FRICTIONLESS ELECTROMAGNETIC BRAKING SYSTEM

BY:AMAR KUMAR

AJIT KUMARAKSHAT RAJ

Contents…. IntroductionWorking PrincipleAdvantages & DisadvantagesApplicationsSummary

INTRODUCTIONElectromagnetic brakes operate electrically,

but transmit torque mechanically. This is why they used to be referred to as electro-mechanical brakes.

Electromagnetic brakes work in a relatively cool condition and satisfy all the energy requirements of braking at high speeds, completely without the use of friction

INTRODUCTION(cont..)All of the torque comes from the magnetic

attraction and coefficient of friction between the steel of the armature and the steel of the brake field.

Braking action is made by varying the strength of the magnetic field.

if the brake was required to have an extended time to stop or slip time, a low coefficient material can be used. Conversely, if the brake was required to have a slightly higher torque (mostly for low RPM applications), a high coefficient friction material could be used.

A electromagnetic brake

WORKING PRINCIPLE

The working principle of the electric retarder is based on the creation of eddy currents within a metal disc rotating between two electromagnets.

This sets up a force opposing the rotation of the disc.

If the electromagnet is not energized, the rotation of the disc is free and accelerates uniformly under the action of the weight to which its shaft is connected.

When the electromagnet is energized, the rotation of the disc is retarded and the energy absorbed appears as heating of the disc.

If the current exciting the electromagnet is varied by a rheostat, the braking torque varies in direct proportion to the value of the current.

A typical retarder consists of stator and rotor. The stator holds 16 induction coils, energized separately in groups of four.

The rotor is made up of two discs, which provide the braking force when subject to the electromagnetic influence when the coils are excited.

Energization The energization of the retarder is operated

by a hand control mounted on the steering column of the vehicle.

This control has five positions: the first is “off”, and the four remaining positions increase the braking power in sequence.

This hand-control system can be replaced by an automatic type that can operate mechanically through the brake pedal.

Thermal DynamicsThermal stability of the electromagnetic

brakes is achieved by means of the convection and radiation of the heat energy at high temperature.

The value of the energy dissipated by the fan can be calculated by the following expression:

The electromagnetic brakes has excellent heat dissipation efficiency owing to the high temperature of the surface of the disc which is being cooled

and also because the flow of air through the centrifugal fan is very rapid.

Therefore, the curie temperature of the disc material could never been reached

It uses electromagnetic force and not mechanical friction

Fully resettable

Can be activated at will via electrical signal

Low maintenance

Operates at any rotational speed

Light weight

Advantages. . .

Disadvantages. . . Braking force diminishes as speed diminishes

with no ability to hold the load in position at standstill.

That could be considered to be a safety issue, but it really means that friction braking may need to be used as well.

These brakes can only be used where the infrastructure has been modified to accept them.

APPLICATIONSIt is used as a stopping mechanism in trains.

It is also used in the smooth breaking and functioning of roller coasters and such fast moving machines.

Summary With all the advantages of electromagnetic brakes over friction brakes, they have been widely used on heavy vehicles where the ‘brake fading’ problem is serious. The same concept is being developed for application on lighter vehicles.

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