Research On Motor Brake Control Strategy Of Distributed Drive Electric Vehicle

As the increasingly growing of energy crisis and environment crisis, new energy vehicles have been widely accepted as the future of the automotive industry. Distributed drive electric vehicle, a kind of electric vehicle driven by several motors distributed in 4 wheels, has better dynamic performance than ordinary electric or hybrid vehicles driven by one or two axles, so it has a promising prospect. During its braking procedure, not only the hydraulic braking system but also the motor braking system is involved, and it is necessary to collaborate both of these two systems to make sure of the braking stability. Meanwhile, all the motor braking force on 4 wheels can be controlled separately. This special c haracter gives motor braking system the potential of helping maintain the vehicle stability with an electric differential braking.To increase the braking stability and handling stability of distributed drive electric vehicle, a motor braking control strategy has been studied based on the vehicle dynamic theories. In this study, the structures of the distributed drive electric vehicle’s driving and braking system was analyzed. The main parameters of driving system were designed, and the systems’ dynamic models were built.The motor braking control strategy for ordinary braking condition was raised. This strategy distributed the front and rear axles’ braking force with constant proportion, which was settled according to ideal front and rear braking force distribution and ECE regulation, as well as maximizing the usage of motor braking. It could guarantee the braking performance and braking stability under the regular braking condition.A motor braking direct yaw moment control strategy was raised. This strat egy could recognize the vehicle’s steering conditions, including under steering, over steering and even lateral slide, and calculate required direct yaw moment based on the fuzzy control theory. By conducting extra motor braking torque on the target wheels, the differential braking could rectify vehicle’s steering state, and keep it in good control.A combined simulation platform was built with Car Sim and Simulink. Following the constructions of national standards and international standards, simulations were carried out to verify the motor braking control strategy. According to the results, the motor braking control strategy for ordinary braking condition could help the distributed drive electric vehicle meet the requirements of braking stability, braking distance and deceleration. When the vehicle is under steering or over steering, the motor braking direct yaw moment control strategy could adjust the motor braking torque and hydraulic braking torque in time, and the electric differential braking could always rectify vehicle’s unstable motion. The simulation results showed that the control strategy was feasible.