GB844560A - Control system for a turbojet engine - Google Patents

Abstract

844,560. Automatic gas-turbine engine control systems. GENERAL MOTORS CORPORATION. Oct. 7, 1958 [Oct. 11, 1957], No. 31946/58. Class 38 (4). [Also in Group XXVI] For a gas-turbine jet engine, an automatic control system comprises means controlling guide vanes 22 and a compressor bleed 29 so as to maintain constant the multiple of engine speed and the square root of inlet air temperature in degrees absolute, co-operating with means controlling a variable area jet pipe nozzle apparatus 16 so as to maintain constant the jet pipe temperature for a given engine speed. The engine is primarily controlled by a conventional fuel controller 33 responsive to engine speed through a shaft 34 and a manual throttle 35 to vary the fuel supplied to burners 12 through a feed-line 37. A mechanical servo 40 responsive to inlet air temperature, sensed by a bellows capsule 41, and to engine speed through a shaft 38, controls an actuator 28 positioning the guide vanes, and an actuator 32 positioning a valve 31 in the compressor bleed. A shaft 46 having an angle of rotation proportional to engine speed, extends from the servo 40 and carries cams 47, 76, 91 scheduling engine speed to the control means for the nozzle 16. The nozzle is positioned by an actuator 21 controlled by an hydraulic valve 59, a piston 58 of which is coupled to a compound linkage 49, 54. The linkage is positioned by the cam 47, a rod 51 applying mechanical feedback from the nozzle and by motors 83, 100 through a rack and pinion 87, 88. The motor 83 is driven by a power amplifier 68 responsive to the out-ofbalance between the voltage of a thermocouple 66 and a voltage from a network 70 representative of the desired turbine outlet temperature scheduled by cam 76. The motor 100 drives the rack 88 to a mean position determined by switches 101, 102 when the rate of change of speed, as determined by a rate amplifier 97 through the cam 91 and potentiometer 94 is such as to actuate a relay 78 which simultaneously disconnects motor 83 and energizes motor 100. At speeds below idle, a switch 106 is closed to energize a relay 81 and cause the motor 83 to drive the nozzle to the open position. The network 70 comprises a centre-tapped potentiometer 73 supplied from the sliders of potentiometers 131-3 controlling the voltage gradient. Cold junction compensation for thermocouple 66 is by temperature-sensitive resistors 129, 130. In a modification, Fig. 7 (not shown), motor 100 and the low-speed switch 106 are not used, the nozzle area at speeds below idle being determined by a cam, and the motor 83 is only operative to correct over-temperature.