Friction Clutch

Introduction

The power is transmitted by friction surfaces between driver and driven shaft. The frictional contact is made by engaging two discs having friction surface made of metal, woven, or ceramic material. The engagement of two friction surface is made by helical compressive spring.

The friction-clutch design, besides allowing for the main requirements (minimum clutch weight, simplicity, of construction, high reliability, and others), should ensure the following:

• Reliable transfer of engine torque to the transmission in all service conditions.
• Smooth starting of the automobile from rest and complete engagement of the clutch.
• Proper disengagement, i.e. complete disconnection of the engine form the transmission with guaranteed clearance between friction surfaces.
• Minimum moment of inertia of driven elements of the clutch, which permits smoother shifting of gears and reduces the wear of the friction surfaces in the synchronizer.
• Necessary heat rejection from friction surfaces.
• Safeguards the transmission against dynamic loads.
• Convenience and ease of control, which are estimated by the effort to be applied to the pedal and pedal movement on disengaging the clutch.

Clutch Frictional Material

Clutch friction linings are subjected to severe rubbing so that generation of heat in relatively short periods takes place. Therefore, the lining material should have a combination of the following properties to withstand the operating conditions.

• Relatively high coefficient of friction under entire operating conditions.
• Maintenance of friction properties during entire working life.
• Relatively high energy absorption for short periods.
• Withstanding high pressure plate compressive loads.
• Withstanding high impacts of centrifugal force during gear changing.
• Adequate shear strength to transmit engine torque.
• High level of endurance in cyclic working without effecting friction properties.
• Good compatibility with cast iron facings over the entire range of operating tempera­ture.
• A high degree of tolerance against interface contamination without affecting its friction take-up and grip characteristics.

Positive Clutch

Introduction

A clutch is a mechanical component is used to transfer power from driver shaft to driven shaft at will of operator. Clutch is very popular in automobile industry to starting of the engine from rest and disconnecting the transmission for shifting gears.

Classification

The clutches are classified as follows 

1. Positive clutches
2. Friction clutches

Positive clutches

Positive clutch transmit power by rigid connection between driver and driven shaft by means of providing jaws on it. These type of clutch is suitable for the applications where quick and simple engagement and disengagement are required. For engagement, driver and driven shaft must be unloaded condition and stationary or relatively slow synchronize speed.

Positive drive means no slip.

In Positive clutches there is no slipping during engagement.

In the absence of slip, there is no relative motion between driver and driven surfaces results no heat generation during engagement and disengagement.

Points to remember

1. Positive clutch is small in size as compare to friction clutch for same power transmitting capacity.
2. In-capable of slipping.
3. The engaging clutch surfaces interlock to produce rigid joint they are suitable for situations requiring simple and rapid disconnection.
4. The engaging surfaces are usually of jaw type.
5. The jaws may be square jaw type or spiral jaw type.
6. Designed empirically by considering compressive strength of the material used.

Advantages of Positive clutches

1. Simple in design
2. No slip occur during power transmission
3. No heat generated during operation
4. Compact in size and low cost.
5. Life is more at slow speed

Disadvantages of Positive clutches 

1. Engagement is possible at very slow synchronize speed or stationary condition.
2. Life is reduce at higher speed engagement

 Types of Positive clutches

Application of Positive Clutches

Positive cluches are suitable for slow speed apllication where higher torque is required.

• Rolling Mill
• Power press