Abstract:
A torque transmitting apparatus includes a cover portion generally defined by a first axis, and a flywheel coupled to the cover portion for rotation therewith. The flywheel is restrained from axial movement relative to the cover portion. The apparatus also includes a pressure plate coupled to the cover portion for rotation therewith, wherein the pressure plate is axially moveable relative to the cover portion. The apparatus also includes an intermediate plate coupled to the cover portion for rotation therewith. The intermediate plate is axially moveable relative to the cover portion and the pressure plate. The apparatus further includes a first clutch disk at least partially interposed between the pressure plate and the intermediate plate, a second clutch disk at least partially interposed between the flywheel and the intermediate plate, an axially acting biasing element for exerting an axial force between the pressure plate and the intermediate plate, and a support member extending through the biasing element.

Description:
TECHNICAL FIELD 
       [0001]    The disclosure generally relates to dual-disk clutches for transmitting torque in automobiles. 
       BACKGROUND 
       [0002]    Friction clutches for use in transmitting rotational torque between a motor vehicle engine and a transmission are well known. One known friction clutch design includes two friction disks, a pressure plate, an intermediate plate, and a clutch cover mounted for rotation about a common axis. The clutch disks, pressure plate and intermediate plate are axially moveable relative to each other so that the pressure plate may be moved relative to the cover to press the two friction disks and the interposed intermediate plate axially against an engine flywheel. A series of drive straps, each generally including one or more resilient elements that are layered to form a leaf spring, are placed around the peripheries of the intermediate plate and pressure plate to provide a biasing force against the plates. During engagement of the clutch, the intermediate plate, pressure plate and friction disks are pressed against the engine flywheel, such that rotation of the flywheel causes rotation of the friction disks. During disengagement of the clutch, the drive straps bias the intermediate plate and pressure plate in a direction away from the flywheel to separate the intermediate plate and pressure plate from the friction disks. 
         [0003]    With many conventional friction clutches, the axial movement of the intermediate plate may be uncontrolled during engagement and disengagement of the clutch. That is, simultaneous engagement of the intermediate plate and the pressure plate with the friction disks and simultaneous disengagement of the friction disks from the interposed intermediate plate may not occur as desired. If the friction disks are engaged sequentially rather than simultaneously, the friction material on one friction disk may be consumed more rapidly than the friction material on the other friction disk, thereby reducing the useful life of the clutch. 
         [0004]    To ensure virtually simultaneous engagement of the friction disks, several designs have been proposed that force the travel of the intermediate plate to closely coincide with pressure plate travel. One known design incorporates a mechanism that includes a separator element bolted to the radially outer side of the intermediate plate and a lever attached to the mid-point of the drive straps that bias the pressure plate. Engagement of the separator element with the lever limits axial movement of the intermediate plate to approximately half of the axial movement of the pressure plate during engagement and disengagement of the clutch. Accordingly, the friction disks are engaged by the intermediate plate and pressure plate nearly simultaneous, providing substantially uniform wear of the friction disks and a smooth engagement of the clutch. 
         [0005]    Further, the previous mechanisms to achieve simultaneous engagement have not been adjustable. Accordingly, there exists a need for a simplified device that can be easily and cost effectively affixed to a clutch to achieve the desired control of intermediate plate travel relative to the pressure plate travel. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    Referring now to the drawings, illustrative embodiments are shown in detail. Although the drawings represent some embodiments, the drawings are not necessarily to scale and certain features may be exaggerated, removed, or partially sectioned to better illustrate and explain the present invention. Further, the embodiments set forth herein are exemplary and are not intended to be exhaustive or otherwise limit or restrict the claims to the precise forms and configurations shown in the drawings and disclosed in the following detailed description. 
           [0007]      FIG. 1  is an environmental view illustrating a clutch mounted in a heavy duty vehicle. 
           [0008]      FIG. 2  is a view of the clutch, taken generally along line  2 - 2  of  FIG. 1 . 
           [0009]      FIG. 3  is a sectional view of the clutch, taken generally along line  3 - 3  of  FIG. 2 . 
           [0010]      FIG. 4  is a sectional view of the clutch, taken generally along line  4 - 4  of  FIG. 2 . 
           [0011]      FIG. 5  is a perspective view of the clutch, taken generally along the view of line  5 - 5  of  FIG. 2 . 
           [0012]      FIG. 6  is an enlarged, partial cut-away view of portion A of  FIG. 5 . 
           [0013]      FIG. 7  is an enlarged view of area  7  of  FIG. 3 , according to an embodiment, with some detail removed for clarity. 
           [0014]      FIG. 8  is a sectional view of the clutch, taken generally along line  3 - 3  of  FIG. 2 , according to another embodiment, with some detail removed for clarity. 
           [0015]      FIG. 9  is an enlarged, partial cut-away perspective view of portion the clutch of  FIG. 8 , similar to the view of  FIG. 6 . 
           [0016]      FIG. 10  is an enlarged view of area  10  of  FIG. 8 , with some detail removed for clarity. 
           [0017]      FIG. 11  is a sectional view of the embodiment of  FIG. 8 , taken generally along line  4 - 4  of  FIG. 2 . 
           [0018]      FIG. 12  is a perspective view of the embodiment of  FIG. 8 , taken generally along the view of line  5 - 5  of  FIG. 2 . 
           [0019]      FIG. 13  is a perspective view of another embodiment of a clutch, with some detail removed for clarity. 
           [0020]      FIG. 14  is an end view of the clutch of  FIG. 13 . 
           [0021]      FIG. 15  is a sectional view taken generally along line  15 - 15  of  FIG. 14 . 
           [0022]      FIG. 16  is an exploded view of the clutch of  FIG. 13 . 
           [0023]      FIG. 17  is a sectional view taken generally along line  17 - 17  of  FIG. 14 , where line  17 - 17  is rotated at the axis of the clutch. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]      FIG. 1  illustrates a vehicle V having a cab C heavy duty clutch  20  which selectively transmits torque from an engine flywheel  24  to a driven shaft  38  of a vehicle transmission T. The flywheel  24  is the driving member providing torque which is selectively transmitted to the transmission T. A standard clutch release assembly  42  is employed for affecting clutch  20  disengagement from the flywheel  24 . Such movement of release assembly R is achieved by depression of a clutch pedal CP in a vehicle cab C, or by an electronic clutch assembly (ECA). The clutch pedal CP may be mechanically linked to release assembly  42 . A full stroke of pedal CP will fully disengage the clutch  20 , moving release assembly  42  to an extreme right position (in the direction of the arrow R). 
         [0025]    Referring to  FIGS. 2-6 , the clutch  20  is illustrated as a double-disk friction clutch generally defined by an axis A-A ( FIG. 3 ). The clutch  20  includes a cover  22  that is detachably secured to the flywheel  24  of the internal combustion engine E. Between the cover  22  and the flywheel  24  is disposed a first friction disk  26  adjacent the flywheel  24  and an the intermediate plate  28  adjacent the first friction disk  26 . A second friction disk  30  is disposed adjacent a transmission-facing side  32  of the intermediate plate  28  and a the pressure plate  34  is disposed adjacent a transmission-facing side  36  of second friction disk  30 . First and second friction disks  26 ,  30  are secured for rotation on the transmission input shaft  38 , but are axially moveable in relation thereto. 
         [0026]    The intermediate plate  28  and the pressure plate  34  are secured for rotation with the cover  22  and, like friction disks  26  and  30 , are axially moveable in relation thereto. In the illustrated exemplary embodiment, the pressure plate  34  abuts a diaphragm spring  40  that moveably connects the pressure plate  34  to a release mechanism  42 . The release mechanism  42  is selectively controlled by a vehicle operator to engage and disengage the clutch  20 . However, it will be appreciated that the clutch  20  can be used with a variety of clamp-load generating release mechanisms besides a diaphragm spring. One well known example is the use of a plurality of levers and compression springs. Another alternative is a centrifugally actuated clutch having both an intermediate plate and a pressure plate. In the centrifugally actuated clutch, the clamping load is generated by pivoted weights, which swing radially outwardly with rotation of the clutch assembly. 
         [0027]    Referring now specifically to  FIGS. 4 and 5 , the intermediate plate  28  and the pressure plate  34  are moveably connected to the cover  22  by first and second drive straps  44  and  46 , respectively. The drive straps  44 ,  46  preferably include a plurality of resilient elements that are layered together to form a leaf spring, as is known. The first drive strap  44  provides a force on the intermediate plate  28  for biasing the intermediate plate  28  in a direction toward the pressure plate  34 . Similarly, the second drive strap  46  provides a force against the pressure plate  34  to ensure that the pressure plate  34  is in continuous contact with the diaphragm spring  40 . In return, the diaphragm spring  40  applies a clamping force against the pressure plate  34  when engagement of the clutch  20  is desired. While  FIGS. 4 and 5  show only one pair of drive straps  44 ,  46  for each of the intermediate plate  28  and the pressure plate  34 , respectively, a plurality of the drive straps  44  and  46  are distributed about the peripheries of the intermediate plate  28  and the pressure plate  34  in the exemplary embodiment illustrated. 
         [0028]    Referring again to  FIG. 4 , a first end  48  of the second drive strap  46  is fixedly secured to a flange portion  50  of the pressure plate  34  by a fastener  52 , such as a rivet or the like. A second end  54  of the second drive strap  46  is removably connected to the cover  22  by a drive strap fastener  56 , such as a threaded bolt or the like. A washer  58  may be disposed between a head  59  of the fastener  56  and the second drive strap  46  to ensure adequate contact pressure is distributed over second end  54  of the second drive strap  46 . 
         [0029]    With continuing reference to  FIG. 4 , a first end  60  of the first drive strap  44  is fixedly secured to the intermediate plate  28  by a fastener  64 , such as a rivet or the like, while a second end  62  of the first drive strap  44  is removably connected to the cover  22 . In the embodiment illustrated, the first drive strap  44  is preferably attached to the cover  22  by the fastener  56 , which may be a threaded bolt or the like. A generally cylindrical sleeve  66  extends between the second end  62  of the first drive strap  44  and the second end  54  of the second drive strap  46 . Accordingly, the first drive strap  44  and the second drive strap  46  are fixedly attached to the cover  22  with a single fastener  56 , although the first drive strap  44  and the second drive strap  46  may not be fixedly attached to the cover  22  with a single fastener. 
         [0030]    Referring to  FIGS. 6 and 7 , the intermediate plate  28  includes a plurality of intermediate attachment portions  70  having an aperture  72  formed therein, and the pressure plate  34  includes a plurality of pressure attachment portions  74  having an aperture  76  formed therein. A plurality of biasing members  80  are interposed between the intermediate plate  28  and the pressure plate  34 . Each biasing member  80  includes a first end  82  that abuts one of the pressure attachment portions  74 , and a second end  84  that abuts one of the intermediate attachment portions  70 . As illustrated in  FIG. 7 , when the friction disks  26 ,  30  contact the flywheel  24 , intermediate plate  28 , and the pressure plate  34 , the biasing members  80  are compressed such that the biasing members  80  exert an axial force (generally parallel to the axis A-A) to urge the pressure plate  34  away from the intermediate plate  28 . In the embodiment illustrated, the clutch  20  includes four biasing members  80 , although other suitable numbers of biasing members may be used. 
         [0031]    Each biasing member  80  includes a first support member  90  interposed therethrough. As illustrated, the first member  90  is slidably interposed through one of the apertures  72  of the intermediate plate  28  and coupled to one of the apertures  76  of the pressure plate  34  to permit the first member  90  to axially translate within the aperture  72  as the intermediate plate  28  moves axially relative to the pressure plate  34 . In the embodiment illustrated, the first member  90  is threadably received within the aperture  76 , although the first member  90  may be coupled with the pressure plate  34  and the intermediate plate  28  in any suitable manner to retain the biasing element  80  in a desired position while permitting the intermediate plate  28  to move axially relative to the pressure plate  34 . 
         [0032]    When the clutch  20  is disengaged, that is, when the release assembly  42  is moved away from the pressure plate  34 , the pressure plate  34  is urged to move away from the flywheel  24  due to the biasing force of the second drive strap  46 . Virtually simultaneously, the intermediate plate  28  automatically moves away from the flywheel  24  due to the biasing force of the first drive strap  44 . Due to the biasing force that the biasing member  80  exerts between the pressure plate  34  and the intermediate plate  28 , the axial distance the intermediate plate  28  moves is approximately one-half the axial distance the pressure plate  34  moves. In this manner, it is ensured that first and second friction disks  26 ,  30  are disengaged virtually simultaneously. 
         [0033]    It will be appreciated that axial movement of the intermediate plate  28  relative to the pressure plate  34  can be easily modified by altering the spring rates of the biasing member  80 , the first drive strap  44 , and the second drive strap  46 . In the embodiment illustrated, the spring rates of the first drive strap and the biasing member are about equal, although other spring rates may be used, as desired. 
         [0034]    Referring to  FIGS. 8-12 , an alternate exemplary embodiment of the inventive system is shown in detail. In this exemplary approach, a clutch  220  is provided that is substantially similar to the clutch  20  described in the first embodiment with a least one exception, namely, the biasing member may be adjustably preloaded, as discussed in greater detail below. 
         [0035]    The clutch  220  includes a cover  222  that is detachably secured to the flywheel  224  of the internal combustion engine E. Between the cover  222  and the flywheel  224  is disposed a first friction disk  226  adjacent the flywheel  224  and an the intermediate plate  228  adjacent the first friction disk  226 . A second friction disk  230  is disposed adjacent a transmission-facing side  232  of the intermediate plate  228  and a pressure plate  234  is disposed adjacent a transmission-facing side  236  of second friction disk  230 . First and second friction disks  226 ,  230  are secured for rotation on the transmission input shaft  238 , but are axially moveable in relation thereto. 
         [0036]    The intermediate plate  228  and the pressure plate  234  are secured for rotation with the cover  222  and, like friction disks  226  and  230 , are axially moveable in relation thereto. In the illustrated embodiment, the pressure plate  234  abuts a diaphragm spring  240  that moveably connects the pressure plate  234  to a release mechanism  242 . The release mechanism  242  is selectively controlled by a vehicle operator to engage and disengage the clutch  20 . However, it will be appreciated that the clutch  220  can be used with a variety of clamp-load generating release mechanisms besides a diaphragm spring. One well known example is the use of a plurality of levers and compression springs. Another illustrative alternative is a centrifugally actuated clutch having both an intermediate plate and a pressure plate. In the centrifugally actuated clutch, the clamping load is generated by pivoted weights, which swing radially outwardly with rotation of the clutch assembly. 
         [0037]    Referring now specifically to  FIGS. 9 ,  11 , and  12 , the intermediate plate  228  and the pressure plate  234  are moveably connected to the cover  222  by first and second the drive straps  244  and  246 , respectively. The drive straps  244 ,  246  preferably include a plurality of resilient elements that are layered together to form a leaf spring, as is known. The first drive strap  244  provides a force on the intermediate plate  228  for biasing the intermediate plate  228  in a direction toward the pressure plate  234 . Similarly, the second drive strap  246  provides a force against the pressure plate  234  to ensure that the pressure plate  234  is in continuous contact with the diaphragm spring  240 . In return, the diaphragm spring  240  applies a clamping force against the pressure plate  234  when engagement of the clutch  220  is desired. While  FIGS. 4 ,  5 , and  9  show only one pair of drive straps  244 ,  246  for each of the intermediate plate  228  and the pressure plate  234 , respectively, a plurality of the drive straps  244  and  246  are distributed about the peripheries of the intermediate plate  228  and the pressure plate  234  in the exemplary embodiment illustrated. 
         [0038]    Referring again to  FIG. 11 , a first end  248  of the second drive strap  246  is fixedly secured to a flange portion  250  of the pressure plate  234  by a fastener  252 , such as a rivet or the like. A second end  254  of the second drive strap  246  is removably connected to the cover  222  by a drive strap fastener  256 , such as a threaded bolt or the like. A washer  258  may be disposed between a head  259  of the fastener  256  and the second drive strap  246  to ensure adequate contact pressure is distributed over second end  254  of the second drive strap  246 . 
         [0039]    With continuing reference to  FIG. 11 , a first end  260  of the first drive strap  244  is fixedly secured to the intermediate plate  228  by a fastener  264 , such as a rivet or the like, while a second end  262  of the first drive strap  244  is removably connected to the cover  222 . In the embodiment illustrated, the first drive strap  244  is preferably attached to the cover  222  by the fastener  256 , which may be a threaded bolt or the like. A generally cylindrical sleeve  266  extends between the second end  262  of the first drive strap  244  and the second end  254  of the second drive strap  246 . Accordingly, the first drive strap  244  and the second drive strap  246  are fixedly attached to the cover  222  with a single fastener  256 , although the first drive strap  244  and the second drive strap  246  may not be fixedly attached to the cover  222  with a single fastener. 
         [0040]    Referring to  FIG. 10 , the intermediate plate  228  includes a plurality of intermediate attachment portions  270  having an aperture  272  formed therein, and the pressure plate  234  includes a plurality of pressure attachment portions  274  having an aperture  276  formed therein. A plurality of biasing members  280  are interposed between the intermediate plate  228  and the pressure plate  234 . Each biasing member  280  includes a first end  282  that abuts one of the pressure attachment portions  274 , and a second end  284  that abuts one of the intermediate attachment portions  270 . As illustrated in  FIG. 8 , when the friction disks  226 ,  230  contact the flywheel  224 , intermediate plate  28 , and the pressure plate  234 , the biasing members  280  are compressed such that the biasing members  280  exert an axial force (generally parallel to the axis B-B) to urge the pressure plate  234  away from the intermediate plate  28 . In the embodiment illustrated, the clutch  220  includes four biasing members  280 , although other suitable numbers of biasing members may be used. 
         [0041]    Each biasing member  280  includes an elongated first member  290  interposed therethrough. The first member  290  has a coupling member  292 , such as a threaded nut attached thereto. The first member  290  includes a collar  294  having a larger diameter than the remainder of the first member  290 . As illustrated, the first member  290  is slidably interposed through one of the apertures  272  of the intermediate plate  228  and threadably received in one of the apertures  276  of the pressure plate  234  to permit the first member  290  to axially translate within the aperture  272  as the intermediate plate  228  moves axially relative to the pressure plate  234 . The first member  290  is threaded to the aperture  276 , generally indicated at  300 . In the embodiment illustrated, the first member  290  is threadably received within the aperture  276  for adjusting the collar  294  axially relative to the pressure plate  234 , although the first member  290  may be coupled with the pressure plate  234  and the intermediate plate  228  in any suitable manner to retain the biasing element  280  in a desired position while permitting the intermediate plate  228  to move axially relative to the pressure plate  234 . 
         [0042]    As best illustrated in  FIG. 10 , when the second friction disk  230  is clamped between the pressure plate  234  and the intermediate plate  228 , the biasing element  280  is compressed. The threaded engagement between the first member  290  and the pressure plate  234  permits the biasing element to be preloaded when in the configuration of  FIG. 10 , as desired. Accordingly, a user may increase or decrease the rate of departure between the pressure plate  234  and the intermediate plate  228  by adjusting the first members  290 . In one embodiment of adjusting the preload, a user may determine a selected first amount of preload force for the biasing member. After operating for a period of time, if the wear on one of the friction disks  226 ,  230  exceeds the other, the first members  290  may be rotated relative to the pressure plate  234  to change the axial position of the first members  290  relative to the pressure plate  234 , thereby changing the preload on the biasing members  288 . This change in preload may result in an increased wear rate on the friction disk that was determined to have the lesser amount of wear as compared to the friction disk that was determined to have the greater amount of wear, thereby increasing the life of the clutch  220 . The coupling member  292  may be used to prevent unwanted rotation of the first member  290 , as is known. 
         [0043]    Although the first members  90 ,  290  are illustrated with threaded surface portions, the first members  90 ,  290  may include any surface features for axially restraining at least one of the pressure plate and the intermediate plate relative to the first member. Further, while the first member  290  illustrated with a collar  294  for axially restraining the biasing element  280  relative to the first member, the first member  290  may include any surface feature suitable for axially restraining the biasing element  280  relative to the first member  290 . 
         [0044]    Referring to  FIGS. 13-16 , an alternate exemplary embodiment of the inventive system is shown in detail. In this exemplary approach, a clutch  420  is provided that is substantially similar to the clutch  20  described in the first embodiment with a least one exception, namely, the drive straps may not be used. Specifically, the first drive straps  44  may omitted and the intermediate plate coupled for rotation with the cover, flywheel and pressure plate as described herein. 
         [0045]    The clutch  420  includes a cover  422  that is detachably secured to a flywheel  424  of an internal combustion engine, such as the internal combustion engine E. Between the cover  422  and the flywheel  424  is disposed a first friction disk  426  adjacent the flywheel  424  and an the intermediate plate  428  adjacent the first friction disk  426 . A second friction disk  430  is disposed adjacent a transmission-facing side  432  of the intermediate plate  428  and a pressure plate  434  is disposed adjacent a transmission-facing side  436  of second friction disk  430 . First and second friction disks  426 ,  430  are secured for rotation on a transmission input shaft  438 , but are axially moveable in relation thereto. 
         [0046]    The intermediate plate  428  and the pressure plate  434  are secured for rotation with the cover  422  and the flywheel  424  and, like friction disks  426  and  430 , are axially moveable in relation thereto. In the illustrated embodiment, the pressure plate  434  abuts a diaphragm spring  440  that moveably connects the pressure plate  434  to a release mechanism  442 . The release mechanism  442  is selectively controlled by a vehicle operator to engage and disengage the clutch  420 . However, it will be appreciated that the clutch  420  can be used with a variety of clamp-load generating release mechanisms besides a diaphragm spring. One well known example is the use of a plurality of levers and compression springs. Another illustrative alternative is a centrifugally actuated clutch having both an intermediate plate and a pressure plate. In the centrifugally actuated clutch, the clamping load is generated by pivoted weights, which swing radially outwardly with rotation of the clutch assembly. As discussed in greater detail below, the flywheel  424  includes a plurality of generally cylindrical apertures  444  for guiding the intermediate plate axially relative to the flywheel  424 . 
         [0047]    The cover  422  includes a plurality of flywheel attachment portions  450 . The intermediate plate  428  includes a plurality of lugs  452  ( FIGS. 13 and 16 ) that are interposed between pairs of the flywheel attachment portions  450  for coupling the intermediate plate  428  for rotation with the cover  422 . The lugs  452  include generally tubular alignment members  454  extending therefrom. As best seen in  FIG. 17 , the intermediate plate  428  is rotatably connected to the cover  222  by a plurality of drive straps  446 . The drive straps  446  may include a plurality of resilient elements that are layered together to form a leaf spring, as is known. The drive strap  458  provides a force against the pressure plate  434  to ensure that the pressure plate  434  is in continuous contact with the diaphragm spring  440 . In return, the diaphragm spring  440  applies a clamping force against the pressure plate  434  when engagement of the clutch  420  is desired. A plurality of the drive straps  446  are distributed about the peripheries of the intermediate plate  428  and the pressure plate  434  in the exemplary embodiment illustrated. 
         [0048]    Referring again to  FIG. 17 , a first end  460  of the drive strap  458  is fixedly secured to a flange portion  462  of the pressure plate  434  by a fastener  464 , such as a rivet or the like. A second end  466  of the drive strap  446  is removably connected to the cover  422  by a drive strap fastener  468 , such as a threaded bolt or the like. 
         [0049]    Referring to  FIGS. 15 and 16 , the intermediate plate  428  includes a plurality of intermediate attachment portions  470  having an aperture  472  formed therein, and the pressure plate  434  includes a plurality of pressure attachment portions  474  having an aperture  476  formed therein. A plurality of biasing members  480  are interposed between the intermediate plate  428  and the pressure plate  434 . Each biasing member  480  includes a first end  482  that abuts one of the pressure attachment portions  474 , and a second end  484  that abuts one of the intermediate attachment portions  470 . When the friction disks  426 ,  430  contact the flywheel  424 , the intermediate plate  428 , and the pressure plate  434 , the biasing members  480  are compressed such that the biasing members  480  exert an axial force (generally parallel to the axis C-C) to urge the pressure plate  434  away from the intermediate plate  428 . In the embodiment illustrated, the clutch  420  includes four biasing members  480 , although other suitable numbers of biasing members may be used. 
         [0050]    Each biasing member  480  includes an elongated first member  490  interposed therethrough. The first member  490  has a coupling member  492 , such as a threaded nut attached thereto. The first member  490  includes a collar  494  having a larger diameter than the remainder of the first member  490 . As illustrated, the first member  490  is slidably interposed through one of the apertures  472  of the intermediate plate  428  and threadably received in one of the apertures  476  of the pressure plate  434  to permit the first member  490  to axially translate within the aperture  472  as the intermediate plate  428  moves axially relative to the pressure plate  434 . The first member  490  is threaded to the aperture  476 , generally indicated at  500 . In the embodiment illustrated, the first member  490  is threadably received within the aperture  476  for adjusting the collar  494  axially relative to the pressure plate  434 , although the first member  490  may be coupled with the pressure plate  434  and the intermediate plate  428  in any suitable manner to retain the biasing element  480  in a desired position while permitting the intermediate plate  428  to move axially relative to the pressure plate  434 . 
         [0051]    As best illustrated in  FIG. 15 , when the second friction disk  430  is clamped between the pressure plate  434  and the intermediate plate  428 , the biasing element  480  is compressed. The threaded engagement between the first member  490  and the pressure plate  434  permits the biasing element to be preloaded when in the configuration of  FIG. 10 , as desired. Accordingly, a user may increase or decrease the rate of departure between the pressure plate  434  and the intermediate plate  428  by adjusting the first members  490 . In one embodiment of adjusting the preload, a user may determine a selected first amount of preload force for the biasing member. After operating for a period of time, if the wear on one of the friction disks  426 ,  430  exceeds the other, the first members  490  may be rotated relative to the pressure plate  434  to change the axial position of the first members  490  relative to the pressure plate  434 , thereby changing the preload on the biasing members  488 . This change in preload may result in an increased wear rate on the friction disk that was determined to have the lesser amount of wear as compared to the friction disk that was determined to have the greater amount of wear, thereby increasing the life of the clutch  420 . The coupling member  492  may be used to prevent unwanted rotation of the first member  490 , as is known. Further, the biasing member  488  may not be preloaded. 
         [0052]    The alignment members  454  extend into the apertures  444  and are axially moveable relative thereto as the intermediate plate  428  moves axially relative to the flywheel  424 . In another embodiment, a plurality of biasing members  490 , such as coil springs, may be interposed between the intermediate plate  428  and the flywheel  424  to urge the intermediate plate  428  to move generally in the direction of the arrow R as the pressure plate  434  moves generally in the direction of the arrow R. The combined force of the biasing members  510  of the clutch  420  may be about equal to the combined force of the biasing members  480  to urge the intermediate plate to move about half of the axial distance moved by the pressure plate  434  relative to the flywheel during clutch engagement and disengagement. 
         [0053]    Although the steps of operating and assembling the clutches  20 ,  220 ,  420  may be listed in an order, the steps may be performed in differing orders or combined such that one operation may perform multiple steps. Furthermore, a step or steps may be initiated before another step or steps are completed, or a step or steps may be initiated and completed after initiation and before completion of (during the performance of) other steps. 
         [0054]    The preceding description has been presented only to illustrate and describe exemplary embodiments of the methods and systems of the present invention. It is not intended to be exhaustive or to limit the invention to any precise form disclosed. It will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the claims. The invention may be practiced otherwise than is specifically explained and illustrated without departing from its spirit or scope. The scope of the invention is limited solely by the following claims.