Research On Multi-Axle Steering Control Strategy For Heavy Semi-trailer Vehicle

Heavy semi-trailer vehicles are widely used in road transportation because they have many advantages such as large transportation volume and high transportation efficiency.However,due to the coupling between the tractor and the trailer through the fifth wheel coupling,the traditional heavy semi-trailer vehicle has inferior path following performance and severe tire wear when turning at low speeds,and it is prone to major traffic accidents due to lateral instability at high speed.The multi-axle steering system has the feature that the tire of the trailer unit can be steered,which can not only improve the tire wear of heavy semi-trailer vehicle,but also reduce the sweeping road width when turning to improve maneuverability,and this can also prevent traffic jams to a certain extent.In addition,the reasonable active control of the tire steering angle can also reduce rearward amplification and improve the lateral stability of the heavy semi-trailer vehicle when driving at high speed.Based on the above advantages,the multi-axle steering system has received widespread attention in the heavy-duty vehicle industry,and how to effectively study the control strategy of the multi-axle steering system to improve the steering performance of the vehicle is a hotspot and core issue of general concern.In view of the problems of severe tire wear at low speeds and inferior lateral stability at high speeds,this article relies on the National Natural Science Foundation of China(51575224)and the Jilin Provincial Science and Technology Development Program(20160101275JC)to consult domestic and foreign literature,and then in-depth analyze the performance requirements of the heavy semi-trailer vehicle such as economy,maneuverability and handling stability,and finally study the multi-axle steering control strategy of the whole vehicle according to the characteristics of the multi-axle steering system,which is to improve the path following ability and tire wear of the trailer unit,taking into account low-speed maneuverability and high-speed lateral stability.Firstly,a combination method of dual model and steady state value is used to identify the stiffness parameters of the simplified vehicle model to improve the control effect of the heavy semi-trailer vehicle;Secondly,the stiffness identification three-dimensional map is used to change the key parameters of the vehicle in real time according to the vehicle state to improve the accuracy of the simplified model;Then,the fuzzy steering control strategy and the variable proportional steering control strategy are proposed to improve the path following performance and tire wear;Finally,the linear quadratic regulator control method is used to strengthen the high-speed lateral stability as the main goal,and the genetic algorithm which overcomes the inefficiency of the traditional adjustment parameter is introduced to optimize the weight coefficient to achieve the optimal control effect.This article mainly conducts research work in the following three aspects:(1)A simplified model of heavy semi-trailer vehicle suitable for vehicle nonlinear characteristics was established,including three-degree-of-freedom vehicle model and five-degree-of-freedom vehicle model.Considering the non-linear characteristics of tire cornering stiffness and body roll stiffness changing with the driving state of the vehicle,a method combining the two vehicle models and the steady-state value was proposed to identify the three dimensional map of stiffness identification at different vehicle speeds and steering wheel angles.In order to verify the accuracy of the simplified vehicle model,an on-line simulation of variable speed and steering conditions was performed and compared with the TruckSim vehicle model,and the results show that the simplified vehicle model can accurately reflect the dynamic characteristics of the vehicle.(2)Two types of low-speed maneuverability control strategies for heavy semi-trailer vehicle,fuzzy steering control strategy and variable proportional steering control strategy,are proposed and compared.The fuzzy steering control strategy uses fuzzy logic theory and trailer steering angle allocation method to determine the steering angle of each tire.The variable proportion steering control strategy first establishes the steering geometric relationship of each tire of the trailer according to the multi-axle steering kinematics model,and uses the trajectory difference to establish offline three dimensional map of variable proportional adjustment parameter and delayed turning time,and then precisely adjust each tire steering angle.In order to verify the effectiveness of the two control strategies,simulations were carried out under the conditions of fixed vehicle speed changing steering angle and fixed steering angle changing vehicle speed,and comparison was made with traditional heavy semi-trailer to verify the effectiveness of the proposed low-speed control strategy.(3)Aiming at the problem that the high-speed driving is prone to lateral instability,a high-speed lateral stability control strategy is proposed based on the linear quadratic regulator.In order to reflect the impact of the actual road on the driver,driver models are introduced to realize the closed-loop simulation of heavy semi-trailer vehicle.Taking the vehicle state related to lateral stability as the linear quadratic regulator performance index,the optimal performance index function is established to solve the optimal control amount,and the tire steering angles of the trailer unit are allocated based on the tire steering angle geometric relationship.In order to overcome the problems of low efficiency and non-global optimization of traditional empirical methods,genetic algorithm was introduced to optimize the weight coefficients.Finally,the effectiveness of the high-speed stability control strategy is verified by high-speed single lane change and double lane change motion simulations.