Three-Dimensional Piston Ring–Cylinder Bore Contact Modeling

Abstract

Increasing durability, preventing knocking combustion, improving fuel efficiency, and reducing pollutant emission characterize the needs for modern internal combustion engine design. These factors are highly influenced by the power cylinder system design. In particular, the piston ring to cylinder bore contact force distribution around the circumference of the piston rings must be optimized under all running conditions. To accomplish this, the ring manufacturers make the ring curvature nonconstant along the circumference. Most existing analytical tools are not able to simulate the variation along the ring circumference. In order to improve the understanding of this contact distribution and provide a high-fidelity ring design tool, a three-dimensional finite element piston ring model was developed to accomplish this variation. The modeling procedure and results are presented in this work. Experiments using a commercially available ring with negative ovality were conducted to validate the model. The ring free-shape profile and the ring cross section geometries were used as inputs to the model. Typical piston ring groove and cylinder wall temperatures were also model inputs to characterize thermal influences on the ring/bore interface forces. The ring/bore conformability was analyzed as a function of the ring radial displacements, cylinder bore constraint forces and thermal load changes to the ring. The model output showed radially separation gaps between the ring front face and the bore. This analysis provides an insight to evaluate the piston ring design. Together with an optimizer, the model can be used as a ring design tool to predict the ring free shape with a specified constraint force distribution pattern. Examples are given to demonstrate the capabilities of this numerical analytical tool. In addition, the 3D ring model can be used to improve the accuracy of existing lubrication, friction, and wear analysis tools and therefore improve the entire internal combustion engine power cylinder system design.