Patent GB-778335-A (GB)
Title: Improvements in hydraulic control systems and aircraft control systems embodying thesame
IPC: B64C13/00
Filed: 1955-05-19
Abstract: 778,335. Fluid-pressure servomotor-control systems. LEDUC, R. May 19, 1955 [May 21, 1954], No. 14489/55. Class 135. An hydraulic servomotor-control system having a controlled member movable in either sense from a neutral position through an appreciable distance substantially proportional to a force applied in the corresponding sense to a controlling member moving a relatively small distance, comprises a piston-type detector valve connected to the controlling member and distributing pressure liquid to the opposite ends of a double-acting jack connected to the controlled member and which on the slightest movement of the valve in either sense from its neutral position sets up an hydraulic pressure difference which acts on the valve in opposition to the force applied thereto and also acts on the jack piston which is so resiliently loaded that its displacement in either sense from neutral is substantially proportional to the pressure difference. As shown, the system comprises a pump 1, Fig. 1, connected by a line 13 to a detector valve 4 comprising a valve piston 5 having identical inner lands 9, 10 between which is a constant volume chamber 12 and smaller identical outer lands 8, 11 between which and the lands 9, 10 are variable volume chambers 6, 7 in constant communication through lines 14, 15 with opposite ends of a double-acting jack 16. The lands 9, 10 control ports 20, 21 connected by lines 18, 19 to a sump 17 and ports 22, 23 connected by lines 14a, 15a to the lines 14, 15 respectively, all the ports in the neutral position of the valve being half covered by the lands 9, 10. The jack piston 25 comprises a central piston 26, two smaller diameter outer pistons 63, 501 and a collar 24 acted upon by equal and opposed springs 29, 30 to resiliently load the piston 25. The piston 25 being connected by a rod 35 to a relay valve 53 having lands 50, 51 controlling the distribution of pressure liquid to the opposite sides of a servomotor piston 61 connected by a rod 48 to the controlled member. A pulsator 32 fitted across the lines 14, 15 reduces the effects of friction in the system and improves the sensitivity of the valve 4 and a pressure regulating valve 2 maintains the pressure in the system constant. When a small axial force is applied, e.g. in the direction of the arrow F to the valve piston 5, the valve piston moves to the right to increase the supply of pressure liquid in the line 15 and reduce it in the line 14 so as to establish a pressure difference in the lines 14, 15 and the chambers 6, 7, which pressure difference acts.on the valve piston 5 in opposition to the applied force and also moves the jack piston 25 to the left in opposition to the spring 29. The piston 25 then moves the relay valve 53 which causes a follow-up movement of the servomotor piston 61 and its rod 48. In Fig. 3, the system is applied to the operation of an aircraft control surface 38, the valve piston 5 being connected for automatic actuation by a device 70, e.g. a pendulum, gyroscope or aneroid capsule sensitive to a flight characteristic of the aircraft, e.g. acceleration, attitude, angular velocity, equivalent air speed, altitude, Mach number, &c. The jack 16, relay valve 53 and servomotor 61 being assembled as a single unit connected by the rod 48 to a lever 41, link 40 and a servomotor 39 to the control surface. The surface 38 may be operated independently by a hand-lever 37 connected by a link 43 to the lever 41. In a modified form of aircraft control system, the lever 41 is replaced by bell-crank levers 45, 47, Fig. 4. A known type of device 46 being fitted between the rod 48 and the lever 45 to give artificial progressive " feel " when under manual control. The device 70 varies the neutral or zero-feel, position of the hand-lever 37 relatively to the control surface 38 proportionately to the force applied by the device 70 to the valve piston 5 so that in the " stick-free " condition the control surface 38 will take up a position corresponding to the zero-feel of the lever 37. Specifications 654,415 and 694,840 are referred to.