Cores and rotating electrical machines

Abstract

A core used in an axial gap type rotating electric machine, comprising: an annular yoke; and a plurality of columnar teeth spaced around the axis of the yoke, wherein the yoke and the plurality of teeth are formed as an integral powder compact, the yoke having a first surface that defines a boundary between the plurality of teeth, a second surface that is opposite to the first surface, and an outer peripheral surface and an inner peripheral surface that connect the first surface and the second surface, and each of the plurality of teeth has an outer region located outward from a first enveloping circle formed by the outer peripheral surface when the core is viewed from a first direction parallel to the axis.

Description

Technical Field

[0001] The present disclosure relates to a core and a rotating electrical machine. This application claims priority based on Japanese Patent Application No. 2023-219625 filed on December 26, 2023, and incorporates by reference all the descriptions set forth in the Japanese application.

Background Art

[0002] Patent Document 1 discloses a core used in an axial-gap type rotating electrical machine. This core includes an annular yoke and a plurality of columnar teeth protruding from the surface of the yoke. Each of the yoke and the plurality of teeth is formed of an integral powder compact. In Patent Document 1, after a powder compact including the yoke and the plurality of teeth is produced by pressure molding soft magnetic powder, grinding is performed on the end surfaces of the respective teeth in the powder compact. By performing grinding on the end surfaces of the respective teeth, variations in height from the back surface of the yoke to the end surfaces of the respective teeth are reduced.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

[0004] The core of the present disclosure is a core used in an axial-gap type rotating electrical machine, and includes 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 integral powder compact. 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. Each of the plurality of teeth includes an external 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.

Brief Description of the Drawings

[0005]

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Embodiments for Carrying Out the Invention

[0006] [Problems to be Solved by the Present Disclosure] The compacted powder body is produced by filling a cavity formed in a mold with powder and then pressure-molding the filled powder. The powder supply to the cavity is performed using a powder box having an opening at the bottom. The powder box reciprocates linearly on the mold. When the powder box moves over the cavity, the powder in the powder box falls into the cavity from the opening of the powder box due to gravity. The bottom surface of the powder box drags a part of the powder filled in the cavity as the powder box reciprocates. Therefore, the area near the powder supply start point from the powder box in the cavity tends to be filled with more powder than the area near the powder supply turning point. When there is a variation in the powder filling amount, in the compacted powder body obtained after pressure molding, variations may occur in the lengths from the back surface of the yoke to the end faces of each of the plurality of teeth.

[0007] In the technique of Patent Document 1, after producing a compacted powder body in a state where the above lengths vary, grinding is performed on the end faces of each of the teeth in the compacted powder body. In the technique of Patent Document 1, a process of performing grinding is required, the number of processes is large, and improvement in productivity is desired.

[0008] One of the objectives of the present disclosure is to provide a core in which the variations in the lengths from the reference surface of the yoke to the end faces of each of the plurality of teeth are small and which is excellent in productivity.

[0009] [Effects of the Present Disclosure] The core of the present disclosure has small variations in the lengths from the reference surface of the yoke to the end faces of each of the plurality of teeth and is excellent in productivity.

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

[0011] (1) The core according to an embodiment of the present disclosure is a core used in an axial-gap type rotating electrical machine, and includes 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 integral compact. 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. Each of the plurality of teeth includes an outer region located outside a first circumscribing circle formed by the outer peripheral surface when the core is viewed from a first direction parallel to the axis.

[0012] The axis of the yoke is the axis of rotational symmetry of the annular yoke. That is, the axis of the yoke is a straight line passing through the center of the annular circle and perpendicular to the first surface of the yoke.

[0013] As described above, the compact is produced by filling a cavity formed in a mold with powder and pressure-molding the filled powder. The cavity has a shape corresponding to the core. The cavity has, for example, 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. The powder box for feeding powder into the cavity reciprocates on the powder constituting the second surface of the yoke.

[0014] In a conventional core as described in Patent Document 1, when the core is viewed from the first direction, each tooth does not include a region located outside a first circumscribing circle formed by the outer peripheral surface of the yoke. In the conventional core, the opening shape of the cavity is the shape of the yoke, that is, annular. If the opening is annular, the contour of the powder group arranged on the opening surface of the cavity is circular. When the contour of the powder group arranged on the opening surface of the cavity is circular, a part of the powder is easily dragged by the powder box as the powder box reciprocates.

[0015] In the core according to the embodiment of the present disclosure, when the core is viewed from the first direction, each tooth includes an outer region located outside a first envelope circle formed by the outer peripheral surface of the yoke. In the core according to the embodiment of the present disclosure, the opening shape of the cavity is the combined shape of the yoke and the outer region, and has an uneven contour. As long as the opening has an uneven contour, the powder group arranged on the opening surface of the cavity has intermittent portions around the axis of the yoke. If there are intermittent portions, it is difficult for the powder to be dragged by the powder box even when the powder box reciprocates. If it is difficult for the powder to be dragged when the powder box reciprocates, it is difficult for the filling amount of the powder into the cavity to be uneven. If it is difficult for the filling amount of the powder to be uneven, in the compacted body obtained after pressure molding, it is difficult for variations to occur in the lengths from the reference surface of the yoke to the end faces of each of the plurality of teeth. Therefore, in the core according to the embodiment of the present disclosure, the variations in the lengths from the reference surface of the yoke to the end faces of each of the plurality of teeth are small.

[0016] In the core according to the embodiment of the present disclosure, when a compacted body is produced by pressure molding the powder, the variations in the lengths from the reference surface of the yoke to the end faces of each of the plurality of teeth are small. Therefore, after the compacted body is produced, it is not necessary to perform grinding on the end faces of each tooth. Therefore, the core according to the embodiment of the present disclosure is excellent in productivity.

[0017] (2) In the core of (1) above, 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 variations in the lengths from the second surface to the first end face in each of the plurality of teeth may be 0.05 mm or less.

[0018] The rotating electrical machine is constructed by housing a stator, in which coils are arranged on each tooth of the core, together with a rotor in a case. At this time, the second surface of the yoke contacts the inner surface of the case. If the variation in the length from the second surface to the first end surface in each of the plurality of teeth is 0.05 mm or less, when the stator and the rotor are housed in the case, the end surfaces of the respective teeth face the magnet at substantially uniform intervals at any position. Therefore, the rotating electrical machine constructed using the above core is excellent in assemblability and has a small torque ripple. Since the torque ripple in the above rotating electrical machine is small, noise and vibration are less likely to increase. Since the torque ripple of the above rotating electrical machine is small, the rotating shaft of the rotor is less likely to vibrate. That is, the frictional force between the rotating shaft of the rotor and the bearing is less likely to vary. Therefore, the mechanical energy loss in the above rotating electrical machine is less likely to increase.

[0019] (3) In the core of the above (1) or (2), each of the plurality of teeth includes a first end surface located at the tip protruding from the first surface in a direction parallel to the shaft, the outer region includes a second end surface which is a surface opposite to the first end surface, and the second end surface may be between the extended surface of the second surface and the first end surface and may be arranged at a distance from the extended surface of the second surface.

[0020] By having a space between the second end surface and the extended surface of the second surface, a wiring space corresponding to this space can be secured. When each tooth includes an outer region, compared with the conventional core, the core becomes larger in the second direction orthogonal to the first direction. However, since the above wiring space is secured using the outer region, the overall increase in size of the stator in which coils are arranged on each tooth of the core is suppressed.

[0021] (4) In the core of the above (3), the second end surface may include a proximal surface 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 surface which is farther from the outer peripheral surface than the proximal surface and is also farther from the extended surface of the second surface.

[0022] The die for pressure molding a core having an external region for each tooth includes a die, a lower punch, and an upper punch, as will be described later. The yoke is formed by having its first surface supported by the die and its second surface pressed by the upper punch. Each tooth is pressed by the lower punch and the upper punch. The second end face is formed by transferring the shape of the convex portion formed on the upper punch. When there is a convex portion on the upper punch, a relatively large stress is generated at the corner of the die that forms the first corner formed by the first surface and the outer peripheral surface of the yoke. When a step is formed on the second end face by a proximal face and a distal face, it is easy to reduce the stress generated in the die.

[0023] (5) In the core according to any one of (1) to (4) above, each of the plurality of teeth includes a first end face located at the tip protruding from the first surface in a direction parallel to the axis, and the ratio of the second length of the external region to the 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 at the location farthest from the axis in the external region.

[0024] The stress generated at the corner of the die that forms the first corner of the yoke is caused by the difference between the molding pressure applied to the external region in each tooth and the molding pressure applied to the region other than the external region. If the above ratio is 60% or more and 90% or less, it is easy to reduce the stress. If the ratio is 90% or less, there is a gap between the second end face, which is the face opposite to the first end face in the external region, and the extension surface of the second surface, and it is easy to secure a wiring space corresponding to this gap. If the ratio is 60% or more, the magnetic flux flowing from the magnet of the rotor into the external region of the tooth is likely to efficiently flow into the yoke.

[0025] (6) In any of the cores from (1) to (5) above, 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 may be 90° or less. The first intersection is the intersection of the side surface of the outer region and the first circumscribed circle. The first tangent line is the tangent line of the first circumscribed circle passing through the first intersection. The second tangent line is the tangent line of the side surface of the outer region passing through the first intersection.

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

[0027] (7) In any of the cores from (1) to (6) above, 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 may be rounded.

[0028] If the first corner is rounded, it is easy to reduce the stress generated at the corner of the die for forming the first corner. If the second corner is rounded, it is easy to reduce the stress generated at the corner of the die for forming 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 forming, relatively large stress is generated at the corner of the die for forming the first corner. If the radius of curvature of the first corner is larger than the radius of curvature of the second corner, it is easy to reduce the stress generated at the corner of the die for forming the first corner.

[0031] (9) In any of the cores from (1) to (8) above, the diameter of the second circumscribed circle surrounding the plurality of teeth may be 15% or more larger than the diameter of the first circumscribed circle.

[0032] The ratio of the diameter of the second enveloping circle to the diameter of the first enveloping circle is correlated with the amount of protrusion along the second direction of the external region with respect to the outer peripheral surface of the yoke. The second direction is a direction orthogonal to the first direction and along the diameter of the yoke. If the diameter of the second enveloping circle is 15% or more larger than the diameter of the first enveloping circle, that is, if the above ratio is 115% or more, the opening shape of the cavity of the mold for manufacturing this core has a contour with a large unevenness difference. The larger the unevenness difference, the more difficult it is for the powder to be dragged into the powder box even when the powder box reciprocates. The larger the unevenness difference, the smaller the variation in the length from the second surface of the yoke to the end face of each of the plurality of teeth.

[0033] (10) The rotating electrical machine according to an embodiment of the present disclosure includes a rotor and a stator facing the rotor in a direction along the rotation axis of the rotor. The stator includes any one of the cores from (1) to (9) above and coils disposed on each of the plurality of teeth in the core.

[0034] Since the rotating electrical machine according to an embodiment of the present disclosure includes the above core, it has excellent assemblability. As described above, the core has a small variation in the length from the second surface of the yoke to the end face of each of the plurality of teeth. Therefore, when the stator and the rotor are housed in the case, the core, the coils, and the rotor are accurately arranged. Further, since the rotating electrical machine according to an embodiment of the present disclosure includes the above core, torque ripple can be reduced and noise and vibration are small.

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

[0036] ≪Core≫ Referring to FIGS. 1 to 6, and FIGS. 12 and 13 as appropriate, the core 1 of the embodiment will be described. The core 1 is used in the axial gap type rotating electrical machine 8 shown in FIG. 13. Typically, the core 1 is used for the core 1 of the stator 7 shown in FIG. 12.

[0037] The core 1 includes an annular yoke 2 and a plurality of columnar teeth 4. Each tooth 4 is arranged at intervals around the axis of the yoke 2. The yoke 2 and the plurality of teeth 4 are formed of an integral compacted body. One of the features of the core 1 of the embodiment is that each tooth 4 has an outer region 40. As shown in FIG. 2, the outer region 40 is a region located outside the first circumscribing circle 61 formed by the outer peripheral surface of the yoke 2 when the core 1 is viewed from the first direction D1. The first direction D1 is a direction parallel to the axis of the yoke 2. Hereinafter, both the direction from the bottom to the top and the direction from the top to the bottom in FIG. 1 are referred to as the first direction D1. Also, the direction orthogonal to the first direction D1 is referred to as the second direction D2. The second direction D2 is a direction along the diameter of the yoke 2 as shown in FIG. 4.

[0038] <Yoke> As shown in FIGS. 1 to 3, the yoke 2 is a plate member having an annular planar shape. The yoke 2 includes a first surface 21, a second surface 22, an outer peripheral surface 23, and an inner peripheral surface 24. The first surface 21 has a boundary with the plurality of teeth 4 and is a surface from which the plurality of teeth 4 project in a direction parallel to the axis of the yoke 2. The second surface 22 is a surface opposite to the first surface 21. The first surface 21 and the second surface 22 are flat surfaces. A shaft hole 25 penetrating the first surface 21 and the second surface 22 is provided at the central portion of the yoke 2. The outer peripheral surface 23 and the inner peripheral surface 24 are surfaces connecting the first surface 21 and the second surface 22. The yoke 2 magnetically couples adjacent teeth 4 among the plurality of teeth 4 arranged at intervals around the axis of the yoke 2.

[0039] As shown in FIG. 2, the yoke 2 is a portion where the first envelope circle 61 formed by the outer peripheral surface 23 is a perfect circle when the core 1 is 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 portions of the core 1 located outside the first envelope circle 61 are part of the teeth 4 described later.

[0040] As shown in FIG. 3, each of the first corner 31 formed by the first surface 21 and the outer peripheral surface 23 and the second corner 32 formed by the first surface 21 and the inner peripheral surface 24 may be rounded. When the first corner 31 is rounded, it is easy to reduce the stress generated at the corner for forming the first corner 31 in the die 91 shown in FIG. 7. When the second corner 32 is rounded, it is easy to reduce the stress generated at the corner for forming the second corner 32 in the die 91. 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, a relatively large stress is generated at the corner for forming the first corner 31 in the die 91. When the radius of curvature of the first corner 31 is larger than the radius of curvature of the second corner 32, it is easy to reduce the stress generated at the corner for forming the first corner 31 in the die 91. 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. Neither the first corner 31 nor the second corner 32 may be rounded.

[0041] <Teeth> As shown in FIG. 1, each of the teeth 4 is a columnar member. The teeth 4 are arranged at intervals around the axis of the yoke 2. Typically, the teeth 4 are arranged at equal intervals around the axis of the yoke 2. The number of teeth 4 may be two or more and can be appropriately selected. 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 3. In the drawings, a core 1 having 12 teeth 4 is illustrated.

[0042] 〔Basic Configuration of Teeth〕 Each tooth 4 has a main region protruding 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 protruding outward from the main region in a direction orthogonal to the axis of the yoke. The outward direction is the direction away from the axis of the yoke 2. The sub-region is an external region 40 located outside the first circumscribing circle 61 when the core 1 is viewed from the first direction D1, as shown in FIG. 2. The external region 40 of this example has a portion located between a first extended surface 51 extending the first surface 21 and a second extended surface 52 extending the second surface 22, as shown in FIG. 5. In other words, the external region 40 of this example has a portion protruding outward from the outer peripheral surface 23 of the yoke 2, as shown in FIGS. 4 and 5.

[0043] Each tooth 4 includes a first end face 41 located at the tip protruding from the first surface 21 in a direction parallel to the axis of the yoke 2. The first end face 41 of this example is a plane 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, among the trapezoidal first end faces 41, the side located distally from the axis of the yoke 2 is formed of a curve. The region between the first end face 41 and the first extended surface 51 in each tooth 4 has a uniform shape in the first direction D1 parallel to the axis of the yoke 2. The tooth 4 having the trapezoidal first end face 41 is a quadrangular prism. The tooth 4 having the trapezoidal first end face 41 easily ensures a large cross-sectional area of the tooth 4. The tooth 4 having the trapezoidal first end face 41 easily ensures a large space between adjacent teeth 4. If a large space between adjacent teeth 4 can be ensured, it is easy to ensure a large arrangement space for the coil 70 shown in FIG. 12, and it is easy to construct a stator 7 (FIGS. 12 and 13) with a high occupancy rate. The shape of the first end face 41 may be triangular such as an isosceles triangle, rectangular, or circular. The region between the first end face 41 and the first extended surface 51 in each tooth 4 may be configured in a tapered shape from the first extended surface 51 toward the first end face 41.

[0044] As used herein, the terms "trapezoidal shape" and "triangular shape" include not only geometric trapezoids and triangles, but also shapes with rounded corners as in this example, including those that are substantially considered trapezoids and triangles. For example, when the contour includes a straight line, it includes a shape in which the intersection of the extension lines of this straight line forms the vertices of a polygon. For example, when the contour includes a curve and a straight line, it includes a shape in which the intersection of the tangent of this curve and the straight line or the extension line of the straight line forms the vertices of a polygon.

[0045] Typically, the shapes and sizes of the respective teeth 4 are the same.

[0046] 〔External Region〕 As shown in FIGS. 2, 4, and 5, the external region 40 includes a second end face 42 that is opposite to the first end face 41. The second end face 42 is a face that extends in a direction intersecting the first direction D1 from the outer peripheral face 23 of the yoke 2. The second end face 42 of this example is along the second direction D2. The second end face 42 of this example is between the first end face 41 and the second extension face 52 and is arranged at an interval from the second extension face 52 as shown in FIGS. 4 and 5.

[0047] The second end face 42 of this example includes a proximal face 421 and a distal face 422 as shown in FIGS. 4 and 5. The proximal face 421 is a face that is located between the first extension face 51 and the second extension face 52 so as to extend along the second face 22 or the outer peripheral face 23 of the yoke 2. The proximal face 421 of this example is located in the vicinity of the second extension face 52. The distal face 422 is a face that is farther from the outer peripheral face 23 than the proximal face and is also located away from the second extension face 52. The distal face 422 of this example is located between the first extension face 51 and the second extension face 52 so as to extend along the side face 43 of the external region 40.

[0048] The second end face 42 of this example is mostly composed of the distal face 422. By having a gap A1 between the distal face 422 and the second extension face 52, a wiring space for the coil 70 shown in FIG. 12 can be secured according to the gap A1. When each tooth 4 includes the outer region 40, compared with the conventional core, the core 1 becomes larger in the second direction D2. However, since the wiring space is secured by using the outer region 40, the overall enlargement of the stator 7 (FIG. 12) configured by arranging the coil 70 on each tooth 4 of the core 1 is suppressed.

[0049] The gap A1 is the gap between the positions that are farthest from the outer peripheral surface 23 among the gaps between the second end face 42 and the second extension face 52. The larger the gap A1 is, the larger the wiring space can be secured. The gap A1 is, for example, 10% or more of the first length L1 from the second face 22 to the first end face 41. The method of measuring the first length L1 of each tooth 4 will be described later. The gap A1 is in a correlation relationship with the second length L2 of the outer region 40. The second length L2 is the length along the first direction D1 at the location that is the most distal from the axis of the yoke 2 in the outer region 40. In other words, the second length L2 is the length along the first direction D1 at the location that is located at the tip protruding outward along the second direction D2 from the main region of the tooth 4 among the side faces 43 of the outer region 40. When the gap A1 becomes larger, the second length L2 becomes smaller. Considering the second length L2, the gap A1 is, for example, 40% or less of the first length L1. The gap A1 is, for example, 10% or more and 40% or less of the first length L1. The gap A1 may be 15% or more and 35% or less, or 20% or more and 30% or less of the first length L1.

[0050] On the second end face 42 of this example, a step is formed by a proximal face 421 and a distal face 422. A die 9 for pressure-molding a core 1 having an external region 40 in each tooth 4 includes a die 91, a lower punch 92, and an upper punch 93, as will be described later with reference to FIG. 11. The yoke 2 is formed by the first face 21 being supported by the die 91 and the second face 22 being pressed by the upper punch 93. Each tooth 4 is pressed by the lower punch 92 and the upper punch 93. The second end face 42 is formed by the shape of the convex portion 934 of the upper punch 93 being transferred. When there is a convex portion 934 on the upper punch 93, a relatively large stress is generated at the corner portion forming the first corner 31 in the die 91. Since the above step is formed on the second end face 42, it is easy to reduce the above stress generated in the die 91.

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

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

[0053] As shown in FIG. 3, when viewing the core 1 in the first direction D1, the angle θ between the first tangent line T1 and the second tangent line T2 at the first intersection point T0 is, for example, 90° or less. The first intersection point T0 is the intersection point between the side surface 43 of the outer region 40 and the first envelope circle 61. The side surface 43 of the outer region 40 is flush with the side surface of the main region in each tooth 4 when viewing the core 1 in the first direction D1. The side surface 43 in this example is a plane flush with the side surface of the main region. The side surface 43 of the outer region 40 is not limited to the plane in this example, and may be a surface with a monotonic curvature or a surface with a changing curvature. The first tangent line T1 is a tangent line of the first envelope circle 61 passing through the first intersection point T0. The second tangent line T2 is a tangent line of the side surface 43 of the outer region 40 passing through the first intersection point T0. If the angle θ is 90° or less, it is easy to reduce the stress generated at the corner forming the first corner 31 in the die 91 of the mold 9 for pressure-molding 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 viewing the core 1 in the first direction D1, the diameter of the second envelope circle 62 surrounding the plurality of teeth 4 is, for example, 15% or more larger than the diameter of the first envelope circle 61. The ratio of the diameter of the second envelope circle 62 to the diameter of the first envelope circle 61 is correlated with the amount of protrusion along the second direction D2 of the outer region 40 with respect to the outer peripheral surface 23 of the yoke 2. If the diameter of the second envelope circle 62 is 15% or more larger than the diameter of the first envelope circle 61, that is, if the above ratio is 115% or more, the opening shape of the cavity of the mold 9 for manufacturing this core 1 has a contour with a large unevenness. The larger the unevenness, as will be described later, 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. The larger the unevenness, the easier it is to reduce the stress generated at the corner forming the first corner 31 in the die 91 of the mold 9 for pressure-molding the core 1.

[0055] If the above ratio is too large, the magnetic characteristics over the entire core 1 may become non-uniform. If the above ratio is 130% or less, the core 1 is likely to have uniform magnetic characteristics over the entire body. The above 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. 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 extension face 52, in this example, the distance A1 between the distal face 422 and the second extension face 52, as described above. The stress generated at the corner for forming the first corner 31 (FIG. 3) of the die 91 (FIG. 7) for pressure-molding the core 1 is caused by the difference between the molding pressure applied to the outer region 40 in each tooth 4 and the molding pressure applied to the region other than the outer region 40. Since the second end face 42 is arranged at a distance from the second extension face 52, the molding pressure on the outer region 40 by the upper punch 93 (FIG. 9) of the die 9 becomes large. If the ratio of the second length L2 to the first length L1 is 60% or more and 90% or less, it is easy to reduce the above stress. If the ratio of the second length L2 to the first length L1 is 90% or less, the interval A1 can be provided, and a wiring space corresponding to this interval A1 can be secured. If the above ratio is 60% or more, the magnetic flux flowing from the magnet 84 of the rotor 80 described later into the outer region 40 easily flows 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 a plurality of teeth〕 Taking the second face 22 of the yoke 2 as a reference plane, the variation in the length from this reference plane to the first end face 41 of each of the plurality of teeth 4 is small. For example, the variation in the first length L1 from the second face 22 to the first end face 41 of each tooth 4 is 0.05 mm or less. For example, assuming that the core 1 is manufactured using a toner cartridge (not shown) that folds back from top to bottom in FIG. 2 after advancing from bottom to top in the drawing of FIG. 2. Even in this case, as shown in FIG. 6, the variation in the first length L1 of the plurality of teeth 4 is 0.05 mm or less.

[0058] The rotating electrical machine 8 shown in Fig. 13 is constructed by housing a stator 7, in which coils 70 are arranged on each tooth 4 of the core 1, together with a rotor 80 in a case 82. At this time, 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 the rotor 80 are housed in the case 82, the first end face 41 of each tooth 4 faces substantially uniformly spaced from any part of the magnet 84. Therefore, the rotating electrical machine 8 constructed using the core 1 is excellent in assemblability and has a small torque ripple. Since the torque ripple in the rotating electrical machine 8 is small, it is difficult for noise and vibration to increase. Since the torque ripple of the rotating electrical machine 8 is small, it is difficult for the rotating shaft 81 of the rotor 80 to vibrate. That is, the frictional force between the rotating shaft 81 of the rotor 80 and the bearing 83 hardly fluctuates. Therefore, it is difficult for the mechanical energy loss in the rotating electrical machine 8 to increase.

[0059] The variation in the first length L1 of the plurality of teeth 4 is obtained as follows. First, in 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 by placing the core 1 on a surface plate equipped with a class 0 surface plate so that the first end face 41 of the tooth 4 faces upward. A plurality of measurement points are selected on the first end face 41 of each tooth 4. The measurement points are set on a straight line passing 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 straight line. The measurement points include the center of gravity of the tooth 4, the edge of the tooth 4 at a position close to the axis of the yoke 2, and the edge of the tooth 4 at a position far from the axis of the yoke 2 on the straight line. The first length L1 of each tooth 4 is the average value of the lengths measured from the surface plate to each measurement point. Next, among the first lengths L1 of the plurality of teeth 4, the maximum length and the minimum length are selected. The variation in the first length L1 of the plurality of teeth 4 is obtained by calculating the difference between the maximum length and the minimum length. It is preferable that the variation in the first length L1 of the plurality of teeth 4 is small. The variation in the first length L1 of the plurality of 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 compacted powder body containing soft magnetic powder. The soft magnetic powder has, for example, a plurality of iron-based particles made of pure iron or an iron-based alloy. The pure iron has a purity of 99% or more, that is, the content ratio of iron (Fe) is 99 mass% or more. The pure iron has effects such as a high saturation magnetic flux density, excellent formability, and being easily densified by pressure molding. Therefore, when it contains iron-based particles made of pure iron, a core 1 with a high saturation magnetic flux density, a core 1 with a high relative density and being dense, a core 1 that is easy to mold during the manufacturing process and has excellent manufacturability can be obtained. Also, due to being dense, it is easy to further increase the saturation magnetic flux density and can be made into a core 1 that is also excellent in mechanical properties such as strength. The iron-based alloy contains additive elements, and the balance is composed of Fe and inevitable impurities. The iron-based alloy contains one or more kinds of additive elements. The additive elements are, for example, silicon (Si), aluminum (Al), and chromium (Cr). The electrical resistance of the iron-based alloy is larger than that of pure iron. Therefore, when it contains iron-based particles made of the iron-based alloy, iron losses such as eddy current loss can be reduced, and a core 1 with low losses can be obtained. It is also possible to use a core 1 that contains both iron-based particles made of pure iron and iron-based particles made of an iron-based alloy.

[0061] The soft magnetic powder generally includes coated particles having an insulating film on the surface of powder particles made of a soft magnetic material. When coated particles are included, iron losses such as eddy current loss can be reduced, and a core 1 with low losses can be obtained. In particular, when it contains coated particles having powder particles made of pure iron and an insulating film, it can have a high saturation magnetic flux density, excellent magnetic properties, and can be made into a core 1 with low losses. The constituent material of the insulating film is an oxide such as, for example, phosphate, silica, magnesium oxide, and 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 is also excellent in 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 compacted powder body to the theoretical density of the compacted powder body constituting the core 1. The above theoretical density can use the true density of the soft magnetic powder constituting the compacted powder body as an equivalent value.

[0063] In the core 1 in which each tooth 4 is provided with an outer region 40, the relative density of the outer region 40 is higher than the relative density of the 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] <<Manufacturing method of core>> The core 1 of the embodiment can be manufactured using the mold 9 shown in FIGS. 7 to 11. The mold 9 includes a die 91 shown in FIG. 7, a lower punch 92 shown in FIG. 8, and an upper punch 93 shown in FIG. 9.

[0065] The die 91 is a cylindrical member. The die 91 includes a central portion 911 and an outer peripheral portion 912. The central portion 911 constitutes 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 for forming the shaft 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 includes a concave portion 913 opening to the upper surface of the die 91 and a through hole 917. The concave portion 913 and the through hole 917 are alternately arranged around the axis of the die 91. The concave portion 913 includes a bottom portion 914, an inner side surface 915, and an outer side surface 916. The inner side surface 915 is also a side surface of the central portion 911. The outer side surface 916 is provided to face the inner side surface 915. The bottom portion 914 connects the inner side surface 915 and the outer side surface 916. The concave portion 913 is for forming most of the yoke 2 in the core 1. The bottom portion 914 constitutes the first surface 21 of the yoke 2. The outer side surface 916 constitutes the outer peripheral surface 23 of the yoke 2. The inner side surface 915 constitutes the inner peripheral surface 24 of the yoke 2. The through hole 917 penetrates the upper and lower portions of the die 91. The through hole 917 is for forming the tooth 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 tooth 4. The circumscribed circle surrounding the plurality of through holes 917 is larger than the circumscribed circle surrounding the plurality of concave portions 913. The circumscribed circle surrounding the plurality of concave portions 913 is constituted by the outer side surface 916 of the concave portion 913. The contour constituting the outer peripheral portion 912 is uneven. The lower punch 92 is inserted into the through hole 917.

[0066] The lower punch 92 includes a base portion 921 and a plurality of columnar portions 922. The base portion 921 is a cylindrical member. The plurality of columnar portions 922 are arranged at intervals around the axis of the base portion 921. Each columnar portion 922 is inserted into the through hole 917 of the die 91. The 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 includes an annular first end face 931. The first end face 931 constitutes the second face 22 of the yoke 2. The upper punch 93 includes a plurality of bulging portions 932 on the outer peripheral surface of the upper punch 93. The plurality of bulging portions 932 are arranged at intervals around the axis of the upper punch 93. Each bulging portion 932 extends along the up and down direction of the upper punch 93. A convex portion 934 is provided at the tip of each bulging portion 932. The convex portion 934 is provided at the location farthest from the axis of the upper punch 93 among the bulging portions 932. The bulging portion 932 includes a second end face 933 having two surfaces that form a step by the convex portion 934. The second end face 933 constitutes the second end face 42 of the outer region 40 of the tooth 4. Among the two surfaces, the surface located proximal to the first end face 931 constitutes the proximal surface 421, and the surface located more distal from the first end face 931 constitutes the distal surface 422.

[0068] By inserting the columnar portion 922 of the lower punch 92 into the through hole 917 of the die 91, a cavity filled with the powder 95 is formed. The powder feeding into the cavity is performed by a powder box (not shown). The powder box has an opening at the bottom. The powder box reciprocates linearly on the die 91. When the powder box moves above the cavity, the powder in the powder box falls into the cavity from the opening of the powder box due to gravity. FIG. 10 shows the state where the cavity is filled with the powder 95. After filling the powder 95 into the cavity, the powder box turns back. At this time of turning back, the bottom surface of the powder box tends to drag a part of the powder 95 filled in the cavity.

[0069] In the mold 9 of this example, as shown in FIG. 10, the opening shape of the cavity has a concavo-convex contour corresponding to the contour of the outer peripheral portion 912 of the die 91. As long as the opening has a concavo-convex contour, the powder 95 group arranged on the opening surface of the cavity has intermittent portions around the axis of the die 91. If there are intermittent portions, it is difficult for the powder 95 to be dragged by the powder box even when the powder box reciprocates. If it is difficult for the powder 95 to be dragged when the powder box reciprocates, it is difficult for the filling amount of the powder 95 into the cavity to be uneven.

[0070] After filling the cavity with the powder 95, as shown in FIG. 11, the powder 95 is pressed by the lower punch 92 and the upper punch 93. If it is difficult for the filling amount of the powder 95 into the cavity to be uneven, it is difficult for variations to occur 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 in the compacted molded body obtained after pressure molding.

[0071] The second end surface 42 of each tooth 4 is formed by transferring the shape of the convex portion 934 provided on the upper punch 93. If there is a convex portion 934 on the upper punch 93, relatively large stress is generated at the corner between the bottom 914 and the outer surface 916 of the concave portion 913 provided on the die 91. The first corner portion 31 of the yoke 2 is formed by this corner portion. If there is a step composed of two surfaces on the second end surface 933, it is easy to reduce the stress generated in the die 91.

[0072] The corners between the bottom 914 and the outer surface 916 and between the bottom 914 and the inner surface 915 of the concave portion 913 provided on the die 91 may be rounded. In this case, the radius of curvature of the corner 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] When the core 1 obtained by the above-described mold 9 is used to produce a compacted molded body by pressure molding the powder 95, 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 is small. Therefore, after producing the compacted molded body, it is not necessary to perform grinding on the first end surface 41 of each tooth 4. Therefore, the core 1 obtained by the above-described mold 9 is excellent in productivity.

[0074] <<Rotating Electric Machine>> Referring to FIGS. 12 and 13, the rotating electric machine 8 of the embodiment will be described. 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. In FIG. 13, a single rotor, double stator type in which one rotor 80 is assembled to be sandwiched between two stators 7 is illustrated. In addition, the rotating electric machine 8 may be in a form including one rotor 80 and one stator 7, or in a form in which one stator 7 is assembled 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 in the core 1. The coil 70 includes a cylindrical portion formed by winding a winding in a spiral shape. The coil 70 in this example is a square cylindrical edge-wound coil with a covering flat wire as the winding. The wiring group 71 of the coil 70 is disposed in a space configured according to the interval A1 between the second end face 42 and the second extension face 52 of the outer region 40 of each tooth 4.

[0076] As shown in FIG. 13, the stator 7 and the 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 peripheries of the stator 7 and the rotor 80. The plate portions are respectively disposed at both ends of the cylindrical portion. The stator 7 and the rotor 80 are housed in the case 82 so as to be sandwiched between the two plate portions. The stator 7 is fixed to the case 82 by fitting a part of the yoke 2 of the core 1 into the plate portion of the case 82. Both plate portions are provided with through holes at their central portions. A bearing 83 is provided in the through hole, and the rotation axis 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 rotation axis 81 is inserted through this bearing. The rotation axis 81 penetrates 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 corresponding to the shape of the first end face 41 of the teeth 4. The rotor body is an annular member and is rotatably supported with respect to the case 82 by a rotating shaft 81. Each magnet 84 is arranged at equal intervals around the axis of the rotor body. Each magnet 84 is magnetized in the direction along the axis of the rotating shaft 81. The magnetization directions of the adjacent magnets 84 around the axis of the rotor body are opposite to each other. When the rotor body rotates, the magnet 84 also rotates together with the rotor body.

[0078] The stator 7 is arranged such that the first end face 41 of the teeth 4 faces the magnet 84 of the rotor 80. The coil 70 of the stator 7 is excited to generate a rotating magnetic field, and the rotor 80 rotates with respect to the stator 7 due to the attractive force or repulsive force caused by the rotating magnetic field. When the rotor 80 rotates, the first end face 41 of the teeth 4 receives the magnetic flux from the rotating magnet 84.

[0079] Since the rotating electrical machine 8 of the embodiment includes the core 1 of the embodiment, it has excellent assemblability. As described above, the core 1 has little variation in the length from the second face 22 of the yoke 2 to the first end face 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 accurately arranged. Further, since the rotating electrical machine 8 of the embodiment includes the core 1 of the embodiment, torque ripple can be reduced, and noise and vibration are small.

[0080] [Test Example 1] In Test Example 1, a core having an external region in each tooth and a conventional core having no external region in each tooth were produced, and the variation in the length from the second face of the yoke to the first end face of each of the plurality of teeth was measured. Sample No. 1-1 is a core having an external region in each tooth. Sample No. 1-2 is a conventional core having no external region in each tooth.

[0081] ≪Description of Samples≫ In Sample No. 1-1, using the mold 9 shown in FIGS. 7 to 11, a powder containing soft magnetic powder was compression-molded to produce a compacted body. The core made of this compacted body is integrally formed with an annular yoke and twelve teeth. Each tooth has an outer region located outside a first circumscribing circle formed by the outer peripheral surface of the yoke when the core is viewed from a first direction parallel to the axis of the yoke. An circumscribing circle surrounding the plurality of teeth is called a second circumscribing circle. The diameter of the second circumscribing circle was 17% larger than the diameter of the first circumscribing circle with respect to the diameter of the first circumscribing circle. The ratio of the diameter of the second circumscribing circle to the diameter of the first circumscribing circle is correlated with the amount of protrusion along a second direction of the outer region with respect to the outer peripheral surface of the yoke. The second direction is a direction orthogonal to the first direction and is a direction along the diameter of the yoke.

[0082] In Sample No. 1-1, each tooth has a first end face located at the tip protruding from the first face of the yoke in a direction parallel to the axis of the yoke, and the outer region has a second end face which is the face opposite to the first end face. The second end face is between the extended face of the second face of the yoke and the first end face, and is arranged at a distance from the extended face of the second face. This distance was 25% of the first length from the second face of the yoke to the first end face of each tooth. That is, the length ratio along the first direction of the portion located farthest from the axis of the yoke in the outer region with respect to the first length was 75%.

[0083] In Sample No. 1-2, the same powder as in Sample No. 1-1 was compression-molded to produce a compacted body. The core made of this compacted body is integrally formed with an annular yoke and twelve teeth. Each tooth does not have a region located outside a first circumscribing circle formed by the outer peripheral surface of the yoke when the core is viewed from the first direction.

[0084] ≪Variation in the length from the second face of the yoke to the first end face of each of the plurality of teeth≫ For each core of the obtained samples, the variation in the length from the second surface of the yoke to the first end face of each of the plurality of teeth was examined as follows. First, in each tooth, the first length L1 from the second surface of the yoke to the first end face of the 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 such that the first end face of the tooth faced upward. On the first end face of each tooth, three or more measurement points were selected. In this example, on the straight line drawn so as to pass through the center of gravity of the tooth and the center of the yoke, measurement points were selected including the center of gravity of the tooth, the edge of the tooth at a position close to the axis of the yoke, and the edge of the tooth at a position far from the axis of the yoke. The length from the surface plate to each measurement point was measured, and the average value of the lengths obtained by the measurement was taken as the first length L1 of each tooth. Next, among the first lengths L1 in the plurality of teeth, the maximum length and the minimum length were selected, and the difference between the maximum length and the minimum length was calculated. This difference was taken as the variation in the length from the second surface of the yoke to the first end face of each of the plurality of teeth. In sample No. 1-1, the variation in the above length was 0.047 mm. In sample No. 1-2, the variation in the above length was 0.099 mm.

[0085] From the results of the above length variation, it can be seen that for a core having an external region in each tooth, the variation in the length from the second surface of the yoke to the first end face of each of the plurality of teeth can be reduced. In a core having an external region in each tooth, the opening shape of the cavity of the mold for producing the core is the shape of the yoke combined with the external region and has an uneven contour. If the opening has an uneven contour, the powder group arranged on the opening surface of the cavity has intermittent portions around the axis of the yoke. If there are intermittent portions, it is considered that even if the powder box reciprocates, it is difficult for the powder to be dragged to the powder box, and it is difficult for the filling amount of the powder into the cavity to be biased. Since it was difficult for the filling amount of the powder to be biased, it is considered that in the compact obtained after pressure molding, it was difficult for the length from the second surface of the yoke to the first end face of each of the plurality of teeth to vary.

[0086] In a conventional core without an external region in each tooth, the opening shape of the cavity of the mold for manufacturing the core is the shape of the yoke, that is, an annular shape. If it is an annular opening, the contour of the powder group arranged on the opening surface of the cavity is a circle, and it is considered that a part of the powder is dragged to the powder box as the powder box reciprocates.

[0087] [Test Example 2] In Test Example 2, cores having external regions in each tooth and different ratios of the second length to the first length were manufactured, and the maximum stress generated in the die during compression molding was measured. The first length is the length from the second surface of the yoke to the first end surface of each tooth. The second length is the length along the first direction of the portion located most distally from the axis of the yoke in the external region. Sample No. 2-1 is a core with the above ratio of 92%. Sample No. 2-2 is a core with the above ratio of 85%. For both Sample No. 2-1 and Sample No. 2-2, the conditions other than the above ratio are the same as those of Sample No. 1-1.

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

[0089] From the above analysis results, it was found that the maximum stress acts on the corner of the die that forms the first corner portion composed of the first surface and the outer peripheral surface of the yoke. In Sample No. 2-1, the maximum stress was 1096 MPa. In Sample No. 2-2, the maximum stress was 1074 MPa.

[0090] From the above analysis results, it can be seen that if the above ratio is 90% or less, the stress generated at the corner of the die that forms the first corner portion of the yoke can be reduced. On the other hand, if it is too small, for example, less than 60% of the above ratio, it becomes difficult for the magnetic flux flowing from the magnet of the rotor into the external region of the tooth to efficiently flow into the yoke.

[0091] [Test Example 3] In Test Example 3, cores each having an external region in each tooth and having different ratios of the second envelope circle to the diameter of the first envelope circle were produced, 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 is 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 is 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 are the same as those of Sample No. 1-1.

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

[0093] From the above analysis results, it was found that the maximum stress acts on the root of the convex part of the upper punch. In Sample No. 3-1, the maximum stress was 2241 MPa. In Sample No. 3-2, the maximum stress was 1153 MPa.

[0094] From the above analysis results, it can be seen that if the diameter of the second envelope circle is 10% or more larger than the diameter of the first envelope circle, the stress generated at the root of the convex part of the upper punch can be reduced. When the above ratio is small, the contact area between the upper punch and the powder constituting the external region becomes small, and it is considered that a relatively large stress is generated at the root of the convex part of the upper punch.

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

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

[0097] From the above analysis results, it was found that the maximum stress acts on the corner of the die for forming the first corner of the yoke. In Specimen No. 4-1, the maximum stress was 1009 MPa. In Specimen No. 4-2, the maximum stress was 983.2 MPa.

[0098] From the above analysis results, it can be seen that if the radius of curvature of the first corner is larger than that of the second corner, the stress generated at the corner of the die for forming the first corner of the yoke can be reduced. During pressure molding, a relatively large stress is generated at the corner of the die for forming the first corner of the yoke. Therefore, it is considered that by increasing the radius of curvature of this corner, the effect of reducing the stress is likely to be exerted.

Explanation of Signs

[0099] 1 Core 2 Yoke 21 First surface, 22 Second surface 23 Outer peripheral surface, 24 Inner peripheral surface 25 Axial hole 31 First corner, 32 Second corner 4 Teeth 40 Outer region 41 First end face, 42 Second end face 421 Near plane, 422 Far plane 43 Side surface 51 First extended surface, 52 Second extended surface 61 First envelope circle, 62 Second envelope circle Interval between A1 and A2 L1 First length, L2 Second length T0 First intersection point, T1 First tangent line, T2 Second tangent line, θ Angle D1 First direction, D2 Second direction 7 Stator, 70 Coil, 71 Wiring group 8 Rotating electrical machine, 80 Rotor, 81 Rotating shaft, 82 Case 83 Bearing, 84 Magnet 9 Mold 91 Die 911 Central part 912 Outer peripheral part 913 Recess, 914 Bottom part, 915 Inner side surface, 916 Outer side surface 917 Through hole 92 Lower punch 921 Base part, 922 Columnar part, 923 End face 93 Upper punch 931 First end face 932 Bulging part, 933 Second end face, 934 Convex part 95 Powder

Claims

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

2. Each of the plurality of teeth has a first end face located at a tip protruding from the first surface in a direction parallel to the axis, the core according to claim 1, wherein 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.

3. Each of the plurality of teeth has a first end face located at a tip protruding from the first surface in a direction parallel to the axis, the outer region has a second end face opposite to the first end face, the core according to claim 1, wherein 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.

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

5. Each of the plurality of teeth has 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, the second length is the length along the first direction at the location farthest from the axis in the outer region, the core according to claim 1.

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

7. The core according to claim 1, wherein each of 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 is rounded.

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

9. The core according to claim 1, wherein a diameter of a second circumscribing circle surrounding the plurality of teeth is 15% or more larger than a diameter of the first circumscribing circle.

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

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