Patent GB-658941-A (GB)
Title: Improvements in self-feeding carburetters for internal combustion engines
Inventor: MORRIS JOHN NEVILLE
IPC: F02M1/00
Filed: 1949-09-07
Abstract: 658,941. Spray carburetters. S. U. CARBURETTER CO., Ltd. Sept. 7, 1949, No. 23127. [Class 7(iii)] In a carburetter of the kind wherein the float chamber 22 is subjected to a depression produced by a venturi 4 of variable effective cross-sectional area which together with a tapered needle 27 controlling a main jet 26 is adjustable by pressureresponsive means which is movable in response to the variation in pressure drop established in the venturi and which may comprise the coaxial nose-piece 8 of a piston 7 loosely fitting within a suction chamber 1 and slidable on a hollow guide 9, an emergency control device, such as a poppet valve 41 actuated by a lever 42 of a float 21, becomes effective, when the fuel level in chamber 22 becomes abnormally low and the depression in the chamber is insufficient to lift fuel, so as to diminish progressively the ratio of depression acting on the means to that obtaining in the venturi such that the means initiates a reduction in cross-sectional area of the venturi with a consequent increase in the depression in chamber 22 whereby inspiration of fuel is recommenced and the control device is arrested in its action. In operation, air enters ports 2 of chamber 1, passes to region 3 and then to an annulus 11 at which occurs the maximum depression communicated via ducts 12, 13 to chamber 1 and via ducts 12, 32 and 33 to chamber 22. Under normal operating conditions a condition of stability is attained when the upward pneumatic load acting on the piston base balances the weight of the piston unit, augmented by a spring 10, and the nosepiece 8 is withdrawn from the venturi such that the resultant effective cross-sectional area of the venturi produces the required degree of depression to lift fuel to chamber 22 and the valve 41 remains inoperative. When the fuel level in chamber 22 is lowered the float drops to fully open a needle valve 20 and raise valve 41 to partially obstruct duct 13, and the evacuation of air from chamber 1 the depression in which decreases to allow the nose-piece to fall to decrease the area of annulus 11 and valve 41 to descend. Restricted communication of chamber 22 is afforded by a jet 34 the air passing through which suffers a reversal in direction to duct 33 to establish a pressure drop across jet 26 and to constitute a metering head which is also available for an enrichment jet 35 interconnected with the throttle valve 5. The degree to which the needle enters jet 26 may be determined by locating the needle head in any one of a series of stops formed in a circular ramp 48 of the piston base. Fluttering of the piston assembly may be prevented by the damping effect of oil 43 retained in the nose-piece and guide 9. An acceleration pump comprising a spring- loaded flexible diaphragm 50 in a chamber 51 communicating with an injector tube 52, may be provided to cause a momentary increase in discharge of fuel past jet 26. It is stated that induction roar is effectively suppressed by reason of the high air flow velocity at the venturi throat and that a simple silencer is sufficient to deal with throttle-edge hiss. Specification 479,114 is referred to.