Truck & Off-Highway Engineering - October 2024 - 21

Off-highway
hybrids are
entering
PRIME
TIME
PROPULSION FEATURE
Cutaway of
John Deere's dieselelectric
drivetrain.
V
ocational off-highway vehicles are piling on the miles with
power provided by an internal combustion engine (ICE)
with additional hybrid technology. " We often get asked the
question, especially by those outside the industry, 'Why
don't we just electrify everything?' The reason is the current challenges
we have with battery-electric vehicles, " Grant Van Tine, product
manager for electric vehicles at John Deere, said during an
August 22 webinar hosted by SAE Media Group.
Van Tine and Mihai Dorobantu, PhD, Eaton Mobility Group's director
of technology planning and government affairs, cited facts,
figures and in-field and in-development examples of why hybrid
innovations are especially relevant today in a session addressing
" The Future Role of Hybrids in Off-Highway Vehicles " (www.sae.
org/webcasts/sae-on-demand).
Since 2015, the John Deere 944 X-Tier electric-drive wheel loader
has showcased hybrid technology instead of an all-electric powertrain,
and with good reason. " Even if we were able to package enough energy
onboard, which would make the machine extremely larger than
what it is now, a 54,000-lb (24,500-kg) battery pack is not something
that can be packaged within the current vehicle frame, " Van Tine said.
An all-electric version of today's 944 loader, according to Van Tine,
would need to be charged multiple times during a typical day's 12hour
shift. A fully electric version would also cost three to four times
higher than the current hybrid machine. " That's just not practical or
feasible for anyone, " he said.
TRUCK & OFF-HIGHWAY ENGINEERING
Increased performance
and lower emissions
explain why hybrid
technology is an appealing
option for certain offhighway
vehicles. Just ask
John Deere.
by Kami Buchholz
Deere's hybrid setup
The current 944 X-Tier wheel loader's powertrain uses a
John Deere 13.5-L diesel engine producing 536 hp (400
kW) that runs at either a limited speed range or a constant
speed. The output shaft connects to a gearbox
that houses the hydraulic pumps and two generators,
which convert the engine's rotational energy into threephase
AC electrical energy. There is no mechanical
transfer of power. Each wheel's electric motor converts
the AC power back to rotational energy and torque in
the final drive. Power electronics control the commands
to the drive system based on operator input.
Recaptured energy is recycled into the system in
certain situations, Van Tine said. " In certain applications,
such as truck loading, we've seen up to a 33%
reduction in fuel consumption compared to a conventional
diesel machine, " he said.
Other benefits associated with the machine's electric
drive system include a longer lifespan for tires, which is
important since the vehicle typically operates in a quarry.
" In abrasive rock environments, wheel spin is bad
and can deteriorate tires. So, independent control of
each wheel can limit the torque when slippage begins
to occur, and that extends tire life, " Van Tine explained.
October 2024 21
JOHN DEERE
http://www.sae.org/webcasts/sae-on-demand http://www.sae.org/webcasts/sae-on-demand
Truck & Off-Highway Engineering - October 2024

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