Abstract:
A clutch assembly for a motor vehicle includes a retainer assembly having an upper and lower portion separable by a separating member. The separable member causes the retainer assembly to contract in response to movement toward a released position. Contracting the retainer assembly in the release position provides for additional clearance between the friction discs and flywheel without a corresponding increase in the length of travel of the retainer assembly. The guide member is stationary relative to the retainer assembly and cooperates with the separating member to cause the retainer assembly to expand and contract during movement to engage and disengage the clutch. Additional movement of the retainer assembly increases clearance to between the flywheel and friction discs without corresponding increase in retainer assembly travel to minimize clutch drag.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates generally to a clutch retainer for a motor vehicle clutch assembly, and specifically to a retainer assembly that expands to maximize pressure plate travel.  
           [0002]    Typically, a clutch is utilized to selectively transmit torque between an engine and a transmission. When the clutch is engaged, clutch levers force pressure plates against clutch disks to engage a flywheel. When the clutch is disengaged, the clutch levers are lifted from the pressure plate to disengage the pressure plates and free the clutch discs from engagement with the flywheel.  
           [0003]    The clutch levers are moved between an engaged and disengaged position by a retainer assembly moved axially along a shaft. The retainer assembly and the clutch levers are biased toward the engaged position by a diaphragm spring. The clutch disks disengage the flywheels when a force is exerted to pull the retainer assembly toward the disengaged position. Clutch straps bias the pressure plates away from the flywheel so that when the retainer assembly is pulled toward the disengaged position the pressure plates disengage the clutch disks.  
           [0004]    The biasing force of the diaphragm spring creates a clamp load against the flywheel. The clamp load determines the amount of torque transfer from the engine to the transmission. The engaged and disengaged positions are obtained by moving the retainer assembly along an axis to transmit a biasing force through a plurality of levers to sandwich the clutch disk between the flywheel and the pressure plate. The biasing force exerted on the pressure plates by the levers is commonly referred to as clamp load. Higher clamp loads provide better torque transfer between the engine and the transmission.  
           [0005]    The clamp load is balanced against the amount of force required to disengage the clutch, commonly referred to as pedal effort. Typically, the clamp load is balanced against an increase in pedal effort. Further, if the pressure plates are not moved far enough away from the flywheel, the pressure plates may not completely disengage the clutch. Such a condition can cause increased wear on the friction disks. As appreciated, pulling the pressure plate further away from the flywheel require greater release assembly travel.  
           [0006]    Accordingly, there is a need for a clutch assembly with increased clearance between the flywheel and friction disks during disengagement without a corresponding increases in release assembly travel.  
         SUMMARY OF THE INVENTION  
         [0007]    An embodiment disclosed in this application is a clutch assembly including a collapsible retainer assembly for increasing clamp pressure plate travel without increasing retainer assembly travel.  
           [0008]    This invention includes a clutch assembly movable between an engaged and disengaged position. This invention provides greater lift off the flywheel by selectively expanding and contracting the retainer arm.  
           [0009]    One embodiment of the retainer assembly includes upper and lower retainer portions with a cam positioned therebetween. The cam includes an arm with a slot associated with a guide member. The guide member is stationary relative to the upper and lower retainer portions. The lower retainer portion actuates levers that force the pressure plates to sandwich the clutch disks therebetween. The upper retainer portion is biased toward the engaged position by the diaphragm spring. A guide member remains stationary relative to the upper and lower retainer portions. A spring biases the upper and lower retainer portions towards the collapsed position. The arm includes a slot supported by a pin positioned on the guide member.  
           [0010]    The cam includes a length and a width, with the length greater than the width.  
           [0011]    In the collapsed position of the retainer assembly, the width of the cam is arranged substantially perpendicular to both the upper and lower retainer portions. The spring along with the lever and diaphragm spring bias the upper and lower retainer assemblies towards each other into the collapsed position.  
           [0012]    The diaphragm spring drives the retainer assembly toward the engaged position causing rotation of the cam about the pin. Rotation of the cam places the length in a position between and perpendicular to the upper and lower retainer portions. This provides the expanded position of the retainer assembly. Contraction of the retainer assembly in the release position provides additional travel distance. The additional distance provided by the contracted retainer assembly increases clearance between the friction discs and flywheel without increasing the travel length of the retainer assembly along the axis  
           [0013]    Another embodiment of the retainer assembly includes upper and lower retainer portions that cooperate to form a cavity. At least two balls are disposed within the cavity and cooperate with a guide member. The guide member includes a ramped portion extending between a first diameter and a second diameter. The first diameter is larger than the second diameter such that movement of the upper and lower retainer assemblies, relative to the guide member changes the configuration of the cavity.  
           [0014]    In the collapsed position, the upper retainer portion is pulled up against a shoulder. In this position, the smaller diameter cooperates with the cavity, trapping the balls in a position allowing the upper and lower portions, to collapse onto each other. Biasing springs within the lower retainer portion bias the balls against the guide member. The lever biases the lower retainer portion towards the upper retainer and the diaphragm spring biases the upper retainer portion toward the lower retainer portion. The upper retainer portion includes slots for receiving the springs in the collapsed position.  
           [0015]    Release of the clutch pedal moves the upper retainer portion toward the engaged position. As the upper retainer portion moves relative to the stationary guide member, the balls are driven along the ramped portion from the smaller diameter towards the larger diameter. Cooperation between the larger diameter and the cavity changes the configuration of the cavity to trap the balls between the upper and lower retainer portions. A slot receives the guide member in the collapsed position. This configuration of the cavity causes the balls to separate the upper and lower retainer portions, thereby attaining the expanded position of the retainer assembly.  
           [0016]    Embodiments of this invention provide for an increased clearance between friction disks and flywheel without increasing the travel distance of the retainer assembly. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows:  
         [0018]    [0018]FIG. 1 is a cross-sectional view of the clutch assembly in a clamp position;  
         [0019]    [0019]FIG. 2 is a cross-sectional view of the clutch assembly in a disengaged position;  
         [0020]    [0020]FIG. 3 is a cross-sectional view of one embodiment of the retainer assembly in a collapsed position;  
         [0021]    [0021]FIG. 4 is a cross-sectional view of the cam;  
         [0022]    [0022]FIG. 5 is a cross-sectional view of the retainer assembly in an expanded position;  
         [0023]    [0023]FIG. 6 is a cross-sectional view of another embodiment of the retainer assembly in the collapsed position; and  
         [0024]    [0024]FIG. 7 is an embodiment of the retainer assembly in an expanded position. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0025]    [0025]FIG. 1 is a cross-sectional view of a clutch assembly  10  including a clutch housing  12  attached to a flywheel  11  to rotate about an axis  14 . Clutch disks  20  are sandwiched between pressure plates  22  and the flywheel  11  to transmit torque from an engine  13  to a transmission  15 . Levers  32  bias the pressure plates  22  into contact with the clutch disks  20 , which in turn engage the flywheel  11 . The levers  32  are support between the clutch housing  12  and the retainer assembly  25 . The retainer assembly  25  is biased toward the flywheel  11  by a diaphragm spring  34 . Clutch straps  21 , shown schematically, bias the pressure plates  22  away from the flywheel  11 . The diaphragm spring  34  overcomes the biasing force of the clutch straps  21  to move the retainer assembly  25  toward the flywheel to an engaged position.  
         [0026]    The retainer assembly  25  is movable along the axis  14  between the engaged position and a disengaged position. In the disengaged, position the retainer assembly  25  releases the levers  32 , and the pressure plates  22  from engagement with the clutch disks  20  and the flywheel  11 . The retainer assembly  25  includes upper and lower portions  24 ,  26  movable between an expanded and a collapsed position. A separating member  31  is disposed between the upper and lower retainer portions  24 ,  26 . The separating member  31  moves the upper and lower retainer portions  24 ,  26  to an expanded position as the retainer assembly  25  moves toward the engaged position.  
         [0027]    A release sleeve  16  connected to a bearing assembly  36  is actuated to move the retainer assembly  25  between engaged and disengaged positions. As appreciated, a worker knowledgeable in the art will understand the operation of the release sleeve  16  and the bearing assembly  36  to selective couple the engine  13  and the transmission  15  (both shown schematically).  
         [0028]    Referring to FIG. 2, the clutch assembly  10  is shown in a disengaged position. In the disengaged position the bearing assembly  36  is pulled away from the flywheel  11 , thereby pulling the release sleeve  16  and the retainer assembly  25  toward the disengaged position. The separating member  31  shifts between the upper and lower retainer portions  24 ,  26  to provide a collapsed position of the retainer assembly  25 .  
         [0029]    The biasing load exerted by the diaphragm spring  34  is overcome by depressing a clutch pedal  37 . It is desirable to have relatively high clamp loads during engagement of the clutch disks  20  with the flywheel  11 . The retainer assembly  25  of this invention contracts to provide greater clearance between pressure plate  22  and flywheel  11  without increasing retainer assembly  25  travel to eliminate the need for additional pedal travel.  
         [0030]    Referring to FIGS.  3 - 5 , an embodiment of the retainer assembly  25  is disclosed and includes the upper and lower retainer portions  24 ,  26  separated by a cam  30 . The lower retainer portion  26  is connected to actuate the lever  32 . The upper retainer portion  24  is biased toward an engaged position by the diaphragm spring  34 . The retainer assembly  25  illustrated in FIG. 3 is in the collapsed position. Movement toward the disengaged position of the clutch assembly  11  coincides with the collapse of the retainer assembly  25 .  
         [0031]    A guide member  28  remains stationary relative to the upper and lower retainer portions  24 ,  26 . A spring  38  biases the upper and lower retainer portions  24 ,  26  towards each other and the collapsed position. The cam  30  includes an arm  45  with a slot  46  engaged to pin  44 . The pin  44  is positioned on the guide member  28 .  
         [0032]    The cam  30  includes a length  42  and a width  40  (FIG. 4). The length  42  is greater than the width  40 . In the collapsed position of the retainer assembly (FIG. 3), the width  40  is arranged substantially perpendicular to both the upper and lower retainer assemblies  24 ,  26 . The spring  38  along with the lever  32  and diaphragm spring  34  biases the upper and lower retainer portions  24 , 26  towards each other into the collapsed position.  
         [0033]    When the clutch pedal  37  is released (FIGS. 1 and 2), the diaphragm spring  34  will act to bias the retainer assembly  25  towards the flywheel  11 . The guide member  28  remains stationary relative to the retainer assemblies  24 ,  26 . Preferably, the guide member  28  is associated with the retainer assembly  25  for preventing relative rotation between the retainer assembly  25  and the clutch housing  12 . A worker skilled in the art would understand that the specific configuration and placement of the guide member  28  is application specific and any type known in the art is within the contemplation of this invention.  
         [0034]    The diaphragm spring  34  drives the retainer assembly  25  toward the engaged position causing rotation of the cam  30  about the pin  44 . Rotation of the cam  30  places the length  42  in a position between and perpendicular to the upper and lower retainer portions  24 , 26  (FIG. 5). This provides the expanded position of the retainer assembly  25 . Expansion of the retainer assembly provides additional travel distance along the axis  14 , forcing the levers  32  into contact with the pressure plates  22 . The additional distance provided by the cam  30  increases the clamp load on the flywheel  11  without increasing the travel length of the retainer assembly  25  along the axis  14 . Subsequent actuation of the clutch pedal  37  pulls the upper retainer assembly  24  upwardly, causing the cam  30  to rotate about the pivot pin  44  to the collapsed position shown in FIG. 3.  
         [0035]    Referring to FIGS. 6 and 7, another embodiment of the retainer assembly  25  is disclosed. In this embodiment, upper and lower retainer portions  70 ,  72  cooperate to form a cavity  48 . At least two spherical members  56  are disposed within the cavity  48  and cooperate with the guide member  68 . The guide member  68  includes a ramped portion  58  extending between a first diameter  50  and a second diameter  52 . The first diameter  50  is larger than the second diameter  52  such that movement of the upper and lower retainer assemblies  70 , 72  relative to the guide member  68  changes the configuration of the cavity  48 .  
         [0036]    In the collapsed position (FIG. 6) the upper retainer portion  24  is pulled up against a shoulder  66 . In this position, the smaller diameter  50  cooperates with the cavity  48 , trapping the spherical members  56  in a position allowing the upper and lower portions  70 , 72  to collapse onto each other. Biasing springs  60  bias the spherical members  56  against the guide member  28 . The lever  32  biases the lower retainer portion  72  towards the upper retainer  70  and the diaphragm spring  34  biases the upper retainer portion  70  toward the lower retainer portion  72 . The upper retainer portion includes slots  62  for receiving the springs  60  in the collapsed position.  
         [0037]    Release of the clutch pedal  37  moves the upper retainer portion  70  toward the engaged position. As the upper retainer portion  24  moves relative to the stationary guide member  68 , the spherical members  56  are driven along the ramped portion  58  from the smaller diameter  52  towards the larger diameter  50 . Cooperation between the larger diameter  50  and the cavity  48  changes the configuration of the cavity to trap the spherical members  56  between the upper and lower retainer portions  70 , 72 . A slot  64  receives the guide member  68  when the retainer assembly  25  is in the collapsed position. This configuration of the cavity  48  separates the upper and lower retainer portions  70 , 72 , thereby attaining the expanded position of the retainer assembly  25 . Expansion of the retainer assembly  25  increases the travel of the levers  32 , resulting in an increase in clamp load exerted on the pressure plates  20 . Further, contraction of the retainer assembly  24  results in greater clearance between the flywheel  11  and pressure plates  22  without a corresponding increase in retainer assembly  24  travel.  
         [0038]    The foregoing description is exemplary and not just a material specification. The invention has been described in an illustrative manner, and should be understood that the terminology used is intended to be in the nature of words of description rather than of limitation. Many modifications and variations of the present invention are possible in light of the above teachings. The preferred embodiments of this invention have been disclosed, however, one of ordinary skill in the art would recognize that certain modifications are within the scope of this invention. It is understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. For that reason the following claims should be studied to determine the true scope and content of this invention.