JP7683418B2 - Control device for internal combustion engine - Google Patents

Description

The present invention relates to a control device for an internal combustion engine.

The internal combustion engine of Patent Document 1 includes multiple cylinders, multiple fuel injection valves, an intake passage, an exhaust passage, and an air-fuel ratio sensor. The cylinders are spaces for burning fuel. The fuel injection valves supply fuel into the cylinders. The intake passages are connected to each cylinder. Air is supplied to each cylinder from the outside via the intake passages. The exhaust passages are connected to each cylinder. Exhaust from each cylinder is discharged to the outside via the exhaust passages. The air-fuel ratio sensor is located in the exhaust passage. The air-fuel ratio sensor detects the air-fuel ratio of the gas flowing through the exhaust passage.

The internal combustion engine of Patent Document 1 is equipped with multiple intake valves, multiple exhaust valves, and a variable valve mechanism. Each intake valve opens and closes the connection between the intake passage and each cylinder. Each exhaust valve opens and closes the connection between the exhaust passage and each cylinder. The variable valve mechanism is capable of adjusting the opening and closing timing of each intake valve and each exhaust valve. The variable valve mechanism is also capable of locking some of the intake valves and some of the exhaust valves in a closed state.

The control device for an internal combustion engine in Patent Document 1 executes a cylinder deactivation process that stops the supply of fuel to some of the multiple cylinders while supplying fuel to the remaining cylinders when a predetermined cylinder deactivation condition is met. In this cylinder deactivation process, the intake valve and exhaust valve corresponding to the cylinder to which the fuel supply is stopped are locked in a closed state by a variable valve device. This also stops the flow of gas from the cylinder to which the fuel supply is stopped to the exhaust passage.

The internal combustion engine control device of Patent Document 1 also determines that there is an abnormality in the intake valve and exhaust valve when the detection value of the air-fuel ratio sensor is equal to or greater than a predetermined threshold value during execution of the cylinder deactivation process, i.e., when the exhaust is excessively lean.

JP 2004-100486 A

A known internal combustion engine has a filter located in the exhaust passage that collects particulate matter contained in the exhaust. In addition, a known configuration for controlling an internal combustion engine with a filter performs a fuel cut process in which fuel supply to some of the cylinders is stopped while fuel is supplied to the remaining cylinders and exhaust is circulated from the cylinders to the exhaust passage. When a fuel cut process is performed for the purpose of regenerating the filter, the intake valve and exhaust valve corresponding to the cylinder to which fuel supply is stopped are opened and closed. As a result, intake air that is not used for combustion, i.e., air containing oxygen, is supplied from the cylinder to the exhaust passage. When oxygen is supplied to the filter located in the exhaust passage in this way, the particulate matter accumulated on the filter is burned, and the filter is regenerated.

The abnormality determination of the intake valve and exhaust valve in Patent Document 1 is based on the premise that the intake valve and exhaust valve corresponding to the cylinder to which fuel supply is stopped are closed. On the other hand, in the fuel cut process for the purpose of filter regeneration described above, the intake valve and exhaust valve corresponding to the cylinder to which fuel supply is stopped are opened and closed. In other words, the behavior of the air-fuel ratio under normal conditions is different between the former and latter due to the difference in the open/closed state of each valve. Therefore, the abnormality determination of the intake valve and exhaust valve in Patent Document 1 cannot be applied to the fuel cut process for the purpose of filter regeneration.

The control device for an internal combustion engine to solve the above problem is a control device applied to an internal combustion engine that includes a plurality of cylinders which are spaces for burning fuel, a plurality of fuel injection valves for supplying fuel into the plurality of cylinders, an exhaust passage connected to the plurality of cylinders, a filter located in the exhaust passage for collecting particulate matter contained in the exhaust, and an air-fuel ratio sensor located in the exhaust passage upstream from the filter and detecting the air-fuel ratio of the gas in the exhaust passage, where "M" and "N" are integers of 1 or more, and the air-fuel ratio sensor detects the air-fuel ratio of the gas in the exhaust passage by detecting the air-fuel ratio of the gas in the exhaust passage. The system executes a fuel cut process that alternates between a stop pattern that stops the supply of fuel to a cylinder while allowing intake air to flow from that cylinder to the exhaust passage, and a combustion pattern that supplies fuel to N consecutive cylinders in the order of the cylinders that reach the combustion stroke while allowing exhaust air to flow from that cylinder to the exhaust passage while continuing to operate the internal combustion engine, and a determination process that determines that there is an abnormality in the fuel cut process when a predetermined period of time has elapsed since the start of the fuel cut process and the detection value of the air-fuel ratio sensor indicates a value richer than a predetermined threshold value.

If the fuel cut process is normal, the gas in the exhaust passage upstream of the filter becomes lean due to the inflow of intake air that is not used for combustion into the exhaust passage. Therefore, with the above configuration, it is possible to determine that there is an abnormality in the fuel cut process based on the detection value of the air-fuel ratio sensor being a value that indicates a richer value than the threshold value.

In addition, in the above configuration, the presence or absence of an abnormality in the fuel cut process is determined based on the detection value of the air-fuel ratio sensor when a predetermined period of time has elapsed since the start of the fuel cut process. This makes it possible to prevent erroneous determination that there is an abnormality in the fuel cut process even if the detection value of the air-fuel ratio sensor temporarily indicates a value richer than the threshold value, for example, immediately after the start of the fuel cut process.

FIG. 1 is a schematic configuration diagram of a vehicle. 4 is a flowchart showing a combustion switching control. 13 is a flowchart showing a determination control. (a) is a time chart showing a change in the execution status of the fuel cut process, (b) is a time chart showing a change in the upstream air-fuel ratio, (c) is a time chart showing a change in the downstream air-fuel ratio, (d) is a time chart showing a change in the normal determination flag, and (e) is a time chart showing a change in the abnormality determination flag.

<General vehicle configuration>
An embodiment of the present invention will now be described with reference to Figures 1 to 4. First, a schematic configuration of a vehicle 100 will be described.

As shown in FIG. 1, the vehicle 100 is equipped with a spark-ignition internal combustion engine 10. The vehicle 100 is equipped with a first motor generator 71 and a second motor generator 72 that function as both an electric motor and a generator. Therefore, the vehicle 100 is a so-called hybrid vehicle.

The internal combustion engine 10 has multiple cylinders 11, a crankshaft 12, an intake passage 21, a throttle valve 22, multiple fuel injection valves 23, multiple ignition devices 24, an exhaust passage 26, a three-way catalyst 27, and a filter 28.

The cylinders 11 are spaces for burning a mixture of fuel and intake air. The internal combustion engine 10 has four cylinders 11. In this specification, when the four cylinders 11 are described collectively, they are simply referred to as cylinders 11, and when the four cylinders 11 are described separately, they are referred to as first cylinder 11A, second cylinder 11B, third cylinder 11C, and fourth cylinder 11D.

The intake passage 21 is connected to the cylinder 11. A portion of the intake passage 21, including the downstream end, branches into four. Each branched passage is connected to each cylinder 11. The intake passage 21 introduces intake air from outside the internal combustion engine 10 to each cylinder 11. An intake valve (not shown) is located at the connection between the intake passage 21 and each cylinder 11. The intake valve opens and closes the connection between the intake passage 21 and the cylinder 11. The throttle valve 22 is located upstream of the branched portion of the intake passage 21. The throttle valve 22 adjusts the amount of intake air flowing through the intake passage 21.

The fuel injection valve 23 is located near the downstream end of the intake passage 21. The internal combustion engine 10 is provided with four fuel injection valves 23 corresponding to the four cylinders 11. The fuel injection valve 23 injects fuel supplied from a fuel tank (not shown) into the intake passage 21. As a result, fuel from the fuel injection valve 23 is supplied to the cylinder 11. The ignition device 24 is located in the cylinder 11. The internal combustion engine 10 is provided with four ignition devices 24 corresponding to the four cylinders 11. The ignition device 24 ignites the mixture of fuel and intake air by spark discharge. The four ignition devices 24 ignite the first cylinder 11A, the third cylinder 11C, the fourth cylinder 11D, and the second cylinder 11B in that order. In other words, the four cylinders 11 undergo the combustion stroke in the following order: first cylinder 11A, third cylinder 11C, fourth cylinder 11D, and second cylinder 11B.

The exhaust passage 26 is connected to the cylinders 11. A portion of the exhaust passage 26, including the upstream end, branches into four. Each branched passage is connected to each cylinder 11. The exhaust passage 26 discharges exhaust from each cylinder 11 to the outside of the internal combustion engine 10. Note that exhaust valves (not shown) are located at the connection points between the exhaust passage 26 and each cylinder 11. The exhaust valves open and close the connection points between the exhaust passage 26 and the cylinders 11.

The three-way catalyst 27 is located downstream of the branched portion of the exhaust passage 26. The three-way catalyst 27 purifies the exhaust gas flowing through the exhaust passage 26. The filter 28 is located downstream of the three-way catalyst 27 in the exhaust passage 26. The filter 28 collects particulate matter contained in the exhaust gas flowing through the exhaust passage 26.

The crankshaft 12 is connected to a piston (not shown) located in each cylinder 11. The crankshaft 12 rotates due to the combustion of a mixture of fuel and intake air in the cylinder 11.

The vehicle 100 includes a first planetary gear mechanism 40 , a ring gear shaft 45 , a second planetary gear mechanism 50 , a reduction mechanism 62 , a differential mechanism 63 , and a plurality of drive wheels 64 .
The first planetary gear mechanism 40 includes a sun gear 41, a ring gear 42, a plurality of pinion gears 43, and a carrier 44. The sun gear 41 is an external gear. The sun gear 41 is connected to the first motor generator 71. The ring gear 42 is an internal gear, and is located coaxially with the sun gear 41. Each pinion gear 43 is located between the sun gear 41 and the ring gear 42. Each pinion gear 43 meshes with both the sun gear 41 and the ring gear 42. The carrier 44 supports the pinion gear 43. The pinion gear 43 is rotatable on its own axis, and is revolved by rotating together with the carrier 44. The carrier 44 is connected to the crankshaft 12.

The ring gear shaft 45 is connected to the ring gear 42. The ring gear shaft 45 is also connected to the drive wheels 64 via a reduction mechanism 62 and a differential mechanism 63. The reduction mechanism 62 reduces the rotational speed of the ring gear shaft 45 and outputs it. The differential mechanism 63 allows a difference in rotational speed to occur between the left and right drive wheels 64.

The second planetary gear mechanism 50 includes a sun gear 51, a ring gear 52, a plurality of pinion gears 53, a carrier 54, and a case 55. The sun gear 51 is an external gear. The sun gear 51 is connected to the second motor generator 72. The ring gear 52 is an internal gear and is located coaxially with the sun gear 51. The ring gear 52 is connected to the ring gear shaft 45. Each pinion gear 53 is located between the sun gear 51 and the ring gear 52. Each pinion gear 53 meshes with both the sun gear 51 and the ring gear 52. The carrier 54 supports the pinion gear 53. The pinion gear 53 is rotatable. The carrier 54 is fixed to the case 55. Therefore, the pinion gear 53 is in a state where it cannot revolve.

The vehicle 100 is equipped with a battery 75, a first inverter 76, and a second inverter 77. The battery 75 is a secondary battery. The first inverter 76 performs AC/DC power conversion between the first motor generator 71 and the battery 75. The first inverter 76 also adjusts the amount of power exchanged between the first motor generator 71 and the battery 75. The second inverter 77 performs AC/DC power conversion between the second motor generator 72 and the battery 75. The second inverter 77 adjusts the amount of power exchanged between the second motor generator 72 and the battery 75.

The vehicle 100 is equipped with an air flow meter 81 , a water temperature sensor 82 , an intake air temperature sensor 83 , a crank angle sensor 84 , an accelerator operation amount sensor 85 , and a vehicle speed sensor 86 .
The air flow meter 81 detects the intake air amount GA, which is the amount of intake air flowing through the intake passage 21 per unit time. The water temperature sensor 82 detects the coolant temperature THW, which is the temperature of the coolant flowing through each part of the internal combustion engine 10. The intake air temperature sensor 83 detects the intake air temperature THA, which is the temperature of the intake air flowing through the intake passage 21. The crank angle sensor 84 detects the crank angle SC, which is the rotational position of the crankshaft 12. The accelerator operation amount sensor 85 detects the accelerator operation amount ACC, which is the amount of operation of the accelerator pedal operated by the driver. The vehicle speed sensor 86 detects the vehicle speed SP, which is the speed of the vehicle 100.

The vehicle 100 is equipped with an upstream air-fuel ratio sensor 87 and a downstream air-fuel ratio sensor 88. The upstream air-fuel ratio sensor 87 is located downstream of the branched portion of the exhaust passage 26 and upstream of the three-way catalyst 27. The upstream air-fuel ratio sensor 87 detects an upstream air-fuel ratio AF1, which is the air-fuel ratio of the gas upstream of the three-way catalyst 27 in the exhaust passage 26. The downstream air-fuel ratio sensor 88 is located downstream of the three-way catalyst 27 and upstream of the filter 28 in the exhaust passage 26. The downstream air-fuel ratio sensor 88 detects a downstream air-fuel ratio AF2, which is the air-fuel ratio of the gas downstream of the three-way catalyst 27 in the exhaust passage 26. Here, the air-fuel ratio is the ratio obtained by dividing the mass of air by the mass of fuel. Therefore, the more air relative to the fuel, the higher the air-fuel ratio, that is, the leaner the fuel. On the other hand, the less air relative to the fuel, the lower the air-fuel ratio, i.e., the richer the fuel state. When the internal combustion engine 10 is running, gas from the four cylinders 11 flows continuously into the exhaust passage 26, so the upstream air-fuel ratio AF1 and the downstream air-fuel ratio AF2 become values close to the average values of the air-fuel ratios in the four cylinders 11.

The vehicle 100 is equipped with a control device 90. The control device 90 obtains a signal indicating the intake air volume GA from the air flow meter 81. The control device 90 obtains a signal indicating the cooling water temperature THW from the water temperature sensor 82. The control device 90 obtains a signal indicating the intake air temperature THA from the intake air temperature sensor 83. The control device 90 obtains a signal indicating the crank angle SC from the crank angle sensor 84. The control device 90 obtains a signal indicating the accelerator operation amount ACC from the accelerator operation amount sensor 85. The control device 90 obtains a signal indicating the vehicle speed SP from the vehicle speed sensor 86. The control device 90 obtains a signal indicating the upstream air-fuel ratio AF1 from the upstream air-fuel ratio sensor 87. The control device 90 obtains a signal indicating the downstream air-fuel ratio AF2 from the downstream air-fuel ratio sensor 88.

The control device 90 calculates the vehicle required output, which is a required value of the output required for the vehicle 100 to travel, based on the accelerator operation amount ACC and the vehicle speed SP. The control device 90 determines the torque distribution of the internal combustion engine 10, the first motor generator 71, and the second motor generator 72 based on the vehicle required output. The control device 90 controls the output of the internal combustion engine 10 and the power running and regeneration of the first motor generator 71 and the second motor generator 72 based on the torque distribution of the internal combustion engine 10, the first motor generator 71, and the second motor generator 72. Specifically, the control device 90 controls the opening degree of the throttle valve 22, the fuel injection amount from the fuel injection valve 23, the ignition timing of the ignition device 24, etc., by outputting a control signal to the internal combustion engine 10. The control device 90 also controls the first motor generator 71 via the first inverter 76 by outputting a control signal to the first inverter 76. Furthermore, the control device 90 controls the second motor generator 72 via the second inverter 77 by outputting a control signal to the second inverter 77.

The control device 90 calculates the engine speed NE, which is the number of revolutions per unit time of the crankshaft 12, based on the crank angle SC. The control device 90 calculates the engine load factor KL based on the engine speed NE and the intake air amount GA. Here, the engine load factor KL represents the ratio of the current cylinder inflow air amount to the cylinder inflow air amount when the internal combustion engine 10 is operated steadily with the throttle valve 22 fully open at the current engine speed NE. Note that the cylinder inflow air amount is the amount of intake air flowing into each cylinder 11 during the intake stroke.

The control device 90 calculates the catalyst temperature TSC, which is the temperature of the three-way catalyst 27, based on the operating conditions of the internal combustion engine 10, such as the intake air charging efficiency and the engine speed NE. The intake air charging efficiency is the value obtained by dividing the mass of intake air actually introduced into the cylinder 11 from the intake passage 21 by the mass of intake air that can be introduced into the cylinder 11 under standard atmospheric conditions. The control device 90 also calculates the filter temperature TF, which is the temperature of the filter 28, based on the operating conditions of the internal combustion engine 10, such as the intake air charging efficiency and the engine speed NE. The control device 90 calculates the PM accumulation amount PS, which is the amount of particulate matter accumulated in the filter 28, based on the engine speed NE, the engine load factor KL, and the filter temperature TF.

The control device 90 executes a fuel cut process to suppress clogging of the filter 28 due to particulate matter. Here, a series of processes in which each of the four cylinders 11 undergoes a combustion stroke once, that is, a period in which the crankshaft 12 rotates twice, is called one combustion cycle. In the fuel cut process, the control device 90 repeats a process of stopping fuel supply to one of the four cylinders 11 while supplying fuel to the remaining three cylinders in one combustion cycle, over multiple consecutive combustion cycles. In addition, the control device 90 opens and closes the intake valves and exhaust valves corresponding to the four cylinders 11 in the fuel cut process. Therefore, in the fuel cut process, the stop pattern and the combustion pattern are alternately repeated while the internal combustion engine 10 continues to operate. Here, the stop pattern refers to stopping the fuel supply to one cylinder 11 while allowing intake air to flow from that cylinder 11 to the exhaust passage 26. The combustion pattern refers to supplying fuel to three cylinders 11 in succession in the order in which the cylinders 11 undergo the combustion stroke, while circulating exhaust gas from the cylinders 11 to the exhaust passage 26.

In the fuel cut process, the air-fuel ratio of the cylinder 11 to which fuel is supplied becomes slightly lower than the theoretical air-fuel ratio AFS, i.e., 14.7. On the other hand, in the fuel cut process, the air-fuel ratio of the cylinder 11 to which fuel supply is stopped becomes much higher than the theoretical air-fuel ratio AFS. As a result, in the fuel cut process, the average value of the air-fuel ratio in the four cylinders 11 becomes higher than the theoretical air-fuel ratio AFS. In this embodiment, in the fuel cut process, the cylinder 11 to which fuel supply is stopped is the third cylinder 11C. In addition, in the fuel cut process, the cylinders 11 to which fuel is supplied are the first cylinder 11A, the second cylinder 11B, and the fourth cylinder 11D. In addition, in the fuel cut process, the control device 90 applies torque to the crankshaft 12 from the first motor generator 71 via the first planetary gear mechanism 40 so as to compensate for the torque of the internal combustion engine 10 that is insufficient due to the stop of combustion of the mixture in the third cylinder 11C.

When the fuel cut process is performed, intake air that is not used for combustion, i.e., air that contains oxygen, is supplied from the third cylinder 11C to the exhaust passage 26. When oxygen flows through the exhaust passage 26 and is supplied to the filter 28 in this way, the particulate matter that has accumulated on the filter 28 is burned, thereby regenerating the filter 28.

The control device 90 may be configured as a circuit including one or more processors that execute various processes according to a computer program (software). The control device 90 may be configured as a circuit including one or more dedicated hardware circuits, such as an application specific integrated circuit (ASIC), that execute at least some of the various processes, or a combination thereof. The processor includes a CPU and memory such as RAM and ROM. The memory stores program code or instructions that are configured to cause the CPU to execute processes. The memory, i.e., computer readable medium, includes any medium that can be accessed by a general-purpose or dedicated computer.

<Combustion switching control>
Next, the combustion switching control performed by the control device 90 will be described. The control device 90 switches the combustion state of the internal combustion engine 10 to one of two states by the combustion switching control. The first of the two combustion states is a state in which the above-mentioned fuel cut processing is performed. The second of the two combustion states is a state in which normal combustion processing is performed in which fuel is supplied to all four cylinders 11. The control device 90 repeatedly executes the combustion switching control from the start of operation of the internal combustion engine 10 to the end of operation of the internal combustion engine 10.

As shown in FIG. 2, when the control device 90 starts the combustion switching control, the control device 90 proceeds to the process of step S11. In step S11, the control device 90 determines whether or not a precondition that is predetermined as a condition for executing the fuel cut process is satisfied. Here, one example of a precondition for the fuel cut process is that the PM accumulation amount PS is equal to or greater than a predetermined specified value. In step S11, if the control device 90 determines that the precondition for the fuel cut process is satisfied (S11: YES), the control device 90 proceeds to the process of step S21.

In step S21, the control device 90 executes a fuel cut process. If the control device 90 is already executing a fuel cut process, the control device 90 continues to execute the fuel cut process. After that, the control device 90 ends the current combustion switching control and proceeds to step S11 again.

On the other hand, in step S11, when the control device 90 determines that the precondition for the fuel cut process is not satisfied (S11: NO), the control device 90 advances the process to step S22.
In step S22, the control device 90 executes the normal combustion process. If the control device 90 is already executing the normal combustion process, the control device 90 continues to execute the normal combustion process. After that, the control device 90 ends the current combustion switching control and proceeds to step S11 again.

<Decision Control>
Next, the judgment control performed by the control device 90 will be described. The control device 90 judges the presence or absence of an abnormality in the fuel cut process through the judgment control. The control device 90 executes the judgment control when the fuel cut process is started. Note that when the control device 90 executes the judgment control for the first time, a normal judgment flag and an abnormality judgment flag, which will be described later, are OFF.

As shown in FIG. 3, when the control device 90 starts the judgment control, it proceeds to the processing of step S61. In step S61, the control device 90 judges whether the duration TX of the fuel cut process is equal to or longer than the first predetermined period TA1. Here, the duration TX is the period from the start of the current fuel cut process to the processing point of step S61. In addition, when setting the first predetermined period TA1, the period from the start of the fuel cut process to the time when the upstream air-fuel ratio AF1 detected by the upstream air-fuel ratio sensor 87 changes due to the fuel cut process is obtained in advance by experiments, etc. Then, a period longer than the obtained period by a certain period is set as the first predetermined period TA1. An example of the first predetermined period TA1 is several hundred msec. In step S61, when the control device 90 judges that the duration TX of the fuel cut process is shorter than the first predetermined period TA1 (S61: NO), it performs the processing of step S61 again. That is, the control device 90 repeats step S61 until the duration TX becomes equal to or greater than the first predetermined period TA1.

On the other hand, in step S61, if the control device 90 determines that the duration TX of the fuel cut process is equal to or longer than the first predetermined period TA1 (S61: YES), the control device 90 proceeds to step S62.

In step S62, the control device 90 determines whether the upstream air-fuel ratio AF1 detected by the upstream air-fuel ratio sensor 87 is equal to or greater than a predetermined first threshold Z1. Here, when setting the first threshold Z1, the air-fuel ratio detected by the upstream air-fuel ratio sensor 87 when a first predetermined period TA1 has elapsed since the start of the fuel cut process is obtained in advance by experiment or the like. Then, an air-fuel ratio that is a certain value lower than the obtained air-fuel ratio is set as the first threshold Z1. An example of the first threshold Z1 is about 17 to 18. In step S62, when the control device 90 determines that the upstream air-fuel ratio AF1 detected by the upstream air-fuel ratio sensor 87 is equal to or greater than the first threshold Z1 (S62: YES), the process proceeds to step S71.

In step S71, the control device 90 determines whether the duration TX of the fuel cut process is equal to or longer than the second predetermined period TA2. Here, when setting the second predetermined period TA2, the period from when the fuel cut process is started until the downstream air-fuel ratio AF2 detected by the downstream air-fuel ratio sensor 88 changes due to the fuel cut process is obtained in advance by experiments or the like. Then, a period longer than the obtained period by a certain period is set as the second predetermined period TA2. As a result, the second predetermined period TA2 is set to a value greater than the above-mentioned first predetermined period TA1. An example of the second predetermined period TA2 is one hundred to several thousand msec. In step S71, when the control device 90 determines that the duration TX of the fuel cut process is less than the second predetermined period TA2 (S71: NO), the control device 90 performs the process of step S71 again. That is, the control device 90 repeats step S71 until the duration TX becomes equal to or longer than the second predetermined period TA2.

On the other hand, in step S71, if the control device 90 determines that the duration TX of the fuel cut process is equal to or longer than the second predetermined period TA2 (S71: YES), the control device 90 proceeds to step S72.

In step S72, the control device 90 determines whether the downstream air-fuel ratio AF2 detected by the downstream air-fuel ratio sensor 88 is equal to or greater than a predetermined second threshold Z2. Here, when setting the second threshold Z2, the air-fuel ratio detected by the downstream air-fuel ratio sensor 88 when the second predetermined period TA2 has elapsed since the start of the fuel cut process is obtained in advance by experiment or the like. Then, an air-fuel ratio that is a certain value lower than the obtained air-fuel ratio is set as the second threshold Z2. An example of the second threshold Z2 is about 17 to 18. In this embodiment, the second threshold Z2 is the same value as the first threshold Z1. In step S72, when the control device 90 determines that the downstream air-fuel ratio AF2 detected by the downstream air-fuel ratio sensor 88 is equal to or greater than the second threshold Z2 (S72: YES), the process proceeds to step S81.

In step S81, the control device 90 performs a normal determination to indicate that the fuel cut process is normal. For example, the control device 90 indicates that the fuel cut process is normal by turning the normal determination flag ON and the abnormality determination flag OFF. Thereafter, the control device 90 ends the current determination control.

On the other hand, in step S62, if the control device 90 determines that the upstream air-fuel ratio AF1 detected by the upstream air-fuel ratio sensor 87 is less than the first threshold value Z1 (S62: NO), the process proceeds to step S82. Also, in step S72, if the control device 90 determines that the downstream air-fuel ratio AF2 detected by the downstream air-fuel ratio sensor 88 is less than the second threshold value Z2 (S72: NO), the process proceeds to step S82.

In step S82, the control device 90 performs an abnormality determination to indicate that the fuel cut process is abnormal. For example, the control device 90 indicates that the fuel cut process is abnormal by turning the abnormality determination flag ON and the normal determination flag OFF. The control device 90 also outputs a control signal to a warning light (not shown) to notify the driver of the vehicle 100 that the fuel cut process is abnormal. The control device 90 then ends the current determination control. In this embodiment, the processes of steps S61, S62, S71, S72, and S82 are the determination process. Note that if a normal determination is made in step S81 or an abnormality is made in step S82, the control device 90 does not perform the determination control again in the current fuel cut process that was the subject of the determination.

<Action of this embodiment>
First, a case where the fuel cut process is normal will be described. Here, as shown in Fig. 4(a), it is assumed that the fuel cut process is not executed before time t11, and normal combustion process is executed. In this case, as shown in Fig. 4(b), the upstream air-fuel ratio AF1 is approximately the stoichiometric air-fuel ratio AFS. Similarly, as shown in Fig. 4(c), the downstream air-fuel ratio AF2 is approximately the stoichiometric air-fuel ratio AFS.

As shown in FIG. 4(a), the fuel cut process is started at time t11. When the fuel cut process is started, intake air that is not used for combustion, air containing oxygen, is supplied from the third cylinder 11C to the exhaust passage 26. Therefore, if the fuel cut process is normal, as shown in FIG. 4(b), the upstream air-fuel ratio AF1 increases after time t11. Similarly, as shown in FIG. 4(c), the downstream air-fuel ratio AF2 increases after time t11. Here, since the downstream air-fuel ratio sensor 88 is located downstream from the upstream air-fuel ratio sensor 87, the downstream air-fuel ratio AF2 increases at a later time than the upstream air-fuel ratio AF1.

Then, as shown in FIG. 4(b), at time t12, which is a first predetermined period TA1 after time t11, the upstream air-fuel ratio AF1 becomes equal to or greater than the first threshold value Z1. Furthermore, as shown in FIG. 4(c), at time t13, which is a second predetermined period TA2 after time t11, the downstream air-fuel ratio AF2 becomes equal to or greater than the second threshold value Z2. As a result, as shown in FIG. 4(d), at time t13, the normality determination flag becomes ON.

Next, a case where the fuel cut process is abnormal will be described. Here, as shown in FIG. 4(a), it is assumed that the fuel cut process is not executed before time t21, and normal combustion process is executed. In this case, as shown in FIG. 4(b), the upstream air-fuel ratio AF1 is approximately the stoichiometric air-fuel ratio AFS. Similarly, as shown in FIG. 4(c), the downstream air-fuel ratio AF2 is approximately the stoichiometric air-fuel ratio AFS.

As shown in FIG. 4(a), the fuel cut process is started at time t21. However, because the fuel cut process is abnormal, the amount of intake air supplied from the cylinder 11 to the exhaust passage 26 is less than when the fuel cut process is normal, even if the fuel cut process is started. Therefore, as shown in FIG. 4(b), at time t22 after the first predetermined period TA1 has elapsed from time t21, the upstream air-fuel ratio AF1 becomes less than the first threshold value Z1. As a result, as shown in FIG. 4(e), the abnormality determination flag is ON at time t22. Note that, similar to the upstream air-fuel ratio AF1, at time t23 after the second predetermined period TA2 has elapsed from time t21, the downstream air-fuel ratio AF2 becomes less than the second threshold value Z2, as shown in FIG. 4(c).

<Effects of this embodiment>
(1) In the internal combustion engine 10, when the fuel cut process is abnormal, the upstream air-fuel ratio AF1 becomes less than the first threshold value Z1, and the downstream air-fuel ratio AF2 becomes less than the second threshold value Z2. Therefore, in this embodiment, it is possible to determine that there is an abnormality in the fuel cut process based on, for example, the upstream air-fuel ratio AF1 being less than the first threshold value Z1, i.e., a value indicating a rich state.

(2) As described above, as shown in FIG. 4(b), the upstream air-fuel ratio AF1 increases after time t11, when the fuel cut process is started. Therefore, even if the fuel cut process is normal, the upstream air-fuel ratio AF1 becomes less than the first threshold value Z1 immediately after time t11.

In this regard, in this embodiment, the presence or absence of an abnormality in the fuel cut process is determined based on the upstream air-fuel ratio AF1 at time t12, which is the first predetermined period TA1 after time t11. This makes it possible to prevent erroneous determination that there is an abnormality in the fuel cut process even if the upstream air-fuel ratio AF1 is less than the first threshold value Z1 immediately after time t11.

(3) In this embodiment, the presence or absence of an abnormality in the fuel cut process is determined based on the upstream air-fuel ratio AF1 detected by the upstream air-fuel ratio sensor 87 and the downstream air-fuel ratio AF2 detected by the downstream air-fuel ratio sensor 88. Therefore, even if the upstream air-fuel ratio AF1 is equal to or greater than the first threshold value Z1 due to an abnormality in the upstream air-fuel ratio sensor 87, if the downstream air-fuel ratio AF2 is less than the second threshold value Z2, an abnormality in the fuel cut process can be appropriately determined.

<Example of change>
This embodiment can be modified as follows: This embodiment and the following modifications can be combined with each other to the extent that there is no technical contradiction.

In the above embodiment, the determination process may be changed.
For example, the first predetermined period TA1 may be the same as the second predetermined period TA2. In this configuration, when the control device 90 makes a positive determination in step S62, the process proceeds to step S72. In other words, the process of step S71 may be omitted.

- For example, in the determination process, the control device 90 may perform only one of the processes of steps S61 and S62 and the processes of steps S71 and S72, and omit the other.

In the above embodiment, the fuel cut process may be changed.
For example, in the fuel cut process, the cylinder 11 to which fuel supply is stopped is not limited to the third cylinder 11C, and may be any one of the first cylinder 11A, the second cylinder 11B, and the fourth cylinder 11D. Furthermore, the cylinder 11 to which fuel supply is stopped and the cylinder 11 to which fuel is supplied may be changed for each combustion cycle.

・For example, in the fuel cut process, the number of cylinders 11 to which fuel supply is stopped and the number of cylinders 11 to which fuel is supplied may be changed as long as they are each 1 or more. Furthermore, the number of cylinders 11 to which fuel supply is stopped and the number of cylinders 11 to which fuel is supplied may be changed for each combustion cycle. Therefore, the fuel cut process may be a process having the following content. Here, "M" and "N" are integers of 1 or more. In the fuel cut process, the stop pattern and the combustion pattern may be alternately repeated while the internal combustion engine 10 continues to operate. Here, the stop pattern is a pattern in which the fuel supply to M consecutive cylinders 11 in the order of the cylinders 11 that will undergo the combustion stroke is stopped while the intake air is circulated from the cylinders 11 to the exhaust passage 26. Also, the combustion pattern is a pattern in which the fuel supply to N consecutive cylinders 11 in the order of the cylinders 11 that will undergo the combustion stroke is supplied while the exhaust air is circulated from the cylinders 11 to the exhaust passage 26. The sum of M and N does not have to match the total number of cylinders 11. Furthermore, if the sum of M and N does not match the total number of cylinders 11, the cylinders 11 to which fuel supply is stopped and the cylinders 11 to which fuel supply is performed may change for each combustion cycle, or there may be no cylinders 11 to which fuel supply is stopped in some combustion cycles.

In the above embodiment, the configuration of the vehicle 100 may be changed.
For example, it is possible to omit one of the upstream air-fuel ratio sensor 87 and the downstream air-fuel ratio sensor 88. Even in this configuration, the control device 90 can determine an abnormality in the fuel cut process based on the detection value of one of the upstream air-fuel ratio sensor 87 and the downstream air-fuel ratio sensor 88 provided in the vehicle 100.

For example, the internal combustion engine 10 may include two or three cylinders 11, or may include five or more cylinders 11.
For example, the vehicle 100 does not need to be equipped with the first motor generator 71 and the second motor generator 72. Even in this configuration, as long as the control device 90 executes the fuel cut process when the vehicle required output is relatively small, there is no problem even if the output of the internal combustion engine 10 is reduced due to the fuel cut process.

REFERENCE SIGNS LIST 10 internal combustion engine 11 cylinder 12 crankshaft 21 intake passage 23 fuel injection valve 24 ignition device 26 exhaust passage 27 three-way catalyst 28 filter 40 first planetary gear mechanism 50 second planetary gear mechanism 62 reduction mechanism 63 differential mechanism 64 drive wheels 71 first motor generator 72 second motor generator 75 battery 76 first inverter 77 second inverter 87 upstream air-fuel ratio sensor 88 downstream air-fuel ratio sensor 90 control device 100 vehicle

Claims (1)

a control device applied to an internal combustion engine including: a plurality of cylinders which are spaces for burning fuel; a plurality of fuel injection valves for supplying fuel into the plurality of cylinders; an exhaust passage connected to the plurality of cylinders; a three-way catalyst located in the exhaust passage and purifying exhaust gas; a filter located in the exhaust passage downstream from the three-way catalyst and collecting particulate matter contained in the exhaust gas; an upstream air-fuel ratio sensor located in the exhaust passage upstream from the three-way catalyst and detecting an upstream air-fuel ratio which is the air-fuel ratio of gas in the exhaust passage; and a downstream air-fuel ratio sensor located in the exhaust passage downstream from the three-way catalyst and upstream from the filter and detecting a downstream air-fuel ratio which is the air-fuel ratio of gas in the exhaust passage,
a fuel cut process in which, while continuing operation of the internal combustion engine, alternately repeats a stop pattern in which fuel supply to M consecutive cylinders is stopped in the order of the cylinders which reach a combustion stroke while allowing intake air to flow from the cylinders to the exhaust passage, and a combustion pattern in which fuel is supplied to N consecutive cylinders in the order of the cylinders which reach a combustion stroke while allowing exhaust air to flow from the cylinders to the exhaust passage, where "M" and "N" are integers equal to or greater than 1;
determining that an abnormality exists in the fuel cut process when one or more of the following is satisfied: the upstream air-fuel ratio is less than a predetermined first threshold value when a predetermined first specified period has elapsed since the start of the fuel cut process; and the downstream air-fuel ratio is less than a predetermined second threshold value when a predetermined second specified period has elapsed since the start of the fuel cut process, the second specified period being a value greater than the first specified period ;
a determination process for determining that the fuel cut process is normal when the upstream air-fuel ratio is equal to or greater than the first threshold value when the first predetermined period has elapsed since the start of the fuel cut process, and when the downstream air-fuel ratio is equal to or greater than the second threshold value when the second predetermined period has elapsed since the start of the fuel cut process.

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