Automotive clutch release bearing

A clutch release bearing comprises an operating member cooperating with a throw-out fork and a drive member coacting with the release members of an associated clutch. The operating member comprises a sleeve mounted on a guide member and having relatively rigid projections running along the bore of the sleeve for sliding engagement with the guide member. Channels for accommodating solid grease are provided between the projections and are open at one end of the sleeve.

BACKGROUND OF THE INVENTION 
The present invention relates generally to clutch release bearings, also 
known as throw-out bearings, of the type particularly adapted for use with 
automotive clutches. 
Such a clutch release bearing generally comprises a drive or thrust member 
which is adapted to coact with the release members of a clutch, in 
particular the fingers of the diaphragm spring in the case of a diaphragm 
friction clutch, an operating member whch is adapted to cooperate with an 
actuating member, in practice, a throw-out fork, and means for securing 
the drive or thrust member axially to the operating member. 
The present invention relates more particularly to such clutch release 
bearings whcih are intended to be slidably received on a guide member 
which in the case of an automotive vehicle is a guide tube surrounding the 
input shaft of the transmission and fixed to the housing of the 
transmission. In such a case the operating member comprises a sleeve which 
is adapted to be entirely axially received on such a guide tube. 
In the course of service the guide member inevitably accumulates dust, dirt 
and grit. The gradual buildup of such dirt may interfere with the proper 
sliding of the clutch release bearing necessary for operation and may even 
bind on the guide member. 
In the case of a so-called self-centering release bearing, which maintains 
its self-centered position once it is obtained, the drive member is 
mounted for limited transverse movement in all directions with respect to 
the operating member, the sleeve of the operating member must be received 
with a relatively close fit on the guide member. 
In my U.S. Pat. No. 4,261,625, assigned to the assignee of the present 
application, there is provided for meeting the apparently contradictory 
requirements of smooth sliding movement and a close fit a sleeve having 
along its inner surface radially inward projections or bosses adapted to 
slidingly engage the guide member and defining between one another 
channels or passages. In practice such projections or bosses are axially 
elongate splines and the passages or channels are axially elongate grooves 
therebetween. 
Taking advantage of the self-lubricating properties of at least some 
plastic synthetic materials and the reduction of the frictional contact 
surface resulting from the splines, it was proposed in my aforementioned 
U.S. patent to provide dry contact, without any lubricant, between the 
sleeve of the clutch release bearing and the guide member on which it is 
received. The ends of the splines are axially outwardly tapering for 
channelling the dirt present on the guide member into the grooves thereby 
avoiding any undesirable contact between the sliding surfaces of the 
bosses or projections and the dirt or grit. 
In practice such an arrangement has given satisfaction and its has the 
advantage of providing accurate location of the clutch release bearing 
with respect to the guide member, the splines on the sleeve of the 
operating member having the desired geometrical configuration for this 
purpose. Indeed, the dummy splines formed on the core of the mold for 
molding such an operating member may be subsequently individually trued. 
For some applications, however, it is imperative to provide a grease 
reservoir between the clutch release bearing and the associated guide 
member. 
Various arrangements have been proposed for this purpose. For example, in 
French patent publication No. 2,145,977 the sleeve of the operating member 
is provided with two radially inwardly resiliently deformable rings 
disposed at the respective ends of the axial bore in specially designed 
grooves in the inner surface of the bore, the rings having ridges engaging 
the guide member and defining the sought after grease reservoir or chamber 
therebetween. Owing to the resilient clamping action exerted by the rings 
the latter are detrimental to good sliding movement of the release bearing 
on the guide member. Further, such an arrangement necessitates the 
machining of annular grooves in the inner wall of the bore through the 
sleeve, and their mounting in the grooves is a rather delicate operation. 
Moreover, such an arrangement is not satisfactory in operation since the 
ridge profile of the rings may cram dirt and grit from the guide member. 
In French patent publication No. 2,230,235 the sleeve of the operating 
member is made of flexible material and comprises at its axial ends 
annular beads which are in resilient engagement with the associated guide 
member and define, as above, a grease reservoir chamber between each 
other. But as in the preceding French patent publication owing to the 
elastic gripping of the guide member the annular beads tend to interfere 
with good sliding movement of the clutch release bearing on the guide 
member. In fact, given the actual flexible nature of the bead material, 
the beads are not suitable for scraping off any dirt or grit which may be 
present on the guide member. 
In French patent publication, the provision of the sought after grease 
chamber translates into an uncertain location of the operating member with 
respect to the guide member, the elastic beads of the operating member 
sleeve enable skewing of the operating member relative to the axis of the 
guide member. 
Admittedly, such skewing may be beneficial in the case of 
non-self-centering release bearings which is precisely the reason it is 
provided on the release bearing of French patent publication No. 
2,230,235. But for the reasons developed above such skewing is normally 
not appropriate for sustained self-centering release bearings which 
maintain their self-centered position once it is attained. 
Indeed, for ensuring the satisfactory position of the release bearing on 
the guide member, it is desirable to provide on the operating member 
relatively rigid projections or in other words an internal sheath or 
portion which is made of relatively rigid material. 
It may be contemplated for the sought after grease chamber to provide on 
the inner surface of the bore of the sleeve of such relatively rigid 
material a recess closed at its axial ends such as is the rule for such 
grease chambers as exemplified by French patent publications Nos. 
2,145,977 and 2,230,235. But when such a sleeve is of molded plastic 
synthetic material which contributes to good sliding on the guide member 
the formation of such a recess gives rise to difficulties which in 
practice are insurmountable. 
Indeed, owing to the sleeve being of relatively rigid material it is 
impossible to unmold the sleeve elastically. Unmolding therefore would 
require the utilization of radially retractable cores making the cost of 
molding prohibitive. 
OBJECT AND SUMMARY OF THE INVENTION 
A general object of the invention is to provide a clutch release bearing 
which enables the foregoing drawbacks of the prior art to be overcome in a 
particularly simple and satisfactory manner. 
According to the invention there is provided such a clutch release bearing 
comprising an operating member adapted to cooperate with an actuating 
member such as a throw-out fork and having a sleeve adapted to slide along 
a guide member, the sleeve having relatively rigid radial projections on 
its inner surface for sliding contact with the guide member, channels 
defined between the projections, the channels being axially open at one 
axial end of the sleeve and axially closed at the other axial end thereof. 
The clutch release bearing, as is conventional, further comprises a drive 
member which is adapted to coact with the release members of the clutch, 
the closed ends of the channels being relatively axially adjacent the 
driven member. The projections are preferably axially elongate splines, 
the closed ends of channels being defined by an annular rib radially flush 
with the projections. 
Thus, according to the invention the splines of U.S. Pat. No. 4,261,625 are 
used for accommodating grease whereas the splines were, in that patent, on 
the contrary, designed for accommodating dirt and grit picked up on the 
guide member. 
The grease chambers of the present invention are defined by axial grooves 
between axial splines which are closed at one of their axial ends. 
The present invention is based on the surprising finding that contrary to 
generally accepted notions, it is not necessary for such grease chambers 
to be closed at both axial ends, but may be closed at only one axial end. 
Indeed, the grease used is virtually solid up to temperatures of the order 
of 80.degree.-100.degree. C., and it retains without any substantial 
deformation its splinelike configuration, complementary to the splines of 
the operating member and it protrudes radially toward the guide member 
when the release member is mounted on the latter. 
Further, because of the gradual movement of the release bearing along the 
guide member away from the clutch as the friction facings of the driven 
disc become worn, there is a systematic cramming or tamping of the 
grease-filled grooves which causes a minimal amount of the grease to be 
driven or flow out into the interstitial between the projections on the 
sleeve of the operating member and the guide member, which space is 
necessary for mounting the operating member on the guide member. 
The present invention resolves the dual problem of unmolding the operating 
member sleeve when made of relatively rigid material or of material made 
relatively rigid and providing a grease chamber on a sustained 
self-centering release bearing and accurate location of the operating 
member with respect to the guide member. Indeed, since the channels 
defining the grease chambers are opened at one of the axial ends, the 
unmolding of the sleeve of the operating member causes no particular 
difficulties. Further, aside from the inevitable play necessary for 
mounting of the operating member on the guide member, the splines 
stringently determine the position of the operating member on the guide 
member and, in addition, ensure good sliding of the operating member on 
the guide member.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The drawings illustrate, by way of example, the application of the 
invention to a sustained self-centering release bearing. 
As is known per se, the clutch release bearing generally comprises an 
operating member 10 which is adapted to cooperate with an actuating member 
which in practice is a throw-out fork, a drive or thrust member 11 which 
is adapted to coact with the release members of a clutch, e.g., the free 
ends of the radial fingers of the diaphragm spring in the case of a 
disphragm friction clutch, and means associated with axially acting 
resilient means for axially securing the drive member 10 to the operating 
member 10. 
For the simplification of the drawings, neither the actuating member nor 
the release members of the clutch are illustrated. 
The operating member 10 comprises a sleeve 12 which extends axially and 
which is adapted to slidingly engage a guide member and a transverse or 
radial flange 13 which is adapted to cooperate with the associated 
actuating member. Also for the sake of simplification the guide member on 
which the clutch release bearing is mounted is not illustrated. 
In the illustrated embodiment the sleeve 12 of the operating member 10 
comprises two coaxial components, i.e., an outer sleeve component 14 of 
metal and an inner sleeve component 16 of relatively rigid synthetic 
plastic material which is preferably glass fiber reinforced. 
The inner sleeve component 16 has a radially outwardly extending collar 17 
which is in mating engagement with a shoulder 19 of the outer sleeve 
component 14 and an inwardly projecting annular crimp 20 at the adjacent 
end of the outer sleeve component 14 bears against the corresponding end 
of the inner sleeve component 16 thereby fixing the axial position of the 
inner sleeve component 16 relative to the outer sleeve component 14. 
The outer sleeve component 14 comprises an external annular shoulder 22 
against which the flange 13 bears, the flange 13 being retained axially in 
position by a ring 23 which is received on outer sleeve component 14 and 
which is held by an inwardly projecting annular crimp 24 af the end of the 
outer sleeve component 14 remote from the crimp 20. 
Two clips 26 for attaching the associated throw-out fork (not shown) are 
fixed to the flange 13 by rivets 25. 
In the illustrated embodiment the drive or thrust member 11 simply 
comprises a ball bearing which is received with radial clearance on sleeve 
12 of the operating member 10 to the side of flange 13 remote from clips 
26. Only the inner race 27 of the ball bearing is in engagement through 
its corresponding endwall with the flange 13. The outer race 28 of the 
ball bearing of the drive member 11 is adapted to coact with the release 
members of the associated clutch (not shown) and has an inwardly rounded 
profile. 
In the illustrated embodiment the means for securing the drive member 11 
axially to the operating member includes axially acting or biasing 
resilient means. In practice, on the side of the drive member 11 remote 
from the flange 13 of operating member is disposed a Belleville type 
washer 30, the inner periphery of the Belleville washer 30 bears axially 
against one of the flanks of a radially outwardly opening groove 31 formed 
in the outer surface of the outer sleeve component 14, and the outer 
periphery of the Belleville washer bears axially against the endwall of 
the inner race 27 of the ball bearing defining the drive member 11. 
The foregoing features are well known per se and as they do not constitute 
novel features of the present invention, they will not be described in 
greater detail herein. 
Likewise, in a manner known per se, the sleeve 12 of the operating member 
10 and more particularly, in the instant embodiment, the inner sleeve 
component 16 has integral longitudinally extending radial projections or 
bosses 32 which are adapted to slidingly engage the associated guide 
member (not shown) and which define between one another longitudinal 
channels 33. According to a feature of the present invention the channels 
33 are axially open at one end of the sleeve 12 and closed at the other 
end of the sleeve. 
In practice the axially closed ends of the channels 33 are located adjacent 
to the drive member 11. In the illustrated embodiment the projections 32 
are axially elongate splines and the channels 33 are grooves closed by a 
circumferentially continuous annular rib 35. In practice the annular rib 
35 lies radially flush with the projections 32 and extends to the 
corresponding free end of the sleeve 12. In other words the splines 
defining projections 32 and the annular rib 35 at one end thereof are in 
one piece and project from the inner surface of the inner sleeve component 
16 of sleeve 12. 
It will be readily understood that the inner sleeve component 16 may be 
easily molded, the central core necessary for forming the axial channels 
33 may be withdrawn axially for unmolding the inner sleeve component 16. 
Preferably, the free ends of the splines axially remote from the annular 
rib 35 are axially outwardly tapered to a point. 
When the present clutch release bearing is mounted on the guide member the 
sleeve 12 of the operating member 10 is in good sliding contact therewith 
through its interior projections 32, with a small amount of radial 
clearance for the purposes of mounting. 
The channels 33 are designed to form grooves between the splines for 
accommodating grease, which grease is solid at ordinary temperatures and 
projects radially as splines for engagement with the guide member. The 
resulting sliding contact is therefore with minimal friction. 
Further, as will be noted, the grease in the channels is in direct 
communication with the ambient air only when the associated release 
bearing effects clutch disengagement. 
The present clutch release bearing is not intended to be limited to the 
illustrated and described embodiment but rather encompasses all variations 
and alternatives understood to those skilled in the art without departing 
from the spirit and scope of the invention. In particular the sleeve and 
the flange of the operating member may be of one-piece synthetic plastic 
construction. Also, the field of the invention is not limited to sustained 
self-centering release bearings but includes all kinds of clutch release 
bearings.