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Practical challenges from both experiment and calculation sides were discussed for determining two piece twin land oil control ring friction. A floating liner engine was used for twin land oil control ring study. Effects of floating liner engine system dynamics and piston skirt friction were addressed and methods to mitigate them were discussed. A deterministic twin land oil control ring model was used for ring friction calculation. Variation of the surface roughness at different spots of the liner and its effects on both hydrodynamic and boundary lubrication predictions were discussed. A multi-point correlation method was introduced to address surface variation effects on the twin land oil control ring model. Ring land width variation between two lands as well as along the circumference and its effects on calculation were shown, and methods to address it were discussed. By taking all these necessary steps in both experiments and calculations, this study shows that a reasonable match can be achieved between the measured and calculated friction, which covers all three lubrication regimes. This study lays a foundation for realistically predicting the friction of piston rings in internal combustion engines.

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Engine bores are finished with a multi-stage honing process and the finished surface roughness contributes significantly to the piston ring hydrodynamic pressure generation, especially for twin-land oil control rings whose land profile is parallel to the liner surface. In this paper, five different honing patterns on a cast iron liner and one on a spray-coated aluminum liner are studied with a floating liner engine and numerical models. The liner temperature and engine speed were varied such that all the lubrication regimes, namely boundary, mixed, and fully hydrodynamic, are present. It is found that the models based on deterministic approach with a patch of carefully measured liner roughness can match the trend of the Stribeck curves for different liner finishes observed in the experiment. Furthermore, the results show that the roughness height and structure of the honing affect the twin-land oil control rings lubrication differently. With the same honing structure, although rougher liner experiences mixed and boundary lubrication in larger range of Gumbel–Hersey number, it renders less friction than the smoother ones in the hydrodynamic regime. With the same plateau roughness height, a more continuous plateau can provide more flow resistance and thus generate higher hydrodynamic pressure at the ring–liner interface and less friction.

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