Truck & Off-Highway Engineering - August 2024 - 22

GEARING UP A NEW
ELECTRIFIED TRUCK
Much of the hardware for the truck is integrated and modular so
that individual components can be replaced and serviced rather
than just full assemblies.
While not production ready, Eaton/BAE's test truck looks much closer to a roadready
product than many prototypes.
ultimately make things easier to manufacture and install
and service. "
Hopkins detailed why adding a gearbox to an electrified
powertrain provides greater flexibility not only in
design but also in overall performance. " For transit, most
of the buses we see do not travel above 45 mph. Now
there are buses that do have to drive up steep hills like in
San Fransisco, " he said. " But in the truck space, a gearbox
helps significantly because you have to be able to do 70
mph and also climb some serious grades. Which is why
we realized right away that going to a gearbox would be
a big advantage over a direct drive architecture. "
There are other advantages, too, such as downsizing
Eaton's four-speed automated manual
transmission is intended specifically for EV applications.
handling, " Webb said. " That may be due to incentives for the first
two, but for the third it's actually now become economically sustainable.
Those are all good duty cycles for BEVs, but for some segments
the infrastructure isn't here yet. Obviously, there's still a lot of challenges
ahead with electrification, and we're not going to tell you that
it's all ready for primetime. But in some market segments, it's really
getting there. "
" We seek to consolidate and simplify because of experience, "
Webb continued. " On the trucking side, a lot of this technology is
new with a lot of OEMs rushing to get products to market and tick
that box. A lot of them are taking a very distributed approach to the
architecture with a lot of boxes, wires and interconnects. It does
make the product electrified, but it's probably not the best way.
" There are too many things that can break, add cost and complexity
and is not easy to manufacture. What we're trying to do is
integrate and use as many advanced commercial technologies as
possible in terms of materials to get heat out, get efficiency up and
22 August 2024
the motor and power electronics. " The truck market is
not as subsidized, it is more TCO and cost sensitive, "
Hopkins said. " Because you need the combination of
excellent startability, we have to ask, 'what is the steepest
grade I can start on with a full load?' You also have to
look at cruising efficiency. "
" It's very difficult to get that out of a direct drive
solution because your motor is being asked to do two
different things: run at high speed very efficiently or
produce a ton of low-end torque, " Hopkins continued.
" So, it's a lot easier once you have multiple speeds to
be able to have a standard motor that doesn't [require]
extreme high-end torque and can be more optimized
to operate at a more moderate speed in the
sweet spot of a motor's efficiency. "
An electric motor's efficiency map is " a lot wider and
more expansive than an ICE sweet spot in terms of peak
efficiency, " Hopkins noted. " But you're still trying to optimize
that motor for peak efficiency where you're doing
the most amount of miles. So, when you get that multiplication
for both those demands, it's very helpful to
have the gearbox. "
Hopkins also explained how introducing a transmission
can reduce overall cost of an electrified powertrain.
TRUCK & OFF-HIGHWAY ENGINEERING
ALL IMAGES: SAE/MATT WOLFE
Truck & Off-Highway Engineering - August 2024

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