Patent Publication Number: US-8531077-B2

Title: Stator coil production method and electric motor equipped with stator coil produced by the same

Description:
CROSS REFERENCE TO RELATED DOCUMENT 
     The present application claims the benefit of priority of Japanese Patent Application No. 2010-111332 filed on May 13, 2010, the disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates generally to a production method of a stator coil for use in an electric motor to be mounted in, for example, automotive vehicles, and an electric motor equipped with a stator coil produced by the production method. 
     2. Background Art 
     Japanese Patent First Publication No. 2009-194994 (corresponding to US2009/0199393 A1, assigned to the same assignee as that of this application) discloses a stator coil production method which bends an insulator-coated conductor wire several times to form a stator coil conductor which is equipped with in-slot portions to be disposed within slots of a stator core and coil-end portions each of which extends between every adjacent two of the in-slot portions and will be a portion of a coil end when the stator coil conductor is wound through the slots of the stator core. This method is achieved using at least three die-punch pairs which are arrayed at regular intervals along a travel path on which the insulator-coated conductor wire travels. The die and the punch of each pair are opposed to each other across the travel path. Specifically, the die and the punch of one of the die-punch pairs are brought close to each other to clamp and press a portion (as will also be referred to as a preplanned coil end portion below) of the insulator-coated conductor wire to form the coil end portion. Simultaneously, the other die-punch pairs are moved in a direction perpendicular to the travel path to form the in-slot portions leading from the coil-end portion. 
     The above stator coil production method includes two steps: one is to input the insulator-coated conductor wire between the die and the punch of each die-punch pair prior to the step of forming the coil end portion and the other is to remove or output the insulator-coated conductor wire from the die-punch pairs after the step of forming the in-slot portions. Such inputting and outputting steps consume much time to move the dies and the punches because of the insulator-coated conductor wire is long, thus resulting in an increase in time required to complete the stator coil conductor. Additionally, the handling of the insulator-coated conductor wire is complicated, which leads to decreased productivity thereof. 
     SUMMARY 
     It is therefore an object to provide a stator coil production method and a production machine which produce a stator coil within a decreased time and are excellent in productivity of the stator coil. 
     According to one aspect of an embodiment, there is provided a method of producing a stator coil of a stator for use in an electric rotating machine using a plurality of shaping press pairs. The stator coil is made up of in-slot portions which are to be disposed in slots of a stator core and coil-end portions which are to be disposed outside the slots and each of which extends between every adjacent two of the in-slot portions. Each of the shaping press pairs has press members opposed to each other across a travel path along which an insulator-coated conductor wire is to travel. The method comprises: (a) a moving step of moving all the shaping press pairs along the travel path; (b) a coil-end portion shaping step of moving the press members of one of the shaping press pairs close to each other to shape a portion of the insulator-coated conductor wire into one of the coil-end portions; and (c) an in-slot portion shaping step of bringing adjacent two of the shaping press pairs close to each other and simultaneously moving one of the adjacent two of the shaping press pairs in a direction substantially perpendicular to a length of the insulator-coated conductor wire to shape a portion of the insulator-coated conductor wire into one of the in-slot portion. 
     Specifically, the coil-end portion shaping step and the in-slot portion shaping step are performed in sequence on the insulator-coated conductor wire which has been inputted into the shaping press pairs while all the shaping press pairs are being moved along the travel path. The coil-end portion is formed by moving the press members of one of the shaping press pairs close to each other to clamp and press a portion of the insulator-coated conductor wire. Subsequently, the in-slot portion is formed by bringing adjacent two of the shaping press pairs close to each other and simultaneously moving one of the adjacent two of the shaping press pairs in the direction substantially perpendicular to the length of the insulator-coated conductor wire to press a portion of the insulator-coated conductor wire. In such a way, the coil-end portions and the in-slot portion may be formed seamlessly, thus resulting in, thus resulting in a decreased production time for the coil conductor and improvement on the productivity thereof. 
     In the preferred mode of the embodiment, the travel path is a looped path. The shaping press pairs are circulated on the looped path. This enables a plurality of insulator-coated conductor wires to be pressed sequentially, thus resulting in improved efficiency in producing stator coils. 
     The press members of each of the shaping press pairs face each other vertically across the travel path. This permits the number of the shaping press pairs required to shaping the in-slot portions and the coil-end portions to be minimized, thus allowing the size of the stator coil production machine and the production cost for the stator coils to be decreased. 
     The press members of each of the shaping press pairs face each other horizontally across the travel path. This arrangement may be achieved easily at decreased costs as compared with the case where the press members of each of the shaping press pairs face each other vertically across the travel path. 
     Ones of the shaping press pairs which are undergoing the in-slot portion shaping step are broken down into a first group and a second group. Each of the shaping press pairs of the first group is disposed between every adjacent two of the shaping press pairs of the second group. The shaping press pairs of the first group are moved in a direction perpendicular to the travel path, while the shaping press pairs of the second group are held from moving in the direction perpendicular to the travel path. This movement of the first and second groups of the shaping press pairs achieves the press operation on the insulator-coated conductor wire to form the in-slot portions. 
     The method further comprises an input step of inputting the insulator-coated conductor wire to the travel path and an output step of outputting the insulator-coated conductor wire from the shaping press pairs. The input step, the coil-end portion shaping step, the in-slot portion shaping step, and the output step are executed in sequence. The output step moves the press members of each of the shaping press pairs away from each other to release the insulator-coated conductor wire. 
     According to another aspect of the embodiment, there is provided an electric motor which comprises: (a) a stator equipped with a stator core in which a plurality of slots are formed; and (b) a stator coil produced by a method of producing a stator coil of a stator for use in an electric rotating machine using a plurality of shaping press pairs. The stator coil is made up of in-slot portions which are to be disposed in slots of a stator core and coil-end portions which are to be disposed outside the slots and each of which extends every adjacent two of the in-slot portions. Each of the shaping press pairs has press members opposed to each other across a travel path along which an insulator-coated conductor wire is to travel. The method comprises: (a) a moving step of moving all the shaping press pairs along the travel path; (b) a coil-end portion shaping step of moving the press members of one of the shaping press pairs close to each other to shape a portion of the insulator-coated conductor wire into one of the coil-end portions; and (c) an in-slot portion shaping step of bringing adjacent two of the shaping press pairs close to each other and simultaneously moving one of the adjacent two of the shaping press pairs in a direction substantially perpendicular to a length of the insulator-coated conductor wire to shape a portion of the insulator-coated conductor wire into one of the in-slot portion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be understood more fully from the detailed description given hereinbelow and from the accompanying drawings of the preferred embodiments of the invention, which, however, should not be taken to limit the invention to the specific embodiments but are for the purpose of explanation and understanding only. 
       In the drawings: 
         FIG. 1  is a partially perspective view which illustrates an insulator-coated flat wire that is a stator coil to be produced by a stator coil production method according to an embodiment; 
         FIG. 2  is a partially perspective view which illustrates a crank-shaped coil end of an assembly of the stator coils of  FIG. 1 ; 
         FIG. 3  is a side view which illustrates one of U-shaped sections of the insulator-coated flat wire of  FIG. 1 ; 
         FIG. 4  is a partially side view of  FIG. 2 ; 
         FIG. 5  is a perspective view which illustrates a stator coil production machine according to an embodiment; 
         FIG. 6  is a perspective view which illustrates an internal structure of the stator coil production machine of  FIG. 5 ; 
         FIG. 7  is a perspective view which illustrates an internal structure of the stator coil production machine of  FIG. 5 ; 
         FIG. 8  is a perspective view which illustrates an array of shaping press pairs installed in the stator coil production machine of  FIG. 5 ; 
         FIG. 9  is an enlarged perspective view which illustrates one of the shaping press pairs of  FIG. 8 ; 
         FIG. 10  is a plane view which illustrates a rotary retainer installed in the stator coil production machine of  FIG. 5 ; 
         FIG. 11  is a perspective view which illustrates a rail cam installed in the stator coil production machine of  FIG. 5 ; 
         FIG. 12  is a plane view of  FIG. 11 ; 
         FIG. 13  is a perspective view which illustrates a cam mechanism installed in the stator coil production machine of  FIG. 5 ; 
         FIG. 14(   a ) is a development view which illustrates an array of shaping press pairs of the stator coil production machine of  FIG. 5  which perform a sequence of steps of shaping a stator coil; 
         FIG. 14(   b ) is a plane view which illustrates a rotary retainer installed in the stator coil production machine of  FIG. 5 ; 
         FIG. 14(   c ) is a plane view which illustrates a rail cam installed in the stator coil production machine of  FIG. 5 ; 
         FIG. 15(   a ) is a development view which illustrates an array of shaping press pairs of the stator coil production machine of  FIG. 5  which are positioned immediately before an input step of inputting an insulator-coated flat wire into the stator coil production machine is commenced; 
         FIG. 15(   b ) is a plane view which illustrates a rotary retainer installed in the stator coil production machine of  FIG. 5  immediately before an input step of inputting an insulator-coated flat wire into the stator coil production machine is commenced; 
         FIG. 15(   c ) is a plane view which illustrates a rail cam installed in the stator coil production machine of  FIG. 5  immediately before an input step of inputting an insulator-coated flat wire into the stator coil production machine is commenced; 
         FIG. 16(   a ) is a development view which illustrates an array of shaping press pairs of the stator coil production machine of  FIG. 5  which travel to the position where an input step of inputting an insulator-coated flat wire into the stator coil production machine is commenced; 
         FIG. 16(   b ) is a plane view which illustrates a rotary retainer installed in the stator coil production machine of  FIG. 5  when an input step of inputting an insulator-coated flat wire into the stator coil production machine is commenced; 
         FIG. 16(   c ) is a plane view which illustrates a rail cam installed in the stator coil production machine of  FIG. 5  when an input step of inputting an insulator-coated flat wire into the stator coil production machine is commenced; 
         FIG. 17(   a ) is a development view which illustrates an array of shaping press pairs of the stator coil production machine of  FIG. 5  which are moved to the position where a coil-end portion shaping step is commenced; 
         FIG. 17(   b ) is a plane view which illustrates a rotary retainer installed in the stator coil production machine of  FIG. 5  when a coil-end portion shaping step is commenced; 
         FIG. 17(   c ) is a plane view which illustrates a rail cam installed in the stator coil production machine of  FIG. 5  when a coil-end portion shaping step is commenced; 
         FIG. 18(   a ) is a development view which illustrates an array of shaping press pairs of the stator coil production machine of  FIG. 5  which are moved to the position where an in-slot portion shaping step is commenced; 
         FIG. 18(   b ) is a plane view which illustrates a rotary retainer installed in the stator coil production machine of  FIG. 5  when an in-slot portion shaping step is commenced; 
         FIG. 18(   c ) is a plane view which illustrates a rail cam installed in the stator coil production machine of  FIG. 5  when an in-slot portion shaping step is commenced; 
         FIG. 19(   a ) is a development view which illustrates an array of shaping press pairs of the stator coil production machine of  FIG. 5  which are moved to the position where an in-slot portion shaping step is being executed; 
         FIG. 19(   b ) is a plane view which illustrates a rotary retainer installed in the stator coil production machine of  FIG. 5  when an in-slot portion shaping step is being executed; 
         FIG. 19(   c ) is a plane view which illustrates a rail cam installed in the stator coil production machine of  FIG. 5  when an in-slot portion shaping step is being executed; 
         FIG. 20(   a ) is a development view which illustrates an array of shaping press pairs of the stator coil production machine of  FIG. 5  which are moved to the position where an in-slot portion shaping step is terminated; 
         FIG. 20(   b ) is a plane view which illustrates a rotary retainer installed in the stator coil production machine of  FIG. 5  when an in-slot portion shaping step is terminated; 
         FIG. 20(   c ) is a plane view which illustrates a rail cam installed in the stator coil production machine of  FIG. 5  when an in-slot portion shaping step is terminated; 
         FIG. 21(   a ) is a development view which illustrates an array of shaping press pairs of the stator coil production machine of  FIG. 5  which are moved to the position where an output step of outputting an insulator-coated flat wire is commenced; 
         FIG. 21(   b ) is a plane view which illustrates a rotary retainer installed in the stator coil production machine of  FIG. 5  when an output step of outputting an insulator-coated fiat wire is commenced; 
         FIG. 21(   c ) is a plane view which illustrates a rail cam installed in the stator coil production machine of  FIG. 5  when an output step of outputting an insulator-coated flat wire is commenced; 
         FIG. 22(   a ) is a development view which illustrates an array of shaping press pairs of the stator coil production machine of  FIG. 5  which passes through the position where an output step of outputting an insulator-coated flat wire is executed; 
         FIG. 22(   b ) is a plane view which illustrates a rotary retainer installed in the stator coil production machine of  FIG. 5  when an output step of outputting an insulator-coated flat wire is executed; 
         FIG. 22(   c ) is a plane view which illustrates a rail cam installed in the stator coil production machine of  FIG. 5  when an output step of outputting an insulator-coated flat wire is executed; 
         FIG. 23  is a perspective view which shows a stator coil production machine according to the second embodiment; and 
         FIG. 24  is a perspective view which shows a modified form of the stator coil production machine of  FIG. 23 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A stator coil production method and a stator coil production machine of an embodiment will be described below which form stepwise coil-end portions in conductor wires (which will also be referred to as coil conductors below) for use in making a stator coil wound through slots of a stator core of an electric rotating machine such as an electric motor, an electric generator, or a motor-generator to be mounted in automotive vehicles. 
     The stator coil will first be described below with reference to  FIGS. 1 to 4 . The stator coil, as referred to herein, is made up of the coil conductors and will also be called a crank-shaped stator coil below.  FIG. 1  is a partially perspective view which illustrates an insulator-coated flat wire  30  that is one of the conductor wires making the stator coil.  FIG. 2  is a partially perspective view which illustrates a crank-shaped coil end of the stator coil which is formed by an assembly of coil-end portions  42  of the insulator-coated flat wires  30 . 
     The insulator-coated flat wires  30  are wound through slot  14  and  15  formed in a stator core  12  of a stator  11 . The stator core  12  is of an annular shape and has an end surface  13  that is one of end surfaces opposed to each other in an axial direction of the stator core  12 . The stator  11 , as referred to herein, is designed for use in an electric motor-generator to drive an automotive vehicle. The electric motor-generator has a rotor (not shown) disposed to be rotatable within an inner periphery of the stator  11 . The rotor has arrayed on an outer circumference thereof a plurality of permanent magnets whose S-poles and N-poles are arrayed alternately in a circumferential direction of the stator core  12 . The rotor is opposed at the outer circumference thereof to the inner circumference of the stator  11  through a small air gap. The stator core  12  is made up of a stack of flat rolled magnetic steel sheets each having a given thickness. The stator coil  20  is formed by three-phase windings. Each of the three-phase windings includes two wave-windings. One of the wave-windings of each of the three-phase windings is wound through the slots  14 , while the other wave-winding is wound through the slots  15 . In other words, the stator coil  20  is of a so-called two-slot per pole per phase type in which each of the three-phase windings is wound through every adjacent two of the slots  14  and  15 . 
     The three phase windings are, for example, distributed wave windings and star-connected to form the stator coil  20 . Each of the three phase windings is made by bending the insulator-coated flat wire  30  and then setting it within the slots  14  or  15  of the stator core  12 . The stator core  12  is of an open-slot structure, but may alternatively be made of an assembly of blocks. 
     The insulator-coated flat wire  30  is made by coating copper wire having a rectangular transverse cross section with enamel such as polyamide-imide and also covering it with an extruded resinous layer made of, for example, polyphenylene sulfide (PPS). The insulator-coated flat wire  30  is, therefore, covered with two types of insulating layers. A total thickness of the insulating layers is 100 μm to 170 μm. The insulator-coated flat wire  30  may alternatively have another known type of insulator-coated structure. The insulator-coated flat wires  30  are arrayed in line within each of the slots  14  and  15  in a depthwise direction thereof, but may alternatively be arranged in an array of rows and columns within each of the slots  14  and  15 . Typically, an insulating sheet is disposed on an inner periphery of each of the slots of the stator core, but omitted in this embodiment because each of the insulator-coated flat wires  30  is covered with the two insulating layers. Each of the insulator-coated flat wires  30  which makes the stator coil  20  includes, as illustrated in  FIG. 1 , in-slot portions  40  to be disposed inside the slots  14  or  15  and coil-end portions  42  each of which extends between adjacent two of the in-slot portions  42 . When the insulator-coated flat wires  30  are set in the stator core  12 , each of the coil-end portions extends over either of the opposed end surfaces of the stator core  12  and connects ends of two of the in-slot portions  42  which lie at an interval of a one-pole pitch away from each other in the circumferential direction of the stator core  12 . 
     Each of the coil-end portions  42  of the insulator-coated flat wire  30  will also be described in detail with reference to  FIG. 3 . 
       FIG. 3  illustrates one of U-shaped sections of each of the insulator-coated flat wires  30 . The U-shaped section includes a head (i.e., the coil-end portion  42 ) and two legs (i.e., the in-slot portions  40 ) extending from ends of the head. The coil-end portion  42  (i.e., the head) has a central top (i.e., the vertex)  1  which lies most outward thereof and extends horizontally (i.e., the circumferential direction of the stator core  12  when the insulator-coated flat wire  30  is set in the stator core  12 ). The top  1  lies at the center between the two adjacent in-slot portions  40 . The coil-end portion  42  is shaped stepwise symmetrically with respect to the top  1 . The top  1  has a transverse section  3 A formed in the center thereof. The transverse section  3 A extends in a thickness-wise direction of the insulator-coated flat wire  30  (i.e., in the radial direction of the stator core  12 ) by approximately the thickness of the insulator-coated flat wire  30 . The transverse section  3 A serves to offset one of halves of a length of the coil-end portion  42  from the other in a direction traversing the length of the coil-end portion  42 , thereby permitting the coil-end portion  42  to which the transverse section  3 A belongs to be laid to overlap an adjacent one of the coil-end portions  42  when the insulator-coated flat wires  30  are wound through the slots  14  and  15  of the stator core  12 . The coil-end portion  42  also includes horizontal sections  2 ,  3 , and  4  and vertical sections  6 ,  7 , and  8 . The horizontal sections  2  to  4  extend in the lengthwise direction of the insulator-coated flat wire  30 , in other words, in the circumferential direction of the stator core  12  and will also be referred to as circumferential sections below. The vertical sections  6  to  8  extend in the transverse direction of the insulator-coated flat wire  30 , in other words, in the axial direction of the stator core  12  and will also be referred to as axial sections below. The coil-end portion  42  also includes corners C 1 , C 2 , C 3 , C 4 , C 5 , C 6 , and C 7 . Each of the corners C 1  to C 6  lies between one of the top  1  and the circumferential sections  2  to  4  and an adjacent one of the axial sections  6  to  8 . Each of the corners C 7  lies between one of the circumferential sections C 7  and a corresponding one of the in-slot portions  40 . The coil-end portion  42  is, as described above, shaped stepwise symmetrically with respect to the top  1  (i.e., the transverse section  3 A). The corners C 1  to C 7  are illustrated in  FIG. 3  as being right-angled corners, but may alternatively be bent or rounded at a radius of curvature selected from a range which permits the coil-end portions  42  to be arranged close to each other over the end surface of the stator core  12 .  FIG. 4  illustrates the crank-shaped coil end formed by an assembly of the coil-end portions  42 . 
     The elongated insulator-coated flat wire  30  is, as will be described later in detail, bent several times to form the coil-end portions  42  lying away from each other at regular intervals in the lengthwise direction of the insulator-coated flat wire  30 , thereby forming one of the wave-wound phase windings. The phase windings are so assembled as to place the coil-end portions  42  close to each other to make the stator coil which exhibits a belt-shape when developed in the circumferential direction of the stator core  12 . The stator coil  20  is inserted at the in-slot portions  40  into the slots  14  and  15  of the stator core  12  to complete the stator  11 . 
     The stator coil  20  is, as described above, so shaped as to have the crank-shaped coil ends and minimize the length of portions (i.e., the crank-shaped coil ends) protruding from either one of the opposed end surfaces of the stator core  12 . The crank-shaped coil ends are, therefore, very difficult to produce. This problem may be alleviated by bending the coil conductor (i.e., the insulator-coated flat wire  30 ) to form the coil-end portions  42  and assembling the coil-end portions  42  before the coil conductor is wound through the stator core  12 . 
     Specifically, the stator  11  is produced by three steps: (1) a coil conductor bending step of bending each of the insulator-coated flat wires  30  to make the in-slot portions  40  and the coil-end portions  42  alternately, (2) a circumferentially-developed stator coil making step of assembling the insulator-coated flat wires  30  so as to lay the coil-end portions  42  to overlap each other in the transverse direction of the insulator-coated flat wires  30  to make the stator coil  20 , as developed in the circumferential direction of the stator core  12 , and (3) a slot insertion step of inserting the in-slot portions  40  into the slots  14  and  15  of the stator core  12  to complete the stator  11 . The feature of the stator coil production method of the embodiment resides on the improvement in the coil conductor bending step. 
     The stator coil production method and the stator coil production machine of the embodiment will be described below in detail with reference to  FIGS. 5 to 13 . 
       FIGS. 5 ,  6  and  7  are perspective views which illustrate a structure of the stator coil production machine designed to make the stator coil  20 . The stator coil production machine is of a cylindrical-surface circulation vertical type and consists of a plurality of shaping press pairs  50 , two rotary retainers  60  which retain the shaping press pairs  50  and rotate them around the center of the stator coil production machine, two rail cams  70 , as illustrated in  FIGS. 11 and 12 , which define paths of travel of the shaping press pairs  50 , and a cam mechanism  80  disposed around arrays of the shaping press pairs  50 . 
     Each of the shaping press pairs  50 , as clearly illustrated in  FIG. 9 , consists of a die  51  and a punch  52  which are aligned with each other and work to create a nip through which the insulator-coated flat wire  30  passes. The die  51  and the punch  52  are mounted on an elongated base  53  to be slidable close to or away from each other. The die  51  and the punch  52  have surfaces facing each other which are contoured to conform with the shape of the stepwise coil-end portion  42 . The die  51  and the punch  52  have cam followers  51   a  and  52   a  secured to surfaces thereof farther away from the mount base  53 . The cam followers  51   a  and  52   a  are each nipped between two of the first to fourth annular guide paths  81  to  84  of the cam mechanism  80 . 
     The mount base  53  also has shafts which extend from opposed ends thereof in a lengthwise direction and on which rollers  54  are mounted to be rotatable within retaining holes  61  of the rotary retainers  60  illustrated in  FIG. 10 . The mount base  53  also has support blocks  55  disposed on ends of the shafts. The support blocks  55  have the width greater than that of the retaining holes  61 . Each of the support blocks  55  has mounted thereon cam followers  56  which are to be disposed within a race  71  of one of rail cams  70 , as illustrated in  FIG. 11 . 
     The stator coil production machine is, as illustrated in  FIG. 8 , equipped with the thirteen (13) shaping press pairs  50  which are arranged at regular intervals in a circular array in parallel to each other. Each of the shaping press pairs  50 , as described above, consists of two press members (i.e., the die  51  and the punch  52 ) and works as press mechanism. The die  51  and the punch  52  face each other in a vertical direction to be movable to form a nip through which the insulator-coated flat wire  30  passes. A leading one of the shaping press pairs  50  into which the insulator-coated flat wire  30  is first inputted has the die  51  disposed below the punch  52 . Similarly, each of the shaping press pairs  50  disposed at an odd-numbered position following the leading one has the die  51  disposed below the punch  52 . Each of the shaping press pairs  50  disposed at an even-numbered position has the die  51  disposed above the punch  52 . In other words, the shaping press pairs  50  are broken down into two types: a first type having the die  51  disposed below the punch  52  and a second type having the die  51  disposed above the punch  52 . The first and second types are arranged alternately in the circumferential direction of the stator coil production machine. 
     The rotary retainers  60  are, as illustrated in  FIG. 5 , made of disc plates secured to opposed ends of a rotating shaft  65 , respectively. Each of the rotary retainers  60 , as clearly illustrated in  FIG. 10 , has the thirteen (13) retaining holes  61  through which the shaping press pairs  50  are retained. Each of the retaining holes  61  is defined by an opening which is cut in the rotary retainer  60  and extends from an outer edge toward the center of the rotary retainer  60 . Each of the retaining holes  61  has a first curved end  61   a  and a second curved end  61   b . The first curved end  61   a  is closer to the center of the rotary retainer  60  than the second curved end  61   b  and oriented to a direction X of rotation of the rotary retainer  60  (i.e., the shaping press pairs  50 ). The second curved end  61   b  is also oriented to the direction X. The length of and the angle which each of the first and second curved ends  61   a  and  61   b  of each of the retaining holes  61  makes with a major portion thereof (i.e., the radial direction of the rotary retainer  60 ) are determined in a given relation to those of a preceding one of the retaining holes  61  in the direction X. 
     The two rollers  54  installed on the ends of each of the mount bases  53  are, as can be seen from  FIG. 6 , disposed in a corresponding one of the retaining holes  61  of the upper rotary retainer  60  and a corresponding one of the retaining holes  61  of the lower rotary retainer  60 , respectively, so that all the shaping press pairs  50  are held in the circular array by the rotary retainers  60  through the support blocks  55 . Each of the shaping press pairs  50  is also movable radially of the rotary retainers  60  along a path, defined by corresponding two of the retaining holes  61  of the rotary retainers  60 . 
     The rail cams  70  are each made of a disc plate which is substantially identical in size with the rotary retainers  60 . Each of the rail cams  70  is disposed outward of one of the rotary retainers  60  in the axial direction of the stator coil production machine in mechanical connection therewith through a coupling mechanism (not shown). The rail cams  70 , as illustrated in  FIGS. 11 and 12 , have the annular races  71  formed by grooves cut in major surfaces facing each other in the axial direction of the stator coil production machine. The annular races  71  serve as rails along which the shaping press pairs  50  supported by the rotary retainers  60  are to travel, that is, define the path of travel of the shaping press pairs  50 . In the annular races  71 , the cam followers  56  on the ends of the mount bases  50  are fit, so that the shaping press pairs  50  may be advanced by the rotary retainers  60  in the direction X along the annular races  71 . 
     Each of the races  71  has an irregularly shaped profile and is made up of a greater circular section  71   a , a smaller circular section  71   b , a great radius-of-curvature varying section  71   c , and a small radius-of-curvature varying section  71   d . The greater circular section  71   a  extends along an outer edge (i.e., a circumference) of the rail cam  70  and is identical in radius of curvature with the outer edge of the rail cam  70 . The smaller circular section  71   b  extends along an inner edge (i.e., a circumference) of a center hole  70   a  of the rail cam  70  and is identical in radius of curvature with the center hole  70   a . The great radius-of-curvature varying section  71   c  extends from an end of the greater circular section  71   a  to an end of the smaller circular section  71   b  at a variable radius of curvature increasing gradually. The small radius-of-curvature varying section  71   d  extends from the other end of the smaller circular section  71   b  to the other end of the greater circular section  71   a  at a variable radius of curvature decreasing gradually. 
     The greater circular section  71   a  defines a first constant-speed path A on which each of the shaping press pairs  50  is to travel in the direction X at a constant speed. The smaller circular section  71   b  defines a second constant-speed path B on which each of the shaping press pairs  50  is to travel in the direction X at a constant speed lower than that in the greater circular section  71   a . The great radius-of-curvature varying section  71   c  defines a decelerating path C on which each of the shaping press pairs  50  is to travel while decelerating gradually in the direction X. The small radius-of-curvature varying section  71   d  defines an accelerating path D on which each of the shaping press pairs  50  is to travel while accelerating gradually in the direction X. The stator coil production machine is designed to have an inlet in substantially the center of the greater circular section  71   a  (i.e., the first constant-speed path A) into which the insulator-coated flat wire  30  is to enter and an outlet in substantially the center of the smaller circular section  71   b  (i.e., the second constant-speed path B) from which the insulator-coated flat wire  30  is to get out. Specifically, each of the shaping press pairs  50  travels half the race  71  within the time for which the insulator-coated flat wire  30  advances from the inlet to the outlet, thereby achieving the coil conductor bending step which bends the insulator-coated flat wire  30  to make the in-slot portions  40  and the coil-end portions  42  alternately. 
     The movement of each of the shaping press pairs  50  along the odd-shaped races  71  of the rail cams  70  is achieved by enabling the rollers  54  of a corresponding one of the mount bases  53  to reciprocate in a corresponding one of combinations of the retaining holes  61  which are cut in the upper and lower rotary retainers  60  and extend in the radial direction thereof. The first curved end  61   a  of each of the retaining holes  61  which is located close to the center of the rotary retainer  60  serves to keep adjacent two of the shaping press pairs  50  placed closest to each other for an increased period of time when the insulator-coated flat wire  70  is discharged from the stator coil production machine, thereby facilitating the ease with which the insulator-coated flat wire  30  is released from the shaping press pairs  50 . The second curved end  61   b  of each of the retaining holes  61  which is located far away from the center of the rotary retainer  60  serves to keep every adjacent two of the shaping press pairs  50  placed closest to each other for an increased period of time when the insulator-coated flat wire  70  is put into the shaping press pairs  50 , thereby facilitating the ease with which the insulator-coated flat wire  30  is supplied into the stator coil production machine. 
     The cam mechanism  80  is, as can be seen from  FIG. 6 , disposed outside the shaping press pairs  50  and surrounds the circular arrays of the shaping press pairs  50 . The cam mechanism  80  is, as clearly illustrated in  FIG. 13 , of a hollow cylindrical shape and consists of six discrete rings  80   a  to  80   f  which will also be referred to as first to sixth rings below. The first to sixth rings  80   a  to  80   f  are laid to overlap each other in the axial direction of the cam mechanism  80  and held, as shown in  FIG. 5 , by a plurality of supports  88  standing on a mount base  90 . 
     Between upwardly located two of the first to sixth rings  80   a  to  80   f , that is, between the first and second rings  80   a  and  80   b , the first guide path  81  is defined in which the cam followers  52   a  of the punches  52  of the shaping press pairs  50  disposed at the odd-numbered positions are fit. Between the fourth and fifth rings  80   d  and  80   e , the second guide path  82  is defined in which the cam followers  51   a  of the dies  51  of the shaping press pairs  50  disposed at the odd-numbered positions are fit. Between the second and third rings  80   b  and  80   c , the third guide path  83  is defined in which the cam followers  51   a  of the dies  51  of the shaping press pairs  50  disposed at the even-numbered positions are fit. Between the fifth and sixth rings  80   e  and  80   f , the fourth guide path  84  is defined in which the cam followers  52   a  of the punches  52  of the shaping press pairs  50  disposed at the even-numbered positions are fit. 
     With the above arrangements of the first to fourth guide paths  81  to  84 , the die  51  and the punch  52  of each of the shaping press pairs  50  located at the odd-numbered positions and the die  51  and the punch  52  of each of the shaping press pairs  50  located at the even-numbered positions will be different in motion from each other. Specifically, the first to fourth guide paths  81  to  84  specify relative positions of the die  51  and the punch  52  of each of the shaping press pairs  50  when being revolved by the rotary retainers  60 . 
     The stator coil production method using the above described stator coil production machine will be described below with reference to  FIGS. 14(   a ) to  22 ( c ).  FIGS. 14(   a ) to  14 ( b ) demonstrate all a sequence of steps of bending the coil conductor (i.e., the insulator-coated flat wire  30 ).  FIG. 14(   a ) is a development diagram which shows the array of the shaping press pairs  50 , as developed in the circumferential direction of the stator coil production machine.  FIG. 14(   b ) is a plane view which shows the rotary retainer  60 .  FIG. 14(   c ) is a plane view which shows the rail cam  70 . Note that  FIG. 14(   a ) schematically represents the shape of the coil-end portions  42  of the insulator-coated flat wire  30  for the sake of simplicity. Arc-shaped thick lines in  FIGS. 14(   b ) and  14 ( c ) drawn outside the rotary retainer  60  and the rail cam  70  indicate a range within which the shaping press pairs  50 , as illustrated in  FIG. 14(   a ), exist. The same is true for the  FIGS. 15(   a ) to  22 ( c ). 
       FIGS. 15(   a ) to  22 ( c ) show an input step of inputting the insulator-coated flat wire  30  into the stator coil production machine (i.e., one of the shaping press pairs  50 ), a coil-end portion shaping step of shaping the coil-end portions  42 , an in-slot portion shaping step of shaping the in-slot portions  40 , and an output step of outputting the insulator-coated flat wire  30  from the stator coil production machine.  FIGS. 15(   a ) to  22 ( c ) represents only four of the shaping press pairs  50 , which will also be expressed by  50 A,  50 B,  50 C, and  50 D below, for the sake of simplicity of illustration. 
     The stator coil production machine is run by an actuator (not shown). Upon turning on of the actuator, the rotating shaft  65  starts to rotate, so that all the shaping press pairs  50  are revolved through the rotary retainers  60  around the rotating shaft  65  at a constant speed. This causes all the shaping press pairs  50  to revolve in the direction X (i.e., the lengthwise direction of the insulator-coated flat wire  30 ) and advance along the travel path defined by the races  71  of the rail cams  70 . The die  51  and the punch  52  of each of the shaping press pairs  50  travel in contact with any of the surfaces of the first to fourth guide paths  81  to  84 , so that the die  51  and the punch  52  move close to or away from each other in the vertical direction (i.e., the axial direction of the stator coil production machine). 
     Input Step 
     During the revolving of the shaping press pairs  50 , some of them traveling along the first constant-speed path A (i.e., the greater circular section  71   a ) of the races  71 , as illustrated in  FIGS. 15(   a ) to  16 ( c ), are in the condition where the die  51  and the punch  52  is placed away from each other in the vertical direction (i.e., the direction in which the die  51  and the punch  52  faces). When one of the shaping press pairs  50  has reached the middle of the greater circular section  71 , the insulator-coated flat wire  70  is inputted to the stator coil production machine. In  FIGS. 15(   a ) and  16 ( a ), the four shaping press pairs  50 A to  50 D are traveling along the first constant-speed path A at constant intervals away from each other. The retaining holes  61  of the rotary retainers  60  through which the shaping press pairs  50 A to  50 D are retained have, as described above, the second curved ends  61   b , thereby causing the adjacent two of the shaping press pairs  50 A to  50 D to be kept closest to each other for a long time. This ensures the stability in inputting the insulator-coated flat wire  30  into one of the shaping press pairs  50 A to  50 D. 
     Coil-End Portion Shaping Step 
     Subsequently, with the rotation of the rotary retainers  60 , the die  51  and the punch  52  of the shaping press pair  50 A into which the insulator-coated flat wire  50  has been inputted, as illustrated in  FIGS. 16(   a ) to  16 ( c ), move close to each other. When the shaping press pair  50 A has reached the position, as illustrated in  FIGS. 17(   a ) to  17 ( c ), a leading portion of the insulator-coated flat wire  30  is clamped and pressed by the die  51  and the punch  52  of the shaping press pair  50 A and then shaped into the stepwise coil-end portion  42  protruding downward, as viewed in  FIG. 17(   a ). Afterwards, the shaping press pair  50 A travels while holding the coil-end portion  42  tightly. 
     Like the shaping press pair  50 A, when each of the following shaping press pairs  50 B to  50 D has reached the position, as illustrated in  FIGS. 17(   a ) to  17 ( c ), a corresponding portion of the insulator-coated flat wire  30  is pressed by the die  51  and the punch  52  and then shaped into the stepwise coil-end portion  42  protruding either in the upward or downward direction, as viewed in  FIG. 17(   a ). Afterwards, each of the shaping press pairs  50 B to  50 D travels while holding a corresponding one of the coil-end portions  42  tightly as it is. With the shaping press pairs  50 A to  50 D, the coil-end portions  42  are formed sequentially which protrude upward and downward alternately. 
     In-Slot Portion Shaping Step 
     After having formed the coil-end portion  42 , the shaping press pair  50 A, as illustrated in  FIGS. 18(   a ) to  18 ( c ), transfers from the first constant-speed path A (i.e., the greater circular section  71   a  of the race  71 ) to the decelerating path C (i.e., the great radius-of-curvature varying section  71   c  of the race  71 ), so that it decelerates gradually. With the gradual deceleration, the interval between adjacent two of the shaping press pairs  50 A to  50 D is, as illustrated in  FIGS. 19(   a ) to  19 ( c ), decreased. This causes the shaping press pairs  50 A to  50 D to approach each other sequentially. The shaping press pairs  50 A and  50 C located at the odd-numbered positions travel straight in the horizontal direction along the first and second guide paths  81  and  82  without moving vertically. The shaping press pairs  50 B and  50 D located at the even-numbered positions enter or advance to the decelerating path C (i.e., the great radius-of-curvature varying section  71   c  of the race  71 ). Upon entering the decelerating path C, each of the shaping press pairs  50 B and  50 D decelerates gradually and moves upward along the third and fourth guide paths  83  and  84 . 
     The above movements of the shaping press pairs  50 A and  50 B cause both a trailing end of the coil-end portion  42  which is held by the shaping press pair  50 A and located close to the shaping press pair  50 B and a leading end of the coil-end portion  42  which is held by the shaping press pair  50 B and located close to the shaping press pair  50 A to be bent. When the shaping press pair  50 A, as illustrated in  FIGS. 20(   a ) to  20 ( c ), has reached the end of the decelerating path C (i.e., the great radius-of-curvature varying section  71   c ), the shaping press pairs A and B are placed closest to each other. This causes a portion of the insulator-coated flat wire  30  between the coil-end portions  42  held by the shaping press pairs  50 A and  50 B to be shaped into the in-slot portion  40  which extends perpendicular to the coil-end portions  42 . 
     With the rotation of the rotary retainers  60 , the in-slot portions  42  are formed sequentially between the shaping press pairs  50 B and  50 C and between the shaping press pairs  50 C and  50 D. 
     Output Step 
     After completion of the in-slot portion shaping step, the shaping press pair  50 A, as illustrated in  FIGS. 21(   a ) to  21 ( c ), transfers from the decelerating path C to the second constant-speed path B (i.e., the smaller circular section  71   b  of the race  71 ) and then travels at the speed lower than that in the first constant-speed path A (i.e., the greater circular section  71   a . When the shaping press pair  50 A enters the second constant-speed path B, the punch  52  moves upward along the first guide path  81 . After a slight delay from the upward movement of the punch  52 , the die  51  moves downward along the second guide path  82  while revolving in the direction X. This causes the coil-end portion  42  to be released from the shaping press pair  50 A. When entering the second constant-speed path B, the shaping press pairs  50  disposed at the odd-numbered positions move in the same manner as the shaping press pair  50 A. 
     When the shaping press pair  50 B following the shaping press pair  50 A, as illustrated in  FIGS. 22(   a ) to  22 ( c ), enters the second constant-speed path B, the punch  52  moves downward along the fourth guide path  84  while revolving in the direction X. After a slight delay from the downward movement of the punch  52 , the die  51  moves upward along the third guide path  83 . This causes the coil-end portion  42  to be released from the shaping press pair  50 B. When entering the second constant-speed path B, the shaping press pairs  50  disposed at the even-numbered positions move in the same manner as the shaping press pair  50 B. 
     In the manner, as described above, when each of the shaping press pairs  50 A to  50 D reaches the middle of the smaller circular section  71   b , the insulator-coated flat wire  30  is outputted from between the die  51  and the punch  42 . 
     When the shaping press pairs  50 A to  50 D are traveling on the second constant-speed path B (i.e., the smaller circular section  71   b  of the race  71 ), the interval between adjacent two thereof is kept constant. The retaining holes  61  of the rotary retainers  60 , as described above, have the first curved ends  61   a , thereby causing the adjacent two of the shaping press pairs  50 A to  50 D to be kept closest to each other for a long time. This ensures the stability in releasing the insulator-coated flat wire  30  from the shaping press pairs  50 A to  50 D. 
     After completion of the output step, the insulator-coated flat wire  30  will be the coil conductor which has the coil-end portions  42  and the in-slot portions  40  formed alternately in the lengthwise direction thereof. 
     The stator coil production method, as described above, offers the following advantages. 
     The input step of inputting the insulator-coated flat wire  30  into the stator coil production machine, the coil-end portion shaping step of shaping the coil-end portions  42  in the insulator-coated flat wire  30 , the in-slot portion shaping step of shaping the in-slot portions  40  in the insulator-coated flat wire  30 , and the output step of outputting the insulator-coated flat wire  30  from the stator coil production machine are performed in sequence while the shaping press pairs  50  which are arrayed at given intervals along the travel path in the stator coil production machine on which the insulator-coated flat wire  30  is to travel are being revolved about the axis of the stator coil production machine. Specifically, the coil-end portion  42  is formed by moving the die  51  and the punch  52  of one of the shaping press pairs  50  close to each other to clamp and press a portion of the insulator-coated flat wire  30 . Subsequently, the in-slot portion  40  is formed by bringing adjacent two of the shaping press pairs  50  one of which belongs to, for example, the one which have just finished the formation of the coil-end portion  42  close to each other and simultaneously moving one of the adjacent two of the shaping press pairs in the direction substantially perpendicular to the length of the insulator-coated conductor wire to press a portion of the insulator-coated conductor wire. In such a way, the coil-end portions  42  and the in-slot portion  40  are formed seamlessly in the insulator-coated flat wire  30 , thus resulting in, thus resulting in a decreased production time for the coil conductor and improvement on the productivity thereof. 
     The stator coil production machine is equipped with the two rail cams  70  in which the circular races  71  are formed. The circular races  71  serve to define the closed looped path. The shaping press pairs  50  circulates the closed looped path to press a plurality of insulator-coated flat wires  30  sequentially, thus resulting in improved efficiency in producing the coil conductors. 
     The stator coil production machine is of a cylindrical-surface circulation vertical type and has the die  51  and the punch  52  of each shaping press pair  50  which face each other across the travel path of the insulator-coated flat wire  30 . This permits the number of the shaping press pairs  50  required to shaping the in-slot portions  40  and the coil-end portions  42  to be minimized, thus allowing the size of the stator coil production machine and the production cost for the coil conductor to be decreased. 
     The stator coil production machine is, as described above, equipped with the shaping press pairs  50 B and  50 D which are located at the even-numbered positions and moved in the vertical direction perpendicular to the length of the insulator-coated flat wire  30  during the in-slot portion shaping step and the shaping press pairs  50 A and  50 C which are located at the odd-numbered positions and not moved in the vertical direction during the in-slot portion shaping step, thereby achieving the press operation on the insulator-coated flat wire  30  to form the in-slot portions  40 . 
     When the output step is entered, the die  51  and the punch  52  of the shaping press pairs  50  having reached near the outlet are brought away from each other to output the insulator-coated flat wire  30 , thereby ensuring the stability in releasing the insulator-coated flat wire  30  after the in-slot portions  40  are formed. 
     The thirteen shaping press pairs  50  are used in the above embodiment, but the required number of the shaping press pairs  50  is preferably determined based on the number of the coil-end portions  42  required to be formed in the insulator-coated flat wire  30 . 
       FIG. 23  illustrates a stator coil production machine according to the second embodiment which is of a horizontally circulation type in which the die  51  and the punch  51  of each shaping press pair  50  are arrayed horizontally so as to face each other across an oval travel path on which the insulator-coated flat wire  30  is to be circulated. The reference numbers as employed in the above embodiment will refer to the same parts, and explanation thereof in detail will be omitted here. 
     Specifically, the stator coil production machine is equipped with a plurality of plate cams  56  which are linked mechanically to each other and circulatable along the oval path. Each of the shaping press pairs  50  located at the even-numbered positions and each of the shaping press pairs  50  located at the odd-numbered positions are conveyed on rails (not shown) different from each other, like the guide paths  81  to  84  in the above first embodiment. The oval travel path has, as clearly illustrated in  FIG. 23 , two straight sections extending parallel to each other. A ball screw  67  (i.e., a mechanical linear actuator) extends along a lower one of the straight sections of the oval travel path, as viewed in the drawing. The ball screw  67  works as a movable retainer to retain and move the shaping press pairs  50  along the straight section of the oval travel path. The ball screw  67  includes a threaded shaft which has a helical raceway  67   a  formed on an outer periphery thereof. The shaping press pairs  50  are engageble with the helical raceway  67   a . Rotation of the ball screw  67  will cause the shaping press pairs  50  to be conveyed along the straight section of the oval travel path. 
     With revolving of the array of the plate cams  67 , some of the shaping press pairs  50  travel along the lower one (which will also be referred to as a bending section below) of the straight sections of the oval travel path to perform the step of bending the insulator-coated flat wire  30 . Specifically, the input step, the coil-end shaping step, the in-slot portion shaping step, and the output step are executed on the insulator-coated flat wire  30  in the straight section of the oval travel path. The interval or pitch (i.e., a screw pitch) between every adjacent two of the helical raceways  67   a  is, as can be seen in  FIG. 23 , is set smaller within an in-slot portion shaping range W where the in-slot portion shaping step is to be executed, so that every adjacent two of the shaping press pairs  50  are brought close to each other when entering the in-slot portion shaping range W. The stator coil production machine also includes pairs of cam blocks  85  (some of them are omitted for the simplicity of illustration) which are arrayed substantially parallel to the bending section of the oval travel path. The cam blocks  85  work to move the die  51  and the punch  52  closer to or away from each other. 
     The bending of the insulator-coated flat wire  30  is achieved by rotating the ball screw  67  to revolve all the shaping press pairs  50  along the oval travel path, inputting the insulator-coated flat wire  30  from an inlet (i.e., a leading portion of the bending section of the oval travel path) between the die  51  and the punch  52  of one of the shaping press pairs  50  which has entered the bending section of the oval travel path (i.e., the input step), and performing a sequence of the coil-end portion shaping step, the in-slot portion shaping step, and the output step in the same manner as described in the first embodiment. Specifically, in the coil-end portion shaping step, the die  51  and the punch  52  are brought close to each other by the cam blocks  85  to press a portion of the insulator-coated flat wire  30  into the coil-end portion  42 . In the in-slot portion shaping step, adjacent two of the shaping press pairs  50  are brought close to each other, while at the same time one of the two adjacent shaping press pairs  50  is moved in a direction perpendicular to the bending section of the oval travel path (i.e., the length of the insulator-coated flat wire  30 ), thereby pressing a portion of the insulator-coated flat wire  50  into the in-slot portion  40 . 
     The stator coil production machine of the second embodiment, like in the first embodiment, works to shape portions of the insulator-coated flat wire  30  into the coil-end portions  42  and the in-slot portions  40  seamlessly sequentially, thus resulting in a decreased production time for the coil conductor and improvement on the productivity thereof. 
       FIG. 24  is a perspective view which shows a modification of the stator coil production machine of  FIG. 23 . 
     The stator coil production machine is equipped with two ball screws  67  lying in the straight sections of the oval travel path. Specifically, the straight sections are used as bending sections where a sequence of the input step, the coil-end shaping step, the in-slot portion shaping step, and the output step are executed on the insulator-coated flat wire  30 . Other arrangements are identical with those in  FIG. 23 , and explanation thereof in detail will be omitted here. 
     While the present invention has been disclosed in terms of the preferred embodiment in order to facilitate better understanding thereof, it should be appreciated that the invention can be embodied in various ways without departing from the principle of the invention. Therefore, the invention should be understood to include all possible embodiments and modifications to the shown embodiments witch can be embodied without departing from the principle of the invention as set forth in the appended claims.