23rd International Colloquium Tribology - January 2022 149 Development of a new fuel efficient, shear stable axle lubricant to meet new U.S. Green House Gas requirements Arjun Goyal BASF Corporation, Florham Park, NJ, USA Corresponding author: arjun.goyal@basf.com Donna Mosher BASF Corporation, Florham Park, NJ, USA 1. Introduction The United States Environmental Protection Agency (EPA) and the National Highway Traffic Safety Administration (NHSTA) on behalf of the Department of Transportation (DOT) have enacted rules to establish the reduction of Green House Gas (GHG) emission (CO2) and fuel consumption of new on-road heavy duty vehicles. To meet these regulations, U.S. Vehicle Builders developed new axle designs with reduced weight, lowering axle ratios and improved gear technology, and lower oil level in axle sump. Current 2021 GHG regulations are met with the existing high performance axle lubricant. Meeting new 2024 GHG (and 2027 GHG) requirements will require axle oils to provide higher efficiency (fuel savings) and reduction in CO 2 reduction (Green House). Reduction in lubricant viscosity can provide fuel savings; however, reduction in viscosity can lead to metal-to-metal contact thus leading to higher component wear and reduced equipment life. Base oil, thickener, and performance package accounts for the majority of finished axle oil formulation. The performance package has minimal contribution to the fuel efficiency. Base oil and thickener provide the required efficiency. 1.1 Performance Package A new performance package to meet long oil drain performance was developed for this program. 1.2 Base Oil Selection It is well known that PAO (polyalfaolefin) base axle oil provides lower traction (efficiency gain) as measured by MTM (Mini Traction Machine) compared to other base oil such as Group III and Group II+. Figure 1 1.3 Thickener Selection BASF proprietary system which provides shear stability and long drain capabilities was used to evaluate various thickeners. The extended length KRL shear test data shows that the candidate oil maintains constant viscosity for 200-hours (predictor of oil viscosity after 500,000 miles (800,000 kms) of no drain service. Figure 2 1.4 SAE J2360 Approval The new candidate oil met the SAE J2360 specification requirements and has been approved by the SAE Lubricants Review Institute (LRI). In addition, the candidate oil met Dana SHAES 256 RevE stringent specification 150 23rd International Colloquium Tribology - January 2022 Development of a new fuel efficient, shear stable axle lubricant to meet new U.S. Green House Gas requirements requirements such as Wet L-37-1 (represents running through the water), High Temperature L-37-1 (operation at high temperature), L-37-1 (extended-length spalling test), and static and dynamic seal tests. 1.5 Cleanliness A 200 hours (four times the requirement for SAE J2360) extended length test was completed on candidate oil to show cleanliness characteristics. The extended length test shows good correlation with cleanliness observed in no-drain 500,000-mile (800,000 km) field performance. Table 1 ASTM D5704 (L-60-1) J2360 Limits (50 hrs) Candidate Oil (200 hrs) Viscosity Increase, 100°C, % 100 max 12 Pentane Insolubles, wt% 3 max 0.9 Toluene Insolubles, wt% 2 max 0.1 Carbon/ Varnish (10=clean) 7.5 min 9.4 Sludge (10=clean) 9.4 min 9.8 1.6 Low and High Temperature Characteristics The candidate oil showed excellent low and high temperature properties indicative of suitability in extreme temperature conditions. Figure 3 1.7 Fuel Efficiency The MTM data comparing traction coefficient (friction losses) are shown below. The candidate oil provided significant reduction in traction coefficient compared to a leading commercial oil. Figure 4 In laboratory dynamometer testing, using a commercial light duty pickup truck axle, efficiency was measured, fuel consumption and CO 2 generation was calculated. The U.S. EPA GEM method was used for the calculation with regional, urban, and multipurpose duty cycles tested. The candidate oil outperformed commercially available oils (80W-90 and 75W-90) by using less fuel and generating less CO 2 . Figure 5 23rd International Colloquium Tribology - January 2022 151 Development of a new fuel efficient, shear stable axle lubricant to meet new U.S. Green House Gas requirements In a controlled over-the-road truck test with a tandem axle (front and rear carriers), the candidate oil provides 0.79% fuel saving and 5.2°C temperature reduction compared to leading commercial oil. Figure 6 1.8 Field Tests The field tests are progressive satisfactorily on this oil in North America in line-haul application. Several test units have accumulated over no-drain 240,000 miles (approx. 400,000 km). The used oil iron content data from one fleet is shown below. The increase in iron content is relatively lower compared to factory-fill oil indicative of reduced component (gear) wear. Figure 7 1.9 Conclusion This paper describes the development of a new lower viscosity, shear stable, synthetic heavy-duty axle lubricant. The lubricant consists of a unique combination of synthetic base oil (PAO) and proprietary viscosity improver (thickener) which results in superior low-and-high temperature properties with excellent extended-length shear stability. The new lubricant meets the SAE J2360 and leading North American axle manufacturers rigorous extended drain specification requirements. The new axle lubricant also shows fuel savings of 0.79% and front axle temperature reduction of 5.2°C over a leading fuel-efficient SAE 75W-90 axle lubricant. Using EPA estimates, the use of new fuel-efficient lubricant is estimated to save over $300 and reduce carbon dioxide (CO 2 ) by over 200 kg per truck per year.