JP6992702B2 - Internal combustion engine control device - Google Patents

Description

The present invention relates to an internal combustion engine control device applied to a spark ignition type internal combustion engine.

Patent Document 1 describes an example of an internal combustion engine using gasoline as fuel. The exhaust purification device of the internal combustion engine includes a three-way catalyst provided in the exhaust passage and a particulate filter arranged downstream of the three-way catalyst in the exhaust passage.

In the internal combustion engine described in Patent Document 1, combustion in the cylinder may be stopped when the load applied to the internal combustion engine is low when the required torque for the internal combustion engine is reduced due to the cancellation of the accelerator operation or the like. be. In such a combustion stop period, a fuel cut process for stopping the fuel injection of the fuel injection valve and a fuel introduction process for injecting fuel from the fuel injection valve and causing the fuel to flow out from the cylinder to the exhaust passage without being burned. One of the processes is selected and executed. According to Patent Document 1, a fuel introduction process is executed when the particulate filter is regenerated. On the other hand, when the regeneration is not performed, the fuel cut process is executed.

In the fuel introduction process, the fuel injected from the fuel injection valve flows through the exhaust passage together with the air. Then, when the fuel is introduced into the three-way catalyst, the temperature of the three-way catalyst rises due to the combustion of the fuel. Then, the high-temperature gas flows into the particulate filter, and the temperature of the particulate filter rises. As a result, the particulate matter collected in the particulate filter is burned.

By the way, in an internal combustion engine, a catalyst diagnosis process for diagnosing whether or not an abnormality caused by deterioration occurs in a three-way catalyst may be executed when combustion is performed in a cylinder. In the catalyst diagnosis process, for example, as described in Patent Document 2, the air-fuel ratio is set to a value on the lean side of the stoichiometric air-fuel ratio to saturate the oxygen occlusion of the three-way catalyst, and then the air-fuel ratio is set to be higher than the stoichiometric air-fuel ratio. Set the value on the rich side to reduce the oxygen storage amount. At this time, the detection time, which is the time required from the time when the air-fuel ratio is set to the value on the rich side of the stoichiometric air-fuel ratio until the oxygen stored in the three-way catalyst is depleted, is detected. The maximum value of oxygen occlusion of the three-way catalyst tends to decrease as the deterioration of the three-way catalyst progresses. That is, the smaller the maximum value of the oxygen storage amount at that time, the shorter the detection time. Therefore, it can be said that the detection time correlates to some extent with the degree of deterioration of the three-way catalyst. Therefore, it is possible to diagnose whether or not an abnormality has occurred in the three-way catalyst based on the detection time.

U.S. Patent Application Publication No. 2014/0041362 JP-A-2015-218646

The three-way catalyst has a characteristic that the maximum value of oxygen occlusion changes depending on the temperature. In particular, when the temperature of the three-way catalyst is equal to or higher than the specified temperature, the maximum value of the oxygen occlusion of the three-way catalyst decreases as the temperature of the three-way catalyst increases. That is, when the temperature of the three-way catalyst is equal to or higher than the specified temperature, the maximum value of oxygen occlusion of the three-way catalyst may become small even though the deterioration of the three-way catalyst has not progressed so much.

If the fuel introduction process is executed during the combustion stop period, the temperature of the three-way catalyst may be higher than the specified temperature. When combustion in the cylinder is restarted and the catalyst diagnosis process is executed under the condition that the temperature of the three-way catalyst is higher than the specified temperature, the above detection time is the actual degree of deterioration of the three-way catalyst. It will be shorter than the time according to. As a result, it may be diagnosed that an abnormality has occurred in the three-way catalyst even though the deterioration of the three-way catalyst has not progressed to the extent that it can be diagnosed as an abnormality.

The internal combustion engine control device for solving the above problems is a spark-ignition type internal combustion engine in which a three-way catalyst is arranged in an exhaust passage and an air-fuel mixture containing fuel injected from a fuel injection valve is burned in a cylinder. Applies to institutions. This internal combustion engine control device sets the air-fuel ratio to a value on the lean side of the stoichiometric air-fuel ratio and then sets the air-fuel ratio to a value on the rich side of the stoichiometric air-fuel ratio when combustion is being performed in the cylinder. Through the implementation of the air-fuel ratio control, a catalyst diagnostic process for diagnosing whether or not an abnormality has occurred in the three-way catalyst is executed. Further, the control device of the internal combustion engine has a fuel cut process for stopping the fuel injection of the fuel injection valve when the combustion in the cylinder is stopped under the condition that the crank shaft of the internal combustion engine is rotating. One of the fuel introduction processes of injecting fuel from the fuel injection valve and causing the fuel to flow out from the cylinder to the exhaust passage without being burned is selected and executed. Then, when the fuel introduction process is executed while the combustion in the cylinder is stopped, the control device of the internal combustion engine restarts the combustion in the cylinder even if the combustion in the cylinder is restarted. The execution of the catalyst diagnostic process is prohibited from the time when it is performed until the specified period elapses.

When the fuel introduction process is executed, the unburned fuel introduced into the three-way catalyst burns, and the temperature of the three-way catalyst rises. When the temperature of the three-way catalyst exceeds the specified temperature, the maximum value of the oxygen occlusion of the three-way catalyst decreases as the temperature of the three-way catalyst increases. Then, when the fuel introduction process is executed, the temperature of the three-way catalyst may exceed the specified temperature. Therefore, if the fuel introduction process is executed during the combustion stop period in the cylinder, the temperature of the three-way catalyst becomes higher than the specified temperature at the time when the stop period ends and the combustion in the cylinder is restarted. There are times when.

According to the above configuration, when the fuel introduction process is executed during the combustion stop period in the cylinder, the specified period elapses even if the stop period ends and the combustion in the cylinder is restarted. Until then, the catalyst diagnostic process will not be executed. That is, it is possible to suppress the execution of the catalyst diagnosis process when the maximum value of the oxygen storage amount of the three-way catalyst is small because the temperature of the three-way catalyst is higher than the specified temperature. As a result, it is possible to prevent the three-way catalyst from being diagnosed as having an abnormality when the deterioration of the three-way catalyst has not progressed to the extent that it can be diagnosed as an abnormality.

Therefore, even if the fuel introduction process is executed during the combustion stop period in the cylinder, it is possible to suppress a decrease in diagnostic accuracy as to whether or not an abnormality has occurred in the three-way catalyst.

FIG. 6 is a configuration diagram showing an outline of a control device including an internal combustion engine control unit which is a control device of the internal combustion engine of the embodiment and a hybrid vehicle equipped with the control device. The figure which shows the functional composition of the internal combustion engine control unit, and the schematic structure of the internal combustion engine mounted on the hybrid vehicle. The flowchart which shows the processing procedure for controlling the fuel injection valve during the period when the combustion of the air-fuel mixture in a cylinder is stopped. The flowchart which shows the processing procedure for determining whether or not the execution of a catalyst diagnosis processing is prohibited. The flowchart which shows the processing procedure for diagnosing whether or not an abnormality has occurred in a three-way catalyst. The graph which shows the relationship between the maximum value of oxygen occlusion in a three-way catalyst and the temperature of a three-way catalyst. Timing chart when the condition to stop the combustion of the air-fuel mixture in the cylinder is not satisfied while the fuel introduction process is being executed.

Hereinafter, an embodiment of the control device for an internal combustion engine will be described with reference to FIGS. 1 to 7.
FIG. 1 illustrates a schematic configuration of a hybrid vehicle. As shown in FIG. 1, the hybrid vehicle includes an internal combustion engine 10, a power distribution integration mechanism 40 connected to the crank shaft 14 of the internal combustion engine 10, and a first motor generator connected to the power distribution integration mechanism 40. It is equipped with 71. A second motor generator 72 is connected to the power distribution integration mechanism 40 via a reduction gear 50, and a drive wheel 62 is connected via a reduction mechanism 60 and a differential 61.

The power distribution integrated mechanism 40 is a planetary gear mechanism, and has a sun gear 41 of an external gear and a ring gear 42 of an internal gear coaxially arranged with the sun gear 41. A plurality of pinion gears 43 that mesh with both the sun gear 41 and the ring gear 42 are arranged between the sun gear 41 and the ring gear 42. Each pinion gear 43 is supported by the carrier 44 in a state where it can rotate and revolve freely. A first motor generator 71 is connected to the sun gear 41. A crank shaft 14 is connected to the carrier 44. A ring gear shaft 45 is connected to the ring gear 42, and both the reduction gear 50 and the reduction mechanism 60 are connected to the ring gear shaft 45.

When the output torque of the internal combustion engine 10 is input to the carrier 44, the output torque is distributed to the sun gear 41 side and the ring gear 42 side. That is, by inputting the output torque of the internal combustion engine 10 to the first motor generator 71, the first motor generator 71 can generate electricity.

On the other hand, when the first motor generator 71 is made to function as an electric motor, the output torque of the first motor generator 71 is input to the sun gear 41. Then, the output torque of the first motor generator 71 input to the sun gear 41 is distributed to the carrier 44 side and the ring gear 42 side. Then, the output torque of the first motor generator 71 is input to the crank shaft 14 via the carrier 44, so that the crank shaft 14 can be rotated. In the present embodiment, rotating the crank shaft 14 by driving the first motor generator 71 in this way is referred to as "motoring".

The reduction gear 50 is a planetary gear mechanism and has a sun gear 51 of an external gear to which a second motor generator 72 is connected and a ring gear 52 of an internal gear coaxially arranged with the sun gear 51. There is. A ring gear shaft 45 is connected to the ring gear 52. Further, a plurality of pinion gears 53 that mesh with both the sun gear 51 and the ring gear 52 are arranged between the sun gear 51 and the ring gear 52. Although each pinion gear 53 is rotatable, it cannot revolve.

Then, when decelerating the vehicle, by making the second motor generator 72 function as a generator, it is possible to generate a regenerative braking force in the vehicle according to the amount of power generated by the second motor generator 72. When the second motor generator 72 is made to function as an electric motor, the output torque of the second motor generator 72 is input to the drive wheels 62 via the reduction gear 50, the ring gear shaft 45, the reduction mechanism 60, and the differential 61. Will be done. As a result, the drive wheels 62 can be rotated, that is, the vehicle can be driven.

The first motor generator 71 transfers electric power to and from the battery 77 via the first inverter 75. The second motor generator 72 transfers power to and from the battery 77 via the second inverter 76.

As shown in FIG. 2, a reciprocating piston 12 is housed in the cylinder 11 of the internal combustion engine 10. The piston 12 is connected to the crank shaft 14 via a connecting rod 13. The intake passage 15 of the internal combustion engine 10 is provided with an air flow meter 80 for detecting the intake air amount GA into the cylinder 11, and the intake air amount in the portion downstream of the air flow meter 80 in the intake passage 15. A throttle valve 16 that rotates to adjust the GA is provided. Further, the internal combustion engine 10 is provided with a fuel injection valve 17 for injecting fuel into a portion downstream of the throttle valve 16 in the intake passage 15. When the intake valve 18 is open, fuel and air are introduced into the cylinder 11 via the intake passage 15. Then, in the cylinder 11, the spark discharge of the ignition device 19 burns the air-fuel mixture containing the air introduced through the intake passage 15 and the fuel injected from the fuel injection valve 17. Then, the exhaust gas generated in the cylinder 11 due to the combustion of the air-fuel mixture is discharged to the exhaust passage 21 when the exhaust valve 20 is open. The exhaust passage 21 is provided with a three-way catalyst 22 and a particulate filter 23 arranged on the downstream side of the three-way catalyst 22. The particulate filter 23 has a function of collecting particulate matter contained in the exhaust gas flowing through the exhaust passage 21.

An air-fuel ratio sensor 81 for detecting the oxygen concentration in the gas flowing through the exhaust passage 21, that is, the air-fuel ratio of the air-fuel mixture is arranged upstream of the three-way catalyst 22 in the exhaust passage 21. Further, a temperature sensor 82 for detecting the temperature of the gas flowing through the exhaust passage 21 and an oxygen sensor 83 are arranged between the three-way catalyst 22 and the particulate filter 23 in the exhaust passage 21. When the oxygen concentration when the air-fuel ratio of the air-fuel mixture provided for combustion in the cylinder 11 is the theoretical air-fuel ratio is set as the boundary oxygen concentration, the detected value of the oxygen sensor 83 is the oxygen concentration of the gas flowing through the exhaust passage 21. Is significantly different between the case where is equal to or higher than the boundary oxygen concentration and the case where the oxygen concentration is less than the boundary oxygen concentration.

In the internal combustion engine 10, when the vehicle is running and the crank shaft 14 is rotating, the combustion of the air-fuel mixture in the cylinder 11 may be stopped. The period during which combustion of the air-fuel mixture in the cylinder 11 is stopped when the crank shaft 14 is rotating is referred to as a "combustion stop period CSP". In the combustion stop period CSP, the piston 12 reciprocates in synchronization with the rotation of the crank shaft 14. Therefore, the air introduced into the cylinder 11 via the intake passage 15 flows out to the exhaust passage 21 without being subjected to combustion.

In the combustion stop period CSP, a fuel cut process for stopping the fuel injection of the fuel injection valve 17 and a fuel for injecting fuel from the fuel injection valve 17 and causing the fuel to flow out from the cylinder 11 to the exhaust passage 21 without being burned. One of the introduction processes is selected and executed. When the fuel introduction process is executed, the fuel injected from the fuel injection valve 17 flows through the exhaust passage 21 together with the air. Then, the fuel is introduced into the three-way catalyst 22. At this time, when the temperature of the three-way catalyst 22 is equal to or higher than the activation temperature, if a sufficient amount of oxygen is present in the three-way catalyst 22 to burn the fuel, the fuel is burned by the three-way catalyst 22. As a result, the temperature of the three-way catalyst 22 rises. Then, the high-temperature gas flows into the particulate filter 23, and the temperature of the particulate filter 23 rises. When oxygen is supplied to the particulate filter 23, when the temperature of the particulate filter 23 becomes equal to or higher than the combustible temperature, the particulate matter collected in the particulate filter 23 is burned.

Next, the control configuration of the hybrid vehicle will be described with reference to FIGS. 1 and 2.
As shown in FIG. 1, the control device 100 of the hybrid vehicle calculates the required torque TQR, which is the torque to be output to the ring gear shaft 45, based on the accelerator opening ACC and the vehicle speed VS. The accelerator opening ACC is an operation amount of the accelerator pedal AP by the driver of the vehicle, and is a value detected by the accelerator opening sensor 84. The vehicle speed VS is a value corresponding to the moving speed of the vehicle, and is detected by the vehicle speed sensor 85. The control device 100 controls the internal combustion engine 10 and the motor generators 71 and 72 based on the calculated required torque TQR.

The control device 100 includes an internal combustion engine control unit 110 that controls the internal combustion engine 10, and a motor control unit 120 that controls the motor generators 71 and 72. The internal combustion engine control unit 110 corresponds to an example of the "internal combustion engine control device" in the present embodiment. When the fuel introduction process is executed during the combustion stop period CSP, the motor control unit 120 controls the drive of the first motor generator 71 for motoring. That is, the rotation speed of the crank shaft 14 can be controlled during the combustion stop period CSP through the execution of motoring.

FIG. 2 illustrates the functional configuration of the internal combustion engine control unit 110. The internal combustion engine control unit 110 has a control unit 111, a prohibition determination unit 112, and a temperature calculation unit 113 as functional units.

The control unit 111 controls the fuel injection valve 17 and the ignition device 19. That is, during the combustion stop period CSP, the control unit 111 stops the spark discharge of the ignition device 19. The control of the fuel injection valve 17 during the combustion stop period CSP will be described later.

On the other hand, when the air-fuel mixture is burned in the cylinder 11, the control unit 111 calculates the required value QPR so that the air-fuel ratio detection value AFS becomes the air-fuel ratio target value AFTr, and fuel injection is performed based on the calculated required value QPR. Drive the valve 17. Further, the control unit 111 causes the ignition device 19 to perform spark discharge at the timing when the piston 12 reaches the vicinity of the compression top dead center. The air-fuel ratio detection value AFS is the air-fuel ratio detected by the air-fuel ratio sensor 81. The air-fuel ratio target value AFTr is a target value of the air-fuel ratio of the air-fuel mixture when the air-fuel mixture is burned in the cylinder 11. For example, the air-fuel ratio target value AFTr is set to the theoretical air-fuel ratio or a value close to the theoretical air-fuel ratio.

Further, when the air-fuel mixture is burned in the cylinder 11, the control unit 111 executes a catalyst diagnosis process for diagnosing whether or not an abnormality accompanying the progress of deterioration of the three-way catalyst 22 has occurred in the three-way catalyst 22. .. When the maximum value of the oxygen storage amount C of the three-way catalyst 22 is set to the maximum storage amount Cmax, the maximum storage amount Cmax becomes smaller as the deterioration of the three-way catalyst 22 progresses. Therefore, as will be described in detail later, in the catalyst diagnosis process, a value having a correlation with the maximum occlusion amount Cmax is acquired, and an abnormality occurs in the three-way catalyst 22 based on the value correlating with the maximum occlusion amount Cmax. It is diagnosed whether or not it is.

The prohibition determination unit 112 determines whether or not to prohibit the execution of the catalyst diagnosis process. The method for determining whether or not to prohibit the execution of the catalyst diagnosis process will be described later.
The temperature calculation unit 113 calculates the catalyst temperature TPSC, which is an estimated value of the temperature of the three-way catalyst 22. It can be inferred that the higher the temperature of the gas passing through the three-way catalyst 22 and toward the particulate filter 23, the higher the temperature of the three-way catalyst 22. Therefore, the temperature calculation unit 113 calculates the catalyst temperature TPSC so that, for example, the higher the temperature of the gas detected by the temperature sensor 82, the higher the temperature of the three-way catalyst 22.

Next, with reference to FIG. 3, the flow of each process executed by the control unit 111 to control the drive of the fuel injection valve 17 during the combustion stop period CSP will be described. The series of processes shown in FIG. 3 is repeated.

In the first step S11 in the series of processes shown in FIG. 3, it is determined whether or not the execution condition of the fuel introduction process is satisfied.
Here, the execution conditions of the fuel introduction process will be described. In the present embodiment, it is determined that the execution condition is satisfied when both of the following two conditions are satisfied.
(Condition 1-1) It can be determined that the temperature of the three-way catalyst 22 is equal to or higher than the specified temperature.
(Condition 1-2) The estimated value of the collected amount of the particulate matter in the particulate filter 23 is equal to or greater than the determined collected amount.

Even if unburned fuel is introduced into the three-way catalyst 22, if the temperature of the three-way catalyst 22 is low, the fuel may not be burned. Therefore, a specified temperature is set as a criterion for determining whether or not the unburned fuel introduced into the three-way catalyst 22 can be burned. That is, the specified temperature is set to a temperature slightly higher than the activation temperature or the activation temperature of the three-way catalyst 22.

The larger the amount of particulate matter collected by the particulate filter 23, the more the clogging of the particulate filter 23 progresses. Therefore, the determined collection amount is set as a criterion for determining whether or not the clogging has progressed to the extent that the particulate filter 23 needs to be regenerated. As the amount of collection increases, the differential pressure between the portion between the three-way catalyst 22 and the particulate filter 23 in the exhaust passage 21 and the portion downstream of the particulate filter 23 in the exhaust passage 21 tends to increase. Therefore, for example, an estimated value of the collected amount can be calculated based on the differential pressure.

When the execution condition of the fuel introduction process is satisfied and the fuel introduction process is started during the combustion stop period CSP, the execution condition of the fuel introduction process is satisfied until the combustion stop period CSP is completed. Is made.

If it is not determined in step S11 that the execution condition of the fuel introduction process is satisfied (NO), since the fuel cut process is being executed, the process is shifted to the next step S12. In step S12, the required value QPR of the fuel injection amount of the fuel injection valve 17 is set to "0". Subsequently, in the next step S13, the drive of the fuel injection valve 17 is controlled based on the calculated required value QPR. In this case, fuel is not injected from the fuel injection valve 17. Then, a series of processes is temporarily terminated.

On the other hand, if it is determined in step S11 that the execution condition of the fuel introduction process is satisfied (YES), the process is shifted to the next step S14 because the fuel introduction process is being executed. To. Then, in step S14, the required value QPR of the fuel injection amount is calculated. The required value QPR of the fuel injection amount when the fuel introduction process is executed is smaller than the required value QPR when burning the air-fuel mixture in the cylinder 11.

When the required value QPR is calculated in step S14, the process proceeds to the next step S13. Then, in step S13, the drive of the fuel injection valve 17 is controlled based on the calculated required value QPR. In this case, fuel is injected from the fuel injection valve 17 even during the combustion stop period CSP. Then, a series of processes is temporarily terminated.

Next, with reference to FIG. 4, the flow of each process executed by the prohibition determination unit 112 for determining whether or not the execution of the catalyst diagnosis process is prohibited will be described. The series of processes shown in FIG. 4 is repeated.

In the first step S21 in the series of processes shown in FIG. 4, it is determined whether or not the fuel injection of the fuel injection valve 17 is stopped. When the control unit 111 is executing the fuel cut process during the combustion stop period CSP, it is determined that the fuel injection of the fuel injection valve 17 is stopped. On the other hand, when the control unit 111 is executing the fuel introduction process even during the combustion stop period CSP, it is not determined that the fuel injection of the fuel injection valve 17 is stopped. Further, when the air-fuel mixture is being burned in the cylinder 11, it is not determined that the fuel injection of the fuel injection valve 17 is stopped.

If it is determined in step S21 that fuel injection has been stopped (YES), the process proceeds to the next step S22. Then, in step S22, the diagnosis prohibition flag FLG is set to off. The diagnosis prohibition flag FLG is a flag that is set to on when the execution of the catalyst diagnosis process is prohibited, and is set to off when the execution of the catalyst diagnosis process is not prohibited. That is, when the fuel cut process is being executed, the catalyst diagnosis process cannot be executed because the fuel injection is not performed in the first place, so that the execution of the catalyst diagnosis process is not prohibited. Then, a series of processes is temporarily terminated.

On the other hand, if it is not determined in step S21 that the fuel injection is stopped (NO), the process proceeds to the next step S23. Then, in step S23, it is determined whether or not the fuel introduction process is being executed. Here, when the air-fuel mixture is being burned in the cylinder 11, it is not determined that the fuel introduction process is being executed. Then, when it is determined that the fuel introduction process is being executed (S23: YES), the process proceeds to the next step S24. In step S24, the diagnosis prohibition flag FLG is set to ON. Then, a series of processes is temporarily terminated.

Here, as will be described in detail later, in the catalyst diagnosis process, a period is provided in which the air-fuel ratio is set to a value on the rich side of the stoichiometric air-fuel ratio. On the other hand, during the fuel introduction process, if fuel is injected from the fuel injection valve 17 so that the air-fuel ratio becomes a value on the rich side of the stoichiometric air-fuel ratio, excess unburned fuel is injected into the three-way catalyst 22. Will be supplied. Therefore, during the execution of the fuel introduction process, the fuel injection valve 17 is not driven so that the air-fuel ratio becomes a value on the rich side of the stoichiometric air-fuel ratio. Therefore, the diagnosis prohibition flag FLG is set to ON.

On the other hand, if it is not determined in step S23 that the fuel introduction process is being executed (NO), it can be determined that the air-fuel mixture is being burned in the cylinder 11, so that the process is next. The process proceeds to step S25. In step S25, it is determined whether or not the current catalyst temperature TPSC is equal to or less than the temperature determination value TPSCTh. The temperature determination value TPSCTh is a value set as a criterion for determining whether or not the temperature of the three-way catalyst 22 is too high for executing the catalyst diagnosis process. The catalyst temperature TPSC is a value calculated by the temperature calculation unit 113.

In step S25, when the catalyst temperature TPSC is higher than the temperature determination value TPSCTh (NO), the process is shifted to step S24. Then, in step S24, when the diagnosis prohibition flag FLG is set to ON, a series of processes is temporarily terminated. On the other hand, when the catalyst temperature TPSC is equal to or less than the temperature determination value TPSCTh (step S25: YES), the process is shifted to step S22. Then, in step S22, when the diagnosis prohibition flag FLG is set to off, a series of processes is temporarily terminated.

When the fuel introduction process is executed during the combustion stop period CSP, the temperature of the three-way catalyst 22 rises. When the combustion stop period CSP is completed and the combustion of the air-fuel mixture in the cylinder 11 is restarted, and the catalyst temperature TPSC at the time of restart is higher than the temperature determination value TPSCTh, the diagnosis prohibition flag FLG is set to ON. Has been done. In this case, when the catalyst temperature TPSC becomes equal to or less than the temperature determination value TPSCTh after that, the diagnosis prohibition flag FLG is set to off, and the execution prohibition of the catalyst diagnosis process is released. That is, in the present embodiment, the period from the time when the combustion of the air-fuel mixture in the cylinder 11 is restarted to the time when the catalyst temperature TPSC becomes the temperature determination value TPSCTh or less corresponds to the "specified period".

When the catalyst temperature TPSC is higher than the temperature determination value TPSCTh, the reason for prohibiting the execution of the catalyst diagnostic process will be described. The maximum storage amount Cmax can be changed not only by the progress of deterioration of the three-way catalyst 22 but also by the temperature of the three-way catalyst 22. That is, as shown in FIG. 6, when the temperature of the three-way catalyst 22 is less than the temperature determination value TPSCTh, the higher the catalyst temperature TPSC, the larger the maximum occlusion value Cmax. However, when the temperature of the three-way catalyst 22 is higher than the specified temperature TPA, the higher the temperature of the three-way catalyst 22, the smaller the maximum occlusion value Cmax.

Therefore, when the catalyst temperature TPSC is higher than the specified temperature TPA, the maximum storage amount Cmax may be small even if the deterioration of the three-way catalyst 22 is not so advanced. When the maximum storage amount Cmax is small due to the high temperature of the three-way catalyst 22, the three-way catalyst 22 can be changed to the three-way catalyst 22 even if the deterioration of the three-way catalyst 22 has not progressed so much by executing the catalyst diagnosis process. It may be diagnosed that an abnormality has occurred. In order to prevent such misdiagnosis, when the catalyst temperature TPSC is higher than the temperature determination value TPSCTh, the execution of the catalyst diagnosis process is prohibited. The temperature determination value TPSCTh is set to a temperature slightly lower than the specified temperature TPA.

Next, with reference to FIG. 5, the flow of the process executed by the control unit 111 for executing the catalyst diagnosis process will be described. The series of processes shown in FIG. 5 is repeated.
In the series of processes shown in FIG. 5, in the first step S31, it is determined whether or not the diagnosis prohibition flag FLG is set to off. When the diagnosis prohibition flag FLG is set to ON (S31: NO), the execution of the catalyst diagnosis process is prohibited, so that the series of processes is temporarily terminated. On the other hand, when the diagnosis prohibition flag FLG is set to off (S31: YES), the process proceeds to the next step S32. In step S32, it is determined whether or not the execution condition of the catalyst diagnosis process is satisfied.

Here, the determination of whether or not the execution condition of the catalyst diagnosis process is satisfied will be described. In the present embodiment, it is determined that the execution condition is satisfied when any of the plurality of conditions shown below is satisfied.
(Condition 2-1) The internal combustion engine 10 is in idle operation.
(Condition 2-2) The fluctuation of the engine load factor is small.
(Condition 2-3) The intake air amount GA is within the specified range.
(Condition 2-4) Warm-up operation is completed, and various sensors 80 to 83 are activated.

Then, in step S32, when it is not determined that the execution condition of the catalyst diagnosis process is satisfied (NO), a series of processes is temporarily terminated. On the other hand, when it is determined that the execution condition of the catalyst diagnosis process is satisfied (S32: YES), the execution of the catalyst diagnosis process is started. In the catalyst diagnosis process, an abnormality occurs in the three-way catalyst 22 through the implementation of air-fuel ratio control in which the air-fuel ratio is set to a value on the lean side of the theoretical air-fuel ratio and then the air-fuel ratio is set to a value on the rich side of the theoretical air-fuel ratio. Whether or not it is diagnosed.

That is, in step S33, lean injection control is performed in which the fuel injection valve 17 is controlled so that the air-fuel ratio of the air-fuel mixture in the cylinder 11 is on the lean side of the stoichiometric air-fuel ratio. Specifically, in the lean injection control, the air-fuel ratio target value AFTr is set to a value on the lean side of the stoichiometric air-fuel ratio. Then, the required value QPR is calculated so that the air-fuel ratio detection value AFS becomes the air-fuel ratio target value AFTr, and the fuel injection valve 17 is driven based on the required value QPR. When the lean injection control is carried out in this way, the oxygen concentration in the exhaust gas becomes higher than when the air-fuel ratio target value AFTr is the stoichiometric air-fuel ratio, so that the oxygen storage amount C of the three-way catalyst 22 is increased.

Subsequently, in the next step S34, it is determined whether or not the oxygen storage amount C of the three-way catalyst 22 is saturated. When the oxygen storage amount C of the three-way catalyst 22 is not yet saturated, oxygen contained in the exhaust gas flowing through the exhaust passage 21 is stored in the three-way catalyst 22. On the other hand, when the oxygen storage amount C of the three-way catalyst 22 is saturated, the oxygen contained in the exhaust gas flowing through the exhaust passage 21 is not stored in the three-way catalyst 22. As a result, the amount of oxygen contained in the exhaust gas flowing downstream of the three-way catalyst 22 in the exhaust passage 21, that is, the exhaust gas passing through the three-way catalyst 22 changes. The change in the amount of oxygen contained in the exhaust passing through the three-way catalyst 22 can be detected by the oxygen sensor 83.

Then, in step S34, when it is not determined that the oxygen storage amount C is saturated (NO), the process is shifted to step S33 described above. That is, the implementation of lean injection control is continued. On the other hand, when it is determined that the oxygen storage amount C is saturated (S34: YES), the process proceeds to the next step S35.

In step S35, rich injection control is performed in which the fuel injection valve 17 is controlled so that the air-fuel ratio of the air-fuel mixture in the cylinder 11 is on the rich side of the stoichiometric air-fuel ratio. Specifically, in the rich injection control, the air-fuel ratio target value AFTr is set to a value on the rich side of the stoichiometric air-fuel ratio. Then, the required value QPR is calculated so that the air-fuel ratio detection value AFS becomes the air-fuel ratio target value AFTr, and the fuel injection valve 17 is driven based on the required value QPR. When the rich injection control is carried out in this way, the oxygen storage amount C of the three-way catalyst 22 is reduced.

Then, in step S36, it is determined whether or not the oxygen stored in the three-way catalyst 22 is depleted. The detection value of the oxygen sensor 83 is inverted before and after the oxygen depletion. Therefore, it is possible to determine whether or not oxygen has been depleted based on the change in the detected value of the oxygen sensor 83.

If it is not determined in step S36 that the oxygen stored in the three-way catalyst 22 has been depleted (NO), the process proceeds to the next step S35. That is, the implementation of rich injection control is continued. On the other hand, when it is determined that oxygen has been depleted (S36: YES), the process proceeds to the next step S37. In step S37, it is determined whether or not the detection time TMd, which is the length of the period from the start of the rich injection control until it can be determined that oxygen is depleted, is equal to or longer than the diagnostic time TMdTh.

The detection time TMd becomes shorter as the maximum occlusion value Cmax is smaller. As described above, the maximum storage amount Cmax becomes smaller as the deterioration of the three-way catalyst 22 progresses. That is, it can be said that the detection time TMd is a value that correlates with the degree of progress of deterioration of the three-way catalyst 22. Then, based on this detection time TMd, the diagnostic time TMdTh is set so that it can be determined whether or not the deterioration of the three-way catalyst 22 has progressed to the extent that an abnormality can be diagnosed.

When the detection time TMd is equal to or longer than the diagnostic time TMdTh (S37: YES), the process proceeds to the next step S38. In step S38, it is diagnosed that no abnormality has occurred in the three-way catalyst 22, that is, the three-way catalyst 22 is normal. Then, a series of processes is temporarily terminated.

On the other hand, when the detection time TMd is less than the diagnostic time TMdTh (S37: NO), the process proceeds to the next step S39. In step S39, it is diagnosed that an abnormality has occurred in the three-way catalyst 22. Then, a series of processes is temporarily terminated.

When the execution of the catalyst diagnosis process is completed, the normal injection control for controlling the fuel injection valve 17 so that the air-fuel ratio of the air-fuel mixture in the cylinder 11 becomes a value close to the stoichiometric air-fuel ratio is executed. Specifically, in the normal injection control, the air-fuel ratio target value AFTr is set to a theoretical air-fuel ratio or a value close to the theoretical air-fuel ratio. Then, the required value QPR is calculated so that the air-fuel ratio detection value AFS becomes the air-fuel ratio target value AFTr, and the fuel injection valve 17 is driven based on the required value QPR.

The operation and effect of this embodiment will be described with reference to FIG. 7.
As shown in FIG. 7, before the timing t11, the air-fuel mixture is burned in the cylinder 11. Therefore, the exhaust gas generated by the combustion of the air-fuel mixture in the cylinder 11 flows through the exhaust passage 21. In this case, the amount of particulate matter collected by the particulate filter 23 increases. Since the condition for stopping the combustion of the air-fuel mixture in the cylinder 11 is satisfied at the timing t11, the combustion stop period CSP is started from the timing t11. Since the estimated value of the collected amount of the particulate matter in the particulate filter 23 calculated at the timing t11 is less than the determined collected amount, the execution condition of the fuel introduction process is not satisfied. Therefore, the fuel cut process is executed from the timing t11. During the execution of the fuel cut process, the air introduced into the cylinder 11 from the intake passage 15 is discharged to the exhaust passage 21 without being subjected to combustion. Therefore, the catalyst temperature TPSC decreases.

Then, when the estimated value of the collected amount of the particulate matter in the particulate filter 23 calculated at the timing t12 is equal to or larger than the determined collected amount, the execution condition of the fuel introduction process is satisfied. That is, at timing t12, the process shifts from the fuel cut process to the fuel introduction process. When the execution of the fuel introduction process is started, the diagnosis prohibition flag FLG is set to ON, and the execution of the catalyst diagnosis process is prohibited.

During the execution of the fuel introduction process, the rotation speed of the crank shaft 14 is controlled by driving the first motor generator 71 by executing the motoring. Therefore, oxygen is appropriately supplied to the three-way catalyst 22 and the particulate filter 23.

Further, from the timing t12, fuel is injected from the fuel injection valve 17 even during the combustion stop period CSP. Moreover, during the combustion stop period CSP, spark discharge is not performed by the ignition device 19. Therefore, the fuel injected from the fuel injection valve 17 flows through the exhaust passage 21 together with the air without being burned. When such unburned fuel is introduced into the three-way catalyst 22, the fuel is burned by the three-way catalyst 22. Therefore, the catalyst temperature TPSC, which is the temperature of the three-way catalyst 22, becomes high. When the high-temperature gas that has passed through the three-way catalyst 22 flows into the particulate filter 23, the temperature of the particulate filter 23 rises.

In the example shown in FIG. 7, the catalyst temperature TPSC exceeds the specified temperature TPA due to the execution of the fuel introduction process. When the temperature of the three-way catalyst 22 becomes high in this way, the maximum occlusion value Cmax of the three-way catalyst 22 becomes smaller than when the catalyst temperature TPSC is less than the specified temperature TPA.

Then, since the condition for stopping the combustion of the air-fuel mixture in the cylinder 11 is not satisfied at the timing t13, the combustion of the air-fuel mixture in the cylinder 11 is restarted from the timing t13. At the timing t13, the catalyst temperature TPSC is higher than the temperature determination value TPSCTh, so that the diagnosis prohibition flag FLG remains set to ON. When the combustion of the air-fuel mixture in the cylinder 11 is restarted, the execution of motoring is terminated.

After the combustion of the air-fuel mixture in the cylinder 11 is restarted, the catalyst temperature TPSC gradually decreases. Then, at the timing t14, the catalyst temperature TPSC becomes equal to or less than the temperature determination value TPSCTh. Then, since the diagnosis prohibition flag FLG is set to off, the execution prohibition of the catalyst diagnosis process is released. After the execution prohibition is lifted in this way, the catalyst diagnosis process is executed when the execution condition of the catalyst diagnosis process is satisfied.

In the present embodiment, even after the timing t13 when the combustion of the mixture in the cylinder 11 is restarted, the catalyst diagnosis process is not executed when the catalyst temperature TPSC is higher than the temperature determination value TPSCTh. As a result, it is possible to prevent the catalyst diagnosis process from being executed when the maximum storage amount Cmax of the three-way catalyst 22 is small because the catalyst temperature TPSC is higher than the specified temperature TPA. As a result, it is possible to prevent the three-way catalyst 22 from being diagnosed as having an abnormality when the deterioration of the three-way catalyst 22 has not progressed to the extent that it can be diagnosed as an abnormality.

Therefore, even if the fuel introduction process is executed during the combustion stop period CSP, it is possible to suppress a decrease in diagnostic accuracy as to whether or not an abnormality has occurred in the three-way catalyst 22.
The above embodiment can be modified and implemented as follows. The above embodiment and the following modified examples can be implemented in combination with each other within a technically consistent range.

-In the fuel introduction process, as described above, the air-fuel ratio of the air-fuel mixture in the cylinder 11 cannot be set to the rich side of the stoichiometric air-fuel ratio. Therefore, it is not possible to execute the catalyst diagnosis process during the fuel introduction process. Therefore, it is not necessary to set the diagnosis prohibition flag FLG to ON during the execution of the fuel introduction process. In this case, when the catalyst temperature TPSC is higher than the temperature determination value TPSCTh when the combustion of the air-fuel mixture in the cylinder 11 is restarted, the diagnosis prohibition flag FLG is set to ON.

-In the above embodiment, when the execution of the fuel introduction process is started during the combustion stop period CSP, the diagnosis prohibition flag FLG is set to ON. However, even during the execution of the fuel introduction process, when the catalyst temperature TPSC is less than the temperature determination value TPSCTh, it is not necessary to set the diagnosis prohibition flag FLG to ON. In this case, it is preferable to set the diagnosis prohibition flag FLG to ON when the catalyst temperature TPSC becomes the temperature determination value TPSCTh or more during the execution of the fuel introduction process.

-The specified period, which is the period during which the execution of the catalyst diagnosis process is prohibited after the restart of the combustion of the air-fuel mixture in the cylinder 11, is from the time when the combustion of the air-fuel mixture in the cylinder 11 is restarted until the specified time elapses. It may be a period of. In this case, the length of the specified period may be fixed at a preset value or may be changed according to the catalyst temperature TPSC at the time of resumption.

-The temperature determination value TPSCTh may be equal to the specified temperature TPA.
When the internal combustion engine 10 is provided with a sensor for detecting the temperature of the three-way catalyst 22, the value detected by the sensor may be used as the catalyst temperature TPSC.

-In the above embodiment, the ignition device 19 is prevented from performing spark discharge during the execution of the fuel introduction process. However, during the execution of the fuel introduction process, the ignition device 19 may be made to perform spark discharge at a time when the air-fuel mixture does not burn in the cylinder 11. For example, when the spark discharge is performed when the piston 12 is located near the bottom dead center, the air-fuel mixture is not burned in the cylinder 11 where the spark discharge is performed. Therefore, even if spark discharge is performed during the fuel introduction process, the fuel injected from the fuel injection valve 17 can be discharged from the cylinder 11 to the exhaust passage 21 without being burned.

-The internal combustion engine to which the control device of the internal combustion engine is applied may include an in-cylinder injection valve which is a fuel injection valve for directly injecting fuel into the cylinder 11. In this case, during the execution of the fuel introduction process, the fuel is injected into the cylinder 11 from the in-cylinder injection valve, and the fuel is discharged to the exhaust passage 21 without being burned. As a result, unburned fuel can be introduced into the three-way catalyst 22.

-The system of the hybrid vehicle may be a system different from the system shown in FIG. 1 as long as the rotation speed of the crank shaft 14 can be controlled by driving the motor.

-The control device for an internal combustion engine may be embodied as a device for controlling an internal combustion engine mounted on a vehicle having no power source other than the internal combustion engine. Even in an internal combustion engine mounted on such a vehicle, combustion of the air-fuel mixture in the cylinder may be stopped under the condition that the crank shaft 14 is rotating due to inertia. When the execution condition of the fuel introduction process is satisfied during the combustion stop period CSP, the fuel introduction process is executed and the temperature of the three-way catalyst 22 rises.

10 ... Internal combustion engine, 11 ... Cylinder, 14 ... Crank shaft, 17 ... Fuel injection valve, 21 ... Exhaust passage, 22 ... Three-way catalyst, 110 ... Internal combustion engine control unit.

Claims (1)

A three-way catalyst is placed in the exhaust passage, and it is applied to a spark-ignition type internal combustion engine that burns the air-fuel mixture containing fuel injected from the fuel injection valve in the cylinder.
Through the implementation of air-fuel ratio control in which the air-fuel ratio is set to a value on the lean side of the theoretical air-fuel ratio and then the air-fuel ratio is set to a value on the rich side of the theoretical air-fuel ratio when combustion is being performed in the cylinder. Execute a catalyst diagnosis process to diagnose whether or not an abnormality has occurred in the three-way catalyst,
When the combustion in the cylinder is stopped under the condition that the crank shaft of the internal combustion engine is rotating, the fuel cut process for stopping the fuel injection of the fuel injection valve and the fuel injection from the fuel injection valve are performed. In the control device of an internal combustion engine, which selects and executes one of the fuel introduction processes for causing the fuel to flow out from the cylinder to the exhaust passage without being burned.
When the fuel introduction process is executed while the combustion in the cylinder is stopped, a specified period elapses from the time when the combustion in the cylinder is restarted even if the combustion in the cylinder is restarted. A control device for an internal combustion engine, characterized in that execution of the catalyst diagnostic process is prohibited until the combustion is performed.

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