Research Of Active Trailer Steering And Differential Braking For Tractor-semitrailer

The maneuverability of tractor-semitrailer is much more complex than that of single vehicle.Under low-speed steering conditions,the trailer of tractor-semitrailer has poor tracking ability to the trajectory of the tractor.Under high-speed conditions,tractor-semitrailer commonly exhibits problems including: yaw instability and rollover instability.In order to improve the ability of path following at low speed,high speed stability and anti-rollover ability under extreme conditions,this paper took the tractor-semitrailer as the research object.The researches on the control of active trailer steering(ATS)and differential braking(DB)were carried out respectively.Studies on the control simulation were carried out based on MATLAB/Simulink and Trucksim software.The main research contents and conclusions of the thesis are as follows:(1)The dynamic model of tractor-semitrailer was studied.Firstly,a five-degree-of-freedom(5DOF)yaw-roll vehicle model was established to describe vehicle motion based on the analysis of the force and motion of tractor-semitrailer.The main vehicle parameters of the 5DOF yaw-roll tractor-semitrailer model were obtained by calling the tractor-semitrailer model generated in Trucksim software and through parameter identification research.In order to verify the correctness of the 5DOF yaw-roll vehicle model,the dynamic responses of the 5DOF vehicle model were compared with that of nonlinear model generated in Trucksim.The results showed that the dynamic model of tractor-semitrailer is credible and can be used in the design and research of active safety controller.(2)The control strategy of low speed active trailer steering for tractor-semitrailer was researched.A shift register was used to construct the target path of the trailer rear axle center.According to the predicted deviation between the actual path and the target path,the steering angles of the trailer wheels were adjusted to reduce the deviation.Simulation of the trailer path following for the tractor-semitrailer were carried out based on the co-simulation platform combining TruckSim and Simulink.Research results showed that the designed controller not only improves the path following performance of the trailer and reduce the width of the turning channel effectively,but also improves the stability of tractor-semitrailer and reduces the abrasion of the trailer tires.(3)The control strategy of high-speed active steering for tractor-semitrailer was researched.A 5DOF vehicle model of tractor-semitrailer with active trailer steering system was established based on the analysis of the force and motion of tractor-semitrailer.On the basis of the linear quadratic regulator theory(LQR),a high-speed trailer steering controller was designed with the optimization objective of the sideslip angle at the center of gravity(CG)and lateral acceleration of the trailer.Control simulation researches were carried out on the model of tractor-semitrailer with active trailer steering built in Matlab and the model generated in Trucksim software respectively.The research results showed that the LQR controller of active trailer steering has certain effect on the linear model.But when the model is the nonlinear vehicle model in Trucksim software,it is not possible for LQR controller to determine the correct trailer wheel angle.In view of this,considering the uncertainty of tractor-semitrailer,a robust controller for active trailer steering was designed based on robust control theory.The effectiveness of the controller was verified by numerical experiments under single lane change and double lane change maneuvers through TruckSim and Simulink co-simulation platform.The simulation results showed that the designed robust controller can effectively improve the roll stability of tractor-semitrailer and the ability of path following for the model considering uncertainties.(4)The control strategy of differential braking for tractor-semitrailer was researched.According to the actual yaw rate and expected yaw rate of the tractor and the trailer,the state of the tractor-semitrailer was judged.The differential braking controller was designed based on the PID control principle to decide additional yaw moments.Then through the analysis of stability of the tractor-semitrailer,the brake wheels were selected reasonably and the brake moment was applied on the wheels to keep the actual rate to the expected yaw rate in a certain range.Finally,the simulations of tractor-semitrailer with differential braking controller under extreme conditions were studied.The simulation results showed that the yaw moment can be directly formed by differential braking,which can effectively improve the stability of tractor-semitrailer and reduce the speed of vehicle.