Patent GB-1183910-A (GB)
Title: Fuel Control for a Gas Turbine Engine
IPC: F02C9/32
Filed: 1968-11-27
Abstract: 1,183,910. Gas turbine engine fuel systems. BENDIX CORP. Nov. 27, 1968 [Dec. 21, 1967], No. 56216/68. Heading F1G. The fuel-flow to a gas turbine engine is controlled by a metering valve which is controlled by a pneumatic control system the output member of which is actuated on the one hand by a first pressureresponsive element responsive to a first pneumatic control pressure representative of the compressor discharge pressure and on the other hand by a second pressure-responsive element responsive to the difference between the first pneumatic control pressure and a second pneumatic control pressure controlled from the first one by a variable area governor valve means actuated as a function of a speed error signal representative of the difference between the engine speed as sensed by a centrifugal governor driven by the compressor-driving turbine and a desired speed selected by a speed control lever, the second pressure-responsive element being connected to the output member through compression resilient means and being adapted to engage a fixed abutment when the difference between the first and second pneumatic control pressures exceeds a predetermined value. Fuel is supplied to the engine through a throttle valve 84 actuated by an evacuated bellows 230 and a bellows 122, the bellows 230 being subjected to an air pressure in a line 138 while the bellows 122 is subjected to the difference between this pressure and an air pressure in a line 150. The pressure drop across the fuel valve 84 is kept constant by by-pass valve 94 controlled by a diaphragm 92 subjected to the pressure drop. Air at compression discharge pressure is bled from an inlet 134 to a low pressure point such as the atmosphere via a throttle valve 200, a fixed restrictor 152 and a throttle valve 154, in series, the line 138 being connected between the valve 200 and the restrictor 152, and the line 150 being connected between the restrictor 152 and the valve 154. When a control lever 62 is turned to accelerate the engine, it moves lever 168, 190 to reduce the opening of valves 154, 200 thereby increasing the pressure in the line 138 and decreasing the pressure difference between lines 138 and 150. The resultant contraction of bellows 122, 230 increases the opening of the fuel valve 84. As the engine accelerates, a governor 180 driven with the compressor moves the lever 190 to fully open valve 200. As the lever 190 moves further, it engages the lever 168 and moves the latter to increase the opening of valve 154. The resultant increase in pressure difference between the lines 138, 150 expands the bellows 122, thereby partially closing the fuel valve 84 until a steady state is reached. When lever 62 is moved to decelerate the engine, whereby the lever 168 is moved to increase the opening of valve 154, the resultant increase of pressure difference between the lines 138, 150 causes the bellows 122 to expand to reduce the opening of the fuel valve 84 until the top 222 of the bellows abuts a stop 224. Thereafter, the bellows 122 is ineffective to control the fuel valve 84, which is closed by the bellows 230 in response to a decrease in compressor discharge pressure, the portion 220 of the bellows 122 between the top 222 and the point of attachment to stem 124 acting merely as a spring. The bellows may be replaced by diaphragms or pistons. Variation in air temperature at the compressor intake is compensated for by a device 240 which senses the temperature and controls a bleed valve 242 connected to the line 138. If the engine overspeeds, the lever 168 opens a valve 231 in parallel with the valve 154.