Wire for piston ring, and manufacturing method of piston ring

A wire for a piston ring, the wire forming a material of the piston ring to be mounted in a ring groove of a piston in an internal combustion engine, the wire comprising:

• a first side surface forming an outer circumferential surface in the piston ring, a second side surface forming an inner circumferential surface in the piston ring, a third side surface connecting the first side surface and the second side surface and forming a surface facing an inner wall of the ring groove on a combustion chamber side in the piston ring, and a fourth side surface connecting the first side surface and the second side surface and forming a surface facing an inner wall of the ring groove on a crank chamber side in the piston ring, wherein
• the first side surface comprises a tapered surface inclined to increase a width toward a first direction that is a direction from a side of the third side surface toward a side of the fourth side surface in a cross section orthogonal to an extending direction of the wire, and a protruding surface connecting the tapered surface and a predetermined surface located on the first direction side of the tapered surface and protruding on a side of a second direction that is a direction from the second side surface toward the first side surface,
• the protruding surface is divided, by a first virtual surface extending from the tapered surface to the first direction side, into a first part connected to the tapered surface and protruding to the second direction side of the first virtual surface, and a second part connecting the first part and the predetermined surface and located on an opposite side of the second direction of the first virtual surface,
• the first part includes a top located on a most second direction side in the first side surface and is formed in a protruding shape on the second direction side, and
• the first side surface including, as the predetermined surface, an inclined surface connecting the protruding surface and the fourth side surface and being inclined to decrease a width toward the first direction in the cross section orthogonal to the extending direction of the wire.

A wire for a piston ring, the wire forming a material of the piston ring to be mounted in a ring groove of a piston in an internal combustion engine, the wire comprising:

• a first side surface forming an outer circumferential surface in the piston ring, a second side surface forming an inner circumferential surface in the piston ring, a third side surface connecting the first side surface and the second side surface and forming a surface facing an inner wall of the ring groove on a combustion chamber side in the piston ring, and a fourth side surface connecting the first side surface and the second side surface and forming a surface facing an inner wall of the ring groove on a crank chamber side in the piston ring, wherein
• the first side surface comprises a tapered surface inclined to increase a width toward a first direction that is a direction from a side of the third side surface toward a side of the fourth side surface in a cross section orthogonal to an extending direction of the wire, and a protruding surface connecting the tapered surface and a predetermined surface located on the first direction side of the tapered surface and protruding on a side of a second direction that is a direction from the second side surface toward the first side surface,
• the protruding surface is divided, by a first virtual surface extending from the tapered surface to the first direction side, into a first part connected to the tapered surface and protruding to the second direction side of the first virtual surface, and a second part connecting the first part and the predetermined surface and located on an opposite side of the second direction of the first virtual surface,
• the first part includes a top located on a most second direction side in the first side surface and is formed in a protruding shape on the second direction side,
• the first side surface includes a cut surface connecting the protruding surface and the fourth side surface,
• the cut surface includes a first undercut surface as the predetermined surface,
• connected to the protruding surface, and a second undercut surface connecting the first undercut surface and the fourth side surface, and
• an inclination angle of the second undercut surface to the second direction is larger than an inclination angle of the first undercut surface to the second direction.

A manufacturing method of a piston ring for manufacturing, from a wire, the piston ring to be mounted in a ring groove of a piston in an internal combustion engine,

• the wire comprising a first side surface forming an outer circumferential surface in the piston ring, a second side surface forming an inner circumferential surface in the piston ring, a third side surface connecting the first side surface and the second side surface and forming a surface facing an inner wall of the ring groove on a combustion chamber side in the piston ring, and a fourth side surface connecting the first side surface and the second side surface and forming a surface facing an inner wall of the ring groove on a crank chamber side in the piston ring,
• the first side surface comprising a tapered surface inclined to increase a width toward a first direction that is a direction from a side of the third side surface toward a side of the fourth side surface in a cross section orthogonal to an extending direction of the wire, and a protruding surface connecting the tapered surface and a predetermined surface located on the first direction side of the tapered surface and protruding on a side of a second direction that is a direction from the second side surface toward the first side surface,
• the protruding surface being divided, by a first virtual surface extending from the tapered surface to the first direction side, into a first part connected to the tapered surface and protruding to the second direction side of the first virtual surface, and a second part connecting the first part and the predetermined surface and located on an opposite side of the second direction of the first virtual surface,
• the first part including a top located on a most second direction side in the first side surface and being formed in a protruding shape on the second direction side,
• the manufacturing method of the piston ring comprising:
• a coiling step of sending out the wire, and applying external force to the wire to form the wire in an annular shape,
• a cutting step of cutting the wire formed in the annular shape to obtain a ring, and
• a polishing step of polishing a surface of the ring, wherein
• in the coiling step, the first part is crushed on a side of the first virtual surface by the external force acting on the first side surface, and the protruding surface is deformed to form a corner portion, and
• in the polishing step, a tip end of the corner portion is polished to form a flat contact surface.