Effect of applied voltages on wear behavior of rolling-sliding steel surface under lubrication with e-Axle fluids

In electric vehicles (EVs), inverters supply shaft voltage to drive motors integrated with e-Axles. These voltages can reach several tens of volts, frequently surpass the dielectric strength of the lubricant film and result in electrical damage. Such damage affects bearing surfaces, which can cause unusual noise, increase in vibration, and a decline in system reliability. This research examined how applying DC voltage influences wear behavior on steel surfaces under rolling-sliding motion, using both base oil and e-Axle fluid formulated with anti-wear additives. A ball-on-disk tribometer was used to replicate bearing conditions under various DC voltage levels. After the friction tests, wear scars and surface topographies were characterized via confocal laser microscopy. The findings showed that higher voltages substantially intensified both wear and electrical damage. Compared to PAO4, the e-Axle fluid led to deeper wear due to the formation of tribofilms from lubricant additives, which facilitated charge buildup and arc discharges. Severe melting was observed on anodic surfaces, while cathodic ones exhibited material transfer. In contrast, PAO4 caused shallower wear scars, owing to its superior electrical insulation, which suppressed arc discharges.