Methodology of Surface Modification for Efficient Journal Bearings

Gu, Thomas

doi:https://doi.org/10.21985/n2-0nr9-1b11

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Methodology of Surface Modification for Efficient Journal Bearings

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Global energy demand is increasingly rapidly in today’s modern world with increasing living standards all around the world. As global energy demand rises, energy efficiency has never been more crucial and that the improvement of tribological systems is critical to the progress of the global future. A large part of the energy demand comes from the industrial and transportation sectors; these fields contain an incredible amount of machinery and power conversion systems that require reliable, durable, and efficient tribological journal bearing lubrication systems. Therefore, enhancements of the lubrication performance of journal bearings is a critical and necessary step to improving global energy efficiency. The research in this dissertation will be analyzing journal bearings in the hydrodynamic and mixed-lubrication regimes, with surface design mechanisms to improve the lubrication performance in each regime. The main objective of this research is to utilize a simulation driven approach to discover micron-scale geometrical surface design improvements of the journal bearing interfaces and uncover their lubrication enhancement mechanisms. The priority is to reduce frictional losses while improving the film thickness between the two surfaces. An advanced numerical lubrication model is used to explain mechanisms of lubrication enhancement or lubrication degradation with the implementation of the surface designs. This dissertation work will build a transient, mixed lubrication Reynolds model, considering Payvar-Salant mass-conservation and Patir-Cheng asperity flow effects with the Greenwood-Tripp pressure gap relationship to be the tools for design simulation and surface parameter optimization. The surface design modifications include indented bearing surface textures/pockets, bearing profile modifications, and journal profile modifications. In aligned journal bearing situations, surface design features can be used to reduce the frictional losses while improving the minimum film thickness. In this work, journal bearings subjected to transient impulse loading had three types of journal bearing surface designs: an indented bearing pocket feature, a protruded bearing lip feature, and a combined design that incorporates both the pocket and lip features on the bearing surface; these features when properly designed were found to considerably improve lubrication performance. A data-driven approach was also employed to assist in the characterization of the pocket effect on the lubrication performance. Each of these features and their lubrication enhancement/degradation mechanisms was explained in depth. It was also shown that an improperly designed bearing may result in a fully hydrodynamic bearing to enter the mixed lubrication regime, causing potential wear on the parts. A surface design strategy was also applied in the context of engine bearings for crankshaft main and connecting rod bearings to enhance their lubrication performance. In misaligned journal bearings, the load bearing capability of the bearing becomes a major issue for the journal bearings due to the fact that much of the load needs to be sustained at the edges of the bearing, causing great potential for wear or seizure of the parts. In these situations, a profile design was developed to help mitigate the damaging lubrication effects of journal misalignment. Misaligned bearings are often operating in the mixed lubrication regime, and with the addition of the profile, it is possible to bring the mixed regime to a hydrodynamic regime where the parts are protected by a full lubricant film. A profile design strategy was suggested based on various types of misalignment examined.

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