Abstract: A new hydraulic actuator with holes in wall based on the principle of hydraulic resistance network which can push or pull the piston to the central position in case of emergency is proposed. The new actuator can be used in the thrust vector control (TVC) system of next generation launch vehicles, and realize the safe centering function after the failure of TVC system. The actuator can realize auto-centering function without electrical control system, position sensor and external force. The design principle and detailed design method are given. By hydraulic resistance network method, the working principle of system is analyzed, and the analytic solutions of pressure gain and load stiffness are obtained. A simulation model is established, and comparative studies are completed. A prototype actuator is produced, and the damage of holes to seal ring is eliminated by optimal design. By comparative experimental studies, the actual auto-centering performances of multi-holes and rectangle holes are tested. The results indicate that these two holes type both can realize the auto-centering function, the control accuracy is high, the movement is stable, and there is no oscillation around the center position. Both simulation and experimental results show that the larger area of hole is, the faster of centering speed will be. And with the increasing of load, the centering speed will be slowly while the offset to center position will be bigger. After 50 h of work, the actuator is aparted and it is proved that the holes in wall do cause some tiny damages to seal ring, however, the working life of actuator can still be guaranteed for the damage can be reduced or even eliminated by some optimal design methods such as using the multi-holes and thickened grid ring proposed in this paper.

Key words: holes in wall, hydraulic actuator, hydraulic cylinder, hydraulic resistance network, servo mechanism