Clutch

It is defined as, "a machine element component used to connect driver shaft to a driven shaft".

•  It will stop driven shaft without altering driven shaft using lever.
• Driver  ↔  anything which produces power is called Primover or Driver.
• Driven Machinery  ↔  anything which consume this power is called Load or Driven Machinery.

Design Considerations

Design consideration factors are described ahead:

1. Coefficient of Friction  ↔  should be high enough to hold load and minimum amount of axial force.
2. Moment of Inertia  ↔  clutch moving components should have less weight to minimize inertia load at high speed.
3. Heat Generated at Contact Surfaces  ↔  heat should dissipate rapidly.
4. Wearing of surfaces  ↔  provision for taking up the wear of contact.
5. Cover Projecting Parts  ↔  guard projecting parts for the provision of easy repair. 

Material Requirement 

The actual friction surface is friction lining which gets in severe rubbing operation. Qualities of material of friction surfaces are:

• It should have high coefficient of friction.
• It should have high resistance (prowear).
• It should withstand a high compression load.
• It should be chemically inert which means oil or air has no effect on them.
• It should have high heat conductivity.
• Have excellent compatibility with cast iron facing. 

Types of Clutches

There are two types of Clutches which are discussed below

1. Positive Type Clutch

It is used when there is no slip between driver and driven shaft (means both have same speed under any condition).

• Power is transmitted using interlock of jaws (or teeth).
• Used where synchronous power transmission required.
• Engagement is not possible at high speed (limited to 600 rpm).

There are two types of Positive Type Clutch:

1. Square Jaw Clutch  ↔  It transmitted power in both direction (CW or CCW).
2. Spiral Jaw Clutch  ↔  Transmit power in one direction (left or right handed). 

2. Friction Type Clutch

Power is transmitted due to friction between surfaces (clutch disk and plane surfaces).

• The driver shaft get contact with other shaft by means of compression springs.

Types of Friction Type Clutch 

a. Cone Clutch 

It consist of inner curve which is attached to the driven shaft and follow cone.

• Male cone is movable and can axially move over the driven member.
• Inner side of female cone (fixed) fits outer side of male cone.
• Slope of cone is small which gives high normal force (angle 8-15 degrees).
• Fork lever is used to dis-engage clutch.

b. Centrifugal Clutch 

It is used to disengage driven shaft at a particular speed.

• It is used engine which has trouble in starting under load.
• It has number of shoes or friction pads arranged radically in symmetric position inside a rim.

Working of Centrifugal Clutch

• Spring produce inward force to kept in original position. 
• As speed increase ↔ centrifugal force increases.
• If centrifugal force = spring force ↔ shoes start floating. 
• If spring force < centrifugal force ↔ shoes moves outward and touch the surface of drum ↔ torque is transmitted.
• As load increases, speed decreases ↔ shoes come to original position.

c. Plate or Disc Clutch

It consist of two flanges. One of them is lined with high friction material and rigidly keyed with driven shaft while the other is free to move along driven shaft due to splined connection.

• Compression springs used to push these flanges against each other.
• Torque is transmitted by friction.

Parts of Plate or Disc Clutch

1. Clutch Plate  ↔  Main component. Single thin metallic disc having both sides frictional surfaces (friction lining) . It is assembled between flywheel and flange.
2. Pressure Plate  ↔  to maintain proper contact between flywheel and clutch plate by means of spring.
3. Springs  ↔  used to move clutch plate towards the flywheel to ensure proper contact between flywheel and clutch plate.
4. Flywheel  ↔  connected to engine output shaft and used to transmit power.  

Working of Disc Clutch 

Single plate is mounted on spline clutch shafts. Flywheel is mounted on engine crankshaft. When paddle is pressed clutch shaft moves in, spring loosen shaft disengaged.

Design of Plate or Disc Clutch

References:

• Material from Class Lectures + Book named Mechanical Engineering Design by Shigley (8th Edition) + my knowledge. 
• Pics and GIF from Google Images.  
• Videos from YouTube.