Patent Publication Number: US-2023163646-A1

Title: Rotary electrical device

Description:
TECHNICAL FIELD 
     The present disclosure relates to a rotary electrical device. 
     BACKGROUND ART 
     A claw pole motor in which a first core and a second core, constituting a stator core, are constituted by iron powder cores is known. The first core includes a disk-shaped connecting bottom plate, a plurality of claw magnetic poles projecting from the peripheral edge of the connecting bottom plate in the axial direction, and a circular yoke portion projecting from the center of the connecting bottom plate in the same direction as the claw magnetic poles. The second core includes a disk-shaped connecting bottom plate joined to the circular yoke of the first core, and a plurality of claw magnetic poles projecting from the peripheral edge of the connecting bottom plate in a direction opposite to plurality of claw magnetic poles of the first core (see Patent Document 1, for example). 
     RELATED-ART DOCUMENTS 
     Patent Documents 
     Patent Document 1: Japanese Laid-open Patent Publication No. 2009-201299 
     SUMMARY OF THE INVENTION 
     Problem to be Solved by the Invention 
     When a stator core is formed by press-forming a magnetic powder core, the pressing direction is typically the axial direction of a motor. Thus, the dimensional accuracy in the axial direction may decrease. For example, as in the conventional technique described above, in a case where the first core and the second core are joined together in the axial direction, an unintended gap may be formed between the joined surfaces or a large error may occur in the height of the cores in the joined state. 
     The present disclosure provides a rotary electrical device that can reduce a decrease in dimensional accuracy in the axial direction. 
     Means to Solve the Problem 
     An aspect of the present disclosure provides a rotary electrical device including a rotor having a substantially hollow cylindrical shape or a substantially solid cylindrical shape and configured to be rotatable; and a stator having a substantially annular shape and disposed in a radial direction of the rotor to surround a rotation axis of the rotor. The stator includes a winding that is wound in a substantially annular shape around the rotation axis, and a stator core that surrounds the winding and is constituted by a magnetic powder core. The stator core includes a plurality of cores facing each other with the winding interposed therebetween in an axial direction of the stator. One core of the plurality of cores includes a yoke that is in contact with or in proximity to one other core of the plurality of cores, and one or more claw magnetic poles that protrude from the yoke toward the rotor in the radial direction. The one or more claw magnetic poles of the one core of the plurality of cores are alternately arranged with claw magnetic poles of the one other core, with which or to which the yoke is in contact or in proximity, in a circumferential direction of the stator. The yoke has at least one yoke surface that is substantially parallel to the axial direction, and the yoke surface of the yoke is in contact with or in proximity to the one other core. 
     With this configuration, a decrease in dimensional accuracy in the axial direction can be reduced. 
     In the above-described rotary electrical device, a length of the yoke surface in the axial direction may be greater than a half of a length of the yoke in the axial direction. 
     With this configuration, the magnetic flux passing through the yoke surface can be increased. 
     In the above-described rotary electrical device, only the yoke surface of the one core may be in contact with or in proximity to the one other core. 
     With this configuration, a decrease in dimensional accuracy in the axial direction can be further reduced. 
     In the above-described rotary electrical device, the yoke surface of the one core may be in contact with or in proximity to the one other core in the circumferential direction. 
     With this configuration, a decrease in dimensional accuracy in the axial direction and in the circumferential direction can be reduced. 
     In the above-described rotary electrical device, the yoke surface of the one core may be in contact with or in proximity to the one other core in the radial direction. 
     With this configuration, a decrease in dimensional accuracy in the axial direction and in the radial direction can be reduced. 
     In the above-described rotary electrical device, in a plan view along the axial direction, the yoke surface may be positioned on a line connecting a center of a width, in the circumferential direction, of at least one claw magnetic pole of the plurality of claw magnetic poles to the rotation axis of the rotor. 
     With this configuration, the magnetic resistance of a magnetic circuit through which the magnetic flux passes can be reduced. 
     In the above-described rotary electrical device, the plurality of cores may have a same shape. 
     With this configuration, the plurality of cores can be formed by the same mold. 
     In the above-described rotary electrical device, the yoke may include a plurality of internal teeth arranged at equal intervals in the circumferential direction, the plurality of internal teeth having a same width in the circumferential direction, and θ α =180/(2·n) and θ β =360/(2·N) may hold, where θ α  represents an angle between a center of a width, in the circumferential direction, of each of the claw magnetic poles and an end, in the circumferential direction, of an internal tooth that is closest to the center of the width, n represents a number of the plurality of claw magnetic poles, and θ β  represents an angle between both ends, in the circumferential direction, of each of the claw magnetic poles, and N represents a number of the plurality of internal teeth. 
     With this configuration, the plurality of cores can be formed in the same shape, and thus, the plurality of cores can be formed by the same mold. 
     In the above-described rotary electrical device, n may be equal to N or may be a multiple of N. 
     With this configuration, ease of assembly of the plurality of cores can be facilitated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a perspective view of an example of a rotary electrical device according to a first embodiment; 
         FIG.  2    is a perspective view of an example of a stator according to the first embodiment; 
         FIG.  3    is a perspective view of an example of a stator unit according to the first embodiment; 
         FIG.  4    is an exploded perspective view of an example of the stator unit according to the first embodiment; 
         FIG.  5    is a plan view of an example of a core according to the first embodiment when viewed in the axial direction; 
         FIG.  6    is a perspective view of an example of a stator unit according to a second embodiment; 
         FIG.  7    is an exploded perspective view of an example of the stator unit according to the second embodiment; 
         FIG.  8    is a plan view of an example of a core according to the second embodiment when viewed in the axial direction; 
         FIG.  9    is a perspective view of an example of a stator unit according to a third embodiment; 
         FIG.  10    is a perspective view of an example of a core according to the third embodiment; 
         FIG.  11    is a perspective view of an example of a stator unit according to a fourth embodiment; 
         FIG.  12    is a plan view of an example of one core according to the fourth embodiment when viewed in the axial direction; 
         FIG.  13    is a plan view of an example of the other core according to the fourth embodiment when viewed in the axial direction; 
         FIG.  14    is a perspective view of an example of a stator unit according to a fifth embodiment; 
         FIG.  15    is a perspective view of an example of a core according to the fifth embodiment; 
         FIG.  16    is a plan view of an example of the core according to the fifth embodiment when viewed in the axial direction; 
         FIG.  17    is an exploded perspective view of an example of a stator unit according to a sixth embodiment; 
         FIG.  18    is a cross-sectional view of a first example configuration of a yoke taken through A-A of  FIG.  14   ; and 
         FIG.  19    is a cross-sectional view of a second example configuration of a yoke taken through A-A of  FIG.  14   . 
     
    
    
     MODE FOR CARRYING OUT THE INVENTION 
     In the following, embodiments will be described. 
       FIG.  1    is a perspective view of an example of a rotary electrical device according to a first embodiment. A motor  1  illustrated in  FIG.  1    is an example of the rotary electrical device. The motor  1  is an outer-rotor-type claw pole motor in which a rotor  10  is disposed radially outward relative to a stator  13 . For example, the motor  1  is mounted on a compressor, a fan, or the like of an air conditioner. 
     The motor  1  includes the rotor  10  and the stator  13 . The rotor  10  has a substantially hollow cylindrical shape and is configured to be rotatable. The stator  13  has a substantially annular shape and is disposed radially inward relative to the rotor  10  to surround a rotation axis AX of the rotor  10 . 
     The rotor  10  is disposed outward in a radial direction of the motor  1  (hereinafter also simply referred to as a “radial direction”) with respect to the stator  13 . The rotor  10  is configured to be rotatable about the rotation axis AX. The rotor  10  includes a rotor core  11  and a plurality of (in this example, 20) permanent magnets  12 . 
     The rotor core  11  has, for example, a substantially cylindrical shape and is disposed such that the rotation axis AX of the motor  1  substantially coincides with the axis of the cylindrical shape. The rotor core  11  has the substantially the same length as the stator  13  in an axial direction of the motor  1  (hereinafter also simply referred to as an “axial direction”). The rotor core  11  is formed of a magnetic material (such as a steel plate, cast iron, or a magnetic powder core). The rotor core  11  may be comprised of one member in the axial direction, or may be comprised of a plurality of members that are stacked in the axial direction (for example, the number of members may correspond to the number of stator units as will be described later). 
     The plurality of (in this example, 20) permanent magnets  12  are arranged on the inner circumferential surface of the rotor core  11  at equal intervals in the circumferential direction. The permanent magnets  12  are arranged so as to be substantially present between one end and the other end of the rotor core  11 . The permanent magnets  12  are, for example, neodymium sintered magnets or ferrite magnets. 
     Both ends of each of the permanent magnets  12  in the radial direction are magnetized to different magnetic poles. From among the plurality of permanent magnets  12 , the inner sides, facing the stator  13  in the radial direction, of two permanent magnets  12  that are adjacent to each other in the circumferential direction are magnetized to different magnetic poles. With this configuration, on the outer side of the stator  13  in the radial direction, permanent magnets  12  whose inner sides in the radial direction are magnetized to N-poles and permanent magnets  12  whose inner sides in the radial direction are magnetized to S-poles are alternately arranged in the circumferential direction. 
     Each of the permanent magnets  12  may be comprised of one magnet member in the axial direction. Alternatively, each of the permanent magnets  12  may be comprised of a plurality of magnet members that are arranged in the axial direction (for example, the number of magnet members may correspond to the number of stator units as will be described later). In this case, the inner sides, facing the stator  13  in the radial direction, of a plurality of magnet members, which constitute a corresponding permanent magnet  12  and are arranged in the axial direction, are all magnetized to the same magnetic pole. 
     Note that the plurality of permanent magnets  12  arranged in the circumferential direction may be replaced with a permanent magnet that is comprised of one member and that is magnetized to have alternately different magnetic poles in the circumferential direction, such as an annular ring magnet, or a plastic magnet. In this case, the permanent magnet comprised of one member in the circumferential direction may also be comprised of one member in the axial direction, such that the permanent magnet may be entirely comprised of one member. In addition, the permanent magnet comprised of one member in the circumferential direction may be separated into a plurality of members in the axial direction, as in the case of the plurality of permanent magnets  12 . Further, when a plastic magnet comprised of one member in the circumferential direction is employed, the rotor core  11  may be omitted. Regardless of whether a permanent magnet is comprised of a plurality of members or one member, the permanent magnet is magnetized such that a predetermined number of magnetic poles is arranged in the circumferential direction. 
       FIG.  2    is a perspective view of an example of a stator according to the first embodiment. Specifically,  FIG.  2    is a diagram illustrating the motor from which the rotor  10  of  FIG.  1    is removed. The stator  13  illustrated in  FIG.  2    is disposed radially inward relative to the rotor  10  (the rotor core  11  and the permanent magnets  12 ). The stator  13  is a member having a substantially annular shape and is disposed to surround the rotation axis AX of the rotor  10 . In this example, the stator  13  includes a plurality of (in this example, three) stator units  14  to  16  that are stacked in the axial direction, and a plurality of (in this example, two) non-magnetic material layers  17  and  18 . 
     The stator  13  includes the stator units  14  to  16  of multiple phases (three phases in this example) having substantially the same structure. Specifically, the stator  13  includes the stator unit  14  of a U-phase, the stator unit  15  of a V-phase, and the stator unit  16  of a W-phase. The plurality of stator units  14  to  16  are offset by an electric angle of 120° in the circumferential direction. 
     Note that the motor  1  (stator  13 ) does not necessarily have three phases, and may have one phase or multiple phases (two phases or four or more phases). 
     The stator  13  includes the non-magnetic material layer  17  between the stator units  14  and  15  that are adjacent to each other in the axial direction, and includes the non-magnetic material layer  18  between the stator units  15  and  16  that are adjacent to each other in the axial direction. The non-magnetic material layer  17  can suppress magnetic flux leakage between the adjacent stator units  14  and  15  of the two different phases. The non-magnetic material layer  18  can suppress magnetic flux leakage between the adjacent stator units  15  and  16  of the two different phases. 
     The non-magnetic material layer  17  is a U-V interphase member provided between the stator unit  14  of the U-phase and the stator unit  15  of the V-phase, which are adjacent to each other in the axial direction. The non-magnetic material layer  17  has, for example, a substantially disk shape or a substantially cylindrical shape having a predetermined thickness in the axial direction, and a through-hole through which an inserting member (not illustrated) is inserted is formed in the central portion of the non-magnetic material layer  17 . The same may apply to the non-magnetic material layer  18 . The non-magnetic material layer  18  is a V-W interphase member provided between the stator unit  15  of the V-phase and the stator unit  16  of the W-phase, which are adjacent to each other in the axial direction. 
       FIG.  3    is a perspective view of an example of a stator unit according to the first embodiment.  FIG.  4    is an exploded perspective view of an example of the stator unit according to the first embodiment. The above-described stator units  15  and  16  have substantially the same configuration as the stator unit  14  illustrated in  FIG.  3    and  FIG.  4   , and thus, the description of the stator units  15  and  16  will be omitted by referring to the description of the stator unit  14 . 
     The stator unit  14  includes a winding  19  that is wound in a substantially annular shape around the rotation axis AX, a stator core  9  that is provided so as to surround the winding  19 , and a through-hole  8  (see  FIG.  3   ) through which an inserting member (not illustrated) is inserted. The stator core  9  is constituted by a magnetic powder core. The stator core  9  constituted by a magnetic powder core can reduce iron loss at high frequencies. The stator core  9  includes a plurality of cores  20  and  40  facing each other with the winding  19  interposed therebetween in the axial direction of the stator  13 . 
     The plurality of cores  20  and  40  are provided so as to surround the winding  19 . The plurality of cores  20  and  40  have the same shape. 
     As illustrated in  FIG.  4   , the core  20  includes a yoke  21 , a plurality of claw magnetic poles  22 , and a center hole  23 . The core  40  includes a yoke  41 , a plurality of claw magnetic poles  42 , and a center hole  43 . 
     Each of the yokes  21  and  41  has an annular shape when viewed in the axial direction, and has a predetermined thickness in the axial direction. The yoke  21  is in contact with or in proximity to the other core  40  that is different from its core  20  among the plurality of cores  20  and  40 . The yoke  21  includes a first yoke portion  24  having a substantially annular shape and a second yoke portion  25  that contacts the other core  40 . The yoke  41  is in contact with or in proximity to the other core  20  that is different from its core  40  among the plurality of cores  20  and  40 . The yoke  41  includes a first yoke portion  44  having a substantially annular shape and a second yoke portion  45  that contacts the other core  20 . 
     The second yoke portion  25  protrudes from an inner circumferential surface  24   a  of the first yoke portion  24  toward the other core  40  by a predetermined amount. In this example, the second yoke portion  25  is a portion that includes a plurality of internal teeth  26  ( 26   a,    26   b,    26   c,  and  26   d ) arranged at intervals in the circumferential direction. The second yoke portion  45  protrudes from an inner circumferential surface  44   a  of the first yoke portion  44  toward the other core  20  by a predetermined amount. In this example, the second yoke portion  45  is a portion that includes a plurality of internal teeth  46  ( 46   a,    46   b,    46   c,  and  46   d ) arranged at intervals in the circumferential direction. 
     The plurality of claw magnetic poles  22  are arranged at equal intervals in the circumferential direction on an outer circumferential surface  24   b  of the first yoke portion  24  of the yoke  21 . The plurality of claw magnetic poles  22  protrude radially outward from the outer circumferential surface  24   b  of the first yoke portion  24  of the yoke  21  toward the rotor  10 . The plurality of claw magnetic poles  42  are arranged on an outer circumferential surface  44   b  of the first yoke portion  44  of the yoke  41  at equal intervals in the circumferential direction. The plurality of claw magnetic poles  42  protrude radially outward from the outer circumferential surface  44   b  of the first yoke portion  44  of the yoke  41  toward the rotor  10 . Each of the claw magnetic poles  22  includes a claw magnetic pole portion  27 , and each of the claw magnetic poles  42  includes a claw magnetic pole portion  47 . 
     The claw magnetic pole portion  27  has a predetermined width, and protrudes from the outer circumferential surface  24   b  of the first yoke portion  24  of the yoke  21  by a predetermined length. The claw magnetic pole portion  47  has a predetermined width, and protrudes from the outer circumferential surface  44   b  of the first yoke portion  44  of the yoke  41  by a predetermined length. 
     Each of the claw magnetic poles  22  further includes a claw magnetic pole portion  28 , and each of the claw magnetic poles  42  further includes a claw magnetic pole portion  48 . This configuration allows the area where magnetic pole surfaces of the claw magnetic poles  22  and  42 , magnetized by the armature current of the winding  19 , and the rotor  10  face each other, to be made relatively large. Therefore, the torque of the motor  1  can be relatively increased, and the output of the motor  1  can be improved. 
     The claw magnetic pole portion  28  of the core  20  protrudes by a predetermined length from the tip of the claw magnetic pole portion  27  toward the other core  40  of the pair of the cores  20  and  40 . For example, the claw magnetic pole portion  28  has a constant width, regardless of the distance from the claw magnetic pole portion  27 . The claw magnetic pole portion  48  of the core  40  protrudes by a predetermined length from the tip of the claw magnetic pole portion  47  toward the other core  20  of the pair of the cores  20  and  40 . For example, the claw magnetic pole portion  48  has a constant width, regardless of the distance from the claw magnetic pole portion  47 . 
     Note that the claw magnetic pole portions  28  and  48  may be omitted. 
     The center hole  23  is a through-hole surrounded by the inner peripheral surfaces of the plurality of internal teeth  26  of the second yoke portion  25 . The center hole  43  is a through-hole surrounded by the inner peripheral surfaces of the plurality of internal teeth  46  of the second yoke portion  45 . The center holes  23  and  43  form the through-hole  8  (see  FIG.  3   ) by combining the cores  20  and  40 . 
     The winding  19  is a conductive wire that is wound in an annular shape when viewed in the axial direction. The winding is also referred to as a coil. Both ends of the winding  19  are electrically connected to external terminals of the motor  1 . The external terminals of the motor  1  are electrically connected to a drive device (for example, an inverter or the like) that drives the motor  1  with electric power supplied from a power source. 
     The winding  19  is disposed between the cores  20  and  40  in the axial direction. The winding  19  is wound such that an outer circumferential portion  19   a  of the winding  19  is located radially inward relative to the outer circumferential surfaces  24   b  and  44   b  of the first yoke portions  24  and  44 , and an inner circumferential portion  19   b  is located radially outward relative to the inner circumferential surfaces  24   a  and  44   a  of the first yoke portions  24  and  44 . 
     The winding  19  contacts at least one of the cores  20  and  40 , thereby improving the heat dissipation performance of the winding  19 . For example, the winding  19  is interposed between the first yoke portion  24  and the first yoke portion  44  while contacting one or both of the first yoke portion  24  and the first yoke portion  44  in the axial direction. The winding  19  may contact one or both of the second yoke portion  25  and the second yoke portion  45 . The winding  19  may contact at least one of the cores  20  and  40  via a bobbin (not illustrated). 
     The winding  19  may be insulated by a known method using a core mold, a bobbin, or the like. Examples of an insulating method include winding an insulating tape around an air core coil and using a mold. As the material of the winding  19 , a round wire, a square wire, or a litz wire can be used. Preferably, a square wire or a round wire wound in an aligned state may be used. 
     As illustrated in  FIG.  3   , the cores  20  and  40  are combined such that the claw magnetic poles  22  of the one core  20  and the claw magnetic poles  42  of the other core  40  are alternately arranged in the circumferential direction. Specifically, the plurality of claw magnetic poles  22  of the one core  20  are alternately arranged with the claw magnetic poles  42  of the other core  40  in the circumferential direction of the stator core  9  (in the circumferential direction of the stator  13 ). Note that the core  20  may include one claw magnetic pole  22 , and the core  40  may include one claw magnetic pole  42 . In this case, alternately arranging the one claw magnetic pole  22  and the one claw magnetic pole  42  in the circumferential direction means that the one claw magnetic pole  22  is located on one side in the circumferential direction, and the claw magnetic pole  42  is located on the other side in the circumferential direction. 
     When an armature current flows through the annular winding  19 , the claw magnetic poles  22  of the one core  20  of the pair of cores  20  and  40 , and the claw magnetic poles  42  of the other core  40  are magnetized to have different magnetic poles. With this configuration, the claw magnetic poles  22 , protruding from the one core  20  of the pair of cores  20  and  40 , are adjacent to the claw magnetic poles  42  protruding from the other core  40  in the circumferential direction, and the claw magnetic poles  22  have a different magnetic pole from the claw magnetic poles  42 . Therefore, in the circumferential direction of the stator core  9  (the pair of cores  20  and  40 ), a combination of the N-pole claw magnetic poles  22  and the S-pole claw magnetic poles  42  and a combination of the N-pole claw magnetic poles  42  and the S-pole claw magnetic poles  22  are alternately generated by the armature current flows through the winding  19 . 
     In a state in which the cores  20  and  40  are combined with the winding  19  being interposed therebetween, the plurality of internal teeth  26  may protrude beyond the core  40  in the axial direction, but are not necessarily required to protrude beyond the core  40  in the axial direction, and the plurality of internal teeth  46  may protrude beyond the core  20  in the axial direction, but are not necessarily required to protrude beyond the core  20  in the axial direction. A spacer may be inserted between the cores  20  and  40  so as to adjust the length of the stator core  9  in the axial direction. 
     A yoke of one core of the pair of cores  20  and  40  has at least one yoke surface that is substantially parallel to the axial direction, and the yoke surface of the one core is in contact with or in proximity to the other core. In this example, the yoke  21  of the core  20  has yoke surfaces  29  that are in contact with or in proximity to yoke surfaces  49  of the yoke  41  of the core  40 , and also has yoke surfaces  30  that are in contact with or in proximity to yoke surfaces  50  of the yoke  41  of the core  40 . 
     The yoke surfaces  29  are surfaces provided on the respective internal teeth  26  ( 26   a,    26   b,    26   c , and  26   d ) of the second yoke portion  25  and facing one circumferential direction (the clockwise direction in  FIG.  3    and  FIG.  4   ). The yoke surfaces  30  are surfaces provided on the respective internal teeth  26  ( 26   a,    26   b,    26   c,  and  26   d ) of the second yoke portion  25  and facing the opposite circumferential direction (the counterclockwise direction in  FIG.  3    and  FIG.  4   ). The yoke surfaces  50  are surfaces provided on the respective internal teeth  46  ( 46   a ,  46   b,    46   c,  and  46   d ) of the second yoke portion  45  and facing one circumferential direction (the clockwise direction in  FIG.  3    and  FIG.  4   ). The yoke surfaces  49  are surfaces provided on the respective internal teeth  46  ( 46   a,    46   b,    46   c,  and  46   d ) of the second yoke portion  45  and facing the opposite circumferential direction (the counterclockwise direction in  FIG.  3    and  FIG.  4   ). 
     Each of the internal teeth  26  is in contact with or in proximity to two internal teeth, of the plurality of internal teeth  46 , adjacent to both sides of a corresponding internal tooth  26  in the circumferential direction. In other words, each of the internal teeth  46  is in contact with or in proximity to two internal teeth, of the plurality of internal teeth  26 , adjacent to both sides of a corresponding internal tooth  46  in the circumferential direction. Specifically, in the case of the internal tooth  26   a  whose one side in the circumferential direction is adjacent to the internal tooth  46   a  and the other side in the circumferential direction is adjacent to the internal tooth  46   d,  a yoke surface  29  of the internal tooth  26   a  is in contact with or in proximity to a yoke surface  49  of the internal tooth  46   a,  and a yoke surface  30  of the internal tooth  26   a  is in contact with or in proximity to a yoke surface  50  of the internal tooth  46   d.  The same applies to the other internal teeth. In this manner, each of the yoke surfaces  29  is in contact with or in proximity to a corresponding yoke surface  49  of the plurality of yoke surfaces  49 , and each of the yoke surfaces  30  is in contact with or in proximity to a corresponding yoke surface  50  of the plurality of yoke surfaces  50 . 
     Further, in this example, the yoke  21  of the core  20  has outer peripheral surfaces  31  that are in contact with or in proximity to the inner circumferential surface  44   a  of the yoke  41  of the core  40 . The yoke  41  of the core  40  has outer peripheral surfaces  51  that are in contact with or in proximity to the inner circumferential surface  24   a  of the yoke  21  of the core  20 . Each of the inner circumferential surfaces  24   a  and  44   a  and the outer peripheral surfaces  31  and  51  is a yoke surface that is substantially parallel to the axial direction. 
     The outer peripheral surfaces  31  are curved surfaces that are provided on the respective internal teeth  26  ( 26   a,    26   b,    26   c,  and  26   d ) of the second yoke portion  25  and face radially outward. The outer peripheral surfaces  51  are curved surfaces that are provided on the respective internal teeth  46  ( 46   a,    46   b,    46   c,  and  46   d ) of the second yoke portion  45  and face radially outward. 
     As described, a yoke of one core of the cores  20  and  40  has at least one yoke surface that is substantially parallel to the axial direction, and the yoke surface of the one core is in contact with or in proximity to the other core. With this configuration, when the cores  20  and  40  are formed by press-forming magnetic powder cores in the axial direction, because the yoke surface is substantially parallel to the pressing direction, the dimensional accuracy of the yoke surface does not readily decrease. Therefore, a decrease in the dimensional accuracy of the stator core  9  in the axial direction can be reduced. 
     Further, each of the second yoke portions  25  and  45  of the cores  20  and  40  is not provided on the entire circumference of the cores  20  and  40 . The second yoke portions  25  and  45  are constituted by the plurality of internal teeth  26  and  46 , respectively, and the total length of the internal teeth  26  and the total length of the internal teeth  46  in the circumferential direction are each approximately half the circumference of a corresponding core. Therefore, the projected area in the axial direction of each of the cores  20  and  40  is reduced. As a result, the pressure by which the magnetic powder cores are press-formed can be reduced, thereby reducing the size of, for example, a pressing device. 
     Further, the cores  20  and  40  and the winding  19  can be brought into contact with each other by fitting the cores  20  and  40  in the axial direction until the yokes  21  and  41  touch the winding  19 . Accordingly, the performance of heat dissipation from the winding  19  to the cores  20  and  40  can be improved. 
     Note that when the yoke surfaces of one core are in contact with the other core, the yoke surfaces of the one core may be joined, fitted, bonded, or pressure-bonded to the other core. In a case where the yoke surfaces of one core are in proximity to the other core, there may be a gap as small as the size of part of a magnetic path. 
     In the first embodiment, the length of each of the yoke surfaces  29  and  30  in the axial direction is greater than a half of the length of the yoke  21  in the axial direction. In this example, the length of each of the yoke surfaces  29  and  30  in the axial direction is substantially the same as the length of the yoke  21  in the axial direction. In the first embodiment, the length of each of the yoke surfaces  49  and  50  is greater than a half of the length of the yoke  41  in the axial direction. In this example, the length of each of the yoke surfaces  49  and  50  is substantially the same as the length of the yoke  41  in the axial direction. With this configuration, the magnetic flux that passes through the yoke surfaces  29 ,  30 ,  49 , and  50  can be increased. Thus, the torque of the motor  1  can be increased, for example. 
     In the first embodiment, only the yoke surfaces (the yoke surfaces  29  and  30  and the outer peripheral surfaces  31 ) of the core  20  are in contact with or in proximity to the core  40 , and only the yoke surfaces (the yoke surfaces  49  and  50  and the outer peripheral surfaces  51 ) of the core  40  are in contact with or in proximity to the core  20 . With this configuration, even when the cores  20  and  40  are constituted by magnetic powder cores press-formed in the axial direction, because the yoke surfaces are substantially parallel to the pressing direction, the dimensional accuracy of the yoke surfaces does not readily decrease. Therefore, a decrease in the dimensional accuracy of the stator core  9  in the axial direction can be further reduced. 
     In the first embodiment, the yoke surfaces  29  and  30  of the core  20  are in contact with or in proximity to the core  40  in the circumferential direction, and the yoke surfaces  49  and  50  of the core  40  are in contact with or in proximity to the core  20  in the circumferential direction. With this configuration, even when the cores  20  and  40  are constituted by magnetic powder cores press-formed in the axial direction, because the yoke surfaces are substantially parallel to the pressing direction, the dimensional accuracy of the yoke surfaces does not readily decrease. Therefore, a decrease in the dimensional accuracy of the stator core  9  in the axial direction can be further reduced. 
     In the first embodiment, the yoke surfaces (in this example, the outer peripheral surfaces  31 ) of the core  20  are in contact with or in proximity to the core  40  in the radial direction, and the yoke surfaces (in this example, the outer peripheral surfaces  51 ) of the core  40  are in contact with or in proximity to the core  20  in the radial direction. With this configuration, even when the cores  20  and  40  are constituted by magnetic powder cores press-formed in the axial direction, because the yoke surfaces are substantially parallel to the pressing direction, the dimensional accuracy of the yoke surfaces does not readily decrease. Therefore, a decrease in the dimensional accuracy of the stator core  9  in the axial direction can be further reduced. 
     In the first embodiment, the plurality of cores  20  and  40  have the same shape. With this configuration, the plurality of cores  20  and  40  can be formed by the same mold. Therefore, the manufacturing cost of the stator core  9  can be reduced, for example. 
       FIG.  5    is a plan view of an example of the core according to the first embodiment when viewed in the axial direction. The above-described core  20  has substantially the same configuration as the core  40  illustrated in  FIG.  5   , and thus, the description of the configuration of the core  20  will be omitted by referring to the description of the core  40 . 
     The core  40  includes the plurality of internal teeth  46  ( 46   a,    46   b,    46   c,  and  46   d ) of the yoke  41 , arranged at equal intervals in the circumferential direction and having the same width in the circumferential direction, and the plurality of claw magnetic poles  42  arranged at equal intervals in the circumferential direction and having the same width in the circumferential direction. 
     An angle θ α  represents an angle between the center  52  of the width, in the circumferential direction, of a claw magnetic pole of the plurality of claw magnetic poles  42  and the end (yoke surface  49  in this example), in the circumferential direction, of an internal tooth that is closest to the center  52  of the width of the claw magnetic pole from among the plurality of internal teeth  46 . More specifically, when viewed in the axial direction, the angle θ α  represents a central angle between a line L 1 , connecting the center  52  of the width of the claw magnetic pole to the rotation axis AX of the rotor  10 , and a line L 2  connecting the end (yoke surface  49  in this example), in the circumferential direction, of the internal tooth that is closest to the center  52  of the width of the claw magnetic pole to the rotation axis AX of the rotor  10 . 
     An angle θ β  represents an angle between both ends (yoke surfaces  49  and  50  in this example), in the circumferential direction, of an internal tooth of the plurality of internal teeth  46 . More specifically, when viewed in the axial direction, the angle θ β  represents a central angle between the line L 2 , connecting one end (yoke surface  49 , in this example), in the circumferential direction, of the internal tooth to the rotation axis AX of the rotor  10 , and a line L 3  connecting the other end (yoke surface  50  in this example), in the circumferential direction, of the internal tooth to the rotation axis AX of the rotor  10 . 
     The plurality of cores  20  and  40  can be formed in the same shape if the following equations hold: 
       θ α =80/(2 ·n )  (Equation 1), and
 
       θ β =360/(2   19  N )  (Equation 2),
 
     where n represents the number of a plurality of claw magnetic poles  42 , and N represents the number of a plurality of internal teeth  46 . Accordingly, plurality of cores  20  and  40  can be formed by the same mold, and thus, the manufacturing cost of the stator core  9  can be reduced, for example. 
     In the example illustrated in  FIG.  5   , n=10 and N=4. Therefore, the plurality of cores  20  and  40  can be formed in the same shape by setting “θ α =9° and θ β =45°” based on the above Equations 1 and 2. 
       FIG.  6    is a perspective view of an example of a stator unit according to a second embodiment.  FIG.  7    is an exploded perspective view of an example of the stator unit according to the second embodiment. The description of the same configurations and effects as those of the above embodiment is omitted or simplified by referring to the above description. 
     In  FIG.  6    and  FIG.  7   , a stator core  9  includes a plurality of cores  20 A and  40 A facing each other with the winding  19  interposed therebetween in the axial direction of the stator  13 . The number and the shape of claw magnetic poles  22  and  42  of a stator unit  14 A differs from those of the stator unit  14  according to the first embodiment. A claw magnetic pole portion  28  has a tapered shape in which the width thereof decreases as the distance from a claw magnetic pole portion  27  increases in the axial direction. A claw magnetic pole portion  48  has a tapered shape in which the width thereof decreases as the distance from a claw magnetic pole portion  47  increases in the axial direction. 
       FIG.  8    is a plan view of an example of a core according to the second embodiment when viewed in the axial direction. The core  20 A has substantially the same configuration as the core  40 A illustrated in  FIG.  8   , and thus, the description of the configuration of the core  20 A is omitted by referring to the description of the core  40 A. 
     In the example illustrated in  FIG.  8   , the number n of claw magnetic poles  42 =8 and the number N of internal teeth  46 =4. Therefore, the plurality of cores  20 A and  40 A can be formed in the same shape by setting “θ α =11.25° and θ β =45°”. 
     The number of claw magnetic poles  42  (n=8) is a multiple of the number of internal teeth  46  (N=4). Therefore, the core  20 A and the core  40 A can be assembled by, for example, inserting an internal tooth  26   a  between an internal tooth  46   d  and an internal tooth  46   a  or between the internal teeth  46   a  and an internal teeth  46   b.  Accordingly, ease of assembly of the core  20 A and the core  40 A can be facilitated. 
       FIG.  9    is a perspective view of an example of a stator unit according to a third embodiment. The description of the same configurations and effects as those of the above embodiments is omitted or simplified by referring to the above description. 
     In  FIG.  9   , a stator core  9  includes a plurality of cores  20 B and  40 B facing each other with the winding  19  interposed therebetween in the axial direction of the stator  13 . The shapes of internal teeth  26  and  46  of a stator unit  14 B differ from those of the stator unit  14 A according to the second embodiment. 
       FIG.  10    is a perspective view of an example of a core according to the third embodiment. The description of the same configurations and effects as those of the above embodiments is omitted or simplified by referring to the above description. The core  20 B has substantially the same configuration as the core  40 B illustrated in  FIG.  10   , and thus, the description of the configuration of the core  20 B is omitted by referring to the description of the core  40 B. 
     Each of the internal teeth  46  ( 46   a,    46   b ,  46   c,  and  46   d ) has a tapered shape in which the width thereof decreases as the distance from an inner circumferential surface  44   a  of a first yoke portion  44  increases in the axial direction. Because each of the internal teeth  26  and  46  has such a tapered shape, the core  20 B and the core  40 B can be readily assembled in the axial direction. 
     In the example illustrated in  FIG.  10   , the number n of claw magnetic poles 42=8 and the number N of internal teeth 46=4. Therefore, the plurality of cores  20 B and  40 B can be formed in the same shape by setting “θ α =11.25° and θ β =45°”. 
       FIG.  11    is a perspective view of an example of a stator unit according to a fourth embodiment. The description of the same configurations and effects as those of the above embodiments is omitted or simplified by referring to the above description. 
     In  FIG.  11   , a stator core  9  includes a plurality of cores  20 C and  40 C facing each other with the winding  19  interposed therebetween in the axial direction of the stator  13 . A stator unit  14 C differs from the stator unit  14 A according to the second embodiment in that the two cores (cores  20 C and  40 C) do not have the same shape. 
       FIG.  12    is a plan view of an example of one of the cores according to the fourth embodiment when viewed in the axial direction.  FIG.  13    is a plan view of an example of the other core according to the fourth embodiment when viewed in the axial direction.  FIG.  12    depicts the core  20 C, and  FIG.  13    depicts the core  40 C. 
     In  FIG.  12   , an angle θ α1  represents an angle between the center  52  of the width, in the circumferential direction, of a claw magnetic pole of a plurality of claw magnetic poles  22  and the end (yoke surface  30  in this example), in the circumferential direction, of an internal tooth that is closest to the center  52  of the width of the claw magnetic pole from among a plurality of internal teeth  26 . More specifically, when viewed in the axial direction, the angle θ α  represents a central angle between a line L 1 , connecting the center  52  of the width of the claw magnetic pole to the rotation axis AX of the rotor  10 , and a line L 2  connecting the end (yoke surface  30  in this example), in the circumferential direction, of the internal tooth that is closest to the center  52  of the width of the claw magnetic pole to the rotation axis AX of the rotor  10 . In the example of  FIG.  12   , the angle θ α1 0°. 
     In  FIG.  12   , an angle θ β  represents an angle between both ends (yoke surfaces  29  and  30  in this example), in the circumferential direction, of an internal tooth of the plurality of internal teeth  26 . More specifically, when viewed in the axial direction, the angle θ β  represents a central angle between the line L 2 , connecting one end (yoke surface  30  in this example), in the circumferential direction, of the internal tooth to the rotation axis AX of the rotor  10 , and a line L 3  connecting the other end (yoke surface  29  in this example), in the circumferential direction, of the internal tooth to the rotation axis AX of the rotor  10 . 
     In  FIG.  13   , an angle θ α2  represents an angle between the center  52  of the width, in the circumferential direction, of a claw magnetic pole of a plurality of claw magnetic poles  42  and the end (yoke surface  49  in this example), in the circumferential direction, of an internal tooth that is closest to the center  52  of the width of the claw magnetic pole from among a plurality of internal teeth  46 . More specifically, when viewed in the axial direction, the angle θ α2  represents a central angle between a line L 1 , connecting the center  52  of the width, in the circumferential direction, of the claw magnetic pole to the rotation axis AX of the rotor  10 , and a line L 2  connecting the end (yoke surface  49  in this example), in the circumferential direction, of the internal tooth that is closest to the center  52  of the width of the claw magnetic pole to the rotation axis AX of the rotor  10 . 
     In  FIG.  13   , an angle θ β  represents an angle between both ends (yoke surfaces  49  and  50  in this example), in the circumferential direction, of an internal tooth of the plurality of internal teeth  46 . More specifically, when viewed in the axial direction, the angle θ β  represents a central angle between the line L 2 , connecting one end (yoke surface  49  in this example), in the circumferential direction, of the internal tooth to the rotation axis AX of the rotor  10 , and a line L 3  connecting the other end (yoke surface  50  in this example), in the circumferential direction, of the internal tooth to the rotation axis AX of the rotor  10 . 
     In a case where the cores have different θ α1  and θ α2 , the value of θ α2  of the core  40 C facing the core  20 C is calculated based on the values of θ α1  and θ β  of the core  20 C. The calculation equation is as follows. 
       θ α2 =2θ α1 +θ β /2  (Equation 3)
 
     Note that the core  20 C and the core  40 C are required to have the same number and shape of internal teeth. 
     For example, when the number N of internal teeth is 4, “θ β =45°” based on Equation 2 above. Therefore, θ α2  of the core  40 C facing the core  20 C having θ α1  of 30° is 37.5° based on Equation 3. For example, when the number N of internal teeth is 4, “θ β =45°” based on Equation 2 above. Therefore, θ α2  of the core  40 C facing the core  20 C having θ α1  of 0° is 22.5° based on Equation 3. 
     In  FIG.  12   , in a plan view along the axial direction, the yoke surface  30  is positioned on the line L 1  connecting the center  52  of the width, in the circumferential direction, of at least one claw magnetic pole  22  of the plurality of claw magnetic poles  22  to the rotation axis AX of the rotor  10 . The magnetic flux, entering from the claw magnetic pole  22  toward the rotation axis AX, is divided between the internal tooth  26   a  side and the internal tooth  46   d  side (see  FIG.  13   ). Therefore, when the yoke surface  30  is positioned on the line L 1 , the magnetic flux passing through the yoke surface  30  is reduced. Accordingly, the magnetic resistance of a magnetic circuit through which the magnetic flux passes can be reduced, and the torque of the motor  1  can be thus increased. 
       FIG.  14    is a perspective view of an example of a stator unit according to a fifth embodiment. The description of the same configurations and effects as those of the above embodiments is omitted or simplified by referring to the above description. 
     In  FIG.  14   , a stator core  9  includes a plurality of cores  20 D and  40 D facing each other with the winding  19  interposed therebetween in the axial direction of the stator  13 . A stator unit  14 D differs from the stator unit  14 A according to the second embodiment in that a plurality of internal teeth  26  do not have the same width in the circumferential direction and a plurality of internal teeth  46  do not have the same width in the circumferential direction. 
       FIG.  15    is a perspective view of an example of a core according to the fifth embodiment.  FIG.  16    is a plan view of an example of the core according to the fifth embodiment when viewed in the axial direction. The description of the same configurations and effects as those of the above embodiments is omitted or simplified by referring to the above description. The core  20 D has substantially the same configuration as the core  40 D illustrated in  FIG.  15    and  FIG.  16   , and thus, the description of the configuration of the core  20 D is omitted by referring to the description of the core  40 D. 
     Each of internal teeth  46   a,    46   b,  and  46   c  protrudes in the axial direction while having a constant curved width (more specifically, a constant arc length) regardless of the distance from an inner circumferential surface  44   a  of a first yoke portion  44 . The curved widths of the internal teeth  46   a ,  46   b,  and  46   c  differ from each other. 
       FIG.  17    is an exploded perspective view of an example of a stator unit according to a sixth embodiment. The description of the same configurations and effects as those of the above embodiments is omitted or simplified by referring to the above description. 
     In  FIG.  17   , a stator core  9  includes a plurality of cores  20 E and  40 E facing each other with the winding  19  interposed therebetween in the axial direction of the stator  13 . In a stator unit  14 E, the shapes of yokes  21  and  41  differ from those of the stator unit  14 A according to the second embodiment. 
     The yoke  21  illustrated in  FIG.  17    has an annular shape when viewed in the axial direction, and has a predetermined thickness in the axial direction. The yoke  21  includes a first yoke portion  24  having a substantially annular shape and a second yoke portion  25  that contacts the other core  40 . In the example illustrated in  FIG.  17   , the first yoke portion  24  is an outer peripheral portion of the yoke  21  having a substantially annular shape, and the second yoke portion  25  is an inner peripheral portion of the yoke  21  having a substantially annular shape. 
     The yoke  41  illustrated in  FIG.  17    has an annular shape when viewed in the axial direction, and has a predetermined thickness in the axial direction. The yoke  41  includes a first yoke portion  44  having a substantially annular shape and a second yoke portion  45  that contacts the other core  20 . In the example illustrated in  FIG.  17   , the first yoke portion  44  is a substantially annular portion of the yoke  21 . The second yoke portion  45  is a cylindrical portion that protrudes from the first yoke portion  44  toward the other core  20  by a predetermined amount. The outer surface of the second yoke portion  45  having a cylindrical shape is in contact with or in proximity to the second yoke portion  25  (the inner peripheral portion of the yoke  21  having a substantially annular shape). 
       FIG.  18    is a cross-sectional view of a first example configuration of a yoke taken through A-A of  FIG.  14   . In  FIG.  18   , a second yoke portion  45  is formed integrally with a first yoke portion  44 .  FIG.  19    is a cross-sectional view of a second example configuration of a yoke taken through A-A of  FIG.  14   . In  FIG.  19   , a second yoke portion  45  is formed separately from a first yoke portion  44 . Similarly, a first yoke portion  24  may be formed integrally with or separately from a second yoke portion  25 . In the embodiments other than  FIG.  14   , a first yoke portion may be formed integrally with or separately from a second yoke portion. 
     Although embodiments have been described above, it will be understood that various modifications may be made to the configurations and details thereof without departing from the spirit and scope of the claims. Various modifications and improvements such as combinations and replacements with part or all of other embodiments are possible. 
     For example, if a yoke portion has surfaces that face each other in the axial direction, the surfaces that face each other in the axial direction do not preferably contact each other. Further, the distance between the surfaces that face each other in the axial direction is preferably set to be greater than the distance between yoke surfaces that are substantially parallel to the axial direction. With this configuration, even if a large dimensional error occurs in the axial direction, the error can be absorbed. 
     For example, in the above-described embodiments, the motor  1  is an outer-rotor-type claw pole motor in which the rotor  10  is disposed radially outward relative to the stator  13 . However, the rotary electrical device according to the present disclosure can be applied to an inner-rotor-type claw pole motor in which a rotor is disposed radially inward relative to a stator. An inner-rotor-type rotary electrical device includes a rotor having a substantially solid cylindrical shape and configured to be rotatable, and a stator having a substantially annular shape and disposed radially outward relative to the rotor to surround the rotation axis of the rotor. 
     This international application is based on and claims priority to Japanese Patent Application No. 2020-083123, filed on May 11, 2020, the entire contents of which are incorporated herein by reference. 
     DESCRIPTION OF THE REFERENCE NUMERALS 
     
         
           1  motor 
           8  through-hole 
           9  stator core 
           10  rotor 
           11  rotor core 
           12  permanent magnet 
           13  stator 
           14  to  16  stator unit 
           17 ,  18  non-magnetic material layer 
           19  winding 
           19   a  outer circumferential portion 
           19   b  inner circumferential portion 
           20 ,  40  core 
           21 ,  41  yoke 
           22 ,  42  claw magnetic pole 
           23 ,  43  center hole 
           24 ,  44  first yoke portion 
           24   a,    44   a  inner circumferential surface 
           24   b,    44   b  outer circumferential surface 
           25 ,  45  second yoke portion 
           26   a,    26   b,    26   c,    26   d,    46   a,    46   b,    46   c,    46   d  internal tooth 
           27 ,  28 ,  47 ,  48  claw magnetic pole portion 
           29 ,  30 ,  49 ,  50  yoke surface 
           31 ,  51  outer peripheral surface 
           52  center of width 
         AX rotation axis 
         L 1 , L 2  line