Cyclic vibration characteristics of a hydraulic free-piston engine

Cyclic vibration characteristics of a single piston hydraulic free-piston engine are investigated. Nonlinear factors of the free-piston vibration are analyzed and a nonlinear vibration model for the freepiston is presented. An approximate solution of the model is given. Vibration characteristics are analyzed and validated by the experiment. Results indicate that the single piston hydraulic free-piston engine is a self-excited vibration system with unsymmetrical restoring forces. Piston cyclic vibration is a solid selfexcited vibration and has stable limit cycles. Amplitude increases with the increase of input power and the decrease of working pressure. Under the steady amplitudes, the piston motion is dissymmetric and maximum velocity is relatively large in the expansion stroke.