Automobile Clutch
Necessity of clutch- Generally the purpose of a clutch is to
disengage and engage the engine from transmission (i.e. gear box) whenever
necessary.
Location of clutch- The clutch is mounted in between engine
and gear box.
Classification- The clutch is classified as
follows-
Requirements of
a good clutch
1. The material of clutch plate should have a good
coefficient of friction.
2. The clutch should have a greater torque transmitting
capacity.
3. As a lot of heat is generated in clutch due to
continuous relative motion between pressure plate, clutch plate and flywheel,
good heat dissipation provision should be provided.
4. To avoid clutch spinning at high speeds, the clutch
should have low moment of inertia.
5. Clutch plate is in contact with rotating flywheel so
it experiences vibrations and jerks frequently. So that a clutch should have a
good vibration and jerk absorption capability and also dynamically balanced.
6. The operation of the clutch pedal should be easy for
the operator and not tiresome, especially for operating for long durations.
Types of Clutch-
I.
Single Plate Clutch- These are the most commonly used clutches especially
in modern light vehicles. As the
name indicates, it contains only one clutch plate.
a. Coil Spring Single
Plate Clutch-
Construction & Working-
The main parts if
Coil spring single plate clutch are- clutch plate, pressure plate, friction
lining, coil springs, flywheel, bearings, etc. the clutch plate contains
friction lining or material on both sides. Pressure plate is bolted to the
flywheel which provides axial force to keep the clutch in an engaged position.
Once the clutch
pedal is operated by driver, clutch springs get compressed and the pressure
plate moves backwards. Due to this, clutch plate becomes free so that engine
shaft and transmission box is disengaged from each other. Now one can shift
gear easily as per the requirement. After shifting the gears when clutch pedal
is released, pressure plate comes back to its original position and power
transmission process continues.
Advantages-
Heat dissipation capacity is better
Load withstanding capacity is good.
Simple in design
Disadvantages-
It requires more space.
More force is required to operate the clutch.
b. Diaphragm
Spring Clutch-
Construction & Working-
Instead of a
series of axial springs, a curved diaphragm is used in this type of clutch.
Diaphragm spring is like a disc having a conical shape. It consists of no. of
radial fingers at its centre. The diaphragm spring is also known as -Belleville
spring. This curved diaphragm exerts an axial
force. The construction for this clutch is very similar to the coil spring
clutch.The diaphragm spring
works on a principle of compressive force. When compressive force is applied,
clutch disengages engine from gear box so that gear can be shifted as per
requirement.
Advantages-
1. Design is very compact and hence requires less space.
2. Instead of coil spring, diaphragm spring is used.
3. Energy storing capacity is more.
4. In worn out conditions also, the spring force is not
decreased.
5. Diaphragm spring acts as both clamping spring and
release levers
6. Easy operation and well-balanced system.
7. The effect of centrifugal forces is very less.
Disadvantages-
If the size of
diaphragm is large then clamping force is insufficient.
I. Multi-plate
Clutch- It is also known as the extension of single plate clutch.
Construction & Working-
In this type, no
of friction plates are used so that friction surface is increased. As friction
surfaces increase the area required to transmit the torque is also increased
and hence torque transmitting capacity of clutch is increased. This clutch is
specifically used where the requirement of torque transmitting capacity is
more.
It includes
pressure plates having teeth at its outer periphery. These plates are meshed with
the grooves on flywheel and free to move inside or outside. When the clutch
pedal is pressed, the axial force binding the clutch plates is removed,
stopping the power being transmitted by the clutch.
Advantages-
1.
Torque
transmitting capacity is more.
2.
Pedal effort
required is less and hence operation becomes easy.
3.
Moment of inertia
of the clutch is decreased.
4.
Better
acceleration is achieved.
Disadvantages-
1.
Weight is more.
2.
It is so expensive.
III. Centrifugal Clutch-
The main parts of centrifugal clutch are-
Shoes: These are the sliding elements which slide into the
guide ways provided on a rim. Shoes are attached with friction lining which
comes in contact with drum while engagement.
Spring: To disengage the clutch at lower speeds, spring
is used.
Spider
or guides: Equally spaced spiders are
mounted on a driver shaft. Suppose there are four guides, then angle between
each pair is 90 degrees. Each guide is holding a spring and allowing
a shoe to slide within it.
Friction
lining: The outer surface area of
shoe is covered with friction lining which helps in making grip with drum
surface.
Drum: The drum of the clutch acts as a cover or casing
which includes all the parts like- guides, springs, shoes, etc.
Construction & Working-
In this type of
clutch, spring force is replaced by a centrifugal force. Centrifugal force is
used to connect two concentric shafts. It consists of a circular rim which
contains no. of shoe mounted on it. These shoes are following radial motion. When
centrifugal force is less, shoe does not change their position at all but when
centrifugal force is equal to spring force, shoes are floating. Depending upon
the engine speed, clutch operates automatically. As the diagram shown above,
the components of centrifugal clutch are as follows-
- It consists of weights A pivoted at B.
- When the engine speed increases the weights fly off due to the centrifugal force, operating the bell crank levels, which press the plate C.
- The movement of plate C presses the spring E, Which ultimately presses the clutch plate D on the flywheel against the spring G.
- This makes the clutch engaged.
- The spring G keeps the clutch disengaged at low speeds at about 500rpm.
- The stop H limits the movement of the weights due to the centrifugal.
Advantages
- It is simple in construction and requires less maintenance.
- The overall cost of the clutch is less and hence it is not expensive.
- Control mechanism is completely eliminated as it is automatically operating clutch.
Disadvantages
- Due to friction and slipping, power loss is observed.
- This clutch cannot operate at high loading conditions.
- As the friction is more, it undergoes overheating.
