Clutch disc assembly

A clutch disc assembly interposed between an input side rotary member and an output side member has a hub, disc-like plates, a friction member, an elastic member and a viscous damper mechanism. The hub is connectable for co-rotation with the output side member. The hub has a flange on its outer circumference. The dlsc-like plates are rotatably mounted on the hub. The friction member is connected to said disc-like plates, for frictional engagement with the input side rotary member. The elastic member is for elastically connecting the flange and the dlsc-like plates whereby the flange and the disc-like plates are rotatable with respect to each other. The viscous damper mechanism includes a fluid medium, for displacing the fluid medium through restrictions in response to angular movements of the dlsc-like plates and the flange with respect to each other.

BACKGROUND OF THE INVENTION 
The present invention relates to a clutch disc assembly used in a vehicle. 
The clutch disc assembly is interposed between an automotive engine and an 
automotive transmission. The clutch disc assembly is used to connect or 
disconnect the power transmission and also to dampen torsional vibration 
as a damper. In general, the clutch disc assembly includes a hub 
connectable to an input shaft of the transmission and having a flange on 
its circumference, a pair of disc-like plates rotatably mounted on the hub 
and disposed on both sides of the flange, friction members fixed to the 
dlsc-like plates for frictional engagement with an input side rotary 
member such as the engine flywheel, coil springs used as elastic members 
for elastically coupling the disc-like plates and the flange in the 
circumferential direction, and a frictional resistance generation 
mechanism interposed between the disc-like plates and the flange. 
In this clutch dlsc assembly, when torsional vibration is transmitted from 
the flywheel thereto, the coil springs are repeatedly compressed and 
expanded so that the pair of disc-like plates and the hub are twisted 
relative to each other. During this angular movement of the disc-like 
plates and the flange relative to each other, frictional resistance is 
generated on the basis of the frictional resistance mechanism, to thereby 
dampen energy of the torsional vibration. 
In such a clutch disc assembly, in order to effectively dampen the 
torsional vibration over a wide operational range, it is preferable that 
magnitude of the frictional resistance be varied depending upon the kinds 
of the torsional vibration. There are two kinds of torsional vibrations, 
for example, torsional vibration having small angular displacement caused 
by the combustion fluctuation of the engine, and low-frequency torsional 
vibration having large angular displacement which is caused when a driver 
suddenly depresses or loosens an accelerator pedal. In order to dampen the 
torsional vibration having small angular displacement, the clutch disc 
assembly has to have low rigidity/small resistance characteristics as a 
damper. In order to dampen the low-frequency torsional vibration having 
large angular displacement, the clutch disc assembly has to have a high 
rigidity/large resistance characteristics as a damper. 
In the conventional clutch disc assembly, the two different torsional 
characteristics may be realized by using a structure where the two 
different frictional forces are generated depending on the different kinds 
of the torsional vibration. However, with the frictional resistance by the 
sliding movement of the frictional member, it would be impossible to 
increase the second stage frictional force to a satisfactory level. It 
would be therefore impossible to sufficiently dampen the low-frequency 
vibration. 
Recently, automotive vehicles have been widely used on highways. Thus, 
frequency of the engagement/disengagement of a clutch has been decreasing 
recently because of more highway use. For this reason, when a service life 
of a clutch disc assembly as a whole is contemplated, a problem of wear of 
friction facings has become less important. Then, a service life of an 
elastic member support portion of the pair of disc-like plates is being 
raised. In other words, when the torsional vibration is generated, the 
elastic member is repeatedly expanded and contracted to thereby wear the 
support portion of the disc-like plates. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to increase the resistance in 
order to dampen the low-frequency vibration. 
It is another object of the present invention is to decrease the wear of 
the disc-like plates due to the expansion/contraction of the elastic 
members. 
A clutch disc assembly according to an aspect of the present invention is 
interposed between an input side rotary member and an output side member; 
and comprises a friction member, disc-like plates, a hub, and a viscous 
damper mechanism. 
The hub is connectable for co-rotation with said output side member and has 
a flange on its outer circumference. The disc-like plates are rotatably 
mounted on the hub. The fiction member is connected to the disc-like 
plates for frictional engagement with the input side rotary member. The 
elastic member is for elastically connecting the flange and the disc-like 
plates whereby the flange and the disc-like plates are rotatable with 
respect to each other. The viscous damper mechanism includes a supply of 
viscous fluid medium and is for displacing the fluid medium through 
restrictions in response to angular movements of the disc-like plates and 
the flange with respect to each other. 
In this clutch disc assembly, when the friction member is frictionally 
engaged with the input side rotary member, the torque transmitted from the 
input side rotary member is transmitted from the friction member and the 
disc-like plates to the flange of the hub through the elastic member. When 
the torsional vibration is input from the input side rotary member, the 
elastic member is repeatedly expanded/contracted between the disc-like 
plate and the flange. At this time, the torsional vibration is dampened by 
the viscous resistance generated by the viscous damper mechanism. 
The viscous damper mechanism generates the viscous resistance by utilizing 
the fluid medium. Thus, it is possible to increase the resistance to 
dampen the low-frequency torsional vibration. 
In the foregoing operation, if the disc-like plates and the hub form a 
fluid chamber containing fluid medium and the elastic member is disposed 
therein, the wear of the disc-like plates is prevented by the fluid medium 
to thereby prolong the service life of the clutch disc assembly.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
First Embodiment 
FIGS. 1 and 2 show a clutch disc assembly in accordance with first 
embodiment of the invention. The line O--O represents a rotary centerline 
of the clutch disc assembly. 
In the figures, the clutch disc assembly is composed mainly of a hub having 
a flange on its outer circumference, a clutch plate 3 and a retaining 
plate 4 which are disposed on both sides of the flange 2 and rotatably 
fitted on the hub 1 from the outer circumferential sides, a plurality of 
coil springs 6 for elastically coupling both plates 3 and 4 with the 
flange 2 in the circumferential direction, and a viscous damper mechanism 
7 disposed within a fluid chamber 5 formed by both the plates 3 and 4 and 
the hub 1, which generates viscous resistance during the relative rotation 
between both the plates (3,4) and the flange 2. 
The hub 1 is, at its central portion, formed with spline teeth 1a for 
engagement with spline portions on an outer circumference of an input 
shaft (output side member) of the transmission (not shown). 
The fluid chamber 5 is filled with a fluid such as oil. The outer 
circumferential wall of the fluid chamber 5 is formed by an outer 
cylindrical wall 4a extending in the axial direction from the retaining 
plate 4. An O-ring 29 is disposed between an edge flange of the outer 
circumferential cylindrical wall 4a and the clutch plate 3 to seal the 
outer circumferential portion of the fluid chamber 5. There are also a 
plurality of cushioning plates 31 fixed to the outer circumferential 
portion of the clutch plate 3 by rivets 30. Frictional facings 9 are fixed 
to both sides of the cushioning plates 31 to be pressed against a flywheel 
(not shown). Sealants 8 are attached between the inner circumferential 
portions of the clutch plate 3 and the retaining plate 4, and the outer 
circumferential surfaces of the hub 1, respectively, to seal the inner 
circumferential portion of the fluid chamber 5. 
As shown in FIG. 2, sector-like cutaways 2a opening radially outwardly are 
formed in the outer circumferential portion of the flange 2. Coil springs 
6 are received into the spring seats 6a provided at both ends of each 
cutaway 2a. The coil spring 6 is arranged within the cutaway 2a such that 
intervals between the adjacent coil turns on the radially outward side are 
larger than those on the radially inward side. Support portions 3b and 4b 
are each tapered radially inward, sector-like, and aligned with the 
intervals between the cutaways 2a. These support portions 3b and 4b are in 
contact with the spring seats 6a of the coil springs 6. 
The viscous damper mechanism 7 is disposed radially inwardly from the coil 
springs 6. The viscous damper mechanism 7 is composed mainly of a pair of 
annular members 12, rectangular plate-like fixed members 13 fixed to the 
flange 2, and a pair of sliders 15 disposed within arcuate chambers 14 
(see FIGS. 2 and 3) formed in the annular members 12. Each of the pair of 
annular members 12, as shown in FIG. 3, has an opening in the inward axial 
directions with respect to the whole device (upwardly in FIG. 3). The 
plurality of arcuate chambers 14 are formed by a plurality of partition 
portions 12a which are formed at a constant interval in the 
circumferential direction. A cutaway 12c is formed in an inner 
circumferential wall at the central portion of each chamber 14. The 
cutaway 12c extends into a part of a side wall of the chamber 14. The pair 
of annular members 12 are fixed to the clutch plate 3 and the retaining 
plate 4 by stud pins 16 at the partitioning portions 12a. The stud pins 16 
are inserted into long holes(not shown) formed in the circumferential 
direction of the flange 2. The long holes formed in the flange 2 ensures 
that the chambers 14 facing each other through the flange 2 communicate 
with each other. 
The fixed members 13 extend in both axial direction of the flange 2 and are 
disposed in the respective arcuate chambers 14. The sliders 15 which are 
in the form of boxes are disposed at both ends of the fixed members 13 in 
the axial direction. Inner and outer walls of the sliders 15 have 
substantially the same shape of the outer and inner walls of the arcuate 
chambers 14 within which the sliders 15 lie so that they may be movable in 
the circumferential direction within the arcuate chambers 14 and divides 
the arcuate chambers into two large partition chambers 20 and 21, as shown 
in FIG. 4. Inside of the sliders 15 are divided into small partition 
chambers 18 and 19 by the-fixed members 13. End walls of the slider 15 
keeps away from both the circumferential sides of the fixed member 13 with 
a given displacement angle. Holes 15a are formed in both end walls of the 
sliders 15 in the circumferential direction. Thus, the large partition 
chambers 20 and the small partition chambers 18 are in communication with 
each other, and the small partition chambers 19 and the large partition 
chambers 21 are in communication with each other. 
The cutaways 12c of the annular members 12 substantially correspond to a 
neutral position of the sliders 15. In the neutral position, the cutaways 
12c are in communication with all the small partition chambers 18 and 19, 
and the large partition chambers 20 and the 21. 
The operation of the clutch disc assembly and characteristics of the 
operation will be described. 
When the friction facings 9 are depressed against, for example, the engine 
flywheel, the torque of the engine flywheel is input to the clutch plate 3 
and the retaining plate 4. The torque is transmitted to the flange 2 of 
the hub 1 through the coil springs 6, and further transmitted to the input 
shaft (not shown). 
The change in torsional rigidity of the coil springs 6 will be explained. 
Assume that the hub 1 is fixed to a base (not shown) and the clutch plate 
3 and the retaining plate 4 is twisted relative to the hub 1. When the 
plates 3 and 4 start the torsional operation relative to the flange 2 (hub 
1), mainly, the outer circumferential side of the coil springs 6 will flex 
to obtain a low rigidity characteristics. When the compression of the coil 
springs 6 is developed, the inner circumferential side of the coil springs 
6 starts to be compressed to obtain a high rigidity characteristics. After 
the stud pins 16 have been brought into contact with ends of the long 
holes of the flange 2, the angular movement of the clutch plate 3 and the 
retaining plate 4 to the flange 2 is finished. 
During the above-mentioned torsional operation, the viscous resistance is 
generated by the viscous damper mechanism 7. Assume that the clutch plate 
3 and the retaining plate 4 are twisted, for example, in direction R.sub.1 
from the neutral position shown in FIG. 4. In this case, the annular 
members 12 and the sliders 15 are rotated together in the rotational 
direction R.sub.1. Thus, the small partition chambers 19 in the sliders 15 
are compressed to be small in volume, and at the same time, the small 
partition chambers 18 are expanded to be large in volume. At this time, 
the fluid will flow radially out from the small partition chambers 19 
through the cutaways 12c of the annular members 12 and into the small 
partition chambers 18 through the cutaways 12c, wherein said cutaways 12c 
opening to the small partition chambers 19 functions as a first choke 
portion. Since the cross-sectional area of the flow paths of the cutaways 
12c is formed to be large, the viscous resistance is small. Accordingly, 
in this case, the small viscous resistance is generated. 
After the torsional angle is increased so that the circumferential walls on 
the rear side of the sliders 15 in the circumferential direction are 
brought into contact with the fixed member 13 (FIG. 5), the large 
partition chambers 21 is contracted to be small in volume, and the large 
partition chambers 20 is expanded to be large in volume. At this time, at 
first, the fluid will flow from the large partition chambers 21 through 
the cutaways 12c. When the torsional operation is advanced, as shown in 
FIG. 6, the communication between the second large partition chambers 21 
and the cutaways 12c is interrupted by the sliders 15. As a result, the 
fluid contained in the large partition chambers 21 will not flow through 
the cutaways 12c so that the fluid contained in the large partition 
chambers 21 will be pressured to flow through the holes 15a and further to 
seed inbetween intimate interfaces between the sliders 15 and the fixed 
members 13, wherein the intimate interfaces function as second choke 
portions. Since the flow path area of the intimate interfaces as the 
second choke portion is small, the viscous resistance is large. 
In the case where the clutch plate 3 and the retaining plate 4 are returned 
on the side R.sub.2 after they have been twisted on the side R.sub.1, 
first of all, the rear ends of the sliders 15 in the circumferential 
direction are separated away from the fixed members 13, and the fluid will 
flow from the cutaways 12c into the small partition chambers 19. When the 
sliders 15 are kept on returning to the side R2, the fluid will flow from 
the cutaways 12c into the large partition chambers 21. Consequently, when 
the components are returned once they have been twisted, the fluid quickly 
returns back to the partition chambers where the fluid has been compressed 
after angular movements. Accordingly, the return operation of the twist 
operation may be smoothly and quickly attained. Incidentally, when the 
rear ends of the sliders 15 separate from the fixed members 13, all the 
partition chambers are in communication with the cutaways 12c so that a 
small viscous resistance is generated. 
Assume that torsional vibration having a small angular displacement is 
transmitted to the viscous damper mechanism 7 due to, for example, 
combustion fluctuations of the engine under the condition that the clutch 
plate 3 and the retaining plate 4 are in the neutral position as shown in 
FIG. 4. In this case, the annular member 12 and the slider 15 move 
relative to the flange 2 in a small-angle range, whereby the fluid goes in 
and out from the small chambers 18 and 19 through the first choke portion 
formed by the cutaways 12c. Therefore, small viscous resistance 
effectively dampens the torsional vibration having a small angular 
displacement. 
Further assume that the torsional vibration having a small angular 
displacement is transmitted to the viscous damper mechanism 7 under the 
condition that the clutch plate 3 and the retaining plate 4 are twisted 
relative to the flange 2 through a certain angle. In this case, the 
annular member 12 and the sliders 15 move relative to the flange 2 in a 
small-angle range where the first and second small partition chambers 18 
and 19 are in fluid communication with the cutaways 12c, so that it is 
possible to obtain a small viscous resistance. Namely, the time when the 
viscous resistance is changed is not determined by the absolute twist 
angle of the clutch plate 3 and the retaining plate 4 relative to the 
flange 2 but by the positional relation between the sliders 15 and the 
fixed members 13. 
Assume that the low-frequency torsional vibration is input to the viscous 
damper mechanism 7 because the driver suddenly depresses or loosen the 
accelerator pedal. Since the low-frequency torsional vibration has a large 
angular displacement, the annular member 12 moves relative to the flange 2 
in a large angle range where the fluid in the large partition chambers 20 
and 21 mainly flows into the small partition chambers 18 and 19 through 
the holes 15 and the intimate interfaces between the fixed member 13 and 
the slider 15, which generates large viscous resistance. 
In this case, since the viscosity of fluid Is utilized, it is possible to 
generate a large viscous resistance in comparison with the frictional 
resistance by the conventional friction member. Accordingly, it is 
possible to effectively dampen the low-frequency torsional vibration. 
As mentioned before, the viscous damper mechanism 7 can effectively dampen 
two different kinds of torsional vibrations by generating different 
magnitudes of the viscous resistance. Also, by the utilization of the 
viscosity, the change of the torsional rigidity may be smooth. 
The viscous damper mechanism 7 is disposed radially inwardly of the coil 
spring 6, and hence it does not suffer the enlargement of the clutch disc 
assembly as a whole. 
The coil springs 6 are lubricated within the fluid chambers 5. Therefore, 
even if the coil springs 6 are repeatedly expanded and compressed and 
might be brought into contact with the support portions 3b and 4b of the 
clutch plate 3 and the retaining plate 4, frictional wear and damage at 
the support portions 3b and 4b would hardly occur. As a result, the 
service life of the clutch disc assembly as a whole may be improved. 
Second Embodiment 
FIGS. 7 and 8 show a clutch disc assembly in accordance with the second 
embodiment of the present invention. The line O--O represents a rotary 
centerline of the clutch disc assembly. 
In the figures, the clutch dlsc assembly is composed mainly of a hub 101 
having a flange 102 on its outer circumference, a clutch plate 103 and a 
retaining plate 104 which are arranged on both sides of the flange 102 and 
rotatably mounted on the hub 101 from the lateral sides, first coil 
springs 106 and second coil springs 107 for elastically coupling both 
plates 103 and 104 with the flange 102 in the circumferential direction 
within a lubrication chamber 105 defined by both plates 103 and 104 and 
the hub 101, and a viscous damper mechanism 108 disposed within the 
lubrication chamber 105 for generating viscous resistance by utilizing the 
lubricant oil contained in the lubrication chamber 105 during the relative 
rotation of both the plates 103 and 104 to the flange 102. The hub 101 
has, at its inner side, spline teeth 101a for engagement with spline 
portions on an outer circumference of the input shaft (output side member) 
of the transmission (not shown). 
The lubrication chamber 105 is filled with fluid such as grease or 
lubricant oil. A bush 109 is used to center the clutch plate 103 and to 
seal an inner circumferential portion of the lubrication chamber 105. The 
retaining plate 104 has, on its outer circumferential portion, a 
cylindrical wall 104a extending toward the clutch plate 103 and in contact 
with the latter. An O-ring 110 is disposed between the clutch plate 103 
and a flange portion of the cylindrical wall 104a to seal the outer 
circumferential portion of the lubrication chamber 105. Also, a plurality 
of cushioning plates 111 are fixed to the outer circumferential portion of 
the clutch plate 103 by rivets 112. Frictional facings 113 are fixed to 
both sides of the cushioning plates 111. When the friction facings 113 are 
depressed on, for example, an engine flywheel (input side rotary member 
not shown), the torque is input to the clutch disc assembly. 
The clutch plate 103 and the retaining plate 104 are coupled with each 
other at the inner circumferential portion by first pins 115 and at the 
outer circumferential portion by second pins 116. 
Three first window holes 102a and three second window holes 102b, smaller 
than the first window holes 102a in both the circumferential direction and 
radial direction, are formed alternatively in radially middle portions of 
the flange 102. The first pins 115 are inserted into an inner peripheral 
portion of the first window hole 102a. When the first pins 115 are brought 
into contact with edges of the first window holes 102a in the 
circumferential direction, the torsion between the clutch plate 103 and 
retaining plate 104 to the flange 102 (and the hub 1) is restricted. Large 
diameter double coil springs 106 and small diameter double coil springs 
107 are disposed within the first window holes 102a and the second window 
holes 102b, respectively. It should be noted that each of the double coil 
springs 106 and 107 is formed by a large diameter coil spring and a small 
diameter coil spring inserted into the respective large diameter coil 
spring. A predetermined interval is provided between spring seats 106a 
located at both ends of each spring 106 and the first window hole 102a. 
Spring seat 107a provided at both ends of the second coil spring 107 are 
brought into contact with both ends of the second window hole 102b in the 
circumferential direction. Drawing portions 103b, 104b and 103c are formed 
at the portions of both the plates 103 and 104 corresponding to the first 
coil springs 106 and the second coil springs 107 for receiving them. 
The viscous damper mechanism 108 are disposed further radially outwardly of 
the coil springs 106 and 107. As shown in FIGS. 9 and 10, the viscous 
damper mechanism 108 is composed of an annular member 118 having a 
plurality of arcuate chambers 119 which have a long hole open radially 
inwardly and extending circumferentially, projections 102c projecting 
radially outward from outer edge of the flange 102 and inserted into the 
arcuate chambers 119 of the annular member 118 through the long hole, and 
cap-shaped sliders 120 disposed movably in the circumferential direction 
of the arcuate chamber 119. 
The annular member 118 is composed of two halves 118a divided in the axial 
direction and is interposed on the inner circumferential side of the 
cylindrical wall 104a between the clutch plate 103 and the outer 
circumferential portion of the retaining plate 104. The second pins 116 
(see FIG. 7) pass through the two halves 118a which form the annular 
member 118. Thus, the annular member 118 is rotated together with the 
clutch plate 103 and the retaining plate 104. As described above and as 
shown in FIG. 10, the parts corresponding to the arcuate chambers 119 of 
the annular members 118 are U-shaped with said long hole opening radially 
inwardly. The outer edge of the flange 102 is inserted into the long hole 
of the arcuate chamber 119, whereby the annular member 118 and the flange 
102 can rotate relative to each other. The fluid filled in the chambers 
119 is the same as the lubricant oil or grease used in the lubrication 
chamber 105. Engagement projections 118b each extending inwardly are 
formed on the inner circumferential edges of the two members 118a of the 
annular member 118 and the engagement projections 118b are engaged with 
annular grooves 102d provided on both sides of the outer circumferential 
portion of the flange 102 to thereby seal the inner circumferential 
portion of the arcuate chamber 119. 
Shape of the outer circumferential wall of the slider 120 corresponds to 
shape of the wall of the arcuate chamber 119 so that the slider 120 can 
move smoothly in the arcuate chamber 119. The arcuate chamber 119 is 
divided into large chambers 123 and 124 by each slider 120. The large 
chambers 123 and 124 are in fluid communication with the small chamber 121 
and the small chamber 122 through cutaway portions formed radially 
inwardly of both sides of stopper portions 120a, respectively. 
The projection 102c of the flange 102 is inserted into the each slider 120 
so that the interior of the slider 120 is divided into small chambers 121 
and 122. The small chambers 121 and 122 is in fluid communication with 
each other through a first choke C.sub.1 between the projection 102c and 
the inner circumferential surface of the slider 120. The slider 120 has 
the stopper portions 120a keeping away from the projection 102c through a 
certain angle in the neutral position. The cutaway portion made in the 
stopper portion 120 is larger in size than the first choke C.sub.1. When 
the slider 120 is moved in the circumferential direction and brought into 
contact with the projection 102c, the cutaway portion is closed. A second 
choke C.sub.2 which is smaller than the first choke C.sub.1 is kept 
between the outer circumferential wall of the slider and the inner 
circumferential wall of the arcuate chamber 119. 
A first side plate 126 and a second side plate 127 are disposed on both 
sides of the flange 102 within the lubrication chamber 105. The first and 
second side plates 126 and 127 are coupled with the clutch plate 103 and 
the retaining plate 104 in an elastic manner in the circumferential 
direction through the first springs 106, and coupled with the flange 102 
in an elastic manner in the circumferential direction through low rigidity 
coil springs 129. As shown in FIG. 8, abutment portions 127a to be brought 
into contact with the spring seats 106a of the first coil springs 106 are 
formed on the outer circumferential plate of the second side plate 127 
(This is the case with respect to the first side plate 126 too). 
Third window holes 102e are formed on an inner circumferential side of each 
second window holes 102b in the flange 102. A low rigidity coil spring 129 
is disposed in the third window hole 102e. Spring seats 129a are provided 
at both ends of the coil spring 129. The spring seats 129a are extending 
in the axial direction and are brought into contact with both ends in the 
circumferential direction of each hole formed in the first and second side 
plates 126 and 127. 
The first and second side plates 126 and 127 are coupled with each other by 
stopper pins 130 which are coupled with each other at the inner 
circumferential portion. The stopper pins 130 pass through fourth window 
holes 102f formed in the inner circumferential portion of the flange 102. 
A predetermined gap is kept in the circumferential direction between the 
stopper pins 130 and the fourth window holes 102f. When the stopper pins 
130 are brought into contact with both ends in the circumferential 
direction of the fourth window holes 102f, the torsional motion is 
restricted between the first and second side plates 126 and 127 to the 
flange 102. A flange portion 109a of the bush 109 is arranged between the 
first side plate 126 and the flange 102. Disc plates 132, 133 and 134 are 
interposed between the flange 102 and the second side plate 127. 
A first disc plate 135 is disposed between the inner circumferential 
portion of the clutch plate 103 and the first side plate 126, and a second 
disc plate 136 is disposed between the second side plate 127 and the 
retaining plate 104. A hole 136a (FIG. 8) extending in the circumferential 
direction is formed in the first disc plate 135 and the second disc plate 
136 so that the stopper pins 130 are movable in the circumferential 
direction. 
The operation of the clutch disc assembly and the characteristics of the 
operation will be described. 
When the friction facings 113 are depressed against, for example, the 
engine flywheel, the torque of the engine side flywheel is input into the 
clutch-plate 103 and the retaining plate 104. The torque is transmitted 
through the first coil springs 106, the second coil springs 107 and the 
low rigidity coil spring 129 to the flange 102 of the hub 101 and further 
to the shaft on the output side. 
The change in torsional rigidity between the clutch plate 103 and the 
retaining plate 104 to the flange 102 will be explained. 
Assume that the hub 101 is fixed to a base (not shown) and the clutch plate 
103 and the retaining plate 104 are twisted to the flange 102 (the hub 
101). When the clutch plate 103 and the retaining plate 104 start 
torsional motion, the lowest rigidity coil springs 129 are compressed. 
When the stopper pins 130 are brought into contact with one of both ends 
in the circumferential direction of the fourth windows 102f of the flange 
102, the relative rotation between the side plates 126 and 127 to the 
flange 102 is finished. When the compression of the first coil springs 106 
is developed, then, the clutch plate 103 and the retaining plate 104 cause 
the second coil springs 107 to be compressed. Thereafter, it is possible 
to obtain the high rigidity characteristics. When the first pins 115 are 
brought into contact with one of both ends in the circumferential 
direction of the first window holes 102c of the flange 102, then, the 
relative movement of both the plates 103 and 104 to the flange 102 is 
finished. 
In the foregoing torsional operation, the viscous resistance is generated 
mainly by the viscous damper mechanism 108 in addition to the slippage 
among the bush 109 and the disc plates 132 to 134 clamped that are between 
the side plates 126 and 127 and the flange 102 and also to the slippage 
between the first and second plates 135 and 136 clamped between the clutch 
plate 103 and the retaining plate 104 and the side plates 126 and 127. 
In the foregoing torsional operation, assume that the clutch plate 103 and 
the retaining plate 104 are displaced in, for example, a rotational 
direction R.sub.1 from the neutral point shown in FIG. 9. The annular 
member 118 and the sliders 120 are moved together in the rotational 
direction R.sub.1. As a result, the small chambers 122 within the sliders 
120 are compressed to be small in size, and at the same time, the small 
chambers 121 is expanded to be large in size. Then, the lubricant oil 
within the first small chambers 121 will flow into the small chambers 122 
through chokes C.sub.1 and also will flow through cutaway portions of the 
stoppers 120a on the R.sub.1 side to the large chamber 124. Since the 
cross-sectional area of the flow path of the choke C.sub.1 is large, the 
viscous resistance is small. 
When the torsional angle is increased, and the stopper portions 120a on the 
R.sub.2 side are brought into contact with the projections 102c, the flow 
of the lubricant oil is stopped between the inside of the sliders 120 and 
the projections 102c. Thus, the sliders 120 are held in a condition that 
the sliders 120 are fixed to the projections 102c. When the torsional 
motion is further continued, the annular member 118 is moved in the 
rotational direction R.sub.1. The large chambers 124 are compressed to be 
small in size, whereas the large chambers 123 are expanded to be large in 
size. The lubricant oil contained within the large chambers 124 will then 
flow into the large chambers 123 through the choke C.sub.2 between the 
inner circumferential wall of the annular member 118 and the outer 
circumferential wall of the sliders 120. At this time, the flow path area 
of the choke C.sub.2 is small, the viscous resistance is large. 
When the clutch plate 103 and the retaining plate 104 are returned after 
the clutch plate 103 and the retaining plate 104 have been twisted in the 
R.sub.1 direction, first of all, the stoppers 120a on the R.sub.2 side of 
the sliders 120 are separated from the projections 102c so that choke 
C.sub.1 functions. For this reason, small viscous resistance is generated. 
Assume that torsional vibration having small angular displacement is 
transmitted to the viscous damper mechanism 108 due to, for example, 
combustion fluctuation of the engine under the condition that the clutch 
plate 103 and the retaining plate 104 are in the neutral position as shown 
in FIG. 9. In this case, the annular member 118 and the slider 120 
reciprocally move relative to the flange 102 in a small-angle range, 
whereby the lubricant oil flows through the first choke C1. Therefore, 
small viscous resistance effectively dampens the torsional vibration 
having small angular displacement. 
Further assume that the torsional vibration having small angular 
displacement is transmitted to the viscous damper mechanism 108 under the 
condition that the clutch plate 103 and the retaining plate 104 are 
twisted relative to the flange 102 through a certain angle. In this case, 
the annular member 118 and the sliders 120 reciprocally moves relative to 
the flange 102 in small-angle range where the lubricant oil flows through 
the first choke C.sub.1, so that it is possible to obtain a small viscous 
resistance. Namely, the time when the viscous resistance is changed is not 
determined by the absolute twist angle of the clutch plate 103 and the 
retaining plate 104 relative to the flange 102, but by the positional 
relation between the sliders 120 and the projection 102c. 
Assume that the low-frequency torsional vibration is input to the viscous 
damper mechanism 108 because the driver suddenly depresses or loosen the 
accelerator pedal. Since the low-frequency torsional vibration has large 
angular displacement, the annular member 118 reciprocally moves relative 
to the flange 102 in a large angle range where the lubricant oil flows 
mainly through the second choke C.sub.2, which generates large viscous 
resistance. 
In this case, since the viscosity of fluid is utilized, it is possible to 
generate a larger viscous resistance in comparison with the frictional 
resistance by the conventional friction member. Accordingly, it is 
possible to effectively dampen the low-frequency torsional vibration. 
As mentioned before, the viscous damper mechanism 108 can effectively 
dampen two different kinds of torsional vibrations by generating different 
magnitudes of the viscous resistance. Also, due to utilization of the 
viscosity, the change of the torsional rigidity may be smooth. 
Also, since the viscous damper mechanism 108 is located most outwardly 
within the lubrication chamber 105, it is possible to generate a large 
hysteresis torque with a small resistance force to thereby make the damper 
mechanism 108 compact. 
Since the first coil springs 106 and the second coil springs 107 are 
lubricated within the lubrication chamber 105, even if these springs 106 
and 107 are repeatedly compressed and expanded, there is almost no fear 
that frictional wear or damage would be caused in the drawing portions 
103b and 104b of the clutch plate 103 and the retaining plate 104. Thus, 
the service life of the clutch disc assembly is prolonged. 
Various details of the invention may be changed without departing from its 
spirits nor its scope. Furthermore, the foregoing description of the 
embodiments according to the present invention is provided for the purpose 
of Illustration only, and not for the purpose of limiting the invention as 
defined by the appended claims and their equivalents.