Which is a purpose of the clutch?

Connect and disconnect engine from transmission for smooth starts and gear changes

In the engaged state of a single plate clutch, how is torque transmitted?

Springs clamp the plate between flywheel and pressure plate; friction carries torque

Hydraulic fluid couples the shafts

What advantage does a diaphragm spring clutch have?

Clamp load stays almost constant as lining wears and pedal effort is lower

Practice · 8 marks

Single plate clutch and diaphragm spring clutch

Short answer

A clutch connects engine and transmission for smooth starts and gear changes. A single plate dry clutch has a friction disc clamped between flywheel and pressure plate by springs. Diaphragm spring clutch uses a dished disc with fingers, giving constant clamp load, lower pedal effort and compactness, unlike coil spring clutches.

What is the purpose of a clutch in an automobile? With a neat sketch describe the construction and working of a single plate dry friction clutch. How does a diaphragm spring clutch differ from a coil spring clutch?

Purpose

The clutch connects and disconnects the engine from the transmission. It lets the driver (1) start the engine without load, (2) move the vehicle smoothly from rest, (3) change gears, and (4) protect the drive line from shock.

Single plate dry clutch

 Engine flywheel   Clutch plate     Pressure plate  Cover
 |==============|  |====lining===|  |=======|=======|
 |  (friction   |<-| disc, hub   |<-| springs push  |
 |   face)      |  | on splined  |  |  plate        |
                    | gearbox in- |  [release lever] <- release
                    | put shaft   |                    bearing

Main parts

Flywheel: drives the clutch cover and provides one friction surface.
Clutch (friction) plate: a steel disc with friction linings riveted on both sides, and a hub that slides on the splined input shaft of the gearbox. Torsional (damper) springs absorb shocks.
Pressure plate: a heavy cast-iron ring pressed against the clutch plate by springs.
Springs, release levers, release (throwout) bearing, and clutch pedal linkage or hydraulic cylinder.

Working

Engaged (pedal released): the springs clamp the clutch plate between the flywheel and the pressure plate, and torque is transmitted by friction to the gearbox shaft.
Disengaged (pedal pressed): the release bearing pushes the levers, which pull the pressure plate back; the clutch plate is free and no torque is transmitted.

The torque transmitted is $T = \mu W R_m n$ , where $\mu$ is the coefficient of friction, $W$ the axial force, $R_m$ the mean radius and $n$ the number of friction surfaces (2).

Diaphragm spring vs coil spring clutch

Point	Coil spring	Diaphragm spring
Spring	Several coil springs with separate release levers	One dished steel disc with radial fingers (acts as both spring and release lever)
Parts	More	Fewer, compact
Pedal effort	Higher; rises as the springs are compressed further	Lower; the spring load falls after a point during release
High-speed behaviour	Springs may bow under centrifugal force and lose clamping load	Not affected by centrifugal force
Clamp load as lining wears	Falls	Remains almost constant
Use	Older and heavy vehicles	Modern cars

✓ Answer checked by Claude Opus 5.5 (high effort)

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Single plate clutch and diaphragm spring clutch

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