Effect of Freeform Honing on the Geometrical Performance of the Cylinder Liner - Numerical Study

Reducing the friction of the internal combustion engine (ICE) is of major interest to reduce fuel consumption and greenhouse gas (GHG) emissions. A huge potential for friction reduction is seen in the piston ring-cylinder liner (PRCL) coupling. Approaching the cylindrical liner shape in the hot operation state will enhance the PRCL conformation. Recently, newly developed freeform honing techniques can help to achieve this perfect cylinder shape. This article presents a numerical study of the effect of freeform honing on the geometrical performance of the liner in the hot operation state. The freeform honed liner (TR) concept is based on the approach of reversing the local deformation of a conventional circular liner. A validated computational model for a gasoline engine is used to compare the geometrical performance of those TR cases with circular, elliptical (EL), and conical elliptical liners (NEL) at different operational points. It was found that the TR concept can reduce the roundness error by 92-95% and the straightness error by 70-75% when the reference load equals the operational one. Quite a good compromise is found to be the initial NEL shape, which probably would be easier for the manufacturing process. In this study, the influence of the reference load on the shape, and with that on friction, is also investigated at different operational loads. It was found that the reference load should be selected at a medium level since commonly the deviations at higher operational loads are less problematic for friction than vice versa. The numerical studies with optimal freeform-shaped cylinder liners - or with the compromise of NEL shapes - show a promising approach to enhance the PRCL conformation and reduce engine friction.