Cooling control method and cooling control device

Abstract

Provided is a cooling control method for cooling an ePT (10) having an inverter (11), an electric motor (12), and a reducer (13) by using an ePT cooling circuit (20), the cooling control method comprising implementing: an outside air temperature acquisition step for acquiring an outside air temperature; a heat quantity comparison step for comparing heat removal amounts, due to cooling water, of the inverter (11) and the reducer (13); and a circulation control step for circulating the cooling water in the order of the inverter (11), the electric motor (12), and the reducer (13) when the outside air temperature is equal to or greater than a first threshold value, and when the outer air temperature is less than the first threshold value and the heat removal amount of the inverter (11) is less than the heat removal amount of the reducer (13), and circulating the cooling water in the order of the reducer (13), the electric motor (12), and the inverter (11) when the outside air temperature is less than the first threshold value and the heat removal amount of the inverter (11) is greater than the heat removal amount of the reducer (13).

Description

Cooling control method and cooling control device

[0001] The present invention relates to a cooling control method and a cooling control device for an electric powertrain.

[0002] An electric powertrain (EPT) mounted on an electric vehicle includes an inverter, an electric motor, and a reducer (speed reducer), and is provided with a cooling system that adjusts the temperatures of the inverter, the electric motor, and the reducer. For example, a cooling system described in Patent Document 1 includes a motor cooling circuit that cools the electric motor, and this motor cooling circuit is provided separately from a battery cooling circuit that cools the battery and an electrical component cooling circuit that cools the electrical components. This cooling system also includes an air conditioning refrigerant circuit that cools the air for air conditioning, which includes a compressor that compresses a refrigerant, an air conditioning evaporator provided upstream of the compressor, and an air-cooled condenser that condenses the refrigerant flowing from the compressor using outside air.

[0003] Japanese Patent Application Laid-Open No. 2020-185891

[0004] However, in the cooling system of Patent Document 1, the air conditioning refrigerant circuit uses an air-cooled condenser, so it cannot exchange heat with the motor cooling circuit or the battery cooling circuit. This prevents the air conditioning system from utilizing the waste heat from the motor cooling circuit or the battery cooling circuit, resulting in a problem of poor electricity consumption (electricity cost) in the electric vehicle. Meanwhile, waste heat from the electric powertrain is sometimes recovered by the heat pump condenser and used to operate the air conditioning system for heating. However, in electric powertrains, inverter temperature management is important, and the coolant is typically circulated through the inverter, electric motor, and reducer in that order. In this case, when the inverter load increases, such as during low outside temperatures or low vehicle speeds, the amount of heat dissipated from the inverter to the coolant in the cooling circuit (the amount of heat released from the inverter to the coolant) becomes excessively large, resulting in a decrease in the amount of heat dissipated from the electric motor and the reducer, and a problem of reduced waste heat recovery efficiency.

[0005] An object of the present invention is to provide a cooling control method and a cooling control device that can improve the efficiency of recovering exhaust heat from an electric powertrain.

[0006] The present invention provides a cooling control method for cooling an electric powertrain having an inverter, an electric motor, and a reducer using a cooling circuit, the method comprising: an outside temperature acquisition step for acquiring an outside temperature; a heat quantity comparison step for comparing the heat quantity of the inverter and the heat quantity of the reducer through the cooling water; and a circulation control step for circulating the cooling water through the inverter, the electric motor, and the reducer in that order when the outside temperature is equal to or higher than a first threshold value and when the outside temperature is less than the first threshold value and the heat quantity of the inverter is less than the heat quantity of the reducer; and for circulating the cooling water through the reducer, the electric motor, and the inverter in that order when the outside temperature is less than the first threshold value and the heat quantity of the inverter is greater than the heat quantity of the reducer. This improves the exhaust heat recovery rate when cooling the electric powertrain.

[0007] 1 is a block diagram showing the general configuration of an electric vehicle according to an embodiment of the present invention. A schematic diagram showing a forward flow of coolant and an example configuration of an ePT cooling circuit. A schematic diagram showing a reverse flow of coolant and an example configuration of an ePT cooling circuit. A schematic diagram of a temperature control system including an ePT cooling circuit, a heat pump, and an air conditioning system. A flowchart showing a cooling control method according to this embodiment. A timing chart showing eWP rotation control and switching control of a switching valve. A diagram showing an example of vehicle speed, outside air temperature, energy loss of the inverter and electric motor, temperatures of the inverter and electric motor, heat release amount of the inverter and electric motor to the outside air, and heat release amount of the inverter and electric motor to the coolant. A diagram showing an example of the vehicle speed of an electric vehicle, the temperature of the coolant flowing into the evaporator, and power consumption in the air conditioning system for this embodiment and a comparative example.

[0008] An embodiment of the present invention will now be described. Fig. 1 is a schematic diagram showing the general configuration of an electric vehicle equipped with a cooling control device of this embodiment. As shown in Fig. 1, the electric vehicle 1 includes an electric power train (ePT 10), an ePT cooling circuit 20, a heat pump 30, an air conditioning system 40, a sensor group 50, and a controller 60.

[0009] The ePT 10 is a device that generates driving force for propelling the electric vehicle 1 and includes an inverter 11, an electric motor 12, and a reducer 13. The inverter 11 converts direct current (DC) input from a battery (not shown) into alternating current (AC) and outputs the AC current to the electric motor 12. It also converts AC current input from the electric motor 12 into DC and inputs the DC current to the battery. The inverter 11 controls the current output to the electric motor 12 based on a speed command input from a controller 60. The electric motor 12 is driven by the AC current input from the inverter 11, and the rotational driving force generated by the driving of the electric motor 12 is transmitted to the drive wheels 14 via the reducer 13. The reducer 13 is a speed reducer that reduces the rotational driving force from the electric motor 12 at a predetermined gear ratio based on the control of the controller 60 and transmits the reduced rotational driving force to the drive wheels 14.

[0010] The ePT cooling circuit 20 is a cooling circuit that cools the ePT 10. Figures 2 and 3 are diagrams showing an example configuration of the ePT cooling circuit 20. Figure 2 shows the flow of cooling water when the cooling water flows through the inverter 11, electric motor 12, and reducer 13 in this order (when the cooling water flows in the forward flow direction). Figure 3 shows the flow of cooling water when the cooling water flows through the reducer 13, electric motor 12, and inverter 11 in this order (when the cooling water flows in the reverse flow direction). As shown in Figures 2 and 3 , the ePT cooling circuit 20 includes a first circulation path 21 that passes through the inverter 11, electric motor 12, and reducer 13, and a second circulation path 24 that includes a pump (eWP 22: Electric Water Pump) and an evaporator 23, which are connected via a switching valve 25.

[0011] The first circulation path 21 is provided with an inverter heat exchanger 211 in contact with the inverter 11, a motor heat exchanger 212 in contact with the electric motor 12, and a reducer heat exchanger 213 in contact with the reducer 13. The inverter heat exchanger 211 recovers heat from the inverter 11 into the coolant, the motor heat exchanger 212 recovers heat from the electric motor 12 into the coolant, and the reducer heat exchanger 213 recovers heat from the reducer 13 into the coolant.

[0012] The eWP 22 is driven at a rotation speed based on a pump rotation command input from the controller 60, and causes the coolant to flow in one direction along the second circulation path 24. The switching valve 25 is switched between a first position and a second position based on a switching command input from the controller 60, thereby switching the circulation direction of the coolant in the first circulation path 21. When the switching valve 25 is switched to the first position, as shown in FIG. 2, the coolant flows through the inverter 11, the electric motor 12, and the reducer 13 in this order in the first circulation path 21. This circulation direction of the coolant is referred to as the forward flow direction. On the other hand, when the switching valve 25 is switched to the second position, as shown in FIG. 3, the coolant flows through the reducer 13, the electric motor 12, and the inverter 11 in this order in the first circulation path 21. This circulation direction of the coolant is referred to as the reverse flow direction.

[0013] The coolant flowing through the ePT cooling circuit 20 will be described in more detail using examples shown in FIGS. 2 and 3 . The coolant discharged from the eWP 22 flows through the evaporator 23 and the switching valve 25. As described above, the switching valve 25 connects the first circuit 21 and the second circuit 24. When the switching valve 25 is in the first position, as shown in FIG. 2 , the coolant flowing into the switching valve 25 flows in the first circuit 21 toward the inverter 11. This allows the coolant to flow forward through the first circuit 21. Furthermore, the coolant circulating through the first circuit 21 and returning to the switching valve 25 from the reducer 13 flows from the switching valve 25 back to the eWP 22 in the second circuit 24. On the other hand, when the switching valve 25 is in the second position, as shown in FIG. 3 , the coolant flowing into the switching valve 25 flows in the first circuit 21 toward the reducer 13. This allows the coolant to flow backward through the first circuit 21. Furthermore, the cooling water that has circulated through the first circulation path 21 and returned from the inverter 11 to the switching valve 25 flows from the switching valve 25 back to the eWP 22 in the second circulation path 24. In this embodiment, whether the cooling water flows in the forward flow direction or the reverse flow direction, the cooling water flows in the second circulation path 24 in the direction from the switching valve 25 back to the eWP 22, thereby causing the cooling water containing the exhaust heat recovered by the ePT 10 to flow to the evaporator 23. The evaporator 23 (chiller) corresponds to the heat exchanger of the present disclosure, and cools the cooling water by dissipating heat from the cooling water to the refrigerant of the heat pump 30.

[0014] In this embodiment, the inverter 11 is provided with a first temperature sensor 111 that measures the temperature of the inverter 11. The reducer 13 is provided with a second temperature sensor 131 that measures the temperature of the reducer 13. An additional temperature sensor may be provided that measures the temperature of the electric motor 12. A water temperature sensor 26 that detects the temperature of the coolant in the ePT cooling circuit 20 is provided downstream of the evaporator 23, between the evaporator 23 and the switching valve 25. In other words, the water temperature sensor 26 measures the temperature of the coolant before it enters the first circulation path 21 that cools the ePT 10.

[0015] FIG. 4 is a schematic diagram of a temperature control system including an ePT cooling circuit 20, a heat pump 30, and an air conditioning system 40. The heat pump 30 is connected to the ePT cooling circuit 20 via an evaporator 23. The heat pump 30 includes an expansion valve 31, a compressor 32, and a condenser 33. The expansion valve 31 expands the refrigerant flowing through the heat pump 30 to a low temperature and low pressure. The refrigerant cooled by the expansion valve 31 exchanges heat with the ePT cooling circuit 20 in the evaporator 23 and is warmed by the exhaust heat of the ePT 10. The compressor 32 compresses the refrigerant transferred from the evaporator 23 and sends it to the condenser 33. The condenser 33 is an air conditioning condenser that, for example, liquefies refrigerant gas to release the heat of the refrigerant.

[0016] The air conditioning system 40 adjusts the temperature inside the vehicle and takes in the heat released by the condenser 33 to use as heat for heating. The air conditioning system 40 may also be equipped with a separate PCT heater. In this case, when sufficient heat is not transferred from the evaporator 23 to the heat pump, the heat from the PCT heater can be used to warm the air.

[0017] The sensor group 50 is various sensors mounted on the vehicle. In this embodiment, the sensor group 50 includes an outside air temperature detection sensor 51 that detects the outside air temperature, a first temperature sensor 111 that measures the temperature of the inverter 11, a second temperature sensor 131 that measures the temperature of the reducer 13, and a water temperature sensor 26 that measures the temperature of the coolant in the ePT cooling circuit 20. Note that other various sensors may also be mounted, such as an accelerator opening sensor that detects the accelerator opening, an acceleration sensor that detects acceleration, a room temperature sensor that detects the temperature inside the vehicle, and an object detection sensor that detects objects around the electric vehicle 1.

[0018] The controller 60 is a computer that controls various operations of the electric vehicle 1, such as driving control of the electric vehicle 1, cooling control of the ePT cooling circuit 20, and air conditioning control of the air conditioning system 40. Note that, although an example in which one controller 60 is provided in the electric vehicle 1 is shown here, a drive control controller for driving control, a cooling control controller for the ePT cooling circuit 20, etc. may also be provided as separate units.

[0019] The controller 60 includes a storage unit 61, such as a memory, that stores various types of information, and one or more processors 62. By reading and executing programs stored in the storage unit 61, the processor 62 functions as an outside air temperature acquisition unit 621, a heat quantity comparison unit 622, a circulation control unit 623, an air conditioning control unit 624, and the like, as shown in FIG. 1 . The circulation control unit 623 also has the functions of a switching control unit 623A and a pump control unit 623B. Note that, in this disclosure, the functions of the processor 62 related to the cooling control device of the ePT 10 will be described, and a description of the functions related to other control of the electric vehicle 1 will be omitted. However, the processor 62 may also have various functions related to various controls of the electric vehicle 1, such as driving and braking.

[0020] The outside air temperature acquisition unit 621 acquires the outside air temperature. Specifically, the outside air temperature detection sensor 51 measures the outside air temperature, and a measurement signal corresponding to the measurement result is input to the controller 60. The outside air temperature acquisition unit 621 acquires the outside air temperature based on the measurement signal.

[0021] The heat quantity comparison unit 622 compares the amount of heat dissipated from the inverter 11 to the coolant in the ePT cooling circuit 20 (the amount of heat removed from the inverter 11 to the coolant) with the amount of heat dissipated from the reducer 13 to the coolant in the ePT cooling circuit 20 (the amount of heat removed from the reducer 13 to the coolant), and determines whether the amount of heat removed from the inverter 11 is greater than the amount of heat removed from the reducer 13. The amount of heat removed from the inverter 11 is calculated from the temperature of the inverter 11 measured by the first temperature sensor 111, the coolant temperature measured by the coolant temperature sensor 26, and the thermal resistance from the inverter 11 to the inverter heat exchanger 211 of the first circulation path 21. The coolant temperature is measured by the coolant temperature sensor 26, which is located between the evaporator 23 and the switching valve 25. The coolant temperature here refers to the temperature of the coolant before it enters the first circulation path 21 that cools the ePT 10 (before it cools the ePT 10). The thermal resistance from the inverter 11 to the inverter heat exchanger 211 is determined by the material of each component between the inverter 11 and the inverter heat exchanger 211 and the contact area between the inverter 11 and the inverter heat exchanger 211 of the first circulation path 21. Ｉ (K), the temperature of the cooling water is T Ｗ(K), the contact area of ​​the inverter heat exchanger 211 with the inverter 11 is S Ｉ (m ２ ), the heat transfer coefficient from the inverter 11 to the inverter heat exchanger 211 is K Ｉ (W / (m ２ When K) is used, the amount of heat dissipated from the inverter 11 to the cooling water is X Ｉ (W) is expressed by the following formula: X Ｉ = S Ｉ ×K Ｉ (T Ｉ -T Ｗ ) … (1)

[0022] Similarly, the amount of heat dissipation of the reducer 13 is calculated from the temperature of the reducer 13 measured by the second temperature sensor 131, the temperature of the cooling water measured by the water temperature sensor 26, and the thermal resistance from the reducer 13 to the reducer heat exchanger 213 of the first circulation path 21. The thermal resistance from the reducer 13 to the reducer heat exchanger 213 is determined by the material of each component intervening between the reducer 13 and the reducer heat exchanger 213, and the contact area between the reducer 13 and the reducer heat exchanger 213 of the first circulation path 21. The temperature of the reducer 13 is calculated as T Ｒ (K), the temperature of the cooling water is T Ｗ (K), the contact area of ​​the reducer heat exchanger 213 with the reducer 13 is S Ｒ (m ２ ), the heat transfer coefficient from the reducer 13 to the reducer heat exchange section 213 is K Ｒ (W / (m ２ ・K)), the amount of heat transferred from the reducer 13 to the cooling water is X Ｒ (W) is expressed by the following formula: X Ｒ = S Ｒ ×K Ｒ (T Ｒ -T Ｗ ) … (2)

[0023] Therefore, the heat quantity comparison unit 622 determines whether the heat quantity of the inverter 11 is greater than the heat quantity of the reducer 13 by determining whether the following formula (3) is satisfied: T Ｉ -T Ｗ >K (T Ｒ -T Ｗ) (3) In the above formula (3), the constant K is K=(S Ｒ ×K Ｒ ) / (S Ｉ ×K Ｉ ) and the contact area S of the inverter heat exchanger 211 with the inverter 11 is previously determined. Ｉ (m ２ ), the heat transfer coefficient K from the inverter 11 to the inverter heat exchanger 211 Ｉ (W / (m ２ K), the contact area S of the reducer heat exchange portion 213 with the reducer 13 Ｒ (m ２ ), the heat transfer coefficient K from the reducer 13 to the reducer heat exchange section 213 Ｒ (W / (m ２ .K)) and store it in the storage unit 61.

[0024] The circulation control unit 623 controls the circulation direction of the ePT cooling circuit 20 according to the outside air temperature acquired by the outside air temperature acquisition unit 621 and the determination result of the heat quantity comparison unit 622. That is, when the outside air temperature is equal to or higher than a first threshold, the circulation control unit 623 sets the circulation direction of the coolant in the ePT cooling circuit 20 to the forward flow direction. Furthermore, even if the outside air temperature is less than the first threshold, the circulation control unit 623 sets the circulation direction of the coolant in the ePT cooling circuit 20 to the forward flow direction if the heat quantity comparison unit 622 determines that the condition of equation (3) is not satisfied. On the other hand, when the outside air temperature is less than the first threshold and the heat quantity comparison unit 622 determines that the condition of equation (3) is satisfied, the circulation control unit 623 sets the circulation direction of the coolant in the ePT cooling circuit 20 to the reverse flow direction.

[0025] As described above, the circulation control unit 623 also functions as the switching control unit 623A and the pump control unit 623B. The switching control unit 623A outputs a switching command to the switching valve 25, switching the switching valve 25 between the first position and the second position. The pump control unit 623B outputs a pump rotation command, including a rotation speed, to the eWP 22, driving the eWP 22 and circulating the cooling water in the ePT cooling circuit 20. When the switching control unit 623A switches the cooling water circulation direction, the pump control unit 623B temporarily stops the flow of cooling water, and the switching control unit 623A switches the switching valve 25 during a period when the cooling water flow rate is zero. In other words, if the circulation direction of the cooling water flowing in one direction through the first circulation path 21 is suddenly changed, the cooling water flowing in one direction due to inertia and the cooling water flowing in the opposite direction by the eWP 22 collide. This causes a sudden increase in water pressure or a sudden decrease in some water pressure, resulting in impact noise and vibration (water hammer, water column separation). In response to this, by switching the switching valve 25 while the flow of cooling water is stopped, the occurrence of water hammer and water column separation can be suppressed.

[0026] The air conditioning control unit 624 adjusts the temperature inside the electric vehicle 1. In this embodiment, when the temperature of the coolant entering the evaporator 23 is equal to or higher than a predetermined second threshold, the air conditioning control unit 624 takes the exhaust heat of the ePT 10, which has been transferred from the ePT cooling circuit 20 to the heat pump 30 via the evaporator 23, into the air conditioning system 40 from the condenser 33. If a PCT heater is separately provided as the air conditioning system 40, the air conditioning control unit 624 may warm up the air using the PCT heater if the temperature of the coolant flowing into the evaporator 23 is below the second threshold, and may drive the heat pump compressor 32 to warm up the air using heat from the ePT cooling circuit 20 when the temperature of the coolant entering the evaporator 23 is equal to or higher than the second threshold.

[0027] [Cooling Control Method] Next, a cooling control method for the ePT 10 in the electric vehicle 1 of this embodiment as described above will be described. Fig. 5 is a flowchart showing the cooling control method of this embodiment. In this embodiment, first, the outside air temperature acquisition unit 621 acquires the outside air temperature measured by the outside air temperature detection sensor 51 (step S1: outside air temperature acquisition step), and determines whether the outside air temperature is less than a predetermined first threshold value (step S2).

[0028] If step S2 returns NO, i.e., if the outside air temperature is equal to or higher than the first threshold, the circulation control unit 623 circulates the cooling water in the forward flow direction in the ePT cooling circuit 20 (step S3: circulation control step). That is, the switching control unit 623A sets the switching valve 25 to the first position, and the pump control unit 623B rotates the eWP 22 at a predetermined rotation speed. As a result, the cooling water circulates through the inverter 11, electric motor 12, and reducer 13 in that order.

[0029] On the other hand, if the determination in step S2 is YES, the heat quantity comparison unit 622 calculates the heat quantity X Ｉ The amount of heat transferred from the reducer 13 to the cooling water is X Ｒ It is determined whether the calculated value is greater than the calculated value, i.e., whether the above-described formula (3) is satisfied (step S4: heat quantity comparison step). If the determination in step S4 is NO, the same process as in step S3 is performed, and the cooling water is circulated in the forward flow direction in the ePT cooling circuit 20.

[0030] On the other hand, if the determination in step S4 is YES, the circulation control unit 623 circulates the cooling water in the reverse direction in the ePT cooling circuit 20 (step S5: circulation control step). That is, the switching control unit 623A sets the switching valve 25 to the second position, and the pump control unit 623B rotates the eWP 22 at a predetermined rotation speed. As a result, the cooling water circulates through the reducer 13, the electric motor 12, and the inverter 11 in that order.

[0031] Further, the heat quantity comparison unit 622 calculates the heat quantity X radiated from the inverter 11 to the cooling water while the electric vehicle 1 is running. Ｉ and the amount of heat dissipated from the reducer 13 to the cooling water X ＲThat is, after the circulation direction of the coolant in the ePT cooling circuit 20 is controlled to the forward flow direction in step S3, the heat quantity comparison unit 622 monitors the amount of heat dissipated from the inverter 11 to the coolant X Ｉ and the amount of heat dissipated from the reducer 13 to the cooling water X Ｒ is monitored to determine whether or not the formula (3) is satisfied and the outside air temperature is less than the first threshold value (step S6: heat quantity comparison step).

[0032] If the determination in step S6 is YES, the circulation control unit 623 switches the circulation direction of the cooling water from the forward flow direction to the reverse flow direction. Figure 6 is a timing chart showing the rotation control of the eWP 22 and the switching control of the switching valve 25. In the rotation control of the eWP 22 (upper graph), the solid line indicates the actual rotation speed of the eWP 22, and the dashed line indicates the rotation speed input to the eWP 22 as a pump rotation command. Furthermore, in the switching control of the switching valve 25 (lower graph), the solid line indicates the actual switching operation of the switching valve 25, and the dashed line indicates the switching command input to the switching valve 25.

[0033] When switching the cooling water circulation direction, the pump control unit 623B first outputs a pump rotation command to the eWP 22 to gradually decrease the rotation speed by a predetermined first change amount α (step S7). Here, as shown in FIG. 6 , the actual rotation speed of the eWP 22 lags behind the pump rotation command. For example, in the example of FIG. 6 , the pump rotation command to gradually decrease the rotation speed by the first change amount α is output at timing T0, and the rotation speed command value of the pump rotation command becomes 0 (rpm) at timing T1. However, due to the inertia of the cooling water and the eWP 22, the actual rotation speed of the eWP 22 does not become 0 (rpm) at timing T1. Instead, the actual rotation speed of the eWP 22 becomes 0 (rpm) at timing T2, a predetermined time after T1. The time from T1 to T2 (first time ΔT1) can be determined by measuring in advance the time until the actual rotation speed of the eWP 22 becomes 0 relative to the first change amount α when gradually decreasing the rotation speed, and storing this time in the storage unit 61. Alternatively, the time ΔT0 from timing T0 to timing T2 may be stored in the storage unit 61. Alternatively, an eWP rotation sensor that measures the actual rotation speed of the eWP 22 may be provided, and timing T2 at which the actual rotation speed measured by the eWP rotation sensor becomes 0 (rpm) may be detected.

[0034] Next, at timing T2 when the actual rotation speed of eWP 22 becomes 0 (rpm), switching control unit 623A outputs a switching command to switching valve 25 to switch from the first position to the second position (step S8). For example, if the time ΔT1 from timing T1 to timing T2 is recorded in storage unit 61, switching control unit 623A reads out the time ΔT1 from storage unit 61 and outputs a switching command to switching valve 25 at timing T2, which is the time ΔT1 after timing T1 when the pump rotation command to set the rotation speed to 0 is output. Alternatively, if the time ΔT0 from timing T0 to timing T2 is recorded in storage unit 61, switching control unit 623A outputs a switching command at timing T2, which is the time ΔT0 after timing T0 when the pump rotation command to gradually decrease the rotation speed is output. Alternatively, if an eWP rotation sensor is separately provided in the eWP 22, the switching control unit 623A outputs a switching command at timing T2 when the actual rotation speed measured by the eWP rotation sensor becomes 0 (rpm).

[0035] Subsequently, the pump control unit 623B outputs a pump rotation command to the eWP 22 to gradually increase the rotation speed at a predetermined rate (step S9). As shown in FIG. 6 , the actual switching of the switching valve 25 from the first position to the second position is delayed relative to the switching command. For example, if a switching command is output at timing T2, the switching valve 25 completes the switching after a time (second time ΔT2) has elapsed. This second time ΔT2 is pre-stored in the memory unit 61. Then, in step S9, the pump control unit 623B outputs a pump rotation command to the eWP 22 to gradually increase the rotation speed of the eWP 22 by a predetermined second change amount β to a predetermined rotation speed, after the second time ΔT2 has elapsed since the switching command was output in step S8. This prevents water hammer and water column separation in the ePT cooling circuit 20. The processes in steps S7 to S9 also correspond to the circulation control steps of the present disclosure.

[0036] Thereafter, the controller 60 determines whether or not to continue cooling the ePT 10 (step S10). For example, when the electric vehicle 1 stops traveling and the user turns off the power, the determination in step S10 is NO, and the cooling of the ePT 10 is terminated. If the determination in step S10 is YES and the electric vehicle 1 continues traveling, the process proceeds to step S11, which will be described later.

[0037] After step S5 or after the determination in step S10 is YES, that is, after the circulation direction of the coolant in the ePT cooling circuit 20 is controlled to the reverse flow direction, the heat quantity comparison unit 622 calculates the amount of heat dissipated from the inverter 11 to the coolant X Ｉ , and the amount of heat dissipated from the reducer 13 to the cooling water X Ｒ The controller 11 monitors the amount of heat dissipation X from the inverter 11 to the coolant, and determines whether the outside air temperature is equal to or higher than the first threshold value or whether the formula (3) is not satisfied (whether the amount of heat dissipation X from the inverter 11 is equal to or lower than the formula (3)) (step S11: heat amount comparison step). Ｉ The amount of heat transferred from the reducer 13 to the cooling water is X Ｒ If the condition of Equation (3) is no longer satisfied, a YES determination is made in step S11. In this case, the circulation control unit 623 switches the circulation direction of the cooling water from the reverse flow direction to the forward flow direction. At this time, similar to steps S7 to S9, the flow rate of the cooling water is temporarily stopped and then the circulation direction is switched. That is, similar to step S7, the pump control unit 623B outputs a pump rotation command to the eWP 22 to gradually decrease the rotation speed by a first change amount α (step S12). Then, similar to step S8, the switching control unit 623A outputs a switching command to the switching valve 25 to switch from the second position to the first position at timing T2 when the actual rotation speed of the eWP 22 becomes 0 (rpm) (step S13). Furthermore, similar to step S9, after a second time ΔT2 has elapsed since the switching command was output, the pump control unit 623B outputs a pump rotation command to the eWP 22 to gradually increase the rotation speed by a second change amount β to a predetermined value (step S14).

[0038] Thereafter, the controller 60 determines whether or not to continue cooling the ePT 10 (step S15), similarly to step S10, and if the determination in step S15 is NO, ends the cooling control. If the determination in step S15 is YES and the traveling of the electric vehicle 1 is to continue, the process proceeds to step S6.

[0039] Next, the above-described cooling control method will be described using an example of a situation in which the electric vehicle 1 switches from low-speed to high-speed traveling. FIG. 7 is a diagram showing an example of the vehicle speed, outside air temperature, energy loss in the inverter 11 and the reducer 13, the temperatures of the inverter 11 and the reducer 13, the amount of heat radiated to the outside air by the inverter 11 and the reducer 13, and the amount of heat dissipated to the coolant by the inverter 11 and the reducer 13 when the electric vehicle 1 switches from low-speed to high-speed traveling. With respect to the energy loss, temperature, amount of heat radiated to the outside air, and amount of heat dissipated in FIG. 7 , the solid line represents data for the inverter 11, and the dashed line represents data for the reducer 13. In FIG. 7 , it is assumed that the outside air temperature acquired in step S1 is constant and less than a first threshold value (the value indicated by the dashed line in the graph of outside air temperature in FIG. 7 ). Therefore, a YES determination is made in step S2. In this example, it is assumed that the electric vehicle 1 starts traveling at a low speed, for example, by starting on a slope. In this case, the energy loss (energy consumption) in the inverter 11 increases, and the temperature of the inverter 11 rises accordingly. Furthermore, the energy loss in the reducer 13 also increases, causing the temperature of the reducer 13 to rise. However, the amount of energy loss in the inverter 11 under high load at low vehicle speeds and low temperatures is greater than the energy loss in the reducer 13, and the temperature of the inverter 11 becomes higher than the temperature of the reducer 13. Note that volume and heat capacity are proportional to each other. Therefore, since the volume of the reducer 13 is larger than that of the inverter 11, the temperature rise of the reducer 13 is delayed compared to that of the inverter 11.

[0040] On the other hand, the heat from the inverter 11 and reducer 13 is cooled by heat dissipation to the surrounding outside air and heat dissipation (heat removal) to the cooling water of the ePT cooling circuit 20, but the amount of heat removed from the high-temperature inverter 11 to the cooling water is greater than the amount of heat removed to the cooling water from the reducer 13. Note that because the volume of the reducer 13 is larger than that of the inverter 11, the amount of heat removed from the reducer 13 to the surrounding outside air is greater than that of the inverter 11.

[0041] Therefore, timing t Ａ After that (timing t Ｃ ), the amount of heat dissipated from the inverter 11 to the coolant is greater than the amount of heat dissipated from the reducer 13 to the coolant, satisfying the condition of formula (3). Therefore, the determination in step S4 is YES, and in step S5, the circulation control unit 623 circulates the coolant in the reverse flow direction.

[0042] Also, the timing t Ｂ In the example shown in FIG. 1, the vehicle speed begins to increase as the electric vehicle 1 starts to travel on a flat road. In this case, the load on the inverter 11 gradually decreases, and the energy loss in the inverter 11 also begins to decrease. As a result, the temperature of the inverter 11 gradually decreases, and the amount of heat released into the surrounding ambient air and the amount of heat removed into the coolant also gradually decrease.

[0043] On the other hand, the energy consumption of the reducer 13 remains substantially constant. The temperature of the reducer 13 increases slightly as the vehicle speed increases, and the amount of heat released into the surrounding outside air and the amount of heat removed by the coolant also increase slightly accordingly.

[0044] And, timing t Ｃ In this state, the amount of heat dissipated from the inverter 11 to the coolant is equal to or less than the amount of heat dissipated from the reducer 13 to the coolant. As a result, the determination in step S11 is YES, and the circulation control unit 623 performs the processes of steps S11 to S13 to switch the circulation direction of the coolant to the forward flow direction.

[0045] In the example of FIG. 7, the timing t Ｃ After that, timing t ＤAfter that, the temperature of the inverter 11 becomes equal to or lower than the temperature of the reducer 13. Ｄ When the cooling water circulation direction is changed from the reverse flow direction to the forward flow direction at timing t Ｃ From timing t Ｄ During this time, the heat from the reducer 13 and electric motor 12, which have higher temperatures, is first dissipated into the coolant. In this case, the temperature of the coolant will rise, and the amount of heat dissipated by the inverter 11 will likely decrease. In contrast, in this embodiment, the direction of circulation of the coolant in the ePT cooling circuit 20 is controlled by comparing the amount of heat dissipated from the inverter 11 to the coolant and the amount of heat dissipated from the reducer 13 to the coolant, rather than by comparing the temperatures of the inverter 11 and the reducer 13. This increases the efficiency of heat recovery from the ePT 10.

[0046] [Efficiency of Exhaust Heat Recovery in the ePT Cooling Circuit 20] Next, the efficiency of exhaust heat recovery in the ePT cooling circuit 20 will be described. FIG. 8 is a diagram showing an example of the vehicle speed of the electric vehicle 1, the temperature of the coolant flowing into the evaporator 23, and the power consumption of the air conditioning system 40 for the present embodiment and a comparative example, in a scenario in which the outside air temperature is below the first threshold, the electric vehicle 1 is traveling at a low vehicle speed, and the air conditioning system 40 is warming up. For the temperature of the coolant flowing into the evaporator 23 in FIG. 8 , the solid line indicates the present embodiment, and the dashed line indicates the comparative example. Furthermore, for the power consumption of the air conditioning system 40 in FIG. 8 , the solid line indicates the power consumption of the PTC heater of the present embodiment. The dashed line indicates the power consumption of the PTC heater of the comparative example. The dashed-dotted line indicates the power consumption of the compressor 32 of the heat pump 30 of the present embodiment. The dashed-dotted line indicates the power consumption of the compressor 32 of the heat pump 30 of the comparative example. The thick dashed line indicates the power consumption effect of the present embodiment compared to the comparative example. The power consumption effect is calculated by subtracting the sum of the power consumption of the PTC heater and the compressor 32 of the present embodiment from the sum of the power consumption of the PTC heater and the compressor 32 of the comparative example. Note that the comparative example shows an example in which the circulation direction of the cooling water is fixed to the forward flow direction.

[0047] In the comparative example, even when the temperature of the inverter 11 is the highest and the temperatures of the electric motor 12 and the reducer 13 decrease in that order, the coolant flows forward. In this case, the amount of heat removed from the inverter 11 to the coolant increases, causing the temperature of the first circulation path 21 between the inverter heat exchanger 211 and the motor heat exchanger 212 to increase. As a result, the difference between the temperature of the coolant flowing into the motor heat exchanger 212 and the temperature of the electric motor 12 decreases, resulting in a decrease in the heat dissipation efficiency of the electric motor 12. Similarly, the temperature of the coolant between the motor heat exchanger 212 and the reducer heat exchanger 213 increases. As a result, the difference between the temperature of the coolant flowing into the reducer heat exchanger 213 and the temperature of the reducer 13 decreases, resulting in a decrease in the heat dissipation efficiency of the electric motor 12. In particular, when the temperature of the coolant flowing into the motor heat exchanger 212 is higher than the temperature of the electric motor 12, heat from the electric motor 12 cannot be recovered. In this case, if the temperature of the cooling water flowing into the reducer heat exchange section 213 becomes higher than the temperature of the reducer 13, the heat of the reducer 13 cannot be recovered.

[0048] On the other hand, in this embodiment, when the amount of heat dissipated by the inverter 11 is greater than the amount of heat dissipated by the reducer 13, the coolant flows in the reverse direction. That is, the heat from the reducer 13 and the electric motor 12, which have lower temperatures, is recovered by the coolant, and then the heat from the inverter 11 is dissipated by the coolant. Because the heat dissipation from the inverter 11, which has the highest temperature, occurs later, the heat from the reducer 13 and the electric motor 12 can be recovered by the coolant. As a result, in this embodiment, the temperature of the coolant in the evaporator 23 increases more quickly. Here, in this embodiment, the time required for the temperature of the coolant in the evaporator 23 to reach or exceed the predetermined second threshold is T3, and in the comparative example, the time required for the temperature of the coolant in the evaporator 23 to reach or exceed the predetermined second threshold is T4. In this embodiment, the time required for the temperature of the coolant in the evaporator 23 to reach or exceed the predetermined second threshold is shortened by ΔT3 compared to the comparative example.

[0049] Furthermore, in order to quickly warm up the interior of the vehicle, the air conditioning system 40 uses a PTC heater to warm up the air when the temperature of the coolant in the evaporator 23 is low. Warming up the air using a PTC heater consumes more power than driving the compressor 32 of the heat pump 30. For this reason, the air conditioning system 40 warms up the air using both the PTC heater and the heat pump 30, which uses the exhaust heat recovered by the evaporator 23, when the temperature of the coolant in the evaporator 23 reaches or exceeds a predetermined second threshold required for warming up the air. Alternatively, the air conditioning system 40 may switch from warming up the air using the PTC heater to warming up the air using the heat pump 30, which uses the exhaust heat recovered by the evaporator 23, when the temperature of the coolant in the evaporator 23 reaches or exceeds the predetermined second threshold required for warming up the air.

[0050] 8, in this embodiment, as described above, heat from the ePT 10 can be efficiently recovered, and the system switches to warm air using the PTC heater and heat pump 30 ΔT3 earlier than in the comparative example. This allows the power of the PTC heater, which consumes a lot of power, to be reduced by ΔT3, resulting in a correspondingly higher power consumption effect.

[0051] [Effects of the Present Embodiment] The electric vehicle 1 of the present embodiment includes an ePT 10 having an inverter 11, an electric motor 12, and a reducer 13, and an ePT cooling circuit 20 that circulates the inverter 11, the electric motor 12, the reducer 13, and the evaporator 23 to cool the ePT 10. The controller 60 of the electric vehicle 1 functions as a cooling control device, and the processor 62 of the controller 60 functions as an outside air temperature acquisition unit 621, a heat quantity comparison unit 622, and a circulation control unit 623 by appropriately reading and executing programs stored in the memory unit 61. The outside air temperature acquisition unit 621 performs an outside air temperature acquisition step (step S1) to acquire the outside air temperature. The heat quantity comparison unit 622 performs heat quantity comparison steps (steps S4, S6, and S11) in the ePT cooling circuit 20 to compare the amount of heat dissipated from the inverter 11 to the coolant with the amount of heat dissipated from the reducer 13 to the coolant. The circulation control unit 623 performs a circulation control step (step S5, steps S7 to S9, and steps S12 to S14) that controls the circulation direction of the coolant based on the outside air temperature, the amount of heat dissipated from the inverter 11 to the coolant, and the amount of heat dissipated from the reducer 13 to the coolant. In this embodiment, in the circulation control step, the circulation control unit 623 circulates the coolant through the inverter 11, the electric motor 12, and the reducer 13 in this order when the outside air temperature is equal to or higher than a first threshold, and when the outside air temperature is lower than the first threshold and the amount of heat dissipated from the inverter 11 to the coolant is equal to or lower than the amount of heat dissipated from the reducer 13 to the coolant. On the other hand, when the outside air temperature is lower than the first threshold and the amount of heat dissipated from the inverter 11 to the coolant is greater than the amount of heat dissipated from the reducer 13 to the coolant, the circulation control unit 623 circulates the coolant through the reducer 13, the electric motor 12, and the inverter 11 in this order.

[0052] In this way, the efficiency of exhaust heat recovery can be improved by changing the circulation direction of the coolant depending on the magnitude of the heat dissipation amounts at the inverter 11 and the electric motor 12 in the ePT cooling circuit 20, and circulating the coolant in order from the configuration with the lowest heat dissipation amount to the configuration with the highest heat dissipation amount. In other words, if the coolant is circulated through the inverter 11 first when the heat dissipation amount of the inverter 11 is high, the temperature of the coolant will become too high and the exhaust heat from the electric motor 12 and the reducer 13 will not be sufficiently recovered. In contrast, if the heat dissipation amount of the inverter 11 is high, the coolant is circulated through the electric motor 12 and the reducer 13, which have lower temperatures, first, and then the coolant is circulated through the inverter 11. This prevents the coolant from being excessively heated, and allows the exhaust heat from the inverter 11, the electric motor 12, and the reducer 13 to be efficiently recovered.

[0053] In this embodiment, in the heat quantity comparison steps (steps S4, S6, and S11), the heat quantity comparison unit 622 determines that the amount of heat dissipated from the inverter 11 to the coolant is greater than the amount of heat dissipated from the reducer 13 to the coolant if formula (3) is satisfied. This allows the heat quantity comparison unit 622 to easily determine the magnitude relationship between the heat dissipation amounts of the inverter 11 and the reducer 13. In other words, the heat dissipation amounts of the inverter 11 and the reducer 13 cannot be directly sensed. In contrast, the heat dissipation amount of the inverter 11 can be calculated using formula (1), and the heat dissipation amount of the reducer 13 can be calculated using formula (2). Using formula (3) derived from formulas (1) and (2), the heat quantity comparison unit 622 can easily determine the magnitude relationship between the heat dissipation amounts of the inverter 11 and the reducer 13 from the temperature of the inverter 11, the temperature of the reducer 13, and the temperature of the coolant before entering the ePT cooling circuit 20.

[0054] In this embodiment, the ePT cooling circuit 20 includes a switching valve 25 that switches between a forward flow direction, in which the cooling water circulates through the inverter 11, the electric motor 12, and the reducer 13 in that order, and a reverse flow direction, in which the cooling water circulates through the reducer 13, the electric motor 12, and the inverter 11 in that order, and an eWP 22 that pumps out the cooling water. In the circulation control steps (steps S7-9, steps S12-14), the circulation control unit 623 stops the eWP 22 using the pump control unit 623B when switching the circulation direction of the cooling water in the ePT cooling circuit 20. While the eWP 22 is stopped, the switching control unit 623A switches the circulation direction using the switching valve 25. This prevents abrupt changes in the circulation direction of the cooling water, thereby reducing the inconvenience of impact noise and vibration caused by water hammer and water column separation.

[0055] At this time, the pump control unit 623B outputs a pump rotation command to the pump to gradually decrease the rotation speed of the eWP 22 by a predetermined first change amount α in step S7 or step S12. Then, when a first time ΔT1 has elapsed after the pump rotation command to set the rotation speed of the eWP 22 to 0 has been output to the eWP 22, the switching control unit 623A switches the circulation direction of the cooling water using the switching valve 25 in step S8 or step S13. This switches the switching valve 25 at the timing when the flow rate of the cooling water becomes 0, making it possible to more reliably suppress problems such as water hammer and impact noise and vibration caused by water column separation.

[0056] Furthermore, the switching control unit 623A outputs a switching command to the switching valve 25 to switch the circulation direction, and after a predetermined second time ΔT2 has elapsed, the pump control unit 623B outputs a pump rotation command to the eWP 22 to gradually increase the rotation speed of the eWP 22 by a predetermined second change amount β. This makes it possible to suppress a sudden change in pressure that would occur if the eWP 22 were driven with the switching valve 25 closed, and to suppress the inconvenience of generating impact noise and vibration due to water hammer or water column separation.

[0057] [Modifications] The present invention is not limited to the above-described embodiment, but also includes the following modifications within the scope of achieving the object of the present invention.

[0058] [Variation 1] In the above embodiment, the heat dissipation amount of the inverter 11 was calculated using equation (1), the heat dissipation amount of the reducer 13 was calculated using equation (2), and whether the heat dissipation amount of the inverter 11 was greater than the heat dissipation amount of the reducer 13 was determined based on whether equation (3) holds. However, the heat dissipation amounts of the inverter 11 and the reducer 13 may be calculated using other methods. For example, in the first circulation path 21 of the ePT cooling circuit 20, water temperature sensors for detecting the temperature of the coolant may be provided at both ends of the inverter heat exchanger 211 that recovers the exhaust heat of the inverter 11 and at both ends of the reducer heat exchanger 213 that recovers the exhaust heat of the reducer 13. In this case, the water temperatures at the inlet and outlet of the inverter heat exchanger 211 are measured, and the amount of heat dissipated from the inverter 11 to the coolant can be calculated based on the difference in water temperature between the inlet and outlet, the specific heat of the coolant, and the flow rate of the coolant. Similarly, the water temperatures at the inlet and outlet of the reducer heat exchanger unit 213 are measured, and the amount of heat dissipated from the reducer 13 to the coolant can be calculated from the water temperature difference between the inlet and outlet, the specific heat of the coolant, and the flow rate of the coolant. The specific heat and flow rate of the coolant are common to the inverter heat exchanger unit 211 and the motor heat exchanger unit 212. Therefore, the heat quantity comparison unit 622 can determine the magnitude relationship between the water temperature difference between the inlet and outlet of the inverter heat exchanger unit 211 and the water temperature difference between the inlet and outlet of the reducer heat exchanger unit 213, thereby determining the magnitude relationship between the amount of heat dissipated by the inverter 11 and the amount of heat dissipated by the reducer 13.

[0059] [Variation 2] In the above embodiment, the ePT cooling circuit 20 includes a first circulation path 21 that circulates through the ePT 10 and a second circulation path 24 that houses the eWP 22 and the evaporator 23, and the first circulation path 21 and the second circulation path 24 are connected by a switching valve 25. However, this is not limiting. For example, if the pump is capable of reversing the coolant delivery direction between forward flow and reverse flow, the second circulation path 24 may be omitted, and the pump and the evaporator 23 may be provided within the first circulation path 21.

[0060] [Modification 3] In the above embodiment, when switching the cooling water circulation direction, the eWP 22 is stopped, the switching valve 25 is switched, and the eWP 22 is driven again. However, if the effects of water hammer or water column separation are not taken into consideration or if other measures are taken, the switching valve 25 may be switched while the eWP 22 is driven. Alternatively, instead of waiting until the rotation of the eWP 22 stops, the switching valve 25 may be controlled to be switched when the rotation speed of the eWP 22 falls below a predetermined value.

[0061] [Variation 4] In the above embodiment, the water temperature sensor 26 for measuring the coolant temperature is provided between the evaporator 23 and the switching valve 25. However, the present invention is not limited to this. For example, water temperature sensors may be provided in the first circulation path 21 between the switching valve 25 and the inverter heat exchanger 211 and between the switching valve 25 and the reducer heat exchanger 213. In this case, if the coolant circulates in the forward flow direction, the coolant temperature may be measured by the water temperature sensor between the switching valve 25 and the inverter heat exchanger 211. Furthermore, if the coolant circulates in the reverse flow direction, the coolant temperature may be measured by the water temperature sensor between the switching valve 25 and the reducer heat exchanger 213.

[0062] 1...electric vehicle, 10...ePT (electric power train), 11...inverter, 12...electric motor, 13...reducer, 20...ePT cooling circuit, 21...first circulation path, 23...evaporator (heat exchange section), 24...second circulation path, 25...switching valve, 26...water temperature sensor, 30...heat pump, 31...expansion valve, 32...compressor, 33...condenser, 40...air conditioning system, 51...outside air temperature detection sensor, 60...controller, 61...memory section, 62...processor, 111...first temperature sensor, 121...second temperature sensor, 131...third temperature sensor, 211...inverter heat exchange section, 212...motor heat exchange section, 213...reducer heat exchange section, 621...outside air temperature acquisition section, 622...heat quantity comparison section, 623...circulation control section, 623A...switching control section, 623B...pump control section, 624...air conditioning control section.

Claims

1. A cooling control method for an electric powertrain of an electric vehicle equipped with an electric powertrain having an inverter, an electric motor, and a reducer, and a cooling circuit that cools the electric powertrain by circulating coolant through the inverter, the electric motor, and the reducer, comprising: an outside air temperature acquisition step of acquiring an outside air temperature; a heat quantity comparison step of comparing, in the cooling circuit, the amount of heat dissipated from the inverter to the coolant with the amount of heat dissipated from the reducer to the coolant; and a circulation control step of controlling the circulation direction of the coolant based on the outside air temperature, the amount of heat dissipated from the inverter to the coolant, and the amount of heat dissipated from the reducer to the coolant, wherein in the circulation control step, when the outside air temperature is equal to or higher than a first threshold, and when the outside air temperature is less than the first threshold and the amount of heat dissipated from the inverter to the coolant is less than the amount of heat dissipated from the reducer to the coolant, the coolant is circulated through the inverter, the electric motor, and the reducer in that order, A cooling control method in which, when the outside air temperature is less than the first threshold value and the amount of heat dissipated from the inverter to the cooling water is greater than the amount of heat dissipated from the reducer to the cooling water, the cooling water is circulated through the reducer, the electric motor, and the inverter in that order.

2. The cooling control method according to claim 1, wherein, in the heat quantity comparison step, if the difference between the temperature of the inverter and the temperature of the cooling water flowing into the electric powertrain is greater than a value obtained by multiplying the difference between the temperature of the reducer and the temperature of the cooling water flowing into the electric powertrain by a predetermined constant, it is determined that the amount of heat dissipated from the inverter to the cooling water is greater than the amount of heat dissipated from the reducer to the cooling water.

3. The cooling circuit is provided with a switching valve that switches between a forward flow direction in which the cooling water is circulated through the inverter, the electric motor, and the reducer in that order, and a reverse flow direction in which the cooling water is circulated through the reducer, the electric motor, and the inverter in that order, and a pump that pumps out the cooling water, and in the circulation control step, when the circulation direction of the cooling water in the cooling circuit is switched, the pump is stopped, and while the pump is stopped, the circulation direction is switched by the switching valve.

4. A cooling control method as described in claim 3, wherein in the circulation control step, a pump rotation command is output to the pump to gradually decrease the rotation speed of the pump by a predetermined first change amount, and after the pump rotation command to set the rotation speed of the pump to 0 is output to the pump, the circulation direction is switched by the switching valve after a predetermined first time has elapsed.

5. A cooling control method as described in claim 3, wherein in the circulation control step, after a switching command to switch the circulation direction is output to the switching valve, a pump rotation command to gradually increase the rotation speed of the pump by a predetermined second change amount is output to the pump after a predetermined second time has elapsed.

6. An electric powertrain having an inverter, an electric motor, and a reducer; a cooling circuit that circulates coolant through the inverter, the electric motor, and the reducer to cool the electric powertrain; an outside air temperature acquisition unit that acquires an outside air temperature; a heat quantity comparison unit in the cooling circuit that compares the amount of heat dissipated from the inverter to the coolant with the amount of heat dissipated from the reducer to the coolant; and a circulation control unit that controls the circulation direction of the coolant based on the outside air temperature, the amount of heat dissipated from the inverter to the coolant, and the amount of heat dissipated from the reducer to the coolant, wherein the circulation control unit circulates the coolant through the inverter, the electric motor, and the reducer in that order when the outside air temperature is equal to or higher than a first threshold, and when the outside air temperature is less than the first threshold and the amount of heat dissipated from the inverter to the coolant is less than the amount of heat dissipated from the reducer to the coolant, A cooling control device that circulates the cooling water through the reducer, the electric motor, and the inverter in the following order when the outside air temperature is less than the first threshold value and the amount of heat dissipated from the inverter to the cooling water is greater than the amount of heat dissipated from the reducer to the cooling water.

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