Core and rotary electric machine

Abstract

A core used in an axial gap type rotary electric machine comprises: an annular yoke; and a plurality of columnar teeth arranged at intervals around the axis of the yoke. The yoke and the plurality of teeth are formed of an integrated powder compact. The yoke comprises a first surface having a boundary with the plurality of teeth, a second surface opposite to the first surface, and an outer peripheral surface and an inner peripheral surface connecting the first surface and the second surface. When viewing the core from a first direction parallel to the axis, each of the plurality of teeth comprises an external region located outside a first envelope circle constituted by the outer peripheral surface.

Description

Cores and rotating electrical machines

[0001] This application claims priority to Japanese Patent Application No. 2023-219625 filed on December 26, 2023, and incorporates by reference the entire contents of that application.

[0002] Patent Document 1 discloses a core used in an axial gap type rotating electric machine. This core includes an annular yoke and a plurality of columnar teeth protruding from the surface of the yoke. The yoke and each of the plurality of teeth are integrally formed into a powder compact. In Patent Document 1, soft magnetic powder is pressure-molded to produce a powder compact including a yoke and a plurality of teeth, and then the end surfaces of each tooth in the powder compact are ground. By grinding the end surfaces of each tooth, variation in height from the back surface of the yoke to the end surfaces of each of the plurality of teeth is reduced.

[0003] Japanese Patent Application Laid-Open No. 2021-100329

[0004] The core disclosed herein is a core for use in an axial gap type rotating electric machine, and includes an annular yoke and a plurality of columnar teeth spaced about the axis of the yoke. The yoke and the plurality of teeth are formed as an integral powder compact. The yoke includes a first surface defining a boundary between the plurality of teeth, a second surface opposite the first surface, and an outer peripheral surface and an inner peripheral surface connecting the first surface and the second surface. Each of the plurality of teeth includes an outer region located outside a first enveloping circle defined by the outer peripheral surface when the core is viewed from a first direction parallel to the axis.

[0005] FIG. 1 is a schematic perspective view showing an example of a core according to an embodiment. FIG. 2 is a schematic bottom view of the core of FIG. 1. FIG. 3 is a schematic plan view of the core of FIG. 1. FIG. 4 is an enlarged view showing one of the teeth provided in the core of FIG. 1. FIG. 5 is a cross-sectional view taken along V-V in FIG. 4. FIG. 6 is a cross-sectional view taken along VI-VI in FIG. 1. FIG. 7 is a schematic perspective view of a die used to manufacture the core according to an embodiment. FIG. 8 is a schematic perspective view of a lower punch used to manufacture the core according to an embodiment. FIG. 9 is a schematic perspective view of an upper punch used to manufacture the core according to an embodiment. FIG. 10 is a schematic top view of a state in which powder has been filled into a cavity formed by the die of FIG. 7 and the lower punch of FIG. 8. FIG. 11 is a schematic cross-sectional view showing a portion of a state in which the die of FIG. 7, the lower punch of FIG. 8, and the upper punch of FIG. 9 are combined. FIG. 12 is a schematic perspective view showing an example of a stator including the core of FIG. 1. FIG. 13 is a schematic perspective view showing an example of a rotating electric machine including the stator of FIG. 12.

[0006] [Problem to be Solved by the Present Disclosure] A powder compact is produced by filling a cavity formed in a die with powder and then pressure-molding the filled powder. Powder is fed into the cavity using a powder box with an opening at the bottom. The powder box moves back and forth linearly above the die. As the powder box moves over the cavity, gravity causes the powder in the powder box to fall into the cavity through the opening of the powder box. As the powder box moves back and forth, the bottom of the powder box drags some of the powder filled into the cavity. Therefore, the area of ​​the cavity near the start point of powder feeding from the powder box tends to be filled with more powder than the area near the turnaround point of powder feeding. If the amount of powder filled is uneven, the length from the back surface of the yoke to each end face of the multiple teeth may vary in the powder compact obtained after pressure molding.

[0007] In the technology of Patent Document 1, a powder compact with the above-mentioned length variations is produced, and then the end surfaces of each tooth in the powder compact are ground. The technology of Patent Document 1 requires a grinding process, which requires a large number of processes, and therefore improvement in productivity is desired.

[0008] An object of the present disclosure is to provide a core that has little variation in the length from the reference surface of the yoke to the end face of each of the plurality of teeth and that is highly productive.

[0009] Effect of the Present Disclosure The core of the present disclosure has small variations in the length from the reference surface of the yoke to the end face of each of the plurality of teeth, and is highly productive.

[0010] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be listed and described.

[0011] (1) A core according to an embodiment of the present disclosure is a core for use in an axial gap type rotating electric machine, and includes an annular yoke and a plurality of columnar teeth spaced about the axis of the yoke. The yoke and the plurality of teeth are formed as an integral powder compact. The yoke includes a first surface defining a boundary between the plurality of teeth, a second surface opposite the first surface, and an outer circumferential surface and an inner circumferential surface connecting the first surface and the second surface. Each of the plurality of teeth includes an outer region located outside a first enveloping circle defined by the outer circumferential surface when the core is viewed from a first direction parallel to the axis.

[0012] The yoke axis is the axis of rotational symmetry of the toroidal yoke, i.e., the yoke axis is a straight line that passes through the center of the toroidal circle and is perpendicular to the first surface of the yoke.

[0013] As described above, a powder compact is produced by filling a cavity formed in a mold with powder and then pressure-molding the filled powder. The cavity has a shape corresponding to the core. For example, the cavity has a shape such that the first surface of the yoke faces downward and the second surface faces upward. The second surface of the yoke is, for example, a flat surface. A powder box that supplies powder to the cavity moves back and forth over the powder that constitutes the second surface of the yoke.

[0014] In a conventional core such as that described in Patent Document 1, when the core is viewed from a first direction, each tooth does not have an area located outside a first enveloping circle formed by the outer peripheral surface of the yoke. In conventional cores, the opening shape of the cavity is the same as the shape of the yoke, i.e., annular. If the opening is annular, the outline of the powder mass arranged on the opening surface of the cavity is circular. If the outline of the powder mass arranged on the opening surface of the cavity is circular, some of the powder is likely to be dragged by the powder box as the powder box moves back and forth.

[0015] In a core according to an embodiment of the present disclosure, when viewed from a first direction, each tooth has an outer region located outward from a first enveloping circle formed by the outer peripheral surface of the yoke. In a core according to an embodiment of the present disclosure, the opening shape of the cavity is a shape combining the yoke and the outer region and has an uneven contour. With an opening having an uneven contour, the powder mass arranged on the opening surface of the cavity has an intermittent portion around the axis of the yoke. The presence of an intermittent portion makes it difficult for the powder to be dragged by the powder box even when the powder box moves back and forth. If the powder is not easily dragged by the powder box when it moves back and forth, unevenness in the amount of powder filled into the cavity is unlikely to occur. If unevenness in the amount of powder filled is unlikely to occur, variation in the length from the reference plane of the yoke to each end face of the multiple teeth is unlikely to occur in the powder compact obtained after pressure molding. Therefore, in a core according to an embodiment of the present disclosure, variation in the length from the reference plane of the yoke to each end face of the multiple teeth is small.

[0016] In the core according to the embodiment of the present disclosure, when the powder is compressed to form a powder compact, there is little variation in the length from the reference surface of the yoke to the end face of each of the multiple teeth. Therefore, after the powder compact is formed, there is no need to grind the end face of each tooth. Therefore, the core according to the embodiment of the present disclosure has excellent productivity.

[0017] (2) In the core of (1) above, each of the plurality of teeth may have a first end face located at a tip protruding from the first surface in a direction parallel to the axis, and the variation in length from the second surface to the first end face of each of the plurality of teeth may be 0.05 mm or less.

[0018] A rotating electric machine is constructed by housing a stator, which is configured by arranging a coil on each tooth of a core, together with a rotor in a case. In this case, the second surface of the yoke contacts the inner surface of the case. If the variation in length from the second surface to the first end face of each of the multiple teeth is 0.05 mm or less, when the stator and rotor are housed in the case, the end faces of each tooth face any part of the magnet at substantially uniform intervals. Therefore, a rotating electric machine constructed using the core is easy to assemble and has small torque ripple. The small torque ripple in the rotating electric machine makes it less likely for noise and vibration to increase. The small torque ripple in the rotating electric machine makes it less likely for the rotor's rotating shaft to wobble. In other words, the frictional force between the rotor's rotating shaft and the bearings is less likely to fluctuate. Therefore, mechanical energy loss in the rotating electric machine is less likely to increase.

[0019] (3) In the core of (1) or (2) above, each of the plurality of teeth may have a first end face located at a tip protruding from the first surface in a direction parallel to the axis, and the external region may have a second end face which is the surface opposite to the first end face, and the second end face may be located between the extension surface of the second surface and the first end face and spaced apart from the extension surface of the second surface.

[0020] By providing a gap between the second end face and the extension of the second face, wiring space corresponding to this gap can be secured. When each tooth has an outer region, the core becomes larger in the second direction perpendicular to the first direction compared to conventional cores. However, by securing the wiring space using the outer region, the overall size of the stator configured by arranging coils on each tooth of the core is suppressed.

[0021] (4) In the core of (3) above, the second end surface may have a proximal surface located between the extension surface of the first surface and the extension surface of the second surface so as to be connected to the second surface or the outer peripheral surface, and a distal surface located farther from the outer peripheral surface than the proximal surface and farther from the extension surface of the second surface.

[0022] As described below, the mold for press-molding the core with an external region on each tooth includes a die, a lower punch, and an upper punch. The yoke is formed by supporting the first surface on the die and pressing the second surface with the upper punch. Each tooth is pressed by the lower punch and the upper punch. The second end surface is formed by transferring the shape of the convex portion formed on the upper punch. If the upper punch has a convex portion, relatively large stress is generated at the corner of the die that forms the first corner portion formed by the first surface and the outer peripheral surface of the yoke. If the second end surface has a step formed by the proximal surface and the distal surface, the above-mentioned stress generated in the die is easily reduced.

[0023] (5) In the core of any one of (1) to (4), each of the plurality of teeth may have a first end face located at a tip end protruding from the first surface in a direction parallel to the axis, and a ratio of a second length of the outer region to a first length of each of the plurality of teeth may be 60% or more and 90% or less. The first length is the length from the second surface to the first end face. The second length is the length along the first direction of a point in the outer region located farthest from the axis.

[0024] Stress generated at the corners of the die that forms the first corners of the yoke is caused by the difference between the molding pressure applied to the outer region of each tooth and the molding pressure applied to the region other than the outer region. If the ratio is 60% or more and 90% or less, the stress is easily reduced. If the ratio is 90% or less, a gap is created between the second end face, which is the surface opposite the first end face in the outer region, and the extended surface of the second face, and wiring space corresponding to this gap is easily secured. If the ratio is 60% or more, magnetic flux flowing from the rotor magnet into the outer region of the teeth is easily able to flow efficiently into the yoke.

[0025] (6) In the core of any one of (1) to (5), when the core is viewed from the first direction, the angle between the first tangent and the second tangent at the first intersection point may be 90° or less. The first intersection point is an intersection point between a side surface of the outer region and the first enveloping circle. The first tangent is a tangent to the first enveloping circle that passes through the first intersection point. The second tangent is a tangent to the side surface of the outer region that passes through the first intersection point.

[0026] If the angle is 90° or less, it is easy to reduce stress generated at the corner of the die that forms the first corner portion of the yoke.

[0027] (7) In any of the cores (1) to (6) above, a first corner formed by the first surface and the outer peripheral surface, and a second corner formed by the first surface and the inner peripheral surface may each be rounded.

[0028] If the first corner is rounded, it is easy to reduce stress generated at the corner of the die that forms the first corner, and if the second corner is rounded, it is easy to reduce stress generated at the corner of the die that forms the second corner.

[0029] (8) In the core of (7) above, the radius of curvature of the first corner may be larger than the radius of curvature of the second corner.

[0030] During pressure molding, a relatively large stress occurs at the corner of the die that forms the first corner portion. If the radius of curvature of the first corner portion is larger than the radius of curvature of the second corner portion, the stress that occurs at the corner of the die that forms the first corner portion can be easily reduced.

[0031] (9) In the core according to any one of (1) to (8) above, the diameter of a second enveloping circle surrounding the plurality of teeth may be 15% or more larger than the diameter of the first enveloping circle.

[0032] The ratio of the diameter of the second envelope circle to the diameter of the first envelope circle correlates with the amount of protrusion of the external region along a second direction relative to the outer peripheral surface of the yoke. The second direction is a direction perpendicular to the first direction and parallel to the diameter of the yoke. If the diameter of the second envelope circle is 15% or more larger than the diameter of the first envelope circle, i.e., the ratio is 115% or more, the opening shape of the cavity of the mold for producing this core has a contour with a large difference in unevenness. The greater the difference in unevenness, the less likely the powder is to be dragged by the powder box even when the powder box moves back and forth. The greater the difference in unevenness, the smaller the variation in length from the second surface of the yoke to each end face of the multiple teeth.

[0033] (10) A rotating electric machine according to an embodiment of the present disclosure includes a rotor and a stator facing the rotor in a direction along a rotation axis of the rotor, the stator including a core according to any one of (1) to (9) above and a coil disposed on each of the plurality of teeth of the core.

[0034] The rotating electric machine according to the embodiment of the present disclosure has excellent assembly properties because it includes the core. As described above, the core has small variation in length from the second surface of the yoke to the end face of each of the multiple teeth. Therefore, when the stator and rotor are housed in the case, the core, coil, and rotor are precisely positioned. Furthermore, because the rotating electric machine according to the embodiment of the present disclosure includes the core, torque ripple can be reduced, and noise and vibration are low.

[0035] [Details of the embodiments of the present disclosure] Specific examples of the core and rotating electric machine of the present disclosure will be described with reference to the drawings. The same reference numerals in the drawings indicate the same or equivalent parts. In each drawing, for the convenience of explanation, some of the configuration may be exaggerated or simplified. The dimensional ratios of each part in the drawings may also differ from the actual ratios. Note that the present invention is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0036] <<Core>> A core 1 according to an embodiment will be described with reference to Figures 1 to 6 and, where appropriate, Figures 12 and 13. The core 1 is used in an axial gap type rotating electric machine 8 shown in Figure 13. Typically, the core 1 is used as the core 1 of a stator 7 shown in Figure 12.

[0037] The core 1 includes an annular yoke 2 and a plurality of columnar teeth 4. The teeth 4 are spaced apart around the axis of the yoke 2. The yoke 2 and the plurality of teeth 4 are formed as an integrated powder compact. One feature of the core 1 of this embodiment is that each tooth 4 includes an outer region 40. As shown in FIG. 2 , the outer region 40 is a region located outside a first enveloping circle 61 formed by the outer peripheral surface of the yoke 2 when viewing the core 1 from a first direction D1. The first direction D1 is a direction parallel to the axis of the yoke 2. Hereinafter, both the bottom-to-top direction and the top-to-bottom direction in FIG. 1 are referred to as the first direction D1. The direction perpendicular to the first direction D1 is referred to as the second direction D2. As shown in FIG. 4 , the second direction D2 is a direction along the diameter of the yoke 2.

[0038] <Yoke> As shown in FIGS. 1 to 3 , the yoke 2 is a plate member having a circular planar shape. The yoke 2 has a first surface 21, a second surface 22, an outer peripheral surface 23, and an inner peripheral surface 24. The first surface 21 defines a boundary between the teeth 4, and is a surface from which the teeth 4 protrude in a direction parallel to the axis of the yoke 2. The second surface 22 is the surface opposite the first surface 21. The first surface 21 and the second surface 22 are flat surfaces. An axial hole 25 penetrating the first surface 21 and the second surface 22 is provided in the center of the yoke 2. The outer peripheral surface 23 and the inner peripheral surface 24 connect the first surface 21 and the second surface 22. The yoke 2 magnetically couples adjacent teeth 4 among the teeth 4 arranged at intervals around the axis of the yoke 2.

[0039] 2 , the yoke 2 is a portion of the core 1 where a first enveloping circle 61 formed by the outer peripheral surface 23 is a perfect circle when viewed from the first direction D1. In other words, the yoke 2 is a portion where the distance A2 between the outer peripheral surface 23 and the inner peripheral surface 24 is constant around the axis of the yoke 2. All of the portions of the core 1 located outward from the first enveloping circle 61 are part of the teeth 4, which will be described later.

[0040] As shown in FIG. 3 , a first corner 31 formed by the first surface 21 and the outer peripheral surface 23 and a second corner 32 formed by the first surface 21 and the inner peripheral surface 24 may each be rounded. Rounding the first corner 31 facilitates reducing stress generated at the corner of the die 91 where the first corner 31 is formed, as shown in FIG. 7 . Rounding the second corner 32 facilitates reducing stress generated at the corner of the die 91 where the second corner 32 is formed. The radius of curvature of the first corner 31 may be larger than the radius of curvature of the second corner 32. During pressure molding, relatively large stress is generated at the corner of the die 91 where the first corner 31 is formed. If the radius of curvature of the first corner 31 is larger than the radius of curvature of the second corner 32, stress generated at the corner of the die 91 where the first corner 31 is formed may be easily reduced. The radius of curvature of the first corner 31 and the radius of curvature of the second corner 32 may be the same. Only the first corner 31 may be rounded. Each of the first corner portion 31 and the second corner portion 32 does not have to be rounded.

[0041] <Teeth> As shown in FIG. 1 , each tooth 4 is a columnar member. Each tooth 4 is arranged at intervals around the axis of the yoke 2. Typically, each tooth 4 is arranged at equal intervals around the axis of the yoke 2. The number of teeth 4 can be two or more and can be selected appropriately. The number of teeth 4 may be three or more, or six or more. When the core 1 is used in a three-phase AC rotating device, the number of teeth 4 is, for example, a multiple of three. The drawings show a core 1 having 12 teeth 4 as an example.

[0042] [Basic Configuration of Teeth] Each tooth 4 has a main region that protrudes from the first surface 21 of the yoke 2 in a direction parallel to the axis of the yoke 2. Each tooth 4 has a sub-region that protrudes outward from the main region in a direction perpendicular to the axis of the yoke 2. The outward direction is the direction away from the axis of the yoke 2. As shown in FIG. 2 , the sub-region is an outer region 40 located outward from the first enveloping circle 61 when viewing the core 1 from the first direction D1. As shown in FIG. 5 , the outer region 40 in this example has a portion located between a first extension surface 51 extending from the first surface 21 and a second extension surface 52 extending from the second surface 22. In other words, the outer region 40 in this example has a portion that protrudes outward from the outer circumferential surface 23 of the yoke 2, as shown in FIGS. 4 and 5 .

[0043] Each tooth 4 has a first end face 41 located at a tip end protruding from the first surface 21 in a direction parallel to the axis of the yoke 2. In this example, the first end face 41 is a surface parallel to the first surface 21. The first end face 41 may be an inclined surface having a slight angle with respect to the first surface 21. The shape of the first end face 41 is, for example, trapezoidal. In this example, the side of the trapezoidal first end face 41 that is distal from the axis of the yoke 2 is configured with a curve. The region between the first end face 41 and the first extension surface 51 of each tooth 4 has a uniform shape in the first direction D1 parallel to the axis of the yoke 2. The tooth 4 with the trapezoidal first end face 41 is a quadrangular prism. The tooth 4 with the trapezoidal first end face 41 easily ensures a large cross-sectional area of ​​the tooth 4. The tooth 4 with the trapezoidal first end face 41 easily ensures a large space between adjacent teeth 4. If a large space can be secured between adjacent teeth 4, it is easy to secure a large space for arranging the coil 70 shown in Fig. 12, and it is easy to construct a stator 7 (Figs. 12 and 13) with a high space factor. The shape of the first end face 41 may be a triangle such as an isosceles triangle, a rectangle, or a circle. The region between the first end face 41 and the first extension surface 51 of each tooth 4 may be configured to taper from the first extension surface 51 toward the first end face 41.

[0044] The terms "trapezoid" and "triangular" used here refer not only to geometric trapezoids and triangles, but also to shapes with rounded corners, such as in this example, and encompass shapes that are essentially considered trapezoids and triangles. For example, if the contour includes straight lines, it also encompasses shapes in which the intersections of the extensions of these lines form the vertices of a polygon. For example, if the contour includes curved and straight lines, it also encompasses shapes in which the intersections of the tangents of these curved lines and the straight lines or the extensions of the straight lines form the vertices of a polygon.

[0045] Typically, the teeth 4 have the same shape and size.

[0046] [External Region] As shown in Figures 2, 4, and 5, the external region 40 has a second end face 42, which is the face opposite to the first end face 41. The second end face 42 is a face extending from the outer peripheral surface 23 of the yoke 2 in a direction intersecting the first direction D1. In this example, the second end face 42 is along the second direction D2. As shown in Figures 4 and 5, the second end face 42 in this example is located between the first end face 41 and the second extension face 52 and is spaced apart from the second extension face 52.

[0047] 4 and 5 , the second end surface 42 in this example has a proximal surface 421 and a distal surface 422. The proximal surface 421 is a surface located between the first extended surface 51 and the second extended surface 52 so as to be continuous with the second surface 22 or the outer peripheral surface 23 of the yoke 2. The proximal surface 421 in this example is located near the second extended surface 52. The distal surface 422 is a surface located farther from the outer peripheral surface 23 than the proximal surface and farther from the second extended surface 52. The distal surface 422 in this example is located between the first extended surface 51 and the second extended surface 52 so as to be continuous with the side surface 43 of the outer region 40.

[0048] In this example, the second end surface 42 is mostly composed of the distal surface 422. By providing a gap A1 between the distal surface 422 and the second extension surface 52, a wiring space for the coil 70 shown in FIG. 12 can be secured in accordance with the gap A1. When each tooth 4 has an outer region 40, the core 1 becomes larger in the second direction D2 compared to conventional cores. However, by securing the wiring space using the outer region 40, the overall size of the stator 7 ( FIG. 12 ) configured in which the coil 70 is disposed on each tooth 4 of the core 1 is suppressed.

[0049] The distance A1 is the distance between the second end surface 42 and the second extension surface 52 at a position farthest from the outer peripheral surface 23. The larger the distance A1, the larger the wiring space that can be secured. The distance A1 is, for example, 10% or more of the first length L1 from the second surface 22 to the first end surface 41. A method for measuring the first length L1 of each tooth 4 will be described later. The distance A1 is correlated with the second length L2 of the outer region 40. The second length L2 is the length along the first direction D1 of a portion of the outer region 40 that is located farthest from the axis of the yoke 2. In other words, the second length L2 is the length along the first direction D1 of a portion of the side surface 43 of the outer region 40 that is located at the tip of the tooth 4 that protrudes outward from the main region along the second direction D2. As the distance A1 increases, the second length L2 decreases. Taking the second length L2 into consideration, the distance A1 is, for example, 40% or less of the first length L1. The distance A1 is, for example, 10% to 40% of the first length L1. The distance A1 may be 15% to 35%, or 20% to 30% of the first length L1.

[0050] In this example, the second end surface 42 has a step formed between the proximal surface 421 and the distal surface 422. The mold 9 for press-molding the core 1, which includes the outer region 40 on each tooth 4, includes a die 91, a lower punch 92, and an upper punch 93, as described below with reference to FIG. 11 . The yoke 2 is formed by supporting the first surface 21 on the die 91 and pressing the second surface 22 with the upper punch 93. Each tooth 4 is pressed with the lower punch 92 and the upper punch 93. The second end surface 42 is formed by transferring the shape of the convex portion 934 of the upper punch 93. If the upper punch 93 has the convex portion 934, a relatively large stress is generated at the corner of the die 91 that forms the first corner portion 31. The step formed on the second end surface 42 makes it easier to reduce the stress generated in the die 91.

[0051] In this example, the outer peripheral surface 23 connecting the second surface 22 and the proximal surface 421 is configured as an inclined surface that approaches the first surface 21 the closer it is to the outer periphery of the yoke 2. In this example, the connecting surface connecting the proximal surface 421 and the distal surface 422 is also configured as an inclined surface that approaches the first surface 21 the closer it is to the outer periphery of the yoke 2. When the outer peripheral surface 23 connecting the second surface 22 and the proximal surface 421 and the connecting surface are inclined surfaces, it is easy to remove the upper punch 93 from the powder compact after pressure molding.

[0052] The second end surface 42 may be formed as a single surface. The second end surface 42 formed as a single surface may be an inclined surface that approaches the first surface 21 toward the outer periphery of the yoke 2. If the second end surface 42 is an inclined surface, it is easy to remove the upper punch 93 from the powder compact after pressure molding.

[0053] As shown in FIG. 3 , when the core 1 is viewed from the first direction D1, the angle θ between the first tangent T1 and the second tangent T2 at the first intersection T0 is, for example, 90° or less. The first intersection T0 is the intersection point between the side surface 43 of the outer region 40 and the first enveloping circle 61. When the core 1 is viewed from the first direction D1, the side surface 43 of the outer region 40 is a surface that is flush with the side surface of the main region of each tooth 4. In this example, the side surface 43 is a flat surface that is flush with the side surface of the main region. The side surface 43 of the outer region 40 is not limited to the flat surface in this example, and may be a curved surface with a monotonous curvature or a curved surface with a changing curvature. The first tangent T1 is a tangent to the first enveloping circle 61 that passes through the first intersection T0. The second tangent T2 is a tangent to the side surface 43 of the outer region 40 that passes through the first intersection T0. If the angle θ is 90° or less, it is easy to reduce stress generated at the corner portion that forms the first corner portion 31 in the die 91 of the mold 9 that pressure-molds the core 1. The angle θ may be less than 90°, 80° or less, or 70° or less.

[0054] [Size of the Outer Region] As shown in FIG. 2 , when the core 1 is viewed from the first direction D1, the diameter of a second enveloping circle 62 surrounding the plurality of teeth 4 is, for example, 15% or more larger than the diameter of the first enveloping circle 61. The ratio of the diameter of the second enveloping circle 62 to the diameter of the first enveloping circle 61 correlates with the amount of protrusion of the outer region 40 in the second direction D2 from the outer peripheral surface 23 of the yoke 2. If the diameter of the second enveloping circle 62 is 15% or more larger than the diameter of the first enveloping circle 61, i.e., if the ratio is 115% or more, the opening shape of the cavity of the mold 9 used to produce the core 1 has a contour with a large difference in concavity and convexity. The larger the difference in concavity and convexity, the smaller the variation in the length from the second surface 22 of the yoke 2 to the first end surface 41 of each of the plurality of teeth 4, as described below. The larger the difference in concavity and convexity, the easier it is to reduce stress generated at the corner of the die 91 of the mold 9 used to pressure-mold the core 1, which forms the first corner portion 31.

[0055] If the ratio is too large, the magnetic properties may become non-uniform throughout the core 1. If the ratio is 130% or less, the core 1 is likely to have uniform magnetic properties throughout the core 1. The ratio may be 115% or more and 130% or less, 118% or more and 127% or less, or 120% or more and 125% or less.

[0056] As shown in FIGS. 4 and 5 , in each tooth 4, the ratio of the second length L2 to the first length L1 is, for example, 60% or more and 90% or less. As described above, the ratio of the second length L2 to the first length L1 is correlated with the distance between the second end face 42 and the second extended surface 52, i.e., the distance A1 between the distal surface 422 and the second extended surface 52 in this example. Stress generated at the corners forming the first corner portions 31 ( FIG. 3 ) in the die 91 ( FIG. 7 ) of the mold 9 used for pressure molding the core 1 is caused by the difference between the molding pressure applied to the outer region 40 of each tooth 4 and the molding pressure applied to a region other than the outer region 40. By arranging the second end face 42 at a distance from the second extended surface 52, the molding pressure applied to the outer region 40 by the upper punch 93 ( FIG. 9 ) of the mold 9 is increased. When the ratio of the second length L2 to the first length L1 is 60% or more and 90% or less, the stress is easily reduced. If the ratio of the second length L2 to the first length L1 is 90% or less, the gap A1 can be provided, and wiring space corresponding to this gap A1 can be secured. If the ratio is 60% or more, magnetic flux flowing into the external region 40 from the magnet 84 of the rotor 80 (described later) is likely to flow efficiently into the yoke 2. The ratio of the second length L2 to the first length L1 may be 65% or more and 85% or less, or 70% or more and 80% or less.

[0057] [Variation in Length of Multiple Teeth] Using the second surface 22 of the yoke 2 as a reference plane, there is small variation in the length from this reference plane to the first end face 41 of each of the multiple teeth 4. For example, the variation in the first length L1 from the second surface 22 to the first end face 41 of each tooth 4 is 0.05 mm or less. For example, suppose the core 1 is manufactured using a powder box (not shown) that moves from bottom to top in FIG. 2 and then turns back from top to bottom in FIG. 2. Even in this case, as shown in FIG. 6, the variation in the first length L1 of the multiple teeth 4 is 0.05 mm or less.

[0058] The rotating electric machine 8 shown in FIG. 13 is constructed by housing a stator 7, which is configured by arranging coils 70 on each tooth 4 of a core 1, together with a rotor 80 in a case 82. In this case, the second surface 22 of the yoke 2 contacts the inner surface of the case 82. If the variation in the first length L1 from the second surface 22 to the first end face 41 of each tooth 4 is 0.05 mm or less, when the stator 7 and rotor 80 are housed in the case 82, the first end face 41 of each tooth 4 faces any portion of the magnet 84 at a substantially uniform interval. Therefore, the rotating electric machine 8 constructed using the core 1 is easy to assemble and has reduced torque ripple. The reduced torque ripple in the rotating electric machine 8 reduces noise and vibration. The reduced torque ripple in the rotating electric machine 8 reduces vibration of the rotating shaft 81 of the rotor 80. In other words, the frictional force between the rotating shaft 81 of the rotor 80 and the bearing 83 is less likely to fluctuate. Therefore, the mechanical energy loss in the rotating electrical machine 8 is unlikely to increase.

[0059] The variation in the first lengths L1 of the multiple teeth 4 is determined as follows. First, for each tooth 4, the first length L1 from the second surface 22 of the yoke 2 to the first end face 41 of the tooth 4 is measured. The measurement is performed using a height gauge equipped with a class 0 surface plate, with the core 1 placed on the surface plate with the first end face 41 of the tooth 4 facing upward. Multiple measurement points are selected on the first end face 41 of each tooth 4. The measurement points are set on a line drawn through the center of gravity of the tooth 4 and the axis of the yoke 2. Three or more measurement points are selected on the line. The measurement points on the line include the center of gravity of the tooth 4, an edge of the tooth 4 close to the axis of the yoke 2, and an edge of the tooth 4 far from the axis of the yoke 2. The first length L1 of each tooth 4 is determined by measuring the length from the surface plate to each measurement point, and the average of the measured lengths. Next, the maximum and minimum first lengths L1 of the multiple teeth 4 are selected. The variation in the first lengths L1 of the teeth 4 is determined by calculating the difference between the maximum length and the minimum length. It is preferable that the variation in the first lengths L1 of the teeth 4 is small. The variation in the first lengths L1 of the teeth 4 is, for example, 0.04 mm or less, or 0.03 mm or less.

[0060] <Constituent Materials> The core 1 is composed of a powder compact containing soft magnetic powder. The soft magnetic powder includes a plurality of iron-based particles made of, for example, pure iron or an iron-based alloy. The pure iron has a purity of 99% or more, i.e., an iron (Fe) content of 99% by mass or more. Pure iron has advantages such as high saturation magnetic flux density, excellent formability, and ease of densification by pressure molding. Therefore, including iron-based particles made of pure iron can result in a core 1 with a high saturation magnetic flux density, a dense core 1 with a high relative density, and easy formability during manufacturing, resulting in a core 1 with excellent manufacturability. Furthermore, the dense core 1 facilitates an increase in saturation magnetic flux density and also provides excellent mechanical properties such as strength. The iron-based alloy contains an additive element, with the remainder consisting of Fe and inevitable impurities. The iron-based alloy contains one or more additive elements. Examples of additive elements include silicon (Si), aluminum (Al), and chromium (Cr). The electrical resistance of an iron-based alloy is greater than that of pure iron. Therefore, if iron-based particles made of an iron-based alloy are included, iron loss such as eddy current loss can be reduced, resulting in a low-loss core 1. The core 1 may also include both iron-based particles made of pure iron and iron-based particles made of an iron-based alloy.

[0061] Soft magnetic powder generally contains coated particles, which are powder particles made of a soft magnetic material and have an insulating coating on their surfaces. The inclusion of coated particles reduces iron loss, such as eddy current loss, and allows for a low-loss core 1. In particular, the inclusion of coated particles, which have powder particles made of pure iron and an insulating coating, allows for a low-loss core 1 with a high saturation magnetic flux density and excellent magnetic properties. The insulating coating is made of an oxide, such as phosphate, silica, magnesium oxide, or aluminum oxide.

[0062] <Relative Density> The relative density of the core 1 is, for example, 90% or more. A core 1 with a relative density of 90% or more has a high saturation magnetic flux density and excellent strength. The relative density of the core 1 may be 93% or more, or 95% or more. The relative density here is the ratio (%) of the actually measured density of the powder compact constituting the core 1 to the theoretical density of the powder compact constituting the core 1. The theoretical density can be used as an equivalent value to the true density of the soft magnetic powder constituting the powder compact.

[0063] In the core 1 having the outer region 40 on each tooth 4, the relative density of the outer region 40 is higher than the relative density of portions other than the outer region 40. The relative density of the outer region 40 is, for example, 93% or more, 95% or more, or 96% or more.

[0064] <<Method of Manufacturing Core>> The core 1 of the embodiment can be manufactured using a mold 9 shown in Figures 7 to 11. The mold 9 includes a die 91 shown in Figure 7, a lower punch 92 shown in Figure 8, and an upper punch 93 shown in Figure 9.

[0065] The die 91 is a cylindrical member. The die 91 has a central portion 911 and an outer peripheral portion 912. The central portion 911 forms a central region including the axis of the die 91 and is a solid body extending to both end faces of the die 91. The central portion 911 is used to form the axial hole 25 of the yoke 2 in the core 1. The outer peripheral portion 912 is located on the outer periphery of the central portion 911. The outer peripheral portion 912 has recesses 913 and through holes 917 that open to the top surface of the die 91. The recesses 913 and through holes 917 are alternately arranged around the axis of the die 91. The recesses 913 have a bottom 914, an inner surface 915, and an outer surface 916. The inner surface 915 is also a side surface of the central portion 911. The outer surface 916 is arranged to face the inner surface 915. The bottom 914 connects the inner surface 915 and the outer surface 916. The recess 913 is for forming the majority of the yoke 2 in the core 1. The bottom 914 forms the first surface 21 of the yoke 2. The outer surface 916 forms the outer peripheral surface 23 of the yoke 2. The inner surface 915 forms the inner peripheral surface 24 of the yoke 2. The through hole 917 penetrates the die 91 from top to bottom. The through hole 917 is for forming the teeth 4 in the core 1. The through hole 917 has the same cross-sectional shape and size as the first end surface 41 of the teeth 4. The envelope circle surrounding the multiple through holes 917 is larger than the envelope circle surrounding the multiple recesses 913. The envelope circle surrounding the multiple recesses 913 is formed by the outer surface 916 of the recesses 913. The contour forming the outer peripheral portion 912 is uneven. A lower punch 92 is inserted into the through hole 917.

[0066] The lower punch 92 includes a base 921 and multiple columnar portions 922. The base 921 is a cylindrical member. The multiple columnar portions 922 are arranged at intervals around the axis of the base 921. Each columnar portion 922 is inserted into a through hole 917 of the die 91. An end face 923 of each columnar portion 922 has the same shape and size as the first end face 41 of the tooth 4. The end face 923 constitutes the first end face 41 of the tooth 4.

[0067] The upper punch 93 is a cylindrical member. The upper punch 93 has an annular first end surface 931. The first end surface 931 constitutes the second surface 22 of the yoke 2. The upper punch 93 has a plurality of bulging portions 932 on its outer peripheral surface. The plurality of bulging portions 932 are arranged at intervals around the axis of the upper punch 93. Each bulging portion 932 extends vertically along the upper punch 93. A protruding portion 934 is provided at the tip of each bulging portion 932. The protruding portion 934 is provided at the portion of the bulging portion 932 that is farthest from the axis of the upper punch 93. The bulging portion 932 has a second end surface 933 having two surfaces that form a step by the protruding portion 934. The second end surface 933 constitutes the second end surface 42 of the outer region 40 of the tooth 4. Of the two surfaces, the surface located proximal to the first end surface 931 constitutes the proximal surface 421 , and the surface located further distal from the first end surface 931 constitutes the distal surface 422 .

[0068] A cavity is formed to be filled with powder 95 by inserting the columnar portion 922 of the lower punch 92 into the through-hole 917 of the die 91. Powder is fed into the cavity using a powder box (not shown). The powder box has an opening at the bottom. The powder box moves back and forth linearly above the die 91. When the powder box moves above the cavity, gravity causes the powder in the powder box to fall into the cavity through the opening of the powder box. Figure 10 shows the state in which the cavity has been filled with powder 95. After the powder 95 has been filled into the cavity, the powder box is folded back. When this folding back occurs, the bottom of the powder box tends to drag some of the powder 95 filled into the cavity.

[0069] In the mold 9 of this example, the cavity opening shape has an uneven contour corresponding to the contour of the outer periphery 912 of the die 91, as shown in Figure 10. With an opening having an uneven contour, the powder 95 arranged on the cavity opening surface has discontinuous portions around the axis of the die 91. The presence of discontinuous portions makes it difficult for the powder 95 to be dragged by the powder box even when the powder box moves back and forth. If the powder 95 is not easily dragged by the powder box when it moves back and forth, unevenness in the amount of powder 95 filled into the cavity is unlikely to occur.

[0070] 11 , the powder 95 is pressed by a lower punch 92 and an upper punch 93. If the amount of powder 95 filled into the cavity is less likely to be uneven, the length from the second surface 22 of the yoke 2 to the first end surface 41 of each of the plurality of teeth 4 in the powder compact obtained after pressure molding is less likely to vary.

[0071] The second end surface 42 of each tooth 4 is formed by transferring the shape of a protrusion 934 provided on the upper punch 93. If the upper punch 93 has a protrusion 934, a relatively large stress is generated at the corner between the bottom 914 and the outer surface 916 of the recess 913 provided in the die 91. This corner forms the first corner 31 of the yoke 2. If the second end surface 933 has a step formed by two surfaces, the above-mentioned stress generated in the die 91 can be easily reduced.

[0072] The corners between the bottom 914 and the outer surface 916 of the recess 913 provided in the die 91 and the corners between the bottom 914 and the inner surface 915 may be rounded. In this case, the radius of curvature of the corners between the bottom 914 and the outer surface 916 may be larger than the radius of curvature of the angle between the bottom 914 and the inner surface 915.

[0073] The core 1 obtained with the above-described die 9 has small variations in the length from the second surface 22 of the yoke 2 to the first end face 41 of each of the plurality of teeth 4 when the powder 95 is press-molded to produce a powder compact. Therefore, after producing the powder compact, there is no need to grind the first end face 41 of each tooth 4. Therefore, the core 1 obtained with the above-described die 9 has excellent productivity.

[0074] <Rotating Electric Machine> A rotating electric machine 8 according to an embodiment will be described with reference to Figs. 12 and 13. The rotating electric machine 8 includes a rotor 80 and a stator 7. The stator 7 faces the rotor 80 in a direction along the rotation axis of the rotor 80. The rotating electric machine 8 can be used as a motor or a generator. Fig. 13 is a cross-sectional view taken along a plane parallel to the rotation axis 81 of the rotating electric machine 8. Fig. 13 illustrates a single-rotor and double-stator type rotating electric machine in which one rotor 80 is assembled so as to be sandwiched between two stators 7. Alternatively, the rotating electric machine 8 may include one rotor 80 and one stator 7, or may include one stator 7 assembled so as to be sandwiched between two rotors 80.

[0075] As shown in Fig. 12, the stator 7 includes a core 1 and a coil 70. The coil 70 is disposed on each tooth 4 of the core 1. The coil 70 includes a cylindrical portion formed by spirally winding a wire. In this example, the coil 70 is a rectangular cylindrical edgewise wound coil in which the wire is a coated rectangular wire. A wiring group 71 of the coil 70 is disposed in a space defined according to the distance A1 between the second end surface 42 and the second extension surface 52 of the outer region 40 of each tooth 4.

[0076] As shown in FIG. 13 , the stator 7 and rotor 80 are housed in a case 82 having a cylindrical internal space. The case 82 includes a cylindrical portion and two plate portions. The cylindrical portion surrounds the outer periphery of the stator 7 and rotor 80. Plate portions are located at both ends of the cylindrical portion. The stator 7 and rotor 80 are housed in the case 82 sandwiched between the two plate portions. The stator 7 is fixed to the case 82 by fitting a portion of the yoke 2 of the core 1 into the plate portions of the case 82. Both plate portions have through holes in their centers. A bearing 83 is provided in the through hole, and a rotating shaft 81 is inserted through the bearing 83. A bearing (not shown) is also provided in the shaft hole 25 of the yoke 2, and the rotating shaft 81 is inserted through this bearing. The rotating shaft 81 passes through the case 82.

[0077] The rotor 80 is a flat member including a plurality of magnets 84 and a rotor body that supports the magnets 84. Each magnet 84 is, for example, flat and has a planar shape that corresponds to the shape of the first end surface 41 of the tooth 4. The rotor body is an annular member that is rotatably supported relative to a case 82 by a rotating shaft 81. The magnets 84 are arranged at equal intervals around the axis of the rotor body. Each magnet 84 is magnetized in a direction along the axis of the rotating shaft 81. The magnetization directions of adjacent magnets 84 around the axis of the rotor body are opposite to each other. When the rotor body rotates, the magnets 84 also rotate together with the rotor body.

[0078] The stator 7 is disposed so that the first end faces 41 of the teeth 4 face the magnets 84 of the rotor 80. The coils 70 of the stator 7 are excited to generate a rotating magnetic field, and the rotor 80 rotates relative to the stator 7 due to the attractive or repulsive force caused by the rotating magnetic field. When the rotor 80 rotates, the first end faces 41 of the teeth 4 receive magnetic flux from the rotating magnets 84.

[0079] The rotating electric machine 8 of the embodiment is easy to assemble because it includes the core 1 of the embodiment. As described above, the core 1 has small variation in length from the second surface 22 of the yoke 2 to the first end surface 41 of each of the plurality of teeth 4. Therefore, when the stator 7 and the rotor 80 are housed in the case 82, the core 1, the coil 70, and the rotor 80 are positioned with high precision. Furthermore, because the rotating electric machine 8 of the embodiment includes the core 1 of the embodiment, torque ripple can be reduced, and noise and vibration are low.

[0080] [Test Example 1] In Test Example 1, a core in which each tooth has an external region and a conventional core in which each tooth does not have an external region were fabricated, and the variation in the length from the second surface of the yoke to the first end face of each of the multiple teeth was measured. Sample No. 1-1 is a core in which each tooth has an external region. Sample No. 1-2 is a conventional core in which each tooth does not have an external region.

[0081] <<Sample Description>> For Sample No. 1-1, a powder compact was produced by pressure-molding a powder containing soft magnetic powder using a mold 9 shown in FIGS. 7 to 11 . The core made of this powder compact was integrally formed with an annular yoke and 12 teeth. When viewing the core from a first direction parallel to the axis of the yoke, each tooth had an outer region located outward from a first envelope circle formed by the outer circumferential surface of the yoke. The envelope circle surrounding the multiple teeth is referred to as a second envelope circle. The diameter of the second envelope circle was 17% larger than the diameter of the first envelope circle, based on the diameter of the first envelope circle. The ratio of the diameter of the second envelope circle to the diameter of the first envelope circle correlates with the amount of protrusion of the outer region along a second direction relative to the outer circumferential surface of the yoke. The second direction is perpendicular to the first direction and is along the diameter of the yoke.

[0082] In Sample No. 1-1, each tooth had a first end face located at the tip protruding from the first surface of the yoke in a direction parallel to the axis of the yoke, and the outer region had a second end face, which was the surface opposite to the first end face. The second end face was located between the extension of the second surface of the yoke and the first end face, and was spaced apart from the extension of the second surface. This space was 25% of the first length from the second surface of the yoke to the first end face of each tooth. In other words, the ratio of the length along the first direction of the portion of the outer region located farthest from the axis of the yoke to the first length was 75%.

[0083] For Sample No. 1-2, a powder compact was produced by pressure-molding the same powder as Sample No. 1-1. The core made of this powder compact was integrally formed with an annular yoke and 12 teeth. When the core was viewed from the first direction, each tooth did not have a region located outside a first enveloping circle formed by the outer peripheral surface of the yoke.

[0084] <<Variation in the Length from the Second Surface of the Yoke to the First End Face of Each of the Multiple Teeth>> The variation in the length from the second surface of the yoke to the first end face of each of the multiple teeth was examined for each sample core as follows. First, the first length L1 from the second surface of the yoke to the first end face of each tooth was measured. The measurement was performed using a height gauge equipped with a class 0 surface plate, with the core placed on the surface plate with the first end face of the tooth facing upward. Three or more measurement points were selected on the first end face of each tooth. In this example, the measurement points were selected on a line drawn through the center of gravity of the tooth and the center of the yoke, including the center of gravity of the tooth, the edge of the tooth close to the axis of the yoke, and the edge of the tooth far from the axis of the yoke. The length from the surface plate to each measurement point was measured, and the average of the measured lengths was defined as the first length L1 of each tooth. Next, the maximum and minimum first lengths L1 for the multiple teeth were selected, and the difference between the maximum and minimum lengths was calculated. This difference was defined as the variation in the length from the second surface of the yoke to the first end surface of each of the plurality of teeth. For Sample No. 1-1, the variation in the length was 0.047 mm. For Sample No. 1-2, the variation in the length was 0.099 mm.

[0085] The above length variation results show that a core with an external region on each tooth can reduce variation in the length from the second surface of the yoke to the first end face of each of the multiple teeth. In a core with an external region on each tooth, the opening shape of the cavity of the mold used to fabricate the core is the combined shape of the yoke and the external region, and has an uneven contour. With an opening with an uneven contour, the powder mass arranged on the opening surface of the cavity has an intermittent portion around the axis of the yoke. The presence of an intermittent portion is thought to have made it difficult for the powder to be dragged by the powder box even when the powder box moves back and forth, reducing the likelihood of unevenness in the amount of powder filled into the cavity. Because unevenness in the amount of powder filled was less likely to occur, it is thought that variation in the length from the second surface of the yoke to the first end face of each of the multiple teeth was less likely to occur in the powder compact obtained after pressure molding.

[0086] In conventional cores that do not have an outer region on each tooth, the opening shape of the cavity in the mold used to manufacture the core is the shape of a yoke, i.e., a ring. With a ring-shaped opening, the outline of the powder mass arranged on the opening surface of the cavity is circular, and it is thought that some of the powder is dragged into the powder box as it moves back and forth.

[0087] [Test Example 2] In Test Example 2, cores were fabricated in which each tooth had an outer region and the ratio of the second length to the first length was different, and the maximum stress generated in the die during pressure molding was measured. The first length was the length from the second surface of the yoke to the first end face of each tooth. The second length was the length along the first direction of the point in the outer region that was located farthest from the axis of the yoke. Sample No. 2-1 was a core in which the ratio was 92%. Sample No. 2-2 was a core in which the ratio was 85%. For both Sample No. 2-1 and Sample No. 2-2, the conditions other than the ratio were the same as those of Sample No. 1-1.

[0088] When the cores of Sample No. 2-1 and Sample No. 2-2 were manufactured, the stress distribution acting on each die was analyzed by CAE (Computer Aided Engineering). From the CAE analysis results, the maximum stress value (MPa) generated in the die was calculated.

[0089] The above analysis results show that the maximum stress acts on the corner of the die that forms the first corner portion defined by the first surface and the outer peripheral surface of the yoke. For Sample No. 2-1, the maximum stress was 1096 MPa. For Sample No. 2-2, the maximum stress was 1074 MPa.

[0090] The analysis results show that if the ratio is 90% or less, the stress generated at the corner of the die that forms the first corner of the yoke can be reduced. On the other hand, if the ratio is too small, for example, less than 60%, the magnetic flux that flows from the rotor magnet into the area outside the teeth does not flow efficiently into the yoke.

[0091] [Test Example 3] In Test Example 3, cores were fabricated in which each tooth had an outer region and the ratio of the second envelope circle to the diameter of the first envelope circle was different, and the maximum stress generated in the upper punch during pressure molding was measured. In Sample No. 3-1, the diameter of the second envelope circle was 6% larger than the diameter of the first envelope circle, based on the diameter of the first envelope circle. In Sample No. 3-2, the diameter of the second envelope circle was 13% larger than the diameter of the first envelope circle, based on the diameter of the first envelope circle. For both Sample No. 3-1 and Sample No. 3-2, the conditions other than the above ratio were the same as for Sample No. 1-1.

[0092] When the cores of Sample No. 3-1 and Sample No. 3-2 were manufactured, the stress distribution acting on the upper punch was analyzed by CAE. From the CAE analysis results, the maximum stress value (MPa) generated in the upper punch was calculated.

[0093] The above analysis results show that the maximum stress acts on the base of the convex portion of the upper punch. For Sample No. 3-1, the maximum stress was 2241 MPa. For Sample No. 3-2, the maximum stress was 1153 MPa.

[0094] The above analysis results show that the stress generated at the base of the convex portion of the upper punch can be reduced if the diameter of the second enveloping circle is 10% or more larger than the diameter of the first enveloping circle. If the above ratio is small, the contact area of ​​the upper punch with the powder constituting the outer region becomes small, and it is thought that relatively large stress is generated at the base of the convex portion of the upper punch.

[0095] [Test Example 4] In Test Example 4, a core was fabricated in which each tooth had an external region, and the first corner formed by the first surface and outer peripheral surface of the yoke and the second corner formed by the first surface and inner peripheral surface were rounded, and the maximum stress generated in the die during pressure molding was measured. Sample No. 4-1 was a core in which the radius of curvature of both the first corner and the second corner was 2.5 mm. Sample No. 4-2 was a core in which the radius of curvature of the first corner was 2.5 mm and the radius of curvature of the second corner was 2.0 mm. For both Sample No. 4-1 and Sample No. 4-2, the conditions other than the above-mentioned radius of curvature were the same as those of Sample No. 1-1.

[0096] When the cores of Sample No. 4-1 and Sample No. 4-2 were manufactured, the stress distribution acting on each die was analyzed by CAE. From the CAE analysis results, the maximum stress value (MPa) generated in the die was calculated.

[0097] The above analysis results show that the maximum stress acts on the corner of the die that forms the first corner of the yoke. For Sample No. 4-1, the maximum stress was 1009 MPa. For Sample No. 4-2, the maximum stress was 983.2 MPa.

[0098] The above analysis results show that if the radius of curvature of the first corner is larger than the radius of curvature of the second corner, the stress generated at the corner of the die used to form the first corner of the yoke can be reduced. Since relatively large stress is generated at the corner of the die used to form the first corner of the yoke during pressure molding, it is thought that increasing the radius of curvature of this corner can easily achieve the effect of reducing that stress.

[0099] DESCRIPTION OF SYMBOLS 1 Core 2 Yoke 21 First surface, 22 Second surface 23 Outer peripheral surface, 24 Inner peripheral surface 25 Shaft hole 31 First corner portion, 32 Second corner portion 4 Teeth 40 Outer region 41 First end surface, 42 Second end surface 421 Proximal surface, 422 Distal surface 43 Side surface 51 First extension surface, 52 Second extension surface 61 First envelope circle, 62 Second envelope circle A1, A2 Distance L1 First length, L2 Second length T0 First intersection point, T1 First tangent, T2 Second tangent, θ Angle D1 First direction, D2 Second direction 7 Stator, 70 Coil, 71 Wiring group 8 Rotating electric machine, 80 Rotor, 81 Rotating shaft, 82 Case 83 Bearing, 84 Magnet 9 Mold 91 Die 911 central portion 912 outer peripheral portion 913 recessed portion 914 bottom portion 915 inner surface 916 outer surface 917 through-hole 92 lower punch 921 base portion 922 columnar portion 923 end surface 93 upper punch 931 first end surface 932 bulging portion 933 second end surface 934 convex portion 95 powder

Claims

1. A core used in an axial-gap type rotating electrical machine, comprising: an annular yoke; and a plurality of columnar teeth arranged at intervals around the axis of the yoke, wherein the yoke and the plurality of teeth are formed of an integral compacted powder body, the yoke includes: a first surface having a boundary with the plurality of teeth; a second surface opposite to the first surface; and an outer peripheral surface and an inner peripheral surface connecting the first surface and the second surface, and each of the plurality of teeth includes an outer region located outside a first circumscribed circle formed by the outer peripheral surface when the core is viewed from a first direction parallel to the axis.

2. Each of the plurality of teeth includes a first end face located at a tip protruding from the first surface in a direction parallel to the axis, and the variation in the length from the second surface to the first end face in each of the plurality of teeth is 0.05 mm or less. The core according to claim 1.

3. Each of the plurality of teeth includes a first end face located at a tip protruding from the first surface in a direction parallel to the axis, the outer region includes a second end face opposite to the first end face, and the second end face is between an extended surface of the second surface and the first end face and is spaced apart from the extended surface of the second surface. The core according to claim 1 or claim 2.

4. The second end face includes: a proximal face located between the extended surface of the first surface and the extended surface of the second surface so as to extend along the second surface or the outer peripheral surface; and a distal face farther from the outer peripheral surface and the extended surface of the second surface than the proximal face. The core according to claim 3.

5. Each of the plurality of teeth includes a first end face located at a tip protruding from the first surface in a direction parallel to the axis, the ratio of the second length of the outer region to the first length of each of the plurality of teeth is 60% or more and 90% or less, the first length is the length from the second surface to the first end face, and the second length is the length along the first direction at the position farthest from the axis in the outer region. The core according to any one of claims 1 to 4.

6. When the core is viewed from the first direction, the angle between the first tangent line and the second tangent line at the first intersection point is 90° or less. The first intersection point is the intersection point between the side surface of the outer region and the first envelope circle. The first tangent line is the tangent line of the first envelope circle passing through the first intersection point. The second tangent line is the tangent line of the side surface of the outer region passing through the first intersection point. The core according to any one of claims 1 to 5.

7. Each of the first corner formed by the first surface and the outer peripheral surface and the second corner formed by the first surface and the inner peripheral surface is rounded. The core according to any one of claims 1 to 6.

8. The radius of curvature of the first corner is larger than the radius of curvature of the second corner. The core according to claim 7.

9. The diameter of the second envelope circle surrounding the plurality of teeth is 15% or more larger than the diameter of the first envelope circle. The core according to any one of claims 1 to 8.

10. A rotor and a stator facing the rotor in a direction along the rotation axis of the rotor. The stator includes the core according to any one of claims 1 to 9 and coils arranged on each of the plurality of teeth in the core. A rotating electrical machine.

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