Experimental Investigation of Surface Modifications for Piston-Ring/Cylinder-Liner Friction Reduction

Micro-dimples on the surface of lubricated sliding contacts can act as mini-hydrodynamic bearings. The pressure generated within these dimples tends to separate the surfaces and reduce the number of asperities in contact, thereby lowering the average coefficient of friction and moving the lubrication condition to the more stable hydrodynamic lubrication regime. An experimental study on the effects of laser surface modifications for friction reduction is presented through the use of several experimental test rigs. Micro-dimples were generated with an Nd-YAG laser on the surface of flat samples for testing in constant speed and reciprocating motion test rigs. These simple geometries were used to investigate the phenomenon and validate existing analytical models. Modifications to the top dead center region of an actual cylinder liner were evaluated with a motored, small-engine dynamometer. The results demonstrated that measurable friction reductions can be achieved using this approach.