| With the continuous development of electric vehicles,pure electric vehicles have gradually become a hot spot for consumers and researchers.Pure electric vehicles are equipped with a braking energy recovery system and no longer use a vacuum booster as a brake booster,which is different from traditional internal combustion engine vehicles.At the same time,pure electric vehicles have no engine braking function on slopes.In order to make pure electric vehicles have the same or even better braking performance than traditional vehicles,it is necessary to redesign the brake assist system of pure electric vehicles,and study the braking force control of pure electric vehicles under different working conditions.In this paper,the pure electric SUV independently driven by front and rear dual motors is the research object.Aiming at the higher demand of pure electric vehicles for the brake assist system,a new type of electronic brake assist system is designed.Constructed a hydraulic brake system scheme.Combining with the characteristics of the vehicle power system parameters in this paper,a braking force distribution strategy based on the ideal I curve is formulated.A speed control strategy of the slope condition is designed,a braking force control algorithm based on model prediction is built,and a vehicle simulation model is established.The specific research content of this paper is as follows:(1)According to the structural characteristics and braking function requirements of pure electric vehicles,a fully decoupled electronic brake assist system with fail-safe is designed,which realizes the decoupling of the brake pedal and the brake master cylinder pressure,and has a traditional brake pedal feel.It can realize the functions of storage and utilization of brake pedal energy and active braking.Relevant parameter design work was carried out on the assist system,the assist motor control algorithm based on backstepping control and vector control was built,and the simulation model was established to verify the target function.(2)Based on the MATLAB/Simulink platform,the electro-hydraulic composite brake system model is built.The pressure coordination control algorithm of the electrohydraulic compound brake system is designed,and the wheel brake cylinder pressure control algorithm based on fuzzy PID adaptive control is constructed,which realizes the precise control of the brake wheel cylinder pressure.(3)According to the characteristics of the vehicle power system parameters in this article,designed a braking force distribution control strategy based on the ideal I curve.The auxiliary vehicle speed control strategy for ramp conditions was formulated,and the energy recovery vehicle speed control and the pure hydraulic braking mode under abnormal conditions were designed.Based on the idea of model prediction,a lower-level braking force control algorithm is built to control the vehicle speed and vehicle slip rate to avoid the dangerous situation of vehicle lockup on low-adhesion roads.(4)The vehicle control strategy simulation platform is built based on MATLAB/Simulink,and the front and rear axle braking force distribution strategy and the ramp assist vehicle speed control strategy formulated in this paper are simulated.The simulation results show that the front and rear axle braking force distribution is reasonable,the braking force switching process does not appear large sudden changes,the front and rear wheel slip rates are basically the same,the road adhesion can be fully utilized,the energy recovery rate during the braking process is high,and the braking force control effect good.The vehicle speed control effect is good in slope conditions,and the battery can recover more energy.In the abnormal situation where the motor cannot work,the hydraulic braking force can stabilize the vehicle speed within a certain limit,and the wheel will not lock on the low-adhesion road. |
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