Lateral stability region conservativeness estimation and torque distribution for FWIA electric vehicle steering

Estimation of the lateral stability region and torque distribution on steering is very important to improve stability in lateral handling for all wheel drive electric vehicles.Based on the built-nonlinear vehicle dynamic model,the lateral stability region of the vehicle related to steering is estimated using Lyapunov function.We obtained stable equilibrium points of non-straight driving according to the estimated lateral stability region and also reconstructed the Lyapunov function matrix,which proved that the closed-loop system composed of yaw rate and lateral velocity is satisfied with negative definite property.In addition,the designed controller dynamically allocates the drive torque in terms of the vertical load and slip rate of the four wheels.The simulation results show that the estimated lateral stability region and the designed controller are satisfactory in handling stability performance against different roads and vehicle parameters.

Design and test of flexible chassis automatic tracking steering system

In order to develop an innovative omnidirectional non-homonymic flexible chassis(FC),the four-wheel steering control method of FC was designed by a new concept called off-centered steering(OCS)and the automatic tracking steering system was analyzed.Novelty of this wheel concept lies in the non-conventional positioning of the steering axis and wheel axis.Additionally,the steering axis of steerable wheel was motorized with an on/off electrometrical brake to overcome a hyper-motorization issue inherent to the wheel’s geometrical properties and hold the steering position.Based on the off-centered steering characteristics of FC,the Wheatstone bridge was applied in the steering control system.The bridge resistances are used to track target steering angles and the actual steering angle,respectively.The output voltage of the bridge is exploited to adjust the wheel’s speed so that steering and automatic tracking could be achieved.Experiments at different speeds,loadings,and target steering angles were conducted.Results showed that the chassis can indeed be controlled independently and its steering range is from-90°to 90°,which indicated the automatic tracking steering system was effective.The electromagnetic lock(EL)can significantly improve the stability of the chassis and reduce the vibration.Loading has no significant effect on the accuracy of the steering angle and the time it takes to complete steering tasks.The time taken to complete a forward steering task showed a linear relationship with the required angles,but was independent of rotation speed;for backward steering,time was related to both target angles and rotation speed.The results presented in this research may provide a reference for the steering control strategies of the four-wheel individual drive and four-wheel(4WID/4WIS)vehicle in the future.

四轮转向电动汽车车架的设计与有限元分析

现有电动汽车底盘普遍为在传统汽车的基础上进行的改进,不能很好的适应电动汽车特有的结构,为更好的实现四轮转向的功能,重新设计了适合四轮转向电动汽车的车架。应用三维软件SolidWorks,通过整车虚拟装配确定了合理的四轮转向电动汽车的车架结构,进而建立了车架的三维模型。运用有限元分析理论,将模型导入Ansys Workbench软件后,建立了车架的有限元模型,对车架在弯曲和扭转工况下的静态结构性能进行了分析,得出相应工况下的应力和应变大小;还进行了模态分析,避免了共振。在满足强度和刚度的条件下对车架结构进行了改进,并通过焊接加工得到了适合四轮转向电动汽车的车架,对以后电动汽车底盘的改进设计提供了参考。