Induction system for internal combustion engine

Claim 1

An induction system for an internal combustion engine having first and second groups of cylinders of which firing orders are respectively discontinuous, comprising: a first collector for supplying air to the first group of cylinders; a second collector for supplying air to the second group of cylinders, said first and second collectors being elongated in parallel to each other and having open ends and closed ends which are arranged reversely to each other; a first main air supply passage fluidly connected to said first collector to form a first air supply line; a second main air supply passage fluidly connected to said second collector to form a second air supply line independent from said first air supply line, said first and second main air supply passages being elongated in the direction transversing the longitudinal axes of said collectors and having downstream ends in communication with said open ends of said first and second collectors; a first throttle valve disposed in said first main air supply passage; a second throttle valve disposed in said second main air supply passage; an additional air supply passage bypassing said first and second throttle valves for supplying additional air to said first and second collectors, said additional air supply passage having a bifurcated downstream end fluidly connected to said first and second air supply lines, said bifurcated downstream end constituted by a balance passage having opposed ends fluidly connected to said first and second main air passages, said balance passage being elongated in parallel to said first and second collectors and having a balance tube comprising a tubular main body with an open end and a closed end and an outward flange at the open end, said tubular main body having at the circumferential peripheral wall thereof a pair of diametrically opposed balance holes, said balance tube being disposed in said balance passage at an approximately central portion thereof in such a manner as to communicate at said open end with an upstream end side of said additional air supply passage and at said balance holes with said opposed ends of said balance passage; and an additional air control valve disposed in said additional air supply passage for controlling air flow therethrough.