Abstract: 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.

Key words: electro-hydraulic servo system, jump phenomenon, limit cycle oscillation, nonlinear vibration