Multi-Steering Control Method And Simulation Of Heavy Vehicle

With the need of construction and production development, heavy multi-axle vehicles have found an increasingly wide application, and multi-axle steering performance directly influences the vehicle's maneuvering stability, active safety and economic efficiency, how to improve the steering performance is one of the significant technologies for heavy multi-axle vehicles. So far, there are quite a few open foreign literatures about multi-axle steering technology, while domestic literatures mainly focus on the optimization of vehicle steering linkage's geometric dimensions and locations, with a few on the research of multi-axle steering strategy, those literatures usually tend to analyze multi-axle vehicle's steering characteristics and propose multi-axle steering control strategy on the basis of simplified linear model, meanwhile neglect the drive's subjective feedback role. Considering the above factors, this peper makes a further more research on the multi-axle steering control strategy.The efficiency of multi-axle steering control strategy directly depends on the accuracy of the multi-axle vehicle's mathematic model, in this paper we utilize from 2DOF to 3DOF model, from linear to nonlinear model, from open-loop model to driver-vehicle closed-loop model to study the multi-axle steering control strategy.On the basis of existing theories, this paper derives linear 3DOF dynamic model for multi-axle vehicle according to Lagrange Equation, through proper transformation, it designs proportional and optimal controller by using output feedback theory that belongs to linear quadratic optimal control theory, and compares the motion of a three-axle vehicle under three different control methods by simulink, the three control methods are proportional and optimal control, proportional control, and front wheel steering control method respectively. The results show that proportional and optimal control method is better than the other two methods, and during adjusting the weighting factors in feedback controller design, we can see the sideslip angle and yaw rate performance index are mutual restrained, when sideslip angle approaches zero, the absolute value of yaw rate becomes large, and vice versa. Therefore, a compromise between the two performance indexes is taken in the proportional and optimal control method to ensure the optimal overall performance.Multi-axle vehicle linear model only applies to small perturbation driving conditions around vehicle equilibrium state, when vehicle drives under extreme circumstances such as at low-adhesion road with high speed, tire cornering characteristic is no longer linear, but with strong nonlinear characteristic, and the linear vehicle model can't describe real vehicle's motion precisely, the controller designed based on the linear vehicle model becomes invalid. Therefore, this paper derives nonlinear 2DOF dynamic model for multi-axle vehicle, the model adopts MF-tyre model, and also considers the reassignment of vertical load between right and left tire, then verifies the nonlinear model's feasibility through comparing linear model and nonlinear model's step response under different driving circumstances. Based on the nonlinear model, this paper designs nonlinear controller by tracking ideal vehicle model, and compares multi-axle steering combined with direct yaw moment control method with zero sideslip angle control method, front wheel steering control method, the results demonstrate that multi-axle steering combined with direct yaw moment control method can control vehicle's motion efficiently, make vehicle with better maneuvering stability.However, considering vehicle itself is a complex system, the dynamic models established previously can't describe the actual physical system accurately, therefore we need to design a robust controller which makes all possible closed-loop systems internal stable and meets performance exceptions. This paper introduces structure single valueμtheory which can overcome uncertainly to design controller, then transforms the vehicle model to unified dynamic model which would be proper forμanalysis and synthesis by LFTs, and two-degree-freedom controller design method was proposed for the multi-axle steering vehicle, this design method on one hand can increase degree of freedom of control system, on the other hand reduce the difficulty of designing controller. The simulation results show that the velocity variations are compensated by feedforward controller independently, and the perturbations introduced by variations of road adhesion, tire cornering stiffness etc are restrained by feedback controller, and the system achieves zero sideslip angle and ideal yaw rate preferably. In conclusion, the control method can assure the good tracing performance and robustness for the vehicle system.In order to further more investigate the multi-axle vehicle's maneuvering stability, this paper derives vehicle-driver closed-loop dynamic model, analyzes and calculates the forward-looking time and coefficients of correction part in the closed-loop system, and judges the closed-loop system's stability by using eigenvalue criterion and stability margin criterion, then discusses the effects of different forward-looking time and different velocity on closed-loop system stability. At last compares closed-loop system's motion using zero sideslip angel control method with front wheel steering control method through simulation under two typical driving circumstances:double lane change text and s-shape text.