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Development of Transaxle Fluid for Electrified Vehicles: Validating Optimized Viscosity through Targeted Hardware Testing
ISSN: 0148-7191, e-ISSN: 2688-3627
Published August 30, 2022 by SAE International in United States
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Reducing powertrain losses is an important technical challenge to further improve the efficiency of electric vehicles as part of measures toward achieving carbon neutrality. One effective method of accomplishing this goal is to reduce the viscosity of transaxle lubricating oil. However, it is generally known that lowering viscosity can cause durability issues such as wear and seizure if the thickness of the lubricating oil film on metal sliding surfaces is insufficient. In gears and bearings, reducing the oil film thickness can increase direct contact with the base metal and may cause surface fatigue peeling.
A new additive formulation for lubricating oil specifically for electrified vehicles has been designed in anticipation of the wider adoption of such vehicles in the future. The result has been a new transaxle fluid that ensures unit durability while reducing viscosity of 40°C to 12.2[mm2/sec]. This low viscosity fluid raises not only the fuel efficiency of hybrid electric vehicles (HEVs) by 1.0% or more under test cycle driving conditions, but also effective in improving the cooling performance of the motor. In addition, it was confirmed that this low viscosity oil satisfied anti-wear and anti-seizure performance of the gear in the high-speed durability test and the differential durability test. Furthermore, it was confirmed in the gear and bearing unit fatigue test that fatigue life was better than the conventional oil.
The developed fluid can contribute to the realization of carbon neutrality by finding widespread use in other electrified vehicles, including plug-in hybrid (PHEVs), battery (BEVs), and fuel cell electric vehicles (FCEVs).
CitationTokozakura, D., Sano, T., Nakamura, T., Tada, A. et al., "Development of Transaxle Fluid for Electrified Vehicles: Validating Optimized Viscosity through Targeted Hardware Testing," SAE Technical Paper 2022-01-1103, 2022, https://doi.org/10.4271/2022-01-1103.
- Huang , Z. , Nategh , S. , Lassila V. et al. Direct Oil Cooling of Traction Motors in Hybrid Drives IEEE International Electric Vehicle Conference Greenville, SC 2012 1 8 10.1109/IEVC.2012.6183163
- Iino , M. , Tada , A. , Masuda , K. , Onumata , Y. et al. Drivetrain Lubricants with High Cooling and Efficiency-Boosting Properties for Electric Vehicles SAE Technical Paper 2021-01-1215 2013 https://doi.org/10.4271/2021-01-1215
- Yungwan , K. , Christopher , C. , Atanu , A. , and Xinggao , F. Understanding Base Oils and Lubricants for Electric Drivetrain Applications SAE Technical Paper 2019-01-2337 2019 https://doi.org/10.4271/2019-01-2337
- Narita , K. and Takekawa , D. Lubricants Technology Applied to Transmissioms in Hybrid Electrica Vehicles and Electric Vehicles SAE Technical Paper 2019-01-2338 2019 https://doi.org/10.4271/2019-01-2338
- Beyer , M. Lubricant Concepts for Electrified Vehicle Transmissions and Axles Tribology Online 14 5 2019
- Kohei , M. , Hajime , N. , Hitoshi , K. , and Osamu , K. Super Low Viscosity ATF; AW-2 SAE Technical Paper 2018-01-1756 2018 https://doi.org/10.4271/2018-01-1756
- Masato , Y. , Toshiaki , I. , Keiichi , N. , and Mitsugu , K. Lubricants Formulation Technology for Fuel Saving Performance in Automatic Transmissions SAE Technical Paper 2015-01-2037 2015 https://doi.org/10.4271/2015-01-2037
- Teruo , M. and Yoshikazu , M. Mobility of Carrier Ions in Electrical Insulating Oil Journal of Electrical Engineers of Japan. A 102 8 1982 459 464
- Shinichi , S. and Makoto , M. Effect of Phosphorus-Based Additives on Rolling Fatigue Journal of Japanese Society of Tribologists 46 7 2001 564 570
- Shinichi , S. and Jyunichi , N. Effect of Sulfur-Based Additives on Rolling Fatigue Journal of Japanese Society of Tribologists 46 7 2001 571 577