| The development of electrification and intelligence of automobiles had put forward higher requirements for the braking system of automobiles.For clean-energy vehicles,the vacuum booster braking system required a vacuum pump to provide a vacuum source,which made the braking system too large,and traditional braking system couldn’t be used to coordinate regenerative brake and friction brake.For intelligent automobile,the vacuum booster braking system couldn’t always guarantee the active brake function.Therefore,the development of new electric power hydraulic booster braking system and its control was an inevitable choice for future automobiles.Relying on the horizontal project "Development of Electric Power Hydraulic Booster Braking System" by the research group and the enterprise.This thesis focused on the structure and modeling of electric power hydraulic booster braking system,control strategy of booster braking system,and researched on booster emergency brake assist system.The main research contents were as follows:(1)In view of the target-matched vehicle and the definition of the braking system function,the structure of the electric power hydraulic booster braking system was proposed and its working principle was introduced.The brake pedal model,hydraulic system model and electric power hydraulic booster model were built.The hydraulic system model mainly included the brake master cylinder model and brake wheel cylinder model,The electric power hydraulic booster model mainly included transmission mechanism model,reaction disc model,booster motor model and friction model.(2)The control strategy of the electric power hydraulic booster braking system was proposed and mainly included three parts: signal filtering,target displacement design and motor servo control.Kalman filtering was used in the signal filtering process to get better control input.By analyzing the working principle of the reaction disk in the vacuum booster,the displacement difference between the pedal push rod and the booster valve body was designed.Used the logic threshold method to distinguish the brake pedal status,For booster motor,three-loop PID and speed feedforward control algorithms were used.Under the environment of Matlab/Simulink and AMESim,the co-simulation model of electric power hydraulic booster braking system was built to verify the above control strategy.(3)Based on NXP’s automotive-grade single-chip MPC5744,the displacement difference sensor and braking system friction test bench were built.Analyzed of the accuracy of displacement difference sensors.Identified the parameters of the Pol-Ind friction model.In friction experiments,particle swarm optimization was used to determine the friction model parameters.(4)The emergency braking assist system of the braking system was designed.Recognized the driver’s braking intention to control the two assist modes of emergency brake and normal brake,and realized the emergency braking assist function to solve the problem of the driver’s excessive braking distance caused by insufficient pedal force in an emergency.The data obtained through the co-simulation model of Simulink and AMESim used the hidden Markov model to identify the braking intention.The recognition accuracy of normal brake and emergency brake intention was high,and based on the vehicle’s driving environment,the emergency brake assist system was simulated and verified. |
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