JP2008038784A - Cylinder-by-cylinder air-fuel ratio control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the deterioration in control accuracy of the cylinder-by-cylinder air-fuel ratio by erroneous learning of a cylinder-by-cylinder air-fuel ratio correction quantity, in a system for controlling the air-fuel ratio of respective cylinders based on a detecting value of one air-fuel ratio sensor arranged in an exhaust confluent part of an internal combustion engine. <P>SOLUTION: The air-fuel ratio of the respective cylinders is estimated based on the detecting value of the air-fuel ratio sensor 37 arranged in the exhaust confluent part 36; the cylinder-by-cylinder air-fuel ratio correction quantity is calculated based on the estimated air-fuel ratio of the respective cylinders; the cylinder-by-cylinder air-fuel ratio correction quantity is learnt by annealing processing; the air-fuel ratio (a fuel injection quantity) of an air-fuel mixture supplied to the respective cylinders, is corrected with respective cylinders based on the cylinder-by-cylinder air-fuel ratio correction quantity and its learning value; and is controlled so as to reduce a variation in the air-fuel ratio between the cylinders. The erroneous learning of the cylinder-by-cylinder air-fuel ratio correction quantity is prevented by prohibiting learning of the cylinder-by-cylinder air-fuel ratio correction quantity, when a state of falling wide of a predetermined range (an allowable range) in the cylinder-by-cylinder air-fuel ration correction quantity of any cylinder, continues for a whole, when controlling this cylinder-by-cylinder air-fuel ratio. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a cylinder of an internal combustion engine having a function of estimating an air-fuel ratio (cylinder-specific air-fuel ratio) of each cylinder based on a detection value of an air-fuel ratio sensor installed in an exhaust gas merging portion where exhaust gases of a plurality of cylinders merge. It is an invention related to another air-fuel ratio control device.

In recent years, as described in Patent Document 1 (Japanese Patent Application Laid-Open No. 2005-207405), a plurality of cylinders based on the output of one air-fuel ratio sensor installed at an exhaust merging portion where exhaust gases from a plurality of cylinders merge. The air-fuel ratio of each cylinder is estimated for each cylinder, and the air-fuel ratio correction amount (cylinder-by-cylinder correction amount) for each cylinder for correcting the variation in the air-fuel ratio for each cylinder is calculated. The correction amount is learned by a smoothing process or the like, and the cylinder-by-cylinder air-fuel ratio control is performed in which the air-fuel ratio (fuel injection amount) of a plurality of cylinders is controlled for each cylinder based on the cylinder-by-cylinder air-fuel ratio correction amount and the learned value. There is something that was made. Further, in the cylinder-by-cylinder air-fuel ratio control system of Patent Document 1, the learning value of the cylinder-by-cylinder air-fuel ratio correction amount is obtained under operating conditions in which it is difficult to estimate the cylinder-by-cylinder air-fuel ratio (it is difficult to calculate the cylinder-by-cylinder air-fuel ratio correction amount). Is used to perform the air-fuel ratio control for each cylinder.
JP 2005-207405 A

  In such a cylinder-by-cylinder air-fuel ratio control system, for example, the estimation accuracy of the cylinder-by-cylinder air-fuel ratio decreases due to a deviation in the sampling timing of the air-fuel ratio sensor output (air-fuel ratio detection timing of each cylinder), or the fuel injection system of each cylinder If the variation in fuel injection amount becomes large due to individual differences (manufacturing variation of fuel injection valves, deterioration over time, etc.), the variation in air-fuel ratio among cylinders will increase, and the cylinder-by-cylinder air-fuel ratio correction amount and its learning value will increase. May be. However, as the cylinder-by-cylinder air-fuel ratio correction amount and its learning value increase, their accuracy is considered to deteriorate. Therefore, if the learning value of the cylinder-by-cylinder air-fuel ratio correction amount is updated indefinitely, the cylinder-by-cylinder air-fuel ratio correction amount is erroneously learned. As a result, the cylinder-by-cylinder air-fuel ratio control may work in the wrong direction, and the accuracy of the cylinder-by-cylinder air-fuel ratio control may deteriorate.

  The present invention has been made in view of such circumstances, and therefore the object of the present invention is to provide a cylinder of an internal combustion engine that can prevent deterioration in accuracy of cylinder-by-cylinder air-fuel ratio control due to erroneous learning of the cylinder-by-cylinder air-fuel ratio correction amount. Another object is to provide a separate air-fuel ratio control apparatus.

  In order to achieve the above object, according to the first aspect of the present invention, an air-fuel ratio sensor for detecting an air-fuel ratio of the exhaust gas is installed at an exhaust merging portion where exhaust gases of a plurality of cylinders of the internal combustion engine merge, Cylinder air-fuel ratio estimating means for estimating the air-fuel ratio of each cylinder based on the detection value of the air-fuel ratio sensor, and air-fuel ratio correction of each cylinder for correcting the inter-cylinder variation of the air-fuel ratio for each of the plurality of cylinders Cylinder-by-cylinder air-fuel ratio correction amount calculating means for calculating the amount (hereinafter referred to as “cylinder-by-cylinder air-fuel ratio correction amount”), cylinder-by-cylinder learning means for learning the cylinder-by-cylinder air-fuel ratio correction amount, And / or cylinder-specific air-fuel ratio control means for performing cylinder-specific air-fuel ratio control that corrects the fuel injection amount of each cylinder based on the learned value to reduce the air-fuel ratio variation between cylinders. In the air-fuel ratio control device, either One or cylinder air-fuel ratio correction amount of two or more cylinders is obtained so as to prohibit the learning prohibition means learning cylinder air-fuel ratio correction amount by the cylinder learning means when out of a predetermined range. In this way, learning of the cylinder-by-cylinder air-fuel ratio correction amount can be prohibited when the cylinder-by-cylinder air-fuel ratio correction amount of any one or more cylinders deviates from the predetermined range (allowable range). Thus, erroneous learning of the cylinder-by-cylinder air-fuel ratio correction amount can be prevented, and deterioration in accuracy of the cylinder-by-cylinder air-fuel ratio control can be prevented.

  In this case, when learning the air-fuel ratio correction amount for each cylinder for each operating region of the internal combustion engine as in claim 2, the air-fuel ratio correction amount for each cylinder of any one or more cylinders falls within a predetermined range. The learning of the cylinder-by-cylinder air-fuel ratio correction amount may be prohibited only for the deviated operation region. In this way, the learning of the cylinder-by-cylinder air-fuel ratio correction amount is prohibited only in the operation region where the cylinder-by-cylinder air-fuel ratio correction amount is outside the predetermined range, thereby preventing erroneous learning of the cylinder-by-cylinder air-fuel ratio correction amount. In other operating regions where the air-fuel ratio correction amount falls within the predetermined range, learning of the cylinder-by-cylinder air-fuel ratio correction amount can be continued to improve the learning accuracy of the cylinder-by-cylinder air-fuel ratio correction amount.

  According to a third aspect of the present invention, learning of the cylinder-by-cylinder air-fuel ratio correction amount by the cylinder-by-cylinder learning unit may be prohibited only for cylinders or cylinder groups in which the cylinder-by-cylinder air-fuel ratio correction amount is outside a predetermined range. In this way, learning of the cylinder-by-cylinder air-fuel ratio correction amount is prohibited only for the cylinders or cylinder groups whose cylinder-by-cylinder air-fuel ratio correction amount is outside the predetermined range, thereby preventing erroneous learning of the cylinder-by-cylinder air-fuel ratio correction amount. For other cylinders or cylinder groups in which the cylinder-by-cylinder air-fuel ratio correction amount falls within the predetermined range, learning of the cylinder-by-cylinder air-fuel ratio correction amount can be continued to improve the learning accuracy of the cylinder-by-cylinder air-fuel ratio correction amount.

  Further, as in claim 4, in the operation region where the cylinder-by-cylinder air-fuel ratio correction amount of any one or more cylinders is out of the predetermined range, The learning of the cylinder specific air-fuel ratio correction amount by the cylinder specific learning means may be prohibited only for the cylinder group. In this way, it is possible to minimize the operation region and the cylinder in which learning of the air-fuel ratio correction amount for each cylinder is prohibited.

  Further, as described in claim 5, when the learning value of the cylinder-by-cylinder air-fuel ratio correction amount of any one or more cylinders is out of a predetermined range, You may make it prohibit learning. Even if it does in this way, the effect similar to the said Claim 1 can be acquired.

  Also in this case, as in the sixth aspect, the learning of the cylinder-by-cylinder air-fuel ratio correction amount is performed only in the operation region in which the learning value of the cylinder-by-cylinder air-fuel ratio correction amount of any one or more cylinders is out of the predetermined range. Or prohibiting learning of the cylinder-by-cylinder air-fuel ratio correction amount only for the cylinder or the cylinder group in which the cylinder-by-cylinder air-fuel ratio correction amount is outside the predetermined range, as in claim 7. As in claim 8, the learning value of the cylinder-by-cylinder air-fuel ratio correction amount is predetermined in the operating region where the learning value of the cylinder-by-cylinder air-fuel ratio correction amount of any one or more cylinders is outside the predetermined range. The learning of the cylinder-by-cylinder air-fuel ratio correction amount may be prohibited only for a cylinder or a cylinder group outside the range. In either case, the same effects as those of the inventions according to claims 2 to 4 can be obtained.

  Several embodiments embodying the best mode for carrying out the present invention will be described below.

A first embodiment of the present invention will be described with reference to FIGS.
First, a schematic configuration of the entire engine control system will be described with reference to FIG.
An air cleaner 13 is provided at the most upstream portion of the intake pipe 12 of an in-line four-cylinder engine 11 that is an internal combustion engine, for example, and an air flow meter 14 that detects the intake air amount is provided downstream of the air cleaner 13. . On the downstream side of the air flow meter 14, a throttle valve 15 whose opening is adjusted by a motor or the like and a throttle opening sensor 16 for detecting the throttle opening are provided.

  Further, a surge tank 17 is provided on the downstream side of the throttle valve 15, and an intake pipe pressure sensor 18 for detecting the intake pipe pressure is provided in the surge tank 17. The surge tank 17 is provided with an intake manifold 19 for introducing air into each cylinder of the engine 11, and a fuel injection valve 20 for injecting fuel is attached in the vicinity of the intake port of the intake manifold 19 of each cylinder. Yes. During engine operation, the fuel in the fuel tank 21 is sent to the delivery pipe 23 by the fuel pump 22 and fuel is injected from the fuel injection valve 20 of each cylinder at each injection timing of each cylinder. A fuel pressure sensor 24 that detects fuel pressure (fuel pressure) is attached to the delivery pipe 23.

  Further, the engine 11 is provided with variable valve timing mechanisms 27 and 28 for changing the opening and closing timings of the intake valve 25 and the exhaust valve 26, respectively. Further, the engine 11 is provided with an intake cam angle sensor 31 and an exhaust cam angle sensor 32 that output a cam angle signal in synchronization with the rotation of the intake cam shaft 29 and the exhaust cam shaft 30, and the rotation of the crank shaft of the engine 11. Is provided with a crank angle sensor 33 for outputting a pulse of a crank angle signal at every predetermined crank angle (for example, every 30 ° C. A).

  On the other hand, an air-fuel ratio sensor 37 for detecting the air-fuel ratio of the exhaust gas is installed in the exhaust gas converging portion 36 where the exhaust manifold 35 of each cylinder of the engine 11 joins. A catalyst 38 such as a three-way catalyst for purifying CO, HC, NOx and the like is provided.

  Outputs of various sensors such as the air-fuel ratio sensor 37 are input to an engine control circuit (hereinafter referred to as “ECU”) 40. The ECU 40 is mainly composed of a microcomputer, and executes various engine control programs stored in a built-in ROM (storage medium), so that the fuel of the fuel injection valve 20 of each cylinder according to the engine operating state. Control injection quantity and ignition timing.

  In the first embodiment, the ECU 40 executes the routines for cylinder-by-cylinder air-fuel ratio control in FIGS. 2 to 5, thereby using the cylinder-by-cylinder air-fuel ratio estimation model to be described later during engine operation. Based on the detected value (the actual air-fuel ratio of the exhaust gas flowing through the exhaust gas merging portion 36), the air-fuel ratio of each cylinder (air-fuel ratio for each cylinder) is estimated, and the average value of the estimated air-fuel ratios of all cylinders is calculated. The value is set to the reference air-fuel ratio (target air-fuel ratio for all cylinders), and the deviation between the estimated air-fuel ratio of each cylinder (the estimated air-fuel ratio for each cylinder) and the reference air-fuel ratio is calculated for each cylinder. A fuel correction coefficient (cylinder-by-cylinder air-fuel ratio correction amount) for the fuel injection amount of each cylinder is calculated so as to decrease, and this cylinder-by-cylinder air-fuel ratio correction amount is learned by smoothing processing, etc. And the fuel injection amount of each cylinder based on the learned value It is, controlled so as to reduce the air-fuel ratio variation among the cylinders fuel ratio of a mixture supplied to each cylinder is corrected for each cylinder (hereinafter, this control of cylinder air-fuel ratio control). At this time, the cylinder-by-cylinder air-fuel ratio correction amount is learned by a smoothing process or the like, and the learned value is updated and stored for each cylinder in a rewritable nonvolatile memory (not shown) such as a backup RAM of the ECU 40. Note that, under operating conditions in which it is difficult to estimate the cylinder-by-cylinder air-fuel ratio (calculation of the cylinder-by-cylinder air-fuel ratio correction amount), the cylinder-by-cylinder air-fuel ratio control is performed using the learning value of the cylinder-by-cylinder air-fuel ratio correction amount. May be.

  Here, a specific example of a model (hereinafter referred to as “cylinder-specific air-fuel ratio estimation model”) that estimates the air-fuel ratio of each cylinder based on the detection value of the air-fuel ratio sensor 37 (the actual air-fuel ratio of the exhaust gas flowing through the exhaust gas merging portion 36). An example will be described.

  Paying attention to the gas exchange in the exhaust gas merging section 36, the detected value of the air-fuel ratio sensor 37 is given a predetermined weight to the estimated air-fuel ratio history of each cylinder and the detected value history of the air-fuel ratio sensor 37 in the exhaust gas merging section 36, respectively. The model is obtained by multiplying and adding, and the air-fuel ratio of each cylinder is estimated using the model. At this time, a Kalman filter is used as an observer.

More specifically, a gas exchange model in the exhaust merging portion 36 is approximated by the following equation (1).
ys (t) = k1 * u (t-1) + k2 * u (t-2) -k3 * ys (t-1) -k4 * ys (t-2)
...... (1)
Here, yS is the detected value of the air-fuel ratio sensor 37, u is the air-fuel ratio of the gas flowing into the exhaust merging section 36, and k1 to k4 are constants.

  In the exhaust system, there are a primary delay element of gas inflow and mixing in the exhaust confluence 36 and a primary delay element due to a response delay of the air-fuel ratio sensor 37. Therefore, in the above equation (1), the history for the past two times is referred to in consideration of these first order lag elements.

When the above equation (1) is converted into a state space model, the following equations (2a) and (2b) are derived.
X (t + 1) = A.X (t) + B.u (t) + W (t) (2a)
Y (t) = C · X (t) + D · u (t) (2b)

  Here, A, B, C, and D are model parameters, Y is a detected value of the air-fuel ratio sensor 37, X is an estimated air-fuel ratio of each cylinder as a state variable, and W is noise.

Further, when the Kalman filter is designed by the above equations (2a) and (2b), the following equation (3) is obtained.
X ^ (k + 1 | k) = A.X ^ (k | k-1) + K {Y (k) -C.A.X ^ (k | k-1)} (3)
Here, X ^ (X hat) is the estimated air-fuel ratio of each cylinder, and K is the Kalman gain. The meaning of X ^ (k + 1 | k) represents that the estimated value of the next time (k + 1) is obtained from the estimated value of time (k).

  As described above, by configuring the cylinder-by-cylinder air-fuel ratio estimation model using the Kalman filter type observer, it is possible to sequentially estimate the air-fuel ratio of each cylinder as the combustion cycle progresses.

  In the first embodiment, the cylinder-by-cylinder air-fuel ratio correction amount calculated based on the deviation between the estimated air-fuel ratio (cylinder-by-cylinder estimated air-fuel ratio) of each cylinder and the reference air-fuel ratio is learned by a smoothing process or the like. Is updated and stored for each cylinder in a rewritable non-volatile memory (not shown) such as a backup RAM of the ECU 40. The larger the cylinder air-fuel ratio correction amount, the worse the learning accuracy. If the learning value of the fuel ratio correction amount is updated indefinitely, there is a possibility that the cylinder-by-cylinder air-fuel ratio correction amount is mislearned and the cylinder-by-cylinder air-fuel ratio control may work in the wrong direction. there is a possibility.

  As a countermeasure, in the first embodiment, the learning of the cylinder-by-cylinder air-fuel ratio correction amount is prohibited when a state in which the cylinder-by-cylinder air-fuel ratio correction amount is out of a predetermined range (allowable range) continues for a while. Therefore, erroneous learning of the cylinder-by-cylinder air-fuel ratio correction amount is prevented.

  The learning of the cylinder-by-cylinder air-fuel ratio control and the cylinder-by-cylinder air-fuel ratio correction amount described above is executed by the ECU 40 in accordance with the routines shown in FIGS. The processing contents of each routine will be described below.

[Air-fuel ratio control routine for each cylinder]
The cylinder-by-cylinder air-fuel ratio control main routine of FIG. 2 is started at every predetermined crank angle (for example, every 30 ° C. A) in synchronization with the output pulse of the crank angle sensor 33. As a role. When this routine is started, first, at step 101, it is determined whether or not an execution condition for the cylinder-by-cylinder air-fuel ratio control is satisfied. As execution conditions for the cylinder-by-cylinder air-fuel ratio control, for example, there are the following conditions (1) to (4).

(1) The air-fuel ratio sensor 37 is in an active state
(2) The air-fuel ratio sensor 37 is not determined to be abnormal (failure)
(3) The engine 11 is in a warm-up state (for example, the cooling water temperature is equal to or higher than a predetermined temperature).
(4) The engine operating range (for example, engine speed and intake pipe pressure) must be an operating range where air-fuel ratio estimation accuracy can be ensured.

  The execution condition of the cylinder-by-cylinder air-fuel ratio control is satisfied when all of these four conditions (1) to (4) are satisfied. If any one of the conditions is not satisfied, the execution condition is not satisfied. If this execution condition is not satisfied, this routine is terminated without performing the subsequent processing.

  On the other hand, if the execution condition is satisfied, the routine proceeds to step 102, where the air-fuel ratio detection timing (sample timing of the output of the air-fuel ratio sensor 37) of each cylinder is set according to the engine load (for example, intake pipe pressure) at that time. Set by map. Note that the air-fuel ratio detection timing of each cylinder may be set by a map according to the engine load and the engine speed.

  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 routine proceeds to step 104, the cylinder-by-cylinder air-fuel ratio control execution routine of FIG. 3 is executed, and this routine is terminated.

[Cylinder-specific air-fuel ratio control execution routine]
The cylinder-by-cylinder air-fuel ratio control execution routine of FIG. 3 is a subroutine executed in step 104 of the cylinder-by-cylinder air-fuel ratio control main routine of FIG. When this routine is started, first, at step 201, the output (air-fuel ratio detection value) of the air-fuel ratio sensor 37 is read. Thereafter, the routine proceeds to step 202 where the air-fuel ratio of the cylinder that is the current air-fuel ratio estimation target is estimated based on the detected value of the air-fuel ratio sensor 37 using the cylinder-by-cylinder air-fuel ratio estimation model. The process of step 202 serves as the cylinder-by-cylinder air-fuel ratio estimating means in the claims. Thereafter, the process proceeds to step 203, 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 routine proceeds to step 204, where the deviation between the estimated air-fuel ratio of each cylinder and the reference air-fuel ratio is calculated, and the cylinder-by-cylinder air-fuel ratio correction amount (fuel correction amount of each cylinder) is calculated so that the deviation becomes smaller. Thereafter, the routine proceeds to step 205, where a cylinder-by-cylinder air-fuel ratio correction amount learning routine of FIG. 4 described later is executed to learn the cylinder-by-cylinder air-fuel ratio correction amount.

  Then, in the next step 206, the air-fuel ratio of the air-fuel mixture supplied to each cylinder is changed to each cylinder by correcting the fuel injection amount of each cylinder using the cylinder-by-cylinder air-fuel ratio correction amount and the learning value thereof. Correction is performed every time and control is performed so as to reduce variation in the air-fuel ratio between cylinders.

[Cylinder-specific air-fuel ratio correction amount learning routine]
The cylinder-by-cylinder air-fuel ratio correction amount learning routine in FIG. 4 is a subroutine executed in step 205 of the cylinder-by-cylinder air-fuel ratio control execution routine in FIG. 3, and plays a role as cylinder-by-cylinder learning means in the claims. When this routine is started, first, at step 301, it is determined whether or not a learning execution condition is satisfied. Here, the learning execution conditions include, for example, the following two conditions (1) and (2).

(1) The air-fuel ratio control for each cylinder is being executed.
(2) The air-fuel ratio fluctuation amount is in a stable operating state with a predetermined value or less. If both of the above two conditions (1) and (2) are satisfied, the learning execution condition is satisfied, and any one of them is not satisfied. If there is a condition, the learning execution condition is not satisfied. If this learning execution condition is not satisfied, this routine is terminated without performing the subsequent processing.

  On the other hand, if the learning execution condition is satisfied, the routine proceeds to step 302, where a learning prohibition determination routine of FIG. 5 described later is executed, and the cylinder-by-cylinder air-fuel ratio correction amount is outside the predetermined range (outside the allowable range). When the state where the cylinder-by-cylinder air-fuel ratio correction amount of any cylinder is outside the predetermined range continues for a predetermined time, the learning prohibition flag is set to ON, meaning that learning is prohibited.

  Then, in the next step 303, it is determined whether or not the learning prohibition flag is set to ON meaning that learning is prohibited. If the learning prohibition flag is set to ON (learning prohibition), the subsequent processing is performed. This routine is terminated without any processing. This prohibits learning of the cylinder specific air-fuel ratio correction amount.

On the other hand, if the learning prohibition flag is OFF (learning permission), the routine proceeds to step 304, and the cylinder-by-cylinder air-fuel ratio correction amount of FIG. 7 stored in the rewritable nonvolatile memory (not shown) of the ECU 40. In the learning map, a learning area (learning area for updating the learning value of the cylinder-by-cylinder air-fuel ratio correction amount) corresponding to the current engine operating area (engine speed and load) is selected. Thereafter, the routine proceeds to step 305, where the smoothing value of the cylinder-by-cylinder air-fuel ratio correction amount is calculated for each cylinder by the following equation using the smoothing coefficient K.
Air-fuel ratio correction amount by cylinder Smoothing value =
{Previous annealing value × (K-1) + Current cylinder air-fuel ratio correction amount} / K

  Thereafter, the process proceeds to step 306, where it is determined whether it is the update timing of the cylinder-by-cylinder air-fuel ratio correction amount learning value. The learning value update timing is set so that the learning value update period is at least longer than the cylinder-by-cylinder correction amount calculation period. If it is determined in this step 306 that it is not the learning value update timing, this routine is immediately terminated.

  On the other hand, if it is determined in step 306 that it is the learning value update timing, the routine proceeds to step 307, where it is determined whether or not the absolute value of the cylinder-by-cylinder air-fuel ratio correction amount smoothing value is equal to or greater than a predetermined value THA. If the absolute value of the smoothed value is smaller than the predetermined value THA, it is determined that it is not necessary to update the learning value, and this routine is terminated.

  If it is determined in step 307 that the absolute value of the cylinder-by-cylinder air-fuel ratio correction amount is greater than or equal to the predetermined value THA, the process proceeds to step 308, where the map is based on the cylinder-by-cylinder air-fuel ratio correction amount annealing value. Thus, the learning value update amount is calculated. The map for calculating the learning value update amount is set so that the learning value update amount increases as the cylinder-by-cylinder air-fuel ratio correction amount smoothing value increases.

  Thereafter, the process proceeds to step 309, and the ECU 40 can rewrite the value obtained by adding the current learning value update amount to the previous cylinder-by-cylinder air-fuel ratio correction amount learning value as a new cylinder-by-cylinder air-fuel ratio correction amount learning value. Update and store in a non-volatile memory (not shown). At this time, the learning value in the learning region selected in step 304 in the cylinder-by-cylinder air-fuel ratio correction amount learning map in FIG. 7 is updated. Note that the cylinder-by-cylinder air-fuel ratio correction amount learning map in FIG. 7 is created for each cylinder.

[Learning prohibition judgment routine]
The learning prohibition determination routine of FIG. 5 is a subroutine executed in step 302 of the cylinder-by-cylinder air-fuel ratio correction amount learning routine of FIG. 4, and serves as learning prohibition means in the claims.

  When this routine is started, first, in step 401, the cylinder-by-cylinder air-fuel ratio correction amount is read, and in step 402, the cylinder-by-cylinder air-fuel ratio correction amount is outside the predetermined range (outside the allowable range). If the air-fuel ratio correction amount for each cylinder is within the predetermined range, learning of the air-fuel ratio correction amount for each cylinder is permitted. In this case, the process proceeds to step 406, the value of the delay time counter T that measures the duration of the state where the cylinder-by-cylinder air-fuel ratio correction amount is outside the predetermined range is reset to 0, and this routine is ended.

  On the other hand, if it is determined in step 402 that the cylinder-by-cylinder air-fuel ratio correction amount is outside the predetermined range, the process proceeds to step 403, where the delay time counter T is incremented and The duration of the state where the air-fuel ratio correction amount is outside the predetermined range is measured. Thereafter, the process proceeds to step 404, where it is determined whether or not the count time of the delay time counter T exceeds a predetermined value. If the count value of the delay time counter T does not exceed the predetermined value, this routine is ended as it is. Thereafter, when the count value of the delay time counter T exceeds a predetermined value, the process proceeds to step 405, the learning prohibition flag is set to ON (learning prohibition), and this routine is terminated.

A control example of the first embodiment described above will be described with reference to the time chart of FIG.
In the example of FIG. 6, at the time t1, the execution condition of the cylinder-by-cylinder air-fuel ratio control is satisfied, the cylinder-by-cylinder air-fuel ratio control is started, and the cylinder-by-cylinder air-fuel ratio correction amount of each cylinder # 1 to # 4 is calculated. . During execution of the cylinder-by-cylinder air-fuel ratio control, it is determined whether or not the cylinder-by-cylinder air-fuel ratio correction amount of each of the cylinders # 1 to # 4 is outside a predetermined range, and any cylinder (# 1 in the example of FIG. 6) is determined. ) At time t2 when the cylinder-by-cylinder air-fuel ratio correction amount is outside the predetermined range, the count-up operation of the delay time counter T is started, and the duration of the state where the cylinder-by-cylinder air-fuel ratio correction amount is outside the predetermined range is started. It is measured.

  Thereafter, at the time t3 when the count value of the delay time counter T exceeds a predetermined value, the learning prohibition flag is set to ON (learning prohibition). Thereafter, learning of the cylinder-by-cylinder air-fuel ratio correction amount is prohibited.

  According to the first embodiment described above, the learning of the cylinder-by-cylinder air-fuel ratio correction amount is prohibited when a state where the cylinder-by-cylinder air-fuel ratio correction amount is outside the predetermined range continues for a while. Thus, erroneous learning of the cylinder-by-cylinder air-fuel ratio correction amount can be prevented, and deterioration in accuracy of the cylinder-by-cylinder air-fuel ratio control can be prevented.

  Note that the present invention is not limited to a configuration in which learning of the cylinder-by-cylinder air-fuel ratio correction amount is prohibited when a state in which the cylinder-by-cylinder air-fuel ratio correction amount is outside the predetermined range continues for a while. The learning of the cylinder-by-cylinder air-fuel ratio correction amount may be prohibited when a state where the cylinder-by-cylinder air-fuel ratio correction amount of any two or more cylinders is outside the predetermined range continues for a while.

  In the present invention, the learning of the cylinder-by-cylinder air-fuel ratio correction amount may be prohibited only for the cylinder or the cylinder group in which the cylinder-by-cylinder air-fuel ratio correction amount is out of the predetermined range. In this way, learning of the cylinder-by-cylinder air-fuel ratio correction amount is prohibited only for the cylinders or cylinder groups whose cylinder-by-cylinder air-fuel ratio correction amount is outside the predetermined range, thereby preventing erroneous learning of the cylinder-by-cylinder air-fuel ratio correction amount. For other cylinders or cylinder groups in which the cylinder-by-cylinder air-fuel ratio correction amount falls within the predetermined range, learning of the cylinder-by-cylinder air-fuel ratio correction amount can be continued to improve the learning accuracy of the cylinder-by-cylinder air-fuel ratio correction amount.

  In the cylinder-by-cylinder air-fuel ratio correction amount learning routine of FIG. 4 described in the first embodiment, the cylinder-by-cylinder air-fuel ratio correction amount learning value is updated for each engine operating region (engine speed and load) (FIG. 7). reference).

  In consideration of this point, in the second embodiment of the present invention shown in FIGS. 8 and 9, when the cylinder-by-cylinder air-fuel ratio correction amount is out of the predetermined range, the cylinder-by-cylinder air-fuel ratio correction amount is predetermined. The learning of the cylinder-by-cylinder air-fuel ratio correction amount is prohibited only in the operation region outside the range, and the learning of the cylinder-by-cylinder air-fuel ratio correction amount is permitted in the other operation regions.

The processing contents of the routines shown in FIGS. 8 and 9 executed in the second embodiment will be described below.
The cylinder-by-cylinder air-fuel ratio correction amount learning routine of FIG. 8 is merely the addition of the determination process of step 303a after step 303 of the cylinder-by-cylinder air-fuel ratio correction amount learning routine of FIG. 4 described in the first embodiment. The processing of these steps is the same.

  In the cylinder-by-cylinder air-fuel ratio correction amount learning routine of FIG. 8, if it is determined in step 301 that the learning execution condition is satisfied, the routine proceeds to step 302, and a learning prohibition determination routine of FIG.

  Then, in the next step 303, it is determined whether or not the learning prohibition flag is set to ON meaning that learning is prohibited. If the learning prohibition flag is set to ON (learning prohibition), the process proceeds to step 303a. It is determined whether or not the current engine operation region (engine speed and load) is a learning prohibition region stored by a learning prohibition determination routine shown in FIG. As a result, if the current engine operation region is the learning prohibited region, this routine is terminated without performing the subsequent processing. Thereby, learning of the cylinder specific air-fuel ratio correction amount is prohibited only in the learning prohibited region.

  On the other hand, if the current engine operation region is not the learning prohibition region in step 303a, it is determined that the cylinder-by-cylinder air-fuel ratio correction amount can be learned, and the process proceeds to step 304 and the subsequent steps. In the same way, the cylinder-by-cylinder air-fuel ratio correction amount learning value in the learning region corresponding to the current engine operation region is updated.

  The learning prohibition determination routine of FIG. 9 is a subroutine executed in step 302 of the cylinder-by-cylinder air-fuel ratio correction amount learning routine of FIG. 8, and is subsequent to step 405 of the learning prohibition determination routine of FIG. 5 described in the first embodiment. Step 407 is simply added, and the other steps are the same.

  In the learning prohibition determination routine of FIG. 9, the learning prohibition flag is set to ON (learning) when a predetermined time elapses when the cylinder-by-cylinder air-fuel ratio correction amount is outside the predetermined range by the processing of steps 401 to 405. Set to (Prohibited). Thereafter, the process proceeds to step 407, where the current engine operation region is stored as a learning prohibition region in a rewritable nonvolatile memory (not shown) of the ECU 40, and thereafter, the cylinder-by-cylinder air-fuel ratio correction amount only for this learning prohibition region. Prohibit learning.

  In the second embodiment described above, learning of the cylinder-by-cylinder air-fuel ratio correction amount is prohibited only in the operation region where the cylinder-by-cylinder air-fuel ratio correction amount is outside the predetermined range, and the cylinder-by-cylinder air-fuel ratio correction amount is erroneously corrected. In other operating regions where the cylinder-by-cylinder air-fuel ratio correction amount falls within the predetermined range while preventing learning, learning of the cylinder-by-cylinder air-fuel ratio correction amount can be continued, and the learning accuracy of the cylinder-by-cylinder air-fuel ratio correction amount can be improved. be able to.

  Note that the present invention is not limited to a configuration in which learning of the cylinder-by-cylinder air-fuel ratio correction amount is prohibited only in the operation region in which the cylinder-by-cylinder air-fuel ratio correction amount is out of the predetermined range. The learning of the cylinder-by-cylinder air-fuel ratio correction amount may be prohibited only in the operation region where the cylinder-by-cylinder air-fuel ratio correction amount is out of the predetermined range.

  In the third embodiment of the present invention shown in FIG. 10 and FIG. 11, in the operation region where the cylinder-by-cylinder air-fuel ratio correction amount is out of the predetermined range, the cylinder in which the cylinder-by-cylinder air-fuel ratio correction amount is out of the predetermined range. Only the learning of the cylinder-by-cylinder air-fuel ratio correction amount is prohibited.

  The cylinder-by-cylinder air-fuel ratio correction amount learning routine of FIG. 10 is merely the addition of the determination process of step 303b after step 303a of the cylinder-by-cylinder air-fuel ratio correction amount learning routine of FIG. 8 described in the second embodiment. The processing of these steps is the same.

  In the cylinder-by-cylinder air-fuel ratio correction amount learning routine of FIG. 10, if it is determined in step 301 that the learning execution condition is satisfied, the routine proceeds to step 302, where a learning prohibition determination routine of FIG.

  Then, in the next step 303, it is determined whether or not the learning prohibition flag is set to ON meaning that learning is prohibited. If the learning prohibition flag is set to ON (learning prohibition), the process proceeds to step 303a. It is determined whether or not the current engine operation region (engine speed and load) is a learning prohibition region stored by a learning prohibition determination routine of FIG. As a result, if it is determined that the current engine operation region is the learning prohibition region, the process proceeds to step 303b, and the cylinder-by-cylinder air-fuel ratio correction amount learning value of the learning prohibition cylinder stored by the learning prohibition determination routine of FIG. If it is an update timing of the cylinder-by-cylinder air-fuel ratio correction amount learning value of the learning-inhibited cylinder, this routine is terminated without performing the subsequent processing. Thereby, learning of the cylinder-by-cylinder air-fuel ratio correction amount is prohibited only in the learning-inhibited region of the cylinder-by-cylinder air-fuel ratio correction amount learning map (see FIG. 7).

  On the other hand, if “No” is determined in step 303a or step 303b, that is, if the current engine operating region is not the learning prohibited region, or the learning value of the cylinder-by-cylinder air-fuel ratio correction amount learning value of the learning prohibited cylinder is determined. If it is not the update timing, it is judged that learning of the cylinder-by-cylinder air-fuel ratio correction amount is possible, the process proceeds to step 304 and the subsequent steps, and the cylinder-by-cylinder air-fuel ratio correction of the cylinders for which learning is permitted is performed in the same manner as in the first embodiment. The cylinder-by-cylinder air-fuel ratio correction amount learning value in the learning region corresponding to the current engine operation region in the amount learning map is updated.

  The learning prohibition determination routine of FIG. 11 is a subroutine executed in step 302 of the cylinder-by-cylinder air-fuel ratio correction amount learning routine of FIG. 10, and the processing of step 407 of the learning prohibition determination routine of FIG. 9 described in the second embodiment. Is changed to the process of step 407a, and the processes of the other steps are the same.

  In the learning prohibition determination routine of FIG. 11, when the state where the cylinder-by-cylinder air-fuel ratio correction amount is outside the predetermined range is reached for a predetermined time by the processing of steps 401 to 405, the learning prohibition flag is turned on (learning). Set to (Prohibited). Thereafter, the process proceeds to step 407a, where the current engine operating region is stored as a learning prohibition region, and the cylinder whose cylinder-by-cylinder air-fuel ratio correction amount is outside the predetermined range is stored as a learning prohibition cylinder. The learning of the cylinder-by-cylinder air-fuel ratio correction amount is prohibited only for the learning prohibition region in the cylinder-by-cylinder air-fuel ratio correction amount learning map.

  In the third embodiment described above, the cylinder-by-cylinder air-fuel ratio correction is performed only for the cylinder in which the cylinder-by-cylinder air-fuel ratio correction amount is outside the predetermined range in the operation region where the cylinder-by-cylinder air-fuel ratio correction amount is outside the predetermined range. Since the learning of the amount is prohibited, it is possible to minimize the operation region and the cylinder in which the learning of the cylinder-by-cylinder air-fuel ratio correction amount is prohibited, and to improve the learning accuracy of the cylinder-by-cylinder air-fuel ratio correction amount.

  Note that the present invention is not limited to a configuration in which learning of the cylinder-by-cylinder air-fuel ratio correction amount is prohibited only for the one cylinder in the operation region where the cylinder-by-cylinder air-fuel ratio correction amount is outside the predetermined range. The learning of the two or more cylinder-by-cylinder air-fuel ratio correction amounts may be prohibited in the operation region in which the cylinder-by-cylinder air-fuel ratio correction amount of any two or more cylinders is out of the predetermined range.

  Further, in the operating region where the cylinder-by-cylinder air-fuel ratio correction amount of any of the cylinders is out of the predetermined range, learning of the cylinder-by-cylinder air-fuel ratio correction amount may be prohibited for the cylinder group to which the cylinder belongs.

  In the first to third embodiments, learning of the cylinder-by-cylinder air-fuel ratio correction amount is prohibited when the cylinder-by-cylinder air-fuel ratio correction amount is out of the predetermined range. The learning of the cylinder-by-cylinder air-fuel ratio correction amount may be prohibited when the other air-fuel ratio correction amount learning value is out of a predetermined range. A fourth embodiment of the present invention that embodies this will be described below.

  In the fourth embodiment, the learning prohibition determination routine of FIG. 12 is executed. First, the cylinder-by-cylinder air-fuel ratio correction amount learning value is read (step 401a), and the cylinder-by-cylinder air-fuel ratio correction amount learning value is predetermined. It is determined whether or not the value is out of the range (step 402a), and the count value of the delay time counter T that measures the duration in which the cylinder-by-cylinder air-fuel ratio correction amount learning value is outside the predetermined range. When the value exceeds a predetermined value, the learning prohibition flag is set to ON which means that learning is prohibited (steps 403 to 405). The other processes are the same as those in the first embodiment.

A control example of the fourth embodiment will be described with reference to the time chart of FIG.
In the example of FIG. 13, at time t1, the cylinder-by-cylinder air-fuel ratio control execution condition is satisfied, the cylinder-by-cylinder air-fuel ratio control is started, and the cylinder-by-cylinder air-fuel ratio correction amount is calculated for each cylinder # 1 to # 4. .

  Thereafter, at time t2, the learning execution condition is satisfied, learning of the air-fuel ratio correction amount for each cylinder is started, and the air-fuel ratio correction amount learning value for each cylinder # 1 to # 4 is updated.

  Thereafter, it is determined whether the cylinder-by-cylinder air-fuel ratio correction amount learning value for each cylinder # 1 to # 4 is outside a predetermined range (outside the allowable range), and the cylinder-by-cylinder air-fuel ratio correction amount learning value for any cylinder is determined. At a time point t3 when it is outside the predetermined range, the count-up operation of the delay time counter T is started, and the duration time in which the cylinder-by-cylinder air-fuel ratio correction amount learning value is outside the predetermined range is measured.

  Thereafter, at the time t4 when the count value of the delay time counter T exceeds a predetermined value, the learning prohibition flag is set to ON (learning prohibition). Thereafter, learning of the cylinder-by-cylinder air-fuel ratio correction amount is prohibited.

  Also in the fourth embodiment described above, the same effect as in the first embodiment can be obtained. Note that the present invention is limited to a configuration in which learning of the cylinder-by-cylinder air-fuel ratio correction amount is prohibited when a state in which the cylinder-by-cylinder air-fuel ratio correction amount learning value of any one cylinder is outside the predetermined range continues for a while. The learning of the cylinder-by-cylinder air-fuel ratio correction amount is prohibited when the cylinder-by-cylinder air-fuel ratio correction amount learning value of any two or more cylinders is outside the predetermined range for a while. good.

  Further, according to the present invention, the learning of the cylinder-by-cylinder air-fuel ratio correction amount may be prohibited only for the cylinder or the cylinder group whose cylinder-by-cylinder air-fuel ratio correction amount learning value is out of the predetermined range. In this way, the learning of the cylinder-by-cylinder air-fuel ratio correction amount is prohibited only for the cylinder or the cylinder group whose cylinder-by-cylinder air-fuel ratio correction amount learning value is outside the predetermined range, thereby preventing erroneous learning of the cylinder-by-cylinder air-fuel ratio correction amount. However, for other cylinders or cylinder groups in which the cylinder-by-cylinder air-fuel ratio correction amount learning value falls within the predetermined range, the learning of the cylinder-by-cylinder air-fuel ratio correction amount is continued to improve the learning accuracy of the cylinder-by-cylinder air-fuel ratio correction amount. be able to.

  In the fifth embodiment of the present invention shown in FIG. 14, when the cylinder-by-cylinder air-fuel ratio correction amount learning value of any cylinder is out of the predetermined range (allowable range), the cylinder-by-cylinder air-fuel ratio correction amount learning value falls within the predetermined range. The learning of the cylinder-by-cylinder air-fuel ratio correction amount is prohibited only for the out-of-operation region, and the learning of the cylinder-by-cylinder air-fuel ratio correction amount is permitted in the other operation regions.

  The learning prohibition determination routine of FIG. 14 executed in the fifth embodiment is simply the addition of the processing of step 407 after step 405 of the learning prohibition determination routine of FIG. 12 described in the fourth embodiment. The process is the same.

  In the learning prohibition determination routine of FIG. 14, the learning prohibition flag is turned on when a state where the learning value of the cylinder air-fuel ratio correction amount for any of the cylinders is outside the predetermined range elapses for a predetermined time by the processing of steps 401 a to 405. Set to (learning prohibited). Thereafter, the process proceeds to step 407, where the current engine operation region is stored as a learning prohibition region in a rewritable nonvolatile memory (not shown) of the ECU 40, and thereafter, the cylinder-by-cylinder air-fuel ratio correction amount only for this learning prohibition region. Prohibit learning. In the fifth embodiment, the cylinder-by-cylinder air-fuel ratio correction amount learning routine of FIG. 8 described in the second embodiment is executed.

  In the fifth embodiment described above, the cylinder-by-cylinder air-fuel ratio correction amount is prohibited by prohibiting learning of the cylinder-by-cylinder air-fuel ratio correction amount only in the operation region where the cylinder-by-cylinder air-fuel ratio correction amount learning value is outside the predetermined range. In other operating regions where the learning value of the cylinder-by-cylinder air-fuel ratio correction amount falls within the predetermined range, the learning of the cylinder-by-cylinder air-fuel ratio correction amount can be continued. Learning accuracy can be increased.

  Note that the present invention is not limited to a configuration in which learning of the cylinder-by-cylinder air-fuel ratio correction amount is prohibited only in the operation region where the cylinder-by-cylinder air-fuel ratio correction amount learning value of any one cylinder is outside the predetermined range. The learning of the cylinder-by-cylinder air-fuel ratio correction amount may be prohibited only in the operation region in which the cylinder-by-cylinder air-fuel ratio correction amount learning value of one or more cylinders is outside the predetermined range.

  In the sixth embodiment of the present invention shown in FIG. 15, in the operating region where the cylinder-by-cylinder air-fuel ratio correction amount learning value of any of the cylinders is out of the predetermined range, the cylinders whose cylinder-by-cylinder air-fuel ratio correction amount learning value is out of the predetermined range. The learning of the cylinder-by-cylinder air-fuel ratio correction amount is prohibited only for.

  The learning prohibition determination routine of FIG. 15 is the same as the processing of step 407a, except that the processing of step 407 of the learning prohibition determination routine of FIG. 14 described in the fifth embodiment is the same.

  In the learning prohibition determination routine of FIG. 15, the learning prohibition flag is turned on when a state where the learning value of the air-fuel ratio correction amount for each cylinder is outside the predetermined range elapses for a predetermined time by the processing of steps 401 a to 405. Set to (learning prohibited). Thereafter, the process proceeds to step 407a, where the current engine operation region is stored as a learning prohibition region, and the cylinder whose cylinder-by-cylinder air-fuel ratio correction amount learning value is out of the predetermined range is stored as a learning prohibition cylinder. The learning of the cylinder-by-cylinder air-fuel ratio correction amount is prohibited only in the learning prohibition region in the cylinder-by-cylinder air-fuel ratio correction amount learning map. In the sixth embodiment, the cylinder-by-cylinder air-fuel ratio correction amount learning routine of FIG. 10 described in the third embodiment is executed.

  In the sixth embodiment described above, in the operation region where the cylinder-by-cylinder air-fuel ratio correction amount learning value of any of the cylinders is out of the predetermined range, only the cylinders for which the cylinder-by-cylinder air-fuel ratio correction amount learning value is out of the predetermined range are used. Since the learning of the separate air-fuel ratio correction amount is prohibited, it is possible to minimize the operation region and the cylinder in which the learning of the individual cylinder air-fuel ratio correction amount is prohibited, and to improve the learning accuracy of the individual air-fuel ratio correction amount. be able to.

  Note that the present invention is limited to a configuration in which learning of the cylinder-by-cylinder air-fuel ratio correction amount is prohibited only for the one cylinder in the operation region in which the cylinder-by-cylinder air-fuel ratio correction amount learning value of any one cylinder is outside the predetermined range. Alternatively, learning of the two or more cylinder-by-cylinder air-fuel ratio correction amounts may be prohibited in an operating region where the cylinder-by-cylinder air-fuel ratio correction amount learning value of any two or more cylinders is outside a predetermined range. .

  Further, in the operation region where the cylinder-by-cylinder air-fuel ratio correction amount learning value of any cylinder is out of a predetermined range, learning of the cylinder-by-cylinder air-fuel ratio correction amount may be prohibited for the cylinder group to which the cylinder belongs.

  In addition, the present invention is not limited to the intake port injection engine, and can be implemented with various modifications without departing from the gist, such as being applicable to a cylinder injection engine.

It is a schematic block diagram of the whole engine control system in Example 1 of this invention. 4 is a flowchart showing a process flow of a cylinder-by-cylinder air-fuel ratio control main routine according to the first embodiment. 4 is a flowchart showing a flow of processing of a cylinder-by-cylinder air-fuel ratio control execution routine according to the first embodiment. 6 is a flowchart illustrating a processing flow of a cylinder-by-cylinder air-fuel ratio correction amount learning routine according to the first embodiment. 6 is a flowchart illustrating a processing flow of a learning prohibition determination routine according to the first exemplary embodiment. 3 is a time chart for explaining a control example of the first embodiment. It is a figure which shows notionally the air-fuel ratio correction amount learning map according to cylinder of Example 1 conceptually. 7 is a flowchart illustrating a processing flow of a cylinder-by-cylinder air-fuel ratio correction amount learning routine according to a second embodiment. 10 is a flowchart illustrating a processing flow of a learning prohibition determination routine according to the second embodiment. FIG. 10 is a flowchart illustrating a processing flow of a cylinder-by-cylinder air-fuel ratio correction amount learning routine according to a third embodiment. 12 is a flowchart illustrating a processing flow of a learning prohibition determination routine according to the third embodiment. 14 is a flowchart illustrating a processing flow of a learning prohibition determination routine according to the fourth embodiment. 10 is a time chart for explaining a control example of the fourth embodiment. 14 is a flowchart illustrating a processing flow of a learning prohibition determination routine according to the fifth embodiment. 18 is a flowchart illustrating a processing flow of a learning prohibition determination routine according to the sixth embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Engine (internal combustion engine), 12 ... Intake pipe, 14 ... Air flow meter, 15 ... Throttle valve, 19 ... Intake manifold, 20 ... Fuel injection valve, 22 ... Fuel pump, 24 ... Fuel pressure sensor, 27, 28 ... Variable valve Timing mechanism 35 ... Exhaust manifold 36 ... Exhaust gas merging section 37 ... Air-fuel ratio sensor 38 ... Catalyst 40 ... ECU (Each cylinder air-fuel ratio estimation means, Cylinder air-fuel ratio correction amount calculation means, Cylinder air-fuel ratio control means , Learning means by cylinder, learning prohibition means)

Claims (8)

An air-fuel ratio sensor for detecting the air-fuel ratio of the exhaust gas is installed at an exhaust gas merging portion where the exhaust gases of a plurality of cylinders of the internal combustion engine merge, and the air-fuel ratio of each cylinder is estimated based on the detection value of the air-fuel ratio sensor And a cylinder-by-cylinder air-fuel ratio estimating means for calculating an air-fuel ratio correction amount (hereinafter referred to as “cylinder-by-cylinder air-fuel ratio correction amount”) for each cylinder for correcting the inter-cylinder variation of the air-fuel ratio for each cylinder. Cylinder air-fuel ratio correction amount calculation means, cylinder-specific learning means for learning the cylinder-by-cylinder air-fuel ratio correction amount, and fuel injection amount of each cylinder is corrected based on the cylinder-by-cylinder air-fuel ratio correction amount and / or its learned value In the cylinder-by-cylinder air-fuel ratio control device of the internal combustion engine, the cylinder-by-cylinder air-fuel ratio control means for executing the cylinder-by-cylinder air-fuel ratio control to reduce the air-fuel ratio variation between the cylinders,
Learning prohibiting means for prohibiting learning of the cylinder-by-cylinder air-fuel ratio correction amount by the cylinder-by-cylinder learning means when the cylinder-by-cylinder air-fuel ratio correction amount of any one or more cylinders is out of a predetermined range; A cylinder-by-cylinder air-fuel ratio control apparatus for an internal combustion engine. The cylinder-specific learning means learns the cylinder-specific air-fuel ratio correction amount for each operating region of the internal combustion engine,
The learning prohibiting means prohibits learning of the cylinder-by-cylinder air-fuel ratio correction amount by the cylinder-by-cylinder learning means only in an operation region where the cylinder-by-cylinder air-fuel ratio correction amount of the one or more cylinders is out of a predetermined range. The air-fuel ratio control apparatus for each cylinder of the internal combustion engine according to claim 1.   2. The learning prohibiting unit prohibits learning of the cylinder-by-cylinder air-fuel ratio correction amount by the cylinder-by-cylinder learning unit only for a cylinder or a cylinder group in which the cylinder-by-cylinder air-fuel ratio correction amount is out of a predetermined range. The cylinder-by-cylinder air-fuel ratio control apparatus according to claim 1. The cylinder-specific learning means learns the cylinder-specific air-fuel ratio correction amount for each operating region of the internal combustion engine,
The learning prohibiting means includes a cylinder or a cylinder in which the cylinder-by-cylinder air-fuel ratio correction amount is out of the predetermined range in an operation region in which the cylinder-by-cylinder air-fuel ratio correction amount is out of the predetermined range. 2. The cylinder-by-cylinder air-fuel ratio control apparatus for an internal combustion engine according to claim 1, wherein learning of the cylinder-by-cylinder air-fuel ratio correction amount by the cylinder-by-cylinder learning unit is prohibited only for the group. An air-fuel ratio sensor for detecting the air-fuel ratio of the exhaust gas is installed at an exhaust gas merging portion where the exhaust gases of a plurality of cylinders of the internal combustion engine merge, and the air-fuel ratio of each cylinder is estimated based on the detection value of the air-fuel ratio sensor And a cylinder-by-cylinder air-fuel ratio estimating means for calculating an air-fuel ratio correction amount (hereinafter referred to as “cylinder-by-cylinder air-fuel ratio correction amount”) for each cylinder for correcting the inter-cylinder variation of the air-fuel ratio for each cylinder. Cylinder air-fuel ratio correction amount calculation means, cylinder-specific learning means for learning the cylinder-by-cylinder air-fuel ratio correction amount, and fuel injection amount of each cylinder is corrected based on the cylinder-by-cylinder air-fuel ratio correction amount and / or its learned value In the cylinder-by-cylinder air-fuel ratio control device of the internal combustion engine, the cylinder-by-cylinder air-fuel ratio control means for executing the cylinder-by-cylinder air-fuel ratio control to reduce the air-fuel ratio variation between the cylinders,
Learning prohibiting means for prohibiting learning of the cylinder-by-cylinder air-fuel ratio correction amount by the cylinder-by-cylinder learning means when the learning value of the cylinder-by-cylinder air-fuel ratio correction amount of any one or more cylinders is out of a predetermined range; A cylinder-by-cylinder air-fuel ratio control apparatus for an internal combustion engine. The cylinder-specific learning means learns the cylinder-specific air-fuel ratio correction amount for each operating region of the internal combustion engine,
The learning prohibiting means sets the cylinder-by-cylinder air-fuel ratio correction amount by the cylinder-by-cylinder learning means only in an operating region where the learning value of the cylinder-by-cylinder air-fuel ratio correction amount of any one or more cylinders is out of a predetermined range. 6. The cylinder-by-cylinder air-fuel ratio control apparatus for an internal combustion engine according to claim 5, wherein learning is prohibited.   6. The learning prohibiting unit prohibits learning of the cylinder-by-cylinder air-fuel ratio correction amount by the cylinder-by-cylinder learning unit only for a cylinder or a cylinder group in which the cylinder-by-cylinder air-fuel ratio correction amount is out of a predetermined range. The cylinder-by-cylinder air-fuel ratio control apparatus for an internal combustion engine according to claim 1. The cylinder-specific learning means learns the cylinder-specific air-fuel ratio correction amount for each operating region of the internal combustion engine,
The learning prohibiting means is configured such that the learning value of the cylinder-by-cylinder air-fuel ratio correction amount is within a predetermined range in an operation region where the learning value of the cylinder-by-cylinder air-fuel ratio correction amount of the one or more cylinders is outside a predetermined range. 6. The cylinder-by-cylinder air-fuel ratio control apparatus for an internal combustion engine according to claim 5, wherein learning of the cylinder-by-cylinder air-fuel ratio correction amount by the cylinder-by-cylinder learning means is prohibited only for cylinders or cylinder groups that are out of range.

Images