Wear Protection for Electrified Transmissions Using e-Fluids without Active Sulfur

In electrified drivetrains, lubricants are commonly in contact with the motor and other electrical components as well as the gears and bearings. Copper, present in these electrical components, is susceptible to corrosion by fluids containing active sulfur, which can lead to catastrophic failure of the unit. Lubricating fluids for electric vehicles (referred to as e-fluids) must not cause corrosion and must maintain high performance while having suitable electrical conductivity, material compatibility, and heat transfer properties. We describe a new formulation without active sulfur that has recently entered the market, which can protect against copper corrosion. We show that this e-fluid can provide suitable wear protection under field trial conditions, and that the e-fluid provides improved wear protection in bearing (FE-8) tests compared to a traditional extreme pressure axle fluid (API GL-4). Surface analysis (X-ray photoelectron spectroscopy) measurements of the component surfaces after testing show that the wear protection arises from the formation of phosphate tribofilms, which are not present after testing with the traditional fluid. We show that the e-fluid provides high resistance to micropitting by gear (FZG) testing. Surface analysis measurements following reciprocating (TE-77) tribological testing again show that the wear protection arises from the formation of phosphate tribofilms, this time comparable to those produced by traditional driveline fluids.