Patent GB-1316778-A (GB)
Title: Apparatus for controlling the ratio between two variables eg two pressures in a gas turbine engine
IPC: F01D17/26
Filed: 1970-06-16
Abstract: 1316778 Gas turbine engine fuel systems; axial-flow compressors DEFENCE SECRETARY OF STATE FOR 16 June 1970 29003/70 Headings F1C and F1G A fluidic circuit for controlling the ratio between two variables comprises fluidic sensing means for detecting any error in the ratio, first fluidic amplifying means for amplifying the error to produce a control pressure and having a variable feedback of the control pressure to the sensing means, the variation of the feedback being dependent indirectly on the ratio between the variables, and a second fluidic amplifying means controlled by the control pressure and having a variable power supply pressure dependent on one of the variables and generating an output pressure arranged to vary a control system upon which the values of the variables depend, the second amplifying means being capable of operation in two modes, one in which the power supply pressure is greater than the power supply pressure and the other in which the control pressure is greater than the power supply pressure and the output pressure is a function of the control pressure. The circuit is used for controlling the ratio between the compressor outlet pressure P4 of a gas turbine engine and the engine inlet total pressure P1, which are supplied to a jet collector 28, the output of which is passed through a fixed orifice 32 as a control pressure Pc to a proportional amplifier 26. The amplifier is also provided with a further control pressure in the form of a reference pressure Pr derived from a fluid potentiometer 20, 18 fed with the pressure P4 and the ambient pressure Po. The potentiometer is adjusted by a pilot's lever 22 and an evacuated bellows 21 subjected to the pressure P1. The amplifier 26 is followed by proportional amplifiers 34, 36 in series, feedback across all three amplifiers being provided via an orifice 60 adjusted by the lever 22. The difference between the pressures Pc and Pr is amplified by the amplifiers 26, 34, 36 to provide an error signal Pc* which is fed to a vortex amplifier 44 having a variable power supply pressure Px supplied via a variable orifice 54 by a fluid potentiometer 58, 56 connected between the pressure P4 and the compressor inlet pressure P3. The output pressure P4s of the amplifier 44 is fed to a capsule 51 of a fuel control system 52. During engine acceleration, Pc* is less than Px, and the vortex amplifier is then in the non- vortexing state whereby P4s is about 0À9 Px. Pc* increases as the required ratio P4/P1 is approached. When Pc* has become greater than Px, the amplifier is in the vortexing state, the resultant reduction in P4s causing the fuel control system to reduce the fuel-flow. A variable orifice 50 in an outlet which vents to Po provides a deceleration limit. The ground idling speed is adjusted by an adjustable orifice 62 in parallel with the orifice 18. A low ground idling setting is obtainable by an orifice 64 controlled by a solenoid 66. In Fig.1 (not shown), the means 62, 64, 66 are omitted, and the pressures Po, P4 applied to the potentiometer 20, 18 are reversed.