Internally assisted clutch

An internally assisted friction clutch having both engagement springs and assister springs extending between a cover and a release sleeve is disclosed. The radially directed forces exerted by the springs continually center and rotatably drive the release sleeve co-axially relative to the cover under normal operating conditions. In order to prevent excessive relative rotation, a plurality of protrusions are formed on the release sleeve which extend into respective recesses formed on the cover. The recesses are sized to be significantly larger than the protrusions so as to cause engagement only when four to five degrees of relative rotational movement or more occurs between the release sleeve and the cover.

BACKGROUND OF THE INVENTION 
This invention relates in general to clutches and in particular to an 
internally assisted friction clutch which normally relies upon the forces 
generated by the engagement and assister springs for centering and 
rotating the release sleeve with the cover, and which further includes one 
or more cooperating protrusions and recesses formed on the release sleeve 
and the cover in order to prevent excessive relative rotation from 
occurring under extreme operating conditions. 
Clutches are well known devices which are used to selectively connect a 
source of rotational power, such as the crankshaft of an engine, to a 
driven mechanism, such as a transmission. Typically, a cover of the clutch 
is connected to a flywheel carried on the end of the engine crankshaft for 
rotation therewith. Between the flywheel and the clutch cover, a pressure 
plate is disposed. The pressure plate is connected for rotation with the 
flywheel and the cover, but is permitted to move axially relative thereto. 
A driven disc assembly is disposed within the clutch between the pressure 
plate and the flywheel. The driven disc assembly is carried on an output 
shaft of the clutch, which is also the input shaft to the transmission. 
When the pressure plate is moved toward the flywheel, the driven disc 
assembly is frictionally engaged therebetween so as to cause the output 
shaft of the clutch to rotate with the flywheel, the cover, and the 
pressure plate. In this manner, the clutch is engaged to transmit power 
from the engine to the transmission to drive the vehicle. When the 
pressure plate is moved away from the flywheel, the driven disc assembly 
is released from such frictional engagement so as to disconnect this 
driving connection. The clutch is typically disengaged to permit a gear 
shifting operation to occur within the transmission. 
A release assembly is provided for selectively moving the pressure plate 
back and forth in the axial direction, so as to engage and disengage the 
clutch as desired. The release assembly includes a generally cylindrical 
release sleeve which is disposed about the output shaft of the clutch. The 
forward end of the release sleeve extends within the clutch. A plurality 
of levers or similar actuating means is typically connected between the 
release sleeve and the cover. Portions of the levers abut the pressure 
plate such that movement of the release sleeve causes corresponding 
movement of the pressure plate. Engagement springs are typically mounted 
between the release sleeve and the cover for urging the release sleeve and 
the pressure plate toward their engaged positions. The rearward end of the 
release sleeve extends through a central opening formed through the cover. 
A bearing assembly is mounted on the rearward end of the release sleeve. A 
manually operable shift lever is connected to the bearing assembly for 
effecting movement of the release sleeve and, therefore, the pressure 
plate. 
More recently, clutches have also been provided with a plurality of 
assister springs mounted between the release sleeve and the cover. The 
assister springs extend generally radially between the cover and the 
release sleeve when the clutch is engaged, thus exerting little or no 
axial force on the release sleeve. However, when the release sleeve is 
moved from its engaged position to its disengaged position, the assister 
springs are moved to an angular orientation. Consequently, the assister 
springs exert some axial force tending to move the release sleeve to its 
disengaged position. 
Thus, it can be seen that the release sleeve rotates with the cover during 
use. Relative rotation between the release sleeve and the cover is 
undesirable because it causes wear on the levers connected therebetween. 
Also, excessive relative rotation can cause the engagement springs to be 
twisted off of their seats on the release sleeve and the cover, thus 
damaging the clutch. In order to prevent such relative rotation, some 
prior clutches have been provided with splines formed on the release 
sleeve which cooperate with corresponding splines formed on the cover. 
Other prior clutches have been provided with enlarged protrusions on the 
inner surface of the cover which extend into slots formed on an enlarged 
portion of the release sleeve. 
In both of these prior clutch structures, the spacing between the engaging 
portions of the cover and the release sleeve is very close. In other 
words, only a very small amount of relative rotation is permitted before 
these portions engage one another to prevent further relative rotation. 
Unfortunately, the release sleeve constantly exerts a certain amount of 
drag relative to the cover because of friction in the bearing assembly. As 
a result of this drag, the engaging portions of these prior clutches 
frequently contact one another during use, even under low torque and speed 
operating conditions. 
Such engagement, while desirable from the standpoint of preventing relative 
rotation, is undesirable because it causes wear between the engaging 
portions. Such engagement is also undesirable because it tends to resist 
axial movement of the release sleeve between the engaged and disengaged 
positions, thus decreasing the effective engagement force generated by the 
engagement springs and increasing the amount of force required to move the 
release sleeve toward the disengaged position. Thus, it would be desirable 
to provide a clutch structure which prevents relative rotation between the 
cover and the release sleeve without frequently causing undesirable 
frictional engagement therebetween. 
SUMMARY OF THE INVENTION 
This invention relates to an internally assisted friction clutch having 
both engagement springs and assister springs extending between a cover and 
a release sleeve. The radially directed forces exerted by the springs 
continually center the release sleeve co-axially relative to the cover. 
Under normal operating conditions, these radially directed forces are 
sufficient to rotatably drive the release sleeve with the cover and 
prevent relative rotation therebetween. This "floating" drive arrangement 
is desirable because there is no continuous mechanical connection between 
the cover and the release sleeve, which can cause wear and affect the 
operation of the clutch. In order to prevent excessive relative rotation 
between the cover and the release sleeve, a plurality of protrusions are 
formed on the release sleeve which extend into respective recesses formed 
on the cover. The recesses are sized to be significantly larger than the 
protrusions so as to cause engagement only when four to five degrees of 
relative rotational movement or more occurs between the release sleeve and 
the cover. 
It is an object of this invention to provide a clutch which normally relies 
upon the forces generated by the engagement and assister springs for 
centering and rotating the release sleeve with the cover. 
It is another object of this invention to provide such a clutch which 
further includes one or more cooperating protrusions and recesses formed 
on the release sleeve and the cover to prevent excessive relative rotation 
when extreme conditions occur. 
Other objects and advantages of this invention will become apparent to 
those skilled in the art from the following detailed description of the 
preferred embodiment, when read in light of the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings, there is illustrated in FIGS. 1 through 3 a 
clutch cover assembly, indicated generally at 10, in accordance with this 
invention. The assembly 10 includes a cover 11 which is adapted to be 
connected to a flywheel (not sown) in a conventional manner for rotation 
therewith about a longitudinal axis. The cover 11 is preferably formed 
from a single piece of material, such as iron by casting. As best shown in 
FIGS. 1 and 4, the main body of the cover 11 is generally annular in shape 
and includes a plurality of engagement spring seats 12 formed integrally 
therewith. The cover 11 further includes a plurality of assister spring 
seats 13 formed integrally therewith. The purpose of these spring seats 12 
and 13 will be discussed below. 
An annular pressure plate 15 is connected to the cover 11 for rotation 
therewith by means of a plurality of spaced lugs and slots, indicated 
generally at 16 in FIGS. 2 and 3. The lug and slot arrangement is 
conventional in the art and permits the cover 11 to rotatably drive the 
pressure plate 15, while allowing the pressure plate 15 to move axially 
relative thereto, as is well known in the art. The pressure plate 15 is 
urged axially toward the cover 11 by a plurality of return springs 17 
disposed about the periphery of the assembly 10. An annular shoulder 15a 
is formed about the pressure plate 15 facing toward the cover 11. 
The clutch cover assembly 10 may include an adjusting ring, as shown at 20 
in FIGS. 1 through 3. The adjusting ring 20 is conventional in the art and 
includes an outer threaded surface which is adapted to cooperate with an 
inner threaded surface formed on the cover 11. Rotation of the adjusting 
ring 20 relative to the cover 11 causes axial movement of the adjusting 
ring 20. A conventional automatic wear adjusting mechanism, indicated 
generally at 21 in FIG. 1, is provided for automatically rotating the 
adjusting ring 20 relative to the cover 11 as wear occurs in the clutch. 
The structure and operation of the adjusting ring 20 and the automatic 
wear adjusting mechanism 21 are described more fully in U.S. Pat. No. 
3,752,286, the disclosure of which is incorporated herein by reference. As 
will become apparent below, however, this invention can be used on 
clutches which are manually adjustable and which are not adjustable. 
A plurality of conventional levers 25 are provided within the clutch cover 
assembly 10. The levers 25 extend generally radially outwardly from the 
axis of rotation and are spaced equidistantly thereabout. The outermost 
ends of the levers 25 have slots formed therethrough to receive respective 
projections formed on the adjusting ring 20. The innermost ends of the 
levers 25 extend into a peripheral groove formed in a release sleeve 26. 
The release sleeve 26 is disposed co-axially about the axis of rotation 
and is axially movable therealong. The structure and operation of the 
release sleeve 26 will be discussed in greater detail below. 
Between their outermost and innermost ends, the levers 25 engage the 
annular shoulder 15a of the pressure plate 15. Thus, as is well known in 
the art, axial movement of the release sleeve 26 causes the levers 25 to 
pivot about the projections of the adjusting ring 20, thereby causing 
axial movement of the pressure plate 15. For example, when the release 
sleeve 26 is moved toward the left when viewing FIGS. 2 and 3, the 
pressure plate 15 is also moved toward the left. This movement causes 
engagement of the clutch. When the release sleeve 26 is moved toward the 
right, the pressure plate 15 is also moved toward the right to disengage 
the clutch. 
As best shown in FIGS. 2, 3, and 5, the release sleeve 26 is formed 
generally in the shape of a hollow cylinder. The release sleeve 26 is 
preferably formed from a single piece of material, such as iron by 
casting. The forward end of the release sleeve 26 extends within the cover 
11 and has the above-mentioned peripheral groove formed thereon for 
receiving the inner ends of the levers 25. A plurality of engagement 
spring seats 27 are formed integrally about the forward end of the release 
sleeve 26. A plurality of assister spring seats 28 are also formed 
integrally about the forward end of the release sleeve 26. 
The rearward end of the release sleeve 26 extends outside of the assembly 
10. A conventional throw-out bearing assembly 29 is secured to the 
rearward end of the release sleeve 26 for axial movement therewith, while 
permitting relative rotational movement. The bearing assembly 29 is 
adapted to be engaged and axially moved by a conventional linkage (not 
shown) so as to permit an operator selectively move the components of the 
assembly 10 between engaged and disengaged positions. 
A conventional engagement spring 30 is supported between each of the 
engagement spring seats 12 formed on the cover 11 and its corresponding 
engagement spring seat 27 formed on the release sleeve 26. In a manner 
which is well known in the art, the engagement springs 30 urge the release 
sleeve 26 toward the left when viewing FIGS. 2 and 3, thus urging the 
pressure plate 15 toward the left into its engaged position, against the 
urging of the return springs 17. The force exerted axially by the 
engagement springs 30 is much larger than the force exerted by the return 
springs 17. Consequently, the release sleeve 26 and the pressure plate 15 
are normally positioned in their engaged positions relative to the cover 
11. 
As discussed above, the release sleeve 26 is moved toward the right to move 
it and the pressure plate 17 to their disengaged positions. To accomplish 
this, an axial force must be exerted on the release sleeve 26 which can 
overcome the urging of the engagement springs 30. This force is supplied 
to the bearing assembly 32 by manual operation of the shift lever 
connected thereto. In order to reduce the amount of such force exerted by 
an operator without significantly reducing the magnitude of the force 
exerted by the engagement springs 30 when the clutch is engaged, a 
plurality of assister springs 31 are provided. The assister springs 31 are 
supported between each of the assister spring seats 13 formed on the cover 
11 and the corresponding assister spring seats 28 formed on the release 
sleeve 26. The structure and operation of the assister springs 31, as well 
as the overall operation of the clutch 10, is described in detail in U.S. 
Pat. No. 4,760,906, the disclosure of which is incorporated herein by 
reference. 
Under normal operating conditions, both the engagement springs 30 and the 
assister springs 31 exert forces radially inwardly against the release 
sleeve 26. This occurs regardless of whether the release sleeve 26 is in 
its engaged position, its disengaged position, or somewhere in between. As 
the release sleeve 26 is moved from the engaged position shown in FIG. 2 
to the disengaged position shown in FIG. 3, the assister springs 31 are 
moved from a generally radial orientation to an angled orientation. As a 
result, the magnitude of the radially inwardly directed force exerted by 
such assister springs 31 decreases as the release sleeve 26 moves closer 
to its disengaged position. At the same time, however, the engagement 
springs 30 are moved from a large angle orientation to a smaller angle 
orientation, thus increasing the magnitude of the radially inwardly 
directed force exerted thereby as the release sleeve 26 moves closer to 
its disengaged position. 
It will be appreciated, therefore, that the combined use of the engagement 
springs 30 and the assister springs 31 continually tends to center the 
release sleeve 26 co-axially relative to the cover 11. Under normal 
operating conditions, these radially directed forces are sufficient to 
rotatably drive the release sleeve 26 with the cover 11 and prevent 
relative rotation therebetween. This "floating" drive arrangement is 
desirable because there is no frequent or continuous mechanical connection 
between the cover 11 and the release sleeve 26. As discussed above, such a 
connection is undesirable because it can cause wear on these components 
and because it can affect the operation of the clutch 10. 
However, in certain unusual situations, the combined radially directed 
forces exerted by the engagement springs 30 and the assister springs 31 
may be insufficient to prevent relative rotation between the cover 11 and 
the release sleeve 26. Such a situation might occur if the bearing 
assembly 29 were to seize or otherwise malfunction. If this situation were 
to occur, the release sleeve 26 would rotate relative to the cover 11 
until either some of the springs 30 or 31 were compressed to a solid 
condition or until the springs 30 or 31 were twisted so far as to fall off 
of their respective seats. Neither of these failure modes is desirable 
because it could cause extensive damage to the clutch. 
Accordingly, a fail safe mechanism is provided to prevent excessive 
rotation of the release sleeve 26 relative to the clutch 11 in the event 
of an abnormal situation, such as described above. The fail safe mechanism 
includes a plurality of protrusions 35 formed integrally on the center or 
sleeve portion of the release sleeve 26. These protrusions 35 extend 
radially outwardly from the release sleeve 26 into corresponding recesses 
36 formed in the cover 11. 
As shown in FIG. 1, the recesses 36 are sized significantly larger than the 
protrusions 35. Thus, the protrusions 35 are received within the recesses 
36 but do not, under normal operating conditions, engage the sides 
thereof. In the event of an abnormal situation, however, the protrusions 
35 will engage the sides of the recesses 36 when the release sleeve 26 has 
rotated a predetermined amount relative to the cover 11. Preferably, the 
protrusions 35 will engage the recesses after four to five degrees of 
relative movement, although a larger range of movement may be desirable in 
some circumstances. In this manner, a positive stop is provided to prevent 
serious damage from occurring to the clutch. 
In accordance with the provisions of the patent statutes, the principle and 
mode of operation of this invention have been explained and illustrated in 
its preferred embodiment. However, it must be understood that this 
invention may be practiced otherwise than as specifically explained and 
illustrated without departing from its spirit or scope.