| 摘要 |
In a corner portion ( 2 ) defined between an outer peripheral surface ( 4 ) and a lower-side surface ( 3 ) of a steel piston ring ( 1 ), a groove ( 5, 6 ) having either an approximately quadrangular shape with a length of one side of 0.05 to 0.4 mm or an approximately quarter circular shape having a radius of 0.05 to 0.4 mm is formed. A sharp edge ( 9 ) formed by the groove ( 5, 6 ) performs an oil scraping function and the groove ( 5, 6 ) works to reduce an oil pressure of a second land or a third land clearance between the cylinder bore and the piston.
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