分布式驱动电动汽车转向工况转矩分配控制研究

针对分布式驱动车辆转向工况在低速下期望提高转向机动性能，高速下期望保证行驶稳定性的需求，充分考虑转向行驶内外侧车轮的转向关系以及车辆动力学，制定了适应车速变化的四轮转矩分配策略，建立了四轮轮毂电机驱动模型以及二自由度参考模型。为了改善分布式驱动转向机动性能，建立自抗扰控制器调整内外侧车轮转矩，形成合理的转速差，减小转向半径，以提高转向机动性；对于高速转向行驶稳定性的需求，通过二次规划方法优化分配各车轮驱动力矩，分析轮胎纵横向附着裕度建立目标函数，并加入附加横摆力矩和路面附着力的限制，进行车轮驱动转矩的在线优化分配，提高车辆转向行驶的稳定性；另外为避免2种控制模式转换时驱动转矩突变，根据车速和稳定性参数制定模糊规则决策2种模式的协调系数，保证2种控制模式的平滑过渡。基于CarSim和MATLAB/Simulink进行联合仿真，并搭建硬件在环平台进行试验，对所提出的方法进行验证。结果表明：在低速转向工况下，提出的分配策略能够调节内外侧车轮产生差速效果，与转矩平均分配的策略相比，转向半径有所减小，提高车辆机动性；高速转向工况下，分配策略能够保证车辆稳定转向，与未考虑稳定性控制的分配策略相比，能更好地跟踪目标轨迹，且横摆角速度控制在参考横摆角速度附近，证明了所提控制策略的有效性。

Torque Distribution in Distributed Drive Electric Vehicles Under Steering Conditions

Regarding the steering conditions of distributed drive vehicles the steering maneuverability is expected to improve at low speeds, driving stability is ensured at high speeds, and the steering relationship between the inner and outer wheels and vehicle dynamics are fully considered. In this study, a four-wheel torque distribution strategy that adapts to varying speeds was developed. In addition, a four-wheel hub motor-driven vehicle model and a 2DOF reference model were established. To improve the maneuverability of distributed drive steering, an active disturbance rejection controller was set up to adjust the torque of the inner and outer wheels to form a reasonable speed difference and reduce the steering radius to improve steering maneuverability. To ensure high-speed steering-based driving stability, a quadratic-programming method was used to optimize the distribution of the driving torque of each wheel, analyze the tire longitudinal and lateral adhesion margins to establish an objective function, and add the restrictions of additional yaw moment and road adhesion to optimize the distribution of wheel drive torque to improve the vehicle's steering stability. In addition, to avoid sudden changes in the driving torque when switching between the two control modes (to ensure smooth transition between the modes), a fuzzy rule was used to determine the coordination coefficients of the two modes based on vehicle speed and stability parameters. CarSim and MATLAB/Simulink were used for joint simulation, and a hardware-in-the-loop platform was set up in the experiments to verify the proposed method. The results show that under low-speed steering conditions, the proposed allocation strategy can adjust the inner and outer wheels to produce a differential effect. Compared with the average torque distribution strategy, the steering radius is reduced and the vehicle's maneuverability is improved. Under high-speed steering conditions, the distribution strategy can ensure stable steering of the vehicle. However, compared with the distribution strategy without stability control, the proposed strategy can better track the target trajectory, and the yaw rate is controlled near the reference yaw rate, thus proving the effectiveness of the proposed control strategy.