JP2008064077A - Control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a catalyst from becoming an overheat state by the occurrence of an abnormal cylinder of largely fluctuating the air-fuel ratio in the lean direction, in a system for controlling the air-fuel ratio of respective cylinders, based on output of an air-fuel ratio sensor arranged in an exhaust confluent part of an internal combustion engine. <P>SOLUTION: The existence of a lean abnormal cylinder of largely fluctuating the air-fuel ratio in the lean direction, is determined based on the air-fuel ratio of the respective cylinders estimated based on the output of the air-fuel ratio sensor 37. When determining that there is the lean abnormal cylinder, reaction heat such as the catalyst 38 becomes the overheat state (a state of being damaged by heat), is not generated by limiting an exhaust gas quantity (an oxygen quantity) flowing in the catalyst 38 by performing limiting operation control for limiting engine output. Thus, even when the air-fuel ratio of exhaust gas flowing in the catalyst 38 is deviated in the lean direction by the occurrence of the lean abnormal cylinder, the catalyst 38 can be prevented from becoming the overheat state. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an internal combustion engine control device having a function of estimating or measuring the air-fuel ratio of each cylinder (air-fuel ratio for each cylinder) based on the output of an air-fuel ratio sensor.

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. There is one that performs cylinder-by-cylinder air-fuel ratio control for controlling the air-fuel ratio (fuel injection amount) of a plurality of cylinders for each cylinder based on the correction amount.
JP 2005-207405 A

  By the way, in the above-described cylinder-by-cylinder air-fuel ratio control system, when air-fuel ratio control becomes difficult due to a failure of a fuel injection valve or the like in any cylinder, the air-fuel ratio of the abnormal cylinder in which the air-fuel ratio control is difficult varies greatly in the lean direction. As a result, the air-fuel ratio of the exhaust gas flowing into the catalyst (that is, the exhaust gas in which the exhaust gas from the abnormal cylinder and the exhaust gas from the normal cylinder are mixed) may shift in the lean direction. If the air-fuel ratio of the exhaust gas flowing into the catalyst deviates in the lean direction, the lean component amount (oxygen amount) flowing into the catalyst increases and the oxidation reaction of rich components such as HC and CO is promoted, and the reaction heat The catalyst may overheat and be damaged.

  The present invention has been made in view of such circumstances, and the object of the present invention is therefore an internal combustion engine that can prevent the catalyst from becoming overheated due to the occurrence of an abnormal air-fuel ratio cylinder. It is to provide an engine control device.

  In order to achieve the above object, according to the first aspect of the present invention, the air-fuel ratio of each cylinder (hereinafter referred to as “cylinder-by-cylinder air-fuel ratio”) is based on the output of an air-fuel ratio sensor that detects the air-fuel ratio of the exhaust gas of the internal combustion engine. In a control apparatus for an internal combustion engine comprising a cylinder-by-cylinder air-fuel ratio detection means for estimating or measuring the air-fuel ratio, and an exhaust gas purification catalyst installed downstream of the air-fuel ratio sensor, an abnormality in the air-fuel ratio is determined based on the cylinder-by-cylinder air-fuel ratio. Limit operation control means for limiting the output and / or rotational speed of the internal combustion engine when it is determined that there is an abnormal cylinder by determining whether there is an abnormal cylinder (hereinafter referred to as "abnormal cylinder"). Is to be executed.

  In this configuration, since the limited operation control is performed to limit the output and rotation speed of the internal combustion engine when it is determined that there is an abnormal cylinder, the air-fuel ratio of the exhaust gas flowing into the catalyst due to the occurrence of the abnormal cylinder is lean. Even when the direction (the direction in which the amount of oxygen flowing into the catalyst increases and the oxidation reaction is promoted) is shifted, the amount of exhaust gas flowing into the catalyst (oxygen amount) can be reduced by limiting the output and rotational speed of the internal combustion engine. By limiting, the reaction heat can be suppressed so that the catalyst does not enter an overheated state (a state damaged by heat), and the catalyst can be prevented from being overheated due to the occurrence of an abnormal cylinder.

  In this case, as in claim 2, when the catalyst overheat determination means determines whether or not there is a possibility that the catalyst is overheated, and when it is determined that there is an abnormal cylinder and the catalyst is likely to be overheated Alternatively, the limited operation control may be executed. In this way, when it is determined that there is an abnormal cylinder and it is determined that there is a possibility that the catalyst will be in an overheated state (a state of being damaged by heat), the limited operation control is executed and the catalyst is in an overheated state. If it is determined that there is no possibility that the catalyst will be overheated even if it is determined that there is an abnormal cylinder, the limited operation control is not performed and the drivability by the limited operation control is determined. Can be avoided.

  Further, as in claim 3, the presence or absence of an abnormal cylinder may be determined for each operation region of the internal combustion engine, and the limited operation control may be performed in the operation region determined to have an abnormal cylinder. In this way, the limited operation control is executed in the operation region determined to have an abnormal cylinder to reliably prevent the catalyst from being overheated, while the limited operation control is not executed in other operation regions. Thus, a decrease in drivability due to the limited operation control can be avoided.

  Further, as a specific method of the limited operation control, the limited operation control may be executed by controlling the throttle opening as in the fourth aspect. For example, when the output or rotational speed of the internal combustion engine becomes equal to or higher than a predetermined value, the throttle opening is controlled in the closing direction (increase direction of the intake air amount) to reduce the output or rotational speed of the internal combustion engine, The output and rotational speed of the internal combustion engine can be limited to a predetermined value or less.

  Further, the limited operation control may be executed by executing the fuel cut control as in claim 5, or the limited operation control is executed by executing the ignition cut control as in claim 6. You may make it do. For example, when the output or rotational speed of the internal combustion engine exceeds a predetermined value, the output or rotational speed of the internal combustion engine is reduced by performing fuel cut control or ignition cut control to reduce the output or rotational speed of the internal combustion engine. Can be limited to a predetermined value or less.

  In the case of a system having a variable valve device that changes the opening / closing characteristics of the intake valve and / or the exhaust valve of the internal combustion engine as in claim 7, the limited operation control is executed by controlling the variable valve device. You may make it do. For example, when the output of the internal combustion engine exceeds a predetermined value, the opening / closing characteristics (opening / closing timing, lift amount, valve opening period, etc.) of the intake valve and exhaust valve are reduced in the variable valve device in a direction in which the output of the internal combustion engine decreases. By changing the output of the internal combustion engine to reduce the output, the output of the internal combustion engine can be limited to a predetermined value or less.

  Further, the limited operation control may be executed by controlling the gear ratio of the transmission as in the eighth aspect. For example, when the rotational speed of the internal combustion engine exceeds a predetermined value, the rotational speed of the internal combustion engine is decreased by changing the speed ratio of the transmission in a direction in which the rotational speed of the internal combustion engine is decreased. The rotation speed can be limited to a predetermined value or less.

  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 cylinder-by-cylinder air-fuel ratio control routine of FIG. 2 to detect the detected value (exhaust gas merging unit) of the air-fuel ratio sensor 37 using the cylinder-by-cylinder air-fuel ratio estimation model described later during engine operation. 36, the air-fuel ratio (cylinder-by-cylinder) of each cylinder is estimated based on the actual air-fuel ratio of the exhaust gas flowing through 36, the average value of the estimated air-fuel ratios of all cylinders is calculated, and the average value is used as the reference air-fuel ratio ( The target air-fuel ratio of all the cylinders is set, 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 so that the deviation is reduced. A fuel correction coefficient (cylinder-by-cylinder air-fuel ratio correction amount) is calculated for each of the fuel injection amounts, and the cylinder-by-cylinder air-fuel ratio correction amount is learned by a smoothing process or the like. By correcting the fuel injection amount for each cylinder, Correcting the air-fuel ratio of the mixture supplied to each cylinder to control so as to reduce the air-fuel ratio variation among the cylinders (hereinafter, this control that 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 a detected value of the air-fuel ratio sensor 37, u is an air-fuel ratio of the gas flowing into the exhaust merging section 36, and k1 to k4 are constants.

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

When the above equation (1) is converted into a state space model, the following equations (2a) and (2b) are derived.
X (t + 1) = A.X (t) + B.u (t) + W (t) (2a)
Y (t) = C · X (t) + D · u (t) (2b)
Here, A, B, C, and D are model parameters, Y is a detected value of the air-fuel ratio sensor 37, X is an estimated air-fuel ratio of each cylinder as a state variable, and W is noise.

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

  As described above, the cylinder-by-cylinder air-fuel ratio estimation model is configured by the Kalman filter type observer, whereby the air-fuel ratio of each cylinder can be sequentially estimated as the combustion cycle proceeds.

  By the way, in the above-described cylinder-by-cylinder air-fuel ratio control system, if the air-fuel ratio control becomes difficult due to a failure of the fuel injection valve 20 or the like in any cylinder, the air-fuel ratio of the abnormal cylinder in which the air-fuel ratio control is difficult becomes large in the lean direction. As a result, the air-fuel ratio of the exhaust gas flowing into the catalyst 38 (that is, the exhaust gas in which the exhaust gas of the abnormal cylinder and the exhaust gas of the normal cylinder are mixed) may shift in the lean direction. If the air-fuel ratio of the exhaust gas flowing into the catalyst 38 deviates in the lean direction, the lean component amount (oxygen amount) flowing into the catalyst 38 increases and the oxidation reaction of rich components such as HC and CO is promoted. The heat of reaction may cause the catalyst 38 to be overheated and damaged.

  Therefore, in the first embodiment, the ECU 40 determines the presence or absence of a lean abnormal cylinder in which the air-fuel ratio varies greatly in the lean direction based on the cylinder-by-cylinder air-fuel ratio, and outputs engine output when it is determined that there is a lean abnormal cylinder. By performing the limited operation control to limit, the amount of exhaust gas (oxygen amount) flowing into the catalyst 38 is limited so that the reaction heat is not generated to the extent that the catalyst 38 is overheated.

  The cylinder-by-cylinder air-fuel ratio control and the limited operation control described above are executed by the ECU 40 according to the routines shown in FIGS. The processing contents of each routine will be described below.

[Air-fuel ratio control routine for each cylinder]
The cylinder-by-cylinder air-fuel ratio control routine shown in FIG. 2 is started at every predetermined crank angle (for example, every 30 ° C. A) in synchronization with the output pulse of the crank angle sensor 33. When this routine is started, first, in step 101, the output (air-fuel ratio detection value) of the air-fuel ratio sensor 37 is read. Thereafter, the routine proceeds to step 102 where the air-fuel ratio of the cylinder that is the current air-fuel ratio estimation target is estimated based on the detected value of the air-fuel ratio sensor 37 using the cylinder-by-cylinder air-fuel ratio estimation model. The processing in step 102 serves as cylinder-by-cylinder air-fuel ratio detection means in the claims.

  Thereafter, the process proceeds to step 103, 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 104, 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 small. .

  Thereafter, the routine proceeds to step 105, 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 of each cylinder based on the cylinder-by-cylinder air-fuel ratio correction amount of each cylinder. Cylinder-by-cylinder air-fuel ratio control is executed to control the variation in air-fuel ratio among the cylinders.

  Thereafter, the routine proceeds to step 106, where it is determined whether or not the deviation between the estimated air-fuel ratio of each cylinder and the reference air-fuel ratio is larger than the lean-side abnormality determination value, and the deviation between the estimated air-fuel ratio and the reference air-fuel ratio is lean A cylinder larger than the abnormality determination value (that is, a cylinder in which the air-fuel ratio greatly varies in the lean direction) is detected as a lean abnormality cylinder. Thereafter, the routine proceeds to step 107, where it is determined whether or not there is a lean abnormal cylinder based on the detection result of step 106. The processing of these steps 106 and 107 serves as an abnormal cylinder determining means in the claims.

  If it is determined in this step 107 that there is no lean abnormal cylinder, this routine is immediately terminated.

  On the other hand, if it is determined in step 107 that there is a lean abnormal cylinder, the routine proceeds to step 108, where a limited operation control routine for limiting engine output is executed by executing a limited operation control routine of FIG. Thus, the amount of exhaust gas (oxygen amount) flowing into the catalyst 38 is limited so that the reaction heat is not generated to the extent that the catalyst 38 is overheated.

[Restricted operation control routine]
The limited operation control routine shown in FIG. 3 is a subroutine executed in step 108 of the cylinder-by-cylinder air-fuel ratio control routine of FIG. 2, and serves as a limited operation control means in the claims. When this routine is started, first, at step 201, it is determined whether or not the engine output is equal to or greater than a predetermined value. In this case, the engine estimated based on one or more of information correlated with the engine output (for example, intake air amount, intake pipe pressure, in-cylinder pressure, filling air rate, engine shaft torque, etc.) You may make it determine whether an output is more than predetermined value. Alternatively, whether or not the engine output is greater than or equal to a predetermined value may be determined based on whether or not one or more of the information correlated with the engine output is greater than or equal to a predetermined value. .

  If it is determined in step 201 that the engine output is smaller than the predetermined value, this routine is terminated without limiting the engine output.

  On the other hand, if it is determined in step 201 that the engine output is equal to or greater than the predetermined value, the process proceeds to step 202a, where the throttle opening is controlled in the closing direction (intake air decreasing direction) to decrease the engine output. As a result, the engine output is limited to a predetermined value or less. Thereby, the amount of exhaust gas (oxygen amount) flowing into the catalyst 38 is limited so that reaction heat that causes the catalyst 38 to be overheated is not generated.

  Instead of the process of step 202a, the process of step 202b is executed, and the valve timing (opening / closing timing) of the intake valve 25 and the exhaust valve 26 is changed in the engine output decreasing direction by the variable valve timing mechanisms 27 and 28. The engine output may be limited to a predetermined value or less by reducing the engine output.

  In the case of a system including a variable valve lift mechanism, the lift amount of the intake valve 25 or the exhaust valve 26 may be changed in the engine output decreasing direction to limit the engine output to a predetermined value or less. Alternatively, in the case of a system equipped with a variable valve working angle mechanism, the working angle (opening period) of the intake valve 25 and the exhaust valve 26 is changed in the engine output decreasing direction to limit the engine output to a predetermined value or less. You may make it do.

  Further, instead of the process of step 202a, the process of step 202c may be executed to perform fuel cut control to reduce the engine output, thereby limiting the engine output to a predetermined value or less.

Further, the engine output may be limited to a predetermined value or less by executing the process of step 202d instead of the process of step 202a and performing the ignition cut control to reduce the engine output.
Further, two or more of the processes in steps 202a to 202d may be executed in combination.

  In the first embodiment described above, when it is determined that there is a lean abnormal cylinder, the limited operation control for limiting the engine output is executed, so that the exhaust gas flowing into the catalyst 38 due to the occurrence of the abnormal cylinder is emptied. Even when the fuel ratio deviates in the lean direction (the direction in which the amount of oxygen flowing into the catalyst 38 increases and the oxidation reaction is promoted), the exhaust gas amount (oxygen amount) flowing into the catalyst 38 is reduced by limiting the engine output. By limiting, it is possible to prevent reaction heat that would cause the catalyst 38 to be overheated, and to prevent the catalyst 38 from being overheated due to the occurrence of an abnormal cylinder.

Next, Embodiment 2 of the present invention will be described with reference to FIG.
In the first embodiment, the limited operation control for limiting the engine output is performed when it is determined that there is a lean abnormal cylinder. In the second embodiment, when it is determined that there is a lean abnormal cylinder, By executing the limited operation control routine shown in FIG. 4, the limited operation control for limiting the engine rotation speed is executed.

  In the limited operation control routine shown in FIG. 4, first, in step 301, it is determined whether or not the engine speed is equal to or higher than a predetermined value. Note that it may be determined whether or not the engine rotational speed is greater than or equal to a predetermined value depending on whether or not information correlated with the engine rotational speed (such as vehicle speed) is greater than or equal to a predetermined value.

  If it is determined in step 301 that the engine rotational speed is lower than the predetermined value, this routine is terminated without limiting the engine rotational speed.

  On the other hand, if it is determined in step 301 that the engine speed is greater than or equal to the predetermined value, the process proceeds to step 302a, where the engine opening speed is controlled by controlling the throttle opening in the closing direction (increase direction of the intake air amount). By reducing the engine speed, the engine speed is limited to a predetermined value or less. Thereby, the amount of exhaust gas (oxygen amount) flowing into the catalyst 38 is limited so that reaction heat that causes the catalyst 38 to be overheated is not generated.

  Instead of the process of step 302a, the process of step 302b is executed to shift up the gear of the transmission and change the gear ratio in the direction of decreasing the engine rotational speed to decrease the engine rotational speed. The rotational speed may be limited to a predetermined value or less.

  Further, instead of the process of step 302a, the process of step 302c may be executed to perform fuel cut control to reduce the engine speed, thereby limiting the engine speed to a predetermined value or less. .

  Further, instead of the process of step 302a, the process of step 302d may be executed to perform the ignition cut control to reduce the engine speed, thereby limiting the engine speed to a predetermined value or less. .

Further, two or more of the processes in steps 302a to 302d may be executed in combination.
In the second embodiment described above, the same effect as that of the first embodiment can be obtained.

Next, Embodiment 3 of the present invention will be described with reference to FIGS.
In the third embodiment, by executing the cylinder-by-cylinder air-fuel ratio control routine shown in FIG. 5, it is determined whether or not there is a lean abnormal cylinder for each engine operating region, and limited operation control is performed in the operating region where it is determined that there is a lean abnormal cylinder. To do.

  In the cylinder-by-cylinder air-fuel ratio control routine shown in FIG. 5, after calculating the estimated air-fuel ratio and the reference air-fuel ratio of each cylinder based on the detection value of the air-fuel ratio sensor 37, the deviation between the estimated air-fuel ratio of each cylinder and the reference air-fuel ratio. And the cylinder-by-cylinder air-fuel ratio correction amount (fuel correction amount of each cylinder) is calculated so that the deviation becomes small (steps 401 to 404).

  Thereafter, by correcting the fuel injection amount of each cylinder based on the cylinder-by-cylinder air-fuel ratio correction amount of each cylinder, the air-fuel ratio of the air-fuel mixture supplied to each cylinder is corrected for each cylinder, and the air-fuel ratio between the cylinders is corrected. The cylinder-by-cylinder air-fuel ratio control is executed to control the variation (step 405).

  Thereafter, the routine proceeds to step 406, where it is determined whether or not the deviation between the estimated air-fuel ratio of each cylinder and the reference air-fuel ratio is larger than the lean-side abnormality determination value, and the deviation between the estimated air-fuel ratio and the reference air-fuel ratio is lean A cylinder larger than the abnormality determination value (that is, a cylinder in which the air-fuel ratio greatly varies in the lean direction) is detected as a lean abnormality cylinder. In that case, for example, as shown in FIG. 6, a lean abnormal cylinder is detected for each of a plurality of engine operation areas divided according to the engine speed and load, and the engine operation area in which the lean abnormal cylinder is detected is detected as an abnormality detection operation. This is an area.

  Thereafter, the process proceeds to step 407, where it is determined whether or not there is a lean abnormal cylinder in any engine operating region based on the detection result in step 406, and there is a lean abnormal cylinder in any engine operating region. If it is determined, the process proceeds to step 408, and it is determined whether or not the current engine operation region is an abnormality detection operation region (an engine operation region determined to have a lean abnormal cylinder).

If it is determined in step 408 that the current engine operation region is the abnormality detection operation region, the process proceeds to step 409 to determine whether or not the catalyst 38 may be overheated (a state damaged by heat). For example, the determination is made based on whether one of the following conditions (1) and (2) is satisfied. The processing in step 409 serves as catalyst overheat determination means in the claims.
(1) There are two or more lean abnormal cylinders
(2) The operation region (for example, the high rotation operation region and the high load operation region shown in FIG. 7) in which the catalyst 38 is likely to be overheated.

  If either one of the above conditions (1) and (2) is satisfied, it is determined that the catalyst 38 may be overheated. However, both of the above conditions (1) and (2) must be satisfied. In this case, it is determined that there is no possibility that the catalyst 38 is overheated.

  That is, if there are two or more lean abnormal cylinders, the air-fuel ratio of the exhaust gas flowing into the catalyst 38 is greatly shifted in the lean direction, the amount of oxygen flowing into the catalyst 38 is increased, and the oxidation reaction is promoted. Therefore, the possibility that the catalyst 38 will be overheated becomes high. Therefore, when there are two or more lean abnormal cylinders, it can be determined that the catalyst 38 may be overheated.

  Further, since the amount of exhaust gas flowing into the catalyst 38 increases in the high rotation operation region and the high load operation region where the intake air amount of the engine 11 is large, the amount of oxygen flowing into the catalyst 38 increases even if there is one lean abnormal cylinder. Thus, the oxidation reaction is promoted, and the possibility that the catalyst 38 is overheated by the heat of reaction increases. Therefore, it can be determined that there is a possibility that the catalyst 38 is overheated in the high rotation operation region and the high load operation region.

  If it is determined in step 408 that the current engine operation region is an abnormality detection operation region, and it is determined in step 409 that the catalyst 38 may be overheated, the process proceeds to step 410, and the above-described operation is performed. By executing the limited operation control routine of FIG. 3 or FIG. 4, the limited operation control for limiting the engine output or the engine speed is executed to limit the exhaust gas amount (oxygen amount) flowing into the catalyst 38. Reaction heat that causes the catalyst 38 to be overheated is prevented from being generated, and the engine operation region is outside the abnormality detection operation region.

  On the other hand, if it is determined in step 408 that the current engine operation region is not the abnormality detection operation region, or if it is determined in step 409 that there is no possibility that the catalyst 38 will be in an overheated state, limited operation is performed. This routine is ended without executing the control.

A control example of the third embodiment described above will be described with reference to the time chart of FIG.
When the air-fuel ratio of the # 1 cylinder greatly varies in the lean direction due to a failure of the fuel injection valve 20 of the # 1 cylinder among the # 1 to # 4 cylinders, the deviation between the estimated air-fuel ratio of the # 1 cylinder and the reference air-fuel ratio At time t1 when the value becomes larger than the lean-side abnormality determination value, it is determined that there is a lean abnormality cylinder, and the deviation between the estimated air-fuel ratio of the # 2 cylinder and the reference air-fuel ratio becomes larger than the lean-side abnormality determination value. At the time t2 when the number of lean abnormal cylinders becomes two, it is determined that there is a possibility that the catalyst 38 is in an overheated state (a state damaged by heat). Thereafter, at the time t3 when it is determined that the engine output is equal to or greater than the predetermined value, the limit operation control for limiting the engine output is started, and the amount of exhaust gas (oxygen amount) flowing into the catalyst 38 is limited. The reaction heat is not generated so as to be overheated.

  In the third embodiment described above, when it is determined that there is a lean abnormal cylinder, it is determined that it is in the abnormality detection operation region, and if it is determined that there is a possibility that the catalyst 38 is in an overheated state, the limited operation control is performed. In this case, it is possible to reliably prevent the catalyst 38 from being overheated. Further, even if it is determined that there is an abnormal cylinder, it is determined that the catalyst 38 is not likely to be overheated. In addition, since the limited operation control is not executed in the operation region other than the abnormality detection operation region, it is possible to avoid a decrease in drivability due to the limited operation control.

  In each of the first to third embodiments, only one of the engine output and the engine rotation speed is limited during the limited operation control. However, both the engine output and the engine rotation speed are limited. You may do it.

  In each of the first to third embodiments, the limit operation control is performed when it is determined that there is a lean abnormal cylinder in which the air-fuel ratio varies greatly in the lean direction. However, the air-fuel ratio varies greatly in the rich direction. The limited operation control may be executed when it is determined that there is a rich abnormal cylinder.

  Further, in each of the first to third embodiments, the present invention is applied to a system that estimates the air-fuel ratio of each cylinder based on the output of one air-fuel ratio sensor installed in the exhaust merge section. The present invention may be applied to a system in which an air-fuel ratio sensor is installed and the air-fuel ratio of each cylinder is measured based on the output of the air-fuel ratio sensor of each cylinder.

It is a schematic block diagram of the whole engine control system in Example 1 of this invention. 3 is a flowchart showing a flow of processing of a cylinder-by-cylinder air-fuel ratio control routine according to the first embodiment. 4 is a flowchart illustrating a process flow of a limited operation control routine according to the first embodiment. 6 is a flowchart showing a flow of processing of a limited operation control routine of Example 2. 12 is a flowchart showing a flow of processing of a cylinder-by-cylinder air-fuel ratio control routine according to a third embodiment. It is a figure explaining an abnormality detection operation field. It is a figure explaining the driving | operation area | region with a high possibility that a catalyst will be in an overheated state. It is a time chart explaining the example of control of the present Example 3.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Engine (internal combustion engine), 12 ... Intake pipe, 16 ... Throttle valve, 20 ... Fuel injection valve, 35 ... Exhaust manifold, 36 ... Exhaust junction, 37 ... Air-fuel ratio sensor, 38 ... Catalyst, 40 ... ECU (cylinder) Separate air / fuel ratio detection means, abnormal cylinder determination means, limited operation control means, catalyst overheat determination means)

Claims (8)

A cylinder-by-cylinder air-fuel ratio detecting means for estimating or measuring an air-fuel ratio of each cylinder (hereinafter referred to as “cylinder-by-cylinder air-fuel ratio”) based on an output of an air-fuel ratio sensor for detecting an air-fuel ratio of exhaust gas from the internal combustion engine; In a control device for an internal combustion engine provided with an exhaust gas purification catalyst installed on the downstream side of the sensor,
Abnormal cylinder determining means for determining the presence or absence of an abnormal air-fuel ratio cylinder (hereinafter referred to as “abnormal cylinder”) based on the cylinder-specific air-fuel ratio;
An internal combustion engine comprising: limiting operation control means for executing limited operation control for limiting the output and / or rotational speed of the internal combustion engine when the abnormal cylinder determining means determines that the abnormal cylinder is present. Control device. A catalyst overheat determination means for determining whether or not the catalyst may be in an overheated state;
The limited operation control means executes the limited operation control when the abnormal cylinder determining means determines that the abnormal cylinder is present and the catalyst overheat determining means determines that the catalyst may be in an overheated state. The control apparatus for an internal combustion engine according to claim 1. The abnormal cylinder determining means determines the presence or absence of the abnormal cylinder for each operating region of the internal combustion engine,
The control apparatus for an internal combustion engine according to claim 1, wherein the limited operation control unit performs the limited operation control in an operation region in which the abnormal cylinder determination unit determines that the abnormal cylinder is present.   4. The control apparatus for an internal combustion engine according to claim 1, wherein the limited operation control means executes the limited operation control by controlling a throttle opening.   5. The control device for an internal combustion engine according to claim 1, wherein the limited operation control unit performs the limited operation control by performing fuel cut control. 6.   6. The control device for an internal combustion engine according to claim 1, wherein the limited operation control means executes the limited operation control by performing ignition cut control. A variable valve device for changing the opening and closing characteristics of an intake valve and / or an exhaust valve of an internal combustion engine;
The control device for an internal combustion engine according to any one of claims 1 to 6, wherein the limited operation control means executes the limited operation control by controlling the variable valve device.   8. The control apparatus for an internal combustion engine according to claim 1, wherein the limited operation control means executes the limited operation control by controlling a speed ratio of the transmission.

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