Abstract:
An object of the present invention is to provide an in-wheel motor driving device which includes a highly adaptable suspension mounting portion, is light weighted, and has reduced drag friction at the time of steering operation. An in-wheel motor driving device comprises: a motor section A which rotates a motor-side rotation member; a speed reducer section B which reduces and transmits rotation of the motor-side rotation member to a wheel-side rotation member; and a wheel hub connected and fixed to the wheel-side rotation member. The above three elements are disposed in series from an inboard side to an outboard side of a vehicle, and suspension mounting brackets are fixed onto an outer surface of the speed reducer section&#39;s housing. Arms of a suspension are attached via the suspension mounting brackets.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to in-wheel motor driving devices incorporating electric motors therein as a driving mechanism for a wheel, and in particular, to suspension mounting structures of these devices. 
       BACKGROUND ART 
       [0002]    A conventional in-wheel motor driving device  101  is disclosed in JP-A-2009-219271 (Patent Literature 1) for example. 
         [0003]    As shown in  FIG. 23 , the in-wheel motor driving device  101  includes a housing  102  which is attached to a vehicle body; a motor section  103  which is placed therein and generates a driving force; a wheel hub bearing section  104  which is connected to a wheel; and a speed reducer section  105  which reduces rotation speed of the motor section  103  and transmits the rotation to the wheel hub bearing section  104 . All of these are disposed in series. 
         [0004]    When mounting the in-wheel motor driving device  101  configured as the above to a vehicle body, generally one of two suspension mechanisms is employed. 
         [0005]    One of them is a method as disclosed in JP-A-H05-116545 (Patent Literature 2) for example; namely, the device is installed to the vehicle body via a knuckle (hub carrier) which fits around a driving unit&#39;s outer circumference and has a suspension arm fitting like those used in conventional engine-driven vehicles. 
         [0006]    The other is a method disclosed in Japanese Patent No. 3440082 (Patent Literature 3), namely, a method in which the suspension arm is fixed directly to a housing of a motor portion. The driving unit in this case includes the motor portion; a wheel hub bearing portion connected to a wheel; a speed reducer portion which slows the rotation of motor portion and transmits the rotation to the wheel hub bearing portion; and a mechanical brake. With this, the suspension arm mounting portion to the vehicle body is made as a separate attachment installable to a housing of the motor portion so that the driving unit has an improved adaptability that it is installable to any vehicle regardless of the shape or characteristics of the motor portion. 
       CITATION LIST 
     Patent Literature 
       [0007]    [Patent Literature 1] JP-A-2009-219271 
         [0008]    [Patent Literature 2] JP-A-H05-116545 
         [0009]    [Patent Literature 3] Japanese Patent No. 3440082 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0010]    Of these mounting methods described above, the former has a problem that it is difficult to incorporate the suspension mounting portion within a limited space inside the wheel since the motor portion&#39;s outer diameter is much bigger than that of the wheel shaft of engine-driven vehicles and the knuckle has to be as big accordingly. Therefore, the knuckle has to be shaped to stay outside of the wheel, or must be disposed at a more laterally inboard position with respect to the vehicle width than the driving unit. These problems of larger knuckle size and restriction on the place where the suspension can be disposed lead to another problem of increased unsprung weight. Further, since the king pin&#39;s axis must be offset to a laterally inboard direction of the vehicle width with respect to the tire&#39;s contact area with the road surface, the device will create a drag friction during steering operation. 
         [0011]    In the latter method where the suspension arm is fixed directly to the motor portion housing, the king pin&#39;s axis and the tire&#39;s contact area with the road surface are undesirably away from each other since the speed reducer section is sandwiched between the motor portion and the wheel (tire) mounting portion. This increases drag friction at the time of steering operation as well as the moment load applied to the motor portion by the tire which is vibrating in up-down and fore-aft directions. In order to deal with this, the mounting portion has to be increased in its thickness to ensure required strength. These have made it difficult to reduce the weight of the device. 
         [0012]    It is therefore an object of the present invention to provide an in-wheel motor driving device which includes a highly adaptable suspension mounting portion, is light weighted, and has reduced drag friction at the time of steering operation. 
       Solution to Problem 
       [0013]    In order to achieve the above-mentioned object, the present invention provides an in-wheel motor driving device including: a motor section which rotates a motor-side rotation member; a speed reducer section which reduces and transmits rotation of the motor-side rotation member to a wheel-side rotation member; and a wheel hub connected and fixed to the wheel-side rotation member. The above three elements are disposed in series from an inboard side to an outboard side of a vehicle. With this arrangement, the speed reducer section includes suspension mounting brackets fixed onto an outer surface of its housing for connection of an arm of a suspension mechanism. 
         [0014]    The suspension mounting brackets may have brake caliper mounting portions. 
         [0015]    Also, one of the suspension mounting brackets may have a knuckle-arm shape for connection with a steering tie rod. 
         [0016]    It is preferable that the suspension mounting bracket has a plurality of surfaces contacting an outer surface of the housing of the speed reducer section, so that an input load will not be born only by fixing bolts which fix the suspension mounting bracket but also born by the suspension mounting bracket. 
         [0017]    The wheel hub may be provided by a hub bearing which incorporates a load sensor. 
         [0018]    The speed reducer section may be provided by a planetary-gear reduction gear system or a cycloid reduction gear system. 
         [0019]    The suspension mechanism may be double wishbone type, strut type, torsion beam type, trailing arm type, or other types. 
         [0020]    The housing of the motor section and the housing of the speed reducer section may be made of a non-ferrous material whereas the suspension mounting bracket may be made of a steel material, for overall weight reduction. 
       Advantageous Effects of Invention 
       [0021]    As described above, according to the in-wheel motor driving device offered by the present invention, arms of the suspension mechanism are fixed onto an outer surface of a housing of the speed reducer section via suspension mounting brackets. 
         [0022]    Therefore, it is now possible to dispose the suspension arm pivot (king pin axis) closely to the tire&#39;s contact surface with the road, and hence it is now possible to reduce drag friction during steering operation and the moment load from the tire. Since the moment load is now reduced, it is now possible to reduce the weight and size of the driving unit. 
         [0023]    Also, by making the suspension mounting bracket as a separate part, the present invention makes it possible to select optimum materials for different members such as strength members, housing members, etc. Not only the materials but also the shape of the members can be optimized with increased freedom. 
         [0024]    For example, it is now possible to use a light material, e.g., an aluminum alloy for large-volume components such as the housing of the motor portion and the housing of the speed reducer section while using a high strength steel material for the bracket to which the suspension is connected. 
         [0025]    Also, by changing the shape of the bracket, it is now possible to connect brake calipers and/or a tie rod of a steering section. Because of this arrangement, customization can be made easily for a front wheel or a rear wheel, or for types and use of the vehicle, only by changing the shape of the bracket. The present invention provides a highly versatile driving unit, making it possible to use the driving unit as a common part. 
         [0026]    Also, by including a detachable bracket, the present invention makes it possible to increase operability in such operations as assembling a suspension to the unit. 
         [0027]    Further, the present invention also makes it possible, by using specifically designed bracket, to make the bracket itself receive an input load from the suspension (tire). The arrangement makes it possible to compensate for the strength of the suspension mounting portion. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0028]      FIG. 1  is a schematic sectional view of an in-wheel motor driving device according to a first embodiment of the present invention. 
           [0029]      FIG. 2  is an enlarged view of a motor section in  FIG. 1 . 
           [0030]      FIG. 3  is an enlarged view of a speed reducer section in  FIG. 1 . 
           [0031]      FIG. 4  is an enlarged view of a wheel hub bearing section in  FIG. 1 . 
           [0032]      FIG. 5  is a sectional view taken in line V-V in  FIG. 1 . 
           [0033]      FIG. 6  is an enlarged view showing a surrounds of an eccentric sections in  FIG. 1 . 
           [0034]      FIG. 7  is a view when a rotary pump in  FIG. 1  is viewed in an axial direction. 
           [0035]      FIG. 8  is a schematic plan view of an electric vehicle which includes in-wheel motor driving devices in  FIG. 1 . 
           [0036]      FIG. 9  is a schematic rear view of the electric vehicle in  FIG. 8 . 
           [0037]      FIG. 10  is a front view of a housing of a speed reducer section as viewed from the wheel hub bearing section. 
           [0038]      FIG. 11  is a perspective view of the housing of the speed reducer section as viewed from the wheel hub bearing section. 
           [0039]      FIG. 12  is a perspective view of the housing of the speed reducer section as viewed from the motor section. 
           [0040]      FIG. 13  is a perspective view, showing an example of a suspension mounting bracket. 
           [0041]      FIG. 14  is a perspective view of the suspension mounting bracket in  FIG. 13  as mounted to a housing of the speed reducer section and viewed from the motor section. 
           [0042]      FIG. 15  is a front view of the suspension mounting bracket in  FIG. 13  as mounted to the housing of the speed reducer section and viewed from the wheel hub bearing section. 
           [0043]      FIG. 16  is a perspective view of the suspension mounting bracket in  FIG. 13  as mounted to the housing of the speed reducer section, with a suspension mounted thereto. 
           [0044]      FIG. 17  is a perspective view, showing another example of the suspension mounting bracket. 
           [0045]      FIG. 18  is a perspective view, showing another example of the suspension mounting bracket. 
           [0046]      FIG. 19  is a perspective view of the suspension mounting bracket in  FIG. 18  as mounted to a housing of the speed reducer section and viewed from the motor section. 
           [0047]      FIG. 20  is a perspective view of a suspension mounting bracket as another example, as mounted to a housing of the speed reducer section and viewed from the motor section. 
           [0048]      FIG. 21  is a perspective view of a suspension mounting bracket as another example, as mounted to a housing of the speed reducer section and viewed from the motor section. 
           [0049]      FIG. 22  is a side view, showing an embodiment of a front wheel driving unit. 
           [0050]      FIG. 23  is a schematic sectional view of a conventional in-wheel motor driving device. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0051]    Hereinafter, embodiments of the present invention will be described based on the attached drawings. 
         [0052]    First, as shown in  FIG. 1 , an in-wheel motor driving device  21  includes a motor section A which generates a driving force; a speed reducer section B which reduces rotating speed of the motor section A and outputs the rotating force; and a wheel hub bearing section C which transmits the output from the speed reducer section B to a driving wheel  14 . The device is installed inside a wheel house  12   a  of a chassis  12  as shown in  FIG. 9 . 
         [0053]    As shown in  FIG. 2 , the motor section A is provided by a radial-gap motor which includes a stator  23  fixed to a housing  22   a;  a rotor  24  disposed inside the stator  23  to face thereto with a radial gap in between; and a motor-side rotation member  25  disposed inside the rotor  24 , being fixed thereto for integral rotation with the rotor  24 . The rotor  24  includes a flange-shaped rotor section  24   a  and a cylindrical hollow section  24   b,  and is supported by roller bearings  36   a,    36   b  rotatably with respect to the housing  22   a.    
         [0054]    The motor-side rotation member  25 , which transmits the driving force from the motor section A to the speed reducer section B, is disposed across the motor section A and the speed reducer section B, and includes eccentric sections  25   a,    25   b  inside the speed reducer section B. The motor-side rotation member  25  has one end fitted into the rotor  24 , and is supported by a roller bearing  36   c  inside the speed reducer section B. The two eccentric sections  25   a,    25   b  are disposed at a 180-degree phase difference so that their centrifugal forces due to their eccentric movement are cancelled by each other. 
         [0055]    As shown in  FIG. 3 , the speed reducer section B includes cycloid discs  26   a,    26   b  which serve as revolving members and are rotatably held by the eccentric sections  25   a,    25   b;  a plurality of outer pins  27  which are held at fixed locations on the housing  22   b  and serving as outer circumferential engager for engagement with the outer circumferential portion of the cycloid discs  26   a,    26   b;  a motion conversion mechanism which transmits rotational movement of the cycloid discs  26   a,    26   b  to a wheel-side rotation member  28 ; and counterweights  29  disposed adjacently to the eccentric sections  25   a,    25   b.  The speed reducer section B includes a speed reducer section lubrication mechanism which supplies lubrication oil to the speed reducer section B. 
         [0056]    The wheel-side rotation member  28  includes a flange section  28   a  and a shaft section  28   b.  The flange section  28   a  has its end surface formed with holes at an equidistant interval on a circle centered on a rotational center of the wheel-side rotation member  28 , for fixing inner pins  31 . The shaft section  28   b  is fitted into and fixed to a wheel hub  32 , and transmits the output from the speed reducer section B to the wheel  14 . The flange section  28   a  of the wheel-side rotation member  28  and the motor-side rotation member  25  are rotatably supported by the roller bearing  36   c.    
         [0057]    As shown in  FIG. 5 , the cycloid discs  26   a,    26   b  have a plurality of waveforms composed of trochoid curves such as epitrochoid curve, on their outer circumferences, and a plurality of through-holes  30   a  penetrating from one end surface to the other end surface. The through-holes  30   a  are made equidistantly on a circle centering on the rotational center of the cycloid discs  26   a,    26   b,  and accommodate inner pins  31  which will be described later. Also, a through-hole  30   b  penetrates the center of the cycloid discs  26   a,    26   b,  and fits around the eccentric sections  25   a,    25   b.    
         [0058]    The cycloid discs  26   a,    26   b  are supported by a roller bearing  41  rotatably with respect to the eccentric sections  25   a,    25   b.  As shown in  FIG. 5 , the roller bearing  41  is provided by a cylindrical roller bearing which includes an inner ring member  42  fitted around outer diameter surfaces of the eccentric sections  25   a,    25   b  and having an inner track surface  42   a  on its outer diameter surface; an outer track surface  43  formed directly on an inner diameter surface of the through-hole  30   b  of the cycloid disc  26   a;  a plurality of cylindrical rollers  44  disposed between the inner track surface  42   a  and the outer track surface  43 ; and a retainer (not illustrated) which keeps the distance between the cylindrical rollers  44 . 
         [0059]    The outer pins  27  are disposed equidistantly on a circular track which centers on the rotational center of the motor-side rotation member  25 . As the cycloid discs  26   a,    26   b  make their revolutions, the wavy curves and the outer pins  27  engage with each other and generate rotational movement of the cycloid discs  26   a,    26   b.  In order to reduce frictional resistance with the cycloid discs  26   a,    26   b,  needle roller bearings  27   a  are provided at places of contact with the outer circumferential surfaces of the cycloid discs  26   a,    26   b.    
         [0060]    The counterweights  29  are disc-like, have a through-hole at a place away from its center for fitting around the motor-side rotation member  25 , and are disposed adjacently to the eccentric sections  25   a,    25   b  respectively, at a 180-degree phase difference therefrom in order to cancel unbalanced inertia couple caused by the rotation of the cycloid discs  26   a,    26   b.    
         [0061]    In the above-described arrangement, there is a relationship expressed by the following equation: 
         [0000]      L 1 ×m 1 ×ε 1 =L 2 ×m 2 ×ε 2 ,
 
         [0000]    where, with reference to  FIG. 6  which shows a center G of the two cycloid discs  26   a,    26   b,  L 1  represents a distance from the center G to the center of the cycloid disc  26   a  in the right side with respect of the center G in the  FIG. 6 ; ml represents a sum of masses of the cycloid disc  26   a,  the roller bearing  41  and the eccentric section  25   a;  ε 1  represents an amount of eccentricity of the center of gravity of the cycloid disc  26   a  from the axis of rotation; L 2  represent the distance from the center G to the counterweight  29 ; m 2  represents the mass of the counterweight  29 ; and ε 2  represents an amount of eccentricity of the center of gravity of the counterweight  29  from the axis of rotation. The same relationship exists between the cycloid disc  26   b  and the counterweight  29  on the left side with respect to the center G in  FIG. 6 . 
         [0062]    The motion conversion mechanism is constituted by a plurality of inner pins  31  held by the wheel-side rotation member  28  and the through-holes  30   a  formed in the cycloid discs  26   a,    26   b.  The inner pins  31  is disposed equidistantly on a circular track centering on the rotational center of the wheel-side rotation member  28 , and has one of its axial end fixed to the wheel-side rotation member  28 . Also, in order to reduce frictional resistance with the cycloid discs  26   a,    26   b,  needle roller bearings  31   a  are provided to make contact with inner wall surfaces of the through-holes  30   a  of the cycloid discs  26   a,    26   b.    
         [0063]    On the other hand, the through-holes  30   a  are formed at locations corresponding to the respective inner pins  31 . Each of the through-holes  30   a  has an inner diameter which is larger, by a predetermined difference, than an outer diameter (a “maximum outer diameter including the needle roller bearing  31   a ”, hereinafter the same will apply) of the inner pins  31 . 
         [0064]    The speed reducer section lubrication mechanism supplies lubrication oil to the speed reducer section B, and includes a lubrication oil path  25   c,  lubrication oil inlets  25   d,  a lubrication oil exit  25   e,  a lubrication oil reservoir  25   f,  a rotary pump  51  and a circulation oil path  25   g.    
         [0065]    The lubrication oil path  25   c  extends axially inside the motor-side rotation member  25 . The lubrication oil inlets  25   d  extend from the lubrication oil path  25   c  toward an outer diameter surface of the motor-side rotation member  25 . In the present embodiment, the lubrication oil inlet  25   d  is provided in each of the eccentric sections  25   a,    25   b.    
         [0066]    Also, the lubrication oil exit  25   e  from which the lubrication oil inside the speed reducer section B is discharged, is provided at least at one location in a bottom portion of the housing  22   b  which supports the speed reducer section B. The lubrication oil reservoir  25   f  is provided in the bottom portion of the housing  22   b  which supports the speed reducer section B. 
         [0067]    The lubrication oil in the lubrication oil reservoir  25   f  is sucked by the rotary pump  51 , and circulated forcibly via the circulation oil path  25   g  and to the lubrication oil path  25   c.    
         [0068]    As shown in  FIG. 7 , the rotary pump  51  is a cycloid pump which includes an inner rotor  52  rotated by rotation of the wheel-side rotation member  28 ; an outer rotor  53  rotated in association with rotation of the inner rotor  52 ; a pump chamber  54 ; an suction port  55 ; and a discharge port  55  communicating with the circulation oil path  25   g.    
         [0069]    The inner rotor  52  has its outer diameter surface formed with a cycloid teeth pattern. Specifically, tooth tip portions  52   a  are composed of epicycloid curves while tooth groove portions  52   b  are composed of hypocycloid curves. The inner rotor  52  rotates integrally with internal pins  31  (wheel-side rotation member  28 ). 
         [0070]    The outer rotor  53  has its inner diameter surface formed with a cycloid teeth pattern. Specifically, tooth tip portions  53   a  are composed of hypocycloid curves while tooth groove portions  53   b  are composed of epicycloid curves. The outer rotor  53  is supported rotatably by the housing  22 . 
         [0071]    The inner rotor  52  rotates on a rotation center c 1 . On the other hand, the outer rotor  53  rotates on a rotation center c 2  which is different from the rotation center c 1  for the inner rotor. Also, it should be noted here that when the inner rotor  52  has as many as n teeth, then the outer rotor  53  has (n+1) teeth. In the present embodiment, n=5. 
         [0072]    A plurality of pump chambers  54  are provided in a space between the inner rotor  52  and the outer rotor  53 . With the above arrangement, as the inner rotor  52  rotates by using the rotation of the wheel-side rotation member  28 , the outer rotor  53  is driven to rotate. Since the inner rotor  52  and the outer rotor  53  rotate on the different rotation centers c 1 , c 2  in this process, the volume of each pump chamber  54  changes constantly. Thus, the lubrication oil from the suction mouth  55  is pumped out of the discharge port  56  to the circulation oil path  25   g.    
         [0073]    As shown in  FIG. 4 , the wheel hub bearing section C includes a wheel hub  32  connected and fixed to the wheel-side rotation member  28 , and a wheel hub bearing  33  which supports the wheel hub  32  rotatably with respect to the housing  22   b  of the speed reducer section B. The wheel hub  32  has a cylindrical hollow section  32   a  and a flange section  32   b.  A driving wheel  14  is fixed to the flange section  32   b  with bolts  32   c.  The shaft section  28   b  of the wheel-side rotation member  28  has its outer diameter surface formed with a spline and a male thread. The hollow section  32   a  of the wheel hub  32  has its inner diameter surface formed with a spline hole. The wheel-side rotation member  28  is threaded into the inner diameter surface of the wheel hub  32 , and a nut  32   d  is threaded to fasten the two members with each other. A brake disc  15  is provided between a tire wheel of the driving wheel  14  and the flange section  32   b  of the wheel hub  32 . 
         [0074]    The wheel hub bearing  33  is provided by a double-row angular contact ball bearing which includes an inside member  33   a  constituted by an outer-side track surface which is integrally formed on an outer diameter surface of the hollow section  32   a  in the wheel hub  32  along a laterally outer side with respect to the vehicle, and an inner ring  33   b  which is fitted around an outer diameter surface of the hollow section  32   a  of the wheel hub  32  along a laterally inner side with respect to the vehicle and has an outer surface formed with an inner-side track surface; two rows of balls  33   c  disposed on the outer-side track surface and the inner-side track surface of the inside member  33   a;  an outer member  33   d  having an inner circumferential surface formed with an outer-side track surface and an inner-side track surface opposed to the outer-side track surface and the inner-side track surface in the inside member  33   a;  a retainer  33   e  which keeps a distance between mutually adjacent balls  33   c;  and sealing members  33   f,    33   g  which seal two axial ends of the wheel hub bearing  33 . 
         [0075]    The outer member  33   d  of the wheel hub bearing  33  is fixed to the housing  22   b  of the speed reducer section B with fastening bolts  71 . 
         [0076]    The outer member  33   d  of the wheel hub bearing  33  has a flange section  33   h  of its outer diameter portion, and a cylindrical section  33   i  on its side facing the speed reducer section B. 
         [0077]    As shown in  FIG. 8 , an electric vehicle  11  equipped with in-wheel motor driving devices according to an embodiment of the present invention includes a chassis  12 , front wheels  13  as steering wheels, rear wheels  14  as driving wheels, and in-wheel motor driving devices  21  which transmit driving forces to the left and the right rear wheels  14  respectively. As shown in  FIG. 9 , the rear wheels  14  are housed inside wheel houses  12   a  of the chassis  12 , and are fixed to a lower portion of the chassis  12  via suspensions  12   b.    
         [0078]    In the present invention, the suspension  12   b  has an end which is connected to the housing  22   b  of the speed reducer section B via a suspension mounting bracket  60 . 
         [0079]    As shown in  FIG. 10 , the housing  22   b  of the speed reducer section B has bolt holes  61   a,    61   b,    61   c  for fixing the suspension mounting brackets  60 . The suspension mounting brackets  60  are bolted onto the housing  22   b  of the speed reducer section B, and ends of suspensions  81 ,  82 ,  83  are connected to the housing  22   b  of the speed reducer section B via the suspension mounting brackets  60 . 
         [0080]    As shown in  FIG. 10 , the housing  22   b  of the speed reducer section B has a generally cylindrical portion  22   c  for housing a speed reducer mechanism of the speed reducer section B which has an input and an output shafts concentric with the motor output shaft “a”; and a lubrication oil reservoir  25   f  which stores lubrication oil. The generally cylindrical portion  22   c  has flat portions  22   d,    22   e  at upper regions of its two sides. The flat portions  22   d,    22   e  which are provided at the upper region of the housing  22   b,  and a lower end surface of the lubrication oil reservoir  25   f  are formed with bolt holes  61   a,    61   b,    61   c  for fixing the suspension mounting brackets  60 . 
         [0081]      FIG. 11  is a perspective view of the housing  22   b  of the speed reducer section B as viewed from a side to which the wheel hub bearing section C is to be mounted.  FIG. 12  is a perspective view from a mounting-surface side of the motor section A. 
         [0082]      FIG. 13  shows a suspension mounting bracket  60  serving as an upper arm bracket  60   a  for connecting an upper arm  81  of the suspension  12   b,  as well as serving as a toe control rod bracket  60   b  for connecting a toe control rod  82 . 
         [0083]      FIG. 14  shows a state in which the upper arm bracket  60   a  and the toe control rod bracket  60   b  are mounted to the flat portions  22   d,    22   e  provided on the upper region of the housing  22   b  of the speed reducer section B. 
         [0084]    Also,  FIG. 15  is a view from a side to which the wheel hub bearing section C is to be mounted. The figure shows a brake disc  15  indicated by broken lines, and a lower arm bracket  60   c  attached to a lower end surface of the lubrication oil reservoir  25   f.  A reference symbol  86  indicates a brake calipers mounting portion which is provided on the housing  22   b  of the speed reducer section B. 
         [0085]      FIG. 16  shows a state where the upper arm  81 , which is a component of the suspension  12   b,  is connected to the upper arm bracket  60   a;  the toe control rod  82  is connected to the toe control rod bracket  60   b;  and a lower arm  83  is connected to the lower arm bracket  60   c.    
         [0086]    The lower arm  83  and the upper arm  81  are spaced from each other, and a shock absorber  84  is disposed in this space to reduce vibration from the road surface. The shock absorber  84  has a lower end which is foxed to the lower arm  83 , and an upper end which is fixed to the chassis  12 . 
         [0087]    The housing  22   b  of the speed reducer section B has a brake mounting portion  86 , to which brake calipers  85  are fixed as shown in  FIG. 16 . 
         [0088]    The brake disc  15  is fixed via the wheel hub bearing section C for integral rotation with the wheel  14 . 
         [0089]    Next,  FIG. 17  shows a bracket  60   d  which has a knuckle-arm shape. This bracket  60   d  may be mounted to the housing  22   b  of the speed reducer section B in place of the toe control rod bracket  60   b,  to constitute a front wheel driving unit. An example of this front wheel driving unit is shown in  FIG. 22 . 
         [0090]    As understood from the above, the driving unit can be used commonly for a front wheel as well as a rear wheel by simply changing the shape of the suspension mounting bracket  60 . 
         [0091]    Next,  FIG. 18  shows a bracket  60   e,  which is a suspension mounting bracket  60  including a brake mounting portion  60   f.    FIG. 19  shows a state in which the bracket  60   e  is mounted. 
         [0092]    The bracket  60   e,  which includes the brake mounting portion  60   f  as described, enables a driving unit to be used as a common driving unit by simply changing the bracket  60   e  according to the shape of the brake. 
         [0093]    Next,  FIG. 20  and  FIG. 21  show embodiments in which the suspension mounting bracket  60  has a seat formed with load bearing portions  60   g  for contact with two surfaces in each of the flat portions  22   d,    22   e  that are made on the housing  22   b  of the speed reducer section B so that an input load from the tire to the suspension  12   b  will not be born only by the bolts which fix the suspension mounting bracket  60  onto the housing  22   b  of the speed reducer section B.  FIG. 20  shows an example arrangement where the load bearing portions  60   g  make contact with a front and a rear surfaces of the seat of the suspension mounting bracket  60  for receiving an axial load whereas  FIG. 21  shows an example arrangement where the load bearing portions  60   g  make contact with an upper and a lower surfaces of the seat of the suspension mounting bracket  60  for receiving a vertical load. Arrows in  FIG. 20  and  FIG. 21  indicate directions of the load. 
         [0094]    As another arrangement, the housing  22   b  of the speed reducer section B may include cylindrical suspension mounting portions which have the flat portions  22   d,    22   e,  with the suspension mounting brackets  60  formed as bottomed cylinders for being fitted by the flat portions  22   d,    22   e  to receive the load. 
         [0095]    Next, there is no specific limitation to materials for the housing  22   a  of the motor section A, the housing  22   b  of the speed reducer section B or the suspension mounting bracket  60 . The most appropriate materials may be selected according to the use and the shape. 
         [0096]    For example, the housing  22   a  of the motor section A and the housing  22   b  of the speed reducer section B may be made of a light-weight material such as an aluminum alloy and resin (including fiber-reinforced resins) whereas the suspension mounting bracket  60  may be made of a steel material for weight reduction. 
         [0097]    Also, heat treatment and/or surface treatment may be performed for reinforcement and other performance improvement such as bruise resistance, corrosion resistance, etc. Examples of such treatment include chromate treatment and alumite treatment. 
         [0098]    In the embodiments described thus far, the suspension mounting brackets  60  are bolted to the housing  22   b  of the speed reducer section B. However, bolting may be replaced by welding. 
         [0099]    There is no specific limitation, either, to the type of the suspension; in other words, the suspension  12   b  may be double wishbone type, strut type, torsion beam type, trailing arm type, or others. 
         [0100]    The wheel hub may be provided by a hub bearing which incorporates a load sensor. 
         [0101]    In the embodiment described above, the cycloid discs  26   a,    26   b  are supported by cylindrical roller bearings. However, the present invention is not limited by this. For example, the bearing may be replaced by slide bearings, cylindrical roller bearings, tapered roller bearings, needle roller bearings, self-aligning roller bearings, deep groove ball bearings, angular contact ball bearings, four-point contact ball bearings, or any other types of bearing regardless of whether they are slide bearings or rolling bearings, whether the bearings includes rollers or balls, or whether the bearings are single row type or double row type. The above applies to any other bearings which are disposed elsewhere in the device, so whatsoever types of bearing may be used. 
         [0102]    It should be noted, however, that deep groove ball bearings have a higher allowable limit in terms of the number of rotations but have a lower load capacity as compared to cylindrical roller bearings. For this reason, a large deep groove ball bearing will have to be utilized in order to achieve a necessary load capacity. Therefore, cylindrical roller bearings will be more suitable as the roller bearing  41  in view of making the in-wheel motor driving devices  21  more compact. 
         [0103]    In the above-described embodiments, the motor section A was provided by a radial gap motor. However, the present invention is not limited to this, and any suitable motor may be employed. For example, an axial gap motor which includes a stator fixed to a housing, and a rotor which is disposed inside the stator to face thereto with an axial gap may be utilized. 
         [0104]    Also, in each of the embodiments described above, the speed reducer section B in the in-wheel motor driving device  21  is implemented by a cycloid reduction gear system. However, the present invention is not limited to this, and any speed reducing mechanism may be employed. Examples include planetary gear speed reducing mechanism and parallel axis gear speed reducing mechanism. 
         [0105]    Further, the electric vehicle  11  shown in  FIG. 8  has the rear wheels  14  serving as driving wheels . However, the present invention is not limited to this, and the front wheels  13  may serve as driving wheels or the vehicle may be a four-wheel drive vehicle. It should be noted here that in the present description, the term “electric vehicle” means any type of vehicle which is driven by electricity. For example, therefore, hybrid cars and similar vehicles should also be included in this category. 
         [0106]    Thus far, embodiments of the present invention have been described with reference to the drawings. However, the present invention is not limited to these illustrated embodiments. Any of these embodiments illustrated thus far may be modified or changed in many ways within the scope or within the equivalence of the present invention. 
       REFERENCE SIGNS LIST 
       [0107]    A motor section 
         [0108]    B speed reducer section 
         [0109]    C wheel hub bearing section 
         [0110]      11  electric vehicle 
         [0111]      12  chassis 
         [0112]      12   a  wheel house 
         [0113]      12   b  suspension 
         [0114]      13  front wheels 
         [0115]      14  rear wheels 
         [0116]      15  disc brake 
         [0117]      22   a  housing of motor section A 
         [0118]      22   b  housing of speed reducer section B 
         [0119]      22   c  generally cylindrical portion 
         [0120]      22   d,    22   e  flat portions 
         [0121]      25   f  lubrication oil reservoir 
         [0122]      60  suspension mounting bracket 
         [0123]      60   a  upper arm bracket 
         [0124]      60   b  toe control rod bracket 
         [0125]      60   c  lower arm bracket 
         [0126]      81  upper arm 
         [0127]      82  toe control rod 
         [0128]      83  lower arm 
         [0129]      84  shock absorber 
         [0130]      85  brake calipers 
         [0131]      24  rotor 
         [0132]      24   a  rotor section 
         [0133]      24   b  hollow section