US Patent 7243596 Spacer expander

In a combined oil ring having a spacer expander to be installed between a pair of upper and lower side rails, a plurality of axially protruding inner peripheral protruding portions are formed on the inner peripheral side of the spacer expander along its peripheral direction. The inner peripheral protruding portions press the inner peripheral surface of the side rails. On the outer peripheral side of the spacer expander, a plurality of slits are formed, and a plurality of connecting portions are located in the peripheral direction isolated by the slits. On the plurality of connecting portions, axially protruding outer peripheral protruding portions are formed.