Piston ring

A piston ring mounted on a piston of an internal combustion engine, comprising:

• an outer circumferential surface provided on an outer circumference of the piston ring;
• an inner circumferential surface provided on an inner circumference of the piston ring;
• an upper surface facing a combustion chamber side in the internal combustion engine among axial end surfaces of the piston ring;
• and a lower surface positioned on a crank chamber side in the internal combustion engine among the axial end surfaces of the piston ring;
• wherein
• the outer circumferential surface includes:
• an outer circumferential end surface including an outer circumferential end portion having a maximum diameter in the piston ring in a cross section orthogonal to a circumferential direction of the the piston ring;
• and a cut surface connecting the outer circumferential end surface and the lower surface so as to form a notched portion extending in the circumferential direction of the piston ring between the outer circumferential end surface and the lower surface;
• the cut surface includes:
• a bottom portion positioned on an innermost side of the cut surface in a radial direction of the piston ring;
• a first surface provided between the outer circumferential end surface and the bottom portion and facing the crank chamber side;
• and a second surface provided between the bottom portion and the lower surface and facing outward in the radial direction;
• the second surface is inclined away from a central axis of the piston ring as it extends toward the crank chamber side;
• an angle of inclination of the second surface with respect to the lower surface in a cross section orthogonal to the circumferential direction of the piston ring is greater than or equal to 50° and less than or equal to 85°;
• when an axial width of the piston ring is h1 and a distance in an axial direction between a connecting portion between the cut surface and the outer circumferential end surface and a connecting portion between the cut surface and the lower surface is H, H/h1 is greater than or equal to 0.2 and less than or equal to 0.4;
• the connecting portion between the cut surface and the lower surface is positioned radially inward of the connecting portion between the cut surface and the outer circumferential end surface;
• and
• the cut surface is configured to allow oil flowing along the second surface to escape to an outer circumferential side of the piston ring.