Patent GB-604594-A (GB)
Abstract: 604,594. Automatic control systems for ventilation of aircraft. MINNEAPOLIS-HONEYWELL REGULATOR CO. June 12, 1945, No. 14840. Convention date, June 22, 1944. [Class 38 (iv)] [Also in Group X] The compressor supplying air to an aircraft cabin normally maintained above atmospheric pressure is controlled by a factor dependent upon engine operation and a factor dependent on the need for air in the cabin. The system is illustrated as applied to the two inboard engines of a four-engined aircraft. One of the inboard engines, 10, Fig. 1, has an exhaust manifold' 30 driving a turbine 28 which drives an air compressor 11 which supplies air to the cabin 152 and to a cooler 14, carburettor 17, throttle 16, a further compressor 18 and intake manifold 19 of the engine 10. The turbine 'speed is controlled by a waste gate 34 in the exhaust conduit, so that speed is reduced as the waste gate is opened. The waste gate is operated through gears 41 by a reversible twophase A.C. motor of which field winding 39 is energized directly from transformer. 45, while field winding 38 is energized by an amplifier 62 such as described in Specification 601,026. The output of amplifier 62 has a phase dependent upon the potentials derived from networks 69, 70 and 71. Network 69 has potentiometer arms 77, 81 positioned respectively in accordance with the position of the waste gate 34 and the variation in velocity of the turbine 28 as obtained from the velocity controller 86. Network 70 has a potentiometer arm 99 controlled by an acceleration controller 101 which varies with any variation in acceleration of the turbine, and a potentiometer arm 104 controlled by two bellows 108, 109, the former of which is evacuated to be affected only by atmospheric pressure and the latter of which is influenced by both atmospheric pressure and air from compressor 11. Network 71 has a potentiometer arm 119 under the control of an evacuated bellows 131 sensitive only to atmospheric pressure and a manually operated potentiometer 133 so that the atmospheric pressure in moving arm 119 sets a lower limit to the level of compressor operation to avoid the air supply to the cabin falling below atmospheric pressure ; network 71 also includes a potentiometer 135 set in accordance with the No. 2 engine controls, potentiometers 140, 139 and 141 being similarly under the control of the other engines. As a consequence of these networks, variations in the velocity or acceleration of the turbine, in the pressure from the compressor 11, or in atmospheric pressure produce a variation in the voltage supplied to amplifier 62 to vary the phase of current in field winding 38 and operate the motor 36 to adjust the waste gate and maintain the air pressure from the compressor constant in accordance with the setting of the manuallycontrolled arm 133 ; the follow-up arm 77  moves until the system is balanced again and the motor 36 stops. The potentiometer resistance 122 includes a suitably positioned conducting bar so that the atmospheric pressure control is constant between altitudes of 8,000 feet and 30,000 feet. The compressor 11 also supplies air to the cabin 152 through a valve 164 operated by a reversible two-phase A.C. motor 166 through gearing 167. One field winding 169 of the motor 166 is continuously energized while the other field winding 170 is energized through amplifier 185 by two networks 200, 201. Network 200 has a potentiometer arm 217 controlled by the bellows 131 responsive only to atmospheric pressure, and a potentiometer arm 216 responsive only to the pressure in the cabin 152. Network 201 has a potentiometer 234 operated from the gearing 167, and a potentiometer arm 239 operated by a timing motor 242 controlled by a manuallyoperated potentiometer 248. As a consequence of these networks, variations in atmospheric and cabin pressures produce a variation in the energization of field winding 170 of motor 166 to adjust the valve 164. The setting of potentiometer 248 is limited by a stop 272 controlled by evacuated bellows 274 so as to be under the influence of atmospheric pressure only and incapable of operation below an altitude of 8,000 feet ; thus the cabin pressure cannot be selected to be below atmospheric pressure. Potentiometer resistance 210 has a suitably positioned conducting bar in its length so that the automatic control is enhanced between altitudes of 8,000 feet and 30,000 feet.  In a modification, the cabin pressure is controlled by varying the outlet valve instead of the input. The cabin, part of whose wall is shown at 355, Fig. 2, is fed with air from the compressor 11 through valve 338 ; the pressure within the cabin, acting on bellows 356, and the pressure in the conduit 150 some way from the cabin, acting on bellows 355 control a switch 351 to open or close the input valve 338 so as to maintain a flow of air into the cabin. The outlet valve 361 is controlled through gears 362 by an A.C. motor 363, one of whose field windings 366 is constantly energized, and the other of whose field windings 364 is controlled by networks 390, 391 through an amplifier 368. Network 390 includes a potentiometer arm 396 controlled by the motor 363 through gearing 362 and a potentiometer arm 399 controlled by an evacuated bellows within the cabin and thus responsive to cabin pressure. Any variation in cabin pressure thus results in an opening or closing of the outlet valve 361 to maintain the pressure constant. Network 391 has a potentiometer arm 413 movable when screw 326 is rotated through gearing 327 by the D.C. motor 425 ; switch arm 420 is manually operable to close the circuit of either of the field windings 429, 430 to rotate the screw 326 and move the arm 413 to'a new position ; the input to the amplifier 370 is thus modified and the motor 363 operates to open or close the valve 361 until a new pressure level is reached as determined by the manual operation of switch 420. The movement of the arm 413 is followed by arm 319 to prevent the compressor being operated at a level insufficient to maintain the cabin pressure. To prevent the difference between atmospheric and cabin pressure becoming too great, a bellows 447 is  open to the atmosphere at 448 and at a predetermined compression actuates switch 441 to operate motor 425 and rotate the screw 326 to move the arm 413 to a position corresponding to a lower cabin pressure. A further correction -may be applied to compensate adjustment of the throttle ; since  cabin pressure determines the extent to which the gate 34 is open and thus the operation of the compressor 11, it may be necessary to close the throttle 16 for engine operation ; the result is a decrease in the exhaust energy leading to a lower pressure corresponding to a given gate position. In order to compensate for this, a further network is added to the networks 69, 70, 71 of Fig. 1 (Fig. 3 not shown) ; this further potentiometer has an arm controlled by the throttle so that a reduction in throttle leads to a closing of the waste gate 34. Specification 605,449 also is referred to.