Power system

Abstract

To suppress increase in nitrogen oxide and appropriately raise a combustion temperature.SOLUTION: A power system S includes: an exhaust valve control section 622 that controls an opening / closing of an exhaust valve 42 in a first cylinder group 21 in a compression stroke of the first cylinder group 21; a recirculation control section 624 that recirculates exhaust gas in a second cylinder group 22 to an intake pipeline 12 and does not recirculate exhaust gas in the first cylinder group 21 to the intake pipeline 12 when the exhaust valve 42 is opened in the compression stroke of the first cylinder group 21; and an injection control section 623 that stops fuel injection to a combustion chamber 242 of the first cylinder group 21 and injects a second injection amount of fuel larger than a first injection amount of fuel that is injected to a combustion chamber 242 of the second cylinder group 22 with the exhaust valve 42 closed in the compression stroke of the first cylinder group 21 to the combustion chamber 242 of the second cylinder group 22 in the case where the exhaust valve 42 is opened in the compression stroke of the first cylinder group 21.SELECTED DRAWING: Figure 3

Description

Technical Field

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

Background Art

[0002] Techniques for raising the temperature of an engine and a purification device during cold start of an engine are known. Patent Document 1 discloses a technique for raising the combustion temperature by increasing the amount of fuel injected into the combustion chamber of an engine, and raising the temperature of the purification device with the exhaust gas that has become hot.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, if the fuel injection amount is increased too much, the output of the engine will become too large, so there is a limit to the injectable amount that can be increased, and the combustion temperature may not be raised sufficiently. In addition, when the injection amount is increased to raise the combustion temperature, nitrogen oxides generated during combustion increase.

[0005] Therefore, the present invention has been made in view of these points, and an object thereof is to suppress an increase in nitrogen oxides and appropriately raise the combustion temperature.

Means for Solving the Problems

[0006] In an aspect of the present invention, there is an exhaust valve control unit that controls opening and closing of exhaust valves of a plurality of cylinders of an engine, a reflux control unit that controls reflux of exhaust of the first cylinder group among the plurality of cylinders and exhaust of a second cylinder group different from the first cylinder group among the plurality of cylinders to an intake pipeline of the engine, and an injection control unit that controls injection of fuel into combustion chambers of each of the plurality of cylinders. When the exhaust valve control unit controls to open the exhaust valves of the first cylinder group during a compression process of the first cylinder group, the reflux control unit controls so that exhaust of the first cylinder group does not reflux to the intake pipeline and exhaust of the second cylinder group refluxes to the intake pipeline. The injection control unit stops fuel injection into the combustion chambers of the first cylinder group and injects fuel in a second injection amount, which is larger than a first injection amount of fuel injected into the combustion chambers of the second cylinder group in a state where the exhaust valves are closed during the compression process of the first cylinder group, into the combustion chambers of the second cylinder group, thereby providing a power system.

[0007] It may include a first reflux pipeline that refluxes exhaust of the first cylinder group to the intake pipeline and a second reflux pipeline that refluxes exhaust of the second cylinder group to the intake pipeline.

[0008] When the exhaust valves are open during an exhaust process of the first cylinder group, the injection control unit may inject fuel in the second injection amount, which is larger than the first injection amount, according to an amount corresponding to a load generated in the engine in a state where the exhaust valves are open during the compression process of the first cylinder group, into the combustion chambers of the second cylinder group.

[0009] The exhaust valve control unit may make a first opening time when the exhaust valves of the first cylinder group are open during the compression process of the first cylinder group the same as a second opening time when the exhaust valves of the second cylinder group are open during the compression process of the second cylinder group.

[0010] When the first opening time is larger than the second opening time by a predetermined time or more, the exhaust valve control unit may open the exhaust valves of the second cylinder group during the compression process of the second cylinder group and close the exhaust valves of the first cylinder group during the compression process of the first cylinder group, thereby making the first opening time the same as the second opening time.

[0011] When the first opening time is greater than or equal to the predetermined time longer than the second opening time, the injection control unit stops fuel injection to the second cylinder group, and injects fuel with a fourth injection amount, which is larger than a third injection amount of fuel injected into the combustion chamber of the first cylinder group in a state where the exhaust valve is closed during the compression process, into the injection unit. The reflux control unit may reflux the exhaust of the first cylinder group in which the exhaust valve is closed during the compression process to the intake air passage, and does not have to reflux the exhaust of the second cylinder group in which the exhaust valve is open during the compression process to the intake air passage.

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

[0013] It has an acquisition unit that acquires the rotational speed of the engine, and when the rotational speed is equal to or lower than a predetermined rotational speed, the exhaust valve control unit may open the exhaust valve during the compression process of the first cylinder group.

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

[0015] It may have a supply control unit that stops the supply of lubricating oil to the piston of the first cylinder group when the exhaust valve opens during the compression process of the first cylinder group.

[0016] When the supply of the lubricating oil to the piston of the first cylinder group is stopped, the supply control unit may reduce the discharge amount of the pump that supplies the lubricating oil to be less than the discharge amount of the pump when the lubricating oil is supplied to the piston of the first cylinder group.

Advantages of the Invention

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

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0019] [Configuration of Power System S] The power system S is a power system using the engine 1. The power system S is a system for shortening the time related to raising the temperature of the engine and the device for purifying the exhaust of the engine when starting the engine 1 during cold start when the temperature of the engine 1 is 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 cylinder of the engine 1. FIG. 3 is a diagram for explaining the configuration of the engine control device 6. The power system S includes the engine 1, an intake pipeline 12, an exhaust pipeline 3, a first reflux pipeline 131, a second reflux pipeline 132, a purification device 34, a supercharger 16, and an engine control device 6. Further, the engine 1 has a plurality of cylinders 2.

[0020] The engine 1 is an internal combustion engine that burns and expands a mixture of fuel and fresh air (air) to generate power. The engine 1 is, for example, a diesel engine mounted on an automobile or a ship, but it may also be a gasoline engine. The plurality of cylinders 2 includes four cylinders: a first cylinder 211, a second cylinder 212, a third cylinder 213, and a fourth cylinder 214. Hereinafter, when it is not necessary to distinguish the first cylinder 211, the second cylinder 212, the third cylinder 213, and the fourth cylinder 214, they are referred to as cylinders 2. Among the plurality of cylinders 2 of the engine 1, the first cylinder 211 and the fourth cylinder 214 are the first cylinder group 21. Among the plurality of cylinders 2 of the engine 1, the second cylinder 212 and the third cylinder 213 are a second cylinder group 22 different from the first cylinder group 21.

[0021] Note that the combustion order of each cylinder in this embodiment 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 set as the first cylinder group 21, and the second cylinder 212 and the third cylinder 213 are set 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. Also, they may be changed according to the number of cylinders of the engine 1. For example, when the engine 1 has six cylinders and the combustion order of each cylinder 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 set as the first cylinder group, and the fourth cylinder, the fifth cylinder, and the sixth cylinder are set 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 the operation cycle of the engine 1. First, when the piston 241 moves downward, the intake valve 41 opens, and fresh air is sucked into the cylinder 2 (intake process). Next, when the piston 241 reaches the bottom dead center, the intake valve 41 closes, and when the piston 241 rises to the top dead center, the air is compressed (compression process). Subsequently, fuel is injected by the injection unit 43, and the fuel mixed with the compressed and heated air burns, and the expanded combustion gas pushes the piston 241 down to the bottom dead center (combustion process). Then, due to inertia and expansion in other cylinders 2, when the piston 241 rises to the top dead center again, the exhaust valve 42 is opened, and the combustion gas is pushed out of the cylinder 2 and discharged into the exhaust pipeline 3 as exhaust gas (exhaust process).

[0023] An oil jet 51 is provided in the cylinder 2. The oil jet 51 injects lubricating oil toward the lower surface 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 by the rotation of the output shaft to supply lubricating oil to the oil jet 51. The pump 52 is, for example, a variable displacement vane pump capable of changing the discharge amount of the lubricating oil, but is not limited thereto.

[0024] The intake pipeline 12 is a pipeline for supplying fresh air to the engine 1. The intake pipeline 12 branches so as to correspond to each cylinder 2 and is a pipeline for supplying fresh air to each cylinder 2. An intercooler 143 is provided in the intake pipeline 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 cooling water or outside air of the engine 1 and the fresh air.

[0025] The exhaust pipe 3 is a pipe for discharging the exhaust gas of the engine 1 to the outside. The exhaust pipe 3 is provided with a turbine 162 of a supercharger 16 that compresses the fresh air supplied to the engine 1. The turbine 162 rotates when the exhaust gas passes through it. The turbine 162 is connected to a compressor 161 of the supercharger 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 a pipe that connects to the first cylinder bank 21 and supplies the exhaust gas of the first cylinder bank 21 to the turbine 162. The second pipe 32 is a pipe that connects to the second cylinder bank 22 and supplies the exhaust gas of the second cylinder bank 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 reflux pipe 131 is a pipe that connects the first pipe 31 and the intake pipe 12 and refluxes the exhaust gas of the first cylinder bank 21 to the intake pipe 12. An exhaust gas cooler 141 is provided in the first reflux pipe 131. The exhaust gas cooler 141 is a heat exchanger that cools the exhaust gas of the first cylinder bank 21 by exchanging heat between the exhaust gas of the first cylinder bank 21 and the cooling water or outside air of the engine 1. A first control valve 151 is provided between the intake pipe 12 and the exhaust gas cooler 141 in the first reflux pipe 131. The first control valve 151 adjusts the flow rate of the exhaust gas of the first cylinder bank 21 flowing into the intake pipe 12. The first control valve 151 adjusts the flow rate of the exhaust gas of the first cylinder bank 21 passing through the first control valve 151 by adjusting the area of the flow path by operating an adjustment valve that adjusts the area of the flow path under the control of the engine control device 6.

[0028] The second recirculation pipeline 132 is a pipeline that connects the second pipeline 32 and the intake pipeline 12 and recirculates the exhaust gas of the second cylinder group 22 to the intake pipeline 12. An exhaust gas cooler 142 is provided in the second recirculation pipeline 132. The exhaust gas cooler 142 is a heat exchanger that cools the exhaust gas of the second cylinder group 22 by exchanging heat between the exhaust gas of 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 pipeline 12 and the exhaust gas cooler 142 in the second recirculation pipeline 132. The second control valve 152 adjusts the flow rate of the exhaust gas of the second cylinder group 22 flowing into the intake pipeline 12. The second control valve 152 is controlled by the engine control device 6, and the flow rate of the exhaust gas of the second cylinder group 22 passing through the second control valve 152 is adjusted by operating an adjustment valve that adjusts the area of the flow path, thereby adjusting the area of the flow path.

[0029] A purification device 34 is provided in the third pipeline 33. The purification device 34 purifies the exhaust gas of the engine 1. The purification device 34 is, for example, a DPD (Diesel Particulate Diffuser) or a selective catalytic reduction denitration device (so-called urea SCR (Selective Catalytic Reduction)), but is not limited thereto. The DPD is a purification device that removes particulate matter (e.g., soot) in the exhaust gas. The DPD has a filter for collecting particulate matter. The selective catalytic reduction denitration device is a purification device that reduces nitrogen oxides in the exhaust gas. The selective catalytic reduction denitration device injects urea water, which is a precursor of ammonia, into the exhaust gas flowing through the third pipeline 33, reacts nitrogen oxides with ammonia, and reduces them to nitrogen and water.

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

[0031] Further, when the engine control device 6 opens the exhaust valve 42 during the compression stroke of the first cylinder bank 21 at the cold start of the engine 1, the engine control device 6 causes the exhaust of the second cylinder bank 22 to flow back into the intake pipe 12 and does not cause the unburned fresh air (air) discharged from the first cylinder bank 21 to flow back. In other words, while the engine control device 6 performs control to open the exhaust valve 42 during the compression stroke of the first cylinder bank 21 at the cold start of the engine 1, the engine control device 6 does not cause the unburned fresh air discharged from the first cylinder bank 21 to flow back. Specifically, the engine control device 6 opens the first control valve 151 and closes the second control valve 152, thereby causing the exhaust of the first cylinder bank 21 to flow back into the intake pipe 12 and not causing the exhaust of the second cylinder bank 22 to flow back into the intake pipe 12.

[0032] Thereby, the engine control device 6 can reduce the oxygen concentration of the air-fuel mixture of fresh air and exhaust gas supplied to the combustion chamber 242 of the second cylinder bank 22, and can suppress an increase in the generated nitrogen oxides. Hereinafter, the specific configuration of the engine control device 6 will be described.

[0033] The engine control device 6 includes 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, and the like. The storage unit 61 stores programs executed by the control unit 62.

[0034] The control unit 62 is a computing resource including a processor such as a CPU (Central Processing Unit). By executing the program stored in the storage unit 61, the control unit 62 realizes 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 the information from the sensor group 11 that acquires information regarding the power system S. For example, the sensor group 11 includes a sensor that acquires the rotational speed of the engine 1 and a sensor that acquires the temperature of the cooling water of the engine 1. The acquisition unit 621 acquires the rotational speed of the engine 1 and the temperature of the cooling water of the engine 1 from the sensor group 11.

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

[0037] The exhaust valve control unit 622 controls the opening and closing of the exhaust valves 42 of the plurality of cylinders 2. The exhaust valve control unit 622 performs the opening and closing control of the exhaust valve 42 of each of the plurality of cylinders 2 according to the process of the operating cycle of the engine 1. Further, the exhaust valve control unit 622 performs the opening and closing control of the exhaust valve 42 in the process of the operating cycle according to 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 valve 42 of the first cylinder group 21 (the first cylinder 211 and the fourth cylinder 214) during the compression process of the first cylinder group 21. Specifically, at the cold start of the engine 1, the exhaust valve control unit 622 opens the exhaust valve 42 during the compression process of the first cylinder group 21, and when the exhaust valve 42 is opened during the compression process of the first cylinder group 21, the exhaust valve 42 is closed during the compression process of the second cylinder group 22 (the second cylinder 212 and the third cylinder 213).

[0038] The exhaust valve control unit 622 determines whether it is at the cold start of the engine 1 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 has not risen. Therefore, when the temperature of the cooling water is equal to or lower than a predetermined water temperature, the exhaust valve control unit 622 determines that it is at the cold start of the engine 1 and opens the exhaust valve 42 during the compression process of the first cylinder group 21. The predetermined water temperature may be determined as appropriate. For example, it is 0 degrees Celsius, but it is not limited thereto. The predetermined water temperature may be the temperature of the outside air. The exhaust valve control unit 622 determines that it is at the cold start 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. By doing so, when the temperature of the cooling water is low and it is necessary to raise 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 and increase the amount of fuel injected into the second cylinder group 22 to a possible state.

[0039] The injection control unit 623 controls each injection unit 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, when the exhaust valve 42 opens during the compression process of the first cylinder group 21, the injection control unit 623 controls the injection unit 43 of the first cylinder group 21 to stop the fuel injection into the combustion chamber 242 of the first cylinder group 21. Thereby, since the exhaust valve 42 opens during the compression process, the injection control unit 623 can suppress the fuel injection into the combustion chamber 242 of the first cylinder group 21 where the temperature of the air-fuel mixture does not reach the combustible temperature.

[0040] When the exhaust valve 42 opens during the exhaust process of the first cylinder group 21, the injection control unit 623 injects fuel with a second injection amount, which is larger 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 when the exhaust valve 42 is closed during the compression process 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 where the exhaust valve 42 is open during the compression process of the first cylinder group 21. More specifically, the injection control unit 623 adds an amount corresponding to the load generated in the engine 1 in a state where the exhaust valve 42 is open during the compression process of the first cylinder group 21 to the first injection amount to determine the second 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 process of the first cylinder group 21, a load is applied to the engine 1. That is, since the expansion stroke is performed in a state where the pressure of the air in the combustion chamber has decreased, negative work is generated in the engine 1, so 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 has been loaded due to the opening of the exhaust valve 42 of the first cylinder group 21 during the compression process 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 cancel out the negative work generated in the engine 1 when the exhaust valve 42 of the first cylinder group 21 is opened during the compression process of the first cylinder group 21. Thereby, 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 a substantial increase in the output of the engine 1. As a result, the combustion temperature of the air-fuel mixture rises, and the temperature of the engine 1 is likely to rise. Also, since the temperature of the exhaust gas of the second cylinder group 22 also rises, the temperature of the purification device 34 is likely to rise.

[0042] The reflux control unit 624 controls the reflux of the exhaust gas of the first cylinder group 21 and the exhaust gas of the second cylinder group 22. For example, when the exhaust valve 42 opens during the compression process of the first cylinder group 21, the reflux control unit 624 causes the exhaust gas of the second cylinder group 22 to flow back into the intake pipe 12 by supplying it to the second reflux pipe 132. The reflux control unit 624 does not cause the exhaust gas of the first cylinder group 21 to flow back into the intake pipe 12 by not supplying it to the first reflux pipe 131. Specifically, the reflux control unit 624 opens the second control valve 152 to supply the exhaust gas of the second cylinder group 22 to the second reflux pipe 132, and closes the first control valve 151 to prevent the exhaust gas of the first cylinder group 21 from being supplied to the first reflux pipe 131.

[0043] Note that the reflux control unit 624 may reduce the amount of exhaust gas of the first cylinder group 21 that flows back into the intake pipe 12 when the exhaust valve 42 opens during the compression process of the first cylinder group 21. For example, when the exhaust valve 42 opens during the compression process of the first cylinder group 21, the reflux control unit 624 makes the opening degree of the first control valve 151 smaller than the opening degree of the first control valve 151 when the exhaust valve 42 is closed during the compression process of the first cylinder group 21.

[0044] In this way, the reflux control unit 624 causes the exhaust gas of the second cylinder group 22, whose oxygen concentration is lower than that of the fresh air, to flow back into the intake pipeline 12. Thereby, the reflux control unit 624 reduces the oxygen concentration in the mixture of fresh air and exhaust gas supplied to the combustion chamber 242 of the second cylinder group 22, so that an increase in nitrogen oxides generated during combustion can be suppressed. Further, since the reflux control unit 624 does not cause the air (fresh air) discharged from the first cylinder group 21, whose oxygen concentration is higher than that of the exhaust gas, to flow back into the intake pipeline 12, an increase in the oxygen concentration of the mixture gas in the combustion chamber 242 of the second cylinder group 22 is suppressed, and an increase in nitrogen oxides generated during combustion can be suppressed.

[0045] The exhaust valve control unit 622 may open the exhaust valve 42 during the compression process of the first cylinder group 21 when the state of the engine 1 satisfies a predetermined condition. FIG. 4 is a diagram for explaining the conditions for opening the exhaust valve 42 during the compression process. The horizontal axis in FIG. 4 indicates the rotational speed R of the engine 1, and the vertical axis indicates the indicated injection amount Q of the fuel to be injected into the combustion chamber 242 of the engine 1.

[0046] When the rotational speed R of the engine 1 is equal to or lower than a predetermined rotational speed R1, the number of combustion times per unit time is smaller than when the rotational speed R is larger than the predetermined rotational speed R1. Therefore, it is difficult for the temperature of the engine 1 and the temperature of the exhaust gas to rise. Therefore, the exhaust valve control unit 622 opens the exhaust valve 42 during the compression process of the first cylinder group 21 when the rotational speed R of the engine 1 is equal to or lower than the predetermined rotational speed R1. The predetermined rotational speed R1 may be appropriately determined according to the specifications and experiments of the engine 1. The specific value of the predetermined rotational speed R1 is, for example, 2000 revolutions per minute in the case of a diesel engine, but is not limited thereto. Thereby, the exhaust valve control unit 622 can easily increase the combustion temperature in the combustion chamber 242 in a situation where it is difficult for the temperature of the engine 1 and the temperature of the exhaust gas to rise.

[0047] When the exhaust valve 42 is opened during the compression process of the first cylinder group 21 while a large load is applied to the engine 1, 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 process of the first cylinder group 21 when the rotational speed R of the engine 1 is equal to or lower than a predetermined rotational speed R1 and the indicated 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 process of the first cylinder group 21 when the indicated injection amount Q is equal to or lower than a determination threshold value N.

[0048] The determination threshold value 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 a determination threshold value N that is smaller than the maximum injection amount M by a predetermined value D. The predetermined value D is determined, for example, based on the specifications or experiments of the engine 1. The specific value of the determination threshold value N is one-fifth (equivalent to 20 percent) of the maximum injection amount M, but is not limited thereto.

[0049] The exhaust valve control unit 622 opens the exhaust valve 42 of the first cylinder group 21 during the compression process of the first cylinder group 21 when the indicated injection amount Q is included in the region shaded with diagonal lines that is equal to or lower than the determination threshold value N. By doing so, the exhaust valve control unit 622 can suppress applying a load to the engine 1 in a state where a large load is applied by opening the exhaust valve 42 during the compression process, and thus can suppress applying an excessive load to the engine 1.

[0050] In addition, in the present embodiment, it is assumed that the determination threshold value N is determined according to the rotational speed R. For example, the storage unit 61 stores a data table associating the rotational speed R with the determination threshold value N. The acquisition unit 621 refers to the storage unit 61 and acquires the determination threshold value N corresponding to the acquired rotational speed R. Then, the exhaust valve control unit 622 determines whether or not the acquired indicated injection amount Q is less than or equal to the determination threshold value N corresponding to the acquired rotational speed R. When the indicated injection amount Q is less than or equal to the determination threshold value N, the exhaust valve control unit 622 opens the exhaust valve 42 during the compression process of the first cylinder group 21. When the indicated injection amount Q is greater than the determination threshold value N, the exhaust valve control unit 622 maintains the exhaust valve 42 in a closed state during the compression process of the first cylinder group 21.

[0051] By the way, if the exhaust valve 42 of the first cylinder group 21 is opened during the compression process of the first cylinder group 21 and the exhaust valve 42 of the second cylinder group 22 is not opened during the compression process 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 the injection part 43 of the second cylinder group 22 may be damaged.

[0052] Therefore, the exhaust valve control unit 622 makes the first opening time when the exhaust valve 42 of the first cylinder group 21 is open during the compression process of the first cylinder group 21 the same as the second opening time when the exhaust valve 42 of the second cylinder group 22 is open during the compression process of the second cylinder group 22. Specifically, when the first opening time is greater than the second opening 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 process of the second cylinder group 22 and closes the exhaust valve 42 of the first cylinder group 21 during the compression process of the first cylinder group 21. The predetermined time may be appropriately determined according to the specifications of the cylinder 2, experiments, etc., and is, for example, 60 seconds, but is not limited thereto. Thereby, when the difference between the first opening time and the second opening time becomes too large, the exhaust valve control unit 622 can reduce the difference between the first opening time and the second opening time.

[0053] The exhaust valve control unit 622 opens the exhaust valve 42 of the second cylinder group 22 during the compression process of the second cylinder group 22 and closes the exhaust valve 42 of the first cylinder group 21 during the compression process of the first cylinder group 21 until the difference between the first opening time and the second opening time becomes less than the switching time which is less 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 process of the first cylinder group 21 and closes the exhaust valve 42 of the second cylinder group 22 during the compression process 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 in which the exhaust valve 42 is opened during the compression process.

[0054] When the exhaust valve control unit 622 switches the cylinder group in which the exhaust valve 42 is opened during the compression process, it is necessary to also switch the cylinder group to which fuel is injected. When the first opening time is greater than or equal to a predetermined time longer than the second opening time, the injection control unit 623 stops fuel injection into the second cylinder group 22. When the injection control unit 623 stops fuel injection into the second cylinder group 22, it injects fuel in a fourth injection amount which is more 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 process. The third injection amount is the amount of fuel injected when the exhaust valve 42 is closed during the compression process of the second cylinder group 22. In this way, the injection control unit 623 can switch the cylinder group in which fuel injection is stopped and the cylinder group in which the injection amount is increased to inject fuel according to the switching of the cylinder group in which the exhaust valve control unit 622 opens the exhaust valve 42 during the compression process.

[0055] When the exhaust valve control unit 622 switches the cylinder group that opens the exhaust valve 42 during the compression process, it is necessary to also switch the cylinder group that recirculates the exhaust. When the first opening time is greater than the second opening time by a predetermined time or more, the recirculation control unit 624 recirculates the exhaust of the first cylinder group 21 in which the exhaust valve 42 is closed during the compression process to the intake pipe 12, and does not recirculate the exhaust of the second cylinder group 22 in which the exhaust valve 42 is open during the compression process 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 of the first cylinder group 21 to the intake pipe 12 and not recirculating the exhaust of 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 according to the switching of the cylinder group in which the exhaust valve control unit 622 opens the exhaust valve 42 during the compression process.

[0056] The exhaust valve control unit 622 opens the exhaust valve 42 of the first cylinder group 21 during the compression process of the first cylinder group 21 while the temperature of the cooling water is below a predetermined value. When the temperature of the cooling water becomes higher than the predetermined water temperature, the exhaust valve control unit 622 keeps the exhaust valve 42 closed during the compression process of the first cylinder group 21 and does not open the exhaust valve 42 during the compression process. Specifically, when the temperature of the cooling water is equal to or higher than a determination temperature that is higher than the predetermined water temperature, the exhaust valve control unit 622 keeps the exhaust valve 42 closed during the compression process of the first cylinder group 21. The determination temperature may be determined according to the specifications and experiments of the engine 1, and is, for example, 40 degrees Celsius, but is not limited thereto. By doing so, the exhaust valve control unit 622 can make the temperature of the engine 1 and the purification device 34 easy to increase until the temperatures of the engine 1 and the purification device 34 are sufficiently increased.

[0057] As described above, since the cooling water temperature corresponds to the temperature of the engine 1 or the purification device 34, 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, not limited to this, 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 process 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 it is during cold start according to whether the temperature of the engine 1 or the purification device 34 is lower than the outside air temperature. Also, the longer the length of the stop time elapsed since the engine 1 stopped, the lower the temperature of the engine 1 drops and approaches the outside air temperature. Therefore, the exhaust valve control unit 622 determines that it is during cold start when the stop time is equal to or longer than a predetermined time, and determines that it is not during cold start 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 process of the first cylinder group 21, no fuel is injected into the combustion chamber 242 of the first cylinder group 21. When no fuel is injected, there is no need to inject lubricating oil into 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 for which the exhaust valve 42 is opened during the compression process. Specifically, the supply control unit 625 stops the supply of lubricating oil to the piston 241 of the first cylinder group 21 when the exhaust valve 42 is opened during the compression process of the first cylinder group 21. More specifically, the supply control unit 625 stops the injection of lubricating oil by the oil jet 51. Thereby, the supply control unit 625 can suppress the supply of unnecessary lubricating oil.

[0059] When the supply control unit 625 stops supplying lubricating oil to the pistons 241 of the first cylinder group 21, it reduces the discharge amount of the pump 52 to be less than the discharge amount of the pump 52 when lubricating oil is being supplied to the pistons 241 of the first cylinder group 21. Thereby, the supply control unit 625 can suppress an excessive load from being applied to the pump 52, enabling the pump 52 to operate with an appropriate load and reducing the risk of the pump 52 malfunctioning. Also, since the load on the pump 52 is reduced, the load on the engine 1 is reduced, and thus the fuel consumption during the process of warming up the engine 1 and the purification device 34 is reduced.

[0060] [Process of warming up the engine 1] FIG. 5 is a flowchart showing an example of the flow of the process of warming up the engine 1. The process of warming up the engine 1 is executed when the non-operating engine 1 starts. Also, it is assumed that the acquisition unit 621 acquires the temperature of the cooling water, the rotational speed R, and the indicated injection amount Q of the engine 1.

[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 starting cold by determining whether the temperature of the cooling water is equal to or lower than the predetermined water temperature. When 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 warming up the engine 1 because the engine 1 is not starting cold and warming up of the engine 1 is unnecessary. The exhaust valve control unit 622 may determine whether the engine 1 is starting cold based on whether the stop time elapsed since the engine 1 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 starting cold. When the engine 1 is starting cold, the exhaust valve control unit 622 determines whether the rotational speed R of the engine 1 is equal to or lower than a predetermined rotational speed R1 (step S2). When the rotational speed R of the engine 1 is greater than the predetermined rotational speed R1 (No in step S2), since the number of combustions per unit time is large and the engine 1 is likely to warm up, the process of warming up the engine 1 is terminated.

[0063] When the rotational speed R of the engine 1 is equal to or lower than a predetermined rotational speed R1 (Yes in step S2), the exhaust valve control unit 622 determines whether the indicated injection quantity Q is equal to or lower than a determination threshold value N (step S3). When the indicated injection quantity Q is greater than the determination threshold value N (No in step S3), since the amount of fuel injected is large and the engine 1 is likely to warm up, the process of warming up the engine 1 is terminated.

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

[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 compression and opening of the second cylinder group 22 (step S5). FIG. 6 is a flowchart showing an example of the flow of the process of compression and opening of 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 process 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 process of the second cylinder group 22 and keeps the exhaust valve 42 of the first cylinder group 21 closed during the compression process of the first cylinder group 21.

[0066] When the exhaust valve 42 of the second cylinder group 22 opens during the compression process of the second cylinder group 22, the reflux control unit 624 refluxes the exhaust of the first cylinder group 21 to the intake pipe 12 (step S53). Specifically, the reflux control unit 624 opens the first control valve 151 to reflux the exhaust of the first cylinder group 21 to the intake pipe 12 and closes the second control valve 152 to prevent the exhaust of the second cylinder group 22 from refluxing to the intake pipe 12.

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

[0068] The exhaust valve control unit 622 executes a process of compression and opening of the first cylinder group 21 when the first opening time is not greater than a predetermined time or more than the second opening time, in other words, when the first opening time is greater 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) (step S6). FIG. 7 is a flowchart showing an example of the flow of the process of compression and opening of 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 process of the first cylinder group 21 (step S62). Specifically, the exhaust valve control unit 622 opens the exhaust valve 42 during the compression process of the first cylinder group 21 and keeps the exhaust valve 42 closed during the compression process of the second cylinder group 22.

[0069] When the exhaust valve 42 of the first cylinder group 21 opens during the compression process of the first cylinder group 21, the reflux control unit 624 refluxes the exhaust of the second cylinder group 22 to the intake pipe 12 (step S63). Specifically, the reflux control unit 624 opens the second control valve 152 to reflux the exhaust of the second cylinder group 22 to the intake pipe 12, and closes the first control valve 151 to prevent the exhaust of the first cylinder group 21 from refluxing to the intake pipe 12.

[0070] The injection control unit 623 injects fuel in a second injection amount into the combustion chamber 242 of the second cylinder group 22 (step S64). Specifically, the injection control unit 623 controls the injection unit 43 of the second cylinder group 22 to inject fuel in a second injection amount that is greater than the first injection amount of fuel injected into the combustion chamber 242 of the second cylinder group 22 with the exhaust valve 42 closed during the compression process of the first cylinder group 21.

[0071] (Modification 1) Although the acquisition unit 621 in the above embodiment acquires the temperature of the cooling water of the engine 1, it is not limited to this, and the temperature of the purification device 34 may be acquired. In this case, the exhaust valve control unit 622 opens the exhaust valve 42 of the first cylinder group 21 during the compression process of the first cylinder group 21 when the temperature of the purification device 34 is lower than the activation temperature at which the purification device 34 is activated and can purify the exhaust.

[0072] (Modification 2) Although the power system S of the above-described embodiment has the first control valve 151 and the second control valve 152, it is not limited thereto, and it may have a three-way valve. For example, instead of the first control valve 151, the power system S has a first three-way valve capable of switching whether to supply the exhaust gas of the first cylinder group 21 to the first reflux pipeline 131 at a branch point where the first reflux pipeline 131 branches from the first pipeline 31. The injection control unit 623 controls the first three-way valve to switch whether to supply the exhaust gas of the first cylinder group 21 to the first reflux pipeline 131. Further, instead of the second control valve 152, the power system S has a second three-way valve capable of switching whether to supply the exhaust gas of the second cylinder group 22 to the second reflux pipeline 132 at a branch point where the second reflux pipeline 132 branches from the second pipeline 32. The injection control unit 623 controls the second three-way valve to switch whether to supply the exhaust gas of the second cylinder group 22 to the second reflux pipeline 132.

[0073] [Effect of Power System S] As described above, in the power system S according to the embodiment, the exhaust valve 42 of the first cylinder group 21 is opened during the compression process of the first cylinder group 21 among the plurality of cylinders 2 of the engine 1, and when the exhaust valve 42 is opened during the compression process of the first cylinder group 21, the fuel injection into the combustion chamber 242 of the first cylinder group 21 is stopped. Then, the power system S injects a second injection amount of fuel, which is larger 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 process of the first cylinder group 21.

[0074] In this way, since the power system S opens the exhaust valve 42 during the compression process of the first cylinder bank 21, a load can be applied to the engine 1. And the power system S can increase the amount of fuel injected into the combustion chamber 242 of the second cylinder bank 22 by an amount corresponding to the load applied to the engine 1 by opening the exhaust valve 42 of the first cylinder bank 21. As a result, the power system S can increase the amount of fuel injected into the combustion chamber 242 of the second cylinder bank 22 more than when the exhaust valve 42 of the first cylinder bank 21 is closed during the compression process of the first cylinder bank 21. As a result, the combustion temperature and the exhaust temperature in the combustion chamber 242 of the second cylinder bank 22 increase, so that the engine 1 and the purification device 34 are more likely to warm up, and the time required for the engine 1 and the purification device 34 to warm up is shortened.

[0075] Also, when the power system S opens the exhaust valve 42 of the first cylinder bank 21 during the compression process of the first cylinder bank 21, the exhaust of the second cylinder bank 22 is refluxed to the intake pipe 12, and the exhaust of the first cylinder bank 21 is not refluxed to the intake pipe 12. As a result, the power system S suppresses the unburned fresh air (air) discharged from the first cylinder bank 21 from being refluxed to the intake pipe 12, and can reflux the exhaust of the second cylinder bank 22 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 bank 22, so that an increase in nitrogen oxides can be suppressed. Note that since no fuel is injected into the first cylinder bank 21, combustion does not occur in the combustion chamber 242 of the first cylinder bank 21. Therefore, since no nitrogen oxides are generated in the first cylinder bank 21, the power system S can suppress the generation of nitrogen oxides in the first cylinder bank 21.

[0076] That is, the power system S opens the exhaust valve 42 during the compression process of the first cylinder bank 21, increases the fuel injection amount to the second cylinder bank 22, refluxes the exhaust of the second cylinder bank 22 to the intake pipe 12, and does not reflux the exhaust of the first cylinder bank 21 to the intake pipe 12. By doing so, 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 required for the engine 1 to warm up while not increasing the generated nitrogen oxides.

[0077] As described above, the present invention has been explained using embodiments. However, 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. For example, all or part of the device can be configured by being functionally or physically dispersed and integrated in any unit. Also, new embodiments resulting from any combination of a plurality of embodiments are included in the embodiments of the present invention. The effects of the new embodiments resulting from the combination have the effects of the original embodiments combined.

Explanation of Reference Numerals

[0078] 1 Engine 3 Exhaust Pipeline 12 Intake Pipeline 16 Supercharger 161 Compressor 162 Turbine 31 First Pipeline 32 Second Pipeline 33 Third Pipeline 34 Purification Device 41 Intake Valve 42 Exhaust Valve 43 Injection Unit 51 Oil Jet 52 Pump 131 First Recirculation Pipeline 132 Second Recirculation Pipeline 141 Exhaust Cooler 142 Exhaust Cooler 143 Intercooler 151 First Control Valve 152 Second Control Valve 21 First Cylinder Bank 22 Second Cylinder Bank 211 First Cylinder 212 Second Cylinder 213 Third Cylinder 214 Fourth Cylinder 241 Piston 242 Combustion Chamber 6 Engine Control Device 61 Storage Unit 62 Control Unit 621 Acquisition Unit 622 Exhaust Valve Control Unit 623 Injection Control Unit 624 Recirculation Control Unit 625 Supply Control Unit

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 an engine, a reflux control unit that controls reflux of exhaust of the first cylinder group and exhaust of a second cylinder group different from the first cylinder group among the plurality of cylinders to an intake pipe of the engine, an injection control unit that controls injection of fuel into combustion chambers of each of the plurality of cylinders, and having, when the exhaust valve control unit controls to open the exhaust valves of the first cylinder group during a compression process of the first cylinder group, the reflux control unit controls so that exhaust of the first cylinder group does not reflux to the intake pipe and exhaust of the second cylinder group refluxes to the intake pipe, the injection control unit, stops fuel injection into the combustion chambers of the first cylinder group, and injects fuel in a second injection amount, which is larger than a first injection amount of fuel injected into the combustion chamber of the second cylinder group with the exhaust valve closed during the compression process of the first cylinder group, into the combustion chamber of the second cylinder group, a power system.

2. a first reflux pipe that refluxes exhaust of the first cylinder group to the intake pipe, a second reflux pipe that refluxes exhaust of the second cylinder group to the intake pipe, and having, the power system according to claim 1.

3. when the exhaust valve is open during an exhaust process of the first cylinder group, the injection control unit injects fuel in the second injection amount, which is larger than the first injection amount, into the combustion chamber of the second cylinder group according to an amount corresponding to a load generated in the engine in a state where the exhaust valve is open during the compression process of the first cylinder group, the power system according to claim 1.

4. the exhaust valve control unit makes the first opening time when the exhaust valve of the first cylinder group is open during the compression process of the first cylinder group the same as the second opening time when the exhaust valve of the second cylinder group is open during the compression process of the second cylinder group, the power system according to claim 1.

5. when the first opening time is larger than the second opening time by a predetermined time or more, the exhaust valve control unit opens the exhaust valve of the second cylinder group during the compression process of the second cylinder group, and closes the exhaust valve of the first cylinder group during the compression process of the first cylinder group to make the first opening time the same as the second opening time, the power system according to claim 4.

6. when the first opening time is larger than the second opening time by the predetermined time or more, the injection control unit stops fuel injection into the second cylinder group, Inject into the combustion chamber of the first cylinder group in a state where the exhaust valve is closed during the compression process, a fuel injection amount that is more than the third injection amount of fuel injected in a state where the exhaust valve is closed during the compression process of the second cylinder group, The reflux control unit refluxes the exhaust of the first cylinder group in which the exhaust valve is closed during the compression process to the intake pipeline, and does not reflux the exhaust of the second cylinder group in which the exhaust valve is open during the compression process to the intake pipeline, The power system according to claim 5.

7. It has an acquisition unit that acquires the temperature of the cooling water of the engine, When the temperature of the cooling water is equal to or lower than a predetermined water temperature, the exhaust valve control unit opens the exhaust valve during the compression process of the first cylinder group. The power system according to claim 1.

8. It has an acquisition unit that acquires the rotational speed of the engine, When the rotational speed is equal to or lower than a predetermined rotational speed, the exhaust valve control unit opens the exhaust valve during the compression process of the first cylinder group. The power system according to claim 1.

9. The acquisition unit acquires the indicated injection amount of fuel injected into the combustion chamber, When the rotational speed is equal to or lower than the predetermined rotational speed and the indicated injection amount is smaller than the maximum injection amount that can be injected into the combustion chamber, the exhaust valve control unit opens the exhaust valve during the compression process of the first cylinder group. The power system according to claim 8.

10. It has a supply control unit that stops the supply of lubricating oil to the piston of the first cylinder group when the exhaust valve opens during the compression process of the first cylinder group, The power system according to claim 1.

11. When the supply of the lubricating oil to the piston of the first cylinder group is stopped, the supply control unit reduces the discharge amount of the pump that supplies the lubricating oil to be less than the discharge amount of the pump when the lubricating oil is supplied to the piston of the first cylinder group. The power system according to claim 10.

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