JP2008144639A - Control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve accuracy of individual cylinder air fuel ratio control and accuracy of individual cylinder air fuel ratio abnormality diagnosis by increasing estimation accuracy of individual cylinder air fuel ratio in a system estimating air fuel ratio of each cylinder (individual cylinder air fuel ratio) based on output of an air fuel ratio sensor installed in an exhaust gas merging part of an engine. <P>SOLUTION: Estimation error of estimated air fuel ratio of each cylinder due to drop of response of the air fuel ratio sensor 37 is accurately corrected by correcting estimated air fuel ratio of each cylinder according to response of the air fuel ratio sensor 37 after accurately correcting estimation error of the estimated air fuel ratio of each cylinder due to change of engine operation conditions by correcting estimated air fuel ratio of each cylinder according to the engine operation conditions (for example, engine speed, load and the like). Accuracy of individual cylinder air fuel ratio control and accuracy of individual cylinder abnormality diagnosis are improved by performing individual cylinder air fuel ratio control and individual cylinder air fuel ratio abnormality diagnosis with using estimated air fuel ratio of each cylinder of which estimation accuracy is improved by the corrections. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a control device for an internal combustion engine that estimates an air-fuel ratio of each cylinder based on a detection value of an air-fuel ratio sensor installed in an exhaust gas merging portion of the internal combustion engine.

In recent years, in order to improve the air-fuel ratio control accuracy of an internal combustion engine, for example, as described in Patent Document 1 (Japanese Patent Laid-Open No. 2005-207405), an exhaust merging portion where exhaust gases of a plurality of cylinders merge is provided. The air-fuel ratio of each cylinder is estimated using a model that associates the detection value of one installed air-fuel ratio sensor (the air-fuel ratio of the exhaust gas merging portion) with the air-fuel ratio of each cylinder, and based on the estimation result, the air-fuel ratio of each cylinder is estimated. 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 between cylinders, and the air-fuel ratio (for example, fuel injection amount) of each cylinder is controlled for each cylinder. There is something.
JP 2005-207405 A

  By the way, in the cylinder-by-cylinder air-fuel ratio estimation in which the air-fuel ratio of each cylinder is estimated based on the detection value of one air-fuel ratio sensor installed in the exhaust gas merging section, the cylinder-by-cylinder is determined according to the operating state of the internal combustion engine (for example, rotational speed, load, etc.). The estimation accuracy of air-fuel ratio estimation may change. For example, in a model method in which the air-fuel ratio of each cylinder is estimated using a model in which the detection value of the air-fuel ratio sensor and the air-fuel ratio of each cylinder are associated with each other, a low-rotation region or an exhaust region where the exhaust gas discharge interval of each cylinder becomes long is used. In the high load region where the gas amount increases, the estimation accuracy of the cylinder-by-cylinder air-fuel ratio estimation tends to be high, and in the high rotation region where the exhaust gas discharge interval of each cylinder becomes short or in the low load region where the exhaust gas amount decreases. The estimation accuracy of cylinder-by-cylinder air-fuel ratio estimation tends to decrease.

  However, in the technique of the above-mentioned Patent Document 1, since the change in the estimation accuracy of the cylinder-by-cylinder air-fuel ratio estimation due to the change in the operating state of the internal combustion engine is not taken into consideration, the estimation of each cylinder is affected by the influence of the operating state of the internal combustion engine. There is a possibility that the estimation accuracy of the air-fuel ratio may be lowered, and accordingly, the control accuracy of the cylinder-by-cylinder air-fuel ratio control based on the estimated air-fuel ratio of each cylinder may be lowered.

  The present invention has been made in view of such circumstances, and therefore the object of the present invention is to accurately determine the estimated air-fuel ratio of each cylinder without being influenced by the operating state of the internal combustion engine. It is an object of the present invention to provide a control device for an internal combustion engine that can improve the control accuracy of the cylinder-by-cylinder air-fuel ratio control based on the estimated air-fuel ratio of the cylinder.

  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 confluence where the exhaust gases of a plurality of cylinders of the internal combustion engine merge. In a control apparatus for an internal combustion engine having a cylinder-by-cylinder air-fuel ratio estimating means for estimating an air-fuel ratio of each cylinder based on a detection value of an air-fuel ratio sensor, the estimated air-fuel ratio of each cylinder is determined by cylinder according to the operating state of the internal combustion engine. The correction is made by the estimated air-fuel ratio correcting means, and the air-fuel ratio of each cylinder is controlled by the cylinder-specific air-fuel ratio control means based on the corrected estimated air-fuel ratio of each cylinder.

  In the cylinder-by-cylinder air-fuel ratio estimation in which the air-fuel ratio of each cylinder is estimated based on the detection value of the air-fuel ratio sensor installed in the exhaust gas merging portion, the estimation accuracy of the cylinder-by-cylinder air-fuel ratio estimation changes according to the operating state of the internal combustion engine. If the estimated air-fuel ratio of each cylinder is corrected according to the operating state of the internal combustion engine, the estimated error of the estimated air-fuel ratio of each cylinder due to the change in the operating state of the internal combustion engine can be corrected with high accuracy. The estimated air-fuel ratio of each cylinder can be obtained with high accuracy regardless of the state. By performing the cylinder-by-cylinder air-fuel ratio control for controlling the air-fuel ratio of each cylinder based on the estimated air-fuel ratio of each cylinder whose estimation accuracy is improved by such correction, the control accuracy of the cylinder-by-cylinder air-fuel ratio control is improved. Can do.

  By the way, in the cylinder-by-cylinder air-fuel ratio estimation in which the air-fuel ratio of each cylinder is estimated based on the detection value of the air-fuel ratio sensor installed in the exhaust gas merging portion, if the responsiveness of the air-fuel ratio sensor decreases due to deterioration over time or the like, The estimation accuracy of the estimation may be reduced.

  Therefore, as described in claim 2, the responsiveness of the air-fuel ratio sensor is detected by the sensor responsiveness detecting means, and the estimated air-fuel ratio of each cylinder is corrected according to the operating state of the internal combustion engine and the responsiveness of the air-fuel ratio sensor. You may do it. In this way, even when the responsiveness of the air-fuel ratio sensor is reduced, each cylinder due to the reduced responsiveness of the air-fuel ratio sensor is corrected by correcting the estimated air-fuel ratio of each cylinder according to the responsiveness of the air-fuel ratio sensor. Therefore, the estimated air-fuel ratio of each cylinder can be accurately obtained by accurately correcting the estimated error of the estimated air-fuel ratio, and the control accuracy of the cylinder-by-cylinder air-fuel ratio control can be further improved.

  Further, as described in claim 3, the presence / absence of abnormality of the air-fuel ratio of each cylinder is determined based on the estimated air-fuel ratio of each cylinder corrected according to the operating state of the internal combustion engine and the responsiveness of the air-fuel ratio sensor. You may make it determine by a diagnostic means. In this way, the cylinder for determining whether or not there is an abnormality in the air-fuel ratio of each cylinder based on the estimated air-fuel ratio of each cylinder whose estimation accuracy is improved by correction according to the operating state of the internal combustion engine and the responsiveness of the air-fuel ratio sensor A separate air-fuel ratio abnormality diagnosis can be performed, and the diagnostic accuracy of the cylinder-specific air-fuel ratio abnormality diagnosis can be improved.

Hereinafter, an embodiment embodying the best mode for carrying out the present invention will be described.
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.

  Further, the ECU 40 executes a cylinder-by-cylinder air-fuel ratio control routine shown in FIG. 2 to be described later, so that the detected value of the air-fuel ratio sensor 37 (the air-fuel ratio of the exhaust gas flowing through the exhaust gas merging portion 36) and the Using a model that associates the air-fuel ratio (hereinafter referred to as “cylinder-by-cylinder air-fuel ratio estimation model”), 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 and the reference air-fuel ratio are estimated. By calculating a deviation from the fuel ratio (the average value or the control target value of the estimated air-fuel ratios of all cylinders), the air-fuel ratio variation of each cylinder is calculated. Then, the air-fuel ratio correction amount (correction amount of the fuel injection amount of each cylinder) is calculated so that the variation in the air-fuel ratio of each cylinder becomes small, 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.

  Here, a specific example of the cylinder-by-cylinder air-fuel ratio estimation model for estimating the air-fuel ratio of each cylinder based on the detection value of the air-fuel ratio sensor 37 (the air-fuel ratio of the exhaust gas flowing through the exhaust gas merging portion 36) 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 merging section 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, the cylinder-by-cylinder air-fuel ratio estimation model is configured by the Kalman filter type observer, whereby the air-fuel ratio of each cylinder can be sequentially estimated as the combustion cycle proceeds.

  Further, the ECU 40 executes a cylinder-by-cylinder air-fuel ratio abnormality diagnosis routine shown in FIGS. 3 and 4 to be described later, thereby using the cylinder-by-cylinder air-fuel ratio estimation model, based on the detected value of the air-fuel ratio sensor 37. Estimating the fuel ratio and calculating the deviation between the estimated air-fuel ratio of each cylinder and the reference air-fuel ratio (the average value of the estimated air-fuel ratio of all the cylinders or the control target value), thereby calculating the variation in the air-fuel ratio of each cylinder. To do. Then, the cylinder-by-cylinder air-fuel ratio abnormality diagnosis is performed in which the air-fuel ratio variation of each cylinder is compared with a predetermined determination value to determine whether the air-fuel ratio of each cylinder is abnormal.

  By the way, the cylinder-by-cylinder air-fuel ratio estimation that estimates the air-fuel ratio of each cylinder using the cylinder-by-cylinder air-fuel ratio estimation model that associates the detection value of one air-fuel ratio sensor 37 installed in the exhaust gas merging section 36 with the air-fuel ratio of each cylinder. Then, the estimation accuracy of the cylinder-by-cylinder air-fuel ratio estimation changes depending on the engine operating state (for example, engine speed, load, etc.). For example, the estimation accuracy of the cylinder-by-cylinder air-fuel ratio estimation tends to be high in a low rotation region where the exhaust gas discharge interval of each cylinder becomes long or a high load region where the amount of exhaust gas increases, and the exhaust gas discharge of each cylinder tends to be high. In the high rotation region where the interval is shortened and in the low load region where the exhaust gas amount is small, the estimation accuracy of the cylinder-by-cylinder air-fuel ratio estimation tends to decrease.

  Further, in the cylinder-by-cylinder air-fuel ratio estimation in which the air-fuel ratio of each cylinder is estimated based on the detection value of the air-fuel ratio sensor 37 installed in the exhaust gas merging portion 36, if the responsiveness of the air-fuel ratio sensor 37 decreases due to deterioration over time, the cylinder There is a possibility that the estimation accuracy of the separate air-fuel ratio estimation is lowered.

  As described above, when the cylinder-by-cylinder air-fuel ratio control or the cylinder-by-cylinder air-fuel ratio abnormality diagnosis is performed using the estimated air-fuel ratio of each cylinder whose estimation accuracy is reduced due to the influence of the engine operating state and the responsiveness of the air-fuel ratio sensor 37, the cylinder There is a possibility that the control accuracy of the separate air-fuel ratio control and the diagnosis accuracy of the abnormality diagnosis for each cylinder may be lowered.

  As a countermeasure, in this embodiment, first, the estimated air-fuel ratio of each cylinder according to the change of the engine operating state is corrected by correcting the estimated air-fuel ratio of each cylinder according to the engine operating state (for example, engine speed, load, etc.). Then, the estimated air-fuel ratio of each cylinder is corrected according to the responsiveness of the air-fuel ratio sensor 37, and the estimated air-fuel ratio of each cylinder due to the decrease in the responsiveness of the air-fuel ratio sensor 37 is corrected. Is accurately corrected. By performing the cylinder-by-cylinder air-fuel ratio control and the cylinder-by-cylinder air-fuel ratio abnormality diagnosis using the estimated air-fuel ratio of each cylinder whose estimation accuracy has been improved by these corrections, the control accuracy of the cylinder-by-cylinder air-fuel ratio control and the cylinder-by-cylinder abnormality diagnosis The diagnostic accuracy is improved.

  The above-described cylinder-by-cylinder air-fuel ratio control and cylinder-by-cylinder air-fuel ratio abnormality diagnosis are executed 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 routine shown in FIG. 2 is executed at a predetermined cycle while the ECU 35 is powered on, and serves as cylinder-by-cylinder air-fuel ratio control means. When this routine is started, first, at step 101, the engine operating state such as the engine speed and load (intake pipe pressure and intake air amount) is read, and then the routine proceeds to step 102 where predetermined air-fuel ratio control for each cylinder is performed. It is determined whether or not an execution condition is satisfied. As a result, when it is determined that the cylinder-by-cylinder air-fuel ratio control execution condition is not satisfied, this routine is terminated without performing the subsequent processing.

  On the other hand, when it is determined in step 102 that the cylinder-by-cylinder air-fuel ratio control execution condition is satisfied, the routine proceeds to step 103, where the output of the air-fuel ratio sensor 37 (air-fuel ratio detection value) is read. Thereafter, the routine proceeds to step 104, where the air-fuel ratio AF (#i of the i-th cylinder #i (i = 1 to 4 in the case of a four-cylinder engine) that is the current air-fuel ratio estimation target using the cylinder-by-cylinder air-fuel ratio estimation model. ) Is estimated based on the detection value of the air-fuel ratio sensor 37. The process of step 104 serves as cylinder-by-cylinder air-fuel ratio estimating means in the claims.

  Thereafter, the routine proceeds to step 105, where the estimated air-fuel ratio AF (#i) of each cylinder is corrected according to the engine operating state (for example, engine speed, load, etc.).

  Specifically, with reference to the map of the correction coefficient KC shown in FIG. 6, the correction coefficient KC (#i of the i-th cylinder #i corresponding to the engine speed NE and the intake pipe pressure PM (or intake air amount). ) And the correction amount FC of the i-th cylinder #i according to the engine speed NE and the intake pipe pressure PM (or intake air amount) with reference to the map of the correction amount FC shown in FIG. i) is calculated. The map of the correction coefficient KC (#i) and the map of the correction amount FC (#i) are set in advance for each cylinder based on test data, design data, and the like.

Then, the estimated air-fuel ratio AF (#i) of the i-th cylinder #i is multiplied by the correction coefficient KC (#i) and the correction amount FC (#i) is added. The estimation error of AF (#i) is corrected.
AF (#i) = AF (#i) × KC (#i) + FC (#i)

If the estimation error of the estimated air-fuel ratio AF (#i) can be corrected to some extent by using only the correction coefficient KC (#i), only the correction coefficient KC (#i) is calculated and the estimated air-fuel ratio AF (#i) May be multiplied by the correction coefficient KC (#i) to correct the estimated air-fuel ratio AF (#i).
AF (#i) = AF (#i) × KC (#i)

Further, when the estimation error of the estimated air-fuel ratio AF (#i) can be corrected to some extent only by the correction amount FC (#i), only the correction amount FC (#i) is calculated and the estimated air-fuel ratio AF (#i) The estimated air-fuel ratio AF (#i) may be corrected by adding the correction amount FC (#i) to
AF (#i) = AF (#i) + FC (#i)
Thereafter, the routine proceeds to step 106, where the estimated air-fuel ratio AF (#i) of each cylinder is corrected according to the responsiveness of the air-fuel ratio sensor 37.

Specifically, a correction coefficient corresponding to the response index Rs of the air-fuel ratio sensor 37 calculated in the sensor abnormality diagnosis routine of FIG. 5 to be described later is calculated by a map or the like, and the estimated air-fuel ratio of each cylinder is calculated using this correction coefficient. By correcting AF (#i), an estimation error of the estimated air-fuel ratio AF (#i) due to a decrease in responsiveness of the air-fuel ratio sensor 37 is corrected. At this time, the estimated air-fuel ratio AF (#i) of each cylinder may be uniformly corrected with the same correction coefficient, but the estimated air-fuel ratio AF (#i) of each cylinder is multiplied by a weight for each cylinder. You may make it correct | amend with the correction coefficient. In addition to the sensor abnormality diagnosis routine, a dedicated process for detecting the responsiveness of the air-fuel ratio sensor 37 may be executed to obtain the responsiveness index Rs of the air-fuel ratio sensor 37.
The processes in these steps 105 and 106 serve as cylinder-by-cylinder estimated air-fuel ratio correction means in the claims.

  Thereafter, the routine proceeds to step 107, where the estimated air-fuel ratio AF (#i) of the i-th cylinder #i and the reference air-fuel ratio (the estimated air-fuel ratios of all cylinders) are corrected according to the engine operating state and the response of the air-fuel ratio sensor 37. By calculating the deviation from the average value or the control target value), the inter-cylinder variation ΔAF (#i) of the air-fuel ratio of the i-th cylinder #i is calculated.

  Thereafter, the process proceeds to step 108, and after calculating the air-fuel ratio correction amount (correction amount of the fuel injection amount of each cylinder) so that the inter-cylinder variation ΔAF (#i) of the air-fuel ratio of each cylinder becomes small, Proceeding to step 109, the fuel injection amount of each cylinder is corrected based on the air-fuel ratio correction amount of each cylinder, whereby the air-fuel ratio of the air-fuel mixture supplied to each cylinder is corrected for each cylinder, and the air-fuel ratio of each cylinder is corrected. The cylinder-by-cylinder air-fuel ratio control is performed so as to reduce the variation among the cylinders.

[Air-fuel ratio abnormality diagnosis routine for each cylinder]
The cylinder-by-cylinder air-fuel ratio abnormality diagnosis routine shown in FIGS. 3 and 4 is executed at a predetermined cycle while the ECU 35 is turned on, and serves as cylinder-by-cylinder air-fuel ratio abnormality diagnosis means. When this routine is started, first, in step 201, the engine operating state such as the engine speed and load (intake pipe pressure and intake air amount) is read, and then the routine proceeds to step 202, where a predetermined cylinder-by-cylinder air-fuel ratio abnormality is detected. It is determined whether a diagnosis execution condition is satisfied. As a result, when it is determined that the cylinder-by-cylinder air-fuel ratio abnormality diagnosis execution condition is not satisfied, this routine is terminated without performing the subsequent processing.

  On the other hand, if it is determined in step 202 that the cylinder-by-cylinder air-fuel ratio abnormality diagnosis execution condition is satisfied, the process proceeds to step 203, the diagnosis execution flag is set to “1”, and the next In steps 204 to 208, the same processing as in steps 103 to 107 in FIG. 2 is executed to obtain the estimated air-fuel ratio AF (#i) based on the detected value of the air-fuel ratio sensor 37. This estimated air-fuel ratio AF (#i) is corrected according to the engine operating state and the responsiveness of the air / fuel ratio sensor 37, and the deviation between the corrected estimated air / fuel ratio AF (#i) and the reference air / fuel ratio is calculated. The variation ΔAF (#i) is calculated. The air-fuel ratio variation ΔAF (#i) calculated in step 107 of FIG. 2 may be read.

  Thereafter, the process proceeds to step 209 in FIG. 4 to determine whether or not the variation ΔAF (#i) in the air-fuel ratio of the i-th cylinder #i is larger than a predetermined determination value F. As a result, if it is determined that the inter-cylinder variation ΔAF (#i) of the air-fuel ratio of the i-th cylinder #i is equal to or less than the determination value F, the process proceeds to step 215, and the abnormality of the air-fuel ratio of the i-th cylinder #i After determining that there is no (normal) and setting the normal flag Xafnorm (#i) of the i-th cylinder #i to “1”, this routine is ended.

  In contrast, if it is determined in step 209 that the air-fuel ratio variation ΔAF (#i) of the air-fuel ratio of the i-th cylinder #i is larger than the determination value F, the process proceeds to step 210 and the i-th cylinder The count value of the delay counter D (#i) of the i-th cylinder #i that measures the elapsed time after the inter-cylinder variation ΔAF (#i) of the air-fuel ratio of #i becomes larger than the determination value F is “1”. Then, the process proceeds to step 211, where it is determined whether or not the count value of the delay counter D (#i) has exceeded a predetermined delay value. It is determined whether or not a predetermined delay time has elapsed since the increase.

  In this step 211, a predetermined delay time has elapsed after the count value of the delay counter D (#i) exceeds a predetermined delay value (that is, the inter-cylinder variation ΔAF (#i) becomes larger than the determination value F). ), The process proceeds to step 212 to start the process of incrementing the count value of the abnormality counter T (#i) of the i-th cylinder #i by “1”, and then proceeds to step 213 to proceed to the abnormality counter T It is determined whether the count value of (#i) has exceeded a predetermined abnormality determination value.

  In this step 213, when it is determined that the count value of the abnormality counter T (#i) is smaller than the abnormality determination value, this routine is ended as it is, and the inter-cylinder variation ΔAF (#i) is determined as the determination value F. When the value is larger than that, the process of incrementing the count value of the abnormality counter T (#i) (steps 201 to 212) is repeated. When the inter-cylinder variation ΔAF (#i) is equal to or less than the determination value F, the count value of the abnormality counter T (#i) is not held but held (held) at the current count value.

  Thereafter, when it is determined in step 213 that the count value of the abnormality counter T (#i) has exceeded the abnormality determination value, the routine proceeds to step 214, where it is determined that the air-fuel ratio of the i-th cylinder #i is abnormal. The abnormal flag Xaffail (#i) of the i-th cylinder #i is set to “1”, and the normal flag Xafnorm (#i) of the i-th cylinder #i is maintained at “0” or reset, so that the driver seat A warning lamp (not shown) provided on the instrument panel is turned on, or a warning is displayed on a warning display part (not shown) of the instrument panel of the driver's seat to warn the driver, The abnormality information (abnormal code or the like) is stored in a rewritable nonvolatile memory such as a backup RAM (not shown) of the ECU 40, and this routine is terminated.

[Sensor abnormality diagnosis routine]
The sensor abnormality diagnosis routine shown in FIG. 5 is executed at a predetermined cycle while the ECU 35 is powered on. When this routine is started, first, at step 301, it is determined whether or not a predetermined sensor abnormality diagnosis execution condition is satisfied. As a result, when it is determined that the sensor abnormality diagnosis execution condition is not satisfied, this routine is terminated without performing the subsequent processing.

  On the other hand, if it is determined in step 301 that the sensor abnormality diagnosis execution condition is satisfied, the process proceeds to step 302, where it is determined whether the fuel cut is started, and the fuel cut is started. When it is determined that the fuel cut has occurred, the routine proceeds to step 303 where the output I1 of the air-fuel ratio sensor 37 at the start of fuel cut is read and stored in the memory of the ECU 40 and the elapsed time from the start of fuel cut is measured by operating the timer. To do.

  Thereafter, the routine proceeds to step 304, where it is determined whether or not the output of the air-fuel ratio sensor 37 has changed to a predetermined value I2, and when it is determined that the output of the air-fuel ratio sensor 37 has changed to a predetermined value I2, step 305 is performed. Then, based on the count value of the timer, the response time T1 required from the start of the fuel cut until the output of the air-fuel ratio sensor 37 changes to the predetermined value I2 is measured.

  Thereafter, the routine proceeds to step 306, where the response time T1 of the air-fuel ratio sensor 37 is converted into a responsiveness index Rs. In this case, for example, by setting the reciprocal of the response time T1 as the response index Rs, the response index Rs is set to be larger as the response of the air-fuel ratio sensor 37 is higher (that is, the response time T1 is shorter). This responsiveness index Rs is used to correct the estimated air-fuel ratio according to the responsiveness of the air-fuel ratio sensor 37 in the cylinder-by-cylinder air-fuel ratio control routine shown in FIG. 2 or the cylinder-by-cylinder air-fuel ratio abnormality diagnosis routine shown in FIGS. Used when The processing in step 306 serves as sensor responsiveness detection means in the claims.

Thereafter, the process proceeds to step 307, where the output change rate ΔI of the air-fuel ratio sensor 37 is calculated from the following equation.
ΔI = (I2 -I1) / T1
The output change rate ΔI may be used as the response index Rs.
Thereafter, the routine proceeds to step 308, where it is determined whether or not the output change rate ΔI of the air-fuel ratio sensor 37 is smaller than a predetermined abnormality determination value Ifc.

  As a result, when it is determined that the output change rate ΔI of the air-fuel ratio sensor 37 is smaller than the abnormality determination value Ifc, it is determined that there is an abnormality in the air-fuel ratio sensor 37, the process proceeds to step 309, and the air-fuel ratio sensor 37 The abnormality flag is set to "1" and a warning lamp (not shown) provided on the instrument panel of the driver's seat is turned on, or a warning display section (not shown) of the instrument panel of the driver's seat The warning information is displayed to warn the driver, and the abnormality information (abnormality code or the like) is stored in a rewritable nonvolatile memory such as a backup RAM (not shown) of the ECU 40, and this routine is terminated.

  On the other hand, if it is determined in step 308 that the output change rate ΔI of the air-fuel ratio sensor 37 is greater than or equal to the abnormality determination value Ifc, it is determined that the air-fuel ratio sensor 37 is not abnormal (normal), This routine ends.

  An execution example of the cylinder-by-cylinder air-fuel ratio abnormality diagnosis of the present embodiment described above will be described with reference to the time chart of FIG. As shown in FIG. 8, at the time t1 when the cylinder-by-cylinder air-fuel ratio abnormality diagnosis execution condition is satisfied, the diagnosis execution flag is set to "1" and the cylinder-by-cylinder air-fuel ratio abnormality diagnosis is started.

  First, the estimated air-fuel ratio AF (#i) of the i-th cylinder #i is obtained based on the detection value of the air-fuel ratio sensor 37, and this estimated air-fuel ratio AF (#i) is determined based on the engine operating state (the engine speed NE and the intake pipe). Pressure PM) and the responsiveness of the air-fuel ratio sensor 37, and calculating the deviation between the corrected estimated air-fuel ratio AF (#i) and the reference air-fuel ratio, the air-fuel ratio variation ΔAF (# i) is calculated.

  At the time t2 when the inter-cylinder variation ΔAF (#i) exceeds a predetermined determination value F, a process of incrementing the count value of the delay counter D (#i) is started, and the count of the delay counter D (#i) is started. When the value exceeds a predetermined delay value t3 (that is, when a predetermined delay time has elapsed after the inter-cylinder variation ΔAF (#i) exceeds the judgment value F), the count value of the abnormality counter T (#i) The process of incrementing is started.

  Thereafter, at time t4 when the count value of the abnormality counter T (#i) exceeds a predetermined abnormality determination value, it is determined that there is an abnormality in the air-fuel ratio of the i-th cylinder #i, and the abnormality flag Xaffail of the i-th cylinder #i (#i) is set to “1”, the diagnosis end flag is set to “1”, and the cylinder-specific abnormality diagnosis is ended.

  In the present embodiment described above, 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 according to the engine operating state (for example, engine speed, load, etc.). As a result, the estimation error of the estimated air-fuel ratio of each cylinder due to a change in the engine operating state can be accurately corrected, and further, the estimated air-fuel ratio of each cylinder is corrected according to the responsiveness of the air-fuel ratio sensor 37. As a result, the estimation error of the estimated air-fuel ratio of each cylinder due to a decrease in the response of the air-fuel ratio sensor 37 can be corrected with high accuracy, without being affected by the engine operating state or the response of the air-fuel ratio sensor 37. The estimated air-fuel ratio of each cylinder can be obtained with high accuracy.

  Further, since the cylinder-by-cylinder air-fuel ratio control and the cylinder-by-cylinder air-fuel ratio abnormality diagnosis are performed using the estimated air-fuel ratio of each cylinder whose estimation accuracy is improved by these corrections, the control accuracy of the cylinder-by-cylinder air-fuel ratio control and the cylinder The diagnostic accuracy of another abnormality diagnosis can be improved.

  In the above embodiment, the estimated air-fuel ratio of each cylinder is corrected according to the engine operating state, and the estimated air-fuel ratio of each cylinder is corrected according to the response of the air-fuel ratio sensor 37. When the influence of the responsiveness of the air-fuel ratio sensor 37 is small (for example, when the responsiveness of the air-fuel ratio sensor 37 is hardly lowered), the correction according to the responsiveness of the air-fuel ratio sensor 37 may be omitted. Further, the method for correcting the estimated air-fuel ratio of each cylinder according to the engine operating state and the method for correcting the estimated air-fuel ratio of each cylinder according to the responsiveness of the air-fuel ratio sensor 37 are limited to the methods described in the above embodiments. Needless to say, it may be changed as appropriate.

  Further, in the above embodiment, the air-fuel ratio of each cylinder is estimated using the cylinder-by-cylinder air-fuel ratio estimation model in which the detection value of the air-fuel ratio sensor 37 is associated with the air-fuel ratio of each cylinder. The estimation method is not limited to the method using the cylinder-by-cylinder air-fuel ratio estimation model, and may be appropriately changed. For example, when the air-fuel ratio dither control for forcibly changing the air-fuel ratio for each cylinder is executed The air-fuel ratio of each cylinder may be estimated based on the output of the air-fuel ratio sensor 37.

Further, the diagnosis method for the cylinder-by-cylinder air-fuel ratio abnormality diagnosis and the method for detecting the response of the air-fuel ratio sensor 37 are not limited to the methods described in the above embodiments, and may be changed as appropriate.
In addition, the present invention is not limited to the four-cylinder engine described in the above embodiment, and can be implemented with various modifications such as being applicable 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 one Example of this invention. It is a flowchart explaining the flow of a process of the air-fuel ratio control routine classified by cylinder. It is a flowchart (the 1) explaining the flow of a process of the air-fuel ratio abnormality diagnosis routine according to cylinder. It is a flowchart (the 2) explaining the flow of a process of the air-fuel ratio abnormality diagnosis routine according to cylinder. It is a flowchart explaining the flow of a process of a sensor abnormality diagnosis routine. It is a figure which shows notionally an example of the map of the correction coefficient KC. It is a figure which shows notionally an example of the map of correction amount FC. It is a time chart explaining the execution example of the air-fuel ratio abnormality diagnosis according to cylinder.

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 (air-fuel ratio estimation for each cylinder) Means, cylinder-specific estimated air-fuel ratio correction means, cylinder-specific air-fuel ratio control means, sensor response detection means, cylinder-specific air-fuel ratio abnormality diagnosis means)

Claims (3)

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 In the control device for an internal combustion engine provided with the cylinder-by-cylinder air-fuel ratio estimating means,
A cylinder-by-cylinder estimated air-fuel ratio correcting unit that corrects an estimated air-fuel ratio of each cylinder estimated by the cylinder-by-cylinder air-fuel ratio estimating unit according to an operating state of the internal combustion engine;
A control apparatus for an internal combustion engine, comprising: cylinder-specific air-fuel ratio control means for controlling the air-fuel ratio of each cylinder based on the estimated air-fuel ratio of each cylinder corrected by said cylinder-specific estimated air-fuel ratio correction means. Sensor responsiveness detecting means for detecting the responsiveness of the air-fuel ratio sensor,
The cylinder-by-cylinder estimated air-fuel ratio correcting means corrects the estimated air-fuel ratio of each cylinder estimated by the cylinder-by-cylinder air-fuel ratio estimating means according to the operating state of the internal combustion engine and the responsiveness of the air-fuel ratio sensor. The control device for an internal combustion engine according to claim 1.   2. A cylinder-by-cylinder air-fuel ratio abnormality diagnosing unit for determining whether there is an abnormality in the air-fuel ratio of each cylinder based on the estimated air-fuel ratio of each cylinder corrected by the cylinder-by-cylinder estimated air-fuel ratio correcting unit. The control apparatus for an internal combustion engine according to 1 or 2.

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