Dead center control of hydraulic free-piston engines

To increase the operation stability of a single piston hydraulic free-piston engine, the dead center control methods of the piston are analyzed. The fundamentals of the piston position control of the single piston hydraulic free-piston engine are investigated theoretically. The contributing factors of the dead center control are analyzed. Based on the simulation and experimental results, the factors of the top dead center (TDC) accurate control, the control strategy for the bottom dead center (BDC) accurate control and its terminal position limit methods are investigated. The results indicate that the main contributing factors of TDC control are the stroke and the initial compression position of the compression stroke. The transferred energy and the dynamics process around BDC of the piston need to be considered in the BDC accurate control strategy. A combinatorial method, i.e. the combination of the heat energy method based on the hydraulic throttle effect and the potential energy method based on the hydraulic fuel bulk elastic modulus, is given for the BDC limiting position control.