Inner rotor and motor

Abstract

This inner rotor 1 comprises a rotor body 2, a polar anisotropic magnet 4 and a plurality of magnetic bodies 3. The rotor body 2 rotates about a rotation axis A1. The polar anisotropic magnet 4 forms a plurality of magnetic poles 41 arranged in the circumferential direction about the rotation axis A1 and is provided on an outer circumferential surface of the rotor body 2. The plurality of magnetic bodies 3 are disposed on the outer circumferential surface of the polar anisotropic magnet 4 at positions respectively corresponding to the plurality of magnetic poles 41.

Description

[Technical Field]

[0001] The technology disclosed herein relates to an inner rotor and a motor. [Background technology]

[0002] Patent Document 1 discloses an inner rotor equipped with a polar anisotropic magnet. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-74888 Summary of the Invention

[0004] However, the strength of the magnetic field generated by a magnet is difficult to increase beyond a certain amount. In other words, the upper limit of the strength of the magnetic field generated by a magnet depends on the physical properties of the magnet material. This makes it difficult to improve the torque of the motor.

[0005] The technology disclosed herein has been made in view of the above points, and its purpose is to improve the torque of the motor.

[0006] The inner rotor disclosed herein comprises a rotor body that rotates around a rotation axis, a polar anisotropic magnet that forms a plurality of magnetic poles arranged circumferentially around the rotation axis and is provided on the outer surface of the rotor body, and a plurality of magnetic bodies that are arranged on the outer surface of the polar anisotropic magnet at positions corresponding to the plurality of magnetic poles.

[0007] The motor disclosed herein includes the inner rotor and a stator that drives the inner rotor.

[0008] The inner rotor can improve the torque of the motor.

[0009] The motor can improve the torque of the motor. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a cross-sectional view of the motor. [Figure 2] FIG. 2 is a cross-sectional view of a polar anisotropic ring magnet and a magnetic body. [Figure 3] FIG. 3 is an enlarged cross-sectional view of the inner rotor. [Figure 4] FIG. 4 is an enlarged cross-sectional view of the polar anisotropic ring magnet and the magnetic body. [Figure 5] FIG. 5 is an enlarged cross-sectional view of the inner rotor of the first modified example. [Figure 6] FIG. 6 is a cross-sectional view of an inner rotor according to the second modification. [Figure 7] FIG. 7 is a cross-sectional view of an inner rotor according to the third modification. [Figure 8] FIG. 8 is a cross-sectional view of an inner rotor according to the fourth modification. DETAILED DESCRIPTION OF THE INVENTION

[0011] Exemplary embodiments will now be described in detail with reference to the drawings. FIG. 1 shows a motor 100 according to an embodiment. The motor 100 includes a rotor 1 that rotates around a predetermined rotation axis A1, and a stator 6 that rotates the rotor 1 around the rotation axis A1. The rotor 1 is an inner rotor that is disposed inside the stator 6. In other words, the motor 100 is an inner rotor type motor. The motor 100 may further include a motor case 7. The motor case 7 houses the rotor 1 and the stator 6. The stator 6 is fixed relative to the motor case 7. The rotor 1 is rotatably supported by the motor case 7.

[0012] Hereinafter, the direction in which the rotation axis A1 extends will be simply referred to as the "rotation axis direction." The circumferential direction centered on the rotation axis A1 will be simply referred to as the "circumferential direction." The radial direction centered on the rotation axis A1 will be simply referred to as the "radial direction." The side toward the rotation axis A1 in the radial direction will be referred to as the "radially inner side." The side opposite the rotation axis A1 in the radial direction will be referred to as the "radially outer side." A cross section perpendicular to the rotation axis A1 will be simply referred to as the "orthogonal cross section." The shape of the orthogonal cross section will be simply referred to as the "cross-sectional shape." The width in the circumferential direction will be simply referred to as the "width."

[0013] The stator 6 includes a stator core 61 and a winding 62. The stator core 61 is made of a soft magnetic material and is formed, for example, from a plurality of laminated electromagnetic steel plates.

[0014] The stator core 61 is formed in an annular shape. Specifically, the stator core 61 is formed in a cylindrical shape. The stator core 61 is fixed to the motor case 7. The stator core 61 is formed with a plurality of teeth 61a that protrude toward the inside of the stator core 61. The plurality of teeth 61a are arranged at intervals in the circumferential direction of the stator core 61. The windings 62 are wound around the plurality of teeth 61a. When a current is supplied to the windings 62, the stator 6 generates a rotating magnetic field that rotates the rotor 1.

[0015] The rotor 1 comprises a rotor body 2, a polar-anisotropic ring magnet 4, and a plurality of magnetic bodies 3. Hereinafter, the polar-anisotropic ring magnet 4 will be simply referred to as the "ring magnet 4." The rotor body 2 rotates around a rotation axis A1. The ring magnet 4 is provided on the outer peripheral surface of the rotor body 2. In other words, the motor 100 is an SPM (Surface Permanent Magnet) motor. The ring magnet 4 forms a plurality of magnetic poles 41 (see FIG. 2) arranged in the circumferential direction. The ring magnet 4 is an example of a polar-anisotropic magnet. The magnetic bodies 3 are provided on the outer peripheral surface 42 (i.e., the radially outer surface) of the ring magnet 4 and concentrate the magnetic flux of the ring magnet 4.

[0016] At least a portion of the rotor body 2 is made of a soft magnetic material. The rotor body 2 includes a rotor core 20 and a shaft 5. The rotor core 20 is made of a soft magnetic material. The rotor core 20 is made of, for example, a plurality of electromagnetic steel plates stacked on top of each other. The rotor core 20 is formed in an annular shape surrounding the rotation axis A1. Specifically, the rotor core 20 is formed in a cylindrical shape with the rotation axis A1 as its axis. The outer peripheral surface of the rotor core 20 forms the outer peripheral surface of the rotor body 2. The cross-sectional shape of the rotor core 20 is the same over the entire length of the rotor core 20 in the rotation axis direction.

[0017] The shaft 5 is fitted inside the rotor core 20. The shaft 5 is fixed to the rotor core 20. The shaft 5 is made of a soft magnetic material. The axis of the shaft 5 coincides with the rotation axis A1. The shaft 5 is rotatably supported by the motor case 7 via bearings or the like. The rotor core 20 rotates together with the shaft 5 around the rotation axis A1.

[0018] The ring magnet 4 is provided on the outer peripheral surface of the rotor core 20. The ring magnet 4 is formed in an annular shape that surrounds the rotor core 20. Specifically, the ring magnet 4 is formed in a cylindrical shape with the rotation axis A1 as its axis. The ring magnet 4 is formed over the entire length of the rotor core 20 in the rotation axis direction. An air gap is formed between the outer peripheral surface 42 of the ring magnet 4 and the inner peripheral surface of the stator core 61.

[0019] The ring magnet 4 is, for example, a bonded magnet. A bonded magnet is formed from a magnetic material containing magnetic powder and a binder that binds the magnetic powder. The magnetic powder is, for example, a powder of neodymium magnet, samarium-iron-nitrogen magnet, samarium-cobalt magnet, ferrite magnet, or alnico magnet, or a mixture of two or more of these powders. The binder is, for example, a thermosetting resin such as epoxy resin, a thermoplastic resin such as polyamide resin, or rubber. For example, a polar anisotropic magnet with a residual magnetic flux density of 0.9 T or less is used as the ring magnet 4.

[0020] The ring magnet 4 is formed by insert molding, for example, by injecting a magnetic material that will become a bonded magnet into a molding die that houses the rotor core 20 and the plurality of magnetic bodies 3.

[0021] Fig. 2 is a cross-sectional view of the ring magnet 4 and magnetic body 3. Fig. 3 is an enlarged cross-sectional view of the rotor 1. Magnetic poles 41 that are alternately arranged in the circumferential direction are formed on the outer peripheral surface 42 of the ring magnet 4. In this example, the ring magnet 4 has six magnetic poles 41. The multiple magnetic poles 41 are arranged at equal intervals in the circumferential direction on the outer peripheral surface 42 of the ring magnet 4.

[0022] 2, the arrow drawn inside the ring magnet 4 indicates the orientation direction of the ring magnet 4. The ring magnet 4 is oriented in a direction extending from the south pole, which is one of two magnetic poles 41 adjacent to each other in the circumferential direction, to the north pole, which is the other magnetic pole 41. The ring magnet 4 is magnetized so that the magnetization direction coincides with the orientation direction.

[0023] The ring magnet 4 concentrates magnetic flux in a portion of the circumferential direction of the outer circumferential surface 42. Therefore, the ring magnet 4 can increase the magnetic flux density of the magnetic poles 41 compared to a radially anisotropic magnet. This can therefore improve the magnet torque of the motor 100.

[0024] Recesses 43 are formed on the outer peripheral surface 42 of the ring magnet 4 at positions corresponding to each magnetic pole 41. The outer peripheral surface 42 of the ring magnet 4 is formed by a plurality of curved surfaces 44 that coincide with the outer peripheral surface of a single imaginary cylinder whose axis is the rotation axis A1, and a plurality of recesses 43 that are recessed radially inward. The curved surfaces 44 and recesses 43 are arranged alternately in the circumferential direction.

[0025] The recesses 43 extend in the direction of the rotation axis and open radially outward. The cross-sectional shape of each recess 43 is the same. Specifically, the cross-sectional shape of the recesses 43 is substantially trapezoidal. The cross-sectional shape of the recesses 43 is symmetrical about an axis of symmetry A2 extending radially.

[0026] 4 is an enlarged cross-sectional view of the ring magnet 4 and the magnetic body 3. The width of the recess 43, i.e., the dimension in the circumferential direction between both circumferential side surfaces of the recess 43, decreases radially inward from the opening of the recess 43. Here, "decreasing radially inward from the opening of the recess 43" includes not only the width of the recess 43 decreasing over the entire radial range of the recess 43, but also the width of the recess 43 decreasing only in the range from the opening of the recess 43 to halfway along the radial direction of the recess 43. In other words, it is sufficient for the recess 43 to have at least a width-reducing portion where the width of the recess 43 decreases radially inward from the opening.

[0027] Specifically, the width of the recess 43 gradually decreases from the opening to the bottom of the recess 43. That is, in this example, the reduced width portion is formed by the entire recess 43. The width b1 of the opening of the recess 43 is the maximum width of the recess 43. The width b2 of the bottom of the recess 43 is the minimum width of the recess 43. The width b1 is at least twice the width b2. More specifically, the width b1 is at least three times the width b2. The width b1 is smaller than the circumferential width b3 (see Figure 1) of the portion of the outer surface 42 of the ring magnet 4 between circumferentially adjacent recesses 43. Hereinafter, the portion of the ring magnet 4 between circumferentially adjacent recesses 43 will be referred to as the "protrusion 46."

[0028] All portions of the recess 43 except for the opening are located inside the edges of both sides of the opening of the recess 43 in the circumferential direction. Specifically, a line segment connecting one circumferential edge of the opening of the recess 43 to the rotation axis A1 is defined as a first line S1, and a line segment connecting the other circumferential edge of the opening of the recess 43 to the rotation axis A1 is defined as a second line S2. The recess 43 has side surfaces 47, 48 on both sides in the circumferential direction. Of the side surfaces on both sides in the circumferential direction of the recess 43, the first side surface 47, which is the side surface on the first line S1 side, is inclined with respect to the first line S1 so as to move away from the first line S1 toward the second line S2 as it moves radially inward. Of the side surfaces on both sides in the circumferential direction of the recess 43, the second side surface 48, which is the side surface on the second line S2 side, is inclined with respect to the second line S2 so as to move away from the second line S2 toward the first line S1 as it moves radially inward.

[0029] In this example, the first side surface 47 of one of the circumferentially adjacent recesses 43 is parallel to the second side surface 48 of the other recess 43. Specifically, one of the circumferentially adjacent recesses 43 is referred to as the first recess 43, and the other recess 43 is referred to as the second recess 43. The first side surface 47, which is the side surface of the first recess 43 facing the second recess 43, is parallel to the second side surface 48, which is the side surface of the second recess 43 facing the first recess 43. Therefore, the circumferential width of the protrusion 46 of the ring magnet 4 is approximately constant throughout the radial direction of the protrusion 46. In this disclosure, "parallel" means substantially parallel. In other words, "parallel" not only means strictly parallel, but also includes a slight tilt due to factors such as dimensional errors.

[0030] The magnetic bodies 3 are arranged at positions corresponding to the magnetic poles 41 (i.e., the recesses 43) of the ring magnet 4. In this example, the rotor 1 has the same number of magnetic bodies 3 as the magnetic poles 41. The magnetic bodies 3 are arranged at positions corresponding to all of the magnetic poles 41.

[0031] The magnetic body 3 is a soft magnetic body. The magnetic body 3 is formed, for example, from multiple electromagnetic steel plates stacked on top of each other. The magnetic permeability of the magnetic body 3 is higher than that of air. Therefore, the magnetic flux of the ring magnet 4 has difficulty passing through the air gap, and instead passes through and concentrates on the magnetic body 3. In other words, the magnetic body 3 is the part of the rotor 1 where the magnetic flux of the ring magnet 4 passes through and concentrates most.

[0032] The magnetic body 3 is fitted into the recess 43 of the ring magnet 4. The cross-sectional shape of the magnetic body 3 is the same as the cross-sectional shape of the recess 43. That is, the cross-sectional shape of the magnetic body 3 is approximately trapezoidal. The cross-sectional shape of the magnetic body 3 is symmetrical about an axis of symmetry A2 (see Figure 3) extending in the radial direction. The d-axis, which is the magnetic central axis of the rotor 1, is set to pass through the magnetic body 3. More specifically, the d-axis passes through the magnetic body 3 and coincides with the axis of symmetry A2.

[0033] The magnetic body 3 has an outer surface 31 exposed radially outward from the recess 43, and an inner surface 32 located within the recess 43. The outer surface 31 faces the stator 6. The outer surface 31 is flush with the curved surface 44 of the ring magnet 4. Specifically, the outer surface 31, together with the curved surface 44, forms the outer surface of a single imaginary cylinder whose axis is the rotation axis A1. The outer surface of the rotor 1 is formed by the curved surface 44 and the outer surface 31.

[0034] The inner surface 32 of the magnetic body 3 is in close contact with the inner surface of the recess 43 of the ring magnet 4 (i.e., the magnetic pole 41). The magnetic body 3 is fixed to the ring magnet 4. For example, when the ring magnet 4 is integrally molded with the magnetic body 3, the inner surface 32 is adhered to the inner surface of the recess 43, thereby fixing the magnetic body 3 to the ring magnet 4. The inner surface 32 includes a bottom surface 32a, which is the surface of the magnetic body 3 opposite to the outer surface 31.

[0035] The width of the magnetic body 3, i.e., the dimension in the circumferential direction between both circumferential side surfaces of the magnetic body 3, decreases from the outer surface 31 toward the radially inner side. Specifically, the width of the magnetic body 3 gradually decreases from the outer surface 31 to the bottom surface 32a. The width of the outer surface 31 is the same as the width b1 of the opening of the recess 43. The width of the outer surface 31 is the maximum width of the magnetic body 3. The width of the bottom surface 32a is the same as the width b2 of the bottom of the recess 43. The width of the bottom surface 32a is the minimum width of the magnetic body 3.

[0036] When a current is supplied to the windings 62 of the stator 6 to form a rotating magnetic field, the magnetic flux generated by the ring magnet 4 interlinks with the windings 62, generating a magnet torque, which causes the rotor 1 to rotate about the rotation axis A1.

[0037] However, the magnetic flux density of the ring magnet 4 is difficult to increase beyond a certain amount once the amount of magnet in the ring magnet 4 exceeds that amount. In other words, the upper limit of the magnetic flux density of the magnetic poles 41 depends on the physical properties of the ring magnet 4. More specifically, the upper limit of the magnetic flux density of the ring magnet 4 depends on the residual magnetic flux density of the material of the ring magnet 4. However, in the rotor of the present disclosure, a magnetic body 3 is provided at each magnetic pole 41 of the ring magnet 4, so the magnetic flux of the ring magnet 4 is concentrated in and out of the magnetic body 3. Therefore, the upper limit of the magnetic flux density in the portion of the outer surface of the rotor 1 corresponding to the magnetic poles 41 depends on the saturation magnetic flux density of the material of the magnetic body 3. Therefore, if a magnetic body 3 with a high saturation magnetic flux density is selected for the rotor of the present disclosure, the magnetic flux density will be high. This can improve the magnet torque of the motor 100, and ultimately the torque of the motor 100.

[0038] Furthermore, the magnetic body 3 is disposed in a recess 43 formed in the outer peripheral surface 42 of the ring magnet 4. This allows the magnetic body 3 to be attached to the ring magnet 4 without protruding radially outward beyond the curved surface 44 of the ring magnet 4. In this case, the air gap formed between the curved surface 44 of the ring magnet 4 and the stator 6 can be reduced. This allows the magnetic flux generated in the stator 6 to flow more easily to the rotor 1, improving the torque of the motor 100. Furthermore, the outer surface 31 of the magnetic body 3 is flush with the curved surface 44 of the ring magnet 4, and no step is formed between the outer surface 31 and the curved surface 44 on the outer peripheral surface of the rotor 1. This reduces air resistance during rotation of the rotor 1, allowing the rotor 1 to rotate efficiently.

[0039] Furthermore, the width of the recess 43 decreases from the opening of the recess 43 toward the radially inward direction. This allows the volume of the portion of the ring magnet 4 adjacent to the recess 43 in the circumferential direction to expand toward the recess 43, thereby increasing the amount of magnet in this portion. Specifically, the volume of the protrusion 46 of the ring magnet 4 can be expanded toward the recess 43 in the circumferential direction, thereby increasing the amount of magnet in the protrusion 46. This therefore improves the magnetic torque of the motor 100. Furthermore, by increasing the width of the opening of the recess 43, the width of the outer surface 31 of the magnetic body 3 can be increased. This makes it less likely that magnetic saturation will occur on the outer surface 31 of the magnetic body 3, and magnetic flux collected from the ring magnet 4 to the magnetic body 3 can more easily enter and exit from the outer surface 31. This therefore further improves the magnetic torque of the motor 100.

[0040] In particular, the first side surface 47 of one of the circumferentially adjacent recesses 43 and the second side surface 48 of the other recess 43 are parallel to each other. This ensures a sufficient width for the outer surface 31 of the magnetic body 3 while also ensuring a sufficient amount of magnetism in the protrusions 46, i.e., the portions of the ring magnet 4 between the circumferentially adjacent recesses 43. This further improves the magnet torque of the motor 100.

[0041] Next, we will explain rotors 1A to 1D of modifications 1 to 4. The basic configuration of rotors 1A to 1D is the same as that of rotor 1. Therefore, the following explanation of rotors 1A to 1D will focus on the differences from rotor 1.

[0042] FIG. 5 is an enlarged cross-sectional view of a rotor 1A according to Modification 1. The ring magnet 4 of the rotor 1A has retaining portions 43a that protrude circumferentially toward the inside of the recess 43 and restrict radially outward movement of the magnetic body 3. In this example, the ring magnet 4 has two retaining portions 43a. The retaining portions 43a are integrally formed with the ring magnet 4. The two retaining portions 43a are formed on both circumferential side surfaces of the recess 43 and face each other. The two retaining portions 43a are formed by reducing the width of a radially intermediate portion 43b of the recess 43. Specifically, the width of the portion of the recess 43 radially outward from the radially intermediate portion 43b decreases radially inward. That is, the width of the portion of the recess 43 radially outward from the radially intermediate portion 43b decreases radially outward. The width of the portion of the recess 43 radially inward from the intermediate portion 43b increases radially inward. That is, the width of the portion of the recess 43 that is radially inward of the intermediate portion 43b is increased as the portion is positioned radially inward, thereby forming two retaining portions 43a with the intermediate portion 43b as their apex.

[0043] The magnetic body 3 has a main body portion 35 that is disposed radially outward of the intermediate portion 43b of the recess 43, and a wide portion 36 that is disposed radially inward of the intermediate portion 43b. The cross-sectional shape of the main body portion 35 matches the cross-sectional shape of the portion of the recess 43 that is disposed radially outward of the intermediate portion 43b. Specifically, the cross-sectional shape of the main body portion 35 is substantially trapezoidal. The width of the main body portion 35 decreases radially inward.

[0044] The wide portion 36 protrudes radially inward from the main body portion 35. The maximum width of the wide portion 36 is greater than the circumferential distance between the two retaining portions 43a, i.e., the width of the intermediate portion 43b of the recess 43. The cross-sectional shape of the wide portion 36 matches the cross-sectional shape of the portion of the recess 43 that is radially inward from the intermediate portion 43b. Specifically, the cross-sectional shape of the wide portion 36 is trapezoidal. The width of the wide portion 36 increases radially inward. The radially inner surface of the wide portion 36 is the bottom surface 32a of the magnetic body 3. The width of the bottom surface 32a is the maximum width of the wide portion 36. The width of the bottom surface 32a is smaller than the width of the outer surface 31, which is the radially outer surface of the main body portion 35.

[0045] When the magnetic body 3 is subjected to centrifugal force during rotation of the rotor 1, the radially outward movement of the wide portion 36 is restricted by the retaining portion 43a. In other words, the magnetic body 3 is prevented from coming off by the retaining portion 43a. Therefore, the magnetic body 3 can be prevented from coming off the ring magnet 4.

[0046] Furthermore, in the protrusion 46 of the ring magnet 4, the amount of magnetism in the radially outer portion close to the stator 6 contributes greatly to the magnet torque. In other words, even if the amount of magnetism in the radially inner portion of the protrusion 46 of the ring magnet 4, which is far from the stator 6, is slightly reduced, the magnet torque does not decrease significantly. Therefore, even though the recess 43 has a wide portion 43c that accommodates the wide portion 36, the magnet torque is unlikely to decrease. In other words, because portion 43c is located at the radially inner end of the recess 43, the amount of magnetism in the radially inner portion of the protrusion 46 is reduced. However, the amount of magnetism in the radially outer portion of the protrusion 46, which contributes greatly to the magnet torque, is not reduced. Therefore, the magnet torque of the motor 100 can be ensured.

[0047] 6 is an enlarged cross-sectional view of rotor 1B of modified example 2. In this example, the shape of wide portion 36 of magnetic body 3 differs from the shape of wide portion 36 of modified example 1. The following description will focus on the differences between rotor 1B and rotor 1A.

[0048] The cross-sectional shape of the portion of the recess 43 that is radially more inward than the intermediate portion 43b is triangular. The width of the portion of the recess 43 that is radially more inward than the intermediate portion 43b decreases radially inward. The cross-sectional shape of the wide portion 36 of the magnetic body 3 matches the cross-sectional shape of the portion of the recess 43 that is radially more inward than the intermediate portion 43b. In other words, the cross-sectional shape of the wide portion 36 of the magnetic body 3 is triangular. The width of the wide portion 36 decreases radially inward.

[0049] In this example as well, when the magnetic body 3 is subjected to centrifugal force during rotation of the rotor 1, the movement of the wide portion 36 outward in the radial direction is restricted by the retaining portion 43a.

[0050] FIG. 7 is a cross-sectional view of a rotor 1C of Modification 3. In this example, the two retaining portions 43a are formed by making the width of the radially outer end of the recess 43 smaller than that of the other portions. Specifically, the width of the portion of the recess 43 radially outer than the radial intermediate portion 43b decreases toward the radially outer side. The width of the portion of the recess 43 radially inner than the intermediate portion 43b decreases toward the radially inner side. As a result, the portion of the recess 43 radially outer than the intermediate portion 43b becomes the retaining portion 43a. The width of the opening of the recess 43 is smaller than the width of the intermediate portion 43b. The width of the opening of the recess 43 is larger than the width of the radially inner end of the recess 43, i.e., the minimum width of the portion of the recess 43 radially outer than the radial intermediate portion 43b.

[0051] The cross-sectional shape of the magnetic body 3 matches the cross-sectional shape of the recess 43. That is, the magnetic body 3 has a portion that matches the cross-sectional shape of a portion of the recess 43 that is located radially inward from the intermediate portion 43b, and a portion that matches the cross-sectional shape of a portion of the recess 43 that is located radially outward from the intermediate portion 43b.

[0052] In this example as well, when the magnetic body 3 is subjected to centrifugal force during rotation of the rotor 1, the magnetic body 3 is restricted from moving radially outward by the retaining portion 43a.

[0053] FIG. 8 is a cross-sectional view of a rotor 1D of Modification 4. The rotor 1D further includes a retaining member 8 that prevents the magnetic bodies 3 arranged in the recesses 43 from coming off. The retaining member 8 is made of, for example, a non-magnetic material such as stainless steel or fiber-reinforced plastics (FRP), or a magnetic material such as iron or steel. The retaining member 8 is formed in an annular shape surrounding the ring magnet 4. Specifically, the retaining member 8 is formed in a cylindrical shape with its axis centered on the rotation axis A1. The retaining member 8 is fixed to the ring magnet 4 with its inner circumferential surface in contact with the curved surface 44 of the ring magnet 4 and the outer surfaces 31 of the multiple magnetic bodies 3. The retaining member 8 prevents the multiple magnetic bodies 3 from moving radially outward when subjected to centrifugal force during rotation of the rotor 1. This prevents the magnetic bodies 3 from coming off the ring magnet 4.

[0054] Other Embodiments As described above, the embodiments and each modified example have been described as examples of the technology disclosed in this application. However, the technology in this disclosure is not limited to these and can be applied to embodiments in which modifications, substitutions, additions, omissions, etc. are made as appropriate. Furthermore, the components described in the embodiments and each modified example can be combined to create new embodiments. Furthermore, the components described in the accompanying drawings and detailed description may include not only components essential for solving the problem, but also components that are not essential for solving the problem in order to exemplify the technology. Therefore, the fact that these non-essential components are described in the accompanying drawings or detailed description should not be interpreted as immediately determining that these non-essential components are essential.

[0055] For example, the rotor body 2 may be formed only with the rotor core 20 without including the shaft 5. The rotor body 2 may be formed only with the shaft 5 without including the rotor core 20. The shaft 5 does not have to be a soft magnetic material. The shaft 5 may be formed integrally with the rotor core 20.

[0056] The residual magnetic flux density of ring magnet 4 is not limited to 0.9 T or less and may exceed 0.9 T. Ring magnet 4 is not limited to a bonded magnet and may be, for example, a sintered magnet formed by sintering magnetic powder. In this case, the magnetic powder may be, for example, a neodymium magnet, a samarium-iron-nitrogen magnet, a samarium-cobalt magnet, a ferrite magnet, or an alnico magnet, or a mixture of two or more of these powders. Ring magnet 4 may be a single polar anisotropic magnet that is continuous in the circumferential direction, or may be multiple polar anisotropic magnets that are divided in the circumferential direction.

[0057] The number of magnetic poles 41 that the ring magnet 4 has is not limited. The shape of the recess 43 of the ring magnet 4 is not limited. For example, the width of the recess 43 may be constant along the radial direction of the recess 43. The width of the recess 43 may increase radially inward. The recess 43 of the ring magnet 4 can be omitted. For example, the outer peripheral surface 42 of the ring magnet 4 may be a curved surface that coincides with the outer peripheral surface of the imaginary cylinder, and the magnetic body 3 may be provided on this curved surface.

[0058] The number of magnetic bodies 3 provided in the rotors 1, 1A to 1D is not limited. The magnetic bodies 3 may be provided on only some of the magnetic poles 41 of the ring magnet 4. The shape of the magnetic bodies 3 is not limited. The outer surface 31 of the magnetic body 3 does not have to be flush with the curved surface 44 of the ring magnet 4. The outer surface 31 of the magnetic body 3 may protrude radially outward from the outer surface 31 of the magnetic body 3, or may be recessed radially inward from the outer surface 31 of the magnetic body 3.

[0059] As described above, the rotors 1, 1A to 1D (inner rotors) relating to the first aspect of the technology of the present disclosure comprise a rotor body 2 that rotates around a rotation axis A1, a ring magnet 4 (polar anisotropic magnet) that forms a plurality of magnetic poles 41 arranged circumferentially around the rotation axis A1 and is provided on the outer surface of the rotor body 2, and a plurality of magnetic bodies 3 that are arranged on the outer surface 42 of the ring magnet 4 at positions corresponding to the plurality of magnetic poles 41.

[0060] With this configuration, the magnetic flux of the ring magnet 4 is concentrated in and out of the magnetic body 3 provided at the magnetic pole 41 of the ring magnet 4. This increases the magnetic flux density in the portion of the outer circumferential surface of the rotor 1 that corresponds to the magnetic pole 41. This improves the magnet torque of the motor 100, and ultimately improves the torque of the motor.

[0061] In addition, in the rotors 1, 1A to 1D relating to the second aspect of the technology of the present disclosure, recesses 43 are formed at positions corresponding to multiple magnetic poles 41 on the outer surface 42 of the ring magnet 4 in the rotors 1, 1A to 1D relating to the first aspect, and the magnetic body 3 is arranged in the recesses 43.

[0062] With this configuration, the magnetic body 3 is arranged without protruding radially outward from the ring magnet 4, thereby reducing the air gap formed between the ring magnet 4 and the stator 6. This makes it easier for the magnetic flux generated in the stator 6 to flow to the rotor 1, thereby improving the torque of the motor 100.

[0063] In addition, in rotors 1, 1A, 1B, and 1D relating to the third aspect of the technology of the present disclosure, in rotors 1, 1A, 1B, and 1D relating to the second aspect, the circumferential width of recess 43 decreases from the opening of recess 43 toward the radially inward direction centered on rotation axis A1.

[0064] With this configuration, the volume of the portion of the ring magnet 4 adjacent to the recess 43 in the circumferential direction can be expanded toward the recess 43, increasing the amount of magnet in this portion. This can therefore improve the magnet torque of the motor 100. Furthermore, the circumferential width of the opening of the recess 43 can be increased, and the circumferential width of the outer surface 31 of the magnetic body 3 exposed from the recess 43 can be increased. This makes it less likely for magnetic saturation to occur on the outer surface 31 of the magnetic body 3, and makes it easier for magnetic flux collected from the ring magnet 4 to enter and exit the outer surface 31. This can therefore further improve the magnet torque of the motor 100.

[0065] Furthermore, in rotors 1, 1A, 1B, 1D relating to the fourth aspect of the technology of the present disclosure, in rotors 1, 1A, 1B, 1D relating to the third aspect, the first recess 43, which is one of the circumferentially adjacent recesses 43, has a first side surface 47, which is the side surface facing the second recess 43, which is the other of the circumferentially adjacent recesses 43, and the second recess 43 has a second side surface 48, which is the side surface facing the first recess 43, and the first side surface 47 and the second side surface 48 are parallel to each other.

[0066] According to this configuration, by making the first side surface 47 and the second side surface 48 parallel to each other, it is possible to ensure a sufficient width of the outer surface 31 of the magnetic body 3 while also ensuring a sufficient amount of magnet in the portions of the ring magnet 4 between the recesses 43 adjacent in the circumferential direction. Therefore, the magnet torque of the motor 100 can be further improved.

[0067] In addition, in rotors 1A to 1C relating to the fifth aspect of the technology of the present disclosure, in rotors 1A to 1C relating to any one of the second to fourth aspects, the ring magnet 4 has a retaining portion 43a that protrudes circumferentially toward the inside of the recess 43 and restricts movement of the magnetic body 3 radially outward around the rotation axis A1.

[0068] According to this configuration, when the magnetic body 3 is subjected to centrifugal force during rotation of the rotor 1, the anti-detachment portion 43a restricts radial outward movement of the magnetic body 3. Therefore, the magnetic body 3 can be prevented from coming off the ring magnet 4 during rotation of the rotor 1.

[0069] Furthermore, a motor 100 according to a sixth aspect of the technique of the present disclosure includes a rotor 1, 1A to 1D according to any one of the first to fifth aspects, and a stator 6 that drives the rotor 1, 1A to 1D.

[0070] This configuration improves the magnet torque of the motor 100, and therefore the torque of the motor. [Explanation of symbols]

[0071] 100 motor 1,1A~1D Inner rotor 2 Rotor body 3 Magnetic material 4 Ring magnets (polar anisotropic magnets) 41 magnetic pole 42 Outer surface 43 Recess 43a Retaining part 47 First aspect 48 Second aspect 6 Stator A1 rotation axis

Claims

1. a rotor body that rotates around a rotation axis; a polar anisotropic magnet provided on the outer circumferential surface of the rotor body, which forms a plurality of magnetic poles arranged in a circumferential direction around the rotation axis; a plurality of magnetic bodies arranged on an outer peripheral surface of the polar anisotropic magnet that faces the stator, the magnetic bodies corresponding to the plurality of magnetic poles and corresponding to the d-axis; a recess is formed on the outer circumferential surface of the polar anisotropic magnet at a position corresponding to the plurality of magnetic poles and the d-axis, The magnetic body is disposed in the recess, a width of the recess in the circumferential direction decreasing from an opening of the recess toward an inner side in a radial direction about the rotation axis, a first recess that is one of the recesses adjacent in the circumferential direction has a first side surface that is a side surface of a second recess that is the other of the recesses adjacent in the circumferential direction, the second recess has a second side surface that faces the first recess, the first side surface and the second side surface are parallel to each other, the circumferential width of the outer surface of the magnetic body is smaller than the circumferential width of the portion of the outer peripheral surface of the polar anisotropic magnet between the circumferentially adjacent recesses, an inner rotor in which the outer surface of the magnetic body is flush with the portions of the outer peripheral surface of the polar anisotropic magnet between the recesses adjacent in the circumferential direction;

2. The inner rotor according to claim 1, The polar anisotropic magnet has an inner rotor having a retaining portion that protrudes inward of the recess in the circumferential direction and restricts movement of the magnetic body outward in the radial direction centered on the rotation axis.

3. The inner rotor according to claim 1; a stator that drives the inner rotor.

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