Patent ID: 8365696

Claim:
A piston device for internal combustion engines comprising a first compression ring and a second compression ring in an outer circumference of a piston, wherein the second compression ring includes a notch extending from the inner circumference to the outer circumference on a lower surface of at least one of a pair of ends of the ring, and a gap between the ring ends at the notch on the second compression ring is larger than a gap between the ring ends of the first compression ring, and a gap between the ring ends at the section other than the notch on the second compression ring is the same or smaller than the gap between the ring ends of the first compression ring, and the second compression ring contains an outer circumferential surface comprised of a tapered surface decreasing the ring radial thickness towards the upper side, and an axial parallel surface formed below the tapered surface, and the boundary between the tapered surface and the axial parallel surface is positioned below the upper surface of the notch in the circumferential positions other than the vicinity of the notch and rising upward from just before the notch so as not to be split by the notch and reaching a position higher than the upper surface of the notch at the notch.