Control device for internal combustion engine

Abstract

The invention provides a control device for an internal combustion engine. Wherein the processing circuit is configured so as to execute: a first process for calculating an imbalance index value indicating the degree of variation in the air-fuel ratio between the plurality of cylinders, and a second process for calculating an imbalance index value indicating the degree of variation in the air-fuel ratio between the plurality of cylinders; a second process of calculating a target air-fuel ratio by correcting the reference air-fuel ratio with the imbalance index value; a third process in which fuel in an amount corresponding to the target air-fuel ratio is injected from the fuel injection valve; and a fourth process for stopping the operation of the internal combustion engine when the stop condition is satisfied. The processing circuit is configured so as to repeat the first to third processes without stopping the operation of the internal combustion engine until an end condition is satisfied, even if a stop condition is satisfied, when a continuation condition indicating a symptom of an abnormality related to a deviation in the air-fuel ratio between the plurality of cylinders is satisfied.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a control device of an internal combustion engine. BACKGROUND

[0002] The internal combustion engine disclosed in Japanese Patent Application Publication No. 2012-97671 has a plurality of cylinders, a fuel injection valve provided for each cylinder, an exhaust passage, and an air-fuel ratio sensor. The exhaust passage is connected to each cylinder. The air-fuel ratio sensor is located midway through the exhaust passage. The air-fuel ratio sensor detects the air-fuel ratio of exhaust gas discharged from each cylinder. A series of periods during which each of the plurality of cylinders undergoes a combustion stroke is referred to as a combustion cycle. A control device of the internal combustion engine calculates an imbalance index value that indicates the degree of deviation of the air-fuel ratio among the plurality of cylinders, based on a change in the detected value of the air-fuel ratio sensor across a predetermined period of a plurality of combustion cycles. The control device stores the imbalance index value in a memory when the imbalance index value is calculated. The control device calculates a target air-fuel ratio based on the latest imbalance index value stored in the memory in each combustion cycle. The control device calculates an instructed injection amount to the fuel injection valve based on the target air-fuel ratio. SUMMARY

[0003] PROBLEMS TO BE SOLVED BY THE INVENTION Sometimes, an internal combustion engine and a control device like those disclosed in the above-described publication are mounted on a hybrid vehicle. In a hybrid vehicle, the vehicle can be made to travel by a motor generator that is a different drive source from the internal combustion engine, so the opportunities for the internal combustion engine to be intermittently stopped increase. As a result, a proper imbalance index value can not be calculated. Therefore, by calculating a target air-fuel ratio and further calculating an instructed injection amount based on an improper imbalance index value, exhaust emission can be deteriorated.

[0004] MEANS FOR SOLVING THE PROBLEMS The control device of the internal combustion engine of one embodiment of the present disclosure is configured to control an internal combustion engine including: an internal combustion engine main body having a plurality of cylinders; and fuel injection valves provided for each of the cylinders. The control device includes a processing circuit. The processing circuit is configured to execute, during operation of the internal combustion engine, a first process of calculating an imbalance index value indicating a degree of imbalance of air-fuel ratios among the plurality of cylinders, on the basis of a change in a parameter indicating an operating state of the internal combustion engine in a predetermined set period; a second process of calculating a target air-fuel ratio by correcting a predetermined reference air-fuel ratio on the basis of the latest imbalance index value; a third process of causing fuel in an indicated injection amount corresponding to the latest target air-fuel ratio to be injected from each of the fuel injection valves; and a fourth process of stopping the operation of the internal combustion engine when a predetermined stop condition is satisfied. The processing circuit is configured to, in a case where a continuation condition that is predetermined as a condition indicating a sign of an abnormality related to imbalance of air-fuel ratios among the plurality of cylinders is satisfied, repeatedly perform the first process, the second process, and the third process without stopping the operation of the internal combustion engine even when the stop condition is satisfied, until a predetermined end condition is satisfied. BRIEF DESCRIPTION OF DRAWINGS

[0005] Figure 1 is a diagram indicating an outline structure of a vehicle.

[0006] Figure 2 is a flowchart of processing steps of a stop process performed by a control device provided in a vehicle of Figure 1 .

[0007] Figure 3 is a flowchart of processing steps of a flag setting process performed by a control device provided in a vehicle of Figure 1 .

[0008] Figure 4 is a diagram indicating contents of injection control performed by a control device provided in a vehicle of Figure 1 . DETAILED DESCRIPTION

[0009] <OVERALL STRUCTURE> Hereinafter, one embodiment of a control device 90 of an internal combustion engine 10 will be described with reference to the accompanying drawings. As shown in Figure 1 , a vehicle 100 is provided with the internal combustion engine 10, a first motor generator 71, a second motor generator 72, a planetary gear mechanism 70, a drive shaft 74, and drive wheels 75. The vehicle 100 is a hybrid vehicle that uses the internal combustion engine 10, the first motor generator 71, and the second motor generator 72 as drive sources.

[0010] The internal combustion engine 10 inputs torque to the planetary gear mechanism 70. The planetary gear mechanism 70 distributes the torque from the internal combustion engine 10 to the first motor generator 71 and the drive shaft 74. The first motor generator 71 generates electric power in accordance with the torque distributed to the first motor generator 71 by the planetary gear mechanism 70. The drive shaft 74 transmits the torque distributed to the drive shaft 74 by the planetary gear mechanism 70 to the drive wheels 75. The second motor generator 72 inputs torque to the drive shaft 74. The torque is transmitted to the drive wheels 75. An example of a vehicle having such a configuration is described in Japanese Patent Application Publication No. 2022-166473.

[0011] The internal combustion engine 10 includes an internal combustion engine main body 10A, a crankshaft 31, and a crank angle sensor 64. The internal combustion engine main body 10A has four cylinders 11. Each cylinder 11 is formed as a space partitioned within the internal combustion engine main body 10A. In each cylinder 11, a mixture of fuel and intake air is combusted by a spark plug 19 provided for each cylinder 11. In correspondence with the combustion of the mixture, the crankshaft 31 rotates. The crank angle sensor 64 outputs a signal corresponding to the rotational position of the crankshaft 31. The internal combustion engine main body 10A includes a water jacket 18 through which cooling water flows.

[0012] The internal combustion engine 10 includes an intake passage 15, a throttle valve 16, and a fuel injection valve 17 provided for each cylinder 11. The intake passage 15 is a passage for introducing intake air to each cylinder 11. The throttle valve 16 adjusts the intake air amount. The fuel injection valve 17 injects and supplies fuel into the corresponding cylinder 11.

[0013] The internal combustion engine 10 includes an exhaust passage 21 and a three-way catalyst 22. The exhaust passage 21 is a passage through which exhaust gas discharged from each cylinder 11 flows. The exhaust passage 21 includes independent passages 21A provided for each cylinder 11 and a merging passage 21B. The plurality of independent passages 21A respectively extend from the corresponding cylinder 11 and merge at the upstream end of the merging passage 21B. The three-way catalyst 22 is located midway through the merging passage 21B. That is, the three-way catalyst 22 is located at a position in the exhaust passage 21 that is on the downstream side compared to the merging positions of the plurality of independent passages 21A. The three-way catalyst 22 purifies hydrocarbon, carbon monoxide, and nitrogen oxides contained in the exhaust gas.

[0014] The internal combustion engine 10 is provided with an upstream air-fuel ratio sensor 62 and a downstream air-fuel ratio sensor 63. The upstream air-fuel ratio sensor 62 is located at a position upstream of the three-way catalyst 22 in the merged passage 21B. The air-fuel ratio of the exhaust gas flowing between the merging point of the plurality of individual passages 21A in the exhaust passage 21 and the three-way catalyst 22 is referred to as an upstream air-fuel ratio AF1. The upstream air-fuel ratio AF1 can also be said to be the air-fuel ratio of the exhaust gas flowing into the three-way catalyst 22. The upstream air-fuel ratio sensor 62 outputs a signal having a voltage value corresponding to the upstream air-fuel ratio AF1. As the upstream air-fuel ratio AF1 changes from rich to lean, the output voltage of the upstream air-fuel ratio sensor 62 increases in a linear manner in proportion to the upstream air-fuel ratio AF1. The downstream air-fuel ratio sensor 63 is located at a position downstream of the three-way catalyst 22 in the merged passage 21B. The air-fuel ratio of the exhaust gas flowing at the position downstream of the three-way catalyst 22 in the merged passage 21B is referred to as a downstream air-fuel ratio AF2. The downstream air-fuel ratio sensor 63 outputs a signal having a voltage value corresponding to the downstream air-fuel ratio AF2. The downstream air-fuel ratio sensor 63 is an oxygen sensor that outputs a voltage that changes greatly with the theoretical air-fuel ratio as a boundary. Examples of the detailed structure of the upstream air-fuel ratio sensor 62 and the downstream air-fuel ratio sensor 63 are disclosed in Japanese Patent Application Publication No. 2012-97671.

[0015] The vehicle 100 is provided with a start switch 67, an accelerator sensor 68, and a vehicle speed sensor 69. The start switch 67 is a switch for a user to turn on or off the main system of the vehicle 100. Hereinafter, the period from when the start switch 67 is turned on to when it is turned off will be referred to as one stroke. The accelerator sensor 68 outputs a signal corresponding to the operation amount of the accelerator pedal of the vehicle 100. The vehicle speed sensor 69 outputs a signal corresponding to the running speed of the vehicle 100.

[0016] The vehicle 100 is provided with a control device 90. The control device 90 is a computer provided with a processing circuit. The processing circuit is provided with a CPU 91 and a memory 92. The memory 92 includes three types of storage devices, namely, a RAM, a ROM, and a nonvolatile memory capable of being electrically rewritten. In the present embodiment, the three types of storage devices will be collectively referred to as the memory 92. The memory 92 stores various programs describing processes that the CPU 91 should execute in advance. The memory 92 stores various data required for the CPU 91 to execute the programs in advance.

[0017] The control device 90 repeatedly acquires signals from various sensors provided on the vehicle 100. The CPU 91 calculates required parameters at all times on the basis of the acquired signals. For example, the CPU 91 converts the signal output from the upstream air-fuel ratio sensor 62 into an upstream air-fuel ratio AF1 according to the voltage value thereof. The CPU 91 calculates the rotational speed of the crankshaft 31, i.e., the engine speed, on the basis of the signal from the crank angle sensor 64. The CPU 91 directly uses the voltage value acquired from the downstream air-fuel ratio sensor 63 for each process. The CPU 91 also processes the signals from the other sensors. Examples of the other sensors are an air flow meter and a cam angle sensor. The air flow meter outputs a signal corresponding to the intake air amount. The cam angle sensor outputs a signal corresponding to the rotational position of an intake camshaft that drives the intake valves. As described in Japanese Patent Application Publication No. 2012-97671, the CPU 91 can calculate the rotational angle of the crankshaft 31, i.e., the crank angle, by combining the signal from the crank angle sensor 64 and the signal from the cam angle sensor. The crank angle takes a value of 0 to 720 degrees with a predetermined rotational position of the crankshaft 31 as a reference.

[0018] The CPU 91 takes the engine 10, the first motor generator 71, and the second motor generator 72 as control targets. The CPU 91 repeatedly calculates a vehicle required torque required for the travel of the vehicle 100 on the basis of the operation amount of the accelerator pedal and the travel speed of the vehicle 100 during one stroke. The CPU 91 distributes the vehicle required torque to the engine 10, the first motor generator 71, and the second motor generator 72 when the vehicle required torque is calculated. The CPU 91 controls the engine 10, the first motor generator 71, and the second motor generator 72 individually on the basis of the distributed torque.

[0019] The CPU 91 operates or stops the operation of the engine 10 in accordance with the torque distributed to the engine 10 during one stroke. The CPU 91 performs various controls for causing the mixture to burn in each cylinder 11 in the case where the engine 10 is operated. The various controls include ignition timing control for controlling the ignition timing of the ignition plug 19, injection control J for controlling the fuel injection of the fuel injection valve 17, and opening degree control for controlling the opening degree of the throttle valve 16. The CPU 91 causes the mixture to burn in each cylinder 11 in turn by these various controls. Hereinafter, the series of periods during which each cylinder 11 undergoes a combustion stroke will be referred to as one combustion cycle. One combustion cycle is a period during which the crank angle is from 0 to 720 degrees.

[0020] As a process for controlling the internal combustion engine 10, the CPU 91 is capable of executing various processes, including the first to fourth processes described later. As one of the processes for controlling the internal combustion engine 10, the CPU 91 is capable of executing a stop process. The CPU 91 initiates the stop process when a predetermined stop condition is met during the operation of the internal combustion engine 10. For example, the stop condition is that the vehicle requires a torque below a predetermined torque. The predetermined torque is predetermined as a value that can be generated solely by the first electric generator 71 and the second electric generator 72, and that satisfies the vehicle state corresponding to the user's requirements.

[0021] like Figure 2 As shown, when the CPU 91 starts the stop process, it first performs step S110. In step S110, the CPU 91 determines whether the allow flag V is on. The allow flag V is a flag indicating whether the internal combustion engine 10 can stop operating. An on allow flag V means that the operation of the internal combustion engine 10 is allowed to stop. An off allow flag V means that the operation of the internal combustion engine 10 is prohibited from stopping. The memory 92 stores the current setting of the allow flag V. If the allow flag V is on (S110: Yes), the CPU 91 causes the process to proceed to step S120.

[0022] In step S120, CPU 91 stops the operation of the internal combustion engine 10. Specifically, CPU 91 stops the execution of various controls for the combustion of the air-fuel mixture. Thus, when the stop condition is met during the operation of the internal combustion engine 10, CPU 91 stops the operation of the internal combustion engine 10, provided that the enable flag V is turned on. This step S120 is the fourth process. After executing the process of step S120, CPU 91 ends the series of processes for stopping. After stopping the operation of the internal combustion engine 10, CPU 91 restarts the operation of the internal combustion engine 10 when a predetermined starting condition is met. The starting condition is, for example, that the vehicle requires a torque greater than a predetermined torque.

[0023] On the other hand, in step S110, if the enable flag V is off (S110: No), the CPU 91 causes the process to proceed to step S130. In step S130, the CPU 91 continues the operation of the internal combustion engine 10. That is, the CPU 91 maintains the execution state of various controls related to the operation of the internal combustion engine 10. Then, the CPU 91 quickly ends the processing in step S130 and ends the stop processing. In other words, if the determination in step S110 is no, the CPU 91 quickly ends the stop processing without performing any special processing. If the determination in step S110 is no and the stop condition is met at the time point when the stop processing ends, the CPU 91 performs the processing in step S110 again.

[0024] CPU91 can perform flag setting processing. Flag setting processing is used to switch the enable flag V on or off. CPU91 starts flag setting processing when the start switch 67 is in the on state. Taking into account the content of flag setting processing, at the time when CPU91 starts flag setting processing, enable flag V is turned on.

[0025] like Figure 3 As shown, during the start flag setting process, CPU 91 first performs step S210. In step S210, CPU 91 determines whether the continuation condition is met. The continuation condition is predefined as a condition indicating an abnormal symptom related to the deviation of the air-fuel ratio among the multiple cylinders 11. In step S210, CPU 91 performs the following processing: First, CPU 91 waits until a new imbalance index value X is calculated in the first process P1 described later. When the calculation of the new imbalance index value X is completed, CPU 91 refers to the first and second values ​​of the imbalance index values ​​X stored in memory 92 in chronological order. The first value is the newly calculated latest imbalance index value X. The second value is the imbalance index value X that is earlier than the first value by a predetermined number. The predetermined number is, for example, 2. CPU 91 divides the value obtained by subtracting the second value from the first value by the continuation judgment period. CPU 91 processes the resulting value as the exponential change rate. The exponential change rate is the rate of change of the imbalance index value X during the continuation judgment period. The continuation judgment period is predefined as the elapsed time from when the CPU 91 calculates the second value until when the first value is calculated. The CPU 91 can calculate the length of the continuation judgment period based on the calculation timing of each imbalance index value X stored in the memory 92. Taking into account the execution period of the first process P1 described later, the continuation judgment period varies according to the internal combustion engine speed. When calculating the exponential change rate, the CPU 91 calculates the exponential average value by referring to the imbalance index values ​​X stored in the memory 92 in chronological order. The exponential average value is the average of multiple imbalance index values ​​X within the continuation judgment period, which is the object of the exponential change rate calculation. When calculating the exponential change rate and the exponential average value, the CPU 91 determines whether the continuation condition is met. The continuation condition is that the exponential change rate is greater than or equal to the continuation judgment value and the exponential average value is greater than or equal to the continuation judgment value. The continuation change rate and the continuation judgment value are predefined based on experiments, etc., as optimal values ​​in terms of understanding the situation where the deviation of the air-fuel ratio among the multiple cylinders 11 subsequently increases.

[0026] If the continuation condition is not met in the determination of whether the continuation condition is valid (S210: No), the CPU91 proceeds to step S240. In step S240, the CPU91 sets the enable flag V to "on". Then, the CPU91 ends the series of processes for flag setting. At this time, if the start switch 67 is in the "on" state, the CPU91 executes the process of step S210 again.

[0027] On the other hand, in step S210, the CPU 91, in a case where the continuation condition is satisfied (S210: YES), causes the process to proceed to step S220. In step S220, the CPU 91 sets the permission flag V to off. Thereafter, the CPU 91 causes the process to proceed to step S230.

[0028] In step S230, the CPU 91 determines whether or not the end condition is satisfied. Specifically, the CPU 91 performs the following process. The CPU 91 calculates the exponential change rate in the same manner as in step S210. The predetermined number of times employed in step S230 can be the same as or different from the predetermined number of times employed in step S210. The predetermined number of times can be, for example, 1. In step S230, the CPU 91 divides the difference between the first value and the second value by the end judgment period instead of the continuation judgment period. The end judgment period is predetermined as the elapsed time from when the CPU 91 calculates the second value to when the first value is calculated. The CPU 91 can calculate the length of the end judgment period in the same manner as the continuation judgment period. In step S230, the CPU 91 calculates, in addition to the exponential change rate, the adjustment change rate, which is the rate of change of the adjustment coefficient Y2 within the end judgment period. The adjustment coefficient Y2 will be described later. The CPU 91 refers to the latest value among the adjustment coefficients Y2 stored in the memory 92 in chronological order and the value calculated before the corresponding amount to the end judgment period with respect to the latest value. The CPU 91 calculates the adjustment change rate by dividing the difference between these two values by the end judgment period. Thereafter, the CPU 91 determines whether or not the end condition is satisfied. The end condition is that the absolute value of the exponential change rate is equal to or less than the exponential judgment value and the absolute value of the adjustment change rate is equal to or less than the adjustment judgment value. The exponential judgment value is predetermined based on experiments or the like as a value that can be regarded as a sufficiently small time variation of the imbalance index value X. Also, the adjustment judgment value is predetermined based on experiments or the like as a value that can be regarded as a sufficiently small time variation of the adjustment change rate.

[0029] The CPU 91, in a case where the end condition is not satisfied in the determination of whether or not the end condition can be established (S230: NO), executes again the process of step S230. The CPU 91 repeatedly performs the process of step S230 until the end condition is satisfied. The CPU 91, when the end condition is satisfied (S230: YES), causes the process to proceed to step S240. The content of the process of step S240 is as already described. The CPU 91, when the switch 67 is switched from on to off during the middle of repeatedly performing the process of step S230, causes the process to proceed to step S240 at that point in time.

[0030] <Details of Injection Control> As Figure 4The injection control J includes a first process Pl, a second process P2, and a third process P3 as shown. The contents of these processes will be described in order.

[0031] The CPU 91 repeatedly executes the first process Pl while the internal combustion engine 10 is operating. In other words, the CPU 91 repeatedly performs the first process Pl during operation of the internal combustion engine 10. The first process Pl is a process of calculating information required in the second process P2, that is, an imbalance index value X. The imbalance index value X is an index value indicating the degree of deviation of the air-fuel ratio among the plurality of cylinders 11. The CPU 91 continues the first process Pl for a predetermined set period. The CPU 91 promptly starts the first process Pl of the next cycle at the end of the set period. That is, the CPU 91 performs the first process Pl for each set period. The set period is a series of periods corresponding to a predetermined set number of combustion cycles. That is, the set period is not specified by an absolute time, but is determined by the speed of change in the crank angle. That is, the set period varies depending on the engine speed. The set number is specified based on experiments or the like as the minimum number of combustion cycles for which an average characteristic from which noise or the like is removed is obtained in relation to the air-fuel ratio in the plurality of cylinders 11. Depending on the set content of the set number, the execution period of one first process Pl can be, for example, 10 seconds or more. As a process in the stage before the first process Pl is performed, the CPU 91 repeatedly acquires the output value of the upstream air-fuel ratio sensor 62, or the upstream air-fuel ratio AF1, at a predetermined sampling interval. The sampling interval is specified by an absolute time. The maximum value of the engine speed at which the internal combustion engine 10 can take is referred to as the maximum speed. The sampling interval is sufficiently short compared to one combustion cycle when the engine speed is the maximum speed. The output value of the upstream air-fuel ratio sensor 62 is one example of a parameter indicating the operating state of the internal combustion engine 10.

[0032] CPU 91 calculates an imbalance index value X each time it executes the first process P1. The calculation method for the imbalance index value X is explained below. During the execution of the first process P1, CPU 91 repeatedly calculates basic index values. The basic index value is obtained by dividing the absolute value of the difference between two consecutively acquired upstream air-fuel ratios AF1 by the sampling interval of the output value of the upstream air-fuel ratio sensor 62. CPU 91 calculates multiple basic index values ​​in one combustion cycle. CPU 91 divides the cumulative value of these multiple basic index values ​​calculated in one combustion cycle by the cumulative count. The cumulative count is the number of basic index values ​​calculated by CPU 91 in one combustion cycle. CPU 91 processes the value obtained by dividing the cumulative value of multiple basic index values ​​by the cumulative count as an intermediate generated value. CPU 91 calculates such intermediate generated values ​​for a set number of combustion cycles. When calculating intermediate generated values ​​for a set number of cycles, CPU 91 divides the cumulative value of these intermediate generated values ​​for the set number of cycles by the set number of cycles. CPU 91 stores the obtained value as the latest imbalance index value X in memory 92. An example of the method for calculating the imbalance index value X is described in the "Obtaining the Air-Fuel Ratio Imbalance Index Value" section of Japanese Patent Application Publication No. 2012-97671. Thus, in the first processing P1, the CPU 91 calculates the imbalance index value X based on the change in the output value of the upstream air-fuel ratio sensor 62 during a set period. According to the calculation method of the basic index value that forms the basis of the imbalance index value X, the greater the degree of deviation in the air-fuel ratio among the multiple cylinders 11, the larger the value of the imbalance index value X. The memory 92 stores the changes in the imbalance index value X together with the calculation time of the imbalance index value X in a time sequence.

[0033] like Figure 4 As shown, CPU 91 repeatedly executes the second process P2 while the internal combustion engine 10 is running. In other words, CPU 91 repeatedly performs the second process P2 during the operation of the internal combustion engine 10. The second process P2 is used to calculate the target air-fuel ratio Y3, which is the information required for the third process P3. CPU 91 performs the second process P2 at predetermined execution intervals, such as one combustion cycle. For example, CPU 91 performs the second process P2 rapidly at the start time of each combustion cycle. In one second process P2, CPU 91 sequentially performs the correction calculation routine P2A, the adjustment coefficient calculation routine P2B, and the target calculation routine P2C.

[0034] The CPU 91 calculates the over-rich correction amount Yl in the correction amount calculation routine P2A. The over-rich correction amount Yl is a correction value for making a reduction correction to the reference air-fuel ratio AFK in the target calculation routine P2C. The reference air-fuel ratio AFK of the present embodiment is predetermined as the stoichiometric air-fuel ratio. As the reference air-fuel ratio AFK, a value other than the stoichiometric air-fuel ratio can also be set. The CPU 91, when calculating the over-rich correction amount Yl, refers to the latest intake air amount, the latest imbalance index value X stored in the memory 92, and a correction map stored in the memory 92. The correction map indicates the relationship of the intake air amount, the imbalance index value X, and the over-rich correction amount Yl. The over-rich correction amount Yl takes a value of zero or more. The correction map basically has the following two characteristics. First, at the same intake air amount, the larger the imbalance index value X, the larger the value of the over-rich correction amount Yl. Second, at the same imbalance index value X, the larger the intake air amount, the larger the value of the over-rich correction amount Yl. The CPU 91 substitutes the latest intake air amount and the latest imbalance index value X in this correction map, and thereby calculates the over-rich correction amount Yl corresponding to the engine operating state at the current time point. The CPU 91 stores the obtained value as the latest over-rich correction amount Yl in the memory 92. The CPU 91 ends the correction amount calculation routine P2A when the over-rich correction amount Yl is calculated. The CPU 91 can also treat a value obtained by multiplying the over-rich correction amount Yl calculated based on the correction map by an appropriate correction coefficient as the final over-rich correction amount Yl. An example of the calculation method of the over-rich correction amount Yl is described in the column of "Determination of the imbalance over-rich correction amount" in Japanese Patent Application Publication No. 2012-97671.

[0035] The CPU 91 calculates the adjustment coefficient Y2 in the adjustment coefficient calculation routine P2B. The adjustment coefficient Y2 is one example of the air-fuel ratio adjustment value. The adjustment coefficient Y2 is a coefficient for adjusting the degree of the decreasing correction of the reference air-fuel ratio AFK in the target calculation routine P2C. The CPU 91 compares the latest output value of the downstream air-fuel ratio sensor 63 with a reference value when calculating the adjustment coefficient Y2. The reference value is predetermined as the value output from the downstream air-fuel ratio sensor 63 when the air-fuel ratio detected by the downstream air-fuel ratio sensor 63 is the reference air-fuel ratio AFK. That is, the reference value of the present embodiment is the value corresponding to the stoichiometric air-fuel ratio. The CPU 91 subtracts a positive first predetermined value from the last value of the adjustment coefficient Y2 stored in the memory 92 in the case where the output value of the downstream air-fuel ratio sensor 63 is larger than the reference value. The CPU 91 stores the resulting value as the new adjustment coefficient in the memory 92. On the other hand, the CPU 91 adds the first predetermined value to the last value of the adjustment coefficient Y2 stored in the memory 92 in the case where the output value of the downstream air-fuel ratio sensor 63 is smaller than the reference value. The CPU 91 stores the resulting value as the new adjustment coefficient Y2 in the memory 92. The CPU 91 stores the last value of the adjustment coefficient Y2 stored in the memory 92 as the new adjustment coefficient Y2 in the memory 92 as it is in the case where the output value of the downstream air-fuel ratio sensor 63 is the same as the reference value. In this way, the CPU 91 updates the adjustment coefficient Y2 based on the comparison result of the output value of the downstream air-fuel ratio sensor 63 and the reference value. The memory 92 stores the changes of the adjustment coefficient Y2 in time series together with the time points when the adjustment coefficient Y2 is calculated. For example, the upper limit value and the lower limit value are defined in such a manner that the air-fuel ratio adjustment value becomes a positive value of 1 or less. The CPU 91 ends the adjustment coefficient calculation routine P2B when a new air-fuel ratio adjustment value is calculated. The adjustment coefficient Y2 corresponds to the "fourth reflection rate" of Japanese Patent Application Publication No. 2012-97671. One example of the calculation method of the adjustment coefficient Y2 is described in the column of "Calculation of the modification amount of the unbalance rich correction amount" of Japanese Patent Application Publication No. 2012-97671.

[0036] The CPU 91 calculates the target air-fuel ratio Y3 in the target calculation routine P2C. The CPU 91 calculates the target air-fuel ratio Y3 on the basis of the latest rich correction amount Yl, the latest adjustment coefficient Y2, and the reference air-fuel ratio AFK. The CPU 91, in calculating the target air-fuel ratio Y3, first multiplies the rich correction amount Yl by the adjustment coefficient Y2. The CPU 91 handles the resulting value as an adjusted correction amount. According to the definitions of the rich correction amount Yl and the adjustment coefficient Y2, the adjusted correction amount is a positive value. The CPU 91, in calculating the adjusted correction amount, subtracts the adjusted correction amount from the reference air-fuel ratio AFK. The CPU 91 subtracts a sub-feedback correction amount and a startup correction amount from the resulting value. The CPU 91 stores the resulting value as the latest target air-fuel ratio Y3 in the memory 92. Then, the CPU 91 ends the target calculation routine P2C. The sub-feedback correction amount is the sum of the outputs of a proportional element, an integral element, and a differential element, which are input with a value obtained by subtracting the output value of the downstream air-fuel ratio sensor 63 from the reference value. The startup correction amount is set on the basis of the temperature of the cooling water of the engine main body 10A at the time of engine startup. As a part of the second processing P2, the CPU 91 calculates these sub-feedback correction amount and startup correction amount through other processing routines. An example of the calculation method of the target air-fuel ratio Y3 is described in the column of "Determination of target air-fuel ratio" of Japanese Patent Application Publication No. 2012-97671. An example of the calculation method of the sub-feedback correction amount is described in the column of "Calculation of sub-feedback amount" of Japanese Patent Application Publication No. 2012-97671. An example of the calculation method of the startup correction amount is described in the column of "Determination of startup correction amount" of Japanese Patent Application Publication No. 2012-97671.

[0037] With regard to the second processing P2, the following can be stated. As described above, the rich correction amount Yl and the adjusted correction amount are positive values. Therefore, in the case where the adjusted correction amount is calculated on the basis of the reference air-fuel ratio AFK in the target calculation routine P2C, the case corresponds to a reduction correction of the reference air-fuel ratio AFK. That is, the CPU 91, in calculating the target air-fuel ratio Y3, performs a reduction correction of the reference air-fuel ratio AFK by the rich correction amount Yl. As described above, in the correction map, the greater the imbalance index value X, the greater the value of the rich correction amount Yl. That is, the CPU 91 calculates the target air-fuel ratio Y3 in such a manner that the greater the imbalance index value X, the greater the degree of reduction correction of the reference air-fuel ratio AFK. The CPU 91, in performing the reduction correction of the reference air-fuel ratio AFK, utilizes the value obtained by multiplying the rich correction amount Yl by the adjustment coefficient Y2. That is, the CPU 91 adjusts the degree of reduction correction of the reference air-fuel ratio AFK by the adjustment coefficient Y2. The CPU 91 changes the degree of reduction correction of the reference air-fuel ratio AFK on the basis of the latest adjustment coefficient Y2, thereby calculating the target air-fuel ratio Y3.

[0038] As Figure 4As shown, the CPU 91 repeatedly executes the third processing P3 while the internal combustion engine 10 is operating. In other words, the CPU 91 repeatedly performs the third processing P3 during the operation of the internal combustion engine 10. The CPU 91 performs the third processing P3 in each combustion cycle.

[0039] The CPU 91 performs the following injection processing routine for each cylinder 11 once in one third processing P3. Any of the four cylinders 11 is referred to as a target cylinder. The contents of the injection processing routine are described below with reference to the target cylinder. The CPU 91 starts the injection processing routine for the target cylinder at a predetermined crank angle before the intake top dead center of the intake of the target cylinder. The CPU 91 first calculates the in-cylinder intake air amount of the target cylinder at the current time point when starting the injection processing routine. The in-cylinder intake air amount is the amount of intake air filled into one cylinder 11. The CPU 91 calculates the in-cylinder intake air amount on the basis of the latest intake air amount and the latest engine speed. The CPU 91 refers to the latest target air-fuel ratio Y3 stored in the memory 92 when calculating the in-cylinder intake air amount. Then, the CPU 91 divides the in-cylinder intake air amount by the target air-fuel ratio Y3. The CPU 91 processes the resulting value as a basic injection amount. The CPU 91 implements feedback correction on the basic injection amount when calculating the basic injection amount. Specifically, the CPU 91 multiplies the basic injection amount by a main feedback coefficient calculated in a processing routine different from the injection processing routine and a main learning value serving as a learning value thereof. The CPU 91 processes the resulting value as an instruction injection amount. The main feedback coefficient and the main learning value are correction values for feedback correcting the fuel injection amount from the fuel injection valve 17 so that the upstream air-fuel ratio AF1 coincides with the target air-fuel ratio Y3. By multiplying these correction values by the basic injection amount, the excess or deficiency of the fuel supply amount to the cylinder 11 on the basis of making the upstream air-fuel ratio AF1 coincide with the target air-fuel ratio Y3 is compensated for. An example of the calculation method of the main feedback coefficient and the main learning value is described in the column of "Main Feedback Control" in Japanese Patent Application Publication No. 2012-97671. An example of the calculation method of the instruction injection amount is described in the column of "Fuel Injection Amount Control" in Japanese Patent Application Publication No. 2012-97671. The CPU 91 causes the fuel injection valve 17 to inject the instruction injection amount at a crank angle corresponding to a previously specified injection timing when calculating the instruction injection amount. The CPU 91 ends the injection processing routine when the fuel injection by the fuel injection valve 17 is completed. The CPU 91 performs such an injection processing routine for each cylinder 11 within one combustion cycle. That is, the CPU 91 causes the instruction injection amount corresponding to the latest target air-fuel ratio Y3 to be injected from each fuel injection valve 17 within one combustion cycle in the third processing P3. The instruction injection amount is the same for each fuel injection valve 17 in the present embodiment. As a result of the CPU 91 repeatedly performing the third processing P3, fuel is supplied to each cylinder 11 in each combustion cycle.

[0040] Effects of Embodiments (1) The CPU 91 sets the permission flag V to off (S220) in a case where the continuation condition of the operation of the internal combustion engine 10 is satisfied (S210: YES). In a case where the stop condition of the internal combustion engine 10 is satisfied in this state, the CPU 91 does not stop the operation of the internal combustion engine 10 but continues the operation of the internal combustion engine 10 until the end condition is satisfied. The CPU 91 repeatedly performs the first process P1, the second process P2, and the third process P3 during the continuation of the operation of the internal combustion engine 10. If such a configuration is adopted, in a case where there is a sign that the deviation of the air-fuel ratios among the plurality of cylinders 11 is becoming large, the CPU 91 updates the imbalance index value X without delay even in a case where the internal combustion engine 10 is intermittently stopped. Therefore, the imbalance index value X always becomes a value that reflects the deviation of the air-fuel ratios among the cylinders 11 at the current time point. Thus, the CPU 91 can always set the optimum target air-fuel ratio Y3 from the viewpoint of suppressing exhaust emission.

[0041] (2) If the time average of the imbalance index value X is large to some extent and the time change rate of the imbalance index value X is large to some extent, the deviation of the air-fuel ratios among the plurality of cylinders 11 is likely to become large thereafter. Therefore, the continuation condition that the index change rate is equal to or larger than the continuation change rate and the index average is equal to or larger than the continuation judgment value is suitable for grasping a sign that the deviation of the air-fuel ratios among the cylinders 11 is becoming large.

[0042] (3) The average of the actual air-fuel ratios in the plurality of cylinders 11 is referred to as a true average air-fuel ratio. As described in Japanese Patent Application Publication No. 2012-97671, in consideration of the structure of the upstream air-fuel ratio sensor 62, the upstream air-fuel ratio sensor 62 can indicate a value that is more rich than the true average air-fuel ratio when the deviation of the air-fuel ratios among the plurality of cylinders 11 is large. On the other hand, in a case where feedback correction is performed in such a manner that the upstream air-fuel ratio AF1 coincides with the target air-fuel ratio Y3, the fuel injection amount is reduced and corrected in such a manner that the rich air-fuel ratio indicated by the upstream air-fuel ratio sensor 62 is eliminated. As a result, the true average air-fuel ratio can be leaner than the reference air-fuel ratio AFK. Such a lean correction is referred to as a lean error correction. In order to compensate for this lean error correction, the CPU 91 reduces and corrects the reference air-fuel ratio AFK on the basis of the imbalance index value X, and thereby sets the target air-fuel ratio Y3. In a case where the update of the imbalance index value X is stalled as the intermittent stop of the internal combustion engine 10 is repeated, the condition in which such a lean error correction cannot be compensated for continues. As described in (1), the CPU 91 of the present embodiment updates the imbalance index value X without stall. Therefore, the CPU 91 can avoid the lean error correction even in a case where the intermittent stop of the internal combustion engine 10 is repeatedly performed.

[0043] (4) As described in Japanese Patent Application Publication No. 2012-97671, the difference between the output value of the downstream air-fuel ratio sensor 63 and the reference value reflects the degree of excess or deficiency of the reduction correction related to the calculation of the target air-fuel ratio Y3. Therefore, the CPU 91 of the present embodiment is able to set the target air-fuel ratio Y3 corresponding to the imbalance index value X to an optimal value in terms of suppressing exhaust emission, by adjusting the degree of the reduction correction related to the target air-fuel ratio Y3 using the adjustment coefficient Y2.

[0044] Suppose that a clogging by a foreign object occurs in one of the fuel injection valves 17. Then, the fuel injection valve 17 supplies less fuel to the cylinder 11 than the indicated injection amount, and further less than the amount of fuel supplied to the other cylinders 11. For example, with such an event, the deviation of the air-fuel ratio among the plurality of cylinders 11 increases with time. Thereafter, if the degree of the deviation gradually stabilizes, the variation of the imbalance index value X gradually becomes small. Thereafter, when the adjustment coefficient Y2 converges to the optimal value, the output value of the downstream air-fuel ratio sensor 63 approaches the reference value. Through such a series of processes, a certain degree of time is required until the output value of the downstream air-fuel ratio sensor 63 substantially coincides with the reference value. Assuming a case where the intermittent stop of the internal combustion engine 10 and the short operation period are repeated, the situation where the adjustment coefficient Y2 cannot converge to the value required to make the output value of the downstream air-fuel ratio sensor 63 approach the reference value can continue. In this regard, the CPU 91 of the present embodiment updates the adjustment coefficient Y2 together with the imbalance index value X without delay. Therefore, the CPU 91 is able to make the adjustment coefficient Y2 quickly become the optimal value even in a situation where the intermittent stop of the internal combustion engine 10 is repeated.

[0045] <Modification Example> The above-described embodiment can be modified and implemented in the following manner. The above-described embodiment and the following modification examples can be combined with each other and implemented within a range where there is no technical contradiction.

[0046] • The imbalance index value X and the method of calculating the same are not limited to the example of the above-described embodiment. The imbalance index value X can indicate the degree of the deviation of the air-fuel ratio among the plurality of cylinders 11. In calculating the imbalance index value X, for example, a parameter indicating the operating state of the internal combustion engine other than the upstream air-fuel ratio AF1, such as the engine speed, can be used.

[0047] • The content of the second processing P2 is not limited to the example of the above-described embodiment. The second processing P2 is only required to be processing that calculates the target air-fuel ratio Y3 by correcting the reference air-fuel ratio AFK based on the imbalance index value X. For example, the reference air-fuel ratio AFK can be increased. When calculating the target air-fuel ratio Y3, one or more of the rich correction amount Yl, the adjustment coefficient Y2, the sub-feedback correction amount, and the start correction amount can not be used. Calculation of a parameter that is not used for correction can be omitted.

[0048] • The content of the third processing P3 is not limited to the example of the above-described embodiment. The third processing P3 is only required to be processing that injects the indicated injection amount corresponding to the target air-fuel ratio Y3 from each fuel injection valve 17. When calculating the indicated injection amount, it is not necessary to implement feedback correction in a manner in which the upstream air-fuel ratio AF1 and the target air-fuel ratio Y3 coincide. The indicated injection amount can be changed for each cylinder 11.

[0049] • The continuation condition is not limited to the example of the above-described embodiment. The continuation condition is only required to be a condition that indicates a sign that the deviation of the air-fuel ratio among the plurality of cylinders 11 is increasing. The continuation condition can be defined by a parameter other than the imbalance index value X.

[0050] • The end condition is not limited to the example of the above-described embodiment. The end condition is only required to be a condition that enables the imbalance index value X to be updated slightly. The sub-feedback correction amount can be handled as the air-fuel ratio adjustment value. As the end condition, the rate of change of the sub-feedback correction amount can be compared with a dedicated adjustment judgment value. The end condition can be defined by either of the imbalance index value X and the air-fuel ratio adjustment value alone, or by a parameter other than these.

[0051] • The overall structure of the internal combustion engine 10 is not limited to the example of the above-described embodiment. The internal combustion engine 10 is only required to have the plurality of cylinders 11 and the fuel injection valve 17 provided for each cylinder 11. The number of cylinders 11 is not limited to four. The upstream air-fuel ratio sensor 62 and the downstream air-fuel ratio sensor 63 can be the same type of sensor.

[0052] • The overall structure of the vehicle 100 is not limited to the example of the above-described embodiment. One or more of the motor generators can be removed from the vehicle 100. If the control device 90 is applied to a vehicle 100 that performs automatic stop and automatic restart of the internal combustion engine 10, it is preferable in terms of updating the imbalance index value X.

[0053] • The control device 90 is not limited to being realized by a processing circuit including the CPU 91 and the memory 92. For example, the control device 90 can also include a dedicated hardware circuit (e.g., an ASIC or the like) that performs at least a portion of the processing performed in the above-described embodiments. That is, the control device 90 can include a processing circuit including any of the following (a) to (c).

[0054] (a) A processing circuit including: one or more processing devices that perform all of the above-described processing in accordance with a program; and one or more program storage devices, such as ROMs, that store the program.

[0055] (b) A processing circuit including: one or more processing devices that perform a portion of the above-described processing in accordance with a program; one or more program storage devices; and one or more dedicated hardware circuits that perform the remaining processing.

[0056] (c) A processing circuit including one or more dedicated hardware circuits that perform all of the above-described processing.

Claims

1. A control device of an internal combustion engine, wherein the internal combustion engine is provided with an internal combustion engine main body having a plurality of cylinders, and a fuel injection valve provided for each of the cylinders, the control device is provided with a processing circuit, the processing circuit is configured to execute, during operation of the internal combustion engine, a first process of calculating an imbalance index value indicating a degree of deviation of air-fuel ratios among the plurality of cylinders, based on a change in a parameter indicating an operating state of the internal combustion engine during a predetermined set period, a second process of calculating a target air-fuel ratio by correcting a predetermined reference air-fuel ratio based on the latest imbalance index value, a third process of causing fuel of an indicated injection amount corresponding to the latest target air-fuel ratio to be injected from each of the fuel injection valves, a fourth process of stopping operation of the internal combustion engine when a predetermined stop condition is satisfied, the processing circuit is configured to, in a case where a continuation condition predetermined as a condition indicating a sign of an abnormality related to deviation of air-fuel ratios among the plurality of cylinders is satisfied, repeatedly execute the first process, the second process, and the third process without stopping operation of the internal combustion engine even when the stop condition is satisfied, until a predetermined end condition is satisfied.

2. The control device of an internal combustion engine according to claim 1, wherein the continuation condition is that a rate of change of the imbalance index value during a predetermined continuation judgment period is equal to or greater than a predetermined continuation change rate, and an average value of the imbalance index value during the continuation judgment period is equal to or greater than a predetermined continuation judgment value.

3. The control device of an internal combustion engine according to claim 1 or 2, wherein the internal combustion engine is further provided with an exhaust passage configured to pass exhaust gas from the plurality of cylinders, including independent passages extending from each of the cylinders and a confluence site at which the independent passages confluence, a three-way catalyst disposed at a position in the exhaust passage that is on a downstream side compared to the confluence site, an upstream air-fuel ratio sensor configured to output a value corresponding to an air-fuel ratio of exhaust gas flowing between the confluence site and the three-way catalyst in the exhaust passage, the first process includes content of calculating the imbalance index value in a manner such that the greater the degree of deviation of air-fuel ratios among the plurality of cylinders, the greater the value, based on a change in an output value of the upstream air-fuel ratio sensor, the second process includes content of calculating the target air-fuel ratio in a manner such that the greater the imbalance index value, the greater the degree of decreasing correction of the reference air-fuel ratio, the third process includes content of calculating the indicated injection amount by implementing feedback correction in a manner such that an air-fuel ratio of exhaust gas flowing into the three-way catalyst coincides with the target air-fuel ratio, the end condition is that an absolute value of a rate of change of the imbalance index value during a predetermined end judgment period is equal to or less than a predetermined index judgment value.

4. The control device of an internal combustion engine according to claim 3, wherein ​ The internal combustion engine further has a downstream air-fuel ratio sensor configured to output a value corresponding to an air-fuel ratio of exhaust gas flowing in a portion of the exhaust passage that is on a downstream side relative to the three-way catalyst, The second processing includes contents of calculating an air-fuel ratio adjustment value that adjusts a degree of reduction correction of the reference air-fuel ratio, based on a comparison result of the output value of the downstream air-fuel ratio sensor and a predetermined reference value, and changing the degree of reduction correction of the reference air-fuel ratio according to the calculated air-fuel ratio adjustment value, thereby calculating the target air-fuel ratio, The end condition is that, on the basis that an absolute value of a rate of change of the imbalance index value during the end judgment period is equal to or less than the index judgment value, an absolute value of a rate of change of the air-fuel ratio adjustment value during the end judgment period is equal to or less than a predetermined adjustment judgment value.

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