Abstract:
A heavy duty clutch release mechanism including a driveline master clutch release yoke where a bearing support shaft is used to minimize bearing end loading. The clutch release yoke is rotatably fixed to the clutch release shaft for rotation and having first and second forks extending adjacent to the release bearing assembly. The yoke includes a number of bearing support shafts having a first end attached to an inboard side of the first and second forks and a second end having a retention flange. The bearing elements are rotatably mounted on the bearing support shafts and engaging the surface of the clutch release bearing.

Description:
This application claims the benefit of U.S. Provisional Application No. 60/431,260, filed Dec. 6, 2002, the entire contents of which are herein incorporated by reference. 

   FIELD OF INVENTION 
   The present invention relates to a driveline master clutch release yoke and more specifically to a driveline master clutch release yoke where a bearing support shaft is used to minimize bearing end loading. 
   BACKGROUND OF THE INVENTION 
   A heavy duty clutch release mechanism known in the art includes a clutch release sleeve, a clutch release bearing and a clutch release yoke. The clutch release lever has a lever engagement feature at a first end. The clutch release bearing engages a second end of the clutch release sleeve and has an inner race rotatably fixed to the second end of the clutch release sleeve. The clutch release yoke has roller assemblies disposed on each of two arms for engagement with an outer race of the clutch release bearing. 
   Unfortunately, the roller assemblies have several problems. Among other things the bearing elements associated with the roller assemblies have been subjected to the build up of contamination over time in combination with excessive end loading. Thus, the roller assemblies have failed sooner than would be optimally desired. 
   SUMMARY OF THE INVENTION 
   The present invention provides a solution to a field problem when a roller assembly with bearing element is used on each fork end of a clutch release yoke. The release yoke includes at least two forks connected by a bridge section. The forks each have an inwardly extending bearing support shaft such that the bearing element supported thereon can engage a clutch release bearing. A retention flange is formed at one end of the bearing support shaft to hold the bearing element in the proper position and to protect the bearing from end loading. Another advantageous result is that the improved retention flange also protects the roller bearing from harmful contamination. As a result premature aging of the roller assembly is minimized. 
   Another advantage is that a positioning snap ring becomes optional since the bearing element can be held between the retention flange and an inner surface of the fork, providing enhanced performance while simplifying assembly and reducing cost. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a rearward facing end view of a clutch release yoke and clutch fork. 
       FIG. 2  is a side view of the release yoke and fork of  FIG. 1  shown in the direction of arrows  2 . 
       FIG. 3  is a partial cross-sectional view of both the prior art roller assembly and the roller assembly of the present invention. 
       FIG. 4  is a sectional side view of the clutch assembly in a released position. 
       FIG. 5  is a sectional side view of the release bearing assembly. 
       FIG. 6  is a cross-sectional view of an embodiment of the roller assembly of  FIG. 3  showing a positioning snap ring. 
       FIG. 7  is a cross-sectional view of an embodiment of the roller assembly of  FIG. 3  showing no positioning snap ring. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring now to the drawings, the preferred illustrative embodiments of the present invention are shown in detail. Although the drawings represent some preferred embodiments of the present invention, the drawings are not necessarily to scale and certain features may be exaggerated to better illustrate and explain the present invention. Further, the embodiments set forth herein are not intended to be exhaustive or otherwise limit or restrict the invention to the precise forms and configurations shown in the drawings and disclosed in the following detailed description. 
     FIG. 1  illustrates a clutch housing  10  pivotably supporting a clutch yoke  12 . Clutch yoke  12  is used to selectively disengage clutch assembly  14 , best shown in  FIG. 4 , through displacement of a clutch release bearing assembly  15 . A clutch linkage  16  disposed between a vehicle operator and the clutch yoke  12  includes an operating lever  17  disposed outside of clutch housing  10 . 
   As illustrated in  FIG. 4 , clutch assembly  14  includes a clutch cover  18  fixed to a flywheel  20 . In turn, flywheel  20  is secured to an engine crankshaft (not shown) for rotation about an axis of rotation  22 . A transmission input shaft  24 , splined on a first end  25 , extends from a transmission case (not shown) along axis  22 . A pressure plate  28  is disposed between the clutch cover  18  and the flywheel  20  for axial movement therebetween, and it is rotatably fixed to the cover. A clutch driven disc  26  is rotatably fixed to the transmission input shaft  24  by way of the splined first end  25 , and positioned between the flywheel  20  and the pressure plate  28  for axially slidable movement between the flywheel and pressure plate. Pressure plate  28  selectively compresses driven disc  26  against flywheel  20 . 
   A clutch release sleeve  31  extends about axis  22  and is slidably and rotatably disposed on the transmission input shaft  24 . It includes a first end  32  disposed between the pressure plate  28  and the clutch cover  18  and a second end  33  disposed on a side of the cover opposite the pressure plate  28 . A plurality of clutch apply levers  30  are circumferentially distributed about axis  22 , and extend radially from first end  32  of the release sleeve  31 . Levers  30  include a radially inwardly disposed ends engaging first end  32  of the release sleeve  31 . A radially outer end of each lever  30  extends between release sleeve  31  and the pressure plate  28  and engages cover  18  directly, or indirectly by way of an adjusting mechanism  34 . 
   As best illustrated in  FIG. 4  bearing release assembly  15  is disposed outside the clutch cover  18  and is connected to second end  33  of sleeve  31 . As shown in  FIG. 5 , an inner race  36  of release bearing assembly  15  is engaged with release sleeve  31  at second end  33  for axial movement therewith. A snap ring  90  helps retain inner race  36  on sleeve  32  and is received in a groove  92  circumferentially disposed about an outer surface of sleeve  31  such that the snap ring is contacts the inner race  36 . An input shaft bushing  37  is press-fit in sleeve  31  in axial alignment with bearing assembly  15 . An outer race  38 , rotatably fixed to a bearing housing  39 , is prevented from rotating relative to clutch housing  10 . The outer race  38  is separated from the inner race by bearing members  35 . 
   As shown in  FIG. 4 , angle springs  40 , which develop the clutch apply loads, are disposed between clutch cover  18  and the first end  32  of sleeve  31 . Both the sleeve  31  and cover  18  have corresponding spring engaging features  42  and  44  respectively. 
   Clutch yoke  12 , shown best in  FIGS. 1 through 3 , straddles clutch release bearing assembly  15  and is secured to two coaxial fork shafts  46  for pivoting about pivot axis  48 , defining a second axis of rotation at a right angle with respect to the axis of rotation  22 . Preferably, pivot axis  48  is closer to the axis of rotation than clutch release bearing assembly outer race  38 . An opposing end  94  of each fork shaft  46  is received within a corresponding opening  96  of clutch housing  10 . One of the fork shafts  46  has an extended axial extent to such that its opposing end is fixed to an operating lever  17  such that movement of operating lever  17  will result in rotation of clutch yoke  12 . Thus, fork shafts  46  each act as a clutch release shaft. 
   A cross member  50  of yoke  12  connects two opposed arms  52  adjacent bearing assembly  15 . Each of the arms  52  have roller assemblies  54  positioned on an inboard side of an arm  52 . Roller assembly  54  engages wear pads  56  on a forward side of bearing assembly  15 . 
   Roller assembly  54  and release bearing assembly  15  are designed as a matched set so that the axial position of sleeve  31  varies as a function of the rotative position of lever  17  exactly as the position of sleeve  31  would vary with the position of lever  17  in a non-roller system. This allows the roller yoke  12  to be installed in a system not explicitly designed for compatibility with a roller fork. The arms  52  of yoke  12  have been widened to make them more resistant to the torsional twisting force introduced by the cantilevered roller assembly  54 . 
   The roller assembly  54  is shown in more detail on the right hand side of  FIG. 3 , where for the purpose of illustration, the prior art roller discussed in the Background of the Invention is shown on the left hand side. Roller assembly  54  includes a bearing element  58  circumferentially disposed about an outer surface of a bearing support shaft  60 . Bearing element  58  is not limited to one particular type of bearing design. For example, if a roller bearing is used, such roller bearings may include needle bearings, ball bearings, sleeve bearings and plastic bearings of various designs. 
   Bearing support shaft is typically made from steel and includes a first end  62  received within a corresponding opening  64  of one of the arms  52  and a second end  66  including a radially outwardly extending retention flange  68 . Typically, the shaft  60  is compression fitted within opening  64  although any securement mechanism, including a threaded arrangement, may be used. Bearing element  58  is disposed between flange  68  and an inner surface  70  of arm  52  adjacent to opening  64 . 
   Two embodiments of the roller assembly  54  are shown in  FIGS. 6 and 7 , respectively. In the embodiment of  FIG. 6 , a roller assembly  54  includes a positioning snap ring  80  disposed between aligned grooves  82  and  84  of the support shaft  60  and bearing element  58 . 
   A more preferred embodiment of roller assembly  54  is illustrated in  FIG. 7 , where there is no positioning snap ring  80 . 
   A roller assembly  54  in accordance with the present invention provides a number of advantages including the reduction of wear on the clutch release bearing assembly. 
   Further, the addition of a retention flange  68  provides a significant improvement over the roller assemblies known in the prior art. For example, as illustrated in  FIG. 7 , it helps to hold bearing element  58  in a proper position independently of any snap ring  80 . Moreover, it protects the bearing element from undesirable end loading. Further, retention flange  68  protects bearing element from harmful contamination. In the illustrated embodiment, the radial extent of retention flange  68  is such that it substantially covers an end portion of bearing element  58  and most specifically covers and protects the portion of bearing element  58  in contact with shaft  60 . In some preferred embodiments, however, it may be desirable to have the radial extent of flange  68  extend even further to provide additional protection to bearing element  58 . 
   The invention operates in the following manner.  FIG. 4  shows the clutch in an engaged position. The position of clutch fork  12  and lever  17  is controlled by the position of release bearing assembly  15 , which is in turn controlled by the travel limits of levers  31  against pressure plate  28 , responsive to the force of springs  40 . When the clutch is released by the operator through linkage  16 , operating lever  17  rotates clutch fork  12 , axially displacing release bearing assembly  15  rearwardly against the force of springs  40  to unload pressure plate  28 . The unloading of pressure plate  28  unclamps driven disc  26 , enabling relative rotation between driven disc  26  and pressure plate and flywheel  28  and  20 . The second or pivot axis  48  is now forward of, or closer to the flywheel  20  than the bearing members. The pivot axis  48  remains closer to the rotative axis than the outer race  38 . 
   As fork  12  is pivoted to the disengaged position, roller assemblies  54  move in a first direction along wear pads  56 . As the clutch is reengaged by the operator, roller assemblies  54  move in a second direction, opposite the first direction, along wear pads  56 . Roller assemblies  54  prevent the undesired wear of sleeve  37  by eliminating substantially all of the frictional drag of fork  12  against pads  56 . 
   The present invention has been particularly shown and described with reference to the foregoing embodiments, which are merely illustrative of the best modes for carrying out the invention. It should be understood by those skilled in the art that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention without departing from the spirit and scope of the invention as defined in the following claims. It is intended that the following claims define the scope of the invention and that the method and apparatus within the scope of these claims and their equivalents be covered thereby. This description of the invention should be understood to include all novel and non-obvious combinations of elements described herein, and claims may be presented in this or a later application to any novel and non-obvious combination of these elements. Moreover, the foregoing embodiments are illustrative, and no single feature or element is essential to all possible combinations that may be claimed in this or a later application.