WASHINGTON — Volvo Group and Mack executives were in the U.S. capital yesterday to show off unique hybrid diesel-electric technology for heavy vehicles.

The internally developed I-SAM system has the potential to be commercially viable, say the companies, though Mack president Paul Vikner said with some passion that government funding is needed to “jump-start” the commercialization process.

At the Swedish Embassy and later at RFK Stadium in Washington, Volvo and sister company Mack Trucks demonstrated a Mack Granite dump truck with hybrid drive ordered by the U.S. Air Force. Four have been built to date for testing purposes, and more are on the way.

Development of the truck was carried out in close co-operation with the USAF which, several years ago, also contracted Mack to develop an aircraft refueller tank truck with hybrid diesel-electric drive. Its drive system is different from the I-SAM system, using an electric motor aft of the transmission, much like a driveline retarder in reverse. The I-SAM answer puts the electric motor in between the engine and transmission as most others do.

Volvo’s solution was named based on its functionality, I-SAM being the acronym for Integrated Starter, Alternator, & Motor. It’s said to have the potential for fuel savings of up to 35 percent depending on application and driving conditions. The first vehicles are expected to enter production in 2009. Volvo is also developing hybrid technology for construction equipment such as wheel loaders, in which the fuel savings can be up to 50 percent.

The I-SAM system is conventional in hybrid terms, consisting of an “electric machine” developing 161 hp and 590 lb ft of torque at its peak sandwiched between a Mack 315-hp MP-7 engine and a Volvo automated mechanical 12-speed direct-drive transmission based loosely on the Volvo I-Shift gearbox. It’s a two-pedal system, having a clutch but no clutch pedal. The system does not employ batteries, instead using capacitors to store energy extracted from the heat of braking.

In a demonstration ride, electric power launched the truck strongly with the diesel kicking in seamlessly within about 20 seconds.

Asked about the price of a Granite equipped with I-SAM, Vikner said the companies really didn’t know yet. Leif Johansson, Volvo Group president and CEO, said it was entirely dependent on volume, and it’s much too early to have that pinned down..