Abstract:
A stator which prevents deformation of component elements of the stator and which effectively removes heat generated by coils at the time of operation. The stator of a motor comprises a stator core having a cylindrical back yoke and teeth projecting out from the back yoke to the inside in the diametrical direction, coils wound around the teeth, an outer cylinder surrounding the back yoke, and heat conducting parts abutting against both an inner circumferential surface of the outer cylinder and coil ends of the coils.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates to a stator provided with an outer cylinder and to a motor. 
         [0003]    2. Description of the Related Art 
         [0004]    Known in the art is a stator comprised of a stator core and an outer cylinder which is arranged so as to surround the stator core and which is shrink fit etc. to fasten it to an outer circumference of the stator core and thereby prevent deformation of the stator core (for example, Japanese Patent Publication No. 2012-143064A). 
         [0005]    In such a stator, art is sought which prevents deformation of component elements of the stator and which effectively removes heat generated by the coils at the time of operation. 
       SUMMARY OF INVENTION 
       [0006]    In an aspect of the invention, a stator of a motor comprises a stator core including a cylindrical back yoke and a tooth projecting radially inside from the back yoke; a coil wound around the tooth an outer cylinder which surrounds the back yoke; and a heat conducting part which contacts an inner circumferential surface of the outer cylinder and a coil end of the coil. 
         [0007]    The stator core may include a plurality of teeth arranged so as to align in a circumferential direction. The stator may comprise a plurality of heat conducting parts arranged so as to align in the circumferential direction. Each of the plurality of heat conducting parts may contact the coil end of the coil wound around each of the plurality of teeth. 
         [0008]    The stator may further comprise a connecting part extending in the circumferential direction of the outer cylinder so as to be connected to the heat conducting part, and contacting the inner circumferential surface of the outer cylinder. The heat conducting part may have a radial direction width equal to or larger than that of the connecting part. 
         [0009]    A step may be formed at the inner circumferential surface of the outer cylinder so as to extend in the circumferential direction. The heat conducting part and the connecting part may be arranged on the step. A fin for dissipating heat or a fluid path for passage of a coolant may be formed at an outer circumferential surface of the outer cylinder. The heat conducting part may include an insulator at a part thereof where the heat conducting part contacts the coil end. 
         [0010]    In another aspect of the invention, a motor comprises the above-mentioned stator. The motor may further comprise a fan for cooling the outer cylinder. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0011]    These and other objects, features, and advantages of the invention will be clarified with reference to the detailed description of illustrative embodiments of the invention shown in the attached drawings, in which: 
           [0012]      FIG. 1  is a side cross-sectional view of a motor according to an embodiment of the invention; 
           [0013]      FIG. 2  is a view of the stator shown in  FIG. 1  as seen from the axially front side; 
           [0014]      FIG. 3  is a view of the stator shown in  FIG. 2 , in which the heat conducting parts are omitted; 
           [0015]      FIG. 4  is a perspective cross-sectional view of a part of the stator shown in  FIG. 2 , in which the heat conducting parts are indicated by dotted lines; 
           [0016]      FIG. 5  is a side cross-sectional view of a motor according to another embodiment of the invention; 
           [0017]      FIG. 6  is a view of the stator shown in  FIG. 5  as seen from the axially front side; 
           [0018]      FIG. 7  is a perspective cross-sectional view of a part of the stator shown in  FIG. 5 , in which the heat conducting parts are indicated by dotted lines; 
           [0019]      FIG. 8  is a view of the stator according to another embodiment of the invention as seen from the axially front side; 
           [0020]      FIG. 9  is a perspective cross-sectional view of a part of the stator shown in  FIG. 8 ; 
           [0021]      FIG. 10  is a view for explaining an outer cylinder according to another embodiment of the invention, which corresponds to  FIG. 9 ; 
           [0022]      FIG. 11  is a view for explaining an outer cylinder according to still another embodiment of the invention, which corresponds to  FIG. 9 ; 
           [0023]      FIG. 12  is a view for explaining an outer cylinder according to still another embodiment of the invention, which corresponds to  FIG. 9 ; and 
           [0024]      FIG. 13  is a view for explaining an insulator provided at the heating conducting part, which corresponds to  FIG. 9 . 
       
    
    
     DETAILED DESCRIPTION 
       [0025]    Below, embodiments of the invention will be explained in detail based on the drawings. First, referring to  FIG. 1 , a motor  10  according to an embodiment of the invention will be explained. Note that, in the following explanation, the axial direction indicates a direction along the axis  0  of the shaft  14  shown in  FIG. 1 , the radial direction indicates a radial direction of a circle centered about the axis  0 , and the circumferential direction indicates a circumferential direction of the circle centered about the axis  0 . Further, for convenience, the direction of the arrow F shown in the figures indicates the frontward in the axial direction (i.e., axially frontward). 
         [0026]    The motor  10  includes a stator  20 , a rotor  12  rotatably arranged radially inside of the stator  20 , and a fan  18  arranged at radially outside of the stator  20 . The rotor  12  includes a shaft  14  and a rotor core  16  fixed to radially outside of the shaft  14 . Magnets (not shown) are held inside of the rotor core  16 . The rotor  12  rotates about the axis O. 
         [0027]    Next, referring to  FIG. 1  to  FIG. 4 , the stator  20  will be explained. The stator  20  includes a stator core  22 , coils  24 , an outer cylinder  26 , and a plurality of heat conducting parts  28  and  29 . 
         [0028]    The stator core  22  is comprised of e.g. a plurality of magnetic steel sheets stacked in the axial direction. The stator core  22  includes a cylindrical back yoke  30  and a plurality of teeth  32  projecting radially inside from the back yoke  30 . In this embodiment, a total of twelve teeth  32  are arranged so as to align in the circumferential direction at substantially equal intervals. 
         [0029]    The coils  24  are respectively wound around the teeth  32 . Each coil  24  includes a coil end  24   a  at the axially front side and a coil end  24   b  at the axially rear side. The coil end  24   a  is a part of the coil  24  wound around the teeth  32 , which projects axially frontward from the tooth  32 . On the other hand, the coil end  24   b  is a part of the coil  24  wound around the teeth  32 , which projects axially rearward from the teeth  32 . 
         [0030]    The outer cylinder  26  is a cylindrical member made of a non-magnetic material such as aluminum or copper. The outer cylinder  26  is arranged so as to surround the back yoke  30  from radially outside, and fixed to the back yoke  30  by e.g. shrinkage fit. The fan  18  generates a flow of air toward the outer cylinder  26 , thereby can cool the outer cylinder  26 . 
         [0031]    The heat conducting parts  28  are arranged at axially front side of the coil ends  24   a.  In this embodiment, a total of twelve heat conducting parts  28  are arranged in the circumferential direction at substantially equal intervals so as to correspond to the positions of the teeth  32 . 
         [0032]    Each of the heat conducting parts  28  is a substantially square plate member having a predetermined thickness, and contacts the inner circumferential surface  26   a  of the outer cylinder  26  at its radially outer end face  28   a.  Further, each of the heat conducting parts  28  contacts the coil end  24   a  of the coil  24  wound around the corresponding tooth  32  at its axially rear end face  28   b  from axially front side. 
         [0033]    On the other hand, the heat conducting parts  29  are arranged at axially rear side of the coil ends  24   b.  Each of the heat conducting parts  29  has a configuration similar to the above-mentioned heat conducting part  28 . Specifically, a total of twelve heat conducting parts  29  are arranged in the circumferential direction at substantially equal intervals so as to correspond to the positions of the teeth  32 . 
         [0034]    Each of the heat conducting parts  29  contacts the inner circumferential surface  26   a  of the outer cylinder  26  at its radially outer end face  29   a.  Further, each of the heat conducting parts  29  contacts the coil end  24   b  of the coil  24  wound around the corresponding tooth  32  at its axially front end face  29   b  from axially rear side. 
         [0035]    For example, one of the heat conducting parts  28  and  29  are integrally formed at the inner circumferential surface  26   a  of the outer cylinder  26 , while the others are fabricated from independent members separated from the outer cylinder  26 , and fixed to the inner circumferential surface  26   a  of the outer cylinder  26  by e.g. welding or adhesion. 
         [0036]    The heat conducting parts  28  and  29  are preferably made of non-magnetic material such as aluminum or copper in order to prevent an eddy current from being generated therein. However, the heat conducting parts  28  and  29  may be made of magnetic material. Further, each of the heat conducting parts  28  and  29  is preferably made of material having high thermal conductivity. 
         [0037]    Thus, in this embodiment, the heat conducting parts  28 ,  29  are provided so as to contact both the outer cylinder  26  and the coil ends  24   a,    24   b  of the coils  24 . According to this configuration, part of heat generated at the coils  24  during the operation of the motor  10  conducts to the outer cylinder  26  through the heat conducting parts  28 ,  29 , and is dissipated to the outside air from the outer cylinder  26 . Therefore, it is possible to improve the heat dissipation effect of the stator  20 . 
         [0038]    Further, in this embodiment, the heat conducting parts  28  which contact the coil ends  24   a  and heat conducting parts  29  which contact the coil ends  24   b  are provided. According to this configuration, it is possible to remove heat from the coil ends  24   a  and  24   b  at both sides in the axial direction of the coils  24  through the heat conducting parts  28  and  29  respectively, so the heat dissipating effect of the stator  20  can be improved more effectively. 
         [0039]    Next, referring to  FIG. 5  to  FIG. 7 , a motor  40  according to another embodiment will be explained. Note that, in various embodiments explained below, elements similar to those in the already-explained embodiments will be assigned the same reference numerals, and detailed explanations thereof will be omitted. 
         [0040]    The motor  40  includes a stator  50  and the rotor  12  rotatably arranged at radially inside of the stator  50 . The stator  50  includes the stator core  22 , the coils  24 , the outer cylinder  26 , and heat conducting rings  52  and  54 . 
         [0041]    The heat conducting ring  52  is a ring-shaped plate member having a predetermined thickness, and is arranged at axially front side of the coil ends  24   a.  Specifically, the heat conducting ring  52  includes heat conducting parts  56  and connecting parts  58 . In this embodiment, a total of twelve heat conducting parts  56  are arranged in the circumferential direction at substantially equal intervals so as to correspond to the positions of the teeth  32 . 
         [0042]    Each of the heat conducting parts  56  is a substantially square plate member, and contacts the inner circumferential surface  26   a  of the outer cylinder  26  at its radially outer end face  56   a.  Further, each of the heat conducting parts  56  contacts the coil end  24   a  of the coil  24  wound around the corresponding tooth  32  at its axially rear end face  56   b  from axially front side. In this embodiment, the radial direction width W 1  of each heat conducting part  56  is set to be larger than the radial direction width W 2  of each connecting part  58 . 
         [0043]    Each of the connecting parts  58  is a substantially arc-shaped plate member, and extends in the circumferential direction between two heat conducting parts  56  adjoining each other in the circumferential direction. The connecting part  58  is integrally connected at one end in the circumferential direction to one heat conducting part  56  positioned at one side in the circumferential direction, while is integrally connected at the other end in the circumferential direction to the other heat conducting part  56  positioned at the other side in the circumferential direction. 
         [0044]    Thus, in this embodiment, a total of twelve connecting parts  58  are arranged in the circumferential direction in series. Each of the connecting parts  58  is arranged so that its outer circumferential surface  58   a  contacts the inner circumferential surface  26   a  of the outer cylinder  26 . 
         [0045]    In this way, the end faces  56   a  of the heat conducting parts  56  and the outer circumferential surfaces  58   a  of the connecting parts  58  define a cylindrical outer circumferential surface  52   a  of the heat conducting ring  52 . The outer circumferential surface  52   a  surface-contacts the inner circumferential surface  26   a  of the outer cylinder  26 . 
         [0046]    On the other hand, the heat conducting ring  54  is arranged at axially rear side of the coil ends  24   b,  and has a configuration similar as the above-mentioned heat conducting ring  52 . Specifically, the heat conducting ring  54  includes a total of twelve heat conducting parts  60  arranged in the circumferential direction at substantially equal intervals so as to correspond to the positions of the teeth  32 ; and a total of twelve connecting parts  62 , each of which extends between two heat conducting parts  60  adjoining each other in the circumferential direction. 
         [0047]    Each of the heat conducting parts  60  contacts the inner circumferential surface  26   a  of the outer cylinder  26  at its radially outer end face  60   a,  while contacts the coil end  24   b  of the coil  24  wound around the corresponding tooth  32  at its axially front end face  60   b  from axially rear side. Further, the radial direction width W 1  of each heat conducting part  60  is set to be larger than the radial direction width W 2  of each connecting part  62 . 
         [0048]    Each of the connecting parts  62  is integrally connected at one end in the circumferential direction to one heat conducting part  60  positioned at one side in the circumferential direction, while is integrally connected at the other end in the circumferential direction to the other heat conducting part  60  positioned at the other side in the circumferential direction. Each connecting part  62  is arranged so that its outer circumferential surface (not shown) contacts the inner circumferential surface  26   a  of the outer cylinder  26 . 
         [0049]    In this way, the end faces  60   a  of the heat conducting parts  60  and the outer circumferential surfaces of the connecting parts  62  define a cylindrical outer circumferential surface (not shown) of the heat conducting ring  54 , which surface-contacts the inner circumferential surface  26   a  of the outer cylinder  26 . 
         [0050]    Note that, the heat conducting rings  52  and  54  may be integrally formed at the inner circumferential surface  26   a  of the outer cylinder  26 . Alternatively, the heat conducting rings  52  and  54  may be made from independent members separated from the outer cylinder  26 , and be fixed to the inner circumferential surface  26   a  of the outer cylinder  26  by welding or shrinkage fit, etc. The heat conducting rings  52  and  54  are preferably made of non-magnetic material such as aluminum or copper, but may be made of magnetic material. Further, the heat conducting rings  52  and  54  are preferably made of material having high thermal conductivity. 
         [0051]    In this embodiment, the heat conducting parts  56 ,  60  are provided so as to contact both the outer cylinder  26  and the coil ends  24   a,    24   b  of the coils  24 . According to this configuration, part of the heat generated at the coils  24  during the operation of the motor  40  conducts to the outer cylinder  26  through the heat conducting parts  56  and  60 , and is dissipated from the outer cylinder  26  to the outside air. Therefore, the heat dissipating effect of the stator  50  can be improved. 
         [0052]    Further, in this embodiment, a ring-shaped heat conducting ring  52  ( 54 ) is constituted by the connecting parts  58  ( 62 ), each of which extends between two heat conducting parts  56  ( 60 ) adjoining each other in the circumferential direction. In addition, the outer circumferential surface  52   a  of the heat conducting ring  52  ( 54 ) contacts the inner circumferential surface  26   a  of the outer cylinder  26 . 
         [0053]    According to this configuration, if the outer cylinder  26  is fixed to the stator core  22  by e.g. shrinkage fit, the ring-shaped heat conducting rings  52  and  54  can contact the inner circumferential surface  26   a  of the deforming outer cylinder  26  so as to reinforce the outer cylinder  26 , thereby can prevent the outer cylinder  26  from being inappropriately deformed (for example, deformed into a non-circular shape). 
         [0054]    Further, each connecting part  58  ( 62 ) is connected to the heat conducting part  56  ( 60 ), and its outer circumferential surface  58   a  contacts the inner circumferential surface  26   a  of the outer cylinder  26 . Due to this, part of heat conducted to the heat conducting parts  56 ,  60  can be conducted to the outer cylinder  26  through the connecting parts  58 ,  62 . Therefore, the heat dissipating effect of the stator  50  can be improved more effectively. 
         [0055]    Further, in this embodiment, the heat conducting ring  52  which contacts the coil ends  24   a  and the heat conducting ring  54  which contacts the coil ends  24   b  are provided. According to this configuration, it is possible to remove heat from the coil ends  24   a  and  24   b  at both sides in the axial direction of the coils  24  through the heat conducting rings  52  and  54 , so the heat dissipating effect of the stator  50  can be improved more effectively. 
         [0056]    Further, in this embodiment, the radial direction width W 1  of each heat conducting part  56  ( 60 ) is set to be larger than the radial direction width W 2  of each connecting part  58  ( 62 ). According to this configuration, since the heat conducting ring  52  ( 54 ) can be configured to have an outer shape similar to the stator core  22 , the component of the stator core  22  can be utilized for the heat conducting ring  52  or  54 . 
         [0057]    This effect will be explained below. The stator core  22  is comprised of a plurality of electrical steel sheets, each of which includes first parts which form the teeth  32  and second parts which form the back yoke  30 . 
         [0058]    As clearly seen from  FIG. 3 , since the radial direction width of each tooth  32  is larger than that of the back yoke  30 , the radial direction width of each of the first parts of the electrical steel sheet is larger than that of the second parts of the electrical steel sheet. Accordingly, the first part and the second part of the electrical steel sheet respectively have dimensions similar to the heat conducting part  56  ( 60 ) and connecting part  58  ( 62 ). 
         [0059]    Therefore, the electrical steel sheet, which constitutes the stator core  22 , can be utilized for the heat conducting ring  52  ( 54 ). According to this configuration, it is possible to reduce the number of components, so the manufacturing cost of the stator  50  can be reduced. 
         [0060]    Note that, in the above-mentioned embodiment, the radial direction width W 1  of each heat conducting part  56  ( 60 ) is set to be larger than the radial direction width W 2  of each connecting part  58  ( 62 ). However, the radial direction width of the heat conducting part may be set to be equal to that of the connecting part. Such an embodiment is shown in  FIG. 8  and  FIG. 9 . 
         [0061]    The stator  50 ′ according to this embodiment includes a heat conducting ring  52 ′. The heat conducting ring  52 ′ is a modification of the heat conducting ring  52  shown in  FIG. 5  to  FIG. 7 , and is comprised of a ring-shaped plate member. The heat conducting ring  52 ′ includes heat conducting parts  56 ′ and connecting parts  58 ′. 
         [0062]    Each of the heat conducting parts  56 ′ contacts the inner circumferential surface  26   a  of the outer cylinder  26  at its radially outer end face  56   a ′, while contacts the coil end  24   a  of the coil  24  wound around the corresponding teeth  32  at its axially rear end face (not shown) from axially front side. Each of the connecting parts  58 ′ extends in the circumferential direction between two heat conducting parts  56 ′ adjoining each other in the circumferential direction, and is integrally connected to these heat conducting parts  56 ′. 
         [0063]    In this embodiment, the heat conducting parts  56 ′ and connecting parts  58 ′ have common radial direction widths W 3 . The heat conducting parts  56 ′ and connecting parts  58 ′ connected in the circumferential direction constitute the ring plate-shaped heat conducting ring  52 ′. 
         [0064]    Such heat conducting ring  52 ′ also can improve the heat dissipating effect of the stator  50 ′, similar as the above-mentioned heat conducting ring  52 , while can prevent the outer cylinder  26  from being unsuitably deformed (for example, into a non-circular shape) by e.g. shrinkage fit. 
         [0065]    Note that, various features can be added to the above-mentioned outer cylinder  26 . Below, referring to  FIG. 10  to  FIG. 12 , outer cylinders according to other embodiments will be explained.  FIG. 10  shows an embodiment where an outer cylinder  64  is provided instead of the outer cylinder  26  in the embodiment shown in  FIG. 9 . 
         [0066]    The outer cylinder  64  includes a plurality of grooves  68  formed at an outer circumferential surface  64   a  of the outer cylinder  64  so as to align in the axial direction. Each of the grooves  68  is provided to be recessed inward from the outer circumferential surface  64   a,  and extends in the circumferential direction. Two grooves  68  adjoining each other in the axial direction define a heat radiating fin  66 . The heat dissipation effect of the outer cylinder  64  can be improved by the fins  66 . 
         [0067]    Note that, the outer cylinder  64  can also be applied to the embodiments shown in  FIG. 4  and  FIG. 7 . In this case, at least one of the fins  66  (or grooves  68 ) is arranged to be adjacent to the heat conducting parts  28  or the heat conducting rings  52 ,  52 ′ at radially outside thereof. 
         [0068]      FIG. 11  shows an embodiment in which an outer cylinder assembly  70  is provided instead of the outer cylinder  26  in the embodiment shown in  FIG. 9 . The outer cylinder assembly  70  includes a first outer cylinder  72  and a second outer cylinder  74  which surrounds the first outer cylinder  72  from radially outside. 
         [0069]    The first outer cylinder  72  includes a groove  76  at its outer circumferential surface  72   a.  The groove  76  is provided to be recessed inward from the outer circumferential surface  72   a,  and continuously extends around the outer circumferential surface  72   a  in a spiral manner. 
         [0070]    The second outer cylinder  74  has a cylindrical inner circumferential surface  74   a,  and is arranged at radially outside of the first outer cylinder  72  so that the inner circumferential surface  74   a  surface-contacts the outer circumferential surface  72   a  of the first outer cylinder  72 . A fluid path  78  extending in a spiral manner is defined by the groove  76  and the inner circumferential surface  74   a.    
         [0071]    The fluid path  78  is fluidly connected to a coolant supply apparatus (not shown) installed at the outside of the stator  50 ′. Coolant supplied from the coolant supply apparatus passes through the fluid path  78 . It is possible to cool the outer cylinder assembly  70  by the coolant passing through the fluid path  78  in this way, so the heat dissipating ability of the stator  50 ′ can be improved. 
         [0072]    Note that, the outer cylinder assembly  70  can also be applied to the embodiments shown in  FIG. 4  and  FIG. 7 . In this case, the fluid path  78  is formed to extend so as to be adjacent to the heat conducting parts  28  or the heat conducting rings  52 ,  52 ′ at radially outside thereof. 
         [0073]      FIG. 12  shows an embodiment in which an outer cylinder  80  is provided instead of the outer cylinder  26  in the embodiment shown in  FIG. 9 . The outer cylinder  80  has a step  82  formed at an inner circumferential surface  80   a  of the outer cylinder  80 . The step  82  extends in the circumferential direction over the entire circumference of the inner circumferential surface  80   a.  The heat conducting ring  52 ′ is arranged on the step  82 . 
         [0074]    According to this configuration, the manufacturer can suitably and easily position the heat conducting ring  52 ′ with respect to the outer cylinder  80  by placing the heat conducting ring  52 ′ on the step  82  before fixing the outer cylinder  80  to the stator core  22  by e.g. shrinkage fit, when producing the stator  50 ′. Note that, the outer cylinder  80  shown in  FIG. 11  can also be applied to the embodiments shown in  FIG. 4  and  FIG. 7 . 
         [0075]    Note that, the above-mentioned heat conducting parts  28 ,  29 ,  56 ,  60 , and  56 ′ may include insulators at their part where they contact the coil ends  24   a,    24   b.  Such an embodiment is shown in  FIG. 13 . In this embodiment, an insulator  84  is coated over an axially rear end face  52   a ′ of the heat conducting ring  52 ′ (i.e., the heat conducting parts  56 ′ and connecting parts  58 ′). 
         [0076]    The insulator  84  electrically insulates the heat conducting parts  56 ′ from the coil ends  24   a.  Due to this, it is possible to prevent a short-circuit current from being generated at the heat conducting ring  52 ′, when voltage is applied to the coils  24 . 
         [0077]    Preferably, the insulator  84  is made of material having high thermal conductivity. Due to this, it is possible to avoid the impairment of the heat conduction from the coil ends  24   a  to the heat conducting parts  56 ′ due to the insulator  84 . 
         [0078]    Note that, in the embodiment shown in  FIG. 1 , the heat conducting parts  28  and  29  are provided. However, only one of the heat conducting parts  28  and heat conducting parts  29  may be provided. Similarly, in the embodiment shown in  FIG. 5 , only one of the heat conducting rings  52  and  54  may be provided. 
         [0079]    Further, in the above-mentioned embodiments, each of the heat conducting rings  52 ,  54 , and  52 ′ is a unitary ring plate. However, the heat conducting ring  52 ,  54 , or  52 ′ may be divided into a plurality of sections in the circumferential direction. 
         [0080]    For example, in the embodiment shown in  FIG. 6 , the heat conducting ring  52  may include a plurality of ring segments arranged in the circumferential direction, wherein each of the ring segments may include a heat conducting part  56  and a connecting part  58  extending from the heat conducting part  56  toward one side in the circumferential direction. 
         [0081]    Further, in the above embodiments, the inside of the outer cylinder  26  may be filled with a resin so as to cover the coil  24 , thereby a so-called molded motor may be constituted. For example, if the inside of the outer cylinder  26  is filled with resin to constitute a molded motor in the embodiments shown in  FIG. 6  and  FIG. 8 , the heat conducting rings  52 ,  54 , and  52 ′ can effectively prevent unsuitable deformation of the outer cylinder due to the resin. 
         [0082]    More specifically, if the inside of the outer cylinder  26  is filled with resin, the resin and outer cylinder  26  greatly differ in coefficient of linear expansion. Further, the resin used for the molded motor is generally a thermosetting resin, and is made to cure by being heated to a high temperature. Therefore, when curing the resin, and then returning it to ordinary temperature, the resin and the outer cylinder  26  pull against each other, thereby the outer cylinder  26  is deformed. 
         [0083]    In this case, if the heat conducting ring  52 ,  54 ,  52 ′ is arranged as shown in  FIG. 6  and  FIG. 8 , the heat conducting ring  52 ,  54 ,  52 ′ will contact the inner circumferential surface  26   a  of a deforming outer cylinder  26  to reinforce the outer cylinder  26 , and prevent the outer cylinder  26  from being deformed unsuitably (for example, deformed into a non-circular shape) due to the resin. 
         [0084]    Further, in the embodiments shown in  FIG. 6  and  FIG. 8 , the outer cylinder  26  may be shrink-fit over the stator core  22  at first, and then the heat conducting ring  52 ,  54 ,  52 ′ may be fixed by shrinkage fit. By assembling in this way, it is possible to correct the deformation of the outer cylinder  26  by the heat conducting ring  52 ,  54 ,  52 ′, when the outer cylinder  26  is deformed by shrinkage fit. 
         [0085]    Above, embodiments of the invention were used to explain the invention, but the above embodiments do not limit the inventions according to the claims. Further, combinations of the features which are explained in the embodiments of the invention may also be included in the technical scope of the invention. However, not all of the combinations of these features are necessarily essential for the solution of the invention. Further, the fact that the above embodiments can be changed or improved in various ways would be clear to a person skilled in the art.