Automobile Clutch



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

  1. It is simple in construction and requires less maintenance.
  2. The overall cost of the clutch is less and hence it is not expensive.
  3. Control mechanism is completely eliminated as it is automatically operating clutch.

Disadvantages

  1. Due to friction and slipping, power loss is observed.
  2. This clutch cannot operate at high loading conditions.
  3. As the friction is more, it undergoes overheating.


 
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