Abstract: A laminated chromium plating layers providing improved wear resistance and fatigue strength for use in mechanical parts of an internal combustion engine. The lamination is formed on a base body and contains a plurality of high hardness chromium plating layer and a plurality of low hardness chromium plating layer, and each high hardness chromium plating layer is formed upon each low hardness chromium plating layer to provide the lamination of alternating high hardness chromium plating layer and low hardness chromium plating layer.

Abstract: A three-piece type oil ring assembly adapted to be fitted in an oil ring groove of a piston disposed within a cylinder comprises a spacer expander in the form of a gapped annulus made of section steel having substantially H-shaped radial cross section, and a pair of upper and lower side rails, each in the form of a gapped flat annulus. The spacer expander includes an axially protruding outer portion disposed on the outer circumference thereof and facing the inner surface of the cylinder, an axially protruding inner portion disposed on the inner circumference thereof and facing the innermost wall of the oil ring groove, and an axially flat connecting portion extending between the outer and inner protruding portions. The outer protruding portion has side rail supporting surfaces formed on the upper and lower ends thereof so as to be inclined toward the axially symmetrical centerline thereof along the radial direction at an acute angle with the radial direction.