Introduction to the Transmission system, Requirements of the transmission system, main units of the transmission system, types of the transmission system, clutch, functions of a clutch, requirements of a clutch, principle of operation of a clutch, friction materials, classification of a clutch, cone clutch, single-plate clutch, multi-plate clutch centrifugal clutch, hydraulic coupling, hydraulic torque converter.

1. Transmission
System
By : Ratnadeepsinh Jadeja

2. Introduction to Transmission system
• The mechanism that transmits the power developed by the engine of the
automobile to the driving wheels is called the transmission system (or
power train).
• It is composed of the clutch, gear box, propeller shaft, universal joints,
rear axle, wheel and tyres.
• The vehicle which have front wheel drive in addition include a second set
of propeller shafts. Universal joints, final drives and differentials for the
front units.

4. Requirements of Transmission system
• The transmission should fulfill the following requirements:
1. Provide means of connection and disconnection of engine with rest of power
train without shock.
2. Provide a varied leverage between the engine and the drive wheels.
3. Provide means to transfer power in the opposite direction.
4. Enable power transmission at varied angles and varied lengths.
5. Enables speed reduction between engine and the drive wheels in the ratio of
about 5:1.
6. Enable diversion of power flow at right angles.
7. Provide means to drive the driving wheels at different speeds when
required.
8. Bear the effect of torque reaction, driving thrust and braking effort
effectively.

5. • The above requirements are fulfilled by the following main units of
transmission system:
1. Clutch
2. Gear box
3. Transfer case
4. Propeller shaft and universal joints
5. Final drive
6. Differential
7. Torque drive
8. Road wheels.

6. Types of Transmission systems
1. Electrical and electromagnetic transmission system
2. Hydraulic transmission system
3. Mechanical transmission system.

7. Units of Transmission systems
1. Clutch unit
• Clutch assembly or fluid coupling
2. Transmission unit
• Gear box
• Transfer case
• Overdrive
• Free wheeling device
• Torque converter etc
3. Driving unit
• Propeller shaft
• Universal joints
• Sprockets and chains
4. Driving axle unit
• Final drive
• Differential
• Half shafts etc.

8. CLUTCH
• A clutch is a mechanism which
enables the rotary motion of one
shaft to be transmitted at will to
second shaft, whose axis is
coincident with that of first.
• The clutch is “disengaged” when
starting the engine, shifting the
gears, stopping the vehicle and
idling the engine.
• The clutch is “engaged” only when
the vehicle is to move and is kept
engaged when the vehicle is moving.

9. Functions of a clutch
1. To permit engagement and
disengagement of a gear when the
vehicle is stationary and the
engine is running.
2. To transmit the engine power to
the road wheels smoothly without
jolt/shock to the transmission
system while setting the wheel in
motion.
3. To permit the engaging of gears
when the vehicle is in motion
without damaging the gear
wheels.

10. Requirements of a clutch.
1. Engage gradually to avoid sudden shock/jerks.
2. Easily operated (i.e. consume minimum physical effort)
3. Dynamically balanced (particularly required in case of high speed engine clutches)
4. Free from slip when engaged.
5. As small as possible so that it will occupy minimum space.
6. Wearing surface should have long life.
7. Easily accessible and have simple means of adjustment.
8. Suitable mechanism to damp vibrations and to eliminate noise produced during the power
transmission.
9. Able to dissipate large amount of heat which is generated during the clutch operation due
to friction.
10. Driven members of the clutch should be made as light as possible.
11. Should have Free pedal play in order to reduce effective clamping load on the carbon thrust
bearing and wear on it.

11. Principle of Operation of a Clutch
• The clutch principle is based on friction. When two friction surfaces are brought in
contact with each other and pressed they are united due to friction between them.
• The friction between two surfaces depends upon, 1. area of the surface, 2. pressure
applied upon them, 3. coefficient of friction of the surface materials.

12. Friction Materials
1. Woven type is made by spinning threads from asbestos fibers, some times on brass
wire, weaving this thread into cloth and then impregnating it with a bonding
material (such as vegetable grains, rubber, synthetic resins etc.).
2. The moulded or compression type of lining is composed of asbestos fibers in their
natural state mixed with a bonding material and then moulded in dies under
pressure and at elevated temperatures. Metallic wires are sometimes included but
only to increase the wearing qualities and to eliminate scoring of the metal faces
against which the lining rubs.
3. Mill board type friction materials mainly include asbestos sheets treated with
different types of impregnants. They are cheap as well as quite satisfactory in
operation.

13. Friction Materials
The following materials are almost
universally used for clutch lining:
1. Leather
2. Cork
3. Fabric
4. Asbestos
5. Reybestos and Ferodo
Properties of a good clutch lining:
1. High coefficient of friction.
2. Good wearing properties.
3. Cheap and easy to manufacture.
4. Good binder in it.
5. High resistance to heat.

14. Classification of clutches
The clutches can be classified as follows:
1. Positive clutches.
2. Gradual engagement clutches.

15. Gradual Engagement Clutches
In such clutches it is possible for one shaft to be revolving rapidly while the other is
either stationary or revolving at lower speed. As the engagement of the clutch proceeds
the speed of the two shafts gradually become same, and when the clutch is fully
engaged the shafts revolve as one. Such clutches are called friction clutches.
Friction clutches are of three type
1. Cone clutch
2. Single plate clutch
3. Multi plate clutch
Other forms of clutches
1. Centrifugal and magnetic clutches
2. Fluid flywheel (Fluid Hydraulic coupling)
3. Hydraulic torque converter.

17. Cone clutch
• The only advantage of cone clutch is that the normal force acting on the friction
surface is greater than the axial force, as compared to the single plate clutch is which
the normal force acting on the friction surfaces is equal to the axial force.
• The cone clutch is practically obsolete, due to the following disadvantages.
1. If the cone angle is made smaller than 20°, the male cone tends to bind in the
female cone and it is difficult to disengage the clutch.
2. A small amount of wear on the cone surfaces results in a considerable amount of
the axial movement of the male cone for which it will be difficult to allow.
• It is only used in the synchromesh units of gear boxes, and in overdrives and some
epicyclic gear boxes.

18. Single Plate Cutch
• Clutch slip occurs if the resisting torque on the driven shafts exceeds the friction
torque at the clutch.
• Single plate clutch divides in two category of elastic member
1. With helical springs
2. With diaphragm spring (Belle ville springs)
• The diaphragm springs offers the following advantages:
1. The operating load is practically uniform and constant on the driven plate.
2. It has a compact design, which results in smaller clutch housing.
3. Release levers are not required, since the diaphragm itself acts as a series of
leavers.
4. Squeaks, rattles and vibrations are mostly eliminated.
5. It can withstand higher rotational speeds since the diaphragm is comparatively less
affected by the centrifugal forces.

20. Single Plate Cutch

21. Multiplate Cutch
• When a great amount of torque is to
be transmitted instead of single
plate we can employ a number of
friction plates. This will increase the
number of mating surfaces, hence it
is called multiplate clutch.
• These clutches are used in heavy
commercial vehicles, racing cars and
motorcycles for transmitting high
torque.

22. Multiplate Cutch

23. Multiplate wet Cutch
• It consists of number of thin plates made of steel fitted to the engine shaft and those
on gear shaft are made of phosphor bronze. These plates are immersed in a bath of oil
and also have grooved surfaces for permitting the oil to flow through them. These
grooves help to dissipate the heat generated during the engagement and release
operation.
• These clutches are generally used in conjunction with or as a part of the automatic
transmission.
Multiplate dry Cutch
• In this type of clutch its different plates are lined with a friction material similar to that
used in case of a single plate.
• The clutches with metal plates are used in tractors or other light powered engine
vehicles.

24. Centrifugal Cutch
• Centrifugal force, instead of spring force, is used for keeping it in engaged position.
Also, it does not require any clutch pedal for operating the clutch. The clutch is
operated automatically depending upon the engine speed.

25. Centrifugal Cutch
• Centrifugal force, instead of spring force, is used for keeping it in engaged position.
Also, it does not require any clutch pedal for operating the clutch. The clutch is
operated automatically depending upon the engine speed.

26. Semi-centrifugal Cutch
• Semi centrifugal clutch uses centrifugal
force as well as spring force for keeping it
in engaged position. The springs are
designed to transmit the torque at normal
speeds, while the centrifugal force assists
in torque transmission at higher speeds.
• The centrifugal force on the pressure plate
can be adjusted by an adjusting screw
provided at the end of the lever.

27. Fluid coupling/Fluid flywheel
• Fluid coupling is a hydraulic unit that replaces a clutch in a semi or fully automatic
system, and transmits the engine torque to a transmission system. Since the coupling
is a major part of the engine flywheel assembly, it is also called a fluid flywheel or
fluid drive acting as an automatic clutch.

28. Fluid coupling/Fluid flywheel
• The efficiency of power transmission may be as high as 98 %
• The efficiency of the hydraulic coupling is defined as the ratio of power output to
power input
• The ratio Wt/Wp is known as speed ratio.
• A fluid coupling always slips by about 2 to 4 percent when transmitting full load. It
means that the turbine is always running slightly slower than the impeller and as such
complete disconnection of the drive is not possible. Thus the fluid coupling is not
suitable for ordinary gear box and is generally used with epicyclic gears to provide a
semi or fully automatic gear box.

29. Hydraulic torque converter
• Hydraulic torque converter is a device used for transmitting increased or decreased
power from one shaft to another. A variable torque is impressed on the driven
member without the use of a gear train or clutch.