GB632170A - Improvements in or relating to apparatus and method of controlling the pressure in an aircraft cabin - Google Patents

Abstract

632,170. Automatic control systems for aircraft cabin pressurizing. DOUGLAS AIRCRAFT CO., Inc. Oct. 7, 1946, Nos. 29835 and 29836. Convention dates, May 13, 1946 and June 10, 1946. [Class 38 (iv] The invention is described with reference to the control of aircraft cabin air pressure and temperature whereby (a) the cabin pressure is a linear function of the pressure altitude of the aircraft, and (b) the differential pressure across the supercharger, at a predetermined value, renders inoperative, temperature sensitive means, inside the cabin, normally controlling the flow of supercharged air through a cooler, so that the load imposed by a refrigerator turbine upon the supercharger is limited to the difference between the maximum safe supercharger load and the load imposed by the cabin pressurization. Pressure control. Fig. 1.-The cabin 21, is supplied with air from supercharger 23 and discharge is effected through the outlet 31, in which the valve 32 is operated by the reversible motor 36, to control the cabin pressure. The motor 36 is controlled, through its fields, from the relay 45 which is subject to the action of the regulators 56, 57, 58 which, respectively, control the differential between the cabin and ambient pressures, the time rate of cabin pressure charge, and the differential limit between the cabin and ambient pressures. The aneroid 63, in regulator 56, tends to maintain the cabin pressure at a predetermined value by its control of the contact arm 65 between the contacts 66, 67, associated with the motor control relay 45. Maintenance of the appropriate, and manually adjustable linear cabin pressure-ambient pressure relationship is effected by the capsule 64 which co-acts with aneroid 63 on the arm 65. Both 63 and 64 are mounted in a container the interior of which is at cabin pressure. The action of regulator 56 may be terminated by the landing gear switch 60 and the thermostat 59, both of which, when operated cause the opening of the outlet valve 32, under the supervision of the rate regulator 57. The latter comprises a capsule 145, of which the interior is at cabin pressure, mounted in a sealed case and which positions the contact arm 154 between the contacts 161, 162. The interior of the aneroid 145 is open to the interior of case 142 through a capillery tube, and arm 154 is moved in accordance with cabin pressure changes so as to (1) veto the action of regulator 56 on the valve 32 and (2) operate the valve 32 to effect a predetermined rate of cabin pressure change when the craft altitude changes at a rate which would tend to cause cabin pressure rate changes beyond desired limits. The cabin pressure limit regulator 58 comprises a capsule 207, subject to the pressure differential between the cabin and atmosphere, which when the differential exceeds a predetermined limit, moves the arm 210 between the contacts 214, 215 to arrest the operation of regulators 56, 57 and simultaneously open the valve 32. Variation of the limiting pressure differential in accordance with the absolute pressures across the capsule 207 is effected by the aneroid 225. Temperature regzclation. Fig. 11.-The air supplied to the cabin; from the supercharger 23, passes through the cooling turbine 284 and heater 285, in a proportion fixed by the valve 287, rotatable by the reversible motor 288 controlled conjointly by the thermostat 306, sensitive to cabin temperature, and the contact arm 321, subject to the pressure difference across the turbine. When the load on the supercharger, as indicated by the pressure differential across it, has risen to a predetermined maximum, the contact arm 321 rotates anti-clockwise and engages contact 332 whereon the motor 288 rotates so as to reduce the amount of air delivered by the turbine 284 until the turbine load becomes equal to the difference between the maximum safe load of the supercharger and the load imposed by the cabin pressurization. The rate of air-flow from the supercharger is supervised by the venturi and piston device 346, 343 and if, upon attaining its maximum speed, the supercharger does not produce the required rate of flow, a switch is operated by the piston device 343 which causes the motor 288 to reduce the passage of air through the cooling turbine.