CLUTCH SYSTEM

CLUTCH SYSTEM

Keys to effective control and transmission of drive torque, speed, and power in many rotating drives ystems are clutches and brakes. Their function is to either transfer torque from an input shaft to an output shaft (clutching) or to stop and hold a load (braking). Though offered as separate components, their functions are often combined into a single unit referred to as a clutch-brake. Clutches and brakes can be categorized by the technique used to engage

or stop the load (friction, electromagnetic, mechanical lockup), and by the

method used to actuate them (mechanical, electric, pneumatic, hydraulic,self-activating) 

DRIVEN MEMBERS

The driven member is the clutch disc with a splined hub

which is free to slide lengthwise along the splines of the

input shaft, but which drives the input shaft through

these same splines.The driving and driven members are held in contact by

spring pressure. This pressure is exerted by a diaphragm

spring in the pressure plate assembly.

OPERATING MEMBERS

The clutch release system consists of the clutch pedal,

the clutch release shaft, the clutch cable, the release

arm and the release bearing. When pressure is applied

to the clutch pedal, the clutch release shaft pushes

against the release bearing by rotating. The bearing

then pushes against the diaphragm spring in the pressure

plate assembly, thereby releasing the clutch.

The clutch allows engine power to be applied gradually when a vehicle is starting out, interrupts power to the transmission to avoid gear clashing when shifting and prevents engine stalling when bringing the vehicle to a stop. Engaging the clutch (clutch pedal fully raised) allows power to transfer from the engine to the transmission and drive wheels. Disengaging the clutch (clutch pedal fully depressed) stops the power transfer and allows the engine to continue turning without force to the drive wheels.

Common clutch-related components are:

 Flywheel – mounts to the engine crankshaft

Clutch Disk – the friction material assembly that provide

s easy engagement and firm torque transference

Pressure Plate – also known as “Clutch Cover” – this is the spring-loaded surface that locks the clutch

Throw-out Bearing – also known as “Release Bearing”

Pilot bearing –centers and supports the transmission input shaft (many cars do not have this bearing)

Clutch Cable – mechanical release mechanism for some vehicles

Clutch Master Cylinder – force-multiplying cylinder for vehicles with hydraulic release mechanisms

Clutch Slave Cylinder – used along with a Master Cylinder for hydraulic release mechanisms

Misc. hoses, lines, brackets, linkages, etc. – varies from vehicle to vehicle

 The flywheel

The flywheel is located at the rear of the engine and is bolted to the crankshaft. It helps absorb power impulses, resulting in a smoothly-idling engine and provides momentum to carry the engine through its operating cycle. The rear surface of the flywheel is machined flat and the clutch components are attached to it.

The pressure plate

The driving member is commonly called the pressure plate. It is bolted to the engine flywheel and its main purpose is to exert pressure against the clutch plate, holding the plate tight against the flywheel and allowing the power to flow from the engine to the transmission. It must also be capable of interrupting the power flow by releasing the pressure on the clutch plate. This allows the clutch plate to stop rotating while the flywheel and pressure plate continues to rotate.The pressure plate consists of a heavy metal plate, coil springs or a diaphragm spring, release levers (fingers), and a cover.When coil springs are used, they are evenly spaced around the metal plate and located between the plate and the metal cover. This places an even pressure against the plate, which in turn presses the clutch plate tight against the flywheel. The cover is bolted tightly to the flywheel and the metal plate is movable, due to internal linkages. The coil springs arearranged to exert direct or indirect tension on the metal plate, depending upon the manufacturer's design. Three release levers (fingers), evenly spaced around the cover, are used on most pressure plates to release the holding pressure of the springs on the clutch plate, allowing it to disengage the power flow.

When a diaphragm spring is used instead of coil springs, the internal linkage is necessarily different to provide an "over-center" action to release the clutch plate from the flywheel. Its operation can be compared to the operation of an oilcan. When depressing the slightly curved metal on the bottom of the can, it goes over-center and gives out a loud "clicking" noise; when released the noise is again heard as the metal returns to its original position. A click is not heard in the clutch operation, but the action of the diaphragm spring is the same as the oil can.

The clutch plate

 of

The clutch plate or driven member consists of a round metal plate attached to a splined hub. The outer portion of the round plate is covered with a friction material of molded or woven asbestos and is riveted or bonded to the plate. The thickness of the clutch plate and/or facings may be warped to give a softer clutch engagement. Coil springs are often installed in the hub to help provide a cushion against the twisting force of clutch engagement. The splined hub is mated to (and turns) a splined transmission shaft when the clutch is engaged.

The release bearing

The release (throw out) bearing is usually a ball bearing unit, mounted on a sleeve, and attached to the release or throwout lever. Its purpose is to apply pressure to the diaphragm spring or the release levers in the pressure plate. When the clutch pedal is depressed, the pressure of the release bearing or lever actuates the internal linkages of the pressure plate, releasing the clutch plate and interrupting the power flow. The release bearing is not in constant contact with the pressure plate. A linkage adjustment clearance should be maintained.