Patent GB-1253203-A (GB)
IPC: F02C9/32
Filed: 1967-10-19
Abstract: 1,253,203. Gas turbine engine fuel systems. JOSEPH LUCAS (INDUSTRIES) Ltd. Oct. 11, 1968 [Oct. 19, 1967], No.47575/67. Heading F1G. A fuel system for a gas turbine engine of the kind comprising a load turbine supplied with gas by a gas generator comprises a centrifugal fuel pump, a control whereby idling or maximum fuel supply can be selected, acceleration control means for controlling the fuel supply in accordance with at least one variable related to the gas generator, a speed-responsive device controlling the fuel supply in accordance with a speed signal obtained from the gas generator, a further speed-responsive device arranged to modify the response of the first speed-responsive device in accordance with the speed of the load turbine, and a further control associated with the further speed-responsive device whereby a limited reduction in speed below the maximum can be selected, the further control being arranged to vary the response of the further speed-responsive device. The invention is described as applied to a two-spool engine forming a gas generator which supplies gas to a free turbine driving a helicopter rotor. Fuel is fed from a fuel pump 10 to burners 13 via throttle valves 18, 25 and a shut-off cock 16. Throttle valve 18 is controlled by governor weights 17 driven from one of the two shafts of the gas generator, a spring abutment 22 being controlled by a cam 23 having two positions corresponding to idling and maximum speeds respectively. The cam 23 is linked to the shut-off cock 16 so that the pilot can select idling and maximum speeds and also complete shut-down. Throttle valve 25 is controlled by a diaphragm 26 subjected on one side to the pressure upstream of the valve 25 and on the other side to a pressure communicated via a duct 37 from a fuel potentiometer comprising by-pass valves 35, 41 connected in series in a by-pass connected between the pump outlet and inlet passages 12, 11. Valve 35 forms part of an acceleration control unit 27 and is positioned by evacuated capsules 29, 30, capsule 29 being subjected to a pressure derived via an air potentiometer 31 from the compressor delivery pressure P 3  and inlet pressure P 1 , while capsule 30 is subjected to the pressure downstream of the first compressor stage or at the inlet thereof or other reference pressure. Valve 41 is positioned by a solenoid 42 in accordance with an electrical signal dependent on the speed of the other of the two shafts of the gas generator and on the exhaust temperature of the gas generator. The response of the throttle valve 18 to the governor weights 17 is modified by a diaphragm 44 acting on the valve through a lever 43. An air potentiometer network, comprising a valve 48, a fixed restrictor 52 and a valve 53 and connected at the upstream end of the network via a duct 47 to the downstream side of the compressor of the gas generator, is connected at opposite ends of the restrictor 52 to opposite sides of the diaphragm 44. Valve 48 is controlled by a diaphragm 49 subjected to the pressure downstream of the valve 48, while valve 53 is controlled by governor weights 60 driven from the free turbine. The effect of the governor weights 60 in thus modifying the response of the throttle valve 18 can be adjusted by the pilot through the cam 62 acting on a spring abutment 63 whereby a limited reduction in the speed of the gas generator can be obtained.