Power System

Abstract

It suppresses the increase in nitrogen oxides and appropriately raises the combustion temperature. [Solution] The power system S has an exhaust valve control unit 622 that controls the opening and closing of the exhaust valve 42 of the first cylinder group 21 during the compression stroke of the first cylinder group 21, a recirculation control unit 624 that recirculates the exhaust of the second cylinder group 22 to the intake line 12 and does not recirculate the exhaust of the first cylinder group 21 to the intake line 12 when the exhaust valve 42 opens during the compression stroke of the first cylinder group 21, and an injection control unit 623 that stops fuel injection into the combustion chamber 242 of the first cylinder group 21 when the exhaust valve 42 opens during the compression stroke of the first cylinder group 21, and injects a second injection amount of fuel into the combustion chamber 242 of the second cylinder group 22, which is greater than a first injection amount of fuel injected into the combustion chamber 242 of the second cylinder group 22 when the exhaust valve 42 is closed during the compression stroke of the first cylinder group 21.

Description

[Technical field]

[0001] The present invention relates to a power system using an engine. [Background technology]

[0002] There are known techniques for warming up the engine and purification device when the engine is started cold. Patent Document 1 discloses a technique for increasing the amount of fuel injected into the engine combustion chamber to raise the combustion temperature, and then using the high-temperature exhaust gas to warm up the purification device. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2000-320386 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, increasing the amount of fuel injected too much results in too much engine power, so there is a limit to how much injection can be increased, and it is sometimes impossible to raise the combustion temperature sufficiently. Also, increasing the injection amount to raise the combustion temperature increases the amount of nitrogen oxides produced during combustion.

[0005] The present invention has been made in consideration of these points, and has an object to suppress an increase in nitrogen oxides and to appropriately increase the combustion temperature. [Means for solving the problem]

[0006] In one aspect of the present invention, a power system is provided that includes an exhaust valve control unit that controls the opening and closing of exhaust valves of a first group of cylinders among a plurality of cylinders of an engine, a recirculation control unit that controls the recirculation of exhaust from the first group of cylinders and exhaust from a second group of cylinders different from the first group of cylinders among the plurality of cylinders to an intake pipe of the engine, and an injection control unit that controls injection of fuel into each of the combustion chambers of the plurality of cylinders, wherein when the exhaust valve control unit controls to open the exhaust valve of the first group of cylinders during a compression stroke of the first group of cylinders, the recirculation control unit controls so that the exhaust from the first group of cylinders is not recirculated to the intake pipe, and the exhaust from the second group of cylinders is recirculated to the intake pipe, and the injection control unit stops fuel injection into the combustion chambers of the first group of cylinders, and injects a second injection amount of fuel into the combustion chambers of the second group of cylinders during the compression stroke of the first group of cylinders when the exhaust valve is closed.

[0007] The engine may include a first recirculation pipe through which exhaust gas from the first group of cylinders is recirculated to the intake pipe, and a second recirculation pipe through which exhaust gas from the second group of cylinders is recirculated to the intake pipe.

[0008] When the exhaust valve opens during the exhaust stroke of the first cylinder group, the injection control unit may inject the second injection amount of fuel, which is greater than the first injection amount by an amount corresponding to a load applied to the engine when the exhaust valve is open during the compression stroke of the first cylinder group, into the combustion chamber of the second cylinder group.

[0009] The exhaust valve control unit may set a first open time during which the exhaust valves of the first cylinder group are open during the compression stroke of the first cylinder group to be the same as a second open time during which the exhaust valves of the second cylinder group are open during the compression stroke of the second cylinder group.

[0010] When the first opening time is greater than the second opening time by a predetermined time or more, the exhaust valve control unit may make the first opening time and the second opening time equal to each other by opening the exhaust valves of the second cylinder group during the compression stroke of the second cylinder group and closing the exhaust valves of the first cylinder group during the compression stroke of the first cylinder group.

[0011] When the first opening time is longer than the second opening time by at least the predetermined time, the injection control unit stops fuel injection to the second cylinder group, and causes the injector to inject a fourth injection amount of fuel, which is greater than a third injection amount of fuel injected when the exhaust valve of the second cylinder group is closed during the compression stroke, into the combustion chamber of the first cylinder group whose exhaust valve is closed during the compression stroke, and the recirculation control unit may recirculate the exhaust from the first cylinder group whose exhaust valve is closed during the compression stroke to the intake pipe, and may not recirculate the exhaust from the second cylinder group whose exhaust valve is open during the compression stroke to the intake pipe.

[0012] The engine may further include an acquisition unit that acquires a temperature of a cooling water of the engine, and the exhaust valve control unit may open the exhaust valve during the compression stroke of the first cylinder group when the temperature of the cooling water is equal to or lower than a predetermined water temperature.

[0013] The engine may further include an acquisition unit that acquires a rotation speed of the engine, and the exhaust valve control unit may open the exhaust valve during the compression stroke of the first cylinder bank when the rotation speed is equal to or lower than a predetermined rotation speed.

[0014] The acquisition unit may acquire a commanded injection amount of fuel to be injected into the combustion chamber, and the exhaust valve control unit may open the exhaust valve during the compression stroke of the first cylinder group when the rotational speed is equal to or lower than the predetermined rotational speed and the commanded injection amount is smaller than a maximum injection amount that can be injected into the combustion chamber.

[0015] The engine may further include a supply control unit that stops the supply of lubricating oil to the piston of the first cylinder bank when the exhaust valve opens during the compression stroke of the first cylinder bank.

[0016] The supply control unit may, when the supply of the lubricating oil to the piston of the first cylinder group is stopped, reduce the discharge rate of the pump supplying the lubricating oil compared to the discharge rate of the pump when the lubricating oil is being supplied to the piston of the first cylinder group. Effect of the Invention

[0017] According to the present invention, it is possible to suppress an increase in nitrogen oxides and to appropriately increase the combustion temperature. [Brief description of the drawings]

[0018] [Figure 1] FIG. 2 is a diagram for explaining the configuration of a power system. [Diagram 2] FIG. 2 is a schematic diagram of an engine cylinder. [Diagram 3] FIG. 2 is a diagram for explaining the configuration of an engine control device. [Figure 4] FIG. 4 is a diagram for explaining a condition for opening an exhaust valve during a compression stroke. [Diagram 5] 4 is a flowchart showing an example of a flow of a process for increasing the temperature of an engine. [Figure 6] 6 is a flowchart showing an example of a process flow for compressing and releasing a second cylinder bank. [Figure 7] 5 is a flowchart showing an example of a process flow for compressing and releasing a first cylinder bank. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] [Configuration of Power System S] The power system S is a power system using an engine 1. The power system S is a system for shortening the time required for the engine and a device for purifying the engine exhaust gas to rise in temperature during a cold start in which the engine 1 is started from a state in which the temperature of the engine 1 is approximately the same as or lower than the temperature around the engine 1. The configuration of the power system S will be described with reference to Figs. 1, 2, and 3. Fig. 1 is a diagram for explaining the configuration of the power system S. Fig. 2 is a schematic diagram of the cylinders of the engine 1. Fig. 3 is a diagram for explaining the configuration of the engine control device 6. The power system S has the engine 1, an intake pipe 12, an exhaust pipe 3, a first return pipe 131, a second return pipe 132, a purification device 34, a turbocharger 16, and an engine control device 6. The engine 1 also has a plurality of cylinders 2.

[0020] The engine 1 is an internal combustion engine that generates power by burning and expanding a mixture of fuel and fresh air (air). The engine 1 is, for example, a diesel engine mounted on an automobile or a ship, but may also be a gasoline engine. The multiple cylinders 2 include four cylinders, a first cylinder 211, a second cylinder 212, a third cylinder 213, and a fourth cylinder 214. Hereinafter, when there is no need to distinguish between the first cylinder 211, the second cylinder 212, the third cylinder 213, and the fourth cylinder 214, they will be referred to as cylinders 2. The first cylinder 211 and the fourth cylinder 214 of the multiple cylinders 2 of the engine 1 are a first cylinder group 21. The second cylinder 212 and the third cylinder 213 of the multiple cylinders 2 of the engine 1 are a second cylinder group 22 different from the first cylinder group 21.

[0021] In this embodiment, the combustion order of the cylinders is the first cylinder 211, the third cylinder 213, the fourth cylinder 214, and the second cylinder 212. Therefore, the first cylinder 211 and the fourth cylinder 214 are defined as the first cylinder group 21, and the second cylinder 212 and the third cylinder 213 are defined as the second cylinder group 22. The first cylinder group 21 and the second cylinder group 22 may be changed according to the combustion order of each cylinder. They may also be changed according to the number of cylinders in the engine 1. For example, if the engine 1 has six cylinders and the combustion order of the cylinders is the first cylinder, the fifth cylinder, the third cylinder, the sixth cylinder, the second cylinder, and the fourth cylinder, the first cylinder, the second cylinder, and the third cylinder are defined as the first cylinder group, and the fourth cylinder, the fifth cylinder, and the sixth cylinder are defined as the second cylinder group.

[0022] The cylinder 2 has an intake valve 41, an exhaust valve 42, an injection unit 43, and a piston 241. The intake valve 41 and the exhaust valve 42 are closed at the start of an operating cycle of the engine 1. First, when the piston 241 descends, the intake valve 41 is opened, and fresh air is drawn into the cylinder 2 (intake stroke). Next, when the piston 241 reaches the bottom dead center, the intake valve 41 is closed, and when the piston 241 ascends to the top dead center, the air is compressed (compression stroke). Next, fuel is injected by the injection unit 43, and the fuel mixed with the compressed and heated air is burned, and the expanded combustion gas pushes the piston 241 down to the bottom dead center (combustion stroke). Then, when the piston 241 ascends again to the top dead center due to inertia and expansion in other cylinders 2, the exhaust valve 42 is opened, and the combustion gas is pushed out of the cylinder 2 and discharged to the exhaust pipe 3 as exhaust gas (exhaust stroke).

[0023] An oil jet 51 is provided in the cylinder 2. The oil jet 51 injects lubricating oil toward the underside of the piston 241 under the control of the engine control device 6. The pump 52 is connected to the output shaft of the engine 1, and operates when the output shaft rotates to supply lubricating oil to the oil jet 51. The pump 52 is, for example, a variable displacement vane pump that can change the amount of lubricating oil discharged, but is not limited to this.

[0024] The intake pipe 12 is a pipe that supplies fresh air to the engine 1. The intake pipe 12 is a pipe that branches so as to correspond to each cylinder 2 and supplies fresh air to each cylinder 2. An intercooler 143 is provided in the intake pipe 12. The intercooler 143 cools the fresh air supplied to the engine 1. The intercooler 143 is a heat exchanger that cools the fresh air by exchanging heat between the fresh air and the cooling water of the engine 1 or outside air.

[0025] The exhaust pipe 3 is a pipe for discharging exhaust gas from the engine 1 to the outside. A turbine 162 of the turbocharger 16 that compresses fresh air supplied to the engine 1 is provided in the exhaust pipe 3. The turbine 162 rotates when the exhaust gas passes through it. The turbine 162 is connected to a compressor 161 of the turbocharger 16. The compressor 161 is provided in the intake pipe 12. The compressor 161 rotates in conjunction with the rotation of the turbine 162 to compress and supercharge the fresh air.

[0026] The exhaust pipe 3 has a first pipe 31, a second pipe 32, and a third pipe 33. The first pipe 31 is connected to the first cylinder group 21 and is a pipe for supplying exhaust gas from the first cylinder group 21 to the turbine 162. The second pipe 32 is connected to the second cylinder group 22 and is a pipe for supplying exhaust gas from the second cylinder group 22 to the turbine 162. The third pipe 33 is a pipe for discharging the exhaust gas that has passed through the turbine 162 to the outside.

[0027] The first recirculation pipe 131 connects the first pipe 31 and the intake pipe 12, and is a pipe for recirculating the exhaust gas of the first cylinder group 21 to the intake pipe 12. The first recirculation pipe 131 is provided with an exhaust cooler 141. The exhaust cooler 141 is a heat exchanger that cools the exhaust gas of the first cylinder group 21 by exchanging heat between the exhaust gas of the first cylinder group 21 and the cooling water of the engine 1 or the outside air. A first control valve 151 is provided between the intake pipe 12 and the exhaust cooler 141 in the first recirculation pipe 131. The first control valve 151 adjusts the flow rate of the exhaust gas of the first cylinder group 21 flowing to the intake pipe 12. The first control valve 151 adjusts the flow rate of the exhaust gas of the first cylinder group 21 passing through the first control valve 151 by operating an adjustment valve that adjusts the flow area of ​​the flow path under the control of the engine control device 6.

[0028] The second recirculation pipe 132 connects the second pipe 32 and the intake pipe 12, and is a pipe for recirculating the exhaust gas from the second cylinder group 22 to the intake pipe 12. The second recirculation pipe 132 is provided with an exhaust cooler 142. The exhaust cooler 142 is a heat exchanger that cools the exhaust gas from the second cylinder group 22 by exchanging heat between the exhaust gas from the second cylinder group 22 and the cooling water of the engine 1 or the outside air. A second control valve 152 is provided between the intake pipe 12 and the exhaust cooler 142 in the second recirculation pipe 132. The second control valve 152 adjusts the flow rate of the exhaust gas from the second cylinder group 22 that flows into the intake pipe 12. The second control valve 152 adjusts the flow rate of the exhaust gas from the second cylinder group 22 that passes through the second control valve 152 by operating an adjustment valve that adjusts the flow area of ​​the flow path under the control of the engine control device 6.

[0029] The third pipe 33 is provided with a purifier 34. The purifier 34 purifies the exhaust gas from the engine 1. The purifier 34 is, for example, a diesel particulate diffuser (DPD) or a selective catalytic reduction denitration device (so-called urea SCR (Selective Catalytic Reduction)), but is not limited thereto. The DPD is a purifier that removes particulate matter (for example, soot) from the exhaust gas. The DPD has a filter that collects the particulate matter. The selective catalytic reduction denitration device is a purifier that reduces nitrogen oxides in the exhaust gas. The selective catalytic reduction denitration device reacts nitrogen oxides with ammonia by injecting urea water, which is a precursor of ammonia, into the exhaust gas flowing through the third pipe 33, thereby reducing the nitrogen oxides to nitrogen and water.

[0030] The engine control device 6 is an ECU (Electronic Control Unit) that controls the engine 1. The engine control device 6 loads the engine 1 by opening the exhaust valve 42 during the compression stroke of the first cylinder group 21 when the engine 1 is cold started. Furthermore, the engine control device 6 increases the amount of fuel injected into the combustion chamber 242 of the second cylinder group 22 compared to a case where the exhaust valve 42 is not opened during the compression stroke of the first cylinder group 21. Furthermore, when the engine 1 is not cold started, that is, in a so-called normal operating state, the engine control device 6 does not perform control to open the exhaust valve 42 during the compression stroke of the first cylinder group 21 or to increase the amount of fuel injected into the combustion chamber 242 of the second cylinder group 22. By performing the control as described above, the engine control device 6 can appropriately increase the combustion temperature without increasing the actual output of the engine 1.

[0031] Furthermore, when the engine control device 6 opens the exhaust valve 42 during the compression stroke of the first cylinder group 21 at the time of cold start of the engine 1, the engine control device 6 recirculates the exhaust gas from the second cylinder group 22 to the intake pipe 12, but does not recirculate the unburned fresh air (air) discharged from the first cylinder group 21. In other words, while the engine control device 6 executes control to open the exhaust valve 42 during the compression stroke of the first cylinder group 21 at the time of cold start of the engine 1, the engine control device 6 does not recirculate the unburned fresh air discharged from the first cylinder group 21. Specifically, the engine control device 6 opens the first control valve 151 and closes the second control valve 152, thereby recirculating the exhaust gas from the first cylinder group 21 to the intake pipe 12, but does not recirculate the exhaust gas from the second cylinder group 22 to the intake pipe 12.

[0032] This enables the engine control device 6 to reduce the oxygen concentration in the mixture of fresh air and exhaust gas supplied to the combustion chamber 242 of the second cylinder bank 22, thereby making it possible to suppress an increase in the amount of nitrogen oxides that is generated. A specific configuration of the engine control device 6 will now be described.

[0033] The engine control device 6 has a storage unit 61 and a control unit 62. The storage unit 61 is a storage medium including a ROM (Read Only Memory), a RAM (Random Access Memory), a hard disk, etc. The storage unit 61 stores a program to be executed by the control unit 62.

[0034] The control unit 62 is a computational resource including a processor such as a CPU (Central Processing Unit). The control unit 62 executes a program stored in the storage unit 61 to realize functions as an acquisition unit 621, an exhaust valve control unit 622, an injection control unit 623, a reflux control unit 624, and a supply control unit 625.

[0035] The acquisition unit 621 acquires information related to the power system S from the sensor group 11. For example, the sensor group 11 includes a sensor that acquires the rotation speed of the engine 1 and a sensor that acquires the temperature of the coolant of the engine 1. The acquisition unit 621 acquires the rotation speed of the engine 1 and the temperature of the coolant of the engine 1 from the sensor group 11.

[0036] The acquisition unit 621 acquires a command injection amount of fuel to be injected into the combustion chamber 242. For example, the acquisition unit 621 acquires a command injection amount corresponding to an operation amount of an operation unit that controls the output of the engine 1. As a specific example, when the engine 1 is mounted on a vehicle, the acquisition unit 621 acquires a larger command injection amount as the depression amount of an accelerator pedal, which is an operation unit, increases. The acquisition unit 621 may also acquire a command injection amount corresponding to a required torque for the engine 1. In this case, the acquisition unit 621 acquires a larger command injection amount as the required torque increases.

[0037] The exhaust valve control unit 622 controls the opening and closing of the exhaust valves 42 of the multiple cylinders 2. The exhaust valve control unit 622 controls the opening and closing of each of the exhaust valves 42 of the multiple cylinders 2 in accordance with the process of the operation cycle of the engine 1. In addition, the exhaust valve control unit 622 controls the opening and closing of the exhaust valves 42 in the process of the operation cycle in accordance with the operating state of the engine 1. The operating state includes, for example, whether the engine 1 is in a cold start state or a normal operating state. For example, the exhaust valve control unit 622 controls the opening and closing of the exhaust valves 42 of the first cylinder group 21 (the first cylinder 211 and the fourth cylinder 214) during the compression stroke of the first cylinder group 21. Specifically, during cold start of engine 1, exhaust valve control unit 622 opens exhaust valve 42 during the compression stroke of first cylinder group 21, and when opening exhaust valve 42 during the compression stroke of first cylinder group 21, keeps exhaust valve 42 closed during the compression stroke of second cylinder group 22 (second cylinder 212 and third cylinder 213).

[0038] The exhaust valve control unit 622 judges whether the engine 1 is in a cold start state based on the temperature of the cooling water. When the temperature of the cooling water is low, it is considered that the temperature of the engine 1 and the purification device 34 is not yet increased. Therefore, when the temperature of the cooling water is equal to or lower than a predetermined water temperature, the exhaust valve control unit 622 judges that the engine 1 is in a cold start state and opens the exhaust valve 42 during the compression stroke of the first cylinder group 21. The predetermined water temperature may be appropriately set, for example, 0 degrees Celsius, but is not limited thereto. The predetermined water temperature may be the temperature of the outside air. The exhaust valve control unit 622 judges that the engine 1 is in a cold start state when the temperature of the cooling water is equal to or lower than the temperature of the outside air detected by the outside air temperature sensor. In this way, when the temperature of the cooling water is low and it is necessary to increase the temperature of the engine 1 and the purification device 34, the exhaust valve control unit 622 can apply a load to the engine 1 to set the amount of fuel injected into the second cylinder group 22 to be increased.

[0039] The injection control unit 623 controls each of the injectors 43 of the first cylinder group 21 and the second cylinder group 22 to control the injection of fuel into the combustion chambers 242 of the first cylinder group 21 and the second cylinder group 22. For example, the injection control unit 623 controls the injector 43 of the first cylinder group 21 to stop fuel injection into the combustion chamber 242 of the first cylinder group 21 when the exhaust valve 42 opens during the compression stroke of the first cylinder group 21. This allows the injection control unit 623 to suppress fuel injection into the combustion chamber 242 of the first cylinder group 21, where the temperature of the mixture does not reach a combustible temperature because the exhaust valve 42 opens during the compression stroke.

[0040] When the exhaust valve 42 opens during the exhaust stroke of the first cylinder group 21, the injection control unit 623 injects a second injection amount of fuel, which is greater than the first injection amount, into the combustion chamber 242 of the second cylinder group 22. The first injection amount is the amount of fuel injected into the combustion chamber 242 of the second cylinder group 22 in a state in which the exhaust valve 42 is closed during the compression stroke of the first cylinder group 21. Specifically, the injection control unit 623 determines the second injection amount according to the load generated in the engine 1 in a state in which the exhaust valve 42 is open during the compression stroke of the first cylinder group 21. More specifically, the injection control unit 623 determines the second injection amount by adding an amount according to the load generated in the engine 1 in a state in which the exhaust valve 42 is open during the compression stroke of the first cylinder group 21 to the first injection amount. The injection control unit 623 controls the injection unit 43 to inject the determined second injection amount of fuel into the combustion chamber 242 of the second cylinder group 22.

[0041] When the exhaust valve 42 of the first cylinder group 21 opens during the compression stroke of the first cylinder group 21, a load is applied to the engine 1. In other words, the expansion stroke is performed with the air pressure in the combustion chamber reduced, and negative work is generated in the engine 1, so that a load is applied to the engine 1. Then, the injection control unit 623 increases the amount of fuel injected into the second cylinder group 22 of the engine 1 that is loaded by the exhaust valve 42 of the first cylinder group 21 opening during the compression stroke of the first cylinder group 21. For example, the injection control unit 623 increases the amount of fuel injected into the combustion chamber 242 of the second cylinder group 22 by an amount that can offset the negative work generated in the engine 1 by the exhaust valve 42 of the first cylinder group 21 opening during the compression stroke of the first cylinder group 21. As a result, the injection control unit 623 can increase the amount of fuel injected into the combustion chamber 242 of the second cylinder group 22 while suppressing an increase in the actual output of the engine 1. As a result, the combustion temperature of the mixture increases, and the temperature of the engine 1 is likely to increase. Furthermore, since the temperature of the exhaust gas from the second cylinder bank 22 also rises, the temperature of the purifier 34 tends to rise.

[0042] The recirculation control unit 624 controls the recirculation of the exhaust gas from the first cylinder group 21 and the exhaust gas from the second cylinder group 22. For example, when the exhaust valve 42 opens during the compression stroke of the first cylinder group 21, the recirculation control unit 624 causes the exhaust gas from the second cylinder group 22 to be supplied to the second recirculation pipe 132, thereby causing the exhaust gas to be recirculated to the intake pipe 12. The recirculation control unit 624 does not cause the exhaust gas from the first cylinder group 21 to be supplied to the first recirculation pipe 131, thereby preventing the exhaust gas from being recirculated to the intake pipe 12. Specifically, the recirculation control unit 624 causes the exhaust gas from the second cylinder group 22 to be supplied to the second recirculation pipe 132 by opening the second control valve 152, and does not cause the exhaust gas from the first cylinder group 21 to be supplied to the first recirculation pipe 131 by closing the first control valve 151.

[0043] The recirculation control unit 624 may reduce the amount of exhaust gas from the first cylinder group 21 recirculated to the intake pipe 12 when the exhaust valve 42 opens during the compression stroke of the first cylinder group 21. For example, the recirculation control unit 624 sets the opening degree of the first control valve 151 when the exhaust valve 42 opens during the compression stroke of the first cylinder group 21 to be smaller than the opening degree of the first control valve 151 when the exhaust valve 42 is closed during the compression stroke of the first cylinder group 21.

[0044] In this way, the recirculation control unit 624 recirculates the exhaust gas from the second cylinder group 22, which has a lower oxygen concentration than the fresh air, to the intake pipe 12. As a result, the recirculation control unit 624 reduces the oxygen concentration in the mixed gas of fresh air and exhaust gas supplied to the combustion chamber 242 of the second cylinder group 22, thereby suppressing an increase in nitrogen oxides generated during combustion. In addition, the recirculation control unit 624 does not recirculate the air (fresh air) discharged from the first cylinder group 21, which has a higher oxygen concentration than the exhaust gas, to the intake pipe 12, thereby suppressing an increase in the oxygen concentration of the mixed gas in the combustion chamber 242 of the second cylinder group 22, and suppressing an increase in nitrogen oxides generated during combustion.

[0045] When the state of the engine 1 satisfies a predetermined condition, the exhaust valve control unit 622 may open the exhaust valve 42 during the compression stroke of the first cylinder bank 21. Fig. 4 is a diagram for explaining the condition for opening the exhaust valve 42 during the compression stroke. The horizontal axis of Fig. 4 indicates the rotation speed R of the engine 1, and the vertical axis indicates the command injection amount Q of fuel to be injected into the combustion chamber 242 of the engine 1.

[0046] When the rotation speed R of the engine 1 is equal to or lower than the predetermined rotation speed R1, the number of combustions per unit time is smaller than when the rotation speed R is higher than the predetermined rotation speed R1, so that the temperature of the engine 1 and the temperature of the exhaust gas are less likely to rise. Therefore, the exhaust valve control unit 622 opens the exhaust valve 42 during the compression stroke of the first cylinder group 21 when the rotation speed R of the engine 1 is equal to or lower than the predetermined rotation speed R1. The predetermined rotation speed R1 may be appropriately determined based on the specifications of the engine 1 and experiments. A specific value of the predetermined rotation speed R1 is, for example, 2000 revolutions per minute in the case of a diesel engine, but is not limited to this. As a result, the exhaust valve control unit 622 can easily increase the combustion temperature in the combustion chamber 242 in a situation where the temperature of the engine 1 and the temperature of the exhaust gas are less likely to rise.

[0047] If the exhaust valve 42 is opened during the compression stroke of the first cylinder group 21 when the engine 1 is under a large load, an excessive load is applied to the engine 1. Therefore, the exhaust valve control unit 622 opens the exhaust valve 42 of the first cylinder group 21 during the compression stroke of the first cylinder group 21 when the rotation speed R of the engine 1 is equal to or lower than a predetermined rotation speed R1 and the command injection amount Q is smaller than the maximum injection amount M that can be injected into the combustion chamber 242. Specifically, the exhaust valve control unit 622 opens the exhaust valve 42 during the compression stroke of the first cylinder group 21 when the command injection amount Q is equal to or lower than a determination threshold value N.

[0048] The judgment threshold N is smaller than the maximum injection amount M that can be injected into the combustion chamber 242 of the engine 1. Specifically, the exhaust valve control unit 622 determines the judgment threshold N to be smaller than the maximum injection amount M by a predetermined value D. The predetermined value D is determined, for example, based on the specifications of the engine 1, experiments, etc. A specific value of the judgment threshold N is one-fifth (equivalent to 20 percent) of the maximum injection amount M, but is not limited to this.

[0049] When the instructed injection amount Q is included in the shaded area equal to or less than the determination threshold value N, the exhaust valve control unit 622 opens the exhaust valve 42 of the first cylinder bank 21 during the compression stroke of the first cylinder bank 21. In this manner, the exhaust valve control unit 622 can suppress the load placed on the engine 1, which is already under a large load, by opening the exhaust valve 42 during the compression stroke, thereby suppressing the load from being placed on the engine 1 excessively.

[0050] In this embodiment, the judgment threshold N is set according to the rotation speed R. For example, the storage unit 61 stores a data table in which the rotation speed R is associated with the judgment threshold N. The acquisition unit 621 acquires the judgment threshold N corresponding to the acquired rotation speed R by referring to the storage unit 61. Then, the exhaust valve control unit 622 judges whether the acquired command injection amount Q is equal to or less than the judgment threshold N corresponding to the acquired rotation speed R. When the command injection amount Q is equal to or less than the judgment threshold N, the exhaust valve control unit 622 opens the exhaust valve 42 during the compression stroke of the first cylinder group 21. When the command injection amount Q is greater than the judgment threshold N, the exhaust valve control unit 622 maintains the exhaust valve 42 closed during the compression stroke of the first cylinder group 21.

[0051] However, if the exhaust valve 42 of the first cylinder group 21 is opened during the compression stroke of the first cylinder group 21 and the exhaust valve 42 of the second cylinder group 22 is not opened during the compression stroke of the second cylinder group 22, the piston 241 of the second cylinder group 22 and the inner wall of the cylinder 2 may wear, or the second cylinder group 22 may overheat and damage the injection part 43 of the second cylinder group 22.

[0052] Therefore, the exhaust valve control unit 622 makes the first open time during which the exhaust valve 42 of the first cylinder group 21 is open during the compression stroke of the first cylinder group 21 equal to the second open time during which the exhaust valve 42 of the second cylinder group 22 is open during the compression stroke of the second cylinder group 22. Specifically, when the first open time is longer than the second open time by a predetermined time or more, the exhaust valve control unit 622 opens the exhaust valve 42 of the second cylinder group 22 during the compression stroke of the second cylinder group 22 and closes the exhaust valve 42 of the first cylinder group 21 during the compression stroke of the first cylinder group 21. The predetermined time may be appropriately determined based on the specifications of the cylinders 2 and experiments, and is, for example, 60 seconds, but is not limited thereto. This makes it possible for the exhaust valve control unit 622 to reduce the difference between the first open time and the second open time when the difference between the first open time and the second open time becomes too large.

[0053] The exhaust valve control unit 622 opens the exhaust valve 42 of the second cylinder group 22 during the compression stroke of the second cylinder group 22 and closes the exhaust valve 42 of the first cylinder group 21 during the compression stroke of the first cylinder group 21 until the difference between the first opening time and the second opening time becomes less than a switching time that is smaller than a predetermined time. The switching time is, for example, 10 seconds, but is not limited thereto. When the difference between the first opening time and the second opening time becomes less than the switching time, the exhaust valve control unit 622 opens the exhaust valve 42 of the first cylinder group 21 during the compression stroke of the first cylinder group 21 and closes the exhaust valve 42 of the second cylinder group 22 during the compression stroke of the second cylinder group 22. In this way, the exhaust valve control unit 622 can make the first opening time and the second opening time the same by switching the cylinder group that opens the exhaust valve 42 during the compression stroke.

[0054] When the exhaust valve control unit 622 switches the cylinder group that opens the exhaust valve 42 during the compression stroke, it is necessary to also switch the cylinder group into which fuel is injected. When the first opening time is greater than the second opening time by a predetermined time or more, the injection control unit 623 stops the fuel injection to the second cylinder group 22. When the fuel injection to the second cylinder group 22 is stopped, the injection control unit 623 injects a fourth injection amount of fuel, which is greater than the third injection amount, into the combustion chamber 242 of the first cylinder group 21 in which the exhaust valve 42 is closed during the compression stroke. The third injection amount is the amount of fuel injected in a state in which the exhaust valve 42 is closed during the compression stroke of the second cylinder group 22. In this way, the injection control unit 623 can switch between the cylinder group for which fuel injection is stopped and the cylinder group for which fuel is injected with an increased injection amount, according to the switching of the cylinder group for which the exhaust valve control unit 622 opens the exhaust valve 42 during the compression stroke.

[0055] When the exhaust valve control unit 622 switches the cylinder group that opens the exhaust valve 42 during the compression stroke, it is necessary to switch the cylinder group that recirculates the exhaust gas. When the first open time is greater than the second open time by a predetermined time or more, the recirculation control unit 624 recirculates the exhaust gas from the first cylinder group 21, whose exhaust valve 42 is closed during the compression stroke, to the intake pipe 12, and does not recirculate the exhaust gas from the second cylinder group 22, whose exhaust valve 42 is open during the compression stroke, to the intake pipe 12. Specifically, the recirculation control unit 624 opens the first control valve 151 and closes the second control valve 152, thereby recirculating the exhaust gas from the first cylinder group 21 to the intake pipe 12 and not recirculating the exhaust gas from the second cylinder group 22 to the intake pipe 12. In this way, the recirculation control unit 624 can switch the cylinder group that recirculates the exhaust gas in response to the exhaust valve control unit 622 switching the cylinder group that opens the exhaust valve 42 during the compression stroke.

[0056] The exhaust valve control unit 622 opens the exhaust valve 42 of the first cylinder group 21 during the compression stroke of the first cylinder group 21 while the temperature of the cooling water is equal to or lower than a predetermined value. When the temperature of the cooling water becomes higher than a predetermined water temperature, the exhaust valve control unit 622 closes the exhaust valve 42 during the compression stroke of the first cylinder group 21 and does not open the exhaust valve 42 during the compression stroke. Specifically, when the temperature of the cooling water is equal to or higher than a judgment temperature higher than the predetermined water temperature, the exhaust valve control unit 622 closes the exhaust valve 42 during the compression stroke of the first cylinder group 21. The judgment temperature may be determined based on the specifications of the engine 1 and experiments, and is, for example, 40 degrees Celsius, but is not limited thereto. In this way, the exhaust valve control unit 622 can make it easy to raise the temperature of the engine 1 and the purification device 34 until the temperature of the engine 1 and the purification device 34 is sufficiently raised.

[0057] As described above, the cooling water temperature corresponds to the temperature of the engine 1 or the purification device 34, so the exhaust valve control unit 622 determines whether the temperature of the engine 1 or the purification device 34 is low based on the temperature of the cooling water. However, the present invention is not limited to this, and the exhaust valve control unit 622 may determine whether to execute control to open the exhaust valve 42 of the first cylinder group 21 during the compression stroke of the first cylinder group 21 by means other than the temperature of the cooling water. For example, the exhaust valve control unit 622 determines whether the engine 1 or the purification device 34 is in a cold start state depending on whether the temperature of the engine 1 or the purification device 34 is lower than the outside air temperature. Also, the longer the stop time that has elapsed since the engine 1 was stopped, the lower the temperature of the engine 1 becomes and the closer it becomes to the outside air temperature. Therefore, the exhaust valve control unit 622 determines that the engine 1 is in a cold start state when the stop time is equal to or longer than a predetermined time, and determines that the engine 1 is not in a cold start state when the stop time is less than the predetermined time. The predetermined time is, for example, 10 hours, but is not limited thereto.

[0058] As described above, when the exhaust valve 42 is opened during the compression stroke of the first cylinder group 21, fuel is not injected into the combustion chamber 242 of the first cylinder group 21. When fuel is not injected, it is not necessary to inject lubricating oil to the piston 241 of the first cylinder group 21. Therefore, the supply control unit 625 does not supply lubricating oil to the piston 241 of the first cylinder group 21 whose exhaust valve 42 is opened during the compression stroke. Specifically, when the exhaust valve 42 is opened during the compression stroke of the first cylinder group 21, the supply control unit 625 stops the supply of lubricating oil to the piston 241 of the first cylinder group 21. More specifically, the supply control unit 625 stops the injection of lubricating oil by the oil jet 51. In this way, the supply control unit 625 can suppress the supply of unnecessary lubricating oil.

[0059] When the supply of lubricating oil to the piston 241 of the first cylinder group 21 is stopped, the supply control unit 625 reduces the discharge rate of the pump 52 to be less than the discharge rate of the pump 52 when lubricating oil is being supplied to the piston 241 of the first cylinder group 21. This allows the supply control unit 625 to prevent an excessive load from being placed on the pump 52, making it possible to operate the pump 52 at an appropriate load, and reducing the risk of the pump 52 breaking down. Furthermore, since the load on the pump 52 is reduced, the load on the engine 1 is reduced, thereby reducing the amount of fuel consumed during the process of raising the temperature of the engine 1 and the purification device 34.

[0060] [Engine 1 heating process] 5 is a flowchart showing an example of the flow of a process for increasing the temperature of the engine 1. The process for increasing the temperature of the engine 1 is executed when the engine 1 that is not operating is started. Also, it is assumed that the acquisition unit 621 acquires the temperature of the coolant of the engine 1, the number of revolutions R, and the instructed injection amount Q.

[0061] The exhaust valve control unit 622 determines whether the temperature of the cooling water is equal to or lower than a predetermined water temperature (step S1). Specifically, the exhaust valve control unit 622 determines whether the engine 1 is in cold start by determining whether the temperature of the cooling water is equal to or lower than a predetermined water temperature. If the temperature of the cooling water is higher than the predetermined water temperature (No in step S1), the exhaust valve control unit 622 ends the process of heating the engine 1 because the engine 1 is not in cold start and it is not necessary to heat the engine 1. The exhaust valve control unit 622 may determine whether the engine 1 is in cold start based on whether the stop time that has elapsed since the engine 1 was stopped is equal to or longer than a predetermined time.

[0062] When the temperature of the cooling water is equal to or lower than a predetermined water temperature (Yes in step S1), the exhaust valve control unit 622 determines that the engine 1 is in cold start. When the engine 1 is in cold start, the exhaust valve control unit 622 determines whether the rotation speed R of the engine 1 is equal to or lower than a predetermined rotation speed R1 (step S2). When the rotation speed R of the engine 1 is higher than the predetermined rotation speed R1 (No in step S2), the exhaust valve control unit 622 ends the process of heating the engine 1 because the number of combustions per unit time is high and the engine 1 is in a state where it is easy for the temperature to rise.

[0063] When the rotation speed R of the engine 1 is equal to or lower than a predetermined rotation speed R1 (Yes in step S2), the exhaust valve control unit 622 determines whether or not the command injection amount Q is equal to or lower than a judgment threshold value N (step S3). When the command injection amount Q is greater than the judgment threshold value N (No in step S3), the amount of injected fuel is large and the engine 1 is in a state where it is easy for the temperature to rise, so the exhaust valve control unit 622 ends the process of raising the temperature of the engine 1.

[0064] When the command injection amount Q is equal to or less than the determination threshold value N (Yes in step S3), the exhaust valve control unit 622 determines whether the first open time is longer than the second open time by a predetermined time or more (step S4). Specifically, the exhaust valve control unit 622 determines whether the first open time during which the exhaust valve 42 of the first cylinder group 21 was open during the compression stroke of the first cylinder group 21 is longer than a predetermined time or more than the second open time during which the exhaust valve 42 of the second cylinder group 22 was open during the compression stroke of the second cylinder group 22.

[0065] When the first opening time is greater than the second opening time by a predetermined time or more (Yes in step S4), the exhaust valve control unit 622 executes a process of compressing and releasing the second cylinder group 22 (step S5). FIG. 6 is a flowchart showing an example of the flow of the process of compressing and releasing the second cylinder group 22. The injection control unit 623 stops fuel injection into the combustion chamber 242 of the second cylinder group 22 (step S51). The exhaust valve control unit 622 opens the exhaust valve 42 of the second cylinder group 22 during the compression stroke of the second cylinder group 22 (step S52). Specifically, the exhaust valve control unit 622 opens the exhaust valve 42 of the second cylinder group 22 during the compression stroke of the second cylinder group 22, and closes the exhaust valve 42 of the first cylinder group 21 during the compression stroke of the first cylinder group 21.

[0066] When the exhaust valve 42 of the second cylinder bank 22 opens during the compression stroke of the second cylinder bank 22, the recirculation control unit 624 recirculates the exhaust gas of the first cylinder bank 21 to the intake pipe 12 (step S53). Specifically, the recirculation control unit 624 opens the first control valve 151 to recirculate the exhaust gas of the first cylinder bank 21 to the intake pipe 12, and closes the second control valve 152 to prevent the exhaust gas of the second cylinder bank 22 from recirculating to the intake pipe 12.

[0067] The injection control unit 623 injects a fourth injection amount of fuel into the combustion chamber 242 of the first cylinder bank 21 (step S54). Specifically, the injection control unit 623 controls the injector 43 of the first cylinder bank 21 to inject a fourth injection amount of fuel into the combustion chamber 242 of the first cylinder bank 21, the fourth injection amount being greater than the third injection amount of fuel injected while the exhaust valve 42 is closed during the compression stroke of the second cylinder bank 22.

[0068] When the first opening time is not longer than the second opening time by a predetermined time or more, in other words, when the first opening time is longer than the second opening time and the difference between the first opening time and the second opening time is less than the predetermined time (No in step S4), the exhaust valve control unit 622 executes a process of compression-releasing the first cylinder group 21 (step S6). FIG. 7 is a flowchart showing an example of the flow of the process of compression-releasing the first cylinder group 21. The injection control unit 623 stops fuel injection into the combustion chamber 242 of the first cylinder group 21 (step S61). The exhaust valve control unit 622 opens the exhaust valve 42 of the first cylinder group 21 during the compression stroke of the first cylinder group 21 (step S62). Specifically, the exhaust valve control unit 622 opens the exhaust valve 42 during the compression stroke of the first cylinder group 21 and closes the exhaust valve 42 during the compression stroke of the second cylinder group 22.

[0069] When the exhaust valve 42 of the first cylinder group 21 opens during the compression stroke of the first cylinder group 21, the recirculation control unit 624 recirculates the exhaust gas of the second cylinder group 22 to the intake pipe 12 (step S63). Specifically, the recirculation control unit 624 opens the second control valve 152 to recirculate the exhaust gas of the second cylinder group 22 to the intake pipe 12, and closes the first control valve 151 to prevent the exhaust gas of the first cylinder group 21 from being recirculated to the intake pipe 12.

[0070] The injection control unit 623 injects the second injection amount of fuel into the combustion chamber 242 of the second cylinder bank 22 (step S64). Specifically, the injection control unit 623 controls the injector 43 of the second cylinder bank 22 to inject the second injection amount of fuel into the combustion chamber 242 of the second cylinder bank 22, the second injection amount being greater than the first injection amount of fuel injected while the exhaust valve 42 is closed during the compression stroke of the first cylinder bank 21.

[0071] (Variation 1) The acquisition unit 621 in the above embodiment acquires the temperature of the cooling water of the engine 1, but is not limited thereto, and may acquire the temperature of the purification device 34. In this case, the exhaust valve control unit 622 opens the exhaust valve 42 of the first cylinder group 21 during the compression stroke of the first cylinder group 21 when the temperature of the purification device 34 is below an activation temperature at which the purification device 34 becomes activated and capable of purifying the exhaust gas.

[0072] (Variation 2) The power system S in the above embodiment has the first control valve 151 and the second control valve 152, but is not limited thereto and may have a three-way valve. For example, the power system S has a first three-way valve, instead of the first control valve 151, at a branch point where the first return pipe 131 branches off from the first pipe 31, which can switch whether or not the exhaust gas from the first cylinder group 21 is supplied to the first return pipe 131. The injection control unit 623 controls the first three-way valve to switch whether or not the exhaust gas from the first cylinder group 21 is supplied to the first return pipe 131. Moreover, the power system S has a second three-way valve, instead of the second control valve 152, at a branch point where the second return pipe 132 branches off from the second pipe 32, which can switch whether or not the exhaust gas from the second cylinder group 22 is supplied to the second return pipe 132. The injection control unit 623 controls the second three-way valve to switch between supplying the exhaust gas from the second cylinder bank 22 to the second return pipe 132 or not.

[0073] [Effects of Power System S] As described above, the power system S according to the embodiment opens the exhaust valve 42 of the first cylinder group 21 of the multiple cylinders 2 of the engine 1 during the compression stroke of the first cylinder group 21, and stops fuel injection into the combustion chamber 242 of the first cylinder group 21 when the exhaust valve 42 opens during the compression stroke of the first cylinder group 21. Then, the power system S injects a second injection amount of fuel, which is greater than the first injection amount of fuel injected into the combustion chamber 242 of the second cylinder group 22, into the combustion chamber 242 of the second cylinder group 22 while the exhaust valve 42 of the first cylinder group 21 is closed during the compression stroke of the first cylinder group 21.

[0074] In this way, the power system S opens the exhaust valve 42 during the compression stroke of the first cylinder group 21, so that a load can be applied to the engine 1. The power system S can increase the amount of fuel injected into the combustion chamber 242 of the second cylinder group 22 by the amount of the load applied to the engine 1 by opening the exhaust valve 42 of the first cylinder group 21. This allows the power system S to increase the amount of fuel injected into the combustion chamber 242 of the second cylinder group 22 compared to when the exhaust valve 42 of the first cylinder group 21 is closed during the compression stroke of the first cylinder group 21. As a result, the combustion temperature and the exhaust temperature in the combustion chamber 242 of the second cylinder group 22 rise, so that the engine 1 and the purification device 34 are more likely to rise in temperature, and the time required for the engine 1 and the purification device 34 to rise in temperature is shortened.

[0075] Furthermore, when the exhaust valve 42 of the first cylinder group 21 is opened during the compression stroke of the first cylinder group 21, the power system S recirculates the exhaust gas of the second cylinder group 22 to the intake pipe 12, but does not recirculate the exhaust gas of the first cylinder group 21 to the intake pipe 12. This allows the power system S to suppress the recirculation of unburned fresh air (air) discharged from the first cylinder group 21 to the intake pipe 12, and allows the exhaust gas of the second cylinder group 22 to be recirculated to the intake pipe 12. As a result, the power system S can reduce the oxygen concentration of the fresh air supplied to the second cylinder group 22, thereby suppressing an increase in nitrogen oxides. Note that, since fuel is not injected into the first cylinder group 21, no combustion occurs in the combustion chamber 242 of the first cylinder group 21. Therefore, nitrogen oxides are not generated in the first cylinder group 21, and the power system S can suppress the generation of nitrogen oxides in the first cylinder group 21.

[0076] That is, the power system S opens the exhaust valve 42 during the compression stroke of the first cylinder bank 21, increases the amount of fuel injected into the second cylinder bank 22, recirculates the exhaust gas from the second cylinder bank 22 to the intake pipe 12, and does not recirculate the exhaust gas from the first cylinder bank 21 to the intake pipe 12. In this manner, the power system can suppress an increase in nitrogen oxides and appropriately raise the combustion temperature. As a result, the power system S can shorten the time it takes to raise the temperature of the engine 1 while preventing an increase in the amount of nitrogen oxides generated.

[0077] Although the present invention has been described above using the embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments, and various modifications and changes are possible within the scope of the gist of the present invention. For example, all or part of the device can be configured by distributing or integrating functionally or physically in any unit. In addition, new embodiments resulting from any combination of multiple embodiments are also included in the embodiments of the present invention. The effect of the new embodiment resulting from the combination combines the effect of the original embodiment. [Explanation of symbols]

[0078] 1 Engine 3 Exhaust pipe 12 Intake pipe 16 Turbocharger 161 Compressor 162 Turbine 31 1st pipeline 32 2nd pipeline 33 3rd pipeline 34 Purification Equipment 41 Intake valve 42 Exhaust valve 43 Injection part 51 Oil Jet 52 Pump 131 First reflux pipe 132 Second reflux pipe 141 Exhaust Cooler 142 Exhaust Cooler 143 Intercooler 151 First control valve 152 Second control valve 21 First cylinder group 22 Second cylinder group 211 1st cylinder 212 2nd cylinder 213 3rd cylinder 214 4th cylinder 241 Piston 242 Combustion chamber 6. Engine control device 61 Storage section 62 Control section 621 Acquisition Department 622 Exhaust valve control section 623 Injection control unit 624 Circulation control section 625 Supply control section

Claims

1. an exhaust valve control unit that controls opening and closing of exhaust valves of a first cylinder group among a plurality of cylinders of the engine; a recirculation control unit that controls the recirculation of exhaust from the first cylinder group and exhaust from a second cylinder group among the plurality of cylinders that is different from the first cylinder group to an intake pipe of the engine; an injection control unit that controls the injection of fuel into each combustion chamber of the plurality of cylinders; having When the exhaust valve control unit controls the exhaust valves of the first cylinder bank to open during the compression stroke of the first cylinder bank, the recirculation control unit performs control so that exhaust gas from the first cylinder group is not recirculated to the intake pipe line and exhaust gas from the second cylinder group is recirculated to the intake pipe line, The injection control unit is stopping fuel injection into the combustion chambers of the first cylinder bank; and injecting a second injection amount of fuel into the combustion chamber of the second cylinder bank, the second injection amount being greater than a first injection amount of fuel injected into the combustion chamber of the second cylinder bank while the exhaust valve is closed during the compression stroke of the first cylinder bank; Power system.

2. a first return pipe that returns exhaust gas from the first cylinder group to the intake pipe; a second return pipe that returns exhaust gas from the second cylinder bank to the intake pipe, 2. The power system of claim 1.

3. When the exhaust valve opens during the exhaust stroke of the first cylinder bank, the injection control unit injects the second injection amount of fuel into the combustion chamber of the second cylinder bank, the second injection amount being greater than the first injection amount by an amount corresponding to a load generated in the engine in a state in which the exhaust valve is open during the compression stroke of the first cylinder bank.

2. The power system of claim 1.

4. The exhaust valve control unit sets a first open time during which the exhaust valves of the first cylinder group are open during the compression stroke of the first cylinder group to be equal to a second open time during which the exhaust valves of the second cylinder group are open during the compression stroke of the second cylinder group.

2. The power system of claim 1.

5. When the first opening time is greater than the second opening time by a predetermined time or more, the exhaust valve control unit opening an exhaust valve of the second bank of cylinders during a compression stroke of the second bank of cylinders; The exhaust valve of the first cylinder bank is closed during the compression stroke of the first cylinder bank, thereby making the first opening time and the second opening time the same.

5. The power system of claim 4.

6. When the first opening time is greater than the second opening time by at least the predetermined time, the injection control unit stopping fuel injection into the second cylinder bank; injecting a fourth injection amount of fuel into a combustion chamber of the first cylinder bank in a state in which the exhaust valve is closed during a compression stroke, the fourth injection amount being greater than a third injection amount of fuel injected into a combustion chamber of the second cylinder bank in a state in which the exhaust valve is closed during a compression stroke, the recirculation control unit recirculates the exhaust gas from the first cylinder bank, whose exhaust valves are closed during the compression stroke, to the intake pipe line, and does not recirculate the exhaust gas from the second cylinder bank, whose exhaust valves are open during the compression stroke, to the intake pipe line.

6. The power system of claim 5.

7. An acquisition unit for acquiring a temperature of the engine cooling water, the exhaust valve control unit opens the exhaust valve during a compression stroke of the first cylinder bank when the temperature of the cooling water is equal to or lower than a predetermined water temperature.

2. The power system of claim 1.

8. An acquisition unit that acquires a rotation speed of the engine, The exhaust valve control unit opens the exhaust valve during a compression stroke of the first cylinder bank when the rotation speed is equal to or lower than a predetermined rotation speed.

2. The power system of claim 1.

9. The acquisition unit acquires an instructed injection amount of fuel to be injected into the combustion chamber, the exhaust valve control unit opens the exhaust valve during a compression stroke of the first cylinder bank when the rotation speed is equal to or lower than the predetermined rotation speed and the instructed injection amount is smaller than a maximum injection amount that can be injected into the combustion chamber.

9. The power system of claim 8.

10. a supply control unit that stops the supply of lubricating oil to the piston of the first cylinder bank when the exhaust valve opens during the compression stroke of the first cylinder bank, 2. The power system of claim 1.

11. the supply control unit, when the supply of the lubricating oil to the piston of the first cylinder group is stopped, reduces a discharge amount of the pump that supplies the lubricating oil to a value smaller than a discharge amount of the pump when the lubricating oil is being supplied to the piston of the first cylinder group.

11. The power system of claim 10.

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