41 abnormality diagnosis, combustion state diagnosis (misfire detection), fuel Various abnormality diagnoses such as property diagnosis are performed. These abnormality diagnoses are performed using the outputs of the air-fuel ratio sensor 37 and the oxygen sensor 41 and parameters (engine fluctuation fluctuations) that change under the influence of the air-fuel ratio. Therefore, when the cylinder-by-cylinder air-fuel ratio control is in an abnormal state, there is a possibility that the abnormality diagnosis is erroneously diagnosed due to the influence.

  As a countermeasure against this, in the first embodiment, when the cylinder-by-cylinder air-fuel ratio correction amount (or the learning value thereof) is out of the predetermined range that is allowed for a while, the cylinder-by-cylinder air-fuel ratio control is performed. By prohibiting the affected abnormality diagnosis, an erroneous diagnosis of the abnormality diagnosis due to unstable cylinder-by-cylinder air-fuel ratio control is prevented. Here, the abnormality diagnosis affected by the cylinder-by-cylinder air-fuel ratio control includes, for example, catalyst 38 deterioration diagnosis, fuel system abnormality diagnosis, air system abnormality diagnosis, air-fuel ratio sensor 37 abnormality diagnosis, oxygen sensor 41 abnormality diagnosis, combustion State diagnosis (misfire detection), fuel property diagnosis, etc., and abnormality diagnosis of at least one of these is prohibited.

  The above-described cylinder-by-cylinder air-fuel ratio control and abnormality diagnosis prevention are performed by the ECU 40 according to the routines shown in FIGS. The processing contents of each routine will be described below.

[Air-fuel ratio control routine for each cylinder]
The cylinder-by-cylinder air-fuel ratio control main routine of FIG. 2 is started at every predetermined crank angle (for example, every 30 ° C. A) in synchronization with the output pulse of the crank angle sensor 33. As a role. When this routine is started, first, in step 101, it is determined whether or not an execution condition for the cylinder-by-cylinder air-fuel ratio control is satisfied. As execution conditions for the cylinder-by-cylinder air-fuel ratio control, for example, there are the following conditions (1) to (4).

(1) The air-fuel ratio sensor 37 is in an active state
(2) The air-fuel ratio sensor 37 is not determined to be abnormal (failure)
(3) The engine 11 is in a warm-up state (for example, the cooling water temperature is equal to or higher than a predetermined temperature).
(4) The engine operating range (for example, engine speed and intake pipe pressure) must be an operating range where air-fuel ratio estimation accuracy can be ensured.

  The execution condition of the cylinder-by-cylinder air-fuel ratio control is satisfied when all of these four conditions (1) to (4) are satisfied. If any one of the conditions is not satisfied, the execution condition is not satisfied. If this execution condition is not satisfied, this routine is terminated without performing the subsequent processing.

  On the other hand, if the execution condition is satisfied, the routine proceeds to step 102, where the air-fuel ratio detection timing (sample timing of the output of the air-fuel ratio sensor 37) of each cylinder is set according to the engine load (for example, intake pipe pressure) at that time. Set by map. Note that the air-fuel ratio detection timing of each cylinder may be set by a map according to the engine load and the engine speed.

  Thereafter, the routine proceeds to step 103, where it is determined whether or not the current crank angle is the air-fuel ratio detection timing set in step 102. If it is not the air-fuel ratio detection timing, this routine is executed without performing the subsequent processing. Exit.

  On the other hand, if the current crank angle is the air-fuel ratio detection timing set in step 102, the routine proceeds to step 104 and the cylinder-by-cylinder air-fuel ratio control execution routine of FIG. 3 is executed. Thereafter, the routine proceeds to step 105, where an abnormality diagnosis prohibition determination routine of FIG. 5 described later is executed, and the cylinder-by-cylinder air-fuel ratio correction amount (or its learned value) of any cylinder is out of the allowable range. When the operation continues for a while, the abnormality diagnosis prohibition flag is set to ON (abnormal diagnosis prohibition), and abnormality diagnosis affected by the cylinder-by-cylinder air-fuel ratio control is prohibited.

[Cylinder-specific air-fuel ratio control execution routine]
The cylinder-by-cylinder air-fuel ratio control execution routine of FIG. 3 is a subroutine executed in step 104 of the cylinder-by-cylinder air-fuel ratio control main routine of FIG. When this routine is started, first, at step 201, the output (air-fuel ratio detection value) of the air-fuel ratio sensor 37 is read. Thereafter, the routine proceeds to step 202 where the air-fuel ratio of the cylinder that is the current air-fuel ratio estimation target is estimated based on the detected value of the air-fuel ratio sensor 37 using the cylinder-by-cylinder air-fuel ratio estimation model. The process of step 202 serves as the cylinder-by-cylinder air-fuel ratio estimating means in the claims. Thereafter, the process proceeds to step 203, where an average value of estimated air-fuel ratios of all cylinders is calculated, and the average value is set as a reference air-fuel ratio (target air-fuel ratio of all cylinders).

  Thereafter, the routine proceeds to step 204, where the deviation between the estimated air-fuel ratio of each cylinder and the reference air-fuel ratio is calculated, and the cylinder-by-cylinder air-fuel ratio correction amount (fuel correction amount of each cylinder) is calculated so that the deviation becomes smaller. Thereafter, the routine proceeds to step 205, where a cylinder-by-cylinder air-fuel ratio correction amount learning routine of FIG. 4 described later is executed to learn the cylinder-by-cylinder air-fuel ratio correction amount.

  Then, in the next step 206, the air-fuel ratio of the air-fuel mixture supplied to each cylinder is changed to each cylinder by correcting the fuel injection amount of each cylinder using the cylinder-by-cylinder air-fuel ratio correction amount and the learning value thereof. Correction is performed every time and control is performed so as to reduce variation in the air-fuel ratio between cylinders.

[Cylinder-specific air-fuel ratio correction amount learning routine]
The cylinder-by-cylinder air-fuel ratio correction amount learning routine of FIG. 4 is a subroutine executed in step 205 of the cylinder-by-cylinder air-fuel ratio control execution routine of FIG. 3, and serves as cylinder-by-cylinder learning means. When this routine is started, first, at step 301, it is determined whether or not a learning execution condition is satisfied. Here, the learning execution conditions include, for example, the following two conditions (1) and (2).

(1) The air-fuel ratio control for each cylinder is being executed.
(2) The air-fuel ratio fluctuation amount is in a stable operating state with a predetermined value or less. If both of the above two conditions (1) and (2) are satisfied, the learning execution condition is satisfied, and any one of them is not satisfied. If there is a condition, the learning execution condition is not satisfied. If this learning execution condition is not satisfied, this routine is terminated without performing the subsequent processing.

On the other hand, if the learning execution condition is satisfied, the routine proceeds to step 304 where the current air-fuel ratio correction amount learning map for each cylinder in FIG. 7 stored in the rewritable nonvolatile memory (not shown) of the ECU 40 A learning area (learning area for updating the learning value of the cylinder-by-cylinder air-fuel ratio correction amount) corresponding to the engine operation area (engine speed and load) is selected. Thereafter, the routine proceeds to step 305, where the smoothing value of the cylinder-by-cylinder air-fuel ratio correction amount is calculated for each cylinder by the following equation using the smoothing coefficient K.
Air-fuel ratio correction amount by cylinder Smoothing value =
{Previous annealing value × (K-1) + Current cylinder air-fuel ratio correction amount} / K

  Thereafter, the process proceeds to step 306, where it is determined whether it is the update timing of the cylinder-by-cylinder air-fuel ratio correction amount learning value. The learning value update timing is set so that the learning value update period is at least longer than the cylinder-by-cylinder correction amount calculation period. If it is determined in this step 306 that it is not the learning value update timing, this routine is immediately terminated.

  On the other hand, if it is determined in step 306 that it is the learning value update timing, the routine proceeds to step 307, where it is determined whether or not the absolute value of the cylinder-by-cylinder air-fuel ratio correction amount smoothing value is equal to or greater than a predetermined value THA. If the absolute value of the smoothed value is smaller than the predetermined value THA, it is determined that it is not necessary to update the learning value, and this routine is terminated.

  If it is determined in step 307 that the absolute value of the cylinder-by-cylinder air-fuel ratio correction amount is greater than or equal to the predetermined value THA, the process proceeds to step 308, where the map is based on the cylinder-by-cylinder air-fuel ratio correction amount annealing value. Thus, the learning value update amount is calculated. The map for calculating the learning value update amount is set so that the learning value update amount increases as the cylinder-by-cylinder air-fuel ratio correction amount smoothing value increases.

  Thereafter, the process proceeds to step 309, and the ECU 40 can rewrite the value obtained by adding the current learning value update amount to the previous cylinder-by-cylinder air-fuel ratio correction amount learning value as a new cylinder-by-cylinder air-fuel ratio correction amount learning value. Update and store in a non-volatile memory (not shown). At this time, the learning value in the learning region selected in step 304 in the cylinder-by-cylinder air-fuel ratio correction amount learning map in FIG. 7 is updated. Note that the cylinder-by-cylinder air-fuel ratio correction amount learning map in FIG. 7 is created for each cylinder.

[Error diagnosis prohibition judgment routine]
The abnormality diagnosis prohibition determination routine of FIG. 5 is a subroutine executed in step 105 of the cylinder-by-cylinder air-fuel ratio control main routine of FIG. 2, and plays a role as diagnosis execution condition determination means in the claims.

  When this routine is started, first, in step 401, the cylinder-by-cylinder air-fuel ratio correction amount (or its learning value) is read, and in step 402, the cylinder-by-cylinder air-fuel ratio correction amount (or the cylinder-by-cylinder air-fuel ratio correction amount) It is determined whether or not the learning value is outside a predetermined range, and if the cylinder-by-cylinder air-fuel ratio correction amount (or the learning value) is within the predetermined range, abnormality diagnosis is permitted. In this case, the routine proceeds to step 406, where the value of the delay time counter T for measuring the duration of the state where the cylinder-by-cylinder air-fuel ratio correction amount (or its learning value) is outside the predetermined range is reset to 0 and this routine is executed. Exit.

  On the other hand, if it is determined in step 402 that the cylinder-by-cylinder air-fuel ratio correction amount (or its learned value) is outside the predetermined range, the process proceeds to step 403 and the delay time counter T is counted. And the duration of the state in which the cylinder-by-cylinder air-fuel ratio correction amount (or its learned value) is outside the predetermined range is measured. Thereafter, the process proceeds to step 404, where it is determined whether or not the count time of the delay time counter T exceeds a predetermined value. If the count value of the delay time counter T does not exceed the predetermined value, this routine is ended as it is. Thereafter, when the count value of the delay time counter T exceeds a predetermined value, the routine proceeds to step 405, the abnormality diagnosis prohibition flag is set to ON (abnormal diagnosis prohibition), and this routine is ended.

[Error diagnosis execution routine]
The abnormality diagnosis execution routine of FIG. 6 is executed at a predetermined cycle during engine operation. When this routine is started, first, at step 501, it is determined whether or not the abnormality diagnosis prohibition flag is set to ON (abnormality diagnosis prohibited), and the abnormality diagnosis prohibition flag is set to ON (abnormality diagnosis prohibited). If not, the process proceeds to step 502, and various abnormality diagnosis routines (abnormality diagnosis means) are executed. If the abnormality diagnosis prohibition flag is set to ON (abnormality diagnosis prohibition), the abnormality diagnosis routine is not executed. This routine ends. This function corresponds to diagnosis prohibition means in the claims.

  When the abnormality diagnosis prohibition flag is ON, only abnormality diagnosis that may be erroneously diagnosed due to the influence of the cylinder-by-cylinder air-fuel ratio control may be prohibited, and other abnormality diagnosis need not be prohibited. Here, abnormality diagnoses that may be erroneously diagnosed under the influence of the cylinder-by-cylinder air-fuel ratio control include, for example, deterioration diagnosis of the catalyst 38, fuel system abnormality diagnosis, air system abnormality diagnosis, abnormality diagnosis of the air-fuel ratio sensor 37, These include abnormality diagnosis of the oxygen sensor 41, combustion state diagnosis (misfire detection), fuel property diagnosis, and the like.

  A control example of the first embodiment described above will be described with reference to time charts of FIGS. FIG. 8 shows an example in which the abnormality diagnosis prohibition flag is turned ON / OFF by comparing the cylinder specific air-fuel ratio correction amount with a predetermined range (allowable range). In this example, at time t1, the execution condition of the cylinder-by-cylinder air-fuel ratio control is established, the cylinder-by-cylinder air-fuel ratio control is started, and the cylinder-by-cylinder air-fuel ratio correction amount of each cylinder # 1 to # 4 is calculated. While this cylinder-by-cylinder air-fuel ratio control is being executed, it is determined whether or not the cylinder-by-cylinder air-fuel ratio correction amount for each of the cylinders # 1 to # 4 is outside a predetermined range (outside the allowable range). In this example, at time t2 when the cylinder-by-cylinder air-fuel ratio correction amount is outside the predetermined range in # 1), the count-up operation of the delay time counter T is started, and the cylinder-by-cylinder air-fuel ratio correction amount is outside the predetermined range. The duration of the state is measured.

  Thereafter, at the time t3 when the count value of the delay time counter T exceeds a predetermined value, the abnormality diagnosis prohibition flag is set to ON (abnormality diagnosis prohibited). Thereafter, abnormality diagnosis that is affected by the cylinder-by-cylinder air-fuel ratio control is prohibited.

  On the other hand, FIG. 9 is an example in which the learning value of the cylinder-by-cylinder air-fuel ratio correction amount is compared with a predetermined range (allowable range) and the abnormality diagnosis prohibition flag is turned ON / OFF. In this example, at time t1, the execution condition of the cylinder-by-cylinder air-fuel ratio control is established, the cylinder-by-cylinder air-fuel ratio control is started, and the cylinder-by-cylinder air-fuel ratio correction amount of each cylinder # 1 to # 4 is calculated.

  Thereafter, at time t2, the learning execution condition is satisfied, learning of the air-fuel ratio correction amount for each cylinder is started, and the air-fuel ratio correction amount learning value for each cylinder # 1 to # 4 is updated.

  Thereafter, it is determined whether the cylinder-by-cylinder air-fuel ratio correction amount learning value for each cylinder # 1 to # 4 is outside a predetermined range (outside the allowable range), and the cylinder-by-cylinder air-fuel ratio correction amount learning value for any cylinder is determined. At a time point t3 when it is outside the predetermined range, the count-up operation of the delay time counter T is started, and the duration time in which the cylinder-by-cylinder air-fuel ratio correction amount learning value is outside the predetermined range is measured.

  Thereafter, at the time t4 when the count value of the delay time counter T exceeds a predetermined value, the abnormality diagnosis prohibition flag is set to ON (abnormality diagnosis prohibition). Thereafter, abnormality diagnosis that is affected by the cylinder-by-cylinder air-fuel ratio control is prohibited.

  According to the first embodiment described above, the cylinder-by-cylinder air-fuel ratio control is performed when the cylinder-by-cylinder air-fuel ratio correction amount (or its learned value) of any cylinder has been outside the predetermined range for a while. Since the affected abnormality diagnosis is prohibited, the erroneous diagnosis of the abnormality diagnosis by the unstable cylinder-by-cylinder air-fuel ratio control can be prevented, and the reliability of the abnormality diagnosis can be improved.

  It should be noted that the present invention provides an abnormality that is affected by the cylinder-by-cylinder air-fuel ratio control when the cylinder-by-cylinder air-fuel ratio correction amount (or its learned value) of any one cylinder is outside a predetermined range for a while. This is not limited to the configuration in which the diagnosis is prohibited, and an abnormality that is affected by the cylinder-by-cylinder air-fuel ratio control when the cylinder-by-cylinder air-fuel ratio correction amount of any two or more cylinders is outside the predetermined range for a while. Diagnosis may be prohibited.

  In addition, if the cylinder-by-cylinder air-fuel ratio correction amount (or its learned value) of any one cylinder is outside the predetermined range for a while, the abnormality diagnosis is not prohibited and the diagnosis result of the abnormality diagnosis is invalidated. You may make it. Even in this case, substantially the same effect can be obtained.

  In the cylinder-by-cylinder air-fuel ratio correction amount learning routine of FIG. 4 described in the first embodiment, the cylinder-by-cylinder air-fuel ratio correction amount learning value is updated for each engine operating region (engine speed and load) (FIG. 7). reference).

  In consideration of this point, in the second embodiment of the present invention shown in FIGS. 10 and 11, when the cylinder-by-cylinder air-fuel ratio correction amount (or the learned value) of any cylinder is out of a predetermined range, An abnormality diagnosis that is affected by the cylinder-by-cylinder air-fuel ratio control is prohibited only in an operation region in which the air-fuel ratio correction amount (or its learned value) is outside a predetermined range, and the abnormality diagnosis is permitted in other operation regions. I have to.

Hereinafter, the processing contents of the routines of FIGS. 10 and 11 executed in the second embodiment will be described.
The abnormality diagnosis prohibition determination routine of FIG. 10 is merely the addition of the processing of step 407 after step 405 of the abnormality diagnosis prohibition determination routine of FIG. is there.

  In the abnormality diagnosis prohibition determination routine of FIG. 10, if a state where the cylinder-by-cylinder air-fuel ratio correction amount (or its learned value) is out of the predetermined range has elapsed by a process of steps 401 to 405, Set the abnormality diagnosis prohibition flag to ON (abnormal diagnosis prohibition). Thereafter, the process proceeds to step 407, where the current engine operation area is stored as an abnormality diagnosis prohibited operation area in a rewritable nonvolatile memory (not shown) of the ECU 40, and this routine is terminated.

  The abnormality diagnosis execution routine of FIG. 11 is merely the addition of the processing of step 503 after step 501 of the abnormality diagnosis execution routine of FIG. 6 described in the first embodiment, and the processing of other steps is the same.

  When this routine is started, first, at step 501, it is determined whether or not the abnormality diagnosis prohibition flag is set to ON (abnormality diagnosis prohibited), and the abnormality diagnosis prohibition flag is set to ON (abnormality diagnosis prohibited). If not, the process proceeds to step 502, and various abnormality diagnosis routines are executed. If the abnormality diagnosis prohibition flag is set to ON (abnormal diagnosis prohibition), the process proceeds to step 503, where the current engine operation region is the non-volatile state of the ECU 40. It is determined whether or not it is an abnormality diagnosis prohibited operation region stored in a memory (not shown).

  As a result, if it is determined that the current engine operation region is not the abnormality diagnosis prohibited operation region stored in the nonvolatile memory (not shown) of the ECU 40, the process proceeds to step 502, and various abnormality diagnosis routines are executed. On the other hand, if the current engine operation region is the abnormality diagnosis prohibited operation region, this routine is terminated without executing the abnormality diagnosis routine. As a result, abnormality diagnosis that is affected by the cylinder-by-cylinder air-fuel ratio control is prohibited only in the abnormality diagnosis prohibited operation region. Alternatively, the diagnosis result of the abnormality diagnosis may be invalidated.

  In the second embodiment described above, abnormality diagnosis that is affected by the cylinder-by-cylinder air-fuel ratio control is prohibited only in the operation region in which the cylinder-by-cylinder air-fuel ratio correction amount (or the learning value thereof) is out of the predetermined range. Therefore, the abnormality diagnosis is prohibited (or invalidated) only in the operation region where the cylinder-by-cylinder air-fuel ratio correction amount (or its learning value) is outside the predetermined range, while preventing the erroneous diagnosis of the abnormality diagnosis. In other operating regions where the fuel ratio correction amount (or its learned value) falls within a predetermined range, abnormality diagnosis can be continued and the abnormality can be detected early when an abnormality occurs.

  Note that the present invention is not limited to a configuration in which abnormality diagnosis is prohibited only in an operating region in which the cylinder-by-cylinder air-fuel ratio correction amount (or the learned value) of any one cylinder is out of a predetermined range. The abnormality diagnosis may be prohibited only in the operation region where the cylinder-by-cylinder air-fuel ratio correction amount (or the learned value) of the cylinder is out of a predetermined range.

  In the third embodiment of the present invention shown in FIG. 12, the cylinder-by-cylinder air-fuel ratio correction amount (or its learning value) of any cylinder is compared with a predetermined range, and the abnormality diagnosis determination condition (determination is determined based on the comparison result). (Threshold) is changed.

  The determination condition change routine of FIG. 12 is executed at a predetermined cycle during engine operation, and serves as determination condition change means in the claims. When this routine is started, first, in step 601, the cylinder-by-cylinder air-fuel ratio correction amount (or its learning value) is read. In the next step 602, the cylinder-by-cylinder air-fuel ratio correction amount (or the cylinder-by-cylinder air-fuel ratio correction amount) It is determined whether or not the learning value is outside a predetermined range. As a result, if it is determined that the cylinder-by-cylinder air-fuel ratio correction amount (or the learned value) of all the cylinders is within the predetermined range, the routine proceeds to step 606, where the cylinder-by-cylinder air-fuel ratio correction amount is outside the predetermined range. The value of the delay time counter T for measuring the duration of the state is reset to 0, and in the next step 607, the determination threshold value for abnormality diagnosis is set to the normal determination threshold value Ka, and this routine is terminated. .

  On the other hand, if it is determined in step 602 that the cylinder-by-cylinder air-fuel ratio correction amount (or its learning value) is outside the predetermined range, the process proceeds to step 603 and the delay time counter T is counted. And the duration of the state in which the cylinder-by-cylinder air-fuel ratio correction amount (or its learned value) is outside the predetermined range is measured. Thereafter, the process proceeds to step 604, where it is determined whether or not the count time of the delay time counter T exceeds a predetermined value. If the count value of the delay time counter T does not exceed the predetermined value, this routine is terminated as it is. Thereafter, when the count value of the delay time counter T exceeds a predetermined value, the routine proceeds to step 605, where the determination threshold value for abnormality diagnosis is set to the determination threshold value Kb where abnormality is difficult to detect, and this routine is terminated. .

  In the third embodiment described above, the cylinder-by-cylinder air-fuel ratio correction amount (or its learned value) of any cylinder is compared with a predetermined range, and the determination threshold for abnormality diagnosis is changed based on the comparison result. Therefore, when the cylinder-by-cylinder air-fuel ratio correction amount (or its learned value) of any one or more cylinders is out of the predetermined range, the abnormality threshold is not easily detected. It becomes possible to change to a strict judgment threshold value, and it is possible to prevent erroneous diagnosis of abnormality diagnosis that is affected by the cylinder-by-cylinder air-fuel ratio control.

  In this case, in an operation region different from an operation region in which the cylinder-by-cylinder air-fuel ratio correction amount (or its learning value) of any one or two or more cylinders is out of the predetermined range, a determination threshold value for abnormality diagnosis is set. The same determination threshold value as that in the operation region when the other air-fuel ratio correction amount is within the predetermined range may be used. In this way, the judgment threshold value for abnormality diagnosis is changed to a strict judgment threshold value that makes it difficult for abnormality to be detected only in the operation region where the cylinder-by-cylinder air-fuel ratio correction amount (or its learned value) is outside the predetermined range. In other operating areas where the cylinder-by-cylinder air-fuel ratio correction amount (or its learning value) falls within the specified range while preventing misdiagnosis of the abnormality diagnosis, the abnormality diagnosis can be continued as usual, and an abnormality occurs. Sometimes the abnormality can be detected early.

  In the present invention, the determination threshold for abnormality diagnosis is changed. However, the diagnosis parameter to be compared with this determination threshold may be changed (corrected). The condition may be changed.

  By the way, the gas recirculation control (exhaust gas recirculation control EGR, blow-by gas recirculation control PCV, evaporation gas purge control PGR, etc.) that affects the air-fuel ratio in cylinder distribution differs for each cylinder in the degree that it affects the air-fuel ratio of each cylinder. There is a possibility that the variation in air-fuel ratio between cylinders is increased. Therefore, if the gas recirculation control is performed in the same way as normal when the cylinder-by-cylinder air-fuel ratio correction amount or its learning value is out of the predetermined range (allowable range), the cylinder-by-cylinder air-fuel ratio correction amount or its learning value becomes more and more abnormal. There is a possibility that the control state of the cylinder-by-cylinder air-fuel ratio control will be further deteriorated.

  In consideration of such circumstances, in the fourth embodiment of the present invention shown in FIGS. 13 and 14, gas recirculation control (exhaust gas recirculation control EGR, blow-by gas recirculation control PCV, evaporation, which affects the air-fuel ratio in cylinder distribution). When the gas purge control PGR or the like is executed, the gas recirculation control is prohibited when the cylinder-by-cylinder air-fuel ratio correction amount (or the learning value thereof) is out of a predetermined range.

  The gas recirculation control prohibition determination routine of FIG. 13 is executed at a predetermined cycle during engine operation. When this routine is started, first, in step 701, the cylinder-by-cylinder air-fuel ratio correction amount (or its learned value) is read. In the next step 702, the cylinder-by-cylinder air-fuel ratio correction amount (or the cylinder-by-cylinder air-fuel ratio correction amount) It is determined whether or not the learning value is outside the predetermined range. If the cylinder-by-cylinder air-fuel ratio correction amount (or the learning value) is within the predetermined range, the gas recirculation control is permitted. In this case, the routine proceeds to step 706, where the value of the delay time counter T for measuring the duration of the state where the cylinder-by-cylinder air-fuel ratio correction amount (or its learned value) is outside the predetermined range is reset to 0 and this routine is executed. Exit.

  On the other hand, if it is determined in step 702 that the cylinder-by-cylinder air-fuel ratio correction amount (or its learning value) is outside the predetermined range, the process proceeds to step 703 and the delay time counter T is counted. And the duration of the state in which the cylinder-by-cylinder air-fuel ratio correction amount (or its learned value) is outside the predetermined range is measured. Thereafter, the process proceeds to step 704, where it is determined whether or not the count time of the delay time counter T has exceeded a predetermined value. If the count value of the delay time counter T has not exceeded the predetermined value, this routine is terminated as it is.

  Thereafter, when the count value of the delay time counter T exceeds a predetermined value, the process proceeds to step 705, where the gas recirculation control prohibition flag is set to ON (gas recirculation control prohibition). Thereafter, the process proceeds to step 707, where the current engine operation region is stored as a gas recirculation control prohibition operation region in a rewritable nonvolatile memory (not shown) of the ECU 40, and this routine is terminated.

  The gas recirculation control execution routine of FIG. 14 is executed at a predetermined cycle during engine operation, and serves as a limiting means in the claims. When this routine is started, first, in step 801, it is determined whether or not the gas recirculation control prohibition flag is set to ON (gas recirculation control prohibition), and the gas recirculation control prohibition flag is ON (gas recirculation control prohibition). If not set, the routine proceeds to step 802, where a gas recirculation control routine is executed to execute at least one of exhaust gas recirculation control EGR, blow-by gas recirculation control PCV, evaporation gas purge control PGR, and the like.

  On the other hand, if the gas recirculation control prohibition flag is set to ON (gas recirculation control prohibition), the routine proceeds to step 803, where the current engine operation region is stored in the nonvolatile memory (not shown) of the ECU 40. It is determined whether or not it is a prohibited operation area.

  As a result, if the current engine operation region is not the gas recirculation control prohibition operation region stored in the nonvolatile memory (not shown) of the ECU 40, the process proceeds to step 802, and the gas recirculation control routine is executed. On the other hand, if the current engine operation region is the gas recirculation control prohibition operation region, this routine is terminated without executing the gas recirculation control routine. This prohibits the gas recirculation control that deteriorates the control state of the cylinder-by-cylinder air-fuel ratio control only in the gas recirculation control prohibition operation region. Alternatively, the control ratio of the gas recirculation control may be reduced.

  According to the fourth embodiment described above, the gas recirculation control is prohibited (or the control ratio is reduced) when the cylinder-by-cylinder air-fuel ratio correction amount (or the learned value) of any cylinder is out of the predetermined range. As a result, it is possible to suppress deterioration of the control state of the cylinder-by-cylinder air-fuel ratio control, and to prevent misdiagnosis of the abnormality diagnosis affected by the cylinder-by-cylinder air-fuel ratio control.

  Moreover, in the fourth embodiment, the gas recirculation control is prohibited (or the control ratio is reduced) only in the operation region where the cylinder-by-cylinder air-fuel ratio correction amount (or the learned value) of any cylinder is out of the predetermined range. Therefore, even when the cylinder-by-cylinder air-fuel ratio correction amount (or the learned value) of any cylinder is out of the predetermined range, depending on the operation region, the gas recirculation control can be executed in the same way as in normal time. The execution frequency of the gas recirculation control can be ensured.

  Note that the present invention is limited to a configuration in which the gas recirculation control is prohibited (or the control ratio is reduced) only in the operation region where the cylinder-by-cylinder air-fuel ratio correction amount (or the learned value) of any one cylinder is out of the predetermined range. In other words, the gas recirculation control is prohibited (or the control ratio is reduced) only in the operation region in which the cylinder-by-cylinder air-fuel ratio correction amount (or the learned value) of any two or more cylinders is out of the predetermined range. good.

  Alternatively, when the processing of step 707 of FIG. 13 and step 803 of FIG. 14 is omitted and the gas recirculation control prohibition flag is set to ON (gas recirculation control prohibition), the gas recirculation control is performed in all operating regions. May be prohibited (or the control ratio is reduced).

  In addition, the present invention prohibits the gas recirculation control (or sets the control ratio) when the cylinder-by-cylinder air-fuel ratio correction amount (or its learned value) of any one of the cylinders is outside the predetermined range for a while. The gas recirculation control is prohibited (or the control ratio is reduced) when the state where the cylinder-by-cylinder air-fuel ratio correction amount of any two or more cylinders is outside the predetermined range continues for a while. ).

  In addition, the present invention is not limited to the intake port injection engine, and can be implemented with various modifications without departing from the gist, such as being applicable to a cylinder injection engine.

It is a schematic block diagram of the whole engine control system in Example 1 of this invention. 4 is a flowchart showing a process flow of a cylinder-by-cylinder air-fuel ratio control main routine according to the first embodiment. 4 is a flowchart showing a flow of processing of a cylinder-by-cylinder air-fuel ratio control execution routine according to the first embodiment. 6 is a flowchart illustrating a processing flow of a cylinder-by-cylinder air-fuel ratio correction amount learning routine according to the first embodiment. 6 is a flowchart illustrating a process flow of an abnormality diagnosis prohibition determination routine according to the first embodiment. 6 is a flowchart illustrating a flow of processing of an abnormality diagnosis execution routine according to the first embodiment. It is a figure which shows notionally the air-fuel ratio correction amount learning map according to cylinder of Example 1 conceptually. 3 is a time chart illustrating a control example (part 1) according to the first embodiment. 6 is a time chart illustrating a control example (No. 2) according to the first embodiment. 7 is a flowchart illustrating a process flow of an abnormality diagnosis prohibition determination routine according to a second embodiment. 6 is a flowchart illustrating a flow of processing of an abnormality diagnosis execution routine according to a second embodiment. 12 is a flowchart illustrating a flow of processing of a determination condition changing routine according to the third embodiment. 12 is a flowchart illustrating a flow of processing of a gas recirculation control prohibition determination routine according to a fourth embodiment. 10 is a flowchart illustrating a flow of processing of a gas recirculation control execution routine according to a fourth embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Engine (internal combustion engine), 12 ... Intake pipe, 14 ... Air flow meter, 15 ... Throttle valve, 19 ... Intake manifold, 20 ... Fuel injection valve, 22 ... Fuel pump, 24 ... Fuel pressure sensor, 27, 28 ... Variable valve Timing mechanism 35 ... Exhaust manifold 36 ... Exhaust gas merging section 37 ... Air-fuel ratio sensor 38 ... Catalyst 40 ... ECU (Each cylinder air-fuel ratio estimation means, Cylinder air-fuel ratio correction amount calculation means, Cylinder air-fuel ratio control means Abnormality diagnosis means, diagnosis prohibition means, diagnosis execution condition determination means, determination condition change means, restriction means)

Claims (10)

An air-fuel ratio sensor for detecting the air-fuel ratio of the exhaust gas is installed at an exhaust gas merging portion where the exhaust gases of a plurality of cylinders of the internal combustion engine merge, and the air-fuel ratio of each cylinder is estimated based on the detection value of the air-fuel ratio sensor And a cylinder-by-cylinder air-fuel ratio estimating means for calculating an air-fuel ratio correction amount (hereinafter referred to as “cylinder-by-cylinder air-fuel ratio correction amount”) for each cylinder for correcting the inter-cylinder variation of the air-fuel ratio for each cylinder. Cylinder-by-cylinder air-fuel ratio correction amount calculating means and cylinder-by-cylinder air-fuel ratio control for correcting the fuel injection amount of each cylinder based on the cylinder-by-cylinder air-fuel ratio correction amount to reduce the air-fuel ratio variation between cylinders. In the air-fuel ratio control apparatus for each cylinder of the internal combustion engine provided with the fuel ratio control means,
An abnormality diagnosis means for performing abnormality diagnosis based on an output of the air-fuel ratio sensor and / or other exhaust gas sensor, or a parameter that changes under the influence of the air-fuel ratio;
When the cylinder-by-cylinder air-fuel ratio correction amount or the learning value of any one or more cylinders is out of a predetermined range, at least one abnormality diagnosis by the abnormality diagnosis unit is prohibited or the diagnosis result is invalidated. And a cylinder-by-cylinder air-fuel ratio control device for an internal combustion engine.   The diagnosis prohibition means performs at least one abnormality diagnosis by the abnormality diagnosis means only for an operating region where the cylinder-by-cylinder air-fuel ratio correction amount or the learning value of any one or two or more cylinders is out of a predetermined range. 2. The cylinder-by-cylinder air-fuel ratio control apparatus for an internal combustion engine according to claim 1, wherein the air-fuel ratio control apparatus is forbidden or invalidates the diagnosis result. An air-fuel ratio sensor for detecting the air-fuel ratio of the exhaust gas is installed at an exhaust gas merging portion where the exhaust gases of a plurality of cylinders of the internal combustion engine merge, and the air-fuel ratio of each cylinder is estimated based on the detection value of the air-fuel ratio sensor And a cylinder-by-cylinder air-fuel ratio estimating means for calculating an air-fuel ratio correction amount (hereinafter referred to as “cylinder-by-cylinder air-fuel ratio correction amount”) for each cylinder for correcting the inter-cylinder variation of the air-fuel ratio for each cylinder. Cylinder-by-cylinder air-fuel ratio correction amount calculating means and cylinder-by-cylinder air-fuel ratio control for correcting the fuel injection amount of each cylinder based on the cylinder-by-cylinder air-fuel ratio correction amount to reduce the air-fuel ratio variation between cylinders. In the air-fuel ratio control apparatus for each cylinder of the internal combustion engine provided with the fuel ratio control means,
An abnormality diagnosis means for performing abnormality diagnosis based on an output of the air-fuel ratio sensor and / or other exhaust gas sensor, or a parameter that changes under the influence of the air-fuel ratio;
Any one or two or more cylinder-by-cylinder air-fuel ratio correction amounts or learning values thereof are compared with a predetermined range, and diagnosis execution condition determination means for determining whether or not abnormality diagnosis can be performed by the abnormality diagnosis means based on the comparison result And a cylinder-by-cylinder air-fuel ratio control apparatus for an internal combustion engine.   The diagnosis execution condition determination unit is configured to detect an abnormality by the abnormality diagnosis unit in an operation region different from an operation region in which the cylinder-by-cylinder air-fuel ratio correction amount or the learning value of the one or more cylinders is out of a predetermined range. 4. The cylinder-by-cylinder air-fuel ratio control apparatus for an internal combustion engine according to claim 3, wherein execution of diagnosis is permitted. An air-fuel ratio sensor for detecting the air-fuel ratio of the exhaust gas is installed at an exhaust gas merging portion where the exhaust gases of a plurality of cylinders of the internal combustion engine merge, and the air-fuel ratio of each cylinder is estimated based on the detection value of the air-fuel ratio sensor And a cylinder-by-cylinder air-fuel ratio estimating means for calculating an air-fuel ratio correction amount (hereinafter referred to as “cylinder-by-cylinder air-fuel ratio correction amount”) for each cylinder for correcting the inter-cylinder variation of the air-fuel ratio for each cylinder. Cylinder-by-cylinder air-fuel ratio correction amount calculating means and cylinder-by-cylinder air-fuel ratio control for correcting the fuel injection amount of each cylinder based on the cylinder-by-cylinder air-fuel ratio correction amount to reduce the air-fuel ratio variation between cylinders. In the air-fuel ratio control apparatus for each cylinder of the internal combustion engine provided with the fuel ratio control means,
An abnormality diagnosis means for performing abnormality diagnosis based on an output of the air-fuel ratio sensor and / or other exhaust gas sensor, or a parameter that changes under the influence of the air-fuel ratio;
Judgment condition changing means for comparing any one or two or more cylinder-by-cylinder air-fuel ratio correction amounts or learning values thereof with a predetermined range and changing judgment conditions for abnormality diagnosis by the abnormality diagnosis means based on the comparison result; A cylinder-by-cylinder air-fuel ratio control apparatus for an internal combustion engine.   The determination condition changing means includes an abnormality diagnosis by the abnormality diagnosis means in an operation region different from an operation region in which the air-fuel ratio correction amount or learning value for each cylinder of the one or more cylinders is out of a predetermined range. 6. The cylinder-by-cylinder air-fuel ratio control apparatus for an internal combustion engine according to claim 5, wherein the determination condition is the same as that in the operation region when the cylinder-by-cylinder air-fuel ratio correction amount is within a predetermined range.   The abnormality diagnosis means performs at least one of catalyst deterioration diagnosis, fuel system abnormality diagnosis, air system abnormality diagnosis, air-fuel ratio sensor abnormality diagnosis, exhaust gas sensor abnormality diagnosis, combustion state diagnosis, and fuel property diagnosis. The cylinder-by-cylinder air-fuel ratio control apparatus for an internal combustion engine according to any one of claims 1 to 6. An air-fuel ratio sensor for detecting the air-fuel ratio of the exhaust gas is installed at an exhaust gas merging portion where the exhaust gases of a plurality of cylinders of the internal combustion engine merge, and the air-fuel ratio of each cylinder is estimated based on the detection value of the air-fuel ratio sensor And a cylinder-by-cylinder air-fuel ratio estimating means for calculating an air-fuel ratio correction amount (hereinafter referred to as “cylinder-by-cylinder air-fuel ratio correction amount”) for each cylinder for correcting the inter-cylinder variation of the air-fuel ratio for each cylinder. Cylinder-by-cylinder air-fuel ratio correction amount calculating means and cylinder-by-cylinder air-fuel ratio control for correcting the fuel injection amount of each cylinder based on the cylinder-by-cylinder air-fuel ratio correction amount to reduce the air-fuel ratio variation between cylinders. In the air-fuel ratio control apparatus for each cylinder of the internal combustion engine provided with the fuel ratio control means,
Means for performing control that affects the air-fuel ratio in cylinder distribution;
When the cylinder-by-cylinder air-fuel ratio correction amount or learning value of any one or more cylinders is out of a predetermined range, the control ratio of the control that affects the air-fuel ratio in the cylinder distribution is reduced or the control is performed. A cylinder-by-cylinder air-fuel ratio control apparatus for an internal combustion engine, comprising: a restricting means for prohibiting.   The limiting means controls the control that affects the air-fuel ratio in the cylinder distribution only in the operation region where the correction amount for each cylinder of the one or more cylinders or the learning value thereof is out of a predetermined range. 9. The cylinder-by-cylinder air-fuel ratio control apparatus for an internal combustion engine according to claim 8, wherein the ratio is reduced or the control is prohibited.   The control for influencing the air-fuel ratio in the cylinder distribution is at least one of exhaust gas recirculation control, blow-by gas recirculation control, and evaporation gas purge control. Air-fuel ratio control device.

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