Patent GB-1423364-A (GB)
Title: Fuel control apparatus for gas turbine engine reheat system
IPC: F02C7/228
Filed: 1972-06-21
Abstract: 1423364 Gas turbine jet engines; re-heat fuel control LUCAS INDUSTRIES Ltd 26 March 1973 [21 June 1972] 29001/72 Heading F1J The invention relates to a fuel control apparatus for a gas turbine engine re-heat system having a plurality of burners, there being a first control means in the form of a three-dimensional  cam 23 responsive to first and second engine operating parameters, namely compressor discharge pressure P2 and compressor intake temperature T1, there being a first variable metering device 17 including a control member 62 responsive to the first control means 23 to regulate fuel flow from the pump to a first re-heat burner. A second control means in the form of an edge cam 72 is responsive to a third engine operating parameter, namely control lever position #, there being second and third variable metering devices 76, 78 each including a control member 70, 71 respectively, responsive to the first and second control means 23 and 72, the second and third metering devices regulating in use, fuel flow from the pump to second and third re-heat burners respectively. The control system shown comprises an inlet 15 from pump (10) at pressure PP and three metering devices 17, 18, 19, the control member 62 of the metering device 17 being formed with an orifice 63 which co-operates with an orifice 61 in a fixed sleeve 60 to define a variable metering orifice through which fuel flows from inlet 15 to outlet 84 at pressure PF1. The axial position of the control member 62 is controlled by a cam follower 69 which co-operates with the three-dimensional cam 23 and with a ballvalve 68 carried on the control member 62. The control member is formed with a stem 66 having a bore 67 controlled by the ball-valve; fuel passes from the inlet 15 through a restriction 65 to a chamber 64 at the right hand side of the control member, the pressure in the chamber 64 and so the axial position of the control member being controlled by the ball-valve 68 and so by the position of the cam 23. The axial positions of the control members 70, 71 of the metering devices 18, 19 are similarly controlled by the cam 23. The control members 70, 71 are however also movable rotationally by means of an edge cam 72 mounted on a shaft 73, cam followers 72a which engage the cam 72 being connected to cause angular rotation of the control members. The axial position of the cam 23 is controlled in dependence on compressor discharge pressure P2 by a servo-device comprising a piston 25 mounted on the shaft 24 of the cam 23, the chamber at one side of the piston being connected to a point intermediate a variable orifice 26 and a fixed orifice 28, and the chamber at the other side of the piston being connected to a point intermediate a variable orifice 29 and a fixed orifice 30. The orifices 26, 29 are controlled by a pivotally mounted lever 31 positioned by a pair of bellows 32, 33, the bellows 32 being subject to pressure intermediate a pair of orifices 34, 35 and bellows 33 to pressure intermediate a pair of orifices 35, 36, the orifice 34 being connected to compressor intake pressure P1 and orifice 36 to compressor discharge pressure P2. The angular position of the three-dimensional cam 23 is controlled by a servodevice 45 in response to compressor intake temperature T1, an angularly pivotable nozzle 52 directing fluid to either one of the passages 54, 55 so controlling the position of spool member 51  and hence the axial position of a piston member 44; the piston member is formed with a rack 43 which engages a pinion 42 which causes rotation of the cam 23. The position of the piston 44 is sensed at 44a and fed back to the input. Throttle valves 82, 76, 78 are associated with the metering devices 17, 18, 19, the throttle valve 82 being controlled by servo-pressure S 1 supplied through inlet 85; the pressure S1 is selected by a shuttle device 120 Fig. 4 (not shown), to be the highest of the pressures PF2, PF3 and PR where PF2 is pressure downstream of throttle valve 76, PF3 is pressure downstream of throttle valve 78 and PR is pressure in the chamber 41 of the metering assembly. Throttle valve 76 is controlled by servopressure S2 applied through inlet 77, pressure S2 being derived from an assembly (81) Fig. 3 (not shown) in dependence on pressures DPI and DP2 which are the pressures downstream of the metering devices 17 and 18 respectively. Throttle valve 78 is similarly controlled by servo-pressure S3 derived from the pressures DPI and DP3 where DP3 is the pressure downstream of the metering device 19.