GB1068361A - Improvements in or relating to hydraulic actuators - Google Patents

Abstract

1,068,361. Fluid-pressure servomotor systems. ELLIOTT BROTHERS (LONDON) Ltd. July 24, 1964 [June 24, 1963], No.25031/63. Heading G3P. An electro-hydraulic system suitable for the actuation of an aircraft control surface 49 has four parallel control channels between a pilot's control column 52 and a lever 46 which actuates a control valve 79 for a hydraulic cylinder 80 operating the control surface and having a feedback lever 78. Each channel terminates in a piston 17, 18, 19, 20 connected by a piston rod 35, 40, 39, 41 with crossheads 38, 42 which are connected together by a tube 43, and any of the pistons may be disconnected automatically on failure of its associated hydraulic or electrical system. The control column, which has a "feel" device 101, actuates four transmitters, e.g. magslips, 56, 57, 58, 59 feeding an amplifier unit 60, and the corresponding output signals from the unit 60 are applied to respective torque motors 63, 73, 74, 75 operating valves 65 which control the individual pistons 17, 18, 19, 20. A separate hydraulic supply system 29, 94, 95, 96 is provided for each piston and the arrangement is such that as, e.g. the pistons 17, 19 are subject to pressure in their chambers 66 the other two pistons are connected to exhaust so that all the pistons assist each other to move the tube 43 in one direction against centering springs 81, 82. The outer sides of the pistons, of smaller effective area, are continuously subject to the hydraulic supply pressures. Electrical resistances 48 provide feedback signals to the unit 60 which also has an input from an auto-stabilizer (not shown). Should the hydraulic supply to one of the pistons fail, a pair of auxiliary pistons 27, 28 normally subject to pressure through holes 23, 24 are no longer effective to hold a flange 32 of an intermediate tube 31 in fixed relationship to the piston so that when the other three pistons are deflected the crosshead assembly moves the piston rod and intermediate tube 31 of the failed piston until balls 36 are moved beyond an internal annulus 37 to release the piston rod from its connection with the piston. The relative movement between the tube 43 and the failed piston will operate a switch 86, 87, 88 or 89 to energize a warning device. After a second piston has failed, the pilot should operate a lever 97 to render operative a connection between the control column 52 and a rod 100 so that the lever 46 is operated by the column. If then a third piston fails the remaining piston will be unable to overcome the springs 81, 82, the tube 43 will consequently be centralized, and control will be effected solely through the link 100. An electrical failure in the control of one of the pistons will result in the other pistons overcoming the hydraulic loading of the auxiliary pistons of the failed piston, this also resulting in release of the locking balls 36.