Coil and method for manufacturing coil

Abstract

The present invention is capable of suppressing temperature rise of a coil. A coil (4) is used in a motor. The coil (4) comprises a first member (41) and a second member (42). The first member (41) is formed of a metal material and has a hollow portion. The first member (41) has a cylindrical shape. The second member (42) is disposed in the hollow portion of the first member (41). The second member (42) includes a phase change part (61) composed of a phase change material. The thickness (X1) between the outer surface (411) and the inner surface (412) of the first member (41) is greater than or equal to the skin depth (X2) determined by the rated frequency of the motor current in the motor.

Description

Coil and Method for Manufacturing Coil

[0001] The present disclosure generally relates to a coil and a method for manufacturing a coil, and more particularly to a coil used in a motor and a method for manufacturing the coil.

[0002] Patent Document 1 discloses a stator used for constructing a rotating electric machine such as an electric motor or a generator. The stator includes a stator core and three-phase coil wires of U-phase, V-phase, and W-phase wound around the stator core in a distributed winding manner. The coil wire has a pipe material forming an outer skin and a heat storage material, which is a low-melting-point metal, filled inside the pipe material.

[0003] Japanese Unexamined Patent Application Publication No. 2020-89232

[0004] By the way, in a coil wire (coil) used in an electric motor (for example, an AC (alternating current) motor) as disclosed in Patent Document 1, it is desired to suppress temperature rise.

[0005] The present disclosure has been made in view of the above circumstances, and an object thereof is to provide a coil and a method for manufacturing a coil capable of suppressing temperature rise.

[0006] The coil according to one aspect of the present disclosure is used in a motor. The coil includes a first member and a second member. The first member is formed of a metal material and has a hollow portion. The first member is cylindrical. The second member is disposed in the hollow portion of the first member and includes a phase change portion formed of a phase change material. The thickness between the outer surface and the inner surface of the first member is not less than the skin depth determined by the rated frequency of the motor current in the motor.

[0007] The method for manufacturing a coil according to one aspect of the present disclosure is a method for manufacturing a coil used in a motor. The method for manufacturing a coil has a first step and a second step. In the first step, a cylindrical first member having a hollow portion is formed of a metal material. In the second step, a material containing a phase change material is injected into the hollow portion of the first member to form a second member including a phase change portion. In the first step, the first member is formed such that the thickness between the outer surface and the inner surface of the first member is not less than the skin depth determined by the rated frequency of the motor current in the motor.

[0008] According to this disclosure, it is possible to suppress the temperature rise of the coil.

[0009] Figure 1 is a schematic diagram showing the configuration of a motor equipped with a coil according to the embodiment. Figure 2 is a schematic cross-sectional view showing the main part of the motor according to the embodiment. Figure 3 is a schematic cross-sectional view showing the coil according to the embodiment. Figure 4 is a schematic diagram for explaining the phase change portion included in the coil according to the embodiment. Figure 5 is an explanatory diagram for explaining the manufacturing method of the coil according to the embodiment. Figure 6 is an explanatory diagram for explaining the manufacturing method of the coil according to the embodiment. Figure 7 is an explanatory diagram for explaining the manufacturing method of the coil according to the embodiment. Figure 8 is an explanatory diagram for explaining the manufacturing method of the coil according to the embodiment. Figure 9 is a graph showing the relationship between the volume fraction and latent heat of vanadium dioxide, which is the material of the phase change portion included in the coil according to Modification 1, and the relationship between the volume fraction and thermal conductivity. Figure 10 is a schematic cross-sectional view showing the coil according to Modification 2.

[0010] Preferred embodiments of this disclosure will be described in detail below with reference to the drawings. Common elements in the embodiments described below are denoted by the same reference numerals, and redundant descriptions of common elements may be omitted. Note that the following embodiments and their variations are only a part of the various embodiments of this disclosure. Furthermore, the following embodiments and their variations can be modified in various ways depending on the design, etc., as long as the objectives of this disclosure are achieved. It is also possible to combine the configurations of the embodiments and their variations as appropriate.

[0011] The figures described in this disclosure are schematic diagrams, and the ratios of the size and thickness of each component in each figure do not necessarily reflect the actual dimensional ratios. Furthermore, the arrows indicating directions in the drawings are examples only and are not intended to specify the direction in which the motor 1 is used. Also, the arrows indicating directions in the drawings are for illustrative purposes only and do not represent actual objects.

[0012] (1) Overview First, an overview of the motor 1 according to this embodiment will be described with reference to Figures 1 to 3.

[0013] Figure 1 is a schematic diagram showing the configuration of a motor 1 equipped with coils 4 according to this embodiment. As shown in Figure 1, the motor 1, which is an AC motor in this embodiment, is equipped with a plurality of coils 4 (nine in the example of Figure 1). In other words, the plurality of coils 4 are used in the motor 1, which is an AC motor.

[0014] Figure 2 is a schematic cross-sectional view showing the main part of the motor 1 according to the embodiment. Figure 3 is a schematic cross-sectional view showing the coil 4 according to the embodiment. As shown in Figures 2 and 3, each of the plurality of coils 4 comprises a first member 41 and a second member 42.

[0015] The first member 41 is made of a metal material and has a hollow portion SP1 (see Figure 5, described later). The first member 41 is cylindrical.

[0016] The second member 42 is positioned in the hollow portion SP1 of the first member 41. The second member 42 includes a phase change portion 61 (see Figure 4, described later) made of a phase change material (PCM).

[0017] As shown in Figure 3, the thickness X1 between the outer surface 411 and the inner surface 412 of the first member 41 is greater than or equal to the skin depth X2, which is determined by the rated frequency of the motor current in the motor 1. In the example in Figure 3, the thickness X1 is greater than the skin depth X2. In this embodiment, the skin depth X2 is the depth relative to the outer surface 411 of the first member 41 (see Figure 3).

[0018] Here, the rated frequency of the motor current is the frequency of the current flowing through the coil 4 of motor 1 when motor 1 is operating at the rated rotational speed specified in the motor 1 catalog or specifications. The rated frequency is determined by the rated rotational speed and the number of poles of motor 1. In the following explanation, the current flowing through coil 4 may be referred to as the motor current.

[0019] In this embodiment, the coil 4 includes a phase change section 61 made of a phase change material such as paraffin inside the coil 4. As a result, when the temperature of the coil 4 rises and reaches a specific temperature, the latent heat of the phase change section 61 suppresses the temperature rise of the coil 4.

[0020] Here, as the frequency of the motor current increases, the current flowing through the coil 4 concentrates on the outside of the coil 4 (the outer surface 411 side) due to the skin effect. In the coil 4 of this embodiment, the thickness X1 of the first member 41, which is made of a metal material such as copper, is greater than or equal to the skin depth X2. In other words, in the coil 4 of this embodiment, the second member 42 including the phase change section 61 is not placed in the region less than the skin depth X2 where the motor current is concentrated. Therefore, it is possible to suppress the increase in copper loss of the coil 4 and the increase in the cross-sectional area of ​​the coil 4 that would occur if the phase change section 61 were included.

[0021] (2) Details The detailed configuration of the motor 1 according to this embodiment will be described below with reference to Figures 1 to 4.

[0022] (2.1) Motor Configuration Motor 1 is, for example, an AC servo motor, and is an inner rotor type three-phase servo motor. Motor 1 transmits rotational force to industrial machinery such as conveying machines or machine tools, or to loads such as robots, and drives the loads. Power is supplied to Motor 1 from, for example, a control device.

[0023] As shown in Figure 1, the motor 1 comprises a stator 2, a rotor 5, and a housing 10. The housing 10 houses the stator 2 and the rotor 5.

[0024] (2.2) Rotor Configuration The rotor 5 has a rotor core 51, a plurality of permanent magnets 52 (eight in the example of Figure 1), and a motor shaft 53.

[0025] The rotor core 51 is located inside the stator 2. The rotor core 51 has a cylindrical shape centered on the motor shaft 53. The rotor core 51 is made of, for example, iron. However, the rotor core 51 may be made of silicon steel, permalloy, or ferrite, etc. The rotor core 51 holds a plurality of permanent magnets 52.

[0026] Multiple permanent magnets 52 are arranged on the outer circumference of the rotor core 51. The multiple permanent magnets 52 are arranged so that north poles and south poles alternate in the circumferential direction of the rotor core 51. The multiple permanent magnets 52 are permanent magnets such as neodymium magnets.

[0027] The motor shaft 53 is fixed to the inner circumference of the rotor core 51. The shape of the motor shaft 53 is cylindrical.

[0028] The interaction between the magnetic fields generated by the multiple permanent magnets 52 and the magnetic fields generated by the current flowing through the multiple coils 4 of the stator 2 causes the rotor core 51 and the motor shaft 53 to rotate around the rotation axis Ax1.

[0029] (2.3) Stator Configuration The overall shape of the stator 2 is cylindrical with the motor shaft 53 at its center. The stator 2 has a stator core 3 (magnetic core) and a plurality of coils 4 (nine in the example in Figure 1).

[0030] The stator core 3 is a magnetic core made of, for example, silicon steel. The stator core 3 has an outer circumference 32 and a plurality of teeth 31 (nine in the example in Figure 1).

[0031] The outer circumference 32 has a cylindrical shape centered on the motor shaft 53.

[0032] Each of the multiple teeth 31 corresponds one-to-one with each of the multiple coils 4. The multiple teeth 31 are arranged at equal intervals (i.e., equal angular intervals) along the circumferential direction of the outer circumference 32. Each of the multiple teeth 31 protrudes from the inner circumferential surface of the outer circumference 32 toward the motor shaft 53 along the radial direction of the motor shaft 53. Each of the multiple teeth 31 is the winding axis of the corresponding coil 4 among the multiple coils 4. In other words, the winding axis direction D1 of the coil 4 (see Figure 2) is along the radial direction of the motor shaft 53.

[0033] Multiple coils 4 are arranged at equal intervals along the circumferential direction of the motor shaft 53. As shown in Figure 2, the coils 4 in this embodiment are made of round wire. Figure 2 is a schematic cross-sectional view obtained by cutting the coils 4 through a virtual plane. Note that the normal direction of the virtual plane in this embodiment is aligned with the axial direction of the motor shaft 53.

[0034] The coil 4 is wound multiple times around the corresponding teeth 31. More specifically, the coil 4 is wound multiple times around the teeth 31 along the winding axis direction D1 of the coil 4. Furthermore, the coil 4 is multi-layered when viewed from the winding axis direction D1 of the coil 4. In other words, the coil 4 is wound around the teeth 31 in a layered manner in the layer direction D2 perpendicular to the winding axis direction D1 when viewed from the winding axis direction D1. Note that in the following explanation, "wound multiple times" may be simply referred to as "wound."

[0035] Furthermore, the term "orthogonal (perpendicular)" as used in this disclosure includes not only a state where the angle between two objects is exactly 90 degrees, but also a state where the two objects intersect within a certain range of difference. In other words, the angle between two orthogonal objects falls within a certain range of difference from 90 degrees (for example, 5 degrees or less). That is, the term "orthogonal" as used in this disclosure includes cases where the angle between two objects is between 85 degrees and 95 degrees.

[0036] The adjacent portions of the coil 4 (the multiple cross-sections of the coil 4 in Figure 2) are electrically insulated by an insulating member 7 made of polyurethane or the like. In Figure 2, the insulating member 7 is shown with dodge hatching.

[0037] As shown in Figure 3, the coil 4 of this embodiment includes a first member 41, a second member 42, and an insulating coating 43. Note that the insulating coating 43 is not shown in Figure 2.

[0038] The first member 41 is made of a metallic material such as copper or aluminum. The first member 41 is cylindrical and has a hollow portion SP1 (see Figure 5, described later). In this embodiment, the first member 41 is cylindrical. The first member 41 functions as a conductive part through which the motor current mainly flows.

[0039] The thickness X1 between the outer surface 411 and the inner surface 412 of the first member 41 is greater than or equal to the skin depth X2, which is determined by the rated frequency of the motor current in the motor 1. In the example shown in Figure 3, the thickness X1 is greater than the skin depth X2. In this embodiment, the skin depth X2 is the depth relative to the outer surface 411 of the first member 41 (see Figure 3). Furthermore, it is preferable that the thickness X1 between the outer surface 411 and the inner surface 412 of the first member 41 is greater than or equal to the skin depth X2, and less than twice the skin depth X2.

[0040] The second member 42 is positioned in the hollow portion SP1 of the first member 41. The second member 42 in this embodiment is cylindrical. Figure 4 is a schematic diagram illustrating the phase change portion 61 included in the coil 4 according to this embodiment. The second member 42 in this embodiment includes a resin portion 63 and a plurality of capsules 62 (see Figure 4) that enclose the phase change portion 61.

[0041] The material of the resin part 63 includes resin materials such as epoxy resin, silicone resin, or polyimide resin. The resin part 63 is filled in the hollow part SP1 of the first member 41.

[0042] Multiple capsules 62 enclose the phase change section 61. In other words, the second member 42 contains multiple capsules 62 that enclose the phase change section 61. The capsules 62 are microcapsules, and the diameter of the capsules 62 is 2 μm to 300 μm. Note that Figure 4 is a perspective view in which a part of the capsule 62 has been broken, and in Figure 4 the phase change section 61 is exposed to the outside of the capsule 62, but in reality the phase change section 61 is not exposed to the outside of the capsule 62.

[0043] The capsule 62 is a microcapsule formed from, for example, acrylic resin or urethane resin. By using the phase change section 61 already enclosed in the capsule 62, the effort required to seal the phase change section 61 can be reduced, and the expansion and contraction of the phase change section 61 can be suppressed.

[0044] The material of the phase change part 61 includes a phase change material. The phase change material of this embodiment is paraffin such as petrolatum, wax, or grease. That is, the phase change part 61 of this embodiment is composed of paraffin. The phase change material that is paraffin melts at a specific temperature and absorbs the thermal energy around the phase change material.

[0045] When the temperature of the coil 4 rises due to Joule heat during the operation of the motor 1 and reaches the melting temperature of the phase change part 61, the phase change part 61 begins to melt. Thereby, the temperature rise of the coil 4 is suppressed until the melting of the phase change part 61 ends.

[0046] Also, the arithmetic mean roughness (Ra) of the inner surface 412 (see FIG. 3) of the first member 41 of this embodiment is larger than the average particle diameter of the plurality of capsules 62 (that is, the average diameter of the plurality of capsules 62). Thereby, the contact area between the inner surface 412 of the first member 41 and the plurality of capsules 62 can be increased, and the thermal conductivity between the inner surface 412 of the first member 41 and the plurality of capsules 62 that enclose the phase change part 61 can be reduced. Therefore, according to the coil 4 of this embodiment, by more surely transmitting the Joule heat generated in the first member 41 to the phase change part 61, the Joule heat can be more surely absorbed by the phase change part 61, so that the temperature rise of the coil 4 can be further suppressed.

[0047] (3) Manufacturing method of the coil Next, a manufacturing method of the coil 4 used in the motor 1 which is an AC motor of this embodiment will be described with reference to FIGS. 5 to 8. FIGS. 5 to 8 are explanatory diagrams for explaining the manufacturing method of the coil 4 according to the embodiment.

[0048] The manufacturing method of the coil 4 of this embodiment has a first step, a second step, and a third step.

[0049] In the first step, a cylindrical first member 41 having a hollow part SP1 is formed of a metal material (see FIG. 5).

[0050] In the first step, the first member 41 is molded such that the thickness X1 of the outer surface 411 and the inner surface 412 of the first member 41 is equal to or greater than the skin depth X2 (see Figure 3) determined by the rated frequency of the motor current in the motor 1.

[0051] For example, in the first step, the first member 41 is formed by additive manufacturing (AM). This makes it easy to manufacture a cylindrical first member 41 having a hollow portion SP1.

[0052] In the second step, a material containing a phase change material is injected into the hollow portion SP1 of the first member 41 to form the second member 42 including the phase change portion 61. More specifically, a resin material of the A stage, which contains a plurality of capsules 62 enclosing the phase change portion 61, is injected into the hollow portion SP1 through an opening 413 (first opening) formed at the first end in the longitudinal direction of the first member 41, and the second member 42 including the phase change portion 61 is formed by thermal curing the resin material of the A stage. Note that the second step in this embodiment is performed with the second opening formed at the second end opposite the first end of the first member 41 closed.

[0053] In the third step, the opening 413 is closed by, for example, using a crimping machine 100 to clamp and crush the first member 41 and the second member 42 (see Figure 7). Then, in the third step, the second member 42 is sealed inside the first member 41 by brazing, laser welding, ultrasonic bonding, projection welding, or TIG (Tungsten Inert Gas) welding on the portion crushed by the crimping machine 100 (see Figure 8).

[0054] Then, in the stator 2 of the motor 1, for example, the raw material for the insulating member 7 (i.e., the insulating member 7 before hardening) is applied to the coil 4, and the coil 4 is wound around the teeth 31 multiple times. After some time has passed since the coil 4 was wound around the teeth 31, the raw material for the insulating member 7 hardens and the insulating member 7 is formed.

[0055] (4) Modifications The following are modifications of the above embodiment.

[0056] (4.1) Modification 1 In the above embodiment, the case in which the phase change material is paraffin was illustrated. However, the phase change material may also be vanadium oxide. In Modification 1, the vanadium oxide is vanadium dioxide. That is, in the coil 4 of Modification 1, the phase change section 61 is made of vanadium dioxide.

[0057] Vanadium dioxide undergoes a crystalline phase change around a certain temperature (for example, 60°C to 70°C). In vanadium dioxide, latent heat is generated as a result of the crystalline phase change.

[0058] In the first modified example, the entire second member 42 is the phase change section 61. However, a part of the second member 42 may be the phase change section 61.

[0059] Figure 9 is a graph showing the relationship between the volume fraction and latent heat of vanadium dioxide, which is the material of the phase change section 61 contained in the coil 4 according to Modification 1, and the relationship between the volume fraction and thermal conductivity. Graph G1 in Figure 9 shows the relationship between the volume fraction and latent heat of vanadium dioxide when copper and vanadium dioxide are combined. Graph G2 in Figure 9 shows the relationship between the volume fraction and thermal conductivity of vanadium dioxide when copper and vanadium dioxide are combined. The horizontal axis of graphs G1 and G2 represents the volume fraction of vanadium dioxide when copper and vanadium dioxide are combined. In the following explanation, the volume fraction of vanadium dioxide when copper and vanadium dioxide are combined may be simply referred to as the "volume fraction of vanadium dioxide".

[0060] As shown in graphs G1 and G2, the magnitude of latent heat and thermal conductivity changes by changing the volume fraction of vanadium dioxide. Note that for many metals, thermal conductivity and electrical conductivity are proportional. In other words, the magnitude of electrical conductivity changes by changing the volume fraction of vanadium dioxide. That is, by changing the amount of the phase change section 61 composed of vanadium dioxide, the magnitude of latent heat and the magnitude of electrical conductivity can be adjusted to manufacture the coil 4. For example, by changing the volume fraction of the first member 41 of this embodiment, which contains copper as a material, and the second member 42, which contains vanadium dioxide as a material, the magnitude of latent heat and the magnitude of electrical conductivity can be adjusted to manufacture the coil 4.

[0061] (4.2) Modification 2 Figure 10 is a schematic cross-sectional view showing a coil 4 according to Modification 2. In the above embodiment, the case in which the coil 4 is a round wire was illustrated. However, the coil 4 is not limited to a round wire. For example, as shown in Figure 10, the coil 4 of Modification 2 is a square wire. That is, in the coil 4 of Modification 2, the first member 41 of the coil 4 is in the shape of a square tube. In addition, in the first step of the manufacturing method of the coil 4 of Modification 2, the first member 41 is formed into a square tube shape.

[0062] This makes it possible to increase the occupancy rate (or packing ratio) of the coil 4 within the motor 1. In the motor 1 of Modification 2, by increasing the packing ratio of the coil 4, it is possible to reduce the losses of the coil 4 and increase the heat capacity of the coil 4, thereby further suppressing the temperature rise of the coil 4.

[0063] Note that the coil 4 in Figure 10 is a rectangular wire with a rectangular cross-section. However, the coil 4 may be a rectangular wire with a cross-section of other polygonal shapes, such as a hexagon. Also, the coil 4 may be a flat rectangular wire.

[0064] (4.3) Other Modifications In the above embodiment, the case in which motor 1 is an inner rotor type motor was illustrated, but motor 1 may be an outer rotor type motor. Also, in the above embodiment, the case in which motor 1 is a servo motor was illustrated, but motor 1 may be a motor other than a servo motor.

[0065] In the above embodiment, the case where motor 1 is an AC motor was illustrated, but motor 1 may also be a DC motor.

[0066] In the above embodiment, the first step in the method for manufacturing the coil 4 is illustrated by forming the first member 41 by additive manufacturing (AM), but the first member 41 may be formed by other methods. For example, the first member 41 may be formed by melting, casting, rolling, extruding, drawing, forging, or other processing using a metal material such as copper or aluminum as a raw material.

[0067] (Aspects) As is clear from the embodiments and modifications described above, the coil (4) according to the first aspect is used in a motor (1). The coil (4) comprises a first member (41) and a second member (42). The first member (41) is made of a metal material and has a hollow portion (SP1). The first member (41) is cylindrical. The second member (42) is arranged in the hollow portion (SP1) of the first member (41). The second member (42) includes a phase change portion (61) made of a phase change material. The thickness (X1) between the outer surface (411) and the inner surface (412) of the first member (41) is greater than or equal to the skin depth (X2) determined by the rated frequency of the motor current in the AC motor.

[0068] According to the second or third embodiment, the temperature rise of the coil (4) can be suppressed.

[0069] In the coil (4) according to the second embodiment, the phase change material is paraffin, as in the first embodiment.

[0070] In the coil (4) according to the third embodiment, the phase change material is vanadium oxide, as in the first embodiment.

[0071] According to this embodiment, the magnitude of latent heat and the magnitude of electrical conductivity can be adjusted.

[0072] In the coil (4) according to the fourth embodiment, as in the second embodiment, the second member (42) includes a plurality of capsules (62) that enclose a phase change section (61). The arithmetic mean roughness of the inner surface (412) of the first member (41) is greater than the average particle size of the plurality of capsules (62).

[0073] According to this embodiment, the thermal conductivity between the inner surface (412) of the first member (41) and the plurality of capsules (62) can be improved.

[0074] In the coil (4) according to the fifth embodiment, the first member (41) is rectangular in shape in any of the first to fourth embodiments.

[0075] According to this embodiment, the occupancy rate of the coil (4) in the AC motor (motor 1) can be increased.

[0076] A coil manufacturing method according to the sixth embodiment is a method for manufacturing a coil (4) used in an AC motor. The coil manufacturing method comprises a first step and a second step. In the first step, a cylindrical first member (41) having a hollow portion (SP1) is formed from a metal material. In the second step, a material containing a phase change material is injected into the hollow portion (SP1) of the first member (41) to form a second member (42) including a phase change portion (61). In the first step, the first member (41) is formed such that the thickness (X1) of the outer surface (411) and inner surface (412) of the first member (41) is equal to or greater than the skin depth (X2) determined by the rated frequency of the motor current in the AC motor.

[0077] According to this embodiment, it is possible to suppress the temperature rise of the coil (4).

[0078] In the coil manufacturing method according to the seventh embodiment, in the sixth embodiment, the first step is to form the first member (41) into a rectangular tube shape.

[0079] According to this embodiment, the occupancy rate of the coil (4) in the AC motor (motor 1) can be increased.

[0080] In the coil manufacturing method according to the eighth embodiment, in the sixth or seventh embodiment, in the second step, a resin material of the A stage containing a phase change material is injected into the hollow portion (SP1) of the first member (41), and the second member (42) containing the phase change portion (61) is formed by thermal curing the resin material.

[0081] In the coil manufacturing method according to the ninth embodiment, in any of the sixth to eighth embodiments, the first step is to form a first member (41) by additive manufacturing.

[0082] According to this embodiment, a cylindrical first member (41) having a hollow portion (SP1) can be easily manufactured.

[0083] The coil of this disclosure can suppress the temperature rise of the coil. Furthermore, the method for manufacturing the coil of this disclosure can easily manufacture the cylindrical component of the coil. Thus, the coil and the method for manufacturing the coil of this disclosure are industrially useful.

[0084] 1 Motor 4 Coil 41 First component 411 Outer surface 412 Inner surface 42 Second component 61 Phase change section 62 Capsule SP1 Hollow section X1 Thickness X2 Skin depth

Claims

1. A coil used in a motor, comprising: a cylindrical first member made of a metal material and having a hollow portion; and a second member disposed in the hollow portion of the first member and including a phase change portion made of a phase change material, wherein the thickness between the outer surface and the inner surface of the first member is greater than or equal to the skin depth determined by the rated frequency of the motor current in the motor.

2. The coil according to claim 1, wherein the phase change material is paraffin.

3. The coil according to claim 1, wherein the phase change material is vanadium oxide.

4. The coil according to claim 2, wherein the second member includes a plurality of capsules containing the phase change portion, and the arithmetic mean roughness of the inner surface of the first member is greater than the average particle diameter of the plurality of capsules.

5. The coil according to any one of claims 1 to 3, wherein the first member is rectangular in shape.

6. A method for manufacturing a coil used in a motor, comprising: a first step of forming a cylindrical first member having a hollow portion out of a metal material; and a second step of injecting a material containing a phase change material into the hollow portion of the first member to form a second member including a phase change portion, wherein in the first step, the first member is formed such that the thickness of the outer surface and inner surface of the first member is equal to or greater than the skin depth determined by the rated frequency of the motor current in the motor.

7. The method for manufacturing a coil according to claim 6, wherein the first step involves forming the first member into a rectangular tube shape.

8. The method for manufacturing a coil according to claim 6 or 7, wherein in the second step, the resin material of the A-stage including the phase change material is injected into the hollow portion of the first member, and the second member including the phase change portion is formed by thermal curing the resin material.

9. The method for manufacturing a coil according to claim 6 or 7, wherein in the first step, the first member is formed by additive manufacturing.

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