Patent GB-672139-A (GB)
Title: Improvements relating to servo control systems
Inventor: WATSON CYRIL DANIEL
IPC: B64C13/24
Filed: 1949-03-04
Abstract: 672,139. Fluid-pressure servomotor-control systems. NATIONAL RESEARCH DEVELOPMENT CORPORATION. March 1, 1950 [March 4, 1949], No. 6037/49. Class 135. A servo control.system has a controlling member 1 movable against spring means to position a control element 63 controlling the supply of power to a servomotor, such as the hydraulic cylinder 12, which adjusts a member to be. operated and resets the control element, the spring means being stressed by the movement of the servomotor in such a direction as to increase the opposition to the movement of the controlling member in its original direction of movement. As applied to the operation of an aircraft control surface, a control column 1 is linked to a floating lever 63 and to a lever 60 having a pivot 61 on the aircraft. The lever 63 operates through a linkage 64 the control member of a reversible delivery variable speed,pump 3 supplying a double-acting hydraulic, cylinder 12 of which the piston rod 11 is pivoted to the floating lever 63 and to a lever 67 at 66. The lever 67 has a pivot 68 on the aircraft and is connected by a link 70 to the control surface. The lever 60 is connected by a rod 4 to a spring box 5 of which the casing is connected for movement by the piston rod 11 through a linkage 7, 9, 10 having a pivot 8 on the aircraft and a link 14 also pivoted on the aircraft. Figs. 2 and 3 show the spring box in detail. The spring 32 is mounted on sleeves 26, 27 with-internal flanges 28, 29 and external flanges 30, 31, the latter being grooved to receive rubber buffers 33, 34 engageable with end plates 23, 24. The sleeve 26 slides on an extension 25 of the end plate 23 and the sleeve 27 on a sleeve 21 mounted on a shouldered member 20. The end plates 23, 24 are connected by side plates 35, 36. The latter have slots 37 in which can slide blocks 38, 39 supporting by pins 44, 45 the upper ends of the double lever 7. Normally the blocks 38 are maintained rigid with the side plates 36 by threaded rods 40, 41 having pivots 56 and maintained in engagement with semi-circular threaded cavities 55 in the sides of the end plate 24 by levers 47, 48. The levers 47, 48 are normally maintained in engagement with the rods 40, 41 by a jack 51 supplied with hydraulic power through an inlet 54. The hydraulic power may be interrupted at will by a solenoidoperated valve to disengage the frame of the spring box from the double lever 7 and so permit adjustment of the controlling member independently of the spring forces. The linkage 7, 9, 10 includes a pin and slot connection 15 which may be adjusted by a pitot or aircraft speed sensitive device to alter the effective leverage of the lever 10 so that equal movements of the control surface at different aircraft speeds result in different stressing of the spring in opposition to movement of the column 1. According to the Provisional Specification, the fulcrum of the lever 8 includes a spindle carrying a pinion maintained in engagement with a fixed rack. Rotation of the spindle and hence movement of the fulcrum is normally prevented by a friction brake which can be released by a solenoid.