Improvements in or relating to hydraulic jacks and power actuated systems including such jacks

摘要

690,219. Hydraulic machines ; Huid-pressure servomotor-control systems. NATIONAL RESEARCH DEVELOPMENT CORPORATION. Aug. 23,1950 [July 9, 1949], No. 18216/49. Classes 69 (ii) and 135 [Also in Group XXX] In a hydraulic servomotor-control system of the kind described in Specification 632,513 suitable for the operation of aircraft control surfaces, a hydraulic vane motor 53 is secured to the threaded shaft 48 which co-operates with the threaded piston 10 to either assist or restrain rotation of the threaded shaft. As shown in Fig. 1, the screw-threaded shaft 48 is made irreversible and the vane motor 53 housed in an extension of the cylinder 11 and connected by ducts 60, 57 to the valve casing. On movement of the pilot valve 17, e.g. to the left on rotation of the shaft 47 either electrically or manually, the main valve 28 moves to the left to connect the pressure duct 13 through the duct 60 simultaneously to the left-hand end of the cylinder I and the vane motor 53 and the exhaust duct 14 through the duct 57 to the vane motor. Thus rotation of the vane motor permits the axial movement of the piston 10 under the pressure applied to its left face. Rotation of the shaft 48 through bevel gears 50, 51, 52 recentres the valve 17 with respect to the valve 28. Under normal operation, a spring-loaded stop 63 is held out of engagement with the splined shaft 42 by liquid pressure. In the event of failure of the liquid pressure the stop 63 engages in a recess 64 on the shaft 42 whence rotation of the shaft 47 moves the valve 17 into engagement with one of the end stops 65, 66 to move the valve 28 to connect the vane motor and the left-hand end of the cylinder 11 with the exhaust duct 14 and lock the shaft 42 to the bevel gear 52, so that the shaft 48 may be rotated and hence the piston 10 axially moved through the gears 52, 51, 50. As shown in Fig. 2, the screw-threaded shaft 48 is made reversible, i.e., rotation of the shaft moves the piston 10 and movement of the piston rotates the shaft. In this case, the duct 60 supplies pressure liquid to the cylinder 11 only, the vane motor being connected to a port 70 in the valve casing by a duct 78 whilst the duct 57 branches into two ducts 73, 74 housing oppositely disposed non-return valves controlling ports 71, 72 in the valve casing. In the neutral position of the valves 17, 28, the port 70 is masked by a land 69 on the valve 28, the vane motor 53 then being hydraulically locked. On movement of the valve 17 to move the valve 28, pressure liquid circulates through the vane motor 53 in the corresponding direction but at a rate which retards the movement of the piston due to the restriction of the ports 70, 71, 72.