Automotive Engineering - December 2024 - 24

New fluids coming for
EV thermal
management
EVs with specially
Balancing low conductivity, corrosion
resistance and optimum heat transfer
in next-generation EV coolants while
meeting new EV safety regulations.
By Lindsay Brooke
M
anaging the heating and cooling of electric vehicle propulsion
systems may seem to be an easy task compared with
combustion engines. After all, ICEs run much hotter-the
thermal optimum for a gasoline engine is around 212 F
(100 C). By comparison, EV batteries normally generate (as a function
of current during charge/discharge cycles) a relatively cool 5986
F (15-30 C). And while motors and power electronics operate hotter,
typically 140-176 F (60-80 C), they still run cooler than ICEs.
But among the myriad complexities of EV thermal management
are batteries' dislike for temperature extremes, new cell chemistries,
heat-generating high-voltage electrical architectures and 800V fast
charging. All are putting greater focus on maintaining stable EV battery
thermal performance and safety. Experts note that compatibility
among the cell chemistry, hardware, and coolant fluid is the key to a
balanced systems solution.
" EV liquid coolant has kind of been an afterthought until recently, "
noted Tom Corrigan, director of EV Technology at Prestone Products
Corp. His team of scientists and engineers is responsible for developing
next-generation thermal-management fluids for OEM and, eventually,
consumer customers. Corrigan said that beyond their vital role
in enabling efficient heat transfer, fluid formulations must be compatible
with every component and material they contact, such as polymeric
seals. They also must provide internal corrosion protection (as
does traditional ICE antifreeze). And perhaps fluids' most vital role is
helping to prevent an extreme failure mode, i.e., thermal runaway,
from spreading throughout the battery pack.
" Low electrical conductivity is a must for thermal-management
fluids which could potentially come into direct contact with high voltage
electronics, " Corrigan asserted.
Low-conductivity coolants taking over
The 'first wave' of EV adoption established the electric-vehicle market
before coolant suppliers had time to develop bespoke thermalmanagement
products, Corrigan explained. " Most EVs on the road
24 December 2024
formulated thermal
management
fluids may move
away from
ionic corrosion
inhibitors, which
were developed
for ICEs.
today are using the same fluids that are used in ICE
vehicles, he said. " We're [Prestone] long established
with many OEM customers, so when those OEMs started
producing EVs, they installed the coolant fluids
they trust for corrosion protection. "
Corrigan sees a shift in the industry's thinking, mainly
driven by EV safety concerns. For motor cooling,
two main strategies are being used today: indirect and
direct cooling. Indirect cooling uses the same waterglycol-based
fluid, with corrosion inhibitors, that is
used for the battery pack. The motor housing serves
as a coolant jacket, allowing the fluid to flow through
it and extract heat indirectly from the motor system.
" The issue with the current additive packages and their
proprietary blend of corrosion inhibitors, is that the industry
had, for a long time, moved towards ionic corrosion
inhibitors for ICEs, " Corrigan explained. Ionic additives
include silicate, organic acid, and phosphate technologies,
all of which increase electrical conductivity.
" With high electrical conductivity, if that fluid were to
come in contact with the high-voltage electronics,
400V or 800V systems, you'll have a pretty violent, catastrophic
reaction, " he said, citing studies that show
that submerging a lithium-ion battery in traditional ICE
coolant results in high heat generation. " There's a good
chance that [heat generation] will cause the coolant to
boil with potential for fire and thermal runaway. "
Such risks, combined with increased thermal performance,
have spurred over 50% of EV manufacturers
to adopt direct cooling strategies for the motor,
according to Corrigan. This method uses an oil-based
'dielectric' fluid, with very low or zero conductivity,
depending on the formula. The fluid flows directly
over the motor coils. Dielectric fluids are also entering
battery thermal management; with direct (also known
AUTOMOTIVE ENGINEERING
PRESTONE PRODUCTS CORP.
Automotive Engineering - December 2024

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