Clutch disc having damper springs

A clutch disc has at least two kinds of torsion damper springs arranged circumferentially around a hub of the clutch disc. First damper springs have a spring constant smaller than that of second damper springs. The first springs and the second springs are not arranged in series, end to end, in a circle, but the first springs are arranged in parallel with the second springs. The first springs are wound around an annular wire guide concentric with the hub. In one embodiment, the annular wire guide extends through the second springs, and the first springs are inserted in the second springs, respectively. In another embodiment, the annular wire guide is mounted on the outer periphery of a flange of the hub outside the second springs.

BACKGROUND OF THE INVENTION 
The present invention relates to clutch discs of friction type clutches. 
A clutch of an automobile disconnects and reconnects the engine from the 
transmission and the drive line. A clutch disc of a friction type clutch 
is provided with a damper mechanism for isolating the vibration caused by 
variation in engine output torque from the transmission. That is, damper 
springs are mounted circumferentially around a flange of a spline hub and 
compressed circumferentially between the hub flange and an assembly of a 
clutch plate and a retaining plate. These damper springs do not have the 
same spring characteristic, but they are classified into groups having 
different spring characteristics, such that the overall spring 
characteristic changes in a sequence of stages in accordance with the 
relative angular displacement occurring between the hub flange and the 
clutch plate assembly. A maximum relative rotational angle within which 
the hub flange and the clutch plate are allowed to relatively displace is 
made as large as possible in order to obtain a good damper effect. 
In a conventional design of such a torsion damper mechanism, the damper 
springs have approximately the same diameter, and are placed in series on 
the same circle. This arrangement limits the space for accommodating the 
damper springs, and limits, also, the relative rotational angle between 
the hub flange and the clutch plate assembly to under about 11 degrees. In 
order to increase the relative rotational angle beyond this limit, it is 
necessary to form, in the hub flange, large openings for accommodating the 
damper springs, but such a large opening size weakens the hub flange and 
causes excessive stress in the damper springs. Because of this 11-degree 
limit, a clutch disc of the conventional type can not sufficiently absorb 
torque fluctuation. This torque fluctuation produces gear noise due to 
backlash in the transmission, especially at low rotational speed and at 
idling. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a clutch disc having an 
arrangement of torsion damper springs which allows a large relative 
rotational displacement between a hub and an assembly of a clutch plate 
and a retaining plate. 
According to the present invention, a clutch disc comprises an assembly of 
a clutch plate having clutch friction facings and a retaining plate, a 
spline hub having a flange disposed between the clutch plate and the 
retaining plate, and damper means arranged between the assembly and the 
flange of the hub for transmitting torque therebetween. The damper means 
comprises first damper means and second damper means. The first damper 
means comprises a plurality of first damper coil springs which are 
arranged circumferentially around the hub and wound around annular wire 
guide concentric with the hub. One end of each of the first damper springs 
is seated on the assembly, and the other end on the hub flange in such a 
manner that each of said first springs is compressed in accordance with a 
relative rotational displacement between the assembly and the hub flange. 
The second damper means comprises a plurality of second damper springs 
having a spring constant greater than that of the first damper springs. 
Each of the second springs is contained in each of a plurality of pockets 
arranged circumferentially around the hub. Each of the pockets is formed 
by three openings which are formed, respectively, in the clutch plate, the 
hub flange, and the retaining plate in such a manner that the second 
springs begin to be compressed when a relative rotational displacement 
between the hub flange and the assembly exceeds a predetermined angle.

DETAILED DESCRIPTION OF THE INVENTION 
One embodiment of the present invention is shown in FIGS. 1 to 4. A spline 
hub 1 having internal splines is integrally formed with an outward flange 
1a. On each side of the flange 1a, a clutch plate 4 and a retaining plate 
5 are mounted through friction washers 2, 3, respectively. The clutch 
plate 4 and the retaining plate 5 are connected by rivet pins 6. 
Cushioning plates 8 having clutch friction facings 7 are fitted to the 
outer periphery of the clutch plate 4. 
Openings, 1b, 4b and 5b are formed, respectively, in the hub flange 1a, the 
clutch plate 4 and the retaining plate 5. In this embodiment, there are 
four sets of the openings 1b, 4b and 5b, as shown in FIG. 1. These four 
sets of the openings are arranged on one and the same circle. Each of four 
springs 9 is contained in a pocket formed by each set of the openings 1b, 
4b and 5b. When the hub flange 1a rotates relative to the assembly of the 
clutch plate 4 and the retaining plate 5 beyond a predetermined angle, the 
springs 9 begins to be compressed. The springs 9 are held in position by 
the openings 4b and 5b. The springs 9 and the openings 1b, 4b and 5b 
constitute a second stage damper B. 
An annular groove 1c is formed circumferentially in the hub flange 1a on 
the retaining plate side. A circle formed by the annular groove 1c passes 
through the center of every spring 9 and is concentric with the spline hub 
1. An annular wire guide 10 is fitted in the annular groove 1c. The 
annular wire guide 10 extends along the annular groove 1c and through the 
openings 1b, and forms the circle concentric with the spline hub 1. Each 
of the openings 4b of the clutch plate 4 has an enlarged middle portion 
4e, and first and second elongate portions 4c, 4d which have a width 
narrower than the middle portion 4e. The first elongate portion 4c extends 
from the middle portion in the direction of the clutch disc rotation along 
the annular wire guide 10, and the second elongate portion 4d extends in 
the opposite direction from the middle portion. The first elongate portion 
4c is longer than the second elongate portion 4d. Each of the openings 5b 
of the retaining plate 5 has an enlarged middle portion 5e, a first 
elongate portion 5c and a second elongate portion 5d having the same 
configurations as the middle portion and the first and second elongate 
portions of the opening 4c. The length along the circumferential direction 
between the end of the first elongate portion 4c and the end of the second 
elongate portion 4d is equal to the length of the opening 1b along the 
circumferential direction. The corresponding length of the opening 5b is 
also equal to the length of the opening 1b along the circumferential 
direction. In a neutral state where no torque is transmitted through the 
disc clutch, the angular position of the opening 1b of each pocket 
coincide with the openings 4b and 5b of that pocket. A coil spring 11 is 
contained in each set of the first and second elongate portions 4c, 4d, 
and the first and second elongate portions 5c, 5d. Each of the springs 11 
is wound around the annular wire guide 10, passes through the inside of 
the spring 9 coaxially, and extends over the full length of the openings 
1b, 4b and 5b from the ends of the first elongate portions of the opening 
4b and 5b to the ends of the second elongate portions of the openings 4b 
and 5b. The springs 11 has a spring constant smaller than that of the 
springs 9. One end of each of the springs 11 is seated on the hub flange 
1a, and the other end on the clutch plate 4 and the retaining plate 5. The 
coil springs 11, the annular wire guide 10, the annular groove 1c, the 
openings 1b, and the openings 4b and 5b with the first and second elongate 
portions constitute a first stage damper A which acts in the full range of 
the relative rotational angle between the hub flange 1a, and the clutch 
plate 4 and the retaining plate 5. 
The operations of this clutch disc is as follows: In the state where the 
clutch disc is incorporated in a clutch, the spline hub 1 is constantly 
engaged with an input shaft of a transmission. On the other hand, the 
clutch plate 4 and the retaining plate 5 rotate integrally with an output 
shaft of an engine, by the aid of the friction between the clutch facings 
7, and the pressure plate of the clutch and the flywheel fixedly connected 
with the output shaft of the engine, when the clutch facings 7 is pressed 
by the pressure plate against the flywheel. 
Torque vibration transmitted during clutch engagement is absorbed by the 
relative rotational movements between the flange 1a of the spline hub 1 
and the assembly of the clutch plate 4 and the retaining plate 5. 
When the hub flange 1a in FIG. 1 rotates with respect to the assembly of 
the clutch plate 4 and the retaining plate 5 in the clockwise direction 
through the action of torque vibration, each of the coil springs 11 is 
compressed by one end of the opening 1b of the hub flange 1a. The coil 
spring 11 is compressed gradually and reaches the state, shown in FIG. 4, 
where one end of the coil spring 11 reaches one end of the spring 9. In 
this state, the relative angular displacement amounts to an angle A1 as 
shown in FIG. 4. When the relative rotational angle exceeds the angle A1 
and enters a zone of an angle B1, the spring 9 begins to be compressed. In 
this zone, the coil spring 11 continues to be compressed along with the 
spring 9. After the start of the compression of the coil spring 11 and 
after the start of the compression of the coil spring 9 as well, the far 
end of the spring 11 in the counterclockwise direction in FIG. 4 is seated 
only on the hub flange 1a, and the other end of the spring 11 in the 
clockwise direction is seated on the clutch plate 4 and the retaining 
plate 5. 
While the clutch plate 5 is being driven and torque is being transmitted, 
the springs 11 are always pushed in the clockwise direction in FIG. 4. 
With the longer length of the first elongate portions 4c and 5c, the 
springs 11 can deflect sufficiently in this direction. Heavy torque is 
transmitted through the compression of the springs 9. 
The maximum relative rotational angle between the hub flange 1a and the 
assembly of the clutch plate and the retaining plate is made larger by 
increasing the size of the openings 1b of the hub flange 1a, as compared 
with the conventional type clutch disc. In the conventional design, the 
first stage damper springs are arranged in series with the second stage 
damper springs circumferentially around the hub. In contrast with this 
conventional design, the first stage springs 11 are arranged in parallel 
with the second stage springs 9 in the clutch disc of the present 
invention. With this arrangement, more space in the hub flange can be used 
for the openings of the springs 9, and the size of the openings can be 
increased. 
FIG. 5 shows relationship between the relative rotational angle and the 
torque. A line x is a relationship according to the conventional type 
clutch disc. A line Y is a relationship according to the clutch disc of 
the present invention. According to the present invention, the hub flange 
1a can rotate more widely with respect to the assembly of the clutch plate 
4 and the retaining plate 5, so that torque vibration is absorbed 
efficiently and the gear backlash noise in a transmission is prevented. 
Another embodiment is shown in FIGS. 6 to 9. In this embodiment, the first 
stage damper A is arranged circumferentially on the outer peripheries of 
the hub flange 1a and the retaining plate 5. The hub flange 1a has a 
plurality of first blocks 13 formed integrally on the outer periphery. The 
retaining plate 5 has a plurality of second blocks 14 on the outer 
periphery. The second blocks 14 are fixed to the retaining plate 5 by the 
rivet pins. The first blocks 13 and the second blocks 14 are arranged 
alternately in a circle concentric with the spline hub 1. An annular wire 
guide 10 concentric with the spline hub 1 is supported by the alternately 
arranged first and second blocks 13 and 14. Either or both of the first 
blocks 13 and the second blocks 14 support the annular wire guide 
slidably. A coil spring 11 is wound around the annular wire guide between 
every neighbouring pair of the first block 13 and the second block 14. One 
end of each of the coil springs 11 is fixed to one of the first block 13, 
and the other end is fixed to the neighbouring second block 14. In this 
embodiment, the openings 4b and 5b do not have the elongate portions but 
have only the middle portions. 
When the hub flange 1a rotates in the clockwise direction in FIG. 6, the 
first blocks 13 rotate together. During this, each of the first blocks 13 
compresses the adjacent spring 11 on the forward side, and at the same 
time, pulls the adjacent spring 11 on the rearward side. The springs 11 on 
the forward side of the first blocks 13, that is, the springs 11 which are 
compressed during a forward rotation of the clutch disc, has a spring 
constant larger than that of the springs 11 on the rearward side of the 
first blocks 13. In other respects, the construction and the operations of 
this embodiment is the same as those of the preceding embodiment. 
Thus, according to the present invention, the maximum relative rotational 
angle between the hub flange and the assembly of the clutch plate and the 
retaining plate is increased without a sacrifice of the rigidity of the 
hub flange, so that engine torque vibrations can be absorbed efficiently 
and gear backlash noises can be prevented.