Clutches
The function of the clutch assembly in car and trucks with manual transmissions or transaxles id to connect or disconnect the flow of power from the engine to the drive line.Although there are many variations in the design of the clutched, all work on the same basic principle.
A clutch is machanism designed to connect or disconnect power from one working part to anther.In a vehicle ,the clutch is used to transmit engine power and to disengage the engine and transmission when shifting gears.It also allows the engine to operate when the vehicle is stopped without placing the transmission in neutral(out of gear).
Clutch Construction
The modern clutch is a single plate,dry disc。It consists of five major parts:flywheel,clutch disc,pressure plate assembly,throw-out bearing,and clutch linkage.Other parts which make up the cluntch assembly are the transmission input shaft and clutch housing.
Flywheel
In addition to providing a base for the starter ring gear,the flywheel forms the foundation on which the other clutch parts are attached.The flywheel used with manual transmision is thick to enable it to absorb a large amount of heat generated by clutch operation.
The clutch side is machined smooth to provide a friction surface.Holes are drilled into the flywheel to provide a means of mounting the clutch assembly.A hole is usually drilled directly into the rear of the crankshaft.This hole allows a bearing to be installed in the center of the flywheel.
The bearing in the center of the flywheel will act as a support for the outboard end of the transmission input shaft. It is referred to as a pilot bearing .T he pilot bearing may be either a ball bearing or a bronze bushing.
Dual Mass FlywheeeL
A dual mass flywheel is sometimes used with diesel engines.To help absorb engine power stroke pulsations,spings mounted inside the flywheel act as a shock absorbing unit when the flywheel sections partially compress ,smoothing out the power flow.They also help to reduce stress on the clutch and transmision parts.
Clutch Disc
The clutch disc is round and or constrcted of thin,high quality steel with a splined hub placed in the center.The hub splinee engage splines on the transmission input shaft.The clutch disc can move back and forth on the shaft,but when the disc is turned ,the shaft must turn also.
Both side of its outer edge are covered with friction material.It is often made of asbestors or other high teperature material and copper wires either woven or molded together.It is riveted to the disc.
To assist in smooth engagement, the disc outer edges are often split and each piece cupped.The friction material is riveted to these segments.When the disc is compressed ,these cupped segments act as a spring –like cusshion.
Pressure Plate
The clutch pressure plate is the same in each type of pressure plate assembly.It is made of a thick piece of cast iron for maximum heat absorption .It is round and about th esame diameter as the clutch disc.One side of the pressure plate is machined smooth .This side will press the clutch disc facing area against the flywheel.The outer side has various shapes to facilitate attachment of spring and release mechanisms.
Release Lever Operating Mechanism
This mechanism consists of a ball bearing normally referred to as a throw-out bearing or release bearing.This bearing is mounted on a sleeve or collar that sides back and forth on a hub that is an integral part of the transmission front bearing retainer.
The throw-out bearing is filled with grease at the factory and does not need servise during its useful life.Another type of throw-out bearing is the graphite type.This bearing employs a ring of graphite to press against a smooth plate fastened to the clutch levers.The throw-out bearing sleeve is moved in and out by a throw-out fork or clutch fork.This fork is usually pivoted on a ball head stud.A return spring pulls the fork away from the pressure plate.
Clutch Operation
The flywheel ,clutch cover,release levers,and pressure plate all revolve as a single unit.The transmission input shaft and the clutch disc are splined together,forming another unit.
The only time the clutch disc will turn is when it is pinched between the flywheeland pressure plate.When the release levers draw the prssure palte away from the flywheel ,the clutch disc will stand still while every thing else continues to revolve.When the pressure plate travels back toward the flywheel ,the discis seized and forced to turn the transmission input shaft.
auther:kelly www.sinodiesel.com
