The influence of lubricant formulation on surface damage under electrified rolling-sliding contact with relevance to electric vehicle drivetrain applications
File(s)
Published version
OA Location
Author(s)
Oh, Jaewoo
Yousuf, Ammad
Spikes, Hugh
Kadiric, Amir
Type
Journal Article
Abstract
Surface damage due to electric potential is one of the primary reliability concerns for electric vehicle drive units. This paper for the first time identifies specific lubricant components which promote such damage. The work can help design new e-Fluids that improve EV reliability. Recent experimental studies have shown substantial effects of electric potential across a lubricated contact on contact friction and surface damage; these studies primarily used either pure base oil or fully formulated commercial lubricants. However, the specific behavior of key additive components, such as friction modifiers (FMs), under electric fields remains poorly understood. In this study, a series of model fluids consisting of base oil and single FMs of different types was systematically designed to isolate the effects of individual additives. Friction and wear properties under DC electric field (2 V and <50 mA) and mixed lubrication conditions were comparatively evaluated using a ball on disc tribometer, suitably modified to apply electric potential across the contact. While base oil alone and base oil +MoDTC solution exhibited only mild surface damage, all six solutions tested containing organic friction modifiers (OFMs) showed pronounced groove wear on the cathodic side. Among these, OFMs with amino group (–NH2), such as oleylamine (OAm), led to the highest friction and wear increase under electrified conditions. A fully formulated e-Fluid containing OAm as a FM exhibited a similar surface damage pattern, despite the presence of other additives in the formulation. Interestingly, this characteristic response was substantially mitigated when the amino group (–NH2) was replaced with a dimethyl-amino group, –N(CH3)2, suggesting that the chemical reactivity and/or steric hindrance of the OFM polar head play a crucial role in the observed phenomena. Based on experimental findings, the underlying wear mechanism is postulated to be electrochemical polishing, a type of corrosive-abrasive wear. It is speculated that OFMs electrochemically react on cathodic metal(oxide) surfaces in the presence of oxygen, promoted by an applied electric field, to form a thin and soft layer that is easily abraded by the oxidized anode surface. This study provides valuable insights into designing electrically robust e-Fluids with desirable tribological properties to improve reliability and efficiency of modern EV drivetrains.
Date Issued
2025-08-30
Date Acceptance
2025-08-18
Citation
Tribology Letters, 2025, 73 (4)
ISSN
1023-8883
Publisher
Springer
Journal / Book Title
Tribology Letters
Volume
73
Issue
4
Copyright Statement
© The Author(s) 2025. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
License URL
Identifier
10.1007/s11249-025-02059-z
Subjects
E-Fluid formulation
Electrified contact
Engineering
Engineering, Chemical
Engineering, Mechanical
Friction modifier
Science & Technology
Technology
Triboelectrochemistry
Wear
Publication Status
Published
Article Number
126
Date Publish Online
2025-08-30