Servomotor pressure control responsive to piston travel

摘要

An arrangement in the dropping of pressure in either chamber of a double acting booster steering servomotor is provided, such pressure drop starting at a predetermined point toward the end of travel of the servomotor piston in either direction. The invention is characterized by a respective bypass valve in each chamber, spring biased to closed position, and engageable by the piston, to be opened gradually. The piston force is exerted on the bypass valves through a respective spring so as to effect the gradual opening instead of the abrupt opening effected in the prior art. Opening of the bypass valves effects connections which shunt the servopump output to the system oil tank via a differential pressure valve as taught in Lang U.S. Pat. No. 3,878,763 to prevent strong mechanical stresses on the steering linkages at the ends of steering movement. Shunt control takes place through desirably small flow lines and bypass valves which heretofore have been found to produce undesirably abrupt operation.