Piston for internal combustion engine, compressor or the like

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.

A method of continuously forming a film of lubricant between a cylinder wall of a cylinder and a piston skirt of a piston reciprocally received in said cylinder, comprising the steps of:

• (a) spacedly providing a plurality of grooves indented all around an outer surface of said piston skirt wall, wherein said grooves are arranged to be extended radially and intervally around said piston skirt wall;
• (b) providing a plurality of indentions indented around said outer surface of said piston skirt wall and arranged to be positioned between said grooves to compensate a coverage of said grooves and increase an effective area for reserving said lubricant;
• (c) spacedly providing a plurality of lubricant channels all around an outer surface of said piston skirt, which are through holes penetrated from an inner surface to said outer surface of said piston skirt wall of said piston skirt;
• (d) producing a suction effect by means of enlarged countersink openings formed at outer ends of said through holes respectively surface when said piston is moving up and down axially along said cylinder, and delivering said lubricant in a cavity defined by said surrounding inner wall of said piston skirt flowing to said openings on said outer surface due to said suction effect;
• (e) retaining said lubricant delivered through said through holes in said grooves and indentions in a maximum period of time when said piston is moving in said cylinder in a reciprocal manner;
• and
• (f) forming a film of said lubricant between said outer surface of said piston skirt and said cylinder wall of said cylinder while said piston is moving reciprocally within said cylinder by ensuring an adequate and continuous supply of said lubricant to be retained in said grooves and indentions so as to substantially reduce said friction between said piston skirt and said cylinder wall.