Air / flash evaporation spray composite cooling system and method for high power-to-mass ratio motor controllers of electric propulsion systems

Abstract

This invention discloses an air / flash spray composite cooling system for an electric propulsion system, comprising a ducted fan, a double-layered housing, and a flash spray system. The double-layered housing is located behind the ducted fan and is coaxially arranged. The airflow from the ducted fan passes through the double-layered housing to dissipate heat from the electrically heated elements inside the housing. The flash spray system, located behind the double-layered housing, includes nozzles, a solenoid valve, and a pressure stabilizing tank. The high-speed airflow generated by the ducted fan is introduced into the controller housing. The high-speed airflow rotates under the action of a spiral flow channel, and the rotating airflow sweeps across the controller, carrying away heat. While precisely cooling the controller, the swirling flow also improves the cooling effect. Furthermore, addressing the problem that forced convection is insufficient for rapid and efficient heat dissipation under power transients, flash spray is used to rapidly cool the controller, achieving temperature skidding and preventing thermal failure of the controller during sudden power increases.

Description

Technical Field

[0001] This invention belongs to the field of heat dissipation system technology, and is particularly applicable to air / flash spray composite cooling system for high power-to-weight ratio motor controllers in electric propulsion systems. Background Technology

[0002] Existing cooling methods specifically designed for electric propulsion system motors primarily utilize high-speed airflow generated within the duct to force-cool the outer casing. This heat dissipation from the internal heat-generating components is achieved through the casing's thermal conductivity. While this method is energy-efficient, the high thermal resistance of the casing prevents rapid removal of heat generated by internal components. For high-power motors, this reaches their cooling limits, posing unprecedented challenges to the design and development of high-power ducted fan motors. Furthermore, existing cooling technologies mainly target individual components such as motor windings, stator, and rotor. However, the controller, as a crucial heat-generating component, suffers from significant cooling issues. Yet, there is a lack of dedicated cooling technologies for high power-to-weight ratio motor controllers on the market.

[0003] Unlike the motors used in traditional new energy vehicles, the power of electric propulsion system motors often changes rapidly due to flight attitude and load, causing the temperature of internal hot components such as controllers to quickly reach their failure temperature. If not cooled quickly, this can easily lead to shortened lifespan and failure of electronic devices. Therefore, there is an urgent need for rapid and efficient cooling methods to remove heat from the controller surface. However, traditional cooling technologies such as forced convection or heat pipes have a long cooling lag, making it difficult to couple and match the cooling system parameters with the transient power changes of the electric propulsion motor, and thus failing to meet the current heat dissipation requirements of electric propulsion motors. Summary of the Invention

[0004] To address the heat dissipation problem of internal hot components in electric propulsion systems, this invention discloses an air / flash spray composite cooling system and method for high power-to-weight ratio motor controllers in electric propulsion systems. High-speed airflow generated by a ducted fan is introduced into the controller housing. The high-speed airflow rotates under the action of a spiral flow channel, and the rotating airflow sweeps across the controller, carrying away heat. While precisely cooling the controller, the swirling flow also improves the cooling effect. Simultaneously, to address the problem that forced convection air cannot achieve rapid and efficient heat dissipation under power transient conditions, flash spray is used to rapidly cool the controller, achieving temperature skidding and preventing thermal failure of the controller during sudden power increases.

[0005] The technical solution adopted in this invention is as follows: an air / flash spray composite cooling system for a high power-to-weight ratio motor controller in an electric propulsion system, characterized in that it includes a ducted fan, a double-layer shell, and a flash spray system;

[0006] The double-layered housing is located behind the ducted fan, and the two are arranged coaxially. The airflow blown out by the ducted fan passes through the double-layered housing to dissipate heat from the electric heating elements inside the housing.

[0007] The flash spray system is located behind the double-layer shell and includes a nozzle, a solenoid valve, and a pressure stabilizing tank. The nozzle's pipeline is connected to the pressure stabilizing tank via the solenoid valve. The pressure stabilizing tank contains liquid CO2. The solenoid valve controls the nozzle to spray atomized liquid CO2 toward the electric heating element. The nozzle is directed toward the electric heating element and the spray axis is tilted toward the direction of the airflow.

[0008] The double-layer shell is a coaxial hollow cylindrical structure consisting of two nested outer shells, forming an annular cavity between the two outer shells. The two outer shells are fixedly connected by a hollow shell connecting structure, which includes multiple hollow shell connecting structures arranged in a circumferential array within the annular cavity. The hollow shell connecting structures extend spirally within the annular cavity between the two outer shells to form a spiral flow channel between every two hollow shell connecting structures. The end of the double-layer shell adjacent to the ducted fan is the air intake, and the end adjacent to the electric heating element is the air-cooled air outlet.

[0009] Furthermore, a heat pipe is provided inside the hollow shell connecting structure. The hot end of the heat pipe is close to the side of the electric heating element, and the cold end of the heat pipe is close to the side of the air outlet, which is used to assist the heat dissipation of the casing.

[0010] The flash spray system has three control circuits: a first circuit, a second circuit, and a third circuit, all of which are connected to the main power supply circuit. A temperature sensor is provided on the surface of the casing of the electric heating element. The temperature sensor is connected in series with a solenoid valve in the first circuit. The solenoid valve is activated based on the temperature sensed by the temperature sensor to control the nozzle to spray liquid refrigerant CO2 toward the electric heating element.

[0011] A pressure sensor is installed inside the pressure stabilizing tank. The second circuit supplies power to the pressure sensor. The pressure sensor senses the internal pressure of the pressure stabilizing tank to maintain sufficient spray pressure for the nozzle operation at all times. When the pressure inside the pressure stabilizing tank is lower than a set threshold, the flow regulating valve at the opening of the pressure stabilizing tank is controlled. Cooling hot air is heated through a spiral channel surrounding the inner shell of the pressure stabilizing tank, causing some of the liquid CO2 to vaporize, thereby raising the pressure inside the pressure stabilizing tank to the set threshold or above.

[0012] Specifically, the pressure stabilizing tank housing includes an outer pressure stabilizing tank housing and an inner pressure stabilizing tank housing nested together. A spiral channel is provided between the outer and inner pressure stabilizing tank housings. The inlet of the spiral channel is controlled by a flow regulating valve, and the inlet of the spiral channel corresponds to the airflow direction of the ducted fan, allowing hot air to pass through. A hot air exhaust port connected to the outlet of the spiral channel is provided on the side of the pressure stabilizing tank away from the ducted fan. The third circuit supplies power to the flow regulating valve, and a third circuit switch is connected to the third circuit. The third circuit switch controls the operation of the flow regulating valve based on the pressure of the pressure sensor.

[0013] Furthermore, the nozzle is a straight stainless steel capillary tube.

[0014] Furthermore, the thickness of the annular cavity is 1cm, and a dustproof net is also provided at the air inlet of the double-layer shell, with a 5mm gap between the dustproof net and the air inlet.

[0015] Furthermore, heat dissipation fins are provided on the outer surface of the housing on which the electric heating element is installed, at the position corresponding to the electric heating element, for auxiliary heat dissipation.

[0016] This invention also claims a method for air / flash spray composite cooling for a high power-to-weight ratio motor controller in an electric propulsion system, employing the aforementioned composite cooling system, the method comprising:

[0017] Under low operating conditions, the ducted fan blows air through the internal annular cavity of the double-layered housing, and then blows it to the electric heating element for air cooling.

[0018] Under high operating conditions, the temperature of the electric heating element is detected by a temperature sensor. When the temperature of the electric heating element exceeds the failure temperature or the temperature of the electric heating element changes rapidly by more than 10 / s, the solenoid valve opens and the nozzle sprays liquid CO2 toward the electric heating element for flash evaporation spray cooling. Under the action of flash evaporation effect and air drag, the liquid CO2 breaks into micron-sized low-temperature droplets. The high-speed droplet group impacts the heat exchange surface of the electric heating element, causing flash evaporation and boiling, thereby quickly removing the heat from the electric heating element.

[0019] When the temperature of the electric heating element is lower than the failure temperature of the electronic components and the temperature change is not drastic, the solenoid valve closes and the nozzle stops spraying liquid CO2.

[0020] In addition, the pressure sensor detects the internal pressure of the pressure stabilizing tank. When the internal pressure of the pressure stabilizing tank is lower than the spray pressure threshold of the nozzle, the flow regulating valve of the pressure stabilizing tank is opened to regulate the amount of hot air entering, so that some liquid CO2 evaporates and the pressure inside the pressure stabilizing tank remains stable. When the pressure sensor detects that the internal pressure of the pressure stabilizing tank reaches or exceeds the spray pressure threshold of the nozzle, the flow regulating valve controls the inlet of the spiral channel to close and stop the hot air from entering.

[0021] It should be noted that compared with traditional mechanical atomization such as water spray, flash spray technology using liquid CO2 as the working fluid has a more intense flash process when the liquid in the tank is at a high superheat (i.e., high fluid temperature), resulting in lower droplet temperatures sprayed from the nozzle, which can further improve the spray cooling capacity.

[0022] The beneficial effects of this invention are:

[0023] 1. Compared with traditional single forced air cooling, the rotating airflow generated by the spiral flow channel to cool the controller under low operating conditions has a better cooling effect; under high power operating conditions, the air / flash spray composite cooling technology to cool the controller can significantly reduce the controller temperature to below the failure temperature of electronic components in a short time; the heat dissipation problem of high power ratio motor controller can be effectively solved by coupling and matching the two heat exchange technologies.

[0024] 2. Utilizing a spiral channel structure design with a double-shell casing, a high-speed airflow is generated within the ducted fan to cool the controller. The system eliminates the need for external fluid pumps or other energy-consuming devices, thereby improving system reliability and saving energy.

[0025] 3. The spray system uses hot air generated by heat exchange through the controller to stabilize the working fluid pressure in the storage tank. No additional pumps or compressors are required for pressurization. The pressure control is precise and the system is safer and more reliable. Waste heat can be reused. The air-cooled heat dissipation and flash boiling heat dissipation systems are coupled into one, making the cooling system more energy-efficient.

[0026] 4. By utilizing the closed-loop control unit of the spray system to control the spray on and off, intelligent control of intermittent flash spray cooling is achieved, while reducing the amount of working fluid used.

[0027] 5. In the cooling system of the present invention, the heat pipe can assist the heat dissipation of the casing, and the fins can enhance the heat conduction at the connection between the controller and the wall, thus assisting in heat dissipation to a certain extent. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the overall air / flash spray composite cooling system for a high power-to-weight ratio motor controller in an electric propulsion system according to the present invention;

[0029] Figure 2 This is a schematic diagram of the vertically unfolded double-shell structure in the composite cooling system of the present invention;

[0030] Figure 3 This is a schematic diagram of the flash spray system in the composite cooling system of the present invention;

[0031] In the diagram: 1-Duct fan blade, 2-Double-layer shell, 3-1-Fin 1, 3-2-Fin 2, 4-1-Controller 1, 4-2-Controller 2, 5-1-Nozzle 1, 5-2-Nozzle 2, 6-1-Pipe 1, 6-2-Pipe 2, 7-Solenoid valve, 8-1-Fixing rod 1, 8-2-Fixing rod 2, 9-Pressure tank, 10-1-Exhaust port 1, 10-2-Exhaust port 2, 11-Air intake, 12-Dustproof net, 13-Air-cooled outlet, 14-Heat pipe, 15-Spiral flow channel, 16-Hollow shell connection structure, 17-1-Temperature sensor 1, 17- 2-Temperature sensor II, 18-Spray system control unit, 19-Pressure sensor, 20-Outer shell of pressure stabilizing tank, 21-Spiral channel, 22-Inner shell of pressure stabilizing tank, 23-Cooling hot air heating control unit, 24-Main circuit, 25-Main circuit switch, 26-First circuit, 27-First circuit switch, 28-Second circuit, 29-Second circuit switch, 30-Third circuit, 31-Third circuit switch, 32-Hot air exhaust port, 33-1-Flow regulating valve I, 33-2-Flow regulating valve II, 34-1-Hot air inlet I, 34-2-Hot air inlet II. Detailed Implementation

[0032] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0033] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "top," "bottom," "inner," and "outer," etc., indicating orientation or positional relationships, are for simplification and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0034] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0035] See Figure 1 This is a schematic diagram of the overall air / flash spray composite cooling system for an electric propulsion system according to the present invention. The composite cooling system includes ducted fan blades 1, a double-layer shell 2, and a flash spray system. The flash spray system includes nozzles, solenoid valves, and a pressure stabilizing tank. See [link to relevant documentation]. Figure 1 In the illustrated embodiment, two electric heating elements, controller 4-1 and controller 4-2, are located inside the housing (electric propulsion motor housing). The nozzle includes nozzle 5-1 and nozzle 5-2. Nozzle 5-1 is positioned towards controller 4-1 and its spray direction forms an angle with respect to the surface of controller 4-1. Nozzle 5-2 is positioned towards controller 4-2 and its spray direction forms an angle with respect to the surface of controller 4-2. Both angles are acute. Preferably, both angles are set to 30°, meaning that the spray axes of nozzles 5-1 and 5-2 are inclined towards the direction of the incoming airflow, causing the two nozzles to spray refrigerant obliquely and in contact with the airflow in the opposite direction, reducing the impact of airflow on the spray. Both nozzles 5-1 and 5-2 are selected as straight stainless steel capillary tubes.

[0036] The nozzle 1 5-1 and nozzle 2 5-2 are connected to the solenoid valve 7 via pipe 2 6-2. The solenoid valve 7 is connected to the pressure tank 9 via pipe 1 6-1. The solenoid valve 7 controls the nozzle to spray atomized liquid CO2 toward the controller. The pressure tank 9 is securely installed outside the housing by fixing rod 1 8-1 and fixing rod 2 8-2, and is located downstream of the air-cooled airflow blown out by the ducted fan blade 1.

[0037] See Figure 1 The double-layered housing 2 is located behind the ducted fan blades 1, and the two are arranged coaxially. The airflow blown out by the ducted fan blades 1 flows through the annular hollow channel of the double-layered housing 2, and then flows out obliquely inward from the inner wall of the double-layered housing 2. After flowing through controller 1 4-1 and controller 2 4-2, it is blown out from the exhaust port at the rear, carrying away heat. The exhaust port can be set as a large opening or multiple small openings. In the illustrated embodiment, the exhaust port includes exhaust port 1 10-1 and exhaust port 2 10-2. See also Figure 1The housing is provided with fin 3-1 at the mounting position corresponding to the controller 4-1, and the housing is provided with fin 3-2 at the mounting position corresponding to the controller 4-2. The fins in the form of ribs accelerate the heat dissipation of the motor housing.

[0038] Figure 2 This is a schematic diagram of the vertically unfolded double-shell structure in the composite cooling system of the present invention. The double-shell 2 is a coaxial hollow cylindrical structure with two outer shells nested together. The circumferential distance between the two outer shells is 1 cm, meaning the thickness of the hollow shell layer of the double-shell 2 is 1 cm. The two nested outer shells are fixedly connected by a hollow shell connecting structure 16. The hollow shell connecting structure 16 is made of lightweight materials such as alloys or the same material as the double outer shells. The hollow shell connecting structure 16 extends spirally in the annular cavity between the two outer shells. A spiral flow channel 15 is formed between every two hollow shell connecting structures 16; the end of the double shell 2 near the duct fan blade 1 is the air inlet 11, and the end near the controller 1 4-1 and controller 2 4-2 is the air-cooled air outlet 13. A dustproof net 12 is also provided at the air inlet 11. The air flow enters the hollow shell layer of the double shell 2 from the air inlet 11 and is guided by the spiral flow channel 15 to form a high-speed rotating airflow, which increases the air-cooling effect. Then it is blown from the air-cooled air outlet 13 to the controller 1 4-1 and controller 2 4-2 for air cooling.

[0039] See Figure 2 The hollow shell connecting structure 16 is equipped with a heat pipe 14. The hot end of the heat pipe 14 is close to the side of controller 1 4-1 and controller 2 4-2, and the cold end of the heat pipe 14 is close to the side of the air outlet 11. The heat pipe is used to assist the heat dissipation of the casing and transfer heat from the controller to the side of the air outlet. Preferably, in the illustrated embodiment, there are six hollow shell connecting structures 16, and the number of spiral flow channels 15 is also six. The spiral flow channels 15 are evenly distributed around the circumference at 60° intervals. The inlet and outlet of the spiral flow channels 15 correspond to the air outlet 11 and the air-cooled air outlet 13, respectively.

[0040] Furthermore, the dustproof net 12 is arranged at the air inlet 11 with a 5mm gap between it and the air inlet 11, which is used to filter the airflow that directly enters the machine casing and block any impurities that may be present in the air.

[0041] Figure 3 This is a schematic diagram of the flash spray system in the composite cooling system of the present invention, combined with... Figure 3 The flash spray system of the present invention is further described in detail as follows: the flash spray system has three control circuits: a first circuit 26, a second circuit 28, and a third circuit 30, and all three control circuits are connected to the main circuit 24. The main circuit 24 is controlled by the main circuit switch 25 to control the supply of control current.

[0042] Temperature sensor 17-1 is mounted on the surface of the casing of controller 4-1, and temperature sensor 17-2 is mounted on the surface of the casing of controller 4-2. Both temperature sensors 17-1 and 17-2 are connected in series in the first circuit 26. The first circuit 26 is also connected to the solenoid valve 7 to control its operation. A first circuit switch 27 is also mounted on the first circuit 26. Controller 4-1, controller 4-2, temperature sensors 17-1 and 17-2, nozzle 5-1, nozzle 5-2, solenoid valve 7, and the first circuit 26 constitute the spray system control unit 18. The first circuit switch 27 controls the operation of the spray system control unit 18. When the temperature sensor detects that the controller temperature is higher than the failure temperature or when the temperature changes drastically by more than 10°C / s, the solenoid valve 7 opens, and the nozzle sprays atomized liquid CO2 refrigerant.

[0043] The pressure stabilizing tank 9 controls the refrigerant pressure to maintain stability, ensuring sufficient injection pressure. A pressure sensor 19 is installed inside the pressure stabilizing tank 9. The second circuit 28 is connected to the pressure sensor 19, and a second circuit switch 29 is installed on the second circuit 28 to control the on / off state of the second circuit. The pressure stabilizing tank 9 uses a cooling hot air heating method to stabilize the refrigerant working fluid pressure inside the tank. See [link to relevant documentation]. Figure 3The pressure stabilizing tank 9 includes an outer shell 20 and an inner shell 22 nested together. A spiral channel 21 is provided between the outer shell 20 and the inner shell 22. The pressure sensor 19 is electrically connected to flow regulating valve 33-1 and flow regulating valve 33-2 and is connected back to the main circuit 24 to form a third circuit 30. A third circuit switch 31 is provided between the pressure sensor 19 and flow regulating valve 33-1 and flow regulating valve 33-2. The third circuit switch 31 controls the operation of flow regulating valve 33-1 and flow regulating valve 33-2. The inlet side of flow regulating valve 33-1 and flow regulating valve 33-2 corresponds to the exhaust port 10-1 and exhaust port 10-2, respectively. The outlet side is connected to the hot air inlet 34-1 and hot air inlet 34-2 of the pressure stabilizing tank, respectively. When flow regulating valve 1 (33-1) and flow regulating valve 2 (33-2) are open, the heated air-cooled airflow blown out from the two exhaust ports can be partially blown into flow regulating valve 1 (33-1) and flow regulating valve 2 (33-2). The amount blown in is controlled by the opening degree of flow regulating valve 1 (33-1) and flow regulating valve 2 (33-2). The heat carried by the air-cooled airflow is used to promote the vaporization of some liquid CO2, thereby maintaining the internal pressure of the pressure stabilizing tank 9. The pressure stabilizing tank 9 has a hot air exhaust port 32 connected to the spiral channel outlet on the side away from the duct fan blades. The second circuit 28, the third circuit 30, the pressure stabilizing tank 9, the spiral channel 21, the hot air exhaust port 32, the flow regulating valve 1 33-1, the flow regulating valve 2 33-2, the hot air inlet 1 34-1, and the hot air inlet 2 34-2 constitute the cooling hot air heating control unit 23 of the pressure stabilizing tank. The flow regulating valve 1 33-1 and the flow regulating valve 2 33-2 are controlled by pressure sensing to heat or block the flow, so as to control the internal pressure of the pressure stabilizing tank 9 to be kept stable at the ejection pressure in real time.

[0044] The specific working method of the air / flash spray composite cooling system of the present invention is as follows:

[0045] When the motor is working under low operating conditions, all circuits are turned on normally, and the ducted fan blade 1 rotates to generate high-speed airflow.

[0046] After passing through the air inlet 11 and the dustproof net 12, the airflow generates a high-speed rotating airflow through the spiral flow channel 15; the high-speed rotating airflow flows out through the air-cooled air outlet 13 to cool controller one and controller two.

[0047] When the motor is operating under high operating conditions, temperature sensor 17-1 and temperature sensor 27-2 monitor the temperature of controller 14-1 and controller 24-2.

[0048] When the temperature exceeds the failure temperature of electronic components, or when a sharp increase in the temperature of the controller's heat exchange surface is detected, with a change exceeding 10°C / s, the spray system control unit 18 opens the solenoid valve 7 to implement flash spray cooling. The refrigerant liquid CO2 is sprayed out through nozzle 1 5-1 and nozzle 2 5-2, and under the action of flash evaporation effect and air drag, it breaks into micron-sized low-temperature droplets. The high-speed droplet group impacts the controller's heat exchange surface, causing flash evaporation and boiling, thereby quickly removing the heat from the controller. Since the flash spray flow rate is small, it is only used under conditions of a sharp increase in motor power, and the environmental impact of the released refrigerant CO2 can be ignored.

[0049] The refrigerant flows out of the pressure tank 9, passes through pipeline 6-1, solenoid valve 7, and pipeline 6-2 to reach nozzle 5-1 and nozzle 5-2, and is sprayed out at an angle to implement cooling. At this time, the second circuit switch 29 is open and the third circuit switch 31 is closed, connecting the third circuit 30.

[0050] Pressure sensor 19 detects a decrease in pressure inside pressure tank 9. It then connects flow regulating valve 1 33-1 and flow regulating valve 2 33-2 through third circuit 30, allowing hot air to be heated through hot air inlet 1 34-1 and hot air inlet 2 34-2, causing some of the liquid refrigerant to evaporate and maintaining stable pressure inside pressure tank 9.

[0051] Temperature sensor 17-1 and temperature sensor 27-2 monitor the temperature of controller 14-1 and controller 24-2 through the first circuit 26;

[0052] When the temperature is below the failure temperature of the electronic components and the temperature change is not drastic, the spray system control unit 18 closes the solenoid valve 7, the flash spray cooling ends, and the refrigerant is no longer output; the pressure sensor 19 monitors the pressure inside the pressure stabilizing tank 9 and keeps it stable, the pressure stabilizing tank cooling hot air heating control unit 23 closes the flow regulating valve 1 33-1 and the flow regulating valve 2 33-2 to stop the hot air heating, the third circuit switch 31 is opened, the third circuit 30 is disconnected, and at the same time the second circuit switch 29 is closed, connecting the second circuit 28 to continuously monitor the pressure inside the pressure stabilizing tank 9, and the operation ends.

[0053] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that, based on the technical solutions of the present invention, various modifications or variations of equivalent structures or equivalent processes that can be made by those skilled in the art without creative effort, or directly or indirectly applied to other related technical fields, are still within the scope of protection of the present invention.

Claims

1. An air / flash evaporation spray compound cooling system for high power-to- mass electric propulsion system electric machines, characterized by, The double-layer shell is coaxial hollow cylindrical structure nested by two layers of shells, an annular cavity is formed between the two layers of shells, the two layers of shells are fixedly connected by a hollow shell connecting structure, the hollow shell connecting structure includes a plurality of hollow shell connecting structures distributed in the annular cavity in a circumferential array, the hollow shell connecting structure extends in a spiral shape in the annular cavity between the two layers of shells to form a spiral flow channel between every two hollow shell connecting structures. The end of the double-layer shell adjacent to the ducted fan is an air inlet, and the end adjacent to the electric heating element is an air outlet. The hollow shell connecting structure is internally provided with a heat pipe, the hot end of the heat pipe is close to one side of the electric heating element, and the cold end of the heat pipe is close to one side of the air inlet. The nozzle is a straight stainless steel capillary tube. The thickness of the annular cavity is 1 cm. The machine shell on which the electric heating element is installed is provided with a heat dissipation fin at a position corresponding to the electric heating element. The air inlet is also provided with a dust screen, and the dust screen is spaced apart from the air inlet by 5 mm.

8. An air / flash spray composite cooling method for an electric propulsion system, the method comprising:

2. The hybrid cooling system of claim 1, further characterized by, In a low working condition, the air flow blown by the ducted fan passes through the internal annular cavity of the double-layer shell, and then blows to the electric heating element for air cooling heat dissipation. ​ 3. The hybrid cooling system of claim 2, further characterized by, ​ 4. The hybrid cooling system of claim 1, further characterized by, ​ 5. The hybrid cooling system of claim 2 or 3, further characterized by, ​ 6. The hybrid cooling system of claim 1, further characterized by, ​ 7. The hybrid cooling system of claim 2 or 3, further characterized by, ​ ​ ​ Under high working conditions, the temperature of the electric heating element is detected by a temperature sensor. When the temperature of the electric heating element exceeds the failure temperature or the temperature of the electric heating element changes rapidly and increases by more than 10 ℃ / s, the electromagnetic valve is opened, the nozzle sprays liquid CO2 towards the electric heating element for flash spray cooling. Under the action of the flash effect and air drag, the liquid CO2 is broken into micron-sized low-temperature droplets. The high-speed droplet group impacts the heat exchange surface of the electric heating element to cause flash evaporation and boiling, thereby quickly taking away the heat of the electric heating element. When the temperature of the electric heating element is lower than the failure temperature of the electronic component and the temperature change is not rapid, the electromagnetic valve is closed, and the nozzle stops spraying liquid CO2.

9. The method of claim 8, further characterized by, The pressure inside the pressure stabilizing tank is detected by a pressure sensor. When the pressure inside the pressure stabilizing tank is lower than the spraying pressure threshold of the nozzle, the flow regulating valve outside the pressure stabilizing tank is opened to heat the cooling hot air to evaporate part of the liquid CO2 and keep the pressure inside the pressure stabilizing tank stable. When the pressure inside the pressure stabilizing tank reaches or exceeds the spraying pressure threshold of the nozzle, the flow regulating valve is closed, and the cooling hot air flowing into the middle layer of the pressure stabilizing tank shell is disconnected.

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