PATENT DOCUMENT

Abstract:
Disclosed is a power transmitting device capable of streamlined structure and control, as well as alleviating energy loss. The device comprises a planetary gear device wherein motive power of an engine and a motor is inputted from a first element and a second element; and a first clutch that transmits, in an interruptible manner, motive power from a second shaft that is linked to the second element, to a first shaft that is linked to a third element and an input shaft, while interrupting motive power from the first shaft or the input shaft to the second shaft. It is possible to switch motive power of the engine and the motor with motive power transmission switching by the first clutch, thus allowing streamlining of structure and control.

Full Description:
TECHNICAL FIELD 
       [0001]    This invention relates to a power transmitting device and, more particularly, to a power transmitting device capable of simplifying structure and control and also suppressing energy loss. 
       BACKGROUND ART 
       [0002]    As a power transmitting device of a hybrid vehicle including an engine and a motor as power source, for example, Non-Patent Literature 1 describes one having a double pinion planetary gear unit and three multiplate wet clutches. According to the techniques disclosed by Non-Patent Literature 1, the three multiplate wet clutches are operated to perform drive-power switching between the engine and the motor. 
       CITATION LIST 
     Non Patent Literature 
       [0003]    Non Patent Literature 1 
         [0004]    “Hybrid System for mini-van 4WD” by Fumimori Imaeda, and 3 others, published by Society of Automotive Engineers of Japan, Paper Number 20024219 May 2002 issued by No. 06-02, pp 8-14 (specially,  FIG. 9  and Table 3) 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0005]    However, the power transmitting device disclosed by Non Patent Literature 1 has disadvantages of complicated structure and complicated control of a power transmitting device because the three multiplate wet clutches must be hydraulically controlled to perform drive-power switching between the engine and the motor. Also, thermal energy is released upon engagement of the multiplate set clutch, resulting in a disadvantage energy loss. 
         [0006]    The present invention has been made to address the aforementioned disadvantages and provides a power transmitting device capable of simplifying structure and control and also suppressing energy loss. 
       Solution to Problem 
       [0007]    To attain this object, a power transmitting device described in claim  1  includes: a planetary gear device having a first element to which power is input from an input shaft connected to an engine, a second element to which power of a motor is input, and a third element meshing with the first element and the second element and transmitting power to a gearbox; a first shaft connected to any element of the three elements and the gearbox; a second shaft connected to the motor and one of the other elements excluding any of the three elements to which the first shaft is connected; and a first clutch transmitting power from the second shaft to the first shaft or the input shaft in an interruptible manner, while blocking transmission of power from the first shaft or the input shaft to the second shaft. As a result, by switching between transmission and interruption of power from the second shaft to the first shaft or the input shaft by the first clutch, distribution of engine power and motor power and drive-power switching can be achieved. This produces advantageous effects of simplifying control and structure of the power transmitting device. 
         [0008]    Also, in the structure of engaging a multiplate wet clutch to perform drive-power switching, thermal energy is released at the time of engagement of the multiplate wet clutch to give rise to energy loss. However, because of a reduced number of multiplate wet clutches, the energy loss is advantageously reduced. 
         [0009]    With the power transmitting device described in claim  2 , the first clutch causes first sprags to engage with the first inner race and the first outer race in order to transmit power while restricting relative rotation of the first inner race and the first outer race in a certain rotation direction. The first load applying device can cause engagement or disengagement of the first sprags to switch between the transmission and the interruption of rotation in the certain direction, resulting in an advantageous effect of shortening the switching time in addition to the advantageous effect of the power transmitting device in claim  1 . 
         [0010]    Since the first sprags are tilted for the transmission and interruption of power in the certain direction, the first inner race and the first outer race can be prevented from idling at the time of switching from the state of blocking the transmission of power to the state of transmitting the power. Accordingly, a shock at the time of switching can be advantageously avoided. 
         [0011]    Further, since power is transmitted through the first sprags, the torque capacity can be increased even if the first clutch is small in size. As a result, a reduction in size of the power transmitting device can be advantageously achieved. 
         [0012]    With the power transmitting device in claim  3 , because of the second clutch which transmits the power from the first shaft or the input shaft to the second shaft, but blocks the transmission of power from the second shaft to the first shaft or the input shaft, the power can be transmitted from the gearbox to the generator motor when inertia traveling (coasting) or the like for advantageous energy regeneration. 
         [0013]    With the power transmitting device in claim  4 , the first urging member applies a urging force to the first sprags to place one of the outer peripheral surface of the first inner race and the inner peripheral surface of the first outer race and one of the engaging faces of each of the first sprags into contact with each other in order to tilt the first sprags in an anti-lock direction of the circumferential directions. The first load applying device applies a load to the first sprags through the cage in opposition to the urging force of the first urging member to tilt the first sprags in a lock direction of the circumferential directions opposite to the anti-lock direction so as to place the two engaging faces of each of the first sprags into contact with the outer peripheral surface of the first inner race and the inner peripheral surface of the first outer race. As a result, the two engaging faces of each of the first sprags are engaged with the outer peripheral surface of the first inner race and the inner peripheral surface of the first outer race to restrict the relative rotation of the first inner race and the first outer race. 
         [0014]    The first sprags are tilted by a balance of the turning moment about the contact point of the outer peripheral surface of the first inner race or the inner peripheral surface of the first outer race and the engaging face of the first sprag. According, the sprag can be tilted with a smaller load than the urging force of the first urging member. As a result, advantageously, the first load applying device can be reduced in size and the load applied to the first sprag can be lowered, resulting in suppression of energy loss. 
         [0015]    With the power transmitting device in claim  5 , the inner cage or the outer cage includes the first retaining potion and the second retaining portion separated from each other in an axis direction. The first sprags are retained by the first retaining portion, while the second sprags are retained by the second retaining portion. The first retaining portion and the second retaining portion are structured to be relatively movable in the circumferential direction, and the second urging member urges the first retaining portion and the second retaining portion toward one of the circumferential directions. As a result, the urging force of the second urging member causes the first face and the second face which are formed on the first retaining portion and the second retaining portion to abut on each other to restrict the relative movement of the first retaining portion and the second retaining portion in one of the circumferential directions. In consequence, the first retaining portion and the second retaining portion can be integrally moved by the urging force of the second urging member, and by the load application of the first load applying device, the first sprags retained in the first retaining portion and the second sprags retained in the second retaining portion can be tilted. 
         [0016]    In this regard, when one of the first sprags and the second sprags are engaged with the first inner race and the first outer race or with the second inner race and the second outer race by the relative movement of the inner cage and the outer cage in the circumferential direction, the other one of the first sprags and the second sprags are retained in the inner cage and the outer cage and disengaged from the first inner race or/and the like. If the inner cage and the outer cage are each formed in an integrated manner, when one of the first sprag and the second sprag engaging with the first inner race and the first outer race or the like is tilted to be more strongly engaged, the tilting motion pushes the inner cage and the outer case to cause further relative movement of the inner cage and the outer cage. Thus, the other of the first sprag and the second sprag may possibly fall out of the inner cage or the outer cage and the inner cage or the outer cage may be possibly damaged. 
         [0017]    As opposed to this, with the power transmitting device in claim  5 , since the first retaining portion and the second retaining portion are structured to be relatively movable in the circumferential direction, if one of the first sprag and the second sprag engaging with the first inner race and the first outer race or the like is tilted so as to engage further strongly, the tilting motion causes only one of the first retaining portion and the second retaining portion to move relative to the other of the first retaining portion and the second retaining portion. As a result, the other of the first retaining portion and the second retaining portion can be prevented from being affected, advantageously leading to prevention of the possibilities that the other of the first sprag and the second sprag falls out of the inner cage or the outer cage and that the inner cage and the outer cage are damaged, in addition to the advantageous effects of claim  3  or  4 . 
         [0018]    With the power transmitting device in claim  6 , first shaft rpm acquiring means and the second shaft rpm acquiring means acquire the rpm of the first shaft and the rpm of the second shaft. The rpm determining means determines whether or not the rpm of the first shaft acquired by the first shaft rpm acquiring means and the rpm of the second shaft acquired by the second shaft rpm acquiring means are in agreement with each other. As a result of the determination, when the rpm of the first shaft and the rpm of the second shaft are in agreement with each other, the load controlling means controls actuation of the first load applying device and presence or absence of application of a load to the first sprags through the cage. Therefore, in addition to the advantageous effects of any of claims  2  to  5 , a shock is advantageously prevented from being produced by inertial torque, which advantageously preventing the driver from feeling a sense of incongruity. 
         [0019]    That is, when the rpm of the first shaft is equal to the rpm of the second shaft, the rpms of the first inner race and the first outer race of the first clutch become also equal to each other. At this stage, if the first sprags engage with the first inner race and the first outer race, since a difference in speed is not produced between the first inner race and the first outer race, producing of inertia torque is prevented to avoid a shock. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0020]      FIG. 1  is a schematic diagram schematically illustrating a vehicle equipped with a power transmitting device in a first embodiment of the present invention. 
           [0021]      FIG. 2  is a schematic diagram schematically illustrating the power transmitting device and the gearbox. 
           [0022]      FIG. 3  is a sectional view of the first clutch. 
           [0023]      FIG. 4  is a sectional view of the first clutch taken along the IV-IV line in  FIG. 3 . 
           [0024]      FIG. 5  is an enlarged sectional view of the portion of the first clutch designated by letter “V” in  FIG. 4 . 
           [0025]      FIG. 6  is a schematic diagram showing the relationship between rpms of the first element, the second element and the third element and travel speed. 
           [0026]      FIG. 7(   a ) is a schematic view schematically illustrating the internal structure of the power transmitting device and the gearbox during the start-up of the engine,  FIG. 7(   b ) is a schematic diagram schematically showing the internal structure of the power transmitting device and the gearbox at vehicle start (low speeds), and  FIG. 7(   c ) is a schematic diagram schematically showing the internal structure of the power transmitting device and the gearbox at vehicle start (high speeds). 
           [0027]      FIG. 8(   a ) is a schematic diagram schematically illustrating the internal structure of the power transmitting device and the gearbox during regeneration,  FIG. 8(   b ) is a schematic diagram schematically showing the internal structure of the power transmitting device and the gearbox when reverse gear is selected, and  FIG. 8(   c ) is a schematic diagram schematically showing the internal structure of the power transmitting device and the gearbox after gear shifting into reverse. 
           [0028]      FIG. 9  is a block diagram illustrating the electrical configuration of the control unit of the power transmitting device. 
           [0029]      FIG. 10  is a flowchart showing the power transmission control processing. 
           [0030]      FIG. 11  is a schematic diagram schematically showing the power transmitting device and the gearbox in the second embodiment. 
           [0031]      FIG. 12  is a schematic diagram schematically showing the power transmitting device in the third embodiment. 
           [0032]      FIG. 13  is a schematic diagram schematically showing the power transmitting device in the fourth embodiment. 
           [0033]      FIG. 14  is a schematic diagram showing the relationship between rpms of the first element, the second element and the third element and travel speed. 
           [0034]      FIG. 15  is a schematic diagram schematically showing the power transmitting device in the fifth embodiment. 
           [0035]      FIG. 16  is a schematic diagram schematically showing the power transmitting device in the sixth embodiment. 
           [0036]      FIG. 17  is a sectional view of the first clutch. 
           [0037]      FIG. 18  is an exploded view of a part of the first clutch. 
           [0038]      FIG. 19(   a ) is a partially enlarged sectional view of the first clutch blocking the transmission of power, shown by enlarging the portion indicated by “XIX” in  FIG. 17  and  FIG. 19(   b ) is a partially enlarged sectional view of the first clutch transmitting the power. 
           [0039]      FIG. 20  is a schematic diagram of the first sprag tilted in the anti-lock direction. 
           [0040]      FIG. 21  is a schematic diagram showing the relationship between rpms of the first element, the second element and the third element and travel speed. 
           [0041]      FIG. 22  is a schematic diagram schematically showing the power transmitting device in the seventh embodiment. 
           [0042]      FIG. 23  is a sectional view of the first clutch. 
           [0043]      FIG. 24(   a ) is a perspective view of important parts of the first retaining portion and the second retaining portion, relative movement of which is restricted,  FIG. 24(   b ) is a sectional view of the first retaining portion, and  FIG. 24(   c ) is a sectional view of the second retaining portion. 
           [0044]      FIG. 25(   a ) is a perspective view of important portions of the first retaining portion and the second retaining portion which are moved relatively,  FIG. 25(   b ) is a sectional view of the first retaining portion, and  FIG. 25(   c ) is a sectional view of the second retaining portion. 
           [0045]      FIG. 26(   a ) is a perspective view of important portions of the first retaining portion and the second retaining portion of which the relative movement is restricted,  FIG. 26(   b ) is a sectional view of the first retaining portion, and  FIG. 26(   c ) is a sectional view of the second retaining portion. 
           [0046]      FIG. 27(   a ) is a sectional view of important portions of the first retaining portion and the second retaining portion which are moved relatively,  FIG. 27(   b ) is a sectional view of the first retaining portion, and  FIG. 27(   c ) is a sectional view of the second retaining portion. 
           [0047]      FIG. 28  is a schematic diagram showing the relationship between rpms of the first element, the second element and the third element and travel speed. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0048]    Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.  FIG. 1  is a schematic diagram schematically illustrating a vehicle  200  equipped with a power transmitting device  1  in a first embodiment of the present invention. Arrows F-B, L-R in  FIG. 1  denote the front and back directions, the right and left directions, respectively, of the vehicle  200 . 
         [0049]    Initially, the structure of the vehicle  200  is described in outline. As shown in  FIG. 1 , the vehicle  200  includes front wheels  201  (left front wheel  201 FL and right front wheel  201 FR), rear wheels (left rear wheel  201 FL and right rear wheel  201 FR), and a unit  210  driving the rear wheels  202 . The unit  210  mainly includes an engine  211  and a later-mentioned generator motor  60  as a power source, a power transmitting device  1  for transmitting power of the engine  211  and the generator motor  60 , and a gearbox  212  to which the power is transmitted from the power transmitting device  1 , which is structured to use the two powers of the engine  211  and the generator motor  60  as circumstances demand, and to deliver the used power through a differential  213  to drive the rear wheels  202 . The unit  210  is structured to have the generator motor  60  also equipped with the ability as a generator and to be capable of regenerating the electric power generated by the generator motor  60 . 
         [0050]    Next, the detail structure of the power transmitting device  1  will be described with reference to  FIG. 2 .  FIG. 2  is a schematic diagram schematically illustrating the internal structure of the power transmitting device  1  and the gearbox  212 .  FIG. 2  shows only the structure shouldering the function of transmitting power for easier understanding. As shown in  FIG. 2 , the power transmitting device  1  mainly includes a planetary gear device  30  connected to an input shaft  2  delivering the power of the engine  211 , and a first clutch  10  and a second clutch  20  which are placed on a power line from the power transmitting device  1  to the rear wheels  202  (drive wheels). The gearbox  212  is placed on the power line from the power transmitting device  1  to the rear wheels  202  (drive wheels). The power applied to the gearbox  212  is output at a predetermined transmission ratio to drive the rear wheels  202  through the differential  213 . 
         [0051]    The planetary gear device  30  includes a sun gear  31 , a carrier  33  rotatably supporting a plurality of pinion gears  32  which mesh with the outer periphery of the sun gear  31 , and a ring gear  34  having the inner periphery meshing with the pinion gears  32 . In the embodiment, the carrier  33  is connected to the input shaft  2  to which the power of the engine  211  is input, which forms a first element. Also, the ring gear  34  is connected to a rotor  62  rotating relative to a stator  61  of the generator motor  60 , which forms a second element. Further, the sun gear  31  is connected to a first shaft  3  transmitting power toward the gearbox  212 , which forms a third element. 
         [0052]    The first clutch  10  is provided for transmitting and interrupting power between the second shaft  4  connected to the ring gear  34  (second element) and the first shaft  3 , and is structured to transmit, in an interruptible manner, power received from the second shaft  4  to the first shaft  3 , but to block transmission of power from the first shaft  3  to the second shaft  4 . 
         [0053]    A detail structure of the first clutch  10  is described with reference to  FIG. 3  and  FIG. 4 .  FIG. 3  is a sectional view of the first clutch  10 .  FIG. 4  is a sectional view of the first clutch  10  taken along the IV-IV line in  FIG. 3 . As shown in  FIG. 3  and  FIG. 4 , the first clutch  10  mainly includes a first inner race  11 , a first outer race  12  surrounding the outer periphery of the first inner race  11 , a plurality of first sprags  13  interposed between the first inner race  11  and the first outer race  12 , a cage  14  retaining the first sprags  13 , and a load applying device  15 . 
         [0054]    The first inner race  11  is a member having a function of transmitting power, and has an outer peripheral surface  11   a  of circular cross section and is structured rotatably about an axis O as illustrated in  FIG. 3  and  FIG. 4 . The first inner race  11  is connected to the first shaft  3  (see  FIG. 2 ). The first outer race  12  is a member having a function for transmitting power in a joint effort with the first inner race  11 , which has an inner peripheral surface  12   a  of circular cross section facing the outer peripheral surface  11   a  of the first inner race  11  as shown in  FIG. 3  and  FIG. 4 . The first outer race  12  is structured rotatably about the axis O similarly to the first inner race  11 . The first outer race  12  is connected to the second shaft  4  (see  FIG. 2 ). 
         [0055]    The first sprag  13  is a member having a function of engaging the first inner race  11  and the first outer race  12  with each other, and has engaging faces  13   a ,  13   b  (see  FIG. 5 ) respectively making contact with the outer peripheral surface  11   a  and the inner peripheral surface  12   a . The plurality of first sprags  13  are arranged at regular intervals in the circumferential direction between the outer peripheral surface  11   a  and the inner peripheral surface  12   a  which face each other as shown in  FIG. 4 . The first sprag  13  is urged in the circumferential direction of the inner peripheral surface  11   a  and the outer peripheral surface  12   a  by a first urging member  16  (see  FIG. 5 ). At this stage, the first urging member  16  is described with reference to  FIG. 5 .  FIG. 5  is an enlarged sectional view of the portion of the first clutch  10  designated by letter “V” in  FIG. 4 . 
         [0056]    The first urging member  16  is a member that exerts an urging force on the first sprag  13  to make the engaging faces  13   a ,  13   b  come into contact with the outer peripheral surface  11   a  and the inner peripheral surface  12   a  in order to allow the first sprag  13  to produce torque in the direction of arrow S in  FIG. 5  (hereinafter referred to as a “self-lock direction”). In the embodiment, as illustrated in  FIG. 5 , the first urging member is structured to include a ribbon spring formed by machining a metallic material to bend it into a wave-like shape, and to be able to effectively use the elasticity to exert the urging force on the first sprag  13 . However, the first urging member  16  may include a coil spring. Because the first urging member  16  exerts the urging force on the first sprag  13 , the first sprag  13  moves in a tilting manner in the self-lock direction to cause the engaging faces  13   a ,  13   b  to come into contact with the outer peripheral surface  11   a  and the inner peripheral surface  12   a . As a result, as shown in  FIG. 5 , frictional force is produced at a contact point A of the inner peripheral surface  12   a  and the engaging face  13   b  and at a contact point B of the outer peripheral surface  11   a  and the engaging face  13   a , and also a positional displacement of each of the contact points A, B in the circumferential direction of the outer peripheral surface  11   a  and the inner peripheral surface  12   a . Thereby, when the first inner race  11  and the first outer race  12  rotate in a predetermined direction, the first sprags  13  engage with the first inner race  11  and the first outer race  12 . 
         [0057]    That is, when the first outer race  12  rotates with respect to the first sprag  13  in the direction of arrow Ro in  FIG. 5  (hereinafter referred to as a “lock direction”) when viewed from the first inner race  11  in rotation relative to the first inner race  11 , the first sprag  13  is engaged with the first inner race  11  and the first outer race  12 . In this manner, the first inner race  11  (see  FIG. 2 ) rotates together with the first outer race  12 . On the other hand, when the first outer race  12  rotates with respect to the first sprag  13  in the opposite direction to arrow Ro in  FIG. 5  (hereinafter referred to as a “free direction”) when viewed from the first inner race  11  in rotation relative to the first inner race  11 , the first sprag  13  is tilted in the anti-self lock direction in opposition to the urging force of the first urging member  16  by the friction force acting on the contract point A, thus disengaging the first sprag  13  from the first inner race  11  and the first outer race  12 . As a result, the first outer race  12  idles around the first inner race  11 . 
         [0058]    When the first inner race  11  rotates with respect to the first sprag  13  in the direction of arrow Ri in  FIG. 5  (the lock direction) when viewed from the first outer race  12  in rotation relative to the first outer race  12 , the first sprag  13  is engaged with the first inner race  11  and the first outer race  12 . As a result, the first outer race  12  rotates together with the first inner race  11  (see  FIG. 2 ). On the other hand, when the first inner race  11  rotates with respect to the first sprag  13  in the opposite direction to arrow Ri in  FIG. 5  (the free direction) when viewed from the first outer race  12  in rotation relative to the first outer race  12 , the first sprag  13  tilts in the anti-self lock direction in opposition to the urging force of the first urging member  16  by the friction force acting on the contract point B, resulting in idling of the first outer race  12  around the first inner race  11  (see  FIG. 2 ). 
         [0059]    Returning to  FIG. 3  and  FIG. 4 , the description is continued. The cage  14  is a member of holding the first sprags  13  in a manner to allow them to tilt in the circumferential direction of the outer peripheral surface  11   a  and the inner peripheral surface  12   a . As shown in  FIG. 3  and  FIG. 4 , the cage  14  includes a retaining portion  14   a  and a load transmitting portion  14   b . The retaining portion  14   a  is a part for retaining the first sprags  13 , which extends in the direction of the axis O as shown in  FIG. 3  and  FIG. 4  so as to hold the top ends of the first sprags  13 . 
         [0060]    The load transmitting portion  14   b  is a part for transmitting the load from the first load applying device  15 , and extends in a direction crossing the direction of axis O as shown in  FIG. 3 . This s allows a reduction in size in the direction of the axis O of the cage  14  as compared with the case of extending the load transmitting portion  14   b  in the direction of the axis O, leading to a reduction in size of the first clutch  10 . The load transmitting portion  14   h  is formed in a cog shape as illustrated in  FIG. 4 , and is structured to receive the load transmitted from the first load applying device  15  through a gear mechanism which is provided between the load transmitting portion  14   b  and a pinion  15   b  described later. This makes it possible to reduce the energy loss occurring in the load transmitting line from the first load applying device  15  to the cage  14 , and to transmit a load to the cage  14  with a high degree of efficiency. 
         [0061]    The first load applying device  15  is a device for applying a load to the first sprag  13  in opposition to the urging force of the first urging member  16  to tilt the first sprag  13  in the anti-self lock direction (the rotation direction opposite to arrow S in  FIG. 5 ), and includes an actuator  15   a  and a pinion  15   b  as shown in  FIG. 3  and  FIG. 4 . 
         [0062]    The actuator  15   a , which is a power source generating a load to be applied to the first sprags  13 , includes an electric motor (AC motor or DC motor) and can be driven by power supplied from a power source (not shown). In this manner, since the actuator  15   a  includes an electric motor, the first load applying device  15  can be simplified in structure and reduced in size as compared with the case of, for example, an actuator  15   a  including a cylinder, a solenoid or the like. If the first load applying device  15  has a complicated structure, the first load applying device  15  will increase in size, resulting in a larger size of the first clutch  10 . However, if it is possible to simplify the structure of the first load applying device  15  and reduce the size of the same, a reduction in size of the first clutch  10  can be achieved. 
         [0063]    The pinion  15   b , which is a member for transmitting power of the actuator  15   a  to the cage  14 , is formed in a cog shape meshing with the load transmitting portion  14   b  of the cage  14  as shown in  FIG. 3  and forms part of the gear mechanism between the load transmitting portion  14   b  and the pinion  15   b . Since the pinion  15   b  transmits the power of the actuator  15   a  to the cage  14 , the load is applied to the first sprags  13  through the cage  14 . In this manner, since the first load applying device  15  applies a load to the first sprag  13  through the cage  14 , the load can be applied to a plurality of the first sprags  13  all at once, resulting in efficient application of a load to the first sprags  13 . 
         [0064]    With the first load applying device  15  structured as described above, the first sprag  13  is tilted in the anti-self lock direction by applying a load to the first sprag  13  in opposition to the urging force of the first urging member  16 , so that the first sprag  13  can be forcibly disengaged from the first inner race  11  and the first outer race  12 . As a result, even when the power transmitted from the generator motor  60  to the second shaft  4  is input to the first outer race  12  of the first clutch  10  so as to rotate the first outer race  12  with respect to the first sprags  13  in the lock direction (the direction of arrow Ro in  FIG. 5 ), the first sprags  13  are forcibly disengaged from the first inner race  11  and the first outer race  12  by the first load applying device  15 , so as to cause the first outer race  12  to idle. As a result, the transmission of power between the first shaft  3  and the second shaft  4  is able to be blocked. Even when the power delivered to the first shaft  3  is input to the first inner race  11  of the first clutch  10  so as to cause the first inner race  11  to rotate with respect to the first sprags  13  in the lock direction (the direction of arrow Ri in  FIG. 5 ), the first load applying device  15  forcibly disengage the first sprags  13  from the first inner race  11  and the first outer race  12  so as to cause the first inner race  11  to idle. As a result, the transmission of power between the first shaft  3  and the second shaft  4  is able to be blocked. 
         [0065]    Returning to  FIG. 2  for describing the second clutch  20 . The second clutch  20  is provided for transmission and interruption of power between the second shaft  4  and the first shaft  3 . The second clutch  20  transmits the power from the first shaft  3  to the second shaft  4 , but blocks the transmission of power from the second shaft  4  to the first shaft  3 . Because the second clutch  20  is structured similarly to the first clutch  10  except for an omission of the first load applying device  15 , details are omitted. 
         [0066]    The second clutch  20  has a second inner race  21  connected to the first shaft  3  and a second outer race  22  connected the second shaft  4 . The second inner race  21  is formed integrally with the first inner race  11  along the axis direction, while the second outer race  22  is formed integrally with the first outer race  12  along the axis direction. The outer diameter of the first inner race  11  is the same as that of the second inner race  21 , while the first outer race  12  and the second outer race  22  are identical in inner diameter. A plurality of second sprags  23  are disposed between the second inner race  21  and the second outer race  22 . The relative rotation of the second inner race  21  and the second outer race  22  causes engagement and disengagement of the second sprags  23  with and from the second inner race  21  and the second outer race  22  to switch between power transmission and power interruption. The generator motor  60  mainly includes a stator  61  and a rotor  62 . The rotor  62  is connected to the ring gear  34  (second element) through the second shaft  4 . 
         [0067]    At this stage, the operation of the planetary gear device  30  is described with reference to  FIG. 6 .  FIG. 6  is a schematic diagram showing the relationship between rpms of the first element, the second element and the third element and travel speed of the vehicle  200 . The horizontal axis in  FIG. 6  represents the travel speed of the vehicle  200 , while the vertical axis represents the rpms of the third element, the first element and the second element. Because the rotor  62  is connected to the ring gear  34  (second element) through the second shaft  4  as illustrated in  FIG. 2 , the rpm of the second element becomes equal to the rpm of the rotor  62  and the second shaft  4 . Because the engine  211  is connected to the carrier  33  (first element) through the input shaft  2 , the rpm of the first element becomes equal to the rpm of the input shaft  2 . Further, because the first shaft  3  is connected to the sun gear  31  (third element) and the drive gear  5   a , the rpm of the third element becomes equal to the rpm of the first shaft  3  and the rpm of the drive gear  5   a .  FIG. 6  illustrates the characteristics in which the rpm of the first element is constant relative to the travel speed of the vehicle  200 , that is, the rpm of the engine  211  and input shaft  2  is constant (R 1 ). 
         [0068]    In  FIG. 6 , when the rpm of the second element is 0 (the rpm of the generator motor  60  (see  FIG. 2 ) is 0), upon reception of the power from the first element (carrier  33 ), the third element (sun gear  31 ) is made speed up (the first element&lt;the third element) as shown in  FIG. 6 . If the numbers of teeth of the sun gear  31  and the ring gear  34  are represented as Za and Zc respectively, the transmission ratio becomes (Za+Zc)/Zc. On the other hand, when the second element (ring gear  34 ) is fixed (rpm=0) and the power from the third element (sun gear  31 ) is input, the first element (carrier  33 ) is slowed down (the first element&lt;the third element) as shown in  FIG. 6 . In this manner, the drive torque of the first element (carrier  33 ) is increased and the transmission ratio becomes Za/(Za+Zc). 
         [0069]    When the rpm of the second element becomes greater than 0 by the generator motor  60  (the rotor  62 ), the third element (sun gear  31 ) produces output in an arbitrary transmission gear ratio in response to the rpm of the second element (ring gear  34 ) as shown in  FIG. 6 .  FIG. 6  shows that, when the rpms of the second element and the first element are equally R 1  (assuming that the travel speed is Vo at this time), the power of the engine  211  input to the first element is output to the third element (sun gear  31 ) as it is. Further, the rpm of the rotor  62  (see  FIG. 2 ) is increased (the rpm of the second element is increased) until the rpm of the second element becomes equal to R 2 , thereupon the rpm of the third element=0. When the rpm of the second element exceeds R 2 , the rpm of the third element&lt;0 becomes. That is, the direction of rotation of the third element (sun gear  31 ) is reversed. 
         [0070]    In this connection, the rpm of the sun gear  31  (the third element) changes to the positive direction as the rpm of the carrier  33  (the first element) changes to the positive direction when the rpm of the ring gear  34  (the second element) is constant, and changes to the negative direction as the rpm of the carrier  33  (the first element) changes to the negative direction. Then, when the rpm of the carrier  33  becomes equal to or lower than a predetermined rpm, the direction of rotation of the sun gear  31  is reversed. 
         [0071]    Returning to  FIG. 2 , the gearbox  212  will be described next. The gearbox  212  is a device that outputs, in an arbitrary transmission gear ratio, the power transmitted to an input shaft  5   c  by a drive gear  5   a  connected to the first shaft  3  of the power transmitting device  1  and a driven gear  5   b  meshing with the drive gear  5   a . The gearbox  212  mainly includes the input shaft  5   c  to which the power is input via the driven gear  5   b , an output shaft  5   d  arranged in parallel to the input shaft  5   c , a plurality of first gear pairs  6 ,  7  placed on the output shaft  5   d  and the input shaft  5   c  and configured to mesh with each other for various transmission ratios, and a second gear pair  8  placed on the output shaft  5   d  and the input shaft  5   c  and meshing with each other. The power delivered to the output shaft  5   d  is structured to be transmitted to the rear wheels  202 . 
         [0072]    The first gear pairs  6 ,  7  of the gearbox  212  include drive gears  6   a ,  7   a  placed on the input shaft  5   c  and driven by the power transmitted to the input shaft  5   c , and driven gears  6   b ,  7   b  placed on the output shaft  5   d  and slave-driven by the drive gears  6   a ,  7   a . The first gear pairs  6 ,  7  are assigned first gear and second gear from largest transmission gear ratio (the number of driven gear teeth the number of drive gear teeth) in increasing order of distance to the driven gear. In the embodiment, the first gear pair  6  is assigned first gear and the first gear pair  7  is assigned second gear. A reverse gear pair  9  including a pinion gear is interposed between the first gear pairs  6 ,  7 . The reverse gear pair  9  has a sliding mesh structure, in which the gear placed on the output shaft  5   d  is slid in the axis direction for meshing in order to allow rearward travel. 
         [0073]    Each of the drive gears  6   a ,  7   a  forming part of the first gear pairs  6 ,  7  is formed integrally with the input shaft  5   c . On the other hand, the driven gears  6   b ,  7   b  respectively opposing and meshing with the drive gears  6   a ,  7   a  are fixed to the output shaft  5   d  through fourth clutches  40  which will be described later. The fourth clutch  40  transmits power from the input shaft  5   c  to the output shaft  5   d , but interrupts power from the output shaft  5   d  to the input shaft  5   c . The fourth clutch  40  is structured to be able to block the transmission of power from the input shaft  5   c  to the output shaft  5   d . Because the fourth clutch  40  is structured similarly to the first clutch  10 , a detailed description is omitted. The same components as those of the first clutch  10  are designated by the same reference signs and a description is omitted in the following. 
         [0074]    A fourth inner race  41  of the fourth clutch  40  is formed integrally with the output shaft  5   d , while a fourth outer race  42  is formed integrally with each of the driven gears  6   b ,  7   b . With the fourth clutch  40 , the power of the engine  211  or the generator motor  60  is transmitted through the input shaft  5   c  and the drive gear  6   a ,  7   a  and then input from the driven gear  6   b ,  7   b . Then, the fourth outer race  42  connected to the driven gear  6   b ,  7   b  rotates with respect to fourth sprags  43  in the lock direction (the direction of arrow Ro in  FIG. 5 ) when viewed from the fourth inner race  41  in rotation relative to the fourth inner race  41 , the fourth sprags  43  are engaged with the fourth inner race  41  and the fourth outer race  42 . As a result, the output shaft  5   d  rotates together with the driven gear  6   b ,  7   b  to transmit the power. On the other hand, when the fourth outer race  42  rotates with respect to the fourth sprags  43  in the free direction (the opposite direction to arrow Ro in  FIG. 5 ) when viewed from the fourth inner race  41  in rotation relative to the fourth inner race  41 , the fourth sprags  43  are disengaged from the fourth inner race  41  and the fourth outer race  42 , so that the driven gear  6   b ,  7   b  idles on the output shaft  5   d.    
         [0075]    After the power is transmitted to the fourth inner race  41  of the fourth clutch  40  from the output shaft  5   d , when the fourth inner race  41  rotates with respect to the fourth sprags  43  in the free direction (the direction opposite to arrow Ri in  FIG. 5 ) when viewed from the fourth outer race  42  in rotation relative to the fourth outer race  42 , the fourth sprags  43  disengage from the fourth inner race  41  and the fourth outer race  42 . As a result, the driven gear  6   b ,  7   b  idles on the output shaft  5   d , so that the transmission of power from the output shaft  5   d  to the input shaft  5   c  is blocked. On the other hand, when the fourth inner race  41  rotates with respect to the fourth sprags  43  in the lock direction (the direction of arrow Ri in  FIG. 5 ) when viewed from the fourth outer race  42  in rotation relative to the fourth outer race  42 , the fourth sprags  43  are engaged with the fourth inner race  41  and the fourth outer race  42 . As a result, the driven gear  6   b ,  7   b  rotate together with the output shaft  5   d  to transmit the power. 
         [0076]    The fourth clutch  40  includes a fourth load applying device  45  structured similarly to the first load applying device  15  (see  FIG. 4 ) of the first clutch  10 , so that, even when the power is transmitted to the fourth inner race  41  or the fourth outer race  42  so as to rotate the fourth inner race  41  or the fourth outer race  42  with respect to the fourth sprags  43  in the lock direction (the direction of arrow Ri or arrow Ro in  FIG. 5 ), the fourth sprags  43  are forcibly disengaged from the fourth inner race  41  and the fourth outer race  42  by the fourth load applying device  45 . As a result, the fourth outer race  42  is able to idle so as to block the transmission of power. 
         [0077]    The drive gear  8   a  forming part of the second gear pair  8  is formed integrally with the input shaft  5   c  through a fifth clutch  50  which will be later. On the other hand, the driven gear  8   b  opposing and meshing with the drive gear  8   a  is fixed to the output shaft  5   d . The fifth clutch  50  transmits power from the output shaft  5   d  to the input shaft  5   c , but blocks the transmission of power from the input shaft  5   c  to the output shaft  5   d . The fifth clutch  50  is structured similarly to the first clutch  10  (see  FIG. 5 ) except for an omission of the first load applying device  15 , and therefore a detailed description is omitted. The same components as those of the first clutch  10  are designated by the same reference signs and a description is omitted in the following. 
         [0078]    A fifth inner race  51  of the fifth clutch  50  is formed integrally with the in shaft  5   c , while a fifth outer race  52  is formed integrally with the drive gear  8   a . With the fifth clutch  50 , after the power of the engine  211  or the generator motor  60  is transmitted to the input shaft  5   c , when the fifth inner race  51  of the fifth clutch  50  rotates with respect to fifth sprags  53  in the free direction (the direction opposite to arrow Ri in  FIG. 5 ) when viewed from the fifth outer race  52  in rotation relative to the fifth outer race  52 , the engagement of the fifth sprags  53  with the fifth inner race  51  and the fifth outer race  52  is released, so that the input shaft  5   c  rotates freely without engaging with the drive gear  8   a , so that the transmission of power from the input shaft  5   c  to the output shaft  5   d  is blocked. On the other hand, when the fifth inner race  51  rotates with respect to the fifth sprags  53  in the lock direction (the direction of arrow Ri in  FIG. 5 ) when viewed from the fifth outer race  52  in rotation relative to the fifth outer race  52 , the fifth sprags  53  are engaged with the fifth inner race  51  and the fifth outer race  52 . As a result, the input shaft  5   c  rotates together with the drive gear  8   a  so as to transmit power. 
         [0079]    After the power is transmitted to the fifth clutch  50  from the output shaft  5   d  through the driven gear  8   b  and the drive gear  8   a , the fifth outer race  52  rotates with respect to the fifth sprags  53  in the lock direction (the direction of arrow Ro in  FIG. 5 ) when viewed from the fifth inner race  51  in rotation relative to the fifth inner race  51 , and then the fifth sprags  53  are engaged with the fifth inner race  51  and the fifth outer race  52 . As a result, the drive gear  8   a  rotates together with the input shaft  5   c  to transmit the power. On the other hand, when the fifth outer race  52  rotates with respect to the fifth sprags  53  in the free direction (the opposite direction to arrow Ro in  FIG. 5 ) when viewed from the fifth inner race  51  in rotation relative to the fifth inner race  51 , the fifth sprags  53  are disengaged from the fifth inner race  51  and the fifth outer race  52 . As a result, the drive gear  8   a  idles on the input shaft  5   c  to block the transmission of power from the output shaft  5   d  to the input shaft  5   c.    
         [0080]    Then, the operation of the power transmitting device  1  and the gearbox  212  in the first embodiment structured as described above will be described with reference to  FIG. 7  and  FIG. 8 .  FIG. 7  and  FIG. 8  schematically show a front view of the internal structure of the power transmitting device  1  and the gearbox  212 .  FIG. 7  and  FIG. 8  indicate power transmission line with arrows P for the sake of easy understanding, and also indicate, with an arrow (solid line), the direction of rotation of each of the ring gear  34 , pinion gear  33 , sun gear  31 , drive gears  6   a ,  7   a  and  8   a , driven gears  6   b ,  7   b  and  8   b , and the first outer race  12 , second outer race  22 , fourth outer race  42  and the fifth outer race  52  of the first clutch  10 , second clutch  20 , fourth clutch  40  and the fifth clutch  50 . An arrow (broken line) extending rightward from an upper portion of the opinion gear  32  (see  FIG. 7(   a ),  FIG. 7(   c ),  FIG. 8(   a ),  FIG. 8(   b )) shows the state of the rotor  62  (see  FIG. 2)  driving the pinion gear  32  through the ring gear  34  in the relationship of the ring gear  34  and the pinion gear  32 . An arrow (broken line) extending leftward from an upper portion of the opinion gear  32  (see  FIG. 7(   b ),  FIG. 8(   c )) shows the state of the rotor  62  (see  FIG. 2)  applying a brake to the pinion gear  32  through the ring gear  34 . An arrow (broken line) extending leftward or rightward from a lower portion of the pinion gear  32  shows the direction of rotation of the sun gear  31 , while an arrow (broken line) extending rightward from the center of the pinion gear  32  shows the direction of rotation of the carrier  33  (see  FIG. 2 ). 
         [0081]    Sign “ON” indicates when the first load applying device  15  and the fourth load applying device  45  are actuated to disengage the first sprags  13  and the fourth sprags  43  from the first inner race  11  and the first outer race  12 , and the fourth inner race  41  and the fourth outer race  42 . Sign “OFF” indicates when the first load applying device  15  and the fourth load applying device  45  are not operated to allow engagements of the first sprags  13  and the fourth sprags  43 . 
         [0082]    As described above, in the embodiment, the first gear pairs  6 ,  7  are arranged from largest transmission gear ratio (the number of driven gear teeth÷the number of drive gear teeth) in increasing order of distance to the driven gear  5   b  (see  FIG. 2 ). Assume that the transmission gear ratios of the first gear pairs  6 ,  7  and the second gear pair  8  are k 1 , k 2  and k 3  in order, the relationship of the transmission gear ratios is k 1 &gt;k 2 &gt;k 3 . The number of teeth of the driven gear  8   b  of the second gear pair  8  is designed to be smaller than the minimum number of gear teeth of those of the driven gears  6   b ,  7   b  of the first gear pairs  6 ,  7  (the number of teeth of the drive gear  7   b  in the embodiment). For this reason, when power is transmitted from the input shaft  5   c  to the output shaft  5   d , assuming that the rotational speeds of the respective driven gears  6   b ,  7   b ,  8   b  are α 1 , α 2 , α 3 , each rotational speed is uniquely determined by the rotational speed of the input shaft  5   c , and α 1 &lt;α 2 &lt;α 3  is obtained from the relationship of the transmission gear ratios. The output shaft  5   d  rotates at rotational speed based on a shift position. 
         [0083]    The operation of the power transmitting device  1  and the gearbox  212  during start-up of the engine  211  and starting of the vehicle  200  will be described next with reference to  FIG. 7 .  FIG. 7(   a ) is a schematic view schematically illustrating the internal structure of the power transmitting device  1  and the gearbox  212  during the start-up of the engine  211 . 
         [0084]    During the start-up of the engine  211 , as shown in  FIG. 7(   a ), the first load applying device  15  (see  FIG. 2)  of the first clutch  10  is rendered non-operative (OFF) and the fourth load applying device  45  (see  FIG. 2 ) of the fourth clutch  40  is rendered operative (ON). In this state, the generator motor  60  (see  FIG. 2 ) is actuated to rotate the rotor  62 , whereupon power is transmitted to the second shaft  4  and the ring gear  34 . By the power transmitted to the second shaft  4 , the first outer race  12  of the first clutch  10  rotates in the lock direction (the direction of arrow Ro in  FIG. 5 ) when viewed from the first inner race  11  in rotation relative to the first inner race  11 . Also, the second outer race  22  of the second clutch  20  rotates in the free direction (the direction of arrow Ro in  FIG. 5 ) when viewed from the second inner race  21  in rotation relative to the second inner race  21 . This engages the first sprags  13  with the first inner race  11  and the first outer race  12  of the first clutch  10 , so as to transmit the power from the second shaft  4  to the first shaft  3 . As a result, the sun gear  31  (third element) connected to the first shaft  3  rotates. 
         [0085]    On the other hand, the power of the rotor  62  (see  FIG. 2 ) is transmitted also to the ring gear  34 . The ring gear  34  receiving the power transmitted meshes with the pinion gear  32  to rotate the sun gear  31 . At this stage, because the power of the rotor  62  is transmitted through the first clutch  10  to the sun gear  31 , the sun gear  31  runs at speeds up to be equal to or greater than a transmission gear ratio of the planetary gear device  30 . As a result, the carrier  33  (see  FIG. 2 ) rotates. In this manner, the power is transmitted to the input shaft  2  connected to the carrier  33 , resulting in start-up of the engine  211 . 
         [0086]    The power transmitted to the first shaft  3  is transmitted through the drive gear  5   a  and the driven gear  5   b  to the input shaft  5   c  of the gearbox  212 . After the power is transmitted to the input shaft  5   c , the driven gears  6   b ,  7   b  of the first gear pairs  6 ,  7  rotate so as to rotate the fourth outer races  42  (see  FIG. 2 ) of the fourth clutches  40  and rotate the fifth inner race  51  (see  FIG. 2 ) of the fifth clutch  50 . The fourth outer race  42  of the fourth clutch  40  rotates in the lock direction (the direction of arrow Ro in  FIG. 5 ) when viewed from the fourth inner race  41  in rotation relative to the fourth inner race  41 . However, because the first load applying device  15  (see  FIG. 2 ) of the fourth clutch  40  is operated (ON), the fourth outer race  42  idles on the fourth inner race  41 . For this reason, the power is not transmitted to the output shaft  5   d . Further, because the fifth inner race  51  (see  FIG. 2 ) of the fifth clutch  50  rotates in the free direction (the direction opposite to arrow Ri in  FIG. 5 ) when viewed from the fifth outer race  52  in rotation relative to the fifth outer race  52 , the fifth inner race  51  rotates freely without engaging with the fifth outer race  52 . Thus, the power is not transmitted to the output shaft  5   d . Accordingly, it is possible to prevent the power from being transmitted to the rear wheels  202  during the start-up of the engine  211 , and to use the generator motor  60  to transmit power from the input shaft  2  to the engine  211  in order to start up the engine  211  even without mounting a cell motor (starter). 
         [0087]    Next, the operation of the power transmitting device  1  and the gearbox  212  during starting of the vehicle  200  will be described with reference to  FIG. 7(   b ) and  FIG. 7(   c ).  FIG. 7(   b ) is a schematic diagram schematically showing the internal structure of the power transmitting device  1  and the gearbox  212  at vehicle start (low speeds), while  FIG. 7(   c ) is a schematic diagram schematically showing the internal structure of the power transmitting device  1  and the gearbox  212  at vehicle start (high speeds). Assuming that low speeds refers to that the travel speed (the horizontal axis in  FIG. 6)  of the vehicle  200  shown in  FIG. 6  is 0&lt;travel speed&lt;Vo and high speeds refers to travel speed≧Vo. 
         [0088]    After the start-up of the engine  211 , while the driving of the rotor  62  (see  FIG. 2 ) is maintained, the rpm of the rotor  62  is adjusted to maintain the rpm of the ring gear  34  (second element) at a value higher (but less than R 2  shown in  FIG. 6 ) than the rpm of the sun gear  31  (first element) (see  FIG. 6 ). As a result, the rpm of the second shaft  4  (equal to the rpm of the second element) is higher than the rpm of the first shaft  3  (equal to the rpm of the third element) (see  FIG. 6 ). As shown in  FIG. 7(   b ), the first load applying device  15  (see  FIG. 2)  of the first clutch  10  is rendered operative (ON), and also the fourth load applying device  45  (see  FIG. 2 ) of the fourth clutch  40  in the first gear pair  6  is rendered non-operative (OFF), as well as the fourth load applying device  45  (see  FIG. 2 ) of the fourth clutch  40  in the first gear pair  7  is rendered operative (ON). 
         [0089]    In this case, the power transmitted to the second shaft  4  causes the first outer race  12  of the first clutch  10  (see  FIG. 2 ) to rotate in the lock direction (the direction of arrow Ro in  FIG. 5 ) when viewed from the first inner race  11  in rotation relative to the first inner race  11 . However, because the first load applying device  15  is operated, the first sprags  13  cannot engage with the first inner race  11  and the first outer race  12 . Also, the second outer race  22  of the second clutch  20  rotates in the free direction (the direction opposite to arrow Ro in  FIG. 5 ) when viewed from the second inner race  21  in rotation relative to the second inner race  21 . From the above, the transmission of power from the second shaft  4  to the first shaft  3  is blocked. 
         [0090]    On the other hand, the power of the engine  211  is transmitted to the carrier  33  (see  FIG. 2 ) (the first element), and then the power is output to the sun gear  31  (the third element). The load of the generator motor  60  is increased to reduce the rpm of the rotor  62  for a reduction in rpm of the ring gear  34  (the second element) or the engine speed of the engine  211  is increased. This causes the motion state of the planetary gear device  30  (see  FIG. 6 ) to move in the right upper direction on the line of the third element. The power transmitted to the sun gear  31  is transmitted to the first shaft  3  and then transmitted through the drive gear  5   a  (see  FIG. 2 ) and the driven gear  5   b  to the input shaft  5   c . The power from the engine  211  and the generator motor  60  is distributed as described above, thus accomplishing forward moving in variable speed conditions in hybrid mode. 
         [0091]    After the power is transmitted to the input shaft  5   c , the driven gears  6   b ,  7   b  of the first gear pairs  6 ,  7  rotate, so that the fourth outer races  42  (see  FIG. 2 ) of the fourth clutches  40  and the fifth inner race  51  of the fifth clutch  50  rotate. The fourth outer races  42  of the fourth clutches  40  rotate in the lock direction (the direction of arrow Ro in  FIG. 5 ) when viewed from the fourth inner race  41  in rotation relative to the fourth inner race  41 . However, since the fourth load applying device  45  (see in  FIG. 2 ) of the fourth clutch  40  of the first gear pair  7  is operated (ON), the fourth outer race  42  (see  FIG. 2 ) of, the fourth clutch  40  of the first gear pair  7  idles on the fourth inner race  41  of the fourth clutch  40 . On the other hand, since the fourth load applying device  45  (see in  FIG. 2 ) of the fourth clutch  40  of the first gear pair  6  is not operated (OFF), the fourth outer race  42  (see  FIG. 2 ) of the fourth clutch  40  of the first gear pair  6  transmits the power to the fourth inner race  41 , thus rotating the output shaft  5   d . The rotational speed of the output shaft  5   d  is α 1  which is equal to the rotational speed of the driven gear  6   b  of the first gear pair  6 . 
         [0092]    On the other hand, in this event, the drive gear  8   a  is rotated through the driven gear  8   b  by the output shaft  5   d . In the embodiment, since a transmission gear ratio (the number of driven gear teeth÷the number of drive gear teeth) k 3  of the second gear pair  8  is set to be smaller than a transmission gear ratio k 1  of the first gear pair  6 , a rotational speed (α 1 ·k 3 =k 3 /k 1 ·α) of the drive gear  8   a  of the second gear pair  8  becomes smaller than the rotational speed (α) of the input shaft  5   c . For this reason, in the fifth clutch  50 , a rotational speed of the fifth outer race  52  (see  FIG. 2 ) becomes slower than the rotational speed α of the fifth inner race  51 . This is tantamount to the state in which the fifth outer race  52  relatively rotates in the free direction (the direction opposite to arrow Ro in  FIG. 5 ). Hence, in the fifth clutch  50 , the fifth sprags  53  cannot engage with the fifth inner race  51  and the fifth outer race  52 , so that the fifth outer race  52  idles on the fifth inner race  51 . In this manner, the rotation (rotational speed α 1 ) of the output shaft  5   d  is transmitted to the rear wheels  202  (see  FIG. 1 ), allowing the Vehicle  200  to move forward. 
         [0093]    When the vehicle  200  is made move forward and then a rpm of the second shaft  4  becomes equal to the rpm (R 1 ) of the first shaft  3  (see  FIG. 6 ), the first load applying device  15  (see  FIG. 2 ) of the first clutch  10  is rendered non-operative (OFF) as illustrated in  FIG. 7(   c ). Note that the fourth load applying device  45  of the fourth clutch  40  is maintained in the state shown in  FIG. 7(   b ). 
         [0094]    When the rpms of the first shaft  3  and the second shaft  4  are the same, the rpms of the first inner race  11  and the first outer race  12  of the first clutch  10  become equal to each other. At this time, if the first load applying device  15  (see  FIG. 2 ) is rendered non-operative, the first sprags  13  are engaged with the first inner race  11  (see  FIG. 5 ) and the first outer race  12 , so that power is transmitted from the second shaft  4  to the first shaft  3 . Because there is no difference in speed between the first inner race  11  and the first outer race  12  when the first sprags  13  engage with them, inertial torque is prevented from being produced to avoid shock. 
         [0095]    After the first load applying device  15  has been rendered non-operative, when the rpm of the third element (the sun gear  31 ) exceeds the rpm of the second element (the ring gear  34 ) (when travel speed&gt;V 0  shown in  FIG. 6 ), the rpm of the first shaft  3  connected to the sun gear  31  exceeds the rpm of the second shaft  4  connected to the ring gear  34 . In the first clutch  10  at this time, the first inner race  11  rotates in the free direction when viewed from the first outer race  12  in rotation relative to the first outer race  12  (see  FIG. 5 ). As a result, the first sprags  13  tilt in the anti-self lock direction, so that the transmission of power from the first shaft  3  to the second shaft  4  is blocked at the first clutch  10 . As a result, the power of the engine  211  is transmitted from the first shaft  3  to the drive gear  5   a  (see  FIG. 2 ), thus achieving forward travel using the power of the engine  211 . 
         [0096]    On the other hand, in the second clutch  20 , the second inner race  21  rotates in the lock direction in rotation relative to the second outer race  22 . As a result, the second sprags  23  are engaged with the second inner race  21  and the second outer race  22 , so that power is transmitted from the second inner race  21  to the second outer race  22 , that is, from the first shaft  3  to the second shaft  4 . In this manner, the generator motor  60  can be functioned as a generator to regenerate the generated electric power as a power source. 
         [0097]    Then, the power transmitted to the drive gear  5   a  (see  FIG. 2 ) is transmitted through the driven gear  5   b  to the input shaft  5   c  to be input to the gearbox  212 . In the gearbox  212 , as illustrated in  FIG. 7(   c ), since the fourth load applying device  45  (see  FIG. 2)  of the fourth clutch  40  in the first gear pair  6  is in the non-operative state (OFF), while the fourth load applying device  45  (see  FIG. 2 ) of the fourth clutch  40  in the first gear pair  7  is in the operative state (ON), the power is transmitted through the first gear pair  6  to the output shaft  5   d  as described earlier. 
         [0098]    Then, for upshifting, the operation of the fourth load applying device  45  (see  FIG. 2 ) of the fourth clutch  40  of the first gear pair  7  higher than the first gear pair  6  is stopped (OFF). As a result, similarly to the fourth clutch  40  of the first gear pair  6 , in the fourth clutch  40  in the first gear pair  7 , the fourth sprags  43  also become allowed to engage with the fourth inner race  41  (see  FIG. 2 ) and the fourth outer race  42 . 
         [0099]    In this connection, since the rotational speed α 2  of the driven gear  7   b  of the first gear pair  7  is faster than the rotational speed α 1  of the driven gear  6   b  of the first gear pair  6  (α 1 &lt;α 2 ), the rotational speed a 2  of the driven gear  7   b  exceeds the rotational seed (α 1 ) of the output shaft  5   d . Thus, in the fourth clutch  40  of the first gear pair  7 , the fourth outer race  42  (see  FIG. 2 ) rotates in the lock direction (the direction of arrow Ro in  FIG. 5 ) when viewed from the fourth inner race  41  in rotation relative to the fourth inner race  41 . As a result, the power is transmitted from the fourth outer race  42  toward the fourth inner race  41 , so that the driven gear  7   b  rotates together with the output shaft  5   d , the output shaft  5   d  rotating at the rotational speed α 2 . 
         [0100]    On the other hand, the rotational speed (α 1 ) of the driven gear  6   b  of the first gear pair  6  becomes slower than the rotation speed (α 2 ) of the output shaft  5   d  (α 1 &lt;α 2 ). Because of this, in the fourth clutch  40  of the first gear pair  6 , the rotational speed of the fourth outer race  42  becomes slower than the rotational speed of the fourth inner race  41 . This is tantamount to the state in which the fourth inner race  41  relatively rotates in the free direction (the direction opposite to arrow Ri in  FIG. 5 ). Hence, in the fourth clutch  40  of the first gear pair  6 , the fourth sprags  43  cannot engage with the fourth inner race  41  and the fourth outer race  42 . As a result, the driven gear  6   b  idles on the output shaft  5   d  so as to transmit no power. Also, through the driven gear  8   b  integrated with the output shaft  5   d , the fifth outer race  52  (see  FIG. 22 ) of the fifth clutch  50  rotates in the free direction (the direction opposite to arrow Ro in  FIG. 5 ) when viewed from the fifth inner race  51  in rotation relative to the fifth inner race  51 , so that the fifth outer race  52  idles on the fifth inner race  51  so as to transmit no power. 
         [0101]    In this manner, when the gearbox  212  upshifts, the shifting gear can be accomplished only by stopping the operation of the fourth load applying device  45  of the fourth clutch  40  of the higher first gear pair  7 , without any operation for lower gears (the first gear pair  6  in the embodiment). Further, in the fourth clutch  40  of the first gear pair  7 , the fourth sprags  43  are tilted in the self lock direction by stopping the operation of the fourth load applying device  45 , so that the relative rotation of the fourth inner race  41  and the fourth outer race  42  in a certain direction of rotation is instantaneously restricted. Accordingly, a reduction in time required for switching is achieved, thus enabling quick gear shifting. Further, because of a reduced time required for switching, idling of the fourth inner race  41  and the fourth outer race  42  do not occur from the state of transmitting no power to the state of transmitting power, leading to prevention of shock during gear shifting. 
         [0102]    Further, because gear shifting is achieved simply by switching between the operative state and the non-operative state of the fourth load applying device  45  of the fourth clutch  40 , the gearbox  212  does not require a complicated engaging mechanism, a shift fork or the like, thus providing reductions in weight and size. This enables incorporation of a plurality of first gear pairs into limited space of the gearbox  212 , and therefore, for example, a multi-speed power transmitting device  1  with 6 or more speeds can be provided. 
         [0103]    For information, after making an idle reduction (the operation of the engine  211  is shut down when the vehicle comes to a stop at a traffic light or the like while moving, in order to reduce the amount of fuel consumed and the emission of exhaust gas), performing the aforementioned sequence of engine start-up and vehicle start allows the vehicle  200  to start moving in a short time after the idle reduction. Specifically, the fourth load applying devices  45  of the fourth clutches  40  in the first gear pairs  6 ,  7  are operated (the state of blocking the transmission of power), and then the engine  211  is started up (see  FIG. 7(   a )). Then, after the engine  211  has started up, the fourth load applying device  45  of the fourth clutch  40  in the first gear pair  6  is rendered non-operative (the transmission of power is allowed) (see  FIG. 7(   b )), thus starting the vehicle  200  moving. The unnecessity of engagement/disengagement operation of a main clutch makes it possible to speedily start a vehicle moving. 
         [0104]    Next, the power transmitting device  1  and the gearbox  212  in regeneration caused during coasting or braking will be described with reference to  FIG. 8(   a ).  FIG. 8(   a ) is a schematic diagram schematically illustrating the internal structure of the power transmitting device  1  and the gearbox  212  during regeneration.  FIG. 8(   a ) illustrates the state after upshifting, that is, in which both the fourth load applying devices  45  of the fourth clutches  40  in the first gear pairs  6 ,  7  are rendered non-operative (OFF). 
         [0105]    In regeneration, the first load applying device  15  (see  FIG. 2 ) of the first clutch  10  is rendered non-operative (OFF) as shown in  FIG. 8(   a ). While the accelerator (not shown) is not operated, as shown in  FIG. 8(   a ), power is input from the output shaft  5   d  (assuming that the rotational speed is a 2 ) to the gearbox  212 . As a result, the power is transmitted from the output shaft  5   d  through the driven gear  8   b  of the second gear pair  8  to the drive gear  8   a , and then to the fifth outer race  52  (see  FIG. 2)  of the fifth clutch  50 . 
         [0106]    In this regard, a rotational speed of the fifth outer race  52  (see  FIG. 2 ) integrated with the drive gear  8   a  is k 3 ·α 2  because a transmission gear ratio of the second gear pair  8  is k 3  and the rotational speed of the driven gear  8   b  is α 2 . On the other hand, since the fifth inner race  51  of the fifth clutch  50  does not receive a drive force from the input shaft  5   c , the rotational speed of the fifth inner race  51  is slower than the rotational speed of the drive gear  8   a . As a result, the fifth outer race  52  rotates in the lock direction (the direction of arrow Ro in  FIG. 5 ) when viewed from the fifth inner race  51  in rotation relative to the fifth inner race  51 , so that the fifth sprags  53  are engaged with the fifth outer race  52  and the fifth inner race  51 . As a result, the power is transmitted from the fifth outer race  52  of the fifth clutch  50  toward the fifth inner race  51 , so that the drive gear  8   a  rotates together with the input shaft  5   c  (rotational speed k 3 ·α 2 ). With the rotation of the drive gear  8   a , the input shaft  5   c  rotates, and also the drive gears  6   a ,  7   a  of the first gear pairs  6 ,  7  rotate (rotational speed k 3 ·α 2 ). 
         [0107]    As a result, the power is transmitted to the driven gears  6   b ,  7   b  meshing with the drive gears  6   a ,  7   a  of the first gear pairs  6 ,  7 , so that the driven gears  6   b ,  7   b  rotate at speeds according to their transmission gear ratios. A rotational speed β 1  of the driven gear  6   b  is k 3 /k 1 ·α 2 , while a rotational speed β 2  of the driven gear  7   b  is k 3 /k 2 ·α 2 . From k 1 &gt;k 2 &gt;k 3 , the rotational speeds β 1 , β 2  of the driven gears  6   b ,  7   b  become both smaller than α 2 . 
         [0108]    On the other hand, because the rotational speed of the output shaft  5   d  is α 2 , in the fourth clutch  40  of the first gear pair  7  the fourth inner race  41  (see  FIG. 2 ) rotates at a speed α 2 . Therefore, in the fourth clutch  40  of the first gear pair  7 , the rotational speed of the fourth inner race  41  is faster than the rotational speed of the fourth outer race  42 , which is tantamount to the state in which the fourth inner race  41  relatively rotates in the free direction (the direction opposite to arrow Ri in  FIG. 5 ). This is the same as the case for the first gear pair  6 . Hence, in the fourth clutches  40  of the first gear pairs  6 ,  7 , the fourth sprags  43  cannot engage with the fourth inner race  41  and the fourth outer race  42 . As a result, the fourth load applying devices  45  of the fourth clutches  40  of the first gear pairs  6 ,  7  are not operated (OFF), so that the power cannot be transmitted from the output shaft  5   d  to the input shaft  5   c.    
         [0109]    The power transmitted to the input shaft  5   c  is transmitted through the driven gear  5   c  (see  FIG. 2 ) and he drive gear  5   a  to the first shaft  3 . 
         [0110]    After the power is transmitted to the first shaft  3 , in the first clutch  10 , the first inner race (see  FIG. 2 ) rotates in the free direction (the direction opposite to arrow Ri in  FIG. 5 ) when viewed from the first outer race  12  in rotation relative to the first outer race  12 , so that the transmission of power is blocked. In the second clutch  20 , the second inner race  21  (see  FIG. 2 ) rotates in the lock direction (the direction of arrow Ri in  FIG. 5 ) when viewed from the second outer race  22  in rotation relative to the second outer race  22 . 
         [0111]    For this reason, the second inner race  21  of the second clutch  20  rotates together with the second outer race  22  so as to transmit the power as shown in  FIG. 8(   a ). In step with the rotation of the second outer race  22  of the second clutch  20 , the second shaft  4 , the ring gear  34  and the rotor  62  (see  FIG. 2)  rotate. As a result, the power input from the output shaft  5   d  is used for the generator motor  60  to functions as a generator. Then, the electric power generated by the generator motor  60  can be regenerated as a power source. On the other hand, the power transmitted to the first shaft  3  rotates the sun gear  31  (third element) connected to the first shaft  3  as shown in  FIG. 8(   a ), and further, rotates the carrier  33  (see  FIG. 2) . In step with the rotation of the carrier  33 , the power is input to the engine  211 , providing engine braking. 
         [0112]    Next, the operation of the power transmitting device  1  and the gearbox  212  when backing up the vehicle  200  will be described in reference with  FIG. 8(   b ) and  FIG. 8(   c ).  FIG. 8(   b ) is a schematic diagram schematically showing the internal structure of the power transmitting device  1  and the gearbox  212  when reverse gear is selected, while  FIG. 8(   c ) is a schematic diagram schematically showing the internal structure of the power transmitting device  1  and the gearbox  212  after gear shifting into reverse. 
         [0113]    Upon selection of reverse gear, the first load applying device  15  (see  FIG. 2 ) of the first clutch  10  of the power transmitting device  1  is actuated (ON) as shown in  FIG. 8(   b ). Then, the motor  60  is driven to rotate the third element (ring gear  34 ) at a higher rpm than R 2  (see  FIG. 6) . As a result, as shown in  FIG. 6  and  FIG. 8(   b ), the third element (sun gear  31 ) rotates in the direction opposite to the direction of rotation for moving forward the vehicle  200  (the direction of rotation of the sun gear  31  shown in  FIG. 8(   a )) (the third element rpm&lt;0 in  FIG. 6) , and the first shaft  3  rotates also in the direction opposite to the direction of rotation for moving forward the vehicle  200 . 
         [0114]    At this time, power is transmitted to the second shaft  4  by driving the rotor  62  (see  FIG. 2 ), so that the first outer race  12  (see  FIG. 5 ) of the first clutch  10  rotates in the lock direction when viewed from the first inner race  11  in rotation relative to the first inner race  11 . However, because the first load applying device  15  (see  FIG. 2 ) is in operation, the transmission of power from the second shaft  4  to the first shaft  3  is blocked in the first clutch  10 . 
         [0115]    Also, the first shaft  3  rotates in the direction opposite to the rotation direction when moving forward the vehicle  200 , so that in the second clutch  20  the second inner race  21  attempts to rotate slightly in the lock direction. However, since the rpm of the second outer race  22  caused by the second shaft  4  is higher than the rpm of the second inner race  21  (the absolute value of the rpm of the second element is larger than the absolute value of the rpm of the third element in a range of travel speed&lt;Vo in  FIG. 6 ), the second outer race  22  rotates in the free direction when viewed from the second inner race  21  in rotation relative to the second inner race  21 . Accordingly, the transmission of power from the second shaft  4  from the first shaft  3  is blocked also in the second clutch  20 . 
         [0116]    Upon selection of reverse gear, in the gearbox  212 , the reverse gear pair  9  makes a connection between the input shaft  5   c  and the output shaft  5   d  as shown in  FIG. 8(   b ). At this stage, since the first shaft  3  rotates in the direction opposite to that when the vehicle  200  moves forward, in spite of reverse gear being selected, the output shaft  5   d  rotates in the same direction as that when the vehicle  200  moves forward (the rotation direction of the output shaft  5   d  shown in  FIG. 8(   b ) is the same as the rotation direction of the output shaft  5   d  shown in  FIG. 8(   a ). That is the rotation direction of the output shaft  5   d  is not changed between when the vehicle  200  moves forward and when reverse gear is selected. 
         [0117]    In this manner, since the output shaft  5   d  can be structured to rotate in the same direction in before and after gear shifting into reverse from when the vehicle  200  moves forward, the gearbox  212  is capable of allowing the meshing of the reverse gear pair  9  without gear rattle provided that at least rpms are commensurate with each other, even without mounting a synchronous mesh mechanism. Even when a synchronous mesh mechanism is mounted in the gearbox  212  in order to improve operability, a size reduction and simplification of the synchronous mesh mechanism can be achieved, leading to a size reduction and simplification of the gearbox  212 . Further, with the size reduction and the simplification of the synchronous mesh mechanism, the amount of energy consumption required for operation of the synchronous mesh mechanism can be reduced. 
         [0118]    After meshing of the reverse gear pair  9  (after gear shifting into reverse), the rpm of the generator motor  60  (see  FIG. 2 ) is reduced in order to reduce the rpm of the second element (ring gear  34 ) to an arbitrary rpm ranging from R 1  to R 2  (see  FIG. 6 ). Thus, the rotation direction of the third element (sun gear  31 ) rotating in the direction opposite to that when the vehicle  200  moves forward is changed to the normal direction (the rotation direction when the vehicle  200  moves forward) (the third element rpm&gt;0 in  FIG. 6 ). As a result, as shown in  FIG. 8(   c ), the rotation direction of the output shaft  5   d  is changed from the rotation direction in  FIG. 8(   b ) and the vehicle  200  starts moving backward. 
         [0119]    Next, the electrical configuration of a control unit  70  of the power transmitting device  1  will be described with reference to  FIG. 9 .  FIG. 9  is a block diagram illustrating the electrical configuration of the control unit  70  of the power transmitting device  1 . The control unit  70  includes a CPU  71 , a ROM  72  and a RAM  73  which are connected to I/O ports  75  through a bus line  74 . The devices, such as the first load applying device  15  and the like, are connected to the I/O ports  75 . 
         [0120]    The CPU  71  is operational equipment for controlling parts connected through the bus line  74  to it. The ROM  72  is a non-rewritable, nonvolatile memory storing fixed value data and the like of a control program (for example, a program using the flowchart shown in  FIG. 10 ) and the like which are executed by the CPU  71 . The RAM  73  is a memory for storing in a rewritable manner various data used for executing the control program. 
         [0121]    A shift switch sensor unit  80  is a device for detecting presence or absence of upshifting operation or downshifting operation of the driver, and outputting the detection result to the CPU  71 . In the embodiment, the shift switch sensor  80  mainly includes a sequential switch built in a shift lever (not shown), and an output circuit (not shown) processing a signal output from the sequential switch and outputting the signal to the CPU  71 . 
         [0122]    A travel speed detector unit  81  is a device for detecting a pulse which is proportional to a rotational speed of an axle, and outputting the detection result to the CPU  71 . The CPU  71  obtains a travel speed of the vehicle  200  from the detection result received from the travel speed detector unit  81 . 
         [0123]    A load applying sensor unit  82  is a device for detecting operation (ON) or non-operation (OFF) of the first load applying device  15 , and outputting the detection result to the CPU  71 , and mainly includes load applying sensors (not shown) respectively detecting operation (ON) and non-operation (OFF) of the first load applying device  15 , and an output circuit (not shown) processing the detection result of each of the load applying sensors and outputting it to the CPU  71 . 
         [0124]    An accelerator sensor unit  83  is a device for detecting the amount of depression of an accelerator (not shown) and an accelerator depression speed, and outputting the detection result to the CPU  71 , and mainly includes an angle sensor (not shown) detecting the amount of accelerator depression, an angular speed sensor (not shown) detecting an accelerator depression speed, and an output circuit (not shown) processing the detection results from the angle sensor and/or the angular speed sensor and outputting them to the CPU  71 . 
         [0125]    A first-shaft rpm sensor unit  84  and a second-shaft rpm sensor unit  85  are devices for detecting rpms of the first shaft  3  (see  FIG. 2 ) and the second shaft  4 , and outputting the detection results to the CPU  71 , and mainly include rpm sensors (not shown), and output circuits (not shown) each of which processes the detection result from the rpm sensor and outputting it to the CPU  71 . 
         [0126]    As examples of other I/O devices  86  shown in  FIG. 8 , an acceleration sensor detecting an acceleration of the vehicle  200  and the like can be shown. The CPU  71  can take account of the detection result on acceleration of the vehicle  200  to determine whether or not an acceleration request is made. 
         [0127]    Next, power transmission control processing in the control unit  70  of the power transmitting device  1  will be described with reference to  FIG. 10 .  FIG. 10  is a flowchart showing the power transmission control processing of the control unit  70  of the power transmitting device  1  in the first embodiment. The processing is executed repeatedly (for example, every 0.2 ms) by the CPU  71  during the turning-on of the power to the control unit  70 . 
         [0128]    For the power transmission control processing, the CPU  71  acquires rpms of the first shaft  3  and the second shaft  4  when starting moving the vehicle  200  (see  FIG. 7(   b ))(S 1 ). In the process, the detection results of the first-shaft rpm sensor unit  84  (see  FIG. 9)  and the second-shaft rpm sensor unit  85  are used as described above. The starting of the vehicle  200  moving is detected by use of each of the detection results of the shift switch sensor unit  80 , the travel speed detection unit  81  and the accelerator sensor unit  83 . 
         [0129]    Then, the CPU  71  performs a comparison between the rpm of the first shaft  3  and the rpm of the second shaft  4  (S 2 ). As a result, if determining that the rpm of the first shaft  3  and the rpm of the second shaft  4  are in disagreement with each other (S 2 : No), the CPU  71  actuates the first load applying device  15  (ON), and then terminates the power transmission control processing. When the rpm of the first shaft  3  is lower than the rpm of the second shaft  4 , the first load applying device  15  is operated to block the transmission of power from the second shaft  4  to the first shaft  3  in order to prevent the planetary gear device  30  from being affected by the first clutch  10 . 
         [0130]    When the rpm of the first shaft  3  is higher than the rpm of the second shaft  4 , in the first clutch  10  the first inner race  11  rotates in the free direction when viewed from the first outer race  12  (see  FIG. 5 ) in rotation relative to the first outer race  12 , so that the first sprags  13  are tilted in the anti-self lock direction. As a result, the transmission of power from the first shaft  3  to the second shaft  4  is blocked without operating the first load applying device  15 . 
         [0131]    On the other hand, when it is determined, as a result of the process S 2 , that the rpm of the first shaft  3  and the rpm of the second shaft  4  are in agreement with each other (S 2 : Yes), the first load applying device  15  is rendered non-operative (OFF) and the power transmission control processing is terminated. When the rpm of the first shaft  3  and the rpm of the second shaft  4  are in agreement with each other, the first load applying device  15  is rendered non-operative, which making it possible to prevent shock from being produced when the operation of the first load applying device  15  is switched, and prevent energy loss. In other words, when the rpm of the first shaft  3  is equal to the rpm of the second shaft  4 , the first inner race  11  and the first outer race  12  of the first clutch  10  (see  FIG. 5 ) become equal in rpm. At this stage, the first load applying device  15  (see  FIG. 2 ) is rendered non-operative. Thereupon, the first sprags  13  engage with the first inner race  11  and the first outer race  12 , but a speed difference is not made between the first inner race  11  and the first outer race  12 . This makes it possible to prevent inertial torque from being produced when the first sprags  13  engage, resulting in avoidance of shock. After the first load applying device  15  has been rendered non-operative, the engine speed of the engine  211  is increased, so that the rpm of the first shaft  3  exceeds the rpm of the second shaft  4 . Thereupon, the first sprags  13  tilt in the anti-self lock direction, so that the transmission of power from the first shaft  3  to the second shaft  4  is blocked. Accordingly, the prevention of energy loss from being caused by the transmission of power from the first shaft  3  to the second shaft  4  can be achieved. Further, since the first load applying device  15  is rendered non-operative when the rpm of the first shaft  3  is equal to or higher than the rpm of the second shaft  4 , this makes it possible to shorten the operating time of the first load applying device  15 , leading to minimization of energy loss produced by operation of the first load applying device  15 . 
         [0132]    Note that, in the flowchart (power transmission control processing) shown in  FIG. 10 , the process in S 1  corresponds to the first shaft rpm acquiring means and second shaft rpm acquiring means described in claim  6 , the process in S 2  corresponds to rpm determining means and the process in S 4  corresponds to load controlling means. 
         [0133]    Next, a power transmitting device  101  in a second embodiment according to the present invention will be described with reference to  FIG. 11 . The first embodiment has described the planetary gear device  30  of the power transmitting device  1  including a single sun gear  31 , a single ring gear  34  and a single carrier  33 . However, the second embodiment describes a planetary gear device  130  which is a complex planetary gear mechanism, having two sun gears  131 ,  132  which are coupled to each other by pinion gears  133 . The same components as those in the first embodiment are designated by the same reference signs and the description is omitted. 
         [0134]      FIG. 11  is a schematic diagram schematically showing the power transmitting device  101  and the gearbox  212  in the second embodiment. The planetary gear device  130  of the power transmitting device  101  includes a first sun gear  131 , a second sun gear  132  placed at a predetermined distance from the first sun gear  131 , and a carrier  134  rotatably supporting a plurality of pinion gears  133  which mesh with the outer periphery of the first sun gear  131  and the second sun gear  132 . In the embodiment, the first sun gear  131  is connected to the input shaft  2  to which the power of the engine  211  is input, which forms a first element. Also, the carrier  134  is connected to the rotor  62  of the generator motor  60 , which forms a second element. Further, the second sun gear  132  is connected to the first shaft  3  transmitting power toward the gearbox  212 , which forms a third element. Note that the operation of the power transmitting device  101  in the second embodiment is similar to the operation of the power transmitting device  1  in the first embodiment, and the description is omitted. 
         [0135]    Next, a third embodiment will be described with reference to  FIG. 12 . The first embodiment has described the power transmitting device  1  structured such that the first shaft  3  is connected to the sun gear  31  of the planetary gear device  30  which includes the carrier  33  (first element), the ring gear  34  (second element) and the sun gear  31  (third element), the second shaft  4  is connected to the ring gear  34 , the first outer race  12  of the first clutch  10  and the second outer race  11  of the second clutch  20  are formed integrally with the second shaft  4 , and the first inner race  11  of the first clutch  10  and the second inner race  21  of the second clutch  20  are formed integrally with the first shaft  3 . 
         [0136]    In comparison with this, the power transmitting device  301  in the first embodiment is similar to the first embodiment in that a carrier  333  (first element), a ring gear  334  (second element), a sun gear  331  (third element) and pinion gears  332  meshing with the sung gear  331  and the ring gear  334  are provided, that the first shaft  3  is connected to the sun gear  331  of a planetary gear device  330 , and that the first outer race  12  of the first clutch  10  and the second outer race  22  of the second clutch  20  are formed integrally with the second shaft  4 , and the first inner race  11  of the first clutch  10  and the second inner race  12  of the second clutch  20  are formed integrally with the first shaft  3 , but differs from the first embodiment in that the second shaft  4  is connected to the carrier  333 . 
         [0137]      FIG. 12  is a schematic diagram schematically showing the internal structure of the power transmitting device  301  in the third embodiment. The same components as those in the first embodiment are designated by the same reference signs and the description is omitted.  FIG. 12  shows only the structure for performing the function of transmitting power for easier understanding. The gearbox  212  shown in  FIG. 2  is omitted in  FIG. 12 . 
         [0138]    The power transmitting device  301 , which is mounted on the vehicle  200  (see  FIG. 1 ), mainly includes the planetary gear device  330  connected to the input shaft  2  transmitting the power of the engine  211 , and the first clutch  10  and the second clutch  20  which are placed on a power line from the planetary gear device  330  to the gear box (not shown), as shown in  FIG. 12 . Note that the relationship between rpms of the first element, the second element and the third element of the planetary gear device  330  and a travel speed of the vehicle  200  is similar to that shown in  FIG. 6 , and the description is omitted. 
         [0139]    The first clutch  10  is provided for transmitting and interrupting power between the second shaft  4  connected to the carrier  333  (first element) and the first shaft  3  connected to the sun gear  331 . The first clutch  10  is structured to transmit, in an interruptible manner, power received from the second shaft  4  to the first shaft  3 , but to block transmission of power from the first shaft  3  to the second shaft  4 . The second clutch  20  is provided for transmitting and interrupting power between the second shaft  4  and the first shaft  3 , and is structured to transmit the power received from the first shaft  3  to the second shaft  4 , but block the transmission of power from the second shaft  4  to the first shaft  3 . 
         [0140]    Next, the operation of the power transmitting device  301  during start-up of the engine  211  will be described. For start-up of the engine, the first load applying device  15  of the first clutch  10  is rendered non-operative (OFF). In this condition, upon actuation of the generator motor  60  to rotate the rotor  62 , the power is transmitted to the ring gear  334  (second element). As shown in  FIG. 6 , as the rpm of the second element (ring gear  334 ) of the planetary gear device  330  increases in the positive direction, the rpm of the third element (sun gear  331 ) increases in the negative direction. Because of this, the power transmitted to the ring gear  334  rotates the sun gear  331  to rotate the first shaft  3 . The power transmitted to the first shaft  3  causes the second inner race  21  of the second clutch  20  to rotate in the lock direction (the direction of arrow Ri in  FIG. 5 ) when viewed from the second outer race  22  in rotation relative to the second outer race  22 . On the other hand, the first inner race  11  of the first clutch  10  rotates in the free direction (the direction opposite to arrow Ri in  FIG. 5 ) when viewed from the first outer race  12  in rotation relative to the first outer race  12 . 
         [0141]    This causes the second sprags  23  to engage with the second inner race  21  and the second outer race  22  of the second clutch  20  so as to transmit the power from the first shaft  3  to the second shaft  4 . As a result, the carrier  333  (first element) connected to the second shaft  4  rotates. Thus, the power is transmitted to the input shaft  2  connected to the carrier  333  to start up the engine  211 . After the start-up of the engine  211 , as in the case described in the first embodiment, forward movement and backward movement of the vehicle  200  (see  FIG. 1 ), up-shifting, down-shifting, coasting and regeneration can be performed. In the power transmitting device  301  in the third embodiment, power switching between the engine  211  and the motor  60  can be provided by use of the first clutch  10  to switch between transmission and interruption of power flowing from the second shaft  4  to the first shaft  3 , as in the case of the first embodiment. 
         [0142]    Next, a fourth embodiment will be described with reference to  FIG. 13 . The first embodiment has described the power transmitting device  1  structured such that the first shaft  3  is connected to the sun gear  31  of the planetary gear device  30  which includes the carrier  33  (first element), the ring gear  34  (second element) and the sun gear  31  (third element), the second shaft  4  is connected to the ring gear  34 , the first outer race  12  of the first clutch  10  and the second outer race  22  of the second clutch  20  are formed integrally with the second shaft  4 , and the first inner race  11  of the first clutch  10  and the second inner race  21  of the second clutch  20  are formed integrally with the first shaft  3 . 
         [0143]    In comparison with this, the fourth embodiment is similar to the first embodiment in that the first outer race  12  of the first clutch  10  and the second outer race  22  of the second clutch  20  are formed integrally with the second shaft  4 , and the first inner race  11  of the first clutch  10  and the second inner race  21  of the second clutch  20  are formed integrally with the first shaft  3 , and describes a structure in which the first shaft  3  is connected to a carrier  433  of a planetary gear device  430  which includes a ring gear  434  (first element), a sun gear  431  (second element), a carrier  433  (third element) and pinion gears  432  meshing with the sun gear  431  and the ring gear  434 , and the second shaft  4  is connected to the sun gear  431 . 
         [0144]      FIG. 13  is a schematic diagram schematically showing the internal structure of the power transmitting device  401  in the fourth embodiment. The same components as those in the first embodiment are designated by the same reference signs and the description is omitted.  FIG. 13  shows only the structure for performing the function of transmitting power for easier understanding. The gearbox  212  shown in  FIG. 2  is omitted in  FIG. 13 . The power transmitting device  401 , which is mounted on the vehicle  200  (see  FIG. 1 ), mainly include, as illustrated in  FIG. 13 , a planetary gear device  430  connected to the input shaft  2  transmitting the power of the engine  211 , and the first clutch  10  and the second clutch  20  which are placed on a power line from the planetary gear device  430  to the gearbox (not shown). 
         [0145]    The ring gear  434  of the planetary gear device  430  is connected to the input shaft  2  to which the power of the engine  211  is input, which forms the first element. The sun gear  431  is connected to the rotor  62  of the generator motor  60 , which forms the second element. In addition, the carrier  433  is connected to the first shaft  3  transmitting the power toward the gearbox (not shown), which forms the third element. 
         [0146]    The first clutch  10  is provided for transmitting and interrupting power between the second shaft  4  connected to the sun gear  431  (second element) and the first shaft  3  connected to the carrier  433 . The first clutch  10  is structured to transmit, in an interruptible manner, power received from the second shaft  4  to the first shaft  3 , but to block transmission of power from the first shaft  3  to the second shaft  4 . The second clutch  20  is provided for transmitting and interrupting power between the second shaft  4  and the first shaft  3 , and is structured to transmit the power received from the first shaft  3  to the second shaft  4 , but block the transmission of power from the second shaft  4  to the first shaft  3 . 
         [0147]    In this connection, the operation of the planetary gear device  430  is described with reference to  FIG. 14 .  FIG. 14  is a schematic diagram showing the relationship between rpms of the first element, the second element and the third element of the planetary gear device  430  and travel speed of the vehicle  200  (see  FIG. 1 ). The horizontal axis in  FIG. 14  represents the travel speed of the vehicle  200 , while the vertical axis represents the rpms of the third element, the first element and the second element. Because the rotor  62  is connected to the sun gear  431  (second element) through the second shaft  4  as illustrated in  FIG. 13 , the rpm of the second element becomes equal to the rpm of the rotor  62  and the second shaft  4 . Because the engine  211  is connected to the ring gear  434  (first element) through the input shaft  2 , the rpm of the first element becomes equal to the rpm of the input shaft  2 . Further, because the first shaft  3  is connected to the carrier  433  (third element) and the drive gear  5   a , the rpm of the third element becomes equal to the rpm of the first shaft  3  and the rpm of the drive gear  5   a .  FIG. 14  illustrates the characteristics in which the rpm of the first element is constant relative to the travel speed of the vehicle  200 , that is, the rpm of the engine  211  and input shaft  2  is constant (R 1 ). 
         [0148]    As shown in  FIG. 14 , in the planetary gear device  430 , when the second element rpm&gt;−R 3  and the second element rpm&lt;R 1  if the power is input from the first element (ring gear  434 ), the third element (carrier  433 ) is decelerated (first element&gt;third element), so that the third element produces output in an arbitrary transmission gear ratio in response to the rpm of the second element. If the rpm of the second element becomes equal to R 1  the power of the engine  211  input to the first element is output to the third element (carrier  433 ) as it is. Further, the rpm of the rotor  62  (see  FIG. 13 ) is increased (the rpm of the second element is increased) until the rpm of the second element rpm&gt;R 1 , thereupon the third element (carrier  433 ) increases in speed (first element&lt;third element), so that the third element produces output in an arbitrary transmission gear ratio in response to the rpm of the second element. 
         [0149]    On the other hand, when the second element rpm=−R 3  the third element rpm=0 results. When the second element rpm&lt;−R 3  the third element rpm&lt;0 results. That is, the direction of rotation of the third element (carrier  433 ) is reversed. In this manner, as in the case of the first embodiment, in the fourth embodiment, it becomes possible that the rotation direction of the output shaft  5   d  (see  FIG. 2 ) is not changed when the vehicle  200  moves forward and when reverse gear is selected. 
         [0150]    As a result, the gearbox  212  (see  FIG. 2 ) is capable of allowing the meshing of the reverse gear pair  9  without gear rattle provided that at least rpms are commensurate with each other, even without mounting a synchronous mesh mechanism. Even when a synchronous mesh mechanism is mounted in the gearbox  212  in order to improve operability, a size reduction and simplification of the synchronous mesh mechanism can be achieved, leading to a size reduction and simplification of the gearbox  212 . Further, with the size reduction and the simplification of the synchronous mesh mechanism, the amount of energy consumption required for operation of the synchronous mesh mechanism can be reduced. 
         [0151]    In the planetary gear device  430 , the rpm of the sun gear  431  (the second element) changes to the positive direction as the rpm of the ring gear  434  (the first element) changes to the negative direction when the rpm of the carrier  433  (the third element) is constant, and changes to the negative direction as the rpm of the ring gear  434  (the first element) changes to the positive direction. Then, when the rpm of the ring gear  434  becomes equal to or lower than a predetermined rpm, the direction of rotation of the sun gear  431  is reversed. 
         [0152]    Next, the operation of the power transmitting device  401  when the vehicle  200  (see  FIG. 1 ) uses the driving force of the generator motor  60  to start moving will be described. Assume that the engine  211  is shutdown. In this case, the first load applying device  15  of the first clutch  10  is actuated (ON). In this state, the generator motor  60  is actuated to rotate the rotor  62 , whereupon the power is transmitted to the second shaft  4  and the sun gear  431 . The power transmitted to the second shaft  4  causes the first outer race  12  of the first clutch  10  to rotate in the lock direction (the direction of arrow Ro in  FIG. 5 ) when viewed from the first inner race  11  in rotation relative to the first inner race  11 . However, because the first load applying device  15  is in operation (ON), the transmission of power from the second shaft  4  through the first clutch  10  to the first shaft  3  is blocked. Further, the second outer race  22  of the second clutch  20  rotates in the free direction (the direction opposite to arrow Ro in  FIG. 5 ) when viewed from the second inner race  21  in rotation relative to the second inner race  21 . As a result, the power of the generator motor  60  is not transmitted from the second shaft  4  to the first shaft  3 . 
         [0153]    On the other hand, the power of the rotor  62  is also transmitted to the sun gear  431 , so that the sun gear  431  to which the power is transmitted meshes with the pinion gears  432  to rotate the carrier  433 . Thus, the power is transmitted to the first shaft  3  connected to the carrier  433 , and then transmitted to the gearbox  212  (see  FIG. 1 ). As a result, the vehicle  200  uses a driving force of the generator motor  60  to start moving. 
         [0154]    Next, the operation of the power transmitting device  401  when the vehicle  200  uses the driving force of the engine  211  to start moving will be described. Assuming that the rotor  62  stops. In this case, after the engine  211  is started up by a starter which is not shown, the first load applying device  15  of the first clutch  10  is rendered non-operative (OFF). In this state, upon increase in the engine speed of the engine  211 , the rpm of the ring gear  434  increases to the positive direction. Along with this, the rpm of the sun gear  431  increases to the negative direction, so that the power is transmitted to the second shaft  4 . The power transmitted to the second shaft  4  causes the first outer race  12  of the first clutch  10  to rotate in the lock direction (the direction of arrow Ro in  FIG. 5 ) when viewed from the first inner race  11  in rotation relative to the first inner race  11 . 
         [0155]    As a result, the power is transmitted from the second shaft  4  through the first clutch  10  to the first shaft  3 , and then transmitted to the gearbox  212  (see  FIG. 1 ). Thus, the vehicle  200  uses the driving force of the engine  211  to start moving. In the fourth embodiment, as in the case described in the first embodiment, forward movement and backward movement of the vehicle  200 , up-shifting, down-shifting, coasting and regeneration can be performed. In this manner, in the power transmitting device  401  in the fourth embodiment, power switching between the engine  211  and the motor  60  can be provided by use of the first clutch  10  to switch between transmission and interruption of power flowing from the second shaft  4  to the first shaft  3 , as in the case of the first embodiment. 
         [0156]    Next, a fifth embodiment will be described with reference to  FIG. 15 . The first embodiment has described the power transmitting device  1  structured such that the first shaft  3  is connected to the sun gear  31  of the planetary gear device  30  which includes the carrier  33  (first element), the ring gear  34  (second element) and the sun gear  31  (third element), the second shaft  4  is connected to the ring gear  34 , the first outer race  12  of the first clutch  10  and the second outer race  22  of the second clutch  20  are formed integrally with the second shaft  4 , and the first inner race  11  of the first clutch  10  and the second inner race  21  of the second clutch  20  are formed integrally with the first shaft  3 . 
         [0157]    In comparison with this, the fifth embodiment describes a structure in which the first outer race  12  of the first clutch  10  and the second outer race  22  of the second clutch  20  are formed integrally with the first shaft  3 , the first inner race  11  of the first clutch  10  and the second inner race  21  of the second clutch  20  are formed integrally with the second shaft  4 , the first shaft  3  is connected to a carrier  533  of a planetary gear device  530  which includes a ring gear  534  (first element), a sun gear  531  (second element), a carrier  533  (third element) and pinion gears  532  meshing with the sun gear  531  and the ring gear  534 , and the second shaft  4  is connected to the sun gear  531 . 
         [0158]      FIG. 15  is a schematic diagram schematically showing the internal structure of the power transmitting device  501  in the fifth embodiment. The same components as those in the first embodiment are designated by the same reference signs and the description is omitted.  FIG. 15  shows only the structure for performing the function of transmitting power for easier understanding. The gearbox  212  shown in  FIG. 2  is omitted in  FIG. 15 . The power transmitting device  501 , which is mounted on the vehicle  200  (see  FIG. 1 ), mainly include, as illustrated in  FIG. 15 , a planetary gear device  530  connected to the input shaft  2  transmitting the power of the engine  211 , and the first clutch  10  and the second clutch  20  which are placed on a power line from the planetary gear device  530  to the gearbox  212  (see  FIG. 1 ). 
         [0159]    The ring gear  534  of the planetary gear device  530  is connected to the input shaft  2  to which the power of the engine  211  is input, which forms the first element. The sun gear  531  is connected to the rotor  62  of the generator motor  60 , which forms the second element. In addition, the carrier  533  is connected to the first shaft  3  transmitting the power toward the gearbox  212 , which forms the third element. 
         [0160]    The first clutch  10  is provided for transmitting and interrupting power between the second shaft  4  connected to the sun gear  531  (second element) and the first shaft  3  connected to the carrier  533 . The first clutch  10  is structured to transmit, in an interruptible manner, power received from the second shaft  4  to the first shaft  3 , but to block the transmission of power from the first shaft  3  to the second shaft  4 . The second clutch  20  is provided for transmitting and interrupting power between the second shaft  4  and the first shaft  3 , and is structured to transmit the power received from the first shaft to the second shaft  4 , but block the transmission of power from the second shaft  4  to the first shaft  3 . Note that the relationship between the rpms of the first element, second element and the third element of the planetary gear device  530  and the travel speed is similar to that shown in  FIG. 14  and the description is omitted. 
         [0161]    Next, the operation of the power transmitting device  501  when the vehicle  200  (see  FIG. 1 ) uses the driving force of the generator motor  60  to start moving will be described. Assume that the engine  211  is shut down. In this case, the first load applying device  15  of the first clutch  10  is actuated (ON). In this state, the generator motor  60  is actuated to rotate the rotor  62 , whereupon the power is transmitted to the second shaft  4  and the sun gear  531 . The power transmitted to the second shaft  4  causes the first inner race  11  of the first clutch  10  to rotate in the lock direction (the direction of arrow Ri in  FIG. 5 ) when viewed from the first outer race  12  in rotation relative to the first outer race  12 . However, because the first load applying device  15  is in operation (ON), the transmission of power from the second shaft  4  through the first clutch  10  to the first shaft  3  is blocked. Further, the second inner race  21  of the second clutch  20  rotates in the free direction (the direction opposite to arrow Ri in  FIG. 5 ) when viewed from the second outer race  22  in rotation relative to the second outer race  22 . As a result, the power of the generator motor  60  is not transmitted from the second shaft  4  to the first shaft  3 . 
         [0162]    On the other hand, the power of the rotor  62  is also transmitted to the sun gear  531 , so that the sun gear  531  to which the power is transmitted meshes with the pinion gears  532  to rotate the carrier  533 . Thus, the power is transmitted to the first shaft  3  connected to the carrier  533 , and then transmitted to the gearbox  212  (see  FIG. 1 ). As a result, the vehicle  200  (see  FIG. 2 ) uses a driving force of the generator motor  60  to start moving. 
         [0163]    Next, the operation of the power transmitting device  501  when the vehicle  200  uses the driving force of the engine  211  to start moving will be described. Assuming that the rotor  62  stops. In this case, after the engine  211  is started up by a starter which is not shown, the first load applying device  15  of the first clutch  10  is rendered non-operative (OFF). In this state, upon increase in the engine speed of the engine  211 , the rpm of the ring gear  534  increases to the positive direction. Along with this, the rpm of the sun gear  531  increases to the negative direction, so that the power is transmitted to the second shaft  4 . The power transmitted to the second shaft  4  causes the first inner race  11  of the first clutch  10  to rotate in the lock direction (the direction of arrow Ri in  FIG. 5 ) when viewed from the first outer race  12  in rotation relative to the first outer race  12 . 
         [0164]    As a result, the power is transmitted from the second shaft  4  through the first clutch  10  to the first shaft  3 , and then transmitted to the gearbox  212  (see  FIG. 1 ). Thus, the vehicle  200  uses the driving force of the engine  211  to start moving. In the fifth embodiment, as in the case described in the first embodiment, forward movement and backward movement of the vehicle  200 , up-shifting, down-shifting, coasting and regeneration can be performed. In this manner, in the power transmitting device  501  in the fifth embodiment, power switching between the engine  211  and the motor  60  can be provided by use of the first clutch  10  to switch between transmission and interruption of power flowing from the second shaft  4  to the first shaft  3 , as in the case of the first embodiment. 
         [0165]    Next, a sixth embodiment will be described with reference to  FIG. 16  to  FIG. 21 . The first embodiment has described the power transmitting device  1  structured such that the first shaft  3  is connected to the sun gear  31  of the planetary gear device  30  which includes the carrier  33  (first element), the ring gear  34  (second element) and the sun gear  31  (third element), and the second shaft  4  is connected to the ring gear  34 . Also, the first outer race  12  of the first clutch  10  and the second outer race  22  of the second clutch  20  are formed integrally with the second shaft  4 , and the first inner race  11  of the first clutch  10  and the second inner race  21  of the second clutch  20  are formed integrally with the first shaft  3 . Also, the first sprags  13  of the first clutch  10  are urged in the direction of engaging with the first inner race  11  and the first outer race  12  by the first urging member  16 , and the first load applying device  15  applies a load in the direction of releasing the engagement of the first sprags  13  with the first inner race  11  and the first outer race  12 . 
         [0166]    In comparison with this, the sixth embodiment describes a structure in which the first outer race  12  of the first clutch  610  and the second outer race  22  of the second clutch  20  are formed integrally with the second shaft  4 , the first shaft  3  is connected to a ring gear  634  of a planetary gear device  630  which includes a sun gear  631  (first element), a carrier  633  (second element), the ring gear  634  (third element) and pinion gears  632  meshing with the sun gear  631  and the ring gear  634 , the second shaft  4  is connected to the carrier  633 , and the input shaft  2  is connected to the sun gear  631 . 
         [0167]      FIG. 16  is a schematic diagram schematically showing the internal structure of the power transmitting device  601  in the sixth embodiment. The same components as those in the first embodiment are designated by the same reference signs and the description is omitted.  FIG. 16  shows only the structure for performing the function of transmitting power for easier understanding, and the gearbox  212  is omitted in  FIG. 16 . The power transmitting device  601 , which is mounted on the vehicle  200  (see  FIG. 1 ), mainly include, as illustrated in  FIG. 16 , a planetary gear device  630  connected to the input shaft  2  transmitting the power of the engine  211 , and a first clutch  610  and the second clutch  20  which are placed on a power line from the engine  211  to the planetary gear device  630 . 
         [0168]    Next, the first clutch  610  will be described with reference to  FIG. 17 .  FIG. 17  is a sectional view in the circumferential direction of the first clutch  610 .  FIG. 18  is an exploded view of a part of the first clutch  610 . 
         [0169]    The first clutch  610  mainly includes the inner race  11  connected to the input shaft  2 , the outer race  12  surrounding the outer periphery of the inner race  11  and connected to the second shaft  4 , a plurality of sprags  613  interposed between the inner race  11  and the outer race  12 , and a cage  614  retaining the sprags  613 , as shown in  FIG. 17  and  FIG. 18 . 
         [0170]    The sprag  613  has engaging faces  613   a ,  613   b  (see  FIG. 18  and  FIG. 19 ) to come respectively into contact with the outer peripheral surface  11   a  and the inner peripheral surface  12   a . As shown in  FIG. 18 , grooves  613   d  are formed respectively in two side faces  613   c  each connecting the two engaging faces  613   a ,  613   b  to each other. The groove  613   d  is a part to which the urging member  616  described later is mounted. 
         [0171]    The cage  614  is a member retaining the sprags  613  with allowing the sprags  613  to tilt in the circumferential direction of the outer peripheral surface  11   a  and the inner peripheral surface  12   a , which includes a retaining portion  614   a  extending in the direction of axis O and in a ring shape and the load transmitting portion  14   b  extending from the retaining portion  614   a  in a direction crossing the direction of axis O. 
         [0172]    The retaining portion  614   a  is a part retaining the sprags  613 , and includes a plurality of holes  614   a   1  bored at regular intervals in the circumferential direction as shown in  FIG. 18 . A portion (around the engaging face  613   a ) of the sprag  613  located close to the inner race  11  is inserted into the hole  614   a   1 , and a gap of an appropriate size is created between the hole  614   a   1  and two front and back faces  613   e  each connecting the two engaging faces  613   a ,  613   b  of the sprag  613  to each other. Thus, the sprags  613  are retained between the outer peripheral surface  11   a  and the inner peripheral surface  12   a  which face each other, while allowed to tilt largely in the circumferential direction by the retaining portion  614   a.    
         [0173]    As shown in  FIG. 17 , the urging member  616  is formed of a ring-shaped coil spring, which is a member causing the urging force to act in a diameter expansion direction. In this regard, the sprag  613  urged by the urging member  616  is explained with reference to  FIG. 19(   a ).  FIG. 19(   a ) is a partially enlarged sectional view of the first clutch  610  blocking the transmission of power, shown by enlarging the portion indicated by “XIX” in  FIG. 17 . In  FIG. 19 , assuming that the outer race  12  is driven by the generator motor  60  (see  FIG. 16)  to rotate in the direction of arrow T (in the counterclockwise direction in  FIG. 19 ). 
         [0174]    The urging member  616  is attached to the grooves  613   d  of the sprag  613 . The urging member  616  causes the urging force to act in the diameter expansion direction in order to tilt the engaging face  613   a  of the sprag  613  in the direction of arrow S in the  FIG. 19  (hereinafter referred to as an “anti-lock direction”) by use of the frictional force, produced on the engaging face  613   b  of the sprag  613  and the inner peripheral surface  12   a  of the outer race  12 . This allows a relative rotation of the inner race  11  and the outer race  12 , thus blocking the transmission of power from the outer race  12  to the inner race  11 . As shown in  FIG. 19(   a ), a clearance is created between the outer peripheral surface  11   a  and the engaging face  613   a . As a result, it is possible to prevent friction from being produced between the outer peripheral surface  11   a  and the engaging face  613   a  of the sprag  613 , thus suppressing energy loss produced by friction. 
         [0175]    Since an appropriately large gap is created between the hole  614   a   1  formed in the retaining portion  614   a  and the two front and back faces  613   e  (see  FIG. 18 ) each connecting the two engaging faces  613   a ,  613   b  to the sprag  613  to each other, the sprags  613  can abut each other by tilting the sprags  613  largely in the anti-lock direction as shown in  FIG. 19(   a ). When the sprags  613  are tilted to a position of an abutment of them, the sprags  613  restrain each other. This allows the ensuring of a satisfactory&#39;clearance between the outer peripheral surface  11   a  and the engaging face  613   a . As a result, in the relative rotation of the inner race  11  and the outer race  12 , the relative rotation of the inner race  11  and the outer race  12  can be prevented from being limited by making the outer peripheral surface  11   a  and the engaging face  613  come into contact with each other to unintentionally cause engagement of the sprags  613  to the outer peripheral surface  11   a  and the inner peripheral surface  12   a.    
         [0176]    Since the grooves  613   d  are formed respectively in the two side faces  613   c  of the sprag  613  each connecting the two engaging faces  613   a ,  613   b  to each other, and the urging member  616  is attached to the grooves  613   d , the urging force of the urging member  616  is capable of tilting the sprags  613  in the anti-lock direction in balanced conditions. 
         [0177]    With the aforementioned first clutch  610 , external forces must be applied to the sprags  613  in opposition to the urging force of the urging member  616  in order to engage the sprags  613  with the inner race  11  and the outer race  12 . Therefore, the first clutch  610  is equipped with the load applying device  15  (see  FIG. 16 ). The load applying device  15  is a device for applying a load to the sprags  613  in opposition to the urging force of the urging member  616  in order to tilt the sprags  613  in the direction opposite to arrow S in  FIG. 19  (hereinafter referred to as the “lock direction”). 
         [0178]    As shown in  FIG. 19(   b ), the application by the load applying device  15  of load acting in the lock direction (the direction opposite to arrow S in  FIG. 19)  to the sprags  613  via the cage  614  in opposition to the urging force of the urging member  616  allows each sprag  613  to tilt in the lock direction approximately around the engaging face  613   b  of the sprag  613 . As a result, the engaging faces  613   a ,  613   b  of the sprag come into contact with the outer peripheral surface  12   a  and the inner peripheral surface  11   a . This produces a friction force at a contact point between the inner peripheral surface  12   a  and the engaging face  613   b  and a contact point between the outer peripheral surface  11   a  and the engaging face  613   a . And also, a positional displacement of each of the contact points in the circumferential direction of the outer peripheral surface  11   a  and the inner peripheral surface  12   a  engages the sprag  613  with the inner race  11  and the outer race  12  to restrict the relative rotation of the inner race  11  and the outer race  12 . As a result, the power is transmitted from the outer race  12  to the inner race  11 , so that the inner race  11  rotates with the rotation (in the direction of arrow T) of the outer race  12 . 
         [0179]    When the sprags  613  engage with the inner race  11  and the outer race  12  to restrict the relative rotation of the inner race  11  and the outer race  12 , and when the outer race  12  rotates in the lock direction (the direction of arrow Lo) when viewed from the inner race  11  in rotation relative to the inner race  11 , even if the load application of the load applying device  15  is halted, the outer race  12  rotates to tilt the sprags  613  in the lock direction, maintaining the engagement of the sprags  613  and the inner race  11  and the outer race  12 . 
         [0180]    On the other hand, when the sprags  613  engage with the inner race  11  and the outer race  12  to restrict the relative rotation of the inner race  11  and the outer race  12 , and when the outer race  12  rotates in the anti-lock direction (the direction opposite to arrow Lo) when viewed from the inner race  11  in rotation relative to the inner race  11 , by halting the load applying device  15  or by reducing the load applied by the load applying device  15 , the sprags  613  tilts in the anti-lock direction (the direction of arrow S in  FIG. 19 ) by the urging force of the urging member  616 . This releases the engagement of the inner race  11  and the outer race  12  and the sprags  613  to block the transmission of power from the outer race  12  to the inner race  11 . 
         [0181]    With the first clutch  610  structured as described above, a load is applied to the sprags  613  by the power transmitting device  15 . This causes the sprags  613  to engage with the inner race  11  and the outer race  12 , so that the relative rotation of the inner race  11  and the outer race  12  in a fixed rotational direction is restricted. On the other hand, upon stopping the load application by the power transmitting device  15 , the urging member  616  applies a urging force to the sprags  613 , so that an engagement of the sprags  613  with the inner race  11  and the outer race  12  is released to allow the inner race  11  and the outer race  12  to relatively rotate in both rotational directions. Thus, switching between the transmission and the interruption of rotation in a fixed direction is made possible. 
         [0182]    Next, the relationship between an urging force and a load acting on the sprag  613  will be described with reference to  FIG. 20 .  FIG. 20  is a schematic diagram of the sprag  613  tilted in the anti-lock direction. As shown in  FIG. 20 , in the sprag  613  released from the engagement with the inner race  11  and the outer race  12 , turning moment to move the sprag  613  to tilt it in the anti-lock direction (a clockwise direction in  FIG. 20 ) is produced around the contact point between the abutting face  613   b  and the inner peripheral surface  12   a  by the urging force (load P) applied by the urging member  616 . When the sprag  613  engages with the inner race  11  and the outer race  12  and revolves round the axis O in step with the rotation of the inner race  11  and the outer race  12 , a centrifugal force K acts on the sprag  613 . With those forces, a pressing load acts on the contact point A. As reaction to this, a reactive force F A  acts on the sprag  613  in the direction of the normal to the inner peripheral surface  12   a  at the contact point A. To oppose this, in order to tilt the sprag  613  in the lock direction, the retaining portion  614   a  applies a load R of the lock direction to the contact point C with the sprag  613 . 
         [0183]    Considering here turning moment M A  around the contact point A acting on the sprag  613 . Since the load P, the load R and the centrifugal force K act on the sprag  613 , the turning moment M A  can be expressed by the following equation (1). 
         [0000]        M   A   =Lp·P+Lk·K−Lr·R   Equation (1)
 
         [0184]    In equation (1), Lp represents a horizontal distance from the contact point A to the point of application of the load P (the groove  613   d ), Lk represents a horizontal distance from the contact point A to the point of application of the centrifugal force K (the center of gravity of the sprag  613 ), and Lr represents a vertical distance from the contact point A to the point of application of the load R (contact point C). Given that the turning moment M A  is a clockwise positive moment about the contact point A. In a strict sense, the loads P, K and R are required to allow for errors caused by the horizontal component and the vertical component of a load, but the error is negligible as compared with the magnitudes of the loads P, K and R. Because of this, given that the loads P and K act in the vertical direction and the load R acts in the horizontal direction. 
         [0185]    In this connection, it is necessary for achieving engagement of the engaging face  613   a  of the sprag  613  with the outer peripheral surface  11   a  that the sprag  613  is tilted in a counterclockwise direction in  FIG. 20  without sliding of the engaging face  613   a  of the sprag  613  on the inner peripheral surface  12   a . That is, M A &lt;0 is required. In the state shown in  FIG. 20 , since the engagement between the sprag  613  and the inner race  11  and the outer race  12  is released, the outer race  12  or the inner race  11  can be rotate around the axis O, but the driving force of the outer race  12  or the inner race  11  alone cannot allow the sprag  613  to revolve about the axis O. Therefore, the centrifugal force K does not act on the sprag  613  (K=0). Given the above facts, a necessary condition for engaging the engaging face  613   a  of the sprag  613  with the outer peripheral surface  11   a  is expressed by the following equation (2) resulting from the substitution of M A &lt;0, K=0 into equation (1). 
         [0000]        R&gt;Lp/Lr·P   Equation (2)
 
         [0186]    Where if Lp&lt;Lr, Lp/Lr&lt;1. Accordingly, a load R&gt;Lp/Lr·P&lt;P results from equation (2). Therefore, even when a load larger than the urging force (load P) of the urging member  616  is not applied to the sprag  613 , the load applying device  15  can allow the sprag  613  to engage with the outer race  12  and the inner race  11 . In consequence, a reduction in size of the load applying device  15  is possible and since a required load is small, minimization of energy loss is possible. In turn, a reduction in size of the first clutch  610  is possible. 
         [0187]    In  FIG. 20 , given that the normal line and the vertical direction in the contact point A form an angle α, the magnitude of a horizontal force component F Ah  of the reactive force F A  acting on the sprag  613  from the inner peripheral surface  12   a  is F A ·sin α, and the orientation is the same as that of the lock direction (counterclockwise direction in  FIG. 20 ). Given that a coefficient of friction at the contact point A is μ, and a vertical force component of the reactive force F A  is F Ap , the magnitude of the friction is μ·F Ap =μ·F A ·cos α, and the orientation is the same as that of the lock direction. 
         [0188]    As described above, of the reactive force F A  acting on the sprag  613  from the inner peripheral surface  12   a  at the contact point A where the inner peripheral surface  12   a  makes contact with the engaging face  613   b , a force component in the loading direction (horizontal direction and the right-and-left direction in  FIG. 20 ) of the load R acting on the sprag  613  through the retaining portion  614   a  by the load applying device  15  is identical in orientation with the lock direction (counterclockwise direction in  FIG. 20 ). Because of this, when the load applying device  15  applies the load R to the sprag  613 , the engaging face  613   b  is prevented from sliding on the inner peripheral surface  12   a , and tilting the sprag  613  approximately around the contact point A with reliability is made possible. In this manner, the application of a load from the load applying device  15  makes it possible to engage the two engaging faces  613   a ,  613   b  of the sprag  613  with the outer peripheral surface  11   a  and the inner peripheral surface  12   a  with reliability. 
         [0189]    Next, the operation of the planetary gear device  630  will be described with reference to  FIG. 21 .  FIG. 21  is a schematic diagram showing the relationship between rpms of the first element, the second element and the third element and travel speed of the vehicle  200 . The horizontal axis in  FIG. 21  represents the travel speed of the vehicle  200 , while the vertical axis represents the rpms of the third element, the first element and the second element. Because the rotor  62  is connected to the carrier  633  (second element) through the second shaft  4  as illustrated in  FIG. 16 , the rpm of the second element becomes equal to the rpm of the rotor  62  and the second shaft  4 . Because the engine  211  is connected to the sun gear  631  (first element) through the input shaft  2 , the rpm of the first element becomes equal to the rpm of the input shaft  2 . Further, because the first shaft  3  is connected to the ring gear  634  (third element) and the drive gear  5   a , the rpm of the third element becomes equal to the rpm of the first shaft  3  and the rpm of the drive gear  5   a .  FIG. 21  illustrates the characteristics in which the rpm of the first element is constant relative to the travel speed of the vehicle  200 , that is, the rpm of the engine  211  and input shaft  2  is constant (R 1 ). 
         [0190]    During the start-up of the engine  211 , the first load applying device  15  of the first clutch  610  (see  FIG. 16 ) is rendered operative to engage the first sprags  613  with the first inner race  11  and the first outer race  12 . In this state, the generator motor  60  is actuated to rotate the rotor  62 , whereupon power is transmitted to the second shaft  4  and the carrier  633 . By the power transmitted to the second shaft  4 , the first outer race  12  of the first clutch  610  rotates in the lock direction (the direction of arrow Lo) when viewed from the first inner race  11  in rotation relative to the first inner race  11 . In this manner, the power is transmitted from the first outer race  12  to the first inner race  11  and the input shaft  2 , resulting in start-up of the engine  211 . 
         [0191]    Also, the rotation of the rotor  62  is transmitted from the carrier  633  to the ring gear  634  to rotate the first shaft  3 . If the gearbox  212  (see  FIG. 1 ) is placed into a state of being capable of transmitting power, the rotation of the first shaft  3  is able to be transmitted to the rear wheels  202 . As a result, concurrently with start-up of the engine  211 , the vehicle  200  can be moved forward (started moving) by use of the power of the generator motor  60 . The engine  211  is started at the same time when the vehicle  200  is started moving, leading to lessening of vibration and shock produced during the start-up of the engine  211 . 
         [0192]    After the vehicle  200  has been started moving, the load of the generator motor  60  is increased to reduce the rpm of the rotor  62  for a reduction in rpm of the carrier  633  (first outer race  12 ), or the engine speed of the engine  211  is increased to increase the rotation of the input shaft  2  (first inner race  11 ), thereby disengaging the first sprag  613  from the first inner race  11  and the first outer race  12 . In this state, the forward movement of the vehicle in hybrid mode in which the engine  211  and the generator motor  60  are operated is realized. 
         [0193]    When the rpm of the second shaft  4  becomes equal to the rpm (R 1 ) of the first shaft  3  after the vehicle  200  has been moved forward and accelerated (see  FIG. 21 ), the first load applying device  15  of the first clutch  610  ( FIG. 16 ) is actuated to engage the first sprags  613  with the first inner race  11  and the first outer race  12 . The three elements of the planetary gear device  630  are rotated simultaneously to achieve the forward movement of the vehicle caused by the power of the engine  211 . Regeneration operation and reverse operation when coasting and braking of the vehicle  200  are similar to those in the first embodiment and the description is omitted. 
         [0194]    Next, a seventh embodiment will be described with reference to  FIG. 22  to  FIG. 28 . In the seventh embodiment, the first outer race of the first clutch  10  and the second outer race  22  of the second clutch  720  are formed integrally with the second shaft  4 . A planetary gear device  730  described includes a carrier  733  (first element), a sun gear  731  (second element), a ring gear  734  (third element) and pinion gears  732  meshing with the sun gear  731  and the ring gear  734 , in which the first shaft  3  is connected to the ring gear  734 , the second shaft  4  is connected to the sun gear  731  and the input shaft  2  is connected to the carrier  733 . 
         [0195]      FIG. 22  is a schematic diagram schematically showing the internal structure of the power transmitting device  701  in the seventh embodiment. The same components as those in the first embodiment are designated by the same reference signs and the description is omitted.  FIG. 17  shows only the structure for performing the function of transmitting power for easier understanding, and the gearbox  212  is omitted in  FIG. 22 . The power transmitting device  701 , which is mounted on the vehicle  200  (see  FIG. 1 ), mainly include, as illustrated in.  FIG. 22 , the planetary gear device  730  to which the input shaft  2  transmitting the power of the engine  211  is connected, and the first clutch  710  and the second clutch  720  which are placed on a power line from the engine  211  to the planetary gear device  730 . 
         [0196]    Next, the first clutch  710  and the second clutch  720  will be described with reference to  FIG. 23 .  FIG. 23  is a sectional view in the circumferential direction of the first clutch  710 . In  FIG. 23 , second sprags  723  (on the reverse side of the sheet of  FIG. 23 ) arranged alongside of first sprags  713  are omitted for the sake of simplifying the drawing. In the embodiment, the first inner race  11  and the second inner race  21  are connect to the input shaft  2  and the first outer race  12  and the second outer race  22  are connected to the second shaft  4 . 
         [0197]    The first sprag  713  of the first clutch  710  is a member having a function for restricting relative rotation of the inner race  11  and the outer race  12 , and a plurality of the first sprags  713  are arranged at regular intervals in the circumferential direction in an accommodating space g between the outer peripheral surface  11   a  and the inner peripheral surface  12   a . The first sprag  713  is structured to have engaging faces  713   a ,  713   b  allowed to be engaged with the outer peripheral surface  11   a  of the inner race  11  and the inner peripheral surface  12   a  of the outer race  12  by the relative rotation of the inner race  11  and the outer race  12  in one direction. 
         [0198]    A plurality of, the second sprags  723  of the second clutch  720 , together with the first sprags  713 , are arranged, alongside the first sprags  713 , at regular intervals in the circumferential direction in the accommodating space g between the outer peripheral surface  11   a  and the inner peripheral surface  12   a . The second sprag  723  is structured to have engaging faces  723   a ,  723   b  allowed to be engaged with the outer peripheral surface  11   a  of the inner race  11  and the inner peripheral surface  12   a  of the outer race  12  by the relative rotation of the inner race  11  and the outer race  12  in the other direction. 
         [0199]    An inner cage  717  is a cylindrical member having a plurality of pockets  717   b  perforated in the circumferential direction and arranged alongside in the axis direction, and retains parts, closer to the inner race  11 , of the first sprags  713  and the second sprags  723  (see  FIG. 24 ) inserted into the pockets  717   b.    
         [0200]    An outer cage  718  is a cylindrical member having a plurality of pockets  718   d  perforated in the circumferential direction and arranged alongside in the axis direction, and retains parts, closer to the outer race  12 , of the first sprags  713  and the second sprags  723  (see  FIG. 24 ) inserted into the pockets  718   b . The outer cage  718  includes a first retaining portion  718   b  (see  FIG. 24 ) retaining the first sprags  713  and a second retaining portion  718   c  separated from the first retaining portion  718   b  in the axis direction and retaining the second sprags  723 . The first retaining portion  718   b  and the second retaining portion  718   c  have pockets  718   d  arranged at regular interval in the circumferential direction so that the first sprags  713  and the second sprags  723  are inserted into the pockets  718   d.    
         [0201]    Returning to  FIG. 22  and describing. The inner cage  717  and the outer cage  718  have cog-shaped load transmission portions  717   a ,  718   a  extending in a direction crossing the axis direction. The load transmission portions  717   a ,  718   a  are parts to which a load is transmitted from a first load applying device  715 . 
         [0202]    The first load applying device  715  is a device for applying a load to the load transmission portions  717   a ,  718   a  to cause the inner cage  717  and the outer cage  718  to relatively rotate or to restrict the relative rotation. The relative rotation of the inner cage  717  and the outer cage  718  caused by the first load applying device  715  allows switching between engagement and disengagement between the first sprags  713  and the first inner race  11  and the first outer race  12  (engagement and disengagement between the second sprags  723  and the second inner race  21  and the second outer race  22 ). The first load applying device  715  includes electric motors  715   a ,  715   c  and pinions  715   b ,  715   d  meshing the load transmission portions  717   a ,  718   a  connected to the electric motors  715   a ,  715   c.    
         [0203]    Next, the structure and the operation of the first retaining portion  718   b  and the second retaining portion  718   c  will be described with reference to  FIG. 24  to  FIG. 27 . Initially, the structure of the first retaining portion  718   b  and the second retaining portion  718   c  is described with reference to  FIG. 24(   a ).  FIG. 24(   a ) is a perspective view of important parts of the first retaining portion  718   b  and the second retaining portion  718   c , relative movement of which is restricted. In from  FIG. 24  to  FIG. 27 , parts of the first sprags  713  and the second sprags  723  retained by the first retaining portion  718   b  and the second retaining portion  718   c  are omitted for simplifying the drawing. 
         [0204]    As shown in  FIG. 24(   a ), the first retaining portion  718   b  has a protrusion  718   e  protruding from the face facing the second retaining portion  718   c  toward the second retaining portion  718   c . The protrusion  718   e  has a first face  718   e   1  formed on one side in the circumferential direction and a third face  718   e   2  formed on the other side. The second retaining portion  718   c  has a recess  718   g  formed in the face facing the first retaining portion  718   b  to receive the protrusion  718   e . The length in the circumferential direction of the recess  718   g  is set longer than that in the circumferential direction of the protrusion  718   e . The recess  718   g  has a second face  718   g   1  formed on one side in the circumferential direction to be allowed to abut on the first face  718   e   1 , and a fourth face  718   g   2  formed on the other side to be allowed to abut on the third face  718   e   2 . A relative movement of the first retaining portion  718   b  and the second retaining portion  718   c  is allowed within a range where the protrusion  718   e  can move within the recess  718   g . However, the second face  718   g   1  of the recess  718   g  abuts on the first face  718   e   1  of the protrusion  717   e , so that a relative movement of the first retaining portion  718   b  and the second retaining portion  718   c  in one of the circumferential directions is restricted. On the other hand, the fourth face  718   g   2  of the recess  718   g  abuts on the third face  718   e   2  of the protrusion  718   e , so that a relative movement of the first retaining portion  718   b  and the second retaining portion  718   c  in the other circumferential direction is restricted. 
         [0205]    Lock portions  718   f ,  718   h  are parts that are formed respectively in the first retaining portion  718   b  and the second retaining portion  718   c  and to which both ends of a second urging member (not shown) are locked. In the embodiment, the lock portions  718   f ,  718   h  formed through from the inner peripheral surface of the first retaining portion  718   b  and the second retaining portion  718   c  to the outer peripheral surface, while the second urging member is formed of a torsion coil spring. The second urging member is locked at its both ends to the lock portions  718   f ,  718   h , and also a ring-shaped part is located along the inner peripheral surface of the outer cage  718  between the first sprag  713  and the second sprag  723 . As a result, the second urging member urges the first retaining portion  718   b  and the second retaining portion  718   c  toward one of the circumferential directions to cause the first face  718   e   1  of the first retaining portion  718   b  to abut on the second face  718   g   1  of the second retaining portion  718   c . When the load applying device  715  (see  FIG. 22 ) applies a load to the second retaining portion  718   c , the first retaining portion  718   b  is moved in attendance upon the second retaining portion  718   c  by the urging force of the second urging portion (not shown), so that the first retaining portion  718   b  and the second retaining portion  718   c  can be moved integrally as the outer cage  718 . 
         [0206]    Next, the operation of the first sprag  713  and the second sprag  723  when the inner cage  717  and the outer cage  718  relatively move in one of the circumferential directions will be described with reference to  FIG. 24(   b ) and  FIG. 24(   c ).  FIG. 24(   b ) is a sectional view in the circumferential direction of the first retaining portion  718   b , while  FIG. 24(   c ) is a sectional view in the circumferential direction of the second retaining portion  718   c.    
         [0207]    As shown in  FIG. 24(   b ), the first load applying device  715  applies a load in the direction of arrow  13  to each of the inner cage  717  and the outer cage  718  (the first retaining portion  718   b ) to move relatively the inner cage  717  and the outer cage  718  (the first retaining portion  718   b ), so that the first sprags  713  inserted into the pockets  717   b ,  718   d  of the inner cage  717  and the first retaining portion  718   b  are tilted. Thereby, the engaging faces  713   a ,  713   b  of the first sprag  713  can come into contact with the outer peripheral surface  11   a  of the inner race  11  and the inner peripheral surface  12   a  of the outer race  12 , resulting in the state of allowing the first sprag  731  to engage with the inner race  11  and the outer race  12 . At this stage, the first sprags  713  are located at a predetermined distance from each other in the circumferential direction between the outer peripheral surface  11   a  and the inner peripheral surface  12   a  which face each other, while preventing an abutting portion  713   c  of one first sprag  713  protruding toward another first sprag  713  located adjacent to it from abutting on the another first sprag  713 . 
         [0208]    Since the second retaining portion  718   c  moves integrally with the first retaining portion  718   b  as described above, a load in the direction of arrow B is applied to each of the inner cage  717  and the outer cage  718  (the second retaining portion  718   c ), whereupon the inner cage  717  and the outer cage  718  (the second retaining portion  718   c ) are relatively moved, so that the second sprags  723  inserted in the pockets  717   b ,  718   d  of the inner cage  717  and the second retaining portions  718   c  are tilted. Hence, at least one of the outer peripheral surface  11   e  of the inner race  11  and the inner peripheral surface  12   a  of the outer race  12  and the engaging face  723   a ,  723   b  of the second sprag  723  go out of contact with each other. As a result, the sprags  723  and the inner race  11  and the outer race  12  become unable to engage with each other. 
         [0209]    In the state shown in  FIG. 24(   b ), when the power is transmitted to the inner race  11  or the outer race  12  to rotate the inner race  11  in the clockwise direction in  FIG. 24  or to rotate the outer race  12  in the counterclockwise direction in  FIG. 24 , the engaging faces  713   a ,  713   b  of the first sprags  713  engage with the outer peripheral surface  11   a  of the inner race  11  and the inner peripheral surface  12   a  of the outer race  12  so as to transmit the power via the first sprags  713 . 
         [0210]    On the other hand, in the second sprags  723 , at least one of the outer peripheral surface  11   a  of the inner race  11  and the inner peripheral surface  12   a  of the outer race  12  and the engaging faces  723   a ,  723   b  of the second sprags  723  goes out of contact with each other, thereby preventing the engaging faces  723   a ,  723   b  of the second sprags  723  from sliding on the outer peripheral surface  11   a  of the inner race  11  and the inner peripheral surface  12   a  of the outer race  12 . This makes it possible to reduce the production of drag torque on the engaging faces  723   a ,  723   b  of the second sprags  723 . Since the engaging faces  723   a ,  723   b  of the second sprags  723  are prevented from sliding on the outer peripheral surface  11   a  of the inner race  11  and the inner peripheral surface  12   a  of the outer race  12 , it is possible to reduce the productions of wearing, heating and the like. 
         [0211]    A relative position of the inner cage  717  and the outer cage  718  is determined while the first sprags  713  engage with the outer peripheral surface  11   a  of the inner race  11  and the inner peripheral surface  12   a  of the outer race  12  (see  FIG. 24(   b )). At this time, the engaging faces  723   a  of the second sprags  723  go out of contact with the outer peripheral surface  11   a  of the inner race  11  as shown in  FIG. 24(   c )). As a result, it is possible to prevent the second sprags  723  from unintentionally engaging with the inner race  11  and the outer race  12  when the first sprags  713  are engaged with the inner race  11  and the outer race  12 . This makes it possible to reliably prevent double-locking in which both the first sprags  713  and the second sprags  723  are engaged with the inner race  11  and the outer race  12 . 
         [0212]    When the torque transmitted through the first sprags  713  increases so as to cause relative movement of the inner cage  717  and the outer cage  718  in the direction of the arrow B, as shown in  FIG. 24(   c ), an abutting portion  723   c  of each second sprag  723  abuts on another second sprag  723  located adjacent to it to restrict a tilting motion beyond the abutting point. As a result, this brings about the state in which the second sprags  723  are held between the inner cage  717  and the outer cage  718  (the second retaining portions  718   c ), so that further relative movement of the inner cage  717  and the outer cage  718  (the second retaining portion  718   c ) is restricted. Accordingly, simplification of device structure can be achieved without a positioning member or the like for controlling the amount of relative movement of the inner cage  717  and the outer cage  718 . 
         [0213]    Next, the operation of the first retaining portion  718   b  and the second retaining portion  718   c  when the first sprags  713  strongly engage with the inner race  11  and the outer race  12  will be described with reference to  FIG. 25 .  FIG. 25(   a ) is a perspective view of important portions of the first retaining portion  718   b  and the second retaining portion  718   c  which are moved relatively.  FIG. 25(   b ) is a sectional view in the circumferential direction of the first retaining portion  718   b .  FIG. 25(   c ) is a sectional view in the circumferential direction of the second retaining portion  718   c.    
         [0214]    In the state shown in  FIG. 24 , when, by high torque, the inner race  11  is rotated clockwise in  FIG. 24  or the outer race  12  is rotated counterclockwise in  FIG. 24 , as shown in  FIG. 25(   b ), the engaging faces  713   a ,  713   b  of the first sprag  713  are strongly engaged with the outer peripheral surface  11   a  of the inner race  11  and the inner peripheral surface  12   a  of the outer race  12 , so that the first sprag  713  is largely tilted. Thereupon, the tilting motion pushes the first retaining portion  718   b  to displace it in the circumferential direction (the counterclockwise direction in  FIG. 25) . On the other hand, the rotation of the inner race  11  in the clockwise direction in  FIG. 24  or the rotation of the outer race  12  in the counterclockwise direction in  FIG. 24  does not allow the second sprags  723  to engage with the inner race  11  and the outer race  12 . For this reason, the second retaining portion  718   c  does not displace in the circumferential direction without being affected by the second sprags  723 . Therefore, the displacement of the first retaining portion  718   b  in the circumferential direction with respect to the inner cage  717  is larger than the displacement of the second retaining portion  718   c  in the circumferential direction with respect to the inner cage  717 . 
         [0215]    In this connection, if the first retaining portion  718   b  and the second retaining portion  718   c  (the outer cage  718 ) are formed integrally as a rigid body, the second retaining portion  718   c  displaces in the circumferential direction with the displacement of the first retaining portion  718   b . In this event, the second sprag  723  may possibly fall out of the outer cage  718  or the inner age  717  or the outer cage  718  may possibly be damaged. 
         [0216]    As opposed to this, the first retaining portion  718   b  and the second retaining portion  718   c  are separated from each other in the axis direction and are structured to be capable of moving relatively in the circumferential direction. Because of this, when the first sprags  713  are tilted to push the first retaining portion  718   b , until the third face  718   e   2  (see  FIG. 25(   a )) abuts on the fourth face  718   g   2 , the first retaining portion  718   b  alone moves relative to the second retaining portion  718   c . As a result, the second retaining portion  718   c  (see  FIG. 25(   c )) can be prevented from being affected by the displacement of the first retaining portion  718   b , leading to prevention of the possibility that the second sprag  723  falls out of the pocket  718   d  of the second retaining portion  718   c  or the inner cage  717  or the second retaining portion  718   c  is damaged. 
         [0217]    Next, the operation of the first sprag  713  and the second sprag  723  when the inner cage  717  and the outer cage  718  relatively move in the other circumferential direction (the direction opposite to that in  FIG. 24 ) will be described with reference to  FIG. 26 .  FIG. 26(   a ) is a perspective view of important portions of the first retaining portion  718   b  and the second retaining portion  718   c  of which the relative movement is restricted.  FIG. 26(   b ) is a sectional view in the circumferential direction of the first retaining portion  718   b .  FIG. 26(   c ) is a sectional view in the circumferential direction of the second retaining portion  718   c.    
         [0218]    The load applying device  715  (see  FIG. 22 ) is actuated to apply a load in the direction of arrow R to each of the inner cage  717  and the outer cage  718  (the first retaining portion  718   b ) to move relatively the inner cage  717  and the outer cage  718  (the first retaining portion  718   b ), so that the first sprags  713  inserted into the pockets  717   b ,  718   d  of the inner cage  717  and the first retaining portion  718   b  are tilted. Thereby, the engaging faces  713   a ,  713   b  of the first sprags  713  go out of contact with at least one of the outer peripheral surface  11   a  of the inner race  11  and the inner peripheral surface  12   a  of the outer race  12 . As a result, the first sprags  713  and the inner race  11  and the outer race  12  become unable to engage with each other. 
         [0219]    Since the second retaining portion  718   c  moves integrally with the first retaining portion  718   b  as described above, the load applying device  715  applies a load in the direction of arrow R to each of the inner cage  717  and the outer cage  718  (the second retaining portion  718   c ) (see  FIG. 26(   c )), whereupon the inner cage  717  and the outer cage  718  (the second retaining portion  718   c ) are relatively moved, so that the second sprags  723  inserted in the pockets  717   b ,  718   d  of the inner cage  717  and the second retaining portions  718   c  are tilted. Hence, the engaging faces  723   a ,  723   b  of the second sprags  723  are made contact with the outer peripheral surface  11   a  of the inner race  11  and the inner peripheral surface  12   a  of the outer race  12 , resulting in the state of allowing the second sprags  723  to engage with the inner race  11  and the outer race  12 . At this stage, the second sprags  723  are located at a predetermined distance from each other in the circumferential direction between the outer peripheral surface  11   a  and the inner peripheral surface  12   a  which face each other, while preventing an abutting portion  723   c  of one second sprag  723  protruding toward another second sprag  723  located adjacent to it from abutting on the another second sprag  723 . 
         [0220]    In the state shown in  FIG. 26(   c ), when the power is transmitted to the inner race  11  or the outer race  12  to rotate the outer race  12  in the clockwise direction in  FIG. 26  or to rotate the inner race  11  in the counterclockwise direction, in  FIG. 26 , the engaging faces  723   a ,  723   b  of the second sprags  723  engage with the outer peripheral surface  11   a  of the inner race  11  and the inner peripheral surface  12   a  of the outer race  12  so as to transmit the power via the second sprags  723 . 
         [0221]    On the other hand, in the first sprags  713  as shown in  FIG. 26(   b ), at least one of the outer peripheral surface  11   a  of the inner race  11  and the inner peripheral surface  12   a  of the outer race  12  and the engaging faces  713   a ,  713   b  of the first sprags  713  goes out of contact with each other, thereby preventing the engaging faces  713   a ,  713   b  of the first sprags  713  from sliding on the outer peripheral surface  11   a  of the inner race  11  and the inner peripheral surface  12   a  of the outer race  12 . This makes it possible to reduce the production of drag torque on the engaging faces  713   a ,  713   b  of the first sprags  713 . Since the engaging faces  713   a ,  713   b  of the first sprags  713  are prevented from sliding on the outer peripheral surface  11   a  of the inner race  11  and the inner peripheral surface  12   a  of the outer race  12 , it is possible to reduce the productions of wearing, heating and the like. 
         [0222]    A relative position of the inner cage  717  and the outer cage  718  is determined while the second sprags  723  engage with the outer peripheral surface  11   a  of the inner race  11  and the inner peripheral surface  12   a  of the outer race  12  (see  FIG. 26(   c )). At this time, the engaging faces  713   a  of the first sprags  713  go out of contact with the outer peripheral surface  11   a  of the inner race  11  as shown in  FIG. 26(   b )). As a result, it is possible to prevent the first sprags  713  from unintentionally engaging with the inner race  11  and the outer race  12  when the second sprags  723  are engaged with the inner race  11  and the outer race  12 . This makes it possible to reliably prevent double-locking in which both the first sprags  713  and the second sprags  723  are engaged with the inner race  11  and the outer race  12 . 
         [0223]    When the torque transmitted through the second sprags  723  increases so as to cause relative movement of the inner cage  717  and the outer cage  718  in the direction of the arrow R, as shown in  FIG. 26(   b ), an abutting portion  713   c  of each first sprag  713  abuts on another first sprag  713  located adjacent to it to restrict tilting motion beyond the abutting point. As a result, this brings about the state in which the first sprags  713  are held between the inner cage  717  and the outer cage  718  (the first retaining portions  718   b ), so that further, relative movement of the inner cage  717  and the outer cage  718  (the first retaining portion  718   b ) is restricted. Accordingly, simplification of device structure can be achieved without a positioning member or the like for controlling the amount of relative movement of the inner cage  717  and the outer cage  718 . 
         [0224]    Next, the operation of the first retaining portion  718   b  and the second retaining portion  718   c  when the second sprags  723  strongly engage with the inner race  11  and the outer race  12  will be described with reference to  FIG. 27 .  FIG. 27(   a ) is a sectional view of important portions of the first retaining portion  718   b  and the second retaining portion  718   c  which are moved relatively.  FIG. 27(   b ) is a sectional view in the circumferential direction of the first retaining portion  718   b .  FIG. 27(   c ) is a sectional view in the circumferential direction of the second retaining portion  718   c.    
         [0225]    In the state shown in  FIG. 26 , when, by high torque, the inner race  11  is rotated counterclockwise in  FIG. 26  or the outer race  12  is rotated clockwise in  FIG. 26 , as shown in  FIG. 27(   c ), the engaging faces  723   a ,  723   b  of the second sprag  723  are strongly engaged with the outer peripheral surface  11   a  of the inner race  11  and the inner peripheral surface  12   a  of the outer, race  12 , so that the second sprag  723  is largely tilted. Thereupon, the tilting motion pushes the second retaining portion  718   c  to displace it in the circumferential direction (the clockwise direction in  FIG. 27) . On the other hand, the rotation of the inner race  11  in the counterclockwise direction in  FIG. 26  or the rotation of the outer race  12  in the clockwise direction in  FIG. 26  does not allow the first sprags  713  to engage with the inner race  11  and the outer race  12 . For this reason, the first retaining portion  718   b  does not displace in the circumferential direction without being affected by the first sprags  713 . Therefore, the displacement of the second retaining portion  718   c  in the circumferential direction with respect to the inner cage  717  is larger than the displacement of the first retaining portion  718   b  in the circumferential direction with respect to the inner cage  717 . 
         [0226]    However, since the first retaining portion  718   b  and the second retaining portion  718   c  are separated from each other in the axis direction and are structured to be capable of moving relatively in the circumferential direction, when the second sprags  723  are tilted to push the second retaining portion  718   c , until the fourth face  718   g   2  (see  FIG. 27(   a )) abuts on the third face  718   e   2 , the second retaining portion  718   c  alone moves relative to the first retaining portion  718   b . As a result, the first retaining portion  718   b  (see  FIG. 27(   b )) can be prevented from being affected by the displacement of the second retaining portion  718   c , leading to prevention of the possibilities that the first sprag  713  falls out of the pocket  718   d  of the first retaining portion  718   b  and that the inner cage  717  or the outer cage  718  is damaged. 
         [0227]    Next, the operation of the planetary gear device  730  will be described with reference to  FIG. 28 .  FIG. 28  is a schematic diagram showing the relationship between rpms of the first element, the second element and the third element and travel speed of the vehicle  200 . The horizontal axis in  FIG. 28  represents the travel speed of the vehicle  200 , while the vertical axis represents the rpms of the third element, the first element and the second element. Because the rotor  62  is connected to the sun gear  731  (second element) through the second shaft  4  as illustrated in  FIG. 22 , the rpm of the second element becomes equal to the rpm of the rotor  62  and the second shaft  4 . Because the engine  211  is connected to the carrier  733  (first element) through the input shaft  2 , the rpm of the first element becomes equal to the rpm of the input shaft  2 . Further, because the first shaft  3  is connected to the ring gear  734  (third element) and the drive gear  5   a , the rpm of the third element becomes equal to the rpm of the first shaft  3  and the rpm of the drive gear  5   a .  FIG. 28  illustrates the characteristics in which the rpm of the first element is constant relative to the travel speed of the vehicle  200 , that is, the rpm of the engine  211  and input shaft  2  is constant (R 1 ). 
         [0228]    During the start-up of the engine  211 , the first load applying device  715  (see  FIG. 22 ) is rendered operative to engage the first sprags  713  and the second sprags  723  with the first inner race  11  and the first outer race  12  (the second inner race  21  and the second outer race  22 ). In this state, the generator motor  60  is actuated to rotate the rotor  62 , whereupon power is transmitted to the first outer race  12  and the second outer race  22 . The relative rotation of the first outer race  12  and the first inner race  11  transmits power to the first inner race  11  and the input shaft  2 , resulting in start-up of the engine  211 . 
         [0229]    After the start-up of the engine  211 , the first load applying device  715  is operated to release the engagement of the first sprags  713  and the second sprags  723  with the first inner race  11  and the first outer race  12  (the second inner race  21  and the second outer race  22 ). In this state, the load of the generator motor  60  is increased to reduce the rpm of the rotor  62  for a reduction in rpm of the sun gear  731  (the first outer race  12 ) or the engine speed of the engine  211  is increased to increase the rotation of the input shaft  2  (the first inner race  11 ). In response to this, the motion state of the planetary gear device  730  moves in the right lower direction on the line of the third element shown in  FIG. 28 . In this motion state, achievement of forward moving of the vehicle in variable speed conditions in hybrid mode using the engine  211  and the generator motor  60  is shown. In this state, since the generator motor  60  at high rpm and in low torque is able to be used to rotate the sun gear  731 , a required load of the generator motor  60  (brake-element capacity) is small. 
         [0230]    When the rpm of the second shaft  4  becomes equal to the rpm (R 1 ) of the first shaft  3  after the vehicle  200  has been moved forward and accelerated (see  FIG. 28 ), the first load applying device  715  ( FIG. 22 ) is actuated to engage the first sprags  713  and the second sprags  723  with the first inner race  11  and the first outer race  12  (the second inner race  21  and the second outer race  22 ). The three elements of the planetary gear device  730  are rotated simultaneously to achieve the forward movement of the vehicle caused by the power of the engine  211 . 
         [0231]    Regeneration operation and reverse operation when coasting and braking of the vehicle  200  are similar to those in the first embodiment and the description is omitted. However, in the energy regeneration on coasting, the generator motor  60  can be operated at high rpm because of the sun gear  731 , resulting in a larger electric-generating capacity. 
         [0232]    Up to this point the present invention has been described based on the embodiments. However, the present invention is not limited to the above embodiments, and it can be easily understood that various improved modifications can be made without departing from the scope of the present invention. 
         [0233]    Each of the aforementioned embodiments has described the example that each of the first load applying device  15 ,  715  and the fourth load applying device  45  is formed of an electric motor (AC electric motor or DC electric motor), but the first load applying device is not necessarily limited to this. It should be understood that another power source can be employed. Other examples of power sources which can be employed include, for example, a DC electric motor, a hydraulic motor, a pneumatic cylinder, a hydraulic cylinder, an AC solenoid, a DC solenoid and the like. 
         [0234]    If the actuator  15   a ,  715   a ,  715   c  (the first load applying device  15 ,  715 ) includes a solenoid, not only the use of a gear mechanism or the like to apply a load to the first sprags  13 ,  613 ,  713 , but also, for example, it may be structured to use an electromagnetic force to apply a load to the first sprags  13 ,  613 ,  713 . 
         [0235]    Each embodiment has described the example that the first clutch  10 ,  610 ,  710  includes a sprag one-way clutch equipped with a function of disengaging the first sprags  13 ,  613 ,  713 , but the first clutch is not necessarily limited to this. Another clutch can be employed as long as it has functions of transmitting power in a certain direction and blocking the transmission of power. Examples of another clutch include a clutch using roller or the like to transmit power. 
         [0236]    Each embodiment has described the example that the second clutch  20 ,  720  is structured to include a sprag one-way clutch, but the second clutch is not necessarily limited to this. Another clutch can be employed as long as it has a function of transmitting power in a certain direction. Examples of another clutch include a clutch using roller or the like to transmit power. 
         [0237]    It should be understood that in each embodiment the first clutch  10 ,  610 ,  710  and the second clutch  20 ,  720  can be replaced with each other. Adoption of the structure of the first clutch  610  into the second clutch  20  makes it possible to prevent disadvantages of simultaneous engagement of the first sprags  613  and the second sprags with the inner race  2  and the outer race  3 . 
         [0238]    The first clutch  710  and the second clutch  720  can prevent the cages (the inner cage  717 , the outer cage  718 ) from being damaged. If this structure can be employed for the first clutch  610 , the same advantageous effects can be realized. This is because, when a load is transmitted by the first clutch  610 , since the first load applying device  15  is operated to engage the first sprags  613 , simultaneously engagement of the first sprags  613  and the second sprags  23  with the first inner race  11  and the first outer race  12  can be inhibited. 
         [0239]    Each embodiment has described the example of using the generator motor  60 , but not so necessary limited. Instead of the generator motor  60 , a motor having a function of generating electric power can be employed as a matter of course. 
         [0240]    Each embodiment has described the example that the engine  211  and the generator motor  60  drive the rear wheels of the vehicle  200 , but the driving is not limited to this. It is should be understood that the front wheels  201  may be driven or the front wheels  201  and the rear wheels  202  may be driven. 
         [0241]    In each embodiment, a clutch for engaging/disengaging the input shaft  2  to which the power from the engine  211  is input is not provided, but it is should be understood that a clutch is arranged for the input shaft  2 . Arranging a clutch for the input shaft  2  makes it possible to disconnect the engine  211  from the planetary gear device  30 ,  130 ,  330 ,  430 ,  530 ,  630 ,  730  in regeneration. As a result, the engine  211  can be prevented from acting as resistance to driving of the generator motor  60 , resulting in an increase in the amount of regeneration without energy loss. 
         [0242]    Each embodiment has described the example of including a parallel-axis gearbox  212 , but a gearbox is not limited to this, and another type of gearbox can be employed as a matter of course. Examples of another gearbox include, for example, a torque converter automatic transmission, a semiautomatic transmission such as a multiplate wet clutch planetary gear type, a dual-clutch transmission (DOT) or the like, and a continuously variable transmission (CVT). Also, a clutch for blocking the transmission of power between the first shaft  3  and the gearbox  212  may be provided as necessary. 
         [0243]    The seventh embodiment has described the example that the second urging member engaged with the lock portions  718   f ,  718   h  is foLffied of a torsion coil spring, but the second urging member is not necessarily limited to this. An elastic member such as rubber and the like may be employed as a matter of course. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           1 ,  101 ,  301 ,  401 ,  501 ,  601 ,  701  power transmitting device 
           2  input shaft 
           3  first shaft 
           4  second shaft 
           10 ,  610 ,  710  first clutch 
           11  first inner race 
           11   a  outer peripheral surface 
           12  first outer race 
           12   a  inner peripheral surface 
           13 ,  613 ,  713  first sprag 
           13   a ,  13   b ,  613   a ,  613   b ,  713   a ,  713   b  engaging face 
           23 ,  723  second sprag 
           23   a ,  23   b ,  713   a ,  713   b  engaging face 
           14 ,  614  cage 
           15 ,  715  first load applying device 
           16 ,  616  first urging member (urging member) 
           20 ,  720  second clutch 
           30 ,  130 ,  330 ,  430 ,  530 ,  630 ,  730  planetary gear device 
           31 ,  331  sun gear (third element) 
           33 ,  333 ,  733  carrier (first element) 
           34 ,  334  ring gear (second element) 
           60  generator motor (motor) 
           131  first sun gear (first element) 
           132  second sun gear (third element) 
           134  carrier (second element) 
           202  rear wheel (drive wheels) 
           211  engine 
           212  gearbox 
           431 ,  531 ,  731  sun gear (second element) 
           433 ,  533  carrier (third element) 
           434 ,  534  ring gear (first element) 
           631  sun gear (first element) 
           633  carrier (second element) 
           634 ,  734  ring gear (third element) 
           717  inner cage (cage) 
           718  outer cage (cage) 
           718   b  first retaining portion 
           718   c  second retaining portion 
           718   e   1  first face 
           718   g   1  second face 
           718   f ,  718   h  lock portions (second urging member is locked) 
         A, B contact point 
         O axis