JP6805980B2 - Internal combustion engine control device - Google Patents

Description

The present invention relates to an internal combustion engine control device for controlling an internal combustion engine provided with a catalyst for purifying exhaust gas discharged from a plurality of cylinders.

In an internal combustion engine, air-fuel ratio control is performed in which the fuel injection amount is adjusted in order to control the air-fuel ratio of the air-fuel mixture in the combustion chamber to a target value. As one of the air-fuel ratio control, there is an air-fuel ratio control that controls the air-fuel ratio so that the atmosphere of the catalyst becomes a stoichiometric atmosphere based on the detection value of the sensor provided downstream of the catalyst, so-called sub-feedback control of the air-fuel ratio. Are known.

Further, for example, Patent Document 1 describes a control device for an internal combustion engine including a three-way catalyst into which the exhaust gas of four cylinders flows. This control device controls the temperature rise of the catalyst by making the air-fuel ratio of one cylinder of the internal combustion engine richer than the stoichiometric air-fuel ratio, and the air-fuel ratio of the remaining three cylinders leaner than the stoichiometric air-fuel ratio. The perturbation control (dither control) is executed for the lean combustion cylinder. This oxidizes the unburned fuel component and incomplete combustion component in the exhaust gas discharged from the rich combustion cylinder by the oxygen in the exhaust gas discharged from the lean combustion cylinder, and raises the temperature of the three-way catalyst by the heat of oxidation. It is aimed at that.

Japanese Unexamined Patent Publication No. 2012-57492

By the way, the ease of hitting the exhaust gas discharged from each cylinder to the sensor may be such that the exhaust gas discharged from a specific cylinder is particularly easy to hit due to the shape of the exhaust passage or the like. Therefore, when the combination of the rich combustion cylinder and the lean combustion cylinder is changed during the execution of the dither control, the exhaust gas discharged from the above-mentioned specific cylinder, so to speak, the cylinder with a strong gas hit is rich exhaust gas. Will change to lean exhaust, and conversely, lean exhaust will change to rich exhaust. When the exhaust gas that hits the sensor changes to rich or lean in this way, the center of the air-fuel ratio control by the sub-feedback control shifts from the stoichiometric, making it difficult to maintain the atmosphere of the catalyst in a state suitable for exhaust gas purification. There is a risk of becoming.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a control device for an internal combustion engine capable of maintaining an atmosphere of a catalyst in a state suitable for exhaust gas purification.

The control device for an internal combustion engine that solves the above problems targets an internal combustion engine provided with a catalyst that purifies the exhaust gas discharged from a plurality of cylinders. Then, the air-fuel ratio control that controls the air-fuel ratio so that the atmosphere of the catalyst becomes a stoichiometric atmosphere based on the detection value of the sensor provided downstream of the catalyst, and the air-fuel ratio control that controls the temperature rise of the catalyst are generated. 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 with respect to the average value of the air-fuel ratio in the plurality of cylinders, and the part of the plurality of cylinders is controlled. The dither control for operating the fuel injection valve corresponding to each cylinder is executed so as to control the air-fuel ratio in the rich combustion cylinder, which is a cylinder different from the cylinder, richer than the target value. In this control device, a plurality of combinations of cylinders set for the rich combustion cylinder and the lean combustion cylinder are set, and a change processing unit that changes the combination of the cylinders at predetermined intervals during execution of the dither control. And a correction value setting processing unit which changes the correction value for the air-fuel ratio control independently for each combination of the cylinders and changes the correction value according to the change of the combination of the cylinders.

According to the same configuration, when the combination of cylinders set for the rich combustion cylinder and the lean combustion cylinder is changed, the correction value for the air-fuel ratio control is also changed according to the change of the combination of the cylinders. It is changed to the correction value according to. Therefore, it is possible to compensate for the deviation of the catalyst atmosphere from the stoichiometric atmosphere by the execution of the dither control by the correction value, and thereby the catalyst atmosphere can be maintained in an atmosphere suitable for exhaust gas purification.

The schematic diagram which shows the control device and the internal combustion engine in one Embodiment. The block diagram which shows the generation processing of the operation signal of the fuel injection valve in the same embodiment. A timing chart showing changes in the dither correction factor and the stoichiometric correction value in the same embodiment. The flowchart which shows the calculation procedure of the stoichiometric correction value in the same embodiment.

Hereinafter, an embodiment of the control device for an internal combustion engine will be described with reference to FIGS. 1 to 4.
As shown in FIG. 1, the internal combustion engine 10 includes four cylinders, such as a first cylinder # 1, a second cylinder # 2, a third cylinder # 3, and a fourth cylinder # 4, which are arranged in series.

The air in the intake passage 12 of the internal combustion engine 10 is sucked into the combustion chambers 14 of the first cylinder # 1 to the fourth cylinder # 4.
A fuel injection valve 16 projects from the combustion chamber 14, and the 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 generated by the spark discharge of the spark plug 18. Burned through ignition. In the present embodiment, the firing order of the cylinders is in the order of the first cylinder # 1 → the third cylinder # 3 → the fourth cylinder # 4 → the second cylinder # 2.

The burned air-fuel mixture is discharged to the exhaust passage 20 as exhaust gas. The exhaust passage 20 is provided with a three-way catalyst 22 that purifies the exhaust gas.
The control device 30 operates various actuators such as a fuel injection valve 16 and a spark plug 18 in order to execute various controls of the internal combustion engine 10. The control device 30 has an upstream air-fuel ratio Af1 detected by a first air-fuel ratio sensor 40 provided upstream of the three-way catalyst 22 and a second air-fuel ratio Af1 provided downstream of the three-way catalyst 22 in order to perform various controls. Refer to the downstream air-fuel ratio Af2 detected by the air-fuel ratio sensor 50. Further, in order to perform various controls, the control device 30 has an engine rotation speed NE detected by the rotation speed sensor 42, an intake air amount Ga detected by the air flow meter 44, a cooling water temperature THW detected by the water temperature sensor 46, and the like. See also. The control device 30 includes a central processing unit (hereinafter referred to as a CPU) 32, a memory 34, and the like, and the CPU 32 executes various controls of the internal combustion engine 10 by executing a program stored in the memory 34.

FIG. 2 shows a part of the processing realized by the CPU 32 executing the program stored in the memory 34.
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 Afp based on the engine rotation speed NE and the engine load KL. To do. Here, in the present embodiment, the target value Afp is set as the stoichiometric air-fuel ratio. Further, in the present embodiment, as the engine load KL, the engine load factor, which is the ratio of the actual filled air amount to the reference value of the filled air amount to the combustion chamber 14 at the current engine rotation speed NE, is used. This engine load factor is calculated based on the intake air amount Ga and the engine rotation speed NE.

The target value setting processing unit M12 sets the target value Afp of the air-fuel ratio of the air-fuel mixture in the combustion chamber 14. In this target value setting processing unit M12, the target value Afp in which both the sub-correction value SB calculated by the sub-feedback processing unit M60 described later and the stoichiometric correction value SH set by the stoichiometric correction value setting processing unit M70 described later are reflected. Is calculated.

The sub-feedback processing unit M60 is a sub-correction value SB for performing so-called air-fuel ratio sub-feedback control based on the downstream air-fuel ratio Af2 detected by the second air-fuel ratio sensor 50 provided downstream of the three-way catalyst 22. Is calculated. In the present embodiment, the sum of the output values of the proportional element, the integrating element, and the differential element, which is input by subtracting the downstream air-fuel ratio Af2 from the theoretical air-fuel ratio, is a sub-correction value for correcting the target value Afp. Calculated as SB. When the downstream air-fuel ratio Af2 is a value leaner than the theoretical air-fuel ratio, this sub-correction value SB corrects the target value Afp to be a value on the rich side as compared with the value before correction. On the contrary, when the downstream air-fuel ratio Af2 is a value richer than the theoretical air-fuel ratio, the sub-correction value SB corrects the target value Afp to be a leaner value than before the correction. By correcting the target value Afp with the sub-correction value SB, the atmosphere of the three-way catalyst 22 is maintained in a stoichiometric atmosphere, and the exhaust gas purification performance of the three-way catalyst 22 is fully exhibited.

The feedback processing unit M14 calculates a feedback correction value KAF for feedback-controlling the upstream air-fuel ratio Af1 detected by the first air-fuel ratio sensor 40 to the target value Afp. In the present embodiment, the sum of the output values of the proportional element, the integrating element, and the differential element, which are input by subtracting the upstream air-fuel ratio Af1 from the target value Afp, is used as the feedback correction value KAF.

The feedback correction processing unit M16 corrects the base injection amount Qb by multiplying the base injection amount Qb by the feedback correction value KAF.
When a request for raising the temperature of the three-way catalyst 22 occurs, the required value output processing unit M20 sets the average value of the air-fuel ratios of the air-fuel ratios # 1 to # 4 of the internal combustion engine 10 to the target value Afp, and is empty between the cylinders. The injection amount correction request value α of the dither control that makes the fuel ratio different is calculated. Here, in the dither control according to the present embodiment, one of the plurality of cylinders is a rich combustion cylinder # R having an air-fuel ratio richer than the target value Afp, and the remaining cylinders have an air-fuel ratio. The lean combustion cylinder #L is leaner than the target value Afp. Then, the injection amount in the rich combustion cylinder #R is multiplied by "1 + α" of the output value of the feedback correction processing unit M16. Further, the injection amount in the lean combustion cylinder #L is multiplied by "1- (α/3)" of the output value of the feedback correction processing unit M16.

The required value output processing unit M20 determines that the cooling water temperature THW is a predetermined temperature Twth or less, and that the integrated value InG of the intake air amount Ga after the internal combustion engine 10 is started is the first threshold value InthL or more. If the logical product is true, it is determined that the dither control execution condition is satisfied.

Here, the condition that the cooling water temperature THW is equal to or lower than the predetermined temperature Twth is a condition for determining that there is a request for raising the temperature of the three-way catalyst 22 at the time of cold start of the internal combustion engine 10. On the other hand, the condition that the integrated value InG is equal to or higher than 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 catalytic activity temperature. This condition is effective because the three-way catalyst 22 promotes the reaction between the unburned fuel component and the incomplete combustion component in the exhaust gas discharged from the rich combustion cylinder and the oxygen in the exhaust gas discharged from the lean combustion cylinder. This is a condition for raising the temperature of the three-way catalyst 22. By the way, the integrated value InG is used as an amount having a correlation with the total amount of heat energy generated by the combustion of the air-fuel mixture in the combustion chamber 14 after the start of the internal combustion engine 10. Further, in the present embodiment, the dither control is executed in the period until the three-way catalyst 22 reaches the active temperature as a whole.

Then, when the above execution condition of the dither control is satisfied, the request value output processing unit M20 calculates the injection amount correction request value α. Specifically, the CPU 32 variably sets the injection amount correction request value α according to the engine rotation speed NE, the engine load KL, and the cooling water temperature THW. Here, the CPU 32 sets the injection amount correction request value α to a larger value when the cooling water temperature THW is low than when it is high. This is because when the cooling water temperature THW is low, there is a need to increase the rate of temperature rise of the three-way catalyst 22 as compared with the case where the cooling water temperature THW is high. Further, when the engine rotation speed NE is low, the CPU 32 sets the injection amount correction request value α to a larger value than when the engine rotation speed NE is high. This is because when the engine rotation speed NE is low, the number of combustion cycles per unit time is small, so that the temperature rise rate of the three-way catalyst 22 by dither control is higher than when the engine rotation speed NE is high. It is considered to be slow. Further, when the engine load KL is high, the CPU 32 sets the injection amount correction request value α to a larger value than when the engine load KL is low. This is because the combustion stability of the air-fuel mixture is higher when the engine load KL is higher than when the engine load is low, so even if the degree of leanness of the lean combustion cylinder and the degree of richness of the rich combustion cylinder are increased, combustion will occur. This is for stability.

The rich correction coefficient calculation processing unit M22 adds "1" to the injection amount correction request value α to correct the output value of the feedback correction processing unit M16 with respect to the rich combustion cylinder #R. Is calculated.

The multiplication processing unit M24 multiplies the injection amount correction request value α by “-1/3”.
The lean correction coefficient calculation processing unit M26 adds "1" to the output value "-α/3" of the multiplication processing unit M24 to correct the output value of the feedback correction processing unit M16 with respect to the lean combustion cylinder #L. The lean correction coefficient LH, which is a coefficient, is calculated.

The dither correction processing unit M28 multiplies the output value of the feedback correction processing unit M16 by the rich correction coefficient RH (= 1 + α), so that the rich cylinder injection amount command value Qp (which is the injection amount command value of the rich combustion cylinder #R) ( R) is calculated.

The dither correction processing unit M30 is a lean cylinder which is an injection amount command value of the lean combustion cylinder #L by multiplying the output value of the feedback correction processing unit M16 by the lean correction coefficient LH (= 1- (α / 3)). The injection amount command value Qp (L) is calculated.

The rich combustion cylinder change processing unit M40 changes the cylinder set in the rich combustion cylinder #R.
As shown in FIG. 3, in the present embodiment, in the cylinder set to the rich combustion cylinder #R, a period until the number of times the combustion stroke is performed reaches a specified value (rich cylinder holding period HP shown in FIG. 3) elapses. Then, the rich combustion cylinder #R is changed to another cylinder through the rich cylinder change period CP.

For example, in the present embodiment, the rich combustion cylinder #R is changed in the order of ignition of the cylinders. Therefore, the rich combustion cylinder #R is repeatedly changed in the order of the first cylinder # 1 → the third cylinder # 3 → the fourth cylinder # 4 → the second cylinder # 2. The rich combustion cylinder change processing unit M40 also sets the lean combustion cylinder #L in accordance with the setting of the rich combustion cylinder #R. In the present embodiment, by implementing the dither control, the combinations of the cylinders set in the rich combustion cylinder #R and the lean combustion cylinder #L are as follows.

-A combination in which the first cylinder # 1 becomes a rich combustion cylinder # R, and the second cylinder # 2, the third cylinder # 3, and the fourth cylinder # 4 become a lean combustion cylinder # L.
-A combination in which the second cylinder # 2 becomes a rich combustion cylinder # R, and the first cylinder # 1, the third cylinder # 3, and the fourth cylinder # 4 become a lean combustion cylinder # L.

-A combination in which the third cylinder # 3 becomes a rich combustion cylinder # R, and the first cylinder # 1, the second cylinder # 2 and the fourth cylinder # 4 become a lean combustion cylinder # L.
-A combination in which the 4th cylinder # 4 becomes a rich combustion cylinder # R, and the 1st cylinder # 1, the 2nd cylinder # 2 and the 3rd cylinder # 3 become a lean combustion cylinder # L.

Further, as shown in FIG. 3, in the rich cylinder change period CP, the dither correction factor is gradually changed in each cylinder in order to avoid a sudden change in the output torque due to the change in the rich combustion cylinder #R. The dither correction factor refers to the rate of increase / decrease in the base injection amount Qb corrected by the dither control, and the dither correction factor in the rich combustion cylinder #R is "injection amount correction required value α × 100%", lean combustion. The dither correction factor in the cylinder #L is a value represented by "-(injection amount correction required value α / 3) x 100%".

In order to gradually change the dither correction factor in each cylinder, the required value output processing unit M20 is set to the current engine operating state (engine rotation speed NE, engine load KL, cooling water temperature THW) in the rich cylinder change period CP. The decrease gradual change process and the increase gradual change process for gradually changing the injection amount correction request value α set accordingly are performed. More specifically, when the injection amount correction request value α set according to the current engine operating state is set to the pre-gradual change request value αb, the pre-slow change request value αb is gradually set toward “0”. As a process for reducing the size, the above-mentioned gradual decrease treatment is performed. Then, when the value after the gradual change processing is set to the required value αa after the gradual change, the dither correction of each cylinder is performed by outputting the required value αa after the gradual change as the injection amount correction required value α. Bring the rate closer to "0%".

Then, when the required value αa after the gradual change becomes “0”, that is, when the dither correction factor of each cylinder becomes “0%”, the rich combustion cylinder change processing unit M40 selects the cylinder set as the rich combustion cylinder #R. change. For example, when the first cylinder # 1 is set to the rich combustion cylinder # R, when the required value αa after gradual change becomes “0” and the dither correction factor becomes “0%” (time t1 in FIG. 3). ), The rich combustion cylinder #R is changed from the first cylinder # 1 to the third cylinder # 3, and the first cylinder # 1 is changed to the lean combustion cylinder #L.

Further, when the required value αa after the gradual change becomes “0”, the required value output processing unit M20 performs injection set according to the current engine operating state (engine rotation speed NE, engine load KL, cooling water temperature THW). When the amount correction request value α is set to the pre-slow change request value αb, the above-mentioned increase and gradual change is performed as a process of gradually increasing the injection amount correction request value α that has become “0” so as to return to the pre-slow change request value αb. Apply processing. Then, when the value after the gradual change processing is set to the required value αa after the gradual change, the required value αa after the gradual change is output as the injection amount correction required value α, whereby the rich combustion cylinder # The dither correction factor of the cylinder set to R is gradually returned to the value of "α x 100%" according to the engine operating state, and the dither correction factor of the cylinder set to the lean combustion cylinder #L is also in the engine operating state. It gradually returns to the value of "-(α / 3) x 100%" according to.

Further, the request value output processing unit M20 divides the required value αa after the slow change by the required value αb before the slow change during the execution of the decrease slow change process and the increase slow change process, and divides the value by the slow change rate RZ. It is calculated as (= αa / αb) and output to the stoichiometric correction value setting processing unit M70. This gradual change rate RZ gradually changes from "1" to "0" when the decrease gradual change process is started, and from "0" to "1" when the increase gradual change process is started. It will change gradually.

The stoichiometric correction value setting processing unit M70 sets the stoichiometric correction value SH based on the cylinder number set in the rich combustion cylinder #R, the engine rotation speed NE, the engine load KL, and the like. The stoichiometric correction value SH is a value described below.

Ease of hitting the exhaust gas discharged from each cylinder to the second air-fuel ratio sensor 50, so to speak, hitting the gas of each cylinder, the exhaust gas discharged from a specific cylinder becomes particularly easy to hit due to the shape of the exhaust passage and the like. May be. Therefore, when the exhaust gas discharged from the rich combustion cylinder #R easily hits the second air-fuel ratio sensor 50, the downstream air-fuel ratio Af2 becomes a value closer to rich, so that the target value Afp of the air-fuel ratio is set through the above sub-feedback control. It is corrected to a value closer to lean. When the target value Afp is corrected to a value closer to lean in this way, the control center of the air-fuel ratio is on the lean side, so that the three-way catalyst 22 tends to have a lean atmosphere, for example, the purification rate of NOx is lowered. There is a risk. Further, when the control center of the air-fuel ratio is on the lean side, the unburned fuel component and the incomplete combustion component in the exhaust gas discharged from the rich combustion cylinder #R are reduced, so that the temperature raising effect by the dither control may be reduced. is there.

On the contrary, when the exhaust gas discharged from the lean combustion cylinder #L easily hits the second air-fuel ratio sensor 50, the downstream air-fuel ratio Af2 becomes a value closer to lean, so the target value Afp of the air-fuel ratio is obtained through the above sub-feedback control. Is corrected to a value closer to rich. When the target value Afp is corrected to a value closer to rich in this way, the control center of the air-fuel ratio is on the rich side, so that the three-way catalyst 22 tends to have a rich atmosphere, for example, the purification rate of HC and CO decreases. There is a risk of Further, when the control center of the air-fuel ratio is on the rich side, oxygen in the exhaust gas discharged from the lean combustion cylinder is reduced, which may also reduce the effect of raising the temperature by dither control.

Therefore, when the three-way catalyst 22 tends to have a lean atmosphere or a rich atmosphere due to the interaction between the gas contact and the sub-feedback control, the target value Afp is corrected so that the atmosphere of the three-way catalyst 22 becomes stoichiometric. As the value, the stoichiometric correction value SH is set. For example, as described above, when the exhaust gas discharged from the rich combustion cylinder #R easily hits the second air-fuel ratio sensor 50 and the downstream air-fuel ratio Af2 becomes a value closer to rich, through the above sub-feedback control. Since the target value Afp of the air-fuel ratio is corrected to a value closer to lean, the three-way catalyst 22 tends to have a lean atmosphere. When the three-way catalyst 22 tends to have a lean atmosphere in this way, a value for correcting the target value Afp to the rich side is set as the stoichiometric correction value SH.

On the contrary, when the exhaust gas discharged from the lean combustion cylinder #L easily hits the second air-fuel ratio sensor 50 and the downstream air-fuel ratio Af2 becomes a value closer to lean, the air-fuel ratio target is achieved through the above sub-feedback control. Since the value Afp is corrected to a value closer to rich, the three-way catalyst 22 tends to have a rich atmosphere. When the three-way catalyst 22 tends to have a rich atmosphere in this way, a value for correcting the target value Afp to the lean side is set as the stoichiometric correction value SH.

In the present embodiment, the stoichiometric correction value SH is added to the target value Afp, and when the stoichiometric correction value SH is a positive value, the target value Afp is corrected to the lean side. Further, when the stoichiometric correction value SH is a negative value, the target value Afp is corrected to the rich side. By the way, the target value Afp may be corrected by multiplying the target value Afp by the stoichiometric correction value SH. In this case, a value larger than "1" is stoichiometrically corrected as a value for correcting the target value Afp to the lean side. The value SH may be set, and a value larger than "0" and smaller than "1" may be set as the stoichiometric correction value SH as a value for correcting the target value Afp to the rich side.

Further, since the gas contact of each cylinder with respect to the second air-fuel ratio sensor 50 changes according to the engine rotation speed NE and the engine load KL, the stoichiometric correction value SH is set based on the engine rotation speed NE and the engine load KL. ..

Further, in the present embodiment, the above dither control is performed, and while the dither control is being executed, the combination of the cylinders set in the rich combustion cylinder #R and the lean combustion cylinder #L is sequentially changed. .. Therefore, when the cylinder having a strong gas contact with the second air-fuel ratio sensor 50 is the rich combustion cylinder #R, the three-way catalyst 22 tends to have a lean atmosphere, so that the above target value Afp is set as the stoichiometric correction value SH. It is necessary to set the value to be corrected on the rich side. On the contrary, when the cylinder having a strong gas contact with the second air-fuel ratio sensor 50 is the lean combustion cylinder #L, the three-way catalyst 22 tends to have a rich atmosphere, so that the stoichiometric correction value SH is the above target value Afp. It is necessary to set a value to correct to the lean side. That is, the stoichiometric correction value SH needs to be changed according to the combination of the cylinders set in the rich combustion cylinder #R and the lean combustion cylinder #L.

Therefore, the stoichiometric correction value SH is a value that corrects the target value Afp so that the atmosphere of the three-way catalyst 22 becomes stoichiometric, and is a value that is variably set according to the engine rotation speed NE and the engine load KL. Is set for each combination of cylinders set in the rich combustion cylinder #R and the lean combustion cylinder #L. The optimum value of the stoichiometric correction value SH is set in advance through experiments and the like.

For example, as shown in FIG. 3 above, the cylinder with strong gas contact with the second air-fuel ratio sensor 50 is the second cylinder # 2, and the second cylinder # 2 is the rich combustion cylinder # R. When it is, the target value Afp is corrected to the rich side by setting a negative value as the stoichiometric correction value SH. On the other hand, when the second cylinder # 2 is the lean combustion cylinder # L, the target value Afp is corrected to the lean side by setting a positive value as the stoichiometric correction value SH.

The operation signal generation processing unit M50 sets the cylinder set to the rich combustion cylinder #R and the lean combustion cylinder #L based on the rich cylinder injection amount command value Qp (R) and the lean cylinder injection amount command value Qp (L). An operation signal MS1 of each fuel injection valve 16 provided in each of the cylinders is generated and output to the corresponding fuel injection valve 16. Then, the amount of fuel injected from the fuel injection valve 16 of the rich combustion cylinder becomes the rich cylinder injection amount command value Qp (R), and the amount of fuel injected from the fuel injection valve 16 of the lean combustion cylinder becomes the lean cylinder injection amount command value. Each fuel injection valve 16 is operated so as to have Qp (L).

Next, the processing of the stoichiometric correction value setting processing unit M70 will be described with reference to FIG.
FIG. 4 shows a procedure for calculating the stoichiometric correction value SH. The process shown in FIG. 4 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" added at the beginning.

In the series of processes shown in FIG. 4, the CPU 32 determines whether or not dither control is being executed (S100). The determination in S100 can be appropriately performed. For example, it can be determined that the dither control is executed when the above-mentioned execution condition of the dither control is satisfied or when the injection amount correction request value α is larger than “0”.

Then, when the dither control is not executed (S100: NO), the CPU 32 temporarily ends this process.
On the other hand, when the dither control is being executed (S100: YES), the CPU 32 acquires the engine rotation speed NE, the engine load KL, the cylinder number set in the rich combustion cylinder #R, and the gradual change rate RZ (the gradual change rate RZ). S110).

Next, the CPU 32 determines whether or not the first cylinder # 1 is set to the rich combustion cylinder # R (S120). Then, when the first cylinder # 1 is set to the rich combustion cylinder # R (S120: YES), the CPU 32 sets the first stoichiometric correction value SH1 to the stoichiometric correction value SH (S130).

The first stoichiometric correction value SH1 is the atmosphere of the three-way catalyst 22 when the first cylinder # 1 is set to the rich combustion cylinder # R and the other cylinders are set to the lean combustion cylinder # L. Is a value for correcting the target value Afp so as to have a stoichiometric atmosphere, and is a value set according to the engine rotation speed NE and the engine load KL.

When it is determined in S120 that the first cylinder # 1 is not set to the rich combustion cylinder # R (S120: NO), the CPU 32 determines whether the second cylinder # 2 is set to the rich combustion cylinder # R. (S140). Then, when the second cylinder # 2 is set to the rich combustion cylinder # R (S140: YES), the CPU 32 sets the second stoichiometric correction value SH2 to the stoichiometric correction value SH (S150).

This second stoichiometric correction value SH2 is the atmosphere of the three-way catalyst 22 when the second cylinder # 2 is set to the rich combustion cylinder # R and the other cylinders are set to the lean combustion cylinder # L. Is a value for correcting the target value Afp so as to have a stoichiometric atmosphere, and is a value set according to the engine rotation speed NE and the engine load KL.

When it is determined in S140 that the second cylinder # 2 is not set to the rich combustion cylinder # R (S140: NO), the CPU32 determines whether or not the third cylinder # 3 is set to the rich combustion cylinder # R. (S160). Then, when the third cylinder # 3 is set to the rich combustion cylinder # R (S160: YES), the CPU 32 sets the third stoichiometric correction value SH3 to the stoichiometric correction value SH (S170).

The third stoichiometric correction value SH3 is the atmosphere of the three-way catalyst 22 when the third cylinder # 3 is set to the rich combustion cylinder # R and the other cylinders are set to the lean combustion cylinder # L. Is a value for correcting the target value Afp so as to have a stoichiometric atmosphere, and is a value set according to the engine rotation speed NE and the engine load KL.

When it is determined in S160 that the third cylinder # 3 is not set to the rich combustion cylinder # R (S160: NO), the CPU 32 sets the fourth stoichiometric correction value SH4 to the stoichiometric correction value SH. (S180).

The fourth stoichiometric correction value SH4 is the atmosphere of the three-way catalyst 22 when the fourth cylinder # 4 is set to the rich combustion cylinder # R and the other cylinders are set to the lean combustion cylinder # L. Is a value for correcting the target value Afp so as to have a stoichiometric atmosphere, and is a value set according to the engine rotation speed NE and the engine load KL.

When the stoichiometric correction value SH is set in any of the processing of S130, the processing of S150, the processing of S170, or the processing of S180, the CPU 32 gradually sets the stoichiometric correction value SH with respect to the set stoichiometric correction value SH. The value obtained by multiplying the variable rate RZ is set as the final stoichiometric correction value SH (S190), and this process is temporarily terminated.

According to the present embodiment described above, the following effects can be obtained.
(1) The stoichiometric correction value SH is set for each combination of cylinders set in the rich combustion cylinder #R and the lean combustion cylinder #L. Therefore, even when the exhaust gas discharged from the rich combustion cylinder #R hits the second air-fuel ratio sensor 50 or the exhaust gas discharged from the lean combustion cylinder #L hits the second air-fuel ratio sensor 50 due to the execution of the dither control, The target value Afp of the air-fuel ratio will be corrected appropriately. That is, by correcting the target value Afp by the stoichiometric correction value SH, it becomes possible to compensate that the atmosphere of the three-way catalyst 22 deviates from the stoichiometric atmosphere, whereby the atmosphere of the three-way catalyst 22 is suitable for exhaust gas purification. The atmosphere can be maintained.

(2) The stoichiometric correction value SH is variably set according to the engine rotation speed NE and the engine load KL. Therefore, the stoichiometric correction value SH can be set more appropriately according to the change per gas of each cylinder with respect to the second air-fuel ratio sensor 50.

(3) When changing the rich combustion cylinder #R, a rich cylinder change period CP was provided to gradually change the dither correction factor in each cylinder. Therefore, when the rich combustion cylinder #R is changed, the fuel injection amount of each cylinder gradually changes. Therefore, a sudden change in output torque due to a change in the rich combustion cylinder #R can be suppressed.

(4) In the present embodiment, in the rich cylinder change period CP, which is a transitional period for changing the rich combustion cylinder #R, each of the above-mentioned gradual change processes (the above-mentioned decrease gradual change process and the above-mentioned increase gradual change process) regarding the injection amount correction required value α By carrying out the change processing), the dither correction factor gradually changes within the rich cylinder change period CP. Here, in the process of S190 shown in FIG. 4, the gradual change rate RZ is set to the stoichiometric correction value SH set according to the combination of the cylinders set in the rich combustion cylinder #R and the lean combustion cylinder #L. By multiplying, the final stoichiometric correction value SH is obtained.

Therefore, as shown in FIG. 3, the stoichiometric correction value SH gradually changes in synchronization with the change in the dither correction factor within the rich cylinder change period CP. Therefore, the target value Afp can be corrected so that the atmosphere of the three-way catalyst 22 becomes a stoichiometric atmosphere even in the transitional period in which the rich combustion cylinder #R is changed.

(5) If the rich combustion cylinder #R is fixed to a specific cylinder without being changed, for example, the deposit amount of the fuel injection valve 16 provided in the rich combustion cylinder #R may increase, or the rich combustion cylinder #R may be fixed. Since the exhaust gas discharged from R always passes through a specific region in the three-way catalyst 22, catalyst deterioration may progress locally. In this regard, in the present embodiment, since the rich combustion cylinder #R is sequentially changed, it is possible to suppress an increase in the deposit amount of the fuel injection valve 16 in such a specific cylinder and the progress of local catalyst deterioration. Can be done.

The above embodiment can also be modified and implemented as follows.
-The stoichiometric correction value SH is variably set based on the engine speed NE and the engine load KL. In addition, for simplicity, the variable setting based on the engine speed NE and the engine load KL is omitted, and at least the stoichiometric correction value is set for each combination of the rich combustion cylinder #R and the lean combustion cylinder #L. SH may be set respectively. Even in this case, deterioration of the catalyst atmosphere due to the change in gas per gas due to the execution of dither control can be suppressed.

-The processing of S190 shown in FIG. 4 may be omitted.
-When changing the rich combustion cylinder #R, the rich cylinder change period CP shown in FIG. 3 above was provided to gradually change the dither correction factor in each cylinder. In addition, the dither correction factor may be changed immediately when the rich combustion cylinder #R is changed by omitting the rich cylinder change period CP. In this case, since the gradual change rate RZ cannot be calculated, the process of S190 shown in FIG. 4 above is omitted.

-The execution conditions for dither control are not limited to those illustrated in the above embodiment, and for example, a sensor for detecting the temperature of the three-way catalyst 22 is provided, and the detection value of the sensor is equal to or higher than a predetermined temperature and lower than the specified temperature. May be an execution condition. 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 the 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 22 reaches the active temperature as a whole. For example, dither control may be performed for the sulfur poisoning recovery treatment even after the three-way catalyst 22 has reached the active temperature throughout.

Further, for example, when entering a temperature region in which the amount of sulfur poisoning is likely to increase in a temperature region higher than the active temperature of the three-way catalyst 22, the three-way catalyst 22 is higher than the temperature region in which the amount of sulfur poisoning is likely to increase. Dither control may be performed to increase the temperature of the.

Further, for example, it may be an execution condition of dither control that a request for raising 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 logical product of the outside air temperature to be less than or equal to the determination value and the engine load to be less than or equal to the predetermined value to be true.

Further, for example, as described below, when a gasoline particulate filter (GPF) equipped with a three-way catalyst is used as a catalyst, it is a condition for executing dither control that there is a request to remove particulate matter clogged in the GPF. It may be. This can be realized, for example, by setting that the difference between the pressure on the upstream side and the pressure on the downstream side of the GPF is equal to or greater than the threshold value.

Further, for example, when the temperature of the upstream end of the three-way catalyst 22 reaches the catalytic activity temperature, dither control is performed unless the temperature becomes excessively high enough to reduce the reliability of the three-way catalyst 22. It may be executed all the time.

-In the above embodiment, the number of lean combustion cylinders # L is larger than the number of rich combustion cylinders # R, but the number is not limited to this. For example, the number of lean combustion cylinders #L and the number of rich combustion cylinders #R may be the same. It is not essential that the total number of lean combustion cylinders # L and the number of rich combustion cylinders # R match 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 is determined. By setting the stoichiometric air-fuel ratio, a cylinder that is neither lean combustion cylinder # L nor rich combustion cylinder # R may be used. By the way, as described below, even when a plurality of catalysts having different exhaust gas purification components are provided, the total of the number of lean combustion cylinders and the number of rich combustion cylinders for which one catalyst purifies the exhaust gas is internal combustion. It will be less than the number of cylinders in the engine.

-The dither control process is not limited to setting the correction amount of the fuel injection amount. For example, the base injection amount calculation processing unit M10 may be separately provided for each of the rich combustion cylinder #R and the lean combustion cylinder #L. In this case, the base injection amount calculation processing unit M10 for the rich combustion cylinder calculates the base injection amount Qb as the open loop operation amount for achieving the rich target air-fuel ratio, and the base injection amount calculation processing for the lean combustion cylinder. Part M10 calculates the base injection amount Qb as the open loop operation amount for achieving a lean target air-fuel ratio. At this time, the average value of the air-fuel ratio of the air-fuel ratio in the combustion chamber 14 of each cylinder may be set to the target value Afp.

-In the above embodiment, the target value Afp of the average value of the air-fuel ratio of the internal combustion engine 10 is set as the theoretical air-fuel ratio, but the present invention is not limited to this. For example, as described above, when a GPF equipped with a three-way catalyst is used as the catalyst, the target value Afp may be leaner than the stoichiometric air-fuel ratio. In this case, the air-fuel ratio of the lean combustion cylinder #L is made leaner than both the theoretical air-fuel ratio and the target value Afp, and the air-fuel ratio of the rich combustion cylinder #R is set to both the theoretical air-fuel ratio and the target value Afp. Make it richer than.

-The catalyst is not limited to the three-way catalyst 22. For example, it may be a gasoline particulate filter (GPF) equipped with a three-way catalyst. The point is that a temperature rise request can occur, and the heat of oxidation when the oxygen in the lean combustion cylinder #L oxidizes the unburned fuel component (HC) and incomplete combustion component (CO) in the rich combustion cylinder #R Anything that can raise the temperature by using

The second air-fuel ratio sensor 50 may be changed to an oxygen sensor whose output voltage changes significantly with the theoretical air-fuel ratio as a boundary.
The control device 30 is not limited to the one that includes the CPU 32 and the memory 34 and executes software processing. For example, a dedicated hardware circuit (for example, ASIC or the like) for hardware processing 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). There may be a plurality of sets of processing devices and memories, and a plurality of dedicated hardware circuits.

(A) A processing device that executes all of the above processing according to a program and a memory for storing the program are provided.
(B) A processing device for executing a part of the above processing according to the program, a memory for storing the program, and a dedicated hardware circuit for executing the remaining processing are provided.

(C) A dedicated hardware circuit for executing all of the above processes is provided.
-The internal combustion engine 10 is not limited to a 4-cylinder internal combustion engine. For example, an in-line 6-cylinder internal combustion engine may be used. Further, for example, a V-type internal combustion engine or the like, which includes a first catalyst and a second catalyst, may have different cylinders for purifying exhaust gas.

-The fuel injection valve 16 is not limited to the one that injects fuel into the combustion chamber 14, and may be, for example, one that injects fuel into the intake passage 12.

10 ... Internal combustion engine, 12 ... Intake passage, 14 ... Combustion chamber, 16 ... Fuel injection valve, 18 ... Spark plug, 20 ... Exhaust passage, 22 ... Three-way catalyst, 30 ... Control device, 32 ... Central processing device (CPU) , 34 ... Memory, 40 ... 1st air-fuel ratio sensor, 42 ... Rotation speed sensor, 44 ... Air flow meter, 46 ... Water temperature sensor, 50 ... 2nd air-fuel ratio sensor, # 1 ... 1st cylinder, # 2 ... 2nd cylinder , # 3 ... 3rd cylinder, # 4 ... 4th cylinder.

Claims (1)

The control target is an internal combustion engine equipped with a catalyst that purifies the exhaust gas discharged from multiple cylinders.
Air-fuel ratio control that controls the air-fuel ratio so that the atmosphere of the catalyst becomes a stoichiometric atmosphere based on the detection value of the sensor provided downstream of the catalyst.
When a temperature rise 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 with respect to the average value of the air-fuel ratio in the plurality of cylinders. , The fuel injection valve corresponding to each of the cylinders is operated so as to control the air-fuel ratio of the rich combustion cylinder, which is a cylinder different from the part of the plurality of cylinders, more richly than the target value. It is a control device that executes dither control and
A plurality of combinations of cylinders set to the rich combustion cylinder and the lean combustion cylinder are set, and a change processing unit that changes the combination of the cylinders at predetermined intervals during execution of the dither control, and a change processing unit.
Control of an internal combustion engine including a correction value setting processing unit in which a correction value for the air-fuel ratio control is independently set for each combination of the cylinders and the correction value is changed according to a change in the combination of the cylinders. apparatus.