Patent GB-918144-A (GB)
Title: Improvements in electro-hydraulic control servo-mechanisms
Inventor: COLHOUN ROBERT SYDNEY
IPC: G05D1/00
Filed: 1959-07-28
Abstract: 918,144. Fluid-pressure servomotor control systems. SHORT BROS. & HARLAND Ltd. July 1, 1960 [July 28, 1959], No. 25886/59. Class 135. [Also in Group XXXIII] An electro-hydraulic servo-system comprises a common input control member and a common output member and at least three independent channels for the transmission of signals from the input control member to the output member, each channel comprising a motor adapted to be controlled by signals developed by movement of the input control member and coupled to operate an hydraulic servo-valve controlling the supply of hydraulic fluid to an hydraulic servomotor mechanically coupled to drive said common output member, means for comparing the position of the servo valve in each of the channels with the position of the hydraulic valve in each of a plurality of the other channels, and warning means responsive to a disparity between the valve positions to indicate the identity of a defective channel. A pilot's control column operates means (not shown) to generate electrical signals fed to input terminals, Fig. 1, and thence to a high-gain amplifier 12 to control a torque motor 13 mechanically connected through shaft 14 to operate a spool valve 15 of an hydraulic servomotor 16 which operates, through shaft 17, an aircraft control surface. Shaft 17 drives the wiper of a potentiometer 18 to provide a feedback signal over line 19 to amplifier 12 and there is also a feedback path between motor 13 and amplifier 12 comprising a shaft 20 which drives a pick-off device 21, the output of which is fed over line 22 to amplifier 12. A further output from pick-off 21 is fed over contact 24 to fault detection apparatus to be described. A datum control voltage is applied to motor 13 over an input 23. In the embodiment three control channels are provided and signals from the control column are applied in parallel to the inputs of three amplifiers and the output shafts of the three servomotors are mechanically connected to the drive mechanism for the control surface. As indicated in Fig. 2 there are three pick-off devices 21, 25 and 26, the output signals from which are amplified at 27, 28 and 29 respectively to provide balanced outputs for energization of three relays A, B and C. Relay A has two pairs of windings a1, a2 and a3, a4 and two sets of contacts A1 and A2. Relays B and C are similarly constructed and the senses in which the windings of the relays are energized are represented in Fig. 2 by arrows. The contacts of the relays A, B and C are associated, in combinations taken two at a time, with three warning circuits 30, 31 and 32 which give warning of faults in the respective channel. Circuit 30 comprises a lamp 33 connected to a D.C. supply through contacts 1 of an electromechanical relay RL1, the winding of which is connected to the D.C. supply through contacts A1 and C2 of the relays A and C and two normally closed contacts 211 and 3<SP>11</SP> associated with warning circuits 31 and 32. The relay has two further contacts 1<SP>1</SP> and 1<SP>11</SP> also associated respectively with circuits 31 and 32 and these circuits have their contacts similarly crossconnected so that if the signal from say pick-off device 25 differs in amplitude in relation to the signals from pick-offs 21 and 26, relays A and B are operated, thus closing their associated contacts to energize relay RL2. This closes contacts 2 to light lamp 34 and opens contacts 2<SP>1</SP> and 2<SP>11</SP> to prevent subsequent energization of the relays RL1 and RL3. A connection 35 is provided in each warning circuit so that the relay remains energized through contact 2 if contacts B<SP>1</SP> and A<SP>2</SP> subsequently open due to the fault in the channel being intermittent. The warning means may in addition isolate automatically a faulty channel by switching off the power supply to that channel and simultaneously de-clutching the defective servomotor.