Patent GB-701092-A (GB)
Title: Hydraulic servo-motor and control valve therefor
IPC: B64C13/00
Filed: 1949-03-28
Abstract: 701,092. Fluid-pressure servomotor-control systems; valves. NORTHROP AIRCRAFT, Inc. March 28, 1949 [March 29, 1948], No. 8381/49. Class 135 In a fluid-pressure servomotor control system for the full-power operation of aircraft control surfaces, the system is made irreversible from loads applied to the control surfaces by the provision of restricted flow passages through the control valve when in its neutral inoperative position so that pressure fluid is supplied to both sides of the servomotor piston to preload it and hold it in a balanced position. As shown applied to the operation of elevons on a large all-wing aircraft, cables 8, Fig. 1, from the pilot's control column pass over pulleys 7 carried by a lever 5 secured to a post 1 pivotally mounted at its ends on the aircraft structure, to actuate through a lever 12 and rod 13 a control valve 16 which supplies pressure liquid to a double-acting servomotor 17. The servomotor has its cylinder operatively con-' nected to the elevon and its piston pivotally secured to the aircraft structure. The valve 16, the body of which is secured to the servomotor cylinder, comprises a valve spool 26, Fig. 3, alidable in a ported sleeve 24 secured in the body between a screwed plug 32 and a spool guide 30. The spool 26 provided with lands 26a, 26b is formed with an axial bore 72 and radial holes 71, 73 connecting its right-hand end with an exhaust duct 51 and blind bores 78, 79, 82, 83 circumferentially disposed around the bore 72 connecting the end faces of the lands 26a, 26b through groups of radial flow-holes 78a, 79a, 82a, 83a with the periphery of the lands. The groups of flow-holes are so arranged that in the neutral position of the spool 26 in relation to its sleeve 24, the inner hole of each group is half uncovered with respect to sleeve recesses 56, 62 to permit pressure liquid supplied through an inlet port 60 to pass through ports 55, 63 communicating with the ends of the servomotor cylinder to preload both faces of the piston. On movement of the spool 26 from its neutral position by the pilot, e.g., to the left, limited by the pin and slot 41, 42, the half holes in groups 82a, 79a are covered whilst the hole groups 78a, 83a are progressively uncovered to connect one end of the servomotor cylinder with pressure liquid and its other end with exhaust, the cylinder moving in the same direction as the spool 26 so that the sleeve 24 follows-up the movement of the spool 26 to restore them to their relative neutral positions. The operating rod 13 is spring-loaded to prevent the valve being damaged by the pilot in the event of failure of the pressure liquid supply. Each elevon is normally operable by two servomotors, each having a separate control valve, but in the event of failure of one servomotor or its control is capable of operation by the other servomotor and its control valve. To prevent hydraulic lock in a motor cylinder in the event of the jamming of a control valve spool in its sleeve, release valves similar to the release valves described in Specification 701,149 may be fitted, and so'allow the other motor and its valve to remain effective. Instead of being pilot-operated the control valve may be operated by an automatic pilot. Specification 629,714, [Group XXXIII], also is referred to. The Specification as open to inspection under Sect. 91 includes a control valve in which the sleeve 24 is dispensed with and the spool is formed with lands 94, Fig. 5 (Cancelled), having recesses 92 and radial holes 93 in lieu of the blind bores and radial flow-holes previously described. This subject-matter does not appear in the Specification as accepted.