Patent GB-1184369-A (GB)
Title: Improvements in control systems for axial flow compressors particularly adapted for use in gas turbine engines
IPC: F04D27/02
Filed: 1967-09-19
Abstract: 1,184,369. Axial flow compressors; gas turbine jet propulsion engines. GENERAL ELECTRIC CO. Sept.19, 1967 [Dec. 22,19661, No. 42616/67. Headings F1C, F1G and F1J. [Also in Division G1] In a gas turbine engine, the engine is controlled in dependance on the Mach number of the gas discharged from its compressor to ensure that the compressor does not stall. In one embodiment of a simple gas turbine engine, Fig. 2, a metering valve 212 controlling the rate of flow of fuel to the combustion chamber 204 and therefore the speed of the rotor of the engine, is primarily controlled by a lever 220 operated by the pilot. The position of the lever is transduced at 222 and converted in signal generator 223 in dependence on the inlet air temperature measured by the sensor 226, to a signal indicative of the required speed. This signal is compared at 228 with a signal indicative of the actual speed, sensed by transducer 230, and the error signal fed via selectors 232, 234, switch 236, and an integrator 238 to a torque motor 218 mechanically connected to the valve 212. An anti-hunting signal is provided by generator 245, and combined with the input to the integrator 238. To prevent the compressor stalling, a signal representative of the Mach number of the gas discharged from the compressor is computed in generator 250 from pressure sensors 246, 248 outputs and compared with signals indicative of the acceleration and deceleration limit. Mach numbers computed in generators 256, 258 from measurements of the rotor speed and inlet gas temperatures. If the actual Mach number exceeds the deceleration limit Mach number or is lower than the acceleration limit Mach number, the corresponding error signal is passed by the corresponding selector 234, or 232, rather than the speed error signal, and is used to control the torque motor 218. A signal representative of the rate of change of Mach number provided by generator 264 is combined with the error signal representative of the difference between the actual and acceleration limit Mach number as a further stall prevention means for rapid acceleration. During starting up of the engine, the Mach number is no longer a valid control parameter for fuel flow. The control is therefore provided by the output from a generator 266, as determined by the rotor speed and inlet temperature. During this period the selectors and associated circuitry are disconnected from the motor 218 by energization of relay 268 the relay being energized by the output from transducer 230, via cut-off 270, arranged to de-energize relay 268 when the speed of the rotor reaches idling speed. In a second embodiment, Fig. 1, of a turbofan engine having an afterburner 40 and a variable nozzle 32, the supply of fuel to the afterburner and the area of the nozzle are determined primarily by movement of a throttle lever 86 by the pilot. The supply to the burners 40 is controlled by a metering valve 72 comprising two movable parts 81, 83, the former moved mechanically in dependence on the outlet pressure of the compressor 18 and the latter by motor 100, energized by movement of the throttle lever 86 past position y. The input to the motor is an error signal indicative of the difference between the required thrust of the engine computed by generators 88, 90, 92 in dependance on the input temperature of the compressor, detected by sensor 52, and the actual position of the valve part, detected by generator 101. The nozzle area is altered by actuators 38 under the control of, a valve 62 moved by motor 60 whose input represents the difference between the actual Mach number of the gas in the compressor, determined by probes 44, 46 and generator 42 and the required Mach number, generated in generator 50 and dependant on the inlet temperature. An anti-hunting signal representing the rate of change of the nozzle area is developed at 69 and combined with the input signal to the motor 60. When the engine is operating in its "dry" condition, with no afterburner operating, the lever 86 being positioned between x and y, the position of the lever is converted into a required nozzle area signal by generator 104, and the motor 60 is controlled by a signal indicative of the difference between the requested nozzle area and the actual nozzle area transduced by generator 68. Also, motor 100 is connected to generator 108 whose output is such that the valve part 83 is maintained in its minimum flow position, and the fuel supply valve 80 is maintained closed. As the lever passes position y indicating that the afterburner is required, the nozzle area comes under the control of the Mach number signal generator. Relay 120 is energized, provided that the turbine rotor speed, measured by generator 116, exceeds a predetermined minimum value pre-set by diode 118, to open valve 80. The fuel is then ignited by means 112 and its ignition sensed by light detector 122. When this occurs the output from circuit 110 energizes relay 124 dis-connecting the motor 100 from generator 108 so that it is again under the control of throttle lever 86. To guard against stalling of the compressor the error signal supplied to motor 60 is compared with a maximum permissible Mach number error signal generated in 128 and the difference used to modify the input to the motor 100 if it exceeds a value set by diode 130. If the nozzle area control mechanism fails and the nozzle does not open sufficiently on ignition of the afterburner, when ignition is detected a minimum nozzle area signal generator 132 produces an output which is compared with the actual nozzle area. If the latter is sufficiently small, indicating that the nozzle has not opened appreciably, a signal is transmitted through diode 136 to a time delay circuit 137 whose output energizes relay 140 dis-connecting the motor 100 from control by the throttle lever and connecting it to the generator 108 so that the valve part is returned to its minimum flow condition. Alternatively the output to the relay could be used to energize relay 124.