WIDTH-REDUCED THREE-PIECE OIL RING

摘要

A width-reduced three-piece oil ring comprising an incomplete torus space expander (10) constituted by a shape steel material having a substantially H-shaped cross section and comprising in turn a projection (12) on the external circumference side expanding axially vertically, a projection (13) on the internal circumference side which is axially longer than the projection on the external circumferences side and expanding axially vertically, an intermediate portion (16) thinned axially and connecting the both projections and slits (11) cut into the intermediate portion (16) alternately from the projection (12) on the external circumference side and the projection (13) on the internal circumference side, and two side rails (20, 20') calming the space expander from the top and bottom thereof. In order to make the friction of the oil ring lower without increasing the tension of the space expander (10) and reduce the oil consumption, upper and lower side rail pressing surfaces (15, 15') for pressing the internal circumferential surfaces (21, 21') of the side rails (20, 20') are formed on the upper and lower surfaces of the axially vertically expanding projection (13) on the internal circumference side which face radially outwardly, and the inclination angle of at least one of the upper and lower side rail pressing surfaces (15, 15') is set less than 15° relative to the axial direction.