GB1416767A - Fuel flow regulator especially for the combustion chamber of an aircraft jet engine - Google Patents

Abstract

1416767 Gas turbine engine fuel control systems SOC NATIONALE D'ETUDE ET DE CONSTRUCTION DE MOTEURS D'AVIATION 11 April 1973 [18 April 1972] 17496/73 Heading FIG The invention relates to a fuel flow regulating device for example of a gas turbine engine fuel system and comprising a needle member 9 having a frusto-conical surface 12a which co-operates with an orifice 12 to define a variable metering orifice. The position of the needle is controlled by means of a piston member 27 mounted on the stem of the needle and disposed within a cylinder 26, the chambers at either side of the piston being indicated at 26a, 26b. The needle is slidably disposed in a bore 10 formed in a partition 44 which is formed in the housing between the chamber 45, which is the chamber downstream of the metering orifice 12, 12a, and the cylinder chamber 26b. In accordance with the invention, filtered fuel is supplied through passages 8, 28, 28a, 28b to the cylinder chambers 26a, 26b at either side of the piston 27; also through passage 49 to an annulus 46 formed in the partition 44 in the bore 10 in which the needle is slidably mounted. This is to ensure that no particles of foreign matter can enter the cylinder chambers 26a, 26b or the bore 10. In the embodiment, fuel enters at inlet 2 and is discharged by pump 3 through passages 4a, 4b to the passage 4 thence through the metering orifice 12, 12a to the chamber 45, thence through passage 17 controlled by a valve-member 18 through the outlet 1 to the combustion section. A filter member 7 comprising a porous sleeve 7a is provided in the passage, fuel passing through the porous sleeve to the chamber 7b, thence through the passage 8 to the cylinder chambers 26a, 26b and annulus 46 in the bore 10. The needle 9 is formed with a second frusto-conical surface 13a which co-operates with an orifice 13 to constitute a second metering orifice through which excess fuel flows from passage 4 to chamber 15 and thence through return passage 16 to the inlet side of the pump 3. The cylinder chambers 26a, 26b are connected through passages 38a, 38b to a pair of oppositely disposed nozzles 37a, 37b which are controlled by a flapper valve 31 pivotally mounted at 31a and controlled by bellows 34, 35 one of which is connected to compressor discharge pressure, the other being evacuated. A member 32 pivotally mounted at 32a co-operates with the flapper valve 31 to form a pair of surfaces between which a member carrying a pair of rollers 33 can move, the member 39 being connected to a pivotally mounted member 40 which carries a follower 40a which co-operates with a cam 41. The cam 41 is rotatable by means responsive to engine parameters such as engine speed, temperature &c. The opposite end 32b of the member 32 engages a spring 36 which also bears against a carrier 9b carried by the needle 9. A device 22 is provided to sense the pressure difference across the metering orifice 12, 12a and controls the pressure of filtered fuel in a passage 23 which in turn controls the position of a valvemember 25 which in turn controls flow of fuel in the passage 4 upstream of the metering orifice 12, 12a back to the suction side of the pump through passage 21; the filter device 23b is similar to the device 7. The assembly 20, 22 serves to maintain the pressure difference across the metering orifice 12, 12a constant. The valve-member 18 which controls flow of fuel from passage 17 to outlet 1 is controlled by a member 19 so as to be open in operation and closed at shut-down.