Cone clutch

Cone Clutch
A cone clutch, as shown in Fig. 5 , was extensively used in automobiles, but now-a-days it has been replaced completely by the disc clutch. It consists of one pair of friction surface only. In a cone clutch, the driver is keyed to the driving shaft by a sunk key and has an inside conical surface or face which exactly fits into the outside conical surface of the driven. The driven member resting on the feather key in the driven shaft, may be shifted along the shaft by a forked lever provided at B, in order to engage the clutch by bringing the two conical surfaces in contact. Due to the frictional resistance set up at this contact surface, the torque is transmitted from one shaft to another. In some cases, a spring is placed around the driven shaft in contact with the hub of the driven. This spring holds the clutch faces in contact and maintains the pressure between them, and the forked lever is used only for disengagement of the clutch. The contact surfaces of the clutch may be metal to metal contact, but more often the driven member is lined with some material like wood, leather, cork or asbestos etc. The material of the clutch faces (i.e. contact surfaces) depends upon the allowable normal pressure and the coefficient of friction.

Design of a Cone Clutch
Consider a pair of friction surfaces of a cone clutch as shown in Fig.6. A little consideration will show that the area of contact of a pair of friction surface is a frustum of a cone.

Let pn = Intensity of pressure with which the conical friction surfaces are held together (i.e. normal pressure between the contact surfaces),
r1 = Outer radius of friction surface, r2 = Inner radius of friction surface,
R = Mean radius of friction surface = (r2 +r1)/2
? = Semi-angle of the cone (also called face angle of the cone) or angle of the friction surface with the axis of the clutch,
? = Coefficient of friction between the contact surfaces, and
b = Width of the friction surfaces (also known as face width or cone face).
Consider a small ring of radius r and thickness dr as shown in Fig.6 .
Let dl is the length of ring of the friction surface, such that,
dl = dr cosec ?
? Area of ring = 2? r. dl = 2? r.dr cosec ?
We shall now consider the following two cases :
1. When there is a uniform pressure, and
2. When there is a uniform wear.
1. Considering uniform pressure We know that the normal force acting on the ring,
?Wn = Normal pressure × Area of ring = pn × 2? r.dr cosec ?
the axial force acting on the ring, ?W = Horizontal component of ?Wn (i.e. in the direction of W)
= ?Wn × sin ? = pn × 2? r.dr cosec ? × sin ? = 2? × pn.r.dr
? Total axial load transmitted to the clutch or the axial spring force required,


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