Electricity has been the military's fuel of choice for the very large - 2,500-ton submarines - and the very small - 12-pound UAVs. But electricity has yet to break into the vast middle ground of tactical vehicles.
Oshkosh hopes to change that with the HEMTT-A3, a hulking hybrid truck that the company says can cut fuel consumption by at least 20 percent, requires less maintenance than current trucks and can double as a power source for field hospitals or command centers.
The "heavy expanded mobility tactical truck" is headed to Army proving grounds this fall to undergo durability, reliability and performance tests.
The U.S. military has spent years examining and testing vehicles that run in part or entirely on electricity, said Paul Skalny, director of the Army's National Automotive Center, but so far, the service has not embraced them.
The Army has a few hybrid electric Humvees for testing purposes - "probably less than 10," Skalny said. And it has tested hybrid utility vehicles, hybrid maneuver vehicles and vehicles powered by fuel cells that generate electricity.
But they haven't generated wide enthusiasm.
"There are no tactical hybrids in the military today," Skalny said.
Oshkosh is optimistic that its vehicle may be the first.
Unlike some hybrids, the HEMTT-A3 runs solely on electricity; there is no parallel mechanical drive train. Instead, a diesel generator produces electricity, which powers electric motors that drive each of the vehicle's four axles, said Gary Schmiedel, Oshkosh's vice president for advanced product engineering.
The generator also produces electricity that is stored in two dozen ultracapacitors. Unlike batteries, the soda-can-size ultracapacitors are electrostatic devices that can charge and discharge in seconds, enabling them to store electricity generated when the vehicle is coasting or braking, and then quickly expend it when the vehicle needs to accelerate.
The motors that drive the axles also act as generators. When they are not pushing the vehicle forward, such as when coasting downhill or braking, they generate electricity, which is directed to the ultracapacitors and stored.
Ultracapacitors, unlike batteries, can be recharged and discharged more than million times without wearing out, Schmiedel said.
The HEMTT-A3's nonconventional power train provides for more flexible vehicle configurations. Without the traditional engine, transmission and drive shaft, "you can move the engine and generator anywhere on the vehicle," Schmiedel said. On the HEMTT-A3, that has freed space for a 40 percent larger cab and allowed engineers to cut 3,000 pounds of weight off the 38,000-pound curb weight vehicle.
The extra cab space and the abundant power supply make it possible to outfit the truck with additional communications gear, computers, GPS receivers and other C4ISR equipment. The hybrid drivetrain also reduces noise and vibration, Schmiedel said.
Oshkosh calls its drivetrain the ProPulse diesel-electric.
"It's built on a power bus that distributes electricity" to the separate motors on each axle, Schmiedel said. "You can have two, three, four axles or more - just keep adding them as the truck gets larger."
The ProPulse system for the four-axle HEMTT-A3 is powerful enough to push the vehicle and 13 tons of cargo up to 65 miles per hour on highways. Oshkosh says in recent tests the vehicle used 24 percent less fuel while cruising at 60 miles per hour than a comparable conventionally powered truck.
Fuel savings increased to 33 percent when the vehicle was driven with lots of stops and starts. Stops and starts kill fuel efficiency in conventional vehicles, but in the HEMTT-A3, the stops generate electricity that is then used to drive the vehicle.
And because the diesel engine drives a generator, not the wheels, it can operate continuously at its most efficient speed.
The ProPulse hybrid drive train "can be integrated into any new vehicle design," the company says. And upgrade kits are available to convert existing vehicles to hybrids.
The HEMTT-A3 offers the military some attractive features beyond its hybrid drivetrain, Oshkosh says.
The truck is capable of loading and unloading itself. It can "pull up to a C-130 and unload the plane without additional equipment," Schmiedel said. And because it can generate electricity, a HEMTT-A3 could unload a field hospital from a C-130, drive it to an operating location and then provide it with 100 kilowatts of "military-grade AC power" - enough electricity to power several dozen homes.
Skalny said the driving cycle and mission profile of HEMTTs may make them good candidates for hybrid powertrains.
The Army also is attracted to hybrid vehicles by their ability to sit silently with electronic systems running on stored electricity, and to travel silently on stored electricity.
But the Army isn't yet convinced that hybrids are the way to go.
A study on the feasibility of a hybrid Stryker brigade illustrates the Army's ambivalence, Skalny said. It concluded that replacing 1,600 conventionally powered vehicles - Humvees, medium tactical trucks, HEMTTs and Strykers - with hybrids would not yield savings in peacetime, but could pay off during war.
Because hybrid vehicles would require less fuel, fewer fuel tankers and fewer troops to man supply convoys would be needed. In addition to saving money, a 1 percent decrease in fuel consumption could keep 6,442 troops off convoy duty and out of harm's way, Skalny said.
But for now, Skalny said, "there isn't a truck out there" that meets Army requirements, in large part because the Army hasn't established firm requirements. "The whole Army has to get together and decide what it wants," he said.
Until it does, the service is more likely to consider hybrids for its fleet of nontactical vehicles - 186,000 leased "administrative" cars and trucks used for routine transportation on military bases.
The Army's Tank-Automotive Research, Development and Engineering Center is in the early stages of a plan that would switch the administrative vehicle fleet to hybrids, electric and fuel cell-powered vehicles, Skalny said.
"That would drive down the cost of those vehicles and have the military be part of the solution" for energy independence, he said.
Meanwhile, Skalny said innovative propulsion systems may be on the verge of taking off in the civilian sector.
"In 2012 or 2013, I think we will see a mini-explosion in hybrid commercial trucks," he said.
If so, the U.S. military may deserve some credit. Military-supported research has pushed hybrids ahead by about two years, he said. ■
E-mail: bmatthews@defensenews.com.
The Army's Future Combat Systems (FCS) program is ready to test a few components that soldiers may have in their hands by 2010.
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