Patent Publication Number: US-11649746-B2

Title: Heat management system for electric vehicle

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Japanese Patent Application No. 2020-054158 filed on Mar. 25, 2020, the contents of which are hereby incorporated by reference into the present application. 
     TECHNICAL FIELD 
     The technology disclosed herein relates to a heat management system for an electric vehicle. The “electric vehicle” herein includes a hybrid vehicle and a fuel-cell vehicle. 
     BACKGROUND 
     A cruising range of an electric vehicle can be increased by suitably utilizing heat of its traction motor and heat of outside air to reduce power consumption of an electric device used for temperature regulation. Japanese Patent Application Publication No. 2019-213337 proposes a heat management system for an electric vehicle that comprehensively manages heat of outside air and heat of a motor, an inverter, and a battery to suitably utilize the heat of each portion of the electric vehicle. 
     The heat management system of Japanese Patent Application Publication No. 2019-213337 includes a first temperature regulation circuit and a second temperature regulation circuit. The first temperature regulation circuit is configured to cool a traction motor and a power converter configured to supply electric power to the motor. The second temperature regulation circuit is configured to regulate the temperature of a cabin. In the first temperature regulation circuit, first heat medium circulates through an oil cooler, a cooler for cooling the power converter (converter cooler), and a radiator. The oil cooler is configured to cool oil for cooling the motor by the first heat medium. In the second temperature regulation circuit, second heat medium circulates between a chiller for air-conditioning in the cabin and an air conditioner outdoor unit. The radiator and the air conditioner outdoor unit are arranged adjacent to each other, thus heat is exchanged also between the first heat medium and the second heat medium. 
     SUMMARY 
     In the heat management system of Japanese Patent Application Publication No. 2019-213337, heat can be exchanged between the radiator in the first temperature regulation circuit (temperature regulation circuit for the motor and the power converter) and the air conditioner outdoor unit in the second temperature regulation circuit (temperature regulation circuit for the cabin). The inventors have considered to actively utilize the radiator (which will hereinafter be termed a first heat exchanger) used to emit the heat of the motor and the power converter to regulate the temperature of the cabin. That is, they have considered to incorporate a second heat exchanger configured to exchange heat between the first heat medium in the first temperature regulation circuit and the second heat medium in the second temperature regulation circuit, a second channel, and a channel valve into the heat management system. Hereinbelow, a channel that connects the oil cooler, the converter cooler, and the first heat exchanger to each other will be termed a first channel. 
     The second channel extends through the second heat exchanger and is connected to an inlet and an outlet of the first heat exchanger. The first channel is also connected to the inlet and the outlet of the first heat exchanger. The first heat exchanger is shared between a circulating system of the first channel and a circulating system of the second channel. The channel valve is configured to select a first valve position and a second valve position. When the first valve position is selected, the channel valve allows a flow of the first heat medium from the first channel to the first heat exchanger and cuts off the flow of the first heat medium from the second channel to the first heat exchanger. When the second valve position is selected, the channel valve allows the flow of the first heat medium from the second channel to the first heat exchanger and cuts off the flow of the first heat medium from the first channel to the first heat exchanger. 
     While the first valve position is selected, the first heat medium that has passed through the oil cooler and the converter cooler can exchange the heat with the outside air in the first heat exchanger, but the first heat medium that has passed through the second heat exchanger cannot exchange the heat with the outside air. While the second valve position is selected, the first heat medium that has passed through the second heat exchanger can exchange the heat with the outside air in the first heat exchanger, but the first heat medium that has passed through the oil cooler and the converter cooler cannot exchange the heat with the outside air. 
     When the temperature of the first heat medium rises due to a temperature rise in the power converter, the channel valve selects the first valve position, by which the heat of the power converter is released in the first heat exchanger. When the temperature of the first heat medium rises due to a temperature rise in the motor (oil), the channel valve also selects the first valve position, by which the heat of the motor (oil) is released in the first heat exchanger. The motor and the first heat medium exchange heat via the oil. A timing when the temperature of the first heat medium rises due to the temperature rise in the power converter differs from a timing when the temperature of the first heat medium rises due to the temperature rise in the motor. If the first valve position is frequently selected in response to the temperature rise in the power converter and the temperature rise in the motor, this makes the first heat medium less frequently circulate between the second heat exchanger and the first heat exchanger. The technology disclosed herein solves this problem. 
     A heat management system disclosed herein is used for an electric vehicle. The heat management system may comprise an oil cooler, an oil pump, a converter cooler, a first heat exchanger, a second heat exchanger, a first channel, a second channel, a channel valve, a bypass channel, and a controller. 
     The oil cooler may be configured to cool oil by first heat medium. The oil is used to cool a traction motor. The oil pump may be configured to circulate the oil between the oil cooler and the traction motor. The converter cooler may be configured to cool a power converter configured to supply electric power to the traction motor by the first heat medium. The first heat exchanger may be configured to exchange heat between the first heat medium and outside air. The second heat exchanger may be configured to exchange heat between second heat medium for an air conditioner of a cabin and the first heat medium. The first channel may extend through the oil cooler and the converter cooler and be connected to an inlet and an outlet of the first heat exchanger. The second channel may extend through the second heat exchanger and be connected to the inlet and the outlet of the first heat exchanger. 
     The channel valve may be configured to select a first valve position and a second valve position. At the first valve position, the channel valve may allow a flow of the first heat medium from the first channel to the first heat exchanger and cuts off the flow of the first heat medium from the second channel to the first heat exchanger. At the second valve position, the channel valve may allow the flow of the first heat medium from the second channel to the first heat exchanger and cuts off the flow of the first heat medium from the first channel to the first heat exchanger. The bypass channel may be configured to allow the first heat medium to bypass the first heat exchanger and circulate between the oil cooler and the converter cooler when the second valve position is selected. The controller may be configured to control the channel valve and the oil pump. The controller may be configured to control the channel valve such that the channel valve selects the first valve position and activate the oil pump in response to the temperature of the first heat medium in the first channel becoming higher than a predetermined upper limit temperature. 
     In the heat management system disclosed herein, the oil pump is activated when the first valve position is selected. Heat of the oil is transferred to the first heat medium, and the heat of the first heat medium is released to the outside air in the first heat exchanger. As a result, both of the temperature of the first heat medium and the temperature of the oil decrease. Thereby, the frequency of the first valve position being selected due to a temperature rise in the motor is reduced, and the first heat medium can circulate more frequently between the second heat exchanger and the first heat exchanger. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a diagram showing a heat management system according to an embodiment; 
         FIG.  2    is a circuit diagram showing a flow of first heat medium at a second valve position; 
         FIG.  3    is a circuit diagram showing a flow of the first heat medium at a first valve position; 
         FIG.  4    is timing charts showing changes in values in a heat management system according to a first embodiment; and 
         FIG.  5    is timing charts showing changes in values in a heat management system according to a second embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Some of the features characteristic to the heat management system disclosed herein will be listed. It should be noted that the respective technical elements are independent of one another, and are useful solely or in combinations. 
     The heat management system disclosed herein is particularly effective for executing a heat pump operation by which heat of the outside air is used for heating air in the cabin. The controller may be configured to execute a heat pump mode in which the channel valve selects the second valve position, the first heat exchanger transfers heat from the outside air to the first heat medium, and the second heat exchanger transfers heat from the first heat medium to the second heat medium. In other words, in the heat pump mode, the controller causes the channel valve to select the second valve position to deliver to the first heat exchanger the first heat medium whose temperature is lower than the temperature of the outside air and deliver to the second heat exchanger the second heat medium whose temperature is lower than the temperature of the first heat medium that has absorbed heat from the outside air. The controller is configured to switch the channel valve from the second valve position to the first valve position and activate the oil pump in response to a difference of temperatures of the first heat medium at the inlet and the outlet becoming smaller than a predetermined temperature difference threshold while executing the heat pump mode. When frost forms on the first heat exchanger, the performance of the first heat exchanger is thereby degraded, and the temperature difference of the first heat medium between at the inlet and the outlet of the first heat exchanger becomes smaller than the predetermined temperature difference threshold. In such a case, the channel valve is switched from the second valve position to the first valve position to deliver the first heat medium heated by the heat of the power converter and the motor (oil) to the first heat exchanger. The heated first heat medium can eliminate the frost on the first heat exchanger. 
     The controller may be configured to inactivate the oil pump in response to the temperature of the oil (oil temperature) becoming lower than a first lower limit temperature while not executing the heat pump mode; and inactivate the oil pump in response to the oil temperature becoming lower than a second lower limit temperature while executing the heat pump mode. The second lower limit temperature may be lower than the first lower limit temperature. In the heat pump mode, it is desirable to prolong, as long as possible, a time period during which the first heat medium is allowed to flow from the second channel to the first heat exchanger. By the lower limit temperature for the oil temperature being set lower in the heat pump mode, a time period required for the temperature of the motor (oil) to reach the upper limit temperature next can be prolonged. Consequently, the time period during which the first heat medium is allowed to flow from the second channel to the first heat exchanger can be prolonged. 
     (First Embodiment) With reference to the drawings, a heat management system  100  according to a first embodiment will be described.  FIG.  1    shows a circuit diagram of the heat management system  100 . The heat management system  100  is mounted on an electric vehicle and is configured to regulate the temperatures of a vehicle-mounted device and a cabin. The heat management system  100  regulates the temperatures of a traction motor  55 , a battery  51  storing electric power for the motor  55 , and a smart power unit (SPU)  46  and a power control unit (PCU)  47  that supply the electric power to the motor  55 . 
     Output of the battery  51  exceeds 200 volts. When outputting large electric power, the battery  51  generates heat. The SPU  46  distributes the electric power of the battery  51  to some devices including the PCU  47 . The SPU  46  includes a DC-DC converter and is configured to step down the voltage of electric power of the battery  51  to supply it to auxiliary equipment (vehicle-mounted low-power device). The PCU  47  is configured to convert the DC power of the battery  51  into AC power to supply it to the motor  55 . The SPU  46  and the PCU  47  also generate heat while operating. Main sources of the heat generated by the SPU  46  and the PCU  47  are switching elements for power conversion. 
     The heat management system  100  mainly functions to cool the motor  55 , the battery  51 , the SPU  46 , and the PCU  47 , but it functions to warm these devices when the vehicle travels in cold climates. 
     The heat management system  100  includes a first heat circuit  10 , a second heat circuit  20 , and a third heat circuit  30 . Heat media respectively flow in the first heat circuit  10 , the second heat circuit  20 , and the third heat circuit  30 . Channels in which the heat media flow are independent from each other among the first heat circuit  10 , the second heat circuit  20 , and the third heat circuit  30 . The heat media in the first heat circuit  10 , the second heat circuit  20 , and the third heat circuit  30  may be constituted of the same material or different materials. Hydrofluorocarbons can be used as the heat media, for example. Herein, the heat medium flowing in the first heat circuit  10  is termed first heat medium, the heat medium flowing in the second heat circuit  20  is termed second heat medium, and the heat medium flowing in the third heat circuit  30  is termed third heat medium. 
     The first heat circuit  10  regulates the temperature of the vehicle-mounted device. The second heat circuit  20  and the third heat circuit  30  regulate the temperature of the cabin. For cooling the vehicle-mounted device, the first heat circuit  10  releases the heat of the first heat medium to the outside air. When a heater for the cabin is turned on, the first heat circuit  10  may heat the second heat medium by utilizing the heat of the outside air. The disclosure herein focuses on cooling the device while heating the air in the cabin. In the present embodiment, descriptions for temperature rise in the device and cooling of the air in the cabin will not be described. 
     The first heat circuit  10  includes a first channel  11 , a second channel  12 , a bypass channel  13 , and a battery channel  14 . As described above, the first heat circuit  10  cools the SPU  46 , the PCU  47 , the motor  55 , and the battery  51 . The motor  55  is cooled by the first heat medium via oil. 
     The first channel  11  extends through the SPU  46 , the PCU  47 , and an oil cooler  45 . One end of the first channel  11  is connected to an inlet  41   i  of a low-temperature radiator  41 , and another end thereof is connected to an outlet  41   o  of the low-temperature radiator  41 . A pump  48  is disposed on the first channel  11 . The pump  48  pumps the first heat medium in the first channel  11 . The first heat medium flows from the pump  48  through the oil cooler  45 , the low-temperature radiator  41 , the SPU  46 , and the PCU  47  in this order. 
     An SPU cooler  46   c  is disposed in the SPU  46 . A PCU cooler  47   c  is disposed in the PCU  47 . The SPU cooler  46   c  and the PCU cooler  47   c  are connected to the first channel  11 . The first heat medium flows through the SPU cooler  46   c  and the PCU cooler  47   c  to cool the SPU  46  and the PCU  47 . 
     An oil circulation path  18  is connected to the oil cooler  45 . The oil circulation path  18  extends inside a transaxle  43 . The transaxle  43  houses the motor  55 . A part of the oil circulation path  18  extends through a sliding portion (i.e., a bearing portion) of the motor  55 . In other words, oil in the oil circulation path  18  also functions as lubricating oil in the motor  55 . An oil pump  44  is disposed on the oil circulation path  18 . The oil pump  44  circulates the oil in the oil circulation path  18 . The oil that has cooled the motor  55  is cooled by the first heat medium in the oil cooler  45 . 
     The first heat medium that has cooled the SPU  46 , the PCU  47 , and the motor  55  (the oil in the oil cooler  45 ) flows through the low-temperature radiator  41 . The heat of the first heat medium is released to the outside air in the low-temperature radiator  41 . The low-temperature radiator  41  exchanges heat between the first heat medium and the outside air. 
     The bypass channel  13  is connected to the first channel  11 . One end of the bypass channel  13  is connected to an upstream part of the first channel  11  via a three-way valve  42 , and another end thereof is connected to a downstream part of the first channel  11 . 
     The first channel  11  is brought into fluid communication with one of the low-temperature radiator  41  and the bypass channel  13  by the three-way valve  42 . The three-way valve  42  is switchable between a first valve position and a second valve position. At the first valve position, the three-way valve  42  allows a flow of the first heat medium from the first channel  11  to the low temperature radiator  41  and cuts off the flow of the first heat medium from the first channel  11  to the bypass channel  13 . At the second valve position, the three-way valve  42  allows the flow of the first heat medium from the first channel  11  to the bypass channel  13  and cuts off the flow of the first heat medium from the first channel  11  to the low-temperature radiator  41 . When the pump  48  is activated with the three-way valve  42  allowing the flow of the first heat medium from the first channel  11  to the low-temperature radiator  41  (i.e., with the three-way valve  42  at the first valve position), the first heat medium circulates through the SPU  46 , the PCU  47 , the oil cooler  45 , and the low-temperature radiator  41 . The heat of the SPU  46 , the PCU  47 , and the motor  55  (the oil) is released to the outside air via the first heat medium. 
     When the pump  48  is activated with the three-way valve  42  allowing the flow of the first heat medium from the first channel  11  to the bypass channel  13  (i.e., with the three-way valve  42  at the second valve position), the first heat medium bypasses the low-temperature radiator  41  and circulates through the SPU  46 , the PCU  47 , and the oil cooler  45 . The temperature of the first heat medium rises due to the heat of the SPU  46 , the PCU  47 , and the motor  55  (the oil). The three-way valve  42  is controlled by a controller  80 . Control over the three-way valve  42  will be described later. 
     The second channel  12  extends through a chiller  52 . One end of the second channel  12  is connected to the inlet  41   i  of the low-temperature radiator  41 , and another end thereof is connected to the outlet  41   o  of the low-temperature radiator  41 . The low-temperature radiator  41  is shared between the first channel  11  and the second channel  12 . A pump  53  is disposed on the second channel  12 . The pump  53  pumps the first heat medium in the second channel  12 . A circulation path  22  of the second heat circuit  20  extends through the chiller  52 . The chiller  52  transfers the heat of the first heat medium to the second heat medium. In other words, the chiller  52  exchanges heat between the first heat medium and the second heat medium. A role of the chiller  52  will be described later. 
     The battery channel  14  is connected to the second channel  12 . The battery channel  14  extends through the battery  51 . One end of the battery channel  14  is connected to the second channel  12  via a three-way valve  49  at a position downstream of the chiller  52 . Another end of the battery channel  14  is connected to the second channel  12  at a position upstream of the pump  53 . 
     The chiller  52  is brought into fluid communication with one of the low-temperature radiator  41  and the battery channel  14  by the three-way valve  49 . The three-way valve  49  is switchable between a first valve position and a second valve position. At the first valve position, the three-way valve  49  allows the flow of the first heat medium from the chiller  52  to the battery channel  14  and cuts off the flow of the first heat medium from the chiller  52  to the low-temperature radiator  41 . At the second valve position, the three-way valve  49  allows the flow of the first heat medium from the chiller  52  to the low-temperature radiator  41  and cuts off the flow of the first heat medium from the chiller  52  to the battery channel  14 . When the pump  53  is activated with the three-way valve  49  allowing the flow of the first heat medium from the chiller  52  to the battery channel  14  (i.e., with the three-way valve  49  at the first valve position), the first heat medium circulates between the chiller  52  and the battery  51 . The first heat medium cools the battery  51 , and then the first heat medium with high temperature is cooled by the second heat medium in the chiller  52 . When the pump  53  is activated with the three-way valve  49  allowing the flow of the first heat medium from the chiller  52  to the low-temperature radiator  41  (i.e., with the three-way valve  49  at the second valve position), the first heat medium flows through the second channel  12  and circulates between the chiller  52  and the low-temperature radiator  41 . The first heat medium circulates between the chiller  52  and the low-temperature radiator  41  in a heat pump mode. The heat pump mode will be described later. 
     A heater  50  is disposed upstream of the battery  51  on the battery channel  14 . When the temperature of the battery  51  decreases due to cold climates and/or the like, the first heat medium is heated by the heater  50 , and then the heated first heat medium heats the battery  51 . 
     As described above, the second heat circuit  20  and the third heat circuit  30  regulate the temperature of the cabin. The second heat circuit  20  is used mainly to cool the air in the cabin. The second heat circuit  20  includes the circulation path  22 , an evaporator  63 , a compressor  66 , an evaporator pressure regulator (EPR)  62 , a condenser  67 , and a modulator  68 . 
     A three-way valve  65  is disposed on the circulation path  22 . The three-way valve  65  switchable between a first valve position and a second valve position. At the first valve position, the three-way valve  65  allows a flow of the second heat medium from the condenser  67  to the evaporator  63 . At the second valve position, the three-way valve  65  allows the flow of the second heat medium from the condenser  67  to the chiller  52 . 
     The three-way valve  65  selects the first valve position to cool the cabin. The second heat medium is compressed in the compressor  66  and turns into a high-temperature gas. This second heat medium is cooled in the condenser  67  and thereby turns into a liquid. Only the second heat medium that is in form of liquid in the modulator  68  flows to the three-way valve  65 . The liquid second heat medium flows through an expansion valve  64  and the evaporator  63 , as a result of which the second heat medium is evaporated and its temperature sharply decreases. The second heat medium with the low temperature cools the air in the cabin. The second heat medium passes through the EPR  62  and is then compressed again in the compressor  66 . 
     In the heat pump mode, the three-way valve  65  is switched to the second valve position to allow the flow of the second heat medium from the condenser  67  to the chiller  52 . The heat pump mode is selected when the air in the cabin is to be heated, which will be described later in detail. The second heat medium is compressed in the compressor  66  and turns into a high-temperature gas. In the heat pump mode, this second heat medium releases the heat to the third heat medium in the condenser  67  and turns into a liquid. Only the second heat medium that is in form of liquid in the modulator  68  flows to the three-way valve  65 . The liquid second heat medium flows through an expansion valve  61  and the chiller  52 , as a result of which the second heat medium is evaporated and its temperature sharply decreases. The second heat medium with low temperature absorbs heat from the first heat medium passing through the chiller  52 , as a result of which the temperature of the second heat medium is increased. This second heat medium is compressed in the compressor  66 , thus its temperature is increased further. This second heat medium releases the heat to the third heat medium in the condenser  67 . 
     The third heat circuit  30  is used mainly to warm the air in the cabin. The third heat circuit  30  includes a circulation path  32 , an electric heater  71 , a heater core  74 , a pump  72 , a high-temperature radiator  75 , and a three-way valve  73 . The air in the cabin is warmed by high-temperature third heat medium flowing in the heater core  74 . 
     When the air in the cabin is to be warmed, the condenser  67 , the electric heater  71 , and the heater core  74  are brought into fluid communication with each other by the three-way valve  73 . As described above, in the heat pump mode, the third heat medium is heated by the high-temperature second heat medium in the condenser  67 . When the heated third heat medium passes through the heater core  74 , it warms the air in the cabin. When the heat of the third heat medium is insufficient, the electric heater  71  heats the third heat medium. 
     When the heat management system  100  has excess heat, the three-way valve  73  allows the flow of the third heat medium from the condenser  67  to the high-temperature radiator  75 . The heat transferred from the second heat medium to the third heat medium via the condenser  67  is released to the outside air in the high-temperature radiator  75 . 
     When a cabin air heating mode is selected in the heat management system  100 , the air in the cabin is warmed by the third heat medium passing through the heater core  74 , as described above. In the cabin air heating mode, the heat of the outside air or the heat of the battery  51  is also utilized. The first heat medium in the first heat circuit  10  is heated by the heat of the outside air or the heat of the battery  51 . In the chiller  52 , the second heat medium is heated by the heated first heat medium. After passing through the chiller  52 , the heated second heat medium is compressed in the compressor  66  and its temperature is thereby increased further. This second heat medium heats the third heat medium in the condenser  67 . The third heat medium warms the air in the cabin in the heater core  74 . A case of utilizing the heat of the outside air will be termed the heat pump mode. 
     The heat pump mode will be described. In the heat pump mode, the first heat medium is heated by the heat of the outside air in the low-temperature radiator  41 , and then the heated first heat medium heats the second heat medium in the chiller  52 . How the heat of the second heat medium warms the air in the cabin is as described above. In disclosure herein, how the heat of the outside air is transferred to the second heat medium for air conditioning in the cabin will be described. The heat pump mode is executed when the temperature of the first heat medium cooled in the chiller  52  is lower than the temperature of the outside air. 
     The heat pump mode is executed by the controller  80 . When the heat pump mode is selected, the controller  80  basically holds the three-way valves  42  and  49  at their second valve positions. How the first heat medium flows at this time is shown in  FIG.  2   .  FIG.  2    shows a part of the circulation path  22  of the second heat circuit  20 , but does not show the other elements of the second heat circuit  20  nor the third heat circuit  30 . 
     In the heat pump mode, the controller  80  controls the three-way valves  42 ,  49  synchronously. In the heat pump mode, the controller  80  basically holds both of the three-way valves  42  and  49  at the second positions. How the first heat medium flows at this time is shown in  FIG.  2   .  FIG.  2    shows a part of the second heat circuit  20  (circulation path  22 ), but does not show the other elements of the second heat circuit  20  nor the third heat circuit  30 . 
     In the heat pump mode, the controller  80  basically holds the three-way valves  42 ,  49  at the second valve positions to allow the flow of the first heat medium from the second channel  12  to the low-temperature radiator  41  and cut off the flow of the first heat medium from the first channel  11  to the low-temperature radiator  41 . As shown by a dashed arrow F 1  in  FIG.  2   , the first heat medium circulates between the chiller  52  and the low-temperature radiator  41 . At this time, the first heat medium in the first channel  11  bypasses the low-temperature radiator  41  and circulates through the SPU  46 , the PCU  47 , and the oil cooler  45 . 
     Firstly, the first heat medium flowing in the second channel  12  will be described. The first heat medium that has been cooled in the chiller  52  flows into the low-temperature radiator  41 . While passing through the low-temperature radiator  41 , the first heat medium is heated by the outside air. The first heat medium that has been heated by the outside air heats the second heat medium in the chiller  52 . As described above, the air in the cabin is warmed by the heat of the second heat medium. In other words, in the heat pump mode, the heat of the outside air is utilized to warm the air in the cabin. The temperature of the first heat medium decreases in the chiller  52 . The first heat medium with the decreased temperature returns to the low-temperature radiator  41  and absorbs heat from the outside air again. 
     In the heat pump mode, as shown by a dashed arrow F 2  in  FIG.  2   , the first heat medium in the first channel  11  does not pass through the low-temperature radiator  41 . The temperature of the first heat medium flowing in the first channel  11  keeps rising. If the temperature of the first heat medium flowing in the first channel  11  becomes excessively high, the first heat medium cannot cool the SPU  46 , the PCU  47 , nor the motor  55 . A temperature sensor  15  is disposed in the first heat circuit  10  between the SPU  46  and the PCU  47 , and the controller  80  monitors the temperature of the first heat medium that has passed through the SPU cooler  46   c . The controller  80  switches the three-way valves  42 ,  49  to their first valve positions in response to the temperature of the first heat medium that has passed through the SPU  46  (a measurement of the temperature sensor  15 ) becoming higher than an upper limit temperature. 
       FIG.  3    shows how the first heat medium flows after the three-way valves  42 ,  49  are switched to the first valve positions. When the three-way valves  42 ,  49  are switched to the first valve positions, the first heat medium is allowed to flow from the first channel  11  to the low-temperature radiator  41  and the first heat medium is stopped from flowing from the second channel  12  to low-temperature radiator  41 . The controller  80  keeps activating the pump  48 . Consequently, as shown by a dashed arrow F 3  in  FIG.  3   , the first heat medium whose temperature has become higher than the upper limit temperature in the first channel  11  flows into the low-temperature radiator  41 . When flowing into the low-temperature radiator  41 , the first heat medium is at a temperature higher than the temperature of the outside air. Thus, the first heat medium passing through the low-temperature radiator  41  releases the heat to the outside air. The SPU  46  and the PCU  47  are cooled by the first heat medium of which temperature has decreased by releasing the heat to the outside air. 
     When switching the three-way valve  42  on the first channel  11  to the first valve position, the controller  80  also switches the three-way valve  49  on the second channel  12  to the first valve position. When the three-way valve  49  is switched to the first valve position, the flow of the first heat medium from the chiller  52  to the low-temperature radiator  41  is cut off. In other words, the flow of the first heat medium from the second channel  12  to the low-temperature radiator  41  is cut off. As described above, in the heat pump mode, the temperature of the first heat medium flowing in the second channel  12  is lower than the temperature of the outside air, and the temperature of the first heat medium flowing in the first channel  11  is higher than the temperature of the outside air. If the first heat medium flowing in the first channel  11  merges with the first heat medium flowing in the second channel  12 , the temperature of the first heat medium flowing in the second channel  12  rises. The controller  80  cuts off the flow of the first heat medium from the second channel  12  to the low-temperature radiator  41  while the first heat medium is allowed to flow from the first channel  11  to the low-temperature radiator  41  for heat exchange between the low-temperature radiator  41  and the first heat medium whose temperature is higher than the temperature of the outside air. This prevents the first heat medium flowing in the first channel  11  from merging with the first heat medium flowing in the second channel  12 . 
     When the three-way valves  42 ,  49  are switched to the first valve positions, the flow of the first heat medium from the chiller  52  to the low-temperature radiator  41  is cut off. The first heat medium that has passed through the chiller  52  does not pass through the low-temperature radiator  41 . For a time period while the three-way valve  42  is held at the first valve position, the use of the heat of the outside air by the heat pump mode is suspended. 
     In the heat pump mode, the controller  80  switches the three-way valves  42 ,  49  to the first valve positions and activates the oil pump  44 . By the oil pump  44  being activated, the heat of the motor  55  is transferred to the first heat medium via the oil. The first heat medium that has absorbed the heat of the SPU  46  and the PCU  47  and the heat of the motor  55  flows into the low-temperature radiator  41  and releases the heat. 
     The controller  80  activates the oil pump  44  in response to the temperature of the oil becoming higher than a predetermined upper limit temperature. In the heat pump mode, however, the controller  80  switches the three-way valve  42  to the first valve position and activates the oil pump  44  even if the temperature of the oil does not reach the upper limit temperature. Such control enables the heat of the motor  55  to be released in the low-temperature radiator  41 . 
     With reference to  FIG.  4   , advantages obtained by switching the three-way valve  42  to the first valve position and activating the oil pump  44  in the heat pump mode will be described. 
     Timing chart (A) in  FIG.  4    shows changes in the temperature of the first heat medium measured by the temperature sensor  15  (see  FIG.  1   ). Timing chart (B) in  FIG.  4    shows changes in the temperature of the oil circulating in the oil circulation path  18 . Timing chart (C) in  FIG.  4    shows on and off timings of the oil pump  44 . In timing charts (A) to (C), changes during the heat pump mode are depicted by solid lines, while changes during times other than the heat pump mode are depicted by dashed lines. 
     As described with reference to  FIG.  2   , the controller  80  basically holds the three-way valves  42 ,  49  at the second valve positions in the heat pump mode. Due to heat generation of the SPU  46 , the PCU  47 , and the motor  55 , the temperature of the first heat medium in the first channel  11  gradually rises as shown in timing chart (A). When the temperature of the first heat medium becomes higher than an upper limit temperature hu (at time t 1 ), the controller  80  switches the three-way valves  42 ,  49  from the second valve positions to the first valve positions. As a result, the first heat medium is allowed to flow from the first channel  11  to the low-temperature radiator  41 , that is, the first heat medium that has absorbed heat from the SPU  46  and the like flows into the low-temperature radiator  41 . Since the first heat medium in the first channel  11  is cooled in the low-temperature radiator  41 , the temperature of the first heat medium gradually decreases. At this time, the flow of the first heat medium from the second channel  12  to the low-temperature radiator  41  is cut off, and the use of the heat of the outside air by the heat pump mode is suspended. 
     As shown in timing chart (B), the temperature of the oil gradually rises by the motor  55  being activated. Firstly, how the temperature of the oil changes during times other than the heat pump mode will be described. The controller  80  switches the three-way valves  42 ,  49  to the first valve positions in response to the temperature of the first heat medium becoming higher than the upper limit temperature hu (at time t 1 ). After time t 1 , the temperature of the first heat medium decreases. 
     A coil is a main source of the heat of the motor  55 , and switching elements are main sources of the heat of the SPU  46  and the PCU  47 . A heat capacity of the motor  55  is higher than those of the switching elements in the SPU  46  and the PCU  47 . Since the motor  55  has the high heat capacity, the temperature of the oil gently rises. Unless the temperature of the oil is higher than an upper limit temperature ou of an appropriate temperature range at time t 1 , the controller  80  does not activate the oil pump  44 . Consequently, as shown by the dashed line in timing chart (B), the temperature of the oil keeps rising even after time t 1 . 
     At time t 2 , the controller  80  returns the three-way valves  42 ,  49  to the second valve positions from the first valve positions. The flow of the first heat medium from the first channel  11  to the low-temperature radiator  41  is thereby cut off. The temperature of the first heat medium in the first channel  11  rises again. Meanwhile, after time t 2 , the first heat medium is allowed to flow from the second channel  12  to the low-temperature radiator  41  again and the heat pump mode restarts. 
     At time to 1 , the temperature of the oil becomes higher than the upper limit temperature ou. Since the temperature of the oil becomes higher than the upper limit temperature ou, the controller  80  activates the oil pump  44  (see timing chart (C)). Consequently, the oil is cooled by the first heat medium, and the temperature of the oil decreases. The controller  80  inactivates the oil pump  44  in response to the temperature of the oil becoming lower than a first lower limit temperature od 1  (at time to 2 ) (see timing chart (C)). Consequently, heat exchange in the oil cooler  45  between the oil and the first heat medium terminates, and the temperature of the oil gradually rises again. The controller  80  activates the oil pump  44  every time the temperature of the oil becomes higher than the upper limit temperature ou (at times to 3 , to 5 ). The controller  80  inactivates the oil pump  44  every time the temperature of the oil becomes lower than the first lower limit temperature od 1  (at times to 4 , to 6 ). 
     While the oil pump  44  is activated, the heat of the oil is transferred to the first heat medium, and thus the temperature of the first heat medium rises (times to 1  to to 2 , times to 3  to to 4 , and times toy to to 6 ). 
     The temperature of the first heat medium reaches the upper limit temperature hu at times t 1 , to 2 , to 4 , and to 6 . Every time the temperature of the first heat medium reaches the upper limit temperature hu, the controller  80  switches the three-way valves  42 ,  49  from the second valve positions to the first valve positions. That is, the three-way valves  42 ,  49  are switched frequently. Every time the three-way valves  42 ,  49  are switched to the first valve positions, the use of the heat of the outside air by the heat pump mode is suspended. If the heat pump mode is frequently suspended in the cabin air heating mode, the controller  80  activates the electric heater  71  (see  FIG.  1   ) to supplement shortage of heat. The electric heater  71  consumes electric power to generate heat. 
     The above-described phenomenon is caused by a fact that the temperature of the oil rises later than the time at which the SPU  46  and the PCU  47  generate heat due to the difference in heat capacity between the PCU  47  (the SPU  46 ) and the motor  55 . In the heat management system  100  according to the embodiment, the controller  80  controls the oil pump  44  such that the three-way valves  42 ,  49  are switched to the first valve positions less frequently in the heat pump mode. 
     Next, control by the controller  80  in the heat pump mode according to the present embodiment will be described. 
     In the heat pump mode, the controller  80  according to the embodiment switches the three-way valves  42 ,  49  from the second valve positions to the first valve positions, and at the same time, activates the oil pump  44 . In the heat pump mode, in response to the temperature of the first heat medium becoming higher than the upper limit temperature hu (at time t 1 ), the controller  80  activates the oil pump  44  in synchronization with the switching of the three-way valves  42 ,  49  to the first valve positions. Consequently, the heat of the oil (heat of the motor  55 ) is transferred to the first heat medium via the oil cooler  45 . The first heat medium that has absorbed the heat of the SPU  46  and the PCU  47  and the heat of the oil (heat of the motor  55 ) flows into the low-temperature radiator  41 , and the heat is released to the outside air. The heat of the oil (heat of the motor  55 ) is also simultaneously released to the outside air via the first heat medium. 
     The controller  80  inactivates the oil pump  44  and switches both of the three-way valves  42 ,  49  to the second valve positions in response to the temperature of the oil becoming lower than a second lower limit temperature od 2  (at time t 2 ). Thereafter, every time the temperature of the first heat medium becomes higher than the upper limit temperature hu, the controller  80  switches the three-way valves  42 ,  49  to the first valve positions and activates the oil pump  44  (at time t 3 ). The controller  80  inactivates the oil pump  44  and switches both of the three-way valves  42 ,  49  to the second valve positions every time the temperature of the oil becomes lower than the second lower limit temperature od 2  (at time t 4 ). In response to the three-way valves  42 ,  49  being switched to the second valve positions, the use of the heat of the outside air by the heat pump mode is restarted and the heat of the outside air is utilized to heat the air in the cabin. 
     As described above, in the heat pump mode, the controller  80  switches the three-way valves  42 ,  49  from the second valve positions to the first valve positions and activates the oil pump  44 . Such control decreases the frequency of the three-way valves  42 ,  49  being switched. The outside air can be utilized efficiently to heat the air in the cabin. 
     When the cabin air heating mode is selected, the temperature of the outside air may be low. If the temperature of the outside air is low and the first heat medium of which temperature is lower than the temperature of the outside air flows through the low-temperature radiator  41 , frost may form. Heat exchange efficiency of the low-temperature radiator  41  is decreased by frost forming on the low-temperature radiator  41 . Use efficiency of the heat of the outside air to heat the air in the cabin is thereby decreased. The decrease in heat exchange efficiency caused by frost formation is detected as a temperature difference of the first heat medium between at the inlet  41   i  and at the outlet  41   o  of the low-temperature radiator  41 . In addition to the above-described control, the controller  80  may switch both of the three-way valves  42 ,  49  to the first valve positions and activate the oil pump  44  in response to the temperature difference of the first heat medium between at the inlet  41   i  and at the outlet  41   o  of the low-temperature radiator  41  becoming smaller than a predetermined temperature difference threshold. This allows the heat of the oil to be utilized to melt the frost on the low-temperature radiator  41 . 
     (Second Embodiment) A heat management system  100  according to a second embodiment will be described. The heat management system  100  according to the second embodiment is the same as the heat management system  100  according to the first embodiment ( FIG.  1   ) in the structure, but is different therefrom in the control executed by the controller  80 . 
     While executing the heat pump mode, the controller  80  periodically switches the three-way valves  42 ,  49  to avoid frost formation on the low-temperature radiator  41 . While executing the heat pump mode, the controller  80  switches the three-way valves  42 ,  49  from the second valve positions to the first valve positions and activates the oil pump  44  periodically. The controller  80  returns the three-way valves  42 ,  49  to the second valve positions from the first valve positions and inactivates the oil pump  44  in response to a predetermined time having passed. Frost formation can be prevented by periodically delivering the first heat medium that has received heat from the oil to the low-temperature radiator  41 . 
     Before switching the three-way valves  42 ,  49  to the first valve positions, the controller  80  activates the oil pump  44  if the temperature of the oil is higher than the temperature of the first heat medium, to increase the temperature of the first heat medium by the heat of the oil. When the three-way valves  42 ,  49  are switched to the first valve positions, the heated first heat medium flows through the low-temperature radiator  41 . A higher defrosting effect can be expected. 
     With reference to  FIG.  5   , an example of process executed by the controller  80  will be described specifically. Timing chart (A) in  FIG.  5    shows changes in the temperature of the first heat medium measured by the temperature sensor  15  (see  FIG.  1   ). Timing chart (B) in  FIG.  5    shows changes in the temperature of the oil circulating in the oil circulation path  18 . Timing chart (C) in  FIG.  5    shows changes in the output of the oil pump  44 . Timing chart (C) in  FIG.  5    shows the output of the oil pump  44  in percentage. 
     While executing the heat pump mode, the controller  80  basically holds both of the three-way valves  42 ,  49  at the second valve positions to heat the air in the cabin by utilizing the heat of the outside air. The controller  80  switches both of the three-way valves  42 ,  49  to the first valve positions on a cycle s 1  and returns both of the three-way valves  42 ,  49  to the second valve positions in response to a predetermined time ds having passed. 
     As described with reference to  FIG.  2   , in the heat pump mode, the controller  80  basically holds the three-way valves  42 ,  49  at the second valve positions. As shown in timing chart (A) in  FIG.  5   , the temperature of the first heat medium in the first channel  11  gradually rises due to the heat of the SPU  46  and the PCU  47 . The motor  55  also generates heat, thus the temperature of the oil rises. At time t 5  in  FIG.  5   , the temperature of the oil becomes higher than the temperature of the first heat medium. In response to the temperature of the oil becoming higher than the first heat medium, the controller  80  activates the oil pump  44 . Heat is thereby transferred from the oil to the first heat medium in the oil cooler  45 . At this time (after time t 5 ), as shown in timing chart (C) in  FIG.  5   , the controller  80  sets an output Op of the oil pump  44  to its maximum (100%). Consequently, as shown between time t 5  and time t 6  in timing chart (A) in  FIG.  5   , the temperature of the first heat medium sharply rises. On the other hand, as shown between time t 5  and time t 6  in timing chart (B) in  FIG.  5   , the rise rate of the temperature of the oil is low. 
     The controller  80  of the heat management system  100  according to the second embodiment activates the oil pump  44  before switching the three-way valves  42 ,  49  to the first valve positions to heat the first heat medium by the heat of the oil. When the controller  80  switches the three-way valves  42 ,  49  to the first valve positions, the first heat medium that has absorbed the heat of the oil flows through the low-temperature radiator  41 . The heat management system  100  according to the second embodiment can defrost the low-temperature radiator  41  by further utilizing the heat of the oil. Simultaneously, the heat of the oil is released to the outside air. 
     As shown in timing chart (C) in  FIG.  5   , the controller  80  gradually decreases the output of the oil pump  44  from time t 6 . Consequently, the flow rate of the oil in the oil circulation path  18  decreases. The amount of heat transferred from the oil to the first heat medium in the oil cooler  45  decreases. As shown in timing chart (B) in  FIG.  5   , the rise rate of the temperature of the oil thus increases again from time t 6 . On the other hand, since the amount of heat the first heat medium absorbs from the oil decreases after time t 6 , the rise rate of the temperature of the first heat medium is lower than that from time t 5  to time t 6 . Consequently, it takes longer for the temperature of the first heat medium to become higher than the upper limit temperature hu. In the example of  FIG.  5   , the temperature of the first heat medium does not reach the upper limit temperature hu even after the cycle s 1  has passed. The controller  80  is configured to switch the three-way valves  42 ,  49  to the first valve positions, regardless of the cycle s 1 , in response to the temperature of the first heat medium becoming higher than the upper limit temperature hu to allow the heat of the first heat medium to be released in the low-temperature radiator  41 . Since the rise rate of the temperature of the first heat medium decreases by the output of the oil pump  44  being gradually decreased, the three-way valves  42 ,  49  do not have to be switched in the midst of the cycle s 1 . In other words, the frequency of the three-way valves  42 ,  49  being switched is not increased. 
     In a case where cooling of the oil should be prioritized, such as when the temperature of the oil is higher than the upper limit temperature ou and/or when the temperature of the motor  55  is higher than a threshold temperature, the controller  80  may not decrease the output of the oil pump  44 . 
     When the cycle s 1  has passed (at time ts), the controller  80  switches the three-way valves  42 ,  49  to the first valve positions. By the three-way valves  42 ,  49  being switched, the first heat medium in the first channel  11  flows into the low-temperature radiator  41  and the heat of the first heat medium is released to the outside air. Consequently, as shown in timing chart (A) in  FIG.  5   , the temperature of the first heat medium decreases after time ts. Since the temperature of the first heat medium decreases, the temperature of the oil also decreases as shown in timing chart (B) in  FIG.  5   . Thereafter, in response to the predetermined time ds having passed (at time t 7 ), the controller  80  returns the three-way valves  42 ,  49  to the second valve positions and inactivates the oil pump  44 . After time t 7 , the temperature of the first heat medium in the first channel  11  and the temperature of the oil rise again. The controller  80  switches the three-way valves  42 ,  49  from the second valve positions to the first valve positions on the cycle s 1 . 
     At time t 8 , the temperature of the oil becomes higher than the temperature of the first heat medium again. The process from time t 5  to time t 7  is repeated from time t 8  to time t 10 . The first heat medium in the first channel  11  repeatedly flows through the low-temperature radiator  41  on the cycle s 1 , and frost formation is thereby prevented. 
     The controller  80  may inactivate the oil pump  44  in response to the temperature of the oil becoming lower than a second lower limit temperature od 2  before the predetermined time ds passes. This prevents the temperature of the oil from decreasing excessively. Moreover, the cycle s 1  and the predetermined time ds are varied depending on conditions such as the capacities of the pump  48  and the oil pump  44 , set temperatures for the oil and the first heat medium in the first channel  11 , etc. For example, when the temperature of the motor  55  is obviously higher than the temperature of the oil, the output of the oil pump  44  may be decreased by shortening the cycle s 1 , to increase the frequency of switching to the first valve positions. 
     Points to be noted relating to the technology described in the embodiments will be listed. The SPU  46  and the PCU  47  are examples of “power converter”. The SPU cooler  46   c  and the PCU cooler  47   c  are examples of “converter cooler”. The low-temperature radiator  41  is an example of “first heat exchanger”, and the chiller  52  is an example of “second heat exchanger”. In the above-described embodiments, the three-way valves  42 ,  49  configure “channel valve”. 
     Variants of the above-described embodiments will be described below. 
     (First Variant) The above-described first embodiment describes the control by the controller  80  while the controller  80  executes the heat pump mode. However, the heat management system  100  is not limited to the configuration shown in  FIG.  1   . For example, the second heat exchanger may be a device configured to transfer heat from the second heat medium to the first heat medium. The controller  80  basically holds the three-way valves  42 ,  49  at the second valve positions to allow the first heat medium to flow from the second channel  12  to the low-temperature radiator  41 , as a result of which the heat of the second heat medium is released in the low-temperature radiator  41  via the first heat medium. The controller  80  switches the three-way valves  42 ,  49  to the first valve positions and activates the oil pump  44 . The first heat medium that has absorbed the heat of the oil is cooled in the low-temperature radiator  41 . The heat of the oil is effectively released to the outside air. 
     (Second Variant) In the first embodiment, the controller  80  determines that frost may form on the low-temperature radiator  41  when the temperature difference of the first heat medium between at the inlet  41   i  and at the outlet  41   o  of the low-temperature radiator  41  becomes smaller than the temperature difference threshold. In response to determining that frost may form, the controller  80  switches the three-way valves  42 ,  49  from the second valve positions to the first valve positions and activates the oil pump  44 . In a second variant, the controller  80  may determine that frost may form based on a speed of the outside air passing through the low-temperature radiator  41 , for example. 
     (Third Variant) In the above-described embodiments, the controller  80  inactivates the oil pump  44  in response to the temperature of the oil becoming lower than the second lower limit temperature od 2  during the heat pump mode. Alternatively, in a third variant, the controller  80  may inactivate the oil pump  44  in response to the temperature of the first heat medium becoming lower than the first lower limit temperature od 1 . 
     (Fourth Variant) In the above-described embodiments, the flow of the first heat medium is controlled by using the two three-way valves  42 ,  49 , but it may be controlled differently. For example, a heat management system  100  that does not include the battery channel  14  may be provided with a stop valve configured to cut off the flow of the first heat medium from the second channel  12  to the low-temperature radiator  41 , in place of the three-way valve  49 . 
     While specific examples of the present disclosure have been described above in detail, these examples are merely illustrative and place no limitation on the scope of the patent claims. The technology described in the patent claims also encompasses various changes and modifications to the specific examples described above. The technical elements explained in the present description or drawings provide technical utility either independently or through various combinations. The present disclosure is not limited to the combinations described at the time the claims are filed. Further, the purpose of the examples illustrated by the present description or drawings is to satisfy multiple objectives simultaneously, and satisfying any one of those objectives gives technical utility to the present disclosure.