Abstract:
A rectifier unit of a vehicle AC generator is comprised of a plurality of metal cases, a plurality of pairs of first and second semiconductor chips and a plurality of pairs of first and second lead wires. The first lead wires are respectively connected to the first semiconductor chips, and the second lead wires are connected to the second semiconductor chips. Each pair of first and second semiconductor chips is disposed in one of the metal cases. The first lead wires are connected to each other to form a first rectifying circuit and second lead wires are connected to form a second rectifying circuit. Therefore, the number of parts for connecting the rectifier circuits can be reduced without providing complicated insulator arrangement.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application is based on and claims priority from Japanese Patent Application 2000-354516, filed Nov. 21, 2000, the contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a rectifier unit of a vehicle AC generator for a passenger car, truck or the like. 
     2. Description of the Related Art 
     It is known well that a vehicle AC generator is provided with a rectifier unit that includes a pair of three-phase full-wave rectifier circuits. For example, such a rectifier unit is comprised of a positive side heat sink and a negative side heat sink. Each heat sink has six diodes that are force-fitted or soldered thereto. The positive side and negative side heat sinks are fixed by a bolt to a frame of the AC generator with an insulation member being interposed between the heat sinks of the pair. However, because this type of the rectifier unit has twelve diodes, the number of parts and manufacturing steps are comparatively large. It is also difficult to make the size of the AC generator compact. 
     JP-A8-205498 and JP-A-7-231656 propose a metal case accommodating two semiconductor chips that are different in polarity from each other in order to reduce the number of parts and the size of the AC generator. However, two semiconductor chips that are different in polarity from each other in a metal case necessitates additional expensive structure to insulate the chips and to distinguish the polarity of the semiconductor chips. 
     SUMMARY OF THE INVENTION 
     Therefore, a main object of the invention is to provide an improved rectifier unit of a vehicle AC generator that is compact and inexpensive. 
     According to a feature of the invention, a rectifier unit of a vehicle AC generator including a plurality of metal cases, a pair of first and second semiconductor chips that has the same polarity with each other disposed in each said metal case, a pair of first and second lead wires connected to the pair of first and second semiconductor chips and a pair of first rectifier circuit connected to the first lead wire and second rectifier circuit connected to the second lead wire. 
     Therefore, the number of metal cases is reduced without providing a complicated insulation arrangement so that manufacturing steps and cost can be reduced. 
     According to another feature of the invention, the rectifier unit may further include a plurality of insulation members. The insulation member is disposed between the first semiconductor chip and the second semiconductor chip disposed in each metal case. 
     According to another feature of the invention, a clad metal member of copper layer, iron-nickel layer and copper layer is disposed between the pair of semiconductor chips and the bottom of the metal case. 
     Therefore, the clad metal member moderates stress caused by a difference in thermal expansion between a solder layer and a pair of the semiconductor chips. 
     According to another feature of the invention, the rectifier unit may further include a pair of heat sinks having a plurality of mounting holes. Each metal case has a knurled outer surface to be force-fitted to one of the mounting holes of the heat sinks. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects, features and characteristics of the present invention as well as the functions of related parts of the present invention will become clear from a study of the following detailed description, the appended claims and the drawings. In the drawings: 
     FIG. 1 is an overview of a vehicle AC generator including a rectifier unit according to a preferred embodiment of the invention; 
     FIG. 2 is a plan view of the rectifier unit according to the preferred embodiment; 
     FIG. 3 is a cross-sectional side view of a pair of semiconductor chips and a metal case of a rectifier element of the rectifier unit according to the preferred embodiment; 
     FIG. 4 is a perspective view of the exterior of the rectifier element shown in FIG. 3; 
     FIG. 5 is a plan view illustrating the inside of the rectifier element shown in FIG. 4; 
     FIG. 6 is a schematic diagram illustrating a step of forming the pair of semiconductor chips shown in FIG. 3; 
     FIG. 7 is a schematic diagram illustrating a variation of the step of forming the semiconductor chips shown in FIG. 6; and 
     FIG. 8 is a circuit diagram of the vehicle AC generator shown in FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As shown in FIG. 1, a vehicle AC generator  1  with a rectifier unit  6  according to a preferred embodiment of the invention is comprised of a stator  2 , a rotor  3 , a pair of frames  4  and  5 , a brush unit  7 , a voltage regulator  8 , a rear cover, etc. 
     The stator  2  is comprised of a stator core  22 , a pair of three-phase stator windings  23   a  and  23   b  and insulators  24  that insulate the pair of stator windings  23   a  and  23   b  from the stator core  22 . The stator windings  23   a  and  23   b  are wound so that they are shifted 30 degree in electric angle from each other. 
     The rotor  3 , a field coil  31  and a pair of front and rear pole cores  32 . The field coil  31  is formed of a cylindrically wound insulator-coated copper wire. The pair of front and rear pole cores  32  has respectively six claw poles and encloses the field coil  31  from opposite ends. The front pole core  32  has a front cooling fan  35  welded to the front end thereof, and the rear pole core  32  has rear cooling fan  36  welded to the rear end thereof. The front cooling fan  35  blows air rearward and radially outward, and the rear cooling fan  36  blows air radially outward. A pair of slip rings  37  and  38  is fixed to a rear end portion of the shaft  33  and electrically connected to the field coil  31  so that the field coil  31  can be supplied field current from the brush unit  7  via the pair of slip rings  37  and  38 . 
     The pair of front and rear frames  4  and  5  accommodates the stator  2  and the rotor  3  therein and supports the stator  2  and the rotor  3  so that the rotor  3  can rotate with the rotor shaft  33  inside the stator  2 . The pair of frames  4  and  5  has air discharge windows  41  and  51  at portions corresponding to portions of the stator windings  23   a  and  23   b  that project from the opposite axial ends of the stator core  22  and also air intake windows at the opposite axial ends of the pair of frames  4  and  5 . 
     The rectifier unit  6  rectifies three-phase AC power generated by the pair of three-phase stator winding  23   a  and  23   b  and provides DC output power. The rectifier unit  6  is comprised of a pair of rectifying circuits  6   a  and  6   b.    
     The rear cover  9  is fixed to the outside of the frame  5  to cover the rectifier unit  6 , the brush unit  7  and the voltage regulator  8 . 
     The vehicle AC generator  1  is driven by an engine via a pulley  20 . When the rotor  3  rotates and field current is supplied to the field coil  31 , the pair of pole cores  32  with the claw poles are excited so that the stator windings  23   a  and  23   b  generate three-phase AC power. 
     As shown in FIG. 2, the rectifier unit  6  is comprised of a pair of a negative heat sink  62  and a positive heat sink  63 , a terminal unit  61 , three negative side rectifier elements  65 , and three positive side rectifier elements  66 . The terminal unit  61  is disposed between the negative heat sink  62  and the positive heat sink  63 , the negative side rectifier elements are fixed to the negative heat sink  62 , and the positive side rectifier elements are fixed to the positive heat sink  63 . 
     The positive heat sink  63  is disposed inside the rear cover  9 . The positive heat sink is an arc-shaped member having approximately the same outside diameter as the inside diameter of the rear cover  9  and has three mounting holes  120  formed at intervals along a circumferential portion thereof. Positive side rectifier elements  66  are respectively force-fitted to the mounting holes  120 . A pair of leads  130   a  and  130   b  extends from each one of the positive side rectifier elements  66  and is respectively welded to connection electrodes  69   a  and  69   b  of the terminal unit  61 . 
     The negative heat sink  62  is an arc member having the outside diameter thereof smaller than outside diameter of the positive heat sink  63  and has three mounting holes  100  formed at intervals along a circumferential portion thereof. Negative side rectifier elements  65  are respectively force-fitted to the mounting holes  100 . A pair of leads also extends from each one of the negative side rectifier elements  65  and is respectively welded to connection electrodes of the terminal unit  61  in the same manner as the positive side rectifier elements  66 . 
     As shown in FIG. 3, the positive side rectifier element  66  includes a metal case  121 , a metal plate  122 , a pair semiconductor chips  123   a  and  123   b  having the same polarity, a lead  130   a  and a lead  130   b.  The metal case  121  has a knurled cylindrical outer surface  124  and a cup-shaped hollow cylindrical portion  125  that has a bottom. The metal plate  122  is soldered to the bottom (a solder layer is indicated by a reference numeral  126 ) of the hollow cylindrical portion  125 . The semiconductor chips  123   a  and  123   b  are soldered to the metal plate  122 , and the leads  130   a  and  130   b  are respectively soldered to the semiconductor chips  123   a  and  123   b.    
     The metal plate  122  is a three-layer-clad metal that is comprised of a copper layer, an iron-nickel layer and a copper layer. The metal plate  122  eases stress caused by a difference in thermal expansion between the solder layer  126  and the semiconductor chips  123   a  and  123   b.  Sealing material  127  is filled in the hollow cylindrical portion  125  to protect the semiconductor chips  123   a  and  123   b.    
     The pair of semiconductor chips  123   a  and  123   b  for the positive side rectifier element  66  is formed of a common semiconductor chip  123 . The conventional chip  123  is cut into two pieces of the same size and shape, as shown in FIGS. 6 and 7. Another pair of semiconductor chips for the negative side rectifier element  65  is also formed of a common semiconductor chip in the same manner as the positive side semiconductor chips  123   a  and  123   b.    
     One of leads that extend from the negative side rectifier element  65  and one of the leads  130   a  that extend from the positive side rectifier elements  66  are jointly connected to the connection electrode  69   a  of the terminal unit  61  to form a three-phase full-wave rectifying circuits  6   a.  One of leads that extend from the negative side rectifier element  65  and one of the leads  130   b  that extend from the positive side rectifier elements  66  are jointly connected to the connection electrode  69   b  of the terminal unit  61  to form the other three-phase full-wave rectifying circuits  6   b.    
     As shown in FIG. 8, phase windings X, Y and Z of the stator winding  23   a  are connected to the three-phase full-wave rectifying circuit  6   a,  and phase windings U, V and W of the stator winding  23   b  are connected to the three-phase full-wave rectifying circuit  6   b.    
     Thus, a pair of negative side semiconductor chips is mounted in each of the metal cases of the negative side rectifier element  65 , and a pair of positive side semiconductor chips is mounted in each of the metal cases of the positive side rectifier element  66 . Therefore, it is not necessary to insulate the pair of semiconductor chips from each other. 
     The negative and positive side rectifier elements  65  and  66  can be fixed to the respective heat sinks by means of soldering instead of force-fitting. 
     In the foregoing description of the present invention, the invention has been disclosed with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes may be made to the specific embodiments of the present invention without departing from the scope of the invention as set forth in the appended claims. Accordingly, the description of the present invention is to be regarded in an illustrative, rather than a restrictive, sense.