Recent announcements from governments and OEMs demonstrate an accelerated transition to electric vehicle production, particularly in passenger cars, but also extending to a portion of commercial vehicles. Lubricant manufacturers must adapt to this new reality. In today’s internal combustion engine (ICE) vehicles, there are typically 50 different places where greases are used. In a typical electric vehicle (EV), there are no more mechanical systems because everything is electric, but up to 100 electric motors have been reported on EVs (average is 80). With so many electric motors, the importance of using the correct greases for these components is more critical than ever.
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Greases in electric vehicles and hybrid vehicles
For HEVs, most starters are permanently engaged and no longer need the shock resistance needed in ICE vehicles because they act like a generator when not starting the vehicle. The bearings of the electric transmission motors may be grease lubricated or, on some HEVs, the electric motors are integrated into the transmission systems which are oil lubricated.
In an electric vehicle, all fats contribute to energy consumption and reduced range. After all, EVs contain almost twice the number of electric motors as ICE vehicles, so fats must be more energy efficient. It is essential that people designing vehicles, especially in commercial environments, decide on the optimum lubrication zone for the electric vehicle and ensure that components are designed to operate in that zone. In other words, lubricating films must be thin enough to avoid churning losses, but not so thin as to reduce component durability.
What fats have to do
In commercial electric vehicles, the greases are subjected to even more stress than in passenger vehicles. Accordingly, newer formulations must be long-lived, low-noise, conductive and insulating as well as energy-efficient.
Conductivity is much more important in electric vehicles and hybrid vehicles. If a grease is too conductive, it can cause current leakage/short circuits. If its conductivity is too low, it can cause net charge buildup and lead to electrically induced bearing damage (EIBD). One of the reasons greases make more sense in electric vehicles than oils is that conductive solids (graphite, metal particles, etc.) can be incorporated into greases but cannot be used in oils.
Optimizing the grease used in rolling element bearings can reduce energy loss, which will extend the range of the EV. Greases are also used for the bearings of the fluid pump which control the temperature of the batteries.
To be more energy efficient, the viscosity of the base oil must be optimized. Greases should produce films thick enough to separate the mating surfaces completely, but not so thick that at higher speeds energy is lost churning through the grease. Synthetic fluid based greases are better than mineral oil, and soft structured greases are also more energy efficient.
The commercial electric vehicle market still has a lot of unknowns, but it’s clear that greases that impact vehicle range will need to be upgraded to have performance and fuel efficiency, durability and lifespan. higher life. As more commercial vehicles transition from ICE engines to electric systems, it will become increasingly important for fleet managers to understand how greases work in these vehicles to optimize their performance in commercial applications.
Gareth Fish, Ph.D., is a Technical Lecturer at The Lubrizol Corp. Visit the Lubrizol website for more information.