Research On Lateral Instability Mechanism Analysis And In The Loop Control Strategy Of Tractor And Double-trailer Combination

Tractor and double-trailer combination has the advantages of large transportation volume,high efficiency and low cost,and has been widely used in foreign countries.With the development of logistics and transport,swap trailer transport will be the next main transport in China in the future.On the one hand,with the characteristics of body length,articulated point and high center of mass,the vehicle combination has many typical accidents such as jackknifing,swing,snaking and rollover,which lead to a great deal of traffic accidents,and hidden dangers to other vehicles on the road.On the other hand,due to the tractor and double-trailer combination has been prohibited driving on the highway currently,the research is relatively small.The corresponding evaluation index,instability mechanism and selection and analysis of various control strategies need to further study.Therefore,the research on the lateral stability and control strategy of tractor and double-trailer combination is an important issue related to the traffic safety and road utilization.The research on the instability mechanism under the typical driving conditions,the corresponding active control strategies and application effect of the vehicle combination are very important.Aiming at the instability of tractor and double-trailer combination in high-speed driving,the related foreign research institutions and universities are studied.Based on the above research,the mechanism of critical rollover instability and control strategy of snaking instability which are prone to appear in tractor-trailer combination are studied.The dynamic modeling,simulation and control strategy were used to solve the problem that the vehicle combination is prone to snaking instability.The evaluation index of the critical rollover of the vehicle combination and its rollover sequence were determined by the nonlinear dynamic model of Truck Sim construction.And the effectiveness of the active control strategy was verified by co-simulation of Truck Sim-Simulink.The specific research contents are as follows:The dynamics model of the tractor and double-trailer combination including the lateral and yaw motions,and the articulation angle between the individual vehicle units was developed.By comparing the handling stability indexes of ordinary cars,tractor and semi-trailer combination,and multi-trailer combination,the evaluation indexes of lateral stability of tractor and double-trailer combination,RWA and Off-tracking,were determined.According to the dynamic model and the evaluation index,the dynamic simulation analysis of the vehicle combination was carried out under step,single lane change and sinusoidal response respectively,and it is found that the vehicle combination prone to snaking instability in high-speed driving.Based on the evaluation index and the energy method,the mechanism and rollover sequence of each vehicle unit were simulated by Truck Sim,which is the multi-body dynamics software.By comparing the numerical values of the lateral acceleration and the tire vertical load at different vehicle speeds and the time sequence of the critical rollover,the tire vertical load can better evaluate the critical rollover sequence,and the sequence of critical rollover in each vehicle unit is obtained.According to the graph theory,the possible instability sequence of each vehicle unit was predicted.According to the energy equation,the total energy of each vehicle unit was solved by the state variables,and used for verification of each sequence of instability.The conclusion is drawn that the rollover sequence of the vehicle combination is the same as the evaluation index.In order to avoid the lateral snaking instability of tractor and double-trailer combination,active control of the rear three vehicle units was carried out according to the vehicle active torque model and active steering model.The weight of the LQR controller was optimized by the genetic algorithm(GA).The relationship between the lateral stability evaluation index RWA and the mass center sideslip angle was taken as the objective function of the fitness function of the GA,which was used to obtain the optimal active torque and the optimal active steering angle.The effects of active braking and active steering control were verified by comparing the state variables without or with the control of the vehicle combination.The comparison of response time,RWA value and sideslip angle in the two control strategies,which show that the active steering control is better to improve the snaking stability of the vehicle combination.In order to validate the control effect of the active steering of the tractor and double-trailer combination,the co-simulation software was used to control software-in-loop(SIL)by Truck Sim-Simulink.According to Ackerman steering principle,the relationship between left and right wheel steer angles of each vehicle unit during steering was determined.The LQR controller optimized by GA was used to control the linear vehicle dynamic model,and the optimal weight coefficient was obtained and had been adjusted for co-simulink control.By comparing the animation effect and the state variables of the vehicle combination without and with the control,it is verified that the active steering control could improve the snaking stability of tractor and double-trailer combination in SIL.According to the similarity model theory,the test bench for tractor-trailer combination was developed,and the gyroscope sensor,digital dynamometer and frequency converter were used to test the system.The single lane change and snake input mode test under different angles,different frequencies and different weights were carried out on the similar model of tractor and double-trailer combination.And the information of state variables was collected.By comparison,the sampling frequency and rank of the Butterworth filter are determined,and the evaluation index that the yaw rate is obtained.Then,according to the variation of yaw rate under different factors,the influence on the lateral stability of tractor-trailer combination is evaluated.It analyzed the mechanism of rollover and analysis of snake instability and in the loop control strategy,which are the important contents of lateral dynamics in multi-trailer combination.It provides an important theoretical basis and solutions in the occurrence of critical rollover,and snaking prevention of the vehicle combination.At the same time,by comparing the simulation results of active torque and active steering control strategy,it can provide reference for the selection of actual control strategy in tractor and double trailer combination.The SIL of co-simulation provides important theoretical basis for practical application.