Four-Wheel Electric Braking System Configuration With New Braking Torque Distribution Strategy for Improving Energy Recovery Efficiency

In this paper, a four-wheel electric braking system configuration is proposed for electric vehicles and its braking performance is compared with other conventional braking system configurations at different initial vehicle speeds and different road conditions in the case of emergency braking. In order to make the vehicle wheel slip ratio track the optimal slip ratio, a control method that combines sliding mode control and extended state observer is designed. Neural-network sliding mode control is designed for the driver's braking command tracking in the normal braking condition. In order to improve braking energy recovery, a new braking torque distribution strategy is developed for the proposed four-wheel electric braking system based on the motor characteristics and vehicle dynamics. The designed braking torque distribution strategy is able to improve the energy recovery by adjusting the braking torque distribution ratio between the front and rear wheel braking torque while tracking the driver's braking command. Numerical simulations have been conducted and the simulation results show that although the braking performance of the four-wheel electric braking system is worse than the conventional braking system at high initial braking speed, it still is able to meet the vehicle braking international standards and simplifies the braking system structure and saves cost. The proposed braking torque distribution strategy can improve energy recovery efficiency compared with the average allocation strategy and deceleration based allocation strategy. The simulation results show that the four-wheel electric braking system configuration with the proposed braking torque distribution strategy is suitable for low to medium speed light electric vehicles.