Patent Publication Number: US-8967349-B2

Title: Lock-up device for torque converter

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. National stage application of International Application No. PCT/JP2012/078647, filed Nov. 5, 2012, which claims priority to Japanese Patent Application No. 2011-265586, filed in Japan on Dec. 5, 2011, the entire contents of which are hereby incorporated by reference. 
     FIELD OF INVENTION 
     The present invention relates to a lock-up device, particularly to a lock-up device for a torque converter, which is configured to transmit torque from a front cover to a transmission-side member through a turbine of the torque converter. 
     BACKGROUND INFORMATION 
     In many cases, a torque converter is provided with a lock-up device for directly transmitting torque from a front cover to a turbine. The lock-up device includes a piston that can be frictionally coupled to the front cover, a drive plate fixed to the piston, a plurality of torsion springs supported by the drive plate, and a driven plate elastically coupled to the piston and the drive plate by the plural torsion springs in the rotational direction. The driven plate is fixed to the turbine. 
     Further, as described in Japanese Laid-open Patent Application Publication No. JP-A-2010-48291, a lock-up device of a so-called multi-plate type using a plurality of clutch plates has been also proposed for increasing the clutch capacity of the lock-up device. 
     When torque is herein transmitted by the lock-up device, reduction in stiffness and expansion in a torsional angle are required for the torsion springs to effectively absorb and attenuate variation in torque inputted thereto from an engine. In view of this, as described in Japanese Laid-open Patent Application Publication No. JP-A-2002-89657, a device has been proposed that pairs of torsion springs among a plurality of torsion springs composing a part of a damper mechanism are configured to act in series through an intermediate member. 
     SUMMARY 
     The intermediate member described in Japanese Laid-open Patent Application Publication No. JP-A-2002-89657 is rotatable relative to both of input-side and output-side members in the damper mechanism. Further in Japanese Laid-open Patent Application Publication No. JP-A-2002-89657, the intermediate member is restricted from moving in both of the axial direction and the radial direction by an input-side plate fixed to a piston composing a part of the lock-up device. 
     Now, particularly in such a lock-up device of the multi-plate type as described in Japanese Laid-open Patent Application Publication No. JP-A-2010-48291, the piston and the damper mechanism are disposed away from each other. In the lock-up device thus structured, the intermediate member cannot be supported by the piston and the input-side plate of the damper mechanism. Further, in the lock-up device of the multi-plate type, the axial space of a clutch part is inevitably increased. Hence, a large axial space cannot be produced for a mechanism for supporting the intermediate member and restricting moving of the intermediate member. 
     It is an object of the present invention to implement a mechanism for restricting moving of an intermediate member with a smaller space, particularly in a lock-up device that a piston and a damper mechanism are disposed in positions away from each other. 
     A lock-up device for a torque converter according to a first aspect of the present invention is a device configured to transmit a torque from a front cover to a transmission-side member through a turbine of the torque converter, and includes a clutch part and a damper mechanism. The clutch part is disposed between the front cover and the turbine, and includes a clutch input member coupled to the front cover, a clutch output member configured to output the torque toward the turbine, a plurality of clutch plates configured to transmit the torque between the clutch input member and the clutch output member, and a piston configured to press the clutch plates against each other. The damper mechanism is configured to transmit the torque from the clutch part to the turbine and to absorb and attenuate a torsional vibration. Further, the damper mechanism includes an input-side member coupled to the clutch output member, an output-side member connected to the turbine, a plurality of elastic members configured to elastically couple the input-side member and the output-side member in a rotational direction, an intermediate member, and a restriction member. The intermediate member is rotatable relative to the input-side member and the output-side member, and is configured to cause at least two of the elastic members to act in series. The restriction member is fixed to the clutch output member, and is disposed such that a part of the intermediate member is interposed between the input-side member and the restriction member in an axial direction. Further, the intermediate member is restricted from moving in a radial direction by the clutch output member while being restricted from moving in the axial direction by the input-side member and the restriction member. 
     In the present device, when a lock-up state is produced, torque from the front cover is inputted into the damper mechanism from the clutch part, and is outputted to the turbine while torsional vibration is absorbed and attenuated. In the damper mechanism, the torque is inputted into the input-side member, and is outputted to the turbine through the plural elastic members and the output-side member. At this time, at least two of the plural elastic members act in series through the intermediate member. Hence, a damper torsional angle can be widely formed and low stiffness can be implemented. Further, the intermediate member is restricted from moving in the radial direction by the clutch output member, while being restricted from moving in the axial direction by the input-side member and the restriction member. 
     It is herein designed that the intermediate member is restricted from moving in the axial direction and the radial direction by the clutch output member and members of the damper mechanism, i.e., the input-side member and the restriction member. Hence, the axial space can be inhibited from being enlarged. Therefore, the present invention effectively works when being applied to a lock-up device of a multi-plate type that a relatively large space is produced for the clutch part. 
     A lock-up device for a torque converter according to a second aspect of the present invention relates to the lock-up device of the first aspect, and wherein the intermediate member is formed in an annular shape and is disposed on an outer peripheral side of the clutch output member. The intermediate member is contactable at an inner peripheral surface thereof to an outer peripheral surface of the clutch output member. 
     Here, the intermediate member is configured to be restricted from moving in the radial direction when the inner peripheral surface of the intermediate member is contacted to the outer peripheral surface of the clutch output member. 
     A lock-up device for a torque converter according to a third aspect of the present invention relates to the lock-up device of the second aspect, and wherein the input-side member is fixed at an inner peripheral part thereof to a turbine-side lateral surface of an outer peripheral part of the clutch output member. Further, the restriction member is formed in an annular shape and is fixed at an inner peripheral part thereof to a front-cover-side lateral surface of the outer peripheral part of the clutch output member. Moreover, the intermediate member is contactable to the input-side member and an outer peripheral part of the restriction member. 
     Here, the intermediate member is restricted from moving toward the turbine by the input-side member, while being restricted from moving toward the front cover by the outer peripheral part of the restriction member. 
     A lock-up device for a torque converter according to a fourth aspect of the present invention relates to the lock-up device of any of the first to third aspects, and wherein the restriction member is made of a plate member with a thickness less than a thickness of the intermediate member. 
     Here, the thickness of the restriction member is smaller than that of the intermediate member. Hence, the axial space can be further inhibited from being enlarged. 
     In the present invention as described above, a mechanism for restricting an intermediate member can be implemented with a smaller space in a lock-up device equipped with a clutch part of a multi-plate type that a piston and a damper mechanism are disposed in positions away from each other. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a partial cross-sectional view of a torque converter equipped with a lock-up device according to an exemplary embodiment of the present invention. 
         FIG. 2  is a diagram illustrating the lock-up device of the torque converter illustrated in  FIG. 1 . 
         FIG. 3  is an enlarged view of a piston and a structure supporting the piston in the lock-up device illustrated in  FIG. 2 . 
         FIG. 4  is an enlarged view of a damper mechanism of the lock-up device illustrated in  FIG. 2 . 
         FIG. 5  is a diagram for explaining an operating oil flow in releasing a lock-up state of the lock-up device. 
         FIG. 6  is a diagram for explaining an operating oil flow directed to a torque converter main body. 
         FIG. 7  is a diagram for explaining an operating oil flow in the lock-up state of the lock-up device. 
         FIG. 8  is a diagram illustrating a power transmission plate support member according to another exemplary embodiment of the present invention. 
         FIG. 9  is an enlarged view of a piston and a structure for supporting the piston according to yet another exemplary embodiment of the present invention. 
         FIG. 10  is a diagram illustrating a mechanism for piston actuation according to further yet another exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
     First Exemplary Embodiment 
     Entire Structure of Torque Converter 
       FIG. 1  is a vertical cross-sectional view of a torque converter  1  employing an exemplary embodiment of the present invention. The torque converter  1  is a device for transmitting torque from a crankshaft of an engine to an input shaft of a transmission. In  FIG. 1 , the engine (not illustrated in the drawing) is disposed on the left side, whereas the transmission (not illustrated in the drawing) is disposed on the right side. A line O-O depicted in  FIG. 1  indicates a rotary axis of the torque converter  1 . 
     The torque converter  1  mainly includes a front cover  2 , a torque converter main body composed of three types of vane wheels (an impeller  3 , a turbine  4  and a stator  5 ), and a lock-up device  6 . 
     Front Cover 
     The front cover  2  is a disc-shaped member that a center boss  8  is fixed to the inner peripheral end thereof by welding. The center boss  8  is a cylindrical member extending in the axial direction, and is inserted into a center hole bored in the crankshaft (not illustrated in the drawings). 
     It should be noted that the front cover  2  is designed to be coupled to the crankshaft of the engine through a flexible plate, although not illustrated in the drawings. In other words, a plurality of bolts  9  are fixed to the engine-side surface of the outer peripheral part of the front cover  2 , while being aligned at equal intervals in the circumferential direction. The outer peripheral part of the flexible plate is fixed to the front cover  2  by nuts screwed onto the bolts  9 . 
     An outer peripheral tubular portion  2   a  is formed in the outer peripheral part of the front cover  2 , while axially extending toward the transmission. The impeller  3  is fixed to the tip end of the outer peripheral tubular portion  2   a  by welding. As a result, the front cover  2  and the impeller  3  form a fluid chamber that operating oil is filled in the inside thereof. 
     Impeller 
     The impeller  3  is mainly composed of an impeller shell  10  and a plurality of impeller blades  11  fixed to the inside of the impeller shell  10 . Further, as described above, the outer peripheral tip end of the impeller shell  10  is welded to the front cover  2 . It should be noted that a tubular portion is formed on the inner peripheral end of the impeller shell  10 , while extending toward the transmission. 
     Turbine 
     The turbine  4  is disposed axially in opposition to the impeller  3  within the fluid chamber. The turbine  4  is mainly composed of a turbine shell  14 , a plurality of turbine blades  15  fixed to the inside of the turbine shell  14 , and a turbine hub  16  fixed to the inner peripheral end part of the turbine shell  14 . The turbine shell  14  and the turbine hub  16  are fixed by a plurality of rivets  17 . 
     The turbine hub  16  has, a disc-shaped flange portion  16   a  to which the inner peripheral end part of the turbine shell  14  is fixed, and a tubular portion  16   b  formed to extend from the inner peripheral part of the flange portion  16   a  toward the front cover  2 . Further, as described above, the turbine shell  14  is fixed to the outer peripheral end part of the flange portion  16   a  by the rivets  17 . Yet further, a spline hole  16   c  is bored in the inner peripheral part of the tubular portion  16   b , and is meshed with a spline shaft formed on the tip end of the input shaft  18  of the transmission. 
     It should be noted that a thrust washer  19  is disposed between the front cover  2  and the tip end of the tubular portion  16   b  of the turbine hub  16 . A plurality of grooves are formed on the turbine-hub- 16  side surface of the thrust washer  19  to penetrate from the inner periphery to the outer periphery. These grooves function as lubricating grooves and oil paths. 
     Stator 
     The stator  5  is a mechanism disposed between the inner peripheral part of the impeller  3  and that of the turbine  4 , and regulates the flow of the operating oil returning to the impeller  3  from the turbine  4 . The stator  5  is integrally formed by forging of resin, aluminum alloy or so forth. The stator  5  is mainly composed of a stator shell  20  formed in an annular shape and a plurality of stator blades  21  formed on the outer peripheral surface of the stator shell  20 . The stator shell  20  is coupled to a stationary shaft  23  through a one-way clutch  22 . 
     It should be noted that an annular recessed portion  20   a  is formed on the front-cover- 2  side surface of the stator shell  20  to be positioned in opposition to the rivets  17 . This recessed portion  20   a  is formed for avoiding interference with the head portions of the rivets  17 . Accordingly, the stator shell  20  and the flange portion  16   a  of the turbine hub  16  can be axially disposed closer to each other, and reduction in axial dimension is enabled. Further, the recessed portion  20   a  partially has a plurality of recesses  20   b  recessing toward the impeller  3 . Accordingly, weight reduction can be achieved. 
     Further, a thrust bearing is disposed between the stator shell  20  and the impeller shell  10 , while another thrust bearing is disposed between the stator shell  20  and the flange portion  16   a  of the turbine hub  16 . 
     Lock-up Device 
     The lock-up device  6  is a device disposed between the front cover  2  and the turbine  4 , and directly transmits power from the front cover  2  to the turbine  4 . The lock-up device  6  includes a clutch part  24  disposed between the front cover  2  and the turbine  4 , and a damper mechanism  25  configured to transmit torque from the clutch part  24  to the turbine. 
     Clutch Part 
     The clutch part  24  is of a hydraulic actuated multi-plate type including a plurality of clutch plates. The clutch part  24  is configured to transmit torque from the front cover  2  to the damper mechanism  25  or block transmission of torque between the front cover  2  and the damper mechanism  25 . As illustrated in an enlarged view of  FIG. 2 , the clutch part  24  includes a clutch input member  26 , a clutch output member  27 , a first clutch plate  28 , a second clutch plate  29  and a piston  30 . 
     The clutch input member  26  is an annular plate member, and is fixed to the front cover  2 . The inner peripheral end part of the clutch input member  26  is bent toward the turbine  4 , and a plurality of grooves are formed on the bent part while being aligned at predetermined intervals in the circumferential direction. 
     The clutch output member  27  is disposed radially outward of the clutch input member  26 . The clutch output member  27  is formed in an annular shape and has a disc portion  27   a  formed in a disc shape, and a tubular portion  27   b  formed to extend from the inner peripheral end part of the disc portion  27   a  toward the front cover  2 . The disc portion  27   a  is fixed to a power transmission plate (to be described) composing a part of the damper mechanism  25  by rivets  32 . A plurality of grooves are formed on the tubular portion  27   b  to extend in the axial direction, while being aligned at equal intervals in the circumferential direction. 
     The first clutch plate  28  is formed in a disc shape, and a plurality of teeth are formed on the inner peripheral end of the first clutch plate  28  to be engaged with the plural grooves formed on the bent part of the clutch input member  26 . With such structure, the first clutch plate  28  is axially movable with respect to and non-rotatable relatively to the clutch input member  26 . 
     The second clutch plate  29  is disposed adjacently to the first clutch plate  28 , while being disposed between the first clutch plate  28  and the clutch input member  26 . The second clutch plate  29  is formed in a disc shape, and a plurality of teeth are formed on the outer peripheral end of the second clutch plate  29  to be engaged with the plural grooves formed on the tubular portion  27   b  of the clutch output member  27 . With such structure, the second clutch plate  29  is axially movable with respect to and non-rotatable relative to the clutch output member  27 . Further, annular friction members are respectively fixed to the both surfaces of the second clutch plate  29 . 
     The piston  30  is disposed radially inward of the clutch output member  27 , while being disposed between the front cover  2  and the inner peripheral part of the turbine  4 . The piston  30  is formed in an annular shape and has a pressure receiving portion  30   a  formed in a disc shape and a pressing portion  30   b  formed on the outer peripheral part of the pressure receiving portion  30   a . The pressure receiving portion  30   a  is configured to be axially moved by hydraulic pressure acting on the front-cover- 2  side surface thereof and that acting on the turbine- 4  side surface thereof. The pressing portion  30   b  extends from the pressure receiving portion  30   a  toward both of the front cover  2  and the turbine  4 . The pressing portion  30   b  is configured to be moved toward the front cover  2  and press the first clutch plate  28  and the second clutch plate  29  between the pressing portion  30   b  and the clutch input member  26 . 
     The piston  30  is supported by a piston support mechanism  34  to be axially movable. The piston support mechanism  34  includes a support boss  35 , a first flange  36  formed in a disc shape and a second flange  37  formed in a disc shape. As described below, the first flange  36  is a plate member composing a part of a lock-up releasing oil chamber. The second flange  37  is a plate member composing a part of a lock-up oil chamber. 
     The support boss  35  is formed in an annular shape, and the tubular portion  16   b  of the turbine hub  16  is inserted in the inside of the support boss  35 . Further, the inner peripheral part of the front-cover- 2  side surface of the support boss  35  is fixed to the front cover  2  by welding. A first seal member  38  and a second seal member  39  are mounted to the outer peripheral surface of the support boss  35 . Further, the inner peripheral surface of the piston  30  slidably makes contact with the second seal member  39 . Yet further, a small diameter portion  35   a , having a diameter less than that of the other part, is formed on the turbine- 4  side part of the outer peripheral surface of the support boss  35 . This small diameter portion  35   a  further protrudes toward the turbine  4  than the turbine- 4  side lateral surface of the support boss  35 , and the protruding part is formed as a protruding portion  35   b  (in the drawings, the protruding portion  35   b  is illustrated in an outwardly bent state). 
     The first flange  36  is disposed on the front-cover- 2  side of the pressure receiving portion  30   a  of the piston  30 , while being fixed to the front cover  2  by swaging a protruding part formed on the front cover  2 . It should be noted that a clearance is produced for circulating the operating oil between the first flange  36  and the front cover  2  except for the part that the both members are fixed to each other. A third seal member  40  is mounted to the outer peripheral surface of the first flange  36 , while making contact with the inner peripheral surface of the pressing portion  30   b  of the piston  30 . The inner peripheral surface of the first flange  36  makes contact with the first seal member  38  mounted to the outer peripheral surface of the support boss  35 . 
     The second flange  37  is disposed on the turbine- 4  side of the pressure receiving portion  30   a  of the piston  30 . A fourth seal member  41  is mounted to the outer peripheral surface of the second flange  37 , while making contact with the inner peripheral surface of the pressing portion  30   b  of the piston  30 . The inner peripheral surface of the second flange  37  is press-fitted to the small diameter portion  35   a  of the support boss  35  and is further swaged by outwardly bending the protruding portion  35   b  by rolling. 
     Structure for Moving Piston 
     As illustrated in  FIG. 2  and  FIG. 3 , which is a partial enlarged view of  FIG. 2 , the piston support mechanism  34  as described above forms the lock-up releasing oil chamber  45  between the pressure receiving portion  30   a  and the first flange  36 , while forming the lock-up oil chamber  46  between the pressure receiving portion  30   a  and the second flange  37 . The inner and outer diameters of the oil chamber  45  and those of the oil chamber  46  are equal to each other. 
     A plurality of first oil paths  51  are formed in the tubular portion  16   b  of the turbine hub  16 , while radially penetrating therethrough. Further, a plurality of second oil paths  52 , a plurality of third oil paths  53  and a plurality of fourth oil paths  54  are formed in the support boss  35 . The second oil paths  52  are formed to radially penetrate through the support boss  35 . Thus, the inner peripheral side of the support boss  35  and the lock-up releasing oil chamber  45  are communicated with each other through the second oil paths  52 . The third oil paths  53  are formed to radially penetrate through the support boss  35 . Thus, the inner peripheral surface of the support boss  35  and the lock-up oil chamber  46  are communicated with each other through the third oil paths  53 . The fourth oil paths  54  are formed to axially penetrate through the support boss  35 . Thus, a space produced on the turbine- 4  side of the support boss  35  and a space produced on the front-cover- 2  side of the support boss  35  are communicated with each other through the fourth oil paths  54 . 
     An annular groove  16   d  is formed on the inner peripheral surface of the tubular portion  16   b  of the turbine hub  16 , whereas an annular recess  16   e  is formed on the outer periphery of the tip end of the tubular portion  16   b . The inner peripheral openings of the first oil paths  51  are located in the bottom surface of the groove  16   d . The inner peripheral openings of the second oil paths  52  are bored to be located in opposition to the recess  16   e.    
     An annular groove  35   c  is formed on the inner peripheral surface of the support boss  35 . The inner peripheral openings of the third oil paths  53  are located in the bottom surface of the groove  35   c . Further, an annular recess  35   d  is formed on the inner peripheral end part of the turbine- 4  side surface of the support boss  35 , while recessing toward the front cover  2 . The recess  35   d  functions as an oil sump part. 
     The turbine- 4  side openings of the fourth oil paths  54  are located in the recess  35   d , whereas the front-cover- 2  side openings of the fourth oil paths  54  are located in the space produced between the front cover  2  and the end surface of the support boss  35 . It should be noted that a plurality of through holes  55  are bored in the inner peripheral end part of the flange portion  16   a  of the turbine hub  16 , while axially penetrating therethrough. The plural through holes  55  are opposed to the recess  35   d  of the support boss  35 . 
     A collar  56  is press-fitted to the inner peripheral part of the tubular portion  16   b  of the turbine hub  16 . A plurality of through holes  57  are bored in the collar  56 , while radially penetrating therethrough. An annular groove  56   a  is formed on the inner peripheral surface of the collar  56 . The outer peripheral openings of the through holes  57  of the collar  56  are opposed to the groove  16   d  formed on the inner surface of the tubular portion  16   b  of the turbine hub  16 . 
     Damper Mechanism 
     As illustrated in  FIG. 4 , the damper mechanism  25  includes a power transmission plate (an input-side member)  61  to which the clutch output member  27  is fixed, an output plate (an output-side member)  62  fixed to the turbine shell  14 , a plurality of torsion springs  63 , an intermediate member  64 , and a restriction plate  65 . It should be noted that  FIG. 4  illustrates only the damper mechanism  25  and the related components thereof, which are extracted from the lock-up device  6 . 
     The power transmission plate  61  is formed in an annular shape and has a disc portion  61   a , an engaging portion  61   b  formed on the outer peripheral end of the disc portion  61   a , and an inner peripheral tubular portion  61   c  formed on the inner peripheral end of the disc portion  61   a  to extend toward the front cover  2 . As described above, the clutch output member  27  is fixed to the disc portion  61   a  by the rivets  32 . The engaging portion  61   b  is engaged with the circumferential end surfaces of the torsion springs  63 . 
     The output plate  62  is engaged with the both circumferential ends of each pair of torsion springs  63  (two torsion springs  63  in the present exemplary embodiment) configured to act in series. Accordingly, the torque inputted from the power transmission plate  61  is transmitted to the output plate  62  through the torsion springs  63 , and is further transmitted to the turbine  4 . 
     The intermediate member  64  is a member for causing each pair of (two) torsion springs in the plural torsion springs  63  to act in series. The intermediate member  64  is formed in an annular shape and has a cross-section formed in an inverted L-shape. The intermediate member  64  is disposed on the outer peripheral side of the clutch output member  27 , and has an inner peripheral end portion  64   a , a lateral support portion  64   b  and an outer support portion  64   c.    
     The inner peripheral end portion Ma extends to the inner peripheral side along the disc portion  61   a  of the power transmission plate  61 . The inner peripheral surface of the inner peripheral end portion  64   a  is contactable to the outer peripheral surface of the clutch output member  27 . Accordingly, the intermediate member  64  is radially positioned. Further, the turbine- 4  side surface of the inner peripheral end portion Ma is contactable to the disc portion  61   a  of the power transmission plate  61 . Accordingly, the intermediate member  64  is restricted from moving toward the turbine  4 . The lateral support portion  64   b  extends to the outer peripheral side from the inner peripheral end portion  64   a , and supports the front-cover- 2  side lateral parts of the torsion springs  63 . Further, pawls (not illustrated in the drawings) are formed to extend from the lateral support portion  64   b  toward the turbine  4 , and support the end surfaces of each pair of torsion springs  63 . The outer support portion  64   c  extends from the outer peripheral end of the lateral support portion  64   b  toward the turbine  4 , and supports the outer peripheral parts of the torsion springs  63 . 
     The restriction plate  65  is formed by a plate with a plate thickness less than that of the intermediate member  64 . The restriction plate  65  is formed in an annular shape, and has a fixation portion  65   a  and an axial restriction portion  65   b.    
     The fixation portion  65   a  is formed in a disc shape, and is fixed to the clutch output member  27  and the power transmission plate  61  by the rivets  32 . The axial restriction portion  65   b  is formed to extend from the fixation portion  65   a  to the outer peripheral side, and is contactable to the front-cover- 2  side surface of the lateral support portion  64   b  of the intermediate member  64 . Accordingly, the intermediate member  64  is restricted from moving toward the front cover  2 . 
     With the structure as described above, the intermediate member  64  is radially positioned by the outer peripheral surface of the clutch output member  27 . Further, the intermediate member  64  is axially positioned by the power transmission plate  61  and the restriction plate  65 . 
     Positioning Structure for Power Transmission Plate 
     As illustrated in  FIG. 4 , a power transmission plate support member  68  is mounted to the inner peripheral side of the power transmission plate  61 . The power transmission plate support member  68  is formed in an annular shape and has a fixation portion  68   a , a first axial restriction portion  68   b , a radial restriction portion  68   c  and a second axial restriction portion  68   d . The power transmission plate support member  68  is disposed on the outer peripheral side than the most inner peripheral part (i.e., a position depicted with P in  FIG. 4 ) in an operating oil outlet of the turbine  4 . 
     The fixation portion  68   a  is fixed to the turbine shell  14 , while being disposed on the outer peripheral side than the pressure receiving portion  30   a  of the piston  30 . The first axial restriction portion  68   b  is formed by partially extending the fixation portion  68   a  to the outer peripheral side. The first axial restriction portion  68   b  is contactable to the turbine- 4  side surface of the disc portion  61   a  of the power transmission plate  61 . The radial restriction portion  68   c  is formed by bending a part of the fixation portion  68   a , i.e., a part on which the first axial restriction portion  68   b  is not formed, toward the front cover  2 . The radial restriction portion  68   c  is contactable to the inner peripheral surface of the inner peripheral tubular portion  61   c  of the power transmission plate  61 . The second axial restriction portion  68   d  is a protruding portion formed on the tip end of the radial restriction portion  68   c  and protrudes to the outer peripheral side. The second axial restriction portion  68   d  is contactable to the tip end of the inner peripheral tubular portion  61   c.    
     With the structure as described above, the power transmission plate  61  and the clutch output member  27  are radially and axially positioned by the power transmission plate support member  68 . 
     Actions 
     When the lock-up state of the lock-up device  6  is released, as illustrated in  FIG. 5 , the lock-up oil chamber  46  is connected to a drain, while the operating oil is supplied to the space between the front cover  2  and the front end part of the turbine hub  16  from a control valve (not illustrated in the drawing). The operating oil is supplied to the lock-up releasing oil chamber  45  via the grooves formed on the thrust washer  19  and the recess  16   e  formed on the outer periphery of the tip end part of the turbine hub  16  and further via the second oil paths  52  of the support boss  35 . Accordingly, the piston  30  is moved toward the turbine  4 , while the pressing portion  30   b  of the piston  30  is separated away from the first clutch plate  28  and the second clutch plate  29 . 
     Further, oil for torque converter actuation is supplied from the space between the input shaft  18  of the transmission and the stationary shaft  23 . As illustrated in  FIG. 6 , the operating oil is directed to the space between the support boss  35  and the front cover  2  via the through holes  55  of the turbine hub  16  and the fourth oil paths  54 . 
     It should be noted that the recess  35   d  is formed between the through holes  55  and the fourth oil paths  54 . Hence, the operating oil, supplied to the support boss  35  side through the through holes  55 , is once accumulated in the recess  35   d , and is then directed toward the fourth oil paths  54 . Therefore, even when the through holes  55  and the fourth oil paths  54  are not axially aligned with each other, the operating oil smoothly flows between these oil paths  55  and  54 . 
     The operating oil, supplied to the space between the support boss  35  and the front cover  2 , is directed to the outer peripheral side through the clearance produced between the front cover  2  and the first flange  36 , and is further directed to the outer peripheral end part of the front cover  2  through the spaces among the first clutch plate  28 , the second clutch plate  29  and the piston  30 . Thereafter, the operating oil is supplied to the torque converter main body. The operating oil within the torque converter main body flows to the control valve (not illustrated in the drawings) through an oil path produced between the stator shell  20  and the impeller shell  10 . 
     In the condition as described above, the torque from the front cover  2  is transmitted from the impeller  3  to the turbine  4  by the operating oil, and is further transmitted to the input shaft  18  of the transmission. 
     By contrast, when the lock-up device is turned into a lock-up state (power transmitted state), the lock-up releasing oil chamber  45  is connected to the drain, while the operating oil is supplied to the inner periphery of the collar  56  through the inside of the input shaft  18  as illustrated in  FIG. 7 . The operating oil is supplied to the lock-up oil chamber  46  through the sequential path of: the through holes  57  of the collar  56 ; the first oil paths  51 ; and the third oil paths  53 . Accordingly, the piston  30  is moved toward the front cover  2 , and the first clutch plate  28  and the second clutch plate  29  are pressed against each other. 
     In the condition as described above, the torque from the front cover  2  is transmitted to the damper mechanism  25  through the sequential path of the clutch input member  26 , the first clutch plate  28  and the second clutch plate  29 , and the clutch output member  27  in this order. 
     In the damper mechanism  25 , the torque inputted into the power transmission plate  61  from the clutch part  24  is transmitted to the turbine  4  through the torsion springs  63  and the output plate  62 , and is further transmitted to the input shaft  18  of the transmission through the turbine hub  16 . 
     In the lock-up device  6  as described above, the power transmission plate  61  is radially and axially positioned by the power transmission plate support member  68 . Further, the intermediate member  64  is restricted from radially moving, while being positioned by the clutch output member  27 . Yet further, the intermediate member  64  is restricted from axially moving, while being positioned by the restriction plate  65  and the power transmission plate  61 . 
     Features 
     The power transmission plate  61  can be radially and axially positioned by the single power transmission plate support member  68 , and therefore, the present device can be simply structured. 
     The power transmission plate support member  68  is fixed to the turbine shell  14 . Hence, a space for disposing one or more other members can be reliably produced between the turbine inner peripheral part and the front cover  2 . In the present exemplary embodiment, members for composing the piston  30  and the oil chambers of the lock-up device are disposed in the space. Therefore, the device can be entirely reduced in the axial dimension thereof. 
     The lock-up state is produced by fixing the clutch input member  26  of the clutch part  24  to the front cover and by moving the piston  30  from the turbine- 4  side to the front-cover- 2  side. Therefore, the device can be reduced in the axial dimension thereof in comparison with a structure that the lock-up state is produced by moving the piston disposed on the front cover side to the turbine side. 
     The clutch output member  27  restricts the intermediate member  64  from radially moving. Hence, it is possible to reduce a space occupied by the lock-up device  6 . Further, the restriction plate  65  with a relatively small thickness and the power transmission plate  61  restrict the intermediate member  64  from axially moving. Hence, axial space saving can be further achieved. Especially, the axial space of a clutch part of a multi-plate type tends to be elongated. Hence, the axial space can be inhibited from being elongated with use of the structure of the present exemplary embodiment. 
     The piston  30  is configured to be moved by supplying the operating oil to the lock-up releasing oil chamber  45  and the lock-up oil chamber  46 , and accordingly, the lock-up state and the lock-up released state are configured to be switched back and forth. Therefore, better responsiveness can be obtained in switching between the states. Further, drag torque can be suppressed in releasing the lock-up state. 
     The lock-up oil chamber  46  is provided independently from the other operating oil circuit. Therefore, stable lock-up torque capacity can be obtained in comparison with a structure configured to produce the lock-up state by utilizing the operating oil to be supplied to the torque converter main body. 
     The inner and outer diameters of the lock-up releasing oil chamber  45  and those of the lock-up oil chamber  46  are equal to each other. Hence, while the operating oil is not being supplied to any of the oil chambers, hydraulic pressures to be produced in the both oil chambers  45  and  46  are equalized by centrifugal force. Therefore, the piston  30  can be maintained in a neutral position. 
     Second Exemplary Embodiment 
       FIG. 8  illustrates another exemplary embodiment of a power transmission plate support member. This power transmission plate support member  70  is composed of a first plate  71  and a second plate  72 . 
     The first plate  71  is formed in an annular shape, and is composed of a fixation portion  71   a , an first axial restriction portion  71   b , a radial restriction portion  71   c  and a second plate support portion  71   d . The structures of the fixation portion  71   a , the first axial restriction portion  71   b  and the radial restriction portion  71   c  are the same as those of the fixation portion  68   a , the first axial restriction portion  68   b  and the radial restriction portion  68   c  in the power transmission plate support member  68  of the first exemplary embodiment. The second plate support portion  71   d  is formed by bending the radial restriction portion  71   c  to the inner peripheral side. 
     The second plate  72  is formed in a disc shape, and the inner peripheral part thereof is fixed to the second plate support portion  71   d  of the first plate  71  by spot welding or so forth. The outer peripheral part of the second plate  72  is disposed to protrude from the radial restriction portion  71   c  of the first plate  71  to the further outer peripheral side. Further, the tip end of the tubular portion  61   c  of the power transmission plate  61  is configured to be contactable to the second plate  72 . In other words, the second plate  72  functions as a second axial restriction portion. 
     With the structure as described above, the power transmission plate  61  and the clutch output member  27  are radially and axially positioned by the first and second plates  71  and  72  composing the power transmission plate support member  70 . 
     Third Exemplary Embodiment 
       FIG. 9  illustrates another exemplary embodiment of the structure for moving the piston. In this exemplary embodiment, a piston support member  75  is mounted to the outer peripheral surface of a tubular portion  16   b ′ of a turbine hub  16 ′. 
     The piston support member  75  is disposed between the front cover  2  and the turbine  4 , and is composed of a disc portion  75   a  functioning as a plate composing a part of a lock-up oil chamber, and a tubular portion  75   b . The outer peripheral part of the disc portion  75   a  extends to reach the first clutch plate  28  and the second clutch plate  29 . The tubular portion  75   b  extends from the inner peripheral end part of the disc portion  75   a  toward the front cover  2 . The tubular portion  16   b ′ of the turbine hub  16 ′ is inserted into the inside of the tubular portion  75   b . Further, the tip end of the tubular portion  75   b  is fixed to the front cover  2  by welding or so forth. 
     A piston  30 ′ is disposed between the front cover  2  and the disc portion  75   a  of the piston support member  75 . The piston  30 ′ has a pressure receiving portion  30   a ′ formed in a disc shape and a pressing portion  30   b ′. The inner peripheral surface of the pressure receiving portion  30   a ′ is slidably supported by the outer peripheral surface of the tubular portion  75   b  of the piston support member  75 . The pressing portion  30   b ′ is formed on the outer peripheral part of the pressure receiving portion  30   a ′ and is capable of pressing the first clutch plate  28  and the second clutch plate  29 . 
     First oil paths  76  and second oil paths  77  are formed in the tubular portion  75   b  of the piston support member  75 . The first oil paths  76  are formed such that the front-cover- 2  side space of the piston  30 ′ and the turbine- 4  side space of the piston support member  75  are communicated with each other. Further, the turbine hub  16 ′ has through holes  55 ′ formed for supplying the operating oil from the control valve to the space produced between the piston  30 ′ and the turbine  4 . The second oil paths  77  are formed such that oil paths (not illustrated in the drawing) formed in the tubular portion  16   b ′ of the turbine hub  16 ′ and a space (lock-up oil chamber)  78  produced between the piston  30 ′ and the disc portion  75   a  of the piston support member  75  are communicated with each other. 
     In the present exemplary embodiment, when the lock-up state of the lock-up device  6  is released, the lock-up oil chamber  78  is configured to be connected to the drain and the operating oil from the control valve is configured to be supplied to the front-cover- 2  side space of the piston  30 ′ via the through holes  55 ′ and the first oil paths  76 . 
     Accordingly, the piston  30 ′ is moved toward the turbine  4 , and the pressing portion  30   b ′ of the piston  30 ′ is separated away from the first clutch plate  28  and the second clutch plate  29 . It should be noted that as with the aforementioned exemplary embodiment, the operating oil, supplied to the front-cover- 2  side space of the piston  30 ′, is directed to the outer peripheral end part of the front cover  2 , and is then supplied to the inside of the torque converter main body. 
     In the condition as described above, torque from the front cover  2  is transmitted from the impeller  3  to the turbine  4  through the operating oil, and is further transmitted to the input shall  18  of the transmission. 
     By contrast, when the lock-up state is produced, the operating oil is configured to be supplied to the lock-up oil chamber  78  via the oil paths formed in the tubular portion  16   b ′ of the turbine hub  16 ′ and the second oil paths  77 . 
     Accordingly, the piston  30 ′ is moved toward the front cover  2 , and the first clutch plate  28  and the second clutch plate  29  are pressed against each other. 
     In the condition as described above, the torque from the front cover  2  is transmitted to the damper mechanism  25  through the path of the clutch input member  26 , the first clutch plate  28  and the second clutch plate  29 , and the clutch output member  27 . 
     Fourth Exemplary Embodiment 
       FIG. 10  illustrates yet another exemplary embodiment. Here, a cone spring  80  is disposed in the lock-up releasing oil chamber  45  of the first exemplary embodiment. The other structures are similar to those of the first exemplary embodiment. 
     The cone spring  80  is mounted for urging the piston  30  toward the turbine  4 . In this case, in producing the lock-up released state, the lock-up state can be released only by supplying a low hydraulic pressure to the lock-up releasing oil chamber  45 . Further, chances are that some load settings of the cone spring  80  eliminate necessity of supplying the operating oil for releasing the lock-up state. 
     Other Exemplary Embodiments 
     The present invention is not limited to the exemplary embodiments as described above, and a variety of changes or modifications can be made without departing from the scope of the present invention. 
     According to the lock-up device of the present invention, a mechanism for restricting an intermediate member can be implemented with a smaller space in a lock-up device equipped with a clutch part of a multi-plate type that a piston and a damper mechanism are disposed in positions away from each other.