Patent GB-852800-A (GB)
Title: Gas turbine engine control system
IPC: H02P23/00
Filed: 1958-12-23
Abstract: 852,800. Electric correspondence control systems. GENERAL MOTORS CORPORATION. Dec. 23, 1958 [Dec. 30, 1957], No. 41460/58. Class 40 (1). [Also in Groups XXVI and XXXV] In a gas turbine jet engine control system comprising means for regulating independent parameters which determine the characteristics of engine operation, e.g. fuel flow rate and jet nozzle area, means for measuring dependent parameters indicative of the mode of engine operation, e.g. engine speed and turbine temperature, and control means which operate the regulating means in accordance with the outputs from the measuring means, non-linear servomechanisms having substantially constant response rates are used in the control means and the regulating means, the response rates of the servo-mechanisms in the control means being faster than those of the servo-mechanisms in the regulating means. As shown, each of the four parameteis, engine speed, turbine temperature, nozzle area and fuel flow rate, is associated with a self-balancing circuit including a bridge powered by the output of an A.C. tachometer generator 51 driven by the turbine shaft 26 via a power take-off 27, accessory drive 24, and shaft 52, said output being fed to a rectifier and regulator assembly 56 which supplies a constant D.C. voltage to the bridge circuits. While the engine is being started, A.C. may be supplied to the system from an independent source via a switch 55; alternatively, the bridges may be energized from a D.C. source 62 via a switch 58. The speeds of response of the servo-mechanisms which operate to rebalance the speed and temperature bridges are arranged to be faster than those of the servo-mechanisms associated with nozzle area and fuel flow regulation. Speed measurement.-The output of tachometer generator 51 actuates a synchronous motor 57 which drives a D.C. generator 63 to impress an E.M.F. proportional to engine speed in opposition to the output from bridge circuit 64. The resultant is supplied to magnetic amplifiers 83, 84, one of which, depending on the sense of the signal, energizes a reversing clutch 88 to connect a shaft 94 through reduction gearing 89 to the motor 57, and shaft 94 moves the wiper 79 of potentiometer 77 to restore the null condition. Temperature measurement.-Turbine temperature is measured by thermocouples 48 in the turbine inlet, the output from the thermocouples being amplified at 49 and fed, in opposition to the output from bridge 66, to magnetic amplifiers 108, 109 to energize a reversing clutch 113 to cause a shaft 119 to be driven by motor 57, through reduction gearing 114, in a direction to move wiper 104 of potentiometer 102 to restore the null condition. Fuel flow control.-This is effected by the manual operation of a power lever 135 which moves wiper 136 of potentiometer 137, thus producing an error signal, which is the difference between the output of bridge 70 and a feed-back signal derived from a D.C. tachometer generator 44 driven by a fluid motor 42 connected in the fuel line 43, and which is fed to magnetic amplifiers 153, 154 to energize a reversing clutch 39 to actuate a control device 37 to vary the speed of operation of a fuel pump 34. Variations of speed and temperature are fed to the bridge by shafts 94 and 119, respectively, shaft 94 moving wiper 147 of potentiometer 142 and shaft 119 varying the value of rheostats 141, 143.  Nozzle area control.-Variations in engine speed and turbine temperature are communicated to bridge 68 by shafts 94 and 119 which control rheostats 123, 125 and potentiometer 124 respectively. Nozzle area is regulated by the axial displacement of a control-ring 19 via four links 21, a pivoted yoke 22, a reciprocable rod 33 and a screw-jack 32 actuated by the accessory drive 24 through a reversing clutch 29. Nozzle area feedback is provided by a potentiometer 46 whose wiper 127, which is coupled to the yoke 22, forms one of the output terminals of bridge 68. The bridge output is fed to magnetic amplifiers 129, 131, one of which energizes the clutch 29 to vary the nozzle area until the bridge is rebalanced.  Modification.-Speed and temperature may limit, instead of monitoring, nozzle area and fuel flow values. Rheostats 141, 143 and potentiometer 142 in bridge 70 are provided with portions of negligible resistance over which the wipers move in the temperature and speed values below the preset limits, and with high-resistance portions which, when the wipers contact them, unbalance the bridge to vary the fuel supply.