GB877811A - Gas turbine engine fuel system - Google Patents

Abstract

877,811. Fluid-pressure servomotor-control systems. ROLLS-ROYCE Ltd. Aug. 24, 1959 [Sept. 1, 1958], No. 28061/58. Class 135. [Also in Group XXVI] In a gas-turbine engine fuel system comprising a throttle valve controlling the flow of pressurized fuel to the engine burners, and wherein the throttle valve obturating member is moved solely by fluid pressure forces acting upon it, one side of the member is subjected to a first fluid pressure which varies in accordance with a first engine variable and its other side, to a second fluid pressure which varies in accordance with a second engine variable. As shown, fuel from a tank 10 passes through a line 12 including a booster pump 13 to the inlet of a centrifugal pump 15 keyed to an engine-driven shaft 17. The pump output is delivered through a channel 47 to a chamber 45 having an outlet orifice 46 controlled by a spindle 48 formed with tapering grooves 54. The spindle 48 is connected to a capsule 50 mounted in a housing 51 to which compressor outlet pressure is delivered through a restrictor 53 so that flow through the orifice 46 is controlled in accordance with compressor outlet pressure. Pressure fluid downstream of the orifice 46 then passes through a passage 62 to a bore 61 in which the obturating member 60 of the throttle valve slides to control a port 63 connected to the engine burners. The chamber 45 is also connected by a passage 65 having a restriction 66 to a further chamber 36. The pressure in this latter chamber acts on the other end of the obturating member 60. The outlet from the chamber 36 leads to a lowpressure chamber 19 connected to the centrifugal pump inlet and is controlled by a shaft 28 formed with metering grooves 43 and moved axially in accordance with engine speed by means of a range speed governor 20. The arms 21 of the governor bear on a stud 23 engageable with the end of the shaft 28 which is loaded by a spring 31. The spring 31 abuts an axially adjustable sleeve 29 having at one end internal gear teeth engageable with planet gears 26 freely rotatable on spindles 251 and meshing with gear teeth on the stud 23 to vary the spring loading. Through the end engagement between the stud 23 and the shaft 28, the rotation of the shaft 17 causes the shaft 28 to rotate which through gears 39, 56, 55, 64 also causes rotation of the shaft 48 and the obturating member 60 to reduce the risk of striction of the shafts 28, 48 and the obturating member. The cross-sectional area of the restriction 66 in the passage 65 is preferably adjustable to compensate for any variation in the density of the fuels that may be used by the engine. On, e.g. increased engine speed, compressor delivery pressure increases causing progressive collapse of the bellows 50 and opening of the orifice 46 to increase the pressure in the bore 61 so that the obturating member 60 moves leftwardly to increase the fuel supply to the burners. At the same time increased engine speed tends to move the shaft 28 leftwardly and when the rise in speed is sufficient to overcome the loading of the spring 31, the pressure drop through the grooves 43 is increased to increase the pressure in the chamber 36 to adjust the obturating member 60 rightwardly until a position of balance is reached between the pressures in the bore 61 and the chamber 36. The booster pump 13 is used during engine starting, the pressure generated by the centrifugal pump although being sufficient to light the burners is insufficient to enable acceleration to take place. As speed increases and the pump 15 takes over, the booster pump 13 is progressively cut out. The obturator member 60 is preferably connected to the pilots throttle lever so that when the engine is shut down the port 63 may be closed to maintain the lines to the burners full with fuel.