Patent GB-728442-A (GB)
Title: Improved fuel control apparatus for gas turbine engines
IPC: F02C9/16
Filed: 1951-11-22
Abstract: 728,442. Automatic control systems for gas turbine engines. GENERAL MOTORS CORPORATION. Nov. 22, 1951 [Dec. 5, 1950], No. 27371/51. Class 38 (4). [Also in Groups XXVI and XXIX] A fuel controller for a gas turbine engine consists of a manually adjustable valve bypassed by a single valve which is automatically adjusted in accordance with altitude and air intake pressure and further automatically modified in accordance with turbine speed plus the rate of change of turbine speed (in order to maintain the turbine speed at a value selected by the pilot), subject to a turbine temperature override sensitive to turbine outlet temperature plus the rate of change of temperature. This override is itself automatically varied to prevent surge, in accordance with turbine speed, inlet air temperature, and turbine outlet temperature. The valve arrangement is similar to that disclosed in Specification 684,581, [Group XXVI], except that to provide the override in respect of the other factors the valve moves within a sleeve which is itself adjustable by being linked to a floating lever (see Group XXVI), adjustable by reversible electric motors 81, 82, through reduction gearing and solenoidoperated clutches. The clutches disengage in the event of an electric power failure and springs can then centralise the lever. Speed control.-The turbine speed is detected by an A.C. tachometer generator 205, Fig. 10, the output of which is applied to a transformer and rectifier 310 via a variable resistor 306, and to a transformer and rectifier 309 via a capacitor 317. A variable resistor 305 is common to both transformers, and together with resistor 306 is ganged to the pilot's control 11. The outputs of the rectifiers are connected in opposition and at the speed selected by the resistors 305, 306, the output is zero. An output varying in magnitude and sign is obtained in accordance with the magnitude and sign of any deviation from this speed. This output energizes a coil 199 of a galvanometer amplifier 200 movable in a magnetic field 201 to move a copper armature 196 to vary the damping on a coil 195 forming the tuned grid circuit of an oscillator valve 184. This valve forms one arm of a bridge, and the controlled impedance of the valve determines the output of the bridge which is fed through a network 175, 176 (which adds a differential component), to a phase-splitter amplifier 156, 166 and output valves 139, 140 to energize one phase of the reversible two-phase servomotor 81 which adjusts the fuel by-pass valve (see Group XXIX). The motor also adjusts a feed-back rheostat 172 to apply a rate signal to the amplifier 166 to improve stability. The output of the bridge is also fed back via a differentiating network 213, 214, 215, 217 to a coil 211 opposing the control coil 199 to improve stability. Temperature control.-The control of motor 82, Fig. 11, which also adjusts the fuel by-pass valve, is similar to that of motor 81 except that the input signal is derived from a thermocouple 240 measuring exhaust gas temperature. The system is set to limit fuel delivery so that the turbine outlet temperature does not exceed 1250‹ F. At all lower temperatures the motor 82 is stalled by a stop, Fig. 1 (not shown), which limits movement of its output shaft. Surge control.-The response of motor 82 is automatically modified in accordance with exhaust gas temperature measured by a second thermocouple 240<SP>11</SP>, inlet temperature measured by a bulb 250, and turbine speed derived from the generator 205 in order to detect incipient surge conditions and reduce the fuel supply. The output of thermocouple 240<SP>11</SP> is amplified by a galvanometer and bridge 200<SP>11</SP> similar to 200 above described and applied to the grid of a mixing valve 253. A coil 241 which biases the motor 82 is in the cathode circuit of valve 253 which also includes part of a resistor 244 adjusted in accordance with the inlet temperature by the bulb 250. Between resistor 244 and the anode of valve 253, the tachometer generator 205 is connected via blocking condensers 245c, 255c.