Abstract:
The present structure does not require a knuckle on the vehicle body side, improves rotational accuracy of an input shaft of a speed reduction unit, increases durability of bearings, and suppresses rotation noise of the bearings by improving the supporting structure of the input shaft of the speed reduction unit. In a drive device for an electric vehicle comprising: a speed reduction unit including an input shaft driven by an electric motor; a hub unit rotationally driven by an output member of the speed reduction unit; and a housing accommodating the electric motor and the speed reduction unit, wherein the input shaft of the speed reduction unit is supported by bearings provided at two locations in the axial direction, the drive device is configured such that the bearings provided at the two locations are both supported by the output member, and the housing is provided with a suspension joining portion.

Description:
TECHNICAL FIELD  
       [0001]    The present invention relates to a drive device for an electric vehicle including an electric motor as a drive source, and particularly to a drive device for an electric vehicle of an in-wheel motor type. 
       BACKGROUND ART 
       [0002]    A conventionally known drive device for an electric vehicle of an in-wheel motor type is made up of an electric motor, a speed reduction unit to which the output of the electric motor is inputted, and a hub unit which is rotationally driven by the speed-reduced output of the speed reduction unit (Patent Literature 1). 
         [0003]    In the drive device for an electric vehicle disclosed in Patent Literature 1, an electric motor is disposed outside the speed reduction unit in the radial direction, and the speed reduction unit in which planetary gear-type units are disposed in two stages in the axial direction is used. The reason why the speed reduction unit is disposed in two stages is for the purpose of increasing the speed reduction ratio. 
         [0004]    A typical configuration of a speed reduction unit of planetary gear type is such that a sun gear is provided on an input shaft in a coaxial manner, and a ring gear is secured around the input shaft in a coaxial manner. A plurality of pinion gears are placed between the sun gear and the ring gear, and a pinion pin that supports each pinion gear is joined to a common carrier. The carrier is integrated with an output member. 
         [0005]    The speed reduction unit is configured such that the pinion gear is caused to revolve while rotating on its axis by the rotation of the input shaft. The rotational speed of the revolving motion is reduced from the rotational speed of the input shaft, and a speed-reduced rotation is transferred to the output member via the carrier. The speed reduction ratio in this case will be Zs/(Zs+Zr). Where, Zs is the number of teeth of the sun gear, and Zr is the number of teeth of the ring gear. 
         [0006]    The input shaft of the speed reduction unit is supported by bearings disposed at two locations in the axial direction, that is, an inboard-side bearing and an outboard side bearing. The inboard-side bearing is attached to a housing of the speed reduction unit, and the outboard-side bearing is attached to the output member of the speed reduction unit. The housing is supported by the vehicle body via the suspension, and the output member is coupled and integrated with an inner member of the hub unit to rotationally drive the vehicle wheel. 
         [0007]    In the above-described drive device for an electric vehicle, the radial load acting on the input shaft of the speed reduction unit is supported by the housing via the inboard-side bearing on the inboard side, and is supported by the output member of the speed reduction unit via the outboard-side bearing on the outboard side. 
         [0008]    On the other hand, the hub unit is joined to a suspension via a knuckle on the vehicle body side in a normal motor vehicle driven by an internal combustion engine. 
       CITATION LIST 
     Patent Literature 
       [0009]    Patent Literature 1: Japanese Patent Laid-Open No. 2001-32888 
       SUMMARY OF INVENTION  
     Technical Problem 
       [0010]    Regarding the supporting structure of the input shaft of the speed reduction unit, while vibration and impact associated with the rotation of the vehicle wheel are transmitted to the outboard-side end portion of the input shaft via the output member and the outboard-side bearing, vibration and impact of the vehicle wheel will not be directly transmitted to the inboard-side end portion since it is supported by a stationary housing via the inboard-side bearing. 
         [0011]    Moreover, since the hub and the hub bearings that support the output member of the speed reduction unit elastically deform due to the effect of the load imposed on the vehicle wheel from the road, the outboard-side bearing is displaced with respect to the original center of the input and output shafts. On the other hand, the housing that supports the inboard-side bearing is not likely to be affected by the load from the vehicle wheel, and therefore the coaxiality between the two bearings that support the input shaft deteriorates or the inclination therebetween occurs. 
         [0012]    For this reason, eccentric load is likely to act on the inboard-side bearing and the outboard-side bearing, thus causing problems such as decline of rotational accuracy of the input shaft, deterioration of the durability of the bearings, and occurrence of rotation noise of the bearings. 
         [0013]    Moreover, in an electric vehicle, since conventionally a knuckle is a required member in the joining structure between the hub unit and the suspension on the vehicle body side, the number of parts is increased accordingly. 
         [0014]    Thus, it is an object of the present invention to provide a structure that does not require a knuckle on the vehicle body side while improving the rotational accuracy of the input shaft and the durability of the bearings and suppressing the rotation noise of the bearings by improving the supporting structure of the input shaft of the speed reduction unit. 
       Solution to Problem 
       [0015]    To solve the above-described problems, the present invention provides a drive device for an electric vehicle, comprising: an electric motor; a speed reduction unit including an input shaft driven by output of the electric motor; a hub unit rotationally driven by an output member of the speed reduction unit; and a housing accommodating the electric motor and the speed reduction unit, wherein the input shaft of the speed reduction unit is supported by bearings provided at two locations in the axial direction, the drive device being configured such that the bearings provided at the two locations are both supported by the output member, and the housing is provided with a suspension joining portion. 
         [0016]    According to the above-described configuration, since the bearings for supporting the input shaft at two locations in the axial direction are attached together to the output member, vibration and impact transmitted from the vehicle wheel to the output member will be imposed on both the bearings at the same time and in the same manner. As a result of this, both the bearings are prevented from being subjected to eccentric load. Moreover, the drive device for an electric vehicle can be attached to the vehicle body by directly joining the above-described suspension joining portion to the vehicle body, and thus a knuckle as an intermediate part is not required. 
         [0017]    The output member may be configured to include flanges disposed on both sides in the axial direction of a speed reduction rotational member such as a pinion gear so that the flanges are coupled and integrated with each other by both end portions of a support pin of the speed reduction rotational member being secured to the flanges, and each of the above-described bearings is placed between the inner radial surface of each flange and the input shaft. 
         [0018]    The above-described “speed reduction rotational member” and “support pin” correspond to the “pinion gear” and the “pinion pin” supporting the pinion gear respectively in the case of a planetary gear type. By attaching each bearing to the inner radial surface of each of the above-described flanges, it is possible to realize a configuration in which both bearings are attached together to the output member. 
         [0019]    Since the above-described speed reduction unit has a configuration in which the flanges on both sides are coupled and integrated with each other by support pins, the pinion gear can be placed between both the flanges. 
         [0020]    Thus, the flanges can be configured to be coupled with each other by a bridge so that the flanges can be securely coupled and integrated with each other by the bridge. 
         [0021]    Since both the flanges are securely engaged and integrated with each other by the above-described bridge, the support stiffness of the support pin such as the pinion pin whose both end portions are coupled to both the flanges is increased. Moreover, by providing the bridge at multiple locations of equally spaced positions in a circumferential direction of the flange, the rotation of the output member becomes smooth, and the rotational accuracy of the input shaft and the rotor of the electric motor fitted and secured to the input shaft is improved. 
       Advantageous Effects of Invention 
       [0022]    As described so far, since the present invention is configured such that a pair of bearings supporting an input shaft of a speed reduction unit are both attached to an output member of the speed reduction unit, both the bearings are prevented from being subjected to eccentric load. As a result of this, the present invention can achieve the effects of improving the rotational accuracy of the input shaft and the durability of the bearings, and further suppressing the rotation noise of the bearings. 
         [0023]    Moreover, since the suspension joining portion is provided in the housing, there is no need of providing a knuckle on the vehicle body side, thus allowing reduction of the number of parts on the vehicle body side. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0024]      FIG. 1  is a cross sectional view of Embodiment 1. 
           [0025]      FIG. 2  is a partially enlarged cross sectional view of Embodiment 1. 
           [0026]      FIG. 3  is an enlarged sectional view taken in X 1 -X 1  line in  FIG. 2 . 
           [0027]      FIG. 4  is a perspective view of a spacer shown in  FIG. 3 . 
           [0028]      FIG. 5  is a cross sectional view taken in X 2 -X 2  line in  FIG. 1 . 
           [0029]      FIG. 6A  is a cross sectional view of a variant of a speed reduction unit portion. 
           [0030]      FIG. 6B  is a cross sectional view taken in X 3 -X 3  line of  FIG. 6A . 
           [0031]      FIG. 7  is a cross sectional view to show a part of Embodiment 2. 
           [0032]      FIG. 8  is a cross sectional view of Embodiment 3. 
           [0033]      FIG. 9  is a side view of Embodiment 3. 
           [0034]      FIG. 10  is a partial cross sectional view of a variant of Embodiment 3. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0035]    Hereafter, embodiments of the present invention will be described based on the appended drawings. 
       Embodiment 1 
       [0036]    A drive device for an electric vehicle relating Embodiment 1 includes, as principal components, an electric motor  11 , a speed reduction unit  12  which is driven by the output power of the electric motor  11 , a hub unit  15  which is rotated by an output member  14  coaxial with an input shaft  13  of the speed reduction unit  12 , and a housing  16  which accommodates the electric motor  11  and the speed reduction unit  12 , as shown in  FIG. 1 . 
         [0037]    The above-described housing  16  includes a cylindrical portion  17  and a front end portion  18  in the radial direction, which is provided at the front end of the cylindrical portion (the end portion of an outboard side, or an end portion on the left side of the figure). A central portion of the front end portion  18  is opened, and a rear end portion of an outer member  21  of the hub unit  15  is fitted into an opening hole  19  so that a flange  22  is secured to the front end portion  18  with a bolt  23 . 
         [0038]    A partition base portion  18   a,  which is concentric with the opening hole  19  and has a larger diameter than that, is provided inside the front end portion  18  of the housing  16 . A dish-shaped partition member  20  is secured to the partition base portion  18   a  with a bolt  20   a.  A center hole  25  is provided at the center of the partition member  20 . The center hole  25  faces an outer radial surface of the input shaft  13  with a gap in a radial direction therebetween. A partition  24  is formed of the above-described partition base portion  18   a  and the partition member  20  joined and secured thereto. The partition  24  has a function of sectioning the interior of the housing  16  into an accommodation space for the electric motor  11  on the outer radial side, and an accommodation space for the speed reduction unit  12  on the inner radial side. 
         [0039]    A suspension joining portion  27  which projects in the axial direction is provided at two centrosymmetric locations on a rear end edge of the cylindrical portion  17  of the housing  16 . In a conventional automobile, the hub unit  15  is joined to the suspension with a knuckle of the vehicle body lying therebetween; however, in the present Embodiment 1, the suspension on the vehicle body side can be directly joined to the suspension joining portion  27  which is a part of the housing  16 . 
         [0040]    Since the housing  16  will achieve the function of the knuckle, it can be described as a structure in which the knuckle is integrated with the housing  16 . In this case, if the outer member  21  of the hub unit  15  becomes necessary to be replaced, the replacement can be performed simply by detaching the bolt  23  without need of detaching the housing  16  from the suspension. 
         [0041]    In the case shown in the figure, the electric motor  11  is a radial-gap-type brushless DC motor, and is made up of a stator  28  secured to an inner radial surface of the cylindrical portion  17  of the housing  16 , and a rotor  29  disposed on an inner radial surface of the stator  28  with a radial gap. The rotor  29  is fitted and secured to the input shaft  13  by a rotor support member  31 . 
         [0042]    The rotor support member  31  is made up of a support member cylindrical portion  31   a  (see  FIG. 2 ) fitted to an inner radial portion of the rotor  29 , and a support member disc portion  31   b  which extends reward along the partition  24  and which is bent to the inner radial direction of the partition. A boss portion  31   c  is provided in an inner radial portion of the support member disc portion  31   b,  and the boss portion  31   c  is fitted to the input shaft  13  and secured to the input shaft  13  with a key locking portion  35 . 
         [0043]    The above-described boss portion  31   c  is inserted into the inner radial side of the center hole  25  of the partition  24 , and an oil seal member  36  is placed between the center hole  25  and the boss portion  31   c  (see  FIG. 2 ). The accommodation portion of the electric motor  11  and the accommodation portion of the speed reduction unit  12  are partitioned and oil-sealed by the partition  24  and the oil seal member  36 . As a result of this, lubricant oil on the speed reduction unit  12  side is prevented from moving to the electric motor  11  side, and thus the electric motor  11  side is kept dry, thus resolving the malfunction that the lubricant oil hinders the rotation of the rotor  29 . 
         [0044]    The speed reduction unit  12  is of a planetary gear type, and is made up of, as shown in  FIG. 2 , the input shaft  13 , the output member  14 , a sun gear  39  which is attached to the outer radial surface of the input shaft with a key locking portion  38 , a ring gear  42  which is disposed along an inner radial surface of a partition cylindrical portion  24   b  in the outer periphery of the sun gear  39 , and which is attached with a key locking portion  41 , and pinion gears  43  which are disposed at three locations equally spaced in the circumferential direction between the ring gear  42  and the sun gear  39 . The pinion gear  43  is supported by a pinion pin  45  via a needle roller bearing  44 . 
         [0045]    The output member  14  includes a coupled shaft portion  47  at an end portion of an outboard side thereof. The coupled shaft portion  47  is spline-coupled to an inner member  46  of the hub unit  15  and secured by a nut  50 . A bearing support portion  49 , which is formed to have a one-step larger diameter than that of the coupled shaft portion  47 , is provided on the inner end side of the coupled shaft portion  47 . 
         [0046]    On an inboard side of the output member  14 , a pair of flanges  52  and  53  which oppose each other in the axial direction are provided with a spacing slightly larger than the width of the pinion gear  43  in the axial direction. A bridge  54  for joining the flanges  52  and  53  to each other in the axial direction is provided at three locations of equally spaced positions in the circumferential direction. The flanges  52  and  53  have a function as a carrier in the speed reduction unit  12  of planetary gear type. 
         [0047]    Providing the bridge  54  at equally spaced positions in the circumferential direction allows the output member  14  to be smoothly rotated, and moreover, to improve the rotational accuracy of the rotor  29  of the electric motor  11  through the output member  14  and the input shaft  13 . 
         [0048]    A shaft hole  51  which is coaxial with the coupled shaft portion  47  is provided at the center of an end surface of the flange  53  of the inboard side. This shaft hole  51  has a length reaching the bearing support portion  49 . 
         [0049]    There are provided pinion gear accommodation portions  55  at the three locations, which are sectioned in the circumferential direction by the pair of the flanges  52  and  53  opposing each other in the axial direction, and the bridges  54  at the three locations in the circumferential direction (see  FIG. 3 ). The pinion gear  43  is accommodated in each pinion gear accommodation portion  55 , and both end portions of the pinion pin  45  are inserted through the flanges  52  and  53 , respectively, and each secured by a locking screw  56 . It can be said that both the flanges  52  and  53  are coupled and integrated with each other not only by the bridge  54 , but also by the pinion pin  45 . 
         [0050]    Since the flanges  52  and  53  are integrated with each other by the bridge  54 , the support stiffness at both ends of the pinion pin  45  increases. 
         [0051]    A thrust plate  57  is placed between each side surface of each pinion gear  43  and each of the flanges  52  and  53  to ensure smooth rotation of the pinion gear  43 . 
         [0052]    A pair of rolling bearings  58  and  59  for supporting the input shaft  13  are provided on both sides of the sun gear  39  between an inner radial surface of each of the flanges  52  and  53  and the outer radial surface of the input shaft  13  opposing each of the inner radial surfaces of the flanges  52  and  53 . By adopting this configuration, the respective rolling bearings  58  and  59  are supported together by the same output member  14 . 
         [0053]    Further, as shown in  FIG. 2 , the positional relationship in the axial direction between each of the rolling bearings  58  and  59 , and a fitting portion between the support member disc portion  31   b  and the input shaft  13  is such that the respective rolling bearings  58  and  59  are disposed together on the outboard side, and form a so-called cantilever support structure as the support structure for the input shaft  13 . 
         [0054]    In contrast to this, in the conventional art (Patent Literature 1), while the bearing on the outboard side is disposed on the outboard side with respect to the fitting portion between the support member disc portion and the input shaft, the bearing on the inboard side is attached to the housing, and therefore is located on the inboard side with respect to the above-described fitting portion. Therefore, the support structure of the input shaft forms a so-called both-end support structure. The cantilever support structure is characterized by a simplified structure compared with the both-end support structure. 
         [0055]    The above-described rolling bearing  58  on the outboard side is configured such that its inner ring is engaged with a stepped portion  61  provided in the input shaft  13 , and its outer ring is engaged with a stepped portion  62  provided in an inner radial surface of the shaft hole  51 . The rolling bearing  59  on the inboard side is configured such that its inner ring is engaged with the boss portion  31   c  of the rotor support member  31  and the key locking portion  35 , and its outer ring is engaged with a retaining ring  63 . 
         [0056]    The sun gear  39  is placed between the respective inner rings of the respective rolling bearings  58  and  59 , and also a spacer  64  is placed between the outer rings. The spacer  64  prevents both the rolling bearings  58  and  59  from being displaced in a direction to approach to each other. 
         [0057]    The spacer  64  is formed into a cylindrical form as shown in  FIGS. 3 and 4 , and is provided, at three locations in the circumferential direction, with window holes  65  which correspond to the shape of the above-described pinion gear accommodation portion  55 . Further, a closure portion  66  between the respective window holes  65  is formed into a shape corresponding to the shape of the bottom plane of the above-described bridge  54 . The spacer  64  is placed between the rolling bearings  58  and  59  on the inner radial surface of the shaft hole  51  in a posture that each window hole  65  corresponds to the pinion gear accommodation portion  55  (see  FIG. 3 ), and is configured to be positioned by screwing a securing screw  67  from an outer radial surface of the bridge  54  into a positioning hole  60  (see  FIG. 4 ). 
         [0058]    The above-described spacer  64  allows to control the bearing pressurization to be applied to both the rolling bearings  58  and  59  by appropriately setting the axial length thereof, thus providing a simple fixed-position pressurization structure. 
         [0059]    When seen in the radial direction, the speed reduction unit  12  is radially disposed to be accommodated on the inner radial side of the electric motor  11  with respect to the partition  24 , and the size in the axial direction is made compact compared with a case where the unit is disposed in the axial direction. 
         [0060]    Here, additionally describing the partition  24 , the partition cylindrical portion  24   b  is placed between the electric motor  11  and the speed reduction unit  12 , which are disposed in the radial direction, and a partition disc portion  24   a  is placed between the speed reduction unit  12  and the support member disc portion  31   b.  A peripheral edge portion of the center hole  25  faces the outer radial surface of the boss portion  31   c  of the rotor support member  31  with a predetermined spacing therebetween. The ring gear  42  of the speed reduction unit  12  is secured to an inner radial surface of the partition base portion  18   a  with the key locking portion  41 . 
         [0061]    The oil seal member  36  is placed between the peripheral edge portion of the above-described center hole  25  and the boss portion  31   c.  The accommodation space for the electric motor  11  of the housing  16  and the accommodation space for the speed reduction unit  12  are partitioned by the presence of the oil seal member  36  and the partition  24 . Since, as a result of this, the lubricant oil on the speed reduction unit  12  side is prevented from moving to the electric motor  11  side, and thus the electric motor side is kept dry, the lubricant oil is prevented from hindering the rotation of the rotor  29 . 
         [0062]    Although, it is described above that both the flanges  52  and  53  of the output member  14  are coupled and integrated by both the bridge  54  and the pinion pin  45 , it is possible to take a structure in which the flange  53  is configured to be a separate body from the output member  14  and both are coupled and integrated by the pinion pin  45 , as shown in  FIGS. 6A and 6B . 
         [0063]    An oil filler port  68  and an oil drainage port  69  for lubricant oil to lubricate the interior of the speed reduction unit  12  are provided in the front end portion of the housing  16 . The lubricant oil is sealed by the above-described oil seal member  36  on the electric motor  11  side, and is sealed by an oil seal member  70 , which is placed between the bearing support portion  49  of the output member  14  and the outer member  21 , on the hub unit  15  side. The oil filler port  68  and the oil drainage port  69  are blocked by a blocking screw  72 . 
         [0064]    Since the electric motor  11  and the speed reduction unit  12 , excepting the rear end portion (the end portion of the inboard side) of the input shaft  13 , fit in the range of the axial length of the cylindrical portion  17  of the housing  16  as shown in  FIG. 1 , a rear cover  73  is fitted to the rear end portion of the cylindrical portion  17  via a seal member  60 . A fin  74  for heat dissipation is provided on an outer side surface of the rear cover  73  so that heat of the electric motor  11  is dissipated to the outside. 
         [0065]    A rotation angle sensor  75  is provided between the center hole of the rear cover  73  and the input shaft  13  that passes through the center hole, and that portion is covered by a sensor cover  77 . The rotation angle sensor  75  shown is a resolver, and whose sensor stator  75   a  is secured into the center hole of the rear cover  73 , and a sensor rotor  75   b  is attached to the input shaft  13 . 
         [0066]    A lead wire  83  of the sensor stator  75   a  is connected to a connector insertion portion  78  provided outside the sensor cover  77 . As the rotation angle sensor  75 , a Hall element can be used besides the above-described resolver. 
         [0067]    A rotational angle of the input shaft  13  detected by the rotation angle sensor  75  is inputted to a control circuit, which is omitted from showing, via the above-described signal wire cable to be used for the rotational control of the electric motor  11 . 
         [0068]    A power supply terminal box  76  for providing power supply to the stator  28  of the electric motor  11  is provided at a position decentered toward an outer peripheral edge of the above-described rear cover  73 , and at a position 90 degrees different from the above-described suspension joining portion  27  (see  FIG. 5 ). 
         [0069]    The power supply terminal box  76  is formed into a cylindrical shape that passes through the rear cover  73 , and is provided with a working hole  80  in an outer peripheral portion of the box. The working hole  80  is usually blocked by a cover  81 . A power supply terminal  82  is provided inside the box at a position opposing the working hole  80 . A lead wire  83  connected to the winding of the stator  28  is connected to the power supply terminal  82 , and also a connection terminal of a power supply cable  84  is connected to the same power supply terminal  82 . These are secured by fastening screws  85 . A cable hole  84   a  is provided at a rear end of the power supply terminal box  76  and the power supply cable  84  is inserted therethrough. 
         [0070]    The hub unit  15  is made up of, as shown in  FIG. 1 , the above-described inner member  46  which is integrated with a hub  86 , a pair of inner rings  87  that are fitted to an outer radial surface of the inner member  46 , the outer member  21  having the flange  22 , an outer ring  88  fitted to an inner radial surface of the outer member  21  and having multiple rows of tracks, and multiple rows of balls  89  to be placed between the inner ring  87  and the outer ring  88 . The vehicle wheel is attached to the hub  86  with hub bolts  90 . 
         [0071]    The coupled shaft portion  47  of the output member  14  is spline-coupled to an inner radial surface of the inner member  46 , and a tip end portion of the coupled shaft portion  47  projecting to the outside from the inner member  46  is secured by the nut  50  as described above. In place of the securing means using the nut  50 , securing means such as press cut joint, diameter expansion caulking, and swing caulking may be adopted. 
         [0072]    Although the above-described hub unit  15  is of a form of so-called first generation, those of a form of the second generation or third generation may be used. 
         [0073]    The driving device for an electric vehicle of Embodiment 1 is configured as described above, and next, the operation thereof will be described. 
         [0074]    When the electric motor  11  is driven by an accelerator at the driving seat being activated, the input shaft  13  is rotated integrally with the rotation of the rotor  29 , and a motor output is inputted to the speed reduction unit  12 . In the speed reduction unit  12 , when the sun gear  39  rotates integrally with the input shaft  13 , the pinion gears  43  revolve around the sun gear  39  while rotating on their own axes. Each of the pinion pins  45  performs speed-reduced rotation at its revolving speed, and thereby rotates the output member  14  at a speed-reduced output shown by the above-described speed reduction ratio. 
         [0075]    The inner member  46  of the hub unit  15  is rotated integrally with the coupled shaft portion  47  of the output member  14 , thereby driving the wheel attached to the hub  86 . 
         [0076]    The above-described input shaft  13  rotates by being supported respectively by the rolling bearing  58  on the outboard side and the rolling bearing  59  on the inboard side at both sides of the pinion gear  43 . Since these rolling bearings  58  and  59  are both attached to the respective flanges  52  and  53  (respective flanges  52  and  53  which are integrated via the pinion pin  45  in the case of  FIGS. 6A and 6B ) which are each integrated with the output member  14 , vibration and impact in the radial direction which are transmitted from the wheel to the output member  14  through the hub unit  15  is imposed onto both the rolling bearings  58  and  59  at the same time and in the same manner. 
         [0077]    Since, as a result of that, both the rolling bearings  58  and  59  can be prevented from being subjected to eccentric load, it is possible to improve the rotational accuracy and durability, and suppress the rotation noise. 
         [0078]    Since the pinion pin  45  of the pinion gear  43  is supported at both end portions thereof by the respective flanges  52  and  53 , the support stiffness increases compared with a conventional case where it is cantilevered. 
         [0079]    The above-described rolling bearings  58  and  59  are disposed on the outboard side with respect to the fitting portion between the rotor support member  31  of the rotor  29  and the input shaft  13 , that is, the key locking portion  35 , so that the support structure becomes simple and easy to be assembled compared with a conventional case where the bearings are disposed on both sides thereof. 
         [0080]    Further, since the lubricant oil in the speed reduction unit  12  is sealed on the electric motor  11  side by the oil seal member  36 , and sealed on the hub unit  15  side by the oil seal member  70 , leakage on the electric motor  11  side and the hub unit side is prevented. As a result of that, on the electric motor  11  side, rotation of the rotor  29  is not hindered, and on the hub unit  15  side, leakage of the lubricant oil to the outside through the hub unit  15  is prevented. 
         [0081]    The heat generated in association with the driving of the electric motor  11  is effectively dissipated by the fin  74  of the rear cover  73 . 
         [0082]    The rotational angle of the input shaft  13 , which is necessary for the rotational control of the electric motor  11 , is detected by the rotation angle sensor  75  and inputted to the control apparatus. 
       Embodiment 2 
       [0083]    Embodiment 2 shown in  FIG. 7  differs in the configuration of the hub unit  15  compared with the above-described Embodiment 1. That is, the flange  22  of the outer member  21  of the hub unit  15  in this case is formed to have a larger diameter than that of the flange  22  (see  FIG. 1 ) of the above-described Embodiment 1. 
         [0084]    A flange cylindrical portion  32  projecting in the axial direction is provided in the inner side surface of the flange  22  with a larger diameter. The flange cylindrical portion  32  extends over an outer radial surface of the flange  53  on the outboard side of the output member  14 . The flange cylindrical portion  32  is fitted to an inner radial surface of the opening hole  19  of the front end portion  18  of the housing  16 . 
         [0085]    Since, compared with the case of Embodiment 1, the opening hole  19  is formed to have a large inner diameter, it is easy to fabricate the partition  24  which is integrated with the front end portion  18 , in the case of this Embodiment 2. For this reason, in the case of Embodiment 2, the partition member  20  (see  FIG. 1 ) which is a separate member is not used. 
         [0086]    A ball of a hub bearing  89   a  on the outboard side is placed between a track groove formed in the outer radial surface of the inner member  46 , and a track groove formed in the inner radial surface of the outer member  21 . Moreover, the ball of the hub bearing  89   b  on the inboard side is placed between a track surface formed in the outer radial surface of the flange  52  and a track groove formed in an inner radial surface of the flange cylindrical portion  32 . 
         [0087]    Letting the radii from “the center” of the ball center of the hub bearing  89   a  on the outboard side, the center of the pinion shaft  45 , and the ball center of the hub bearing  89   b  on the inboard side be r 1 , r 2 , and r 3 , respectively, these sizes have a relationship as r 1 &lt;r 3 , and r 2 &lt;r 3 . Other configurations are the same as those of the case of Embodiment 1. 
         [0088]    As describe above, setting the ball PCD (pitch circle diameter) of the hub bearing  89   b  on the inboard side to be larger than the ball PCD of the hub bearing  89   a  on the outboard side results in increasing in the bearing stiffness of the hub unit  15 . 
         [0089]    It is noted that the hub unit  15  in this case can be said to be a variant form of the so-called third generation. 
         [0090]    Although, in the illustrated case, each of the balls of the hub bearings  89   a  and  89   b  is configured to be in direct contact with the track groove, it is also possible to configure such that a bearing in which the track groove is provided in each of its inner ring and outer rings is used, and these track rings are fitted to the aforementioned opposite members. 
       Embodiment 3 
       [0091]    Embodiment 3 shown in  FIGS. 8 to 10  differs from Embodiment 1 in the configurations of the hub unit  15 , the rotation angle sensor  75 , the power supply terminal box  76 , and the connector insertion portion  78 . 
         [0092]    That is, the hub unit  15  in this case is formed such that the flange  22  of the outer member  21  has a larger diameter than in the case of Embodiment 1. For this reason, there is no need of adopting a supplementary housing  16   b  as in Embodiment 1, and the single housing  16  which has a similar structure to that of a main housing  16   a  is used. The flange  22  with a larger diameter is secured to the housing  16  with the bolt  23 . 
         [0093]    The ball  89   a  on the outboard side constituting the hub bearing is placed between the track groove provided in the outer radial surface of the inner member  46  and the track groove provided in the inner radial surface of the outer member  21 . Further, the ball  89   b  on the inboard side is placed between the track groove provided in the outer radial surface of the output member  14  and the track groove provided in the inner radial surface of the outer member  21 . It can be said to be a variant type of the so-called third-generation. 
         [0094]    The rotation angle sensor  75  is provided between opposite surfaces in the axial direction of the support member disc portion  31   b  of the rotor support member  31 , and the partition disc portion  24   a.  A sensor rotor  91   a  is made up of a magnet which is attached to the support member disc portion  31   b  with a vis  92 . Moreover, a sensor stator  91   b  is made up of a Hall element attached to the opposite surface of the partition disc portion  24   a  with a vis  93 . Both oppose each other via an axial gap. 
         [0095]    As shown in  FIG. 10 , the cross sectional shape of the sensor rotor  91   b  may be formed into a reverse L-shape, and a radial gap may be formed between the horizontal portion of the sensor rotor  91   b  and the sensor stator  91   a.    
         [0096]    The power supply terminal box  76  and the connector insertion portion  78  are both provided in the housing  16  (see  FIG. 9 ). The power supply terminal box  76  is configured such that an accommodation recessed portion  94  is provided within the range of the wall thickness of a rear end surface of the housing  16 , and the power supply terminal  82  is provided inside the accommodation recessed portion  94 . A communication hole  95  in communication with the interior of the housing  16  is provided in a deep part of the accommodation recessed portion  94 . The opening surface of the accommodation recessed portion  94  is blocked by a cover member  96 . The cover member  96  is provided with a cable hole  97  for passing the power supply cable  84 . 
         [0097]    Further, the working hole  80  is provided in the wall surface of the housing  16 . This working hole  80  is usually blocked by the cover  81 . The lead wire  83  on the electric motor  11  side is connected to the power supply terminal  82  through the communication hole  95 , and the power supply cable  84  is drawn in through the cable hole  97  so that its connection terminal is connected to the power supply terminal  82 . Both are coupled to the power supply terminal  82  with a fastening screw  85 . 
         [0098]    The connector insertion portion  78  is provided in the rear end surface of the housing  16  side-by-side with the power supply terminal box  76 , as shown in  FIG. 9 . The connector insertion portion  78  is configured such that a recessed portion  99  is provided in the rear end surface of the housing  16 , and a lead wire hole  100  which brings a deep part of the recessed portion  99  and the interior of the housing  16  into communication is provided (see  FIG. 8 ). A lead wire  101  of the rotation angle sensor  75  is connected to the interior of the recessed portion  99  through the lead wire hole  100 . The connector (not shown) of the signal cable is inserted into the connector insertion portion  78 . 
         [0099]    As described above, the configuration in which both the power supply terminal box  76  and the connector insertion portion  78  are provided in the housing  16  can simplify the configuration of the rear cover  73  so that it can be made up of a thin metal plate, a plastic plate, and the like. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           11  Electric motor 
           12  Speed reduction unit 
           13  Input shaft 
           14  Output member 
           15  Hub unit 
           16  Housing 
           17  Cylindrical portion 
           18  Front end portion 
           18   a  Partition base portion 
           19  Opening hole 
           20  Partition member 
           20   a  Bolt 
           21  Outer member 
           22  Flange 
           23  Bolt 
           24  Partition 
           24   a  Partition disc portion 
           24   b  Partition cylindrical portion 
           25  Center hole 
           26  Fin 
           27  Suspension joining portion 
           28  Stator 
           29  Rotor 
           31  Rotor support member 
           31   a  Support member cylindrical portion 
           31   b  Support member disc portion 
           31   c  Boss portion 
           32  Flange cylindrical portion 
           35  Key locking portion 
           36  Oil seal member 
           38  Key locking portion 
           39  Sun gear 
           41  Key locking portion 
           42  Ring gear 
           43  Pinion gear 
           44  Needle roller bearing 
           45  Pinion pin 
           46  Inner member 
           47  Coupled shaft portion 
           48  Rolling bearing 
           49  Bearing support portion 
           50  Nut 
           51  Shaft hole 
           52 ,  53  Flange 
           54  Bridge 
           55  Pinion gear accommodation portion 
           56  Locking screw 
           57  Thrust plate 
           58 ,  59  Rolling bearing 
           60  Positioning hole 
           61 ,  62  Stepped portion 
           63  Retaining ring 
           64  Spacer 
           65  Window hole 
           66  Closure portion 
           67  Securing screw 
           68  Oil filler port 
           69  Oil drainage port 
           79  Oil seal member 
           71  Groove 
           72  Blocking screw 
           73  Rear cover 
           74  Fin 
           75  Rotation angle sensor 
           75   a  Sensor stator 
           75   b  Sensor rotor 
           76  Power supply terminal box 
           76   a  Power supply terminal 
           77  Sensor cover 
           78  Connector insertion portion 
           79  Insertion hole 
           80  Working hole 
           81  Cover 
           82  Power supply terminal 
           83  Lead wire 
           84  Power supply cable 
           84   a  Cable hole 
           85  Fastening screw 
           86  Hub 
           87  Inner ring 
           88  Outer ring 
           89  Ball 
           89   a,    89   b  Hub bearing 
           90  Hub bolt 
           91   a  Sensor rotor 
           91   b  Sensor stator 
           92 ,  93  Vis 
           94  Accommodation recessed portion 
           95  Communication hole 
           96  Cover member 
           97  Cable hole 
           99  Recessed portion 
           100  Lead wire hole