JP2018131961A - Control device and control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control device and a control method which prevents the lowering of a proportion of exhaust with respect to air intake on EGR upon the driving of an additional supercharger.SOLUTION: An internal combustion engine includes: a cylinder; an intake valve; an exhaust valve; a variable valve mechanism; a first supercharger including a turbine of an exhaust passage and a first compressor of an intake passage; a second supercharger including a second compressor of the intake passage; an EGR passage which connects the exhaust passage and the intake passage without passing through the cylinder; and an EGR valve which adjusts a gas flow rate passing through the interior of the EGR passage according to an opening and closing movement. A control device controls the variable valve mechanism such that a change manner can be made to be a first manner or a second manner in which a proportion of exhaust on an inner part of the cylinder when the exhaust valve is closed becomes more than the first manner, controls the variable valve mechanism so as to totally close the EGR valve when an intake pressure of a connection part of the suction passage and the EGR passage is higher than an exhaust pressure of a connection part of the exhaust passage and the EGR passage (S103) and controls the variable valve mechanism such that the change manner is made to be the second manner (S104).SELECTED DRAWING: Figure 2

Description

  The present invention relates to a control device and a control method, and more particularly to a control device and a control method for an internal combustion engine.

  Conventionally, there has been an internal combustion engine equipped with an exhaust gas recirculation (EGR) system that reintakes part of exhaust gas generated in the internal combustion engine. In some of such internal combustion engines, an additional supercharger is provided in addition to a turbocharger that increases the pressure of intake air by the energy of exhaust gas. For example, as an additional supercharger, an electric compressor that increases the pressure of intake air with an electric motor may be used (see, for example, Patent Document 1).

JP, 2014-234808, A

  In such a configuration, when the electric compressor is driven, the pressure on the intake side may be higher than the pressure on the exhaust side. In such a case, in the EGR system, the pressure on the exhaust side becomes lower than the pressure on the intake side, so that the exhaust cannot be guided to the intake side. For this reason, there has been a problem that the EGR rate, which is the ratio of the exhaust to the intake air taken into the cylinder of the internal combustion engine, decreases.

  The present invention has been made to solve the above-described problems, and the object thereof is to reduce the ratio of exhaust to intake air in EGR even when an additional supercharger provided in an internal combustion engine is driven. It is an object of the present invention to provide a control device and a control method that can prevent this.

  The control device according to the present invention is a control device for an internal combustion engine. The internal combustion engine is provided in a cylinder, an intake valve, an exhaust valve, a variable valve mechanism that can change a change amount of a lift amount of at least one of the intake valve and the exhaust valve, a turbine provided in the exhaust passage, and an intake passage. A first supercharger including a first compressor, a second supercharger including a second compressor provided in the intake passage, an EGR passage connecting the exhaust passage and the intake passage without passing through the cylinder, and an opening / closing operation And an EGR valve for adjusting the flow rate of the gas passing through the EGR passage.

  The control device may control the variable valve mechanism so that the change mode is the first mode, or the second mode in which the ratio of exhaust inside the cylinder when the exhaust valve is closed is greater than the first mode. When the intake pressure at the connection portion between the intake passage and the EGR passage is higher than the exhaust pressure at the connection portion between the exhaust passage and the EGR passage, the EGR valve is controlled to be fully closed, and the variable valve mechanism And the change mode is set as the second mode.

  Preferably, the control device controls to open the EGR valve when the intake pressure becomes lower than the exhaust pressure, and controls the variable valve mechanism to set the change mode as the first mode.

  Preferably, the second aspect is an aspect in which the exhaust valve is closed earlier than the first aspect, or an upper limit value of the lift amount of the exhaust valve is made smaller than that in the first aspect.

  Preferably, the second mode is a mode in which the intake valve is opened earlier than the first mode, or an upper limit value of the lift amount of the intake valve is set to be larger than that in the first mode.

  A control method according to another aspect of the present invention is a control method for an internal combustion engine. The internal combustion engine is provided in a cylinder, an intake valve, an exhaust valve, a variable valve mechanism that can change a change amount of a lift amount of at least one of the intake valve and the exhaust valve, a turbine provided in the exhaust passage, and an intake passage. A first supercharger including a first compressor, a second supercharger including a second compressor provided in the intake passage, an EGR passage connecting the exhaust passage and the intake passage without passing through the cylinder, and an opening / closing operation And an EGR valve for adjusting the flow rate of the gas passing through the EGR passage.

  The control method is such that the control device of the internal combustion engine controls the variable valve mechanism to change the change mode to the first mode, or the ratio of exhaust inside the cylinder when the exhaust valve is closed is higher than the first mode. When the intake pressure at the connection portion between the intake passage and the EGR passage is higher than the exhaust pressure at the connection portion between the exhaust passage and the EGR passage, the EGR valve is fully closed. And controlling the variable valve mechanism to change the change mode to the second mode.

  According to this invention, when the intake pressure is higher than the exhaust pressure, the EGR valve in the EGR passage is fully closed. For this reason, intake air can be prevented from flowing into the exhaust side. In addition, when the intake pressure is higher than the exhaust pressure, the variable valve mechanism is controlled so that the ratio of exhaust inside the cylinder when the exhaust valve is closed is higher than when the intake pressure is lower than the exhaust pressure. The As a result, it is possible to provide a control device and a control method capable of preventing a reduction in the ratio of exhaust to intake air in the EGR even when the second supercharger which is an additional supercharger is driven. it can.

It is a figure which shows the outline of an example of a structure of the engine in this Embodiment. It is a flowchart which shows the flow of the EGR rate reduction | decrease suppression process in this Embodiment. It is a figure which shows the control state of the variable valve mechanism in this Embodiment. It is a figure which shows the change of the value relevant to the control at the time of acceleration. It is a figure for demonstrating the effect in this Embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

[Configuration around the engine in the present embodiment]
FIG. 1 is a diagram schematically showing an example of the configuration of the engine 10 in the present embodiment. Referring to FIG. 1, engine 10 is assumed to be a diesel engine in the present embodiment. However, the present invention is not limited to this, and other types of engines such as gasoline engines may be used.

  The engine 10 includes a plurality of combustion chambers 11 and one or more intake valves 12 and exhaust valves 13 for each combustion chamber 11. The combustion chamber 11 is a space surrounded by a cylinder, a cylinder head, and a piston in a reciprocating engine such as a diesel engine such as the engine 10 of the present embodiment. The part forming the space of the combustion chamber 11 is called a cylinder for convenience. The engine 10 of this embodiment operates as follows. (1) After the intake valve 12 is opened and the exhaust valve 13 is closed, intake air is drawn into the combustion chamber 11. (2) The intake valve 12 is closed and the intake air in the combustion chamber 11 is compressed. (3) After compression, fuel is injected into the combustion chamber 11 and combusted to expand the combustion gas, thereby generating power. (4) The exhaust valve 13 is opened, and the combustion gas in the combustion chamber 11 is discharged as exhaust.

  The intake air drawn from the intake port is drawn into the turbocharger 23 via the air cleaner 21 and the intake passage 22. The turbocharger 23 includes a turbine provided in the exhaust passage and a compressor provided in the intake passage, and raises the pressure of the intake air by a compressor that is operated by energy applied to the turbine from the exhaust in the exhaust passage.

  The intake air whose pressure has been increased by the turbocharger 23 enters the intercooler 25 via the intake passage 24. The intercooler 25 cools the intake air whose temperature has increased in the turbocharger 23 due to adiabatic compression.

  When the electric compressor 27 is driven via the intake passage 26, the intake air cooled by the intercooler 25 is sucked into the electric compressor 27 by closing the bypass valve 28, and the electric compressor 27 is not driven. The bypass valve 28 is opened and flows into the intake passage 29. The electric compressor 27 increases the pressure of intake air by a compressor operated by an electric motor. The electric compressor 27 assists when the supercharging pressure of the turbocharger 23 does not increase the exhaust energy and does not reach the supercharging pressure required according to the vehicle speed, accelerator opening, etc. during vehicle acceleration. Thus, the driving state (ON state) is established.

  The intake air whose pressure has been further increased by the electric compressor 27 or the intake air that has passed through the bypass valve 28 is controlled in flow rate by the diesel throttle 19 via the intake passage 29 and flows into the intake manifold 14. The diesel throttle 19 is a valve that adjusts the amount of intake air flowing into the combustion chamber 11, and is controlled according to the amount of exhaust gas that is recirculated, which will be described later. The intake air that has flowed into the intake manifold 14 flows into the combustion chamber 11 via any one of the intake valves 12 that are sequentially opened at a predetermined valve timing.

  Exhaust gas in the combustion chamber 11 flows into the exhaust manifold 15 via an exhaust valve 13 opened at a predetermined valve timing. Exhaust gas collected by the exhaust manifold 15 flows into the turbine side of the turbocharger 23. Exhaust gas that gives energy to the turbine by the turbocharger 23 is discharged from the exhaust port via the exhaust passage 31.

  The variable valve mechanism 16 changes the change mode (opening / closing timing and maximum lift amount) of the lift amount of at least one of the intake valve 12 and the exhaust valve 13 according to the situation.

  A part of the exhaust collected by the exhaust manifold 15 enters the EGR cooler 33 via the connection passage 32 for guiding the exhaust for EGR to the intake side. The EGR cooler 33 cools the hot exhaust gas.

  The exhaust gas cooled by the EGR cooler 33 is controlled in flow rate by the EGR valve 35 via the connection passage 34 and further returned to the intake manifold 14 via the connection passage 36. The EGR valve 35 is a valve that adjusts the amount of exhaust gas returned to the intake side, and is controlled according to the operating state of the engine 10. The exhaust gas returned to the intake manifold 14 flows into the combustion chamber 11 together with the intake air flowing into the intake manifold 14.

  The ECU (Electronic Control Unit) 100 is a device that controls the engine 10. The pressure sensor 17 provided in the intake manifold 14 detects the pressure of the connection portion on the intake side of the EGR system (in this embodiment, the pressure of the intake manifold 14). The pressure sensor 18 provided in the exhaust manifold 15 detects the pressure at the exhaust-side connection portion of the EGR system (in this embodiment, the pressure of the exhaust manifold 15). ECU 100 receives detection signals from pressure sensors 17 and 18 and the like.

  The ECU 100 controls the variable valve mechanism 16, the diesel throttle 19, the bypass valve 28, the EGR valve 35, and the electric compressor 27 according to sensor values such as values indicated by detection signals from the pressure sensors 17 and 18. .

[Description of EGR rate decrease suppression processing]
In the configuration as described above, the EGR rate may decrease during operation of the electric compressor 27. Specifically, when the electric compressor 27 is operated, the intake pressure of the intake manifold 14 may become higher than the exhaust pressure of the exhaust manifold 15.

  In such a case, the exhaust on the side of the exhaust manifold 15 having a low pressure cannot be guided to the side of the intake manifold 14 having a high pressure. For this reason, the EGR rate that is the ratio of the exhaust to the intake air sucked into the combustion chamber 11 is lowered.

  Therefore, in the present embodiment, when the pressure on the intake manifold 14 side, that is, on the intake side, is higher than the pressure on the exhaust manifold 15 side, that is, on the exhaust side, the EGR valve 35 is controlled to close, and the exhaust valve The variable valve mechanism 16 is controlled so that the ratio of the exhaust gas inside the combustion chamber 11 when 13 is closed is higher than the normal control when the pressure on the intake side is lower than the pressure on the exhaust side. As a result, even when an additional supercharger such as the electric compressor 27 is driven, it is possible to prevent the ratio of exhaust to intake air in the EGR from decreasing.

  FIG. 2 is a flowchart showing the flow of the EGR rate decrease suppression process in the present embodiment. Referring to FIG. 2, this EGR rate decrease suppression process is read from a main process repeatedly executed at a predetermined cycle by ECU 100 and executed as a subroutine, for example.

  First, the ECU 100 determines whether or not the electric compressor 27 is being driven (step (hereinafter, step is referred to as S) 101). If it is determined that the engine is not being driven (NO in S101), the ECU 100 ends the EGR rate decrease suppression process and returns the process to be executed to the caller process.

  On the other hand, when it is determined that the electric compressor 27 is being driven (YES in S101), the pressure Pin of the intake manifold 14 is calculated in accordance with the detection signal from the pressure sensor 17, and the exhaust manifold is in accordance with the detection signal from the pressure sensor 18. The pressure Pex of 15 is calculated, and it is determined whether or not the pressure Pin> the pressure Pex (S102).

  When it is determined that the pressure Pin> the pressure Pex (YES in S102), the ECU 100 controls the EGR valve 35 to be fully closed (S103). Next, the ECU 100 turns on a VVT (Variable Valve Timing) flag (S104). Thereafter, the ECU 100 ends the EGR rate decrease suppression process and returns the process to be executed to the caller process.

  FIG. 3 is a diagram showing a control state of the variable valve mechanism 16 in the present embodiment. Referring to FIG. 3, the variable valve mechanism 16 is configured to be able to switch between two cams for opening and closing the exhaust valve 13. Each of the two cams has shapes A and B in which the lift amount of the exhaust valve 13 is changed, and the shape B is the shape A in which the ratio of the exhaust gas in the combustion chamber 11 when the exhaust valve 13 is closed is the shape A. More shapes than the above. In the present embodiment, the change modes of the exhaust valve 13 corresponding to the shapes A and B are the broken line and the solid line in FIG. 3, respectively. Thus, the shape B has a shape in which the closing timing of the exhaust valve 13 is earlier than that in the shape A and the maximum lift amount is small. When the VVT flag is on, the ECU 100 controls the variable valve mechanism 16 to switch to the shape B cam. As a result, the exhaust speed is reduced, and the exhaust valve 13 is closed with more exhaust remaining in the combustion chamber 11.

  Returning to FIG. 2, if it is determined that the pressure Pin> the pressure Pex is not satisfied (NO in S102), the ECU 100 returns the EGR valve 35 to the normal control (S111). In this normal control of the EGR valve 35, the EGR valve 35 is controlled so as to have an EGR rate calculated from various conditions such as the engine speed, the intake air amount, and the intake and exhaust pressures and temperatures. .

  Next, the ECU 100 turns off the VVT flag (S112). Thereafter, the ECU 100 ends the EGR rate decrease suppression process and returns the process to be executed to the caller process.

  Referring to FIG. 3 again, when the VVT flag is in the OFF state, ECU 100 returns variable valve mechanism 16 to normal control. In the normal control of the variable valve mechanism 16, the cam of the exhaust valve 13 is switched from the cam of the shape B to the cam of the shape A.

  FIG. 4 is a diagram illustrating changes in values related to control during acceleration. Referring to FIG. 4, when the accelerator is depressed greatly as shown in the first graph, and there is a large acceleration request, the torque for acceleration is increased as shown in the second graph. In order to generate a larger amount, the ECU 100 controls the electric compressor 27 to be turned on.

  When the electric compressor 27 is turned on, the pressure Pin of the intake manifold 14 rises relatively large, as shown by the third graph. Thereby, the pressure Pin exceeds the pressure Pex of the exhaust manifold 15.

  In such a state, the control of S103 and S104 in FIG. 2 is performed, so that the EGR valve 35 is fully closed and the VVT flag is set as shown in the fifth and fourth graphs. It is turned on.

  Thereafter, when the pressure Pex of the exhaust manifold 15 exceeds the pressure Pin of the intake manifold 14 as shown in the third graph by the increase in the rotational speed of the engine 10, the control of S111 and S112 in FIG. As a result, the EGR valve 35 and the variable valve mechanism 16 are returned to the normal control as shown in the graphs of the fifth and fourth stages.

  Thereafter, when the exhaust energy increases and the turbocharger 23 reaches the required supercharging pressure, the ECU 100 turns off the electric compressor 27 as shown in the second graph. Be controlled.

  FIG. 5 is a diagram for explaining the effect of the present embodiment. Referring to FIG. 5, “with VVT” in the figure indicates the case where the control of the VVT flag of S104 and S112 in FIG. 2 is present, and “without VVT” indicates the control of the VVT flag of S104 and S112 of FIG. Indicates no case.

  The first graph in FIG. 5 is the same as the third graph in FIG. When the electric compressor 27 is driven and the pressure Pin of the intake manifold 14 is higher than the pressure Pex of the exhaust manifold 15, the EGR valve 35 is fully closed, but if the VVT flag is not turned on, 2 in FIG. As indicated by the broken-line graph at the stage, the in-cylinder EGR rate, that is, the EGR rate inside the combustion chamber 11 becomes almost zero. Further, as indicated by the broken line graph in the third row in FIG. 5, the NOx emission amount increases significantly as the EGR rate decreases.

  On the other hand, when the EGR valve 35 is fully closed and the VVT flag is turned on, the in-cylinder EGR rate of the in-cylinder EGR rate is greater than the pressure Pex, as shown by the solid line graph in FIG. Compared to when it is small, it can maintain almost the same value. Further, as shown by the solid line graph in the third stage of FIG. 5, the NOx emission amount is substantially the same value as when the pressure Pin is smaller than the pressure Pex because the EGR rate does not substantially decrease. Can be maintained.

[Modification]
(1) In the above-described embodiment, as shown in FIG. 1, the configuration for EGR is an EGR that recirculates exhaust gas from upstream of the turbine of the turbocharger 23 to downstream of the compressor of the turbocharger 23, so-called HPL (High Pressure Loop) -EGR.

  However, the present invention is not limited to this, and the embodiment described above is applied to EGR for recirculating exhaust gas from the downstream of the turbine of the turbocharger 23 to the upstream of the compressor of the turbocharger 23, so-called LPL (Low Pressure Loop) -EGR. Can do. Moreover, it is applicable to the structure provided with HPL-EGR and LPL-EGR. Furthermore, the present invention can be applied to a configuration including a plurality of turbochargers.

  (2) In the above-described embodiment, the variable valve mechanism 16 is configured to make the change mode (the closing timing and the maximum lift amount) of the lift amount of the exhaust valve 13 variable. Specifically, by switching the cam of the exhaust valve 13 from the shape A to the shape B in S104 of FIG. 2, the closing timing of the exhaust valve 13 is made earlier and the maximum lift amount is made smaller than in the case of the shape A. I did it.

  However, the present invention is not limited to this, and when the pressure Pin of the intake manifold 14 is higher than the pressure Pex of the exhaust manifold 15, the ratio of exhaust inside the combustion chamber 11 when the exhaust valve is closed is higher than when the pressure is low. In other words, the variable valve mechanism 16 may have another configuration as long as the exhaust can be kept in the combustion chamber 11 as much as possible at the time of transition from the exhaust stroke to the intake process.

  For example, the maximum lift amount of the exhaust valve 13 may be left as it is, and the closing timing may be advanced, the opening timing of the intake valve 12 may be advanced, or the opening timing of the intake valve 12 may be accelerated. In addition, the maximum lift amount may be increased, or both the exhaust valve 13 and the intake valve 12 may be controlled as described above.

  (3) In the above-described embodiment, the auxiliary supercharger for the turbocharger 23 that is the main supercharger is the electric compressor 27. However, the present invention is not limited to this, and the auxiliary supercharger may be a mechanical supercharger that is driven by power from the output shaft of the engine 10.

[Summary]
The embodiment described above is summarized below. As shown in FIG. 1, the ECU 100 is a control device for the engine 10. The engine 10 includes a combustion chamber 11, an intake valve 12, an exhaust valve 13, a variable valve mechanism 16, a turbocharger 23, an electric compressor 27, connection passages 32, 34 and 36, and an EGR valve 35. . The intake valve 12 opens and closes an intake passage to the combustion chamber 11. The exhaust valve 13 opens and closes an exhaust passage from the combustion chamber 11. The variable valve mechanism 16 changes at least one of the change modes (opening / closing timing and maximum lift amount) of at least one of the intake valve 12 and the exhaust valve 13. The turbocharger 23 includes a turbine provided in the exhaust passage and a compressor provided in the intake passage, and raises the pressure of the intake air by a compressor that is operated by energy applied to the turbine from the exhaust in the exhaust passage. The electric compressor 27 increases the pressure of the intake air by a compressor that is provided in the intake passage and operates with energy different from the energy from the exhaust. The connection passages 32, 34, and 36 connect the exhaust passage and the intake passage. The EGR valve 35 is provided in the connection passages 32, 34 and 36 and opens and closes the connection passages 32, 34 and 36.

  As shown in FIG. 2, the ECU 100 identifies the pressure Pin of the intake manifold 14 that is the connection portion of the connection passage 36 of the intake passage, and sets the pressure Pex of the exhaust manifold 15 that is the connection portion of the connection passage 32 of the exhaust passage. Specifically, when the pressure Pin is higher than the pressure Pex, the EGR valve 35 is controlled to be closed, and the ratio of the exhaust gas inside the combustion chamber 11 when the exhaust valve 13 is closed is such that the pressure Pin is higher than the pressure Pex. The variable valve mechanism 16 is controlled so as to be higher than the normal control when it is low.

  Thereby, when the pressure Pin is higher than the pressure Pex, the EGR valve 35 of the connection passages 32, 34, and 36 is closed. For this reason, intake air can be prevented from flowing into the exhaust side. Further, when the pressure Pin is higher than the pressure Pex, the ratio of the exhaust inside the combustion chamber 11 when the exhaust valve 13 is closed is higher than that in the normal control when the pressure Pin is lower than the pressure Pex. The variable valve mechanism 16 is controlled. For this reason, when the pressure Pin is higher than the pressure Pex, the control of the variable valve mechanism 16 increases the ratio of the exhaust to the intake air inside the combustion chamber 11 when the exhaust valve 13 is closed, compared to the normal control. As a result, it is possible to prevent the EGR rate from decreasing even when the electric compressor 27 is driven.

  In addition, when the pressure Pin becomes lower than the pressure Pex, the ECU 100 returns the EGR valve 35 to the normal control and returns the variable valve mechanism 16 to the normal control.

  Further, when the pressure Pin is higher than the pressure Pex, the ECU 100 controls the variable valve mechanism 16 so as to close the exhaust valve 13 early or reduce the maximum lift amount of the exhaust valve 13.

  Further, the ECU 100 may control the variable valve mechanism 16 so that the intake valve 12 is opened early or the maximum lift amount of the intake valve 12 is increased when the pressure Pin is higher than the pressure Pex.

  In the above-described embodiment, the invention has been described as a control device such as the ECU 100. However, the present invention is not limited to this, and the invention can be understood as a method in which the control device controls an internal combustion engine such as the engine 10 or a program for the control device that controls the internal combustion engine.

  The embodiments disclosed this time are also scheduled to be implemented in appropriate combinations. The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description of the embodiments but by the scope of claims for patent, and is intended to include meanings equivalent to the scope of claims for patent and all modifications within the scope.

  DESCRIPTION OF SYMBOLS 10 Engine, 11 Combustion chamber, 12 Intake valve, 13 Exhaust valve, 14 Intake manifold, 15 Exhaust manifold, 16 Variable valve mechanism, 17, 18 Pressure sensor, 19 Diesel throttle, 21 Air cleaner, 22, 24, 26, 29 Intake passage , 23 Turbocharger, 25 Intercooler, 27 Electric compressor, 28 Bypass valve, 31 Exhaust passage, 32, 34, 36 Connection passage, 33 EGR cooler, 35 EGR valve, 100 ECU.

Claims (5)

A control device for an internal combustion engine,
The internal combustion engine
Cylinders,
An intake valve;
An exhaust valve;
A variable valve mechanism for changing a change mode of a lift amount of at least one of the intake valve and the exhaust valve;
A first supercharger including a turbine provided in the exhaust passage and a first compressor provided in the intake passage;
A second supercharger including a second compressor provided in the intake passage;
An EGR passage connecting the exhaust passage and the intake passage without going through the cylinder;
An EGR valve that adjusts the flow rate of gas passing through the EGR passage by an opening and closing operation;
The controller is
By controlling the variable valve mechanism, the change mode is the first mode, or the second mode in which the ratio of the exhaust inside the cylinder when the exhaust valve is closed is larger than the first mode. Is possible,
When the intake pressure at the connection portion between the intake passage and the EGR passage is higher than the exhaust pressure at the connection portion between the exhaust passage and the EGR passage, the EGR valve is controlled to be fully closed and the variable The control apparatus which controls a valve mechanism and sets the change mode as the second mode.   When the intake pressure becomes lower than the exhaust pressure, the control device controls the EGR valve so that a ratio of exhaust to intake inside the cylinder becomes a ratio calculated from a predetermined condition regarding the internal combustion engine. The control device according to claim 1, wherein the control mode is returned to normal control, and the variable valve mechanism is controlled to set the change mode as the first mode.   The said 2nd aspect is an aspect which closes the said exhaust valve earlier than the said 1st aspect, or an aspect which makes the upper limit of the lift amount of the said exhaust valve smaller than the said 1st aspect. Control device.   The said 2nd aspect is an aspect which opens the said intake valve earlier than the said 1st aspect, or is an aspect which makes the upper limit of the lift amount of the said intake valve larger than the said 1st aspect. Control device. A control method for an internal combustion engine comprising:
The internal combustion engine
Cylinders,
An intake valve;
An exhaust valve;
A variable valve mechanism for changing a change mode of a lift amount of at least one of the intake valve and the exhaust valve;
A first supercharger including a turbine provided in the exhaust passage and a first compressor provided in the intake passage;
A second supercharger including a second compressor provided in the intake passage;
An EGR passage connecting the exhaust passage and the intake passage without going through the cylinder;
An EGR valve that adjusts the flow rate of gas passing through the EGR passage by an opening and closing operation;
In the control method, the control device for the internal combustion engine includes:
By controlling the variable valve mechanism, the change mode is the first mode, or the second mode in which the ratio of the exhaust inside the cylinder when the exhaust valve is closed is larger than the first mode. Possible steps,
When the intake pressure at the connection portion between the intake passage and the EGR passage is higher than the exhaust pressure at the connection portion between the exhaust passage and the EGR passage, the EGR valve is controlled to be fully closed and the variable Controlling the valve mechanism to change the change mode to the second mode.

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