Automobile Clutch-Working & Types.pdf

Clutch-Working & Types

1. Clutches

2. Objectives
•Describe the various clutch components
and their functions.
•Name and explain the advantages of the
different types of pressure plate
assemblies.
•List the safety precautions that should be
followed during clutch servicing.
continued…

3. Objectives
•Explain how to perform basic clutch
maintenance.
•Name the six most common problems
that occur with clutches.
•Explain the basics of servicing a clutch
assembly.
continued…

4. Drive Trains
Front-Wheel
Drive Vehicle
Rear-Wheel
Drive Vehicle

5. Automotive Clutch
•Used to connect and disconnect the
engine and manual transmission or
transaxle
•Allows the driver to control power flow
between the engine and transmission or
transaxle

6. •Vehicles with manual transmissions
require a clutch
•Power flow from one unit to another can
be controlled with a drive disc and a driven
disc

7. Clutch
Theory
Clutch is
engaged
Clutch is
disengaged

12. Introduction
Clutches
In order to change gear, the drive between the engine and the gearbox must
be temporarily disconnected. The vehicle clutch enables the driver to do this.
A clutch is a component that is designed to connect together two rotating shafts.
Clutches can be classified as one of two types - positive engagement (dog clutch) or
gradual engagement (friction clutch). Positive engagement clutches normally use teeth
in order to provide a positive connection, whereas gradual engagement clutches use
friction

13. The clutch is situated between the engine and the transmission gearbox.
In this example depressing the clutch pedal will engage and disengage
the engine from the transmission. The clutch is designed to gradually
and smoothly transmit power from the engine to the transmission to
enable a vehicle to start off under full control.

Note: The ability of a clutch to transmit torque (clutch capacity) is
normally between 1.2 and 1.4 times the maximum torque of the engine.
Commercial vehicles usually have a capacity between 1.5 and 2.5. If
the clutch is too light, slipping will take place and lead to premature
failure. Too large a clutch will tend to cause the engine to stall and is
inefficient

14. Requirements of a vehicle clutch

• it must connect power smoothly
• it must transmit power without slipping
• it must disengage quickly and smoothly
• it must have good heat radiating properties
• it must be well balanced
• it must be trouble free and have a long service
life
• it must be easy to inspect, adjust and repair.

15. Basic Clutch
Parts
The clutch assembly consists of
two major items, cover assembly
(containing pressure plate and
spring) and the clutch friction
plate or disc which is trapped
between the engine fly wheel and
the cover assembly

16. Simplified Clutch

17. Clutch Components
continued…

18. Clutch Action (Disengaged)
•When driver presses the clutch pedal,
clutch release mechanism pulls or
pushes on the clutch fork
•Fork moves the release bearing into the
center of the pressure plate
•Pressure plate face pulls away from the
clutch disc
•Clutch disc and transmission input do
not turn

19. Clutch Action (Disengaged)

20. Clutch Action (Engaged)
•When driver releases the clutch pedal,
spring pressure inside the pressure
plate pushes forward on the clutch disc
•This locks the flywheel, disc, pressure
plate, and transmission input together
•Engine rotates the transmission input

21. Clutch Action (Engaged)

24. Coil spring type
The cover assembly is bolted to the flywheel and rotates at engine speed. The friction disc is
splined to the gearbox input shaft. Trapped between the pressure plate and flywheel by spring
pressure, the disc will transmit power to the transmission.

Depressing the clutch pedal will cause the lever to move the release bearing and relieve the
pressure exerted by the spring on the disc. This will cause the disc to spin freely between the
flywheel and the pressure plate. Power cannot therefore be transmitted to the transmission

25. Diaphragm spring type
There are two main types of clutch cover assembly. The type illustrated uses
coil springs to trap the friction disc between the pressure plate and the flywheel.
The clutch cover uses a diaphragm spring

26. •Components:
–pilot bearing
–flywheel
–clutch disc
–pressure plate
–release bearing
–clutch housing (bell housing)
–clutch release mechanisms
–clutch start switch

27. Clutch Components
•Clutch housing
–Connects engine
and transmission
and houses the
clutch assembly.
continued…

28. Clutch (Bell) Housing
•Bolts to the rear of the engine
•Encloses the clutch assembly
•Made of aluminum, magnesium, or cast
iron
•Transmission bolts to the back of the
clutch housing

29. Clutch Components
•Flywheel
–Acts as balancer for
the engine.
–Adds inertia to the
rotating crankshaft.
–Provides a surface
for the clutch to
contact.
continued…
Some flywheel have
Ring gear for starter engagement
Some vehicles have dual mass flywheel

30. Flywheel
•A mounting place for the
clutch
•The pressure plate bolts to
the flywheel face
•Flywheel face is precision
machined to a smooth
surface, where it contacts
the clutch disc
•Normally made of iron for
good wear and heat
dissipation

31. 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
splined to the clutch
shaft.
–When engaged, the
clutch disc drives the
input shaft.
continued…

32. Clutch Disc
•Consists of a splined metal hub and a
round metal plate covered with friction
material (lining)
•“Splined” to the transmission input shaft
•Disc is free to slide back and forth on the
shaft

33. 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.
continued…

34. Clutch Components
Clutch disc

continued…

35. Clutch Disc
The central hub is splined to
fit on the gearbox input shaft
and is free to rotate a limited
distance in relation to the
friction faces. This movement
is governed by torsion
dampers made usually from
coil springs or rubber inserts
and reduces initial shock at
power take up.

36. There is a tendency for the disc to
stick to the flywheel or pressure
plate when released in much the
same way that two sheets of
glass are hard to separate due to
air pressure. Grooves in the
friction faces help air to enter the
gap forming when the pressure
plate moves away from the disc.

37. 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.
continued…

38. Clutch Disc Torsion Springs
•Help absorb some of the vibration and
shock produced by clutch engagement
•Small coil springs located between the
clutch disc hub and the friction disc

39. Clutch Disc Facing Springs
•Flat, metal springs located under the disc’s
friction material
•Springs have a light wave (curve)
–allow the friction material to flex inward
slightly during clutch engagement
–flexing smoothes engagement

40. Clutch Disc Friction Material
•Made of heat-resistant substances
•Grooves cut in the material aid cooling
•Rivets are commonly used to bond the friction material to both sides
of the metal body of the disc
•Leather ,cork,fabric,Asbestos
–Reybestos and ferodo > most suitable, Widely used
–Non asbestos clutch
•Glass fibre mixed with special rubber
•Kavalar with brass wire
•Sintered metal friction

41. Pressure Plate
•Spring loaded device
•Locks or unlocks the clutch disc and the
flywheel
•Clutch disc fits between the flywheel
and pressure plate
•Two basic types:
–coil spring
–diaphragm spring

42. Clutch Components
Diaphragm Coil
Spring Spring
continued…

43. Components
•Small coil springs
–clamp clutch disc between face and
flywheel
•Face
–large ring that contacts the clutch disc
•Release levers
–allow the release bearing to move the face
–hinged inside the pressure plate

44. Diaphragm Spring Pressure
Plate
•Uses a single diaphragm spring instead of
several coil springs
•Diaphragm spring is a large, round disc of
spring steel which rides on a pivot ring part
way in from the outer edge
•Pushing in on the center of the spring
bends the outer edge away from the
engine, releasing the clutch disc

45. Diaphragm Spring Pressure
Plate

46. Clutch Components
•Release bearing
–Is operated by the
clutch linkage.
–Presses against the
pressure plate to
release the clutch.
continued…

47. Release Bearing
•Usually a ball bearing and collar
assembly that reduces friction between
the pressure plate levers and the clutch
fork
•A few imported vehicles use a graphite
bearing
–ring shaped block of graphite presses on a
smooth, flat plate on the clutch release
levers

48. 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.
continued…

49. Pilot Bearing
•Made of a solid bronze bushing, roller or
ball bearing
•Prevents the transmission shaft and
clutch disc from wobbling when the
clutch is released

50. Clutch Linkage
•Clutch linkage
transfers the clutch
pedal movement to
the release
bearing.
–Mechanical clutch
linkage uses
shafts, levers, or a
cable.
continued…

51. Clutch Cable
Mechanism

52. Clutch Cable Mechanism
•Uses a steel cable inside a flexible
housing to transfer pedal movement to the
clutch fork
•One end usually has a threaded sleeve for
clutch adjustment

53. Clutch Linkage Mechanism

54. Clutch Linkage Mechanism
•Uses levers and rods to transfer motion
from the clutch pedal to the clutch fork
•A bellcrank may be used to reverse the
movement of the clutch pedal
•A release rod transfers motion to the fork
and allows adjustment

55. Clutch Linkage
Hydraulic clutch linkage consists of a
master cylinder, hydraulic tubing, and a
slave cylinder.
continued…

56. Hydraulic Clutch Release
Mechanism
•Uses a simple hydraulic circuit to transfer
clutch pedal action to the clutch fork
•Components:
–clutch cylinder
–hydraulic line
–slave cylinder

57. Clutch Cylinder
•Produces hydraulic pressure for the
system
•Mounted to the firewall or cowl
•Push rod links the clutch pedal and the
cylinder piston
•Most systems use brake fluid

58. Clutch Cylinder

59. Slave Cylinder
Uses hydraulic
pressure to cause
clutch fork
movement

60. Multiplate Clutch Assembly
Drum Piston Seals Return Springs
Unlined Plates
Snap Ring
Lined Discs
Pressure Plate
A typical clutch
assembly contains
the apply piston,
piston return springs,
and the clutch plates.

61. 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.

continued…

62. Common Clutch Problems
•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

continued…

63. 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.
continued…

64. 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.

continued…

65. Common Clutch Problems
•Causes for damaged release bearings
–Misalignment
–Overheating
–Slippage
–Component damage

continued…

66. 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.

continued…

67. 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.

continued…

68. Flywheel service
•Visually inspect for hot spots, grooves,
scoring and cracks
•Check with dial indicator for run out and
crank end play
•Most flywheels can (should) be
resurfaced
–Must remove dowel pins
•Inspect ring gear

69. Clutch Service Checks
Measuring flywheel runout and
Crankshaft endplay
continued…

70. Clutch Service Checks
Measuring clutch housing face runout
continued…

71. Hydraulic Clutch Problems
•Soft clutch pedal or excessive pedal travel
–Is usually caused by low fluid level.
–May be caused by a faulty master or slave
cylinder.
•Hard pedal
–Is commonly caused by binding linkage or
swollen cups in the master or slave cylinder.

continued…

72. Clutch disc service
•Inspect for wear similar to brake pads
•Common to have loose or broken
springs
•Common failure due to oil
contamination
–Must find cause BEFORE repair

73. Clutch disc service
•Clutch disc will normally have a flywheel
side
•Disc must be centered with clutch
alignment tool before pressure plate
bolted down
•Make sure new disc fits on input shaft of
the transmission before you install it

74. Pressure plate service
•Mark relation to flywheel if reused
•Remove bolts slowly in criss-cross pattern
•Inspect fingers for parallelism, cracking or
uneven wear
•Inspect friction surface for hot spots,
cracks etc and with straight edge for
warpage
•Must be torqued to specs and in sequence
•Uses hard bolts

75. Release bearing service
•Very common failure - isolated by lightly
applying clutch and listening
•Inspect for looseness or roughness
•Most are sealed but some were lubeable
•Clutch fork must be lubed at pivot point
and bearing contact points
•Bearing retainer and input shaft should be
lubed
•Clutch fork must be secured at the pivot
point

76. Pilot servicing
•Should always be changed with clutch
•Can be isolated by applying clutch in gear
•Special pullers may be used for removal
–Can be removed with grease
•Should be lightly lubed on installation