Patent GB-837858-A (GB)
Title: Improvements in integrated hydraulic power actuator
IPC: G05D1/00
Filed: 1957-11-01
Abstract: 837,858. Automatic steering control systems. GENERAL ELECTRIC CO. Nov. 1, 1957 [Nov. 5, 1956 (2)], No. 34160/57. Class 38 (4). [Also in Group XXIX] A combined manual and automatic control system for operating a control surface comprising a power actuator having a housing, a power piston movable therein, connections to the surface to transmit motion of the power piston, a power valve spool controlling the supply of hydraulic fluid to the actuator, and manual and automatic position input means, including an autopilot, is characterized in that movement of the valve spool is controlled by a linkage operatively connected to the valve spool, and both the manual and automatic position input means are operatively coupled to the linkage for simultaneously introducing separate position control input signals thereto to control the valve spool so that displacement of the latter relative to the actuator housing will determine the positioning of the control surface, whereby only the autopilot control reflects upon the manual control. In the arrangement shown an aircraft control surface 10 is moved by a power piston 24 controlled by a pilot valve 32, which may be operated through a follow-up linkage 52, 53, 54 by: (a) the autopilot 16 operating solenoids S 1 , S 2  controlling a pilot valve 44 and piston 42 connected by a pivot A to link 52; (b) a transient damper 18 operating solenoids S 3 , S 4  controlling a pilot valve 36 and piston 38 connected by a pivot D to link 54; or (c) a pilot's control lever 14 connected to piston 42. The system may operate in the following modes: (a) Manual operation without damping.- Switch 35 is moved to position " M," a solenoid S 6  and valve 34 cutting off the supply of pressure liquid to a locking mechanism 40 whereby a spring-loaded plunger is caused to engage and lock damper piston 38, and a by-pass 50 is opened to allow free movement of autopilot piston 42. Displacement of the pilot's lever 14 is transmitted through piston 42 and linkage 52, 53, 54 to valve spool 32. (b) Autopilot operation.-Switch 35 is moved to position "A," a solenoid S 6  and valve 48 admitting pressure liquid to control valve 44. The system operates in a similar manner to mode (a), piston 42 being operated by valve 44 and a follow-up synchro F 2  being operative. Control lever 14 moves in correspondence with piston 42. (c) Damper operation.-Switch 35 is moved to pisition "D," energizing solenoid S 6  and opening valve 34 to disengage the locking plunger from piston 38. Solenoids S 3'  S 4  control valve 36 and piston 38 operates valve spool 32 through link 54. A follow-up synchro F 1  is operative under these conditions. (d) Fully automatic operation.-With switch 35 in the position shown, the outputs from pistons 38, 42 are combined, pivot D being fixed for autopilot inputs, and pivot A for damper inputs. In a second embodiment, Fig. 2 (not shown), the piston 38 is integral with a moving sleeve (56) for valve spool 32, and the linkage 52, 53, 54 is replaced by a single lever (58). In a further embodiment, Fig. 3 (not shown), the power actuator comprises a fixed piston and moving cylinder, and the signals from the damper amplifier 41 are fed into a canceller amplifier (152) by which the damping motions are prevented from being fed to the control lever 14 under fully automatic control conditions.