Abstract
The reduction of frictional power losses in power transmitting gears takes a crucial role in the design of energy- and resource-efficient drivetrains. Water-containing lubricants like glycerol and polyalkylene glycols have shown great potential in achieving friction within the superlubricity regime with coefficients of friction lower than 0.01 under elastohydrodynamic lubrication. Additionally, a bio-based production of the base stocks can lead to the development of green lubricants. However, one challenge associated with the application of water-containing lubricants to gearboxes is the evaporation of water and its impact on the lubricant properties. In this study, the influence of water evaporation on elastohydrodynamic friction and film thickness was investigated for three water-containing polyalkylene glycols. Two nominal water contents of 20 wt% and 40 wt% and two viscosities were considered. The results show that the friction increases continuously with higher evaporated water content, while the overall friction level remains low in nearly water-free states. A similar trend is observed for film thickness, where the strong increase in viscosity results in a notable increase in film thickness. Nevertheless, the sensitivity of friction and film thickness to water evaporation is low for small amounts of evaporated water. This allows generous thresholds for permissible variations in water content.
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Acknowledgements
The presented results are based on the research project CHEPHREN (Nos. 03EN4005A and 03EN4029A) supported by the Federal Ministry for Economic Affairs and Climate Action (BMWK) and supervised by Project Management Jülich (PtJ).
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Conceptualization, methodology, formal analysis and investigation, and writing—original draft preparation: Stefan HOFMANN; writing—review and editing: Thomas LOHNER; funding acquisition: Karsten STAHL; supervision: Thomas LOHNER and Karsten STAHL
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Stefan HOFMANN. He got bachelor and master degrees in mechanical engineering at Technical University of Munich, Munich, Germany. Since 2020 he is working as research associate at gear research center (FZG) in the Department “EHL-Tribological-Contact and Efficiency”. He is specialized in the fields of gear tribology with focus on elastohydrodynamically lubricated rolling-sliding contacts. Surface coatings like diamond-like carbon (DLC) as well as water-containing lubricants are the mainstream of his research. Therefore, he applies experimental measurement techniques such as optical interferometry or thin-film sensor technology to study the complex mechanisms and interactions within elastohydrodynamic contacts.
Thomas LOHNER. He is a postdoctoral researcher and the head of the Department “EHL-Tribological Contact and Efficiency” at the Gear Research Center (FZG) of the Technical University of Munich (TUM), Munich, Germany. He is specialized in the fields of gear tribology, efficiency, and heat balance of geared transmissions. His interests in gear tribology include elastohydrodynamics, lubrication regimes, roughness, friction, wear, and tribofilms. In the field of gearbox efficiency and heat balance, he focuses on power loss, lubricant flow, and temperature, specifically in relation to lubricants, lubrication methods, coatings, surfaces, materials, and gear geometry. His research conducted is both theoretical and experimental in nature, encompassing basic and applied research.
Karsten STAHL. Since 2011 he is full time professor at the Gear Research Center (FZG) at the Technical University of Munich, Munich, Germany. His research topics include the development of methods and tools of reliable determination of fatigue life, efficiency, and vibration characteristics of gears and transmission elements.
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Hofmann, S., Lohner, T. & Stahl, K. Influence of water evaporation on elastohydrodynamic lubrication with water-containing polyalkylene glycols. Friction 12, 2370–2388 (2024). https://doi.org/10.1007/s40544-024-0916-1
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DOI: https://doi.org/10.1007/s40544-024-0916-1