Patent GB-988845-A (GB)
Title: Gas turbine engine fuel system
Inventor: JOHNSON CHRISTOPHER LYNLEY
IPC: F02C7/22
Filed: 1964-02-04
Abstract: 988,845. Gas turbine engine fuel systems. ROLLS-ROYCE Ltd. Feb. 4, 1964, No. 4777/64. Heading F1G. [Also in Division G3]  A gas turbine engine fuel system comprises a fixed body 10 having a chamber 11 therein, fuel at high pressure being supplied to the chamber through inlet 12. A rotor shaft 13 adapted to be driven by the engine is rotatably mounted in the body 10, a rotor 14 in the form of a disc being secured to or integral with the rotor shaft. The rotor 14 is formed with two valve bores 30, 31, the axes of the bores being disposed at right angles to the axis of the rotor shaft and valve members 32, 33 are disposed in the bores 30, 31 respectively, see Fig. 2. The rotor shaft 13 is also formed with an axial bore 15 and an axiallymovable valve member 16 is disposed therein, the valve member 16 being connected by a rod 17 to a bellows assembly 19. The valve member 16, which is shown in two different positions in Fig. 1 is non-rotatable and co-operates with a series of small bores 44 in the rotor 14 so as to constitute part of a fuel metering orifice. The bellows assembly 19 comprises a first portion 21 which is evacuated and a second portion 22 which is connected by line 23 to pressure P 1  which is functionally related to the pressure at the inlet of the engine compressor. The space 25 between the bellows and the wall of the bellows chamber is connected by line 24 to the space between a pair of restrictions in a conduit opposite ends of which are connected to pressures which are functionally related to pressures Pi and P 2  at the inlet and outlet ends of the engine compressor. The valve members 32, 33 are pivotally connected to bifurcated arms 34, each pair of arms having thrust pads 35 which are disposed at the opposite sides of a swash plate 36, the arrangement being such that as the rotor rotates the valve members 32, 33 are caused to be oscillated circumferentially within the respective bore, such oscillation reducing the tendency for the valves to stick in the valve bores. Each of the valve members 32, 33 has also pivoted thereto an arm 37 which carries a governor weight 40, see Fig. 3, the governor weights in operation tending to move the valve members outwardly of the respective bores 30, 31. Movement of the valve 32 outwardly of the bore 30, that is, to the left as seen in Fig. 2, is resisted by a spring 46 which is disposed within bore 45 in the valve member and is connected between a pin 47 secured to the valve member and to a pin 38 secured to the rotor 14. Movement of the valve member 32 outwardly of the bore is also resisted by pressure of fuel referred to as "servo pressure" communicated to the valve bore 45 from chamber 49 see Fig. 5, by way of duct 48. Fuel from the chamber 11 passes into a "figureeight" shaped passage 41 in the rotor 14, see Fig. 2, thence to a passage 42 which communicates with the valve bore 30, the valve member 32 being formed with a reduced diameter portion 43 in the region of the passage 42, whereby fuel may flow from the chamber 11 through the passages 41, 42 to the reduced diameter portion 43 of the valve member 32, the fuel then passing through the small bores 44 into the space within the bore 15 of the rotor shaft. The number of the small bores 44 available for fuel flow is dependent on the axial position of the valve member 32 and thus on engine rotational speed and also on the axial position of the valve member 16 and thus on pressures at the compressor inlet and outlet. A portion of fuel from the space within the valve bore 15 may pass through outlet 63 to the pilot burner of the combustion equipment, but the main portion passes through duct 66 to the reduced diameter portion 65 of the valve member 33 the fuel then passing to an annular chamber 68 which itself communicates with a passage 67 and thence to the main burners of the combustion equipment. The flow of fuel through the duct 66 is controlled by the axial position of the valve member 33 and this is dependent in part on the centrifugal force of the respective governor weight 40 and in part on the pressure drop across the metering orifice, the righthand end of the valve member 33 being subject to pressure of fuel within the chamber 11, that is, upstream of the metering orifice, and the lefthand end of the valve member 33 being subject by way of duct 64, to pressure of fuel within the valve bore 15, that is, pressure downstream of the metering orifice. The bores 44 may be of 0À025 inch diameter and may be arranged over an area 0À4 inch long by 0À1 inch wide. The servo pressure which acts within the valve bore 45 is derived from chamber 49, see Fig. 5. The chamber 49 is separated from a chamber 50 by a diaphragm 51, the chamber 50 communicating with the chamber 11 by way of duct 52. The diaphragm 51 carries at its centre a valve member 53, the valve having an axial bore 55 and co-operating with a valve seat 54 so that the chambers 49, 50 are interconnected when the valve member is off its seat. The diaphragm 51 is acted on at its right-hand side by a spring 56 the loading of which is controlled by means of the spring seat 57 and cam 60 by means of a pilot's throttle lever which is connected to the spindle 61. Thus the loading of the spring 56 will determine the value of the servo pressure in the chamber 49 and hence that in the valve bore 45 which acts to assist the action of the spring 46. The datum setting of the governor 40 is thus controlled by the pilot's throttle lever. The governor weight 40 of the valve member 33 may be formed of aluminium or other low density material so as to compensate approximately for differences in density of the fuel flowing through the chamber 11.