clutch assembly, clutch exploded view, sub parts functions

1. Clutch

4. Components of an Automobile
Automobile
Power Unit
Transmission System
Basic Structure
Controls
Auxiliaries
Superstructure
Power
Plant
Running
Gear
Framework
Or
Automobile
Chassis

5. Components of an Automobile
Automobile
Power Unit
Transmission System
Basic Structure
Controls
Auxiliaries
Superstructure
Transmission System
Clutch
Manual Transmission & Transaxles
Automatic transmission
Propeller shafts and drive shafts
Differential
Power
Plant
Gearbox

6. Some New Terms
• Transmission refers to
– rear-wheel drive vehicles
– A separate differential is used with a transmission.
• Transaxle usually refers
– to front-wheel-drive vehicles
– that have a differential built into the unit.

7. The Chassis
• Transmission is the mechanism which is used to transfer
the power developed by engine to the wheels of an
automobile.
• Often transmission refers simply to the gearbox that uses
gears and gear trains to provide speed and torque
conversions from a rotating power source to another device.
Transmission System

8. Typical drive train components for a
rearwheel-drive car.

9. The Clutch
• A clutch is a device for disconnecting and connecting rotating
shafts.
• In a vehicle with a manual gearbox, the driver pushes down the
clutch when changing gear, thus disconnecting the engine from
the gearbox.
• It allows a temporary neutral position for gear changes and also a
gradual way of taking up drive from rest.
• The clutch assembly is located between the engine and the
transmission/transaxle.

10. The Clutch
• Most clutches used in the modern motor car are called friction
clutches.
• This means that they rely on the friction created between two
surfaces to transmit the drive from the engine to the gearbox.
• The clutch fulfils a number of different tasks.

11. The Clutch
• The four main ones are:
– To connect & transmit engine torque to the transmission/
transaxle/gearbox ;
– To provide a smooth engagement & disengagement between
the engine and the transmission/transaxle;
– To dampen & absorb engine impulses and drive train
vibrations
– To provide the vehicle with a temporary neutral.

12. The Clutch
• If the vehicle had no clutch and the engine
was always connected to the transmission, then
– the engine would stop every time the vehicle was brought to
a stop.
• The clutch engages the transmission gradually by allowing a
certain amount of slippage between the transmission’s input
shaft and the flywheel.

13. What happens when the clutch is
engaged

14. Requirements of a clutch
• A clutch must transmit drive smoothly with no drag.
– Drag is where the clutch is not fully disengaged and rubs
together, still transmitting some drive.
• A clutch must transmit drive smoothly with no slip
once it is fully engaged.
– Slip is where drive is not fully transmitted and the friction
surfaces slide over each other, producing a loss of turning
effort.
• A friction clutch must be able to transmit all of the engine
torque to the rest of the transmission system without slip.

15. Three methods that increase the torque
transmitting ability of a friction clutch

16. Parts of a Clutch
• The main component parts of a clutch are:
– driven plate, sometimes referred to as the clutch, centre or
friction plate;
– pressure plate which comes complete with the clutch cover,
springs or diaphragm to provide the force to press the
surfaces together;
– release bearing which provides the bearing surface which,
when the driver operates the clutch pedal, disconnects the
drive between the engine and the gearbox;
– flywheel, the main driving member of the clutch.

17. Parts of a Clutch

18. Parts of a Clutch
(1) Flywheel

19. Parts of a Clutch
• The flywheel, an important part of the engine, is also the main driving
member of the clutch.
• It is heavy, or has a large mass, which creates inertia.
• It is normally made of nodular or gray cast iron, which has a high
graphite content (about 3%) to lubricate the engagement of the clutch.
• On a running engine, the crankshaft speeds up as a cylinder fires, then
slows due to internal engine friction until the next cylinder fires.
(1) Flywheel

20. Parts of a Clutch
• The inertia provided by the flywheel mass tends to keep
crankshaft speed more constant.
• Whenever friction exists between two moving parts, heat is
generated.
• The flywheel absorbs some of the heat created by clutch
operation by acting as a heat sink for the clutch friction disc.
• The flywheel has two sets of bolt holes drilled into it.
(1) Flywheel

21. Parts of a Clutch
• The inner set is used to fasten the flywheel to the crankshaft, and
the outer set provides a mounting plate for the pressure plate
assembly.
• An external ring gear is pressed or welded onto the flywheel
along its outer circumference.
• When the starter motor is engaged, the starter-drive gear
meshes with the flywheel ring gear.
(1) Flywheel

22. Parts of a Clutch
• Through gear reduction, the flywheel transfers starter motor
rotation to the crankshaft to crank the engine.
• The face on the transmission side of the flywheel has a smooth,
machined area that creates the application surface for the clutch
friction disc.
• This surface must be properly finished to allow adequate slippage
as the clutch engages and disengages, and to prevent slippage
when the clutch is engaged.
(1) Flywheel

23. Parts of a Clutch
Engaged Disengaged

24. Parts of a Clutch

25. Multi Plate Clutch

26. Parts of a Clutch
(2) Clutch Disc

27. Parts of a Clutch
(2) Clutch Disc

28. Parts of a Clutch
(2) Clutch Disc

29. Parts of a Clutch
(2) Clutch Disc
• The clutch disc is also called a driven center plate or a friction
disc.
• The clutch disc provides the friction material needed to transmit
engine torque from the flywheel and pressure plate to the input
shaft of the transmission.
• The central alloy-steel—splined hub is separate from the steel
disc (Central Plate). Drive is transmitted from the steel disc to the
hub through heavy torsional coil springs.

30. Parts of a Clutch
(2) Clutch Disc
• This spring hub arrangement dampens torsional vibrations from
the engine.
• It also absorbs shock loads imposed on the drive line by sudden
or violent clutch engagement.
• Waved spring steel segments located between the friction
facings cause the facings to spread apart slightly when the clutch
is disengaged and to compress as it is engaged.

31. Parts of a Clutch
(2) Clutch Disc

32. Parts of a Clutch
(2) Clutch Disc
• This gives a cushioning effect during clamping of the clutch disc in the
pressure plate.
• These waved springs allow a progressive application of the pressure
plate clamping force as the waved springs are being compressed when
the pedal is being released.
• The result is smoother engagement of the clutch when starting from a
stop.
• These springs reduce chatter when the clutch is engaged and also
reduce the chance of the clutch disc sticking to the flywheel and
pressure plate surfaces when the clutch is disengaged.

33. Parts of a Clutch
(2) Clutch Disc
• The clutch disc is splined to the transmission’s input shaft and
receives the driving motion from the flywheel and pressure plate
assembly and transmits that motion to the transmission input
shaft.
• Friction material is riveted to both sides of the clutch disc—one
side touches the flywheel of the engine and the other side
touches the friction surface of the pressure plate.

34. Parts of a Clutch
(2) Clutch Disc
• There are two types of friction facings :- Molded & Woven
• Molded friction facings are preferred because they withstand
greater pressure plate loading force without damage.
• Woven friction facings are used when additional cushioning
action is needed for clutch engagement. Woven materials are
softer , but they may not last as long as molded materials.

35. Parts of a Clutch
(2) Clutch Disc
• Friction materials operate in high heat and pressure.
• For many years, asbestos was the most common material used in
both clutch and brake linings.
• However, it is no longer used because inhaling tiny particles of
asbestos causes lung damage.
• Today, clutch friction material may contains particles of cotton,
brass, rope, and wire to prolong the life of the clutch disc and to
provide torsional strength.

36. Parts of a Clutch
(2) Clutch Disc
• Grooves are cut across the face of the friction facings.
• This promotes clean disengagement of the driven disc from the
flywheel and pressure plate; it also promotes better cooling.

37. Parts of a Clutch
(3) Pressure Plate Assembly
• The purpose of the pressure plate assembly is twofold.
• First, it must squeeze the clutch disc onto the flywheel with
sufficient force to transmit engine torque efficiently.
• Second, it must move away from the clutch disc so the clutch disc
can stop rotating, even though the flywheel and pressure plate
continue to rotate.

38. Parts of a Clutch
(3) Pressure Plate Assembly
• Basically, there are two types of pressure plate assemblies:
– those with coil springs and
– those with a diaphragm spring.
• Both types have a stamped steel cover that bolts to the flywheel
and acts as a housing to hold the parts together. In both, there is
also the pressure plate, which is a heavy, flat ring made of
nodular or gray cast iron.

39. Parts of a Clutch
(3) Pressure Plate Assembly
• A coil spring pressure plate assembly uses coil springs and release
levers to move the pressure plate back and forth.
• The springs exert pressure to hold the pressure plate tightly
against the clutch disc and flywheel.
• This forces the clutch disc against the flywheel.
• The release levers release the holding force of the springs. There
are usually three of them.
Coil Spring Pressure Plate Assembly

40. Parts of a Clutch
(3) Pressure Plate Assembly
• To disengage the clutch, the release bearing pushes the inner
ends of the release levers forward toward the flywheel.
• Each end of the lever moves in the opposite direction. When
force pushes one end of the lever down, the other end moves up.
• In a coil spring pressure plate, the release lever yokes act as
fulcrums for the levers, and the outer ends of the release levers
move backward, pulling the pressure plate away from the clutch
disc.
Coil Spring Pressure Plate Assembly

41. Parts of a Clutch
(3) Pressure Plate Assembly
• This compresses the springs and releases the clamping of the
clutch disc between the pressure plate and flywheel.
• When the clutch is engaged, the release bearing moves away
from the pressure plate.
• This allows the pressure plate springs to push the pressure plate
and clutch disc against the flywheel, allowing power transfer
from the engine to the transmission.
Coil Spring Pressure Plate Assembly

42. Parts of a Clutch
(3) Pressure Plate Assembly
Coil Spring Pressure Plate Assembly

43. Parts of a Clutch
(3) Pressure Plate Assembly
Diaphragm Spring Pressure Plate Assembly

44. Parts of a Clutch
(3) Pressure Plate Assembly
Engaged Disengaged

45. Parts of a Clutch
4. Clutch Release Bearing

46. Parts of a Clutch
4. Clutch Release Bearing
• The clutch release bearing is also called a throwout bearing.
• Its function is to smoothly and quietly move the pressure plate
release levers or diaphragm spring through the engagement and
disengagement process.
• When the driver depresses the clutch pedal, the movement is
passed to the release bearing by either hydraulics or cable and
the release bearing then pushes or pulls the diaphragm spring
(depending on whether the clutch is a ‘push’ or ‘pull’ design)

47. Parts of a Clutch
4. Clutch Release Bearing
• The outer part of the release bearing is held (by the release lever)
so it does not rotate, and the inner race of the bearing rotates
with the diaphragm spring and clutch cover.

48. Coil Spring vs. Diaphragm spring
• A number of early clutches used coil springs to provide the
clamping effort. Over a period of time, coil spring tension and
length would change due to wear and tear. When this happened,
an uneven clamping force could be produced at the pressure
plate. This uneven clamping force might lead to clutch drag, slip
or vibrations.
• To overcome these problems a spring mechanism called ‘a
diaphragm’ was developed. This diaphragm spring is a single
metal plate, made into a series of sprung steel fingers. It is
slightly dished in shape.

49. Coil Spring vs. Diaphragm spring
• When one end of the fingers is pressed by the clutch release
bearing, the fingers pivot about a fulcrum(like a seesaw). This
moves the opposite end of the diaphragm fingers in the other
direction. When this happens, the pressure plate is moved away
from the friction plate and disengages the clutch.
• When the driver lifts his foot off the clutch pedal, the ends of the
fingers of the diaphragm spring are released. Because the steel
fingers are sprung, they return to their original position and
reapply pressure to the friction plate. This then reconnects the
drive. Because the spring diaphragm fingers are made from a
single piece of metal, an even clamping force can be produced.
This overcomes many of the problems created when using coil
spring mechanisms.

50. Freeplay
• When the clutch is engaged, no force should be placed on the
release bearing where it touches the diaphragm springs of the
pressure plate.
• A small clearance or gap is normally needed at the pedal end.
This is called ‘clutch pedal freeplay’.
• Clutch pedal freeplay is needed for two reasons:
– It makes sure that the release bearing is not continuously pressed against
the rotating fingers of the diaphragm spring. This will help reduce wear on
both the diaphragm spring fingers and the clutch release bearing itself.
– It ensures that the clutch mechanism is fully engaged.

51. Freeplay
• If freeplay didn’t exist, then the bearing might be pushing on the
clutch release springs. This would partly disengage the clutch
friction plate. This would then cause the drive plate to slip and to
wear out early.
• If too much freeplay exists, then when the clutch pedal is pressed
by the driver, the clutch might not fully disengage. This would
mean that the friction plate is still being gripped slightly between
the pressure plate and The flywheel. If this happens, the engine
could not be fully disconnected from the gearbox. This can make
changing gear difficult. If the clutch friction plate does not fully
disengage, this is referred to as clutch drag.