Patent GB-908629-A (GB)
Title: Fuel control for gas turbine engines
IPC: F02C9/16
Filed: 1961-06-20
Abstract: 908,629. Fluid-pressure servomotor control systems. BENDIX CORPORATION. June 20, 1961 [Aug. 8, 1960], No. 22329/61. Class 135. [Also in Group XXVI] In a fuel control system for a gas turbine engine, the effective flow area of the fuel conduit is controlled by a governor-controlled valve which is actuated as a function of engine speed, and as a function of the position of a throttle member controlling the operation of the engine, the fuel pressure upstream of the fuel nozzle being controlled by a regulator which is responsive to compressor generated air pressure such as the discharge pressure of the air compressor, the regulator comprising a valve which is arranged to control fuel flow in the conduit. The control unit shown in Fig. 1 comprises a casing 36 having a fuel inlet 38 and a fuel outlet 40. A positive displacement fuel pump 48 is disposed within the casing and is driven at the speed of the engine compressor 22 by means of a drive connection 70. Fuel passes from the inlet 38 through duct 46 to the inlet of the pump and discharges therefrom through duct 50 into chamber 52, the fuel then passing through variable orifice 54 into duct 56 through the valve member 58 and check valve 60 to outlet orifice 40. A by-pass duct 64 having an inlet orifice 62 controlled by a valve 94 is provided between the duct 50 and the duct 46 leading to the pump inlet. The valve 94 is connected to two diaphragms 74, 76, the space above the upper diaphragm 76 being subjected to compressor discharge pressure P c  by means of line 92, the space 86 between the diaphragms being open to atmospheric pressure P a  by means of vent 88, and the lower side of the lower diaphragm being subjected to fuel pump pressure P 1 . The valve 94 is also loaded in a closing direction by means of a spring 96. The orifice 54 is controlled by means of an annular member 108, the position of which is controlled by means of a centrifugal governor 98 driven from the engine compressor 22. The governor spring 112 bears against a tubular member 114 the position of which is adjustable, so as to vary the loading of the governor spring, by means of a cam 130 secured at the end of the throttle valve 58. The valve 58 which is rotated by means of the throttle lever 122 comprises a slot 128 which is arranged so as to increase the area of the fuel flow passage as the lever is moved from the cut-off to the idle positions, but between idle and maximum speed positions moves the member 114 downwardly so as to increase the loading of the governor spring 112. A needle valve 144 is disposed in the fuel duct 42 leading to the fuel burners 44, the position of the valve being set manually in accordance with a given altitude setting. Alternatively the needle valve may be controlled automatically either by means of a temperature-sensitive device or a pressureresponsive device. The fuel burners 44 are utilized as fixed fuel metering orifices. An orifice 120 is provided so as to allow fuel to flow to the burners 44 even when the orifice 54 is closed. The apparatus shown in Fig. 2 is similar to that of Fig. 1 except that a pressure type of governor is utilized in place of the centrifugal type. Fuel enters the casing 36 through inlet 38 and is delivered by the pump 48 through duct 50, the duct being controlled by a port 162 in a valve member 164. The fuel then enters the chamber 166 and passes through the orifice 168 to passage 170 which is controlled by a port 172 in the valve member 164. The fuel then passes through the spring-loaded check valve 60 and issues through outlet port 40. A fuel pressure regulator 72 controls the flow of fuel through the by-pass duct 64 as in Fig. 1. The valve 164 is rotated by means of the throttle lever 122, the valve port 172 being shaped so that the flow area therethrough increases gradually as the throttle lever is moved from the start to the idle position, the flow area being constant as the throttle is moved from the idle to the maximum speed position. The effective area of the orifice 168 is controlled by the valve member 174 which is actuated by the pressure governor which comprises a diaphragm 178 which is subjected at its left-hand side to the fuel pump pressure P 1  which is communicated through duct 190. The right-hand side of the diaphragm 178 is subjected to the pressure P 2  of fuel in the chamber 166, i.e. the fuel pressure downstream of the port 162. A passage 192 controlled by a spring-loaded check valve 194, is provided so as to permit fuel at a predetermined pressure P 1  to pass into the chamber 166 so as to prevent the pressure difference P 1 -P 2  from exceeding a predetermined maximum value. The port 162 in the valve member is shaped so that as the valve member is rotated by the throttle lever, the port presents a progressively increasing opening so as to permit a greater flow of fuel to the engine. An orifice 198 is provided so as to maintain fuel flow to the engine when the orifice 168 is closed. A passage 204 controlled by a spring-loaded ball valve is provided between the ducts 50 and 46, the valve opening should pressure P 2  exceed a predetermined value. The fuel control unit shown in Fig. 3 is similar to that of Fig. 2 except that it is modified by the addition of a second governor mechanism for controlling the speed of a separate power turbine. The orifice 168 is controlled by the valve member 174 which is controlled by means of a diaphragm 178 as in Fig. 2 in response to the fuel pressure differential P 1 -P 2 . The valve is also controlled by means of a lever 210 which is pivotally mounted at 212 and is normally held away from the orifice 168 by a light spring 216. The lever is also actuated in dependence on the position of a throttle lever 218 and the speed of the separate power turbine. A positive displacement hydraulic fluid pump 240 is provided and is driven by the separate power turbine so that the pump delivers fluid at a rate proportional to the speed of that turbine. The control fluid pressure #H is applied through a line 236 to one side of a diaphragm 226, the other side of the diaphragm being subjected to atmospheric pressure P a . A lever 224 is held against the diaphragm 226, the lever being rigid with the arm 220 of a bell-crank lever, the second arm 222 of the bell-crank lever being adapted to engage the pivoted lever 210 and so to control the effective area of the orifice 168. The pressure of the control fluid in line 236 is dependent on the position of a throttle lever 218 which controls a valve 242 which is connected between the line 236 and the tank 238. In Fig. 4 a maximum speed governor 248 responsive to the speed of the separate power turbine is provided. The duct 92 by which compressor discharge pressure P c  is applied through orifice 272 to the chamber 84 of the pressure regulator 72 is connected by means of duct 274 and port 276 to the interior of the governor casing 250, the casing being vented to atmosphere through port 278. The port 276 is normally closed by a flapper valve 270 which forms part of a U-shaped lever 266 pivotally mounted at 268, the second arm of the lever being disposed between the governor arms 258 and the control spring 262. Should the speed of the separate power turbine exceed a predetermined value, the U-shaped lever will pivot in an anti-clockwise direction so opening port 276 and the duct 92 and chamber 86 will be vented to atmosphere. The pressure differential P c -P a  across the diaphragm 76 will thereby be reduced and the valve member 94 will move away from the orifice 62 so that more fuel will pass through the by-pass passage 64 and so less fuel passes to the combustion chambers.