Abstract:
A stator of a vehicle AC generator includes a stator core having a plurality of slots and a stator winding having a plurality of circumferentially aligned U-shaped conductor segments. One group of the U-shaped conductor segments have first turn portions and another group of U-shaped conductor segments have second turn portions enclosed by the first turn portions. The first turn portions and the second turn portions are shifted from one another in the circumferential direction to provide a distance therebetween for insulation as well as cooling air.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application is based on and claims priority from Japanese Patent Application Hei 10-335640 filed on Nov. 26, 1998, the contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an AC generator for a vehicle and, particularly, a stator winding arrangement thereof. 
     2. Description of the Related Art 
     WO92/06527 discloses an ac generator&#39;s stator having U-shaped conductor segments inserted into respective stator&#39;s slots from an end of a stator core so that turn portions can be disposed circumferentially at one end of the stator. As the number of the conductor segments disposed in each slot increases, the number of the turn portions increases. In the stator having four conductor members in each slot, two conductor members are disposed at the front of the slot and two conductor members are disposed at the rear of the slot. Two conductor members extending from one slot in the same circumferential direction have respective turn portions aligned circumferentially. Therefore, as the number of the aligned turn portions increases the distance therebetween decreases, thereby making cooling effect of the stator winding worse. In other words, as the distance between the aligned turn portions decreases, cooling air supplied by an inside cooling fan can not smoothly flow from radially outward between the turn portions. 
     SUMMARY OF THE INVENTION 
     A main object of the invention is to provide an improved stator having conductor segments that can be cooled effectively. 
     According to an aspect of the invention, a stator of a vehicle AC generator includes a stator core having a plurality of slots and a stator winding including a plurality of circumferentially aligned U-shaped conductor segments. 
     The conductor segments are grouped into two: first segments having first turn portions, and second segments having second turn portions which are enclosed by the first turn portions. The first turn portions and second turn portions are shifted from one another in the circumferential direction. 
     In the stator, each of the first segments has two inclined portions having the same length which respectively extend from two slots and join together at the first turn portion, and each of the second segments has two inclined portions having different lengths which respectively extend from two slots and join together at the second turn portion. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects, features and characteristics of the present invention as well as the functions of related parts of the present invention will become clear from a study of the following detailed description, the appended claims and the drawings. In the drawings: 
     FIG. 1 is a partially cross-sectional side view of an ac generator for a vehicle according to a preferred embodiment of the invention; 
     FIG. 2 is a fragmentary cross-sectional plan view of a stator of the ac generator according to the preferred embodiment of the invention; 
     FIG. 3 is a perspective view of a pair of U-shaped conductor segments of the ac generator according to the preferred embodiment; 
     FIG. 4 is a fragmentary schematic side view of the stator; 
     FIG. 5 is a fragmentary schematic front view of the stator; 
     FIG. 6 is a fragmentary schematic side view of a variation of the stator; and 
     FIG. 7 is a fragmentary schematic side view of another variation of the stator. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In FIG. 1, an AC generator  1  includes stator  2 , rotor  3 , frame  4 , rectifier  5  and others. 
     Stator  2  includes stator core  22 , a plurality of base segment units  23  and insulators  24  insulating conductor segments  23  from stator core  22 . 
     Rotor  3  includes field coil  8  formed of a cylindrically wound magnet wire and a pair of front and rear pole cores  7  each of which has six claw poles extending to enclose field coil  8 . A mixed flow cooling fan  11  is welded by a welder to the front surface of front pole core  7 , and a centrifugal cooling fan  12  is welded to the rear surface of rear pole core  7 . 
     Frame  4  accommodates stator  2  and rotor  3 . Rotor  3  is supported by frame  4  to be rotatable with shaft  6  and disposed inside stator  2  spaced at a prescribed air gap. Frame  4  has a plurality of air-intake windows  42  at portions opposite coil-ends of the stator winding and a plurality of air-discharge windows  41 . 
     AC generator  1  is rotated by pulley  20 , which is driven by an engine (not shown) through a belt. When field coil  8  is energized by an outside electric source, the claw poles of pole cores  7  are excited, so that three-phase electric voltage is generated in the stator winding and converted into a DC power by rectifier  5 . 
     In FIGS. 2 and 3, the stator winding is disposed in the plurality of slots and is composed of a plurality of sets of an even number (e.g. four) of conductor members each slot. One set of four conductor members in one slot is, as shown in FIG. 2, has four conductor members aligned in four radial layers: innermost layer, inner middle layer, outer middle layer, and outermost layer. 
     Electric conductor  231   a  in the innermost layer of one slot  25  is paired with conductor member  231   b  in the outermost layer in another slot  25  that is a pole pitch spaced apart therefrom in the clockwise direction. In the same manner, conductor segment  232   a  in the inner middle layer of the same one slot  25  is paired with conductor member  232   b  in the outer middle layer in the same another slot  25  that is a pole pitch spaced apart therefrom in the clockwise direction. The paired conductor members  231   a - 231   b  and  232   a - 232   b  are joined by continuous portions via turn portions  231   c  and  232   c  at one end of stator core  22 . 
     Therefore, the continuous portion that joins conductor member  231   b  in the outermost layer and conductor member  231   a  in the innermost layer via turn portion  231   c  encloses the continuous portion that joins conductor member  232   b  in the outer middle layer and conductor member  232   a  in the inner middle layer via turn portion  232   c  at the one end of stator core  22 . Thus, in the one end of stator core  22 , turn portion  232   c , which is a joining portion of the one paired conductor members, is enclosed by turn portion  231   c , which is a joining portion of the another paired conductor members disposed in the same two slots as the former conductor members. Thus, each of internal coil ends is formed by joining the conductor member  232   a  extending from the inner middle layer and the conductor member  232   b  extending from the outer middle layer, and each of external coil ends is formed by joining the conductor member  231   a  extending from the innermost layer and the conductor member  231   b  extending from the outermost layer. 
     Turn portions  231   c  included in the external coil-ends and turn portions  232   c  included in the internal coil-ends are shifted in the circumferential direction from each other to prevent the external and internal coil ends from overlapping with each other. 
     On the other hand, conductor member  232   a  in the inner middle layer is paired with conductor member  231   a ′ in the innermost layer of another slot that is a pole pitch spaced apart from the slot having conductor member  232   a  in the clockwise direction. In the same manner, conductor member  231   b ′ in the outermost layer of one slot  25  is paired with conductor member  232   b  in the outer middle layer of the slot that is a pole pitch spaced apart from the slot having conductor member  231   b ′ therein in the clockwise direction. These conductor members are welded to one another at the other end of stator core  22 . 
     Accordingly, external connection portion  233   b  of outermost conductor member  231   b ′ and outer middle conductor member  232   b  and internal connection portion  233   a  of innermost conductor member  231   a  and inner middle conductor member  232   a  are shifted from each other in the circumferential direction. Thus, two coaxial and adjoining coil-end-rings are formed. 
     As shown in FIG. 3, innermost conductor member  231   a  and outermost conductor member  231   b  form U-shaped large segment  231 , and inner middle conductor member  232   a  and outer middle conductor member  232   b  form U-shaped small segment  232 . A pair of large and small segments  231  and  232  form base segment unit  23 . Large and small segments  231  and  232  have axially extending straight in-slot portions and inclined portions  232   f ,  232   g ,  232   f , and  232   g . Coil-ends extending axially from opposite ends of stator core  22  are formed by the inclined portions. When cooling fans  11  and  12  are rotated, cooling air can pass through gaps formed between the inclined portions. 
     The above described structure is applied to all the segment units  23  disposed in all slots  25 . In the coil ends at the end of stator core  22  opposite the turn portions, edge  231   e ′ of the outermost conductor member  231   b ′ and edge  232   e  of outer middle conductor member  232   b  are welded together, and edge  232   d  of inner middle conductor member  232   a  and edge  231   d ′ of another outermost conductor member are welded together by a welder such as a super sonic welder or an arc welder, or soldered together to form external connection portions  233   b  and internal connection portion  233   a , which are coated with insulation material to bridge a plurality of connection portions  233   b  and  233   a . It is desirable to apply as thick insulation coatings as possible to only connection portions  233   b  and  233   a.    
     As shown in FIGS. 4 and 5, turn portion  231   c  of the external coil-end joins inclined portion  231   f  extending from slot  251  and inclined portion  231   f  extending from slot  252  that is a pole pitch spaced apart therefrom. In the same manner, turn portion  232   c  of internal coil-end joins inclined portion  232   f  extending from slot  251  and inclined portion  232   f  extending from slot  252 . Two inclined portions  231   f  disposed opposite sides of turn portion  231   c  and two turn portions  232   f  disposed opposite sides of turn portion  232   c  are portions of conductor members extending from slots  251  and  252 . Two turn portions  231   c  and  232   c  are disposed not to overlap with each other by changing the ratio of length of respective inclined portions. For example, as shown in FIG. 5, the ratio of the length between inclined portion  231   f  extending from slot  251  and inclined portion  231   f  extending from slot  252  and the ratio of the length between inclined portion  232   f  extending from slot  251  and inclined portion  232   f  extending from slot  252  are different. Two turn portions  231   c  and  232   c  can be also shifted in the circumferential direction, so that each of turn portions  232   c  of the internal coil-ends are disposed between two turn portions  231   c  of the external coil-ends when viewed from an outside portion in the axial direction of stator core  22 . 
     As shown in FIG. 4, one of two inclined portions  231   f  of large segment  231  extending from slot  251  is made shorter than the other inclined portion  231   f  extending from slot  252  so that turn portion  231   c  is located near slot  251 . On the other hand, one of two inclined portions  232   f  of small segment  232  extending from slot  251  is made longer than the other inclined portion  232   f  extending from slot  252  so that turn portion  232   c  included in the internal coil-end is located near slot  252 . It is, of course, possible to locate turn portion  231   c  included in external coil-end near slot  252  and turn portion  232   c  included in internal coil-end near slot  251 . It is also possible to locate turn portion  231   c  offset from the center between slot  251  and slot  252  as described above while turn portion  232   c  is located at the center between slot  251  and slot  252 , as shown in FIG.  6 . 
     As shown in FIG. 7, the length of two inclined portions  231   f  extending from turn portion  231   c  is made equal so that turn portion  231   c  can be located at the center between slot  251  and slot  252  while one of inclined portions  232   f  extending from turn portion  232   c  of small segment  232  is made longer than the other inclined portion  232   f  so that turn portion  232   c  is offset from the center between slot  251  and slot  252 . 
     Thus, all the turn portions included in the external and internal coil-ends are disposed in double rings so that a sufficient circumferential distance between the coil-ends can be provided, thereby reducing resistance of passages of cooling air supplied by cooling fans  11  and  12  from the inside thereof to the outside thereof. The turn portions included in the internal coil-ends are exposed to the cooling air, so that the internal coil-ends can receive a sufficient amount of cooling air. 
     Since turn portions  231   c  and turn portions  232   c  are offset from the center between two slots (e.g.  251  and  252 ), the stator winding has mesh-like coil-ends surrounding rotor  3  with evenly distributed small gaps. As a result, noise caused by the cooling air passing through the stator winding can be effectively reduced. 
     As a variation, a stator winding having more than four conductor members in each slots and turn portions disposed in three rings can be provided according to the invention. 
     In the foregoing description of the present invention, the invention has been disclosed with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes may be made to the specific embodiments of the present invention without departing from the broader spirit and scope of the invention as set forth in the appended claims. Accordingly, the description of the present invention in this document is to be regarded in an illustrative, rather than restrictive, sense.