OIL RING, METHOD OF PRODUCING THE SAME, AND PISTON STRUCTURE USING THE OIL RING

摘要

An oil ring (1) has an annular oil ring body (10) and a coil expander (20). The oil ring body (10) has a pair of rail portions arranged at its axially upper and lower portions and has a fit joint. The coil expander (20) is assembled to the inner periphery side of the oil ring body (10). A radial cross-section of an outer periphery sliding surface(f) of each of the pair of rail portions (12) has at its center a substantially straight line region (f1) with a length of 0.05 mm or greater and curved regions (f2) formed on both sides of the straight line region (f1).