Research On Vehicle Braking Control Strategy For Complex Road Environments

With the development trend of intelligent,electrified and networked vehicles,the requirements for intelligent braking of vehicles are gradually increasing.In this paper,in order to further improve the safety and comfort of vehicle braking,we study the intelligent vehicle longitudinal braking control under complex environmental conditions,which focuses on automatic emergency braking system and electric power-assisted braking system.In the automatic emergency braking system,a more accurate and effective road identification algorithm is proposed,and the ABS system and the safe distance model are optimized to improve the collision avoidance strategy of the automatic emergency braking system.In the electric power-assisted braking system,the control algorithm of the power-assisted motor is optimized,and the physical modeling method based on AMESim is proposed to improve the structural framework of the electric power-assisted braking system.Finally,the coordinated control strategy of automatic emergency braking system and electric power-assisted braking system is proposed with remarkable effect.Details are shown as follows:1.Aiming at the problem of road information identification of automatic emergency braking system,this paper proposes a road identification algorithm considering the range of vehicle optimal slip rate under different road conditions.The vehicle longitudinal dynamics model is established,and the peak adhesion coefficient of the pavement is obtained based on the table look-up method and the weighting method,while the optimal slip rate range for each level of pavement is obtained by dividing the pavement class.In addition,a safe vehicle distance model considering vehicle and road parameters is proposed in combination with comfort requirements.The optimal slip rate factor is also added to the ABS control logic to determine the vehicle braking control mode in order to improve the control strategy of the vehicle automatic emergency braking system.The above algorithm is verified by building a co-simulation model of emergency braking system based on Simulink,AMESim and Carsim.The results show that the identification accuracy of the road identification algorithm in this paper can reach more than 95%,which meets the identification accuracy and response requirements of automatic emergency braking system.The maximum lateral deflection of the vehicle underμ-split road conditions is only 0.056m,and the slip rate under docking road conditions is within the best range of 0.1-0.2,which meets the braking performance of the vehicle based on the automatic emergency braking system onμ-split road and docking road.At the same time,the test based on C-NCAP standard shows that the automatic emergency braking strategy in this paper has good collision avoidance capability.2.In order to realize the composite coordinated braking of hydraulic brake and electric brake,this paper designs the control strategy of permanent magnet synchronous motor based on three closed-loop control to improve the electric power-assisted braking system.The motor-assist physical module and hydraulic system module are established based on AMESim,and the motor-assist algorithm model is built in Simulink to test the braking performance of the system under different vehicle speed,road surface,slope and wind speed conditions.The experimental results show that the system meets the GB 7528-2017 road test testing standards,which include a safe braking distance of less than 100 meters under high-speed conditions,a full average deceleration rate higher than 6m/s~2 under medium-speed conditions,and a car that can avoid pedestrian collisions under low-speed conditions,verifying the accuracy and effectiveness of the electric power-assisted braking system in this paper.3.When the automatic emergency braking system and electric power-assisted braking system work simultaneously,the ABS module dynamically adjusts the wheel cylinder pressure,resulting in fluctuations in the master cylinder pressure under the electric power-assisted braking system and a continuous high pressure situation.In order to avoid damage to the booster mechanism as well as to further improve the braking efficiency,considering that the master cylinder pressure is directly affected by the brake master cylinder push rod position and the booster motor,this paper designs a master cylinder push rod coordinated following control strategy by optimizing the permanent magnet synchronous motor control algorithm,which corrects the pressure on the basis of the push rod displacement to ensure that the master cylinder pressure is maintained in a reasonable range.Simulation results show that the coordinated algorithm optimally controls master cylinder pressure and wheel cylinder pressure to ensure that the vehicle brakes at the optimal slip rate,verifying the effectiveness of the coordinated control algorithm,which improves vehicle braking safety while also improving the comfort of the vehicle.