Motor core, stator, tooth piece, radial-gap motor, production method for motor core, and production method for stator
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Filing Date
- 2026-01-06
- Publication Date
- 2026-04-07
Abstract
Description
Motor core, stator, tooth piece, radial gap motor, motor core manufacturing method, and stator manufacturing method
[0001] The present invention relates to a motor core, a stator, a tooth piece, a radial gap motor, a method for manufacturing a motor core, and a method for manufacturing a stator.
[0002] A radial gap motor uses a motor core (stator core) with multiple teeth extending from a circular back yoke, and in this motor core, a winding is wound around each tooth to generate a magnetic field.
[0003] JP 2018-168413 A
[0004] Because the motor core has multiple adjacent teeth, the windings are wound around each tooth using a method called nozzle winding. In nozzle winding, the winding is wound around each tooth by winding the nozzle around the teeth while unwinding the wire from the tip of the nozzle. However, with this type of nozzle winding, there is a limit to how high the winding density can be, making it difficult to increase the magnetic flux density.
[0005] Therefore, a method has been devised to increase magnetic flux density by manufacturing a motor core by joining multiple split cores (see, for example, Patent Document 1). The split core is composed of an arc-shaped back yoke and one tooth extending from the back yoke. With a split core, there are no obstacles around the teeth, so windings can be wound around the teeth at high density. Therefore, by winding windings around the teeth of each split core and then joining the multiple split cores, the windings are wound at high density, resulting in a high magnetic flux density.
[0006] When manufacturing a motor core in this manner, it is conceivable to wind a winding around the teeth of each split core, then arrange the multiple split cores in a circular shape, and then join adjacent split cores by welding, adhesive, or the like. However, unless the positional accuracy of adjacent split cores is extremely high, misalignment will occur between adjacent split cores, resulting in low circularity of the back yoke. For this reason, after joining the multiple split cores, it is necessary to cut the inner and outer peripheral surfaces of the back yoke to improve the circularity of the back yoke.
[0007] Furthermore, powder molded bodies are sometimes used as motor cores, but it is difficult to cut powder molded bodies with high precision. Therefore, if multiple split cores made of powder molded bodies are joined using the method described above, it is difficult to subsequently cut the inner and outer surfaces of the back yoke to increase the roundness of the back yoke.
[0008] Therefore, an object of the present disclosure is to provide a motor core, a stator, a tooth piece, a radial gap motor, a method for manufacturing a motor core, and a method for manufacturing a stator that can obtain high magnetic flux density and easily increase the roundness of the back yoke.
[0009] [1] The motor core according to the present disclosure is a motor core for a radial gap motor, and includes an annular back yoke and a plurality of tooth pieces formed separately from the back yoke, the plurality of tooth pieces being joined to the back yoke so as to extend radially inward from the back yoke.
[0010] In this motor core, the multiple tooth pieces are formed separately from the back yoke, so windings can be wound around each of the multiple tooth pieces before joining the multiple tooth pieces to the back yoke. This allows windings to be wound densely around each of the multiple tooth pieces, resulting in high magnetic flux density. Moreover, because the back yoke is formed in an annular shape, there is no problem with loss of roundness due to joining. This makes it easy to improve the roundness of the back yoke.
[0011] [2] In the motor core described in [1], the back yoke and the plurality of teeth may be powder-compressed compacts. In this motor core, the back yoke and the plurality of teeth are powder-compressed compacts, making it difficult to cut them with high precision. However, as described above, the back yoke is not divided, so the problem of reduced roundness due to joining does not occur. Therefore, the roundness of the back yoke can be easily improved.
[0012] [3] In the motor core according to [1] or [2], the length of the back yoke in the axial direction of the back yoke may be longer than the length of the plurality of teeth in the axial direction. In this motor core, the length of the back yoke in the axial direction is longer than the length of the plurality of teeth in the axial direction. As a result, a step is formed in which the back yoke is higher than the plurality of teeth in the axial direction, and this step increases the magnetic flux, thereby obtaining a higher magnetic flux density.
[0013] [4] In the motor core according to any one of [1] to [3], the back yoke may extend beyond the plurality of teeth in the axial direction of the back yoke to at least one side. In this motor core, the back yoke extends beyond the plurality of teeth in the axial direction to at least one side. As a result, a step is formed in which the back yoke is higher in the axial direction than the plurality of teeth, and this step increases the magnetic flux, thereby achieving a higher magnetic flux density.
[0014] [5] In the motor core according to any one of [1] to [4], each of the plurality of tooth pieces may have a body portion around which a winding is wound and a flange portion located at the end of the body portion opposite the back yoke, and the length of the flange portion in the axial direction of the back yoke may be longer than the length of the body portion in the axial direction. In this motor core, the length of the flange portion in the axial direction is longer than the length of the body portion in the axial direction. Therefore, a step is formed in which the flange portion is higher than the body portion in the axial direction, and this step increases the magnetic flux, thereby achieving a higher magnetic flux density.
[0015] [6] In the motor core according to any one of [1] to [5], each of the plurality of tooth pieces may have a body portion around which a winding is wound and a flange portion located at an end of the body portion opposite the back yoke, and the flange portion may extend beyond the body portion to at least one side in the axial direction of the back yoke. In this motor core, the flange portion extends beyond the body portion to at least one side in the axial direction. As a result, a step is formed in which the flange portion is higher than the body portion in the axial direction, and this step increases the magnetic flux, thereby achieving a higher magnetic flux density.
[0016] [7] In the motor core according to any one of [1] to [6], the back yoke may have a plurality of recesses formed on the inner peripheral surface of the back yoke, and each of the plurality of tooth pieces may be fitted into a corresponding one of the recesses. In this motor core, each of the plurality of tooth pieces is fitted into a corresponding one of the plurality of recesses formed on the inner peripheral surface of the back yoke, thereby increasing the bonding strength between the back yoke and the plurality of tooth pieces and improving the positional accuracy of the plurality of tooth pieces relative to the back yoke.
[0017] [8] In the motor core described in [7], each of the plurality of tooth pieces may have a protrusion that fits into each of the plurality of recesses. In this motor core, the protrusions of each of the plurality of tooth pieces fit into each of the plurality of recesses formed in the inner peripheral surface of the back yoke, thereby increasing the bonding strength between the back yoke and the plurality of tooth pieces and improving the positional accuracy of the plurality of tooth pieces relative to the back yoke.
[0018] [9] In the motor core described in [8], the recessed portions may be dovetail grooves and the protruding portions may be dovetail tenons. In this motor core, the recessed portions are dovetail grooves and the protruding portions are dovetail tenons, which can prevent the multiple tooth pieces from coming off the back yoke and increase the bonding strength between the back yoke and the multiple tooth pieces.
[0019]
[10] In the motor core described in [7], each of the plurality of tooth pieces may have a trunk portion around which a winding is wound and a base portion located on the back yoke side of the trunk portion and fitted into each of the plurality of recesses, and the length of the base portion in the circumferential direction of the back yoke may be longer than the length of the trunk portion in the circumferential direction. In this motor core, since the length of the base portion in the circumferential direction is longer than the length of the trunk portion in the circumferential direction, the plurality of tooth pieces can be stably joined to the back yoke and the plurality of tooth pieces can be prevented from collapsing relative to the back yoke.
[0020]
[11] In the motor core according to [7] or
[10] , each of the plurality of tooth pieces may have a trunk portion around which a winding is wound and a base portion located on the back yoke side of the trunk portion and fitted into each of the plurality of recesses, and the base portion may extend beyond the trunk portion to at least one side in the circumferential direction of the back yoke. In this motor core, since the base portion extends beyond the trunk portion to at least one side in the circumferential direction, the plurality of tooth pieces can be stably joined to the back yoke and the plurality of tooth pieces can be prevented from collapsing relative to the back yoke.
[0021]
[12] In the motor core according to any one of [1] to
[11] , each of the plurality of tooth pieces has a winding surface on which a winding is wound, and the winding surface has a first winding surface portion and a second winding surface portion that face each other in the axial direction of the back yoke, and a third winding surface portion and a fourth winding surface portion that face each other in the circumferential direction of the back yoke, and at least one of the first winding surface portion and the third winding surface portion, the first winding surface portion and the fourth winding surface portion, the second winding surface portion and the third winding surface portion, and the second winding surface portion and the fourth winding surface portion may be connected in a curved shape. In this motor core, at least one of the first and third winding surface portions, the first and fourth winding surface portions, the second and third winding surface portions, and the second and fourth winding surface portions on the winding surfaces of the plurality of teeth is connected in a curved shape, so that when the winding is wound around each of the winding surfaces of the plurality of teeth, the winding can be easily aligned along the winding surface. This makes it possible to prevent the winding from floating off the winding surface, thereby increasing the magnetic flux density.
[0022]
[13] The tooth piece according to the present disclosure is joined to an annular back yoke to form a motor core according to any one of [1] to
[12] .
[0023] Since these tooth pieces are joined to the annular back yoke to form the motor core described above, windings can be wound on them before joining them to the back yoke. This allows the windings to be wound densely around the tooth pieces, resulting in high magnetic flux density. Moreover, since the back yoke to which the tooth pieces are joined does not need to be divided, the problem of reduced roundness due to joining does not occur. This makes it easy to improve the roundness of the back yoke.
[0024]
[14] The tooth piece according to
[13] , further comprising a winding surface on which the wire is wound, the winding surface having a first winding surface portion and a second winding surface portion that face each other and a third winding surface portion and a fourth winding surface portion that are adjacent to the first winding surface portion and the second winding surface portion, and at least one of the first winding surface portion and the third winding surface portion, the first winding surface portion and the fourth winding surface portion, the second winding surface portion and the third winding surface portion, and the second winding surface portion and the fourth winding surface portion may be connected in a curved shape. In this tooth piece, at least one of the first winding surface portion and the third winding surface portion, the first winding surface portion and the fourth winding surface portion, the second winding surface portion and the third winding surface portion, and the second winding surface portion and the fourth winding surface portion is connected in a curved shape, so that when the wire is wound around the winding surface of the tooth piece, the wire can be easily aligned along the winding surface. This makes it possible to suppress the winding from floating from the winding surface, thereby increasing the magnetic flux density.
[0025]
[15] A stator according to the present disclosure is a stator for a radial gap motor, comprising the motor core according to any one of [1] to
[12] and a winding wound around each of the plurality of teeth of the motor core. Because this stator includes the motor core described above, it is possible to obtain a high magnetic flux density and easily increase the roundness of the back yoke.
[0026]
[16] A radial gap motor according to the present disclosure includes the stator described in
[15] and a rotor rotatably disposed relative to the stator. Because this radial gap motor includes the stator described above, it is possible to obtain a high magnetic flux density and easily improve the roundness of the back yoke.
[0027]
[17] A motor core manufacturing method according to the present disclosure is a motor core manufacturing method for manufacturing a motor core described in any one of [1] to
[12] , and includes a preparation step of preparing an annular back yoke and a plurality of tooth pieces configured separately from the back yoke, and a joining step of joining the plurality of tooth pieces to the back yoke so that they extend radially inward from the back yoke.
[0028] In this motor core manufacturing method, multiple tooth pieces formed separately from the back yoke are joined to the back yoke, so that windings can be wound around each of the multiple tooth pieces before joining the multiple tooth pieces to the back yoke. This allows windings to be wound densely around each of the multiple tooth pieces, resulting in high magnetic flux density. Moreover, because the back yoke is formed in an annular shape, there is no problem with loss of roundness due to joining. This makes it easy to improve the roundness of the back yoke.
[0029]
[18] A method for manufacturing a stator according to the present disclosure is a method for manufacturing a stator as described in
[15] , and includes a preparation step of preparing a circular back yoke and a plurality of tooth pieces configured separately from the back yoke, a winding step of winding a winding around each of the plurality of tooth pieces, and a joining step of joining the plurality of tooth pieces to the back yoke so that the tooth pieces extend radially inward from the back yoke after the winding step.
[0030] In this stator manufacturing method, a winding is wound around each of the multiple tooth pieces, which are formed separately from the back yoke, before joining them to the back yoke. This allows the winding to be wound densely around each of the multiple tooth pieces, resulting in a high magnetic flux density. Moreover, because the back yoke is formed in an annular shape, there is no problem with loss of roundness due to joining. This makes it easy to improve the roundness of the back yoke.
[0031] A high magnetic flux density can be obtained and the roundness of the back yoke can be easily improved.
[0032] FIG. 1 is a schematic cross-section of a radial gap motor according to an embodiment. FIG. 2 is a perspective view of a motor core according to a first embodiment. FIG. 3 is a plan view of the motor core according to the first embodiment. FIG. 4 is a perspective view of a back yoke shown in FIGS. 2 and 3. FIG. 5 is a perspective view of a tooth piece shown in FIGS. 2 and 3. FIG. 6 is a cross-sectional view of the tooth piece shown in FIGS. 2 and 3. FIG. 7 is a perspective view of a motor core according to a second embodiment. FIG. 8 is a plan view of a motor core according to the second embodiment. FIG. 9 is a perspective view of the back yoke shown in FIGS. 6 and 7. FIG. 10 is a perspective view of the tooth piece shown in FIGS. 6 and 7. FIG. 11 is a perspective view of a motor core according to a third embodiment. FIG. 12 is a perspective view of the back yoke shown in FIG. 11. FIG. 13 is a cross-sectional view of the motor core shown in FIG. 11. FIG. 14 is a perspective view of a motor core according to a fourth embodiment. FIG. 15 is a perspective view of the back yoke shown in FIG. 14. FIG. 16 is a cross-sectional view of the motor core shown in FIG. 14. FIG. 17 is a perspective view of a motor core according to a fifth embodiment. Fig. 18 is a perspective view of the tooth piece shown in Fig. 17. Fig. 19 is a cross-sectional view of the tooth piece shown in Fig. 17. Fig. 20 is a cross-sectional view of the tooth piece shown in Fig. 17. Fig. 21 is a perspective view of a motor core according to a sixth embodiment. Fig. 22 is a plan view of the motor core according to the sixth embodiment. Fig. 23 is a perspective view of the back yoke shown in Figs. 21 and 22. Fig. 24 is a perspective view of the tooth piece shown in Figs. 21 and 22. Fig. 25 is a cross-sectional view of the motor core shown in Figs. 21 and 22.
[0033] Preferred embodiments of the present disclosure will be described in detail below with reference to the drawings. In the drawings, identical or corresponding parts are designated by the same reference numerals, and duplicate explanations will be omitted. Also, in the drawings, dimensional proportions and the like have been appropriately changed to make the explanation easier to understand.
[0034] [Radial Gap Motor] Fig. 1 is a schematic cross-sectional view of a radial gap motor according to an embodiment. As shown in Fig. 1, the radial gap motor 1 according to this embodiment includes a stator 2, a rotor 3 arranged rotatably relative to the stator 2, and a shaft 4 fixed to the rotor 3. The stator 2 and the rotor 3 are arranged to be spaced apart in the radial direction of the shaft 4. A shaft hole 5 through which the shaft 4 is inserted is formed in the center of the rotor 3.
[0035] [Stator] The stator 2 according to this embodiment is the stator of the radial gap motor 1. The stator 2 includes a motor core 6 and windings 7 wound around the motor core 6. The motor core 6 is the portion of the stator 2 excluding the windings 7, and is also called a stator core.
[0036] [Motor Core of First Embodiment] Figure 2 is a perspective view of the motor core according to the first embodiment. Figure 3 is a plan view of the motor core according to the first embodiment. As shown in Figures 1 to 3, the motor core 6 according to this embodiment includes an annular back yoke 10 and a plurality of tooth pieces 20 that are formed separately from the back yoke 10 and joined to the back yoke 10. In this embodiment, the motor core 6 is described as including four tooth pieces 20, but the number of tooth pieces 20 is not particularly limited as long as it is two or more.
[0037] FIG. 4 is a perspective view of the back yoke shown in FIGS. 2 and 3. As shown in FIGS. 1 to 4, the back yoke 10 is formed in an annular shape without being divided into multiple parts. Here, the axial direction of the back yoke 10 is referred to as the axial direction D1, the radial direction of the back yoke 10 is referred to as the radial direction D2, and the circumferential direction of the back yoke 10 is referred to as the circumferential direction D3. The axial direction D1 is also the thickness direction of the back yoke 10 (the rotational axis direction of the rotor 3 in the radial gap motor 1). The radial direction D2 is also the radial direction of the annulus formed by the back yoke 10 (the radial direction of the rotor 3 in the radial gap motor 1). The circumferential direction D3 is also the circumferential direction of the annulus formed by the back yoke 10 (the rotational direction of the rotor 3 in the radial gap motor 1).
[0038] The outer peripheral surface 11 of the back yoke 10 is formed in a perfect circle shape. Note that a perfect circle shape includes not only a completely perfect circle shape, but also an approximately perfect circle shape that has been deformed due to manufacturing errors, etc. The inner peripheral surface 12 of the back yoke 10 may be formed in a perfect circle shape, or may be polygonal in order to make it easier to join multiple tooth pieces 20 to the back yoke 10.
[0039] A plurality of recesses 13 are formed on the inner peripheral surface 12 of the back yoke 10. The recesses 13 are positioned at equal intervals in the circumferential direction D3. The number of recesses 13 is the same as the number of tooth pieces 20. Each of the recesses 13 extends outward from the inner peripheral surface 12 of the back yoke 10 in the radial direction D2 and penetrates the back yoke 10 in the axial direction D1.
[0040] The back yoke 10 is, for example, a powder compact formed by pressing soft magnetic powder coated with an insulating material. The powder compact back yoke 10 can be molded, for example, using a commercially available powder compacting device. The soft magnetic powder material is, for example, pure iron, iron-silicon, or iron-cobalt. The average particle size of the soft magnetic powder is, for example, 3 μm to 300 μm, 30 μm to 200 μm, or 50 μm to 150 μm. The insulating material is, for example, an insulating coating containing phosphoric acid, silicone, or the like. The average particle size of the soft magnetic powder is measured using a robot shifter (model number: RPS-205) manufactured by Seishin Enterprise Co., Ltd. The back yoke 10 may also be a laminate formed by stacking multiple electromagnetic steel sheets.
[0041] Figure 5 is a perspective view of the tooth piece shown in Figures 2 and 3. Figure 6 is a cross-sectional view of the tooth piece shown in Figures 2 and 3. As shown in Figures 1 to 6, a plurality of tooth pieces 20 are joined to an annular back yoke 10 to form a motor core 6. Each of the plurality of tooth pieces 20 is a portion around which a winding 7 is wound. Each of the plurality of tooth pieces 20 is fitted into a respective one of a plurality of recesses 13 formed on the inner peripheral surface 12 of the back yoke 10. The plurality of tooth pieces 20 are joined to the back yoke 10 so as to extend inward in the radial direction D2 from the back yoke 10.
[0042] Each of the multiple tooth pieces 20 has a body portion 21 around which the winding 7 is wound, a flange portion 22 located at the end of the body portion 21 opposite the back yoke 10, and a base portion 23 located on the back yoke 10 side of the body portion 21 (the side opposite the flange portion 22). Each of the multiple tooth pieces 20 is joined to the back yoke 10 by fitting the base portion 23 into a respective one of multiple recesses 13 formed in the inner circumferential surface 12 of the back yoke 10. The body portion 21 and the base portion 23 extend linearly in the radial direction D2. The cross-sectional shapes of the body portion 21 and the base portion 23 in a direction perpendicular to the radial direction D2 are, for example, rectangular.
[0043] The trunk portion 21 has a winding surface 24 around which the winding 7 is wound. The winding surface 24 is the surface of the trunk portion 21 around the radial direction D2 and is the surface of the trunk portion 21 that extends from the inner circumferential surface 12 of the back yoke 10 to the flange portion 22. The winding surface 24 has a first winding surface portion 24a and a second winding surface portion 24b that face each other in the axial direction D1, and a third winding surface portion 24c and a fourth winding surface portion 24d that face each other in the circumferential direction D3. The first winding surface portion 24a and the second winding surface portion 24b are adjacent to the third winding surface portion 24c on one side in the circumferential direction D3, and the first winding surface portion 24a and the second winding surface portion 24b are adjacent to the fourth winding surface portion 24d on the other side in the circumferential direction D3. Furthermore, the third winding surface portion 24c and the fourth winding surface portion 24d are adjacent to the first winding surface portion 24a on one side in the axial direction D1, and the third winding surface portion 24c and the fourth winding surface portion 24d are adjacent to the second winding surface portion 24b on the other side in the axial direction D1.
[0044] The flange portion 22 forms the inner circumferential surfaces of the stator 2 and the motor core 6. The length of the flange portion 22 in the circumferential direction D3 is longer than the length of the trunk portion 21 in the circumferential direction D3. The flange portion 22 extends beyond the trunk portion 21 to at least one side in the circumferential direction D3. In other words, when viewed from the radial direction D2, the flange portion 22 protrudes from the trunk portion 21 to at least one side in the circumferential direction D3. In this embodiment, the flange portion 22 extends beyond the trunk portion 21 to both sides in the circumferential direction D3. In other words, when viewed from the radial direction D2, the flange portion 22 protrudes from the trunk portion 21 to both sides in the circumferential direction D3.
[0045] The plurality of tooth pieces 20 are, for example, powder compacts formed by pressing soft magnetic powder coated with an insulating material. The plurality of tooth pieces 20, which are powder compacts, can be molded, for example, using a commercially available powder compacting device. The soft magnetic powder material is, for example, pure iron, iron-silicon, or iron-cobalt. The average particle size of the soft magnetic powder is, for example, 3 μm to 300 μm, 30 μm to 200 μm, or 50 μm to 150 μm. The insulating material is, for example, an insulating coating containing phosphoric acid, silicone, or the like. The average particle size of the soft magnetic powder is measured using a robot shifter (model number: RPS-205) manufactured by Seishin Enterprise Co., Ltd. The plurality of tooth pieces 20 may also be a laminate formed by stacking multiple electromagnetic steel sheets.
[0046] [Method for Manufacturing Motor Core and Stator] Next, a method for manufacturing the motor core and stator according to this embodiment will be described. This method is a method for manufacturing the motor core 6 and stator 2 described above.
[0047] The manufacturing method of the motor core and the stator includes a preparing step, a winding step, and a joining step.
[0048] In the preparation step, an annular back yoke 10 and a plurality of tooth pieces 20 configured as separate bodies from the back yoke 10 are prepared.
[0049] The winding process can be performed at any timing before the joining process. For example, the winding process may be performed before, after, or simultaneously with the preparation process. In the winding process, the winding 7 is wound around each of the multiple tooth pieces 20. Winding the winding 7 around each of the multiple tooth pieces 20 can be performed by, for example, spindle winding, nozzle winding, flyer winding, or the like, which rotates the tooth pieces 20 to wind the winding 7 around the winding surfaces 24 of the tooth pieces 20.
[0050] The joining process is performed after the preparation process and the winding process. In the joining process, each of the multiple tooth pieces 20 is fitted into each of the multiple recesses 13 formed on the inner peripheral surface 12 of the back yoke 10. The multiple tooth pieces 20 are then joined to the back yoke 10 so that the multiple tooth pieces 20 extend inward in the radial direction D2 from the back yoke 10. The multiple tooth pieces 20 can be joined to the back yoke 10 by, for example, welding, adhesive bonding, etc.
[0051] This completes the manufacture of the motor core 6 and the stator 2. Note that by not performing the winding process, it is possible to manufacture only the motor core 6 without the windings 7.
[0052] As described above, in the motor core 6 according to this embodiment, the tooth pieces 20 are configured separately from the back yoke 10, so the windings 7 can be wound around each of the tooth pieces 20 before joining the tooth pieces 20 to the back yoke 10. This allows the windings to be wound densely around each of the tooth pieces 20, thereby obtaining a high magnetic flux density. Moreover, because the back yoke 10 is formed in an annular shape, the problem of reduction in roundness that accompanies joining does not occur. This makes it possible to easily improve the roundness of the back yoke 10.
[0053] Furthermore, in this motor core 6, the back yoke 10 and the multiple tooth pieces 20 are powder-compressed compacts, making it difficult to cut them with high precision. However, as described above, the back yoke 10 is not divided, so the problem of reduced roundness that accompanies joining does not occur. Therefore, the roundness of the back yoke 10 can be easily improved.
[0054] Furthermore, in this motor core 6, each of the multiple tooth pieces 20 is fitted into each of the multiple recesses 13 formed on the inner surface 12 of the back yoke 10, thereby increasing the bonding strength between the back yoke 10 and the multiple tooth pieces 20 and improving the positional accuracy of the multiple tooth pieces 20 relative to the back yoke 10.
[0055] Since the tooth pieces 20 according to this embodiment are joined to the annular back yoke 10 to form the motor core 6 described above, the windings 7 can be wound around the tooth pieces 20 before joining them to the back yoke 10. This allows the windings 7 to be wound around the tooth pieces 20 at high density, thereby obtaining high magnetic flux density. Moreover, since the back yoke 10 to which the tooth pieces 20 are joined does not need to be divided, the problem of reduced roundness that accompanies joining does not occur. This makes it easy to improve the roundness of the back yoke 10.
[0056] The stator 2 according to this embodiment includes the motor core 6 described above, and therefore a high magnetic flux density can be obtained and the roundness of the back yoke 10 can be easily improved.
[0057] The radial gap motor 1 according to this embodiment includes the stator 2 described above, and therefore a high magnetic flux density can be obtained and the roundness of the back yoke 10 can be easily improved.
[0058] In the motor core manufacturing method according to this embodiment, multiple tooth pieces 20 formed separately from the back yoke 10 are joined to the back yoke 10, so that the windings 7 can be wound around each of the multiple tooth pieces 20 before joining the multiple tooth pieces 20 to the back yoke 10. This allows the windings to be wound densely around each of the multiple tooth pieces 20, thereby obtaining high magnetic flux density. Moreover, because the back yoke 10 is formed in an annular shape, there is no problem with a decrease in roundness that accompanies joining. This makes it possible to easily improve the roundness of the back yoke 10.
[0059] In the method for manufacturing a stator according to this embodiment, the windings 7 are wound around each of the plurality of tooth pieces 20, which are formed separately from the back yoke 10, before joining the tooth pieces 20 to the back yoke 10. This allows the windings 7 to be wound densely around each of the plurality of tooth pieces 20, thereby obtaining a high magnetic flux density. Moreover, because the back yoke 10 is formed in an annular shape, the problem of reduction in roundness that accompanies joining does not occur. This makes it possible to easily improve the roundness of the back yoke 10.
[0060] [Motor Core of Second Embodiment] Next, a motor core according to a second embodiment will be described. The motor core according to the second embodiment is basically the same as the motor core according to the first embodiment (see FIGS. 2 to 6), but differs from the motor core according to the first embodiment in the joining structure between the back yoke and the multiple teeth. Therefore, only the differences from the motor core according to the first embodiment will be described below, and descriptions of the same aspects as those of the motor core according to the first embodiment will be omitted.
[0061] Fig. 7 is a perspective view of a motor core according to a second embodiment. Fig. 8 is a plan view of the motor core according to the second embodiment. As shown in Figs. 7 and 8, a motor core 6A according to the second embodiment includes an annular back yoke 10A and a plurality of tooth pieces 20A that are formed separately from the back yoke 10A and joined to the back yoke 10A.
[0062] FIG. 9 is a perspective view of the back yoke shown in FIGS. 7 and 8 . As shown in FIGS. 7 to 9 , the back yoke 10A is formed in an annular shape without being divided into multiple parts. A plurality of recesses 13A are formed on the inner peripheral surface 12A of the back yoke 10A instead of the plurality of recesses 13 of the first embodiment. Each of the plurality of recesses 13A is shorter in the circumferential direction D3 than each of the plurality of recesses 13 of the first embodiment. That is, each of the plurality of recesses 13A is narrower than each of the plurality of recesses 13 of the first embodiment. Each of the plurality of recesses 13A is, for example, a dovetail groove. Each of the plurality of recesses 13A being a dovetail groove means, for example, that each of the plurality of recesses 13A is formed in a triangular shape that widens outward in the radial direction D2 (toward the outer peripheral surface 11), has a portion whose width in the circumferential direction D3 increases from the inner peripheral surface 12A toward the outer peripheral surface 11, or has a surface that faces outward in the radial direction D2 (toward the outer peripheral surface 11) relative to the circumferential direction D3.
[0063] Figure 10 is a perspective view of the tooth piece shown in Figures 7 and 8. As shown in Figures 7 to 10, each of the multiple tooth pieces 20A is fitted into a corresponding one of multiple recesses 13A formed in the inner circumferential surface 12A of the back yoke 10A. The multiple tooth pieces 20A are joined to the back yoke 10A so as to extend inward in the radial direction D2 from the back yoke 10A.
[0064] Each of the tooth pieces 20A has a body portion 21 around which the winding 7 is wound, a flange portion 22 located at the end of the body portion 21A opposite the back yoke 10A, and a protrusion portion 23A located on the back yoke 10 side of the body portion 21A (the side opposite the flange portion 22). Each of the tooth pieces 20A is joined to the back yoke 10A by fitting the protrusion portion 23A into a respective one of a plurality of recesses 13A formed on the inner peripheral surface 12A of the back yoke 10A. The protrusions 23A are dovetails corresponding to the respective recesses. The protrusions 23A being dovetails means, for example, that the protrusions 23A are formed in a triangular shape that widens outward in the radial direction D2 (toward the outer peripheral surface 11), have a portion whose width in the circumferential direction D3 increases toward the protruding tip, and have a surface that faces outward in the radial direction D2 more than in the circumferential direction D3.
[0065] The respective convex portions 23A of the multiple tooth pieces 20A can be fitted into the respective multiple recesses 13A formed on the inner surface 12A of the back yoke 10A, for example, by inserting the respective convex portions 23A of the multiple tooth pieces 20A through the openings on one side of each of the multiple recesses 13A in the axial direction D1, and sliding each of the multiple tooth pieces 20A in the axial direction D1 relative to the back yoke 10A.
[0066] The motor core 6A and the stator including the motor core 6A can be manufactured by the same method as the above-described method for manufacturing the motor core and the stator.
[0067] As described above, in the motor core 6A of this embodiment, the convex portions 23A of each of the multiple tooth pieces 20A are fitted into multiple recesses 13A formed on the inner surface 12A of the back yoke 10A, thereby increasing the bonding strength between the back yoke 10A and the multiple tooth pieces 20A and improving the positional accuracy of the multiple tooth pieces 20A relative to the back yoke 10A.
[0068] Furthermore, in this motor core 6A, each of the multiple recesses 13A formed on the inner surface 12A of the back yoke 10A is a dovetail groove, and each of the protrusions 23A of the multiple tooth pieces 20A is a dovetail, thereby preventing the multiple tooth pieces 20A from coming loose from the back yoke 10A and increasing the bonding strength between the back yoke 10A and the multiple tooth pieces 20A.
[0069] [Motor Core of Third Embodiment] Next, a motor core according to a third embodiment will be described. The motor core according to the third embodiment is basically the same as the motor core according to the first embodiment (see FIGS. 2 to 6), but differs from the motor core according to the first embodiment in that the back yoke is longer in the axial direction than the plurality of teeth. For this reason, only the differences from the motor core according to the first embodiment will be described below, and descriptions of the same aspects as those of the motor core according to the first embodiment will be omitted.
[0070] Fig. 11 is a perspective view of a motor core according to the third embodiment. As shown in Fig. 11, a motor core 6B according to the third embodiment includes an annular back yoke 10B and a plurality of tooth pieces 20 that are formed separately from the back yoke 10B and joined to the back yoke 10B.
[0071] FIG. 12 is a perspective view of the back yoke shown in FIG. 11. FIG. 13 is a cross-sectional view of the motor core shown in FIG. 11. As shown in FIGS. 11 to 13, the back yoke 10B differs from the back yoke 10 of the first embodiment only in that it is longer in the axial direction D1 than the back yoke 10 of the first embodiment. The length L1 of the back yoke 10B in the axial direction D1 is longer than the length L2 of the plurality of tooth pieces 20 in the axial direction D1. The back yoke 10B extends to at least one side in the axial direction D1 beyond the plurality of tooth pieces 20. In other words, when viewed from the radial direction D2, the back yoke 10B protrudes from the plurality of tooth pieces 20 to at least one side in the axial direction D1. In this embodiment, the back yoke 10B extends to both sides in the axial direction D1 beyond the plurality of tooth pieces 20. In other words, when viewed from the radial direction D2, the back yoke 10B protrudes from the plurality of tooth pieces 20 to both sides in the axial direction D1.
[0072] The motor core 6B and the stator including the motor core 6B can be manufactured by the same method as the above-described method for manufacturing the motor core and the stator.
[0073] As described above, in the motor core 6B according to this embodiment, the length L1 of the back yoke 10B in the axial direction D1 is longer than the length L2 of the plurality of tooth pieces 20 in the axial direction D1, and the back yoke 10B extends to both sides in the axial direction D1 further than the plurality of tooth pieces 20. As a result, a step is formed in the axial direction D1 where the back yoke 10B is higher than the plurality of tooth pieces 20, and this step increases the magnetic flux, thereby achieving a higher magnetic flux density.
[0074] [Motor Core of Fourth Embodiment] Next, a motor core according to a fourth embodiment will be described. The motor core according to the fourth embodiment is basically the same as the motor core according to the second embodiment (see FIGS. 7 to 10 ), but differs from the motor core according to the second embodiment in that the back yoke is longer in the axial direction than the plurality of teeth. For this reason, only the differences from the motor core according to the second embodiment will be described below, and descriptions of the same aspects as those of the motor core according to the second embodiment will be omitted.
[0075] Fig. 14 is a perspective view of a motor core according to the fourth embodiment. As shown in Fig. 14, a motor core 6C according to the fourth embodiment includes an annular back yoke 10C and a plurality of tooth pieces 20A that are formed separately from the back yoke 10C and joined to the back yoke 10C.
[0076] FIG. 15 is a perspective view of the back yoke shown in FIG. 14. FIG. 16 is a cross-sectional view of the motor core shown in FIG. 14. As shown in FIGS. 14 to 16, the back yoke 10C differs from the back yoke 10A of the second embodiment only in that it is longer in the axial direction D1 than the back yoke 10A of the second embodiment. The length L3 of the back yoke 10C in the axial direction D1 is longer than the length L4 of the plurality of tooth pieces 20A in the axial direction D1. The back yoke 10C extends to at least one side in the axial direction D1 beyond the plurality of tooth pieces 20A. In other words, when viewed from the radial direction D2, the back yoke 10B protrudes from the plurality of tooth pieces 20 to at least one side in the axial direction D1. In this embodiment, the back yoke 10C extends to both sides in the axial direction D1 beyond the plurality of tooth pieces 20A. In other words, when viewed from the radial direction D2, the back yoke 10B protrudes from the plurality of tooth pieces 20 to both sides in the axial direction D1.
[0077] The motor core 6C and the stator including the motor core 6C can be manufactured by the same method as the above-described method for manufacturing the motor core and the stator.
[0078] As described above, in the motor core 6C according to this embodiment, the length L3 of the back yoke 10C in the axial direction D1 is longer than the length L4 of the plurality of tooth pieces 20A in the axial direction D1, and the back yoke 10C extends further on both sides in the axial direction D1 than the plurality of tooth pieces 20A. As a result, a step is formed in the axial direction D1 where the back yoke 10C is higher than the plurality of tooth pieces 20A, and this step increases the magnetic flux, thereby achieving a higher magnetic flux density.
[0079] [Motor Core of Fifth Embodiment] Next, a motor core according to a fifth embodiment will be described. The motor core according to the fifth embodiment is basically the same as the motor core according to the third embodiment (see FIGS. 11 to 13 ), but differs from the motor core according to the third embodiment in that the shapes of the body portions and flange portions of each of the multiple tooth pieces are different. For this reason, only the differences from the motor core according to the third embodiment will be described below, and descriptions of the same aspects as those of the motor core according to the third embodiment will be omitted.
[0080] Fig. 17 is a perspective view of a motor core according to the fifth embodiment. As shown in Fig. 17, a motor core 6D according to the fifth embodiment includes an annular back yoke 10B and a plurality of tooth pieces 20D formed separately from the back yoke 10B and joined to the back yoke 10B.
[0081] Fig. 18 is a perspective view of the tooth piece shown in Fig. 17. Figs. 19 and 20 are cross-sectional views of the tooth piece shown in Fig. 17. As shown in Figs. 17 to 20, each of the multiple tooth pieces 20D has a body portion 21D that is joined to the back yoke 10B and around which the winding 7 is wound, a flange portion 22D located at the end of the body portion 21D opposite the back yoke 10B, and a base portion 23D located on the back yoke 10 side of the body portion 21D. The base portion 23D has the same external shape as the body portion 21D.
[0082] The trunk portion 21D has a winding surface 24D around which the winding 7 is wound. The winding surface 24D is the surface of the trunk portion 21D around the radial direction D2 and is the surface of the trunk portion 21D that extends from the inner circumferential surface 12 of the back yoke 10D to the flange portion 22D. The winding surface 24D has a first winding surface portion 24Da and a second winding surface portion 24Db that face each other in the axial direction D1, and a third winding surface portion 24Dc and a fourth winding surface portion 24Dd that face each other in the circumferential direction D3. The first winding surface portion 24Da and the second winding surface portion 24Db are adjacent to the third winding surface portion 24Dc on one side in the circumferential direction D3, and the first winding surface portion 24Da and the second winding surface portion 24Db are adjacent to the fourth winding surface portion 24Dd on the other side in the circumferential direction D3. Furthermore, the third winding surface portion 24Dc and the fourth winding surface portion 24Dd are adjacent to the first winding surface portion 24Da on one side in the axial direction D1, and the third winding surface portion 24Dc and the fourth winding surface portion 24Dd are adjacent to the second winding surface portion 24Db on the other side in the axial direction D1.
[0083] At least one of the first winding surface portion 24Da and the third winding surface portion 24Dc, the first winding surface portion 24Da and the fourth winding surface portion 24Dd, the second winding surface portion 24Db and the third winding surface portion 24Dc, and the second winding surface portion 24Db and the fourth winding surface portion 24Dd is connected in a curved surface shape. In this embodiment, all of the first winding surface portion 24Da and the third winding surface portion 24Dc, the first winding surface portion 24Da and the fourth winding surface portion 24Dd, the second winding surface portion 24Db and the third winding surface portion 24Dc, and the second winding surface portion 24Db and the fourth winding surface portion 24Dd are connected in a curved surface shape.
[0084] The flange 22D differs from the flange 22 of the third embodiment only in that it is longer in the axial direction D1 than the flange 22 of the third embodiment. The length L5 of the flange 22D in the axial direction D1 is longer than the length L6 of the trunk 21D in the axial direction D1. The flange 22D extends to at least one side in the axial direction D1 beyond the trunk 21D. In other words, when viewed from the radial direction D2, the flange 22D protrudes from the trunk 21D to at least one side in the axial direction D1. In this embodiment, the flange 22D extends to both sides in the axial direction D1 beyond the trunk 21D. In other words, when viewed from the radial direction D2, the flange 22D protrudes from the trunk 21D to both sides in the axial direction D1.
[0085] The motor core 6D and the stator including the motor core 6D can be manufactured by the same method as the above-described method for manufacturing the motor core and the stator.
[0086] As described above, in the motor core 6D according to the present embodiment, on the winding surface 24D of each of the plurality of tooth pieces 20D, at least one of the first winding surface portion 24Da and the third winding surface portion 24Dc, the first winding surface portion 24Da and the fourth winding surface portion 24Dd, the second winding surface portion 24Db and the third winding surface portion 24Dc, and the second winding surface portion 24Db and the fourth winding surface portion 24Dd is connected in a curved shape, so that when the winding 7 is wound around each of the winding surfaces 24 of the plurality of tooth pieces 20D, the winding 7 can be easily aligned along the winding surface 24D. This makes it possible to suppress floating of the winding 7 from the winding surface 24D, thereby increasing the magnetic flux density.
[0087] Furthermore, in this motor core 6D, the length L5 of the flange 22D in the axial direction D1 is longer than the length L6 of the body 21D in the axial direction D1, and the flange 22D extends further to at least one side in the axial direction D1 than the body 21D. Therefore, a step is formed in the axial direction D1 where the flange 22D is higher than the body 21D, and this step increases the magnetic flux, thereby achieving a higher magnetic flux density.
[0088] In tooth piece 20D according to the present embodiment, at least one of first winding surface portion 24Da and third winding surface portion 24Dc, first winding surface portion 24Da and fourth winding surface portion 24Dd, second winding surface portion 24Db and third winding surface portion 24Dc, and second winding surface portion 24Db and fourth winding surface portion 24Dd is connected in a curved shape on winding surface 24, so that when winding wire 7 is wound around winding surface 24D of tooth piece 20D, winding wire 7 can be easily aligned along winding surface 24D. This makes it possible to suppress floating of winding wire 7 from winding surface 24D, thereby increasing magnetic flux density.
[0089] [Motor Core of Sixth Embodiment] Next, a motor core according to a sixth embodiment will be described. The motor core according to the sixth embodiment is basically the same as the motor core according to the first embodiment (see FIGS. 2 to 6), but differs from the motor core according to the first embodiment in the shape of the multiple recesses in the back yoke and the shape of the body portions of each of the multiple tooth pieces. Therefore, only the differences from the motor core according to the first embodiment will be described below, and descriptions of the same aspects as those of the motor core according to the first embodiment will be omitted.
[0090] Fig. 21 is a perspective view of a motor core according to the sixth embodiment. Fig. 22 is a plan view of the motor core according to the sixth embodiment. As shown in Figs. 21 and 22 , a motor core 6E according to the sixth embodiment includes an annular back yoke 10E and a plurality of tooth pieces 20E that are formed separately from the back yoke 10E and joined to the back yoke 10E.
[0091] Figure 23 is a perspective view of the back yoke shown in Figures 21 and 22. As shown in Figures 21 to 23, the back yoke 10E is formed in an annular shape without being divided into multiple pieces. A plurality of recesses 13E are formed on the inner peripheral surface 12E of the back yoke 10E, instead of the multiple recesses 13 of the first embodiment. Each of the multiple recesses 13E is longer in the circumferential direction D3 than each of the multiple recesses 13 of the first embodiment. In other words, each of the multiple recesses 13E is wider than each of the multiple recesses 13 of the first embodiment.
[0092] Figure 24 is a perspective view of the tooth piece shown in Figures 21 and 22. Figure 25 is a cross-sectional view of the motor core shown in Figures 21 and 22. As shown in Figures 21 to 25, each of the multiple tooth pieces 20E is fitted into each of the multiple recesses 13E formed in the inner circumferential surface 12E of the back yoke 10E. The multiple tooth pieces 20E are joined to the back yoke 10E so as to extend inward in the radial direction D2 from the back yoke 10E.
[0093] Each of the plurality of tooth pieces 20E has a body portion 21 around which the winding 7 is wound, a flange portion 22 located at the end of body portion 21A opposite to back yoke 10, and a base portion 23E located on the back yoke 10E side of body portion 21A (opposite flange portion 22). Each of the plurality of tooth pieces 20E is joined to back yoke 10E by fitting base portion 23E into each of a plurality of recesses 13E formed in an inner peripheral surface 12E of back yoke 10E.
[0094] The base portion 23E is longer in the circumferential direction D3 than the base portion 23 of the first embodiment. That is, the base portion 23E is also wider than the base portion 23 of the first embodiment. The length L7 of the base portion 23E in the circumferential direction D3 is longer than the length L8 of the trunk portion 21 in the circumferential direction D3. The base portion 23E extends to at least one side in the circumferential direction D3 beyond the trunk portion 21. That is, when viewed from the radial direction D2, the base portion 23E protrudes from the trunk portion 21 to at least one side in the circumferential direction D3. In this embodiment, the base portion 23E extends to both sides in the circumferential direction D3 beyond the trunk portion 21. That is, when viewed from the radial direction D2, the base portion 23E protrudes from the trunk portion 21 to both sides in the circumferential direction D3.
[0095] The motor core 6E and the stator including the motor core 6E can be manufactured by the same method as the above-described method for manufacturing the motor core and the stator.
[0096] As described above, in the motor core 6E according to this embodiment, the length L7 of the base portion 23E in the circumferential direction D3 is longer than the length L8 of the body portion 21 in the circumferential direction D3, and the base portion 23E extends to at least one side in the circumferential direction D3 beyond the body portion 21. This allows the multiple tooth pieces 20E to be stably joined to the back yoke 10E, and also prevents the multiple tooth pieces 20E from collapsing relative to the back yoke 10E.
[0097] The present disclosure is not limited to the above-described embodiments, and modifications can be made as appropriate without departing from the spirit of the present disclosure.
[0098] The present disclosure is applicable to a motor core, a stator, a tooth piece, a radial gap motor, a method for manufacturing a motor core, and a method for manufacturing a stator.
[0099] 1... Radial gap motor, 2... Stator, 3... Rotor, 4... Shaft, 5... Shaft hole, 6, 6A, 6B, 6C, 6D, 6E... Motor core, 7... Winding, 10, 10A, 10B, 10C, 10D, 10E... Back yoke, 11... Outer peripheral surface, 12, 12A, 12E... Inner peripheral surface, 13, 13A, 13E... Recess, 20, 20A, 20D, 20E... Teeth piece, 21, 21A, 21D... Body part, 22, 22D... Flange part, 23, 23E... Base part, 23A... Convex part, 24, 24D... Winding surface, 24a, 24Da... First volume Winding surface portion, 24b, 24Db...second winding surface section, 24c, 24Dc...third winding surface section, 24d, 24Dd...fourth winding surface section, D1...axial direction, D2...radial direction, D3...circumferential direction.
Claims
1. This is the motor core of a radial gap motor. A circular back yoke, It comprises a plurality of teeth pieces that are configured separately from the back yoke, The plurality of teeth are joined to the back yoke so as to extend radially inward from the back yoke. Motor core.
2. The back yoke and the plurality of teeth are compacted molded bodies. The motor core according to claim 1.
3. The length of the back yoke in the axial direction is longer than the length of the plurality of teeth pieces in the axial direction. The motor core according to claim 1.
4. The back yoke extends beyond the plurality of teeth pieces to at least one side in the axial direction of the back yoke. The motor core according to claim 1.
5. Each of the aforementioned multiple teeth pieces is, The body around which the winding wire is wound, The torso has a flange portion located at the end opposite to the back yoke, The length of the flange portion in the axial direction of the back yoke is longer than the length of the body portion in the axial direction. The motor core according to claim 1.
6. Each of the aforementioned multiple teeth pieces is, The body around which the winding wire is wound, The torso has a flange portion located at the end opposite to the back yoke, The flange extends beyond the body portion to at least one side in the axial direction of the back yoke. The motor core according to claim 1.
7. The back yoke has a plurality of recesses formed on the inner circumferential surface of the back yoke, Each of the plurality of teeth is fitted into each of the plurality of recesses. The motor core according to claim 1.
8. Each of the plurality of teeth pieces has a protrusion that fits into each of the plurality of recesses. The motor core according to claim 7.
9. The aforementioned recess is a dovetail groove, The aforementioned protrusion is a dovetail joint. The motor core according to claim 8.
10. Each of the aforementioned multiple teeth pieces is, The body around which the winding wire is wound, The torso has a base portion located on the back yoke side and fitted into each of the plurality of recesses, The length of the base of the back yoke in the circumferential direction is longer than the length of the body in the circumferential direction. The motor core according to claim 7.
11. Each of the aforementioned multiple teeth pieces is, The body around which the winding wire is wound, The torso has a base portion located on the back yoke side and fitted into each of the plurality of recesses, The base extends beyond the torso portion to at least one side of the back yoke in the circumferential direction. The motor core according to claim 7.
12. Each of the aforementioned multiple teeth pieces has a winding surface around which the winding is wound, The aforementioned winding surface is The first and second winding surfaces of the back yoke are opposite each other in the axial direction, The back yoke has a third and fourth winding portion facing each other in the circumferential direction, At least one of the first and third curved surfaces, the first and fourth curved surfaces, the second and third curved surfaces, and the second and fourth curved surfaces are connected in a curved manner. The motor core according to claim 1.
13. A tooth piece that, when joined to an annular back yoke, forms a motor core according to any one of claims 1 to 12.
14. Having a winding surface around which the winding is wound, The aforementioned winding surface is The first and second curved surfaces are opposite each other, It has a first winding surface portion and a third winding surface portion and a fourth winding surface portion adjacent to the second winding surface portion, At least one of the first and third curved surfaces, the first and fourth curved surfaces, the second and third curved surfaces, and the second and fourth curved surfaces are connected in a curved manner. The tooth piece according to claim 13.
15. It is the stator of a radial gap motor, A motor core according to any one of claims 1 to 12, The motor core comprises windings wound around each of the plurality of teeth pieces, stata.
16. The stator described in claim 15, The system comprises a rotor rotatably arranged relative to the stator, Radial gap motor.
17. A method for manufacturing a motor core according to any one of claims 1 to 12, A preparation step involves preparing an annular back yoke and a plurality of teeth pieces that are constructed separately from the back yoke. The process includes joining the plurality of teeth pieces to the back yoke so that they extend radially inward from the back yoke, A method for manufacturing a motor core.
18. A method for manufacturing a stator as described in claim 15, A preparation step involves preparing an annular back yoke and a plurality of teeth pieces that are constructed separately from the back yoke. A winding step in which a winding wire is wound around each of the plurality of teeth pieces, The process includes, after the winding step, joining the plurality of teeth pieces to the back yoke so that they extend radially inward from the back yoke, A method for manufacturing a stator.