A partnership with the US Air Force has enabled Volvo Group to prove its I-SAM hybrid technology is viable for heavy-duty applications, the company announced at a recent gathering in the US capital.

I-SAM (Integrated Starter Alternator Motor) technology can deliver fuel savings of up to 35% depending on application and driving conditions, announced Leif Johansson, president and CEO of Volvo Group. Mack Trucks has received four contracts from the US Air Force to develop hybrid-powered trucks and plans to take the technology to the commercial truck market.

A number of heavy-duty hybrids will be built in 2007, with customer field testing set to commence in 2008 and serial production in 2009. Johansson said there is a substantial potential market for heavy-duty hybrids in North America and Europe: 20,000 refuse; 80,000 construction; and 200,000 urban delivery vehicles are already in operation, he pointed out.

Sten-Ake Aronsson, head of Volvo Powertrain in North America, said the heavy-duty hybrid trucks consist of: a traditional diesel engine; a Volvo I-Shift automated mechanical transmission; an electronic motor that generates electric power (about 160 hp); a power/electronics box; an energy storage box; and a powertrain control unit. The electric motor helps provide torque and regenerates energy during braking. This energy is stored in the ultracapacitators and used in place of diesel fuel when powering the vehicle.

The electric motor delivers full torque as soon as the throttle is applied, improving efficiency, Aronsson pointed out. While powered by the electric motor, the vehicle operates nearly soundlessly, which makes it ideal for applications in urban areas where noise is a concern.

Customers can downsize their diesel engine, thanks to the 160 hp of muscle provided by the electric motor, Aronsson pointed out.

Paul Vikner, president and CEO of Mack Trucks, said Mack is leading the hybrid charge for Volvo Group, thanks to its partnership with the US Air Force. Mack’s four contracts with the military are worth US$6.8 million and include the construction of six vehicles.

Motortruck had the opportunity to ride along in a Mack Granite Axle Back hybrid dump truck in the parking lot of RFK stadium in Washington, D.C. The truck was loaded to about 50,000 lbs and had a 365 hp MP7 engine under the hood.

As promised, the electric motor delivered immediate torque right out of the gate. Combined with the diesel engine’s traditional torque band, the hybrid dump truck provides a more efficient torque curve, resulting in improved overall performance. We launched solely in electric mode, with the diesel engine kicking in at about 850 RPM. We took the Granite for a short drive around the parking lot, braking periodically and watching the ultracapacitors charge under braking thanks to a specially-rigged laptop that revealed the ultracapacitors’ voltage. For the most part, the ultracapacitors hovered at around 600 volts, discharging power while accelerating and recharging under braking.

This particular truck required the diesel engine to continue running while idling, but that won’t be the case with production models, pointed out Mack engineers. The diesel engine will shut down while production model hybrids are at a standstill, resulting in further fuel savings and noise-free idling. Even when starting from sixth gear, the electric motor has enough power to launch the hybrid on its own. In fact, it’s been known to climb a 5% grade while loaded with no assistance from the diesel engine for about 200 feet before depleting the ultracapacitors.