Fabrication Of Electro Magnetic Brake report Download
The purpose of the present report is to design an electromagnetic brake for a given braking torque and speed, validate it experimentally, provide a conceptual design, and study its integration in automobiles.
The project plan is decomposed as follows:
– Theoretical analysis: An analytical model is derived for the electromagnetic brake and its fundamental physics are investigated. The model provides a preliminary sizing of the brake and critical information about the sensitivity to design parameters.
– Experimental validation: A test bed has been built based on specifications from numerical data calculated and data has been gathered and compared to the numerical analysis data. The objective is to validate the accuracy of numerical analysis and to explain potential divergences. This validation is necessary to establish the ability of numerical analysis to model electromagnetic brakes.
– Expansion of the concept: Several additional innovations are analyzed and incorporated in the integrated brake in order to make the concept more complete and more relevant to real world applications.
– Integration study: The use of the integrated brake in conventional and hybrid automobiles is investigated. Specifications for the respective sizing of the friction, regenerative and eddy-current brake are derived through an optimization study and the gains achieved are analyzed.
Electromagnetic brakes have been used as supplementary retardation equipment in addition to the regular friction brakes on heavy vehicles. The working principle and characteristics of electromagnetic brakes are given below.
General Principle of Brake System
The principle of braking in road vehicles involves the conversion of kinetic energy into thermal energy (heat). When stepping on the brakes, the driver commands a stopping force several times as powerful as the force that puts the car in motion and dissipates the associated kinetic energy as heat. Brakes must be able to arrest the speed of a vehicle in short periods of time regardless how fast the speed is. As a result, the brakes are required to have the ability to generating high torque and absorbing energy at extremely high rates for short periods of time. Brakes may be applied for a prolonged periods of time in some applications such as a heavy vehicle descending a long gradient at high speed. Brakes have to have the mechanism to keep the heat absorption capability for prolonged periods of time.
The working principle of the electric retarder is based on the creation of eddy currents within a metal disc rotating between two electromagnets, which 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. It was the Frenchman Raoul Sarazin who made the first vehicle application of eddy current brakes. The development of this invention began when the French company Telma, associated with Raoul Sarazin, developed and marketed several generations of electric brakes based on the functioning principles described above (Reverdin, 1974).
A typical retarder consists of stator and rotor. The stator holds 16 induction coils, energized separately in groups of four. The coils are made up of varnished aluminum wire mounded in epoxy resin. The stator assembly is supported resiliently through anti-vibration mountings on the chassis frame of the vehicle. The rotor is made up of two discs, which provide the braking force when subject to the electromagnetic influence when the coils are excited. Careful design of the fins, which are integral to the disc, permit independent cooling of the arrangement.
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