Electric Vehicles (EVs) are emerging as the future of transportation as the marketmoves towards electrification. However, materials and lubricants for EVs have not
been optimized over decades of tribological research like it has been done for internal
combustion engine vehicles (ICEVs). Although EVs are more efficient than
ICEVs, energy losses and tribological challenges in electric motors (EMs) are still
considerable, so characterization of EM-specific friction and wear behavior is important.
Particularly, greased bearings in EMs are subject to a wide range of operational
requirements and corresponding micro-environments. Consequently, greases
must function effectively in these conditions. Here, the tribological performance of
four market-available EM greases was characterized by measuring friction and wear
of silicon nitride sliding on hardened 52100 steel. The EM greases evaluated had
similar viscosity grade, but different combinations of polyurea or lithium thickener
with mineral or synthetic base oil. Measurements were performed across a range of
temperatures and surface roughness conditions to capture behavior across multiple
lubrication regimes. Results enabled direct comparison of market-available products
across different application-relevant metrics and the analysis methods developed can
be used as a baseline for future studies of EM grease performance.