Patent GB-893682-A (GB)
Title: Improvements in or relating to aircraft cabin pressure control systems
Inventor: MOLLOY LOUIS BRYAN
IPC: B64D13/04
Filed: 1959-04-20
Abstract: 893,682. Fluid-pressure servomotor-control systems. NORMALAIR Ltd. April 1, 1960 [April 20, 1959], No. 13316/59. Class 135. [Also in Group XXXV] The pressure in an aircraft cabin 76, Fig. 5, is controlled by one or, as shown, two outlet valves 78, 79 and a relief valve 80 ; the outlet valves 78, 79 are actuated by diaphragms 83 the undersides of which are open to cabin pressure whilst the opposite sides, which form control chambers 82, are spring - loaded, each being open to cabin pressure via a restriction 91 and/or ambient pressure via a restriction 92 and duct 99 under the control of a pilot valve 93. The connection between restriction 92 and duct 99 is sealed off by an evacuated capsule 96 when the pressure is below that corresponding to e.g. 9,000 feet altitude. In each chamber 82 are three potentiometers 85, 86, 87 controlled by movement of the associated outlet valve; potentiometers 85 are connected to a control unit 100 and provide negative feed-back signals which are differentiated therein to give rate of change of valve movement; potentiometers 86 provide equalization of valve travel whilst potentiometers 87 are connected to means 101 indicating the relative openings of the outlet valves. Unit 100, which is connected with sensing means in units 1, 55 and 42, gives signal current amplification, phase discrimination and rectification ; the differentiated feedback and valve movement equalization signals are passed to D.C. motors 94 actuating the pilot valves 93, which motors can be moved through a small angle, defined by stops, on either side of the axis of symmetry; the motors incorporate permanent magnets biasing the armatures towards the axis of symmetry. Signals from the transducer units 1, 55 and 42 are fed into a transformer and algebraically summed. The outlet valves may be of the butterfly-type actuated by air motors controlled by electrical signals. Sensing units.-Transducer unit 1 senses altitude and consists of absolute capsules 3, Fig. 1, subject to cabin pressure, which through a spring-loaded slotted link 8 actuates an I-shaped armature 14 pivoted at 15 associated with a core 16 having windings 17, 18, 19 and adjustable stops 21, 22; the core, which is partially rotatable by a knob 32 through worm gearing 24, 25 is connected by a spring 27 to the armature. A further knob 36 oppositely adjusts altitude and rate of change of pressure potentiometers 39, 41 which regulate the excitation of the transducer. Transducer unit 42, Fig. 5, senses cabin differential pressure and comprises capsules subjected internally to ambient pressure and externally to cabin pressure, which capsules operate an armature similar to that in unit 1, the core of which is adjustable through a worm gear to obtain the desired setting of the transducer. Transducer unit 55, which senses the rate of change of cabin pressure, has two chambers 61, 62, Fig. 3, in its casing formed by a division 57 on which is mounted a capsule 59 actuating an armature 14 ; the chambers are interconnected by a restriction 60. The chamber 61 opens into the capsule 59 and chamber 62 is open to cabin pressure; the chamber 61 communicates with the cabin through relief valves 71, 73. In another form the division is dispensed with and the remaining chamber is open to the cabin via a restriction. The rate of change at which the sensing means becomes effective is varied by moving the knob 36, Fig. 1. The transducers, which may be variously arranged in a common casing, may be flexibly mounted, and may consist of bar armatures moving in coils.