Patent ID: 7415961

Claim:
A piston for performing a reciprocal movement in a cylinder having a cylinder wall with a predetermined amount of lubricant, comprising: a piston ring and a piston skirt having a piston skirt wall having an outer surface, an inner surface and a cavity defined by said surrounding inner surface, a plurality of lubricant reservoirs including a plurality of grooves and indentions indented all around said outer surface of said piston skirt wall, wherein each of said grooves has a length shorter than a circumference of said piston skirt and is extended radially and intervally around said piston skirt wall, wherein said indentions are arranged to be positioned between said grooves to compensate a coverage of said grooves and increase an effective area for reserving said lubricant, and a plurality of lubricant channels which are through holes spacedly provided all around said outer surface of said piston skirt and adjacent to said grooves and indentions, wherein each of said through holes extends from an inner surface to said outer surface of said piston skirt wall and has an enlarged countersink opening formed at an outer end thereof, whereby a suction effect is achieved to deliver said lubricant in said cavity flowing to said opening on said outer surface when said piston is moving up and down axially along said cylinder so as to ensure said lubricant reaching said outer surface rapidly and retaining in said grooves and indentions for effectively and continuously forming a film of said lubricant between said outer surface of said piston skirt and said cylinder wall of said cylinder, wherein said indentions provided between said grooves maximally increase an oil film area between said piston skirt and said cylinder wall.