Patent Publication Number: US-2019190357-A1

Title: Stator, stator manufacturing method and motor

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority to Japanese Patent Application No. 2016-172342 filed on Sep. 2, 2016 and is a Continuation Application of PCT Application No. PCT/JP2017/031390 filed on Aug. 31, 2017. The entire contents of each application are hereby incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a stator, a stator manufacturing method and a motor. 
     2. Description of the Related Art 
     A stator of a motor includes a plurality of teeth radially installed thereon, and an annular part connecting radially outer sides of the teeth in an annular shape. In the stator, an inclined part is formed on an end portion of each core piece of each divided laminate core, and pairs of core pieces with different shapes are alternately laminated with one another. 
     However, by merely chamfering a corner portion of an arc protrusion in a lamination direction as in the conventional stator mentioned above, it cannot be rotated smoothly in some cases when the core pieces are rotated in a state where the shape of the core piece constituting the stator is changed. 
     SUMMARY OF THE INVENTION 
     According to an example preferred embodiment of the present invention, a stator includes an annular core with a center that is a vertically extending central axis and a conductive wire that is wound around the core, in which the core includes core pieces in which at least a first laminate member and a second laminate member are laminated, the first laminate member includes a first tooth portion extending in a radial direction and a first core back portion connected to a radially outer side of the first tooth portion and extending in a circumferential direction, the second laminate member includes a second tooth portion extending in the radial direction and a second core back portion connected to a radially outer side of the second tooth portion and extending in the circumferential direction, positions of both circumferential ends of the first core back portion are different from positions of both circumferential ends of the second core back portion, the first core back portion has an inclined or curved shape at a lower side of one side thereof in the circumferential direction or the other side thereof in the circumferential direction which overlaps the core piece adjacent thereto, the second core back portion has an inclined or curved shape at a lower side of the other side thereof in the circumferential direction or one side thereof in the circumferential direction which overlaps the core piece adjacent thereto, the inclined or curved shape of the first core back portion is at a portion protruding in the circumferential direction with respect to the second core back portion in a plan view, and the inclined or curved shape of the second core back portion is at a portion protruding in the circumferential direction with respect to the first core back portion in a plan view. 
     The above and other elements, features, steps, characteristics and advantages of the present disclosure will become more apparent from the following detailed description of the example embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of a motor according to an example embodiment of the present disclosure. 
         FIG. 2  is a plan view of a laminate member of a core piece according to an example embodiment of the present disclosure. 
         FIG. 3  is a plan view of laminate members of laminated core pieces according to an example embodiment of the present disclosure. 
         FIG. 4  is a plan view of annularly connected core pieces according to an example embodiment of the present disclosure. 
         FIG. 5  is an enlarged view of a connection portion of adjacent core pieces according to an example embodiment of the present disclosure. 
         FIG. 6  is a view showing an area, in which core back portions of adjacent core pieces overlap each other in a lamination direction according to an example embodiment of the present disclosure. 
         FIG. 7  is a cross-sectional view of a connection portion of adjacent core pieces according to an example embodiment of the present disclosure. 
         FIG. 8  is a plan view of a core piece according to a modified example embodiment of the present disclosure. 
         FIG. 9  is a cross-sectional view of a connection portion of core pieces according to a modified example embodiment of the present disclosure. 
         FIG. 10  is a flowchart showing a process of manufacturing a stator according to an example embodiment of the present disclosure. 
         FIG. 11  is a view showing a laminate member formed on a plate member used in a process of manufacturing a stator according to an example embodiment of the present disclosure. 
         FIG. 12  is view showing laminate members of core pieces in a process of manufacturing a stator according to an example embodiment of the present disclosure. 
         FIG. 13  is a view showing a divided stator having a coil formed by winding a conductive wire around teeth of a core piece in a process of manufacturing a stator according to an example embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, example embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. The example embodiments described below are only exemplary examples of the present disclosure, but the technical scope is not limited thereby. Further, the same reference numerals may be assigned to the same components, and the descriptions thereof may be omitted. 
     The exemplary embodiments of the present invention relate to a configuration of a stator (also referred to as a “stator core”) used in a motor and a method of manufacturing the stator. In the description, the term “core piece” refers to an element including a tooth portion around which a conductive wire is not wound and a core back portion having an annular shape in a connected state. The term “core” refers to a group of a plurality of annularly connected core pieces. The term “divided stator” refers to a core piece around which the conductive wire is wound. The term “stator” refers to a group of a plurality of divided stators in an annularly connected state. Further, each layer of the core piece, which defines the core piece by being laminated, refers to a “laminate member.” Further, the term “laminate member” does not necessarily refer to only a layer of the member of the core piece, but may include a plurality of layers of the members having the same or similar shapes and consecutively laminated. 
     Further, for convenience of description in the specification, in laminate members laminated in a manufacturing process, a direction in which the laminate members are laminated refers to an “upper side” or an “upper direction,” and a direction in which laminate members, which are already laminated, are positioned refers to a “lower side” or a “lower direction.” In most cases, the lower side opposing the upper side is positioned on a lower side in a gravity direction. Further, a direction in which the laminate members of the core piece are laminated refers to a “lamination direction.” In the following description, the lamination direction is parallel to a central axis of rotation of the motor, but the lamination direction and the central axis are not necessarily parallel to each other. 
       FIG. 1  is a cross-sectional view of a motor  80  of one embodiment of the present invention. As shown in  FIG. 1 , the motor  80  preferably includes a shaft  81 , a rotor  82 , a stator  83 , a housing  84 , a bearing holder  85 , a first bearing  86 , a second bearing  87 , an insulator  88 , a coil-drawing line  89 , a coil  90 , and the like. The shaft  81  and the rotor  82  are preferably integrated with each other by, for example, the shaft  81  being press fit through the rotor  82 . The shaft  81  has a cylindrical shape having a center that is a central axis extending in one direction. The rotor  82  is positioned at a middle of the shaft  81 . The rotor  82  is rotatable about the stator  83 . The stator  83  is disposed to surround the rotor  82  in an axial direction. The stator  83  includes the coil  90  which is preferably formed by winding a conductive wire around the core of the stator  83 . The housing  84  is engaged with an outer circumferential surface of the stator  83  and accommodates the shaft  81 , the rotor  82 , the stator  83 , the bearing holder  85 , the first bearing  86 , the second bearing  87 , the insulator  88 , the coil-drawing line  89 , and the coil  90  which compose the motor  80 . The bearing holder  85  supports the second bearing  87 . The bearing holder  85  is engaged with the housing  84 . The first bearing  86  is preferably disposed at a lower portion of the housing  84  and supports one side of the shaft  81 . The second bearing  87  supports the other side of the shaft  81 . The insulator  88  is disposed between the stator  83  and a conductive wire of the coil  90  to insulate the stator  83  and the conductive wire of the coil  90 . 
       FIG. 2  is a plan view of one laminate member  10   a  of a core piece  10  which defines the stator  83 .  FIG. 3  is a plan view of the laminated core pieces  10 .  FIG. 4  is a plan view of a core  1  in a state in which the core pieces  10  are annularly connected. 
     As shown in  FIG. 4 , a center point of a circle of an outer circumferential surface or an inner circumferential surface defined by the core  1  is C 1 . Straight lines A 1 , A 2 , and A 3  shown in  FIGS. 2 and 3  each are lines extending in a radial direction through the center point C 1 . An inner angle between the straight line A 1  and the straight line A 2  and an inner angle between the straight line A 1  and the straight line A 3  are preferably about 15°, for example. An inner angle between tooth portions  40  of adjacent core pieces  10  is preferably about 30°, for example. An inner angle between the tooth portions  40  of the adjacent core pieces  10 , an inner angle between the straight lines A 1  and A 2 , and an inner angle between the straight lines A 1  and A 3  vary according to the number of core pieces  10  forming the core  1 . The core  1  according to the present preferred embodiment of the present invention preferably includes the twelve core pieces  10 , and thus, as described above, each of the inner angles between the tooth portions  40  of the adjacent core pieces  10  is preferably about 30°. Further, the number of core pieces  10  of the core  1  may be arbitrarily changed as desired. 
     As shown in  FIG. 2 , the laminate member  10   a  of the core piece  10  includes the tooth portion  40  and the core back portion  20 . The core piece  10  is preferably formed by laminating the plurality of laminate members  10   a  with a predetermined thickness. The tooth portion  40  is linearly symmetrical with respect to the straight line A 1  passing through the center point C 1 . The tooth portion  40  has a shape in which an end on an inner side in a radial direction extends in a circumferential direction, and has an inner circumferential surface  41  on the inner side in the radial direction. 
     As shown in  FIG. 3 , one laminate member and another laminate member of the core piece  10  are laminated so that the tooth portion  40  does not protrude. Since circumferential lengths of one circumferential end of one laminate member and another circumferential end of another laminate member are different from each other, one side protrudes from another side. 
     The core back portion  20  is an element defining an annular portion of the core  1 . The core back portion  20  is preferably connected with a radially outer side of the tooth portion  40  and has a shape extending in a circumferential direction. 
     The core back portion  20  includes a circular arc-shaped protrusion  21  and a radially straight portion  22  formed at one end thereof in the circumferential direction. The radially straight portion  22  has a shape of a straight line extending in a radial direction through the center point C 1 . The radially straight portion  22  protrudes outward from the straight line A 1  in a circumferential direction. The circular arc-shaped protrusion  21  preferably has a shape of protruding circumferentially outward of a radially straight line passing through the center point C 1  and the radially straight portion  22 . The circular arc-shaped protrusion  21  has a circular arc shape partially overlapping a circle having a center that is an intersection point C 2  between the straight line A 2  and an outer circumferential recess  26   b  of the core back portion  20 . An end on a circumferential inner side of the circular arc-shaped protrusion  21  is connected with an end on the circumferential outer side of the radially straight portion  22 , and the circular arc-shaped protrusion  21  and the circumferential end of the radially straight portion  22  become one circumferential end of the core back portion  20 . 
     Further, the circular arc-shaped protrusion  21  may not necessarily have a circular arc shape if so desired. For example, the core back portion  20  may be a protrusion with an arc shape of an ellipse or a gently curved protrusion instead of the circular arc-shaped protrusion  21 . But a portion corresponding to the circular arc-shaped protrusion  21  of one end of the core back portion  20  is in contact with a contact portion  23  of an adjacent core piece at one point. 
     The core back portion  20  preferably includes the contact portion  23  and a radially straight portion  24  provided at the other end thereof in the circumferential direction. Like the radially straight portion  22 , the radially straight portion  24  preferably has a shape extending in a radial direction through the center point C 1 . Unlike the radially straight portion  22 , the radially straight portion  24  has a shape of being recessed circumferentially inward of the straight line A 3 . The contact portion  23  has a straight shape with an inclined surface recessed circumferentially inward of the radially straight portion  24 . An inner angle between the radially straight portion  22  and the contact portion  23  is preferably about 135°. An end on a circumferential inner side of the contact portion  23  is connected with an end on a circumferential outer side of the radially straight portion  24 , and the contact portion  23  and one circumferential end of the radially straight portion  24  become the other circumferential end of the core back portion  20 . 
       FIG. 5  is an enlarged view of a connection portion of laminate members  10   a  and  11   a  of the core pieces  10  and  11  adjacent to each other. As shown in  FIG. 5 , an inner angle P 2  between the radially straight portion  24  and the contact portion  23  is preferably about 135°. 
     Further, the contact portion  23  may not necessarily have a straight line shape. For example, the contact portion  23  may be a shape of a circular arc-shaped protrusion or recess or a curved part. But a portion corresponding to the contact portion  23  of the other end of the core back portion  20  is in contact with the circular arc-shaped protrusion  21  of the adjacent core piece at one point. The contact portion  23  refers to a linear recess as a representation corresponding to the circular arc-shaped protrusion. 
     As shown in  FIG. 5 , one end of the laminate member  10   a  of the core piece  10  is preferably in contact with the other end of the laminate member  11   a  of the adjacent core piece  11 . Specifically, the circular arc-shaped protrusion  21  of the core piece  10  and the contact portion  23  of the core piece  11  are in contact with each other at one contact point P 1 . The radially straight portion  22  of the core piece  10  and the radially straight portion  24  of the core piece  11  are spaced apart from each other. But the radially straight portion  22  of the core piece  10  and the radially straight portion  24  of the core piece  11  are not necessarily spaced apart from each other and may be in contact with each other. 
     As described above, in the core piece  10  and the core piece  11  which are adjacent to each other, the circular arc-shaped protrusion  21  of the laminate member  10   a  of the core piece  10  and the contact portion  23  of the laminate member  11   a  of the core piece  11  are in contact with each other at one point. When the core piece  10  rotates outward of the radial direction with respect to the core piece  11 , the radially straight portion  22  and the radially straight portion  24  are not in contact with each other, but the circular arc-shaped protrusion  21  and the contact portion  23  are in contact with each other at one point. Even when the core piece  11  and the core piece  10  relatively rotate, the core piece  10  and the core piece  11  are in contact with each other at one point, and thus a frictional resistance between the core piece and the core piece  11  decreases. Therefore, compared to a configuration in which core pieces adjacent to each other are in surface contact with each other or in contact with each other at a plurality of points as in the conventional art, the core pieces can rotate while connected with each other. 
     Further, when the core piece  10  rotates with respect to the core piece  11 , a center of rotation is a center C 2  of a circular arc of the circular arc-shaped protrusion  21 . In the laminate members of the core piece  10 , since the center C 2  coincides with a lamination direction, the core piece  10  may smoothly rotate about the center C 2  as an axis. 
     Further, in the laminate members  10   a  and  11   a  of the core pieces  10  and  11 , an inner angle between the radially straight portion  24  and the contact portion  23  is preferably about 135°, and thus the core piece  10  may rotate within a wide range when rotating with respect to the core piece  11  while being in contact with the core piece  11  at one point. Further, the inner angle P 2  is not necessarily limited to 135° and may be changed within a range of about 130° to about 140°. Even when the inner angle P 2  is an arbitrary angle in a range of about 130° to about 140°, the core pieces can be rotated in a sufficiently wide range while being in contact with each other at one point. 
     An outer circumferential surface of the core back portion  20  is engaged with a housing (not shown) when a motor is assembled. The core back portion  20  includes a central recess  29 , outer circumferential surfaces  25   a  and  25   b , and outer circumferential recesses  26   a  and  26   b  provided at an outer circumferential portion thereof. 
     The central recess  29  is incised inward in the radial direction at a position at which an outer circumferential surface of the core back portion  20  and the straight line A 1  intersect with each other. The central recess  29  extends in a groove shape in a vertical direction in which the laminate members are laminated. 
     Each of the outer circumferential surfaces  25   a  and  25   b  preferably has a circular arc shape including a center that is the center point C 1 . The outer circumferential surfaces  25   a  and  25   b  are connected with both circumferential sides of the central recess  29 . The outer circumferential surfaces  25   a  and  25   b  are portions which are in contact with the inner circumferential surface of the housing while the stator including the core  1  around which the conductive wire is wound is engaged with an inner side of the housing. 
     The outer circumferential recesses  26   a  and  26   b  are connected with circumferential end sides on the outer circumferential surfaces  25   a  and  25   b . The outer circumferential recesses  26   a  and  26   b  are recessed from the outer circumferential surfaces  25   a  and  25   b  inward in a radial direction. The outer circumferential recesses  26   a  and  26   b  include a circular arc shape having a smaller diameter than that of the outer circumferential surfaces  25   a  and  25   b  and having the center point C 1  the same as that of the outer circumferential surfaces  25   a  and  25   b . When the stator is fitted to an inner side of the housing, the outer circumferential recesses  26   a  and  26   b  are not in contact with an inner circumferential surface of the housing, and thus gaps are defined between the inner circumferential surface of the housing and the outer circumferential recesses  26   a  and  26   b.    
     The outer circumferential surface of the core back portion  20  of the core piece  10  is preferably engaged with the housing as a stator, as described above, the outer circumferential surfaces  25   a  and  25   b  are in contact with an inner circumferential surface of the housing, and the central recess  29  and the outer circumferential recesses  26   a  and  26   b  are not in contact with the inner circumferential surface of the housing. Therefore, accuracy of a size of the outer circumferential surface of the core back portion  20  increases. Further, the core back portion  20  may not necessarily have the outer circumferential recesses  26   a  and  26   b . When the core back portion  20  has in a shape having the outer circumferential recesses  26   a  and  26   b , dimensions of the outer circumferential surfaces  25   a  and  25   b  more effectively increase. 
     The core back portion  20  preferably includes inner circumferential surfaces  27   a  and  27   b  and inner circumferential recesses  28   a  and  28   b  provided on an inner circumferential surface thereof. The inner circumferential surfaces  27   a  and  27   b  preferably include a circular arc shape having a center that is the center point C 1 . The inner circumferential surfaces  27   a  and  27   b  are connected with both circumferential sides of the tooth portion  40 . The inner circumferential recesses  28   a  and  28   b  are connected with circumferential end sides of the inner circumferential surfaces  27   a  and  27   b . The inner circumferential recesses  28   a  and  28   b  are recessed from the inner circumferential surfaces  27   a  and  27   b  outward in the radial direction. The inner circumferential recesses  28   a  and  28   b  preferably include a circular arc shape having an inner diameter smaller than that of the inner circumferential surfaces  27   a  and  27   b  having the center that is the center point C 1  the same or substantially the same as that of the inner circumferential surfaces  27   a  and  27   b.    
     As shown in  FIG. 3 , when the core piece  10  including a plurality of laminate members which are laminated is viewed from above, since positions of both circumferential ends of the core back portion  20  are different from each other among the laminate members, the laminate member disposed on a lower side is partially shown. When viewed from above, a circular arc-shaped protrusion  121 , a radially straight portion  122 , an outer circumferential recess  126   a , and an inner circumferential recess  128   a  of the laminate member disposed below the laminate member disposed on the top are shown at the contact portion  23 , which is defined short in a circumferential direction of the core back portion  20 , and a circumferential outer side of the radially straight portion  24 . The circular arc-shaped protrusion  121 , the radially straight portion  122 , the outer circumferential recess  126   a , and the inner circumferential recess  128   a  of the laminate members of the core piece  10  overlap an adjacent core piece in a lamination direction. 
       FIG. 6  is a view showing the core back portions  20  of the core pieces  10  and  11  adjacent to each other overlap each other in a lamination direction, and particularly, a view showing an overlapping area. A circular arc-shaped protrusion  221 , a radially straight portion  222 , an outer circumferential recess  226   a , and an inner circumferential recess  228   a  of the laminate member of the core piece  11  are preferably laminated on the circular arc-shaped protrusion  121 , the radially straight portion  122 , the outer circumferential recess  126   a , and the inner circumferential recess  128   a  of the laminate member of the core piece  10 . The laminate member of the core piece  10  is disposed under the laminate member of the core piece  11 . As shown in  FIG. 6  with inclined lines, the core piece  10  and the core piece  11  overlap in an area R. A boundary of the area R is determined by the circular arc-shaped protrusion  221 , the radially straight portion  222 , the outer circumferential recess  226   a , and the inner circumferential recess  228   a , which are laminate members of the core piece  11  positioned on an upper side, and the circular arc-shaped protrusion  121 , the radially straight portion  222 , the outer circumferential recess  226   a , and the inner circumferential recess  228   a , which are laminate members of the core piece  10  positioned on a lower side. But the outer circumferential recess  226   a  and the inner circumferential recess  228   a , the outer circumferential recess  226   a , and the inner circumferential recess  228   a  preferably overlap each other in the lamination direction. 
     For example, an area of the area R is greater than an area of a circumferentially cross-sectional area of the core back portion  20  at a position of the straight line A 3 . Further, the cross-section of the core back portion  20  is calculated by multiplying a circumferential length of the core back portion  20  and a thickness of the laminate member. The reason why the area R is formed as described above is as follows. 
     One circumferential end of each of the laminate members of the core piece  10  is in contact with the other circumferential end of each of the laminate members of the core piece  11  at one point. For this reason, as compared with when one circumferential end of the core piece  10  is in surface contact with the other circumferential end of the core piece  11 , a magnetic path is defined by circumferential ends of the core pieces  10  and  11  so that an amount of magnetic flux flowing therein is narrow. Therefore, the area greater than or equal to the magnetic path which is narrowed due to the area R is able to be secured. Further, since the radially straight portion  22  and the radially straight portion  24  are not in contact with each other in a circumferential direction in an assembled state, the magnetic path is not provided at a position at which the radially straight portion  22  and the radially straight portion  24  are in contact with each other. 
     Even when one circumferential end of the laminate member of the core piece  10  is not in contact with the other circumferential end of the laminate member of the core piece  11  adjacent thereto, is in surface contact therewith, or is in contact with at a plurality of points, the magnetic path is defined in the area R, and thus the magnetic property is improved. 
     Further, it is preferable that the area R be less than or equal to about 5 times the circumferential cross-sectional area of the core back portion  20 . Therefore, an area in which the core back portions  20  of the adjacent core piece  10  overlap in the lamination direction is sufficiently secured, and thus a sufficient magnetic path is able to be secured. Further, because a frictional resistance is prevented from being excessively generated in the lamination direction of the core back portion  20  of the adjacent core piece  10 , the adjacent core pieces are able to rotate in a manufacturing process. 
       FIG. 7  is a cross-sectional view of the connection portion of the core pieces  10  and  11  adjacent to each other. As shown in  FIG. 7 , the core piece  10  is preferably defined by laminate members  10   a  to  10   d  which are laminated. The core piece  11  is preferably defined by laminate members  11   a  to  11   d  which are laminated. Ends of the core piece  10  and the core piece  11  face each other and preferably have uneven portions. The uneven portion of the end of the core piece  10  is engaged and connected with the uneven portion of the end of the core piece  11 . 
     An end  32   a  of the radially straight portion  22  or the circular arc-shaped protrusion  21  is preferably provided at a circumferential end of the laminate member  10   a  of the core piece  10 . An end  35   a  of the radially straight portion  24  or the contact portion  23  is preferably defined at a circumferential end of the laminate member  11   a  of the core piece  11  to face the end  32   a . An upper recess  31   a , which is more recessed from an upper surface of a circumferential inner side of the core piece  10 , is provided at an upper side of the circumferential inner side of the end  32   a . A lower surface  34   a  is positioned under the circumferential inner side of the end  32   a . An inclination  33   a  is provided between the end  32   a  and the lower surface  34   a . When viewed from above, the inclination  33   a  is positioned at the circular arc-shaped protrusion  121  protruding from the upper laminate member in the circumferential direction, the radially straight portion  122 , the outer circumferential recess  126   a , and the inner circumferential recess  128   a  (see  FIG. 6 ). The inclination  33   a  is preferably formed by a chamfering process in the manufacturing process, for example. 
     The laminate member of the core piece  10  is preferably formed by punching a plate member in the manufacturing process, for example. In this case, a burr protruding downward is formed on a lower surface of the laminate members. Since the burr causes interference in accurate lamination when the laminate members are laminated, the above-described chamfering is performed. Further, the inclination  33   a  is formed by the chamfering, and thus the core pieces are able to be smoothly rotated. Further, the lower side of the core piece  10  may be formed to have a curved shape instead of the inclination  33   a.    
     A gap  61  may be defined between a lower surface  34   a  of the laminate member  10   a  and an upper recess  31   b  of the laminate member lib in a lamination direction. Similarly, a gap  62  is defined between the laminate member lib and the laminate members  10   c , and a gap  63  is provided between the laminate member  10   c  and the laminate member  11   d . The gaps  61 ,  62 , and  63  preferably have a distance of greater than or equal to about 5 μm to less than or equal to about 20 μm so that magnetic paths are appropriately defined. Further, in order to form the more appropriate magnetic path, the gaps preferably have a distance of greater than or equal to about 5 μm to less than or equal to about 10 μm, for example. 
     The gaps  61 ,  62 , and  63  preferably have long and short distances rather than the same distance. For example, in the present embodiment, the gaps  61  and  63  have a distance of 5 μm, and the gap  62  has a distance of about 10 μm. An effective magnetic path is secured at a portion at which a distance in the lamination direction of the laminated portion of the adjacent core pieces is short, and a frictional resistance decreases at a portion at which a distance in the lamination direction is long. Therefore, when the effective magnetic path is provided, the magnetic property is secured, and the core pieces are able to be easily rotated in the manufacturing process. 
     Further, a lower recess is preferably provided on a lower side of a circumferential inner side of the circumferential end  32   a  of the laminate member  10   a , similar to the upper recess  31   a . Further, the lower recess may be provided on the laminate member  10   a  instead of the upper recess  31   a.    
     A stator, a core, and a core piece of the present invention are not limited to the above-described embodiment, and various forms made based on the embodiment may be included. For example, the stator, the core, and the core piece of the present invention may be components having the modified embodiments described below. Further, the same components as those in the above-described embodiment will be designated with the same name or numeral references, and the description thereof may be omitted. 
       FIG. 8  is a plan view of laminate members  12   a  defining a core piece  12  as a modified embodiment according to the present invention. As shown in  FIG. 8 , the shapes of both circumferential ends of the laminate member  12   a  of the modification are different from those of the laminate member  10   a  (see  FIG. 2 ) according to the above-describe embodiment of the present invention. 
     Specifically, the laminate member  12   a  has a circular arc-shaped protrusion  21   a  provided at one circumferential end of the core back portion  20   a  thereof. The laminate members  12   a  preferably includes a contact portion  23   a  defined at the other circumferential end of the core back portion  20   a . The laminate member  12   a  of the modification does not have radially straight portions defined at both ends thereof. 
     Even in the case of this configuration, ends in a circumferential direction of the adjacent core pieces are in contact with each other at one point, and the same effect as that of the above-described embodiment is obtained. The core piece  12  of the modification is used, and thus the laminate members of the core piece are able to be easily manufactured. 
     However, as described in the above-described embodiment, when the laminate member includes the radially straight paths  22  and  24 , and one core piece is rotated in a direction in which an inner side in the radial direction gets close to the other core piece, the radially straight paths  22  and  24  come into contact with each other. Therefore, one core piece is able to be prevented from rotating in a direction in which the radially inner side gets close to the other core piece. 
       FIG. 9  is a cross-sectional view of a connection portion of core pieces  13  and  14  in a modified embodiment according to the present invention. As shown in  FIG. 9 , when compared to the core pieces  10  and  11  (see  FIG. 7 ) according to the above-described embodiment, the core pieces  13  and  14  of the modification preferably have a different lamination shape in the vicinity of circumferential ends thereof. 
     Specifically, a lower protrusion  36   a  additionally protruding downward from a lower surface  34   a  is preferably defined on a lower side of a circumferential inner side of the end  32   a  of a laminate member  13   a  of the core piece  13 . A second upper recess  37   b , which overlaps the lamination member  13   a  in the lamination direction and is more recessed than the upper recess  31   b , is provided at an upper side of a circumferential inner side of the end  32   b  of a laminate member  14   b  of the core piece  14 . The lower protrusion  36   a  and the second upper recess  37   b  face each other in a lamination direction and are engaged with each other. Therefore, uneven portions engaged with each other are defined at a portion at which laminate members of the adjacent core pieces  13  and  14  overlap each other in the lamination direction, and thus the core piece  13  and the core piece  14  are prevented from being separated. 
     Next, a method of manufacturing a stator of a embodiment of the present invention will be described with referent to  FIGS. 10 to 13 . Further, although the laminate members are arranged in a transverse direction of a plate member corresponding to number of annularly connected cores in practice, only a portion of them are shown in  FIGS. 11 to 13 , and the others are omitted for the sake of simplicity. Hereinafter, in a plane which is horizontal to a gravity direction, a direction horizontal to a transfer direction of the plate member refers to a “transverse direction.” 
       FIG. 10  is a flowchart showing a process of manufacturing a stator according to a preferred embodiment of the present invention. In the process of manufacturing the stator, a process of separating a laminate member from a plate member, which is a base material, (S 100 ) is performed first. When the laminate member is separated, the separated laminate member is laminated on the laminate member (S 110 ). 
       FIG. 11  is a view showing laminate members  101   a ,  101   b ,  101   c ,  101   d ,  102   a ,  102   b ,  102   c ,  102   d ,  103   a ,  103   b ,  103   c ,  103   d ,  104   a ,  104   b ,  104   c , and  104   d  of core pieces provided on a plate member  2 . The laminate members  101   a ,  101   b ,  101   c , and  104   d  are arranged in each lamination layer. The laminate members  101   a ,  101   b ,  101   c , and  104   d  are arranged in a first layer, the laminate members  102   a ,  102   b ,  102   c , and  102   d  are arranged in a second layer, the laminate members  103   a ,  103   b ,  103   c , and  103   d  are arranged in a third layer, and the laminate members  104   a ,  104   b ,  104   c , and  104   d  are arranged in a fourth layer, and thus the core piece is formed. In the process of separating the laminate members, the laminate members in the same layer are simultaneously or sequentially separated. 
     When all of the laminate members are not laminated (N of S 120 ), the plate member  2  is transferred in a transfer direction S (see  FIG. 11 ), then the laminate members to be laminated are transferred to a separation position (S 130 ). For example, before separation of the laminate members  102   a ,  102   b ,  102   c , and  102   d  in the second layer is performed, the laminate members  102   a ,  102   b ,  102   c , and  102   d  formed on the plate member  2  are positioned right above the separated laminate members,  101   b ,  101   c , and  101   d  in the first layer. Further, a separation of the laminate members  102   a ,  102   b ,  102   c , and  102   d  is performed (S 100 ) so that the laminate members  102   a ,  102   b ,  102   c , and  102   d  are laminated on the laminate members  101   a ,  101   b ,  101   c , and  101   d    104   d.    
       FIG. 12  is a view showing core pieces in which laminate members are laminated in a process of manufacturing a stator. When all of the laminate members are laminated (Y of S 120 ), as shown in  FIG. 12 , core pieces  15   a ,  15   b ,  15   c , and  15   d  in which the laminate members are laminated are arranged in a transverse direction. In this state, conductive wires are wound around tooth portions  40  of the core pieces  15   a ,  15   b ,  15   c , and  15   d , and thus a coil  70  is formed (S 140 ). When the conductive wires are wound around the tooth portions  40  of the core pieces  15   a ,  15   b ,  15   c , and  15   d , the core pieces  15   a ,  15   b ,  15   c , and  15   d  may be rotated in a direction in which tooth portions  40  of the adjacent core pieces are spaced apart from each other, and thus a wide space provided around the tooth portions  40  allows the conductive wires to be easily wound around the tooth portion  40 . In this case, the circular arc-shaped protrusion  21  and the contact portion  23  of the adjacent core pieces are in contact with each other at one point, and the core pieces are rotated about a center C 2  while changing a contact position.  FIG. 13  is a view showing divided stators on which a coil  70  is formed by winding a conductive wire around tooth portions  40  of core pieces  15   a ,  15   b ,  15   c , and  15   d . When the conductive wires are wound around the tooth portions  40 , the divided stators of the core pieces  15   a  to  15   d  around which the conductive wires are wound are rotated, and the core back portions  20  are annularly connected (S 150 ). Thus, the stator having the core  1 , on which the conductive wire is wound, shown in  FIG. 4  is formed. 
     Further, the plate member  2  used in a manufacturing configuration may not be necessarily one plate member but may be two or more plate members if so desired. 
     As such, the embodiments and the modifications of the present invention have been described in detail. The above-descriptions are only exemplary and the present invention is not limited thereto and may be widely interpreted within the range in which those skilled in the art understand. For example, the above embodiments and each modification may be implemented in combination with each other. 
     Features of the above-described preferred embodiments and the modifications thereof may be combined appropriately as long as no conflict arises. 
     While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.