JP4600699B2 - Cylinder-by-cylinder air-fuel ratio control apparatus for internal combustion engine - Google Patents

Description

  The present invention relates to a cylinder-by-cylinder air-fuel ratio control apparatus for an internal combustion engine having a function of estimating an air-fuel ratio of each cylinder based on a detection value of one air-fuel ratio sensor installed in an exhaust gas collection portion of the internal combustion engine.

  In recent years, as described in Patent Document 1 (Japanese Patent No. 3217680), in order to improve air-fuel ratio control accuracy by reducing air-fuel ratio variation between cylinders of an internal combustion engine, the behavior of the exhaust system of the internal combustion engine is described. Is set by the observer who inputs the detection value (the air-fuel ratio of the exhaust gas flowing through the exhaust gas collection unit) installed in the exhaust collection unit to the model and observes its internal state. The air-fuel ratio of each cylinder is estimated, and the fuel injection amount of each cylinder is corrected according to the deviation between the estimated air-fuel ratio of each cylinder and the target value, so that the air-fuel ratio of each cylinder matches the target value. There is something. Further, in Patent Document 1, a delay until the exhaust gas discharged from each cylinder reaches the vicinity of the air-fuel ratio sensor and the air-fuel ratio is detected (hereinafter referred to as “exhaust system response delay”) is an engine operating state. In the engine design and manufacturing process, a map that defines the relationship between the exhaust system response delay and the engine operating state is created, and the sample timing of the air-fuel ratio sensor output ( The air-fuel ratio detection timing of each cylinder) is changed by the map according to the engine operating state.

However, the cause for changing the response delay of the exhaust system is not only the engine operating state, but also the response delay of the exhaust system changes due to deterioration with time of the response of the air-fuel ratio sensor.
Therefore, in Patent Document 2 (Japanese Patent Laid-Open No. 10-73049), a delay parameter indicating the degree of response deterioration of the air-fuel ratio sensor is calculated by measuring the response delay of the air-fuel ratio sensor after the start of fuel cut, and the air-fuel ratio sensor output is calculated. The sample timing (air-fuel ratio detection timing of each cylinder) is changed in consideration of both the deterioration parameter and the engine operating state.
Japanese Patent No. 3217680 (see [0008], [0013], [0162] to [0164], etc.) JP-A-10-73049 (second page, etc.)

  However, the length of the exhaust passage (exhaust manifold) from the exhaust port of each cylinder to the air-fuel ratio sensor is different for each cylinder, and the flow of exhaust gas in each cylinder is complicated by the engine speed and the amount of air charged in the cylinder. The exhaust system response delay also changes due to engine manufacturing variations and aging, so the relationship between the exhaust system response delay of each cylinder and the engine operating state can be accurately mapped during the engine design and manufacturing process. It is difficult to make it. Therefore, it is difficult to accurately correct the sample timing of the air-fuel ratio sensor output (air-fuel ratio detection timing of each cylinder) with the techniques of Patent Documents 1 and 2 above.

  In view of the above, an object of the present invention is to provide a system for estimating the air-fuel ratio of each cylinder based on the detection value of one air-fuel ratio sensor installed in the exhaust collecting portion of the internal combustion engine. It is to be able to learn accurately the deviation in sample timing (air-fuel ratio detection timing of each cylinder).

In order to achieve the above object, the invention according to claim 1 is provided with an air-fuel ratio sensor for detecting an air-fuel ratio of the exhaust gas at an exhaust gas collecting portion where the exhaust gas of each cylinder of the internal combustion engine collects and flows. Based on the detection value of the air-fuel ratio sensor detected at each air-fuel ratio detection timing of each cylinder, the air-fuel ratio of each cylinder is estimated by the cylinder-specific air-fuel ratio estimation means, and each cylinder is estimated by the cylinder-specific air-fuel ratio control means. The fuel correction amount of each cylinder is calculated based on the deviation between the air-fuel ratio and the reference air-fuel ratio, and the fuel injection amount of each cylinder is corrected with the fuel correction amount to control the air-fuel ratio of each cylinder (hereinafter referred to as “by cylinder”). in-cylinder air-fuel ratio control apparatus for an internal combustion engine so as to) that the air-fuel ratio control ", by changing the air-fuel ratio detecting timing in the cylinder air-fuel ratio control estimates the air-fuel ratio of each cylinder, fuel changes in the estimated air-fuel ratio of before and after correction Is intended but where the structure includes a learning means for learning the air-fuel ratio detection timing which becomes air-fuel ratio change amount according to the fuel correction amount, as appropriate air-fuel ratio detection timing for detecting the air-fuel ratio in each cylinder .

If the accuracy of the estimated air-fuel ratio of each cylinder is good, the fuel correction amount of each cylinder is accurately reflected in the amount of change in the estimated air-fuel ratio, and the amount of change in the estimated air-fuel ratio before and after fuel correction corresponds to the fuel correction amount. It should be the amount of change (hereinafter referred to as “fuel correction amount equivalent”) .
Focusing on this characteristic, in the invention according to claim 1, the air-fuel ratio detection timing of each cylinder is changed during the cylinder-by-cylinder air-fuel ratio control, and the air-fuel ratio before and after fuel correction of each cylinder at the air-fuel ratio detection timing is changed. The air-fuel ratio detection timing at which the estimated air-fuel ratio change amount before and after fuel correction becomes equivalent to the fuel correction amount is learned by the learning means as the appropriate air-fuel ratio detection timing. An appropriate air-fuel ratio detection timing can be learned during air-fuel ratio control, and the air-fuel ratio detection timing of each cylinder can be corrected to an appropriate air-fuel ratio detection timing based on the learning result. The fuel ratio can be accurately estimated.

Further, if the accuracy of the estimated air-fuel ratio of each cylinder is good, the degree of variation in estimated air-fuel ratio between cylinders and the degree of variation in fuel correction amount are reduced.
Focusing on this characteristic, as in claim 2, the air-fuel ratio detection timing of each cylinder is changed during the air-fuel ratio control for each cylinder to estimate the air-fuel ratio of each cylinder, and the degree of variation in the estimated air-fuel ratio between the cylinders In addition, the air-fuel ratio detection timing at which the variation degree of the fuel correction amount is minimized or less than a predetermined value may be learned as an appropriate air-fuel ratio detection timing. Even in this case, it is possible to learn the appropriate air-fuel ratio detection timing during the cylinder-by-cylinder air-fuel ratio control, and to set the air-fuel ratio detection timing of each cylinder to the appropriate air-fuel ratio detection timing based on the learning result. Thus, the air-fuel ratio of each cylinder can be accurately estimated.

In this case, considering that the appropriate air-fuel ratio detection timing changes according to the operating state of the internal combustion engine, the appropriate air-fuel ratio detection timing is learned for each operating state of the internal combustion engine as in claim 3. It is good to do. In this way, the accuracy of the learned value of the air-fuel ratio detection timing can be improved.

In the inventions according to the first to third aspects, the method for estimating the air-fuel ratio of each cylinder based on the detection value of the air-fuel ratio sensor is described in Patent Documents 1 and 2 and other known documents. However, as described in claim 4 , the detected value of the air-fuel ratio sensor is obtained by multiplying the history of the estimated air-fuel ratio of each cylinder and the history of the detected value of the air-fuel ratio sensor by a predetermined weight. It may be modeled as an addition, and the air-fuel ratio of each cylinder may be estimated using the model. In this way, since the model for estimating the air-fuel ratio for each cylinder is an autoregressive model for predicting the detection value of the air-fuel ratio sensor from the past detection value, the air-fuel ratio for each cylinder is accurately determined from the detection value of the air-fuel ratio sensor. It can be estimated well. In addition, since a simple model can be obtained, there is an advantage that the complexity of modeling can be eliminated and the calculation load of the in-vehicle computer can be reduced.

  Hereinafter, the best mode for carrying out the present invention will be described with reference to several examples.

  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 collecting portion 36 where the exhaust manifold 35 of each cylinder of the engine 11 gathers. 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 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 the present embodiment, the ECU 40 executes a cylinder-by-cylinder air-fuel ratio control routine, which will be described later, so that the detected value of the air-fuel ratio sensor 37 (flows through the exhaust collecting portion 36) using a cylinder-by-cylinder air-fuel ratio estimation model to be described later. Estimate the air-fuel ratio of each cylinder based on the actual air-fuel ratio of the exhaust gas, calculate the average value of the estimated air-fuel ratio of all cylinders, and set the average value as the reference air-fuel ratio (target air-fuel ratio of all cylinders) At the same time, the deviation between the estimated air-fuel ratio of each cylinder and the reference air-fuel ratio is calculated for each cylinder, and the fuel correction amount (correction amount of the fuel injection amount) of each cylinder is calculated so that the deviation becomes small, By correcting the fuel injection amount of each cylinder based on the calculation result, the air-fuel ratio of the air-fuel mixture supplied to each cylinder is corrected for each cylinder so as to reduce the variation in air-fuel ratio among the cylinders ( Hereinafter, this control is referred to as cylinder-by-cylinder air-fuel ratio control).

  Here, a specific example of a model (hereinafter referred to as “cylinder-specific 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 actual air-fuel ratio of the exhaust gas flowing through the exhaust collecting portion 36). An example will be described.

  Focusing on the gas exchange in the exhaust collecting section 36, the detected value of the air-fuel ratio sensor 37 is set to a predetermined weight for the estimated air-fuel ratio history of each cylinder and the detected value history of the air-fuel ratio sensor 37 in the exhaust collecting 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 collecting 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 collecting 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 collecting portion 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.

  Next, a method for setting the air-fuel ratio detection timing of each cylinder (sample timing of the output of the air-fuel ratio sensor 37) will be described. In the first embodiment, the delay until exhaust gas discharged from each cylinder reaches the vicinity of the air-fuel ratio sensor 37 and the air-fuel ratio is detected (hereinafter referred to as “response delay of the exhaust system”) depends on the engine operating state. In consideration of the change, the air-fuel ratio detection timing of each cylinder is set by a map according to the engine operating state (for example, engine load, engine speed, etc.), and the output of the air-fuel ratio sensor 37 is taken into the ECU 40. Yes. In general, as the engine load decreases, the response delay of the exhaust system increases. Therefore, the air-fuel ratio detection timing of each cylinder is set to shift to the retard side as the engine load decreases.

  However, the length of the exhaust manifold 35 from the exhaust port of each cylinder to the air-fuel ratio sensor 37 is different for each cylinder, and the exhaust gas flow of each cylinder is in the engine operating state (engine rotation speed, in-cylinder charged air amount, etc.). ), And the exhaust system response delay also changes due to manufacturing variations and aging of the engine 11. Therefore, in the engine design and manufacturing process, the exhaust system response delay (the air-fuel ratio of each cylinder) It is difficult to accurately map the relationship between the detection timing and the engine load. For this reason, the air-fuel ratio detection timing of each cylinder may deviate from the proper air-fuel ratio detection timing.

  If the air-fuel ratio detection timing of each cylinder shifts, the estimation accuracy of the air-fuel ratio of each cylinder deteriorates, and even if the cylinder-by-cylinder air-fuel ratio control is continued, the variation in the estimated air-fuel ratio between the cylinders will not become forever. (See FIG. 4).

Therefore, in the first embodiment, an air-fuel ratio detection timing deviation determination routine shown in FIG. 5 described later is executed, so that the air-fuel ratio detection timing is based on the degree of variation in estimated air-fuel ratio between cylinders during cylinder-by-cylinder air-fuel ratio control. The presence or absence of deviation is determined.
Hereinafter, processing contents of each routine 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 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, at 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 the 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 determined 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. The map for setting the air-fuel ratio detection timing is learned and corrected by an air-fuel ratio detection timing deviation learning correction routine shown in FIGS.

  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 process proceeds to step 104, and the output of the air-fuel ratio sensor 37 (air-fuel ratio detection value) is read. Thereafter, the routine proceeds to step 105, 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 processing in step 105 serves as cylinder-by-cylinder air-fuel ratio estimation means in the claims. Thereafter, the routine proceeds to step 106, where the average value of the estimated air-fuel ratios of all cylinders is calculated, and the average value is set as the reference air-fuel ratio (target air-fuel ratio of all cylinders).

  Thereafter, the routine proceeds to step 107, where the deviation between the estimated air-fuel ratio of each cylinder and the reference air-fuel ratio is calculated, the fuel correction amount of each cylinder is calculated so that the deviation becomes smaller, and then the routine proceeds to step 108, where By correcting the fuel injection amount of each cylinder based on the fuel correction amount of the cylinder, the air-fuel ratio of the air-fuel mixture supplied to each cylinder is corrected for each cylinder so that variations in the air-fuel ratio among the cylinders are reduced. To do.

[Air-fuel ratio detection timing deviation determination routine]
First, a method for determining the deviation of the air-fuel ratio detection timing will be described with reference to the time charts of FIGS. FIG. 3 is a control example when the air-fuel ratio detection timing of each cylinder is correct, and FIG. 4 is a control example when the air-fuel ratio detection timing of each cylinder is shifted.

  As shown in FIG. 3, when the air-fuel ratio detection timing of each cylinder is correct, the air-fuel ratio of each cylinder can be accurately estimated based on the detection value of the air-fuel ratio sensor 37. The deviation between the estimated air-fuel ratio of each cylinder and the reference air-fuel ratio (hereinafter, this deviation is referred to as “estimated air-fuel ratio deviation”) is reduced, and the variation in estimated air-fuel ratio among the cylinders is reduced.

  On the other hand, as shown in FIG. 4, when the air-fuel ratio detection timing of each cylinder is shifted, the accuracy of the estimated air-fuel ratio of each cylinder calculated from the detection value of the air-fuel ratio sensor 37 deteriorates. Even if the air-fuel ratio control is continued, the estimated air-fuel ratio deviation of each cylinder does not become forever, and the variation in estimated air-fuel ratio among the cylinders does not become small.

  Focusing on such characteristics, in the first embodiment, by executing the air-fuel ratio detection timing deviation determination routine of FIG. 5, the air-fuel ratio detection timing is determined depending on whether or not the degree of variation in the estimated air-fuel ratio between the cylinders is large. The presence or absence of deviation is determined. This routine is started every predetermined crank angle (for example, every 30 ° C. A) in synchronization with the output pulse of the crank angle sensor 33. When this routine is started, it is first determined in step 201 whether or not the cylinder-by-cylinder air-fuel ratio control is being performed. If the cylinder-by-cylinder air-fuel ratio control is not being performed, the routine is terminated without performing the subsequent processing. To do.

  On the other hand, if the cylinder-by-cylinder air-fuel ratio control is being performed, the routine proceeds to step 202, where it is determined whether or not the degree of variation in the estimated air-fuel ratio between the cylinders is large, for example, one of the following conditions (A1) and (A2) Or by both.

(A1) Whether the variation in estimated air-fuel ratio between cylinders is large depending on whether the deviation between the maximum estimated air-fuel ratio and the minimum estimated air-fuel ratio among the estimated air-fuel ratios of each cylinder is a predetermined value or more Determine whether.
(A2) It is determined whether or not the degree of variation in the estimated air-fuel ratio among the cylinders is large depending on whether the standard deviation of the estimated air-fuel ratio of all the cylinders is equal to or greater than a predetermined value.

  If it is determined in step 202 that the degree of variation in the estimated air-fuel ratio between the cylinders is large, the process proceeds to step 203, where it is determined that the air-fuel ratio detection timing has deviated, and this routine is terminated. If the degree of variation in the estimated air-fuel ratio between the cylinders is small (determined as “No” in step 202), it is determined that the air-fuel ratio detection timing is correct, and this routine is terminated.

[Air-fuel ratio detection timing deviation learning correction routine]
First, a learning correction method for deviation in the air-fuel ratio detection timing will be described with reference to FIGS. 8 and 9 are diagrams for explaining the effect of fuel injection amount correction (fuel correction) when the air-fuel ratio detection timing is different from the correct timing. When the air-fuel ratio detection timing is correct, the air-fuel ratio of each cylinder can be accurately estimated. Therefore, if the fuel injection amount of a predetermined cylinder is corrected by a predetermined amount, the air-fuel ratio of that cylinder should change by an amount corresponding to the fuel correction amount. It is. Focusing on this characteristic, in the first embodiment, the air-fuel ratio detection timing of each cylinder is changed by executing the air-fuel ratio detection timing deviation learning correction routine of FIG. 6 and FIG. The air-fuel ratio before and after fuel correction of each cylinder is estimated, and the air-fuel ratio detection timing at which the amount of change in the estimated air-fuel ratio before and after fuel correction is equivalent to the fuel correction amount is learned as the appropriate air-fuel ratio detection timing. .

  The air-fuel ratio detection timing deviation learning correction routine shown in FIGS. 6 and 7 is started after the air-fuel ratio detection timing deviation determination routine shown in FIG. 5 ends, and serves as learning means in the claims. When this routine is started, first, at step 301, it is determined whether or not the air-fuel ratio detection timing is determined to be shifted by the air-fuel ratio detection timing shift determination routine of FIG. If not, the routine is terminated without performing the subsequent processing.

  On the other hand, if it is determined that the air-fuel ratio detection timing is deviated, the process proceeds to step 302, and whether or not the number of delay corrections (the number of times the air-fuel ratio detection timing is corrected to the retard side) is less than the specified number. If the number of delay corrections is less than the specified number, the process proceeds to step 303, and the air-fuel ratio detection timing is corrected to the retard side by a predetermined crank angle. Thereafter, the routine proceeds to step 304, where the air-fuel ratio before and after fuel correction of the cylinder at the air-fuel ratio detection timing after retardation correction is estimated, and the change amount of the estimated air-fuel ratio before and after fuel correction is calculated.

  Thereafter, the process proceeds to step 305, and it is determined whether or not the change amount of the estimated air-fuel ratio substantially matches the fuel correction amount equivalent, so that whether or not the current air-fuel ratio detection timing is an appropriate air-fuel ratio detection timing. Determine whether. As a result, when it is determined that the current air-fuel ratio detection timing is not an appropriate air-fuel ratio detection timing, the process returns to step 302, and the above-described retardation correction of the air-fuel ratio detection timing is repeated. If it is determined that the amount of change in the estimated air-fuel ratio substantially coincides with the fuel correction amount equivalent and the air-fuel ratio detection timing has reached an appropriate air-fuel ratio detection timing before the number of retardation corrections reaches the specified number, Proceeding to 306, the air-fuel ratio detection timing at that time is learned as an appropriate air-fuel ratio detection timing, and the learned value is updated and stored in a learning value storage area of a rewritable nonvolatile memory such as a backup RAM of the ECU 40. At this time, considering that the appropriate air-fuel ratio detection timing changes according to the engine operating state, as shown in FIG. 10, the learning value of the air-fuel ratio detection timing is set to the engine operating state (for example, engine load and engine speed). ) Update and store every time. Thereafter, the process proceeds to step 307, and this routine in which the count value of the number of retardation corrections is reset is terminated.

  On the other hand, if the air-fuel ratio detection timing does not reach an appropriate air-fuel ratio detection timing even if the retardation correction of the air-fuel ratio detection timing is repeated a specified number of times, the process proceeds to step 308 in FIG. It is determined whether or not the number of times (the number of times the air-fuel ratio detection timing has been corrected to the advance side) is less than the specified number of times, and if the number of advance angle corrections is less than the specified number of times, the process proceeds to step 309 and the air-fuel ratio detection timing is set. A predetermined crank angle is corrected from the initial position before the retard correction to the advance side. Thereafter, the process proceeds to step 310, where the air-fuel ratio before and after fuel correction of the cylinder at the air-fuel ratio detection timing after advance angle correction is estimated, and the change amount of the estimated air-fuel ratio before and after fuel correction is calculated.

  Thereafter, the process proceeds to step 311 to determine whether or not the current air-fuel ratio detection timing is an appropriate air-fuel ratio detection timing by determining whether or not the amount of change in the estimated air-fuel ratio substantially matches the fuel correction amount equivalent. Determine whether. As a result, when it is determined that the current air-fuel ratio detection timing is not an appropriate air-fuel ratio detection timing, the process returns to step 308 to repeat the advance correction of the air-fuel ratio detection timing described above. If it is determined that the amount of change in the estimated air-fuel ratio substantially matches the fuel correction amount and the air-fuel ratio detection timing has reached an appropriate air-fuel ratio detection timing before the advance angle correction count reaches the specified number of times, Proceeding to 312, the air-fuel ratio detection timing at that time is learned as an appropriate air-fuel ratio detection timing, and the learned value is updated and stored in a rewritable nonvolatile memory such as a backup RAM of the ECU 40. Thereafter, the process proceeds to step 313, and the routine in which the count value of the advance angle correction count is reset is terminated.

  The learning map of the air-fuel ratio detection timing created by this routine is used as a map for setting the air-fuel ratio detection timing in step 102 of the cylinder-by-cylinder air-fuel ratio control routine of FIG.

  If the advance correction of the air-fuel ratio detection timing is repeated a specified number of times, but the air-fuel ratio detection timing does not reach the proper air-fuel ratio detection timing (that is, the proper air-fuel ratio detection timing cannot be learned) In Step 308, “No” is determined, and this routine is finished.

  In the first embodiment described above, the presence / absence of a deviation in the air-fuel ratio detection timing is determined based on the degree of variation in the estimated air-fuel ratio between the cylinders during the cylinder-by-cylinder air-fuel ratio control. In addition, it is possible to accurately determine the deviation of the air-fuel ratio detection timing.

  Moreover, in the first embodiment, the air-fuel ratio detection timing of each cylinder is changed during the air-fuel ratio control for each cylinder, the air-fuel ratio before and after fuel correction of each cylinder at the air-fuel ratio detection timing is estimated, and before and after fuel correction. Since the air-fuel ratio detection timing at which the change amount of the estimated air-fuel ratio is equivalent to the fuel correction amount is learned as the appropriate air-fuel ratio detection timing, the proper air-fuel ratio detection timing is learned during the cylinder-by-cylinder air-fuel ratio control. The air-fuel ratio detection timing of each cylinder can be corrected to an appropriate air-fuel ratio detection timing based on the learning result, and the air-fuel ratio of each cylinder can be accurately estimated.

Further, in the first embodiment, the air-fuel ratio detection timing is learned for each engine operation state (for example, engine load and engine speed) in consideration of the fact that the appropriate air-fuel ratio detection timing changes according to the engine operation state. Since it did in this way, the precision of the learning value of an air fuel ratio detection timing can be improved.
However, it goes without saying that the present invention may learn the average deviation of the air-fuel ratio detection timing.

  As shown in FIG. 3, when the air-fuel ratio detection timing of each cylinder is correct, the air-fuel ratio of each cylinder can be accurately estimated based on the detection value of the air-fuel ratio sensor 37. As the fuel correction amount increases, the deviation between the estimated air-fuel ratio of each cylinder and the reference air-fuel ratio (estimated air-fuel ratio deviation) decreases, and the variation in estimated air-fuel ratio among the cylinders decreases.

  On the other hand, as shown in FIG. 4, when the air-fuel ratio detection timing of each cylinder is shifted, the accuracy of the estimated air-fuel ratio of each cylinder calculated from the detection value of the air-fuel ratio sensor 37 deteriorates. Even if the fuel correction amount of each cylinder increases after the start of air-fuel ratio control, the estimated air-fuel ratio deviation of each cylinder does not decrease, and the variation in estimated air-fuel ratio among the cylinders does not decrease.

  Focusing on this characteristic, in the second embodiment of the present invention, by executing the air-fuel ratio detection timing deviation determination routine of FIG. Whether or not there is a deviation in the air-fuel ratio detection timing is determined based on the degree of variation in the estimated air-fuel ratio. This routine is started every predetermined crank angle (for example, every 30 ° C. A) in synchronization with the output pulse of the crank angle sensor 33. When this routine is started, it is first determined in step 401 whether or not the cylinder-by-cylinder air-fuel ratio control is being performed. If the cylinder-by-cylinder air-fuel ratio control is not being performed, this routine is terminated without performing the subsequent processing. To do.

  On the other hand, if the cylinder-by-cylinder air-fuel ratio control is being performed, the routine proceeds to step 402, where it is determined whether or not fuel correction of a predetermined level or more is being performed, for example, one of the following conditions (B1) to (B3): Or it judges by two or more.

(B1) Whether or not fuel correction more than a predetermined value is being performed depending on whether or not the deviation between the maximum fuel correction value and the minimum fuel correction value among the fuel correction values for each cylinder is equal to or greater than a predetermined value Determine.
(B2) It is determined whether or not fuel correction greater than or equal to a predetermined value is being performed based on whether or not the standard deviation of fuel correction amounts for all cylinders is greater than or equal to a predetermined value.
(B3) It is determined whether or not fuel correction greater than or equal to a predetermined value is being performed based on whether or not the elapsed time after the start of fuel correction is greater than or equal to a predetermined time.

  If it is determined in step 402 that the fuel correction of a predetermined value or more has not been performed, the present routine is terminated. If it is determined that the fuel correction of the predetermined value or more is being performed, the process proceeds to step 403. Whether or not the degree of variation in the estimated air-fuel ratio between the cylinders is large is determined based on, for example, one or both of the following conditions (C1) and (C2).

(C1) Whether the variation in estimated air-fuel ratio between cylinders is large depending on whether the deviation between the maximum estimated air-fuel ratio and the minimum estimated air-fuel ratio among the estimated air-fuel ratios of each cylinder is a predetermined value or more Determine whether.
(C2) It is determined whether or not the degree of variation in the estimated air-fuel ratio among the cylinders is large depending on whether the standard deviation of the estimated air-fuel ratio of all the cylinders is equal to or greater than a predetermined value.

  If it is determined in step 403 that the degree of variation in the estimated air-fuel ratio between the cylinders is large, the process proceeds to step 404, where it is determined that the air-fuel ratio detection timing has deviated, and this routine is terminated. If the degree of variation in the estimated air-fuel ratio between the cylinders is small (if “No” is determined in step 403), it is determined that the air-fuel ratio detection timing is correct, and this routine is terminated.

  Also in the second embodiment described above, it is possible to accurately determine the deviation of the air-fuel ratio detection timing during the cylinder-by-cylinder air-fuel ratio control.

  If the accuracy of the estimated air-fuel ratio of each cylinder is good, in the operating state where the increase / decrease direction of the fuel correction amount of each cylinder and the increase / decrease direction of the estimated air-fuel ratio are the same behavior, It is considered that the accuracy of the estimated air-fuel ratio is poor.

  Focusing on this characteristic, in the third embodiment of the present invention, by executing the air-fuel ratio detection timing deviation determination routine of FIG. 12, during the cylinder-by-cylinder air-fuel ratio control, the fuel correction amount increase / decrease direction of each cylinder and the estimated sky The presence or absence of a deviation in the air-fuel ratio detection timing is determined based on the increase / decrease direction of the fuel ratio. This routine is started every predetermined crank angle (for example, every 30 ° C. A) in synchronization with the output pulse of the crank angle sensor 33. When this routine is started, it is first determined in step 501 whether or not the cylinder-by-cylinder air-fuel ratio control is being performed. If the cylinder-by-cylinder air-fuel ratio control is not being performed, this routine is terminated without performing the subsequent processing. To do.

  On the other hand, if the cylinder-by-cylinder air-fuel ratio control is being performed, the routine proceeds to step 502, where it is determined whether or not fuel correction of a predetermined value or more is being performed, for example, either one of the following conditions (D1), (D3) or Judge by both.

(D1) Whether or not fuel correction more than a predetermined value is being performed depending on whether or not the deviation between the maximum fuel correction value and the minimum fuel correction value among the fuel correction values for each cylinder is equal to or greater than a predetermined value Determine.
(D2) It is determined whether or not fuel correction greater than a predetermined value is being performed based on whether or not the fuel correction amount of the specific cylinder is greater than or equal to a predetermined value.

  If it is determined in step 502 that the fuel correction of a predetermined value or more is not performed, the present routine is terminated. If it is determined that the fuel correction of the predetermined value or more is being performed, the process proceeds to step 503. Whether or not the fuel correction amount increase / decrease direction of each cylinder and the estimated air / fuel ratio increase / decrease behavior are opposite, for example, the deviation between the change rate of the fuel correction amount and the estimated air / fuel ratio of each cylinder Judgment is made based on whether or not it is equal to or greater than a predetermined value. As a result, if it is determined that the increase / decrease direction of the fuel correction amount of each cylinder is opposite to the increase / decrease direction of the estimated air / fuel ratio, the routine proceeds to step 504, where it is determined that the air / fuel ratio detection timing has shifted. To end this routine. If the increase / decrease direction of the fuel correction amount of each cylinder and the increase / decrease direction of the estimated air-fuel ratio are the same (when determined “No” in step 503), the air-fuel ratio detection timing is correct. Judgment is made and this routine is terminated.

  Also in the third embodiment described above, it is possible to accurately determine the deviation in the air-fuel ratio detection timing during the cylinder-by-cylinder air-fuel ratio control.

  If the air-fuel ratio detection timing of each cylinder is correct, the air-fuel ratio of each cylinder can be accurately estimated based on the detection value of the air-fuel ratio sensor 37. Therefore, as shown in FIG. The degree of variation in estimated air-fuel ratio between them (estimated air-fuel ratio deviation of each cylinder) is minimized, and the degree of variation in fuel correction amount between cylinders is also minimized.

  Focusing on this characteristic, the fourth embodiment of the present invention changes the air-fuel ratio detection timing of each cylinder during the air-fuel ratio control for each cylinder by executing the air-fuel ratio detection timing deviation learning correction routine shown in FIG. Thus, the air-fuel ratio of each cylinder is estimated, and the air-fuel ratio detection timing at which the degree of variation in estimated air-fuel ratio between cylinders and the degree of variation in fuel correction amount are minimized is learned as an appropriate air-fuel ratio detection timing.

  This routine is started after the presence or absence of a deviation in the air-fuel ratio detection timing is determined by the air-fuel ratio detection timing deviation determination routine described in any of the first to third embodiments, and serves as a learning means in the claims. Fulfill. When this routine is started, first, at step 601, it is determined whether or not the air-fuel ratio detection timing is determined to be shifted by the air-fuel ratio detection timing shift determination routine, and it is determined that the air-fuel ratio detection timing is shifted. If not, this routine is terminated without performing the subsequent processing.

  On the other hand, if it is determined that the air-fuel ratio detection timing is deviated, the process proceeds to step 602, where the air-fuel ratio detection timing is set to the most advanced angle position (correctable advance side limit position). Thereafter, the process proceeds to step 603, where the degree of variation in the estimated air-fuel ratio between the cylinders is calculated by either (E1) or (E2) below.

(E1) The deviation between the maximum estimated air-fuel ratio and the minimum estimated air-fuel ratio among the estimated air-fuel ratios of each cylinder is calculated, and this is used as the degree of variation in estimated air-fuel ratio between cylinders.
(E2) The standard deviation of the estimated air-fuel ratio of all cylinders is calculated, and this is used as the degree of variation in the estimated air-fuel ratio between the cylinders.

Thereafter, the process proceeds to step 604, and the degree of variation in the fuel correction amount between the cylinders is calculated by either (F1) or (F2) below.
(F1) A deviation between the maximum fuel correction amount and the minimum fuel correction amount among the fuel correction amounts of the respective cylinders is calculated, and this is set as a variation degree of the fuel correction amount between the cylinders.
(F2) The standard deviation of the fuel correction amount of all cylinders is calculated, and this is used as the degree of variation in the fuel correction amount between the cylinders.

  Thereafter, the process proceeds to step 604, the air-fuel ratio detection timing is corrected to the retard side by a predetermined crank angle, and then the process proceeds to step 605, where the air-fuel ratio detection timing after the delay angle correction is the most retarded position (correctable retard angle). It is determined whether or not the limit position on the side has been exceeded. If not, the process returns to step 603 to repeat the above-described processing. Thus, the process of calculating the degree of variation in the estimated air-fuel ratio between the cylinders and the degree of variation in the fuel correction amount by advancing the air-fuel ratio detection timing little by little from the most advanced position to the most retarded position is repeated.

  After that, when the air-fuel ratio detection timing corrected in step 605 exceeds the most retarded position, the determination result in step 606 becomes “Yes”, and the process proceeds to step 607, where the estimated empty space between the cylinders calculated so far is obtained. From the degree of variation in the fuel ratio and the degree of variation in the fuel correction amount, the optimum point of the air-fuel ratio detection timing at which they are minimized is searched, and in the next step 608, the optimum point of the air-fuel ratio detection timing is determined. Are updated and stored in the learning value storage area of the rewritable nonvolatile memory. At this time, considering that the appropriate air-fuel ratio detection timing changes according to the engine operating state, the learning value of the optimum point of the air-fuel ratio detection timing is updated for each engine operating state (for example, engine load and engine speed). Remember to remember.

In the fourth embodiment described above, the optimum point of the air-fuel ratio detection timing can be learned with high accuracy during the cylinder-by-cylinder air-fuel ratio control.
In the fourth embodiment, the air-fuel ratio detection timing is changed from the most advanced position to the most retarded position, but the degree of variation in estimated air-fuel ratio between cylinders and the degree of variation in fuel correction amount are below a predetermined value. At this stage, the process of calculating the degree of variation may be terminated, and the position where the degree of variation becomes a predetermined value or less may be learned as an appropriate air-fuel ratio detection timing.

  As shown in FIG. 15, the timing at which the output of the air-fuel ratio sensor 37 first changes to a level corresponding to the air-fuel ratio after resuming injection is determined only by the first injection cylinder at the time of fuel cut return, Not affected by the cylinder.

  Focusing on this characteristic, in the fifth embodiment of the present invention, by executing the air-fuel ratio detection timing deviation learning correction routine shown in FIG. An appropriate air-fuel ratio detection timing in the first injection cylinder at the time of fuel cut return (hereinafter referred to as “fuel cut return cylinder”) is learned based on the timing at which the air-fuel ratio changes to a predetermined level.

  This routine 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, and serves as a learning means in the claims. When this routine is started, first, in step 701, it is determined whether or not the fuel cut return (fuel cut end) is within a predetermined period. If it is not within the predetermined period, the subsequent learning process is not performed. This routine ends. This predetermined period is set to a period slightly longer than the period until the output of the air-fuel ratio sensor 37 first changes to a predetermined level corresponding to the air-fuel ratio after restarting the injection when the fuel cut is restored. Note that even when the amount of change in engine operating conditions (engine speed, load, etc.) exceeds a predetermined value within this predetermined period, this routine may be terminated without performing the subsequent learning process. . This is because the learning accuracy decreases when the engine operating condition changes greatly.

  On the other hand, if it is within a predetermined period from the fuel cut return, the process proceeds to step 702, the fuel cut return cylinder is stored in a memory such as the RAM of the ECU 40, and then the process proceeds to step 703, where the output of the air-fuel ratio sensor 37 is It waits until it changes to the predetermined level corresponding to an air fuel ratio. This predetermined level may be variably set by a map or the like according to engine operating conditions (engine speed, load, fuel correction amount, etc.).

  Thereafter, when the output of the air-fuel ratio sensor 37 changes to a predetermined level corresponding to the air-fuel ratio after resuming injection, the routine proceeds to step 704, where the output of the air-fuel ratio sensor 37 reaches a predetermined level corresponding to the air-fuel ratio after resuming injection. Calculate the appropriate air-fuel ratio detection timing for the fuel cut return cylinder based on the amount of deviation between the crank angle when changed (crank counter value) and the crank angle when the fuel cut return cylinder resumes injection (crank counter value) To do. At this time, engine operating conditions (engine speed, load, etc.) may be taken into consideration.

  Thereafter, the process proceeds to step 705, and the air-fuel ratio detection timing is updated and stored in a learning value storage area of a rewritable nonvolatile memory such as a backup RAM of the ECU 40. At this time, considering that the appropriate air-fuel ratio detection timing changes according to the engine operating state, the learning value of the air-fuel ratio detection timing is updated and stored for each engine operating state (for example, engine load and engine speed). It is good to make it.

Also in the fifth embodiment described above, the optimum point of the air-fuel ratio detection timing can be learned with high accuracy during the cylinder-by-cylinder air-fuel ratio control.
Needless to say, the deviation in the air-fuel ratio detection timing detected in the specific cylinder may be learned as the average deviation in the air-fuel ratio detection timing of the other cylinders.

Next, Embodiment 6 of the present invention will be described with reference to FIGS.
In the sixth embodiment, as data for evaluating the deviation of the air-fuel ratio detection timing, the relationship between the change amount of the estimated air-fuel ratio of at least one cylinder and the change amount of the fuel correction amount (air-fuel ratio correction amount) of that cylinder is expressed. A correlation value as an index is used.

  This correlation value is represented by the product of the change amount of the estimated air-fuel ratio of one cylinder and the change amount of the fuel correction amount of that cylinder, or the sum of this product for a plurality of cylinders. In the sixth embodiment, the product of the change amount of the estimated air-fuel ratio of each cylinder and the change amount of the fuel correction amount is integrated by the number of all cylinders to obtain the correlation value.

  Further, in the sixth embodiment, the correlation value is calculated at a plurality of timings per 720 ° C., for example, six timings (base timing, base timing + 180 ° C., base timing −180 ° C. A, base timing + 360 ° C. A, Base timing + 90 ° C., base timing −90 ° C.), among the correlation values calculated at each timing, it is determined that the timing with the largest correlation value is the air-fuel ratio detection timing with the least deviation. ing.

  As described in the third embodiment, if the increase / decrease direction of the fuel correction amount of each cylinder and the increase / decrease direction of the estimated air-fuel ratio are opposite, it is considered that the accuracy of the estimated air-fuel ratio of each cylinder is poor. If the increase / decrease direction of the fuel correction amount of each cylinder and the increase / decrease direction of the estimated air-fuel ratio are opposite, the sign of the change amount of the estimated air-fuel ratio of each cylinder (±) and the sign of the change amount of the fuel correction amount (± ) Is opposite, the product of both becomes a negative value, and the correlation value which is the sum of the number of cylinders of this product becomes smaller. Therefore, the smaller the correlation value, the larger the deviation of the air-fuel ratio detection timing, and the larger the correlation value, the smaller the deviation of the air-fuel ratio detection timing. From this relationship, in the sixth embodiment, the correlation value is calculated at a plurality of timings per 720 ° C., and the timing with the largest correlation value is determined as the air-fuel ratio detection timing with the least deviation, and the air-fuel ratio detection is performed. The timing is corrected by learning.

  The deviation determination / learning correction of the air-fuel ratio detection timing of the sixth embodiment described above is executed by the ECU 40 according to FIGS. 17 to 22. The processing contents of these routines will be described below.

  The air-fuel ratio detection timing deviation determination routine of FIG. 17 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. When this routine is started, it is first determined in step 801 whether or not the cylinder-by-cylinder air-fuel ratio control is being performed. If the cylinder-by-cylinder air-fuel ratio control is not being performed, this routine is terminated without performing the subsequent processing. To do.

  On the other hand, if the cylinder-by-cylinder air-fuel ratio control is in progress, the routine proceeds to step 802, where whether or not fuel correction of a predetermined value or more is being performed is the same as in step 502 of FIG. Judge by method. If it is determined in step 802 that the fuel correction of a predetermined value or more is not performed, the present routine is terminated. If it is determined that the fuel correction of the predetermined value or more is being performed, the process proceeds to step 803. The correlation value calculation routine of FIG. 18 is executed.

  When the correlation value calculation routine of FIG. 18 is started, it is first determined in step 811 whether or not it is a correlation value calculation timing (for example, every 720 ° C. A). This routine is terminated without performing it.

On the other hand, if it is the correlation value calculation timing, the routine proceeds to step 812, where differences ΔFAF (1) to ΔFAF (N), which are changes in the fuel correction coefficient (fuel correction amount) of each cylinder, are calculated.
ΔFAF (k) = ΔFAF (k) [i] −ΔFAF (k) [i−1]
Here, ΔFAF (k) is ΔFAF of the k-th cylinder (k = 1 to N), ΔFAF (k) [i] is current ΔFAF (k), and ΔFAF (k) [i-1] is the previous time ΔFAF (k).

  Thereafter, the routine proceeds to step 813, where the estimated air-fuel ratio difference calculation routine of FIG. 19 is executed to calculate the difference ΔPHI which is the change amount of the estimated air-fuel ratio of each cylinder at the following timings (T1) to (T6). .

(T1) Estimated air-fuel ratio difference ΔPHIbase of each cylinder at base timing
ΔPHIbase (k) = PHIbase (k) [i] −PHIbase (k) [i−1] (k = 1 to N)
PHIbase (k) is an estimated air-fuel ratio of the k-th cylinder estimated at the base timing. The base timing is a reference air-fuel ratio detection timing, and is learned and corrected by an air-fuel ratio detection timing deviation learning correction routine shown in FIG.

(T2) Estimated air-fuel ratio difference ΔPHIp180 of each cylinder at base timing + 180 ° C.
ΔPHIp180 (k) = PHIp180 (k) [i] −PHIp180 (k) [i−1] (k = 1 to N)
PHIp180 (k) is the estimated air-fuel ratio of the k-th cylinder estimated at the timing of base timing + 180 ° C.

(T3) Base timing-difference ΔPHIm180 of estimated air-fuel ratio of each cylinder at 180 ° C A
ΔPHIm180 (k) = PHIm180 (k) [i] −PHIm180 (k) [i−1] (k = 1 to N)
PHIm180 (k) is an estimated air-fuel ratio of the k-th cylinder estimated at a timing of base timing −180 ° C.

(T4) Difference in estimated air-fuel ratio of each cylinder at base timing + 360 ° C. ΔPHIp360
ΔPHIp360 (k) = PHIp360 (k) [i] −PHIp360 (k) [i−1] (k = 1 to N)
PHIp360 (k) is an estimated air-fuel ratio of the k-th cylinder estimated at a timing of base timing + 360 ° C.

(T5) Estimated air-fuel ratio difference ΔPHIp90 of each cylinder at base timing + 90 ° C.
ΔPHIp90 (k) = PHIp90 (k) [i] −PHIp90 (k) [i−1] (k = 1 to N)
PHIp90 (k) is an estimated air-fuel ratio of the k-th cylinder estimated at the timing of base timing + 90 ° C.

(T6) Base timing -difference ΔPHIm90 in estimated air-fuel ratio of each cylinder at 90 ° C. A
ΔPHIm90 (k) = PHIm90 (k) [i] −PHIm90 (k) [i−1] (k = 1 to N)
PHIm90 (k) is an estimated air-fuel ratio of the k-th cylinder estimated at a base timing of −90 ° C.

Here, the estimated air-fuel ratios PHIbase (k) to PHIm90 (k) of the k-th cylinder at the respective timings (T1) to (T6) are calculated by the equivalence ratio φ.
Equivalent ratio φ = theoretical air / fuel ratio / estimated air / fuel ratio = 1 / excess air ratio

  After calculating the difference ΔPHI of the estimated air-fuel ratio of each cylinder at each timing (T1) to (T6), the process proceeds to step 814 in FIG. 18, and the instantaneous correlation value calculation routine in FIG. 20 is executed to execute each timing (T1). The instantaneous correlation value dCOR in (T6) is calculated.

(T1) Instantaneous correlation value dCORbase at base timing
dCORbase = Σ {ΔFAF (k) × ΔPHIbase (k)} (k = 1 to N)
Here, Σ means integration from the first cylinder to the Nth cylinder (hereinafter the same).
(T2) Instantaneous correlation value dCORp180 at base timing + 180 ° C A
dCORp180 = Σ {ΔFAF (k) × ΔPHIp180 (k)} (k = 1 to N)
(T3) Base timing-instantaneous correlation value dCORm180 at 180 ° C A
dCORm180 = Σ {ΔFAF (k) × ΔPHIm180 (k)} (k = 1 to N)
(T4) Base timing + instantaneous correlation value dCORp360 at 360 ° C A
dCORp360 = Σ {ΔFAF (k) × ΔPHIp360 (k)} (k = 1 to N)
(T5) Instantaneous correlation value dCORp90 at base timing + 90 ° C A
dCORp90 = Σ {ΔFAF (k) × ΔPHIp90 (k)} (k = 1 to N)
(T6) Base timing-instantaneous correlation value dCORm90 at 90 ° C A
dCORm90 = Σ {ΔFAF (k) × ΔPHIm90 (k)} (k = 1 to N)

  After calculating the instantaneous correlation value dCOR at each timing (T1) to (T6), the process proceeds to step 815 in FIG. 18, and the integrated correlation value calculation routine in FIG. 21 is executed, and at each timing (T1) to (T6). The integrated correlation value sumCOR is calculated.

(T1) Integrated correlation value sumCORbase (i) at base timing
sumCORbase (i) = sumCORbase (i-1) + dCORbase
(SumCORbase (i-1): previous sumCORbase)
(T2) Base timing + accumulated correlation value sumCORp180 (i) at 180 ° C A
sumCORp180 (i) = sumCORp180 (i-1) + dCORp180
(SumCORp180 (i-1): previous sumCORp180)
(T3) Base timing—integrated correlation value sumCORm180 (i) at 180 ° C. A
sumCORm180 (i) = sumCORm180 (i-1) + dCORm180
(SumCORm180 (i-1): previous sumCORm180)
(T4) Integrated correlation value sumCORp360 (i) at base timing + 360 ° C A
sumCORp360 (i) = sumCORp360 (i-1) + dCORp360
(SumCORp360 (i-1): previous sumCORp360)
(T5) Integrated correlation value sumCORp90 (i) at base timing + 90 ° C A
sumCORp90 (i) = sumCORp90 (i-1) + dCORp90
(SumCORp90 (i-1): previous sumCORp90)
(T6) Base timing-integrated correlation value sumCORm90 (i) at 90 ° C A
sumCORm90 (i) = sumCORm90 (i-1) + dCORm90
(SumCORm90 (i-1): previous sumCORm90)

  After calculating the integrated correlation value sumCOR at each timing (T1) to (T6), the process proceeds to step 816 in FIG. 18 to increment the integration period calculation counter C that counts the number of integrations of the instantaneous correlation value dCOR. In 817, it is determined whether or not the value of the integration period calculation counter C (the number of integrations of the instantaneous correlation value dCOR) has reached a set value CMAX (for example, 25). End the routine.

  Thereafter, when the value of the integration period calculation counter C (the number of integrations of the instantaneous correlation value dCOR) reaches the set value CMAX, the process proceeds to step 818 to execute the air-fuel ratio detection timing deviation learning correction routine of FIG. The deviation in the air-fuel ratio detection timing is corrected by learning as follows. First, in step 831, the integrated correlation values sumCORbase (i), sumCORp180 (i), sumCORm180 (i), sumCORp360 (i), sumCORp90 (i), sumCORm90 (i) at six timings (T1) to (T6) are calculated. Select the maximum integrated correlation value from the list.

Thereafter, the process proceeds to step 832, and the correction amount Lcrnk of the air-fuel ratio detection timing is selected as follows according to the timing at which the integrated correlation value becomes maximum.
(T1) When base correlation integrated correlation value sumCORbase (i) is maximum
Air-fuel ratio detection timing correction amount Lcrnk = 0
(T2) When base correlation + accumulated correlation value sumCORp180 (i) at 180 ° C A is maximum
Air-fuel ratio detection timing correction amount Lcrnk = + 180 ° C. A
(T3) Base timing-When integrated correlation value sumCORm180 (i) at 180 ° C is maximum
Air-fuel ratio detection timing correction amount Lcrnk = −180 ° C.
(T4) When the integrated correlation value sumCORp360 (i) at base timing + 360 ° C is maximum
Air-fuel ratio detection timing correction amount Lcrnk = + 360 ° C.
(T5) When the integrated correlation value sumCORp90 (i) at base timing + 90 ° C is maximum
Air-fuel ratio detection timing correction amount Lcrnk = + 30 ° C.
(T6) Base timing-When the integrated correlation value sumCORm90 (i) at 90 ° C is maximum
Air-fuel ratio detection timing correction amount Lcrnk = −30 ° C. A

  Here, when the integrated correlation value sumCORbase (i) of the base timing is maximum, it means that the deviation of the air-fuel ratio detection timing is minimized at the base timing. Therefore, in this case, the correction amount Lcrnk of the air-fuel ratio detection timing is set to zero.

  On the other hand, when the integrated correlation value of the base timings ± 180 ° C.A and + 360 ° C. A is maximum, it means that the air-fuel ratio detection timing is shifted by 180 ° C. or more. Such a large shift causes the wrong cylinder air-fuel ratio to be estimated and corrected. Therefore, it is necessary to urgently correct the shift in the air-fuel ratio detection timing. Therefore, in this case, the correction amount Lcrnk of the air-fuel ratio detection timing is set to ± 180 ° C. and + 360 ° C., and large deviations in the air-fuel ratio detection timing are corrected all at once.

  Further, when the integrated correlation value at the base timing ± 90 ° C. A is maximum, it means that the current air-fuel ratio detection timing is close to an appropriate timing. Therefore, in this case, importance is attached to the correction accuracy of the air-fuel ratio detection timing, and the deviation of the air-fuel ratio detection timing is corrected in increments of ± 30 ° C. A.

  In the next step 833, the correction amount Lcrnk of the air-fuel ratio detection timing stored in a rewritable nonvolatile memory such as a backup RAM is updated with the value selected in step 832. Thereafter, the process proceeds to step 819 in FIG. 18 to reset the integration period calculation counter C, and then proceeds to step 820 to reset the integration correlation values at the respective timings (T1) to (T6), and this routine is ended. .

  An example of the learning correction of the air-fuel ratio detection timing of the sixth embodiment described above is shown in FIG. The example of FIG. 23 shows a control example when the cylinder-by-cylinder air-fuel ratio control is started in a state where the air-fuel ratio of the # 1 cylinder is shifted. In the example of FIG. 23, the integrated correlation value at the timings (T1) to (T6) after the start of the cylinder-by-cylinder air-fuel ratio control has the maximum integrated correlation value sumCORp90 at the base timing + 90 ° C. Therefore, Deviation is corrected in small increments by + 30 ° C. Thereby, the air-fuel ratio detection timing is accurately corrected to the optimal timing.

In the sixth embodiment described above, the process of obtaining the instantaneous correlation value by integrating the product of the difference in fuel correction coefficient of each cylinder and the difference in estimated air-fuel ratio by the number of all cylinders at a plurality of timings per 720 ° C. After calculating the accumulated correlation value at a plurality of timings by integrating the instantaneous correlation value at each timing for a predetermined period, the timing with the largest accumulated correlation value is determined as the air-fuel ratio detection timing with the least deviation. Thus, the deviation in the air-fuel ratio detection timing is learned and corrected, so that the deviation in the air-fuel ratio detection timing can be learned and corrected with high accuracy.
In addition, in the sixth embodiment, since the instantaneous correlation values are integrated for a predetermined period, there is an advantage that the influence of instantaneous noise can be reduced.

In the sixth embodiment, the product of the difference between the fuel correction coefficients of each cylinder and the difference between the estimated air-fuel ratios is integrated by the number of all the cylinders to obtain the correlation value. However, only for one specific cylinder, Alternatively, correlation values may be obtained for a plurality of cylinders smaller than the total number of cylinders.
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. 3 is a flowchart showing a flow of processing of a cylinder-by-cylinder air-fuel ratio control routine according to the first embodiment. It is a time chart which shows the example of control when the air-fuel ratio detection timing of each cylinder is correct. It is a time chart which shows the example of control when the air-fuel ratio detection timing of each cylinder has shifted. 6 is a flowchart showing a flow of processing of an air-fuel ratio detection timing deviation determination routine according to the first embodiment. 6 is a flowchart showing a flow of processing of an air-fuel ratio detection timing deviation learning correction routine according to the first embodiment (No. 1). 6 is a flowchart showing a flow of processing of an air-fuel ratio detection timing deviation learning correction routine of the first embodiment (No. 2). 3 is a time chart illustrating a method for detecting a deviation in air-fuel ratio detection timing according to the first embodiment. 3 is a time chart for explaining a learning correction method for an air-fuel ratio detection timing shift according to the first embodiment. The figure which shows notionally the learning map of the air fuel ratio detection timing of Example 1. FIG. 6 is a flowchart showing a flow of processing of an air-fuel ratio detection timing deviation determination routine of Embodiment 2. 12 is a flowchart illustrating a flow of processing of an air-fuel ratio detection timing deviation determination routine according to a third embodiment. 12 is a time chart for explaining a learning correction method for an air-fuel ratio detection timing shift according to a fourth embodiment. 12 is a flowchart showing a flow of processing of an air-fuel ratio detection timing deviation learning correction routine of Example 4. 10 is a time chart for explaining a learning correction method for an air-fuel ratio detection timing shift according to the fifth embodiment. FIG. 10 is a flowchart illustrating a process flow of an air-fuel ratio detection timing deviation learning correction routine according to a fifth embodiment. It is a flowchart which shows the flow of a process of the air-fuel ratio detection timing deviation determination routine of Example 6. It is a flowchart which shows the flow of a process of the correlation value calculation routine of Example 6. It is a flowchart which shows the processing content of the estimated air-fuel ratio difference calculation routine of Example 6. 18 is a flowchart showing the processing contents of an instantaneous correlation value calculation routine of Example 6. 18 is a flowchart illustrating processing contents of an integrated correlation value calculation routine according to the sixth embodiment. FIG. 16 is a flowchart illustrating a process flow of an air-fuel ratio detection timing deviation learning correction routine according to a sixth embodiment. 18 is a time chart illustrating an example of air-fuel ratio detection timing deviation learning correction according to the sixth 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 collecting part 37 ... Air-fuel ratio sensor 38 ... Catalyst 40 ... ECU (Cylinder-specific air-fuel ratio estimation means, Cylinder-specific air-fuel ratio control means, learning means)

Claims (4)

An air-fuel ratio sensor for detecting an air-fuel ratio of the exhaust gas is installed in an exhaust gas collecting portion where the exhaust gas of each cylinder of the internal combustion engine flows and flows, and the air-fuel ratio sensor detected at each air-fuel ratio detection timing of each cylinder A cylinder-by-cylinder air-fuel ratio estimating means for estimating the air-fuel ratio of each cylinder based on the detected value of each cylinder, and calculating a fuel correction amount for each cylinder based on the deviation between the estimated air-fuel ratio of each cylinder and the reference air-fuel ratio The cylinder-by-cylinder air-fuel ratio is provided with cylinder-by-cylinder air-fuel ratio control means for controlling the air-fuel ratio of each cylinder by correcting the fuel injection amount with the fuel correction amount (hereinafter referred to as “cylinder-by-cylinder air-fuel ratio control”). In the control device,
During said cylinder air-fuel ratio control by changing the air-fuel ratio detecting timing estimates the air-fuel ratio of each cylinder, the air-fuel ratio variation amount of change estimated air-fuel ratio before and after the fuel correction corresponding to the fuel correction amount A cylinder-by-cylinder air-fuel ratio control apparatus for an internal combustion engine, comprising: learning means for learning the air-fuel ratio detection timing to become an air-fuel ratio detection timing appropriate for detecting the air-fuel ratio of each cylinder . The learning means estimates the air-fuel ratio of each cylinder by changing the air-fuel ratio detection timing of each cylinder during the cylinder-by-cylinder air-fuel ratio control, and determines the degree of variation in the estimated air-fuel ratio between the cylinders and the degree of variation in the fuel correction amount. 2. The cylinder-by-cylinder air-fuel ratio control apparatus for an internal combustion engine according to claim 1, wherein an air-fuel ratio detection timing at which the air-fuel ratio becomes a minimum or a predetermined value or less is learned as the appropriate air-fuel ratio detection timing. It said learning means, cylinder air-fuel ratio control apparatus for an internal combustion engine according to claim 1 or 2, characterized in that to learn the proper air-fuel ratio detection timing for each operating state of the internal combustion engine. The cylinder-by-cylinder air-fuel ratio estimation means models the detection values of the air-fuel ratio sensor as the estimated air-fuel ratio history of each cylinder and the history of detection values of the air-fuel ratio sensor multiplied by a predetermined weight, respectively. However, the cylinder air-fuel ratio control apparatus for an internal combustion engine according to any of claims 1 to 3, characterized in that for estimating the air-fuel ratio of each cylinder by using the model.

Images