Two-piece type oil ring assembly

A two-piece type oil ring assembly adapted to be mounted in an oil ring groove of a piston disposed within a cylinder, the oil ring groove having a lower side and the oil ring assembly comprising:

• a single spacer expander in the form of a split annulus and a single side rail in the form of a flat split annulus,
• said spacer expander having an upper surface, a lower surface, and a radial section, said radial section forming a substantially L-shaped configuration with a lower surface having substantial portions thereof making plane contact with the lower side of said oil ring groove, an outer crest portion and an inner crest portion, said outer crest portion being closer to the cylinder than said inner crest portion, said outer crest portion having an inner and outer periphery, said inner crest portion being closer to an end of the oil ring groove than said outer crest portion, said inner crest portion having an inner and outer periphery, said outer crest portion and said inner crest portion being integrally connected by a trough portion, said inner crest portion being axially taller than said outer crest portion,
• said upper and lower surfaces and being formed with a multiplicity of radial slots extending alternatively from the outer periphery of said outer crest portion to the outer periphery of said inner crest portion and from the inner periphery of said inner crest portion to the inner periphery of said outer crest portion, said outer and inner crest portions being substantially axially inflexible,
• said spacer expander being provided with a plurality of oil grooves radially passing through said spacer expander, at least one of said oil grooves being adjacent to one of said slots, said side rail having a lower surface placed on said outer crest portion and an inner periphery supported by said inner crest portion.