Automotive Engineering - December 2022 - 15

TECHNOLOGY REPORT
system. The Bolt was equipped with a
screen that demonstrated when the
DMD system was active and pulsing the
electric motor. In low-load city driving,
where the system is going to be most
active, the pulsing of the motor was just
as imperceptible as Tula's cylinder deactivation
in an ICE demonstration truck.
The screen readout in the Bolt clearly
demonstrated when the system was
active and when the motor was functioning
normally, but there was no clear
change in perceptible NVH that would
tip off the driver that the DMD system
had been engaged. The readout on the
screen also indicated what the overall
efficiency of the system was during various
loads. It showed that the DMD system
did indeed keep the motor's output
in the " sweet spot " for longer periods
of time when it was active.
Mark Wilcutts, director of DMD
Systems, discussed the process the company
used to produce acceptable NVH
levels in the cabin while DMD was active.
" We've been doing NVH work on this car
for about six months, " he explained.
" When we started, we had our inverter in
place and were starting to drive the car
just to validate functionality. But our initial
impressions when the system was functioning
were 'that's obnoxious, that's
shaking my hands off the steering wheel.' "
Wilcutts uses this analogy: " You've got
a bunch of big rocks and then you've got
to knock the big ones into smaller ones,
and then the smaller ones into pebbles.
So, we started by finding the biggest
problem and think about how we want to
write an algorithm and create calibration
for it. Then that gets better but then we
notice three or four other problems that
we didn't notice before. Then we have to
write another set of algorithms to compensate
for that. That's basically what's
been going on over the last six months. "
Tula has been using GMUTS (General
Motors's Driveline Noise and Vibration
Vehicle Level Allocatable Test) to validate
its NVH testing as well as accelerometers
and microphones for its own internal NVH
scale. When compared to their NVH measurements
with the stock Bolt motor control,
company engineers feel that they are
nearly within standard deviation of where
AUTOMOTIVE ENGINEERING
The DMD system offers a claimed 25% reduction in losses on the MCT EV drive cycle.
While copper losses when the motor is being pulsed do increase, the reductions in core and inverter
losses more than offset the increased copper losses.
they started when the DMD system is
functioning. " There were some areas that
there are 6.5's and sevens. I don't think
anything was above a 7.75, " said Wilcutts.
" I would say we are 80 to 85 percent of
the way there (on NVH reduction) now. "
Heavy-duty implications
While the DMD system does offer most
of its benefits at low load, it still can
offer efficiency gains on larger scale
electrified vehicles. The company is
working with a truck OEM to develop
the DMD system for a commercial application.
Bailey also stressed that
" There is nothing that limits DMD application
to just mobility. "
John Fuerst, senior VP, DMD and
Engineering, expanded on DMD's potential
for commercial and off-highway applications.
He explained that DMD could
be used in agricultural applications. " For
example, a high-horsepower tractor that
spends a significant portion of its life driving
a fairly low-load accessory drive using
a small amount of the machine's peak
power, " he said. " If you've got a significant
portion of the application that's operating
at low load, then the DMD can
provide some real benefits. " Tula reportedly
is in talks with a U.S.-based ag
equipment company about implementing
the DMD system on their machines.
Matt Wolfe
December 2022 15
BOTH IMAGES: TULA

Automotive Engineering - December 2022

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