Compression ring
To provide a long-life compression ring without an increase in the outer peripheral abrasion near the gap regardless of the ring material or the presence or absence of the outer peripheral hard coating, in an annular compression ring having a pair of gap faces opposed to each other to form a free gap and a nominal diameter d1 equal to an inner diameter of a cylinder to which the compression ring is attached to along with a piston, a self tangential force is 5N to 50N, and a radius of curvature R1 and the nominal diameter d1 satisfy a relationship: −0.01≤(2 R 1− d 1)/ d 1<0.002 where the radius of curvature R1 is that of outer peripheral arcs of gap end portions in a free shape state before the compression ring is attached to the cylinder, and the gap end portions are defined in ranges between the gap faces and positions where a center angle from a midpoint of the free gap is 35°.
1. A combination comprising a compression ring, a piston, and a cylinder, wherein
the compression ring is an annular compression ring having a pair of gap faces opposed to each other to form a free gap and a nominal diameter d 1 equal to an inner diameter of the cylinder to which the compression ring is attached to along with the piston,
a self tangential force of the compression ring is 5 N to 50 N, and
a radius of curvature R 1 and the nominal diameter d 1 of the compression ring satisfy a relationship:
−0.01≤(2 R 1− d 1)/ d 1<0.002
where the radius of curvature R 1 is that of an outer peripheral arcs of gap end portions in a free shape state before the compression ring is attached to the cylinder, and
the gap end portions are defined in ranges between the gap faces and positions where a center angle from a midpoint of the free gap is 35°.
2. The combination of the compression ring, the piston, and the cylinder according to claim 1 , wherein the radius of curvature R 1 and the nominal diameter d 1 of the compression ring satisfy a relationship:
−0.01≤(2 R 1− d 1)/ d 1<0.
3. The combination of the compression ring, the piston, and the cylinder according to claim 1 , wherein
an ovality of the compression ring defined as a difference (d 3 −d 4 ) and the nominal diameter d 1 satisfy a relationship:
−0.013≤( d 3− d 4)/ d 1<0
where d 3 is a diameter in a first axial direction through the midpoint of the closed gap and d 4 is a diameter in a second axial direction orthogonal to the first axial direction when the compression ring is inserted into an annular flexible tape and the flexible tape is drawn to close the compression ring until the closed gap becomes a predetermined gap in a case where the compression ring is attached to the cylinder.
4. The combination of the compression ring, the piston, and the cylinder according to claim 1 , wherein, the compression ring has less than 35% of a light passing ratio in a light tightness test defined by ISO 6621-2:2003(E), where the light passing ratio is a ratio of a circumferential length of a light passing portion excluding the closed gap to an inner peripheral length of a ring gauge used in the light tightness test, the light passing portion being between an inner peripheral face of the ring gauge and an outer peripheral face of the compression ring.
5. The combination of the compression ring, the piston, and the cylinder according to claim 4 , wherein radial gaps between the outer peripheral face of the compression ring in the light passing portion and the inner peripheral face of the ring gauge at outer peripheral positions 1 mm away from the pair of gap faces are smaller than 0.13% of the nominal diameter d 1 .
6. The combination of the compression ring, the piston, and the cylinder according to claim 1 , wherein the compression ring comprises at least one coating selected from the group consisting of a plating film, an ion plating film, and a nitrided layer on at least an outer peripheral sliding surface.
7. The combination of the compression ring, the piston, and the cylinder according to claim 6 , wherein the ion plating film is at least one film selected from the group consisting of CrN, Cr 2 N, TiN, CrCN, TiCN, and a diamond like carbon.
8. The combination of the compression ring, the piston, and the cylinder according to claim 1 , wherein the radius of curvature R 1 and the nominal diameter d 1 of the compression ring satisfy a relationship:
−0.004≤(2 R 1− d 1)/ d 1≤−0.001.
9. A combination comprising a compression ring, a piston, and a cylinder, wherein
the compression ring is an annular compression ring having a pair of gap faces opposed to each other to form a free gap and a nominal diameter d 1 equal to an inner diameter of the cylinder to which the compression ring is attached to along with the piston,
a self tangential force of the compression ring is 5 N to 50 N, and
a radius of curvature R 1 and the nominal diameter d 1 of the compression ring satisfy a relationship:
−0.01≤(2R1 −d 1)/ d 1<0.002
where the radius of curvature R 1 is that of an outer peripheral arcs of gap end portions in a free shape state before the compression ring is attached to the cylinder, and
the gap end portions are defined in ranges between the gap faces and positions where a center angle from a midpoint of the free gap is 35°; and wherein
the compression ring has less than 35% of a light passing ratio in a light tightness test defined by ISO 6621-2:2003(E), where the light passing ratio is a ratio of a circumferential length of a light passing portion excluding the closed gap to an inner peripheral length of a ring gauge used in the light tightness test, the light passing portion being between an inner peripheral face of the ring gauge and an outer peripheral face of the compression ring.