JP2018105296A - Control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control device of an internal combustion engine which can make compatible both the temperature rise performance of a catalyst and the stabilization of combustion suitably.SOLUTION: When a temperature rise requirement of a three-dimensional catalyst 22 arises, a CPU 32 performs dither control for setting a first cylinder #1 to a rich combustion cylinder which makes an air-fuel ratio richer than a theoretical air-fuel ratio, and setting second to fourth cylinders #2 to #4 to lean combustion cylinders which make air-fuel ratios leaner than the theoretical air-fuel ratio. Then, on condition that a variation not smaller than a prescribed value occurs in time series data of a rotational speed accompanied by combustion in each cylinder, the CPU 32 reduces a richening degree of the rich combustion cylinder and leaning degrees of the lean combustion cylinders while maintaining the dither control.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a control device for an internal combustion engine that controls an internal combustion engine that includes a catalyst that purifies exhaust gas discharged from a plurality of cylinders.

  For example, Patent Document 1 describes a control device for an internal combustion engine including a three-way catalyst into which exhaust from four cylinders flows. This control device is a rich combustion cylinder in which the air-fuel ratio of one cylinder of the internal combustion engine is richer than the stoichiometric air-fuel ratio as catalyst warm-up (temperature rise) control, and the air-fuel ratio of the remaining three cylinders is the stoichiometric air-fuel ratio. Perturbation control (dither control) is executed to make the lean combustion cylinder leaner than the fuel ratio. This oxidizes unburned fuel components and incomplete combustion components in the exhaust discharged from the rich combustion cylinder with oxygen in the exhaust discharged from the lean combustion cylinder, and raises the temperature of the three-way catalyst by the oxidation heat It is aimed at.

JP 2012-57492 A

  By the way, when the dither control is executed, there is a possibility that combustion of the air-fuel mixture in each cylinder becomes unstable due to the dither control. On the other hand, if the dither control is stopped to stabilize the combustion when the combustion becomes unstable, the temperature of the catalyst cannot be raised early. Also, if dither control is performed after the catalyst temperature reaches the activation temperature, when the combustion becomes unstable, the dither control is stopped to stabilize the combustion, thereby increasing the catalyst temperature early. In addition to the fear that the catalyst cannot be made, the temperature of the catalyst may decrease.

  The present invention has been made in view of such a situation, and an object of the present invention is to provide a control device for an internal combustion engine that can achieve a suitable balance between raising the temperature of the catalyst early and stabilizing the combustion. It is to provide. Another object of the present invention is to provide a control device for an internal combustion engine that can stabilize the combustion while suppressing a decrease in the temperature of the catalyst due to the stop of the tether control. In short, an object of the present invention is to provide a control device for an internal combustion engine that can achieve a suitable balance between the temperature rise performance of a catalyst and the stabilization of combustion.

Hereinafter, means for solving the above-described problems and the effects thereof will be described.
1. The control device for an internal combustion engine targets an internal combustion engine including a catalyst whose purification target is exhaust discharged from a plurality of cylinders, and when a temperature increase request for the catalyst occurs, one of the plurality of cylinders The lean air-fuel ratio in the lean combustion cylinder, which is a part of the cylinder, is controlled to be leaner than the target value for the average value of the air-fuel ratio in the plurality of cylinders, and is a cylinder different from the some of the plurality of cylinders Dither control processing for operating the fuel injection valve corresponding to each cylinder so as to control the air-fuel ratio in a rich combustion cylinder to be richer than the target value, and rotation of the crankshaft when the dither control processing is performed On condition that the fluctuation becomes equal to or greater than a predetermined value, the air-fuel ratio of the lean combustion cylinder is leaner than the target value, the air-fuel ratio of the rich combustion cylinder is richer than the target value, and the plurality of cylinders Decreasing process for reducing the difference between the air-fuel ratio in the lean combustion cylinder and the target value and the difference between the air-fuel ratio in the rich combustion cylinder and the target value while maintaining the average value of the air-fuel ratio in the lean combustion cylinder And execute.

  In the above configuration, the combustion state is improved by reducing the lean degree of the lean combustion cylinder and the rich degree of the rich combustion cylinder on condition that the rotational fluctuation becomes equal to or greater than a predetermined value when the dither control processing is performed. Plan. In addition, since the dither control itself is continued at this time, it is possible to increase the temperature of the catalyst earlier and to suppress the decrease in the temperature of the catalyst as compared with the case where the dither control is stopped. For this reason, in the above configuration, it is possible to achieve a suitable balance between raising the temperature of the catalyst early and stabilizing the combustion, and stabilizing the combustion while suppressing a decrease in the temperature of the catalyst. That is, according to the above configuration, it is possible to achieve a suitable balance between the temperature rise performance of the catalyst and the stabilization of combustion.

2. 2. The control apparatus for an internal combustion engine according to claim 1, wherein after the reduction process is executed, the reduction process is executed again on the condition that the rotational fluctuation is equal to or greater than a predetermined value.
In the above configuration, on the condition that the crankshaft rotational fluctuation is equal to or greater than a predetermined value, the lean combustion cylinder leaning degree and the rich combustion cylinder enrichment degree are decreased only once in order to gradually reduce the leaning degree and the richness degree of the rich combustion cylinder. Compared to the case, it is easy to set the amount of decrease once. For this reason, it is possible to prevent the lean degree and the rich degree from being excessively reduced and corrected while stabilizing the combustion.

  3. 3. The control apparatus for an internal combustion engine according to claim 1 or 2, wherein the reduction process is performed by setting a decrease amount of the difference when the difference is reduced on the condition that the rotation fluctuation is equal to or greater than a predetermined value. This is a process for increasing the frequency when the frequency becomes high compared to when it is low.

  In the above configuration, the amount of reduction in the lean combustion cylinder and the amount of reduction in the richness of the rich combustion cylinder are larger than when the frequency of the rotational fluctuation is high, so it is reduced regardless of the frequency. Compared with the case where the amount is set uniformly, it is possible to make the reduction amount as small as possible while improving the combustion state. This is because when the frequency is high, the degree of instability of combustion tends to be greater than when the frequency is low, and in order to stabilize combustion, there is a tendency that it is desirable to increase the amount of decrease. .

  4). In the control apparatus for an internal combustion engine according to any one of 1 to 3, the plurality of the rotation fluctuations greater than or equal to the predetermined period are not detected within a predetermined period after the reduction process is executed. An increase that increases the difference between the air-fuel ratio in the lean combustion cylinder and the target value and the difference between the air-fuel ratio in the rich combustion cylinder and the target value while maintaining the average value of the air-fuel ratio in the cylinder at the target value Execute the process.

  In the above configuration, the lean combustion cylinder lean is increased by increasing the leaning degree of the lean combustion cylinder and the enrichment degree of the rich combustion cylinder on the condition that a rotational fluctuation exceeding a predetermined value is not detected. The degree of enrichment and the degree of enrichment of the rich combustion cylinder can be increased. For this reason, compared with the case where an increase process is not performed, temperature rising performance can be made high, such as increasing the rate of temperature increase of the catalyst, while stabilizing combustion.

  5. 5. The control device for an internal combustion engine according to claim 4, wherein after the increase process is executed, the increase process is executed again on condition that the rotation fluctuation of the predetermined value or more is not detected within the predetermined period.

  In the above configuration, on the condition that more than a predetermined fluctuation in rotation is not detected, the degree of leaning of the lean combustion cylinder and the degree of enrichment of the rich combustion cylinder are increased stepwise, compared with a case where it is increased only once. It is possible to increase the degree of leaning and the degree of enrichment as much as possible while stabilizing the combustion.

  6). 6. The control apparatus for an internal combustion engine according to 4 or 5, wherein the increase process is performed by increasing the difference when the difference is increased on condition that the rotation fluctuation of the predetermined value or more is not detected within the predetermined period. When the frequency at which the rotational fluctuation is greater than or equal to a predetermined value is low, the rotational fluctuation is made larger than when it is high.

  In the above configuration, the amount of increase in the lean combustion cylinder and the richness of the rich combustion cylinder is increased more than when the frequency of rotation fluctuation is low, so that the increase is uniform regardless of the frequency. As compared with the case of setting to, the increase amount can be increased as much as possible while improving the combustion state. This is because when the frequency is low, the degree of instability of combustion tends to be lower than when the frequency is high, and the amount of increase can be increased while stabilizing the combustion.

  7). In the control apparatus for an internal combustion engine according to any one of 4 to 6, the difference between the air-fuel ratio in the lean combustion cylinder and the target value, and the difference between the air-fuel ratio in the rich combustion cylinder and the target value, The base request value, which is the base value of the request value, is variably set according to the operating state of the internal combustion engine, and the base request value is input, and the request value is limited to be equal to or less than the guard value. And the dither control process determines the difference between the air-fuel ratio of the lean combustion cylinder and the target value, and the difference between the air-fuel ratio of the rich combustion cylinder and the target value as the required value. The decreasing process is to decrease the guard value, and the increasing process is to increase the guard value toward the base required value.

  In the above configuration, by setting the base request value variably according to the operating state of the internal combustion engine, lean combustion is performed in order to increase the temperature of the catalyst at an early stage in each operating state as compared to the case where the base setting value is not set variably Appropriate values can be finely set as the lean degree of the cylinder and the rich degree of the rich combustion cylinder. In the above configuration, by executing the decrease process and the increase process, it is possible to bring the actual required value closer to the base required value as much as possible while stabilizing the combustion.

The figure which shows the control apparatus and internal combustion engine concerning 1st Embodiment. The block diagram which shows the production | generation process of the operation signal of the fuel injection valve concerning the embodiment. The flowchart which shows the procedure of the calculation process of the injection quantity correction | amendment request value concerning the embodiment. 6 is a flowchart showing a procedure of various counter update processing according to the embodiment; The time chart which prescribes | regulates the rotation fluctuation between cylinders and the rotation fluctuation between cycles concerning the embodiment. The flowchart which shows the procedure of the reduction process of the guard value concerning the embodiment. The flowchart which shows the procedure of the increase process of the guard value concerning the embodiment. The time chart which shows transition of the injection quantity correction | amendment request value concerning the embodiment. The flowchart which shows the procedure of the reduction process of the guard value concerning 2nd Embodiment. The flowchart which shows the procedure of the update process of the various counters concerning 3rd Embodiment. The flowchart which shows the procedure of the increase process of the guard value concerning the embodiment.

<First Embodiment>
Hereinafter, a first embodiment of a control device for an internal combustion engine will be described with reference to the drawings.

  As shown in FIG. 1, the internal combustion engine 10 includes four cylinders, a first cylinder # 1 to a fourth cylinder # 4. Air in the intake passage 12 of the internal combustion engine 10 is taken into the combustion chambers 14 of the first cylinder # 1 to the fourth cylinder # 4. A fuel injection valve 16 protrudes into the combustion chamber 14, and an air-fuel mixture of the fuel injected from the fuel injection valve 16 and the air sucked into the combustion chamber 14 from the intake passage 12 is spark discharge of the ignition device 18. Is used for combustion. The air-fuel mixture provided for combustion is discharged into the exhaust passage 20 as exhaust. A three-way catalyst 22 for purifying exhaust gas is provided in the exhaust passage 20.

  The control device 30 controls the internal combustion engine 10 and controls various actuators such as the fuel injection valve 16 and the ignition device 18 in order to control the control amounts (torque, exhaust components). The control device 30 controls the control amount by controlling the air-fuel ratio Af detected by the air-fuel ratio sensor 40 provided upstream of the three-way catalyst 22 and the crankshaft rotational speed NE detected by the rotational speed sensor 42. The intake air amount Ga detected by the air flow meter 44 and the water temperature THW detected by the water temperature sensor 46 are referred to. The control device 30 includes a central processing unit (CPU 32) and a memory 34, and the control amount is controlled by the CPU 32 executing a program stored in the memory 34.

FIG. 2 shows a part of processing realized by the CPU 32 executing the program stored in the memory 34.
Based on the rotational speed NE and the load KL, the base injection amount calculation processing unit M10 calculates the base injection amount Qb as an open loop operation amount for controlling the air-fuel ratio of the air-fuel mixture in the combustion chamber 14 to the target value Af *. . Here, in the present embodiment, the target value is the stoichiometric air-fuel ratio. Further, as the load KL, in the present embodiment, a load factor that is a ratio of the actual charged air amount to the reference value of the charged air amount to the combustion chamber 14 at the current rotational speed NE is exemplified. The load factor is calculated based on the intake air amount Ga and the rotational speed NE.

  The target value setting processing unit M12 sets a target value Af * of the air-fuel ratio of the air-fuel mixture in the combustion chamber 14. The feedback processing unit M14 calculates an operation amount KAF for performing feedback control of the air-fuel ratio Af detected by the air-fuel ratio sensor 40 to the target value Af *. In the present embodiment, the operation amount KAF is defined as the sum of the output values of the proportional element, the integral element, and the derivative element, which are input by subtracting the air-fuel ratio Af from the target value Af *.

The feedback correction processing unit M16 corrects the base injection amount Qb by multiplying the base injection amount Qb by the operation amount KAF.
When the temperature increase request of the three-way catalyst 22 is generated, the request value output processing unit M20 sets the average value of the air-fuel ratio in each cylinder # 1 to # 4 of the internal combustion engine 10 as the target value Af *, but between the cylinders. A dither control injection amount correction request value α for varying the air-fuel ratio is calculated. Here, in the dither control according to the present embodiment, the first cylinder # 1 is a rich combustion cylinder that makes the air-fuel ratio richer than the target value Af *, and the second to fourth cylinders # 2 to # 4 are set. The lean combustion cylinder is set so that the air-fuel ratio is leaner than the target value Af *. The injection amount in the rich combustion cylinder is “1 + α” times the output value of the feedback correction processing unit M16, and the injection amount in the lean combustion cylinder is “1− (α / 3)” times the output value. .

  The correction coefficient calculation processing unit M22 adds the injection amount correction request value α to “1” to calculate the correction coefficient of the output value of the feedback correction processing unit M16 for the first cylinder # 1. The multiplication processing unit M24 multiplies the injection amount correction request value α by “−1/3”, and the correction coefficient calculation processing unit M26 adds the output value of the multiplication processing unit M24 to “1”, For the fourth cylinders # 2 to # 4, the correction coefficient of the output value of the feedback correction processing unit M16 is calculated.

  The dither correction processing unit M28 calculates the injection amount command value Q * of the first cylinder # 1 by multiplying the output value of the feedback correction processing unit M16 by the correction coefficient “1 + α”. The dither correction processing unit M30 multiplies the output value of the feedback correction processing unit M16 by a correction coefficient “1- (α / 3)” to thereby determine the injection amount command values for the second to fourth cylinders # 2 to # 4. Q * is calculated.

  The operation signal generation processing unit M32 generates an operation signal MS1 of each fuel injection valve 16 based on the injection amount command value Q *, outputs the operation signal MS1 to the corresponding fuel injection valve 16, and is injected from each fuel injection valve 16. Each fuel injection valve 16 is operated so that the fuel amount becomes the injection amount command value Q *.

Next, processing of the request value output processing unit M20 will be described with reference to FIGS.
FIG. 3 shows a procedure for calculating the injection amount correction request value α. The process shown in FIG. 3 is realized by the CPU 32 repeatedly executing the program stored in the memory 34 at a predetermined cycle. In the following, the step number is represented by a number with “S” at the beginning.

  In the series of processes shown in FIG. 3, the CPU 32 first determines whether or not the flag F1 is “1” (S10). The flag F1 becomes “1” when the dither control is executed, and becomes “0” when the dither control is not executed. When determining that the flag F1 is “0” (S10: NO), the CPU 32 determines that the water temperature THW is equal to or lower than the predetermined temperature Twth and that the integrated value InG of the intake air amount Ga from the start of the internal combustion engine 10 is the first value. It is determined whether or not a logical product with being equal to or greater than one threshold value InthL is true (S12). This process is for determining whether or not the execution condition for the dither control is satisfied. Here, the condition that the water temperature THW is equal to or lower than the predetermined temperature Twth is a condition for determining that there is a request for increasing the temperature of the three-way catalyst 22 when the internal combustion engine 10 is cold started. On the other hand, the condition that the integrated value InG is greater than or equal to the first threshold value InthL is a condition for determining that the temperature at the upstream end of the three-way catalyst 22 has reached the catalyst activation temperature. This promotes the reaction between the unburned fuel component and the incomplete combustion component in the exhaust from the rich combustion cylinder and the oxygen in the exhaust from the lean combustion cylinder by the three-way catalyst 22, and effectively the three-way catalyst 22. Is a condition for raising the temperature. Incidentally, the integrated value InG is used as an amount having a correlation with the total amount of thermal energy generated by the combustion of the air-fuel mixture in the combustion chamber 14 after the internal combustion engine 10 is started.

  When determining that the logical product is true (S12: YES), the CPU 32 sets the flag F1 to “1” (S14). Then, the CPU 32 calculates a base correction request value α0 that is a base value of the injection amount correction request value α (S16). Specifically, the CPU 32 variably sets the base correction request value α0 according to the rotational speed NE, the load KL, and the water temperature THW. Here, the CPU 32 sets the base correction request value α0 to a larger value when the water temperature THW is low than when the water temperature THW is high. This is because when the water temperature THW is low, there is a need to increase the temperature increase rate of the three-way catalyst 22 than when the water temperature THW is high. Further, the CPU 32 sets the base correction request value α0 to a larger value when the rotational speed NE is low than when the rotational speed NE is high. This is because, when the rotational speed NE is low, the number of combustion cycles per unit time is small, so that the temperature increase rate of the three-way catalyst 22 by dither control is low compared to the case where the rotational speed NE is high. Is. Further, the CPU 32 sets the base correction request value α0 to a larger value when the load KL is high than when the load KL is low. This is because the stability of combustion is higher when the load KL is higher than when the load KL is low, so that the lean degree of the lean combustion cylinder and the rich degree of the rich combustion cylinder are easily increased.

  Then, the CPU 32 determines whether or not the logical sum of the fact that the inter-cylinder variation counter Can, which will be described later, has reached the threshold value Canth, and the history that the inter-cycle variation counter Cac has reached the threshold value Cacth is true. Is determined (S18). When determining that the logical sum is false (S18: NO), the CPU 32 sets the guard value αth of the injection amount correction request value α as the base correction request value α0 (S20). This process is for setting the injection amount correction request value α to the base correction request value α0 when the rotation fluctuation of the crankshaft does not increase immediately after the start of the dither control.

  When completing the process of S20 or determining that the logical sum is true (S18: YES), the CPU 32 determines whether or not the base correction request value α0 is larger than the guard value αth (S22). ). When determining that the value is equal to or less than the guard value αth (S22: NO), the CPU 32 substitutes the base correction request value α0 for the injection amount correction request value α (S26). On the other hand, when determining that the value is larger than the guard value αth (S22: YES), the CPU 32 substitutes the guard value αth for the injection amount correction request value α (S24).

  When the processes of S24 and S26 are completed, the CPU 32 performs a gradual change process on the injection amount correction request value α to suppress a rapid change in the injection amount correction request value α (S27). Note that when the flag F1 is switched from “0” to “1” and the injection amount correction request value α is calculated for the first time, the CPU 32 regards the initial value of the injection amount correction request value α as zero.

  On the other hand, when determining that the flag F1 is “1” (S10: YES), the CPU 32 determines whether or not the integrated value InG is greater than or equal to a second threshold value InthH that is greater than the first threshold value InthL (S28). ). This process determines whether or not a dither control end condition is satisfied. Here, the second threshold value InthH is set to a value when the three-way catalyst 22 is in an active state throughout. When determining that it is less than the second threshold value InthH (S28: NO), the CPU 32 proceeds to the process of S16, and when determining that it is greater than or equal to the second threshold value InthH (S28: YES), the flag F1 is set to zero. (S30).

Note that when the processes of S27 and S30 are completed or when a negative determination is made in S12, the CPU 32 once ends the series of processes shown in FIG.
FIG. 4 shows a procedure for updating various counters such as the inter-cylinder variation counter Can and the inter-cycle variation counter Cac. The process shown in FIG. 4 is realized by the CPU 32 repeatedly executing the program stored in the memory 34 at a cycle of 180 ° CA, for example.

  In the series of processes shown in FIG. 4, the CPU 32 first determines the time T30 (n) required for rotation in the “0-30 ° CA” section of the cylinder that has become the most recently (hereinafter, this time) compression top dead center. Whether or not the absolute value of the difference from the time T30 (n−1) required for the rotation of the “0 to 30 ° CA” section of the cylinder that became the compression top dead center one time before is equal to or greater than the threshold value Tth1 Is determined (S30). FIG. 5 exemplifies times T30 (n) and T30 (n−1) when the cylinder at the compression top dead center is the first cylinder # 1. The process of S30 in FIG. 4 is a process of determining whether or not a difference greater than or equal to a predetermined value (rotation fluctuation between cylinders) occurs in the rotation speed caused by combustion between cylinders whose combustion strokes are chronologically changed. The CPU 32 variably sets the threshold value Tth1 based on the rotational speed NE and the load KL. Here, the threshold value Tth1 is variably set according to the rotational speed NE in order to quantify the rotation fluctuation between the cylinders, rather than the magnitude of the difference between the times T30 (n) and T30 (n-1). This is because it is more appropriate to evaluate the magnitude of the ratio between one of them and the other. For this reason, the CPU 32 sets the threshold value Tth1 to a smaller value when the rotational speed NE is high than when the rotational speed NE is low. The reason why the threshold value Tth1 is variably set according to the load KL is that the stability of combustion is higher when the load KL is high than when the load KL is low, on the premise that the dither control is not performed. That is, by setting the threshold value Tth1 to a larger value when the load KL is low than when the load KL is high, the CPU 32 suppresses detection of the inter-cylinder rotation fluctuation due to the instability of combustion not caused by dither control.

  When determining that the CPU 32 is equal to or greater than the threshold value Tth1 (S30: YES), the CPU 32 increments the inter-cylinder variation counter Can that counts the number of detections of inter-cylinder rotation variation, and counts the number of times that no rotation variation is detected. The combustion counter Cn is initialized (S32).

  When completing the process of S32 or making a negative determination in S30, the CPU 32 proceeds to the process of S34. In the process of S34, the CPU 32 determines that the time T90 (n) required for the rotation of the section “0 to 90ATDC” in the cylinder that has become the compression top dead center this time and “0 to 90ATDC before one combustion cycle in the cylinder”. It is determined whether or not the absolute value of the difference from the time T90 (n−1) required for the rotation of the section “” is equal to or greater than the threshold value Tth2. FIG. 5 exemplifies times T90 (n) and T90 (n−1) when the cylinder at the compression top dead center is the first cylinder # 1 this time. The process of S34 in FIG. 4 is a process for determining whether or not a difference greater than a predetermined value (rotational fluctuation between cycles) occurs in the rotational speed due to combustion in a specific cylinder in each of the combustion cycles that are preceded and followed in time series. It is. The CPU 32 variably sets the threshold value Tth2 based on the rotational speed NE and the load KL. Here, the reason why the threshold value Tth2 is variably set is the same as the reason why the threshold value Tth1 is variably set.

  When determining that the threshold value is greater than or equal to the threshold Tth2 (S34: YES), the CPU 32 increments an inter-cycle variation counter Cac that counts the number of detections of inter-cycle rotation variation, and initializes a normal combustion counter Cn (S36).

  When the CPU 32 completes the process of S36 or makes a negative determination in S34, the CPU determines that the inter-cylinder rotation fluctuation is not detected and the inter-cycle rotation fluctuation is detected in the current control cycle of the series of processes shown in FIG. It is determined whether or not the logical product of not being performed is true (S38). When determining that the logical product is true (S38: YES), the CPU 32 increments the normal combustion counter Cn (S40).

Note that the CPU 32 once ends the series of processes shown in FIG. 4 when the process of S40 is completed or when a negative determination is made in S38.
FIG. 6 shows the procedure of the guard value αth reduction process. The process shown in FIG. 6 is realized by the CPU 32 repeatedly executing the program stored in the memory 34 at a predetermined time period.

  In the series of processes shown in FIG. 6, the CPU 32 first determines whether the logical sum of whether the inter-cylinder variation counter Can is equal to or greater than the threshold value Canth and that the inter-cycle variation counter Cac is equal to or greater than the threshold value Cacth is true. Is determined (S50). This process determines whether a condition for reducing the guard value αth is satisfied. When determining that the logical sum is true (S50: YES), the CPU 32 corrects the guard value αth by a predetermined amount Δ1 (S52). Then, the CPU 32 determines whether or not the guard value αth after the decrease correction is smaller than the lower limit value αthL (S54). Here, the lower limit value αthL is set to a value larger than zero. When determining that the CPU 32 is smaller than the lower limit value αthL (S54: YES), the CPU 32 substitutes the lower limit value αthL for the guard value αth (S56).

  When the process of S56 is completed or when a negative determination is made in S54, the CPU 32 initializes the inter-cylinder variation counter Can and the inter-cycle variation counter Cac (S58). Note that the CPU 32 once ends the series of processes shown in FIG. 6 when the process of S58 is completed or when a negative determination is made in S50.

  FIG. 7 shows a procedure for increasing the guard value αth. The processing shown in FIG. 7 is realized by the CPU 32 repeatedly executing the program stored in the memory 34 at a predetermined time period.

  In the series of processes shown in FIG. 7, the CPU 32 first determines whether or not the guard value αth is smaller than the base correction request value α0 (S60). When determining that the value is smaller than the base correction request value α0 (S60: YES), the CPU 32 determines whether or not the normal combustion counter Cn is greater than or equal to the threshold value Cnth (S62). The processing of S60 and S62 is for determining whether or not a condition for increasing the guard value αth is satisfied. If the CPU 32 determines that the threshold value is greater than or equal to the threshold Cth (S62: YES), the CPU 32 increases the guard value αth by a predetermined amount Δ2 (S64).

  Next, the CPU 32 determines whether or not the guard value αth is larger than the base correction request value α0 (S66). When determining that the value is larger than the base correction request value α0 (S66: YES), the CPU 32 substitutes the base correction request value α0 for the guard value αth (S68). When the process of S68 is completed or when a negative determination is made in S66, the CPU 32 initializes the combustion counter Cn (S70).

When the process of S70 is completed or when a negative determination is made in S60 and S62, the CPU 32 once ends the series of processes shown in FIG.
Here, the operation of the present embodiment will be described.

FIG. 8 shows changes in the inter-cylinder fluctuation counter Can, the cycle fluctuation counter Cac, the normal combustion counter Cn, and the injection amount correction request value α.
As shown in FIG. 8, when the dither control is started at time t1, the injection amount correction request value α changes toward the base correction request value α0. In this example, since the base correction request value α0 is large, the injection amount correction request value α is increased stepwise by the upper limit change amount Δmax by the gradual change processing that limits the change in the injection amount correction request value α. Show. FIG. 8 shows an example in which neither inter-cylinder rotational fluctuation nor inter-cycle rotational fluctuation is detected until time t2 when the injection amount correction required value α reaches the base correction required value α0.

  FIG. 8 shows an example in which only the rotation fluctuation between cylinders is detected after time t3 in order to simplify the description. This can occur when combustion is unstable in each combustion cycle in only one specific cylinder among the cylinders # 1 to # 4. However, in reality, when a rotational fluctuation caused by misfire or the like continuously occurs in a single cylinder, some kind of fail-safe processing can be performed. However, in the example shown in FIG. 8, for the sake of convenience of explanation, the fail-safe process or the like is not included.

  As shown in FIG. 8, the normal combustion counter Cn is initialized every time the cylinder rotation fluctuation occurs. On the other hand, as illustrated at times t4, t5, and t6, when the inter-cylinder variation counter Can becomes equal to or greater than the threshold value Canth, the guard value αth is corrected to decrease by a predetermined amount Δ1, and the inter-cylinder variation counter Can is initialized. The predetermined amount Δ1 is set to a value smaller than the upper limit change amount Δmax. At time t5, it is initialized that the inter-cylinder variation counter Can is larger than the threshold value Canth. This is a phenomenon caused by the processing cycle shown in FIG. 6 being a time cycle.

  FIG. 8 shows an example in which the base correction request value α0 decreases at time t7, thereby eliminating the inter-cylinder rotation fluctuation. In this case, although the normal combustion counter Cn increases, the guard value αth is not increased since the base correction request value α0 and the injection amount correction request value α coincide before time t8. However, when the base correction request value α0 increases at time t8, since the injection amount correction request value α (in this case, the guard value αth) is smaller than the base correction request value α0, the guard value αth is corrected to increase by a predetermined amount Δ2. The normal combustion counter Cn is initialized. Thereafter, when the normal combustion counter Cn becomes equal to or greater than the threshold value Cnth again, the guard value αth is again increased by the predetermined amount Δ2.

  As described above, in this embodiment, when the combustion becomes unstable during the execution of the dither control, the injection amount correction request value α is decreased stepwise to improve the combustion state. The temperature raising process of the original catalyst 22 is continued. Thereby, suitable coexistence with raising the temperature of the three-way catalyst 22 at an early stage and stabilization of combustion can be aimed at.

According to the embodiment described above, the following effects can be obtained.
(1) Each time the combustion becomes unstable, the injection amount correction request value α is decreased stepwise. Thereby, compared with the case where it reduces only once, it is easy to set the amount of decrease (predetermined amount (DELTA) 1) of 1 degree small. For this reason, it is possible to prevent the lean degree and the rich degree from being excessively reduced and corrected while stabilizing the combustion.

  (2) The guard value αth is increased on condition that the normal combustion counter Cn is equal to or greater than the threshold value Cnth. Thereby, compared with the case where it does not increase, the rate of temperature rise of the three-way catalyst 22 can be increased while stabilizing the combustion.

  (3) The guard value αth is increased stepwise based on the normal combustion counter Cn. Thereby, compared with the case where it increases only once, the lean degree and the rich degree can be increased as much as possible while stabilizing the combustion.

  (4) The base correction request value α0 is variably set according to the operating state of the internal combustion engine 10, and the base correction request value α0 is subjected to guard processing using the guard value αth. In this way, by variably setting the base correction request value α0 in accordance with the operating state of the internal combustion engine 10, the temperature of the three-way catalyst 22 is increased earlier in each operating state than when not variably set. In the above, appropriate values can be finely set as the lean degree of the lean combustion cylinder and the rich degree of the rich combustion cylinder.

  (5) The increase amount (predetermined amount Δ1) of the guard value αth when increasing the guard value αth based on the normal combustion counter Cn is higher than the upper limit change amount Δmax for limiting the change rate of the injection amount correction request value α. I made it smaller. Accordingly, it is possible to suppress the combustion from becoming unstable again by increasing the injection amount correction request value α based on the normal combustion counter Cn.

<Second Embodiment>
Hereinafter, the second embodiment will be described with reference to the drawings with a focus on differences from the first embodiment.

In the present embodiment, the leaning degree and the decreasing rate of the enriching degree are variably set according to the combustion state.
FIG. 9 shows the procedure of the guard value αth reduction process. The processing shown in FIG. 9 is realized by the CPU 32 repeatedly executing the program stored in the memory 34 at a predetermined time period. In FIG. 9, processes corresponding to the processes shown in FIG. 6 are denoted by the same step numbers and description thereof is omitted.

  In the series of processes shown in FIG. 9, when the CPU 32 makes an affirmative determination in S50, the guard value αth is variably set according to the larger one of the inter-cylinder variation counter Can and the inter-cycle variation counter Cac. A decrease correction is made according to the fixed amount Δ1 (S52a). Here, the CPU 32 sets the predetermined amount Δ1 to a larger value than when the larger one of the inter-cylinder variation counter Can and the inter-cycle variation counter Cac is large. Then, when the process of S52a is completed, the CPU 32 proceeds to the process of S54.

  The CPU 32 proceeds to the process of S58 when the process of S56 is completed or when a negative determination is made at S50 in addition to a negative determination at S54. Accordingly, the inter-cylinder variation counter Can and the inter-cycle variation counter Cac when the process of S52a is executed indicate the frequency of the inter-cylinder rotation variation and the inter-cycle rotation variation within the control cycle of the series of processes in FIG. .

  According to the present embodiment, the degree of leaning and the degree of enrichment can be reduced according to the low stability of combustion by variably setting the rate of decrease of the guard value αth as described above.

<Third Embodiment>
Hereinafter, the third embodiment will be described with reference to the drawings with a focus on differences from the second embodiment.

In the present embodiment, the leaning degree and the increasing speed of the enriching degree are also variably set according to the combustion state.
FIG. 10 shows a procedure for updating various counters such as the inter-cylinder variation counter Can and the inter-cycle variation counter Cac. The process shown in FIG. 10 is realized by the CPU 32 repeatedly executing the program stored in the memory 34 at a cycle of 180 ° CA, for example. In FIG. 10, processes corresponding to the processes shown in FIG. 4 are given the same step numbers and description thereof is omitted.

  In the series of processes shown in FIG. 10, when the determination is positive in S30, the CPU 32 increments the inter-cylinder variation counter Can but does not initialize the normal combustion counter Cn (S32a). If the determination in S34 is affirmative, the CPU 32 increments the cycle-to-cycle variation counter Cac but does not initialize the normal combustion counter Cn (S36a). Such a change is for quantifying the frequency at which no rotation fluctuation between cylinders or no rotation fluctuation between cycles is detected by the normal combustion counter Cn.

  FIG. 11 shows a procedure for increasing the guard value αth. The processing shown in FIG. 11 is realized by the CPU 32 repeatedly executing the program stored in the memory 34 at a predetermined time period. In FIG. 11, processes corresponding to the processes shown in FIG. 7 are assigned the same step numbers and description thereof is omitted.

  In the series of processes shown in FIG. 11, when the determination is positive in S62, the CPU 32 increases and corrects the guard value αth by the predetermined amount Δ2 variably set by the normal combustion counter Cn (S64a). Here, the CPU 32 sets the predetermined amount Δ2 to a larger value when the normal combustion counter Cn is large than when it is small. Note that the CPU 32 proceeds to S70 when the process of S68 is completed or when a negative determination is made at S60 or S62 in addition to a negative determination at S66. This is a setting for setting the normal combustion counter Cn at the time when the process of S64a is executed to a frequency at which no inter-cylinder rotation fluctuation or inter-cycle rotation fluctuation is detected within the control cycle of the series of processes in FIG.

  According to the present embodiment, the degree of leaning and the degree of enrichment can be increased according to the low stability of combustion by variably setting the increasing rate of the guard value αth as described above.

<Correspondence>
The correspondence relationship between the items in the above embodiment and the items described in the column “Means for Solving the Problems” is as follows. In the following, the correspondence relationship is shown for each number of solution means described in the “means for solving the problem” column.

  [1] The dither control processing includes a correction coefficient calculation processing unit M22, a multiplication processing unit M24, a correction coefficient calculation processing unit M26, and dither correction processing units M28 and M30 when the injection amount correction request value α is not “0”. This corresponds to the processing of the operation signal generation processing unit M32. The reduction process corresponds to the processes of S52 and 52a. [2] The reduction process corresponds to the processes of S52 and 52a. [3] The variable setting of the reduction amount is realized by the process of S52a. [4] The predetermined period corresponds to an appearance interval of adjacent combustion strokes in time series, in other words, corresponds to a rotation period of 180 ° CA. That is, the processing of FIG. 4 is performed every 180 ° CA, and when the inter-cylinder rotation fluctuation and the inter-cycle rotation fluctuation are not detected within the period, the normal combustion counter Cn is incremented, and based on this, the guard value αth Is corrected to increase by a predetermined amount Δ2. This corresponds to increasing the guard value αth on the condition that the inter-cylinder rotation fluctuation and the cycle rotation fluctuation are not detected during the rotation period of 180 ° CA. The increase process corresponds to the process of S64, 64a. [5] The increase process corresponds to the processes of S64 and 64a. [6] The variable setting of the increase amount is realized by the process of S64a. [7] The request value setting process corresponds to the process of S16, and the guard process corresponds to the processes of S22 to S26. The required value of the difference between the air-fuel ratio and the target value in the lean combustion cylinder corresponds to “1- (α0 / 3)”, and the required value of the difference between the air-fuel ratio in the rich combustion cylinder and the target value is “ 1 + α0 ”. Here, it can be considered that the required value of the difference is set by the process of setting the base correction required value α0 in the process of S16.

<Other embodiments>
In addition, you may change at least 1 of each matter of the said embodiment as follows.
"About reduction processing"
As the decrease process, the guard value αth is decreased on condition that the logical sum of the fact that the inter-cylinder variation counter Can is equal to or greater than the threshold value Canth and that the inter-cycle variation counter Cac is equal to or greater than the threshold value Cacth is true. Not limited to things. For example, the guard value αth may be decreased on the condition that the inter-cycle variation counter Cac becomes equal to or greater than the threshold value Cacth without using the inter-cylinder variation counter Can. Further, for example, the guard value αth may be decreased on the condition that the inter-cylinder variation counter Can becomes equal to or greater than the threshold value Canth without using the inter-cycle variation counter Cac. Further, for example, without providing the inter-cylinder variation counter Can and the inter-cycle variation counter Cac, the guard value αth is decreased on the condition that the total value of the inter-cylinder rotation variation and the inter-cycle rotation variation is equal to or greater than a threshold value. It may be a thing.

  The reduction process is not limited to one that reduces the injection amount correction request value α stepwise. For example, the injection amount correction request value α may be reduced to the lower limit value αthL when the rotational fluctuation becomes greater than or equal to a predetermined value. However, in this case, it is desirable to execute a process of increasing the injection amount correction request value α in a stepwise manner on the condition that the rotational fluctuation does not exceed a predetermined value.

  In the process of S52a of FIG. 9, the predetermined amount Δ1 is variably set according to the larger value of the inter-cylinder variation counter Can and the inter-cycle variation counter Cac, but this is not restrictive. For example, the predetermined amount Δ1 may be variably set according to the total value of the inter-cylinder variation counter Can and the inter-cycle variation counter Cac.

About increase processing
As an increase process, the normal combustion counter Cn that is incremented on condition that the logical product of the fact that the inter-cylinder rotational fluctuation is not detected and the inter-cycle rotational fluctuation is not detected is true is determined to be greater than or equal to the threshold Cnth. The condition is not limited to increasing the guard value αth. For example, the normal combustion counter Cn may be incremented on the condition that the inter-cylinder rotational fluctuation is not detected and the inter-cycle rotational fluctuation is not detected. Further, for example, the normal combustion counter Cn may be incremented on the condition that the inter-cylinder rotational fluctuation is not detected without referring to the inter-cycle rotational fluctuation.

  The increasing process is not limited to increasing the injection amount correction request value α step by step. For example, in the third embodiment, the injection amount correction request value α may be increased only once in a state where the base correction request value α0 does not change.

About the base request value
It is not essential to variably set the base correction request value α0 based on the rotational speed NE, the load KL, and the water temperature THW. For example, it may be variably set based on only two of the three parameters of the rotational speed NE, the load KL, and the water temperature THW, or may be variably set based on only one of the three parameters, for example. May be.

  It is not essential to variably set the base correction request value α0 based on the above parameters. When the variable setting process using the above parameters for the base correction request value α0 is not performed, the base correction request value α0, the injection amount correction request value α, and the guard value αth need not be distinguished. That is, for example, the guard value αth reduction process in the above-described embodiment may be changed to the injection amount correction request value α reduction process.

"Execution conditions for dither control"
The execution conditions of the dither control are not limited to those exemplified in the above embodiment, and for example, a sensor for detecting the temperature of the three-way catalyst is provided, and the detected value of the sensor is not less than a predetermined temperature and not more than a specified temperature. It is good also as conditions. However, the present invention is not limited to this, and dither control may be executed from the start of the internal combustion engine 10 on condition that the internal combustion engine 10 is cold started for the purpose of simplifying the control.

  The execution period of the dither control is not limited to the period until the three-way catalyst reaches the activation temperature throughout. For example, the dither control may be executed for the sulfur poisoning recovery process even after the three-way catalyst reaches the activation temperature throughout. Also, for example, when entering a temperature range where the sulfur poisoning amount is likely to increase in a temperature range higher than the activation temperature of the three-way catalyst, dither control is performed to make the temperature of the three-way catalyst higher than that temperature range. May be. For example, the execution condition may be that a request to raise the temperature of the exhaust pipe is generated in order to suppress adhesion of condensed water to the exhaust pipe. This can be realized, for example, by setting the execution condition that the logical product of the outside air temperature being equal to or less than the determination value and the load being equal to or less than the predetermined value is true. Further, for example, when GPF is used as a catalyst as described in the “About catalyst” section below, the execution condition may be that a request to remove particulate matter clogged with GPF is generated. This can be realized by setting the execution condition that the difference between the pressure on the upstream side of the GPF and the pressure on the downstream side is equal to or greater than a threshold value. Also, for example, when the temperature of the upstream end of the three-way catalyst has reached the catalyst activation temperature, dither control is always performed unless the temperature is excessively high enough to reduce the reliability of the three-way catalyst. May be. In these embodiments, stopping the dither control when combustion becomes anxious does not necessarily prevent the temperature of the catalyst from being raised at an early stage, but may cause a decrease in the temperature of the catalyst. There is also. And in that case, changing the degree of leaning or the degree of enrichment in the manner of the above embodiment can suppress the decrease in the temperature of the catalyst while ensuring the stability of combustion and ensure the temperature rise performance. Has technical significance.

“Number of lean and rich combustion cylinders”
In the above embodiment, the number of lean combustion cylinders is greater than the number of rich combustion cylinders, but the present invention is not limited to this. For example, the number of lean combustion cylinders and the number of rich combustion cylinders may be the same. Note that it is not essential that the sum of the number of lean combustion cylinders and the number of rich combustion cylinders matches the number of cylinders of the internal combustion engine 10. For example, the air-fuel ratio in the combustion chamber 14 of a specific cylinder By setting the fuel ratio, a cylinder that is neither a lean combustion cylinder nor a rich combustion cylinder may be used. Incidentally, as described in “Internal combustion engine” below, even when a plurality of catalysts with different exhaust purification targets are provided, the number of lean combustion cylinders for which one catalyst purifies exhaust and the rich combustion cylinders. The sum with the number is smaller than the number of cylinders of the internal combustion engine.

About dither control
The dither control process is not limited to a process for setting a correction amount for the injection amount. For example, the base injection amount calculation processing unit M10 may be provided separately for the rich combustion cylinder and the lean combustion cylinder. In this case, the base combustion amount calculation processing unit M10 for the rich combustion cylinder calculates a base injection amount Qb as an open loop operation amount for obtaining a rich target air-fuel ratio, and a base injection amount calculation process for the lean combustion cylinder. The part M10 calculates a base injection amount Qb as an open loop manipulated variable for achieving a lean target air-fuel ratio. At this time, the average value of the air-fuel ratio of the air-fuel mixture in the combustion chamber 14 of each cylinder may be set to the target value Af *. In this case, the net exhaust components of all the cylinders may deviate from the exhaust components when the average value of the exhaust air / fuel ratio is the target value, but this may be compensated by air / fuel ratio feedback control.

  Incidentally, the exhaust air-fuel ratio of the target exhaust is defined using a virtual mixture. That is, the unburned fuel concentration (for example, HC), the incomplete combustion component concentration (for example, CO), and the oxygen concentration of the exhaust gas generated when the virtual air-fuel mixture is made of only fresh air and fuel and burned are subject to the target exhaust gas. And the exhaust air / fuel ratio is defined as the air / fuel ratio of the virtual air / fuel mixture. However, the combustion of the virtual mixture here is not limited to combustion in which at least one of the unburned fuel concentration, the incomplete combustion component concentration, and the oxygen concentration becomes zero or a value that can be regarded as zero, but the unburned fuel concentration and incomplete fuel concentration. Combustion in which both the combustion component concentration and the oxygen concentration are greater than zero is also included. The average value of the exhaust air / fuel ratio of the plurality of cylinders is the exhaust air / fuel ratio when the entire exhaust gas discharged from the plurality of cylinders is the target exhaust gas. Incidentally, in the above embodiment, the average value of the exhaust air-fuel ratios of all the cylinders is controlled to the target value.

“Target value”
In the above embodiment, the target value of the average value of the air-fuel ratio of the internal combustion engine is the stoichiometric air-fuel ratio, but it is not limited to this. For example, when using a GPF having a three-way catalyst as a catalyst as described in the “About catalyst” column, the lean air-fuel ratio may be used. In this case, the air-fuel ratio of the lean combustion cylinder is leaner than both the theoretical air-fuel ratio and the target value, and the air-fuel ratio of the rich combustion cylinder is richer than both the theoretical air-fuel ratio and the target value.

About catalyst
The catalyst is not limited to the three-way catalyst 22. For example, a gasoline particulate filter (GPF) provided with a three-way catalyst may be used. In short, a temperature increase request may occur, and the temperature can be increased by utilizing the oxidation heat when oxidizing the unburned fuel component and the incomplete combustion component of the rich combustion cylinder with oxygen of the lean combustion cylinder. Anything is acceptable.

"About control devices"
The control device is not limited to one that includes the CPU 32 and the memory 34 and executes software processing. For example, a dedicated hardware circuit (for example, an ASIC) that performs hardware processing on at least a part of the software processed in the above embodiment may be provided. That is, the control device may have any of the following configurations (a) to (c). (A) A processing device that executes all of the above processing according to a program, and a memory that stores the program. (B) A processing device that executes part of the above processing according to a program, a memory that stores the program, and a dedicated hardware circuit that executes the remaining processing. (C) A dedicated hardware circuit that performs all of the above processes is provided. Here, a plurality of sets of processing devices and memories and dedicated hardware circuits may be provided.

"About internal combustion engines"
The internal combustion engine is not limited to a 4-cylinder internal combustion engine. For example, an in-line 6-cylinder internal combustion engine may be used. In this case, considering that the appearance cycle of adjacent combustion strokes in time series is 120 ° CA, the processing cycle in FIG. 4 may be set to 120 ° CA, for example. Further, for example, a V-type internal combustion engine or the like may include a first catalyst and a second catalyst, and the cylinders from which exhaust gas is purified are different from each other.

"others"
The fuel injection valve is not limited to one that injects fuel into the combustion chamber 14, and may be one that injects fuel into the intake passage 12, for example. It is not essential to perform air-fuel ratio feedback control when performing dither control.

DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine, 12 ... Intake passage, 14 ... Combustion chamber, 16 ... Fuel injection valve, 18 ... Ignition device, 20 ... Exhaust passage, 22 ... Three-way catalyst, 30 ... Control device, 32 ... CPU, 34 ... Memory, 40 ... Air-fuel ratio sensor, 42 ... Rotational speed sensor, 44 ... Air flow meter, 46 ... Water temperature sensor.

Claims (7)

An internal combustion engine provided with a catalyst that purifies exhaust discharged from a plurality of cylinders is a control target,
When a temperature increase request for the catalyst occurs, the air-fuel ratio in the lean combustion cylinder, which is a part of the plurality of cylinders, is controlled to be leaner than the target value for the average value of the air-fuel ratio in the plurality of cylinders. The fuel injection valve corresponding to each cylinder is operated so that the air-fuel ratio in the rich combustion cylinder, which is a cylinder different from the some of the plurality of cylinders, is controlled to be richer than the target value. Dither control processing,
The air-fuel ratio of the lean combustion cylinder is set to be leaner than the target value, and the air-fuel ratio of the rich combustion cylinder is set to the target value on condition that the crankshaft rotational fluctuation during the dither control process is greater than or equal to a predetermined value. The difference between the air-fuel ratio in the lean combustion cylinder and the target value, and the air-fuel ratio in the rich combustion cylinder and the target, while maintaining the average value of the air-fuel ratio in the plurality of cylinders at the target value. A control device for an internal combustion engine that executes a reduction process for reducing a difference from the value.   2. The control device for an internal combustion engine according to claim 1, wherein after the reduction process is executed, the reduction process is executed again on condition that the rotation fluctuation becomes equal to or greater than a predetermined value.   The reduction process increases the amount of reduction of the difference when the difference is reduced on the condition that the rotational fluctuation is greater than or equal to a predetermined value when the frequency of the rotational fluctuation is greater than or equal to the predetermined value. 3. The control device for an internal combustion engine according to claim 1, wherein the control device is a process.   The lean combustion is performed while maintaining the average value of the air-fuel ratios in the plurality of cylinders at the target value on the condition that the rotation fluctuation more than the predetermined value is not detected within a predetermined period after the reduction process is executed. The internal combustion engine according to any one of claims 1 to 3, wherein an increase process is executed to increase a difference between an air-fuel ratio in a cylinder and the target value and a difference between the air-fuel ratio in the rich combustion cylinder and the target value. Control device.   5. The control device for an internal combustion engine according to claim 4, wherein after the increase process is executed, the increase process is executed again on condition that the rotation fluctuation of the predetermined value or more is not detected within the predetermined period.   In the increase process, the increase amount of the difference when the difference is increased on the condition that the rotation fluctuation of the predetermined value or more is not detected within the predetermined period is low when the frequency of the rotation fluctuation becomes a predetermined value or less. The control device for an internal combustion engine according to claim 4 or 5, wherein the control device is larger than a case where the height is higher. The base required value, which is the base value of the required value of the difference between the air-fuel ratio in the lean combustion cylinder and the target value, and the difference between the air-fuel ratio in the rich combustion cylinder and the target value, is set as the operating state of the internal combustion engine. A required value setting process to variably set according to the
Performing a guard process that takes the base request value as input and restricts the request value to be equal to or less than a guard value;
The dither control process controls the difference between the air-fuel ratio of the lean combustion cylinder and the target value, and the difference between the air-fuel ratio of the rich combustion cylinder and the target value to the required value,
The reduction process is to reduce the guard value;
The control device for an internal combustion engine according to any one of claims 4 to 6, wherein the increasing process is to increase the guard value toward the base required value.