Clutches

Semi Centrifugal --->For small torque transmission, clutch springs should not to be so stiff as to cause any strain to the driver while disengaging.For high powered engines the action of disengaging the clutch become fatiguing to the driver, to obviate this troubleThese clutch springs are designed to transmit the torque at normal speeds, while for higher speeds, centrifugal force assist in torque transmission

FUNCTION 1. To engage and disengage the transmission from

engine to the remaining part of transmission. a) starting and running the engine at a sufficiently

high speed to generate sufficient power necessary for moving the vehicle from rest.

b) Shifting the gear so that damage to gear teeth can be avoided.

c) Stopping the vehicle after applying brakes.2. The second function of the clutch is to allows

the engine to take up the driving load of the vehicle gradually and with out shok.

Requirements of clutch1. Transmit maximum torque of the engine .2. Engage gradually to avoid sudden jerks.3. Able to dissipate large amount of heat generated during

clutch operation.4. Dynamically balabced particularly in the case of high

speed engine clutch.5. To damp vibrations and to eliminate noise produced

during power transmission.6. As small as possible so that it will occupy minimum space.7. Easy to operate requiring as little exertion on the part of

the driver.8. Light in weight.9. Trouble free and have large life.10. Easy to inspect, adjust and repair.

Clutch Components

Clutch Components Clutch housing

Connects engine and transmission and houses the clutch assembly.

Flywheel Acts as balancer for the

engine. Adds inertia to the

rotating crankshaft. Provides a surface for

the clutch to contact.

Clutch Components Clutch (input) shaft

Projects from the front of the transmission.

Usually has a pilot that rides in a bearing or bushing in the end of the crankshaft.

The clutch disc is plined to the clutch shaft. When engaged, the

clutch disc drives the input shaft.

Clutch Components Clutch disc

Is covered with friction material. Transmits power from the engine

crankshaft to the transmission input shaft.

Torsional coil springs or rubber grommets allow the disc to rotate slightly in relation to the pressure plate while they absorb the torque forces.

Clutch Components Clutch disc (cont’)

The clutch facings are riveted to wave springs, or cushioning springs, which cause the contact pressure on the facings to rise gradually when the clutch is engaged.

These springs eliminate chatter by dampening the clutch engagement.

Clutch ComponentsClutch disc

Clutch Components Pressure plate assembly

Squeezes clutch disc onto flywheel. Can be engaged or disengaged. Acts like a spring-loaded clamp. Two common types, the coil spring and diaphragm (Belleville) spring design.

Clutch Components Release bearing

Is operated by the clutch linkage.

Presses against the pressure plate to release the clutch.

Clutch Components Pilot bearings

The purpose of the pilot bushing or bearing is to support the outer end of the transmission’s input shaft.

Allows the input shaft to rotate in the crankshaft.

Clutch Linkage Clutch linkage

transfers the clutch pedal movement to the release bearing. Mechanical clutch

linkage uses shafts, levers, or a cable.

Clutch LinkageHydraulic clutch linkage consists of a master cylinder, hydraulic tubing, and

a slave cylinder.

Clutch Operation The pressure plate is a large spring-

loaded plate that engages the clutch by pressing the disc against the flywheel.

The pressure plate moves away from the flywheel when the clutch pedal is depressed.

Clutch Operation The clutch release bearing is operated

by the clutch linkage. When the clutch pedal is depressed,

the bearing moves toward the flywheel, depressing the pressure plate fingers and moving the pressure plate away from the clutch disc.

A clutch enables two co-axial shafts to be engaged or disengaged while at rest or in relative motion.

Friction Clutches

Types of Friction Clutches

1. Disc or plate clutches2. Cone clutches3. Centrifugal clutches

T

TW (axial thrust)W

Friction plate

Friction lining Pressure

plates

springs

Single-plate Friction Clutch (Disengaged position)

Driving shaft

Driven shaft

Flat-plate friction clutches

Single-plate Friction Clutch (Engaged position)

T

TW (axial thrust)

WFriction plate

Friction lining

Pressure plates

springs

Driving shaft

Driven shaft

Flat-plate friction clutches

An example is the clutch found in most automobiles.

Flat-plate friction clutches

Torsional springs

Splined boss (hub)

Friction lining

Clutch plate or friction plate

Pressure plate

Diaphragm spring

Clutch housing

Pressure plate and housing

In a multi plate clutch, the torque is transmitted by friction between several pairs of co-axial annular driving faces maintained in contact by an axial thrust.

Both sides of each plate are lined with friction material, so that a single-plate clutch has two pairs of driving faces in contact.

Multi plate clutches

n = no. of pairs of driving faces.

Then, for a plate clutch, the maximum torque transmitted is

mWrnT

Multi plate clutches

No. of driving pairs n = 6

driver driven

Pressure plates

Friction plates

21 43 65

Multi plate clutch

Driving shaft

Driven shaft

Friction lining

α

The maximum torque transmitted =

α = semi-apex angle of the cone

Only one pair of driving surfaces is possible, n =1

Cone clutch

T = μWrm cosecα

w

Centrifugal clutch

Driving shaft

Driven shaft

Friction lining

Total friction torque , T = nµR(F-P)

F=mrω2

ω

ω

P

R

Common Clutch Problems Clutch slippage

Definition: With the clutch engaged, engine speed increases but vehicle speed does not.

Before disassembly: Check linkage. Check for worn or binding parts. Check engine mounts.

Other causes for clutch slippage Oil-soaked or worn disc facings Warped flywheel or pressure plate Weak pressure plate springs Contact between the release bearing and the

fingers of the pressure plate

Common Clutch Problems Clutch chatter

Definition: Shaking or shuddering when clutch is engaged.

Before Disassembly: Check engine mounts. Check for leaks from rear main seal,transmission input shaft seal, and clutch slave cylinder.

Common Clutch Problems Clutch noises

These noises are usually caused by bad bearings or bushings.

To diagnose, determine whether the noise changes with the clutch engaged or disengaged.

Causes for damaged release bearings Misalignment Overheating Slippage Component damage

Common Clutch Problems Clutch vibrations

Are usually caused by worn engine mounts, loose bolts, excessive flywheel runout, or flywheel and/or pressure plate assembly imbalance.

Dragging clutch Is usually caused by linkage problems,

incorrect pedal adjustments, or defective clutch assembly

Common Clutch Problems Pulsating clutch pedal

Is usually caused by broken or bent release levers, misaligned bell housing, or warped pressure plate, flywheel, or clutch disc.

Binding clutch Is usually caused by binding linkage or

cables, defective clutch assembly, or improper installation.

Dry clutches generally last less well though, but the point of having them is they're smaller and lighter. A wet clutch needs to be big with more clutch plate area because the oil lubricates the plates as well as cooling them, so you need more area to offer the same amount of grip as an equivalent dry clutch. That reduced weight and size of the dry clutch is important on high performance bikes, so you get them on race bikes and a few road bikes, most notably Ducati superbikes. In fact in general use, Ducati dry clutches don't feel a lot different to wet clutches, you can slip them when pulling away normally just the same, and they'll take a few fast getaways too, especially if you let them cool again in between.

Car clutches are nearly all dry, because they have much more torque than bikes (it's torque that determines clutch size, not power) and would have to be obstructively big if they were wet. But more pragmatically, dry clutches are cheaper and they work well enough in most cars anyway

There's a sort of truth... Wet clutches are more durable, certainly, the oil helps keep the temperatures low and more evenly distributed, and pick up as you let the lever out is smoother too. They do still wear and fail when abused though - older Yamahas used to be notorious for it, and I remember when speed testing them in the 90s you could only do a few quarter mile runs before they'd permanently give up.