Rotor member, rotor, and motor

Abstract

To provide a technique for suppressing a temperature rise of a rotor member in the rotor member for a motor.SOLUTION: A rotor member for a motor includes a rotor core portion formed of ceramic and having a support portion for supporting a magnet, and a shaft portion connected to the rotor core portion and formed of ceramic, in which the shaft portion has a plurality of crystal grains and a grain boundary liquid phase surrounded by the crystal grains, and in a cross section of the shaft portion, a proportion of the grain boundary liquid phase is less than 10% in terms of an area ratio.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a rotor member, a rotor, and a motor. [Background technology]

[0002] BACKGROUND ART Rotor members for motors have been known for some time (for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-40996 [Patent Document 2] International Publication No. 2018 / 147052 Summary of the Invention [Problem to be solved by the invention]

[0004] However, even with the prior art such as Patent Documents 1 and 2, there is still room for improvement in the technology for suppressing temperature rise in rotor members for motors.

[0005] An object of the present invention is to provide a technique for suppressing a temperature rise in a rotor member for a motor. [Means for solving the problem]

[0006] The present invention has been made to solve at least part of the above-mentioned problems, and can be realized in the following aspects.

[0007] (1) One aspect of the present invention provides a rotor member for a motor, comprising: a rotor core portion formed of ceramic and having a support portion for supporting a magnet; and a shaft portion formed of ceramic and connected to the rotor core portion, the shaft portion having a plurality of crystal grains and a grain boundary liquid phase surrounded by the crystal grains, wherein the grain boundary liquid phase occupies less than 10% of a cross section of the shaft portion in terms of area ratio.

[0008] According to this configuration, the rotor core and shaft of the rotor member are each made of ceramic. This reduces iron loss generated in the rotor member and suppresses an increase in mechanical loss due to friction, thereby suppressing heat generation due to iron loss and mechanical loss. Furthermore, the proportion of the grain boundary liquid phase in the cross section of the shaft is less than 10% by area. This allows heat to be easily transferred in the shaft, making it easier to release heat generated in the rotor core to the outside of the motor via the shaft. This therefore suppresses temperature rise in the rotor member.

[0009] (2) In the rotor member of the above aspect, the average grain size of the crystal grains in the shaft portion may be 5.0 μm or less. With this configuration, the average grain size of the crystal grains in the shaft portion is 5.0 μm or less, so that the strength of the shaft portion is relatively high, thereby making it possible to suppress breakage.

[0010] (3) In the rotor member of the above embodiment, the shaft portion may have a surface roughness Ra of 15 μm or less. With this configuration, the surface roughness Ra of the shaft portion is relatively small, thereby reducing the frictional force between the shaft portion and the portion that rotatably supports the shaft portion. This allows the rotor member to rotate at a higher speed.

[0011] (4) According to another aspect of the present invention, a rotor for a motor is provided. This rotor includes the rotor member described above, a magnet supported by the support portion, and a magnetic portion provided in the rotor core portion and formed of a metal or a ceramic having soft magnetic properties, the magnet forming a magnetic circuit passing through the magnetic portion. According to this configuration, the rotor core portion is provided with a magnetic portion through which the magnetic circuit formed by the magnet passes. The rotor member provided in the rotor core portion has relatively small iron loss and mechanical loss, and therefore is less likely to increase in temperature. This suppresses the temperature increase in the magnetic portion provided in the rotor core portion, thereby suppressing performance degradation of the magnetic portion.

[0012] (5) According to yet another aspect of the present invention, a motor is provided. The motor includes the rotor member described above, a magnet supported by the support, and a stator for the motor, disposed outside the rotor core and having windings for generating a magnetic field. With this configuration, the motor includes a rotor member made of ceramic, so iron loss and mechanical loss in the rotor are relatively small. This suppresses temperature rise in the rotor, thereby suppressing temperature rise in the entire motor.

[0013] The present invention can be realized in various forms, for example, in the form of an apparatus that uses a rotor member, a method for manufacturing a rotor member, a method for manufacturing a rotor or motor that includes a rotor member, or a computer program that causes a computer to execute the manufacturing of a rotor member. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a cross-sectional view of a motor including a rotor member according to a first embodiment. [Figure 2] FIG. 2 is a perspective view of a rotor member according to the first embodiment. [Figure 3] FIG. 2 is a perspective view of a rotor according to the first embodiment. [Figure 4] FIG. 2 is a cross-sectional view of the rotor of the first embodiment. [Figure 5]FIG. 2 is a diagram schematically illustrating a cross section of a shaft portion of the first embodiment. [Figure 6] 5A to 5C are diagrams illustrating evaluation results regarding the rotor member of the first embodiment. [Figure 7] FIG. 10 is a cross-sectional view of a rotor of a comparative example. [Figure 8] FIG. 10 is a cross-sectional view of a motor including a rotor member according to a second embodiment. [Figure 9] FIG. 10 is a perspective view of a rotor member according to a second embodiment. [Figure 10] FIG. 10 is a perspective view of a rotor according to a second embodiment. [Figure 11] FIG. 6 is a cross-sectional view of a rotor according to a second embodiment. [Figure 12] 10A and 10B are diagrams illustrating a magnetic circuit formed in a rotor according to a second embodiment. [Figure 13] 10A and 10B are diagrams illustrating evaluation results regarding the rotor member of the second embodiment. [Figure 14] FIG. 10 is a cross-sectional view of a rotor of a comparative example. [Figure 15] FIG. 4 is a cross-sectional view of a first modified example of the rotor member of the first embodiment. [Figure 16] FIG. 4 is a cross-sectional view of a second modified example of the rotor member of the first embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0015] First Embodiment 1 is a cross-sectional view of a motor including a rotor member according to a first embodiment. A rotor member 100 according to this embodiment is used in a motor 1 that outputs rotational torque when power is supplied. The motor 1 includes a rotor 10 having the rotor member 100, a stator 20, and a motor case 30. The rotor 10 is provided on a central axis C1 of the motor 1 so as to be rotatable about the central axis C1.

[0016] Fig. 2 is a perspective view of a rotor member of this embodiment. Fig. 3 is a perspective view of the rotor of this embodiment. Fig. 4 is a cross-sectional view of the rotor of this embodiment. The rotor member 100 is made of ceramic and includes a rotor core portion 110 having a support portion 111 for supporting a magnet 130, and a shaft portion 120 made of ceramic and connected to the rotor core portion 110. The rotor 10 includes the rotor member 100 and the magnet 130. The rotor member 100 of this embodiment is made of a single ceramic member.

[0017] As shown in Fig. 2, the rotor core portion 110 has a generally cylindrical shape. The support portions 111 are recessed portions formed on a side surface 112 of the rotor core portion 110, which has a generally cylindrical shape. In this embodiment, four support portions 111 are formed on the side surface 112 of the rotor core portion 110, lined up along the circumferential direction of the rotor core portion 110.

[0018] The shaft portion 120 has two shaft portions 121 and 122. The two shaft portions 121 and 122 are formed so as to protrude from two end faces 113 and 114 of the rotor core portion 110, which has a substantially cylindrical shape (see FIG. 1). Each of the shaft portions 121 and 122 has a substantially rod shape with its longitudinal direction aligned with the central axis C100 of the rotor member 100. The outer diameter of each of the shaft portions 121 and 122 is smaller than the outer diameter of the rotor core portion 110.

[0019] In this embodiment, the shaft portion 120 has a surface roughness Ra of 15 μm or less. The end of each of the shaft portions 121, 122 opposite to the side connected to the rotor core portion 110 is rotatably supported by two bearings 310, 320, which will be described later (see FIG. 1). As a result, friction between each of the shaft portions 121, 122 and the bearings 310, 320 is relatively small, making it easier for the rotor 10 to rotate relative to the stator 20 and allowing it to rotate at higher speeds. The end of each of the shaft portions 121, 122 opposite to the side connected to the rotor core portion 110 is exposed to the outside of the motor case 30, which will be described later (see FIG. 1).

[0020] The rotor member 100 of this embodiment is made of ceramic. The ceramic forming the rotor member 100 of this embodiment is at least one of oxide, carbide, and nitride. Specifically, the rotor member 100 is made of at least one of oxide-based ceramics such as alumina (Al2O3), silica (SiO2), titanium oxide (TiO2), zirconia (ZrO2), and magnesia (MgO); carbide-based ceramics such as silicon carbide (SiC), boron carbide (B4C), titanium carbide (TiC), and chromium carbide (CrC); and nitride-based ceramics such as aluminum nitride (AlN), silicon nitride (Si3N4), titanium nitride (TiN), and sialon (SiAlON). The material forming the rotor member 100 is identified using X-ray diffraction (XRD) and energy dispersive X-ray analysis (EDS). The rotor member 100 of this embodiment is made of a mixture of alumina and zirconia.

[0021] FIG. 5 is a schematic diagram illustrating a cross section of the shaft portion of this embodiment. FIG. 5 is a schematic diagram of an SEM image of a cross section of the shaft portion 120 exposed by etching, captured by a scanning electron microscope (SEM). The shaft portion 120 of this embodiment has a plurality of crystal grains 120a and a grain boundary liquid phase 120b surrounded by the crystal grains 120a. In this embodiment, the area ratio of the grain boundary liquid phase 120b in the cross section of the shaft portion 120 is less than 10% (i.e., the area ratio of the crystal grains 120a in the cross section of the shaft portion 120 is 90% or more). When the area ratio of the grain boundary liquid phase in the cross section is less than 10%, as in the shaft portion 120 of this embodiment, the crystal grains are in contact with each other in a relatively large area, which facilitates heat transfer. Alternatively, the thickness of the grain boundary liquid phase, which conducts heat less easily than the crystal grains, does not exceed a certain thickness, which does not hinder heat transfer. As a result, the shaft portion 120 of this embodiment has a structure that allows heat to be easily transmitted. The proportion of the grain boundary liquid phase 120b in the cross section of the shaft portion 120 is calculated using analysis results obtained by energy dispersive X-ray analysis (EDS) on the cross section of the shaft portion 120 as shown in FIG. 5. Specifically, for example, in a square analysis area with sides of 100 μm, the analysis results of the energy dispersive X-ray analysis are subjected to image processing to classify the area into parts representing crystal grains 120a and black parts representing the grain boundary liquid phase 120b, and the proportion of the area occupied by the grain boundary liquid phase 120b in the analysis area is calculated. Note that the proportion of the area occupied by the grain boundary liquid phase 120b in the cross section of the shaft portion 120 is 0% or more in terms of area ratio.

[0022] In this embodiment, the average grain size of the crystal grains 120a in the shaft portion 120 is 5.0 μm or less. In this embodiment, the average grain size of the crystal grains 120a in the shaft portion 120 is measured using a linear intercept method. Specifically, a plurality of square measurement ranges, e.g., three to five, each 500 μm on a side, are set on the cross section of the shaft portion 120. Next, the number of particles present on the diagonal of each set measurement range is counted, and the length of the diagonal of the measurement range is divided by the number of counted particles to calculate the average grain size of the crystal grains in each measurement range. Finally, the average grain size of the crystal grains in the shaft portion 120 is calculated using the average grain size of the crystal grains calculated for each measurement range. The average grain size of the crystal grains in the shaft portion 120 is, for example, 0.5 μm or more.

[0023] The magnet 130 is supported by a support portion 111 of the rotor core portion 110. In this embodiment, the magnet 130 is supported by the rotor core portion 110 by being fitted into the support portion 111 of the rotor core portion 110, i.e., a recessed portion formed on the side surface 112 of the rotor core portion 110. In other words, the motor 1 of this embodiment is a so-called SPM motor in which the magnet 130 is mounted on the surface of the rotor core portion 110. The magnet 130 may be fixed to the recessed portion of the support portion 111 with an adhesive (resin), or may be fixed (for example, welded) directly to the rotor core portion 110 without using an adhesive.

[0024] The stator 20 has a stator core portion 210 and a winding 220 (see FIG. 1). The stator 20 is disposed outside the rotor core portion 110 and is fixed to the motor case 30, which will be described later, inside the motor case 30. The stator core portion 210 is formed to have a substantially cylindrical shape and has a plurality of protrusions 211 on the inside. The stator core portion 210 is formed by stacking a plurality of electromagnetic steel plates.

[0025] The windings 220 are conductor wires covered with an insulator, and are wound around each of the plurality of protrusions 211 of the stator core portion 210. When electricity supplied from outside the motor 1 flows through the windings 220, the windings 220 generate a magnetic field.

[0026] The motor case 30 is a hollow member that houses the rotor 10 and the stator 20. Two bearings 310, 320 are provided in the motor case 30. The bearings 310, 320 are provided on two opposing bracket portions 301, 302 of the motor case 30. One of the two shaft portions 121, 122, the shaft portion 121, is inserted through the bearing 310, and the other of the two shaft portions 121, 122, the shaft portion 122, is inserted through the bearing 320. As a result, the rotor 10 is rotatably supported by the motor case 30.

[0027] Next, an example of a manufacturing method for the rotor member 100 of this embodiment will be described. In the manufacturing method for the rotor member 100, first, predetermined amounts of ceramic particles and a sintering aid are weighed out as main raw materials. In the rotor member 100 of this embodiment, the area ratio of the grain boundary liquid phase 120b in the cross section of the shaft portion 120 can be adjusted by adjusting the amount of the sintering aid to be weighed out. For example, adding approximately 3 to 15 wt% of YO, Nd, SiO, SiC, AlN, or the like as a sintering aid reduces the area ratio of the grain boundary liquid phase 120b in the cross section of the shaft portion 120. Furthermore, in the rotor member 100 of this embodiment, the average grain size of the crystal grains 120a in the shaft portion 120 can be set to 5.0 μm or less by adjusting the average grain size of the ceramic particles and the firing temperature of the processed green body (described later), as well as by controlling the particle size of the sintering aid and the dispersion state of the sintering aid in the slurry (described later). For example, the average particle size of the ceramic particles as the main raw material is set to 1 to 3 μm or less, the firing temperature of the processed green body is set to 1650 to 1800° C., and the particle size of the sintering aid and the dispersion state of the sintering aid in the slurry are controlled to set the average particle size of the crystal grains 120a in the shaft portion 120 to 5.0 μm or less. Note that the methods for reducing the area ratio of the grain boundary liquid phase 120b in the cross section of the shaft portion 120 and the methods for setting the average particle size of the crystal grains 120a in the shaft portion 120 to 5.0 μm or less are not limited to these.

[0028] Next, the weighed materials are placed in a ball mill together with ethanol and milled and mixed for a predetermined time to produce a slurry. The produced slurry is then extrusion-molded to form an extruded body having a generally cylindrical shape. The extruded body is then processed to form the shaft portion 120, the support portion 111, and other portions, to produce a processed body having the shape of the rotor member 100. The processed body is then fired by heating under predetermined conditions (e.g., a firing temperature in the range of 1650 to 1800°C) to produce a fired body. Finally, the surface of the portion of the fired body that will become the shaft portion 120 is polished to a surface roughness Ra of 15 μm or less. The rotor member 100 is thus produced. Note that the manufacturing method for the rotor member 100 shown here is merely an example and is not limited to this manufacturing method. The surface roughness Ra of the portion that will become the shaft portion 120 is, for example, 1 μm or more.

[0029] Next, an evaluation test of the rotor member in this embodiment will be described. In this evaluation test, 13 types of rotor members (hereinafter referred to as "samples") for use in SPM motors were fabricated, differing in any of the following: rotor member material, grain boundary liquid phase area ratio, structure, average grain size, surface roughness, presence or absence of magnetic parts, or material, and each of the 13 samples was evaluated for "iron loss," "rotation strength," and "rotation efficiency."

[0030] FIG. 6 is a diagram illustrating the evaluation results of the rotor member of this embodiment. Of the 13 types of samples used in this evaluation test, Samples 1 to 10 and Sample 13 were manufactured by a method similar to the manufacturing method of the rotor member 100 of this embodiment. For each of Samples 1 to 10 and Sample 13, the ceramic particle material used as the main raw material was selected so as to achieve the composition of the "material" shown in FIG. 6. Sample 11 was manufactured by stacking multiple electromagnetic steel sheets. Sample 12 was manufactured by extruding and processing epoxy resin. The volume ratio of Si2N4 to TiN in Sample 5 and the volume ratio of Al2O3 to ZrO2 in Samples 8 to 10 were all 7:3.

[0031] The "area ratio of grain boundary liquid phase" shown in FIG. 6 is a value indicating the area ratio of the grain boundary liquid phase in the cross section of the shaft portion for each of Samples 1 to 10 and Sample 13. The "area ratio of grain boundary liquid phase" was measured using a method similar to the method used to calculate the proportion of the grain boundary liquid phase 120b in the cross section of the shaft portion 120 in this embodiment. The "structure" shown in FIG. 6 indicates the relationship between the rotor core portion and the shaft portion for each of Samples 1 to 13.

[0032] The "average grain size" shown in FIG. 6 indicates the average grain size of the ceramic crystal grains forming each of Samples 1 to 13. The "average grain size" was measured using a method similar to the method for measuring the average grain size (linear intercept method) in the rotor member 100 of this embodiment. The "surface roughness" shown in FIG. 6 indicates the surface roughness Ra of the shaft portion for each of Samples 1 to 13. The surface roughness Ra of the shaft portion was measured using a stylus-type surface roughness tester specified in JIS B0633:2001. The "magnetic portion" shown in FIG. 6 indicates whether or not a magnetic portion is provided in the rotor core portion for each of Samples 1 to 10, and if a magnetic portion is provided, the material of the magnetic portion. None of Samples 1 to 10 has a magnetic portion.

[0033] FIG. 7 is a cross-sectional view of a rotor of a comparative example. In this evaluation test, the "iron loss" and "rotation efficiency" shown in FIG. 6 each show the results of a comparison with a motor equipped with a rotor 90 of a comparative example (hereinafter simply referred to as the "motor of the comparative example"). As shown in FIG. 7, the rotor 90 of the comparative example includes a rotor core portion 91, a magnet 92, and a shaft portion 93 connected to the rotor core portion 91. In the rotor 9 of the comparative example, the rotor core portion 91 and the shaft portion 93 equipped in the rotor member 900 are formed from laminated electromagnetic steel plates, and the magnet 92 is mounted on a surface 911 of the rotor core portion 91.

[0034] The "iron loss" shown in Figure 6 was calculated using the method of JIS C 4034-2-1. Specifically, the loss of each motor was measured using the method of JIS C 4034-2-1 for the motors equipped with each of Samples 1 to 13 and the motor of the comparative example. Next, the loss of each motor was calculated by subtracting the copper loss calculated using the current flowing through the motor and the mechanical loss calculated from friction, etc., from the measured loss. The calculated loss values ​​of each motor were classified into the following symbols A and B based on the magnitude of the iron loss of each of Samples 1 to 13 compared to the motor of the comparative example. A: Less than 95% of the motor in the comparison example B: 95% or more of the motor in the comparative example

[0035] The "rotational strength" shown in Figure 6 indicates the durability of the rotor components against the centrifugal force and stress acting during rotation. The "rotational strength" was measured using the following method. First, the rotation speed of the motors equipped with each of Samples 1 to 13 was gradually increased, and the rotation speed at which the rotor components broke was measured. Next, the magnitude of the rotation speed was taken as the "rotational strength" and classified into the following symbols: S, A, B, and C. S: The rotation speed at which the fracture occurred was between 15,000 rpm and 20,000 rpm. A: The rotation speed at which the fracture occurred was between 10,000 rpm and 15,000 rpm. B: The rotation speed at which the fracture occurred was between 5,000 rpm and 10,000 rpm. C: The rotation speed at which the fracture occurred was less than 5000 rpm

[0036] The "rotational efficiency" shown in Figure 6 indicates the ratio of output to input in a motor, i.e., the efficiency of the motor. To measure the "rotational efficiency," first, the output of a motor equipped with each of Samples 1 to 13 and a motor of the comparative example was measured when rotated at a predetermined rotation speed. The degree of the magnitude of the output measured for a motor equipped with each of Samples 1 to 13 relative to the output measured for the motor of the comparative example was taken as the "rotational efficiency" and was classified into the symbols A and B shown below. A: Greater than 1% improvement compared to the comparison motor B: Less than 1% improvement compared to the comparison motor

[0037] In the "iron loss" shown in Figure 6, it was confirmed that Samples 1 to 10 and Sample 13, which are made of ceramic, exhibited better performance than Sample 11, which is made of electromagnetic steel sheet. Sample 11, which is made of electromagnetic steel sheet, is prone to iron loss such as hysteresis loss and eddy current loss, while Samples 1 to 10 and Sample 13, which are made of ceramic, are less likely to generate iron loss. This suppresses heat generation in the rotor components, making it difficult for Samples 1 to 10 and Sample 13 to experience a rise in temperature.

[0038] Among Samples 1 to 10 and Sample 13, which are ceramic "materials," a comparison of Samples 1 to 10, which have an "area ratio of grain boundary liquid phase" of less than 10%, and Sample 13, which has an "area ratio of grain boundary liquid phase" of 10%, confirmed a difference in "rotational strength." Specifically, it was confirmed that Samples 1 to 10, which have an "area ratio of grain boundary liquid phase" of less than 10%, have greater strength than Sample 13, which has an "area ratio of grain boundary liquid phase" of 10%. As described above, when a ceramic member has an area ratio of grain boundary liquid phase of less than 10% in the cross section, the crystal grains come into contact with each other in a relatively large area, which facilitates heat transfer. Alternatively, the thickness of the grain boundary liquid phase, which conducts heat less easily than the crystal grains, does not exceed a certain thickness, which makes it less likely to impede heat transfer. Therefore, it is believed that Samples 1 to 10, in which the "area ratio of the grain boundary liquid phase" is less than 10%, have superior heat transfer properties compared to Sample 13, in which the "area ratio of the grain boundary liquid phase" is 10%.

[0039] In the "rotation strength" shown in Figure 6, it was confirmed that, among Samples 1 to 10, Samples 4 to 10, which have an "average particle size" of 5 μm or less, exhibit superior performance to Samples 1 to 3, which have an "average particle size" of more than 5 μm. In addition, it was confirmed that, among Samples 4 to 10, which have an "average particle size" of 5 μm or less, Samples 8 to 10, which have an "average particle size" of 2 μm or less, exhibit even superior performance to Samples 4 to 7, which have an "average particle size" of more than 2 μm but less than 5 μm.

[0040] In the "rotation efficiency" shown in Figure 6, it was confirmed that, among Samples 1 to 10, Samples 8 to 10, which have a "surface roughness" of 15 μm or less, exhibit superior performance to Samples 1 to 7, which have a "surface roughness" of more than 15 μm. This is thought to be because, as the surface roughness Ra of the shaft portion decreases, the frictional force between the rotor member and the bearing that rotatably supports the rotor member decreases, reducing loss due to frictional force in the input to the motor and resulting in greater output for the same input.

[0041] According to the rotor member 100 of this embodiment described above, the rotor core portion 110 and the shaft portion 120 included in the rotor member 100 are each formed of ceramic. This reduces iron loss generated in the rotor member 100 and suppresses an increase in mechanical loss due to friction, thereby suppressing heat generation due to iron loss and mechanical loss. Furthermore, in the cross section of the shaft portion 120, the proportion of the grain boundary liquid phase 120b is smaller than the proportion of the crystal grains 120a. This allows heat to be easily conducted in the shaft portion 120, making it easier to dissipate heat generated in the rotor core portion 110 to the outside of the motor 1 via the shaft portion 120. This makes it possible to suppress a temperature rise in the rotor member 100.

[0042] Furthermore, according to the rotor member 100 of this embodiment, the grain boundary liquid phase 120b accounts for less than 10% of the cross section of the shaft portion 120 in terms of area ratio, which improves the durability of the rotor member against centrifugal forces and stresses acting during rotation, thereby enabling the rotor member to rotate at higher speeds.

[0043] Furthermore, according to the rotor member 100 of this embodiment, the average grain size of the crystal grains 120a in the shaft portion 120 is 5.0 μm or less. This makes the strength of the shaft portion 120 relatively high, thereby preventing damage to the rotor member 100 due to centrifugal force or stress during rotation. This allows the rotor member 100 to rotate at a higher speed.

[0044] Furthermore, according to the rotor member 100 of this embodiment, the shaft portion 120 has a surface roughness Ra of 15 μm or less. This reduces the frictional force between the shaft portion 120 and the bearings 310, 320 that rotatably support the shaft portion 120. This reduces loss due to frictional force in the input to the motor 1, allowing for a larger output for the same input. Furthermore, the rotor member 100 can be rotated at a higher speed.

[0045] Furthermore, according to the motor 1 of this embodiment, the motor 1 includes the rotor member 100 made of ceramic, which reduces iron loss and mechanical loss in the rotor 10. This suppresses a temperature rise in the rotor 10, thereby suppressing a temperature rise in the entire motor 1.

[0046] Second Embodiment 8 is a cross-sectional view of a rotor including a rotor member according to the second embodiment. The rotor member included in the rotor according to the second embodiment differs from the rotor member according to the first embodiment (FIG. 1) in that it includes a magnetic portion.

[0047] Similar to the rotor 10 of the first embodiment, the rotor 40 of the second embodiment is provided in a motor 2 that includes a stator 20 and a motor case 30. The rotor 40 includes a rotor member 400, a magnet 430, and a magnetic portion 440. The rotor 40 is provided on the central axis C2 of the motor 2 so as to be rotatable about the central axis C2.

[0048] Fig. 9 is a perspective view of a rotor member of this embodiment. Fig. 10 is a perspective view of the rotor of this embodiment. Fig. 11 is a cross-sectional view of the rotor of this embodiment. The rotor member 400 includes a rotor core portion 410 formed of ceramic and having a support portion 411 for supporting a magnet 430, and a shaft portion 420 formed of ceramic and connected to the rotor core portion 410. In the rotor member 400 of this embodiment, the rotor core portion 410 and the shaft portion 420 are formed of a single ceramic member, similar to the rotor member 100 of the first embodiment.

[0049] As shown in FIG. 9 , the rotor core portion 410 has a substantially cylindrical shape. The support portion 411 of the rotor core portion 410 has an insertion hole with an opening formed in one end face 412 of two end faces 412, 413 of the substantially cylindrical rotor core portion 410. In this embodiment, the opening portion of the support portion 411 is formed to have an annular shape, and a plurality of magnets 430 are provided in the support portion 411. The one end face 412 of the rotor core portion 410 has an opening portion of an insertion hole 414 into which a magnetic portion 440 is inserted. The opening portion of the insertion hole 414 is located inside the opening portion of the support portion 411. In this embodiment, a plurality of insertion holes 414 are formed so that one magnetic portion 440 is disposed across two adjacent magnets 430 among the plurality of magnets 430 supported by the support portion 411 (see FIG. 9 ).

[0050] The shaft portion 420 has two shaft portions 421, 422. The two shaft portions 421, 422 are formed so as to protrude from two end faces 412, 413 of the rotor core portion 410, which has a substantially cylindrical shape (see FIG. 8). Each of the shaft portions 421, 422 has a substantially rod shape with its longitudinal direction aligned with the central axis C400 of the rotor member 400. The outer diameter of each of the shaft portions 421, 422 is smaller than the outer diameter of the rotor core portion 410. The end of each of the shaft portions 421, 422 opposite to the end connected to the rotor core portion 410 is exposed to the outside of the motor case 30.

[0051] The shaft portion 420 of this embodiment, like the shaft portion 120 of the first embodiment, has a plurality of crystal grains and a grain boundary liquid phase surrounded by the crystal grains. In this embodiment, the proportion of the grain boundary liquid phase in the cross section of the shaft portion 420 is less than 10% in terms of area ratio. The average grain size of the crystal grains in the shaft portion 420 is 5.0 μm or less.

[0052] The rotor member 400 of this embodiment is made of ceramic. The ceramic forming the rotor member 400 of this embodiment is at least one of oxide, carbide, and nitride. The rotor member 400 of this embodiment is made of a mixture of alumina and zirconia.

[0053] The magnets 430 are supported by support portions 411 of the rotor core portion 410. In this embodiment, the ten magnets 430 are supported by the rotor core portion 410 by being inserted into insertion holes formed in the support portions 411 of the rotor core portion 410. In other words, the motor 2 of this embodiment is a so-called IPM motor in which the magnets 430 are mounted inside the rotor core portion 410. The magnets 430 may be fixed to the insertion holes formed in the support portions 411 with an adhesive (resin), or may be fixed (for example, welded) directly to the rotor core portion 410 without using an adhesive.

[0054] The magnetic portion 440 is provided in the rotor core portion 410 and is made of a metal or a soft magnetic ceramic. Materials for forming the magnetic portion 440 include iron (Fe), cobalt (Co), nickel (Ni), nanocrystalline soft magnetic materials having nano-sized crystals in an amorphous alloy, electromagnetic steel sheets, and soft magnetic ceramics such as ferrite (Fe2O3). The magnetic portion 440 of this embodiment is made of electromagnetic steel sheets. Ten magnetic portions 440 are inserted into ten insertion holes 414 of the rotor core portion 410, respectively.

[0055] Fig. 12 is a diagram illustrating a magnetic circuit formed in the rotor. For convenience of illustration, Fig. 12 shows only the cross section of rotor 40 also shown in Fig. 11. In this embodiment, magnet 430 forms a magnetic circuit Mgc that passes through magnetic portion 440.

[0056] Next, an example of a manufacturing method for the rotor member 400 of this embodiment will be described. The manufacturing method for the rotor member 400 is a method similar to the manufacturing method for the rotor member 100 of the first embodiment. The manufacturing method for the rotor member 400 differs from the manufacturing method for the rotor member 100 in that a portion that becomes the shaft portion 420, a portion that becomes the support portion 411, an insertion hole 414 into which the magnetic portion 440 is inserted, and the like are processed in a molded extrusion molded body to produce a processed molded body having the shape of the rotor member 400. Note that the manufacturing method for the rotor member 400 shown here is an example, and the manufacturing method is not limited to this.

[0057] Next, an evaluation test of the rotor member in this embodiment will be described. In this evaluation test, five types of samples of rotor members used in IPM motors were fabricated, and the "iron loss," "rotational strength," and "rotational efficiency" were evaluated for each of the five samples in the same manner as in the evaluation test of the first embodiment.

[0058] Fig. 13 is a diagram illustrating the evaluation results for the rotor member of this embodiment. Each of Samples 14 to 18 used in this evaluation test was produced by a method conforming to the manufacturing method for rotor member 400 of this embodiment. For each of Samples 14 to 18, the material of the ceramic particles as the main raw material was selected so as to have the composition of the "material" shown in Fig. 13. The volume ratio of Al2O3 to ZrO2 in Samples 14 to 18 was all 7:3.

[0059] The "area ratio of grain boundary liquid phase" shown in FIG. 13 is a value indicating the area ratio of the grain boundary liquid phase in the cross section of the shaft portion for each of Samples 14 to 18. The "average grain size" shown in FIG. 13 is a value indicating the average grain size of the ceramic crystal grains forming the sample for each of Samples 14 to 18. The "surface roughness" shown in FIG. 13 is a value indicating the surface roughness Ra of the shaft portion for each of Samples 14 to 18. The "area ratio of grain boundary liquid phase," "average grain size," and "surface roughness" shown in FIG. 13 were measured using the same methods as those used in the evaluation tests of the first embodiment.

[0060] The "magnetic portion" shown in Fig. 13 indicates the material forming the magnetic portion provided in the rotor core portion for each of Samples 14 to 18. Sample 14 is provided with a magnetic portion formed from ferrite, and Sample 15 is provided with a magnetic portion formed from a nanocrystalline soft magnetic material. Samples 16 to 18 are each provided with a magnetic portion formed from an electromagnetic steel sheet.

[0061] Fig. 14 is a cross-sectional view of a rotor of a comparative example. In this evaluation test, the "iron loss" and "rotation efficiency" shown in Fig. 13 each show the results of a comparison with a rotor 95 of a comparative example. As shown in Fig. 14, the rotor 95 of the comparative example includes a rotor member 950 having a rotor core portion 96 and a shaft portion 97, and a plurality of magnets 98. In the rotor 95 of the comparative example, the rotor core portion 96 and the shaft portion 97 are formed from laminated electromagnetic steel plates, and the magnets 98 are inserted into support portions 961 of the rotor core portion 96.

[0062] As in the first embodiment, the "iron loss" shown in Fig. 13 was evaluated using the same threshold values ​​as in the first embodiment, with an IPM motor including the rotor member 950 of the comparative example as the evaluation standard. As a result, as shown in Fig. 13, it was confirmed that, in terms of "iron loss," each of Samples 14 to 18, whose "material" was ceramic, exhibited superior performance (evaluation "A") compared to the IPM motor including the rotor member 950 of the comparative example.

[0063] As in the first embodiment, the "rotation strength" shown in Fig. 13 was determined by gradually increasing the rotation speed of the motors including each of Samples 14 to 18, measuring the rotation speed at which the rotor member broke, and using the same threshold value as in the first embodiment. As a result, as shown in Fig. 13, it was confirmed that, in terms of "rotation strength," each of Samples 14 to 18, whose "material" was ceramic, exhibited superior performance (determined "S") compared to the IPM motor including the rotor member 950 of the comparative example.

[0064] As in the first embodiment, the "rotation efficiency" shown in Fig. 13 was evaluated using the same threshold values ​​as in the first embodiment, with an IPM motor including comparative rotor member 950 as the evaluation standard. As a result, as shown in Fig. 13, it was confirmed that, in "rotation efficiency," each of Samples 14 to 18, whose "material" was ceramic, exhibited superior performance (evaluation "A") compared to the IPM motor including comparative rotor member 950.

[0065] According to the rotor member 400 of this embodiment described above, the rotor core portion 410 and the shaft portion 420 included in the rotor member 400 are each formed of ceramic. This reduces iron loss generated in the rotor member 400 and suppresses an increase in mechanical loss due to friction, thereby suppressing heat generation due to iron loss and mechanical loss. Furthermore, the proportion of the grain boundary liquid phase in the cross section of the shaft portion 420 is smaller than the proportion of the crystal grains. This allows heat to be easily conducted in the shaft portion 420, making it easier to dissipate heat generated in the rotor core portion 410 to the outside of the motor 2 via the shaft portion 420. This makes it possible to suppress a temperature rise in the rotor member 400.

[0066] Furthermore, according to the rotor 40 of this embodiment, the rotor core portion 410 is provided with a magnetic portion 440 through which the magnetic circuit Mgc formed by the magnets 430 passes. The rotor member 400 including the rotor core portion 410 is less likely to increase in temperature because iron loss and mechanical loss are relatively small. This also suppresses temperature increases in the magnetic portion 440 provided in the rotor core portion 410, thereby suppressing performance degradation of the magnetic portion 440.

[0067] <Modification of this embodiment> The present invention is not limited to the above-described embodiment, and can be embodied in various forms without departing from the spirit of the invention. For example, the following modifications are also possible.

[0068] [Variation 1] In the above-described embodiment, the rotor member is formed from a mixture of alumina and zirconia. However, the ceramic forming the rotor member is not limited to this. As described above, the ceramic forming the rotor member is preferably at least one of oxide, carbide, and nitride, but is not limited to these. When the ceramic forming the rotor member is at least one of oxide, carbide, and nitride, the rotor member becomes relatively lightweight and relatively strong. Therefore, not only is breakage during use suppressed, but the rotor member is also easily manufactured due to its excellent workability during manufacturing.

[0069] [Variation 2] In the above-described embodiment, the ceramic forming the rotor member has an average crystal grain size of 5.0 μm or less. The average crystal grain size of the ceramic forming the rotor member may be greater than 5.0 μm. When the average crystal grain size is 5.0 μm or less, the strength of the rotor member becomes relatively high, and when the average crystal grain size is 2.0 μm or less, the strength of the rotor member becomes even higher.

[0070] [Variation 3] In the above-described embodiment, the shaft portion has a surface roughness Ra of 15 μm or less. The surface roughness Ra of the shaft portion may be greater than 15 μm, but is preferably 15 μm or less, and more preferably 10 μm or less. When the surface roughness Ra of the shaft portion is reduced, the frictional force between the portion that rotatably supports the shaft portion and the shaft portion is reduced, making it easier for the rotor member to rotate.

[0071] [Variation 4] In the above-described embodiment, the rotor member has the rotor core portion and the shaft portion formed from a single ceramic member. However, the relationship between the rotor core portion and the shaft portion is not limited to this.

[0072] FIG. 15 is a cross-sectional view of a first modified example of the rotor member of the first embodiment. In the rotor member 100 shown in FIG. 15, the rotor core portion 110 and the shaft portion 120, in which the proportion of the grain boundary liquid phase in the cross section is less than 10% in terms of area ratio, are separate members. Specifically, the rotor core portion 110 has a through hole 115 on a central axis C100 of the rotor member 100. The shaft portion 120 is inserted into the through hole 115 and fixed to the rotor core portion 110. Even in the rotor member 100 configured as described above, because the rotor core portion 110 and the shaft portion 120 are made of ceramic, iron loss can be reduced and an increase in mechanical loss can be suppressed. In addition, because heat is easily conducted in the shaft portion 120, a temperature rise in the rotor member 100 can be suppressed.

[0073] 16 is a cross-sectional view of a second modified example of the rotor member of the first embodiment. In the rotor member 100 shown in FIG. 16, the rotor core portion 110 and the shaft portions 121 and 122 are separate members. The shaft portions 121 and 122, in which the grain boundary liquid phase accounts for less than 10% of the cross section in terms of area ratio, are connected to two end faces 113 and 114 of the rotor core portion 110, each of which has a substantially cylindrical shape, by an adhesive or the like (not shown). Even in the rotor member 100 having such a configuration, because the rotor core portion 110 and the shaft portion 120 are made of ceramic, iron loss can be reduced and an increase in mechanical loss can be suppressed. In addition, because heat is easily conducted in the shaft portion 120, a temperature rise in the rotor member 100 can be suppressed.

[0074] This aspect has been described above based on embodiments and modifications. However, the above-described embodiments are intended to facilitate understanding of this aspect and are not intended to limit this aspect. This aspect may be modified or improved without departing from the spirit and scope of the claims, and equivalents thereof are included in this aspect. Furthermore, if a technical feature is not described as essential in this specification, it may be deleted as appropriate.

[0075] <Application example 1> A rotor member for a motor, comprising: a rotor core portion formed of ceramic and having a support portion for supporting the magnet; a shaft portion connected to the rotor core portion and made of ceramic, the shaft portion has a plurality of crystal grains and a grain boundary liquid phase surrounded by the crystal grains, In the cross section of the shaft portion, the proportion of the grain boundary liquid phase is less than 10% in terms of area ratio. A rotor member characterized by: <Application example 2> The rotor member according to Application Example 1, The shaft portion has an average grain size of the crystal grains of 5.0 μm or less. A rotor member characterized by: <Application example 3> The rotor member according to Application Example 1 or Application Example 2, The shaft portion has a surface roughness Ra of 15 μm or less. A rotor member characterized by: <Application Example 4> A rotor for a motor, comprising: The rotor member according to any one of Application Examples 1 to 3, a magnet supported by the support portion; a magnetic portion provided in the rotor core portion and formed of a metal or a ceramic having soft magnetic properties, The magnet forms a magnetic circuit passing through the magnetic portion. A rotor characterized by: <Application example 5> A motor, The rotor member according to any one of Application Examples 1 to 3, a magnet supported by the support portion; a stator for the motor, the stator being disposed outside the rotor core and having a winding for generating a magnetic field; A motor characterized by: [Explanation of symbols]

[0076] 1, 2...Motor 10,40...Rotor 20...Stator 100,400...Rotor parts 110,410...Rotor core part 111,411...Support part 120,420...shaft section 130,430...Magnet 440...Magnetic part 220...winding Mgc...magnetic circuit

Claims

1. A rotor member for a motor, comprising: a rotor core portion formed of ceramic and having a support portion for supporting the magnet; a shaft portion connected to the rotor core portion and made of ceramic, the shaft portion has a plurality of crystal grains and a grain boundary liquid phase surrounded by the crystal grains, In a cross section of the shaft portion, the proportion of the grain boundary liquid phase is less than 10% in terms of area ratio. A rotor member characterized by:

2. 2. The rotor member according to claim 1, The shaft portion has an average grain size of the crystal grains of 5.0 μm or less. A rotor member characterized by:

3. 3. The rotor member according to claim 1 or 2, The shaft portion has a surface roughness Ra of 15 μm or less. A rotor member characterized by:

4. A rotor for a motor, comprising: The rotor member according to claim 1 or 2; a magnet supported by the support portion; a magnetic portion provided in the rotor core portion and formed of a metal or a ceramic having soft magnetic properties, The magnet forms a magnetic circuit passing through the magnetic portion. A rotor characterized by:

5. A motor, The rotor member according to claim 1 or 2; a magnet supported by the support portion; a stator for the motor, the stator being disposed outside the rotor core and having a winding for generating a magnetic field; A motor characterized by:

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