Abstract:
A DC motor has a conductive case and an arrangement for electrically connecting the shaft and case of the DC motor that is grounded. The arrangement includes a conductive member and a pressing member that presses the conductive member against the shaft, thereby grounding the shaft.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application is based on and claims priority from Japanese Patent Application 2000-054701, filed Feb. 29, 2000 and 2000-290878, filed Sep. 25, 2000, the contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an electric motor for a vehicle or an acoustic device. 
     2. Description of the Related Art 
     An ordinary electric motor for a vehicle such as a windshield wiper motor or a washer pump motor has a noise suppressing circuit that is comprised of a pair of noise suppressing coils and a capacitor. The noise suppressing circuit is effective to reduce electromagnetic noises generated at a commutator of the motor. However, if such the motor employs a pair of resinous bearing holders for supporting a pair of bearings that rotatably supports a shaft of a rotor, the resinous bearing holders electrically insulate the shaft from a ground. As a result, electro-magnetic noises may be radiated from an end of the shaft that extends from a case of the motor. 
     JP-U-6-9355 discloses an arrangement of grounding a shaft. In the arrangement, a metal bearing is in direct contact with a yoke that is grounded. 
     However, if the shaft is vibrated in the radial direction of the motor, the contact between the metal bearing and the yoke may be broken repeatedly, and the electro-magnetic noises cannot be effectively reduced. 
     SUMMARY OF THE INVENTION 
     A main object of the invention is to provide an electric motor that has an improved arrangement for reducing such electro-magnetic noises. 
     According to a main feature of the invention, a motor includes a conductive case, a member for grounding said case, a shaft and means for pressing a conducting member between the shaft and the case. 
     Therefore, the contact between the shaft and the case may not be broken even if the shaft is vibrated repeatedly. 
     The means may include a resilient contact member integrated with the case. 
     The means may include a conductive bearing holder fixed to the case and having a resilient contact member in contact with the bearing. 
     The means may include a magnetic core and a permanent magnet disposed to generate a magnetic force to press the contact member against the bearing. 
     The means may also include a spring washer held between the bearing and a collar formed on the shaft or a bearing-holding washer having a resilient projecting member. 
     The means may include a oil seal made of a conductive material. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects, features and characteristics of the present invention as well as the functions of related parts of the present invention will become clear from a study of the following detailed description, the appended claims and the drawings. In the drawings: 
     FIG. 1 is a cross-sectional view of a main portion of a DC motor according to a first embodiment of the invention; 
     FIG. 2 is a cross-sectional view of a main portion of a DC motor according to a second embodiment of the invention; 
     FIG. 3 is a cross-sectional view of a main portion of a DC motor according to a third embodiment of the invention; 
     FIG. 4 is a cross-sectional view of a main portion of a DC motor according to a fourth embodiment of the invention; 
     FIG. 5 is a front view illustrating a contact member of the DC motor according to the fourth embodiment; 
     FIG. 6 is an enlarged fragmentary cross-sectional side view illustrating a contact member of a DC motor according to a fifth embodiment of the invention; 
     FIG. 7A is a cross-sectional view of a main portion of a DC motor according to a sixth embodiment of the invention, and FIG. 7B is a fragmentary enlarged view of a contact member of the DC motor according to the sixth embodiment; 
     FIG. 8A is a front view of the contact member of the DC motor according to the sixth embodiment, and FIG. 8B is a fragmentary enlarged cross-sectional side view of a main portion of the contact member; 
     FIG. 9 is a schematic diagram illustrating the contact member in contact with a shaft of the DC motor according to the sixth embodiment; 
     FIG. 10 is a fragmentary enlarged cross-sectional view of a main portion of a DC motor according to a seventh embodiment of the invention; 
     FIG. 11A is a plan view of a conductive washer of the DC motor according to the seventh embodiment of the invention, and FIG. 11B is a side view of the washer shown in FIG. 11B; 
     FIG. 12 is a fragmentary enlarged cross-sectional view of a main portion of a DC motor according to an eighth embodiment of the invention; 
     FIG. 13 is a fragmentary enlarged cross-sectional view of a main portion of a DC motor according to a variation of the eighth embodiment of the invention; 
     FIG. 14 is a fragmentary enlarged cross-sectional view of a main portion of a DC motor according to a variation of the eighth embodiment of the invention; 
     FIG. 15 is a fragmentary enlarged cross-sectional view of a main portion of a DC motor according to a variation of the eighth embodiment of the invention; 
     FIG. 16 is a fragmentary enlarged cross-sectional view of a main portion of a DC motor according to a ninth embodiment of the invention; 
     FIG. 17A is a cross-sectional view of a main portion of a DC motor according to a tenth embodiment of the invention, and FIG. 17B is a fragmentary enlarged view of a contact member of the DC motor shown in FIG. 17A; 
     FIG. 18A is a front view of the contact member of the DC motor according to the tenth embodiment, and FIG. 18B is a fragmentary enlarged cross-sectional side view of a main portion of the contact member shown in FIG. 18A; and 
     FIG. 19 is a schematic diagram of a DC motor including a noise suppressing circuit. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A DC motor according to a first embodiment of the invention is described with reference to FIG.  1 . The DC motor has a cup-shaped cylindrical motor case  1  and a disk-shaped cover  2 , both of which are made of a conductive metal member. A plurality of permanent magnets is disposed in the motor case  1 . A through hole  1   a  is formed at the center of the motor case  1 , and a resinous bearing holder  4  is fitted to the through hole  1   a.  The bearing holder  4  has a spherical inside surface  4   a  whose diameter increases toward the axial center thereof. A bearing  5  is disposed inside the spherical inner surface. The bearing  5  is an oil retaining bearing made of a porous sintered alloy and has a spherical outside surface that is fitted to the spherical inside surface  4   a  of the bearing holder  4 . 
     The cover  2  has a pair of through holes  2   a  and  2   b  formed at symmetric portions away form the center thereof. An injection-molded resinous support member  6  is fixed to the inside surface of the cover  2 . The support member  6  has a pair of terminal holders  6   a  and  6   b  that project outward through the pair of through holes  2   a  and  2   b  and a bearing holder  6   c  disposed at the center thereof to be paired with the bearing holder  4 . The bearing holder  6   c  has the same spherical inside surface as the bearing holder  4 , and a bearing  7  having the same outside surface as the bearing  5  is fitted to the bearing holder  6   c.  Because of the spherical surfaces of the bearings  5  and  7  and the bearing holders  4  and  6   c,  the shaft  9  can be easily aligned to the center of the motor. 
     The bearing  7  is also paired with the bearing  5  to rotatably support the shaft  9 . In more detail, the bearing  5  supports the front or left portion of the shaft  9 , and the bearing  7  supports the rear or right end of the shaft  9 . The rotor  8  includes an armature  10  and a commutator  11 . The armature  10  is comprised of a magnetic core  10   a  and an armature coil (not shown). The axial center X of the core  10   a  is disposed a distance L off to the front or left side with respect to the axial center Y of the permanent magnets  3 . Therefore, the armature  10  is pulled by the permanent magnets  3  to the right. Even if the motor and the shaft  9  is vibrated in the radial direction of the motor, the rear end  9   b  of the shaft  9  is always brought in contact with the inside surface of the cover  2  under pressure. The commutator  11  is disposed between the armature  10  and the rear bearing  7 . The terminal holder  6   a  holds a high-side terminal  12   a,  and the terminal holder  6   b  holds a low-side terminal  12   b.  The terminals  12   a  and  12   b  extend outward from inside of the cover  2  in the axial direction of the motor. 
     A pair of brush springs  13  and  31  is fixed to the resinous support member  6  at a portion thereof around the commutator  11 . The pair of brush springs  13  and  31  is made of a metal plate. 
     The brush spring  13  has an anchor portion  13   a  that is fixed to the resinous support member  6 , a spring portion  13   b  that extends from an end of the anchor portion  13   a  in the radial direction of the motor to the commutator  11  and a connection bar  13   c  that extends from the other end of the anchor portion  13   a.  The anchor portion  13   a  extends in the axial direction and held between two members of the resinous support member  6 , and the connection bar  13   c  is connected to the inside end of the terminal  12   a.  The anchor portion  13   a,  the spring portion  13   b  and the connection bar  13   c  are cut from the same metal plate. 
     The brush spring  31  also has an anchor portion  31   a  that is fixed to the resinous support member  6  in the same manner as the anchor portion  13   a,  a spring portion  31   b  that extends from an end of the anchor portion  31   a  to the commutator  11  and a connection bar  31   c  that extends from the other end of the anchor portion  31   a,  which also contacts the inside surface of the cover  2 . The connection bar  31   c  is connected to the inside or left end of the terminal  12   b.    
     Each of the spring portions  13   b  and  31   b  has a brush  15  at the tip thereof, which is brought in contact with the commutator  11  under pressure. 
     The terminal  12   a  and the brush spring  13  are disposed in the high-side circuit, and the terminal  12   b  and the brush spring  31  are disposed in the low-side or ground level circuit. 
     When a DC voltage is applied across the terminal  12   a  and the terminal  12   b,  DC power is supplied to the armature  10  through the brush springs  13  and  31 , brushes  15  and the commutator  11  to rotate the rotor  8 . 
     Although the brush  15  and the commutator  11  generate electric noises, the motor case  1  and the cover  2  prevent electro-magnetic noises from radiating from the case  1 . Because, the motor case  1  and the cover  2  are grounded through the brush spring  31  and the terminal  12   b  that are connected to the ground level circuit. Although the front end  9   a  of the shaft  9  extends outward, the electro-magnetic noises do not radiate from the front end  9   a  because the rear end  9   b  is connected to the cover  2  that is grounded. 
     A DC motor according to a second embodiment of the invention is described with reference to FIG.  2 . 
     In the meantime, the same reference numeral in the following drawings corresponds to the same portion or component as shown in FIG.  1 . 
     The DC motor according to the second embodiment is comprised of a cup-shaped cylindrical motor case  41  that has a small cylindrical portion  41   a  at the center of the bottom thereof. The motor case  41  is made of a conductive magnetic material (iron sheet), and a conductive bearing  42  is fitted to the inside of the small cylindrical portion  41   a.  A shaft collar  43  is formed at the shaft  9  between the armature  10  and the bearing  42 , and a conductive washer  44  is disposed between the bearing  42  and the shaft collar  43 . 
     The axial center X of the core  10   a  is disposed a distance M off to the rear or right side with respect to the axial center Y of the permanent magnets  3 . Therefore, the armature  10  is pulled by the permanent magnets  3  to the left. Even if the motor and the shaft  9  is vibrated in the radial direction of the motor, the front end of the washer  44  is always brought in contact with the inside surface of the cover  2  under pressure. 
     A DC motor according to a third embodiment of the invention is described with reference to FIG.  3 . 
     The cover  2  of the first embodiment is replaced with a cover  51 . The cover  51  has a center through hole  51   a.  A resilient conductive contact member  52  is fixed to the cover  51  so that an end thereof can be pressed against the rear end surface  9   c  of the shaft  9 . Even if the motor and the shaft  9  is vibrated in the radial direction of the motor, the rear end of the shaft is always brought in contact with the cover  51  under pressure. Therefore, it is not necessary to arrange the axial position of the armature with respect to the permanent magnets. 
     A DC motor according to a fourth embodiment of the invention is described with reference to FIGS. 4 and 5. 
     A contact member  61  is fixed to the bottom of the motor case  2  instead of the shaft&#39;s rear end  9   b  of the first embodiment. The contact member  61  is made of a resilient conductive plate having an end  61   a  in contact with the outer periphery of the shaft  9  under pressure. Therefore it is not necessary to arrange the axial position of the armature with respect to the permanent magnets. 
     A DC motor according to a fifth embodiment of the invention is described with reference to FIG.  6 . 
     Instead of the through hole  2   b  and the connection bar  31   c  of the low-side brush spring  31  connected to the cover  2  of the first embodiment, the cover  2  has a cut-and-raised portion  2   c  that resiliently contacts the low-side terminal  12   b.    
     A DC motor according to a sixth embodiment of the invention is described with reference to FIGS.  7 A and  7 B-FIG.  9 . 
     The DC motor is integrated into a pump unit. A motor case  71  is comprised of a cup-shaped member made of a conductive magnetic plate. The motor case  71  has a small cylindrical portion  71   a  projecting outward from the bottom thereof. The cylindrical portion  71   a  has a partly spherical inside surface  71   b.  A bearing-holding washer  72 , which has a partly spherical or conical inside surface  72   a,  is fixed to the inside surface  71   b.  The bearing  5  is held between the spherical or conical inside surfaces  71   b  and  72   a,  so that the shaft  9  is rotatably supported by the bearings  5  and  7 . 
     The motor is accommodated in a pump housing  73 . The pump housing  73  has a cavity  73   a  to which the motor case  1  is fitted. A through hole  73   b  is formed at the bottom of the pump housing  73 , and an oil seal  74  is inserted therein. The front end  9   a  of the shaft  9  extends outward from the pump housing  73  through the oil seal  74 . 
     A conductive earth plate  75  is fixed to the outside surface of the bottom of the motor case  1 . As shown in FIGS. 8A and 8B, the earth plate  75  has a disk portion  75   a,  a cylindrical portion  75   b  and a pair of contact portions  75   c.  The pair of contact portions  75   c  is disposed opposite to each other at a slightly shorter distance than the outside diameter of the shaft  9 . As shown in FIG. 8B, the disk portion  75   a  has six slant spring arms  75   d  that are cut and extended from the disk portion  75   a  at circumferentially equal intervals. As shown in FIG. 7B, the disk portion  75   a  is held between the outside surface of the bottom of the motor case  71  and the pump housing  73 . Because of the slant spring arms  75   d , the disk portion  75   a  is securely connected to the motor case  71  even if there is a small gap between the motor case  71  and the pump housing  73 . The cylindrical portion  75   b  is fitted to the through hole  73   b,  and the pair of the contact portions  75   c  contacts the outer periphery of the front end of the shaft  9  at an angle of about 180° from each other, as shown in FIG.  9 . An impeller  6  is fixed to the front tip  9   a  of the shaft  9 . 
     Even if the shaft  9  is vibrated at a high rotation speed, the pair of contact portions  75   c  completely follows the shaft  9  so that the shaft  9  can be securely grounded. 
     A DC motor according to a seventh embodiment of the invention is described with reference to FIG.  10  and FIGS. 11A and 11B. 
     Rather than the earth plate  75  of the DC motor according to the sixth embodiment shown in FIG. 7, a conductive washer  81  is disposed between the bearing and a collar  9   d  formed on the shaft  9 . The washer  81  has a pair of spring arms  81   a  cut and extended from the annular base portion thereof. The washer  81  is fit to the outer periphery of the shaft  9 . Because of the pair of spring arms  81   a , the washer  81  can securely contact both the collar  9   d  and the bearing  5  even if there is a small gap between the collar  9   d  and the bearing  5 . 
     A DC motor according to an eighth embodiment of the invention is described with reference to FIG.  12 . 
     In this embodiment, the earth plate  75  of the DC motor according to the sixth embodiment shown in FIG. 7 is omitted. A bearing-fixing washer  91  is disposed between the bearing  5  and the collar  9   d  formed on the shaft  9 . The washer  91  is made of a conductive disk plate that has a conical or spherical inside surface  91   a  at the center thereof and a plurality of resilient contact arms  91   b  that extends from the rear end of the bearing-fixing washer  91  along the rear surface of the bearing  5 . Accordingly, the contact arms  91   b  are pressed against the front surface of the collar  9   d.  In other words, the contact arms  91   d  respectively extend from the rear end of the bearing-fixing washer  91  radially inward into the gap between the bearing  5  and the shaft collar  9   d  and compressed by the bearing  5  and the collar  9   d.  The contact arms  91   b  securely contact the collar  9   d  and the bearing  5 . Because the contact arms  91   a  are formed from a portion of the washer  91 , no additional member is necessary to ground the shaft  9 . Further, the contact arms are automatically lubricated by lubrication oil oozing from the bearing  5 . 
     Variations of the eighth embodiment of the invention are respectively described with reference to FIGS. 13-15. 
     The contact arms  91   b  can be substituted by resilient contact arms  91   c , as shown in FIG.  13 . The contact arms  91   c  slantwise extend from the rear end of the bearing-contact washer  91  radially outward to press against the outer periphery of the shaft collar  9   d.    
     The contact arms  91   b  and the shaft collar  9   d  can be substituted by resilient contact arms  91   d  and a shaft collar  9   e,  as shown in FIG.  14 . The contact arms  91   d  extend radially outward from the rear end of the bearing-contact washer  91  to press the front surface of the shaft collar  9   e.  For this purpose, the outside diameter of the shaft collar  9   d  is much larger than the outside diameter of the bearing  5 . 
     The contact arms  91   b  can be also substituted by resilient contact arms  91   e,  as shown in FIG.  15 . The contact arms  91   e  extend from the rear end of the bearing-contact washer  91  radially inward into the gap between the bearing  5  and the collar  9   d.  The contact arms have a plurality of resilient semispherical projections  91   f  on the rear surface thereof that are pressed against the front surface of the shaft collar  9   d.    
     A DC motor according to a ninth embodiment of the invention is described with reference to FIG.  16 . 
     The earth plate  75  of the DC motor according to the sixth embodiment shown in FIG. 7 is omitted. The oil seal  74  is made of a conductive material, and the oil seal  74  disposed in contact with the motor case  71 . The conductive material of the oil seal  74  is a compound of rubber and conductive powder. The oil seal  74  has ring-shaped lips  74   a  and  74   b  to which the shaft  9  is press-fitted and a flat rear surface in contact with the small cylindrical portion  71   a.    
     The conductive oil seal can be also formed of a nonconductive rubber oil seal and a conductive film that covers a portion of the oil seal to connect the shaft  9  and the motor case  71 . 
     A DC motor according to a tenth embodiment of the invention is described with reference to FIGS. 17A-18B. 
     The earth plate  75  of the DC motor according to the sixth embodiment shown in FIG. 7 is substituted by another earth plate shown in FIGS. 18A and 18B. The earth plate  95  has a disk portion  95   a,  a cylindrical portion  95   b  that projects forward from the disk portion  95   a,  a bottom portion  95   c  having six radially extending contact tongues  95   d . The contact tongues  95   d  slantwise extend forward from the bottom portion to the shaft  9 . As shown in FIG. 18A, the tip ends of the six contact tongues form an inscribed circle that has a smaller diameter than the outside diameter (represented by a two-dot-chain line) of the shaft  9 . The disk portion  95   a  has six slant spring arms  95   e  at circumferentially equal intervals. The disk portion  95   a  is held between the outside surface of the motor case  71  and the pump housing  73 , as shown in FIG.  17 B. Because of the spring arms  95   e,  the disk portion is securely connected to the motor case  71 . The cylindrical wall portion  95   b  is fitted to the through hole  73   b,  and the shaft  9  is inserted into the inscribed circle formed by the six contact tongues  95   d . Therefore, the contact tongues  95   d  are bent and pressed against the shaft  9 , so that the shaft  9  can be grounded through the earth plate  95 , the motor case  71  and the cover  2 . The number of the contact tongues may be changed from six to four, eight or any other number as desired. 
     As shown in FIG. 19, a noise suppressing circuit  16  that includes a pair of coils  20   a  and  20   b  and a capacitor  21  can be connected to the pair of terminals  12   a  and  12   b  of one of the DC motor according to the embodiments described above. The noise suppressing circuit  16  is accommodated in a circuit case  17  that has a pair of external pins  19   a  and  19   b  respectively connected to the noise suppressing circuit  16 . The coil  20   a  is connected between the external pin  19   a  and the high-side terminal  12   a,  and the coil  20   b  is connected between the external pin  19   b  and the low-side terminal  12   b.  The capacitor  21  is connected across the external pins  19   a  and  19   b.    
     If a DC voltage is applied across the external pins  19   a  and  19   b,  direct current is supplied from the external pin  19   a  through the coil  20   a,  the high-side terminal  12   a,  the high-side brush spring  13 , the high-side brush  15 , the commutator  11 , the armature  10 , the commutator  11 , the low-side brush  15 , the low-side brush spring  14 , the low-side terminal  12   b  and the coil  20   b  to the external pin  19   b.  Although electro-magnetic noises are generated between the brushes and the commutator, the noises are reduced by the noise suppressing circuit. 
     The invention described above can be applied to various rotary electric machines, such as an induction motor or other type of AC motor, as far as it has a case and a rotor accommodated in the case. 
     In the foregoing description of the present invention, the invention has been disclosed with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes may be made to the specific embodiments of the present invention without departing from the broader spirit and scope of the invention as set forth in the appended claims. Accordingly, the description of the present invention is to be regarded in an illustrative, rather than a restrictive, sense.