Piston for internal combustion engine

A piston for an internal combustion engine comprising:

• a piston body which is reciprocable relative to an inner wall of a cylinder bore;
• a pair of skirts which extend downward from the piston body;
• a pair of piston pin bosses which retains a piston pin;
• a pair of side walls which connect the skirts together;
• and
• resin-coated layers disposed on surfaces of the skirts which face the inner wall of the cylinder bore,
• wherein each of the skirts includes a central skirt portion, an upper skirt portion, and a lower skirt portion, the central skirt portion being a central portion of the skirt in a center axial direction of the piston body, having a largest diameter, and also having a surface area extending parallel to a center axis of the piston body, the upper skirt portion being curved to have an outer diameter which gradually decreases from an upper boundary of the central skirt portion toward the center axis of the piston body above the upper boundary, the lower skirt portion being curved to have an outer diameter which gradually decreases from a lower boundary of the central skirt portion toward the center axis of the piston body below the lower boundary,
• wherein each of the resin-coated layers has formed therein a plurality of recesses which retain oil therein,
• wherein ones of the recesses which are arranged close to the upper boundary or the lower boundary are located at a given distance away from the upper boundary or the lower boundary, and
• wherein the upper skirt portion and the lower skirt portion are shaped to have a first distance and a second distance, the first distance being a distance from the upper boundary to a portion of the upper skirt portion where a given value of the radius decrease is created on an imaginary plane, the imaginary plane being defined to extend parallel to the center axial direction of the piston body and pass through the skirt, and wherein the first distance is selected to be longer than the second distance that is a distance from the lower boundary to a portion of the lower skirt portion where the given value of the radius decrease is created on the imaginary plane.