中文摘要：

转向轮转向角是车辆自主导航系统关键的控制参数，三位四通比例电磁换向阀实现闭环电控液压转向被广泛采用。由于地面对转向轮的回正力作用，电磁阀阀芯由中位滑至侧位实现转向控制动作的起始瞬间，转向轮容易产生“回摆”现象，难以通过转向角闭环控制消除，影响转向轮伺服控制系统精度。为此，首先对转向“回摆”问题进行动力学分析，得出电磁阀开通瞬间转向轮受力不平衡是造成拖拉机转向轮产生回摆的主要原因；接着提出一种在液压回路中添加平衡阀来消除转向轮“回摆”的方法，分析了其工作原理及调试方法，通过实车试验进行对比验证。结果表明：添加平衡阀维持了电磁换向阀开通瞬间转向轮受力平衡，较好地克服了转向轮回摆问题，提高了拖拉机转向轮转向角闭环控制精度，系统＆#177;10°阶跃响应静态闭环跟踪测试超调量12．6％，平均峰值时间0．8s，且都在1．5s内达到期望值（此设定期望值偏差是0．5°）。

英文摘要：

Precision steering control is key to automatic navigation control for agricultural vehicles where normally 3-posi-tion 4-way directional solenoid valves are adopted to achieve electro-hydraulically controlled steering control.Due to the counter-torque from the ground the tractor’ s front wheels are liable to short-time jerk the moment the valve is opened before following the valve’ s control, which cannot be avoided by the closed-loop control and may cause severe interfer-ences to the precision steering control.First, this paper conducts a in-depth dynamics analysis of the cause of this jerk action and concludes that it is caused by the imbalance in the wheels’ torque.Then, this paper thus proposes addition of two balancing valves to the original system to establish back pressure in the cylinder to maintain torque balance of the front wheels to avoid this jerk action when the solenoid valve operates, analyzes its working principle and debugging method, and verified through real car comparison test.The rest results show that this steering system with back-pressure function maintains steering wheel force balance when solenoid valve is opening, to better overcome the jerk problem, aching smooth steering operation and improve the wheel steering loop control precision of the tractor.The system’ s over-shoot of ＆#177;10°step response closed-loop tracking test is 12.6%, the average peak time 0.8s, and reach expectations and stable in 1 .5 s （ the setting expectations deviation is 0 .5 °in here ） .