| Compared with traditional two-axle single-unit vehicles,tractor-semitrailer use a combination of tractors and semi-trailers,connected through the traction points.During the braking process,the movements of the tractor and the semi-trailer are coupled and interact with each other,which is more complicated and difficult to predict.In this paper,the research status of the braking control methods of Tractor-Semitrailer at home and abroad is analyzed,and then proposes a brake force distribution control strategy of Tractor-Semitrailer based on optimal distribution of slip rates.First of all,in order to provide a feasible braking force control method,a theoretical analysis of the braking vehicle model is carried out to establish a simplified vehicle non-linear model of single-wheel and monorail vehicle trains.The linearized model is obtained by performing linearization at the equilibrium points of the two simplified vehicle models.Which can use the Lyapunov stability judgment method to analyze the stability of the linearized vehicle model,then can obtained the conclusion of the range of the slip ratio when the system is stable and the influence of the vehicle parameters(such as speed and normal load)on the system stability.Secondly,in order to improve the braking performance and lateral stability during tractor-semitrailer braking,the objective function of the weighted sum of slip ratios of each axis is established,with considering the interaction between the tractor and the trailer,then the optimization brake force distribution strategy based on slip ratio is proposed.Since the objective function involves the longitudinal forces of the axles of the tractor-semitrailer,the extended Kalman filter method is used to estimate the tire forces of each axle.The braking force of the tractor and the trailer is compared in real time to adjust the weight coefficient in the objective function to each axis.The minimum value of the sum of weighted sums of the migration rates is the target,resulting in an optimized target slip rate.The PID control braking force distribution is used to achieve the desired slip ratio,and the braking force between the tractor front axle,the rear axle and the trailer axle of the distribution tractor is optimized.The optimized distribution scheme was verified and analyzed by Matlab/Simulink an TruckSim co-simulation platform.Based on the estimated tire force,the pavement adhesion coefficient was estimated in real time based on the forgetting factor least-squares method,and the adhesion of dry and wet road surfaces was tested with braking performance under both straight and curve conditions.The results show that the proposed brake force optimal distribution strategy can significantly improve vehicle braking performance and lateral stability under different braking conditions. |
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