GB1244553A - Fuel controls for gas turbine engines - Google Patents

Abstract

1,244,553. 553. Gas turbine engine fuel systems. UNITED AIRCRAFT CORP. March 11, 1969 [March 29, 1968] , No.12673/69. Heading F1G. A gas turbine engine fuel control comprises fuel metering means, regulating means responsive to a number of engine operating variables for regulating the fuel metering means, sensing means for sensing the pressure of the engine working medium, and means responsive to the sensing means solely when the pressure exceeds a predetermined value for positioning the fuel metering means independently of the regulating means at a velocity dependent on the magnitude by which the pressure of the working medium exceeds the predetermined value. A pump 18 supplies fuel to the engine via a throttle valve 46 having a servopiston 56 controlled by a pilot valve 48. A computer 32 applies a signal force indicative of the ratio of the rate of fuel flow to the compressor discharge pressure and influenced also by the engine intake temperature and pressure and engine speed to a multiplication linkage 40, 42, 44 connected to the pilot valve 48. A signal indicative of the compressor discharge pressure is fed to the multiplication linkage by varying the position of roller 42, whereby the pilot valve is positioned in accordance with the product of the two signals, i. e. the rate of fuel flow. Feedback is applied by a spring 50. The compressor discharge pressure signal is obtained by applying the compresor discharge pressure via a line 26 to a bellows 78, an evacuated bellows 76 connecting the pressure to an absolute value. The bellows operate a pivoted flapper 84 for differentially throttling leak-off nozzles 90, 92 located downstream of respective restrictors 98, 100 connected to the discharge side of pump 18, whereby the pressures applied to opposite sides of a servopiston 110 are correspondingly differentially varied. The piston 110 moves the roller 42 via linkage 112, 114. Feedback is applied through linkage 116 and spring 118. A further linkage 122 connected to the piston 110 carries an arm 124 which is normally separated from lever 44. If the compressor discharge pressure exceeds a predetermined value, the arm 124 bears against the lever 44 and turns it to bring the pilot valve 48 into a position in which it reduces the opening of the throttle valve 46, whereby the compressor discharge pressure is reduced. The predetermined value is set by a cam 132 which can be adjusted by a manual control 134 which rotates it or by an evacuated bellows 138 which moves it axially. The bellows 138, which senses ambient pressure or altitude, may be replaced by a sensor responsive to the engine inlet temperature. The two signals fed to the multiplication linkage may be transposed.