Core piece, stator core, stator, and rotating electric machine

Abstract

Provided is a core piece that constitutes a stator core for an axial gap type rotating electric machine, the core piece comprising a column-shaped first member extending in a direction along an axis of the stator core, wherein a peripheral surface of the first member has, on at least part of the surface contacting a winding of a coil, a plurality of grooves along a direction in which the winding is wound.

Description

Core piece, stator core, stator, and rotating electric machine

[0001] This disclosure relates to a core piece, a stator core, a stator, and a rotating electric machine. This application claims priority to Japanese Patent Application No. 2022-116664 filed on July 21, 2022, and incorporates by reference all of the contents of that application.

[0002] Patent Documents 1 to 3 disclose a stator core and a stator for an axial gap motor. The stator core includes teeth, a yoke portion, and a flange portion. The stator includes coils arranged on the teeth of the stator core. The coils are formed by winding wires around the teeth. Generally, the circumferential surfaces of the teeth on which the coils are arranged are formed as flat surfaces.

[0003] JP 2009-44829 A JP 2009-124794 A JP 2009-142095 A

[0004] The core piece according to the present disclosure is a core piece constituting a stator core for an axial gap type rotating electric machine, and comprises a columnar first member extending in a direction along the axis of the stator core, and the peripheral surface of the first member has a plurality of grooves along the direction in which the winding is wound, on at least a portion of the surface that contacts the coil winding.

[0005] FIG. 1 is a perspective view showing an outline of a core piece according to the first embodiment. FIG. 2 is a top view showing an outline of a core piece according to the first embodiment. FIG. 3 is a view of the core piece according to the first embodiment as seen from the inner peripheral surface side. FIG. 4 is a cross-sectional view showing a state in which the core piece is cut along line IV-IV in FIG. 3. FIG. 5 is a cross-sectional view showing a state in which the core piece is cut along line V-V in FIG. 3. FIG. 6 is a cross-sectional view showing a state in which the core piece is cut along line VI-VI in FIG. 3. FIG. 7A is a schematic cross-sectional view showing multiple grooves provided on the inner peripheral surface of the first member in the core piece according to the first embodiment. FIG. 7B is a schematic cross-sectional view showing an example in which the cross section of the winding is elliptical, which is a modification of the first embodiment. FIG. 8 is a schematic cross-sectional view showing another example of multiple grooves, which is a modification of the first embodiment. FIG. 9 is a perspective view showing an outline of a core piece having multiple grooves on the outer peripheral surface of the first member, which is another modification of the first embodiment. FIG. 10 is a top view showing the opening edge of a die of a mold for manufacturing the core piece according to the first embodiment. FIG. 11 is a cross-sectional view showing an outline of a mold for manufacturing a first member in the core piece according to the first embodiment. FIG. 12 is a cross-sectional view showing an outline of a mold for manufacturing a second member in the core piece according to the first embodiment. FIG. 13 is a cross-sectional view showing an outline of a mold for manufacturing a third member in the core piece according to the first embodiment. FIG. 14 is a perspective view showing an outline of a core piece according to another modification of the first embodiment, in which the protruding portion of the second member has a groove in which the winding start end of the winding is disposed. FIG. 15 is a perspective view showing an outline of a core piece according to another modification of the first embodiment, in which the protruding portion of the second member has a step in which the winding start end of the winding is disposed. FIG. 16 is a perspective view showing an outline of a stator core according to the second embodiment. FIG. 17 is a perspective view showing an outline of a stator according to the third embodiment. FIG. 18 is a cross-sectional view showing an outline of a rotating electric machine according to the fourth embodiment. FIG. 19 is a cross-sectional view showing an outline of a rotating electric machine according to the fifth embodiment.

[0006] [Problem to be Solved by the Present Disclosure] When a motor is driven, a current flows through the coil, causing the coil to generate heat. In order to downsize the motor while maintaining the motor's output, it is necessary to increase the current flowing through the coil. As the amount of heat generated by the coil increases, it is desirable to suppress the temperature rise of the coil.

[0007] An object of the present disclosure is to provide a core piece capable of suppressing a temperature rise in the coil. Another object of the present disclosure is to provide a stator core, a stator, and a rotating electric machine capable of suppressing a temperature rise in the coil.

[0008] [Effects of the Present Disclosure] The core pieces according to the present disclosure can suppress a rise in the temperature of the coil.

[0009] <Description of Embodiments of the Present Disclosure> First, embodiments of the present disclosure will be listed and described.

[0010] (1) A core piece according to an embodiment of the present disclosure is a core piece constituting a stator core for an axial gap type rotating electric machine, and includes a columnar first member extending in a direction along the axis of the stator core, and the peripheral surface of the first member has a plurality of grooves along the direction in which the winding is wound, on at least a portion of the surface that contacts the coil winding.

[0011] The core piece of the present disclosure can suppress the temperature rise of the coil. In the core piece of the present disclosure, the coil is arranged on a first member. The circumferential surface of the first member has multiple grooves. The winding is arranged in a state where it fits into each groove. Therefore, the contact area between the winding and the first member is increased compared to when the circumferential surface of the first member is configured as a flat surface. As a result of improved heat dissipation from the winding to the first member, the coil can be cooled effectively.

[0012] Furthermore, when winding the winding around the first member, the winding is held in each groove, preventing the winding from becoming unbalanced. Winding the winding evenly along the grooves improves the coil space factor. Improving the coil space factor is effective in reducing the size and increasing the output of rotating electrical machines.

[0013] (2) In the core lamination described in (1) above, the width of each of the plurality of grooves may be greater than or equal to ¼ of the major axis of the winding and less than or equal to the major axis, and the depth of each of the plurality of grooves may be greater than or equal to ¼ of the minor axis of the winding and less than or equal to the minor axis.

[0014] The core pieces (2) are sufficiently held in place with the windings fitted into the grooves.

[0015] (3) In the core piece described in (1) or (2) above, the cross section of the winding may be circular, the cross section of each of the plurality of grooves may be arc-shaped, and the radius of the circle of the cross section of the winding may be the same as the radius of the arc of the cross section of the groove.

[0016] The core piece (3) above can easily ensure a sufficient contact area between the winding and the first member, because the cross-sectional shape of the groove corresponds to the cross-sectional shape of the winding.

[0017] (4) In the core piece described in any one of (1) to (3) above, the plurality of grooves may have a connecting surface between two adjacent grooves that is continuous with the inner peripheral surface of the groove, and the connecting surface may be composed of a flat surface or a rounded curved surface.

[0018] (4) The core pieces have a connecting surface that is formed of a flat surface or the curved surface, and therefore does not have a sharp shape, so that chipping is unlikely to occur at the connecting surface.

[0019] (5) In the core piece described in any one of (1) to (4) above, the circumferential surface may have an inner circumferential surface positioned close to the axis of the stator core and an outer circumferential surface positioned far from the axis of the stator core, and the plurality of grooves may be provided on at least one of the inner circumferential surface and the outer circumferential surface.

[0020] The core piece (5) above has multiple grooves on at least one of the inner and outer circumferential surfaces of the first member, which can suppress the temperature rise of the coil. In particular, the inner circumferential surface of the core piece is close to the inner circumferential surfaces of adjacent core pieces around the axis of the stator core, which makes it easy for heat to build up in the coil. In other words, the temperature rise of the winding in contact with the inner circumferential surface of the first member is large. Therefore, when multiple grooves are provided on the inner circumferential surface of the first member, the temperature rise of the coil can be more effectively suppressed. The outer circumferential surface of the core piece has a longer length around the axis of the stator core than the inner circumferential surface. Therefore, when multiple grooves are provided on the outer circumferential surface of the first member, the winding is more likely to be stably held in each groove.

[0021] (6) The core piece described in any one of (1) to (5) above comprises: a plate-shaped second member provided at a first end of the first member in a direction along the axis; and a plate-shaped third member provided at a second end of the first member in a direction along the axis; the peripheral surface of the first member is connected to the second member and the third member; the second member has a protruding portion that protrudes outward from the peripheral surface of the first member; and the third member has a protruding portion that protrudes outward from the peripheral surface of the first member; and the first member, the second member, and the third member may be configured as an integrally molded powder compact.

[0022] The core piece of (6) above has the protrusions of the second and third members at each end of the first member, so that the coil arranged on the first member can be held between the two protrusions. Also, the core piece of (6) above is composed of a powder compact in which the first, second, and third members are integrally molded, so that the core piece is easy to manufacture and to handle as a single member.

[0023] (7) In the core piece described in (6) above, the protruding portion of the second member or the protruding portion of the third member may have a groove or a step in which a winding start end of the winding is placed.

[0024] In the core piece (7) described above, the winding start end of the winding is positioned in the groove or step, so that when winding is performed in multiple layers, the second and subsequent layers of winding can be prevented from interfering with the winding start end. Therefore, the core piece (7) described above allows one more turn of winding to be wound than a core piece without a groove or step. In other words, the space factor of the coil is improved.

[0025] (8) A core piece according to an embodiment of the present disclosure is a core piece constituting a stator core for an axial gap type rotating electric machine, comprising: a columnar first member extending in a direction along the axis of the stator core; a plate-shaped second member provided at a first end of the first member in the direction along the axis; and a plate-shaped third member provided at a second end of the first member in the direction along the axis, wherein the first member has a circumferential surface connecting the second member and the third member, the second member has a protruding portion that protrudes outward beyond the circumferential surface of the first member, and the third member has a protruding portion that protrudes outward beyond the circumferential surface of the first member, the first member, the second member, and the third member are formed as an integrally molded powder compact, and the circumferential surface of the first member has an inner circumferential surface that is located close to the axis of the stator core, and an outer circumferential surface that is located far from the axis of the stator core, At least one of the inner peripheral surface and the outer peripheral surface has a plurality of grooves along the direction in which the winding is wound, on at least a portion of the surface that contacts the coil winding, the width of each of the plurality of grooves is greater than or equal to 1 / 4 of the major axis of the winding and less than or equal to the major axis, the depth of each of the plurality of grooves is greater than or equal to 1 / 4 of the minor axis of the winding and less than or equal to the minor axis, and the protrusion of the second member or the protrusion of the third member has a groove or step in which the starting end of the winding of the winding is positioned.

[0026] The core piece of (8) above has the configurations described in (1), (2), (5), (6), and (7) above. The core piece of (8) above exhibits the respective effects of the above configurations.

[0027] (9) A stator core according to an embodiment of the present disclosure is a stator core for an axial gap type rotating electric machine, and has a plurality of core pieces arranged in a ring shape, each of which is a core piece according to any one of (1) to (8) above.

[0028] The stator core of the present disclosure includes the above-described core pieces, thereby making it possible to suppress temperature rise in the coils.

[0029] (10) A stator according to an embodiment of the present disclosure is a stator for an axial gap type rotating electric machine, and includes the stator core described in (9) above, and a coil arranged on each of the first members in the stator core.

[0030] The stator of the present disclosure includes the above-described stator core, thereby making it possible to suppress temperature rise in the coil.

[0031] (11) A rotating electric machine according to an embodiment of the present disclosure is an axial gap type rotating electric machine having a rotor and a stator, the rotor and the stator being arranged facing each other in a direction along the axis, and the stator being the stator described in (10) above.

[0032] The rotating electric machine of the present disclosure includes the above-described stator, thereby making it possible to suppress temperature rise in the coil.

[0033] Details of the embodiments of the present disclosure will be described below with reference to the drawings. The same reference numerals in the drawings denote the same components.

[0034] First Embodiment [Core] A core lamination 1 according to a first embodiment will be described with reference to FIGS. 1 to 9 . As will be described later with reference to FIG. 16 , a plurality of core laminations 1 are arranged in an annular shape to form a stator core 7. As will be described later with reference to FIG. 17 , this stator core 7 has a coil 80 arranged in each first member 10 of each core lamination 1 to form a stator 8. As will be described later with reference to FIGS. 18 and 19 , this stator 8 is used in an axial gap type rotating electric machine 9. As shown in FIG. 1 , the core lamination 1 of this embodiment includes a columnar first member 10. The first member 10 extends in a direction along the axis of the stator core 7. One of the features of the core lamination 1 of this embodiment is that a plurality of grooves 40 are formed in the circumferential surface 11 of the first member 10. The windings 81 of the coil 80 are wound along the grooves 40, as will be described later with reference to FIG. 7A . In the following, the direction along the axis of the stator core may be referred to as the "axial direction," the direction perpendicular to the axial direction of the stator core may be referred to as the "radial direction," and the direction around the axis of the stator core may be referred to as the "circumferential direction."

[0035] 1, the core piece 1 of this embodiment further includes a plate-shaped second member 20 and a plate-shaped third member 30. The second member 20 is provided at a first end of the first member 10 in the axial direction. The third member 30 is provided at a second end of the first member 10 in the axial direction. Details of the core piece 1 will be described below.

[0036] The direction along the radial direction of the stator core 7 in the core lamination 1 is the X-axis direction. The direction along the axial direction of the stator core 7 in the core lamination 1 is the Z-axis direction. The direction perpendicular to both the X-axis direction and the Z-axis direction of the core lamination 1 is the Y-axis direction. Within the X-axis direction, the direction approaching the axis of the stator core 7 in the core lamination 1 is the X1 direction, and the direction away from the axis of the stator core 7 is the X2 direction. The X1 direction is the inner circumferential direction of the stator core 7. The X2 direction is the outer circumferential direction of the stator core 7. Within the Z-axis direction, the direction from the third member 30 toward the second member 20 in the first member 10 is the Z1 direction, and the direction from the second member 20 toward the third member 30 in the first member 10 is the Z2 direction. The end of the first member 10 in the Z1 direction is the first end of the first member 10. The end of the first member 10 in the Z2 direction is the second end of the first member 10. In the Y-axis direction, a first direction of the stator core 7 in the core lamination 1 is defined as a Y1 direction, and a second direction of the stator core 7 is defined as a Y2 direction.

[0037] [First Member] The first member 10 is a columnar member extending in the Z-axis direction. The first member 10 forms teeth in either the case where the core laminations 1 form a stator core 7 of a double stator / single rotor configuration in an axial gap type rotating electric machine 9, or the case where the core laminations 1 form a stator core 7 of a single stator / double rotor configuration in an axial gap type rotating electric machine 9. An axial gap type rotating electric machine 9 of a double stator / single rotor configuration is assembled so that one rotor 90 is sandwiched between two stators 8, as shown in FIG. 18 . An axial gap type rotating electric machine 9 of a single stator / double rotor configuration is assembled so that one stator 8 is sandwiched between two rotors 90, as shown in FIG. 19 . Hereinafter, for convenience of explanation, a double stator / single rotor may be referred to as a DS / SR, and a single stator / double rotor may be referred to as a SS / DR.

[0038] The shape of the first member 10 may be, for example, a rectangular prism or a cylindrical shape. A rectangular prism is, for example, a quadrangular prism, where the cross-section cut along a plane perpendicular to the Z-axis direction is a square. A quadrangular prism is, for example, a trapezoidal prism, where the cross-section is a trapezoid. The cross-section may or may not be uniform in the Z-axis direction. The term "trapezoid" refers not only to a geometric trapezoid, but also to shapes with rounded corners, as in this example, that are essentially considered trapezoids. The term "trapezoid" includes trapezoids with both legs of the same length, such as an isosceles trapezoid, as well as trapezoids with both legs of different lengths, such as a right-angled trapezoid. This also applies to the second member 20 and the third member 30, which will be described later.

[0039] As shown in Figures 1 and 4, the shape of the first member 10 in this embodiment is a trapezoidal columnar shape, in which the cross-sectional shape is trapezoidal. The cross-sectional shape has a longer side in the X2 direction and a shorter side in the X1 direction. The cross-sectional shape of the first member 10 is uniform in the Z-axis direction. If the shape of the first member 10 is a trapezoidal columnar shape, it is easy to ensure a large cross-sectional area. Furthermore, it is easy to reduce the dead space of the core laminations 1, and it is easy to configure a stator 8 with a high space factor.

[0040] As shown in FIGS. 1 and 3 , the first member 10 has a circumferential surface 11 that is connected to the second member 20 and the third member 30. As shown in FIG. 4 , the circumferential surface 11 of the first member 10 has an outer circumferential surface 12, an inner circumferential surface 13, a first side surface 14a, and a second side surface 14b. The outer circumferential surface 12 is located in the X2 direction. That is, the outer circumferential surface 12 is located far from the axis of the stator core 7. The inner circumferential surface 13 is located in the X1 direction. That is, the inner circumferential surface 13 is located close to the axis of the stator core 7. The first side surface 14a and the second side surface 14b are located on opposite sides of each other in the circumferential direction of the stator core 7 of the core lamination 1. That is, the first side surface 14a is located in a first direction in the circumferential direction of the stator core 7 of the core lamination 1. The second side surface 14b is located in a second direction in the circumferential direction of the stator core 7 of the core lamination 1. The positional relationship between the outer peripheral surface 12, the inner peripheral surface 13, the first side surface 14a, and the second side surface 14b is the same for the second member 20 and the third member 30 described later.

[0041] The outer peripheral surface 12 is connected to the outer peripheral edge of the first side surface 14 a and the outer peripheral edge of the second side surface 14 b. The inner peripheral surface 13 is connected to the inner peripheral edge of the first side surface 14 a and the inner peripheral edge of the second side surface 14 b. That is, the first side surface 14 a and the second side surface 14 b are connected to the outer peripheral surface 12 and the inner peripheral surface 13.

[0042] The length between the first side surface 14a and the second side surface 14b on the outer peripheral surface 12, i.e., the length of the outer peripheral surface 12 along the Y-axis direction, is longer than the length between the first side surface 14a and the second side surface 14b on the inner peripheral surface 13, i.e., the length of the inner peripheral surface 13 along the Y-axis direction. In this embodiment, the outer peripheral surface 12 has a curved surface that is convex in the X2 direction. The outer peripheral surface 12 may be configured as a flat surface. In this embodiment, the inner peripheral surface 13 has a curved surface that is convex in the X1 direction. The inner peripheral surface 13 may have a curved surface that is convex in the X2 direction, or may be configured as a flat surface. The bending radii of the outer peripheral surface 12 and the inner peripheral surface 13 may be the same or different from each other.

[0043] Each of the first side surface 14a and the second side surface 14b has a first parallel surface 141, a second parallel surface 142, and a first inclined surface 143. The first parallel surfaces 141 of the first side surface 14a and the second side surface 14b are parallel to each other. The second parallel surfaces 142 of the first side surface 14a and the second side surface 14b are parallel to each other. The first parallel surface 141 of the first side surface 14a and the second parallel surface 142 of the first side surface 14a are parallel to each other. The first parallel surface 141 and the second parallel surface 142 are parallel to the X-axis direction of the core lamination 1. The X-axis direction refers to the direction along a straight line that passes through the center of the stator core 7 and bisects the core lamination 1 in the circumferential direction of the stator core 7. The first parallel surface 141 is contiguous with the outer peripheral surface 12. The second parallel surface 142 is contiguous with the inner peripheral surface 13. The first inclined surface 143 is contiguous with the first parallel surface 141 and the second parallel surface 142.

[0044] The length of the first parallel surface 141 and the second parallel surface 142 along the X-axis direction depends on the size of the core piece 1, and is preferably, for example, 0.3 mm or more and 25 mm or less. If the length is equal to or greater than the lower limit, damage to the mold 5 caused by contact between the lower punch 55 and the die 50, which will be described later with reference to FIGS. 10 and 12 , can be suppressed. While a method for manufacturing the core piece 1 will be described later, if the length is equal to or greater than the lower limit, sufficient pressure can be applied to the raw material powder constituting the core piece 1. If the length is equal to or less than the upper limit, the cross-sectional area of ​​the first member 10 can be increased, thereby improving torque and suppressing iron loss in the axial gap type rotating electric machine 9. The length of the first parallel surface 141 and the second parallel surface 142 along the X-axis direction is further preferably equal to or greater than 0.4 mm and 20 mm or less, and particularly preferably equal to or greater than 0.5 mm and 15 mm or less. The above-mentioned preferred ranges of the lengths along the X-axis direction of the first parallel plane 141 and the second parallel plane 142 on each of the first side surface 14a and the second side surface 14b of the first member 10 are also the same for the first parallel plane 241 and the second parallel plane 242 on each of the first side surface 24a and the second side surface 24b of the second member 20, which will be described later, and the first parallel plane 341 and the second parallel plane 342 on each of the first side surface 34a and the second side surface 34b of the third member 30.

[0045] As shown in FIG. 4 , the first inclination angle θ11 and the second inclination angle θ12 of the first inclined surface 143 are preferably, for example, 5° to 20°. When the first inclination angle θ11 and the second inclination angle θ12 are 5° to 20°, it is easy to wind the winding 81 (described later) around the circumferential surface 11 of the first member 10. The first inclination angle θ11 and the second inclination angle θ12 are preferably 5.5° to 18°, and particularly preferably 6° to 16°. The first inclination angle θ11 and the second inclination angle θ12 are preferably the same angle, but may be different. The first inclination angle θ1 refers to the angle between the first inclined surface 143 and an extension E11 of the first parallel surface 141 on the first side surface 14a. The second inclination angle θ12 refers to the angle between the first inclined surface 143 and an extension E12 of the first parallel surface 141 on the second side surface 14b.

[0046] (Grooves) As shown in FIG. 1 , the circumferential surface 11 of the first member 10 has a plurality of grooves 40. As shown in FIG. 7A , the plurality of grooves 40 may be provided on at least a portion of the surface that contacts the winding 81 of the coil 80. The "at least a portion of the surface that contacts the winding 81 of the coil 80" includes corners of two adjacent surfaces on the circumferential surface 11. In this embodiment, the plurality of grooves 40 are provided on the inner circumferential surface 13 of the circumferential surface 11. The grooves 40 are aligned along the direction in which the winding 81 of the coil 80 is wound. Hereinafter, the direction in which the winding 81 is wound may be referred to as the "winding direction." FIG. 7A is a cross-sectional view of the inner circumferential surface 13, taken along a plane perpendicular to the inner circumferential surface 13 and parallel to the Z-axis direction. The plurality of grooves 40 are aligned in the Z-axis direction. Each groove 40 extends in the inner circumferential surface 13 in a direction perpendicular to the Z-axis direction. The grooves 40 extend in a direction parallel to the winding direction of the winding 81 and may be inclined with respect to the Z-axis direction. The winding 81 is disposed in a state of being fitted into each groove 40. The increased contact area between the winding 81 and the first member 10 improves heat dissipation from the winding 81 to the first member 10. As a result, the coil 80 is cooled effectively, and a temperature rise in the coil 80 is suppressed.

[0047] The cross section of the winding 81 is, for example, circular or elliptical. In this embodiment, the cross section of the winding 81 is circular. The cross section of the winding 81 is a cross section cut along a plane perpendicular to the direction along the length of the winding 81. The winding 81 includes a copper wire and an insulating coating covering the copper wire. The coil 80 is a multilayer wound coil in which the winding 81 is wound in line in multiple layers. The winding 81 has a major axis 81a and a minor axis 81b. The major axis 81a is the longest diameter in the cross section of the winding 81. The minor axis 81b is the longest diameter among the diameters perpendicular to the major axis 81a. When the cross section of the winding 81 is circular, the major axis 81a and the minor axis 81b are each equal to the diameter 81d.

[0048] The cross-sectional shape of the groove 40 may be any shape as long as the winding 81 contacts the inner circumferential surface of the groove 40 at two or more points. The cross-section of the groove 40 in this embodiment is arc-shaped, as shown in FIG. 7A . The cross-section of the groove 40 is a cross-section cut along a plane perpendicular to the extension direction of the groove 40. The inner circumferential surface of the groove 40 is formed of an arc-shaped surface. In this embodiment, the radius of the circle in the cross-section of the winding 81 is the same as the radius of the arc in the cross-section of the groove 40. In other words, the cross-sectional shape of the groove 40 corresponds to the cross-sectional shape of the winding 81. By having the winding 81 substantially in close contact with the inner circumferential surface of the groove 40, it is easy to ensure a sufficient contact area between the winding 81 and the first member 10.

[0049] The groove 40 need only be large enough to accommodate the winding 81. When the cross section of the winding 81 is circular, the width 40w of the groove 40 is, for example, greater than or equal to ¼ of the diameter 81d of the winding 81 and less than or equal to the diameter 81d. The width 40w is the opening width of the groove 40 that opens to the circumferential surface 11. When the width 40w is greater than or equal to ¼ of the diameter 81d and less than or equal to the diameter 81d, the winding 81 can be easily and sufficiently held. The width 40w may be greater than or equal to ½ of the diameter 81d and less than or equal to the diameter 81d. Furthermore, the width 40w may be greater than or equal to ¾ of the diameter 81d and less than or equal to ¾ of the diameter 81d. The deeper the depth 40d of the groove 40, the easier it is for the winding 81 to be sufficiently held in place in the groove 40. The depth 40d of the groove 40 can be determined according to the width 40w of the groove 40 so that the winding 81 can easily fit within the groove 40. The depth 40d of the groove 40 is, for example, greater than or equal to ¼ and less than the diameter 81d of the winding 81. The depth 40d is the distance from the opening edge to the bottom of the groove 40. When the depth 40d is greater than or equal to ¼ and less than the diameter 81d, the winding 81 is easily and sufficiently held. The depth 40d may also be greater than or equal to ⅓ and less than ½ of the diameter 81d.

[0050] In the first member 10 shown in FIG. 7A , the diameter of the winding 81 is the same as the diameter of the groove 40. That is, the cross section of the groove 40 is formed in an arc shape that conforms to the circular shape of the winding 81. The outer peripheral surface of the winding 81 coincides with the inner peripheral surface of the groove 40, and the contact area between the winding 81 and the groove 40 is largest relative to the width 40w. Expressing this relationship as a range, the width 40w and depth 40d of the groove 40 may satisfy the following relationship (1) or (2) with respect to the diameter 81d of the winding 81. Here, the diameter 81d is simply represented as "D"). (1) When the width 40w is 0.25D or greater and D or less, the depth 40d is 0.016D or greater and 0.5D or less. (2) When the width 40w is 0.6D or greater and 0.8D or less, the depth 40d is 0.1D or greater and 0.2D or less.

[0051] In this embodiment, the grooves 40 have a coupling surface 42 that is continuous with the inner circumferential surface of the groove 40 between two adjacent grooves 40. As shown in FIG. 7A , the coupling surface 42 in this embodiment is configured as a flat surface. Because the coupling surface 42 is configured as a flat surface, no sharp corners are formed between adjacent grooves 40. Because the coupling surface 42 is not sharp, chipping is less likely to occur on the coupling surface 42. Furthermore, even if the winding 81 comes into contact with the coupling surface 42 when winding the winding 81 around the first member 10, damage to the winding 81 can be suppressed. Furthermore, corners between the inner circumferential surface of the groove 40 and the coupling surface 42 may be rounded. The coupling surface 42 may be configured as a rounded curved surface. Even if the coupling surface 42 is configured as the curved surface, the coupling surface 42 does not have a sharp shape, so chipping is less likely to occur on the coupling surface 42. Furthermore, damage to the winding 81 when winding the winding 81 around the first member 10 can be suppressed.

[0052] The cross section of the winding 81 may be elliptical, as shown in FIG. 7B . When the cross section of the winding 81 is elliptical, the winding 81 is wound, for example, with its major axis 81a parallel to the circumferential surface 11. The cross section of the groove 40 is shaped to conform to the elliptical shape of the winding 81. The width 40w of the groove 40 is, for example, greater than or equal to ¼ of the major axis 81a of the winding 81 and less than or equal to the major axis 81a. The width 40w may be, for example, greater than or equal to ¾ of the major axis 81a and less than or equal to ¾ of the major axis 81a. The depth 40d of the groove 40 is, for example, greater than or equal to ¼ of the minor axis 81b of the winding 81 and less than or equal to the minor axis 81b. The depth 40d may further be, for example, greater than or equal to ⅓ of the minor axis 81b and less than or equal to ½ of the minor axis 81b. Unlike the example shown in FIG. 7B , the winding 81 may be wound, for example, with its minor axis 81b parallel to the circumferential surface 11. 7B may have the major axis 81a and the minor axis 81b interchanged. In this case, the width 40w of the groove 40 may be greater than or equal to ¼ of the minor axis 81b of the winding 81 but less than the minor axis 81b, and the depth 40d of the groove 40 may be greater than or equal to ¼ of the major axis 81a of the winding 81 but less than the major axis 81a.

[0053] The cross section of the groove 40 may be triangular, as shown in Fig. 8. The inner peripheral surface of the triangular groove 40 is formed by two linearly inclined surfaces. The winding 81 contacts the inner peripheral surface of the groove 40 at two points.

[0054] The plurality of grooves 40 may be provided on any of the outer peripheral surface 12, inner peripheral surface 13, first side surface 14a, and second side surface 14b of the circumferential surface 11 shown in FIG. 4 . For example, as shown in FIG. 9 , the plurality of grooves 40 may be provided on the outer peripheral surface 12. Furthermore, the plurality of grooves 40 may be provided on both the inner peripheral surface 13 and the outer peripheral surface 12. The plurality of grooves 40 may be provided at corners of two adjacent surfaces. For example, the plurality of grooves 40 may be provided near a corner between at least one of the first side surface 14a and the second side surface 14b and the inner peripheral surface 13. Furthermore, the plurality of grooves 40 may be provided near a corner between at least one of the first side surface 14a and the second side surface 14b and the outer peripheral surface 12.

[0055] When multiple grooves 40 are provided on the inner circumferential surface 13, they can be formed by a lower punch 55, which will be described later with reference to FIG. 12 . When multiple grooves 40 are provided on the outer circumferential surface 12, they can be formed by an upper punch 54, which will be described later with reference to FIG. 11 . When multiple grooves 40 are provided on at least one of the first side surface 14a and the second side surface 14b, they can be formed by the inner circumferential surface of the mold hole 50h of the die 50, which will be described later with reference to FIG. 10 . When multiple grooves 40 are provided on at least one of the first side surface 14a and the second side surface 14b, the grooves 40 may be damaged by rubbing against the inner circumferential surface of the mold hole 50h when the core piece 1 is removed from the mold hole 50h of the die 50. Furthermore, the frictional resistance between the core piece 1 and the inner circumferential surface of the mold hole 50h increases, making it difficult to remove the core piece 1 from the mold hole 50h. When multiple grooves 40 are provided on the inner circumferential surface 13, the grooves 40 are formed by the lower punch 55, making them less likely to be damaged. When a plurality of grooves 40 are provided on the outer peripheral surface 12, the grooves 40 are formed by the upper punch 54, so that the grooves 40 are less likely to be damaged.

[0056] 1 and 3 , the second member 20 is a plate-shaped member provided at a first end in the Z-axis direction of the first member 10. When the core laminations 1 form the stator core 7 for the axial gap type rotating electric machine 9 of the DS / SR configuration, the second member 20 forms a yoke. When the core laminations 1 form the stator core 7 for the axial gap type rotating electric machine 9 of the SS / DR configuration, the second member 20 forms a flange.

[0057] In this embodiment, the second member 20 has a trapezoidal plate shape. The trapezoidal plate shape is a trapezoidal cross section obtained by cutting the second member 20 along a plane perpendicular to the Z-axis direction. The cross section may or may not be uniform in the Z-axis direction. Note that the shape of the second member 20 may be a rectangular plate when the core laminations 1 form a stator core 7 for an axial gap type rotating electric machine 9 of SS / DR configuration.

[0058] As shown in FIGS. 1 to 3 , the second member 20 has a protruding portion 21. The protruding portion 21 protrudes outward from the circumferential surface 11 of the first member 10. The protruding portion 21 may protrude outward from the circumferential surface 11 of the first member 10 in a portion of the circumferential surface 11 of the first member 10, or may protrude outward from the circumferential surface 11 of the first member 10 over the entire circumferential circumference of the first member 10. In this embodiment, the protruding portion 21 has a first protruding portion 211 and a second protruding portion 212. The first protruding portion 211 protrudes in a second circumferential direction of the stator core 7. The second protruding portion 212 protrudes in the second circumferential direction of the stator core 7. Note that the protruding portion 21 may not have the first protruding portion 211 and the second protruding portion 212, and may have a portion protruding in the X1 direction and a portion protruding in the X2 direction. The protruding portion 21 may have a portion that protrudes in the X1 direction and a portion that protrudes in the X2 direction, in addition to the first protruding portion 211 and the second protruding portion 212. In this case, the protruding portion 21 is provided in an annular shape along the circumferential direction of the first member 10.

[0059] When the core laminations 1 form a stator core 7 for an axial gap type rotating electric machine 9 of a DS / SR configuration, the protruding lengths of the first protruding portions 211 and the second protruding portions 212 of the second member 20 are longer than the protruding lengths of the first protruding portions 311 and the second protruding portions 312 of the third member 30 described below. When the core laminations 1 form a stator core 7 for an axial gap type rotating electric machine 9 of a SS / DR configuration, the protruding lengths of the first protruding portions 211 and the second protruding portions 212 of the second member 20 may be the same as the protruding lengths of the first protruding portions 311 and the second protruding portions 312 of the third member 30. The protruding length refers to the length that protrudes in a direction perpendicular to the circumferential surface 11 of the first member 10. When the circumferential surface 11 has a curved surface, the protruding length refers to the length along the normal direction of the curved surface.

[0060] As shown in FIG. 3 , the second member 20 has a first end surface 26 and a second end surface 27. As shown in FIG. 5 , the second member 20 has an outer peripheral surface 22, an inner peripheral surface 23, a first side surface 24 a, and a second side surface 24 b. As described above, the positional relationship between the outer peripheral surface 22, the inner peripheral surface 23, the first side surface 24 a, and the second side surface 24 b is the same as the positional relationship between the respective surfaces in the first member 10. The first end surface 26 and the second end surface 27 are disposed facing each other. The first end surface 26 is located in the Z1 direction. The first end surface 26 is located on the opposite side from the first member 10. The second end surface 27 is located in the Z2 direction. The second end surface 27 is located on the first member 10 side. The positional relationship between the first end surface 26 and the second end surface 27 is the same in the third member 30 described below.

[0061] The outer peripheral surface 22 is contiguous with the outer peripheral edge of the first side surface 24a, the outer peripheral edge of the second side surface 24b, the outer peripheral edge of the first end surface 26 (see FIG. 3), and the outer peripheral edge of the second end surface 27 (see FIG. 3). The outer peripheral surface 22 of the second member 20 is contiguous with the outer peripheral surface 12 of the first member 10 (see FIG. 4). The inner peripheral surface 23 is contiguous with the inner peripheral edge of the first side surface 24a, the inner peripheral edge of the second side surface 24b, the inner peripheral edge of the first end surface 26, and the inner peripheral edge of the second end surface 27. The inner peripheral surface 23 of the second member 20 is contiguous with the inner peripheral surface 13 of the first member 10 (see FIG. 4). The first side surface 24a and the second side surface 24b are contiguous with the outer peripheral surface 22 and the inner peripheral surface 23. The first end surface 26 is continuous with the outer peripheral surface 22, the first side surface 24a, the second side surface 24b, and the inner peripheral surface 23. The second end surface 27 is continuous with the outer peripheral surface 22, the first side surface 24a, the second side surface 24b, the inner peripheral surface 23, and the peripheral surface 11 of the first member 10.

[0062] The length between the first side surface 24a and the second side surface 24b on the outer peripheral surface 22 is longer than the length between the first side surface 24a and the second side surface 24b on the inner peripheral surface 23. The length between the first side surface 24a and the second side surface 24b on the outer peripheral surface 22 of the second member 20 is longer than the length between the first side surface 14a and the second side surface 14b on the outer peripheral surface 12 of the first member 10. The length between the first side surface 24a and the second side surface 24b on the inner peripheral surface 23 of the second member 20 is the same as the length between the first side surface 14a and the second side surface 14b on the inner peripheral surface 13 of the first member 10.

[0063] In this embodiment, the outer peripheral surface 22 has a curved surface that is convex in the X2 direction. However, the outer peripheral surface 22 may be configured as a flat surface. In this embodiment, the inner peripheral surface 23 has a curved surface that is convex in the X1 direction. However, the inner peripheral surface 23 may have a curved surface that is convex in the X2 direction, or may be configured as a flat surface. The bending radii of the outer peripheral surface 22 and the inner peripheral surface 23 may be the same or different from each other.

[0064] Each of the first side surface 24a and the second side surface 24b has a first parallel surface 241, a second parallel surface 242, and a first inclined surface 243. The first parallel surfaces 241 of the first side surface 24a and the second side surface 24b are parallel to each other. The second parallel surfaces 242 of the first side surface 24a and the second side surface 24b are parallel to each other. The first parallel surface 241 of the first side surface 24a and the second parallel surface 242 of the first side surface 24a are parallel to each other. The first parallel surface 241 and the second parallel surface 242 are surfaces parallel to the X-axis direction of the core piece 1. The first parallel surface 241 is contiguous with the outer peripheral surface 22. The second parallel surface 242 is contiguous with the inner peripheral surface 23. The first inclined surface 243 is contiguous with the first parallel surface 241 and the second parallel surface 242.

[0065] As shown in FIG. 5 , the first inclination angle θ21 and the second inclination angle θ22 of the first inclined surface 243 are preferably, for example, 5° to 20°. When the first inclination angle θ21 and the second inclination angle θ22 are 5° to 20°, it is easy to arrange the core laminations 1 in an annular shape and to form the stator core 7. The first inclination angle θ21 and the second inclination angle θ22 are preferably 5.5° to 18°, and particularly preferably 6° to 16°. The first inclination angle θ21 and the second inclination angle θ22 are preferably the same angle, but may be different. The first inclination angle θ21 refers to the angle between the first inclined surface 243 and an extension E21 of the first parallel surface 241 on the first side surface 24a. The second inclination angle θ22 refers to the angle between the first inclined surface 243 and an extension E22 of the first parallel surface 241 on the second side surface 24b.

[0066] When the core laminations 1 constitute a stator core 7 for an axial gap type rotating electric machine 9 of DS / SR configuration, a first core lamination 1 and a second core lamination 1 adjacent to each other in the circumferential direction of the stator core 7 are in contact with each other at the first side surface 24a of the second member 20 of the first core lamination 1 and the second side surface 24b of the second member 20 of the second core lamination 1. In this case, the first inclined surface 243 of the first side surface 24a preferably has a portion 244 that protrudes outward from the first imaginary plane V21. The first inclined surface 243 of the second side surface 24b preferably has a portion 244 that protrudes outward from the second imaginary plane V22.

[0067] The first imaginary plane V21 is a plane connecting the first connection point and the second connection point on the first side surface 24a of the first protruding portion 211. The first connection point on the first side surface 24a is a connection point between the first parallel surface 241 and the first inclined surface 243 of the first side surface 24a. The second connection point on the first side surface 24a is a connection point between the second parallel surface 242 of the first side surface 24a and the inner circumferential surface 23. The second imaginary plane V22 is a plane connecting the first connection point and the second connection point on the second side surface 24b of the second protruding portion 212. The first connection point on the second side surface 24b is a connection point between the first parallel surface 241 and the first inclined surface 243 of the second side surface 24b. The second connection point on the second side surface 24b is a connection point between the second parallel surface 242 of the second side surface 24b and the inner circumferential surface 23. The first imaginary plane V21 and the second imaginary plane V22 are indicated in FIG. 5 by two-dot chain lines extending diagonally relative to the paper surface.

[0068] The magnetic path area of ​​the stator core 7 is likely to be increased by the first inclined surface 243 on each of the first side surface 24a and the second side surface 24b having the protruding portion 244. The reason for this is as follows. For example, in the case of core pieces in which the first side surface 24a and the second side surface 24b each have the first parallel surface 241, the second parallel surface 242, and the first inclined surface 243, and the first inclined surface 243 does not have the protruding portion 244, the following occurs. When the core pieces are arranged in an annular shape, if the first side surface 24a of the first core piece and the second side surface 24b of the second core piece that are adjacent in the circumferential direction of the stator core 7 are brought into contact with each other, the first corner of the first core piece and the second corner of the second core piece come into contact with each other. The first corner is the corner between the first side surface 24a and the inner circumferential surface 23. The second corner is the corner between the second side surface 24b and the inner circumferential surface 23. Therefore, the first side surface 24a of the first core piece 1 and the second side surface 24b of the second core piece cannot be in sufficient contact with each other. That is, the contact area between the first side surface 24a of the first core piece 1 and the second side surface 24b of the second core piece is reduced.

[0069] In contrast, the first side surface 24a of the core piece 1 has a first parallel surface 241, a second parallel surface 242, and a first inclined surface 243, and the first inclined surface 243 has a portion 244 that protrudes beyond the first imaginary plane V21. The second side surface 24b of the core piece 1 has a first parallel surface 241, a second parallel surface 242, and a first inclined surface 243, and the first inclined surface 243 has a portion 244 that protrudes beyond the second imaginary plane V22. When the core pieces 1 are arranged in an annular shape, even if the first side surface 24a of the first core piece 1 and the second side surface 24b of the second core piece 1 are brought into contact with each other, the first corner of the first core piece 1 and the second corner of the second core piece 1 can be prevented from coming into contact with each other. Therefore, the first side surface 24a of the first core piece 1 and the second side surface 24b of the second core piece 1 can be brought into sufficient contact with each other. That is, the contact area between the first side surface 24a of the first core lamination 1 and the second side surface 24b of the second core lamination 1 increases.

[0070] When the core laminations 1 constitute a stator core 7 for an axial gap type rotating electric machine 9 of the DS / SR configuration, as described above, the first core laminations 1 and the second core laminations 1 adjacent in the circumferential direction of the stator core 7 contact each other at the first side surface 24a of the second member 20 of the first core laminations 1 and the second side surface 24b of the second member 20 of the second core laminations 1. In this case, it is preferable that the first side surface 24a and the second side surface 24b of the core laminations 1 have a step 240 that allows them to fit together, as shown in FIG. 3 . This makes it easier to increase the magnetic path area of ​​the stator core 7. The first core laminations 1 and the second core laminations 1 adjacent in the circumferential direction of the stator core 7 fit together at the step 240 of the first side surface 24a of the first protruding portion 211 of the second member 20 of the first core laminations 1 and the step 240 of the second side surface 24b of the second protruding portion 212 of the second member 20 of the second core laminations 1. Therefore, the first core laminations 1 and the second core laminations 1 can be brought into sufficient contact with each other, thereby increasing the contact area between adjacent core laminations 1 in the circumferential direction of the stator core 7. The step 240 of the first side surface 24a is provided on the first end face 26 side. The step 240 of the first side surface 24a is configured to become farther away from the first side surface 14a of the first member 10 as it moves from the first end face 26 to the second end face 27. On the other hand, the step 240 of the second side surface 24b is provided on the second end face 27 side. The step 240 of the second side surface 24b is configured to become farther away from the second side surface 14b of the first member 10 as it moves from the second end face 27 to the first end face 26.

[0071] Although not shown, the first side surface 24a of the core lamination 1 may have at least one of a recess and a protrusion, rather than a step. The second side surface 24b may have at least one of a protrusion corresponding to the recess of the first side surface 24a and a recess corresponding to the protrusion of the first side surface 24a. That is, both the first side surface 24a and the second side surface 24b may have unevenness. Alternatively, one of the first side surface 24a and the second side surface 24b may have only a recess, and the other side surface may have only a protrusion. The number and shape of the recesses and protrusions are not particularly limited.

[0072] Although not shown, each of the first side surface 24a and the second side surface 24b of the core piece 1 may have a second inclined surface in contact with each other, rather than a step or unevenness. For example, the second inclined surface of the first side surface 24a may be inclined outward from the first end surface 26 toward the second end surface 27. The second inclined surface of the second side surface 24b may be inclined outward from the second end surface 27 toward the first end surface 26.

[0073] When the core pieces 1 constitute a stator core 7 for an axial gap type rotating electric machine 9 of SS / DR configuration, the core pieces 1 are arranged in an annular shape without contacting each other. In this case, each of the first side surface 24a and the second side surface 24b does not need to have any of the step 240, recessed portion, protruding portion, or second inclined surface that can fit together with each other.

[0074] The corners between the first side surface 24a and the first end surface 26 and the corners between the first side surface 24a and the second end surface 27 are rounded. The corners between the second side surface 24b and the first end surface 26 and the corners between the second side surface 24b and the second end surface 27 are rounded.

[0075] When the core laminations 1 form a stator core 7 for an axial gap rotating electric machine 9 of a DS / SR configuration, the first end surface 26 is formed, for example, as a flat surface. When the core laminations 1 form a stator core 7 for an axial gap rotating electric machine 9 of a SS / DR configuration, the first end surface 26 may be formed as a flat surface or as a convex surface facing the Z1 direction. Such core laminations 1 can form an axial gap rotating electric machine 9 with low noise and vibration. The reason for this is as follows. In an axial gap rotating electric machine 9 of a SS / DR configuration, a stator 8 and a rotor 90 are arranged facing each other as shown in FIG. 19 . The stator 8 includes a stator core 7 and a coil 80 as shown in FIG. 17 . The stator core 7 is formed by arranging multiple core laminations 1 in an annular shape as shown in FIG. 16 . The coil 80 is arranged on the first member 10 (see FIG. 1 ) of each core lamination 1 as shown in FIG. 17 . If the first end surface 26 of the second member 20 of the core lamination 1 is formed in a convex shape, in the axial gap type rotating electric machine 9 shown in Fig. 19, a sudden change in the magnetic flux of the magnet 95 of the rotor 90 that is received by the core lamination 1 is easily suppressed. Therefore, the cogging torque is easily reduced. The small cogging torque makes it difficult for noise and vibration to increase.

[0076] It is preferable that the corners between the first end face 26 and the inner peripheral surface 23 and the corners between the first end face 26 and the outer peripheral surface 22 are chamfered. These chamfered corners are less likely to be damaged. These chamfers may be C-chamfered or R-chamfered.

[0077] 1 and 3 , the third member 30 is a plate-shaped member provided at a second end in the Z-axis direction of the first member 10. The third member 30 forms a flange portion in either case where the core laminations 1 form the stator core 7 for the axial gap type rotating electric machine 9 of the DS / SR configuration or where the core laminations 1 form the stator core 7 for the axial gap type rotating electric machine 9 of the SS / DR configuration.

[0078] In this embodiment, the third member 30 has a trapezoidal plate shape. The trapezoidal plate shape is a trapezoidal cross section obtained by cutting the third member 30 along a plane perpendicular to the Z-axis direction. The cross section may or may not be uniform in the Z-axis direction. The third member 30 may also have a rectangular plate shape. For example, in the core piece 1, the first member 10 may have a trapezoidal columnar shape, and at least one of the second member 20 and the third member 30 may have a rectangular plate shape.

[0079] As shown in FIGS. 1 to 3 , the third member 30 has a protruding portion 31. The protruding portion 31 protrudes outward from the circumferential surface 11 of the first member 10. The protruding portion 31 may protrude outward from the circumferential surface 11 of the first member 10 in a portion of the circumferential surface 11 of the first member 10, or may protrude outward from the circumferential surface 11 of the first member 10 over the entire circumferential circumference of the first member 10. In this embodiment, the protruding portion 31 has a first protruding portion 311 and a second protruding portion 312. The first protruding portion 311 protrudes in a first direction in the circumferential direction of the stator core 7. The second protruding portion 312 protrudes in a second direction in the circumferential direction of the stator core 7. Note that the protruding portion 31 may not have the first protruding portion 311 or the second protruding portion 312, and may have at least one of a portion protruding in the X1 direction and a portion protruding in the X2 direction. The protruding portion 31 may have a portion that protrudes in the X1 direction and a portion that protrudes in the X2 direction, in addition to the first protruding portion 311 and the second protruding portion 312. In this case, the protruding portion 31 is provided in an annular shape along the circumferential direction of the first member 10.

[0080] As described above, when the core laminations 1 configure the stator core 7 for the axial gap type rotating electric machine 9 of the DS / SR configuration, the protruding length of the first protruding portion 311 and the second protruding portion 312 of the third member 30 is shorter than the protruding length of the first protruding portion 211 and the second protruding portion 212 of the second member 20. As described above, when the core laminations 1 configure the stator core 7 for the axial gap type rotating electric machine 9 of the SS / DR configuration, the protruding length of the first protruding portion 311 and the second protruding portion 212 of the third member 30 may be the same as the protruding length of the first protruding portion 211 and the second protruding portion 212 of the second member 20.

[0081] As shown in Fig. 3, the third member 30 has a first end surface 36 and a second end surface 37. As shown in Fig. 6, the third member 30 has an outer peripheral surface 32, an inner peripheral surface 33, a first side surface 34a, and a second side surface 34b. As described above, the positional relationship between the outer peripheral surface 32, the inner peripheral surface 33, the first side surface 34a, and the second side surface 34b is the same as the positional relationship between the respective surfaces in the first member 10. As described above, the positional relationship between the first end surface 36 and the second end surface 37 is the same as the positional relationship between the respective surfaces in the second member 20.

[0082] The outer peripheral surface 32 is contiguous with the outer peripheral edge of the first side surface 34a, the outer peripheral edge of the second side surface 34b, the outer peripheral edge of the first end surface 36 (see FIG. 3), and the outer peripheral edge of the second end surface 37 (see FIG. 3). The outer peripheral surface 32 of the third member 30 is contiguous with the outer peripheral surface 12 of the first member 10 (see FIG. 4). The inner peripheral surface 33 is contiguous with the inner peripheral edge of the first side surface 34a, the inner peripheral edge of the second side surface 34b, the inner peripheral edge of the first end surface 36, and the inner peripheral edge of the second end surface 37. The inner peripheral surface 33 of the third member 30 is contiguous with the inner peripheral surface 13 of the first member 10 (see FIG. 4). The first side surface 34a and the second side surface 34b are contiguous with the outer peripheral surface 32 and the inner peripheral surface 33. The first end surface 36 is continuous with the outer peripheral surface 32, the first side surface 34a, the second side surface 34b, and the inner peripheral surface 33. The second end surface 37 is continuous with the outer peripheral surface 32, the first side surface 34a, the second side surface 34b, the inner peripheral surface 33, and the peripheral surface 11 of the first member 10.

[0083] The length between the first side surface 34a and the second side surface 34b at the outer peripheral surface 32 is longer than the length between the first side surface 34a and the second side surface 34b at the inner peripheral surface 33. The length between the first side surface 34a and the second side surface 34b at the outer peripheral surface 32 of the third member 30 is longer than the length between the first side surface 14a and the second side surface 14b at the outer peripheral surface 12 of the first member 10. The length between the first side surface 34a and the second side surface 34b at the outer peripheral surface 32 of the third member 30 is shorter than the length between the first side surface 24a and the second side surface 24b at the outer peripheral surface 22 of the second member 20. The length between the first side surface 34a and the second side surface 34b at the inner peripheral surface 33 of the third member 30 is the same as the length between the first side surface 14a and the second side surface 14b at the inner peripheral surface 13 of the first member 10. That is, the length between the first side surface 14a and the second side surface 14b on the inner surface 13 of the first member 10, the length between the first side surface 24a and the second side surface 24b on the inner surface 23 of the second member 20, and the length between the first side surface 34a and the second side surface 34b on the inner surface 33 of the third member 30 are all identical to each other.

[0084] In this embodiment, the outer peripheral surface 32 has a curved surface that is convex in the X2 direction. However, the outer peripheral surface 32 may be configured as a flat surface. In this embodiment, the inner peripheral surface 33 has a curved surface that is convex in the X1 direction. However, the inner peripheral surface 33 may have a curved surface that is convex in the X2 direction, or may be configured as a flat surface. The bending radii of the outer peripheral surface 32 and the inner peripheral surface 33 may be the same or different from each other.

[0085] The bend radii of at least two of the outer peripheral surfaces 12, 22, and 32 may be the same. Of course, the bend radii of the outer peripheral surfaces 12, 22, and 32 may all be the same. The bend radii of the outer peripheral surfaces 12, 22, and 32 may all be different. The bend radii of the inner peripheral surfaces 13, 23, and 33 may at least be the same. Of course, the bend radii of the inner peripheral surfaces 13, 23, and 33 may all be the same. The bend radii of the inner peripheral surfaces 13, 23, and 33 may all be different.

[0086] Each of the first side surface 34a and the second side surface 34b has a first parallel surface 341, a second parallel surface 342, and a first inclined surface 343. The first parallel surfaces 341 of the first side surface 34a and the second side surface 34b are parallel to each other. The second parallel surfaces 342 of the first side surface 34a and the second side surface 34b are parallel to each other. The first parallel surface 341 of the first side surface 34a and the second parallel surface 342 of the first side surface 34a are parallel to each other. The first parallel surface 341 and the second parallel surface 342 are surfaces parallel to the X-axis direction of the core piece 1. The first parallel surface 341 is contiguous with the outer peripheral surface 32. The second parallel surface 342 is contiguous with the inner peripheral surface 33. The first inclined surface 343 is contiguous with the first parallel surface 341 and the second parallel surface 342.

[0087] As shown in FIG. 6 , the first inclination angle θ31 and the second inclination angle θ32 of the first inclined surface 343 are preferably, for example, 5° or greater and 20° or less. When the first inclination angle θ31 and the second inclination angle θ32 are 5° or greater and 20° or less, density variation of the core pieces 1 can be suppressed. The first inclination angle θ31 and the second inclination angle θ32 are preferably 5.5° or greater and 18° or less, and particularly preferably 6° or greater and 16° or less. The first inclination angle θ31 and the second inclination angle θ32 are preferably the same angle, but may be different. The first inclination angle θ31 refers to the angle between the first inclined surface 343 and an extension E31 of the first parallel surface 341 on the first side surface 34a. The second inclination angle θ32 refers to the angle between the first inclined surface 343 and an extension E32 of the first parallel surface 341 on the second side surface 34b.

[0088] At least two of the first inclination angles θ11, θ21, and θ31 may be the same. At least two of the second inclination angles θ12, θ22, and θ32 may be the same. Of course, the first inclination angles θ11, θ21, and θ31 may all be the same. The second inclination angles θ12, θ22, and θ32 may all be the same. Note that the first inclination angles θ11, θ21, and θ31 may all be different. The second inclination angles θ12, θ22, and θ32 may all be different.

[0089] The corners between the first side surface 34a and the first end surface 36 and the corners between the first side surface 34a and the second end surface 37 are rounded. The corners between the second side surface 34b and the first end surface 36 and the corners between the second side surface 34b and the second end surface 37 are rounded.

[0090] The first end surface 36 may be flat as shown in FIG. 3 or convex toward the Z2 direction, regardless of whether the core laminations 1 are used to form the stator core 7 for an axial gap rotating electric machine 9 of a DS / SR configuration or an axial gap rotating electric machine 9 of a SS / DR configuration. A convex first end surface 36 can provide an axial gap rotating electric machine 9 with reduced noise and vibration. The reason for this is as follows. In an axial gap rotating electric machine 9, a stator 8 and a rotor 90 are arranged facing each other, as shown in FIG. 18 or 19 . The stator 8 includes a stator core 7 and a coil 80, as shown in FIG. 17 . The stator core 7 is formed by arranging a plurality of core laminations 1 in an annular shape, as shown in FIG. 16 . The coil 80 is disposed on the first member 10 of each core lamination 1, as shown in FIG. 17 . In the axial gap type rotating electric machine 9 shown in Figures 18 and 19, the first end face 36 of the third member 30 of the core lamination 1 is provided in a convex shape, which tends to suppress sudden changes in the magnetic flux of the magnet 95 of the rotor 90 that is received by the core lamination 1. This tends to reduce cogging torque. The small cogging torque also tends to prevent increases in noise and vibration.

[0091] It is preferable that the corners between the first end face 36 and the inner peripheral surface 33 and the corners between the first end face 36 and the outer peripheral surface 32 are chamfered. These chamfered corners are less likely to be damaged. These chamfers may be C-chamfered or R-chamfered.

[0092] [Seams] As shown in FIG. 3 , a first seam between the second end surface 27 of the protruding portion 21 of the second member 20 and the circumferential surface 11 of the first member 10, and a second seam between the second end surface 37 of the protruding portion 31 of the third member 30 and the circumferential surface 11 of the first member 10, are rounded. In this embodiment, the first seam includes the seam between the first protruding portion 211 of the second member 20 and the circumferential surface 11 of the first member 10, and the seam between the second protruding portion 212 of the second member 20 and the circumferential surface 11 of the first member 10. These seams are rounded. The second seam includes the seam between the first protruding portion 311 of the third member 30 and the circumferential surface 11 of the first member 10, and the seam between the second protruding portion 312 of the third member 30 and the circumferential surface 11 of the first member 10. These seams are rounded. Since each joint has a rounded shape, the core piece 1 is less likely to be damaged starting from the joint.

[0093] The bending radius of the first joint and the second joint is preferably 0.2 mm or more and 4.0 mm or less. When the bending radius of the first joint and the second joint is 0.2 mm or more, the load on the mold during manufacturing of the core laminations 1 is reduced. When the bending radius of the first joint and the second joint is 4.0 mm or less, it is easy to wind the coil 80 when constructing the stator 8 described later with reference to FIG. 17 , and therefore it is easy to increase the number of turns of the coil 80. The bending radius of the first joint and the second joint is further preferably 0.3 mm or more and 3.0 mm or less, and particularly preferably 0.5 mm or more and 2.0 mm or less. The bending radius of the first joint and the second joint may be the same or different from each other.

[0094] [Area Ratio] The total area of ​​the outer peripheral surfaces 12, 22, and 32 of each of the first member 10, the second member 20, and the third member 30 is preferably more than 1 time and not more than 4 times the total area of ​​the inner peripheral surfaces 13, 23, and 33 of each of the first member 10, the second member 20, and the third member 30. Core pieces 1 whose total area of ​​the outer peripheral surfaces 12, 22, and 32 is more than 1 time the total area of ​​the inner peripheral surfaces 13, 23, and 33 are easy to arrange in an annular shape and to form the stator core 7. Core pieces 1 whose total area of ​​the outer peripheral surfaces 12, 22, and 32 is not more than 4 times the total area of ​​the inner peripheral surfaces 13, 23, and 33 are easy to manufacture. Because the ratio of the total area of ​​the inner peripheral surfaces 13, 23, and 33 is relatively large, the area extruded by the lower punch 55 is large when the core pieces 1 are extracted from the mold 5. Therefore, damage to the core pieces 1 when they are extracted from the mold 5 is easily suppressed. The total area of ​​the outer peripheral surfaces 12, 22, 32 is preferably 1.2 to 3.8 times the total area of ​​the inner peripheral surfaces 13, 23, 33, and more preferably 1.5 to 3.5 times.

[0095] The core piece 1 of this embodiment is composed of a powder compact in which the first member 10, the second member 20, and the third member 30 are integrally molded. "Integratedly molded" means that the first member 10, the second member 20, and the third member 30 are formed continuously by molding, without, for example, mechanical connection using screws or bonding with an adhesive. The powder compact contains a plurality of soft magnetic particles. The powder compact is composed of an aggregate of soft magnetic particles. The powder compact is obtained by compression molding soft magnetic powder containing a plurality of soft magnetic particles. The soft magnetic particles are iron-based particles made of pure iron or an iron-based alloy. Pure iron refers to iron (Fe) with a purity of 99% by mass or more. The iron-based alloy contains at least one element of Si (silicon) and Al (aluminum), with the remainder being Fe and unavoidable impurities. The iron-based alloy is, for example, at least one selected from the group consisting of an Fe-Si based alloy, an Fe-Al based alloy, and an Fe-Si-Al based alloy. An example of an Fe-Si alloy is silicon steel. An example of an Fe-Si-Al alloy is sendust. Because the above materials are relatively soft, the soft magnetic particles are easily deformed during the formation of the powder compact. As a result, the core piece 1 has high density and excellent dimensional accuracy. The powder compact is preferably composed of an aggregate of multiple coated soft magnetic particles having an insulating coating on the surface of the soft magnetic particles. In other words, the powder compact is preferably formed by compression molding of coated soft magnetic powder having multiple coated soft magnetic particles. If an insulating coating is formed, the insulating coating easily ensures electrical insulation between particles. Therefore, the iron loss of the powder compact caused by eddy current loss can be reduced. The soft magnetic particles are as described above. Examples of insulating coatings include phosphate coatings and silica coatings.

[0096] [Relative Density] The relative density of the powder compact is preferably 85% or more. A powder compact with a relative density of 85% or more is excellent in magnetic properties such as saturation magnetic flux density, and mechanical properties such as strength. The relative density of the powder compact is more preferably 90% or more, and particularly preferably 93% or more. The relative density of the powder compact may be less than 100%. "Relative density" refers to the ratio (%) of the actual density of the powder compact to the true density of the soft magnetic particles that make up the powder compact.

[0097] [Relative Density Difference] Of the first, second, and third portions of the core lamination 1, the difference in relative density between the first and second portions and the third portion is preferably 5.0% or less. Because the difference in relative density is small, the core lamination 1 has substantially uniform physical properties, such as magnetic properties, within the core lamination 1. The smaller the difference in relative density between the first and second portions and the third portion, the more preferable. The difference in relative density between the first and second portions and the third portion is more preferably 4.0% or less, and particularly preferably 3.0% or less. Here, as shown in FIG. 2 , the core lamination 1 is divided into three portions by an imaginary plane Va along the second parallel surface 142 of the first side surface 14a (see FIG. 4) and an imaginary plane Vb along the second parallel surface 142 of the second side surface 14b (see FIG. 4). The portion located in the first circumferential direction is referred to as the first portion, the portion located in the second circumferential direction is referred to as the second portion, and the portion located between the first and second portions is referred to as the third portion.

[0098] Among the first member 10, the second member 20, and the third member 30, the difference in relative density between the member with the highest relative density and the member with the lowest relative density is preferably 5.0% or less. Because the difference in relative density is small, the physical properties, such as magnetic properties, of this core piece 1 are substantially uniform within the core piece 1. The smaller the difference in relative density between the member with the highest relative density and the member with the lowest relative density, the more preferable. The difference in relative density between the member with the highest relative density and the member with the lowest relative density is more preferably 4.0% or less, and particularly preferably 3.0% or less.

[0099] It is preferable that the difference in relative density between the first and second regions and the third region is 5.0% or less, and that the difference in relative density between the member with the highest relative density and the member with the lowest relative density is 5.0% or less.

[0100] [Manufacturing Method] The core piece 1 according to the first embodiment can be manufactured by a core piece manufacturing method including a filling step and a molding step. In the filling step, raw material powder is filled into the cavity of a die 5. In the molding step, the raw material powder in the cavity is compression molded. First, the die 5 will be described with reference to Figs. 10 to 13, and then each step will be described.

[0101] [Mold] The mold 5 includes a die 50, an upper punch 54, and a lower punch 55. The die 50 and the lower punch 55 form a cavity into which the raw material powder is filled.

[0102] (Die) The die 50 has a mold hole 50h. An upper punch 54 and a lower punch 55 are arranged in the mold hole 50h so as to face each other. The inner peripheral shape of the mold hole 50h corresponds to the shape of the core piece 1. The upper punch 54 can be driven independently in the vertical direction relative to the die 50. The lower punch 55 can be driven independently in the vertical direction relative to the die 50.

[0103] The mold cavity 50h has a first hole 51 shown in FIGS. 10 and 11, a second hole 52 shown in FIGS. 10 and 12, and a third hole 53 shown in FIGS. 10 and 13. FIG. 10 shows the opening edge of the mold cavity 50h of the die 50 on the upper punch 54 side. For ease of explanation, the die 50 is hatched in FIG. 10. FIGS. 11 to 13 are cross-sectional views showing the state in which the raw material powder filled in the cavity is pressure-molded by the upper punch 54 and the lower punch 55. The cut position of the cross-sectional view in FIG. 11 corresponds to the position indicated by the XI-XI cutting line in FIG. 10. The cut position of the cross-sectional view in FIG. 12 corresponds to the position indicated by the XII-XII cutting line in FIG. 10. The cut position of the cross-sectional view in FIG. 13 corresponds to the position indicated by the XIII-XIII cutting line in FIG. 10.

[0104] The first hole portion 51 has an inner peripheral surface that forms the first side surface 14a and the second side surface 14b of the first member 10. The second hole portion 52 has an inner peripheral surface that forms the first side surface 24a, the second side surface 24b, the first end surface 26, and the second end surface 27 of the second member 20. The third hole portion 53 has an inner peripheral surface that forms the first side surface 34a, the second side surface 34b, the first end surface 36, and the second end surface 37 of the third member 30. The first hole portion 51, the second hole portion 52, and the third hole portion 53 are formed continuously in a direction perpendicular to the direction in which the upper punch 54 and the lower punch 55 face each other. Specifically, the second hole portion 52 is connected to a first end side of the first hole portion 51 in the perpendicular direction. The third hole portion 53 is connected to a second end side of the first hole portion 51 in the perpendicular direction.

[0105] The first hole portion 51 includes a first straight portion 511, a second straight portion 512, and a tapered portion 513. The first straight portion 511, the tapered portion 513, and the second straight portion 512 are formed in a continuous sequence from the upper side where the upper punch 54 is inserted toward the lower side where the lower punch 55 is inserted. Similarly, the second hole portion 52 includes a first straight portion 521, a second straight portion 522, and a tapered portion 523. The first straight portion 521, the tapered portion 523, and the second straight portion 522 are formed in a continuous sequence from the upper side where the upper punch 54 is inserted toward the lower side where the lower punch 55 is inserted. Similarly, the third hole portion 53 includes a first straight portion 531, a second straight portion 532, and a tapered portion 533. The first straight portion 531, the tapered portion 533, and the second straight portion 532 are formed in a continuous sequence from the upper side where the upper punch 54 is inserted toward the lower side where the lower punch 55 is inserted. The first straight portions 511, 521, 531 form the portions near the outer peripheral surface of the core piece 1. The second straight portions 512, 522, 532 form the portions near the inner peripheral surface of the core piece 1. The tapered portions 513, 523, 533 form the portions between the outer peripheral surface and the inner peripheral surface of the core piece 1.

[0106] When forming a plurality of grooves 40 on the first side surface 14 a or the second side surface 14 b of the first member 10 , it is sufficient to provide the inner peripheral surface of the first hole portion 51 with irregularities corresponding to the plurality of grooves 40 .

[0107] (Upper Punch) The upper punch 54 has a first upper punch portion 541 shown in FIG. 11 , a second upper punch portion 542 shown in FIG. 12 , and a third upper punch portion 543 shown in FIG. 13 . The first upper punch portion 541 has a first lower end surface 541 e. The first lower end surface 541 e forms the outer peripheral surface 12 of the first member 10. The second upper punch portion 542 has a second lower end surface 542 e. The second lower end surface 542 e forms the outer peripheral surface 22 of the second member 20. The third upper punch portion 543 has a third lower end surface 543 e. The third lower end surface 543 e forms the outer peripheral surface 32 of the third member 30. The first upper punch portion 541, the second upper punch portion 542, and the third upper punch portion 543 may be formed in a continuous manner, or may be formed independently of each other so as to be able to move up and down independently. When the first upper punch portion 541, the second upper punch portion 542, and the third upper punch portion 543 are formed continuously, the first lower end surface 541e, the second lower end surface 542e, and the third lower end surface 543e are formed continuously. The shape of the first lower end surface 541e corresponds to the shape of the outer peripheral surface 12 of the first member 10. The shape of the second lower end surface 542e corresponds to the shape of the outer peripheral surface 22 of the second member 20. The shape of the third lower end surface 543e corresponds to the shape of the outer peripheral surface 32 of the third member 30.

[0108] When forming multiple grooves 40 on the outer peripheral surface 12 of the first member 10 as shown in Figure 9, it is sufficient to provide unevenness corresponding to the multiple grooves 40 on the first lower end surface 541e of the first upper punch portion 541.

[0109] (Lower Punch) The lower punch 55 has a first lower punch portion 551 shown in FIG. 11 , a second lower punch portion 552 shown in FIG. 12 , and a third lower punch portion 553 shown in FIG. 13 . The first lower punch portion 551 has a first upper end surface 551 e. The first upper end surface 551 e forms the inner circumferential surface 13 of the first member 10. The second lower punch portion 552 has a second upper end surface 552 e. The second upper end surface 552 e forms the inner circumferential surface 23 of the second member 20. The third lower punch portion 553 has a third upper end surface 553 e. The third upper end surface 553 e forms the inner circumferential surface 33 of the third member 30. The first lower punch portion 551, the second lower punch portion 552, and the third lower punch portion 553 may be formed in a continuous manner, or may be formed independently of each other so as to be able to move up and down independently. When the first lower punch portion 551, the second lower punch portion 552, and the third lower punch portion 553 are formed continuously, the first upper end surface 551e, the second upper end surface 552e, and the third upper end surface 553e are formed continuously. The shape of the first upper end surface 551e corresponds to the shape of the inner circumferential surface 13 of the first member 10. The shape of the second upper end surface 552e corresponds to the shape of the inner circumferential surface 23 of the second member 20. The shape of the third upper end surface 553e corresponds to the shape of the inner circumferential surface 33 of the third member 30.

[0110] When forming multiple grooves 40 on the inner peripheral surface 13 of the first member 10 as shown in Figure 1, it is sufficient to provide unevenness corresponding to the multiple grooves 40 on the first upper end surface 551e of the first lower punch portion 551.

[0111] [Filling Step] Raw material powder is filled into the cavity formed by the die 50 and the lower punch 55. The raw material powder may be the soft magnetic powder or coated soft magnetic powder described above. In addition to the soft magnetic powder or coated soft magnetic powder, the raw material powder may also contain a binder and a lubricant. A lubricant may be applied to the inner peripheral surface of the die hole 50h of the die 50.

[0112] [Forming step] The raw material powder in the cavity is compression-molded by the upper punch 54 and the lower punch 55. The direction in which the raw material powder is compressed is along the radial direction of the stator core 7. The higher the pressure during compression molding, the higher the relative density of the core pieces 1 produced. The pressure is preferably, for example, 700 MPa or more, and more preferably 980 MPa or more.

[0113] [Other Steps] After the molding step, a heat treatment may be performed as needed. For example, by removing distortion by the heat treatment, a low-loss core piece 1 can be manufactured. Alternatively, for example, the binder or lubricant may be removed by the heat treatment. When the raw material powder contains the coated soft magnetic particles described above, the heat treatment temperature is preferably equal to or lower than the decomposition temperature of the insulating coating.

[0114] The core lamination 1 of this embodiment can suppress a temperature rise in the coil 80. The core lamination 1 has a plurality of grooves 40 on the circumferential surface 11 of the first member 10. The winding 81 is arranged so as to fit into each groove 40. The increased contact area between the winding 81 and the first member 10 improves heat dissipation from the winding 81 to the first member 10. The coil 80 is effectively cooled. Furthermore, when the winding 81 is wound around the first member 10, the winding 81 is held in each groove 40, which prevents the winding 81 from becoming unbalanced. The winding 81 is wound uniformly along the grooves 40, which improves the space factor of the coil 80. The improved space factor of the coil 80 allows the axial gap type rotating electric machine 9 to be made smaller and have higher output.

[0115] <<Modification>> The core piece 1 of this embodiment may have a groove 61 or a step 62 in which the winding start end 81s of the winding 81 is disposed, in the protruding portion 21 of the second member 20 or the protruding portion 31 of the third member 30, as shown in FIG. 14 or FIG. 15 .

[0116] <<Modification 1>> In Modification 1, an example in which the protruding portion 21 of the second member 20 has a groove 61 will be described with reference to Fig. 14 . In this example, the groove 61 is provided in the second end surface 27 (see Fig. 3 ) of the first protruding portion 211. The groove 61 extends from the outer peripheral surface 22 of the first protruding portion 211 along the outer peripheral surface 11 of the first member 10. The groove 61 opens to the outer peripheral surface 22. The winding 81 passes through this groove 61 and is wound around the outer peripheral surface 11. The size of the groove 61 only needs to be large enough to accommodate the winding start end 81s. The width and depth of the groove 61 only need to be equal to or greater than the diameter of the winding 81.

[0117] <<Modification 2>> In Modification 2, an example in which the protruding portion 21 of the second member 20 has a step 62 will be described with reference to Fig. 15 . In this example, the protruding portion 21 has a third protruding portion 213 in addition to a first protruding portion 211 and a second protruding portion 212. The third protruding portion 213 protrudes in the X2 direction. The step 62 is provided on the third protruding portion 213. The step 62 is recessed in the Z1 direction with respect to the first protruding portion 211 and the second protruding portion 212. The winding 81 is wound around the circumferential surface 11 from the step 62. The distance in the Z-axis direction between the first protruding portion 211 and the second protruding portion 212 and the step 62 may be equal to or greater than the diameter of the winding 81.

[0118] By arranging the winding start end 81s of the winding 81 in the groove 61 or step 62 described above, it is possible to prevent the second and subsequent layers of the winding 81 from interfering with the winding start end 81s when winding the winding 81 in multiple layers. Therefore, the winding 81 can be wound by one more turn compared to a core piece without the groove 61 or step 62.

[0119] <<Embodiment 2>> [Stator Core] A stator core 7 according to embodiment 2 will be described with reference to FIG. 16 . The stator core 7 of this embodiment has a plurality of core laminations 1 arranged in an annular shape. Each of the plurality of core laminations 1 is the core lamination 1 according to embodiment 1. The plurality of core laminations 1 are combined in an annular shape such that, among circumferentially adjacent core laminations 1, the step 240 on the first side surface 24 a of the second member 20 of a first core lamination 1 and the step 240 on the second side surface 24 b of the second member 20 of a second core lamination 1 fit together. This stator core 7 is used in an axial gap type rotating electric machine 9 of a DS / SR configuration shown in FIG. 18 .

[0120] It is preferable that the variation in the length between the first end surface and the second end surface in the Z-axis direction of each of the multiple core pieces 1 is 0.1 mm or less. The length between the first end surface and the second end surface in the Z-axis direction is the maximum length between the first end surface 26 of the second member 20 and the first end surface 36 of the third member 30.

[0121] If the variation in length between the first end face 26 of the second member 20 and the first end face 36 of the third member 30 in each of the multiple core laminations 1 is 0.1 mm or less, the variation in length is very small. Therefore, the stator core 7 can constitute an axial gap type rotating electric machine 9 with low noise and vibration. The reason for this is as follows. In the axial gap type rotating electric machine 9, the stator 8 and the rotor 90 are arranged facing each other, as shown in FIG. 18 . The small variation in the length of the stator core 7 reduces the variation in the gap between the stator 8 and the rotor 90. The small variation in the gap reduces torque ripple. The small torque ripple makes it difficult for noise and vibration to increase. The variation in length is determined as follows. For each core lamination 1, the length from the first end face 26 of the second member 20 to the first end face 36 of the third member 30 is measured. This length is the maximum length of the core lamination 1 along the Z-axis direction. The difference between the maximum and minimum values ​​of the length for each of the plurality of core pieces 1 is calculated. This difference is defined as the variation in the length. The variation in the length between the first end face 26 of the second member 20 and the first end face 36 of the third member 30 for each of the plurality of core pieces 1 is preferably 0.05 mm or less, and particularly preferably 0.01 mm or less.

[0122] In the stator core 7 of this embodiment, the plurality of core laminations 1 constituting the stator core 7 are each formed of the core laminations 1 of the first embodiment, and therefore, the temperature rise of the coils 80 can be suppressed.

[0123] Third Embodiment [Stator] A stator 8 according to a third embodiment will be described with reference to Fig. 17 . The stator 8 of this embodiment includes a stator core 7 and a coil 80. The stator core 7 according to the second embodiment can be used as the stator core 7. The coil 80 is wound around the first member 10 of each core lamination 1 of the stator core 7. This stator 8 is used in an axial gap type rotating electric machine 9 of a DS / SR configuration shown in Fig. 18 .

[0124] Each coil 80 has a cylindrical portion formed by winding a wire. Note that Fig. 17 shows only the cylindrical portion of each coil 80 in a simplified manner, and both ends of the wire are not shown. The stator core 7 can be produced by winding a wire around the first member 10 of each core lamination 1.

[0125] The stator 8 according to the third embodiment includes the stator core 7 according to the second embodiment, and therefore, the temperature rise of the coil 80 can be suppressed.

[0126] Fourth Embodiment [Rotating Electric Machine] A rotating electric machine 9 according to a fourth embodiment will be described with reference to FIG. 18 . FIG. 18 is a cross-sectional view taken along a plane parallel to the rotation axis 91 of the rotating electric machine 9 and passing through the center of the stator 8. This also applies to FIG. 19 , which will be referred to in a fifth embodiment described later. The rotating electric machine 9 according to this embodiment is an axial gap type rotating electric machine. The rotating electric machine 9 according to this embodiment is a DS / SR type including one rotor 90 and two stators 8. In the rotating electric machine 9, the rotor 90 and the stators 8 are arranged axially opposite each other. The one rotor 90 is assembled so as to be sandwiched between the two stators 8. The stator 8 according to the third embodiment described above can be used for each stator 8. The rotating electric machine 9 can be used as a motor or a generator. The rotating electric machine 9 includes a case 92.

[0127] The case 92 has a cylindrical internal space that houses the stator 8 and the rotor 90. The case 92 includes a cylindrical portion 921 and two plates 922. The cylindrical portion 921 surrounds the outer peripheries of the stator 8 and the rotor 90. A plate 922 is disposed on each end of the cylindrical portion 921. The two plates 922 are fixed to both end surfaces of the cylindrical portion 921 so as to sandwich the stator 8 and the rotor 90 from both sides in the axial direction. Both plates 922 have a through hole in their center. A bearing 93 is provided in the through hole. The rotating shaft 91 is inserted into the through hole via this bearing 93. The rotating shaft 91 passes through the case 92.

[0128] The rotor 90 includes a magnet 95 and a rotor body. In this embodiment, the rotor 90 is a flat-plate-shaped member. The number of magnets 95 may be multiple, as in this embodiment, or may be one, unlike this embodiment. When the number of magnets 95 is multiple, the specific number of magnets 95 may be the same as the number of core pieces 1. The multiple magnets 95 are arranged at equal intervals around the circumferential direction of the rotor body. In this embodiment, each magnet 95 is flat and has a planar shape corresponding to the planar shape of the first end surface 36 of the third member 30 in each core piece 1. Note that each magnet 95 may be a convex lens shape having a convex surface facing each stator 8. When there is only one magnet 95, the magnet 95 has an annular shape. In each magnet 95, south and north poles are arranged alternately around the circumferential direction. The rotor body supports the multiple magnets 95. The rotor body is an annular-shaped member. The rotor body is rotatably supported by a rotating shaft 91. The magnets 95 are arranged at equal intervals around the circumferential direction of the rotor body. Each magnet 95 is magnetized in a direction along the axis of the rotating shaft 91. The magnetization directions of adjacent magnets 95 around the circumferential direction of the rotor body are opposite to each other. The rotating magnetic field generated by the stator 8 causes the magnets 95 to repeatedly attract and repel each core piece 1, causing the rotor 90 to rotate.

[0129] The stator 8 is arranged so that the first end face 36 of the third member 30 in each core lamination 1 faces the magnet 95 of the rotor 90. When the rotor 90 rotates, the first end face 36 of the third member 30 in each core lamination 1 receives magnetic flux from the rotating magnet 95. If the first end face 36 of the third member 30 in each core lamination 1 is configured in a convex shape as described above, as shown in FIG. 3 , noise and vibration of the rotating electric machine 9 can be reduced. The reason for this is as follows. By providing the first end face 36 of the third member 30 in each core lamination 1 in a convex shape, sudden changes in the magnetic flux of the magnet 95 of the rotor 90 received by each core lamination 1 are easily suppressed. Therefore, cogging torque is easily reduced. The small cogging torque makes it less likely that noise and vibration will increase.

[0130] The rotating electric machine 9 according to the fourth embodiment includes the stator 8 according to the third embodiment, and therefore can suppress the temperature rise of the coil 80 .

[0131] Fifth Embodiment [Rotating Electric Machine] A rotating electric machine 9 according to a fifth embodiment will be described with reference to Fig. 19 . The rotating electric machine 9 of this embodiment is an axial gap type rotating electric machine. The rotating electric machine 9 of this embodiment differs from the rotating electric machine 9 of the fourth embodiment mainly in that it is an SS / DR type having two rotors 90 and one stator 8. In the rotating electric machine 9, the rotor 90 and the stator 8 are arranged facing each other in the axial direction. One stator 8 is assembled so as to be sandwiched between the two rotors 90. The following description will focus on the differences from the fourth embodiment. Description of the same configuration as the fourth embodiment will be omitted.

[0132] Each rotor 90 includes a rotor body, a plurality of magnets 95, and a back yoke 98. The rotor body and the plurality of magnets 95 are the same as those in the fourth embodiment. The back yoke 98 is provided between the rotor 90 and the plate 922. The back yoke 98 is a flat plate-shaped member. The back yoke 98 is made of a powder compact similar to the core lamination 1 described above, or a laminated steel plate.

[0133] The stator 8 includes a plurality of core laminations 1 arranged in an annular shape, a coil 80 wound around the first member 10 of each core lamination 1, and a support member that holds the plurality of core laminations 1. The support member is not shown. Each core lamination 1 has the same configuration for the second member 20 and the third member 30. That is, the protruding amounts of the first protrusions 211 and the second protrusions 212 on the second member 20 are the same as the protruding amounts of the first protrusions 311 and the second protrusions 312 on the third member 30. Furthermore, the first side surface 24a of the first protrusions 211 and the second side surface 24b of the second protrusions 212 on the second member 20 do not have the steps described above. The coil 80 is the same as in the third embodiment. The support member holds the plurality of core laminations 1 so that the core laminations 1 are spaced equally apart. This support member prevents circumferentially adjacent core laminations 1 from contacting each other.

[0134] The rotating electric machine 9 according to the fifth embodiment includes the stator 8 like the rotating electric machine 9 according to the fourth embodiment, and therefore, the temperature rise of the coil 80 can be suppressed.

[0135] 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 of the claims. For example, a rotating electric machine may include one rotor and one stator.

[0136] <<Supplementary Notes>> The following supplementary notes are further disclosed in relation to the above-described embodiments of the present disclosure.

[0137] [Supplementary Note 1] A core piece constituting a stator core for an axial gap type rotating electric machine, comprising: a columnar first member extending in the axial direction of the stator core; a plate-shaped second member provided at a first end of the first member in the axial direction; and a plate-shaped third member provided at a second end of the first member in the axial direction, wherein the first member has a circumferential surface connecting the second member and the third member, the second member has a protruding portion that protrudes outward beyond the circumferential surface of the first member, and the third member has a protruding portion that protrudes outward beyond the circumferential surface of the first member, and each of the first member, the second member, and the third member has: an outer circumferential surface located at a position far from the axis of the stator core; an inner circumferential surface located at a position close to the axis of the stator core; a first side surface located in a first direction in the circumferential direction of the stator core and connecting to the outer circumferential surface and the inner circumferential surface; and a second side surface located in a second direction in the circumferential direction of the stator core and connected to the outer peripheral surface and the inner peripheral surface, wherein in each of the first member, the second member, and the third member, the length between the first side surface and the second side surface on the outer peripheral surface is longer than the length between the first side surface and the second side surface on the inner peripheral surface, wherein the first side surface and the second side surface in each of the first member, the second member, and the third member each have a first parallel surface connected to the outer peripheral surface, a second parallel surface connected to the inner peripheral surface, and a first inclined surface connected to the first parallel surface and the second parallel surface, wherein in each of the first member, the second member, and the third member, the first parallel surface of the first side surface and the first parallel surface of the second side surface are parallel, the second parallel surface of the first side surface and the second parallel surface of the second side surface are parallel, and the first parallel surface of the first side surface and the second parallel surface of the first side surface are parallel, a core piece, wherein the first member, the second member, and the third member are configured as an integrally molded powder compact, and the peripheral surface of the first member has a plurality of grooves along the winding direction of the coil winding on at least a part of the surface that contacts the coil winding.

[0138] The core piece according to Supplementary Note 1 has excellent productivity.

[0139] A conventional core piece is formed, for example, by combining a powder compact in which a first member and a second member are integrally molded with a third member configured separately from the powder compact. Alternatively, a conventional core piece is formed, for example, by combining a powder compact in which a first member and a third member are integrally molded with a second member configured separately from the powder compact. In other words, a conventional core piece must be formed by fabricating and combining at least two members. Therefore, the number of steps required to manufacture a conventional core piece is large, and the manufacturing time is long. Furthermore, the manufacturing of a conventional core piece requires at least two molds.

[0140] On the other hand, the core piece according to Supplementary Note 1 is composed of a powder compact in which the first member, the second member, and the third member are integrally molded, so there is no need to combine multiple members. Therefore, the core piece according to Supplementary Note 1 can be manufactured with fewer steps and in a shorter time than conventional core pieces. Furthermore, since the core piece according to Supplementary Note 1 is composed of a powder compact in which the first member, the second member, and the third member are integrally molded, it can be manufactured using a single mold. Therefore, costs required for mold manufacturing and maintenance can be reduced, so the core piece according to Supplementary Note 1 can be manufactured at low cost.

[0141] The powder compact is manufactured by pressing raw material powder filled into a die cavity of a metal mold with an upper punch and a lower punch. A powder compact in which the first, second, and third members are integrally molded can be manufactured by orienting the pressing direction and removal direction along the radial direction of the stator core, as described in the manufacturing method above. The outer and inner peripheral surfaces of the core pieces are formed by the lower end surface of the upper punch and the upper end surface of the lower punch. The first and second side surfaces of the core pieces, and the first and second end surfaces in the axial direction of the stator core, are formed by the inner peripheral surface of the die cavity. In this case, even if the second and third members each have protrusions, the protrusions do not get caught on the inner peripheral surface of the die cavity. Therefore, the core pieces can be removed from the metal mold.

[0142] Furthermore, the core piece according to Supplementary Note 1 has a high relative density. The reason for this is as follows: As described above, the first parallel surface and the second parallel surface can be formed by a straight portion in the die cavity of the mold along the pressure direction of the upper and lower punches. Therefore, sufficient pressure can be applied to the raw material powder that constitutes the core piece. In addition, the first inclined surface can be formed by a tapered portion in the die cavity of the mold that intersects with the pressure direction of the upper and lower punches. By having a straight portion in the die cavity, contact between the upper and lower punches and the inner peripheral surface of the tapered portion is suppressed. Therefore, the life of the mold is extended, and the number of core pieces that can be produced with one mold is increased.

[0143] [Appendix 2] The core piece described in Appendix 1, wherein in each of the first member, the second member, and the third member, the angle between the extension of the first parallel surface of the first side surface and the first inclined surface is 5° or more and 20° or less, and the angle between the extension of the first parallel surface of the second side surface and the first inclined surface is 5° or more and 20° or less.

[0144] In the core piece of Supplementary Note 2, the angle formed in the first member satisfies the above range, making it easy to wind a winding on the circumferential surface of the first member and to form a stator. In the core piece of Supplementary Note 2, the angle formed in the second member satisfies the above range, making it easy to arrange the core piece in an annular shape and to form a stator core. In the core piece of Supplementary Note 2, the angle formed in the third member satisfies the above range, making it possible to suppress density variations within the core piece.

[0145] [Supplementary Note 3] The protruding portion of the second member and the protruding portion of the third member each have a first protruding portion protruding in a first circumferential direction and a second protruding portion protruding in a second circumferential direction, the protruding amount of the first protruding portion on the second member is greater than the protruding amount of the first protruding portion on the third member, the protruding amount of the second protruding portion on the second member is greater than the protruding amount of the second protruding portion on the third member, the first inclined surface of the first protruding portion on the second member has a portion protruding outward from a first imaginary plane, the first inclined surface of the second protruding portion on the second member has a portion protruding outward from a second imaginary plane, the first imaginary plane is a plane that connects a connection point between the first parallel surface and the first inclined surface and a connection point between the second parallel surface and the inner circumferential surface on the first side surface of the first protruding portion on the second member, A core piece described in Appendix 1 or Appendix 2, wherein the second imaginary surface is a plane connecting the connection point between the first parallel surface and the first inclined surface and the connection point between the second parallel surface and the inner surface on the second side surface of the second protrusion in the second member.

[0146] The core pieces of Supplementary Note 3 are easy to form a stator core with a large magnetic path area for the following reasons.

[0147] The stator core is formed by arranging a plurality of core pieces in an annular shape. Some stator cores are formed by assembling first core pieces and second core pieces that are adjacent to each other in the circumferential direction so as to be in contact with each other.

[0148] For example, in the case of a core piece in which the first side surface of the first protruding portion and the second side surface of the second protruding portion each have a first parallel surface, a second parallel surface, and a first inclined surface, and the first inclined surface does not have the protruding portion, the following occurs: When the core pieces are arranged in an annular shape, if an attempt is made to bring the first side surface of the first protruding portion of the second member of the first core piece into contact with the second side surface of the second protruding portion of the second member of the second core piece, a first corner of the first core piece comes into contact with a second corner of the second core piece. The first corner is a corner between the first side surface of the first protruding portion of the second member and the inner circumferential surface. The second corner is a corner between the second side surface of the second protruding portion of the second member and the inner circumferential surface. Therefore, the first side surface of the first protruding portion of the second member of the first core piece and the second side surface of the second protruding portion of the second member of the second core piece cannot be brought into sufficient contact.

[0149] In contrast, in the core pieces of Supplementary Note 3, the first side surface of the first protruding portion and the second side surface of the second protruding portion each have a first parallel surface, a second parallel surface, and a first inclined surface, and the first inclined surface has a portion that protrudes beyond the first imaginary plane and the second imaginary line. When the core pieces are arranged in an annular shape, even if the first side surface of the first protruding portion of the second member of the first core piece is brought into contact with the second side surface of the second protruding portion of the second member of the second core piece, contact between the first corner of the first core piece and the second corner of the second core piece can be prevented. Therefore, the first side surface of the first protruding portion of the second member of the first core piece and the second side surface of the second protruding portion of the second member of the second core piece can be brought into sufficient contact.

[0150] [Appendix 4] A core piece according to Appendix 3, wherein the first side surface of the first protrusion in the second member has one selected from the group consisting of at least one of a recess and a protrusion, a step, and a second inclined surface, and the second side surface of the second protrusion in the second member has one selected from the group consisting of at least one of a protrusion corresponding to the recess of the first side surface and a recess corresponding to the protrusion of the first side surface, a step corresponding to the step of the first side surface, and a second inclined surface corresponding to the second inclined surface of the first side surface.

[0151] The core pieces of Supplementary Note 4 make it easy to form a stator core with a large magnetic path area. The reason is as follows: the first core pieces and the second core pieces that are adjacent to each other in the circumferential direction of the stator core can be fitted together at the steps or the concaves and convexes, or can be brought into contact with each other at the second inclined surfaces. Therefore, the first core pieces and the second core pieces can be brought into sufficient contact with each other, and the contact area between the first core pieces and the second core pieces can be increased.

[0152] [Appendix 5] The core piece according to Appendix 3 or Appendix 4, wherein the third member has a first end face arranged on the opposite side to the side facing the second member, and the first end face is provided in a convex shape toward the opposite side.

[0153] The core pieces of Supplementary Note 5 can be used to construct a rotating electric machine with low noise and vibration. The reasons are as follows: In the rotating electric machine, a stator and a rotor are arranged facing each other. The stator is configured by arranging a coil in each first member of the stator core. The stator core is configured by arranging a plurality of core pieces in an annular shape. Because the first end faces of the core pieces are convex, sudden changes in the magnetic flux of the rotor magnet that the core pieces receive are easily suppressed. Because sudden changes in magnetic flux are easily suppressed, cogging torque is easily reduced. Because the cogging torque is small, noise and vibration are less likely to increase.

[0154] [Appendix 6] The core piece according to any one of Appendices 1 to 5, wherein the outer peripheral surface of each of the first member, the second member, and the third member has a curved surface that is convex in a direction away from the axis of the stator core, and the inner peripheral surface of each of the first member, the second member, and the third member has a curved surface that is convex in a direction approaching the axis of the stator core.

[0155] The core piece of Supplementary Note 6 can suppress variations in density within the core piece.

[0156] [Appendix 7] A core piece according to any one of Appendices 1 to 6, wherein a first seam between the protruding portion of the second member and the peripheral surface of the first member and a second seam between the protruding portion of the third member and the peripheral surface of the first member are rounded.

[0157] In the core piece of Appendix 7, the first joint and the second joint are rounded, so that each joint is less likely to be damaged.

[0158] [Appendix 8] The core piece according to appendix 7, wherein the bending radius of the first seam and the bending radius of the second seam are 0.2 mm or more and 4.0 mm or less.

[0159] In the core piece of Supplementary Note 8, the bending radius of the first joint and the second joint is 0.2 mm or more, which reduces the load on the mold during manufacturing of the core piece.In the core piece of Supplementary Note 8, the bending radius of the first joint and the second joint is 4.0 mm or less, which makes it easy to wind a coil when constructing a stator, and therefore makes it easy to increase the number of turns of the coil.

[0160] [Appendix 9] The core piece according to any one of Appendices 1 to 8, wherein each of the second member and the third member has a first end face arranged on the opposite side from the sides facing each other, and in each of the second member and the third member, a corner between the outer peripheral surface and the first end face and a corner between the inner peripheral surface and the first end face are chamfered.

[0161] In the core piece of Supplementary Note 9, the corners are chamfered, so that the corners are less likely to be damaged.

[0162] [Appendix 10] The core piece according to any one of Appendices 1 to 9, wherein the total area of ​​the outer peripheral surface of each of the first member, the second member, and the third member is more than 1 time and not more than 4 times the total area of ​​the inner peripheral surface of each of the first member, the second member, and the third member.

[0163] The core pieces of Supplementary Note 10 are easy to arrange in an annular shape and to form a stator core because the total area of ​​the outer peripheral surfaces is more than one time the total area of ​​the inner peripheral surfaces. The core pieces are easy to manufacture because the total area of ​​the outer peripheral surfaces is four times or less the total area of ​​the inner peripheral surfaces. Because the ratio of the total area of ​​the inner peripheral surfaces is relatively large, the area from which the lower punch pushes the core pieces when removing them from the mold is large. Therefore, damage to the core pieces when removing them from the mold is easily suppressed.

[0164] [Appendix 11] The core piece according to any one of Appendices 1 to 10, wherein, among the regions obtained by dividing the core piece into three by an imaginary plane along the second parallel plane of the first side surface and an imaginary plane along the second parallel plane of the second side surface, the difference in relative density between a first region located in the first circumferential direction and a second region located in the second circumferential direction, and a third region located between the first region and the second region, is 5.0% or less.

[0165] The core piece of Appendix 11 has a small difference in relative density, and therefore the physical properties such as magnetic properties are substantially uniform within the core piece.

[0166] [Appendix 12] The core piece according to any one of Appendices 1 to 11, wherein the difference in relative density between the first member, the second member, and the third member having the highest relative density and the member having the lowest relative density is 5.0% or less.

[0167] The core piece of Appendix 12 has a small difference in relative density, and therefore the physical properties such as magnetic properties are substantially uniform within the core piece.

[0168] [Appendix 13] The core piece according to any one of Appendices 1 to 12, wherein the powder compact has a relative density of 85% or more.

[0169] The core piece of Appendix 13 has a relative density of 85% or more, which means that it is high-density. The core piece of Appendix 13 can be used to construct an axial gap type rotating electric machine with excellent magnetic properties such as saturation magnetic flux density. Furthermore, the core piece of Appendix 13 has excellent mechanical properties such as strength.

[0170] [Appendix 14] The core piece according to any one of Appendices 1 to 13, wherein the powder compact is composed of an aggregate of a plurality of coated soft magnetic particles having an insulating coating on the surface of the soft magnetic particles, and the soft magnetic particles are iron-based particles made of at least one metal selected from the group consisting of pure iron, Fe—Si-based alloys, Fe—Al-based alloys, and Fe—Si—Al-based alloys.

[0171] The core piece of Appendix 14 has high density and excellent dimensional accuracy. This is because the material is relatively soft, and the soft magnetic particles are easily deformed during molding of the powder compact.

[0172] REFERENCE SIGNS LIST 1 core piece 10 first member 11 peripheral surface, 12 outer peripheral surface, 13 inner peripheral surface 14a first side surface, 14b second side surface 141 first parallel surface, 142 second parallel surface, 143 first inclined surface 20 second member 21 protruding portion 211 first protruding portion, 212 second protruding portion, 213 third protruding portion 22 outer peripheral surface, 23 inner peripheral surface, 24a first side surface, 24b second side surface 240 step 241 first parallel surface, 242 second parallel surface, 243 first inclined surface, 244 protruding portion 26 first end surface, 27 second end surface 30 third member 31 protruding portion, 311 first protruding portion, 312 second protruding portion 32 outer peripheral surface, 33 inner peripheral surface 34a first side surface, 34b second side surface 341 First parallel surface 342 Second parallel surface 343 First inclined surface 36 First end surface 37 Second end surface 40 Groove 40w Width 40d Depth 42 Connecting surface 5 Mold 50 Die 50h Mold hole 51 First hole portion 511 First straight portion 512 Second straight portion 513 Tapered portion 52 Second hole portion 521 First straight portion 522 Second straight portion 523 Tapered portion 53 Third hole portion 531 First straight portion 532 Second straight portion 533 Tapered portion 54 Upper punch 541 First upper punch portion 541e First lower end surface 542 Second upper punch portion 542e Second lower end surface 543 Third upper punch portion 543e Third lower end surface 55 Lower punch 551 DESCRIPTION OF SYMBOLS First lower punch portion, 551e First upper end surface 552 Second lower punch portion, 552e Second upper end surface 553 Third lower punch portion, 553e Third upper end surface 61 Groove, 62 Step 7 Stator core, 8 Stator 80 Coil 81 Winding, 81s Winding start end 81a Major axis, 81b Minor axis 81d Diameter 9 Rotating electric machine 90 Rotor, 91 Rotating shaft, 92 Case 921 Cylindrical portion, 922 Plate 93 Bearing, 95 Magnet, 98 Back yoke E11, E12, E21, E22, E31, E32 Extension plane Va, Vb Virtual plane, V21 First virtual plane, V22 Second virtual plane θ11, θ21, θ31 First inclination angle θ12, θ22, θ32 Second inclination angle

Claims

1. A core piece constituting a stator core for an axial gap type rotating electric machine, a columnar first member extending in a direction along the axis of the stator core; The circumferential surface of the first member has a plurality of grooves along the direction in which the winding is wound on at least a part of a surface that contacts the winding of the coil. Core piece.

2. a width of each of the plurality of grooves is equal to or greater than ¼ of a major axis of the winding and equal to or less than the major axis; The core piece according to claim 1 , wherein a depth of each of the plurality of grooves is greater than or equal to ¼ of a minor axis of the winding and less than or equal to the minor axis.

3. The cross section of the winding is circular, Each of the plurality of grooves has a cross section in the shape of a circular arc; 3. A core piece according to claim 1 or 2, wherein a radius of a circle of a cross section of said winding is the same as a radius of a circular arc of a cross section of said groove.

4. The plurality of grooves each have a connecting surface between two adjacent grooves, the connecting surface being continuous with an inner circumferential surface of the groove, The core piece according to claim 1 or 2, wherein the connecting surface is configured as a flat surface or a rounded curved surface.

5. The peripheral surface is an inner circumferential surface disposed near an axis of the stator core; an outer circumferential surface disposed at a position far from the axis of the stator core; The core piece according to claim 1 or 2, wherein the plurality of grooves are provided on at least one of the inner peripheral surface and the outer peripheral surface.

6. a plate-shaped second member provided at a first end of the first member in a direction along the axis; a plate-shaped third member provided at a second end of the first member in a direction along the axis, the circumferential surface of the first member is connected to the second member and the third member, the second member has a protruding portion that protrudes outward from the peripheral surface of the first member, the third member has a protruding portion protruding outward from the peripheral surface of the first member, The core piece according to claim 1 or 2, wherein the first member, the second member, and the third member are configured as an integrally molded powder compact.

7. The core piece according to claim 6 , wherein the protruding portion of the second member or the protruding portion of the third member has a groove or a step in which a winding start end of the winding is placed.

8. A core piece constituting a stator core for an axial gap type rotating electric machine, A columnar first member extending in a direction along the axis of the stator core; a plate-shaped second member provided at a first end of the first member in a direction along the axis; a plate-shaped third member provided at a second end of the first member in a direction along the axis, the first member has a peripheral surface connected to the second member and the third member, the second member has a protruding portion that protrudes outward from the peripheral surface of the first member, the third member has a protruding portion protruding outward from the peripheral surface of the first member, the first member, the second member, and the third member are formed as an integrally molded powder compact, The peripheral surface of the first member is an inner circumferential surface disposed near an axis of the stator core; an outer circumferential surface disposed at a position far from the axis of the stator core; At least one of the inner circumferential surface and the outer circumferential surface has a plurality of grooves along a direction in which the winding of the coil is wound, on at least a part of a surface that contacts the winding of the coil, a width of each of the plurality of grooves is equal to or greater than ¼ of a major axis of the winding and equal to or less than the major axis; a depth of each of the plurality of grooves is equal to or greater than ¼ of a minor axis of the winding and equal to or less than the minor axis; the protruding portion of the second member or the protruding portion of the third member has a groove or a step in which a winding start end of the winding is placed, Core piece.

9. A stator core for an axial gap type rotating electric machine, A plurality of core pieces arranged in an annular shape; Each of the plurality of core pieces is the core piece according to claim 1 or 2. Stator core.

10. A stator for an axial gap type rotating electric machine, The stator core according to claim 9 , a coil disposed on each of the first members in the stator core, Stator.

11. An axial gap type rotating electric machine including a rotor and a stator, the rotor and the stator being disposed facing each other in a direction along an axis, The stator is a stator according to claim 10. Rotating electric motor.