Fleet Maintenance - 24

What is a GEM?

"Manufacturers will
have to carefully
monitor fleet sales
to ensure they are
promoting powertrain
technologies and
vehicle configurations
optimized for
the best possible
fuel economy."

Federal emissions standards must be monitored
through standardized and consistent testing. Enter
the greenhouse gas emissions model, or GEM.
By Erica Schueller

The U.S. Environmental Protection Agency
(EPA) has provisions in place requiring heavy
duty truck and engine manufacturers to
conduct annual compliance testing on the
equipment they manufacture. This testing
helps to ensure original equipment manufacturers (OEMs) are meeting current emissions and fuel efficiency requirements.

cles sold and has values attributed to specific
configurations and options," says Kelly Gedert,
director, product marketing, Freightliner and
Detroit components for heavy truck manufacturer Daimler Trucks North America. "The
tool works in real-time and calculates values
as orders are processed. Once a vehicle is
built, the values are loaded to the database."

The greenhouse gas emissions model, more
commonly known as GEM, is a simulation tool
used by all classes of vehicle manufacturers
to calculate vehicle fuel efficiency. The simulation model uses data from the drivetrain
- engine, transmission, and axles - as well as
other emissions reduction technologies.

Since the calculation takes into account the
cumulative score of all assets in production
for the OEM, the GEM results may be below or
above the threshold for meeting emissions and
fuel efficiency requirements on a single vehicle.

More specifically, the calculation takes into
account things like aerodynamic drag, tire
rolling resistance, equipment lightweighting, idle reduction technologies, etc.
A truck OE has a cumulative score and cannot exceed the Family Emissions Limits (FEL).
Calculations are determined based on current vehicles in production. This means that
all vehicle options from an OEM must work
toward improving vehicle technologies and
offer higher efficiency products to fleets.
"GEM is based on the entire portfolio of vehi-

"Some of the vehicles will have GEM simulation
results that are below the standard for their
configuration, while others will be above the
standard," explains Carl Hergart, director of
powertrain and advanced engineering, Paccar
Technical Center. The Paccar Technical Center
provides testing and development for the company's Kenworth, Peterbilt, and DAF trucks. "Final
compliance for an OEM is determined after all
the vehicles are built for a given model year."
The final GEM score for all vehicles manufactured by an OEM is calculated into CO2 credits,
notes Hergart. These CO2 credits are totaled
annually to confirm if the OEM remained in
compliance with federal emissions regulations.

Michael Noonan, director, certification
and compliance, Navistar

APPLICATION CONSIDERATIONS

Duty cycle plays a role in the calculation as well.
"Since each vehicle type is modeled in GEM
against a unique duty cycle, different technologies will provide significant improvements
on some types of vehicles and nearly none on
others," advises Johan Agebrand, director of
product marketing for heavy truck maker Volvo
Trucks North America. "For example, engine
stop-start technology, which stops the engine
when the vehicle comes to a stop in traffic or at a
stoplight, will provide up to a 17 percent improvement in GEM on an urban vocational vehicle
and nearly zero improvement on a high-roof
sleeper cab tractor due to the different
amounts of stop-and-go operation
in their respective duty cycles."
This means that as vehicles are built,
it will impact that GEM rating. As
truck manufacturers continue to
introduce new products, they need
to ensure their entire fleet sold
meets the criteria set forth by federal emissions standards. With that,
OEMs look to encourage fleets to
specify fuel-efficient technologies.
Jim Nachtman, director, heavy duty
marketing for Navistar, provides the
example of a recent aerodynamics and
fuel efficiency package now available
for the company's line of International
trucks. He advises specifying the
package can provide up to 8.2 percent
better fuel economy. "Improvements
to the customer's bottom line will
encourage more customers to spec
these technologies," Nachtman says.
"Longer term, further refinement in
engine and transmission integration,
aerodynamics, and programming will
all deliver improved fuel economy
while meeting the GEM regulations."
®

Continued adoption of automated manual transmissions (AMTs),
data capture and utilization, and
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24 Fleet Maintenance | February 2020

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