JP2021120543A - Control system for internal combustion engine - Google Patents

Abstract

To suppress variation in air-fuel ratio caused between a first cylinder group and a second cylinder group.SOLUTION: An internal combustion engine includes: a first exhaust gas passage between a first cylinder group and a turbine wheel; and a second exhaust gas passage between a second cylinder group and the turbine wheel. Also, the internal combustion engine includes an EGR passage connecting the first exhaust gas passage and the air intake passage among the first exhaust gas passage and the second exhaust gas passage. A control device controls, when the opening degree of the waste gate valve is small, an intake-side variable valve mechanism and an exhaust-side variable valve mechanism such that a valve overlap period is short compared to the case of large opening degree.SELECTED DRAWING: Figure 2

Description

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

The internal combustion engine described in Patent Document 1 includes a turbocharger. The turbocharger is equipped with a turbine wheel provided in the exhaust passage. Further, the internal combustion engine includes a first exhaust passage from the first cylinder group, which is a part of the plurality of cylinders, to the turbine wheel, and a turbine from the second cylinder group, which is the remaining cylinder of the plurality of cylinders. It has a second exhaust passage leading to the wheel. Further, the internal combustion engine includes an EGR passage connecting the first exhaust passage and the intake passage of the first exhaust passage and the second exhaust passage.

Japanese Unexamined Patent Publication No. 2012-127294

The present inventor has experimentally confirmed that the following events occur in an internal combustion engine including a turbocharger, a first exhaust passage and a second exhaust passage, and an EGR passage connecting the first exhaust passage and the intake passage. bottom.

-During the valve overlap period in which the intake valve and the exhaust valve are opened at the same time, there is a difference between the exhaust pressure of the first exhaust passage and the exhaust pressure of the second exhaust passage, and as a result, the intake passage to the first There is also a difference between the amount of intake air introduced into the 1-cylinder group and the amount of intake air introduced from the intake passage into the second cylinder group.

-As a result of a difference between the amount of intake air introduced from the intake passage into the first cylinder group and the amount of intake air introduced from the intake passage into the second cylinder group, between the first cylinder group and the second cylinder group. The air-fuel ratio varies.

The difference between the exhaust pressure of the first exhaust passage and the second exhaust pressure of the second exhaust passage during the valve overlap period becomes larger as the opening degree of the wastegate valve becomes smaller.
An object of the present invention is to suppress variations in the air-fuel ratio that occur between the first cylinder group and the second cylinder group.

The internal combustion engine control system for solving the above problems includes a changing mechanism for changing the valve overlap period, which is a period during which the intake valve and the exhaust valve are opened at the same time, and a control device for controlling the changing mechanism. , EGR passage connecting the exhaust passage and the intake passage, a turbine wheel provided in the exhaust passage, a bypass passage connecting the upstream side and the downstream side of the turbine wheel in the exhaust passage, and the bypass passage. A control system for a multi-cylinder internal combustion engine equipped with a turbocharger having a wastegate valve. Among a plurality of cylinders, some cylinders are designated as the first cylinder group and the remaining cylinders are designated as the second cylinder group. When, the exhaust passage includes a first exhaust passage which is a passage from the first cylinder group to the turbine wheel and a second exhaust passage from the second cylinder group to the turbine wheel, and the EGR passage includes the second exhaust passage. The intake passage is connected to either one of the first exhaust passage and the second exhaust passage, and the control device is compared with the case where the opening degree of the wastegate valve is small as compared with the case where the opening degree is large. Therefore, the change mechanism is controlled so that the valve overlap period is shortened.

In the above configuration, when the opening degree of the wastegate valve is small, the valve overlap period is shortened as compared with the case where the opening degree is large. Therefore, even if there is a difference between the exhaust pressure of the first exhaust passage and the exhaust pressure of the second exhaust passage during the valve overlap period, the intake amount introduced from the intake passage to the first cylinder group The difference between the intake amount introduced from the intake passage to the second cylinder group is less likely to occur. As a result, it is possible to suppress variations in the air-fuel ratio between the first cylinder group and the second cylinder group.

The schematic which shows the control system of an internal combustion engine. The flowchart which shows the setting control of a valve overlap period. Explanatory drawing which shows the exhaust pressure of the 1st exhaust passage and the exhaust pressure of the 2nd exhaust passage. The relationship diagram which shows the relationship between a valve overlap period and an air-fuel ratio.

Hereinafter, embodiments of an internal combustion engine control system applied to a vehicle will be described with reference to FIGS. 1 to 4.
As shown in FIG. 1, the internal combustion engine 10 includes an intake pipe 20, an intake manifold 25, an engine body 30, an exhaust manifold 40, an exhaust pipe 49, a turbocharger 70, an air cleaner 51, an intercooler 52, and a throttle valve 53. ing. The intake pipe 20 introduces intake air from the outside of the internal combustion engine 10. The air cleaner 51 is attached in the middle of the intake pipe 20.

The turbocharger 70 is attached to a portion of the intake pipe 20 on the downstream side of the air cleaner 51. The turbocharger 70 includes a housing 71. The housing 71 includes an intake flow passage 72 that connects the internal space on the upstream side and the internal space on the downstream side of the turbocharger 70 in the intake pipe 20.

The intercooler 52 is attached to a portion of the intake pipe 20 on the downstream side of the turbocharger 70. The intercooler 52 cools the intake air flowing through the inside of the intercooler 52. The throttle valve 53 is attached to the downstream end of the intake pipe 20. The throttle valve 53 adjusts the intake amount, which is the amount of intake air flowing through the intake pipe 20.

The intake manifold 25 includes one collecting pipe 26 and four branch pipes 27. The upstream end of the collecting pipe 26 is attached to the throttle valve 53. Each branch pipe 27 extends from the downstream end of the collecting pipe 26.

The downstream ends of the four branch pipes 27 are connected to the engine body 30. The engine body 30 includes four cylinders 33, eight intake ports 31, and eight exhaust ports 32. The four cylinders 33 are arranged in parallel on the left and right in FIG. When the cylinders 33 are described separately, the cylinders 33A, the cylinders 33B, the cylinders 33C, and the cylinders 33D will be described in order from the left side in FIG.

Each intake port 31 connects one cylinder 33 and the internal space of one branch pipe 27. The intake port 31 introduces intake air from the branch pipe 27 to the cylinder 33. Two intake ports 31 are provided for one cylinder 33. Note that FIG. 1 shows only one intake port 31 for one cylinder 33 for convenience.

Each exhaust port 32 connects one cylinder 33 to the outside of the engine body 30. The exhaust port 32 exhausts exhaust gas from the cylinder 33 to the outside of the engine body 30. Two exhaust ports 32 are provided for one cylinder 33. Note that FIG. 1 shows only one exhaust port 32 for one cylinder 33 for convenience. Further, when the exhaust port 32 is described separately, the exhaust port 32A, the exhaust port 32B, the exhaust port 32C, and the exhaust port 32D will be described in order from the left side in FIG.

The engine body 30 includes eight intake valves 36, eight exhaust valves 37, and four fuel injection valves 35. The intake valve 36 is arranged one by one at the connection portion of the intake port 31 and the cylinder 33. The intake valve 36 adjusts the intake amount, which is the amount of intake air flowing through the connection portion of the intake port 31 and the cylinder 33, by controlling the opening degree of the connection portion between the intake port 31 and the cylinder 33. Note that FIG. 1 shows only one intake valve 36 for one cylinder 33 for convenience.

The exhaust valve 37 is arranged one by one at the connecting portion of the exhaust port 32 and the cylinder 33. The exhaust valve 37 adjusts the amount of exhaust gas, which is the amount of exhaust gas flowing through the connection portion between the exhaust port 32 and the cylinder 33, by controlling the opening degree of the connection portion between the exhaust port 32 and the cylinder 33. Note that FIG. 1 shows only one exhaust valve 37 for one cylinder 33 for convenience. One fuel injection valve 35 is arranged in each cylinder 33. The fuel injection valve 35 injects fuel supplied from a fuel tank (not shown) into the cylinder 33.

The exhaust manifold 40 includes four branch pipes 41, one first collecting pipe 46, and one second collecting pipe 47. The upstream ends of the four branch pipes 41 are attached to the engine body 30. The internal space of the branch pipe 41 is connected to each of the four exhaust ports 32. When the branch pipe 41 is described separately, the branch pipe 41A, the branch pipe 41B, the branch pipe 41C, and the branch pipe 41D are described in order from the left side in FIG.

The downstream end of the branch pipe 41A and the downstream end of the branch pipe 41D are connected. The upstream end of the first collecting pipe 46 is connected to the connecting portion of the branch pipe 41A and the branch pipe 41D. The downstream end of the branch pipe 41B and the downstream end of the branch pipe 41C are connected. The upstream end of the second collecting pipe 47 is connected to the connecting portion of the branch pipe 41B and the branch pipe 41C. The downstream end of the first collecting pipe 46 and the downstream end of the second collecting pipe 47 are attached to the housing 71.

The turbocharger 70 includes a compressor wheel 81, a shaft 82, and a turbine wheel 83. The compressor wheel 81 is arranged in the middle of the intake flow passage 72. One end of the shaft 82 is connected to the compressor wheel 81. The turbine wheel 83 is connected to the other end of the shaft 82.

The housing 71 includes an exhaust flow passage 75 through which exhaust gas flows. The exhaust flow passage 75 includes a first exhaust introduction path 76, a second exhaust introduction path 77, and an exhaust discharge path 78. The first exhaust introduction path 76 extends from the internal space of the first collecting pipe 46 toward the turbine wheel 83. The first exhaust introduction path 76 introduces the exhaust gas that has passed through the internal space of the first collecting pipe 46 into the turbine wheel 83. Further, the second exhaust introduction path 77 extends from the internal space of the second collecting pipe 47 toward the turbine wheel 83. The second exhaust introduction path 77 introduces the exhaust gas that has passed through the internal space of the second collecting pipe 47 into the turbine wheel 83. The exhaust discharge path 78 extends from the turbine wheel 83 toward the outside of the housing 71. The exhaust discharge path 78 discharges the exhaust gas circulated through the turbine wheel 83 to the outside of the housing 71. An exhaust pipe 49 is attached to the housing 71. The internal space of the exhaust pipe 49 is connected to the exhaust discharge path 78.

The housing 71 includes a bypass passage 85 that connects a portion of the exhaust flow passage 75 upstream of the turbine wheel 83 and a portion downstream of the turbine wheel 83. The bypass passage 85 includes a first bypass passage 86, a second bypass passage 87, and a downstream bypass passage 88. The upstream end of the first bypass passage 86 is connected in the middle of the first exhaust introduction passage 76. The upstream end of the second bypass passage 87 is connected in the middle of the second exhaust introduction path 77. The downstream end of the first bypass passage 86 and the downstream end of the second bypass passage 87 are connected. The upstream end of the downstream bypass passage 88 is connected to the connecting portion of the first bypass passage 86 and the second bypass passage 87. The downstream end of the downstream bypass passage 88 is connected in the middle of the exhaust discharge passage 78.

The turbocharger 70 includes a wastegate valve 89 provided in the bypass passage 85. The wastegate valve 89 is arranged at a connecting portion of the first bypass passage 86, the second bypass passage 87, and the downstream bypass passage 88. The waste gate valve 89 is for exhaust flowing through the first bypass passage 86 and the second bypass passage 87 by controlling the opening degree of the waste gate valve 89 with respect to the downstream ends of the first bypass passage 86 and the second bypass passage 87. Adjust the amount of exhaust gas. The larger the opening degree of the wastegate valve 89, the larger the displacement, which is the amount of exhaust gas flowing through the first bypass passage 86 and the second bypass passage 87.

In the present embodiment, the internal space of the intake pipe 20, the internal space of the intake manifold 25, the intake flow passage 72, and the intake port 31 are intake passages. Further, the exhaust port 32, the internal space of the exhaust manifold 40, the exhaust flow passage 75, and the internal space of the exhaust pipe 49 are the exhaust passages.

The cylinder 33A and the cylinder 33D are the first cylinder group 11A, and the cylinder 33B and the cylinder 33C are the second cylinder group 11B. Further, the exhaust port 32A, the internal space of the branch pipe 41A, the exhaust port 32D, the internal space of the branch pipe 41D, the internal space of the first collecting pipe 46, and the first exhaust introduction path 76 are the turbine wheels from the first cylinder group 11A. It is the first exhaust passage 12A which is a passage to 83. Further, the exhaust port 32B, the internal space of the branch pipe 41B, the exhaust port 32C, the internal space of the branch pipe 41C, the internal space of the second collecting pipe 47, and the second exhaust introduction path 77 are the turbine wheels from the second cylinder group 11B. It is a second exhaust passage 12B which is a passage up to 83.

The internal combustion engine 10 includes an EGR tube 56, an EGR valve 57, and an EGR cooler 58. One end of the EGR pipe 56 is attached in the middle of the branch pipe 41D in the exhaust manifold 40. The other end of the EGR pipe 56 is attached in the middle of the collecting pipe 26 in the intake manifold 25. The EGR pipe 56 returns the exhaust gas flowing through the branch pipe 41D to the collecting pipe 26. The internal space of the EGR pipe 56 is the EGR passage 56A.

The EGR valve 57 is attached in the middle of the EGR pipe 56. The EGR valve 57 adjusts the exhaust amount, which is the amount of exhaust gas flowing from the branch pipe 41D side to the collecting pipe 26 side in the EGR passage 56A. The EGR cooler 58 is arranged closer to the collecting pipe 26 than the EGR valve 57 in the EGR pipe 56. The EGR cooler 58 cools the exhaust gas flowing through the EGR passage 56A.

The internal combustion engine 10 includes a hydraulically driven intake-side variable valve mechanism 61 and a hydraulically driven exhaust-side variable valve mechanism 62. The intake side variable valve mechanism 61 changes the relative rotation angle of the intake side camshaft with respect to the rotation angle of the crankshaft by changing the internal hydraulic circuit of the intake side variable valve mechanism 61. As a result, the timing at which the intake valve 36 opens and closes is changed with respect to the rotation angle of the crankshaft. The exhaust-side variable valve mechanism 62 changes the relative rotation angle of the exhaust-side camshaft with respect to the rotation angle of the crankshaft by changing the internal hydraulic circuit of the exhaust-side variable valve mechanism 62. As a result, the timing at which the exhaust valve 37 opens and closes with respect to the rotation angle of the crankshaft is changed.

The variable valve mechanism 61 on the intake side can change the length of the valve overlap period, which is the period during which the intake valve 36 and the exhaust valve 37 are simultaneously opened by changing the timing at which the intake valve 36 opens and closes. Is. Further, the exhaust side variable valve mechanism 62 can change the length of the valve overlap period by changing the timing at which the exhaust valve 37 opens and closes. Therefore, the intake side variable valve mechanism 61 and the exhaust side variable valve mechanism 62 function as a changing mechanism for changing the valve overlap period.

The internal combustion engine 10 includes an accelerator opening sensor 91 for detecting an accelerator operation amount X1 which is an operation amount of the accelerator pedal operated by the driver. Further, the internal combustion engine 10 includes a crank angle sensor 92 for detecting the engine rotation speed X2, which is the rotation speed of the crankshaft. The internal combustion engine 10 includes an air flow meter 93 that detects an intake amount X3, which is an amount of intake air flowing through the intake pipe 20 per unit time.

A signal indicating the accelerator operation amount X1 is input to the control device 100 from the accelerator opening sensor 91. Further, a signal indicating the engine rotation speed X2 is input to the control device 100 from the crank angle sensor 92. A signal indicating the intake air amount X3 is input to the control device 100 from the air flow meter 93. Further, the control device 100 calculates the engine load factor KL based on the engine rotation speed X2 and the intake air amount X3. Here, the engine load factor KL is the ratio of the current cylinder inflow air amount to the cylinder inflow air amount when the internal combustion engine 10 is steadily operated with the throttle valve 53 fully open at the current engine rotation speed X2. Represents. The cylinder inflow air amount is the amount of intake air flowing into each cylinder 33 in the intake process.

The control device 100 includes a throttle control unit 101 that controls the throttle valve 53. The throttle control unit 101 controls the throttle valve 53 by outputting the control signal S1 to the throttle valve 53. Then, the throttle control unit 101 adjusts the intake amount, which is the amount of intake air that flows from the upstream side to the downstream side of the throttle valve 53 through the throttle valve 53. The throttle control unit 101 controls the throttle valve 53 based on the accelerator operation amount X1 and the engine rotation speed X2 and the like.

The control device 100 includes an EGR control unit 102 that controls the EGR valve 57. The EGR control unit 102 controls the EGR valve 57 by outputting the control signal S2 to the EGR valve 57. Then, the EGR control unit 102 adjusts the exhaust amount, which is the amount of exhaust gas flowing from the branch pipe 41D side to the collecting pipe 26 side of the EGR valve 57 through the EGR valve 57. The EGR control unit 102 controls the EGR valve 57 based on the accelerator operation amount X1 and the engine rotation speed X2 and the like.

The control device 100 includes a WGV control unit 103 that controls the wastegate valve 89. The WGV control unit 103 calculates the opening degree A, which is the target opening degree of the wastegate valve 89, based on the accelerator operation amount X1 and the engine rotation speed X2 and the like. The WGV control unit 103 controls the wastegate valve 89 by outputting the control signal S3 to the turbocharger 70 based on the opening degree A. Then, the WGV control unit 103 adjusts the exhaust amount, which is the amount of exhaust gas flowing through the first bypass passage 86 and the second bypass passage 87 through the wastegate valve 89.

The control device 100 includes a change mechanism control unit 104 that controls the intake side variable valve mechanism 61 and the exhaust side variable valve mechanism 62. The change mechanism control unit 104 controls the intake side variable valve mechanism 61 by outputting the control signal S6 to the intake side variable valve mechanism 61. Then, the change mechanism control unit 104 changes the timing at which the intake valve 36 opens and closes with respect to the rotation angle of the crankshaft through the intake side variable valve mechanism 61. The change mechanism control unit 104 controls the intake side variable valve mechanism 61 based on the engine rotation speed X2.

Further, the change mechanism control unit 104 controls the exhaust side variable valve mechanism 62 by outputting the control signal S7 to the exhaust side variable valve mechanism 62. Then, the change mechanism control unit 104 changes the timing at which the exhaust valve 37 opens and closes with respect to the rotation angle of the crankshaft through the exhaust side variable valve mechanism 62. The change mechanism control unit 104 controls the exhaust side variable valve mechanism 62 based on the engine rotation speed X2.

The control device 100 includes an injection control unit 105 that controls the fuel injection valve 35. The injection control unit 105 controls the fuel injection valve 35 by outputting the control signal S5. The injection control unit 105 controls the fuel injection valve 35 based on the accelerator operation amount X1 and the engine rotation speed X2 and the like.

The control device 100 can be configured as a circuit (cyclery) including one or more processors that execute various processes according to a computer program (software). The control device 100 is configured as one or more dedicated hardware circuits such as an application specific integrated circuit (ASIC) that executes at least a part of various processes, or a circuit including a combination thereof. You may. The processor includes a CPU and a memory such as a RAM and a ROM. The memory stores a program code or an instruction configured to cause the CPU to execute the process. Memory or computer-readable medium includes any medium accessible by a general purpose or dedicated computer.

Next, an event that occurs in the internal combustion engine 10 will be described.
Since exhaust pulsation occurs in the first exhaust passage 12A and the second exhaust passage 12B, as shown in FIG. 3, the exhaust pressures E1, F1, and the first exhaust pressures E1, F1, and the second of the connection portion with the first cylinder group 11A in the first exhaust passage 12A. The exhaust pressures E2 and F2 of the connection portion with the second cylinder group 11B in the two exhaust passages 12B fluctuate. Here, since the EGR passage 56A is connected to the first exhaust passage 12A and the EGR passage 56A is not connected to the second exhaust passage 12B, the fluctuations of the exhaust pressures E1 and F1 are the exhaust pressures E2 and F2. Is different from the fluctuation of. Then, in the valve overlap period in which the intake valve 36 and the exhaust valve 37 are opened at the same time, for example, a difference occurs between the exhaust pressure E1 and the exhaust pressure E2. As a result, there is a difference between the intake amount introduced from the intake port 31 into the first cylinder group 11A and the intake amount introduced from the intake port 31 into the second cylinder group 11B. Then, the air-fuel ratio varies between the first cylinder group 11A and the second cylinder group 11B.

Here, in the case where the opening degree A of the wastegate valve 89 is a relatively small first opening degree, the exhaust pressure of the connection portion with the first cylinder group 11A in the first exhaust passage 12A is set to the exhaust pressure E1 and the second The exhaust pressure at the connection portion with the second cylinder group 11B in the exhaust passage 12B is defined as the exhaust pressure E2. Further, when the opening degree A of the wastegate valve 89 is a second opening degree larger than the first opening degree, the exhaust pressure of the connecting portion with the first cylinder group 11A in the first exhaust passage 12A is set to the exhaust pressure F1. The exhaust pressure at the connection portion with the second cylinder group 11B in the second exhaust passage 12B is defined as the exhaust pressure F2. As shown in FIG. 3, the difference between the exhaust pressure E1 and the exhaust pressure E2 during the valve overlap period is larger than the difference between the exhaust pressure F1 and the exhaust pressure F2. Then, due to the variation in the exhaust pressure, there is also a difference between the intake amount introduced from the intake port 31 into the first cylinder group 11A and the intake amount introduced from the intake port 31 into the second cylinder group 11B. It is easy to occur. As a result, the smaller the opening degree A of the wastegate valve 89, the larger the variation in the air-fuel ratio between the first cylinder group 11A and the second cylinder group 11B.

Further, since the intake port 31, the cylinder 33, and the exhaust port 32 are communicated with each other during the valve overlap period, the exhaust pressure of the exhaust port 32 tends to affect the intake amount introduced from the intake port 31 to the cylinder 33. Therefore, in the valve overlap period, for example, if there is a difference between the exhaust pressure E1 and the exhaust pressure E2, the intake amount introduced into the first cylinder group 11A and the second cylinder group are affected by the difference. There is a tendency for a difference to occur with the amount of intake air introduced in 11B. As a result, as shown in FIG. 4, the longer the valve overlap period, the more empty the air-fuel ratio G1 which is the air-fuel ratio of the first cylinder group 11A and the air-fuel ratio G2 which is the air-fuel ratio of the second cylinder group 11B. The variation in fuel ratio becomes large.

Therefore, the variation in the air-fuel ratio between the first cylinder group 11A and the second cylinder group 11B tends to increase as the opening degree A of the wastegate valve becomes smaller and the valve overlap period becomes longer.

Next, with reference to FIG. 2, the setting control of the valve overlap period executed by the control device 100 will be described. The control device 100 executes setting control at predetermined intervals from the start of the operation of the control device 100 to the end of the operation.

As shown in FIG. 2, when the change mechanism control unit 104 starts a series of setting control, the process of step S11 starts. In step S11, the change mechanism control unit 104 determines whether or not a variable condition for allowing the change in the length of the valve overlap period is satisfied. As the variable condition, for example, the hydraulic pressure supplied to the intake side variable valve mechanism 61 and the exhaust side variable valve mechanism 62 is required to drive the intake side variable valve mechanism 61 and the exhaust side variable valve mechanism 62. The conditions are that the hydraulic pressure is equal to or higher than the threshold pressure, and that the combustion state of the fuel in the cylinder 33 is not unstable. The change mechanism control unit 104 determines that the variable condition is satisfied when all the conditions defined as the variable condition are satisfied. In step S11, when it is determined that the variable condition is not satisfied (S11: NO), the change mechanism control unit 104 ends the current setting control. On the other hand, in step S11, when the change mechanism control unit 104 determines that the variable condition is satisfied (S11: YES), the process proceeds to step S12.

In step S12, the change mechanism control unit 104 calculates the base period C of the valve overlap period based on the engine rotation speed X2 and the engine load factor KL. Here, the change mechanism control unit 104 stores in advance a base period map for calculating the base period C. The base period map is a map showing the base period C in association with the engine speed X2 and the engine load factor KL. The change mechanism control unit 104 calculates the base period C with reference to the base period map. After that, the change mechanism control unit 104 advances the process to step S13.

In step S13, the change mechanism control unit 104 acquires the opening degree A of the wastegate valve 89 at the time of processing in step S13 calculated by the WGV control unit 103. After that, the change mechanism control unit 104 advances the process to step S14.

In step S14, the change mechanism control unit 104 determines whether or not the opening degree A is larger than the predetermined threshold value B. In step S14, when the change mechanism control unit 104 determines that the opening degree A is equal to or less than the threshold value B (S14: NO), the process proceeds to step S22. On the other hand, in step S14, when the change mechanism control unit 104 determines that the opening degree A is larger than the threshold value B (S14: YES), the process proceeds to step S21.

In step S21, the change mechanism control unit 104 sets the base period C calculated in step S12 as the setting period D of the valve overlap period. Then, the change mechanism control unit 104 controls the intake side variable valve mechanism 61 and the exhaust side variable valve mechanism 62 so that the valve overlap period becomes the set period D. After that, the change mechanism control unit 104 ends the current setting control.

As described above, when the change mechanism control unit 104 determines in step S14 that the opening degree A is equal to or less than the threshold value B (S14: NO), the process proceeds to step S22. In step S22, the change mechanism control unit 104 sets the valve overlap period setting period D as a period shorter than the base period C calculated in step S12 by a predetermined period α. Then, the change mechanism control unit 104 controls the intake side variable valve mechanism 61 and the exhaust side variable valve mechanism 62 so that the valve overlap period becomes the set period D. After that, the change mechanism control unit 104 ends the current setting control.

The operation of this embodiment will be described.
In the internal combustion engine 10, when the opening degree A of the wastegate valve 89 is equal to or less than the threshold value B, the intake side variable valve mechanism 61 and the exhaust side are possible so that the valve overlap period is shorter than when the wastegate valve 89 is not. The variable valve mechanism 62 is controlled. That is, when the difference between the exhaust pressure of the connection portion with the first cylinder group 11A in the first exhaust passage 12A and the exhaust pressure of the connection portion with the second cylinder group 11B in the second exhaust passage 12B becomes large, The valve overlap period is shortened. As a result, the difference between the intake amount introduced from the intake port 31 into the first cylinder group 11A and the intake amount introduced from the intake port 31 into the second cylinder group 11B is less likely to occur.

The effect of this embodiment will be described.
In the internal combustion engine 10, the difference between the intake amount introduced from the intake port 31 into the first cylinder group 11A and the intake amount introduced from the intake port 31 into the second cylinder group 11B is unlikely to occur. As a result, it is possible to suppress the variation in the air-fuel ratio between the first cylinder group 11A and the second cylinder group 11B. It should be noted that the variation in the air-fuel ratio between the first cylinder group 11A and the second cylinder group 11B may worsen the fuel combustion state and emissions in the first cylinder group 11A and the second cylinder group 11B. Can be suppressed.

This embodiment can be modified and implemented as follows. The present embodiment and the following modified examples can be implemented in combination with each other within a technically consistent range.
-In the above embodiment, the EGR passage 56A may be connected to the second exhaust passage 12B instead of the first exhaust passage 12A. As a specific example, one end of the EGR pipe 56 may be attached to the branch pipe 41C in the exhaust manifold 40.

-In the above embodiment, the number of cylinders 33 in the engine body 30 may be changed. Similarly, the number of intake ports 31 and exhaust ports 32 in the engine body 30 may be changed.
-In the above embodiment, the passage configuration of the first exhaust passage 12A and the second exhaust passage 12B can be changed. For example, the exhaust manifold 40 may be omitted, and the housing 71 of the turbocharger 70 may be attached to the engine body 30. In this case, the engine body 30 may include a first assembly passage connecting the exhaust port 32A and the exhaust port 32D, and a second assembly passage connecting the exhaust port 32B and the exhaust port 32C. Further, the EGR passage 56A may be connected to either the first gathering passage or the second gathering passage described above.

In the above embodiment, the change mechanism control unit 104 may control either the intake side variable valve mechanism 61 or the exhaust side variable valve mechanism 62 when changing the valve overlap period. Further, in changing the valve overlap period, the internal combustion engine 10 may include at least one of the intake side variable valve mechanism 61 and the exhaust side variable valve mechanism 62.

-In the above embodiment, the intake side variable valve mechanism 61 may change the valve overlap period by changing the lift amount of the intake valve 36. Specifically, the valve overlap period can be changed if the timing of opening and closing the intake valve 36 is adjusted with respect to the rotation angle of the crankshaft as the lift amount of the intake valve 36 is changed. The same applies to the exhaust side variable valve mechanism 62.

-In the above embodiment, the setting control of the valve overlap period can be changed. For example, in step S22, the period α may be set so that the smaller the opening degree A, the larger the period α. In this case, the intake side variable valve mechanism 61 and the exhaust side variable valve mechanism 62 are controlled so that the smaller the opening degree A is with respect to the threshold value B, the shorter the valve overlap period. Further, for example, the determination process in step S14 may be omitted and the valve overlap period may be adjusted. As a specific example, the change mechanism control unit 104 may control the intake side variable valve mechanism 61 and the exhaust side variable valve mechanism 62 so that the valve overlap period becomes shorter as the opening degree A becomes smaller.

A ... Opening B ... Threshold 10 ... Internal combustion engine 11A ... 1st cylinder group 11B ... 2nd cylinder group 12A ... 1st exhaust passage 12B ... 2nd exhaust passage 20 ... Intake pipe 30 ... Engine body 31 ... Intake port 32 ... Exhaust Port 33 ... Cylinder 35 ... Fuel injection valve 36 ... Intake valve 37 ... Exhaust valve 40 ... Exhaust manifold 56 ... EGR pipe 56A ... EGR passage 61 ... Intake side variable valve mechanism 62 ... Exhaust side variable valve mechanism 70 ... Turbocharger 81 … Compressor wheel 82… Shaft 83… Turbine wheel 85… Bypass passage 89… Wastegate valve 100… Control device

Claims (1)

A change mechanism that changes the valve overlap period, which is the period during which the intake valve and the exhaust valve are opened at the same time, a control device that controls the change mechanism, an EGR passage that connects the exhaust passage and the intake passage, and the EGR passage. A multi-cylinder equipped with a turbine wheel provided in the exhaust passage, a bypass passage connecting the upstream side and the downstream side of the turbine wheel in the exhaust passage, and a turbocharger having a wastegate valve provided in the bypass passage. It is a control system for internal combustion engines.
When some of the cylinders are in the first cylinder group and the remaining cylinders are in the second cylinder group,
The exhaust passage includes a first exhaust passage which is a passage from the first cylinder group to the turbine wheel and a second exhaust passage from the second cylinder group to the turbine wheel.
The EGR passage connects either one of the first exhaust passage and the second exhaust passage to the intake passage.
The control device is a control system for an internal combustion engine that controls the changing mechanism so that when the opening degree of the wastegate valve is small, the valve overlap period is shorter than when the opening degree is large.

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