GB866722A - Improvements in or relating to fuel systems for gas turbine engines - Google Patents

Abstract

866,722. Gas turbine plant. BRISTOL SIDDELEY ENGINES Ltd. Aug. 28, 1959 [Sept. 4, 1958], No. 28433/58. Class 110 (3). In a fuel system for a gas turbine engine including a device responsive to variations of air intake ram pressure and atmospheric pressure and arranged to override throttle control means of the engine to prevent the reduction of selected engine speed, by the throttle control means, below a minimum value required to maintain adequate combustion under the conditions to which the device is responsive, the device is inoperative until the air intake ram pressure has increased to a predetermined value, the atmospheric pressure has decreased to a predetermined value or the combined effect on the device of increased air intake ram pressure and decreased atmospheric pressure has reached a predetermined value. The invention is described with reference to a governor-controlled fuel system described in Specification 866,721 which, briefly, comprises an engine-driven governor 9 having a shaft 8 arranged to bear axially against an arm 7 carried by a lever 4. The lever 4 carries a half-ball valve 1 which controls the fuel flow between the ducts 2, 3. The arm 7 is also acted upon by an adjustable spring device comprising two angularly adjustable springs 14, 15. The springs are adjusted by means of plates 20, 21 mounted on a common shaft 22. The plates 20, 21 and shaft 22 are shown in laterally separated positions for convenience of illustration. The shaft 22 is turned by a lever 23 connected to a throttle control lever. An arm 27 fast with the shaft 22 actuates a pivoted pawl 29 mounted in the housing 35 of the idling device. The housing 35 is open to atmospheric pressure at 32 and contains a capsule unit consisting of two pressure-responsive capsules 31, 33 positioned back to back. One of the capsules 33 is open to air intake total pressure at 34 and expands in response to the difference between air intake total pressure and atmospheric pressure and thus to air intake ram pressure. The other capsule 31 is evacuated and expands in response to atmospheric pressure i.e. altitude. The combined effective length of the capsule, unit therefore changes on variation of the air intake ram pressure or the atmospheric pressure or on variation of air intake ram pressure and atmospheric pressure together. On expansion or contraction of the capsule unit the rod 36 pivots the lever 30 about the pivot 37. The end of the lever 30 remote from the rod 36 is in the form of a stepped cam or ratchet with the surface of each step of the cam or ratchet normal to a radial line through the pivot 37. As the throttle. lever is moved towards the closed or idling position, the pawl 29 is pivoted upwardly. Under certain conditions of atmospheric pressure and air intake total pressure, the length of the capsule unit 31, 33 is such that the cam lever 30 is pivoted and engaged by the pawl 29. When this occurs no further movement of the throttle control lever can move the shaft 22, but the throttle lever can be brought into contact with the stop 25 by overriding spring-loaded pawls 26. In modification, Fig. 2 (not shown the end of the capsule unit engages a cam operated by the throttle lever and the other end valve opening means. The arrangement is such that after a certain amount of movement in the valve closing direction, the lever has no effect on the valve opening. The invention may be applied to a fuel system controlled by the flow of fuel. Arrangements in which the capsules 31, 33 are arranged side by side are also described.