| 摘要 |
A generally circular compression piston ring having an outer peripheral surface, an inner peripheral surface, and a pair of end faces splitting the circular shape in a radial direction thereof for defining a gap portion. The ring has a first portion including a notched portion formed at the inner peripheral surface and extending over a predetermined circumferential length portion starting from the end face, and a second portion other than the first portion. The second portion has a radial thickness ranging from 2.0 mm to 6.0 mm. The notched portion is a plane shape gradually reaching the outer peripheral surface toward the end face. The end face has a radial thickness ranging from 0.2 times to less than 0.5 times as large as the radial thickness of the second portion. The outer peripheral surface defines a center serving as a center of a center angle, and the predetermined circumferential length portion is defined by the center angle ranging from 26.5 degrees to 14 degrees.
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