Research On Planning And Control Algorithm For Emergency Collision Avoidance Of Tractor Semi-Trailer

Emergency braking technologies for tractor semi-trailer has become mature and already commercialized.However,there are few studies on the steering-based or steering-braking-based collision avoidance technology for tractor semi-trailer,though this method can extremely shorten the collision avoidance distance under medium and high-speed conditions.An important reason for this situation is that tractor semi-trailer is prone to rollover and jackknifing during emergency steering conditions.If these instability patterns cannot be handled well,it will be difficult to realize the steering collision avoidance,or the steering-braking collision avoidance.Aiming at the problem that the tractor semi-trailer is prone to instability when steering to avoid collision,the method of emergency steering-based and steering-brake-based to avoid collision is studied by optimal control.Firstly,a 7 degrees-of-freedom dynamics model which can accurately describe the dynamic characteristics of tractor semi-trailer is established and verified by simulation.The instability mode and mechanism of tractor semi-trailer are analyzed and the tire slip angle and the lateral acceleration of the vehicle is choose as the stability constraints of trajectory planning and nonlinear model predictive control.Secondly,an analysis of the collision avoidance limit of semi-trailer trains is carried out to fully explore the collision avoidance potential of vehicles.On the basis of ensuring the stability of the vehicle,the collision avoidance limit of the vehicle steering-based and braking-steering-based collision avoidance is calculated based on the optimal control algorithm.When calculating the steering collision avoidance limit,the phenomenon of trailer tracking-off is used,and the required constraints are simplified at the same time.According to the analysis of the collision avoidance limit of different roads adhesion coefficients and load conditions,it is found that steering-based and steering-braking-based to avoid collisions is less sensitive to road adhesion coefficients and load changes.Therefore,a decision planning algorithm that comprehensively considers the advantages of steering-braking-based collision avoidance is proposed,and simulation verification is carried out.The results show that the algorithm can handle more extreme dangerous conditions,and the limit of steering-braking-based collision avoidance is half less than the braking collision avoidance limit under medium-high speed conditions.Thirdly,aiming at the characteristic that tractor semi-trailer is prone to instability when steering,a nonlinear model predictive controller(NMPC)that integrated steering and braking is designed,which can directly consider the actuator and state constraints.The effectiveness of the proposed planning control algorithm is proved by simulation.Considering that NMPC is difficult to run in real time,a linear time-varying model predictive control(LTV-MPC)is designed.By comparing with nonlinear model predictive control,we can find that its control precision decreases slightly,but it meets the requirement of trajectory tracking accuracy and can run in real time.Finally,the proposed planning and control algorithm is verified in a real vehicle.The results show that the proposed planning trajectory can improve the collision avoidance limit of the vehicle under the condition of ensuring the stable driving of the vehicle,and the proposed control algorithm can accurately track the planned trajectory.Instability of tractor semi-trailer often leads to serious accidents,to realize the vision of zero casualties,this paper broadens the handling ability of tractor semi-trailer to deal with dangerous scenarios from theory and practice.