Automobile subject in Mechanical engineering

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.