Patent GB-1331983-A (GB)
Title: Control apparatus for a gas turbine engine
IPC: F02C9/32
Filed: 1970-04-25
Abstract: 1331983 Gas turbine plant controlling power turbine JOSEPH LUCAS (INDUSTRIES) Ltd  19 April 1971 [ 25 April 1970] 19988/70 Heading F1G [ Also in Division G1] In a gas turbine engine wherein nozzles 26 move to control the passage of gas from a gas generator to a power turbine, movement of the nozzles is dependent on engine operating conditions e.g. combustion temperature. As shown in Fig 1, movement of the nozzles effected by an arm 45 controlled by pistons 41, 46 in an oil circuit which includes electrically operated valves 29, 30 controlled by windings 97, 73. The arm 45 is also moved by a cam 49 driven by an electric motor 50. The control arrangement discloses the conditions whereby the windings 97, 73 and motor 50 are energised. A fuel system comprises a displacement pump 10 which feeds fuel sprayers 13 through a network which includes restrictors 11, 12, a pressurising valve 16 and a stop cock 15. A spill valve 21 across the pump includes a closure member operated by a motor also in dependence on operating conditions. The control circuit 24 shown in detail in Fig 2 includes probes 51, 52 giving outputs proportional to the speeds of gas generator and power turbine. The signal from probe 51 adjusted for intake temperature by a temperature sensitive resistor 55 feeds one input 58a of a differential amplifier 58. A second input 58b is fed by a signal set by a power demand lever 63, and a third input 58c receives a signal indicative of a minimum power demand. The output of amplifier 58 gives the difference between power supplied and power demanded and is fed via amplifier 59 as one of three inputs of a diode network 70 whose output if large enough actuates the motor 23 through transistors 65, 66 thereby shutting the spill valve 21 and increasing fuel flow to the engine. A signal derived from sensor 52 and indicative of turbine speed is applied to a differential amplifier 69 together with a reference signal. The output which decreases with speed, is applied to the diode network 70 and if less positive than the signal from amplifier 59 controls the transistor 65 and hence the valve 21. When the output of amplifier 69 is negative the spill valve 21 is fully open thereby diminishing the fuel flow. The output of circuit 54 is also applied to a power turbine speed meter 106 and to an interlock on a gearbox 108 to prevent change-down above a certain speed. The output of the circuit 69 is also applied via diode 72 to a relay 115 to energise a solenoid 73 and shut valve 30 thereby causing the nozzles to move so that the gas flow tends to reverse the direction of rotation of the power turbine. Thermocouples 74 measure combustion temperature which is displayed at 110, and the signal is amplified at 77 being corrected for lag by circuit 103. This signal is fed to a comparator 78 which provides an output for signals above a given limit. An amplifier 80 has an output which is constant up to a certain value and thereafter increases with the temperature modified speed signal derived from sensor 51. This output forms one input to a differential amplifier 81 whose other input is derived from amplifier 77 via an ambient temperature sensitive circuit 82, 83. The output from amplifier 81 if positive indicates an unacceptably high combustion temperature and this signal is passed to a switching circuit 93 and a control circuit 111 to control motor 50 in a direction to cause an increased flow of gas to the power turbine. A negative signal from 81 indicates an unacceptably low combustion temperature and is passed through switching circuit 90 to operate motor 50 in the other sense. The output from amplifier 58 is applied to a switching circuit 96 to control solenoid 97 to open valve 29 when the signal exceeds a given value. The solenoid 97 is also operated in unison with a switch 102 when a brake lever 117 is actuated to provide a low idling speed for the engine. The output from amplifier 58 may be utilised to control the motor 50 in advance of any temperature change. This is effected by a positive signal passing through diode 94 to switching circuit 93 to increase the gas flow, and by a negative signal passing through diode 95 to modify the signal at 111. Under steady conditions there is no output from amplifier 58.