It is anticipated that many future electrified vehicle transmissions and axles will incorporate the electric motor within the unit housing. In such an arrangement, the lubricant will be in direct contact with powered motor windings, which raises new concerns regarding its electrical conductivity and its propensity to corrode copper. The heat produced at the motor windings will challenge the lubricant's heat transfer ability and its thermal stability. Expected high temperature excursions warrant the use of new plastics, which may give rise to new compatibility concerns. In this paper we share our learnings regarding the electrical properties of lubricants and discuss new methods to characterize copper corrosion. We review the factors that affect the heat transfer characteristics of lubricants and illustrate how improving heat transfer will favor the use of lower viscosity lubricants. We also share our early efforts to quantify lubricant compatibility with higher temperature plastics using tensile strength measurements. Finally, we discuss how these new concerns will shift the perception of what is required for lubricants used in different types of electrified transmission hardware.

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A new method for monitoring the corrosion of copper by lubricating fluid additives through the measurement of the electrical resistance of copper wires is presented. The effect of base oil and lubricant additive components upon the corrosion rate of copper is discussed. The information on corrosion generated by this method provides details of the corrosion processes that are not obtained from traditional corrosion tests and insight as to how to formulate oils to better protect copper and copper alloys.

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In this paper, a new method, measuring the change in resistance of a thin copper wire, has been applied to provide a way to monitor a corrosion reaction in situ. Two different corrosion inhibitors used in commercial automatic transmission fluids have been studied at 110 °C, 120 °C, 130°C, and 150 °C using this new test method coupled with a more traditional coupon test to allow surface analysis to be carried out. Both inhibitors were found to be equally as effective up to temperatures of 130°C; however, the evidence provided shows that at 150°C, the thiadiazole inhibitor is breaking down leading to severe pitting on the surface. Corrosion performance therefore, cannot be assumed to be effective at all temperatures, and the current method provides a convenient quantitative screening method for inhibitor evaluation.

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