Helically-shaped intake port of an internal combustion engine

Claim 1

An intake port of a spark-ignition internal combustion engine, which intake port includes a helical portion having an upper wall, a helically curved peripheral side wall, and an outlet at the bottom of the helix, wherein an intake valve is arranged at said outlet, and said peripheral side wall extends circumferentially about an axis of said intake valve, and an inlet passage portion tangentially connected at one end to said helical portion and having an inlet at its other end, said inlet passage portion being defined by an upper wall, a bottom wall, a first side wall, and a second side wall, said second side wall being more remote from the axis of said intake valve than said first side wall and being connected to the peripheral side wall of said helical portion, wherein said first side wall of said inlet passage portion has an inclined wall portion at said other end, the direction in which said wall portion is inclined being such as to make the width of said inlet passage portion above the lower edge of the inclined wall portion at any point along said inlet passage portion narrower than the width of said inlet passage portion below said inclined wall portion at said point, the width of said inclined wall portion increasing gradually towards said helical portion to comprise the entire first side wall at said one end of said inlet passage portion which is tangentially connected to said helical portion such that the cross-sectional shape of the passage at the entrance to the helical portion is trapezoidal, and the intake port comprising a valve guide projecting into said helical portion from the upper wall of said helical portion and having a circumferential wall, an upper part of said first side wall being tangentially connected to the circumferential wall of said valve guide, and a lower part of said first side wall being connected to the peripheral side wall of said helical portion so as to deflect part of the flow through the intake port downwards toward the outlet of the helical portion while allowing the remainder of the flow to pass around the helically curved peripheral side wall, thereby introducing said part of the flow directly into the combustion chamber with minimum flow resistance while allowing said remainder of the flow to develop a strong swirl motion in the helical portion of the intake port.