Abstract:
An in-wheel motor drive device includes a motor part, a speed reducer part, a wheel bearing part, a casing, and a lubrication mechanism that supplies lubricating oil to the motor and speed reducer parts. A rotation shaft of a motor in the motor part drives an input shaft of a speed reducer. The speed reducer part reduces a rotation speed of the input shaft and transmits the rotation to an output shaft. The lubrication mechanism includes an oil path in the speed reducer part, which discharges oil inside the speed reducer part to the motor part, and an oil path in the motor part, which discharges oil inside the motor part to an oil tank together with the oil from the speed reducer part. The motor part includes a partition plate that guides the oil from the speed reducer part to the oil path in the motor part.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an in-wheel motor drive device, in which, for example, an output shaft of an electric motor and a wheel bearing are connected to each other via a speed reducer. 
       BACKGROUND ART 
       [0002]    There has been known a related-art in-wheel motor drive device having a structure described in, for example, Patent Literature 1. As illustrated in  FIG. 12 , an in-wheel motor drive device  101  described in Patent Literature 1 includes a motor part  103  configured to generate driving force inside a casing  102  to be mounted on a vehicle body via a suspension device (suspension), a wheel bearing part  104  to be connected to a wheel, and a speed reducer part  105  arranged between the motor part  103  and the wheel bearing part  104  and configured to reduce a speed of rotation of the motor part  103  to transmit the rotation to the wheel bearing part  104 . 
         [0003]    In the in-wheel motor drive device  101  having the above-mentioned configuration, a small-sized motor of a low-torque high-rotation type is employed in the motor part  103  from the viewpoint of device compactness. The motor part  103  is a radial gap motor including a stator  106  fixed to the casing  102 , a rotor  107  arranged on a radially inner side of the stator  106  at an opposed position with a gap, and a rotation shaft  108  of the motor, which is arranged on a radially inner side of the rotor  107  to rotate integrally with the rotor  107 . 
         [0004]    Meanwhile, the wheel bearing part  104  requires a large torque for driving the wheel. Therefore, a cycloid speed reducer capable of obtaining a high speed reduction ratio with a compact size is employed in the speed reducer part  105 . The cycloid speed reducer mainly includes an input shaft  110  of the speed reducer having a pair of eccentric portions  109   a  and  109   b , a pair of curved plates  111   a  and  111   b  arranged at the eccentric portions  109   a  and  109   b  of the input shaft  110  of the speed reducer, respectively, a plurality of outer pins  112  configured to engage with outer peripheral surfaces of the curved plates  111   a  and  111   b  to cause rotational motion of the curved plates  111   a  and  111   b , and a plurality of inner pins  114  configured to engage with inner peripheral surfaces of through-holes of the curved plates  111   a  and  111   b  to transmit the rotational motion of the curved plates  111   a  and  111   b  to an output shaft  113  of the speed reducer. 
         [0005]    The in-wheel motor drive device  101  described in Patent Literature 1 includes a lubrication mechanism configured to supply lubricating oil to the motor part  103  and to the speed reducer part  105 . The lubrication mechanism includes a rotary pump  115  configured to force-feed the lubricating oil, and has a structure to circulate the lubricating oil inside the motor part  103  and the speed reducer part  105 . The lubrication mechanism configured to circulate the lubricating oil inside the motor part  103  and the speed reducer part  105  from the rotary pump  115  mainly includes the rotary pump  115 , an oil path  116  in an upper portion of the casing, an oil path  117  in the rotation shaft  108  of the motor, oil holes  118  in the rotor  107 , an oil path  122  in the input shaft  110  of the speed reducer, an oil path  124  in an outer pin housing  123 , oil paths  125  and  119  in a lower portion of the casing, an oil tank  120 , and an oil path  121  in a lower portion of the casing. The outline arrows in the lubrication mechanism indicate lubricating oil flow. 
         [0006]    In the lubrication mechanism having the above-mentioned configuration, when the rotary pump  115  rotates, the lubricating oil stored in the oil tank  120  is sucked through the oil path  121  in the lower portion of the casing into the rotary pump  115  and supplied to the inside of the motor part  103  and the speed reducer part  105 . The lubricating oil force-fed from the rotary pump  115  passes through the oil path  116  in the upper portion of the casing and the oil path  117  in the rotation shaft  108  of the motor and is discharged by pump pressure and centrifugal force through the oil holes  118  of the rotor  107  to cool the stator  106 . Meanwhile, the lubricating oil having passed through the oil path  122  in the input shaft  110  of the speed reducer, which communicates with the oil path  117  in the rotation shaft  108  of the motor, and discharged to the inside of the speed reducer part  105  passes through the oil path  124  in the outer pin housing  123  and the oil path  125  in the lower portion of the casing to reach the motor part  103 . The lubricating oil having cooled the stator  106  is discharged to the oil tank  120  through the oil path  119  in the lower portion of the casing together with the lubricating oil having entered the motor part  103  from the speed reducer part  105 . 
       CITATION LIST 
       [0007]    Patent Literature 1: JP 2011-189919 A 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0008]    Incidentally, the related-art in-wheel motor drive device  101  described above needs to be accommodated inside a wheel of a vehicle and needs to reduce the unsprung weight. Further, downsizing is an essential requirement for providing a large passenger compartment space. Such downsizing of the in-wheel motor drive device itself may cause difficulty in securing enough volume for the oil tank  120  arranged in the lower portion of the casing  102 . Thus, the lubricating oil is stored inside the motor part  103 . The lubricating oil stored inside the motor part  103  is a sum total of the lubricating oil having cooled the motor part  103  and the lubricating oil having lubricated the speed reducer part  105  and entered the motor part  103  through the oil path  125  in the lower portion of the casing. 
         [0009]    When the amount of lubricating oil to be enclosed is increased to secure a necessary amount of lubricating oil for the motor part  103  and the speed reducer part  105 , an oil surface M (see the two-dot chain line of  FIG. 12 ) of the lubricating oil stored inside the motor part  103  becomes higher, with the result that the rotor  107  is partially immersed in the lubricating oil. Further, the rotary pump  115  rotates in synchronization with the output shaft  113  of the speed reducer. Thus, immediately after activation of the motor, the rotation speed of the rotary pump  115  increases with an increase in the motor rotation speed, and the amount of lubricating oil to be discharged from the rotary pump  115  also increases. Therefore, the amount of lubricating oil to be discharged through the oil holes  118  of the rotor  107  also increases. 
         [0010]    Further, the lubricating oil is fluid having viscosity, and the rotor  107  rotates at a high speed of 15,000 min −1  or more. Therefore, the lubricating oil brought into contact with the rotor  107  (lubricating oil in the vicinity of the rotor) is dragged in a rotating direction of the rotor  107  and pulled upward. Further, when the rotation speed of the rotor  107  increases, the amount of lubricating oil brought into contact with the rotor  107  increases, and a load acting between the rotor  107  and the lubricating oil due to the viscosity of the lubricating oil also increases. Therefore, stirring resistance of the lubricating oil increases. 
         [0011]    As illustrated in  FIG. 13 , an increase in stirring resistance may cause the lubricating oil stored inside the motor part  103  to be pulled upward in the rotating direction (see the solid line arrow of  FIG. 13 ) of the rotor  107 . As a result, the oil surface M is significantly inclined with respect to a horizontal plane. The oil tank  120  arranged in the lower portion of the casing  102  is arranged on a rear (close to the right side in  FIG. 13 ) in a traveling direction of a vehicle to cope with a suspension configuration of the vehicle, an inclination of the lubricating oil due to inertia during acceleration and deceleration of the vehicle, and a change in oil surface at the time of ascending a slope. Therefore, when the oil surface M of the lubricating oil is significantly inclined as described above, the lubricating oil becomes less likely to flow into the oil tank  120 . 
         [0012]    As described above, when the lubricating oil stored inside the motor part  103  becomes less likely to flow into the oil tank  120 , the amount of lubricating oil in the oil tank  120  is reduced along with the rotation of the rotary pump  115 . As a result, the amount of lubricating oil to be discharged from the rotary pump  115  is reduced, and hence the rotary pump  115  may be difficult to discharge the necessary amount of lubricating oil for the motor part  103  and the speed reducer part  105 . 
         [0013]    The present invention has been proposed in view of the above-mentioned problems. It is an object of the present invention to provide an in-wheel motor drive device exhibiting high quality and excellent durability through improvement in lubricating performance in the speed reducer part. 
       Solution to Problem 
       [0014]    As a technical measure to achieve the above-mentioned object, according to one embodiment of the present invention, there is provided an in-wheel motor drive device, comprising: a motor part; a speed reducer part; a wheel bearing part; a casing; and a lubrication mechanism configured to supply lubricating oil to the motor part and to the speed reducer part, the speed reducer part being configured to reduce a speed of rotation of a motor in the motor part and transmit the rotation to an output shaft of a speed reducer, and the wheel bearing part being connected to the output shaft of the speed reducer, the lubrication mechanism comprising: an oil path in the speed reducer part, which is configured to discharge lubricating oil inside the speed reducer part to the motor part; and an oil path in the motor part, which is configured to discharge lubricating oil inside the motor part to an oil tank together with the lubricating oil from the speed reducer part, the motor part comprising a partition plate configured to guide the lubricating oil from the speed reducer part to the oil path in the motor part. 
         [0015]    According to the present invention, even when the lubricating oil brought into contact with the rotor of the motor part is dragged in a rotating direction of the rotor and pulled upward, and the stirring resistance increases, the lubricating oil to be discharged to the motor part from the speed reducer part and the lubricating oil to be brought into contact with the rotor can be separated by the partition plate arranged in the motor part. Through such separation, the lubricating oil from the speed reducer part can be guided to the oil path in the motor part without being affected by the dragging of the lubricating oil brought into contact with the rotor. Thus, the lubricating oil from the speed reducer part becomes more likely to flow into the oil tank. Therefore, the amount of discharge of the rotary pump can be secured. As a result, the lubrication performance of the speed reducer part in the in-wheel motor drive device can be improved. 
         [0016]    According to one embodiment of the present invention, it is preferred that the oil path in the speed reducer part extend in an axial direction to communicate with the motor part, that the partition plate be arranged so as to be opposed to the oil path in the speed reducer part, and that the oil path in the motor part be arranged immediately below the partition plate. With such a configuration, the lubricating oil to be discharged to the motor part from the speed reducer part and the lubricating oil to be brought into contact with the rotor can easily be separated. Therefore, the lubricating oil from the speed reducer part can be smoothly guided to the oil path in the motor part. 
         [0017]    According to one embodiment of the present invention, it is preferred that the motor part comprise a stator fixed to the casing and a rotor arranged at the rotation shaft of the motor, and that the partition plate extended toward the rotor have a large number of small holes in an extension portion which is closely arranged so as to be opposed to an oil hole formed in the rotor. With such a configuration, the lubricating oil to be brought into contact with the rotor becomes more likely to flow out through the small holes. Thus, the dragging of the lubricating oil brought into contact with the rotor can be reduced. Therefore, the stirring resistance of the lubricating oil, which is generated by the rotation of the rotor, can be reduced. 
         [0018]    According to one embodiment of the present invention, it is preferred that the partition plate be made of an insulating material. With such a configuration, the partition plate can be arranged close to the stator in the motor part. Thus, a sufficient volume for the motor part can be secured in a range of from the oil path in the speed reducer part to the oil path in the motor part. Therefore, the lubricating oil from the speed reducer part can easily be guided to the oil path in the motor part. 
         [0019]    According to one embodiment of the present invention, it is preferred that the lubrication mechanism comprise a pump configured to force-feed the lubricating oil and an oil tank. With such a configuration, the lubricating oil can easily be supplied to the motor part. 
       Advantageous Effects of Invention 
       [0020]    According to the present invention, even when the lubricating oil brought into contact with the rotor of the motor part is dragged in a rotating direction of the rotor and pulled upward, and the stirring resistance increases, the lubricating oil to be discharged to the motor part from the speed reducer part and the lubricating oil to be brought into contact with the rotor can be separated by the partition plate arranged in the motor part. Through such separation, the lubricating oil from the speed reducer part can be guided to the oil path in the motor part without being affected by the dragging of the lubricating oil brought into contact with the rotor. Thus, the lubricating oil discharged from the speed reducer part to the motor part becomes more likely to flow into the oil tank. Therefore, the amount of discharge of the rotary pump can be secured. As a result, the lubrication performance of the speed reducer part in the in-wheel motor drive device can be improved, thereby being capable of achieving the in-wheel motor drive device exhibiting high quality and excellent durability. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0021]      FIG. 1  is a longitudinal sectional view for illustrating an overall configuration of an in-wheel motor drive device according to an embodiment of the present invention. 
           [0022]      FIG. 2  is a sectional view taken along the line P-P of  FIG. 1 . 
           [0023]      FIG. 3  is an enlarged sectional view for illustrating relevant parts of a speed reducer part of  FIG. 1 . 
           [0024]      FIG. 4  is an explanatory view for illustrating a load acting on a curved plate of  FIG. 1 . 
           [0025]      FIG. 5  is a transverse sectional view for illustrating a rotary pump of  FIG. 1 . 
           [0026]      FIG. 6  is a sectional view taken along the line Q-Q of  FIG. 1 . 
           [0027]      FIG. 7  is a sectional view taken along the line R-R of  FIG. 1 . 
           [0028]      FIG. 8  is a longitudinal sectional view for illustrating an overall configuration of an in-wheel motor drive device according to another embodiment of the present invention. 
           [0029]      FIG. 9  is a sectional view taken along the line S-S of  FIG. 8 . 
           [0030]      FIG. 10  is a plan view for illustrating a schematic configuration of an electric vehicle on which in-wheel motor drive devices are mounted. 
           [0031]      FIG. 11  is a rear sectional view for illustrating the electric vehicle of  FIG. 10 . 
           [0032]      FIG. 12  is a longitudinal sectional view for illustrating an overall configuration of a related-art in-wheel motor drive device. 
           [0033]      FIG. 13  is a sectional view taken along the line T-T of  FIG. 12 . 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0034]    An in-wheel motor drive device according to one embodiment of the present invention is described in detail with reference to the drawings. 
         [0035]      FIG. 10  is a schematic plan view of an electric vehicle  11  on which in-wheel motor drive devices  21  are mounted, and  FIG. 11  is a schematic sectional view of the electric vehicle  11  as viewed from a rear side. As illustrated in  FIG. 10 , the electric vehicle  11  comprises a chassis  12 , front wheels  13  serving as steered wheels, rear wheels  14  serving as driving wheels, and the in-wheel motor drive devices  21  configured to transmit driving force to the rear wheels  14 . As illustrated in  FIG. 11 , each rear wheel  14  is accommodated inside a wheel housing  12   a  of the chassis  12  and fixed below the chassis  12  via a suspension device (suspension)  12   b.    
         [0036]    In the suspension device  12   b , a horizontally extending suspension arm supports the rear wheels  14 , and a strut comprising a coil spring and a shock absorber absorbs vibrations that each rear wheel  14  receives from the ground to suppress vibrations of the chassis  12 . In addition, a stabilizer configured to suppress tilting of a vehicle body during turning and other operations is provided at connecting portions of the right and left suspension arms. In order to improve the property of following irregularities of a road surface to transmit the driving force of the rear wheels  14  to the road surface efficiently, the suspension device  12   b  is an independent suspension type capable of independently moving the right and left wheels up and down. 
         [0037]    The electric vehicle  11  does not need to comprise a motor, a drive shaft, a differential gear mechanism, and other components on the chassis  12  because the in-wheel motor drive devices  21  configured to drive the right and left rear wheels  14 , respectively, are arranged inside the wheel housings  12   a . Accordingly, the electric vehicle  11  has the advantages in that a large passenger compartment space can be provided and that rotation of the right and left rear wheels  14  can be controlled, respectively. It is necessary to reduce the unsprung weight in order to improve traveling stability and NVH characteristics of the electric vehicle  11 . In addition, the in-wheel motor drive device  21  is required to be downsized to provide a large passenger compartment space. 
         [0038]    Therefore, the in-wheel motor drive device  21  of this embodiment has the following structure.  FIG. 1  is a longitudinal sectional view for illustrating a schematic configuration of the in-wheel motor drive device  21 .  FIG. 2  is a sectional view taken along the line P-P of  FIG. 1 .  FIG. 3  is an enlarged sectional view for illustrating a speed reducer part B.  FIG. 4  is an explanatory view for illustrating a load acting on a curved plate  26   a .  FIG. 5  is a transverse sectional view for illustrating a rotary pump  51 . Prior to the description of a characteristic configuration of this embodiment, an overall configuration of the in-wheel motor drive device  21  is described. 
         [0039]    As illustrated in  FIG. 1 , the in-wheel motor drive device  21  comprises a motor part A configured to generate driving force, the speed reducer part B configured to reduce a speed of rotation of the motor part A to output the rotation, and a wheel bearing part C configured to transmit the output from the speed reducer part B to the rear wheels  14  (see  FIG. 10  and  FIG. 11 ) serving as driving wheels. The motor part A and the speed reducer part B are accommodated in a casing  22  and mounted inside the wheel housing  12   a  (see  FIG. 11 ) of the electric vehicle  11 . The casing  22  has a divided structure constructed by a motor housing accommodating the motor part A and a speed reducer housing accommodating the speed reducer part B, and is unified through fastening with a bolt. 
         [0040]    The motor part A is a radial gap motor comprising a stator  23   a  fixed to the casing  22 , a rotor  23   b  arranged on a radially inner side of the stator  23   a  at an opposed position with a gap, and a rotation shaft  24  of the motor, which is arranged on a radially inner side of the rotor  23   b  so as to rotate integrally with the rotor  23   b . The stator  23   a  is constructed by winding a coil  23   d  on an outer periphery of a magnetic core  23   c , and the rotor  23   b  is constructed by a permanent magnet or a magnetic member. The rotor  23   b  rotates at a high speed of 15,000 min −1  or more through energization with respect to the coil  23   d  of the stator  23   a.    
         [0041]    The rotation shaft  24  of the motor has a holder portion  24   d , which integrally extends toward a radially outer side, to hold the rotor  23   b . The holder portion  24   d  has a configuration with an annularly formed concave groove having the rotor  23   b  fitted and fixed therein. The rotation shaft  24  of the motor is rotatably supported by a rolling bearing  36   a  at one end portion in its axial direction (right side in  FIG. 1 ) and by a rolling bearing  36   b  at another end portion in the axial direction (left side in  FIG. 1 ) with respect to the casing  22 . 
         [0042]    An input shaft  25  of the speed reducer is rotatably supported by a rolling bearing  37   a  at one approximately central portion in its axial direction (right side in  FIG. 1 ) and by a rolling bearing  37   b  at another end portion in the axial direction (left side in  FIG. 1 ) with respect to an output shaft  28  of the speed reducer. The input shaft  25  of the speed reducer has eccentric portions  25   a  and  25   b  inside the speed reducer part B. The two eccentric portions  25   a  and  25   b  are arranged with a 180° phase shift to mutually cancel out centrifugal force caused by eccentric motion. The input shaft  25  of the speed reducer and the above-mentioned rotation shaft  24  of the motor are connected to each other by spline fitting, and driving force of the motor part A is transmitted to the speed reducer part B. 
         [0043]    The speed reducer part B comprises curved plates  26   a  and  26   b  serving as revolving members rotatably held at the eccentric portions  25   a  and  25   b  of the input shaft  25  of the speed reducer, a plurality of outer pins  27  configured to engage with outer peripheral portions of the curved plates  26   a  and  26   b , a motion conversion mechanism configured to transmit rotational motion of the curved plates  26   a  and  26   b  to the output shaft  28  of the speed reducer, and a counterweight  29 , which is arranged at the input shaft  25  of the speed reducer and adjacent to the eccentric portions  25   a  and  25   b.    
         [0044]    The output shaft  28  of the speed reducer comprises a flange portion  28   a  and a shaft portion  28   b . A plurality of inner pins  31  are fixed to the flange portion  28   a  at equal intervals on a circumference about a rotation axis of the output shaft  28  of the speed reducer. Further, the shaft portion  28   b  is connected to a hub wheel  32  serving as an inner member of the wheel bearing part C by spline fitting so as to transmit torque, and is configured to transmit output of the speed reducer part B to the rear wheel  14 . The output shaft  28  of the speed reducer is rotatably supported on an outer pin housing  60  by rolling bearings  46 . 
         [0045]    As illustrated in  FIG. 2  and  FIG. 3 , the curved plates  26   a  and  26   b  have a plurality of wave patterns formed of trochoidal curves such as epitrochoidal curves in the outer peripheral portions, and through-holes  30   a  and  30   b  each extending from one end surface to another end surface. The plurality of through-holes  30   a  are formed at equal intervals on the circumference about the rotation axis of the curved plates  26   a  and  26   b  and are configured to receive the above-mentioned inner pins  31 . The through-hole  30   b  is formed at a center of each of the curved plates  26   a  and  26   b , and the eccentric portions  25   a  and  25   b  are fitted therein. 
         [0046]    The curved plates  26   a  and  26   b  are rotatably supported by rolling bearings  41  with respect to the eccentric portions  25   a  and  25   b , respectively. The rolling bearing  41  is a cylindrical roller bearing comprising an inner ring  42  being fitted onto each of the outer peripheral surfaces of the eccentric portions  25   a  and  25   b  and having an inner raceway surface  42   a  formed on the outer peripheral surface, an outer raceway surface  43  directly formed at the inner peripheral surface of the through-hole  30   b  of each of the curved plates  26   a  and  26   b , a plurality of cylindrical rollers  44  arranged between the inner raceway surface  42   a  and the outer raceway surface  43 , and a cage  45  configured to retain the cylindrical rollers  44 . The inner ring  42  has a flange portion  42   b  projecting toward a radially outer side from both ends of the inner raceway surface  42   a  in the axial direction. 
         [0047]    The outer pins  27  are provided at equal intervals on the circumference about the rotation axis of the input shaft  25  of the speed reducer. As a result of revolving motion of the curved plates  26   a  and  26   b , curved wave patterns are engaged with the outer pins  27  to cause rotational motion of the curved plates  26   a  and  26   b . The outer pins  27  are held rotatably on the outer pin housing  60  by needle roller bearings  27   a , and the outer pin housing  60  is mounted to the casing  22  under a floating state (not shown) of being rotationally stopped and elastically supported. With this, contact resistance between the outer pins  27  and the curved plate  26   a  and between the outer pins  27  and the curved plate  26   b  can be reduced. 
         [0048]    The counterweight  29  has an approximately fan shape, has a through-hole into which the input shaft  25  of the speed reducer is fitted, and is arranged at a position adjacent to each of the eccentric portions  25   a  and  25   b  with a 180° phase shift with respect to the eccentric portions  25   a  and  25   b  in order to cancel out unbalanced inertia couple caused by the rotation of the curved plates  26   a  and  26   b . When a central point in the rotation axis direction between the two curved plates  26   a  and  26   b  is denoted by G (see  FIG. 3 ), a relationship of L 1 ×m 1 ×ε 1 =L 2 ×m 2 ×ε 2  is satisfied on the right side of the central point G, where L 1  is the distance between the central point G and the center of the curved plate  26   a , m 1  is the sum of the mass of the curved plate  26   a , the mass of the rolling bearing  41 , and the mass of the eccentric portion  25   a, ε   1  is the amount of eccentricity of the center of gravity of the curved plate  26   a  from the rotation axis, L 2  is the distance between the central point G and the counterweight  29 , m 2  is the mass of the counterweight  29 , and ε 2  is the amount of eccentricity of the center of gravity of the counterweight  29  from the rotation axis. The relationship of L 1 ×m 1 ×ε 1 =L 2 ×m 2 ×ε 2  allows for inevitably occurring errors. The same relationship is established between the curved plate  26   b  and the counterweight  29  on the left side of the central point G. 
         [0049]    The motion conversion mechanism comprises the plurality of inner pins  31 , which are held on the output shaft  28  of the speed reducer and extend in the axis direction, and the through-holes  30   a  formed in the curved plates  26   a  and  26   b . The inner pins  31  are provided at equal intervals on the circumference about the rotation axis of the output shaft  28  of the speed reducer, and each have one end in the axial direction fixed to the flange portion  28   a  of the output shaft  28  of the speed reducer. In order to reduce the frictional resistance between the inner pins  31  and the curved plate  26   a  and between the inner pins  31  and the curved plate  26   b , needle roller bearings  31   a  are provided at positions of contact with the inner wall surfaces of the through-holes  30   a  in the curved plates  26   a  and  26   b . The through-holes  30   a  are arranged at positions corresponding to the plurality of inner pins  31 , respectively, and an inner diameter of each through-hole  30   a  is set larger by a predetermined dimension than an outer diameter of each inner pin (maximum diameter including the needle roller bearings  31   a ). 
         [0050]    A stabilizer  31   b  is provided at other ends of the inner pins  31  in the axial direction. The stabilizer  31   b  comprises an annular portion  31   c  having a circular ring shape, and a cylindrical portion  31   d  extending in the axial direction from the inner peripheral surface of the annular portion  31   c . The other ends of the plurality of inner pins  31  in the axial direction are fixed to the annular portion  31   c . The load applied to some of the inner pins  31  from the curved plates  26   a  and  26   b  is supported by all the inner pins  31  through the flange portion  28   a  and the stabilizer  31   b . Therefore, the stress acting on the inner pins  31  can be reduced, thereby being capable of improving the durability. 
         [0051]    The state of the load acting on each of the curved plates  26   a  and  26   b  is described with reference to  FIG. 4 . An axial center O 2  of the eccentric portion  25   a  is eccentric with respect to an axial center O of the input shaft  25  of the speed reducer by an amount of eccentricity e. The curved plate  26   a  is mounted to the outer periphery of the eccentric portion  25   a , and the eccentric portion  25   a  rotatably supports the curved plate  26   a . Accordingly, the axial center O 2  is also an axial center of the curved plate  26   a . The outer periphery of the curved plate  26   a  is formed of a wavy curve, and the curved plate  26   a  has radially concave and wavy recesses  26   c  equiangularly. On the periphery of the curved plate  26   a , the plurality of outer pins  27  configured to engage with the recesses  26   c  are arranged in the circumferential direction about the axial center O. 
         [0052]    In  FIG. 4 , when the eccentric portion  25   a  rotates in a counterclockwise direction on the drawing sheet together with the input shaft  25  of the speed reducer, the eccentric portion  25   a  revolves about the axial center O. Therefore, the recesses  26   c  of the curved plate  26   a  successively come into circumferential contact with the outer pins  27 . As a result, as indicated by the arrows, the curved plate  26   a  is subjected to a load Fi from each of the plurality of outer pins  27  to rotate in a clockwise direction. 
         [0053]    The curved plate  26   a  has the plurality of through-holes  30   a  formed in the circumferential direction about the axial center O 2 . The inner pin  31  configured to be joined to the output shaft  28  of the speed reducer, which is arranged coaxially with the axial center O, is inserted through each through-hole  30   a . The inner diameter of each through-hole  30   a  is larger by a predetermined dimension than the outer diameter of each inner pin  31 , and hence the inner pins  31  do not impede the revolving motion of the curved plate  26   a , and the inner pins  31  utilize the rotational motion of the curved plate  26   a  to allow the output shaft  28  of the speed reducer to rotate. Then, the output shaft  28  of the speed reducer has a higher torque and a lower number of rotations than the input shaft  25  of the speed reducer, and the curved plate  26   a  is subjected to a load Fj from each of the plurality of inner pins  31 , as indicated by the arrows in  FIG. 4 . A resultant force Fs of the plurality of loads Fi and Fj is applied to the input shaft  25  of the speed reducer. 
         [0054]    The direction of the resultant force Fs varies depending on the geometric conditions such as the wavy shape of the curved plate  26   a  and the number of the recesses  26   c , and on the effect of centrifugal force. Specifically, an angle α formed between the resultant force Fs and a reference line X that is orthogonal to a straight line Y connecting the rotation axial center O 2  and the axial center O and passes through the axial center O 2  varies within a range of from approximately 30° to approximately 60°. The plurality of loads Fi and Fj vary in load direction and load magnitude during one rotation (360°) of the input shaft  25  of the speed reducer. As a result, the resultant force Fs acting on the input shaft  25  of the speed reducer also varies in load direction and load magnitude. One rotation of the input shaft  25  of the speed reducer in the counterclockwise direction causes speed reduction of the wavy recesses  26   c  of the curved plate  26   a  and rotation of the curved plate  26   a  by one pitch in the clockwise direction, resulting in the state of  FIG. 4 . This process is repeated. 
         [0055]    As illustrated in  FIG. 1 , a bearing  33  for the wheel in the wheel bearing part C is a double-row angular contact ball bearing comprising an inner member, an outer ring  33   b , a plurality of balls  33   c , a cage  33   d , and sealing members  33   e . The inner member is constructed by the hub wheel  32  having an inner raceway surface  33   f  directly formed on an outer peripheral surface thereof, and an inner ring  33   a  which is fitted over a small-diameter step portion  32   a  of the outer peripheral surface of the hub wheel  32  and has an inner raceway surface  33   g  formed on an outer peripheral surface of the inner ring  33   a . The outer ring  33   b  is fitted and fixed to an inner peripheral surface of the casing  22 , and has outer raceway surfaces  33   h  and  33   i  formed on an inner peripheral surface thereof. The plurality of balls  33   c  serve as rolling elements arranged between the inner raceway surface  33   f  of the hub wheel  32  and the outer raceway surface  33   h  of the outer ring  33   b , and between the inner raceway surface  33   g  of the inner ring  33   a  and the outer raceway surface  33   i  of the outer ring  33   b . The cage  33   d  is configured to hold a space between the adjacent balls  33   c . The sealing members  33   e  are configured to seal the bearing  33  for the wheel from both ends in the axial direction. The rear wheel  14  is connected and fixed to the hub wheel  32  of the bearing  33  for the wheel by a bolt  34 . 
         [0056]    Next, the entire lubrication mechanism is described. The lubrication mechanism is configured to supply lubricating oil to the motor part A to cool the motor part A, and is configured to supply the lubricating oil to the speed reducer part B. As illustrated in  FIG. 1 , the lubrication mechanism mainly comprises the rotary pump  51 , oil paths  22   a ,  24   a , and  24   b  and oil holes  24   c  formed in the motor part A, an oil path  25   c  and oil holes  25   d  and  25   e  formed in the speed reducer part B, and an oil tank  22   d  arranged in a lower portion of the casing  22 . A suction port  55  and a discharge port  56  of the above-mentioned rotary pump  51  are formed in the motor housing of the casing  22 . Further, the oil tank  22   d  is formed integrally with the motor housing of the casing  22 . 
         [0057]    The oil path  22   a  formed in the casing  22  extends from the rotary pump  51  toward a radially outer side and is bent to extend in the axial direction. The oil path  22   a  is further bent to extend toward a radially inner side to be connected to the oil path  24   a . The oil path  24   a  extends inside the rotation shaft  24  of the motor along the axial direction to be connected to the oil path  25   c . The oil paths  24   b  of the rotation shaft  24  of the motor communicate with the oil path  24   a  extending along the axial direction, and extend to the holder portion  24   d  located on the radially outer side to communicate with a gap  24   e  formed between the holder portion  24   d  and the rotor  23   b . The oil holes  24   c  are formed in end surfaces of the holder portion  24   d  on an in-board side and an out-board side and communicate with the gap  24   e  between the holder portion  24   d  and the rotor  23   b  to be open to the inside of the motor part A. 
         [0058]    The oil path  25   c  extends inside the input shaft  25  of the speed reducer along the axial direction. The oil holes  25   d  communicate with the oil path  25   c  extending along the axial direction, and extend toward the outer peripheral surface of the input shaft  25  of the speed reducer to be open to the inside of the speed reducer part B. The oil hole  25   e  communicates with the oil path  25   c  extending along the axial direction, and is open to the inside of the speed reducer part B from an axial end of the input shaft  25  of the speed reducer. 
         [0059]    Between the motor part A and the speed reducer part B of the casing  22 , there is formed an oil path  22   b  which communicates with the inside of the motor part A and the inside of the speed reducer part B. In a bottom portion of the casing  22  at a position of the motor part A, there is formed an oil path  22   f  configured to discharge the lubricating oil inside the motor part A to the oil tank  22   d . The oil tank  22   d  is arranged at a lower position of the casing  22  on a rear (close to the right side in  FIG. 6 ) in a traveling direction of a vehicle to cope with a suspension configuration of the vehicle, an inclination of the lubricating oil due to inertia during acceleration and deceleration of the vehicle, and a change in oil surface at the time of ascending a slope. Further, the casing  22  has an oil path  22   e  configured to return the lubricating oil from the oil tank  22   d  to the rotary pump  51 . The rotary pump  51  configured to forcibly circulate the lubricating oil is arranged between the oil path  22   e  and the oil path  22   a  of the casing  22 . 
         [0060]    As illustrated in  FIG. 5 , the rotary pump  51  is a cycloid pump comprising an inner rotor  52  configured to rotate using the rotation of the output shaft  28  of the speed reducer (see  FIG. 1 ), an outer rotor  53  configured to be driven to rotate in conjunction with the rotation of the inner rotor  52 , pump chambers  54 , the suction port  55  communicating with the oil path  22   e , and the discharge port  56  communicating with the oil path  22   a . An increase in size of the in-wheel motor drive device  21  can be prevented by arranging the rotary pump  51  inside the casing  22 . 
         [0061]    The outer peripheral surface of the inner rotor  52  has a tooth profile formed of cycloid curves. To be more specific, each tooth tip portion  52   a  has an epicycloid curve shape, and each tooth groove portion  52   b  has a hypocycloid curve shape. The inner rotor  52  is fitted to the outer peripheral surface of the cylindrical portion  31   d  (see  FIG. 1  and  FIG. 3 ) provided to the stabilizer  31   b  to rotate integrally with the output shaft  28  of the speed reducer. The inner peripheral surface of the outer rotor  53  has a tooth profile formed of cycloid curves. To be more specific, each tooth tip portion  53   a  has a hypocycloid curve shape, and each tooth groove portion  53   b  has an epicycloid curve shape. The outer rotor  53  is rotatably supported in the casing  22 . 
         [0062]    The inner rotor  52  rotates about a rotation center c 1 , whereas the outer rotor  53  rotates about a rotation center c 2 . The inner rotor  52  and the outer rotor  53  rotate about the different rotation centers c 1  and c 2 , and hence the volume of each pump chamber  54  changes continuously. Thus, the lubricating oil flowing through the suction port  55  is force-fed through the discharge port  56  to the oil path  22   a.    
         [0063]    A flow of the lubricating oil with the lubrication mechanism having the above-mentioned configuration is described. In  FIG. 1 , the outline arrows in the lubrication mechanism indicate the flow of the lubricating oil. To cool the motor part A, the lubricating oil force-fed from the rotary pump  51  flows through the oil paths  22   a  and  24   a , and partially passes through the oil path  24   b  and the gap  24   e  by centrifugal force caused by rotation of the rotation shaft  24  of the motor and by pump pressure, thereby cooling the rotor  23   b . Further, the lubricating oil is discharged through the oil holes  24   c  of the holder portion  24   d , thereby cooling the stator  23   a . The motor part A is cooled in such a manner. 
         [0064]    Meanwhile, to lubricate the speed reducer part B, the lubricating oil force-fed from the rotary pump  51  passes through the oil paths  22   a ,  24   a , and  25   c , and is partially discharged through the oil holes  25   d  and  25   e  to the speed reducer part B by centrifugal force caused by rotation of the input shaft  25  of the speed reducer and pump pressure. The lubricating oil having been discharged through the oil holes  25   d  is supplied through oil holes  42   c  (see  FIG. 3 ), which are formed in the inner rings  42  of the cylindrical rolling bearings  41  configured to support the curved plates  26   a  and  26   b , to the inside of the bearing. Further, the lubricating oil moves to the radially outer side through an oil path  60   a  formed in the outer pin housing  60  while lubricating abutment portions of the curved plates  26   a  and  26   b  with the inner pins  31  and the outer pins  27 . The lubricating oil discharged through the oil holes  25   e  is supplied to, for example, the rolling bearing  37   b  configured to support the input shaft  25  of the speed reducer. The speed reducer part B is lubricated in such a manner. 
         [0065]    The lubricating oil having cooled the motor part A and lubricated the speed reducer part B moves to a lower portion along the inner wall surface of the casing  22  by the gravity. The lubricating oil having moved to the lower portion of the speed reducer part B moves to the motor part A through the oil path  22   b . Further, the lubricating oil having moved to the lower portion of the motor part A, together with the lubricating oil from the speed reducer part B, is discharged through the oil path  22   f  and temporarily stored in the oil tank  22   d . As described above, the oil tank  22   d  is arranged, and hence the lubricating oil which cannot temporarily be discharged by the rotary pump  51  can be stored in the oil tank  22   d . As a result, an increase in torque loss of the speed reducer part B can be prevented. 
         [0066]    The overall configuration of the in-wheel motor drive device  21  of this embodiment is as described above. Characteristic configurations thereof are described below. 
         [0067]    With regard to the in-wheel motor drive device  21  of this embodiment, it has been conceived to provide a partition plate  80 , which is configured to guide the lubricating oil from the speed reducer part B to the oil path  22   f  in the motor part A, to the motor part A. As illustrated in  FIG. 6  and  FIG. 7 , the partition plate  80  has an arcuate band plate shape and is arranged so as to be opposed to the two oil paths  22   b , which are formed in the casing  22  located between the motor part A and the speed reducer part B, in the axial direction. The oil path  22   f  extending to the oil tank  22   d  is formed at a part immediately below the partition plate  80  and close to one of the oil paths  22   b.    
         [0068]    The partition plate  80  has an outer peripheral portion which is arranged closely along an inner wall surface of the casing  22 , and an inner peripheral portion which is arranged on the out-board side of the holder portion  24   d  for the rotor  23   b  so as to be opposed to the oil hole  24   c  of the holder portion  24   d  for the rotor  23   b  (see  FIG. 1 ). The partition plate  80  is fixed at a predetermined location of the casing  22  in an appropriate manner such as fastening with a screw. A material of the partition plate  80  may be a metal having a nonmagnetic property or a resin having an insulating property. 
         [0069]    The in-wheel motor drive device  21  needs to be accommodated inside a wheel of a vehicle and needs to reduce the unsprung weight. Further, downsizing is an essential requirement for providing a large passenger compartment space. Such downsizing of the in-wheel motor drive device itself may cause difficulty in securing enough volume for the oil tank  22   d  arranged in the lower portion of the casing  22 . Thus, the lubricating oil is stored inside the motor part A. The lubricating oil stored inside the motor part A is a sum total of the lubricating oil having cooled the motor part A and the lubricating oil having lubricated the speed reducer part B and entered the motor part A through the oil hole  22   b.    
         [0070]    When the amount of the lubricating oil to be enclosed is increased to secure a necessary amount of the lubricating oil for the motor part A and the speed reducer part B, as illustrated in  FIG. 1 , an oil surface N of the lubricating oil stored inside the motor part A becomes higher, with the result that the rotor  23   b  is partially immersed in the lubricating oil. Further, the rotary pump  51  rotates in synchronization with the output shaft  28  of the speed reducer. Thus, immediately after activation of the motor, the rotation speed of the rotary pump  51  increases with an increase in motor rotation speed, and the amount of lubricating oil to be discharged from the rotary pump  51  also increases. Therefore, the amount of lubricating oil to be discharged through the oil holes  24   c  of the holder portion  24   d  of the rotor  23   b  also increases. 
         [0071]    Further, the lubricating oil is fluid having viscosity, and the rotor  23   b  rotates at a high speed of 15,000 min −1  or more. Therefore, the lubricating oil brought into contact with the holder portion  24   d  for the rotor  23   b  (lubricating oil which is present in the vicinity of the holder portion) is dragged in a rotating direction of the rotor  23   b  and pulled upward, and hence the oil surface N of the lubricating oil is significantly inclined with respect to a horizontal plane. When the oil surface N of the lubricating oil brought into contact with the holder portion  24   d  for the rotor  23   b  is significantly inclined as described above, the lubricating oil becomes less likely to flow into the oil tank  22   d.    
         [0072]    In the in-wheel motor drive device  21  according to this embodiment, the partition plate  80  is interposed between a region comprising the holder portion  24   d  for the rotor  23   b  and the stator  23   a  and a region comprising the oil path  22   b  located between the speed reducer part B and the motor part A. Thus, the lubricating oil to enter the motor part A from the speed reducer part B through the oil path  22   b  and the lubricating oil to be brought into contact with the holder portion  24   d  for the rotor  23   b  can be separated. Through such separation, the lubricating oil from the speed reducer part B can be smoothly guided to the oil path  22   f  in the motor part A without being affected by the dragging of the lubricating oil brought into contact with the holder portion  24   d  for the rotor  23   b . As a result, even when the oil tank  22   d  is arranged on a rear (close to the right side in  FIG. 6 ) in the traveling direction of a vehicle, the lubricating oil from the speed reducer part B becomes more likely to flow into the oil tank  22   d . Therefore, the amount of discharge of the rotary pump  51  can be secured. As a result, the lubrication performance of the speed reducer part B in the in-wheel motor drive device  21  can be improved. 
         [0073]    The partition plate  80  is also arranged close to the coil  23   d  of the stator  23   a . In a case where the material of the partition plate  80  is a nonmagnetic metal, it is necessary to set an axial gap with the coil  23   d  of the stator  23   a  to a minimum dimension which prevents a flow of current to the partition plate  80 . Therefore, it is effective to have an insulating resin as the material of the partition plate  80 . When the partition plate  80  is made of a resin, the partition plate  80  can easily be arranged close to the coil  23   d  of the stator  23   a . Thus, a sufficient volume for the motor part A can be secured in a range of from the oil path  22   b  in the speed reducer part B to the oil path  22   f  in the motor part A. Therefore, the lubricating oil from the speed reducer part B can easily be guided to the oil path  22   f  in the motor part A. 
         [0074]      FIG. 8  is an illustration of an overall configuration of the in-wheel motor drive device  21  according to another embodiment of the present invention, and characteristic configurations thereof are described below. 
         [0075]    With regard to the in-wheel motor drive device  21  according to this embodiment, the inner peripheral portion of the partition plate  80  described above is extended toward a radially inner side, and an extension portion  81  is arranged close to the holder portion  24   d  for the rotor  23   b . As illustrated in  FIG. 9 , the extension portion  81  of the partition plate  80  has a semi-circular band plate shape opposed to a lower half of the rotor  23   b . As described above, when the extension portion  81  of the partition plate  80  is arranged close to the holder portion  24   d  for the rotor  23   b , the amount of lubricating oil to be dragged by the rotation of the rotor  23   b  is reduced through limitation to the lubricating oil interposed between the holder portion  24   d  for the rotor  23   b  and the extension portion  81  of the partition plate  80 . Therefore, the dragging of the lubricating oil can be reduced. 
         [0076]    As described above, dragging of the lubricating oil can be reduced, and hence the stirring resistance of the lubricating oil generated by the rotation of the rotor  23   b  can be reduced. The stirring resistance of the lubricating oil is reduced, and hence, even when the lubricating oil stored inside the motor part A is pulled in the rotating direction of the rotor  23   b , an inclination of the oil surface N of the lubricating oil may be smaller. As a result, even when the oil tank  22   d  is arranged on a rear in the traveling direction of a vehicle (close to the right side in  FIG. 9 ), the lubricating oil becomes more likely to flow into the oil tank  22   d . The amount of discharge of the rotary pump  51  can be secured by sufficiently securing the amount of lubricating oil in the oil tank  22   d . Therefore, the lubricating performance of the motor part A in the in-wheel motor drive device  21  can be improved. 
         [0077]    When the extension portion  81  of the partition plate  80  is to be arranged close to the holder portion  24   d  of the rotor  23   b  in the axial direction, the axial oscillation of the rotor  23   b  rotating at high speed needs to be taken into account. The axial gap between the holder portion  24   d  of the rotor  23   b  and the extension portion  81  of the partition plate  80  is only necessary to be set to the extent that interference with the rotor  23   b  due to the axial oscillation of the rotor  23   b  can be avoided. 
         [0078]    Further, the extension portion  81  of the partition plate  80  has a large number of small holes  82  formed in a scattered dot pattern. Through formation of the large number of small holes  82  in the extension portion  81  of the partition plate  80 , the lubricating oil having been discharged through the oil hole  24   c  of the holder portion  24   d  for the rotor  23   b  and being present on the rotor side of the extension portion  81  of the partition plate  80  becomes more likely to flow through the small holes  82  into the motor part A arranged on the non-rotor side with respect to the extension portion  81  of the partition plate  80 . As a result, an increase in amount of lubricating oil interposed between the holder portion  24   d  for the rotor  23   b  and the extension portion  81  of the partition plate  80  is prevented. Therefore, it contributes to reduction of the dragging of the lubricating oil and to reduction of the stirring resistance. 
         [0079]    Lastly, the overall operation principle of the in-wheel motor drive device  21  of this embodiment is described. 
         [0080]    As illustrated in  FIG. 1  to  FIG. 3 , in the motor part A, for example, the coil of the stator  23   a  is supplied with AC current to generate electromagnetic force, which in turn allows the rotor  23   b  formed of a permanent magnet or a magnetic member to rotate. The input shaft  25  of the speed reducer, which is connected to the rotation shaft  24  of the motor, therefore rotates to cause the curved plates  26   a  and  26   b  to revolve about the rotation axis of the input shaft  25  of the speed reducer. Then, the outer pins  27  come into engagement with the curved wave patterns of the curved plates  26   a  and  26   b  to allow the curved plates  26   a  and  26   b  to rotate on their axes in a direction reverse to the rotation of the input shaft  25  of the speed reducer. 
         [0081]    The inner pins  31  inserted through the through-holes  30   a  come into contact with the inner wall surfaces of the through-holes  30   a  in conjunction with the rotational motion of the curved plates  26   a  and  26   b . The revolving motion of the curved plates  26   a  and  26   b  is therefore prevented from being transmitted to the inner pins  31 , and only the rotational motion of the curved plates  26   a  and  26   b  is transmitted to the wheel bearing part C through the output shaft  28  of the speed reducer. In this process, the speed of the rotation of the input shaft  25  of the speed reducer is reduced by the speed reducer part B, and the rotation is transmitted to the output shaft  28  of the speed reducer. Therefore, a necessary torque can be transmitted to the rear wheels  14  even in a case where the motor part A of a low-torque high-rotation type is employed. 
         [0082]    When the number of the outer pins  27  and the number of wave patterns of the curved plates  26   a  and  26   b  are denoted by Z A  and Z B , respectively, the speed reduction ratio in the speed reducer part B is calculated by (Z A −Z B )/Z B . In the embodiment illustrated in  FIG. 2 , Z A =12 and Z B =11 are given. Thus, a very high speed reduction ratio of 1/11 can be obtained. The in-wheel motor drive device  21  that is compact and has a high speed reduction ratio can be obtained by using the speed reducer part B capable of obtaining a high speed reduction ratio without requiring a multi-stage configuration. Moreover, the needle roller bearings  27   a  and  31   a  are provided to the outer pins  27  and the inner pins  31 , respectively (see  FIG. 3 ), to reduce the frictional resistance between those pins and the curved plates  26   a  and  26   b , thereby improving the transmission efficiency of the speed reducer part B. 
         [0083]    In this embodiment, there has been exemplified a case where the oil path  24   b  is formed in the rotation shaft  24  of the motor, the oil hole  25   d  is formed in each of the eccentric portions  25   a  and  25   b , and the oil hole  25   e  is formed in the axial end of the input shaft  25  of the speed reducer. The present invention is not limited thereto, and the oil paths and holes may be formed at any positions in the rotation shaft  24  of the motor and the input shaft  25  of the speed reducer. Further, there has been given an example in which a cycloid pump is used as the rotary pump  51 , but the present invention is not limited thereto. Any rotary pump that is driven using the rotation of the output shaft  28  of the speed reducer may be employed. Further, the rotary pump  51  may be omitted so that the lubricating oil is circulated only by centrifugal force. 
         [0084]    There has been given an example in which the two curved plates  26   a  and  26   b  of the speed reducer part B are arranged with a 180° phase shift. However, the number of curved plates may be arbitrarily set. In a case where three curved plates are arranged, for example, the three curved plates may be arranged with a 120° phase shift. There has been given an example in which the motion conversion mechanism comprises the inner pins  31  fixed to the output shaft  28  of the speed reducer and the through-holes  30   a  formed in the curved plates  26   a  and  26   b . However, the present invention is not limited thereto. Any configuration may be applied as long as the rotation of the speed reducer part B can be transmitted to the hub wheel  32 . For example, the motion conversion mechanism may comprise inner pins fixed to the curved plates  26   a  and  26   b  and holes formed in the output shaft  28  of the speed reducer. With regard to the in-wheel motor drive device  21  of this embodiment, there has been given an example in which the speed reducer of the cycloid type is employed. However, the present invention is not limited thereto. A planetary speed reducer, a parallel shaft speed reducer, and other speed reducers are applicable. 
         [0085]    The description as to the operation in this embodiment focuses on the rotation of each member. In fact, however, power containing a torque is transmitted from the motor part A to the rear wheels  14 . Accordingly, the power after speed reduction as described above is converted into a high torque. There has been given a case where electric power is supplied to the motor part A to drive the motor part and the power from the motor part A is transmitted to the rear wheels  14 . Contrary to this, however, when a vehicle decelerates or descends a slope, power from the rear wheel  14  side may be converted at the speed reducer part B into high-rotation low-torque rotation so that the rotation is transmitted to the motor part A for electric power generation in the motor part A. Further, the electric power generated in the motor part A may be stored in a battery so that the electric power is used to drive the motor part A later or to operate other electric devices provided in the vehicle. 
         [0086]    In this embodiment, there has been given an example in which a radial gap motor is employed in the motor part A. However, the present invention is not limited thereto, and a motor having arbitrary configuration is applicable. For example, there may be used an axial gap motor comprising a stator to be fixed to a casing, and a rotor arranged on the inner side of the stator at an opposed position with an axial gap. In addition, there has been given an example in which the rear wheels  14  of the electric vehicle  11  illustrated in  FIG. 9  and  FIG. 10  serve as driving wheels. However, the present invention is not limited thereto, and the front wheels  13  may be used as driving wheels or a four-wheel drive vehicle may be used. It should be understood that “electric vehicle” as used herein is a concept encompassing all vehicles that may obtain driving force from electric power and also encompasses, for example, a hybrid car. 
         [0087]    The present invention is not limited to the above-mentioned embodiment. As a matter of course, the present invention may be carried out in various modes without departing from the gist of the present invention. The scope of the present invention is defined in the scope of claims, and encompasses equivalents described in claims and all changes within the scope of claims.