Patent GB-917506-A (GB)
Title: Improvements in or relating to engine fuel systems
Inventor: BASFORD KENNETH ARNOLD
IPC: F02C7/22
Filed: 1960-10-03
Abstract: 917,506. Gas turbine engine fuel systems. ROLLS-ROYCE Ltd. Sept. 29, 1961 [Oct. 3, 1960], No. 33927/60. Class 110 (3). The invention relates to a fuel system for a gas turbine engine supplying power to a pair of driven devices, one of which at least is capable of being disconnected from the engine under certain operating conditions, the fuel system comprising a pair of parallel fuel delivery paths leading to the engine, each path containing an associated throttle valve to vary the rate of fuel flow through the path, the throttle valves being coupled for movement together in the opening sense and for movement together in the closing sense, the system also being arranged so that when one driven device is disconnected from the engine, fuel flow through one of the parallel paths is prevented. The invention is described with reference to an aircraft gas turbine engine which drives a propeller 11 and may also drive an air compressor 12 through a disengageable clutch 13, the air supplied by the compressor being utilized to drive helicopter rotor blades to assist the aircraft take-off. In flight, the compressor 12 is disengaged and the rotor blades then rotate automatically. Fuel is supplied from tank 14 through boost pump 15, filter 15a and main fuel pump 16, through control unit 17 and lines 18, 19 to the burners 21. The unit 17 is shown in Fig. 2 with the filter 15a incorporated therein. Fuel flows from inlet 35 through the filter 15a through pipe 36 and duct 43 to chamber 80 from which it discharges through outlet 81 to the main fuel pump 16. Fuel from the main pump 16 flows through pipe 37 into the control unit 17, flowing into the duct 38 past a pressurizing valve 39 to a throttle arrangement. The valve 39 is acted on in the closing direction by a spring and by the pressure of fuel in the low pressure duct 43 acting on the piston 41. The throttle arrangement comprises two throttle valves 45, 48 disposed in parallel to control fuel flow from the duct 38 to the duct 47, the two valves being coupled together as indicated at 50 so that they move in the same sense. The throttle arrangement also includes a selector valve 51 which is operated by a link 17b which is interconnected with a lever 30 which controls operation of the clutch 13, the arrangement being such that when the clutch 13 is engaged, whereby the compressor 12 is driven, the selector valve 51 is open so that fuel flows past the second valve 48 and through duct 49 to the duct 47; when the clutch 13 is disengaged, the selector valve 51 is closed so that the fuel flow path 49 is closed off. Fuel from the duct 47 flows past a shut-off valve 55 to the pipes 18, 19, the fuel flow to the main fuel pipe 19 being controlled by a pressurizing valve 56 which is loaded in the closing sense by a spring 57 and by pressure of fuel in the low pressure duct 43 acting on piston 62. The fuel system downstream of the valve 55 is arranged to be connected to a drain 59 when the valve 55 is closed. Flow of fuel past the throttle valves 45, 48 is controlled in dependence on atmospheric pressure by a pair of capsules 65, 66 disposed in the chamber 80, the capsule 65 being evacuated and the capsule 66 being connected to compressor intake pressure through line 67. The capsules are connected to a rod 68 which acts on a pivoted lever 69, the lever also being acted upon by a tappet 70 which is loaded towards the lever by a spring and by pressure of fuel in the duct 47 acting on piston 71, and which is loaded away from the lever by pressure of fuel in the duct 38 upstream of the throttle valves 45, 48. The lever 69 has a half-ball valve 77 which controls a bleed outlet 78 of a servo-mechanism controlling the delivery of the main fuel pump 16. When the bleed flow through the outlet 78 increases, the pump delivery is reduced and vice versa. An adjustable by-pass 53 is provided across the throttle valve 45 and a similar by-pass 54 is provided across the valve 48. Operating fluid may be supplied from the duct 38 through line 82 to the governor 23 which may be as set forth in Specification 917,505. The engine may be of the two-spool type, the low pressure spool driving the propeller 11 and the compressor 12.