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Draw the neat sketch of epicyclic gear train and explain how it works.

In an epicyclic gear train, the axes of the shafts, over which the gears are mounted, may move relative to a fixed axis. A simple epicyclic gear train is shown in Fig. where a gear A and the arm C have a common axis at 1 about which they can rotate. The gear B meshes with gear A and has its axis on the arm at O2, about which the gear B can rotate. If the arm is fixed, the gear train is simple and gear A can drive gear B or viceversa, but if gear A is fixed and the arm is rotated about the axis of gear A (i.e.

What is the necessity of clutch? State its types.

Necessity: A clutch is necessary for the transmission of power of shafts and machines which must be started and stopped frequently. Its application is also found in cases in which power is to be delivered to machines partially or fully loaded. The force of friction is used to start the driven shaft from rest and gradually brings it up to the proper speed without excessive slipping of the friction surfaces.

In automobiles, friction clutch is used to connect the engine to the driven shaft. It may be noted that -

Compare brakes and dynamometers (two points).

Brakes : A brake is a device by means of which artificial frictional resistance is applied to a moving machine member, in order to retard or stop the motion of a machine.

Types : Hydraulic brakes

1.Electric brakes  2.Mechanical brakes.

The brake absorbs either kinetic energy of the moving member or potential energy given up by objects being lowered by hoists, elevators etc.

The energy absorbed by brakes is dissipated in the form of heat.

Explain: (i) Uniform pressure theory. (ii) Uniform wear theory in clutches and bearing.

(i) Uniform pressure theory:
 When the mating component in clutch, bearing are new, then the contact between
surfaces may be good over the whole surface.
It means that the pressure over the rubbing surfaces is uniform distributed.
 This condition is not valid for old clutches, bearings because mating surfaces may
have uneven friction.
The condition assumes that intensity of pressure is same.
P = W/A =Constant; where, W= load, A= area
(ii) Uniform wear theory in clutches and bearings:


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