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Lubricants
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Tribology of Electric Vehicles
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Tribology of Electric Vehicles

A special issue of Lubricants (ISSN 2075-4442).

Deadline for manuscript submissions: 31 August 2025 | Viewed by 8605

Special Issue Editors

Dr. Peter M. Lee

E-Mail Website
Guest Editor
Tribology Research and Evaluations, Fuels and Lubricants Division, Southwest Research Institute, San Antonio, TX, USA
Interests: tribology; electric vehicles; EV fluids; rheology
Dr. Carlos Sanchez

E-Mail Website
Guest Editor
Tribology Research and Evaluations, Fuels and Lubricants Division, Southwest Research Institute, San Antonio, TX, USA
Interests: tribology; electric vehicles; EV fluids; rheology

Special Issue Information

Dear Colleagues,

The shift towards electrification in the automotive industry has presented new challenges in the field of lubrication. While the number of moving parts in a battery electric vehicle (BEV) has reduced significantly versus those in internal combustion engine (ICE) vehicles, the tribological concerns facing electric vehicles (EVs) reach beyond traditional ICE vehicles. BEVs are significantly heavier than ICE vehicles, placing more load on the wheel bearings and tires. In addition, the driveline fluids, historically made to protect gears from scuffing and pitting and provide traction characteristics for clutches, now have to operate at greatly increased rotational speeds, operate in an environment with stray electric currents, and in many cases act as a coolant in direct contact with the motor and inverter. They must also continue to protect the gears from pitting and scuffing. These challenging requirements have created a need for new base fluids and additives.

Traditional test methods for ICE fluids are not entirely suitable for understanding the behavior of EV fluids. Early research has shown that the presence of the electric field has an effect on material performance in terms of friction and wear. Fluid properties such as viscosity are also affected. This collection of manuscripts will present various approaches to studying EV fluid and grease properties. Test method development, analysis of initial findings, and thoughtful discussions will be presented.

Dr. Peter M. Lee
Dr. Carlos Sanchez
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Lubricants is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • tribology
  • electric vehicles
  • EV fluids
  • rheology

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Published Papers (6 papers)

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Research

21 pages, 10268 KiB  
Article
Tribological Performance Comparison of Lubricating Greases for Electric Vehicle Bearings
by Deepika Shekhawat, Ayush Jain, Nitesh Vashishtha, Arendra Pal Singh and Rahul Kumar
Lubricants 2025, 13(3), 108; https://doi.org/10.3390/lubricants13030108 - 1 Mar 2025
Viewed by 418
Abstract
EV motors and machine elements operate at higher speeds, generate significant heat and noise (vibration), and subject lubricants (bearings) to multiple degrading factors, requiring thermal stability, wear protection, mitigating wear mechanisms like pitting and scuffing, and low electrical conductivity to prevent arcing damage [...] Read more.
EV motors and machine elements operate at higher speeds, generate significant heat and noise (vibration), and subject lubricants (bearings) to multiple degrading factors, requiring thermal stability, wear protection, mitigating wear mechanisms like pitting and scuffing, and low electrical conductivity to prevent arcing damage to bearings. This study evaluates the tribological performance of four types of greases—PUEs, PUPao, PUEth (polyurea-based), and LiPAO (lithium–calcium complex-based)—to determine their suitability for electric motor bearings. Key performance metrics include tribological properties, electrical resistivity, leakage, bearing noise, and wear behavior. A four-ball wear test ranks the greases by scar diameter as PUPao < PUEs < PUEth < LiPAO, while the coefficient of friction is observed in the range of 0.15–0.18, with LiPAO exhibiting the lowest friction. Electrical resistivity tests reveal that PUEs grease has the lowest resistivity. Electrical leakage tests, conducted with a voltage differential across bearings, assess pitting damage, with PUEth and LiPAO showing evidence of surface pitting. Optical microscopy and scanning electron microscopy analysis is carried out to examine the pitting. In bearing noise tests, PUEs demonstrates the lowest noise levels, whereas LiPAO produces the highest. Visual and microscopic examination of the greases further characterizes their lubricating properties. Based on overall performance, the greases are ranked in suitability for electric motor applications as PUEs > PUPao > PUEth > LiPAO. The findings highlight the critical need for selecting appropriate grease formulations to ensure optimal bearing performance under varying operational conditions. Full article
(This article belongs to the Special Issue Tribology of Electric Vehicles)
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15 pages, 4740 KiB  
Article
MoS2 Additives in Lithium Grease for Electrified Systems
by Mohsen Tajedini, M. Humaun Kabir, Rouzhina Azhdari, Reza Bahrami, Hung-Jue Sue and Hong Liang
Lubricants 2025, 13(3), 106; https://doi.org/10.3390/lubricants13030106 - 28 Feb 2025
Viewed by 207
Abstract
This study investigates the effectiveness of micron- and nano-sized molybdenum disulfide (MoS2) particles as additives in lithium (Li) grease under electrified conditions. By systematically applying electric current and high temperatures as experimental parameters, we evaluated the frictional and wear performance of [...] Read more.
This study investigates the effectiveness of micron- and nano-sized molybdenum disulfide (MoS2) particles as additives in lithium (Li) grease under electrified conditions. By systematically applying electric current and high temperatures as experimental parameters, we evaluated the frictional and wear performance of the grease formulations. Our results showed that micron MoS2 (M-MoS2) particles outperform their nano counterparts in reducing friction in the range of room temperature to 40 °C. Meanwhile, at 80 °C, nano-sized MoS2 (N-MoS2) particles provide better surface protection. The superior performance of M-MoS2 is attributed to their particle size, which improves the ability to form a more stable and robust lubricating film under the given electrical conditions. In terms of wear, both MoS2-added greases showed substantial improvements, with a 93% reduction in wear at 40 °C and an 85% at 80 °C under an applied 3 A current. Surface characterization revealed that M-MoS2 resulted in a smoother surface with less severe pitting and melted pools compared to the base grease. EDX analysis showed the existence of oxygen, molybdenum, and sulfur in M-MoS2, indicating the presence and stability of MoS2 on the wear track. These findings suggest that MoS2 additives have great potential for improving the efficiency and durability of lubricants in electrically and thermally demanding applications. Full article
(This article belongs to the Special Issue Tribology of Electric Vehicles)
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11 pages, 2457 KiB  
Article
Low-Foaming/Aeration and Low-Traction Electric Drivetrain Fluid (EDF) Solutions for High-Speed E-Mobility
by Philip Ma, Donna Mosher and Chad Steele
Lubricants 2025, 13(2), 53; https://doi.org/10.3390/lubricants13020053 - 28 Jan 2025
Viewed by 707
Abstract
The use of electrically driven drivetrains is increasing for passenger cars and light-, medium-, and heavy-duty trucks. Off-the-shelf automatic transmission fluids (ATFs) are still being used as electric drivetrain fluids (EDFs). EDFs are trending toward lower viscosity for better energy efficiency and better [...] Read more.
The use of electrically driven drivetrains is increasing for passenger cars and light-, medium-, and heavy-duty trucks. Off-the-shelf automatic transmission fluids (ATFs) are still being used as electric drivetrain fluids (EDFs). EDFs are trending toward lower viscosity for better energy efficiency and better heat transfer capacity, while satisfying all the other challenging requirements, such as gear/bearing scuffing/wear protection, oxidative stability, copper corrosion, and coating/seal material compatibility. In this paper, we will highlight the importance of low foaming, low aeration, and low traction coefficient which are critical for the performance of the EDF during high-speed applications, measured using metrics such as energy efficiency, heat transfer capacity, and longer oil drain interval. Full article
(This article belongs to the Special Issue Tribology of Electric Vehicles)
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14 pages, 9081 KiB  
Article
Non-Polar Chain-Enabled Suspension of Carbon Nanoparticles in Base Oil
by M. Humaun Kabir, Darrius Dias, Evan Johnson, Joe Kosmoski and Hong Liang
Lubricants 2024, 12(11), 373; https://doi.org/10.3390/lubricants12110373 - 29 Oct 2024
Cited by 2 | Viewed by 1078
Abstract
The transition to electric vehicles (EVs) has introduced new challenges in lubrication, demanding innovative solutions to ensure consistent performance. One promising approach is the use of nanoparticle additives, which have the potential to improve lubrication performance significantly. However, achieving a stable suspension of [...] Read more.
The transition to electric vehicles (EVs) has introduced new challenges in lubrication, demanding innovative solutions to ensure consistent performance. One promising approach is the use of nanoparticle additives, which have the potential to improve lubrication performance significantly. However, achieving a stable suspension of these nanoparticles in lubricating oils remains a critical challenge, as suspension stability is essential for maintaining consistent performance and maximizing the benefits of these advanced additives. In this study, carbon nanoparticles (CNPs) were modified with dodecylamine (DDA) to achieve stable suspension in nonpolar fluids. The successful functionalization was confirmed by the FTIR results, which showed characteristic peaks of various bonding. The suspension stability tests demonstrated that DDA-CNPs remained suspended for over 60 days in the Polyalphaolefin (PAO) oil, whereas unmodified CNPs were sedimented within 3–7 days. The rheological behavior was measured under different shear rates and temperatures. Viscosity measurements indicated that DDA-CNPs maintained a lower value compared to base PAO. The lubricants’ friction coefficient (COF) was also determined under various speeds and loads. The addition of DDA-CNPs at a concentration of 0.05 wt.% resulted in a significant reduction in COF, with values decreasing by 26% compared to base PAO oil under a load of 1 N. Additionally, the COF for DDA-CNPs was consistently lower than that of PAO, with reductions ranging from 15% to 18% across all tested speeds. The Stribeck curve further highlighted the improved performance of DDA-CNPs across boundary, mixed, and hydrodynamic lubrication regimes. These findings suggest that DDA-CNPs significantly improve the lubrication performance of PAO oil, making them suitable for advanced lubrication applications in automotive and industrial systems. Full article
(This article belongs to the Special Issue Tribology of Electric Vehicles)
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22 pages, 12430 KiB  
Article
Electrification of a Mini Traction Machine and Initial Test Results
by Peter Lee, Carlos Sanchez, Michael Moneer and Andrew Velasquez
Lubricants 2024, 12(10), 337; https://doi.org/10.3390/lubricants12100337 - 30 Sep 2024
Viewed by 1873
Abstract
Electric vehicles (EVs) continue to evolve, and sales continue to increase as the world pushes toward improved sustainability. This drives the need for research to understand the unique environments in which fluids operate within the Electric Drive Units (EDUs) of EVs in order [...] Read more.
Electric vehicles (EVs) continue to evolve, and sales continue to increase as the world pushes toward improved sustainability. This drives the need for research to understand the unique environments in which fluids operate within the Electric Drive Units (EDUs) of EVs in order to improve durability and reduce frictional losses. However, for this to happen, test rigs are required to operate with an electric current passing across the test parts and through the lubricant. Very few electrified test rigs currently exist, with most being adaptations of rigs undertaken by academia and independent and national research labs. In this work, the PCS Mini Traction Machine (MTM) was modified to supply a voltage across a tribological contact. New parts for the MTM were designed in collaboration with the instrument manufacturer. Work was undertaken in both the author’s labs and the manufacturer’s labs with the aim of bringing a commercially available unit to market as quickly as possible. A test matrix was completed on the MTM utilizing a range of temperatures, loads, and voltage inputs for three different lubricants commonly used in EDUs. The test matrix consisted of 36 test conditions, with some runs performed in triplicate, resulting in 81 tests for each oil and a total matrix of 243 tests. The test matrix was run to obtain the results and to test the robustness of the rig design. After testing was completed, the MTM disc wear scars were measured. The results from these measurements indicate that the application of alternating current (AC) and direct current (DC) causes a significant increase in the wear scar compared to non-electrified test conditions. This, in turn, results in increased traction values under non-electrified conditions. It was also noted that the repeatability of the traction curves and end-of-test wear was reduced under both AC and DC electrified conditions. Full article
(This article belongs to the Special Issue Tribology of Electric Vehicles)
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16 pages, 10786 KiB  
Article
Exploring the Boundaries of Electrically Induced Bearing Damage in Grease-Lubricated Rolling Contacts
by Jack R. Janik, Sudip Saha, Robert L. Jackson and German Mills
Lubricants 2024, 12(8), 268; https://doi.org/10.3390/lubricants12080268 - 28 Jul 2024
Cited by 3 | Viewed by 3053
Abstract
As public attention is increasingly drawn toward more sustainable transportation methods, the popularity of electric vehicles (EVs) as part of the solution is rapidly expanding. Operating conditions within EVs can be severe compared to standard combustion powertrains, and the risk of electrical arcing [...] Read more.
As public attention is increasingly drawn toward more sustainable transportation methods, the popularity of electric vehicles (EVs) as part of the solution is rapidly expanding. Operating conditions within EVs can be severe compared to standard combustion powertrains, and the risk of electrical arcing across mechanical surfaces from electric leakage currents incites additional concern. This study employed a series of electro-tribological tests utilizing various moving patterns to improve understanding of the driving conditions for electrically induced bearing damage (EIBD). Rolling ball-on-disk tests were performed with different polyurea-thickened greases. Rotational tests were initially run at various speeds and test durations, but electrical damage was limited. However, electrical damage was unmistakable when a reciprocating motion was used at different track lengths and speeds. These results suggest that the conditions associated with the track length, such as the number of directional changes and speed-dependent film thickness, play a considerable role in forming electrical damage. This work provides critical insights into the mechanisms of EIBD in EVs and other electrical systems. It highlights the importance of understanding the operational conditions that contribute to EIBD, which can lead to improved designs and maintenance practices, ultimately enhancing the efficiency and lifespan of these systems. Full article
(This article belongs to the Special Issue Tribology of Electric Vehicles)
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