INTAKE PORT STRUCTURE OF ENGINE AND DESIGNING METHOD

PURPOSE:To allow the intake port of an engine to put intake flow in a specified direction without being affected by a translation section by preventing intake resistance from increasing due to the change in a port cross area shape at the translation section between the axis lines of the intake port and a valve and setting the incidence angle of the axis line of the intake port CONSTITUTION:The port axis AP at the throat section 4a of an intake port 4 is defined by a small incidence angle thetaP and a straight line or a curve of a large radius R of curvature in the interval L from an outlet side opening to a portion in the upper section separated a specified length from the outlet side opening, and an axis transient section of a small radius (r) of curvature whose center of curvature is positioned in the intake port is provided between the port axis AP and a valve axis VP. The shape and area of the cross section of the port in the interval L are defined so as to become nearly the same on a defined plane perpendicular to the port axis AP at the end of the upper section, perpendicular to the valve axis VP at the lower section and gradually changed between them.