Piston ring

A piston ring having an annular shape opened at a piston ring gap portion, the piston ring being placed inside a ring groove formed in an outer peripheral portion of a piston configured to reciprocate inside a bore along an axis direction of the bore, the piston ring being configured to slide with an outer peripheral portion of the piston ring being pressed against an inner peripheral surface of the bore, the piston ring comprising:

• a plurality of first ring pieces placed inside the ring groove in a stacking manner such that the first ring pieces adhere to each other in the axis direction;
• and
• a closing member,
• wherein
• the first ring pieces include respective piston ring gap portions each having end surfaces separated from each other via a ring gap having a predetermined dimension in a circumferential direction of the first ring pieces,
• the respective piston ring gap portions of the first ring pieces are displaced from each other in the circumferential direction,
• the closing member is provided to close the piston ring gap portions of the first ring pieces in a radial direction of the first ring pieces,
• the piston ring gap portion of a first ring piece on an uppermost side in the axis direction among the first ring pieces has a pair of first end surfaces separated from each other via a first predetermined ring gap in the circumferential direction,
• the first predetermined ring gap as a space between the first end surfaces gradually decreases inwardly in a radial direction of the first ring piece on the uppermost side,
• the closing member includes a first plug piece between the first end surfaces, and
• the first plug piece is configured to move inwardly, by a pressure applied to an outer peripheral side of the first ring piece on the uppermost side, from a first radial position to a second radial position in the radial direction of the first ring piece while an airtight state where the first plug piece is in contact with the first end surfaces is maintained.