Abstract:
A method of manufacturing a stator core for a dynamo-electric machine by preparing a cylindrical laminated body by winding into a helical shape a continuous first sheet formed by press-punching from a strip-shaped first magnetic steel sheet material, preparing a plurality of second sheets by press-punching from a thicker second magnetic steel sheet material, bending the second sheets into an annular shape and stacking the second sheets bent into the annular shape on both axial ends of the laminated body and integrating the stacked sheets by laser welding.

Description:
This is a divisional of application Ser. No. 10/430,327 filed May 7, 2003 now abandoned. The entire disclosure of the prior application, application Ser. No. 10/430,327 is considered part of the disclosure of the accompanying divisional application and is hereby incorporated by reference. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a method for manufacturing a stator core for a dynamoelectric machine such as an automotive alternator, for example, and particularly to a method for manufacturing a stator core formed by laminating a press-formed magnetic steel sheet material. 
   2. Description of the Related Art 
     FIG. 8  is a plan explaining a process for forming a laminated body by a first sheet in a conventional stator for an automotive alternator described in Japanese Patent Laid-Open No. 2001-112197 (Gazette), for example,  FIG. 9  is a cross section taken along line IX-IX in  FIG. 8  viewed from the direction of the arrows,  FIG. 10  is a plan showing a second sheet in the conventional stator for an automotive alternator,  FIG. 11  is a cross section taken along line XI-XI in  FIG. 10  viewed from the direction of the arrows,  FIG. 12  is an exploded perspective showing a process for inserting conductor segments into a stator core in the conventional stator for an automotive alternator, and  FIG. 13  is a partial cross section explaining a mounted state of a stator winding in the conventional stator for an automotive alternator. 
   A conventional stator  1  is constituted by: a cylindrical stator core  2  in which slots  3  are formed at a predetermined pitch in a circumferential direction so as to open onto an inner circumferential side; a stator winding  4  installed in the slots  3  of the stator core  2 ; and insulators  5  mounted inside each of the slots  3 . 
   The stator core  2  is provided with: a laminated body  7  constituted by a first sheet  6 ; and second sheets  8  disposed at first and second axial ends of the laminated body  7 . 
   As shown in  FIG. 8 , the laminated body  7  is formed into a cylindrical shape by winding up the first sheet  6  for a predetermined number of winds into a helical shape, the first sheet  6  being formed by using a press die to punch recess portions  6   a  at a predetermined pitch in a strip-shaped magnetic steel sheet material. Here, the recess portions  6   a  are superposed in an axial direction of the laminated body  7 , constituting first slot portions  3   a . In the laminated body  7 , the first sheet  6  is laminated with the press punch direction aligned, as shown in  FIG. 9 , and burrs  6   b  extending in the press punch direction remain on each layer of the first sheet  6  on inner wall surfaces of the first slot portions  3   a.    
   As shown in  FIG. 10 , the second sheets  8  are each formed into an annular shape by using a press die to punch a flat sheet composed of a magnetic steel sheet material having a sheet thickness greater than that of the first sheet  6 . Here, second slot portions  3   b  corresponding in position to the first slot portions  3   a  are simultaneously press-formed. As shown in  FIG. 11 , chamfered portions  8   a  are formed on edge portions of the second slot portions  3   b  on a first end side of the second sheets  8 . Moreover, the second sheets  8  are formed so as to be equal in diameter to the laminated body  7 . 
   The second sheets  8  are disposed at first and second end surfaces of the laminated body  7  such that the positions of the first slot portions  3   a  and the second slot portions  3   b  align and the chamfered portions  8   a  face away from the laminated body  7 , and the stator core  2  is prepared by applying several strips of laser welding so as to extend in an axial direction from a first end portion to a second end portion on the outer circumferential surfaces thereof. Moreover, the first and second slot portions  3   a  and  3   b  align in an axial direction, constituting the slots  3 . 
   As shown in  FIGS. 12 and 13 , the stator winding  4  is constructed using a plurality of conductor segments  9  by joining together end portions of the conductor segments  9  by a joining method such as welding, etc. The conductor segments  9  are each prepared by bending into a U shape a short length of copper wire having an electrically-insulating coating. Here, large and small first and second conductor segments  9   a  and  9   b  form a basic unit and a plurality of these units are used. The conductor segments  9  are housed in the slots  3  so as to be surrounded by the insulators  5  such that the insulators  5  are interposed between the conductor segments  9  and inner wall surfaces of the slots  3 . Together with the electrically-insulating coating covering the copper wire of the conductor segments  9 , these insulators  5  ensure electrical insulation between the conductor segments  9  and the stator core  2 . 
   The conductor segments  9  and the insulators  5  are inserted into the slots  3  of the stator core  2  in a direction aligned with the press punch direction of the first sheet  6 , in other words, from top to bottom in  FIG. 13 . The stator winding  4  is prepared by bending first end portions of the conductor segments  9  extending outward from the slots  3  of the stator core  2  as indicated by the arrow in  FIG. 13  and joining the first end portions to second end portions of conductor segments  9  separated by a predetermined pitch. 
   In the conventional stator  1  constructed in this manner, because the second sheets  8  having a thick sheet thickness are disposed on the first and second axial end portions of the laminated body  7 , the rigidity of the stator core  2  is increased. Thus, the occurrence of deformation and peeling of the first sheet  6  having a thin sheet thickness is prevented during insertion of the conductor segments  9 . When the stator  1  is fixed by being held from first and second axial ends by a frame, the occurrence of warping in outer circumferential portions of the stator core  2  is reliably prevented. Because the rigidity of the stator core  2  is increased, the sheet thickness of the first sheet  6  constituting the laminated body  7  can be reduced. Thus, iron loss which is proportional to the square of the sheet thickness of the steel sheets is reduced, enabling increased efficiency to be achieved in the dynamoelectric machine. 
   Because opening edge portions of the slots  3  at the first and second axial end surfaces of the stator core  2  are constituted by the chamfered portions  8   a  of the second sheets  8 , damage to the electrically-insulating coating of the conductor segments  9  caused by the burrs  6   b  is avoided during insertion of the conductor segments  9 , during bending or joining of the end portions of the conductor segments  9 , and during shaping of coil ends of the stator winding  4  after joining of the conductor segments  9 , thereby improving electrical insulation. 
   In the conventional stator for an automotive alternator, because the stator core  2  is prepared, as described above, by preparing the laminated body  7  by winding the strip-shaped first sheet  6  in which the recess portions  6   a  (the first slot portions  3   a ) are formed by press-punching into a helical shape for a predetermined number of winds, preparing the thick annular second sheets  8  in which the second slot portions  3   b  are formed by press-punching, forming the chamfered portions  8   a  on the edge portions of the second slot portions  3   b  of the second sheets  8  by chambering, disposing the faced second sheets  8  at first and second ends of the laminated body  7 , and integrating the laminated body  7  and the second sheets  8  by welding, the following problems arise, preventing cost reductions: 
   First, because the annular second sheets  8  are prepared from a flat magnetic steel sheet material by press-punching, the second sheets  8  cannot be prepared from the magnetic steel sheet material efficiently, increasing the amount of magnetic steel sheet material. 
   Second, because the chamfered portions  8   a  are formed on the edge portions of the second slot portions  3   b  by chambering the annular second sheets  8 , slot opening portions are narrow, lowering chambering precision, thereby lowering yield. 
   SUMMARY OF THE INVENTION 
   The present invention aims to solve the above problems and an object of the present invention is to provide a method for manufacturing a stator core for a dynamoelectric machine enabling cost reductions to be achieved by preparing a second sheet constituting an end plate in a straight shape by press-punching and preparing an annular end plate by bending the straight second sheet to prepare the end plate from a magnetic steel sheet material efficiently and suppress increases in material quantities, and in addition, by forming an chamfered portion on an edge portion of a recess portion by chambering the straight second sheet to increase chambering precision and enable improved yield. 
   With the above object in view, according to one aspect of the present invention, there is provided a method for manufacturing a stator core for a dynamoelectric machine, the method including the step of preparing a cylindrical laminated body by preparing a continuous first sheet in which first recess portions are formed at a predetermined spacing by press-punching from a strip-shaped first magnetic steel sheet material and winding the first sheet into a helical shape such that the first recess portions are superposed in an axial direction. Also, the method includes the step of preparing a second sheet having a predetermined length in which second recess portions are formed at a predetermined spacing by press-punching a second magnetic steel sheet material having a sheet thickness greater than that of the first magnetic steel sheet material. Further, the method includes the steps of bending the second sheet into an annular shape, stacking the second sheets bent into the annular shape on both axial ends of the laminated body such that the second recess portions are superposed on the first recess portions in an axial direction, and integrating the laminated body and the second sheets stacked together by applying several strips of welding on an outer circumferential surface of the laminated body and the second sheets so as to extend from a first end to a second end in an axial direction. 
   Therefore, the method enables the second sheet for an end plate to be prepared from the second magnetic sheet material efficiently, thereby enabling cost reduction to be achieved. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective showing a stator for an automotive alternator using a stator core manufactured by a method for manufacturing a stator core according to Embodiment 1 of the present invention; 
       FIG. 2  is a perspective showing the stator core manufactured by the method for manufacturing a stator core according to Embodiment 1 of the present invention; 
       FIG. 3  is a cross section taken along line III-III in  FIG. 2  viewed from the direction of the arrows; 
       FIG. 4  is a perspective explaining the method for manufacturing a stator core according to Embodiment 1 of the present invention; 
       FIG. 5  is a perspective explaining the method for manufacturing the stator core manufactured by the method for manufacturing a stator core according to Embodiment 1 of the present invention; 
       FIG. 6  is a perspective explaining the method for manufacturing the stator core manufactured by the method for manufacturing a stator core according to Embodiment 1 of the present invention; 
       FIG. 7  is a perspective showing a stator core manufactured by a method for manufacturing a stator core according to Embodiment 2 of the present invention; 
       FIG. 8  is a plan explaining a process for forming a laminated body by a first sheet in a conventional stator for an automotive alternator; 
       FIG. 9  is a cross section taken along line IX-IX in  FIG. 8  viewed from the direction of the arrows; 
       FIG. 10  is a plan showing a second sheet in the conventional stator for an automotive alternator; 
       FIG. 11  is a cross section taken along line XI-XI in  FIG. 10  viewed from the direction of the arrows; 
       FIG. 12  is an exploded perspective showing a process for inserting conductor segments into a stator core in the conventional stator for an automotive alternator; and 
       FIG. 13  is a partial cross section explaining a mounted state of a stator winding in the conventional stator for an automotive alternator. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Preferred embodiments of the present invention will now be explained with reference to the drawings. 
   Embodiment 1 
     FIG. 1  is a perspective showing a stator for an automotive alternator using a stator core manufactured by a method for manufacturing a stator core according to Embodiment 1 of the present invention,  FIG. 2  is a perspective showing the stator core manufactured by the method for manufacturing a stator core according to Embodiment 1 of the present invention,  FIG. 3  is a cross section taken along line III-III in  FIG. 2  viewed from the direction of the arrows, and  FIGS. 4 to 6  are perspectives explaining the method for manufacturing a stator core according to Embodiment 1 of the present invention. 
   In  FIGS. 1 to 3 , a stator  10  is constituted by: a cylindrical stator core  11  in which slots  12  are formed at a predetermined pitch in a circumferential direction so as to open onto an inner circumferential side; and a stator winding  13  installed in the slots  12  of the stator core  11 . 
   The stator core  11  is constructed by laminating a pair of end plates  17  composed of a magnetic steel sheet onto first and second axial ends of a laminated body  16  formed by laminating a magnetic steel sheet material and integrating by laser welding, for example. 
   The stator winding  13  is prepared by mounting three winding phase portions  15  into groups of the slots  12  so as to be offset by one slot each, each winding phase portion  15  being formed by installing one conductor wire  14  composed of a copper wire coated with an electrical insulator into a wave winding in every third slot  12 . Each of the winding phase portions  15  is formed by preparing an annular unit by winding one conductor wire  14  for a predetermined number of winds, preparing a star-shaped unit by shaping the annular unit into a star shape, and mounting the star-shaped unit into the slots  12  of the stator core  11 . 
   Next, a method for manufacturing the stator core  11  will be explained. 
   First, a single-strip first sheet  20  in which first recess portions  20   a  are formed at a predetermined pitch is prepared by press-forming a hoop material composed of a first magnetic steel sheet material having a thickness of 0.50 mm, for example, using a press die. Then, as shown in  FIG. 4 , the cylindrical laminated body  16  is prepared by winding the first sheet  20  into a helical shape for a predetermined number of winds. At this time, the first recess portions  20   a  are superposed in an axial direction of the laminated body  16  to constitute the slots  16   a.    
   Second sheets  21  having a predetermined length in which second recess portions  21   a  are formed at a predetermined pitch are each prepared by press-forming a flat plate composed of a second magnetic steel sheet material having a thickness of 1.00 mm, for example, using a press die. Here, the length of the second sheets  21  is equivalent to the circumferential length of the stator core  11 . Next, as shown in  FIG. 5 , these straight second sheets  21  are faced using a press die to form chamfered portions  21   b  on edge portions of the second recess portions  21   a  on a first surface side of each of the second sheets  21 . Then, the second sheets  21  formed with the chamfered portions  21   b  are each bent into an annular shape. In addition, annular end plates  17  are prepared by abutting first and second end surfaces of the second sheets  21  and joining the abutted portions  21   c  by tungsten inert-gas (TIG) welding. 
   Next, the pair of end plates  17 , as shown in  FIG. 6 , are superposed onto the first and second axial end portions, respectively, of the laminated body  16  such that the chamfered portions  21   b  face outward and the second recess portions  21   a  are aligned with the slots  16   a . The stator core  11  shown in  FIG. 2  is prepared by applying several strips of laser welding (weld portions  18 ) on outer circumferential surfaces thereof so as to extend in an axial direction from the first end portion to the second end portion. Moreover, the slots  16   a  and the second recess portions  21   a  line up in an axial direction to constitute the slots  12 . 
   As shown in  FIG. 3 , burrs  20   b  extending in the press punch direction remain on each layer of the first sheet  20  on inner wall surfaces of the slots  12  of the stator core  11 . A powdered form of an electrically-insulating resin such as an epoxy resin, for example, is electrostatically coated onto the stator core  11 , then melted by heating, the electrically-insulating resin being formed so as to cover the entire surface of the stator core  11 . 
   In the stator  10  constructed in this manner, opening edge portions of the slots  12  at the first and second end surfaces of the stator core  11  are constituted by the chamfered portions  21   b , and the burrs  20   b  formed by press-punching are present only inside the slots  12 . Thus, damage to the electrically-insulating coating of the conductor wires  14  caused by the burrs  20   b  is avoided during mounting of the stator winding  13  and during shaping of coil ends of the stator winding  13 , thereby improving electrical insulation. 
   Because end plates  17  having a thick sheet thickness are disposed on the first and second end portions of the stator core  11 , the rigidity of the stator core  11  is increased. Thus, the occurrence of deformation and peeling of the first sheet  20  having a thin sheet thickness is prevented during insertion of the stator winding  13 . When the stator  10  is fixed by being held from first and second axial ends by a frame, the occurrence of warping in outer circumferential portions of the stator core  11  is reliably prevented. In addition, because the rigidity of the stator core  11  is increased, the sheet thickness of the first sheet  20  constituting the laminated body  16  can be reduced. Thus, iron loss which is proportional to the square of the sheet thickness of the steel sheets is reduced, enabling increased efficiency to be achieved in the dynamoelectric machine. 
   Because the end plates  17  are prepared by joining together the abutted portions  21   c  of the second sheets  21  by TIG welding, magnetic flux can be passed through the end plates  17  effectively, enabling output to be stabilized. 
   Because the laminated body  16  constituting the stator core  11  is prepared by winding into a helical shape a single-strip first sheet  20  formed by pressing a hoop material composed of the first magnetic steel sheet material, the first sheet  20  can be prepared from the first magnetic steel sheet material efficiently, enabling the amount of magnetic material used to be reduced, thereby enabling cost reductions. 
   Because the end plates  17  constituting the stator core  11  are prepared by bending into an annular shape second sheets  21  having a predetermined length formed by pressing a flat plate composed of the second magnetic steel sheet material, then TIG welding the first and second end surfaces of the bent second sheets  21  placed in contact with each other, the second sheets  21  can be prepared from the second magnetic steel sheet material efficiently. In this case, five times as many end plates  17  can be prepared as when the annular end plates are press-formed directly from the second magnetic steel sheet material, significantly reducing the amount of magnetic material used, thereby enabling cost reductions. Furthermore, because the abutted portions  21   c  of the second sheets  21  are joined together, handling of the end plates  17  is facilitated when the end plates  17  are being superposed onto the laminated body  16 , improving manufacture. 
   When the chamfered portions are formed by chamfering annular end plates, as in the related art, the slot opening portions are narrow, making it hard to perform high-precision chamfering, thereby reducing yield. According to Embodiment 1, because the chamfered portions  21   b  are formed on the edge portions of the second recess portions  21   a  by chamfering the straight second sheets  21 , the slot opening portions are wide, making high-precision chamfering possible, thereby enabling reliability to be increased. 
   Moreover, in Embodiment 1 above, the abutted portions  21   c  of the second sheets  21  are joined together by TIG welding, but the abutted portions  21   c  of the second sheets  12  do not necessarily have to be joined together; the first and second end surfaces of the second sheets  21  constituting the abutted portions  21   c  through which magnetic flux flows need only be placed in contact with each other. 
   In Embodiment 1 above, the stator winding  13  is constructed by preparing annular units by winding single conductor wires  14  each composed of a copper wire coated with an electrical insulator for a predetermined number of winds, preparing star-shaped units by shaping the annular units into a star shape, and mounting the star-shaped units into the slots  12  of the stator core  11 , but the stator winding is not limited to this construction and it goes without saying that the stator winding may also be constructed using the conductor segments  9  shown in the conventional technique. 
   In Embodiment 1 above, insulators are not mounted to the slots  12 , but it goes without saying that insulators may be mounted to each of the slots  12 . 
   Embodiment 2 
   In a stator core  11 A according to Embodiment 2, as shown in  FIG. 7 , the abutted portions  21   c  of the second sheets  21  constituting the end plates  17  are aligned with one of several strip-shaped weld portions  18  integrating the laminated body  16  and the end plates  17 . In other words, the abutted portions  21   c  are joined together simultaneously when laser welding is applied in order to integrate the laminated body  16  and the end plates  17 . 
   Moreover, the rest of this embodiment is constructed in a similar manner to Embodiment 1 above. 
   A method for manufacturing the stator core  11 A will now be explained. 
   First, a single-strip first sheet  20  in which first recess portions  20   a  are formed at a predetermined pitch is prepared by press-forming a hoop material composed of a first magnetic steel sheet material having a thickness of 0.35 mm, for example, using a press die. Then, the cylindrical laminated body  16  is prepared by winding the first sheet  20  into a helical shape for a predetermined number of winds. 
   Second sheets  21  having a predetermined length in which second recess portions  21   a  are formed at a predetermined pitch are each prepared by press-forming a flat plate composed of a second magnetic steel sheet material having a thickness of 0.80 mm, for example, using a press die. Next, these second sheets  21  are faced using a press die to form chamfered portions  21   b  on edge portions of the second recess portions  21   a  on a first surface side of each of the second sheets  21 . Then, the second sheets  21  formed with the chamfered portions  21   b  are each bent into an annular shape. 
   Next, the second sheets  21  which have been bent into an annular shape and in which the first and second end surfaces are abutted are superposed onto the first and second axial end portions, respectively, of the laminated body  16  such that the chamfered portions  21   b  face outward and the second recess portions  21   a  are aligned with the slots  16   a . The stator core  11 A shown in  FIG. 7  is prepared by applying several strips of laser welding (weld portions  18 ) on outer circumferential surfaces thereof so as to extend in an axial direction from the first end portion to the second end portion. Here, one of the strips of laser welding is applied at the position of the abutted portions  21   c  of the second sheets  21 . Thus, the second sheets  21  are joined together at the abutted portions  21   c  to form the end plates  17 . 
   In addition, a powdered form of an electrically-insulating resin such as an epoxy resin, for example, is electrostatically coated onto the stator core  11 A, then melted by heating, the electrically-insulating resin being formed so as to cover the entire surface of the stator core  11 A. 
   Consequently, similar effects to those in Embodiment 1 above can also be achieved in Embodiment 2. 
   In Embodiment 2, because the abutted portions  21   c  of the second sheets  21  constituting the end plates  17  are joined together simultaneously when laser welding is applied to integrate the laminated body and the end plates, a single welding process is sufficient, thereby simplifying the manufacturing process. 
   Moreover, because the first and second end surfaces of the second sheets  21  in the end plates  17  are placed in contact at the abutted portions  21   c , the flow of the magnetic flux is not inhibited. Furthermore, in addition to the outer circumferential surface of the second sheets  21 , the abutted portions  21   c  may also be welded on the end surfaces on an opposite side from the laminated body  16  during laser welding. In that case, magnetic flux can be passed through the end plates  17  effectively, enabling output to be stabilized.