Abstract:
A method for forming a loop winding having a plurality of meandering parts and disposed in a stator of a motor which includes: disposing the loop winding between a first die unit having a plurality of first dies and a second die unit having a plurality of second dies; and press forming the loop winding between the first dies and the second dies by relatively moving the first die unit and the second die unit toward each other, wherein the press forming step is so performed as to provide the loop winding with a plurality of meandering parts and, simultaneously, to reduce the loop winding in the radial direction.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a Divisional Application which claims the benefit of pending U.S. patent application Ser. No. 11/878,767, filed on Jul. 26, 2007, and claims priority of Japanese Patent Application No. 2006-204510, filed on Jul. 27, 2006, and Japanese Patent Application No. 2007-119376, filed on Apr. 27, 2007. The disclosures of the prior applications are hereby incorporated herein in their entirety by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a forming machine for forming a meandering loop winding used as a stator winding in a motor and to a method of forming the meandering loop winding. 
         [0004]    2. Description of the Related Art 
         [0005]    As a hybrid powered vehicle motor or an electric vehicle motor, the permanent magnet type alternating current synchronous motor or brushless DC motor in which permanent magnets are used in a rotor is widely used. As one of this type of motors, a permanent magnet type three-phase synchronous motor having a stator in which windings on a concentrated winding mode are wound around stator cores provided respectively for three phases (U phase, V phase, and W phase) so as to perform three-phase driving of a rotor having permanent magnets by the stator has been known, as for example described in Japanese Patent Laid-open No. Hei 11-299137. 
         [0006]    In addition, a permanent magnet type three-phase synchronous motor having a stator in which windings for three phases (U phase, V phase, and W phase) are wound in wavy forms by disposing them in the manner of threadingly extending between teeth (claw poles) adjacent to each other in the circumferential direction so as to perform three-phase driving of a rotor by the stator has been known, as for example described in Japanese Patent Laid-open No. 2002-165396. 
         [0007]    In the above-mentioned three-phase synchronous motors according to the related art, the windings are needed on the basis of each of the three phases. Therefore, it is difficult to suppress an increase in the number of component parts required to constitute the stator, and much labor is needed for winding the respective windings for the three phases. Moreover, in the stator having the windings on the wave winding mode, it is difficult to enhance the winding occupation factor between the adjacent teeth. Further, it is difficult to reduce the size in the axial direction of the motor by reducing the height at the coil end, in order to enhance the mountability onto a vehicle or the like. 
         [0008]    In order to solve these problems in the related art, the present applicant has previously proposed a motor stator in which stator rings for three phases and loop windings for two phases are alternately disposed in the manner of sequentially stacking along a direction parallel to the axis and in which each of the loop windings is provided with a plurality of meandering parts so as to increase the magnetic flux generated by the stator (refer to Japanese Patent Application No. 2005-306778). 
         [0009]    The stator in the permanent magnet type three-phase synchronous motor or claw pole motor according to the previous patent application mentioned above is configured by use of the loop windings having a plurality of meandering parts. However, such a loop winding having meandering parts was not generally used in the past, and, therefore, establishment of a method for forming such a meandering loop winding is being desired. 
       SUMMARY OF THE INVENTION 
       [0010]    Accordingly, it is an object of the present invention to provide a forming machine for efficiently manufacturing a loop winding having a plurality of meandering parts. 
         [0011]    It is another object of the present invention to provide a method of forming a meandering loop winding, for efficiently manufacturing a loop winding having a plurality of meandering parts. 
         [0012]    In accordance with an aspect of the present invention, there is provided a forming machine for forming a loop winding having a plurality of meandering parts and disposed in a stator of a motor, the forming machine including: a first die unit having a plurality of first dies spaced from each other at regular intervals in a circumferential direction; and a second die unit having a plurality of second dies which are spaced from each other at the same intervals as the regular intervals in a circumferential direction and which are each disposed between adjacent ones of the first dies, wherein each of the second dies has a winding holding part for holding a loop winding; and the first die unit and the second die unit are each provided with a winding diameter reducing means for reducing the loop winding in the radial direction according to a displacement of the first die unit in an axial direction relative to the loop winding held by the winding holding parts. 
         [0013]    According to this configuration, the first and second die units are each provided with the winding diameter reducing means for reducing the loop winding in the radial direction according to the displacement of the first die unit in the axial direction in forming the meandering loop winding; therefore, it is possible to largely reduce the elongation of the loop winding during forming of the meandering parts in the loop winding, and to remarkably enhance the productivity in the press forming. 
         [0014]    Preferably, the number of the first dies and the number of the second dies are equal to or greater than the number of poles of the stator in the motor. With the numbers of the first dies and the second dies set to be equal to or greater than the number of the poles of the stator in the motor, the meandering parts of the loop winding can be securely disposed adjacently to each of the poles of the stator. 
         [0015]    Preferably, a holding surface, facing an outer peripheral part of the loop winding, of each of the winding holding parts has a radius of curvature equal to or greater than the radius of curvature of the outer peripheral part before working of the loop winding, and a holding surface, facing an inner peripheral part of the loop winding, of each of the winding holding parts has a radius of curvature equal to or smaller than the radius of curvature of the inner peripheral part after the working of the loop winding. 
         [0016]    With the radii of curvature of the holding surfaces of the winding holding parts thus set appropriately, it is possible to securely hold the loop winding, without exerting any irrational stress on the loop winding which is varied in diameter through the process of press forming (working). 
         [0017]    Preferably, the winding diameter reducing means includes a plurality of first rollers each of which is radially displaceably provided adjacent to each of the first dies, a plurality of first roller guides which are provided in the second die unit and which are each suitable for rolling thereon of each of the first rollers, a plurality of second rollers each of which is radially displaceably provided adjacent to each of the second dies, and a plurality of second roller guides which are provided in the first die unit and which are each suitable for rolling thereon of each of the second rollers; and a roller rolling surface of each of the first and second roller guides is a curved surface. 
         [0018]    Since the roller rolling surface of each of the first and second roller guides constituting the winding diameter reducing means is formed to be a curved surface, the first and second rollers roll on the curved surface shaped roller rolling surfaces of the first and second roller guides according to the displacement in the axial direction of the first die unit. Therefore, it is possible to reduce the winding diameter according to the extent of working of the loop winding, and to form the plurality of meandering parts without exerting any irrational stress on the loop winding. 
         [0019]    In accordance with another aspect of the present invention, there is provided a method of forming a loop winding having a plurality of meandering parts and disposed in a stator of a motor, the method including the steps of: disposing the loop winding between a first die unit having a plurality of first dies and a second die unit having a plurality of second dies; and press forming the loop winding between the first dies and the second dies by relatively moving the first die unit and the second die unit toward each other, wherein the press forming step is so performed as to provide the loop winding with a plurality of meandering parts and, simultaneously, to reduce the loop winding in the radial direction. 
         [0020]    According to this configuration, it is possible to form the plurality of meandering parts in the loop winding and simultaneously to reduce the loop winding in the radial direction, by the press forming step. Therefore, it is possible to efficiently form the loop winding having a plurality of meandering parts, without exerting any irrational stress on the loop winding. 
         [0021]    The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description and appended claims with reference to the attached drawings showing some preferred embodiments of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1  is an exploded perspective view of a stator having a meandering loop winding to which the present invention is applied; 
           [0023]      FIG. 2  is a perspective view of the stator in its assembled state; 
           [0024]      FIGS. 3A to 3C  illustrate a method of forming a loop winding; 
           [0025]      FIG. 4  is a bottom view of an upper die unit before working; 
           [0026]      FIG. 5  is a plan view of a lower die unit before working; 
           [0027]      FIG. 6  shows sectional views of the upper die unit and the lower die unit before working, wherein the upper die unit is shown in a sectional view taken along line A-O-A of  FIG. 4 , and the lower die unit is shown in a sectional view taken along line B-O-B of  FIG. 5 ; 
           [0028]      FIG. 7  shows sectional views of the upper die unit and the lower die unit immediately before the start of working; 
           [0029]      FIG. 8  is a bottom view of the upper die unit after completion of working; 
           [0030]      FIG. 9  is a plan view of the lower die unit after completion of working; 
           [0031]      FIG. 10  shows sectional views of the upper die unit and the lower die unit after completion of working, wherein the upper die unit is shown in a sectional view taken along line A-O-A of  FIG. 8 , and the lower dieunit is shown in a sectional view taken along line B-O-B of  FIG. 9 ; 
           [0032]      FIG. 11  is a diagram showing the relationship between the amount of variation in the axial direction of the loop winding and the amount of variation in the radial direction of the loop winding; 
           [0033]      FIG. 12  shows the relationship between the radii of curvature of holding surfaces of a winding holding part and the radius of curvature of the loop winding, before working; 
           [0034]      FIG. 13  shows the relationship between the radii of curvature of the holding surfaces of the winding holding part and the radius of curvature of the loop winding, after completion of working; 
           [0035]      FIG. 14  is an enlarged sectional view showing a pressing part and the loop winding; 
           [0036]      FIG. 15  shows sectional views of a reforming machine before reforming pressing, wherein like  FIG. 6 , the left half sectional view shows the section before reforming of a meandering part of the meandering loop winding, and the right half sectional view shows the section before reforming of a non-meandering part; 
           [0037]      FIG. 16  shows sectional views of the reforming machine after reforming pressing, wherein like  FIG. 10 , the left half sectional view shows a reformed section of the meandering part of the meandering loop winding, and the right half sectional view shows the reformed section of the non-meandering part; 
           [0038]      FIG. 17A  shows the positional relationship between dies and the loop winding before reforming pressing, and 
           [0039]      FIG. 17B  shows the positional relationship between the dies and the loop winding after the reforming pressing. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0040]    Now, preferred embodiments of the present invention will be described in detail below referring to the drawings. First, before describing a forming machine for forming a meandering loop winding according to an embodiment of the present invention, a stator in which a loop winding formed by the forming machine based on the present invention is mounted will be described referring to  FIGS. 1 to 3 . This annular stator  2  constitutes, for example, a permanent magnet type alternating current synchronous motor (also called a brushless DC motor or a claw pole type motor) to be mounted on a hybrid powered vehicle as a vehicle drive source together with an engine. For example, in a parallel hybrid powered vehicle with a structure in which an engine, a claw pole type motor and a transmission are connected in series, the drive force of at least either one of the engine and the claw pole type motor is transmitted through the transmission to drive wheels of the vehicle. 
         [0041]    In addition, when a drive force is transmitted from the drive wheel side to the claw pole type motor when the vehicle is decelerated, the claw pole type motor functions as a generator to generate the so-called regenerative braking force, whereby the kinetic energy of the vehicle body is recovered as electrical energy (regenerative energy). Further, also when the output of the engine is transmitted to the claw pole type motor, the claw pole type motor functions as a generator to generate electrical energy. 
         [0042]    Referring to  FIG. 1 , there is shown an exploded perspective view of the annular stator  2  to which a meandering loop winding is mounted.  FIG. 2  is a perspective view of the stator  2  after assembled. As shown in  FIG. 1 , the annular stator  2  includes a U-phase stator ring (teeth ring)  4 , a V-phase stator ring (teeth ring)  6 , a W-phase stator ring (teeth ring)  8 , a U-phase loop winding  22 , and a W-phase loop winding  26 . 
         [0043]    The U-phase stator ring  4  has a plurality (in this embodiment, ten) of U-phase teeth (U-phase claw poles)  10  spaced from each other at regular intervals in the circumferential direction, and a plurality of connecting parts  12  spaced from each other in the circumferential direction. Each of the U-phase teeth  10  is projected to one side (the right side in  FIG. 1 ) in the axial direction. The V-phase stator ring  6  has a plurality (in this embodiment, ten) of V-phase teeth  14  spaced from each other at regular intervals in the circumferential direction, and a plurality of connecting parts  16  spaced from each other in the circumferential direction. Each of the V-phase teeth  14  is projected to both sides in the axial direction. 
         [0044]    The W-phase stator ring  8  has a plurality (in this embodiment,  10 ) of W-phase teeth  18  spaced from each other at regular intervals in the circumferential direction, and a plurality of connecting parts  20  spaced from each other in the circumferential direction. Each of the W-phase teeth  18  is projected to the other side (the left side in  FIG. 1 ) in the axial direction. Namely, the U-phase teeth  10  and the W-phase teeth  18  are projected in such directions as to come close to each other. It is to be noted here that the U-phase teeth  10 , the V-phase teeth  14  and the W-phase teeth  18  are disposed at relatively staggered positions so that they do not overlap with each other when the U-phase stator ring  4 , the V-phase stator ring  6  and the W-phase stator ring  8  are laminated and joined at their connecting parts  12 ,  16 ,  20 . 
         [0045]    The U-phase loop winding  22  is configured by winding a wire in a loop form, and has a plurality (in this embodiment, ten) of meandering parts  24  meandering in the axial direction of the stator  2 . Similarly, the W-phase loop winding  26  also has a plurality (in this embodiment, ten) of meandering parts  28  meandering in the axial direction of the stator  2 . When the connecting parts  12 ,  16 ,  20  of the stator rings  4 ,  6 ,  8  are aligned, the U-phase loop winding  22  and the W-phase loop winding  26  are disposed at predetermined positions in the circumferential direction and the stator rings  4 ,  6 ,  8  are fixed together by bolts, the annular stator  2  is completed as shown in  FIG. 2 . 
         [0046]    As is clear from observation of  FIGS. 1 and 2 , the teeth  10 ,  14 ,  18  are arranged in a predetermined sequence (U-phase teeth  10 , W-phase teeth  18 , V-phase teeth  14 , U-phase teeth  10 , . . . ) in the circumferential direction; in this case, each meandering part  24  of the U-phase loop winding  22  is disposed between each pair of teeth  10  and  14  adjacent to each other in the circumferential direction, and each meandering part  28  of the W-phase loop winding  26  is disposed between each pair of teeth  14  and  18  adjacent to each other in the circumferential direction. In other words, one of the U-phase teeth  10  is disposed in the U-phase meandering part  24 , one of the W-phase teeth  18  is disposed in the W-phase meandering part  28 , and one of the V-phase teeth  14  is disposed between the U-phase meandering part  24  and the W-phase meandering part  28  adjacent to each other in the circumferential direction. 
         [0047]    The meandering parts  24  of the U-phase loop winding  22  and the meandering parts  28  of the W-phase loop winding  26  are projected in mutually different directions, and the U-phase loop winding  22  and the W-phase loop winding  26  are disposed at positions relatively staggered in the circumferential direction so as to have a phase difference in terms of electrical angle of 240°. This ensures that the loop windings  22 ,  26  for two phases so disposed as to threadingly extend between the circumferentially adjacent teeth  10 ,  14  or  14 ,  18  are so formed as to constitute short-pitch windings at a so-called electrical angle of not more than 120°. 
         [0048]    The loop windings having a plurality of meandering parts as above-described are not in general use, and, therefore, establishment of a method for manufacturing such loop windings is being desired. In view of this, there may first be contemplated a method in which a wire is wound around a former designed according to the shape of the slot, and the wound wire is pressed with a die designed according to the slot shape from at least one outer side to achieve the desired forming. In this method, however, the wire is wound around the former on the basis of each turn of the winding, so that handling properties are bad. Further, in the case of a complicatedly shaped slot, it is difficult to wind the wire and, therefore, the number of working steps is increased. 
         [0049]    In order to solve this problem, there is a method in which a winding formed in a loop form is pressed from at least one side by a die shaped according to the slot shape, to achieve the desired forming. However, when the meandering parts are formed by pressing, the winding is reduced in diameter, so that it is difficult to restrict the winding to the required diameter size. In addition, since the amount of displacement in working in the radial direction is different from that in the axial direction, the winding would be elongated. 
         [0050]    The present invention has been made in order to solve these problems. Now, a forming machine for forming a loop winding in an embodiment of the present invention, which has a means for reducing the loop winding in the radial direction according to the progress of forming of the loop winding, will be described in detail below referring to  FIGS. 4 to 13 . 
         [0051]    Prior to description of the forming machine, the method of forming a loop winding will be described briefly, referring to  FIGS. 3A to 3C . First, as shown in  FIG. 3A , a cylindrical body  15  having a groove  17  in the axial direction is prepared. A wire  19  is wound around the cylindrical body  15  to form, for example, a loop winding  21  in three rows and three layers. Symbol  23  denotes the starting end of the winding, while symbol  25  denotes the trailing end of the winding. After the loop winding is thus formed by winding the wire  19  around the cylindrical body  15 , a binding band is inserted into the groove  17 , and the group of loops (turns) are bound together, to form a loop winding  21 . Thereafter, a jig is inserted, and the loop winding  21  is detached from the cylindrical body  15  (see  FIG. 3B ). Then, as shown in  FIG. 3C , the starting end  23  and the trailing end  25  of the winding are formed as desired, to complete the loop winding  21 . 
         [0052]      FIG. 4  is a bottom view of an upper die unit (first die unit) before working, and  FIG. 5  is a plan view of a lower die unit (second die unit) before working. The upper die unit and the lower die unit together constitute a die set.  FIG. 6  shows sectional views of the upper die unit (first die unit) and the lower die unit (second die unit) before working, wherein the upper die unit is shown in a sectional view taken along line A-O-A of  FIG. 4 , while the lower die unit is shown in a sectional view taken along line B-O-B of  FIG. 5 .  FIG. 7  shows sectional views of the upper die unit and the lower die unit immediately before the start of working. 
         [0053]    First, referring to  FIGS. 4 and 6 , the structure of the upper die unit (first die unit)  30  will be described. A plurality (in this embodiment, ten) of die support parts  34  are fixed to a base  32  of the upper die unit  30  in the state of being spaced from each other at regular intervals in the circumferential direction. A guide rail  40  is mounted to each die support part  34  through a pair of brackets  36 ,  38 . A slider  42  is mounted so that it can be slid in the radial direction of a loop winding  82  to be formed, along the guide rail  40 . 
         [0054]    A first die (forming part)  44  is attached to each slider  42 . Each first die  44  includes a die base  46  and a pressing part  48 . As shown in  FIG. 14 , the pressing part  48  is formed to be longer than the thickness a of the loop winding  82  (namely, b&gt;a) so as to securely hold the loop winding  82 . A roller  52  is rotatably mounted on the die base  46  through a pair of brackets  50 . In this embodiment, the upper die unit  30  has ten first dies  44  spaced from each other at regular intervals in the circumferential direction, so that the first dies  44  are spaced from each other by 36° along the circumferential direction. 
         [0055]    Further, a plurality (in this embodiment, ten) of roller guides  54  are fixed to the upper die unit  30 ; in this case, the roller guides  54  are spaced from each other at regular intervals in the circumferential direction, and each thereof is disposed at the middle between the adjacent first dies  44 ,  44 . Each roller guide  54  is provided at its tip with a roller rolling surface  56  in the form of a curved surface. The roller rolling surface  56  has a configuration in which (as viewed in section) a steeply inclined substantially rectilinear portion  56   a  provided on the outer side in the radial direction and a moderately inclined substantially rectilinear portion  56   c  provided on the inner side in the radial direction are connected to each other by an arcuate portion  56   b.    
         [0056]    Now, referring to  FIGS. 5 and 6 , the structure of the lower die unit (second die unit)  60  will be described. A plurality (in this embodiment, ten) of die support parts  64  are fixed to a base  62  of the lower die unit  60  in the state of being spaced from each other at regular intervals in the circumferential direction. Each die support part  64  is provided with a guide rail  66 , and a second die (forming part)  68  is mounted so that it can be slid in the radial direction of the loop winding  82 , along the guide rail  66 . 
         [0057]    Each second die  68  includes a die base  70  slidable along the guide rail  66 , and a winding pressing member  72 . Though not particularly shown, the winding pressing member  72  is bolted to the die base  70  after the loop winding  82  is held by the second die  68 . A roller  70  is rotatably mounted on the die base  70  through a pair of brackets  74 . The roller  76  of each second die  68  is made to conform to rolling on the roller rolling surface  56  of the roller guide  54  provided in the upper die unit  30 ; therefore, the second dies  68  are spaced from each other by 36° along the circumferential direction, and each thereof is disposed at the middle in the circumferential direction between the adjacent first dies  44 ,  44 . 
         [0058]    Further, a plurality (in this embodiment, ten) of roller guides  78  are fixed to the lower die unit  60 ; in this case, the roller guides  78  are spaced from each other at regular intervals in the circumferential direction, and each thereof is disposed at the middle between the adjacent second dies  68 ,  68 . Each roller guide  78  is provided at its tip with a roller rolling surface  80  in the form of a curved surface. The roller rolling surface  80  has a configuration in which (as viewed in section) a steeply inclined substantially rectilinear portion  80   a  provided on the outer side in the radial direction and a moderately inclined substantially rectilinear portion  80   c  provided on the inner side in the radial direction are connected to each other by an arcuate portion  80   b . Each roller guide  78  is provided oppositely to each roller  52  mounted on the upper die unit  30  so that each roller  52  in the upper die unit  30  can roll on the roller rolling surface  80  of each roller guide  78  in the lower die unit  60 . 
         [0059]    Now, a method of forming a loop winding by the loop winding forming machine according to the present embodiment as above-described will be described below. First, as shown in  FIG. 6 , the loop winding  82  is held by the die bases  70  of the second dies  68  of the lower die unit  60 , and the pressing members  72  are bolted to the die bases  70 . As a result, the loop winding  82  is securely held by the second dies  68  of the lower die unit  60 . Starting from this condition, the upper die unit  30  is lowered to the position shown in  FIG. 7 , and forming (working) of the loop winding  82  is started. At the start of forming (working) as shown in  FIG. 7 , each roller  52  in the upper die unit  30  makes contact with the steeply inclined substantially rectilinear portion  80   a  of the roller rolling surface  80  of each roller guide  78  in the lower die unit  60 , and each roller  76  in the lower die unit  60  makes contact with the steeply inclined substantially rectilinear portion  56   a  of the roller rolling surface  56  of each roller guide  54  in the upper die unit  30 . In the beginning stage of forming (working), therefore, the loop winding  82  is reduced in the radial direction only slightly, relative to the amount of variation in the axial direction thereof, as shown in  FIG. 11 . 
         [0060]    As the upper die unit  30  is moved further in the axial direction, each roller  52  rolls on the arcuate portion  80   b  of each roller rolling surface  80 , while each roller  76  rolls on the arcuate portion  56   b  of each roller rolling surface  56 . Therefore, the amount of displacement for reducing in the radial direction of the loop winding  82  relative to the amount of displacement in the axial direction of the upper die unit  30  increases gradually. As the press working proceeds further, each roller  52  rolls on the moderately inclined substantially rectilinear portion  80   c  of each roller rolling surface  80 , while each roller  76  rolls on the moderately inclined substantially rectilinear portion  56   c  of each roller rolling surface  80 . Therefore, the amount of displacement in the radial direction relative to the amount of displacement in the axial direction of the loop winding  82  varies along the curve as shown in  FIG. 11 . 
         [0061]    Thus, by adopting the roller rolling surfaces  56 ,  80  which are each in the shape of a specially shaped curved surface, the ratio of the amount of displacement in the radial direction of the loop winding  82  to the amount of displacement in the axial direction of the loop winding  82  can be varied continuously. Therefore, a plurality of meandering parts  83  can be easily and automatically formed in the loop winding  82  as shown in  FIG. 11 , without exerting any irrational stress on the loop winding  82 . 
         [0062]      FIG. 8  shows a bottom view of the upper die unit  30  after completion of forming (working), and  FIG. 9  shows a plan view of the lower die unit  60  after completion of forming (working). It is seen that the rollers  52 ,  76  have been moved to the inner side in the radial direction, as compared to their locations before the forming (working) shown in  FIGS. 4 and 5 .  FIG. 10  shows sectional views of the upper die unit  30  and the lower die unit  60  upon completion of the forming (working), wherein the upper die unit  30  is shown in a sectional view taken along line A-O-A of  FIG. 8 , and the lower die unit  60  is shown in a sectional view taken along line B-O-B of  FIG. 9 . 
         [0063]    Now, a preferred shape of the winding holding part in the lower die unit  60  will be described, referring to  FIGS. 12 and 13 .  FIG. 12  shows the winding holding parts  70 ,  72  before working of the loop winding  82 , and  FIG. 13  shows the winding holding parts  70 ,  72  after the working of the loop winding  80 . As is clear from  FIGS. 12 and 13 , a holding surface  72   a , facing an outer peripheral part  82   a  of the loop winding  82 , of the winding holding part  72  is preferably configured to have a radius of curvature equal to or greater than the radius of curvature of the outer peripheral part  82   a  before working of the loop winding  82 . 
         [0064]    In addition, a holding surface  70   a , facing an inner peripheral part  82   b  of the loop winding  82 , of the winding holding part  70  is preferably configured to have a radius of curvature equal to or smaller than the radius of curvature of the inner peripheral part  82   b  after working of the loop winding  82 . Where the radii of curvature of the winding holding parts are set in this manner, gaps  84  are formed between the inner periphery side winding holding surface  70   a  and the inner peripheral part  82   b  of the loop winding  82  before working as shown in  FIG. 12 , and gaps  86  are formed between the outer periphery side winding holding surface  72   a  and the outer peripheral part  82   a  of the loop winding  82  after working as shown in  FIG. 13 . When the radii of curvature of the winding holding surfaces in the lower die unit  60  are set in this manner, the loop winding  82  can be securely held, without exerting any irrational stress on the loop winding  82  before or after the working. 
         [0065]    Preferably, after the above-described press working, reforming is conducted for enhancing the shape accuracy of the loop winding  82  provided with the meandering parts  83 . The reforming is carried out by use of a reforming machine  95  including an upper die unit  90  and a lower die unit  96  shown in  FIG. 15 .  FIG. 15  shows sectional views of the upper die unit  90  and the lower die unit  96  before reforming, and  FIG. 16  shows sectional views of the upper die unit  90  and the lower die unit  96  after reforming. As best shown in  FIG. 17A , the upper die unit  90  has a plurality of first dies  92  and a plurality of second dies  94  which are formed alternately along the circumferential direction. 
         [0066]    As best shown in  FIG. 17A , the lower die unit  96  has a plurality of third dies  98  for receiving the first dies  92  and a plurality of fourth dies  100  for receiving the second dies  94 , the third and fourth dies  98  and  100  being formed alternately along the circumferential direction. Incidentally, the third die  98  functions also as a knock-out in taking out the loop winding after the reforming. As shown in  FIG. 15 , the loop winding  82  having the meandering parts  83  is set between an inner diameter frame and an outer diameter frame of the reforming machine  95  including the upper die unit  90  and the lower die unit  96 . Then, the upper die unit  90  is lowered to press the loop winding  82 . As a result, as shown in  FIG. 16  and  FIG. 17B , the loop winding  82  is pressed between the first and third dies  92 ,  98  and between the second and fourth dies  94 ,  100 , whereby the shape accuracy of the loop winding  82  having the meandering parts  83  can be conditioned. 
         [0067]    In the preferred embodiment described above, the numbers of the first and second dies  44 ,  68  used in the initial meandering part pressing work and the numbers of the first, second, third and fourth dies  92 ,  94 ,  98 ,  100  used in the reforming are equal to the number of the poles of the stator of the motor (the number of the teeth). However, the present invention is not limited to this number. The numbers of the first and second dies used in the initial meandering part pressing work or the numbers of the first to fourth dies used in the reforming may be equal to or greater than the number of poles of the stator of the motor. 
         [0068]    In addition, the means for controlling the relative positions of the upper die unit  30  and the lower die unit  60  is not limited to the rollers and roller guides described in the above embodiment. For example, the positional relationships between the relevant component parts may be feedback controlled by additionally using air cylinder, hydraulic cylinders, motors or the like. 
         [0069]    The present invention is not limited to the details of the above described preferred embodiments. The scope of the invention is defined by the appended claims and all changes and modifications as fall within the equivalence of the scope of the claims are therefore to be embraced by the invention.