Modeling Piston Ring-Pack Lubrication With Consideration of Ring Structural Response 2005-01-1641

The lubrication of the piston ring-pack is directly related to the engine friction and oil consumption. Non-axisymmetric characteristics of the power cylinder system, most noticeably cylinder bore distortion, piston secondary motion, and ring gaps, can introduce circumferential variations to ring/liner lubrication and overall performance of the ring-pack in friction and oil consumption. In order to be able to optimize the piston ring-pack in a more fundamental way, it is necessary to develop physical understanding of the effects of these non-axisymmetric properties and effective numerical tools.

In this study, a comprehensive model has been developed for the lubrication of a piston ring-pack. By employing a finite element analysis, this model is capable of evaluating the in-plane structural response of a ring to external forces. A newly developed one-dimensional hydrodynamic lubrication sub-model is implemented to calculate the lubrication force at each cross-section.

The model has been applied to a light-duty diesel engine in a high-speed and full-load condition. In the discussion, emphases are placed on the oil transport along the liner, and the effects of the piston tilt motion, ring twist and bore distortion on the lubrication. Under the extreme condition of the leading edge of the second ring being flooded during down-strokes, considerable down-scraping of oil by the top ring is observed for all the cases tested. Bore distortion is found to have significant influence on the oil transport. Because of the reduced conformability of the top ring caused by the bore distortion, a relatively large amount of oil is left on the liner by the top ring during intake stroke. Under the impact of increasing gas pressure acting on the back, the top ring can carry some oil to the upper region of liner, and even up-scraping of oil is observed. Both up and down-scraping of oil by the top ring are found to increase with the amplitude of bore distortion.