Internal combustion engine misfire detection device

Abstract

To suppress false detection on accidental fire of an opposite cylinder, though the accidental fire of the opposite cylinder does not occur.SOLUTION: An engine control unit 300 as an accidental fire detection device of an internal combustion engine executes opposite cylinder accidental fire detection processing for detecting occurrence of the opposite cylinder accidental fire as abnormality that accidental fire occurs every 360°CA, on the basis of a rotation fluctuation amount of a crank shaft 59. The engine control unit 300 stops the opposite cylinder accidental fire detection processing when specific cylinder stop processing is executed to stop fuel supply to a set of opposite cylinders in which expansion strokes are separated by 360°CA and to supply the fuel to the remaining cylinders.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Patent Document 1 discloses a misfire detection device that detects opposed cylinder misfires in a six-cylinder internal combustion engine. Opposed cylinder misfires refer to misfires that occur every 360° CA. In other words, when opposed cylinder misfires occur, misfires occur in two cylinders whose expansion strokes are 360° CA apart, i.e., in both opposed cylinders. The misfire detection device detects opposed cylinder misfires based on the amount of rotational fluctuation of the crankshaft.

[0003] Furthermore, Patent Document 2 discloses a control device for an internal combustion engine that performs control to raise the temperature of a catalyst by stopping fuel supply to specific cylinders among multiple cylinders of the internal combustion engine and supplying fuel to the remaining cylinders.

[0004] In a six-cylinder internal combustion engine, when a specific cylinder stopping process is executed to stop fuel supply to a specific cylinder and supply fuel to the remaining cylinders as disclosed in Patent Document 2, fuel supply to a pair of opposing cylinders is stopped. This is to suppress torque fluctuations by evenly allocating two combustion-stopped cylinders during a period in which all six cylinders have their ignition timing once each, i.e., during a period in which the crankshaft rotates twice. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 10-54294 [Patent Document 2] Patent Publication No. 2021-60027 Summary of the Invention [Problem to be solved by the invention]

[0006] In a six-cylinder internal combustion engine, when a specific cylinder stop process is being performed to stop the fuel supply to a pair of opposing cylinders, the rotational fluctuation of the crankshaft behaves in a manner similar to that observed when the opposing cylinders are misfiring, which may result in a false detection that the opposing cylinders are misfiring even when they are not. [Means for solving the problem]

[0007] The means for solving the above problems and their effects will be described below. A misfire detection device for an internal combustion engine for solving the above problems is applied to an internal combustion engine having six cylinders. This misfire detection device executes an opposed cylinder misfire detection process that detects the occurrence of opposed cylinder misfire, which is an abnormality in which a misfire occurs every 360° CA, based on the rotational fluctuation amount of the crankshaft. In addition, this misfire detection device stops the opposed cylinder misfire detection process when a specific cylinder stop process is executed that stops the fuel supply to a pair of opposed cylinders whose expansion strokes are 360° CA apart and supplies fuel to the remaining cylinders.

[0008] The misfire detection device stops the opposed cylinder misfire detection process when a specific cylinder stop process is being performed in which the behavior of the rotational fluctuation amount of the crankshaft is similar to the behavior of the rotational fluctuation amount when an opposed cylinder misfire occurs, thereby making it possible to suppress erroneous detection that an opposed cylinder misfire is occurring based on the behavior of the rotational fluctuation amount caused by the specific cylinder stop process. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram showing the configuration of a hybrid vehicle equipped with an engine control unit that is an embodiment of a misfire detection device. [Diagram 2] FIG. 2 is a schematic diagram for explaining the crank angle signal. [Diagram 3] FIG. 3 is a graph showing the behavior of the rotation fluctuation amount of the crankshaft when a misfire occurs in the opposed cylinder. [Figure 4] FIG. 4 is an explanatory diagram for explaining a calculation mode of the rotation fluctuation amount. [Diagram 5] FIG. 5 is a flowchart showing a series of processes for detecting an opposed cylinder misfire and determining an abnormality. [Figure 6] FIG. 6 is a time chart explaining the action of the engine control unit of the embodiment, in which FIG. 6(a) shows whether or not a specific cylinder stop process is being executed, FIG. 6(b) shows the cumulative number of revolutions Σrev, and FIG. 6(c) shows the progress of the misfire count value cnt. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, one embodiment of a misfire detection device for an internal combustion engine will be described with reference to Figs. <About the configuration of vehicle 10> As shown in FIG. 1, the vehicle 10 is equipped with an engine 50. The engine 50 is a six-cylinder engine equipped with six cylinders, #1 to #6, as shown in FIG. 1. The vehicle 10 is also equipped with a battery 30 that stores electric power. The vehicle 10 is further equipped with a first motor generator 11 and a second motor generator 12. The first motor generator 11 and the second motor generator 12 are motors that generate driving force in response to power supplied from the battery 30, and also function as generators that receive external power and generate electric power to charge the battery 30.

[0011] The vehicle 10 is further provided with a planetary gear mechanism 13 having three rotating elements, a sun gear 14, a planetary carrier 15, and a ring gear 16. A crankshaft 59, which is an output shaft of the engine 50, is connected to the planetary carrier 15 of the planetary gear mechanism 13. A first input shaft 25, which is connected to a rotating shaft of the first motor generator 11, is connected to the sun gear 14 of the planetary gear mechanism 13. A counter drive gear 17 is integrally provided to the ring gear 16 of the planetary gear mechanism 13. A counter driven gear 18 is meshed with the counter drive gear 17. A reduction gear 19 is meshed with the counter driven gear 18. A second input shaft 26, which is connected to a rotating shaft of the second motor generator 12, is connected to the reduction gear 19.

[0012] A final drive gear 20 is connected to the counter driven gear 18 so as to be rotatable together with the counter driven gear 18. A final driven gear 21 is meshed with the final drive gear 20. A drive shaft 24 of drive wheels 23 is connected to the final driven gear 21 via a differential mechanism 22.

[0013] <About the System Control Unit 100> The system control unit 100 includes a storage device in which a program is stored, and a processing circuit that executes the program stored in the storage device to perform various controls. The system control unit 100 is connected to a power control unit 200 and an engine control unit 300.

[0014] <About the power control unit 200> The first motor generator 11 and the second motor generator 12 are connected to the battery 30 via a power control unit 200. The power control unit 200 includes a control circuit, an inverter, and a converter. The power control unit 200 operates based on a command from the system control unit 100. The power control unit 200 adjusts the amount of power supplied from the battery 30 to the first motor generator 11 and the second motor generator 12, and the amount of charge from the first motor generator 11 and the second motor generator 12 to the battery 30. The vehicle 10 is provided with a connector 31 that can be connected to an external power source 40. Therefore, the battery 30 can also be charged by the power supplied from the external power source 40. That is, the vehicle 10 is a plug-in hybrid vehicle.

[0015] <About the engine control unit 300> The engine control unit 300 controls the engine 50 based on commands from the system control unit 100. The engine control unit 300 includes a storage device in which programs are stored, and a processing circuit that executes the programs stored in the storage device to perform various types of control.

[0016] The engine control unit 300 receives detection signals from various sensors that detect the operating state of the engine 50. The sensors that input detection signals to the engine control unit 300 include a crank position sensor 134 that detects the rotation angle of the crankshaft 59.

[0017] 2, a crank rotor 58 is attached to a crankshaft 59. The crank rotor 58 has 34 teeth 56 spaced at equal intervals, with one missing tooth portion 57 where the interval between adjacent teeth 56 is wider. The crank position sensor 134 is provided facing the periphery of the crank rotor 58 so as to face the teeth 56 of the crank rotor 58.

[0018] The crank position sensor 134 is a magnetic resistance element type sensor consisting of a sensor circuit incorporating a magnet and a magnetic resistance element. When the crank rotor 58 rotates in conjunction with the rotation of the crankshaft 59, the teeth 56 of the crank rotor 58 and the crank position sensor 134 move toward or away from each other. This changes the direction of the magnetic field acting on the magnetic resistance element in the crank position sensor 134, causing a change in the internal resistance of the magnetic resistance element. The sensor circuit converts this change in resistance value into a voltage and compares it with a threshold value to shape the waveform into a rectangular wave consisting of Lo and Hi signals, and outputs the waveform as the crank angle signal Scr.

[0019] As shown in FIG. 2, specifically, the crank position sensor 134 outputs a Lo signal when facing a tooth 56. The crank position sensor 134 outputs a Hi signal when facing a gap between the teeth 56. Therefore, when a Hi signal corresponding to the missing tooth portion 57 is detected, a Lo signal corresponding to the tooth 56 is detected thereafter. Then, a Lo signal corresponding to the tooth 56 is detected every 10° CA thereafter. After 34 Lo signals are detected in this manner, a Hi signal corresponding to the missing tooth portion 57 is detected again. Therefore, the rotation angle from when the Hi signal corresponding to the missing tooth portion 57 is sandwiched until the Lo signal corresponding to the next tooth 56 is detected is 30° CA in crank angle.

[0020] The interval from when a Hi signal corresponding to the missing tooth portion 57 is followed by a Lo signal corresponding to the tooth 56 to when the next Hi signal corresponding to the missing tooth portion 57 is followed by a Lo signal is 360° CA in crank angle.

[0021] The engine control unit 300 calculates the crank angle and the engine speed based on the crank angle signal Scr. The engine control unit 300 also calculates the time required for the crank angle to change by a certain amount as an index value of the rotation fluctuation amount of the crankshaft 59. A period corresponding to T30 is shown in FIG. 2. T30 is the time required for the crank angle to change by 30° CA.

[0022] The engine control unit 300 calculates the engine rotation speed, which is the rotation speed of the crankshaft 59, based on the crank angle signal Scr input from the crank position sensor .

[0023] Also connected to the engine control unit 300 is an intake air temperature sensor 135 that detects the temperature of the intake air taken into the combustion chamber of the engine 50. Furthermore, also connected to the engine control unit 300 is a water temperature sensor 136 that detects the temperature of the cooling water for the engine 50.

[0024] 1, a main switch 130 that allows the driver of the vehicle 10 to start and stop the system of the vehicle 10 is connected to the system control unit 100. An accelerator position sensor 131 that detects an accelerator operation amount and a brake sensor 132 that detects a brake operation amount are also connected to the system control unit 100. A vehicle speed sensor 133 that detects the vehicle speed, which is the speed of the vehicle 10, is also connected to the system control unit 100.

[0025] Further, the current, voltage, and temperature of the battery 30 are input to the power control unit 200. The power control unit 200 calculates a state of charge index value SOC, which is the ratio of the remaining charge to the charge capacity of the battery 30, based on the current, voltage, and temperature.

[0026] The engine control unit 300 and the power control unit 200 are each connected to the system control unit 100. The system control unit 100, the power control unit 200, and the engine control unit 300 mutually exchange and share information based on detection signals input from sensors and calculated information.

[0027] Based on this information, the system control unit 100 outputs commands to the engine control unit 300 and controls the engine 50 through the engine control unit 300. The system control unit 100 also outputs commands to the power control unit 200 based on this information. As a result, the system control unit 100 controls the first motor generator 11 and the second motor generator 12 and controls the charging of the battery 30 through the power control unit 200. In this way, the system control unit 100 controls the vehicle 10 by outputting commands to the power control unit 200 and the engine control unit 300.

[0028] <Regarding control of vehicle 10> Next, the control of the vehicle 10 performed by the system control unit 100 will be described in more detail.

[0029] The system control unit 100 calculates a required output, which is a required value of the output of the vehicle 10, based on the accelerator operation amount and the vehicle speed. The system control unit 100 then determines the torque distribution of the engine 50, the first motor generator 11, and the second motor generator 12 according to the required output and a state of charge index value SOC of the battery 30. The system control unit 100 then controls the output of the engine 50 and power running / regeneration by the first motor generator 11 and the second motor generator 12. The system control unit 100 switches the driving mode of the vehicle 10 depending on the magnitude of the state of charge index value SOC.

[0030] When the state of charge index value SOC exceeds a certain level, the system control unit 100 selects a motor driving mode in which the vehicle runs using the driving force from the second motor generator 12 and the driving force from the first motor generator 11 without operating the engine 50. In other words, the system control unit 100 selects the motor driving mode when the remaining charge of the battery 30 is sufficient.

[0031] On the other hand, when the state of charge index value SOC falls below a certain level, the system control unit 100 selects a hybrid driving mode in which the engine 50 is used in addition to the first motor generator 11 and the second motor generator 12.

[0032] Even if the state of charge index value SOC exceeds a certain level, the system control unit 100 selects the hybrid driving mode in the following cases. When the vehicle speed exceeds the upper limit of the motor driving mode.

[0033] When a large amount of power is needed temporarily, such as during rapid acceleration with a large amount of accelerator pedal operation. When engine 50 needs to be started. When the hybrid driving mode is selected, the system control unit 100 causes the first motor generator 11 to function as a starter motor when starting the engine 50. Specifically, the system control unit 100 causes the first motor generator 11 to rotate the sun gear 14, thereby rotating the crankshaft 59 and starting the engine 50.

[0034] Furthermore, when the hybrid driving mode is selected, the system control unit 100 switches the control during vehicle stop according to the magnitude of the state of charge index value SOC. Specifically, when the state of charge index value SOC is equal to or greater than a threshold value, the system control unit 100 stops the operation of the engine 50 and does not drive the first motor generator 11 and the second motor generator 12. That is, the system control unit 100 stops the operation of the engine 50 during vehicle stop to suppress idling. Note that, when the state of charge index value SOC of the battery 30 is less than a threshold value, the system control unit 100 operates the engine 50. Then, the first motor generator 11 is driven by the output of the engine 50 to function as a generator.

[0035] When the hybrid driving mode is selected, the system control unit 100 switches the control according to the state of charge index value SOC even during driving. When the state of charge index value SOC of the battery 30 is equal to or greater than the threshold value when starting or during light load driving, the system control unit 100 starts and drives the vehicle 10 only by the driving force of the second motor generator 12. In this case, the engine 50 is stopped, and the first motor generator 11 does not generate power. On the other hand, when the state of charge index value SOC of the battery 30 is less than the threshold value when starting or during light load driving, the system control unit 100 starts the engine 50, causes the first motor generator 11 to generate power, and charges the generated power to the battery 30. In this case, the vehicle 10 runs by part of the driving force of the engine 50 and the driving force of the second motor generator 12. During steady running, when the state of charge index value SOC of the battery 30 is equal to or higher than the threshold value, the system control unit 100 operates the engine 50 in a state of high operating efficiency, and runs the vehicle 10 mainly with the output of the engine 50. At this time, the power of the engine 50 is divided between the drive wheels 23 side and the first motor generator 11 side via the planetary gear mechanism 13. As a result, the vehicle 10 runs while generating power with the first motor generator 11. Then, the system control unit 100 drives the second motor generator 12 with the generated power, and the power of the second motor generator 12 assists the power of the engine 50. On the other hand, during steady running, when the state of charge index value SOC of the battery 30 is less than the threshold value, the system control unit 100 increases the engine rotation speed. Then, the power generated by the first motor generator 11 is used to drive the second motor generator 12, and the surplus power is charged to the battery 30. During acceleration, the system control unit 100 increases the engine rotation speed and uses the electric power generated by the first motor generator 11 to drive the second motor generator 12. This causes the vehicle 10 to accelerate using the power of the engine 50 and the power of the second motor generator 12. During deceleration, the system control unit 100 stops the operation of the engine 50.The system control unit 100 then causes the second motor generator 12 to function as a generator, and the generated electric power is charged to the battery 30. In the vehicle 10, the resistance caused by such power generation is used as a brake. Such power generation control during deceleration is called regenerative control.

[0036] <Diagnosis of misfire abnormalities> The engine control unit 300 performs an abnormality diagnosis to diagnose misfire abnormality in the engine 50. Specifically, the engine control unit 300 detects opposed cylinder misfire, which is an abnormality in which misfire occurs every 360° CA. If the frequency of opposed cylinder misfire is high, the engine control unit 300 diagnoses that a misfire abnormality due to opposed cylinder misfire has occurred.

[0037] Fig. 3 shows the behavior of the rotation fluctuation of the crankshaft 59 when an opposing cylinder misfire occurs. Fig. 3 shows the length of time required for the crank angle to change by a certain amount due to combustion in each cylinder for each cylinder. Specifically, T120, which is the time required for the crank angle to change by 120° CA after ignition, is shown for each cylinder.

[0038] FIG. 3 shows an example where a misfire occurs in cylinders #2 and #5. The expansion strokes of cylinders #2 and #6 are 360°CA apart. That is, FIG. 3 shows the behavior of the rotation fluctuation when opposing cylinder misfire occurs between cylinders #2 and #5. In the cylinder where a misfire occurs, the expansion of the combustion gas does not occur. Therefore, as shown in FIG. 3, in cylinders #2 and #5, the time T120 required for the crank angle to change by 120°CA is longer than that of cylinders #1, #3, #4, and #6 where no misfire occurs.

[0039] Therefore, the engine control unit 300 uses T120 calculated based on the crank angle signal Scr as an index value of the rotation fluctuation amount. Specifically, as shown in Fig. 3, the engine control unit 300 detects that a behavior in which T120 becomes longer in a cylinder whose expansion stroke is 360° CA away appears, and detects a misfire in the opposing cylinder.

[0040] Specifically, as shown in FIG. 4, the engine control unit 300 calculates T120[0] to T120[5] as T120 corresponding to the combustion stroke of each cylinder. FIG. 4 shows the calculation mode of the rotation fluctuation index value used to detect the opposing cylinder misfire, with T120 for the #5 cylinder as T120[0]. Note that, as shown in FIG. 4, T120[0] is calculated as T30[0], which is the time required for the crank angle to change by 30° CA from #6TDC, which is the top dead center of the #6 cylinder. As shown in FIG. 4, T120[0] is the sum of T30[0], T30[1] which is the T30 at the 30° CA immediately before, T30[2] which is the T30 at the 30° CA two before, and T30[3] which is the T30 at the 30° CA three before. As shown in FIG. 4, T120[0] to T120[5] are each the sum of four consecutive T30s.

[0041] Then, the engine control unit 300 calculates ΔT120, which is the difference between ΔT120 in the cylinders whose ignition timings are adjacent to each other. In the example shown in Fig. 4, the difference obtained by subtracting T120[1], which is the previous T120, from T120[0] is calculated as ΔT120[0].

[0042] If there is no misfire in cylinder #5 and no misfire in cylinder #4, T120[0] and T120[1] will be roughly the same length, so the value of ΔT120[0] will be close to "0". On the other hand, if there is a misfire in cylinder #5 and no misfire in cylinder #4, T120[0] will be longer than T120[1], so ΔT120[0] will be a large value. In other words, ΔT120 is an index value of the amount of rotational fluctuation between cylinders whose ignition timing is adjacent to each other, and is an index value for detecting the occurrence of a misfire.

[0043] 4, in order to detect the opposing cylinder misfire, the engine control unit 300 also calculates ΔT120[3], which is an index value for detecting misfire in the #2 cylinder whose expansion stroke is 360° CA away from the #5 cylinder. Then, the engine control unit 300 calculates ΣT120[0], which is the sum of ΔT120[0] and ΔT120[3].

[0044] When misfires occur in both cylinder #5 and cylinder #2 and an opposing cylinder misfire occurs, both ΔT120[0] and ΔT120[3] become large values, so ΣT120[0] becomes a very large value.

[0045] In addition to ΣT120[0], the engine control unit 300 also calculates ΣT120[1] and ΣT120[2] using the same calculation method, and calculates the average value of these, ΔT120A. If ΣT120A is equal to or greater than the threshold value X1, the engine control unit 300 determines that an opposed cylinder misfire has occurred, thereby detecting the occurrence of an opposed cylinder misfire. The engine control unit 300 repeatedly executes this opposed cylinder misfire detection process while the engine 50 is operating.

[0046] In addition to detecting opposing cylinder misfires, the engine control unit 300 also detects misfires in a single cylinder using ΔT30, which is the difference in T30, and ΔT180, which is the difference in T180, as well as random misfires, which are misfires that occur irregularly.

[0047] <About specific cylinder shutoff processing> The engine control unit 300 may execute a specific cylinder stop process to stop the fuel supply to a pair of opposing cylinders that are 360° CA apart in the expansion stroke among the six cylinders, and operate the engine 50 with fuel supplied to the remaining four cylinders. Such a specific cylinder stop process is executed to burn and remove particulate matter deposited on a particulate filter provided in the exhaust passage of the engine 50. By operating the engine 50 with the fuel supply to some cylinders stopped, the air that has passed through the cylinders to which the fuel supply has been stopped can be sent to the exhaust purification catalyst and the particulate filter. This promotes the oxidation reaction of the particulate matter, and the particulate matter can be burned and removed.

[0048] The reason why the cylinders to which the fuel supply is stopped are a pair of opposing cylinders whose expansion strokes are separated by 360° CA is to suppress torque fluctuations by evenly allocating two combustion-stopped cylinders over the period of two rotations of crankshaft 59.

[0049] Incidentally, when engine 50 executes a specific cylinder stop process that stops the fuel supply to a pair of opposed cylinders, the rotation fluctuation of crankshaft 59 behaves in the same manner as when opposed cylinder misfire occurs as shown in Fig. 2. Therefore, engine control unit 300 erroneously detects that opposed cylinder misfire occurs even when opposed cylinder misfire does not occur.

[0050] <Abnormality diagnosis for opposing cylinder misfire> In order to suppress erroneous detection as described above, the engine control unit 300 stops the opposed cylinder misfire detection process for detecting the occurrence of an opposed cylinder misfire while the specific cylinder stop process is being performed.

[0051] 5 is a flowchart showing the flow of a series of processes for abnormality diagnosis regarding opposed cylinder misfire, which is executed by the engine control unit 300. The engine control unit 300 executes this routine every time the TDC of each cylinder is reached.

[0052] 5, the engine control unit 300 first determines whether or not the specific cylinder stop process is being performed in the process of step S100. If the engine control unit 300 determines that the specific cylinder stop process is not being performed (step S100: NO), the engine control unit 300 advances the process to step S110.

[0053] In the process of step S110, the engine control unit 300 updates the cumulative number of rotations Σrev. The cumulative number of rotations Σrev is a value that is counted up by one each time the crankshaft 59 rotates once during the operation of the engine 50 through this routine. That is, the cumulative number of rotations Σrev is a value obtained by accumulating the number of rotations of the crankshaft 59. Specifically, in the process of step S110, the engine control unit 300 grasps the rotation phase of the crankshaft 59 based on the crank angle signal Scr. Then, the engine control unit 300 counts up the cumulative number of rotations Σrev by one each time the crankshaft 59 rotates once. For example, when it is detected that the crank angle signal Scr has crossed 0° CA, and when it is detected that the crank angle has crossed 360° CA, the engine control unit 300 counts up the cumulative number of rotations Σrev by one.

[0054] Next, in the process of step S120, the engine control unit 300 determines whether or not an opposed cylinder misfire has occurred. Specifically, the engine control unit 300 executes the opposed cylinder misfire detection process described above.

[0055] When it is determined in the process of step S120 that an opposed cylinder misfire has occurred (step S120: YES), the engine control unit 300 advances the process to step S130.

[0056] In the process of step S130, the engine control unit 300 updates the misfire count value cnt. The misfire count value cnt is a value indicating the number of times that it has been determined through this routine that an opposed cylinder misfire has occurred. Specifically, in the process of step S130, the engine control unit 300 adds "1" to the misfire count value cnt, and sets the sum as the new misfire count value cnt. That is, in this case, the engine control unit 300 increases the misfire count value cnt by "1". Then, the engine control unit 300 advances the process to step S140.

[0057] In the process of step S140, the engine control unit 300 determines whether the cumulative number of revolutions Σrev is equal to or greater than the second threshold value X2. For example, the second threshold value X2 is set to "200." In the process of step S140, when it is determined that the cumulative number of revolutions Σrev is equal to or greater than the second threshold value X2 (step S140: YES), the engine control unit 300 advances the process to step S150.

[0058] Then, in the process of step S150, the engine control unit 300 judges whether the misfire count value cnt is equal to or greater than the third threshold value X3. When it is judged in the process of step S150 that the misfire count value cnt is equal to or greater than the third threshold value X3 (step S150: YES), the engine control unit 300 advances the process to step S160. In the process of step S160, the engine control unit 300 judges that a misfire abnormality due to opposed cylinder misfire has occurred, and performs an abnormality diagnosis. Note that here, a state in which the occurrence frequency of opposed cylinder misfire exceeds an allowable range is regarded as a misfire abnormality due to opposed cylinder misfire. The third threshold value X3 is set as a threshold value of the misfire count value cnt for judging such a misfire abnormality. For example, the third threshold value X3 is set to "10".

[0059] When the abnormality diagnosis is made in this way, the engine control unit 300 records in a storage device information indicating that a misfire abnormality has occurred due to an opposed cylinder misfire. The engine control unit 300 also turns on a warning light and displays on the display at the driver's seat that a misfire abnormality has occurred.

[0060] If an abnormality is diagnosed through the process of step S160, the engine control unit 300 advances the process to step S170. In the process of step S170, the engine control unit 300 resets the cumulative number of revolutions Σrev and the misfire count value cnt to "0". Then, the engine control unit 300 temporarily ends this routine. Note that if an abnormality is diagnosed, this routine will not be executed until repairs are performed and the information indicating the occurrence of a misfire abnormality is cleared.

[0061] Moreover, when it is determined in the process of step S150 that the misfire count value cnt is less than the third threshold value X3 (step S150: NO), the engine control unit 300 advances the process to step S170 without executing the process of S160.

[0062] In addition, in step S140, when it is determined that the cumulative number of revolutions Σrev is less than the second threshold value X2 (step S140: NO), the engine control unit 300 ends this diagnosis routine once. That is, in this case, the engine control unit 300 ends this routine once without performing an abnormality diagnosis.

[0063] As described above, by repeatedly executing this routine, the engine control unit 300 determines whether or not to determine an abnormality each time the cumulative number of revolutions Σrev reaches the second threshold value X2. The determination of whether or not to determine an abnormality is made based on the misfire count value cnt indicating the number of times that the occurrence of opposed cylinder misfire was determined before the cumulative number of revolutions Σrev reached the second threshold value X2. That is, in this routine, abnormality diagnosis is made based on the results of the processing from step S110 to step S130 in the opposed cylinder misfire detection processing.

[0064] When it is determined in the process of step S100 that the specific cylinder stop process is being performed (step S100: YES), the engine control unit 300 does not execute the processes of steps S110 to S130. Then, the engine control unit 300 proceeds directly to the process of step S140. That is, in this case, the cumulative number of revolutions Σrev is not updated, the opposed cylinder misfire detection process is not executed, and the misfire count value cnt is not updated. As a result, a positive determination is not made in the process of step S140, and the abnormality diagnosis is not performed.

[0065] In this way, when the specific cylinder stop process is being performed, the engine control unit 300 stops the opposed cylinder misfire detection process for detecting the occurrence of an opposed cylinder misfire.

[0066] <Action of this embodiment> Next, the operation of this embodiment will be described with reference to Fig. 6. When the engine 50 of the vehicle 10 is operating, the cumulative number of revolutions Σrev is incremented by "1" each time the crankshaft 59 rotates once, as shown in Fig. 6(b). Also, as shown in Fig. 6(c), the misfire count value cnt is increased each time an occurrence of an opposed cylinder misfire is detected through the opposed cylinder misfire detection process. In the example shown in Fig. 6, opposed cylinder misfires are detected at such a low frequency that an abnormality diagnosis is not made.

[0067] As shown in FIG. 6(a), when the specific cylinder stop process is started at time t1, as described above, the engine control unit 300 stops updating the cumulative rotation count Σrev, executing the opposed cylinder misfire detection process, and updating the misfire count value cnt.

[0068] In FIG. 6, as a comparative example, the dashed line shows an example in which updating of the cumulative number of revolutions Σrev, execution of the opposed cylinder misfire detection process, and updating of the misfire count value cnt are continued without being stopped.

[0069] In the comparative example, as shown by the dashed line in FIG. 6(b), the cumulative number of revolutions Σrev continues to increase even while the specific cylinder stop process is being executed. Also, as shown by the dashed line in FIG. 6(c), the misfire count value cnt continues to increase even while the specific cylinder stop process is being executed. Note that while the specific cylinder stop process is being executed, it is determined that the opposed cylinder misfire has occurred every time the opposed cylinder misfire detection process is executed. Therefore, the increase rate of the misfire count value cnt becomes greater than that before time t1. Then, when it is determined that the cumulative number of revolutions Σrev is equal to or greater than the second threshold value X2 at time t2, the misfire count value cnt is compared with the third threshold value X3. As a result, it is determined that a misfire abnormality due to the opposed cylinder misfire has occurred at time t2 based on the fact that the misfire count value cnt is equal to or greater than the third threshold value X3, and an erroneous abnormality diagnosis is made.

[0070] In contrast, in the present embodiment, while the specific cylinder stop process is being performed, the engine control unit 300 stops updating the cumulative number of revolutions Σrev, executing the opposed cylinder misfire detection process, and updating the misfire count value cnt. Therefore, as shown by the solid lines in Figures 6(b) and 6(c), the cumulative number of revolutions Σrev and the misfire count value cnt do not increase.

[0071] Then, as shown in FIG. 6(a), when the specific cylinder stop process ends at time t3, updating of the cumulative number of revolutions Σrev, execution of the opposed cylinder misfire detection process, and updating of the misfire count value cnt are resumed.

[0072] At time t4, when it is determined that the cumulative number of revolutions Σrev is equal to or greater than the second threshold value X2, the misfire count value cnt is compared with the third threshold value X3. In this case, since the misfire count value cnt at time t4 is less than the third threshold value X3, an erroneous abnormality diagnosis is not made.

[0073] <Effects of this embodiment> (1) When executing a specific cylinder stop process in which the behavior of the rotation fluctuation amount of the crankshaft 59 becomes similar to the behavior of the rotation fluctuation amount when an opposed cylinder misfire occurs, the engine control unit 300 stops the opposed cylinder misfire detection process. This makes it possible to suppress erroneous detection that an opposed cylinder misfire has occurred based on the behavior of the rotation fluctuation amount caused by the specific cylinder stop process.

[0074] (2) It is also possible to prevent erroneous abnormality diagnoses based on false positive results. <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.

[0075] An example has been shown in which the update of the cumulative number of revolutions Σrev, the execution of the opposed cylinder misfire detection process, and the update of the misfire count value cnt are stopped when the specific cylinder stop process is being performed. In contrast, if the opposed cylinder misfire detection process is stopped when the specific cylinder stop process is being performed, it is possible to suppress erroneous detection that an opposed cylinder misfire has occurred. Therefore, the same effect can be obtained by stopping the opposed cylinder misfire detection process when the specific cylinder stop process is being performed, without being limited to the above-mentioned aspect. For example, when the specific cylinder stop process is being performed, all misfire detection processes, including the opposed cylinder misfire detection process and other misfire detection processes, may be stopped.

[0076] The vehicle 10 is not limited to a plug-in hybrid vehicle. It may be a hybrid vehicle that does not have a configuration for performing external charging. Also, it may be a vehicle that runs only on the driving force of the engine 50.

[0077] In the above example, the occurrence of a misfire abnormality is diagnosed based on the fact that the misfire count value cnt is equal to or greater than the third threshold value X3 when the cumulative rotation count Σrev is equal to or greater than the second threshold value X2. Alternatively, the misfire rate may be calculated by dividing the misfire count value cnt by the second threshold value X2 when the cumulative rotation count Σrev is equal to or greater than the second threshold value X2. In other words, the occurrence of a misfire abnormality may be diagnosed based on the fact that the misfire rate is equal to or greater than a threshold value.

[0078] The routine of Fig. 5 may be executed by the system control unit 100 to diagnose misfire abnormality. In this case, the system control unit 100 serves as a misfire detection device.

[0079] In the above embodiment, the engine control unit 300, which is the misfire detection device, executes software processing. However, this is merely an example. For example, the misfire detection device may include a dedicated hardware circuit (e.g., ASIC, etc.) that processes at least a part of the software processing executed in the above embodiment. That is, the misfire detection device may have any of the following configurations (a) to (c). (a) The misfire detection device includes a processing circuit that executes all processing according to a program, and a storage device that stores the program. That is, the misfire detection device includes a software execution device. (b) The misfire detection device includes a processing circuit that executes a part of the processing according to a program, and a storage device. Furthermore, the misfire detection device includes a dedicated hardware circuit that executes the remaining processing. (c) The misfire detection device includes a dedicated hardware circuit that executes all processing. Here, the software execution device and / or the dedicated hardware circuit may be multiple. That is, the above processing may be executed by a processing circuitry that includes at least one of one or more software execution devices and one or more dedicated hardware circuits. The storage device that stores the program, i.e., the computer-readable medium, includes any available medium that can be accessed by a general-purpose or dedicated computer. [Explanation of symbols]

[0080] 10. Vehicle 11…First motor generator 12...Second motor generator 30…Battery 31…Connector 40…External power supply 50…Engine 59…Crankshaft 100...System control unit 130…Main switch 131...Accelerator position sensor 132...Brake sensor 133...Vehicle speed sensor 134...Crank position sensor 135…Intake air temperature sensor 136...Water temperature sensor 200…Power control unit 300…Engine control unit

Claims

[Claim 1] Applied to an internal combustion engine with six cylinders, a misfire detection device for an internal combustion engine that performs an opposed cylinder misfire detection process to detect the occurrence of opposed cylinder misfire, which is an abnormality in which a misfire occurs every 360° CA, based on a rotational fluctuation amount of a crankshaft, executes an abnormality diagnosis process for determining that a misfire abnormality has occurred when a misfire count value, which is the number of times that the occurrence of a misfire in the opposed cylinder is determined in the opposed cylinder misfire detection process, becomes equal to or greater than a threshold value before an accumulated number of rotations of the crankshaft reaches a predetermined number of rotations; When a specific cylinder stop process is being executed in which fuel supply to a pair of opposing cylinders whose expansion strokes are 360° CA apart is stopped and fuel is supplied to the remaining cylinders, the opposing cylinder misfire detection process is stopped to stop updating the misfire count value and to stop updating the cumulative number of revolutions. A misfire detection device for internal combustion engines.

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