Abstract: The free piston motion of a single piston hydraulic free-piston engine is not restricted by any mechanical linkages. To protect the mechanical structure from damaging, a hydraulic throttle control method for free piston extreme position of the single piston hydraulic free-piston engine is investigated. The fundamentals of the hydraulic throttle control method for free piston extreme position are analyzed. The mathematic model of the hydraulic control circuit has been built up. The working characteristics and the contributed factors of the throttle control method are analyzed based on experiments and simulations. The results indicate that the throttle effect of the check valve, the dump port throttle and the oil bulk modulus should be considered in the throttle control method for free piston extreme position of the single piston hydraulic free-piston engine. The first pressure peak in the compress chamber of expansion stroke is caused by the check valve. The second pressure peak is caused by the dump port throttle and the oil bulk modulus. The duration of the high pressure wave after the first pressure peak is reduced by increasing the dump port flow area. The damage of the free piston and the engine body is effetely prevented by the dump port throttle and the oil bulk modulus.

Key words: Free-piston engines, Limit position, Position control, Throttle controls