Coordinated Control under Transitional Conditions in Hybrid Braking of Electric Vehicle 2018-01-1869

In the hybrid brake system of electric vehicle, due to the limitation of the motor braking force when the motor is at high speed and the failure of the regenerative braking force when the motor is at low speed, there are three transitional conditions in hybrid braking: the hydraulic brake system intervenes the braking, the hydraulic brake system withdraws the braking and the regenerative braking force withdraws the braking. Due to the response speed of the hydraulic system is slower than that of the motor, there is a large braking impact (the derivative of braking deceleration) in the transitional conditions of hybrid braking, which deteriorates the smoothness and comfort in braking. Aiming at the impact caused by the poor cooperation between the hydraulic braking force and the motor braking force, a coordinated strategy of double closed-loop feedback and motor force correction is proposed in this paper. The double closed-loop feedback strategy relies on the motor force to compensate the tracking error of hydraulic pressure of the hydraulic brake system. The purpose of the motor force correction strategy is to allow the motor to consistently have the compensation capability under all transitional conditions. Simulation and hardware in-loop test were carried out based on Integrated-electro-hydraulic brake system (I-EHB). The HIL test results show that the proposed strategy can greatly reduce the impact degree when the two kinds of braking force switch. The impact degree of hydraulic braking force intervention decreased from the initial 28.26 m/s³ to 18.39 m/s³, decreased by 34.9%, the impact degree of regenerative braking withdrawal reduced from the initial −60.94 m/s³ to 16.84 m/s³, reduced by 72.3%, which improved the comfort in vehicle braking and provided a reference for the practical application of the strategy.