Outer rotor and motor

Abstract

This outer rotor comprises: a holding member having a cylindrical part extending in an axial direction and a bottom part extending in a radial direction from an end part on one side of the cylindrical part in the axial direction; a cylindrical back yoke held on an inner peripheral surface of the cylindrical part of the holding member; and a plurality of magnets fixed on an inner peripheral surface of the back yoke. In the holding member, the cylindrical part covers at least a part of an outer peripheral surface of the back yoke, and the bottom part covers an end part on one side of the back yoke in the axial direction. The back yoke and / or the holding member has protrusions that are positioned between the plurality of magnets and determine a circumferential spacing of the plurality of magnets. The plurality of magnets are in contact with the holding member in the axial direction.

Description

Outer rotor and motor

[0001] The present invention relates to an outer rotor and a motor.

[0002] An outer rotor having a cylindrical back yoke and a plurality of magnets fixed to the inner peripheral surface of the back yoke is known. For example, Patent Document 1 discloses an outer rotor type electric motor as an in-wheel motor for a saddle-ride type electric vehicle, which has a back yoke portion and a plurality of ferrite magnets supported on the back yoke portion. In this electric motor, the plurality of ferrite magnets are fixed to the back yoke portion with an adhesive, arranged circumferentially on the inner peripheral surface of the back yoke portion.

[0003] JP 2013-126859 A

[0004] In the electric motor disclosed in Patent Document 1, multiple ferrite magnets are arranged circumferentially on the inner peripheral surface of the back yoke. However, the multiple ferrite magnets are not positioned circumferentially relative to the back yoke. This can result in uneven circumferential spacing between the multiple ferrite magnets. This can increase noise or vibrations generated by motor rotation.

[0005] In response to this, there is a demand for a configuration that allows multiple magnets to be positioned accurately on the inner peripheral surface of the back yoke.

[0006] An object of the present invention is to provide an outer rotor and a motor that can accurately position a plurality of magnets on the inner peripheral surface of a back yoke and reduce vibrations or noise generated by the rotation of the motor.

[0007] An outer rotor according to an exemplary embodiment of the present invention is an outer rotor including: a retaining member having a cylindrical portion extending in the axial direction and a bottom portion extending radially from one axial end of the cylindrical portion; a cylindrical back yoke held on the inner circumferential surface of the cylindrical portion of the retaining member; and a plurality of magnets fixed on the inner circumferential surface of the back yoke. The cylindrical portion of the retaining member covers at least a portion of the outer circumferential surface of the back yoke, and the bottom portion covers one axial end of the back yoke. At least one of the back yoke and the retaining member has protrusions located between the plurality of magnets and determining the circumferential spacing of the plurality of magnets. The plurality of magnets are in axial contact with the retaining member.

[0008] A motor according to an exemplary embodiment of the present invention includes an outer rotor having the above-described configuration and a stator positioned inside the outer rotor.

[0009] According to an exemplary embodiment of the outer rotor and motor of the present invention, it is possible to provide an outer rotor and motor that can accurately position multiple magnets on the inner surface of the back yoke, thereby reducing vibrations or noise generated by the rotation of the motor.

[0010] Fig. 1 is a diagram showing an example of a schematic configuration of a motor as viewed in the axial direction. Fig. 2 is a diagram showing an example of a configuration of an outer rotor as viewed in the axial direction. Fig. 3 is a cross-sectional view taken along line III-III in Fig. 2. Fig. 4 is a partially enlarged cross-sectional view taken along line IV-IV in Fig. 3. Fig. 5 is a perspective view showing a schematic configuration of a holding member.

[0011] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The same or corresponding parts in the drawings are designated by the same reference numerals, and their description will not be repeated. Furthermore, the dimensions of the components in each drawing do not faithfully represent the actual dimensions of the components, the dimensional ratios of the components, etc.

[0012] In the following description, the direction in which the axis P of the outer rotor 1 extends is referred to as the "axial direction AD." The circumferential direction centered on the axis P is referred to as the "circumferential direction CD," and the radial direction centered on the axis P is referred to as the "radial direction RD." Furthermore, the direction described as "one axial direction" in the specification is shown as the "+X direction" in the drawings, and the direction described as "the other axial direction" is shown as the "-X direction" in the drawings. Furthermore, the directions shown in the drawings are defined merely for the convenience of explanation, and do not limit the orientation of the motor according to the present invention when used or assembled.

[0013] Furthermore, in the following description, the expressions "fix," "connect," and "attach" (hereinafter referred to as "fixing") include not only cases where members are directly fixed to each other, but also cases where members are fixed via other members. In other words, in the following description, the expression "fixing" includes both direct and indirect fixing of members to each other.

[0014] 1 is a diagram showing an example of a schematic configuration of a motor 100 as viewed in an axial direction AD. The motor 100 has an outer rotor 1 and a stator 2 located inward of the outer rotor 1. The motor 100 is used, for example, as an in-wheel motor disposed in the drive wheel of an electric motorcycle.

[0015] The outer rotor 1 is cylindrical with a bottom extending along the axis P. The stator 2 is annular and extends along the axis P, and is located radially inward of the cylindrical portion of the outer rotor 1 in the radial direction RD. The outer rotor 1 rotates about the axis P relative to the stator 2. In other words, the motor 100 of this embodiment is a so-called outer rotor motor. The configuration of the stator 2 is the same as that of a conventional motor. Therefore, a detailed description of the stator 2 will be omitted.

[0016] (Outer rotor) Fig. 2 is a diagram showing an example of the configuration of the outer rotor 1 as viewed in the axial direction AD. Fig. 3 is a cross-sectional view taken along line III-III in Fig. 2. Fig. 4 is an enlarged partial cross-sectional view taken along line IV-IV in Fig. 3. As shown in Figs. 2 and 3, the outer rotor 1 has a back yoke 10, a holding member 20, and a plurality of magnets 30.

[0017] The back yoke 10 is a cylindrical member made of a magnetic material. The back yoke 10 is made of, for example, a plurality of disk-shaped magnetic steel plates stacked in the axial direction AD. That is, the back yoke 10 has a plurality of magnetic steel plates stacked in the axial direction AD. This makes it possible to easily form the back yoke 10. Note that the back yoke 10 may be made cylindrical by combining a plurality of metal blocks instead of a plurality of disk-shaped electromagnetic steel plates.

[0018] 2 and 4, the inner peripheral side of the back yoke 10 has a polygonal shape when the back yoke 10 is viewed in the axial direction AD. That is, the inner peripheral surface of the back yoke 10 has a plurality of back yoke planar portions 10a aligned in the circumferential direction CD. As will be described later, magnets 30 are fixed to the plurality of back yoke planar portions 10a on the inner peripheral surface of the back yoke 10 in a state aligned in the circumferential direction CD.

[0019] The multiple magnets 30 are rectangular parallelepiped members. The multiple magnets 30 are members that generate a bipolar magnetic field, such as ferrite magnets or neodymium magnets. One surface of each of the multiple magnets 30 in the axial direction AD is fixed to the back yoke planar portion 10a. As described above, the inner peripheral surface of the back yoke 10 has multiple back yoke planar portions 10a aligned in the circumferential direction CD. The surface of each of the multiple magnets 30 that is fixed to the back yoke 10 is flat, and this flat surface is fixed to the back yoke planar portion 10a.

[0020] This allows the magnet 30 to be fixed in closer contact with the back yoke flat portion 10a of the inner peripheral surface of the back yoke 10. This allows more magnetic flux to flow from the magnet 30 to the back yoke 10. Furthermore, by fixing the flat surface of the magnet 30 on the back yoke flat portion 10a, the magnet 30 can be easily positioned relative to the back yoke 10.

[0021] The length of the long side of the magnet 30 is shorter than the length in the axial direction AD of the back yoke 10. The multiple magnets 30 are fixed on the back yoke planar portion 10a in a state where they are positioned inward in the axial direction AD from both ends of the back yoke 10 in the axial direction AD. In other words, the multiple magnets 30 do not protrude in the axial direction AD from the back yoke 10.

[0022] As shown in FIG. 4 , the outer circumferential side of the back yoke 10 has a circular shape recessed inward in the radial direction RD at multiple locations in the circumferential direction CD when viewed in the axial direction AD. Specifically, the back yoke 10 has multiple back yoke recesses 10b arranged in the circumferential direction CD on its outer circumferential surface. The back yoke recesses 10b have a V-shaped cross section and are groove-like extending in the axial direction AD. When viewed in the axial direction AD, the multiple back yoke recesses 10b are located on the outer circumferential surface of the back yoke 10 outward in the radial direction RD from the central portion in the circumferential direction CD of the inner back yoke planar portion 10a. As shown in FIG. 4 , the outer circumferential side of the back yoke 10 is held by a holding member 20, which will be described later. Therefore, the holding member 20 is located on the outer circumferential surface of the back yoke 10, including the back yoke recesses 10b.

[0023] As shown in FIG. 4 , the back yoke recess 10b is located at a position overlapping with the central portions of the multiple magnets 30 in the circumferential direction CD of the back yoke 10 when viewing the back yoke 10 in the radial direction RD. The magnetic flux generated by the multiple magnets 30 flows in an arc shape connecting adjacent magnets 30 in the circumferential direction CD within the back yoke 10 when viewing the back yoke 10 in the axial direction AD, as shown by the dashed arrows in FIG. 4 . Meanwhile, not much magnetic flux flows through the central portions of the magnets 30 in the circumferential direction CD of the back yoke 10. By locating the back yoke recess 10b on the outer peripheral surface of the back yoke 10 as in the above-described configuration, the flow of magnetic flux as described above can be prevented from being obstructed by the back yoke 10. This allows the weight of the back yoke 10 to be reduced without degrading the magnetic characteristics of the motor 100.

[0024] Fig. 5 is a perspective view showing a schematic configuration of the holding member. As shown in Fig. 5, the holding member 20 is a cylindrical member with a bottom that holds the back yoke 10. The holding member 20 is a member made of a non-magnetic material. The holding member 20 is, for example, a cast part made of aluminum material, or a resin molded part made of resin material. For example, the holding member 20 is molded integrally with the back yoke 10 by insert molding.

[0025] As described above, the retaining member 20 and the back yoke 10 are made of different types of materials. The retaining member 20 is integrally molded with the back yoke 10. Welding different types of materials together is difficult, and the holding force of adhesives is weak. In contrast, by integrally molding the retaining member 20 with the back yoke 10 as described above, the back yoke 10 can be firmly held by the retaining member 20 without using welding or adhesive.

[0026] As shown in FIG. 5 , the holding member 20 has a cylindrical portion 21, a bottom portion 22, and a wall portion 23. The cylindrical portion 21, the bottom portion 22, and the wall portion 23 are a single member. The cylindrical portion 21 is cylindrical, and as shown in FIG. 4 , the back yoke 10 is disposed on the inner peripheral surface. As described above, the back yoke 10 has a back yoke recess 10b recessed in the radial direction RD on its outer peripheral surface. The cylindrical portion 21 of the holding member 20 covers the outer peripheral surface of the back yoke 10 and is also located within the back yoke recess 10b. This allows the weight of the back yoke 10 to be reduced. Furthermore, because a portion of the cylindrical portion 21 of the holding member 20 is positioned within the back yoke recess 10b on the outer peripheral surface of the back yoke 10, movement of the back yoke 10 in the circumferential direction CD relative to the holding member 20 can be suppressed. This allows the holding member 20 to more reliably hold the back yoke 10.

[0027] Specifically, the cylindrical portion 21 of the holding member 20 has, on its inner circumferential side, a back yoke accommodating recess 21a in which the back yoke 10 is accommodated. The cylindrical portion 21 has, on the inner circumferential surface of the back yoke accommodating recess 21a, multiple retention protrusions 21b that are accommodated in back yoke recesses 10b located on the outer circumferential surface of the back yoke 10. The multiple retention protrusions 21b are positioned at equal intervals in the circumferential direction CD on the inner circumferential surface of the cylindrical portion 21. In this embodiment, the back yoke recesses 10b are groove-shaped with a V-shaped cross section and extending in the axial direction AD. Therefore, the retention protrusions 21b are also ridges with a triangular cross section that extend in the axial direction AD. The multiple retention protrusions 21b are a single member with the cylindrical portion 21. By having the multiple retention protrusions 21b on the cylindrical portion 21 of the holding member 20, movement of the back yoke 10 in the circumferential direction CD relative to the holding member 20 can be suppressed.

[0028] The bottom portion 22 extends inward in the radial direction RD from an end portion on one side of the axial direction AD of the cylindrical portion 21, and has an annular shape when the holding member 20 is viewed in the axial direction AD. The bottom portion 22 covers the end portion on one side of the axial direction AD of the back yoke 10. The wall portion 23 is cylindrical and extends in the axial direction AD from the bottom portion 22 along the cylindrical portion 21, at a position inward in the radial direction RD from the cylindrical portion 21. In other words, the wall portion 23 is located inward in the radial direction RD with respect to the cylindrical portion 21. As a result, an annular groove 24 is formed between the wall portion 23 and the cylindrical portion 21 when the holding member 20 is viewed in the axial direction AD. The end portion on one side of the axial direction AD of the back yoke 10 is positioned within this groove 24. Note that in this embodiment, the wall portion 23 is integral with the lower portion of the cylindrical portion 21, but may also extend in the axial direction AD from the bottom portion 22 separately from the cylindrical portion 21.

[0029] The wall portion 23 of the holding member 20 having the above configuration covers the end portion of the back yoke 10 on one side in the axial direction AD (+X direction). This allows the back yoke 10 to be positioned in the radial direction RD relative to the holding member 20. Therefore, the back yoke 10 and the multiple magnets 30 fixed on the inner peripheral surface of the back yoke 10 can be positioned with high precision in the radial direction RD. This allows for a reduction in vibration or noise caused by the rotation of the motor 100.

[0030] Furthermore, by positioning the back yoke 10 in the groove 24 located between the wall portion 23 and the cylindrical portion 21, the back yoke 10 can be held in a position relative to the holding member 20 in the axial direction AD.

[0031] The wall portion 23 has, at its tip on the other side in the axial direction AD, a plurality of recesses 23a capable of accommodating portions of the magnets. The recesses 23a are aligned at equal intervals in the circumferential direction CD at the tip of the wall portion 23. In other words, the wall portion 23 has a plurality of protrusions 23b located between adjacent recesses 23a in the circumferential direction CD. The protrusions 23b protrude from the wall portion 23 in the other side in the axial direction AD and are located between the plurality of magnets 30 whose portions are accommodated in the recesses 23a. The magnets 30 are rectangular-shaped members. Therefore, the recesses 23a are rectangular when the holding member 20 is viewed in the radial direction RD.

[0032] 4, the multiple protrusions 23b are located between adjacent back yoke recesses 10b of the back yoke 10 when viewed in the radial direction RD of the back yoke 10. In other words, the multiple protrusions 23b are located between adjacent holding protrusions 21b of the cylindrical portion 21 when viewed in the radial direction RD of the back yoke 10. This allows the magnet 30 to be positioned so that the back yoke recesses 10b overlap the central portion of the magnet 30 in the circumferential direction CD when viewed in the radial direction RD of the back yoke 10, as described above.

[0033] 3 , the holding member 20 exposes the inner circumferential surface of the back yoke 10 and also exposes at least a portion of the end face 10 c on the other side of the axial direction AD of the back yoke 10. That is, at least a portion of the end face 10 c on the other side of the axial direction AD of the holding member 20 of the back yoke 10 is exposed to the holding member 20.

[0034] This allows the exposed end surface 10c of the back yoke 10 to be positioned relative to, for example, a molding die when the holding member 20 is molded together with the back yoke 10. Therefore, the back yoke 10 can be easily positioned relative to the holding member 20.

[0035] The multiple magnets 30 are fixed to the inner peripheral surface of the back yoke 10 with an adhesive. A portion of each of the multiple magnets 30 is positioned within the recess 23a of the wall portion 23 of the holding member 20 that holds the back yoke 10. The multiple magnets 30 are in contact with the inner surface of the recess 23a of the wall portion 23. In other words, the multiple magnets 30 are in contact with the holding member 20 in the axial direction AD. As a result, the multiple magnets 30 are positioned in the axial direction AD with respect to the holding member 20.

[0036] The thickness of the magnets 30 in the radial direction RD is greater than the thickness of the wall portions 23 and protrusions 23b of the holding member 20 in the radial direction RD. In other words, the thickness of the wall portions 23 and protrusions 23b of the holding member 20 in the radial direction RD is smaller than the thickness of the magnets 30 in the radial direction RD.

[0037] This prevents the wall portion 23 and the protrusion 23b of the holding member 20 from protruding further inward in the radial direction RD than the magnet 30 and coming into contact with the stator 2. This allows the magnet 30 to be brought closer in the radial direction RD to the stator 2. This makes it possible to improve the magnetic characteristics of the motor 100 and thereby improve the performance of the motor 100 while making the motor 100 more compact in the radial direction RD.

[0038] With the above configuration, the outer rotor 1 shown as an example in this embodiment includes a holding member 20 having a cylindrical portion 21 extending in the axial direction AD and a bottom portion 22 extending in the radial direction RD from one end of the cylindrical portion 21 in the axial direction AD, a cylindrical back yoke 10 held on the inner circumferential surface of the cylindrical portion 21 of the holding member 20, and a plurality of magnets 30 fixed on the inner circumferential surface of the back yoke 10. The cylindrical portion 21 of the holding member 20 covers at least a portion of the outer circumferential surface of the back yoke 10, and the bottom portion 22 covers the end of the back yoke 10 on one side in the axial direction AD. At least one of the back yoke 10 and the holding member 20 has protrusions 23b located between the plurality of magnets 30 and determining the spacing of the plurality of magnets 30 in the circumferential direction CD. The plurality of magnets 30 are in contact with the holding member 20 in the axial direction AD.

[0039] As a result, the spacing in the circumferential direction CD of the magnets 30 fixed on the inner peripheral surface of the back yoke 10 held by the holding member 20 can be determined by the protrusions 23b, and the magnets 30 can be positioned in the axial direction AD by the holding member 20. Therefore, the magnets 30 can be positioned with high precision relative to the back yoke 10, which reduces vibrations or noise caused by the rotation of the motor 100.

[0040] In this embodiment, the holding member 20 has a wall portion 23 that extends from the bottom portion 22 to the other side of the axial direction AD around the inner periphery of the back yoke 10. The protrusions 23b protrude in the axial direction AD from the wall portion 23 of the holding member 20 and are positioned between the plurality of magnets 30. The plurality of magnets 30 are in contact with the end of the wall portion 23 on the other side of the axial direction AD.

[0041] As a result, the plurality of magnets 30 can be positioned in the circumferential direction CD by the protrusions 23b protruding in the axial direction AD from the wall portion 23 of the holding member 20, and the plurality of magnets 30 can be positioned in the axial direction AD by the wall portion 23 of the holding member 20. Therefore, the configuration of the holding member 20 allows the magnets 30 to be accurately positioned relative to the back yoke 10. Therefore, a configuration that can reduce vibration or noise generated by rotation of the motor 100 can be easily realized.

[0042] Furthermore, the magnets 30 are positioned in the circumferential direction CD by the protrusions 23b of the holding member 20. This prevents the back yoke 10, to which the magnets 30 are fixed, from rotating in the circumferential direction CD relative to the holding member 20.

[0043] While the embodiments of the present invention have been described above, the above-described embodiments are merely examples for carrying out the present invention. Therefore, the present invention is not limited to the above-described embodiments, and can be practiced by appropriately modifying the above-described embodiments within the scope of the spirit thereof.

[0044] In the above embodiment, an in-wheel motor placed inside the drive wheel of an electric motorcycle is described as an application example of motor 100. However, the motor of this embodiment may be applied to other configurations as long as the configuration is one to which an outer rotor motor can be applied.

[0045] In the above embodiment, the holding member 20 has protrusions 23b positioned between the magnets 30 to determine the spacing in the circumferential direction CD of the magnets 30. However, the back yoke may have protrusions on its inner circumferential surface positioned between the magnets to determine the spacing in the circumferential direction CD of the magnets. In this case, it is preferable that either the back yoke or the holding member has a protrusion that protrudes in the radial direction RD relative to the other in order to prevent the back yoke from rotating relative to the holding member.

[0046] In the above embodiment, the holding member 20 has a recess 23a capable of accommodating a portion of the magnet 30 at the tip of the wall portion 23 on the other side in the axial direction AD. However, the holding member may have a recess in the wall portion capable of accommodating the entire magnet. Also, the holding member may not have a recess capable of accommodating a portion of the magnet.

[0047] In the above embodiment, the holding member 20 is molded integrally with the back yoke 10 by insert molding. However, the holding member may be molded separately from the back yoke, and the back yoke may be attached to the inner surface of the holding member after molding.

[0048] In the above embodiment, the magnets 30 are fixed onto each of the plurality of back yoke planar portions 10a on the inner peripheral surface of the back yoke 10. However, the magnets may be fixed onto only some of the plurality of back yoke planar portions on the inner peripheral surface of the back yoke.

[0049] In the above embodiment, the multiple magnets 30 do not protrude in the axial direction AD relative to the back yoke 10. However, at least one of the two ends of at least one of the multiple magnets in the axial direction AD may be located at the same position in the axial direction AD as the end of the back yoke in the axial direction AD. Also, at least one of the two ends of at least one of the multiple magnets in the axial direction AD may protrude outward in the axial direction AD beyond the end of the back yoke in the axial direction AD.

[0050] In the above embodiment, the back yoke recess 10b has a V-shaped cross section and is a groove-like shape extending in the axial direction AD. However, the back yoke recess may have a cross section of another shape, such as a U-shaped cross section. Furthermore, instead of being groove-shaped, the back yoke recess may have a shape in which only a portion of the outer peripheral surface of the back yoke in the axial direction AD is recessed. The back yoke does not have to have a back yoke recess.

[0051] (Configuration Example) The present technology can also be configured as follows.

[0052] (1) An outer rotor having a retaining member having a cylindrical portion extending in the axial direction and a bottom portion extending radially from one axial end of the cylindrical portion, a cylindrical back yoke held on the inner peripheral surface of the cylindrical portion of the retaining member, and a plurality of magnets fixed on the inner peripheral surface of the back yoke, wherein the cylindrical portion of the retaining member covers at least a portion of the outer peripheral surface of the back yoke and the bottom portion covers one axial end of the back yoke, at least one of the back yoke and the retaining member has protrusions located between the plurality of magnets and determining the circumferential spacing of the plurality of magnets, and the plurality of magnets are in axial contact with the retaining member.

[0053] (2) In the outer rotor described in (1), the retaining member further has a wall portion extending from the bottom portion to the other axial direction around the inner periphery of the back yoke, the protrusion portion protrudes axially from the wall portion of the retaining member and is positioned between the plurality of magnets, and the plurality of magnets are in contact with the end portion on the other axial side of the wall portion.

[0054] (3) In the outer rotor described in (2), the radial thickness of the wall portion and the protrusion portion of the holding member is smaller than the radial thickness of the magnet.

[0055] (4) In the outer rotor described in (2), the wall portion of the holding member covers an end portion on one axial side of the inner circumferential surface of the back yoke.

[0056] (5) In the outer rotor described in any one of (1) to (4), the retaining member and the back yoke are each made of different types of material, and the retaining member is integrally molded with the back yoke.

[0057] (6) In the outer rotor described in (5), at least a portion of the end face of the back yoke on the other axial side of the holding member is exposed to the holding member.

[0058] (7) In the outer rotor described in any one of (1) to (6), the back yoke has a back yoke recess that is recessed radially on its outer peripheral surface, and the cylindrical portion of the retaining member covers the outer peripheral surface of the back yoke and is also located within the back yoke recess.

[0059] (8) In the outer rotor described in (7), the back yoke recess is located at a position overlapping with a central portion of the plurality of magnets in the circumferential direction of the back yoke when the back yoke is viewed in the radial direction.

[0060] (9) In the outer rotor described in any one of (1) to (8), the inner surface of the back yoke has a plurality of back yoke flat portions arranged in the circumferential direction, and the surfaces of the plurality of magnets that are fixed to the back yoke are flat, and the flat surfaces are fixed onto the back yoke flat portions.

[0061] (10) In the outer rotor described in any one of (1) to (9), the back yoke has a plurality of magnetic steel plates stacked in the thickness direction.

[0062] (11) A motor having the stator according to any one of (1) to (10) and a stator positioned inside the outer rotor.

[0063] The configuration of the present invention is applicable to an outer rotor having a retaining member, a cylindrical back yoke held on the inner surface of the cylindrical portion of the retaining member, and a plurality of magnets fixed on the inner surface of the back yoke.

[0064] REFERENCE SIGNS LIST 1 outer rotor 2 stator 10 back yoke 10a back yoke flat portion 10b back yoke recess 10c end face on other axial side 20 holding member 21 cylindrical portion 21a back yoke accommodating recess 21b holding protrusion 22 bottom portion 23 wall portion 23a recess 23b protrusion 24 groove 30 magnet 100 motor P axis

Claims

1. An outer rotor comprising: a retaining member having a cylindrical portion extending in the axial direction and a bottom portion extending radially from one axial end of the cylindrical portion; a cylindrical back yoke retained on the inner peripheral surface of the cylindrical portion of the retaining member; and a plurality of magnets fixed on the inner peripheral surface of the back yoke, wherein the cylindrical portion of the retaining member covers at least a portion of the outer peripheral surface of the back yoke and the bottom portion covers one axial end of the back yoke, at least one of the back yoke and the retaining member has protrusions located between the plurality of magnets and determining the circumferential spacing of the plurality of magnets, and the plurality of magnets are in axial contact with the retaining member.

2. An outer rotor as set forth in claim 1, wherein the retaining member further has a wall portion extending from the bottom portion in the other axial direction around the inner periphery of the back yoke, the protrusion protrudes axially from the wall portion of the retaining member and is positioned between the plurality of magnets, and the plurality of magnets are in contact with the end portion of the wall portion on the other axial side.

3. An outer rotor according to claim 2, wherein the radial thickness of the wall portion and the protrusion portion of the retaining member is smaller than the radial thickness of the magnet.

4. An outer rotor according to claim 2, wherein the wall portion of the retaining member covers one axial end of the inner peripheral surface of the back yoke.

5. An outer rotor according to claim 1, wherein the retaining member and the back yoke are made of different types of materials, and the retaining member is integrally molded with the back yoke.

6. An outer rotor according to claim 5, wherein at least a portion of the end face of the back yoke on the other axial side of the holding member is exposed to the holding member.

7. An outer rotor according to claim 1, wherein the back yoke has a back yoke recess that is recessed in the radial direction on its outer circumferential surface, and the cylindrical portion of the retaining member covers the outer circumferential surface of the back yoke and is also located within the back yoke recess.

8. An outer rotor according to claim 7, wherein the back yoke recess is located at a position overlapping with a central portion of the plurality of magnets in the circumferential direction of the back yoke when the back yoke is viewed in the radial direction.

9. An outer rotor according to claim 1, wherein the inner peripheral surface of the back yoke has a plurality of back yoke flat portions arranged in the circumferential direction, and the surfaces of the plurality of magnets that are fixed to the back yoke are flat, and the flat surfaces are fixed onto the back yoke flat portions.

10. An outer rotor according to claim 1, wherein the back yoke has a plurality of magnetic steel plates laminated in the thickness direction.

11. A motor comprising: an outer rotor according to any one of claims 1 to 10; and a stator positioned inside the outer rotor.

Images