Control device for internal combustion engine

Abstract

To enable abnormality in a fuel cut process to be determined.SOLUTION: A control device executes a fuel cut process where, given that M and N are integers greater than or equal to 1, a stop pattern to distribute intake air from cylinders to an exhaust passage while consecutively stopping fuel supply to M number of cylinders in the order of proximity to a combustion stroke and a combustion pattern to distribute exhaust gas from the cylinders to the exhaust passage while consecutively supplying the fuel to N number of cylinders in the order of proximity to the combustion stroke are alternately repeated with an internal combustion engine continuously operated. Also, the control device executes a determination process to determine that the fuel cut process has abnormality when an upstream air-fuel ratio AF1 detected with an upstream air-fuel ratio sensor is richer than a predetermined first threshold Z1 after the elapse of a first predetermined period TA1 since the fuel cut process is started.SELECTED DRAWING: Figure 3

Description

Technical Field

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

Background Art

[0002] The internal combustion engine of Patent Document 1 includes a plurality of cylinders, a plurality of fuel injection valves, an intake passage, an exhaust passage, and an air-fuel ratio sensor. A cylinder is a space for burning fuel. The fuel injection valve supplies fuel into the cylinder. The intake passage is connected to each cylinder. Intake air to each cylinder is supplied from the outside through the intake passage. The exhaust passage is connected to each cylinder. Exhaust from each cylinder is discharged to the outside through the exhaust passage. 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.

[0003] Further, the internal combustion engine of Patent Document 1 includes a plurality of intake valves, a plurality of exhaust valves, and a variable valve device. Each intake valve opens and closes the connection portion between the intake passage and each cylinder. Each exhaust valve opens and closes the connection portion between the exhaust passage and each cylinder. The variable valve device can adjust the opening and closing timing of each intake valve and each exhaust valve. Further, the variable valve device can lock some of the intake valves and some of the exhaust valves in a closed state.

[0004] When a predetermined cylinder stop condition is satisfied, the control device for the internal combustion engine of Patent Document 1 executes a cylinder stop process in which the supply of fuel to some of the plurality of cylinders is stopped while fuel is supplied to the remaining cylinders. In this cylinder stop process, the intake valve and the exhaust valve corresponding to the cylinder whose fuel supply is stopped are locked in a closed state by the variable valve device. Thereby, the flow of the gas flowing from the cylinder whose fuel supply is stopped to the exhaust passage is also stopped.

[0005] Further, during the execution of the cylinder stop process, when the detection value of the air-fuel ratio sensor is equal to or greater than a predetermined threshold value, that is, when the exhaust is excessively lean, the control device for the internal combustion engine of Patent Document 1 determines that there is an abnormality in the intake valve and the exhaust valve.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] As an internal combustion engine, a configuration is known that includes a filter located in an exhaust passage for collecting particulate matter contained in exhaust gas. Also, regarding the control of an internal combustion engine equipped with a filter, a configuration is known in which a fuel cut process is performed to stop the supply of fuel to some of a plurality of cylinders while supplying fuel to the remaining cylinders and allowing exhaust gas to flow from the cylinders to the exhaust passage. When performing the fuel cut process for the purpose of filter regeneration, the intake valve and the exhaust valve corresponding to the cylinders where the fuel supply is stopped are opened and closed. As a result, intake air that is not used for combustion, that is, air containing oxygen, is supplied from the cylinders to the exhaust passage. When oxygen is thus supplied to the filter located in the exhaust passage, the particulate matter deposited on the filter burns and the filter is regenerated.

[0008] The abnormality determination of the intake valve and the exhaust valve in Patent Document 1 is based on the premise that the intake valve and the exhaust valve corresponding to the cylinders where the fuel supply is stopped are in the closed state. On the other hand, in the fuel cut process for the purpose of the above-described filter regeneration, the intake valve and the exhaust valve corresponding to the cylinders where the fuel supply is stopped are opened and closed. That is, due to the different opening and closing states of each valve between the former and the latter, the behavior of the air-fuel ratio during normal operation is also different. Therefore, the abnormality determination of the intake valve and the exhaust valve in Patent Document 1 cannot be applied to the fuel cut process for the purpose of filter regeneration.

Means for Solving the Problems

[0009] A control device for an internal combustion engine for solving the above problems 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 upstream of the filter in the exhaust passage for detecting the air-fuel ratio of the gas in the exhaust passage. The control device is applied to an internal combustion engine and includes a stop pattern in which, when "M" and "N" are integers of 1 or more, intake air is allowed to flow from the cylinders to the exhaust passage while stopping the fuel supply to M consecutive cylinders in the order of the cylinders approaching the combustion stroke, and a combustion pattern in which, while continuously supplying fuel to N consecutive cylinders in the order of the cylinders approaching the combustion stroke, exhaust gas is allowed to flow from the cylinders to the exhaust passage. A fuel cut process is repeatedly performed alternately while continuing the operation of the internal combustion engine. When the detected value of the air-fuel ratio sensor is a value indicating richer than a predetermined threshold when a predetermined period has elapsed since the start of the fuel cut process, a determination process for determining that there is an abnormality in the fuel cut process is executed.

[0010] If the fuel cut process is normal, due to the inflow of intake air not used for combustion into the exhaust passage, the gas in the exhaust passage upstream of the filter from the view of the filter becomes lean. Therefore, according to the above configuration, based on the fact that the detected value of the air-fuel ratio sensor is a value indicating richer than the threshold, it can be determined that there is an abnormality in the fuel cut process.

[0011] In addition, in the above configuration, the presence or absence of an abnormality in the fuel cut process is determined based on the detected value of the air-fuel ratio sensor when a predetermined period has elapsed since the start of the fuel cut process. Thereby, for example, even if the detected value of the air-fuel ratio sensor temporarily becomes a value indicating richer than the threshold due to being immediately after the start of the fuel cut process, it is possible to suppress an erroneous determination that there is an abnormality in the fuel cut process.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0013] <Schematic Configuration of Vehicle> Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 to 4. First, the schematic configuration of the vehicle 100 will be described.

[0014] As shown in FIG. 1, the vehicle 100 includes a spark ignition internal combustion engine 10. The vehicle 100 includes a first motor generator 71 and a second motor generator 72 that have both the functions of an electric motor and a generator. Therefore, the vehicle 100 is a so-called hybrid vehicle.

[0015] The internal combustion engine 10 includes a plurality of cylinders 11, a crankshaft 12, an intake passage 21, a throttle valve 22, a plurality of fuel injection valves 23, a plurality of ignition devices 24, an exhaust passage 26, a three-way catalyst 27, and a filter 28.

[0016] The cylinder 11 is a space for burning a mixture of fuel and intake air. The internal combustion engine 10 includes four cylinders 11. In this specification, when the four cylinders 11 are collectively described, they are simply referred to as cylinders 11, and when the four cylinders 11 are separately described, they are referred to as the first cylinder 11A, the second cylinder 11B, the third cylinder 11C, and the fourth cylinder 11D.

[0017] The intake passage 21 is connected to the cylinder 11. A part including the downstream end in the intake passage 21 branches into four. Each of the branched passages is connected to each cylinder 11. The intake passage 21 introduces intake air from outside the internal combustion engine 10 into each cylinder 11. Note that an intake valve (not shown) is located at the connection point between the intake passage 21 and each cylinder 11. The intake valve opens and closes the connection point between the intake passage 21 and the cylinder 11. The throttle valve 22 is located on the upstream side when viewed from the branched part in the intake passage 21. The throttle valve 22 adjusts the amount of intake air flowing through the intake passage 21.

[0018] 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, the 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 air-fuel mixture by spark discharge. Note that the four ignition devices 24 perform ignition in the order of the first cylinder 11A, the third cylinder 11C, the fourth cylinder 11D, and the second cylinder 11B. In other words, the four cylinders 11 undergo the combustion stroke in the order of the first cylinder 11A, the third cylinder 11C, the fourth cylinder 11D, and the second cylinder 11B.

[0019] The exhaust passage 26 is connected to the cylinder 11. A part including the upstream end in the exhaust passage 26 branches into four. Each of the branched passages is connected to each cylinder 11. The exhaust passage 26 discharges exhaust gas from each cylinder 11 to the outside of the internal combustion engine 10. Note that an exhaust valve (not shown) is located at the connection point between the exhaust passage 26 and each cylinder 11. The exhaust valve opens and closes the connection point between the exhaust passage 26 and the cylinder 11.

[0020] The three-way catalyst 27 is located on the downstream side when viewed from 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 on the downstream side when viewed from 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.

[0021] The crankshaft 12 is connected to pistons (not shown) located in each cylinder 11. The crankshaft 12 rotates due to the combustion of the air-fuel mixture in the cylinder 11.

[0022] 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 gears 43. The pinion gears 43 are rotatable about their own axes and are revolvable by rotating together with the carrier 44. The carrier 44 is connected to the crankshaft 12.

[0023] The ring gear shaft 45 is connected to the ring gear 42. Also, the ring gear shaft 45 is connected to the drive wheels 64 via the reduction mechanism 62 and the 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.

[0024] 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 positioned coaxially with the sun gear 51. The ring gear 52 is connected to the ring gear shaft 45. Each pinion gear 53 is positioned 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 gears 53. The pinion gears 53 are rotatable about their own axes. The carrier 54 is fixed to the case 55. Therefore, the pinion gears 53 are in a state where they cannot revolve.

[0025] The vehicle 100 includes 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. Also, the first inverter 76 adjusts the amount of power transfer 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 transfer between the second motor generator 72 and the battery 75.

[0026] The vehicle 100 includes 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 water temperature THW, which is the temperature of the coolant water 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 operation amount 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.

[0027] 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 on the downstream side when viewed from the branched part of the exhaust passage 26 and on the upstream side when viewed from the three-way catalyst 27. The upstream air-fuel ratio sensor 87 detects the upstream air-fuel ratio AF1, which is the air-fuel ratio of the gas on the upstream side of the three-way catalyst 27 in the exhaust passage 26. The downstream air-fuel ratio sensor 88 is located on the downstream side when viewed from the three-way catalyst 27 and on the upstream side when viewed from the filter 28 in the exhaust passage 26. The downstream air-fuel ratio sensor 88 detects the downstream air-fuel ratio AF2, which is the air-fuel ratio of the gas on the downstream side 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 there is relative to the fuel, the higher the air-fuel ratio, that is, the leaner the fuel state. On the other hand, the less air there is relative to the fuel, the lower the air-fuel ratio, that is, the richer the fuel state. When the internal combustion engine 10 is driving, since the gas from the four cylinders 11 continuously flows into the exhaust passage 26, the upstream air-fuel ratio AF1 and the downstream air-fuel ratio AF2 become values close to the average value of the air-fuel ratios in the four cylinders 11.

[0028] Vehicle 100 is equipped with a control device 90. The control device 90 acquires a signal indicating the intake air amount GA from an air flow meter 81. The control device 90 acquires a signal indicating the coolant water temperature THW from a coolant water temperature sensor 82. The control device 90 acquires a signal indicating the intake air temperature THA from an intake air temperature sensor 83. The control device 90 acquires a signal indicating the crank angle SC from a crank angle sensor 84. The control device 90 acquires a signal indicating the accelerator operation amount ACC from an accelerator operation amount sensor 85. The control device 90 acquires a signal indicating the vehicle speed SP from a vehicle speed sensor 86. The control device 90 acquires a signal indicating the upstream air-fuel ratio AF1 from an upstream air-fuel ratio sensor 87. The control device 90 acquires a signal indicating the downstream air-fuel ratio AF2 from a downstream air-fuel ratio sensor 88.

[0029] Based on the accelerator operation amount ACC and the vehicle speed SP, the control device 90 calculates a vehicle required output, which is a required value of the output necessary for the vehicle 100 to travel. Based on the vehicle required output, the control device 90 determines the torque distribution among the internal combustion engine 10, the first motor generator 71, and the second motor generator 72. Based on the torque distribution among the internal combustion engine 10, the first motor generator 71, and the second motor generator 72, the control device 90 controls the output of the internal combustion engine 10, the power running and regeneration of 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. Also, the control device 90 controls the first motor generator 71 via the first inverter 76 by outputting a control signal to the first inverter 76. Further, 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.

[0030] The control device 90 calculates the engine rotational 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 ratio KL based on the engine rotational speed NE and the intake air amount GA. Here, the engine load ratio KL represents the ratio of the current cylinder inflow air amount to the cylinder inflow air amount when the internal combustion engine 10 is in steady operation with the throttle valve 22 fully open at the current engine rotational speed NE. Note that the cylinder inflow air amount is the amount of intake air flowing into each cylinder 11 during the intake stroke.

[0031] The control device 90 calculates the catalyst temperature TSC, which is the temperature of the three-way catalyst 27, based on the operating state of the internal combustion engine 10 such as the intake filling efficiency and the engine rotational speed NE. Note that the intake filling efficiency is a value obtained by dividing the mass of the intake air actually introduced from the intake passage 21 into the cylinder 11 by the mass of the intake air that can be introduced into the cylinder 11 under the state of standard atmosphere. Further, the control device 90 calculates the filter temperature TF, which is the temperature of the filter 28, based on the operating state of the internal combustion engine 10 such as the intake filling efficiency and the engine rotational speed NE. The control device 90 calculates the PM deposition amount PS, which is the deposition amount of particulate matter in the filter 28, based on the engine rotational speed NE, the engine load ratio KL, and the filter temperature TF.

[0032] 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 the four cylinders 11 each undergo a combustion stroke, that is, the period during which the crankshaft 12 rotates twice, is referred to as one combustion cycle. In the fuel cut process, the control device 90 repeats, in a plurality of consecutive combustion cycles, a process of stopping the fuel supply to one of the four cylinders 11 in one combustion cycle while supplying fuel to the remaining three cylinders. Further, in the fuel cut process, the control device 90 opens and closes the intake valves and exhaust valves corresponding to the four cylinders 11. Therefore, in the fuel cut process, the stop pattern and the combustion pattern are alternately repeated while continuing the operation of the internal combustion engine 10. Here, the stop pattern is to stop the fuel supply to one cylinder 11 and allow intake air to flow from the cylinder 11 to the exhaust passage 26. The combustion pattern is to continuously supply fuel to three cylinders 11 in the order of the cylinders 11 undergoing the combustion stroke and allow exhaust gas to flow from the cylinders 11 to the exhaust passage 26.

[0033] In the fuel cut process, the air-fuel ratio of the cylinders 11 to which fuel is supplied becomes slightly lower than the theoretical air-fuel ratio AFS, that is, 14.7. On the other hand, in the fuel cut process, the air-fuel ratio of the cylinders 11 to which the fuel supply is stopped becomes extremely higher than the theoretical air-fuel ratio AFS. As a result, in the fuel cut process, the average value of the air-fuel ratios in the four cylinders 11 becomes higher than the theoretical air-fuel ratio AFS. In the present embodiment, in the fuel cut process, the cylinder 11 to which the fuel supply is stopped is the third cylinder 11C. Also, 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. Note that the control device 90 applies torque from the first motor generator 71 to the crankshaft 12 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 combustion stop of the air-fuel mixture in the third cylinder 11C in the fuel cut process.

[0034] When the fuel cut process is executed, the intake air not being used for combustion, i.e., the air containing oxygen, is supplied from the third cylinder 11C to the exhaust passage 26. When oxygen is thus supplied to the filter 28 through the exhaust passage 26, the particulate matter deposited on the filter 28 burns, thereby regenerating the filter 28.

[0035] Note that the control device 90 can be configured as a circuitry including one or more processors that execute various processes according to a computer program (software). Note that the control device 90 may be configured as a circuitry including one or more dedicated hardware circuits such as an application specific integrated circuit (ASIC) that execute at least a part of the various processes, or a combination thereof. The processor includes a CPU and memories such as a RAM and a ROM. The memory stores program codes or instructions configured to cause the CPU to execute processes. The memory, i.e., the computer-readable medium, includes any medium accessible by a general-purpose or dedicated computer.

[0036] <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 the state in which the above-described fuel cut process is being executed. The second of the two combustion states is the state in which a normal combustion process of supplying fuel to all of the four cylinders 11 is being executed. The control device 90 repeatedly executes the combustion switching control from when the driving of the internal combustion engine 10 is started until the driving of the internal combustion engine 10 is ended.

[0037] As shown in FIG. 2, when the control device 90 starts the combustion switching control, it proceeds with the process of step S11. In step S11, the control device 90 determines whether a pre-determined prerequisite condition for executing the fuel cut process is satisfied. Here, an example of the prerequisite condition for the fuel cut process is that the PM deposition amount PS is equal to or greater than a pre-determined specified value. In step S11, when the control device 90 determines that the prerequisite condition for the fuel cut process is satisfied (S11: YES), the process proceeds to step S21.

[0038] In step S21, the control device 90 executes the fuel cut process. Note that when the control device 90 has already executed the fuel cut process, it continues to execute the fuel cut process. Thereafter, the control device 90 ends the current combustion switching control and proceeds with the process to step S11 again.

[0039] On the other hand, in step S11, when the control device 90 determines that the prerequisite condition for the fuel cut process is not satisfied (S11: NO), the process proceeds to step S22. In step S22, the control device 90 executes the normal combustion process. Note that when the control device 90 has already executed the normal combustion process, it continues to execute the normal combustion process. Thereafter, the control device 90 ends the current combustion switching control and proceeds with the process to step S11 again.

[0040] <Judgment Control> Next, the judgment control performed by the control device 90 will be described. The control device 90 determines the presence or absence of an abnormality in the fuel cut process by 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, the normal judgment flag and the abnormality judgment flag described later are OFF.

[0041] As shown in FIG. 3, when the control device 90 starts the determination control, it proceeds to the process of step S61. In step S61, the control device 90 determines whether or not the continuation period TX of the fuel cut process is equal to or longer than a first predetermined period TA1 that is preset. Here, the continuation period TX is the period from the start of the current fuel cut process to the time of the process in step S61. Also, when setting the first predetermined period TA1, the period from the start of the fuel cut process until 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 through experiments or the like. Then, a period that is a certain period longer than the obtained 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 determines that the continuation period TX of the fuel cut process is less than the first predetermined period TA1 (S61: NO), it performs the process of step S61 again. That is, the control device 90 repeats step S61 until the continuation period TX becomes equal to or longer than the first predetermined period TA1.

[0042] On the other hand, in step S61, when the control device 90 determines that the continuation period TX of the fuel cut process is equal to or longer than the first predetermined period TA1 (S61: YES), it proceeds with the process to step S62.

[0043] In step S62, the control device 90 determines whether or not the upstream air-fuel ratio AF1 detected by the upstream air-fuel ratio sensor 87 is equal to or higher than a first threshold value Z1 that is preset. Here, when setting the first threshold value 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 through experiments 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 value Z1. An example of the first threshold value 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 higher than the first threshold value Z1 (S62: YES), it proceeds with the process to step S71.

[0044] In step S71, the control device 90 determines whether the continuous period TX of the fuel cut process is equal to or longer than a second predetermined period TA2 that is preset. Here, when setting the second predetermined period TA2, the period from when the fuel cut process starts 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 through experiments or the like. Then, a period that is a certain period longer than the obtained period is set as the second predetermined period TA2. As a result, the second predetermined period TA2 is set to a value larger than the above-described first predetermined period TA1. An example of the second predetermined period TA2 is several hundred to several thousand msec. In step S71, when the control device 90 determines that the continuous period TX of the fuel cut process is less than the second predetermined period TA2 (S71: NO), the process of step S71 is performed again. That is, the control device 90 repeats step S71 until the continuous period TX becomes equal to or longer than the second predetermined period TA2.

[0045] On the other hand, in step S71, when the control device 90 determines that the continuous period TX of the fuel cut process is equal to or longer than the second predetermined period TA2 (S71: YES), the process proceeds to step S72.

[0046] 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 higher than a second threshold value Z2 that is preset. Here, when setting the second threshold value Z2, the air-fuel ratio detected by the downstream air-fuel ratio sensor 88 when a period of the second predetermined period TA2 has elapsed since the start of the fuel cut process is obtained in advance through experiments 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 value Z2. An example of the second threshold value Z2 is about 17 to 18. In the present embodiment, the second threshold value Z2 is the same value as the first threshold value 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 higher than the second threshold value Z2 (S72: YES), the process proceeds to step S81.

[0047] In step S81, the control device 90 makes a normal determination indicating that the fuel cut process is normal. For example, the control device 90 indicates that the fuel cut process is normal by turning on the normal determination flag and turning off the abnormal determination flag. Thereafter, the control device 90 ends the current determination control.

[0048] On the other hand, 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 less than the first threshold value Z1 (S62: NO), the process proceeds to step S82. Also, 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 less than the second threshold value Z2 (S72: NO), the process proceeds to step S82.

[0049] In step S82, the control device 90 makes an abnormal determination indicating that the fuel cut process is abnormal. For example, the control device 90 indicates that the fuel cut process is abnormal by turning on the abnormal determination flag and turning off the normal determination flag. Also, the control device 90 outputs a control signal to a warning lamp (not shown) to notify the driver of the vehicle 100 or the like that the fuel cut process is abnormal. Thereafter, the control device 90 ends the current determination control. In the present embodiment, the processes of step S61, step S62, step S71, step S72, and step S82 are determination processes. Note that when a normal determination is made in step S81 or an abnormal determination is made in step S82, the control device 90 does not perform a determination control again in the current fuel cut process that is the determination target.

[0050] <Operation of the Present Embodiment> First, the 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 the normal combustion process is being executed. In this case, as shown in FIG. 4(b), the upstream air-fuel ratio AF1 is about the theoretical air-fuel ratio AFS. Similarly, as shown in FIG. 4(c), the downstream air-fuel ratio AF2 is about the theoretical air-fuel ratio AFS.

[0051] As shown in FIG. 4(a), at time t11, the fuel cut process is started. When the fuel cut process is started, the intake air not used for combustion, the 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 becomes higher after time t11. Similarly, as shown in FIG. 4(c), the downstream air-fuel ratio AF2 becomes higher after time t11. Here, since the downstream air-fuel ratio sensor 88 is located on the downstream side as viewed from the upstream air-fuel ratio sensor 87, the timing at which the air-fuel ratio of the downstream air-fuel ratio AF2 becomes higher than that of the upstream air-fuel ratio AF1 is delayed.

[0052] Then, as shown in FIG. 4(b), at time t12 after the elapse of the first predetermined period TA1 from time t11, the upstream air-fuel ratio AF1 becomes equal to or higher than the first threshold value Z1. Further, as shown in FIG. 4(c), at time t13 after the elapse of the second predetermined period TA2 from time t11, the downstream air-fuel ratio AF2 becomes equal to or higher than the second threshold value Z2. As a result, as shown in FIG. 4(d), the normal determination flag becomes ON at time t13.

[0053] Next, the 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 and the normal combustion process is being executed before time t21. In this case, as shown in FIG. 4(b), the upstream air-fuel ratio AF1 is about the stoichiometric air-fuel ratio AFS. Similarly, as shown in FIG. 4(c), the downstream air-fuel ratio AF2 is about the stoichiometric air-fuel ratio AFS.

[0054] As shown in FIG. 4(a), at time t21, the fuel cut process is started. However, since the fuel cut process is abnormal, even if the fuel cut process is started, the amount of intake air supplied from the cylinder 11 to the exhaust passage 26 is less than that in the case where the fuel cut process is normal. Therefore, as shown in FIG. 4(b), at time t22 after the elapse of the first predetermined period TA1 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), at time t22, the abnormality determination flag is turned ON. Note that, similar to the upstream air-fuel ratio AF1, as shown in FIG. 4(c), at time t23 after the elapse of the second predetermined period TA2 from time t21, the downstream air-fuel ratio AF2 becomes less than the second threshold value Z2.

[0055] <Effects of the present 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 the present embodiment, based on the fact that the upstream air-fuel ratio AF1 is less than the first threshold value Z1, that is, a value indicating rich, etc., it can be determined that there is an abnormality in the fuel cut process.

[0056] (2) As described above, as shown in FIG. 4(b), after the time t11 when the fuel cut process is started, the upstream air-fuel ratio AF1 increases. 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.

[0057] In this regard, in the present 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 after the elapse of the first predetermined period TA1 from time t11. Thereby, even if the upstream air-fuel ratio AF1 becomes less than the first threshold value Z1 due to being immediately after time t11, it is possible to suppress erroneously determining that there is an abnormality in the fuel cut process.

[0058] (3) In this embodiment, it is determined whether there is an abnormality in the fuel cut process 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, for example, 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, the abnormality in the fuel cut process can be appropriately determined.

[0059] <Modified Example> This embodiment can be implemented with the following modifications. This embodiment and the following modified examples can be implemented in combination with each other within a technically consistent range.

[0060] · In the above embodiment, the determination process may be changed. For example, the first predetermined period TA1 may be the same value as the second predetermined period TA2. In this configuration, when the control device 90 makes an affirmative determination in step S62, the process may proceed to step S72. That is, the process of step S71 may be omitted.

[0061] · For example, the control device 90 may perform only one of the processes of step S61 and step S62 and the processes of step S71 and step S72 in the determination process, and omit the other.

[0062] · In the above embodiment, the fuel cut process may be changed. For example, in the fuel cut process, the cylinder 11 in which the 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. Further, for each combustion cycle, the cylinder 11 in which the fuel supply is stopped and the cylinder 11 in which the fuel supply is performed may be changed.

[0063] · For example, in the fuel cut process, if the number of cylinders 11 where fuel supply is stopped and the number of cylinders 11 where fuel supply is performed are each 1 or more, the number of cylinders 11 where fuel supply is stopped and the number of cylinders 11 where fuel supply is performed may be changed. Further, for each combustion cycle, the number of cylinders 11 where fuel supply is stopped and the number of cylinders 11 where fuel supply is performed may be changed. Therefore, the fuel cut process may be any process with the following content. Here, let "M" and "N" be integers of 1 or more. In the fuel cut process, it is sufficient that the stop pattern and the combustion pattern are alternately repeated while continuing the operation of the internal combustion engine 10. Here, the stop pattern is a pattern in which, in the order of the cylinders 11 approaching the combustion stroke, fuel supply to M consecutive cylinders 11 is stopped while allowing intake air to flow from the cylinder 11 to the exhaust passage 26. Also, the combustion pattern is a pattern in which, in the order of the cylinders 11 approaching the combustion stroke, fuel is supplied to N consecutive cylinders 11 while allowing exhaust gas to flow from the cylinder 11 to the exhaust passage 26. Note that the total value of M and N does not necessarily have to match the total number of cylinders 11. Further, when the total value of M and N does not match the total number of cylinders 11, for each combustion cycle, the cylinders 11 where fuel supply is stopped and the cylinders 11 where fuel supply is performed may be changed, or there may be no cylinders 11 where fuel supply is stopped in some combustion cycles.

[0064] · In the above embodiment, the configuration of the vehicle 100 may be changed. For example, one of the upstream air-fuel ratio sensor 87 and the downstream air-fuel ratio sensor 88 may be omitted. Even with 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.

[0065] · 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 may not be provided with the first motor generator 71 and the second motor generator 72. Even in this configuration, if the control device 90 executes the fuel cut process when the vehicle demand output is relatively small, it does not matter if the output of the internal combustion engine 10 decreases due to the fuel cut process.

Explanation of Signs

[0066] 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 wheel 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

【Claim 1】 A control device applied to an internal combustion engine, comprising: 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 for purifying exhaust gas; a filter located downstream of the three-way catalyst in the exhaust passage for collecting particulate matter contained in the exhaust gas; an upstream air-fuel ratio sensor located upstream of the three-way catalyst in the exhaust passage for detecting an upstream air-fuel ratio which is the air-fuel ratio of the gas in the exhaust passage; and a downstream air-fuel ratio sensor located downstream of the three-way catalyst and upstream of the filter in the exhaust passage for detecting a downstream air-fuel ratio which is the air-fuel ratio of the gas in the exhaust passage. A fuel cut process in which, when "M" and "N" are integers of 1 or more, a stop pattern in which intake air is circulated from the cylinders to the exhaust passage while stopping fuel supply to M consecutive cylinders in the order of the cylinders approaching the combustion stroke, and a combustion pattern in which exhaust gas is circulated from the cylinders to the exhaust passage while supplying fuel to N consecutive cylinders in the order of the cylinders approaching the combustion stroke, are alternately repeated while continuing the operation of the internal combustion engine. When one or more of the following conditions are met: the upstream air-fuel ratio is less than a predetermined first threshold when a predetermined first period has elapsed since the start of the fuel cut process; and the downstream air-fuel ratio is less than a predetermined second threshold when a predetermined second period, which is a value larger than the first period, has elapsed since the start of the fuel cut process, it is determined that there is an abnormality in the fuel cut process. 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 when the first period has elapsed since the start of the fuel cut process, and the downstream air-fuel ratio is equal to or greater than the second threshold when the second period has elapsed since the start of the fuel cut process. A control device for an internal combustion engine.

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