JP2016014354A - Internal combustion engine control unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To execute appropriate accidental fire countermeasures in response to a deceleration state step by step and efficiently suppress an accidental fire if a vehicle decelerates during EGR.SOLUTION: An ECU 50 functions to execute a first accidental fire countermeasure control, a second accidental fire countermeasure control, and an accidental fire variable control. In the first accidental fire countermeasure control, the ECU 50 suppresses an accidental fire by an increase in a fuel injection quantity, setting of ignition timing to a retard position or the like without changing valve characteristics of an intake valve 14. In the second accidental fire countermeasure control, the ECU 50 suppresses an accidental fire by a control to change the valve characteristics of the intake valve 14. In the accidental fire countermeasure variable control, the ECU 50 executes only the first accidental fire countermeasure control if residual EGR gas flowing in each cylinder is present during deceleration and an engine load is higher than a load determination value A, and executes at least the second accidental fire countermeasure control if the residual EGR gas flowing in each cylinder is present during deceleration and the engine load is lower than the load determination value A.

Description

  The present invention relates to a control device for an internal combustion engine applied to an automobile or the like, and more particularly to a control device for an internal combustion engine equipped with an EGR mechanism.

  As a related technique, for example, as disclosed in Patent Document 1 (Japanese Patent Laid-Open No. 2013-011271), a control device for an internal combustion engine provided with an EGR (Exhaust Gas Recirculation) mechanism is known. In this related technology, the amount of EGR gas in the cylinder is estimated, and the misfire limit EGR gas amount is calculated based on the operating state of the engine. If there is a possibility of misfire, the misfire is suppressed by combining the fuel injection amount increase control, the intake valve small lift control, and the like.

JP 2013-011271 A

  In the related art described above, the misfire limit EGR gas amount is calculated based on the operating state of the engine, and control to be executed is selected from a plurality of types of misfire avoidance control based on the calculation result. However, in the related art, when deceleration is performed during EGR, for example, the optimum type of misfire avoidance control to be selected according to the state of deceleration is not specifically studied. In addition, the control that maximizes the misfire suppression effect has not been specifically studied, and there is room for improvement. For this reason, in the related technology, there is a problem that it is difficult to efficiently execute effective misfire countermeasures when a situation in which misfire is likely to occur due to deceleration during EGR occurs.

  The present invention provides a control device for an internal combustion engine capable of effectively suppressing misfire by executing appropriate misfire countermeasures stepwise in accordance with the state of deceleration when deceleration is performed during EGR. There is.

A first invention is an EGR mechanism capable of recirculating external EGR gas from an exhaust system of an internal combustion engine to an intake system;
A variable valve mechanism that can change the valve characteristics including the lift amount of the intake valve;
A controller for controlling the EGR mechanism and the variable valve mechanism,
The controller is
A first misfire countermeasure that executes any one or more of a change in fuel injection amount, a change in fuel injection timing, a change in ignition timing, and a tumble flow reduction control without changing the valve characteristic of the intake valve. Means,
Second misfire countermeasure means for suppressing misfire by control for changing valve characteristics of the intake valve including control for reducing the lift amount of the intake valve;
Misfire prediction means for predicting the possibility of misfire based on the amount of in-cylinder EGR when the internal combustion engine is decelerated and there is external EGR gas flowing into the cylinder;
A determination value setting means for setting a load determination value based on an external EGR amount when the occurrence of misfire is predicted by the misfire prediction means;
Control selection means for operating the first misfire countermeasure means when the engine load is larger than the load judgment value, and for activating at least the second misfire countermeasure means when the engine load is smaller than the load judgment value; I have.

  According to the second invention, the control selection means is configured to operate only the second misfire countermeasure means when the engine load is smaller than the load determination value.

  According to a third aspect of the invention, the control selection means is configured to activate both the first misfire countermeasure means and the second misfire countermeasure means when the engine load is smaller than the load determination value.

According to a fourth aspect of the invention, the load determination value is higher in the EGR region determined based on the engine load and the external EGR amount than in the reference region, which is a high load and low EGR amount region. A first region that is a low load and high EGR amount region, a second region that is a lower load and higher EGR amount region than the first region, and a lower load and higher load than the second region A third region that is an EGR amount region;
The control selection means determines which region the operating state belongs to based on the engine load and the external EGR amount, and when belonging to the first region, operates only the first misfire countermeasure means, When belonging to the second area, only the second misfire countermeasure means is activated, and when belonging to the third area, both the first misfire countermeasure means and the second misfire countermeasure means are activated.

  According to a fifth aspect of the invention, the second misfire countermeasure means includes a control for reducing the lift amount of the intake valve and the opening timing of the intake valve as compared to when the second misfire countermeasure means is not in operation. Control for retarding and control for advancing the closing timing of the intake valve are executed.

  According to the sixth aspect of the invention, the second misfire countermeasure means performs control for reducing the lift amount of the intake valve as compared to when the first misfire countermeasure means is not operated, and opens the intake valve. One of a control for retarding the valve timing and a control for advancing the closing timing of the intake valve is executed.

  According to a seventh aspect, the control device calculates a timing at which the discharge of the external EGR gas remaining in the intake system ends, and stops the first misfire countermeasure means and the second misfire countermeasure means when the timing comes. It is configured to do.

  According to an eighth aspect of the invention, the load determination value is changed based on the engine speed.

  In the ninth aspect, the minimum load that is reached during deceleration is predicted based on the operation state of the accelerator, and the predicted load is used as the engine load by the control selection means.

  According to the first invention, misfire is determined based on the in-cylinder EGR amount at the time of deceleration, and when there is a possibility of misfire, the external EGR limit is estimated from the load state, and the first misfire countermeasure means and the first 2 Selection of misfire countermeasure means can be appropriately switched. In other words, the second misfire countermeasure means for reducing the lift amount of the intake valve has a high misfire suppression effect, but reduces the intake air amount, which may cause a torque step. For this reason, when the engine load at the time of deceleration is large, the control selection means can first take the countermeasure against misfire while suppressing the torque step by selecting the first misfire countermeasure means. On the other hand, when the engine load during deceleration is small, the second misfire countermeasure means having a high misfire suppression effect can be selected. Therefore, for example, when deceleration is performed during EGR, an appropriate misfire countermeasure can be executed in stages according to the deceleration state, and misfire can be efficiently suppressed. Further, by selecting the misfire countermeasure means according to the situation, it is possible to minimize the reduction in fuel consumption, drivability, torque limitation, etc. that are likely to occur due to the individual means.

  According to the second aspect of the present invention, for example, when it is determined that the influence of the fuel consumption reduction is larger than the effect of the first misfire countermeasure means, the first misfire countermeasure means is avoided from being forcibly used during sudden deceleration. Can do.

  According to the third invention, when the external EGR limit is greatly reduced, the second misfire countermeasure means having a high misfire suppression effect can be selected in addition to the first misfire countermeasure means. As a result, the maximum misfire suppression effect can be obtained by the synergistic effect of the two types of misfire countermeasures, and misfire can be stably suppressed even in a low load and high external EGR amount.

  According to the fourth aspect, the first to third areas can be set according to the degree of necessity of countermeasures against misfire. Based on the region to which the operating state belongs, it is possible to select whether to use only the first misfire countermeasure means, only the second misfire countermeasure means, or both misfire countermeasure means. Thus, for example, when deceleration is performed during EGR, the control can be switched to three stages according to the state of deceleration. Therefore, the control can be adapted with high accuracy to the degree of necessity of misfire countermeasures.

  According to the fifth aspect, the second misfire countermeasure means includes control for reducing the lift amount of the intake valve, control for retarding the valve opening timing of the intake valve, and control for advancing the valve closing timing of the intake valve. Are executed in combination. Therefore, the synergistic effect of these three types of control can sufficiently compensate for the shortage of ignition energy that is largely insufficient in a low load and high EGR amount state, and can greatly improve the external EGR limit.

  According to the sixth aspect of the invention, the second misfire countermeasure means executes control to reduce the lift amount of the intake valve, retards the opening timing of the intake valve, and advances the closing timing of the intake valve. Either one of the cornering controls can be executed. Thereby, the external EGR limit can be improved.

  According to the seventh aspect, the first misfire countermeasure means and the second misfire countermeasure means can be stopped at an appropriate timing when the residual EGR gas in the intake system runs out. Therefore, misfire caused by the residual EGR gas can be stably suppressed while avoiding excessive or insufficient misfire countermeasures.

  According to the eighth aspect of the invention, it is possible to improve the consistency between the load determination value and the misfire countermeasure means by reflecting the influence of the change in the engine speed on the load determination value.

  According to the ninth aspect, the misfire countermeasure means can be selected by predicting the minimum load to be reached by deceleration. Therefore, for example, even during sudden deceleration, it is possible to select in advance a misfire countermeasure means that matches the final ultimate load. That is, the response delay of the misfire countermeasure can be suppressed, and the necessary misfire countermeasure can be executed at an appropriate timing.

It is a block diagram for demonstrating the system configuration | structure of the engine by Embodiment 1 of this invention. In Embodiment 1 of this invention, it is explanatory drawing which shows an example of the valve characteristic of the intake valve implement | achieved by 2nd misfire countermeasure control. It is a characteristic line figure which shows the lift amount of the intake valve implement | achieved by small lift amount control. It is a characteristic diagram which shows the relationship between the lift amount of an intake valve, and a tumble ratio. It is explanatory drawing which shows typically the influence which the presence or absence of small lift amount control has on the spark between the plug gaps of a spark plug. It is a characteristic diagram which shows the influence which the presence or absence of small lift amount control has on the secondary voltage waveform of ignition. It is a characteristic diagram which shows the relationship between the lift amount of an intake valve, and an external EGR limit. It is a characteristic diagram which shows the relationship between energy required for ignition, engine load, and in-cylinder EGR rate. It is a characteristic diagram which shows the relationship between IVO and in-cylinder temperature. It is a characteristic diagram which shows the state of the engine load and pump loss which increase by IVO retardation control. It is a characteristic diagram which shows the relationship between an engine load and an internal EGR rate. It is a characteristic diagram which shows the relationship between IVO and an external EGR limit. It is a characteristic diagram which shows the relationship between IVC and the flow velocity between plug gaps. It is a characteristic diagram which shows the relationship between IVC and in-cylinder temperature. It is a characteristic diagram which shows the relationship between IVC and an external EGR limit. It is explanatory drawing which shows the effect of 2nd misfire countermeasure control compared with a normal state. It is explanatory drawing which shows the effect at the time of performing each 1st misfire countermeasure control and 2nd misfire countermeasure control independently, and the effect at the time of combining. It is explanatory drawing which shows typically an example of the state in which deceleration is performed during EGR. In Embodiment 1 of this invention, it is a timing chart which shows an example of misfire countermeasure variable control. In Embodiment 1 of this invention, it is a timing chart which shows another example of misfire countermeasure variable control. In Embodiment 2 of this invention, it is explanatory drawing which shows the division of the EGR area | region for switching selection of misfire countermeasure control. It is explanatory drawing which shows the three-dimensional data map which classifies an EGR area | region based on an engine load, an external EGR rate, and an engine speed. In Embodiment 2 of this invention, it is a flowchart which shows an example of the control performed by ECU. It is a timing chart which shows misfire countermeasure variable control by Embodiment 2 of this invention. In Embodiment 3 of this invention, it is a flowchart which shows an example of the control performed by ECU.

Embodiment 1 FIG.
[Configuration of Embodiment 1]
Hereinafter, Embodiment 1 of the present invention will be described with reference to FIGS. FIG. 1 is a configuration diagram for explaining a system configuration of an engine according to Embodiment 1 of the present invention. The system according to the present embodiment includes an engine 10 as an internal combustion engine. Although FIG. 1 illustrates a four-cylinder engine, the present invention can be applied to an internal combustion engine having an arbitrary number of cylinders. Each cylinder 12 of the engine 10 includes a fuel injection valve, an intake valve 14, an exhaust valve 16, a spark plug 18 and the like (not shown).

  The engine 10 also includes an intake passage 20 that sucks intake air into each cylinder 12 and an exhaust passage 22 that discharges exhaust gas from each cylinder 12. The intake passage 20 is provided with a throttle valve 24 for adjusting the intake air amount. A catalyst 26 for purifying exhaust gas is provided in the exhaust passage 22. A supercharger 28 is provided between the intake passage 20 and the exhaust passage 22 to supercharge intake air using exhaust pressure. The supercharger 28 includes a turbine 28 a disposed in the exhaust passage 22 and a compressor 28 b disposed in the intake passage 20. The present invention is also applicable to a naturally aspirated internal combustion engine that is not equipped with a supercharger.

  The engine 10 includes an LPL (Low Pressure Loop) type EGR mechanism 30 that can recirculate external EGR gas from an exhaust system to an intake system. The EGR mechanism 30 includes an EGR passage 32 and an EGR valve 34. The EGR passage 32 takes out the exhaust gas from the exhaust passage 22 on the downstream side of the catalyst 26, and causes this exhaust gas to flow into the intake passage 20 on the upstream side of the compressor 28b as external EGR gas. The EGR valve 34 adjusts the flow rate (EGR amount) of the external EGR gas flowing through the EGR passage 32.

  The engine 10 also includes a variable valve mechanism 36 that can change the valve characteristics of the intake valve 14. Here, the valve characteristic means a parameter controlled by the second misfire countermeasure control described later, among the lift amount, the valve opening timing (IVO) and the valve closing timing (IVC) of the intake valve 14. As the variable valve mechanism 36, for example, as described in Japanese Patent Application Laid-Open No. 2006-97602, a variable valve operating mechanism that can change the operating angle with the opening / closing timing of the valve may be used. The variable valve mechanism 36 is a combination of a variable valve timing system (VVT) that changes the phase and a variable valve mechanism of variable working angle as described in, for example, Japanese Patent Application Laid-Open No. 2000-87769. You may comprise by.

  The system according to the present embodiment includes a sensor system 40 that detects the operating state of the engine 10 and the vehicle, and an ECU (Electronic Control Unit) 50 as a control device that controls the engine 10 based on the output of the sensor system 40. ing. The sensor system 40 includes various sensors including a crank angle sensor, an air flow sensor, an accelerator opening sensor, and the like. The crank angle sensor is a sensor for detecting the rotational speed of the crankshaft (engine rotational speed) and the crank angle. The air flow sensor detects an intake air amount, and the accelerator opening sensor detects a driver's accelerator operation amount (accelerator opening).

  The ECU 50 includes a storage circuit in which various control programs are stored in advance, an arithmetic processing unit (CPU) that executes control based on the control programs, and an input / output circuit that inputs and outputs signals to the arithmetic processing unit. It has. Each sensor of the sensor system is connected to the input side of the ECU 50. Various actuators including a fuel injection valve and a spark plug 18, an EGR valve 34, a variable valve mechanism 36, and the like of each cylinder are connected to the output side of the ECU 50.

  The ECU 50 calculates the intake air amount, the engine rotation speed, the engine load, and the like based on the output of the sensor system 40, and drives each actuator based on these calculation results. Further, the ECU 50 determines whether or not an EGR request is generated based on the operating state of the engine 10. When an EGR request is generated, the target EGR amount is set based on the operating state, and the opening degree of the EGR valve 34 is feedback-controlled so that the actual EGR amount follows the target EGR amount.

[Features of Embodiment 1]
When the vehicle is decelerated during EGR, the ECU 50 closes the EGR valve 34 and stops the EGR. However, the residual EGR gas remaining in the intake passage 20 on the downstream side of the EGR valve 34 causes a phenomenon (EGR delay) that flows into the cylinder even after the EGR is stopped, causing a misfire. In particular, in the LPL type EGR mechanism 30, the amount of residual EGR gas is larger than that of, for example, an HPL (High Pressure Loop) type EGR mechanism, and thus misfire is easily induced. For this reason, it is preferable to execute some misfire countermeasure control when residual EGR gas is present during deceleration.

  However, the capability required for misfire countermeasure control varies depending on the degree of deceleration. Therefore, in the present embodiment, when there is residual EGR gas at the time of deceleration, the misfire countermeasure variable control that selects one or both of the first misfire countermeasure control and the second misfire countermeasure control according to the degree of deceleration. Run. Hereinafter, these controls will be described. In the present specification, the first misfire countermeasure control and the second misfire countermeasure control may be collectively referred to as “misfire countermeasure control”.

(First misfire countermeasure control)
The first misfire countermeasure control is to suppress misfire by using another control without changing the valve characteristic of the intake valve 14, and corresponds to the first misfire countermeasure means of the present embodiment. Examples of the first misfire countermeasure control include control for enriching the air-fuel ratio from the normal state (that is, control for increasing the fuel injection amount), control for retarding the ignition timing from the normal state, and the like. Here, the normal state is a state corresponding to when the first misfire countermeasure control is not executed.

  In the system in which fuel is directly injected into the cylinder, control for retarding the fuel injection timing from the normal state may be employed as the first misfire countermeasure control. Further, in a system including a tumble control valve (TCV) that generates a tumble flow in the cylinder, control for reducing the tumble ratio from the normal state by TCV may be employed as the first misfire countermeasure control. Furthermore, the first misfire countermeasure control may be configured by combining a part of each of the above controls.

(Second misfire countermeasure control)
The second misfire countermeasure control is to suppress misfire by changing the valve characteristic of the intake valve 14 using the variable valve mechanism 36, and corresponds to the second misfire countermeasure means of the present embodiment. FIG. 2 is an explanatory diagram showing an example of the valve characteristic of the intake valve realized by the second misfire countermeasure control in the first embodiment of the present invention. As shown in this figure, in the second misfire countermeasure control, at least the lift amount, preferably all of the three parameters including the lift amount of the intake valve 14 and IVO and IVC are controlled. Hereinafter, the control of each parameter is referred to as small lift amount control, IVO retardation control, and IVC advance control.

(Small lift control)
Next, with reference to FIG. 3 to FIG. 7, the small lift amount control and the effect thereof will be described. FIG. 3 is a characteristic diagram showing the lift amount of the intake valve realized by the small lift amount control. FIG. 4 is a characteristic diagram showing the relationship between the lift amount of the intake valve and the tumble ratio. FIG. 5 is an explanatory diagram schematically showing the influence of the presence or absence of the small lift amount control on the spark between the plug gaps of the spark plug. FIG. 6 is a characteristic diagram showing the influence of the presence or absence of small lift amount control on the secondary voltage waveform of ignition. FIG. 7 is a characteristic diagram showing the relationship between the lift amount of the intake valve and the external EGR limit. The external EGR limit means the maximum external EGR rate that can be realized without causing misfire.

  In the small lift amount control, as shown in FIGS. 2 and 3, the lift amount of the intake valve 14 is set to a small lift amount smaller than the normal state (normal lift amount). The normal lift amount is a lift amount used when the second misfire countermeasure control is not executed. When the lift amount decreases, the tumble flow (tumble ratio) in the cylinder decreases as shown in FIG. As a result, when the air-fuel mixture is ignited, as shown in FIG. 5, the flow velocity of the airflow passing between the plug gaps of the spark plug 18 is lowered, so that the spark between the plug gaps is hardly flowed by the airflow. That is, since the spark break between the plug gaps is suppressed, as shown in FIG. 6, the discharge maintaining time becomes long.

  Therefore, according to the small lift amount control, for example, in a case where a large amount of energy is required for ignition, such as when the EGR rate is high at a low load, dispersion of ignition energy is suppressed, and high ignition of the air-fuel mixture is achieved. Energy can be added locally. Thereby, the certainty of ignition can be improved, misfire can be suppressed, and the external EGR limit can be improved. Further, as shown in FIG. 7, the small lift amount control can greatly increase the external EGR limit only by slightly decreasing the lift amount, and has high sensitivity to the external EGR limit.

(IVO retard angle control)
Next, IVO retardation control and its effect will be described with reference to FIGS. FIG. 8 is a characteristic diagram showing a relationship among energy required for ignition, engine load, and in-cylinder EGR rate. FIG. 9 is a characteristic diagram showing the relationship between IVO and in-cylinder temperature. FIG. 10 is a characteristic diagram showing the state of the engine load and the pump loss that are increased by the IVO retardation control. FIG. 11 is a characteristic diagram showing the relationship between the engine load and the internal EGR rate. FIG. 12 is a characteristic diagram showing the relationship between the IVO and the external EGR limit.

  In a state where the EGR rate is high, the oxygen concentration in the cylinder decreases, so that the energy required for ignition increases. As a result, the ignition energy is relatively short, and misfire is likely to occur. In particular, in a state where the EGR rate is high at a low load, as shown in FIG. 8, much energy is required to raise the in-cylinder temperature to a temperature at which the air-fuel mixture can be ignited. Therefore, in the IVO retardation control, as shown in FIGS. 2 and 9, the IVO is retarded from the normal state (normal IVO) (so-called delay opening control). The normal IVO is an IVO used when the second misfire countermeasure control is not executed. According to the IVO retardation control, the piston descends with the intake valve 14 closed, and the cylinder volume increases, so that the air sucked into the cylinder expands, and the pressure and temperature of the air decrease. . As a result, the temperature difference between the wall surface of the combustion chamber and the air increases, and the amount of heat received from the wall surface to the air increases, so that the in-cylinder temperature can be raised from the normal state as shown in FIG. As a result, the temperature of the air-fuel mixture can be increased and ignition can be easily performed, and the external EGR limit can be improved.

  In addition, the biggest factor that the external EGR limit decreases in the low load region is that the internal EGR rate is high. Since the amount of fresh air is small in the low load region, the internal EGR rate tends to be relatively high even if the internal EGR amount is minimized by eliminating the overlap period of the intake valve and the exhaust valve. On the other hand, if the IVO is retarded, the pump loss and the engine load at the same torque increase as shown in FIG.

  As a result, since the amount of fresh air increases as the engine load increases, the internal EGR rate can be relatively lowered as shown in FIG. Therefore, according to the IVO retard angle control, even if the misfire limit of the in-cylinder EGR rate obtained by combining the external EGR rate and the internal EGR rate is constant, the internal EGR rate can be reduced and the external EGR limit can be improved accordingly. it can. In addition, as shown in FIG. 12, the IVO retardation control can increase the external EGR limit as the IVO is retarded, and has high sensitivity to the external EGR limit.

(IVC advance angle control)
Next, IVC advance angle control and its effects will be described with reference to FIGS. FIG. 13 is a characteristic diagram showing the relationship between the IVC and the flow velocity between the plug gaps. FIG. 14 is a characteristic diagram showing the relationship between IVC and in-cylinder temperature. FIG. 15 is a characteristic diagram showing the relationship between IVC and external EGR limit. In the IVC advance angle control, as shown in FIGS. 2 and 13, the IVC is advanced from the normal state (normal IVC) (so-called early closing control). The normal IVC is an IVC that is used when the second misfire countermeasure control is not executed, and is generally set on the retard side from the bottom dead center.

  According to the IVC advance angle control, as shown in FIG. 13, the intake stroke can be completed early, and the flow velocity of the gas in the cylinder can be quickly attenuated. That is, if the intake stroke is completed early, the decay time of the gas in the cylinder becomes long, so that the gas flow rate can be sufficiently reduced. Thereby, compared with a normal state, the flow velocity of the airflow which flows between plug gaps at the time of ignition falls. Therefore, for the same reason as the small lift amount control, the certainty of ignition can be improved and the external EGR limit can be improved. Further, as shown in FIG. 15, the IVC advance angle control can increase the external EGR limit as the IVC is advanced, and has high sensitivity to the external EGR limit.

  In IVC advance control, it is preferable to advance IVC from the normal state and set it near the bottom dead center. Here, “near” means a small crank angle range in which the same effect as when IVC is set to the bottom dead center can be obtained. Since the actual compression ratio is improved by advancing the IVC to the vicinity of the bottom dead center, as shown in FIG. 14, the temperature of the air-fuel mixture at the time of ignition can be increased from the normal state. Therefore, in addition to the effects shown in FIG. 13, it is possible to realize an easily ignited state and further improve the external EGR limit.

  In the IVC advance control, the IVC may be advanced, and it is not always necessary to set the IVC near the bottom dead center. That is, the IVC advance control of the present invention includes control for advancing the IVC in a direction away from the bottom dead center in a system in which the normal IVC is set on the advance side with respect to the bottom dead center.

(Comparison of two types of misfire countermeasure control)
Next, the characteristics of the first misfire countermeasure control and the second misfire countermeasure control will be compared with reference to FIGS. 16 and 17. FIG. 16 is an explanatory diagram showing the effect of the second misfire countermeasure control in comparison with the normal state. FIG. 17 is an explanatory diagram showing an effect when the first misfire countermeasure control and the second misfire countermeasure control are executed independently and an effect when they are combined. Note that FIG. 17 illustrates control for enriching the air-fuel ratio as the first misfire countermeasure control. Further, the EGR resistance improvement allowance corresponds to, for example, the external EGR limit improvement allowance, and represents the effect of suppressing misfire on the basis of the normal state.

  As shown in FIG. 16, in the best mode that combines the second misfire countermeasure control, in particular, the small lift amount control, the IVO retardation control, and the IVC advance control, the external EGR limit is greatly improved as compared with the normal state. Can be made. In particular, in the operating region where the engine speed is about 3600 rpm, the external EGR limit in the normal state is about 2%, whereas the external EGR limit in the second misfire countermeasure control is greatly improved to about 20%. confirmed. On the other hand, as shown in FIG. 17, the first misfire countermeasure control has an effect margin smaller than that of the second misfire countermeasure control, but can suppress misfire and improve the EGR resistance.

  The effect of the second misfire countermeasure control is very large compared to the first misfire countermeasure control (riching the air-fuel ratio) for the following reason. Generally, the air-fuel ratio that provides the best ignitability, that is, the target air-fuel ratio when enriching the air-fuel ratio is 12.5 to 13. Since this air-fuel ratio is close to the target air-fuel ratio (theoretical air-fuel ratio) in the normal state, the degree of improvement in ignitability (effect margin) obtained by enriching the air-fuel ratio is relatively small. However, since the upper limit torque is not limited as compared with the second misfire countermeasure control, the first misfire countermeasure control can be easily applied to a region where the engine load is relatively large.

  On the other hand, in the second misfire countermeasure control, a large synergistic effect can be obtained by combining the small lift amount control, the IVO retardation control, and the IVC advance control. In other words, these three types of control can sufficiently compensate for the shortage of ignition energy that is largely insufficient in a low load and high EGR state. Therefore, misfire can be effectively suppressed even when the external EGR rate is high at a low load, such as when deceleration is performed during EGR by the LPL type EGR mechanism 30. In addition, since only the valve characteristics of the intake valve 14 are changed, it is possible to minimize a reduction in fuel consumption and drivability. Further, when the first misfire countermeasure control and the second misfire countermeasure control are combined, the external EGR limit can be further improved by a synergistic effect of both.

  Note that the effect of the second misfire countermeasure control is most prominently exhibited in the best mode in which the small lift amount control, the IVO retardation control, and the IVC advance control are combined as described above. However, this effect can be exhibited at least by small lift amount control. Therefore, in the second misfire countermeasure control of the present invention, the small lift amount control and the IVO retard angle control may be combined without adopting the IVC advance angle control. Further, in the second misfire countermeasure control, the small lift amount control and the IVC advance angle control may be combined without adopting the IVO retard angle control. Furthermore, the second misfire countermeasure control may be configured only by the small lift amount control.

  Next, the limitation of each control will be considered. Since the effect margin is relatively small as described above, the first misfire countermeasure control is difficult to apply to a situation where the external EGR limit rapidly decreases, for example, sudden deceleration. Further, since the first misfire countermeasure control is likely to reduce the fuel consumption due to an increase in the fuel injection amount, the retard of the ignition timing, etc., it is desired to avoid using it in a situation where these control amounts become large.

  On the other hand, the second misfire countermeasure control can sufficiently suppress misfire even when the external EGR limit rapidly decreases. However, when the second misfire countermeasure control is executed, the intake air amount is limited according to the valve characteristics of the intake valve 14 even if the throttle valve 24 is largely opened. That is, since the second misfire countermeasure control has a characteristic of limiting the upper limit torque, it is difficult to apply to the region where the engine load is large.

(Variable control against misfire)
Based on the characteristics of each misfire countermeasure control described above, the misfire countermeasure variable control is executed in the present embodiment. In the misfire countermeasure variable control, when the engine 10 is decelerated and there is residual EGR gas flowing into the cylinder and there is a possibility of misfire, the load judgment value A is first determined based on the external EGR rate. Set. When the engine load is larger than the load determination value A, only the first misfire countermeasure control is executed. When the engine load is smaller than the load determination value A, at least the second misfire countermeasure control is executed.

  Generally, the external EGR limit tends to decrease as the engine load decreases. Moreover, in misfire countermeasure control, the capability to raise an external EGR limit is requested | required in order to suppress misfire, so that an external EGR limit falls. That is, in the operating region on the high load side, the external EGR limit is relatively high, so that misfire can be suppressed only by the first misfire countermeasure control. Further, since the external EGR limit is low in the low load side operation region, it is necessary to greatly increase the external EGR limit by the second misfire countermeasure control.

  For this reason, the load determination value A includes an operation region on the high load side where the misfire can be suppressed only by the first misfire countermeasure control, and a low load that requires the second misfire countermeasure control. It is set to a load value that distinguishes the operation region on the side. Note that “misfire suppression is possible” means “external EGR limit can be made higher than the current external EGR rate”.

  Further, in the misfire countermeasure control, it is necessary to increase the external EGR limit so that the external EGR rate is higher than the external EGR rate. For this reason, the load determination value A is set to a larger value as the external EGR rate is higher, and is configured to expand the application range of the second misfire countermeasure control. Further, the external EGR limit changes not only with the engine load and the external EGR rate but also with the engine speed. For this reason, it is preferable to change the load determination value A based on the engine speed. On the other hand, the load determination value A may be corrected in consideration of, for example, the allowable limit of the fuel consumption reduction amount reduced by the first misfire countermeasure control, the allowable limit of the torque limit amount restricted by the second misfire countermeasure control, and the like. Good. A specific example of the load determination value A will be described later in the second and third embodiments.

  Next, a basic operation of the misfire countermeasure variable control will be described with reference to FIGS. FIG. 18 is an explanatory diagram schematically illustrating an example of a state in which deceleration is performed during EGR. FIG. 19 is a timing chart showing an example of misfire countermeasure variable control in Embodiment 1 of the present invention. FIG. 19 exemplifies a case in which only the first misfire countermeasure control and the second misfire countermeasure control are switched from the state in which only the first misfire countermeasure control is executed during deceleration during EGR.

  As shown in FIG. 18, for example, when rapid deceleration is performed during steady operation, the EGR limit is greatly reduced from a value during steady operation (for example, approximately 25%) to approximately 5%. At this time, the ECU 50 closes the EGR valve 34 and stops the EGR. However, if residual EGR gas is present due to an EGR delay or the like, the ECU 50 executes a misfire countermeasure variable control. In the misfire countermeasure variable control, as shown in FIG. 19, for example, the occurrence of misfire is predicted and the second misfire countermeasure control is not performed in the section a where the engine load is larger than the load determination value A described above. Only the first misfire countermeasure control is executed. Note that the state in which the occurrence of misfire is predicted is a state in which, for example, the in-cylinder EGR rate is larger than the EGR misfire limit (dotted line), as shown in the lower part of FIG. Moreover, in this Embodiment, it is good also as a structure which estimates the timing when an in-cylinder EGR rate becomes larger than an EGR misfire limit, and performs misfire countermeasure control slightly before this timing.

  Here, the internal EGR rate is estimated based on, for example, the engine rotation speed, the intake air amount, the valve timings of the intake valve 14 and the exhaust valve 16, and the like. The external EGR rate is estimated based on, for example, a target EGR rate (or a target opening of the EGR valve 34) by EGR control. Further, the EGR misfire limit, which is a limit value of the in-cylinder EGR rate that can suppress misfire, is estimated based on, for example, engine load, engine speed, and the like. Therefore, the possibility of misfire can be predicted by calculating the in-cylinder EGR rate by adding the internal EGR rate and the external EGR rate, and comparing the calculated in-cylinder EGR rate with the EGR misfire limit. In an operation state in which the internal EGR can be ignored, the surge tank EGR rate may be used as the external EGR rate, or the external EGR rate may be used as the in-cylinder EGR rate.

  On the other hand, for example, in the section b where the degree of deceleration increases and the engine load becomes smaller than the load determination value A, both the first misfire countermeasure control and the second misfire countermeasure control are executed. FIG. 19 illustrates deceleration where the engine load gradually increases. On the other hand, when the engine load falls below the load determination value A from the start of deceleration due to sudden deceleration or the like, the section a does not exist, and both the first misfire countermeasure control and the second misfire countermeasure control are executed from the beginning. Is done.

  Further, when the deceleration state continues to some extent, the discharge of residual EGR gas proceeds and the external EGR rate decreases. At this time, the ECU 50 reflects the decrease in the external EGR rate in the load determination value A and decreases the load determination value A. Accordingly, for example, in the section c in FIG. 19, the engine load becomes relatively larger than the load determination value A, so the second misfire countermeasure control is stopped and only the first misfire countermeasure control is executed.

  Further, the ECU 50 may be configured to calculate a timing at which the discharge of the residual EGR gas is finished and finish the misfire countermeasure control when the timing comes. This timing is a timing at which the external EGR gas remaining in the intake passage 20 is replaced with fresh air. That is, the timing can be calculated by a calculation model or the like based on, for example, the volume downstream of the EGR valve 34 in the intake passage 20 and the intake air amount. The volume is stored in advance in the ECU 50. According to this control, the misfire countermeasure control can be accurately terminated at the timing when the residual EGR gas disappears. Therefore, it is possible to avoid an excess or deficiency of the misfire countermeasure control and to stably suppress misfire caused by the residual EGR gas.

  Thus, according to the misfire countermeasure variable control, misfire is determined based on the in-cylinder EGR rate at the time of deceleration, and when there is a possibility of misfire, the external EGR limit is estimated from the load state, and the first misfire is performed. Selection between countermeasure control and second misfire countermeasure control can be appropriately switched. That is, the second misfire countermeasure control for reducing the lift amount of the intake valve 14 has a high misfire suppression effect, but reduces the intake air amount, which may cause a torque step. For this reason, in the misfire countermeasure variable control, when the engine load during deceleration is large, first, the first misfire countermeasure control is selected, so that the misfire countermeasure can be performed while suppressing the torque step. Thereby, it is possible to maintain good drivability while executing misfire countermeasures.

  On the other hand, when the engine load during deceleration is small, in addition to the first misfire countermeasure control, the second misfire countermeasure control having a high misfire suppression effect can be selected. As a result, the maximum misfire suppression effect can be obtained by the synergistic effect of the two types of misfire countermeasure control, and misfire can be stably suppressed even in a low load and high external EGR rate. Therefore, for example, when deceleration is performed during EGR, an appropriate misfire countermeasure can be executed in stages according to the deceleration state, and misfire can be efficiently suppressed. Further, by selecting the control according to the situation, it is possible to minimize the reduction in fuel consumption, drivability, torque limitation, etc. that are likely to occur due to individual misfire countermeasure control.

  A specific example of the above effect will be described with reference to the bottom row in FIG. The dotted line in the figure illustrates the EGR misfire limit by the conventional misfire countermeasure control. The solid line illustrates the EGR misfire limit by the misfire countermeasure variable control. First, in the conventional control, when deceleration is performed while EGR gas remains, the actual in-cylinder EGR rate becomes larger than the EGR misfire limit, and misfire is likely to occur. On the other hand, in the present embodiment, the EGR misfire limit is greatly improved by the first misfire countermeasure control and the second misfire countermeasure control, and the EGR misfire limit is higher than the in-cylinder EGR rate even during rapid deceleration, for example. Can be held.

(Other control examples)
In the present embodiment, the misfire countermeasure variable control shown in FIG. 20 may be adopted. FIG. 20 is a timing chart showing another example of the misfire countermeasure variable control in the first embodiment of the present invention. In this misfire countermeasure variable control, when the engine load is smaller than the load determination value A, only the second misfire countermeasure control is executed without executing the first misfire countermeasure control. Therefore, at the time of deceleration where the engine load changes from a state larger than the load determination value A to a small state, the first misfire countermeasure control is first executed and then the second misfire countermeasure control is switched.

  According to the modified example configured as described above, substantially the same effect as the misfire countermeasure variable control shown in FIG. 19 can be obtained. Further, according to this modification, for example, when it is determined that the influence of the fuel consumption reduction or the like is larger than the effect of the first misfire countermeasure control, it is avoided that the first misfire countermeasure control is forcibly used during sudden deceleration. be able to. In the present invention, the controls shown in FIGS. 19 and 20 may be combined. This control will be described in the second embodiment.

Embodiment 2. FIG.
Next, a second embodiment of the present invention will be described with reference to FIGS. The present embodiment is characterized in that the selection of the first misfire countermeasure control and the second misfire countermeasure control is changed in four areas. FIG. 21 is an explanatory diagram showing divisions of the EGR region for switching selection of misfire countermeasure control in the second embodiment of the present invention. FIG. 22 is an explanatory diagram showing a three-dimensional data map that divides the EGR region based on the engine load, the external EGR rate, and the engine rotation speed.

  As shown in FIGS. 21 and 22, the ECU 50 stores a three-dimensional data map in advance. This data map divides an EGR area determined based on, for example, an engine load, an external EGR rate, and an engine speed into four areas A0, A1, A2, and A3. As described above, in the misfire countermeasure control, the smaller the engine load and the higher the external EGR rate, the higher the external EGR limit is required. Accordingly, the areas A0 to A3 are divided in consideration of this requirement.

  Specifically, first, the reference area A0 corresponds to a normal operation area where deceleration is not performed. Region A0 is the region with the highest load and low EGR rate among the regions. Therefore, in the region A0, the misfire countermeasure control is not necessary because the external EGR limit is maintained higher than the external EGR rate without executing the misfire countermeasure control. The first region A1 is a region having a lower load and a higher EGR rate than the reference region A0. For this reason, in the area A1, the external EGR limit is lower than in the area A0, and the margin of the external EGR limit with respect to the external EGR rate is reduced. However, in region A1, since the amount of decrease in the external EGR limit is not so large, misfire can be suppressed only by the first misfire countermeasure control.

  The second region A2 is a region having a lower load and a higher EGR rate than the region A1. For this reason, in the region A2, the amount of decrease in the external EGR limit is larger than that in the region A1, and the margin for the external EGR limit is further reduced. This allowance exceeds the application range of the first misfire countermeasure control, but is the application range of the second misfire countermeasure control. Therefore, in the area A2, misfire can be suppressed only by the second misfire countermeasure control. The third region A3 is a region having a lower load and a higher EGR rate than the region A2, and has the highest load and a low EGR rate among the regions. In the region A3, the external EGR limit is extremely reduced with respect to the external EGR rate. Therefore, it is required to increase the external EGR limit as much as possible by both the first misfire countermeasure control and the second misfire countermeasure control.

  Also, the external EGR limit changes depending on the engine speed. For this reason, in the present embodiment, the range of the regions A0 to A3 is changed based on the engine rotational speed using a three-dimensional data map. Thereby, the influence by the change of engine rotational speed is reflected in each area | region A0-A3, and the consistency with each area | region and misfire countermeasure control can be improved. In the present invention, it is not always necessary to use the engine rotation speed. For example, the area may be divided by a two-dimensional data map based on the engine load and the external EGR rate. Also, other parameters that affect the external EGR limit (for example, intake air temperature, intake air pressure, etc.) may be added to the argument of the data map.

  In the misfire countermeasure variable control, when there is residual EGR gas at the time of deceleration, by referring to the data map based on the engine load, the external EGR rate, and the engine speed, it is possible to determine which region the operation state belongs to. Identify. Then, based on the region to which the operating state belongs, specific misfire countermeasure control is selected and executed as described later. The above-described regions A1 to A3 correspond to the load determination value A in the first embodiment. More specifically, the boundary between the first area A1 and the second area A2 corresponds to the load determination value described in claims 1 and 2. The boundary between the first region A1 and the third region A3 corresponds to the load determination value described in claims 1 and 3.

[Specific Processing for Realizing Embodiment 2]
Next, specific processing of misfire countermeasure variable control will be described with reference to FIG. FIG. 23 is a flowchart showing an example of control executed by the ECU in the second embodiment of the present invention. Note that the routine shown in this figure is repeatedly executed during engine operation.

  In the routine shown in FIG. 23, first, in step S100, it is determined whether or not the external EGR is being executed. When this determination is established, the process proceeds to step S104. If the determination in step S100 is not established, the process proceeds to step S102, and it is determined whether or not the external EGR gas is remaining (during tailing). When the determination in step 102 is established, the process proceeds to step S104. If the determination in step S104 is not established, there is no external EGR gas flowing into the cylinder, and thus this routine ends.

  Next, in step S104, the accelerator operation state (for example, accelerator opening, operation, and speed) is read by the accelerator opening sensor. In step S106, it is determined whether the vehicle is decelerating based on the operation state of the accelerator. When the determination in step S106 is established, load prediction control is executed in step S108. In the load prediction control, the minimum load that is reached during deceleration is predicted based on the operation state of the accelerator, and the predicted load is used as the engine load used in the misfire countermeasure variable control. According to the load prediction control, during deceleration, for example, it can be predicted that the greater the accelerator opening, operation, or speed, the greater the engine load will decrease and the minimum load that will be reached.

  Next, in step S110, the current engine speed and external EGR rate are read. In a state where the EGR valve 34 is closed at the start of deceleration, the residual EGR gas is gradually replaced with fresh air, so that the external EGR rate is gradually reduced. For this reason, the latest external EGR rate includes, for example, the target EGR rate before starting deceleration, the amount of residual EGR gas at the time when the EGR valve 34 is closed, and the integrated intake air amount after the EGR valve 34 is closed. It can be calculated based on

  Next, in step S112, by referring to the data map based on the predicted load in step S108, the engine rotational speed, and the external EGR rate, which of the areas A0 to A3 will be the future area is determined. Identify. Here, the future region means a region where the operation state at that time is predicted to belong when the engine load reaches the predicted load. After specifying the area, the process proceeds to step S118.

  On the other hand, if it is determined in step S106 that the vehicle is not decelerating, the load prediction control is not executed and the region to which the current operating state belongs is specified. Specifically, first, in step S114, the current engine speed, external EGR rate, and engine load are read. Next, the current region is specified by referring to the data map based on these read values, and the process proceeds to step S118.

  Next, in step S118, it is determined whether or not the specified area is the area A0. This determination process corresponds to a process for predicting the possibility of misfire. That is, in this embodiment, the possibility of misfire is predicted based on the external EGR rate by using the external EGR rate as the in-cylinder EGR rate. If the determination in step S118 is established, the possibility of misfire is small, and misfire countermeasure control is not necessary, so this routine is terminated without doing anything. If the determination in step S118 is not established, the occurrence of misfire is predicted, so the process proceeds to step S120 to determine whether or not the specified region is the region A1. If the determination in step S120 is established, this is a region where the possibility of misfire is relatively low. Therefore, in this case, the process proceeds to step S122, and only the first misfire countermeasure control is executed.

  If the determination in step S120 is not established, the process proceeds to step S124, and it is determined whether or not the specified area is the area A2. If the determination in step S124 is established, this is a region where the possibility of misfire is relatively high. Therefore, in this case, the process proceeds to step S126, and only the second misfire countermeasure control is executed. If the determination in step S124 is not established, the specified area is the area A3, and therefore the possibility of misfire is very high. Therefore, in this case, the process proceeds to step S130, and both the first misfire countermeasure control and the second misfire countermeasure control are executed.

  Next, with reference to FIG. 24, a specific operation by the above control will be described. FIG. 24 is a timing chart showing misfire countermeasure variable control according to Embodiment 2 of the present invention. In this figure, the solid line exemplifies the case where rapid deceleration (see FIG. 21) that reaches the region A3 during EGR is performed. Moreover, the dotted line has illustrated the case where the slow deceleration of the grade which reaches | attains area | region A1 during EGR was performed.

  First, at the time of sudden deceleration, the accelerator opening (driver's torque request) decreases rapidly, and the load factor (= air amount) gradually decreases accordingly. Further, at the start of deceleration, the EGR valve 34 is closed, but the external EGR rate gradually decreases with a delay from the start of deceleration as the residual EGR gas continues to flow into the cylinder. As a result, during the period from when the rapid deceleration is started until the external EGR rate starts to decrease, the tendency of the high EGR rate with a low load gradually increases. Migrate with A3. The selection of the misfire countermeasure control changes from the first misfire countermeasure control → the second misfire countermeasure control → both misfire countermeasure controls in accordance with the transition of the region.

  Next, when the discharge of residual EGR gas proceeds and the external EGR rate starts to decrease, the region to which the operating state belongs shifts from A3 to A2 to A1. Along with this, the selection of the misfire countermeasure control changes from both of the misfire countermeasure controls → second misfire countermeasure control → first misfire countermeasure control. When the operating state finally reaches the area A0, the first misfire countermeasure control and the second misfire countermeasure control are ended.

  On the other hand, during slow deceleration, the load factor decreases slowly. As a result, the region to which the operating state belongs only shifts to A1, and only the first misfire countermeasure control is executed as the misfire countermeasure control. However, at the time of slow deceleration, the discharge of the residual EGR gas is delayed, so that the external EGR rate becomes high for a relatively long time. Along with this, the time during which the first misfire countermeasure control is executed in the region A1 also becomes longer.

  Thus, according to this Embodiment, area | region A0-A3 can be set according to the necessity level of misfire countermeasures. Based on the region to which the operating state belongs, it is possible to select whether to execute only the first misfire countermeasure control, execute only the second misfire countermeasure control, or execute both misfire countermeasure controls. Thereby, for example, when deceleration is performed during EGR, an appropriate misfire countermeasure can be executed step by step according to the state of deceleration, and misfire can be efficiently suppressed. Moreover, in the present embodiment, the control can be switched in three stages according to the necessity of misfire countermeasures. Therefore, the same effects as those of the first embodiment can be obtained, and the control can be adapted with high accuracy to the degree of necessity for the misfire countermeasure.

  Moreover, in this Embodiment, as shown to step S108 in FIG. 23, load prediction control is performed. Accordingly, it is possible to select a misfire countermeasure control by predicting a future region to be reached by deceleration. Therefore, for example, even during sudden deceleration, the misfire countermeasure control suitable for the final reach area can be executed in advance. That is, it is possible to suppress a response delay in misfire countermeasure control and execute necessary misfire countermeasure control at an appropriate timing.

Embodiment 3 FIG.
Next, Embodiment 3 of the present invention will be described with reference to FIG. The present embodiment is characterized in that sequential processing for always specifying the latest region is executed based on the current operating state without executing load prediction control. FIG. 25 is a flowchart showing an example of control executed by the ECU in the third embodiment of the present invention. The routine shown in this figure adds the process of step S200 to the routine shown in FIG. 23, and excludes the processes of steps S104 to S112. For this reason, the description of the steps described above will be omitted as appropriate.

  In the routine shown in FIG. 25, first, in step S200, it is determined whether or not the vehicle is decelerating. If the vehicle is decelerating, the process proceeds to step S100. If the vehicle is not decelerating, this routine is terminated. In the next process, if any of the determinations in steps S100 and S102 is established, the process proceeds to step S114. And in step S114, S116, the area | region where the present driving | running state belongs is specified. Next, in steps 118 to S130, misfire countermeasure control is selected based on the identified region. The routine shown in FIG. 25 is repeatedly executed during engine operation as in FIG. 23. Steps S100 to S130 in FIG. 25 are repeatedly executed from the start of deceleration until the end thereof. . In this embodiment configured as described above, substantially the same effect as that of the second embodiment can be obtained.

  In the first to third embodiments, the first misfire countermeasure control, the second misfire countermeasure control, and the misfire countermeasure variable control are specific examples of the first misfire countermeasure means, the second misfire countermeasure means, and the control selection means, respectively. ing. Further, steps S108, S110, S112, and S118 in FIG. 23 and steps S114, S116, and S118 in FIG. 25 show specific examples of misfire prediction means. Further, step S112 in FIG. 23 and step S116 in FIG. 25 show specific examples of the judgment value setting means.

  In the first to third embodiments, the case where the “in-cylinder EGR rate” and the “external EGR rate” are used for the control is illustrated. However, the present invention is not limited to the EGR rate, and “in-cylinder EGR amount” and “external EGR amount” may be used for control. In the embodiment, a gasoline engine equipped with an LPL type EGR mechanism 30 is exemplified. However, the present invention is not limited to this, and may be applied to an HPL type EGR mechanism or a diesel engine.

10 Engine (Internal combustion engine)
12 cylinder 14 intake valve 16 exhaust valve 18 spark plug 20 intake passage 22 exhaust passage 24 throttle valve 26 catalyst 28 supercharger 30 EGR mechanism 32 EGR passage 34 EGR valve 36 variable valve mechanism 40 sensor system 50 ECU (control device)
A Load judgment value A0, A1, A2, A3 area (load judgment value)

Claims (9)

An EGR mechanism capable of recirculating external EGR gas from the exhaust system of the internal combustion engine to the intake system;
A variable valve mechanism that can change the valve characteristics including the lift amount of the intake valve;
A controller for controlling the EGR mechanism and the variable valve mechanism,
The controller is
A first misfire countermeasure that executes any one or more of a change in fuel injection amount, a change in fuel injection timing, a change in ignition timing, and a tumble flow reduction control without changing the valve characteristic of the intake valve. Means,
Second misfire countermeasure means for suppressing misfire by control for changing valve characteristics of the intake valve including control for reducing the lift amount of the intake valve;
Misfire prediction means for predicting the possibility of misfire based on the amount of in-cylinder EGR when the internal combustion engine is decelerated and there is external EGR gas flowing into the cylinder;
A determination value setting means for setting a load determination value based on an external EGR amount when the occurrence of misfire is predicted by the misfire prediction means;
Control selection means for activating the first misfire countermeasure means when the engine load is larger than the load judgment value, and activating at least the second misfire countermeasure means when the engine load is smaller than the load judgment value;
The control apparatus of the internal combustion engine provided with.   2. The control device for an internal combustion engine according to claim 1, wherein the control selection unit is configured to operate only the second misfire countermeasure unit when the engine load is smaller than the load determination value.   2. The control of the internal combustion engine according to claim 1, wherein the control selection unit is configured to operate both the first misfire countermeasure unit and the second misfire countermeasure unit when the engine load is smaller than the load determination value. apparatus. In the EGR region determined based on the engine load and the external EGR amount, the load determination value includes a reference region that is a region with a high load and a low EGR amount, and a high EGR amount with a lower load than the reference region. A first region that is a region, a second region that is a lower load and a higher EGR amount than the first region, and a second region that is a lower load and a higher EGR amount than the second region. 3 areas,
The control selection means determines which region the operating state belongs to based on the engine load and the external EGR amount, and when belonging to the first region, operates only the first misfire countermeasure means, When belonging to the second area, only the second misfire countermeasure means is operated, and when belonging to the third area, both the first misfire countermeasure means and the second misfire countermeasure means are activated. Item 2. A control device for an internal combustion engine according to Item 1.   The second misfire countermeasure means includes a control for reducing a lift amount of the intake valve, a control for delaying a valve opening timing of the intake valve, and The control apparatus for an internal combustion engine according to any one of claims 1 to 4, wherein the control is performed to advance the valve closing timing of the intake valve.   The second misfire countermeasure means performs control to reduce the lift amount of the intake valve and retards the valve opening timing of the intake valve as compared to when the first misfire countermeasure means is not in operation. 5. The control device for an internal combustion engine according to claim 1, wherein any one of control for advancing the closing timing of the intake valve is executed.   The control device is configured to calculate a timing at which the discharge of the external EGR gas remaining in the intake system ends, and to stop the first misfire countermeasure means and the second misfire countermeasure means when the timing comes. The control apparatus for an internal combustion engine according to any one of claims 1 to 6.   The control device for an internal combustion engine according to any one of claims 1 to 7, wherein the load determination value is changed based on an engine rotational speed.   The internal combustion engine according to any one of claims 1 to 8, wherein a minimum load that is reached during deceleration is predicted based on an accelerator operation state, and the predicted load is used as the engine load by the control selection unit. Engine control device.

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