GB659917A - Improvements in fuel supply systems for aircraft engines - Google Patents

Abstract

659,917. Regulating; spray carburetters. HOBSON, Ltd., H. M., and GREENLAND, L. S. March 16, 1949, No. 7182. [Classes 7(iii) and 7(vi)] [Also in Group XXIX] In an aircraft engine fuel supply system of the type in which fuel is delivered through a metering orifice whose area is varied by a variable datum boost control device as a function of boost pressure, and in which the pressure across the orifice is maintained as a function of engine speed, the metering orifice is defined by two relatively movable members, one of which is arranged to be moved manually on operation of a pilot's lever to change the selected boost, and the other is adjusted by means responsive to induction pressure and temperature, and exhaust back-pressure, i.e. atmospheric pressure, and the boost control device includes a resetting piston which adjusts the member coupled to the pilot's lever to correct the fuel flow in accordance with the reduction in boost pressure above full-throttle height. Fuel is delivered bv a pump 1 to the metering orifice defined by a sleeve 3 and a needle 4 whence it passes through a passage 5 to a discharge point at the supercharger intake incorporating a regulating valve 6. The valve 6 is actuated by a diaphragm 15 loaded at its upper side by pressure at the inlet to an engine-driven impeller 11 which discharges into the conduit 2 feeding the metering orifice whereby the pressure across the orifice is related to engine speed. The engine throttle valve 29 is actuated in the idling range by an eccentric 26 on a pilot's control shaft 25 and at other times by a servopiston 28 controlled by a piston valve 48 actuated by a bellows 42 subjected to boost pressure and damped by liquid 51. The datum is varied by a floating lever 39 linked to the shaft 25, to the resetting piston 45 and to the bellows and the sleeve 3. The needle 4 is actuated through a lever 56 by a capsule 57 responsive to temperature in the induction pipe 158 and by a diaphragm 59 exposed on its upper side to atmospheric pressure and on its lower side to boost pressure. The arrangement is such that at idling boosts, when no adjustment of the metering orifice in accordance with exhaust back-pressure is required, the diaphragm 59 will have depressed the needle 4 to such an extent that a flange 54 on the needle will have been brought into contact with a stop 61. During operation below full-throttle height, the metering sleeve 3 is set according to the selected pressure, but above that height, i.e. when the servopiston 28 has reached the limit of its travel, the sleeve is adjusted by the resetting piston 45 which is also controlled by the valve 48 but which, below fullthrottle height, is spring-urged against a stop 47. An adjustable needle 64 in a passage byepassing the metering orifice controls the fuel flow for slow-running. A mixture control valve 36 linked to the shaft 25 is open below cruising boost to weaken the mixture, but is closed above that boost. Specifications 429,682, 567,106, [Group XXIX], 567,239 and 585,275 are referred to.