Spring clutch

A friction clutch assembly is disclosed having an annular spring compressed between a clutch cover and a plurality of externally located release levers. The spring has tongues cooperating with indentations on the outside of the cover to centrally locate the spring and prevent it from rotating relative to the cover. An abutment may be formed on the cover for engagement by the spring to indicate when the clutch is in a fully worn position.

BACKGROUND OF THE INVENTION 
This invention relates to friction clutch assemblies in general and is 
particularly directed to a resiliently loaded lever operating mechanism 
for these devices. 
Lever operating mechanisms for friction type clutches require a certain 
amount of axial space in order to permit the levers to perform their 
desired function of engaging and disengaging the clutch. To reduce the 
axial length of the clutch assembly, it is common practice to provide an 
annular belleville type spring for applying the required resilient load. 
One method is to locate the spring internally between the clutch cover and 
pressure plate with the levers arranged to exert a pull against the 
pressure plate to overcome the spring load against the pressure plate. 
Another method used is to position the spring externally between the 
clutch cover and levers so that the levers carry the full spring load. 
The latter design is desirable over the former because the spring is 
located entirely outside the cover. This eliminates contact between the 
spring and pressure plate thereby preventing direct conduction of heat 
from the pressure plate to the spring. Another advantage in this 
arrangement is the fact that the spring is in constant contact with the 
levers at all times whether in the releasing or engaging position. This 
eliminates the need for close fit of the levers or any additional means 
for holding the levers against rattling. With any design using a spring as 
described above, it is essential to properly locate the spring relative to 
the clutch operating parts so that it will function in its intended 
manner. 
While arrangements exist which permit satisfactory operation and control of 
such springs, they have been complex and require more space than presently 
available in vehicle applications. 
SUMMARY OF THE INVENTION 
The present invention is an externally located actuating mechanism for a 
friction clutch assembly comprising a plurality of radially extending 
release levers and an annular spring ring positioned between the levers 
and the clutch cover. The cover has support means for centering and 
retaining the spring with integral stops provided on the support means to 
prevent the spring from bottoming out when the clutch is in a fully worn 
condition.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIGS. 1 and 2 of the drawings, in a preferred embodiment, a 
friction clutch is shown generally at 10 having a central axis X--X. 
Clutch 10 comprising an annular cover 12 having a peripheral flange 
portion 13 secured to the rear face of a standard flywheel 14 by a 
plurality of circumferentially spaced bolts 16 so that the cover 12 
rotates with the flywheel 14. Cover 12 further comprises a rim portion 18 
extending in a generally axial direction and an end wall 20 extending 
radially inwardly from the rim portion 18 and terminating in an angular 
disposed ramp 22. The radially inner portion of ramp 22 defines a central 
opening 24 in the cover end wall 20. 
An annular space 26 is provided between flywheel 14 and the cover 12 for 
receiving a pressure plate 28. A driven disc 30 is adapted to be clamped 
between the pressure plate 28 and the flywheel 14. 
Driven disc 30 comprises a central hub 32 having a support plate 34 secured 
thereto with friction facing 36 fastened on opposite sides of the outer 
peripheral portion of the support plate 34. Central hub 32 is splined to 
the outer end of a transmission input shaft 38 with the friction facing 36 
positioned between the pressure plate 28 and flywheel 14. The splined 
connection permits the driven disc 30 to move freely in an axial direction 
relative to the input shaft 38 while being rotatable with it. 
Pressure plate 28 is axially movable into engagement with driven disc 30 to 
clamp the same to the flywheel 14 to drivingly connecting the rotatable 
drive and driven members of the clutch. A plurality of circumferentially 
spaced drive straps 40 rotatably connect the pressure plate 28 to the 
cover 12 and permit limited axial movement of the pressure plate 28 
relative to the cover 12. Drive straps 40 further serve as means to lift 
the pressure plate 28 away from the flywheel when the clutch 10 is moved 
to its disengaged position. The opposite ends of drive straps 40 are 
connected to the cover 12 and pressure plate 28 in a conventional manner. 
A lever operating mechanism is provided to move the pressure plate 28 
axially relative to the cover 12 into and out of engagement with the 
driven disc 30. The lever operating mechanism is disposed wholly outside 
the cover 12 and comprises a plurality of radially extending levers 42 
pivotally connected to the cover 12 by pivot pins 44. Lever outer ends 46 
engage a head 48 formed on a screw 50 threadedly fastened to the pressure 
plate 28. 
Resilient means are provided to apply an axially engaging force to pressure 
plate 28 to normally urge the same into clamping engagement with the 
driven disc 30. The resilient means is designed to maintain a 
substantially constant engaging pressure regardless of wear on the driven 
disc friction facing 36. In a preferred embodiment, the resilient means is 
an annular spring washer 54 of the belleville type compressed between the 
cover 12 and levers 42. Spring washer 54 in its unstressed state, is 
conical in shape having an inner peripheral portion 60, an intermediate 
cone-shaped portion 62 and an outer peripheral portion 64. Inner and outer 
peripheral portions 60 and 64 are axially spaced and approach the same 
plane as spring 54 is placed under compression. Spring washer 54 is 
designed to have the inner peripheral portion 60 (fixed) react against the 
cover 12 and the outer peripheral portion 64 (movable) engage and be 
movable with the levers 42. Because of the spring washer movement, the 
cover ramp 22 is sufficiently angled to permit clearance during operation. 
Levers 42 are arranged to be depressed against the action of spring washer 
54 by a throw-out bearing 66 operating against inner ends 68 of levers 42. 
Operation of throw-out bearing 66 causes levers 42 to pivot about pins 44 
so that the outer ends 46 respond by moving the pressure plate 28 to clamp 
the driven disc 30 against flywheel 14. 
To equally distribute load and stress from the washer to the levers 42, an 
annular collector ring 70 is provided. Collector ring 70 is cup-shaped in 
cross-section and comprising an annular axially extending rim 72 
encircling the outer peripheral portion 64 of spring washer 54 and a 
radially inwardly extending annular base 74. Base 74 is adapted to be 
positioned between the back face of spring washer 54 and adjacent front 
face of levers 42. Thus, base 74 transfers the reaction load of the spring 
washer 54 to the levers 42. Base 74 is disposed at a slight angle to 
provide clearance for the spring washer outer peripheral portion 64 when 
the levers 42 are pivoted to their clutch disengaged position. 
Collector ring 70 has sufficient clearance with respect to washer outer 
peripheral portion 64 to permit it to move freely during the various 
clutch operating stages. Since levers 42 are in constant contact with the 
collector ring base 74, they serve to maintain the collector ring 70 in 
place against the spring washer 54. If desired, spring washer 54 may act 
directly against the levers 42. However, it has been found that, rather 
than concentrating the engaging load directly under the levers 42, an 
equal distribution of load results by providing the annular collector 70. 
Restraint means are attached to cover 12 for cooperating with positioning 
means attached to spring washer 54 to concentrically locate the spring 
washer 54 with respect to the clutch axis X--X and prevent relative 
rotational movement between it and cover 12. The restraint means comprises 
a plurality of circumferentially spaced tabs 76 extending inwardly from 
the cover ramp 22 toward the clutch axis X--X. Integrally formed on the 
inner end of each tab 76 is a lip 78 which extends outwardly in a 
direction parallel to the clutch axis X--X. Lips 78, as shown in FIG. 4, 
further comprise indentations 80 for receiving the positioning means 
formed as an integral part of spring washer 54. The indentation results in 
angularly disposed and spaced shoulders 82 provided therein. 
The positioning means on spring washer 54 comprise a plurality of 
circumferentially spaced tongues 84 extending inwardly from the spring 
washer inner peripheral portion 60. Tongues 84 are equal in number and of 
such size as to closely fit the contour of indentations 80. The spacing is 
such as to provide the necessary clearance for spring washers 54 as it 
flattens during its operation. The spaced outer edges of the tongue inner 
ends form stops 86 engageable with the inside surface of angular shoulders 
82 of indentations 80. The tolerances are such that top surface of 
indentation 80 and mating bottom surface of tongues 84 cooperate to 
centrally position the spring washer 54 about the clutch axis X--X. 
Further, the tongue spaced outer edges or stops 86 cooperate with the 
mating internal surfaces of the angled shoulders 82 to prevent spring 
washer 54 from rotating relative to the cover 12. 
With the arrangement thus far described, it will be seen that the addition 
of tongues 84 on spring washer inner peripheral portion 60 results in a 
substantial increase in the distance from the spring washer outer 
periphery 64 to the inner edge of the tongues 84. This results in a 
radially lengthening of the spring washer intermediate portion 62 at the 
circumferentially spaced tongue locations allowing more deflection in the 
spring washer 54 without increasing load. 
Reference is made to the graph shown in FIG. 7 to show the comparison 
between the spring washer 54 of the present invention and a standard 
belleville washer. The deflection curve indicated by dotted lines A was 
developed from a standard belleville washer. As a comparison, the solid 
line B depicts the deflection curve developed from the tongued belleville 
washer 54 illustrated in FIGS. 1-6. The peak load is indicated at P and 
the negative rate portion of the curve is indicated at N. 
In the preferred embodiment, the inner bottom edges of spring washer 
tongues 84 engage and act against the outer surface of tab 76 while the 
outer spring washer peripheral portion 64 reacts against the insides of 
levers 42 through collector ring 70. Thus, tongues 84 provide a plurality 
of circumferentially spaced reaction surfaces on the interior of spring 
washer 54 while the action surface on the exterior is annular. 
Referring to FIG. 4, it will be seen that, in cross-section, cover ramp 22, 
tabs 76 and lips 78 define substantially L-shaped legs with spring washer 
tongues 84 being wholly within the area of lip 78. An alternate embodiment 
illustrated in FIG. 6 provides an integral abutment on at least one of the 
lips 78 engageable by the spring washer tongues 84 to indicate when the 
clutch 10 is in a fully worn position. Preferably, to maintain balance and 
proper indication of wear, each lip 78 should be provided with an integral 
abutment. The abutment comprises an outwardly extending flange 88 (see 
FIG. 1--dotted lines). Flange 88 is integral with lip 78 and extends in a 
direction substantially perpendicular to clutch axis X--X. The radially 
outermost inner edge of lip 78 forms a fixed stop 90 which is designed to 
engage the outer surface of spring washer tongue 84 and act to keep spring 
washer 54 from bottoming out or achieving an over-center position when the 
clutch is in a fully worn position. 
Flange 88 is bent over at a preselected angle so that fixed stop 90 is 
located at a point corresponding to the fully worn position of the clutch. 
While flange 88 is shown extending in a direction perpendicular to the 
clutch axis X--X, it is possible that it could be angularly disposed to 
either side in order to position the stop 90 in a desired location. The 
presence of flange 88 and position of stop 90 allows spring washer 54 to 
stop at a position that would coincide with allotted facing wear of driven 
disc 30. At this point the levers 42 would sense free travel or no-load 
effect. This would indicate to an operator that the clutch is worn. 
In the normally engaged position of the clutch 10 as illustrated in FIG. 2, 
spring washer 54 is arranged with relation to the remainder of the clutch 
mechanism so that pressure will be exerted against its inner and outer 
peripheries 60 and 64 respectively. As indicated, it is assembled under 
initial compression so as to bring its inner and outer peripheries closer 
together in an axial direction. During clutch release operation its 
peripheries will be further deflected toward a common plane 
(flattening-out) as illustrated in dotted lines R in FIG. 6. As the 
friction facings 30 wear, the peripheral portions move further apart 
axially tending to approach the free or relaxed condition of the spring 
washer. The location of the flange 88 and stop 90 thereon are designed so 
that the outer surface of spring washer tongue 84 will come in contact 
with stop 90 and prevent spring washer 54 from reaching a position beyond 
that shown by dotted lines W in FIG. 6. The dotted line W indicates the 
position of spring washer 54 when the clutch is in a fully worn position. 
In this position spring washer 54 will no longer be responsive to apply a 
biasing force against the insides of levers 42. 
It is obvious that other types of annular spring washers may be used in 
place of the cone type shown, e.g., slotted, finger, curved types as well 
as single or stacked versions of the wave washer type. 
From the foregoing description, it is apparent that the advantages of the 
present invention result from the combined relationship of the restraint 
portion formed on the clutch cover 12 and the positioning means 
constructed on the spring washer 54. The arrangement is such as to provide 
a satisfactory operative connection for the parts in a limited axial 
space. Further, the provision of the collector ring 70 to equally 
distribute load to the levers 42 and the alternate wear indicator feature 
result in additional advantages in a clutch of this type. 
Having thus described preferred embodiments of the present invention, it 
should be understood that the invention is not to be limited to the 
specific construction and arrangement described. It will be apparent to 
those skilled in the art that modifications or alterations may be made 
without departing from the spirit and scope of the invention as set forth 
in the appended claims.