Clutch system and used and advanced Note.pdf

Clutch system

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CLUTCH SYSTEM

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CLUTCH SYSTEM



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PURPOSE OF THE CLUTCH

The automotive drive train or power train carries power from the engine to the drive wheels. In vehicles with a manual transmission or manual
transaxle, the power flows through a clutch. This device couples and uncouples the manual transmission or transaxle and the engine. The
clutch is usually operated by the driver’s foot. Some clutches have a power-assist device to reduce drive effort. Various electronics devices
may be used so that the clutch operates automatically.
The clutch is located between the engine flywheel and the transmission or transaxle. Movement of a foot pedal operates the clutch. When the
driver pushes the clutch pedal down, the clutch disconnects or disengages from the engine flywheel. No engine power can flow through to
the transmission or transaxle. When the driver releases the clutch pedal, the clutch engages. This allows power to flow through.


Manual Transmission

Manual Transaxle

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FUNCTION
OF
CLUTCH SYSTEM
 Clutch can be
disengaged (pedal are
pressed). This allows
engine cranking and
permits the engine to
run freely without
delivering power to the
transmission.

 While clutch disengaged (pedal are pressed), it permits
the driver to shift the transmission into various gears.
This allows the driver to select the proper gear (1
st
, 2
nd
,
3
rd
, 4
th
, 5
th
, or neutral) for the operating condition.

 While engaging (pedal are moving up), the clutch slip
momentarily. This provides smooth engagement and
lessens the shock on gears, shafts, and other drive-train
parts. As the engine develops enough torque to
overcome the inertia of the vehicle, the drive wheels
turn and the vehicle begins to move.

 When clutch are
engaged (pedal are
totally released), the
clutch transmits power
from the engine to the
transmission. All
slipping has stopped.

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SO WHAT IS FRICTION?

Friction is the resistance to motion between two objects in contact with each other. It varies with the force applied between the sliding
surfaces (the load), the roughness of the surfaces and the material of which the surface are made. The amount of the friction also depends on
whether a fluid such as oil is between the surfaces to provide lubrication. The three types of friction are dry, greasy and viscous.

THE PASCAL’S LAW IN VEHICLE HYDRAULIC SYSTEM

WHAT IS PASCAL’S LAW?

The Pascal’s Law means that when there is a force towards any point of an enclosed fluid the pressure will be distributed equally throughout
the system.

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HYDRAULICS PRESSURE

Hydraulic is the use of a liquid under pressure to transfer force or motion or to increase an applied force. Pressure on a liquid is called
hydraulic pressure. It is hydraulic pressure that forces the brake shoe or pads into contact with the rotating drum or disc to produce braking.
Increasing the pressure on a gas will compress it into a smaller volume. However, increasing the pressure on a liquid will not compress it. The
liquid is incompressible. This makes it possible to use the pressure on liquids in hydraulic system to transmit force or motion.

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TYPES OF CLUTCH SYSTEM

Different types of clutch system use in automotive industries



FRICTION CLUTCH

Single plate clutch Multi plate clutch Cone clutch

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CENTRIFUGAL CLUTCH ELECTROMAGNETIC CLUTCH





HOW THE CLUTCH CONSTRUCTION

The typical clutch consists of three basic parts. These are the engine flywheel, a friction disc, and a pressure plate. The flywheel and the
pressure plate are the drive or driving members. They attach to and rotate with the engine crankshaft. The friction disc is the driven member
(also called the driven plate and the driven disc). It is about 305 mm or less in diameter and splined to the clutch shaft or transmission input
shaft. Both must turn together, but the friction disc can slide back and forth on the shaft splines.
The pressure plate, with one or more springs, attaches to the clutch cover. This pressure-plate assembly bolts to the flywheel while the clutch
is engaged. The transmission input shaft has the same centerline as the engine crankshaft. The small end of the input shaft rides in a pilot
bearing or bushing in the end of the crankshaft. The transmission front bearing or transmission input shaft bearing support the other end of
the input shaft.

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CLUTCH OPERATION

Disengaging the clutch (pushing the clutch pedal down) moves the pressure plate away from the friction disc. Releasing the clutch pedal
engages the clutch. Spring force clamps the friction disc between the pressure plate and the flywheel. Then the friction disc and transmission
input shaft turn with the flywheel. In many clutches, when the driver depresses the clutch pedal, linkage to the clutch fork causes it to pivot.
The fork pushes against the release bearing or throws out bearing. This forces the release bearing inward against release fingers or levers in
the pressure-plate assembly. These pivot to push the pressure plate away from the friction disc. As the pressure plate moves away from the
friction disc, a slight air gap opens between the pressure plate and the friction disc. Another gap appears between the friction disc and the
flywheel. These gaps disengage the clutch so no power flows through it. The typical friction disc travels about 1.5 mm as it moves from
engaged to disengaged.

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CLUTCH COMPONENTS

FRICTION DISC


















Friction disc has a hub and plate, cushion springs and dampening springs. The slightly-waved cushion springs attach to the plate. The friction
facings attach to the cushion springs. When the clutch engages, the cushion springs compress slightly to take up the shock of engagement.
The dampening springs or torsional springs are heavy coil springs set in a circle around the hub. The hub is driven through these springs they
help reduce the torsional vibration caused by the engine power impulses. This smoothes the power flow to the transmission. There are
grooves on both sides of the friction-disc facings. These grooves prevent the facings from sticking to the flywheel face and pressure plate
when the clutch disengages. The grooves break any vacuum that might form and cause the facings to stick. They also help cool the facings.
The facings on many friction discs are made of cotton and asbestos fibers woven or molded together. Then the material is saturated with
resins or other binding agents. Copper wire is woven or pressed into the facings of some friction discs to give them added strength. However,
asbestos is a health hazard and is being replaced with other materials. Some friction discs have ceramic-metallic faces.

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Elastic Clutch Disc with sited segments Elastic Clutch Disc with spring under liner
Clutch disc with Torsional damping Clutch disc with ceramic sinter linings (for
extreme high operational demands

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COIL-SPRING CLUTCH

The clamping force in the pressure-plate assembly is provided by a single diaphragm spring or by several coil spring. These are set in a circle
between the cover and the pressure plate. Depressing the clutch pedal forces the release bearing against the release levers. Three are shown
in the diagram. These pivot on eyebolts. Struts then carry the motion to the pressure plate. It moves away from the friction disc, compressing
the springs against the clutch cover. This disengages the clutch. Releasing the clutch pedal allows the coil springs to extend. They again
clamp the friction disc between the pressure plate and the flywheel. This engages the clutch.
The coil spring must be strong enough to prevent clutch slippage. However, the stronger the springs, the harder the driver must push on the
pedal clutch. One solution is to use a semi-centrifugal clutch. It has weights on the ends of the release levers. As speed increases, centrifugal
force causes the weights to add to the force of the springs.

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DIAPHRAGM-SPRING CLUTCH

The diaphragm-spring clutch is used with most manual transaxle and in many rear-wheel-drive vehicles. A diaphragm spring supplies the force
that holds the friction disc against the flywheel. The spring has tapered fingers pointing inward from a solid ring. These act as release levers
to take up the spring force as the clutch disengages. The diaphragm acts like the bottom of an oil can. After it is pushed inward, it will ‘spring’
back when the applying force is released. As the driver depressed the clutch pedal, the release bearing pushes against the fingers on the
diaphragm spring. This causes the diaphragm to pivot about the inner pivot ring and dish inward. As it does so, the outer section moves in the
opposite direction and pushes the pressure plate away from the friction disc. This disengages the clutch. Spring force varies according to the
size and thickness of the diaphragm spring.

Some cars use a diaphragm-spring pull clutch. The release bearing has a flange that rides on the inside surface of the diaphragm-spring
fingers. Depressing the clutch pedal causes the fork to pull the release bearing and fingers outward. This pulls s the pressure plate away from
the friction disc and disengages the clutch.

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RELEASE BEARING

When the drive depresses the clutch pedal, the clutch linkages moves the release bearing or throw out bearing. The bearing travel pushes or
pulls the release levers or fingers inward or outward to disengage the clutch. The type of clutch linkage determines the type of release
bearing. Most are ball bearing, but they vary in construction and operation. Depressing the clutch pedal forces the release bearing against
the release levers. This starts the release bearing rotating. Letting up the clutch pedal moves the release bearing away from the pressure
plate. The release bearing must travel far enough so there is some clearance or free play between the release levers and the bearing. If not,
the bearing continues rotating. Then this type of release bearing will overheat and fail. It may also cause the clutch to slip.

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TYPES OF CLUTCH LINKAGE

The parts that connect the clutch pedal to the release bearing make up the clutch linkage. It is either mechanical (rod or cable) or hydraulic.
They all convert a light force applied to the clutch pedal into a greatly increased force that moves the release bearing.

Mechanical Clutch Linkage

On many vehicles, it is simpler for the manufacturer to install a cable system than to develop a rod arrangement. The cable operates the
release bearing by movement of the clutch fork. The fork passes through a boot or dust cover that seals the fork opening in the clutch
housing. This prevents dirt, dust and water from entering the clutch through the opening. Cable linkage requires routine clutch adjustment.

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Hydraulic Clutch Linkage

Hydraulically-operated clutch linkage is used when the clutch location makes it difficult to run a rod or cable to it. Hydraulic clutch linkage is
also used on high performance engines. These have strong springs in the pressure-plate assembly and would require high pedal effort.
Operation of the hydraulic-clutch linkage begins when the driver depresses the clutch pedal. This forces a pushrod into the master cylinder.
Pressurized fluid is then forced from the master cylinder, through a hydraulic line, to a servo or slave cylinder. A servo is a device that
converts hydraulic pressure to mechanical movement. The pressurized fluid then pushes a piston and pushrod out of the servo. The pushrod
movement operates the clutch fork and disengages the clutch. The hydraulic system can be designed so alight force on the clutch pedal
produces a heavy force on the clutch fork. This is done by using a small piston in the master cylinder and a large piston in the servo.
Operation of hydraulic clutch linkage is similar to a hydraulic brake system.

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HYDRAULICS PRESSURE

Hydraulic is the use of a liquid under pressure to transfer force or motion or to increase an applied force. Pressure on a liquid is called
hydraulic pressure. It is hydraulic pressure that forces the fork to push the pressure plate away from the friction disc. Increasing the pressure
on a gas will compress it into a smaller volume. However, increasing the pressure on a liquid will not compress it. The liquid is
incompressible. This makes it possible to use the pressure on liquids in hydraulic system to transmit force or motio



Master Cylinder

This component has the task to create the fluid pressure for the
hydraulic part of the clutch operation


Master Cylinder



Slave cylinder

This component has the task to transfer the fluid pressure from
the master cylinder to operate the shifter



Slave Cylinder

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CLUTCH TROUBLE-DIAGNOSIS

COMPLAINT POSSIBLE CAUSE
Clutch slips while
engaged
a. Incorrect clutch-linkage adjustment
b. Broken or weak pressure springs
c. Binding in clutch linkage
d. Broken engine mount
e. Worn friction-disc facings
f. Grease or oil on disc facings
g. Incorrectly adjusted release levers
h. Warped friction disc
Clutch chatters or
grabs
While engaging
a. Binding in clutch linkage
b. Broken engine mount
c. Oil or grease on disc facings or glazed or loose facings
d. Binding of friction-disc hub on clutch shaft
e. Broken disc facings, springs, or pressure plate
f. Warped friction disc
Clutch spins or drags
While disengaged
a. Incorrect linkage adjustment or operation
b. Warped friction disc or pressure plate
c. Loose friction-disc facings
d. Improper release-lever adjustment
e. Broken engine mount
Clutch noisy while
engaged
a. Friction-disc hub loose
b. Friction-disc dampener springs broken or weak
c. Misalignment of engine and transmission

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Clutch noisy while
disengaged
a. Release bearing worn, binding or out of lubricant
b. Release levers not properly adjusted
c. Pilot bearing in crankshaft worn or out of lubricant
d. Diaphragm spring worn or damaged
Clutch-pedal pulsates
a. Engine and transmission not aligned
b. Flywheel not seated on crankshaft flange or flywheel bent
c. Clutch housing distorted
d. Release levers not evenly adjusted
e. Warped pressure plate or friction disc
f. Pressure-plate assembly misaligned
g. Broken diaphragm spring
Rapid friction-disc
facing wear
a. Driver ‘drives’ the clutch
b. Excessive and incorrect use of clutch
c. Cracks in flywheel or pressure-plate face
d. Weak or broken pressure springs
e. Warped pressure plate or friction disc
f. Improper linkage adjustment
g. Clutch linkage binding
Clutch pedal stiff
a. Clutch linkage lacks lubricant
b. Clutch pedal binds in floor mat
c. Misaligned linkage parts
d. Overcenter spring out of adjustment
e. Bent clutch pedal
Hydraulic-clutch
troubles
a. Gear clashing and difficulty shifting in or out of gear

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NOTES.

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