A combined oil control ring comprising a pair of annular side rails each having a gap, and an axially corrugated spacer expander arranged between the side rails; the corrugated spacer expander having on the inside seating tabs for pushing inner peripheral surfaces of the side rails; the side-rail-pushing surface of each seating tab being provided with a nitrided layer; an entire surface of each spacer expander except for those provided with the nitrided layer being coated with a plating film; and the plating film having Vickers hardness HV0.01 of 300 or less.

In this piston ring combination, a second outer peripheral surface, which is the outer peripheral surface of a second ring, has a second protruding surface curved into a convex shape, and a pair of third outer peripheral surfaces, which are the outer peripheral surfaces of a pair of segments, each have a third outer peripheral area in which a third protruding surface is formed, the third protruding surfaces being curved into convex shapes. In at least one of the pair of third outer peripheral surfaces, the peripheral edge on a crank-chamber side is positioned farther outward in the diametrical direction than the peripheral edge on a combustion-chamber side, and a peak of the third protruding surface is positioned nearer to the crank chamber than the center of the third outer peripheral surface.

In this piston ring combination, a second outer peripheral surface, which is the outer peripheral surface of a second ring, has a second protruding surface curved into a convex shape, and a pair of third outer peripheral surfaces, which are the outer peripheral surfaces of a pair of segments, each have a third outer peripheral area in which a third protruding surface is formed, the third protruding surfaces being curved into convex shapes. In at least one of the pair of third outer peripheral surfaces, the peripheral edge on a crank-chamber side is positioned farther outward in the diametrical direction than the peripheral edge on a combustion-chamber side, and a peak of the third protruding surface is positioned nearer to the crank chamber than the center of the third outer peripheral surface.

A combined oil control ring comprising a pair of annular side rails each having a gap, and an axially corrugated spacer expander arranged between the side rails; the corrugated spacer expander having on the inside seating tabs for pushing inner peripheral surfaces of the side rails; the side-rail-pushing surface of each seating tab being provided with a nitrided layer; an entire surface of each spacer expander except for those provided with the nitrided layer being coated with a plating film; and the plating film having Vickers hardness HV0.01 of 300 or less.

A combined oil control ring comprising a pair of circular side rails each having a gap, and a waved spacer expander longitudinally sandwiched by the side rails, which has seating tabs for pushing inner surfaces of the side rails on the inner side, (a) the radial thickness a.sub.1 of the side rail being 50-90% of the height a.sub.9 of the spacer expander, or (b) the height a.sub.10 of the seating tab being 23-60% of the height a.sub.9 of the spacer expander.