A number of embodiments of a piston may have a shape that provides enhanced piston guidance. In such embodiments, the piston shape may include an axial profile that is configured to provide certain thrust load characteristics.
1. 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.
2. An internal combustion engine, comprising:
a bore wall at least partially defining a bore; and
a piston that moves in the bore in response to a combustion event that provides a rod force component and a thrust force component, the thrust force component urging the piston against a major thrust side of the bore wall, the piston comprising:
a head portion; and
a skirt portion, the skirt portion having a substantially circumferential skirt wall that is operable to bear against the bore wall in a thrust plane, the skirt wall including an upper skirt point along a major thrust side of the thrust plane spaced apart from a lower skirt point along the major thrust side of the thrust plane, the portion of the skirt wall proximal to the lower skirt point having substantially greater radial flexibility than the portion of the skirt wall proximal to the upper skirt point, and the upper skirt point and the lower skirt point bearing substantially equivalent lateral loads when the piston is urged against the major thrust side of the bore wall.
3. The engine of claim 2 , wherein the skirt wall includes an intermediate skirt point along the major thrust side of the thrust plane, the intermediate skirt point bearing substantially equivalent lateral loads as the upper skirt point and the lower skirt point when the piston is urged against a major thrust side of the bore wall.
4. The engine of claim 2 , wherein the skirt wall includes a lower skirt portion, an intermediate skirt portion, and an upper skirt portion, the intermediate skirt portion including a concave curvature in the thrust plane.
5. The engine of claim 4 , wherein the lower skirt portion includes a maximum radius that is in an interference fit with the wall when the engine is at an operating temperature.
6. The engine of claim 5 , wherein the lower skirt portion is spring-loaded against major and minor thrust sides of the bore wall when in the interference fit with the wall.
7. The engine of claim 6 , wherein when the lower skirt portion is spring-loaded against major and minor thrust sides of the wall, the lower skirt portion and the upper skirt portion are operable to substantially uniformly distribute a thrust load when the piston is urged against a major thrust side of the bore wall.