Piston structure for internal combustion engine

A piston structure for a four-valve four-stroke internal combustion engine in which a pair of intake valves and a pair of exhaust valves are provided in a cylinder head at positions around a spark plug, located approximately on a cylinder central axis, and are disposed into a V-shape facing a combustion chamber, comprising:

• a piston crown of a piston, said piston crown comprising
• a pair of intake valve recesses and a pair of exhaust valve recesses respectively facing head portions of the intake valves and head portions of the exhaust valves;
• an intake-side inclined flat surface which is a single plane defined by bottom surfaces of said pair of intake valve recesses;
• an intake-side common flat surface which extends from said bottom surfaces of said pair of intake valve recesses toward a center of said piston crown such that said bottom surfaces are continuous with each other;
• an exhaust-side inclined flat surface which is a single plane defined by bottom surfaces of said pair of exhaust valve recesses;
• and
• an exhaust-side common flat surface which extends from said bottom surfaces of said pair of exhaust valve recesses toward the center of said piston crown such that said bottom surfaces are continuous with each other,
• wherein said intake-side inclined flat surface and said exhaust-side inclined flat surface are formed into a pent-roof shape with a ridge line at an intersection therebetween,
• wherein said exhaust-side inclined flat surface extends into said pair of intake valve recesses, and
• wherein said ridge line is located on a side of said piston crown corresponding to said pair of intake valve recesses.