中文摘要：

传统主动前轮转向系统理想变传动比曲线非光滑，会导致电机转矩波动等问题．本文基于车辆模型，通过对比分析5种拟合变传动比曲线的性质，设计光滑的拟合变传动比曲线．分析表明，改进型S函数变传动比曲线与理想变传动比曲线非常接近，并且其使电机角加速度突变最小，从而能使电机转矩的突变最小，具有最优综合性能．在MATLAB／Simulink中仿真结果验证了改进型S函数变传动比曲线的优良性能．

英文摘要：

In traditional Active Front Steering System, the ideal variable steering ratio curve has the defect of non-smooth property, thus inducing torque fluctuation of the electric motor. This paper aims at designing a smooth fitting variable steering ratio curve based on vehicle model, through a comparative anal-ysis of five different kinds of fitting variable steering ratio curves. The analysis indicates that the modified sigmoid fitting curve has the best overall performance due to its closeness to the ideal curve and mininal in-fluence on the torque fluctuation of the electric motor. Furthermore, simulation in MATLAB/Simulink validates the good property of the modified sigmoid fitting curve.