Automotive Engineering - May 2022 - 29

Q&
Integrating a plug-in hybrid Jeep
At no other time in the auto industry's history has the role of
vehicle integration and synthesis been so important. The
growth of electronic content, the melding of mechanical and
electrical engineering and the increased focus on electrified
propulsion have made integration/synthesis teams vital to ensuring
that design spec and requirements are maintained
through prototypes, testing and validation in order to meet
market standards and exceed customer expectations.
Eunjoo Hopkins is vehicle synthesis manager on the 2022
Jeep Grand Cherokee 4xe (called " 4-by-e " by Stellantis engineers;
see p.11). She joined the former FiatChrysler in 2009 as
a powertrain engineer and only recently
moved over to vehicle integration.
" I've worked in propulsion systems for
most of my career here thus far, including
the [Chrysler] Pacifica Hybrid, " she
told SAE Media during the Grand
Cherokee 4xe media launch in Texas. " I
moved into integration/synthesis because
I wanted to experience the other
aspects of vehicle development. "
Integration, she explained, " is all
about what we call 'the sciences' -
aerodynamics, safety, NVH, vehicle
dynamics. We have to make sure we
meet the 'science' goals established for
the program, all the way back to component
design, " she noted. For the
Grand Cherokee 4xe, that includes
metrics such as foundation braking feel
as well as regen braking. Calibration
falls under powertrain, however. " If
there is a metric we don't meet, we go
back and redesign the component, "
Hopkins asserted. " We're also responsible
for holding ride-and-drives with
our executives to get their inputs and
buy-in to make sure our products meet
customer expectations. "
Highlights of our conversation with
Hopkins follow.
Eunjoo Hopkins
If there is a metric
we don't meet, we
go back and redesign
the component.
Is most of the Grand Cherokee 4xe's
PHEV powertrain carried over from the
Jeep Wrangler 4xe?
Yes, but with more refinements. Being
able to pick up the propulsion system
from Wrangler allowed us to move the
program along much more quickly. The
challenge, however, was the different
electrical architectures of the two vehicles.
The Wrangler's architecture is
very different from the WL [internal
AUTOMOTIVE ENGINEERING
code for the new Grand Cherokee] in how it does 'wake up' and
'sleep,' for example. That's where a lot of complication came in
for us, in integrating [the hybrid system] with the vehicle architecture.
Grand Cherokee and Grand Wagoneer have all-new
electrical architectures, as Tom Seel [Grand Cherokee vehicle
line engineer] has noted.
The PHEV system combines P1 and P2 electric machine positions.
What do you call that combination?
We call it a 'P1-P2!' Integrating the hybrid transmission into the
Grand Cherokee, seamlessly, is where our learnings from
Wrangler came in. To make its engagement
and disengagement smooth in all
operating modes, including engine-on/
engine-off and at launch, required a lot of
hard work in terms of control-algorithms
and calibration. The vehicle has a separate
transmission controller, which 'plays
nice' with the supervisory controller.
A key to any electrified Jeep is thorough
and robust sealing of the battery,
controllers and the high-voltage harness
from water intrusion. Did sealing
the Grand Cherokee pose challenges?
We used industry standard specifications
for sealing. We didn't do anything
special. We made sure that we validated
those requirements at the VP [prototype]
stage. When we hand-build our
prototype vehicles, we use as much of
the actual factory processes as possible.
Before we put this vehicle through our
first water fording test, we contacted all
the DREs [design release engineers] to
make sure the parts they supplied truly
did pass the component-level testing.
The WL team drove the Grand
Cherokee 4xe over the 22-mile
Rubicon Trail on electric power only.
How much did regen braking play a
role in getting through that journey?
That's interesting. Doing the Rubicon
Trail is a low-speed event; not a lot of
power is used. When you tip out of the
throttle, you're using the electric machine
to absorb that energy.
On that run, we typically used the
forward motion of the vehicle and the
driver's foot to modulate vehicle speed.
In the end I believe we still had some
battery energy left.
May 2022 29
A
LINDSAY BROOKE
Automotive Engineering - May 2022

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