Patent GB-920661-A (GB)
Title: Gas turbine engine fuel system
Inventor: JOHNSON CHRISTOPHER LINLEY
IPC: F02C9/16
Filed: 1960-06-02
Abstract: 920,661. Gas turbine engine fuel systems; speed governors. ROLLS-ROYCE Ltd. May 26, 1961 [June 2, 1960], No. 19618/60. Classes 57 and 110 (3). A gas turbine engine fuel system comprises in flow series a fuel reservoir 10, a centrifugal main fuel pump 14, a fuel control unit 21 for metering the flow of fuel in accordance with one or more engine variables, and a fuel circuit incorporating spill burners 110, a centrifugal circulating pump 106 being provided for circulating the fuel in the fuel circuit. A top speed emergency governor device also being provided so as to reduce the amount of fuel when the engine speed exceeds a predetermined value, the governor device being responsive to the pressure of the high pressure side of the circulating pump. Fuel delivered by the main fuel pump 14 passes through duct 18 into the chamber 20 within the control unit, the fuel then passing through a metering orifice 43, 45 before discharging from the control unit through outlet duct 63, 87. The control unit comprises a cylindrical member 27 which is axially and rotatably mounted within a bore 28 in the unit. The outer race of the ball bearing 30 in which the member 27 is mounted is connected by means of members 31, 32 to a pair of bellows 33, 34 which are disposed within a chamber 22 which is supplied with air through passage 42 which is connected to a passage 38 between restrictions 40, 41 therein, the passage 38 being connected to a supply of air at the delivery pressure P 2  of the compressor or at a pressure functionally related thereto. Each bellows 33, 34 is divided into two compartments 35, 36, the compartments 35 being evacuated and the compartments 36 being supplied with air under pressure from the passage 38 downstream of the second restriction 40. The downstream end of the passage 38 communicates by way of a hole 39 with the compressor inlet. The cylindrical member 27 will thus move axially as the pressure supplied to the passage 38 varies. The member 27 is formed with triangular-shaped apertures 43 which co-operate with an annular gap 45 to define a fuel metering orifice. The gap 45 is formed between a fixed wall and an axiallymovable and rotatable sleeve 44 which is mounted on the cylindrical member 27, the sleeve 44 having a radially-extending flange 46 to which are connected push-rods 47 which pass through apertures 26 in the wall 25. The push-rods are connected to a ring member 48 against which act the lever arms of governor weights 49, the weights being carried by a governor housing 68. The annular gap 45 will thus be varied in dependence on engine speed. The loading of the spring 54 which acts on the sleeve 44 in opposition to the governor 49 may be varied by means of the control lever 50 which adjusts the position of the cam 50<SP>1</SP>. Fuel supplied to the chamber 20 passes through the metering orifice 43, 45 to the space within the cylindrical member 27 and then discharges through outlet 63, the outlet being controlled by a cylindrical throttle member 60. The throttle member 60 is formed with an extension 61 having a flange 66 against which bear the lever arms of centrifugal governor weights 67 so that the position of the throttle member 60 is dependent on engine speed. The throttle member is also provided with two surfaces 64, 65, the pressure of the metered fuel acting on the surface 64, and the pressure of the fuel upstream of the metering orifice acting on the surface 65, so that the position of the throttle member 60 is also dependent on the pressure drop across the metering orifice. The governor housing 68 is connected by means of rods 70 to a gear 71 which is rotatably mounted on a fixed shaft 72, the gear 71 being driven from the engine by means of a compound gear 73. Rotatably mounted on the rods 70 are compound gears 74, 75, the gear 74 engaging with a fixed gear 76 mounted on the fixed shaft 72 and the gear 75 engaging with a gear 77 secured to the throttle extension 61, the gear 75 being elongated to permit axial movement of the gear 77. The throttle member 60 is connected by a rod 78 to a slider 80 whereby the cylindrical member 27 is rotatably driven. A second cylindrical member 82 is connected to the member 27 at the side thereof remote from the metering orifice, the member 82 being disposed within a chamber 83 which is connected by means of a pipe 84 to the space within the cylindrical member 27 whereby the member 27 is pressure balanced axially. The space within the chamber 83 is also connected by means of a duct 85 and solenoid valve 86 to the line 87, a restriction 88 being disposed in the duct. Fuel discharges from the control unit through the lines 63 and 87 to the emergency governor 90 which comprises a sleeve 121 disposed within a valve body 120. The sleeve is provided with ports 124 which co-operate with the annular passage 125 to which fuel is delivered by the duct 87, also with ports 126 which communicate with an annular passage 127 which communicates with the outlet pipe 91. The sleeve is rotated by means of gearing 123, 122, and is loaded upwardly by means of the spring 128. The sleeve valve is also loaded upwardly by the fuel pressure within it and downwardly by the pressure of fuel delivered by the centrifugal circulating pump 106 through the line 112. Normally, fuel passes from the line 87, through the ports 124 to the line 91, but should the engine speed exceed a predetermined value, the increase in pressure of fuel at the outlet of the pump 106 will cause the sleeve 121 to move downwardly so as to reduce the fuel supply to the spill burners 110. The governor outlet 9] communicates with the shut-off cock 92 which comprises a valve member 94 disposed within a valve body 93, the cock being shown in the " Open " position in Fig. 1. The valve member 94 comprises three reduced diameter portions 96, 97, 98, also an axial bore 95 and is movable by means of a rack and pinion 100, 101. In the " Open " position, fuel from the line 91 passes through the reduced portion 98 and discharges through the line 103 which divides into two paths 105, 107, the line 105 leading to the inlet of the circulating pump 106, fuel discharging from the pump through line 111 to the reduced portion 96 of the valve body 94 and thence through line 115 to the annular passage 116 within the spill burner 110, some of the fuel discharging through the nozzle 117, the remainder, i.e. the " spill flow " passing into the chamber 108 and returning by way of lines 107, 105 to the inlet of the circulating pump. Fuel passes also from the reduced portion 96 through line 112 to the upper side of the governor sleeve 121. When the shut-off cock is moved to the " Closed " position shown in Fig. 2, the reduced portion 98 is displaced from the inlet duct 91 and reduced portion 97 is aligned therewith, fuel from the line 91 now passing into reduced portion 97 and discharging through outlet duct 104 back to the inlet of the main fuel pump 14. Also, fuel delivered by the circulating pump 106 into the line 111 now passes into the axial bore 95 in the valve body 94 and passes through non-return valve 113 to the pump passage 114.