Patent Publication Number: US-7902701-B2

Title: Automotive alternator

Description:
CROSS REFERENCE TO THE RELATED APPLICATIONS 
     This application is a Divisional of U.S. patent application Ser. No. 11/965,283 filed Dec. 27, 2007, which claims benefit of Japanese Patent Application No. 2007-152936, filed Jun. 8, 2007. The above-noted application is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an automotive alternator and particularly relates to a rectifier cooling construction. 
     2. Description of the Related Art 
     In conventional automotive alternators, positive-side unidirectional conducting elements and negative-side unidirectional conducting elements have been supported by a positive-side cooling plate and a negative-side cooling plate so as to be positioned approximately in a common plane that is perpendicular to a rotating shaft, cooling fins have been formed so as to project from an opposite side of a first cooling plate from the side on which the unidirectional conducting elements are supported, and a second cooling plate has been fixed to a casing member, such that the cooling fins have been cooled by a cooling fan (see Patent Literature 1, for example). 
     Patent Literature 1: Japanese Patent No. 13342978 (Gazette) 
     In conventional automotive alternators, because the positive-side cooling plate and the negative-side cooling plate have been disposed so as to line up radially, the following problems have arisen, preventing effective cooling of rectifying apparatuses: 
     First, cooling airflows that have been sucked in through ventilating apertures due to rotation of the cooling fan reach the cooling fan through gaps between the positive-side cooling plate and the negative-side cooling plate and gaps between the cooling plate that is positioned inside and a bearing box. Sufficient cross-sectional area cannot be ensured in the gaps at these two positions as air channels through which the cooling airflows may pass, giving rise to pressure loss due to reductions in air channel cross-sectional area as the cooling airflows flow in. 
     Cooling airflow flow channels that extend from the ventilating apertures to the cooling fan are also divided by the positive-side cooling plate and the negative-side cooling plate. Thus, portions of the cooling airflows are discharged externally without passing through the cooling fins, reducing the volume of cooling airflow that passes through the cooling fins compared to the intake and discharge capacity of the cooling fan. 
     Because installation space for the cooling plate on the inside is also narrower, the number of cooling fins must be reduced, reducing heat radiating area. 
     SUMMARY OF THE INVENTION 
     The present invention aims to solve the above problems and an object of the present invention is to provide an automotive alternator that improves rectifier cooling by adapting arrangement of cooling plates and also by positioning radiating fins downstream from a cooling fan in a cooling airflow flow channel. 
     In order to achieve the above object, according to one aspect of the present invention, there is provided an automotive alternator including: a rotor that is fixed to a rotating shaft; a case that rotatably supports the rotating shaft and that envelops the rotor; a stator that is constituted by: a cylindrical stator core that is held by the case and that surrounds the rotor; and a stator coil that is mounted to the stator core; a rectifier that has: a positive-side heatsink that has a flat, arc-shaped positive-side base portion; a positive-side rectifying element that is mounted to a front surface of the positive-side base portion; a negative-side heatsink that has a flat, arc-shaped negative-side base portion; and a negative-side rectifying element that is mounted to a front surface of the negative-side base portion, the positive-side heat sink and the negative-side heat sink being disposed inside the case at a first end of the rotor so as to be separated axially such that the front surfaces of the positive-side base portion and the negative-side base portion face each other; and a cooling fan that is fixed to a first end surface of the rotor. An air intake aperture is disposed through the case so as to face whichever heatsink of the positive-side heatsink and the negative-side heatsink is disposed farther away from the rotor, and an air discharge aperture is disposed through the case so as to be positioned radially outside the cooling fan, and a plurality of radiating fins are disposed so as to project from a rear surface of the base portion of whichever heatsink of the positive-side heatsink and the negative-side heatsink is disposed nearer to the rotor. The heatsink that is disposed nearer to the rotor is disposed such that the plurality of radiating fins are positioned radially outside the cooling fan, and a cooling airflow that flows out from the cooling fan passes through the plurality of radiating fins. 
     According to the present invention, because the positive-side heatsink and the negative-side heatsink are disposed so as to be separated axially such that the front surfaces of the positive-side base portion and the negative-side base portion face each other, space can be enlarged on an inner radial side of the positive-side heatsink and the negative-side heatsink. Thus, because cooling airflows that have been sucked in through the air intake aperture due to rotation of the cooling fan pass through an enlarged gap between the positive-side heatsink and the bearing box to reach the cooling fan, pressure loss is reduced, enabling the volume of cooling air that the cooling fan supplies and discharges to be increased. Because the positive-side heatsink and the negative-side heatsink do not divide the cooling airflow flow channel that extends from the air intake aperture to the cooling fan, the volume of cooling air that passes through the radiating fins is increased. 
     Because the radiating fins are positioned radially outside the cooling fan, high-speed cooling airflows that have flowed out from the cooling fan flow through the radiating fins, improving heat radiating performance. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross section of an overall configuration of an automotive alternator according to Embodiment 1 of the present invention; 
         FIG. 2  is a partial cross section that explains cooling airflows in the automotive alternator according to Embodiment 1 of the present invention; 
         FIG. 3  is a partial cross section of a vicinity of a rectifier of an automotive alternator according to Embodiment 2 of the present invention; 
         FIG. 4  is a partial cross section of a vicinity of a rectifier of an automotive alternator according to Embodiment 3 of the present invention; 
         FIG. 5  is a partial cross section of a vicinity of a rectifier of an automotive alternator according to Embodiment 4 of the present invention; 
         FIG. 6  is a partial cross section of a vicinity of a rectifier of an automotive alternator according to Embodiment 5 of the present invention; 
         FIG. 7  is a partial cross section of a vicinity of a rectifier of an automotive alternator according to Embodiment 6 of the present invention; 
         FIG. 8  is a partial cross section of a vicinity of a rectifier of an automotive alternator according to Embodiment 7 of the present invention; 
         FIG. 9  is a partial cross section of a vicinity of a rectifier of an automotive alternator according to Embodiment 8 of the present invention; 
         FIG. 10  is a projection in which a rear-end cooling fan, radiating fins that are disposed radially outside the rear-end cooling fan, and rear-end coil ends are projected onto a plane that is perpendicular to a central axis of a rotating shaft in an automotive alternator according to Embodiment 9 of the present invention; 
         FIGS. 11A and 11B  are schematic diagrams that explain how cooling airflows that have flowed out from the cooling fan flow through the radiating fins; 
         FIGS. 12A ,  12 B, and  12 C are projections in which radiating fins that are disposed radially outside a rear-end cooling fan and rear-end air discharge apertures are projected onto a plane that is perpendicular to a central axis of a rotating shaft in an automotive alternator according to Embodiment 10 of the present invention; 
         FIG. 13  is a projection in which a rear-end cooling fan, radiating fins that are disposed radially outside the rear-end cooling fan, and rear-end air discharge apertures are projected onto a plane that is perpendicular to a central axis of a rotating shaft in an automotive alternator according to Embodiment 11 of the present invention; 
         FIGS. 14A and 14B  are schematic diagrams that explain how cooling airflows that have flowed out from between the radiating fins flow through the discharge apertures; 
         FIG. 15  is a schematic diagram that explains how cooling airflows that have flowed out from between the radiating fins flow through the discharge apertures in an automotive alternator according to Embodiment 11 of the present invention; 
         FIG. 16  is a projection in which a rear-end cooling fan, radiating fins that are disposed radially outside the rear-end cooling fan, rear-end coil ends, and rear-end air discharge apertures are projected onto a plane that is perpendicular to a central axis of a rotating shaft in an automotive alternator according to Embodiment 12 of the present invention; and 
         FIG. 17  is a schematic diagram that explains how cooling airflows that have flowed out from the cooling fan flow through the radiating fins. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiment 1 
       FIG. 1  is a cross section of an overall configuration of an automotive alternator according to Embodiment 1 of the present invention, and  FIG. 2  is a partial cross section that explains cooling airflows in the automotive alternator according to Embodiment 1 of the present invention. 
     In  FIG. 1 , an automotive alternator includes: a case  3  that is constituted by a front bracket  1  and a rear bracket  2  that are each approximately bowl-shaped and made of aluminum; a rotating shaft  8  that is rotatably supported by bearings  6  and  7  that are housed in front-end and rear-end bearing boxes  4  and  5  that are disposed at central axial positions of the front bracket  1  and the rear bracket  2 ; a pulley  9  that is fixed to a first end of the rotating shaft  8  that projects outward at a front end of the case  3 ; a claw-pole rotor  10  that is fixed to the rotating shaft  8  so as to be rotatably disposed inside the case  3 ; a stator  11  that is held by an inner wall surface of the case  3  so as to surround the rotor  10 ; a rectifier  12  that is electrically connected to a stator coil  19  of the stator  11  and that rectifies alternating current that is generated in the stator coil  19  into direct current; and a voltage regulator  13  that adjusts magnitude of alternating voltage that is generated in the stator coil  19 . 
     The rotor  10  has: a field coil  15  that generates magnetic flux on passage of electric current; and a pole core  16  that is disposed so as to cover the field coil  15  and in which magnetic poles are formed by the magnetic flux. The rotating shaft  8  is inserted through a central axial position of the pole core  16  and fixed, and front-end and rear-end cooling fans  17   a  and  17   b  are fixed to two axial end surfaces of the pole core  16 . 
     The stator  11  includes: a stator core  18  that is held between the front bracket  1  and the rear bracket  2  and that is disposed so as to surround the rotor  10 ; and a stator coil  19  that is mounted to the stator core  18 . Here, a rotating magnetic field is applied to the stator coil  19  due to rotation of the rotor  10 , generating electromotive force in the stator coil  19 . 
     The rectifier  12  includes: a positive-side heatsink  20  onto which a plurality of positive-side rectifying elements  23   a  have been mounted; a negative-side heatsink  21  onto which a plurality of negative-side rectifying elements  23   b  have been mounted; and a circuit board  22 . The positive-side heatsink  20  is made of a good thermally conducting material such as aluminum, etc., and has: a flat, arc-shaped positive-side base portion  20   a ; and positive-side radiating fins  20   b  that are each disposed so as to project vertically from a rear surface of the positive-side base portion  20   a , that are disposed so as to extend radially on an inner circumferential side and an outer circumferential side of the rear surface of the positive-side base portion  20   a , and that are disposed in a radial pattern on the rear surface of the positive-side base portion  20   a . The negative-side heatsink  21  is made of a good thermally conducting material such as aluminum, etc., and has: a flat, arc-shaped negative-side base portion  21   a ; and negative-side radiating fins  21   b  that are each disposed so as to project vertically from a rear surface of the negative-side base portion  21   a , that are disposed so as to extend radially on an outer circumferential side of the rear surface of the negative-side base portion  21   a , and that are disposed in a radial pattern on the rear surface of the negative-side base portion  21   a . The plurality of positive-side and negative-side rectifying elements  23   a  and  23   b  are mounted so as to line up circumferentially on the front surface of each of the base portions  20   a  and  21   a , and are connected by a circuit board  22  so as to constitute a rectifier circuit. 
     The negative-side heatsink  21  is disposed inside the rear bracket  2  such that the front surface of the negative-side base portion  21   a  is positioned in a plane that is perpendicular to a central axis of the rotating shaft  8 , such that the rear surface of the negative-side base portion  21   a  faces toward the rotor  10 , such that the negative-side radiating fins  21   b  are positioned radially outside the rear-end cooling fan  17   b  so as to face coil ends  19   b  of the stator coil  19 , and such that an arc center of the negative-side base portion  21   a  is approximately aligned with the central axis of the rotating shaft  8 . The positive-side heatsink  20  is disposed inside the rear bracket  2  such that the front surface of the positive-side base portion  20   a  is positioned in a plane that is perpendicular to a central axis of the rotating shaft  8 , such that the rear surface of the positive-side base portion  20   a  faces toward the rotor  10 , such that the positive-side base portion  20   a  is positioned behind the negative-side base portion  21   a  so as to face the negative-side base portion  21   a , and such that an arc center of the positive-side base portion  20   a  is approximately aligned with the central axis of the rotating shaft  8 . 
     Front-end air intake apertures  1   a  are disposed through the front bracket  1  in a vicinity of the front-end bearing box  4 , and front-end air discharge apertures  1   b  are disposed radially outside the front-end cooling fan  17   a . Rear-end air intake apertures  2   a  are disposed through the rear bracket  2  so as to face the positive-side heatsink  20 , and rear-end air discharge apertures  2   b  are disposed radially outside the rear-end cooling fan  17   b.    
     In an automotive alternator that is configured in this manner, electric current is first supplied from a battery (not shown) through brushes  14  and the slip rings (not shown) to the field coil  15  of the rotor  10 , generating magnetic flux. Magnetic poles are formed in the pole core  16  by this magnetic flux. At the same time, rotational torque from an engine is transmitted from an output shaft of the engine through a belt (not shown) and the pulley  9  to the rotating shaft  8 , rotating the rotor  10 . Thus, a rotating magnetic field is applied to the stator coil  19  of the stator  11 , generating an electromotive force in the stator coil  19 . This alternating-current electromotive force is rectified into direct current by the rectifier  12  and charges the battery or is supplied to an electric load. Magnitude of the alternating voltage that is generated in the stator  11  is also adjusted by the voltage regulator  13 . 
     The cooling fans  17   a  and  17   b  are rotated together with the rotation of the rotor  10 . Thus, at the rear end, as indicated by arrows in  FIG. 2 , a cooling airflow is sucked inside the rear bracket  2  through the rear-end air intake apertures  2   a . This cooling airflow flows radially inward through the positive-side radiating fins  20   b  of the positive-side heatsink  20 , and then flows alongside the rotating shaft  8  toward the rotor  10 . Another cooling airflow flows radially inward between the positive-side heatsink  20  and the negative-side heatsink  21 . The cooling airflows that have flowed to the rotor  10  are deflected centrifugally by the rear-end cooling fan  17   b . Then, a portion of the cooling airflows flows radially outward through the negative-side radiating fins  21   b  of the negative-side heatsink  21 , and is discharged through the rear-end air discharge apertures  2   b . A remainder of the cooling airflows cools the coil ends  19   b  of the stator coil  19 , and is discharged through the rear-end air discharge apertures  2   b . Thus, heat that is generated by the positive-side and negative-side rectifying elements  23   a  and  23   b  of the rectifier  12  is absorbed into the cooling airflows that flow through the radiating fins  20   b  and  21   b , suppressing temperature increases in the positive-side and negative-side rectifying elements  23   a  and  23   b.    
     At the front end, cooling airflows are also sucked inside the front bracket  1  through the front-end air intake apertures  1   b , are deflected centrifugally by the front-end cooling fan  17   a , cool the coil ends  19   a  of the stator coil  19 , and are then discharged through the front-end air discharge apertures  1   b . Thus, heat that is generated by the stator coil  19 , is absorbed into the cooling airflows, suppressing temperature increases in the stator  11 . 
     According to Embodiment 1, the negative-side heatsink  21  is disposed inside the rear bracket  2  such that the negative-side radiating fins  21   b  are positioned radially outside the cooling fan  17   b , and the positive-side heatsink  20  is disposed inside the rear bracket  2  so as to be positioned axially rearward facing the negative-side heatsink  21 . Thus, clearances between the positive-side and negative-side heat sinks  20  and  21  and the rear-end bearing box  5  are enlarged, reducing pressure loss in the ventilation channels for the cooling airflows that are formed due to the rotation of the rear-end cooling fan  17   b , and enabling the volume of cooling air that is moved by the rear-end cooling fan  17   b  to be increased. The ventilation channels for the cooling airflows that are formed due to the rotation of the rear-end cooling fan  17   b  are not divided by the positive-side and negative-side heat sinks  20  and  21 , increasing the volume of cooling air that passes through the radiating fins  20   b  and  21   b . Because the positive-side and negative-side heat sinks  20  and  21  are disposed on an outer circumferential side inside the rear bracket  2 , installation space for the radiating fins  20   b  and  21   b  is wider, enabling the number of fins to be increased and heat radiating area to enlarged. 
     The negative-side radiating fins  21   b  are positioned radially outside the rear-end cooling fan  17   b . In other words, the radiating fins  21   b  are disposed closely downstream from the rear-end cooling fan  17   b  in the ventilation channel for the cooling airflows. Closely downstream from the rear-end cooling fan  17   b , the flow velocity of the cooling airflows is approximately equal to the rotational speed of the rear-end cooling fan  17   b . The rotational speed of the rear-end cooling fan  17   b  has a velocity that is several times the flow velocity of cooling airflows that flow through cooling airflow ventilation channels that are far from the rear-end cooling fan  17   b . Thus, high-speed cooling airflows flow through the negative-side radiating fins  21   b  that are disposed closely downstream from the rear-end cooling fan  17   b , improving heat radiating performance. 
     Because the negative-side radiating fins  21   b  are disposed closely downstream from the rear-end cooling fan  17   b  in the cooling airflow ventilation channel, heat radiating performance can also be improved since approximately all of the cooling airflow that has been sucked into rear-end cooling fan  17   b  flows through the negative-side radiating fins  21   b.    
     Because the coil ends  19   b  of the stator coil  19  and the negative-side radiating fins  21   b  are disposed so as to face each other closely downstream from the rear-end cooling fan  17   b  in the cooling airflow ventilation channel, the coil ends  19   b  of the stator coil  19  and the negative-side radiating fins  21   b  are cooled simultaneously, enabling the stator  11  and the rectifier  12  to be cooled effectively. 
     Embodiment 2 
       FIG. 3  is a partial cross section of a vicinity of a rectifier of an automotive alternator according to Embodiment 2 of the present invention. 
     In  FIG. 3 , in a positive-side heatsink  20 A, positive-side radiating fins  20   b  are each disposed so as to project vertically from a front surface of a positive-side base portion  20   a , are disposed so as to extend radially on an inner circumferential side and an outer circumferential side of the front surface of the positive-side base portion  20   a , and are disposed in a radial pattern on the front surface of the positive-side base portion  20   a . Positive-side rectifying elements  23   a  are mounted onto the front surface of the positive-side base portion  20   a  so as to line up circumferentially at a position between the positive-side radiating fins  20   b  that are arranged on the inner circumferential side and the positive-side radiating fins  20   b  that are arranged on the outer circumferential side. The positive-side heatsink  20 A is disposed inside the rear bracket  2  such that the front surface faces a negative-side heatsink  21 . Moreover, the rest of this embodiment is configured in a similar manner to Embodiment 1 above. 
     Consequently, similar effects to those in Embodiment 1 above can also be achieved in Embodiment 2. 
     Embodiment 3 
       FIG. 4  is a partial cross section of a vicinity of a rectifier of an automotive alternator according to Embodiment 3 of the present invention. 
     In  FIG. 4 , in a positive-side heatsink  20 B, positive-side radiating fins  20   b  are each disposed so as to project radially vertically from an inner circumferential end surface of a positive-side base portion  20   a , are disposed so as to extend axially on the inner circumferential end surface of the positive-side base portion  20   a , and are disposed in a radial pattern on the inner circumferential end surface of the positive-side base portion  20   a . Positive-side rectifying elements  23   a  are mounted onto a front surface of the positive-side base portion  20   a  so as to line up circumferentially. The positive-side heatsink  20 B is disposed inside the rear bracket  2  such that the front surface faces a negative-side heatsink  21 . Moreover, the rest of this embodiment is configured in a similar manner to Embodiment 1 above. 
     Consequently, similar effects to those in Embodiment 1 above can also be achieved in Embodiment 3. 
     According to Embodiment 3, because the positive-side radiating fins  20   b  are disposed so as to project radially inward from the inner circumferential end surface of the positive-side base portion  20   a , axial length of the automotive alternator can be reduced, enabling reductions in the size of the automotive alternator. 
     Moreover, in Embodiments 1 through 3 above, radiating fins are disposed on the positive-side heatsink, but the radiating fins may also be omitted and a positive-side heatsink configured using only a base portion. 
     In Embodiments 1 through 3 above, the negative-side heatsink is disposed such that negative-side radiating fins are positioned closely downstream from the rear-end cooling fan  17   b  in the cooling airflow ventilation channel, but the positive-side heatsink may also be disposed such that the positive-side radiating fins are positioned closely downstream from the rear-end cooling fan  17   b  in the cooling airflow ventilation channel. 
     Embodiment 4 
       FIG. 5  is a partial cross section of a vicinity of a rectifier of an automotive alternator according to Embodiment 4 of the present invention. 
     In  FIG. 5 , a positive-side heatsink  24  is made of a good thermally conducting material such as aluminum, etc., and has: a flat, arc-shaped positive-side base portion  24   a ; and positive-side radiating fins  24   b  that are each disposed so as to project vertically from a rear surface of the positive-side base portion  24   a , that are disposed so as to extend radially from an outer circumferential side of the rear surface of the positive-side base portion  24   a , and that are disposed in a radial pattern on the rear surface of the positive-side base portion  24   a . A negative-side heatsink  25  is constituted by only a flat, arc-shaped negative-side base portion  25   a  that is made of a good thermally conducting material such as aluminum, etc. A plurality of positive-side and negative-side rectifying elements  23   a  and  23   b  are mounted so as to line up circumferentially on a front surface of each of the base portions  24   a  and  25   a , and are connected by a circuit board  22  so as to constitute a rectifier circuit. 
     The positive-side heatsink  24  is disposed inside a rear bracket  2  such that the front surface of the positive-side base portion  24   a  is positioned in a plane that is perpendicular to a central axis of a rotating shaft  8 , such that the rear surface of the positive-side base portion  24   a  faces toward a rotor  10 , such that the positive-side radiating fins  24   b  are positioned radially outside a rear-end cooling fan  17   b  so as to face coil ends  19   b  of a stator coil  19 , and such that an arc center of the positive-side base portion  24   a  is approximately aligned with the central axis of the rotating shaft  8 . An inner circumferential end surface of the negative-side base portion  25   a  of the negative-side heatsink  25  is fixed to an outer circumferential wall surface of the rear bracket  2  such that the front surface of the negative-side base portion  25   a  faces toward rear-end air discharge apertures  2   b.    
     Moreover, the rest of this embodiment is configured in a similar manner to Embodiment 1 above. 
     According to Embodiment 4, cooling airflows are sucked into the rear bracket  2  through the rear-end air intake apertures  2   a  due to rotation of the rear-end cooling fan  17   b , and are deflected centrifugally by the rear-end cooling fan  17   b . Then, a portion of the cooling airflows flows radially outward through the positive-side radiating fins  24   b  of the positive-side heatsink  24 , and is discharged through the rear-end air discharge apertures  2   b . A remainder of the cooling airflows cools the coil ends  19   b  of the stator coil  19 , and is discharged through the rear-end air discharge apertures  2   b.    
     Heat that is generated by the negative-side rectifying elements  23   b  is transferred to the rear bracket  2  by means of the negative-side base portion  25   a  of the negative-side heatsink  25 , and is radiated from the surface of the rear bracket  2 . 
     Consequently, similar effects to those in Embodiment 1 above can also be achieved in Embodiment 4. 
     According to Embodiment 4, because it is not necessary to dispose a negative-side heatsink behind the positive-side heatsink  24 , cross-sectional area of the cooling airflow ventilation channel can be enlarged, enabling the volume of cooling air to be increased, and axial dimensions of the automotive alternator can also be reduced. 
     Moreover, in Embodiment 4 above, the negative-side rectifying elements  23   b  are mounted to an outer wall surface of the rear bracket  2  by means of the negative-side heatsink  25 , but the negative-side rectifying elements  23   b  may also be mounted directly to the outer wall surface of the rear bracket  2 . In that case, the number of parts is reduced, simplifying assembly processes. 
     Embodiment 5 
       FIG. 6  is a partial cross section of a vicinity of a rectifier of an automotive alternator according to Embodiment 5 of the present invention. 
     In  FIG. 6 , a positive-side heatsink  24  is made of a good thermally conducting material such as aluminum, etc., and has: a flat, arc-shaped positive-side base portion  24   a ; and positive-side radiating fins  24   b  that are each disposed so as to project vertically from a rear surface of the positive-side base portion  24   a , that are disposed so as to extend radially from an outer circumferential side of the rear surface of the positive-side base portion  24   a , and that are disposed in a radial pattern on the rear surface of the positive-side base portion  24   a . A plurality of positive-side rectifying elements  23   a  are mounted onto a front surface of the positive-side base portion  24   a  so as to line up circumferentially. The negative-side heatsink  26  has: a flat, arc-shaped negative-side base portion  26   a  that is made of a good thermally conducting material such as aluminum, etc.; and negative-side radiating fins  26   b  that are each disposed so as to project vertically from a front surface of the negative-side base portion  26   a , that are disposed so as to extend radially on an inner circumferential side and an outer circumferential side of the front surface of the negative-side base portion  26   a , and that are disposed in a radial pattern on the front surface of the negative-side base portion  26   a . A plurality of negative-side rectifying elements  23   b  are mounted onto the front surface of the negative-side base portion  26   a  so as to line up circumferentially at a position between the negative-side radiating fins  26   b  that are arranged on the inner circumferential side and the negative-side radiating fins  26   b  that are arranged on the outer circumferential side. The positive-side and negative-side rectifying elements  23   a  and  23   b  that are mounted onto the front surface of the base portions  24   a  and  26   a  are connected by a circuit board  22  so as to constitute a rectifier circuit. 
     The positive-side heatsink  24  is disposed inside a rear bracket  2  such that the front surface of the positive-side base portion  24   a  is positioned in a plane that is perpendicular to a central axis of a rotating shaft  8 , such that the rear surface of the positive-side base portion  24   a  faces toward a rotor  10 , such that the positive-side radiating fins  24   b  are positioned radially outside a rear-end cooling fan  17   b  so as to face coil ends  19   b  of a stator coil  19 , and such that an arc center of the positive-side base portion  24   a  is approximately aligned with the central axis of the rotating shaft  8 . The negative-side heatsink  26  is mounted to an inner wall surface of the rear bracket  2  with a material  27  that has good thermal conductivity interposed such that the front surface of the negative-side base portion  26   a  is positioned in a plane that is perpendicular to a central axis of the rotating shaft  8 , such that the front surface of the negative-side base portion  26   a  faces toward the rotor  10 , such that the negative-side base portion  26   a  is positioned behind the positive-side base portion  24   a  so as to face the positive-side base portion  24   a , and such that an arc center of the negative-side base portion  26   a  is approximately aligned with the central axis of the rotating shaft  8 . Greases, resins, or radiating sheets, etc., that have high thermal conductivity can be used for the material  27  that has good thermal conductivity. 
     Moreover, the rest of this embodiment is configured in a similar manner to Embodiment 1 above. 
     According to Embodiment 5, cooling airflows are sucked into the rear bracket  2  through the rear-end air intake apertures  2   a  due to rotation of the rear-end cooling fan  17   b , flow through the negative-side radiating fins  26   b  to an inner circumferential side, flow along the rotating shaft  8  toward the rotor  10 , and are then deflected centrifugally by the rear-end cooling fan  17   b . Then, a portion of the cooling airflows flows radially outward through the positive-side radiating fins  24   b  of the positive-side heatsink  24 , and is discharged through the rear-end air discharge apertures  2   b . A remainder of the cooling airflows cools the coil ends  19   b  of the stator coil  19 , and is discharged through the rear-end air discharge apertures  2   b.    
     Consequently, similar effects to those in Embodiment 1 above can also be achieved in Embodiment 5. 
     According to Embodiment 5, because the negative-side base portion  26   a  is mounted to the inner wall surface of the rear bracket  2  by means of the material  27  that has good thermal conductivity, heat that is generated by the negative-side rectifying elements  23   b  is transferred to the rear bracket  2  by means of the negative-side base portion  26   a  and the material  27  that has good thermal conductivity, and is radiated from the surface of the rear bracket  2 . As a result, because radiating effects from the front surface of the rear bracket  2  are added to radiating effects from the negative-side radiating fins  26   b , heat radiating performance is improved. 
     Embodiment 6 
     In Embodiment 6, as shown in  FIG. 7 , a flat rib  28  is disposed on an air intake portion of a rear bracket  2 . 
     Moreover, the rest of this embodiment is configured in a similar manner to Embodiment 5 above. 
     According to Embodiment 6, because the flat rib  28  is disposed on the air intake portion of the rear bracket  2 , surface area of the rear bracket  2  is increased, and radiation from the front surface of the rear bracket  2  is facilitated, further improving heat radiating performance. 
     Moreover, the shape of the rib  28  is not limited to being flat, and may also be a rod shape. 
     Embodiment 7 
     In Embodiment 7, as shown in  FIG. 8 , projecting height of negative-side radiating fins  26   b  from a negative-side base portion  26   a  of a negative-side heatsink  26 A is lowered. 
     Moreover, the rest of this embodiment is configured in a similar manner to Embodiment 5 above. 
     According to Embodiment 7, because there are radiating effects from the front surface of the rear bracket  2 , heat radiating area of the negative-side radiating fins  26   b  can be reduced. As a result, pressure loss can be reduced, enabling the volume of cooling air that is sucked in by the rear-end cooling fan  17   b  to be increased, and axial length of the automotive alternator can also be reduced. 
     Embodiment 8 
     In Embodiment 8, as shown in  FIG. 9 , in a negative-side heatsink  26 B, negative-side radiating fins  26   b  are each disposed so as to project radially vertically from an inner circumferential end surface of a negative-side base portion  26   a , are disposed so as to extend axially on the inner circumferential end surface of the negative-side base portion  26   a , and are disposed in a radial pattern on the inner circumferential end surface of the negative-side base portion  26   a . Negative-side rectifying elements  23   b  are mounted onto a front surface of the negative-side base portion  26   a  so as to line up circumferentially. The negative-side heatsink  26 B is mounted to an inner wall surface of the rear bracket  2  with a material  27  that has good thermal conductivity interposed such that the front surface of the negative-side base portion  26   a  is positioned in a plane that is perpendicular to a central axis of the rotating shaft  8 , such that the front surface of the negative-side base portion  26   a  faces toward the rotor  10 , such that the negative-side base portion  26   a  is positioned behind the positive-side base portion  24   a  so as to face the positive-side base portion  24   a , and such that an arc center of the negative-side base portion  26   a  is approximately aligned with the central axis of the rotating shaft  8 . 
     Moreover, the rest of this embodiment is configured in a similar manner to Embodiment 5 above. 
     According to Embodiment 8, because the negative-side radiating fins  26   b  project radially inward from the inner circumferential end surface of the negative-side base portion  26   a , axial length of the automotive alternator can be reduced. 
     Moreover, in Embodiments 5 through 8 above, radiating fins  26   b  are disposed on the negative-side base portion  26   a , but the negative-side radiating fins  26   b  may also be omitted. 
     Now, in Embodiments 1 through 8 above, arrangements of positive-side heatsinks and the negative-side heatsinks have been explained, but shapes of radiating fins of heatsinks that are disposed in close proximity to a rear-end cooling fan  17   b  will be explained below. 
     Embodiment 9 
       FIG. 10  is a projection in which a rear-end cooling fan, radiating fins that are disposed radially outside the rear-end cooling fan, and rear-end coil ends are projected onto a plane that is perpendicular to a central axis of a rotating shaft in an automotive alternator according to Embodiment 9 of the present invention, and  FIGS. 11A and 11B  are schematic diagrams that explain how cooling airflows that have flowed out from the cooling fan flow between the radiating fins. Moreover, numeral  29  in  FIG. 10  represents a blade of a rear-end cooling fan  17   b , and arrow A indicates a direction of rotation of a rotor  10 . Arrows C in  FIG. 11  indicate directions of flow of cooling airflows. 
     In  FIG. 10 , radiating fins  30  are formed such that a cross section of each that is perpendicular to a central axis of the rotating shaft  8  has a long, thin rectangular shape, and are arranged in a row at a uniform pitch circumferentially. The radiating fins  30  that are arranged in a row circumferentially are disposed radially outside a rear-end cooling fan  17   b  so as to face rear-end coil ends  19   b . The respective radiating fins  30  intersect at an angle of inclination α with straight lines B that extends in a radial pattern in a radial direction from a center of rotation O of the rotor  10 . Here, the angle of inclination α is an angle that is formed by a center line in a thickness direction of a radiating fin  30  and a straight line B that extends radially from the center of rotation O of the rotor  10  and passes through the radiating fin  30  in a plane that is perpendicular to a central axis of a rotating shaft  8 . Moreover, in the case of radiating fins that have long, thin rectangular cross sections, the center lines in the thickness direction of the radiating fins correspond to longitudinal directions. 
     Cooling airflows flow out from the rotating cooling fan  17   b  in directions that are inclined forward in the direction of rotation relative to the straight lines B. Thus, if the radiating fins  30  are inclined forward in the direction of rotation relative to the straight lines B, when the cooling airflows flow out from the cooling fan  17   b  and reach the radiating fins  30 , their directions of flow are changed slightly by the radiating fins  30  as they flow between the radiating fins  30 , as indicated by the arrows C in  FIG. 11A . On the other hand, if the radiating fins  30  are inclined backward in the direction of rotation relative to the straight lines B, when the cooling airflows flow out from the cooling fan  17   b  and reach the radiating fins  30 , their directions of flow are changed dramatically by the radiating fins  30  as they flow between the radiating fins  30 , as indicated by the arrows C in  FIG. 11B . 
     Thus, because the directions of flow of the cooling airflows that have flowed out from the cooling fan  17   b  and have reached the radiating fins  30  are changed dramatically by the radiating fins  30  if the radiating fins  30  are inclined backward in the direction of rotation relative to the straight lines B that extend radially from the center of rotation O of the rotor  10 , pressure loss is greatly increased, reducing the volume of cooling air. 
     From the above, it is preferable for the radiating fins  30  to be parallel to the straight lines B that extend radially from the center of rotation O of the rotor  10 , or to be inclined forward in the direction of rotation relative to the straight lines B. Since the directions of outflow of the cooling airflows from the cooling fan  17   b  differ depending on the shape of the blades  29  and the rotational speed of the rotor  10 , it is particularly desirable for the angle of inclination α of the radiating fins  30  relative to the straight lines B to be set so as to match the directions of outflow of the cooling airflows from the cooling fan  17   b  in an operating state in which the automotive alternator is mainly used. 
     Moreover, the radiating fins that are arranged in a radial pattern on an outer circumferential side of a rear surface of a base portion in Embodiments 1 through 8 above correspond to fins that are parallel to the straight lines B. 
     Embodiment 10 
       FIGS. 12A ,  12 B, and  12 C are projections in which radiating fins that are disposed radially outside a rear-end cooling fan and rear-end air discharge apertures are projected onto a plane that is perpendicular to a central axis of a rotating shaft in an automotive alternator according to Embodiment 10 of the present invention. 
     In  FIGS. 12A ,  12 B, and  12 C, radiating fins  30  are arranged in a row circumferentially at an angle of inclination α, and air discharge ribs  31  are arranged in a row circumferentially at an angle of inclination β. 
     Now, if the angle of inclination α of the radiating fins  30  is equal to the angle of inclination β of the air discharge ribs  31 , the directions of flow of the cooling airflows that have flowed out from between the radiating fins  30  are parallel to the air discharge ribs  31 , as shown in  FIG. 12A , minimizing collisions between the cooling airflows and the air discharge ribs  31  and changes in directions of flow of the cooling airflows, etc., and also minimizing pressure loss. 
     If the angle of inclination α of the radiating fins  30  is greater than the angle of inclination β of the air discharge ribs  31 , portions of the cooling airflows that have flowed out from between the radiating fins  30  collide with wall surfaces of the air discharge ribs  31  that are rearward relative to the direction of rotation, as shown in  FIG. 12B , and their directions are changed slightly as they are discharged. Thus, collisions between the cooling airflows and the air discharge ribs  31  and changes in directions of flow of the cooling airflows, etc., are reduced, also reducing pressure loss. 
     If the angle of inclination β of the air discharge ribs  31  is greater than the angle of inclination α of the radiating fins  30 , as shown in  FIG. 12C , wall surfaces of the air discharge ribs  31  that are forward relative to the direction of rotation may act so as to obstruct the cooling airflows that have flowed out from between the radiating fins  30 . Thus, collisions between the cooling airflows and the air discharge ribs  31  and changes in directions of flow of the cooling airflows, etc., are increased, increasing pressure loss, and also reducing the volume of cooling air. 
     From the above, it is preferable for the radiating fins  30  and the air discharge ribs  31  to be disposed such that the angle of inclination α of the radiating fins  30  is greater than or equal to the angle of inclination β of the air discharge ribs  31 . 
     Embodiment 11 
       FIG. 13  is a projection in which a rear-end cooling fan, radiating fins that are disposed radially outside the rear-end cooling fan, and rear-end air discharge apertures are projected onto a plane that is perpendicular to a central axis of a rotating shaft in an automotive alternator according to Embodiment 11 of the present invention, and  FIGS. 14A and 14B  are schematic diagrams that explain how cooling airflows that have flowed out from between the radiating fins flow through the discharge apertures. 
     In Embodiment 11, as shown in  FIG. 13 , fillet surfaces  30   a  and  31   a  are formed on respective corner portions of radiating fins  30 A and air discharge ribs  31 A. 
     Now, in the case of air discharge ribs  31  in which fillet surfaces are not formed on corner portions, as shown in  FIG. 14B , cooling airflows collide with the air discharge ribs  31 , and then detachment occurs at the corner portions of the air discharge ribs  31 , increasing pressure loss. As a result, reductions in the volume of cooling air and increases in wind noise occur due to collisions. In the case of radiating fins  30 , the cooling airflows also collide with the radiating fins  30  and then detachment occurs at the corner portions of the radiating fins  30 , giving a similar result. 
     In Embodiment 11, as shown in  FIG. 14A , because the cooling airflows collide with the air discharge ribs  31 A and then flow along the fillet surfaces  31   a , the occurrence of detachment of the cooling airflows is suppressed, reducing pressure loss. As a result, reductions in the volume of cooling air and increases in wind noise due to collisions are suppressed. Similarly, because the fillet surfaces  30   a  are formed on the corner portions of the radiating fins  30 A, the occurrence of detachment of the cooling airflows is suppressed because the cooling airflows collide with the radiating fins  30 A then flow along the fillet surfaces  30   a.    
     Because the fillet surfaces  30   a  and  31   a  are formed on the corner portions of the radiating fins  30 A and the air discharge ribs  31 A, inflow and outflow of the cooling airflows can be enlarged without reducing the surface area of the radiating fins  30 A and the air discharge ribs  31 A, thereby suppressing pressure loss. 
     Moreover, in Embodiment 11 above, the corner portions of the radiating fins  30 A and the air discharge ribs  31 A are formed so as to have a curved shape, but corner portions  30   b  and  31   b  of radiating fins  30 B and air discharge ribs  31 B may also be chamfered to form a tapered shape, as shown in  FIG. 15 . 
     Embodiment 12 
       FIG. 16  is a projection in which a rear-end cooling fan, radiating fins that are disposed radially outside the rear-end cooling fan, rear-end coil ends, and rear-end air discharge apertures are projected onto a plane that is perpendicular to a central axis of a rotating shaft in an automotive alternator according to Embodiment 12 of the present invention, and  FIG. 17  is a schematic diagram that explains how cooling airflows that have flowed out from the cooling fan flow between the radiating fins. 
     In  FIG. 16 , radiating fins  32  are formed such that a cross section of each that is perpendicular to a central axis of the rotating shaft  8  is a thin curved body in which an angle relative to a straight line B gradually decreases, and are arranged in a row at a uniform pitch circumferentially. The radiating fins  32  that are arranged in a row circumferentially are disposed radially outside a rear-end cooling fan  17   b  so as to face rear-end coil ends  19   b . Air discharge ribs  31  that define air discharge apertures  2   b  are inclined at an angle β forward in a direction of rotation A relative to the straight lines B. 
     Since the rear bracket  2  is produced using molding, or die casting, there is a limit to the angle of inclination β of the air discharge ribs  31 . If the angle of inclination β of the air discharge ribs  31  is large, the number of air discharge ribs  31  must be reduced, reducing the cross-sectional area of the air discharge apertures  2   b . At the same time, the faster the rotational speed of the rotor  10 , the more tangential to the rotor  10  the directions of outflow of the cooling airflows from the cooling fan  17   b  become. 
     Collisions between the cooling airflows and the radiating fins  32  and changes in the directions of the cooling airflows are minimized as the cooling airflows flow in between the radiating fins  32  if the radiating fins  32  are disposed parallel to the directions of flow of the cooling airflows, and pressure loss is also minimized. For this reason, it is desirable for an angle of inclination α in  on an inflow side of the radiating fins  32  to be increased so as approach being tangential to the rotor  10 , and for an angle of inclination α out  on an outflow side to approach the angle of inclination β of the air discharge ribs  31 . 
     In Embodiment 12, because the angle of inclination α in  on the inflow side of the radiating fins  32  is set so as to be greater than the angle of inclination α out  on the outflow side, the angle of inclination α in  on the inflow side of the radiating fins  32  can be made to approach being tangential to the rotor  10 , and the angle of inclination α out  on the outflow side can be made to approach the angle of inclination β of the air discharge ribs  31 . Thus, pressure loss is reduced when the cooling airflows flow into the radiating fins  32 , and the pressure loss is also reduced when the cooling airflows flow into the air discharge apertures  2   b.    
     Because inflow end portions and outflow end portions of the radiating fins  32  are linked into smooth curved surfaces such that the angle of inclination α decreases gradually, the cooling airflows flow smoothly along the curved surfaces of the radiating fins  32  as they flow through the radiating fins  32 , as indicated by arrows in  FIG. 17 , reducing pressure loss that results from changes in direction of the cooling airflows. 
     Thus, according to the present invention, because high-speed cooling airflows on the outflow side of the cooling fan are used directly for the cooling of the radiating fins, a high-performance automotive alternator in which heat radiating performance is high can be achieved. 
     The number and cross-sectional shapes of the radiating fins of the heatsinks are not limited to those of the above embodiments. 
     Similar effects can also be achieved if an insulating coating is applied to the radiating fins of the heatsinks.