A Mixed Lubrication Model of Piston Rings on Cylinder Liner Contacts Considering Temperature-Dependent Shear Thinning and Elastic–Plastic Contact

Abstract

This work develops a numerical methodology for predicting the performance of an automotive piston ring system by considering contact and lubrication mechanics. The rough surface contact mechanics and lubrication occurs on a scale much smaller than the size of the piston rings and therefore the key aspect of the model is an algorithm that simultaneously solves the multiple mechanisms at different scales. The finite element method will be used to model the mechanical deformations of the piston ring surfaces at large scales. The quasi-steady state model includes heat generation due to solid and viscous friction. This heat generation will then be used to predict the temperature rise and thermal effects in the lubricant and component. A statistical rough surface method that renders asperities as elastic–plastic wavy surfaces predicts the solid contact area. The modified Reynolds equation will be solved to consider the effects of mixed hydrodynamic lubrication while using flow factors formulated for actual piston and ring surfaces. The lubricant viscosity depends both on temperature and shear rate. This will allow for the regimes of boundary, mixed, and full-film lubrication to be considered. The model predicts friction for various loads and speeds that are then compared to experimental measurements. Although the contacts operate mostly in the mixed lubrication regime, the model and experiments show changes in friction with load, speed, and temperature.

Keywords

• rough surface elastic-plastic contact
• sinusoidal asperity
• boundary lubrication
• flow factors
• shear thinning
• thermal heating