Abstract:
An alternator for use in an automobile is driven by an internal combustion engine. The alternator includes a pulley that is coupled to a rotating shaft of the engine via a driving belt such as a poly-V belt. Plural pulley grooves to be engaged with the driving belt are formed on the pulley between a front flange and a rear flange. A projected surface of a front frame is located around the outer periphery of the rear flange, so that the driving belt is correctly positioned between the front and the rear flanges, guided by the projected surface. Two overlaps in the axial direction between the pulley and the front frame are formed to reduce an amount of water entering into the alternator through a gap between the pulley and the front frame.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application is based upon and claims benefit of priority of Japanese Patent Application No. 2004-327599 filed on Nov. 11, 2004, the content of which is incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to an alternator for use in an automotive vehicle, and more particularly to such an alternator having a driving pulley with end flanges.  
         [0004]     2. Description of Related Art  
         [0005]     Generally, an alternator for use in an automobile is driven by an engine via a driving belt coupled to a pulley of the alternator. When a so-called poly-V belt having plural V-shaped projections is used as the driving belt, the poly-V belt has to be correctly positioned relative to plural pulley grooves formed on the pulley. That is, the plural V-shaped projections of the driving belt have to be engaged with the plural pulley grooves, so that the V-belt is correctly positioned in the axial direction within a width of the pulley. For this purpose, a pulley having end flanges formed at both axial ends of the pulley is proposed, as exemplified in JP-B2-3509292.  
         [0006]     It is not easy, however, to make end flanges having a relatively large diameter, especially when the pulley is made of a steel plate by stamping. If the diameter of the flanges is not sufficiently large, the poly-V belt may not be correctly positioned relative to an axial width of the pulley. Further, water may enter into a bearing of the alternator through an axial gap between the pulley and an axial end of a bearing holder. The bearing may be damaged with the water, and thereby noises may be generated and a life of the alternator may be shortened.  
       SUMMARY OF THE INVENTION  
       [0007]     The present invention has been made in view of the above-mentioned problem, and an object of the present invention is to provide an improved alternator having a pulley with end flanges, wherein a poly-V belt is correctly positioned around the pulley and an amount of water entering into the alternator is reduced.  
         [0008]     The alternator includes a frame composed of a front frame and a rear frame, a stator fixedly contained in the frame, a rotor rotatably supported in the frame inside the stator and a pulley connected to the rotor at an front side of the frame. A rotating shaft of an engine and the pulley are coupled by a driving belt (such as a poly-V belt) to drive the alternator by the engine. The pulley has a cylindrical shape and includes plural pulley grooves to be engaged with projections formed on an inner surface of the driving belt, a first flange formed at an front end of the pulley and a second flange formed at a rear end of the pulley. The diameter of the second flange is made larger than the outer diameter of the pulley grooves and smaller than the diameter of the first flange. A projected portion is circularly formed on a front end of the frame so that the projected portion is positioned at a radial outside of the second flange. Windows for sucking cooling air into the frame are formed at a radial outside of the projected portion.  
         [0009]     A gap L 1  between the inner diameter of the projected portion and the diameter of the second flange is made smaller than a thickness (in the radial direction) of the driving belt. A front end surface of the projected portion is positioned at a front side of a rear end of the second flange, thereby making an overlap L 2  therebetween. A front end surface of the projected portion is positioned at a front side of a rear end surface of the pulley, thereby making another overlap L 3  therebetween.  
         [0010]     Since the gap L 1  is smaller than the thickness of the driving belt, and since the front end surface of the projected portion is positioned in a front side of the rear end of the second flange, the driving belt can be correctly positioned between two flanges, guided by the front end surface of the projected portion even if the diameter of the second flange is not sufficiently large. Since there are two overlaps L 2  and L 3  between the front frame and the pulley, an amount of water entering into a bearing in the front frame is reduced. Since the cooling air sucking windows are formed radially outside of the projected portion, cooling air smoothly flows into the frame.  
         [0011]     Other objects and features of the present invention will become more readily apparent from a better understanding of the preferred embodiment described below with reference to the following drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1  is a cross-sectional view showing an entire structure of an alternator according to the present invention;  
         [0013]      FIG. 2  is a plan view showing the alternator, viewed form direction II shown in  FIG. 1 ; and  
         [0014]      FIG. 3  is a partial cross-sectional view showing a rear end frame and a pulley used in the alternator, in an enlarged scale. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0015]     A preferred embodiment of the present invention will be described with reference to accompanying drawings. As shown in  FIG. 1 , an alternator  1  is composed of a rotor  2 , a stator  3 , a frame formed by a front frame  4  and a rear frame  5 , a brush device  6 , a rectifier  7 , a voltage regulator  8 , a pulley  9  and other associated components. The pulley  9  is positioned at a front side of the alternator  1 , while components such as the brush device  6  are positioned at a rear side of the alternator  1 . The front side and the rear side are indicated in  FIG. 1  with an arrow.  
         [0016]     The rotor  2  includes a pair of rotor cores  22 ,  23  firmly connected to a rotor shaft  24  and a rotor winding  21  wound on the rotor cores  22 ,  23 . Each rotor core  22 ,  23  has a boss connected to the rotor shaft  24  and six claw-shaped poles. A cooling fan  25  for sucking cooling air in the axial direction and blowing the sucked cooling air in axial and radial directions is connected to a front surface of the front rotor core  22 . Another cooling fan  26  (a centrifugal fan) for sucking cooling air in the axial direction and blowing the sucked cooling air in the radial direction is connected to a rear surface of the rear rotor core  23 . The cooling fans  25 ,  26  are connected to respective rotor cores  22 ,  23  by welding or the like.  
         [0017]     A pair of slip-rings  27 ,  28  are formed at the rear end of the rotor shaft  24 , and brushes  61 ,  62  held in the brush device  6  slidably contact the slip-rings  27 ,  28 . Excitation current is supplied to the rotor winding  21  from the rectifier  7  through the brushes  61 ,  62  and the slip-rings  27 ,  28 .  
         [0018]     The stator  3  is composed of a cylindrical stator core  31  and stator winding  32  disposed in slots formed in the stator core  31 . The stator winding  32  forms a three-phase armature winding. The rectifier  7  rectifies three-phase alternating current generated in the stator winding  32  into a direct current output. The rectifier  7  is composed of heat-sink plates and rectifier elements mounted on and soldered to the heat-sink plates.  
         [0019]     The frame composed of the front frame  4  and the rear frame  5  contains therein the stator  3  and the rotor  2 . The stator  3  is fixedly contained in the frame, and the rotor  2  is rotatably supported in the frame inside the stator  3 . The stator  3  is sandwiched between the front frame  4  and the rear frame  5 , and both frames  4 ,  5  are connected to each other with bolts  34  inserted into four supporting portions  420  formed at equal intervals around the outer periphery of the frames  4 ,  5 .  
         [0020]     The voltage regulator  8  controls the output voltage, which otherwise changes according to rotational speed and loads of the alternator  1 , to a substantially constant level. The pulley  9  is connected to the front end of the rotor shaft  24  with nut  81 , and the rotor  2  is driven by an engine via a driving belt coupling the engine to the pulley  9 . The brush device  6 , the rectifier  7  and the voltage regulator  8  mounted on the rear side of the rear frame  5  is covered with a rear cover  82 .  
         [0021]     Now, a structure of the pulley  9  and the front end of the front frame  4  will be described in detail with reference to  FIGS. 2 and 3 . The front flame  4  includes a bearing holder  400  in which a bearing  36  is contained. A collar  29  is sandwiched between the rear end surface of the pulley  9  and an inner ring of the bearing  36 , and the pulley  9  is firmly connected to the rotor shaft  24  by fastening the nut  81 .  
         [0022]     The pulley  9  is made of a steel plate, for example, by stamping. The cylindrically shaped pulley  9  includes plural pulley grooves  91 , a first flange  92  formed at the front end and a second flange  93  formed at the rear end of the pulley  9 . The outer diameter ΦB of the second flange  93  is lager than the outer diameter of the pulley grooves  91  and smaller than the outer diameter ΦA of the first flange  92 . Plural projections formed on the inside surface of the driving belt  100  engage with the plural grooves  91 . The width of the driving belt  100  is correctly positioned between the first flange  92  and the second flange  93 , guided by both flanges  92 ,  93 .  
         [0023]     A projected portion  41  is circularly formed on the front end of the front frame  4  and positioned outside of the second flange  93 . A gap L 1  between the outer diameter ΦB of the second flange  93  and the inner diameter of the projected portion  41  is made smaller than a thickness (in the radial direction) of the driving belt  100 . It is preferable to make the gap L 1  considerably smaller than the thickness of the driving belt  100 , taking into consideration that the driving belt  100  is made of a material having a certain resiliency. For example, the gap L 1  is made smaller than 3 mm. Windows 42 for introducing cooling air into the frame are made at a radial outside of the projected portion  41 .  
         [0024]     As shown in  FIG. 3 , the front end surface  41   a  of the projected portion  41  is positioned at a front side of the rear end surface  93   a  of the second flange  93 . In other words, there is a small overlap L 2  in the axial direction between the rear end surface  93   a  of the second flange  93  and the front end surface  41   a  of the projected portion  41 . The rear end surface  9   a  of the pulley  9  is positioned at a rear side of the front end surface  41   a  of the projected portion  41 . In other words, there is a small overlap L 3  in the axial direction between the rear end surface  9   a  of the pulley  9  and the front end surface  41   a  of the projected portion  41 .  
         [0025]     The outer diameter ΦB of second flange  93  is smaller than the outer diameter ΦA of the first flange  92 . Therefore, when the driving belt  100  is coupled to the pulley  9 , the driving belt  100  may not be properly guided by the second flange  93  and may shift toward the front frame  4 . If this happens, the rear side of the driving belt  100  contacts the front surface  41   a  of the projected portion  41  and is properly guided to a correct position. The gap L 1  is smaller than the thickness of the driving belt  100 , and there is the overlap L 2  between the rear end surface  93   a  of the second flange  93  and the front end surface  41   a  of the projected portion  41 . Therefore, the side of the driving belt  100  surely interferes with the front end surface  41   a  of the projected portion  41  if the driving belt  100  shifts toward the front frame  4  when coupling the driving belt  100  to the pulley  9 . In this manner, the driving belt  100  is always correctly positioned between the first flange  92  and the second flange  93 .  
         [0026]     Since there is the overlap L 3  between the front end surface  41   a  of the projected portion  41  and the rear end surface  9   a  of the pulley  9 , water is prevented from easily entering into the bearing  36  when the alternator  1  is mounted on an automobile so that the rotor shaft  24  becomes parallel to the horizontal direction. Thus, an amount of water entering into the bearing  36  is reduced. Since the projected portion  41  is formed at a radial inside of the cooling air sucking windows  42 , the projected portion  41  does not interfere with a cooling airflow entering into the windows  42 , rather the cooling airflow is properly guided by the projected portion  41 .  
         [0027]     The present invention is not limited to the embodiment described above, but it may be variously modified. For example, the pulley  9  may be made by machining or forging though it is explained that the pulley  9  is made of a steel plate by stamping in the above embodiment. While the present invention has been shown and described with reference to the foregoing preferred embodiment, 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.