Patent GB-692993-A (GB)
Title: Control for cabin pressure regulator
IPC: B64D13/02
Filed: 1949-04-12
Abstract: 692,993. Ventilating. GARRETT CORPORATION. April 12, 1949 [April 20, 1948] No. 9917/49..Class 137 FAl.so in Group XXIX] Aircraft pressurizing control apparatus comprises an air flow opening having control means,. an adjuster to adjust the control means to a desired setting and overriding adjusting means responsive to ambient air pressure to adjust said control. means to a setting corresponding to ambient air pressure and meansacting when said overriding adjusting means is in operation to render said adjuster inoperative and means for starting and stopping said overriding adjusting means operated manually, through part of the aircraft engaging the ground or by an increase in cabin pressure. Air is fed into an aircraft cabin by a blower or compressor 11 and leaves through an outlet 12 controlled by a balanced valve 13 comprising disc shaped closures 14 mounted on an axial shaft 15 mounted on diaphragms or spiders 15a as described in Specification 650,766, [Groug XXIX]. The end of shaft 15 is connected to diaphragm 17 forming part of a control chamber 18. A spring 19 urges diaphragm 17 leftwardly and therefore the position of closures 14 depends on cabin air pressure on the left side of the diaphragm and spring 19 plus control chamber air on the right. Air enters chamber 18 from the aircraft cabin through orifice 20 and leaves through isobaric control valve I or differential control valve D, these valves having their ports connected to the ambient atmosphere through a duct 21. Isobaric valve I is controlled by an aneroid bellows A mounted at one end on a bracket 23 and connected at its other end to a lever 24 pivoted at 26 to bracket 27. A tension spring 28 connected to lever 24 resists compression of bellows A. The tension in the spring 28 is adjusted by longitudinal movement of a rod 29 by a reversible motor 34, having field windings 30, 31 through shaft 33, worm 32 and gear 36. When winding 30 is energized rod 29 moves leftward to reduce tension in spring 28, energization of winding 31 having the reverse effect. Valve I, Fig. 2, comprises a conical closure 37 which closes port 38 and is secured to a cup member 39 having a lip 42 engaging a flange 41 on a tubular mem. ber 40 secured to lever 24, the members 39, 40 being urged apart by a spring 43. Within. cup member 39 is a normally open switch 44 formed by a contact 45 mounted on an insulator 46 and an earthed contact 47. The switch is closed when the bellows A expand. Control valve D is attached to differential bellows B and is similar to valve I but both contacts 45<SP>1</SP>, 47<SP>1</SP> are insulated and normally closed. The interior of bellows B is connected, through tube 50 and duct 21, with the atmosphere. The control for valve 13 will be adjusted by a preselector so that a desired pressure is achieved in cabin 10 after a predetermined time even though ambient pressure has dropped below this pressure as the aircraft climbed. If the aircraft descends so that the atmospheric pressure exceeds that for which the preselector is set, ambient pressure acting through valve I will activate an overriding adjuster so as to adjust the control to correspond to the ambient pressure. If the aircraft climbs again the preselector will again become operative and will alter the pressure gradually back to the selected value. Motor windings 30, 31 are energized through switches 51, 52 respectively. When bridging contact 57 is moved leftwardly, Fig. 1, in normal pressurized flight, thereby connecting contacts 66, 67, and the cabin ambient pressure differential is within the prescribed limits, energization of a relay 68 will close a circuit including contact 68', conductor 69, contact 66, contact 57, contact 67, stationary contact 70<SP>1</SP>, moving contact 71, conductor 72, closed switch 44<SP>1</SP>. conductor 72<SP>1</SP>, switch 52 and conductor 73 which connects the moving contact 63 of switch 52 with motor winding 31. When switch 44 is closed due to expansion of bellows A electromagnet 75 is energized, moving contact 71 out of engagement with stationary contact 70<SP>1</SP> and moving a movable contact 77 into engagement with contact 78, thus bridging the contacts 60, 59 so that winding 30 is energized and the tension in spring 28 is reduced. Power source 56 is connected to contact 80 and if contact 63 is in engagement with contact 80 current will flow from source 56 to winding 31. Electromagnet 81, energized through resistor 82, will pull movable contact 53 down against the tension of a spring 83, but normally the current in resistor 82 is diverted through a conductor 84 and contacts 85 and 86 to ground. Electromagnet 87 is normally energized through a resistor 88 and holds contact 63 against spring 89 to engage contact 64. Conductor 90 connects the junction of resistor 88 and electromagnet 87 to a contact 91 adjacent movable contact 86 and opposite contact 85 contact 86 is connected to lever 24 so that movement of lever 24 as the bellows A expands and contracts alters contact 86 and hence controls switches 51 and 52. Under normal pressurized flying conditions the slight movements of lever 24 and hence contact 86 do not result in its engaging either of contacts 85, 91. If bridging contact 57 is moved rightwardly, Fig. 1, it connects contacts 59, 60 to carry current from power source 56 through conductors 58, 61 to winding 30. Energization of relay 62 connects power source 55 through switch 51 to energize winding 30 and reduce tension in spring 28. When the pilot moves the overriding switch P into the position shown in dotted lines or when the undercarriage, as the aeroplane lands, causes switch 95 to move into dotted'line position 95<SP>1</SP>, the motor of jack 92 operates so as to move strut 93, which carries a bracket 94 on which is mounted contact 57, rightwardly, Fig. 1, to engage shaft 15 and open valve 13. Cabin pressure selector S comprises a lever 105 which can be moved through a series of positions along a resistance 106 whose ends are connected to the ends of resistance 107 which is swept by a contact lever 108 connected to a gear segment 109 driven by a worm 110 on the shaft of motor 34. Contact levers 105 and 108 are connected in series with the winding 111 of polarized switch 112 and, if they are not in the same relative positions along resistances 106, 107, current will flow through winding 111 of switch 112. When contact lever 105 is moved towards H<SP>1</SP> i.e. lower pressure, contact 113 of switch 112, which is connected through a pulser 116 to power source 117, will move to engage contact 114 and hence energize relay 62 and hence motor winding 30 to reduce tension in spring 28. Similarly, on moving contact lever 105 towards L<SP>1</SP>, relay 68 will be energized and hence winding 31 to increase the tension in spring 28. Pulser 116 comprises a continuously rotating drum 118 of insulating material to which is affixed a serrated metal cylindrical contact 119 continuously connected to contact 113. A brush 120 connected to a power source 117 intermittently engages contact 119 so that relays 62 and 63 are not energized continuously and adjustment of spring 28 takes place gradually. A control system of this type may be used in conjunction with a cabin pressure control of the type described in Specification 621,669, [Group XXIX], as shown in Fig. 5. Specification 521,623, [Group XXIX], also is referred to.