Automotive Engineering - April 2023 - 9

TECHNOLOGY REPORT
" J2908 sets test specifics such as environmental conditions, battery state of charge
and vehicle warmup and preconditioning. "
the distribution of blended drivetrain
output to individual axles. " So we
came about this with a very technology-agnostic
approach, " Duoba said.
" Another thing that was important
was that this was compatible to ISO
standard [ISO 20762], he added. " I
would say the SAE standard is a little bit
more specific and a little bit tighter on
what you're doing and what you're not
doing. But it is definitely compatible with
the ISO and you should come up up with
the same [peak power value]. "
Duoba said the J2908 sets test specifics
such as environmental conditions,
battery state of charge and vehicle
warmup and preconditioning. Vehicles
with temporary, extra-power " boost "
functions can use those settings to derive
the peak-power rating, but he said
the boost feature must be readily accessible
to the driver.
Duoba said that because of the comAE
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plexities of hybrid and all-electric drivelines,
the new J2908 procedure relies on
a wheel-power test (WPT) figure that
measures power at the driven axle(s).
Rather than using an engine dynamometer,
" You can use a chassis dynamometer
or a wheel dynamometer. OEMs
have both, " Duoba said. " It's up to everybody
to figure out what the best way to
get the most accurate numbers. "
Duoba would like to see automakers
begin using the J2908 procedure, conceding
that adoption " might take some
time. " He noted that Volkswagen may
be the first automaker to deploy the
standard. On the consumer web page
listing power for the 2023 ID.4 electric
vehicle, Volkswagen's power-rating
disclaimer states, " Maximum hp calculated
via peak performance of the
electric motor(s) at peak battery power
pursuant to SAE J2908. " Duoba said
feedback from industry is vital to continue
refinement and improvements.
The J2908 procedure has been under
Duoba's study since early 2013. Current
simulation techniques and technology
might allow testers to generate comparatively
accurate measures of an
electrified drivetrain's peak system
power, Duoba conceded, " But I'm like,
'No - I just can't do it. We have to do a
physical test. "
The standard can be accessed here:
https://www.sae.org/standards/content/
j2908_202301
Bill Visnic
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Automotive Engineering - April 2023

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