Patent Publication Number: US-2012043840-A1

Title: Electric motor and motor with a reduction gear

Description:
TECHNICAL FIELD 
     The present invention relates to an electric motor installed, for example, in a vehicle, and to an electric motor with a gear reduction using such a motor. 
     The present application claims priority based on the patent application 2009-112131, filed on May 1, 2009 in Japan, the content of which is incorporated herein by reference. 
     BACKGROUND ART 
     An electric motor, for example, has a plurality of segmented permanent magnets disposed on the inner peripheral surface of a cylindrically shaped yoke with a bottom, and an armature that is rotatably provided further to the inside in the radial direction than the permanent magnetic. The armature has an armature core that is fitted and fixed to the outside of a rotary shaft, and a commutator provided with a plurality of segments. The armature core is provided with a plurality of teeth that extend toward the outside in the radial direction, with a plurality of long slots provided between the teeth in the axial direction. Windings are passed through from these slots, wound as concentrated winding or distributed windings for each of the teeth. 
     The windings are electrically conductive with the segments of the commutator. Brushes are in sliding contact with each segment, so that electrical current is supplied to the windings via the brushes. When electrical current is supplied to the windings, a magnetic field is formed, and the armature is rotated by magnetic attractive force and repulsive force occurring between this magnetic field and the permanent magnets. 
     In the case of using a segmented permanent magnet, because air gaps are formed between each of the permanent magnets, the change in the magnetic flux becomes large at the boundaries of the two ends of the permanent magnetic in the peripheral direction. For this reason, when each of the teeth passes the ends of a permanent magnet, there is a large change in the forces of magnetic attraction and magnetic repulsion with respect to each tooth, resulting in an increase in cogging torque. 
     Given this, art has been proposed (for example, refer to Patent Document 1 and Patent Document 2) in which the air gap between the permanent magnets and the armature core is made gradually larger from the center of the permanent magnets toward both ends of the permanent magnets in the peripheral direction, so as to reduce the change in the magnetic forces of attraction and repulsion when each of the teeth passes the ends of the permanent magnets. 
     Art has also been proposed (for example, refer to Patent Document 3) in which the material thickness of the permanent magnets at both ends thereof in the peripheral direction is made greater than the material thickness at the center part, while maintaining the air gap with respect to the armature core, so as to prevent cracking of the permanent magnets. 
     Patent Document 1: Japanese Unexamined Patent Application, First Publication No. JPA S56-94958 
     Patent Document 2: Japanese Unexamined Patent Application, First Publication No. JPA 2005-20914 
     Patent Document 3: Japanese Unexamined Patent Application, First Publication No. JPA H9-224337 
     DISCLOSURE OF INVENTION 
     Problem to be Solved by the Invention 
     In the above-described prior art, however, because the segmented permanent magnets are formed in the shape of roof tiles, there is a restriction on the thickness to which the permanent magnets can be processed. For this reason, the permanent magnets must be made larger than necessary, and particularly in the case of forming rare earth magnets made of neodymium sintered magnets or the like, machining is difficult, and it is difficult to achieve a thin material thickness. 
     Given this, the present invention was made in consideration of the above-described situation, and provides an electric motor and an electric motor with a reduction gear, which is lightweight, compact, and low-cost, using the smallest required permanent magnets, while reducing the cogging torque, and which provides improved motor characteristics. 
     Means for Solving the Problem 
     (1) To solve the above-described problem, an electric motor according to a first aspect of the present invention includes: a bottomed cylindrical yoke; six flat-sheet permanent magnets fixed to an inner peripheral surface of the yoke; an armature rotatably supported further inward in the radial direction from the permanent magnets, and one pair of brushes which supply electricity to the armature, wherein the armature has a rotary shaft; an armature core which is fitted and fixed to the outside of the rotary shaft; and a commutator provided adjacently to the armature core with nine segments disposed in the peripheral direction, and the armature core has: nine teeth extending toward the outside in the radial direction and 9 slots formed between the teeth and extending along the axial direction, wherein windings are wound around each of the teeth and the end part of the windings connected to the segments, the permanent magnets are disposed on flat sections of a peripheral wall of the yoke, which is formed to be polygonal seen in plan view in the axial direction, a first bearing section which rotatably supports one end of the rotary shaft is integrally formed on a bottom part of the yoke, a brush holder accommodating section capable of accommodating a brush holder unit that holds the brushes is integrally formed at an opening of the yoke, and electricity is supplied to the windings by a sliding contact by the brushes with the segments. 
     In this manner, by using flat-sheet permanent magnets in a 6-pole, 9-slot, 9-segment electric motor, the need for complex processing of the permanent magnets is eliminated. For this reason, even in the case in which rare earth magnets are used as the permanent magnets, it is possible to easily make thin permanent magnets by machining and the like. It is possible, therefore, to achieve light weight and low cost, and to achieve an electric motor that is overall compact. 
     Also, by forming the peripheral wall of the yoke in a polygonal shape when seen in plan view in the axial direction and disposing the permanent magnets on the flat portions, it is possible to securely hold even flat-sheet permanent magnets to the inner peripheral surface of the yoke. It is additionally possible to cause the air gap between the permanent magnets and the armature core to increase gradually from the center of the permanent magnet toward both ends thereof in the peripheral direction. For this reason, it is possible to reduce the change in the magnetic forces of attraction and repulsion as each of the teeth passes the two ends of a permanent magnet, thereby enabling a reduction of the cogging torque. 
     It is also possible to increase the outer diameter of the armature core to the extent that the thickness of the permanent magnets is reduced, without increasing the outer diameter of the yoke. For this reason, it is possible to reserve more space for windings than conventionally, enabling an improvement in torque performance by increasing the number winding turns. 
     By integrally forming the brush holding accommodating section that accommodates the brush holder unit with the yoke, it is possible to achieve a more compact electric motor than in the case in which a separate brush holder unit is mounted to the electric motor. 
     (2) In the electric motor according to the first aspect of the present invention, the brush holder unit may be formed to enable fitting and holding inside the brush holder accommodating section, and a second bearing unit which rotatably supports the other end of the rotary shaft may be integrally formed on the brush holder unit. 
     By adopting this constitution, positioning of the brush holder unit is facilitated. Also, because the brush holder accommodating section is formed integrally with the yoke, it is easy to position the brush holder unit with respect to the yoke. 
     For this reason, it is possible to perform precise relative positioning between the first bearing section formed integrally on the bottom wall of the yoke and the second bearing unit of the brush holder unit. It is therefore possible to prevent undue stress on the rotary shaft or on the bearings, and also possible to prevent an increase in the torque load on the rotary shaft due to relative positioning offset at each of the bearing sections. 
     (3) In the electric motor according to the first aspect of the present invention, the brush holder unit and the brush holder accommodating section may be formed to have a shape that is an elongated circle seen in plan view, a peripheral wall of the brush holder accommodating section having two flat sections and arc-shaped sections that link the flat sections in the peripheral direction, wherein of the flat sections of the yoke, two flat sections that are in mutual opposition with the rotary shaft as the center and a flat section of the brush holder accommodating section may be flush. 
     By adopting this constitution, it is possible to achieve a flattened and compact electric motor. 
     (4) In the electric motor according to the first aspect of the present invention, the one pair of brushes may be disposed, on both ends in the longitudinal direction of the brush holder unit, to be in opposition about the rotary shaft as the center, and a resilient member which impels the brushes toward the commutator may be provided in the brush holder unit. 
     By adopting this constitution, it is possible to achieve a further flattened and compact electric motor. 
     (5) In the electric motor according to the first aspect of the present invention, an outer flange may be integrally formed at the opening edge of the brush holder accommodating section, a depression may be formed at least at one position in a connecting part between the peripheral wall of the brush holder accommodating section and the outer flange, and a protrusion capable of being placed in the depression may be provided in the outer peripheral edge of the brush holder unit. 
     By adopting this constitution, it is possible to perform accurate positioning of the brush holder unit with respect to the brush holder accommodating section. For this reason, it is possible to improve the installation precision of the brush holder unit, and improve the ease of installing the brush holder unit. 
     (6) In the electric motor according to the first aspect of the present invention, in the yoke a circular section having a shape that is substantially circular seen in plan view in the axial direction may be formed in a region between the proximity of the bottom wall of the peripheral wall and the first bearing section. 
     In the case in which the peripheral wall of the yoke is made polygonal when seen in plan view in the axial direction and the first bearing section is formed on the bottom wall of the yoke, if the yoke is formed, for example, by deep drawing of a metal sheet, there is a risk that, when forming the flat sections of the peripheral wall, the first bearing section will be pulled, and the roundness of the first bearing section will worsen. Also, to improve the roundness of the first bearing section, the number of pressing operations increases, thereby risking an increase in processing cost. 
     However, by forming a circular section in a region from the proximity of the bottom wall of the peripheral wall of the yoke up to the first bearing section, it is possible to achieve uniform pulling around the entire periphery of the first bearing section when operations such as deep drawing are performed, thereby enabling an improvement of the roundness of the first bearing section and a reduction of the processing cost. 
     (7) In the electric motor according to the first aspect of the present invention, the permanent magnets may be formed to be long in the axial direction and also may be disposed so that sides in the short direction are at an inclination with respect to a straight line along the axial direction. 
     By adopting this constitution, it is possible to skew the permanent magnets with respect to the teeth. For this reason, it is possible to further reduce the change in magnetic flux of the permanent magnet with respect to the teeth when the armature rotates and therefore it is possible to further reduce the cogging torque. 
     (8) In the electric motor according to the first aspect of the present invention, the peripheral wall of the yoke may be formed to be a hexagon seen in plan view in the axial direction. 
     By adopting this constitution, it is possible to make the peripheral wall of the yoke flat, while securely holding six permanent magnets to the peripheral wall of the yoke. 
     (9) In the electric motor according to the first aspect of the present invention, the peripheral wall of the yoke may be formed to be a dodecagon seen in plan view in the axial direction. 
     By adopting this constitution, it is possible to make the spacing between the angles about the center of the rotary shaft of the peripheral wall that opposes the rotary shaft smaller, compared to forming the peripheral wall of the yoke to have a hexagonal shape when seen in plan view in the axial direction. For this reason, it is possible to further reduce the size of the overall yoke, while securely holding the flat sheet-like permanent magnets to the peripheral wall of the yoke. 
     (10) In the electric motor according to the first aspect of the present invention, a positioning protrusion may be formed on the inner surface of the peripheral wall of the yoke, between each permanent magnet. 
     By adopting this constitution, because it is possible to easily position the permanent magnets, it is possible to improve the ease of mounting the permanent magnets. 
     (11) In the electric motor according to the first aspect of the present invention, the other end of the rotary shaft may protrude from the brush holder unit, and a linking section which transmits rotation of the rotary shaft to an external apparatus may be provided at protruding position, and the linking section may be able to be attached to and removed from the external apparatus. 
     By adopting this constitution, in the case in which an electric motor is mounted to an external apparatus, it is possible to improve the general usefulness of the electric motor, without the need to provide a motor for each external apparatus. 
     (12) A motor with a gear reduction according to a second aspect of the present invention includes: the motor of the first aspect of the present invention and an external apparatus provided with a reduction mechanism, wherein the other end of the rotary shaft protrudes from the brush holder unit, and a linking section which transmits rotation of the rotary shaft to the external apparatus is provided at protruding position, and the reduction mechanism and the rotary shaft of the armature are linked via the linking section. 
     By adopting this constitution, it is possible to not only achieve light weight, compactness, and reduced cost by using the smallest required permanent magnets, while reducing the cogging torque, but also to provide a motor with a reduction gear that provides improved motor characteristics. 
     Effect of the Invention 
     According to the present invention, by using flat-sheet permanent magnets in a 6-pole, 9-slot, 9-segment electric motor, the need for complex processing of the permanent magnets is eliminated. For this reason, even in the case of using, for example, rare earth magnets as the permanent magnets, it is easy to form thin permanent magnets by machining or the like. It is therefore possible to achieve lightweight permanent magnets at a low cost, and to achieve compactness for the overall electric motor. 
     Also, by forming the peripheral wall of the yoke to be a polygonal shape seen in plan view in the axial direction and disposing the permanent magnets in the flat sections, even when using flat sheet-like permanent magnets, secure mounting thereof to the inner peripheral wall of the yoke is possible. Additionally, it is possible to gradually increase the air gap between the permanent magnets and the armature core from the center of the permanent magnet towards both ends thereof in the peripheral direction. By doing this, it is possible to reduce the change in the magnetic forces of attraction and repulsion as each tooth passes the ends of the permanent magnet, thereby enabling a reduction of the cogging torque. 
     It is also possible to make the outer diameter of the armature core larger to the extent that the material thickness of the permanent magnets is reduced, without increasing the outer diameter of the yoke. For this reason, it is possible to reserve more space for windings than conventionally, enabling an improvement in torque performance by increasing the number of winding turns. 
     Because the brush holder accommodating section that accommodates the brush holder unit is formed integrally with the yoke, the electric motor is more compact than in the case in which a separate brush holder unit is mounted to the electric motor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an oblique view of a motor with a reduction gear according to a first embodiment of the present invention. 
         FIG. 2  is an exploded oblique view of a motor with a reduction gear according to the first embodiment of the present invention. 
         FIG. 3A  is an exploded oblique view of an electric motor in the first embodiment of the present invention. 
         FIG. 3B  is a drawing showing the electric motor in the first embodiment of the present invention, this showing an enlarged view of the armature in  FIG. 3A . 
         FIG. 4A  is a front elevation showing the motor case in the first embodiment of the present invention. 
         FIG. 4B  is a drawing showing the motor case in the first embodiment of the present invention, this showing a cross-sectional view along the line A-A in  FIG. 4A . 
         FIG. 5  is a plan view of the brush holder unit in the first embodiment of the present invention. 
         FIG. 6  is an exploded oblique view of the worm reduction mechanism in an embodiment of the present invention. 
         FIG. 7  is a cross-sectional view of the motor case in a second embodiment of the present invention. 
         FIG. 8A  is a side elevation showing the motor case in a third embodiment of the present invention. 
         FIG. 8B  is a drawing showing the motor case in the third embodiment of the present invention, this showing a cross-sectional view along the line B-B in  FIG. 8A . 
         FIG. 9A  is a side elevation showing the motor case in a fourth embodiment of the present invention. 
         FIG. 9B  is a drawing showing the motor case in the fourth embodiment of the present invention, this showing a cross-sectional view along the line C-C in  FIG. 9A . 
         FIG. 10A  is a drawing showing the motor case in a fifth embodiment of the present invention. 
         FIG. 10B  is a drawing showing the motor case in the fifth embodiment of the present invention, this showing a cross-sectional view along the line D-D in  FIG. 10A . 
         FIG. 11  is a side cross-sectional view showing another form of the yoke section in the fifth embodiment of the present invention. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     First Embodiment 
     Motor with a Reduction Gear 
     The first embodiment of the present invention will be described below, based on  FIG. 1  to  FIG. 6 . 
       FIG. 1  is an oblique view of motor with a reduction gear  1 .  FIG. 2  is an exploded oblique view of the motor with a reduction gear  1 .  FIG. 3A  and  FIG. 3B  show the electric motor  2 ,  FIG. 3A  being an exploded oblique view, and  FIG. 3B  being an enlarged view of the armature  6  of  FIG. 3A . 
     As shown in  FIG. 1  to  FIG. 3B , the motor with a reduction gear  1  is used, for example, as the drive source for a power window of a vehicle, and is provided with an electric motor  2  and a worm reduction mechanism  3  linked to the rotary shaft  12  of the electric motor  2 , a connector unit  4  being provided to supply electrical power to the electric motor  2 . 
     Electric Motor 
       FIG. 4A  and  FIG. 4B  show the motor case  5 ,  FIG. 4A  being a front elevation thereof, and  FIG. 4B  being a cross-sectional view thereof, along the line A-A of  FIG. 4A . 
     As shown in detail in  FIG. 3A ,  FIG. 3B ,  FIG. 4A , and  FIG. 4B , the electric motor  2  is provided with an armature  6  that can freely rotate, within the motor case  5 , which is shaped as a bottomed cylinder, and a brush holder unit  7  is fitted and held into the inside of the opening  5   a  in the motor case  5 . 
     Motor Case 
     The motor case  5  is formed by deep drawing using pressing operations or the like of a metal sheet, and has a yoke section  8  shaped as a bottomed cylinder, and a brush holder accommodating section  9  formed integrally on one end of the opening  8   a  of the yoke section  8  in the shape of an elongated circle. That is, the opening  9   a  of the brush holder accommodating section  9  is the opening  5   a  of the motor case  5 . 
     The peripheral wall  81  of the yoke section  8  is formed as a hexagonal shape when seen in plan view in the axial direction, and has six flat sections  81   a,  and arc-shaped sections  81   b  that join the flat sections  81   a.  A segmented permanent magnet  10  is formed on the inside surface of each of the flat sections  81   a.  That is, the peripheral wall  81  of the yoke section  8  plays the role of forming a magnetic path between the permanent magnets  10 , and is provided with the six permanent magnets  10 . 
     The permanent magnets  10  are formed as flat sheets made of rare earth magnets, such as neodymium sintered magnets. The permanent magnets  10  are formed to have a rectangular shape extending in the axial direction when seen in plan view, and have front and rear surfaces  10   a  that are mutually opposing in the thickness direction, mutually parallel long surfaces  10   b  that are disposed at both ends of the front and rear surfaces  10   a  in the short direction, and mutually parallel short surfaces  10   c  that are disposed at both ends of the front and rear surface  10   a  in the long direction. 
     The arc-shaped sections  81   b  of the yoke section  8  are formed so as to correspond to the air gaps K formed between long surfaces  10   b  of the permanent magnets  10 . 
     A bearing section  11  is integrally formed with the bottom wall  82  of the yoke section  8 , protruding outwardly in the axial direction at substantially the center thereof. The bearing section  11  is formed to have the shape of a bottomed cylinder, and also so that the bottom wall  11   a  faces outwardly. The bearing section  11  rotatably supports one end of the rotary shaft  12 . The bottom wall  82  is formed by a substantially round flat surface formed on the periphery of the bearing section  11 . 
     A thrust plate  13  is placed on the bottom wall  11   a  inside the bearing section  11 . A sliding bearing  14  is press fit and held in the inner peripheral surface  11   b  of the bearing section  11 . Additionally, a steel ball  15  is provided between the thrust plate  13  and the sliding bearing  14 . The thrust load of the rotary shaft  12  is received by the thrust plate  13  via the steel ball  15 . 
     A circular section  16  having a substantially circular shape seen in plan view in the axial direction is formed over the region from the proximity of the bottom wall  82  of the peripheral wall  81  up to the bearing section  11  in the yoke section  8 . By the formation of the circular section  16 , a rounded section  16   a  is formed in the connecting section between the peripheral wall  81  and the bottom wall  82  (refer to  FIG. 4B ). 
     A brush holder accommodating section  9  that is integrally formed at an end of the opening  8   a  of the yoke section  8  is formed so as to be a substantially elongated circular shape in the axial direction, which is long in the direction that is perpendicular to the axial direction. The brush holder accommodating section  9  has a pair of flat walls  91  that are rectangularly shaped when seen in plan view and are disposed so as to be in opposition about the rotary shaft  12  as the center, and a pair of arc-shaped walls  92  that join both ends of the flat walls  91  in the peripheral direction, that is, the ends in the longitudinal direction. 
     The pair of flat walls  91  is provided so as to be flush with each of the flat sections  81   a  of the yoke section  8 , which are disposed so as to be opposite, with the rotary shaft  12  as a center. A stepped wall  93  is formed between the arc-shaped wall of the brush holder accommodating section  9  and the peripheral wall  81  of the yoke section  8 . The stepped wall  93  makes continuity from the peripheral wall  81  of the yoke section up until the arc-shaped wall  92  of the brush holder accommodating section  9 . 
     An outer flange  17  for the purpose of connecting and holding the electric motor  2  to the worm reduction mechanism  3  is formed on the end of the opening  9   a  of the brush holder accommodating section  9 . This outer flange  17  is formed in substantially the shape of a pentagon when viewed in plan view in the axial direction, lengthened along the longitudinal direction of the brush holder accommodating section  9 , and also so that a part that is a vertex is positioned in the longitudinal direction. 
     The width E 1  of the outer flange  17  in the short direction is set to be slightly larger than the distance between the pair of flat walls  91  of the brush holder accommodating section  9 . 
     The part that is a vertex of and is on one end of the outer flange  17  in the longitudinal direction has formed on it one bolt hole  18   a.  Cutout parts  19  on either side of and sandwiching the bolt hole  8   a  are formed on one end of the outer flange  17  in the longitudinal direction. 
     A flat chamfered part  20  is formed on both sides of the other end of the outer flange  17  in the longitudinal direction. Bolt holes  18   b  and  18   c  are formed inside these flat chamfered parts  20  in the longitudinal direction. 
     Two depressions  21  each are formed on the inside of the connecting parts  17   a  between the outer flange  17  and the brush holder accommodating section  9 . These depressions  21  are disposed so as to be distributed around the rotary shaft  12  as the center. The depressions  21  are for the purpose of positioning the brush holder unit  7  (to be described in detail later). 
     Armature 
     As shown in  FIG. 3A  and  FIG. 3B , the armature  6  provided so as to be freely rotatable inside the motor case  5  has an armature core  61  that is fitted over the outside at a position opposite the yoke section  8  of the rotary shaft  12 , an armature coil  62 , which is wound on the armature core  61 , and a commutator  63 , which is disposed at the other end of the rotary shaft  12  and also fitted over the outside at a position opposite the brush holder accommodating section  9 . The armature core  61  is laminated in the axial direction with a plurality of ribbon-like metal plates  64 . 
     Nine T-shaped teeth  65  are formed along the peripheral direction on the outer periphery of the metal plates  6  at a uniform spacing in a radial manner. The end parts of the teeth  65  extend in the peripheral direction, and are formed on the outer periphery of the armature core  61 . That is, end parts of the teeth  65  are in a condition in which they oppose in the radial direction the front and rear  10   a  of the permanent magnets  10  that are disposed on the peripheral wall  81  of the yoke section  8 . 
     Whereas the end parts of the teeth  65  are formed as arcs when seen in plan view in the axial direction, the front and rear surfaces  10   a  of the permanent magnets  10  that oppose them are formed to be flat. For this reason, moving from the center of the permanent magnet  10  toward the long side surface  10   b  in the peripheral direction, the air gap between the permanent magnet  10  and the armature core  61  gradually increases. 
     Insulators  67  are attached to the teeth  65  constituted as noted above. The insulators  67  are for the purpose of insulating the armature coils  62  from the armature core  61 , and are formed to have a shape that is substantially a channel. Two insulators  67  are attached from the both sides in the axial direction of one tooth  65 , and the overall teeth, with the exception of the end parts are covered by the insulators  67 . 
     By fitting and holding a plurality of metal plates  64  over the outside of the rotary shaft  12 , nine slots  66  that are shaped line ant paths that extend in the axial direction are formed between adjacent teeth  65  on the outer periphery of the armature core  61 . 
     Windings  62   a  of enamel-covered wire are inserted between these slots  66 , and the windings  62   a  are wound, via the insulators  67  that are made of an insulating material. By doing this, a plurality of armature coils  62  are formed on the outer periphery of the armature core  61 . 
     The commutator  63  is fitted and fixed to the outer periphery of the other end of the rotary shaft  12 . Nine segments  68  formed of an electrically conductive material are mounted to the outer peripheral surface of the commutator  63 . 
     The segments  68  are pieces of metal plate that are long in the axial direction, and are mutually insulated and fixed in parallel with a uniform spacing therebetween along the peripheral direction. 
     The electric motor  2  of the first embodiment, therefore, has six permanent magnets  10 , nine slots  66 , and nine segments  68 , making it a 6-pole, 9-slot, 9-segment electric motor. 
     An integrally formed a riser  69  that is bent to bend around towards the outer radius side is formed on the armature core  61  end of each segment  68 . The winding  62   a  that is the beginning end of the armature coil  62  is hung over the riser  69  and the winding  62   a  is held to the riser  69  by fusing. By doing this, there is conductivity between a segment  68  and its corresponding armature coil  62 . 
     Brush Holder Unit 
       FIG. 5  is a plan view of the brush holder unit  7 . 
     As shown in  FIG. 3A  and  FIG. 3B , a brush  2  provided in the brush holder unit  7  accommodated by the brush holder accommodating section  9  makes sliding contact with the segments  68 . The brush holder unit  7  has a box-shaped unit body  70  with an opening  70   a.  The unit body  70  is accommodated in the brush holder accommodating section  9  so that the opening  70   a  faces the armature core  61 . 
     The bottom wall  71  of the unit body  70  closes off the opening  9 a of the brush holder accommodating section  9  when the brush holder unit  7  is accommodated into the brush holder accommodating section  9 . The bottom wall  71  of the unit body  70  is formed as an elongated circle, so as to match the cross-sectional shape of the brush holder unit  9 , and has a pair of flat sides  71   a  and a pair of arc-shaped sides  71   b.    
     A protrusion  72  is formed at four positions on the arc-shaped sides  71   b  that are opposite the depressions  21  formed in the brush holder accommodating section  9 . 
     These protrusions  72  are formed with a size that can be placed into the depressions  21 , and have a width in the peripheral direction that is slightly shorter than the width of the depressions  21 . That is, the brush holder unit  7  is positioned in the axial direction by the protrusions  72  into the depressions  21  of the brush holder accommodating section  9 . 
     Brush holder sections  73  are provided in the unit body  70 , at the center part in the short direction and on both sides in the longitudinal direction. The brush holder sections  73  are formed with a shape that is substantially a cube that is open on the longitudinal direction end. The brush holder sections  73  are disposed so that the longitudinal direction thereof is along the radial direction. 
     Brushes  22  are provided within the brush holder sections  73  facing toward the center in the radial direction and so as to be able to freely protrude and be buried therewithin. For this reason, the brushes are disposed so as to be in opposition along the longitudinal direction of the unit body about the rotary shaft  12  as the center. 
     The brushes  22  make sliding contact with the segments  68  of the commutator  63  so as to supply electrical current to the armature coil  62 . The brushes  22  are impelled toward the segments  68  by coil springs  23  disposed adjacently in the short direction of the brush holder section  73 . 
     A slit  74  is formed in the brush holder section  73 , along the longitudinal direction, on the surface opposite from the bottom wall  71  (the surface in front in  FIG. 5 ). One end of a pigtail lead  24  is connected to each of the brushes  22  via the slit  74 . The pigtail leads  24  are dressed in an L-shape when seen in plan view so as to run along the outer periphery of the bottom wall  71  from the brushes  22 . The other ends of the pigtail leads  74  are connected to the power-supplying section  25  provided on the flat side  71   a  side of the bottom wall  71 . The power-supplying section  25  is electrically connected to the connector unit  4 . 
     Although it is not illustrated in  FIG. 5 , a smoothing capacitor to smooth the supplied electric current or a choke coil for noise suppression may be provided on the pigtail leads  24  running between the brushes  22  and the power-supplying section  25 . 
     A protruding section  75  is formed on the bottom wall  71  of the unit body  70  facing the outside in the axial direction at the center part, that is, facing the side opposite from the armature core  61 . At the center of the protruding section  75  is integrally formed a bearing section  76  that has a substantially spherical cross-section. 
     The bearing section  76  is for rotatably supporting the other end of the rotary shaft  12 , and has a sliding bearing  26  press fit thereinto. The sliding bearing  26  has an outer shape that is substantially spherical, and inclines when the bearing section  76  is installed. By the inclined movement of the sliding bearing  26 , it is possible to accommodate the rotary shaft  12  even if its axis is offset. A plurality of slits  76   a  are formed in the peripheral direction with a uniform spacing in the peripheral direction on the peripheral wall of the bearing section  76 , so as to provide some degree of tolerance for manufacturing errors in the inner diameter of the bearing section  76  and the outer diameter of the sliding bearing  26 . 
     The peripheral wall  77  of the unit body  70  is formed so as to rise upward from the outer peripheral part of the bottom wall  71 . The peripheral wall  77  is the integral formation of one pair of flat sections  77   a  and one pair of arc-shaped section  77   b  linking the flat sections  77   a,  so as to follow along the outer peripheral surface of the brush holder accommodating section  9 . That is, the peripheral wall  77  serves as a socket-and-spigot part for making a socket-and-spigot joining of the brush holder unit  7  with the brush holder accommodating section  9  of the motor case  5 . 
     Openings  78  are formed at the centers of the arc-shaped sections  7     7 b  in the peripheral direction, that is, at positions on the arc-shaped sections  77   b  that are opposite the brush holder sections  73 . By forming the openings  78 , the task of installing the brushes  22  into the brush holder sections  73  is facilitated. 
     The other end of the rotary shaft  12  protrudes, via the sliding bearing  26  provided on the brush holder sections  73 , toward the worm reduction mechanism  3 . On this protruding other end of the rotary shaft  12  is mounted a joint motor  27  formed into a three-leafed shape. 
     The joint motor  27  forms one end of a joint unit  29  that transmits to the worm reduction mechanism  3  rotational force of the rotary shaft  12  to the worm reduction mechanism  3 , and has a main section  51  that is substantially a circular plate. A square hole  52  is formed in a large part of the center of the main section  51  in the radial direction. 
     Two flat sections  53  are formed in the other end of the rotary shaft  12 , these flat sections  53  being press fit into the square hole  52  of the main section  51  of the joint motor  27 . By doing this, it is possible to join the rotary shaft  12  and the joint motor  27  so as to prevent mutual rotation and also so as to enable movement in the axial direction. 
     Protrusions  54  having substantially sector shapes seen in plan view in the axial direction are provided at three positions on the outer peripheral wall of the main section  51  facing outwardly in the radial direction. These protrusions  54 , by mating removably with a joint frame  28  that is described later and that forms the other end of the joint unit  29 , transmit the rotational force of the rotary shaft  12  to the worm reduction mechanism  3 . 
     Connector Unit 
     The electric motor  2  constituted as noted above is secured by bolts  105  and held to the worm reduction mechanism  3  with a connector unit  4  therebetween. 
     The connector unit  4  is for the purpose of making electrical connection between an external power supply (not shown) and the motor with a gear reduction  1 . The connector unit  4  has a base section  41  formed as an elongated circle to oppose the bottom wall  71  of the brush holder unit  7 , and a connection section  42  provided so as to protrude from one end of the base section  41 . 
     An opening  43  through which the joint motor  27  can be passed is formed in the center of the base section  41  in the radial direction. A rising part  44  formed so as to rise upward substantially perpendicular toward the worm reduction mechanism  3  is formed on the connector section  42  side of the aperture  43  of the base section  41 . A board  45  is fixed to the rising part  44 . 
     A detection element (not shown) is mounted for the purpose of detection the rotational position of the connector unit  4  is mounted to the board  45 . The detection signal from the detection element is output to an external controller via the connector section  42 . Rotational control of the electric motor  2  is performed by this detection signal. 
     The connector section  42  has a cylindrical receptacle  46  that enables mating and removal of a connector (not shown) from an external power supply (not shown) or the like. One end of a plurality of terminals  47  used for a power supply or a sensor are provided so as to protrude inside the receptacle  46 . The terminals  47  include those that make electrical connection with the board  45  by extending from the receptacle  46  up to the board  45  bent toward the worm reduction mechanism  3  side via the base section  41 , and those that make electrical connection with the power-supplying section  25  of the brush holder unit  7  by extending from the receptacle  46  up to the power-supplying section  25  bent toward the electric motor  2  side via the base section  41 . 
     Of the terminals  47 , those that make connection to the board  45  are used as terminals for a sensor, and those that make connection to the power-supplying section  25  are used as terminals for a power supply. By doing this, the electrical power of an external power supply is supplied to the electric motor  2  via the brush holder unit  7 . 
     Worm Reduction Mechanism 
       FIG. 6  is an exploded oblique view of the worm reduction mechanism  3 . 
     As shown in  FIG. 1 ,  FIG. 2 , and  FIG. 6 , the worm reduction mechanism  3  houses, within a gear casing  30 , a worm shaft  33  that is linked to the rotary shaft  12  of the electric motor  2 , a worm wheel  34  that meshes with the worm shaft  33 , and a drive unit  35  that outputs the rotation of the worm wheel  34 . 
     The gear casing  30  is an integral formation of a gear accommodating section  31  that accommodates the worm shaft  33 , the worm wheel  34 , and the drive unit  35  with the receiving section  48  that is disposed at a position corresponding to the electric motor  2  and that can receive the base section  41  of the connector unit  4 . 
     The receiving section  48  is formed to have the shape of a box with an opening on the electric motor  2  side. The inner peripheral wall of the receiving section  48  is formed so as to have a cross-sectional shape that is substantially an elongated circle, so as to match the base section  41  of the connector unit  4 . A depression  49  that receives the part of the connector unit  4  that connects the base section  41  and the connector part  42  is formed in the peripheral wall  48   a  of the receiving section  48 . 
     The gear accommodating section  31  has a worm shaft accommodating section  36  for accommodating the worm shaft  33 , and a worm wheel accommodating section  37  for accommodating the drive unit  35 . A toothed part  33   a  is formed over a major portion of the center of the worm shaft  33  in the axial direction, this toothed part  33 a meshing with the worm wheel  34 . 
     The worm shaft accommodating section  36  is formed to have a substantially cylindrical shape, and extends along the axial direction of the rotary shaft  12 . An end nut  38  is press fit into an opening  36   a  at the end of the worm shaft accommodating section  36  opposite from the receiving section  48 , so as to block the opening  36   a.    
     A sliding bearing  101   a  that rotatably supports one end of the worm shaft  33 , and a steel ball  102  for receiving the thrust load of the worm shaft  33  are provided on the inside of the end nut  38 . The sliding bearing  101 a is pressed into and held in the receiving section  48 . The steel ball  102  is prevented by the end nut  38  from falling off from the worm shaft accommodating section  36 , and it is possible by the end nut  38  to adjust the position of the worm shaft  33  in the thrust direction. 
     The receiving section  48  side of the worm shaft accommodating section  36  passes and communicates with the receiving section  48 . A sliding bearing  101   b  for rotatably supporting the other end of the worm shaft  33  is fit into and fixed to the receiving section  48  side end of the worm shaft accommodating section  36 . The other end of the worm shaft  33  protrudes toward the receiving section  48  side via the sliding gear  101   b.  A location on this other end of the worm shaft  33  that protrudes is splined, and the joint frame  28  that forms the other side of the joint unit  29  is fit thereto by a spline mating. 
     The joint frame  28  has a main section  55  that is formed to be a substantially circular plate. At the center of the main section  55  in the radial direction is formed an insertion through hole  56  through which the other end of the worm shaft  33  can be passed. The insertion through hole  56  is splined, and by this the joint frame  28  and the worm shaft  33  are fit together by a spline mating. 
     Protrusions  57  that protrude along the axial direction are integrally formed with the surface of the main part  55  on the electric motor  2  side at three positions. 
     Each of the protrusions  57  is constituted so as to be interposed between the three protrusions  54  of the joint motor  27 . That is, when the joint motor rotates by the drive of the electric motor  2 , the protrusions  54  of the joint motor  27  and the protrusions  57  of the joint frame  28  engage in the peripheral direction, so that the joint motor  27  and the joint frame  28  rotate as one. In this manner, the joint motor  27  and the joint frame  28  are each formed so as to be attachable and removable in the axial direction and also to be able to engage in the rotational direction, so that the rotational force of the rotary shaft  12  is transmitted to the worm shaft  33 . 
     A steel ball  58  is provided between the rotary shaft  12  and the worm shaft  33 . This steel ball  58  makes direct contact with the rotary shaft  12  and the worm shaft  33 , and plays the role of preventing an increase in sliding resistance therebetween, while also playing the role of restricting the axial direction of the shafts  12  and  38 . 
     The worm wheel accommodating section  37  is formed to have a shape that is substantially a bottomed cylinder. A center shaft  111  that is inserted from the rear side (lower side in  FIG. 6 ) and that protrudes toward the inside is provided at the bottom part  37   a  of the worm wheel accommodating section  37  at the center part in the radial direction. The worm wheel  34  is accommodated in the worm wheel accommodating section  37  in the condition in which it is rotatably supported by the center shaft  111 . 
     The worm wheel  34  is formed to be substantially a circular plate, and has formed on the outer peripheral surface thereof a toothed part  34   a  that meshes with the worm shaft  33 . At the center in the radial direction of the worm wheel  34  is formed an insertion through hole  112  for the passing through of the center shaft  111 . The center shaft  111  passes through the worm wheel  34  and protrudes outwardly from the worm wheel  34 . 
     Also, in the worm wheel  34 , on the surface of the worm wheel accommodating section  37  that is opposite the bottom part  37   a,  there are formed, in the area surrounding the insertion hole  112 , housing depressions  113  that are sector shaped when seen in plan view in the axial direction. By forming the housing depressions  113  at three positions on the worm wheel  34 , three walls  113   a  are formed in a radial manner in the area surrounding the insertion through hole  11 . Because each of the housing depressions  113  is formed to have a sector shape seen in plan view in the axial direction, the walls  113   a  broaden toward the outside in the radial direction from the inside in the radial direction when seen in plan view in the axial direction. 
     These housing depressions  113  house a rubber damper  114 . The damper  114  is constituted by six damper pieces  115  disposed at a uniform spacing in the peripheral direction, and a ring part  116  that is disposed on the inside of the damper pieces  115  in the radial direction and that join the six damper pieces  115 . 
     The damper pieces  115  are formed to have a semi-cylindrical shape in cross-section, and with a size so that two of the damper pieces  115  can be housed within one housing depression  113  of the worm wheel  34 . By doing this, movement of the damper  114  in the direction of rotation is restricted by the walls  113 a of the worm wheel  34 . 
     The drive unit  35  is rotatably supported by the center shaft  111  on the opposite side of the worm wheel with the damper  114  therebetween. The drive unit  35  has a base plate  117  that is shaped substantially as a circular plate. The diameter of the base plate  117  is set to be a size that can cover over the end of the damper pieces  115  of the damper  114 . 
     Protrusions  118  are formed so as to protrude at three positions spaced uniformly in the peripheral direction on the surface of the base plate  117  opposite the damper  114 . Each of the protrusions  118  interposes between two damper pieces  115  that are housed in each of the housing depressions  113  of the worm wheel  34 . 
     That is, when the worm wheel  34  rotates, the walls  113   a  of the worm wheel  34  and the protrusions  118  of the drive unit  35  engage in the peripheral direction, with the damper pieces  115  therebetween, so that the worm wheel  34  and the drive unit  35  rotate as one. 
     Because the rotational force of the worm wheel  34  is transmitted to the drive unit  35  via the damper  114 , it is possible to soften the shock acting on the worm wheel  34  and the drive unit  35 . 
     On the side of the base plate  117  opposite the damper  114 , the output section  119  is provided so as protrude as a column. The output section  119  is constituted by a base section  122  that is a circular plate, and a linking section  123  that is provided so as to protrude from the base section  122 . The linking section  123  is linked to, for example, a power window apparatus (not shown) of a vehicle. By doing this, the rotation of the worm wheel  34  can be transmitted to the power window apparatus. 
     An insertion through hole  121  for passing a shaft is provided in the output section  119  and in the base plate  117 . The center shaft  111  is passes through this insertion through hole  121  and the drive unit  35  is rotatably supported. 
     A cover  131  having a shape that is substantially circular and that closes off the opening  37   b  is provided on the worm wheel accommodating section  37 . The cover  131  prevents the intrusion of dust or water drops and the like into the inside of the worm wheel accommodating section  37 , and also plays the role of restricting the movement of the drive unit  35  in the removal direction. The cover  131  has a cover piece  132  shaped substantially annularly, and the output section  119  of the drive unit  35  protrudes outward from the center of this cover piece  132 . 
     A rubber sealing member  133  for improving the tight sealing inside the worm wheel accommodating section  37  is provided on the inner peripheral edge of the cover  131 . By a sliding contact between this sealing member  133  and the base section  122  of the output section  119 , it is possible to prevent the intrusion of dust or water drops and the like into the inside of the worm wheel accommodating section  37 . 
     A plurality of engaging pieces  134  are provided on the outer peripheral edge of the cover  131 . These engaging pieces  134  are formed so as to be elastically deformable, and extend outward toward the bottom part  37   a  of the worm wheel accommodating section  37 , so as to run along the outer peripheral surface of the worm wheel accommodating section  37 . 
     An engagement protrusion  135  is formed on the outer peripheral surface of the worm wheel accommodating section  37  at a position corresponding to the engagement pieces  134 . By the engagement of this engagement protrusion  135  with an engagement piece  134 , the cover  131  is fixed, and movement of the drive unit  35  in the direction of removal is restricted. 
     In addition, one bolt seat  141 a is formed in the worm shaft accommodating section  36  of the gear casing  30 , and bolt seats  141   b  are formed at two positions in the worm wheel accommodating section  37 . These bolt seats  141   a  and  141   b  are used, for example, to tighten and hold the motor with a gear reduction  1  to a power window apparatus (not shown). The bolt seats  141   a  and  141   b  have insertion through holes  142   a  and  142   b  for passing bolts (not shown). Flanged bushings  143  are inserted into the insertion through holes  142   a  and  142   b.    
     Operating Effect 
     The operating effect of the motor with a gear reduction  1  is described below. 
     When electrical power is supplied to the electric motor  2  via the connector unit  4 , a magnetic field is formed in the armature core  61 , and magnetic forces of attraction and repulsion are generated with respect to the permanent magnets  10  disposed in the yoke section  8  so that the armature  6  rotates. 
     Because there is a skew with respect to the permanent magnet  10  axial direction and they are formed as flat sheets, proceeding from the center of the permanent magnets  10  toward the long surface  10   b  on both sides in the peripheral direction, the air gap between the permanent magnets  10  and the armature core  61  gradually increases. 
     For this reason, it is possible to reduce the change in the magnetic flux at the boundaries of the two ends of the permanent magnets in the peripheral direction, so that the cogging torque is reduced. By reducing the cogging torque, it is possible to reduce the vibration and noise when the electric motor  2  is driven. 
     By the rotation of the armature  6 , the worm shaft  33  that is linked to the rotary shaft  12  via the joint unit rotates. Next, the worm wheel  34  that meshes with the worm shaft  33  rotates. When the worm wheel  34  rotates, the drive unit  35  that is formed as one therewith rotates. When this occurs, because the damper  114  is provided between the worm wheel  34  and the drive unit  35 , the shock occurring between the worm wheel  34  and the drive unit  35  is softened. 
     In the case in which, for example, a power window apparatus (not shown) is linked to the drive unit  35 , even if some external force is applied to the power window apparatus, because of the damper  114  the shock transmitted to the worm wheel  34  from the drive unit  35  can be softened. 
     Effect 
     According to the first embodiment of the present invention, therefore, in a 6-pole, 9-slot, 9-segment electric motor  2 , by using flat plates as the segmented permanent magnets  10 , it is not necessary to perform complex processing of the permanent magnets  10 . For this reason, even in the case, for example, in which a rare earth magnet such as neodymium sintered magnets are used as the permanent magnets  10 , it is possible by machining to achieve thin permanent magnets  10 . It is therefore possible to reduce both the weight and the cost of the permanent magnets  10 , and to reduce the overall size of the electric motor  2 . 
     In the motor case  5 , the peripheral wall  81  of the yoke section  8  is formed so as to be hexagonal when seen in plan view in the axial direction, and the peripheral wall  81  is constituted by flat sections  81   a  and arc-shaped sections  81   b.  By then disposing the permanent magnets  10  on the flat sections  81   a,  it is possible to securely fix even flat plate permanent magnets  10  to the inner peripheral wall of the yoke section  8 . Because an arc-shaped section  81   b  is formed between each of the flat sections  81   a,  it is possible to improve the rigidity of the yoke section  8  and to reduce the vibration or operating noise when the electric motor  2  is driven. 
     Additionally, it is possible to increase the outer diameter of the armature core  61  to the extent that the permanent magnets  10  are made thinner, without increasing the outer diameter of the yoke section  8 . For this reason, it is possible to reserve more winding space for the winding  62   a  than conventionally, so that in forming the armature coil  62 , it is possible to increase the number of winding turns, thereby enabling an improvement in the torque performance of the electric motor  2 . 
     Additionally, by making the permanent magnets  10  flat plates, moving from the center the permanent magnet  10  to the long side surface  10   b  on both ends in the peripheral direction, the air gap between the permanent magnet  10  and the armature core  61  gradually increases. For this reason, it is possible to reduce the change in the forces of magnetic attraction and repulsion with respect to each of the teeth  65  of the armature  6  as they pass both ends of the permanent magnet  10 , thereby enabling a reduction in the cogging torque. 
     By integrally forming the brush holder accommodating section  9  that accommodates the brush holder unit  7  with the yoke section  8 , the motor case  5  is constituted by the yoke section  8  and the brush holder accommodating section  9 . By doing this, the electric motor  2  can be made more compact than in the case of mounting a separate brush holder unit  7  to the electric motor  2 . 
     The brush holder unit  7  is fitted to the brush holder accommodating section  9  using a socket-and-spigot joint, and a bearing section  76  that rotatably supports the other end of the rotary shaft  12  is integrally formed on the brush holder accommodating section  9 . By doing this, it is not only possible to perform accurate positioning of the brush holder unit  7  with respect to the yoke section  8 , but also easy to establish the position of each of the bearing sections  11  and  76  with the bearing section  11  formed on the yoke section  8  as the reference. It is therefore possible to perform precise relative positioning of the bearing sections  11  and  76 . It is therefore possible to prevent undue stress from being applied to the rotary shaft  12  or the bearing sections  11  and  76 . In addition, it is possible to prevent an increase in the torque load on the rotary shaft  12  due to relative offset between the bearing sections  11  and  76 , thereby enabling an improvement in the motor characteristics of the electric motor  2 . 
     In addition to forming the brush holder accommodating section  9  to have substantially the shape of an elongated circle in the axial direction, the brush holder unit  7  that is accommodated in the brush holder accommodating section  9  is formed to have a shape that is substantially an elongated circled seen in plan view in the axial direction. The flat walls  91  of the brush holder accommodating section  9  and the flat sections  81   a  of the yoke section  8  that are disposed so as to be opposite about the rotary shaft  12  as the center are formed so as to be mutually flush. By doing this, it is possible to make an electric motor  2  that overall flat and compact. 
     Also, by disposing each of the brush holder sections  73  in the center of the brush holder unit  7  in the axial direction and on both ends in the longitudinal direction, it is possible to make an electric motor  2  that is further flattened and compact. 
     In addition, coil springs  23  that impel the brushes  22  toward the commutator  63  are disposed so as to be adjacent thereto in the short direction of the brush holder section  73 . For this reason, compared with the case of disposing a resilient member (spring) that impels the brushes  22  on the end part in the longitudinal direction, it is possible to make the length of the brush holder section  73  shorter. It is therefore possible to make the length of the brush holder unit  7  shorter. 
     Additionally, an outer flange  17  is formed on the opening  9  end of the brush holder accommodating section  9 , and a depressions  21  are formed in the connecting parts  17   a  between the outer flange  17  and the arc-shaped wall  92  of the brush holder accommodating section  9 . Protrusions  72  are formed at position that correspond to the depressions  21  of the brush holder unit  7 . By placing the protrusions  72  in the depressions  21  of the brush holder accommodating section  9  at the time of assembling the brush holder unit  7 , it is possible to easily and accurately position the brush holder unit  7  in the axial direction. 
     For this reason, the precision of assembling the brush holder unit and the ease of the task of assembly are improved. 
     A circular section  16  having a substantially circular shape seen in plan view in the axial direction is formed over the region from the proximity of the bottom wall  82  of the peripheral wall  81  up to the bearing section  11  in the yoke section  8 . By the formation of the circular section  16 , a rounded part  16   a  is formed in the connecting part between the peripheral wall  81  and the bottom wall  82  (refer to  FIG. 4B ). 
     In the case forming the motor case  5  by deep drawing by pressing operations or the like, there is the risk that the metal plate used as the blank is pulled to the flat section  81   a  on the peripheral wall  81 , thereby worsening the roundness of the bearing section  11 . Also, to improve the roundness of the bearing section  11 , the number of pressing operations increases, thereby risking an increase in the processing cost. 
     However, because of the formation of the circular section  16  on the motor case  5 , the bearing section  11  is uniformly pulled over the entire outer periphery at the time of deep drawing. Also, because it is possible by the rounded part  16   a  to achieve a large spacing between the bearing section  11  and the peripheral wall  81 , it is possible to reduce the influence on the roundness of the bearing section  11  by the formation the peripheral wall  81 . For this reason, it is easy to improve the roundness of the bearing section  11 , and possible to reduce the processing cost. 
     Additionally, the rotary shaft  12  of the electric motor  2  and the worm shaft  33  of the worm reduction mechanism  3  are linked via the joint unit  29 . For this reason, even in the case of mounting the electric motor  2  not to the worm reduction mechanism  3 , but rather to another reduction mechanism or external apparatus, the need to redesign the rotary shaft  12  of the electric motor  2  is eliminated. For this reason, the general usefulness of the electric motor  2  is improved. Furthermore, by mounting the joint motor  27  that forms one side of the joint unit to the rotary shaft  12  of the electric motor  2  beforehand, the assembly of the electric motor  2  and worm reduction mechanism  3  is facilitated, and the ease of assembly is improved. 
     In the first embodiment described above, although the description was for the case in which segmented permanent magnets  10  are formed as flat plates from rare earth magnets such as neodymium sintered magnets and also formed to have substantially a rectangular shaped when seen in plan view, and to be long in the axial direction, this is not a restriction, and the permanent magnets  10  may be formed using neodymium bonded magnets or ferrite magnets. 
     Second Embodiment 
     Next, the second embodiment of the present invention will be described, based on  FIG. 7 . 
       FIG. 7  is a vertical cross-sectional view of the motor case of the second embodiment. Aspects that are the same as in the first embodiment are described with the assignment of the same reference numerals and the descriptions thereof are omitted (this is true of the other embodiments to follow). 
     In the second embodiment, the motor with a reduction gear  1  is used as the drive source for, for example, a power window apparatus of a vehicle, and has an electric motor  2  and a worm reduction mechanism  3  linked to a rotary shaft  12  of the electric motor  2 . The basic features such as provision of a connector unit for the purpose of supplying electrical power to the electric motor  2 , the brush holder unit  7  being fitted into a held in the opening  5   a  side of the motor case  5 , the rotatable provision of an armature  6  on the opening  5   a  side of the motor case  5 , the constitution as an electric motor having 6 poles, 9 slots, and  9  segments, the worm reduction mechanism  3  having housed within a gear casing  30  a worm shaft  33  linked to the rotary shaft  12  of the electric motor, a worm wheel  34  meshing with the worm shaft  33 , and a drive unit  35  that outputs the rotation of the worm wheel  34  are the same as in the first embodiment (this applying to the other embodiments to follow). 
     As shown in  FIG. 7 , the point of difference between the first embodiment and the second embodiment is that, whereas the permanent magnets  10  of the above-described first embodiment are formed so as to be substantially rectangular when seen in plan view and long in the axial direction, the permanent magnets  310  of the second embodiment are formed to have a shape that is substantially a parallelogram when seen in plan view and long in the axial direction. 
     More specifically, the permanent magnets  310  are disposed so that the long side surfaces  310   b  thereof are inclined with respect to a straight line L 1  that is along the axial direction, and also so that the one surface of the front and rear surfaces  310   a  makes contact with a flat section  81   a  of the yoke section  8 . The permanent magnets  10  are arranged in a row so that one short side surface  301   c  of each is positioned on the one and the same flat plane. That is, the permanent magnets  310  are in a skewed condition. 
     According to the above-described second embodiment, therefore, it is possible to achieve the same type of effect as with the above-described first embodiment. In addition, the permanent magnets  310  are formed so as to be in the shape of parallelograms seen in plan view and are disposed so as to be skewed with respect to the teeth  65  of the armature  6 . 
     Third Embodiment 
     Next, the third embodiment of the present invention will be described, based on  FIG. 8A  and  FIG. 8B . 
       FIG. 8A  and  FIG. 8B  show a motor case  205  of the third embodiment,  FIG. 8A  being a side view, and  FIG. 8B  being a cross-sectional view along the line B-B in  FIG. 8A . 
     As shown in  FIG. 8A  and  FIG. 8B , the point of difference between the first embodiment and the third embodiment is that, whereas in the first embodiment the yoke section  8  is formed with a shape that is substantially hexagon seen in plan view in the axial direction, the yoke section  208  in the third embodiment is formed with a shape that is substantially a dodecagon seen in plan view in the axial direction. 
     The motor case  205  is formed by deep drawing a metal plate by pressing operations and the like, and is constituted by a yoke section  208  that is a bottomed cylindrical shape, and a brush holder accommodating section  9  in the shape of an elongated circle formed integrally with the end of an opening  208   a  of the yoke section  208 . 
     The peripheral wall  281  of the yoke section  208  is constituted by six first flat sections  281   a  formed instead of the flat sections  81   a  of the peripheral wall  81  of the yoke section  8  in the first embodiment, and six second flat sections  281   b  formed instead of the arc-shaped sections  81   b.    
     The first flat sections  281   a  and the second flat sections  281   b  are in the condition of being alternately disposed in the peripheral direction. Because the second flat sections  281   b  are formed in place of the arc-shaped sections of the first embodiment, the width W 1  thereof in the peripheral direction is set to be smaller than the width W 2  of the first flat sections  281   a  in the peripheral direction. 
     A segmented permanent magnet  10  is disposed on each of the first flat sections  281   a.  The permanent magnets  10  may be formed with a shape that is substantially a parallelogram seen in plan view that is long in the axial direction, and may alternatively be formed as rectangles. 
     According to the third embodiment, therefore, in addition to the same type of effect as with the first embodiment, the yoke section  208  is smaller than the yoke section  8  of the first embodiment to the extent that the yoke section  208  is formed to have a shape that is substantially a dodecagon seen in plan view in the axial direction. 
     More specifically, second flat sections  281   b  are formed in the peripheral wall  281  of the yoke section  208  instead of the arc-shaped sections  81   b  that are formed in the first embodiment. By doing this, the second flat sections  281   b  are positioned more toward the inside in the radial direction than the arc-shaped sections  81   b.  That is, the yoke section  208  is in form of the yoke section  8  of the first embodiment, but with the corners (arc-shaped sections  81   b ) pressed in. For this reason, the distance E 2  (refer to  FIG. 8B ) between opposing angles about the rotary shaft  12  as the center can be made smaller than the distance E 3  (refer to  FIG. 4A ) between the arc-shaped sections  81   b  opposing about the rotary shaft  12  as the center in the yoke section  8  of the first embodiment. 
     Fourth Embodiment 
     Next, the fourth embodiment of the present invention will be described, base on  FIG. 9A  and  FIG. 9B . 
       FIG. 9A  and  FIG. 9B  show a motor case  305  of the fourth embodiment,  FIG. 9A  being a side view, and  FIG. 9B  being a cross-sectional view along the line C-C in  FIG. 9A . 
     As shown in  FIG. 9A  and  FIG. 9B , the point of difference between the first embodiment and the fourth embodiment is that positioning protrusions  311  for positioning the permanent magnets  310  are formed on the yoke section  8  of the first embodiment. 
     More specifically, the peripheral wall  381  of the yoke section  308  in the motor case  305  is formed to have a shape that is substantially hexagonal seen in plan view in the axial direction, and is constituted by six flat sections  381   a  and arc-shaped sections  381   b  that are linked to these flat sections  381   a.  The permanent magnets  10  are provided on the inner surface of each of the flat sections  381   a.    
     A plurality of positioning protrusions  311  are provided on the arc-shaped sections  381   b  of the yoke section  308  so as to protrude toward the inside in the radial direction. Two positioning protrusions  311  are formed along the axial direction on each arc-shaped section  381   b,  and positioning protrusions  311  that are adjacent in the peripheral direction are positioned on one and the same flat plane. The positioning protrusions  311  are formed by using a fixture or the like to press the arc-shaped sections  381   b  inwardly in the radial direction from the outside in the radial direction. For this reason, depressions  311   a  are formed in the outer periphery of the arc-shaped sections  381   b  at locations opposite the positioning protrusions  311 . 
     The permanent magnet  10  disposed on each flat section  381  is formed so that the permanent magnet  10  is securely sandwiched by the positioning protrusions  311  positioning the both sides of the permanent magnet  10 . That is, each positioning protrusions  311  is formed between each of the permanent magnets  10 , and the positioning of the permanent magnet  10  in the peripheral direction is performed. 
     According to the above-described fourth embodiment, therefore, in addition to the same type of effect as with the first embodiment, it is possible to easily position the permanent magnets  10 . For this reason, it is possible to improve the ease of the task of mounting the permanent magnets  10 . 
     Although the above-described fourth embodiment is for the case of forming two each of the positioning protrusions  311  along the axial direction on each of the arc-shaped sections of the yoke section  308  and disposing the permanent magnets  10  having a shape that is substantially rectangular seen in plan view on the flat sections  381   a,  this is not a restriction, and the two positioning protrusions  311  formed on each of the arc-shaped sections  381   b  of the yoke section  308  may be disposed so as to be offset in the axial direction, and permanent magnets  310  having a shape that is substantially a parallelogram seen in plan view may be used in place of the permanent magnets  10  that are substantially rectangular seen in plan view. 
     Fifth Embodiment 
     Next, the fifth embodiment of the present invention will be described, based on  FIG. 10A ,  FIG. 10B , and  FIG. 11 . 
       FIG. 10  and  FIG. 10B  show the motor case  405  of the fifth embodiment, with  FIG. 10A  being a side view and  FIG. 10B  being a cross-sectional view along the line D-D in  FIG. 10A . 
     As shown in  FIG. 10A  and  FIG. 10B , the point of difference between the fourth embodiment and the fifth embodiment is that, whereas the motor case  305  in the fourth embodiment had formed a plurality of positioning protrusions for positioning the permanent magnets  10  in the yoke section  308  in the peripheral direction, the motor case  405  in the fifth embodiment has positioning ridges  411  in the yoke section  408  in place of the positioning protrusions  311 . 
     The positioning ridges  411  are formed on the inner surface  481  of the yoke section  40  so as to pass in the axial direction across each of the flat sections  481   a.  That is, the peripheral wall  481  of the yoke section  408  is constituted by the flat sections  481   a  and the positioning ridges  411 . The flat sections  481  a and the positioning ridges  411  are disposed alternately in the peripheral direction. 
     The positioning ridges  411  are formed using a fixture or the like to press the peripheral wall  481  inwardly in the radial direction from the outside in the radial direction. For this reason, depressions  481   b  are formed in the peripheral direction in the peripheral wall  481  between each of the flat sections  481   a.    
     According to the above-described fifth embodiment, therefore, it is possible to achieve the same type of effect as with the fourth embodiment. In addition, because the positioning ridges  411  are formed so as to pass over the entire peripheral wall  481  in the axial direction, the short direction sides of the permanent magnets are securely sandwiched. For this reason, it is possible to perform reliable positioning of the permanent magnets  10 . 
     The above-described fifth embodiment is described for the case in which the peripheral wall  481  is pressed inwardly in the radial direction from the outside in the radial direction using a fixture or the like, so as to form the positioning ridges  411 . Additionally, the description is for the case in which the permanent magnets  10  are disposed on the flat sections  481   a  of the peripheral wall  481 . In this case, as shown in  FIG. 11 , a machined part  482  may be formed on the inner surface of the flat section  481  by cutting, so as to enable more precise positioning of the permanent magnets  10 . 
       FIG. 11  is a side cross-sectional view of another form of the yoke section  40  of the fifth embodiment. 
     As shown in  FIG. 11 , in the case of forming the machined parts  482  in the inner surface of the flat sections  481   a  by cutting, the need to form the positioning ridges  411  precisely is eliminated. Also, in the case in which the machined parts  482  are formed in the inner surface of the flat sections  481   a,  it is desirable to set the material thickness of the peripheral wall  481  of the yoke section  408  to a thickness that accounts for the allowance for machining 
     In the above-described fifth embodiment, the description is for the case in which the positioning ridges  411  are formed so as to run along the axial direction. This is not a restriction, however, and the positioning ridges  411  may be formed at an inclination with respect to the axial direction. By doing this, it is possible to dispose the permanent magnets  310  that have a shape that is substantially a parallelogram seen in plan view on the flat sections  481   a  in place of the permanent magnets  10  having a shape that is substantially rectangular seen in plan view. 
     The present invention is not restricted to the above-described embodiments, which may be subjected to various modifications, within the scope of the present invention. 
     Additionally, in the above-described embodiments, the descriptions are for the case in which, in the motor cases  5 ,  205 ,  305 , and  405 , two each of depressions  21  are formed in the connection parts  17   a  between an outer flange  17  and the arc-shaped wall  92  of the brush holder accommodating section  9 , and in which four protrusions  72  that correspond to the depressions  21  are formed in the brush holder unit  7 . This is not a restriction, however, and at least one depression  21  can be formed in the brush holder accommodating section  9 , with at least one protrusion  72  formed in the brush holder unit  7 . 
     In the above-described embodiments, the descriptions are for the case in which the depressions  21  are formed in the connecting parts  17 a with the arc-shaped walls  92  of the brush holder accommodating section  9  and protrusions  72  are formed in positions of the brush holder unit  7  that correspond to the depressions  21 , and when the brush holder unit  7  is assembled, by placing the protrusions  72  into the depressions  21  of the brush holder accommodating section  9 , positioning of the brush holder unit  7  in the axial direction is done (refer to  FIG. 2 ). These are not restrictions, however, and the peripheral wall  77  of the brush holder unit  7  may be caused to make contact with the stepped wall  93  (refer to  FIG. 4B ) formed between the arc-shaped wall  92  of the brush holder accommodating section  9  and the peripheral wall  81  of the yoke section  8  so as to perform positioning in the axial direction. In this case, the depressions  21  need not be formed in the motor cases  5 ,  205 ,  305 , and  405 , and the protrusions  72  need not be formed in the brush holder unit  7 . 
     Also, in the above-described embodiments, the descriptions are for the case in which a worm reduction mechanism  3  is linked to the electric motor  2 . This is not a restriction, however, and in place of a worm reduction mechanism  3  linked to the electric motor  2 , an actuator mechanism using a trapezoidal screw other external equipment, for example, may be linked thereto. 
     INDUSTRIAL APPLICABILITY 
     The present invention, in addition to enabling the achievement of light weight, compactness, and low cost using the smallest required permanent magnets while reducing the cogging torque, can be applied to an electric motor capable of improving performance, and to a motor with a gear reduction. 
     REFERENCE SYMBOLS 
     
         
           1  Motor with a reduction gear 
           2  Electric motor 
           3  Worm reduction mechanism 
           4  Connector unit 
           5 ,  205 ,  305 ,  405  Motor case 
           6  Armature 
           7  Brush holder unit 
           8 ,  208 ,  308 ,  408  Yoke section (yoke) 
           8   a,    9   a,    208   a  Opening 
           9  Brush holder accommodating section 
           10 ,  310  Permanent magnet 
           11  Bearing section (first bearing section) 
           12  Rotary shaft 
           16  Circular section 
           17  Outer flange 
           17   a  Connecting part 
           21  Depression 
           22  Brush 
           23  Coil spring (resilient member) 
           27  Joint motor (linking part) 
           28  Joint frame 
           29  Joint unit 
           33  Worm shaft 
           34  Worm wheel 
           61  Armature 
           62  Armature coil 
           62   a  Winding 
           63  Commutator 
           65  Teeth 
           66  Slot 
           68  Segment 
           72  Protrusion 
           76  Bearing section (second bearing section) 
           77 ,  81 ,  281 ,  381 ,  481  Peripheral wall 
           77   a,    81   a,    381   a,    481   a  Flat part 
           77   b,    381 b Arc-shaped part 
           82  Bottom wall 
           91  Flat wall 
           92  Arc-shaped wall 
           93  Stepped wall 
           281   a  First flat section 
           281   b  Second flat section 
           311  Positioning protrusion 
           411  Positioning ridge (position protrusion)