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.
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 emission reduction technologies.
More specifically, the calculation takes into account things like aerodynamic drag, tire rolling resistance, equipment lightweighting, idle reduction technologies, etcetera.
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 vehicles 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.”
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.
“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 Hegart. These CO2 credits are totaled annually to confirm if the OEM remained in compliance with federal emissions regulations.
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 idle reduction technologies are all methods OEMs have looked toward in order to address the continuing shift to higher efficiency.
Continued monitoring
The latest round of federal emissions standards – known as Phase 2 – will continue to drive these technology changes.
“Phase 2 has increased the amount of inputs that need to be analyzed and reported on,” Daimler’s Gedert says. “In Phase 1, the categories were mainly around aero[dynamics], tire rolling resistance, weight, and speed. In addition, we now also review engine fuel maps, transmission types, axle ratios, accessory load, intelligent controls, and other technologies.”
“The GHG Phase 2 regulation requires manufacturers to assign a GEM score to each individual vehicle sold,” says Michael Noonan, director, certification and compliance for Navistar. “This is an expansion upon Phase 1 in that the actual powertrain and vehicle configuration sold is now considered. Due to this change, 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.”
OEs utilize validation through computer simulations, as well as track testing to ensure that the equipment produced meets the standards set.
“Our vehicles and components are subjected to thousands of hours and millions of miles of lab, test track, and on-road testing, the latter being performed both by the Volvo Group and our customers,” Volvo’s Agebrand says.
The supplier side
Suppliers selected by OEs are equally responsible for their role in ensuring the entire vehicle meets the criteria put forth by the emissions regulations. Because of this, truck manufacturers have a trusted working relationship with suppliers to ensure the products specified in today’s trucks are meeting these criteria.
“Collecting all inputs required to exercise GEM in time for certification means manufacturers and suppliers have to align product development schedules, deployment schedules, change management, and testing,” Paccar’s Hergart says. “OEMs, being the integrators of all technology building blocks, need to have adequate oversight of the component level tests to ensure the integrity and accuracy of the data.”
“With the introduction of GHG Phase 2, many of our suppliers will now have to support product compliance through the submission of certification data for the components they supply,” Navistar’s Noonan advises. “Through this process, it offers us a unique opportunity to help guide the development, optimization, and selection of components and technologies for each application we offer.”
