Abstract: In order to improve the accuracy of the nonlinear response of the angular transmission ratio of the steer-by-wire vehicle at high speed, the objective function of steer-by-wire were analyzed, and the calculation process of variable transmission ratio was deduced. The effects of constant yaw velocity gain, constant lateral acceleration gain, vehicle speed and steering wheel input on the mapping results of front wheel angle were discussed, and the variable transmission ratio strategy based on fuzzy inference system was established. Aiming at the deficiency of ideal transmission ratio in vehicle stability control, the method of front wheel compensation angle is used to make the final decision of front wheel angle. In the verification process, the vehicle mathematical model of steer by-wire was built, typical steering input conditions were selected, and the overall system design was co-simulated and compared with the dynamic simulation software. Experimental results show that the designed transmission ratio strategy can meet the requirements of steering wheel indicators,reduce yaw speed and centroid sideshow angle, and effectively reduce the operating burden of the driver. The active steering strategy based on improved sliding mode control reduces overshoot by 9% compared with saturation function exponential reaching law sliding mode control, which improves vehicle driving safety.

Key words: Steer-by-wire system; Variable transmission ratio design; Sliding mode control; Active front steering; Variable exponential approach

摘要： 为了提高线控转向车辆在高速工况下角传动比非线性响应的准确性，分析线控转向的 功能指标，推导可变传动比的计算过程，讨论固定横摆角速度增益、固定侧向加速度增益、 车速、方向盘输入对前轮转角映射结果的影响，建立基于模糊推理系统的可变传动比策略， 针对理想传动比在车辆稳定性控制层面上的不足，采用前轮补偿角的方法进行最终前轮转角 的决策。在验证过程中，搭建线控转向整车数学模型，选取典型转向输入工况，结合动力学 仿真软件对总体系统设计进行联合仿真对比分析。实验结果分析证明，设计后的传动比策略 可以实现方向盘指标需求，降低横摆角速度和质心侧偏角，有效减轻驾驶员的操作负荷，基 于改进滑模控制的主动转向策略相比饱和函数指数趋近律滑模控制，超调量降低了 9%，提高 汽车行驶安全。

关键词: 线控转向系统；可变传动比设计；滑模控制；主动前轮转向；变指数趋近律