Hybrids not Mil-Spec

Technology limitations stall military hybrids

The U.S. military has long sought diesel-electric hybrids that would improve fuel economy, offer a reduced logistical burden and provide the ability to export power, among other advantages.

But after more than a decade of research and development, and despite much recent hype, military hybrids are still years away from mass production.

None of the current military hybrid engine efforts has any specific goals or timelines to deliver an operational vehicle. “Right now, we do not have a current hybrid program that targets fielding,” says Gus Khalil, team leader of hybrid-electric research at the Army’s Tank Automotive Research, Development and Engineering Center, or TARDEC.

But there is potential for civilian uses... note that garbage trucks have frequent stops, and could use regenerative braking.

"Oshkosh Truck Corp. and General Dynamics Land Systems have pressed on with hybrids despite the technological problems and the military’s waning support.

Oshkosh has pinned its hopes on the development of a hybrid drive for the heavy expanded mobility tactical truck, or HEMTT. The technology is jointly funded by Oshkosh, the Army and the Energy Department, which is interested in commercial and civilian applications of large hybrids, such as municipal garbage collection.

The Army uses the HEMTT for heavy cargo hauling. The hybrid HEMTT, which Oshkosh calls the A3, uses ultra-capacitors, rather than batteries, to store diesel-generated AC power, an adaptation that effectively skirts the problem that doomed the hybrid Humvee. Ultra-capacitors are safer and more efficient than batteries, company officials said, but store less energy per unit of weight than batteries and are more complex.

“When we’re coasting to a slower speed, when we have ‘regenerative braking,’ the rolling of the truck turns traction motors into generators, says Gary Schmiedel, Oshkosh vice president for advanced products. The ultra-capacitors can store 1.5 mega-joules of energy that way, he notes. “With that energy, I can add 190 horsepower to the truck for 10 seconds or 19 horsepower for 100 seconds. That saves fuel."