Patent GB-621670-A (GB)
Title: Improvements in and relating to pressure cabin systems for aircraft
IPC: B64D13/04
Filed: 1942-07-21
Abstract: 621,670. Fluid-pressure servomotor-control systems. BOEING AIRCRAFT CO. July 21, 1942, No. 10203. Convention date, Oct. 18, 1941. [Class 135] [Also in Group XXXV] A system for controlling aircraft cabin pressures and maintaining adequate ventilation therein comprises a compressor driven through variable speed means regulable automatically by means responsive to the flow through the system and also, if desired, manually. As shown in Fig. 1, air delivered by a compressor 7 passes to the cabin 9 through a conduit 90 and escapes from the cabin through an orifice controlled in the manner described in Specification 621,669. The compressor is driven by the aircraft propelling unit 8 or an auxiliary power plant driving through a variable speed gear, e.g. a hydraulic coupling 83, and reduction gear 71. The coupling 83 comprises two plates 81, 82 arranged close to each other in a casing to which oil is continuously supplied through a valve 84 and exhausted through a conduit 86. The valve 84 is regulated to adjust the quantity of oil in the casing to vary the transmission ratio by a double-acting power piston 1 under the control of an auxiliary valve 11. This valve is actuated by a floating lever 12 connected on the one hand to the piston-rod 10 and on the other to a spring-loaded diaphragm 13. One side of the diaphragm is connected by a pipe 96 with the conduit 90 while the other is connected by a pipe 95 with a sub-venturi 94 within a venturi in the conduit 90 so that a reduction in flow increases the opening of the valve 84 to introduce more oil into the chamber 83 and speed up the compressor. Should the compressor tend to overspeed, a governor-controlled arm 73 moves a lever 72 into contact with a member 14 on the auxiliary valve spindle to move the valve and initiate a correcting movement. The governor may actuate a further auxiliary valve in the conduit 85. The spring 24 loading the diaphragm may be adjusted by hand from a remote point by a member 88. The pipe 95 may be connected by a pipe 97 to the outflow control so that when the valve 92 is closed down sufficiently, cabin pressure is admitted to the pipe 95 so that the piston 1 is moved in the direction to increase the speed of the compressor. Alternatively, a throttle connecting pipes 95, 96 may be fitted and made adjustable manually from the cabin or by a power piston controlled by a valve actuated by a diaphragm subject to cabin pressure and atmospheric pressure under the control of the outflow controller. In another form, the throttle is actuated by a reversible electric motor controlled by a double-ended rheostat, the movable contact of which is movable with the outflow control valve. Fig. 8 shows a constructional form of the diaphragm 13. The diaphragm 13 separates two bellows 21, 22 connected respectively to the pipes 95, 96. An evacuated bellows 23 enclosing a spring 24 is arranged in the bellows 22 to convert a constant volume control into a constant weight control. The variable speed gear shown may be replaced by a hydraulic gear comprising a variable delivery pump and hydraulic motor, by a gear comprising a roller displaceable between reversed conical rollers, or by an epicyclic variable speed gear. In the latter case, the valve 84 is used to throttle variably a pipe connecting the suction and delivery parts of a pump driven by the planet carrier. The planets mesh with a sun-wheel connected to the compressor drive reduction gear and with internal teeth on an annulus having external teeth meshing with a pinion driven by the engine 8. As shown in Fig. 4, the compressor 7 is driven by a variable speed electric motor in circuit with a generator driven by the engine 8 and rheostats 40, 44. The movable arm of the rheostat 44 is adjusted by a bimetallic thermostatic strip 41 in the pipe 90 connecting the compressor to the cabin 9, while the movable arm 4 of the rheostat 40 is adjusted by a pair of spring-loaded opposed diaphragms 13 subject to the full bore and throat pressures of a venturi in the conduit 90. The rheostat 40 itself may be adjusted by a hand-operated member 88 and by a speed governor acting through a floating lever 74. When the compressor is driven by an auxiliary power plant, its speed may be controlled by coupling the power plant throttle to the piston 1. In another arrangement (Fig. 7, not shown), the arm 4 is formed as a floating lever and co-operates with a rheostat modified to control a reversible variable speed electric motor connected with the floating lever and adjusted to regulate the control member of a variable delivery pump forming part of a hydraulic variable speed gear in the compressor drive. The controlling diaphragm may be controlled by variations in flow of fluid entering the compressor or leaving the cabin. Specification 521,623 also is referred to.