may2022 - 42

GUE ST EDITORIA L
their core with the inclusion of highly effective
corrosion-inhibiting technology.
This offers demonstrable benefits for protection
of copper connections, exposed motor
wiring, and circuit boards. Corrosion can occur
in copper components directly exposed to the
oil but surprisingly also in unlubricated components
above the oil because of corrosive vapors.
A suitable e-fluid prevents this from occurring.
Specialized tests have been devised to
screen for such corrosion protection. Lubrizol's
wire corrosion test uses bare wires and tests
circuit boards to assess the protection abilities
of the fluid.
The life of the e-motor and other electrical
components is only as good as the life of the
insulation, and thorough testing of the e-fluid
ensures that resins and plastics are not
damaged by it.
E-fluids generally have a lower viscosity than
Photo: Lubrizol
The EV e-fluids
revolution
Electric motor lubrication technology
is advancing at a rapid pace to help
fleets get the most value out of their
electric vehicle investments.
While many know about the growing adoption
of electric vehicles (EVs), few are aware
that the lubrication technology for electric
motors and other powertrain components is
advancing at a similarly rapid pace. Called
driveline e-fluids, these represent a significant
technological advancement over traditional
lubricants and will help fleets get the most out
of their electrified investments.
Until recently, commercialized automatic
transmission fluids (ATF) have been the lubricant
of choice, but these are increasingly less
suitable to meet the specific demands of the electric
powertrain. Costly examples exist in fleet
garages where a traditional gear oil had been
used in error. These can corrode copper wiring,
traditional fluids for a few reasons:
ÜA thinner fluid offers less resistance to
moving parts, which improves the efficiency
of the drive components and preserves
battery range.
leading to motor burnouts and vehicle failure.
Because of their cost, fleets need EVs operating
as much as possible and failure is unacceptable.
Lubrizol's research found replacing ATF with
dedicated e-fluids formulated with the right
additives can help alleviate these problems by
protecting copper and electrical components
while still providing gear protection. The key
is to ensure that only the most suitable components
are used in the fluid design phase.
It's also worth noting that ATFs and e-fluids
are not interchangeable. Though some ATF
technology is marketed as appropriate for electric
vehicles, the fact is that they were designed
for traditional drivetrains. Improvements in
aspects of fluid design such as supplements
or " boosters " to existing additive packages are
sometimes offered, but do not make them suited
for the unique demands of an e-drivetrain.
E-fluids, by contrast, are developed as part
of the transmission design process and are a
technical component of the driveline-just
like mechanical components. It's evidence that
OEMs are turning toward dedicated e-fluids for
electric powertrains.
By Michael Gahagan
TECHNOLOGY MANAGER-DRIVELINE,
THE LUBRIZOL CORPORATION
Michael Gahagan is Technology Manager-Driveline for The
Lubrizol Corporation in Wickliffe, Ohio.
Advances in driveline e-fluids
Transmission fluids can be subject to extreme
heat, especially when there is heavy current
draw on the electrics in contact with the oil.
E-fluids are therefore designed to be more
stable to oxidation and thermal breakdown
than many traditional fluids. Traditional fluids
over time can also degrade to form corrosive
sludge, adversely affecting the efficiency of
component operation.
Where an unsuitable lubricating fluid is
in contact with electrical equipment, there is
always a risk of component corrosion, which is
especially accelerated at high temperatures. In
contrast, e-fluids have corrosion protection at
42 Fleet Maintenance | May 2022
ÜLess-viscous oils are generally better at
carrying away heat, which benefits the e-motor.
A cooler e-motor is more efficient, and
there is a beneficial effect on the lifetime of
oil-cooled components because they have
not had to run so hot for so long.
The thermal properties of an oil are more
important than ever, and engineers must
study the fluid's thermal conductivity, heat
capacity, fluid density, and viscosity profiles
against temperature.
The electrical properties of lubricants are
just as important in e-fluids as values such as
viscosity, element content, and other performance
characteristics. Three values typically
measured for an e-fluid are:
ÜElectrical conductivity: how much electric
current can be passed through an oil.
ÜRelative permittivity (or dielectric constant)
related to the tendency of the oil not to store
electrical charge.
ÜDielectric breakdown strength, which is
related to the ability of the oil itself to resist
electric spark discharges.
Although the permittivity and dielectric
breakdown values appear similar for many
fluids, the electrical conductivity is highly
dependent on the fluid viscosity and additives
present. In general, most e-fluids are
expected to be lower in electrical conductivity
than traditional fluids, though it must be high
enough to avoid electrostatic buildup.
The fluids are expected to protect steel gears,
bearings, and other contacting surfaces from
wear, which can be a challenge because specific
additives can corrode the copper. To avoid
this, judicious anti-wear chemical components
are added to e-fluids. E-fluids are expected
to provide suitable frictional performance
to minimize noise, vibration, and harshness
(NVH). The quieter-running feature expected
of EVs is enhanced by stable friction modifiers,
which eliminate NVH issues that can be caused
by less suitable fluids.
may2022

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