Motor cooling system and motor cooling method

Abstract

To provide a motor cooling system and a motor cooling method with high cooling performance. [Solution] The motor 10 comprises a rotor 11 having a permanent magnet section 112 and a stator 13 having an electromagnet section, a cooling fluid 30 for cooling the motor 10, and a tubular flow path 20 through which the cooling fluid 30 flows. The flow path 20 has a discharge section 21 that discharges the cooling fluid 30 toward the rotor 11 from a discharge port 211, and the cooling fluid 30 discharged toward the rotor 11 forms a liquid film 31 on the rotor surface where the gas-liquid interface is saturated.

Description

[Technical Field]

[0001] The present invention relates to a motor cooling system and a motor cooling method. [Background technology]

[0002] In today's society, where electrification is promoted with the aim of reducing carbon emissions, motors are known as a necessary technological element for the stable and efficient use of energy resources. Because motors generate heat due to losses, they are often equipped with cooling mechanisms.

[0003] Conventionally, as disclosed in Patent Document 1, for example, an axial motor is known that guides a refrigerant injected from outside the case to the rotor surface. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2007-20382 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, in motors with high power density, which are expected to be applied in fields such as electric vehicles and electric aircraft, conventional cooling methods have been insufficient. Motors with high power density require higher cooling performance because the absolute amount of heat generated due to losses increases. In particular, the permanent magnets in motors lose or cease to be magnetic if they exceed a certain temperature, so it is necessary to maintain an appropriate temperature. Furthermore, permanent magnets have a lower thermal conductivity compared to the coil core of an electromagnet, and since their magnetic force decreases or is lost if they exceed the Curie temperature, high cooling performance is required to maintain an appropriate temperature. In other words, how to cool the permanent magnets is crucial for improving the performance of motors.

[0006] This invention has been made in consideration of these circumstances, and aims to provide a motor cooling system and a motor cooling method with high cooling performance. [Means for solving the problem]

[0007] To achieve the above objectives, the present invention provides the following means. The motor cooling system of the present invention comprises a motor having a rotor having a permanent magnet and a stator having an electromagnet; a cooling fluid for cooling the motor; and a tubular flow path through which the cooling fluid flows. The flow path has a discharge section that discharges the cooling fluid toward the rotor from an outlet, and the cooling fluid discharged toward the rotor forms a liquid film on the rotor surface in a liquid phase state where the gas-liquid interface is saturated.

[0008] The present invention relates to a motor cooling method for a motor comprising a rotor having a permanent magnet and a stator having an electromagnet, wherein the cooling fluid for cooling the motor is discharged from a discharge port toward the rotor from a tubular flow path through which the cooling fluid flows, and the cooling fluid discharged toward the rotor forms a liquid film on the rotor surface with a saturated gas-liquid interface. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a motor cooling system and a motor cooling method with high cooling performance. [Brief explanation of the drawing]

[0010] [Figure 1] This is a cross-sectional view showing a motor cooling method according to the first embodiment of the present invention. [Figure 2] This is a cross-sectional view showing a motor cooling method according to modified example A of the present invention. [Figure 3] This is a cross-sectional view showing a motor cooling method according to modified example B of the present invention. [Figure 4] They are a cross-sectional view and a path diagram showing a motor cooling system according to a second embodiment of the present invention. [Figure 5] It is a diagram showing coordinates of a magnet in the theoretical description of an embodiment of the present invention. [Figure 6] It is a diagram showing a temperature distribution of a magnet with respect to a heat transfer coefficient of a cooling index in the theoretical description of an embodiment of the present invention. [Figure 7] It is a diagram showing a heat transfer coefficient of liquid methane based on flow rate and rotation speed in Example 1 of the present invention. [Figure 8] It is a diagram showing a liquid film thickness required for cooling liquid methane based on flow rate and rotation speed in Example 1 of the present invention. [Figure 9] It is a diagram showing a heat transfer coefficient of liquid nitrogen based on flow rate and rotation speed in Example 2 of the present invention. [Figure 10] It is a diagram showing a liquid film thickness required for cooling liquid nitrogen based on flow rate and rotation speed in Example 2 of the present invention. [Figure 11] It is a diagram showing a heat transfer coefficient of liquid hydrogen based on flow rate and rotation speed in Example 3 of the present invention. [Figure 12] It is a diagram showing a liquid film thickness required for cooling liquid hydrogen based on flow rate and rotation speed in Example 3 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] In the present embodiment, the drawings are schematic diagrams for explaining the configuration in an easy-to-understand manner, and the dimensional ratios and the like of each component may differ from actual ones. In the present specification, a direction orthogonal to the rotation shaft of a motor 10 is defined as a radial direction R. A direction along the rotation shaft of the motor 10 is defined as an axial direction S. In FIGS. 1 to 4, the description will be given with the upper side of the radial direction R as the + side, the lower side as the - side, the right side of the axial direction S as the + side, and the left side as the - side.

[0012] [First Embodiment] A motor 10 according to the first embodiment of the present invention will be described with reference to Figure 1. Figure 1 is a cross-sectional view of a motor 10 equipped with a cooling method according to the first embodiment.

[0013] <Configuration of the first embodiment> The motor 10 is a high-power-density axial motor comprising a rotor 11, a shaft 12, and a stator 13. A discharge section 21, formed at one end of a flow path 20 through which a cooling fluid 30 flows, is inserted into the motor 10.

[0014] The rotor 11 is the part that corresponds to the rotating body (rotor) of an axial motor. This rotor 11 comprises a rotor body 111 and a permanent magnet 112 embedded in the rotor body 111. The central part 113 of the rotor body 111 is connected and fixed to a connection part 123 of the shaft 12, which will be described later.

[0015] The rotor 11 is provided with a rotational speed measuring means (not shown) for measuring the rotational speed of the rotor 11 and a temperature measuring means for measuring the temperature of the rotor 11. Furthermore, if the rotational speed of the rotor 11 and the temperature of the rotor 11 are known, the rotational speed measuring means and temperature measuring means may be provided in locations other than the rotor 11.

[0016] The rotor body 111 is formed in a plate shape that extends parallel to the radial direction R, and is made of, for example, a steel member. Furthermore, the rotor body 111 is formed in a substantially circular shape when viewed from the front in the axial direction S.

[0017] The permanent magnet portion 112 is a part formed by embedding a permanent magnet, for example, made primarily from a magnetic material such as neodymium, into the rotor body portion 111. The permanent magnet portion 112 may be formed in a substantially ring shape that is concentric with the rotor body portion 111 when viewed from the axial direction S, or it may be formed so that multiple arc-shaped permanent magnet portions 112 are arranged at predetermined equally spaced arcs. Furthermore, the permanent magnet portion 112 may be formed to be substantially the same thickness as the rotor body portion 111 when viewed from the radial direction R, or it may be formed to be a different thickness.

[0018] The shaft 12 is the part that corresponds to the rotation axis of the axial motor. This shaft 12 comprises a shaft body portion 121, a bearing end portion 122, a connecting portion 123 to which the central portion 113 of the rotor body portion 111 is connected and fixed, and an output end portion 124.

[0019] The shaft body portion 121 is, for example, a steel member formed in a rod shape extending in the axial direction S.

[0020] The bearing end 122 is the input side (-S side) end of the shaft body 121 and is rotatably connected to a bearing (not shown), such as a ball bearing.

[0021] The connecting portion 123 is a predetermined part of the shaft body portion 121 and is fixed to the central portion 113 of the rotor body portion 111.

[0022] The output end 124 is the output side (+S side) of the shaft body 121 and is connected to an external device (not shown). The output end 124 is also inserted into a bearing (not shown), such as a ball bearing, and is held rotatably. In this example, the output terminal 124 is connected to an external device and provides output to the external device. However, the bearing terminal 122 and the output terminal 124 may be reversed, or both may be used as terminals that provide output to an external device.

[0023] The stator 13 is the part that corresponds to the magnetic field generating section (stator) of an axial motor. This stator 13 is constructed by a first stator 131 and a second stator 132, flanking the rotor 11.

[0024] The first stator 131 is formed in a wall shape parallel to the radial direction R, and is made of, for example, a steel member, and is formed in substantially the same shape as the rotor body 111. The first stator surface 1311, which is the surface of the first stator 131 facing the rotor 11 (+S side), is positioned at a predetermined distance L away from the first surface 114 (-S side) of the rotor 11. This first stator 131 is equipped with a first electromagnet 1312. Furthermore, the first stator 131 has a first insertion hole 1313 that is approximately circular in shape when viewed from the axial direction S. The input side (-S side) of the shaft body 121 is inserted through this first insertion hole 1313 without contact.

[0025] The first electromagnet section 1312 is formed by placing an electromagnet, constructed by winding coil wires around a core made of magnetic material, on the surface 1311 of the first stator. When viewed from the front in the axial direction S, the first electromagnet section 1312 is formed to be substantially the same shape as the permanent magnet section 112 of the rotor 11. Furthermore, the first electromagnet section 1312 is designed to generate a magnetic field when power supplied to the motor 10 from an external source is passed through it.

[0026] The second stator 132 is formed in a wall shape parallel to the radial direction R, and is made of, for example, a steel member, and is formed in substantially the same shape as the rotor body 111 and the first stator 131. The second stator surface 1321, which is the side of the second stator 132 facing the rotor 11 (-S side), is positioned at a predetermined distance L away from the second surface 115 (+S side) of the rotor 11. This second stator 132 is equipped with a second electromagnet section 1322. Furthermore, the second stator 132 has a second insertion hole 1323 that is approximately circular in shape when viewed from the axial direction S. The output side (+S side) of the shaft body 121 is inserted through this second insertion hole 1323 without contact.

[0027] The second electromagnet section 1322 is formed by placing an electromagnet, constructed by winding coil wires around a core made of magnetic material, on the surface 1321 of the second stator. When viewed from the front in the axial direction S, the second electromagnet section 1322 is formed to be substantially the same shape as the permanent magnet section 112 of the rotor 11. Furthermore, the second electromagnet section 1322 is designed to generate a magnetic field when power supplied to the motor 10 from an external source is passed through it.

[0028] Therefore, the rotor 11 is positioned such that the permanent magnet portion 112 faces the first electromagnet portion 1312 and the second electromagnet portion 1322, and is sandwiched between the first stator 131 and the second stator 132. The shaft 12 and the rotor 11 fixed to the shaft 12 rotate in the circumferential direction C of the shaft 12 when power is supplied to the first electromagnet portion 1312 and the second electromagnet portion 1322 of the stator 13. The circumferential direction C is the direction of rotation with the rotation axis of the motor 10 as the central axis.

[0029] The flow path 20 is, for example, a steel pipe through which the cooling fluid 30 can flow. A discharge section 21 is formed at the downstream end of the flow path 20. In addition, a flow rate adjustment section 24 and a temperature change section 23, as shown in Figure 4 below, are provided along the flow path 20.

[0030] The cooling fluid 30 is a fluid containing liquid methane, which can also be used as a propellant for electric aircraft, for example, and has the property that its temperature in the liquid phase state 30a is lower than the temperature of the rotor 11.

[0031] The discharge section 21 is the part of the motor 10 that supplies and discharges cooling fluid 30 to the rotor 11 for cooling. The discharge port 211 at the end of the flow path 20 is formed to discharge the cooling fluid 30 to the first surface 114 of the rotor 11 near the connection point 123 with the shaft 12, which is the rotation center of the rotor 11. In Figure 1, the discharge section 21 is provided with multiple discharge ports 211 for the flow paths 20 at the connection point 123 with the shaft 12.

[0032] The cooling fluid 30 is normally in a liquid phase state 30a within the flow path 20. In this invention, the cooling fluid 30 in liquid phase state 30a released from the discharge section 21 stretches the high-temperature rotor 11 from the center outward due to the centrifugal force caused by the rotation of the rotor 11, forming a thin liquid film 31. The temperature of the cooling fluid 30 in liquid phase state 30a and the flow rate of the cooling fluid 30 released from the discharge section 21 are adjusted so that when cooling the rotor 11, the thin liquid film 31 can easily evaporate to a thickness sufficient to form a saturated state at its gas-liquid interface with the surrounding vapor and exhibit sufficient cooling capacity.

[0033] In a space filled with the vapor of the cooling fluid 30, when the cooling fluid 30 in a properly adjusted liquid phase state 30a comes into contact with the high-temperature rotor 11 and is heated, the gas-liquid interface of the liquid film 31 becomes saturated. Because the liquid film 31 of the properly adjusted cooling fluid 30 evaporates very easily, it rapidly removes heat from the heated surface of the rotor 11. This high cooling performance makes it possible to lower the temperature inside the permanent magnet section 112, which has low thermal conductivity.

[0034] During cooling, the gap L between the rotor 11 and the stator 13 becomes a two-phase flow state consisting of a liquid film 31 in liquid phase state 30a and a gaseous phase state 30b consisting of generated vapor. Near the outer circumference of the rotor 11, almost all of the cooling fluid 30 in liquid phase state 30a becomes a refrigerant in gaseous phase state 30b, consisting of superheated vapor or moist vapor containing liquid droplets, and is discharged from the discharge section 142, which will be described later in Figure 4.

[0035] In conventional cooling methods, a problem is that the cooling capacity is lost when the liquid film of the cooling fluid 30 dries out. On the other hand, in cooling methods like the one disclosed in Patent Document 1, where the cooling fluid 30 is released in large quantities to the outside of the motor as a liquid phase even after cooling, the cooling performance is low and it was not possible to lower the temperature inside the permanent magnet section 112, which has low thermal conductivity. In this invention, by supplying an appropriate amount of liquid according to the rotational speed and temperature of the rotor 11, it is possible to form an optimal liquid film 31 in which the gas-liquid interface is constantly saturated.

[0036] In this invention, a control unit (not shown) is provided that controls the flow rate adjustment unit 24 and the temperature change unit 23 by a feedback circuit based on the rotational speed and temperature of the rotor 11 obtained by the aforementioned rotational speed measurement means and rotational temperature measurement means of the rotor 11. By controlling the flow rate and temperature of the cooling fluid 30 with this control unit, an optimal liquid film 31 is formed so that the gas-liquid interface is constantly saturated.

[0037] <Operation of the First Embodiment> The motor 10 constructed in this manner receives an operation command and energizes the first electromagnet section 1312 and the second electromagnet section 1322 of the stator 13, causing the rotor 11 and shaft 12 to rotate in the circumferential direction C. The output end 124 of the shaft 12 transmits the rotational motion in the circumferential direction C as power to external equipment.

[0038] The energization of the first electromagnet section 1312 and the second electromagnet section 1322, and the motion of the rotor 11 in the circumferential direction C, generate heat due to losses. Therefore, the cooling fluid 30 in a liquid phase state 30a is discharged from the discharge port 211 of the discharge section 21 toward the vicinity of the center of the first surface 114 near the connection point 123 with the shaft 12, which is the rotation center of the heated rotor 11. The cooling fluid 30 in a liquid phase state 30a is subjected to centrifugal force accompanying the rotational motion of the rotor 11 in the circumferential direction C, and stretches toward the outer circumference (radial direction R) of the rotor 11. The stretched cooling fluid 30 in a liquid phase state 30a forms a very thin liquid film 31 on the first surface 114 of the rotor 11. The liquid film 31 formed by the cooling fluid 30 in a liquid phase state 30a evaporates by absorbing heat from the first surface 114 of the rotor 11, and transitions to a refrigerant in a moist gas phase state 30b containing superheated vapor or liquid droplets. At this time, the liquid film 31 easily evaporates because the gas-liquid interface is saturated. The transition to the gas phase state 30b due to evaporation, i.e., the latent heat, efficiently absorbs heat from the rotor 11, thereby efficiently cooling the permanent magnet section 112, which has low thermal conductivity, and maintaining it at an appropriate temperature.

[0039] <Effects of the First Embodiment> According to the cooling method for the motor 10 of the first embodiment, the control unit controls the flow rate and temperature of the cooling fluid 30, thereby releasing the cooling fluid 30 to the rotor 11 to form a liquid film 31 that is constantly saturated or subcooled. As a result, the rotor 11 can be efficiently cooled using latent heat. The permanent magnet portion 112 of the rotor 11 is efficiently cooled using latent heat, maintaining an appropriate temperature and preventing a decrease or loss of magnetic force.

[0040] Furthermore, according to the cooling method for the motor 10 of the first embodiment, the contact area between the cooling fluid 30 and the first surface 114 of the rotor 11 is increased by forming a liquid film 31, thereby enabling more efficient cooling of the rotor 11. In addition, since the liquid film 31 is formed using the centrifugal force in the outer circumferential direction accompanying the rotation of the rotor 11, the liquid film 31 can be formed efficiently.

[0041] Furthermore, according to the cooling method for the motor 10 of the first embodiment, since liquid methane, which can also be used as a propellant for electric aircraft and the like, is used as the cooling fluid 30, it is easy to implement.

[0042] Although the first embodiment of the present invention has been described in detail above with reference to the drawings, the specific configuration is not limited to this embodiment, and design changes and the like are also included within the scope of the gist of the present invention. Furthermore, the components shown in the above-described embodiment and the following modifications can be combined as appropriate. In the following explanation, components that are common to those already explained will be denoted with the same symbols, and redundant explanations will be omitted.

[0043] <Variation A> Figure 2 is a cross-sectional view showing the motor 10A of modified example A.

[0044] In modified example A, a flow path 20 is formed inside the shaft body portion 121A of the shaft 12A. In Figure 2, the flow path 20 is a flow path for the cooling fluid 30 formed in a spiral shape extending along the axial direction S, and has an outlet 211A at a position approximately in the same plane as the first surface 114 of the rotor 11, forming an outlet portion 21A. The flow path 20 may also be formed to extend linearly along the axial direction S.

[0045] The discharge port 211A is a plurality of holes formed on the side surface of the shaft body 121A. It is provided to discharge the cooling fluid 30 in a liquid phase state 30a that flows inside the flow path 20 toward the first surface 114 of the rotor 11.

[0046] According to the cooling method for the motor 10A in modified example A, it is not necessary to provide a flow path 20 in the stator 13 and the housing (not shown). Furthermore, since the cooling fluid 30 can be introduced closer to the rotational axis of the rotor 11 than in the first embodiment, the cooling fluid 30 can cool the entire rotor 11.

[0047] Furthermore, according to the cooling method for the motor 10A described in modified example A, since the flow path 20 is formed in a spiral shape, the centrifugal force associated with the rotational motion of the rotor 11 toward the circumferential direction C promotes the flow of the cooling fluid 30 in the liquid phase state 30a toward the outlet 211A.

[0048] <Variation B> Figure 3 is a cross-sectional view showing the motor 10B of modified example B. This motor 10B includes a second discharge section 21B in addition to the discharge section 21 of the first embodiment.

[0049] The second discharge section 21B has a second discharge port 211B at the end of the flow path 20 inserted through the second stator 132, which protrudes to supply and discharge cooling fluid 30 from the second stator 132 to the vicinity of the connection portion 123 between the second stator 132 and the shaft 12, which is the rotation center on the second surface 115 side of the rotor 11.

[0050] The second discharge section 21B supplies and discharges cooling fluid 30 to the second surface 115 side of the rotor 11, which is the back side of the rotor 11 of the discharge section 21, and its configuration is the same as that of the discharge section 21. The flow path 20 forming the discharge section 21 and the second discharge section 21B may be configured with separate flow rate adjustment section 24, temperature variable section 23, and control unit, or the flow rate adjustment section 24, temperature variable section 23, and the control unit described later may be common, and a branch section (not shown) may be provided in one flow path 20 to divide the cooling fluid 30 between the discharge section 21 side and the second discharge section 21B side. The flow rate adjustment section 24 and temperature variable section 23 may be provided downstream of the branch section, and the temperature and flow rate of the cooling fluid 30 on the discharge section 21 side and the second discharge section 21B side may be controlled to be different. Furthermore, as in modified example A, the flow path 20 may be provided from both sides in the axial direction S of the shaft 12, and modified example A may be configured to discharge and supply the cooling fluid 30 from both sides of the rotor 11.

[0051] According to the cooling method for the motor 10B of modified example B, the motor 10B can be cooled more efficiently by forming a liquid film 31 on both the first surface 114 and the second surface 115 of the rotor 11.

[0052] In the first embodiment, the motor 10 is an axial motor, but the shape and configuration of the motor 10 are not limited to this. For example, motor 10 may be a radial motor. Furthermore, the motor 10 may be another device that generates rotational motion by magnetic force, such as a magnetic clutch. In that case, the discharge port 211 is formed to discharge the cooling fluid 30 toward the rotor that generates heat.

[0053] [Second Embodiment] A cooling system 1 for a motor 10 according to a second embodiment of the present invention will be described with reference to Figure 4. Figure 4 shows a cooling system 1 for a motor 10 equipped with the cooling mechanism of the first embodiment. Modifications A and B can also be realized with a similar cooling system 1 by providing a flow path 20 in the shaft 12 and configuring the system to discharge and supply cooling fluid 30 from both sides of the rotor 11.

[0054] <Configuration of the second embodiment> The cooling system 1 comprises a motor 10, a flow path 20, a cooling fluid 30, and a control unit (not shown). The control unit is a program-executable computer having a processor such as a CPU, a storage unit capable of storing programs and data, a memory capable of reading programs, an arithmetic unit that processes signals from sensors and the like, and a calculation unit that determines the optimal flow rate, temperature, etc., of the cooling fluid 30.

[0055] The motor 10 is enclosed inside a housing 14, for example, made of steel, which is formed in a roughly rectangular box shape when viewed from the side in the radial direction R. The housing portion 14 corresponds to the motor case of the axial motor. This housing portion 14 includes an insertion portion 141 and an discharge portion 142.

[0056] In the example shown in Figure 4, the insertion section 141 is an opening provided on the input side (-S side) wall of the housing section 14, through which the shaft 12 and discharge section 21 are inserted. This insertion section 141 is closed using an airtight material or the like while the shaft 12 and discharge section 21 are inserted.

[0057] The discharge section 142 is an opening provided on the wall surface of the housing section 14 parallel to the axial direction S, and is connected to the flow path 20, which will be described later. This discharge section 142 is provided so that the cooling fluid 30, after cooling the motor 10, has vaporized (into a gaseous state 30b) and is discharged to the outside of the housing section 14.

[0058] The flow path 20 includes a main path section 22 connected to the discharge section 142, a temperature control section 23 for adjusting the temperature of the cooling fluid 30 in the flow path 20, a flow rate adjustment section 24 for adjusting the flow rate of the cooling fluid 30 in the flow path 20, and a power supply section 25.

[0059] The main body of the circulation path 22 is a single circulation path constructed, for example, with steel piping, and is the main body of the circulation path 20 through which the cooling fluid 30 can flow. The refrigerant and cooling fluid 30 in a gaseous state 30b that flow through the main body of the circulation path 22 flow in one direction F from the upstream end 221, which is the opening of the discharge section 142 provided at one upstream end of the main body of the circulation path 22, to the downstream end 222, which is the opening provided at the other downstream end.

[0060] The temperature-variable unit 23 is a condensing device, such as a radiator or Peltier element, that is provided to cool or adjust the temperature of the refrigerant in the gas phase state 30b within the flow path 20. This temperature-variable unit 23 is located in the middle of the main flow path 22. The temperature-variable unit 23 is also provided to communicate with the control unit, and upon receiving an operation command, it cools the refrigerant in the gas phase within the main flow path 22 until it becomes a cooling fluid 30 that can be cooled by the motor 10. The control unit may measure the temperature of the cooling fluid 30 using a temperature measuring unit (not shown), and based on the result, the input threshold, the result of the calculation unit, etc., send an operation command to the temperature control unit 23 for adjusting the temperature of the cooling fluid 30.

[0061] The flow rate adjustment unit 24 is a transfer device, such as a valve or pump, that is provided to adjust the flow rate of the cooling fluid 30 in the flow path 20. This flow rate adjustment unit 24 is located in the path of the main path 22 and downstream of the temperature change unit 23. The flow rate adjustment unit 24 is also provided to communicate with the control unit, and upon receiving an operation command, it transfers the cooling fluid 30 in the main path 22 downstream. The control unit may measure the flow rate of the cooling fluid 30 using a flow rate measuring unit (not shown) and send an operation command to the flow rate adjustment unit 24 based on the result, the input threshold, the result of the calculation unit, etc. Alternatively, the control unit may calculate or measure the rotational speed of the rotor 11 and send an operation command to the flow rate adjustment unit 24 based on the result, the input threshold, the result of the calculation unit, etc.

[0062] The power supply unit 25 is a power supply device, such as a battery, that is provided to supply electricity to equipment in the distribution path 20. This power supply unit 25 is located inside the cooling system 1 and supplies power to the temperature control unit 23, the flow rate adjustment unit 24, and the motor 10.

[0063] <Operation of the second embodiment> In the motor cooling system 1 constructed in this manner, the liquid film 31 formed by the cooling fluid 30 in liquid phase state 30a released from the discharge section 21, where the gas-liquid interface is saturated, absorbs heat from the first surface 114 of the rotor 11 and transitions to the gas phase state 30b. As the cooling fluid 30 transitions to the gas phase state 30b, the pressure inside the housing section 14 increases, and the refrigerant in the gas phase state 30b flows from the discharge section 142 into the main body section 22 of the flow path 20. The refrigerant in the gas phase state 30b inside the main body section 22 is cooled by the temperature change section 23 and transitions to the cooling fluid 30 in liquid phase state 30a. The cooling fluid 30 in liquid phase state 30a is adjusted by the flow rate adjustment section 24 to a predetermined flow rate formed on the first surface 114 of the rotor 11, transported downstream, and released from the discharge section 21, once again forming a liquid film 31 on the first surface 114 where the gas-liquid interface is saturated.

[0064] The thickness of the liquid film 31 in the saturated and subcooled states varies depending on the rotational speed of the rotor 11 and the flow rate and temperature of the cooling fluid 30. This liquid film 31 absorbs heat from the contact surface with the first surface 114 of the rotor 11. Therefore, if the liquid film 31 is formed thickly (large in the axial direction S), the contact area per unit flow rate decreases, resulting in reduced cooling efficiency. On the other hand, if the liquid film 31 is formed thinly (small in the axial direction S), the contact area per unit flow rate increases, resulting in improved cooling efficiency. Specifically, the optimal condition is a liquid film thickness at which the liquid film 31 completely transitions to the gaseous state 30b just before it reaches the radial R (outer circumference of the rotor 11) end of the first surface 114 of the rotor 11. Therefore, the control unit can operate the flow rate adjustment unit 24 based on the measurement results of the flow rate of the cooling fluid 30 and the calculation results of the rotational speed of the rotor 11 to form a liquid film 31 with an optimal thickness that saturates the gas-liquid interface.

[0065] <Effects of the second embodiment> According to the motor 10 cooling system 1 of the second embodiment, the refrigerant, which has absorbed heat from the first surface 114 of the rotor 11 and become a gaseous state 30b, is cooled by the temperature-changing section 23 until it becomes a cooling fluid 30 in a liquid state 30a, and is supplied to and released from the rotor 11, thereby allowing it to absorb heat again from the first surface 114 of the rotor 11. Since the cooling fluid 30 is not discarded but circulates within the cooling system 1, it has a low environmental impact and low operating costs.

[0066] Furthermore, according to the motor 10 cooling system 1 of the second embodiment, the rotor 11 can be cooled even more efficiently because a liquid film 31 with an optimal thickness is formed by calculations in the control unit, adjustment of the flow rate by the flow rate adjustment unit 24, and adjustment of the temperature of the temperature change unit 23.

[0067] Although a second embodiment of the present invention has been described in detail above with reference to the drawings, the specific configuration is not limited to this embodiment, and design modifications and the like are also included within the scope of the gist of the present invention. Furthermore, the components shown in the above-described embodiment and the following modifications can be combined as appropriate.

[0068] For example, a portion of the refrigerant that has entered the gas phase state 30b may be cooled by the outside air surrounding the housing 14 and stored as a liquid phase at the bottom of the housing 14. To prevent this, a heating section may be provided in the housing 14 to convert the stored refrigerant into a gas phase. [Examples]

[0069] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples. In the following embodiment, the conditions for the cooling fluid 30 required for cooling the magnet (permanent magnet portion 112) were analyzed and calculated.

[0070] The cooling of the permanent magnet portion 112 will be examined using the model shown in Figure 5, which consists of the permanent magnet portion 112 and the liquid film 31 of the cooling fluid 30 formed on the surface of the permanent magnet portion 112. If we define the bottom surface of the magnet in the model as zero and the thickness of the magnet as x0, then it can be represented as any coordinate x within the magnet. At this time, the temperature distribution related to the permanent magnet part 112 is derived by the following equation (1). As shown in equation (1), the temperature distribution T related to the permanent magnet part 112 is given by the thickness x0 of the magnet, an arbitrary coordinate x within the magnet, the amount of heat generated q, and the temperature T of the cooling fluid. f The thermal conductivity of the magnet, k, and the heat transfer coefficient of the cooling index, h, are given by these factors.

[0071]

number

[0072] Figure 6 shows the temperature distribution of the magnet against the heat transfer coefficient h, which is a cooling index. The horizontal axis of Figure 6 represents the thickness of the magnet x0 (an arbitrary coordinate x inside the magnet), as shown in Figure 5. The vertical axis of Figure 6 represents the amount of heat generated inside the magnet. The dashed line (Keeping below the temp) extending parallel to the horizontal axis of Figure 6 represents the upper limit of the appropriate temperature at which the magnetic force of the magnet is maintained. From Figure 6, the heat transfer coefficient is at least less than or equal to the dashed line, which is 3.0 × 10⁻⁶. 4 W / m 2 It becomes clear that / K is necessary.

[0073] The discharge flow rate of the cooling fluid 30 required to achieve the heat transfer coefficient of the cooling index is derived by the following equations (2)-(4). Thickness of the liquid film 31 formed by the cooling fluid 30 (size in the axial direction S) δ N This is derived by the following equation (2). As shown in equation (2), the liquid film thickness δ N The rotational speed is given by the fluid flow rate Q, the fluid's kinematic viscosity v, the rotor radius r, and the rotor's rotational speed ω.

[0074]

number

[0075] Here, it can be assumed that the liquid film 31 formed by the cooling fluid 30 in a liquid phase state (saturated or subcooled state) 30a evaporates (transitions to the gas phase) to the extent that it absorbs heat from the rotor 11, and therefore the thermal conductivity k of the cooling fluid liquid Thus, the relationship shown in equation (3) below holds.

[0076]

number

[0077] Then, by integrating and averaging the heat transfer coefficients based on equations (2) and (3), the average heat transfer coefficient of the liquid film 31 on the magnet can be determined by the following equation (4), where R1 is the shaft radius and R2 is the rotor radius.

[0078]

Num.

[0079] In this example, the cooling fluid was evaluated based on the above mathematical formula (4) and various conditions.

[0080] <Example 1 / Liquid Methane> In Example 1, evaluation was performed when liquid methane was used as the cooling fluid 30. This liquid methane is a cryogenic fluid used as a fuel for motors having high power density such as those installed in electric aircraft.

[0081] Figure 7 is a diagram showing the heat transfer coefficient of liquid methane based on flow rate and rotational speed. The horizontal axis of Figure 7 indicates the rotational speed of the rotor 11, and the vertical axis indicates the flow rate of liquid methane. The heat map scale shown on the right side of Figure 7 indicates the thermal conductivity of liquid methane represented by the shading in Figure 7. The white line on the heat map of Figure 7 indicates that the thermal conductivity of liquid methane is 3×10 4 W / (m 2 K), which is an isoline.

[0082] Figure 8 is a diagram showing the liquid film thickness required for cooling liquid methane (required liquid film thickness) based on flow rate and rotational speed. The horizontal axis of Figure 8 indicates the rotational speed of the rotor 11, and the vertical axis indicates the flow rate of liquid methane. The heat map scale shown on the right side of Figure 8 indicates the required liquid film thickness of liquid methane represented by the shaded areas in Figure 8. The white line on the heat map of Figure 8 corresponds to the isoline where the thermal conductivity of liquid methane shown in Figure 7 is 3×10 4 W / (m 2 K), which is an isoline where the required liquid film thickness of liquid methane is 6.12 μm.

[0083] Therefore, in Example 1, the control unit is set so as to discharge liquid methane at a flow rate at which the thickness of the liquid film 31 becomes 6.12 μm for a predetermined rotational speed. Thereby, the cooling system 1 can cool the motor 10 more efficiently.

[0084] <Example 2 / Liquid Nitrogen> Example 2 involved an evaluation of the case where liquid nitrogen was used as the cooling fluid 30. This liquid nitrogen is a fluid commonly used as an cryogenic fluid.

[0085] Figure 9 shows the heat transfer coefficient of liquid nitrogen based on flow rate and rotational speed. The horizontal axis of Figure 9 represents the rotational speed of rotor 11, and the vertical axis represents the flow rate of liquid nitrogen. The heat map lines shown to the right of Figure 9 represent the thermal conductivity of liquid nitrogen in shades within Figure 9. The white line on the heat map in Figure 9 represents the thermal conductivity of liquid nitrogen at 1 × 10⁻⁶. 4 W / (m 2 These are contour lines that satisfy the condition K).

[0086] Figure 10 shows the required liquid nitrogen film thickness based on flow rate and rotational speed. The horizontal axis of Figure 10 represents the rotational speed of the rotor 11, and the vertical axis represents the liquid nitrogen flow rate. The heat map lines shown on the right of Figure 10 indicate the required liquid nitrogen film thickness at the areas of light and dark areas within Figure 10. The white lines on the heat map in Figure 10 represent the thermal conductivity of liquid nitrogen shown in Figure 9, which is 1 × 10⁻⁶. 4 W / (m 2 This is the contour line corresponding to K), where the required liquid nitrogen film thickness is 14.45 μm.

[0087] Therefore, in Example 2, the control unit is set to release liquid nitrogen at a flow rate such that the thickness of the liquid film 31 becomes 14.45 μm for a predetermined rotational speed. This allows the cooling system 1 to cool the motor 10 even more efficiently.

[0088] <Example 3 / Liquid Hydrogen> Example 3 involved an evaluation of the case where liquid hydrogen was used as the cooling fluid 30. This liquid hydrogen is a cryogenic fluid used as fuel for motors with high power density, such as those in electric aircraft.

[0089] Figure 11 shows the heat transfer coefficient of liquid hydrogen based on flow rate and rotational speed. The horizontal axis of Figure 11 represents the rotational speed of rotor 11, and the vertical axis represents the flow rate of liquid hydrogen. The heat map lines shown on the right of Figure 11 represent the thermal conductivity of liquid hydrogen in varying shades within Figure 11. The white line on the heat map in Figure 11 represents the thermal conductivity of liquid hydrogen at 1 × 10⁻⁶. 4 W / (m 2 These are contour lines that satisfy the condition K).

[0090] Figure 12 shows the required liquid hydrogen film thickness based on flow rate and rotational speed. The horizontal axis of Figure 12 represents the rotational speed of the rotor 11, and the vertical axis represents the flow rate of liquid hydrogen. The heat map line shown on the right of Figure 12 indicates the required liquid hydrogen film thickness at the areas of light and dark areas in Figure 12. The white line on the heat map of Figure 12 represents the thermal conductivity of liquid hydrogen shown in Figure 11, which is 1 × 10⁻⁶. 4 W / (m 2 This is the contour line corresponding to K), where the required liquid hydrogen film thickness is 10.36 μm.

[0091] Therefore, in Example 3, the control unit is set to release liquid hydrogen at a flow rate such that the thickness of the liquid film 31 becomes 10.36 μm for a predetermined rotational speed. This allows the cooling system 1 to cool the motor 10 even more efficiently.

[0092] According to the embodiment, the material and properties of the cooling fluid 30 are not particularly limited, as long as it is a fluid (for example, liquid methane, liquid nitrogen, and fluorine-based inert fluids) that has properties such that the temperature of the saturated or subcooled state is lower than the temperature of the heat loss caused by the motor 10. Furthermore, the cooling system 1 can efficiently cool the motor 10 by forming a liquid film 31 of an optimal thickness according to the properties of the cooling fluid 30. [Explanation of symbols]

[0093] 1. Cooling System 10 motors 11 rotors 12 shafts 13 ステーター 20 Circulation Road 21, 21A, 21B Emission Section 23 Ministry of Warmth 24 Flow Adjustment Department 30 Cooling fluid 31 Liquid film 112 Permanent Magnet Department 113 Central Department 131 First ステーター 132 The second ステーター 211 Export S-axis direction

Claims

1. A motor comprising a rotor having a permanent magnet and a stator having an electromagnet, A cooling fluid for cooling the motor, It comprises a tubular flow path through which the cooling fluid flows, The aforementioned distribution channels are It has a discharge section that discharges the cooling fluid from the discharge port toward the rotor, The cooling fluid released onto the rotor forms a liquid film on the rotor surface in a liquid phase state where the gas-liquid interface is saturated. Motor cooling system.

2. A flow rate adjustment unit for adjusting the flow rate of the cooling fluid, The system includes a flow rate adjustment unit and a control unit that controls the operation of the motor, The control unit controls the operation of the flow rate adjustment unit based on the results calculated by the calculation unit, and sets the flow rate of the cooling fluid. A motor cooling system according to claim 1.

3. A temperature control unit that adjusts the temperature of the cooling fluid, It comprises a control unit that controls the operation of the temperature-changing unit and the motor, The control unit controls the operation of the temperature change unit based on the results calculated by the calculation unit and sets the temperature of the cooling fluid. A motor cooling system according to claim 1.

4. The stator comprises a first stator and a second stator, which are provided to sandwich the rotor. The discharge portion is formed in the shape of a nozzle inserted into at least one of the first stator and the second stator, The aforementioned discharge port is positioned to face the central part of the rotor. A motor cooling system according to claim 1.

5. Multiple discharge sections are provided and are inserted into the first stator and the second stator, respectively. A motor cooling system according to claim 4.

6. The rotor is fixed to a shaft that serves as the axis of rotation. The aforementioned flow path is a path formed inside the shaft, The discharge port is a hole formed on the side of the shaft and near the surface of the rotor. A motor cooling system according to claim 1.

7. The aforementioned flow path is formed as a spiral-shaped path extending axially inside the shaft. A motor cooling system according to claim 6.

8. The cooling fluid includes any of the following: liquid methane, liquid nitrogen, liquid nitrogen, or a fluorine-based inert fluid. A motor cooling system according to claim 1.

9. A method for cooling a motor comprising a rotor having a permanent magnet and a stator having an electromagnet, The cooling fluid for cooling the motor is discharged from a tubular flow path toward the rotor via an outlet, and the cooling fluid discharged toward the rotor forms a saturated liquid film at the gas-liquid interface on the rotor surface. Motor cooling methods.

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