Patent ID: 7506575

Claim:
An apparatus, comprising: an internal combustion engine having at least one wall defining a bore; and a piston disposed to reciprocate in the bore, the piston comprising a head portion and a skirt portion, the piston having a substantially circumferential outer surface and at least a portion of the outer surface bearing against the wall in a thrust plane, wherein the outer surface includes a lower skirt portion, an intermediate skirt portion, and an upper skirt portion having a maximum radius in the thrust plane that is less than a maximum radius of the lower skirt portion in the thrust plane, the intermediate skirt portion including a concave curvature in the thrust plane to at least partially define the only region of concavity in the thrust plane of the skirt portion when the piston is substantially at an operating temperature; wherein the outer surface transitions from the substantially convex curvature of the lower skirt profile to the substantially concave curvature of the intermediate skirt profile to account for a change in rigidity of the piston; and wherein the lower skirt portion and the upper skirt portion are operable to substantially uniformly distribute a thrust load from the piston to the major thrust side of the wall.