US Patent 7373873 Low friction, high durability ringless piston and piston sleeve

A cylinder liner and ringless piston adapted to be combined therewith in an internal combustion engine are provided that have superior wear resistance, superior scuffing resistance, and superior properties for abating friction loss between the inside surface of the cylinder and the sliding surface of the ringless piston. These embodiments can also include a cylinder liner which has at least some portion of the inner circumferential surface coated with an iron oxide film, a metallic nitride film, or other physical vapor deposition or chemical vapor deposition film, combined with a ringless piston with at least some portion of the exterior surface being coated with a metallic nitride film or other vapor deposition film.