复合工况下四轮驱动电动汽车操纵稳定性控制

Handling and Stability Control of Four-wheel Drive Electric Vehicle under Combined Slip Conditions

设计一个考虑车辆侧纵向耦合的模型预测控制器(Model predictive control,MPC)用于提升四轮驱动电动汽车在复合工况下的操纵性和稳定性。基于传统UniTire轮胎模型,推导面向控制器设计的复合工况UniTire轮胎模型解析表达式;基于前后轮侧偏角相平面提出一种新的车辆稳定性评价标准,通过前后轮侧偏角的位置到坐标原点的距离判断车辆的稳定性,给出定量的稳定性指标;采用MPC控制器结构将车辆操纵性控制、稳定性控制以及四轮滑移率约束作为目标函数,采用复合工况UniTire轮胎模型表达式和双轨车辆模型构建预测模型,并且通过稳定指标和轮胎滑移率实时调整各个目标的权重以达到最优的控制效果;通过Simulink-CarSim联合仿真和硬件在环(HiL)测试对算法进行验证,结果表明,该控制器能够根据车辆稳定性指标动态调节跟踪权重,有效提升车辆的操纵性和稳定性。并且由于复合UniTire轮胎模型的使用,极限工况下控制器决策的四轮力矩更小,有效地抑制轮胎滑移率的增加。

A model predictive controller(MPC)considering combined slip conditions is designed to improve the handling and stability of four-wheel drive electric vehicles.Firstly,the UniTire model is simplified and deduced,and the analytical expressions of the combined UniTire model which can be used for the controller design are obtained.Secondly,based on the analysis of the tire slip angle phase plane,a new vehicle stability evaluation standard is proposed.The vehicle stability can be judged by the distance from the position of the front and rear tire slip angles to the coordinate origin,and the quantitative stability index can be obtained.Then,the MPC structure is used to take the vehicle handling control,stability control and four-wheel slip ratio constrains as the objective function.Combined Uni Tire model and the double-track vehicle model are used as the prediction model,and the weight of each objective is adjusted in real time through the stability index and tire slip ratio to achieve the optimal control effect.Finally,the algorithm is verified by Simulink-CarSim simulation and hardware in the loop(Hi L)test.The results show that the controller can dynamically adjust the tracking weight according to the vehicle stability index,and improve the handling and stability of the vehicle.Due to the application of the combined UniTire model,the four-wheel torque decided by the controller under the harsh condition is smaller,which effectively inhibits the increase of tire slip ratio.