Patent GB-875277-A (GB)
Title: Improvements in or relating to diaphragm carburettors
IPC: F02M17/04
Filed: 1959-11-13
Abstract: 875,277. Spray carburetters. TILLOTSON MANUFACTURING CO. Nov. 13, 1959 [June 18, 1959], No. 38532/59. Class 7(3). A carburetter comprises a fuel-air mixing passage 12, Fig. 2, a recess forming with a diaphragm 42 a fuel chamber 40, a fuel inlet 72, Fig. 5, in communication with the chamber, a valve 74 for the inlet actuated by the diaphragm for controlling flow of liquid fuel from a supply into the chamber, a main fuel delivery system including an accelerating fuel well 90 for delivering fuel from the chamber into the mixing passage at 87 and a secondary fuel delivery system for delivering fuel to the mixing passage, the secondary fuel delivery system comprising a passage 116 communicating with the well and arranged so that fuel flow through the secondary system effects delivery of fuel from the chamber into the well. As shown in Fig. 5, the fuel flow from the supply, by means of a pump or gravity, is controlled by the diaphragm 42 acting, via lever 60 pivoted at 53, on the valve member 66, loosely slidable in member 64 The fuel flows into the chamber 40 through the gap between the cone portion 74 and valve seating 70 made of neoprene or similar material. On starting the engine, when the throttle plate 28, Fig. 2, is opened and the choke plate 22 in the air inlet 14 is closed, the pressure in the Venturi 18 will drop and the diaphragm 42 will be forced upwards by atmospheric pressure through vent 47 in cap 46. Fuel will therefore flow into the chamber 40 and thence into the mixing passage througl the primary system via port 108, Fig. 6, meter ing device 102, 104, well 90, ball valve 94 contained by bar 97, and nozzle 87. Under idling conditions when the choke is open and the throttle partially closed the pressure in the Venturi 18 will be high and thus force the bal 94 against the seating 86. The pressure on the down flow side of the throttle plate howeve will be low and fuel will flow from the fue chamber through the secondary system via metering device 102, 104, well 90, passage 116, chamber 112, a similar metering device, a passage 136, Fig. 7, to the secondary ports 138, 140. At the same time as the fuel is supplied to the mixing passage via the secondary system, the wall 90 is filled with fuel from the chamber 40 which is then available for immediate injection, via the main nozzle 87, into the mixing passage when the throttle plate is opened. An air bleed 120 between the well 90 and the air inlet 14 is provided to allow rapid injection of fuel from the well to the mixing passage, and mix a small amount of air with the fuel before passing to the mixing passage from either the secondary ports or the main nozzle. A modification particularly adaptable as an updraft carburetter is shown in Figs. 11, 12, wherein the well is formed by the passages 144, 116a and the air bleed is formed by passages 166, 172 between the chamber 112a and the air inlet 14a. A modified form of ball valve is also shown. An auxiliary metering device may be formed by providing a restriction in the ends of passage 116a, both acting on the secondary system, and the lower also acting on the fuel injected from the well on opening the throttle. A modified fuel passage between the fuel chamber 40a and the duct 106a, Fig. 11, may be provided whereby a port 162<SP>1</SP> in an elevated position above the duct 106 and in communication with it by a passage 178 provides a hydrostatic head of fuel in the vertical passage 178 assisting the flow through the secondary system and also maintaining fuel in the chamber 40a at a higher level. An alternative valve arrangement to that shown in Fig. 12 may be provided which consists of a fine capillary tube connecting passage 144 to the mixing passage 12a. A liquid seal prevents air entering when the secondary system is operating. As a further alternative the air bleed may be provided with a restriction and enter into the secondary passage after the secondary metering device. A further modification is shown in Fig. 23 wherein the fuel enters chamber 212 from chamber 40d and maintains a fuel well reservoir up to the line XX, a metering device 219 being provided for the main fuel nozzle. A number of modifications of the fuel inlet valve, and of the delivery ball valve, are described.