23rd International Colloquium Tribology - January 2022 493 Novel, bio-based Group V basestocks for EV applications: customizable performance with reduced CO 2 footprint Arthur Coen Oleon NV, Ertvelde, Belgium Corresponding author: arthur.coen@oleon.com Ben Deweert Oleon NV, Ertvelde, Belgium Anne-Elise Lescoffit Oleon SAS, Venette, France Marion Kerbrat Oleon SAS, Venette, France 1. Introduction Strengthening fuel economy and emission control regulations are steering the automotive industry to look at electric vehicles to reduce CO 2 and other GHG emissions. OEMs are continuously optimizing electric drivetrain designs to increase drive range, accelerate charging rates and improve transmission efficiency. Performance characteristics of EV fluids can be enhanced by selecting the right base stock. Because of specific challenges, like the need to lower fluid viscosity and decreasing the additives treat rate, the base oil must largely carry the many technical EV requirements by itself. By optimizing viscosity profiles, increasing heat transfer capacity, lowering volatility and improving electrical and material compatibility, multi-purpose basestocks like Group V oils can help address many of the industrial requirements. Simultaneously, the awareness for the carbon intensity of the different automotive components themselves is increasing. Eco-design is a valuable tool to design sustainable solutions right from the start, considering both the product footprint and handprint in a full life cycle. By designing new Group V base oils from renewable, sustainably sourced building blocks, LCA studies (ISO 14040 & 14044) showed that these fluids may reduce the product carbon footprint, in particular when biogenic carbon is subtracted, compared to petrochemical alternatives. 2. Novel Group V basestock for EV Group V base stocks and in particular esters are an incredibly versatile product group. Customizable to a very high degree as they provide a mean to create complex organic structures from simple building blocks like acids and alcohols. The complexity is to strike the right balance between sometimes opposing properties, both from a technical as an environmental perspective. 2.1 Eco-design and Product Carbon Footprint Eco-design is the integration of environmental aspects into the product development process, by balancing ecological and economic requirements. Eco-design considers environmental aspects at all stages of the product development process. We used life cycle analysis as a methodology to select the most sustainable new developments. The analysis highlighted the contribution of the different steps in the process on the product carbon footprint. The main contributors, in a cradle to gate scenario, are the origin of the raw materials and the production step, so efforts have been focusing on these contributors first. It was shown that with careful selection of sustainably sourced raw materials and by exploring new production methods significant improvements are possible. 2.2 Technical performance and product handprint Embedding the assessment of the product carbon footprint in product development is a fundamental first step to lay a strong and credible basis for future innovation. Maybe even more important however is the contribution a product can have during use-phase, this is generally referred to as the handprint of the product. What positive contribution can a product make in terms of efficiency improvements or fuel economy improvements compared to an alternative technology or solution? Many challenges come with the development of electrical vehicles but reducing the size and weight of the e-motor is the main driver of e-motor development currently. By doing so, heat dissipation area is decreased, so the im- 494 23rd International Colloquium Tribology - January 2022 Novel, bio-based Group V basestocks for EV applications: customizable performance with reduced CO 2 footprint provement of e-motor cooling becomes crucial in order to achieve increasing power density. This led to the concept of oil cooling for the electric motor, instead of the standard water jacket cooling. This creates a need to design a multipurpose fluid that functions as lubricant for the transmission and bearings as always, and at the same time is a coolant for the electric motor. The following performance characteristics have been reviewed in the search for a suitable base oil for such a multipurpose fluid: 2.2.1 Thermal properties Studies have demonstrated that there is little differentiation in the thermal properties (specific heat capacity, thermal conductivity) between the main different base oil technologies. Also within the ester product group our analysis has shown equivalent conclusions. This means the cooling power is mainly determined by the viscosity and can be significantly improved by lowering the viscosity of the fluid. Esters demonstrate a high customizable nature with wide flexibility in viscosity design, whilst maintaining a low volatility and strong lubricant film formation. The heat transfer capacity in our study has been characterized by the Mouromtseff number: (1) Figure 1: Relationship between viscosity, cooling power and flash point 2.2.2 Dielectric properties The electrical compatibility of fluids with the e-motor and other drivetrain components is key for EV performance. Some research showed the dielectric properties of finished fluids is strongly impacted by the formulation and types of additives used, while the base oil seems to play a secondary role. The typical range of the electrical volume resistivity (ASTM D1169 at 20°C) for the Group V esters in our research is between 0.5 and 200 GΩ.m and varied with the viscosity. Figure 2: Electrical volume resistivity of different esters 2.2.3 Material compatibility The requirement for copper compatibility has strongly increased for electric vehicles, especially when the copper windings are in direct contact with the cooling fluid. An extended copper corrosion test (ASTM D130) was performed for 400h at 100°C to better mimic the EV conditions. The research proved excellent compatibility of Group V esters, with minimal impact on the copper strip and no copper leaching (ICP). The elastomer compatibility of esters needs special attention. By selecting suitable seals, coatings and plastics in combination with the right Group V base oil or/ and blending with other base stocks, strategies can be developed to eliminate compatibility issues. 2.2.4 Transmission Efficiency Transmission efficiency is a key focus area for the industry. MTM traction curves were used to simulate powertrain efficiency by mimicking the behavior in the elasto-hydrodynamic lubrication regime of gears. Results showed superior lubricity performance for the Group V esters. Figure 3: MTM traction curves - 75°C, 16N, 2 m/ s 23rd International Colloquium Tribology - January 2022 495 Novel, bio-based Group V basestocks for EV applications: customizable performance with reduced CO 2 footprint 3. Conclusion Our study has shown that newly developed low viscous Group V ester base stocks can possibly play an important role in the development of multipurpose driveline and battery fluids for future electrical vehicles. These new developments have the potential to improve both the handprint through optimized viscosity profiles, more efficient cooling and higher transmission efficiencies as well as having a positive impact on the product carbon footprint through careful selection of renewable, sustainably sourced and produced building blocks. References [1] Boyde, S., “Esters”, Synthetics, Mineral Oils, and Bio-Based Lubricants, Chemistry and Technology, 3 rd Ed. CRC Press, 2021 [2] El Bahi, H., “ Comprehensive study of cooling and lubrication of electric drive units based on an innovative MP fluid”, SAE powertrains, fuels and lubricants summit, September 2021 [3] Murr, T., “Lubricants solutions for combined thermal cycles of electrirfied powertrains”, SAE powertrains, fuels and lubricants summit, September 2021