Comparison of the Braking Performance of Electromechanical and Hydraulic ABS Systems

Abstract

The benefits potentially available by replacing conventional hydraulic ABS brake systems with electromechanical brake-by-wire systems (EMB) are extensive and have been well documented. They include increased functionality, packaging and design flexibility, reduced assembly costs, and elimination of hydraulic fluids [1, 2]. A characteristic of most ABS systems is a sequence of discontinuous build-hold-dump pressure cycles, whereas EMB systems will allow continuous control of brake torque. In this paper, the antilock performance of an EMB using a continuous brake torque control strategy is compared against that of a current state-of-the-art hydraulic ABS system. The comparison was performed using a half-car model developed in the Simulink environment. The hydraulic system characteristics were identified from ABS test data on a recent production vehicle and the simulated ABS logic was also validated using this data. A simple model of the dynamics of an EMB actuator with clamp force control was developed, and validated against limited test results from a prototype EMB system. A continuous gain-scheduled PID wheel slip controller was developed for the EMB to replace the conventional ABS logic. Brake system performances were compared using an Antilock Performance Index (API). The results of the comparison indicate that an EMB with continuous slip control has the potential to perform better than a conventional ABS system, provided a suitably robust wheel slip controller and algorithm for determining the appropriate target slip are available.