GB805139A - Improvements in hydraulic servo-systems - Google Patents

Abstract

805,139. Hydraulic control systems on aircraft. LEDUCE, R. March 29,1956 [March 30, 1955], No. 9976/56. Class 4. An hydraulic control system on aircraft for operating servo-motors 7, 8 comprises one or more stand-by systems which are automatically brought into operation upon a failure or loss in pressure in a main system. The main hydraulic circuit consists of a reservoir 3, a pump 1, an accumulator 5, parallel feed lines 9, 10 and return lines 17, 19. The stand-by circuit consists of a reservoir 4, a pump 2, an accumulator 6, a branched feed line 15 and return lines 16, 18. The motors 7 and 8 have collector chambers 11 and 12 respectively receiving the main and stand-by feed lines 9, 10 and 15. The stand-by feed is controlled in response to main feed pressure by a single feed selector device 14 common to both servo-motors while a separate return selector device 20 controls the disposal of liquid returned from each servomotor to the reservoir 3 via lines 17, 19 or to the reservoir 4 via lines 16, 18. Selector 14 comprises a cylinder housing a differential area piston, Fig. 1a (not shown) the face of the piston of larger area being subjected to liquid pressure from line 9 and the face of smaller area being subjected to pressure from accumulator 6. The accumulators 5 and 6 are maintained at the same pressure and this ensures that the piston in selector 14 holds shut a needle valve between accumulator 6 and line 15. Should pressure in the main circuit fail, the piston will unseat the needle valve to keep the servo-motors 7 and 8 supplied with pressure liquid from accumulator 6. A further pressure responsive device is located between lines 9 and 15 which, on loss of pressure in the main circuit, operates a switch to energize a warning signal. Each selector device 20 comprises also a differential area piston so that the flow of liquid from the servomotors is automatically directed to the appropriate reservoir. To ensure that the, or each, stand-by circuit is " exercised " it is made to operate jacks 21, 21a, for operating the undercarriage through a separate circuit branched from feed line 15 through a feed line 26, selector valves 24, 24a and connections 22, 22a. A stand-by system is provided comprising selector valves 25, 25a connections 23, 23a and feed lines 28, 28a branched from feed line 9, so that during the " exercising " period if the circuit incorporating line 15 fails the undercarriage can be operated from accumulator 5. A further embodiment, Fig. 3 (not shown) discloses two stand-by hydraulic circuits in addition to a main circuit.