Abstract: There is provided a highly heat conductive piston ring for an internal combustion engine capable of exhibiting a gas seal function and a heat transfer function for a long period of time in a stable manner when used in an automobile gasoline engine having a high compression ratio. The highly heat conductive piston ring for an internal combustion engine is a piston ring for an internal combustion engine having an Mn—Cr steel as a base material, the Mn—Cr steel including C in the range of from 0.52 to 0.65 mass %, Si in the range of from 0.15 to 0.35 mass %, Mn in the range of from 0.60 to 1.00 mass %, Cr in the range of from 0.60 to 1.00 mass %, P in the range of 0.04 mass % or less, S in the range of 0.04 mass % or less, a slight amount of components (total content of Al, Ni, and Cu) in the range of from 0.05 to 3.0 mass %, and a remnant being Fe and unavoidable impurities.

Abstract: There is provided a highly heat conductive piston ring for an internal combustion engine capable of exhibiting a gas seal function and a heat transfer function for a long period of time in a stable manner when used in an automobile gasoline engine having a high compression ratio. The highly heat conductive piston ring for an internal combustion engine is a piston ring for an internal combustion engine having an Mn—Cr steel as a base material, the Mn—Cr steel including C in the range of from 0.52 to 0.65 mass %, Si in the range of from 0.15 to 0.35 mass %, Mn in the range of from 0.60 to 1.00 mass %, Cr in the range of from 0.60 to 1.00 mass %, P in the range of 0.04 mass % or less, S in the range of 0.04 mass % or less, a slight amount of components (total content of Al, Ni, and Cu) in the range of from 0.05 to 3.0 mass %, and a remnant being Fe and unavoidable impurities.

Abstract: An internal combustion engine oil ring which stably retains, for a long period, the function of scraping excess oil from a cylinder inner wall surface and letting the excess oil flow down to an underside of a piston and ensures reduction in the amount of oil consumption when an internal combustion engine is driven. An internal combustion engine oil ring is provided, whose main body includes, along an inner peripheral surface, a coil expander receiving recess having a generally semicircular shape in cross-section in an oil ring axial direction, an inner peripheral surface of the coil expander receiving recess has an oil return groove formed along an inner peripheral direction for smoothly returning scraped oil to an underside of a piston, and an outer peripheral shape of the groove is composed of a straight line and a curved line continuous therewith in cross-section in the oil ring axial direction.