Abstract:
Power differential transfer device for automatically changing the power transfer system to two wheel drive, four wheel drive or differential locking and includes a first cage disposed between a drive member and a first driven member for frictionally engaging with the first driven member for relative rotation and accommodating a first rolling member in an opening, a second cage provided between the drive member and a second driven member for frictionally engaging with the second driven member for relative rotation and accommodating a second rolling member in an opening. The first cage includes a projection for engaging with a recess provided in the second cage to allow a relative rotation by a limited angle.

Description:
[0001]     This application is based on and claims priority under 35 U.S.C.§119 with respect to Japanese Application No. 2004-187389 filed on Jun. 25, 2004, the entire content of which is incorporated herein by reference.  
       FIELD OF THE INVENTION  
       [0002]     This invention generally relates to a power differential transfer device, and more particularly to a power differential transfer device having a differential function and the same or similar locking function to a differential gear device and capable of automatically changing from two wheel drive to four wheel drive or vise versa.  
       BACKGROUND OF THE INVENTION  
       [0003]     Known transfer device such as front differential device for ATV includes a power differential transfer device for changing drive mode among two wheel drive, four wheel drive and differential lock mode by manually operating or electrically controlling the clutch mechanism.  
         [0004]     Among such known arts, a U.S. Pat. No. 6,896,085 B2 discloses a power switching apparatus having a power change over device for changing over the power distribution between drive member and two, right and left driven members. In this device, the a circumferential connecting surface of the drive member and respective circumferential connecting surfaces of the two driven members are wedge connected through rollers by rotating the edge surface of the cage which is forcibly moved in axial direction by an electromagnetic force so as to be in friction contact with the driven members when the change over means is set at on-mode. According to this simple construction, the change over between full two wheel drive and full four-wheel drive modes can be easily performed.  
       SUMMARY OF THE INVENTION  
       [0005]     According to one aspect of the invention, a power differential transfer device includes a drive member having an inner cam face, a first driven member disposed coaxially with the drive member at an inside of the drive member and having a first outer cam face at an outer peripheral surface, a second driven member disposed coaxially with the drive member at the inside of the drive member and being adjacent to the first driven member in an axial direction, the second driven member having a second outer cam face at the outer peripheral surface, a plurality of first rolling members disposed in an annular space formed by a plurality of wedge shaped spaces between the inner cam face and the first outer cam face in a circumferential direction for wedge connection between the drive member and the first driven member, a plurality of second rolling members disposed in an annular space formed by a plurality of wedge shaped spaces between the inner cam face and the second outer cam face in a circumferential direction for wedge connection between the drive member and the second driven member, a first cage frictionally engaging with the first driven member directly or indirectly for permitting relative rotation therewith and having a plurality of first openings for accommodating the plurality of first rolling members respectively therein; and a second cage frictionally engaging with the second driven member directly or indirectly for permitting relative rotation therewith and having a plurality of second openings for accommodating the plurality of second rolling members respectively therein.  
         [0006]     The power differential transfer device of the invention includes a feature that the first cage includes a projection extending to the second cage side, the second cage includes a recess for receiving the projection of the first cage and that the projection of the first cage and the recess of the second cage allow a relative rotation therebetween by a predetermined angle. The predetermined angle is defined by an angle between a first line connecting a rotation axis of the drive member and the center of one of the plurality of first rolling member at a wedge connection position and a second line between the rotation axis of the drive member and one of the plurality of center of the second rolling member at a non-wedge connection position within the wedged space where the first rolling member is situated, or an angle between a third line connecting the rotation axis of the drive member and the center of the second rolling member at the wedge connection position and a fourth line connecting the rotation axis of the drive member and the center of the first rolling member at the non-wedge connection position within the wedge space where the second rolling member is situated.  
         [0007]     According to another aspect of the present invention, the power differential transfer device includes a drive member having a circumferential connection surface in an inner peripheral surface, a first driven member disposed coaxially with the drive member in the inner periphery side of the drive member and having an inner cam face at an outer peripheral surface of the first driven member, a second driven member disposed coaxially with the drive member at the inner peripheral side of the drive member and disposed adjacent the first driven member in an axial direction, the second driven member having an inner cam face at an outer peripheral surface of the second driven member, a first rolling member disposed in an annular space formed by a plurality of wedge shaped spaces between the drive member and the first driven member in a circumferential direction for wedge connection between the drive member and the first driven member, a second rolling member disposed in an annular space formed by a plurality of wedge shaped spaces between the drive member and the first driven member in a circumferential direction for wedge connection between the drive member and the second driven member, a first cage frictionally engaging with the first driven member for relative rotation therewith directly or indirectly and having an opening for accommodating the first rolling member therein and a second cage member frictionally engaging with the second driven member for relative rotation therewith directly or indirectly and having an opening for accommodating the second rolling member therein. The feature of this structure according to the aspect of the invention is that the first cage includes a projection extending to the second cage side, the second cage includes a recess for receiving the projection of the first cage and that the projection of the first cage and the recess of the second cage allow a relative rotation therebetween by a predetermined angle. This predetermined angle is defined by an angle between a first line connecting a rotation axis of the drive member and the center of the first rolling member at a wedge connection position and a second line between the rotation axis of the drive member and the center of the second rolling member at a non-wedge connection position within the wedged space where the first rolling member is situated, or an angle between a third line connecting the rotation axis of the drive member and the center of the second rolling member at the wedge connection position and a fourth line connecting the rotation axis of the drive member and the center of the first rolling member at the non-wedge connection position within the wedge space where the second rolling member is situated.  
         [0008]     The wedged space means a space formed in wedge shape between an outer surface of the drive member and the outer surface of the first and the second driven members seen in an axial direction. In other words, the space between the surfaces of the drive member and the driven members is formed from the smallest to the largest with a wedge shape.  
         [0009]     The wedge connection means a connection between the drive member and the driven members by the rolling member which rolls from the larger space in wedge space to the smaller space to engage the drive member and the driven member by wedge action. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING FIGURES  
       [0010]     The foregoing and additional features and characteristics of the present invention will become more apparent from the following detailed description considered with reference to the accompanying drawing figures in which like reference numerals designate like elements and wherein:  
         [0011]      FIG. 1  is a schematic view of a vehicle with a power differential transfer device according to a first embodiment of the present invention;  
         [0012]      FIG. 2  is a cross sectional view of the power differential transfer device according to the first embodiment of the invention, but only showing schematically;  
         [0013]      FIG. 3  is a cross sectional view of the power differential transfer device according to the first embodiment of the invention taken along A-A line of  FIG. 2 ;  
         [0014]      FIG. 4  is a schematic view of a first cage and a second cage used in the power differential transfer device of the first embodiment of the invention, showing a plane view, left side view and right side view for each cage;  
         [0015]      FIG. 5  is a schematic view of a first spring used in the power differential transfer device of the first embodiment of the invention, showing a plane view and a side view;  
         [0016]      FIG. 6  is a view explaining operations of the first cage and the second cage used in the power differential transfer device of the first embodiment of the invention, showing a state of neutral position of the first and second cages;  
         [0017]      FIG. 7  is a view explaining operations of the first cage and the second cage used in the power differential transfer device of the aspect of the invention, each showing a state of vehicle straight forward running;  
         [0018]      FIG. 8  is a view similar to  FIG. 7 , but explaining operations of the first cage and the second cage used in the power differential transfer device of the first embodiment of the invention, each showing a state of vehicle forward running with left turning;  
         [0019]      FIG. 9  is a view explaining operations of the first cage and the second cage used in the power differential transfer device of the first embodiment of the invention, each showing a state of vehicle rearward straight running;  
         [0020]      FIG. 10  is a view explaining operations of the first cage and the second cage used in the power differential transfer device of the aspect of the invention, each showing a state of vehicle straight forward running with engine braking; and,  
         [0021]      FIG. 11  is a schematic view explaining a predetermined permissible angle of relative rotation between the first cage and the second cage used in the power differential transfer device of the first embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]     A first embodiment of the present invention is explained hereinafter referring to attached drawings.  
         [0023]      FIG. 1  is a schematic view of a vehicle with a power differential transfer device according to the first embodiment of the present invention.  FIG. 2  is a cross sectional view of the power differential transfer device, but only showing schematically.  FIG. 3  is a cross sectional view of the power differential transfer device according to the embodiment of the invention taken along A-A line of  FIG. 2 .  
         [0024]      FIG. 4  is a schematic view of a first cage and a second cage used in the power differential transfer device of the embodiment of the invention, each showing a plane view, left side view and right side view.  FIG. 4  shows various views of the cages according to the embodiment, in which  FIG. 4  (A) shows a plane view of the first cage  71 , (B) shows a left side view of the first cage, (C) shows a right side view of the first cage, (D) shows a plane view of the second cage  72 , (E) shows a left side view of the second cage and (F) shows a right side view of the second cage.  
         [0025]      FIG. 5  is a schematic view of a first spring  65  used in the power differential transfer device of the embodiment of the invention, showing a plane view and a side view.  FIG. 5  (A) shows a plane view of the first spring and Fig. (B) shows a side view of the first spring of this embodiment. In  FIG. 3 , the first housing and the second housing are omitted from the drawing for more easily understanding the spring.  
         [0026]     First the vehicle as a whole will be explained in accordance with  FIG. 1 . A vehicle includes an engine  1 , a transmission  2  connected to the output side of the engine  1 , a drive shaft  3  connected to the output side of the transmission  2 , a power differential transfer device  4  connected at the front end of the drive shaft  3 . The vehicle further includes a front left side wheel  6  connected to one end of a front wheel shaft  5 . The other end of the shaft  5  is connected to the power differential transfer device  4 . A front right side wheel  8  is connected to one end of a right side front wheel shaft  7 . The other end of the shaft  7  is connected to the power differential transfer device  4 . A differential gear unit  10  is connected to the rear end of the drive shaft  3 . A rear left side wheel  12  is connected to one end of a rear wheel shaft  11 . The other end of the rear wheel shaft  11  is connected to the differential gear unit  10  and a rear right side wheel  14  is connected to one end of another (right side) rear wheel shaft  13 . The other end of the shaft  13  is connected to the differential gear unit  10 .  
         [0027]     Rotational torque from the engine  1  is always transmitted to the differential gear unit  10  at the rear side wheels  12  and  14  and also always transmitted to the power differential transfer device  4  at the front side wheels  6  and  8 . The power differential transfer device  4  transmits the engine torque through four routes, (A) to right and left side wheel shafts  7 ,  5 , (B) to only right side wheel shaft  7 , (C) to only left side wheel shaft  5  and (D) not to transmit the engine torque to both front right and left side wheel shafts  7 ,  5  by switching operation based on the road surface conditions detected through left side front wheel  6  and left side wheel shaft  5  and through right side front wheel  8  and right side wheel shaft  7  by only mechanical operation, without any manual or electrical controlling. This will be later explained in detail.  
         [0028]     The power differential transfer device  4  will be explained hereinafter. In  FIG. 2 , the power differential transfer device  4  includes a pinion gear shaft  21 , a drive member  30 , a first housing  41 , a second housing  42 , bolt  43 , bearings  51 ,  52 ,  53  and  54 , a first rolling member  61 , a second rolling member  62 , a first driven member  63 , a second driven member  64 , a first spring  65 , a second spring  66 , a first cage  71 , a second cage  72 , a first friction member  81  and a second friction member  82 .  
         [0029]     The pinion gear shaft  21  is rotatably supported on the second housing  42  through the bearings  53  and  54 . The pinion gear shaft  21  includes a pinion gear  21   a  between a portion supported by the bearing  53  and a portion supported by the bearing  54 . The pinion gear  21   a  engages with a ring gear  34 . The pinion gear shaft  21  is connected to the drive shaft  3  (shown in  FIG. 1 ).  
         [0030]     The drive member  30  is an assembly of a case  31 , a first cover  32  and a second cover  33 , the ring gear  34 , screws  35  and  36  for connecting the first and the second covers  32  and  33  to the case  31  and a bolt  37  for connecting the ring gear  34  to the case  31 . These components  31  to  37  are rotated as a unit. The drive member  30  is rotatably supported by the first and second housings  41  and  42  through the bearings  51  and  52 . The bearing  51  is supported by the first housing  41  and the bearing  52  is supported by the second housing  42 .  
         [0031]     The case  31  is a cylindrical member having a plurality of inner cam faces  31   a  at the inner peripheral surface thereof. The inner cam faces  31   a  form a polygon. Inside of the case  31 , a plurality of first and second rolling members  61  and  62  are provided, the number of which corresponds to the number of the inner cam face, i.e., the number of the side of the polygon, for example, if the polygon is a hexagon, then the number of the rolling member  61  and  62  is  12  in total (6+6). The first cover  32  is connected to the left side end of the case  31  by the screw  35 , while the second cover  33  is connected to the right side end of the case  31  by the screw  36 . The first cover  32  is supported by the first housing  41  through the first bearing  51 . The second cover  33  is supported by the second housing  42  through the second bearing  52 . The ring gear  34  is attached to the outer peripheral portion of the case  31  by the bolt  37  and is engaged with the pinion gear  21   a . Thus the drive member  30  is always driven by the rotation of the drive shaft  3  shown in  FIG. 1 .  
         [0032]     The first housing  41  and the second housing  42  are integrally connected together by the bolt  43 .  
         [0033]     The first driven member  63  is provided at inner peripheral side of the case  31  to the first cover  31 . The first driven member  63  is in spline connection with the front left wheel shaft  5  and rotated together with the wheel shaft  5 . The second driven member  64  is provided at the inside of the case  31  to the second cover  33 . The second driven member  64  is in spline connection with the front right wheel shaft  7  and rotated together with the wheel shaft  7 . The first and second driven members  63  and  64  are coaxially provided with the center axis of the drive member  30 . The first driven member  63  is provided with a hub portion  63   a  at the first cover  32  side. The hub portion  63   a  is relatively rotatably inserted into a stepped portion  32   a  provided at the inner peripheral portion of the first cover  32  at left side thereof. The second driven member  64  is provided with a hub portion  64   a  at the second cover  33  side. The hub portion  64   a  is relatively rotatably inserted into a stepped portion  33   a  provided at the inner peripheral portion of the second cover  33  at left side thereof. Thus the first and second driven members  63  and  64  are held to the drive member  30  for relative rotation with the drive member  30  (case  31 , first cover  32  and second cover  33 ). The drive member  30  (case  31  and ring gear  34 ) and the first and second driven members  63  and  64  are coaxially provided. A spacer (not shown) may be provided between the first and second driven members  63  and  64  for keeping the space therebetween.  
         [0034]     The first driven member  63  is provided with a first outer cam face  63   b , which is in contact with the first rolling member  61  at the outer peripheral surface of the first driven member  63 . Similarly, the second driven member  64  is provided with a second outer cam face  64   b , which is in contact with the second rolling member  62  at the outer peripheral surface of the second driven member  64 . The outer cam face  63   b  of the first driven member  63  and the outer cam face  64   b  of the second driven member  64   b  are provided coaxially with the case  31  (cam faces  31   a ). In an annular space  91  provided among the outer cam face  63   b  of the first driven member  63  and the outer cam face  64   b  of the second driven member  64   b  and the inner cam faces  31   a , a plurality of wedged space  91   a  ( FIG. 3 ) are formed, which gradually become narrower toward both peripheral directions (both rotation directions).  
         [0035]     The first rolling member  61  is spherical in shape and accommodated in an opening  71   a  provided at the first cage  71  in the annular space  91 . The first rolling member  61  contacts with the inner cam face  31   a  of the case  31  and contacts with the circumferential connection portion  63   b  of the first driven member  63  at the opposite side. The first cage  71  restricts the movement of the circumferential connection portion  63   b  in rotational and axial directions. Similarly, the second rolling member  62  is spherical in shape and accommodated in an opening  72   a  provided at the second cage  72  in the annular space  91 . The second rolling member  62  contacts with the inner cam face  31   a  of the case  31  and contacts with the circumferential connection portion  64   b  of the second driven member  64  at the opposite side. The second cage  72  restricts the movement of the circumferential connection portion  64   b  in rotational and axial directions. The shape of the first and second rolling members  61  and  62  may not be limited to the spherical shape but may be a roller.  
         [0036]     The first cage  71  is a cylindrical member and provided in the annular space  91  at the first cover  32  side. (See  FIG. 2  and  FIG. 4 .). The first cage  71  includes a recess  71   b  at the first cover  32  side for inserting a pawl  65   a  provided at the first spring  65 . The second cage  72  is a cylindrical member and provided in the annular space  91  at the second cover  33  side. (see  FIG. 2  and  FIG. 4 ). The second cage  72  includes a recess  72   b  at the second cover  33  side for inserting a pawl  66   a  provided at the second spring  66 .  
         [0037]     The first cage  71  includes a projection  71   c  extending toward the second cage  72  side. The second cage  72  includes a recess  72   c  provided at a position capable of engaging with the projection  71   c  of the first cage  71 . The projection  71   c  and the recess  72   c  permit a predetermined relative rotation. This permitted relative rotation is determined to half of the angle formed between a first line L 1  connecting the rotation axis of the drive member  30  and the center of the first rolling member  61  at the engaging position in vehicle forward driving and a second line L 2  connecting the rotation axis of the drive member  30  and the center of the first rolling member  61  at the engaging position in vehicle rearward driving. In other words, as shown in  FIG. 8  or  FIG. 11 , such angle is defined by an angle α formed between a third line L 3  connecting the rotation axis A of the drive member  30  when the vehicle is turning to the left in forward direction (see  FIG. 8  (A)) and a fourth line L 4  connecting the rotation axis A of the drive member  30  and the center of second rolling member  62  at a position in the annular space  91   a  equivalent to the first rolling member  61 , where no wedge connection is made when the vehicle is turning to left in forward direction (see  FIG. 8  (C)). The angle           is also defined by a fifth line connecting the rotation axis of the drive member  30  and the center of second rolling member  62  at a position in the annular space  91   a  equivalent to the second rolling member  62 , where wedge connection is made when the vehicle is turning to right in forward direction and a sixth line connecting the rotation axis of the drive member  30  and the center of the first rolling member  61  at a position in the annular space  91   a , where no wedge connection is made when the vehicle is turning to right in forward direction. (See  FIG. 8  and  FIG. 11 ).  FIG. 11  shows mainly the first cage seen from the left side thereof.  
         [0038]     The first spring  65  is of ring type wound around the outer periphery of the first friction member  81  and internally in contact with the outer periphery of the first friction member  81  under slidable rotation therewith for frictional rotation by the elastic force. (See  FIG. 2  and  FIG. 5 ). Similarly, the second spring  66  is of ring type wound around the outer periphery of the second friction member  82  and internally in contact with the outer periphery of the second friction member  82  under slidable rotation therewith for frictional rotation by the elastic force. The first spring  65  includes a pawl portion  65   a , which is engaged with the recess portion  71   b  of the first cage  71 . The second spring  66  includes a pawl portion  66   a , which is engaged with the recess portion  71   b  of the first cage  71 .  
         [0039]     The first cage  71  frictionally engages with the first driven member  63  having the outer cam face  63   b  through the first friction member  81  and the first spring  65  for relative rotation and is rotated by the rotation of the first driven member  63 . Similarly, the second cage  72  frictionally engages with the second driven member  64  having the outer cam face  64   b  through the second friction member  82  and the second spring  66  for relative rotation and is rotated by the rotation of the second driven member  64 . In other words, the first and second cages  71  and  72  are not frictionally engaged with the drive member  30  (case  31 ) both directly and indirectly. Thus the cages  71  and  72  are not rotated with the drive member  30 .  
         [0040]     The first friction member  81  is fixed to an area on the outer periphery surface other than the outer cam face  63   b  at the first cover  32  side. The first friction member  81  is frictionally engaged with the first spring  65  for relative rotation therewith. The first friction member  81  is fixed to an area on the outer periphery surface other than the outer cam face  63   b  at the first cover  32  side. The second friction member  82  is frictionally engaged with the second spring  66  for relative rotation therewith.  
         [0041]     The operation of the first embodiment of the invention will be explained with the attached drawings.  FIGS. 6 through 10  explain the operation of the first and second cages used in the power differential transfer device, wherein each (A) shows a partial side view of the first cage seen from the left side, (B) shows a partial plane view of the first and second cages and (C) shows a partial side view of the second cage seen from the right side.  FIG. 6  shows a neutral position and  FIG. 7  shows a vehicle forward straight running condition,  FIG. 8  shows a vehicle left turning condition in vehicle forward running,  FIG. 9  shows a vehicle rearward straight running condition and  FIG. 10  shows a vehicle forward straight running under engine braking.  
         [0042]     In  FIG. 6  (neutral position), when the rotational speed (rpm) between the engine side (drive member  30  side) and the tire side (driven members  63  and  64  side) has no rotational speed difference, the drive member  30 , the first driven member  63  and the second driven member  64  are not rotated and accordingly, the first and second rolling members  61  and  62  are positioned in the annular space  91  at the area where the distance of the inner cam face  31   a  from the outer surface of the circumferential connection surfaces  63   b  and  64   b  is the largest and both first and second driven members  63  and  64  are not wedge connected with the drive member  30 .  
         [0043]     In  FIG. 7  (vehicle forward straight running), when the vehicle is going straight ahead and the engine rpm is higher than that of the front wheels due to, for example, a wheel slipping, a difference in rotation speed between the drive member  30  and the first and second driven members  63  and  64  occurs. Due to this difference, the drive member  30  and the driven members  63  and  64  are immediately in wedge connected. Then the drive torque from the drive member  30  is transmitted to the first and second driven members  63  and  64 . Then the vehicle drive system becomes the four-wheel drive condition. The first and second rolling members  61  and  62  are forced to move in a normal rotational direction of the drive member  30  by the inner cam face  31   a  of the drive member  30 . The first rolling member  61  becomes in contact with the edge of the opening  71   a  of the first cage  71  in a normal rotational direction. Since the first and second driven members  63  and  64  are wedge connected with the drive member  30  by the first and second rolling members  61  and  62 , the torque transmitted to the first and second driven members  63  and  64  become equal which assures the stability in straight forward running.  
         [0044]     In  FIG. 8  (left turning in forward running), when the vehicle is running forward and making a left turn, and if the engine rpm is higher than that of wheel side, a rotational difference between the drive member  30  and the left side first driven member  63  occurs. The drive member  30  and the first driven member  63  are immediately wedge connected by the first rolling member  61  and then the torque is transmitted to the first driven member  63 . The first rolling member  61  is forced to move in a normal rotational direction of the drive member by the cam action of the inner cam face  31   a  provided at the drive member  30 . The first rolling member  61  becomes in contact with the edge of the opening  71   a  of the first cage  71  in a normal rotational direction. The first cage  71  is then forced to move in a normal rotational direction by the first rolling member  61 . On the other hand, since the rotational speed of the second driven member  64  at the right side is higher than that of the first driven member  63  at the right side due to over-run of the front right wheel, the recess  72   c  of the second cage  72  is engaged with the projection  71   c  of the first cage  71 . A slip is generated between the second spring  66  and the second friction member  82  to generate rotation difference between the second cage  72  and the second driven member  64 . The second rolling member  62  is engaged with the second cage  72  not to wedge connect the drive member  30  and the second driven member  64 . Thus the torque will not be transmitted to the second driven member  64  to assuredly perform the differential function.  
         [0045]     The attached drawings do not show the condition of vehicle left turn driving, but in this condition, the rotational difference is generated between the drive member  30  and the second driven member at the right side and the drive member  30  and the second driven member  64  are immediately wedge connected by the second rolling member  62  to transmit the torque to the second driven member  64 . The second rolling member  62  is forced to move in the rotational direction of the drive member  30  by the cam action of the inner cam face  31   a  provided at the drive member  30 . The second rolling member  62  becomes in contact with the edge of the opening  72   a  of the second cage  72  in a normal rotational direction. The second cage  72  is then forced to move in a normal rotational direction by the second rolling member  62 . On the other hand, since the rotational speed of the first driven member  63  at the left side is higher than that of the second driven member  64  at the right side due to over-run of the front left wheel, the recess  72   c  of the second cage  72  is engaged with the projection  71   c  of the first cage  71 . A slip is generated between the first spring  65  and the first friction member  81  to generate rotation difference between the first cage  71  and the first driven member  63 . The first rolling member  61  is engaged with the first cage  72  not to wedge connect the drive member  30  and the first driven member  63 . Thus the torque will not be transmitted to the second driven member  64  to assuredly perform the differential function.  
         [0046]     In  FIG. 9  (rearward straight running), when the vehicle is running straight rearward and the engine side rpm is higher than that of the wheel side, a rotational difference is generated between the drive member  30  and the first and second driven members  63  and  64 . Then the drive member  30  and the first and second driven members  63  and  64  are immediately wedge connected to transmit the torque to the first and second driven members  63  and  64 . The vehicle becomes an engine braking running condition. The first and second rolling members  61  and  62  are forced to move in a reverse rotational direction of the drive member  30  by the cam action of the inner cam face  31   a  provided at the drive member  30 . The first rolling member  61  becomes in contact with the edge of the opening  71   a  of the first cage  71  in a reverse rotational direction and at the same time the second rolling member  62  becomes in contact with the edge of the opening  72   a  of the second cage  72  in a reverse rotational direction. The first and the second driven members  63  and  64  are wedge connected with the drive member  30  by the first and the second rolling members  61  and  62 . Thus the torque transmitted to the first and the second driven members  63  and  64  is equal. Accordingly, the vehicle can run stable in forward straight running.  
         [0047]     According to the first embodiment of this invention, even under the four wheel driving condition, the relative rotational displacement of the first cage  71  and the second cage  72  holding the first and the second rolling members  61  and  62  in a rotational direction can be permitted to a predetermined proper amount in order not to reduce the differential function. Further wedge connection with the inner cam face in the other direction, which may occur by the outer wheel over-run at the vehicle turning motion can be eliminated to keep the first rolling member  61  (or the second rolling member  62 ) which corresponds to the outer wheels under the vehicle turning motion to non-driving position. This will assuredly enable the differential function.  
         [0048]     Further, when the rotational difference is generated between the first and second driven members  63  and  64  and the drive member  30 , the first and second driven members  63  and  64  and the drive member  30  are immediately wedge connected by the first and the second rolling members  61  and  62 . (ball clutch mechanism) The engagement and disengagement of the drive member  30  with the first and the second driven members  63  and  64  can be easily and lightly to be performed.  
         [0049]     Further, the power differential transfer device does not house the differential gear unit and accordingly the device is simple, compact in structure and lightweight.  
         [0050]     Next a modification of the first embodiment will be explained hereinafter. In this modification, the first and the second driven members include cam face and the drive member (case) includes a circumferential connection surface instead of providing the circumferential connection surface ( 63   b ) at the first and the second driven members and providing the inner cam face ( 31   a ) at the drive member  30  (case  31 ). In other words, the frictional slidable connection between the first cage and the first driven member is performed at the circumferential connection surface between the case and the first rolling member and cam action is performed at the contact surface between the first driven member and the first rolling member. Similarly, the frictional slidable connection between the second cage and the second driven member is performed at the circumferential connection surface between the drive member (case) and the second rolling member and cam action is performed at the contact surface between the second driven member and the second rolling member. In this case, the first and the second cages are frictionally engaged with the drive member (case) directly or indirectly for relative rotation to rotate the drive member (case) as a unit. In other words, the first cage and the second cage having cam faces are not frictionally engaged, neither directly nor indirectly. Thus the first and the second driven members are not rotated with the first and the second cages. This modification can perform the same function and the same results can be obtained.