The document discusses the requirements and components of a clutch mechanism. It provides details on: 1. The key requirements of a clutch include transmitting maximum engine torque without slippage, dissipating large amounts of heat generated, engaging gradually without jerks, being dynamically balanced, damping vibrations, having minimum inertia when disengaged, and requiring minimal force to disengage. 2. The main components of a clutch are the clutch plate, friction facings, pressure plate, springs, throwout bearing, and release levers. The clutch plate transfers torque via friction facings attached to its steel plate. The pressure plate applies pressure to the clutch plate via springs. 3. Different types of clutches include single

1. Clutch: Requirements
►Definition: Mechanism which enables to transfer rotary motion of one shaft to another
coincident shaft when desired.
●1 Should transmit maximum engine torque under all conditions.
--Should not slip when fully-engaged.
--Clutches are designed to transmit 125-150% of maximum engine torque.
►Requirements:
●2 Should dissipate large amounts of heat generated.
--Clutch temperature is a major factor limiting clutch-capacity.
--Rubbing faces should have sufficient area & mass to absorb heat.
--Clutch faces should maintain reasonable coefficient-of-friction.
--Friction material should not crush at high-temperatures & clamping-loads.
--Clutch should have proper ventilation or cooling.
●3 Should engage gradually without sudden jerks.
●4 Should be dynamically-balanced for high-speed operation.
●5 Should damp vibrations and eliminate noise produced in transmission.
●6 Should have minimum inertia to avoid its spinning when disengaged.
--Else it causes hard-shifting & gear-clashing in spite of synchronizer.
●7 Should have sufficient free-pedal-play.
--This reduces effective clamping-load on carbon-thrust-bearing & its wear thereof.
●8 Should require minimum force to disengage. Should not be tiresome to the driver.
●9 Should of smallest possible size to occupy minimum space.

2. Clutch Parameters
►1 Torque: It is directly proportional to: (T = μWR)
●1 Coefficient-of-Friction(μ):
--Dynamic-μ is slightly lesser than static-μ.
-- μ varies with temperature, pressure, rubbing-velocity.
--Usually around 0.35 – 0.4.
●2 Axial-Force Applied(W):
--Normal force which driver can exert without undue strain is 100-120 N.
●3 Clutch-Radius(R):
--Larger the clutch-radius, more space it occupies.
►2 Slip: Variation of rotational-speed expressed as percentage. (s% = (N1-N2)/N1 *100)
--Clutch-Slip represents loss of energy and consequent increase in fuel consumption.
►3 Free-Pedal-Play: Part of clutch-pedal movement that is purposely kept idle without
pressing the thrust-bearing, to avoid rapid wear of thrust-bearing & clutch-pedal.
--Of 75 mm clutch pedal travel, 25 mm typically is free-play.
--It changes due to wear of:
●1 friction-lining, due to continuous use. This decreases free-pedal-play.
If free-pedal-play is less, clutch cannot engage fully.
●2 throwout-bearing’s carbon-ring, due to driver always resting his foot on clutch-pedal.
This increases free-pedal-play. Excess free-pedal-play clutch cannot disengage fully.

3. 1. Clutch-Plate
--It consists of a steel plate with splined central hub.
--Annular friction-facings are attached to steel plate by rivets.
--Special resins are used to bind friction-facings.
--Curved cushion-springs are attached between center-plate & friction-facing as they:
(1) provide axial cushioning.
(2) cause smoother engagement because on engagement, load applied first has to
compress these springs to flat, causing longer distance travel for clutch-plate.
(3) result in longer life for clutch-facing because of more uniform contact pressure
causing uniform wear and uniform heat generation over entire friction-surface.
--Dampening-springs are provided in the clutch-plate. These are torsional coil-springs to
absorb torsional-vibrations due to engine power-stroke torque pulses.
--Clutch-plates are usually perforated to dissipate large amount of heat generated.
Clutch Components
●1 Clutch-Plate or Friction-Plate
●2 Clutch-Facing or Friction-Lining
●3 Pressure-Plate
●4 Springs
●5 Throwout Bearing
●6 Release Levers
●7 Clutch-Cover & Straps

4. 2. Clutch-Facing
►Requirements:
(1) Good Anti-Wear Property: Clutch-facing-wear depends on at engagement time:
●rubbing-speed (should be <30 m/s) ●pressure-intensity (should be < 100 kPa)
(2) Presence of Good Binder:
(3) High Coefficient of Friction:
(4) High Resistance to Heat: Should withstand 330oC.
(5) Cheap & Easy to Manufacture:
►Types:
(1) Millboard Type:
(2) Molded Type:
(3) Woven Type:
a) Solid-Woven Type:
b) Laminated Type:
►Common Clutch-Facing Materials:
(1) Leather (μ = 0.27):
(2) Cork (μ = 0.32):
(3) Fabric (μ = 0.40):
(4) Asbestos (μ = 0.20): Has anti-heat characteristics.
(5) Reybestos & Ferodo (μ = 0.35):
(6) Non-Asbestos:
a) SW3-AF (μ = 0.28 @50C – 0.36 @250C) b) HWK 200 (μ = 0.39-0.40)
c) Graphitic materials d) Sintered metal-friction materials

5. Clutch-Components
●3 Pressure-Plate:
--Requirements:
Should be sufficiently rigid:
(1) so as not to distort under pressure of clutch-springs.
(2) to provide uniform pressure to clutch-plate.
Should have sufficient thermal-conductivity to absorb & conduct away heat generated.
Should have sufficient mass.
--Material: High-tensile grey-iron
●4 Springs:
--Requirements:
Should have high stiffness, so that sufficient spring-force is left after their
extension due to wear of clutch-facings. But higher stiffness causes driver-fatigue.
--Material: Oil-tempered spring-steel wire (normal-duty); silico-chrome steel (heavy-duty)
--Insulating washers are used to reduce heat conduction from pressure-plate to springs.
●5 Throwout Bearing:
--Used to transfer force at pedal from stationary-linkage to rotating-clutch.
--Material: (1) Thrust-ball-bearing with grease lubrication
(2) Graphite-impregnated ball-bearing which doesn’t require any lubrication.
●6 Release Levers:
--Coil-spring-clutch has 3 or 4 release-levers around the pressure-plate.
--On back of pressure-plate, numbers of lugs are cast to locate & support release-levers.

6. Clutch-Components
●7 Clutch-Cover:
--Function:
(1) Houses pressure-plate assembly.
(2) Provides pivot for release-levers
(3) Takes reaction of springs
(4) Dissipates heat through its holes.
--Material: It is a steel-pressing bolted onto flywheel.
●8 Straps:
--Holds together clutch-cover & pressure-plate.
--Its one-end bolts to pressure-plate; its other-end is connected to cover.
--When clutch is engaged, straps deflect, transmitting drive from cover to pressure-plate
without any friction between them.
--Usually 4 straps are arranged around the pressure-plate.
Clutch Troubles
●1 Clutch-Slip: Big difference between input & output speeds
●2 Clutch-Drag or Spin: Do not disengage completely
●3 Clutch-Judder: Vibration during engagement
●4 Clutch-Rattle: Peculiar noises
●5 Knock: Noise especially during idling
●6 Pulsation of Clutch-Pedal:

7. Clutch Types
►1. Friction-Clutch
●1. Cone-Clutch
►2. Fluid-Flywheel or Hydraulic Coupling
■1. Dry-Clutch
■2. Wet-Clutch
●2. Single-Plate-Clutch
●3. Multi-Plate-Clutch
●4. Semi-Centrifugal-Clutch
●5. Centrifugal-Clutch
◘1. Coil-Type
Clutch-Actuation Types
●1. Mechanical
●2. Electro-magnetic
●3. Hydraulic
●4. Vacuum
●5. Electronic (ECU-Controlled Clutch-By-Wire)
◘2. Diaphragm-Type

8. Cone Clutch
●Clutch Engaged: Male-cone is pressed inside female-cone by springs.
Friction-surfaces are in contact. Has torque/speed transfer.
●Clutch Disengaged: Male-cone is pulled-out of female-cone by lever operated through
clutch-pedal. Contact-surfaces are separated. No torque/speed transfer.
●Adv: (1) Normal-force acting on contact-surfaces is larger than axial-force.
Compared to in single-plate clutch, where normal-force is equal to axial-force.
●Disadv: Obsolete because
(1) If cone-angle is <20, difficult to disengage clutch, as male-cone binds to female-cone.
(2) Small wear on cone-surfaces requires large amount of axial-movement of male-cone.
Single-Plate Clutch: Coil Type
●Construction:
--Friction-plate is held between flywheel & pressure-plate.
--Friction-plate is mounted on a splined-hub, thus free to slide over gear-box shaft.
--Friction-lining is attached to both sides of friction-plate to provide 2 torque surfaces.
--Number of circumferentially arranged springs provide axial-force for clutch engagement
--A pedal pulls pressure-plate against spring-force when clutch is disengaged.
●Adv: (1) As pedal movement is less compared to cone-clutch, gear-changing is easier.
(2) More reliable than cone-clutch as there is no clutch-binding.
●Disadv: (1) Compared to cone-clutch, springs have to be stiffer, requiring greater force
by the driver to disengage.

9. Single-Plate Clutch: Diaphragm Type
●Construction:
--Diaphragm-spring is conically-bent in its free state. When assembled it is bent to flat
condition, due to which it exerts load on pressure-plate.
--Diaphragm-spring is supported on a fulcrum retaining-ring; thus it acts as simple lever.
--Pressure-plate is movable axially, but fixed radially w.r.t cover due to equally-spaced
lugs on back-surface of pressure-plate.
●Operation:
--Drive from flywheel is transmitted through cover, pressure-plate, friction-plate to gear-
box input-shaft.
--Depressing clutch-pedal, actuates release-fingers by release-ring. This pivots spring
about its fulcrum, relieving spring-load on outside-diameter, disconnecting the drive.
●Adv:
(1) Stores energy more compact; thus clutch size is reduced.
(2) Less affected by centrifugal-forces, hence withstands higher rpm.
Coil-spring distorts in transverse-direction at high rpm.
(3) Non-linear load-deflection curve; as clutch-facing wears, force on plate increases.
Coil-spring has linear load-deflection; as clutch-facing wears, force on plate decreases.
(4) Diaphragm acts as both clamping-spring & release-lever. Thus extra parts (struts,
eye-bolts, levers) are eliminated. Thus higher efficiency, with no squeaks & rattles.
●Disadv:
(1) For heavy-vehicles single diaphragm-spring cannot provide sufficient clamping-force.
Hence used in smaller-vehicles with clutch-size < 270 mm.

10. Multi-Plate Clutch
●Construction:
--Number of friction-surfaces are increased, to increase clutch torque-capacity.
--Like single-plate clutch, except all friction-plates are in 2 sets:
(1) One set of friction-plates slides in grooves on flywheel.
(2) Other set slides on splines on pressure-plate-hub. Alternate plates belongs to a set.
●Applications:
(1) Heavy transport vehicles, racing-cars (due to high torque-capacity)
(2) Scooters, motor-cycles (due to limited space availability).
Semi-Centrifugal Clutch
●Features:
--Clutch-springs keep the clutch engaged, and transmit torque at low & normal speeds.
--At high-speeds, centrifugal-force assists in clutch-engagement.
--This reduces driver-fatigue as to disengage clutch, he needs to apply force only against
the weaker spring-force instead of combined (spring & centrifugal) force.
●Construction:
--3-hinged-weighted-levers are arranged at equal intervals.
--Lever has fulcrum at A, hinged to pressure-plate at B, weighted at C.
--D is the adjusting-screw to adjust maximum centrifugal force on pressure-plate.
--Levers are mounted on needle-roller-bearings at pressure-plate, to reduce friction.
--At higher-speeds, weight C moves about A as fulcrum, thus pressing pressure-plate.
--Centrifugal-force at C is proportional to speed-squared so adequate pressure is applied

11. Centrifugal Clutch
●Features:
--Springs are eliminated totally; only centrifugal-force applies pressure to engage clutch.
--Clutch is operated automatically (no clutch-pedal) depending upon engine-speed.
--Car can be started & stopped in gear without engine-stall. Driving becomes very easy.
●Construction:
--As speed increases, weight-A flies, causing bell-crank-lever-B to press plate-C.
This force is transmitted to friction-plate-D (by springs-E), which presses to flywheel-F.
--Spring-G keeps clutch disengaged at low-speeds. Stop-H limits centrifugal-force.

12. ●Adv:
(1) No wear on moving parts.
(2) No adjustments to be made.
(3) No maintenance necessary, except oil-level.
(4) Simple design.
(5) No jerk on transmission when gear engages. It damps all shocks & strains.
(6) No skill required for operating it.
(7) Car can start & stop in gear.
Fluid-Flywheel
●Construction:
--It has 2 rotors:
(1) Driving-rotor is connected to flywheel
(2) Driven-rotor is free to slide on splines of transmission-shaft.
There is no direct connection between the two.
--Both rotors are always filled with viscous-fluid.
--Rotors have radial ribs to form a number of passages which
(1) avoid eddies formation
(2) guide fluid-flow in the desired direction.
●Mechanism:
--As fluid-particle moves from smaller to larger radius position in driving-rotor, it gains KE
--When this fluid-particle moves to driven-rotor, it transfers its KE to it, causing it to rotate
●Disadv: (1) There is drag on gear-box-shaft even when driven-rotor is stationary.
This makes gear-changing difficult. To avoid this, epicyclic-gear-box is used.

13. Wet Clutch
--Same as dry-clutch, except friction-plates are wetted by oil-circulation.
--Oil helps clutch-cooling, though it reduces coefficient-of-friction.
●For multi-plate-clutch: this method cannot be used due to poor oil-distribution to remote
friction-surfaces. It requires:
●For single-plate-clutch: oil is sprayed through holes in clutch-plate by a nozzle.
(1) oil-pump, for oil flow through internal passages to rim of clutch-plate-hub.
(2) clutch-brake, to overcome viscous-drag and permit shifting from 1st to neutral
or reverse gear when vehicle is standing still.
--Clutch-brake is applied at end of clutch-release-stroke by using pull-type release.
●Adv: (compared to dry-clutch)
(1) Lower clutch temperatures. Since metal-to-oil heat transfer is much higher than
metal-to-air, clutch can tolerate much longer engagement time.
(2) Longer life
(3) Used in trucks having lower torque-peaks in drive-train.
●Disadv: (compared to dry-clutch)
(1) Lower torque-capacity, due to lower coefficient-of-friction for friction-material
operating in oil.

14. Clutch Actuation
►Mechanical:
-On pressing clutch-pedal, shaft-A turns  moves fork-lever  turns shaft-B  actuates
release-lever  presses thrust-bearing  pivots clutch-levers  disengages clutch.
--Leverage ratio of 10:1 to 12:1 is employed.
--Pedal force of 100-120 N, pedal-travel of 75 mm is required.
►Electro-Magnetic:
--Flywheel incorporates a winding to which current is supplied from battery-dynamo.
--When winding is energized, it attracts pressure-plate, engaging the clutch.
When winding is de-energized, clutch disengages.
--At low speeds, since winding-force is small, springs are provided to clutch-disengage.
--Adv: (1) Used for remote clutch operation since no linkages are required.
--Disadv: (1) Higher initial cost (2) Higher heat generation in magnetic-coil and clutch.
►Hydraulic:
--When clutch-pedal is pressed, fluid under pressure from master-cylinder reaches
slave-cylinder (mounted on clutch itself).
--This fluid pushes slave-cylinder-push-rod which operates clutch-release-fork to
disengage the clutch.
--Adv: (1) Used for heavy-clutches where driver-force becomes excessive
(2) Used also when clutch-pedal & clutch have to located far away from each other

15. Clutch Actuation
►Vacuum-Operated:
●Construction:
--A reservoir is connected to engine-manifold through non-return-valve.
--The reservoir is further connected to vacuum-cylinder through solenoid-valve.
--The solenoid is operated from battery.
--A switch in gear-lever turns on when driver holds gear-lever to change gears.
--Vacuum-cylinder contains a piston, exposed to atmospheric-pressure on one side.
--The piston is connected through linkage to clutch. Movement of piston operates clutch.
●Mechanism:
--During part-throttle, vacuum in intake-manifold opens non-return-valve, and fills the
reservoir with vacuum.
During full-throttle, increased pressure in intake-manifold closes non-return-valve,
isolating the reservoir with vacuum in it. Thus reservoir contains vacuum at all times.
--When clutch is engaged, gear-lever-switch is open, solenoid-valve remains at bottom.
Atmospheric-pressure acts on both sides of piston in vacuum-cylinder.
--When gear-lever-switch is on, energized-solenoid pulls the valve up, connecting the
vacuum-cylinder to vacuum in the reservoir. Piston moves due to unequal pressures.
--When gear-lever is released, its switch is off, thus engaging the clutch.
►Clutch-By-Wire:
--A sensor on clutch-pedal measures exact pedal-position and transmits to ECU.
--ECU, based on other sensors information, operates the clutch through an actuator.
--There is no mechanical link between clutch-pedal and the clutch.