Automotive Engineering - October 2021 - 26

'Retuning'
lubricants
FOR EV
DUTY
Multiple bearing
types in electric
propulsion systems, with
increased interest in
ceramics, is driving new
grease developments.
" M
y focus is lubricating grease; I've been
doing it for 32 years, " explained Dr.
Gareth Fish with a high degree of pride.
Lubrizol's top expert on the subject.
Globally recognized in the lubricants field, Dr. Fish has authored
more than 70 technical papers on grease and tribology
and has four U.S. patents. He finds the industry's
shift to electrified vehicles and its impact on automotive
greases " an extremely interesting and challenging time. "
Broad challenges include strategic supply - the
lubricants industry competes with the battery industry
for lithium - and sustainability by reducing grease's
environmental footprint, Dr. Fish noted. Removing the
internal combustion engine and its ancillary systems
from vehicles is an obvious trend with major impact;
Lubrizol provides the industry with significant technology
development and R&D support. " Today we have
50-60 greases, about 2 kilograms (4.4 lb.) in total, on
a standard, mid-size passenger vehicle, " Dr. Fish noted.
" On a hybrid-electric vehicle you'll have a similar
number, because the vast majority of componentry
will not change. Moving to electric vehicles [EVs] there
will be some significant changes, such as elimination
of crankcase oil. But the overall volume of greases will
stay the same as today, about 2 kilograms. "
While EVs retain traditional grease-intensive chassis
components such as CV joints, wheel hubs and bearings,
their propulsion systems' grease requirements are
anything but traditional. " Drive motors in electric vehicles
must operate at high rpm to be efficient - 18,000
26 October 2021
Lubrizol's top grease expert talks
about how the electric vehicle
trend is driving innovations and
creating opportunities.
by Lindsay Brooke
to 20,000 rpm, " Dr. Fish explained. " When you get to those high
speeds, noise becomes critical, so you need low-noise greases. You
also have to have durability, and these motors can get hot, which requires
wider temperature-range greases. You need a special premium
grease for those electric drive motors. Add to that it may be electrically-conductive
as well - all of these create challenges. "
The EV movement is creating the need for new grease formulations,
he said. " For wheel bearings alone, there are additional loads
caused by the heavy battery packs. Then there is electrical conductivity.
If your electric drive motor has ceramic rolling elements in its
bearings, it has different behavior and so needs different lubrication
than bearings with caged steel balls and steel races. The requirement
is basically hardware-specific, " Dr. Fish explained.
He noted that as an AC induction motor rotates, it will create stray
currents within the system. Those stray currents build up charge on the
motor shaft. " At some point, that current has to go somewhere; it can
be grounded away by some means (such as slip rings), " he observed.
" If you don't handle this properly, you can basically build up charge
that will discharge through the bearing, which ends up damaging the
bearing. Or you get current flowing through the bearing which can
cause a softening of the rolling elements. So, you need to guard
against that. "
He explained that Lubrizol is working with industry to help implement
greases for future technologies. " We've talked with a couple of
motor manufacturers; they're still unsure where everything is going to
go. We've also talked to bearing manufacturers and some of them believe
the best way to insulate electric-motor shafts is to use ceramic
rolling elements, but they're high-cost. So they're looking for other
solutions, one of which is conducting grease. But the technology of
conducting grease today makes this a non-trivial problem. "
AUTOMOTIVE ENGINEERING
LINDSAY BROOKE
Automotive Engineering - October 2021

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