JP2016041922A - Internal combustion engine cylinder-specific air-fuel ratio control unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to avoid continuation of cylinder-specific air-fuel-ratio control in a state in which an air fuel ratio of each cylinder of an engine cannot be correctly controlled.SOLUTION: Cylinder-specific air-fuel-ratio estimation for estimating an air fuel ratio of each cylinder is implemented on the basis of a detection value of an air-fuel ratio sensor 36 installed in an exhaust gas collection portion 34a of an engine 11, and cylinder-specific air-fuel-ratio control for controlling the air-fuel ratio of each cylinder is implemented so as to reduce a variation in the air fuel ratio among the cylinders on the basis of the estimated air-fuel ratio of each cylinder. Furthermore, it is determined whether or not an accidental fire occurs to the engine 11, and the cylinder-specific air-fuel-ratio estimation and the cylinder-specific air-fuel-ratio control are stopped and a cylinder-specific correction value under the cylinder-specific air-fuel-ratio control is reset when it is determined that an accidental fire occurs to the engine 11. As a result, it is possible to prevent the cylinder-specific air-fuel-ratio control from being continued as usual in a state in which the air-fuel ratio of each cylinder cannot be correctly controlled due to the influence of the accidental fire.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a cylinder-by-cylinder air-fuel ratio control apparatus for an internal combustion engine that estimates the air-fuel ratio of each cylinder of the internal combustion engine and controls the air-fuel ratio of each cylinder based on the estimated air-fuel ratio.

  As a technique for reducing variation in air-fuel ratio between cylinders of an internal combustion engine, for example, as described in Patent Document 1 (Japanese Patent Laid-Open No. 2013-253593), an air-fuel ratio sensor installed in an exhaust collection portion of an internal combustion engine is used. Some cylinders perform air-fuel ratio control for each cylinder in which the air-fuel ratio of each cylinder is estimated based on a detected value and the air-fuel ratio of each cylinder is controlled based on the estimated air-fuel ratio of each cylinder. Further, in Patent Document 1, it is determined whether or not there is a deviation in the air-fuel ratio detection timing based on the estimated air-fuel ratio during the cylinder-by-cylinder air-fuel ratio control, and when it is determined that there is a deviation in the air-fuel ratio detection timing, The air-fuel ratio detection timing correction for correcting the above is performed.

JP 2013-253593 A

  By the way, if misfire of the internal combustion engine (for example, continuous misfire in a specific cylinder) occurs during cylinder-by-cylinder air-fuel ratio control, the estimation accuracy of the air-fuel ratio of each cylinder may deteriorate due to the influence. In such a case, the estimated air-fuel ratio of each cylinder diverges, and the air-fuel ratio of each cylinder cannot be correctly controlled (control so as to reduce the variation in air-fuel ratio between cylinders). There is a possibility of inviting.

  Further, if the internal combustion engine accelerates rapidly and then decelerates rapidly, the exhaust flow velocity may greatly decrease, and the exhaust flow may stagnate. If the flow of exhaust gas near the air-fuel ratio sensor stagnate during cylinder-by-cylinder air-fuel ratio control, the air-fuel ratio sensor output amplitude will be reduced due to this, and the air-fuel ratio sensor output at each air-fuel ratio detection timing of each cylinder will be set correctly. It may be difficult to read. In such a case, an erroneous estimation cylinder (correspondence between each cylinder and the estimated air-fuel ratio) occurs, and the air-fuel ratio of each cylinder cannot be controlled correctly, which may lead to deterioration of exhaust emissions. is there. If the air-fuel ratio detection timing correction is performed in such a state, the estimation accuracy of the air-fuel ratio of each cylinder may be further deteriorated.

  Therefore, the problem to be solved by the present invention is that of an internal combustion engine that can suppress the deterioration of exhaust emission by avoiding that the cylinder-by-cylinder air-fuel ratio control is continued in a state where the air-fuel ratio of each cylinder cannot be controlled correctly. An object is to provide a cylinder-by-cylinder air-fuel ratio control device.

  In order to solve the above-mentioned problem, the invention according to claim 1 is directed to an air-fuel ratio for detecting the air-fuel ratio of the exhaust gas in the exhaust collecting portion (34a) through which the exhaust gas of each cylinder of the internal combustion engine (11) flows. For each cylinder, a sensor (36) is installed and the cylinder-by-cylinder air-fuel ratio estimation is performed to estimate the air-fuel ratio of each cylinder based on the detected value of the air-fuel ratio sensor (36) detected at each air-fuel ratio detection timing of each cylinder. An internal combustion engine comprising air-fuel ratio estimation means (39) and cylinder-by-cylinder air-fuel ratio control means (39) for performing 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 In the cylinder-by-cylinder air-fuel ratio control apparatus, when the misfire determination means (39) for determining whether or not the internal combustion engine (11) has misfired and the misfire determination means (39) determine that the internal combustion engine (11) has misfired, Cylinder air-fuel ratio estimation and cylinder air-fuel ratio control Chino is obtained by a structure in which a stop means (39) to stop at least one.

  By stopping the estimation of the air-fuel ratio for each cylinder (the calculation of the estimated air-fuel ratio of each cylinder is stopped), the update of the correction value for each cylinder by the cylinder-by-cylinder air-fuel ratio control can be stopped. Even if only the estimation is stopped, the air-fuel ratio control for each cylinder can be almost the same as when the correction value for each cylinder is stopped.

  Therefore, if it is determined that the internal combustion engine has misfired, if the cylinder-by-cylinder air-fuel ratio estimation and the cylinder-by-cylinder air-fuel ratio control are stopped, the cylinder-by-cylinder air-fuel ratio control is normally performed in a state where the air-fuel ratio of each cylinder cannot be controlled correctly due to misfire. It is possible to prevent the exhaust emission from deteriorating by avoiding being continued on the street.

  According to a third aspect of the present invention, an air-fuel ratio sensor (36) for detecting an air-fuel ratio of the exhaust gas is installed in an exhaust collecting portion (34a) through which exhaust gases of the cylinders of the internal combustion engine (11) flow. Then, the cylinder-by-cylinder air-fuel ratio estimating means (39) for executing the cylinder-by-cylinder air-fuel ratio estimation for estimating the air-fuel ratio of each cylinder based on the detection value of the air-fuel ratio sensor (36) detected at each air-fuel ratio detection timing of each cylinder. ), Cylinder-by-cylinder air-fuel ratio control means (39) for controlling the air-fuel ratio of each cylinder based on the estimated air-fuel ratio of each cylinder, and estimation of each cylinder during cylinder-by-cylinder air-fuel ratio control In a cylinder-by-cylinder air-fuel ratio control apparatus for an internal combustion engine, comprising a detection timing correction means (39) for executing air-fuel ratio detection timing correction for correcting the air-fuel ratio detection timing based on the air-fuel ratio, the exhaust gas of the internal combustion engine (11) Flow is stagnant ( (Referred to as “exhaust flow stagnation state”), and when the exhaust flow stagnation state is determined by the exhaust flow determination means (39), the cylinder-by-cylinder air-fuel ratio estimation and cylinder A stop means (39) for stopping at least one of the separate air-fuel ratio control and the air-fuel ratio detection timing correction is provided.

  If the cylinder-by-cylinder air-fuel ratio estimation and the cylinder-by-cylinder air-fuel ratio control are stopped when it is determined that the exhaust flow stagnation state, the cylinder-by-cylinder air-fuel ratio control is performed in a state where the air-fuel ratio of each cylinder cannot be controlled correctly due to the stagnation of the exhaust flow. Deterioration of exhaust emission can be suppressed by avoiding continuing as usual. Even if the air-fuel ratio detection timing correction is stopped, it is possible to suppress the deterioration of the estimation accuracy of the air-fuel ratio of each cylinder and to suppress the deterioration of the control accuracy of the cylinder-by-cylinder air-fuel ratio control.

FIG. 1 is a diagram showing a schematic configuration of an engine control system in Embodiment 1 of the present invention. FIG. 2 is a block diagram illustrating the air-fuel ratio control function. FIG. 3 is a diagram showing the behavior of the estimated air-fuel ratio of each cylinder, the correction value for each cylinder, and the actual air-fuel ratio. FIG. 4 is a flowchart showing the flow of the misfire determination routine. FIG. 5 is a flowchart illustrating a flow of processing of the execution condition determination routine according to the first embodiment. FIG. 6 is a flowchart showing the flow of processing of the cylinder-by-cylinder air-fuel ratio control routine. FIG. 7 is a flowchart showing the flow of processing of the air-fuel ratio detection timing determination routine. FIG. 8 is a flowchart showing the flow of processing of the air-fuel ratio detection timing deviation learning correction routine. FIG. 9 is a flowchart showing the flow of processing of the local learning execution routine. FIG. 10 is a flowchart showing the flow of processing of the local learning index calculation routine. FIG. 11 is a flowchart showing the flow of processing of the global learning execution routine. FIG. 12 is a flowchart showing the flow of processing of the global learning index calculation routine. FIG. 13 is a diagram showing an assumed cylinder when it is assumed that the air-fuel ratio detection timing is changed. FIG. 14 is a flowchart showing the flow of the rapid acceleration / deceleration determination routine. FIG. 15 is a flowchart illustrating a flow of processing of an execution condition determination routine according to the second embodiment. FIG. 16 is a time chart showing an execution example (part 1) of the control of the second embodiment. FIG. 17 is a time chart showing an execution example (No. 2) of the control of the second embodiment.

  Hereinafter, some embodiments embodying the mode for carrying out the present invention will be described.

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 in-line four-cylinder engine 11 that is an internal combustion engine, for example, has four cylinders, a first cylinder # 1 to a fourth cylinder # 4, and an air cleaner 13 is provided at the most upstream portion of the intake pipe 12 of the engine 11. An air flow meter 14 for detecting the intake air amount is provided on the downstream side of the air cleaner 13. A throttle valve 15 whose opening is adjusted by a motor or the like and a throttle opening sensor 16 for detecting the opening (throttle opening) of the throttle valve 15 are provided on the downstream side of the air flow meter 14.

  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 that introduces air into each cylinder of the engine 11, and a fuel injection valve that injects fuel toward the intake port in the vicinity of the intake port of the intake manifold 19 of each cylinder. 20 is attached. 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 valve timing (opening / closing timing) 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 every predetermined crank angle (for example, every 30 CA) in synchronization with the rotation of the shaft is provided.

On the other hand, in the exhaust pipe 34 of the engine 11, exhaust gas in the exhaust collecting portion 34 a (the portion where the exhaust manifold 35 of each cylinder gathers or the downstream side thereof) flows. An air-fuel ratio sensor 36 for detecting the fuel ratio is provided. A catalyst 37 such as a three-way catalyst for purifying CO, HC, NO _{x and the} like in the exhaust gas is provided on the downstream side of the air-fuel ratio sensor 36. A cooling water temperature sensor 38 for detecting the cooling water temperature is attached to the cylinder block of the engine 11.

  Outputs of these various sensors are input to an electronic control unit (hereinafter referred to as “ECU”) 39. The ECU 39 is mainly composed of a microcomputer, and executes various engine control programs stored in a built-in ROM (storage medium), thereby depending on the engine operating state, the fuel injection amount, the ignition timing. The throttle opening (intake air amount) and the like are controlled.

  At this time, the ECU 39 sets the air-fuel ratio of the air-fuel mixture so that the air-fuel ratio of the exhaust gas matches the target air-fuel ratio based on the output of the air-fuel ratio sensor 36 when a predetermined air-fuel ratio F / B control execution condition is satisfied. Air-fuel ratio F / B control for F / B control (for example, fuel injection amount) is executed. Here, “F / B” means “feedback” (hereinafter the same).

  Specifically, as shown in FIG. 2, first, the air-fuel ratio deviation calculating unit 40 calculates the deviation between the detected air-fuel ratio (the air-fuel ratio of the exhaust gas detected by the air-fuel ratio sensor 36) and the target air-fuel ratio, The air-fuel ratio F / B control unit 41 calculates an air-fuel ratio correction coefficient so that the deviation between the detected air-fuel ratio and the target air-fuel ratio becomes small. The injection amount calculation unit 42 calculates the fuel injection amount based on the base injection amount, the air-fuel ratio correction coefficient, etc. calculated based on the engine speed and engine load (intake pipe negative pressure, intake air amount, etc.). The fuel injection valve 20 of each cylinder is controlled based on the fuel injection amount.

  Further, the ECU 39 executes an air-fuel ratio control routine for each cylinder shown in FIG. 6 to be described later, thereby setting the air-fuel ratio of each cylinder based on the detection value of the air-fuel ratio sensor 36 detected at each air-fuel ratio detection timing of each cylinder. Cylinder air-fuel ratio estimation is performed for each cylinder, and cylinder-by-cylinder air-fuel ratio control is performed to control the air-fuel ratio of each cylinder for each cylinder based on the estimated air-fuel ratio of each cylinder.

  Specifically, as shown in FIG. 2, first, the cylinder-by-cylinder air-fuel ratio estimation unit 43 uses a detection value of the air-fuel ratio sensor 36 (exhaust gas flowing through the exhaust collecting unit 34 a) using a cylinder-by-cylinder air-fuel ratio estimation model described later. Based on the actual air-fuel ratio), the air-fuel ratio of each cylinder is estimated for each cylinder, the reference air-fuel ratio calculating unit 44 calculates the average value of the estimated air-fuel ratios of all the cylinders, and the average value is used as the reference air-fuel ratio. Set. Thereafter, the cylinder-by-cylinder air-fuel ratio deviation calculating unit 45 calculates the deviation between the estimated air-fuel ratio of each cylinder and the reference air-fuel ratio for each cylinder, and the cylinder-by-cylinder air-fuel ratio control unit 46 calculates the estimated air-fuel ratio of each cylinder and the reference air-fuel ratio. For example, a fuel correction amount (a fuel injection amount correction amount) is calculated for each cylinder as a cylinder specific correction value so that the deviation from the air-fuel ratio becomes small. By correcting the fuel injection amount of each cylinder for 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 to reduce the air-fuel ratio variation among the cylinders.

  Here, a specific model for estimating the air-fuel ratio of each cylinder based on the detected value of the air-fuel ratio sensor 36 (actual air-fuel ratio of the exhaust gas flowing through the exhaust collecting portion 34a) (hereinafter referred to as "cylinder-specific air-fuel ratio estimation model"). An example will be described.

  Paying attention to the gas exchange in the exhaust collecting portion 34a, the detected value of the air-fuel ratio sensor 36 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 36 in the exhaust collecting portion 34a. The model is obtained by multiplying and adding, and the air-fuel ratio of each cylinder is estimated using this model. At this time, a Kalman filter is used as an observer.

More specifically, a gas exchange model in the exhaust collecting portion 34a 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 36, u is an air-fuel ratio of the gas flowing into the exhaust collecting portion 34a, and k1 to k4 are constants.

  In the exhaust system, there are a first-order lag element for gas inflow and mixing in the exhaust collecting portion 34 a and a first-order lag element due to a response delay of the air-fuel ratio sensor 36. 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 36, 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.

  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 36) will be described. The delay until the exhaust gas discharged from each cylinder reaches the vicinity of the air-fuel ratio sensor 36 and the air-fuel ratio is detected (hereinafter referred to as “exhaust system response delay”) varies depending on the engine operating state. Considering this, in this embodiment, 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 36 is taken into the ECU 39. I am doing so. 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 36 is different for each cylinder, and the flow of exhaust gas in each cylinder is in the engine operating state (engine rotation speed, in-cylinder charged air amount, etc.). ). Moreover, since the exhaust system response delay also changes due to manufacturing variations and aging of the engine 11, the response delay of the exhaust system of each cylinder (air-fuel ratio detection timing of each cylinder) and the engine load in the engine design and manufacturing process. It is difficult to map these relationships with high accuracy. 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. Become.

  Therefore, the ECU 39 executes the routines shown in FIGS. 7 to 12 to be described later, thereby determining whether there is a deviation in the air-fuel ratio detection timing based on the estimated air-fuel ratio during the cylinder-by-cylinder air-fuel ratio control. The air-fuel ratio detection timing correction is performed to correct the air-fuel ratio detection timing when it is determined that there is a deviation in the air-fuel ratio detection timing.

  For example, the local learning for correcting the air-fuel ratio detection timing is executed so that the variation (fluctuation) of the detection value of the air-fuel ratio sensor 36 is maximized within one cycle (720 CA) of the engine 11. After the execution of the local learning, the air-fuel ratio detection timing is determined based on the relationship between the change in the estimated air-fuel ratio of at least one cylinder and the change in the cylinder-specific correction value (for example, fuel correction amount) of the cylinder during the cylinder-by-cylinder air-fuel ratio control. The global learning for correcting is performed. In this global learning, the change in the estimated air-fuel ratio of at least one cylinder and the change in the estimated air-fuel ratio in each of the cases where each cylinder number assumed for the estimated air-fuel ratio of each cylinder is virtually changed in plural ways. A correlation value with a change in the cylinder-specific correction value of the cylinder number is calculated, and the air-fuel ratio detection timing is corrected so that this correlation value becomes maximum.

  When the air-fuel ratio detection timing of each cylinder deviates, the correct air-fuel ratio detection timing of a certain cylinder is not necessarily near the current air-fuel ratio detection timing of that cylinder. For example, the current air-fuel ratio of the next combustion cylinder It is assumed that the detection timing is delayed to the retarded angle side, or the current air-fuel ratio detection timing of the previous combustion cylinder is advanced to the advanced angle side. For example, as shown in FIG. 3B, the correct air-fuel ratio detection timing of a certain cylinder (assumed to be the first cylinder # 1) reaches the current air-fuel ratio detection timing of the other cylinder (assumed to be the third cylinder # 3). In the case of deviation, the timing at which the actual air-fuel ratio of the first cylinder # 1 is best detected is not the current air-fuel ratio detection timing of the first cylinder # 1, but the current air-fuel ratio detection timing of the third cylinder # 3. It becomes. In this case, the cylinder is corrected by the cylinder-specific correction value (for example, fuel correction amount) of the first cylinder # 1 calculated based on the estimated air-fuel ratio of the first cylinder # 1 estimated based on the current air-fuel ratio detection timing of the first cylinder # 1. When the separate air-fuel ratio control is performed, the actual air-fuel ratio of the first cylinder # 1 changes according to the change of the cylinder-specific correction value of the first cylinder # 1. However, the estimated air-fuel ratio of the first cylinder # 1 does not change according to the change of the correction value for each cylinder of the first cylinder # 1, and the estimated air-fuel ratio of the third cylinder # 3 is corrected for each cylinder of the first cylinder # 1. It will change as the value changes.

  Focusing on this characteristic, in the present embodiment, by global learning, the change in the estimated air-fuel ratio of at least one cylinder and the change in the cylinder-specific correction value (for example, fuel correction amount) of the cylinder during the cylinder-by-cylinder air-fuel ratio control. Since the air-fuel ratio detection timing is corrected based on the above relationship, the deviation of the air-fuel ratio detection timing can be corrected. In addition, in the case where each cylinder number assumed for the estimated air-fuel ratio of each cylinder is virtually changed in plural ways, the change of the estimated air-fuel ratio of at least one cylinder and the cylinder number after the change of the estimated air-fuel ratio are changed. A correlation value with a change in the cylinder specific correction value (for example, fuel correction amount) is calculated, and the air-fuel ratio detection timing is corrected based on the correlation value. This eliminates the need to actually calculate the correlation value by sequentially shifting the current air-fuel ratio detection timing, and uses only the estimated air-fuel ratio of each cylinder at the current air-fuel ratio detection timing and the correction value for each cylinder based on that. Based on this, it is possible to simultaneously calculate and compare the correlation values when the assumed cylinder is virtually replaced. Thereby, even when the optimal air-fuel ratio detection timing is greatly deviated from the current air-fuel ratio detection timing, the deviation of the air-fuel ratio detection timing can be corrected in a short time.

  Further, for example, the correct air-fuel ratio detection timing of a certain cylinder (assumed to be the first cylinder # 1) is the current air-fuel ratio detection timing of other consecutive cylinders (assumed to be the second cylinder # 2 and the fourth cylinder # 4). The air-fuel ratio detection timing at which the actual air-fuel ratio of the first cylinder # 1 can be detected with the highest accuracy when shifted to the middle is not the current air-fuel ratio detection timing of the first cylinder # 1, but the second cylinder # 2. And the current air-fuel ratio detection timing of the fourth cylinder # 4. In this case, since the estimated air-fuel ratio at the timing most correlated with the change in the cylinder-by-cylinder correction value of the first cylinder # 1 cannot be obtained in the estimation at the current air-fuel ratio detection timing, the optimum air-fuel ratio detection is performed. The timing may not be corrected. Therefore, it is desirable that any of the detection values of the air-fuel ratio sensor 36 at the air-fuel ratio detection timing of each cylinder accurately detect any of the actual air-fuel ratios of each cylinder.

  Thus, in this embodiment, the air-fuel ratio detection timing is corrected by local learning so that the variation (variation) in the detection value of the air-fuel ratio sensor 36 is maximized within one cycle (720 CA) of the engine 11. . Thus, when the actual air-fuel ratio of each cylinder varies, the air-fuel ratio fluctuates within one cycle, but the fluctuation can be detected to the maximum, and the air-fuel ratio sensor 36 at the air-fuel ratio detection timing of each cylinder. Any one of the detected values can accurately detect any of the actual air-fuel ratios of the respective cylinders. Thereby, since any of the estimated air-fuel ratios of the respective cylinders can detect any of the actual air-fuel ratios of the respective cylinders, the deviation of the air-fuel ratio detection timing can be accurately corrected in the global learning.

  By the way, if misfire of the engine 11 (for example, continuous misfire in a specific cylinder) occurs during cylinder-by-cylinder air-fuel ratio control, the estimation accuracy of the air-fuel ratio of each cylinder may deteriorate due to the influence. In such a case, the estimated air-fuel ratio of each cylinder diverges, and the air-fuel ratio of each cylinder cannot be correctly controlled (control so as to reduce the variation in air-fuel ratio between cylinders). There is a possibility of inviting.

As a countermeasure, in the first embodiment, the ECU 39 executes the routines shown in FIGS. 4 and 5 to be described later to determine whether the engine 11 has misfired. When it is determined that the engine 11 has misfired, The cylinder-by-cylinder air-fuel ratio estimation and the cylinder-by-cylinder air-fuel ratio control are stopped, and the cylinder-by-cylinder correction value by the cylinder-by-cylinder air-fuel ratio control is reset.
Hereinafter, the processing content of each routine of FIG. 4 thru | or FIG. 12 which ECU39 performs in the present Example 1 is demonstrated.

[Misfire detection routine]
The misfire determination routine shown in FIG. 4 is started at every predetermined crank angle (for example, every 30 CA) in synchronization with the output pulse of the crank angle sensor 33, and serves as misfire determination means in the claims.

  When this routine is started, first, in step 101, the crankshaft of the engine 11 rotates 30 CA at a predetermined timing (for example, every predetermined misfire determination crank angle section) based on the output signal of the crank angle sensor 33. 30 CA time T30, which is the time required, is calculated.

Thereafter, the process proceeds to step 102, where a time change amount DMF (information on engine rotation fluctuation), which is a difference between the current 30CA time T30 (i) and the previous 30CA time T30 (i-1), is calculated.
Thereafter, the process proceeds to step 103, where it is determined whether the time change amount DMF is larger than the misfire determination value.

  If it is determined in step 103 that the time change amount DMF is equal to or less than the misfire determination value, the process proceeds to step 104, where it is determined that the engine 11 has not misfired, and the misfire flag is reset to “0”. This routine ends.

  On the other hand, if it is determined in step 103 that the time change amount DMF is larger than the misfire determination value, the process proceeds to step 105 where it is determined that the engine 11 has misfired and the misfire flag is set to “1”. After setting to, this routine is terminated. It should be noted that when the number of times that the time change amount DMF is continuously determined to be larger than the misfire determination value (the number of consecutive times) exceeds a predetermined value, it is determined that there is a misfire, or The misfire may be determined to be present when the number of times that the change amount DMF is determined to be larger than the misfire determination value (the number of integration) exceeds a predetermined value.

  Further, in the routine of FIG. 4, the time change amount DMF is compared with the misfire determination value to determine the presence or absence of misfire. However, the misfire determination method is not limited to this, and may be changed as appropriate. The presence or absence of misfire may be determined by comparing the engine rotation fluctuation amount with the misfire determination value.

[Execution condition judgment routine]
The execution condition determination routine shown in FIG. 5 is started every predetermined crank angle (for example, every 30 CA) in synchronization with the output pulse of the crank angle sensor 33. When this routine is started, first, at step 201, it is determined whether or not a misfire flag = 0 (no misfire).

  If it is determined in step 201 that the misfire flag = 0 (no misfire), the process proceeds to step 202, in which the air-fuel ratio sensor 36 is usable (for example, whether the air-fuel ratio sensor 36 is normal and active). Determine whether.

  If it is determined in step 202 that the air-fuel ratio sensor 36 can be used, the process proceeds to step 203 where the engine operating state (for example, engine load and engine speed) is within a predetermined range (for example, the air-fuel ratio estimation accuracy is reduced). It is determined whether it is within the area that can be secured.

  If all the determinations in steps 201 to 203 are “Yes” (that is, if all the conditions in steps 201 to 203 are satisfied), the process proceeds to step 204 and the execution condition of the cylinder-by-cylinder air-fuel ratio control is satisfied. This routine is terminated after the execution condition flag is set to “1”.

  On the other hand, if it is determined in step 201 that the misfire flag = 1 (with misfire), the process proceeds to step 205, and the cylinder-specific correction value (fuel correction amount) of each cylinder is set to a predetermined value (for example, an initial value). (Or the value before the misfire detection). Thereafter, the routine proceeds to step 206, where it is determined that the execution condition of the cylinder-by-cylinder air-fuel ratio control is not satisfied, the execution condition flag is reset to “0”, and this routine is ended. By these processes, when it is determined that the engine 11 has misfired (misfire flag = 1), the execution condition of the cylinder-by-cylinder air-fuel ratio control is not satisfied (execution condition flag = 0), and the cylinder-by-cylinder air-fuel ratio estimation and cylinder The separate air-fuel ratio control is stopped and the cylinder-specific correction value for each cylinder is reset. Therefore, in the first embodiment, the routine of FIG. 5 or the like serves as a stopping means in the claims.

  If “No” is determined in step 202 or 203, the process proceeds to step 206, where it is determined that the execution condition of the air-fuel ratio control for each cylinder is not satisfied, and the execution condition flag is reset to “0”. After that, this routine is finished.

[Air-fuel ratio control routine for each cylinder]
The cylinder-by-cylinder air-fuel ratio control routine shown in FIG. 6 is started at predetermined crank angles (for example, every 30 CA) in synchronization with the output pulse of the crank angle sensor 33, and serves as cylinder-by-cylinder air-fuel ratio control means. Play a role.

  When this routine is started, first, in step 301, it is determined whether or not the execution condition of the cylinder-by-cylinder air-fuel ratio control is satisfied, depending on whether or not the execution condition flag is set to “1”.

  If it is determined in step 301 that the execution condition of the cylinder-by-cylinder air-fuel ratio control is not satisfied (execution condition flag = 0), this routine is executed without executing the processing related to the cylinder-by-cylinder air-fuel ratio control in and after step 302. finish. Thus, when it is determined that the engine 11 has misfired (misfire flag = 1) and the execution condition of the cylinder-by-cylinder air-fuel ratio control is not established (execution condition flag = 0), the cylinder-by-cylinder air-fuel ratio estimation is performed. The cylinder-by-cylinder air-fuel ratio control is stopped.

  On the other hand, if it is determined in step 301 that the execution condition of the cylinder-by-cylinder air-fuel ratio control is satisfied (execution condition flag = 1), the processing related to the cylinder-by-cylinder air-fuel ratio control in step 302 and subsequent steps is as follows. And run.

  First, in step 302, the air-fuel ratio detection timing of each cylinder (sample timing of the output of the air-fuel ratio sensor 36) is set by a map according to the engine load (for example, intake pipe pressure) at that time. 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 corrected by a local learning execution routine shown in FIG. 9 and a global learning execution routine shown in FIG.

  Thereafter, the routine proceeds to step 303, where it is determined whether or not the current crank angle is the air-fuel ratio detection timing set in step 302. 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 302, the process proceeds to step 304, and the output (air-fuel ratio detection value) of the air-fuel ratio sensor 36 is read.

  Thereafter, the routine proceeds to step 305, 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 36 using the cylinder-by-cylinder air-fuel ratio estimation model. The processing in step 305 serves as cylinder-by-cylinder air-fuel ratio estimation means in the claims.

Thereafter, the process proceeds to step 306, where an average value of estimated air-fuel ratios of all cylinders is calculated, and the average value is set as a reference air-fuel ratio (target air-fuel ratio of all cylinders).
Thereafter, the process proceeds to step 307, where the deviation between the estimated air-fuel ratio of each cylinder and the reference air-fuel ratio is calculated, and the fuel correction amount is calculated as a cylinder-specific correction value for each cylinder so that the deviation becomes small.

  Thereafter, the routine proceeds to step 308, where the fuel injection amount of each cylinder is corrected based on the fuel correction amount of each cylinder, thereby correcting the air-fuel ratio of the air-fuel mixture supplied to each cylinder for each cylinder. Control is performed to reduce the variation in air-fuel ratio.

[Air-fuel ratio detection timing determination routine]
The air-fuel ratio detection timing determination routine shown in FIG. 7 is started every predetermined crank angle (for example, every 30 CA) in synchronization with the output pulse of the crank angle sensor 33. When this routine is started, first, at step 401, it is determined 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 executed without performing the subsequent processing. finish.

  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 value or more is being performed, for example, one of the following conditions (A1) to (A3) Determine by one or more.

(A1) 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.
(A2) 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 the fuel correction amount for all cylinders is greater than or equal to a predetermined value.
(A3) It is determined whether or not a fuel correction of a predetermined value or more is being performed based on whether or not an elapsed time after the start of the fuel correction is a predetermined time or more.

If it is determined in step 402 that the predetermined fuel correction or more has not been performed, the present routine is immediately terminated.
On the other hand, if it is determined in step 402 that fuel correction of a predetermined value or more is being performed, the process proceeds to step 403 to determine whether the degree of variation in the estimated air-fuel ratio between the cylinders is large, for example, under the following condition ( Judgment is made based on one or both of B1) and (B2).

(B1) Whether the variation in the estimated air-fuel ratio among the 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.
(B2) 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 small, it is determined that the air-fuel ratio detection timing is correct, and this routine is immediately terminated.
On the other hand, if it is determined in step 403 that the degree of variation in the estimated air-fuel ratio between the cylinders is large, it is determined that the air-fuel ratio detection timing may be shifted, and the process proceeds to step 404. In this step 404, it is determined whether or not 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, for example, the change rate of the fuel correction amount of each cylinder and the change of the estimated air-fuel ratio. It is determined by whether or not the deviation from the rate is a predetermined value or more.

  If it is determined in step 404 that the fuel correction amount increase / decrease direction of each cylinder is the same as the estimated air / fuel ratio increase / decrease direction, it is determined that the air / fuel ratio detection timing is correct, and this routine is directly executed. finish.

  On the other hand, if it is determined in step 404 that 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 process proceeds to step 405 and the air / fuel ratio detection timing is shifted. This routine is terminated after the deviation determination flag is set to “1”.

[Air-fuel ratio detection timing deviation learning correction routine]
The air-fuel ratio detection timing deviation learning correction routine shown in FIG. 8 is started every predetermined crank angle (for example, every 30 CA) in synchronization with the output pulse of the crank angle sensor 33. When this routine is started, first, in step 501, it is determined whether or not the local learning completion flag is set to “1”, and it is determined that the local learning completion flag is set to “1”. In step 502, the counter is incremented after the local learning is completed.

  Thereafter, the routine proceeds to step 503, where it is determined whether or not the air-fuel ratio detection timing is determined to be shifted by the air-fuel ratio detection timing determination routine of FIG. 7 depending on whether or not the shift determination flag is set to “1”. To do.

  If it is not determined in step 503 that the air-fuel ratio detection timing has shifted (if the shift determination flag = 0), this routine is terminated without performing the processing from step 504 onward.

  On the other hand, when it is determined in step 503 that the air-fuel ratio detection timing has shifted (when the shift determination flag = 1), the process proceeds to step 504, where the local learning completion flag is “0” or It is determined whether or not the count value of the counter after completion of the local learning is equal to or greater than a predetermined value T1.

  If it is determined in step 504 that the local learning completion flag is “0”, or if the count value of the counter after completion of local learning is determined to be greater than or equal to the predetermined value T1, the process proceeds to step 505. . In step 505, the count value of the local learning completion counter is reset to “0”, the local learning completion flag is reset to “0”, and the local learning execution counter is counted up.

  Thereafter, the process proceeds to step 506, and the cylinder-specific correction value (fuel correction amount) of each cylinder is held at the previous value, and then the process proceeds to step 507, where a local learning execution routine of FIG. Thus, local learning for correcting the air-fuel ratio detection timing is executed so that the variation in the detection value of the air-fuel ratio sensor 36 is maximized.

  On the other hand, if it is determined in step 504 that the local learning completion flag is “1” and it is determined that the count value of the counter after completion of the local learning has not reached the predetermined value T1, step 508 is executed. Then, it is determined whether or not the count value of the counter after completion of the local learning is equal to or greater than a predetermined value T2. Here, the predetermined value T2 is a value smaller than the predetermined value T1 (T2 <T1).

  If it is determined in step 508 that the count value of the counter after completion of the local learning has not reached the predetermined value T2, a sufficient time is required for the cylinder-by-cylinder air-fuel ratio control to stabilize after the local learning is completed. It is determined that it has not elapsed, and this routine is terminated.

  Thereafter, if it is determined in step 508 that the count value of the counter after the completion of local learning is equal to or greater than the predetermined value T2, a sufficient time for the cylinder-by-cylinder air-fuel ratio control to stabilize after the local learning is completed. In step 509, the global learning execution counter is counted up.

  Thereafter, the routine proceeds to step 510, where a global learning execution routine of FIG. 11 described later is executed, and the air-fuel ratio is determined based on the relationship between the change in the estimated air-fuel ratio of each cylinder and the change in the correction value (fuel correction amount) for each cylinder. Global learning for correcting the detection timing is executed.

[Local learning execution routine]
The local learning execution routine shown in FIG. 9 is a subroutine executed in step 507 of the air-fuel ratio detection timing deviation learning correction routine of FIG.

  In this routine, local learning for correcting the air-fuel ratio detection timing is performed so that the variation in the detection value of the air-fuel ratio sensor 36 is maximized within one cycle. In this local learning, the air-fuel ratio detection timing is corrected so that the value corresponding to the dispersion of the detection value of the air-fuel ratio sensor 36 detected at each air-fuel ratio detection timing of each cylinder becomes maximum.

When this routine is started, first, in step 601, it is determined whether or not the count value of the local learning execution counter is equal to or less than a predetermined value (for example, a value corresponding to 30 cycles).
If it is determined in step 601 that the count value of the local learning execution counter is equal to or smaller than the predetermined value, the process proceeds to step 602, the local learning index calculation routine of FIG. 10 is executed, and the local learning index is set as follows. To calculate. Assuming that the air-fuel ratio detection timing of the first cylinder # 1 is the following timings L1 to L6 [CA], the dispersion of the detection value of the air-fuel ratio sensor 36 detected at each air-fuel ratio detection timing of each cylinder will be described. A corresponding value (hereinafter referred to as “dispersion of detected air-fuel ratio”) is calculated, and this detected air-fuel ratio dispersion is used as a local learning index.

  (1) When the air-fuel ratio detection timing of the first cylinder # 1 is assumed to be the first timing L1 = Dca1 -90 (timing advanced by 90 CA from the current air-fuel ratio detection timing Dca1 of the first cylinder # 1) The detected air-fuel ratio variance V (Dca1-90) is calculated by the following equation.

  Here, N is the number of cylinders per air-fuel ratio sensor 36 (for example, 4), and φ (k) is a detected value of the air-fuel ratio sensor 36 at k [CA]. Mean φ (k) is the average value of {φ (k), φ (k + 720 / N * 1), φ (k + 720 / N * 2), φ (k + 720 / N * 3)} It is. Φ (k) is calculated by an equivalence ratio (reciprocal of excess air ratio).

  (2) When the air-fuel ratio detection timing of the first cylinder # 1 is assumed to be the second timing L2 = Dca1−60 (timing advanced by 60 CA from the current air-fuel ratio detection timing Dca1 of the first cylinder # 1) The variance V (Dca1-60) of the detected air-fuel ratio is calculated by the following equation.

  (3) When the air-fuel ratio detection timing of the first cylinder # 1 is assumed to be the third timing L3 = Dca1-30 (timing advanced by 30 CA from the current air-fuel ratio detection timing Dca1 of the first cylinder # 1) The detected air-fuel ratio variance V (Dca1-30) is calculated by the following equation.

  (4) Dispersion of the detected air-fuel ratio when the air-fuel ratio detection timing of the first cylinder # 1 is assumed to be the fourth timing L4 = Dca1 (the same timing as the current air-fuel ratio detection timing Dca1 of the first cylinder # 1) V (Dca1) is calculated by the following equation.

  (5) Detection when it is assumed that the air-fuel ratio detection timing of the first cylinder # 1 is the fifth timing L5 = Dca1 + 30 (timing delayed by 30 CA from the current air-fuel ratio detection timing Dca1 of the first cylinder # 1) The air-fuel ratio dispersion V (Dca1 + 30) is calculated by the following equation.

(6) 第１気筒＃１の空燃比検出タイミングを、第６のタイミングＬ6 ＝Ｄca1 ＋６０（第１気筒＃１の現在の空燃比検出タイミングＤca1 から６０ＣＡ遅角したタイミング）と仮定した場合の検出空燃比の分散Ｖ(Dca1+60) は、次式により算出する。

(6) Detection when the air-fuel ratio detection timing of the first cylinder # 1 is assumed to be the sixth timing L6 = Dca1 + 60 (timing delayed by 60 CA from the current air-fuel ratio detection timing Dca1 of the first cylinder # 1) The air-fuel ratio dispersion V (Dca1 + 60) is calculated by the following equation.

  In this way, when the air-fuel ratio detection timing of the first cylinder # 1 is assumed to be the respective timings L1 to L6, after calculating the variance V (Local learning index) of the detected air-fuel ratio, the process proceeds to step 603 in FIG. move on. In this step 603, when the air-fuel ratio detection timing of the first cylinder # 1 is assumed to be the respective timings L1 to L6, the detected air-fuel ratio variance V (Local learning index) is normalized.

  Specifically, the variances V (Dca1-90), V (Dca1-60), V (Dca1-30) of the detected air-fuel ratio when the air-fuel ratio detection timing of the first cylinder # 1 is assumed to be the respective timings L1 to L6. ), V (Dca1), V (Dca1 + 30), V (Dca1 + 60) are assigned higher scores (for example, 5 to 0 points) in descending order. Those points Point (Dca1-90), Point (Dca1-60), Point (Dca1-30), Point (Dca1), Point (Dca1 + 30), Point (Dca1 + 60) are normalized indices (detection sky). Data obtained by normalizing the dispersion V of the fuel ratio).

V (Dca1-90) → Point (Dca1-90)
V (Dca1-60) → Point (Dca1-60)
V (Dca1-30) → Point (Dca1-30)
V (Dca1) → Point (Dca1)
V (Dca1 + 30) → Point (Dca1 + 30)
V (Dca1 + 60) → Point (Dca1 + 60)

  Thereafter, the process proceeds to step 604, where the air-fuel ratio detection timing of the first cylinder # 1 is assumed to be the respective timings L1 to L6. The current normalized index is added to the integrated value to update the integrated value of the normalized index.

  Thereafter, when it is determined in step 601 that the count value of the local learning execution counter has exceeded a predetermined value, it is determined that the integrated value of the normalization index for a predetermined period has been calculated, and the flow proceeds to step 605 to determine each timing. The timing at which the integrated value of the normalization index among the L1 to L6 is maximized is selected as the optimum timing.

  Thereafter, the process proceeds to step 606, where the selected optimal timing (timing at which the integrated value of the normalization index during the predetermined period becomes maximum) is learned as the air-fuel ratio detection timing of the first cylinder # 1, and the first cylinder # 1. The air-fuel ratio detection timings of the other cylinders (second cylinder # 2 to fourth cylinder # 4) are learned on the basis of the air-fuel ratio detection timing. These learning values are updated and stored in a learning value storage area of a rewritable nonvolatile memory such as a backup RAM of the ECU 39.

  Thereafter, the process proceeds to step 607 where the count value of the local learning execution counter is reset to “0”, the deviation determination flag is reset to “0”, and the local learning completion flag is set to “1”. Thereafter, the process proceeds to step 608, the cylinder-specific correction value (fuel correction amount) of each cylinder is reset to a predetermined value (for example, an initial value or a value before deviation determination), and this routine ends.

[Global learning execution routine]
The global learning execution routine shown in FIG. 11 is a subroutine executed in step 510 of the air-fuel ratio detection timing deviation learning correction routine of FIG.

  In this routine, global learning for correcting the air-fuel ratio detection timing is executed based on the relationship between the change in the estimated air-fuel ratio of each cylinder and the change in the correction value for each cylinder (fuel correction amount). In this global learning, the change in the estimated air-fuel ratio of each cylinder and the cylinder number after the change in the estimated air-fuel ratio in each of the cases where each cylinder number assumed for the estimated air-fuel ratio of each cylinder is virtually changed in several ways. A correlation value with a change in the cylinder specific correction value (fuel correction amount) is calculated, and the air-fuel ratio detection timing is corrected so that the correlation value becomes maximum.

  When this routine is started, first, in step 701, it is determined whether or not it is a global learning index calculation timing (for example, every 720CA). If it is determined that it is not a global learning index calculation timing, steps 702 and thereafter are performed. This routine is terminated without performing any processing.

  On the other hand, if it is determined in step 701 that it is the global learning index calculation timing, the process proceeds to step 702, and whether or not the count value of the global learning execution counter is equal to or less than a predetermined value (for example, a value corresponding to 30 cycles). Determine.

  If it is determined in step 702 that the count value of the global learning execution counter is equal to or smaller than the predetermined value, the process proceeds to step 703, the global learning index calculation routine of FIG. 12 is executed, and the global learning index is set as follows. To calculate. When the air-fuel ratio detection timing of the first cylinder # 1 is assumed to be the following timings G1 to G4 [CA], the correlation value between the change of the estimated air-fuel ratio of each cylinder and the change of the fuel correction amount is calculated, This correlation value is used as a global learning index.

Specifically, in step 711, the estimated air-fuel ratio change amount Δφ of each cylinder at the current air-fuel ratio detection timing and the fuel correction amount change amount ΔCmp of each cylinder are calculated by the following equations.
Δφ ^ # i (t) = φ ^ # i (t) −φ ^ # i (tn)
ΔCmp # i (t) = Cmp # i (t) −Cmp # i (tn)

  Here, φ ^ # i (t) is the current calculated value of the estimated air-fuel ratio of the i-th cylinder #i, and φ ^ # i (tn) is n times before the estimated air-fuel ratio of the i-th cylinder #i. It is a calculated value. Cmp # i (t) is the current calculated value of the fuel correction amount for the i-th cylinder #i, and Cmp # i (tn) is the calculated value n times before the fuel correction amount for the i-th cylinder #i. is there. Note that n is a predetermined integer value of 1 or more.

  Thereafter, the process proceeds to step 712, and assuming that the air-fuel ratio detection timing of the first cylinder # 1 is the following timings G1 to G4 [CA], the estimated air-fuel ratio change and the fuel correction amount change of each cylinder respectively. (A sum of products of the estimated amount of change Δφ of the estimated air-fuel ratio and the amount of change ΔCmp of the fuel correction amount).

  (1) When the air-fuel ratio detection timing of the first cylinder # 1 is assumed to be the first timing G1 = Dca1 (the same timing as the current air-fuel ratio detection timing Dca1 of the first cylinder # 1), FIG. As shown in a), the estimated air-fuel ratio φ ^ # 1 of the first cylinder # 1 at the current air-fuel ratio detection timing is calculated as the estimated air-fuel ratio of the first cylinder # 1. The estimated air-fuel ratio φ ^ # 3 of the third cylinder # 3 at the current air-fuel ratio detection timing is calculated as the estimated air-fuel ratio of the third cylinder # 3, and the fourth cylinder # 4 at the current air-fuel ratio detection timing. Is calculated as the estimated air-fuel ratio of the fourth cylinder # 4, and the estimated air-fuel ratio φ ^ # 2 of the second cylinder # 2 at the current air-fuel ratio detection timing is that of the second cylinder # 2. Calculated as the estimated air-fuel ratio.

Accordingly, the correlation value Cor (Dca1) when the air-fuel ratio detection timing of the first cylinder # 1 is assumed to be the first timing G1 = Dca1 can be calculated by the following equation.
Cor (Dca1) = Δφ ^ # 1 (t) × ΔCmp # 1 (t) + Δφ ^ # 3 (t) × ΔCmp # 3 (t)
+ Δφ ^ # 4 (t) × ΔCmp # 4 (t) + Δφ ^ # 2 (t) × ΔCmp # 2 (t)

  (2) When the air-fuel ratio detection timing of the first cylinder # 1 is assumed to be the second timing G2 = Dca1 +180 (a timing delayed by 180 CA from the current air-fuel ratio detection timing Dca1 of the first cylinder # 1) As shown in FIG. 13B, the estimated air-fuel ratio φ ^ # 1 of the first cylinder # 1 at the current air-fuel ratio detection timing is calculated as the estimated air-fuel ratio of the second cylinder # 2. Further, the estimated air-fuel ratio φ ^ # 3 of the third cylinder # 3 at the current air-fuel ratio detection timing is calculated as the estimated air-fuel ratio of the first cylinder # 1, and the fourth cylinder # 4 at the current air-fuel ratio detection timing. Is calculated as the estimated air-fuel ratio of the third cylinder # 3, and the estimated air-fuel ratio φ ^ # 2 of the second cylinder # 2 at the current air-fuel ratio detection timing is that of the fourth cylinder # 4. Calculated as the estimated air-fuel ratio.

Accordingly, the correlation value Cor (Dca1 + 180) when the air-fuel ratio detection timing of the first cylinder # 1 is assumed to be the second timing G2 = Dca1 + 180 can be calculated by the following equation.
Cor (Dca1 + 180) = Δφ ^ # 3 (t) × ΔCmp # 1 (t) + Δφ ^ # 4 (t) × ΔCmp # 3 (t)
+ Δφ ^ # 2 (t) × ΔCmp # 4 (t) + Δφ ^ # 1 (t) × ΔCmp # 2 (t)

  (3) When the air-fuel ratio detection timing of the first cylinder # 1 is assumed to be the third timing G3 = Dca1 + 360 (a timing delayed by 360 CA from the current air-fuel ratio detection timing Dca1 of the first cylinder # 1) As shown in FIG. 13 (c), the estimated air-fuel ratio φ ^ # 1 of the first cylinder # 1 at the current air-fuel ratio detection timing is calculated as the estimated air-fuel ratio of the fourth cylinder # 4. Further, the estimated air-fuel ratio φ ^ # 3 of the third cylinder # 3 at the current air-fuel ratio detection timing is calculated as the estimated air-fuel ratio of the second cylinder # 2, and the fourth cylinder # 4 at the current air-fuel ratio detection timing. Is estimated as the estimated air-fuel ratio of the first cylinder # 1, and the estimated air-fuel ratio φ ^ # 2 of the second cylinder # 2 at the current air-fuel ratio detection timing is the same as that of the third cylinder # 3. Calculated as the estimated air-fuel ratio.

Accordingly, the correlation value Cor (Dca1 + 360) when the air-fuel ratio detection timing of the first cylinder # 1 is assumed to be the third timing G3 = Dca1 + 360 can be calculated by the following equation.
Cor (Dca1 + 360) = Δφ ^ # 4 (t) × ΔCmp # 1 (t) + Δφ ^ # 2 (t) × ΔCmp # 3 (t)
+ Δφ ^ # 1 (t) × ΔCmp # 4 (t) + Δφ ^ # 3 (t) × ΔCmp # 2 (t)

  (4) When the air-fuel ratio detection timing of the first cylinder # 1 is assumed to be the fourth timing G4 = Dca1 +540 (timing delayed by 540CA from the current air-fuel ratio detection timing Dca1 of the first cylinder # 1) As shown in FIG. 13 (d), the estimated air-fuel ratio φ ^ # 1 of the first cylinder # 1 at the current air-fuel ratio detection timing is calculated as the estimated air-fuel ratio of the third cylinder # 3. Further, the estimated air-fuel ratio φ ^ # 3 of the third cylinder # 3 at the current air-fuel ratio detection timing is calculated as the estimated air-fuel ratio of the fourth cylinder # 4, and the fourth cylinder # 4 at the current air-fuel ratio detection timing is calculated. Is calculated as the estimated air-fuel ratio of the second cylinder # 2, and the estimated air-fuel ratio φ ^ # 2 of the second cylinder # 2 at the current air-fuel ratio detection timing is the same as that of the first cylinder # 1. Calculated as the estimated air-fuel ratio.

Accordingly, the correlation value Cor (Dca1 + 540) when the air-fuel ratio detection timing of the first cylinder # 1 is assumed to be the fourth timing G4 = Dca1 + 540 can be calculated by the following equation.
Cor (Dca1 + 540) = Δφ ^ # 2 (t) × ΔCmp # 1 (t) + Δφ ^ # 1 (t) × ΔCmp # 3 (t)
+ Δφ ^ # 3 (t) × ΔCmp # 4 (t) + Δφ ^ # 4 (t) × ΔCmp # 2 (t)

  In this way, when the air-fuel ratio detection timing of the first cylinder # 1 is assumed to be the respective timings G1 to G4, the correlation value Cor (Global learning) between the change of the estimated air-fuel ratio of each cylinder and the change of the fuel correction amount, respectively. After calculating the index, the process proceeds to step 704 in FIG. In this step 704, when the air-fuel ratio detection timing of the first cylinder # 1 is assumed to be the respective timings G1 to G4, the correlation value Cor is obtained by adding the current correlation value Cor to the previous integration value Cor. Update the accumulated value of. At this time, only the positive value of the correlation value Cor may be integrated, or only the negative value of the correlation value Cor may be integrated.

  Thereafter, when it is determined in step 702 that the count value of the global learning execution counter has exceeded a predetermined value, it is determined that the integrated value of the correlation value Cor for a predetermined period has been calculated, and the process proceeds to step 705, where each timing Among the G1 to G4, the timing at which the integrated value of the correlation value Cor for a predetermined period is maximized is selected as the optimum timing.

  Thereafter, the process proceeds to step 706, where the selected optimum timing (timing at which the integrated value of the correlation value Cor during the predetermined period becomes maximum) is learned as the air-fuel ratio detection timing of the first cylinder # 1, and the first cylinder # 1. The air-fuel ratio detection timings of the other cylinders (second cylinder # 2 to fourth cylinder # 4) are learned on the basis of the air-fuel ratio detection timing. These learning values are updated and stored in a learning value storage area of a rewritable nonvolatile memory such as a backup RAM of the ECU 39.

  Thereafter, the process proceeds to step 707, where the count value of the global learning execution counter is reset to “0”, the deviation determination flag is reset to “0”, and the local learning completion flag is reset to “0”. After the local learning is completed, the count value of the counter is reset to “0”, and this routine ends.

These routines shown in FIGS. 7 to 12 serve as detection timing correction means in the claims.
Note that the F / B gain of cylinder-by-cylinder air-fuel ratio control may be increased during the period from the completion of local learning to the completion of global learning. In this case, only the F / B gain of a specific cylinder may be increased, or a different F / B gain may be set for each cylinder.

  In addition, after the local learning is performed (that is, after the air-fuel ratio detection timing is corrected by the local learning), the air-fuel ratio detection timing is set to the combustion interval (4 In the case of a cylinder, 180CA) or a global learning that corrects each multiple thereof is executed, so that the air-fuel ratio detection timing of each cylinder is replaced with the air-fuel ratio detection timing of each cylinder, and the air-fuel ratio detection timing of each cylinder is changed. You may make it correct | amend to the correct air fuel ratio detection timing.

  In the first embodiment described above, the cylinder-by-cylinder air-fuel ratio estimation and the cylinder-by-cylinder air-fuel ratio control are stopped when it is determined that the engine 11 has misfired. Therefore, the air-fuel ratio of each cylinder is correctly controlled by misfire. It is possible to prevent the deterioration of exhaust emissions by preventing the cylinder-by-cylinder air-fuel ratio control from being continued as usual in a state where it is not possible.

  In the first embodiment, when it is determined that the engine 11 has misfired, the cylinder-by-cylinder air-fuel ratio estimation and the cylinder-by-cylinder air-fuel ratio control are stopped, and the cylinder-by-cylinder air-fuel ratio control is corrected. ) Is reset. As a result, when the cylinder-by-cylinder air-fuel ratio control is resumed, the cylinder-by-cylinder air-fuel ratio control can be started in a state in which the cylinder-by-cylinder correction value is reset (that is, a state in which the influence of misfire is eliminated).

  In the first embodiment, when it is determined that the engine 11 has misfired, both the cylinder-by-cylinder air-fuel ratio estimation and the cylinder-by-cylinder air-fuel ratio control are stopped. However, the present invention is not limited to this. Only one of the fuel ratio estimation and the cylinder-by-cylinder air-fuel ratio control may be stopped.

  By stopping the estimation of the air-fuel ratio for each cylinder (stopping the calculation of the estimated air-fuel ratio for each cylinder), the update of the correction value for each cylinder by the cylinder-by-cylinder air-fuel ratio control can be stopped. Even if only the estimation is stopped, the air-fuel ratio control for each cylinder can be almost the same as when the correction value for each cylinder is stopped. Therefore, even if only one of the cylinder-by-cylinder air-fuel ratio estimation and the cylinder-by-cylinder air-fuel ratio control is stopped, the cylinder-by-cylinder air-fuel ratio control is continued as usual in a state where the air-fuel ratio of each cylinder cannot be controlled correctly due to misfire. It is possible to prevent the exhaust emission from deteriorating.

  Next, Embodiment 2 of the present invention will be described with reference to FIGS. However, description of substantially the same parts as those in the first embodiment will be omitted or simplified, and different parts from the first embodiment will be mainly described.

  If the engine 11 suddenly decelerates after sudden acceleration, the exhaust flow velocity may drop significantly, and the exhaust flow may stagnate. If the flow of exhaust gas in the vicinity of the air-fuel ratio sensor 36 stagnate during the cylinder-by-cylinder air-fuel ratio control, the amplitude of the air-fuel ratio sensor 36 output decreases due to the influence, and the air-fuel ratio sensor 36 at each air-fuel ratio detection timing of each cylinder. It may be difficult to read the output correctly. In such a case, an erroneous estimation cylinder (correspondence between each cylinder and the estimated air-fuel ratio) occurs, and the air-fuel ratio of each cylinder cannot be controlled correctly, which may lead to deterioration of exhaust emissions. is there. If the air-fuel ratio detection timing correction is performed in such a state, the estimation accuracy of the air-fuel ratio of each cylinder may be further deteriorated.

  As a countermeasure against this, in the second embodiment, the ECU 39 executes the routines shown in FIGS. 14 and 15 to be described later to determine whether or not the exhaust flow of the engine 11 is stagnant (hereinafter referred to as “exhaust flow stagnant state”). When the exhaust flow stagnation state is determined, the cylinder-by-cylinder air-fuel ratio estimation, the cylinder-by-cylinder air-fuel ratio control, and the air-fuel ratio detection timing correction are stopped.

At this time, in the second embodiment, the exhaust flow stagnation state is determined when the engine 11 suddenly decelerates after sudden acceleration. If the engine 11 suddenly decelerates after rapid acceleration, the exhaust flow velocity decreases greatly, and the exhaust flow stagnate. Therefore, it is determined that the exhaust flow is stagnant (the exhaust flow velocity is greatly decreased) during sudden deceleration after the rapid acceleration. be able to.
Hereinafter, the processing content of each routine of FIG.14 and FIG.15 which ECU39 performs in the present Example 2 is demonstrated.

[Rapid acceleration / deceleration judgment routine]
The rapid acceleration / deceleration determination routine shown in FIG. 14 is started at every predetermined crank angle (for example, every 30 CA) in synchronization with the output pulse of the crank angle sensor 33, and serves as exhaust flow determination means in the claims. .

  When this routine is started, first, in step 801, the intake air amount GN [g / rev] and the intake air based on the output signals of the air flow meter 14 and the intake pipe pressure sensor 18 at every predetermined timing (for example, every TDC). The amount GA [g / s] is calculated.

Thereafter, the process proceeds to step 802, and the difference between the current intake air amount GN (i) and the previous intake air amount GN (i-1) is calculated to obtain a predetermined period (for example, between TDCs) of the intake air amount GN. The change amount dGN is obtained, and the difference between the current intake air amount GA (i) and the previous intake air amount GA (i-1) is calculated, whereby the change amount of the intake air amount GA over a predetermined period (for example, between TDCs). Obtain dGA.
dGN = GN (i) −GN (i−1)
dGA = GA (i) −GA (i−1)

  Thereafter, the process proceeds to step 803, where it is determined whether or not the rapid deceleration flag after rapid acceleration is set to “1”. This rapid deceleration flag after rapid acceleration is set to “1” when it is determined in step 808 described later that rapid deceleration after rapid acceleration has occurred.

  If it is determined in step 803 that the rapid deceleration flag after rapid acceleration = 0, the process proceeds to step 804, in which it is determined whether the rapid acceleration flag is set to “1”. The rapid acceleration flag is set to “1” when it is determined in step 806, which will be described later, that rapid acceleration is being performed.

  If it is determined in step 804 that the rapid acceleration flag = 0, the process proceeds to step 805, where the change amount dGN is larger than a predetermined increase determination value KN1 (> 0) and the change amount dGA is determined to be a predetermined increase determination. It is determined whether or not the value is greater than the value KA1 (> 0) (dGN> KN1 and dGA> KA1).

  If it is determined in this step 805 that dGN ≦ KN1 or dGA ≦ KA1, it is determined that there is no sudden acceleration, and this routine is terminated while the rapid acceleration flag is maintained at “0”.

  Thereafter, if it is determined in step 805 that dGN> KN1 and dGA> KA1, the process proceeds to step 806, where it is determined that there is sudden acceleration, and the rapid acceleration flag is set to “1”. This routine ends.

  Thereafter, if it is determined in step 804 that the rapid acceleration flag = 1, the process proceeds to step 807, where the change amount dGN is smaller than a predetermined decrease determination value KN2 (<0) and the change amount dGA is predetermined. It is determined whether or not it is smaller than the decrease determination value KA2 (<0) (dGN <KN2 and dGA <KA2).

  If it is determined in this step 807 that dGN ≧ KN2 or dGA ≧ KA2, it is determined that there is no sudden deceleration after sudden acceleration, and the rapid deceleration flag after sudden acceleration is maintained at “0”. This routine is terminated.

  Thereafter, if it is determined in step 807 that dGN <KN2 and dGA <KA2, the process proceeds to step 808, where it is determined that the vehicle is suddenly decelerating after rapid acceleration (that is, exhaust gas stagnation). The subsequent rapid deceleration flag is set to “1” and the rapid acceleration flag is reset to “0”, and then this routine is terminated.

  Thereafter, if it is determined in step 803 that the rapid deceleration flag after rapid acceleration = 1, the process proceeds to step 809, during rapid deceleration after rapid acceleration (rapid deceleration flag after rapid acceleration = 1). It is determined whether or not a predetermined time has elapsed since the determination.

If it is determined in step 809 that the predetermined time has not elapsed since it was determined that the vehicle was suddenly decelerating after rapid acceleration (the flag for rapid deceleration after rapid acceleration = 1), the process proceeds to step 810 and changes are made. It is determined whether the amount dGN is larger than a predetermined value KN3 (> 0) and the change amount dGA is larger than a predetermined value KA3 (> 0) (dGN> KN3 and dGA> KA3). Here, the predetermined values KN3 and KA3 may be fixed values set in advance, but may be set in accordance with the elapsed time after determining the sudden deceleration after the rapid acceleration.
If it is determined in this step 810 that dGN≤KN3 or dGA≤KA3, the routine ends while the rapid deceleration flag after rapid acceleration is maintained at "1".

  Thereafter, when it is determined in step 809 that a predetermined time has elapsed since it is determined that the vehicle is suddenly decelerating after sudden acceleration (a flag during rapid deceleration after rapid acceleration = 1), or in step 810, dGN> KN3 If it is determined that dGA> KA3, the routine proceeds to step 811 where it is determined that the engine is not suddenly decelerating after rapid acceleration (that is, the exhaust flow stagnation state) and the rapid deceleration flag after rapid acceleration is set to “0”. After the reset to, this routine ends.

  In the routine of FIG. 14, both the change amount dGN and the change amount dGA are used in steps 805, 807, and 810. However, the present invention is not limited to this, and only one of the change amount dGN and the change amount dGA is used. May be used.

  Specifically, in step 805, it is determined whether dGN> KN1, and if it is determined that dGN> KN1, the process may proceed to step 806. Alternatively, in step 805, it is determined whether dGA> KA1, and if it is determined that dGA> KA1, the process may proceed to step 806.

  In step 807, it is determined whether dGN <KN2, and if it is determined that dGN <KN2, the process may proceed to step 808. Alternatively, it may be determined in step 807 whether or not dGA <KA2, and if it is determined that dGA <KA2, the process may proceed to step 808.

  In step 810, it is determined whether dGN> KN3. If it is determined that dGN> KN3, the process may proceed to step 811. Alternatively, in step 810, it is determined whether dGA> KA3, and if it is determined that dGA> KA3, the process may proceed to step 811.

[Execution condition judgment routine]
The execution condition determination routine of FIG. 15 executed in the second embodiment changes the process of step 201 of the routine of FIG. 5 described in the first embodiment to the process of step 201a, and also performs the process of step 205 of the routine of FIG. The processing is omitted, and the processing of each step other than that is the same as FIG.

  In the execution condition determination routine of FIG. 15, first, in step 201a, it is determined whether or not the rapid deceleration flag after rapid acceleration = 0. If it is determined in step 201a that the rapid deceleration flag after rapid acceleration = 0, the process proceeds to step 202 to determine whether or not the air-fuel ratio sensor 36 is usable. If it is determined that it is possible, the process proceeds to step 203 to determine whether or not the engine operating state is within a predetermined region.

  If all the determinations in steps 201a to 203 are “Yes” (that is, if all the conditions in steps 201a to 203 are satisfied), the process proceeds to step 204, and the execution condition for the cylinder-by-cylinder air-fuel ratio control is satisfied. This routine is terminated after the execution condition flag is set to “1”.

  On the other hand, if it is determined in step 201a that the rapid deceleration flag after rapid acceleration = 1 (the rapid deceleration after rapid acceleration), the routine proceeds to step 206 where the cylinder-by-cylinder air-fuel ratio control is performed. After determining that the execution condition is not satisfied and resetting the execution condition flag to “0”, this routine is terminated. By these processes, when it is determined that the engine 11 is suddenly decelerated after sudden acceleration (that is, an exhaust flow stagnation state), the execution condition of the cylinder-by-cylinder air-fuel ratio control is not satisfied (execution condition flag = 0), and the cylinder While the separate air-fuel ratio estimation and the cylinder-by-cylinder air-fuel ratio control are stopped, the air-fuel ratio detection timing correction is stopped as the cylinder-by-cylinder air-fuel ratio control is stopped. Therefore, in the second embodiment, the routine of FIG. 15 or the like serves as stop means in the claims.

An execution example of the control of the second embodiment described above will be described with reference to the time charts of FIGS.
As shown in FIGS. 16 and 17, the change amount dGN of the intake air amount GN and the change amount dGA of the intake air amount GA are calculated at every predetermined timing (for example, every TDC).

  Then, at the time point t1 when it is determined that the change amount dGN is greater than the increase determination value KN1 and the change amount dGA is greater than the increase determination value KA1 (dGN> KN1 and dGA> KA1), it is determined that there is a sudden acceleration. Then, the rapid acceleration flag is set to “1” (not shown).

  Thereafter, at the time t2 when it is determined that the change amount dGN is smaller than the decrease determination value KN2 and the change amount dGA is smaller than the decrease determination value KA2 (dGN <KN2 and dGA <KA2), (In other words, the exhaust flow stagnation state is determined), and the rapid deceleration flag after rapid acceleration is set to “1”. As a result, it is determined that the execution condition of the cylinder-by-cylinder air-fuel ratio control is not satisfied, and the execution condition flag is reset to “0”, so that the cylinder-by-cylinder air-fuel ratio estimation, cylinder-by-cylinder air-fuel ratio control, and air-fuel ratio detection timing correction are performed. To stop.

  After that, as shown in FIG. 16, at the time t3 when a predetermined time has elapsed since it was determined that the vehicle was suddenly decelerated after sudden acceleration (the flag for sudden deceleration after sudden acceleration = 1), In other words, it is determined that the exhaust flow stagnation state is not established, and the rapid deceleration flag after rapid acceleration is reset to “0”. Alternatively, as shown in FIG. 17, after the rapid acceleration at time t3 when the change amount dGN is larger than the predetermined value KN3 and the change amount dGA is larger than the predetermined value KA3 (dGN> KN3 and dGA> KA3). It is determined that it is not during sudden deceleration, and the rapid deceleration flag after rapid acceleration is reset to “0”. Accordingly, it is determined that the execution condition of the cylinder-by-cylinder air-fuel ratio control is satisfied, and the execution condition flag is set to “1”, so that the cylinder-by-cylinder air-fuel ratio estimation, the cylinder-by-cylinder air-fuel ratio control, and the air-fuel ratio detection timing are set. Resume correction.

  In the second embodiment described above, it is determined whether or not the exhaust flow stagnation state is based on whether or not the engine 11 is suddenly decelerated after sudden acceleration, and when the engine 11 is suddenly decelerated after sudden acceleration (exhaust flow stagnation state). When the determination is made, cylinder-by-cylinder air-fuel ratio estimation, cylinder-by-cylinder air-fuel ratio control, and air-fuel ratio detection timing correction are stopped. Thereby, it is possible to prevent the cylinder-by-cylinder air-fuel ratio control from continuing normally in a state where the air-fuel ratio of each cylinder cannot be controlled correctly due to the stagnation of the exhaust flow, and to suppress the deterioration of exhaust emission.

  In the second embodiment, when the amount of change in the intake air amount changes from a state larger than a predetermined increase determination value to a state smaller than a predetermined decrease determination value, a sudden deceleration after the rapid acceleration (exhaust flow) (Stagnation state). As a result, it is possible to accurately determine the time of sudden deceleration (exhaust gas flow rate lowered state) after sudden acceleration based on the intake air amount detectable by the sensor.

  Furthermore, in the second embodiment, when a predetermined time has elapsed since it was determined that the vehicle is suddenly decelerating after sudden acceleration (exhaust flow stagnation state) or when the amount of change in the intake air amount is greater than a predetermined value, It is determined that it is not at the time of sudden deceleration after sudden acceleration (exhaust flow stagnation state). In this way, a predetermined time elapses after it is determined that the vehicle is suddenly decelerating after sudden acceleration (a state in which the exhaust gas flow rate is reduced), or the amount of change in the intake air amount exceeds a predetermined value, and The cylinder-by-cylinder air-fuel ratio control can be resumed after the stagnation is eliminated and the amplitude of the output of the air-fuel ratio sensor 36 increases to some extent.

  In the second embodiment, when it is determined that the vehicle is suddenly decelerating after sudden acceleration (exhaust flow stagnation state), all cylinder-by-cylinder air-fuel ratio estimation, cylinder-by-cylinder air-fuel ratio control, and air-fuel ratio detection timing correction are all stopped. However, the present invention is not limited to this, and one or two of the cylinder-by-cylinder air-fuel ratio estimation, the cylinder-by-cylinder air-fuel ratio control, and the air-fuel ratio detection timing correction may be stopped.

  As described above, since the cylinder-by-cylinder air-fuel ratio estimation is stopped (the calculation of the estimated air-fuel ratio of each cylinder is stopped), the update of the cylinder-specific correction value for each cylinder by the cylinder-by-cylinder air-fuel ratio control can be stopped. Even if only the cylinder-by-cylinder air-fuel ratio estimation is stopped, the cylinder-by-cylinder air-fuel ratio control can be brought into a state substantially the same as that in which the cylinder-by-cylinder correction value calculation is stopped. Even if only the air-fuel ratio detection timing correction is stopped, it is possible to suppress the deterioration of the estimation accuracy of the air-fuel ratio of each cylinder and to suppress the deterioration of the control accuracy of the cylinder-by-cylinder air-fuel ratio control.

  Further, in the second embodiment, it is determined whether or not the vehicle is suddenly decelerating after sudden acceleration (exhaust gas flow rate lowered state) based on the intake air amount. However, the present invention is not limited to this. Based on the accelerator opening, the throttle opening, the intake pressure, and the like, it may be determined whether or not the vehicle is suddenly decelerating after sudden acceleration.

  In the second embodiment, the routine shown in FIG. 14 determines whether or not a predetermined time has elapsed since it was determined that the vehicle was suddenly decelerated after sudden acceleration (step 809), and the amount of change in the intake air amount. Both of the processes (step 810) for determining whether or not is greater than a predetermined value are performed, but either one of the processes may be omitted.

  In the second embodiment, the cylinder-by-cylinder air-fuel ratio estimation, the cylinder-by-cylinder air-fuel ratio control, and the air-fuel ratio detection timing correction are stopped when it is determined that there is a sudden deceleration after sudden acceleration. Alternatively, the cylinder-by-cylinder air-fuel ratio estimation, the cylinder-by-cylinder air-fuel ratio control, and the air-fuel ratio detection timing correction may be stopped when it is determined that the exhaust flow is in a stagnation state, even at times other than sudden deceleration after sudden acceleration.

Further, the method of correcting the air-fuel ratio detection timing when it is determined that there is a deviation in the air-fuel ratio detection timing is not limited to the method described in the first and second embodiments, and may be changed as appropriate.
In the first and second embodiments, the present invention is applied to a four-cylinder engine. However, the present invention is not limited to this, and the present invention can be applied to a two-cylinder engine, a three-cylinder engine, or an engine having five or more cylinders. good.

  In addition, the present invention is not limited to the intake port injection type engine, but is an in-cylinder injection type engine or a dual injection type engine having both a fuel injection valve for intake port injection and a fuel injection valve for in-cylinder injection. It can also be applied to.

  DESCRIPTION OF SYMBOLS 11 ... Engine (internal combustion engine), 12 ... Intake pipe, 34 ... Exhaust pipe, 34a ... Exhaust collecting part, 36 ... Air-fuel ratio sensor, 39 ... ECU (Air-fuel ratio estimation means by cylinder, Air-fuel ratio control means by cylinder, Detection timing (Correction means, misfire determination means, stop means, exhaust flow determination means)

Claims (6)

An air-fuel ratio sensor (36) for detecting the air-fuel ratio of the exhaust gas is installed in the exhaust collecting part (34a) where the exhaust gas of each cylinder of the internal combustion engine (11) flows and flows. Cylinder-by-cylinder air-fuel ratio estimation means (39) for executing cylinder-by-cylinder air-fuel ratio estimation for estimating the air-fuel ratio of each cylinder based on the detected value of the air-fuel ratio sensor (36) detected every time; In a cylinder-by-cylinder air-fuel ratio control apparatus for an internal combustion engine, comprising: a cylinder-by-cylinder air-fuel ratio control means (39) for performing cylinder-by-cylinder air-fuel ratio control for controlling the air-fuel ratio of each cylinder based on an estimated air-fuel ratio;
Misfire determination means (39) for determining the presence or absence of misfire in the internal combustion engine (11);
Stop means (39) for stopping at least one of the cylinder-by-cylinder air-fuel ratio estimation and the cylinder-by-cylinder air-fuel ratio control when the misfire judgment means (39) determines that the internal combustion engine (11) has misfired. And a cylinder-by-cylinder air-fuel ratio control apparatus for an internal combustion engine.   The stop means (39) resets the cylinder specific correction value by the cylinder specific air-fuel ratio control when the misfire determination means (39) determines that the internal combustion engine (11) has misfired. The cylinder-by-cylinder air-fuel ratio control apparatus for an internal combustion engine according to claim 1. An air-fuel ratio sensor (36) for detecting the air-fuel ratio of the exhaust gas is installed in the exhaust collecting part (34a) where the exhaust gas of each cylinder of the internal combustion engine (11) flows and flows. Cylinder-by-cylinder air-fuel ratio estimation means (39) for executing cylinder-by-cylinder air-fuel ratio estimation for estimating the air-fuel ratio of each cylinder based on the detected value of the air-fuel ratio sensor (36) detected every time; Cylinder air-fuel ratio control means (39) for executing cylinder-by-cylinder air-fuel ratio control for controlling the air-fuel ratio of each cylinder based on the estimated air-fuel ratio, and the estimated air-fuel ratio of each cylinder during the cylinder-by-cylinder air-fuel ratio control. A cylinder-by-cylinder air-fuel ratio control apparatus for an internal combustion engine, comprising detection timing correction means (39) for executing air-fuel ratio detection timing correction for correcting the air-fuel ratio detection timing based on
Exhaust flow determination means (39) for determining whether or not the exhaust flow of the internal combustion engine (11) is stagnant (hereinafter referred to as "exhaust flow stagnant state");
When it is determined by the exhaust flow determination means (39) that the exhaust flow is stagnant, at least one of the cylinder-by-cylinder air-fuel ratio estimation, the cylinder-by-cylinder air-fuel ratio control, and the air-fuel ratio detection timing correction is stopped. A cylinder-by-cylinder air-fuel ratio control apparatus for an internal combustion engine, comprising: a stop means (39).   The air-fuel ratio for each cylinder of the internal combustion engine according to claim 3, wherein the exhaust flow determination means (39) determines the exhaust flow stagnation state when the internal combustion engine (11) is suddenly decelerated after sudden acceleration. Control device.   When the amount of change in the intake air amount of the internal combustion engine (11) changes from a state larger than a predetermined increase determination value to a state smaller than a predetermined decrease determination value, the exhaust flow determination means (39) 5. The cylinder-by-cylinder air-fuel ratio control apparatus for an internal combustion engine according to claim 4, wherein it is determined that the vehicle is suddenly decelerated after sudden acceleration.   The exhaust flow determining means (39) determines that the predetermined amount of time has elapsed since it was determined to be suddenly decelerated after the rapid acceleration, or the amount of change in the intake air amount of the internal combustion engine (11) is greater than a predetermined value. 6. The cylinder-by-cylinder air-fuel ratio control apparatus for an internal combustion engine according to claim 5, wherein it is determined that it is not at the time of sudden deceleration after the sudden acceleration.

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