Patent GB-1390749-A (GB)
Title: Fuel control units for gas turbine engines
IPC: F02C9/32
Filed: 1973-04-17
Abstract: 1390749 Gas turbine engine fuel systems; jet-propulsion engines SOC NATIONALE D'ETUDE ET DE CONSTRUCTION DE MOTEURS D'AVIATION 17 April 1973 [19 April 1972] 18349/73 Headings F1G and F1J A gas turbine engine fuel control unit comprises a housing 8 containing hydromechanical elements 12, electro-mechanical elements 13 and electronic elements 10 immersed in a fuel bath which is renewed by a circulation of fuel between escape or return flows caused by the operation of the hydromechanical elements and a fuel return conduit 26, the electronic elements being housed in a removable cover 9 and fixed to the upper part of a support 11, the lower part of which supports the electro-mechanical elements. The elements 10, 13 are cooled by the fuel bath. Fuel delivered by an engine driven pump 3 passes via duct 14 to a metering device 16 comprising a needle 19 controlling, in opposite senses, a metering orifice 22 leading, via ducts 27, 1 to the burners and a bypass orifice 23 leading via the interior of a device 44 to the interior 25 of the housing 8 and thence via the return conduit 26 to the suction side of the pump 3. The device 44 comprises a pivoted blade 45 controlled via bellows 48 by the compressor delivery pressure and acting to differentially throttle two opposed nozzles connected by ducts 49, 50 to respective spaces on opposite sides of the actuating piston 42 of the needle 19, the two spaces being connected via respective restrictors to the duct 27. The blade 45 thus controls the position of the needle 19, negative feedback being provided by a spring 5 1 having a pivoted abutment 46 which is coupled to the blade 45 by rollers 47 which are positioned vertically by a cam 54 adjusted by a motor 55 forming one of the electro-mechanical elements 13 and controlled in accordance with various engine variables by the electronic computer 10. Feedback to the motor 55 is provided by a  transducer 56 sensing the position of the cam 54. The pressure drop across the metering orifice 22 is maintained constant by a by-pass valve 40 which returns fuel from the duct 14 to the space 25 under the control of a bellows 39 subjected to a pressure controlled by a device 37 which is subjected to the pressure drop. A three-way cock connected to the throttle lever 5 opens a shut-off cock 28. The supply of fuel as a pressure fluid for operating the jacks which control the variable-area jet nozzle of the engine is controlled by a slide valve 59 which is positioned by the pressures prevailing in chambers 58a, 58b, these pressures being determined by a pivoted blade 61a moving between opposed vent nozzles 62a, 62b which are connected to the respective chambers downstream of respective restrictors 60a, 60h. Negative feedback is applied by springs 65a, 65b as a function of the position of the valve 59. The blade 61a is controlled by a torque motor 64 controlled by the computer 10 in accordance with engine variables. The computer 10 receives inputs from an inductive potentiometer 67, indicative of the position of the throttle lever 5, from a capacitive potentiometer 66 indicative of the position of the valve 59 and from a tachogenerator 68 which signals the engine speed in the form of a corresponding electrical frequency. In addition, various temperatures are signalled to the computer through a connector 74 which also serves for the connection of the electrical supply and the piping conveying the compressor delivery pressure to the bellows 48. The computer 10 comprises electronic modules 75 plugged into a printed circuit board 69 and connected by flexible printed circuit tapes to the electro-mechanical elements 13. The elements 13 are connected mechanically by quickrelease couplings such as 4b and 30c to the hydromechanical elements, excpet in the case of the capacitive potentiometer 66, where the rod 66a merely extends into a cavity of the potentiometer without a mechanical connection. After removal of the cover 9, the electronic, electromechanical and hydromechanical elements can be individually removed.