Intake system of a multi-cylinder internal combustion engine

A multi-cylinder internal combustion engine, each cylinder having a combustion chamber and an intake valve which has a valve head, said engine comprising:

• at least one intake passage common to at least two cylinders and comprising a collecting portion having an inlet, and at least two branch intake passages branched off from said collecting portion, each of said branch intake passages having an upper wall and a bottom wall and being connected to a respective one of said combustion chambers via a corresponding one of said intake valves;
• fuel supply means arranged in the inlet of said collecting portion;
• a common connecting passage;
• at least two branch connecting passages each being connected to said common connecting passage and having an opening which opens into a respective one of said branch intake passages, wherein the opening of each of said branch connecting passages is tangentially connected to an inner wall of a respective one of said branch intake passages, said wall extending circumferentially about an axis of said corresponding intake valve;
• and
• at least two rotatable throttle valves each being arranged in a respective one of said branch intake passages at a position upstream of the opening of a corresponding one of said branch connecting passages and having a lower edge and an upper edge which cooperates with the upper wall of said corresponding branch intake passage to form therebetween a mixture flow passage, the cross sectional area of which is increased as the corresponding throttle valve is rotated in accordance with an increase in the level of the load of said engine, the lower edge of each of said throttle valves cooperating with the bottom wall of said corresponding branch intake passage to prevent flow between the lower edge of said throttle valve and the bottom wall of said corresponding branch intake passage at least when the valves are opened less than a predetermined degree.