Patent Publication Number: US-2022239190-A1

Title: Motor, fan, air conditioner, and manufacturing method of motor

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a U.S. national stage application of International Patent Application No. PCT/JP2019/029332 filed on Jul. 26, 2019, the disclosure of which is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a motor, a fan, an air conditioner, and a manufacturing method of the motor. 
     BACKGROUND 
     Conventionally, a motor having a stator covered with a mold resin is known (see, for example, Patent Reference 1). 
     PATENT REFERENCE 
     Patent Reference 1 
     International Publication WO 2017/183162 (see  FIG. 1 ) 
     Recently, with an increasing output of the motor, reduction in vibration and noise of the motor is required. 
     SUMMARY 
     The present invention is intended to solve the above-described problem, and an object of the present invention is to reduce vibration and noise of a motor. 
     A motor according to an aspect of the present invention includes a rotor that has a rotation shaft, a rotor core fixed with respect to the rotation shaft, a magnet attached to the rotor core, and a bearing attached to the rotation shaft. The magnet constitutes a first magnetic pole, and a part of the rotor core constitutes a second magnetic pole. The motor also includes an annular stator surrounding the rotor from outside in a radial direction about a center axis of the rotation shaft, a bearing holding member holding the bearing, and a resin portion covering the stator and the bearing holding member. The bearing holding member is composed of a metal or a resin different from the resin portion. 
     According to the present invention, the bearing is held by the bearing holding member, and the bearing holding member and the stator are covered with the resin portion. Thus, the coaxiality between the stator and the rotor can be improved. Accordingly, vibration and noise of the motor can be reduced. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a partial sectional view illustrating a motor of a first embodiment. 
         FIG. 2  is a sectional view illustrating a rotor of the first embodiment. 
         FIG. 3  is a plan view illustrating a stator core of the first embodiment. 
         FIGS. 4(A) and 4(B)  are a plan view and a side view illustrating a stator of the first embodiment, respectively. 
         FIG. 5  is an enlarged sectional view illustrating a part of the motor of the first embodiment. 
         FIGS. 6(A), 6(B) , and  6 (C) are a front view, a sectional view, and a rear view illustrating a bearing holding member of the first embodiment, respectively. 
         FIG. 7  is a diagram illustrating a mold stator of the first embodiment as viewed from an opening side. 
         FIG. 8  is a sectional view illustrating a mold used in a manufacturing process of the motor of the first embodiment. 
         FIG. 9  is a flowchart illustrating the manufacturing process of the motor of the first embodiment. 
         FIG. 10  is an enlarged diagram illustrating a part of a bearing holding member of a modification. 
         FIG. 11  is an enlarged sectional view illustrating a part of a motor of a second embodiment. 
         FIG. 12  is a diagram illustrating a mold stator of the second embodiment as viewed from an opening side. 
         FIG. 13(A)  is an enlarged sectional view illustrating a part of a motor of a third embodiment, and  FIG. 13(B)  is a perspective view illustrating a contact portion of the third embodiment. 
         FIG. 14  is an enlarged sectional view illustrating a part of a motor of a fourth embodiment. 
         FIG. 15(A)  is an enlarged sectional view illustrating a part of a motor of a fifth embodiment, and  FIG. 15(B)  is a perspective view illustrating a bearing holding member of the fifth embodiment. 
         FIG. 16  is a sectional view illustrating a rotor of a modification. 
         FIG. 17(A)  is a diagram illustrating an air conditioner to which the motor of each embodiment is applicable, and  FIG. 17(B)  is a sectional view illustrating an outdoor unit. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present invention will be described in detail below with reference to the figures. The present invention is not limited to these embodiments. 
     First Embodiment 
     (Configuration of Motor  1 ) 
       FIG. 1  is a partial sectional view illustrating a motor  1  of a first embodiment. The motor  1  is, for example, a brushless DC motor that is used in a fan of an air conditioner. 
     The motor  1  includes a rotor  2  having a rotation shaft  11  and a mold stator  4 . The rotation shaft  11  is a shaft for rotation of the rotor  2 . The mold stator  4  has an annular stator  5  surrounding the rotor  2 , a circuit board  6 , a bearing holding member  3 , and a mold resin portion  40  as a resin portion that covers these components. 
     In the description below, a direction of an axis C 1 , which is a center axis of the rotation shaft  11 , is referred to as an “axial direction”. A circumferential direction (indicated by an arrow R 1  in  FIG. 3  and other figures) about the axis C 1  of the rotation shaft  11  is referred to as a “circumferential direction”. A radial direction about the axis C 1  of the rotation shaft  11  is referred to as a “radial direction”. 
     The rotation shaft  11  protrudes from the mold stator  4  to the left in  FIG. 1 . For example, an impeller  505  of a fan ( FIG. 17(A) ) is attached to an attachment portion  11   a  famed at the protruding portion of the rotation shaft  11 . Thus, the protruding side (the left side in  FIG. 1 ) of the rotation shaft  11  is referred to as a “load side”, while the opposite side (the right side in  FIG. 1 ) of the rotation shaft  11  is referred to as a “counter-load side”. 
     (Configuration of Rotor  2 ) 
       FIG. 2  is a sectional view illustrating the rotor  2 . As illustrated in  FIG. 2 , the rotor  2  has the rotation shaft  11 , a rotor core  20  fixed with respect to the rotation shaft  11 , a plurality of magnets  23  embedded in the rotor core  20 , and a resin portion  25  provided between the rotation shaft  11  and the rotor core  20 . The number of magnets  23  is five in this example. The magnet  23  is also referred to as a main magnet. 
     The rotor core  20  is a member having an annular shape about the axis C 1 . An inner circumference of the rotor core  20  faces the rotation shaft  11  with a space therebetween. The rotor core  20  is famed of a plurality of stacking elements that are stacked in the axial direction and integrally fixed by crimping, welding, bonding, or the like. The stacking elements are, for example, electromagnetic steel sheets. Each stacking element has a thickness of 0.1 mm to 0.7 mm. 
     The rotor core  20  has a plurality of magnet insertion holes  21  in the circumferential direction. The magnet insertion holes  21  are arranged at equal intervals in the circumferential direction and disposed at equal distances from the axis C 1 . The number of magnet insertion holes  21  is five in this example. The magnet insertion holes  21  are famed along an outer circumference of the rotor core  20  and pass through the rotor core  20  in the axial direction. 
     The magnet  23  is inserted in each magnet insertion hole  21 . The magnet  23  is a rare earth magnet that contains samarium (Sm), iron (Fe), and nitrogen (N). Alternatively, the magnet  23  may be a rare earth magnet that contains neodymium (Nd), iron, and boron (B). These rare earth magnets are characterized by large magnetic force. The magnet  23  is in the form of a flat plate, and has a rectangular shape in a cross section perpendicular to the axial direction in this example. The shape of the magnet  23  is not limited to such a shape, but may be other shapes. 
     Five magnets  23  are arranged so that the same magnetic poles face the outer circumferential side of the rotor core  20 . In a region of the rotor core  20  between the magnets  23  adjacent in the circumferential direction, a magnetic pole opposite to those of the magnets  23  is famed. 
     Thus, five first magnetic poles P 1  and five second magnetic poles P 2  are alternately arranged in the circumferential direction in the rotor  2 . Each first magnetic pole P 1  is famed by the magnet  23 , while each second magnetic pole P 2  is famed by a portion of the rotor core  20 . The first magnetic pole P 1  is also referred to as a magnet magnetic pole, while the second magnetic pole P 2  is also referred to as a virtual magnetic pole. Such a rotor  2  is called a consequent pole rotor. 
     Hereinafter, the team “magnetic poles” denotes both the first magnetic poles P 1  and the second magnetic poles P 2 . The number of poles of the rotor  2  is  10 . The magnetic poles P 1  and P 2  of the rotor  2  are arranged at equal angular intervals in the circumferential direction with a pole pitch of 36 degrees (360 degrees/10). A boundary between the first magnet pole P 1  and the second magnetic pole P 2  is defined as a pole boundary M. 
     The outer circumference of the rotor core  20  has a so-called flower shape in a cross section perpendicular to the axial direction. In other words, the outer circumference of the rotor core  20  has its maximum outer diameter at a pole center of each of the magnetic poles P 1  and P 2  and its minimum outer diameter at the pole boundary M, and extends in an arc shape from the pole center to the pole boundary M. The outer circumference of the rotor core  20  is not limited to the flower shape, but may be a circular shape. The inner circumference of the rotor core  20  has a circular shape in a cross section perpendicular to the axial direction. 
     In the consequent pole rotor  2 , the number of magnets  23  can be halved as compared with a non-consequent pole rotor having the same number of poles. Since the number of the expensive magnets  23  is small, the manufacturing cost of the rotor  2  is reduced. 
     Although the number of poles of the rotor  2  is  10  in this example, it is sufficient that the number of poles of the rotor  2  is an even number of four or more. Moreover, although one magnet  23  is disposed in each magnet insertion hole  21  in this example, two or more magnets  23  may be disposed in each magnet insertion hole  21 . 
     The magnet insertion hole  21  extends linearly in a direction perpendicular to a straight line extending in the radial direction and passing through a center of the magnetic insertion hole  21  in the circumferential direction, i.e., the pole center. An opening (flux barrier)  22  for suppressing a leakage magnetic flux between the adjacent magnetic poles is famed at each of both sides of the magnet insertion hole  21  in the circumferential direction. The magnet insertion hole  21  may have a V shape such that its center in the circumferential direction protrudes toward the axis C 1  side. 
     The resin portion  25  is provided between the rotation shaft  11  and the rotor core  20 . The resin portion  25  holds the rotation shaft  11  and the rotor core  20  in such a manner that the rotation shaft  11  and the rotor core  20  are apart from each other. The resin portion  25  is desirably composed of a thermoplastic resin such as polybutylene terephthalate (PBT). 
     The resin portion  25  has an annular inner ring portion  26  that is fixed to an outer circumference of the rotation shaft  11 , an annular outer ring portion  28  that is fixed to the inner circumference of the rotor core  20 , and a plurality of ribs  27  that connect the inner ring portion  26  and the outer ring portion  28 . The ribs  27  are arranged at equal intervals in the circumferential direction about the axis C 1 . The number of ribs  27  is, for example, half the number of poles, and is five in this example. 
     The rotation shaft  11  is fitted into an inner side of the inner ring portion  26  of the resin portion  25 . The ribs  27  are arranged at equal intervals in the circumferential direction and radially extend outward in the radial direction from the inner ring portion  26 . A hollow portion  29  is famed between the ribs  27  that are adjacent to each other in the circumferential direction. In this example, the number of ribs  27  is half the number of poles, and a position of each rib  27  in the circumferential direction is coincident with the pole center of the second magnetic pole P 2 , but the number and positions of the ribs  27  are not limited thereto. 
     As illustrated in  FIG. 1 , a sensor magnet  24  is disposed to face the rotor core  20  in the axial direction. The sensor magnet  24  is held by the resin portion  25 . The sensor magnet  24  has magnetic poles, the number of which is the same as the number of poles of the rotor  2 . A magnetic field of the sensor magnet  24  is detected by a magnetic sensor mounted on the circuit board  6 , and thereby a position of the rotor  2  in the circumferential direction, i.e., a rotational position of the rotor  2  is detected. 
     The rotor  2  is not limited to the configuration in which the rotor core  20  and the rotation shaft  11  are connected by the resin portion  25  as described above. For example, the rotor  2  may have a central hole famed in the rotor core  20 , and the rotation shaft  11  may be fitted into the central hole. 
     (Configuration of Mold Stator  4 ) 
     The mold stator  4  includes the stator  5  and the mold resin portion  40  as described above. The stator  5  surrounds the rotor  2  from outside in the radial direction. The stator  5  includes a stator core  50 , an insulating portion  52  provided on the stator core  50 , and coils  53  wound on the stator core  50  via the insulating portion  52 . 
     The mold resin portion  40  is desirably composed of a thermosetting resin such as a bulk molding compound (BMC). However, the mold resin portion  40  may be composed of a thermoplastic resin such as PBT or polyphenylene sulfide (PPS). The mold resin portion  40  has mounting legs  45  on its outer circumference. The mounting legs  45  are provided for mounting the motor  1  on a frame of an air conditioner or the like. 
     The mold resin portion  40  has a rotor housing portion  41  at its center in the radial direction, and the rotor  2  is housed in the rotor housing portion  41 . An opening  42  is famed on the load side of the rotor housing portion  41 . The rotor  2  is inserted into the rotor housing portion  41  through the opening  42 . 
     At an end surface of the mold resin portion  40  on the load side, a step portion  43  is famed along a peripheral edge of the opening  42 . A bracket  15  is attached to the step portion  43 . The bracket  15  is composed of a metal such as a hot-dip zinc-aluminum-magnesium alloy-plated steel sheet. A bearing  12 , which is one of the bearings that support the rotation shaft  11 , is held by the bracket  15 . A cap  14  for preventing the entry of water or the like is attached to the outside of the bracket  15 . 
     The bearing holding member  3  that holds the other bearing  13  is provided on a side of the mold resin portion  40  opposite to the opening  42 , i.e., on the counter-load side. A configuration of the bearing holding member  3  will be described later. 
       FIG. 3  is a plan view illustrating the stator core  50 . The stator core  50  is famed of a plurality of stacking elements that are stacked in the axial direction and integrally fixed by crimping, welding, bonding, or the like. The stacking elements are, for example, electromagnetic steel sheets. Each stacking element has a thickness of 0.1 mm to 0.7 mm. 
     The stator core  50  has a yoke  51   a  extending annularly in the circumferential direction about the axis C 1 , and a plurality of teeth  51   b  extending inward in the radial direction from the yoke  51   a.  A tooth tip end  51   c  on an inner side of each tooth  51   b  in the radial direction faces the outer circumference of the rotor  2  ( FIG. 1 ). Although the number of teeth  51   b  is  12  in this example, the number of teeth  51   b  is not limited to  12 . 
     The stator core  50  is formed of a plurality of core portions  51  each of which includes one tooth  51   b  and which are connected together. The core portions  51  are divided by split surface portions  51   d  famed in the yoke  51   a.  Each split surface portion  51   d  extends outward in the radial direction from an inner circumference of the yoke  51   a.  A thin-walled connection portion  51   e,  which is a plastically deformable thin-walled portion, is famed between an outer end of each split surface portion  51   d  and the outer circumference of the yoke  51   a.    
     The thin-walled connection portion  51   e  is a connection portion that connects the core portions  51  adjacent to each other in the circumferential direction. That is, the stator core  50  has a configuration in which a plurality of core portions  51  are connected in the circumferential direction at the thin-walled connection portions  51   e.  The stator core  50  can be expanded into a strip shape by plastic defamation of the thin-walled connection portions  51   e.    
     The coils  53  can be wound around the teeth  51   b  in a state where the stator core  50  are expanded in a strip shape. After the winding of the coils  53  is completed, the strip-shaped stator core  50  is bent in an annular shape, and both ends W of the stator core  50  are welded to each other. The connection portion that connects adjacent core portions  51  is not limited to the thin-walled connection portion  51   e,  but may be, for example, a crimping portion. 
       FIG. 4(A)  is a plan view illustrating the stator  5 .  FIG. 4(B)  is a side view illustrating the stator  5 . In  FIG. 4(A) , two of the teeth  51   b  of the stator  5  are indicated by broken lines. 
     The coil  53  is, for example, a magnet wire, and is wound around the tooth  51   b  via the insulating portion  52 . The insulating portion  52  is composed of a thermoplastic resin such as PBT, for example. The insulating portion  52  is famed by integrally molding the thermoplastic resin with the stator core  50  or by assembling a molded body of the thermoplastic resin to the stator core  50 . 
     The insulating portion  52  has wall portions on inner and outer sides of the coils  53  in the radial direction, and the wall portions guide the coils  53  from both sides in the radial direction. A plurality of terminals  57  are mounted on the insulating portion  52 . Ends of the coils  53  are connected to the terminals  57  by, for example, fusing (thermal caulking), soldering, or the like. 
     The insulating portion  52  is also provided with a plurality of protrusions  56  for fixing the circuit board  6 . The protrusions  56  are inserted through attachment holes famed in the circuit board  6 . The circuit board  6  is fixed to the stator  5  by thermally welding the tips of the protrusions  56  inserted through the attachment holes of the circuit board  6 . A combination of the stator  5  and the circuit board  6  is referred to as a stator assembly. 
     As shown in  FIG. 1 , the circuit board  6  is disposed on one side of the stator  5  in the axial direction, i.e., the counter-load side of the stator  5  in this example. The circuit board  6  is a printed circuit board on which a drive circuit  61  such as a power transistor for driving the motor  1  is mounted, and lead wires  63  are wired on the circuit board  6 . The lead wires  63  on the circuit board  6  are drawn to the outside of the motor  1  through a lead wire outlet component  62  attached to an outer circumferential portion of the mold resin portion  40 . 
     (Configuration of Bearing Holding Member  3 ) 
     Next, the bearing holding member  3  will be described.  FIG. 5  is an enlarged view illustrating a part of the motor  1 . As illustrated in  FIG. 5 , the bearing  13  is a rolling bearing and has an outer ring  13   a,  an inner ring  13   b,  and rolling elements  13   c.  The inner ring  13   b  of the bearing  13  is attached to the rotation shaft  11  by interference fit. The outer ring  13   a  of the bearing  13  is attached to the bearing holding member  3  by clearance fit. 
     The bearing holding member  3  is composed of a metal. More specifically, the bearing holding member  3  is composed of a hot-dip zinc-aluminum-magnesium alloy-plated steel sheet. Since the hot-dip zinc-aluminum-magnesium alloy-plated steel sheet can be subjected to press-working, its workability is excellent and high dimensional accuracy can be easily obtained. In addition, the hot-dip zinc-aluminum-magnesium alloy-plated steel sheet has higher thermal conductivity as compared to a general resin such as BMC or PBT. 
     The bearing holding member  3  may also be composed of an aluminum alloy such as ADC12 (JIS H5302). An aluminum alloy such as ADC12 can be processed by die-casting, and thus a degree of freedom in the shape is higher as compared to the case where the bearing holding member  3  is famed by extrusion molding or the like. Thus, the number of steps for forming the bearing holding member  3  can be reduced, and the manufacturing cost of the motor  1  can be reduced. An aluminum alloy such as ADC12 has higher thermal conductivity as compared to a general resin such as BMC or PBT. 
     The bearing holding member  3  is provided in the mold stator  4  so as to cover a side (more specifically, the counter-load side) of the rotor housing portion  41  in the radial direction. The rotor  2  including the bearings  12  and  13  is housed in the rotor housing portion  41 . 
     The bearing holding member  3  has a flange portion  31  located on an outer side of the bearing  13  in the radial direction and a plate-shaped portion  32  located on an inner side of the flange portion  31  in the radial direction. The plate-shaped portion  32  protrudes from the flange portion  31  on a side in the axial direction, more specifically, on a side facing away from the stator  5 . 
     On an inner circumferential side of the flange portion  31 , a bearing facing portion  33  is famed to face an outer circumferential surface of the outer ring  13   a  of the bearing  13  in the radial direction. The bearing facing portion  33  has an inner circumferential surface having a cylindrical shape about the axis C 1 . The outer ring  13   a  of the bearing  13  is attached to an inner side of the bearing facing portion  33  by clearance fit. 
     On the stator  5  side of the plate-shaped portion  32 , a bearing contact portion  34  is formed to contact an end surface of the outer ring  13   a  of the bearing  13  in the axial direction. The bearing contact portion  34  is a flat contact surface perpendicular to the axis C 1  in this example. 
     A separation portion  35  is formed adjacent to and on an inner side of the bearing contact portion  34  in the radial direction. The separation portion  35  is distanced in the axial direction from the inner ring  13   b  of the bearing  13  and from an end surface of the rotation shaft  11 . In other words, the bearing holding member  3  contacts the outer ring  13   a  of the bearing  13 , but contacts neither the inner ring  13   b  of the bearing  13  nor the rotation shaft  11 . This suppresses generation of a current passing through the rolling elements  13   c of the bearing  13 .    
       FIG. 6(A)  is a front view of the bearing holding member  3  as viewed from the stator  5  side.  FIG. 6(B)  is a sectional view of the bearing holding member  3 .  FIG. 6(C)  is a rear view of the bearing holding member  3  as viewed from a side opposite to the stator  5 . 
     As illustrated in  FIG. 6(A) , the flange portion  31  of the bearing holding member  3  is famed in an annular shape about the axis C 1 . As illustrated in  FIG. 6(B) , the flange portion  31  has a first surface  31   a  on the stator  5  side and a second surface  31   b  on a side opposite to the first surface  31   a.    
     The plate-shaped portion  32  is located at a center of the bearing holding member  3  in the radial direction and protrudes in the axial direction from the second surface  31   b  of the flange portion  31 . As illustrated in  FIG. 6(C) , the plate-shaped portion  32  is formed in a disk shape about the axis C 1 . 
     As illustrated in  FIG. 6(B) , a hollow portion  39  that houses the bearing  13  ( FIG. 5 ) is famed at a center of the bearing holding member  3  in the radial direction. An outer circumference of the hollow portion  39  is defined by the bearing facing portion  33 . The bearing facing portion  33  of the flange portion  31  has an inner circumferential surface having a cylindrical shape about the axis C 1 , as described above. 
     The bearing contact portion  34  and the separation portion  35  described above are located on one end of the hollow portion  39  in the axial direction. The bearing contact portion  34  has a flat surface perpendicular to the axis C 1  in this example, but the bearing contact portion  34  is not limited to such a shape. The bearing contact portion  34  may be any portion in contact with the end surface of the outer ring  13   a  ( FIG. 5 ) of the bearing  13  in the axial direction. 
     The separation portion  35  has a flat surface perpendicular to the axis C 1  in this example, but the separation portion  35  is not limited to such a shape. It is sufficient that the separation portion  35  is distanced in the axial direction from both of the inner ring  13   b  of the bearing  13  and the rotation shaft  11  ( FIG. 5 ). 
       FIG. 7  is a diagram illustrating the mold stator  4  as viewed from the opening  42  side. When the mold stator  4  is viewed from the opening  42  side, the bearing facing portion  33 , the bearing contact portion  34 , and the separation portion  35  can be seen at the center of the rotor housing portion  41  in the radial direction. 
     The mounting legs  45  are foiled at the outer circumference of the mold resin portion  40 . In this example, four mounting legs  45  are famed at intervals of 90 degrees about the axis C 1 . However, the number of mounting legs  45  is not limited to four and only needs to be one or more. The mounting legs  45  are provided with holes  46  through which screws for fixing the motor  1  to a frame of an air conditioner or the like are inserted. 
     (Manufacturing Method of Motor  1 ) 
     Next, a manufacturing method of the motor  1  will be described.  FIG. 8  is a sectional view illustrating a mold  100  used in a manufacturing process of the motor  1 . The mold  100  has an upper mold  101  and a lower mold  102  that can be opened and closed, and a cavity  104  is famed between the molds  101  and  102 . The upper mold  101  is provided with a heat-dissipation-member housing portion  103  for housing the bearing holding member  3 . 
     The lower mold  102  has a center core  105  in the cavity  104 . The center core  105  protrudes in the axial direction from a bottom of the cavity  104 . The center core  105  has a core shaped portion  106  having an outer shape corresponding to the rotor core  20  ( FIG. 1 ) and a bearing shaped portion  107  having an outer shape corresponding to the bearing  13 . 
     A larger-diameter portion  108  is famed at a lower end portion of the center core  105 , and the larger-diameter portion  108  overhangs outward in the radial direction from the center core  105 . The larger-diameter portion  108  is a portion corresponding to the opening  42  ( FIG. 1 ) of the mold stator  4 . 
     A gate  110  is formed in the lower mold  102 . The gate  110  is a flow passage through which a resin is injected into the cavity  104 . Pins  109  extending in the axial direction are famed on an outer circumferential portion of the cavity  104 . The pins  109  are used to form the holes  46  of the mold resin portion  40 . 
       FIG. 9  is a flowchart illustrating the manufacturing process of the motor  1 . In the manufacturing process of the motor  1 , a plurality of stacking elements are stacked in the axial direction and integrally fixed by crimping or the like, thereby forming the stator core  50  (step S 101 ). 
     Then, the insulating portion  52  is attached to or molded integrally with the stator core  50 , and then the coils  53  are wound on the stator core  50  via the insulating portion  52  (step S 102 ). In this way, the stator  5  is famed. 
     Subsequently, the circuit board  6  is attached to the stator  5  (step S 103 ). At this time, the protrusions  56  ( FIG. 4(B) ) of the insulating portion  52  of the stator  5  are inserted through the attachment holes of the circuit board  6 , and the tips of the protrusions  56  are thermally welded, so that the circuit board  6  is fixed to the stator  5 . In this way, the stator assembly including the stator  5  and the circuit board  6  is completed. 
     Then, the upper mold  101  of the mold  100  is moved upward to open the cavity  104 , and the stator assembly is set in the cavity  104  (step S 104 ). The stator  5  is mounted around the center core  105  of the mold  100 , as illustrated in  FIG. 8 . 
     Then, the bearing holding member  3  is set on the center core  105  of the mold  100  (step S 105 ). The bearing holding member  3  is supported by the bearing shaped portion  107  of the center core  105 . 
     Then, the upper mold  101  is moved downward to close the cavity  104 , and molding is performed (step S 106 ). That is, the mold resin in a molten state is injected into the cavity  104  through the gate  110 . The mold resin injected into the cavity  104  covers the stator  5  and the circuit board  6 , and also covers the outer circumference side of the bearing holding member  3 . 
     After the mold resin is injected into the cavity  104 , the mold resin in the cavity  104  is cured by heating the mold  100 , in a case where a thermosetting resin is used as the mold resin. In this way, the mold resin portion  40  is formed. That is, the mold stator  4  in which the stator  5  and the circuit board  6  are covered with the mold resin portion  40  is formed. 
     Aside from steps S 101  to S 106 , the rotor  2  is foiled. That is, a plurality of stacking elements are stacked in the axial direction and integrally fixed by crimping or the like, thereby foaming the rotor core  20 . Then, the magnets  23  are inserted into the magnet insertion holes  21 . Furthermore, the rotation shaft  11 , the rotor core  20 , the magnets  23 , and the sensor magnet  24  are integrally formed with a resin that foams the resin portion  25 . Thereafter, the bearings  12  and  13  are attached to the rotation shaft  11 , and the rotor  2  is formed. 
     Thereafter, the rotor  2  is inserted into the rotor housing portion  41  through the opening  42  of the mold stator  4 , and the bracket  15  is fitted to the step portion  43  on the peripheral edge of the opening  42  (step S 107 ). Thus, the bearing  13  is attached to the bearing holding member  3 , and the bearing  12  is attached to the bracket  15 . Further, the cap  14  is attached to the outside of the bracket  15 . Consequently, the motor  1  is completed. 
     (Functions) 
     As illustrated in  FIG. 5 , the bearing  13  is held by the bearing holding member  3 , and the bearing holding member  3  and the stator  5  are integrally held by the mold resin portion  40 . Thus, the coaxiality between the stator  5  and the rotor  2  can be improved by forming the bearing holding member  3  with high dimensional accuracy using the above-described aluminum alloy or the like. As a result, vibration and noise of the motor  1  can be reduced. 
     In particular, in the motor  1  having the consequent pole rotor  2 , the first magnetic pole P 1  as the magnet magnetic pole and the second magnetic pole P 2  as the virtual magnetic pole have different inductances, and vibration and noise tend to increase due to the imbalance of inductance. In the first embodiment, the coaxiality between the stator  5  and the rotor  2  is improved, and thus it is possible to effectively reduce vibration and noise of the motor  1  having the consequent pole rotor  2 . 
     The other bearing  12  is held by the metal bracket  15  ( FIG. 1 ), and the bracket  15  is fitted to the step portion  43  of the mold resin portion  40 . Since the bracket  15  and the bearing holding member  3  are integrally held by the mold resin portion  40  together with the stator  5 , the coaxiality between the stator  5  and the rotor  2  can be further improved, and thus the effect of reducing vibration and noise of the motor  1  can be enhanced. 
     The bearing contact portion  34  of the bearing holding member  3  contacts the outer ring  13   a  of the bearing  13 , but the separation portion  35  contacts neither the inner ring  13   b  of the bearing  13  nor the rotation shaft  11 . Thus, the current passing through the rolling elements  13   c  of the bearing  13  can be suppressed. Therefore, it is possible to prevent damage, called electric corrosion, to surfaces of the rolling element  13   c  and raceway surfaces of the outer ring  13   a  and inner ring  13   b.    
     Since the bearing holding member  3  is covered with the mold resin portion  40  together with the stator  5  and the circuit board  6 , and a part of the bearing holding member  3  is exposed to the outside of the mold resin portion  40 , heat generated by the coils  53  of the stator  5  and the circuit board  6  can be efficiently dissipated through the bearing holding member  3  to the outside. 
     (Effects of Embodiment) 
     As described above, the motor  1  of the first embodiment includes the rotor  2 , the stator  5 , the bearing holding member  3  that holds the bearing  13  of the rotor  2 , and the mold resin portion  40  as the resin portion that covers the bearing holding member  3  and the stator  5 . Thus, the coaxiality between the stator  5  and the rotor  2  can be improved, and thereby vibration and noise of the motor  1  can be reduced. 
     Since the bearing holding member  3  has the bearing facing portion  33  that faces the bearing  13  in the radial direction, the bearing  13  can be held by the bearing facing portion  33 . 
     Since the bearing facing portion  33  has a cylindrical surface, the bearing  13  can be attached to the bearing facing portion  33  by, for example, clearance fit, and thus the bearing  13  can be held in a stable state. 
     Since the bearing holding member  3  has the bearing contact portion  34  that contacts the bearing  13  in the axial direction, the bearing holding member  3  can be positioned in the axial direction by the contact between the bearing  13  and the bearing contact portion  34 . 
     The bearing contact portion  34  of the bearing holding member  3  contacts the outer ring  13   a  of the bearing  13 , but the separation portion  35  contacts neither the inner ring  13   b  of the bearing  13  nor the rotation shaft  11 . Thus, the current passing through the rolling elements  13   c  of the bearing  13  can be suppressed, and the occurrence of electric corrosion can be suppressed. 
     In the case where the bearing holding member  3  is composed of a hot-dip zinc-aluminum-magnesium alloy-plated steel sheet, the bearing holding member  3  can be subjected to the press-working, and thus high dimensional accuracy can be easily obtained. In addition, the hot-dip zinc-aluminum-magnesium alloy-plated steel sheet has higher thermal conductivity than a general resin such as BMC or PBT, and thus heat dissipation property can be improved. 
     In the case where the bearing holding member  3  is composed of an aluminum alloy such as ADC 12 , the bearing holding member  3  can be processed by die-casting, and thus a degree of freedom in the shape is higher as compared to the case where the bearing holding member  3  is famed by extrusion molding or the like. Thus, the number of steps for forming the bearing holding member  3  can be reduced, and the manufacturing cost of the motor  1  can be reduced. In addition, since an aluminum alloy such as ADC12 has higher thermal conductivity than a general resin such as BMC or PBT, the heat dissipation property can be improved. 
     Since the mold resin portion  40  is composed of a thermosetting resin such as BMC, the mold resin portion  40  can be famed by low-pressure molding, and thus it is possible to suppress defamation of the circuit board  6  due to the molding pressure. 
     Since the magnet  23  of the rotor  2  is famed of a rare earth magnet that contains samarium, iron, and nitrogen, a large magnetic force can be obtained, and the output of the motor  1  can be improved. When the magnet  23  is famed of a rare earth magnet that contains neodymium, iron, and boron, a large magnetic force can be obtained as well, and the output of the motor  1  can be improved. 
     When the magnets  23  generate a large magnetic force, an exciting force in the radial direction acting between the rotor  2  and the stator  5  increases. However, since the coaxiality between the rotor  2  and the stator  5  is improved by the bearing holding member  3 , vibration and noise due to the exciting force in the radial direction can be reduced. 
     Modification 
       FIG. 10  is an enlarged diagram illustrating a part of a bearing holding member  3  of a modification of the first embodiment. In this modification, a grease G is provided in a gap between the bearing facing portion  33  of the bearing holding member  3  and the outer ring  13   a  of the bearing  13 . As the grease G, a general grease for bearings can be used. 
     By the action of the grease G, the bearing  13  is smoothly inserted into the inside of the bearing facing portion  33  when the rotor  2  is mounted in the mold stator  4  (step S 107  in  FIG. 9 ). In addition, the bearing  13  is applied with pressure from the bearing facing portion  33  via the grease G, and is held in a stable state inside the bearing facing portion  33 . This can suppress the creep phenomenon in which the outer ring  13   a  of the bearing  13  rotates relative to the bearing holding member  3 . 
     Second Embodiment 
     Next, a second embodiment will be described.  FIG. 11  is an enlarged sectional view illustrating a part of a motor  1  of the second embodiment. The motor  1  of the second embodiment differs from the motor  1  of the first embodiment in the configuration of a bearing holding member  3 A. 
     In the bearing holding member  3  of the first embodiment, the bearing facing portion  33  has the cylindrical surface (see  FIG. 6(A) ). In contrast, in the bearing holding member  3 A of the second embodiment, the bearing facing portion  33  has a plurality of protrusions  38  that are arranged with spaces therebetween in the circumferential direction. 
       FIG. 12  is a diagram illustrating a mold stator  4  of the second embodiment as viewed from an opening  42  side. In  FIG. 12 , the mold resin portion  40  is not illustrated. The bearing holding member  3 A has an inner circumferential surface  37  having a cylindrical shape. The inner circumferential surface  37  faces the bearing  13  with a space therebetween in the radial direction. The protrusions  38  are famed at a plurality of positions on the inner circumferential surface  37 . 
     The protrusions  38  protrude inward in the radial direction from the inner circumferential surface  37 , and inner end surfaces of the protrusions  38  in the radial direction face the bearing  13 . The inner end surfaces of the protrusion  38  in the radial direction constitute parts of a cylindrical surface about the axis C 1 . The protrusions  38  are famed at equal intervals in the circumferential direction. Four protrusions  38  are famed at intervals of 90 degrees in the circumferential direction in this example. However, the number of protrusions  38  only needs to be two or more. 
     The protrusions  38  are integrally formed with other portions of the bearing holding member  3 A using the same material. However, the protrusions  38  may be famed as separate members from other portions of the bearing holding member  3 A and may be fixed thereto by adhesion or the like. The material of the bearing holding member  3 A is the same as that of the bearing holding member  3  described in the first embodiment. 
     The motor of the second embodiment is configured in a similar manner to the motor  1  of the first embodiment except for the points described above. 
     In the second embodiment, the bearing holding member  3 A faces the bearing  13  at the protrusions  38  arranged in the circumferential direction. Thus, the bearing  13  can be easily inserted into the bearing holding member  3 A when the rotor  2  is mounted in the mold stator  4  (step S 107  in  FIG. 9 ). An area at which the protrusions  38  face the bearing  13  is small, and the pressure acting between the protrusions  38  and the bearing  13  is high, and thus the effect of suppressing creep can be enhanced. 
     In the second embodiment, the grease G may be provided between the bearing  13  and the protrusions  38 , as described in the modification of the first embodiment. 
     Third Embodiment 
     Next, a third embodiment will be described.  FIG. 13(A)  is an enlarged sectional view illustrating a part of a motor  1  of the third embodiment. The motor  1  of the third embodiment differs from the motor  1  of the first embodiment in the configuration of a bearing holding member  3 B. 
     The bearing holding member  3 B of the third embodiment has a contact portion  36  on the first surface  31   a  of the flange portion  31 , and the contact portion  36  contacts the circuit board  6 . The contact portion  36  is integrally famed with other portions of the bearing holding member  3 B using the same material. However, the contact portion  36  may be famed as a separate member from other portions of the bearing holding member  3 B and may be fixed thereto by adhesion or the like. The material of the bearing holding member  3 B is the same as that of the bearing holding member  3  described in the first embodiment. 
     The contact portion  36  is famed in an annular shape about the axis C 1  as illustrated in  FIG. 13(B) , on the first surface  31   a  of the flange portion  31 . The shape, number, and position of the contact portion(s)  36  are not limited as long as the contact portion  36  contacts the circuit board  6 . 
     In this example, the contact portion  36  contacts the circuit board  6 . However, it is sufficient that the contact portion  36  contacts a part of the stator assembly including the stator  5  and the circuit board  6 . For example, the contact portion  36  may contact the insulating portion  52  of the stator  5 . 
     The motor of the third embodiment is configured in a similar manner to the motor  1  of the first embodiment except for the points described above. 
     In the third embodiment, since the contact portion  36  of the bearing holding member  3 B contacts a part of the stator assembly, the bearing holding member  3 B can be positioned in the axial direction with high accuracy. Thus, the quality of the motor  1  can be improved. 
     Further, since the contact portion  36  of the bearing holding member  3 B contacts the circuit board  6 , heat generated by electronic components of the circuit board  6  can be transferred to the bearing holding member  3 B, and can be efficiently dissipated to the outside of the motor  1 . 
     In the third embodiment, the grease G may be provided around the bearing  13 , as described in the modification of the first embodiment. The bearing facing portion  33  may be constituted by a plurality of protrusions  38 , as described in the second embodiment. 
     Fourth Embodiment 
     Next, a fourth embodiment will be described.  FIG. 14  is an enlarged sectional view illustrating a part of a motor  1  of the fourth embodiment. The motor  1  of the fourth embodiment differs from the motor  1  of the first embodiment in the configuration of a bearing holding member  3 C. 
     The bearing holding member  3  of the first embodiment is composed of a metal. In contrast, the bearing holding member  3 C of the fourth embodiment is composed of a resin. 
     The bearing holding member  3 C is composed of a thermoplastic resin such as polyphenylene sulfide (PPS). Since a thermoplastic resin can be subjected to injection molding, high dimensional accuracy can be obtained more easily than metal or ceramics, and the manufacturing cost can be reduced. By forming the bearing holding member  3 C using a thermoplastic resin having high thermal conductivity such as PPS, heat dissipation property can be improved. 
     The bearing holding member  3 C may be famed of a thermosetting resin such as BMC, for example. By forming the bearing holding member  3 C using the same type of material as that of the mold resin portion  40 , the occurrence of cracking due to a difference in linear expansion coefficient between the bearing holding member  3 C and the mold resin portion  40  can be suppressed, and the resistance to heat shock can be improved. Furthermore, by forming the bearing holding member  3 C using a thermosetting resin having high thermal conductivity such as BMC, heat dissipation property can be improved. 
     In this case, the bearing holding member  3 C is desirably composed of a resin that has a higher strength than the mold resin portion  40 . BMC, which forms the mold resin portion  40 , contains unsaturated polyester as a main component and a reinforcing material such as glass fibers added thereto. The bearing holding member  3 C is desirably famed of BMC in which the adding amount of the reinforcing material is larger than that of BMC forming the mold resin portion  40 , for example. The shape of the bearing holding member  3 C is the same as that of the bearing holding member  3  of the first embodiment. 
     The motor of the fourth embodiment is configured in a similar manner to the motor  1  of the first embodiment except for the points described above. 
     In the fourth embodiment, by forming the bearing holding member  3 C using a thermoplastic resin, the manufacturing cost of the motor can be reduced. Alternatively, by forming the bearing holding member  3 C using a thermosetting resin, the resistance to heat shock can be enhanced. In addition, by using thermoplastic or thermosetting resin having high thermal conductivity, heat dissipation property can be enhanced. 
     In the fourth embodiment, the grease G may be provided around the bearing  13 , as described in the modification of the first embodiment. The bearing facing portion  33  may be constituted by a plurality of protrusions  38 , as described in the second embodiment. The bearing holding member  3 C may be provided with the contact portion  36  in contact with the stator assembly, as described in the third embodiment. 
     Fifth Embodiment 
     Next, a fifth embodiment will be described.  FIG. 15(A)  is an enlarged sectional view illustrating a part of a motor  1  of the fifth embodiment. The motor  1  of the fifth embodiment differs from the motor  1  of the first embodiment in the configuration of a bearing holding member  3 D. 
       FIG. 15(B)  is a perspective view illustrating the bearing holding member  3 D of the fifth embodiment. The bearing holding member  3 D is a member that has an annular shape about the axis C 1 . The sectional shape of the bearing holding member  3 D is, for example, a quadrilateral, but is not limited thereto. An inner circumferential surface of the bearing holding member  3 D constitutes a bearing facing portion  33  that faces the outer ring  13   a  of the bearing  13  in the radial direction. 
     As shown in  FIG. 15(A) , the mold resin portion  40  of the fifth embodiment covers the bearing holding member  3 D from outside in the radial direction and also covers the counter-load side of the rotor housing portion  41 . The mold resin portion  40  has a bearing contact portion  401  that contacts the end surface of the outer ring  13   a  of the bearing  13  in the axial direction. 
     The bearing holding member  3 D is composed of a metal such as a hot-dip zinc-aluminum-magnesium alloy-plated steel sheet or an aluminum alloy, as is the case with the bearing holding member  3  of the first embodiment. However, the bearing holding member  3 D may be composed of a thermoplastic resin or a thermosetting resin, as is the case with the bearing holding member  3 C of the fourth embodiment. 
     The motor of the fifth embodiment is configured in a similar manner to the motor  1  of the first embodiment except for the points described above. 
     In the fifth embodiment, the bearing holding member  3 D is an annular member, and thus it is easy to manufacture the bearing holding member  3 D. Thus, the coaxiality between the rotor  2  and the stator  5  can be enhanced, and vibration and noise can be reduced while reducing the manufacturing cost. 
     In the fifth embodiment, the grease G may be provided around the bearing  13 , as described in the modification of the first embodiment. The bearing facing portion  33  may be constituted by a plurality of protrusions  38 , as described in the second embodiment. The bearing holding member  3 D may be provided with the contact portion  36  in contact with the stator assembly, as described in the third embodiment. 
     (Modification of Rotor) 
     Next, a rotor of a modification that is applicable to each embodiment will be described.  FIG. 16  is a sectional view illustrating a rotor  2 A of the modification. The above-described rotor  2  of the first embodiment is of a consequent-pole type having the magnet magnetic poles and the virtual magnetic poles. In contrast, the rotor  2 A of the modification is a non-consequent-pole type in which all the magnetic poles are constituted by magnet magnetic poles. 
     The rotor  2 A has a rotor core  201  centered on the axis C 1 . The rotor core  201  is famed of a plurality of stacking elements that are stacked in the axial direction and integrally fixed by crimping, welding, bonding, or the like. The stacking elements are, for example, electromagnetic steel sheets. Each stacking element has a thickness of 0.1 mm to 0.7 mm. The rotor core  201  has a central hole  202  at its center in the radial direction. The rotation shaft  11  is fixed to the central hole  202 . 
     A plurality of magnet insertion holes  21  are famed along an outer circumference of the rotor core  20 . The magnet insertion holes  21  are arranged at equal intervals in the circumferential direction. The shape of each magnet insertion hole  21  is as described in the first embodiment. Openings  22  are famed on both sides of the magnet insertion hole  21  in the circumferential direction. The number of magnet insertion holes  21  is 10 in this example, but is not limited to 10. 
     The magnet  23  is inserted in each magnet insertion hole  21 . The magnet  23  is in the form of a flat plate, and has a rectangular shape in a cross section perpendicular to the axial direction. The material and shape of the magnet  23  are as described in the first embodiment. 
     The magnets  23  adjacent to each other in the circumferential direction are arranged so that the opposite magnetic poles face the outer circumferential side of the rotor core  201 . Thus, all the magnetic poles of the rotor  2  are constituted by the magnets  23 . In this example, the rotor  2 A has 10 magnets  23 , and the number of magnetic poles of the rotor  2 A is 10. 
     The non-consequent pole rotor  2 A has a larger number of magnets  23  than the consequent pole rotor  2 , but has the advantage of being less likely to cause vibration and noise. 
     The motor of the modification is configured in a similar manner to the motor  1  of the first embodiment except that the rotor  2 A is of the non-consequent-pole type. The non-consequent pole rotor  2 A of the modification may be applied to the motors of the second to fifth embodiments. 
     Even in the motor  1  having the non-consecutive-pole rotor  2 A, the coaxiality between the rotor  2 A and the stator  5  can be improved by the provision of the bearing holding member  3  of each embodiment. Thus, vibration and noise can be reduced. 
     (Air Conditioner) 
     Next, an air conditioner to which the motor  1  of each of the above-described embodiments and modifications is applicable will be described.  FIG. 17(A)  is a diagram illustrating a configuration of an air conditioner  500  to which the motor  1  of the first embodiment is applied. The air conditioner  500  includes an outdoor unit  501 , an indoor unit  502 , and a refrigerant pipe  503  connecting the units  501  and  502 . 
     The outdoor unit  501  includes an outdoor fan  510  which is, for example, a propeller fan. The indoor unit  502  includes an indoor fan  520  which is, for example, a cross flow fan. The outdoor fan  510  has the impeller  505  and a motor  1 A that drives the impeller  505 . The indoor fan  520  includes an impeller  521  and a motor  1 B that drives the impeller  521 . Each of the motors  1 A and  1 B is constituted by the motor  1  described in the first embodiment. A compressor  504  that compresses a refrigerant is also illustrated in  FIG. 17(A) . 
       FIG. 17(B)  is a sectional view of the outdoor unit  501 . The motor  1 A is supported by a frame  509  disposed in a housing  508  of the outdoor unit  501 . The impeller  505  is attached to the rotation shaft  11  of the motor  1  via a hub  506 . 
     In the outdoor fan  510 , the impeller  505  rotates by the rotation of the rotor  2  of the motor  1 A to blow air to the outside of a room. During a cooling operation of the air conditioner  500 , heat is released when the refrigerant compressed by the compressor  504  is condensed in a condenser, and the heat is released to the outside of the room by the air blown by the outdoor fan  510 . 
     Similarly, in the indoor fan  520  ( FIG. 17(A) ), the impeller  521  rotates by the rotation of the rotor  2  of the motor  1 B to blow air to the inside of the room. During the cooling operation of the air conditioner  500 , the refrigerant takes heat from the air when the refrigerant evaporates in an evaporator, and the air is blown into the room by the indoor fan  520 . 
     In the motor  1  of the first embodiment described above, vibration and noise are reduced. Thus, the quietness of the air conditioner  500  can be improved by constituting the motors  1 A and  1 B using the motor  1  of the first embodiment. 
     Each of the motors  1 A and  1 B is constituted by the motor  1  of the first embodiment, but it is sufficient that at least one of the motors  1 A and  1 B is constituted by the motor  1  of the first embodiment. Further, any of the motors of the second to fifth embodiments may be used as the motor  1 A, the motor  1 B or both. 
     The motor  1  described in each embodiment can be mounted on any electric apparatuses other than the fan of the air conditioner. 
     Although the desirable embodiments of the present invention have been specifically described above, the present invention is not limited to the above-described embodiments, and various modifications or changes can be made to those embodiments without departing from the scope of the present invention.