Patent Abstract:
A clutch release assembly for use in a motor vehicle includes a bearing and a housing retaining the bearing. The housing has disposed on its exterior two L-shaped lugs are formed on opposite sides of the housing and extending radially therefrom. The lugs each define a circumferential engagement surface in a plane normal to the axis and face toward the bearing. An axially extending engagement surface is normal to the circumferential engagement surface wherein the tips of the arms of a clutch yoke engage the circumferential engagement surface to axially displace the release assembly. The axially extending surfaces prevent rotation of the housing by engagement with the tips of the arms.

Full Description:
FIELD OF THE INVENTION 
     This invention relates to release assemblies for use with clutches for manual transmissions, and particularly release assemblies for medium and heavy duty trucks. 
     BACKGROUND OF THE INVENTION 
     Pull type friction clutches for medium and heavy duty trucks commonly have a release assembly with a bearing housing with a square lower portion and a release fork with machined tines. The release assembly is concentric with and circumscribes the transmission input shaft. The release assembly is axially displaced by a clutch yoke or fork in the course of disengaging and re-engaging the clutch. The yoke acts against the bearing housing to displace the bearing and release the clutch. As the release force is diminished, the spring force of the clutch acts against the yoke, through the bearing housing, to restore the yoke and the associated shift linkage to the engaged position. The machined tines engage the square lower portion of the housing, thereby preventing rotation of the housing about the transmission input shaft. Preventing rotation of the housing is necessary to ensure that the tips of the yoke engage the contact pads on the housing. The contact pads are fixed to lugs extending from the sides of the housing. The contact pads are formed of a suitable wearable material which sustains relative motion of the yoke tips without damaging the yoke tips. After a period of use, the release assembly is removed and replaced. A reason commonly necessitating the removal and replacement of the release assembly is the wearing of the contact pads. 
     Customer expectations of increasingly longer periods of service-free operation require improvement of the yoke to release assembly interface durability. It is also desired to eliminate the need to provide a machined interface between the yoke and the release assembly to prevent rotation of the bearing housing. While U.S. Pat. No. 5,911,296, assigned to the assignee of the present invention, discloses one approach to improving the yoke to release assembly interface durability, it does not teach how to prevent the rotation of the bearing housing without employing a machined yoke to release assembly interface. 
     SUMMARY OF THE INVENTION 
     The present invention discloses a release assembly restricting rotation of a housing of the release assembly without requiring the provision of machined surfaces on either the yoke or the release assembly. 
     The present invention also discloses a release assembly providing improved durability at the yoke to release assembly interface. 
     A clutch release assembly for use in a motor vehicle includes a bearing having an inner race and an outer race and having a release sleeve formed integral with the inner race and having an axis of rotation around which the outer race rotates relative to the inner race. A cover formed of metal receives at least in part the bearing assembly. The cover has a radially inwardly extending flange partially closing a first end. The cover has an open second end. The radially inwardly extending flange has an inner diameter sized to permit the release sleeve to pass therethrough and to prevent the bearing from passing therethrough. A housing is fixed to the second end of the cover. The housing, together with the cover, defines a cylindrical cavity therein centered on the axis of rotation. The bearing is disposed within the cylindrical cavity and is oriented to have its release sleeve extending past the radially inwardly extending flange. The housing is formed of metal. A low friction bushing is fixedly disposed within the cylindrical cavity and has an inside diameter smaller than an inside diameter of the inner race. A spring is axially disposed between the bushing and the bearing assembly. The spring is sized to engage the outer race and biases the outer race against the cover. Two L-shaped lugs are formed on opposite sides of one of the cover and the housing and extend radially therefrom. The lugs each define a circumferential engagement surface in a plane normal to the axis and face toward the bearing. An axially extending engagement surface is normal to the circumferential engagement surface wherein the tips of the arms of a clutch yoke engage the circumferential engagement surface to axially displace the release assembly. The axially extending surfaces prevent rotation of the housing by engagement with the tips of the arms. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of a drive train, including an engine, a transmission and an axle in their relative vehicle locations. 
     FIG. 2 is a sectional view of a clutch assembly including a first embodiment of a release assembly. 
     FIG. 3 is an exploded perspective view of the release assembly of FIG.  2 . 
     FIG. 4 is partial perspective side view of a second embodiment of a release assembly. 
     FIG. 5 is an exploded perspective view of a third embodiment of a release assembly. 
     FIG. 6 is a sectional side view the embodiment of FIG.  5 . 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     A frictional drive or clutch  10  is disposed between an engine  12  and a transmission  14 . Clutch  10  rotates about an axis of rotation  15 . A clutch linkage  16  is used by a vehicle operator to selectively disengage and re-engage clutch  10 . A clutch yoke  18 , comprising part of the clutch linkage and alternatively referred to as a clutch fork, is at an end of the clutch linkage  16 . Yoke  18  engages a release assembly  20  of clutch  10 . Release assembly  20  is slidably and rotatably disposed over input shaft  22  of transmission  14 . Release assembly rides on a stationary sleeve or quill  23  extending from transmission  14 . Quill  23  is radially disposed between input shaft  22  and release assembly  20 . Although as shown, quill  23  is stationary, extending from the transmission housing bearing cover, release assembly  20  could alternatively be employed in combination with a dynamic quill which rotates with the input shaft, or with no quill at all. 
     Clutch  10  also includes a flywheel  24  rotatably coupled to the crank shaft  25  of engine  12  for unitary rotation therewith. A driven disc  26  is slidably disposed over the splines of input shaft  22  for unitary rotation therewith. Driven disc  26  is axially disposed between flywheel  24  and a pressure plate  28 . A clutch cover  30  is mounted directly to flywheel  24  and substantially encloses pressure plate  28 . Cover  30  can be cast or stamped. A diaphragm spring  32  disposed between pressure plate  28  and cover  30  biases pressure plate  28  toward flywheel  24 , compressing driven disc  26  between pressure plate  28  and flywheel  24 , and causing input shaft  22  to rotate as a unit with flywheel  24  and pressure plate  28 . Diaphragm spring  32  has fingers  34  which extend radially inwardly from an outer annular portion  36 . Tips of fingers  34  are engaged by a retainer  38  disposed at an end of release assembly  20 . Retainer  38  is kept in engagement with release assembly by a snap ring  39 . Annular portion  36  engages cover  30  at an outer diameter, and engages pressure plate  28  at an inner diameter. An anti-rotation strap  40  connects pressure plate  28  with cover  30 , rotatively fixing pressure plate  28  to flywheel  14  and cover  30 , while allowing relative axial motion between pressure plate  28  and cover  30 . 
     While a diaphragm type clutch is shown in FIG. 2, it is to be appreciated that a lever type arrangement could alternatively be employed. Lever type clutches are well known. In an exemplary lever type clutch (not shown) a plurality of pressure springs is disposed between a retainer disposed at an end of release assembly  20  and cover  30 . A plurality of levers, six in one embodiment, radiate outwardly from the retainer. The radially inwardly disposed tips of the levers engage the retainer. The levers in turn pivot on their radially outwardly disposed ends on a fulcrum provided on the cover. An intermediate point on the levers engages pressure plate  28 . The pressure springs are oriented to force the retainer and the tips of levers away from the cover, and thereby bias pressure plate  28  toward flywheel  24  and engaging driven disc  26 . 
     A hub of driven disc  26  has internal splines slidably disposed over external splines of input shaft  22 . A plate having friction material disposed on both sides thereof is rotatably connected to the hub. Commonly, damping springs are disposed between the hub and the plate. 
     A first embodiment of release assembly  20  includes a bearing cover  42 , a bushing  44 , a ball bearing  46 , a bearing housing  48  and a pre-load/anti-rotation spring  50 . Yoke  18  has two arms  52  in engagement with release assembly  20 . Rollers  54 , disposed on an inboard side and at an end of each arm, engage bearing housing  48 . 
     Bearing  46  is preferably a ball bearing so as to be able to sustain thrust loads. Bearing  46  is also preferably sealed to prevent or at least minimize the risk of potentially damaging debris entering the bearing and damaging the rollers, and/or the bearing races. Bearing  46  includes an outer race  56  and an inner race  58 . Ball shaped rollers are disposed between outer race  56  and inner race  58 . Outer race  56  is intended to be non-rotating relative to bearing housing  48 . Inner race  58  is formed integral with a release sleeve portion  62 . Release sleeve portion  62  extends axially from bearing  46  and defines an end of release assembly  20 . Release sleeve portion  62  has a snap ring groove  64  proximate to an end thereof. 
     Bearing housing  48  has an end plate portion  66  disposed at a first end of a cylindrical bushing carrier portion  68  of housing  48 . End plate portion  66  is substantially flat and annular in shape as shown in the FIG.  3 . Bushing carrier portion  68  is formed integral and unitary with end plate portion  66 . Bearing housing  48  is cast of steel, and heat treated. Housing  48  is not machined. One or more gussets  70  extend between end plate portion  66  and bushing carrier portion  68  to stiffen end plate portion  66 . Housing  48  has a pair of L-shaped anti-rotation lugs  72  formed on opposite sides of bushing carrier portion  68 . Lugs  72  are formed integral and unitary with carrier portion  68  as part of bearing housing  48 . Anti-rotation lugs  72  each have an axially extending portion  74  and a circumferentially extending portion  76 . Axially extending portion  74  and circumferentially extending portion  76  meet at a right angle. Circumferentially extending portion  76  is disposed at a second end of bushing carrier portion opposite the first end. There are a plurality of reinforcing ribs on a side of portions  76  facing the second end to help sustain the axial clutch release loads. Counterbores are provided on each end of housing  48  to help retain bushing  44 . 
     Bushing  44  is formed of a low friction material such as polytetra fluoroethylene (PTFE). Bushing  44  extends the full length of housing  48 , and is formed within the inner diameter cavity  82  of housing  48  by insert molding it in the inner diameter cavity. The insert molding eliminates any need to machine the internal diameter of housing  48 . Axial retention of bushing  44  in housing  48  is ensured by forcing some of the plastic into the space provided by the counterbores at the ends of housing  48 . Bushing  44  is provided with a plurality of axially extending debris channels  84 . The inside diameter of bushing  44  is sized to slide freely over quill  23 . 
     Bearing cover  42  is stamped of steel. Cover  42  has an enclosure portion  86  in which substantially all of bearing  46  is disposed. Enclosure portion  86  has an inside diameter somewhat larger than an outside diameter of outer race  56  to facilitate receipt of race  56  by cover  42 . At a first end of bearing cover  42  and of enclosure portion  86 , an outer diameter lip  88  extends axially away from enclosure portion  86  before cover  42  is attached to housing  48 . Lip  88  is crimped over an outer diameter of plate portion  66  to fix cover  42  to housing  48 . At a second end, a radially inwardly extending flange  90  extends across the sealed gap between outer race  56  and inner race  58  to provide bearing  46  with an additional element of protection from debris intrusion. 
     In an installed condition, release assembly  20  is positioned by yoke  18 . Axially extending portions  74  of lugs  72  are located a distance above axis  15  equal to the radius of rollers  54 . Thus, rollers  54  engage circumferentially extending portions  76  at locations defining a line passing through and normal to axis  15 . Such an engagement location facilitates axial movement of the bearing without tending to tip or pivot release assembly  20  with respect to input shaft  22  and quill  23 . 
     The axial movement of rollers  54  is achieved by the pivoting of yoke  18 . Yoke  18  pivots about a shaft  92  retained within a clutch housing (not shown) which substantially surrounds clutch  10 . An inboard side of rollers  54  limits lateral movement of release assembly  20  relative to input shaft  22 . Pivot shaft  92  may be rotatively mounted to permit rotation relative to the clutch housing, or alternatively, if provision is made to enable rotation between shaft  92  and yoke  18 , shaft  92  may be rotatively fixed to the clutch housing. It is to be appreciated that the pivoting motion of yoke  18  results in a slight offset of the location of a line between the centers of rollers  54  and axis  15  as rollers  54  move through their arcuate path. The length of arms  52  is chosen so that for the axial travel required, the resultant off-set is of minimal effect. However, it should be appreciated that as the friction material of driven disc  26  wears, release assembly  20  will be drawn closer to flywheel  24 . With increased movement of release assembly  20  toward flywheel  24 , yoke  18  pivots further from an upright position. The increased pivoting results in a larger gap between rollers  54  and the axially extending portion  74  of lugs  72 . The gap permits pivoting rotation of release assembly  20  to produce contact between one of rollers  54  and a corresponding one of axially extending portions  74 . The pivoting effectively doubles the size of the gap. The length of the circumferentially extending portions  76  must be sufficient so that in a worn disk condition, rollers  54  are able to maintain engagement with portions  76 . An inadequate length may result in only one of portions  76  being engaged by yoke, with assembly  20  resultantly cocking and not sliding freely. Employing an adjusting mechanism which compensates for the wear of the friction elements of driven disc  26 , such as that disclosed in U.S. Pat. No. 5,566,804, would reduce the range of yoke pivoting which would otherwise be required. 
     Pre-load/anti-rotation spring  50  is in the form of a wave spring. Pre-load/anti-rotation spring  50  biases outer race  56  into engagement with cover  42 . The second end of cover  42  is configured so that when bearing  46  is pressed thereagainst, the outer race  56  engages the cover and the inner race  58  does not. This causes outer race  56  to resist rotation relative to cover  42  and housing  48 . 
     In operation, the invention operates as a conventional release assembly in that it moves in an axial direction responsive to operator inputs to the linkage  16  releasing and re-engaging clutch  10 . The force of the clutch apply spring, whether it be diaphragm spring  32  or pressure springs, resists the force applied against release assembly  20  by yoke  18 . Travel and free play or lash of yoke  18  in an engaged or unloaded condition must be limited so that rollers  54  cannot move past the ends of axially extending portions  74  of lugs  72 . Retainer  38  and inner race  58  will tend to rotate with pressure plate  28 , diaphragm spring  32  and cover  30 . Housing  48  and cover  42  will be prevented from rotation because of engagement of at least one axially extending portion  74  with yoke, and outer race  56  will resist rotation relative to housing  48 . 
     An alternative to axially extending portion  74  for preventing rotation of housing  48 ′ is shown in FIG.  4 . Flats  74 ′ normal to a line between rollers  54  and located adjacent the engagement surfaces of circumferentially extending portion  76 ′, and are located only a short distance from the inboard ends of rollers  54 . Flats  74 ′ are so close to rollers  54  that they engage the ends of rollers  54  when housing  48 ′ begins to rotate. 
     FIGS. 5 and 6 show an alternative configuration for a bearing eliminating the need for a machined fork and bearing interface. Release assembly  100  includes a bearing  110 . A housing  112 , similar to cover  42  but longer, receives bearing  110 . A wave spring  114  and a plastic bushing  116  are also received by housing  110 . The contents of housing  112  are retained therein by a retaining collar  118 . A wear ring  120  is fixed to a radially outwardly extending thrust ring  122  of housing  112 . 
     Bearing  110  is substantially like bearing  46 , having an outer race  124 , an inner race  126  and a plurality of balls disposed therebetween. Bearing  46  also has an axially extending sleeve portion  128  formed integral with the inner race. Sleeve portion  128  similarly has a snap ring groove  130 . 
     Housing  112  comprises in its largest part a cylindrical portion  132 . At a first end of housing  112  there is a radially inwardly extending flange  134 . At a second end of housing  112 , there is a radially outwardly extending annular thrust ring  122 . Housing  112 , including flange  134  and ring  122 , is stamped from a single piece of steel as a single unit. 
     Bushing  116  is also preferably formed from a low friction plastic such as polytetra fluoroethylene (PTFE). It should be appreciated that alternative materials, including metals such as bronze, may be used for the bushings. The exemplary embodiment has an inner wall  138  and an outer wall connected by a plurality of connecting spokes  142 . The outer diameter of bushing  116  and the outer diameter of outer race  124  are approximately the same, permitting cylindrical portion  132  to be of a constant diameter. 
     Wave spring  114  is disposed between bushing  116  and bearing  110 . Wave spring  114  biases the outer race  124  against flange  134 , causing outer race  124  to resist rotating relative to housing  112 . 
     Retaining collar  118  holds bearing  110 , wave spring  114  and bushing  116  inside housing  112 . Retaining collar  118  is fixed against thrust ring  122  by three small rivets  144  on the second end of housing  112 . An axially extending engagement portion  146  of retaining collar  118  extends axially into the cavity of cylindrical portion  132  and contacts an end of bushing  116 . With retaining collar  118  fixed to housing  112 , engagement portion  114  acts against bushing  116  to compress wave spring  114 . 
     Wear ring  120  is affixed to a side of thrust ring  122  opposite retaining collar  118  by the same rivets  144  used to fix retaining collar  118  to thrust ring  122 . The material of which wear ring  120  is made depends on the design of the yoke  18  engaging wear ring  120 . If yoke  18  employs rollers, a hardened material would be most appropriate for wear ring. If a sliding contact between wear ring  120  and the tips of arms without rollers is anticipated, then friction material would be most appropriate for use as wear ring  120 . 
     In operation, thrust ring  122  is engaged by yoke rollers  54 . Force between rollers  54  and thrust ring  122  causes housing  112  to resist rotation induced by the rotation of inner race. Rotational indexing of housing  112  occurs with clutch  10  in an engaged condition when the loads between yoke  18  and release assembly  20  are lowest. The indexing of housing  112  result in rollers  54  contacting wear ring  120  in different spots around wear ring  120  for each release of the clutch. Use of a yoke without rollers would be benefitted as well by release assembly  100 . As noted above, wear ring would be formed of frictional material. The regular indexing of housing  112  results in wear being distributed around wear ring  120 . The distribution of wear means that a wear ring  120 , and release assembly  20  can be used much longer than a convention release assembly having relatively small friction pads. Of course wear ring  120 , and supporting thrust ring  122  must be sufficiently large to accommodate the change in position of rollers  54  relative to axis  15  with the pivoting of yoke  18 . As noted above, the change in position becomes more pronounce with the wear of the friction material on driven disc  24 . 
     The embodiments disclosed herein have been discussed for the purpose of familiarizing the reader with the novel aspects of the invention. Although preferred embodiments of the invention have been shown and disclosed, many changes, modifications and substitutions may be made by one having ordinary skill in the art without necessarily departing from the spirit and scope of the invention as described in the following claims.

Technology Classification (CPC): 5