Modeling and control of electromagnetic brakes for enhanced braking capabilities for automated highway systems

In automatic highway systems, a faster response and a robust braking system are crucial part of the overall automatic control of the vehicle. This paper describes electromagnetic brakes as a supplementary system for regular friction brakes. This system provides better response time for emergency situations, and in general keeps the friction brake working longer and safer. A modified mathematical model for electromagnetic brakes is proposed to describe their static characteristics (angular speed versus brake torque). The performance of the modified mathematical model is better than the other three models available in the literature. To control the brakes, a robust sliding mode controller is designed to maintain the wheel slip at a given value. Simulations show that the controller designed is capable of controlling the vehicle with parameter deviations and disturbances . INTRODUCTION The principle of braking in road vehicles involves the conversion of kinetic energy into heat. This high energy conversion demands a large rate of heat dissipation so that stable performance can be maintained. By using the electromagnetic brake as supplementary retardation equipment, the friction brakes can be used less frequently and therefore never reach high temperatures. The brake linings can have a longer life span, and the potential “brake fade” problem can be avoided. In this paper, a new mathematical model for electromagnetic brakes is proposed to describe their static characteristics (angular speed versus brake torque). The performance of the new mathematical model is better than the other three models available in the literature in a least-square sense. A robust sliding mode controller is designed that achieves wheel-slip control for vehicle motion. The objective of this brake control system is to keep the wheel slip at an ideal value so that the tire can still generate lateral and steering forces as well as shorter stopping distances. The system shows the nonlinearities and uncertainties. Hence, a nonlinear control strategy based on sliding mode, which is a standard approach to tackle the parametric and modeling uncertainties of a nonlinear system, is chosen for slip control. Simulation will be performed to confirm the effectiveness of the controller. GENERAL PRINCIPLE OF ELECTROMAGNETIC BRAKES The conventional friction brake can absorb and convert enormous energy values, but only on the condition that the temperature of the friction contact materials is controlled. Electromagnetic brakes work in a relatively cool condition and satisfy all the energy requirements of braking at high speeds. Electromagnetic brakes can be applied separately completely without the use of friction brakes. Due to their specific method of installation, electromagnetic brakes can avoid problems that friction brakes face as we mentioned before. Typically, electromagnetic brakes have been mounted in the transmission line of vehicles [1,5]. The propeller shaft is divided and fitted with a sliding universal joint and is connected to the coupling flange on the brake. The brake is fitted into the chassis of the vehicle by means of anti-vibration mounting. The working principle of the electric retarder is based on the creation of eddy currents within a metal disc rotating between two electromagnets, 391 0-7803-4269-0/97/S10.00