Patent Publication Number: US-2017355051-A1

Title: Driving Apparatus and Tire-Wheel Assembly Including Driving Apparatus

Description:
INCORPORATION BY REFERENCE 
     The disclosure of Japanese Patent Application No. 2016-118357 filed on Jun. 14, 2016 including the specification, drawings and abstract is incorporated herein by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a driving apparatus and a tire-wheel assembly including the driving apparatus. 
     2. Description of Related. Art 
     There is a known driving apparatus configured such that the speed of rotation output from a motor is reduced by a speed-reducer and a rotary driving force generated by the motor is transmitted to a rotary shaft. Japanese Patent Application Publication No. 2016-97761 (JP 2016-97761 A) describes an in-wheel motor driving apparatus including an input shaft (output shaft), a motor portion (motor), and a speed-reducer, as an example of the above-described driving apparatus. The speed-reducer reduces the speed of rotation output from the motor portion, and outputs the rotation having a reduced speed to the input shaft. In the in-wheel motor driving apparatus, the motor portion and the speed-reducer are disposed side by side along the axial direction of the input shaft. 
     The driving apparatus described in JP 2016-97761. A is configured such that the motor and the speed-reducer are disposed side by side along the axial direction of the output shaft. This configuration increases the width of the driving apparatus in the axial direction. This makes it difficult to achieve desired size reduction of the driving apparatus. 
     SUMMARY OF THE INVENTION 
     One object of the invention is to provide a driving apparatus configured to achieve desired size reduction thereof and a tire-wheel assembly including the driving apparatus. 
     A driving apparatus according to an aspect of the invention includes an output shaft, a motor, and a speed-reducer. The motor includes a stator having an annular shape, and a rotor having an annular shape. The rotor is disposed radially inward of the stator or disposed radially outward of the stator. The speed-reducer is disposed radially inward of the motor. The speed-reducer is configured to reduce the speed of rotation output from the rotor and transmit a rotary driving force of the rotor to the output shaft. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and further features and advantages of the invention will become apparent from the following description of example embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements and wherein: 
         FIG 1  is a plan view schematically illustrating a drive-train of a vehicle; 
         FIG. 2  is a sectional view illustrating a driving apparatus according to an embodiment of the invention; and 
         FIG. 3  is a sectional view illustrating a driving apparatus according to another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Hereinafter, example embodiments of the invention will be described in detail with reference to the accompanying drawings.  FIG. 1  is a plan view schematically illustrating a drive-train of a vehicle  1 . As illustrated in  FIG. 1 , the vehicle  1  is a four-wheel-drive vehicle, and includes four tire-wheel assemblies including a pair of front tire-wheel assemblies  2   FR ,  2   FL , and a pair of rear tire-wheel assemblies  3   RR ,  3   RL . The pair of front tire-wheel assemblies  2   FR ,  2   FL  includes a front right tire-wheel assembly  2   FR  and a front left tire-wheel assembly  2   FL . The pair of rear tire-wheel assemblies  3   RR ,  3   RL , includes a rear right tire-wheel assembly  3   RR  and a rear left tire-wheel assembly  3   RL . Each of the front right tire-wheel assembly  2   FR , the front left tire-wheel assembly  2   FL , the rear right tire-wheel assembly  3   RR , and the rear left tire-wheel assembly  3   RL  include a wheel  4  and a tire  5 . 
     The front right tire-wheel assembly  2   FR  is rotationally driven by a front-right-tire-wheel-assembly driving apparatus  7   FR  including a front-right-tire-wheel-assembly driving motor  6   FR  (motor). The front left tire-wheel assembly  2   FL  is rotationally driven by a front-left-tire-wheel-assembly driving apparatus  9   FL  including a front-left-tire-wheel-assembly driving motor  8   FL  (motor). The front-right-tire-wheel-assembly driving motor  6   FR  is an in-wheel three-phase alternating-current (AC) electric motor incorporated in the wheel  4  of the front right tire-wheel assembly  2   FR . The front-left-tire-wheel-assembly driving motor  8   FL  is an in-wheel three-phase AC electric motor incorporated in the wheel  4  of the front left tire-wheel assembly  2   FL . 
     The rear right tire-wheel assembly  3   RR  is rotationally driven by a rear-right-tire-wheel-assembly driving apparatus  11   RR  including a rear-right-tire-wheel-assembly driving motor  10   RR . The rear left tire-wheel assembly  3   RL  is rotationally driven by a rear-left-tire-wheel-assembly driving apparatus  13   RL  including a rear-left-tire-wheel-assembly driving motor  12   RL . The rear-right-tire-wheel-assembly driving motor  10   RR  is an in-wheel three-phase AC electric motor incorporated in the wheel  4  of the rear right tire-wheel assembly  3   RR . The rear-left-tire-wheel-assembly driving motor  12   RL  is an in-wheel three-phase AC electric motor incorporated in the wheel  4  of the rear left tire-wheel assembly  3   RL . In the present embodiment, the rear right tire-wheel assembly  3   RR  and the rear left tire-wheel assembly  3   RL  have a direct-drive configuration, that is, the rear right tire-wheel assembly  3   RR  and the rear left tire-wheel assembly  3   RL  are rotationally driven directly by the rear-right-tire-wheel-assembly driving motor  10   RR  and the rear-left-tire-wheel-assembly driving motor  12   RL , respectively. 
     The vehicle  1  further includes a steering operation mechanism  14  configured to steer the front right tire-wheel assembly  2   FR  and the front left tire-wheel assembly  2   FL . The steering operation mechanism  14  includes a steering wheel  15 , a steering shaft  16 , a first pinion shaft  17 , a rack shaft  18 , and two tie rods  19 . The steering shaft  16  rotates in response to a steering operation of the steering wheel  15 . The first pinion shaft  17  is coupled to the steering shaft  16  so as to rotate together with the steering shaft  16  in an integrated manner. The first pinion shaft  17  has first pinion teeth  17   a . The first pinion teeth  17   a  are meshed with first rack teeth  18   a  of the rack shaft  18 . The tie rods  19  are coupled to respective axial end portions of the rack shaft  18 . The front right tire-wheel assembly  2   FR  and the front left tire-wheel assembly  2   FL  are coupled to the rack shaft  18  via the tie rods  19  and knuckle arms (not illustrated). 
     As the steering wheel  15  is steered, the first pinion shaft  17  rotates together with the steering shaft  16 , and the rotation of the first pinion shaft  17  is converted into a reciprocating motion of the rack shaft  18 . Thus, the steered angle of the front right tire-wheel assembly  2   FR  and the front left tire-wheel assembly  2   FL  changes, and the front right tire-wheel assembly  2   FR  and the front left tire-wheel assembly  2   FL  are steered. The vehicle  1  further includes a steering assist mechanism  20  configured to apply a steering assist force to the steering operation mechanism  14 . The steering assist mechanism  20  includes a second pinion shaft  21 , a steering assist motor  22 , and a steering assist speed-reducer  23 . The second pinion shaft  21  is rotationally driven by the steering assist motor  22 . The steering assist speed-reducer  23  reduces the speed of rotation output from the steering assist motor  22 , and transmits a rotary driving three generated by the steering assist motor  22  to the second pinion shaft  21 . The second pinion shaft  21  has second pinion teeth  21   a . The second pinion teeth  21   a  are meshed with second rack teeth  18   b  of the rack shaft  18 . 
     As the steering assist motor  22  is driven, the speed of rotation output from the steering assist motor  22  is reduced by the steering assist speed-reducer  23 , and a rotary driving force generated by the steering assist motor  22  is transmitted to the second pinion shaft  21 . Thus, the second pinion shaft  21  rotates, and the rotation of the second pinion shaft  21  is converted into a reciprocating motion of the rack shaft  18 . In this way, the steering assist force is applied to the steering operation mechanism  14  by the steering assist mechanism  20 . 
     The vehicle  1  further includes an electronic control unit (ECU)  24 , an inverter module  25 , and a battery  26 . The ECU  24  is, for example, a microcomputer including a central processing unit (CPU) and memories (e.g., a read-only memory (ROM), a random-access memory (RAM), and a non-volatile memory). The ECU  24  controls the driving of the front-right-tire-wheel-assembly driving motor  6   FR , the front-left-tire-wheel-assembly driving motor  8   FL , the rear-right-tire-wheel-assembly driving motor  10   RR , the rear-left-tire-wheel-assembly driving motor  12   RL , and the steering assist motor  22 , via the inverter module  25 . 
     The inverter module  25  includes a plurality of three-phase inverter circuits configured to individually drive the front-right-tire-wheel-assembly driving motor  6   FR , the front-left-tire-wheel-assembly driving motor  8   FL , the rear-right-tire-wheel-assembly driving motor  10   RR , the rear-left-tire-wheel-assembly driving motor  12   RL , and the steering assist motor  22 . The inverter module  25  drives the front-right-tire-wheel-assembly driving motor  6   FR  and the front-left-tire-wheel-assembly driving motor  8   FL , with electric power supplied from the battery  26 . Thus, the front-right-tire-wheel-assembly driving motor  6   FR  and the front-left-tire-wheel-assembly driving motor  8   FL  are rotationally driven, so that the front right tire-wheel assembly  2   FR  and the front left tire-wheel assembly  2   FL  rotate. In addition, the inverter module  25  drives the rear-right-tire-wheel-assembly driving motor  10   RR  and the rear-left-tire-wheel-assembly driving motor  12   RL , with electric power supplied from the battery  26 . Thus, the rear-right-tire-wheel-assembly driving motor  10   RR  and the rear-left-tire-wheel-assembly driving motor  12   RL  are rotationally driven, so that the rear right tire-wheel assembly  3   RR  and the rear left tire-wheel assembly  3   RL  rotate. In addition, the inverter module  25  drives the steering assist motor  22 , with electric power supplied from the battery  26 . Thus, a steering assist force is applied to the steering operation mechanism  14 . 
     Next, with reference to  FIG. 2 , the detailed configuration of the front-right-tire-wheel-assembly driving apparatus  7   FR  incorporated in the wheel  4  of the front right tire-wheel assembly  2   FR  will be described.  FIG. 2  is a sectional view illustrating the front-right-tire-wheel-assembly driving apparatus  7   FR  according to an embodiment of the invention. Because the front right tire-wheel assembly  2   FR  and the front left tire-wheel assembly  2   FL  have almost the same configuration, the configuration of the front right tire-wheel assembly  2   FR  will be described by way of example, and description on the configuration of the front left tire-wheel assembly  2   FL  will be omitted. 
     With reference to  FIG. 2 , the front-right-tire-wheel-assembly driving apparatus  7   FR  includes an output shaft  31 , the front-right-tire-wheel-assembly driving motor  6   FR , a speed-reducer  32 , and a housing  33 . The output shaft  31  is coupled to the wheel  4 . The speed-reducer  32  reduces the speed of rotation output from the front-right-tire-wheel-assembly driving motor  6   FR , and transmits a rotary driving force generated by the front-right-tire-wheel-assembly driving motor  6   FR  to the output shaft  31 . The housing  33  accommodates the output shaft  31 , the front-right-tire-wheel-assembly driving motor  6   FR,  the speed-reducer  32 , and so forth. 
     Hereinafter, the direction in which a central axis L of the output shaft  31  extends will be simply referred to as “axial direction”. In the axial direction, the direction toward the inside of the vehicle  1  will be simply referred to as “axially-inward direction”, and the direction toward the outside of the vehicle  1  will be simply referred to as “axially-outward direction”. The radial direction of the output shaft  31  will be simply referred to as “radial direction”. In the radial direction, the direction toward the central axis L will be simply referred to as “radially inward direction”, and the direction away from the central axis L will be simply referred to as “radially outward direction”. 
     The housing  33  is made of a metal material containing, for example, aluminum. The housing  33  includes an annular portion  34  having an annular plate shape, a cylindrical portion  35  having a cylindrical shape, and a closing member  36  having an annular plate shape. The annular portion  34  is centered at the output shaft  31 . The cylindrical portion  35  protrudes in the axially-inward direction from a peripheral edge of the annular portion  34 , and opens on the opposite side of the housing  33  from the annular portion  34 . The closing member  36  closes the opening of the cylindrical portion  35 . The closing member  36  of the housing  33  is fastened to the cylindrical portion  35  with a bolt  37 . The annular portion  34 , the cylindrical portion  35 , and the closing member  36  of the housing  33  define an internal space  38  in which the output shaft  31 , the front-right-tire-wheel-assembly driving motor  6   FR , the speed-reducer  32 , and so forth are accommodated. 
     A first recess portion  34   a  and a second recess portion  34   b  are provided in the annular portion  34  of the housing  33 . The first recess portion  34   a  is recessed in the axially-outward direction from an axially-inner-side surface of the annular portion  34 . The second recess portion  34   b  is recessed in the axially-outward direction from the bottom of the first recess portion  34   a . The second recess portion  34   h  has a radial width (opening width) that is smaller than the radial width (opening width) of the first recess portion  34   a . A through-hole  34   c  extending through the second recess portion  34   b  in the axial direction is provided in the central portion of the bottom of the second recess portion  34   b.    
     The output shaft  31  has one end portion  31   a  located on the axially-outer side and the other end portion  31   b  located on the axially-inner side. The one end portion  31   a  of the output shaft  31  passes through the annular portion  34  of the housing  33  (the through-hole  34   c  of the second recess portion  34   b ), and is located outside the housing  33 . The other end portion  31   b  of the output shaft  31  is located in the internal space  38  of the housing  33 . The output shaft  31  is supported by a hub bearing  39  provided in the housing  33  so as to be rotatable relative to the housing  33 . The detailed configuration of the hub bearing  39  will be described later in detail. 
     In the present embodiment, the front-right-tire-wheel-assembly driving motor  6   FR  is an inner rotor motor. The front-right-tire-wheel-assembly driving motor  6   FR  includes a stator  41  having an annular shape, a rotor  42  having an annular shape, and a motor shaft  43  having a columnar shape. The stator  41  is fixed to an inner peripheral surface of the cylindrical portion  35  of the housing  33 . The rotor  42  having an annular shape is disposed radially inward of the stator  41 . The motor shaft  43  is disposed radially inward of the rotor  42 , and is coupled to the rotor  42 . The stator  41  is fastened to the inner peripheral surface of the cylindrical portion  35  of the housing  33  with a bolt  44 . The stator  41  is provided with stator coils including a U-phase coil, a V-phase coil, and a W-phase coil that respectively correspond to the U-phase, V-phase, and W-phase of the front-right-tire-wheel-assembly driving motor  6   FR . 
     The motor shaft  43  is disposed coaxially with the output shaft  31 . The motor shaft  43  has one end portion  43   a  located on the axially-outer side and the other end portion  43   b  located on the axially-inner side. The one end portion  43   a  of the motor shaft  43  is rotatably coupled to the other end portion  31   b  of the output shaft  31  via a bearing  45 . The other end portion  43   b  of the motor shaft  43  extends through the closing member  36  of the housing  33 , and is drawn outside the housing  33 . The other end portion  43   b  of the motor shaft  43  is supported by a bearing  46  attached to an inner wall surface of the closing member  36  so as to be rotatable relative to the closing member  36 . Thus, the motor shaft  43  is supported so as to be rotatable relative to the housing  33 , and is rotatable relative to the output shaft  31 . 
     In the present embodiment, the rotor  42  is coupled to the motor shaft  43  via a coupling member  47 . More specifically, the coupling member  47  includes an annular portion  48  having an annular plate shape, a cylindrical portion  49 , a flange portion  50 , and a boss portion  51 . The cylindrical portion  49  protrudes in a cylindrical shape in the axially-outward direction from a peripheral edge of the annular portion  48 . The flange portion  50  protrudes in the radial direction from an axially-outer-side end portion of the cylindrical portion  49 . The boss portion  51  extends toward one side in the axial direction (in the present embodiment, in the axially-outward direction) from an inner peripheral edge of the annular portion  48 . 
     The coupling member  47  is coupled to the motor shaft  43  so as to be rotatable together with the motor shaft  43  in an integrated manner, when the boss portion  51  is connected to the motor shaft  43  via a key  52 . The rotor  42  is supported by the cylindrical portion  49  and the flange portion  50  of the coupling member  47 . That is, the cylindrical portion  49  and the flange portion  50  of the coupling member  47  constitute a supporting portion that supports the rotor  42 . In the present embodiment, the rotor  42  is fastened to the flange portion  50  with a bolt  53 . Thus, the rotor  42  is prevented from being detached from the coupling member  47 . The rotor  42  and the motor shaft  43  are coupled together via the coupling member  47  so as to be rotatable together with each other in an integrated manner. 
     In the front-right-tire-wheel-assembly driving motor  6   FR , as the rotor  42  is rotationally driven, a rotary driving force of the rotor  42  is transmitted to the motor shaft  43  via the coupling member  47 . Thus, the motor shaft  43  is rotationally driven. As the motor shaft  43  is rotationally driven, the rotary driving force of the motor shaft  43  is transmitted to the speed-reducer  32 . The speed-reducer  32  is disposed radially inward of the front-right-tire-wheel-assembly driving motor  6   FR . The speed-reducer  32  reduces the speed of rotation output from the motor shaft  43 , and transmits the rotary driving force of the motor shaft  43  to the output shaft  31 . In the present embodiment, the speed-reducer  32  includes a planetary gear mechanism  64  including a sun gear  60 , a ring gear  61  having an annular shape, planet gears  62 , and a carrier  63 . The sun gear  60  is coupled to the one end portion  43   a  of the motor shaft  43  so as to be rotatable together with the motor shaft  43  in an integrated manner. The ring gear  61  is non-rotatably disposed around the sun gear  60 . The planet gears  62  are disposed between the sun gear  60  and the ring gear  61  so as to be meshed with both the sun gear  60  and the ring gear  61 . The carrier  63  is coupled to the output shaft  31  so as to be rotatable together with the output shaft  31  in an integrated manner. The carrier  63  holds the planet gears  62  so as to allow the planet gears  62  to rotate about their axes, and holds the planet gears  62  so as to allow the planet gears  62  to turn around the axis of the sun gear  60 . 
     In the present embodiment, the sun gear  60  is provided so as to be integral with the one end portion  43   a  of the motor shaft  43 . The sun gear  60  is coupled to the rotor  42  via the motor shaft  43  and the coupling member  47  so as to be rotatable together with the rotor  42  in an integrated manner. The carrier  63  includes a carrier annular portion  65  having an annular plate shape. The carrier annular portion  65  is disposed apart from the output shaft  31  in the axially-outward direction, between the coupling member  47  of the front-right-tire-wheel-assembly driving motor  6   FR  and the other end portion  31   b  of the output shaft  31 . The carrier  63  is fixed to the output shaft  31  when the carrier annular portion  65  and the other end portion  31   b  of the output shaft  31  are fastened together with a bolt  66 . Each of the planet gears  62  includes a planet gear shaft  67  and a gear portion  69 . The planet gear shaft  67  is supported between the other end portion  31   b  of the output shaft  31  and the carrier annular portion  65 . The gear portion  69  is rotatably supported by the planet gear shaft  67  via a bearing  68 . 
     The front-right-tire-wheel-assembly driving apparatus  7   FR  further includes a ring-gear supporting member  71  having a generally cylindrical shape. The ring gear  61  is non-rotatably supported by the ring-gear supporting member  71 . The ring gear  61  is fixed to the housing  33  via the ring-gear supporting member  71 . The ring-gear supporting member  71  is preferably made of a metal material having a higher strength than that of the housing  33  (e.g., chrome molybdenum steel). 
     The ring-gear supporting member  71  includes a first cylindrical portion  72 , a second cylindrical portion  73  having a cylindrical shape, and a base portion  74  having an annular shape. The first cylindrical portion  72  is located on the axially-outer side, and is inserted in the second recess portion  34   b  of the annular portion  34  of the housing  33 . The second cylindrical portion  73  is located on the axially-inner side, and extends through a region between the planet gears  62  and the rotor  42  (the cylindrical portion  49  of the coupling member  47 ) in the axial direction. The base portion  74  is connected to the first cylindrical portion  72  and the second cylindrical portion  73 , at a position between the first cylindrical portion  72  and the second cylindrical portion  73 . 
     The first cylindrical portion  72  of the ring-gear supporting member  71  is inserted in the second recess portion  34   b  so as to come into contact with a side wall and a bottom wall of the second recess portion  34   b  of the annular portion  34  of the housing  33 . The first cylindrical portion  72  of the ring-gear supporting member  71  has an inner peripheral surface that is flush with an inner peripheral surface of the base portion  74  of the ring-gear supporting member  71 . The hub bearing  39  is disposed radially inward of the first cylindrical portion  72  and the base portion  74  of the ring-gear supporting member  71 . The inner peripheral surfaces of the first cylindrical portion  72  and the base portion  74  of the ring-gear supporting member  71  constitute a bearing-supporting portion  75  that supports the hub bearing  39 . Hereinafter, the configurations of the output shaft  31 , the hub bearing  39 , and the bearing-supporting portion  75  of the ring-gear supporting member  71  will be described in detail. 
     In the present embodiment, the hub bearing  39  includes a double-row angular contact ball bearing. The hub bearing  39  includes an inner ring  76 , an outer ring  77 , and a plurality of rolling elements  78 A,  78 B. The rolling elements  78 A,  78 B are disposed between the inner ring  76  and the outer ring  77 . In the present embodiment, the plurality of the rolling elements  78 A,  7813  includes a plurality of the first rolling elements  78 A and a plurality of the second rolling elements  78 B. The first rolling elements  78 A are disposed on the axially-inner side, and are arranged along the circumferential direction of the inner ring  76  of the hub bearing  39 . The second rolling elements  78 B are disposed on the axially-outer side, and are arranged along the circumferential direction of the inner ring  76  of the hub bearing  39 . 
     The inner ring  76  of the hub bearing  39  is fitted to an outer peripheral surface of the output shaft  31  so as to be rotatable together with the output shaft  31  in an integrated manner. In the present embodiment, the output shaft  31  has a receiving portion  31   c  that is in contact with an axially-inner-side end portion of the inner ring  76  of the hub bearing  39 , and receives the inner ring  76  of the hub bearing  39  in the axial direction. This receiving portion  31   c  of the output shaft  31  serves also as a positioning portion that sets the position at which the inner ring  76  of the hub bearing  39  is disposed. 
     The outer ring  77  of the hub bearing  39  is non-rotatably supported by the bearing-supporting portion  75  of the ring-gear supporting member  71 . The inner ring  76  is rotatably supported by the outer ring  77  of the hub bearing  39  via the rolling elements  78 A,  78 B. That is, the bearing-supporting portion  75  of the ring-gear supporting member  71  supports the output shaft  31  via the hub bearing  39  such that the output shaft  31  is rotatable. The second cylindrical portion  73  of the ring-gear supporting member  71  has an inner peripheral portion  73   a  facing the planet gears  62  at its axially-inner-side end portion, and supports the ring gear  61  at the inner peripheral portion  73   a . In the present embodiment, the ring gear  61  is provided so as to be integral with the inner peripheral portion  73   a  of the second cylindrical portion  73 . That is, the inner peripheral portion  73   a  of the second cylindrical portion  73  constitutes the ring gear-supporting portion  79  that supports the ring gear  61 . 
     The base portion  74  of the ring-gear supporting member  71  includes an outer annular protrusion  80  and an inner annular protrusion  81 . The outer annular protrusion  80  protrudes in an annular shape radially outward from an outer peripheral surface of the base portion  74 . The inner annular protrusion  81  protrudes in an annular shape radially inward from the inner peripheral surface of the base portion  74 . The outer annular protrusion  80  of the base portion  74  is configured to be fitted in the first recess portion  34   a  of the housing  33 , and is in contact with a side wall and a bottom wall of the first recess portion  34   a . The outer annular protrusion  80  is fastened to the bottom portion of the first recess portion  34   a  with a bolt  82 . More specifically, a first bolt insertion hole  83  is selectively provided in the outer annular protrusion  80 . In addition, a second bolt insertion hole  84  is provided in the bottom portion of the first recess portion  34   a  in the housing  33 , at a position at which the second bolt insertion hole  84  is aligned with the first bolt insertion hole  83 . The bolt  82  is inserted in the first bolt insertion hole  83  and the second bolt insertion hole  84  from the outer annular protrusion  80 -side toward the annular portion  34  of the housing  33 . In this way, the ring-gear supporting member  71  is fixed to the housing  33 . 
     The inner annular protrusion  81  of the base portion  74  is configured to protrude radially inward so as to come into contact with an axially-inner-side end portion of the hub bearing  39  in the axial direction. The inner annular protrusion  81  of the ring-gear supporting member  71  is in contact with at least the outer ring  77  of the hub bearing  39  in the axial direction. The inner annular protrusion  81  constitutes a load-receiving portion  85  configured to receive axial loads applied to the output shaft  31 , via the hub bearing  39 . 
     As described above, the ring-gear supporting member  71  has, in addition to the function of fixing the ring gear  61  to the housing  33 , the function of supporting the hub bearing  39  and the function of receiving axial loads applied to the output shaft  31 , via the hub bearing  39 . The ring-gear supporting member  71  is disposed in a region radially inward of the front-right-tire-wheel-assembly driving motor  6   FR  and radially outward of the speed-reducer  32 . The ring-gear supporting member  71  defines a first accommodation chamber  90  in which the front-right-tire-wheel-assembly driving motor  6   FR  is accommodated and disposed. The first accommodation chamber  90  is disposed radially outward of the ring-gear supporting member  71 . The ring-gear supporting member  71  defines a second accommodation chamber  91  in which the output shaft  31  and the speed-reducer  32  are accommodated and disposed. The second accommodation chamber  91  is disposed radially inward of the ring-gear supporting member  71 . More specifically, the second accommodation chamber  91  is defined by a region surrounded by an inner wall surface of the ring-gear supporting member  71 . The first accommodation chamber  90  is defined by a region interposed between an outer wall surface of the ring-gear supporting member  71  and an inner wall surface of the cylindrical portion  35  of the housing  33 . 
     When configuration in which the first accommodation chamber  90  and the second accommodation chamber  91  are defined is employed, the front-right-tire-wheel-assembly driving apparatus  7   FR  may be assembled through the following steps. That is, first, the output shaft  31 , the hub bearing  39 , the planet gears  62 , and so forth are installed in the second accommodation chamber  91  defined by the ring-gear supporting member  71 , whereby an assembly unit in which these components are disposed in an integrated manner is formed (sub-assembly). Subsequently, the assembly unit (sub-assembly) is attached to the housing  33 , and then the front-right-tire-wheel-assembly driving motor  6   FR  is installed in the first accommodation chamber  90  defined between the housing  33  and the ring-gear supporting member  71 . When the configuration in which the first accommodation chamber  90  and the second accommodation chamber  91  are defined in the housing  33  is employed, it becomes easier to install each of the constituent components that are accommodated and disposed in the housing  33 . 
     Referring to  FIG. 2  again, outside the housing  33 , a wheel coupling member  95  to be coupled to the wheel  4  is attached to the one end portion  31   a  of the output shaft  31  so as to be rotatable together with the output shaft  31  in an integrated manner. The wheel coupling member  95  includes a boss portion  97  having a cylindrical shape, and a flange portion  98  having an annular plate shape. The boss portion  97  is coupled to the one end portion  31   a  of the output shaft  31  through a key  96 . The flange portion  98  extends radially outward from an axially-outer-side end portion of the boss portion  97 . 
     The flange portion  98  has a bolt insertion hole  100  through which the bolt  99  for attaching the wheel coupling member  95  to the wheel  4  is inserted. A seal member  101  is provided between the wheel coupling member  95  and the annular portion  34  of the housing  33 . A nut  102  is screwed to the one end portion  31   a  of the output shaft  31 , so that the wheel coupling member  95  is prevented from detaching from the output shaft  31 . 
     Outside the housing  33 , a rotation angle detection sensor  103  (in the present embodiment, a resolver) for detecting a rotation angle of the motor shaft  43  is attached to the other end portion  43   b  of the motor shaft  43 . When the output shaft  31  is rotationally driven with the wheel coupling member  95  coupled to the wheel  4 , a rotary driving force of the output shaft  31  is transmitted to the wheel coupling member  95 , so that the wheel coupling member  95  rotates. As the wheel coupling member  95  is rotationally driven, a rotary driving force of the wheel coupling member  95  is transmitted to the wheel  4 , so that the wheel  4  rotates. In this way, the front right tire-wheel assembly  2   FR  rotates. 
     In the front-right-tire-wheel-assembly driving apparatus  7   FR  according to the present embodiment, the speed-reducer  32  is disposed radially inward of the front-right-tire-wheel-assembly driving motor  6   FR . Thus, it is possible to appropriately reduce the axial width of the front-right-tire-wheel-assembly driving apparatus  7   FR . Thus, it is possible to provide the front-right-tire-wheel-assembly driving apparatus  7   FR  configured to achieve desired size reduction thereof. In addition, in the front-right-tire-wheel-assembly driving apparatus  7   FR  according to the present embodiment, the first accommodation chamber  90  and the second accommodation chamber  91  are defined by the ring-gear supporting member  71 , in the internal space  38  of the housing  33 . The front-right-tire-wheel-assembly driving motor  6   FR  is accommodated and disposed in the first accommodation chamber  90 . The output shaft  31  and the speed-reducer  32  are accommodated and disposed in the second accommodation chamber  91 . Thus, it is possible to define each of the regions in which the front-right-tire-wheel-assembly driving motor  6   FR , the output shaft  31 , and the speed-reducer  32  are accommodated and disposed. Thus, it becomes easier to install the front-right-tire-wheel-assembly driving motor  6   FR , the output shaft  31 , and the speed-reducer  32  in the housing  33 . As a result, it becomes possible to achieve desired size reduction of the front-right-tire-wheel-assembly driving apparatus  7   FR  and increase the efficiency of producing the front-right-tire-wheel-assembly driving apparatus  7   FR . 
     In the front-right-tire-wheel-assembly driving apparatus  7   FR  according to the present embodiment, the ring-gear supporting member  71  for fixing the ring gear  61  to the housing  33  includes the bearing-supporting portion  75  (the first cylindrical portion  72  and the base portion  74  of the ring-gear supporting member  71 ) that supports the hub bearing  39 , at a position between the output shaft  31  and the bearing-supporting portion  75 . Thus, it is not necessary to use another member for supporting the hub bearing  39  between the output shaft  31  and the ring-gear supporting member  71 , and thus the number of components can be reduced. As a result, it is possible to achieve further size reduction of the front-right-tire-wheel-assembly driving apparatus  7   FR . 
     In addition, in the front-right-tire-wheel-assembly driving apparatus  7   FR  according to the present embodiment, the ring-gear supporting member  71  includes the load-receiving portion  85  (the inner annular protrusion  81  of the base portion  74  of the ring-gear supporting member  71 ) for receiving axial loads applied to the output shaft  31 , via the hub bearing  39 . With this configuration, the axial loads applied to the output shaft  31  can be received by the load-receiving portion  85  of the ring-gear supporting member  71 . With the configuration in which the ring-gear supporting member  71  includes the load-receiving portion  85 , it is possible to make the axial thickness of the load-receiving portion  85  smaller than that in a case where the load-receiving portion  85  is provided separately from the ring-gear supporting member  71 . Furthermore, the load-receiving portion  85  can be formed using a part of the ring-gear supporting member  71 . Thus, it is possible to reduce the number of components. As a result, it is possible to achieve further size reduction of the front-right-tire-wheel-assembly driving apparatus  7   FR , from this viewpoint. 
       FIG. 3  is a sectional view illustrating a front-right-tire-wheel-assembly driving apparatus  7   FR  according to another embodiment of the invention. In  FIG. 3 , the same configurations as those described with reference to  FIG. 1  and  FIG. 2  will be denoted by the same reference symbols as those in  FIG. 1  and  FIG. 2 , and description thereof will be omitted. In the front-right-tire-wheel-assembly driving apparatus  7   FR  according to the present embodiment, an inner ring  76  of the hub bearing  39  includes a first portion  76 A configured to support a plurality of the first rolling elements  78 A and a second portion  76 B configured to support a plurality of the second rolling elements  78 B. The first portion  76 A of the inner ring  76  is integral with the output shaft  31 . The second portion  76 B of the inner ring  76  is integral with the boss portion  97  of the wheel coupling member  95 . The outer ring  77  of the hub bearing  39  is integral with the first cylindrical portion  72  and the base portion  74  of the ring-gear supporting member  71 . 
     With this configuration as well, it is possible to exhibit the same effects as those described in the foregoing embodiment. In the front-right-tire-wheel-assembly driving apparatus  7   FR  according to the present embodiment, it is possible to form the inner ring  76  of the hub bearing  39  using a part of the output shaft  31  and a part of the boss portion  97  of the wheel coupling member  95 , and to form the outer ring  77  of the hub bearing  39  using a part of the ring-gear supporting member  71 . Thus, in the front-right-tire-wheel-assembly driving apparatus  7   FR  according to the present embodiment, the number of components is smaller than that in a case where the inner ring  76  and the outer ring  77  of the hub bearing  39  are individually provided. As a result., it becomes possible to achieve cost reduction. 
     While the example embodiments of the invention have been described so far, the invention may be implemented in various other embodiments. For example, in each of the foregoing embodiments, the front-right-tire-wheel-assembly driving motor  6   FR  is an inner rotor motor. However, the front-right-tire-wheel-assembly driving motor  6   FR  may be, instead of an inner rotor motor, an outer rotor motor including a stator  41  having an annular shape, and a rotor  42  having an annular shape and disposed radially outward of the stator  41 . When this configuration is employed, for example, the stator  41  is fixed to the ring-gear supporting member  71  (an outer peripheral surface of the second cylindrical portion  73 ) and the rotor  42  is disposed between the stator  41  and the inner wall surface of the cylindrical portion  35  of the housing  33 . 
     In each of the foregoing embodiments, a driving apparatus having the same configuration as that of the driving apparatuses  7   FR,    9   FL , may be installed in each of the rear right tire-wheel assembly  3   RR  and the rear left tire-wheel assembly  3   RL . In addition, in each of the foregoing embodiments, the boss portion  51  of the coupling member  47  may be spline-fitted to the motor shaft  43  without using the key  52 , or may be serration-fitted to the motor shaft  43  without using the key  52 . The boss portion  51  of the coupling member  47  may be fastened to the motor shaft  43  with a bolt, without using the key  52 . 
     In the foregoing embodiments, the huh bearing  39  includes a double-row angular contact ball bearing. Alternatively, the hub bearing  39  may include, instead of a double-row angular contact ball bearing, a double-row tapered roller bearing. Further, it is possible to make a variety of design changes within the scope of the appended claims. 
     In the configuration of the invention, the speed-reducer is disposed radially inward of the motor. Thus, it is possible to appropriately reduce the axial width of the driving apparatus. As a result, it is possible to provide the driving apparatus configured to achieve desired size reduction thereof.