POWER SYSTEM AND METHOD OF CONTROLLING POWER SYSTEM

Abstract

A power system including: a power unit, a supply pump for feeding liquid oil for lubricating the power unit; a supply flow path for guiding, to the power unit, the oil fed from the supply pump; a return pump for returning the oil having flowed through the power unit; a return flow path for guiding, to the return pump, the oil having flowed through the power unit; a circulation flow path for guiding, to the supply pump, the oil returned by the return pump; a bypass flow path connecting the supply flow path and the return flow path; and an on-off valve for opening and closing the bypass flow path.

Claims

1. A power system comprising: a power unit; a supply pump configured to feed oil in a liquid form for lubricating the power unit; a supply flow path configured to guide, to the power unit, the oil fed from the supply pump; a return pump configured to return the oil having flowed through the power unit; a return flow path configured to guide, to the return pump, the oil having flowed through the power unit; a circulation flow path configured to guide, to the supply pump, the oil returned by the return pump; a bypass flow path connecting the supply flow path and the return flow path; and an on-off valve configured to open and close the bypass flow path.

2. The power system according to claim 1, wherein a capacity of the return pump is larger than a capacity of the supply pump.

3. The power system according to claim 2, wherein the oil led out from the power unit is mixed with gas, and the circulation flow path is provided with a gas-liquid separator configured to separate the gas from the oil.

4. The power system according to claim 1, wherein the on-off valve comprises a relief valve that is pushed by the oil to open when a pressure of the oil supplied from the supply pump reaches a predetermined pressure upper limit value.

5. The power system according to claim 1, further comprising: a motor configured to drive the supply pump and the return pump.

6. The power system according to claim 5, wherein the motor is a sole motor, and the power system further comprises a power transmission mechanism configured to transmit a rotational driving force of the motor to the supply pump and the return pump.

7. The power system according to claim 5, further comprising: a controller comprising one or more processors that execute computer-executable instructions stored in a memory, wherein the one or more processors execute the computer-executable instructions to cause the controller to control the motor to set torque of the motor to predetermined target torque in a state where the on-off valve is opened.

8. The power system according to claim 7, wherein the one or more processors cause the controller to control the motor to set a rotational speed of the supply pump to a target rotational speed in a state where the on-off valve is closed.

9. The power system according to claim 1, wherein the power unit comprises: a bearing that rotatably supports a rotor; and a lubrication flow path configured to allow the oil to flow through the bearing.

10. A method of controlling a power system, wherein the power system comprises: a power unit; a supply pump configured to feed oil in a liquid form, for lubricating the power unit; a supply flow path configured to guide, to the power unit, the oil fed from the supply pump; a return pump configured to return the oil having flowed through the power unit; a return flow path configured to guide, to the return pump, the oil having flowed through the power unit; a circulation flow path configured to guide, to the supply pump, the oil returned by the return pump; a bypass flow path connecting the supply flow path and the circulation flow path; an on-off valve configured to open and close the bypass flow path; a motor configured to drive the supply pump and the return pump; and a controller comprising one or more processors that execute computer-executable instructions stored in a memory, the method comprising: causing, by the one or more processors executing computer-executable instructions, the controller to control the motor to set torque of the motor to predetermined target torque in a state where the on-off valve is opened.

11. The method of controlling the power system according to claim 10, wherein the one or more processors cause the controller to control the motor to set a rotational speed of the supply pump to a target rotational speed in a state where the on-off valve is closed.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIG. 1 is a schematic diagram of a power system according to an embodiment of the present invention;

[0012] FIG. 2 is a block diagram of a controller of the power system;

[0013] FIG. 3 is a flowchart showing a method of controlling a power system according to an embodiment of the present invention;

[0014] FIG. 4 is a schematic view for explaining the flow of oil in the power system;

[0015] FIG. 5 is a schematic view for explaining the flow of oil in the power system;

[0016] FIG. 6 is a schematic diagram of a power system according to a comparative example; and

[0017] FIG. 7 is a timing chart for explaining a method of controlling the power systems.

DETAILED DESCRIPTION OF THE INVENTION

[0018] In the case of starting up the power system in a low-temperature environment (for example, an environment at or below the freezing point), the pressure of oil flowing through the interior of a power unit may become excessively high because the viscosity of the oil is relatively high. In the case of such a low temperature environment, it is necessary to supply oil to the power unit after increasing the temperature of the oil to reduce the viscosity of the oil. However, a heating device to be provided in the power system to raise the temperature of the oil increases the manufacturing cost and weight of the power system. The present disclosure has been made in view of such problems, and can provide a power system and a method of controlling the power system that can suppress an excessive increase in the pressure of oil flowing through the interior of a power unit and can efficiently increase the temperature of the oil while suppressing an increase in manufacturing cost and weight.

[0019] FIG. 1 is a schematic diagram of a power system 10 according to an embodiment of the present invention. The power system 10 is mounted on an aircraft, for example. The aircraft is, for example, an electric vertical take-off and landing (eVTOL) aircraft. The aircraft is not limited to the electric vertical takeoff and landing aircraft. The power system 10 is not limited to the example of being mounted on an aircraft, and may be mounted on a ship, a vehicle, or the like. The power system 10 may be provided in a stationary power generation apparatus.

[0020] As shown in FIG. 1, the power system 10 includes a power unit 12, an oil supply unit 14, and an oil collection unit 16. The power unit 12 includes a rotating electric machine 18 and a gas turbine engine 20. The rotating electric machine 18 can drive, for example, VTOL rotors (not shown) of an electric vertical takeoff and landing aircraft.

[0021] The rotating electric machine 18 includes a rotating electric machine main body 22, bearings 24, a partition wall member 26, and a casing 28. The rotating electric machine main body 22 includes a rotor 30 and a stator 32. The rotor 30 includes a rotation shaft 30a and a magnet portion 30b provided on an outer circumference of the rotation shaft 30a. The rotation shaft 30a is coupled to, for example, a shaft member 20a of the gas turbine engine 20. The magnet portion 30b is, for example, a permanent magnet. The stator 32 is formed in an annular shape. The rotor 30 is inserted into a hole of the stator 32. The stator 32 includes an electromagnetic coil 32a and a stator core 32b. The rotor 30 and the stator 32 are not limited to the above-described configuration.

[0022] For example, at the time of starting the gas turbine engine 20, alternating current is supplied to the electromagnetic coil 32a of the stator 32 to rotate the rotor 30 so that the rotating electric machine 18 functions as a motor 66 for rotating the shaft member 20a of the gas turbine engine 20. Further, the rotating electric machine 18 functions as a generator that generates electric power by rotation of the rotor 30 rotated by a driving force of the gas turbine engine 20. In the rotating electric machine 18, the rotor 30 and the stator 32 generate heat. Specifically, in the rotating electric machine 18, the magnet portion 30b of the rotor 30 and the electromagnetic coil 32a of the stator 32 are particularly likely to become high in temperature.

[0023] The bearings 24 includes a first bearing 24a and a second bearing 24b. The first bearing 24a rotatably supports one end of the rotation shaft 30a. The second bearing 24b rotatably supports the other end of the rotation shaft 30a. Each of the first bearing 24a and the second bearing 24b is, for example, a rolling bearing. Each of the first bearing 24a and the second bearing 24b may be a plain bearing.

[0024] The partition wall member 26 is formed in a tubular shape. The rotor 30 is disposed inside the partition wall member 26, and the stator 32 is disposed outside the partition wall member 26. The partition wall member 26 is made of, for example, a ceramic material. The partition wall member 26 may be fixed to the casing 28. The partition wall member 26 separates a space in which the rotor 30 is disposed from a space in which the stator 32 is disposed in a liquid-tight and air-tight manner. The casing 28 accommodates the rotating electric machine main body 22 and the bearings 24.

[0025] The oil supply unit 14 supplies liquid oil to the rotating electric machine 18 (power unit 12). Examples of the oil include gas turbine oil. The oil cools the heat-generating portions (the rotor 30 and the stator 32) of the rotating electric machine 18 and lubricates the bearings 24. The oil supply unit 14 includes a supply pump 34 and a supply flow path 36. The supply flow path 36 guides oil from the supply pump 34 to the rotating electric machine 18.

[0026] The rotating electric machine 18 is provided with a rotor cooling flow path 38, a stator cooling flow path 40, a lubrication flow path 42, a reservoir 46, a first discharge flow path 48, a second discharge flow path 50, and a third discharge flow path 52.

[0027] The oil guided from the supply flow path 36 flows separately into the rotor cooling flow path 38, the stator cooling flow path 40, and the lubrication flow path 42. That is, the rotor cooling flow path 38, the stator cooling flow path 40, and the lubrication flow path 42 are arranged in parallel. The partition wall member 26 separates the rotor cooling flow path 38 and the stator cooling flow path 40. Therefore, the oil flowing through the rotor cooling flow path 38 and the oil flowing through the stator cooling flow path 40 are not mixed with each other along the way.

[0028] The rotor cooling flow path 38 allows the oil guided from the supply flow path 36 to flow through the rotor 30. The rotor cooling flow path 38 includes a path formed inside the rotor 30. In this case, the rotor 30 can be efficiently cooled by the oil flowing through the interior of the rotor 30. The rotor cooling flow path 38 is opened to the atmosphere. Therefore, the oil flowing through the rotor cooling flow path 38 is mixed with gas (air).

[0029] The stator cooling flow path 40 allows the oil guided from the supply flow path 36 to flow through the stator 32. The stator cooling flow path 40 is formed so as to surround the stator 32. In this case, the oil can be brought into contact with the electromagnetic coil 32a of the stator 32, and thus the stator 32 can be efficiently cooled. The stator cooling flow path 40 is not opened to the atmosphere. Therefore, the oil flowing through the stator cooling flow path 40 is not mixed with gas (air).

[0030] The lubrication flow path 42 includes a first lubrication flow path 42a and a second lubrication flow path 42b. The first lubrication flow path 42a allows the oil guided from the supply flow path 36 to flow to the first bearing 24a. The oil that has flowed through the first lubrication flow path 42a is blown to the first bearing 24a by the pressure applied by the supply pump 34. The oil blown from the first lubrication flow path 42a to the first bearing 24a is mixed with gas (air). The second lubrication flow path 42b supplies the oil guided from the supply flow path 36 to the second bearing 24b. The oil that has flowed through the second lubrication flow path 42b is blown to the second bearing 24b the pressure applied by the supply pump 34. The oil blown from the second lubrication flow path 42b to the second bearing 24b is mixed with gas (air).

[0031] The reservoir 46 is formed, for example, in the bottom of the casing 28. The reservoir 46 includes a first reservoir 46a and a second reservoir 46b. The first reservoir 46a is positioned, for example, below the first bearing 24a (in the direction of gravity with respect to the first bearing 24a). The second reservoir 46b is positioned, for example, below the second bearing 24b (in the direction of gravity with respect to the second bearing 24b). The size, shape, position, and the like of the reservoir 46 can be appropriately set.

[0032] The first discharge flow path 48 guides the oil that has flowed through the first bearing 24a to the first reservoir 46a. The second discharge flow path 50 guides the oil that has flowed through the second bearing 24b to the second reservoir 46b. The third discharge flow path 52 guides the oil that has flowed through the rotor cooling flow path 38 to the second reservoir 46b. The oil that flows through the first discharge flow path 48, the second discharge flow path 50, and the third discharge flow path 52 is mixed with gas (air). That is, the reservoir 46 stores a gas-liquid mixture fluid in which liquid oil and gaseous air are mixed.

[0033] The oil collection unit 16 includes a return flow path 53, a lead-out flow path 54, a return pump 55, a circulation flow path 56, a gas-liquid separator 58, and a tank 60. The return flow path 53 is connected to the first reservoir 46a, the second reservoir 46b, and the return pump 55. The return flow path 53 is also connected to the stator cooling flow path 40 via the lead-out flow path 54. That is, the oil that has flowed through the stator cooling flow path 40 joins the gas-liquid mixture fluid flowing through the return flow path 53 via the lead-out flow path 54.

[0034] The return pump 55 returns the gas-liquid mixture fluid stored in the first reservoir 46a and the second reservoir 46b. The capacity of the return pump 55 is larger than the capacity of the supply pump 34. In other words, the maximum amount of oil discharged per unit time from the return pump 55 is larger than the maximum amount of oil discharged per unit time from the supply pump 34.

[0035] The circulation flow path 56 guides, to the supply pump 34, the oil collected by the return pump 55. The circulation flow path 56 is provided with a gas-liquid separator 58 and a tank 60. The gas-liquid separator 58 separates a gaseous component from the gas-liquid mixture fluid fed from the return pump 55. The liquid oil from which the gaseous component is separated by the gas-liquid separator 58 is stored in the tank 60.

[0036] The power system 10 further includes a bypass flow path 62, a relief valve (on-off valve) 64, one motor 66, and a power transmission mechanism 68. The bypass flow path 62 connects the supply flow path 36 to the return flow path 53. The relief valve 64 opens and closes the bypass flow path 62. The relief valve 64 opens as a valve body (not shown) of the relief valve 64 is pushed by the oil supplied from the supply pump 34 when the pressure of the oil reaches a predetermined pressure upper limit value. In other words, the relief valve 64 closes the bypass flow path 62 as long as the pressure of the oil supplied from the supply pump 34 (the discharge pressure of the supply pump 34) is lower than the pressure upper limit value.

[0037] The motor 66 drives the supply pump 34 and the return pump 55. The power transmission mechanism 68 transmits the rotational driving force of the motor 66 to the supply pump 34 and the return pump 55. In the present embodiment, the power transmission mechanism 68 includes a first mechanism 68a that transmits the rotational driving force of the motor 66 to the return pump 55, and a second mechanism 68b that transmits the rotational driving force that has transmitted from the motor 66 to the return pump 55 further to the supply pump 34. The power transmission mechanism 68 may include, for example, a speed reduction mechanism. The configuration of the power transmission mechanism 68 can be set as appropriate.

[0038] FIG. 2 is a block diagram of a controller 72 of the power system 10. As shown in FIG. 2, the power system 10 further includes a sensor 70 and a controller 72. The sensor 70 detects various kinds of information of the power system 10. The detection signals of the sensor 70 are sequentially transmitted to the controller 72. The sensor 70 includes, for example, a temperature sensor. In this case, the temperature sensor detects, for example, the temperature of the oil flowing through a portion of the supply flow path 36 between the supply pump 34 and the relief valve 64. The sensor 70 may include a pressure sensor that detects the pressure of the oil (the discharge pressure of the supply pump 34), a torque sensor that detects the torque of the motor 66, rotational speed sensors that detect the rotational speeds of the supply pump 34 and the return pump 55, a rotational speed sensor that detects the rotational speed of the gas turbine engine 20, and the like.

[0039] The controller 72 includes a computation unit 74 and a storage unit 76. The computation unit 74 can be constituted by a processor such as a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), or the like. More specifically, the computation unit 74 can be constituted by a processing circuit (processing circuitry).

[0040] The computation unit 74 includes a control unit 78, a motor control unit 80, an information acquisition unit 82, and a determination unit 84. The control unit 78, the motor control unit 80, the information acquisition unit 82, and the determination unit 84 can be realized by the computation unit 74 executing programs stored in the storage unit 76.

[0041] At least a part of the control unit 78, the motor control unit 80, the information acquisition unit 82, and the determination unit 84 may be realized by an integrated circuit such as an application specific integrated circuit (ASIC) or a field-programmable gate array (FPGA). At least a part of the control unit 78, the motor control unit 80, the information acquisition unit 82, and the determination unit 84 may be constituted by an electronic circuit including a discrete device.

[0042] The storage unit 76 may constituted by a volatile memory (not shown), and a nonvolatile memory (not shown). As the volatile memory, there may be cited, for example, a RAM (Random Access Memory). Such a volatile memory is used as a working memory of the processor, and temporarily stores data necessary for performing processing or calculations. As the nonvolatile memory, there may be cited, for example, a ROM (Read Only Memory), a flash memory, or the like. The nonvolatile memory is used as a storage memory, and stores programs, tables, maps, and the like. At least a portion of the storage unit 76 may be provided in the processor, the integrated circuit, or the like, in the manner described above.

[0043] The control unit 78 controls the entirety of the power system 10. The motor control unit 80 controls the motor 66. The information acquisition unit 82 acquires various kinds of information based on the detection signals transmitted from the sensor 70 to the controller 72. Examples of the various kinds of information include the temperature of the oil, the pressure of the oil (the discharge pressure of the supply pump 34), the torque of the motor 66, the rotational speed of the supply pump 34, the rotational speed of the return pump 55, the rotational speed of the gas turbine engine 20, and the like. The determination unit 84 determines whether or not the relief valve 64 is in the closed state based on the information acquired by the information acquisition unit 82.

[0044] Next, a description will be given concerning a method for controlling the power system 10. Specifically, a description will be given concerning a method for controlling the power system 10 in the case of starting up the power system 10 in a low-temperature environment (for example, an environment at or below the freezing point). FIG. 3 is a flowchart showing a method of controlling the power system 10 according to an embodiment of the present invention.

[0045] As shown in FIG. 3, in step S1, the control unit 78 starts up the power system 10. Specifically, the motor control unit 80 controls the motor 66 to drive each of the supply pump 34 and the return pump 55. When the supply pump 34 is driven, the supply pump 34 feeds the oil stored in the tank 60 to the supply flow path 36. In the low temperature environment, the pressure of the oil fed by the supply pump 34 tends to be higher than the pressure upper limit value because the temperature of the oil is low (the viscosity is high). In the case where the pressure of the oil is higher than the pressure upper limit value, the relief valve 64 is opened by the oil fed from the supply pump 34 to the supply flow path 36.

[0046] FIG. 4 is a schematic view for explaining the flow of oil in the power system 10. Specifically, FIG. 4 is an explanatory diagram showing the flow of oil in the case that the relief valve 64 is in the open state. As shown in FIG. 4, in the case of the relief valve 64 being opened, most of the oil is guided to the return flow path 53 via the bypass flow path 62. The oil guided to the return flow path 53 is returned to the supply pump 34 by the return pump 55 via the circulation flow path 56 (the gas-liquid separator 58 and the tank 60). That is, most of the oil discharged from the supply pump 34 circulates through a path that returns to the supply pump 34 via the supply flow path 36, the bypass flow path 62, the return flow path 53, the return pump 55, and the circulation flow path 56. In this case, the oil is heated by the supply pump 34 when flowing through the supply pump 34, and is heated by the return pump 55 when flowing through the return pump 55. That is, the oil is heated by the supply pump 34 and the return pump 55.

[0047] In the state where the relief valve 64 is open, a small amount of oil flows to the rotating electric machine 18. The oil that has flowed to the rotating electric machine 18 is divided into the rotor cooling flow path 38, the stator cooling flow path 40, and the lubrication flow path 42, and then flows through the return flow path 53 to be returned by the return pump 55. Since the amount of oil flowing through the interior of the rotating electric machine 18 is relatively small, the oil causes no excessive force acting on the components of the rotating electric machine 18.

[0048] The control unit 78 also starts up the gas turbine engine 20 to rotate the shaft member 20a of the gas turbine engine 20 at a predetermined rotational speed for idling. In accordance therewith, the rotor 30 and the stator 32 generate heat, and the temperature of the oil flowing through the rotating electric machine 18 can be increased. After the power system 10 is started up, the process proceeds to step S2.

[0049] In step S2, the information acquisition unit 82 acquires a variety of information. Specifically, the information acquisition unit 82 acquires various kinds of information based on the detection signals transmitted from the sensor 70 to the controller 72. The process then proceeds to step S3.

[0050] In step S3, the determination unit 84 determines whether or not the relief valve 64 is in the closed state. Specifically, for example, the determination unit 84 determines that the relief valve 64 is in the closed state in the case where the temperature of the oil is equal to or higher than a predetermined target temperature. The target temperature is set based on the pressure upper limit value of the relief valve 64. The viscosity of the oil increases as the temperature decreases. Therefore, the pressure of the oil supplied from the supply pump 34 increases as the temperature decreases (as the viscosity increases). That is, there is a correlation between the temperature of the oil and the pressure of the oil. In the present embodiment, the target temperature is set to the temperature of the oil at which the relief valve 64 is switched from the open state to the closed state. The temperature of the oil is acquired by the information acquisition unit 82.

[0051] When the determination unit 84 determines that the relief valve 64 is not in the closed state (is in the open state) (NO in step S3), the process proceeds to step S4.

[0052] In step S4, the motor control unit 80 performs constant torque control. Specifically, the motor control unit 80 controls the motor 66 to set the torque of the motor 66 to the predetermined target torque. The process then proceeds to step S5.

[0053] In step S5, the determination unit 84 determines whether or not the control unit 78 has received a signal for stopping the power system 10. The control unit 78 receives a signal for stopping the power system 10, for example, in the case where the user operates a stop switch of the power system 10. In the case where the determination unit 84 determines that the control unit 78 has not received a signal for stopping the power system 10 (NO in step S5), the process returns to step S2.

[0054] In the case where the determination unit 84 determines in step S3 that the relief valve 64 is in the closed state (YES in step S3), the process proceeds to step S6.

[0055] FIG. 5 is a schematic view for explaining the flow of oil in the power system 10. Specifically, FIG. 5 is an explanatory diagram showing the flow of oil in the case that the relief valve 64 is in the closed state. As shown in FIG. 5, in the case of the relief valve 64 being closed, the oil is not guided to the bypass flow path 62. In other words, the entire amount of the oil fed from the supply pump 34 to the supply flow path 36 flows to the rotating electric machine 18. The oil that has flowed to the rotating electric machine 18 flows separately to the rotor cooling flow path 38, the stator cooling flow path 40, and the lubrication flow path 42. The oil flowing through the rotor cooling flow path 38 cools the rotor 30, and is then guided to the second reservoir 46b via the third discharge flow path 52 by the centrifugal force generated by the rotation of the rotor 30 and the influence of gravity. Gas (air) is mixed in the oil flowing through the third discharge flow path 52. That is, a gas-liquid mixture fluid of the oil and air flows through the third discharge flow path 52.

[0056] The oil flowing through the stator cooling flow path 40 cools the stator 32 and is then guided to the return flow path 53 via the lead-out flow path 54.

[0057] The oil flowing through the first lubrication flow path 42a is blown to the first bearing 24a by the pressure applied by the supply pump 34. Thus, the first bearing 24a is lubricated by the oil. The oil that has flowed through the first bearing 24a flows down to the first reservoir 46a via the first discharge flow path 48 due to the influence of gravity. Gas (air) is mixed in the oil flowing through the first discharge flow path 48. That is, a gas-liquid mixture fluid of the oil and air flows through the first discharge flow path 48.

[0058] The oil flowing through the second lubrication flow path 42b is blown to the second bearing 24b by the pressure applied by the supply pump 34. Thus, the second bearing 24b is lubricated by the oil. The oil that has flowed through the second bearing 24b flows down to the second reservoir 46b via the second discharge flow path 50 due to the influence of gravity. Gas (air) is mixed in the oil flowing through the second discharge flow path 50. That is, a gas-liquid mixture fluid of the oil and air flows through the second discharge flow path 50.

[0059] The gas-liquid mixture fluid stored in the first reservoir 46a and the second reservoir 46b is fed to the gas-liquid separator 58 via the return flow path 53 by the return pump 55. The gas-liquid mixture fluid fed to the gas-liquid separator 58 is separated into oil and gas (air) by the gas-liquid separator 58. The oil from which the gaseous component is separated by the gas-liquid separator 58 is guided to the tank 60.

[0060] In step S6, the motor control unit 80 performs constant rotational speed control. Specifically, the motor control unit 80 controls the motor 66 to set the rotational speed of the supply pump 34 to the target rotation speed. The target rotational speed is determined in advance, for example. The target rotational speed may be set based on the required output of the power unit 12. The process then proceeds to step S5.

[0061] In step S5, when the determination unit 84 determines that the control unit 78 has received the signal for stopping the power system 10 (YES in step S5), the process proceeds to step S7. In step S7, the control unit 78 stops the power system 10. Specifically, the motor control unit 80 controls the motor 66 to stop the driving of each of the supply pump 34 and the return pump 55. Thereafter, the process shown in FIG. 3 is completed.

[0062] FIG. 6 is a schematic diagram of a power system 100 according to a comparative example. As shown in FIG. 6, in the power system 100 according to the comparative example, the bypass flow path 62 is connected to a portion of the circulation flow path 56 between the tank 60 and the supply pump 34. The configuration of the power system 100 other than the bypass flow path 62 is the same as the configuration of the power system 10 according to the present embodiment.

[0063] In the power system 100 according to the comparative example, in the case of the relief valve 64 being opened, most of the oil fed from the supply pump 34 to the supply flow path 36 is returned to the supply pump 34 via the bypass flow path 62 and the circulation flow path 56. In this case, the oil is heated solely by the supply pump 34.

[0064] FIG. 7 is a timing chart for explaining methods of controlling the power systems 10, 100. In FIG. 7, the broken line illustrates a timing chart of the power system 100 according to the comparative example, and the solid line illustrates a timing chart of the power system 10 according to the present embodiment.

[0065] As shown in FIG. 7, in the comparative example, when the power system 100 is started up at time to in the low temperature environment, most of the oil fed from the supply pump 34 to the supply flow path 36 is returned to the supply pump 34 via the bypass flow path 62 and the circulation flow path 56 because the relief valve 64 is opened. That is, the oil is heated by the supply pump 34.

[0066] The motor control unit 80 controls the motor 66 to set the rotational speed of the supply pump 34 to a predetermined rotational speed n1. Therefore, the viscosity of the oil decreases with the increase in the temperature of the oil, and the torque of the motor 66 decreases. That is, in the power system 100 according to the comparative example, even when the viscosity of the oil decreases, the rotational speed of the supply pump 34 is maintained at the rotational speed n1. In other words, in the comparative example, even if the viscosity of the oil decreases, the thermal energy supplied from the supply pump 34 to the oil does not change.

[0067] In the comparative example, at time to, the control unit 78 controls the power unit 12 to set the rotational speed of the gas turbine engine 20 to a predetermined rotational speed na (rotational speed for idling). Thus, the rotor 30 and the stator 32 of the rotating electric machine 18 generate heat, and thus the temperature of the small amount of oil guided from the supply flow path 36 to the rotating electric machine 18 is increased by the rotor 30 and the stator 32 of the rotating electric machine 18. The small amount of the oil thus heated is returned to the supply pump 34 via the return flow path 53, the return pump 55, and the circulation flow path 56.

[0068] In the comparative example, the temperature of the oil reaches the temperature T1 (target temperature) at time t2. At time t2, the discharge pressure of the supply pump 34 (pressure of the oil) becomes lower than the upper limit oil pressure P1, and the relief valve 64 is closed. That is, the bypass flow path 62 is closed by the relief valve 64.

[0069] At time t2, the control unit 78 controls the power unit 12 to set the rotational speed of the gas turbine engine 20 to the rotational speed nb (target rotational speed of the engine). Thus, the bearings 24 of the rotating electric machine 18 can be lubricated with a sufficient amount of oil (at stable flow rate), and therefore the output of the power unit 12 can be increased.

[0070] In the comparative example, when the relief valve 64 is closed, the motor control unit 80 controls the motor 66 to set the rotational speed of the supply pump 34 to the rotational speed n2 (target rotational speed). Then, at time t4, the temperature of the oil rises to a temperature T2, the torque of the motor 66 decreases to a torque N2, and the discharge pressure of the supply pump 34 (pressure of the oil) decreases to the pressure P2.

[0071] On the other hand, in the power system 10 according to the present embodiment, when the power system 10 is started up at time to in the low temperature environment, most of the oil fed from the supply pump 34 to the supply flow path 36 is returned to the supply pump 34 via the bypass flow path 62, the return flow path 53, the return pump 55, and the circulation flow path 56 because the relief valve 64 is in the open state. That is, the oil is heated by the supply pump 34 and the return pump 55.

[0072] The motor control unit 80 controls the motor 66 to adjust the torque of the motor 66 to a predetermined torque N1 (target torque). Therefore, as the viscosity of the oil decreases, the rotational speed of each of the supply pump 34 and the return pump 55 increases. That is, in the present embodiment, as the viscosity of the oil decreases, the thermal energy supplied to the oil from each of the supply pump 34 and the return pump 55 can be increased.

[0073] In the present embodiment, as in the comparative example, at time to, the control unit 78 controls the power unit 12 to set the rotational speed of the gas turbine engine 20 to a predetermined rotational speed na (rotational speed for idling). Thus, the rotor 30 and the stator 32 of the rotating electric machine 18 generate heat, and thus the temperature of the small amount of oil guided from the supply flow path 36 to the rotating electric machine 18 is increased by the rotor 30 and the stator 32 of the rotating electric machine 18. The small amount of the oil thus heated is returned to the supply pump 34 via the return flow path 53, the return pump 55, and the circulation flow path 56.

[0074] In the present embodiment, the temperature of the oil reaches the temperature T1 (target temperature) at time t1 earlier than time t2. At time t1, the discharge pressure of the supply pump 34 (pressure of the oil) becomes lower than the upper limit oil pressure P1, and the relief valve 64 is closed. That is, the bypass flow path 62 is closed by the relief valve 64.

[0075] At time t1, the control unit 78 controls the power unit 12 to set the rotational speed of the gas turbine engine 20 to the rotational speed nb (target rotational speed of the engine). Thus, the bearings 24 of the rotating electric machine 18 can be lubricated with a sufficient amount of oil (at stable flow rate), and therefore the output of the power unit 12 can be increased.

[0076] In the present embodiment, when the relief valve 64 is closed, the motor control unit 80 controls the motor 66 to set the rotational speed of the supply pump 34 to the rotational speed n2 (target rotational speed). Then, at time t3 earlier than time t4, the temperature of the oil rises to the temperature T2, the torque of the motor 66 decreases to a torque N2, and the discharge pressure of the supply pump 34 (pressure of the oil) decreases to the pressure P2.

[0077] According to the present embodiment, in the case where the power system 10 is started in a low temperature environment, the relief valve 64 can be opened, and thus it is possible to suppress oil having high viscosity from being guided to the rotating electric machine 18. This can suppress an excessive increase in the pressure of the oil flowing through the interior of the rotating electric machine 18. In addition, in the case of the relief valve 64 being opened, most of the oil fed from the supply pump 34 to the supply flow path 36 can be returned to the supply pump 34 via the bypass flow path 62, the return flow path 53, the return pump 55 and the circulation flow path 56. Thus, the temperature of the oil can be increased by the supply pump 34 and the return pump 55, and therefore, a heating device such as a heater does not have to be added. Therefore, the temperature of the oil can be efficiently raised while suppressing an increase in the manufacturing cost and weight of the power system 10. As such, a better power system 10 and a better method of controlling the power system 10 can be provided.

[0078] The present embodiment is not limited to the above-described configuration. The determination unit 84 may determine that the relief valve 64 is in the closed state when the discharge pressure of the supply pump 34 (pressure of the oil) becomes lower than the pressure upper limit value. The determination unit 84 may determine that the relief valve 64 is in the closed state when the rotation speed of the supply pump 34 is equal to or higher than the target rotation speed.

[0079] The power system 10 is not limited to an example proved with the relief valve 64 that closes when the pressure of the oil becomes lower than the pressure upper limit value, and may be provided with a solenoid valve (on-off valve) instead of the relief valve 64. In this case, the controller 72 controls the solenoid valve to close to block the bypass flow path 62 when the pressure of the oil reaches the pressure upper limit value.

[0080] The power system 10 may drive the supply pump 34 and the return pump 55 by the rotational driving force of the rotor 30 of the rotating electric machine 18. In this case, the motor 66 and the motor control unit 80 of the power system 10 are omitted. The power system 10 may include a motor for driving the supply pump 34 and a motor for driving the return pump separately.

[0081] The following supplementary notes are further disclosed in relation to the above embodiment.

Supplementary Note 1

[0082] The power system (10) of the present disclosure includes: the power unit (12), the supply pump (34) configured to feed liquid oil for lubricating the power unit; the supply flow path (36) configured to guide, to the power unit, the oil fed from the supply pump; the return pump (55) configured to return the oil having flowed through the power unit; the return flow path (53) configured to guide, to the return pump, the oil having flowed through the power unit; the circulation flow path (56) configured to guide, to the supply pump, the oil returned by the return pump; the bypass flow path (62) connecting the supply flow path and the return flow path; and the on-off valve (64) configured to open and close the bypass flow path.

[0083] According to such a configuration, in the case where the power system is started up in a low temperature environment, the on-off valve can be opened, and thus it is possible to suppress oil having high viscosity from being guided to the power unit. This can suppress an excessive increase in the pressure of the oil flowing through the interior of the power unit. In addition, in the case of the on-off valve being opened, most of the oil fed from the supply pump to the supply flow path can be returned to the supply pump via the bypass flow path, the return flow path, the return pump and the circulation flow path. Thus, the temperature of the oil can be increased by the supply pump and the return pump, and therefore, a heating device such as a heater need not be added. Therefore, the temperature of the oil can be efficiently raised while suppressing an increase in the manufacturing cost and weight of the power system. Thus, a better power system can be provided.

Supplementary Note 2

[0084] In the power system according to Supplementary Note 1, the capacity of the return pump may be larger than the capacity of the supply pump.

[0085] According to such a configuration, the oil can be efficiently heated by the supply pump and the return pump.

Supplementary Note 3

[0086] In the power system according to Supplementary Note 2, the oil led out from the power unit may be mixed with gas, and the circulation flow path may be provided with the gas-liquid separator (58) configured to separate the gas from the oil.

[0087] According to such a configuration, a mixture of oil and gas can be smoothly guided to the gas-liquid separator by the return pump having the larger capacity than the capacity of the supply pump. In addition, the oil from which the gaseous component has been removed by the gas-liquid separator can be returned to the supply pump.

Supplementary Note 4

[0088] In the power system according to any one of Supplementary Notes 1 to 3, the on-off valve may be the relief valve that is pushed by the oil to open when the pressure of the oil supplied from the supply pump reaches the predetermined pressure upper limit value.

[0089] According to such a simple configuration, it is possible to suppress the pressure of the oil flowing through the interior of the power unit from becoming excessively large.

Supplementary Note 5

[0090] The power system according to any one of Supplementary Notes 1 to 4 may further include the motor (66) for driving the supply pump and the return pump.

[0091] According to such a configuration, the degree of freedom in layout of the supply pump and the return pump can be increased as compared with the case where the supply pump and the return pump are driven by the power generated by the power unit.

Supplementary Note 6

[0092] In the power system according to Supplementary Note 5, the motor may be a sole motor, and the power system may further include the power transmission mechanism (68) that transmits a rotational driving force of the motor to the supply pump and the return pump.

[0093] According to such a configuration, the power system can be configured to be compact as compared with the case where a motor for driving the supply pump and a motor for driving the return pump are separately provided.

Supplementary Note 7

[0094] The power system according to Supplementary Note 5 or 6 may further include the motor control unit (80) configured to control the motor, and in a state where the on-off valve is opened, the motor control unit may control the motor to set torque of the motor to predetermined target torque.

[0095] According to such a configuration, as the viscosity of the oil decreases with an increase in the temperature of the oil, the thermal energy transferred to the oil from each of the supply pump and the return pump can be increased. Thus, the time required for raising the temperature of the oil can be shortened.

Supplementary Note 8

[0096] In the power system according to Supplementary Note 7, in a state where the on-off valve is closed, the motor control unit may control the motor to set the rotational speed of the supply pump to a target rotational speed.

[0097] According to such a configuration, it is possible to supply oil to the power unit at a stable flow rate in the state where the on-off valve is closed.

Supplementary Note 9

[0098] In the power system according to any one of Supplementary Notes 1 to 8, the power unit may include the bearing (24) rotatably supporting the rotor (30), and the lubrication flow path (42) allowing the oil to flow through the bearing.

[0099] According to such a configuration, the bearing can be lubricated by the oil.

Supplementary Note 10

[0100] The method of the present disclosure of controlling a power system, wherein the power system comprises: the power unit; the supply pump configured to supply liquid oil for lubricating the power unit; the supply flow path configured to guide, to the power unit, the oil supplied from the supply pump; the return pump configured to return the oil having flowed through the power unit; the return flow path configured to guide, to the return pump, the oil having flowed through the power unit; the circulation flow path configured to guide, to the supply pump, the oil returned by the return pump; the bypass flow path connecting the supply flow path and the circulation flow path; the on-off valve configured to open and close the bypass flow path; the motor configured to drive the supply pump and the return pump; and the motor controller configured to control the motor, the method comprising controlling the motor by the motor controller to set torque of the motor to predetermined target torque in a state where the on-off valve is opened.

[0101] According to such a method, a better method for controlling a power system can be provided.

Supplementary Note 11

[0102] In the method of controlling the power system according to Supplementary Note 10, in the state where the on-off valve is closed, the motor control unit may control the motor to set the rotational speed of the supply pump to a target rotational speed.

[0103] Although the present disclosure has been described in detail, the present disclosure is not limited to the above-described embodiments. These embodiments can be subjected to various addition, replacement, change, partially deletion, and the like without departing from the gist of the present disclosure or without departing from the gist of the present disclosure derived from the contents described in the claims and equivalents thereof. These embodiments may also be implemented in combination. For example, in the above-described embodiments, the order of operations and the order of processes are shown as examples, and the present invention is not limited thereto. The same applies to a case where numerical values or mathematical expressions are used in the description of the above-described embodiments.