Abstract:
A vehicular AC generator has a stator coil formed by connection of four-turn phase coils by serially inserting coil conductors into slots separated by intervals of three slots, the coil conductors being arranged four in a line in a radial direction. This minimizes the crossover connection portions of the turns, to attendantly prevent a deterioration of the cooling capacity.

Description:
This is a divisional of application Ser. No. 09/561,969 filed May 1, 2000, now U.S. Pat. No. 6,285,105 the disclosure of which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a vehicular AC generator adapted to prevent cooling ability from being deteriorated by crossover connection portions of each of turns of phase windings of a stator coil. More particularly, this invention relates to a coil winding structure for decreasing or omitting crossover connection portions of each of turns of phase windings of a stator coil. 
     2. Description of the Related Art 
     FIG. 8 is sectional diagram showing the configuration of a conventional vehicular AC generator. 
     The conventional vehicular AC generator is configured so that a Lundell-type rotor  7  is rotatably mounted within a case  3  consisting of an aluminum front bracket  1  and an aluminum rear bracket  2  by means of a shaft  6 , and that a stator  8  is fixed to the inner wall of the case  3  in such a manner as to cover the outer periphery of the rotor  7 . 
     The shaft  6  is rotatably supported by the front bracket  1  and the rear bracket  2 . A pulley  4  is fixed to one end of this shaft  6 , so that the rotating torque of an engine can be transmitted to the shaft  6  by means of a belt (not shown). 
     Slip rings  9  for supplying electric current to the rotor  7  are fixed to the other end of the shaft  6 . A pair of brushes  10  are accommodated in a brush holder  11 , which is disposed in the case  3 , in such a way as to slide in contact with the slip rings  9 . A regulator  19  for regulating the output voltage of the stator  8  is attached to a heat sink  17  fitted on the brush holder  11 . A rectifier  12  electrically connected to the stator  8  and adapted to rectify an alternating current generated in the coil the stator  8  to a direct current is mounted within the case  3 . 
     The rotor  7  comprises a rotor coil  13  which generates magnetic flux when an electric current flows therein, and a pair of pole cores  20  and  21  disposed so as to cover the rotor coil  13  in which magnetic poles are formed by the magnetic flux generated by the rotor coil  13 . The pole cores  20  and  21  are made of iron, each has a plurality of claw-like magnetic pole pieces  22  and  23  circumferentially provided along the outer circumferential edge thereof at an equiangular pitch in such a way as to protrude therefrom. The pole cores  20  and  21  are fixed to the shaft  6  in such a manner as to face each other so that the magnetic pole pieces  22  and  23  engage with each other. Moreover, fans  5  are fixed to both axial ends of the rotor  7 . 
     The stator  8  comprises a stator core  15  and a stator coil  16  composed of wires wound around this stator core  15  in which an alternating current is generated by alternating the magnetic flux of the rotor  7  owing to the rotation of the rotor  7 . 
     In the conventional AC generator configured in this manner, an electric current is supplied from a battery (not shown) to the rotor coil  13  by means of the brushes  10  and the slip rings  9 , so that the magnetic flux is generated. The claw-like magnetic poles  22  of the pole core  20  are magnetized to N polarities by this magnetic flux. The claw-like magnetic poles  23  of the pole core  21  are magnetized to S polarities by this magnetic flux. On the other hand, the rotatinal torque of the engine is transmitted to the shaft  6  by means of the belt and the pulley  4 , so that the rotor  7  is rotated. Thus, a rotating magnetic field is given to the stator coil  16 . Then, an electromotive force is generated in the stator coil  16 . This AC electromotive force is transmitted to and rectified by the rectifier  12  to a direct current, its voltage is regulated by the regulator  18 . Then, the battery is recharged. 
     The rotor coil  13 , the stator coil  16 , the rectifier  12  and the regulator  18  emit heat at all times during power generation. The heating values of these elements are 60W, 50W, 120W and 6W, respectively, at a high-temperature rotation point in the case of an AC generator of the class that has a rated output current of 100 A. 
     Thus, intake openings  1   a  and  2   a  and exhaust openings  1   b  and  2   b  are provided in the front bracket  1  and the rear bracket  2  so as to cool heat generated by power generation. As indicated by arrows in FIG. 8, at the rear side of the generator, outside air is sucked by the rotation of the fans  5  from the intake openings  2   a  respectively provided in such a way as to face a heat sink  19  of the rectifier  12  and the heat sink  17  of the regulator  18  and flows along the axis of the shaft  6 . Consequently, the air cools the rectifier  12  and the regulator  18 . Thereafter, each of the flows of the air is turned by the corresponding fan  5  to a centrifugal direction. Thus, the air cools the rear-side coil end of the stator coil  16 . Then, the air is discharged to the outside through the exhaust openings  2   b.  On the other hand, at the front side of the generator, outside air is sucked by the rotation of the fans  5  from the intake openings  1   a  in the axial direction. Thereafter, each of the flows of the air is turned by the corresponding fan  5  to a centrifugal direction. Thus, the air cools the front-side coil end of the stator coil  16 . Then, the air is discharged to the outside through the exhaust openings  1   b.    
     Next, the structure of the conventional stator  8  will be concretely described hereinbelow with reference to FIGS. 9 to  13 . FIG. 9 is a rear elevation illustrating the coil connection employed in the conventional stator. FIG. 10 is a perspective view of a primary part of the conventional stator, viewed from the rear side thereof. FIG. 11 is a perspective view of the primary part of the conventional stator, viewed from the front side thereof. FIGS. 12 and 13 are schematic diagrams illustrating a method of winding the conventional stator coils. 
     The stator core  15  is formed like a cylinder and has a plurality of teeth  15   a  (each having a rectangular section) provided along the circumference thereof at an equiangular pitch in such a manner as to inwardly radially project therefrom. A slot  15   b  for accommodating the coil therein is formed between each pair of adjacent teeth  15   a.  Each of the slots  15   b  extends in parallel with the axial direction and is opened to the inner circumference of the stator core  15 . In the case of this conventional generator, the rotor  7  has 12 magnetic pole pieces, and the stator  8  has 36 slots  15   b.  Thus, the number of slots per magnetic pole and per phase is 1. 
     Each of the stator coils  16  is constituted by (nearly U-shaped) coil pieces  30  as follows. Each of the coil pieces  30  has a pair of leg portions  30   a  connected by a nearly V-shaped connecting portion  30   b.  The leg portions  30   a  of each of the coil pieces  30  are inserted into two slots  15   b,  whose slot numbers are different from each other by three, from the rear side of the stator core  15 . Then, open-end portions  30   c  extending toward the front side of the stator core  15  are joined together. Thus, the stator coils  16  are constructed. Incidentally, a coil conductor is constructed by connecting and integrating the coil pieces  30 . 
     Two coil pieces  30  are inserted into each set of the two slots  15   b,  whose slot numbers are by 3, from the rear side of the stator core  15 , as shown in FIG.  12 . At that time, 4 leg portions  30   a  are accommodated in each of the slots  15   b  in such a manner as to be radially arranged in a line, as illustrated in FIG.  9 . Further, the leg portions  30   a  of the outer-circumference-side coil piece  30  are inserted into a first place, which is closest to the outer circumference, in one of the slots  15   b,  whose slot numbers differ from each other by 3, and into the second place closest to the outer circumference, in the other slot  15   b.  On the other hand, the leg portions  30   a  of the inner-circumference-side coil piece  30  are inserted into a third place, which is the third closest place to the outer circumference, in one of the slots  15   b,  whose slot numbers differ from each other by 3, and into a fourth place, which is the fourth closest place to the outer circumference, in the other slot  15   b.    
     Moreover, after the leg portions  30   a  of each of the coil pieces  30  are inserted into the slots  15   b  as shown in FIG. 12, the open-end portions thereof extending toward the front side of the stator core  15  are bent in such a way as to outwardly open (that is, bent outwardly circumferentially). Furthermore, the open-end portion  30   c  of the coil piece  30  extending to the front side of the stator core  15  from the second outmost place in the corresponding slot  15   b  is made to overlap with the open-end portion  30   c  of another coil piece  30  extending to the front side from the first outmost place in another slot  15   b,  whose slot number differs from that of the former slot  15   b  by 3, as illustrated in FIGS. 11 and 13. Then, these open-end portions  30   c  are crimped with a clip  29 . Subsequently, these open-end portions  30   c  are soldered to each other. Thus, two outer-circumference-side coils, each of which consists of the connected six outer-circumference-side coil pieces  30 , are produced. Similarly, the open-end portion  30   c  of the coil piece  30  extending to the front side of the stator core  15  from the fourth outmost place in the corresponding slot  15   b  is made to overlap with the open-end portion  30   c  of another coil piece  30  extending to the front side from the third outmost place in another slot  15   b,  whose slot number differs from that of the former slot  15   b  by 3, as illustrated in FIGS. 11 and 13. Then, these open-end portions  30   c  are crimped with a clip  29 . Subsequently, these open-end portions  30   c  are soldered to each other. Consequently, two inner-circumference-side coils, each of which consists of the connected six inner-circumference-side coil pieces  30 , are produced. 
     Thus, in the two outer-circumference-side coils and the two inner-circumference-side coils inserted into adjacent two sets of two slots  15   b  selected at intervals of three slots, these coils are cut at the adjoining rear-side coil-end portions of these coils, as illustrated in FIG.  9 . Subsequently, an end portion u 1 ′ of one of the inner-circumference-side coils is joined with an end portion u 2  of one of the outer-circumference-side coils. Moreover, another end portion u 2 ′ of this outer-circumference-side coil is joined with an end portion u 3  of the other inner-circumference-side coil. Furthermore, another end portion u 3 ′ of this inner-circumference-side coil is joined with an end portion u 4  of the other outer-circumference-side coil. Thus, a four-turn coil corresponding to one phase is obtained. Further, the end portion u 1  of the former inner-circumference-side coil is connected to the rectifier  12  as a lead wire. Moreover, the end portion u 4 ′ of the latter outer-circumference-side coil is connected to a neutral point in a star three-phase connection among this coil and coils respectively corresponding to other two phases. 
     Furthermore, similarly, the coils respectively corresponding to other two phases are produced. 
     Further, each of the u 1 ′-u 2  connection portion, the u 2 ′-u 3  connection portion and the u 3 ′-u 4  connection portion is not constituted by the connecting portion of the coil piece. Instead, these connection portions are formed outside the coil end portions, as crossover connection portions, as illustrated in FIG.  10 . Incidentally, although three crossover connection portions are shown in FIG. 10, the stator actually has coils respectively corresponding to three phases. Thus, the stator has nine crossover connection portions. 
     In the case of the stator  8  constructed in this manner, the coil pieces  30  are inserted into the slots  15   b  from the rear side thereof. Moreover, the open-end portions  30   c  extending to the front side thereof are connected to each other as described above. Thus, the coil pieces  30  have almost the same shape. This results in increase in productivity of stators and easiness in being shaped after the fabrication thereof. Consequently, this reduces time and effort to perform the step of shaping the coil after the coil pieces are inserted into slots and connected to each other. 
     Moreover, connection portions for connecting the open-end portions  30   c  of the coil pieces  30  are concentrated at the front side of the stator. This enhances the workability in a process of connecting the open-end portions. 
     Incidentally, each of the nearly U-shaped coil pieces  30  is folded back nearly at the center of the corresponding connecting portion  30   b.  Both leg portions  30   a  of each of the coil pieces  30  are deviated from the folded-back portion in such a way as to suitably be accommodated in the slots  15   b.  Thus, each of the coil pieces  30  is inserted at a predetermined angle with respect to the circumference of the stator  8 . Further, the longitudinal direction of each of the coil pieces  30  is a radial direction of the stator  8  at the folded-back portion thereof. In the slots  15   b,  one of the leg portions  30   a  is placed along a radius extending from the center of the stator core  15 , while the other leg portion  30   a  is placed along a different radius of the stator core  15 . 
     In this case of the stator  8  constructed in this manner, three crossover connection portions are necessary for connecting between 4-turn coils constituting each phase coil. Consequently, the conventional vehicular AC generator has a problem in that it is necessary for forming the crossover connection portions to cut, bend and draw the coil pieces  30  excessively and that thus, the workability thereof is deteriorated. 
     Thus, an improved stator structure for reducing the number of the crossover connection portions between 4-turn coils constituting each phase coil has been proposed. 
     FIG. 14 is a rear elevation illustrating the coil connection of an improved stator applied to a conventional vehicular AC generator. FIG. 15 is a perspective view of a primary part of the improved stator applied to the conventional vehicular AC generator viewed from the rear side thereof. 
     As shown in FIGS. 14 and 15, two coil pieces  30  are inserted from the rear side of the stator core  15  into each of the slots  15   b  whose slot numbers differ by three from each other. At that time, four leg portions  30   a  are axially arranged in a line and accommodated in each of the slots  15   b.  Further, two leg portions  30   a  of each of the coil pieces  30  are sequentially inserted into the second outermost place in a slot  15   b  and the third outermost place in another slot  15   b,  which is the third slot from the former slot  15   b  in the clockwise circumferential direction in FIG.  14 . Moreover, two leg portions  30   a  of another coil piece  30  are serially inserted into the first outermost place in a slot  15   b  and into the fourth outermost place in another slot  15   b,  which is the third slot from the former slot  15   b  in the clockwise circumferential direction in FIG. 14, in such a manner as to stride over the connecting portion  30   c  of the coil piece  30  having leg portions precedingly inserted into the second outermost place in a slot  15   b  and into the third outermost place in another slot  15   b,  which is the third slot from the former slot  15   b.  Thus, the rear-side coil end portion is configured by stacking the connecting portions  30   c  of the coil pieces  30  as two layers as shown in FIG.  15 . 
     Subsequently, in the case of each coil piece  30  having leg portions respectively inserted into the second outermost place in a slot  15   b  and into the third outermost place in another slot  15   b,  the open-end portions thereof extending from the slot  15   b  toward the front side of the stator core  15  are bent in such a way as to outwardly open, that is, bent outwardly. Furthermore, in the case of each coil piece  30  having leg portions respectively inserted into the first outermost place in a slot  15   b  and into the fourth outermost place in another slot  15   b,  the open-end portions thereof extending from the slot  15   b  toward the front side of the stator core  15  are bent inwardly. 
     Furthermore, the open-end portion  30   c  of the coil piece  30  extending to the front side of the stator core  15  from the second outmost place in the corresponding slot  15   b,  as indicated by dotted lines in FIG. 14, is made to overlap with the open-end portion  30   c  of another coil piece  30  extending to the front side from the first outmost place in another slot  15   b,  whose slot number differs from that of the former slot  15   b  by 3 in the counterclockwise circumferentially, as illustrated in FIG.  14 . Then, these open-end portions  30   c  are crimped with a clip. Subsequently, these open-end portions  30   c  are soldered to each other. Similarly, the open-end portion  30   c  of the coil piece  30  extending to the front side of the stator core  15  from the third outmost place in the corresponding slot  15   b,  as indicated by dotted lines in FIG. 14, is made to overlap with the open-end portion  30   c  of another coil piece  30  extending to the front side from the fourth outmost place in another slot  15   b,  whose slot number differs from that of the former slot  15   b  by 3 in the clockwise circumferentially, as illustrated in FIG.  14 . Then, these open-end portions  30   c  are crimped with a clip. Subsequently, these open-end portions  30   c  are soldered to each other. 
     Subsequently, the connecting portion  30   b  (thus, the rear-side coil end portions) is cut off from the coil piece  30  having leg portions respectively inserted into the second outermost place in one slot of the one set of the slots  15   b,  whose slot number differs from each other by three, and into the third outermost place in another slot  15   b.  Furthermore, the connecting portion  30   b  (thus, the rear-side coil end portions) is cut off from the coil piece  30  having leg portions respectively inserted into the first outermost place in one slot of the one set of the slots  15   b,  whose slot number differs from each other by three, and into the fourth outermost place in another slot  15   b.    
     Then, end portions u 2 ′ cut off from the coil peace  30  is connected to end portion u 3  of cut off from the coil peace  30 . Thus, first and second coils each which consists of twelve connected coil pieces  30  are connected at this u 2 ′-u 3  connection portion. Consequently, a four-turn coil constituted by connecting 24 coil pieces  30  is obtained. 
     Further, end portions u 1  and u 4 ′ of the coil pieces  30 , which are cut off therefrom, respectively extend from the second and fourth places in the slots  15   b  to the rear side of the stator core  15 , as illustrated in FIG.  15 . The end portion u 1  acts as a lead wire, and the end portion u 4 ′ is connected to a neutral point. 
     Furthermore, coils corresponding to other two phases are similarly produced. Further, the end portion u 1  of the cut coil piece  30  is connected to the rectifier  12  as a lead wire. Moreover, the end portion u 4 ′ of the coil piece  30  is connected to a neutral point in a star three-phase connection among this coil and coils respectively corresponding to other two phases. Thus, a stator  8 A is obtained. 
     Incidentally, although one u 2 ′-u 3  connection portion served for crossover connection portion is shown in FIG. 15, the stator has coils respectively corresponding to three phases. Thus, the stator has three crossover connection portions. 
     In the improved stator coil  16 A constructed in this manner, the number of the crossover connection portions is reduced to three. 
     Thus, the work load of cutting, bending and drawing the coil pieces  30  so as to form the crossover connection portion is alleviated. Consequently, the workability thereof is considerably enhanced. 
     In this conventional vehicular AC generator, each of constituent phase coils of the stator coils  16  of the stator  8  is constituted by a four-turn coil. The crossover connection portion of each turn is provided at the side opposite to the part connecting the open-end portions  30   c.  Moreover, the crossover connection portion of each turn protrudes outwardly axially from the coil end portion. 
     Although the height of the coil end portion at the side of the connecting portion  30   b  of each of the coil pieces  30  (namely, the dimension of a part projecting from the end surface of the stator core  15 ) can be reduced, the crossover connection portion of each turn outwardly axially protrudes from the aligned coil end portions, so that the wind resistance at the discharge side of each of the fans increases. Consequently, the total air quantity of the fans decreases, and the cooling ability of the generator is degraded. Especially, when the axial height of the rear-side coil end portion is large, the ability to cool rear-side internal fittings, such as the rectifier  12  and the regulator  18 , is adversely affected. 
     Furthermore, unaligned large coil end portions are placed at the discharge side of the fans. Thus, the conventional vehicular AC generator has a problem in that higher-order discomfort interference noises are generated between the coil end portion and the fan  5  or the coil end portion and the shoulder of each of the claw-like magnetic pole piece  23  of the pole core  21  and that thus, wind noises are loud. 
     Moreover, the conventional vehicular AC generator has another problem in that it is necessary for connecting 4-turn coils to cut, bend and draw the coil pieces  30  and that thus, the workability thereof is extremely deteriorated. 
     Additionally, the conventional vehicular AC generator has another problem in that, owing to vibrations thereof, a break is liable to occur in the crossover connection portions and that thus, the risk of power-generation failure is increased. 
     On the other hand, in the stator coil  16 A of the improved stator  8 A, the number of the crossover connection portion between four-turn coil constituting each of constituent phase coils is reduced to one. Thus, the work load of cutting, bending and drawing the coil pieces  30  so as to form the crossover connection portion is alleviated. Consequently, the workability in winding the stator coil is considerably enhanced. However, in the stator coil  16 A, apex portions  30   d  of the connecting portions  30   b  of the coil pieces  30  are axially stacked as two layers and are circumferentially arranged, so that the height of the coil end portion is large and the wind resistance at the discharge side of each of the fans increases. Consequently, the total air quantity of the fans decreases, and the cooling ability of the generator is degraded. 
     Furthermore, the apex portions  30   d  of the connecting portions  30   b  are axially stacked as two layers, so that inner connecting portions  30   b  are covered by outer connecting portions  30   b.  Thus, in the soldering process of the open-end portions of the coil pieces  30 , even if the stator core  15  is chucked and a plane jig is held to the apex portions  30   d  of the connecting portions  30   b,  the open-end portions  30   c  thereof are of unequal height. In this case, even if the length of the leg portions of each coil piece  30  is preliminary adjusted so as to be able to make the open-end portions  30   c  of uniform height by holding the plane jig to the apex portions  30   d  of the connecting portions  30   b,  the open-end portions  30   c  thereof are of unequal height as the plane jig is not in contact with the apex portions  30   d  of the inner connecting portions  30   b.  Consequently, as the inner coil pieces  30  are soldered in such an unstable condition, the workability in soldering between the open-end portions  30   c,  that is, the workability in winding the stator coil is extremely deteriorated. 
     SUMMARY OF THE INVENTION 
     The present invention is accomplished to solve the aforementioned problems of the conventional vehicular AC generator. Accordingly, an object of the present invention is to provide a vehicular AC generator, which enhances the workability in winding the stator coil and prevents deterioration in ability to cool devices and increase in wind noises due to the projection of crossover connection portions from coil end portions by devising a coil winding structure so as to reduce and omit the crossover connection portions of turns of each constituent phase coil and to expose apex portions of connecting portions of coil pieces. 
     To achieve the foregoing object, according to an aspect of the present invention, there is provided a vehicular AC generator comprising: 
     a shaft rotatably supported on a pair of brackets; 
     a rotor fixed to the shaft and disposed in said pair of brackets; 
     a stator disposed at an outer-circumference-side of said rotor and fixed to said pair of brackets; 
     internal fittings placed at a rear side of said rotor; and 
     a fan driven by a rotation of said shaft and for forming a flow of cooling air flowing along an axis of said shaft, 
     wherein said stator comprising: 
     a stator core in which a plurality of slots, whose grooves extend in an axial direction, are circumferentially provided at an equiangular pitch so as to open on an inner circumference side thereof; and 
     a stator coil formed by AC connection of four-turn phase coils constructed by serially inserting coil conductors into said slots separated by a predetermined interval of said slots, said coil conductors being arranged four in a line in a radial direction, 
     and wherein each of said phase coils comprises: 
     nearly U-shaped first coil pieces, which constitute said coil conductors, inserted from an axial side into two adjacent sets of two of said separated slots, respectively, so that said first coil pieces are respectively positioned at a third outermost place in one slot of each of said two sets and at a second outermost place in the other slot of each of said two sets, and remaining first coil pieces inserted from an axial side into remaining sets of two of said separated slots, respectively, so that one of said remaining first coil pieces is respectively positioned at a first outermost place in one slot of each of said remaining sets and at a second outermost place in the other slot of each of said remaining sets and that another of said remaining first coil pieces is respectively positioned at a third outermost place in said one slot of each of said remaining sets and at a fourth outermost place in the other slot of each of said remaining sets; 
     second coil pieces, which constitute said coil conductors, inserted into said two sets of two of said separated slots, respectively, so that said second coil pieces are respectively positioned at a first outermost place in said one slot of each of said two sets and at a fourth outermost place of the other slot of each of said two sets and that end portions of said second coil piece extend from each slot of said two sets to both axial sides; 
     a two-turn first coil formed by connecting an end portion of each of said first coil pieces, which extend from the second outermost place in each of said slots to an axial opposite side and are bent circumferentially outwardly, to a corresponding end portion of said first and second coil pieces, which extend from the first outermost place of said slot, whose slot number differs from that thereof by the predetermined interval of said slots, to the axial opposite side and are bent circumferentially outwardly; 
     a two-turn second coil formed by connecting an end portion of each of said first and second coil pieces, which extend from the fourth outermost place in said slots to the axial opposite side and are bent circumferentially outwardly, to a corresponding end portion of said first coil pieces, which extends from the third outermost place in said slot, whose slot number differs from that thereof by the predetermined interval of said slots, to the axial opposite side and is bent circumferentially outwardly; and 
     a crossover connection portion between said first and second coils formed by connecting one of first and second sets of end portions of said second coil pieces, said first set of end portions of said second coil piece extending from the first outermost place in said one slot of each of said two sets to the axial side, said second set of end portions of said second coil piece extending from the fourth outermost place in the other slot of each of said two sets to the axial side, the other set of end portions being used as a lead wire and a wire connected to a neutral point formed among said phase coils. 
     According to another aspect of the present invention, there is provided a vehicular AC generator comprising: 
     a shaft rotatably supported on a pair of brackets; 
     a rotor fixed to said shaft and disposed in said pair of brackets; 
     a stator disposed at an outer-circumference-side of said rotor and fixed to said pair of brackets; 
     internal fittings placed at a rear side of said rotor; and 
     a fan driven by a rotation of said shaft and for forming a flow of cooling air flowing along an axis of said shaft, 
     wherein said stator comprises: 
     a stator core in which a plurality of slots, whose grooves extend in an axial direction, are circumferentially provided at an equiangular pitch so as to open on an inner circumference side thereof; and 
     a stator coil formed by AC connection of four-turn phase coils constructed by serially inserting coil conductors into said slots separated by a predetermined interval of said slots, said coil conductors being arranged four in a line in a radial direction, 
     and wherein each of said phase coils comprises: 
     one of nearly U-shaped first coil pieces, which constitute said coil conductors, inserted from an axial side into one set of two of said separated slots so that said first coil piece is respectively positioned at a first outermost place in one slot of said one set and at a third outermost place in the other slot of said one set, and remaining first coil pieces inserted from an axial side into remaining sets of two of said separated slots, respectively, so that one of said remaining first coil pieces is respectively positioned at a first outermost place in one slot of each of said remaining sets and at a fourth outermost place in the other slot of each of said remaining sets and that another of said remaining first coil pieces is respectively positioned at a second outermost place in said one slot of each of said remaining sets and at a third outermost place in the other slot of each of said remaining sets; and 
     second coil pieces, which constitute said coil conductors, inserted into said one set of two of said separated slots so that said second coil pieces are respectively positioned at a second outermost place in said one slot of said one set and at a fourth outermost place of the other slot of said one set and that end portions of said second coil piece extend from each slot of said one set to both axial sides, 
     wherein one of said remaining first coil pieces, which are respectively inserted from the axial side into the first outermost place in one slot of each of said remaining sets and the fourth outermost place in the other slot of each of said remaining sets, is respectively placed in each gap formed between another of said remaining first coil pieces, which are respectively inserted from the axial side into the second outermost place in said one slot of each of said remaining sets and the third outermost place in the other slot of each of said remaining sets, at said connecting portion thereof by setting heights of apex portion of said connecting portion at an equal value, 
     wherein a four-turn coil is formed by connecting an end portion of each of said first and second coil pieces, which extend from the second outermost place in each of said slots to an axial opposite side and are bent circumferentially outwardly, to a corresponding end portion of said first coil pieces, which extend from the first outermost place of said slot, whose slot number differs from that thereof by the predetermined interval of said slots, to the axial opposite side and are bent circumferentially inwardly and by connecting an end portion of each of said first and second coil pieces, which extend from the fourth outermost place in said slots to the axial opposite side and are bent circumferentially inwardly, is connected to a corresponding end portion of said first coil pieces, which extends from the third outermost place in said slot, whose slot number differs from that thereof by the predetermined interval of said slots, to the axial opposite side and is bent circumferentially outwardly, 
     and wherein an end portion of said second coil piece extending from the second outermost place in said one slot of said one set to the axial side and an end portion of said second coil piece extending from the fourth outermost place in the other slot of said one set to the axial side are used as a lead wire and a wire connected to a neutral point formed among said phase coils. 
     According to another aspect of the present invention, there is provided a vehicular AC generator comprising: 
     a shaft rotatably supported on a pair of brackets; 
     a rotor fixed to said shaft and disposed in said pair of brackets; 
     a stator disposed at an outer-circumference-side of said rotor and fixed to said pair of brackets; 
     internal fittings placed at a rear side of said rotor; and 
     a fan driven by a rotation of said shaft and for forming a flow of cooling air flowing along an axis of said shaft, 
     wherein said stator comprises: 
     a stator core in which a plurality of slots, whose grooves extend in an axial direction, are circumferentially provided at an equiangular pitch so as to open on an inner circumference side thereof; and 
     a stator coil formed by AC connection of four-turn phase coils constructed by serially inserting coil conductors into said slots separated by a predetermined interval of said slots, said coil conductors being arranged four in a line in a radial direction, 
     and wherein each of said phase coils comprises: 
     one of nearly U-shaped first coil pieces, which constitute said coil conductors, inserted from an axial side into one set of two of said separated slots so that said first coil piece is respectively positioned at a first outermost place in one slot of said one set and at a fourth outermost place in the other slot of said one set, and remaining first coil pieces inserted from an axial side into remaining sets of two of said separated slots, respectively, so that one of said remaining first coil pieces is respectively positioned at a first outermost place in one slot of each of said remaining sets and at a third outermost place in the other slot of each of said remaining sets and that another of said remaining first coil pieces is respectively positioned at a second outermost place in said one slot of each of said remaining sets and at a fourth outermost place in the other slot of each of said remaining sets; and 
     second coil pieces, which constitute said coil conductors, inserted into said one set of two of said separated slots so that said second coil pieces are respectively positioned at a second outermost place in said one slot of said one set and at a third outermost place of the other slot of said one set and that end portions of said second coil piece extend from each slot of said one set to both axial sides, 
     wherein a four-turn coil is formed by connecting an end portion of each of said first and second coil pieces, which extend from the second outermost place in each of said slots to an axial opposite side and are bent circumferentially outwardly, to a corresponding end portion of said first coil pieces, which extend from the first outermost place of said slot, whose slot number differs from that thereof by the predetermined interval of said slots, to the axial opposite side and are bent circumferentially inwardly and by connecting an end portion of each of said first coil pieces, which extend from the fourth outermost place in said slots to the axial opposite side and are bent circumferentially outwardly, to a corresponding end portion of said first and second coil pieces, which extends from the third outermost place in said slot, whose slot number differs from that thereof by the predetermined interval of said slots, to the axial opposite side and is bent circumferentially inwardly; 
     and wherein end portions of said second coil piece extending from the second outermost place in said one slot of said one set to the axial side and from the third outermost place in the other slot of said one set to the axial side are used as a lead wire and a wire connected to a neutral point formed among said phase coils. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other features, objects and advantages of the present invention will become apparent from the following description of preferred embodiments with reference to the drawings in which like reference characters designate like or corresponding parts throughout several views, and in which: 
     FIG. 1 is a rear elevation illustrating the coil connection of a stator applied to a vehicular AC generator, which is a first embodiment of the present invention; 
     FIG. 2 is a perspective view of a primary part of the stator applied to the vehicular AC generator, which is the first embodiment of the present invention, viewed from the rear side thereof; 
     FIG. 3 is a sectional diagram showing the vehicular AC generator, which is the first embodiment of the present invention; 
     FIG. 4 is a rear elevation illustrating the coil connection of a stator applied to a vehicular AC generator, which is a second embodiment of the present invention; 
     FIG. 5 is a perspective view of a primary part of the stator applied to the vehicular AC generator, which is the second embodiment of the present invention, viewed from the rear side thereof; 
     FIG. 6 is a rear elevation illustrating the coil connection of a stator applied to a vehicular AC generator, which is a third embodiment of the present invention; 
     FIG. 7 is a perspective view of a primary part of a stator applied to a vehicular AC generator, which is the third embodiment of the present invention; 
     FIG. 8 is a sectional diagram showing the conventional vehicular AC generator; 
     FIG. 9 is a rear elevation illustrating the coil connection applied to a conventional stator; 
     FIG. 10 is a perspective view of a primary part of the conventional stator, viewed from the rear side thereof; 
     FIG. 11 is a perspective view of the primary part of the conventional stator, viewed from the front side thereof; 
     FIGS. 12 and 13 are schematic diagrams illustrating a method of winding the conventional stator coils; 
     FIG. 14 is a rear elevation illustrating the coil connection of another conventional stator applied to the conventional vehicular AC generator; and 
     FIG. 15 is a perspective view of a primary part of another conventional stator applied to the conventional vehicular AC generator. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, the preferred embodiments of the present invention will be described in detail by referring to the accompanying drawings. 
     First Embodiment 
     FIG. 1 is a rear elevation illustrating the coil connection of a stator applied to a vehicular AC generator, which is the first embodiment of the present invention. FIG. 2 is a perspective view of a primary part of the stator applied to the vehicular AC generator, which is the first embodiment of the present invention, viewed from the rear side thereof. 
     A stator  35  of the first embodiment consists of a stator core  15  and a stator coil  36 . Similarly as in the case of the conventional stator coil  16 , the stator coil  36  is constituted by (nearly U-shaped) coil pieces  30  as follows. Each of the coil pieces  30  has a pair of leg portions  30   a  connected by a nearly V-shaped connecting portion  30   b.  The leg portions  30   a  of each of the coil pieces  30  are inserted into two slots  15   b,  whose slot numbers are different from each other by three, from the rear side of the stator core  15 . Then, open-end portions  30   c  extending toward the front side of the stator core  15  are joined together. However, the number of crossover connection portions of each phase coil is reduced to 1 by devising a coil wiring method. 
     Next, the structure of the stator  35  will be described hereinbelow with reference to FIGS. 1 and 2. 
     Two coil pieces  30  are inserted from the rear side of the stator core  15  into each set of the slots  15   b  whose slot numbers differ by three from each other. At that time, four leg portions  30   a  are radially arranged in a line and accommodated in each of the slots  15   b.  Further, two leg portions  30   a  of each of the outer-circumference-side coil piece  30  are respectively inserted into the first outermost place in a slot  15   b  and the second outermost place in another slot  15   b,  which is the third slot from the former slot  15   b  in the clockwise circumferential direction in FIG.  1 . On the other hand, two leg portions  30   a  of each of the inner-circumference-side coil piece  30  are respectively inserted into the third outermost place in a slot  15   b  and the fourth outermost place in another slot  15   b,  which is the third slot from the former slot  15   b  in the clockwise circumferential direction in FIG.  1 . Thus, a rear-side coil end portion  36   r  is configured by arranging in the circumferential direction the apex portions (return portion) of the connecting portions  30   b  of the coil pieces  30  aligned in two rows in the radial direction as shown in FIG.  2 . 
     Incidentally, the slot inserting positions, into which leg portions of a coil piece  30  are inserted, in each of adjacent two sets of the slots  15   b,  whose slot numbers differ from each other by three, are set to differ from those in other sets of such two slots  15   b.  Namely, in the former set of two slots  15   b,  the leg portions of one coil piece  30  are respectively inserted into the first outermost place in one of these two slots  15   b  from the outer-circumference and into the fourth outermost place in the other slot  15   b,  whose slot number differs from that of the former slot  15   b  by three in the clockwise circumference direction in FIG.  1 . Moreover, the leg portions of another coil piece  30  are respectively inserted into the third outermost place in one of these two slots  15   b  and into the second outermost place in the other slot  15   b,  whose slot number differs from that of the former slot  15   b  by three in the clockwise circumferential direction in FIG.  1 . 
     Additionally, the former coil piece  30  corresponds to a second coil piece, which has leg portions respectively inserted into the first outermost place in one of these two slots  15   b  from the outer-circumference and into the fourth outermost place in the other slot  15   b,  whose slot number differs from that of the former slot  15   b  by three in the clockwise circumference direction in FIG.  1 . The other coil piece  30  corresponds to a first coil piece. 
     Further, each of the coil pieces  30  is folded back at the apex portion  30   d  of the connecting portion  30   b  so that a pair of leg portions  30   a  thereof are deviated from each other in the radial direction in FIG.  1 . Moreover, each of coil pieces  30 A and  30 B, which has leg portions respectively inserted into the third outermost place in one of two slots  15   b  and into the second outermost place in the other slot  15   b  whose slot number differs from that of the former slot  15   b  by three in the clockwise circumferential direction, is adapted so that the direction, in which the leg portions thereof are folded back at the apex portion  30   d  of the connecting portion  30   b,  is opposite to such a direction in the case of other coil pieces  30  so as to suppress the interference from those coil pieces  30 . 
     Consequently, the rear-side coil end portion  36   r  is configured by arranging in the circumferential direction the apex portions (return portion) of the connecting portions  30   b  of the coil pieces  30  aligned in two rows in the radial direction as shown in FIGS. 1 and 2. 
     Furthermore, after the leg portions of each of the coil pieces  30  are inserted into the slots  15   b,  the open-end sides extending toward the front side are outwardly bent. Further, as indicated by dotted lines in FIG. 1, the open-end portion  30   c  of the coil piece  30 , which extends to the front side from the second outermost place of a slot  15   b,  is made to overlap with the open-end portion  30   c  of another coil piece  30  extending to the front side from the first outmost place in another slot  15   b,  whose slot number differs from that of the former slot  15   b  by three. Then, these open-end portions  30   c  are crimped with a clip. Subsequently, these open-end portions  30   c  are soldered to each other. Thus, two-turn outer-circumference-side coil (namely, a first coil), which consists of twelve connected outer-circumference-side coil pieces  30 , are produced. Similarly, the open-end portion  30   c  of the coil piece  30  extending to the front side of the stator core  15  from the fourth outmost place in the corresponding slot  15   b  is made to overlap with the open-end portion  30   c  of another coil piece  30  extending to the front side from the third outmost place in another slot  15   b,  whose slot number differs from that of the former slot  15   b  by 3, as indicated by dotted lines in FIG.  1 . Then, these open-end portions  30   c  are crimped with a clip. Subsequently, these open-end portions  30   c  are soldered to each other. Consequently, two-turn inner-circumference-side coil (namely, a second coil), which consists of twelve connected inner-circumference-side coil pieces  30 , are produced. 
     Then, the connecting portions  30   b  (thus, the rear-side coil end portions) are cut off from each coil piece  30  having leg portions respectively inserted into the first outermost place in one slot of two sets of the slots  15   b  and into the fourth outermost place in another slot  15   b,  whose slot number differs by three from that of the former slot  15   b  in the clockwise circumferential direction in FIG.  1 . Subsequently, end portions u 2 ′ and u 3  of each coil piece  30 , which are cut off and extend from the first outermost place in the slot  15   b,  are made to overlap with each other and joined together. Thus, a four-turn coil corresponding to a phase is produced. Thus, in a one-phase constituent coil of the stator coil  36 , end portions u 1  and u 4 ′ of each of the cut coil pieces  30  extend from the fourth outermost place in the slot  15   b  to the rear side of the stator core  15 , as shown in FIG.  2 . 
     Moreover, coils corresponding to other two phases are similarly produced. Furthermore, the end portion u 1  of the cut coil piece  30  is connected to the rectifier  12  as a lead wire. Moreover, the end portion u 4 ′ of another coil piece  30  is connected to a neutral point in a star three-phase connection among this coil and coils respectively corresponding to other two phases. 
     Further, each of the u 1 ′-u 2  connection portion and the u 3 ′-u 4  connection portion, which are necessary for the conventional stator coil  16 , are replaced with the coil pieces  30 A and  30 B, each of which has leg portions respectively inserted into the third outermost place in one of the slots  15   b  and into the second outermost place in another slot  15   b,  whose slot number differs from that of the former slot  15   b  by three in the circumferential direction. Thus, only one crossover connection portion u 2 ′-u 3  still remains in the stator. Incidentally, because the stator actually has coils respectively corresponding to three phases, the stator has three crossover connection portions. 
     In this first embodiment, the coil pieces  30  are inserted into the slots  15   b  from the rear side thereof, similarly as in the conventional generator. Moreover, the open-end portions  30   c  extending to the front side thereof are connected to each other as described above. Thus, stator coils  36  are produced. Consequently, the coil pieces  30  have almost the same shape. This results in increase in productivity of stators and easiness in being shaped after the fabrication thereof. Consequently, this reduces time and effort to perform the step of shaping the coil after the coil pieces are inserted into slots and connected to each other. Furthermore, connection portions for connecting the open-end portions  30   c  of the coil pieces  30  are concentrated at the front side of the stator. This enhances the workability in a process of connecting the open-end portions. 
     According to the first embodiment, the number of the crossover connection portions between 4-turn coils constituting constituent phase coil of the stator coil  36  is reduced to 1. Thus, the work load of cutting, bending and drawing the coil pieces  30  so as to form the crossover connection portion is alleviated. Consequently, the workability thereof is considerably enhanced. Moreover, the risk of a break in the crossover connection portion due to vibrations of the vehicular AC generator is reduced. Consequently, an occurrence of power-generation failure owing to the break in the crossover connection portion is prevented. 
     Further, the crossover connection portion u 2 ′-u 3  is configured by overlapping and connecting the end portions u 2 ′ and u 3  of each coil piece  30 , which extend toward the rear side thereof from the first outermost place in the slots  15   b  after cut off at the connecting portions. Thus, this crossover connection portion is placed at the outer-diameter-side of the coil end portion and positioned between the coil end portion and the bracket. Therefore, neither the height of the coil end portion nor the wind resistance at the discharge side of the fan  5  is increased by forming the crossover connection portion. Consequently, the total air quantity of the fans is restrained from decreasing, so that the temperature of each part of the generator is prevented from rising. Moreover, the connecting portion  30   b  of the coil piece  30 , which serves to reduce the height of the coil end portion, is placed at the rear side of the stator. Thus, the wind resistance decreases at the discharge side of the rear-side fan. Consequently, the rear-side internal fittings, such as the rectifier  12  and the regulator  18 , are efficiently cooled. 
     Furthermore, the rear-side coil end portions have no axial projections due to the crossover connection portion. This prevents the generation of higher-order discomfort interference noises between the coil end portion and the fan  5  or the coil end portion and the shoulder of the claw-like magnetic pole  23  of the pole core  21 . Consequently, wind noises are reduced. 
     Additionally, in the conventional generator, a mixed condition of the crossover connection portion and the constituent coils of the coil end portions is apt to damage the coils. However, in the case of this stator coil  36 , the crossover connection portion is placed at the outside-diameter side of the coil end portion, so that the coils are prevented from being damaged and that high quality output and performance are achieved. 
     Furthermore, the apex portions  30   d  of the connecting portions  30   b  of coil pieces  30  constituting the stator coil  36  are aligned as two rows in the radial direction and are arranged in the circumferential direction, so that the height of the coil end portion is small and the wind resistance at the discharge side of each of the fans decreases. Consequently, the total air quantity of the fans increases, and the cooling ability of the generator is enhanced. 
     The apex portions  30   d  of the connecting portions  30   b  are exposed in the axial direction, so that the open-end portions  30   c  thereof are of the same uniform height by chucking the stator core  15  and holding a plane jig to the apex portions  30   d  of the connecting portions  30   b  of all coil pieces  30  in the jointing process of the open-end portions of the coil pieces  30  before the open-end portions  30   c  are jointed. Thus, when the open-end portions  30   c  are jointed, the height of the open-end portions  30   c  are maintained uniformly, so that the open-end portions  30   c  are jointed in such a stable condition and the workability in jointing between the open-end portions  30   c  is enhanced. 
     Furthermore, the height of the coil end portion constituted by the connecting portions  30   b  of the coil pieces  30  in the axial direction is smaller than that of the coil end portion constituted by jointing the open-end portions  30   c  thereof. The coil end portion constituted by the connecting portions  30   b  of the coil pieces  30  is disposed at the rear side. Thus, the height of the rear-side coin end portion  36   r  is lower than that of a front-side coil end portion  36   f  so that the wind resistance at the rear side decreases, that is, the air quantity at the rear side increases. Consequently, the rear-side internal fittings, such as the rectifier  12  and the regulator  18 , are efficiently cooled. 
     As the fans  5  are disposed at both axial ends of the rotor  7 , a front-side cooling air path in which the outer air is sucked in from the intake openings  1   a,  cools the front-side coil end portion of the stator coil  36  and then is discharged to the outside from the exhaust opening  1   b  and a rear-side cooling air path in which the outer air is sucked in from the intake openings  2   a,  respectively, cooling the rectifier  12  and the regulator  18 , cools the rear-side coil end portion of the stator coil  36  and then is discharged to the outside from the exhaust opening  2   b  are formed, realizing the good cooling ability. 
     In the first embodiment, it is to be desired that the axial lap amount between the front-side coil end portion and the fan  5  is larger than that between the rear-side coil end portion and the fan  5 . Accordingly, the rear-side cooling air path has a high wind resistance as the rectifier  12  and the regulator  18  are disposed in the rear-side cooling air path. On the other hand, the front-side cooling air path has a low wind resistance as there is no internal fittings in the front-side cooling air path. Thus, the wind resistance of the rear-side cooling air path due to the rear-side coil end portion is restrained from increasing by decreasing the axial lap amount between the rear-side coil end portion and the fan  5 , so that the rectifier  12  and the regulator  18  are efficiently cooled by the cooling air flowing through the rear-side cooling air path. On the other hand, the wind resistance of the front-side cooling air path is not particularly increased even if the axial lap amount between the front-side coil end portion and the fan  5  is increased, because the front-side cooling air path has a low wind resistance due to no internal fittings. Further, since there is no internal fittings in the front-side cooling air path, it is possible to suppress temperature increases in the cooling air flowing through the front-side cooling air path and the area of the front-side coil end portion on which the cooling air hits is increased. Thus, the large area of the front-side coil end portion is exposed to the cooling air, enabling temperature increases in the stator coil to be efficiently suppressed. 
     Furthermore, in the first embodiment, it is to be desired that gaps between the apex portion of the rear-side coil end portion and the opposite plane of the rear bracket  2  opposite to the apex portion thereof, between the apex portion thereof and the rectifier  12  and between the apex portion thereof and the regulator  18  are uniformly formed in the circumferential direction. Accordingly, the cooling air paths constituted by the apex portion of the coil end portion and the opposite plane of the rear bracket  2 , and by the apex portion of the coil end portion and the rectifier  12  and the regulator  18  are formed so as to have a uniform gap in the circumferential direction, respectively. Thus, it is possible to suppress fluctuations in the wind resistance of the cooling air paths in the circumferential direction. Consequently, overall wind resistance of the cooling air path is reduced, enabling the good cooling ability of the rectifier  12  and the regulator  18  to be secured. 
     Furthermore, in the first embodiment, it is to be desired that the front-side exhaust wind volume is larger than the rear-side exhaust wind volume. Accordingly, the front-side exhaust air which is possible to cool the coil end portion efficiently increases in wind volume compared with the rear-side exhaust air, enabling. Consequently, the stator coil is efficiently cooled, enabling temperature increases in the rectifier  12  and the regulator  18  to be suppressed. Furthermore, the front-side exhaust wind volume having a low wind resistance increases compared with the rear-side exhaust wind volume having a high wind resistance, preventing wind noise from being deteriorated. 
     Incidentally, in the foregoing description of the first embodiment, it has been described that the leg portions of the nearly U-shaped coil pieces are inserted into the first outermost place in one of two slots  15   b,  whose slot numbers differ from each other by three, and into the fourth outermost place in the other slot  15   b,  whose slot number differs from that of the former one  15   b  in the clockwise circumferential direction in FIG. 1, and that the connecting portions  30   b  (namely, the rear-side coil end portions) of the coil pieces  30  are, thereafter, cut off. However, the present invention is not limited to this generator. The generator according to be present invention may be adapted so that rod-like coil pieces are inserted into the first outermost place in one of two slots  15   b,  whose slot numbers differ from each other by three, and into the fourth outermost place in the other slot  15   b,  whose slot number differs from that of the former one  15   b  in the clockwise circumferential direction in FIG. 1 in such a way as to axially extend to both sides thereof. This obviates the necessity of cutting off the connecting portions  30   b  of the coil pieces  30 . 
     Further, in the first embodiment, it has been described that the crossover connection portion u 2 ′-u 3  is configured by overlapping and connecting the end portions u 2 ′ and u 3  of each coil piece  30 , which extend toward the rear side thereof from the first outermost place in the slots  15   b  after cut off at the connecting portions. However, the crossover connection portion u 2 ′-u 3  may be configured by overlapping and connecting the end portions u 1  and u 4 ′ of each coil piece  30 , which extend toward the rear side thereof from the fourth outermost place in the slots  15   b  after cut off at the connecting portions. In this case, the end portions u 2 ′ and u 3  of each coil piece  30 , which extend toward the rear side thereof from the first outermost place in the slots  15   b  after cut off at the connecting portions, are connected to the rectifier  12  as a lead wire and to a neutral point in a star three-phase connection among this coil and coils respectively corresponding to other two phases, respectively. 
     Furthermore, in the first embodiment, it has been described that the apex portions  30   d  of the connecting portions of the coil pieces  30  constituting the stator coil  36  are radially aligned in two rows and are arranged in the circumferential direction. However, the apex portions  30   d  may be arranged in a single row in the circumferential direction, enabling the same effects to be achieved. 
     Furthermore, in the first embodiment, it has been described that the fans  5  are fixed to both axial ends of the rotor  7 . However, the fans  5  are not necessarily disposed at both axial ends of the rotor  7 . The fan  5  may be fixed to the only rear-side axial end of the rotor  7 . In this case, though cooling efficiency in the front-side coil end portion is reduced, a flow of the cooling air is formed by the rotation of the fan  5  at the rear side, cooling the rectifier  12  and the regulator  18  and then cooling the rear-side coil end portion, enabling temperature increases in the stator coil to be suppressed. Further, the fan  5  is disposed at only the rear side of the rotor  7 , enabling costs to be lowered. 
     Second Embodiment 
     FIG. 4 is a rear elevation illustrating the coil connection of a stator applied to a vehicular AC generator, which is the second embodiment of the present invention. FIG. 5 is a perspective view of a primary part of the stator applied to the vehicular AC generator, which is the second embodiment of the present invention, viewed from the rear side thereof. 
     As shown in FIGS. 4 and 5, two coil pieces  30  are inserted from the rear side of the stator core  15  into each of the slots  15   b  whose slot numbers differ by three from each other. At that time, four leg portions  30   a  are radially arranged in a line and accommodated in each of the slots  15   b.  Further, two leg portions  30   a  of each of the coil pieces  30  are sequentially inserted into the second outermost place in a slot  15   b  and the third outermost place in another slot  15   b,  which is the third slot from the former slot  15   b  in the clockwise circumferential direction in FIG.  4 . Moreover, two leg portions  30   a  of another coil piece  30  are serially inserted into the first outermost place in a slot  15   b  and into the fourth outermost place in another slot  15   b,  which is the third slot from the former slot  15   b  in the clockwise circumferential direction in FIG. 4, in such a manner as to get the apex portion (return portion) of the connecting portion  30   b  thereof between the apex portions of the connecting portions  30   b  of the coil pieces  30  having leg portions precedingly inserted into the second outermost place in a slot  15   b  and into the third outermost place in another slot  15   b,  which is the third slot from the former slot  15   b.  Thus, the rear-side coil end portion is configured by arranging the apex portions of the connecting portions  30   b  of the coil pieces  30  in a single row in the circumferential direction as shown in FIG.  5 . 
     Incidentally, the slot inserting positions, into which leg portions of a coil piece  30  are inserted, in one set of the slots  15   b,  whose slot numbers differ from each other by three, are set to differ from those in other sets of such two slots  15   b.  Namely, in the one set of two slots  15   b,  the leg portions of one coil piece  30  are respectively inserted into the first outermost place in one of the two slots  15   b  from the outer-circumference and into the third outermost place in the other slot  15   b,  whose slot number differs from that of the former slot  15   b  by three in the clockwise circumference direction in FIG.  4 . Moreover, the leg portions of the other coil piece  30  are respectively inserted into the second outermost place in one of the two slots  15   b  and into the fourth outermost place in the other slot  15   b,  whose slot number differs from that of the former slot  15   b  by three in the clockwise circumferential direction in FIG.  4 . 
     Additionally, the coil piece  30  corresponds to a second coil piece, which has leg portions respectively inserted into the second outermost place in one of these two slots  15   b  from the outer-circumference and into the fourth outermost place in the other slot  15   b,  whose slot number differs from that of the former slot  15   b  by three in the clockwise circumference direction in FIG.  4 . The other coil piece  30  corresponds to a first coil piece. 
     Subsequently, in the case of each coil piece  30  having leg portions respectively inserted into the second outermost place in a slot  15   b  and into the third outermost place in another slot  15   b,  the open-end portions thereof extending from the slot  15   b  toward the front side of the stator core  15  are bent in such a way as to outwardly open, that is, bent outwardly. Furthermore, in the case of each coil piece  30  having leg portions respectively inserted into the first outermost place in a slot  15   b  and into the fourth outermost place in another slot  15   b,  the open-end portions thereof extending from the slot  15   b  toward the front side of the stator core  15  are bent inwardly. Further, in the case of each coil piece  30  having leg portions respectively inserted into the first outermost place in a slot  15   b  and into the third outermost place in another slot  15   b,  the open-end portion thereof extending from the first outermost place in the slot  15   b  toward the front side of the stator core  15  is bent inwardly, and the open-end portion thereof extending from the third outermost place in the slot  15   b  toward the front side of the stator core  15  is bent outwardly. Moreover, in the case of each coil piece  30  having leg portions respectively inserted into the second outermost place in a slot  15   b  and into the fourth outermost place in another slot  15   b,  the open-end portion thereof extending from the second outermost place in the slot  15   b  toward the front side of the stator core  15  is bent outwardly, and the open-end portion thereof extending from the fourth outermost place in the slot  15   b  toward the front side of the stator core  15  is bent inwardly. 
     Furthermore, the open-end portion  30   c  of the coil piece  30  extending to the front side of the stator core  15  from the second outmost place in the corresponding slot  15   b,  as indicated by dotted lines in FIG. 4, is made to overlap with the open-end portion  30   c  of another coil piece  30  extending to the front side from the first outmost place in another slot  15   b,  whose slot number differs from that of the former slot  15   b  by 3 in the counterclockwise circumferentially, as illustrated in FIG.  4 . Then, these open-end portions  30   c  are crimped with a clip. Subsequently, these open-end portions  30   c  are soldered to each other. Similarly, the open-end portion  30   c  of the coil piece  30  extending to the front side of the stator core  15  from the third outmost place in the corresponding slot  15   b,  as indicated by dotted lines in FIG. 4, is made to overlap with the open-end portion  30   c  of another coil piece  30  extending to the front side from the fourth outmost place in another slot  15   b,  whose slot number differs from that of the former slot  15   b  by 3 in the clockwise circumferentially, as illustrated in FIG.  4 . Then, these open-end portions  30   c  are crimped with a clip. Subsequently, these open-end portions  30   c  are soldered to each other. 
     Thus, a first two-turn coil and a second two-turn coil each consisting of twelve connected coil pieces  30  are connected at the connecting portion  30   b  of the coil piece  30 C having leg portions respectively inserted into the first outermost place in one slot  15   b  and into the third outermost place in another slot  15   b,  whose slot number differs from that of the former slot  15   b.  Thus, a four-turn coil constituted by connecting 24 coil pieces  30  is obtained. 
     Subsequently, the connecting portion  30   b  (thus, the rear-side coil end portions) is cut off from the coil piece  30  having leg portions respectively inserted into the second outermost place in one slot of the one set of the slots  15   b,  whose slot number differs from each other by three, and into the fourth outermost place in another slot  15   b.  Then, end portions u 1  and u 4 ′ of the coil piece  30 , which are cut off therefrom, respectively extend from the second and fourth places in the slot  15   b  to the rear side of the stator core  15 , as illustrated in FIG.  5 . The end portion u 1  acts as a lead wire, and the end portion u 4 ′ is connected to a neutral point. 
     Furthermore, coils corresponding to other two phases are similarly produced. Further, the end portion u 1  of the cut coil piece  30  is connected to the rectifier  12  as a lead wire. Moreover, the end portion u 4 ′ of this coil piece  30  is connected to a neutral point in a star three-phase connection among this coil and coils respectively corresponding to other two phases. Thus, a stator  35 A is obtained. 
     Further, the u 2 ′-u 3  connection portion is necessary for the stator coil  36  of the aforementioned first embodiment. However, in the case of the stator coil  36 A of the second embodiment, the connecting portion  30   b  of the coil piece  30 C corresponds to the u 2 ′-u 3  connecting portion. Incidentally, the coil piece  30 C has leg portions respectively inserted into the first outermost place in one of the slots  15   b  and into the third outermost place in the other slot  15   b,  whose slot number differs from that of the former slot  15   b  by three in the circumferential direction. Thus, the second embodiment obviates the crossover connection portion. 
     According to this second embodiment, the connecting portion  30   b  of the stator coil  30 C is substituted for the crossover connection portion between the four-turn coils constituting each constituent phase coil of the stator coil  36 A. Consequently, the second embodiment obviates the crossover connection portion. 
     Thus, the second embodiment obviates the work of cutting, bending and drawing the coil pieces so as to form the crossover connection portion. Consequently, the workability thereof is considerably enhanced. 
     Moreover, the risk of a break in the crossover connection portion due to vibrations of the vehicular AC generator is eliminated. Consequently, an occurrence of power-generation failure owing to the break in the crossover connection portion is prevented. 
     Further, because the crossover connection portion is eliminated, the height of the coil end portion is reduced. Thus, the wind resistance at the discharge side of the fan  5  is decreased. Consequently, the total air quantity of the fans is restrained from decreasing, so that the temperature of each part of the generator is prevented from rising. Especially, the rear-side internal fittings, such as the rectifier  12  and the regulator  18 , are efficiently cooled. 
     Furthermore, the coil end portions have no axial projections due to the crossover connection portion. This prevents the generation of higher-order discomfort interference noises between the coil end portion and the fan  5  or the coil end portion and the shoulder of the claw-like magnetic pole  23  of the pole core  21 . Consequently, wind noises are reduced. 
     Additionally, if the crossover connection portion is placed between the coil end portion and the bracket, similarly as in the aforementioned first embodiment, an insulation failure between the crossover connection portion and the bracket may occur. However, such an insulation failure does not occur in the second embodiment. 
     Further, the second embodiment eliminates the risk of damage to the coils due to the mixed condition of the crossover connection portion and the coil of the coil end portion. Consequently, the second embodiment achieves high quality output and high performance. 
     Furthermore, because the apex portions of the connecting portions  30   b  of the coil pieces  30  constituting the stator coil  36 A are arranged in a single row in the circumferential direction, the height of the coil end portion is reduced and the wind resistance at the discharge side of the fan is reduced. As a result, the total air quantity of the fans is increased, enabling cooling ability in the AC generator to be enhanced. 
     Furthermore, because the apex portions of the connecting portions  30   b  are exposed in the axial direction, the open-end portions  30   c  of the coil pieces  30  are soldered to each other in such a stable condition that the stator core  15  is chucked and the connecting portions  30   b  of the coil pieces  30  are held, enabling the workability in soldering between the open-end portions  30   c  to be enhanced. 
     Incidentally, in the foregoing description of the second embodiment, it has been described that the leg portions of the nearly U-shaped coil pieces are inserted into the second outermost place in one of two slots  15   b,  whose slot numbers differ from each other by three, and into the fourth outermost place in the other slot  15   b,  whose slot number differs from that of the former one  15   b  in the clockwise circumferential direction in FIG. 4, and that the connecting portion  30   b  (namely, the rear-side coil end portion) of the coil pieces  30  is, thereafter, cut off. However, the present invention is not limited to this generator. The generator according to be present invention may be adapted so that rod-like coil pieces are inserted into the second outermost place in one of two slots  15   b,  whose slot numbers differ from each other by three, and into the fourth outermost place in the other slot  15   b,  whose slot number differs from that of the former one  15   b  in the clockwise circumferential direction in FIG. 4 in such a way as to axially extend to both sides thereof. This obviates the necessity of cutting off the connecting portion  30   b  of the coil piece  30 . 
     Further, in the foregoing description of the second embodiment, it has been described that the end portions u 1  and u 4 ′ of the coil piece  30 , which respectively extend toward the rear side thereof from the second and fourth outermost places in the slots  15   b  after cut off therefrom, serve as a lead wire connected to the rectifier  12  and a wire connected to a neutral point among this coil and coils respectively corresponding to other two phases. However, the end portions u 1  and u 4 ′ may be respectively used as a wire connected to the neutral point and a lead wire connected to the rectifier  12 . 
     Third Embodiment 
     FIG. 6 is a rear elevation illustrating the coil connection of a stator applied to a vehicular AC generator, which is the third embodiment of the present invention. FIG. 7 is a perspective view of a primary part of the stator applied to the vehicular AC generator, which is the third embodiment of the present invention, viewed from the rear side thereof. 
     As shown in FIGS. 6 and 7, two coil pieces  30  are inserted from the rear side of the stator core  15  into each set of the slots  15   b  whose slot numbers differ by three from each other. At that time, four leg portions  30   a  are radially arranged in a line and accommodated in each of the slots  15   b.  Further, two leg portions  30   a  of each of the coil piece  30  are sequentially inserted into the first outermost place in a slot  15   b  and the third outermost place in another slot  15   b,  which is the third slot from the former slot  15   b  in the clockwise circumferential direction in FIG.  6 . Moreover, two leg portions  30   a  of another coil piece  30  are serially inserted into the second outermost place in a slot  15   b  and into the fourth outermost place in another slot  15   b,  which is the third slot from the former slot  15   b  in the clockwise circumferential direction in FIG.  6 . Thus, at the rear-side coil end portion, the apex portions of the connecting portions  30   b  of the coil pieces  30  are aligned in two rows in the radial direction and are arranged in the circumferential direction as shown in FIG.  7 . 
     Incidentally, the slot inserting positions, into which leg portions of a coil piece  30  are inserted, in one set of the slots  15   b,  whose slot numbers differ from each other by three, are changed to those in the other sets of such two slots  15   b.  Namely, in this set of the slots  15   b,  the leg portions of one coil piece  30  ( 30 D) are respectively inserted into the first outermost place in one of these two slots  15   b  from the outer-circumference and into the fourth outermost place in the other slot  15   b,  whose slot number differs from that of the former slot  15   b  by three in the clockwise circumference direction in FIG.  6 . Moreover, the leg portions of the other coil piece  30  are respectively inserted into the second outermost place in one of the two slots  15   b  and into the third outermost place in the other slot  15   b,  whose slot number differs from that of the former slot  15   b  by three in the clockwise circumferential direction in FIG.  6 . 
     Additionally, the coil piece  30  corresponds to a second coil piece, which has leg portions respectively inserted into the second outermost place in one of these two slots  15   b  from the outer-circumference and into the third outermost place in the other slot  15   b,  whose slot number differs from that of the former slot  15   b  by three in the clockwise circumference direction in FIG.  6 . The other coil piece  30  corresponds to a first coil piece. 
     Subsequently, in the case of each coil piece  30  having leg portions respectively inserted into the first outermost place in a slot  15   b  and into the third outermost place in another slot  15   b,  the open-end portions thereof extending from the slot  15   b  toward the front side of the stator core  15  are bent inwardly. Furthermore, in the case of each coil piece  30  having leg portions respectively inserted into the second outermost place in a slot  15   b  and into the fourth outermost place in another slot  15   b,  the open-end portions thereof extending from the slot  15   b  toward the front side of the stator core  15  are bent in such a way as to outwardly open. Further, in the case of the coil piece  30  having leg portions respectively inserted into the first outermost place in a slot  15   b  and into the fourth outermost place in another slot  15   b,  the open-end portion thereof extending from the first outermost place in the slot  15   b  toward the front side of the stator core  15  are bent inwardly, and the open-end portion thereof extending from the fourth outermost place in the slot  15   b  toward the front side of the stator core  15  are bent outwardly. Moreover, in the case of the coil piece  30  having leg portions respectively inserted into the second outermost place in a slot  15   b  and into the third outermost place in another slot  15   b,  the open-end portion thereof extending from the second outermost place in the slot  15   b  toward the front side of the stator core  15  are bent outwardly, and the open-end portion thereof extending from the third outermost place in the slot  15   b  toward the front side of the stator core  15  are bent inwardly. 
     Furthermore, the open-end portion  30   c  of the coil piece  30  extending to the front side of the stator core  15  from the first outmost place in the corresponding slot  15   b,  as indicated by dotted lines in FIG. 6, is made to overlap with the open-end portion  30   c  of the coil piece  30  extending to the front side from the second outmost place in another slot  15   b,  whose slot number differs from that of the former slot  15   b  by three in the counterclockwise circumferentially, as illustrated in FIG.  6 . Then, these open-end portions  30   c  are crimped with a clip. Subsequently, these open-end portions  30   c  are soldered to each other. Similarly, the open-end portion  30   c  of the coil piece  30  extending to the front side of the stator core  15  from the third outmost place in the corresponding slot  15   b,  as indicated by dotted lines in FIG. 6, is made to overlap with the open-end portion  30   c  of the coil piece  30  extending to the front side from the fourth outmost place in another slot  15   b,  whose slot number differs from that of the former slot  15   b  by three in the counterclockwise circumferentially, as illustrated in FIG.  6 . Then, these open-end portions  30   c  are crimped with a clip. Subsequently, these open-end portions  30   c  are soldered to each other. 
     Thus, a first two-turn coil and a second two-turn coil consisting of twelve connected coil pieces  30  are connected at the connecting portion  30   b  of the coil piece  30 D having leg portions respectively inserted into the first outermost place in one slot  15   b  and into the fourth outermost place in another slot  15   b,  whose slot number differs from that of the former slot  15   b.  Thus, a four-turn coil constituted by connecting  24  coil pieces  30  is obtained. 
     Subsequently, the connecting portion  30   b  (thus, the rear-side coil end portion) is cut off from the coil piece  30  having leg portions respectively inserted into the second outermost place in one slot of a set of the slots  15   b  and into the third outermost place in another slot  15   b,  whose slot number differs by three from that of the former slot  15   b.  Then, end portions u 1  and u 4 ′ of the coil piece  30 , which are cut off therefrom and respectively extend from the second and third places in the slots  15   b  to the rear side of the stator core  15 , as illustrated in FIG.  6 . The end portion u 1  acts as a lead wire, and the end portion u 4 ′ is connected to a neutral point. 
     Furthermore, coils corresponding to other two phases are similarly produced. 
     Further, the end portion u 1  of the cut coil piece  30  is connected to the rectifier  12  as a lead wire. Moreover, the end portion u 4 ′ of this coil piece  30  is connected to a neutral point in a star three-phase connection among this coil and coils respectively corresponding to other two phases. Thus, a stator  35 B is obtained. 
     Further, the u 2 ′-u 3  connection portion is necessary for the stator coil  36  of the aforementioned first embodiment. However, in the case of the stator coil  36 B of the third embodiment, the connecting portion  30   b  of the coil piece  30 D corresponds to the u 2 ′-u 3  connection portion. Incidentally, the coil piece  30 D has leg portions respectively inserted into the first outermost place in one of the slots  15   b  and into the fourth outermost place in another slot  15   b,  whose slot number differs from that of the former slot  15   b  by three in the circumferential direction. Thus, the third embodiment obviates the crossover connection portion. 
     According to this third embodiment, the connecting portion  30   b  of the stator coil  30 D is substituted for the crossover connection portion between the four-turn coils constituting each constituent phase coil of the stator coil  36 B. Consequently, the third embodiment obviates the crossover connection portion. 
     Thus, the third embodiment obviates the work of cutting, bending and drawing the coil pieces so as to form the crossover connection portion. Consequently, the workability thereof is considerably enhanced. 
     Moreover, the risk of a break in the crossover connection portion due to vibrations of the vehicular AC generator is eliminated. Consequently, an occurrence of power-generation failure owing to the break in the crossover connection portion is prevented. 
     Further, because the crossover connection portion is eliminated, the height of the coil end portion is reduced. Thus, the wind resistance at the discharge side of the fan  5  is decreased. Consequently, the total air quantity of the fans is restrained from decreasing, so that the temperature of each part of the generator is prevented from rising. Especially, the rear-side internal fittings are efficiently cooled. 
     Furthermore, the coil end portions have no axial projections due to the crossover connection portion. This prevents the generation of higher-order discomfort interference noises between the coil end portion and the fan  5  or the coil end portion and the shoulder of the claw-like magnetic pole  23  of the pole core  21 . Consequently, wind noises are reduced. 
     Additionally, if the crossover connection portion is placed between the coil end portion and the bracket, similarly as in the aforementioned first embodiment, an insulation failure between the crossover connection portion and the bracket may occur. However, such an insulation failure does not occur in the third embodiment. 
     Further, the third embodiment eliminates the risk of damage to the coils due to the mixed condition of the crossover connection portion and the coil of the coil end portion. Consequently, the third embodiment achieves high quality output and high performance. 
     Furthermore, the coil pieces  30  of each phase coil is configured by having nearly the same shape. Thus, there is little overlap between the coil pieces. Consequently, the height of the coil end portion is reduced to a small value. Moreover, the damage to the coil is reduced. 
     Furthermore, because the apex portions of the connecting portions  30   b  of the coil pieces  30  constituting the stator coil  36 B are arranged in a single row in the circumferential direction, the height of the coil end portion is reduced and the wind resistance at the discharge side of the fan is reduced. As a result, the total air quantity of the fans is increased, enabling cooling ability in the AC generator to be enhanced. 
     Furthermore, because the apex portions of the connecting portions  30   b  are exposed in the axial direction, the open-end portions  30   c  of the coil pieces  30  are soldered to each other in such a stable condition that the stator core  15  is chucked and the connecting portions  30   b  of the coil pieces  30  are held, enabling the workability in soldering between the open-end portions  30   c  to be enhanced. 
     Incidentally, in the foregoing description of the third embodiment, it has been described that the leg portions of the nearly U-shaped coil pieces  30  are inserted into the second outermost place in one of two slots  15   b,  whose slot numbers differ from each other by three, and into the third outermost place in the other slot  15   b,  whose slot number differs from that of the former one  15   b  in the clockwise circumferential direction in FIG. 6, and that the connecting portions  30   b  (namely, the rear-side coil end portions) of the coil pieces  30  are, thereafter, cut off. However, the present invention is not limited to this generator. The generator according to be present invention may be adapted so that the rod-like coil pieces are inserted into the second outermost place in one of two slots  15   b,  whose slot numbers differ from each other by three, and into the third outermost place in the other slot  15   b,  whose slot number differs from that of the former one  15   b  in the clockwise circumferential direction in FIG. 6 in such a way as to axially extend to both sides thereof. This obviates the necessity of cutting off the connecting portions  30   b  of the coil pieces  30 . 
     Further, in the foregoing description of the third embodiment, it has been described that the end portions u 1  and u 4 ′ of the coil piece  30 , which respectively extend toward the rear side of the stator core  15  from the second and third outermost places in the slots  15   b  after cut off therefrom, serve as a lead wire connected to the rectifier  12  and a wire connected to a neutral point among this coil and coils respectively corresponding to other two phases. However, the end portions u 1  and u 4 ′ may be respectively used as a wire connected to the neutral point and a lead wire connected to the rectifier  12 . 
     Incidentally, in the foregoing descriptions of the aforementioned embodiments, the three phase AC generators having the slots, of which the number corresponding to each phase and to each pole is 1, have been described. However, needless to say, the present invention can be applied to a three phase AC generator having slots of which the number corresponding to each phase and to each pole is 2 or more, and to other multi-phase AC generators, such as a six phase AC generator. Further, as the number of slots corresponding to each phase and to each pole and the number of phases increase, the number of crossover connections increases, so that the advantageous effects of the present invention are brought into the fore. 
     Moreover, each of the aforementioned embodiments uses a round coil having a circular section as the coil piece  30 . However, a flat coil having a rectangular section may be used as the coil piece  30 . 
     Furthermore, in each of the embodiments, the open-end portions  30   c  of the coil pieces  30  are made to overlap with each other, and then crimped by using the a clip, and subsequently, soldered to each other. Thus, the coil pieces are connected to each other by soldering. However, means for connecting the open-end portions  30   c  of the coil pieces  30  is not limited to soldering. For example, the open-end portions  30   c  may be connected to each other by welding. 
     Furthermore, in each of the embodiments, the after-treatment of the coil end portion is described nowhere. However, the coil end portion may be impregnated with any insulating resin. In this case, insulating ability in the connected portions is enhanced. Moreover, because the crossover connection portion is integrally fixed to the coil end portion, the risk of a brake in the crossover connection portion due to vibration of the vehicular AC generator is reduced. 
     The vehicular AC generator of the present invention is constructed as described above, and thus has the following advantageous effects. 
     According to the present invention, there is provided a vehicular AC generator which comprises: 
     a shaft rotatably supported on a pair of brackets; 
     a rotor fixed to the shaft and disposed in the pair of brackets; 
     a stator disposed at an outer-circumference-side of the rotor and fixed to the pair of brackets; 
     internal fittings placed at a rear side of the rotor; and 
     a fan driven by a rotation of the shaft and for forming a flow of cooling air flowing along an axis of the shaft, 
     wherein the stator comprising: 
     a stator core in which a plurality of slots, whose grooves extend in an axial direction, are circumferentially provided at an equiangular pitch so as to open on an inner circumference side thereof; and 
     a stator coil formed by AC connection of four-turn phase coils constructed by serially inserting coil conductors into the slots separated by a predetermined interval of the slots, the coil conductors being arranged four in a line in a radial direction, 
     and wherein each of the phase coils comprises: 
     nearly U-shaped first coil pieces, which constitute the coil conductors, inserted from an axial side into two adjacent sets of two of the separated slots, respectively, so that the first coil pieces are respectively positioned at a third outermost place in one slot of each of the two sets and at a second outermost place in the other slot of each of the two sets, and remaining first coil pieces inserted from an axial side into remaining sets of two of the separated slots, respectively, so that one of the remaining first coil pieces is respectively positioned at a first outermost place in one slot of each of the remaining sets and at a second outermost place in the other slot of each of the remaining sets and that another of the remaining first coil pieces is respectively positioned at a third outermost place in the one slot of each of the remaining sets and at a fourth outermost place in the other slot of each of the remaining sets; 
     second coil pieces, which constitute the coil conductors, inserted into the two sets of two of the separated slots, respectively, so that the second coil pieces are respectively positioned at a first outermost place in the one slot of each of the two sets and at a fourth outermost place of the other slot of each of the two sets and that end portions of the second coil piece extend from each slot of the two sets to both axial sides; 
     a two-turn first coil formed by connecting an end portion of each of the first coil pieces, which extend from the second outermost place in each of the slots to an axial opposite side and are bent circumferentially outwardly, to a corresponding end portion of the first and second coil pieces, which extend from the first outermost place of the slot, whose slot number differs from that thereof by the predetermined interval of the slots, to the axial opposite side and are bent circumferentially outwardly; 
     a two-turn second coil formed by connecting an end portion of each of the first and second coil pieces, which extend from the fourth outermost place in the slots to the axial opposite side and are bent circumferentially outwardly, to a corresponding end portion of the first coil pieces, which extends from the third outermost place in the slot, whose slot number differs from that thereof by the predetermined interval of the slots, to the axial opposite side and is bent circumferentially outwardly; and 
     a crossover connection portion between the first and second coils formed by connecting one of first and second sets of end portions of the second coil pieces, the first set of end portions of the second coil piece extending from the first outermost place in the one slot of each of the two sets to the axial side, the second set of end portions of the second coil piece extending from the fourth outermost place in the other slot of each of the two sets to the axial side, the other set of end portions being used as a lead wire and a wire connected to a neutral point formed among the phase coils. 
     Thus, the number of the crossover connection portions of the first and second coils corresponding to the phases is reduced to 1. Thus, the number of axial projections provided on the aligned coil end portions is decreased. Further, the wind resistance at the discharge side of the fan is reduced. Consequently, the cooling ability of the generator is enhanced. Moreover, the discomfort higher-order interference noises generated between the coil end portion and the rotor or the coil end portion and the fan are reduced. Furthermore, the wind noises are decreased. Moreover, the number of crossover connection portions formed by connecting the end portions of the second coil piece is reduced. Consequently, an occurrence of power generation failure due to a break in the crossover connection portions, which is caused by vibrations, is prevented. 
     According to an embodiment of the present invention, the second coil pieces are constructed by which nearly U-shaped coil pieces respectively are inserted from the axial side into the two sets of two of the separated slots so that the U-shaped coil pieces are respectively positioned at a first outermost place in one slot of each of the two sets and at a fourth outermost place in the other slot of each of the two sets, and each of the U-shaped coil pieces is cut off at each connecting portion ( 30   b ) thereof after inserted into the slots. Thus, the work of cutting, bending and drawing the second coil piece is reduced. Further, a process of assembling the stator coil is simplified. The assemblability of the stator is enhanced. 
     According to another embodiment of the present invention, each of the first coil pieces is formed by being folded at a connecting portion thereof, and wherein a direction, in which the first coil pieces respectively inserted into a first outermost place in one slot of each set of two of the separated slots and into a second outermost place in the other slot is folded at the connecting portion thereof, is the same with a direction, in which the first coil pieces respectively inserted into a third outermost place in one slot of each set of two of the separated slots and into a fourth outermost place in the other slot is folded at the connecting portion thereof, and is opposite to a direction, in which the first coil pieces respectively inserted into a third outermost place in one slot of each set of two of the separated slots and into a second outermost place in the other slot is folded at the connecting portion thereof. Thus, the interference between the crossover connection portion and the first coil is suppressed. Consequently, the size of the coil end portions is reduced. 
     According to another embodiment of the present invention, the crossover connection portion is formed in such a manner as to have a height which is less than that of a coil end portion constructed by a connecting portion of each of the first coil pieces. Thus, there is no axial projections of the crossover connection portion in the aligned coil end portions. Further, the wind resistance at the discharge side of the fan is decreased. The cooling ability of the generator is enhanced. 
     According to the present invention, there is provided a vehicular AC generator which comprises: 
     a shaft rotatably supported on a pair of brackets; 
     a rotor fixed to the shaft and disposed in the pair of brackets; 
     a stator disposed at an outer-circumference-side of the rotor and fixed to the pair of brackets; 
     internal fittings placed at a rear side of the rotor; and 
     a fan driven by a rotation of the shaft and for forming a flow of cooling air flowing along an axis of the shaft, 
     wherein the stator comprises: 
     a stator core in which a plurality of slots, whose grooves extend in an axial direction, are circumferentially provided at an equiangular pitch so as to open on an inner circumference side thereof; and 
     a stator coil formed by AC connection of four-turn phase coils constructed by serially inserting coil conductors into the slots separated by a predetermined interval of the slots, the coil conductors being arranged four in a line in a radial direction, 
     and wherein each of the phase coils comprises: 
     one of nearly U-shaped first coil pieces, which constitute the coil conductors, inserted from an axial side into one set of two of the separated slots so that the first coil piece is respectively positioned at a first outermost place in one slot of the one set and at a third outermost place in the other slot of the one set, and remaining first coil pieces inserted from an axial side into remaining sets of two of the separated slots, respectively, so that one of the remaining first coil pieces is respectively positioned at a first outermost place in one slot of each of the remaining sets and at a fourth outermost place in the other slot of each of the remaining sets and that another of the remaining first coil pieces is respectively positioned at a second outermost place in the one slot of each of the remaining sets and at a third outermost place in the other slot of each of the remaining sets; and 
     second coil pieces, which constitute the coil conductors, inserted into the one set of two of the separated slots so that the second coil pieces are respectively positioned at a second outermost place in the one slot of the one set and at a fourth outermost place of the other slot of the one set and that end portions of the second coil piece extend from each slot of the one set to both axial sides, 
     wherein one of the remaining first coil pieces, which are respectively inserted from the axial side into the first outermost place in one slot of each of the remaining sets and the fourth outermost place in the other slot of each of the remaining sets, is respectively placed in each gap formed between another of the remaining first coil pieces, which are respectively inserted from the axial side into the second outermost place in the one slot of each of the remaining sets and the third outermost place in the other slot of each of the remaining sets, at the connecting portion thereof by setting heights of apex portion of the connecting portion at an equal value, 
     wherein a four-turn coil is formed by connecting an end portion of each of the first and second coil pieces, which extend from the second outermost place in each of the slots to an axial opposite side and are bent circumferentially outwardly, to a corresponding end portion of the first coil pieces, which extend from the first outermost place of the slot, whose slot number differs from that thereof by the predetermined interval of the slots, to the axial opposite side and are bent circumferentially inwardly and by connecting an end portion of each of the first and second coil pieces, which extend from the fourth outermost place in the slots to the axial opposite side and are bent circumferentially inwardly, is connected to a corresponding end portion of the first coil pieces, which extends from the third outermost place in the slot, whose slot number differs from that thereof by the predetermined interval of the slots, to the axial opposite side and is bent circumferentially outwardly, 
     and wherein an end portion of the second coil piece extending from the second outermost place in the one slot of the one set to the axial side and an end portion of the second coil piece extending from the fourth outermost place in the other slot of the one set to the axial side are used as a lead wire and a wire connected to a neutral point formed among the phase coils. 
     Thus, the connecting portion of the first coil pieces, which are positioned at the first outermost place in one slot of one set of two of the separated slots and at the third outermost place in the other slot of the one set, is substituted for the crossover connection portions of the phase coils. Consequently, there is no axial projection in the aligned coil end portions. Thus, the wind resistance at the discharge side of the fan is decreased. The cooling ability of the generator is improved. Moreover, the higher-order discomfort interference noises generated between the coil end portion and the rotor or the coil end portion and the fan are reduced. Furthermore, the work of connecting the crossover connection portion, namely, the work of cutting, bending and drawing the coil pieces is omitted. Thus, the assemblability of the stator is enhanced. Furthermore, power generation failure due to a break in the crossover connection portions formed by connecting end portions is prevented. Furthermore, the connecting portions of the first coil pieces constituting the coil end portion are arranged in the circumferential direction by setting heights of apex portion of the connecting portion at an equal value, enabling cooling ability of the AC generator to be enhanced. 
     Further, according to an embodiment of the present invention, the second coil pieces are constructed by which a nearly U-shaped coil piece is inserted from the axial side into the one set of two of the separated slots so that the U-shaped coil piece is respectively positioned at a second outermost place in one slot of the one set and at a fourth outermost place in the other slot of the one set, and the U-shaped coil piece is cut off at a connecting portion thereof after inserted into the slots. Thus, the process of producing the stator coil is simplified. Consequently, the workability is enhanced. 
     Additionally, according to another aspect of the present invention, there is provided another a vehicular AC generator which comprises: 
     a shaft rotatably supported on a pair of brackets; 
     a rotor fixed to the shaft and disposed in the pair of brackets; 
     a stator disposed at an outer-circumference-side of the rotor and fixed to the pair of brackets; 
     internal fittings placed at a rear side of the rotor; and 
     a fan driven by a rotation of the shaft and for forming a flow of cooling air flowing along an axis of the shaft, 
     wherein the stator comprises: 
     a stator core in which a plurality of slots, whose grooves extend in an axial direction, are circumferentially provided at an equiangular pitch so as to open on an inner circumference side thereof; and 
     a stator coil formed by AC connection of four-turn phase coils constructed by serially inserting coil conductors into the slots separated by a predetermined interval of the slots, the coil conductors being arranged four in a line in a radial direction, 
     and wherein each of the phase coils comprises: 
     one of nearly U-shaped first coil pieces, which constitute the coil conductors, inserted from an axial side into one set of two of the separated slots so that the first coil piece is respectively positioned at a first outermost place in one slot of the one set and at a fourth outermost place in the other slot of the one set, and remaining first coil pieces inserted from an axial side into remaining sets of two of the separated slots, respectively, so that one of the remaining first coil pieces is respectively positioned at a first outermost place in one slot of each of the remaining sets and at a third outermost place in the other slot of each of the remaining sets and that another of the remaining first coil pieces is respectively positioned at a second outermost place in the one slot of each of the remaining sets and at a fourth outermost place in the other slot of each of the remaining sets; and 
     second coil pieces, which constitute the coil conductors, inserted into the one set of two of the separated slots so that the second coil pieces are respectively positioned at a second outermost place in the one slot of the one set and at a third outermost place of the other slot of the one set and that end portions of the second coil piece extend from each slot of the one set to both axial sides, 
     wherein a four-turn coil is formed by connecting an end portion of each of the first and second coil pieces, which extend from the second outermost place in each of the slots to an axial opposite side and are bent circumferentially outwardly, to a corresponding end portion of the first coil pieces, which extend from the first outermost place of the slot, whose slot number differs from that thereof by the predetermined interval of the slots, to the axial opposite side and are bent circumferentially inwardly and by connecting an end portion of each of the first coil pieces, which extend from the fourth outermost place in the slots to the axial opposite side and are bent circumferentially outwardly, to a corresponding end portion of the first and second coil pieces, which extends from the third outermost place in the slot, whose slot number differs from that thereof by the predetermined interval of the slots, to the axial opposite side and is bent circumferentially inwardly; 
     and wherein end portions of the second coil piece extending from the second outermost place in the one slot of the one set to the axial side and from the third outermost place in the other slot of the one set to the axial side are used as a lead wire and a wire connected to a neutral point formed among the phase coils. 
     Thus, the connecting portion of the first coil pieces, which are positioned at the first outermost place in one slot of one set of two of the separated slots and at the fourth outermost place in the other slot of the one set, is substituted for the crossover connection portions of the phase coils. Consequently, the aligned coil end portion has no axial projections formed on the crossover connection portion. Therefore, the wind resistance at the discharge side of the fan is reduced. Moreover, the cooling ability of the generator is enhanced. Furthermore, the higher-order discomfort interference noises generated between the coil end portion and the rotor or the coil end portion and the fan are reduced. The wind noises are decreased. Additionally, the work of connecting the crossover connection portion, that is, the work of cutting, bending and drawing the coil pieces is omitted. Consequently, the assemblability of the stator is enhanced. Furthermore, the crossover connection portions formed by connecting end portions of coil pieces are omitted. Consequently, an occurrence of power generation failure owing to a break in the crossover connection portion, which is caused y vibrations, is prevented. 
     Further, according to an embodiment of the present invention, the second coil pieces are constructed by which a nearly U-shaped coil piece is inserted from the axial side into the one set of two of the separated slots so that the U-shaped coil piece is respectively positioned at a second outermost place in one slot of the one set and at a third outermost place in the other slot of the one set, and the U-shaped coil piece is cut off at a connecting portion thereof after inserted into the slots. Thus, two leg portions of one coil piece are respectively inserted from an axial side into a set of slots, whose slot numbers differ from each other by a predetermined number, and then the inserted coil piece is cut off at the connecting portion thereof. Consequently, the process of producing the stator coil is simplified. The workability is enhanced. 
     Moreover, according to an embodiment of the present invention, a coil end portion constituted by a connecting portion of the first coil piece is placed at a rear side. Thus, the height of the rear-side coil end portion is reduced. Consequently, the internal devices, such as the rectifier and the regulator, to be cooled are effectively cooled. 
     Moreover, according to an embodiment of the present invention, an axial height of a rear-side coil end portion in a axial direction is lower than that of a front-side coil end portion and an axial lap amount between the front-side coil end portion and the fan is larger than that between the rear-side coil end portion and the fan. Thus, since there is no internal fittings in the front-side cooling path, the front-side coil end portion is efficiently cooled by the front-side cooling air suppressed temperature increases, enabling temperature increases in the stator coil to be suppressed. 
     Moreover, according to an embodiment of the present invention, gaps between the apex portion of the rear-side coil end portion and the internal fittings and between the apex portion of the rear-side coil end portion and an apex-facing surface of the bracket facing to the apex of the rear-side coil end portion are uniformly formed in a circumferential direction. Thus, it is possible to suppress fluctuations in the wind resistance of the cooling air path in the circumferential direction. Consequently, overall wind resistance of the cooling air path is reduced, enabling temperature increases in the internal fittings to be suppressed. 
     Moreover, according to an embodiment of the present invention, the apex portions of the connecting portions of the first coil pieces are exposed in an axial direction. Thus, the open-end portions of the first and second coil pieces are of the same uniform height by chucking the stator core and holding the connecting portions thereof in the jointing process before the open-end portions are jointed. Consequently, the open-end portions are jointed in a stable condition and the workability in jointing between the open-end portions is enhanced. 
     Moreover, according to an embodiment of the present invention, the fan is fixed to a rear-side axial end of the rotor. Thus, the rear-side cooling air path in which the cooling air flows is formed, enabling temperature increases in the internal fittings to be suppressed. 
     Moreover, according to an embodiment of the present invention, the fans are fixed to both axial end of the rotor. Thus, the rear-side and front-side cooling air path in which the cooling air flows are formed, enabling cooling ability in the AC generator to be enhanced. 
     Moreover, according to an embodiment of the present invention, front-side exhaust wind volume is larger than rear-side exhaust wind volume. Thus, it is possible to cool the front-side coil end portion efficiently, enabling temperature increases to suppressed. Further, the front-side exhaust wind volume having a low wind resistance increases compared with the rear-side exhaust wind volume having a high wind resistance, preventing wind noise from being deteriorated. 
     Although the preferred embodiments of the present invention have been described above, it should be understood that the present invention is not limited thereto and that other modifications will be apparent to those skilled in the art without departing from the sprint of the invention. 
     The scope of the present invention, therefore, should be determined solely by the appended claims.