Patent GB-673891-A (GB)
Title: Improvements in hydraulic servo motors
IPC: B64C13/24
Filed: 1949-06-10
Abstract: 673,891. Fluid-pressure servomotor-control systems. HOBSON, Ltd., H. M., and TYLER, S. R. June 5, 1950 [June 10, 1949], No. 15503/49. Class 135. In a hydraulic power unit of the kind in which an output member 14 is moved by a hydraulic actuator, such as a jack or a rotary type hydraulic motor, under the control of a valve 15 operated by a manually operated input member 25 so as to follow up the movements of the input member, normally closed venting valves 34, 35, one associated with each end of the actuator are provided to connect the associated end of the actuator with an exhaust outlet 36, one or other of these venting valves being opened by a member 30 directly coupled to the input member on movement of the input member in either direction from a neutral position, and a flexible connection is provided between the input member and the control valve 15 which connection yields on seizure of the control valve and permits stops 44, 45 on the input member to impart manual movement to the actuator. As applied to the control of an aircraft control surface, the output member 14 which is connected to the control surface is coupled to a cylinder 13 slidable over a piston 10 connected to a fixed structure 12. The cylinder 13 is unitary with a housing 16 for the control valve 15. The valve 15 has an extension 27 with inwardly extending abutments 127. Washers pressed apart by a spring 28 are restrained against outward movement by the abutments 127 and collars 26 on the input member 25. The input member 25 operates through a lever 30 pivoted on the housing 16 and a push rod 33, the spring-loaded exhaust valves 34, 35 adapted to connect opposite ends of the cylinder 13 with an exhaust line 36. The latter leads through a spring-loaded valve 40 normally maintained open by the supply pressure in the line 37 acting on a spring-loaded piston 38 to an exhaust outlet 41. The valve 40 contains a spring-loaded relief valve 50 which permits the escape of surplus liquid due to thermal expansion when the valve 40 is closed, a passage 52 through the valve 40 leading to the outlet 41. The stops 44, 45 on the input member 25 engage the housing 16 and so give direct manual operation if the pressure supply fails. At the same time one of the valves 34, 35 is opened positively by the rod 33 to permit liquid to leave the corresponding end of the cylinder 13, the other valve opening under suction. The valves 21, 22 prevent the cylinder 13 from being drained through the valve 15 when open. If the valve 15 seizes in an open position, reverse movement of the input member 25 opens one of the valves 34, 35 to vent the liquid being supplied to one end of the cylinder 13 and the output member 14 is moved positively through one of the stops 44, 45. Movement of the input member in the opposite direction allows one of the valves 34, 35 to close temporarily so that the uncontrolled liquid supply is effective on the corresponding end of the cylinder 13 to move the output member 14. The piston 10 contains a pressurizing piston 47. The cylinder 13 may be fixed and the piston 10 movable in which case a follow-up linkage is provided between the piston and the control valve 15. The invention is applicable to duplicated systems comprising two jacks connected in tandem or in parallel or two hydraulic motors connected to a common shaft either positively or through a differential gear.