The Assessor Mag Autumn 2024 Web - Flipbook - Page 30
JOURNAL
DATA
UNDERFLOOR,
TRACTION BATTERY
DAMAGE ASSESSMENT
By Andrew Marsh FIMI, Hon IAEA fellow.
arger battery packs
typically used in pure
electric drive vehicles
tend to be 昀椀tted on the
underside. While this
ensures a signi昀椀cant mass – anywhere
from 300 to 700kg – is located as
low as possible, there are a growing
number of issues associated with
battery pack damage as a secondary
consequence of impact.
L
This article will concentrate on cars, but
some of the aspects discussed apply to
LCVs as well.
Packaging
This term is used to describe how
everything and everyone can 昀椀t inside
the vehicle skin. If we think back to
pure internal combustion powered
vehicles, the fuel tank was commonly
昀椀tted to the underside of passenger
car boot area. For front end impact this
of course made little difference, until
we consider the front end ploughed
into the rear end of such a vehicle.
Whizzy mechanisms to release the fuel
tank during impact were toyed with,
but in the main it gradually moved to
between the rear wheels behind the
rear seat backrest, or, as hatchbacks
became more popular combined with
widespread migration to front wheel
drive, under the 昀氀oor just ahead of the
rear wheels.
Why?
This was the safety zone in the event of
major impact damage, where the fuel
tank was least likely to by damaged. It
is easier (but not easy) to package fuel
lines along the underside and into the
engine bay than to package a large
tank.
Some deviations – Honda managed to
make an ultra-shallow tank, overcoming
the issues of liquid surge under
cornering / braking / accelerating, to 昀椀t
it beneath the front seats. This enabled
the rear end to be opened up, allowing
the rear seats to fold in all sorts of
ways. Please note: I’ve just mentioned
30
that things like the Honda Jazz are
quite lively. Who knew.
Most vehicle manufacturers have from
pure internal combustion power to
electri昀椀ed powertrains to pure electric
powertrains, knowing the full range of
product gave the maximum protection
from the demands of certain regional
governments. Unlike manufacturers
who only build pure electric vehicles,
the multi powertrain approach means
昀椀tting all sorts of parts inside the
very same model skin. Further, the
parts and sub-assemblies wherever
possible, would be shared across as
many applications as possible to offset investment and reduce part cost
due to higher component production
volumes.
This is the ‘kit’ of parts. Such ‘kits’,
sometimes called platforms, have
manufacturer speci昀椀c names such as
CMP, EMP, CMF, STLA, MQB Evo,
MEB, CLAR and more.
Battery manufacturers complain
Right back in 2010, as the process
of creating brand-new business
models for many established vehicle
manufacturers began, all of them
decided to create special limited
production / low production volume
pure electric vehicles, and to convert
existing or soon to arrive regular ‘kits’
to include electri昀椀cation.
The result has been a blizzard of
product which has been arriving
on the market since 2018, and the
pace of arrivals has not slowed until
the effective battery electric vehicle
(‘BEV’) delay arrived in 2024. Going
forwards we will continue to see a
mix of products powered by an array
of possible powertrains in spite of
Government ‘rules’ / mandates.
Right back at the start the battery
manufacturers struggled to produce
convincing traction batteries that stood
any change of 昀椀tting inside a vehicle,
that offered anything like a usable
range and were expensive. From the
manufacturer perspective they were
frustrated to consider huge assemblies
which weighed so much, making
conversion dif昀椀cult. As the battery
manufacturers noted, most of the
problems were due to manufacturers
not approaching the problem with an
open mind.
Much has changed since then, and a
‘formula’ has emerged:
• Under昀氀oor traction battery, 昀椀tted
within the wheelbase. This leaves
the 昀氀oor skin as a barrier between
the battery upper case and the
occupants.
• Shorter front chassis legs, usually
integrated with the strut tower, with
signi昀椀cant material added to sweep
outboard to meet the sills. This is
designed to direct impact energy
into the A pillar / sill area.
• Signi昀椀cant increase of UHS
reinforcements for the side structure,
to minimise side intrusion. Usually,
the battery pack case will also have
sacri昀椀cial side elements to protect
the interior.
• Shorter rear chassis leg crush zones,
because greater instant torque from
an electric motor suits rear drive
better than front drive, so there can
be a signi昀椀cantly larger rear drive
module to protect than an internal
combustion engine powertrain
remote diff module.
So, the battery is protected from front
end impact, side impact and rear end
impact. For the underside, the traction
battery is on its own.
Package compromise
The biggest package constraint is the
overall height. For a conventional
low-riding car, the passenger
compartment 昀氀oor was usually not
lower than the lower edge of the sill.
Now the large traction battery has
the lower-case skin on the ground
clearance line, and is at the same
height as the sill lower edge.
THE ASSESSORS JOURNAL | AUTUMN 2024 | www.iaea-online.org/news/the-assessor
