GB760173A - Improvements in or relating to jet turbine engines - Google Patents

Abstract

760,173. Automatic control systems for jet turbines. WESTINGHOUSE ELECTRIC INTERNATIONAL CO. July 13, 1954, No. 20442/54. Class 38 (4). The opening of the fuel valve 9, Fig. 5, and the area of the exhaust nozzle 8 of a jet turbine are controlled by manual operation of a lever 19 and automatically controlled by a tachometer alternator 20 responsive to engine speed and a thermocouple 26 responsive to engine temperature. Alternator 20 also provides electrical power for the control system. In a frequency discriminator 28 associated with alternator 20 a direct voltage dependent on frequency, produced by a rectifier in series with a condenser of suitable capacity, is opposed to a reference direct voltage, also produced by rectification, and a speed-setting direct voltage produced by a potentiometer 17 operated by a lever 19. The resultant output which is of one polarity or the other according to whether speed is above or below that selected by lever 19 is applied to a modulator circuit 33 which produces an alternating output of corresponding magnitude and phase sense which is applied to a thermionic valve amplifier 36. A.C. output from amplifier 36 biases in opposite senses a pair of A.C. operated valves in a thermionic valve amplifier 37 to unbalance the energization of a pair of solenoid-operated hydraulic valves. As a result, a hydraulic servomotor is operated through a hydraulic relay in a stage 14 to adjust the nozzle area by operation of members 13. The arrangement is such that when speed is below the selected value the nozzle area is increased and when speed is above the selected value the nozzle area is decreased. Feed-back to the input of modulator 33 is provided from a potentiometer 116 adjusted with members 13. A rectifier CR123a is arranged so that feedback is greater when the nozzle area is being increased so that this is effected more slowly than when nozzle area is being decreased. The output of discriminator 28 is also applied through a line 31a to a modulator 34 producing an A.C. output, of magnitude and phase corresponding to its input, which through a two-valve amplifier 44 biases a pair of A.C. operated thyratrons in a stage 45 so as to alter relatively the points in each cycle at which they fire and thereby produce a D.C. output of corresponding magnitude and polarity to energize a D.C. servomotor 16 adjusting fuel valve 9. The arrangement is such that when speed is below the selected value the fuel valve opening is increased and when speed is above the selected value the fuel valve opening is decreased. A further voltage dependent on rate of change of the output of discriminator 28 may be applied to modulator 34. Feed-back through line 124 to the input of modulator 34 is provided from a potentiometer 121 adjusted with valve 9. A further feed-back dependent on the rate of adjustment of valve 9 is provided through a line 126 so that the effect of sudden advance of lever 19 is delayed. In a stage 29 the voltage of thermocouple 26 is opposed to a reference direct voltage and a temperature-setting direct voltage from a potentiometer 18 operated by lever 19 and the resultant output is applied to a vibratory converter the A.C. output of which is amplified and applied to a demodulator producing a direct voltage output dependent in magnitude and polarity on the magnitude and sense of temperature deviation from the selected value. This output is applied to modulator 34 and through a line 32a to modulator 33, the arrangement being such that below the selected temperature the supply of fuel is increased and the nozzle area decreased, while above the selected temperature the effects are reversed. Negative feed-back is applied to stage 29 through line 104. The maximum input of either polarity from the temperature responsive circuit is limited by biased rectifiers CR102a, CR102b. The maximum input applied through line 31a from the speed-responsive circuit in a sense tending to increase the-fuel supply is limited by a biased rectifier CR102c. Inductancecapacity filter circuits (not shown) are associated with the speed and temperature-responsive circuits. Rectifiers CR103a, CR103b are so arranged that at low settings of lever 19 the speed deviation signal overrides the temperature deviation so far as control of fuel supply is concerned. Under these conditions during acceleration the speed and temperature deviation signals combine to open the nozzle wide. When a predetermined maximum temperature is exceeded, however, at about 75 per cent full speed, the temperature deviation signal overrides all other signals.