Physical Model of Tire-Road Contact Under Wet Conditions |
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Authors: | Löwer J Wagner P Unrau H-J Bederna C Gauterin F |
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Affiliation: | 1.System and Component Design, KTH Royal Institute of Technology, 100 44, Stockholm, Sweden ;2.Department of Mechanical Engineering, The University of Tokyo, Tokyo, 113-8656, Japan ;3.Axel Christiernsson International AB, 449 11, Nol, Sweden ;4.Department of Electromechanical, Systems and Metal Engineering, Ghent University, 9000, Ghent, Belgium ; |
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Abstract: | Four non-halogenated ionic liquids (ILs) with trihexyl(tetradecyl)phosphonium cation are tested as lubricant additives to polypropylene (PP) and lithium-complex (LiX) greases. In pin-on-disk tests at elevated temperatures, the addition of an IL with bis(oxalato)borate (BOB]) anion reduces wear by up to 50% when compared to the neat LiX base grease; an IL with bis(mandelato)borate (BMB]) anion reduces friction by up to 60% for both PP and LiX. Elemental analysis reveals that oxygen-rich tribofilms help to reduce wear in case of BOB], while the friction reduction observed for BMB] is likely caused by adsorption processes. We find that temperature has a pronounced effect on additive expression, yet additive concentration is of minor importance under continuous sliding conditions. In contrast, rolling-sliding experiments at 90 °C show that the traction performance of LiX grease is dependent on additive concentration, revealing a reduction in traction by up to 30 and 40% for BMB]- and BOB]-containing ILs at concentrations of 10 wt%. Finally, an IL with dicyanamide anion reduces friction and increases wear in pin-on-disk tests at room temperature, while an IL with bis-2,4,4-(trimethylpentyl)phosphinate anion increases wear, showing only limited potential as grease additives. Overall, this work demonstrates the ability of non-halogenated ILs to significantly extend grease performance limits. |
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