Executive Summary
Many TLT readers report that their organizations have already implemented gear lubricant strategies specifically tailored for electric or hybrid vehicle transmissions. Energy efficiency is the top motivating factor, with material/electrical compatibility and load-carrying performance as other important considerations. Readers report a variety of challenges in lubricating these gear systems, with efficiency, high speed, high load and excessive heat listed as common occurrences. Lubricant formulation is key in addressing these challenges.

Q.1. Please describe one tribological challenge you have encountered when lubricating high-speed gear systems in electric or hybrid vehicles. What approach or solution was used to address it?

Thermal effects on the contact. We are currently trying to solve this.
 
I have seen aeration in lubrication due to high speed operation. Also, the need to have lower viscosity product to reduce churning losses but also needing optimized additive system to avoid metal-to-metal contact with low viscosity oils.

Make sure you have a high quality surface finish, particularly in thin lubricants.

Minimizing the energy consumption of a component in the power transfer system is not necessarily defined in the OEM standards.

One key tribological challenge in high-speed electric vehicle (EV) gear systems has been micropitting due to high rotational speeds combined with the use of lower-viscosity fluids for efficiency. Under these conditions, maintaining sufficient film thickness in elastohydrodynamic lubrication (EHL) regimes becomes difficult, especially during transient loads. We addressed this by optimizing the formulation toward stronger surface protection rather than just viscosity, using base oils with better film strength at high shear and an additive package focused on antiwear and micropitting resistance. This approach improved gear surface durability in testing without sacrificing efficiency.

Balancing several fluid requirements: viscosity, efficiency, pour point and flash point and hitting everything. Solution was the addition of some ester to improve efficiency without compromising other aspects.

Frosting damage. The typical mitigations.

Copper corrosion.

Balance between viscosity and efficiency and gear protection. Innovative base stocks to enable low viscosity and low volatility were the solution.

Has your organization already implemented gear lubricant strategies specifically tailored for electric or hybrid vehicle transmissions?
Yes 74%
No 26%
Based on an informal poll sent to 15,000 TLT readers.



Selection of lubricant viscosity for improving efficiency and reliability of EV drivetrains presents a number of challenges. On one hand, under low-speed/high-torque conditions representative of acceleration, a higher viscosity fluid is preferable for protecting contacting surfaces and reducing load-dependent losses. On the other, under high-speed/low-torque conditions representative of cruising a lower viscosity fluid may be preferable to reduce churning and drag losses. The balance of these competing requirements depends strongly on vehicle duty. This is further complicated by the influence of viscosity on oil distribution within the casing, which can lead to lower viscosity fluids causing greater churning losses under certain conditions. We are developing computationally efficient numerical tools to estimate transmission efficiency over entire drive cycles to assess the relative contributions of the different power losses.

Corrosion foam.

We have many challenges: copper corrosion, foam, lubricity, dielectric fluids formulation and extreme heat. Among these the foam is a very challenging issue now, because defoamers settle down after six months shelf life.

Excess fluid heating. Addressed by dropping viscosity to minimize churn and used additives to make the performance more robust.

Need for low viscosity/low volatility base stocks. Searched existing base stock solutions for optimized properties and researched potential next generation base stock technologies.

Foaming.

Transmission efficiency under high-speed condition, load-carrying performance using FZG A10.

For plug-in hybrid electric vehicles (PHEV), the oils’ high-speed foam and the demulsibility issues. So we need to develop dedicated PHEV fluids for this particular vehicle.

This occurs when the set of machine tools becomes old or without proper lubrication; to avoid any incident it is required to demand proper combination and parameters and grades of lubricant. With proper grade and required parameters, tribology remains functional and movable.

None, get the OEMs to address.

In high-speed EV/hybrid electric vehicle (HEV) gearboxes and e-axles, the key tribological challenge is ensuring robust gear and bearing protection with lower-viscosity fluids (while controlling foam and maintaining copper/yellow-metal compatibility).

Noise, vibration and harshness (NVH) and low-viscosity requirements. Range improvement versus film strength. Reduced oil-film strength at startup. Protection under instantaneous torque (a unique EV challenge).

Gear scuffing. Addressed with jet lubrication to gear mesh.

Q.2. How is your organization preparing for or adapting to increasing sustainability expectations in gear lubricant selection for future mobility applications?

Development of in-house tribological methodology.
 
Yes, we are working on sustainable axle lubricants.
 
We must balance the defined sustainability expectations with the real-world longevity requirements of the end-user.

Tribological challenge and solution: In high-speed EV and hybrid gear systems, micropitting caused by high speeds and low-viscosity lubricants is a common issue. We addressed it by optimizing base oils and additive packages to enhance surface protection under EHL conditions, improve antiwear performance and ensure electrical compatibility. This increased gear durability without reducing efficiency. Sustainability adaptation: We are moving toward biobased and lower-carbon footprint lubricants, reducing hazardous additives and extending service life to meet evolving sustainability expectations while maintaining performance for future mobility applications.

We have developed an oil for flex fuel vehicles.

Creation of good quality product carbon footprint (PCF) data is essential. It can be a long process, but we are putting in the work now so we are ready for the future. Esters can have very high biobased contents, but it is about fine tuning them to improve their sustainability. In-use benefits are also very important and creating good quality data here is also a must.

Research on sustainable lubricants.

Explore the use of biobased esters and sulfur carriers.

Nothing special, other than noting options if someone is willing to pay a premium for them.

We are increasingly focused on the feasibility of more sustainable base fluids, such as water-based fluids.
 
Selection criteria: 1.) Low viscosity lube. 2) Biobased lubricant. 3.) Synthetic and ester-based lubricants. 4.) Direct cooling lubricant. Now we do not consider re-refined based products.

Performance is the key.

Engagement with the major OEMs to understand their needs and participate in the development of new test methods.

Optimizing lubricant formulation application to down-sized and high-speed gearbox.

In the long term, using re-refined base oil (RRBO) to reduce the greenhouse gas (GHG) carbon footprint (CFP) of the future lubricants is the coming trend—we should do the preparation in advance.

Which of the following factors most influences your organization’s decision when selecting gear lubricants for electric vehicle or hybrid applications?
Load-carrying performance                 50%
Thermal and oxidative stability                  39%
Energy efficiency (low viscosity, reduced churning losses) 93%
Material/electrical compatibility                   68%
Environmental or sustainability considerations          36%
Cost                                 39%
Based on an informal poll sent to 15,000 TLT readers. Total exceeds 100% because respondents were allowed to choose more than one answer.

It demands required grades and parameters of lubrication tribology. Using green lubrication or biodegradable lubricants, criteria can be driven toward net zero for poor economy.

Choosing OEM approved products that meet energy requirements.

We’re adapting by designing e-fluids that deliver efficiency plus longevity: optimized viscosity and friction to cut energy losses, materials-benign additive strategies that support durability and longer drain intervals and a development approach anchored in testing, compliance and traceability—so lubricant selection aligns with OEM sustainability expectations for future mobility.

Target low-toxicity, low-metal, ash-free additives. Develop ethylene-octene copolymers (POE)/bio-ester/polyalkylene glycol (PAG) blends that meet EV electrical and thermal requirement. Assess carbon footprint of raw materials, production, use phase and disposal. Others including nano materials, electrical exposure testing and extended compatibility testing.

Editor’s Note: Sounding Board is based on an informal poll sent to 15,000 TLT readers. Views expressed are those of the respondents and do not reflect the opinions of the Society of Tribologists and Lubrication Engineers. STLE does not vouch for the technical accuracy of opinions expressed in Sounding Board, nor does inclusion of a comment represent an endorsement of the technology by STLE.