Patent GB-945353-A (GB)
Title: Fuel control for gas turbine engines
Inventor: FLEMING ROBERT STEWART
IPC: F02C9/16
Filed: 1960-03-28
Abstract: 945,353. Fluid-pressure servomotor systems. HOLLEY CARBURETOR CO. March 28, 1960, No. 10846/60. Heading G3P. [Also in Division F1] The fuel supply to a gas turbine engine is by way of centrifugal and gear pumps in series to a passage 28 leading to a metering valve 34 having ports 40 coacting with ports 38 in a fixed sleeve 36, and thence through a passage 46, spring-loaded valve 354 and cut-off valve (not shown) controlled by a power lever 282 to the burners. The metering valve 34, the pressure difference across which is governed by a by-pass valve 52 having compensation for fuel temperature variation, is arranged for rotary and axial movements to control fuel flow for acceleration, deceleration and steady running. Axial movement is caused by variation of pressure in a chamber 72 occasioned by movement of a valve 60 coacting with a seat on the metering valve so that the latter follows up the movement of the valve 60. The valve 60 is actuated by a lever 62 coacting with a spring- loaded, moving cylinder 270 and with a cam 144 which can be moved axially and rotated. Rotation is effected by a servopiston (not shown) having a depending rod 160 coacting with a helical slot to convert axial to rotary motion, and the servopiston is controlled by a valve carried by a lever 196 which is operable by a movable cylinder 194 and subject to a feedback force applied by rollers 206 movable by the servopiston and loaded by a spring having fuel temperature compensation. Both movable cylinders 270 and 194 are subject to a speed-responsive pressure governed by a centrifugal valve carried by an engine driven rotor rotor 216. Rotation of the metering valve is effected by a servopiston and helical slot arrangement similar to that for rotating the cam 144 but controlled in this case by compressor outlet pressure acting on a bellows assembly 210 which incorporates a valve to limit the pressure applied.. Should the rotary and axial positioning of the metering valve become such as to give an excessive flow a valve 75 is operated to limit the pressure in the chamber 72. Axial positioning of the cam 144 is by a lever 172 which is rocked by axial movement of a further cam 256 adjusted by a servopiston under the control of compressor inlet pressure. The cam 256 is rotated by the power lever 282 and coacts with a follower 284 which, through a further servopiston (not shown), effects adjustment of a lever 314 to vary the spring loading on the cylinder 270. At low fuel flow rates closure of the valve 354 results in the opening of a minimum flow valve 372 by-passing the metering valve 34. During steady state operation the lever 62 is out of contact with the cam 144 and fuel flow is controlled by compressor outlet pressure governing the rotational position of the metering valve and. engine speed, compressor inlet pressure, and power lever position governing the axial position of the metering valve through the cylinder 270 subject to the speed responsive pressure and to its spring loading controlled by the lever 314 under the control of the lever 284. Movement of the power lever to accelerate the engine results in compression of the spring loading the cylinder 270 and consequent engagement of the lever 62 with the cam 144 which then governs the axial positioning of the metering valve during acceleration, whilst during deceleration the force of the spring loading on the cylinder 270,is relaxed such that the valve 60 rests against a stop 73 causing the metering valve to adopt its lowermost position and control is effected solely by rotational movement of the metering valve in response to compressor outlet pressure. In a modification, the lever 172 is omitted and the axial position of the cam 144 is determined by means responsive to compressor inlet temperature, whilst in a further modification the cam 256 is positioned axially by temperature instead of by compressor inlet pressure.