Exploring Electrically Conductive Nanoparticle Additives in Greases for Electric Vehicle Applications

Abstract

Global transportation trends favor renewable alternatives, with electric vehicles (EVs) emerging as a popular choice. However, EV adoption is challenged by range anxiety and infrastructure. Optimizing tribological contacts within gears and rolling element bearings in electric drivetrain systems is essential to ensuring safe, efficient, and sustainable EV performance. Compared to internal combustion engine (ICE) vehicles, EVs offer more responsive performance at the cost of increased mechanical and thermal expectations. In addition to traditional wear and fatigue, current leakage can induce electrical damage along the surfaces of mechanical contacts. Bearing manufacturers have implemented solutions, such as insulating bearing surfaces or increasing the bulk lubricant conductivity, to mitigate this electrical damage without compromising friction or wear resistance. Both solutions can prevent the damaging discharge of accumulated energy across bearing surfaces, but altering bearing conductivity does not require modifying or adding mechanical components. Studies have indicated that blending conductive nanoparticles (NPs) into grease can reduce pitting damage caused by electrical exposure. This research compares the performance of various NP-enriched polyurea greases with electrified rolling ball-on-disk tests. Systematic variations in speed and moving profiles are employed to determine conditions that increase the probability of surface damage. Results reaffirm the potential for conductive NPs to mitigate electrical damage. However, incorporating these particles requires suspension in a colloid solution, introducing additional liquid hydrocarbons to the grease mixture. Oscillatory amplitude sweeps demonstrate that the increased liquid content effectively lowers the NP-enriched grease's crossover (flow) point compared to neat grease. This observation underscores the intricate relationship between tribological performance, rheological behavior, and electrical resistance necessary for lubricants to succeed in electrical applications.