Patent GB-850477-A (GB)
Title: Improved gas turbine engine fuel system
Inventor: JUBB ALBERT
IPC: F02C9/34
Filed: 1957-08-01
Abstract: 850,477. Gas turbine engine fuel systems. ROLLS-ROYCE Ltd. July 14, 1958 [Aug. 1, 1957; Dec. 20, 1957; June 11, 1958], Nos. 24413/57, 39765/57 and 18736/58. Class 110 (3). [Also in Group XXIX] In a gas turbine engine fuel system for controlling the supply of pressurized fuel from a source thereof to a burner of the gas turbine engine, a fuel supply control unit is provided having means which afford a metering orifice, means also being provided for supplying pressurized fuel from the source to the burner via the control unit and the orifice. Means are also provided for varying the size of the metering orifice in accordance with engine rotational speed, and independently in proportion to the ratio of the outlet and intake pressures P 2  and P 1  respectively of a compressor of the engine, further means being provided for metering the fuel flow to the burner in accordance with the pressure drop across the metering orifice. In Fig. 4, fuel is supplied under pressure from a swash-plate type fuel pump through a duct 24 to a first control unit 25 in which is mounted a rotatable sleeve 61 formed with a toothed flange 62 which engages with a gear-wheel 63 by which the sleeve is rotated. The flange 62 is formed with a cylindrical portion 65 on which governor weights 66 having operating arms 67 are pivotally mounted. The governor arms 67 engage the flange 68 of an axially-slidable cylindrical sleeve 69 which moves axially between stops 73, 74 against the load of spring 71. The adjacent ends of sleeves 61 and 69 cooperate to form an adjustable annular slot 70, the right-hand edge of the slot being movable axially in dependence on engine speed. Within the sleeve 61 is slidably mounted a piston 76 having a rod 77 which is formed with a cylindrical sleeve 78 having triangular apertures 79 therein, the apertures 79 co-operating with the annular slot 70 to afford variable area orifices. Fuel supplied through duct 24 passes to the inside of the sleeve 61 and acts against the lefthand face of the piston 76, escape of fuel from within the sleeve being controlled by valve 82a co-operating with sleeve outlet 82b. The position of valve 82a is controlled by a bellows 84 disposed in chamber 85, compressor outlet pressure being applied to the chamber 85 through duct 86 and restriction 87, and the chamber being connected to the compressor intake through restriction 88 and duct 89. The bellows 84 is connected to the valve 82a by means of lever 83 and the position of the valve and so of the triangular slots 79 in the sleeve 78 are positioned in dependence on P 1  F (P 2 /P 1 ). Fuel flows through the outlet 82b through the passage 91 to the space within the sleeve 78, through the variable orifices defined by the triangular slots 79 and the annular slot 70 into the space 93. Metered fuel then flows through duct 37 into the second control unit 38. Highpressure (unmetered) fuel is also supplied to the control unit 38 through duct 42. The control unit 38 comprises a piston 94 slidable in sleeve 94<SP>1</SP>, the piston being formed with rod and housing 105a. The control unit also comprises a rotatable cylinder 97 which is driven by the engine through pinion 95, the cylinder having mounted therein two governor weights 100, 101, the operating arms 102, 103 of which bear against a cup member 104 slidable in the housing 105a against pressure of spring 105. The position of piston 94 with respect to the fuel outlet ducts 107, 106 leading to the main burner and pilot burner respectively is therefore controlled in dependence on the pressure difference across the variable orifice formed by the triangular slot 79 and the annular slot 70, and on the engine speed by means of the governor device 100, 101. The outlet to the main burner is connected via the duct 23 to one face of the control-piston of the variable swash-plate fuel pump, fuel pump outlet pressure being applied to the opposite face of the piston; when the outlet duct 107 tends to be closed by the piston 94 the fuel pump outlet pressure will rise and the fuel pump servo-piston 19 will move to the right, acting on the swash-plate so as to reduce the pump output. The gear-wheel 63 is driven by the geared flange 98 formed on the housing 97. The compression of the spring 71 which bears on the sleeve 69 is varied by means of the pilot's control-lever 108 acting through the pinion 75a and rack on the cup member 75. In Fig. 5 fuel is supplied under pressure by pump 213 from tank 210 to the space 216 within the control unit 215. A cylindrical member 217 having an internal blanking wall 217a and terminating in a sharp edge 217b projects through a wall of the control unit, a sleeve member 218 being mounted on the cylindrical member so as to be free for rotational and axial movement thereon. The sleeve 218 is formed with four triangular apertures 218a and carries a toothed gear-wheel 218b. A further sleeve member 219 is mounted in a bore 220 in an internal wall 221 of the control unit in axial alignment with the sleeve 218. The sleeve 219 is formed with a closed end 219a and with partannular sharp-edged orifices 219c. A gearwheel 219b is formed integrally with the sleeve 219. Slidably mounted within the sleeves 218, 219 is an open-ended cylinder 222 which terminates at its left-hand end in a sharp edge 222a, the edges 217b and 222a co-operating to form an annular slot which with the triangular apertures 218a, produce four part-annular orifices 223. The area of each orifice is controlled in accordance with P 1  F (P  2 (P  1 ) by means of a bellows 226 disposed within chamber 227 which receives air under pressure P 2  from the compressor outlet through duct 232 and restriction 232a, and discharges to the compressor intake through restriction 231a and duct 231. The bellows 226 is connected to a shaft 224 by means of a coupling which allows relative rotational movement but which does not allow relative axial movement between the parts. The shaft 224 is formed with a gear-wheel 224b having cheek-plates 224a on either side thereof, the gear-wheel 218b of the sleeve 218 engaging with the wheel 224b between the cheek-plates. Axial movement of the shaft 224 due to movement of the bellows 226 is thereby communicated to the sleeve 218 so causing variation in area of the orifices 223 by movement of the triangular apertures 218a. The sleeve 218 and so the shaft 224 are caused to rotate by means of splined shaft 239 engaging with the gearwheel 218b. The cylinder 222 is caused to move axially within the sleeves 218 and 219, so varying the width of the annular slot formed between edges 217b, 222a by means of a governor 234. The shaft 236 is driven from the shaft 239 by means of gearing 239a, 236a and is formed with two cup-shaped members 234a, 235a, governor weights 234c being pivotally mounted within cup member 234a. The governor arms act on an axially-movable sleeve 241 which carries pins 241a which co-operate with the forked end of a link 225, the other forked end of the link engaging with pins 222b on the cylinder 222. The governor controlspring 243 is disposed between the pilot's control lever 244 and a lever mounted on the spindle 225a. The pressure difference across the orifice 223 is communicated to either side of the closed end wall 219a of the sleeve 219, the orifices 219c of which control the openings to the annular outlets 228, 229 to the pilot burner 228b and main burner 229b respectively. The governor 235 comprises weights 235c pivotally mounted within cup member 235a, the governor arms acting on an axially-movable sleeve 247 which co-operates with pivoted levers 248b and 248a, the lever 248a co-operating with a collar 251a secured to the closed end of sleeve 219. The levers 248b, 248a may have a spring 250 disposed therebetween as shown, the two levers abutting by means of stops 248c, 248d so as to move as one above a certain speed. Alternatively the levers may be formed as a single unit. The governor 235 functions to produce a pres-. sure drop across the part-annular orifices 223 in accordance with the square of the rotational speed. In Fig. 7 the casing of the control unit is divided into two chambers 314, 315 by means of a partition 316, the two chambers being interconnected by a bore 317 in the partition. Fuel is supplied to the chambers through duct 312 by means of fuel pump 313, the fuel outlets to the pilot and main burners being through ducts connected to the annular ports 363, 364 respectively within the partition 316. A sleeve 340 is supported within the partition with freedom for rotational and axial. movement, the sleeve being formed with four circumferentially-spaced apertures 362 which co-operate with the annular ports 363, 364. The sleeve 340 is secured on a shaft 341 to which are secured a flanged sleeve 374 and a sleeve formed with a gear-wheel 342. The gear-wheel is rotatably driven from the pinion 320 by an epicyclic gear-train. The shaft 341 carries at its other end a transverse pin 343 which engages grooves 345 in a sleeve member 346 which is rotatably mounted in bearings 348, 350, the sleeve 346 engaging within the sleeve 340 and being formed with triangular apertures 347. A further sleeve 357 is mounted on the sleeve 346 with freedom for axial movement but constrained against rotational movement, the left-hand edge of the sleeve 357 cooperating with the right-hand edge of the bearing 350 to form a circumferential slot 358 of variable area. The slot 358 co-operates with the triangular apertures 347 to form variable area orifices, the end wall 340<SP>1</SP> of the sleeve 340 being subjected on its outer side to the pressure of the fuel pump discharge and on its inner side to the pressure at the downstream side of the orifices 347, 358. The sleeve 340 therefore tends to move to the left as a result of this pressure difference. The sleeve 340, however, tends to be moved to the right by means of the governor 373 which bears 'a