Assessing the Likelihood of Binding in Distorted Stepped Radius Cylinder Bores 2014-01-0395

Interference assessments of a stepped-radius power-train component moving within a deformed stepped bore often arise during engine and transmission development activities. For example, when loads are applied to an engine block, the block distorts. This distortion may cause a cam or crankshaft to bind or wear prematurely in its journals as the part rotates within them. Within an automatic transmission valve body, care must be taken to ensure valve body distortion under oil pressure, assembly, and thermal load does not cause spool valves to stick as they translate within the valve body. In both examples, the mechanical scenario to be assessed involves a uniform or stepped radius cylindrical part maintaining a designated clearance through a correspondingly shaped but distorted bore. These distortions can occur in cross-sections (“out-of-round”) or along the bore (in an “s” or “banana” shaped distortions).

To assess clearance in a deformed (stepped or uniform) bore, a new optimization based technique is proposed. This paper defines an optimization process that determines an axis assessed as producing the largest clearance between the stepped surface and points defining the bore surfaces. This clearance is calculated for clouds of points representing undeformed and deformed cylindrical bores. From this clearance, shrinkage (or expansion) of a stepped-bore or single-radius bore is estimated. These clearance data are useful in understanding when a part may stick or bind as a result of projected stepped-bore distortion.