Control device for internal combustion engine

Abstract

To provide a control device of an internal combustion engine 10 capable of curbing a reduction in a NOx purification rate associated with a termination of a temperature increasing treatment which stops fuel supply to a cylinder #2.SOLUTION: A CPU 72: enriches an air-fuel ratio of cylinders #1 to #4 so that the same is increased to a theoretical air-fuel ratio in stages after stopping a fuel cut treatment for all the cylinders; executes a temperature increase treatment for a GPF 34 through the fuel cut treatment for the cylinder #2 and enrichment of an air-fuel mixture for the cylinders #1, #3 and #4; enriches the air-fuel ratio of the cylinders #1 to #4 so that the same is increased to the theoretical air-fuel ratio in stages after stopping the temperature increase treatment; and makes the air-fuel ratio of the cylinders #1 to #4 after stopping the temperature increase treatment larger than the air-fuel ratio after stopping the fuel cut treatment for all the cylinders.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a control device for an internal combustion engine. [Background technology]

[0002] A so-called fuel cut process is well known, which stops the fuel supply to an internal combustion engine when a vehicle is decelerating, etc. When the fuel cut process is executed, a catalyst provided in an exhaust system of the internal combustion engine stores a large amount of oxygen, and therefore, when the fuel cut process is stopped, the catalyst's ability to reduce NOx decreases.

[0003] Therefore, as disclosed in the following Patent Document 1, it has been proposed to make the air-fuel ratio of the mixture richer than the stoichiometric air-fuel ratio when the fuel cut process is stopped. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2015-10489 A Summary of the Invention [Problem to be solved by the invention]

[0005] The inventors have considered performing a regeneration process for the aftertreatment device when the shaft torque of the internal combustion engine is not zero. Specifically, as the regeneration process, they considered a temperature rise process in which fuel supply is stopped only to some cylinders, the air-fuel ratio of the remaining cylinders is made richer than the theoretical air-fuel ratio, and unburned fuel and oxygen are supplied to the exhaust. They have found that the NOx reduction ability of the catalyst decreases even when the temperature rise process is stopped. [Means for solving the problem]

[0006] Means for solving the above problems and their effects will be described below. 1. A control device for an internal combustion engine applied to a multi-cylinder internal combustion engine equipped with an after-treatment device in an exhaust passage, the after-treatment device including a catalyst having oxygen storage capacity, and executing a temperature rise process for raising the temperature of the after-treatment device and a return-time process, the temperature rise process including a stop process and a rich process, the stop process being a process for stopping the supply of fuel to some of the multiple cylinders, the rich process being a process for making the air-fuel ratio of the mixture in cylinders other than the some of the multiple cylinders less than the theoretical air-fuel ratio, and the return-time process being a process for making the concentration of unburned fuel in the exhaust discharged into the exhaust passage higher than the equivalent concentration when the temperature rise process is stopped, the equivalent concentration being the concentration of unburned fuel that reacts with the oxygen in the exhaust just right.

[0007] When the temperature rise process is performed, the stop process is performed, so that a large amount of oxygen may flow into the catalyst compared to when the stop process is not performed. Even if a larger amount of unburned fuel flows into the catalyst due to the rich process than when the rich process is not performed, the amount of oxygen stored in the catalyst may be larger than when the temperature rise process is not performed. In that case, the NOx reduction ability of the catalyst may decrease after the temperature rise process is stopped. Therefore, in the above configuration, when the temperature rise process is stopped, the return process is performed. As a result, a larger amount of unburned fuel is supplied to the catalyst than the amount of unburned fuel that reacts with the oxygen in the exhaust gas without excess or deficiency, so that the amount of oxygen stored in the catalyst can be quickly reduced. Therefore, the decrease in the NOx purification rate due to the stop of the temperature rise process can be suppressed.

[0008] 2. A control device for an internal combustion engine as described in 1 above, wherein the rich processing changes the air-fuel ratio of the mixture in the different cylinders to be below an upper limit air-fuel ratio and above a lower limit air-fuel ratio depending on the temperature of the aftertreatment device, and the return processing includes processing for setting the air-fuel ratio of at least one of the multiple cylinders to a post-specific stop air-fuel ratio, and the post-specific stop air-fuel ratio is greater than the lower limit air-fuel ratio and less than the theoretical air-fuel ratio.

[0009] Although the amount of oxygen stored in the catalyst may be greater by performing the temperature rise process compared to when the temperature rise process is not performed, the temperature rise process includes rich processing, and therefore the NOx reduction ability is higher compared to when the rich processing is not performed. Therefore, if the specific stop air-fuel ratio is made excessively rich in the return process, the fuel consumption rate may become unnecessarily high. Therefore, in the above configuration, the specific stop air-fuel ratio is made larger than the lower limit air-fuel ratio, thereby suppressing the increase in the fuel consumption rate.

[0010] 3. A control device for an internal combustion engine as described in 1 or 2 above, wherein the rich processing changes the air-fuel ratio of the mixture in the different cylinders to a value lower than an upper limit air-fuel ratio and higher than a lower limit air-fuel ratio depending on the temperature of the aftertreatment device, and the return processing includes processing for setting the air-fuel ratio of at least one of the multiple cylinders to a post-specific stop air-fuel ratio, and the post-specific stop air-fuel ratio is smaller than the upper limit air-fuel ratio.

[0011] When the amount of oxygen stored in the catalyst increases due to the execution of the temperature rise process, if the air-fuel ratio of the mixture is not made rich by a certain amount when the temperature rise process is stopped, the NOx purification rate may decrease. This is preferably greater than the minimum degree of enrichment required to maintain the temperature of the post-treatment device at the target value. Therefore, in the above configuration, the specific post-stop air-fuel ratio is made smaller than the upper limit air-fuel ratio, so that the decrease in the NOx purification rate caused by the stop of the temperature rise process can be suitably suppressed.

[0012] 4. A control device for an internal combustion engine described in any one of 1 to 3 above, wherein when the temperature increase process is not performed, a feedback process is performed in which the detection value of an air-fuel ratio sensor upstream of the after-treatment device is feedback-controlled to a target value, and a switching process is performed in which the target value is alternately shifted from one of two values, a feedback rich air-fuel ratio less than the stoichiometric air-fuel ratio, and a feedback lean air-fuel ratio greater than the stoichiometric air-fuel ratio, to the other, and the return process includes a process of setting the air-fuel ratio of at least one of the multiple cylinders to a post-specific stop air-fuel ratio, and the post-specific stop air-fuel ratio is smaller than the feedback rich air-fuel ratio.

[0013] In the above configuration, the amount of oxygen stored in the catalyst can be controlled to an appropriate amount by the switching process. However, when the difference between the feedback rich air-fuel ratio and the stoichiometric air-fuel ratio is increased, it is easy to make it difficult to control the amount of oxygen stored. Therefore, the feedback rich air-fuel ratio tends to be set to a value that is smaller than the stoichiometric air-fuel ratio. Therefore, if the air-fuel ratio after the specific stop is set to about the feedback lean air-fuel ratio, the oxygen in the catalyst cannot be quickly reduced when the temperature rise process is stopped, and there is a risk that the NOx purification rate will decrease. Therefore, in the above configuration, the air-fuel ratio after the specific stop is set smaller than the feedback rich air-fuel ratio, so that the oxygen in the catalyst can be quickly reduced when the temperature rise process is stopped.

[0014] 5. The control device for an internal combustion engine according to any one of 2 to 4 above, wherein the return process is a process for making the air-fuel ratio of the mixture in all of the plurality of cylinders the air-fuel ratio after the specific stop.

[0015] In the above configuration, by setting the air-fuel ratio of the mixture in all cylinders to the post-specific stop air-fuel ratio when the temperature rise process is stopped, the oxygen in the catalyst can be reduced more quickly when the temperature rise process is stopped, compared to when only some of the cylinders are set to the post-specific stop air-fuel ratio.

[0016] 6. A control device for an internal combustion engine described in any one of 1 to 5 above, wherein an all-cylinder fuel cut process is executed, the all-cylinder fuel cut process is a process for stopping the supply of fuel to all cylinders of the multi-cylinder internal combustion engine, and the return process includes a process for setting the air-fuel ratio of the mixture in each of the multiple cylinders to a post-total-stop air-fuel ratio which is smaller than the post-specific-stop air-fuel ratio after the all-cylinder fuel cut process is stopped, and the post-specific-stop air-fuel ratio is the air-fuel ratio of the mixture in the multiple cylinders after the temperature rise process is stopped and is an air-fuel ratio which is smaller than the theoretical air-fuel ratio.

[0017] The state of the catalyst immediately after the temperature increase process is stopped tends to require less fuel to suppress the decrease in the NOx purification rate compared to the state of the catalyst immediately after the all-cylinder fuel cut process is stopped. Nevertheless, if the air-fuel ratio after the full stop and the air-fuel ratio after the specific stop are made the same, there is a risk of the fuel consumption rate being unnecessarily decreased. Therefore, in the above configuration, by making the air-fuel ratio after the specific stop larger than the air-fuel ratio after the full stop, it is possible to suppress both the decrease in the NOx purification rate and the increase in the fuel consumption rate.

[0018] 7. A control device for an internal combustion engine as described in any one of 1 to 6 above, which executes an oxygen storage amount calculation process using an intake amount variable, which is a variable indicating the intake air amount of the internal combustion engine, as input, and the return time process includes a process of setting the air-fuel ratio of at least one of the plurality of cylinders to the air-fuel ratio after a specific stop, and the return time process includes a change process of gradually increasing the air-fuel ratio after the specific stop as the oxygen storage amount decreases.

[0019] When a large amount of fuel flows into the catalyst when the oxygen storage amount is small, even if there is an adequate amount of oxygen to react with the fuel, some of the fuel may flow out downstream of the catalyst. Therefore, in the above configuration, the air-fuel ratio after the specific stop is increased stepwise as the oxygen storage amount decreases. This makes it possible to quickly eliminate the state in which the oxygen storage amount is large and the NOx purification rate is likely to decrease, while suppressing the outflow of fuel downstream of the catalyst.

[0020] 8. The control device for an internal combustion engine as described in claim 7, wherein the return processing includes forced rich processing, and the change processing includes processing for changing the air-fuel ratio after the specific stop from a first rich air-fuel ratio to a second rich air-fuel ratio when the oxygen storage amount transitions from a state greater than a specified value to a state equal to or less than the specified value, the first rich air-fuel ratio being smaller than the second rich air-fuel ratio, and the forced rich processing is processing for making the air-fuel ratio after the specific stop the first rich air-fuel ratio for a predetermined period from the stop of the temperature rise processing, even if the oxygen storage amount is equal to or less than the specified value.

[0021] In the above configuration, when the oxygen storage amount transitions to a state below a specified value, the air-fuel ratio after the specific stop is changed to a second rich air-fuel ratio, thereby suppressing the outflow of fuel downstream of the catalyst. However, the inventors found that, even if the calculated oxygen storage amount is below a specified value after the temperature rise process is stopped, the NOx purification rate may decrease if the second rich air-fuel ratio is used. Therefore, in the above configuration, by providing a forced rich process, the air-fuel ratio after the specific stop is temporarily set to the first rich air-fuel ratio even if the oxygen storage amount at the time the temperature rise process is stopped is below a specified value. This makes it possible to suppress the decrease in the NOx purification rate. [Brief description of the drawings]

[0022] [Figure 1] 1 is a diagram showing a configuration of a control device and a drive system of a vehicle according to an embodiment; [Diagram 2] FIG. 2 is a block diagram showing a part of the process executed by the control device according to the embodiment. [Diagram 3] 4 is a flowchart showing a procedure of a process executed by the control device according to the embodiment. [Figure 4] 4 is a flowchart showing a procedure of a process executed by the control device according to the embodiment. [Diagram 5] 4 is a flowchart showing a procedure of a process executed by the control device according to the embodiment. [Figure 6] 4 is a time chart showing the operation of the embodiment; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Hereinafter, the first embodiment will be described with reference to the drawings. As shown in FIG. 1, an internal combustion engine 10 includes four cylinders #1 to #4. A throttle valve 14 is provided in an intake passage 12 of the internal combustion engine 10. A port injection valve 16 that injects fuel into an intake port 12a, which is a downstream portion of the intake passage 12, is provided in the intake port 12a. Air drawn into the intake passage 12 and fuel injected from the port injection valve 16 flow into a combustion chamber 20 when an intake valve 18 opens. Fuel is injected into the combustion chamber 20 from an in-cylinder injection valve 22. A mixture of air and fuel in the combustion chamber 20 is combusted in response to a spark discharge from an ignition plug 24. The combustion energy generated at this time is converted into the rotational energy of a crankshaft 26.

[0024] The air-fuel mixture subjected to combustion in the combustion chamber 20 is discharged as exhaust gas into an exhaust passage 30 when an exhaust valve 28 is opened. A three-way catalyst 32 having an oxygen storage capacity and a gasoline particulate filter (GPF 34) are provided in the exhaust passage 30. In this embodiment, the GPF 34 is assumed to be a filter that collects particulate matter (PM) and supports a three-way catalyst having an oxygen storage capacity.

[0025] The crankshaft 26 is mechanically connected to a carrier C of a planetary gear mechanism 50 constituting a power split device. A rotating shaft 52a of a first motor generator 52 is mechanically connected to a sun gear S of the planetary gear mechanism 50. A rotating shaft 54a of a second motor generator 54 and a driving wheel 60 are mechanically connected to a ring gear R of the planetary gear mechanism 50. An AC voltage is applied to terminals of the first motor generator 52 by an inverter 56. An AC voltage is applied to terminals of the second motor generator 54 by an inverter 58.

[0026] The control device 70 operates the operation parts of the internal combustion engine 10, such as the throttle valve 14, the port injection valve 16, the in-cylinder injection valve 22, and the spark plug 24, in order to control the torque and the exhaust component ratio as the controlled variable of the internal combustion engine 10. The control device 70 also operates the inverter 56 to control the rotation speed, which is the controlled variable of the first motor generator 52. The control device 70 also operates the inverter 58 to control the torque, which is the controlled variable of the second motor generator 54. FIG. 1 shows the operation signals MS1 to MS6 of the throttle valve 14, the port injection valve 16, the in-cylinder injection valve 22, the spark plug 24, and the inverters 56 and 58. The control device 70 refers to the intake air amount Ga detected by the air flow meter 80, the output signal Scr of the crank angle sensor 82, and the water temperature THW detected by the water temperature sensor 84 in order to control the controlled variable of the internal combustion engine 10. The control device 70 also refers to an upstream air-fuel ratio Afu detected by an upstream air-fuel ratio sensor 86 provided upstream of the three-way catalyst 32, and a downstream air-fuel ratio Afd detected by a downstream air-fuel ratio sensor 88 provided downstream of the three-way catalyst 32. The control device 70 also refers to an output signal Sm1 of a first rotation angle sensor 90 that detects the rotation angle of the first motor-generator 52, in order to control the control amount of the first motor-generator 52. The control device 70 also refers to an output signal Sm2 of a second rotation angle sensor 92 that detects the rotation angle of the second motor-generator 54, in order to control the control amount of the second motor-generator 54. The control device 70 also refers to an accelerator operation amount ACCP, which is the amount of depression of the accelerator pedal detected by an accelerator sensor 94.

[0027] The control device 70 includes a CPU 72, a ROM 74, and a peripheral circuit 76, which are capable of communicating with each other via a communication line 78. Here, the peripheral circuit 76 includes a circuit for generating a clock signal that regulates the internal operation, a power supply circuit, a reset circuit, etc. The control device 70 controls the controlled variable by the CPU 72 executing a program stored in the ROM 74.

[0028] In the following, the processes executed by the control device 70 will be described in detail in the order of basic process, regeneration process of the GPF 34, and return coefficient calculation process which is part of the process of FIG. (Basic processing) 2 shows the process executed by the control device 70. The process shown in FIG.

[0029] The base injection amount calculation process M10 is a process for calculating a base injection amount Qb, which is a base value of the fuel amount for making the air-fuel ratio of the mixture in the combustion chamber 20 the target air-fuel ratio, based on the charging efficiency η. In detail, when the charging efficiency η is expressed as a percentage, for example, the base injection amount calculation process M10 may be a process for calculating the base injection amount Qb by multiplying the fuel amount QTH per 1% of the charging efficiency η for making the air-fuel ratio the target air-fuel ratio by the charging efficiency η. The base injection amount Qb is a fuel amount calculated based on the amount of air charged in the combustion chamber 20 to control the air-fuel ratio to the target air-fuel ratio. In this embodiment, the target air-fuel ratio is the theoretical air-fuel ratio. The charging efficiency η is calculated by the CPU 72 based on the intake air amount Ga and the rotation speed NE. The rotation speed NE is calculated by the CPU 72 based on the output signal Scr.

[0030] The feedback coefficient calculation process M12 is a process for calculating and outputting a feedback correction coefficient KAF. The feedback correction coefficient KAF is a value obtained by adding "1" to the correction ratio δ of the base injection amount Qb as a feedback manipulated variable, which is a manipulated variable for feedback-controlling the upstream air-fuel ratio Afu to the target value Afu*. In more detail, the feedback coefficient calculation process M12 sets the correction ratio δ to the sum of the output values ​​of the proportional element and the differential element, which input the difference between the upstream air-fuel ratio Afu and the target value Afu*, and the output value of the integral element, which holds and outputs an integrated value of the difference.

[0031] The switching process M14 is a process for alternately switching the target value Afu* from one of two values, the feedback rich air-fuel ratio Afr and the feedback lean air-fuel ratio Afl, to the other. The switching process M14 is a process for switching the target value Afu* to the feedback rich air-fuel ratio Afr when the logical sum of the following conditions is true:

[0032] This condition is that the oxygen storage amount OS is equal to or greater than the upper limit value OSfl for switching. The downstream air-fuel ratio Afd is equal to or greater than "Afs+Δ". Here, the stoichiometric point Afs corresponds to the theoretical air-fuel ratio. The minute amount Δ is, for example, about 0.1 to 0.3.

[0033] The switching process M14 is a process for switching the target value Afu* to the feedback lean air-fuel ratio Afl when the logical sum of the following conditions is true: This condition means that the oxygen storage amount OS is equal to or less than the lower limit value OSfr for switching.

[0034] The downstream air-fuel ratio Afd is equal to or less than "Afs-Δ". The switching process M14 includes a process for calculating the oxygen storage amount OS based on the intake air amount Ga and the upstream air-fuel ratio Afu.

[0035] The storage amount calculation process M16 is a process for calculating the oxygen storage amount OS of the three-way catalyst 32 based on a required injection amount Qd and an intake air amount Ga, which will be described later. The return coefficient calculation process M18 is a process for calculating a return coefficient Kc, which is a correction coefficient for increasing the base injection amount Qb when returning from an all-cylinder fuel cut process M22a (to be described later) or the like, to a value greater than "1".

[0036] The required injection amount calculation process M20 is a process for multiplying the base injection amount Qb by the feedback correction coefficient KAF and the return time coefficient Kc to calculate the amount of fuel required in one combustion cycle (required injection amount Qd).

[0037] The injector operation process M22 is a process that outputs an operation signal MS2 to the port injector 16 to operate the port injector 16, and outputs an operation signal MS3 to the in-cylinder injector 22 to operate the in-cylinder injector 22. In particular, the injector operation process M22 is a process that sets the amount of fuel injected from the port injector 16 and the in-cylinder injector 22 within one combustion cycle to an amount corresponding to the required injection amount Qd.

[0038] The injector operation process M22 also includes an all-cylinder fuel cut process M22a. The all-cylinder fuel cut process M22a is a process for stopping fuel injection into all of the cylinders #1 to #4. The all-cylinder fuel cut process M22a is executed, for example, under the following conditions.

[0039] This is a condition that there is a demand for applying friction torque from the internal combustion engine 10 to the drive wheels 60. This is a condition for executing a diagnostic process that includes the stop of fuel injection as one of the execution conditions.

[0040] This condition indicates that the accelerator pedal was released when the temperature of the GPF 34 was rising due to high-load driving. In this case, the fuel cut process is executed in order to supply oxygen to the GPF 34 to burn and remove the PM that has been captured by the GPF 34 when the temperature of the GPF 34 has risen due to the driver's driving behavior.

[0041] (GPF34 recycling process) The control device 70 basically performs the process shown in Fig. 2, but during regeneration processing of the GPF 34 to intentionally increase the temperature of the GPF 34, the control device 70 changes the process shown in Fig. 2. This will be described below.

[0042] The procedure of the playback process is shown in Fig. 3. The process shown in Fig. 3 is realized by the CPU 72 repeatedly executing a program stored in the ROM 74, for example, at a predetermined interval. In the following, the step number of each process is represented by a number preceded by "S."

[0043] In the series of processes shown in FIG. 3, the CPU 72 first acquires the rotation speed NE, the charging efficiency η, and the water temperature THW (S10). Next, the CPU 72 calculates an update amount ΔDPM of the accumulation amount DPM based on the rotation speed NE, the charging efficiency η, and the water temperature THW (S12). Here, the accumulation amount DPM is the amount of PM trapped in the GPF 34. In detail, the CPU 72 calculates the amount of PM in the exhaust gas discharged to the exhaust passage 30 based on the rotation speed NE, the charging efficiency η, and the water temperature THW. The CPU 72 also calculates the temperature Tgpf of the GPF 34 based on the rotation speed NE and the charging efficiency η. Then, the CPU 72 calculates the update amount ΔDPM based on the amount of PM in the exhaust gas and the temperature of the GPF 34. Note that when the process of S22 described later is executed, the temperature Tgpf and the update amount ΔDPM may be calculated based on the increase coefficient Kr.

[0044] Next, the CPU 72 updates the accumulation amount DPM according to the update amount ΔDPM (S14). Next, the CPU 72 determines whether or not the execution flag F is "1" (S16). When the execution flag F is "1", it indicates that the temperature increase process for burning and removing PM in the GPF 34 is being executed, and when it is "0", it indicates that the temperature increase process is not being executed. When the CPU 72 determines that the execution flag F is "0" (S16: NO), it determines whether or not the logical sum of the accumulation amount DPM being equal to or greater than the regeneration execution value DPMH and the period during which the process of S22 described below is interrupted is true (S18). The regeneration execution value DPMH is set to a value at which the amount of PM trapped by the GPF 34 has increased and it is desired to remove PM.

[0045] When it is determined that the logical sum is true (S18: YES), the CPU 72 determines whether or not a condition that the logical product of the following condition (a) and condition (b), which are execution conditions for the temperature increase process, is true, is established (S20).

[0046] Condition (A): An engine torque command value Te*, which is a command value of the torque for the internal combustion engine 10, is equal to or greater than a lower limit torque TethL and equal to or greater than an upper limit torque TethH. Condition (A): The rotation speed NE of the internal combustion engine 10 is equal to or higher than the lower limit speed NEthL and equal to or higher than the upper limit speed NEthH.

[0047] In an operating state in which the upper limit torque TethH and the upper limit speed NEthH are exceeded, the exhaust gas temperature is high to begin with, and the deposition amount DPM is unlikely to increase even if the process of S22 described below is not executed.

[0048] When the CPU 72 determines that the logical product is true (S20: YES), it executes the temperature increase process and assigns "1" to the execution flag F (S22). As the temperature increase process according to this embodiment, the CPU 72 stops the injection of fuel from the port injection valve 16 and the in-cylinder injection valve 22 of the cylinder #2, and makes the air-fuel ratio of the mixture in the combustion chamber 20 of the cylinders #1, #3, and #4 richer than the theoretical air-fuel ratio. This process is a process for first increasing the temperature of the three-way catalyst 32. That is, by discharging oxygen and unburned fuel into the exhaust passage 30, the unburned fuel is oxidized in the three-way catalyst 32 to increase the temperature of the three-way catalyst 32. Secondly, it is a process for increasing the temperature of the GPF 34 and supplying oxygen to the high-temperature GPF 34 to oxidize and remove the PM captured by the GPF 34. That is, when the temperature of the three-way catalyst 32 becomes high, the temperature of the GPF 34 increases as high-temperature exhaust gas flows into the GPF 34. Then, oxygen flows into the high-temperature GPF 34, whereby the PM trapped by the GPF 34 is oxidized and removed.

[0049] Specifically, the CPU 72 assigns "0" to the required injection amount Qd for the port injector 16 and the in-cylinder injector 22 of the cylinder #2. On the other hand, the CPU 72 assigns a value obtained by multiplying the base injection amount Qb by the increase coefficient Kr to the required injection amount Qd for the cylinders #1, #3, and #4.

[0050] The CPU 72 sets the boost coefficient Kr so that the unburned fuel in the exhaust discharged from the cylinders #1, #3, #4 into the exhaust passage 30 reacts just right with the oxygen discharged from the cylinder #2. In more detail, the CPU 72 sets the value of the boost coefficient Kr to a value that is larger when the temperature Tgpf of the GPF 34 is low than when it is high. That is, in the early stage of the regeneration process of the GPF 34, the CPU 72 sets the air-fuel ratio of the mixture in the cylinders #1, #3, #4 to a value that is as close as possible to the amount that reacts just right in order to raise the temperature of the three-way catalyst 32 early.

[0051] On the other hand, when the CPU 72 determines that the execution flag F is "1" (S16: YES), it determines whether or not the accumulation amount DPM is equal to or smaller than the stop threshold value DPML (S24). The stop threshold value DPML is set to a value at which the amount of PM trapped in the GPF 34 becomes small enough that the regeneration process may be stopped. When the CPU 72 determines that the accumulation amount DPM is larger than the stop threshold value DPML (S24: NO), it proceeds to the process of S20.

[0052] On the other hand, when the detected value is equal to or less than the stop threshold value DPML (S24: YES) or when a negative determination is made in the process of S20, the CPU 72 stops or interrupts the process of S22 and assigns "0" to the execution flag F (S26). Here, when a positive determination is made in the process of S24, the process of S22 is deemed completed and stopped, whereas when a negative determination is made in the process of S20, the process of S22 is interrupted at a stage where it has not yet been completed.

[0053] When the CPU 72 completes the processes of S22 and S26, or when a negative determination is made in the process of S18, the CPU 72 temporarily ends the series of processes shown in FIG. (Details of the recovery coefficient calculation process) 4 shows a process for calculating the return coefficient Kc after the all-cylinder fuel cut process M22a is stopped. The process shown in FIG. 4 is realized by the CPU 72 repeatedly executing a program stored in the ROM 74 at a predetermined interval, for example.

[0054] In the series of processes shown in FIG. 4, the CPU 72 first determines whether the all-cylinder fuel cut process M22a has ended (S30). If the CPU 72 determines that the all-cylinder fuel cut process M22a has ended (S30: YES), the CPU 72 assigns the maximum coefficient KL to the return coefficient Kc (S32). This process is intended to quickly reduce oxygen at the upstream end of the three-way catalyst 32. The CPU 72 then waits for a predetermined period of time (S34: NO). Here, the predetermined period may be, for example, one combustion cycle or two combustion cycles. In this way, if the interval is the rotation angle of the crankshaft 26, it becomes easy to determine the number of times that the fuel injection is increased and corrected by the maximum coefficient KL.

[0055] When the predetermined period has elapsed (S34: YES), the CPU 72 assigns the intermediate coefficient KM to the return coefficient Kc (S36). The intermediate coefficient KM is smaller than the maximum coefficient KL. Then, the CPU 72 waits until the oxygen storage amount OS becomes equal to or smaller than the specified value OSH (S38: NO). The specified value OSH is set according to the lower limit value of the value at which unburned fuel may flow out downstream of the three-way catalyst 32 if the return coefficient Kc is set to the intermediate coefficient KM. Here, the specified value OSH does not mean that it is smaller than the amount of oxygen that reacts with the unburned fuel flowing into the three-way catalyst 32 without excess or deficiency due to the intermediate coefficient KM. When the oxygen storage amount OS becomes small, even if the amount of oxygen stored is enough to react with the unburned fuel flowing into the three-way catalyst 32 without excess or deficiency, the unburned fuel may flow out downstream of the three-way catalyst 32 due to a decrease in reaction rate.

[0056] When the CPU 72 determines that the oxygen storage amount OS is equal to or less than the specified value OSH (S38: YES), it assigns the minimum coefficient KS to the return coefficient Kc (S40). Then, the CPU 72 waits until the oxygen storage amount OS is equal to or less than a predetermined value OSS (S42). The predetermined value OSS is set to a value for determining that the effect of the all-cylinder fuel cut process M22a has been eliminated and the state of the three-way catalyst 32 has returned to a normal state. When the CPU 72 determines that the oxygen storage amount OS is equal to or less than the predetermined value OSS (S42: YES), it assigns "1" to the return coefficient Kc (S44).

[0057] When the CPU 72 completes the process of S44 or makes a negative determination in the process of S30, the CPU 72 temporarily ends the series of processes shown in FIG. Fig. 5 shows the procedure of the process for calculating the return coefficient Kc after the temperature increase process is stopped. The process shown in Fig. 5 is realized by the CPU 72 repeatedly executing a program stored in the ROM 74, for example, at a predetermined interval. For convenience, the same step numbers are given to the processes in Fig. 5 that correspond to those shown in Fig. 4.

[0058] In the series of processes shown in FIG. 5, the CPU 72 determines whether the execution flag F has been switched from "1" to "0" (S50). This process is a process for determining whether the temperature increase process has been stopped. If the CPU 72 determines that the execution flag F has been switched (S50: YES), it assigns the intermediate coefficient KM to the return coefficient Kc (S36). Then, the CPU 72 waits for a predetermined period of time (S52: NO). Here, the predetermined period is an integral multiple of the interval at which the compression top dead center occurs. Specifically, it may be one combustion cycle, for example. If the predetermined period of time has elapsed (S52: YES), the CPU 72 waits until the oxygen storage amount OS becomes equal to or less than the specified value OSH (S38: NO), and assigns the minimum coefficient KS to the return coefficient Kc (S40). If the oxygen storage amount OS is already equal to or less than the specified value OSH at or before the predetermined period has elapsed, the CPU 72 assigns the minimum coefficient KS to the return coefficient Kc after the predetermined period has elapsed.

[0059] When the process of S44 is completed or when a negative determination is made in the process of S50, the CPU 72 temporarily ends the series of processes shown in FIG. Here, the operation and effects of this embodiment will be described.

[0060] FIG. 6 shows the transition of the air-fuel ratio of the cylinders #1, #3, and #4 according to the return coefficient Kc. As shown in Fig. 6, when the all-cylinder fuel cut process M22a is executed at time t1, the oxygen storage amount OS increases. Note that the air-fuel ratios of cylinders #1, #3, and #4 are not shown during the period from time t1 to time t2 when the all-cylinder fuel cut process M22a is executed, because the injection amount is zero and the air-fuel ratios cannot be defined.

[0061] When the all-cylinder fuel cut process M22a is stopped at time t2, the CPU 72 sets the return coefficient Kc to the maximum coefficient KL, so that the air-fuel ratio of the mixture in the cylinders #1, #3, and #4 becomes very small. The air-fuel ratio here may be, for example, "10" or less. By allowing a large amount of unburned fuel to flow into the three-way catalyst 32 in this way, oxygen at the upstream end of the three-way catalyst 32 can be quickly consumed after the all-cylinder fuel cut process M22a is stopped. Then, at time t3 when a predetermined period has elapsed, the CPU 72 sets the return coefficient Kc to the intermediate coefficient KM, so that the air-fuel ratio of the mixture in the cylinders #1, #3, and #4 increases. The air-fuel ratio here may be, for example, about "11 to 13".

[0062] Then, at time t4 when the oxygen storage amount OS becomes equal to or smaller than the specified value OSH, the CPU 72 assigns the minimum coefficient KS to the return coefficient Kc. As a result, the air-fuel ratios of the mixtures in the cylinders #1, #3, and #4 are lower than the theoretical air-fuel ratio, but are further increased. The air-fuel ratio here may be, for example, about "13 to 14".

[0063] Then, at time t5 when the oxygen storage amount OS becomes equal to or less than the predetermined value OSS, the CPU 72 assigns "1" to the return coefficient Kc. The CPU 72 then calculates the required injection amount Qd according to the feedback correction coefficient KAF. As a result, the air-fuel ratio of the mixture in the cylinders #1, #3, and #4 is feedback-controlled to the target value Afu*. In other words, it is controlled to a feedback rich air-fuel ratio Afr and a feedback lean air-fuel ratio Afl. The feedback rich air-fuel ratio Afr is greater than the air-fuel ratio of the mixture in the cylinders #1, #3, and #4 when the minimum coefficient KS is assigned to the return coefficient Kc.

[0064] On the other hand, when the temperature increase process is started at time t6, the CPU 72 makes the air-fuel ratio of the mixture in the cylinders #1, #3, and #4 richer than the theoretical air-fuel ratio. The air-fuel ratio at this time is set to an appropriate value within the region Ar according to the temperature Tgpf of the GPF 34. The upper limit value of the region Ar is greater than the air-fuel ratio realized by the minimum coefficient KS and smaller than the feedback rich air-fuel ratio Afr. The lower limit value of the region Ar is smaller than the air-fuel ratio realized by the maximum coefficient KL.

[0065] After time t7 when the temperature increase process is stopped, the CPU 72 assigns the intermediate coefficient KM to the return coefficient Kc. Then, at time t8 when the oxygen storage amount OS becomes equal to or less than the specified value OSH, the CPU 72 assigns the minimum coefficient KS to the return coefficient Kc. Then, at time t9 when the oxygen storage amount OS becomes equal to or less than the specified value OSS, the CPU 72 assigns "1" to the return coefficient Kc. Then, the CPU 72 calculates the required injection amount Qd according to the feedback correction coefficient KAF. As a result, the air-fuel ratio of the mixture in the cylinders #1, #3, and #4 is feedback-controlled to the target value Afu*.

[0066] In this way, by setting the return coefficient Kc to the intermediate coefficient KM when the temperature increase process is stopped, it is possible to suppress a decrease in the purification rate of NOx by the three-way catalyst 32 after the temperature increase process is stopped. According to the present embodiment described above, the following actions and effects can be obtained.

[0067] (1) After the temperature rise process is stopped, the value of the return coefficient Kc is increased, and then gradually decreased within a range greater than "1". When a large amount of fuel flows into the three-way catalyst 32 when the oxygen storage amount OS is small, even if the amount of oxygen stored in the three-way catalyst 32 is equal to or greater than the amount that can react with the fuel without excess or deficiency, some of the fuel may flow out downstream of the three-way catalyst 32. In response to this, in this embodiment, the return coefficient Kc is gradually decreased. This makes it possible to quickly eliminate a state in which the oxygen storage amount OS is large and the NOx purification rate is likely to decrease, and to suppress fuel from flowing out downstream of the three-way catalyst 32.

[0068] (2) The CPU 72 sets the return coefficient Kc to the intermediate coefficient KM for a predetermined period after the temperature rise process is stopped, even if the oxygen storage amount OS is equal to or less than the specified value OSH. This is because, after the temperature rise process is stopped, if the return coefficient Kc is set to the minimum coefficient KS, the NOx purification rate may decrease even if the calculated oxygen storage amount OS is equal to or less than the specified value OSH. More specifically, this is because, in cases such as when the intake air amount Ga becomes excessively large due to a sudden increase in the accelerator operation amount ACCP, the NOx purification rate may decrease. In other words, by setting a period in which the coefficient Kc is set to the intermediate coefficient KM, the decrease in the NOx purification rate can be suppressed.

[0069] (3) The value of the return time coefficient Kc when the temperature rise process is stopped is set to be smaller than the value of the return time coefficient Kc when the all-cylinder fuel cut process M22a is stopped. The state of the three-way catalyst 32 immediately after the temperature rise process is stopped tends to require a smaller amount of fuel to suppress the decrease in the NOx purification rate compared to the state of the three-way catalyst 32 immediately after the all-cylinder fuel cut process M22a is stopped. Nevertheless, if the value of the return time coefficient Kc when the temperature rise process is stopped is set to be equal to the value of the return time coefficient Kc when the all-cylinder fuel cut process is stopped, there is a risk of the fuel consumption rate being unnecessarily decreased. In contrast, in this embodiment, the value of the return time coefficient Kc when the temperature rise process is stopped is set to be smaller than the value of the return time coefficient Kc when the all-cylinder fuel cut process M22a is stopped, so that both the decrease in the NOx purification rate and the increase in the fuel consumption rate can be suppressed.

[0070] <Correspondence> The correspondence between the matters in the above embodiment and the matters described in the above "Means for solving the problem" column is as follows. In the following, the correspondence is shown for each number of the means for solving the problem described in the "Means for solving the problem" column. [1] The post-treatment device corresponds to the three-way catalyst 32 and the GPF 34. The catalyst corresponds to the three-way catalyst 32. The temperature increase process corresponds to the process of S22. The return process corresponds to the process of FIG. 5. [2, 3] The specific post-stop air-fuel ratio corresponds to the air-fuel ratio when the return coefficient Kc is set to the intermediate coefficient KM or the minimum coefficient KS. The upper limit air-fuel ratio and the lower limit air-fuel ratio correspond to the upper limit value and the lower limit value of the region Ar shown in FIG. 6. [4] The feedback process corresponds to the feedback coefficient calculation process M12 and the injector operation process M22. The switching process corresponds to the switching process M14. The specific post-stop air-fuel ratio corresponds to the air-fuel ratio when the return coefficient Kc is set to the intermediate coefficient KM or the minimum coefficient KS. [5] After the temperature increase process is stopped, the increase coefficient is set in all cylinders by the process of FIG. 5. [6] The all-cylinder fuel cut process corresponds to the all-cylinder fuel cut process M22a. The post-all-stop air-fuel ratio corresponds to the air-fuel ratio when the maximum coefficient KL is used. [7] The storage amount calculation process corresponds to the storage amount calculation process M16. The change process corresponds to the processes of S38 to S44. [8] The first rich air-fuel ratio corresponds to the air-fuel ratio realized by the intermediate coefficient KM. The second rich air-fuel ratio corresponds to the air-fuel ratio realized by the minimum coefficient KS. The forced rich process corresponds to the process of S36 being executed when the determination in the process of S52 is negative.

[0071] <Other embodiments> This embodiment can be modified as follows: This embodiment and the following modifications can be combined with each other to the extent that no technical contradiction occurs.

[0072] "About air-fuel ratio after specific stop" The specific post-stop air-fuel ratio is not limited to the air-fuel ratio realized by the intermediate coefficient KM used after the all-cylinder fuel cut processing M22a is stopped and the air-fuel ratio realized by the minimum coefficient KS. In other words, it is not essential that the value of the return coefficient Kc is the same as the value used after the all-cylinder fuel cut processing M22a is stopped.

[0073] The air-fuel ratio after the specific stop is not limited to one consisting of two values. For example, it may consist of three or more values ​​and be decreased stepwise as the amount of oxygen storage decreases. Even in this case, it is desirable that the maximum value of the air-fuel ratio after the specific stop is less than the feedback rich air-fuel ratio Afr. Also, making the minimum value of the air-fuel ratio after the specific stop greater than the air-fuel ratio realized by the maximum coefficient KL is effective in suppressing an increase in the fuel consumption rate.

[0074] The post-specific stop air-fuel ratio is not limited to a plurality of values ​​that increase with a decrease in the oxygen storage amount OS. For example, if the internal combustion engine is capable of suppressing and controlling the rate of increase in the intake air amount Ga after the temperature increase process, it may be a fixed value. Such an internal combustion engine may be installed in a vehicle that does not need to immediately increase the output of the internal combustion engine 10 in response to the required driving force value, such as a series hybrid vehicle described in the "Vehicle" section below.

[0075] It is not essential that the post-specific stop air-fuel ratio be set between the upper limit air-fuel ratio and the lower limit air-fuel ratio of the air-fuel ratios of the cylinders #1, #3, and #4 during the temperature rise process. "About forced rich processing" In the above embodiment, the predetermined period in the process of S52 is an integer multiple of the interval between occurrences of the compression top dead center, and the integer is a predetermined fixed value, but this is not limited to this. For example, the integer may be variable depending on the amount of oxygen storage OS.

[0076] It is not essential to perform the forced rich process. This is not limited to the case where the air-fuel ratio after a specific stop is a fixed value, as described in the section "Regarding the air-fuel ratio after a specific stop". For example, if the internal combustion engine is capable of suppressing and controlling the rate of increase in the intake air amount Ga after the temperature increase process, even if the air-fuel ratio after a specific stop is reduced according to the oxygen storage amount, the coefficient KS may be set to the minimum coefficient from the beginning if the oxygen storage amount OS is equal to or less than a predetermined value OSS.

[0077] "About air-fuel ratio after complete shutdown" The air-fuel ratio after total stop is not limited to three values. For example, it may have four or more values ​​and be increased stepwise as the oxygen storage amount OS decreases. It may also have two values. Furthermore, it may have one value if the internal combustion engine is capable of suppressing and controlling the increase speed of the intake air amount Ga after the all-cylinder fuel cut process. Such an internal combustion engine may be mounted on a vehicle or the like that does not require the output of the internal combustion engine 10 to be increased immediately according to the required value of driving force, such as a series hybrid vehicle described in the "Vehicle" section below.

[0078] "About the switching process" In the above embodiment, the switching process M14 calculates the oxygen storage amount independently of the storage amount calculation process M16, but this is not limiting. For example, the oxygen storage amount OS calculated by the storage amount calculation process M16 may be used as an input.

[0079] The condition for switching the target value Afu* to the feedback lean air-fuel ratio Afl is not limited to the logical sum of the oxygen storage amount OS being equal to or less than the switching lower limit value OSfr and the downstream air-fuel ratio Afd being equal to or less than "Afs-Δ". For example, it may be that the oxygen storage amount OS is equal to or less than the switching lower limit value OSfr. Also, it may be that the downstream air-fuel ratio Afd is equal to or less than "Afs-Δ".

[0080] The condition for switching the target value Afu* to the feedback rich air-fuel ratio Afr is not limited to the logical sum of the oxygen storage amount OS being equal to or greater than the switching upper limit value OSfl and the downstream air-fuel ratio Afd being equal to or greater than "Afs+Δ". For example, it may be that the oxygen storage amount OS is equal to or greater than the switching upper limit value OSfl. Also, it may be that the downstream air-fuel ratio Afd is equal to or greater than "Afs+Δ".

[0081] "About the storage amount calculation process" The storage amount calculation process is not limited to the process of calculating the oxygen storage amount OS based on the intake air amount Ga and the required injection amount Qd. For example, instead of the intake air amount Ga, the charging efficiency η may be input as an intake air amount variable that indicates the intake air amount of the internal combustion engine 10, and the rotation speed NE and the upstream air-fuel ratio Afu may also be input.

[0082] "About temperature rise treatment" In the process of S22, the number of cylinders to which fuel supply is stopped in one combustion cycle is one, but this is not limited to one. For example, the number may be two.

[0083] In the above embodiment, the cylinders to which the fuel supply is stopped in each combustion cycle are fixed to a predetermined cylinder, but this is not limited to the above. For example, the cylinders to which the fuel supply is stopped may be changed at a predetermined cycle.

[0084] The temperature increase process is not limited to a process with a period of one combustion cycle. For example, in the case of four cylinders as in the above embodiment, a period of five times the interval between occurrences of the compression top dead center may be set as a period, and one cylinder may be provided to stop the fuel supply during the same period. In this way, the cylinder to which the fuel supply is stopped can be changed at a period of five times the interval between occurrences of the compression top dead center.

[0085] "About the conditions for temperature rise processing" In the above embodiment, the above conditions (A) and (B) are exemplified as the predetermined conditions for executing the temperature increase process when a request for executing the temperature increase process is made, but the predetermined conditions are not limited to these. For example, the two conditions (A) and (B) may include only one of them.

[0086] "Estimation of deposition volume" The process of estimating the deposition amount DPM is not limited to the example shown in Fig. 3. For example, the deposition amount DPM may be estimated based on the intake air amount Ga and the pressure difference between the upstream and downstream sides of the GPF 34. Specifically, the deposition amount DPM may be estimated to be a larger value when the pressure difference is large than when it is small, and even if the pressure difference is the same, the deposition amount DPM may be estimated to be a larger value when the intake air amount Ga is small than when it is large. Here, when the pressure downstream of the GPF 34 is regarded as a constant value, the detected value of the pressure upstream of the GPF 34 can be used instead of the pressure difference.

[0087] "About post-processing device" The aftertreatment device is not limited to one having a GPF 34 downstream of the three-way catalyst 32, but may be one having a three-way catalyst 32 downstream of the GPF 34. Also, it is not limited to one having both the three-way catalyst 32 and the GPF 34. For example, it may be one having only the GPF 34. Even if the aftertreatment device is composed of only the three-way catalyst 32, if the temperature of the aftertreatment device needs to be increased during the regeneration process, it is effective to execute the process exemplified in the above embodiment and their modified examples. Note that, when the aftertreatment device is equipped with a GPF downstream of the three-way catalyst 32, the GPF is not limited to a filter carrying a three-way catalyst, but may be only a filter.

[0088] "About the control device" The control device is not limited to a device equipped with a CPU 72 and a ROM 74 and executing software processing. For example, the control device may be equipped with a dedicated hardware circuit such as an ASIC that performs hardware processing of at least a part of what was processed by software in the above embodiment. That is, the control device may have any of the following configurations (a) to (c). (a) A processing device that executes all of the above processing according to a program, and a program storage device such as a ROM that stores the program. (b) A processing device and a program storage device that execute a part of the above processing according to a program, and a dedicated hardware circuit that executes the remaining processing. (c) A dedicated hardware circuit that executes all of the above processing. Here, there may be a plurality of software execution devices equipped with a processing device and a program storage device, and a plurality of dedicated hardware circuits.

[0089] "About the vehicle" The vehicle is not limited to a series-parallel hybrid vehicle, but may be, for example, a parallel hybrid vehicle or a series hybrid vehicle. However, the vehicle is not limited to a hybrid vehicle, and may be, for example, a vehicle in which the power generating device of the vehicle is only the internal combustion engine 10. [Explanation of symbols]

[0090] 10. Internal combustion engine 20…Combustion chamber 30…Exhaust passage 32...Three-way catalyst 34…GPF 50...Planetary gear mechanism 52…First motor generator 54…Second motor generator 70...Control device 86...Upstream air-fuel ratio sensor 88...Downstream air-fuel ratio sensor

Claims

1. The present invention is applied to a multi-cylinder internal combustion engine equipped with an after-treatment device in an exhaust passage, The aftertreatment device includes a catalyst having an oxygen storage capacity and a filter that collects particulate matter, a temperature increasing process for increasing the temperature of the aftertreatment device in order to remove particulate matter trapped by the filter from the filter; Recovery processing and Run The temperature increase process includes a stop process and a rich process, the stop processing is processing for stopping the supply of fuel to some of the multiple cylinders, the rich processing is a processing for making an air-fuel ratio of the mixture in a cylinder other than the part of the cylinders among the plurality of cylinders less than a stoichiometric air-fuel ratio, the return process is a process for making a concentration of unburned fuel in the exhaust gas discharged into the exhaust passage higher than an equivalent concentration when the temperature increase process is stopped, A control device for an internal combustion engine, wherein the equivalent concentration is a concentration of unburned fuel that reacts with oxygen in the exhaust gas just enough.

2. the rich processing changes the air-fuel ratio of the mixture in the different cylinder to be equal to or lower than an upper limit air-fuel ratio and equal to or higher than a lower limit air-fuel ratio in accordance with a temperature of the post-treatment device, the return process includes a process of setting an air-fuel ratio of at least one cylinder among the plurality of cylinders to an air-fuel ratio after a specific stop, 2. The control device for an internal combustion engine according to claim 1, wherein the specific post-stop air-fuel ratio is greater than the lower limit air-fuel ratio and less than the stoichiometric air-fuel ratio.

3. the rich processing changes the air-fuel ratio of the mixture in the different cylinder to be equal to or lower than an upper limit air-fuel ratio and equal to or higher than a lower limit air-fuel ratio in accordance with a temperature of the post-treatment device, the return process includes a process of setting an air-fuel ratio of at least one cylinder among the plurality of cylinders to an air-fuel ratio after a specific stop, 3. The control device for an internal combustion engine according to claim 1, wherein the specific post-stop air-fuel ratio is smaller than the upper limit air-fuel ratio.

4. a feedback process for feedback-controlling a detection value of an air-fuel ratio sensor upstream of the aftertreatment device to a target value when the temperature increase process is not executed; a switching process for alternately switching the target value from one of two values, a feedback rich air-fuel ratio less than the stoichiometric air-fuel ratio and a feedback lean air-fuel ratio greater than the stoichiometric air-fuel ratio, to the other; the return process includes a process of setting an air-fuel ratio of at least one cylinder among the plurality of cylinders to an air-fuel ratio after a specific stop, 4. The control device for an internal combustion engine according to claim 1, wherein the specific post-stop air-fuel ratio is smaller than the feedback rich air-fuel ratio.

5. 5. The control device for an internal combustion engine according to claim 2, wherein the return process is a process for making the air-fuel ratio of the mixture in all of the plurality of cylinders the air-fuel ratio after the specific stop.

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