JP2008128161A - Control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve estimation accuracy of the each cylinder air-fuel ratio when responsiveness of an air-fuel ratio sensor is deteriorated, in a system for estimating the air-fuel ratio (the each cylinder air-fuel ratio) of respective cylinders based on output of the air-fuel ratio sensor arranged in an exhaust confluent part of an engine. <P>SOLUTION: An estimation error in the each cylinder air-fuel ratio by output reduction in the air-fuel ratio sensor 37, is corrected by correcting an estimate of the each cylinder air-fuel ratio by using correction gain, by learning the correction gain corresponding to an output reduction quantity of the air-fuel ratio sensor 37, by calculating the correction gain corresponding to a deterioration degree of the responsiveness of the air-fuel ratio sensor 37, and by detecting the deterioration degree of the responsiveness of the air-fuel ratio sensor 37 in a high load region of the engine 11. Variations of the air-fuel ratios among cylinders are also calculated, by calculating a deviation between the estimated air-fuel ratio and the reference air-fuel ratio of the respective cylinders after a correction. Thus, the estimation accuracy of the each cylinder air-fuel ratio when the responsiveness of the air-fuel ratio sensor is deteriorated, detecting accuracy of the variations of the air-fuel ratios among the cylinders, is improved. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an internal combustion engine control device having a function of estimating an air-fuel ratio of each cylinder based on an output of an air-fuel ratio sensor installed at an exhaust gas merging portion where exhaust gases of a plurality of cylinders of the internal combustion engine merge. is there.

  In recent years, in order to improve the air-fuel ratio control accuracy of an internal combustion engine, as described in Patent Document 1 (Japanese Patent No. 3357572), one installed in an exhaust merging section where exhaust gases of a plurality of cylinders merge The air-fuel ratio of each cylinder (air-fuel ratio for each cylinder) is estimated using a model that associates the output of the air-fuel ratio sensor (the air-fuel ratio of the exhaust gas merging portion) with the air-fuel ratio of each cylinder. A cylinder-by-cylinder air-fuel ratio control is performed in which the air-fuel ratio correction amount of each cylinder is calculated so as to reduce the variation in the air-fuel ratio of each cylinder and the air-fuel ratio (for example, fuel injection amount) of each cylinder is controlled for each cylinder. There is what I did.

Furthermore, in the technique of Patent Document 1, in order to prevent the estimation accuracy of the cylinder-by-cylinder air-fuel ratio from deteriorating due to the deterioration of the response of the air-fuel ratio sensor, the response speed of the air-fuel ratio sensor is determined, Accordingly, the timing at which the air-fuel ratio is detected by the air-fuel ratio sensor is corrected.
Japanese Patent No. 3357572 (first page, etc.)

  By the way, when the responsiveness of the air-fuel ratio sensor deteriorates, the output value of the air-fuel ratio sensor may also decrease. However, in the technique of Patent Document 1, since the influence of the output reduction of the air-fuel ratio sensor when the responsiveness of the air-fuel ratio sensor deteriorates is not considered at all, the air-fuel ratio when the responsiveness of the air-fuel ratio sensor deteriorates is not considered. There is a possibility that the estimation accuracy of the cylinder-by-cylinder air-fuel ratio based on the output of the air-fuel ratio sensor may decrease due to the decrease in the output of the sensor.

  The present invention has been made in consideration of such circumstances. Accordingly, the object of the present invention is to provide an internal combustion engine capable of improving the estimation accuracy of the cylinder-by-cylinder air-fuel ratio when the response of the air-fuel ratio sensor is deteriorated. It is to provide a control device.

  In order to achieve the above object, according to a first aspect of the present invention, an air-fuel ratio sensor is installed in an exhaust gas merging portion where exhaust gases of a plurality of cylinders of an internal combustion engine merge, and each cylinder is based on the output of the air-fuel ratio sensor. In a control device for an internal combustion engine that estimates the air-fuel ratio of the engine (hereinafter referred to as “cylinder-by-cylinder air-fuel ratio”), the degree of deterioration of the response of the air-fuel ratio sensor is detected by the sensor response deterioration degree detection means in the high load region of the internal combustion engine. Thus, the correction gain learning means learns a correction gain corresponding to the decrease in the output of the air-fuel ratio sensor based on the detected deterioration degree of the responsiveness of the air-fuel ratio sensor, and the cylinder-by-cylinder air-fuel ratio is determined using the learned correction gain. The estimated value is corrected.

  In a high load region where the exhaust gas amount of the internal combustion engine increases, the responsiveness of the air-fuel ratio sensor to the change in air-fuel ratio can be detected with high accuracy. Furthermore, when the responsiveness of the air-fuel ratio sensor deteriorates, the output of the air-fuel ratio sensor decreases according to the degree of deterioration. Therefore, by using the degree of deterioration of the responsiveness of the air-fuel ratio sensor detected in the high load region, it is possible to accurately learn a correction gain corresponding to the output decrease of the air-fuel ratio sensor. By correcting the estimated value of the air-fuel ratio, it is possible to accurately correct the estimation error of the cylinder-by-cylinder air-fuel ratio due to the decrease in the output of the air-fuel ratio sensor. Can be improved.

  Further, as described in claim 2, the degree of deterioration of the responsiveness of the air-fuel ratio sensor is detected for each of a plurality of learning regions divided according to the operating state of the internal combustion engine, and the responsiveness of the air-fuel ratio sensor is detected for each learning region. A correction gain corresponding to the output decrease of the air-fuel ratio sensor may be learned based on the degree of deterioration of the air-fuel ratio, and the estimated value of the cylinder-by-cylinder air-fuel ratio may be corrected using the correction gain for each learning region. In this way, it is possible to accurately correct the estimation error of the cylinder-by-cylinder air-fuel ratio due to the decrease in the output of the air-fuel ratio sensor without being influenced by the operating state of the internal combustion engine.

  Further, as described in claim 3, when estimating the air-fuel ratio for each cylinder based on the output of the air-fuel ratio sensor, the timing at which the air-fuel ratio sensor detects the air-fuel ratio in accordance with the degree of deterioration of the responsiveness of the air-fuel ratio sensor. You may make it correct | amend. In this way, the timing at which the air-fuel ratio sensor detects the air-fuel ratio can be changed according to the degree of deterioration of the response of the air-fuel ratio sensor and set to an appropriate timing. The estimation accuracy of the cylinder-by-cylinder air-fuel ratio can be further improved.

  Further, as described in claim 4, the variation in the air-fuel ratio of each cylinder may be detected based on the estimated value of the air-fuel ratio for each cylinder after correction using the correction gain. In this way, it is possible to improve the detection accuracy of the variation in the air-fuel ratio among the cylinders when the responsiveness of the air-fuel ratio sensor is deteriorated.

  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 crank of the engine 11. A crank angle sensor 33 that outputs a pulse of a crank angle signal at every predetermined crank angle (for example, every 30 ° C. A) in synchronization with the rotation of the shaft is provided.

  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.

  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.

  In addition, the ECU 40 executes each routine for cylinder-by-cylinder air-fuel ratio control described later with reference to FIGS. 2 to 5, thereby detecting the detected value of the air-fuel ratio sensor 37 during the engine operation (the exhaust gas flowing through the exhaust gas merging section 36). The air-fuel ratio (cylinder-specific air-fuel ratio) of each cylinder is determined based on the detected value of the air-fuel ratio sensor 37 using a model (hereinafter referred to as “cylinder-specific air-fuel ratio estimation model”) that associates the air-fuel ratio of each cylinder with the air-fuel ratio. By estimating and calculating the deviation between the estimated air-fuel ratio of each cylinder and the reference air-fuel ratio (the average value or control target value of the estimated air-fuel ratios of all cylinders), the variation in the air-fuel ratio of each cylinder is calculated. Then, the air-fuel ratio correction coefficient (correction coefficient of the fuel injection amount of each cylinder) is calculated so that the variation in the air-fuel ratio of each cylinder is reduced, and the fuel injection amount of each cylinder is calculated based on the calculation result. By correcting the air-fuel ratio, the air-fuel ratio of the air-fuel mixture supplied to each cylinder is corrected for each cylinder, and the cylinder-by-cylinder air-fuel ratio control is performed to control the variation in the air-fuel ratio among the cylinders.

  By the way, when the responsiveness of the air-fuel ratio sensor 37 deteriorates, the output value of the air-fuel ratio sensor 37 may also decrease, and due to the decrease in the output of the air-fuel ratio sensor 37, the cylinder-by-cylinder air-fuel ratio based on the output of the air-fuel ratio sensor 37 The estimation accuracy of may decrease.

  As a countermeasure, in the first embodiment, the deterioration degree of the responsiveness of the air-fuel ratio sensor 37 is detected in the high load region of the engine 11 and the correction gain corresponding to the deterioration degree of the responsiveness of the air-fuel ratio sensor 37 is calculated. Thus, a correction gain corresponding to the output decrease of the air-fuel ratio sensor 37 is obtained and learned, and the estimated value of the cylinder-by-cylinder air-fuel ratio is corrected using this correction gain.

  In the high load region where the exhaust gas amount of the engine 11 increases, the responsiveness of the air-fuel ratio sensor 37 to the change in the air-fuel ratio can be detected with high accuracy. Furthermore, when the responsiveness of the air-fuel ratio sensor 37 deteriorates, the output of the air-fuel ratio sensor 37 decreases according to the degree of deterioration. Therefore, by obtaining a correction gain according to the degree of deterioration of the responsiveness of the air-fuel ratio sensor 37 detected in the high load region, the correction gain according to the output decrease of the air-fuel ratio sensor 37 can be learned with high accuracy. By correcting the estimated value of the cylinder-by-cylinder air-fuel ratio using this correction gain, the estimation error of the cylinder-by-cylinder air-fuel ratio due to the decrease in the output of the air-fuel ratio sensor 37 can be accurately corrected.

  Hereinafter, processing contents of each routine for cylinder-by-cylinder air-fuel ratio control of FIGS. 2 to 5 executed by the ECU 40 will be described.

[Air-fuel ratio control routine for each cylinder]
The cylinder-by-cylinder air-fuel ratio control routine shown in FIG. 2 is executed at a predetermined cycle while the ECU 40 is powered on. When this routine is started, first, at step 101, the output of the air-fuel ratio sensor 37 (air-fuel ratio detection value) is read, then the routine proceeds to step 102, where a cylinder-by-cylinder air-fuel ratio estimation routine of FIG. Thus, the air-fuel ratio of each cylinder is estimated based on the detected value of the air-fuel ratio sensor 37, and the estimated air-fuel ratio of each cylinder is corrected using the correction gain.

  Thereafter, the process proceeds to step 103, and the deviation between the estimated air-fuel ratio of each cylinder after correction using the correction gain and the reference air-fuel ratio (the average value or control target value of the estimated air-fuel ratios of all cylinders) is calculated. Then, the variation between cylinders in the air-fuel ratio of each cylinder is calculated. The processing in step 103 serves as a cylinder-to-cylinder variation detecting means in the claims.

  Thereafter, the process proceeds to step 104, and after calculating the air-fuel ratio correction coefficient (correction coefficient of the fuel injection amount of each cylinder) so that the cylinder variation of the air-fuel ratio of each cylinder is reduced, the process proceeds to step 105. By correcting the fuel injection amount of each cylinder based on the air-fuel ratio correction coefficient of the cylinder, the air-fuel ratio of the air-fuel mixture supplied to each cylinder is corrected for each cylinder, and the variation in the air-fuel ratio of each cylinder is reduced. The cylinder-by-cylinder air-fuel ratio control is performed so that the control is performed.

[Individual air-fuel ratio estimation routine]
The cylinder-by-cylinder air-fuel ratio estimation routine shown in FIG. 3 is a subroutine executed in step 102 of the cylinder-by-cylinder air-fuel ratio control routine shown in FIG. When this routine is started, first, at step 201, it is determined whether or not the responsiveness of the air-fuel ratio sensor 37 has deteriorated based on the diagnosis result of a sensor responsiveness deterioration diagnosis routine (not shown). Specifically, the response time T of the air-fuel ratio sensor 37 is measured by a method described later, and the response time T is compared with a predetermined deterioration determination value (or the previous value of the response time T) to determine the response of the air-fuel ratio sensor 37. The presence or absence of sex deterioration is determined.

  If it is determined in step 201 that the responsiveness of the air-fuel ratio sensor 37 has not deteriorated, the process proceeds to step 202 and the correction gain is set to “1.0”. In this case, the estimated air-fuel ratio of each cylinder is not substantially corrected.

  On the other hand, if it is determined in step 201 that the responsiveness of the air-fuel ratio sensor 37 has deteriorated, the routine proceeds to step 203 where a correction gain learning routine shown in FIG. The degree of responsiveness deterioration of the air-fuel ratio sensor 37 is detected in the load region, and a correction gain corresponding to the output decrease of the air-fuel ratio sensor 37 is learned based on the degree of responsiveness deterioration of the air-fuel ratio sensor 37.

  Thereafter, the process proceeds to step 204, 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, and then the process proceeds to step 205. By multiplying the estimated air-fuel ratio of each cylinder by a correction gain, the estimated air-fuel ratio of each cylinder is corrected to obtain the final estimated air-fuel ratio of each cylinder. The processing in step 205 serves as cylinder-by-cylinder air-fuel ratio correction means in the claims.

[Correction gain learning routine]
The correction gain learning routine shown in FIG. 4 is a subroutine executed in step 203 of the cylinder-by-cylinder air-fuel ratio estimation routine shown in FIG. 3, and serves as correction gain learning means in the claims. When this routine is started, first, at step 301, it is determined whether or not the engine operating state is in a high load region, for example, whether the engine load K (intake air amount, intake pipe pressure, etc.) is a predetermined value HK or more. Judge by whether or not. If it is determined in step 301 that the engine operating state is not in the high load region, this routine is terminated without performing the processing related to correction gain learning in step 302 and subsequent steps.

  Thereafter, when it is determined in step 301 that the engine operating state is in the high load region, the processing related to correction gain learning in step 302 and subsequent steps is executed as follows. First, in step 302, a sensor responsiveness deterioration degree detection routine of FIG. 5 described later is executed to detect the deterioration degree R of the responsiveness of the air-fuel ratio sensor 37 in the high load region of the engine 11.

  Thereafter, the process proceeds to step 303, and a correction gain corresponding to the output decrease of the air-fuel ratio sensor 37 is obtained by calculating a correction gain corresponding to the degree of deterioration R of the responsiveness of the air-fuel ratio sensor 37 using a map or a mathematical expression. The correction gain is learned by storing the correction gain in a rewritable nonvolatile memory such as a backup RAM of the ECU 40.

[Sensor responsiveness degradation degree detection routine]
The sensor responsiveness deterioration degree detection routine shown in FIG. 5 is a subroutine executed in step 302 of the correction gain learning routine of FIG. 4, and serves as a sensor responsiveness deterioration degree detection means in the claims. . When this routine is started, first, at step 401, it is determined whether or not the deterioration degree detection execution flag is set to “1”. This deterioration degree detection execution flag is set to “1” every time the engine 11 is started (for example, every time the power of the ECU 40 is turned on). Alternatively, the deterioration degree detection execution flag may be set to “1” every time the accumulated travel distance or the accumulated time from the previous detection of the responsiveness deterioration degree of the air-fuel ratio sensor 37 exceeds a predetermined value.

  If it is determined in step 401 that the deterioration degree detection execution flag is set to “1”, the processing relating to the deterioration degree detection in and after step 402 is executed as follows. First, in step 402, it is determined whether or not the fuel cut has been started. When it is determined that the fuel cut has been started, the process proceeds to step 403 and the timer is activated to measure the elapsed time from the start of the fuel cut. .

  Thereafter, the routine proceeds to step 404, where it is determined whether the output of the air-fuel ratio sensor 37 has exceeded a predetermined lean determination value, and when it is determined that the output of the air-fuel ratio sensor 37 has exceeded the lean determination value, step 405 is performed. Then, as shown in FIG. 6, the response time T required from the start of fuel cut until the output of the air-fuel ratio sensor 37 exceeds the lean determination value is measured based on the count value of the timer.

Thereafter, the process proceeds to step 406, where the current response deterioration ΔR is obtained based on the difference between the current response time T (i) of the air-fuel ratio sensor 37 and the previous response time T (i-1). The responsiveness deterioration degree R (i) of the current air-fuel ratio sensor 37 is obtained by adding the current responsiveness deterioration amount ΔR to the responsiveness deterioration degree R (i-1) of the air-fuel ratio sensor 37.
R (i) = R (i-1) + ΔR

  The response deterioration of the current air-fuel ratio sensor 37 is based on the difference between the current response time T (i) of the air-fuel ratio sensor 37 and the initial response time T0 (response time when the response is not deteriorated). The degree R (i) may be obtained.

The responsiveness deterioration degree R (i) of the air-fuel ratio sensor 37 thus obtained is stored in a rewritable nonvolatile memory such as a backup RAM of the ECU 40.
Thereafter, the process proceeds to step 407, the deterioration degree detection execution flag is reset to “0”, and this routine is terminated.

  On the other hand, if it is determined in step 401 that the deterioration degree detection execution flag has been reset to “0”, this routine is terminated without executing the processing relating to the deterioration degree detection in and after step 402.

  In this routine, as shown in FIG. 6, the response time T required from the start of the fuel cut until the output of the air-fuel ratio sensor 37 exceeds the predetermined lean determination value is obtained. The response time T required until the output of the fuel ratio sensor 37 exceeds a predetermined rich determination value may be obtained.

  Alternatively, as shown in FIG. 7, when the operating state of the engine 11 is in a steady state, the fuel injection amount is forcibly increased (or decreased) and the air-fuel ratio is forcibly made rich (or lean). ), The response time T required until the output of the air-fuel ratio sensor 37 exceeds a predetermined rich determination value (or lean determination value) may be obtained.

  In the first embodiment described above, the degree of deterioration of the responsiveness of the air-fuel ratio sensor 37 is detected in the high load region of the engine 11 and the correction gain corresponding to the degree of deterioration of the responsiveness of the air-fuel ratio sensor 37 is calculated. Thus, the correction gain corresponding to the output decrease of the air-fuel ratio sensor 37 is obtained and learned, and the estimated value of the cylinder-by-cylinder air-fuel ratio is corrected using this correction gain. It is possible to accurately correct the estimation error of the cylinder-by-cylinder air-fuel ratio, and to improve the estimation accuracy of the cylinder-by-cylinder air-fuel ratio when the response of the air-fuel ratio sensor is deteriorated, and hence the detection accuracy of the variation in the air-fuel ratio of each cylinder be able to.

Next, Embodiment 2 of the present invention will be described with reference to FIG.
In the second embodiment, when the cylinder-by-cylinder air-fuel ratio is estimated based on the output of the air-fuel ratio sensor 37 by executing a cylinder-by-cylinder air-fuel ratio estimation routine of FIG. The timing at which the air-fuel ratio sensor 37 detects the air-fuel ratio is corrected according to the degree of deterioration.

  In the cylinder-by-cylinder air-fuel ratio estimation routine shown in FIG. 8, if it is determined in step 201 that the responsiveness of the air-fuel ratio sensor 37 has deteriorated, the routine proceeds to step 203, and the above-described correction gain learning routine of FIG. Is executed to detect the degree of deterioration of the responsiveness of the air-fuel ratio sensor 37 in the high load region of the engine 11, and according to the output decrease of the air-fuel ratio sensor 37 based on the degree of deterioration of the responsiveness of the air-fuel ratio sensor 37. Learn correction gain.

  Thereafter, the process proceeds to step 203a, and the timing at which the air-fuel ratio sensor 37 detects the air-fuel ratio is corrected according to the degree of deterioration of the responsiveness of the air-fuel ratio sensor 37. As a result, the timing at which the air-fuel ratio sensor 37 detects the air-fuel ratio is changed according to the degree of deterioration of the responsiveness of the air-fuel ratio sensor 37 and set to an appropriate timing. The processing in step 203a serves as air-fuel ratio detection timing correction means in the claims.

  After that, after estimating the air-fuel ratio of the cylinder that is the target of air-fuel ratio estimation this time based on the detection value of the air-fuel ratio sensor 37 using the cylinder-by-cylinder air-fuel ratio estimation model, a correction gain is respectively applied to the estimated air-fuel ratio of each cylinder. By multiplying, the estimated air-fuel ratio of each cylinder is corrected to obtain the final estimated air-fuel ratio of each cylinder (steps 204 and 205).

  In the second embodiment described above, when the air-fuel ratio for each cylinder is estimated based on the output of the air-fuel ratio sensor 37, the air-fuel ratio sensor 37 detects the air-fuel ratio according to the degree of deterioration of the responsiveness of the air-fuel ratio sensor 37. The timing at which the air-fuel ratio sensor 37 detects the air-fuel ratio can be changed according to the degree of deterioration of the responsiveness of the air-fuel ratio sensor 37 and set to an appropriate timing. The estimation accuracy of the cylinder-by-cylinder air-fuel ratio when the response of the sensor 37 is deteriorated can be further improved.

  In each of the first and second embodiments, the estimated value of the cylinder-by-cylinder air-fuel ratio is always corrected using the correction gain learned in the high load region. However, when correcting the estimated value of the cylinder-by-cylinder air-fuel ratio, The correction gain learned in the high load region may be corrected according to the engine operating state (for example, engine load) at that time, and the estimated value of the air-fuel ratio for each cylinder may be corrected using the correction gain.

Next, Embodiment 3 of the present invention will be described with reference to FIGS.
In the third embodiment, the degree of responsiveness deterioration of the air-fuel ratio sensor 37 is set for each of a plurality of learning regions divided according to the operating state of the engine 11 by executing routines shown in FIGS. Detecting a correction gain corresponding to a decrease in the output of the air-fuel ratio sensor 37 based on the degree of deterioration of the responsiveness of the air-fuel ratio sensor 37 for each learning region, and for each cylinder using the correction gain for each learning region The estimated value of the air-fuel ratio is corrected.

  In the cylinder-by-cylinder air-fuel ratio estimation routine shown in FIG. 9, if it is determined in step 501 that the responsiveness of the air-fuel ratio sensor 37 has deteriorated, the routine proceeds to step 503, and the correction gain learning routine in FIG. The degree of responsiveness deterioration of the air-fuel ratio sensor 37 is detected for each of the plurality of learning regions divided according to the operating state (for example, engine load) of the engine 11, and the response of the air-fuel ratio sensor 37 is detected for each learning region. The correction gain corresponding to the output decrease of the air-fuel ratio sensor 37 is learned based on the degree of deterioration of the property.

  Thereafter, the process proceeds to step 504, where the air-fuel ratio of the cylinder that is the current air-fuel ratio estimation target is estimated based on the detection value of the air-fuel ratio sensor 37 using the cylinder-by-cylinder air-fuel ratio estimation model, and then the process proceeds to step 505. It is determined whether the engine operating area is one of a plurality of learning areas divided according to the engine operating state (for example, engine load).

  Proceeding to step 506, the estimated air-fuel ratio of each cylinder is corrected by multiplying the estimated air-fuel ratio of each cylinder by the correction gain of the learning region corresponding to the current engine operation region, so that the final estimated air-fuel ratio of each cylinder is corrected. Ask for.

  In the correction gain learning routine shown in FIG. 10, first, in step 601, it is determined whether the current engine operation area is one of a plurality of learning areas divided according to the engine operation state (for example, engine load). To do.

  Thereafter, the routine proceeds to step 602, where the aforementioned sensor responsiveness deterioration degree detection routine of FIG. 5 is executed to detect the responsiveness deterioration degree R of the air-fuel ratio sensor 37 in the learning region corresponding to the current engine operation region. .

  Thereafter, the process proceeds to step 603, and the correction gain corresponding to the deterioration degree R of the responsiveness of the air-fuel ratio sensor 37 in the learning region corresponding to the current engine operation region is calculated by a map or a mathematical formula, whereby the air-fuel ratio sensor 37. The correction gain corresponding to the output decrease is obtained, and the correction gain is learned by storing the correction gain in a rewritable nonvolatile memory such as a backup RAM of the ECU 40. At this time, the learning value of the correction gain in the learning region corresponding to the current engine operation region is updated.

  In the third embodiment described above, the degree of deterioration of the responsiveness of the air-fuel ratio sensor 37 is detected for each of the plurality of learning regions divided according to the operating state of the engine 11, and the air-fuel ratio sensor 37 is detected for each learning region. Since the correction gain corresponding to the output decrease of the air-fuel ratio sensor 37 is learned based on the deterioration degree of the responsiveness, the estimated value of the cylinder-by-cylinder air-fuel ratio is corrected using the correction gain for each learning region. The estimation error of the cylinder-by-cylinder air-fuel ratio due to the decrease in the output of the air-fuel ratio sensor 37 can be accurately corrected regardless of the engine operating state.

  In the first to third embodiments, the air-fuel ratio of each cylinder is estimated using the cylinder-by-cylinder air-fuel ratio estimation model that associates the detected value of the air-fuel ratio sensor 37 with the air-fuel ratio of each cylinder. The cylinder-by-cylinder air-fuel ratio estimation method is not limited to the method using the cylinder-by-cylinder air-fuel ratio estimation model, and may be changed as appropriate. For example, air-fuel ratio dither control for forcibly changing the air-fuel ratio for each cylinder is performed. The air-fuel ratio of each cylinder may be estimated based on the output of the air-fuel ratio sensor 37 when executed.

  In the first to third embodiments, the present invention is applied to a four-cylinder engine. However, the present invention may be applied to a two-cylinder engine, a three-cylinder engine, or an engine having five or more cylinders.

It is a schematic block diagram of the whole engine control system in Example 1 of this invention. 3 is a flowchart showing a flow of processing of a cylinder-by-cylinder air-fuel ratio control routine according to the first embodiment. 3 is a flowchart showing a process flow of a cylinder-by-cylinder air-fuel ratio estimation routine according to the first embodiment. 5 is a flowchart illustrating a processing flow of a correction gain learning routine according to the first embodiment. 6 is a flowchart illustrating a flow of processing of a sensor responsiveness deterioration degree detection routine according to the first embodiment. 6 is a time chart for explaining a method for detecting a response time of the air-fuel ratio sensor according to the first embodiment. It is a time chart for demonstrating the other detection method of the response time of the air fuel ratio sensor of Example 1. FIG. 6 is a flowchart illustrating a processing flow of a cylinder-by-cylinder air-fuel ratio estimation routine according to a second embodiment. 12 is a flowchart showing a flow of processing of a cylinder-by-cylinder air-fuel ratio estimation routine according to a third embodiment. 12 is a flowchart illustrating a processing flow of a correction gain learning routine according to the third embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Engine (internal combustion engine), 12 ... Intake pipe, 15 ... Throttle valve, 20 ... Fuel injection valve, 35 ... Exhaust manifold, 36 ... Exhaust junction, 37 ... Air-fuel ratio sensor, 40 ... ECU (sensor response deterioration degree) Detecting means, correction gain learning means, cylinder-by-cylinder air-fuel ratio correcting means, inter-cylinder variation detecting means)

Claims (4)

An air-fuel ratio sensor is installed at an exhaust gas merging portion where exhaust gases from a plurality of cylinders of an internal combustion engine merge, and the air-fuel ratio of each cylinder (hereinafter referred to as “cylinder-specific air-fuel ratio”) is estimated based on the output of the air-fuel ratio sensor. In a control device for an internal combustion engine,
Sensor responsiveness deterioration degree detecting means for detecting the deterioration degree of the responsiveness of the air-fuel ratio sensor in a high load region of the internal combustion engine;
Correction gain learning means for learning a correction gain according to the output decrease of the air-fuel ratio sensor based on the deterioration degree of the response of the air-fuel ratio sensor detected by the sensor responsiveness deterioration degree detection means;
A control apparatus for an internal combustion engine, comprising: a cylinder-by-cylinder air-fuel ratio correction unit that corrects the estimated value of the cylinder-by-cylinder air-fuel ratio using the correction gain learned by the correction gain learning unit. An air-fuel ratio sensor is installed at an exhaust gas merging portion where exhaust gases from a plurality of cylinders of an internal combustion engine merge, and the air-fuel ratio of each cylinder (hereinafter referred to as “cylinder-specific air-fuel ratio”) is estimated based on the output of the air-fuel ratio sensor. In a control device for an internal combustion engine,
Sensor responsiveness deterioration degree detection means for detecting the deterioration degree of the responsiveness of the air-fuel ratio sensor for each of a plurality of learning regions divided according to the operating state of the internal combustion engine;
Correction gain learning means for learning a correction gain corresponding to the output decrease of the air-fuel ratio sensor based on the degree of deterioration of the responsiveness of the air-fuel ratio sensor detected by the sensor responsiveness deterioration degree detection means for each learning region; ,
A control apparatus for an internal combustion engine, comprising: a cylinder-by-cylinder air-fuel ratio correction unit that corrects an estimated value of the cylinder-by-cylinder air-fuel ratio using a correction gain learned by the correction gain learning unit for each learning region. .   When estimating the cylinder-by-cylinder air-fuel ratio based on the output of the air-fuel ratio sensor, the air-fuel ratio sensor detects the air-fuel ratio sensor according to the deterioration degree of the response of the air-fuel ratio sensor detected by the sensor responsiveness deterioration degree detection means. 3. The control apparatus for an internal combustion engine according to claim 1, further comprising air-fuel ratio detection timing correction means for correcting timing for detecting the fuel ratio.   Inter-cylinder variation detecting means for detecting inter-cylinder variation in the air-fuel ratio of each cylinder based on the estimated value of the cylinder-by-cylinder air-fuel ratio after being corrected by the cylinder-by-cylinder air-fuel ratio correcting unit. The control apparatus for an internal combustion engine according to any one of claims 1 to 3.

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