Motor cooling system

Abstract

In a motor cooling system that cools a motor using a refrigerant containing oil in CO2, oil in the motor is reliably discharged. A motor cooling system (100) mounted on a vehicle (200) is provided with: a compressor (3) for compressing a refrigerant containing oil in CO2; a heat exchanger (5) for cooling the refrigerant compressed by the compressor (3); an electric machine (1) for driving the vehicle (200); refrigerant passages (23, 24) for supplying the refrigerant cooled by the heat exchanger (5) into the motor (1); and a control device (80) configured so as to control the compressor (3), the control device (80) being configured so as to control the compressor (3) so as to generate a supercritical refrigerant in order to supply the supercritical refrigerant from the refrigerant passage (24) into the motor (1) when the supercritical refrigerant supply condition is satisfied.

Description

Technical Field

[0001] This invention relates to an electric motor cooling system for cooling an electric motor in a vehicle. Background Technology

[0002] In recent years, the practical application of electric vehicles has led to the development of small, high-performance motors. These high-performance motors require, in particular, increased output and torque per unit volume. Furthermore, with the increase in motor output and torque, efficient motor cooling is also required. Based on these requirements, technologies such as air cooling, water cooling, and oil cooling for motors have been developed.

[0003] As a method for cooling an electric motor, a method of directly supplying refrigerant to the motor is considered. For example, Patent Document 1 describes a motor cooling structure that uses a refrigerant (ATF (Automatic Transmission Fluid), etc.) to cool magnets embedded in the rotor of the motor. This motor cooling structure forms a refrigerant passage extending from the magnets within the axial rotor of the motor, and cools the magnets by supplying refrigerant through this passage.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent document 1: Japanese Patent Application Publication No. 2022-114761.

[0007] The technical problem that the invention aims to solve

[0008] Here, when using refrigerant to cool the motor, a method of supplying refrigerant between the rotor and stator is considered. In this case, the stirring resistance of the refrigerant between the rotor and stator varies quadratically with the motor speed. That is, as the motor speed increases, the stirring resistance becomes very large. Therefore, in motors of electric vehicles and the like, which operate at ultra-high speeds, there is a tendency to generate large resistance. In particular, when a high-viscosity fluid is used as the refrigerant, very large resistance is generated.

[0009] Therefore, the inventors of this invention considered using a refrigerant composed of low-viscosity CO2 (hereinafter sometimes referred to as "CO2 refrigerant," or simply "refrigerant") to balance reduced stirring resistance and improved cooling performance. Such a CO2 refrigerant has high insulation properties, and furthermore, as it is a so-called natural refrigerant, its impact on the environment and human health has been taken into consideration.

[0010] However, the refrigerants described above typically contain a small amount of oil (PAG, etc.). This is because a compressor is used to ensure the refrigerant supplied to the motor is in the desired state, but oil is required for lubrication within the compressor. Furthermore, the bearings supporting the rotating shaft of the motor also use lubricating oil. Consequently, not only CO2 but also oil enters the motor; that is, oil enters the gap between the rotor and stator, thereby forming an oil film (in other words, oil accumulation) in this gap, creating a technical problem of increased stirring resistance. Summary of the Invention

[0011] The present invention was made to solve the problems of the prior art mentioned above, and its purpose is to reliably discharge the oil inside the motor in a motor cooling system that uses a refrigerant containing oil in CO2 to cool the motor.

[0012] Technical means for solving technical problems

[0013] To achieve the above objectives, the present invention relates to a motor cooling system for a vehicle, comprising: a compressor for compressing a refrigerant containing oil in CO2; a heat exchanger for cooling the refrigerant compressed by the compressor; a motor for driving the vehicle; a refrigerant passage for supplying the refrigerant cooled by the heat exchanger into the motor to cool the motor; and a control device configured to at least control the compressor, the control device being configured to control the compressor to generate supercritical refrigerant in order to supply supercritical refrigerant into the motor from the refrigerant passage when predetermined conditions are met.

[0014] According to the present invention configured in this way, by supplying a supercritical refrigerant into the motor, the compatibility of the supercritical refrigerant can be utilized to draw in oil within the motor and effectively discharge the oil along with the refrigerant. This removes the oil film (in other words, oil buildup) formed within the motor and suppresses the increase in stirring resistance caused by oil within the motor.

[0015] In this invention, it is preferred that the control device is configured to control the compressor to generate a refrigerant in a supercritical state when the specified conditions are met, and to control the compressor to generate a refrigerant in a liquid state when the specified conditions are not met.

[0016] In this invention, when the specified conditions are not met, the control device limits the supply of supercritical refrigerant by supplying liquid refrigerant into the motor; that is, it prevents the unnecessary supply of supercritical refrigerant. This reduces the load on the compressor used to generate the supercritical refrigerant and suppresses the increase in resistance caused by supplying supercritical refrigerant into the motor.

[0017] In this invention, preferably, the control device is configured to, after a predetermined condition is met, terminate the supply of supercritical refrigerant when a predetermined time has elapsed since the start of supplying supercritical refrigerant into the motor, and control the compressor to generate liquid refrigerant in order to supply liquid refrigerant into the motor.

[0018] According to the present invention configured in this way, by supplying supercritical refrigerant for a certain period of time, the supply of supercritical refrigerant can be stopped when the oil discharge in the motor is completed. As a result, the load on the compressor used to generate supercritical refrigerant can be reduced. That is, the power consumption of the compressor can be suppressed.

[0019] In this invention, preferably, the refrigerant passage has a first passage and a second passage. The first passage is used to supply supercritical refrigerant to the motor, and the second passage is used to supply liquid refrigerant to the motor. The motor cooling system also has a valve disposed in the first passage and / or the second passage. The control device is configured such that, when a predetermined condition is met, the control valve supplies supercritical refrigerant to the motor from the first passage, and when the predetermined condition is not met, the control valve supplies liquid refrigerant to the motor from the second passage.

[0020] According to the present invention configured in this way, by switching the refrigerant flow path (first path, second path) by controlling the valve, the refrigerant supplied to the motor can be easily switched between a supercritical refrigerant and a liquid-phase refrigerant.

[0021] In this invention, preferably, the motor cooling system also includes a motor speed sensor for detecting the motor speed, and the control device is configured to determine that a predetermined condition is met when the speed (motor speed) detected by the motor speed sensor is less than a predetermined speed.

[0022] According to the present invention configured in this way, a supercritical refrigerant can be supplied when the motor is rotating at low speed, and the increase in resistance caused by supplying a supercritical refrigerant into the motor can be effectively suppressed.

[0023] In this invention, preferably, the control device is configured such that, during the period when a supercritical refrigerant is supplied to the motor under specified conditions, when the rotational speed is above a specified speed, the supply of supercritical refrigerant is terminated, and in order to supply liquid refrigerant to the motor, the compressor is controlled to generate liquid refrigerant.

[0024] According to this invention, when the motor speed increases (typically during acceleration), the operation of the compressor used to generate the supercritical refrigerant is stopped, thereby suppressing the compressor's power consumption. As a result, power can be transferred to the motor, accurately meeting the vehicle's acceleration requirements.

[0025] In this invention, preferably, the motor cooling system further includes at least one of an acceleration sensor, a camera, a distance sensor, and a GPS sensor. The acceleration sensor detects the acceleration of the vehicle, the camera captures images of the vehicle's surroundings, the distance sensor detects the distance between the vehicle and objects existing in the vehicle's surroundings, and the GPS sensor detects the vehicle's current position. The control device is configured to predict the vehicle's stopping based on signals obtained from at least one of the acceleration sensor, camera, distance sensor, and GPS sensor, and to determine that a predetermined condition is met when the vehicle's stopping is predicted.

[0026] In this invention, considering that generating supercritical refrigerant in the compressor requires a certain amount of time, the compressor for generating supercritical refrigerant is started in advance, anticipating the moment the vehicle stops before the motor actually starts rotating at low speed. Therefore, supercritical refrigerant can be reliably supplied even when the motor is rotating at low speed, accurately balancing the suppression of increased resistance caused by supplying supercritical refrigerant to the motor and ensuring oil discharge from the motor by supercritical refrigerant.

[0027] In this invention, preferably, the motor cooling system also includes a pedal sensor that detects pedal operations performed by the driver to apply braking force to the vehicle, and the control device is configured to determine that a predetermined condition is met when the pedal operation is detected by the pedal sensor.

[0028] In this invention, considering that generating supercritical refrigerant in the compressor requires a certain amount of time, the compressor for generating supercritical refrigerant begins operation in advance, at the moment the pedal sensor detects pedal operation for braking the vehicle before the motor actually rotates at low speed. Therefore, supercritical refrigerant can be reliably supplied even when the motor is rotating at low speed, reliably suppressing the increase in resistance caused by supplying supercritical refrigerant to the motor and ensuring oil discharge from the motor by supercritical refrigerant.

[0029] In this invention, preferably, the motor cooling system also includes an oil tank and an oil level sensor. The oil tank stores oil, and the oil level sensor detects the level of the oil stored in the oil tank. The control device is configured to determine that a predetermined condition is met when the level detected by the oil level sensor is above a first predetermined value and below a second predetermined value that is greater than the first predetermined value.

[0030] According to the present invention configured in this way, the supply of refrigerant in a supercritical state is controlled by determining the oil level based on the first and second predetermined values. When there is a relatively large amount of oil in the motor, compressor sintering and other problems caused by insufficient oil in the refrigerant can be prevented, and the oil in the motor can be reliably discharged.

[0031] In this invention, preferably, the motor has a rotor and a stator, a rotating shaft connected to the rotor, and a sliding bearing supporting the rotating shaft, and is configured to supply refrigerant from a refrigerant passage to the space between the rotor and the stator. The motor cooling system also has a refrigerant passage different from the refrigerant passage for supplying refrigerant to the sliding bearing, and an oil passage for supplying oil to the sliding bearing.

[0032] The effects of the invention

[0033] According to the present invention, in a motor cooling system that uses a refrigerant containing oil in CO2 to cool the motor, the oil inside the motor can be reliably discharged. Attached Figure Description

[0034] Figure 1 This is a schematic structural diagram of a vehicle using an electric motor cooling system according to an embodiment of the present invention.

[0035] Figure 2 This is a schematic structural diagram of the motor cooling system according to an embodiment of the present invention.

[0036] Figure 3 This is an enlarged schematic structural diagram of the motor periphery of the motor cooling system according to an embodiment of the present invention.

[0037] Figure 4 This is a block diagram illustrating the electrical structure of a motor cooling system according to an embodiment of the present invention.

[0038] Figure 5 This is a timing diagram illustrating the control of an embodiment of the present invention.

[0039] Figure 6 This is a flowchart illustrating the control process of an embodiment of the present invention.

[0040] Figure 7 This is a timing diagram illustrating the control of a modified example of an embodiment of the present invention.

[0041] Figure 8 This is a flowchart illustrating a modified example of an embodiment of the present invention.

[0042] Symbol Explanation

[0043] 1 motor

[0044] 3 compressors

[0045] 5 heat exchangers

[0046] 6 fuel tanks

[0047] 11 rotors

[0048] 12 stators

[0049] 13 rotating axes

[0050] 15 sliding bearings

[0051] 21-24, 26 Refrigerant passages

[0052] 25 Mixed Fluid Path

[0053] 27 oil passages

[0054] 30 Cooling valve

[0055] 31 Discharge valve

[0056] 80 control device

[0057] 100 motor cooling system

[0058] 200 vehicles. Detailed Implementation

[0059] Hereinafter, the motor cooling system according to an embodiment of the present invention will be described with reference to the accompanying drawings.

[0060] [Overall Structure]

[0061] First, refer to Figure 1 This is a schematic structural diagram of a vehicle that uses the motor cooling system of this embodiment.

[0062] like Figure 1 As shown, the vehicle 200 is, for example, an electric vehicle, and has a motor cooling system 100. The motor cooling system 100 mainly includes: a motor 1 that generates power to drive the vehicle 200; a compressor 3 that compresses the refrigerant supplied to the motor 1; and a heat exchanger 5 that includes a condenser, a fan, etc., for cooling the refrigerant compressed by the compressor 3.

[0063] The motor cooling system 100 circulates the refrigerant in the refrigeration cycle. Specifically, it circulates CO2 refrigerant (hereinafter sometimes simply referred to as "refrigerant"), which is a natural refrigerant. This CO2 refrigerant contains not only CO2 but also oils such as PAG (refrigeration oil) (and may also contain additives). Because of the use of this CO2 refrigerant, the compressor 3 is configured to compress the refrigerant to a very high pressure. The motor 1 uses the refrigerant compressed by the compressor 3 (typically a liquid refrigerant) for cooling the rotor and stator; and for lubricating the sliding bearings supporting the rotating shaft. In this case, the motor 1 functions as an expansion valve and evaporator in the refrigeration cycle. For example, in the motor cooling system 100, high-temperature liquid refrigerant is supplied from the compressor 3 to the heat exchanger 5, low-temperature liquid refrigerant is supplied from the heat exchanger 5 to the motor 1, and high-temperature gaseous refrigerant is supplied from the motor 1 to the compressor 3. Furthermore, the refrigerant compressed by the compressor 3 can also be used for air conditioning in air conditioners, battery cooling, etc.

[0064] [Structure of the motor cooling system]

[0065] Next, refer to Figures 2 to 4 The motor cooling system 100 of this embodiment will be described in detail.

[0066] first, Figure 2 This is a schematic structural diagram of the motor cooling system 100 according to this embodiment. Figure 2 As shown, in addition to the motor 1, compressor 3, and heat exchanger 5 described above, the motor cooling system 100 also includes: an oil tank 6 for storing oil; refrigerant passages 21-24, 26 for refrigerant (CO2 refrigerant) flow; a mixed fluid passage 25 for a mixture of refrigerant and oil; and an oil passage 27 for oil flow. Furthermore, as... Figure 2 As shown, the motor 1 has a rotating shaft 13 and a pair of sliding bearings 15 supporting the rotating shaft 13.

[0067] Refrigerant passage 21 is a passage for supplying refrigerant from compressor 3 to motor 1 and the like via heat exchanger 5. Downstream of heat exchanger 5, it branches into refrigerant passage 22, refrigerant passage 23, and refrigerant passage 24. A refrigerant pressure sensor 51 for detecting the pressure of the refrigerant is provided in refrigerant passage 21.

[0068] Refrigerant passage 22 is for supplying refrigerant to the sliding bearing 15, and refrigerant passages 23 and 24 are for supplying refrigerant to the motor 1. Specifically, refrigerant passage 23 is for supplying liquid-phase refrigerant to the motor 1 (equivalent to the "second passage" in this invention), and refrigerant passage 24 is for supplying supercritical refrigerant to the motor 1 (equivalent to the "first passage" in this invention). The refrigerant supplied from refrigerant passage 22 to the sliding bearing 15 is used for lubrication of the sliding bearing 15; the refrigerant supplied from refrigerant passage 23 to the motor 1 is used for cooling within the motor 1; and the refrigerant supplied from refrigerant passage 24 to the motor 1 is used for draining oil from within the motor 1.

[0069] In addition, a check valve 35 is provided in the refrigerant passage 22. Furthermore, a cooling valve 30 is provided in the refrigerant passage 23, which can switch the supply / cut-off of refrigerant based on the passage by opening and closing, and a discharge valve 31 is provided in the refrigerant passage 24, which can switch the supply / cut-off of refrigerant based on the passage by opening and closing.

[0070] Furthermore, it is not limited to installing valves (cooling valve 30 and discharge valve 31) in refrigerant passages 23 and 24 respectively; that is, it is not limited to using two valves. In other examples, a valve may be installed in either of the refrigerant passages 23 and 24, or a three-way valve may be installed at the branch point of the refrigerant passages 23 and 24, using such a valve to allow refrigerant to flow in either of the refrigerant passages 23 and 24.

[0071] The mixing fluid passage 25 is a passage for supplying a mixture of refrigerant and oil discharged from the motor 1 to the oil tank 6. The oil tank 6 is configured to separate the oil (gas-liquid separation) from the mixture supplied from the mixing fluid passage 25 and store the separated oil. On the other hand, the remaining refrigerant (which also contains a small amount of oil) is supplied to the compressor 3 through the refrigerant passage 26. In addition, an oil level sensor 52 is provided in the oil tank 6 to detect the level of the stored oil.

[0072] Oil passage 27 is a passage for supplying oil stored in oil tank 6 to sliding bearing 15. The oil supplied to sliding bearing 15, together with the aforementioned refrigerant, is used for lubrication of sliding bearing 15. Oil passage 27 is equipped with oil pump 33 for pressurizing oil, oil pressure sensor 53 for detecting oil pressure, and check valve 36.

[0073] Furthermore, in the motor cooling system 100 described above, since the refrigerant is supplied (specifically, ejected) into the motor 1 through refrigerant passages 23 and 24 and its pressure is reduced, the motor 1 functions as an expansion valve in the refrigeration cycle. Additionally, since the refrigerant supplied in this way undergoes heat exchange within the motor 1 (during which the refrigerant absorbs heat and evaporates), the motor 1 functions as an evaporator in the refrigeration cycle.

[0074] then, Figure 3 This is an enlarged schematic structural diagram showing the area around the motor 1 in the motor cooling system 100 of this embodiment. Specifically, Figure 3 This is a cross-sectional view of motor 1 viewed along the axial direction. Furthermore, in Figure 3 The diagram illustrates the state of supercritical refrigerant being supplied from refrigerant passage 24 into motor 1.

[0075] like Figure 3 As shown, the motor 1 of the motor cooling system 100 includes: a rotor 11 and a stator 12; a rotating shaft 13 connected to the rotor 11 and one end connected to the drive axle (not shown) of the vehicle 200; a pair of sliding bearings 15 supporting the rotating shaft 13 of the motor 1; and a housing 14 housing the rotor 11, stator 12, rotating shaft 13 and sliding bearings 15.

[0076] Additionally, a side of the housing 14 of the motor 1 is provided for sealing the rotating shaft 13 connected to the drive axle, etc. Figure 3 The left side of the image shows a sealing member 18 (on one side where the sliding bearing 15 is located). This sealing member 18 is configured to prevent leakage of fluid from the gap between the portion of the rotating shaft 13 extending outward from the housing 14 and the housing 14. The sealing member 18 is configured as a mechanical seal that supplies oil from the aforementioned oil passage 27 to prevent fluid leakage.

[0077] Furthermore, such as Figure 3 As shown, in the motor cooling system 100, the refrigerant passage 22 is configured to supply refrigerant to a pair of sliding bearings 15 in the motor 1, and the refrigerant passage 23 is configured to supply refrigerant (in liquid phase) to the gap between the rotor 11 and the stator 12 in the motor 1. In particular, the refrigerant passage 23 branches into two passages downstream of the cooling valve 30, and refrigerant is supplied to the gap between the rotor 11 and the stator 12 from these two passages.

[0078] Furthermore, the refrigerant passage 24 branches into four refrigerant passages 24a to 24d at the branch 24x located downstream of the discharge valve 31, and refrigerant (supercritical refrigerant) is supplied to the motor 1 from these refrigerant passages 24a to 24d respectively. Specifically, refrigerant passages 24a and 24b are configured to supply refrigerant to the gap between the rotor 11 and the stator 12, especially to the central portion of the rotor 11 and the stator 12 in the axial direction, while refrigerant passages 24c and 24d are configured to supply refrigerant from the sides of the rotor 11 and the stator 12.

[0079] Here, as described in the "Technical Problem to be Solved by the Invention" above, since the refrigerant (CO2 refrigerant) contains oil, and since the sliding bearing 15 uses oil, not only CO2 but also oil enters the gap between the rotor 11 and the stator 12, thereby forming an oil film in the gap (in other words, oil accumulation) (see reference). Figure 3 (See arrow A1 in the diagram). As a result, an increase in stirring resistance occurs in motor 1.

[0080] To address this technical problem, in this embodiment, supercritical refrigerant is supplied to the motor 1 through refrigerant passage 24. Supercritical refrigerant has high compatibility with oil, thus effectively drawing in oil. Therefore, by supplying supercritical refrigerant to the gap between rotor 11 and stator 12, oil located in this gap can be accurately drawn in by the refrigerant, and the drawn-in oil, along with the refrigerant, is discharged from the mixing fluid passage 25. As a result, the oil film formed in the gap between rotor 11 and stator 12 can be removed, preventing an increase in stirring resistance. Furthermore, in this embodiment, refrigerant is supplied to areas within the motor 1 prone to stirring resistance (see reference 24d) using four refrigerant passages 24a to 24d. Figure 3 (The refrigerant supply status is shown).

[0081] Next, refer to Figure 4 The electrical structure of the motor cooling system 100 of this embodiment will be described. Figure 4 This is a block diagram showing the electrical structure of the motor cooling system 100 in this embodiment.

[0082] like Figure 4 As shown, the motor cooling system 100 has a control device 80 configured to perform various controls within the system. The control device 80 is a computer comprising a memory 80b having one or more processors 80a (typically a CPU), various programs (including basic control programs such as an OS, and application programs that start on the OS and perform specific functions) and various data such as ROM and RAM stored on the processor 80a for interpretation and execution.

[0083] In addition, the motor cooling system 100 includes the aforementioned sensors 51-53 (see reference). Figure 2 In addition to the motor speed sensor 54, which detects the rotational speed of the motor 1 (the rotational speed of the rotor 11 and the rotating shaft 13, which is synonymous with rotational speed), the vehicle speed sensor 55, which detects the speed of the vehicle 200, the acceleration sensor 56, which detects the acceleration of the vehicle 200, the throttle sensor 57, which detects the operation of the accelerator pedal in the vehicle 200 (especially the accelerator pedal opening), the brake sensor 58, which detects the operation of the brake pedal in the vehicle 200, the camera 59, which captures the surroundings of the vehicle 200 (typically the front), the distance sensor 60, which detects the distance between the vehicle 200 and objects in its surroundings (typically the vehicle in front), and the GPS (Global Positioning System) sensor 61, which detects the current position of the vehicle 200.

[0084] For example, the distance sensor 60 is a millimeter-wave radar, lidar, ultrasonic sensor, etc., and in a typical example, LiDAR (Light Detection and Ranging) is used. The GPS sensor 61 includes a GPS receiver, a gyroscope sensor, etc. In addition, the throttle sensor 57 and the brake sensor 58 are examples of the "pedal sensors" in this invention.

[0085] Based on the detection signals from these sensors 51-61, the control device 80 supplies control signals to the motor 1, compressor 3, cooling valve 30, discharge valve 31, oil pump 33, and oil level warning light 34. The oil level warning light 34 is used to warn that the oil level (detected by oil level sensor 52) stored in the oil tank 6 is below a specified value.

[0086] In this embodiment, the control device 80 mainly controls the compressor 3 to generate refrigerant in liquid phase or supercritical state, and controls the opening and closing of the switching cooling valve 30 and the discharge valve 31 to supply the refrigerant in liquid phase or supercritical state from the refrigerant passage 23 or the refrigerant passage 24 to the motor 1.

[0087] [Control Methods]

[0088] Next, in this embodiment, the control of the motor cooling system 100 by the control device 80 will be specifically described.

[0089] In this embodiment, the control device 80 determines whether supercritical refrigerant should be supplied to the motor 1 (this is used to determine whether the "prescribed conditions" in this invention are met). If it is determined that supercritical refrigerant should be supplied to the motor 1, the compressor 3 is controlled to generate supercritical refrigerant, and the cooling valve 30 is closed while the discharge valve 31 is opened to supply the supercritical refrigerant to the motor 1 through the refrigerant passage 24. As a result, oil located in the gap between the rotor 11 and the stator 12 is drawn in by the supercritical refrigerant supplied to the motor 1, and this oil is discharged together with the refrigerant. This removes the oil film (in other words, oil accumulation) formed in the gap between the rotor 11 and the stator 12, preventing an increase in stirring resistance.

[0090] In contrast, when the control device 80 determines that supercritical refrigerant should be supplied to the motor 1, i.e., when liquid refrigerant should be supplied to the motor 1, it controls the compressor 3 to generate liquid refrigerant and controls the opening of the cooling valve 30 and the closing of the discharge valve 31 to supply the liquid refrigerant to the motor 1 through the refrigerant passage 23. This avoids unnecessarily supplying supercritical refrigerant to the motor 1. Consequently, the load on the compressor 3 used to generate supercritical refrigerant is reduced, and the increase in resistance caused by supplying supercritical refrigerant to the motor 1 is suppressed. Furthermore, compared to supplying supercritical refrigerant to the motor 1, supplying liquid refrigerant to the motor 1 tends to reduce refrigerant stirring resistance. This is because when liquid refrigerant is supplied to the motor 1, the refrigerant changes from a liquid phase to a gas phase (including a gas-liquid mixture) within the motor 1.

[0091] Furthermore, the control device 80, after a predetermined time has elapsed since the start of supplying supercritical refrigerant to the motor 1 as described above, terminates the supply of supercritical refrigerant and controls the opening and closing of the compressor 3 and the switching valve 30 and the discharge valve 31 to supply liquid refrigerant to the motor 1. Thus, by supplying supercritical refrigerant for a certain period, the supply of supercritical refrigerant terminates when the oil discharge from the motor 1 is complete. This reduces the load on the compressor 3 used to generate supercritical refrigerant. From this perspective, the predetermined time is determined based on the time during which supercritical refrigerant should be supplied before the oil discharge from the motor 1 is complete.

[0092] Furthermore, when the following exemplified determination condition (an example equivalent to the "prescribed condition" in this invention, hereinafter appropriately referred to as the "supercritical refrigerant supply condition") is met, the control device 80 controls the supply of the supercritical refrigerant to the motor 1. When the supercritical refrigerant supply condition is not met, the control device 80 controls the supply of the liquid refrigerant to the motor 1. Additionally, when supplying supercritical refrigerant, the control device 80 sets the "discharge increase request flag" to ON in order to increase the discharge rate of the compressor 3.

[0093] In the first example, the control device 80 determines that the supercritical refrigerant supply condition is met when the motor speed detected by the motor speed sensor 54 is lower than the specified speed. This is done to suppress the increase in resistance caused by supplying supercritical refrigerant into the motor 1, and to supply supercritical refrigerant while the motor 1 is rotating at a low speed. This is because the stirring resistance of the refrigerant is smaller at low speeds compared to high speeds. Furthermore, from this perspective, when the motor speed is lower than the specified speed, the control device 80, while supplying supercritical refrigerant into the motor 1, stops the supply of supercritical refrigerant when the motor speed reaches or exceeds the specified speed. To supply liquid refrigerant into the motor 1, the compressor 3 is controlled, and the opening and closing of the cooling valve 30 and the discharge valve 31 are switched. Moreover, the specified speed is set based on the premise that the stirring resistance of the refrigerant (especially the supercritical refrigerant) is lower than the specified motor speed.

[0094] As a second example, the control device 80 predicts the stopping of the vehicle 200 based on signals obtained from at least one of the acceleration sensor 56, camera 59, distance sensor 60, and GPS sensor 61. If the stopping of the vehicle 200 is predicted, it determines that the supercritical refrigerant supply condition is met. In this second example, to suppress the increase in resistance caused by supplying supercritical refrigerant to the motor 1, it is also generally sought to supply supercritical refrigerant when the motor 1 is rotating at a low speed. In particular, in this second example, considering that it takes a certain amount of time for the compressor 3 to generate supercritical refrigerant, the operation of the compressor 3 for generating supercritical refrigerant is started in advance at the moment when the vehicle 200 is predicted to stop, before the motor 1 actually reaches a low speed (i.e., before the vehicle 200 almost stops). Furthermore, when the stopping of the vehicle 200 is predicted in this way, the control device 80 sets the "stop prediction flag" to ON.

[0095] As a third example, when the control device 80 detects a pedal operation by the driver to apply braking force to the vehicle 200, specifically when the brake sensor 58 detects a brake pedal depressing operation, it determines that the supercritical refrigerant supply condition has been met. In this third example, in order to suppress the increase in resistance caused by supplying supercritical refrigerant to the motor 1, it is also generally sought to supply supercritical refrigerant when the motor 1 is rotating at a low speed. In particular, in this third example, considering that it takes a certain amount of time for the compressor 3 to generate supercritical refrigerant, the operation of the compressor 3 for generating supercritical refrigerant is started in advance at the moment when the brake pedal is depressed before the motor 1 actually reaches a low speed (i.e., before the vehicle 200 almost stops).

[0096] As a fourth example, the control device 80 determines that the supercritical refrigerant supply condition is met when the oil level detected by the oil level sensor 52 is above the first liquid level (first predetermined value) and below the second liquid level (second predetermined value), which is higher than the first liquid level. Here, firstly, the case where the oil level is below the second liquid level refers to a situation where the oil level in the oil tank 6 is relatively low, which can be interpreted as meaning there is a relatively large amount of oil in the motor 1. In this case, the oil in the motor 1 should be discharged through the supercritical refrigerant. Secondly, the case where the oil level is above the first liquid level refers to a situation where the refrigerant contains an amount of oil sufficient to reliably operate the compressor 3. That is, when the compressor 3 is operated to generate supercritical refrigerant, the compressor 3 can be reliably lubricated with the oil contained in the refrigerant to prevent sintering or other defects in the compressor 3. In this way, by controlling the supply of refrigerant in a supercritical state based on the determination results of the oil level using the first and second liquid levels, when there is a relatively large amount of oil in the motor 1, it is possible to prevent the compressor 3 from sintering due to insufficient oil in the refrigerant, and to reliably discharge the oil in the motor 1.

[0097] Furthermore, in the above, four examples of determination conditions were shown as supercritical refrigerant supply conditions, but it is not limited to using only one of these four determination conditions; any two or more of these four determination conditions can be used in combination.

[0098] Next, refer to Figure 5 The control process performed by the control device 80 in this embodiment will be explained. Figure 5 This is a timing diagram illustrating the control in this embodiment. Figure 5 From top to bottom, the following parameters are displayed: ON / OFF of the stop prediction flag, motor speed, ON / OFF of the brake pedal, ON / OFF of the discharge increase request flag, opening and closing of the discharge valve 31, and the time variation of opening and closing of the cooling valve 32. Here, the first to third examples described above are used as examples of supercritical refrigerant supply conditions.

[0099] First, at time t11, the control device 80 predicts the stopping condition of the vehicle 200 based on signals obtained from at least one of the acceleration sensor 56, camera 59, distance sensor 60, and GPS sensor 61, thereby setting the stop prediction flag to ON. Then, at time t12, the motor speed is less than a predetermined speed N1, and the brake pedal is ON (i.e., the brake pedal is depressed). At this time t12, the control device 80 sets the discharge increase requirement flag ON, controls the compressor 3 to generate supercritical refrigerant, and controls the opening of the discharge valve 31 and the closing of the cooling valve 30 to supply the supercritical refrigerant from the refrigerant passage 24 to the motor 1.

[0100] Subsequently, at time t13, a predetermined time T1 has elapsed since the start of supplying supercritical refrigerant to motor 1. Therefore, at time t13, control device 80 terminates the supply of supercritical refrigerant and supplies liquid refrigerant to motor 1. Specifically, control device 80 sets the discharge increase requirement flag to OFF, controls compressor 3 to generate liquid refrigerant, and controls the closing of discharge valve 31 and the opening of cooling valve 30 to supply liquid refrigerant from refrigerant passage 23 to motor 1.

[0101] Furthermore, as described above, when the brake pedal is depressed, the motor 1 generates heat due to its regenerative operation. However, at this time, the discharge rate of the compressor 3 increases, thereby increasing the amount of refrigerant supplied to the motor 1. Therefore, the heat generated during regeneration can be accurately addressed. In addition, the regenerative power generated by the motor 1 can be used to increase the work done by the compressor 3.

[0102] Next, refer to Figure 6 A flowchart illustrating the specific control process of this embodiment will be described. This process is repeatedly executed by the control device 80 at a predetermined cycle. Specifically, the processor 80a within the control device 80 reads and executes a program stored in the memory 80b, thereby realizing the control involved in this process. Here, the first to fourth examples described above are used as examples of supercritical refrigerant supply conditions.

[0103] First, in step S10, the control device 80 acquires data from the aforementioned sensors 51 to 61 (…). Figure 4The system detects various information, including the detected values. Then, the control device 80 proceeds to step S11, determining whether the oil level detected by the oil level sensor 52 is above the first liquid level and below the second liquid level. If the control device 80 determines that the oil level is above the first liquid level and below the second liquid level (step S11: Yes), it proceeds to step S12. Conversely, if the control device 80 does not determine that the oil level is above the first liquid level and below the second liquid level (step S11: No), i.e., the oil level is below the first liquid level or above the second liquid level, it terminates the control involved in this process. In this case, the control device 80 does not control the supply of supercritical refrigerant to the motor 1 (the same applies below).

[0104] Next, in step S12, the control device 80 determines whether the stop prediction flag is ON. Here, the control device 80 predicts the stopping of the vehicle 200 based on signals obtained from at least one of the acceleration sensor 56, camera 59, distance sensor 60, and GPS sensor 61. Then, if the control device 80 predicts that the vehicle 200 will stop, it sets the stop prediction flag to ON.

[0105] In one example, when the acceleration detected by the acceleration sensor 56 decreases to less than a predetermined value (i.e., when vehicle 200 decelerates relatively significantly), the control device 80 predicts that vehicle 200 will stop. In another example, the control device 80 predicts that vehicle 200 will stop when the brake lights of the vehicle ahead are illuminated, when the traffic light ahead is red, or when a road sign ahead indicates a temporary stop, as captured by the camera 59. In yet another example, the control device 80 predicts that vehicle 200 will stop when the distance to the vehicle ahead, detected by the distance sensor 60, decreases to less than a predetermined value (equivalent to the vehicle ahead decelerating relatively significantly and the distance between them shortening). In another example, the control device 80, in addition to referring to the current position of the vehicle 200 detected by the GPS sensor 61, also refers to map data from the navigation system installed on the vehicle 200, and if it determines that the current position of the vehicle 200 is a location where it needs to stop or slow down (intersection, traffic light, downhill lane), it predicts that the vehicle 200 will stop. Furthermore, the examples listed here can be appropriately combined for implementation.

[0106] The result of step S12 is that if the control device 80 determines that the stop prediction flag is ON (step S12: Yes), it proceeds to step S13. If it does not determine that the stop prediction flag is ON (step S12: No), that is, if the stop prediction flag is OFF, the control involved in this process ends.

[0107] Next, in step S13, the control device 80 determines whether the motor speed detected by the motor speed sensor 54 is less than the specified speed N1. As a result, if the control device 80 determines that the motor speed is less than the specified speed N1 (step S13: Yes), it proceeds to step S14; if it does not determine that the motor speed is less than the specified speed N1 (step S13: No), that is, if the motor speed is greater than or equal to the specified speed N1, the control involved in this process ends.

[0108] Next, in step S14, the control device 80 determines whether the brake pedal is ON. In this case, the control device 80 determines whether the brake pedal is depressed by the brake sensor 58. As a result, if the control device 80 determines that the brake pedal is ON (step S14: Yes), that is, the brake pedal is depressed, it proceeds to step S15. Conversely, if the control device 80 does not determine that the brake pedal is ON (step S14: No), that is, the brake pedal is not depressed, it terminates the control involved in this process.

[0109] Next, in step S15, since all the conditions in steps S11 to S14 are met, i.e., the supercritical refrigerant supply condition is met, the control device 80 sets the discharge increase requirement flag to ON and controls the compressor 3 to generate supercritical refrigerant. Then, in step S16, the control device 80 controls the opening of the discharge valve 31 and the closing of the cooling valve 30 to supply supercritical refrigerant from the refrigerant passage 24 to the motor 1.

[0110] Next, in step S17, the control device 80 determines whether the motor speed detected by the motor speed sensor 54 is less than the specified speed N1. If the control device 80 does not determine that the motor speed is less than the specified speed N1 (step S17: No), that is, if the motor speed is greater than or equal to the specified speed N1, it proceeds to step S19. In step S19, the control device 80 terminates the supply of refrigerant in the supercritical state and controls the closing of the discharge valve 31 and the opening of the cooling valve 30 to supply liquid-phase refrigerant from the refrigerant passage 23 into the motor 1. At this time, the control device 80 also sets the discharge increase requirement flag to OFF and controls the compressor 3 to generate liquid-phase refrigerant. Then, the control device 80 terminates the control involved in this process.

[0111] In contrast, if the control device 80 determines that the motor speed is less than the specified speed N1 (step S17: Yes), it proceeds to step S18 to determine whether a specified time T1 has elapsed since the start of supplying supercritical refrigerant to the motor 1. If the control device 80 determines that the specified time T1 has elapsed (step S18: Yes), it proceeds to step S19, performs the same control as described above, and terminates the control involved in this process. On the other hand, if the control device 80 does not determine that the specified time T1 has elapsed (step S18: No), it returns to step S16. In this case, the control device 80 continues to supply supercritical refrigerant.

[0112] Furthermore, in the above process, four determination processes, S11 to S14, were performed when determining the supercritical refrigerant supply conditions. However, it is not limited to performing all four determination processes; it is sufficient to perform at least one of the four determination processes.

[0113] [Functions and Effects]

[0114] Next, the function and effects of the motor cooling system 100 in this embodiment will be explained.

[0115] In this embodiment, the motor cooling system 100 installed in the vehicle 200 includes: a compressor 3 for compressing a refrigerant containing oil in CO2; a heat exchanger 5 for cooling the refrigerant compressed by the compressor 3; a motor 1 for driving the vehicle 200; refrigerant passages 23 and 24 for supplying the refrigerant cooled by the heat exchanger 5 into the motor 1; and a control device 80 configured to control the compressor 3 to generate a supercritical refrigerant, in order to supply a supercritical refrigerant from the refrigerant passage 24 into the motor 1 when a supercritical refrigerant supply condition is met.

[0116] According to this embodiment, by supplying a supercritical refrigerant into the motor 1, the compatibility of the supercritical refrigerant can be utilized to draw in oil within the motor 1, and the oil and refrigerant can be effectively discharged together. This removes the oil film (in other words, oil accumulation) formed within the motor 1 (especially in the gap between the rotor 11 and the stator 12), suppressing the increase in stirring resistance caused by the oil within the motor 1.

[0117] Furthermore, in this embodiment, the control device 80 is configured to control the compressor 3 to generate supercritical refrigerant when the supercritical refrigerant supply conditions are met, and to control the compressor 3 to generate liquid refrigerant when the supercritical refrigerant supply conditions are not met. In this embodiment, the control device 80 limits the supply of supercritical refrigerant, that is, it avoids unnecessarily supplying supercritical refrigerant. This reduces the load on the compressor 3 used to generate supercritical refrigerant and suppresses the increase in resistance caused by supplying supercritical refrigerant into the motor 1.

[0118] Furthermore, in this embodiment, the control device 80 is configured to, after the supercritical refrigerant supply conditions are met, terminate the supply of supercritical refrigerant when a predetermined time T1 has elapsed since the start of supplying supercritical refrigerant to the motor 1, and control the compressor 3 to generate liquid refrigerant in order to supply liquid refrigerant to the motor 1. Thus, by supplying supercritical refrigerant for a certain period of time, the supply of supercritical refrigerant can be terminated when the oil discharge from the motor 1 is complete, reducing the load on the compressor 3 used to generate supercritical refrigerant. In other words, the power consumption of the compressor 3 can be suppressed.

[0119] Furthermore, in this embodiment, the motor cooling system 100 includes: a refrigerant passage 23 for supplying liquid-phase refrigerant to the motor 1; a refrigerant passage 24 for supplying supercritical refrigerant to the motor 1; a cooling valve 30 disposed in the refrigerant passage 23; and a discharge valve 31 disposed in the refrigerant passage 24. The control device 80 is configured to control the discharge valve 31 to supply supercritical refrigerant from the refrigerant passage 24 to the motor 1 when the supercritical refrigerant supply condition is met, and to control the cooling valve 30 to supply liquid-phase refrigerant from the refrigerant passage 24 to the motor 1 when the supercritical refrigerant supply condition is not met. Therefore, by controlling the cooling valve 30 and the discharge valve 31, the refrigerant flow path (refrigerant path 23, 24) is switched, thereby making it easy to switch the refrigerant supplied to the motor 1 between a supercritical refrigerant and a liquid refrigerant.

[0120] Furthermore, in this embodiment, the motor cooling system 100 also includes a motor speed sensor 54 for detecting the motor speed, and the control device 80 is configured to determine that the supercritical refrigerant supply condition is met when the motor speed is less than a predetermined speed N1. Therefore, supercritical refrigerant can be supplied when the motor 1 is rotating at low speed, effectively suppressing the increase in resistance caused by supplying supercritical refrigerant into the motor 1.

[0121] Furthermore, in this embodiment, the control device 80 is configured such that, during the period when supercritical refrigerant is supplied to the motor 1 under supercritical refrigerant supply conditions, when the motor speed reaches a predetermined speed N1 or higher, the supply of supercritical refrigerant is terminated, and the compressor 3 is controlled to generate liquid refrigerant in order to supply liquid refrigerant to the motor 1. Therefore, when the motor speed increases (typically during acceleration), the operation of the compressor 3 for generating supercritical refrigerant is terminated, thereby suppressing the power consumption of the compressor 3. As a result, power can be transmitted to the motor 1, accurately meeting the acceleration requirements of the vehicle 200.

[0122] In this embodiment, the motor cooling system 100 also includes at least one of the following: an acceleration sensor 56 for detecting the acceleration of the vehicle 200, a camera 59 for capturing images of the area around the vehicle 200, a distance sensor 60 for detecting the distance between the vehicle 200 and objects existing around the vehicle, and a GPS sensor 61 for detecting the current position of the vehicle 200. The control device 80 is configured to predict the stopping of the vehicle 200 based on signals acquired from at least one of the acceleration sensor 56, the camera 59, the distance sensor 60, and the GPS sensor 61, and, if the stopping of the vehicle 200 is predicted, to determine that the supercritical refrigerant supply condition has been met. In this embodiment, considering that it takes a certain amount of time to generate supercritical refrigerant in the compressor 3, the operation of the compressor 3 for generating supercritical refrigerant is started in advance at the moment when the stopping of the vehicle 200 is predicted before the motor 1 actually starts rotating at low speed. Therefore, it is possible to reliably supply supercritical refrigerant when the motor 1 is rotating at low speed, and to accurately balance suppressing the increase in resistance caused by supplying supercritical refrigerant into the motor 1 and ensuring the discharge of oil from the motor 1 caused by supercritical refrigerant.

[0123] In addition, in this embodiment, the motor cooling system 100 also includes a brake sensor 58, which detects brake pedal operation performed by the driver to apply braking force to the vehicle 200. The control device 80 is configured to determine that the supercritical refrigerant supply condition is met when the brake sensor 58 detects brake pedal operation. In this embodiment, considering that it takes a certain amount of time to generate supercritical refrigerant in the compressor 3, the operation of the compressor 3 for generating supercritical refrigerant is also started in advance at the moment when the brake pedal is depressed before the motor 1 actually starts rotating at low speed. As a result, supercritical refrigerant can be reliably supplied even when the motor 1 is rotating at low speed, and the increase in resistance caused by supplying supercritical refrigerant to the motor 1 can be accurately balanced with ensuring that oil discharge from the motor 1 caused by supercritical refrigerant is prevented.

[0124] Furthermore, in this embodiment, the motor cooling system 100 also includes an oil tank 6 for storing oil and an oil level sensor 52 for detecting the oil level stored in the oil tank 6. The control device 80 is configured such that when the oil level detected by the oil level sensor 52 is above a first liquid level and below a second liquid level (> the first liquid level), it is determined that the supercritical refrigerant supply condition is met. Based on this determination result using the first and second liquid levels, the supply of supercritical refrigerant is controlled, thereby preventing the compressor 3 from burning out due to insufficient oil in the refrigerant when there is a relatively large amount of oil in the motor 1, and reliably discharging the oil from the motor 1.

[0125] [Variation Example]

[0126] In the above-described embodiments, a third example of the supercritical refrigerant supply condition uses the condition of whether a pedal operation performed by the driver to apply braking force to the vehicle 200 has been performed. Specifically, in this third example, the braking pedal depressing operation detected by the brake sensor 58 is used as the pedal operation performed by the driver to apply braking force to the vehicle 200. In this third example, it is envisioned that the invention be applied to a vehicle that performs a so-called two-pedal operation, where the vehicle is driven by depressing the accelerator pedal and braked by depressing the brake pedal. In contrast, a modified example applies the invention to a vehicle that performs a so-called single-pedal operation, where the vehicle is driven by depressing the accelerator pedal and braked by depressing the accelerator pedal. In this modified example, the control device 80 uses the accelerator pedal depressing operation detected by the throttle sensor 57 as the pedal operation performed by the driver to apply braking force to the vehicle 200 to determine the supercritical refrigerant supply condition.

[0127] Reference Figure 7 and Figure 8 Specifically explain the control methods involved in this variation. First, Figure 7 This is a timing diagram representing the control of a variant example. Figure 7 From top to bottom, the following parameters are represented: ON / OFF of the stop prediction flag, motor speed, differential value of accelerator pedal opening, ON / OFF of the discharge increase requirement flag, opening and closing of discharge valve 31, and time variation of opening and closing of cooling valve 32. Furthermore, only the control method described in the above-described embodiment will be explained here. Figure 5 The differences between them.

[0128] In a modified example, at time t22, the differential value of the accelerator pedal opening detected by the throttle sensor 57 is less than 0. This means that in the vehicle 200 performing so-called one-pedal operation, braking force is applied to the vehicle 200 by depressing the accelerator pedal. At this time t22, the stop prediction flag is set to ON, and the motor speed is less than the specified speed N1. Therefore, at time t22, the control device 80 sets the discharge increase requirement flag to ON, controls the compressor 3 to generate supercritical refrigerant, and controls the opening of the discharge valve 31 and the closing of the cooling valve 30 to supply the supercritical refrigerant from the refrigerant passage 24 to the motor 1.

[0129] then, Figure 8 This is a flowchart illustrating a modified embodiment of the present invention. This process is also repeatedly executed by the control device 80 at a predetermined cycle. Specifically, the processor 80a within the control device 80 reads and executes a program stored in the memory 80b, thereby implementing the control involved in this process.

[0130] Figure 8 Steps S20-S23 and S25-S29 are respectively with Figure 6 Steps S10-S13 and S15-S19 are the same, so their descriptions are omitted. Here, we will mainly describe step S24. In step S24, the control device 80 calculates the differential value of the accelerator pedal opening detected by the throttle sensor 57 and determines whether this differential value is less than 0. Here, in the vehicle 200 where a so-called one-pedal operation is being performed, the control device 80 determines whether the accelerator pedal has been depressed. The result of step S24 is that if the control device 80 determines that the differential value of the accelerator pedal opening is less than 0 (step S24: Yes), it proceeds to step S25; if it does not determine that the differential value of the accelerator pedal opening is less than 0 (step S24: No), i.e., the accelerator pedal has not been depressed, the control involved in this process ends.

[0131] According to this variation, considering that it takes a certain amount of time to generate supercritical refrigerant in compressor 3, the operation of compressor 3 for generating supercritical refrigerant can be started in advance at the moment when the accelerator pedal is depressed before motor 1 actually starts rotating at low speed. As a result, supercritical refrigerant can be reliably supplied when motor 1 is rotating at low speed, and the increase in resistance caused by supplying supercritical refrigerant to motor 1 can be accurately balanced with ensuring that oil discharge from motor 1 caused by supercritical refrigerant is prevented.

Claims

1. An electric motor cooling system, mounted in a vehicle, characterized in that, have: A compressor used to compress refrigerant containing oil in CO2; A heat exchanger for cooling the refrigerant after it has been compressed by the compressor; An electric motor used to drive the vehicle; A refrigerant passage for supplying the refrigerant cooled by the heat exchanger into the motor to cool the motor; as well as A control device configured to control at least the compressor. The control device is configured to control the compressor to generate the supercritical refrigerant in order to supply the supercritical refrigerant from the refrigerant passage to the motor when specified conditions are met.

2. The motor cooling system according to claim 1, characterized in that, The control device is configured to control the compressor to generate the refrigerant in a supercritical state when the specified conditions are met, and to control the compressor to generate the refrigerant in a liquid state when the specified conditions are not met.

3. The motor cooling system according to claim 1, characterized in that, The control device is configured to, after the specified conditions are met, terminate the supply of the supercritical refrigerant when a specified time has elapsed since the start of supplying the supercritical refrigerant into the motor, and control the compressor to generate the liquid refrigerant in order to supply the liquid refrigerant into the motor.

4. The motor cooling system according to claim 1, characterized in that, The refrigerant passage has a first passage and a second passage. The first passage is used to supply the refrigerant in a supercritical state to the motor, and the second passage is used to supply the refrigerant in a liquid state to the motor. The motor cooling system also includes valves disposed in the first passage and / or the second passage. The control device is configured to, when the specified conditions are met, control the valve to supply the refrigerant in a supercritical state to the motor from the first passage, and when the specified conditions are not met, control the valve to supply the refrigerant in a liquid state to the motor from the second passage.

5. The motor cooling system according to claim 1, characterized in that, The motor cooling system also includes a motor speed sensor for detecting the motor's rotational speed. The control device is configured to determine that the specified condition is met when the rotational speed detected by the motor speed sensor is less than the specified rotational speed.

6. The motor cooling system according to claim 5, characterized in that, The control device is configured such that, during the period when the prescribed conditions are met and the refrigerant in a supercritical state is supplied to the motor, when the rotational speed is above the prescribed speed, the supply of the refrigerant in a supercritical state is terminated, and in order to supply the refrigerant in a liquid state to the motor, the compressor is controlled to generate the refrigerant in a liquid state.

7. The motor cooling system according to claim 1, characterized in that, The motor cooling system also includes at least one of an accelerometer, a camera, a distance sensor, and a GPS sensor. The accelerometer detects the vehicle's acceleration, the camera captures images of the vehicle's surroundings, the distance sensor detects the distance between the vehicle and objects in the vehicle's vicinity, and the GPS sensor detects the vehicle's current position. The control device is configured to predict the stopping of the vehicle based on signals obtained from at least one of the acceleration sensor, the camera, the distance sensor, and the GPS sensor, and to determine that the predetermined condition is met when the stopping of the vehicle is predicted.

8. The motor cooling system according to claim 1, characterized in that, The motor cooling system also includes a pedal sensor that detects pedal operations performed by the driver to apply braking force to the vehicle. The control device is configured to determine that the predetermined condition is met when the pedal operation is detected by the pedal sensor.

9. The motor cooling system according to claim 1, characterized in that, The motor cooling system also includes an oil tank and an oil level sensor. The oil tank stores the oil, and the oil level sensor detects the oil level in the tank. The control device is configured to determine that the specified condition is met when the liquid level detected by the oil level sensor is above a first specified value and less than a second specified value that is greater than the first specified value.

10. The motor cooling system according to claim 1, characterized in that, The motor has a rotor and a stator, a rotating shaft connected to the rotor, and a sliding bearing supporting the rotating shaft, and is configured to supply refrigerant from the refrigerant passage to the space between the rotor and the stator. The motor cooling system also has a refrigerant passage, which is different from the refrigerant passage, for supplying the refrigerant to the sliding bearing, and an oil passage for supplying the oil to the sliding bearing.

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