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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].

To achieve carbon neutrality by reducing carbon dioxide (CO2) emissions, vehicles with an internal combustion engine have started to be replaced by electrification vehicles such as hybrid electric vehicles (HEVs), plug-in HEVs (PHEVs), and battery EVs (BEVs) worldwide, which have motors in their transaxles (T/As). Reducing transmission torque loss in the transaxles is effective to reduce CO2 emissions, and lowering the viscosity of lubrication fluids in T/As is a promising method for reducing churning and drag loss. However, lowering viscosity generally leads to thin oil films and makes the lubrication condition severe, resulting in worse anti-fatigue and anti-seizure performance. To deal with these issues, we made improvements on the additive formulation of fluid, such as the addition of an oil-film-forming polymer, chemical structure change of calcium detergents, and an increase of anti-wear additives including phosphorus and sulfur.