| Automobiles are developing rapidly in the direction of light weight,electrification,intelligence,networking and sharing,which also puts forward new challenges and higher requirements for the automobile braking system.The application of traditional vacuum boosters in future vehicles is greatly restricted,electric brake booster systems have become the optimal choice for automobile brake systems.This paper relies on the school enterprise cooperation project "theoretical design scheme of electric brake booster",takes an electric brake booster system developed by the research group as the research object,mainly focusing on the nonlinear friction existing in the system,and carries out the research on friction force compensation control.The main research contents are as follows:(1)According to the functional requirements,the electric brake booster system is designed,the main structural components of the system are introduced,including the brushless DC motor,mechanical transmission mechanism,hydraulic system,etc.The mechanical transmission mechanism includes two-stage gear reducer,trapezoidal screw,booster valve body and reaction plate.The kinematic equation model and friction model of each part of the system are established,and the simulation model of reaction disk and hydraulic system are built in AMEsim software.(2)A update Pol-Ind friction model is proposed for the discontinuity of friction state switching in the standard Pol-Ind friction model.The parameters of the friction model are identified step by step based on the experimental data.Among them,the static parameters of the model are identified by least square method and simulated annealing particle swarm optimization algorithm,and the dynamic parameters are identified by using the characteristics of the model.(3)A three loop PID controller of BLDCM is built,and the position tracking error feedback control is used to reduce the influence of friction and inertia.Then,on the basis of feedback control,for friction and inertia interference,the friction feed-forward and speed acceleration feed-forward control modules are introduced to eliminate the adverse effects of friction on the system and improve the position tracking accuracy of the system.Finally,in order to further improve the control accuracy and robustness of the system,the modeling error caused by the external environment and the uncertainty of the system is considered,and the adaptive sliding mode controller of the system friction is derived.(4)The simulation analysis of friction compensation controller is carried out.To verify the feasibility of the friction compensation controller,the simulation model of the electric brake assist system is built in Matlab/Simulink.The output response characteristics of the system with step signal,sine signal and trapezoid wave input are analyzed.The simulation results are shown that the composite control strategy of feedforward + PID control and adaptive sliding mode control can achieve great compensation control effect.Among them,the adaptive sliding mode controller has faster response speed and position tracking accuracy,the rise time of step response is about 0.024 s,and the position tracking error of the output response of sine signal and trapezoid wave signal is reduced to micron level,which is more in line with the requirements of fast response and accurate pressure building of electric brake assist system. |
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