电液伺服系统是非线性动力学系统，在工作过程中容易出现非线性振动、噪声、冲击和爬行等异常现象，而且诱因不易确定，严重影响系统的稳定性。根据非线性动力学原理，建立电液伺服系统的非线性动力学模型。通过理论研究，探索非线性液压弹簧力和非线性摩擦力等非线性因素对系统动力学特性的影响规律。指出非线性液压弹簧力作用可以用Duffing方程描述，非线性摩擦力作用可以用Van Der Pol方程描述。用研究非线性动力学系统的有效方法：时间历程、频闪采样、功率谱等，对实测信号进行深入分析，多方位揭示电液伺服系统非线性振动的机理及诱因。结果表明，非线性液压弹簧力引起的“跳跃现象”和非线性摩擦力引起的极限环型振荡的共同作用是导致系统发生非线性振动的一个主要诱因，值得关注。

The electro-hydraulic servo system(EHSS) is a nonlinear dynamics system. When it is in the work, the anomalies are easy to happen, such as nonlinear vibration, noise, impact, crawl and so on. These anomalies seriously affect the stability of EHSS. Miserably, the incentives are not easy to determine. Based on the principle of the nonlinear dynamics, the nonlinear dynamical model of EHSS is established. Then, the influence laws of nonlinear hydraulic spring force(NHSF) and nonlinear friction(NF) etc on dynamic characteristics of EHSS are explored through theoretical study. Two conclusions are put forward. The effect of NHSF can be described by Duffing equation, and the effect of NF can be described by Van Der Pol equation. Moreover, the measured signals are deeply analyzed by means of the methods, such as time-course, stroboscopic sampling, power spectrum and so on. Then, the mechanism and incentive of nonlinear vibration of EHSS are revealed. Results indicated that the nonlinear vibration of the EHSS is mainly due to the interaction of the “jump phenomenon” caused by NHSF and the limit cycle oscillation caused by NF.