Patent Publication Number: US-7221070-B2

Title: Electric appliance with terminal

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application is based upon and claims the benefit of priority of Japanese Patent Application No. 2004-131705 filed on Apr. 27, 2004, the content of which is incorporated herein by reference. 
   FIELD OF THE INVENTION 
   The present invention relates to an electric appliance with a terminal having a soldering portion for soldering another terminal thereon and a soldering method for the terminal. 
   BACKGROUND OF THE INVENTION 
   JP-2003-284292-A discloses a brush holder for a dynamoelectric appliance in which a terminal is soldered. The brush holder has a holder body and a power input connector that are integrally formed. A terminal is embedded over the holder body and the power input connector. One end of the terminal is electrically connected to a circuit board disposed in the holder body by soldering. 
   Conventionally, a soldering of the terminal includes steps of putting a solder piece on the terminal and radiating a laser light to the solder piece to heat and melt the solder piece. Commonly the terminal has a smooth (burnishing) surface that reflects the laser light to decrease the heating efficiency for melting the solder piece. This extends the time for the soldering. 
   SUMMARY OF THE INVENTION 
   The object of the present invention, in view of the above issues, is to provide an electric appliance with terminal having a soldering portion for soldering another terminal thereon and a soldering method for the terminal that can shorten a time for the soldering. 
   To achieve the above object, an electric appliance has a first terminal and a second terminal electrically connected to the first terminal. The first terminal has a soldering portion for soldering the second terminal thereon. The soldering portion has a smooth face and a rough face disposed on one imaginary plane. The rough face has a flat portion and a plurality of concavities disposed on the flat portion at intervals. Further, the soldering portion may have a through hole adjacent to the rough face to insert the second terminal. The first terminal is embedded in an insulator. The insulator has an opening exposing the soldering portion therein. The insulator includes a frame forming a housing of an electric appliance. A seal seals a connection gap at a margin of the frame in the housing. A partition wall may be disposed between the soldering portion and the seal. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other features and advantages of the present invention will be appreciated, as well as methods of operation and the function of the related parts, from a study of the following detailed description, the appended claims, and the drawings, all of which form a part of this application. In the drawings: 
       FIG. 1  is a cross-sectional view showing a motor (electric appliance with terminal) according to an embodiment of the present invention; 
       FIG. 2  is a plan view of the brush holder seen in a direction of arrow II in  FIG.1 ; 
       FIG. 3  is a plan view of the brush holder seen in a direction of arrow III in  FIG. 1 ; 
       FIG. 4  is a plan view of the brush holder not disposing the electric devices thereon and seen in a direction of arrow IV in  FIG. 1 ; 
       FIG. 5  is a plan view of the brush holder not disposing the electric devices thereon and seen in a direction of arrow V in  FIG. 1 ; 
       FIG. 6A  is a perspective view showing a connecting portion; 
       FIG. 6B  is a perspective view showing the connecting portion; 
       FIG. 7A  is a plan view showing the connecting portion; 
       FIG. 7B  is a cross sectional view taken along a line VIIB—VIIB in  FIG. 7A ; 
       FIG. 8A  is a plan view showing the rough face; 
       FIG. 8B  is a cross sectional view taken along a line VIIIB—VIIIB in  FIG. 8A ; 
       FIG. 9  is a plan view showing a soldering process; and 
       FIG. 10  is a cross-sectional view taken along a line X—X for explaining the soldering process. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   An embodiment of the present invention will be described with reference to accompanying drawings. 
   A motor (a dynamoelectric appliance)  1  shown in  FIG. 1  generates a driving power of a power window system mounted on a vehicle. The wiper motor  1  includes a motor unit  2  and a rotation-reducing unit  3 . 
   The motor unit  2  includes a yoke housing  4 , a pair of magnets  5 , an armature  6 , a brush holder  7  and a pair of brushes  8 . The yoke housing  4  has a cup shape partially depressed in a radial direction thereof. The plurality of magnets  5  is fixed on an inner peripheral surface of the yoke housing  4 . The armature  6  is rotatably enclosed in the yoke housing  4  at a position radially inward of the magnets  5 . The yoke housing  4  has a bearing  10  at a center of its bottom. The bearing  10  rotatably holds one end portion of a rotation shaft  9  of the armature  6 . 
   An opening  4   a  of the yoke housing  4  has a pair of flanges  4   b  extending outward in a radial direction thereof. A gear housing  21  of the rotation-reducing unit  3  is assembled to the opening  4   a  of the yoke housing  4  by screws  11 . As shown in  FIGS. 2 and 3 , the opening  4   a  (the flanges  4   b ) of the yoke housing  4  and an opening  21   a  of the gear housing  21  interpose the brush holder  7  therebetween. 
   The brush holder  7  is made of synthetic resin (preferably a thermosetting resin). The brush holder  7  includes a holder body (a frame portion)  7   a  having a circular plate shape, an extension  7   b  extending radially outward from the holder body  7   a  and a connector body (connector portion)  7   c  extending out of the wiper motor  1  to provide an electrical connection with an outer electric appliance. 
   The holder body  7   a  is provided with a frame mount  7   d  extending over an entire periphery thereof and connected to the extension  7   b.  The opening  4   a  of the yoke housing  4  and the opening  21   a  of the gear housing  21  interpose the frame mount  7   d  and the extension  7   b  therebetween. 
   The frame mount  7   d  and the extension  7   b  have a seal  15  integrally formed thereon. The seal  15  is made of an elastic and electrically insulating material such as elastomer. The seal  15  covers a surface of the frame mount  7   d  and the extension  7   b  and is interposed between the openings  4   a  and  21   a  of the yoke housing  4  and the gear housing  21 . Specifically, the seal  15  seals an interstice between the openings  4   a  and  21   a  to prevent foreign matters such as water drops and dust particles from entering in the yoke housing  4  and the gear housing  21 . 
   A center portion of the holder body  7   a  holds a bearing  12  that rotatably supports another end portion of the rotation shaft  9 . The holder body  7   a  further has a pair of brush retainers  7   e  disposed in such a manner of interposing the rotation shaft  9  therebetween. Each the brush retainers  7   e  supports the brushes  8  to be in slide contact with the rectifier  13  integrally rotating with the rotation shaft  9  to supply electric power to the rectifier  13 . 
   As shown in  FIGS. 2 and 4 , the holder body  7   a  has coil-holding hollows  41 ,  42  at a side of the brush retainers  7   e  (at a side of the motor unit  2 ). The coil-holding hollows  41 ,  42  hold cylinder-shaped choke coils  31 ,  32  to limit a noise in the electric power. The coil-holding hollows  41 ,  42  are disposed close to the frame mount  7   d  and diagonally on the holder body  7   a  in such a manner of interposing the rotation shaft  9  therebetween. As shown in  FIGS. 3 and 4 , a bottom of each the coil-holding hollows  41 ,  42  has through holes  41   a,    42   a  penetrating the holder body  7   a.  The through holes  41   a,    42   a  respectively lead one side leads of the choke coils  31 ,  32  to a side of the rotation-reduction unit  3 . Another side leads of the choke coils  31 ,  32  are connected to pigtails  8   a  extending from the brushes  8 . 
   As shown in  FIGS. 2 and 4 , the holder body  7   a  has a capacitor-holding hollow  43  at a side of the brush retainers  7   e.  The capacitor-holding hollow  43  holds two rectangular-shaped capacitors  33 ,  34  side by side. The capacitors  33 ,  34  also limit a noise in the electric power. The capacitor-holding hollow  43  is disposed close to the coil-holding hollow  41  and close to the frame mount  7   d.  As shown in  FIGS. 3 and 4 , a bottom of the capacitor-holding hollow  43  has four through holes  43   a – 43   d  in a row. The through holes  43   a,    43   d,  which are outermost ones in the row, respectively lead one side leads of the capacitors  33 ,  34  to the side of the rotation-reduction unit  3 . Another side leads (not shown) of the choke coils  31 ,  32  are connected to a grounding terminal  35 . The grounding terminal  35  has a pair of protrusions bent to form grounding slips  35   a.  The grounding slips  35   a  protrude out of the frame mount  7   d  to be in contact with the yoke housing  4  through which the grounding terminals are grounded. 
   As shown in  FIGS. 2 and 4 , the holder body  7   a  has a breaker-holding hollow  44  at a side of brush retainers  7   e.  The breaker-holding hollow  44  holds a rectangular-shaped circuit breaker  36  for an overcurrent protection. The breaker-holding hollow  44  is disposed at a peripheral portion of the holder body  7   a  and opposite to the capacitor-holding hollow  43  in such a manner that the capacitor-holding hollow  43  and the breaker-holding hollow  44  interpose the rotation shaft  9  therebetween. A bottom of the breaker-holding hollow  44  and a portion close to the bottom thereof have two openings  44   a,    44   b.  The openings  44   a,    44   b  are arranged to expose contact portions  38   a,    39   c  of a second and third terminals  38 ,  39  that will be described below. The openings  44   a,    44   b  respectively expose connection leads  36   a,    36   b  of the circuit breaker  36  to be in contact with the contact portions  38   a,    39   c  of the second and third terminals  38 ,  39 . 
   As shown in  FIGS. 3 and 5 , the holder body  7   a  has fitting projections  45 ,  46  at the side of the rotation-reduction unit  3 . The fitting projections  45 ,  46  are disposed at both sides in a longitudinal direction of the holder body  7   a  to interpose the rotation shaft  9  therebetween. The fitting projections  45 ,  46  have flat top faces that are disposed on one imaginary plane. The fitting projections  45 ,  46  each have fitting holes  45   a,    46   a  opening on the top faces and extending in parallel with the rotation shaft  9 . The fitting holes  45   a,    46   a  are on a line that extends in a longitudinal direction of the holder body  7   a  and crosses with the center of the rotation shaft  9 . The fitting holes  45   a,    46   a  are for inserting fitting projections  21   b  of the gear housing  21  (refer to  FIG. 1 ). The fitting projections  21   b  also extend in parallel with the rotation shaft  9 . The engagement of the fitting holes  45   a,    46   a  and the fitting projections  21   b  restricts deviation of the brush holder  7  and the gear housing  21  from each other. 
   As shown in  FIGS. 3 ,  5 ,  6 A and  6 B, the holder body  7   a  has a first to third connection faces  51 – 53  at respective portions close to the fitting projections  45 ,  46 . The first connection face  51  is at a rear of the coil-holding hollow  41  and the capacitor-holding hollow  43 . The second connection face  52  is at the rear of the capacitor-holding hollow  43  and at a side of the first connection face  51 . The third connection face  53  is at a rear side of the coil-holding hollow  42 . The first connection face  51  has an opening  51   a  communicated with the through hole  41   a  of the coil-holding hollow  41  and the through holes  43   a,    43   b  of the capacitor-holding hollow  43 . The second connection face  52  has an opening  52   a  communicated with the through holes  43   c,    43   d  of the capacitor-holding hollow  43 . The third connection face  53  has an opening  53   a  communicated with the through hole  42   a  of the coil-holding hollow  42 . 
   As shown in  FIG. 6A , the holder body  7   a  has a wall portion  54  extending along the peripheral portion thereof, specifically at a boundary between the first and second connection faces  51 ,  52  and the seal  15 . The wall portion  54  is integrally formed with the holder body  7   a.  The wall portion  54  protrudes beyond the connection faces  51 ,  52  and the seal  15 . Specifically, top faces of the wall portion  54  and the fitting projection  45  are on one imaginary plane. The wall portion  54  continuously extends from the fitting projection  45  to the boundary at a side of the first and second connection faces  51 ,  52 . As shown in  FIG. 6B , the holder body  7   a  also has a wall portion  55  extending along the peripheral portion thereof, specifically at a boundary between the third connection face  53  and the seal  15 . The wall portion  55  is also integrally formed with the holder body  7   a.  The wall portion  55  protrudes beyond the connection face  53  and the seal  15 . Specifically, top faces of the wall portion  55  and the fitting projection  46  are on one imaginary plane. The wall portion  55  continuously extends from the fitting projection  46  to the boundary at a side of the third connection face  53 . 
   As shown in  FIGS. 2–5 , a first terminal  37  and the second terminal  38  are embedded in the holder body  7   a,  the extension  7   b  and the connector body  7   c  of the brush holder  7  by insert molding. The first and second terminals  37 ,  38  each extend from the connector body  7   c  through the extension  7   b  to respective portions of the holder body  7   a.  The first and second terminals  37 ,  38  are disposed side by side in the connector body  7   c  and the extension  7   b,  and in a separate arrangement in the holder body  7   a.  The third terminal  39  is embedded in the holder body  7   a  by insert molding. The first, second and third terminals  37 – 39  each are made of metal plate. 
   The connector body  7   c  exposes one end of the first terminal  37  and the opening  51   a  of the first connection face  51  exposes another end of the first terminal  37  to provide a contact portion  37   a.  The connector body  7   c  also exposes one end of the second terminal  38  and the opening  44   a  in the breaker-holding hollow  44  exposes another end of the second terminal  37  to provide the contact portion  38   a.  The opening  52   a  of the second connection face  52  exposes one end of the third terminal  39  to provide a contact portion  39   a.  The opening  53   a  of the third terminal  53  and the opening  44   b  of the breaker-holding hollow  44   b  expose another end of the third terminal  39  to provide contact portions  39   b,    39   c.  The contact portion  37   a  of the first terminal  37  has insert holes  37   b – 37   d  in communication with the through hole  41   a,    43   a,    43   b  at corresponding positions. The contact portion  39   a  of the third terminal  39  has insert holes  39   d,    39   e  in communication with the through holes  43   c,    43   d  at corresponding positions. The contact portion  39   b  of the third terminal  39  has an insert hole  39   f  in communication with the through hole  42   a  at a corresponding position. As shown in  FIGS. 6A and 6B , the surfaces of the contact portions  37   a,    39   a,    39   b  exposing the openings  51   a – 53   a  and the sealing surface of the seal  15  are on one imaginary plane. Namely, the surfaces of the contact portions  37   a,    39   a,    39   b  are retracted relative to the wall portions  54  and  55 . 
   As shown in  FIG. 5 , the contact portion  37   a  has a smooth face  61  and rough faces  64   a – 64   c  formed continuously with each other. The contact portion  39   a  has a smooth face  62  and rough faces  65   a – 65   b  formed continuously with each other. The contact portion  39   b  has a smooth face  63  and rough faces, or matte faces,  66  formed continuously with each other. Specifically, the rough faces  64   a – 64   c  each are adjacent to the through holes  37   b – 37   d , the rough faces  65   a ,  65   b  each are adjacent to the through holes  39   d ,  39   e  and the rough face  66  is adjacent to the through bole  39   f.    
   The rough face  64   a – 64   c  on the contact portion  37   a  will now be described in the following. As shown in  FIG. 7A , the rough face  64   a – 64   c  are defined in an approximately semicircular (arc) shape that are close to the through holes  37   b – 37   d  to surround half circumferences thereof. The rough faces  64   a – 64   c  are disposed at radially inner positions relative to the through holes  37   b – 37   d  in the radial direction of the holder body  7   a.  The arrangement of the rough faces  64   a – 64   c  is adjusted to a radiation direction of laser lights in a soldering process of the contact portion  37   a  as described below (refer to FIG.  10 ). As shown in  FIG. 7B , the rough face  64   b  has a flat face  64   d  continuous to the smooth face  61  and a plurality of dents (concavities)  64   e  formed on the flat face  64   d.  The contact portion  37   a  has a stack of a plating layer  71 , a core plate  72  and a plating layer  73  from one surface to another one. Each of the above-described grooves  64   e  has a depth making the dents  64   e  not reaching the core plate  72 . 
   As shown in  FIGS. 8A ,  8 B, each of the dents  64   e  are a quadrangular pyramid-shaped that are formed in stamping the terminal  37  with a stamping die (not shown). Desirably, the dents  64   e  are disposed at a small interval (at 0.2 mm for example). The rough faces  64   a,    64   c  on the contact portion  37   a  and the rough faces  65   a,    65   b,    66  on the contact portions  39   a,    39   b  are formed similarly as the rough face  64   b  on the contact portion  37   a.    
   The terminals  37 – 39  are in electric connection to the circuit breaker  36 , the choke coils  31 ,  32  and the capacitors  33 ,  34  as follows. The circuit breaker  36  is connected by electric soldering to the contact portions  37   a,    39   a  of the second and third terminal  38 ,  39  exposed at the openings  44   a,    44   b.  One side leads  31   a,    32   a  of the choke coils  31 ,  32  are introduced in the through holes  37   b,    39   f  of the first and third terminal  37 ,  39  exposed in the openings  51   a,    53   a  and connected by solder  67 ,  68  to the contact portions  37   a,    39   b.  In this embodiment, the above-described electric connections, namely soldering, are processed after assembling the seal  15  relative to the brush holder  7 . 
   As shown in  FIG. 9 , the above-described soldering is processed by a laser-processing machine. Specifically, solder wires are fed to the through holes  37   b,    37   c,    39   e,    39   f  on contact portions  37   a,    39   a,    39   b  outward in a radial direction of the holder body  7   a,  which is shown by arrows in the figure and will be referred to as “feeding direction” below. The laser-processing machine radiates laser lights in the feeding direction to melt the solder wire. As shown in  FIG. 10 , the a processing head  83  of the laser-processing machine radiates the laser lights to the contact portion  37   a  ( 39   a,    39   b ) at an angle that is inclined by approximately 15 degrees relative to an normal direction of the contact portion  37   a  ( 39   a,    39   b ). As shown in  FIG. 9 , the processing head  83  radiates the laser lights in the feeding direction on radiation areas  81  adjacent to the through holes  37   b,    37   c,    39   e,    39   f  to heat them. The radiation areas  81  are defined at positions at both sides of the through holes  37   b,    37   c,    39   e,    39   f  in a direction perpendicular to the feeding direction. Thus, the temperature increases of the radiation areas  81  are prominent at the rough faces  64   a,    64   b,    65   b,    66 . Further, temperatures of preheating areas  82  located short of the radiation areas  81  in the feeding direction also increase. 
   The rough faces  64   a,    64   b,    65   b,    66  has an irregular surface realized by the plurality of dents  64   e  to be subjected to the laser lights and to be heated efficiently. This is because the laser lights enter on the surface of the rough faces  64   a,    64   b,    65   b,    66  at varied angles to restrict heat generated by the laser lights from radiating outward. Thus, the heating efficiency by the laser lights is larger relative to smooth faces  61 – 63 . Further, the rough faces  64   a,    64   b,    65   b,    66  are subjected to laser radiation at larger area are than they were made flat. Accordingly, the solder wires melt in a short time are efficiently heated on the rough faces  64   a,    64   b,    65   b,    66  and spread onto the smooth faces  61 – 63  continued to the rough faces  64   a,    64   b,    65   b,    66  to form the solder  67 – 70  in a short time. 
   Conventional soldering is processed with flux to clean the contacts, to restrict the oxidation, to improve the soldering state by decreasing surface tension of the melt solder. In this embodiment, the flux is contained in the solder wire, or the solder  67 – 70 . The flux and the solder melt by the heat in soldering process sometimes spread and/or splatter over designed areas. In this embodiment, the contact portions  37   a,    39   a  are surrounded by the wall portion  54  and the contact portion  39   b  is surrounded by the wall portion  55  to prevent the flux and solder from spreading and/or flattering to the periphery of the holder body  7   a,  namely the seal  15 . Thus, the wall portions  54 ,  55  prevent solder and flux with high temperature from adhering on the seal  15  not to deform the seal  15  and to secure a sealing quality between the opening  4   a  of the yoke housing  4  and the opening  21  a of the gear housing  21 . 
   As shown in  FIGS. 6A and 6B , the wall portions  54 ,  55  have curved side faces  54   a,    55   a  along peripheries of soldering areas on which the solders  67 – 70  are soldered. The curved side faces  54   a,    54   b  have radiuses approximately equal to those of the soldering areas. The curved side faces  54   a,    55   a  do not restrict for the solder  67 – 70  spreading on the soldering areas to form a conical shape suitable for securing a good electric contact. Even when the solder  67 – 70  spreading on the soldering areas come in contact with the curved side faces  54   a,    55   a,  the curved side faces  54   a,    55   a  do not hinder the solder  67 – 70  from forming the conical shape. 
   The rotation-reduction unit  3  has a gear housing  21 , a worm axis  22 , a worm wheel  23  and a clutch  24 . The gear housing  21  is made of a synthetic resin and has a shape for enclosing the worm axis  22 , the worm wheel  23  and the clutch  24  therein. The gear housing  21  has the opening  21   a  to be faced with the opening  4   a  (flange portion  7   b ) of the yoke housing  4 . The gear housing  21  and the yoke housing  4  interpose the brush holder  7  therebetween and are fixed to each other with the bolts  11 . 
   The worm axis  22  is rotatably supported by a pair of bearings  25 ,  26  provided in a given position in the gear housing  21 , and is engaged via the clutch  24  with the rotation shaft  9 . The clutch  24  transmits a driving force of the rotation shaft  9  to the worm axis  22  and prevents the rotational force of the worm axis  24  from transmitting to the rotation shaft  9  by locking the rotation of the worm axis  24 . That is, the clutch  24  prevents an outer force acting on an output axis  27  from rotating the motor  1 . 
   The worm axis  22  is engaged with the worm wheel  23 . The worm wheel  23  is in driving connection with the output axis  27  disposed perpendicular to the worm axis  22 . The output axis  27  is in driving connection with a conventional X-armed type regulator for opening and closing the power windows. Thus, the rotation of the output axis  27  operates the regulator to open and close the power windows. 
   The present embodiment has the following advantages. 
   (a) The contact portions  37   a,    39   a,    39   b  subjected to the laser lights has a larger efficiency at rough faces  64 – 66  in absorbing heat generated by the laser lights to melt the solder wire in a short time. Further, the rough face  64 – 66  formed continuously to the smooth faces  61 – 63  helps the solder melt on the rough faces  64 – 66  to spreads to the smooth faces  61 – 63 . That is, the soldering on the contact portions  37   a,    39   a,    39   b  can be processed in a short time. 
   (b) The rough face  64   a  is formed with a flat face  64   d  continuously formed to the smooth face  61  and a plurality of dents  64   e  formed on the flat face  64   d.  Thus, the rough face  64   a  is easily manufactured by stamping the flat face  64   d  continuous to the smooth face  61 . 
   (c) The terminals  37 – 39  have through holes  37   b – 37   d,    39   d – 39   f  for introducing one leads  31   a – 34   a  of the choke coils  31 ,  32  and the capacitors  33 ,  34 . The rough faces  64   a – 64   c,    65   a,    65   b,    66  are disposed close to the through holes  37   b – 37   d,    39   d – 39   f  of the contact portions  37   a,    39   a,    39   b.  Thus, it is possible to heat positions close to the through holes  37   b – 37   d,    39   d  – 39   f  of the contact portions  37   a,    39   a,    39   b  efficiently by the laser lights to solder the leads  31   a – 34   a  of the electric devices  31 – 34  introduced in the through holes  37   b – 37   d,    39   d – 39   f  in a short time and securely. 
   (d) The contact portions  37   a,    39   a,    39   b  are surrounded by wall portions  54 ,  55  that protrude beyond the contact portions  37   a,    39   a,    39   b.  Thus, the wall portions  54 ,  55  restrict solder wire melt on the contact portions  37   a,    39   a,    39   b  from spreading over the contact portions  37   a,    39   a,    39   b.    
   (e) In soldering on the contact portions  37   a,    39   a,    39   b,  laser lights are intensively radiated on the rough faces  64   a – 64   c,    65   a,    65   c,    66  (the radiation areas shown in  FIG. 9 ) having a large efficiency in absorbing heat generated by the laser lights. This assembly helps the solder to be melted fast. 
   (Modified Embodiments) 
   The above embodiments can be modified as follows, for example. 
   (1) The terminals  37 – 39  embedded in the brush holder  7  in the embodiment may be separately formed and assembled in the terminals  37 – 39 . 
   (2) The dents  64   e  having a quadrangular pyramid shape in the embodiment. The shapes of the dents, however, are not limited to the quadrangular pyramid-shape. For example, the dents may have a groove shape formed on a flat face. 
   (3) The above-described embodiment is applied to a motor  1  for the power window system. The present invention, however, can also be applied to motors for other apparatus such as a wiper motor for a windshield wiper system. 
   (4) The above-described embodiment is applied to a motor  1  having a motor unit  2  and a rotation-reduction unit  3  in a body. The present invention, however, can also be applied to a motor without any rotation-reduction unit (deceleration mechanism) therein. 
   The present invention further has the following advantages. 
   (f) The dents  64   e  are easily formed by stamping than forming protrudes. This decreases the manufacturing cost of the brush holder  7 . 
   (g) The dents  64   e  having a quadrangular pyramid shapes can be formed at a large density in an area, because it is easy to provide the stamping form with quadrangular pyramid-shaped projections. 
   (h) The manufacturing cost of the brush holder  7  by integrally forming the wall portions  54 ,  55  with the holder body  7   a  by injection molding. 
   This description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.