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Brakes, Clutches and Couplings

BRANCH-MECHANICAL ENGG.

SEMESTER-6^TH SEM

NAME-Er.MANAS RANJAN MOHANTA

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Purpose

A clutch is designed with the following requirements

Allow the vehicle to come to a stop while the transmission remains in gear
Allow the driver to smoothly take off from a dead stop
Allow the driver to smoothly change gears
Must not slip under heavy loads and full engine power

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Types of clutch

1) Positive clutches

When positive drive is required then positive clutches are used. The simplest type of positive clutch is the jaw clutch which transmits the torque from one shaft to another shaft through interlocking jaws.

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Single plate clutch

It consists of various elements

pressure plate,
friction plate (clutch plate),
driving shaft,
splined driven shaft,
splined hub,
brass bush etc.

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It consists of various elements, such as pressure plate, friction plate (clutch plate), driving shaft, splined driven shaft, splined hub, brass bush etc.

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Friction plate has a ring of friction material on either side. Friction plate is attached to splined hub which is free to slide axially on splined driven shaft and rotates along with driven shaft.
The spring is placed between pressure plate and cover. Brass bush is press fitted inside the pressure plate so that it can rotate freely on driven shaft.

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Multi plate clutch

It consists of two sets of plates the driving plates and driven plates arranged alternately, driving shaft, spring, splined driven shaft etc.

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It consists of more than one driving as well as driven plates. So the number of pair of contacting surfaces is more than two.

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Cone clutch

It consists of driving shaft, splined driven shaft, outer cone (cup), inner cone (cone), helical compression spring etc. The outer cone (cup) is keyed to the driving shaft and inner cone is free to slide axially on the splined driven shaft.

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To engage the clutch axial force is provided by a helical compression spring. Clutch is disengaged by means of fork fitted in shifting collar or groove on the outer surface of cone, leather, cork or asbestos is used as friction lining.

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Centrifugal clutch

It is works on the principle of centrifugal force. Centrifugal force is increases with the increase in speed.

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It consists of spider having radial guide, sliding shoes, helical tension springs co-axial drum
The spider having four equally spaced radial guides is keyed to the driving shaft. Sliding shoes can slide radially in guides.
The sliding shoes are covered with frictional material from outer side. These shoes are held against spider on driving shaft by helical tension springs and all these assembly is enclosed in coaxial drum which is mounted on driven shaft.

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��Coupling

Shafts are mostly available up to 7 meter length due to transport difficulty. To get a greater length, it is necessary to joint two or more pieces of the shaft using coupling.
Purposes of Coupling used are,
To connect shafts of motor and generator which are manufactured separately and to provide for disconnection for repairs.
To reduce the transmission of shock loads from one shaft to another.
To allow misalignment of the shaft or to introduce mechanical flexibility.
To introduce protection against overloads.

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Types of couplings

(1) Rigid coupling

It is used to connect two shafts which are perfectly in axial alignment. These couplings do not allow any relative rotation between the two shafts.
There are basic three types of rigid coupling as follows,
Sleeve or muff coupling
Clamp or split muff or compression coupling

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(2) Sleeve or Muff coupling

Construction
This is the simplest type of rigid coupling. It is made from cast iron and very simple to design and manufacture. It consists of a hollow cylinder (muff) whose inner diameter is the same as diameter of the shaft.

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The hollow cylinder (muff) is fitted over the ends of the two shafts with the help of taper sunk key. A key and sleeve (muff) useful to transmit rower from one shaft to the other shaft. It has no projecting parts.

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3) Split muff coupling (clamp coupling)

Construction

In this coupling, the muff or sleeve is made into two halves parts of cast iron and they are join together by bolts as shown in Figure. Both the halves are held together by means of M.S stud OR nut/Bolts.

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There are basic two types,
(1) Unprotected type flange coupling
The projected portion of one of the flange and corresponding recess on other flange are help to bring the shafts into line and to maintain alignment.

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(2) Protected type flange coupling
In order to prevent catching clothes of workmen in coupling the flange is provided with a shroud which shelters the bolt head & nuts . This coupling is called protected type flange coupling.

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(2) Flexible couplings

This coupling is used to protect the driving and driven machine members against harmful effects produce due to misalignment of shafts, vibration, and sudden shock load or shaft expansion.
There are basic three types of flexible coupling as follows,
Bushed pin type flange coupling

Oldham coupling
Universal coupling

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a) Bush pin type flange coupling

This is a modified form of protected type flange coupling

This type of coupling has a pins and it work as a coupling bolts. The rubber or leather bushes are used over the pins. The coupling is having two halves are dissimilar in construction. The pins are rigidly fastened by nuts to one of the flange and kept loose in the other flange.

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(b) Oldham’s coupling

Construction
It consists of two flanges A and B with slots and a central floating disc as shown in fig.
Use
Connecting two parallel shafts but not in alignment, and their axes are at small distance apart.

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Construction
It consists of two similar forks keyed on the ends of the two shafts. These two forks are assembled to a central block by pin. A central block having two arms at right angle to each other.

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Brakes

Brake is a device by means of which an artificial frictional resistance is applied to a moving body in order to retard or stop the motion of a body.
During braking process, the brake absorbs either kinetic energy or potential energy or both by an object.

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(a) Single block or shoe brake

Construction
It consists of blocks which are pressed against the surface of a rotating drum by means of lever.

The friction between friction lining on the block and drum retards the rotation of the drum. The block or shoe is made up of softer material than the rim of the drum.

The material of the block for light and slow vehicles is wood and rubber and for heavy and fast vehicles it is cast steel.

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b) Pivoted block brake

Construction
A pivoted block brake is shown in figure 11.15. Unlike single block brake, in this the shoe is pivoted to lever to get uniform wear.

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This load produces the bending of the shaft. It can be prevented by using a double block or shoe brake having two blocks on the two sides of the drum.

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(B) Band brake

Construction
It consists of a rope, belt or flexible steel band lined with frictional material which is wrapped partly round the drum.
Working
When band is pressed against the external surface of drum, the frictional force between drum and band will induce braking torque on the drum.
There are two types of band brake,
(a) Simple band brake
(b) Differential band brake

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(a) Simple band brake

Construction
In this brake one end of the band is attached at the fulcrum of the lever while the other end is at a distance 'b' from fulcrum.

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(b) Differential band brake

Construction
In a differential band brake, neither end of the band is attached to the fulcrum of the lever. The two ends of band are attached to the two points on opposite side of the fulcrum as shown in figure

The lever AOC is pivoted at fulcrum '0' and two ends of band are attached at points A and B.

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Construction
It consists of number of wooden blocks fixed inside a flexible steel band.

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It consists of two semicircular shoes S₁and S₂ pivoted at the fixed fulcrum O₁ and O₂ respectively. The outer surfaces of the shoes are lined with friction material

One end of the shoe is pivoted at fulcrum while the other end is subjected to the actuating force. The actuating force on both the shoes is applied by hydraulic cylinder or cam mechanism.