| Electromechanical brake is a main branch of brake-by-wire systems. It propels actuator by electric power to produce clamping force quickly and stably against the wheel rotor rotation. As a result, it can simplify the quantity of components of vehicle braking system greatly and be convenient for other mechanism layout. This thesis main discuss the performence of vehicle braking control based on the electromechanical brake actuator.In this paper, the response characteristics of the electromechanical brake actuator are analyzed firstly. Analyzed the dynamic behavior of EMB, the planetary gear train is simplified as an 8-degree freedom deceleration model consisting of the revolution of planetary gears and the ratation of all gears and plannet carrier. According to the force transmission route, the clamping force load is as a 2-degree freedom model with the relative motion between brake pad and caliper. Then the high order model of EMB actuator is established considering the backlashes among gear teeth, the variation of gear mesh stiffness and damping and various frictions. Further, the EMB actuator model is replaced by a fixed transmission ration and a clamping force curve depending on the dynamic displacement of brake pad.This thesis analyzes the energy distribution and transmission efficiency through considering the static friction, coulomb friction and viscous friction of EMB actuator.Secondly, the logic threshold anti-lock braking control algorithm is designed based on the EMB actuator. The road identifying utilizes the minimum deviation between effective adhesion coefficient and magic tire adhesion coefficient to determine the curent road. The vehicle speed estimation adopts wheelspeed signal with variable slop method to calculate the reference speed. The simulation result indicates that the single wheel brake algorithm is effective in single-road brake, road-transition brake and switch beteween general brake and ABS.Thirdly, the vehicle model and the observer are established to estimate the state parameters. Carried outthe dynamic analysis of vehicle, the 8-degree freedom vehicle model congsists of the rotation of four wheel, the longitudinal and lateral movement of vehicle and the yawing and rolling of vehicle. It is possible that vehicle velocitys including longitudinal velocity and lateral velocity are estimated based on the mensurability of wheelspeed, lateral acceleration and yaw velocity.According to the estimated state parameters, the vertical load of each wheel can be calculated.Finaly, the total brake force is distributied based on the proportion of the estimated vertical load. Simulation result shows that the braking performance of vehicle meets the requirments of braking laws.Furthermore, this paper analyzes four control modes of EMB actuator failure in braking process, which the simulation results of all modes meet the requirments of brake laws. The vehicle yawing control adopt fuzzy method to calculate the compensation yawing moment, then the vehicle is corrected to the desire driving path through differential braking of EMB actuators. |
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