JP2016089749A - Internal combustion engine control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an internal combustion engine control device capable of suppressing the occurrence of a misfire caused by the introduction of EGR gas.SOLUTION: A control device comprising: a variable valve lift mechanism 36 capable of switching an intake cam over between a large lift cam and a small lift cam; and an EGR device 42 performing an exhaust gas recirculation operation for recirculating part of burned gas discharged from within each cylinder of an internal combustion engine 10 into the cylinder, executes a switching operation for operating the variable valve lift mechanism 36 to switch the intake cam from the large lift cam to the small lift cam when a deceleration request such that a load of the internal combustion engine 10 falls below a misfire lower limit load is issued during the introduction of EGR gas. In the switching operation, the control device controls start timing of the switching operation so as to complete the switching operation at timing at which the load of the internal combustion engine 10 reaches the misfire lower limit load using time until the load of the internal combustion engine 10 reaches the misfire lower limit load and time required for the switching operation.SELECTED DRAWING: Figure 11

Description

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

  Conventionally, for example, Japanese Unexamined Patent Application Publication No. 2013-11271 discloses a technique for preventing misfire at the time of deceleration due to introduction of EGR gas in an engine equipped with an EGR device. In this technique, the in-cylinder inflow EGR gas amount is estimated, and the misfire limit EGR amount is calculated based on the engine operating state. And when these are compared and it is estimated that a misfire will generate | occur | produce, misfire avoidance control is performed. In the misfire avoidance control, for example, airflow enhancement control is performed to reduce the lift amount of the intake valve and increase the flow velocity of the intake air flowing into the cylinder.

JP 2013-11271 A International Publication No. 2012/004850 JP 2000-87769 A

  However, if the lift amount of the intake valve is reduced when the engine is decelerated as in the prior art described above, the valve control cannot catch up at the time of re-acceleration, and a misfire may occur due to an insufficient air amount.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a control device for an internal combustion engine that can suppress the occurrence of misfire due to the introduction of EGR gas.

In order to achieve the above object, a first invention is a control device for an internal combustion engine,
A variable valve lift mechanism capable of switching the lift amount of the intake valve between a large lift amount and a small lift amount;
An exhaust gas recirculation device for performing an exhaust gas recirculation operation for recirculating part of the burned gas exhausted from the cylinder of the internal combustion engine into the cylinder;
In an operating state in which the lift amount of the intake valve is controlled to the large lift amount and the exhaust gas recirculation operation is being performed, a low load request is issued that is below the misfire limit lower limit load, which is the lower limit of the load at which misfire does not occur. Control means for performing a switching operation of operating the variable valve lift mechanism to switch the lift amount of the intake valve from the large lift amount to the small lift amount,
The control means, when the load of the internal combustion engine reaches the misfire limit lower limit load based on the time until the load of the internal combustion engine reaches the misfire limit lower limit load and the time required for the switching operation, The start time of the switching operation is controlled so that the switching operation is completed.

  According to the first aspect of the present invention, in an operating state in which the lift amount of the intake valve is controlled to be a large lift amount and the exhaust gas recirculation operation is being executed, a low value lower than the misfire limit lower limit load that is the lower limit of the load that does not cause misfire. When a load request is issued, a switching operation for switching the lift amount of the intake valve from the large lift amount to the small lift amount by operating the variable valve lift mechanism is performed. At this time, based on the time until the load of the internal combustion engine reaches the misfire limit lower limit load and the time required for the switching operation, the switching operation is completed when the load of the internal combustion engine reaches the misfire limit lower limit load, The start time of the switching operation is controlled. According to such a configuration, when switching to an acceleration request exceeding the misfire limit lower limit load is performed before the switching operation to the small lift amount is actually started, the switching operation is not performed, and therefore suction is performed at the time of reacceleration. It is possible to suppress a situation where misfire occurs due to an insufficient amount of air.

It is a figure for demonstrating the system configuration | structure of the internal combustion engine in Embodiment 1 of this invention. It is a time chart for demonstrating the relationship between the load of an internal combustion engine, and the switching operation of a variable valve lift mechanism. It is a figure for demonstrating the method for determining the switching time of an intake cam. It is a figure which shows the relationship of the hydraulic pressure response time with respect to a hydraulic pressure. 6 is a flowchart showing a routine for control executed by an ECU 50 in a second embodiment. 6 is a flowchart showing a routine for control executed by an ECU 50 in a second embodiment. It is a figure which shows the driving | operation area | region map used for priority arbitration. It is a figure for demonstrating the change of the valve opening characteristic of an intake valve at the time of performing priority arbitration. It is a figure which shows the change of the amount of intake air with respect to throttle opening. It is a figure which shows the misfire tolerance at the time of EGR introduction with respect to the operation amount of a variable valve timing mechanism. It is a time chart which shows the change of various state quantities at the time of performing priority arbitration.

Embodiment 1 FIG.
Embodiment 1 of the present invention will be described with reference to FIGS.

[Configuration of Embodiment 1]
FIG. 1 is a diagram for explaining a system configuration of an internal combustion engine 10 according to Embodiment 1 of the present invention. The control device of the present embodiment includes an internal combustion engine 10 configured as a spark ignition type gasoline engine. An intake passage 12 and an exhaust passage 14 communicate with each cylinder of the internal combustion engine 10.

  An air cleaner 16 is attached in the vicinity of the inlet of the intake passage 12. An air flow meter 18 that outputs a signal corresponding to the flow rate of air (fresh air) sucked into the intake passage 12 is provided in the intake passage 12 on the downstream side of the air cleaner 16. A compressor 20 a of the turbocharger 20 is installed in the intake passage 12 on the downstream side of the air flow meter 18. The compressor 20a is integrally connected to a turbine 20b disposed in the exhaust passage 14 via a connecting shaft.

  An electronically controlled throttle valve 22 is provided in the intake passage 12 downstream of the compressor 20a. Further, the intake passage 12 downstream of the throttle valve 22 is configured as an intake manifold 24 connected to an intake port (not shown) of each cylinder. The intake manifold 24 includes a collecting portion that functions as a surge tank 24a, and an intake branch pipe 24b that connects the surge tank 24a and each intake port. The surge tank 24a is provided with an intercooler 26 for cooling the air compressed by the compressor 20a.

  Each cylinder of the internal combustion engine 10 has a fuel injector 30 for injecting fuel into an intake port, an ignition plug 32 for igniting an air-fuel mixture in a combustion chamber, an intake valve (not shown), and an exhaust valve (not shown). ) And are provided. The intake valve and the exhaust valve are provided with a hydraulic variable valve timing mechanism (VVT) 34 that can advance or retard the opening / closing timing with a constant operating angle. The intake valve is provided with a hydraulic variable valve lift mechanism (VVL) 36 for changing the valve lift amount, which is the valve opening characteristic of the intake valve. The variable valve lift mechanism 36 according to the present embodiment switches the large lift cam corresponding to the large lift amount and the small lift cam corresponding to the small lift amount (both not shown) to thereby change the operating angle together with the lift amount of the intake valve. This is a mechanism for changing to two stages. The variable valve timing mechanism 34 and the variable valve lift mechanism 36 are operated by a common hydraulic device (not shown). The hydraulic device is provided with a hydraulic pressure sensor 38 for detecting the hydraulic pressure. Note that the configurations of the variable valve timing mechanism 34 and the variable valve lift mechanism 36 are well known in many documents, and thus detailed description thereof is omitted.

  The exhaust passage 14 downstream of the turbine 20b is provided with a catalyst (for example, a three-way catalyst) 40 for purifying exhaust gas and a muffler 41 for silencing. The internal combustion engine 10 shown in FIG. 1 includes a low-pressure loop (LPL) type exhaust gas recirculation device (EGR device) 42. The EGR device 42 includes an EGR passage 44 that connects the exhaust passage 14 downstream of the catalyst 40 and the intake passage 12 upstream of the compressor 20a. In the middle of the EGR passage 44, an EGR cooler 46 and an EGR valve 48 are provided in order from the upstream side of the flow of EGR gas when introduced into the intake passage 12. The EGR cooler 46 is provided for cooling the EGR gas flowing through the EGR passage 44, and the EGR valve 48 is provided for adjusting the flow rate of the EGR gas.

  Furthermore, the system of the present embodiment includes an ECU 50 (Electronic Control Unit) as control means. The ECU includes at least an input / output interface, a memory, and an arithmetic processing unit (CPU). The input / output interface is provided to capture sensor signals from various sensors attached to the internal combustion engine or a vehicle on which the internal combustion engine is mounted, and to output operation signals to various actuators provided in the internal combustion engine. Various sensors for acquiring the engine operating state, such as a crank angle sensor for acquiring the rotational position of the crankshaft and the engine rotational speed, in addition to the air flow meter 18 and the hydraulic pressure sensor 38 described above, are sensors that the ECU captures signals. Is included. In addition to the throttle valve 22, the spark plug 32, the fuel injector 30, the variable valve timing mechanism 34, the variable valve lift mechanism 36, and the EGR valve 48, there are various actuators for controlling the engine operation. An actuator is included. The memory stores various control programs and maps for controlling the internal combustion engine. The CPU reads out and executes a control program or the like from the memory, and generates operation signals for various actuators based on the acquired sensor signals.

[Operation of Embodiment 1]
As described above, the system of the present embodiment includes the variable valve lift mechanism 36 that can switch the valve lift amount of the intake valve in two stages by switching between the large lift cam and the small lift cam. The operating region of the internal combustion engine 10 is divided into a region where the large lift cam is used and a region where the small lift cam is used. In the internal combustion engine 10 of the present embodiment, first, the engine rotational speed and the engine load are calculated using the air flow meter 18, the crank angle sensor, the accelerator position sensor, and the like, and the operation state specified from these values is any lift cam. The switching operation by the variable valve lift mechanism 36 is performed depending on whether it belongs to the region.

  Specifically, in the internal combustion engine 10 of the present embodiment, the control state of the variable valve lift mechanism 36 is controlled to be switched to the large lift cam during light load operation including idling. During such a large lift control, the closing timing (IVC) of the intake valve is delayed, and a so-called Atkinson cycle in which the operation is performed with a small amount of air by returning the air once sucked. Thereby, reduction of pumping loss can be aimed at. On the other hand, during acceleration, the control state of the variable valve lift mechanism 36 is controlled so as to be switched to the small lift cam. In such a small lift control, the intake air is not blown back, so that the charging efficiency of the intake air can be increased and the acceleration performance can be improved.

  Further, in the internal combustion engine 10 of the present embodiment, an exhaust gas recirculation operation for the purpose of improving fuel efficiency is performed. Specifically, when the operating state of the internal combustion engine 10 belongs to a predetermined EGR introduction region, the EGR valve 48 is opened. By such an exhaust gas recirculation operation, a part of the burned gas exhausted from the cylinder to the exhaust passage 14 is caused to flow to the intake passage 12 through the EGR passage 44. The recirculated burned gas (EGR gas) is sucked into the cylinder of the internal combustion engine 10 together with fresh air and is used for combustion.

  Here, if a deceleration request is issued during the introduction of EGR gas, there is a risk of misfire due to insufficient intake air amount. As a countermeasure against this misfire, it is conceivable to switch the intake cam of the variable valve lift mechanism 36 from the large lift cam to the small lift cam for the purpose of enhancing the misfire resistance by improving the combustion state. Therefore, in the system according to the present embodiment, when EGR gas is introduced into the intake cam for a large working angle, the target load at the time of deceleration of the internal combustion engine 10 is the lower limit load (misfire limit lower limit). When it is determined that the intake valve is lower than the load), control is performed to switch the intake cam of the variable valve lift mechanism 36 from the large lift cam to the small lift cam.

  However, depending on the operating state of the internal combustion engine 10, it may be assumed that an acceleration request is made immediately after a deceleration request is issued. FIG. 2 is a time chart for explaining the relationship between the load of the internal combustion engine 10 and the switching operation of the variable valve lift mechanism 36. This figure shows an example in which the target load temporarily falls below the misfire limit lower limit due to the deceleration request, but the actual load as a result increases without falling below the misfire limit lower limit due to the subsequent acceleration request. In such a change in the target load, (a) in the figure shows a case where the intake cam is switched from the large lift cam to the small lift cam at a time point a immediately after the target load falls below the misfire limit lower limit. In this way, if the intake cam switching is started at time point a immediately after the target load falls below the misfire limit lower limit load, the intake cam is unnecessarily switched, resulting in a shortage of intake air during reacceleration. This leads to a reduction in fuel consumption due to the occurrence of misfire due to or transient control during switching.

  Therefore, in the system of the present embodiment, when it is determined that the target load at the time of a low load request due to deceleration of the internal combustion engine 10 is less than the misfire limit lower limit load when the EGR gas is introduced into the large lift cam, the actual load is The start timing of the switching operation is delayed so that the switching operation of the intake cam to the small lift cam is completed when the misfire limit lower limit load is reached. (B) in FIG. 2 shows an example of the case where the start of the intake cam switching is delayed to the time point b, and as a result, an acceleration request is issued before the time point b, resulting in the failure to switch the intake cams. ing. As described above, according to the system of the present embodiment, the number of intake cam lifetime changes can be reduced, so that a reduction in fuel consumption due to the change can be suppressed and components can be protected.

  Note that the start time of the switching operation is determined by the following calculation. FIG. 3 is a diagram for explaining a method for determining the intake cam switching timing. In FIG. 3, (1) in the figure is the time X at which deceleration starts, (2) in the figure is the time Y at which the actual load reaches the misfire limit lower limit, and (3) in the figure is the small intake cam from the large lift cam. This is the switching time Z required for switching to the lift cam, and the switching operation start time T is calculated by T = (Y−X−Z). The switching time Z is calculated as the sum of the hardware operation time, the control time, the hydraulic response time, and the operation variation. The oil pressure response time changes corresponding to the oil pressure. FIG. 4 is a diagram showing the relationship of the hydraulic response time with respect to the hydraulic pressure. As shown in this figure, the hydraulic response time tends to become shorter as the hydraulic pressure becomes higher, that is, as the oil temperature becomes lower and the rotation speed becomes higher. Here, the hydraulic pressure response time corresponding to the detected value of the hydraulic pressure sensor 38 can be specified using the relationship shown in FIG.

  If switching of the intake cam is started at such timing, the start of switching of the intake cam can be delayed as much as possible to suppress unnecessary switching. In addition, for necessary switching, the switching of the intake cam can be completed at the timing when the actual load reaches the lower limit of misfire, so that the occurrence of misfire due to deceleration during the introduction of EGR gas is effectively suppressed. Can do.

  In the system of the first embodiment described above, the variable valve lift mechanism 36 has been described as an example of a mechanism that switches between two large and small intake cams, but other mechanisms may be used as long as the valve lift amount can be varied. .

  In the system of the first embodiment described above, the start time T is determined as T = (Y−X−Z). However, the intake cam is switched in the range until the actual load reaches the misfire limit lower limit. Can be completed, the start time T may be shorter than (Y-X-Z).

Embodiment 2. FIG.
A second embodiment of the present invention will be described with reference to FIGS.

[Features of Embodiment 2]
The system of the present embodiment can be realized by causing the ECU 50 to execute routines shown in FIGS. 5 and 6 described later using the hardware configuration shown in FIG.

  As described above, the system of the present embodiment is configured such that the variable valve timing mechanism 34 and the variable valve lift mechanism 36 are operated by a common hydraulic device. For this reason, when the VVT operation request by the variable valve timing mechanism 34 and the intake cam switching operation request by the variable valve lift mechanism 36 are issued at the same time when the hydraulic pressure is low, both mechanisms are operated at the same time. There is a possibility that it cannot be made.

  Therefore, in the system according to the present embodiment, when the operation requests of the variable valve timing mechanism 34 and the variable valve lift mechanism 36 are issued at the same time, it is determined whether or not these mechanisms can be operated at the same time. Judgment will be made. When it is determined that these mechanisms cannot be operated at the same time, the operation with high misfire resistance at the time of introduction of EGR gas is preferentially executed. Hereinafter, specific processing of such control will be described in detail with reference to flowcharts.

  FIG. 5 is a flowchart showing a routine for control executed by the ECU 50 in the second embodiment. In this routine, first, when the introduction of EGR gas is started in step S1, in the next step S2, it is determined whether or not there is a VVT operation request to the variable valve timing mechanism 34 due to the deceleration request of the internal combustion engine, and the deceleration of the internal combustion engine. It is determined whether or not there is a request for switching from the large lift cam to the small lift cam of the variable valve lift mechanism 36 upon request.

  In the next step S3, it is determined whether the VVT operation request by the variable valve timing mechanism 34 and the switching request by the variable valve lift mechanism 36 are issued at the same time based on the determination result in the step S2. As a result, when it is determined that the operation requests of both mechanisms are not issued at the same time, the process proceeds to step S5 described later, and the operation of the mechanism for which the operation request is issued is performed.

  On the other hand, if it is determined in step S3 that the operation requests for both mechanisms are issued at the same time, the process proceeds to the next step S4 so that these mechanisms can be operated at the same time. It is determined whether or not. Specifically, it is determined whether or not the current oil pressure detected by the oil pressure sensor 38 is equal to or greater than a predetermined value X. As the predetermined value X, a preset value is read as a hydraulic pressure value capable of operating the variable valve timing mechanism 34 and the variable valve lift mechanism 36 at the same time. As a result, when the establishment of hydraulic pressure ≧ predetermined value X is recognized, it is determined that both mechanisms can be operated at the same time, and the process proceeds to the next step S5, where the variable valve timing mechanism 34 performs phase variable operation and The intake cam switching operation by the variable valve lift mechanism 36 is performed at the same time. Specifically, the variable valve timing mechanism 34 is operated in accordance with an operation map that defines the relationship between the operation state specified from the engine speed and the engine load and the control amount of the variable valve timing mechanism 34. Further, the variable valve lift mechanism 36 performs the same operation as the operation in the first embodiment described above, and is switched to the small lift cam by the switching operation by the start time T.

  On the other hand, if the establishment of hydraulic pressure ≧ predetermined value X is not recognized in step S4, it is determined that these mechanisms cannot be operated at the same time, and the process proceeds to the next step S6 where the variable valve timing mechanism 34 Priority arbitration is performed between the phase variable operation and the intake cam switching operation by the variable valve lift mechanism 36. FIG. 6 is a flowchart showing a routine for control executed by the ECU 50 in the second embodiment. In step S6, specifically, the routine shown in FIG. 6 is executed.

  In the routine shown in FIG. 6, first, in step S10, priority arbitration is performed between the phase variable operation by the variable valve timing mechanism 34 and the intake cam switching operation by the variable valve lift mechanism 36. FIG. 7 is a diagram illustrating an operation region map used for priority arbitration. FIG. 8 is a diagram for explaining a change in the valve opening characteristic of the intake valve when priority arbitration is performed. 8A shows the case where the advance amount of the intake valve phase is the maximum and switching to the small lift cam, and FIG. 8B shows the case where the advance amount of the intake valve phase is minimized. (C) in FIG. 8 shows a case where the advance amount of the intake valve phase is minimum and the switching is made to the small lift cam. Each is shown.

  In the operation region map shown in FIG. 7, the region (A) belonging to the region from the low rotation medium load to the low rotation high load, the region (B) belonging to the region from the low rotation low load to the low rotation medium load, and the high rotation region Priority arbitration is performed separately for the (C) region belonging to. More specifically, if the EGR gas is introduced when the current operating state belongs to the region (A) in the figure, the intake air amount is insufficient only by controlling the throttle valve 22 and the wastegate valve (not shown). For this reason, at the time of deceleration, it is necessary to increase the intake and intake efficiency and the supercharging pressure by the operation of the variable valve timing mechanism 34, thereby increasing the operation amount (advance amount) of the variable valve timing mechanism 34.

  (A) in FIG. 8 shows an example in which switching from the state of the (A) region to the small lift cam is performed with priority. FIG. 9 is a diagram showing changes in the intake air amount with respect to the throttle opening. As shown in FIG. 9, it can be seen that when the intake cam is switched from the first lift cam to the small lift cam in a high load range where the throttle opening is large, the amount of intake air is greatly reduced. Further, as shown in FIG. 8A, when priority is given to switching to the small lift cam, the IVC after switching to the small lift cam deviates from the bottom dead center aim, so the amount of intake air is small. Insufficient misfire can not be suppressed.

  On the other hand, (b) in FIG. 8 shows that the variable valve timing mechanism 34 is preferentially operated so that the IVC after switching from the state of the (A) region to the small lift cam is aimed at the bottom dead center. The example at the time of switching to a lift cam is shown. In this case, since the IVC after switching to the small lift cam becomes the target bottom dead center, the effect of suppressing misfire is enhanced.

  If the current operating state belongs to the region (B) in the figure, the intake air amount can be controlled by controlling the throttle valve 22 and the wastegate valve (not shown) even if EGR gas is introduced. it can. For this reason, at the time of deceleration, the operation amount (advance amount) of the variable valve timing mechanism 34 becomes small.

  (C) in FIG. 8 shows an example in which switching from the state of the (B) region to the small lift cam is performed with priority. In this case, in this case, the IVC after switching to the small lift cam becomes the target bottom dead center, so the effect of suppressing misfire is enhanced.

  When the current operating state belongs to the region (C) in the figure, the engine rotation speed is high and the hydraulic pressure is high. Therefore, the phase variable operation by the variable valve timing mechanism 34 and the intake cam switching by the variable valve lift mechanism 36 are switched. Operations can be performed at the same time, and there is no need for priority arbitration.

  As described above, in step S10, the variable valve timing mechanism 34 and the variable valve lift mechanism 36 switch the intake cam according to which region of the operation region map shown in FIG. Which of these is prioritized is determined.

  If it is determined in step S10 that the current operation state belongs to the (A) region, it is determined that the phase variable operation by the variable valve timing mechanism 34 should be prioritized, and the process proceeds to the next step S11. In step S11, the variable valve timing mechanism 34 is varied to the retard side until the advance amount becomes a VVT predetermined value or less. Note that the VVT predetermined value uses an operation amount for IVC to be near the bottom dead center when switching to the small lift cam. FIG. 10 is a diagram illustrating the misfire resistance when the EGR is introduced with respect to the operation amount of the variable valve timing mechanism 34. (A) and (b) shown in this figure correspond to the operations of (a) and (b) shown in FIG. As shown in this figure, it is understood that the misfire resistance is increased by changing the intake valve to the small lift cam after changing the variable valve timing mechanism 34 to a position where the VVT is not more than the predetermined value.

  When the process of step S11 is completed, the process proceeds to the next step S12. In step S12, it is determined whether or not the current time has reached a predetermined switching timing time. The predetermined switching timing time is the switching timing considering the start time T in the first embodiment. As a result, when it is recognized that the current time ≧ the predetermined switching timing time is established, the process proceeds to the next step S13, and switching to the small lift cam is immediately performed.

  On the other hand, if the establishment of the current time ≧ predetermined switching timing time is not recognized in step S12, the process proceeds to the next step S14 to determine whether or not the VVT predetermined value is different from the map value of the deceleration destination. Is done. As a result, if it is recognized that VVT predetermined value ≠ map value is established, the process proceeds to the next step S15 and the variable valve timing mechanism 34 is operated toward the map value until a predetermined switching timing time is reached. After the process of step S15, or when the predetermined value ≠ map value is not recognized in step S14, the process proceeds to the next step S16, and the switching operation to the small lift cam is executed at a predetermined switching timing time. The

  When the intake cam of the variable valve lift mechanism 36 is switched to the small lift cam in step S13 or step S16, the process proceeds to step S17. In step S17, it is determined whether or not the current operation amount of the variable valve timing mechanism 34 has reached the map value. As a result, when the operation amount has not yet reached the map value, the process proceeds to the next step S18, and the variable valve timing mechanism 34 is operated to the map value.

  If it is determined in step S10 that the current operating state belongs to the region (B), it is determined that the switching operation of the intake cam by the variable valve lift mechanism 36 should be prioritized, and the next step S19. Migrate to In step S19, the variable valve timing mechanism 34 is operated toward the position where the operation amount becomes the map value until the predetermined switching timing time elapses. Then, when the predetermined switching timing time is reached in step S20, the operation of the variable valve timing mechanism 34 is stopped. Then, in the next step S21, the switching operation to the small lift cam is executed at a predetermined switching timing time. When the process of step S21 is completed, the process proceeds to step S17, and the operation of the variable valve timing mechanism 34 is performed.

  The effect of the priority arbitration described above will be described using a time chart. FIG. 11 is a time chart showing changes in various state quantities when priority arbitration is performed. In the example shown in this figure, the solid line indicates the case where the priority arbitration is executed according to the routine shown in FIG. 6, the one-dot chain line indicates the comparative example in which the switching to the small lift cam is executed at the highest speed, and the chain line indicates the operation of the variable valve timing mechanism 34. Comparative examples in which are executed at the fastest speed are shown.

  In the operation example shown in FIG. 11, when a deceleration request is issued at time t1, the variable valve timing mechanism 34 is operated so that the operation amount becomes equal to or less than the VVT predetermined value. At time t2, the operation of the variable valve timing mechanism 34 is stopped and the switching operation of the intake cam by the variable valve lift mechanism 36 is started. Then, at time t3 when the engine load reaches the misfire limit lower limit, the switching to the small lift cam is completed. After time t3, the variable valve timing mechanism 34 is operated to the map value. According to such an operation, since the misfire limit tolerance at the time of introducing the EGR gas can be set high, the EGR rate that can be introduced in a steady state can be improved.

DESCRIPTION OF SYMBOLS 10 Internal combustion engine 12 Intake passage 14 Exhaust passage 16 Air cleaner 18 Air flow meter 20 Turbo supercharger 20a Compressor 20b Turbine 22 Throttle valve 24 Intake manifold 24a Surge tank 24b Intake branch pipe 26 Intercooler 30 Fuel injector 32 Spark plug 34 Variable valve timing mechanism 36 Variable valve lift mechanism 38 Hydraulic sensor 40 Catalyst 41 Muffler 42 EGR device 44 EGR passage 46 EGR cooler 48 EGR valve 50 ECU (Electronic Control Unit)

Claims (1)

A variable valve lift mechanism capable of switching the lift amount of the intake valve between a large lift amount and a small lift amount;
An exhaust gas recirculation device for performing an exhaust gas recirculation operation for recirculating part of the burned gas exhausted from the cylinder of the internal combustion engine into the cylinder;
In an operating state in which the lift amount of the intake valve is controlled to the large lift amount and the exhaust gas recirculation operation is being performed, a low load request is issued that is below the misfire limit lower limit load, which is the lower limit of the load at which misfire does not occur. Control means for performing a switching operation of operating the variable valve lift mechanism to switch the lift amount of the intake valve from the large lift amount to the small lift amount,
The control means, when the load of the internal combustion engine reaches the misfire limit lower limit load based on the time until the load of the internal combustion engine reaches the misfire limit lower limit load and the time required for the switching operation, A control device for an internal combustion engine, wherein the start timing of the switching operation is controlled so that the switching operation is completed.

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