Patent ID: 7856956

Claim:
A spark ignition engine comprising: a cylinder; a cylinder head; a piston; a sleeve formed in a blind cylindrical shape; an auxiliary chamber formed at a bottom part of the sleeve; an ignition plug fitted to the cylinder head through the sleeve; a set of ignition electrodes for the ignition plug facing a single chamber type combustion chamber in the cylinder; and one or more nozzle holes allowing the auxiliary chamber to communicate with the combustion chamber, wherein: the bottom of the sleeve is projected to the inside of the combustion chamber from an explosion surface of the cylinder head; an ignition position of the ignition electrodes is set near the explosion surface; the ignition position is configured to be in a position lower than a residual gas that remains in the auxiliary chamber at a time of ignition before the piston reaches top dead center; and a ratio of a volume of the auxiliary chamber to that of the combustion chamber when the piston reaches top dead center is set within a range of 0.010 to 0.015.