Patent Publication Number: US-2015076945-A1

Title: Stator for rotating electric machine

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based on and claims priority from Japanese Patent Application No. 2013-193775 filed on Sep. 19, 2013, the content of which is hereby incorporated by reference in its entirety into this application. 
     BACKGROUND 
     1 Technical Field The present invention relates to stators for rotating electric machines that are used in, for example, motor vehicles as electric motors and electric generators. 
     2 Description of Related Art 
     Japanese Patent Application Publication No. JP2013059156A discloses a stator for a rotating electric machine The stator includes an annular stator core and a stator coil mounted on the stator core. The stator coil is comprised of first to third phase windings that are Y-connected to define a neutral point therebetween. Moreover, to facilitate the process of connecting the first to the third phase windings to form a connection portion which represents the neutral point and improve the reliability of the formed connection portion, there are employed first and second neutral wires in the stator coil. The first neutral wire, which is a single continuous electric conductor wire, extends to connect the first and second phase windings. The second neutral wire, which is also a single continuous electric conductor, extends to connect the third phase winding to the first neutral wire. More specifically, a joining portion of the second neutral wire is arranged to extend along the circumferential direction of the stator core and in contact with a joining portion of the first neutral wire. The joining portions of the first and second neutral wires are joined to each other by brazing or welding. 
     However, with the above arrangement of the first and second neutral wires, there is no member or part of the stator radially supporting the connection portion of the stator coil. Therefore, radial vibration transmitted from outside to the stator may cause the connection portion of the stator coil to greatly vibrate in the radial direction. Accordingly, when the rotating electric machine is used in a vehicle where the machine is subjected to high radial vibration, electrical connection failure may occur such as breakage of the connection portion of the stator coil or damage of insulating coats of the first and second neutral wires due to stress induced therein. 
     Further, when the above arrangement is applied to other cases where the stator coil includes more than one connection portion between the phase windings (e.g., the stator coil includes a plurality of Y-connections or a A-Y connection), the probability of electrical connection failure occurring in the stator coil will accordingly increase. 
     To prevent electrical connection failure from occurring in the stator coil, one may consider firmly fixing the connection portion of the stator coil using insulating resin or binding the connection portion to a coil end part of the stator coil with threads. However, in those cases, the manufacturing cost of the stator would be increased due to increase in the man-hours required for manufacturing the stator, the amount of the insulating resin used for the stator coil, or the parts count of the stator. 
     Moreover, in some embodiments disclosed in the above patent document, the first and second neutral wires are arranged so as to be axially aligned with each other. However, with this arrangement, the axial height of the connection portion of the stator coil will be increased, thereby reducing the axial gap between the connection portion and an internal wall of a frame which receives the stator therein. Consequently, the environmental resistance of the rotating electric machine is lowered. In addition, the resistance of the rotating electric machine to radial vibration is also lowered. 
     Furthermore, with the arrangements of the first and second neutral wires disclosed in the above patent document, it is difficult to stably hold the first and second neutral wires in joining the joining portions thereof. Therefore, to facilitate the process of joining the joining portions of the first and second neutral wires by, for example, welding, it is necessary to strip the joining portions of their respective insulating coats over a wide range. Accordingly, after joining the joining portions of the first and second neutral wires, it is necessary to apply an increased amount of insulating resin onto the joining portions so as to secure electrical insulation thereof. Consequently, the manufacturing cost of the stator will be accordingly increased. 
     SUMMARY 
     According to an exemplary embodiment, there is provided a stator for a rotating electric machine. The stator includes an annular stator core and a stator coil. The stator core has a plurality of slots formed therein. The slots are spaced from one another in a circumferential direction of the stator core. The stator coil includes first to third phase windings mounted on the stator core and a connection portion located outside the slots of the stator core. The connection portion is formed of a first connection wire connecting the first and second phase windings and a second connection wire connecting the third phase winding to the first connection wire. The first connection wire is arranged so as to extend in the circumferential direction of the stator core. The second connection wire is bent to include a bend and an intersecting part that extends from the bend to the first connection wire so as to intersect the first connection wire. The intersecting part of the second connection wire is joined to the first connection wire with a joint formed therebetween. 
     With the above configuration, when radial vibration is transmitted to the connection portion of the stator coil, one of the first and second connection wires will function as a strut to support the other of the first and second connection wires, thereby suppressing radial vibration of the connection portion. It is preferable that the intersecting part of the second connection wire extends in a radial direction of the stator core so as to intersect the first connection wire at right angles. 
     Preferably, the bend of the second connection wire is formed radially outside the first connection wire, and the intersecting part of the second connection wire extends from the bend to the first connection wire. 
     It is preferable that each of opposite end portions of the first connection wire is led out from a radially inner part of a corresponding one of the slots of the stator core. 
     It is also preferable that the first connection wire is axially positioned between the stator core and the intersecting part of the second connection wire. 
     It is also preferable that at the joint, a cut is formed in either or both of the first and second connection wires for positioning them with respect to each other. Further, the cut may be formed in the shape of a recess only in the second connection wire so that the first connection wire is fitted in the cut. Alternatively, at the joint, each of the first and second connection wires may have a cut formed therein in the shape of a recess so that: the first connection wire is fitted in the cut formed in the second connection wire; and the second connection wire is fitted in the cut formed in the first connection wire. 
     It is also preferable that each of the first and second connection wires has a substantially rectangular cross section. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be understood more fully from the detailed description given hereinafter and from the accompanying drawings of one exemplary embodiment, which, however, should not be taken to limit the invention to the specific embodiment but are for the purpose of explanation and understanding only. 
       In the accompanying drawings: 
         FIG. 1  is a schematic cross-sectional view of an automotive alternator which includes a stator according to the exemplary embodiment; 
         FIG. 2  is a schematic perspective view illustrating the configuration of electric conductor segments forming a stator coil of the stator; 
         FIG. 3  is a schematic perspective view illustrating a process of inserting the electric conductor segments into slots formed in a stator core of the stator; 
         FIG. 4  is a schematic perspective view illustrating pairs of end portions of the electric conductor segments joined at a front-side coil end part of the stator coil; 
         FIG. 5  is a schematic perspective view illustrating the configuration of electric conductor segments forming the stator coil according to a first modification; 
         FIG. 6  is a schematic circuit diagram of the stator coil which is comprised of a pair of three-phase coils; 
         FIG. 7  is a schematic perspective view illustrating the configuration of electric conductor segments forming lead wires of the stator coil; 
         FIG. 8  is a schematic axial end view illustrating the configuration of a connection portion representing a neutral point of the stator coil; 
         FIG. 9  is a schematic view of the connection portion of the stator coil from the radially inside; 
         FIG. 10  is a schematic perspective view illustrating the configuration of the connection portion of the stator coil; 
         FIG. 11  is a schematic axial end view illustrating the configuration of the connection portion of the stator coil according to a second modification; 
         FIG. 12  is a schematic axial end view illustrating the configuration of the connection portion of the stator coil according to a third modification; 
         FIG. 13  is a schematic perspective view illustrating a cut formed in the connection portion of the stator coil according to a fourth modification; 
         FIG. 14  is a schematic perspective view illustrating a cut formed in the connection portion of the stator coil according to a fifth modification; 
         FIG. 15  is a schematic perspective view illustrating cuts formed in the connection portion of the stator coil according to a sixth modification; 
         FIG. 16  is a schematic circuit diagram of the stator coil according to a seventh modification; and 
         FIG. 17  is a schematic axial end view illustrating the configuration of the connection portion of the stator coil according to an eighth modification. 
     
    
    
     DESCRIPTION OF EMBODIMENT 
       FIG. 1  shows the overall configuration of an automotive alternator  1  which includes a stator  3  according to an exemplary embodiment. The alternator  1  is designed to be used in a motor vehicle, such as a passenger car or a truck. 
     As shown in  FIG. 1 , the alternator  1  includes, in addition to the stator  3 , a rotor  2 , a frame  4 , a rectifier  5 , a voltage regulator  11  and a pulley  20 . 
     The rotor  2  includes a rotating shaft  6 , a pair of Lundell-type magnetic pole cores  21  and a field coil  24 . The rotating shaft  6  is rotatably supported by the frame  4  via bearings. The rotating shaft  6  has the pulley  20  mounted on a front end portion (i.e., a left end portion in  FIG. 1 ) thereof, so that it can be driven by an internal combustion engine (not shown in the figures) of the vehicle via the pulley  20 . Each of the magnetic pole cores  21  has a plurality of magnetic pole claws. The field coil  24  is made of, for example, an insulation-treated copper wire and wound into an annular shape. The magnetic pole cores  21  are fixed on the rotating shaft  6  with the field coil  24  held between the magnetic pole cores  21 . In addition, on a rear end portion (i.e., a right end portion in  FIG. 1 ) of the rotating shaft  6 , there are provided a pair of slip rings via which field current is supplied to the field coil  24  during rotation of the rotor  2 . 
     The stator  3  includes an annular (or hollow cylindrical) stator core  31  and a stator coil  32  mounted on the stator core  31 . The detailed configuration of the stator  3  will be described later. 
     The frame  4  has both the rotor  2  and the stator  3  retained therein so that the stator  3  surrounds a radially outer periphery of the rotor  2  with a predetermined radial gap formed therebetween. 
     The rectifier  5  rectifies three-phase AC power outputted from the stator coil  32  into DC power and outputs the obtained DC power via output terminals thereof. 
     The voltage regulator  11  regulates the voltage of the DC power outputted from the rectifier  5 . 
     Moreover, in the present embodiment, the alternator  1  further includes a pair of cooling fans  22  and  23  that are respectively provided on axial end faces of the magnetic pole cores  21  of the rotor  2 . The cooling fans  21  and  22  suck cooling air into the alternator  1  via suction openings  41  formed in front and rear end walls of the frame  4  and discharge the cooling air out of the alternator  1  via discharge openings  42  formed in a circumferential wall (or side wall) of the frame  4 . With the cooling air, it is possible to cool the stator coil  32 , the rectifier  5  and the regulator  11  during operation of the alternator  1 . In addition, it should be noted that though not shown in  FIG. 1 , the discharge openings  42  are formed not only in a front part but also in a rear part of the frame  4 . 
     After having described the overall configuration of the alternator  1 , the detailed configuration of the stator  3  according to the present embodiment will be described with reference to  FIGS. 2-10 . 
     In the present embodiment, the annular stator core  31  is formed by laminating a plurality of steel sheets in the axial direction. In the radially inner surface of the stator core  31 , there are formed a plurality of slots  310  so as to penetrate the stator core  31  in the axial direction. Moreover, the slots  310  are spaced from one another in the circumferential direction of the stator core  31  at a constant pitch and each extend in a radial direction of the stator core  31 . That is, for each of the slots  310 , the depth direction of the slot  310  coincides with the radial direction of the stator core  31 . 
     The stator coil  32  is mounted on the stator core  31  so as to be partially received in the slots  310  of the stator core  31  with insulating sheets  34  interposed between the stator coil  32  and those internal walls of the stator core  31  which define the slots  310 . Moreover, as shown in  FIG. 1 , the stator coil  32  has a front-side coil end part  32 F protruding from a front end face (or a first axial end face) of the stator core  31  and a rear-side coil end part  32 R protruding from a rear end face (or a second axial end face) of the stator core  31 . 
     The stator coil  32  can be considered as being formed by connecting electric conductors received in the slots  310  of the stator core  31 . That is, as illustrated in  FIGS. 2-3 , in each of the slots  310  of the stator core  31 , there are received an even number (e.g., four in the present embodiment) of electric conductors in alignment with each other in the radial direction of the stator core  31  (or in the depth direction of the slot  310 ). Hereinafter, for the sake of convenience of explanation, the four electric conductors are sequentially referred to as an innermost conductor, an inner-middle conductor, an outer-middle conductor and an outermost conductor from the radially inside to the radially outside of the slot  310 . In addition, in the present embodiment, each of the electric conductors has a substantially rectangular cross section. 
     Moreover, the electric conductors received in the slots  310  of the stator core  31  are electrically connected to one another in a predetermined pattern. 
     Specifically, referring to  FIG. 2 , for one of the slots  310 , the innermost conductor  331   a  in the slot  310  is electrically connected, via a connecting conductor  331   c , to the outermost conductor  331   b  in another one of the slots  310  which is positioned away from the slot  310  by one magnetic pole pitch in the clockwise direction; the connecting conductor  331   c  is located on a first axial side of the stator core  31  (i.e., the lower side in  FIG. 2  and the rear side in  FIG. 1 ). In addition, it should be noted that “the clockwise direction” hereinafter denotes the clockwise direction with the point of sight located on the first axial side of the stator core  31 . 
     Similarly, for one of the slots  310 , the inner-middle conductor  332   a  in the slot  310  is connected, via a connecting conductor  332   c , to the outer-middle conductor  332   b  in another one of the slots  310  which is positioned away from the slot  310  by one magnetic pole pitch in the clockwise direction; the connecting conductor  332   c  is also located on the first axial side of the stator core  31 . 
     Consequently, on the first axial side of the stator core  31 , each of the connecting conductors  332   c  that respectively connect pairs of the inner-middle conductors  332   a  and the outer-middle conductors  332   b  is partially surrounded by a corresponding one of the connecting conductors  331   c  that respectively connect pairs of the innermost conductors  331   a  and the outermost conductors  331   b . As a result, all the connecting conductors  332   c  together form an axially inner layer of the rear-side coil end part  32 R of the stator coil  32 ; all the connecting conductors  331   c  together form an axially outer layer of the rear-side coil end part  32 R of the stator coil  32 . 
     Moreover, for one of the slots  310 , the inner-middle conductor  332   a  in the slot  310  is electrically connected, on a second axial side of the stator core  31  (i.e., the upper side in  FIG. 2  and the front side in  FIG. 1 ), to the innermost conductor  331   a ′ in another one of the slots  310  which is positioned away from the slot  310  by one magnetic pole pitch in the clockwise direction. More specifically, the inner-middle conductor  332   a  is electrically connected to the innermost conductor  331   a ′ by joining, for example by TIG welding or ultrasonic welding, a pair of connecting conductors  332   g  and  331   g ′ that respectively extend from the inner-middle conductor  332   a  and the innermost conductor  331   a ′. In addition, it should be noted that the superscript [&#39;] (i.e., apostrophe) is attached to some of the electric conductors hereinafter only for the sake of convenience of explanation and ease of understanding. 
     Similarly, for one of the slots  310 , the outermost conductor  331   b ′ in the slot  310  is electrically connected, on the second axial side of the stator core  31 , to the outer-middle conductor  332   b  in another one of the slots  310  which is positioned away from the slot  310  by one magnetic pole pitch in the clockwise direction. More specifically, the outermost conductor  331   b ′ is electrically connected to the outer-middle conductor  332   b  by joining, for example by TIG welding or ultrasonic welding, a pair of connecting conductors  331   g ′ and  332   g  that respectively extend from the outermost conductor  331   b ′ and the outer-middle conductor  332   b.    
     Consequently, on the second axial side of the stator core  31 , each of joints  333   a  formed between end portions  332   d  of the connecting conductors  332   g  and end portions  331   d ′ of the connecting conductors  331   g ′ is offset from a corresponding one of joints  333   b  formed between end portions  331   e ′ of the connecting conductor  331   g ′ and end portions  332   e  of the connecting conductors  332   g  both in the radial and circumferential directions of the stator core  31 . As a result, as shown in  FIG. 4 , all the joints  333   a  fall on the same circle to form a radially inner layer of the front-side coil end part  32 F of the stator coil  32 ; all the joints  333   b  fall on the same circle to form a radially outer layer of the front-side coil end part  32 F. 
     Moreover, in the present embodiment, the stator coil  32  is formed of a plurality of substantially U-shaped electric conductor segments  30 . Further, the electric conductor segments  30  are comprised of a plurality of pairs of large and small electric conductor segments  331  and  332 . More specifically, as shown in  FIG. 2 , each connected set of the innermost conductor  331   a , outermost conductor  331   b , connecting conductor  331   c  on the first axial side of the stator core  31  and connecting conductors  331   g  on the second axial side of the stator core  31  is formed in one piece construction by using one of the large electric conductor segments  331 . On the other hand, each connected set of the inner-middle conductor  332   a , outer-middle conductor  332   b , connecting conductor  332   c  on the first axial side of the stator core  31  and connecting conductors  332   g  on the second axial side of the stator core  31  is formed in one piece construction by using one of the small electric conductor segments  332 . 
     In other words, each of the large electric conductor segments  331  has a pair of in-slot portions  331   a  and  331   b  respectively received in two slots  310  of the stator core  31  which are circumferentially apart from each other by one magnetic pole pitch, a turn portion  331   c  that connects the pair of in-slot portions  331   a  and  331   b  on the first axial side of the stator core  31 , and a pair of oblique portions  331   g  that respectively protrude from the pair of in-slot portions  331   a  and  331   b  on the second axial side of the stator core  31  and extend obliquely at predetermined angles with respect to the axial direction of the stator core  31 . In addition, the turn portion  331   c  includes a pair of oblique portions  331   f  that extend obliquely at predetermined angles with respect to the axial direction of the stator core  31 . Similarly, each of the small electric conductor segments  332  has a pair of in-slot portions  332   a  and  332   b  respectively received in two slots  310  of the stator core  31  which are circumferentially apart from each other by one magnetic pole pitch, a turn portion  332   c  that connects the pair of in-slot portions  332   a  and  332   b  on the first axial side of the stator core  31 , and a pair of oblique portions  332   g  that respectively protrude from the pair of in-slot portions  332   a  and  332   b  on the second axial side of the stator core  31  and extend obliquely at predetermined angles with respect to the axial direction of the stator core  31 . In addition, the turn portion  332   c  includes a pair of oblique portions  332   f  that extend obliquely at predetermined angles with respect to the axial direction of the stator core  31 . 
     Consequently, with the large and small electric conductor segments  331  and  332 , the stator coil  32  is formed in a lap winding manner on the stator core  31 . Moreover, all of the turn portions  331   c  of the large electric conductor segments  331  and the turn portions  332   c  of the small electric conductor segments  332  together constitute the rear-side coil end part  32 R of the stator coil  32 ; all of the oblique portions  331   g  of the large electric conductor segments  331  and the oblique portions  332   g  of the small electric conductor segments  332  together constitute the front-side coil end part  32 F of the stator coil  32  (see  FIG. 1 ). In addition, during rotation of the rotor  2 , the flow of cooling air created by the cooling fans  22  and  23  passes through the front-side and rear-side coil end parts  32 F and  32 R of the stator coil  32 , thereby cooling them. 
     In addition, as shown in  FIG. 5 , the stator coil  32  may also be formed of a plurality of identical electric conductor segments  30  which are substantially U-shaped. Further, with the identical electric conductor segments  30 , the stator coil  32  may be formed in a wave winding manner on the stator core  31 . 
     In the present embodiment, the electric conductor segments  30  are electrically connected in the above-described manner to form a pair of first and second three-phase coils  32 A and  32 B as shown in  FIG. 6 . Moreover, the first and second three-phase coils  32 A and  32 B together constitute the stator coil  32 . 
     In other words, in the present embodiment, the stator coil  32  is comprised of the pair of three-phase coils  32 A and  32 B. In addition, the first and second three-phase coils  32 A and  32 B are mounted on the stator core  31  so as to be different in phase from each other by 30° in electrical angle. 
     As shown in  FIG. 6 , the first three-phase coil  32 A includes three phase windings x, y and z, which are Y-connected with each other. The phase winding x has its opposite end portions respectively led out as lead wires Xb and Xc from the rear-side coil end part  32 R of the stator coil  32 . The phase winding y has its opposite end portions respectively led out as lead wires Yb and Yc from the rear-side coil end part  32 R. The phase winding z has its opposite end portions respectively led out as lead wires Zb and Zc from the rear-side coil end part  32 R. The lead wires Xb, Yb and Zb are electrically connected to the rectifier  5  of the alternator  1 . On the other hand, the lead wires Xc, Yc and Zc are joined together to define a neutral point N1 of the first three-phase coil  32 A. 
     Similarly, the second three-phase coil  32 B includes three phase windings u, v and w, which are Y-connected with each other. The phase winding u has its opposite end portions respectively led out as lead wires Ub and Uc from the rear-side coil end part  32 R of the stator coil  32 . The phase winding v has its opposite end portions respectively led out as lead wires Vb and Vc from the rear-side coil end part  32 R. The phase winding w has its opposite end portions respectively led out as lead wires Wb and We from the rear-side coil end part  32 R. The lead wires Ub, Vb and Wb are electrically connected to the rectifier  5  of the alternator  1 . On the other hand, the lead wires Uc, Vc and We are joined together to define a neutral point N2 of the second three-phase coil  32 B. 
     Moreover, in the present embodiment, the lead wires Xb, Yb, Zb, Ub, Vb and Wb, which are led out from the rear-side coil end part  32 R of the stator coil  32  and electrically connected to the rectifier  5 , are formed using electric conductor segments  30 ′ as shown in  FIG. 7 . 
     Specifically, compared to the above-described substantially U-shaped electric conductor segments  30 , each of the electric conductor segments  30 ′ is not bent back at the turn portion, thus having two straight portions extending parallel to each other. Each of the electric conductor segments  30 ′ is inserted in a corresponding one of the slots  310  of the stator core  31  from the first axial side of the stator core  31  (i.e., the upper side in  FIG. 7  and the rear side in  FIG. 1 ), so as to have one end portion thereof protruding from the corresponding slot  310  on the second axial side (i.e., the lower side in  FIG. 7  and the front side in  FIG. 1 ). The end portion is then bent to extend obliquely at a predetermined angle with respect to the axial direction of the stator core  31 . Thereafter, the end portion is joined to a corresponding one of the oblique portions of the electric conductor segments  30  (i.e., the oblique portions  331   g  of the large electric conductor segments  331  and the oblique portions  332   g  of the small electric conductor segments  332  in  FIG. 2 ), thereby making up a portion of the front-side coil end part  32 F of the stator coil  32  as shown in  FIG. 4 . On the other hand, the other end portions of the electric conductor segments  30 ′, which remain on the first axial side of the stator core  31 , make up the lead wires Xb, Yb, Zb, Ub, Vb and Wb; those lead wires Xb-Zb and Ub-Wb protrude from the rear-side coil end part  32 R of the stator coil  32 . 
     Accordingly, with the electric conductor segments  30 ′, it is possible to easily form the lead wires Xb-Zb and Ub-Wb. In addition, like the electric conductor segments  30 , each of the electric conductor segments  30 ′ also has a substantially rectangular cross section. 
     Next, a connection portion M of the first three-phase coil  32 A which represents the neutral point N1 will be described in detail. 
     In addition, in the present embodiment, the second three-phase coil  32 B has the same configuration and features as the first three-phase coil  32 A. Therefore, for the sake of avoiding redundancy, description of a connection portion M of the second three-phase coil  32 B which represents the neutral point N2 will be omitted hereinafter. 
     As described previously, in the present embodiment, the first three-phase coil  32 A includes the phase windings x, y and z that are Y-connected to define the neutral point N1 therebetween (see  FIG. 6 ). Further, the lead wires Xc, Yc and Zc, which are respectively drawn from the phase windings x, y and z, are connected together to form the connection portion M which represents the neutral point N1. 
     Specifically, in the present embodiment, as shown in  FIGS. 8-10 , the lead wires Xc and Yc are together implemented by a first connection wire Na which is a single continuous electric conductor wire. The first connection wire Na is arranged so as to extend in the circumferential direction of the stator core  31 . The lead wire Zc is implemented by a second connection wire Nb which is also a single continuous electric conductor wire. The second connection wire Nb is bent to include a bend Nb  1  formed radially outside the first connection wire Na and an intersecting part m that extends from the bend Nb1 to the first connection wire Na so as to intersect the first connection wire Na. Further, the intersecting part m is joined, for example by welding, to the first connection wire Na to form a joint (or junction) Nc therebetween. 
     That is, in the present embodiment, the connection portion M of the first three-phase coil  32 A, which represents the neutral point N1, is formed of the first and second connection wires Na and Nb. The first connection wire Na connects the phase windings x and y. The second connection wire Nb connects the phase winding z to the first connection wire Na. The first connection wire Na extends in the circumferential direction of the stator core  31 . The second connection wire Nb includes the intersecting part m that extends so as to intersect the first connection wire Na and is jointed to the first connection wire Na to form the joint Nc therebetween. Consequently, when radial vibration is transmitted to the connection portion M of the first stator coil  32 A, the second connection wire Nb will function as a strut to support the first connection wire Na, thereby suppressing radial vibration of the connection portion M. 
     Moreover, in the present embodiment, as shown in  FIG. 8 , the intersecting part m of the second connection wire Nb extends to the first connection wire Na from the bend Nb  1  that is formed radially outside the first connection wire Na. Consequently, when radial vibration is transmitted to the connection portion M of the first stator coil  32 A, the second connection wire Nb will support the first connection wire Na from the radially outside, thereby suppressing the amplitude of radial vibration of the connection portion M in the radially outward direction. As a result, it is possible to secure a sufficient gap between the joint Nc and the internal wall of the frame  4  in which the stator  3  is received, thereby improving the environmental resistance of the alternator  1 . 
     Furthermore, in the present embodiment, as shown in  FIG. 9 , the first connection wire Na is axially positioned between the stator core  31  and the intersecting part m of the second connection wire Nb. Consequently, it is possible to reduce the axial height of the entire first connection wire Na that extends in the circumferential direction of the stator core  31 , thereby improving the vibration resistance of the entire connection portion M of the first three-phase coil  32 A. 
     In addition, in the present embodiment, each of the first and second connection wires Na and Nb has a substantially rectangular cross-sectional shape. Consequently, it is possible to improve the vibration resistance of each of the first and second connection wires Na and Nb, thereby more reliably suppressing radial vibration of the connection portion M. 
     The above-described stator  3  according to the present embodiment has the following advantages. 
     In the present embodiment, the stator  3  includes the annular stator core  31  and the stator coil  32 . The stator core  31  has the slots  310  formed therein. The slots  310  are spaced from one another in the circumferential direction of the stator core  31 . The stator coil  32  includes the phase windings x, y and z and the connection portion M located outside the slots  310  of the stator core  31 . The connection portion M is formed of the first connection wire Na that connects the phase windings x and y and the second connection wire Nb that connects the phase winding z to the first connection wire Na. The first connection wire Na is arranged so as to extend in the circumferential direction of the stator core  31 . The second connection wire Nb is bent to include the bend Nb1 and the intersecting part m that extends from the bend Nb1 to the first connection wire Na so as to intersect the first connection wire Na. The intersecting part m of the second connection wire Nb is joined to the first connection wire Na to form the joint Nc therebetween. 
     With the above configuration, when radial vibration is transmitted to the connection portion M, the second connection wire Nb will function as a strut to support the first connection wire Na, thereby suppressing radial vibration of the connection portion M. 
     Moreover, in the present embodiment, the bend Nb1 of the second connection wire Nb is formed radially outside the first connection wire Na, and the intersecting part m of the second connection wire Nb extends from the bend Nb1 to the first connection wire Na. 
     With above configuration, when radial vibration is transmitted to the connection portion M, the second connection wire Nb will support the first connection wire Na from the radially outside, thereby suppressing the amplitude of radial vibration of the connection portion M in the radially outward direction. As a result, it is possible to secure a sufficient gap between the connection portion M and the internal wall of the frame  4  in which the stator  3  is received, thereby improving the environmental resistance of the alternator  1 . 
     Furthermore, in the present embodiment, the first connection wire Na is axially positioned between the stator core  31  and the intersecting part m of the second connection wire Nb. 
     With the above configuration, it is possible to reduce the axial height of the entire first connection wire Na that extends in the circumferential direction of the stator core  31 , thereby improving the vibration resistance of the entire connection portion M. 
     In the present embodiment, each of the first and second connection wires Na and Nb is configured to have a substantially rectangular cross section. 
     With the above configuration, it is possible to improve the vibration resistance of each of the first and second connection wires Na and Nb, thereby more reliably suppressing radial vibration of the connection portion M. 
     While the above particular embodiment has been shown and described, it will be understood by those skilled in the art that various modifications, changes, and improvements may be made without departing from the spirit of the invention. 
     (1) For example, in the previous embodiment, the intersecting part m of the second connection wire Nb is arranged to extend obliquely with respect to the first connection wire Na (see  FIG. 8 ). 
     However, as shown in  FIG. 11 , the intersecting part m of the second connection wire Nb may be arranged to extend in a radial direction of the stator core  31 , thereby intersecting the first connection wire Na at right angles. With this arrangement, when radial vibration is transmitted to the connection portion M, the second connection wire Nb will support the first connection wire Na in the radial direction, thereby more effectively suppressing radial vibration of the connection portion M. 
     (2) It is preferable that each of opposite end portions of the first connection wire Na (i.e., the lead wire Xc+the lead wire Ye) is led out (or protrudes) from a radially inner part of a corresponding one of the slots  310  of the stator core  31 , as shown in  FIG. 12 . In this case, it is possible to locate the joint Nc formed between the first connection wire Na and the intersecting part m of the second connection wire Nb in close vicinity to the radially inner periphery of the stator core  31 . Consequently, it is possible to more reliably secure a sufficient gap between the joint Nc and the internal wall of the frame  4  in which the stator  3  is received, thereby further improving the environmental resistance of the alternator  1 . 
     (3) It is preferable to form, at the joint Nc, a cut in either or both of the first and second connection wires Na and Nb, thereby positioning them with respect to each other. With the cut, it is possible to reduce the axial height of the joint Nc, thereby widening the gap between the joint Nc and the internal wall of the frame  4  and thus improving the environmental resistance of the alternator  1 . Moreover, with the cut, it is also possible to stably hold the first and second connection wires Na and Nb relative to each other in joining them to form the joint Nc therebetween. Accordingly, in joining the first and second connection wires Na and Nb by, for example, welding, it is unnecessary to strip the first and second connection wires Na and Nb of their respective insulating coats over a wide range. Consequently, after joining the first and second connection wires Na and Nb, it is unnecessary to apply a large amount of insulating resin to cover the joint Nc and the stripped portions of the first and second connection wires Na and Nb. As a result, it is possible to reduce the manufacturing cost of the stator  3 . In addition, it is also unnecessary to bind the first and second connection wires Na and Nb to the rear-side coil end part  32 R of the stator coil  32  with threads. In other words, it unnecessary to employ any additional member for holding the first and second connection wires Na and Nb. As a result, it is possible to further reduce the manufacturing cost of the stator  3 . 
     Specifically, as shown in  FIG. 13 , a cut K may be formed in the shape of a recess only in the second connection wire Nb so that the first connection wire Na can be fitted in the cut K. In addition, it is easy to form such a cut K in a distal end portion of the second connection wire Nb. 
     Alternatively, as shown in  FIG. 14 , a cut K may be formed in the shape of a recess only in the first connection wire Na so that the second connection wire Nb can be fitted in the cut K. 
     Otherwise, as shown in  FIG. 15 , each of the first and second connection wires Na and Nb may have a cut K formed therein in the shape of a recess so that: the first connection wire Na can be fitted in the cut K formed in the second connection wire Nb; and the second connection wire Nb can be fitted in the cut K formed in the first connection wire Na. In this case, it is possible to more stably hold the first and second connection wires Na and Nb in joining them to form the joint Nc therebetween. 
     (4) In the previous embodiment, each of the phase windings x-z and u-w of the stator coil  32  is formed of the electric conductor segments  30  and  30 ′ which have the substantially rectangular cross-sectional shape. However, each of the phase windings x-z and u-w of the stator coil  32  may also be formed of electric conductor segments which have other cross-sectional shapes (e.g., a substantially circular cross-sectional shape). 
     Furthermore, each of the phase windings x-z and u-w of the stator coil  32  may be formed of, instead of the electric conductor segments, a single continuous electric conductor wire which has a suitable cross-sectional shape (e.g., a substantially rectangular or circular cross-sectional shape). 
     (5) In the previous embodiment, the stator coil  32  is comprised of the first and second three-phase coils  32 A and  32 B each of which is Y-connected (see  FIG. 6 ). 
     However, as shown in  FIG. 16 , the stator coil  32  may also be comprised of a pair of three-phase windings  32 A and  32 B each of which is connected in a Δ-Y combined manner (or is A-Y-connected). In this case, in the stator coil  32 , there are a total of six connection portions M, at each of which three phase windings can be connected in the manner described in the previous embodiment. 
     Moreover, the stator coil  32  may also be comprised of a pair of three-phase windings one of which is Y-connected while the other is Δ-Y-connected. 
     Furthermore, the stator coil  32  may include only one three-phase coil which is either Y-connected or Δ-Y-connected. 
     (6) In the previous embodiment, the first connection wire Na is axially positioned between the stator core  31  and the intersecting part m of the second connection wire Nb (see  FIG. 8 ). 
     However, it is also possible to axially position the intersecting part m of the second connection wire Nb between the stator core  31  and the first connection wire Na. 
     (7) In the previous embodiment, the bend Nb1 of the second connection wire Nb is formed radially outside the first connection wire Na and the intersecting part m of the second connection wire Nb extends from the bend Nb1 to the first connection wire Na (see  FIG. 8 ). 
     However, as shown in  FIG. 17 , the bend Nb  1  of the second connection wire Nb may be formed radially inside the first connection wire Na. In this case, the intersecting part m of the second connection wire Nb extends from the radially inside to the radially outside of the first connection wire Na. 
     (8) In the previous embodiment, the lead wires Xc and Yc are together implemented by the first connection wire Na while the lead wire Zc is alone implemented by the second connection wire Nb. 
     However, it is also possible to implement the lead wires Yc and Zc (or alternatively the lead wires Xc and Zc) together by the first connection wire Na while implementing the lead wire Xc (or alternatively the lead wire Yc) alone by the second connection wire Nb. 
     (9) In the previous embodiment, the present invention is applied to the stator  3  of the automotive alternator  1 . 
     However, the invention can also be applied to stators of other rotating electric machines, such as a stator of an electric motor and a stator of a motor-generator that can selectively function either as an electric motor or as an electric generator.