Abstract:
An automotive alternator mounted on a vehicle for generating electric power includes front and rear frames, a cylindrical stator and a rotor. The cylindrical stator is contained in the frames, and the rotor is rotatably supported in the cylindrical stator. A rectifier device for rectifying alternating current generated in the stator into direct current is mounted on a rear surface of the rear frame and covered with a rear cover. To sufficiently cool minus rectifier elements positioned at a place not easily cooled only by the outside cooling air introduced into the alternator, a base portion of the minus rectifier element is contacted to the rear frame thereby to establish heat conduction therebetween. A resilient heat-conductive member is disposed between the base plate and the rear frame to absorb any dimensional discrepancies therebetween.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims benefit of priority of Japanese Patent Application No. 2007-167956 filed on Jun. 26, 2007, the content of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an alternator for use in an automotive vehicle. 
     2. Description of Related Art 
     An automotive alternator having a minus rectifier element, a base portion of which extends toward a rear frame and contacts the rear frame for better dissipating heat, has been known hitherto. An example of such an alternator is disclosed in JP-A-2002-519987. In this alternator, a plus cooling fin on which plus rectifier elements are mounted and a minus cooling fin on which minus rectifier elements are amounted are connected to a rear frame, forming a two-story structure. A base portion of each minus rectifier element extends from the minus cooling fin toward the rear frame and contacts the rear frame, thereby to better cool the minus rectifier element. Since the plus rectifier elements are positioned at a place better cooled by cooing air in this structure, it is not necessary for the plus rectifier elements to devise a structure for better cooling. 
     In the rectifier cooling structure mentioned above, the following problems are involved. (1) It is very difficult to establish a close contact between a base portion of the minus rectifier element and a seat portion of the rear frame for all of the minus rectifier elements. This is because a length of the base portion extending from the fin cannot be made uniform for all minus rectifier elements since the minus rectifier element is forcibly inserted into a hole of the minus cooling fin. If there is a minus rectifier element not contacting the rear frame, that element is not sufficiently cooled and may be damaged by heat. (2) If it is tried to establish the contact with the rear frame for all of the minus rectifier elements, some of the rectifier elements may be pushed against the rear frame with a force unbearable by the rectifier element. (3) In order to establish the close contact between the minus rectifier element and the rear frame for all of them, the length of the base portion extending from the minus cooling fin has to be very precisely controlled for all of the minus rectifier elements. This requires an impermissibly high manufacturing cost. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an improved automotive alternator, in which rectifier elements are well cooled by heat conduction to a frame. 
     The alternator is mounted on an automotive vehicle and driven by an engine thereby to generate electrical power. The alternator includes a front frame, a rear frame, a rotor and a cylindrical stator. The cylindrical stator is contained in the front and rear frames, and the rotor is rotatably supported in the cylindrical stator. A rectifier device for rectifying alternating current generated in the stator into direct current is mounted on an outside surface of the rear frame and covered by a rear cover. The rectifier device includes a plus cooling fin on which plus rectifier elements are mounted and a minus cooling fin on which minus rectifier elements are mounted. 
     The minus cooling fin is connected to the rear surface of the rear frame, and the plus cooling fin is overlapped on the minus cooling fin with a certain space therebetween. Both cooling fins are cooled down by outside air introduced into the alternator in both the radial and axial directions. To sufficiently cool the minus rectifier elements disposed inside of the plus rectifier elements, a base portion of the minus rectifier element is contacted to the rear frame in the following manner. 
     The base portion of the minus rectifier element is extended through the minus cooling fin toward the rear frame. A seat portion is formed on the rear frame by depressing part of the rear frame, so that the base portion contacts the seat portion. To establish a close contact between the seat portion and the base portion, a resilient heat-conductive member is disposed between the base portion and the seat portion. In this manner, good heat conduction is realized between each of the minus rectifier elements and the rear frame even if there is a deviation among lengths of the base portions of the minus rectifier elements extending from the minus cooling fin, because such deviation is absorbed by the resiliency of the resilient heat-conductive member. The resilient heat conductive-member may be made in various ways. For example, it may be made of a porous resin into which conductive grease is impregnated or may be made of a resilient metallic plate. 
     According to the present invention, the minus rectifier elements positioned at a place not easily cooled are effectively cooled by both the outside cooling air introduced into the alternator and heat conduction to the rear frame. Other objects and features of the present invention will become more readily apparent from a better understanding of the preferred embodiments described below with reference to the following drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view showing an automotive alternator as a first embodiment of the present invention; 
         FIG. 2  is a plan view showing a rectifier device used in the alternator shown in  FIG. 1 ; 
         FIG. 3  is a perspective view showing a way of mounting a resilient heat-conductive member between a rectifier element and a frame; 
         FIG. 4  is a perspective view showing another example of the resilient heat-conductive member made of metallic fibers; 
         FIG. 5  is a perspective view showing yet another example of the resilient heat-conductive member made of a metallic plate; 
         FIG. 6  is a perspective view showing yet another example of the resilient heat-conductive member made of a metallic plate having cutouts; 
         FIG. 7  is a perspective view showing yet another example of the resilient heat-conductive member made of a metallic cylinder having bellows; 
         FIG. 8  is a plan view showing a rectifier device as a second embodiment of the present invention; and 
         FIG. 9  is a partial cross-sectional view showing a rectifier element used in the rectifier device shown in  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A first embodiment of the present invention will be described with reference to  FIGS. 1-7 . An alternator  100  shown in  FIG. 1  is mounted on an automobile vehicle and driven by an engine of the vehicle through a driving belt. The alternator  100  includes: a rotor  2  having a pulley  1  that is driven by the engine through a driving belt; a stator  4  in a cylindrical shape functioning as an armature; a front frame  3   a  having a bearing  3   c  and a rear frame  3   b  having a bearing  3   d ; the rotor  4  being rotatably supported by the bearings  3   c ,  3   d  in an inner bore of the stator  4 ; a rectifier device  5  for converting alternating current generated in the stator  4  to direct current; a brush holder  7  holding brushes for supplying field current to a field coil  2   a  of the rotor  2 ; a regulator  9  for controlling output voltage; a connector case  6  having a terminal for electrically communicating with devices mounted on the vehicle; and a rear cover  8  made of resin covering the rectifier device  5 , the regulator  9  and the brush holder  7  disposed on a rear surface of the rear frame  3   b . A front side and a rear side of the alternator  100  are indicated with an arrow in  FIG. 1 . 
       FIG. 2  is a plan view showing the rectifier device  5 , on which the brush holder  7  and the connector case  6  are mounted. The rectifier device  5  includes a minus cooling fin  503 , on which minus rectifier elements are mounted, a plus cooling fin  501 , on which plus rectifier elements  502  are mounted, and a terminal plate  513 . The rectifier device  5  constitutes two pairs of three-phase full-wave rectifiers with six plus side rectifier elements (which are referred to as the plus rectifier elements  502 ) and six minus side rectifier elements (which are referred to as the minus rectifier elements  504 ). 
     The terminal plate  513  is made of resin for insulating the plus cooling fin  501  from the minus cooling fin  503 , and includes conductive members for leading alternating current generated in the stator  4  to the plus rectifier elements  502  and the minus rectifier elements  504 . The minus cooling fin  503  is disposed to face the rear surface of the rear frame  3   b , and the plus cooing fin  501 , which has a smaller outer peripheral size than the minus cooling fin  503 , is disposed on the minus cooling fin  503  with a certain space formed therebetween, thereby forming a two-story structure. The plus rectifier elements  502  are press-fitted into respective holes formed in the plus cooling fin  501 , and its lead terminals are extended toward the minus cooling fin  503 . The minus rectifier elements  504  are press-fitted into respective holes formed in the minus cooling fin  503 , and its lead terminals are extended toward the plus cooling fin  501 . The lead terminals of all the rectifier elements  502 ,  504  are electrically connected to the conductive members of the terminal plate  513 . 
     The direct current output is taken out from a bolt  506  connected to the plus cooling fin  501  after the alternating current generated in the stator  4  is rectified by the rectifier device  5 . The rectifier device  5  is connected to a bearing box  30  of the rear frame  3   b  with bolts, for example, together with the rear cover  8 . Both of the cooling fins  501 ,  503  are made of aluminum or copper. 
     Openings  801  for introducing cooling air in the axial direction around the plus rectifier elements  502  are formed in the rear cover  8 . Ribs  501   a ,  501   b  standing in the axial direction from the plus cooling fin  501  are formed on outer and inner peripheral portions of the plus cooling fin  501  thereby to increase an cooling area of the plus cooling fin  501 . The plus rectifier elements  502  are cooled down by the cooling air introduced from the openings  801 , and heat generated therein is dissipated through the plus cooling fin  501 . 
     Sub fins  503   a  extending in the radial direction from an outer peripheral portion of the minus cooling fin  503  are formed thereby to increase an cooling area of the minus cooling fin  503 . As shown in  FIG. 1 , an axial opening  802  is formed between an outer periphery of the rear frame  3   b  and the rear cover  8 . A radial passage  810  is formed between the rear surface of the rear frame  3   b  and the minus cooling fin  503 . The axial opening  802  and the radial passage  810  are connected to each other. When a fan  21  rotates together with the rotor  2 , cooling air is introduced into the alternator from the openings  801  formed in the rear cover  8  and from the axial opening  802 . The cooling air is further introduced into the alternator through openings  803  formed in the rear frame  3   b  to cool the rotor  2  and the stator  4 . The minus cooling fin  503  is cooled by the cooling air thus introduced, and particularly by the cooling air passing through the axial opening  802  and the radial passage  810 . 
     Now, a resilient heat conductive member  510  disposed between a base portion  504   a  of the minus rectifier element  504  and the rear frame  3   b  will be described. As shown in  FIG. 1 , a seat portion  300  is formed on the rear frame  3   b  by depressing the rear frame  3   b . The base portion  504   a  of the minus rectifier element  504  extends through the minus cooling fin  503  toward the rear frame  3   b  and contacts the seat portion  300  via the resilient heat conductive member  510 . The resilient heat conductive member  510  is held in the depression forming the seat portion  300 . Heat generated in the minus rectifier element  504  is effectively conducted to the rear frame  3   b  via the resilient heat-conductive member  510 . 
     Each of the minus rectifier elements  504  has the same structure as described above. The minus rectifier elements  504  are sufficiently cooled by the cooling air introduced into the alternator and by the heat conduction to the rear frame  3   b . Since the minus rectifier elements  504  resiliently contact the rear frame  3   b , good contact is secured for all the minus rectifier elements  504  even if there is a certain deviation among the lengths of the respective base portions  504   a  extending through the minus cooling fin  503 . Thus, all the minus rectifier elements  504  are well cooled without fail. 
     Some more details of the resilient heat-conductive member  510  will be described with reference to  FIG. 3 . In the example shown in  FIG. 3 , the resilient heat-conductive member  510  is made of porous resin into which heat-conductive grease is impregnated. The base portion  504   a  of the minus rectifier element  504  that is press-fitted into a hole of the minus cooling fin  503  extends from the minus cooling fin  503 . The bottom surface of the depression formed in the rear frame  3   b  serves as the seat portion  300  that contacts the base portion  504   a  via the resilient heat-conductive member  510 . The base portion  504   a  of the minus rectifier element  504  surely contacts the seat portion  300  by the resiliency of the resilient heat-conductive member  510 . 
     The resilient heat-conductive member  510  shown in  FIG. 3  may be variously modified. Some modified forms are shown in  FIGS. 4-7 . A resilient heat-conductive member  510   a  shown in  FIG. 4  is made by rounding and tangling metallic fibers in a ball-shape. By pushing the resilient heat-conductive member  510   a  between the base portion  504   a  and the seat portion  300 , a good heat contact is established. A resilient heat-conductive member  510   b  shown in  FIG. 5  is made of a metallic plate having waves depressed and projected in the axial direction of the rotor  2 . By pushing the resilient heat-conductive member  510   b  in the axial direction, a good heat contact is established between the base portion  504   a  and the seat portion  300 . 
     A resilient heat-conductive member  510   c  shown in  FIG. 6  is made by forming cutouts raised in the axial direction on a metallic plate. In this particular example, four cutouts are formed. By pushing the cutouts in the axial direction, a good heat contact is similarly established. A resilient heat-conductive member  510   d  shown in  FIG. 7  is made of a metallic cylinder having bellows deformable in the axial direction. By pushing the resilient heat-conductive member  510   d  in the axial direction, a good heat contact is similarly established. 
     A second embodiment of the present invention will be described with reference to  FIGS. 8 and 9 . In this embodiment, the minus cooling fin is divided into two portions  5031  and  5032 , as shown in  FIG. 8 . A base surface of the base portion  504   a  of the minus rectifier element  504  is made flush with a surface of the minus cooling fin  5031  ( 5032 ), which in turn closely contacts the rear frame  3   b , as shown in  FIG. 9 . Accordingly, the base portion  504   a  directly contacts the rear frame  3   b , establishing a good heat conduction from the minus rectifier element  504  to the rear frame  3   b . Other structures and functions of the rectifier device  5  are the same as those of the first embodiment. In the second embodiment, the base surface of the base portion  504   a  is made flush with the surface of the minus cooling fin  503 , and the minus cooling fin  503  is divided into two portions and connected to the rear frame  3   d  with respective bolts. Therefore, the influence of the deviation in the axial dimensions between the base portion  504   a  and the minus cooling fin on the heat conductivity is alleviated in the second embodiment. 
     The present invention is not limited to the embodiments described above, but it may be variously modified. For example, though the base portion  504   a  is part of the minus rectifier element  504  in the foregoing embodiments, the base portion  504   a  may be made as a part separate from the minus rectifier element  504  and attached to the minus rectifier element  504 . The ribs  501   a ,  501   b  formed on the plus cooling fin  501  and the sub fins  503   a  of the minus cooling fin  503  may be eliminated in certain applications. 
     While the present invention has been shown and described with reference to the foregoing preferred embodiments, it will be apparent to those skilled in the art that changes in form and detail may be made therein without departing from the scope of the invention as defined in the appended claims.