GB640958A - Improvements in or relating to control systems for gas-turbine power-plants - Google Patents

Abstract

,640,958. Gas turbine plant. ROLLS-ROYCE, Ltd. Nov. 28, 1947, No. 31590. [Class 110(iii)] [Also in Groups XXIX and XXXIII] A gas turbine plant having a power output shaft on which the torque loading may be varied is controlled by temperature responsive means located in the gas flow 'through the turbine system which varies the torque loading on the output shaft and by a constant speed governor, driven by a rotor in the plant which varies the fuel supply. The temperature responsive means maintains the gas flow temperature at a selected value by increasing the torque loading on decrease of the gas-flow temperature and vice versa. In the plant shown, Fig. 1, the fuel supply to the burners 13 is controlled by a throttle valve 25 which is operated by the piston of a servomotor 29 the movements, of which are determined by a centrifugal governor 30 driven from the engine shaft 16 through the gearing 21. The governor 30 is loaded by a spring 31 which has an abutment 32 the position of which can be varied by a control arm 33 through a rack and pinion mechanism. The arrangement is such that the fuel flow is controlled so as to maintain the speed of the rotor at the value pre-set by the control arm 33. The variable pitch airscrew 17 driven through a reduction gear from the engine shaft 16' is controlled by a resistance thermometer 41 through a hydraulic servo-mechanism 19 and piston valve 38. The resistance thermometer is mounted in the exhaust unit 20 and is connected to an A.C. bridge circuit 42 such as an Owen's bridge as shown in Fig. 2. The bridge comprises in the same arm as the resistance thermometer 41 a variable inductance 43, by which the balanced condition of the bridge circuit can be adjusted. Variation of the temperature in the exhaust unit 20 will alter the balanced condition of the bridge and the output from the bridge after passing through a phase discriminating and amplifying device 46 is arranged to control the direction of rotation of the motor 40 which operates the piston valve 38. The arrangement is such that when the temperature of the exhaust gases rises above the datum value, the valve 38 is moved to cause a decrease of pitch of the airscrew blades 17 and vice versa. The variable inductance 43 is controlled by the arm 45. The control arms 33 and 45 are connected together and to a main control member so that for each load there is a pre-selected temperature. Modifications in which the temperature responsive means is a quartz rod or thermo-couple and the speed responsive means a fluid centrifugal device driven by the engine rotor are also described. The variable pitch screw described is suitable for aircraft or marine propulsion but for land vehicle use a variable speed transmission mechanism or torque converter is described. Where the power plant drives an external load through a fixed gear ratio, it is necessary to vary the load to vary the torque.