Patent Publication Number: US-7219417-B2

Title: Method of producing bus bars for centralized power distribution unit

Description:
CROSS REFERENCE TO RELATED DOCUMENTS 
   This is a Division of Application Ser. No. 10/281,202 filed Oct. 28, 2002, now U.S. Pat. No. 6,894,410, which claims the benefit of Japanese Patent Application No. 2001-330026 filed Oct. 26, 2001. The entire disclosure of the prior application is hereby incorporated by reference herein in its entirety. 

   BACKGROUND OF THE INVENTION 
   1. Field of Invention 
   The present invention relates to a centralized power distribution unit which is used for performing centralized power distribution on stator windings of a vehicular thin brushless motor. 
   2. Description of Related Art 
   Recently, automobiles with good fuel economy have been in high demand. As one example of automobile manufacturers&#39; efforts to meet these demands, hybrid cars with super low fuel consumption have been developed. In particular, a hybrid car has been proposed recently which is provided with an auxiliary power mechanism (a motor assist mechanism) in which an engine provides the main power and a DC brushless motor assists the engine upon acceleration or the like. 
   The motor assist mechanism is subject to much constraint in installation, since a brushless motor constituting the motor assist mechanism is disposed in a limited space, for example, a space between an engine and a transmission in an engine compartment. Thus, such a brushless motor is required to have a thin configuration. 
   A thin brushless motor to be used in the motor assist mechanism of a vehicle includes a rotor directly connected to a crankshaft of the engine, and a ring-like stator enclosing the rotor. The stator includes many magnetic poles that have windings on cores, a stator holder that contains the magnetic poles, and a centralized distribution unit that concentratedly distributes currents to the windings. 
   As shown in  FIG. 34A , a conventional centralized power distribution unit used in a three-phase DC brushless motor includes three ring-like bus bars  101 ,  102 , and  103 . Each of the ring-like bus bars  101 ,  102 , and  103  includes a ring-like body  104 , a terminal portion  105  projecting outwardly in a radial direction on an outer periphery of the ring-like body  104 , and a plurality of tabs  106  each projecting inwardly in the radial direction on an inner periphery of the ring-like body  104 . Each terminal portion  105  is electrically connected through an electric wire to a battery while each tab  106  is electrically connected through a respective electric wire to an end of a respective winding. When the three ring-like bus bars  101 ,  102 , and  103  are energized, currents are concentratedly distributed to the windings corresponding to a U phase, a V phase, and a W phase. Consequently, the motor is driven. 
   SUMMARY OF THE INVENTION 
   When the conventional centralized power distribution unit is to be produced, press moldings must be conducted on a conductive metal plate  107  using different molds to form ring-like bus bars  101 ,  102 , and  103  for the three phases as shown in  FIG. 34B . 
   In order to obtain the ring-like bus bars  101 ,  102 , and  103 , the conductive metal plate  107  must have a size which is at least as larger than the outer diameters of the bus bars  101 ,  102 , and  103 . Most of the portions of the metal plate other than the portions which are stamped out into the ring-like shape become wasted. Therefore, conventionally, as seen from the above, the conductive metal plate  107  includes a very large useless portion and hence is wasteful. This is a cause of increased production costs of a centralized power distribution unit. 
   The invention has been made in view of the above-discussed problem. It is an object of the invention to provide a centralized power distribution unit for a vehicular thin brushless motor which can be produced at a small amount of waste of a metal material and at a low cost. It is another object of the invention to provide a method of producing bus bars which are preferably used as excellent components of the centralized power distribution unit. 
   In order to attain these objects, in the invention, a centralized power distribution unit for a vehicular thin brushless motor includes: a plurality of bus bars each having a terminal portion to be connected to a battery, and tabs to be respectively connected to windings of a stator, the bus bars being disposed correspondingly with phases of the motor; and a resin insulating layer that covers the bus bars. The centralized power distribution unit can intensively distribute a current to the windings, and has a ring-like shape. Each of the bus bars is shaped into a substantially annular shape by bending a molded material which is obtained by stamping out a conductive metal plate into a strip-like shape. In a thickness direction, diameters of the bus bars are set to be different from one another depending on the phase, and the bus bars are stacked in a radial direction of the centralized power distribution unit, being separated from one another by a predetermined gap. 
   According to the invention, therefore, the bus bars can be configured by materials which are stamped out into a strip-like shape, so that it is not required to use a considerably large conductive metal plate and the bus bars can be obtained with a reduced amount of wasted material. In the case of a strip-like shape, the bus bars can be obtained in a state where the bus bars are densely placed, and hence the amount of wasted material can be reduced. Therefore, the material cost of the bus bars can be reduced, with the result that the centralized power distribution unit can be produced at a low cost. 
   In the invention, in a method of producing bus bars used in a centralized power distribution unit of the above-mentioned invention, press molding using a mold is conducted to simultaneously stamp out the bus bars respectively corresponding to the phases from a common conductive metal plate. 
   According to the invention, therefore, the material loss is remarkably reduced as compared with that in a conventional method. Therefore, the material cost of the bus bars can be reduced, and the cost of the mold can be lowered. As a result, the centralized power distribution unit can be produced at a low cost. 
   Preferably, when a linear bus bar body is stamped out by the press molding, the terminal portion and the tabs are integrally formed in a state where the terminal portion and the tabs are coupled to the bus bar body. In this case, a step of welding or the like is not necessary, and hence the production cost can be reduced as compared with the case where a terminal portion and tabs which are previously produced are later attached to the bus bar body. Therefore, the use of such bus bars enables the centralized power distribution unit to be produced at a low cost. 
   Preferably, the bus bars are stamped out in a state where the bus bar bodies are placed in parallel, and in a state where both ends of the bus bar bodies are substantially aligned with one another. According to the configuration, the material loss in the stamping process is reduced, so that further cost reduction can be attained. 
   Preferably, when the bus bars are laid out in parallel in a row on a conductive metal plate in order to be stamped from the conductive metal plate, the terminal portion and the tabs of one(s) of the bus bars which is (are) positioned at an outermost side(s) are directed to a center of the bus bar row. In this case, a conductive metal plate of a smaller width can be used as compared with the case where the terminal portion and tabs of the outermost one(s) of the bus bars are directed to the outer side of the bus bar row. Therefore, the material loss in the stamping process is further reduced, so that still further cost reduction can be attained. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other features of the present invention will become apparent to one skilled in the art to which the present invention relates upon consideration of the invention with reference to the accompanying drawings, wherein: 
       FIG. 1  is a schematic side elevation view of a thin brushless motor; 
       FIG. 2  is a schematic wiring diagram of the thin brushless motor; 
       FIG. 3  is a perspective view of a centralized distribution unit; 
       FIG. 4  is a front elevation view of the centralized distribution unit; 
       FIG. 5  is a rear elevation view of the centralized distribution unit; 
       FIG. 6A  is a cross sectional view of the centralized distribution unit; 
       FIG. 6B  is an enlarged cross sectional view of a terminal portion of the unit; 
       FIG. 6C  is an enlarged perspective view of the terminal portion shown in  FIG. 6B ; 
       FIG. 7  is a plan elevation view of a terminal portion of the centralized distribution unit; 
       FIG. 8  is a perspective view of an insulating holder; 
       FIG. 9  is a front elevation view of the insulating holder in which bus bars are inserted; 
       FIG. 10  is an enlarged front elevation view of a part of the insulating holder; 
       FIG. 11  is a front elevation view of bus bars from which the insulating holder is omitted; 
       FIG. 12  is an enlarged front elevation view of a part of the insulating holder, illustrating a bus bar non-containing section in the holder; 
       FIG. 13A  is a cross sectional view of the insulating holder taken along line  13   a — 13   a  in  FIG. 9 ; 
       FIG. 13B  is a cross sectional view of the insulating holder taken along line  13   b — 13   b  in  FIG. 9 ; 
       FIG. 13C  is a cross sectional view of the insulating holder taken along line  13   c — 13   c  in  FIG. 9 ; 
       FIG. 14A  is a cross sectional view of the centralized distribution unit taken along line  14   a — 14   a  in  FIG. 4 ; 
       FIG. 14B  is a perspective view of the centralized distribution unit shown in  FIG. 14A ; 
       FIG. 15A  is a cross sectional view of the centralized distribution unit taken along line  15   a — 15   a  in  FIG. 4 ; 
       FIG. 15B  is a perspective view of the centralized distribution unit shown in  FIG. 15A ; 
       FIG. 16A  is a cross sectional view of the centralized distribution unit taken along line  16   a — 16   a  in  FIG. 4 ; 
       FIG. 16B  is a perspective view of the centralized distribution unit shown in  FIG. 16A ; 
       FIG. 17A  is a cross sectional view of the centralized distribution unit taken along line  17   a — 17   a  in  FIG. 4 ; 
       FIG. 17B  is a perspective view of the centralized distribution unit shown in  FIG. 17A ; 
       FIG. 18A  is a cross sectional view of a first press apparatus, illustrating the apparatus in an open position; 
       FIG. 18B  is a perspective view of a part of a strip-like blank to be pressed by the first press apparatus shown in  FIG. 18A ; 
       FIG. 19A  is a cross sectional view of the first press apparatus, illustrating the apparatus in a closed position; 
       FIG. 19B  is a perspective view of a strip-like blank that has been pressed in the first press apparatus shown in  FIG. 19A ; 
       FIG. 20A  is a cross sectional view of a second press apparatus, illustrating the apparatus in an open position; 
       FIG. 20B  is a perspective view of a strip-like blank that has been pressed in the second press apparatus shown in  FIG. 20A ; 
       FIG. 21A  is a plan elevation view of a strip-like blank, illustrating the blank in a state before a terminal portion of the bus bar is bent; 
       FIG. 21B  is a longitudinal sectional view of the blank taken along line  21   b - 21   b  in  FIG. 21B ; 
       FIG. 22  is a rear elevation view of the insulating holder; 
       FIG. 23A  is an enlarged plan elevation view of a bearing recess; 
       FIG. 23B  is an enlarged perspective view of the bearing recess shown in  FIG. 23A ; 
       FIG. 24  is a cross sectional view of an insert-molding mold, illustrating the mold in which the insulating holder is set; 
       FIG. 25  is a cross sectional view of the insert-molding mold similar to  FIG. 24 , illustrating the mold into which a molten resin material is poured; 
       FIG. 26  is a cross sectional view of the insert-molding mold similar to  FIG. 25 , illustrating the mold in which a holder support pin and an upper mold member support are retracted; 
       FIG. 27  is a cross sectional view of the insert-molding mold similar to  FIG. 26 , illustrating the mold in an open position; 
       FIG. 28  is a plan view of a conductive metallic plate to be punched into the strip-like blanks, illustrating a process for producing the centralized distribution unit; 
       FIG. 29  is a perspective view of the blanks shown in  FIG. 28 , illustrating the terminal portion of each of bus bars being bent; 
       FIG. 30  is a perspective view of ring-like blanks that are formed by bending the blanks shown in  FIG. 29 , illustrating the bus bars being inserted into the insulating holder; 
       FIG. 31  is a perspective view of the blanks shown in  FIG. 30 , illustrating tabs of the bus bars being bent inward; 
       FIG. 32  is a perspective view of the blanks shown in  FIG. 3   1 , illustrating a part of the terminal portions being sealed by a sealing material; 
       FIG. 33  is a view showing another example of a process of stamping out strip-like molded materials from a conductive metal plate; 
       FIG. 34A  is a perspective view of conventional ring-like bus bars; and 
       FIG. 34B  is a plan view of a conductive metallic plate from which the conventional ring-like bus bars are to be punched out. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   As shown in  FIG. 1 , a three-phase thin DC brushless motor  11  to be used in a hybrid automobile is disposed between an engine  12  and a transmission  13 . The thin DC brushless motor  11  includes a rotor  14  connected, e.g., directly connected, to a crankshaft of the engine  12 , and a ring-like stator  15  enclosing the rotor  14 . The stator  15  includes a plurality of magnetic poles that have windings  16  on cores, a stator holder  18  that contains the magnetic poles, and an annular centralized distribution unit  17  that concentratedly distributes currents to the windings  16 . 
     FIG. 2  shows a schematic diagram of the stator  15 . As shown in  FIG. 2 , an end of each phase winding  16  is connected to one of bus bars  22   a ,  22   b , and  22   c  formed in the centralized distribution unit  17  while the other end is connected to a ring-like conductive member (not shown). 
   As shown in  FIGS. 3 to 6 , a continuous annular insulating holder  21  ( FIGS. 6A and 6B ) made of synthetic resin is embedded in the centralized distribution unit  17 . The insulating holder  21  may be made of, for example, PBT (polybutyrene terephthalate), PPS (polyphenylene sulfide), or the like. 
   In this embodiment, the insulating holder  21  is made of a PPS containing a glass fiber of 40% by weight. The reason why the insulating holder  21  is made of such a material is that the material is superior in its electrical properties (dielectric strength). In particular, in the thin DC brushless motor  11  in the present embodiment, since voltages to be applied to the respective phase bus bars  22   a ,  22   b , and  22   c  are high, it is important to maintain the dielectric strength in the respective bus bars  22   a ,  22   b , and  22   c . The dielectric strength in this case is required to be above 2000V. In addition, PPS has a high mechanical strength as well as a high heat resistance in comparison with a common resin such as a PP (polypropylene) or the like. 
   As shown in  FIGS. 8 ,  9 , and  10 , the insulating holder  21  is provided on one side with holding grooves  23   a ,  23   b , and  23   c  extending in the circumferential direction. The holding grooves  23   a ,  23   b , and  23   c  are disposed in parallel at a given distance in the radial direction of the insulating holder  21 . The bus bars  22   a ,  22   b , and  22   c  corresponding to the respective phases are individually inserted into the respective holding grooves  23   a ,  23   b , and  23   c , respectively. The respective bus bars  22   a ,  22   b , and  22   c  are stacked on each other in the radial direction of the centralized distribution unit  17  with the bus bars being spaced from each other at a given distance. Accordingly, the respective holding grooves  23   a ,  23   b , and  23   c  serve to hold the respective bus bars  22   a ,  22   b , and  22   c  in the precise positions. The insulating holder  21  and bus bars  22   a ,  22   b , and  22   c  are entirely covered with a resin insulation layer  25 . This covering accomplishes individual insulation between the respective bus bars  22   a ,  22   b , and  22   c.    
   The resin insulation layer  25  is made of a PPS containing a glass fiber, similar to the insulating holder  21 . The reason why this material is used in the resin insulation layer  25  is that the material is superior in its electric properties (dielectric strength), heat resistance, and mechanical strength, similar to the reason it is used in the insulating holder  21 . The material in the resin insulation layer  25  utilizes a synthetic resin. 
   In this embodiment, the bus bar  22   a  at the inside layer corresponds to a W phase, the bus bar  22   b  at the intermediate layer to a U phase, and the bus bar  22   c  at the outside layer to a V phase, respectively. For convenience of explanation, the W phase bus bar  22   a  is referred to as the “inside bus bar  22   a ” hereinafter, the U phase bus bar  22   b  as the “intermediate bus bar  22   b ,” and the V phase bus bar  22   c  as the “outside bus bar  22   c ,” respectively. 
   The respective bus bars  22   a ,  22   b , and  22   c  will be explained below. The respective bus bars  22   a ,  22   b , and  22   c  are formed beforehand by punching out a conductive metallic plate made of a copper or a copper alloy into a strip-like blank using a press apparatus, and bending the blank in the thickness direction to form a discontinuous annular configuration from which a part of an arc is removed (substantially a C-shape). The diameters of the respective bus bars  22   a ,  22   b , and  22   c  are set to be larger in order from the inside layer to the outside layer. The formed respective bus bars  22   a ,  22   b , and  22   c  are inserted into the respective holding grooves  23   a ,  23   b , and  23   c . This makes it easy to assemble the respective bus bars  22   a ,  22   b , and  22   c  in the insulating holder  21 . 
   As shown in  FIGS. 8 to 11 , the respective bus bars  22   a ,  22   b , and  22   c  are provided with respective pluralities of projecting tabs  41   a ,  41   b , and  41   c  to which the respective windings  16  are connected. The respective tabs  41   a ,  41   b , and  42   c  are punched out from the conductive metallic plate simultaneously when the respective bus bars  22   a ,  22   b , and  22   c  are punched out from the plate by the press apparatus. Consequently, the respective bus bars  22   a ,  22   b , and  22   c  and the respective tabs  41   a ,  41   b , and  41   c  are formed integrally together as one piece by a single pressing step. This simplifies the production process in comparison with a process in which the respective tabs  41   a ,  41   b , and  41   c  are coupled to the respective bus bars  22   a ,  22   b , and  22   c  by welding. 
   Six of each of tabs  41   a ,  41   b , and  41   c  are provided on the respective bus bars  22   a ,  22   b , and  22   c . The respective tabs  41   a ,  41   b , and  41   c  in the respective phase are arranged at an even angular distance (i.e., 60 degrees with respect to the center) in the circumferential direction of the respective bus bars  22   a ,  22   b , and  22   c . Removed portions  42  of the respective bus bars  22   a ,  22   b , and  22   c  are displaced from each other by an angle of 20 degrees in the circumferential direction. Consequently, eighteen of the tabs  41   a  to  41   c  in total are arranged at an even angular distance of 20 degrees with respect to the center in the circumferential direction of the centralized distribution unit  17 . As shown in  FIG. 11 , in the present embodiment, in the case where the removed portion  42  of the outside bus bar  22   c  is set to be a reference, the intermediate bus bar  22   b  is arranged away from the reference by +20 degrees in the clockwise direction. Meanwhile, the inside bus bar  22   a  is arranged away from the reference by −20 degrees in the counterclockwise direction. 
   The respective tabs  41   a ,  41   b , and  41   c  of the respective bus bars  22   a , and  22   b , and  22   c  are bent into L-shapes in cross section to direct the distal ends of them to the center of the centralized distribution unit  17 . 
   Each distal end of the respective tabs  41   a ,  41   b , and  41   c  projects inwardly in the radial direction from the inner periphery of the centralized distribution unit  17 . Each winding  16  is connected to a respective projecting portion. The respective tabs  41   a ,  41   b , and  41   c  are different in length. The distal end of each of the respective tabs  41   a ,  41   b , and  41   c  is arranged on the same distance from the center of the centralized distribution unit  17 . Accordingly, the respective tabs  41   a ,  41   b , and  41   c  of the respective bus bars  22   a ,  22   b , and  22   c  are longer in length in the radial direction of the centralized distribution unit in order from the inside bus bar  22   a  to the outside bus bar  22   c.    
   As shown in  FIGS. 15A and 15B , the tabs  41   b  of the intermediate bus bar  22   b  are, at the section covered by the resin insulation layer  25 , provided with a curved portion  44  raised in the height direction of the walls  43   a ,  43   b ,  43   c , and  43   d  that define the holding grooves  23   a ,  23   b , and  23   c . The curved portion  44  goes around the top side of the inside bus bar  22   a  (i.e., another bus bar) in the resin insulation layer  25 . The curved portion  44  can provide an increased distance between the tabs  41   b  and the adjacent bus bar. 
   As shown in  FIGS. 16A and 16B , the tabs  41   c  of the outside bus bar  22   c  are, at the section covered by the resin insulation layer  25  provided with a curved portion  45  raised in the height direction of the walls  43   a  to  43   d . The curved portion  45  goes around the top sides of the intermediate bus bar  22   b  as well as the inside bus bar  22   a  (i.e., other bus bars) in the resin insulation layer  25 . The curved portion  45  can provide an increased distance between the tabs  41   c  and the adjacent bus bars. Since the curved portion  45  goes around two bus bars  22   a  and  22   b , the curved portion  45  is longer than the curved portion  44  of the tab  41   b  on the intermediate bus bar  22   b.    
   As shown in  FIGS. 14A and 14B , the tabs  41   a  of the inside bus bar  22   a  have no curved portion on the proximal end, but rather have a right-angled portion. The tabs  41   a  are not required to be at an increased distance, since there is no adjacent bus bar for the tabs to go around. 
   As shown in  FIGS. 14A and 14B , inside projecting pieces  47  are formed integrally with wall  43   b , and are positioned between tab forming sections of the inside bus bar  22   a  from tab non-forming sections of the intermediate bus bar  22   b  adjacent the inside bus bar  22   a . The inside projecting pieces  47  can provide an increased creepage distance between the inside bus bar  22   a  and the intermediate bus bar  22   b  adjacent the inside bus bar  22   a . Six inside projecting pieces  47  in total, made of a synthetic resin, are provided on the wall  43   b  and arranged at an even spacing in the circumferential direction of the insulating holder  21 . The respective inside projecting pieces  47  correspond in position to the respective tabs  41   a  formed on the inside bus bar  22   a . The portions of wall  43   b  having the inside projecting pieces  47  are higher than the portions of wall  43   b  that space the tab non-forming sections of the inside bus bar  22   a  and intermediate bus bar  22   b.    
   As shown in  FIGS. 15A and 15B , an outside projecting piece  48  is formed integrally with wall  43   c  that spaces a tab forming section of the intermediate bus bar  22   b  from a tab non-forming section of the outside bus bar  22   c  adjacent the intermediate bus bar  22   b . The outside projecting piece  48  can provide an increased distance between the intermediate bus bar  22   b  and the outside bus bar  22   c  adjacent the intermediate bus bar  22   b . Six outside projecting pieces  48  in total, made of a synthetic resin, are provided on the wall  43   c  and arranged at an even spacing in the circumferential direction of the insulating holder  21 . The respective outside projecting pieces  48  correspond to the respective tabs  41   b  formed on the intermediate bus bar  22   b . The portions of wall  43   c  having the outside projecting piece  48  are higher than the portions of wall  43   c  that space the tab non-forming sections of the intermediate bus bar  22   b  and outside bus bar  22   c.    
   As shown in  FIGS. 3 to 7 , the respective bus bars  22   a ,  22   b , and  22   c  are provided on their sides with respective terminal portions  50   w ,  50   u , and  50   v  formed integrally together with the respective bus bars. The respective terminal portions  50   w ,  50   u , and  50   v  project outwardly from the resin insulation layer  25 . The respective terminal portions  50   w ,  50   u , and  50   v  are connected through electric power source cables  51  shown in  FIG. 1  to a battery (not shown) for the thin DC brushless motor  11 . The respective terminal portions  50   w ,  50   u , and  50   v  are punched out simultaneously when the bus bars  22   a ,  22   b , and  22   c  are punched out from the conductive metallic plate by a press apparatus. Accordingly, the respective terminal portions  50   w ,  50   u , and  50   v  are formed integrally together as one-piece with the bus bars  22   a ,  22   b , and  22   c , respectively, by a single pressing process. This can simplify the production process in comparison with a procedure in which the respective terminal portions  50   u ,  50   v , and  50   w  are welded to the respective bus bars  22   a ,  22   b , and  22   c.    
   As shown in  FIGS. 6 and 7 , the respective terminal portions  50   u ,  50   v , and  50   w  are provided on the distal ends with bolt through-holes that permit attachment bolts (not shown) for the electric power source cables  51  to pass. Resin-containing sections  53  are formed integrally together with the outer periphery of the resin insulation layer  25  to enclose the outer peripheries from the proximal ends to the central portions of the respective terminal portions  50   u ,  50   v , and  50   w . The resin-containing sections  53  are filled with sealing material  54  made of an insulative thermosetting resin. The sealing material  54  embeds portions disposed near the proximal ends away from the bolt through-holes  52  and exposed from the resin insulation layer  25  on the respective terminal portions  50   u ,  50   v , and  50   w . Waterproof-ness and airtight-ness functions are enhanced by the sealing material  54  embedding the parts of the respective terminal portions  50   u ,  50   v , and  50   w . In the present embodiment, the sealing material  54  is preferably a silicone-based thermosetting resin. Alternatively, the thermosetting resin may be any resin other than a silicone-based resin. 
     FIG. 28  is a developed view of the bus bars  22   a ,  22   b , and  22   c . As shown in  FIG. 28 , the respective terminal portions  50   u ,  50   v , and  50   w  are disposed substantially on longitudinally central parts of the respective bus bars  22   a ,  22   b , and  22   c . The numbers of the respective tabs  41   a ,  41   b , and  41   c  on opposite sides of the respective terminal portions  50   u ,  50   v , and  50   w  are preferably the same. In more detail, three tabs  41   a ,  41   b , and  41   c  are provided on one side of the respective terminal portions  50   u ,  50   v , and  50   w  while three tabs  41   a ,  41   b , and  41   c  are provided on the other side of the respective terminal portions  50   u ,  50   v , and  50   w . The reason why the same numbers of the tabs  41   a , 41   b , and  41   c  are provided on the opposite sides of the terminal portions  50   u ,  50   v , and  50   w  is to permit equal amounts of current to flow in the tabs  41   a ,  41   b , and  41   c.    
   As shown in  FIGS. 6 and 8 , the respective terminal portions  50   u ,  50   v , and  50   w  include embedded sections  55  covered by the sealing material  54  on their proximal ends, and exposed sections  56  having the bolt through-holes  52  and not covered by the sealing material  54  on their distal ends. The embedded sections  55  are pressed to form central ramp portions  55   a . These central ramp portions  55   a  can save material in comparison with central right-angled portions, and reduce weights of the bus bars  22   a ,  22   b , and  22   c.    
   Slits  57   a  and  57   b  are provided on opposite sides of the embedded portions of the respective terminal portions  50   u ,  50   v , and  50   w . Both slits  57   a  and  57   b  extend in the longitudinal directions of the respective terminal portions  50   u ,  50   v , and  50   w . The two slits  57   a  and  57   b  reduce a part of the embedded section  55 , thereby making a width of the reduced portion narrower than that of a non-reduced portion. Such structure can make a difference in reducing heat contraction between the resin insulation layer  25  and the bus bars  22   a  to  22   c  when the resin insulation layer encloses the insulating holder  25  during insert molding. The number and width of the slits  57   a  and  57   b  may be changed without lowering mechanical strengths of the respective terminal portions  50   u ,  50   v , and  50   w . For example, two slits  57   a  and  57   b  may be provided on the opposite sides of the embedded section  55 , respectively. 
   As shown by cross hatching in  FIG. 8 , parts of the exposed section  56  and embedded section  55  on the respective terminal portions  50   u ,  50   v , and  50   w  are covered by tinning. In more detail, tinning covers an area from the distal end of the exposed section  56  to the central ramp portion  55   a  of the embedded section  55 . This tinning can prevent the bus bars  22   a ,  22   b , and  22   c  from being subject to corrosion by oxidation. 
   After the respective terminal portions  50   u ,  50   v , and  50   w  are bent by a first press apparatus  60  shown in  FIGS. 18 and 19 , a second press apparatus  61  shown in  FIG. 20  further bends them. 
   The first press apparatus  60  will be explained below with reference to  FIGS. 18 and 19 . As shown in  FIGS. 18 and 19 , the first press apparatus  60  bends the respective terminal portions  50   u ,  50   v , and  50   w . The first press apparatus  60  includes a stationary lower die member  62  and a movable upper die member  63 . When the upper die member  63  moves down toward the lower die member  62 , both dies are closed. Conversely, when the upper die member  63  moves up away from the lower die member  62 , both dies are opened. 
   The lower die member  62  is provided on the upper surface with a lower forming V-shaped recess  62   a  and a lower forming V-shaped protrusion  62   b  adjacent the recess  62   a . A pilot pin  64  is formed at the top of the lower forming protrusion  62   b . When the pilot pin  64  passes through a pilot hole  65  formed in the central ramp portion  55   a  of each of the terminal portions  50   u ,  50   v , and  50   w , the respective terminal portions  50   u ,  50   v , and  50   w  are positioned. 
   On the other hand, the upper die member  63  is provided on the lower surface with an upper forming V-shaped protrusion  63   a  and an upper forming V-shaped recess  63   b  adjacent the protrusion  63   a . The upper forming protrusion.  63   a  is opposed to the lower forming recess  62   a  while the upper forming recess  63   b  is opposed to the lower forming protrusion  62   b . When the upper die member  63  moves down toward the lower die member  62  to the closed position, the upper forming protrusion  63   a  engages the lower forming recess  62   a . The upper forming recess  63   b  is provided on the bottom surface with an escape recess  66 . When the lower and upper die members  62  and  63  are driven to the closed position, the pilot pin  64  enters the escape recess  66 , thereby preventing the pilot pin  64  and upper die member  63  from interfering with each other. 
   Next, a second press apparatus  61  will be explained below by referring to  FIG. 20 . As shown in  FIG. 20 , the second press apparatus  61  bends boundary sections between the respective terminal portions  50   u ,  50   v , and  50   w  and the respective bus bars  22   a ,  22   b , and  22   c . The second press apparatus  61  comprises a stationary lower die member  67  and a movable upper die member  68 . When the upper die member  68  moves down toward the lower die member  67 , both dies are closed. Conversely, when the upper die member  68  moves up away from the lower die member  67 , both dies are opened. 
   The lower die member  67  is provided on the upper surface with a lower forming protrusion  67   a  that engages the embedded section  55  on the respective terminal portions  50   u ,  50   v , and  50   w . An insertion pin  69  is formed near the lower forming protrusion  67   a  on the lower die member  67  to position the terminal portions  50   u ,  50   v , and  50   w . When the respective terminal portions  50   u ,  50   v , and  50   w  are set on the lower die member  67 , the insertion pin  69  passes through the respective bolt through-hole  52 . When the insertion pin  69  passes through the bolt through-hole  52 , the respective terminal portions  50   u ,  50   v , and  50   w  are prevented from being displaced. 
   The upper die member  68  is provided on the lower surface with an upper forming recess  68   a  opposing the lower forming protrusion  67   a . When the upper and lower die members  68  and  67  are driven to the closed position, the upper forming recess  68   a  engages the lower forming protrusion  67   a . The thickness of the portion of the upper die member  68  other than the portion at which the upper forming recess  68   a  is formed is designed so that the insertion pin  69  on the lower die member  67  does not interfere with the upper die member  68  when the upper and lower die members are driven to the closed position. 
   As shown in  FIG. 18   a  and  FIGS. 21A and 21B , a plurality of notches  59  extending in the lateral (width) direction are formed on the areas to be bent on the respective terminal portions  50   u ,  50   v , and  50   w  by the first and second press apparatuses  60  and  61 . Each notch  59  is formed in a surface of a strip-like blank  92  punched out from the conductive metallic plate before forming the respective terminal portions  50   u ,  50   v , and  50   w . In the present embodiment, one notch is formed in one surface of the strip-like blank  92  corresponding to the respective terminal portions  50   u ,  50   v , and  50   w , while three notches are formed in the other surface of the blank  92 . The strip-like blank  92  is bent inwardly at the notch  59 . 
   Next, a process for bending the respective terminal portions  50   u ,  50   v , and  50   w  by using the first and second press apparatuses  60  and  61  mentioned above will be explained. 
   As shown in  FIGS. 18A and 18B , when the upper and lower die members  63  and  62  of the first press apparatus  60  are driven to the opened position, the strip-like blanks  92  punched out from the conductive metallic plate are put on the lower die member  62 . The pilot pin  64  on the lower die member  62  passes through the pilot hole  65  formed in a respective strip-like blank  92  to prevent or reduce displacement of the blank  92 . 
   As shown in  FIGS. 19A and 19B , when the upper and lower die members  63  and  62  are driven to the closed position, the strip-like blank  92  is clamped between the lower forming recess  62   a  and the upper forming protrusion  63   a  and between the lower forming recess  62   b  and the upper forming protrusion  63   b . Thus, the respective strip-like blanks  92  are bent at the portions corresponding to the respective terminal portions  50   u ,  50   v , and  50   w  to form the respective terminal portions  50   u ,  50   v , and  50   w . Thereafter, the upper and lower die members  63  and  62  are driven to the opened position and the strip-like blank  92 , in which the respective terminal portion  50   u ,  50   v , or  50   w  is formed, is removed from the lower die member  62 . 
   As shown in  FIGS. 20A and 20B , when the upper and lower die members  68  and  67  of the second press apparatus  61  are driven to the opened position, the respective terminal portion  50   u ,  50   v , or  50   w  formed by the first press apparatus  60  engages the lower die member  62 . The insertion pin  69  passes through the bolt through-hole  52  formed in the respective terminal portions  50   u ,  50   v , or  50   w  to prevent or reduce displacement of the blank  92 . 
   When the upper and lower die members  68  and  67  are driven to the closed position, an end of the strip-like blank  92 , namely a portion corresponding to the respective bus bars  22   a ,  22   b , or  22   c , is clamped between the lower forming protrusion  67   a  and the upper forming recess  68   a  to bend at a right angle the boundary areas between the respective bus bar  22   a ,  22   b , or  22   c  and the respective terminal portion  50   u ,  50   v , or  50   w . Thereafter, the upper and lower die members  68  and  67  are driven to the opened position and the strip-like blank  92 , in which the respective terminal portion  50   u ,  50   v , or  50   w  is formed, is removed from the lower die member  67 . 
   As shown in  FIGS. 24 to 27 , the resin insulation layer  25  for covering the insulating holder  21  is formed by an insert-molding mold  70 . The insert-molding mold  70  comprises a stationary lower mold member  71  and a movable upper mold member  72 . The upper mold member  72  can move to and from the lower mold member  71 . When the upper mold member  72  moves down to the lower mold member  71 , the mold  70  is placed in a closed position. When the upper mold member  72  moves up from the lower mold member  71 , the mold  70  is placed in an open position. 
   A forming recess  71   a  in the lower mold member  71  is opposed to a forming recess  72   a  in the upper mold member  72 . When the lower and upper mold members  72  and  71  are driven to the closed position, the forming recesses  72   a  and  71   a  define an annular cavity  73 . A molten resin material  90  is poured through a gate (not shown) into the cavity  73  to form the resin insulation layer  25 . 
   The upper mold member  72  is provided with upper mold member supports  80  that push an upper surface of the insulating holder  21  to be contained in the cavity  73 . The upper mold member supports  80  can move out from and into an inner top surface of the upper forming recess  72   a . Although not shown in the drawings, a plurality of upper mold member supports  80  (eighteen in the present embodiment) are provided in the upper mold member  72 . The upper mold member supports  80  are arranged at an even spacing on the circumference of the insulating holder  21 , except for the portions where the terminal portions  50   u ,  50   v , and  50   w  are located. When the upper mold member supports  80  are advanced out from the upper forming recess  72   a , a plurality of latch grooves  81  formed in the ends of the supports  80  engage the wall  43   b  that spaces the inside bus bar  22   a  from the intermediate bus bar  22   b , and also engage the wall  43   c  that spaces the intermediate bus bar  22   b  from the outside bus bar  22   c . Under this engagement condition, distal end surfaces of the upper mold member supports  80  come into contact with upper end edges of the respective bus bars  22   a ,  22   b , and  22   c . Consequently, the upper mold member supports  80  push the insulating holder  21  (an upper portion of the holder  21  in  FIG. 24 ). 
   The lower mold member  71  is provided with holder support pins  74  that support the insulating holder  21  to be contained in the cavity  73 . The holder support pins  74  can move out from a bottom surface of the lower forming recess  71  a into the cavity  73  and move from the cavity  73  into the bottom surface. Although not shown in the drawings, a plurality of holder support pins  74  (thirty-six pins in the present embodiment) are provided in the lower mold member  71 . The holder support pins  74  are arranged at an even spacing on the circumference of the insulating holder  21 . Each holder support pin is preferably formed into a stick-like configuration having a tapered end. Preferably, the tapered end of each holder support pin  74  has a taper angle of about 30 to 150 degrees. 
   As shown in  FIG. 22 , and  FIGS. 23A and 23B , when the holder support pins  74  move out from the bottom surface of the lower forming recess  71  a into the cavity  73 , the distal ends of the pins  74  engage bearing recesses  75  in the lower surface of the insulating holder  21 . This engagement can prevent displacement of the insulating holder  21  in the radial direction of the cavity  73  when the insulating holder  21  is contained in the cavity  73 . The insulating holder  21  is fixed at a proper position in the cavity  73  by the holder support pins  74  and upper mold member supports  80 . Consequently, the resin insulation layer  25  is formed around the insulating holder  21  at a uniform thickness. 
   Each bearing recess  75  has a taper that reduces the recess in diameter toward the inner top part. Thus, the holder support pin  74  finally engages the bearing recess  75  while the pin  74  is being guided along the inner periphery of the bearing recess  75 . Accordingly, when the insulating holder  21  is set in the lower forming recess  71   a  in the lower mold member  71 , the holder support pin  74  does not fail to engage the bearing recess  75 . 
   Two arcuate ribs  76   a  and  76   b  are formed around the holder support pin  74  on the bottom surface of the insulating holder  21 . The ribs  76   a  and  76   b  make a virtual depth of the bearing recess  75  larger. This reduces the chance of the holder support pin  74  disengaging from the bearing recess  75  inadvertently and reduces the chance of the insulating holder  21  displacing in the cavity  73 . 
   A plurality of notches  77   a  and  77   b  (two notches in the present embodiment) are formed between the ribs  76   a  and  76   b . The formation of the notches  77   a  and  77   b  allows the resin for forming the resin insulating layer  25  to easily move toward the bearing recesses  75  via the notches  77   a  and  77   b  in the state where the holder support pin  74  is extracted from the bearing recess  75  during the process of insert molding the resin insulation layer  25 . In the centralized power distribution unit  17  in the final production step, the bearing recesses  75  are filled with the resin insulation layer  25 . The numbers of the ribs  76   a  and  76   b  and the notches  77   a  and  77   b  can be arbitrarily changed. When the ribs  76   a  and  76   b  are formed as one rib having a C-like shape, for example, the notches  77   a  and  77   b  can be configured as one notch. 
   As shown in  FIGS. 22 ,  23 , and in  FIGS. 14 to 16 , the insulating holder  21  is provided, in its bottom surface, with a plurality of communication holes  78  communicating with the holding grooves  23   a ,  23   b , and  23   c . The communication holes  78  facilitate the flow of resin for forming the resin insulation layer  25  into the respective holding grooves  23   a ,  23   b , and  23   c  during insert molding. The plural communication holes  78  are provided on the periphery of the insulating holder  25 . In more detail, the respective communication holes  78  are arranged along the holding grooves  23   a ,  23   b , and  23   c . In addition, as shown in  FIG. 10 , the respective communication holes  78  are shifted from each other in the circumferential direction of the insulating holder  21 . This means that only one communication hole  78  is disposed on the same line in the radial direction of the insulating holder  21 . 
   As shown in  FIGS. 22 and 24 , the insulating holder  21  is provided on the inner surface with positioning projections  82  the distal ends of which come into contact with the inner surface of the lower forming recess  71   a  when the insulating holder  21  is set in the lower mold member  71 . The plural positioning projections  82  are arranged at an even spacing in the circumferential direction of the insulating holder  21 . When all of the positioning projections  82  come into contact with the inner surface of the lower forming recess  71   a , displacement of the insulating holder  21  in its circumferential direction can be substantially eliminated. 
   As shown in  FIGS. 9 ,  12 , and  13 , the respective holding grooves  23   a  to  23   c  in the insulating holder  21  are divided into a bus bar containing section  83  that accommodates the bus bars  22   a  to  22   c  and a bus bar non-containing section  84  that does not accommodate the bus bars. First reinforcement ribs  85  are provided at a given distance in the circumferential direction of the insulating holder  21  on the holding grooves  23   a ,  23   b , and  23   c  in the bus bar non-containing section  84 . The respective first reinforcement ribs  85  are formed integrally together with bottom surfaces and inner side surfaces of the walls  43   a  to  43   d . partitioning the respective holding grooves  23   a ,  23   b , and  23   c.    
   The communication holes  78  that serve to facilitate to flow the molten resin material  90  into the respective holding grooves  23   a ,  23   b , and  23   c  are formed in the bottom surface of the respective holding grooves  23   a ,  23   b , and  23   c  in the respective sections  83  and  84 . Thus, the molten resin material  90  easily flows into the respective holding grooves  23   a ,  23   b , and  23   c.    
   Three holding grooves  23   a ,  23   b , and  23   c  are provided in the bus bar containing section  83  in the insulating holder  21  while two holding grooves  23   a  and  23   b  are provided in the bus bar non-containing section  84  in the insulating holder  21 . That is, there is no holding groove  23   c  at the outermost side in the bus bar non-containing section  84 . The bus bar non-containing section  84  in the insulating holder  21  is narrower than the bus bar containing section  83 . 
   Furthermore, the bus bar non-containing section  84  in the insulating holder  21  is provided on the outer periphery with a second reinforcement rib  86  extending in the circumferential direction of the insulating holder  21 . The second reinforcement rib  86  is formed into an arcuate shape and a radius of curvature of the rib  86  is set to be the same as the radius of the insulating holder  21 . 
   Next, a process for insert-molding the centralized distribution unit  17  by using the insert-molding mold  70  described above will be explained below. 
   When the mold  70  is driven to the opened position, the insulating holder  21  is put in the lower forming recess  71   a  in the lower mold member  71 . The holder support pins  74  projecting from the lower forming recess  71   a  engage the bearing recesses  75  in the insulating holder  21  at the distal ends. Thus, the insulating holder  21  is supported in the lower mold member  71  with the holder  21  being spaced at a certain distance from the bottom surface of the lower forming recess  71   a . At this time, the respective plural positioning projections  82  on the insulating holder  21  come into contact with the inner periphery of the lower forming recess  71   a  at the distal end surfaces. This substantially prevents displacement of the insulating holder  21  in the radial direction. 
   As shown in  FIG. 24 , when the upper mold member  72  moves down toward the lower mold member  71  to close the mold  70 , the cavity  73  is defined in the mold  70 . When the mold  70  is closed, the distal end surfaces of the upper mold member supports  80  projecting from the upper forming recess  72   a  come into contact with the upper ends of the bus bars  22   a ,  22   b , and  22   c . Further, the latch grooves  81  in the distal end surfaces of the upper mold member supports  80  engage the walls  43   b  and  43   c  that partition the respective holding grooves  23   a ,  23   b , and  23   c . Consequently, the upper mold member supports  80  push the insulating holder  21  and the bus bars  22   a ,  22   b , and  22   c . As described above, the insulating holder  21  is constrained from upward and downward movement by the plural holder support pins  74  and plural upper mold member supports  80 . 
   As shown in  FIG. 25 , molten resin material  90  for forming the resin insulation layer  25  is poured through a gate (not shown) formed in one of the mold members, e.g., the lower mold member  71 , into the cavity  73 . At this time, the molten resin material  90  that is poured to cover the insulating holder  21  flows through openings of the respective holding grooves  23   a ,  23   b , and  23   c  into their interiors. In addition, the molten resin material  90  flows through the communication holes  78  in the insulating holder  21  into the holding grooves  23   a ,  23   b , and  23   c . Even if the molten resin material  90  is applied under pressure to the holding grooves  23   a ,  23   b , and  23   c  in the bus bar non-containing section  84  (see  FIG. 12 ) in the insulating holder  21 , the first and second reinforcement ribs  85  and  86  prevent or reduce deformation of the walls  43   a  to  43   d.    
   When the molten resin material  90  substantially fills the cavity  73 , as shown in  FIG. 26 , the holder support pins  74  retract into the lower mold member  71  and the upper mold member supports  80  retract into the upper mold member  72 . Although the insulating holder  21  is fully floated in the cavity  73  without any supports, the insulating holder  21  will not incline in the cavity  73  since the molten resin material  90  is being poured into the cavity  73 . In addition, the molten resin material  90  will fill the holes caused by the retraction of the holder support pins  74  and upper mold member supports  80 . Furthermore, the molten resin material  90  flows into the bearing recesses  75  in which the holder support pins have engaged, the spaces around the bearing recesses  75 , and the spaces between and around the upper ends of the walls  43   b  and  43   c . Thus, the molten resin material  90  covers the insulating holder  21 . 
   As shown in  FIG. 27 , after a given period of time has passed and the molten resin material  90  has cooled and solidified, the insulation layer  25  is formed. Thereafter, the upper mold member  72  and the lower mold member  71  are separated and placed in the opened position, and the centralized distribution unit  17 , in which the insulating holder  21  and the resin insulation layer  25  are integrated together, is removed from the mold  70 . 
   An exemplary process for producing the centralized distribution unit  17  is explained below. 
   (Step of punching a conductive metallic plate) 
   As shown in  FIG. 28 , in order to form the bus bars  22   a ,  22   b , and  22   c  for a three-phase motor, three strip-like blanks  92  are formed from one rectangular conductive metal plate  91 . In this case,the tabs  41   a ,  41   b , and  41 c, and the terminal portions  50   u ,  50   v , and  50   w  are stamped out in a state where they are coupled to the respective strip-like blanks  92 , by a press machine which is not shown. 
   As shown in  FIG. 28 , the strip-like blanks  92  which are stamped out from the conductive metal plate  91  are laid out along the longitudinal direction of the conductive metal plate  91  so that they are parallel to one another. The two strip-like blanks  92  which are positioned in the outermost side are placed so that the tabs  41   a  and  41   c  and the terminal portions  50   v  and  50   w  are directed to the center of the bus bar row. According to the configuration, the three strip-like blanks  92  can be densely laid out (laid out without forming large gaps) in the one conductive metal plate  91 . As a result, the unused areas formed among the strip-like blanks  92  are narrowed. Therefore, the amount of wasted material is reduced, and the width of the conductive metal plate  91  which is required for obtaining the strip-like blanks  92  can be shortened. 
   The three strip-like blanks  92  are formed so as to have an approximately same length. In the one conductive metal plate  91 , the strip-like blanks  92  are laid out so that their both ends are substantially aligned with one another. According to the configuration, in the one conductive metal plate  91 , the unused areas formed in the vicinities of the both ends of the three strip-like blanks  92  are narrowed. As a result, the amount of wasted material is reduced, and the length of the conductive metal plate  91  which is required for obtaining the strip-like blanks  92  can be shortened. Among the tabs protruding from each of the strip-like blanks  92 , the two tabs which are positioned at endmost portions are formed integrally with the end portions of the strip-like blanks  92 , respectively. Therefore, the lengths of the strip-like blanks  92  can be shortened as compared with the case where, for example, a bus bar structure of a complete annular shape is employed. This also contributes to the reduced length of the conductive metal plate  91  which is required for obtaining the strip-like blanks  92 . 
   In this way, the strip-like blanks  92  are produced from the conductive metal plate  91  before the bending process are applied to the bus bars  22   a  to  22   c . Since the strip-like blanks  92  for forming the bus bars  22   a ,  22   b , and  22   c  have a substantially linear shape as shown in  FIG. 29 , they can be stamped out in parallel. This remarkably contributes to a reduced material cost, and to an improved yield as compared with the case where the strip-like blanks  92  are annularly stamped out. 
   (First Bending of the Bus Bars) 
   As shown in  FIG. 29 , the first and second press apparatuses  60  and  61  mentioned above bend the portions corresponding to the terminal portions  50   u ,  50   v , and  50   w in the strip-like blanks  92 . 
   (Second Bending of the Bus Bars) 
   As shown in  FIG. 29 , the portions corresponding to the bus bars  22   a ,  22   b , and  22   c  in the strip-like blanks  92  in which the terminal portions  50   u ,  50   v , and  50   w  have been formed are bent in the thickness direction to form annular shapes. This bending work is carried out by a bending device (not shown). Thus, the bus bars  22   a ,  22   b , and  22   c  are formed into substantially annular shapes beforehand, before attaching the bus bars  22   a ,  22   b , and  22 c to the insulating holder  21 . 
   (Step of Inserting the Bus Bars) 
   As shown in  FIG. 30 , the respective bus bars  22   a ,  22   b , and  22   c  are inserted into the insulating holder  21  that has already been produced. At this time, the bus bars are inserted into the insulating holder  21  in order from the outermost position to the innermost position. That is, the outside bus bar  22   a , intermediate bus bar  22   b , and inside bus bar  22   c  are inserted into the insulating holder  21  in that order. If the inside bus bar  22   c  is inserted into the insulating holder  21  before inserting the intermediate bus bar  22   b , the prior bus bar interferes with entrance of the latter bus bar. 
   (Third Bending of the Bus Bars) 
   As shown in  FIG. 31 , the respective tabs  41   a ,  41   b , and  41   c  are bent so that their distal ends are directed to the center of the insulating holder  21  with the respective bus bars  22   a  to  22   c  being attached to the insulating holder  21 . The curved portions  44  and  45  are formed on the proximal ends of tabs of the the intermediate bus bar  22   b  and outside bus bar  22   c , respectively. 
   (Insert Molding) 
   As shown in  FIG. 32 , the resin insulation layer  25  is formed on the outer periphery of the insulating holder  21  to which the bus bars  22   a ,  22   b , and  22   c  have been already attached. This forming process may be carried out by using the insert-molding mold  70  mentioned above. Thereafter, the centralized distribution unit  17  is taken out from the insert-molding mold  70 . Finally, the sealing material  54  fills the resin containing sections  53  ( FIG. 5 ) formed in the resin insulation layer  25 . 
   Accordingly, effects including the following effects may be obtained according to the above-described embodiment. 
   (1) The bus bars  22   a ,  22   b , and  22   c  are formed by stamping out into a strip-like shape from the one conductive metal plate  91 . In this case, the bus bars  22   a ,  22   b , and  22   c  are stamped out from the conductive metal plate  91 , in the state where the bus bars are densely laid out. Therefore, the required area of the conductive metal plate  91  can be made smaller than that in the case where the bus bars  22   a ,  22   b , and  22   c  are stamped out into a ring-like shape. Consequently, the material loss is reduced as compared with that in a conventional method, so that the material cost of the bus bars  22   a ,  22   b , and  22   c  can be lowered. As a result, the centralized power distribution unit  17  can be economically produced. 
   (2) The bus bars  22   a ,  22   b , and  22   c  are simultaneously stamped out from the common conductive metal plate  91  by using a mold. In this case, the used area of the conductive metal plate  91  can be reduced to about a half of that in the case where the bus bars  22   a ,  22   b , and  22   c  are stamped out into a ring-like shape, and the material loss is reliably suppressed. Therefore, the material cost of the bus bars  22   a ,  22   b , and  22   c  can be reduced. Unlike the conventional art, it is not required to use different molds for respective rings. Therefore, the mold cost can be reduced. As a result, the centralized power distribution unit  17  can be more economically produced. 
   (3) The tabs  41   a ,  41   b , and  41   c , and the terminal portions  50   w ,  50   w , and  50   v  are integrally formed, coupled with the bodies of the bus bars  22   a ,  22   b , and  22   c , respectively. In this case, it is not necessary to attach the tabs  41   a ,  41   b , and  41   c , and the terminal portions  50   w ,  50   w , and  50   v  in a subsequent step by welding or the like. Therefore, the number of steps of producing the bus bars  22   a ,  22   b , and  22   c  can be reduced. As a result, the centralized power distribution unit  17  can be more economically produced. 
   (4) The bus bars  22   a ,  22   b , and  22   c  are stamped out from the conductive metal plate  91  in the state where both ends of the bus bars are substantially aligned with one another, and in the state where the bus bars are placed in parallel. In the conductive metal plate  91 , therefore, material loss in the areas of the ends in the longitudinal direction and the sides in the width direction of the bus bars  22   a ,  22   b , and  22   c  is reduced. Consequently, the material cost of the bus bars  22   a ,  22   b , and  22   c  can be further lowered, so that the centralized power distribution unit  17  can be still more economically produced. 
   (5) Among the bus bars  22   a ,  22   b , and  22   c , the bus bars  22   a  and  22   c  which are positioned in the outermost side are laid out in parallel so that the terminal portions  50   w  and  50   v  and the tabs  41   a  and  41   c  are directed to the center of the bus bar row. According to this configuration, in the conductive metal plate  91 , the material loss in the areas of the ends in the longitudinal direction of the bus bars  22   a ,  22   b , and  22   c  is reduced. Consequently, the material cost of the bus bars  22   a ,  22   b , and  22   c  can be further lowered. As a result, the centralized power distribution unit  17  can be still more economically produced. 
   The above-described embodiment of the invention may be modified in, for example, the following ways. 
   In the above-described embodiment, the terminal portions  50   w ,  50   u , and  50   v , and the tabs  41   a ,  41   b , and  41   c  are formed integrally with the bodies of the bus bars  22   a ,  22   b , and  22   c , respectively. Alternatively, the terminal portions  50   w ,  50   u , and  50   v , and/or the tabs  41   a ,  41   b , and  41   c  may be formed by stamping as members separated from the bodies of the bus bars  22   a ,  22   b , and  22   c . For example, as shown in  FIG. 33 , the bus bars  22   a ,  22   b , and  22   c  are laid out in parallel. The terminal portions  50   u ,  50   v , and  50   w  are laid out in parallel with the bodies of the bus bars  22   a ,  22   b , and  22   c , between the tabs  41   a ,  41   b , and  41   c  disposed on the bodies of the bus bars  22   a ,  22   b , and  22   c . According to the configuration, the bus bars  22   a ,  22   b , and  22   c  can be placed more densely, and hence the amount of wasted material in the width direction of the conductive metal plate  91  is further reduced. Therefore, the area of the conductive metal plate  91  which is required for stamping out the bus bars  22   a ,  22   b , and  22   c  can be made smaller than that in the above-described embodiment. In this case, the terminal portions  50   w ,  50   u , and  50   v , and the tabs  41   a ,  41   b , and  41   c  are later attached to the bodies of the bus bars  22   a ,  22   b , and  22   c . As a method of conducting the later attachment, specifically, welding, brazing, soldering, screw fixation, or the like may be used. 
   In the above-described embodiment, the terminal portion  50   w ,  50   u , or  50   v , and the tabs  41   a ,  41   b , or  41   c  are formed on the same side edge of the corresponding one of the bus bars  22   a ,  22   b , and  22   c . Alternatively, the terminal portion  50   w ,  50   u , or  50   v , and the tabs  41   a ,  41   b , or  41   c  may be formed on different side edges. 
   In the above-described embodiment, the invention is applied to the centralized power distribution unit  17  for the three-phase thin DC brushless motor  11 . The invention is not limited to this, and may be applied to a centralized power distribution unit for a motor in which the phase number is larger than three (or smaller than three). In accordance with the phase number, the numbers of the bus bars and the holding grooves may be increased or decreased. 
   In this case, for example, four bus bars for a four-phase motor may be stamped out from a common conductive metal plate  91 , or five bus bars for a five-phase motor may be stamped out from a common conductive metal plate  91 . 
   In addition to the technical concepts explicitly described above, several technical concepts can be grasped from the embodiment described above. The technical concepts will be described together with their effects. 
   (1) In a method of producing bus bars used in a centralized power distribution unit, the terminal portion and the tabs are formed on a same side edge of the bus bar body. According to the configuration, the stamping can be performed so that the terminal portion and the tabs of one(s) of the bus bars which are positioned in the outermost side among the bus bars which are placed in parallel are directed to the center of the bus bar row. Therefore, the material loss in the process of stamping out the bus bars from the conductive metal plate can be reduced, so that the centralized power distribution unit for a vehicular thin brushless motor can be produced at a low cost. 
   As described above in detail, according to the invention, it is possible to provide a centralized power distribution unit for a vehicular thin brushless motor which can be produced in a relatively simple manner, and which has high reliability. 
   According to the invention, the material cost of the bus bars, and the mold cost can be reduced, and hence the centralized power distribution unit for a vehicular thin brushless motor can be produced at a low cost. 
   According to the invention, the number of steps of producing the bus bars can be reduced, and hence the centralized power distribution unit for a vehicular thin brushless motor can be produced at a low cost. 
   According to the invention, the loss of the metal material for producing the bus bars can be further reduced, and hence the centralized power distribution unit for a vehicular thin brushless motor can be produced at a lower cost. 
   While the invention has been described in conjunction with the specific embodiments described above, many equivalent alterative, modifications and variations may become apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention as set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention. 
   The entire disclosure of Japanese Patent Application No. 2001-330026 filed on Oct. 26, 2001 including the specification, claims, drawings and summary is incorporated herein by reference in its entirety.