JP2018096243A - Device for controlling internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent misfire at the time of switching to NOx purge drive and maintain combustion stability.SOLUTION: A device for controlling an internal combustion engine controls closing operation of a throttle valve 17 and EGR valve 33 depending on a degree of misfire based on variation in retard time of ignition when executing NOx purge drive, and properly sets the closing operation of the throttle valve 17 and EGR valve 33 while suppressing misfire regardless of variation in ignition retard time when switching the drive to NOx purge drive.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a control device for an internal combustion engine that maintains the stability of combustion when switching the operation of the internal combustion engine.

  As a technique for reducing nitrogen oxide (NOx) contained in exhaust gas of an internal combustion engine (for example, diesel engine), NOx in exhaust gas is occluded (adsorbed) during operation at a lean air-fuel ratio, and the stoichiometric air-fuel ratio or rich 2. Description of the Related Art There is known an exhaust purification device that includes a NOx storage catalyst that releases and reduces NOx stored during operation at an air-fuel ratio.

  In an exhaust purification device equipped with a NOx storage catalyst, when the lean air-fuel ratio operation continues for a predetermined time, fuel is injected separately from the main injection to temporarily increase the exhaust temperature, and the stored NOx is released. An operation for purifying and reducing (NOx purge operation) is performed, and the regeneration of the NOx storage catalyst is performed (see Patent Document 1).

  In the NOx purge operation, in order to easily enrich the exhaust gas, the throttle valve is throttled to suppress the intake air amount, and the exhaust gas recirculation (EGR) is reduced to ensure the combustion stability. For this reason, in the conventionally proposed technology, when shifting from the normal operation to the NOx purge operation, the throttle valve and the EGR valve are controlled to be closed simultaneously.

  When the internal combustion engine is operated, for example, the ignition delay time changes depending on the composition of the intake air, temperature, pressure, etc., and there is a possibility that misfire may occur. However, in the NOx purge operation, the current situation is that the throttle valve and the EGR valve are controlled to be closed simultaneously regardless of the degree of misfire.

JP 2003-314314 A

  The present invention has been made in view of the above situation, and appropriately closes the throttle valve and the EGR valve during the operation of raising the temperature of the exhaust gas of the internal combustion engine (when switching the operation) regardless of the change in the ignition delay time. An object of the present invention is to provide a control device for an internal combustion engine that can be set and maintain the stability of combustion.

  In order to achieve the above object, a control apparatus for an internal combustion engine according to a first aspect of the present invention communicates with a throttle valve for adjusting an intake air amount in an intake passage communicating with a cylinder of the internal combustion engine and a cylinder of the internal combustion engine. An EGR passage that circulates exhaust gas in the exhaust passage to the intake passage; an EGR valve that adjusts a circulation amount of exhaust gas in the EGR passage; and when the temperature of the exhaust gas discharged from the internal combustion engine is raised, the throttle valve And the valve operating means for closing the EGR valve, the throttle valve by the valve operating means, and the EGR based on the misfiring degree which is the degree of misfiring due to the change in the ignition delay time of the internal combustion engine. And a valve control means for controlling the closing operation of the valve.

  In the present invention according to claim 1, when the temperature of the exhaust gas of the internal combustion engine is raised (NOx purge, regeneration of the diesel particulate filter, warm air, etc.), according to the misfire degree based on the change in the ignition delay time. The closing operation of the throttle valve and the EGR valve can be controlled, and the closing operation of the throttle valve and the EGR valve can be appropriately controlled while suppressing misfire.

  For this reason, during the operation of raising the temperature of the exhaust gas of the internal combustion engine (during operation switching), the closing operation of the throttle valve and the EGR valve is appropriately set to maintain the combustion stability regardless of the change in the ignition delay time. be able to.

  According to a second aspect of the present invention, there is provided the control device for an internal combustion engine according to the first aspect, wherein the valve control means obtains a reference state of a misfire degree of the internal combustion engine, and the reference The closing operation of the throttle valve and the EGR valve is controlled based on the misfire degree with respect to the state.

  According to the second aspect of the present invention, the closing operation of the throttle valve and the EGR valve can be controlled according to the reference state of the misfire degree, and the valve can be closed in a state where no misfire occurs. That is, the order of closing the throttle valve and the EGR valve can be set in a state where no misfire occurs. As for the reference state, for example, the fuel state (ignition delay, misfire) when it is assumed that the throttle valve and the EGR valve are closed in this order is estimated, and a reference index capable of keeping exhaust gas within an allowable range without misfire is mapped. It is obtained by setting.

  According to a third aspect of the present invention, there is provided the control device for an internal combustion engine according to the second aspect, wherein the valve control means is configured such that when the misfire degree is low with respect to the reference state, The EGR valve is closed after the throttle valve is closed.

  In the present invention according to claim 3, when the degree of misfire is low, in order to reduce the inflow of fresh air (in order to suppress leaning) so as to be advantageous for increasing the temperature, in order of the throttle valve and the EGR valve Misfire can be suppressed by closing the valve.

  According to a fourth aspect of the present invention, there is provided the control apparatus for an internal combustion engine according to the second aspect, wherein the valve control means is configured such that when the misfire degree is high with respect to the reference state, The throttle valve is closed after the EGR valve is closed.

  In the present invention according to claim 4, when the degree of misfire is high, the misfire can be suppressed by closing the EGR valve and the throttle valve in this order so that the intake pressure is lowered after the EGR rate is lowered. it can. In this case, since the throttle valve is closed later, the exhaust air / fuel ratio tends to become leaner. Therefore, it is possible to enrich the exhaust air / fuel ratio by adding fuel within a range that does not affect the torque.

  An internal combustion engine control apparatus according to a fifth aspect of the present invention is the internal combustion engine control apparatus according to any one of the first to fourth aspects, wherein the exhaust passage on the downstream side of the EGR passage is arranged in the exhaust passage on the downstream side of the EGR passage. Is provided with a NOx occlusion catalyst that stores NOx when the exhaust air-fuel ratio is lean and reduces and purifies NOx occluded when the exhaust air-fuel ratio is stoichiometric or rich, and raises the temperature of the exhaust gas of the internal combustion engine This operation is a NOx purge operation for releasing NOx stored in the NOx storage catalyst.

  In the present invention according to claim 5, during the NOx purge operation, the closing operation of the throttle valve and the EGR valve can be appropriately controlled while suppressing misfire.

  According to a sixth aspect of the present invention, there is provided a control device for an internal combustion engine according to any one of the first to fifth aspects, wherein the valve control means includes an intake oxygen concentration, an intake air The misfire degree is derived based on at least one of a temperature, an intake pressure expectation, and a fuel injection amount.

  In the present invention according to claim 6, when any one or all of intake oxygen concentration, intake air temperature, intake pressure expectation, and fuel injection amount are changed to a high value, it is determined that the ignition delay becomes small and the misfire degree becomes low. When these change to low, it can be determined that the ignition delay becomes large and the degree of misfire increases.

  The control device for an internal combustion engine according to the present invention appropriately controls the closing operation of the throttle valve and the EGR valve during the operation of raising the exhaust gas temperature of the internal combustion engine (when switching the operation) regardless of the change in the ignition delay time. It becomes possible to maintain the stability of combustion.

It is a schematic block diagram showing the system | strain of the control apparatus of the internal combustion engine which concerns on one Example of this invention. It is a block block diagram of a valve control means. It is a conceptual map explaining the relationship between ignition delay and valve closing timing. It is a flowchart of the control apparatus of the internal combustion engine which concerns on one Example of this invention. It is a time chart of operation | movement of the control apparatus of the internal combustion engine which concerns on one Example of this invention.

  The configuration of an embodiment of the present invention will be described with reference to FIG. FIG. 1 shows a schematic configuration representing a system of a control device for an internal combustion engine according to an embodiment of the present invention.

  As shown in the figure, an exhaust pipe 2 of a multi-cylinder diesel engine (engine) 1 as an internal combustion engine mounted on a vehicle has a NOx storage catalyst 21 as a device to be heated and a diesel particulate filter. 22 is provided. A piston 5 is provided in a cylinder (cylinder) of the engine 1 so as to freely reciprocate, and a combustion chamber 7 is formed between the piston 5 and the cylinder head 6. The crankshaft is driven by the reciprocating motion of the piston 5.

  An intake pipe 12 is connected to the cylinder head 6 via an intake port, and the intake port is opened and closed by an intake valve. Further, the exhaust pipe 2 is connected to the cylinder head 6 through an exhaust port. The exhaust port is opened and closed by an exhaust valve. The cylinder head 6 is provided with a fuel injection valve 9 for directly injecting fuel into the combustion chamber 7 of each cylinder. The fuel injection valve 9 is supplied with fuel from a common rail (not shown). The fuel injection valve 9 is driven based on an injection signal from the valve control means 10, and a predetermined amount of fuel is injected into the combustion chamber 7 (inside the cylinder) at a predetermined time.

  A turbocharger 15 is provided in the middle of the intake pipe 12 and the exhaust pipe 2, and the turbocharger 15 is provided with a turbine on the exhaust pipe 2 side, and a compressor connected to the turbine is provided on the intake pipe 12 side. When the exhaust gas of the engine 1 is sent from the exhaust pipe 2 to the turbocharger 15, the turbine rotates by the flow of the exhaust gas, and the compressor rotates with the rotation of the turbine to supercharge the intake air in the intake pipe 12. .

  An intercooler 16 is disposed in the intake pipe 12 on the downstream side of the turbocharger 15, and the supercharged intake air is cooled by the intercooler 16 and sent to the combustion chamber 7. A throttle valve 17 that opens and closes the intake pipe 12 is provided in the intake pipe 12 on the downstream side of the intercooler 16.

  One end of a high-pressure EGR pipe 31 (EGR passage) is connected to the exhaust pipe 2 on the upstream side of the turbocharger 15, and the other end of the high-pressure EGR pipe 31 is on the downstream side of the throttle valve 17 (downstream side of the turbocharger 15). It communicates with the tube 12. An EGR valve 33 that adjusts the circulation amount of the exhaust gas is provided at a connection portion between the high pressure EGR pipe 31 and the intake pipe 12.

  By opening the EGR valve 33, a part of the exhaust gas flowing through the exhaust pipe 2 upstream of the turbocharger 15 is introduced into the high-pressure EGR pipe 31, and the exhaust gas introduced into the high-pressure EGR pipe 31 is downstream of the turbocharger 15. To the intake pipe 12 on the side. By recirculating a part of the exhaust gas to the intake air, the combustion temperature in the combustion chamber 7 of the engine 1 can be lowered and the amount of NOx emission can be reduced.

  The NOx occlusion catalyst 21 occludes NOx when the exhaust air-fuel ratio is lean, and reduces and purifies NOx occluded when the exhaust air-fuel ratio is stoichiometric or rich. When the lean air-fuel ratio operation is continued for a predetermined time, NOx is stored in the NOx storage catalyst 21. Therefore, post-injection is performed to inject fuel separately from the main injection, and the stored NOx is released to purify and reduce ( NOx purge operation) is performed.

  When the NOx purge operation is performed, in order to easily enrich the exhaust gas, the throttle valve 17 is throttled to suppress the intake amount, and the exhaust gas recirculation (EGR) is reduced to ensure the combustion stability. Yes. For this reason, when shifting from the normal operation to the NOx purge operation, the throttle valve 17 and the EGR valve 33 are closed. The closing operation of the throttle valve 17 and the EGR valve 33 is performed at a predetermined timing according to a command from the valve control means 10 (valve operating means).

  When the internal combustion engine is operated, for example, the ignition delay time changes depending on the composition of the intake air, temperature, pressure, fuel injection amount, and the like. When performing the NOx purge operation, the timing of the closing operation of the throttle valve 17 and the EGR valve 33 can be considered as a background to the change in the ignition delay time. Conventionally, the throttle valve 17 and the EGR valve 33 are closed at the same time in order to eliminate the risk of misfire due to a change in the ignition delay time.

  When performing the NOx purge operation, closing the throttle valve 17 before the EGR valve 33 reduces the increase in fresh air and can suppress the increase in NOx. On the other hand, if the EGR valve 33 is closed later, there is a risk of misfire.

  In the NOx purge operation, when there is a request to suppress the air amount, if there is no risk of misfire (if the degree of misfire is low), the throttle valve 17 is closed before the EGR valve 33 in order to reduce fresh air. Is preferred. When the degree of misfire increases, the throttle valve 17 and the EGR valve 33 are simultaneously closed by closing the EGR valve 33 early. Furthermore, when the degree of misfire increases, it is preferable to close the EGR valve 33 first. In this case, since the start timing of the NOx purge operation is determined, it is preferable to delay the closing timing of the throttle valve 17 so that the EGR valve 33 is closed before the throttle valve 17.

  As described above, when the NOx purge operation is performed, the misfire is controlled by controlling the closing operation of the throttle valve 17 and the EGR valve 33 with respect to the change in the ignition delay time (with respect to the misfire degree that is a risk of misfire). Can be eliminated. In the present embodiment, based on such a background, even if the ignition delay time changes, the closing operation of the throttle valve 17 and the EGR valve 33 is appropriately controlled to eliminate misfire, and the combustion of the NOx purge operation is prevented. I try to maintain stability.

  The valve control means will be specifically described with reference to FIGS. FIG. 2 shows a block configuration of the valve control means 10, and FIG. 3 shows a map concept for explaining the relationship between the ignition delay (degree of misfire) and the closing timing of the throttle valve 17 and the EGR valve 33.

  As shown in FIG. 2, the valve control means 10 is provided with a valve operating means 25 that outputs a closing operation command to the throttle valve 17 and the EGR valve 33. Further, the valve control means 10 includes a misfire degree deriving means 26 for deriving an expected ignition delay time, and a reference setting means 27 for obtaining a reference state of the misfire degree.

  In the misfire degree deriving means 26, as shown in FIG. 3, for example, when the throttle valve 17 is closed and then the EGR valve 33 is closed, the estimated intake oxygen concentration, the estimated intake air temperature, the estimated intake pressure, the fuel injection amount Based on the above, an expected ignition delay (expected ignition delay time) is obtained. In the reference setting means 27, a reference state (reference ignition delay A: reference state of misfire degree) that allows exhaust gas performance to fall within an allowable range without misfire is set.

  Although omitted in FIG. 1, the engine 1 includes sensors such as an intake air temperature sensor, an intake manifold pressure sensor, a water temperature sensor, an air flow sensor, an exhaust temperature sensor, a throttle opening sensor, and the like. The estimated intake pressure and the fuel injection amount are detected and calculated based on the detection information of these sensors.

  As shown in FIG. 2, the valve control means 10 determines whether the misfire degree is low or high based on the estimated intake oxygen concentration, intake temperature, estimated intake pressure, and fuel injection amount with respect to the reference state of the misfire degree. And determining means 28 for sending the determination result to the valve operating means 25 is provided.

  The closing operation of the throttle valve 17 and the EGR valve 33 in the NOx purge operation will be specifically described based on FIG. 3, FIG. 4, and FIG.

  FIG. 4 is a flowchart of an internal combustion engine control apparatus according to an embodiment of the present invention. FIG. 5 is an EGR opening degree, throttle opening degree, EGR rate (intake manifold) in the internal combustion engine control apparatus according to an embodiment of the present invention, It is a time chart explaining the passage time change of intake manifold pressure, fresh air flow, and catalyst air-fuel ratio. 5A shows a state in which the misfire degree is lower than the reference ignition delay A in FIG. 3 (a), FIG. 5B shows the misfire degree in FIG. 3 almost equal to the reference ignition delay A (b). In this case, FIG. 5 (c) shows a state (c) in FIG. 3 where the misfire degree is higher than the reference ignition delay.

  As shown in FIG. 4, it is determined whether or not there is a request for NOx purge operation in step S1, and if it is determined that there is a request for NOx purge operation in step S1, the situation of the misfire degree is determined in step S2. The That is, the misfire degree status is grasped based on the estimated intake oxygen concentration, the estimated intake air temperature, the estimated intake pressure, and the fuel injection amount in the reference operation (the throttle valve and the EGR valve are simultaneously closed in this example).

  After the misfire degree is grasped, in step S3, the misfire degree with respect to the reference state (reference ignition delay A in FIG. 4) is compared, that is, it is determined whether the misfire degree is lower than the reference state. For example, assuming that the intake oxygen concentration in the reference state (reference ignition delay A in FIG. 4), the intake temperature, the intake pressure, and the fuel injection amount are respectively medium, the fuel injection amount remains medium. When the expectation of the intake oxygen concentration, the intake air temperature, and the expectation of the intake pressure increase, the misfire degree becomes lower than the reference state (for example, (a) in FIG. 4).

  If it is determined in step S3 that the misfire degree is lower than the reference state, in step S4, the throttle valve 17 is closed, and then the EGR valve 33 is closed, and the process returns. That is, since the assumed ignition delay is short and the risk of misfire is small, misfire does not occur even if the EGR valve 33 is closed after the throttle valve 17 is closed.

  In this case, as shown in FIG. 5A, the throttle opening is fully closed at time t1 when the NOx purge operation is started, and the EGR opening is fully closed at time t2 when a predetermined time has elapsed. Prior to time t2, the catalyst air-fuel ratio becomes rich, the EGR rate is maintained high, the intake manifold pressure is reduced, and an increase in fresh air is avoided. At time t3, the NOx purge operation ends, the EGR opening and the throttle opening increase, the intake manifold pressure increases, and the catalyst air-fuel ratio becomes lean.

  For this reason, the throttle valve 17 and the EGR valve 33 can be closed so that misfire does not occur in accordance with a state where the risk of misfire is small. In addition, the air-fuel ratio of the catalyst can be enriched at an early stage while avoiding an increase in fresh air (the post injection amount is reduced, and the outflow of the reducing agent at the catalyst can be suppressed).

  Returning to the flowchart of FIG. 4, if it is determined in step S3 that the misfire degree is not lower than the reference state, it is determined in step S5 whether the misfire degree is substantially equal to the reference state. If the fuel injection amount remains medium and the intake air oxygen concentration, intake air temperature, and intake pressure are medium, the misfire degree is substantially equal to the reference state (for example, (b) in FIG. 4). Specifically, the misfire degree is slightly higher.

  If it is determined in step S5 that the misfire degree is substantially equal to the reference state, the throttle valve 17 and the EGR valve 33 are closed substantially simultaneously in step S6. Actually, since the misfire degree is slightly higher, the throttle valve 17 is closed after a little delay, and a return is made. Since the misfire degree is substantially equal to the reference state and the throttle valve 17 and the EGR valve 33 are closed at the same time, no misfire occurs.

  In this case, as shown in FIG. 5B, the EGR opening is fully closed at time t1 when the NOx purge operation is started, and the throttle opening is fully closed at time t2 at substantially the same time. The catalyst air-fuel ratio becomes rich, the EGR rate decreases, the intake manifold pressure decreases, and an increase in fresh air can be avoided. At time t3, the NOx purge operation ends, the EGR opening and the throttle opening increase, the intake manifold pressure increases, and the catalyst air-fuel ratio becomes lean.

  For this reason, the throttle valve 17 and the EGR valve 33 can be closed and operated so as to prevent misfire in accordance with the reference state that is the reference ignition delay.

  Returning to the flowchart of FIG. 4, if it is determined in step S5 that the misfire degree is not substantially equal to the reference state, it is determined in step S7 whether the misfire degree is higher than the reference state. If the fuel injection amount remains medium and the likelihood of the intake oxygen concentration, the intake air temperature, and the intake pressure are low, the misfire degree becomes higher than the reference state (for example, (c) in FIG. 4).

  If it is determined in step S7 that the degree of misfire is higher than the reference state, in step S8, the EGR valve 33 is closed and then the throttle valve 17 is closed, and the process returns. If it is determined in step S7 that the misfire degree is not higher than the reference state, a return is made. That is, since the assumed ignition delay is long and there is a high risk of misfire, the misfire can be prevented by closing the throttle valve 17 after the EGR valve 33 is closed.

  In this case, as shown in FIG. 5C, the EGR opening is fully closed at time t1 when the NOx purge operation is started, and the throttle opening is fully closed at time t2 when a predetermined time has elapsed. The catalyst air-fuel ratio becomes rich immediately before reaching time t2, the EGR rate decreases before reaching time t2, the intake manifold pressure is maintained until time t2, and fresh air slightly increases. At time t3, the NOx purge operation ends, the EGR opening and the throttle opening increase, the intake manifold pressure increases, and the catalyst air-fuel ratio becomes lean.

  For this reason, since there is a high risk of misfire, the throttle valve 17 and the EGR valve 33 can be closed to prevent misfire by reducing the intake manifold pressure after the EGR rate is lowered and preventing misfire. In this case, since the fresh air flow rate temporarily increases, it is possible to enrich the exhaust air-fuel ratio by adding fuel within a range that does not affect the torque. As a result, it is possible to cover the delay in enrichment with the highest priority given to the prevention of torque reduction due to misfire.

  As described above, when the NOx purge operation is performed, the closing operation of the throttle valve 17 and the EGR valve 33 is controlled according to the misfire degree based on the change in the ignition delay time, and the throttle valve 17 and the EGR are controlled while suppressing the misfire. The closing operation of the valve 33 can be appropriately controlled.

  For this reason, at the time of switching to the NOx purge operation (at the time of operation switching), the closing operation of the throttle valve 17 and the EGR valve 33 is appropriately set regardless of the change in the ignition delay time to prevent misfire, and combustion stability Can be maintained.

  Then, the closing operation of the throttle valve 17 and the EGR valve 33 can be controlled according to the reference state of the misfire degree, and the closing order of the throttle valve 17 and the EGR valve 33 can be set in a state where no misfire occurs. .

  That is, when the degree of misfiring is low, the valves are closed in the order of the throttle valve 17 and the EGR valve 33 in order to reduce the inflow of fresh air so as to be advantageous for NOx purge (in order to suppress leaning). Misfire can be suppressed. If the degree of misfire is high, the misfire can be suppressed by closing the valves in the order of the EGR valve 33 and the throttle valve 17 so that the intake pressure is lowered after the EGR rate is lowered.

  In the above-described embodiment, the NOx purge operation of the NOx storage catalyst 21 is described as an example of the operation for raising the temperature of the exhaust of the engine. However, as the operation for raising the temperature of the exhaust, the diesel particulate filter 22 is used. Regeneration operation and warm-up operation of the engine 1 can be applied.

  The present invention can be used in the industrial field of control devices for internal combustion engines.

1 Multi-cylinder diesel engine (engine)
2 Exhaust pipe 5 Piston 6 Cylinder head 7 Combustion chamber 9 Fuel injection valve 10 Valve control means 12 Intake pipe 15 Turbocharger 16 Intercooler 17 Throttle valve 21 NOx storage catalyst 22 Diesel particulate collection filter 31 High pressure EGR pipe 33 EGR valve

Claims (6)

A throttle valve for adjusting the amount of intake air in the intake passage communicating with the cylinder of the internal combustion engine;
An EGR passage that circulates exhaust gas in an exhaust passage communicating with a cylinder of the internal combustion engine to the intake passage;
An EGR valve that adjusts a circulation amount of exhaust gas in the EGR passage;
A valve operating means for closing the throttle valve and the EGR valve when raising the temperature of the exhaust gas discharged from the internal combustion engine;
The throttle valve by the valve operating means and the valve control means for controlling the closing operation of the EGR valve based on the misfire degree which is the degree of misfire due to the change in the ignition delay time of the internal combustion engine. A control device for an internal combustion engine. The control apparatus for an internal combustion engine according to claim 1,
The valve control means includes
A control apparatus for an internal combustion engine, characterized in that a reference state of a misfire degree of the internal combustion engine is obtained and a closing operation of the throttle valve and the EGR valve is controlled based on the misfire degree with respect to the reference state. The control apparatus for an internal combustion engine according to claim 2,
The valve control means includes
The control device for an internal combustion engine, wherein when the misfire degree is low with respect to the reference state, the EGR valve is closed after the throttle valve is closed. The control apparatus for an internal combustion engine according to claim 2,
The valve control means includes
The control apparatus for an internal combustion engine, wherein when the misfire degree is high with respect to the reference state, the throttle valve is closed after the EGR valve is closed. The control device for an internal combustion engine according to any one of claims 1 to 4,
The exhaust passage on the downstream side of the EGR passage is provided with a NOx storage catalyst that stores NOx when the exhaust air-fuel ratio is lean and reduces and purifies NOx stored when the exhaust air-fuel ratio is stoichiometric or rich. And
The control device for an internal combustion engine, wherein the operation for raising the temperature of the exhaust gas of the internal combustion engine is a NOx purge operation for releasing NOx stored in the NOx storage catalyst. The control apparatus for an internal combustion engine according to any one of claims 1 to 5,
The valve control means includes
The control apparatus for an internal combustion engine, wherein the misfire degree is derived based on at least one of an intake oxygen concentration, an intake air temperature, an intake pressure expectation, and a fuel injection amount.

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