Improving the efficiency of electric vehicle (EV) transmissions can help to
extend the driving range of EVs, and the EV oil used in these transmissions
plays an important role. In this study, in order to enhance energy efficiency,
we examined the effects of lowering viscosity, traction, and friction in EV oil.
While friction modifiers (FMs) have been widely used as friction reduction
technologies in the field of tribology for many years, we previously developed a
new FM that reduces friction in drive units. We found that a combination of
lowering viscosity and using the developed FM was effective for better energy
efficiency. The oil formulated with the developed FM improved efficiency by
approximately +0.8% to +0.9% compared to commercial EV oil.
EV oil also requires cooling performance. We assumed that reducing heat
generation through friction reduction would improve cooling performance and
examined the effect of lowering viscosity, traction, and friction. Consequently,
it was found that a combination of lowering traction and applying the developed
FM is effective for reduction in parasitic heat losses. We also examined
durability, which is an issue when reducing viscosity. The results suggested
that the oil formulated with the developed FM had good durability for gears and
bearings. Thus, we succeeded in developing an ultra-low-viscosity EV oil that
has excellent energy efficiency and high cooling performance.