Axial clearance type motor

Abstract

An axial-gap type motor is provided that can reduce the cogging torque and torque ripple included in the output torque while suppressing a decrease in the output torque. A plurality of pressed powder teeth (32) extend in the radial direction of the stator core and each has a trapezoidal shape in which the circumferential length of the radially outer end portion of the pressed powder tooth is greater than the circumferential length of the radially inner end portion of the pressed powder tooth. A plurality of field magnets (22) are arranged such that the circumferential length of the radially inner end portion (22b) of the magnet is greater than or equal to the circumferential length of the radially outer end portion (22a) of the magnet, and when the rotor (2) and the stator core (30) rotate relative to each other about the rotation axis (P), a part of the field magnet (22) first overlaps with the radially inner portion (U) of the pressed powder tooth of the pressed powder tooth (32), and when the field magnet (22) is at the q-axis position relative to the pressed powder tooth (32), adjacent ones of the field magnets (22) respectively overlap with one pressed powder tooth (32).

Description

Technical Field

[0001] This teaching relates to an axial-gap motor. Background Art

[0002] In known axial-gap motors, a rotor including a plurality of field magnets and capable of rotating about a rotation axis and a stator including a stator core and stator coils are located in the axial direction of the rotation axis. A known example of such an axial-gap motor is the axial-gap motor disclosed in Patent Document 1.

[0003] In such an axial-gap motor, the rotor includes an annular back yoke attached to a shaft and a plurality of permanent magnets provided on a surface of the back yoke close to the stator. As in Patent Document 1 for example Figure 1 As shown, each permanent magnet has an arc shape. The rotor is located in the axial direction of the rotation axis of the rotor with respect to the stator.

[0004] The stator core of the stator includes an annular back yoke provided substantially orthogonally to the shaft and compression powder iron core teeth provided on a surface of the back yoke close to the rotor. The plurality of teeth extend along the shaft and are arranged around the shaft. Coils are wound around each tooth around the axis. The teeth are fixed to the back yoke by press fitting or adhesion for example.

[0005] As in for example Patent Document 1 Figure 1 As shown, each tooth has a triangular shape.

[0006] Citation List

[0007] Patent Document

[0008] Patent Document 1: Japanese Patent No. 5040407 Summary of the Invention

[0009] Technical Problem

[0010] For example, from the viewpoint of miniaturization, it is required that an axial-gap motor having the above configuration has as high an output torque as possible. As disclosed in Patent Document 1, in such a case of increasing the output torque of the axial-gap motor, the size of the permanent magnet of the rotor is preferably as large as possible.

[0011] In the case where the permanent magnet of the rotor and the teeth of the stator are formed into the shapes described in Patent Document 1, although the output torque of the axial-gap motor can be increased, the cogging torque and torque ripple included in the output torque of the axial-gap motor will also increase.

[0012] The cogging torque and torque ripple included in the output torque significantly affect the performance of the motor. Therefore, it is necessary to reduce the cogging torque and torque ripple included in the output torque. However, if the cogging torque and torque ripple included in the output torque are reduced, the output torque itself will also decrease. To this end, there is a need for an axial gap motor that can reduce the cogging torque and torque ripple included in the output torque while suppressing the reduction of the output torque.

[0013] Therefore, an object of the present teaching is to provide an axial gap type motor capable of reducing cogging torque and torque ripple included in output torque while suppressing a decrease in output torque.

[0014] Solution to the problem

[0015] The inventors of the present teachings have studied a configuration of an axial gap type motor that can reduce cogging torque and torque ripple included in the output torque while suppressing a decrease in the output torque. Through intensive studies, the inventors have arrived at the following configuration.

[0016] An axial gap motor according to one embodiment of the present teachings is an axial gap electric motor comprising: a rotor including multiple field magnets and rotatable about a rotation axis; a cylindrical stator core located axially relative to the rotor in the rotation axis direction, the stator core comprising a yoke and a plurality of teeth arranged circumferentially about the rotation axis relative to the yoke; and a stator coil wound around each of the plurality of teeth. Each of the plurality of teeth is formed from pressed particles. When the plurality of teeth are viewed in the axial direction, each of the plurality of teeth extends in the radial direction of the stator core and has a trapezoidal shape, wherein the circumferential length of the radially outer end of the tooth located at the radially outer end of the tooth is greater than the circumferential length of the radially inner end of the tooth located at the radially inner end of the tooth. Each pair of circumferentially adjacent teeth in the plurality of teeth forms a slot capable of accommodating the stator coil and having a rectangular shape when the plurality of teeth are viewed in the axial direction. In each of the plurality of field magnets, a circumferential length of a radially inner end portion of the magnet located at an inner end of the field magnet in the radial direction is greater than or equal to a circumferential length of a radially outer end portion of the field magnet located at an outer end of the field magnet in the radial direction, and when the rotor and the stator core rotate relative to each other around the rotation axis, when the plurality of field magnets and the plurality of teeth are viewed in the axial direction, a portion of the field magnet first overlaps with a radially inner portion of the tooth located on the inner side of a center of a corresponding one of the teeth in the radial direction, and when the field magnet is located at a q-axis position relative to the tooth, when the plurality of field magnets and the plurality of teeth are viewed in the axial direction, each group of adjacent ones of the field magnets overlaps with one of the teeth.

[0017] The teeth are formed of pressed particles, and when observing the teeth in the axial direction, the teeth extend in the radial direction of the stator core and each has a trapezoidal shape, where the circumferential length of the radially outer end of the tooth is greater than the circumferential length of the radially inner end of the tooth. In each of the field magnets, the circumferential length of the radially inner end of the magnet is greater than or equal to the circumferential length of the radially outer end of the magnet. With these shapes of the teeth and the field magnets, when the rotor rotates relative to the stator about the rotation axis and the rotor and the stator are observed in the axial direction, the field magnets first overlap with the radially inner part of the teeth. The output torque of the axial-gap type motor is significantly affected by the magnetic flux generated by the field magnets in the radially inner part of the teeth. As described above, when the rotor and the stator rotate relative to each other about the rotation axis and the rotor and the stator are observed in the axial direction, the field magnets first overlap with the radially inner part of the teeth. Therefore, a decrease in the output torque of the axial-gap type motor can be suppressed.

[0018] In addition, in the above configuration, when the field magnets are located at the q-axis position relative to the teeth and the plurality of field magnets and the plurality of teeth are observed in the axial direction, two adjacent ones of the plurality of field magnets respectively overlap with one tooth. Therefore, a significant change in the magnetic flux generated by the plurality of field magnets in the teeth can be suppressed. In this way, the change in the magnetic flux generated in the teeth of the stator by the field magnets of the rotor is suppressed, so that the torque ripple generated in the rotor can be suppressed. Therefore, the cogging torque and the torque ripple included in the output torque of the axial-gap motor can be reduced.

[0019] Therefore, an axial-gap type motor can be provided, which can reduce the cogging torque and the torque ripple included in the output torque while suppressing a decrease in the output torque.

[0020] On the other hand, the axial-gap type motor according to the present teachings preferably includes the following configuration. The plurality of field magnets are configured such that when the rotor and the stator core are observed in the axial direction and the field magnets are located at the q-axis position relative to the teeth, the field magnets cover the circumferential ends of the teeth extending in the radial direction.

[0021] With this configuration, when the field magnets are located at the q-axis position relative to the teeth and the rotor and the stator core are observed in the axial direction, the field magnets of the rotor overlap with the circumferential ends of the teeth of the stator core. Therefore, a significant change in the magnetic flux generated by the field magnets in the teeth at the q-axis position can be suppressed.

[0022] In addition, compared with the case where the field magnets of the rotor do not overlap with the circumferential ends of the teeth of the stator core when the field magnets are located at the q-axis position relative to the teeth, the above configuration can increase the output torque of the axial-gap type motor.

[0023] Therefore, an axial-gap type motor can be provided, which can reduce the cogging torque and the torque ripple included in the output torque while suppressing a decrease in the output torque.

[0024] On the other hand, the axial-gap type motor according to the present teachings preferably includes the following configuration. Each of the plurality of field magnets has a size sufficient such that when the rotor and the stator core are viewed along the axial direction, at least one magnet radially inner end of the plurality of field magnets always overlaps radially inside each tooth of the plurality of teeth when the rotor and the stator core rotate relative to each other about the rotation axis.

[0025] Therefore, when the rotor and the stator core rotate relative to each other about the rotation axis, a significant change in the magnetic flux generated in the teeth of the stator core due to the field magnets of the rotor at the q-axis position can be suppressed. In addition, compared with the case where the magnet radially inner end does not always overlap the plurality of teeth when the rotor rotates relative to the stator core about the rotation axis when the rotor and the stator core are viewed along the axial direction, the output torque of the axial-gap type motor can be increased.

[0026] On the other hand, the axial-gap type motor according to the present teachings preferably includes the following configuration. Each of the plurality of field magnets has a rectangular shape in which, when the rotor is viewed along the axial direction, the circumferential length of the magnet radially inner end is equal to the circumferential length of the magnet radially outer end.

[0027] Therefore, the region where the field magnets of the rotor overlap the teeth of the stator core when the rotor and the stator core are viewed along the axial direction can be maximized, while reducing the cogging torque and torque ripple included in the output torque when the rotor and the stator core rotate relative to each other about the rotation axis.

[0028] Therefore, an axial-gap type motor can be provided that can reduce the cogging torque and torque ripple included in the output torque while suppressing a decrease in the output torque.

[0029] On the other hand, the axial-gap type motor according to the present teachings preferably includes the following configuration. Each of the plurality of field magnets is configured such that when the rotor and the stator core are viewed along the axial direction, the magnet radially inner end is located outside the tooth radially inner end in the radial direction.

[0030] Therefore, compared with the case where the magnet radially inner end of the field magnet is located inside the tooth radially inner end in the radial direction when the rotor and the stator core are viewed along the axial direction, the output torque can be increased.

[0031] The terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the invention.

[0032] The term "and / or" used herein includes any and all combinations of one or more of the associated listed items.

[0033] It should be further understood that when used in this specification, the terms "comprising", "comprises" or "having" and their variants specify the presence of the stated features, steps, elements, components and / or their equivalents, but do not preclude the presence or addition of one or more other steps, operations, elements, components and / or groups thereof.

[0034] It should be further understood that the terms "mounted", "connected", "coupled" and / or their equivalents are used broadly and include both direct and indirect mounting, connection and coupling. Further, "connected" or "coupled" is not limited to physical or mechanical connection or coupling, but may include direct or indirect connection or coupling.

[0035] Unless defined otherwise, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0036] It will be further understood that terms such as those defined in commonly used dictionaries should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and this disclosure, and should not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0037] In describing the present invention, it will be understood that several techniques and steps are disclosed. Each of these has its respective benefits, and each can also be used in combination with one or more or in some cases all of the other disclosed techniques.

[0038] Accordingly, for clarity, this specification will avoid repeating every possible combination of the individual steps in an unnecessary manner. However, the specification and claims should be read with the understanding that such combinations are fully within the scope of the present invention and the claims.

[0039] Embodiments of an axial-gap type motor in accordance with this teaching will be described herein.

[0040] In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to one of ordinary skill in the art that the present invention may be practiced without these specific details.

[0041] This disclosure should be regarded as illustrative of the present invention and is not intended to limit the present invention to the specific embodiments shown by the following figures or the specification.

[0042] [Axial-gap type motor]

[0043] The axial-gap motor of the present invention refers to a motor in which a rotor and a stator are arranged in the axial direction of the rotation axis of the rotor and the rotor rotates around the rotation axis. The rotor includes a plurality of field magnets arranged in the circumferential direction around the rotation axis. The stator includes a plurality of teeth arranged in the circumferential direction around the rotation axis. A stator coil is wound around each of the plurality of teeth. The plurality of field magnets of the rotor and the plurality of teeth of the stator are opposed to each other in the axial direction. Therefore, the axial-gap motor has a gap (axial gap) in the axial direction between the plurality of field magnets and the plurality of teeth.

[0044] [Pressed particles]

[0045] The pressed particles of the present invention refer to fine particles including magnetic material particles. For example, a pressed powder tooth is formed by pressing the pressed particles. A base yoke can be formed of the pressed particles.

[0046] [Outer end of tooth in radial direction]

[0047] The outer end of tooth in radial direction of the present invention refers to a part of the tooth extending in the radial direction of the stator core, and the outer end of tooth in radial direction is located at the outer end in the radial direction. The circumferential length of the outer end of tooth in radial direction refers to, for example, the circumferential length of the outermost part of the outer end of tooth in radial direction.

[0048] [Inner end of tooth in radial direction]

[0049] The inner end of tooth in radial direction of the present invention refers to a part of the tooth extending in the radial direction of the stator core, and the inner end of tooth in radial direction is located at the inner end in the radial direction. The circumferential length of the inner end of tooth in radial direction refers to, for example, the circumferential length of the innermost part of the inner end of tooth in radial direction.

[0050] [Inner part of tooth in radial direction]

[0051] The inner part of tooth in radial direction of the present invention refers to a part of the tooth extending in the radial direction of the stator core, and the inner part of tooth in radial direction is located inside the center of the tooth in the radial direction. The inner part of tooth in radial direction includes the inner end of tooth in radial direction.

[0052] [Outer end of magnet in radial direction]

[0053] The outer end of magnet in radial direction of the present invention refers to a part of the field magnet located at the outer end in the radial direction of the field magnet in the radial direction of the stator core. The circumferential length of the outer end of magnet in radial direction refers to, for example, the circumferential length of the outermost part of the outer end of magnet in radial direction.

[0054] [Inner end of magnet in radial direction]

[0055] The inner end of magnet in radial direction of the present invention refers to a part of the field magnet located at the inner end in the radial direction of the field magnet in the radial direction of the stator core. The circumferential length of the inner end of magnet in radial direction refers to, for example, the circumferential length of the innermost part of the inner end of magnet in radial direction.

[0056] [q-axis position]

[0057] The state where the magnetic field is in the q-axis position relative to the teeth means that when observing the rotor and stator cores in the axial direction, the center of the teeth in the circumferential direction is at a position overlapping with the center of the interval between two of the plurality of field magnets of the rotor that are adjacent to each other in the circumferential direction.

[0058] Advantageous effects of the present invention

[0059] According to an embodiment of the present teaching, an axial-gap type motor can be provided that can reduce the cogging torque and torque ripple included in the output torque while suppressing a decrease in the output torque. Description of the drawings

[0060] Figure 1 Figure 1 is a view of the axial-gap type motor according to the embodiment observed in the first direction.

[0061] Figure 2 Figure 2 is a cross-sectional view taken along line II-II in Figure 1 .

[0062] Figure 3 Figure 3 is a view showing a schematic configuration of the base yoke.

[0063] Figure 4A Figure 4A is a perspective view showing a schematic configuration of the pressed powder teeth.

[0064] Figure 4B Figure 4B is a view of the pressed powder teeth observed in the axial direction.

[0065] Figure 5 Figure 5 is a perspective view showing a schematic configuration of the resin bobbin.

[0066] Figure 6 Figure 6 is a perspective view showing a state where the pressed powder teeth are inserted into the accommodation space of the resin bobbin for the pressed powder teeth and the stator coil is wound around the side surface of the resin bobbin.

[0067] Figure 7 Figure 7 is a view of the stator observed in the first direction.

[0068] Figure 8 Figure 8 is a view of the stator observed in the second direction.

[0069] ​​​​​​​​​​​​​​​​​​​Figure 9 Figure 9 is a view showing a state where the rotor rotates about the rotation axis relative to the stator when viewed in the axial direction.

[0070] Figure 10 Figure 10 (a) shows the positional relationship between the field magnet and the pressed powder teeth of the stator according to the embodiment, Figure 10 (b) shows the positional relationship between the trapezoidal field magnet and the pressed powder of the stator, Figure 10 (c) shows the positional relationship between the field magnet having a width narrower than that of the field magnet of the present embodiment and the pressed powder teeth of the stator.

[0071] Figure 11 Figure 11 is a view schematically showing that when the field magnet is located on the q-axis with respect to the pressed powder teeth, the intersection point between the trapezoidal field magnet and the pressed powder teeth changes as the inclination of the hypotenuse of the trapezoidal field magnet changes when the field magnet and the pressed powder teeth are viewed in the axial direction.

[0072] Figure 12 Figure 12 is a view showing Figure 11 the relationship between the intersection point, the average torque of the output torque of the axial-gap type motor, and the torque ripple and cogging torque included in the output torque in the case where the intersection point changes as shown. DETAILED DESCRIPTION

[0073] Embodiments will be described below with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and their description will not be repeated. The dimensions of the components in the drawings do not strictly represent the actual dimensions of the components and the dimensional ratios of the components.

[0074] Hereinafter, the direction in which the rotation axis P of the axial-gap type motor 1 extends will be referred to as the "axial direction", and hereinafter, the radial direction of the rotor of the axial-gap type motor 1 will be referred to as the "radial direction". The direction in which the rotor 2 of the axial-gap type motor 1 rotates about the rotation axis P will be referred to as the "circumferential direction". The radial direction is a direction orthogonal to the rotation axis P of the axial-gap type motor 1.

[0075] Hereinafter, the direction in which the stator 3 and the rotor 2 are arranged in sequence in the axial direction will be referred to as the first direction. The direction in which the rotor 2 and the stator 3 are arranged in sequence in the axial direction will be referred to as the second direction.

[0076] <OVERALL CONFIGURATION>

[0077] Refer to Figure 1 and Figure 2 to describe the axial-gap type motor 1 according to the first embodiment. Figure 1 ​​​​​​​is a plan view showing a schematic configuration of the axial-gap type motor 1. Figure 1 is a view of the stator 3 of the axial-gap type motor 1 observed in the first direction. Figure 2 is a cross-sectional view showing a cross-section of the axial-gap type motor 1 taken along the line II-II in the radial direction.

[0078] As Figure 2 shown, the axial-gap type motor 1 according to the present embodiment is, for example, a motor in which the rotor 2 and the stator 3 are arranged in the axial direction and the rotor 2 rotates about the rotation axis P.

[0079] The axial-gap type motor 1 includes a rotor 2 and a stator 3. The rotor 2 and the stator 3 face each other in the axial direction. The rotor 2 and the stator 3 are provided with a predetermined gap 4 in the axial direction.

[0080] The rotor 2 rotates about the rotation axis P with respect to the stator 3. The rotor 2 includes a rotor yoke 21 and a plurality of field magnets 22.

[0081] The rotor yoke 21 is, for example, a cap-shaped member made of a ferromagnetic steel plate. That is, the rotor yoke 21 includes a bottomed cylindrical rotor yoke protrusion 21a and an annular rotor yoke flange 21b provided so as to surround the rotor yoke protrusion 21a.

[0082] A rotor shaft (not shown) passes through the rotor yoke protrusion 21a. The rotor shaft is connected to the rotor yoke protrusion 21a. Therefore, the rotor yoke 21 rotates integrally with the rotor shaft. The axis of the rotor shaft coincides with the rotation axis P. The protruding direction of the rotor yoke protrusion 21a is the second direction in the axial direction of the rotation axis P. The rotor yoke protrusion 21a and the rotor yoke flange 21b are integrally formed. In the axial-gap type motor 1, the rotor yoke protrusion 21a is located inside a later-described annular stator 3 in the radial direction.

[0083] The rotor yoke may have a shape other than the cap shape, such as a disk shape or a cylindrical shape. The rotor yoke may have any shape as long as the rotor yoke can rotate together with the rotor shaft while holding the later-described field magnets 22.

[0084] The field magnet 22 is a rectangular flat plate member. The field magnet 22 is fixed to the rotor yoke flange 21b. In the present embodiment, the field magnet 22 is fixed on the surface of the rotor yoke flange 21b in the protruding direction of the rotor yoke convex portion 21a. On the rotor yoke flange 21b, a plurality of field magnets 22 are arranged at regular intervals in the circumferential direction. Therefore, when the rotor 2 rotates about the rotation axis P, the field magnets 22 also rotate about the rotation axis P. The field magnet 22 will be described in detail later.

[0085] The field magnet 22 may be fixed to the rotor yoke flange 21b in any manner such as adhesion, threading, welding, or deposition. The field magnet 22 may have other shapes such as circular, or may have a shape other than a plate shape such as a rod shape.

[0086] The field magnet 22 generates magnetic flux in the thickness direction. That is, in the present embodiment, the direction of the magnetic flux generated by the field magnet 22 is the axial direction of the rotor 2. The direction of the magnetic flux generated by the field magnet 22 may be changed according to the configuration of the motor.

[0087] The stator 3 is integrally configured in a cylindrical shape. The stator 3 and the rotor 2 are arranged in the axial direction such that the rotor yoke protrusion 21a is located inside the stator 3 in the radial direction. The stator 3 includes a stator core 30, a stator coil 33, and a plurality of resin bobbins 34. The stator core 30 includes a base yoke 31 and a plurality of pressed powder teeth 32 (teeth). In the stator 3 of the present embodiment, the base yoke 31 is a member separated from the plurality of pressed powder teeth 32.

[0088] Figure 3 is a plan view showing a schematic configuration of the base yoke 31. The base yoke 31 is made of an annular plate-shaped magnetic material such as an electromagnetic steel sheet, for example. The base yoke 31 may be formed by laminating electromagnetic steel sheets in the thickness direction, or may be made of, for example, pressed powder or amorphous material as long as the base yoke 31 is a magnetic material.

[0089] The base yoke 31 includes a plurality of tooth holes 35 as a plurality of insertion holes arranged in the circumferential direction. The pressed powder teeth 32 described later are respectively inserted into the plurality of tooth holes 35. The stator 3 includes slots 37, each of which is located between adjacent ones of the pressed powder teeth 32. The stator coil 33 wound around the pressed powder teeth 32 is accommodated in the slots 37. In this embodiment, as Figure 1 shown by the dashed line in, when the stator 3 is observed in the axial direction, each slot 37 has a rectangular shape. That is, the cross section of the pressed powder tooth 32 is trapezoidal to form a rectangular slot 37 when the stator 3 is observed in the axial direction, which will be described in detail later. Although Figure 1 only one slot 37 is shown, rectangular slots 37 are respectively formed between every two adjacent pressed powder teeth 32.

[0090] As Figure 1As shown, when the stator 3 is observed in the axial direction, the tooth holes 35 extend in the radial direction of the base yoke 31. When the stator 3 is observed in the axial direction, in each tooth hole 35, the circumferential length of the tooth hole radially outer end portion 35a including the end face of the base yoke 31 constituting the outer end in the radial direction of the corresponding tooth hole 35 is greater than the circumferential length of the tooth hole radially inner end portion 35b including the end face of the base yoke 31 constituting the inner end in the radial direction of the corresponding tooth hole 35. That is, each tooth hole 35 has a trapezoidal shape, and when the stator 3 is observed in the axial direction, the width of the trapezoidal shape in the circumferential direction increases toward the outside of the base yoke 31 in the radial direction.

[0091] Each tooth hole 35 has a slit 35c extending in the radial direction in the innermost circumferential portion of the annular plate-shaped base yoke 31. Therefore, the tooth hole 35 opens to the inside of the base yoke 31. The width of the slit 35c in the circumferential direction is smaller than the circumferential length of the tooth hole radially inner end portion 35b of the tooth hole.

[0092] The base yoke 31 includes a plurality of positioning portion insertion holes 36 arranged in the circumferential direction. The press powder tooth positioning portions 34c of the resin bobbin 34 described later are respectively inserted into the plurality of positioning portion insertion holes 36. The base yoke 31 has the same number of positioning portion insertion holes 36 as the number of tooth holes 35. The positioning portion insertion holes 36 are located outside the tooth holes 35 in the radial direction of the base yoke 31. That is, in a state where the press powder teeth 32 are inserted into the tooth holes 35, the positioning portion insertion holes 36 are located outside the press powder teeth 32 in the radial direction.

[0093] In the present embodiment, the positioning portion insertion hole 36 is constituted by a cut formed in the tooth hole radially outer end portion 35a of the tooth hole 35. That is, the positioning portion insertion hole 36 is continuously formed in at least a part of the tooth hole radially outer end portion 35a. The circumferential length of the positioning portion insertion hole 36 is smaller than the circumferential length of the tooth hole radially outer end portion 35a.

[0094] The positioning portion insertion hole may be located inside the tooth hole 35 in the radial direction of the base yoke 31. That is, in a state where the press powder teeth 32 are inserted into the tooth holes 35, the positioning portion insertion hole 36 may be located inside the press powder teeth 32 in the radial direction.

[0095] Figure 4A is a perspective view showing a schematic configuration of the press powder teeth 32. Figure 4B is a view of the press powder tooth joint portion 32 observed in the axial direction. The press powder teeth 32 are composed of fine particles including magnetic material particles. Specifically, the press powder teeth 32 are formed by molding the particles into a cylindrical shape with a molding die under a predetermined pressure.

[0096] The pressed powder tooth 32 is a columnar member having a trapezoidal cross-section and extending in the axial direction along the rotation axis P. The pressed powder tooth 32 is inserted into the tooth hole 35 of the base yoke 31 such that the thickness direction of the base yoke 31 coincides with the axial direction of the pressed powder tooth 32. Accordingly, the pressed powder teeth 32 are arranged relative to the base yoke 31 in the circumferential direction around the rotation axis P.

[0097] In a state where the pressed powder tooth 32 is inserted into the tooth hole 35 of the base yoke 31, when the pressed powder tooth 32 is viewed in the axial direction along the rotation axis P, the pressed powder tooth 32 extends in the radial direction of the stator 3, and the circumferential length of each pressed powder tooth radially outer end portion 32a (tooth radially outer end portion) located at the outer end in the radial direction of the corresponding pressed powder tooth 32 is greater than the circumferential length of each pressed powder tooth radially inner end portion 32b located at the corresponding pressed powder tooth 32 in the radial direction.

[0098] Each pressed powder tooth 32 includes a pressed powder tooth bottom surface 41, a pressed powder tooth upper surface 42, and a pressed powder tooth side surface 43. The pressed powder tooth side surface 43 is the surface of the pressed powder tooth radially inner end portion 32b that constitutes the short side of the trapezoidal cross-section. The pressed powder tooth upper surface 42 is the surface of the pressed powder tooth radially outer end portion 32a that constitutes the long side of the cross-section. And the pressed powder tooth side surface 43 is the surface of the pressed powder tooth circumferential end portion 32c (tooth circumferential end portion) that constitutes the hypotenuse connecting the pressed powder tooth bottom surface 41 and the pressed powder tooth upper surface 42 in the cross-section. The pressed powder tooth circumferential end portion 32c is located at the end of each of the pressed powder teeth 32 in the circumferential direction and extends in the radial direction of the stator core 30 when the pressed powder tooth 32 is attached to the base yoke 31. In the present embodiment, the cross-sectional shape and cross-sectional area of the pressed powder tooth 32 are the same in the axial direction of the rotation axis P.

[0099] In each columnar pressed powder tooth 32, at least one of the longitudinal dimension or the lateral dimension of the cross-section may gradually decrease in the axial direction. That is, each pressed powder tooth 32 may have a draft angle in the axial direction.

[0100] In the axial-gap type motor 1 having the above configuration, each pressed powder tooth 32 can have a trapezoidal shape having the following dimensional relationships.

[0101] Assume

[0102] The number of slots of the stator 3: S,

[0103] Offset: w,

[0104] The distance from the center of the stator core 3 to the pressed powder tooth bottom surface 41: r1, and

[0105] Distance from the center of the stator core 3 to the upper surface 42 of the pressed powder tooth: r2,

[0106] The pressed powder tooth 32 may have a trapezoidal shape defined as follows:

[0107] Core height: r1 - r2

[0108] Angle formed by the hypotenuse: 2π / S

[0109] Upper surface length: 2×(r2 - w / sin(π / S))×tan(π / S)

[0110] Bottom surface length: 2×(r1 - w / sin(π / S))×tan(π / S)

[0111] The trapezoidal pressed powder teeth 32 satisfying the above relationships are inserted into the tooth holes 35 of the base yoke 31 such that the pressed powder tooth side surfaces 43 of the pressed powder teeth 32 adjacent to each other in the circumferential direction are parallel. Thus, a space for winding the stator coil 33 around the pressed powder teeth 32 can be obtained between the pressed powder teeth 32 adjacent to each other in the circumferential direction.

[0112] The expression "parallel" includes not only the case where the pressed powder tooth side surfaces 43 of adjacent pressed powder teeth 32 do not completely intersect each other, but also the case where the angle formed by the pressed powder tooth side surfaces 43 of adjacent pressed powder teeth 32 is less than 90 degrees.

[0113] With the above configuration, the space factor of the stator coil 33 in the stator 3 increases, so that the number of windings of the stator coil 33 in the same cross-sectional area can be increased. Thus, the output torque of the axial-gap type motor 1 can be improved. In addition, since the space factor of the stator coil 33 can be increased as described above, the size of the stator coil 33 can be increased, and square wire or flat wire can be wound as the stator coil 33. When the space factor of the stator coil 33 increases, the resistance of the stator coil 33 can be reduced, and the copper loss, which is the cause of the stator coil 33 heating, can also be reduced.

[0114] With the above configuration, although a large winding diameter is required to equalize the resistance of the stator coil 33, an Al coil can also be wound. Thus, the weight of the axial-gap type motor 1 can be reduced.

[0115] Each of the plurality of pressed powder teeth 32 is provided with a resin bobbin 34. Figure 5 is a perspective view showing a schematic configuration of the resin bobbin 34. The resin bobbin 34 is a bottomed cylindrical resin member. Specifically, the resin bobbin 34 includes a side surface 34a, a bottom surface 34b, and a pressed powder tooth positioning portion 34c. In the present embodiment, the side surface 34a, the bottom surface 34b, and the pressed powder tooth positioning portion 34c are integrally formed.

[0116] The side surface 34a is configured to define a compacted powder tooth receiving space S, which has a trapezoidal cross-sectional shape and is capable of receiving a compacted powder tooth 32 having a trapezoidal cross-sectional shape. The bottom surface 34b is located on one side of the resin bobbin 34 in the axial direction with respect to the side surface 34a, and defines one side of the compacted powder tooth receiving space S in the axial direction. The other side of the compacted powder tooth receiving space S in the axial direction is constituted by an opening 34d surrounded by the side surface 34a of the resin bobbin 34. The axial direction coincides with the axial direction of the rotation axis P in the axial-gap type motor 1.

[0117] The length of the compacted powder tooth receiving space S in the axial direction is smaller than the length of the compacted powder tooth 32 in the axial direction. Therefore, in a state where the compacted powder tooth 32 is received in the compacted powder tooth receiving space S, the compacted powder tooth 32 protrudes in the axial direction with respect to the side surface 34a.

[0118] The compacted powder tooth positioning portion 34c is a protrusion extending from the side surface 34a constituting the opening 34d in the axial direction. The compacted powder tooth positioning portion 34c has a shape capable of inserting the compacted powder tooth positioning portion 34c into the positioning portion insertion hole 36 of the base yoke 31.

[0119] Figure 6 is a perspective view showing a state in which the compacted powder tooth 32 is inserted into the compacted powder tooth receiving space S of the resin bobbin 34 and the stator coil 33 is wound around the side surface 34a of the resin bobbin 34. As Figure 6 shown, the compacted powder tooth 32 is inserted into the compacted powder tooth receiving space S of the resin bobbin 34 such that the compacted powder tooth 32 is covered by the resin bobbin 34. The stator coil 33 is wound around the side surface 34a of the resin bobbin 34. Therefore, the compacted powder tooth 32 is electrically insulated from the stator coil 33.

[0120] Figure 7 is a view showing a state in which the resin bobbin 34 and the compacted powder tooth 32 are attached to the base yoke 31 when viewed in the first direction. Figure 8 is a view showing a state in which the resin bobbin 34 and the compacted powder tooth 32 are attached to the base yoke 31 when viewed in the second direction. As Figure 7 and Figure 8As shown, a resin bobbin 34 in which a compacted powder tooth 32 is received in a compacted powder tooth accommodation space S and a stator coil 33 is wound around a side surface 34a is attached to a base yoke 31 such that a compacted powder tooth positioning portion 34c is inserted into a positioning portion insertion hole 36 of the base yoke 31. Accordingly, the compacted powder tooth 32 is positioned in a tooth hole 35 of the base yoke 31 such that a radially inner end portion 32b of the compacted powder tooth 32 contacts a radially inner end portion 35b of the tooth hole 35. Thus, the resin bobbin 34 and the compacted powder tooth 32 are positioned relative to the base yoke 31.

[0121] When the stator 3 is viewed in the axial direction, grooves 37 having a rectangular shape are formed between resin winding shafts 34 that are adjacent to each other in the circumferential direction and cover the compacted powder teeth 32. Accordingly, the stator coil 33 wound around the side surface 34a of the resin bobbin 34 is received in the grooves 37.

[0122] With the above-described configuration, the stator 3 is configured such that the compacted powder teeth 32 are respectively inserted into a plurality of tooth holes 35 of the base yoke 31.

[0123] Although not specifically shown, the stator 3 having the above-described configuration can be resin molded by insert molding using resin.

[0124] In the above-described manner, in the final step of stator assembly, by resin molding the base yoke 31 and the compacted powder teeth 32 of the stator 3, stress concentration generated on the base yoke 31 and the compacted powder teeth 32 due to torque reaction forces generated by the axial-gap type motor 1 can be suppressed. This can obtain the strength of the brittle compacted powder teeth 32.

[0125] <Field Magnet>

[0126] Now, reference will be made to Figure 9 and Figure 10 to describe in detail the field magnet 22 of the rotor 2. Figure 9 is a diagram showing a state in which the rotor 2 rotates about a rotation axis P relative to the stator 3 when viewed in the axial direction. Figure 10 (a) shows the positional relationship between the field magnet 22 according to the present embodiment and the compacted powder tooth 32 of the stator 3, Figure 10 (b) shows the positional relationship between the trapezoidal field magnet 122 and the compacted powder tooth 32 of the stator 3, Figure 10 (c) shows the positional relationship between the field magnet 222 having a width narrower than that of the field magnet 22 according to the present embodiment and the compacted powder tooth 32 of the stator 3. Figure 10 (a), Figure 10 (b), Figure 10 (c) show the states in which the field magnets 22, 122, 222 move relative to the compacted powder tooth 32 in the circumferential direction in the order of a top view, a middle view, and a bottom view, respectively.

[0127] In the axial-gap type motor 1 according to the present embodiment, the rotor 2 is positioned axially away from the stator 3 having the above-described configuration. By the magnetic flux generated in the sintered powder teeth 32 by energizing the stator coil 33 and the magnetic flux generated by the field magnet 22 of the rotor 2, the rotor 2 is subjected to a force in the rotational direction about the rotation axis P. In the axial-gap type motor 1, the torque generated by this rotation of the rotor 2 is output as the output torque.

[0128] As Figure 9 shown by the white arrow in Figure 9 FIG., the field magnet 22 of the rotor 2 rotates about the rotation axis P relative to the sintered powder teeth 32 of the stator 3. For ease of explanation,

[0129] the rotor yoke 21 of the rotor 2 and the resin bobbin 34 of the stator 3 are omitted, and the stator coil 33 is indicated by a dashed line.

[0130] The field magnet 22 is a rectangular plate member. The circumferential length of the magnet radially inner end portion 22b located at the inner end of the field magnet 22 in the radial direction is equal to the circumferential length of the magnet radially outer end portion 22a located at the outer end of the field magnet 22 in the radial direction. As long as the circumferential length of the magnet radially inner end portion 22b is equal to the circumferential length of the magnet radially outer end portion 22a, the field magnet may have an arcuate side or may not have parallel sides in a plan view.

[0131] A plurality of field magnets 22 are arranged at regular intervals in the circumferential direction on the rotor yoke flange 21b of the rotor yoke 21. In the field magnet 22, the magnet radially inner end portion 22b is located outside the sintered powder tooth radially inner end portion 32b of the rotor 2 in the radial direction. That is, when the rotor 2 and the stator 3 are observed in the axial direction, the sintered powder tooth radially inner end portion 32b of the sintered powder teeth 32 includes a portion that does not overlap with the magnet radially inner end portion 22b of the field magnet 22. In the field magnet 22, the magnet radially outer end portion 22a is located outside the sintered powder tooth radially outer end portion 32a of the rotor 2 in the radial direction.

[0132] When the rotor 2 rotates relative to the stator 3 about the rotation axis P such that the field magnet 22 overlaps the sintered powder teeth 32 when the magnet 22 and the sintered powder teeth 32 are observed in the axial direction as Figure 10 shown, the magnet radially inner end portion 22b of the field magnet 22 first overlaps the sintered powder tooth radially inner portion U located inside the center of the sintered powder teeth 32 in the radial direction. When the field magnet 22 is at the q-axis position relative to the sintered powder teeth 32, when the field magnet 22 and the sintered powder teeth 32 are observed in the axial direction, the field magnets 22 adjacent to each other in the circumferential direction overlap one sintered powder tooth 32.

[0133] This configuration can increase the rotational force generated in the rotor 2 by the magnetic flux generated in the pressed powder teeth 32 and the magnetic flux generated in the field magnet 22 when the stator coil 33 is energized. Therefore, compared with an axial-gap type motor without the above configuration, the output torque can be increased.

[0134] In addition, when the field magnet 22 and the pressed powder teeth 32 are viewed in the axial direction, it is possible to prevent a sharp increase in the overlapping area where the field magnet 22 overlaps with the pressed powder teeth 32. Therefore, it is possible to reduce the cogging torque and torque ripple included in the output torque of the axial-gap type motor 1.

[0135] On the other hand, as Figure 10 (b) shows, for example, in the case of using the following trapezoidal field magnet 122 as the field magnet, in the trapezoidal field magnet, the circumferential length of the radially outer end portion 122a of the magnet is greater than the circumferential length of the radially inner end portion 122b of the magnet in a plan view. When the rotor rotates relative to the stator 3 about the rotation axis P such that the field magnet 122 starts to overlap with the pressed powder teeth 32 when viewed in the axial direction, the circumferential end portion 122c of each field magnet 122 overlaps with the side surface 43 of the pressed powder teeth of the pressed powder teeth 32 at the central portion in the radial direction.

[0136] Therefore, in the combination of the field magnet 122 and the pressed powder teeth 32 shown in Figure 10 (b), when the field magnet 122 overlaps with the pressed powder teeth 32 when viewed in the axial direction, the overlapping area increases sharply. Therefore, the cogging torque and torque ripple included in the output torque of the axial-gap type motor increase.

[0137] In the case shown in Figure 10 (b), when the field magnet 122 is at the q-axis position relative to the pressed powder teeth 32, when the field magnet 122 and the pressed powder teeth 32 are viewed in the axial direction, adjacent field magnets 122 in the circumferential direction overlap with one pressed powder tooth 32. Therefore, in the field magnet 22 of the present embodiment, a torque sufficient as the output torque of the axial-gap type motor can be obtained.

[0138] As Figure 10 (c) shows, in the case of using a field magnet 222 having a width smaller than that of the field magnet 22 of the present embodiment as the field magnet, when the field magnet 222 is at the q-axis position relative to the pressed powder teeth 32, when the field magnet 222 and the pressed powder teeth 32 are viewed in the axial direction, adjacent field magnets 222 in the circumferential direction do not overlap with one pressed powder tooth 32. Therefore, in the configuration of Figure 10 (c), the output torque of the axial-gap type motor is smaller than that in the case of the field magnet 22 of the present embodiment.

[0139] In Figure 10 the combination of the field magnet 222 and the pressed powder tooth 32 shown in (c), in a manner similar to Figure 10 (b), when the rotor rotates relative to the stator 3 about the rotation axis P such that when the field magnet 222 and the pressed powder tooth 32 are viewed in the axial direction, when the field magnet 222 starts to overlap with the pressed powder tooth 32, the circumferential end 222c of the magnet of the field magnet 222 overlaps with the pressed powder tooth side surface 43 of the pressed powder tooth 32 at the central portion in the radial direction.

[0140] Therefore, in Figure 10 the combination of the field magnet 222 and the pressed powder tooth 32 shown in (c), in the case where the field magnet 222 overlaps with the pressed powder tooth 32 when viewed in the axial direction, the overlapping area also increases sharply. Therefore, the cogging torque and torque ripple included in the output torque of the axial-gap motor increase.

[0141] In Figure 10 the configuration shown in (c), when the rotor rotates relative to the stator 3 about the rotation axis P, when the rotor and the stator 3 are viewed in the axial direction (for example, the q-axis position), the radially inner end 222b of the magnet of the field magnet 222 does not overlap with the radially inner portion of the pressed powder tooth of the pressed powder tooth 32 in some cases. On the other hand, in Figure 10 the configuration of the present embodiment shown in (a), when the rotor 2 rotates relative to the stator 3 about the rotation axis P, when the rotor 2 and the stator 3 are viewed in the axial direction, the radially inner end 22 of at least one of the plurality of field magnets 22 always overlaps with the radially inner portion U of the pressed powder tooth of the pressed powder tooth 32.

[0142] Therefore, compared with the configuration of Figure 10 (c) in a state where the radially inner end 222b of the magnet of the field magnet 222 does not overlap with the radially inner portion of the pressed powder tooth of the pressed powder tooth 32, the output torque of the axial-gap motor can be increased, and the cogging torque and torque ripple included in the output torque can be reliably reduced.

[0143] Figure 11 is a view schematically showing the change of the intersection point between the trapezoidal field magnet and the pressed powder tooth 32 with the change of the inclination of the hypotenuse of the trapezoidal field magnet when the field magnet is located at the q-axis with respect to the pressed powder tooth 32 and the field magnet and the pressed powder tooth 32 are viewed in the axial direction. Figure 12 is a graph showing the relationship between the intersection point, the average torque of the output torque of the axial-gap motor, and the torque ripple and cogging torque included in the output torque in the case of the change of the intersection point as shown in Figure 11 . Figure 12 The intersection points A to E in Figure 11The intersections A to E schematically shown therein.

[0144] As Figure 12 shown, when the field magnet is in the q-axis position relative to the pressed powder tooth 32, the intersection of the field magnet and the pressed powder tooth 32 is located on the upper surface 42 of the pressed powder tooth when viewed in the axial direction, and the average torque is greater and the torque ripple and cogging torque are smaller compared to the case where the intersection is located on the side surface 43 of the pressed powder tooth.

[0145] Therefore, the field magnet 22 of the rotor 2 is preferably configured such that when the field magnet 22 is in the q-axis position relative to the pressed powder tooth 32 and the rotor 2 and the stator 3 are viewed in the axial direction, the field magnet 22 covers the circumferential end portion 32c of the pressed powder tooth 32.

[0146] (Other embodiments)

[0147] Although the present embodiment has been described above, the present embodiment is merely an example. Therefore, the present teachings are not limited to the above-described embodiment, and the embodiment can be modified as needed without departing from the gist of the present teachings.

[0148] In the present embodiment, the pressed powder tooth 32 is a columnar member having a substantially trapezoidal cross-section. Alternatively, the pressed powder tooth may be a columnar member having other cross-sectional shapes. For example, the corner portion of the pressed powder tooth may have a rounded portion or a chamfered portion.

[0149] In the embodiment, each resin bobbin 34 includes a side surface 34a, a bottom surface 34b, and a pressed powder tooth positioning portion 34c. Alternatively, the resin bobbin may not have a bottom surface. The resin bobbin may not have a portion of the side surface having a trapezoidal cross-sectional shape. The resin bobbin may not have a pressed powder tooth positioning portion.

[0150] In the present embodiment, in the field magnet 22, the magnet radially inner end portion 22b is located radially outside the radially inner end portion 32b of the pressed powder tooth in the radial direction of the rotor 2. Alternatively, in the field magnet, the magnet radially inner end portion may be located at the same position as the radially inner end portion of the pressed powder tooth in the radial direction, or may be located radially inside the radially inner end portion of the pressed powder tooth.

[0151] In the present embodiment, the field magnet 22 is configured to cover the circumferential end portion 32c of the pressed powder tooth 32 when the rotor 2 and the stator 3 are viewed in the axial direction and the field magnet 22 is in the q-axis position relative to the pressed powder tooth 32. Alternatively, the field magnet may be configured to cover a part of the circumferential end portion of the pressed powder tooth when the rotor and the stator are viewed in the axial direction and the field magnet is in the q-axis position relative to the pressed powder tooth.

[0152] In the present embodiment, the plurality of field magnets 22 have a sufficient size to allow at least one of the plurality of field magnets 22 to always overlap with each of the radially inner portions U of the compacted powder teeth 32 of the plurality of compacted powder teeth 32 when the rotor 2 rotates about the rotation axis relative to the stator core 30 and is viewed in the axial direction. Alternatively, in the plurality of field magnets, when the rotor and the stator core are viewed in the axial direction and the rotor rotates about the rotation axis relative to the stator core, at least one of the radially inner ends 22b of the magnets of the plurality of field magnets may not always overlap with each of the radially inner portions of the compacted powder teeth of the plurality of compacted powder teeth.

[0153] In the present embodiment, when the rotor 2 rotates relative to the stator 3 about the rotation axis P such that the field magnet 22 overlaps with the compacted powder tooth 32 when the field magnet 22 and the compacted powder tooth 32 are viewed in the axial direction, the radially inner end 22b of the magnet of the field magnet 22 first overlaps with the radially inner portion U of the compacted powder tooth 32 of the compacted powder tooth 32. Alternatively, when the field magnet overlaps with the compacted powder tooth, a portion of the field magnet other than the radially inner end of the magnet may first overlap with the compacted powder tooth.

[0154] In the embodiment, in the case where the rotor 2 rotates about the rotation axis P relative to the stator 3, when the rotor 2 and the stator 3 are viewed in the axial direction, at least one of the radially inner ends 22 of the magnets of the plurality of field magnets 22 always overlaps with the radially inner portion U of the compacted powder tooth 32 of the compacted powder tooth 32. Alternatively, a portion of the field magnet 22 other than the radially inner end 22b of the magnet may also overlap with the compacted powder tooth.

[0155] List of Reference Numerals

[0156] 1 Axial-gap type motor

[0157] 2 Rotor

[0158] 3 Stator

[0159] 4 Gap

[0160] 21 Rotor yoke

[0161] 21a Rotor yoke projection

[0162] 21b Rotor yoke flange

[0163] 22, 122, 222 Field magnet

[0164] 22a, 122a Radially outer end of magnet

[0165] 22b, 122b, 222b Radially inner end of magnet

[0166] 122c, 222c Circumferential end of magnet

[0167] 30 Stator core

[0168] 31 Base yoke

[0169] 32 Pressed powder tooth (tooth)

[0170] 32a Radially outer end of the pressed powder tooth (radially outer end of the tooth)

[0171] 32b Radially inner end of the pressed powder tooth (radially inner end of the tooth)

[0172] 32c Circumferential end of the pressed powder tooth (circumferential end of the tooth)

[0173] 33 Stator coil

[0174] 34 Resin bobbin

[0175] 34a Side surface

[0176] 34b Bottom surface

[0177] 34c Pressed powder tooth positioning part

[0178] 34d Opening

[0179] 35 Tooth hole

[0180] 35a Radially outer end of the tooth hole

[0181] 35b Radially inner end of the tooth hole

[0182] 35c Slit

[0183] 36 Positioning part insertion hole

[0184] 37 Slot

[0185] 41 Bottom surface of the pressed powder tooth

[0186] 42 Upper surface of the pressed powder tooth

[0187] 43 Side surface of the pressed powder tooth

[0188] P Axis of rotation

[0189] S Pressed powder tooth accommodation space

[0190] U Radially inner part of the pressed powder tooth

Claims

1. An axial-gap type motor, comprising: a rotor including a plurality of field magnets and capable of rotating about a rotation axis, the plurality of field magnets being arranged in a circumferential direction; a cylindrical stator core located in the axial direction of the rotation axis with respect to the rotor, the stator core including a yoke and a plurality of teeth, the plurality of teeth being arranged in the circumferential direction around the rotation axis with respect to the yoke; and a stator coil wound around each of the plurality of teeth, wherein, each of the plurality of teeth is formed of pressed particles, when observing the plurality of teeth in the axial direction, each of the plurality of teeth extends in the radial direction of the stator core and has a trapezoidal shape, in which trapezoidal shape, the circumferential length of the radially outer end portion of the tooth located at the outer end of the tooth in the radial direction is greater than the circumferential length of the radially inner end portion of the tooth located at the inner end of the tooth in the radial direction, each pair of the plurality of teeth adjacent to each other in the circumferential direction forms a slot, the slot being capable of accommodating the stator coil and having a rectangular shape when observing the plurality of teeth in the axial direction, and in each of the plurality of field magnets, the circumferential length of the magnet radially inner end portion located at the inner end of the field magnet in the radial direction is greater than or equal to the circumferential length of the field magnet radially outer end portion located at the outer end of the field magnet in the radial direction, and when the rotor and the stator core rotate relative to each other about the rotation axis, when observing the plurality of field magnets and the plurality of teeth in the axial direction, a part of the field magnet first overlaps with the radially inner part of the corresponding one of the teeth located at the center of the tooth in the radial direction, and when the field magnet is in the q-axis position with respect to the tooth, when observing the plurality of field magnets and the plurality of teeth in the axial direction, each group of adjacent ones of the plurality of field magnets overlaps with one of the teeth.

2. The axial-gap type motor according to claim 1, wherein, each of the plurality of field magnets is configured to cover the tooth circumferential end portion when observing the rotor and the stator core in the axial direction and when the field magnet is in the q-axis position with respect to the tooth, the tooth circumferential end portion being located at the end of the tooth in the circumferential direction and extending in the radial direction.

3. The axial-gap type motor according to claim 1, wherein, each of the plurality of field magnets has a size sufficient to always overlap the radially inner part of each of the plurality of teeth with the magnet radially inner end portion of at least one of the plurality of field magnets when the rotor and the stator core rotate relative to each other about the rotation axis when observing the rotor and the stator core in the axial direction.

4. The axial-gap type motor according to claim 1, wherein, each of the plurality of field magnets has a rectangular shape, in which rectangular shape, the circumferential length of the magnet radially inner end portion is equal to the circumferential length of the magnet radially outer end portion when observing the rotor in the axial direction.

5. The axial-gap type motor according to any one of claims 1 to 4, wherein, each of the plurality of field magnets is arranged such that when the rotor and the stator core are viewed along the axial direction, a radially inner end portion of the magnet is located outside a radially inner end portion of the tooth in the radial direction.

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