Abstract:
There is provided a winding to be wound at a stator of a rotary electric machine. The winding is produced from a flat wire having a rectangular cross section along a plane perpendicular to a length-wise direction. The flat wire is coated with an electric insulating layer and is bent to have curves at given portions of the flat wire in the length-wise direction. The curves are located on an axial outer side of the stator. The cross section of the flat wire has four corners, among which mutually-adjacent two corners are lager in curvatures than remaining mutually-adjacent two corners. The mutually-adjacent two corners whose curvatures are smaller are positioned on a circumferential outer side of each of the curves and the mutually-adjacent two corners whose curvatures are larger are positioned on a circumferential inner side of each of the curves.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a divisional of U.S. application Ser. No. 14/081,419 filed Nov. 15, 2013, which is based on and claims priority under 35 U.S.C. 119 from Japanese Patent Application No. 2012-250769 filed on Nov. 15, 2012, the entire contents of which are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    [Technical Field of the Invention] 
         [0003]    The present invention mainly relates to a stator winding for use in a rotary electric machine, and, in particular, to such a stator winding which is preferably used in a vehicle alternator. 
         [0004]    [Related Art] 
         [0005]    A stator winding based on conventional art for use in a rotary electric machine is formed, for example, by bending linear conductors that are applied with insulation coating. In bending the linear conductors, the insulation coating is expanded in the outer surface of a curve which is formed by bending each of the conductors. As a result, the insulation coating is sometimes problematically damaged (e.g., refer to patent document JP-B-4506895). 
         [0006]    In order to meet the recent needs of enhancing the performance of a rotary electric machine, a stator is required to increase the space factor in the slots. For this purpose, there is an increasing need of using a flat wire, as a material for forming a stator winding, which has a rectangular cross section. However, compared to a round wire having a circular cross section, a flat wire, when bent, causes a significant expansion in the insulation coating in the outer surface of the curve mentioned above, and accordingly has a high probability of suffering from damages in the insulation coating. Therefore, additional measures may have to be taken against this, such as increasing the thickness of the insulation coating of the flat wire, or reinforcing the insulation coating of the flat wire after being bent, or the like. 
         [0007]    Further, from a standpoint of reducing cost incurred in the materials, only round wires may be purchased and rolled into flat wires only when used for a stator winding that is required to achieve a high space factor. 
         [0008]    In this case, the coating characteristics will be impaired in the process of rolling the round wire into a flat wire. Therefore, the probability of damaging the insulation coating will become higher. 
       SUMMARY 
       [0009]    Hence, in consideration of the foregoing, it is desired to reduce the probability of damaging the insulation coating in the outer surfaces of curves of a flat wire that forms a stator winding. 
         [0010]    As one exemplary embodiment, there is provided a winding to be wound at a stator of a rotary electric machine. The winding is produced from a flat wire having a rectangular cross section along a plane perpendicular to a length-wise direction, being coated with an electric insulating layer, and being bent to have curves (or curved sections) at given portions of the flat wire in the length-wise direction, the curves being located on an axial outer side of the stator, wherein the cross section of the flat wire has four corners, among which mutually-adjacent two corners are lager in curvatures than remaining mutually-adjacent two corners, and the mutually-adjacent two corners whose curvatures are smaller than the others are positioned on a circumferential outer side of each of the curves and the mutually-adjacent two corners whose curvatures are larger than the others are positioned on a circumferential inner side of each of the curves. 
         [0011]    When a flat wire is bent, the amount of expansion of the flat wire varies depending on the portions, such as an inner portion or surfaces, of the flat wire. The amount of expansion becomes smaller as the curvature becomes smaller in the corners of the cross section of the flat wire. Therefore, the two smaller-curvature corners are ensured to reside in the outer surface of the curve mentioned above, in which the expansion is significant, to minimize the amount of expansion in the insulation coating in the outer surface. Thus, the probability of damaging the insulation coating is reduced in the outer surface of the curve of the stator winding that uses a flat wire as a material. 
         [0012]    In the following description, a flat wire in which the curvature of two adjacent corners in the cross section is larger than that of the remaining two corners, may be referred to as a deformed flat wire. Also, throughout the specification, when the term “cross section” is used, it refers to a cross section perpendicular to the longitudinal direction. 
         [0013]    As another embodiment, there is provided a method of manufacturing the winding according to the foregoing. The method includes preparing a round wire with electrically insulating coating, the round wire having a round section along a plane perpendicular to a length-wise direction thereof; and rolling the round wire at two stages a first rolling stage and a second rolling stage following the first rolling stage, at the first rolling stage of which the round wire is rolled into a deformed flat wire having an isosceles trapezoid cross section. 
         [0014]    Thus, further rolling is performed using the flat wire as an intermediate material having an isosceles trapezoid cross section, so that a deformed flat wire can be easily formed. Specifically, plastic flow is easily caused, by rolling, in between the legs of the isosceles trapezoid cross section, i.e. near the surface of a portion in which the length between the legs is large. Accordingly, the metal is permitted to plastically flow into the two corners which are desired to have large curvature, thereby easily forming a deformed flat wire. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    In the accompanying drawings: 
           [0016]      FIG. 1  is a partial perspective view illustrating a part of a stator, according to an embodiment of the present invention; 
           [0017]      FIG. 2  is a partial perspective view illustrating insertion of a wire segment into a slot; 
           [0018]      FIG. 3  is a perspective view illustrating a curved profile of the wire segment; 
           [0019]      FIG. 4  is a cross-sectional view taken along a line IV-IV of  FIG. 3 , and 
           [0020]      FIGS. 5A and 5B  are explanatory views illustrating a first rolling stage and a second rolling stage, respectively. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0021]    With reference to  FIGS. 1-5A and 5B , hereinafter is described a preferred embodiment of the present invention. 
         [0022]    With reference to the drawings, a configuration of a stator winding  1  of the embodiment is described. 
         [0023]    The stator winding  1  is obtained by connecting a number of wire segments  3  (hereinafter also just referred to as segments  3 ), each having a curve (or a curved section)  2 , in an electrically conductive manner. Specifically, the segments  3  before being connected are mounted to slots  5  of a stator core  4  and deformed. Then, predetermined connecting portions  6  of the respective segments  3  are connected to each other in an electrically conductive manner. In order to avoid complication, the connecting portions in the drawings are indicated by  6 Aa,  6 Ba,  6 Ab and  6 Bb, which will be described later, instead of being simply indicated by  6 . An integral body of the stator winding  1  and the stator core  4  provided in this way forms a stator  7  of a rotary electric machine. For example, the stator  7  is used in a vehicle alternator. 
         [0024]    Each segment  3  is formed of a flat wire having a rectangular cross section  11  and having a surface applied with an insulation coating  8 . For example, a flat wire is substantially bent into a shape of a V to form the curve (or the curved section)  2  at the bottom of the V shape. 
         [0025]    As shown in  FIG. 4  and  FIGS. 5A and 5B , the rectangular cross section  11  of the flat wire as a material of the segment  3  has four corners  12   a ,  12   b ,  12   c  and  12   d . Of these corners, the two adjacent corners  12   a  and  12   b  have a larger curvature than the remaining two corners  12   c  and  12   d . In short, the flat wire is a deformed flat wire. In cases where each of the four corners  12   a ,  12   b ,  12   c  and  12   d  is produced as part of a circle of a radius r, the curvature is defined as 1/r. 
         [0026]    Specifically, for example, as shown in  FIGS. 3 and 4 , the rectangular cross section  11  of the deformed flat wire as a material of the segment  3  has two short sides  13   a  and  13   b  that are parallel to each other. Of these short sides  13   a  and  13   b , one short side  13   a  has the two corners  12   a  and  12   b  whose curvature CV 1  is made larger than that CV 2  of the two corners  12   c  and  12   d  of the other short side  13   b  (refer to  FIG. 4 ). As shown in  FIGS. 2 and 3 , each of the curves  2  is made to have a circumferential direction CR and a radial direction RA. For example, the short side  13   a  is ensured to reside in the inner surface of the curve  2  in the radial direction RA and the short side  13   b  is ensured to reside in the outer surface of the curve  2  in the radial direction RA. 
         [0027]    Each segment  3  includes a V-shaped portion  15  and two linear portions  16  extending parallel to each other from the ends of the V-shaped portion  15  to display line symmetry (see  FIGS. 2 and 3 ). The V-shaped portion  15  functions as an intermediate portion connecting the two linear portions. In order to avoid complication, the linear portions in the drawings are indicated by  16 Aa,  16 Ba,  16 Ab and  16 Bb, which will be described later, instead of being simply indicated by  16 . 
         [0028]    Two types of the segment  3  are used here, one type being a segment  3 A having the curve  2  of a larger curvature, and the other type being a segment  3 B having the curve  2  of a smaller curvature. The curve  2  of the segment  3 A is arranged confronting the inner surface of the curve  2  of the segment  3 B. The segments  3 A and  3 B, when inserted into the slots  5 , form a single wire unit  17  (hereinafter also just referred to as unit  17 ). In the embodiment, the curve  2  is twisted so that both linear portions of each segment are allowed to be inserted at different layers (levels) of the respective slots  5 , as shown in  FIG. 2 . Hence, the circumferential direction of each curve  2  is not parallel with that of the stator 
         [0029]    In one unit  17 , the linear portions  16  on one side A of the curves  2  of the respective segments  3 A and  3 B are inserted into a slot  5  so as to be located radially inward of the slot, while the linear portions  16  on the other side B of the curves  2  are inserted into another slot  5  so as to be located radially outward of the slot (see FIG.  2 ). Hereinafter, of the two linear portions  16  of the segment  3 A, the one located radially inward of the slot  5  is referred to as a linear portion  16 Aa, and the one located radially outward of another slot  5  is referred to as a linear portion  16 Ab. Also, of the two linear portions  16  of the segment  3 B, the one located radially inward of the slot  5  is referred to as a linear portion  16 Ba, and the one located radially outward of another slot  5  is referred to as a linear portion  16 Bb. 
         [0030]    The slot  5  into which the linear portions  16 Aa and  16 Ba are inserted is different from the slot  5  into which the linear portions  16 Ab and  16 Bb are inserted. 
         [0031]    These two slots  5  are interposed by two different slots  5 . Specifically, the unit  17  is outstretched on both sides of the curve  2  in the circumferential direction and inserted into the stator core  4 , bridging three teeth  20 . The linear portions  16 Aa,  16 Ba,  16 Ab and  16 Bb of the unit  17  have respective folds  19  which are parallel to long sides  18  of the rectangular cross section  11 . The linear portions  16 Aa,  16 Ba,  16 Ab and  16 Bb are bent at the respective folds  19  (see  FIG. 4  and  FIGS. 5A and 5B ). 
         [0032]    The linear portions  16 Aa,  16 Ba,  16 Ab and  16 Bb have respective end portions which are projected from the slots  5  in the axial direction, i.e. projected in a direction opposite to the curve  2 , to form the respective connecting portions  6 . Here, the connecting portions  6  at the ends of the linear portions  16 Aa,  16 Ba,  16 Ab and  16 Bb are designated as connecting portions  6 Aa,  6 Ba,  6 Ab and  6 Bb, respectively. The connecting portion  6 Aa is connected, in an electrically conductive manner, to the connecting portion  6 Ba of a unit  17  which is inserted into a slot  5 , being interposed by three teeth  20  on the one side A in the circumferential direction. 
         [0033]    The connecting portion  6 Ba is connected, in an electrically conductive manner, to the connecting portion  6 Aa of a unit  17  which is inserted into a slot  5 , being interposed by three teeth  20  on the other side B in the circumferential direction. The connecting portion  6 Ab is connected, in an electrically conductive manner, to the connecting portion  6 Bb of a unit  17  which is inserted into a slot  5 , being interposed by three teeth  20  on the other side B in the circumferential direction. The connecting portion  6 Bb is connected, in an electrically conductive manner, to the connecting portion  6 Ab of a unit  17  which is inserted into a slot  5 , being interposed by three teeth  20  on the one side A in the circumferential direction. 
         [0034]    Thus, in the stator  7 , the end portions of the linear portions  16 Aa,  16 Ba,  16 Ab and  16 Bb and the V-shaped portions  15  form coil ends axially projected from both axial sides of the stator core  4 . Then, a rotor is arranged radially inside of the stator  7  to thereby form a rotary electric machine. 
         [0035]    Referring to  FIGS. 5A and 5B , hereinafter is described a method of fabricating the stator winding  1  of the embodiment, in particular, a method of forming the deformed flat wire that is a material of the wire segment  3 . 
         [0036]    The deformed flat wire is fabricated by rolling a round wire applied with insulation coating and having a circular cross section. In the rolling, the round wire is rolled in two stages (two-stage rolling) using various rollers  22 . In the following description, the material supplied in a first rolling stage performed firstly may be referred to as an initial material  23 . Also, the material resulting from the first rolling stage may be referred to as an intermediate material  24 . Further, the material resulting from a second rolling stage may be referred to as a final material  25 . 
         [0037]    First, a round wire is prepared as the initial material  23 , and then the intimal material  23  is subjected to the first rolling stage. 
         [0038]    In the first rolling stage, a round wire as the initial material  23  is rolled into a flat wire as the intermediate material  24  whose cross section is in an isosceles trapezoid shape. Then, in the second rolling stage, the intermediate material  24  is rolled into a deformed flat wire as the final material  25 . In a isosceles trapezoid cross section  27  of the intermediate material  24 , two bases  28   a  and  28   b  substantially parallel to each other correspond to the short sides  13   a  and  13   b , respectively, in the rectangular cross section  11  of the final material  25 . Similarly, two legs  29  correspond to the long sides  18  in the rectangular cross section  11 . 
         [0039]    Further, of the two bases  28   a  and  28   b , the longer base  28   a  has two corners  30   a  and  30   b  which correspond to the two corners  12   a  and  12   b  (i.e., two first corners), respectively, having a larger curvature in the rectangular cross section  11 . The shorter base  28   b  has two corners  30   c  and  30   d  which correspond to the two corners  12   c  and  12   d  (i.e., two second corners), respectively, having a smaller curvature in the rectangular cross section  11 . 
         [0040]    In the second rolling stage, a portion  32  is chiefly subjected to rolling. The portion  32  is a portion near the base  28   a , in which the length between the legs  29  is large. Also, in the second rolling stage, the deformation volume of the intermediate material  24  is larger in the portion  32  near the base  28   a  between the legs  29 , than in a portion near the base  28   b . Therefore, camber is likely to be caused in the final material  25  in which the short sides  13   a  and  13   b  reside in the outer and inner surfaces, respectively. For this reason, in the second rolling stage, the rollers  22  are arranged to minimize the occurrence of camber. 
         [0041]    The stator winding  1  of the embodiment uses a deformed flat wire as the final material  25 . The deformed flat wire is bent to form the curve  2 . In bending the deformed flat wire, the two smaller-curvature corners  12   c  and  12   d  are ensured to reside in the outer surface of the curve  2 , and the two larger-curvature corners  12   a  and  12   b  are ensured to reside in the inner surface of the curve  2 . 
         [0042]    Thus, the two smaller-curvature corners  12   c  and  12   d  are permitted to reside in the outer surface of the curve  2 , in which the insulation coating  8  is significantly expanded by the bending. With this configuration, expansion of the insulation coating  8  is minimized in the outer surface of the curve  2 . As a result, the probability of damaging the insulation coating  8  is reduced in the outer surface of the curve  2  of the stator winding  1  that uses a flat wire as a material. 
         [0043]    The deformed flat wire as the final material  25  is fabricated by rolling a round wire as the initial material  23  in two stages, the round wire having a circular cross section and applied with insulation coating. In the preceding first rolling stage, the round wire is rolled into the intermediate material  24  whose cross section is in an isosceles trapezoid shape. 
         [0044]    Thus, the intermediate material  24  having a cross section in an isosceles trapezoid shape is subjected to rolling to thereby easily form a deformed flat wire as the final material  25 . Specifically, plastic flow is easily caused, by rolling, in between the legs  29  of the isosceles trapezoid cross section, i.e. near the surface of the portion  32  in which the length between the legs  29  is large. Accordingly, the metal is permitted to plastically flow into the two corners  30   a  and  30   b  which are desired to have large curvature, thereby easily forming a deformed flat wire. 
         [0045]    The two-stage rolling is performed with the sequential transition of the material from the initial material  23  to the intermediate material  24  and further to the final material  25 . In this two-stage rolling, the final material  25  can be formed without having to do so much rolling in the intermediate material  24  with respect to the two corners  30   c  and  30   d  which are desired to have smaller curvature. Thus, compared to the case where the initial material  23  is rolled into the final material  25  without forming the intermediate material  24 , the probability of damaging the insulation coating is further reduced in the corners  30   c  and  30   d.    
         [0046]    [Modifications] 
         [0047]    The mode of the stator winding  1  and a method of fabricating the same is not limited to the embodiment described above, but may be variously modified. 
         [0048]    For example, according to the fabrication method of the embodiment, the stator winding  1  is rolled in two stages. Alternative to this two-stage rolling, a single-stage rolling may be performed in which the deformed flat wire as the final material  25  is fabricated from the round wire as the initial material  23 , without forming the intermediate material  24 . In this case, the number of the stages is reduced and the cost incurred in the fabrication is reduced. 
         [0049]    The present invention may be embodied in several other forms without departing from the spirit thereof. The embodiment and modifications described so far are therefore intended to be only illustrative and not restrictive, since the scope of the invention is defined by the appended claims rather than by the description preceding them. All changes that fall within the metes and bounds of the claims, or equivalents of such metes and bounds, are therefore intended to be embraced by the claims.