JP2016044575A - Cylinder air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide such a system for performing a cylinder-different air-fuel ratio control as is enabled to suppress an air-fuel ratio detecting timing (or a sample timing of an air-fuel ratio sensor output) due to the change of an exhaust flow speed.SOLUTION: On the basis of such a detection value of an air-fuel ratio sensor 36 as is detected at each air-fuel ration detecting timing of each cylinder of an engine 11, the air-fuel ratio of each cylinder is estimated to control the air-fuel ratio of each cylinder on the basis of the estimated air-fuel ratio of each cylinder. At this time, an air-fuel ratio detection timing is corrected in accordance with exhaust flow changing factors (an ignition timing, a fuel injection timing and a load changing amount) or the running conditions for causing the change of the exhaust flow speed. As a result, in accordance with the change of the phase of the output waveform of the air-fuel sensor 36 (i.e., the change in the proper air/fuel ratio detection timing of each cylinder), the air-fuel ratio of each cylinder is suppressed from deviating from the proper air-fuel ratio detection timing.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. At that time, the delay until the exhaust gas discharged from each cylinder reaches the vicinity of the air-fuel ratio sensor and the air-fuel ratio is detected (response delay of the exhaust system) changes depending on the load and the rotational speed of the internal combustion engine. In consideration, the air-fuel ratio detection timing (sample timing of the air-fuel ratio sensor output) of each cylinder is set according to the load and the rotational speed.

JP 2013-253593 A

  By the way, the exhaust flow velocity may change depending on operating conditions other than the load and rotation speed of the internal combustion engine (for example, ignition timing). When the exhaust flow velocity changes, the response delay of the exhaust system changes accordingly, and the air-fuel ratio Since the phase of the output waveform of the sensor changes, the appropriate air-fuel ratio detection timing of each cylinder also changes.

  For this reason, even when the air-fuel ratio detection timing of each cylinder is set according to the load and rotation speed of the internal combustion engine during the cylinder-by-cylinder air-fuel ratio control, if the exhaust flow velocity changes due to operating conditions other than the load and rotation speed, There is a possibility that the air-fuel ratio detection timing of each cylinder deviates from the proper air-fuel ratio detection timing. When the air-fuel ratio detection timing of each cylinder shifts, the estimation accuracy of the air-fuel ratio of each cylinder decreases, and the air-fuel ratio of each cylinder is correctly controlled (control is performed so as to reduce the air-fuel ratio variation between cylinders). It becomes difficult.

  Accordingly, an object of the present invention is to provide a cylinder-by-cylinder air-fuel ratio control apparatus for an internal combustion engine that can suppress a deviation in the air-fuel ratio detection timing due to a change in the exhaust flow velocity of the internal combustion engine.

  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. An air-fuel ratio detection timing setting means (39) for setting an air-fuel ratio detection timing of each cylinder according to at least one of the load and the rotational speed of the internal combustion engine (11); A cylinder-by-cylinder air-fuel ratio estimating means (39) for estimating 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, and each of the cylinders based on the estimated air-fuel ratio of each cylinder. In the cylinder-by-cylinder air-fuel ratio control device for an internal combustion engine that includes a cylinder-by-cylinder air-fuel ratio control means (39) for controlling the air-fuel ratio of the cylinder, the air-fuel ratio detection timing setting means (39) is an exhaust flow velocity of the internal combustion engine (11). Factors that change It is obtained so as to correct the air-fuel ratio detection timing according to the operating conditions (hereinafter referred to as "exhaust flow rate change factor") that.

  In this configuration, the exhaust flow rate changes according to the exhaust flow rate change factor, and the phase of the output waveform of the air-fuel ratio sensor changes (that is, the appropriate air-fuel ratio detection timing of each cylinder changes). Thus, the air-fuel ratio detection timing can be corrected, and deviation of the air-fuel ratio detection timing of each cylinder from the appropriate air-fuel ratio detection timing can be suppressed. As a result, even if the exhaust gas flow rate changes due to operating conditions other than the load and rotation speed of the internal combustion engine, the deviation of the air-fuel ratio detection timing due to the change in the exhaust gas flow rate can be suppressed. The reduction in accuracy can be suppressed, and the air-fuel ratio of each cylinder can be correctly controlled (control so as to reduce the variation in air-fuel ratio between cylinders).

FIG. 1 is a diagram showing a schematic configuration of an engine control system in one embodiment of the present invention. FIG. 2 is a block diagram illustrating the air-fuel ratio control function. FIG. 3 is a flowchart showing the flow of processing of the cylinder-by-cylinder air-fuel ratio control routine. FIG. 4 is a flowchart showing the flow of processing of the air-fuel ratio detection timing setting routine. FIG. 5 is a diagram conceptually showing an example of the map of the base air-fuel ratio detection timing Sb. FIG. 6 is a diagram conceptually showing an example of a map of the correction amount S1 according to the ignition timing. FIG. 7 is a diagram conceptually showing an example of a map of the correction amount S2 corresponding to the fuel injection timing. FIG. 8 is a diagram conceptually showing an example of a map of the correction amount S3 corresponding to the load change amount. FIG. 9 is a time chart showing an execution example of the air-fuel ratio detection timing correction according to the ignition timing. FIG. 10 is a time chart showing an execution example of the air-fuel ratio detection timing correction according to the fuel injection timing.

Hereinafter, an embodiment embodying a mode for carrying out the present invention will be described.
First, a schematic configuration of the entire engine control system will be described with reference to FIG.
An 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 for introducing air into each cylinder of the engine 11, and fuel is injected into the intake port at or near the intake port connected to the intake manifold 19 of each cylinder. A fuel injection valve 20 is attached. Alternatively, a fuel injection valve 20 that directly injects fuel into the cylinder may be attached to each cylinder of the engine 11. 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), so that the fuel injection amount and the fuel injection are determined according to the engine operating state. The timing, ignition timing, throttle opening (intake air amount), etc. 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. 3 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. In consideration of 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 speed and load), and the output of the air-fuel ratio sensor 36 is taken into the ECU 39. ing. In general, as the load on the engine 11 decreases, the response delay of the exhaust system increases, so the air-fuel ratio detection timing of each cylinder is set to shift to the retard side as the load on the engine 11 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.). ). In addition, since the response delay of the exhaust system 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 load in the engine design and manufacturing process. It is difficult to map the relationship accurately. For this reason, the air-fuel ratio detection timing of each cylinder may deviate from the proper air-fuel ratio detection timing.

  Therefore, the ECU 39 performs air-fuel ratio detection timing determination for 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, and when it is determined that there is a deviation in the air-fuel ratio detection timing Correct 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.

  Alternatively, after the local learning is executed (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 ( (In the case of four cylinders, 180 CA) or a global learning that corrects multiple times of each is performed to replace the air-fuel ratio detection timing of each cylinder with the air-fuel ratio detection timing of the other cylinders. May be corrected to the correct air-fuel ratio detection timing.

  By the way, the exhaust flow rate may change depending on operating conditions (for example, ignition timing) other than the load of the engine 11 and the rotational speed. When the exhaust flow rate changes, the response delay of the exhaust system changes accordingly, and the air-fuel ratio sensor. Since the phase of the output waveform 36 changes, the appropriate air-fuel ratio detection timing of each cylinder also changes.

  For this reason, even if the air-fuel ratio detection timing of each cylinder is set according to the load and rotation speed of the engine 11 during the cylinder-by-cylinder air-fuel ratio control, if the exhaust flow velocity changes due to operating conditions other than the load and rotation speed, There is a possibility that the air-fuel ratio detection timing of each cylinder deviates from the proper air-fuel ratio detection timing. When the air-fuel ratio detection timing of each cylinder shifts, the estimation accuracy of the air-fuel ratio of each cylinder decreases, and the air-fuel ratio of each cylinder is correctly controlled (control is performed so as to reduce the air-fuel ratio variation between cylinders). It becomes difficult.

  As a countermeasure, in this embodiment, the ECU 39 executes an air-fuel ratio detection timing setting routine shown in FIG. 4 to be described later, thereby operating conditions (hereinafter referred to as “exhaust flow rate change factor”) that cause the exhaust flow rate of the engine 11 to change. ), The air-fuel ratio detection timing is corrected.

  In this way, the exhaust flow rate changes in accordance with the exhaust flow rate change factor, and the phase of the output waveform of the air-fuel ratio sensor 36 changes (that is, the appropriate air-fuel ratio detection timing of each cylinder changes). Correspondingly, the air-fuel ratio detection timing can be corrected, and the deviation of the air-fuel ratio detection timing of each cylinder from the appropriate air-fuel ratio detection timing can be suppressed.

  In this embodiment, the engine 11 ignition timing, the fuel injection timing, and the load change amount are used as the exhaust flow velocity change factors, and the air-fuel ratio detection timing is determined according to these ignition timing, fuel injection timing, and load change amount. I am trying to correct.

  When the ignition timing (for example, the retard amount from the base ignition timing) changes, the exhaust pressure changes due to the change in the combustion timing, and the exhaust flow velocity changes. Therefore, the ignition timing becomes an exhaust flow velocity change factor.

  In addition, when the fuel injection timing changes (for example, switching between intake stroke injection and compression stroke injection), the combustion state changes and the exhaust flow velocity changes, so the fuel injection timing depends on the exhaust flow velocity change factor. Become.

Furthermore, when the amount of change in load (for example, the amount of change in intake air amount over a predetermined period) changes, the amount of change in exhaust gas amount over a predetermined period changes, and the exhaust flow rate changes. It becomes a flow velocity change factor.
Hereinafter, the processing content of each routine of FIG.3 and FIG.4 which ECU39 performs by a present Example is demonstrated.

[Air-fuel ratio control routine for each cylinder]
The cylinder-by-cylinder air-fuel ratio control routine shown in FIG. 3 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, at step 101, it is determined whether or not an execution condition for the cylinder-by-cylinder air-fuel ratio control is satisfied. The execution conditions of the cylinder-by-cylinder air-fuel ratio control include, for example, the following conditions (1) to (3).
(1) The air-fuel ratio sensor 36 is in an active state
(2) The air-fuel ratio sensor 36 is not judged to be abnormal (failure)
(3) The engine operating range (for example, engine speed and intake pipe pressure) must be an operating range where air-fuel ratio estimation accuracy can be ensured.

  The execution condition of the cylinder-by-cylinder air-fuel ratio control is satisfied when all of these three conditions (1) to (3) are satisfied. If any one of the conditions is not satisfied, the execution condition is not satisfied. If the execution condition is not satisfied, this routine is terminated without performing the processing after step 102.

  On the other hand, if the execution condition is satisfied, the routine proceeds to step 102 where an air-fuel ratio detection timing setting routine shown in FIG. 4 described later is executed to detect the air-fuel ratio detection timing of each cylinder (sample timing of the output of the air-fuel ratio sensor 36). ) Is set.

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

  On the other hand, if the current crank angle is the air-fuel ratio detection timing set in step 102, the process proceeds to step 104, and the output (air-fuel ratio detection value) of the air-fuel ratio sensor 36 is read.

  Thereafter, the routine proceeds to step 105, where the air-fuel ratio of the cylinder that is the current air-fuel ratio estimation target is estimated based on the detected value of the air-fuel ratio sensor 36 using the cylinder-by-cylinder air-fuel ratio estimation model. The processing in step 105 serves as cylinder-by-cylinder air-fuel ratio estimation means in the claims.

Thereafter, the routine proceeds to step 106, where the average value of the estimated air-fuel ratios of all cylinders is calculated, and the average value is set as the reference air-fuel ratio (target air-fuel ratio of all cylinders).
Thereafter, the routine proceeds to step 107, where the deviation between the estimated air-fuel ratio of each cylinder and the reference air-fuel ratio is calculated, 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 108 where the air-fuel ratio of the air-fuel mixture supplied to each cylinder is corrected for each cylinder by correcting the fuel injection amount for each cylinder based on the fuel correction amount for each cylinder. Control is performed to reduce the variation in air-fuel ratio.

[Air-fuel ratio detection timing setting routine]
The air-fuel ratio detection timing setting routine shown in FIG. 4 is a subroutine executed in step 102 of the cylinder-by-cylinder air-fuel ratio control routine shown in FIG. 3, and serves as air-fuel ratio detection timing setting means in the claims. .

When this routine is started, first, in step 201, outputs of various sensors and calculation information of the ECU 39 (for example, ignition timing, fuel injection timing, etc.) are read.
Thereafter, the routine proceeds to step 202, where the base air-fuel ratio detection timing Sb of each cylinder is calculated from a map (see FIG. 5) according to the current load (for example, intake pipe pressure) of the engine 11. The base air-fuel ratio detection timing Sb of each cylinder may be calculated from a map according to the engine speed and load. The map for calculating the base air-fuel ratio detection timing Sb is learned and corrected by an unillustrated routine for correcting an air-fuel ratio detection timing deviation learning (for example, a local learning execution routine or a global learning execution routine).

  Thereafter, the routine proceeds to step 203, where the correction amount S1 corresponding to the current ignition timing (for example, the retard amount from the base ignition timing) is calculated with reference to the map of the correction amount S1 corresponding to the ignition timing shown in FIG. To do. In the map of the correction amount S1 in FIG. 6, the correction amount S1 decreases (the advance amount of the air-fuel ratio detection timing increases) as the ignition timing becomes retarded (that is, the retardation amount from the base ignition timing increases). Is set). The map of the correction amount S1 is created in advance based on tests and design data, and stored in the ROM of the ECU 39.

  Thereafter, the routine proceeds to step 204, where the correction amount S2 corresponding to the current fuel injection timing is calculated with reference to the map of the correction amount S2 corresponding to the fuel injection timing shown in FIG. The map of the correction amount S2 in FIG. 7 is set so that the correction amount S2 is smaller (the advance amount of the air-fuel ratio detection timing is larger) when the fuel injection timing is the compression stroke than when the fuel injection timing is the intake stroke. ing. The map of the correction amount S2 is created in advance based on tests and design data, and stored in the ROM of the ECU 39.

  Thereafter, the process proceeds to step 205, where the correction amount S3 corresponding to the current load change amount is calculated with reference to the map of the correction amount S3 corresponding to the load change amount shown in FIG. Here, the load change amount is, for example, a change amount dGN of the intake air amount GN during a predetermined period (for example, between TDCs). The map of the correction amount S3 in FIG. 8 is set so that the correction amount S3 increases (the retardation amount of the air-fuel ratio detection timing increases) as the load change amount increases. The map of the correction amount S3 is created in advance based on tests and design data, and is stored in the ROM of the ECU 39.

Thereafter, the routine proceeds to step 206, where the correction amounts S1 to S3 are used to correct the base air-fuel ratio detection timing Sb to obtain the final air-fuel ratio detection timing S. Thus, the air-fuel ratio detection timing is corrected according to the ignition timing, the fuel injection timing, and the load change amount.
S = Sb + S1 + S2 + S3

  In the present embodiment described above, the air-fuel ratio detection timing is corrected in accordance with the exhaust flow velocity change factors (ignition timing, fuel injection timing, and load change amount), which are operating conditions that cause the exhaust flow velocity of the engine 11 to change. I have to. In this way, the exhaust flow rate changes in accordance with the exhaust flow rate change factor, and the phase of the output waveform of the air-fuel ratio sensor 36 changes (that is, the appropriate air-fuel ratio detection timing of each cylinder changes). Correspondingly, the air-fuel ratio detection timing can be corrected, and the deviation of the air-fuel ratio detection timing of each cylinder from the appropriate air-fuel ratio detection timing can be suppressed. Thereby, even if the exhaust gas flow rate changes due to operating conditions other than the load and rotation speed of the engine 11 (ignition timing, fuel injection timing, and load change amount), the deviation of the air-fuel ratio detection timing due to the change in the exhaust gas flow rate is suppressed. Therefore, it is possible to suppress a decrease in the estimation accuracy of the air-fuel ratio of each cylinder, and to correctly control the air-fuel ratio of each cylinder (control to reduce the air-fuel ratio variation between the cylinders).

  Specifically, when the ignition timing changes, the exhaust pressure changes due to the change in combustion timing, and the exhaust flow velocity changes, so the phase of the output waveform of the air-fuel ratio sensor 36 changes. For example, as shown in FIG. 9, when the ignition timing is retarded, the exhaust gas flow rate increases, and the phase of the output waveform of the air-fuel ratio sensor 36 changes in the advance direction (see the broken line in FIG. 9).

  Therefore, in this embodiment, the correction amount S1 is calculated according to the ignition timing (for example, the retard amount from the base ignition timing), and the base air-fuel ratio detection timing is corrected using this correction amount S1 to obtain the final empty By obtaining the fuel ratio detection timing, the air fuel ratio detection timing is corrected according to the ignition timing. In this way, the exhaust flow rate changes due to a change in the ignition timing (for example, the ignition timing retardation during the catalyst warm-up control), and the phase of the output waveform of the air-fuel ratio sensor 36 changes. The fuel ratio detection timing can be corrected, and the deviation of the air fuel ratio detection timing of each cylinder can be suppressed.

  Further, when the fuel injection timing changes, the combustion state changes and the exhaust flow velocity changes, so the phase of the output waveform of the air-fuel ratio sensor 36 changes. For example, as shown in FIG. 10, when the fuel injection timing changes from the intake stroke to the compression stroke (that is, switching from the intake stroke injection to the compression stroke injection), the exhaust gas flow rate increases, and the output waveform of the air-fuel ratio sensor 36 increases. The phase changes in the advance direction (see the broken line in FIG. 10).

  Therefore, in this embodiment, the correction amount S2 is calculated according to the fuel injection timing, the base air-fuel ratio detection timing is corrected using this correction amount S2, and the final air-fuel ratio detection timing is obtained, whereby the fuel injection The air-fuel ratio detection timing is corrected according to the timing. In this way, in response to a change in the fuel injection timing (for example, switching from intake stroke injection to compression stroke injection), the exhaust flow velocity changes, and the phase of the output waveform of the air-fuel ratio sensor 36 changes. The air-fuel ratio detection timing can be corrected, and the deviation of the air-fuel ratio detection timing of each cylinder can be suppressed.

  Further, when the load change amount changes, the change amount of the exhaust gas amount for a predetermined period changes, and the exhaust flow velocity changes, so the phase of the output waveform of the air-fuel ratio sensor 36 changes. Therefore, in this embodiment, the correction amount S3 is calculated according to the load change amount (for example, the intake air amount change amount), and the base air-fuel ratio detection timing is corrected using this correction amount S3 to obtain the final air-fuel ratio. By obtaining the detection timing, the air-fuel ratio detection timing is corrected according to the load change amount. In this way, the air-fuel ratio detection timing is corrected in response to a change in the output waveform phase of the air-fuel ratio sensor 36 due to a change in the exhaust flow velocity according to the load change amount during the engine 11 transition. This can suppress the deviation of the air-fuel ratio detection timing of each cylinder.

  In the above embodiment, the ignition timing, the fuel injection timing, and the load change amount are used as the exhaust flow velocity change factors, and the air-fuel ratio detection timing is corrected according to these ignition timing, fuel injection timing, and load change amount. Like to do. However, the present invention is not limited to this. For example, the air-fuel ratio detection timing may be corrected according to two or one of the ignition timing, the fuel injection timing, and the load change amount.

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 above embodiment, and may be changed as appropriate.
In the above embodiment, the present invention is applied to a four-cylinder engine. However, the present invention is not limited to this, and the present invention may be applied to a two-cylinder engine, a three-cylinder engine, or an engine having five or more cylinders.

  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 detection timing setting means, Cylinder-specific air-fuel ratio estimation means, Cylinder-specific Air-fuel ratio control means)

Claims (4)

An air-fuel ratio sensor (36) for detecting an air-fuel ratio of the exhaust gas is installed in an exhaust collecting portion (34a) where exhaust gases of the cylinders of the internal combustion engine (11) flow and merge to load the internal combustion engine (11). And an air-fuel ratio detection timing setting means (39) for setting an air-fuel ratio detection timing of each cylinder according to at least one of the rotation speed and the air-fuel ratio sensor detected at each air-fuel ratio detection timing of each cylinder Cylinder air-fuel ratio estimating means (39) for estimating the air-fuel ratio of each cylinder based on the detected value of (36), and cylinder-by-cylinder for controlling the air-fuel ratio of each cylinder based on the estimated air-fuel ratio of each cylinder In the air-fuel ratio control apparatus for each cylinder of the internal combustion engine provided with the air-fuel ratio control means (39),
The air-fuel ratio detection timing setting means (39) corrects the air-fuel ratio detection timing in accordance with an operating condition (hereinafter referred to as “exhaust flow rate change factor”) that causes a change in the exhaust flow rate of the internal combustion engine (11). A cylinder-by-cylinder air-fuel ratio control apparatus for an internal combustion engine.   The air-fuel ratio detection timing setting means (39) uses the ignition timing of the internal combustion engine (11) as the exhaust flow velocity change factor, and corrects the air-fuel ratio detection timing according to the ignition timing. Item 2. The air-fuel ratio control apparatus for each cylinder of the internal combustion engine according to Item 1.   The air-fuel ratio detection timing setting means (39) uses the fuel injection timing of the internal combustion engine (11) as the exhaust flow velocity change factor, and corrects the air-fuel ratio detection timing according to the fuel injection timing. The air-fuel ratio control apparatus for each cylinder of the internal combustion engine according to claim 1 or 2.   The air-fuel ratio detection timing setting means (39) uses a change amount of the load of the internal combustion engine (11) as the exhaust flow velocity change factor, and corrects the air-fuel ratio detection timing according to the change amount of the load. 4. A cylinder-by-cylinder air-fuel ratio control apparatus for an internal combustion engine according to any one of claims 1 to 3.

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