Patent GB-856145-A (GB)
Title: Dual input servo valve
IPC: F15B13/043
Filed: 1957-02-13
Abstract: 856,145. Fluid-pressure servomotor control systems. MOOG SERVOCONTROLS Inc., [formerly MOOG VALVE CO. Inc.]. Feb. 13, 1957 [Feb. 13, 1956], No. 5008/57. Class 135. A valve for controlling hydraulic machinery, e.g. hydraulically operated aircraft control surfaces, consists of a spool 41 adapted to be driven hydraulically by pressure differences applied through conduits 96, 97 and also mechanically by means which shift the position of opposed yielding means 78 relative to the valve body, the displacement of said spool relative to the body being responsive to the algebraic sum of the hydraulically and mechanically induced displacements of said spool. The spool valve 41 shown is adapted to control primary and secondary hydraulic circuits feeding a pair of servo-pistons mounted in tandem upon a common piston rod which is connected to the aircraft control surface to be actuated. Annular recesses 56, 58 in a sleeve 39 surrounding the spool 41 are connected to opposite ends of one of the servo-pistons whilst annular recesses 69, 71 are connected to the two ends of the other servo-piston. The pressure supply and drain connections of the primary system are connected respectively to annular recesses 50 and 52, 53 whilst the corresponding connections of the secondary system are connected to annular recesses 63 and 65, 66. Variation of the pressures in the conduits 96, 97 to cause hydraulic displacement of the spool 41 is caused by displacement of a flapper 100 relative to a pair of nozzles 101, 102 fed from the secondary system through the recess 63, conduits 109, 105, a valve 106, and a conduit 107 having branches 110, 111, with restrictions. Displacement of the flapper 100, which is mounted in a flexure tube 103, is effected by electrical signals derived from an automatic pilot or stabilizer and passed through an electronic amplifier to a solenoid or torque motor 99. Movement of the aircraft control surface causes operation of an electrical position signal generator which provides a feedback signal which is fed to the electronic amplifier. The mechanical input to the spool valve 41 is from a pilot's control column connected through a floating lever with a link 25 which is connected to a lever 79 with a fixed pivot on a bracket 81. The floating lever is also connected with the rod of the servo-pistons to provide a mechanical feedback. A link 83 extends between the lever 79 and a second lever 80 pivotally mounted on a bracket 82 whereby abutments 75 for the resilient means or springs 78 at each end of the spool 41 are moved simultaneously in the same direction. Tubular elements 77 movable with the abutments 75 have lost motion relative to the spool 41 whereby the latter is moved positively should it tend to stick. The degree of lost motion corresponds to the deflection required of the spool 41 for full opening of the ports whilst stops 86, 87 for the lever 79 limit the displacement of the members 75, 77 to twice the movement of the spool which is necessary for full opening of the ports so that, with the spool 41 deflected to its maximum extent in one direction under the influence of the hydraulic actuation, overriding control can be exercised by the pilot to displace the spool to the opposite extreme of its travel. To disable the electrical control of the spool 41 a switch is opened which de-energizes a solenoid 113 to allow a spring 114 to operate the valve 106 to interrupt communication between the conduits 105, 107 thereby cutting off the supply of fluid to the nozzles 101, 102. To control the spool 41 electrically without the mechanical input a switch is closed to energize a solenoid 113 to cause a valve 128 to apply hydraulic pressure to the space between a pair of plungers 117, 118 which are thereby forced apart to engage stops 122, 124 on the levers 79, 80. It is possible for the pilot to overcome the force exerted by the plungers 117, 118. It is stated that pressure repeating power amplifiers may be interposed between the nozzles and the drive chambers at the ends of the spool 41. Specifications 849,445 and 854,287 are referred to.