Patent GB-1231791-A (GB)
Filed: 1967-02-16
Abstract: 1,231,791. Gas turbine engine fuel systems. JOSEPH LUCAS (INDUSTRIES) Ltd. April 29, 1968 [Feb.16, 1967], No.7501/67. Heading F1G. . The invention relates to a gas turbine engine fuel control system comprising a control unit which controls the supply of fuel in accordance with a number of engine operating parameters, the parameters being engine speed and two pressures obtaining at different stages of the engine compressor, the two pressures being applied to a flexible device which acts to control the flow of fuel. In accordance with the invention, means are provided for modifying the response of the flexible device to the two pressures, the means comprising a device which is responsive to a further pressure obtained from a further stage of the engine compressor, the device being also responsive to the position of a manually set member. The device is arranged to actuate a valve in a passage which affords communication between passages through which said higher and lower pressures are applied to the flexible device, so as to modify the ratio of these pressures which is exerted upon the flexible device. In the embodiment the fuel control unit 11 comprises an inlet 10 and an outlet 12, the fuel metering device comprising an axially movable sleeve 14 formed with an orifice 15 which cooperates with a variable orifice formed between a fixed sleeve 16 and an axially movable sleeve 17. The fuel-flow is also controlled by a further sleeve 20 which moves axially in dependence on engine speed. The axial position of the sleeve 14 is controlled by means of a flexible device 18 in response to pressures at two different stages of the engine compressor. The axial position of the sleeve 17 is controlled in dependence on engine speed by means of a centrifugal governor device, the spring loading of which is controlled by a manual control 21. The flexible device 18 comprises a pair of bellows, one being evacuated and the other being subjected internally to a compressor pressure communicated through line 23. The bellows assembly is disposed within a chamber to which a further and higher compressor pressure is communicated through line 24. The lines 23 and 24 are inter-connected, restrictions 25, 26, 27, 28 being disposed as shown. The lines 24 and 23 are also inter-connected by a line 33 which is controlled by a valve member 32 at one end of a pivotally mounted lever, the other end of the lever being controlled by a bellows 35 and a bellows 36. The interior of the bellows 35 is connected through lines 35a and 41 to a further compressor pressure, in this case the pressure at the compressor inlet. The bellows 36 is evacuated. The bellows assembly 35, 36 is disposed within a chamber 34 to which the higher compressor pressure in line 24 is communicated through lines 43, 44, the outlet from the chamber 34 being controlled by a throttle valve 37 which is itself controlled by the manual lever 21 through the linkage 38. The connection between the lines 43, 44 is controlled by a valve member 39 which is pivotally mounted within a chamber 45 and is controlled by a bellows assembly 40, 42, the bellows 40 being connected to line 41 and so to compressor intake pressure, and the bellows 42 being evacuated. A further control is provided to limit the compressor pressure which is sensed in line 24. A line 47 communicates with line 24 downstream of the restrictor 27, the outlet of lines 47 to chamber 48 and so to atmosphere being controlled by a valve member 50 on a pivotally mounted lever. The lever is controlled by a bellows 52 to which the compressor pressure existing in line 24 is communicated through line 53, and by a spring-loading 51.