Piston ring for internal combustion engine

Claim 1

For use in an internal combustion engine having an oblong piston mounted to reciprocate within an oblong cylinder having arcuate end portions, a piston ring adapted to be received within a peripheral groove on the piston, the piston ring in its free state before installation having straight side portions of equal length each having one end merging with a relatively longer arcuate portion of the ring, the other ends of said straight portions merging with first and second relatively shorter arcuate portions of the piston ring, said shorter arcuate portions defining between them a gap, the free shape of the piston ring having the following characteristics: 0-0'=γR-γC α=90°×γC/γR β<α AD=BC ∠0'AD=90°=∠0'A'D' D0"=D'0"'=γR where 0=center of the radius of the arcuate end portions of the cylinder 0'=center of the radius of the relatively longer arcuate portion of the piston ring 0"=center of the radius of the first relatively shorter arcuate portion of the piston ring 0"'=center of the radius of the second relatively shorter arcuate portion of the piston ring γR: radius of the relatively longer arcuate portion of the piston ring γC: radius of the arcuate end portions of the cylinder A and D: ends of one straight portion of the piston ring A' and D': ends of the other straight portion of the piston ring B and C: ends of one straight portion of the cylinder α: angle between the longitudinal axis of the piston ring and a line between 0' and the point where either straight side portion of the piston ring merges with the relatively longer arcuate portion of the ring E: end of the first relatively shorter arcuate portion of the piston ring E': end of the second relatively shorter arcuate portion of the piston ring β: ∠D0"E=∠D'0"'E'.