Patent GB-1383705-A (GB)
Title: Aircraft air-conditioning system
IPC: B64D13/06
Filed: 1972-03-16
Abstract: 1383705 Automatic control of temperature GARRETT CORP 16 March 1972 [17 March 1971] 12409/72 Heading G3R An aircraft air-conditioning system includes a turbine engine (auxiliary power unit-APU) 10 Fig. 2 also Fig. 3 (not shown), having high and low pressure spools and arranged to produce shaft power and bleed air, air conditioning means 11 arranged to receive and condition bleed air and supply it to one or more temperature controlled zones 12, and "interface" automatic control means 14 which are arranged to provide a temperature demand signal to the air conditioning means to cause adjustment of the temperature of conditioned bleed air and to increase the speed of the LP spool whereby to increase the flow rate of conditioned air to the zone or zones if the air conditioning means cannot satisfy the temperature demand signal without such an increase. Bleed air may also be obtained from the aircrafts main propulsion engines in addition to that from the turbine engine 10. The bleed air provides high pressure and temperature and is extracted from the flow between the LP and HP compressors. Zone inlet temperature is adjusted by:- (i) modulating the outlet temperature of air conditioning packs 11 by adjusting the APU turbine engine by-pass and ram air doors; (ii) by adjusting a trim heat valve; (iii) by adjusting the LP spool speed in a range between 78% and 93% of maximum rated speed.  The air conditioning packs may comprise conventional turbo-compressor refrigeration units. INTERFACE CONTROL SYSTEM, Fig. 6, also Fig. 8 (not shown). A zone temperature controller 39 (e.g. for zone I) comprises an actual temperature sensor 41 located in the zone of a desired temperature selector 40 connected to a summer 42 to produce a temperature error signal. A "zone inlet demand signal" is derived from the error signal by an integrating channel 43 and a proportional channel 44 and, together with similar signals in respect of the other zones, is fed on a minimum demand discriminator 57. In addition this demand signal is fed via a limiter 45 to a summer 46 which compares it with a signal from a zone inlet temperature sensor 47 to provide a zone inlet temperature error signal (trim heating demand signal) which is used to adjust the trim heat control valve 49. The trim heating demand, signals in respect of all of the zones are fed to a trim heating descriminator 56. This passes the largest signal to a filter 53 which produces an APU speed demand signal which is fed via stabilizing network 50 to a maximum speed discriminator 58. Likewise the minimum demand discriminator 57 passes the lowest inlet temperature demand signal via a filter 59 to the discriminator 58. The maximum speed discriminator 58 passes the largest input speed demand signal thereto as an output signal which is used to control the speed of the LP spool of the APU turbine engine 29. The demand temperature signal from discriminator 57 is also fed via a limiter 76 to an air conditioning pack temperature controller 51 where it is compared with a signal from a pack outlet temperature sensor 79. The resulting difference signal is used to adjust the turbine (29) by-pass and-ram air doors 62 to supply the demanded air temperature via ducts to the respective zone. Individual adjustment of the inlet air temperature to other zones demanding higher temperature is effected by adjustment of the respective trim heat valves 49.