Combustion chamber of an internal combustion engine

Claim 1

An internal combustion engine comprising a cylinder block having a cylinder bore therein; a piston having a flat top face and being reciprocally movable in said cylinder bore; a cylinder head fixed onto said cylinder block and having an inner wall overlying the adjacent end of the cylinder bore, said inner wall having a flat wall portion and a concave wall portion, said flat wall portion circumferentially extending along a part of the periphery of said inner wall and defining a flat squish area on one side of the axis of said cylinder bore between said flat wall portion and said flat top face of said piston, said concave wall portion and said flat top face of the piston defining a combustion chamber when said piston is at its top dead center position, which combustion chamber has a central axis parallel to and offset on an opposite side of the axis of said cylinder bore; an intake valve arranged on said concave wall portion; an exhaust valve arranged on said concave wall portion; and a spark plug having a spark gap arranged in said combustion chamber, wherein the improvement comprises: a projection having a concave bottom wall and a flat side wall extending from a region of the surface of the concave wall portion of said inner wall of the cylinder head located between the axis of the cylinder bore and said central axis of the combustion chamber, the flat side wall being inclined at an acute angle with respect to said central axis of the combustion chamber and facing the squish area, and a threaded bore extending through said projection perpendicular to said flat side wall, the spark plug being mounted in said threaded bore with its spark gap located close to the plane of said flat side wall approximately at a point on said central axis of the combustion chamber which is midway between the intersections of said central axis with the concave wall portion of the inner wall of the cylinder head and the flat top face of the piston when the piston is at its top dead center position, wherein the cross-sectional area of the projection progressively decreases with distance from said inclined flat side wall on the opposite side of the combustion chamber from the squish area, such that the concave bottom wall of the projection becomes flush with the concave wall portion of said cylinder head surrounding the projection prior to reaching the plane of said flat wall portion of said cylinder head, wherein the volume of the combustion chamber on said opposite side of the inclined side wall is approximately the same as the volume on the side facing the squish area.