GB1201227A - Improvements in or relating to carburettors for internal combustion engines - Google Patents

Abstract

1,201,227. Carburetters. P. AUGUST. Nov.30, 1968, No.45948/68. Heading F1B. A downdraught carburetter comprises a main induction passage for the downward flow of mixture, a tube open at both ends located in a lower part of the passage so that there is defined between the passage and the tube an open-topped annular chamber for the collection of fuel condensate running down the walls of the passage, the chamber being in communication with heating means for evaporating the condensate, and means for leading the evaporated fuel from the heating means to the engine, the tube being located in front of or masking a main outlet orifice from a duct for idling mixture such that the idling mixture discharges through the orifice into the chamber when the carburetter is in use. In the downdraught carburetter shown, fuel condensate is collected in the annular space 11 between a tube 10 and the main induction passage 1. Idling mixture from a duct 4 also enters the annular space 11 via a regulating screw 6. Heated extra combustion air is supplied to the idling mixture either through a bore 7 in the regulating screw 6 or through a passage 8 controlled by a regulating screw 9, or through both of these means. The condensate and idling mixture pass via a bore 11 into a heating chamber 12 which is heated by means not shown to evaporate the condensate. The heated mixture is led from the chamber 12 to the locality of the inlet valves via a narrow pipe 14 extending through the induction manifold. Preferably the pipe 14 is heated by known means. When the main throttle valve 2 is closed as shown, a thickened portion 3 closes by-pass holes 5 leading from the duct 4. The upper edge 10<SP>1</SP> of the tube 10 is chamfered so that the valve 2, when opened, canenter the tube either freely or with slight grazing. During over-run, i.e., when the throttle valve 2 is closed while the engine speed is above a predetermined value, the supply of idling fuel to the duct 4 is cut off, a throttle valve 13 in the pipe 14 is closed, and a throttle valve 15 is opened to admit air through a tube 18 to facilitate combustion (during the first few seconds) of the fuel which remains in the induction manifold. During the remainder of the over -run, the engine is starved of fuel, so that there is no, or substantially no, emission of carbon monoxide or hydrocarbon. This control may be effected pneumatically or hydraulically but preferably by electromagnetic means which are energized when the engine speed exceeds a predetermined value, say about 1800 to 2000 r.p.m., so sensed by an electronic device connected to the ignition coil, while a switch connected to the throttle valve 2 is closed on closure of the throttle valve. When the engine speed falls below a second predetermined value, say about 1100 to 1500 r.p.m., or the throttle valve 2 is re-opened the electromagnetic means is de-energized. In about the first half second after the throttle valve 2 is re-opened, the mixture entering the induction manifold is very weak but is enriched before it enters the inlet valves by heated mixture from the heating chamber 12 passing through the pipe 14.