Clutch discs
The clutch disc transfers the engine torque to the input shaft of the transmission by
means of frictional contact. Power flows from the flywheel and from the contact plate via
the clutch linings (1), the cushion spring (2) and the disc adaptor (3)
into the torsion damper and from there to the transmission shaft via the gear teeth of the
hub (4).
Clutch linings
The linings consist of threads which are embedded in a matrix made of resin, rubber and
fillers such as carbon black, graphite and kaolin. The thread is mainly made of glass
fibres and a brass or copper wire. Other fibres such as polyacylonitrile, aramid,
cellulose or others may be added depending on the manufacturer.
Sachs produces its own linings. These and products of other lining manufacturers are
evaluated using test specifications which accurately simulate vehicle use. This ensures
that the right lining is used for every vehicle, also taking expense into account.
The most important criteria for evaluating clutch linings are:
• Friction coefficient, particularly the minimum value at extreme load;
• Rotational speed at which they burst;
• Wear of linings themselves and of the mating surfaces;
• Distortion at thermal load;
• Specific gravity as the influencing variable for the moment of inertia;
• Responsiveness of the torque structure;
• Tendency to self-generated friction vibrations (shear) and friction noises
The lining spring is a corrugated segment of sheet metal with a spring deflection of 0.3 to 1 mm which is riveted to the two linings as well as to the driving disc. Six to nine such springs are arranged around the circumference. The lining spring characteristic curve is divided into three sections:
A: Start of torque transfer. The smooth rise gives the driver time to reduce the high pedal speed, when moving through the free travel of the pedal, to the low response speed when moving off.
B: Response range for usual starting torques. One third of the maximum contact pressure is needed for this. The flexible adaptation of the lining to the mating surfaces ensures a constant contact pattern which is a prerequisite for low lining wear and favourable shear properties.
C: Residual suspension in the range from 70 % to 100 % of the maximum contact
pressure.
It is used to compensate for the contact plate protection at high thermal load and to
suppress friction noises.
Torsion damper
Every combustion engine produces vibrations in the power train of a vehicle which may
make rattling noises in the transmission and droning noises in the body at certain speeds
and under certain operation conditions. A torsion damper installed in the clutch dampens
these vibrations thus reducing the annoying sounds or eliminating them completely.
The torsion damper is generally integrated into the clutch disc.
It is inserted into the flywheel, which is then referred to as a dual mass flywheel, for more demanding applications in passenger vehicles. The torsion damper comprises several helical springs arranged towards the circumference and permits a limited distortion between crankshaft and transmission input shaft.
The springs are fed into windows. Usually two spring sets are connected in series - an outer one for driving mode (5) and an inner for idling mode (6) - to form one component. The characteristic curve of the torsion damper has a pull and a push section which are limited by stops (7). The stops record torque peaks and prevent the springs becoming blocked.
The characteristic curve is only travelled through almost completely when the load changes. A small vibration angle is set at constant travel. A friction device (8) reduces the vibration angle at the resonance throughput. The optimal torsion damper characteristic curve is determined for every new vehicle model coming onto the market by means of calculations and test drives. The procedure is known as the tuning of the power train.
Survey of clutch discs
The lining springs / torsion damper combinations for series production are listed in
the table arranged according to the standardised clutch disc diameters.
If necessary, additional measurements may be performed. All current transmission input
shaft profiles are available. We recommend that our customer services department be
consulted to help select the most suitable torsion damper.