GB1205233A - Fuel flow control systems for gas turbine engines - Google Patents

Abstract

1,205,233. Gas turbine fuel systems. DOWTY FUEL SYSTEMS Ltd. May 2, 1968 [April 14, 1967], No.17282/67. Heading F1G. A gas turbine engine fuel system comprises a flow regulating valve arranged between a source of fuel under pressure and a burner assembly, a linkage arranged to control the opening of the valve as a function of two input signals, of which one input signal is applied to the linkage by means responsive to a pressure signal of a variable operating characteristic of the engine, and of which the other input signal is applied to the linkage by a movable member, first control means for moving the movable member in accordance with a signal derived from two or more other variable operating characteristics of the engine, one of which is the setting of a manual control, second control means for moving the movable member directly from the manual control, and means for holding one of the control means stationary while the other control means is operative. A pump 13, Fig.1 supplies fuel to a burner assembly 20 via a regulating valve 35 and a pressurizing valve 15. The valve 35 is operated by a piston 36, the upper side of which is directly connected to the delivery line 12 of the fuel pump while the lower side is connected to the delivery line 12 via a fixed restrictor 38. The pressure at the lower side is controlled by a half-ball valve 41 carried by a lever 42 pivoted at 46, a feedback spring 44 being connected between the valve and the lever. The pressure difference across the valve 35 is maintained constant by means of a valve 77 operated by a piston 78 controlled by the pressure difference. A pressure signal of an engine-operating variable such as the compressor delivery pressure acts via a capsule 48 opposed by an evacuated capsule 50 on a lever 49 pivoted at 51 and acting on the lever 42 through a movable roller 52. Electrical signals indicative of such variables as rotational speeds (leads 21, 22), engine intake temperature (lead 23) and jet pipe temperature (lead 24), and a signal (leads 25, 26) from a manual control lever 28 are fed to a computer 19 which supplies an electrical output signal via leads 17, 18 to a coil 65 to operate a flapper 59 which differentially throttles opposed nozzles 60, 61 which are connected via respective fixed restrictors 62, 63 to the pump delivery line 12, whereby a piston 57 is correspondingly moved. Feedback springs 68, 69 are connected between the piston 57 and the flapper 59. The piston 57 acts through a lever 53 pivoted at a pin 58 to move the roller 52. A governor-controlled spill valve 84 limits engine speed. If the electric supply fails or the computer 19 malfunctions, the lever 53 can be operated directly by the manual control lever 28 through a cam 31 and a follower 32. For this purpose, the pivot pin 58 is withdrawn manually from the lever 53. A switch 71 having a contact maker 70, Fig.2, movable with the pin 58 then cuts the supply both to the coil 65 and to a solenoid valve 74. The valve 74 now opens the right hand side of the piston 57 to low-pressure, and the piston is biased to the right hand end of its cylinder. During direct operation by the manual control lever 28, the lever 53 pivots about a point 56.