Abstract:
A one-way clutch having a lock-up function, comprises an outer race, an inner race radially spaced apart from the outer race and disposed within the outer race concentrically for relative rotation, a cam surface provided on an inner peripheral surface of the outer race or an outer peipheral surface of the inner race, a track surface provided on the outer peripheral surface of the inner race or the inner peripheral surface of the outer race in a confronting relationship to the cam surface, a plurality of roller members disposed between the outer race and the inner race and adapted to transmit torque between the outer race and the inner race, springs for biasing the roller members toward one circumferential direction, a side plate for holding the roller members and the springs with predetermined intervals along a circumferential direction, and a control member for acting on the roller members to effect lock-up control, and wherein the control member controls the one-way clutch to lock up the one-way clutch in both directions or one direction by urging the roller members radially against the outer peripheral surface of the inner race or the inner peripheral surface of the outer race to frictionally engage the former with the latter or by releasing the roller members.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an improvement in a one-way clutch used in a transmission, particularly an automatic transmission of a motor vehicle, an agricultural machine, a construction machine, an industrial machine and the like. More particularly, the present invention relates to a one-way clutch having a lock-up function. 
     2. Related Background Art 
     A conventional one-way clutch used in an automatic transmission has an outer race and an inner race which are rotated relative to each other, and sprags or rollers for transmitting torque between the outer race and the inner race are engaged by a cam surface provided on a track surface of the outer race or the inner race, thereby transmitting rotational torque only in one direction. Further, such a one-way clutch is idly rotated in reverse direction. 
     Such a one-way clutch cannot be used in case that rotation must be transmitted in both of two directions. In such cases, by combining the one-way clutch with a multi plate clutch such as a multi-plate frictional engaging device for effecting lock-up, a clutch is designed so that a rotary member is idly rotated only in one direction or the rotary member is prevented from being idly rotated in both of two directions, on demand. 
     However, in such an arrangement, the function for effecting idle rotation only in one direction and the function for preventing idle rotation in both directions must be shared with two members, with the result that there arise problems such as an increase in the number of parts, complexity, bulkiness, an increase in weight and an increase in cost. 
     SUMMARY OF THE INVENTION 
     Accordingly, an object of the present invention is to provide a one-way clutch having a lock-up function, which has both a function for effecting idle rotation only in one direction and a function for preventing rotation in both directions, in order to solve problems such as an increase in the number of parts, complexity, bulkiness, an increase in weight and an increase in cost. 
     To achieve the above object, the present invention provides a one-way clutch having a lock-up function, comprising an outer race, an inner race radially spaced apart from the outer race and disposed within the outer race concentrically for relative rotation, a cam surface provided on an inner peripheral surface of the outer race or an outer peripheral surface of the inner race, a track surface provided on the outer peripheral surface of the inner race or the inner peripheral surface of the outer race in a confronting relationship to the cam surface, a plurality of roller members disposed between the outer race and the inner race and adapted to transmit torque between the outer race and the inner race, springs for biasing the roller members toward one circumferential direction, a side plate for holding the roller members and the springs at predetermined intervals along a circumferential direction, and a control member for acting on the roller members to effect lock-up control, and wherein the control member controls the one-way clutch to lock-up the one-way clutch in both directions or one direction by urging the roller members radially against the outer peripheral surface of the inner race or the inner peripheral surface of the outer race to frictionally engage the former with the latter or by releasing the roller members. 
     According to the present invention, when a torque transmitting member normally fixed or secured only in one direction is urged against the inner race, a friction force is generated at a contact area between the torque transmitting member and the inner race, with the result that the torque transmitting member follows the rotational direction of the inner race regardless of the urging force of the spring, thereby locking-up the one-way clutch. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a view for explaining an operating principle of the present invention; 
     FIG. 2 is an exploded perspective view of a one-way clutch according to a first embodiment of the present invention; 
     FIG. 3 is a partial radial sectional view of the one-way clutch according to the first embodiment of the present invention; 
     FIG. 4 is an axial sectional view showing an example of an oil path arrangement useful in various embodiments of the present invention; 
     FIG. 5 is an axial sectional view showing another example of an oil path arrangement useful in various embodiments of the present invention; 
     FIG. 6 is an axial sectional view showing a further example of an oil path arrangement useful in various embodiments of the present invention; 
     FIG. 7 is an axial sectional view showing a still further example of an oil path arrangement useful in various embodiments of the present invention; 
     FIG. 8 is a partial radial sectional view of a one-way clutch according to a second embodiment of the present invention; 
     FIG. 9 is a radial sectional view of a one-way clutch according to a third embodiment of the present invention; 
     FIG. 10 is a perspective view of an urging piece used in the third embodiment; 
     FIG. 11 is a radial sectional view of a one-way clutch according to a fourth embodiment of the present invention; 
     FIG. 12 is a radial sectional view of a one-way clutch according to a fifth embodiment of the present invention; 
     FIG. 13 is a radial sectional view of a one-way clutch according to a sixth embodiment of the present invention; 
     FIG. 14 is a perspective view of an urging piece used in the sixth embodiment; 
     FIG. 15 is a radial sectional view of a one-way clutch according to a seventh embodiment of the present invention; 
     FIG. 16 is a perspective view of an urging member used in the seventh embodiment; 
     FIG. 17 is a radial sectional view of a one-way clutch according to an eighth embodiment of the present invention; and 
     FIG. 18 is a perspective view showing an urging member of FIG. 7 in detail. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will now be fully explained in connection with embodiments thereof with reference to the accompanying drawings. Incidentally, it should be noted that embodiments described hereinbelow are explained only as examples of the present invention and do not limit the present invention. Further, in the drawings, the same elements are designated by the same reference numerals. 
     (Operating Principle) 
     Before explaining embodiments, a principle of the present invention will be described with reference to FIG. 1. A conventional one-way clutch has only a single cam surface by which rollers as torque transmitting members are engaged. However, in the present invention, there are provided symmetrical (in a left-and-right direction) cam surfaces  101 ,  102 . Each of substantially cylindrical roller members or rollers  140  is always biased toward the left cam surface  101  by a corresponding spring  103  having one end held by a spring holding member  104 . 
     An urging member or urging plate  150  is disposed above the roller  140 . Normally, the urging plate  150  is in an elevated position not in contact with the roller  140 , or no external force acts on the urging plate  150  so that, if the urging plate is contacting with the roller  140 , movement of the roller  140  is not obstructed. 
     In a condition that the urging plate  150  is in the elevated position, when an inner race  120  rotates in an anti-clockwise direction, i.e., a left direction L in FIG. 1, the roller  140  is pushed by the spring to engage with the left cam surface  101 , thereby securing the inner race  120 . On the other hand, when rotated in a clockwise direction, i.e., a right direction R, the inner race  120  can idly be rotated. 
     When the urging plate  150  is lowered, the roller  140  is urged against the inner race  120 , thereby generating a friction force in a contact area between the roller and the inner race. This friction force causes the roller  140  to follow the rotation of the inner race  120 . When the inner race  120  is rotated in the left direction L, the roller  140  is engaged by the left cam surface  101 . When rotated in the right direction R, the friction force between the roller  140  and the inner race shifts the roller  140  in the right direction in opposition to a biasing force of the spring, thereby eventually engaging the roller with the right cam surface  102 . Thus, depending upon the operation of the urging plate  150 , the inner race  120  is locked-up (secured) in both directions or in one direction. 
     (First Embodiment) 
     FIG. 2 is an exploded perspective view of a one-way clutch having a lock-up function (referred to merely as “one-way clutch” hereinafter) according a first embodiment of the present invention. A one-way clutch  1  has an inner race  2 , and an outer race  3  capable of being rotated relatively and coaxially disposed radially outwardly of the inner race  2 . Incidentally, in various embodiments (described later) including the first embodiment, the outer race is non-driven. Only the inner race is driven. 
     Annular side plates  7  are disposed between the outer race  3  and the inner race  2 , and oil pressure introduction ports  11  for introducing oil pressure supplied from an oil-hydraulic circuit (not shown) are formed in the side plates  7 . Further, annular oil passages  12  are formed in the outer race  3  at both axial sides. 
     The oil pressure introduced into the oil passages  12  is transmitted through a plurality of radial through holes  14  formed in partition walls  15  at predetermined positions, thereby urging the urging members  9  which will be described later. 
     As can be seen from FIG. 2, two urging members are arranged side by side in an axial direction to urge both axial ends of a corresponding roller. 
     FIG. 3 is a partial axial sectional view of the one-way clutch  1  of FIG.  2 . As shown in FIG. 3, a cam portion  8  is provided on a portion of the inner peripheral surface of the outer race  3  radially inwardly of the oil passages  12  and has pairs of opposed cam surfaces  8   a ,  8   b  having substantially equal but opposite inclinations. The pairs of the cam surfaces  8   a ,  8   b  are equidistantly spaced apart from the adjacent pair along the circumferential direction. 
     A plurality of rollers  4  corresponding to the pairs of cam surface  8   a ,  8   b  are disposed between the cam portion  8  and the outer peripheral surface of the inner race  2 . Each roller  4  has a substantially cylindrical shape and is rotatable along the circumferential direction. The rollers  4  are held by the side plates  7  so as not to be dislodged in the axial direction. 
     The rollers  4  are biased toward one direction, i.e., toward the respective cam surfaces  8   a  by corresponding springs  5  such as accordion springs. The springs  5  have one end secured by fixed plates  6  integrally protruded from a cage. 
     Urging members  9  comprised of spring members having predetermined elasticity are disposed between corresponding rollers  4  and the partition walls  15 . The urging members serving as urging plates of the lock-up mechanism of the one-way clutch  1  are arranged to straddle the single roller  4 . Accordingly in correspondence to the number of rollers  4 , a plurality of urging members  9  are provided along the circumferential direction. 
     A friction material  10  is adhered, by an adhesive, to an inner surface of each urging member  9 , i.e., surface facing the corresponding roller  4  in order to easily obtain a friction force. However, if a sufficient friction force can be by direct contact with the inner surface, the friction material need not be provided. Both circumferential ends  9   a  of each urging member  9  are bent outwardly so that the ends  9   a  are supported by holding projections  13  integrally protruding from the corresponding side plate  7  not to be overlapped with the ends of the adjacent urging member. Each holding projection  13  has a central curved portion  13   a  curved upwardly. The end  9   a  of the urging member  9  is prevented from being contacted with the end  9   a  of the adjacent urging member  9  by this curved portion  13   a . As a result, when the urging member  9  as a control member for effecting lock-up is displaced downwardly, since both circumferential ends of the urging member  9  are held by the holding projections  13 , excessive deformation of the urging member  9  can be prevented. 
     In the one-way clutch having such a construction, each urging member  9  is operated as follows. First, the oil pressure F introduced from the oil pressure introduction port  11  is transmitted to a rear surface of the urging member  9  through the oil passage  12  and the through hole  14  to flex the urging member  9 , thereby urging the urging member toward the inner race  2 . In this case, the holding projections  13  act as fulcrums when the urging member  9  is flexed. As a result, the urging member  9  urges the corresponding roller  4  against the outer peripheral surface of the inner race  2  via the friction material  10 . This condition is shown by the solid line in FIG.  3 . With dependence upon the rotational direction of the inner race  2 , the roller  4  is engaged by the cam surface  8   a  or the cam surface  8   b  thereby locking-up the one-way clutch. 
     On the other hand, in order to release the lock-up by stopping the operation of the urging member  9 , the oil pressure may merely be released. When the oil pressure is released, each urging member is lifted up to its original position by its own elastic force. This condition of the urging member  9  is shown by the broken line in FIG.  3 . In the condition that the oil pressure is being applied, the force of the oil pressure is greater than the elastic force of the urging member  9 . 
     As shown in FIG. 3, each roller  4  can be shifted between the cam surface  8   a  and the cam surface  8   b  by a distance D between two lock positions. In the actual operation of the one-way clutch  1 , all of the rollers  4  are urged by the urging members  9  substantially simultaneously. However, a plurality of oil passages may be provided as independent units so that only some rollers  4  can be urged. 
     Now, a relationship between the oil pressure and the urging member  9  will be described with reference to FIG.  4 . FIG. 4 is an axial sectional view of the one-way clutch  1  according to the first embodiment. 
     In FIG. 4, the annular side plates  7  are fitted into both axial sides of the one-way clutch  1  to keep the oil passages  12  of the outer race  3  in a liquid-tight condition. Since each side plate  7  is slidingly contacted with the inner peripheral surface of the outer race  3  and the outer peripheral surface of the inner race  2  and is provided at both its radial ends with annular flanges  7   a  extending axially inwardly (see FIG.  2 ), the side plate  7  has a function as an end bearing to maintain concentricity between the outer race  3  and the inner race  2 . Incidentally, upper flanges  7   a  of the side plates  7  are fitted into the oil passages  12 . 
     The oil introduction ports  11  formed in the two side plates  7  provided on both axial sides of the clutch are connected to oil tubes  18  connected to an oil hydraulic circuit (not shown). The oil entered into the oil passage  12  from the corresponding oil tube  18  and oil introduction port  11  passes through the through hole  14  and acts on the rear surface of the urging member  9  to urge the urging member downwardly. It is designed so that the pressure is held while retaining a very small gap or clearance defined by a stepped portion  3   a  of the outer race  3 , side plate  7 , urging member  9  and allowing movement of the urging member  9 . An oil seal is provided between the oil tube  18  and the oil introduction port  11  to seal the boundary between them. The urging member  9  and the friction material  10  can be displaced between the surface of the roller  4  and the stepped portion  3   a  of the outer race  3 . 
     Incidentally, FIG. 4 shows a condition that the oil pressure is not applied. 
     In the above explanation, while an example that the urging members  9  as the urging plates are installed in both axial side grooves of the outer race  3  was explained, so long as the roller  4  is not inclined (for example, when a diameter of the roller is considerably greater than the width of the roller), the urging member may be installed only at one axial side of the outer race. Further, it should be understood that the oil passage arrangement shown in FIG. 4 can be applied to various embodiments which will be described later. 
     (Other Examples of Oil Passage Arrangement) 
     FIG. 5 is a sectional view similar to FIG.  4 . Although the fundamental arrangement is the same as that shown in FIG. 4, there are no through holes  14  in FIG.  5 . Accordingly, the oil introduced from each oil introduction port  11  of the side plate  7  enters into the oil passage  12  and provides the oil pressure required for urging the urging member  9  against the roller  4 . According to an example shown in FIG. 5, since the oil paths are reduced, the construction is made simpler. 
     FIG. 6 is a sectional view similar to FIG.  4 . In this example, oil passages of the outer race  3  differ from those in FIG.  4 . 
     In FIG. 6, annular side plates  7  are fitted into both axial sides of a one-way clutch  40  to keep oil passages  12  of an outer race  3  in a liquid-tight condition. Similar to FIG. 4, each side plate  7  has a function as an end bearing to prevent a roller  4  from dislodging in the axial direction and to maintain concentricity between the outer race  3  and the inner race  2 . 
     The two oil passages  12  provided in the outer race  3  at its axial sides communicate with each other through a communication passage  15 . Accordingly, the oil tube  18  and the oil introduction port  11  may be provided for only one of the side plates  7 . 
     The oil entering into the oil passage  12  from the oil introduction port  11  formed in the side plate  7  also enters into the opposite oil passage  12  and applies predetermined pressure onto the urging members  9  through the through holes  14 . 
     FIG. 6 shows a condition where the oil pressure is not applied. Incidentally, as mentioned above, in the example shown in FIG. 6, two oil passages  12  provided at both axial sides are communicated with each other through the communication passage  15  extending axially through the outer race. At least one communication passage  15  is provided in the circumferential direction of the outer race  3 . The oil pressure in the oil passages  12  is made uniform by the presence of the communication passages  15 , thereby applying substantially uniform hydraulic forces to the urging members  9 . According to the example of the oil passage arrangement shown in FIG. 6, since the oil tube  18  and the oil introduction port  11  may be provided only at one side, the arrangement is made simpler. 
     FIG. 7 is a sectional view similar to FIG.  5 . In this example, an oil passage arrangement of the outer race  3  differs from those in FIGS. 4 to  6  the constructions of urging members  39  also differ. Also in a one-way clutch  50  shown in FIG. 7, each side plate  7  has a function as an end bearing. 
     In the example shown in FIG. 7, similar to FIG. 6, two oil passages  12  provided at both axial sides communicate with each other by a communication passage  15  extending axially through the outer race. At least one communication passage  15  is provided in the circumferential direction of the outer race  3 . The oil pressure in the oil passages  12  is made uniform by the presence of the communication passage  15 , thereby applying substantially uniform hydraulic forces to the urging members  9 . 
     In the example shown in FIG. 7, unlike the aforementioned embodiments in which two urging members are arranged independently in the axial direction, each urging member  39  is constituted by interconnecting two urging portions  39   b  via connecting portions  39   a , as shown in FIG.  18 . According to the example of the oil passage arrangement shown in FIG. 7, similar to the example of FIG. 6, since the oil tube  18  and the oil introduction port  11  may be provided only at one side, the arrangement is made simpler. Further, an urging force for the urging member  39  acts on the integrally formed urging member  39  uniformly. Particularly, since the hydraulic force is distributed via the connecting portions  39   a , the urging force of the urging portions  39   b  against the roller  4  becomes uniform and synchronism can be achieved. 
     Incidentally, the arrows shown in FIGS. 4 to  7  indicate flows of oil introduced from the oil introduction ports. 
     (Second Embodiment) 
     FIG. 8 is a partial radial sectional view of a one-way clutch  20  according to a second embodiment of the present invention. Since fundamental construction and operation are the same as those of the first embodiment, explanation thereof will be omitted. 
     In the second embodiment, unlike the first embodiment, the design is such that one elongated urging member  19  applies urging forces to three rollers  4 . In case of the second embodiment, a plurality of urging members  19  are disposed equidistantly along a circumferential direction. 
     Similar to the first embodiment, both circumferential ends of each urging member  19  have ends bent outwardly so that the ends  9   a  are supported by holding projections  13 . According to the second embodiment, the number of parts is reduced and the apparatus is made simpler. 
     (Third Embodiment) 
     FIG. 9 is a partial radial sectional view of a one-way clutch  60  according to a third embodiment of the present invention. Since fundamental construction and operation are the same as those of the first embodiment, explanation thereof will be omitted. 
     In the third embodiment, as each urging member, in place of a plate-shaped member, an urging piece is used. Similar to the first and second embodiments, one oil passage is provided. Further, each urging piece is associated with one roller  4 . 
     A cam portion  8  of an outer race  3  is provided with a plurality of through holes  54  extending radially and disposed equidistantly along a circumferential direction, and the urging pieces  55  are fitted into the corresponding through holes  54 . As shown in FIG. 10, each urging piece  55  has a substantially rectangular body  55   b  provided at its lower surface with a bottom portion  55   c  to which a friction material  10  is adhered. 
     The body  55   b  of each of the plurality of urging pieces  55  has a pair of arm portions  55   a  protruding from an upper part of the body outwardly and downwardly in opposite directions. Below the arm portions  55   a , recessed portions  55   d  are formed in side surfaces of the body  55   b . The urging piece  55  is formed from material having predetermined elasticity, such as resin. 
     In the third embodiment, the oil pressure is applied through oil pressure introduction ports  11  of the outer race  3 , the oil pressure passes in the oil passages  12  to urge the urging pieces  55  to abut the urging pieces against the rollers  4  via the friction materials  10 , thereby locking-up the one-way clutch  60 . Incidentally, FIG. 9 shows the urging pieces  55  in a non-lock-up condition. 
     When the oil pressure is released to release the lock-up, each urging piece  55  is returned to its original position mainly due to elastic forces or spring forces of the arm portions  55   a . A stopper member  56  is integrally formed (or formed as a discrete part) on an upper surface (opposite to the surface on which the friction material  10  is adhered) of the urging piece  55 . Due to the presence of the stopper member  56 , the urging piece  55  is maintained in an elevated position between an upper wall of the oil passage  12  of the outer race  3  and the cam portion  8  holding the arm portions  55   a.    
     (Fourth Embodiment) 
     FIG. 11 is a radial sectional view of a one-way clutch  70  according to a fourth embodiment of the present invention. 
     In the fourth embodiment, the design is an example of one elongated urging piece  63  a straddling plurality of rollers, the illustrative design being such that one urging piece applies an urging force to three rollers  4 . 
     Arm portions  63   a  are provided on both circumferential ends of each urging piece  63 . When the urging piece is operated by oil pressure, the arm portions are supported by portions of the cam portion  8  adjacent to a through hole  64  formed in the cam portion  8 . According to the fourth embodiment, the number of parts is reduced and the apparatus is made simpler. A stopper member  56  is integrally formed (or formed as a discrete part) on an upper surface (opposite to the surface on which the friction material  10  is adhered) of the urging piece  63 . Due to the presence of the stopper member  56 , the urging piece  63  is maintained in an elevated position between an upper wall of the oil passage  12  of the outer race  3  and the cam portion  8  holding the arm portions  63   a.    
     (Fifth Embodiment) 
     FIG. 12 is a partial radial sectional view of a one-way clutch  80  according to a fifth embodiment of the present invention. Since fundamental construction and operation are the same as those of the first embodiment, explanation thereof will be omitted. 
     In the fifth embodiment, similar to the fourth embodiment, as each urging member, in place of a plate-shaped member, a block-shaped urging piece  65  is used. Each urging piece  65  is associated with one roller  4 . 
     A cam portion  8  of an outer race  3  is provided with a plurality of through holes  64  extending radially and disposed equidistantly along a circumferential direction, and the urging pieces  65  are fitted into the corresponding through holes  64 . A friction material  10  is adhered to a lower surface of each urging piece  65 . 
     Each of urging pieces  65  has a rectangular window portion  66  extending axially through the urging piece. A spring  67  is fitted into each window portion  66 . Further, a projection  68  integrally formed with a side plate  73  and protruding axially is fitted into each window portion  66 . The spring  67  is disposed between the projection  68  and an inner surface of the window portion  66 . “A” in FIG. 12 is a partial sectional view showing a condition that the urging piece  65  is held by the projection  68  of the side plate  73 . 
     According to the fifth embodiment having the above-mentioned arrangement, in a condition that the oil pressure is not applied, each urging piece  65  is in a position shown in FIG.  12 . In this case, since each spring  67  applies the biasing force to the projection  68  within the window portion  66 , the urging piece  65  is biased outwardly (radially upwardly) by the projection  68 . Accordingly, the urging piece  65  is held at a position where the urging piece does not urge the corresponding roller  4 . 
     When the oil pressure is supplied to the oil introduction port  11  (not shown) and the oil passage  12 , due to the hydraulic force, the urging piece  65  is shifted downwardly in opposition to the biasing force of the spring  67 . Accordingly, the lower surface of the urging piece  65  abuts against the periphery of the roller  4 , thereby urging the roller  4  against the outer peripheral surface of the inner race  2 . 
     When the oil pressure is released, as mentioned above, the urging piece  65  is shifted upwardly by the biasing force of the spring  67  to be spaced apart from the peripheral surface of the roller  4 . 
     (Sixth Embodiment) 
     FIG. 13 is a partial radial sectional view of a one-way clutch  90  according to a sixth embodiment of the present invention. Since fundamental construction and operation are the same as those of the first embodiment, explanation thereof will be omitted. FIG. 14 is a perspective view of an urging member  91  used in this sixth embodiment. 
     In the sixth embodiment, as each urging member, in place of a plate-shaped member, an urging piece  91  is used. Each urging piece  91  is associated with one roller  4 . 
     A cam portion  8  of an outer race  3  is provided with a plurality of through holes  94  extending radially and disposed equidistantly along a circumferential direction, and the urging pieces  91  are fitted into the corresponding through holes  94 . As shown in FIG. 14, each urging piece  91  is integrally formed by two urging portions  92  spaced apart from each other with a predetermined interval, and a bridge portion  93  for interconnecting ends of the urging portions  92 , and friction materials  10  are adhered to lower surfaces of the urging portions  92 . Incidentally, the urging portions  92  and the bridge portion  93  may be formed as discrete members. 
     Unlike in above-mentioned embodiments, the urging piece according to this embodiment is not formed by an elastic member such as a spring. The reason is that, when the oil pressure is released, an upper surface of the bridge portion  93  abuts against a cam surface of an outer race  3 , and, when the oil pressure is applied, the bridge portion abuts against the roller  4  to prevent further movement of the roller. When the oil pressure is not applied, the urging piece  91  may be in a free condition. 
     In the sixth embodiment, when the oil pressure is applied through the oil introduction port  11  of the outer race  3 , the oil passes through the oil passage  12  to urge the urging piece  91  to abut the urging piece against the roller with the interposition of the friction material  10 , thereby locking-up the one-way clutch  90 . Incidentally, FIG. 13 shows the urging piece  91  in a non-lock-up condition. 
     When the oil pressure is released to release the lock-up, the urging members  91  become free thereby releasing the urging against the rollers  4 . 
     (Seventh Embodiment) 
     FIG. 15 is a radial sectional view of a one-way clutch  100  according to a seventh embodiment of the present invention. Since fundamental construction and operation are the same as those of the first embodiment, explanation thereof will be omitted. Further, FIG. 16 is a perspective view of an urging member used in this embodiment. 
     In the seventh embodiment, an elongated plate-shaped member  109  is used as an urging member. FIG. 16 is a partial perspective view showing an urging member  109  in detail. The urging member  109  is formed from an elongated belt-shaped material and has bent portions  109   a  bent outwardly and inwardly, upper flat portions  109   c  contiguous to respective bent portions  109   a , and lower flat portions  109   b  connected to the upper flat portions  109   c  via adjacent bent portions  109   a . When it is considered that one bent portion  109   a , one upper flat portion  109   c  and one lower flat portion  109   b  constitute one unit, a plurality of units are contiguous to each other to form an annular urging member  109 . It should be understood that the numbers of the bent portions  109   a  and the flat portions  109   b ,  109   c  can freely be selected. 
     The urging member  109  having the above-mentioned construction is assembled in the one-way clutch  100  in a condition that the lower flat portions  109   b  to which the friction materials  10  are adhered are opposed to the rollers  4  and the upper flat portions  109   c  are held by holding portions  108  provided on the cam portion of the outer race  3 . In this case, since side surfaces  109   d  of the bent portions  109   a  adjacent to each upper flat portion  109   c  pinch both ends of the corresponding holding portion  108 , the urging member  109  is positively held by the holding portions  108 . 
     In the seventh embodiment, when the oil pressure is applied through the oil introduction ports  11  of the outer race  3 , the oil passes the oil passages  12  to urge the lower flat portions  109   b  of the urging members  109 , with the result that the friction materials  10  abut against the rollers  4 , thereby locking-up the one-way clutch  100 . Incidentally, FIG. 15 shows the urging member  109  in a non-lock-up condition. 
     When the oil pressure is released to release the lock-up, the urging members  109  are returned to their original positions by elasticity of the bent portions  109   a , thereby releasing the urging against the rollers  4 . 
     (Eighth Embodiment) 
     FIG. 17 is an axial sectional view of a one-way clutch  110  according to an eighth embodiment of the present invention. 
     In the eighth embodiment, rollers  4  are urged by an annular band  111  surrounding an inner race  2 . 
     The band  111  has an anchor tab  114  having one end supported by an anchor fixing portion  115 , and an apply tab  113  connected to an apply hydraulic unit  112  and adapted to receive oil pressure. When the oil pressure from the hydraulic unit  112  secured to the fixing portion  115  is applied, the apply tab  113  is urged against the anchor tab  114  via a piston  116 , and the band urges the rollers  4  against the outer peripheral surface of the inner race  2 , thereby locking-up the one-way clutch  110 . A friction material for obtaining a required frictional force is adhered to an inner peripheral surface of the band  111  by an adhesive. 
     In the various embodiments as mentioned above, by urging the rollers  4  by means of the urging members, the rollers  4  are urged between the cam surface and the outer peripheral surface of the inner race, thereby locking-up the one-way clutch. Accordingly, even when the inner race is rotated in either one direction or the other direction, the lock-up can be achieved. 
     Further, in the embodiments of the present invention, while an example that the outer race is not driven and the inner race is driven was explained, the inner race may be non-driven and the outer race may be driven. Also, both the outer and inner races may be driven. 
     Furthermore, although it was described for all of the embodiments that the urging members or the urging pieces may be provided at at least one side of the rollers in the axial direction, it is preferable that they are provided at both sides of the rollers in the axial direction in order to prevent the rollers from being inclined. 
     The configurations of the oil passages, side plates, and urging members or urging pieces described above can freely be combined, and, thus, it should be noted that the present invention is not limited to the above-mentioned embodiments. 
     It will be appreciated that the one-way clutch having the lock-up function of the present invention functions both as a one-way clutch and as a lock-up clutch, whereby simplicity of the apparatus, reduction in the number of parts, compactness and reduction in weight can be achieved.