Patent Abstract:
An object is to reduce various losses occurring in a speed-reduction/differential gear apparatus for electric vehicles including a planetary-gear speed reducer and a differential device, thereby improving transmission efficiency of the driving force and increasing travel distance of the electric vehicle per battery charge. A speed-reduction/differential gear apparatus for electric vehicles includes a planetary-gear speed reducer and a differential device. A planetary gear mechanism in the speed reducer includes a speed-reducer-side carrier which has its inner diameter surface supported by a speed-reducer-side carrier support bearing. The invention provides proper mesh between in the pair of engaging teeth, leading to decrease in loss torque.

Full Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to speed-reduction/differential gear apparatuses for motor-driven electric vehicles, and in particular to one which has decreased loss in torque thereby having improved transmission efficiency leading to increased mileage per electric charge. 
     2. Description of the Related Art 
     A conventional speed-reduction/differential gear apparatus for electric vehicles is typically constituted by a combination of an electric motor, a planetary-gear speed reducer and a planetary-gear differential device. The speed reducer includes an input shaft which is integral with a motor shaft of the electric motor, and the differential device receives speed-reduced output from the speed reducer, as an input (Patent Literature 1). 
     In the differential device, an output is differentially distributed to two distribution members, i.e., the sun gear and the carrier. At the center of the sun gear, there is inserted and connected a first output shaft. The first output shaft coaxially penetrates the speed reducer&#39;s input shaft and the motor shaft which is integral with the reducer input shaft, connects to a motor-side constant-velocity joint, which is connected one of the driving wheels. On the other hand, the carrier is connected to a second output shaft. The second output shaft is connected to a differential-side constant-velocity joint, which is connected to another driving wheel. 
     In the above-described speed reducer and differential device, needle roller bearings are generally used for pinion gears which are included in the planetary gear mechanisms, as described in Patent Literature 1 and 2. An example is shown in  FIG. 7 . 
       FIG. 7  relates to a support structure for a pinion gear  1  in a speed reducer. A needle roller bearing  3  is placed between the pinion gear  1  and a pinion shaft  2 . The pinion shaft  2  has its two ends supported by a carrier  4  and by a disc region  5  of a differential-side ring gear respectively. Thrust washers  6 ,  6  are placed between an end surface of the pinion gear  1  and the carrier  4 , and between another end surface and a disc region  5 . Lubrication to the needle roller bearing  3  is performed through an oil hole  7  which is made in the pinion shaft  2 . 
     CITATION LIST 
     Patent Literature 
     
         
         Patent Literature 1: JP-A H08-42656 Gazette 
         Patent Literature 2: JP-A H06-323404 Gazette 
       
    
     SUMMARY OF THE INVENTION 
     1. Technical Problem 
     According to the Patent Literature 1, the speed reducer&#39;s planetary gear mechanism has a carrier support structure in which the speed-reducer-side carrier is only connected to a speed-reducer-side pinion pin. In other words, it is not supported by a casing via a bearing. Although the speed-reducer-side carrier is integral with the differential-side ring gear, the differential-side ring gear is engaged only with a differential-side pinion gear. 
     Therefore, neither the speed-reducer-side carrier nor the differential-side ring gear is not positively positioned at any specific radial locations, and therefore there can be cases where they make eccentric rotation. This also results in tilt, causing undesirable gear engagement which may lead to excessive wear in teeth surface. 
     In addition, in the support structure for the pinion gear  1  in the speed reducer shown in  FIG. 7 , the thrust washers  6 ,  6  make contact with end surfaces of the retainer of the needle roller bearing  3 , end surfaces of the pinion gear  1 , the carrier  4 , and the disc region  5 , resulting in slip loss at these regions of contact. 
     Therefore, an object of the present invention is to reduce various losses occurring in the apparatus as described above, thereby to improve transmission efficiency of the driving force and to increase travel distance of the electric vehicle per battery charge. 
     2. Solution to the Problem 
     In order to achieve the above-stated object, the present invention provides a speed-reduction/differential gear apparatus for electric vehicles, which includes: an electric motor; a planetary-gear speed reducer and a planetary-gear differential device which are disposed coaxially with the motor; a casing which houses the above-mentioned components; and a coaxially disposed first and second output shafts. The first output shaft penetrates a motor shaft of the electric motor, has its two end portions supported by the casing via respective output shaft support bearings. Driving force from the electric motor receives speed reduction by the speed reducer and is outputted to the differential device. The speed-reduced driving force is outputted to two distribution members by the differential device in accordance with a size of load; one of the distribution members is connected with the first output shaft whereas the other of the distribution members is connected with the second output shaft. With the arrangement described above, the speed-reduction/differential gear apparatus for electric vehicles further includes a speed-reducer-side carrier support bearing between a speed-reducer-side carrier which constitutes part of a planetary gear mechanism of the speed reducer, and the casing. 
     According to the arrangement described above, the speed-reducer-side carrier is positively positioned radially, and is prevented from making eccentric rotation. This provides proper mesh between gear teeth, leading to decrease in loss torque. 
     Specifically, this can be achieved by the following arrangement; the speed-reducer-side carrier has a boss; the speed-reducer-side carrier support bearing is placed between an outer diameter surface of the boss and the casing; and a motor shaft support bearing is placed between an inner diameter surface of the boss and the motor shaft of the electric motor. 
     Further, there may be another arrangement; interior space of the casing is divided by a partition wall into an electric motor encasing section and a speed reducer and differential device encasing section; the partition wall has a shaft hole through which the motor shaft is inserted; the boss of the speed-reducer-side carrier is inserted between the shaft hole and the motor shaft; and the carrier support bearing is between an outer diameter surface of the boss and the shaft hole. 
     Also, where the planetary gear mechanism of the speed reducer includes pinion gears and pinion gear shafts, there may be an arrangement that a deep groove ball bearing is placed between each pair of the speed-reducer-side pinion gear and the speed-reducer-side pinion gear shaft. The arrangement enables to supply lubricant oil from a width surface of the deep groove ball bearing. Thus, it is no longer necessary, unlike in cases where a needle roller bearing is utilized, for supplying lubricant from the pinion shaft. Where oil bath lubrication is employed, the above arrangement makes it possible to lower the height of oil surface, which leads to decreased agitation torque of the lubricant oil. 
     Another arrangement may be that the speed-reducer-side pinion shaft has one end supported by a speed-reducer-side carrier and another end supported by a disc region of a differential-side ring gear; a side plate is placed between the speed-reducer-side carrier and an end surface of an inner ring of the deep groove ball bearing, and a sideplate is placed between a disc region of the differential-side ring gear and another end surface of the inner ring of the deep groove ball bearing. 
     The side plates as described above do not make sliding contact with the speed-reducer-side pinion gear or bearing&#39;s outer ring. This makes it possible to reduce torque loss caused by the sliding contact. 
     3. Advantageous Effects of the Invention 
     As understood from the above, the present invention reduces various losses occurring in the apparatus, and therefore the invention is capable of improving transmission efficiency of the driving force and increasing travel distance of the electric vehicle per battery charge. 
     Another arrangement is that a speed-reducer-side carrier support bearing is placed between a speed-reducer-side carrier which constitute part of the planetary gear mechanism in the speed reducer, and the casing. This provides positive radial positioning and prevents eccentric rotation of the speed-reducer-side carrier. This provides proper mesh between each gear teeth, leading to decrease in loss torque. Actual measurements of the transmission efficiency revealed improvement by a one percent at a maximum. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectional view of Embodiment 1. 
         FIG. 2  is an enlarged sectional view of a portion of the same. 
         FIG. 3  is a sectional view taken in lines X 1 -X 1  in  FIG. 1 . 
         FIG. 4  is an enlarged sectional view of a portion of a speed-reducer-side pinion support structure in Embodiment 1. 
         FIG. 5  is a sectional view of a portion of a variation made to the arrangement shown in  FIG. 4 . 
         FIG. 6  is a sectional view taken in lines X 2 -X 2  in  FIG. 1 . 
         FIG. 7  is an enlarged sectional view of a portion of a conventional speed-reducer-side pinion support structure. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, embodiments of the present invention will be described based on the attached drawings. 
     Embodiment 1 
     A speed-reduction/differential gear apparatus for electric vehicles according to Embodiment 1 includes, as shown in  FIG. 1  and  FIG. 2 , an electric motor  11 , a planetary-gear speed reducer  12  and planetary-gear differential device  13  which are disposed coaxially with each other; a casing  14  which houses the above-listed components; and a first output shaft  15   a  and a second output shaft  15   b  which are disposed coaxially with each other. The first output shaft  15   a  is connected to an outer ring  16  (hereinafter called motor-side outer ring  16 ) of a motor-side constant-velocity joint whereas the second output shaft  15   b  is connected to an outer ring  17  (hereinafter called differential-side outer ring  17 ) of a differential-side constant-velocity joint. 
     The motor-side outer ring  16  and the differential-side outer ring  17  respectively have cups  16   a ,  17   a  and stems  16   b ,  17   b . Spaces between the respective pair of cups  16   a ,  17   a  and the stems  16   b ,  17   b  are partitioned by cup bottom plates  16   c ,  17   c . The stem  16   b  and the stem  17   b  have axially penetrating serrated holes  18 ,  19  respectively. 
     The first output shaft  15   a  penetrates a hollow motor shaft  21  of the electric motor  11 . The first output shaft  15   a  has an end on the electric motor  11  side, which is inserted into the serrated hole  18  in the stem  16   b  of the motor-side outer ring  16 , thereby integrally connected therewith by serration connection. Further, at the end portion of the stem  16   b  where the first output shaft  15   a  is inserted, an anti-backoff pin  20  is inserted radially to prevent the first output shaft  15   a  from backing off. 
     Also, the first output shaft  15   a  has an end on the differential device  13  side, which is inserted into a bearing hole  48   b  made in a boss  48   a  in a differential-side carrier  48  to be described later (see  FIG. 2 ). Between an inserting end of the second output shaft  15   b  and an inner diameter surface of the bearing hole  48   b , there is disposed an output shaft support bearing  22  which is provided by a needle roller bearing. 
     The casing  14  is an assembly of a motor casing  14   a  which houses the electric motor  11 ; a speed-reduction/differential casing  14   b  which houses the speed reducer  12  and the differential device  13 ; and a casing lid  14   c  on the differential device  13  side. 
     Each of the motor casing  14   a  and the speed-reduction/differential casing  14   b  has their one end closed and another end open. The closed end of the speed-reduction/differential casing  14   b  is coaxially and sealingly fitted and connected to the open end of the motor casing  14   a  whereas the casing lid  14   c  is sealingly fitted and connected to the open end of the speed-reduction/differential casing  14   b.    
     The closed end of the speed-reduction/differential casing  14   b  serves as a partitioning wall  14   d  which divides an interior space of the casing  14 ; i.e. the partitioning wall  14   d  divides the space into an encasing section for the electric motor  11 , and an encasing section for the speed reducer  12  and the differential device  13 . The partitioning wall  14   d  has a center with a bearing hole  14   e.    
     The closed end (left end) of the motor casing  14   a  has a center with a shaft hole  23 . Inside the shaft hole  23 , there is provided an axially protruding boss  24 . The motor shaft  21  has its end inserted into an inner end&#39;s inner diameter surface of the boss  24 , via a motor shaft support bearing  25 , which is provided by a deep-groove ball bearing, disposed between the two members. 
     At the motor shaft support bearing  25 , the first output shaft  15   a  comes out of the end of the motor shaft  21  to protrude to the outside of the motor casing  14   a , and to this protrusion the stem  16   b  of the motor-side outer ring  16  is connected. Also, between an inner diameter surface of the boss  24  and the first output shaft  15   a , there is placed a first output shaft support bearing  26 , and on an outer side thereof, an oil seal  27  is provided. The oil seal  27  provides sealing against lubricant oil inside the motor casing  14   a.    
     The electric motor  11  housed in the motor casing  14   a  is constituted by a stator  28  which is fixed to an inner circumferential surface of the motor casing  14   a , and a rotor  29  which is inside the stator and is assembled integrally with the motor shaft  21 . The motor shaft  21  has its one end supported by the motor shaft support bearing  25 . 
     The motor shaft  21  has another end supported by a motor shaft support bearing  31  which is provided by a deep groove ball bearing placed between the shaft and the partitioning wall  14   d , i.e., the closed wall of the speed-reduction/differential casing  14   b . From this motor shaft support bearing  31 , an end of the motor shaft  21  protrudes toward the speed reducer  12 , serving as a speed reducer input shaft  30 . 
     The speed-reduction/differential casing  14   b  coaxially houses the speed reducer  12  and the differential device  13  in this order from the partitioning wall  14   d  side. 
     The speed reducer  12  is constituted by a speed-reducer-side sun gear  35  (see  FIG. 2  and  FIG. 3 ) which is provided integrally with the speed reducer input shaft  30  around an outer circumferential surface of a tip-end of the shaft; a speed-reducer-side ring gear  36  which is on the outer diameter side of the sun gear and is coaxially fixed to an inner diameter surface of the speed-reduction/differential casing  14   b ; and speed-reducer-side pinion gears  37  and a speed-reducer-side carrier  38  (see  FIG. 1  and  FIG. 2 ) which are disposed between the sun gear  35  and the ring gear  36 , along the circumferential direction at three equidistant locations. 
     The speed-reducer-side pinion gears  37  engage with the sun gear  35  and the ring gear  36 . Also, each pinion gear  37  is supported by the speed-reducer-side pinion shaft  41  via a deep groove ball bearing  39 . The pinion shaft  41  has an axially penetrating lubrication hole  42 . 
     As shown in  FIG. 2 , the speed-reducer-side pinion shaft  41  has its one end supported by the speed-reducer-side carrier  38 , and another end supported by a disc region  44   a  of a differential-side ring gear  44  which will be described later. Side plates  32 ,  33  are placed, i.e., one between the speed-reducer-side carrier  38  and an end surface of an inner ring  39   a  (see  FIG. 4 ) of the deep groove ball bearing  39 , and the other between the other end surface of the inner ring and the disc region  44   a  of the differential-side ring gear  44  (see  FIG. 4 ). 
     These side plates  32 ,  33  have an outer diameter which is smaller than that of the inner ring  39   a , so as to avoid contact with an outer ring  39   b  or with the pinion gear  37 . Also, none of the inner ring  39   a , the speed-reducer-side carrier  38  and the differential-side ring gear  44  makes relative rotation with respect to the side plates  32 ,  33 , so there is no slip loss at the side plates  32 ,  33 . 
     If the side plates  32 ,  33  are not employed, then slip loss may be avoided by a different arrangement. Specifically, as shown in  FIG. 5 , the inner ring  39   a  is given a greater width than that of the speed-reducer-side pinion gear  37  so as to avoid contact between the speed-reducer-side carrier  38  and the disc region  44   a  of the differential-side ring gear  44 . 
     As shown in  FIG. 2 , the speed-reducer-side carrier  38  is fitted between the partitioning wall  14   d , which represents the closed end of the speed-reduction/differential casing  14   b , and the speed-reducer-side pinion gear  37 , with a radial gap around the speed reducer input shaft  30 . In its inner diameter section, the speed-reducer-side carrier  38  has a boss  38   a  protruding toward the electric motor  11 , and this boss  38   a  is inserted between the speed reducer input shaft  30  which is integral with the motor shaft  21 , and the bearing hole  14   e  of the partitioning wall  14   d.    
     A carrier support bearing  43  which is provided by a deep groove ball bearing is disposed between an outer diameter surface of the boss  38   a  and the bearing hole  14   e . Also, the motor shaft support bearing  31  is disposed between an inner diameter surface of the boss  38   a  and the speed reducer input shaft  30 . The carrier support bearing  43  positions the speed-reducer-side carrier  38  with respect to the casing  14 . Also, the motor shaft support bearing  31  positions the motor shaft  21  with respect to the casing  14  via the carrier support bearing  43 . 
     The speed-reducer-side carrier  38  has an outer circumferential edge, which has a plurality of connection tabs  40  (see  FIG. 1  and  FIG. 3 ) each bent toward the differential device  13 , at a space along its circumferential direction. These connection tabs  40  are inserted into the ring gear disc region  44   a  of the differential-side ring gear  44 , to fasten the speed-reducer-side carrier  38  and the differential-side ring gear  44  with each other. 
     As shown in  FIG. 1 ,  FIG. 2  and  FIG. 6 , the differential device  13  is constituted by: the differential-side ring gear  44 ; a differential-side sun gear  45  which is radially inside thereof and is coaxially therewith; double-pinion differential-side pinion gears  46   a ,  46   b  engaged with each other and disposed between the ring gear  44  and the sun gear  45 ; differential-side pinion shafts  47 ,  47   b  which support these pinion gears  46   a ,  46   b ; and a differential-side carrier  48  which supports these pinion shafts  47   a ,  47   b.    
     The differential-side ring gear  44  includes a disc region  44   a ; a circumferential region  44   b  which is an outer circumferential edge of the disc region  44   a  bent outward (toward the casing lid  14   c ); and a gear region  44   c  formed on an inner diameter surface of the circumferential region  44   b . The disc region  44   a  is fittingly disposed coaxially around an outer circumference of the first output shaft  15   a , with a radial gap (see  FIG. 2 ). A thrust bearing  63  is disposed between the disc region  44   a  and the differential-side sun gear  45 . 
     The differential-side sun gear  45  has a serrated hole  50  in its center, into which the first output shaft  15   a  is inserted, thereby integrated with the first output shaft  15   a  by means of serration connection. 
     An end of the first output shaft  15   a  which protrudes outward from the serration connection is inserted into the bearing hole  48   b  in the boss  48   a  of the differential-side carrier  48 . Between this inserting region and an inner diameter surface of the bearing hole  48   b , there is disposed a first output shaft support bearing  22  which is provided by a needle roller bearing. The boss  48   a  is supported by the casing  14  which includes the casing lid  14   c , via a differential-side carrier support bearing  54  to be described later. The differential-side sun gear  45  has an axial lubrication hole  62 . 
     The double-pinion gears  46   a ,  46   b  have the same size and the same number of teeth as each other. As shown in  FIG. 6 , they engage with each other. One pinion gear  46   a  of the two has a greater PCD than the other pinion gear  46   b , and engages with the ring gear  44  whereas the other pinion gear  46   b  which has a smaller PCD engages with the sun gear  45 . Needle roller bearings  58   a ,  58   b  are disposed between each pair made by the pinion gears  46   a ,  46   b  and the pinion shafts  47   a ,  47   b . Each of the pinion shafts  47   a ,  47   b  has an oil hole  66 . 
     As shown in  FIG. 2 , the differential-side carrier  48  is disposed along an inner side surface of the casing lid  14   c  and provides support, together with a differential-side carrier assist member  49  which is disposed along the disc region  44   a  of the differential-side ring gear  44 , to two ends of both pinion shafts  47   a ,  47   b . The differential-side carrier  48  includes an outer circumferential edge which has a plurality of locations each having a fastening protrusion  59  (see  FIG. 1  and  FIG. 6 ) protruding toward the differential-side carrier assist member  49 . Each of the fastening protrusions  59  has a tip formed with a small projection  60  (see  FIG. 1 ), which is inserted into a fastening hole  61  in the differential-side carrier assist member  49 . This fastens the differential-side carrier  48  and the differential-side carrier assist member  49  with each other. 
     As shown in  FIG. 1  and  FIG. 2 , the boss  48   a  is at a center of the differential-side carrier  48 , protruding outward. The axial bearing hole  48   b  in the boss  48   a  is at an inner end (at the end of the differential device  13  side), and as has been described earlier, the end of the first output shaft  15   a  is inserted into the bearing hole  48   b , in a rotatable manner via the first output shaft support bearing  22 . 
     The boss  48   a  has a closed outer end, at a center of which there is integrally provided the second output shaft  15   b  which was described earlier. The second output shaft  15   b  is inserted into the serrated hole  19  in the stem  17   b  of the differential-side outer ring  17 , and therefore fastened with the stem by means of serration connection. Also, in the stem  17   b , an anti-backoff pin  70  penetrates the second output shaft  15   b  radially, to prevent the shaft from backing off. 
     A differential-side carrier support bearing  54  which is provided by a deep groove ball bearing is placed between the boss  48   a  in the differential-side carrier  48  and a boss  53  in the casing lid  14   c , so that the differential-side carrier  48  and the second output shaft  15   b  are supported by the casing  14  including the casing lid  14   c.    
     The differential-side carrier support bearing  54  has a holding ring  55  which is fastened by a bolt  56  to an outer side surface of the boss  53  of the casing lid  14   c . An oil seal  57  is placed between the holding ring  55  and the boss  48   a , sealing the speed-reduction/differential casing  14   b , thereby keeping lubrication oil inside. 
     The speed-reduction/differential gear apparatus for electric vehicles according to Embodiment 1 has the arrangement as described thus far. Next, description will cover functions thereof. 
     As the electric motor  11  (see  FIG. 1 ) is driven, the motor shaft  21  rotates. Simultaneously, the speed reducer input shaft  30  and the speed-reducer-side sun gear  35 , which are integral with the motor shaft  21 , rotate. The speed-reducer-side pinion gears  37  which are engaged with the speed-reducer-side sun gear  35 , rotates while revolving. This revolving movement causes the speed-reducer-side carrier  38  to make rotation at a reduced speed, and this slower rotation is outputted to the differential-side ring gear  44  on the differential device  13  side. 
     Where the number of teeth in the speed-reducer-side sun gear  35  is represented by Zs and the number of teeth in the speed-reducer-side ring gear  36  is represented by Zr, the speed reduction is made at a ratio of Zs/(Zs+Zr) as is well known. 
     A load received by one of the wheels of the vehicle is applied to the differential-side sun gear  45  via the motor-side constant-velocity joint which includes the motor-side outer ring  16  and the first output shaft  15   a  whereas a load received by the other wheel is applied to the differential-side carrier  48  via the differential-side constant-velocity joint which includes the differential-side outer ring  17  and the second output shaft  15   b . When the loads applied to the two wheels are equal to each other, the differential-side sun gear  45 , the pinion gears  46   a ,  46   b  and the carrier  48  rotate in an integral fashion, i.e., there is no relative rotation amongst them in response to the rotational input from the ring gear  44 . Thus, the rotational input is distributed evenly, i.e., a portion thereof is passed on the differential-side sun gear  45  and the first output shaft  15   a , to the motor-side outer ring  16  while another portion is passed on the differential-side carrier  48  and the second output shaft  15   b , to the differential-side outer ring  17 , causing the left and the right wheels to turn at the same speed via their respective constant-velocity joints. 
     On the other hand, when there is a difference between the loads which are applied to the left and the right wheels, the rotational input resulting from rotation and revolution of the pinion gears  46   a ,  46   b  is differentially distributed to the left and the right wheels through the above-mentioned routes, and then through the motor-side outer ring  16  or through the differential-side outer ring  17 , in accordance with a load difference. 
     In other words, in a case where the load which is passed on to the motor-side outer ring  16  and is applied to the first output shaft  15   a  becomes relatively larger, causing the sun gear  45  which is integral with the shaft to rotate at a number of rotations Ns and this number is smaller than a number of input rotations Nr of the ring gear  44  by ΔN, the carrier  48  rotates at a number of rotations Nc, which is expressed as:
 
 Nc=Nr +λ/(1−λ)·Δ N  
 
In other words, the second output shaft  15   b  rotates at a higher speed. In the above equation, λ represents gear ratio (=Zs/Zr) whereas Zs represents the number of teeth in the sun gear  45 , and Zr represents the number of teeth in the ring gear  44 .
 
     On the other hand, in a case where the load which is passed on to the differential-side outer ring  17  and is applied to the second output shaft  15   b  becomes relatively larger, causing the carrier  48  which is integral with the shaft to rotate at a number of rotations Nc and this number is smaller than the number of input rotations Nr by ΔN, the sun gear  45  rotates at the number of rotations Ns which is expressed as:
 
 Ns=Nr +(1−λ)/λ·Δ N  
 
In other words, the first output shaft  15   a  rotates at a higher speed.
 
     During these operations, the speed-reducer-side carrier  38  and the differential-side ring gear  44  which is integrally fastened thereto make their rotations under a positively positioned state, being supported by the casing  14  via the speed-reducer-side carrier support bearing  43 . The arrangement, therefore, prevents each gear in each planetary gear mechanism in the speed reducer  12  and the differential device  13  from making eccentric rotation. 
     Also, the speed-reducer-side pinion gears  37  and their support bearings, i.e., the deep groove ball bearings  39  are prevented from making slip loss which may otherwise caused by the side plates  32 ,  33 . 
     The speed-reduction/differential gear apparatus for electric vehicles according to Embodiment 1 utilizes oil-bath lubrication. Specifically, lubrication oil for both of the motor casing  14   a  and the speed-reduction/differential casing  14   b  fills inside the casing  14  to the level indicated by an oil surface level symbol L. The stator  28  of the electric motor  11  is below the oil surface L but the rotor  29  is not. In this arrangement, rotation of the rotor  29  will not agitate the lubricant oil, so the arrangement decreases loss caused by the agitation. 
     In the speed reducer  12 , the speed-reducer-side carrier  38  has the connection tabs  40  and the speed-reducer-side pinion gear  37  on its outer circumference, and they splash the lubricant oil during their rotation as they pass through the body of lubricant oil below the oil surface L. The lubricant oil is splashed inside the speed reducer  12  and lubricates the parts inside. Part of the oil finds a way to a lubrication hole  42  in the speed-reducer-side pinion shaft  41  and moves axially. 
     Since the speed-reducer-side pinion gear  37  is supported by the deep groove ball bearing  39 , splashed lubrication oil is supplied from the width surface of the deep groove ball bearing  39 . For this reason, there is no need for an arrangement to provide lubrication from inside the speed-reducer-side pinion shaft  41 . 
     In the differential device  13 , the differential-side carrier  48  has the fastening protrusions  59 , the differential-side pinion gears  46   a ,  46   b , etc., on its outer circumference, and they splash lubrication oil. The lubricant oil is splashed inside the differential device  13  and lubricates the parts inside. Part of the oil finds a way to a lubrication hole  62  made in the differential-side sun gear  45  and moves axially. 
     During the above-described operation, the oil seals  27 ,  57  on both of the left and right sides prevent the lubrication oil from leaking out of the casing  14 . Also, lubricant oil which reached the motor casing  14   a  and the speed-reduction/differential casing  14   b  communicate with each other inside the casing  14  through a communication hole  65  in the closed wall of the speed-reduction/differential casing  14   b.    
     REFERENCE SIGNS LIST 
     
         
           11  electric motor 
           12  speed reducer 
           13  differential device 
           14  casing 
           14   a  motor casing 
           14   b  speed-reduction/differential casing 
           14   c  casing lid 
           14   d  partitioning wall 
           14   e  bearing hole 
           15   a  first output shaft 
           15   b  second output shaft 
           16  motor-side outer ring 
           16   a  cup 
           16   b  stem 
           16   c  cup bottom plate 
           17  differential-side outer ring 
           17   a  cup 
           17   b  stem 
           17   c  cup bottom plate 
           18  serrated hole 
           19  serrated hole 
           20  anti-backoff pin 
           21  motor shaft 
           22  first output shaft support bearing 
           23  shaft hole 
           24  boss 
           25  motor shaft support bearing 
           26  first output shaft support bearing 
           27  oil seal 
           28  stator 
           29  rotor 
           30  speed reducer input shaft 
           31  motor shaft support bearing 
           32  side plate 
           33  side plate 
           35  speed-reducer-side sun gear 
           36  speed-reducer-side ring gear 
           37  speed-reducer-side pinion gear 
           38  speed-reducer-side carrier 
           38   a  boss 
           39  deep groove ball bearing 
           39   a  inner ring 
           39   b  outer ring 
           40  connection tab 
           41  speed-reducer-side pinion shaft 
           42  lubrication hole 
           43  speed-reducer-side carrier support bearing 
           44  differential-side ring gear 
           44   a  disc region 
           44   b  circumferential region 
           44   c  gear region 
           45  differential-side sun gear 
           46   a ,  46   b  differential-side pinion gear 
           47   a ,  47   b  differential-side pinion shaft 
           48  differential-side carrier 
           48   a  boss 
           48   b  bearing hole 
           49  differential-side carrier assist member 
           50  serrated hole 
           52  serration-connected region 
           53  boss 
           54  differential-side carrier support bearing 
           55  holding ring 
           56  bolt 
           57  oil seal 
           58   a ,  58   b  needle roller bearing 
           59  fastening protrusion 
           60  small projection 
           61  fastening hole 
           62  lubrication hole 
           63  thrust bearing 
           65  communication hole 
           66  oil hole 
           70  anti-backoff pin

Technology Classification (CPC): 5