Lockup device for fluid-type torque transmission device

A lockup device 7 having a dual friction surface to make it possible to arrange a friction coupling part on the outside with respect to the radial direction is provided. The lockup device 7 has a clutch plate 71, a drive plate 72, a driven plate 73, a plurality of torsion springs 74, a spring holder 80, a piston 75, and a piston coupling mechanism 76. The piston 75 radially extends to the position of a friction coupling part 71c of the clutch plate 71. The mounting radius of the torsion springs 74 is shorter than a radius extending to the radial position of the outer circumferential edge of the piston 75 or the friction coupling part 71c. The protrusions 72d of the drive plate 72 mate with the recessions 71e of the clutch plate 71 at a radial position that is farther from the rotational axis than mounting radius of the torsion springs 74.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a lockup device for a fluid-type torque transmission device. More specifically, the present invention relates to a lockup device provided in a fluid-type torque transmission device equipped with a front cover having a friction surface, an impeller that is fixed to the front cover and forms a fluid chamber, and a turbine arranged opposite the impeller inside the fluid chamber.

2. Background Information

A conventional torque converter has three types of bladed wheels (an impeller, a turbine, and a stator) arranged therein. A torque converter represents one type of fluid-type torque transmission device because it transmits torque through fluid enclosed therein. A torque converter is often provided with a lockup device. The lockup device is usually disposed in the space between the turbine and a front cover, which form a fluid chamber of the torque converter. The lockup device is a mechanism that serves to couple mechanically the front cover and the turbine together such that torque can be transmitted directly from the front cover to the turbine. Normally, the lockup device has a circular disc shaped piston, a drive plate, a driven plate, and a torsion spring. The piston can be pressed against the front cover. The drive plate is fixed to an outer circumferential part of the piston. The driven plate is fixed to the turbine. The torsion spring serves to couple elastically the drive plate and the driven plate together in the rotational direction.

When the lockup device is engaged, torque is transmitted from the front cover to the piston and from the piston to the turbine through the torsion spring. The torsion spring is compressed in the rotational direction between the drive plate and the driven plate and acts to absorb and damp torsional vibrations.

There have already been proposals for such a lockup device that has a plurality of friction surfaces to increase the torque transmission capacity. One such device has a drive plate, a driven plate, a plurality of torsion springs, and a piston. The drive plate is provided with a friction coupling part. The driven plate is joined together with the turbine. The plurality of torsion springs elastically couple the drive plate and driven plate together in the rotational direction. The piston presses the friction coupling part against the front cover. Here, the driven plate holds the outside circumference and rotationally facing ends of the torsion springs. The drive plate has an abutting part for abutting against the rotationally facing end parts of the torsion springs so that it can compress the torsion springs in the rotational direction. The friction coupling part of the drive plate is disposed axially between the piston and the front cover.

In this lockup device, the drive plate is an annular plate having the friction coupling part and abutting part formed integrally thereon. The abutting part of the drive plate is arranged such that it can abut against the torsion springs in the vicinity of the mounting radius of the torsion springs. Meanwhile, the friction coupling part of the drive plate must be arranged at a position that is more inward in the radial direction than the position of the abutting part because the friction coupling part is sandwiched axially between the piston and the front cover. Consequently, the friction coupling part cannot be positioned on the radially outside portion of the drive plate. Thus, the torque transmission capacity of the lockup device cannot be increased.

When such a lockup device is in the engaged state, torque is transmitted from the front cover to the drive plate and from the drive plate to the turbine through the torsion springs. In this state, the torsion springs are compressed in the rotational direction of the torque converter between the drive plate and the driven plate and act to absorb and damp torsional vibrations. The torsion springs also move radially outward due to centrifugal force and slide against the driven plate, which holds the torsion springs. Consequently, wearing of the torsion springs and the driven plate becomes a problem.

In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved lockup device for a fluid-type torque transmission device that overcomes the aforementioned problems. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.

SUMMARY OF THE INVENTION

The object of the present invention is to make it possible to arrange the friction coupling part on the outside with respect to the radial direction in a lockup device having a dual friction surface. Another object of the present invention is to reduce sliding of the torsion springs against other members in a lockup device.

A lockup device for a fluid-type torque transmission device in accordance with a first aspect of a preferred embodiment of the present invention is equipped with a front cover, an impeller, and a turbine. The front cover has a friction surface. The impeller is fixed to the front cover and forms a fluid chamber therewith. The turbine is arranged opposite the impeller inside the fluid chamber. The lockup device is equipped with a clutch member, a piston, a plurality of elastic members, a drive member, and a driven member. The clutch member has a friction coupling part that can be pressed against the friction surface of the front cover. The piston is arranged between the front cover and the turbine and presses the friction coupling part against the friction surface. The elastic members are arranged in the rotational direction. The drive member has an abutting part and a mating member. The abutting part abuts against rotationally facing ends of the elastic members in such a manner that torque can be transmitted. The mating member is positioned farther outward in the radial direction than the abutting part and mates with the clutch member in such a manner that the drive member cannot rotate relative to the clutch member. The driven member is fixed to the turbine and receives torque from the plurality of elastic members.

In this lockup device, the clutch member has a friction coupling part. The drive member has an abutting part and a mating part. The abutting part abuts against the rotationally facing ends of the elastic members in such a manner that torque can be transmitted. The mating part is positioned farther outward in the radial direction than the abutting part and mates with the clutch member in such a manner that the drive member cannot rotate relative to the clutch member. As a result, the mating part of the drive member can be arranged on the outside with respect to the radial direction and the friction coupling part of the clutch member can be arranged on the outside with respect to the radial direction.

A lockup device for a fluid-type torque transmission device in accordance with a second aspect of the present invention is the transmission device of the first aspect, wherein, the clutch member is an annular plate and the outside radius of the clutch member is larger than a mounting radius of the elastic members.

With this lockup device the friction coupling part of the clutch member can be positioned even further to the outside because the outer circumferential portion of the clutch member is positioned further to the outside than a mounting radius of the elastic members.

A lockup device for a fluid-type torque transmission device in accordance with a third aspect of the present invention is the transmission device of the first or second aspects, wherein the drive member has an annular part, a plurality of mating parts and a plurality of abutting parts. The plurality of mating parts is formed on the outside edge of the annular part and extends radially outward. The plurality of abutting parts is formed on an inner circumferential section of the annular part and extends in the axial direction.

A lockup device for a fluid-type torque transmission device in accordance with a fourth aspect of the present invention is the transmission device of any one of the first to third aspects, wherein the drive member is positioned in the axial and radial directions by the driven member. With this lockup device, the axial and radial positioning of the drive member is stable because the drive member is positioned in the axial and radial directions by the driven member.

A lockup device for a fluid-type torque transmission device in accordance with a fifth aspect of the present invention is the transmission device of the fourth aspect, wherein the driven member has a first driven member and a second driven member. The first driven member is fixed to the turbine. The second driven member is fixed to the first driven member and serves to position the drive member in the axial and radial directions.

A lockup device for a fluid-type torque transmission device in accordance with a sixth aspect of the present invention is the transmission device of any one of the first to fifth aspects, wherein the driven member limits the rotation of the drive member to a prescribed angular range when the drive member rotates relative to the driven member. With this lockup device, any desired torsional characteristic can be obtained because the compression of the elastic members disposed between the drive member and the driven member can be limited to a prescribed angular range.

A lockup device for a fluid-type torque transmission device in accordance with a seventh aspect is equipped with a front cover having a friction surface, an impeller that is fixed to the front cover and forms a fluid chamber therewith, and a turbine arranged opposite the impeller inside the fluid chamber. The lockup device is equipped with a clutch member, a plurality of elastic members, a drive member, a driven member, an intermediate member, and a piston. The clutch member has a friction coupling part that can be pressed against the friction surface of the front cover. The elastic members are arranged in the rotational direction. The drive member mates with the clutch member such that it cannot rotate relative to the clutch member and can transmit torque to the plurality of elastic members. The driven member is fixed to the turbine and receives torque from the plurality of elastic members. The intermediate member supports at least the radially outward facing side of each of the elastic members and can rotate relative to the driven member and drive member. The piston is arranged between the front cover and the turbine and serves to press the friction coupling part against the friction surface.

With this lockup device, the elastic members are compressed in the rotational direction when the drive member and driven member rotate relative to each other. When this occurs, the elastic members do move radially outward, but it is difficult for the elastic members to slide against the drive member and driven member because each of the elastic members is supported by the intermediate member on at least its radially outward facing side and one axially facing side. Consequently, wear of the elastic members, drive member, and driven member can be reduced.

A lockup device for a fluid-type torque transmission device in accordance with a eighth aspect of the present invention is the transmission device of the seventh aspect, wherein the plurality of elastic members has a plurality of pairs of elastic members arranged such that the elastic members operate in series in the rotational direction. The intermediate member has a transmitting part arranged between each pair of elastic members. With this lockup device, torsional vibration absorbing performance can be achieved similar to that obtained with elastic members that are relatively long in the rotational direction because the plurality of elastic members acts in series.

A lockup device for a fluid-type torque transmission device in accordance with a ninth aspect of the present invention is the transmission device of the seventh or eighth aspects, wherein the intermediate member is positioned in the radial direction by the driven member. With this lockup device, the radial positioning of the intermediate member is stable because the intermediate member is positioned by the driven member in the radial direction.

A lockup device for a fluid-type torque transmission device in accordance with a tenth aspect of the present invention is the transmission device of any one of the seventh to ninth aspects, wherein the intermediate member is positioned in the axial direction by the driven member. With this lockup device, the axial positioning of the intermediate member is stable because the intermediate member is positioned by the driven member in the axial direction.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring initially toFIG. 1, a torque converter1having a lockup device7is illustrated in accordance with a first embodiment of the present invention. The embodiment of the present invention is described below based on the drawings.

(1) Basic Structure of Torque Converter

FIG. 1shows a vertical cross-sectional schematic view of the torque converter1in accordance with a preferred embodiment of the present invention. The torque converter1serves to transmit torque from a crankshaft2of an engine to an input shaft3of a transmission. The engine, which is not shown in the figures, is arranged on the left side of FIG.1and the transmission, which is also not shown, is arranged on the right side of FIG.1. The line O—O shown inFIG. 1is the rotational axis of the torque converter1.

The torque converter1chiefly has a flexible plate4and a torque converter main body5. The flexible plate4is made of a relatively thin, circular disc-shaped member and serves both to transmit torque and to absorb bending vibrations transmitted to the torque converter main body5from the crankshaft2. Therefore, the flexible plate4is provided with sufficient rigidity in the rotational direction for transmitting torque but its rigidity is relatively low in the bending or axial direction.

The torque converter main body5is equipped with a front cover11to which an outer circumferential part of the flexible plate4is fixed. The torque converter main body5also has three types of bladed wheels (an impeller21, a turbine22, and a stator23) and the lockup device7. A fluid chamber defined by the front cover11and the impeller21is filled with a fluid and divided into a fluid operating chamber6and an annular space8. The fluid operating chamber6is torus shaped and defined by the impeller21, the turbine22, and the stator23. The lockup device7is disposed in the annular space8.

The front cover11is a circular disc-shaped body having a roughly cylindrical center boss16that extends in the axial direction. The center boss16is fixed to an inside circumferential part of the front cover11by welding or the like. The center boss16is inserted into a center hole of the crankshaft2.

An outer cylindrical part11athat extends axially toward the transmission is formed on an outer circumferential part of the front cover11. The outer circumferential rim of an impeller shell26of the impeller21is fixed to the tip of the outer cylindrical part11aby welding or the like. The front cover11and the impeller21form a fluid chamber the inside of which is filled with fluid. The impeller21chiefly has the impeller shell26, a plurality of impeller blades27, and an impeller hub28. The impeller blades27are fixed to the inside of the impeller shell26. The impeller hub28is fixed by welding or the like to an inner circumferential part of the impeller shell26.

The turbine22is arranged inside the fluid chamber so as to face the impeller21in the axial direction. The turbine22chiefly has a turbine shell30, a plurality of turbine blades31, and a turbine hub32. The turbine blades31are fixed to the surface of the turbine shell30that axially faces the impeller21. The turbine hub32is fixed to the inner circumferential rim of the turbine shell30. The turbine hub32includes a flange part32aand a boss part32b. The turbine shell30and the turbine hub32, as well as a driven plate73(discussed later), are preferably fixed together with a plurality of rivets33at the flange part32aof the turbine hub32. Splines that mate with the input shaft3are formed on the internal surface of the boss part32bof the turbine hub32. Thus, the turbine hub32is made to rotate integrally with the input shaft3.

The stator23is installed axially between an inner circumferential part of the impeller21and an inner circumferential part of the turbine22. The stator23serves to redirect the flow of the fluid returning to the impeller21from the turbine22. The stator23is preferably made of resin or aluminum alloy that has been cast as a single unit. The stator23chiefly has a ring-shaped stator carrier35and a plurality of stator blades36provided on the outer circumferential surface of the stator carrier35. The stator carrier35is supported by a cylindrical stationary shaft39with a one-way clutch37disposed therebetween. The stationary shaft39extends axially toward the transmission between the outer circumferential surface of the input shaft3and the inner circumferential surface of the impeller hub28.

A fluid passage16athrough which fluid can pass in the radial direction is formed in the center boss16. The fluid passage16aprovides communication between the space on the inside of the center boss16that communicates with a center hole3aof the input shaft3and the space8on the outside of the center boss16. A first thrust bearing41is disposed axially between the center boss16and the turbine hub32and bears a thrusting force that is produced due to the rotation of the turbine22. A second thrust bearing42is disposed between the turbine hub32and an inner circumferential part of the stator23(more specifically, the one-way clutch37). In the section where the second thrust bearing42is provided, a first port18is formed which allows fluid to communicate in the radial direction between both sides thereof. In short, the first port18links the fluid operating chamber6with the fluid passage between the input shaft3and the stationary shaft39. There is also a third thrust bearing43disposed axially between the stator23(more specifically, the stator carrier35) and the impeller21(more specifically, the impeller hub28). In the section where the third thrust bearing43is provided, a second port19is formed which allows fluid to communicate in the radial direction between both sides thereof. In short, the second port19links the fluid operating chamber6with the fluid passage between the stationary shaft39and the impeller hub28. Also, each fluid passage is connected to a hydraulic circuit, which is not shown in the figures, and fluid can be supplied and discharged to and from each of the fluid passage16aand ports18and19independently.

(2) Structure of Lockup Device

The lockup device7is arranged in the space8between the turbine22and the front cover11and serves to couple mechanically the turbine22and the front cover11together when necessary. The lockup device7has both a clutch function and an elastic coupling function. The lockup device7chiefly has a clutch plate71(clutch member), a drive plate72(drive member), the driven plate73(driven member), a plurality of torsion springs74(elastic member), a spring holder80(intermediate member), a piston75, and a piston coupling mechanism76.FIG. 2is a cross-sectional view of the portion of the torque converter1that contains the lockup device7.FIG. 3is an exploded perspective view of the clutch plate71, the drive plate72, the driven plate73, the plurality of torsion springs74, and the spring holder80of the lockup device7.FIG. 4is an exploded perspective view of the piston75and the piston coupling mechanism76.

Driven Plate

Referring toFIGS. 2 and 3, the driven plate73has a first driven plate77and a second driven plate78. The first driven plate77is an annular plate member whose inner circumferential part is fixed along with the turbine shell30to the flange part32aof the turbine hub32with the plurality of rivets33. The first driven plate77has an annular part77a, a plurality of claw parts77b, a cylindrical part77c, and an annular part77d. The claw parts77bare formed on the outside edge of the annular part77a. The cylindrical part77cextends axially toward the transmission from the inside edge of the annular part77a. The annular part77dis formed on the end of the cylindrical part77cthat is closer to the transmission. The annular part77dhas a plurality of holes77e, a plurality of fluid holes77f, and a plurality of holes77g. The plurality of holes77eis formed in an inner circumferential part of the annular part77d. The plurality of fluid holes77fis formed to the radial outside of the holes77e. The plurality of holes77gis formed to the radial outside of the fluid holes77f. The holes77eare provided for rivets33to pass through. The fluid holes77fserve to secure the flow of fluid in both axial directions through the first driven plate77. The holes77gare used for fixing the second driven plate78with a plurality of rivets79to the first driven plate77. The cylindrical part77chas a plurality of cut-and-raised parts77hformed near the edge of the transmission side thereof so as to point radially outward. In this embodiment, there are preferably four cut-and-raised parts77harranged with equal spacing in the rotational direction. The annular part77ahas a plurality of protrusions77ithat protrude toward the transmission side of the annular part77ain the axial direction and extend in a radial manner, preferably from the cylindrical part77cto the claw parts77b. The protrusions77iare formed in pairs in positions corresponding to the circumferential spaces between the cut-and-raised parts77h. Similarly to the protrusions77i, the claw parts77bare also formed in positions corresponding to the circumferential spaces between the cut-and-raised parts77h. Thus, in this embodiment, there are preferably four claw parts77barranged with equal spacing in the rotational direction. The claw parts77bhave a C-shaped cross section that protrudes toward the transmission in the axial direction. The circumferential spaces between the claw parts77bconstitute spring housing sections77j, of which, similar to the claw parts77b, there are preferably four in this embodiment. There are preferably two torsion springs74arranged inside each spring housing section77j. Thus, there are preferably a total of four pairs of torsion springs74(eight springs) arranged in the rotational direction.

The second driven plate78is an annular plate member arranged on the side of the first driven plate77that faces the engine in the axial direction. An inner circumferential part thereof is fixed to the first driven plate77with the plurality of rivets79. The second driven plate78has an annular part78a, a plurality of holes78bformed in an inner circumferential part of the annular part78a, and a plurality of cut-and-raised parts78cformed on an outer circumferential portion. The holes78bare formed in positions corresponding to the holes77gof the first driven plate77and the rivets79are passed therethrough. The cut-and-raised parts78care formed so as to bulge out toward the transmission from positions corresponding to the claw parts77bof the first driven plate77. In this embodiment, there are preferably four of these cut-and-raised parts78c.

Drive Plate

The drive plate72is a member that can rotate relative to the driven plate73and is sandwiched axially between the first driven plate77and the second driven plate78. The drive plate72is an annular plate member having an annular part72a, a plurality of protrusions72b, a plurality of claw parts72c, and a plurality of protrusions72d. The protrusions72bare formed on the inside edge of the annular part72aand extend radially inward therefrom. The claw parts72c(abutting parts) are formed in positions corresponding to the circumferential spaces between the protrusions72band extend axially from the annular part72atoward the transmission. The plurality of protrusions72d(mating parts) is formed on the outside edge of the annular part72aand extends radially outward therefrom.

The claw parts72cextend toward the transmission in the axial direction and are formed in positions corresponding to the claw parts77bof the first driven plate77. There are preferably four claw parts72cin this embodiment and they are arranged in the C-shaped portions of the claw parts77bof the first driven plate77. The circumferential width of the claw parts72cis narrower than the circumferential width of the cut-and-raised parts78cof the second driven plate78. The inner circumferential edge parts of the claw parts72care formed so as not to interfere with the outer circumferential face of the cut-and-raised parts78c.

The protrusions72bare formed circumferentially between the claw parts72cand project radially inward. There are preferably four protrusions72bin this embodiment and they extend further inward in the radial direction than the rotationally facing edge sections of the cut-and-raised parts78cof the second driven plate78. Thus, when the drive plate72rotates relative to the driven plate73, the protrusions72btouch against the rotationally facing edge sections of the cut-and-raised parts78csuch that the relative rotation between the drive plate72and the driven plate73is limited to a prescribed angular range. The inside edge of the drive plate72(i.e., the inside edge portion located circumferentially between the protrusions72band the claw parts72c) fits around the outside edge of the cut-and-raised parts78dof the second driven plate78. In short, the drive plate72is positioned in the radial direction by the driven plate73(more specifically, the second driven plate78). The engine-side surface of the drive plate72touches against the transmission-side surface of the outer circumferential part of the second driven plate78. As a result, the drive plate72is also positioned in the axial direction by the driven plate73. The protrusions72dare formed so as to project radially outward from positions corresponding to the claw parts72cand the protrusions72b.

Spring Holder

The spring holder80is a member that can rotate relative to the drive plate72and the driven plate73and is disposed on the side of the first driven plate77that faces the transmission in the axial direction. The spring holder80is an annular plate member having an annular part80a, a cylindrical part80b, a plurality of claw parts80c, and a plurality of protrusions80d. The cylindrical part80bis formed on the outside edge of the annular part80aand extends in the axial direction toward the engine. The plurality of claw parts80c(transmitting parts) is formed on the inside edge of the annular part80a. The plurality of protrusions80dis arranged circumferentially on both sides of each claw part80c. The end of the cylindrical part80bthat is closer to the engine has a narrowed form.

The claw parts80care formed by bending back the inside edge of the annular part80atoward the outside. In other words, the claw parts80care formed by bending in the direction of the engine protrusions that extend axially inward from the annular part80asuch that the ends of the claw parts80copposite the annular part80aextend toward the cylindrical part80b. The claw parts80care arranged in positions corresponding to the circumferential center portions of the spring housing sections77jof the first driven plate77. The circumferential width of the inside portion of the claw parts80cis smaller than circumferential width of the cut-and-raised parts77hof the first driven plate77.

The protrusions80dare arranged circumferentially on both sides of each claw part80cand protrude radially inward from the annular part80a. The width of the portions circumferentially between the protrusions80d(i.e., the width of the portions circumferentially between the protrusions80dwhere the claw parts80care not formed) is larger than the circumferential width of the cut-and-raised parts77hof the first driven plate77. The plurality of protrusions80dis arranged so as to be sandwiched axially between the cut-and-raised parts77hand the protrusions77iof the first driven plate77. More specifically, the surface of each protrusion80dthat faces the transmission in the axial direction is supported by a cut-and-raised part77hof the first driven plate77and the surface of the annular part80athat faces the engine is supported by the protrusions77iof the first driven plate77. As a result, the spring holder80is positioned in the axial direction by the driven plate73(more particularly, the first driven plate77). Also, the inside edges of the protrusions80dfit around the outside surface of the cylindrical part77cof the first driven plate77. In short, the driven plate73(more particularly, the first driven plate77) supports the radially inside portion of the spring holder80such that the spring holder80can rotate relative thereto and also positions the spring holder80in both the axial and radial directions.

Torsion Springs

The torsion springs74have a plurality (preferably eight in this embodiment) of coil springs arranged in pairs in the spring housing sections77jof the first driven plate77. The rotationally facing ends of each pair of the torsion springs74are supported, either directly or through a spring seat, on the rotationally facing edge sections of the claw parts77b, which serve to transmit torque. The claw parts80cof the spring holder80are arranged so as to be sandwiched circumferentially between the two torsion springs74disposed in each spring housing section77j. The claw parts80cserve to support either directly or through a spring seat the mutually facing ends of the two torsion springs74, i.e., the ends between which the claw parts80care sandwiched. Moreover, the radially outside portion and the transmission facing portion of the torsion springs74are supported by the annular part80aand the cylindrical part80bof the spring holder80.

Thus, when the drive plate72and the driven plate73rotate relative to each other, the pairs of the torsion springs74are compressed between the rotationally facing edge sections of the claw parts72cof the drive plate72and the rotationally facing edge sections of the claw parts77bof the driven plate73. When this occurs, the claw parts80cof the spring holder80act to press against the adjacent rotationally facing ends of the torsion springs74due to the compression of the torsion springs74. In short, the pairs of the torsion springs74housed in the spring housing sections77jare made to act in series in the rotational direction.

Clutch Plate

The clutch plate71functions chiefly as a friction coupling part that couples with and releases from the front cover11. It is installed axially between the driven plate73and the front cover11. The clutch plate71is an annular plate member having an annular part71aand a cylindrical part71bthat extends from the outside edge of the annular part71atoward the turbine22in the axial direction. The inner circumferential portion of the annular part71aconstitutes the friction coupling part71cand is in close proximity to the friction surface11bof the front cover11. Friction facings71dare attached to both axial surfaces of the friction coupling part71c. The cylindrical part71bhas a plurality (preferably eight in this embodiment) of recessions71eformed in the transmission-facing edge thereof so as to correspond to the protrusions72dof the drive plate72. The protrusions72dmate with the recessions71esuch that relative rotation is not possible. In short, the clutch plate71mates with the drive plate72such that it cannot rotate relative to the drive plate72.

Piston

Referring now toFIGS. 2 and 4, the piston75is a circular disc-shaped member with a center hole formed therein and serves to engage and disengage the clutch. The piston75is positioned on the radial outside of the center boss16. The outer circumferential portion of the piston75constitutes a pressing part75a. The pressing part75ais a flat, annular section disposed on the transmission side of the friction coupling part71cof the clutch plate71. Consequently, when the piston75moves toward the engine, the pressing part75apresses the friction coupling part71cagainst the friction surface11bof the front cover11. Meanwhile, the inner circumferential portion of the piston75is provided with a cylindrical part75bthat extends toward the engine in the axial direction. The internal surface of the cylindrical part75bfits around the external surface of the center boss16such that it can move in the axial direction. A seal ring82is provided between the external surface of the center boss16and the cylindrical part75bso that fluid does not flow between the engine side of the piston75and the transmission side of the piston75within the space8.

Next, the relative positioning of the clutch plate71, the drive plate72, the torsion springs74, and the piston75is explained. The clutch plate71has the friction coupling part71cand is positioned in the radial direction such that it is aligned with the friction surface11bof the front cover11. The pressing part75aof the piston75extends to the radial position of the friction coupling part71cso that it can press against the friction coupling part71c. The mounting radius of the torsion springs74is shorter than a radius extending to outside edge of the piston75or the friction coupling part71c. The claw parts72cof the drive plate72are arranged at a radial position that is roughly the same as the mounting radius of the torsion springs74. The protrusions72dof the drive plate72are arranged at a radial position that is farther from the rotational axis than the mounting radius of the torsion springs74(in this embodiment, farther from the rotational axis than outside edges of the piston75and the friction coupling part71c) and mate with the recessions71eof the clutch plate71.

Piston Coupling Mechanism

The piston coupling mechanism76functions to couple the piston75to the front cover11in such a manner that the piston rotates integrally with the front cover11but can move relative to the front cover11in the axial direction. With respect to the radial direction, the piston coupling mechanism76is provided at an intermediate position between the pressing part75aand the cylindrical part75bof the piston75. The piston coupling mechanism76has a piston lug plate83, a cover lug plate84, and a return plate85.

The piston lug plate83is an annular plate that is fixed to the engine side of the piston75with a plurality of rivets86. The piston lug plate83has an annular part83aand a plurality of claw parts83bthat project toward the engine in the axial direction from the inside edge of the annular part83a. The claw parts83bare arranged circumferentially and there are preferably eighteen of them in this embodiment. The cover lug plate84is an annular plate that is fixed to the turbine side of the front cover11by welding. The cover lug plate84has an annular part84aand a plurality of recessions84bformed so as to recess inward from the outside edge of the annular part84a.

The recessions84bare arranged in positions corresponding to the claw parts83bof the piston lug plate83and the claw parts83bmate therewith such that the two lug plates83and84cannot rotate relative to each other but can move in the axial direction relative to each other. Thus, the piston75can move relative to the front cover11in the axial direction but not in the rotational direction. When the recessions84band the claw parts83bare in the mated state, a plurality (preferably eighteen in this embodiment) of slit parts87, i.e., slit-shaped gaps, are formed radially-between the claw parts83band the recessions84b.

The return plate85is an annular plate that is fixed along with the piston lug plate83to the engine side of the piston75with rivets86. The return plate85has an annular part85a, a plurality of protrusions85b, and a plurality of claw parts85c. The protrusions85bproject radially inward from the inside edge of the annular part85a. The plurality of claw parts85care formed circumferentially between the protrusions85b. There are three protrusions85bin this embodiment and the tips of these protrusions85btouch against the transmission facing surface of the annular part84aof the cover lug plate84. There are preferably nine claw parts85cin this embodiment and these claw parts85care shaped such that they extend toward the engine in the axial direction from the inside edge of the annular part85a. The tips of the claw parts85c(i.e., the portion closer to the engine) are provided with cut-and-raised parts85dthat catch in slit parts87and serve to limit the distance to which the piston75can move toward the transmission in the axial direction.

Thus, when the piston75moves toward the engine in the axial direction, the return plate85can apply a force that pushes the piston75toward the transmission in the axial direction because protrusions85bdeform elastically. Moreover, when the piston75moves toward the transmission in the axial direction, the return plate85can limit the movement of the piston75toward the transmission because cut-and-raised parts85dof claw parts85ctouch against the inner circumferential rim of the recessions84bof the cover lug plate84(more particularly, against slit parts87).

(3) Operation of Torque Converter

The operation of the torque converter is described with reference primarily toFIGS. 1 and 2.

Immediately after the engine is started, fluid is supplied to the inside of the torque converter main body5through the fluid passage16aand the second port19and fluid is discharged from the first port18. The fluid supplied through the fluid passage16aflows radially outward between the front cover11and the piston75within the space8.

The fluid passes through the axial spaces on both sides of the clutch plate71and finally flows into the fluid operating chamber6.

During this process, the piston75moves toward the turbine22because the hydraulic pressure is higher in the space8than in the fluid operating chamber6and because of the force applied by protrusions85bof the return plate85. The piston75stops when cut-and-raised parts85dof the return plate85of the piston coupling mechanism76abut against the rim part of the slit parts87. When the lockup device7is disengaged in this manner, torque is transmitted between the front cover11and the turbine22by the fluid drive between the impeller21and the turbine22.

Under these conditions, there are times when changes in the hydraulic pressure within the torque converter1cause a force to act on the piston75such that it moves toward the front cover11. However, since the return plate85pushes the piston in the direction of separation from the front cover11, it is difficult for the piston75to move toward the engine.

When the gear ratio of the torque converter1increases and the rotational speed of the input shaft3reaches a prescribed speed, fluid from the space8is discharged through the fluid passage16a. As a result, the hydraulic pressure of the fluid operating chamber6becomes higher than the hydraulic pressure of the space8and the piston75moves toward the engine. As a result, the pressing part75aof the piston75presses the friction coupling part71cof the clutch plate71against friction surface11bof the front cover11. Since the piston75rotates integrally with the front cover11due to the piston coupling mechanism76, torque is transferred from the front cover11to the clutch plate71. Meanwhile, since the piston lug plate83of the piston coupling mechanism76is close to the cover lug plate84because the piston75has moved toward the engine, the protrusions85bof the return plate85touch against the transmission facing surface of the annular part84aof the cover lug plate84and deform elastically. The torque of the front cover11is transmitted from the drive plate72(which is mated with the clutch plate71such that it cannot rotate relative to the clutch plate) to the driven plate73through the torsion springs74. In short, torque is transmitted from the drive plate72to the driven plate73through the torsion springs74. In other words, the front cover11is mechanically coupled with the turbine22and the torque of the front cover11is imparted directly to the input shaft3through the turbine22. When this occurs, the relative rotation between the drive plate72and the driven plate73causes the torsion springs74to be compressed between the rotationally facing edge surfaces of the claw parts72cof the drive plate72and the rotationally facing edge surfaces of the claw parts77bof the first driven plate77while the claw parts80cof the spring holder80are sandwiched between spring pairs. In other words, the spring holder80rotates relative to the drive plate72and the driven plate73and functions to cause the pairs of the torsion springs74to act in series in the rotational direction. The side of the torsion springs74that faces radially outward and the side of the same that faces toward the transmission are supported by the spring holder80and cannot easily slide with respect to the drive plate72and the driven plate73. The rotation of the drive plate72with respect to the driven plate73is limited to a prescribed angular range because the protrusions72b(which are provided on the inner circumference of the drive plate72) touch against the rotationally facing edge sections of the cut-and-raised parts78c(which are provided on the second driven plate78). Since both surfaces of the friction coupling part71cof the clutch plate71are provided with friction facings71d, the torque transmission capacity is larger than for lockup devices having a single friction surface.

(4) Features of Lockup Device

This embodiment of the lockup device7has the following features.

Friction Coupling Part Arranged on Outside with Respect to Radial Direction

In this embodiment of the lockup device7, the clutch plate71has the friction coupling part71cand the drive plate72has the claw parts72cthat abut against the rotationally facing ends of the torsion springs74in such a manner that torque can be transmitted. Further, the protrusions72dare positioned farther to the outside in the radial direction than the claw parts72cand mate with the recessions71eof the clutch plate71in such a manner that the drive plate72cannot rotate relative to the clutch plate71. Consequently, the protrusions72dof the drive plate72can be arranged on the outside with respect to the radial direction. As a result, the friction coupling part71cof the clutch plate71can be arranged on the outside with respect to the radial direction and the torque transmission capacity of the lockup device7can be increased. Furthermore, the assembly of the lockup device is simple because the drive plate72can be assembled to the clutch plate71by simply mating the protrusions72dof the drive plate72with the recessions71eof the clutch plate71.

Drive Plate Supported by Driven Plate

In this embodiment of the lockup device7, the drive plate72mates with the driven plate73(more specifically, with the cut-and-raised parts78cof the second driven plate78) in such a manner that it can rotate relative to the driven plate73and is positioned in the axial and radial directions by the driven plate73. Consequently, the axial and radial positions of the drive plate72are stable. As a result, the axial and radial positions of the clutch plate71, which mates with the drive plate72in such a manner that it cannot rotate relative thereto, are also stable.

Limited Relative Rotation Angle Between Drive Plate and Driven Plate

In this embodiment of the lockup device7, the protrusions72dof the drive plate72touch against the rotationally facing end parts of the cut-and-raised parts78cof the second driven plate78and prohibit relative rotation between the drive plate72and the driven plate73when the relative rotation between the two plates72and73reaches a prescribed angle. In short, the cut-and-raised parts78cof the second driven plate78function as stoppers with respect to the protrusions72dof the drive plate72. Thus, the cut-and-raised parts78cof the second driven plate78function both to position the drive plate72in the axial and radial directions and as stoppers for stopping the drive plate72. As a result, since the compression of the torsion springs74can be limited to a prescribed angular range, any desired torsional characteristic can be obtained and increases in the number of parts can be suppressed.

Sliding of Torsion Springs Against other Parts an be Reduced

In this embodiment of the lockup device7, the transmission-facing side and radially outward facing side of each torsion spring74is supported by the spring holder80. As a result, it is difficult for the torsion springs74to slide against the drive plate72and the driven plate73. Also, since the torsion springs74have a plurality of pairs (preferably four in this embodiment) of coil springs arranged so as to act in series in the rotational direction, torsional vibration absorbing performance can be achieved which is similar to that obtained with torsion springs that are long in the rotational direction.

Spring Holder Supported by Drive Plate

In this embodiment of the lockup device7, the spring holder80mates with the first driven plate77in such a manner that it can rotate relative to the first driven plate77and the inner circumferential portion of the spring holder80is positioned in the radial and axial directions by the cylindrical part77c, the cut-and-raised parts77h, and the protrusions77iof the first driven plate77. As a result, the radial and axial positions of the spring holder80are stable. Furthermore, since only the inner circumferential portion of the spring holder80touches against the first driven plate77, there are few sections where sliding occurs. Thus, wear between the spring holder80and the first driven plate77can be reduced. Wear between the spring holder80and the drive plate72can also be reduced because the lockup device is structured in such a manner that the spring holder80does not slide against the drive plate72.

Other Embodiments

An embodiment of the present invention has been described based on the drawings, but the specific features of the present invention are not limited to those of the previously described embodiment. Modifications are possible so long as the gist of the invention is not exceeded.

For example, instead of applying the lockup device of the present invention to a torque converter, it can be applied to a fluid coupling or other fluid-type torque transmission device.

EFFECTS OF THE INVENTION

With the lockup device of the present invention, the friction coupling part can be arranged on the outside with respect to the radial direction. Furthermore, sliding of the torsion springs against other members can be reduced.

As used herein, the following directional terms “forward, rearward, above, downward, vertical, horizontal, below, and transverse” as well as any other similar directional terms refer to those directions of a vehicle equipped with the present invention. Accordingly, these terms, as utilized to describe the present invention should be interpreted relative to a vehicle equipped with the present invention.

This application claims priority to Japanese Patent Application No. 2002-073007. The entire disclosure of Japanese Patent Application No. 2002-073007 is hereby incorporated herein by reference.