Induction system for multi-cylinder engine

Abstract

An induction system for a multi-cylinder internal combustion engine that improves fuel efficiency and reduces the emission of unwanted exhaust gas constituents, particularly at the low and medium load conditions. The engine induction system comprises a plurality of separate carburetor barrels which, at least under some running conditions, serve cylinders separately from each other through main induction passages. One carburetor barrel is provided with a different fuel discharge system than the other carburetor barrels for accomodating a certain engine operating condition. A separate sub-intake system connects this carburetor barrel with other cylinders not normally served by the particular carburetor barrel in question. This sub-intake system has a substantially smaller cross-sectional area in the main intake system so that the charge drawn into the cylinders through the sub-intake system enters at a substantially higher velocity. This improves combustion by creating turbulence under at least some operating conditions. In a specific illustrated embodiment, the one carburetor barrel is provided with a choke valve so as to provide cold starting enrichment for all of the cylinders served by this carburetor barrel during cold starting. In accordance with the invention, means are provided for achieving a corresponding flow resistance in the carburetor barrels which do not have the cold starting device so that under other engine operating conditions the flow resistance between the various carburetor barrels is equal. In one embodiment this is done by providing a somewhat smaller venturi section in the other carburetor barrels. In another embodiment, this is done by changing the initial setting of the throttle valve of the one carburetor barrel from the others so as to provide the appropriate resistance differential.