Magnetic core and method for manufacturing same, magnetic core with coil, and rotary electric machine

Abstract

This magnetic core comprises a core back part and a tooth part, said core back part having a front surface facing a first direction toward the rotation axis of a rotary electric machine when the magnetic core is incorporated in the rotary electric machine. The tooth part includes a tooth body part extending from the front surface in the first direction and a tooth tip part provided at the tip of the tooth body part. The tooth tip part has a back surface facing the reverse direction of the first direction. The tooth body part has an end surface that faces a second direction along the rotation axis when the magnetic core is incorporated in the rotary electric machine. The end surface has a recessed curved surface that smoothly connects the end surface to the front surface of the core back part or the back surface of the tooth tip part, and the curved surface is formed by a first curved surface formation part that is a part of the tooth body part.

Description

Magnetic core and manufacturing method thereof, magnetic core with coil, and rotating electric machine

[0001] The present invention relates to a technique for mitigating the occurrence of magnetic saturation in a rotating electric machine.

[0002] A known example of a conventional rotating electric machine is the motor described in Patent Document 1. The motor described in Patent Document 1 includes a stator and a rotor disposed inside the stator so that its center of rotation coincides with the axis of the stator. The stator includes a stator core and a stator coil wound around a plurality of teeth. The stator core is a powder magnetic core made of powder containing particles of a magnetic material. The stator core is integrally molded by compacting the powder at a predetermined pressure using a molding die.

[0003] The stator core has a yoke and a plurality of teeth. The yoke is formed in a cylindrical shape. Each tooth extends from the inner peripheral surface of the yoke toward the inside of the yoke. The plurality of teeth are formed on the inner peripheral surface of the yoke and are arranged at equal intervals in the circumferential direction. A stator coil is wound around each of the plurality of teeth.

[0004] The stator core has a cylindrical yoke divided into a plurality of pieces in the circumferential direction, and the stator core has a plurality of yoke pieces formed by the division, each of which includes one tooth.

[0005] The teeth have a tooth body portion formed in a rectangular prism shape extending from the inner peripheral surface of the yoke toward the inside of the yoke, and a tooth tip portion located at the tip of the tooth body portion. The teeth are formed in a roughly T-shape when viewed from the axial direction of the stator. The teeth face the rotor. A stator coil is wound around the tooth body portion.

[0006] JP 2017-060395 A

[0007] In recent years, there has been a demand for improving the output torque of motors in order to increase the output of devices driven by the motor. To improve the output torque of a motor equipped with a stator core having the above-described configuration, it is necessary to increase the magnetic flux generated by energizing the stator coil. This magnetic flux flows within the stator core.

[0008] On the other hand, particularly in small motors, magnetic saturation is more likely to occur in the stator core as the stator core becomes smaller. When magnetic saturation occurs in the stator core, the magnetic flux flowing through the stator core cannot be increased, and there is a limit to how much the motor's output torque can be improved.

[0009] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a magnetic core capable of reducing the occurrence of magnetic saturation, a manufacturing method thereof, a magnetic core with a coil, and a rotating electrical machine.

[0010] A magnetic core according to one embodiment of the present invention is used in a rotating electric machine. The magnetic core includes a core back portion having a front surface that faces a first direction toward the rotation axis of the rotating electric machine when the magnetic core is incorporated into the rotating electric machine, and teeth portions. The teeth portions include tooth main bodies extending in the first direction from the front surface and tooth tip portions provided at the ends of the tooth main bodies. The tooth tip portions have back surfaces that face the opposite direction to the first direction. The tooth main bodies have end surfaces that face a second direction along the rotation axis when the magnetic core is incorporated into the rotating electric machine. The end surfaces have concave curved surfaces that smoothly connect to the front surface of the core back portion or the back surface of the tooth tip portions, and the curved surfaces are formed by first curved surface forming portions that are part of the tooth main bodies.

[0011] Conventionally, the end faces of the tooth main body portions and the front faces of the core back portions or the back faces of the tooth tips are connected by flat surfaces. In this case, a corner is formed at the connection point between the end faces of the tooth main body portions and the front faces of the core back portions or the back faces of the tooth tips. When a magnetic core is incorporated into a rotating electric machine and current is applied to the coils wound around the tooth main body portions, magnetic flux is generated inside the magnetic core through the tooth main body portions. This magnetic flux flows from the tooth main body portions toward the front faces of the core back portions or the back faces of the tooth tips. In this case, the flow of magnetic flux attempts to take the shortest path inside the magnetic core. Conventionally, because a corner is formed at the connection point between the end faces of the tooth main body portions and the front faces of the core back portions or the back faces of the tooth tips, the corner obstructs the flow of magnetic flux that attempts to flow along the shortest path. This increases magnetic resistance in the magnetic circuit near the corner, making it difficult for magnetic flux to flow near the corner. This results in localized magnetic saturation at the corner.

[0012] On the other hand, with the magnetic core, the end face of the tooth main body portion has a concave curved surface that smoothly connects the end face to the front face of the core back portion or the back face of the tooth tip portion, and the curved surface is formed by a first curved surface forming portion that is part of the tooth main body portion. Therefore, with the magnetic core, unlike conventional cores, no corners are formed in the first direction, and magnetic flux can pass through the first curved surface forming portion and flow along a short path. This reduces magnetic resistance in the magnetic circuit. As a result, local magnetic saturation can be alleviated. Furthermore, the area through which magnetic flux flows can be expanded in the direction perpendicular to the first direction in the core back portion or the tooth tip portion. This allows the core back portion to be effectively utilized as a magnetic circuit. As a result, the output torque of a rotating electric machine equipped with the magnetic core can be further improved.

[0013] In the above magnetic core, the end face of the tooth main body portion includes a first flat surface which is a surface parallel to the first direction, and the first curved surface forming portion protrudes from the first flat surface toward the second direction and may be located only on the second direction side of the first flat surface.

[0014] According to the above configuration, the first curved surface portion is formed without reducing the cross-sectional area of ​​the tooth main body in the second direction. Therefore, even if the first curved surface portion is formed, the saturation magnetic flux density of the magnetic flux flowing inside the tooth main body does not decrease. Therefore, a decrease in the output torque of the rotating electric machine can be suppressed.

[0015] In the magnetic core, the tooth main body portion may have a side surface that faces a circumferential direction centered on the rotation axis of a rotary electric machine when the magnetic core is incorporated into the rotary electric machine. In this configuration, the side surface has a concave curved surface that smoothly connects the side surface to the front surface of the core back portion or the back surface of the tooth tip portion, and the curved surface is formed by a second curved surface forming portion that is a part of the tooth main body portion.

[0016] According to the above configuration, unlike conventional rotors, no corners are formed in the circumferential direction, and magnetic flux can pass through the first curved surface portion, thereby allowing it to flow in a short path. This reduces the magnetic resistance in the magnetic circuit, and as a result, the occurrence of local magnetic saturation can be further alleviated.

[0017] In the above-mentioned magnetic core, the side surface may include a second flat surface that is a surface parallel to the first direction, and the second curved surface forming portion may protrude circumferentially from the second flat surface and be located only on the circumferential side of the second flat surface.

[0018] According to the above configuration, the second curved surface portion is formed without reducing the cross-sectional area of ​​the tooth main body in the circumferential direction. Therefore, even if the second curved surface portion is formed, the saturation magnetic flux density of the magnetic flux flowing inside the tooth main body does not decrease. Therefore, a decrease in the output torque of the rotating electric machine can be suppressed.

[0019] In the magnetic core, the tooth main body may have a side surface facing a third direction, which is a circumferential direction about the rotation axis when the magnetic core is incorporated into a rotating electric machine, and a slope connecting the end face and the side surface. In this configuration, the slope has a tapered curved surface that smoothly connects itself to an edge of the curved surface in the third direction, and the tapered curved surface is formed by a third curved surface forming portion that is a part of the tooth main body.

[0020] With this configuration, no corners are formed at the connection between the end faces and side faces of the tooth main bodies on the core back side, allowing magnetic flux to flow more easily, further reducing the occurrence of localized magnetic saturation.

[0021] The magnetic core may be a compact formed from soft magnetic powder.

[0022] According to the above configuration, the magnetic core can be easily manufactured.

[0023] A method for manufacturing a magnetic core according to one embodiment of the present invention includes a finishing step in which the magnetic core is finished by polishing using spherical media, and prior to the finishing step, the magnetic core is manufactured so that the radius of curvature of the curved surface of the end face is already larger than the diameter of the media used in the finishing step.

[0024] According to the above manufacturing method, because the radius of curvature of the first curved surface is larger than the radius of the media, the media can contact every corner of the curved surface of the end face of the tooth main body portion in the finishing process. This allows burrs formed on the curved surface of the end face of the tooth main body portion in a previous stage of the finishing process to be removed in the finishing process. This prevents damage to the coil when it is wound around the tooth main body portion after the magnetic core is completed. Furthermore, when an insulating film is applied to the surface of the magnetic core after the finishing process, the insulating film can be made thinner, increasing the slot space factor of the coil and improving the output efficiency of the rotating electric machine.

[0025] A method for manufacturing a magnetic core according to one embodiment of the present invention includes a finishing step in which the magnetic core is finished by polishing using spherical media, and prior to the finishing step, the magnetic core is manufactured so that the radius of curvature of the curved surface on the side surface is already larger than the diameter of the media used in the finishing step.

[0026] According to the above manufacturing method, because the minimum value of the radius of curvature of the second curved surface is larger than the radius of the media, the media can contact every corner of the curved surface of the side surface of the tooth main body portion in the finishing process. This allows burrs formed on the curved surface of the side surface of the tooth main body portion in a stage prior to the finishing process to be removed in the finishing process. This prevents damage to the coil when it is wound around the tooth main body portion after the magnetic core is completed. Furthermore, when an insulating film is applied to the surface of the magnetic core after the finishing process, the insulating film can be made thinner, increasing the slot space factor of the coil and improving the output efficiency of the rotating electric machine.

[0027] According to the present invention, the occurrence of magnetic saturation can be reduced.

[0028] FIG. 1 is an external perspective view of a brushless motor 100 using a magnetic core 1. FIG. 2 is a perspective schematic view showing a portion of the brushless motor 100 in a cutaway view. FIG. 3 is a perspective view of the magnetic core 1. FIG. 4 is a cross-sectional view of the magnetic core 1 and an enlarged cross-sectional view of the first curved surface portion R11 and its vicinity. FIG. 5 is a cross-sectional view showing the magnetic flux flowing through a magnetic core 50 according to a comparative example in a motor including the magnetic core 50 according to a comparative example. FIG. 6 is a cross-sectional view showing the magnetic flux flowing through the magnetic core 1 in the brushless motor 100. FIG. 7 is a cross-sectional view showing the magnetic flux flowing through two adjacent magnetic cores 1 in the brushless motor 100. FIG. 8 is a cross-sectional view showing an example of a manufacturing process for the magnetic core 1. FIG. 9 is a diagram showing the relationship between the radius of curvature CR1 of the first curved surface CS1 and the radius RA of the medium M. FIG. 10 is a cross-sectional view showing the interior of a barrel B during the finishing process. FIG. 11 is a perspective view of a magnetic core 1a. FIG. 12 is a perspective view of a magnetic core 1b. 13 is a cross-sectional view of the magnetic core 1b and an enlarged cross-sectional view of the vicinity of the second curved surface forming portion R21. FIG. 14 is a diagram showing the relationship between the radius of curvature CR2 of the second curved surface CS2 and the radius RA of the medium M.

[0029] [First Embodiment] (Configuration of Brushless Motor 100) First, the configuration of a brushless motor 100 according to a first embodiment of the present invention will be described below with reference to the drawings. Fig. 1 is a perspective view of the exterior of brushless motor 100. Fig. 2 is a perspective schematic view showing brushless motor 100 with a portion cut away.

[0030] In this specification, directions are defined as follows, by way of example. Of the radial directions centered on the rotation axis AR of brushless motor 100, the direction from tooth tip end 32 toward rotation axis AR of brushless motor 100 is defined as a first direction DIR1. First direction DIR1 is the direction toward rotation axis AR of brushless motor 100 when magnetic core 1 is incorporated into brushless motor 100. Of the axial directions along rotation axis AR of brushless motor 100, the direction in which shaft 21 protrudes outside housing 15 through opening OP is defined as a second direction DIR2. Of the circumferential directions centered on rotation axis AR of brushless motor 100, the clockwise direction with respect to rotation axis AR of brushless motor 100 as viewed in second direction DIR2 is defined as a third direction DIR3. The opposite direction of second direction DIR2 is defined as a fourth direction DIR4.

[0031] As shown in Fig. 2, the brushless motor 100 includes a rotor 20, a stator 10, bearings 14, and a housing 15. In this embodiment, the brushless motor 100 is an inner rotor type. That is, the stator 10 is disposed around the rotor 20. The brushless motor 100 is an example of a rotating electric machine of the present invention. The brushless motor 100 may also be an outer rotor type. That is, the rotor 20 may be disposed around the stator 10.

[0032] The rotating electric machine may have a structure in which a rotor is rotated by electricity, or may have a structure in which electricity is generated by the rotation of the rotor. Rotating electric machines include brushless motors, permanent magnet synchronous motors, permanent magnet synchronous generators, etc.

[0033] The rotor 20 includes a shaft 21 and a rotor member 22. The shaft 21 is cylindrical. The rotor member 22 is cylindrical. The shaft 21 and the rotor member 22 have the same central axis, which forms a rotation axis AR.

[0034] The rotor member 22 has a soft magnetic material 23 and a hard magnetic material 24. The rotor member 22 is attached to the outer peripheral surface of the shaft 21 in the radial direction centered on the rotation axis AR. More specifically, the soft magnetic material 23 is attached to the outer peripheral surface of the shaft 21 in the radial direction centered on the rotation axis AR. The hard magnetic material 24 is attached to the outer peripheral surface of the soft magnetic material 23 in the radial direction centered on the rotation axis AR.

[0035] The soft magnetic material 23 is a soft magnetic material. The hard magnetic material 24 is a magnetized hard magnetic material. The hard magnetic material is magnetized when an external magnetic field is applied. After that, even if the application of the magnetic field is stopped, the hard magnetic material does not lose its magnetization.

[0036] The bearing 14 supports the shaft 21 so that it can rotate in the circumferential direction about the rotation axis AR. More specifically, the bearing 14 has a first bearing 14a and a second bearing 14b. In this embodiment, the first bearing 14a and the second bearing 14b are each a ball bearing. The first bearing 14a and the second bearing 14b are each cylindrical and extend along the rotation axis AR. The central axes of the first bearing 14a and the second bearing 14b are the rotation axis AR. In other words, the central axes of the first bearing 14a and the second bearing 14b coincide with the central axis of the shaft 21. However, the first bearing 14a and the second bearing 14b are not limited to being ball bearings.

[0037] The second bearing 14b is located in the fourth direction DIR4 from the first bearing 14a. The first bearing 14a is located in the second direction DIR2 from the rotor member 22. The second bearing 14b is located in the fourth direction DIR4 from the rotor member 22. The second bearing 14b supports the end of the shaft 21 in the fourth direction DIR4.

[0038] The stator 10 includes a coil 13 and a magnetic core 1. That is, in this embodiment, the magnetic core 1 is used in the stator 10. The magnetic core according to the present invention may also be used as a part of a rotor.

[0039] As shown in FIG. 1, the housing 15 has a first housing 15a and a second housing 15b. As shown in FIGS. 1 and 2, the first housing 15a is cylindrical. The central axis of the first housing 15a is the rotation axis AR. The first housing 15a is positioned in the second direction DIR2 from the second housing 15b. The first housing 15a also has an opening OP. As a result, the shaft 21 protrudes from the opening OP in the second direction DIR2. That is, in this embodiment, the brushless motor 100 is a single-shaft type. Note that the brushless motor 100 is not limited to a single-shaft type and may be a double-shaft type.

[0040] The first housing 15a supports the first bearing 14a, the plurality of magnetic cores 1, and the plurality of coils 13. The second housing 15b supports the second bearing 14b. In this embodiment, the material of each of the first housing 15a and the second housing 15b is stainless steel (SUS). However, the material of each of the first housing 15a and the second housing 15b is not limited to stainless steel (SUS), and may be any material with high rigidity.

[0041] In this embodiment, the number of coils 13 and the number of magnetic cores 1 are each nine. Note that in FIG. 2 , reference symbols are assigned to only representative magnetic cores 1 and coils 13 among the nine magnetic cores 1 and nine coils 13. The nine coils 13 and nine magnetic cores 1 are aligned in the circumferential direction centered on the rotation axis AR. The nine magnetic cores 1 are arranged around the hard magnetic material 24 with a gap between them. Note that the number of coils 13 and the number of magnetic cores 1 are not limited to nine.

[0042] The coil 13 is made of a conductive material such as copper. The coil 13 has a structure in which the surface of a copper wire is covered with an insulating coating. Because the surface of the copper wire is covered with an insulating coating, the coil 13 is electrically insulated from the magnetic core 1. However, at the two end portions of the coil 13, the surface of the copper wire is not covered with the insulating coating and the copper wire is exposed.

[0043] A current is supplied to the coil 13 from a power supply (not shown). When a current flows through the coil 13, the coil 13 generates a magnetic field. The magnetic core 1 is magnetized by both the magnetic field generated by the hard magnetic material 24 and the magnetic field generated by the coil 13. The rotation of the rotor 20 is controlled by controlling the current supplied from the power supply (not shown).

[0044] (Configuration of magnetic core 1) The configuration of the magnetic core 1 according to the first embodiment of the present invention will be described below with reference to the drawings. Fig. 3 is a perspective view of the magnetic core 1. Fig. 4 is a cross-sectional view of the magnetic core 1 and an enlarged cross-sectional view of the vicinity of the first curved surface forming portion R11. Note that in Fig. 3, only representative slopes SL among the four slopes SL are denoted by reference symbols. Note that the cross section of the magnetic core 1 in Fig. 4 is a plane that passes through the first flat surface FS1 of the first end surface ES1 of the tooth main body portion 31 and is perpendicular to the first flat surface FS1 of the first end surface ES1 of the tooth main body portion 31.

[0045] 3, the magnetic core 1 includes a core back portion 2 and teeth portions 3. The core back portion 2 and teeth portions 3 are included in the magnetic core 1, which is a single member. Here, a single member means a member having a structure that cannot be separated without being damaged.

[0046] The magnetic core 1 is a soft magnetic material. In this embodiment, the magnetic core 1 is a molded body formed from soft magnetic powder. That is, each of the core back portion 2 and the teeth portion 3 is a molded body formed from soft magnetic powder. The material of the soft magnetic powder includes, for example, iron and a binder. The binder is, for example, a resin. The soft magnetic powder is, for example, a mixture of iron powder and epoxy resin powder, which is an example of binder powder. Such a magnetic core 1 is manufactured, for example, by compression molding. In addition, an insulating film (not shown) is applied to the surface of the magnetic core 1 that comes into contact with another member. Note that the magnetic core 1 does not have to be a molded body formed from soft magnetic powder.

[0047] The core back portion 2 has a front surface IS2 facing the first direction DIR1, a back surface OS2 facing the opposite direction to the first direction DIR1, two side surfaces connecting the front surface IS2 and the back surface OS2, the two side surfaces being aligned in the third direction DIR3, and two end surfaces connecting the front surface IS2 and the back surface OS2, the two end surfaces being aligned in the second direction DIR2. In this embodiment, the front surface IS2, the two side surfaces aligned in the third direction DIR3, and the two end surfaces aligned in the second direction DIR2 are all flat surfaces. The front surface IS32 is a curved surface that is concavely curved in the opposite direction to the first direction DIR1. The back surface OS2 is a curved surface that is convexly curved in the opposite direction to the first direction DIR1. The back surface OS2 forms a part of the outer peripheral surface of the stator 10. When magnetic core 1 is incorporated into brushless motor 100, the side surface connecting front surface IS2 and rear surface OS2 is magnetically connected to the side surface connecting front surface IS2 and rear surface OS2 of an adjacent magnetic core 1. Note that the front surface IS2, the two side surfaces aligned in third direction DIR3, and the two end surfaces aligned in second direction DIR2 may each include at least a portion of a curved surface. Also, the rear surface OS2 may include at least a portion of a flat surface.

[0048] The tooth portions 3 have a shape extending in the first direction DIR1 from the core back portion 2. More specifically, the tooth portions 3 have tooth main body portions 31 extending in the first direction DIR1 from the front surface IS2 and tooth tip portions 32 provided at the tips of the tooth main body portions 31. As shown in FIG. 2 , coils 13 are wound around the tooth main body portions 31. When the magnetic core 1 is incorporated into the brushless motor 100, the tooth tip portions 32 face the hard magnetic material 24 of the rotor 20 across an air gap. In this embodiment, the positions of the ends of the rotor member 22 in the second direction DIR2 are equal to the positions of the ends of the tooth main body portions 31 in the second direction DIR2. Furthermore, the position in the fourth direction DIR4 of the end of the rotor member 22 in the fourth direction DIR4 is equal to the position in the fourth direction DIR4 of the end of the tooth main body portion 31 in the fourth direction DIR4. Note that the position in the second direction DIR2 of the end of the rotor member 22 in the second direction DIR2 does not have to be equal to the position in the second direction DIR2 of the end of the tooth main body portion 31 in the second direction DIR2. Furthermore, the position in the fourth direction DIR4 of the end of the rotor member 22 in the fourth direction DIR4 does not have to be equal to the position in the fourth direction DIR4 of the end of the tooth main body portion 31 in the fourth direction DIR4.

[0049] As shown in FIG. 3 , each tooth tip portion 32 has a front surface IS32 facing the first direction DIR1, a back surface OS32 facing the opposite direction to the first direction DIR1, two side surfaces connecting the front surface IS32 and the back surface OS32, the two side surfaces being aligned in the third direction DIR3, and two end surfaces connecting the front surface IS32 and the back surface OS32, the two end surfaces being aligned in the second direction DIR2. In this embodiment, the back surface OS32, the two side surfaces being aligned in the third direction DIR3, and the two end surfaces being aligned in the second direction DIR2 are all flat surfaces. The front surface IS32 is a concavely curved surface in the first direction DIR1. The front surface IS32 is aligned along the outer circumferential surface of the rotor 20. The back surface OS32, the two side surfaces being aligned in the third direction DIR3, and the two end surfaces being aligned in the second direction DIR2 may each include a curved surface. Additionally, the front surface IS32 may include a flat surface.

[0050] In this embodiment, the tooth main body 31 has a shape of a quadrangular prism extending in the first direction DIR1 with each corner chamfered. More specifically, as shown in Fig. 4 , the tooth main body 31 has a first end face ES1 facing the second direction DIR2, a second end face ES2 facing the fourth direction DIR4, a first side face SS1 facing the third direction DIR3, a second side face SS2 facing the opposite direction to the third direction DIR3, and four slopes SL connecting the first end face ES1 or the second end face ES2 to the first side face SS1 or the second side face SS2. In this embodiment, each of the first end face ES1 and the second end face ES2 includes a first flat surface FS1 that is a surface parallel to the first direction DIR1. Each of the first side surface SS1 and the second side surface SS2 includes a second flat surface FS2 that is a surface parallel to the first direction DIR1. Note that each of the first end surface ES1 and the second end surface ES2 does not necessarily have to include the first flat surface FS1 that is a surface parallel to the first direction DIR1. Also, each of the first side surface SS1 and the second side surface SS2 does not necessarily have to include the second flat surface FS2 that is a surface parallel to the first direction DIR1. Also, the first end surface ES1 or the second end surface ES2 corresponds to the "end surface" in the present invention. The first side surface SS1 or the second side surface SS2 corresponds to the "side surface" in the present invention.

[0051] When the magnetic core 1 is viewed in the first direction DIR1, the outer edge of the tooth main body portion 31 is surrounded by the outer edge of the core back portion 2. When the magnetic core 1 is viewed in the first direction DIR1, the outer edge of the tooth main body portion 31 is surrounded by the outer edge of the tooth tip portion 32. Note that the tooth main body portion 31 does not have to have a shape in which each corner of a quadrangular prism extending in the first direction DIR1 is chamfered.

[0052] In this embodiment, as shown in Figures 3 and 4, four first curved surface forming portions R1 are formed on the tooth main body 31. The four first curved surface forming portions R1 are part of the tooth main body 31. One of the four first curved surface forming portions R1 is formed at an end of the tooth main body 31 in the first direction DIR1 and at an end of the tooth main body 31 in the second direction DIR2. One of the four first curved surface forming portions R1 is formed at an end of the tooth main body 31 in the opposite direction to the first direction DIR1 and at an end of the tooth main body 31 in the second direction DIR2. One of the four first curved surface forming portions R1 is formed at an end of the tooth main body 31 in the first direction DIR1 and at an end of the tooth main body 31 in the fourth direction DIR4. One of the four first curved surface forming portions R1 is formed at the end of the tooth main body 31 in the opposite direction to the first direction DIR1 and at the end of the tooth main body 31 in the fourth direction DIR4. In this embodiment, the four first curved surface forming portions R1 have a symmetrical structure with respect to each other. Therefore, a description of the two first curved surface forming portions R1 formed at the end of the tooth main body 31 in the fourth direction DIR4 will be omitted. Note that the number of first curved surface forming portions R1 does not have to be four. Furthermore, the first curved surface forming portions R1 do not have to have a symmetrical structure with respect to each other.

[0053] First, we will explain the first curved surface portion R1 formed on the end of the tooth main body 31 in the first direction DIR1 and on the end of the tooth main body 31 in the second direction DIR2. Hereinafter, this first curved surface portion R1 will be referred to as the first curved surface portion R11.

[0054] The first curved surface forming portion R11 protrudes from the first flat surface FS1 of the first end surface ES1 in the second direction DIR2. The first curved surface forming portion R11 is located only on the second direction DIR2 side of the first flat surface FS1 of the first end surface ES1. More specifically, the first curved surface forming portion R11 has a first curved surface CS1. The first curved surface CS1 of the first curved surface forming portion R11 is concavely curved. In this embodiment, the first curved surface CS1 of the first curved surface forming portion R11 is curved in an arc shape in a cross section perpendicular to the third direction DIR3. The first curved surface CS1 of the first curved surface forming portion R11 has a single radius of curvature CR1. The first curved surface CS1 of the first curved surface forming portion R11 does not have to be curved in an arc shape in a cross section perpendicular to the third direction DIR3. Furthermore, the first curved surface CS1 of the first curved surface forming portion R11 may have a plurality of radii of curvature CR1.

[0055] The first curved surface CS1 of the first curved surface forming portion R11 is a part of the first end surface ES1. The first curved surface CS1 of the first curved surface forming portion R11 is smoothly connected to the back surface OS32 of the tooth tip portion 32. Therefore, the tooth main body portion 31 is smoothly connected to the back surface OS32 of the tooth tip portion 32 via the first curved surface CS1 of the first curved surface forming portion R11. In this embodiment, as shown in FIG. 3 , edges E are formed on the end of the first curved surface CS1 of the first curved surface forming portion R11 in the third direction DIR3 and on the end of the first curved surface CS1 of the first curved surface forming portion R11 in the opposite direction to the third direction DIR3.

[0056] Next, we will explain the first curved surface portion R1 formed on the end of the tooth main body 31 in the opposite direction to the first direction DIR1 and on the end of the tooth main body 31 in the second direction DIR2. Hereinafter, this first curved surface portion R1 will be referred to as the first curved surface portion R12.

[0057] As shown in FIG. 4 , the first curved surface forming portion R12 protrudes in the second direction DIR2 from the first flat surface FS1 of the first end face ES1. The first curved surface forming portion R12 is located only on the second direction DIR2 side of the first flat surface FS1 of the first end face ES1. More specifically, the first curved surface forming portion R12 has a first curved surface CS1. The first curved surface CS1 of the first curved surface forming portion R12 is concavely curved. In this embodiment, the first curved surface CS1 of the first curved surface forming portion R12 is curved in an arc shape in a cross section perpendicular to the third direction DIR3. The first curved surface CS1 of the first curved surface forming portion R12 has a single radius of curvature CR1. The first curved surface CS1 of the first curved surface forming portion R12 does not have to be curved in an arc shape in a cross section perpendicular to the third direction DIR3. Furthermore, the first curved surface CS1 of the first curved surface forming portion R12 may have a plurality of radii of curvature CR1.

[0058] The first curved surface CS1 of the first curved surface forming portion R12 is a part of the first end surface ES1. The first curved surface CS1 of the first curved surface forming portion R12 is smoothly connected to the front surface IS2 of the core back portion 2. Therefore, the tooth main body portion 31 is smoothly connected to the front surface IS2 of the core back portion 2 via the first curved surface CS1 of the first curved surface forming portion R12. In this embodiment, an edge E is formed on an end of the first curved surface CS1 of the first curved surface forming portion R12 in the third direction DIR3 and on an end of the first curved surface CS1 of the first curved surface forming portion R12 in the opposite direction to the third direction DIR3.

[0059] The magnetic core 1 can mitigate the occurrence of magnetic saturation. As a comparative example, a magnetic core 50 in which the first curved surface forming portion R1 is not formed in the tooth main body portion 31 will be described with reference to the drawings. FIG. 5 is a cross-sectional view showing the state of magnetic flux flowing through the magnetic core 50 according to the comparative example in a motor including the magnetic core 50 according to the comparative example. Note that in FIG. 5, only representative magnetic field lines MFL out of the multiple magnetic field lines MFL are denoted by reference symbols. Also, for the sake of explanation, the boundary lines between the tooth main body portion 31 and the core back portion 2 and the boundary lines between the tooth main body portion 31 and the tooth tip portion 32 are omitted in FIG. 5.

[0060] In the brushless motor 100, when current is applied to the coil 13 wound around the tooth main body portion 31, magnetic flux is generated in the tooth main body portion 31. This magnetic flux flows from the tooth main body portion 31 toward the front surface IS2 of the core back portion 2 or the back surface OS32 of the tooth tip portion 32. The direction of the magnetic flux flow can be changed by changing the direction of the current flowing through the coil 13. At this time, the magnetic flux tries to flow along the shortest path inside the magnetic core 50 according to the comparative example. In the magnetic core 50 according to the comparative example, angles A were formed at the portions where the first end surface ES1 of the tooth main body portion 31 was connected to the front surface IS2 of the core back portion 2 and the back surface OS2 of the tooth tip portion 32, respectively.

[0061] In the magnetic core 50 according to the comparative example, the flow of magnetic flux was impeded by the angle A, forcing the magnetic flux to take a detour near the angle A, making it difficult to flow. As a result, residual stress was generated near the angle A, increasing the magnetic resistance in the magnetic circuit and causing local magnetic saturation at the angle A. Therefore, when the magnetic core 50 according to the comparative example was used in a motor, the output torque of the motor could not be improved.

[0062] Next, the magnetic core 1 will be described with reference to the drawings. Fig. 6 is a cross-sectional view showing the magnetic flux flowing through the magnetic core 1 in the brushless motor 100. For ease of explanation, the boundary between the tooth main body 31 and the core back portion 2 and the boundary between the tooth main body 31 and the tooth tip portion 32 are omitted in Fig. 6. Furthermore, in Fig. 6, only a representative magnetic field line MFL among the multiple magnetic field lines MFL is denoted by a reference symbol.

[0063] In the magnetic core 1, the tooth main body 31 is formed with a first curved surface forming portion R11 having a concavely curved first curved surface CS1. The first curved surface CS1 of the first curved surface forming portion R11 smoothly connects to the back surface OS32 of the tooth tip 32. As shown in FIG. 6 , the tooth main body 31 is formed with the first curved surface forming portion R11, allowing magnetic flux to flow along the shortest path without detours near the first curved surface forming portion R11. Therefore, in the magnetic core 1, magnetic flux flows more easily near the first curved surface forming portion R11 than in the magnetic core 50 according to the comparative example. This reduces the occurrence of magnetic saturation near the first curved surface forming portion R11.

[0064] Furthermore, since the first curved surface forming portion R11 is formed on the tooth main body portion 31, the magnetic core 1 can more effectively receive the magnetic flux generated by the hard magnetic material 24 and including a component in the second direction DIR2 or the fourth direction DIR4. This effect becomes more pronounced when the end of the rotor member 22 in the second direction DIR2 is located further in the second direction DIR2 than the end of the tooth main body portion 31 in the second direction DIR2 and the distance in the second direction DIR2 between the end of the rotor member 22 in the second direction DIR2 and the end of the tooth main body portion 31 in the second direction DIR2 is longer, or when the end of the rotor member 22 in the fourth direction DIR4 is located further in the fourth direction DIR4 than the end of the tooth main body portion 31 in the fourth direction DIR4 and the distance in the fourth direction DIR4 between the end of the rotor member 22 in the fourth direction DIR4 and the end of the tooth main body portion 31 in the fourth direction DIR4 is longer.

[0065] Because the first curved surface CS1 of the first curved surface forming portion R11 is curved concavely, more coil 13 can be wound around tooth main body portion 31 than when the first curved surface CS1 of the first curved surface forming portion R11 is curved convexly. This increases the slot space factor of coil 13, and improves the output torque of brushless motor 100.

[0066] Furthermore, in the magnetic core 1, the first curved surface-forming portion R11 protrudes in the second direction DIR2 from the first flat surface FS1 of the first end face ES1 and is located only on the second direction DIR2 side of the first flat surface FS1 of the first end face ES1. In other words, the first curved surface-forming portion R11 is formed without reducing the cross-sectional area of ​​the tooth main body 31 in the second direction DIR2. Therefore, even if the first curved surface-forming portion R11 is formed, the saturation magnetic flux density of the magnetic flux flowing inside the tooth main body 31 does not decrease. This prevents a decrease in the output torque of the brushless motor 100.

[0067] In the magnetic core 1, the tooth main body 31 is formed with a first curved surface forming portion R12 having a concavely curved first curved surface CS1. The first curved surface CS1 of the first curved surface forming portion R12 is smoothly connected to the front surface IS2 of the core back portion 2. Because the tooth main body 31 is formed with the first curved surface forming portion R12, magnetic flux can flow along the shortest path without detours near the first curved surface forming portion R12. Therefore, in the magnetic core 1, magnetic flux flows more easily near the first curved surface forming portion R12 than in the magnetic core 50 according to the comparative example. This reduces the occurrence of magnetic saturation near the first curved surface forming portion R12.

[0068] Because the first curved surface CS1 of the first curved surface forming portion R12 is curved concavely, more coil 13 can be wound around tooth main body portion 31 than when the first curved surface CS1 of the first curved surface forming portion R12 is curved convexly. This increases the slot space factor of coil 13, and improves the output torque of brushless motor 100.

[0069] The first curved surface forming portion R12 formed on the tooth main body portion 31 enables the area in which magnetic flux flows to be expanded in the direction perpendicular to the first direction DIR1 for the core back portion 2. More specifically, when the magnetic core 1 is incorporated into the brushless motor 100, adjacent magnetic cores 1 are connected by their respective core back portions 2. Hereinafter, one of these adjacent magnetic cores 1 will be referred to as magnetic core 11, and the other will be referred to as magnetic core 12.

[0070] When magnetic flux generated in the tooth main body portion 31 of the magnetic core 11 by passing current through the coil 13 wound around the tooth main body portion 31 of the magnetic core 11 flows from the tooth main body portion 31 of the magnetic core 11 toward the front surface IS2 of the core back portion 2 of the magnetic core 11, magnetic flux is formed in the direction from the core back portion 2 of the magnetic core 11 toward the core back portion 2 of the magnetic core 12 (third direction DIR3).

[0071] While magnetic flux tends to flow along the shortest path, repulsive forces act between multiple magnetic fluxes, causing them to spread in directions (second direction DIR2 and fourth direction DIR4) perpendicular to the first direction DIR1 and third direction DIR3. In the magnetic core 50 according to the comparative example, the first curved surface-forming portion R1 is not formed on the core back portion 2 side of the tooth main body portion 31, so an angle A is formed at the portion where the first end face ES1 of the tooth main body portion 31 and the front face IS2 of the core back portion 2 connect. This angle A obstructs the flow of magnetic flux that tends to spread in the second direction DIR2 and the fourth direction DIR4, making it impossible to expand the area through which magnetic flux flows in the second direction DIR2 and the fourth direction DIR4 for the core back portion 2, and therefore preventing effective use of the core back portion 2 as a magnetic circuit. If the area through which the magnetic flux flows cannot be expanded, this leads to an increase in magnetic resistance in the magnetic circuit, which becomes a factor that reduces the output efficiency of the motor when the magnetic core 50 according to the comparative example is used in a motor.

[0072] Next, the magnetic core 1 will be described with reference to the drawings. Fig. 7 is a cross-sectional view showing the state of magnetic flux flowing through two adjacent magnetic cores 1 in the brushless motor 100. Note that in Fig. 7, only representative magnetic field lines MFL among the multiple magnetic field lines MFL are denoted by reference symbols.

[0073] In the magnetic core 11, the first curved surface forming portion R12 is formed on the tooth main body 31, so that the flow of magnetic flux is not obstructed by corners near the first curved surface forming portion R12, and the magnetic flux easily spreads in the second direction DIR2. Furthermore, in the magnetic core 12, the first curved surface forming portion R12 is formed on the tooth main body 31, so that the flow of magnetic flux is not obstructed by corners near the first curved surface forming portion R12, and the magnetic flux easily spreads in the second direction DIR2. In other words, in the magnetic core 11, the magnetic flux is easily emitted toward the magnetic core 12, and in the magnetic core 12, the magnetic flux is easily introduced from the magnetic core 11. This suppresses an increase in magnetic resistance in the magnetic circuit. Therefore, a decrease in the output efficiency of the brushless motor 100 is suppressed.

[0074] Furthermore, in the magnetic core 1, the first curved surface-forming portion R12 protrudes in the second direction DIR2 from the first flat surface FS1 of the first end face ES1 and is located only on the second direction DIR2 side of the first flat surface FS1 of the first end face ES1. In other words, the first curved surface-forming portion R12 is formed without reducing the cross-sectional area of ​​the tooth main body 31 in the second direction DIR2. Therefore, even if the first curved surface-forming portion R12 is formed, the saturation magnetic flux density of the magnetic flux flowing inside the tooth main body 31 does not decrease. This prevents a decrease in the output torque of the brushless motor 100.

[0075] (Method for manufacturing magnetic core 1) A method for manufacturing a magnetic core 1 according to a first embodiment of the present invention will be described below with reference to the drawings. FIG. 8 is a cross-sectional view showing an example of a manufacturing process for the magnetic core 1. FIG. 9 is a diagram showing the relationship between the radius of curvature CR1 of the first curved surface CS1 and the radius RA of the medium M. Note that in FIG. 9, only a representative first curved surface CS1 out of the four first curved surfaces CS1 is labeled with a reference symbol. FIG. 10 is a cross-sectional view showing the inside of the barrel B during the finishing process.

[0076] As shown in FIG. 8 , first, a soft magnetic powder SMP, a mixture of iron powder and epoxy resin powder, is filled into a mold DI. Next, the soft magnetic powder SMP filled in the mold DI is compressed with a punch P to compression-molde the soft magnetic powder SMP. The punch P has a convexly curved convex surface CON. In this embodiment, the number of convex surfaces CON is four. As a result, when the soft magnetic powder SMP is compression-molded, four first curved surface forming portions R1 are formed on the tooth main body portion 31. At this stage, burrs are formed on the surface of the compression-molded soft magnetic powder SMP due to the presence of a small gap between the mold DI and the punch P and the rough surface of the punch P. As shown in FIG. 9 , the radius of curvature CR1 of the first curved surface CS1 of the compression-molded soft magnetic powder SMP is greater than the radius RA of the medium M. In addition, when the first curved surface CS1 of the compression-molded soft magnetic powder SMP has a plurality of radii of curvature CR1, the minimum value of the plurality of radii of curvature CR1 needs to be larger than the radius RA of the medium M.

[0077] In this manufacturing method, after the soft magnetic powder SMP is compression-molded, a finishing process is performed in which the magnetic core 1 is polished. As shown in FIG. 10 , in the finishing process, the compression-molded soft magnetic powder SMP, media M, a grinding aid (not shown), and water W are first placed inside a hollow barrel B. The media M has a spherical shape with a radius RA. In this embodiment, there is one compression-molded soft magnetic powder SMP and one media M, but there may be multiple compression-molded soft magnetic powder SMP and multiple media M. When there are multiple media M, the magnetic core 1 can be efficiently finished. When there are multiple compression-molded soft magnetic powder SMP, multiple magnetic cores 1 can be simultaneously finished.

[0078] In the finishing step, the barrel B is rotated to bring the media M into contact with the compression-molded soft magnetic powder SMP, thereby polishing the compression-molded soft magnetic powder SMP. In the finishing step, the compression-molded soft magnetic powder SMP is polished with the media M, thereby removing burrs formed on the surface of the compression-molded soft magnetic powder SMP in the stage prior to the finishing step, and finishing the magnetic core 1. Note that the method of polishing the compression-molded soft magnetic powder SMP with the media M in the finishing step is not limited to rotating the barrel B, and may also be by vibrating the barrel B. Furthermore, the barrel B is not essential in the finishing step, as long as the compression-molded soft magnetic powder SMP is polished with the media M. Similarly, the grinding aid and water W are not essential in the finishing step.

[0079] The magnetic core 1 is a molded body made of soft magnetic powder. Therefore, compared to a magnetic core formed by laminating electromagnetic steel sheets, the first curved surface forming portion R1 can be easily formed as shown in the manufacturing method of the magnetic core 1. As a result, the magnetic core 1 can be easily manufactured.

[0080] According to the manufacturing method of the magnetic core 1, burrs formed on the first curved surface CS1 before the finishing process can be removed in the finishing process. More specifically, the radius of curvature CR1 of the first curved surface CS1 of the compression-molded soft magnetic powder SMP is larger than the radius RA of the media M. This allows the media M to contact every corner of the first curved surface CS1 in the finishing process, and burrs formed on the first curved surface CS1 in the stage prior to the finishing process can be removed in the finishing process. This prevents damage to the coil 13 when it is wound around the tooth main body 31 after the magnetic core 1 is completed.

[0081] Furthermore, as shown in the magnetic core 1, when an insulating film is applied to the surface of the magnetic core 1 after the finishing process, the insulating film can be made thinner since there are no burrs. This increases the slot space factor of the coil 13, and improves the output efficiency of the brushless motor 100.

[0082] [First Modification] (Configuration of Magnetic Core 1a) The configuration of a magnetic core 1a according to a first modification of the present invention will be described below with reference to the drawings. FIG. 11 is a perspective view of the magnetic core 1a. Note that in FIG. 11, reference numerals are assigned only to representative first curved surface forming portions R1 and first curved surfaces CS1 among the four first curved surface forming portions R1 and four first curved surfaces CS1, respectively. Regarding the magnetic core 1a according to the first modification, only the differences from the magnetic core 1 according to the first embodiment will be described, and the rest will be omitted.

[0083] As shown in FIG. 11, the magnetic core 1a differs from the magnetic core 1 in that the tooth main body 31 has four third curved surface forming portions R3.

[0084] The four third curved surface-forming portions R3 are parts of the tooth main body 31. One of the four third curved surface-forming portions R3 is formed at an end of the tooth main body 31 facing in the opposite direction to the third direction DIR3 and at an end of the tooth main body 31 facing in the second direction DIR2. One of the four third curved surface-forming portions R3 is formed at an end of the tooth main body 31 facing in the opposite direction to the third direction DIR3 and at an end of the tooth main body 31 facing in the fourth direction DIR4. One of the four third curved surface-forming portions R3 is formed at an end of the tooth main body 31 facing in the third direction DIR3 and at an end of the tooth main body 31 facing in the second direction DIR2. One of the four third curved surface-forming portions R3 is formed at an end of the tooth main body 31 facing in the third direction DIR3 and at an end of the tooth main body 31 facing in the fourth direction DIR4. In this modification, the four third curved surface forming portions R3 have a symmetrical structure with respect to one another. Note that the number of third curved surface forming portions R3 does not have to be four. Furthermore, the third curved surface forming portions R3 do not have to have a symmetrical structure with respect to one another.

[0085] Each of the four third curved surface forming portions R3 has a third curved surface CS3. The third curved surface CS3 of each of the four third curved surface forming portions R3 is part of each of the four slopes SL. The third curved surface CS3 of each of the four third curved surface forming portions R3 is tapered. More specifically, the third curved surface CS3 of each of the four third curved surface forming portions R3 tapers toward the core back portion 2 on the core back portion 2 side of the tooth main body 31. Furthermore, the third curved surface CS3 of each of the four third curved surface forming portions R3 tapers toward the tooth tip portion 32 on the tooth tip portion 32 side of the tooth main body 31. The third curved surface CS3 smoothly connects to the edge E of the first curved surface CS1 in the third direction DIR3.

[0086] The magnetic core 1a described above also achieves the same effect as the magnetic core 1. Furthermore, in the magnetic core 1a, the tooth main body 31 is formed with the third curved surface forming portion R3, which allows the magnetic flux to flow more easily without being obstructed by corners at the portion where the first end face ES1 or the second end face ES2 of the tooth main body 31 connects to the first side face SS1 or the second side face SS2 on the core back 2 side or the tooth tip 32 side of the tooth main body 31. This further mitigates the occurrence of local magnetic saturation.

[0087] [Second Modification] (Configuration of Magnetic Core 1b) The configuration of a magnetic core 1b according to a second modification of the present invention will be described below with reference to the drawings. FIG. 12 is a perspective view of the magnetic core 1b. FIG. 13 is a cross-sectional view of the magnetic core 1b and an enlarged cross-sectional view of the vicinity of the second curved surface forming portion R21. Note that the cross-section of the magnetic core 1b in FIG. 13 is a plane that passes through the second flat surface FS2 of the second side surface SS2 of the tooth main body portion 31 and is perpendicular to the second flat surface FS2 of the second side surface SS2 of the tooth main body portion 31. FIG. 14 is a diagram showing the relationship between the radius of curvature CR2 of the second curved surface CS2 and the radius RA of the medium M. Note that in FIG. 14, only a representative second curved surface CS2 out of the four second curved surfaces CS2 is denoted by a reference symbol. Regarding the magnetic core 1b according to the second modification, only the differences from the magnetic core 1a according to the first modification will be described, and the rest will be omitted.

[0088] As shown in FIGS. 12 and 13, the magnetic core 1b differs from the magnetic core 1a in that the tooth main body 31 has four second curved surface forming portions R2.

[0089] The four second curved surface forming portions R2 are parts of the tooth main body 31. One of the four second curved surface forming portions R2 is formed at an end of the tooth main body 31 in the first direction DIR1 and at an end of the tooth main body 31 facing in the opposite direction to the third direction DIR3. One of the four second curved surface forming portions R2 is formed at an end of the tooth main body 31 facing in the opposite direction to the first direction DIR1 and at an end of the tooth main body 31 facing in the opposite direction to the third direction DIR3. One of the four second curved surface forming portions R2 is formed at an end of the tooth main body 31 facing in the first direction DIR1 and at an end of the tooth main body 31 facing in the third direction DIR3. One of the four second curved surface forming portions R2 is formed at an end of the tooth main body 31 facing in the opposite direction to the first direction DIR1 and at an end of the tooth main body 31 facing in the third direction DIR3. In this modification, the four second curved surface forming portions R2 have a symmetrical structure with respect to each other. Therefore, a description of the two second curved surface forming portions R2 formed at the end of the tooth main body portion 31 in the third direction DIR3 will be omitted. Note that the number of second curved surface forming portions R2 does not have to be four. Furthermore, the second curved surface forming portions R2 do not have to have a symmetrical structure with respect to each other.

[0090] First, we will explain the second curved surface portion R2 formed on the end of the tooth main body 31 in the first direction DIR1 and on the end of the tooth main body 31 in the opposite direction to the third direction DIR3. Hereinafter, this second curved surface portion R2 will be referred to as the second curved surface portion R21.

[0091] The second curved surface forming portion R21 protrudes from the second flat surface FS2 of the second side surface SS2 in the opposite direction of the third direction DIR3. The second curved surface forming portion R21 is located only on the opposite side of the third direction DIR3 from the second flat surface FS2 of the second side surface SS2. More specifically, the second curved surface forming portion R21 has a second curved surface CS2. The second curved surface CS2 of the second curved surface forming portion R21 is concavely curved. In this modification, the second curved surface CS2 of the second curved surface forming portion R21 is curved in an arc shape in a cross section perpendicular to the second direction DIR2. The second curved surface CS2 of the second curved surface forming portion R21 has a single radius of curvature CR2. The second curved surface CS2 of the second curved surface forming portion R21 does not have to be curved in an arc shape in a cross section perpendicular to the second direction DIR2. Furthermore, the second curved surface CS2 of the second curved surface forming portion R21 may have a plurality of radii of curvature CR2.

[0092] The second curved surface CS2 of the second curved surface forming portion R21 is part of the second side surface SS2. The second curved surface CS2 of the second curved surface forming portion R21 is smoothly connected to the back surface OS32 of the tooth tip portion 32. Therefore, the tooth main body 31 is connected to the back surface OS32 of the tooth tip portion 32 via the second curved surface CS2 of the second curved surface forming portion R21.

[0093] Next, we will explain the second curved surface portion R2 formed on the end of the tooth main body 31 opposite to the first direction DIR1 and the end of the tooth main body 31 opposite to the third direction DIR3. Hereinafter, this second curved surface portion R2 will be referred to as the second curved surface portion R22.

[0094] The second curved surface forming portion R22 protrudes from the second flat surface FS2 of the second side surface SS2 in the opposite direction of the third direction DIR3. The second curved surface forming portion R22 is located only on the opposite side of the third direction DIR3 from the second flat surface FS2 of the second side surface SS2. More specifically, the second curved surface forming portion R22 has a second curved surface CS2. The second curved surface CS2 of the second curved surface forming portion R22 is concavely curved. In this modification, the second curved surface CS2 of the second curved surface forming portion R22 is curved in an arc shape in a cross section perpendicular to the second direction DIR2. The second curved surface CS2 of the second curved surface forming portion R21 has a single radius of curvature CR2. The second curved surface CS2 of the second curved surface forming portion R22 does not have to be curved in an arc shape in a cross section perpendicular to the second direction DIR2. Furthermore, the second curved surface CS2 of the second curved surface forming portion R22 may have a plurality of radii of curvature CR2.

[0095] The second curved surface CS2 of the second curved surface forming portion R22 is part of the second side surface SS2. The second curved surface CS2 of the second curved surface forming portion R22 is smoothly connected to the front surface IS2 of the core back portion 2. Therefore, the tooth main body portion 31 is smoothly connected to the front surface IS2 of the core back portion 2 via the second curved surface CS2 of the second curved surface forming portion R22.

[0096] The manufacturing method of the magnetic core 1b according to this modification is the same as the manufacturing method of the magnetic core 1 according to the first embodiment. However, as shown in Fig. 14, the radius of curvature CR2 of the second curved surface CS2 of the compression-molded soft magnetic powder SMP is larger than the radius RA of the medium M. Note that, when the second curved surface CS2 of the compression-molded soft magnetic powder SMP has multiple radii of curvature CR2, it is sufficient that the minimum value of the multiple radii of curvature CR2 is larger than the radius RA of the medium M.

[0097] The magnetic core 1b described above also achieves the same effects as the magnetic core 1a. Furthermore, in the magnetic core 1b, the tooth main body 31 is formed with a second curved surface-forming portion R21 having a concavely curved second curved surface CS2. The second curved surface CS2 of the second curved surface-forming portion R21 smoothly connects to the back surface OS32 of the tooth tip 32. By forming the second curved surface-forming portion R21 on the tooth main body 31, magnetic flux can flow along the shortest path without detours near the second curved surface-forming portion R21. Therefore, in the magnetic core 1b, magnetic flux flows more easily near the second curved surface-forming portion R21 than in the magnetic core 50 according to the comparative example. This reduces the occurrence of magnetic saturation near the second curved surface-forming portion R21.

[0098] Because the second curved surface CS2 of the second curved surface forming portion R21 is curved concavely, more coil 13 can be wound around tooth main body portion 31 than when the second curved surface CS2 of the second curved surface forming portion R21 is curved convexly. This increases the slot space factor of coil 13, and improves the output torque of brushless motor 100.

[0099] Furthermore, in the magnetic core 1b, the second curved surface-forming portion R21 protrudes from the second flat surface FS2 of the second side surface SS2 in the direction opposite to the third direction DIR3 and is located only on the opposite side of the second flat surface FS2 of the second side surface SS2 in the third direction DIR3. In other words, the second curved surface-forming portion R21 is formed without reducing the cross-sectional area of ​​the tooth main body portion 31 in the direction opposite to the third direction DIR3. Therefore, even if the second curved surface-forming portion R21 is formed, the saturation magnetic flux density of the magnetic flux flowing inside the tooth main body portion 31 does not decrease. This prevents a decrease in the output torque of the brushless motor 100.

[0100] In the magnetic core 1b, the tooth main body 31 is formed with a second curved surface forming portion R22 having a concavely curved second curved surface CS2. The second curved surface CS2 of the second curved surface forming portion R22 is smoothly connected to the front surface IS2 of the core back portion 2. By forming the second curved surface forming portion R22 on the tooth main body 31, magnetic flux can flow along the shortest path without detours near the second curved surface forming portion R22. Therefore, in the magnetic core 1b, magnetic flux flows more easily near the second curved surface forming portion R22 than in the magnetic core 50 according to the comparative example. This reduces the occurrence of magnetic saturation near the second curved surface forming portion R22.

[0101] Because the second curved surface CS2 of the second curved surface forming portion R22 is curved concavely, more coil 13 can be wound around tooth main body portion 31 than when the second curved surface CS2 of the second curved surface forming portion R22 is curved convexly. This increases the slot space factor of coil 13, and improves the output torque of brushless motor 100.

[0102] According to the manufacturing method of the magnetic core 1b, burrs formed on the second curved surface CS2 before the finishing process can be removed in the finishing process. More specifically, the radius of curvature CR2 of the second curved surface CS2 of the compression-molded soft magnetic powder SMP is greater than the radius RA of the media M. This allows the media M to contact every corner of the second curved surface CS2 in the finishing process, and burrs formed on the second curved surface CS2 in the stage prior to the finishing process can be removed in the finishing process. This prevents damage to the coil 13 when it is wound around the tooth main body 31 after the magnetic core 1b is completed.

[0103] [Other Embodiments] The magnetic core according to the present invention is not limited to the magnetic core 1, the magnetic core 1a, or the magnetic core 1b, and can be modified within the scope of the present invention. In addition, the structures of the magnetic core 1, the magnetic core 1a, or the magnetic core 1b may be arbitrarily combined.

[0104] The rotating electric machine may include the magnetic core 1, the magnetic core 1a, or the magnetic core 1b, and may include a brush.

[0105] The present invention has the following configuration.

[0106] (1) A magnetic core for use in a rotary electric machine, comprising: a core back portion having a front surface that faces a first direction toward a rotation axis of the rotary electric machine when the magnetic core is incorporated into the rotary electric machine; and teeth portions, wherein the teeth portions include: a tooth main body portion extending in the first direction from the front surface; and a tooth tip portion provided at a tip of the tooth main body portion, wherein the tooth tip portion has a back surface that faces a direction opposite to the first direction, and the tooth main body portion has an end surface that faces a second direction along the rotation axis when the magnetic core is incorporated into the rotary electric machine, and the end surface has a concave curved surface that smoothly connects the end surface to the front surface of the core back portion or the back surface of the tooth tip portion, and the curved surface is formed by a first curved surface forming portion that is a part of the tooth main body portion.

[0107] (2) The magnetic core according to (1), wherein the end face includes a first flat surface that is a surface parallel to the first direction, and the first curved surface forming portion protrudes from the first flat surface toward the second direction and is located only on the second direction side of the first flat surface.

[0108] (3) A magnetic core according to (1) or (2), wherein the tooth main body portion has a side surface facing in a circumferential direction centered on the rotation axis when the magnetic core is incorporated into the rotating electric machine, the side surface having a concave curved surface that smoothly connects the side surface to the front surface of the core back portion or the back surface of the tooth tip portion, and the curved surface is formed by a second curved surface forming portion that is part of the tooth main body portion.

[0109] (4) The magnetic core according to (3), wherein the side surface includes a second flat surface that is a surface parallel to the first direction, and the second curved surface forming portion protrudes from the second flat surface in the circumferential direction and is located only on the circumferential side of the second flat surface.

[0110] (5) A magnetic core described in any one of (1) to (4), wherein the tooth main body portion has a side surface facing a third direction that is a circumferential direction centered on the rotation axis when the magnetic core is incorporated into the rotating electric machine, and a slope connecting the end face and the side surface, and the slope has a tapered curved surface that smoothly connects itself to an edge of the curved surface in the third direction, and the tapered curved surface is formed by a third curved surface forming portion that is part of the tooth main body portion.

[0111] (6) The magnetic core according to any one of (1) to (5), which is a molded body formed from soft magnetic powder.

[0112] (7) A magnetic core with a coil, comprising: the magnetic core according to any one of (1) to (6); and a coil wound around the tooth main body portion.

[0113] (8) A rotating electrical machine comprising the magnetic core according to any one of (1) to (6).

[0114] (9) A method for manufacturing a magnetic core, comprising a finishing step of finishing the magnetic core described in any one of (1) to (6) by polishing using spherical media, and manufacturing the magnetic core in a stage prior to the finishing step so that the radius of curvature of the curved surface of the end face is already larger than the diameter of the media used in the finishing step.

[0115] (10) A method for manufacturing a magnetic core, comprising a finishing step of finishing the magnetic core described in (3) or (4) by polishing using spherical media, and manufacturing the magnetic core in a stage prior to the finishing step so that the radius of curvature of the curved surface of the side surface is already larger than the diameter of the media used in the finishing step.

[0116] 1, 11, 12, 1a, 1b: magnetic core 2: core back portion 3: teeth portion 10: stator 13: coil 14: bearing 14a: first bearing 14b: second bearing 15: housing 15a: first housing 15b: second housing 20: rotor 21: shaft 22: rotor member 23: soft magnetic material 24: hard magnetic material 31: teeth main body portion 32: teeth tip portion 100: brushless motor A: angle B: barrel CON: convex surface CR1, CR2: radius of curvature CS1: first curved surface CS2: second curved surface CS3: third curved surface DI: mold DIR1: first direction DIR2: second direction DIR3: third direction DIR4: fourth direction ES1: first end face ES2: Second end surface FS1: First flat surface FS2: Second flat surface IS2, IS32: Front surface M: Media MFL: Magnetic field lines OP: Opening OS2, OS32: Back surface P: Punch R1, R11, R12: First curved surface forming portion R2, R21, R22: Second curved surface forming portion R3: Third curved surface forming portion RA: Radius SMP: Soft magnetic powder SS1: First side surface SS2: Second side surface SL: Slope W: Water

Claims

1. A magnetic core for use in a rotating electric machine, comprising: a core back portion having a front surface that faces a first direction toward a rotation axis of the rotating electric machine when the magnetic core is assembled into the rotating electric machine; and a teeth portion, wherein the teeth portion includes a teeth main body portion extending in the first direction from the front surface, and a teeth tip portion provided at a tip of the teeth main body portion, wherein the teeth tip portion has a back surface that faces in a direction opposite to the first direction, and the teeth main body portion has an end face that faces a second direction along the rotation axis when the magnetic core is assembled into the rotating electric machine, the end face having a concave curved surface that smoothly connects the end face to the front surface of the core back portion or the back surface of the teeth tip portion, the curved surface being formed by a first curved surface forming portion that is part of the teeth main body portion.

2. A magnetic core as described in claim 1, wherein the end face includes a first flat surface that is a surface parallel to the first direction, and the first curved surface forming portion protrudes from the first flat surface in the second direction and is located only on the second direction side of the first flat surface.

3. A magnetic core as described in claim 1 or claim 2, wherein the tooth main body portion has a side surface that faces in a circumferential direction centered on the rotation axis when the magnetic core is incorporated into the rotating electric machine, the side surface having a concave curved surface that smoothly connects the side surface to the front surface of the core back portion or the back surface of the tooth tip portion, the curved surface being formed by a second curved surface forming portion that is part of the tooth main body portion.

4. A magnetic core as described in claim 3, wherein the side surface includes a second flat surface that is a surface parallel to the first direction, and the second curved surface forming portion protrudes from the second flat surface in the circumferential direction and is located only on the circumferential side of the second flat surface.

5. A magnetic core as described in any of claims 1 to 4, wherein the tooth main body portion has a side surface facing a third direction which is a circumferential direction centered on the rotation axis when the magnetic core is incorporated into the rotating electric machine, and a slope connecting the end face and the side surface, the slope having a tapered curved surface which smoothly connects itself to an edge of the curved surface in the third direction, and the tapered curved surface is formed by a third curved surface forming portion which is part of the tooth main body portion.

6. A magnetic core according to any one of claims 1 to 5, which is a compact formed from soft magnetic powder.

7. A magnetic core with a coil, comprising: a magnetic core according to any one of claims 1 to 6; and a coil wound around the tooth main body portion.

8. A rotating electrical machine comprising a magnetic core according to any one of claims 1 to 6.

9. A method for manufacturing a magnetic core, comprising a finishing step of polishing the magnetic core according to any one of claims 1 to 6 using spherical media, and manufacturing the magnetic core in a stage prior to the finishing step such that the radius of curvature of the curved surface of the end face is already larger than the diameter of the media used in the finishing step.

10. A method for manufacturing a magnetic core, comprising a finishing step of polishing the magnetic core according to claim 3 or 4 using spherical media, and manufacturing the magnetic core prior to the finishing step such that the radius of curvature of the curved surface of the side surface is already larger than the diameter of the media used in the finishing step.

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