Patent GB-597286-A (GB)
Title: Improvements in fluid pressure operated remote control systems
IPC: B64C13/00
Filed: 1945-08-13
Abstract: 597,286. Fluid - pressure servomotor control systems; valves. HOBSON (AIRCRAFT & MOTOR) COMPONENTS, Ltd., H. M., DODSON, E., and WESTBURY, R. Aug. 13, 1945, No. 20738. [Class 135] [Also in Group XXXII] A fluid-pressure servomotorcontrol system applied, e.g. to the operation of aircraft flaps, comprises a sender unit 13, Fig. 2, having a dashpot 39, Figs. 2, 3, producing a time lag in the system and receiver units 17, Figs. 6, 7, each of which operates a hydraulic jack 14 and its associated flap 15. The sender unit comprises a piston valve operable in a bore having ports 125, 116, 120 which communicate with a conduit 25, a signal pressure line 16 and an exhaust line 20 respectively. A valve 24 within the unit controls a pressure-reducing ball-valve 28 for establishing in the conduit a pressure below that in a highpressure supply line 12, but a predetermined value above that in the signal line due to a spring 30. A chamber 33 open to the exhaust line houses a balancing spring 27 disposed between a flange on the piston 26 and an abutment 44 on the hollow extension 43 of the rod of the dashpot piston 38. The extension 43 communicates with the chamber 33 via a valve 41 and with both sides of the dashpot piston through holes 49, 50 and discs 46 having staggered holes therethrough respectively. The dashpot piston is connected by a link 37 to a lever 34, which is coupled by a spring 40 to a hand-lever 100 and to a link 52 attached to a plunger 51 exposed to the pressure in the conduit. Each receiver unit 17 comprises a piston valve 53 having one end open to signal-line pressure and the other end, which is connected to its rod 55 and loaded by a spring 54, open to exhaust pressure. The rod 55 is pivoted to one end of a lever 57 whose other end 58 is connected to a servo-valve 59. Intermediat its ends the lever is connected to a relay valve 61 having ports 62, 63 communicating through passages 64, 65 with the signal and exhaust lines respectively. A reduced portion 67 of the relay valve communicates through a passage 66 with the right-hand side of a piston 68 connected to the valve 59 which slides in a moving sleeve 70 having ports 71, 73, 72 which communicate with the two sides of the jack piston 75 and a second exhaust line 21 respectively. The sleeve 70 is formed at one end with a rack 76 which engages a pinion 77 and through a chain-and-sprocket drive 78, Fig. 7, and a lever 19 a " follow-up " motion is imparted to the sleeve. To lower the flaps, the hand-lever 100 is moved anticlockwise, to a position indicating the desired final position of the flaps, thus tensioning the spring 40 and through the lever 34 and the link 37 urging the dashpot piston to the left to give an initial compression to the spring 27 and open the valve 41. Exhaust fluid enters the extension 43 and both sides of the dashpot piston 38, the continued loading of the spring 40 moving the dashpot piston further to the left, thus increasing the loading on the spring 27 and moving the piston valve 26 to the left. The movement of the valve 26 connects the conduit 25 to the signal line to increase the pressure therein and lower the pressure in the conduit which permits the valve 24, assisted by the spring 30, to move to the left to open the reducing valve 28 to allow fluid from the supply main to enter the signal line until the lever 34 again abuts against the lever 100, and the spring 27 is compressed the desired amount to balance the increased pressure in the signal line. The valve 26 then returns to its normal position, the pressure difference between the conduit and the signal line is restored and the valve 24 moves to the right and the valve 28 closes. The increased signal line pressure moves the valve 53 in the receiver unit to the right which, through the lever 57, moves the relay valve 61 to expose the right-hand side of the piston 68 to signal line pressure which moves, together with the valve 59, to the left to connect the right-hand side of the jack piston through ports 73, 72 with the exhaust line 21. The jack piston whose left-hand side is open to the pressure in the supply line 12, then moves into its cylinder to actuate the flap. To raise the flaps, the lever 100 is moved clockwise which carries the lever 34 with it together with the link 37. The spring 27 then urges the dashpot piston to the right to permit right-ward movement of the valve 26 to connect the signal line with the exhaust line 20. At the same time the link 52 moves the plunger 51 to increase the pressure in the conduit 25 and move the valve 24 to the right to connect the conduit through channels 31 with the exhaust line. This continues until the dashpot piston reaches its final position ; the spring 27 is fully relieved and balances the reduced pressure in the signal line when the valve 26 returns to its neutral position and the pressure difference between the conduit and the signal line is again restored. The decreased pressure in the signal line causes the valve 53 in the receiver unit to move to the left, the relay valve to open the right-hand side of the piston 68 to exhaust and the spring 69 to move the valve 59 to the right to connect the supply line 12 through ports 71, 73 with the righthand side of the jack piston to move the jack piston out of its cylinder. In a modification of the dashpot, a liner having a passage 80, Fig. 5, and a hole 79 is inserted in the dashpot cylinder to give further communication between the two sides of its piston such that the dashpot effect is decreased over part of the stroke to increase the speed of operation of the flaps when near their fully-raised positions. Specifications 483,049, 551,257 and 574,148 are referred to.