线控转向系统转角反步控制算法研究

为实现商用车线控转向，设计一套新的线控转向系统架构及其转角跟踪控制算法。新的线控转向系统采用丝杠螺母结构中的丝杠直接控制纵拉杆，螺母通过带轮机构被电机驱动。对线控转向系统结构进行运动学分析，推导转向系统可变传动比，采用前轮转角为状态变量，建立线控转向系统二阶动力学模型。基于转角跟踪目标，采用反步控制算法，设计线控转向系统转角跟踪控制器，通过反馈系统线性化处理系统参数不确定和环境干扰问题，实现准确的目标转角跟踪，并建立李雅普诺夫函数，证明了采用反步控制的线控转向系统是渐进稳定的。搭建采用“丝杠螺母+带轮机构”架构的线控转向实车底盘测试台架，选取蛇形和混合工况进行控制算法验证。研究结果表明：与滑模控制算法的测试结果对比可知，反步控制算法绝对平均跟踪误差值降低了71.88%~79.57%，跟踪误差标准偏差值降低了71.32%~78.50%；线控转向系统反步控制转角跟踪算法能够减少系统收敛到原点的时间，抑制系统的抖振，提高车辆线控转向系统转角跟踪的操纵灵活性。

Backstepping Control Algorithm for Steer-by-wire Angle Tracking

To meet the steering-angle tracking requirements of commercial vehicles, a novel steer-by-wire system was developed, and the corresponding control law was designed. The steer-by-wire system uses a screw to drive the drag rod, where the nut is driven by the motor through a pulley mechanism. Considering the variable transmission ratio of the steering system, a steering-angle tracking backstepping controller was proposed for the steer-by-wire system, in which the front wheel angle is used as the state variable. Based on Lyapunov function, it was proved that the steer-by-wire system with backstepping controller is stable. A steer-by-wire system test bench with a "screw nut & pulley mechanism" architecture was constructed on the vehicle chassis. Typical serpentine and mixed cycles were selected to verify the control algorithm. It was experimentally demonstrated that the mean absolute tracking error and standard deviation of the tracking error of the backstepping controller are reduced by 71.88%-79.57% and 71.32%-78.50% compared with those of the sliding mode controller. It can be concluded that the proposed steering-angle tracking algorithm can reduce the response time, and prevent the chattering of the system. Therefore, the designed controller is a suitable solution for the angle tracking of steer-by-wire system.