Abstract:
A clutch assembly in a torque converter including a piston plate operatively arranged to apply axial pressure to a clutch in the clutch assembly. An annular member can be rotationally connected to a cover of the torque converter and rotationally connected to an outer circumference of the clutch. A first seal can be disposed between the piston plate and an inner circumference of the drive plate to form a seal between the piston plate and the inner circumference. In some aspects, the annular member is a drive plate arranged to transmit torque from said cover to said clutch and the annular member is fixedly secured to said cover by a weld. In other aspects, the first clutch plate is axially displaceable with respect to the annular member and the piston plate is axially displaceable with respect to the annular member.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Application No. 60/796,429 filed May 1, 2006. 
     
     FIELD OF THE INVENTION 
       [0002]    The invention relates generally to a seal for a torque converter, and, more particularly, to a drive plate member that interacts with a slipping clutch, and seals the piston plate. 
       BACKGROUND OF THE INVENTION 
       [0003]    It is well known that a torque converter is used to transmit torque from an engine to a transmission of a motor vehicle.  FIG. 1  illustrates a general block diagram showing the relationship of the engine  7 , torque converter  10 , transmission  8 , and differential/axle assembly  9  in a typical vehicle. 
         [0004]    The three main components of the torque converter are the pump  37 , turbine  38 , and stator  39 . The torque converter becomes a sealed chamber when the pump is welded to cover  11 . The cover is connected to flexplate  41  which is, in turn, bolted to crankshaft  42  of engine  7 . The cover can be connected to the flexplate using lugs or studs welded to the cover. The welded connection between the pump and cover transmits engine torque to the pump. Therefore, the pump always rotates at engine speed. The function of the pump is to use this rotational motion to propel the fluid radially outward and axially towards the turbine. Therefore, the pump is a centrifugal pump propelling fluid from a small radial inlet to a large radial outlet, increasing the energy in the fluid. Pressure to engage transmission clutches and the torque converter clutch is supplied by an additional pump in the transmission that is driven by the pump hub. 
         [0005]    In torque converter  10  a fluid circuit is created by the pump (sometimes called an impeller), the turbine, and the stator (sometimes called a reactor). The fluid circuit allows the engine to continue rotating when the vehicle is stopped, and accelerate the vehicle when desired by a driver. The torque converter supplements engine torque through torque ratio, similar to a gear reduction. Torque ratio is the ratio of output torque to input torque. Torque ratio is highest at low or no turbine rotational speed (also called stall). Stall torque ratios are typically within a range of 1.8-2.2. This means that the output torque of the torque converter is 1.8-2.2 times greater than the input torque. Output speed, however, is much lower than input speed, because the turbine is connected to the output and it is not rotating, but the input is rotating at engine speed. 
         [0006]    Turbine  38  uses the fluid energy it receives from pump  37  to propel the vehicle. Turbine shell  22  is connected to turbine hub  19 . Turbine hub  19  uses a spline connection to transmit turbine torque to transmission input shaft  43 . The input shaft is connected to the wheels of the vehicle through gears and shafts in transmission  8  and axle differential  9 . The force of the fluid impacting the turbine blades is output from the turbine as torque. Axial thrust bearings  31  support the components from axial forces imparted by the fluid. When output torque is sufficient to overcome the inertia of the vehicle at rest, the vehicle begins to move. 
         [0007]    After the fluid energy is converted to torque by the turbine, there is still some energy left in the fluid. The fluid exiting from small radial outlet  44  would ordinarily enter the pump in such a manner as to oppose the rotation of the pump. Stator  39  is used to redirect the fluid to help accelerate the pump, thereby increasing torque ratio. Stator  39  is connected to stator shaft  45  through one-way clutch  46 . The stator shaft is connected to transmission housing  47  and does not rotate. One-way clutch  46  prevents stator  39  from rotating at low speed ratios (where the pump is spinning faster than the turbine). Fluid entering stator  39  from turbine outlet  44  is turned by stator blades  48  to enter pump  37  in the direction of rotation. 
         [0008]    The blade inlet and exit angles, the pump and turbine shell shapes, and the overall diameter of the torque converter influence its performance. Design parameters include the torque ratio, efficiency, and ability of the torque converter to absorb engine torque without allowing the engine to “run away.” This occurs if the torque converter is too small and the pump can&#39;t slow the engine. 
         [0009]    At low speed ratios, the torque converter works well to allow the engine to rotate while the vehicle is stationary, and to supplement engine torque for increased performance. At high speed ratios, the torque converter is less efficient. The torque ratio of the torque converter gradually reduces from a high of about 1.8 to 2.2, to a torque ratio of about 1 as the turbine rotational speed approaches the pump rotational speed. Torque ratio of 1 is called the coupling point. At this point, the fluid entering the stator no longer needs redirected, and the one way clutch in the stator allows it to rotate in the same direction as the pump and turbine. Because the stator is not redirecting the fluid, torque output from the torque converter is the same as torque input. The entire fluid circuit will rotate as a unit. 
         [0010]    Maximum torque converter efficiency is limited to 92-93% based on losses in the fluid. Therefore torque converter clutch  49  is employed to mechanically connect the torque converter input to the output, improving efficiency to near 100%. Clutch piston plate  17  is hydraulically applied when commanded by the transmission controller. Piston plate  17  is sealed to turbine hub  19  at its inner diameter by o-ring  18  and to cover  11  at its outer diameter by friction material ring  51 . These seals create a pressure chamber and force piston plate  17  into engagement with cover  11 . This mechanical connection bypasses the torque converter fluid circuit. 
         [0011]    The mechanical connection of torque converter clutch  49  transmits many more engine torsional fluctuations to the drivetrain. As the drivetrain is basically a spring-mass system, torsional fluctuations from the engine can excite natural frequencies of the system. A damper is employed to shift the drivetrain natural frequencies out of the driving range. The damper includes springs  15  in series to lower the effective spring rate of the system, thereby lowering the natural frequency. 
         [0012]    Torque converter clutch  49  generally comprises four components: piston plate  17 , cover plates  12  and  16 , springs  15 , and flange  13 . Cover plates  12  and  16  transmit torque from piston plate  17  to compression springs  15 . Cover plate wings  52  are formed around springs  15  for axial retention. Torque from piston plate  17  is transmitted to cover plates  12  and  16  through a riveted connection. Cover plates  12  and  16  impart torque to compression springs  15  by contact with an edge of a spring window. Both cover plates work in combination to support the spring on both sides of the spring center axis. Spring force is transmitted to flange  13  by contact with a flange spring window edge. Sometimes the flange also has a rotational tab or slot which engages a portion of the cover plate to prevent over-compression of the springs during high torque events. Torque from flange  13  is transmitted to turbine hub  19  and into transmission input shaft  43 . 
         [0013]    Energy absorption can be accomplished through friction, sometimes called hysteresis, if desired. Hysteresis includes friction from windup and unwinding of the damper plates, so it is twice the actual friction torque. The hysteresis package generally consists of diaphragm (or Belleville) spring  14  which is placed between flange  13  and one of cover plates  16  to urge flange  13  into contact with the other cover plate  12 . By controlling the amount of force exerted by diaphragm spring  14 , the amount of friction torque can also be controlled. Typical hysteresis values are in the range of 10-30 Nm. 
         [0014]    Some torque converters implement a clutch pack consisting of several clutch plates. The current design of such multi-plate torque converter clutches feature a driven plate member located radially outside of the clutch plates. A second plate welded to the cover acts as a seal member that engages a portion of the piston plate. (e.g., U.S. Pat. No. 6,264,018 (Matsuoka). 
         [0015]      FIG. 7  is a cross-sectional view of torque converter  110 , embodying one configuration of a torque converter with a continuous slip clutch with drive plate  112  attached to front cover  116 . Drive plate  112  is conventionally attached to front cover  116  using a laser weld or some other attachment means known in the art. Weld  122  indicates the typical location of the welding point used to attach drive plate  112  to front cover  116 . Drive plate  112  can be an annular stamped component having an L-shaped cross section profile comprised of sheet steel. Outer clutch plates  124  and  130  and inner clutch plate  128  are associated with drive plate  112  at the outer circumference of the plates, where drive plate  112  functions as a retaining means for these clutch plates. Clutch plates  132  are associated with damper plate  138  at the inner circumference of the plates. Clutch plates  124 ,  128  and  130  are driven axially by drive plate  112  to interact with inner clutch plates  132 . Consequently, torque is transmitted by frictional engagement of clutch plates  124 ,  128  and  132  with clutch plates  132 , and the rotational connection of clutch plates  132  to damper  138  transfers torque. Clutch plates  124 ,  128 ,  130  and  132  can be manufactured from sheet steel and include friction paper  126  on the contact surfaces of the clutch plates. Clutch plates  124 ,  128 ,  130  and  132  comprise the clutch pack, where clutch plates  124 ,  128 ,  130  are retained by drive plate  112  on the outer circumference of the clutch plates with the assistance of retaining ring  134 . The clutch plates of the clutch pack are disposed on drive plate  112  and damper plate  138  in such a way to facilitate the axial displacement of individual clutch plates to enable the clutch plates to be acted upon by axial displacement of piston plate  118 . Axial displacement among the clutch plates permits the clutch pack to engage or disengage, i.e., bypass the torque converter fluid circuit or not. 
         [0016]    Piston plate  118  with apply side  158  and release side  156 , is the component that transfers torque generated in the pressure chamber to clutch plates  124 ,  128 ,  130  and  132 . Pressure developed on apply side  158  of piston plate  118  in the pressure chamber causes the piston plate to move axially toward clutch plate  124 , which in turn transfers torque to the clutch pack and bypasses the fluid circuit in the torque converter. Fluid pumped by a pump in the transmission is directed to the pressure chamber that axially moves piston plate  118  to engage the clutch pack, which ultimately bypasses the fluid circuit in the torque converter. Sealing member  114  engages piston plate  118  to form a pressure chamber that enables fluid pumped into the chamber on the apply side of the piston plate to axial move the piston plate to facilitate the bypass of the fluid circuit. 
         [0017]    Sealing member  114  can be welded to front cover  116  in any method known in the art Sealing member  114  is an annular element with an L-shaped cross section profile. O-ring  120 , placed between the underside of sealing member  114  and piston plate  118 , is one method of sealing pressure and fluid inside the pressure chamber formed on apply side  158  of piston plate  118 . The arrangement shown in  FIG. 7  is the conventional method of sealing the piston plate, wherein a separate sealing member, such as sealing member  114  is implemented. 
         [0018]    Contemporary multi-plate torque converter clutches require second plate  114  rotationally connected to front cover  116 , typically by a weld, to seal the pressure chamber behind the piston plate. Requiring a separate plate to seal the piston plate increases the material costs since additional steel is needed to make the second plate. Moreover, the time needed to weld a second plate to the torque converter cover increases manufacturing time and increases the complexity of the torque converter manufacturing process. The formation of a second sealing plate is one area that results in additional manufacturing time. Also, the time needed to weld the second plate to the cover is additional waste that could be eliminated if the second sealing plate could be rendered superfluous. 
         [0019]    Thus, there is a long-felt need to provide a sealing member for the apply side of a piston plate in a torque converter that can eliminate the need for a separate second sealing plate. There is a further need for a piston plate sealing member that can reduce the complexity, costs, assembly time, and overall manufacturing costs for a piston plate sealing member by providing a drive plate that can simultaneously seal the apply side of the piston plate and associate with the clutch plates on a multi-plate torque converter clutch. 
       SUMMARY OF THE INVENTION 
       [0020]    The invention broadly comprises a clutch assembly in a torque converter including a piston plate operatively arranged to apply axial pressure to a clutch in the clutch assembly. An annular member can be rotationally connected to a cover of the torque converter and rotationally connected to an outer circumference of the clutch. A first seal can be disposed between the piston plate and an inner circumference of the drive plate to form a seal between the piston plate and the inner circumference. In some aspects, the annular member is a drive plate arranged to transmit torque from said cover to said clutch, and the annular member is fixedly secured to said cover by a weld. The clutch assembly can further comprise a first clutch plate with an outer circumference where the annular member is rotationally connected to the first clutch plate proximate the outer circumference. In some aspects, the first clutch plate is axially displaceable with respect to the annular member and the piston plate is axially displaceable with respect to the annular member. The clutch can be a continuous slip clutch with a plurality of second clutch plates where the plurality of second clutch plates is axially displaceable with respect to the annular member. The piston plate can further comprise an inner circumferential end where the torque converter further comprises a space between the cover and the piston plate and a second seal is disposed proximate the inner circumferential end, where the first and second seals substantially seal the space. The torque converter can be arranged to modify pressure in the space to axially displace the piston plate. The seal can be selected from the group consisting of a U-shaped seal and an L-shaped seal, where the said seal can be rubber or an o-ring. 
         [0021]    The invention also broadly comprises a drive plate for a clutch in a torque converter which includes an axially disposed segment rotationally connected to an outer circumference of the clutch and rotationally connected to a cover for the torque converter. A sealing element can be disposed between the inner circumferential end of the drive plate and a piston plate that is engage with the clutch, where a seal is formed between a seal the inner circumferential end and the piston plate. In some aspects, the drive plate is arranged to transmit torque from the cover to the clutch and the piston plate is arranged to axially engage the clutch. 
         [0022]    The invention further comprises a clutch assembly in a torque converter which includes a piston plate operatively arranged to apply axial pressure to a clutch in the clutch assembly. Also, a drive plate with an inner circumference can be fixedly secured to a cover of the torque converter and rotationally connected to an outer circumference of at least one clutch plate in the clutch, and comprising an inner circumference. A seal can be disposed between the piston plate and the inner circumference of the drive plate and in contact with the piston plate and the inner circumference of the drive plate, where the piston plate is axially displaceable with respect to the annular member. 
         [0023]    It is a general object of the present invention to provide a torque converter with a drive plate and piston plate sealing member that eliminates manufacturing costs and time. 
         [0024]    It is another object of the present invention to provide a torque converter that combines the tasks of a drive plate and piston plate sealing member into one component. 
         [0025]    These and other objects and advantages of the present invention will be readily appreciable from the following description of preferred embodiments of the invention and from the accompanying drawings and claims. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]      FIG. 1  is a general block diagram illustration of power flow in a motor vehicle, intended to help explain the relationship and function of a torque converter in the drive train thereof; 
           [0027]      FIG. 2  is a cross-sectional view of a prior art torque converter, shown secured to an engine of a motor vehicle; 
           [0028]      FIG. 3  is a left view of the torque converter shown in  FIG. 2 , taken generally along line  3 - 3  in  FIG. 2 ; 
           [0029]      FIG. 4  is a cross-sectional view of the torque converter shown in  FIGS. 2 and 3 , taken generally along line  4 - 4  in  FIG. 3 ; 
           [0030]      FIG. 5  is a first exploded view of the torque converter shown in  FIG. 2 , as shown from the perspective of one viewing the exploded torque converter from the left; 
           [0031]      FIG. 6  is a second exploded view of the torque converter shown in  FIG. 2 , as shown from the perspective of one viewing the exploded torque converter from the right; 
           [0032]      FIG. 7  is a partial cross-sectional view of a torque converter with a multi-plate clutch; 
           [0033]      FIG. 8  is a partial cross-sectional view of a torque converter with a multi-plate clutch of the present invention; 
           [0034]      FIG. 9  is an enlarged cross-sectional view of a torque converter, similar to that shown in  FIG. 8 , taken generally from the region designated as circle  9  and  10  shown in  FIG. 8 , showing the present invention; and, 
           [0035]      FIG. 10  is an enlarged cross-sectional view of a torque converter, similar to that shown in  FIG. 8 , taken generally from the region designated as circle  9  and  10  shown in  FIG. 8 , showing an alternative embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0036]    At the outset, it should be appreciated that like drawing numbers on different drawing views identify identical, or functionally similar, structural elements of the invention. While the present invention is described with respect to what is presently considered to be the preferred aspects, it is to be understood that the invention as claimed is not limited to the disclosed aspects. 
         [0037]    Furthermore, it is understood that this invention is not limited to the particular methodology, materials and modifications described and as such may, of course, vary. It is also understood that the terminology used herein is for the purpose of describing particular aspects only, and is not intended to limit the scope of the present invention, which is limited only by the appended claims. 
         [0038]    Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this invention belongs. Although any methods, devices or materials similar or equivalent to those described herein can be used in the practice or testing of the invention, the preferred methods, devices, and materials are now described. 
         [0039]      FIG. 8  is a vertical cross-sectional view of torque converter  110  of the present invention. In this view, sealing member  114  and drive plate  112  (both shown in  FIG. 7 ) have been eliminated. The sealing member  114  and drive plate  112  have been replaced by drive plate  146  that extends toward the center of front cover  116  to surface  162  of piston plate  118 . The functions of both elements, sealing member  114  and drive plate  112 , are accomplished by a single element, drive plate  146 . Drive plate  146  is rotationally connected to front cover  116  and rotationally connected to the outer circumference of the clutch shown represented by clutch plates  124 ,  128 ,  130  and  132 . Specifically, drive plate  146  is rotationally connection to the outer circumference of clutch plates  124 ,  128  and  130 , and damper plate  138  is rotationally connected to clutch plates  132 . As clutch plates  124 ,  128  and  130  are compressed axially, friction between plates  124 ,  128  and  130  acting upon clutch plates  132  transfers torque to damper plate to  138 . 
         [0040]    By rotationally connected, or secured, we mean that the plate and the shell are connected such that the two components rotate together, that is, the two components are fixed with respect to rotation. Rotationally connecting two components does not necessarily limit relative movement in other directions. For example, it is possible for two components that are rotationally connected to have axial movement with respect to each other via a spline connection. However, it should be understood that rotational connection does not imply that movement in other directions is necessarily present. For example, two components that are rotationally connected can be axially fixed one to the other. The preceding explanation of rotational connection is applicable to the discussions infra. In the discussions infra, a connection is assumed to be a rotational connection unless otherwise specified. 
         [0041]    The seal on drive plate  146  that facilitates the sealing of the pressure chamber behind apply side  158  of piston plate  118  can be performed by any seal known in that art. Represented in  FIGS. 8 and 9  by members  148 ,  150 , and in  FIG. 10  by lip seal  152  are two possible sealing candidates. It should be understood that the seal between drive plate inner circumferential end  160  and piston plate  162  can include, but is not limited to sealing members  148 ,  150  and  152 , i.e., other alternative sealing means known in the art can be substituted for the sealing means shown and described. In some aspects, drive plate  146  is also associated with the clutch plates of the continuous slip clutch assembly at a position distal to inner circumferential end  160 . Disposing sealing element  148 ,  150  or  152  at inner circumferential end  160  of the drive plate, and the clutch plates at an end distal to the periphery of drive plate  146 , enables drive plate  146  to interact with the clutch plates and piston plate  118  simultaneously. 
         [0042]    The pressure chamber formed by interaction between inner circumferential end  160  of drive plate  146  and surface  162  of piston plate  118  enables fluid pressure to be generated on apply side  158  of piston plate  118 . It is this fluid pressure that is generated in the pressure chamber by a separate pump connected to the transmission that can force piston plate  118  to move axially toward clutch plates  124 ,  128 ,  130  and  132 . If enough pressure is generated in the pressure chamber on apply side  158 , piston plate  118  will fully engage the clutch plates and the torque converter fluid circuit will be bypassed. As pressure in the pressure chamber on apply side  158  is decreased, piston plate  118  displaces axially away from clutch plates  124 ,  128 ,  130  and  132 , which in turn disengages the clutch and stops the bypass of the torque converter fluid circuit. The seal at inner circumferential end  160  of drive plate  146  remains in constant contact with surface  162  of piston plate  118  as this axial movement of piston plate  118  occurs. The interaction between the seal at inner circumferential end  160  and surface  162  prevents the loss of pressure and fluid from the pressure chamber, and facilitates the transfer of fluid pressure on apply side  158  to piston plate  118 , which cause frictional engagement of the clutch plates to cause bypass of the fluid circuit in the torque converter. The interaction of the sealed inner circumferential end  160  of drive plate  146  can be a frictional engagement, and preferably the interaction should allow axial movement of piston plate  118 . 
         [0043]      FIG. 9  is an enlarged cross-sectional view of drive plate  146  that seals apply side  158  of piston plate  118  of the present invention. Drive plate  146  has the dual function of retaining and associating at the outer circumference of clutch plates  124 ,  128 ,  130  and indirectly  132 , and sealing apply side of piston plate  118 . The number of clutch plates of the continuous slip clutch assembly shown is variable. It is within the spirit and scope of the present invention to have one clutch plate or a plurality of clutch plates associated with drive plate  146 . The clutch plates of the conventional multi-plate torque converter clutch shown in  FIG. 7  are similar to the clutch plates of the embodiment shown in  FIGS. 8 ,  9  and  10 , and thus identical reference numbers have been used. This is true of other elements of the torque converter of the present invention that are similar to the contemporary torque converter shown in  FIG. 7  in that parts that are similar in  FIGS. 8 ,  9  and  10  have retained the reference numbers used in  FIG. 7 . 
         [0044]    Drive plate  146  is an annular component formed from a sheet steel blank that has been stamped into a plate having a L-shaped cross section profile. This configuration is only one possible shape for drive plate  146 , and variations in shape of this element are considered within the spirit and scope of the instant invention. Where previous drive plates were welded to front cover  116  and remain flush with the interior surface of front cover  116  and did not extend to surface  162  of piston plate  118 , drive plate  146  of the instant invention extends toward the center axis of front cover  116  to surface  162  of piston plate  118 . By extending drive plate  146  to surface  162  of piston plate  118 , separate sealing member  114  (shown in  FIG. 7 ) can be eliminated, thus resulting in a reduction of material costs and production time. Eliminating sealing member  114  reduces production time by doing away with the manufacturing steps of forming sealing member  114  and attaching the sealing member to front cover  116 . Drive plate  112  (shown in  FIG. 7 ) and drive plate  146  of the current invention are attached to front cover  116  in a similar fashion, i.e., welding. Thus, by consolidating the tasks of the drive plate and piston sealing member into one component  146 , the step of welding a separate sealing member is completely eliminated and manufacturing time is reduced and material costs are reduced. 
         [0045]    Drive plate  146  seals piston plate  118  with ring  150 , which has an L-shaped cross section, and o-ring  148 . The L-shape of ring  150  creates a lip that retains o-ring  148 . The combination of ring  150  and o-ring  148  forms a seal against surface  162  of piston plate  118  that prevents leakage of fluid from the pressure chamber on apply side  158  of piston plate  118 . In the sealing method shown in  FIG. 9 , O-ring  148  can be formed of a compliant yet resilient material such as rubber, latex, plastic, or other flexible substances, but it is not limited to such substances. Retaining ring  150  can be constructed of various substances including rubber, steel, aluminum, other metals, and various alloys, but ring  150  is generally associated with o-ring  148  in a commercially available sealing assembly that is known in the art. 
         [0046]    Inner circumferential end  160  of drive plate  146  is shown proximate surface  162  of piston plate  118 . The relationship between inner circumferential end  160  and surface  162  can be altered to accommodate the different substances that may be used in sealing assembly composed of  148  and  150 , or  152 . If the sealing assembly chosen to seal inner circumferential end  160  and surface  162  of piston plate  118  relies only upon an o-ring similar to o-ring  148  it may be appropriate to extend inner circumferential end  160  of drive plate  146  to contact surface  162  of piston plate  118 , or nearly contact surface  162 . However, it should be appreciate that numerous other sealing methods known in the art can be used to complete the seal between piston plate  118  and drive plate  146 . 
         [0047]    Bent segment  164  in drive plate  146  is formed in a shape shown to add resiliency and durability to drive plate  146  and the seal between drive plate  146  and piston plate  118 , particularly inner circumferential end  160  and surface  162 . The shape of bent segment  164  on drive plate  146  is also intended to give clearance for the axial movement of piston plate  118 . Bent segment  164  can be various other shapes and the shape will be related to numerous factors that include but are limited to: the torque converter application, the resiliency needed in the drive plate, and on the clearance required for axial movement of the piston plate. It should be appreciated, that bent segment  164  can take on various other configurations, and thus it is considered within the spirit and scope of the invention to have drive plate  146  in various configurations prior to reaching the sealing surface  162  of piston plate  118 . In some aspects, bent segment  164  can be eliminated entirely and drive plate  146  can be a flat plate, excluding the clutch engagement portion of plate  146 , which should remain flexed or bent for clutch plate engagement. 
         [0048]      FIG. 10  is an enlarged cross section of an alternative embodiment of drive plate  146  of the present invention, where drive plate  146  implements lip seal  152  to seal the pressure chamber on apply side  158  of piston plate  118  at surface  162 . This alternative embodiment of drive plate  146  can be an annular component formed from a sheet steel blank that has been stamped into a plate having an L-shaped cross section profile. The shape, however, can be varied and it should be understood that variations the shape of drive plate  146  are considered within the spirit and scope of the invention. Where previous drive plates where welded to front cover  116  and remain flush with the interior surface of front cover  116 , drive plate  146  extends toward the center of front cover  116  to surface  162  of piston plate  118 . Fluid pressure on apply side  158  is sealed against leakage by lip seal  152  engaging surface  162  of piston plate  118 . Lip seal  152  has a U-shaped cross section profile which enables lip seal  152  to envelop inner circumferential end  160  of drive plate  146 . Lip seal  152  can be formed of a compliant yet resilient material such as rubber, latex, plastic, or other flexible substances, but it is not limited to such substances. For example lip seal  152  could take a form similar to that shown in  FIG. 9  where a stiff ring is used to reinforce the seal. Such reinforcing rings can compensate for gaps between inner circumferential end  160  of drive plate  146  and surface  162  of piston plate  118 . Tight interaction between inner circumferential end  160  and the interior surfaces of lip seal  152 , and tight interaction between surface  162  and the exterior surface of lip seal  152 , seals inner circumferential end  160  to surface  162  to form the pressure chamber on apply side  158 . However, it should be appreciated that numerous other sealing methods known in the art can be used to complete the seal between piston plate  118  and drive plate  146 . 
         [0049]    In the alternative embodiment of drive plate  146  shown in  FIG. 10 , bent segment  164  can add resiliency to plate  146  and affords piston plate  118  sufficient clearance to move axially. Bent segment  164  can be configured in various other shapes that are not shown in  FIGS. 9 and 10 . One of ordinary skill in the art would understand that the clearance and resiliency concerns that need to be considered in forming drive plate  146  would permit numerous configurations that would be considered equivalent approaches to that disclosed here. In some aspects, multiple bends in bent segment  164  of drive plate  146  can be used, similar to the embodiment shown in  FIG. 9 , to accommodate a particular seal. However, it should be understood that drive plate  146  is not limited to any particular shape. 
         [0050]    Thus, it is seen that the objects of the invention are efficiently obtained, although changes and modifications to the invention should be readily apparent to those having ordinary skill in the art, without departing from the spirit or scope of the invention as claimed. Although the invention is described by reference to a specific preferred embodiment, it is clear that variations can be made without departing from the scope or spirit of the invention as claimed.