Function of the clutch
As a result of further developments in vehicle construction, today’s clutch components must satisfy a host of requirements that have a significant influence on the comfort behaviour of the vehicle. These include soft start-up, swift gear shifting, vibration damping and noise minimisation. The designers have squared up to these requirements. A modern clutch is typified by speed resistance, high transmission reliability, low overall height, low engagement forces and a long lifespan. The main components of a clutch are: Clutch pressure plate, disc flywheel and friction disc.
Together with flywheel and friction disc, the clutch pressure plate forms a friction system and is mounted to the flywheel by bolts in the housing. The pressure plate ensures that the engine torque is transferred via the friction disc to the transmission intake shaft. In the 70’s, the diaphragm spring clutch has consistently eliminated bolt springs from the passenger car. The contact force required for transferring engine torque is now provided by a slotted diaphragm spring. The diaphragm spring is significantly noticeable to the driver, because he needs to apply less pressure on the pedal due to the lower engaging force. Depending on clutch structure and actuation type, there is either the drawn or the compressed diaphragm spring clutch.
The LuK conventional diaphragm spring clutch is a compressed clutch. In this case, the polygon hub is bolted to the V-belt pulley on the crankshaft. The force flow is transferred through clutch housing into the flywheel bolted to it. The contact plate is attached to the clutch housing by plate springs. The cams on the contact plate project through the openings in the housing. The outer diaphragm spring are supported on these cam. It is attached to the housing by bolts and wire rings. The disengage bearing is arranged on the cylindrical outer diameter of the polygon hub and can move. The torque is transferred to the transmission intake shaft through the friction disc. This is a hollow shaft and sits on crankshaft stump between clutch and engine.
Diaphragm spring
A core component of every design detailed here is the diaphragm spring. It is flatter and lighter than coil springs. Especially important is the characteristic curve of the diaphragm spring, which differs substantially from the linear curve of a coil spring. Precise modeling of the diaphragm spring’s inner and outer diameters, its thickness, opening angle and material hardness allows a characteristic curve to be produced as represented by the continuous curve. While the clamp load with a coil spring clutch decreases linearly with decreasing facing thickness due to wear, here it initially increases and then drops again. The clutch is designed to begin to slip before the wear limit of the facing is reached. The necessity of a clutch replacement is thus signaled in due time, so that further damage, e.g. by the scoring of the facing rivets, is avoided. Moreover, because of the diaphragm spring characteristic curve the requisite pedal forces are less than with coil spring clutches.
Designs
Depending on the design and actuation system of a clutch, one distinguishes between:
• the pushed diaphragm spring clutch and
• the pulled diaphragm spring clutch
Standard diaphragm
The clutch cover encloses the diaphragm spring and the pressure plate. The pressure plate is linked to the clutch cover via tangential leaf springs. They are riveted to the pressure plate at three tabs.
Tangential leaf springs perform three basic functions:
• Lifting the pressure plate during clutch disengagement
• Transmitting the engine torque from the cover to the pressure plate
• Centering the pressure plate
The diaphragm spring is clamped between the pressure plate and the clutch cover so as to produce the load required to clamp the clutch disc non-positively between the flywheel and pressure plate. In so doing, it is supported by a ring or – optionally a rib – in the clutch cover. A ring fixed with studs serves as the mating bearing surface. The outer diameter of the diaphragm spring is seated on the pressure plate. If the clutch is actuated, the release bearing pushes onto the tips of the diaphragm spring fi ngers. The pressure plate lifts and the clutch disc is disengaged.
Diaphragm spring clutch with keyhole tabs
Figure shows a diaphragm spring clutch with keyhole tabs. This design is a further development of the standard diaphragm spring clutch shown in last picture. The keyhole tabs are modeled in such a way that they pull the studs outward. As a result, no clearance occurs at the diaphragm spring despite worn diaphragm spring mountings. The advantage of this design is uniform lift throughout the entire clutch life.
Diaphragm spring clutch with support spring
The diaphragm spring clutch with support spring is a special version. The diaphragm spring is supported against the cover by a ring, which can optionally be replaced by a rib in the clutch cover. The support spring serves as a mating bearing surface. This design allows for a playfree and lossless mounting of the diaphragm spring with automatic wear adjustment. Otherwise this type does not differ from those shown.Boltless diaphragm spring clutch
Another special type is the boltless diaphragm spring clutch shown in picture. Similar to the design with support spring, the diaphragm spring is supported against the cover by a ring, which can be optionally replaced by a rib in the clutch cover. As with a pin clutch mechanism, a wire ring serves as the mating bearing surface. As a special feature, however, the ring is retained by tabs formed from the clutch cover. By analogy with the keyhole design, here too, the tabs are preloaded, so as to provide automatic compensation for the wear occurring at the diaphragm spring mount and to prevent clearance of the diaphragm spring mount throughout the entire clutch service life.
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