Hybrid Class 8 trucks coming soon from Wal-Mart

  • 19-Jun-2008 04:33 EDT
II Wal-Mart truck.jpg
Wal-Mart's fleet drivers log more than 850 million mi (1.37 billion km) per year, collectively, with the average Wal-Mart driver logging 115,000 mi (185,000 km) annually.

­The notion that hybrid-electric technology only makes sense on vehicles with stop-and-go duty cycles could be dispelled after a dual-mode diesel-electric Class 8 truck hits the highway in early 2009.

"Putting a demonstrator hybrid-electric Class 8 truck in real world driving scenarios—on hills and flat terrain and all kinds of duty cycles—will provide a considerable amount of feedback on fuel economy and other potential paybacks. This project could prove that the heavy-duty truck industry is an appropriate fit for hybrid-electric technologies," said Michael Roeth, Director of Global Advanced Engineering for Navistar, Inc. at the truck engineering facility in Fort Wayne, IN.

Transforming a Class 8 International ProStar truck into a hybrid means replacing the flywheel, starter, transmission, clutch, and alternator with hybrid components, including a 620-to-12 V power converter, a battery pack (ranging in size from 20 to 60 kW·h), a 180-kW generator, and a traction motor rated at 180 kW continuous and 360 kW peak, according to Vern Caron, Director of Commercial Vehicle System Electronics at ArvinMeritor.

The truck will be fitted with its hybrid hardware in July, followed by six months of fine-tuning work. "Remember this is a demo-vehicle, so we will be designing, developing, and testing control algorithms, doing performance evaluations of the drivetrain, as well as evaluating the sub-systems," said Dennis Kramer, Program Manager of Electric Drivetrains for ArvinMeritor.

ArvinMeritor's dual-mode diesel-electric drivetrain will employ the electric motor primarily during low-speed—typically below 50 mph (80 km/h)—operating conditions such as accelerating from a stop.

"We expect that the truck will operate in zero-emissions mode for 20 miles or 20 minutes, whichever comes first. When the battery state-of-charge drops to approximately 15%, the Cummins diesel engine will be started and the generator will be used to recharge the battery," said Caron. Two lithium-ion battery packs will be located along the side rails behind the fuel tanks.

At highway speeds, typically above 50 mph (80 km/h), the operation switches to parallel mode, which is primarily diesel-mechanical. During hill climbs, passing situations, as well as other high-demand times, the electrical system can provide additional power. If the vehicle is being decelerated, the traction motor can provide regenerative braking.

When the project started in late 2006, the price for a gallon of diesel fuel was $2.50, but that price soared beyond $4.00 in mid-2008. "The basic objective of doing a Class 8 hybrid truck is to allow for at least a 15 percent fuel economy improvement," said Caron, adding, "We expect that as the price of components decreases due to higher volumes and the cost of fuel increases that our customers will see a payback on their investment in two years or less."

Retailer Wal-Mart, with more than 3600 discount stores, super centers, and neighborhood markets in the U.S., is expected to take delivery of the Class 8 ProStar demonstrator hybrid truck in early 2009. "We are continually looking for new, innovative ways to improve the fuel economy and reduce the emissions of our fleet," said Chris Sultemeier, Wal-Mart's Senior Vice President of Transportation. Wal-Mart's transportation-greening effort entails the development and use of "diesel hybrid trucks that we anticipate will help us exceed our goal to increase fleet efficiency by 25 percent," according to Sultemeier.­

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