Patent ID: 7302884

Claim:
A piston comprising a head portion and a skirt portion, the piston having an axial profile in a thrust plane, the axial profile, when the piston is substantially at an operating temperature, includes: a lower skirt profile; an intermediate skirt profile adjacent the lower skirt profile, at least a portion of the intermediate skirt profile having a concave curvature in the thrust plane; and an upper skirt profile adjacent the intermediate skirt profile, wherein the lower skirt profile has a maximum radius that is greater than a maximum radius of the upper skirt profile, wherein the skirt portion defined by the lower skirt profile has substantially greater radial flexibility than the skirt portion defined by the upper skirt profile, wherein at least a portion of the lower skirt profile has a substantially convex curvature in the thrust plane and at least a portion of the upper skirt profile has a substantially convex curvature in the thrust plane, wherein the intermediate skirt profile joins the lower skirt portion at an inflection point between the substantially concave curvature of the intermediate skirt profile and the substantially convex curvature of the lower skirt profile, and wherein the axial profile 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.