Technology limitations stall military hybrids

ByDavid Axe

techolimits 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.

TARDEC, a division of the Research, Development and Engineering Command, in Warren, Mich., is the military’s main research center for vehicle technologies.

Khalil and other TARDEC engineers have been developing hybrid-electric engines and testing vehicle demonstrators since 1992.

Across the Defense Department, there are around 30 hybrid-electric demonstrator vehicles in some form of testing. These demonstrators range from hybrid models of existing vehicles, such as Humvees, M-113 armored personnel carriers and M-2 Bradley infantry fighting systems, to new designs such as the Marine Corps’ reconnaissance, surveillance and targeting vehicle, or RST-V.

Some of these demonstrators are more promising than others. Some even offer new niche capabilities. But all have failed to achieve the combination of performance, toughness, price and utility that the military demands of its vehicles.

“We found out way back when, that you cannot just take what is being developed out there for commercial cars and put it in military vehicles,” Khalil says. “The space available on military vehicle platforms is extremely tight and the demand of the user is different than that of the average driver on the road.”

“Hybrid technologies may seem like an easy undertaking, especially with the automotive industry making headway to reduce [gasoline] consumption by way of hybrid platforms,” a TARDEC document says. “It is not so easy for the military. Our vehicles have larger electric- and use-loads than standard commercial vehicles, so adopting commercial technology for military use is not always possible. Additionally, our vehicles operate in conditions that most commercial vehicles do not.”

“Generally speaking, size and weight are challenges for everything we do,” Khalil says. “The weight is limited and that is dictated by how you transport the vehicle from one place to another. And there are definite limits on [a vehicle’s internal] volume. You need components that deliver very high power, but fit in the vehicles, and are light enough not to exceed weight limits.”

Another concern is cooling. The area under the vehicle armor is a very hot environment for electronics. “In order to make hybrid technology survive, the Army needs to cool the components. In order to properly cool the components, you have to add some type of cooling system — which then adds more weight to the vehicle,” the TARDEC document says.

The enormous challenges facing military hybrids have discouraged some manufacturers from investing in demonstrators. Other companies are gambling on hybrids that are, at best, compromises — that meet some military requirements while failing others.

AM General, which builds the ubiquitous Humvee, has eased up on military hybrids after several years of serious investment. “We were developing a hybrid Humvee, but the Army canceled the contract a couple years back after some prototypes were built,” says one company official, who asked to remain anonymous. He says the limitations of batteries were a major factor in the Army’s decision to cancel the contract. “Now there isn’t a clear direction from the Army or the Defense Department on hybrid programs … Besides, the focus these days is on armor, not alternative fuels.”

AM General spokesman Craig MacNabb is more diplomatic: “We are exploring all the alternative fuels options, which is to say, bio-diesel, alcohol, hybrid-electric and fuel cells. We’re looking at all of them, but none of them are quite soup yet.”

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. And when I’m all done at the end of the mission, I can take whatever energy is still stored in the capacitor and export it.”

The hybrid HEMTT design favors missions that involve a lot of starting and stopping to provide the regenerative braking that tops off the capacitors. But when cruising at a steady speed over a long distance, as is common during convoy missions, the HEMTT A3 performs better than a conventional truck, Schmiedel explains. The hybrid truck, however, is more expensive than diesel-engine models.

Where the hybrid HEMTT shines most brightly is in its physical profile, he says. While hybrids must cram a greater volume of components into a given space than conventional vehicles, many of a hybrid’s components function separately from each other, and can be positioned more flexibly than large conventional drive-trains. Like most hybrids, the HEMTT A3 relies on individual induction motors instead of a drive shaft, torque converters and axles. This lets the A3 designers adapt the HEMTT for easier cargo transfer from aircraft such as the C-130.

“We came up with a strategy that gets the load handling system of the truck to the same elevation as the C-130 cargo hold,” Schmiedel says. “We were only able to do that with a hybrid system. A conventional truck has some significant drive-train components in the center of the truck, but by going with the hybrid approach, we were able to embed the load handling system within the profile of the airplane.”

General Dynamics Land Systems, which designed the RST-V in 1999 to fit into the compact cabin of the V-22 Osprey tilt-rotor, promotes the layout flexibility of individual hybrid induction motors versus integrated conventional drive-trains.

“The key technology is the in-hub permanent magnetic motors which allow you to pull the entire drive train from the belly of vehicle into the wheel hubs,” says GDLS Director for Advanced Programs Bill Riker. “You don’t have any propulsion shaft, just a folding A-frame suspension that can collapse into itself. Essentially, you have a vehicle that has the same wheel-width and stability as a Humvee — actually, better stability — and the folding suspension enables it to shrink down to about 60 inches to be internally transportable by V-22.”

Two RST-V demonstrators were slated to deploy to Iraq early this year, but testing in 2005 revealed software and mechanical problems. Navy officials said that the reliability problems are typical of any vehicle development program.

In addition to layout advantages, Oshkosh and GDLS tout their demonstrators’ power-export capabilities. Both the HEMTT A3 and RST-V generate three-phase AC power that is compatible with a wide range of computers, sensors and network terminals used by military command posts. The latest incarnations of HEMTT A3 and RST-V offer more utility as mobile generators. HEMTT A3 exports as much as 100 kilowatts of power. RST-V exports 30 kilowatts.

Power export is not a new capability — AM General’s hybrid Humvee demonstrated it years ago, albeit at a modest 15 kilowatts, and naval vessels have practiced it for decades.

But with command posts going digital, demand for power has skyrocketed in the last 10 years, points out Khalil. The ballooning logistical requirements have planners eager to trim command post overhead. The Army has decided it wants vehicles that can haul and power electronic equipment. But the service remains far from committing to a production contract.

Both Oshkosh and GDLS are counting on their demonstrators’ physical flexibility and power export capabilities to eventually win over Army managers, despite performance and reliability problems. But neither company seems too eager to discuss fuel efficiency.

According to the anonymous AM General official, fuel efficiency is only one of many reasons for the Army’s interest in hybrids.

“Under certain operating conditions you can achieve some fuel economy,” Khalil says. “But we’re not doing hybrid-electrics just to save fuel.”

For the time being, the military seems content to just study and test hybrids while holding off on issuing formal requirements for a particular need that hybrids might fill. Khalil stresses that for any of the current hybrid demonstrators to make a quick transition to production, the military would have to write requirements tailored to the vehicle’s strengths.

“There are challenges, and there are issues, but they don’t seem insurmountable,” Khalil says. “If someone from a program office told us they wanted something in production in two years, we would have it into production.”

The HEMTT A3 has been rigorously tested and is ready for production now, Oshkosh officials aver.

Riker says the four RST-V demonstrators manufactured to date have traveled more than 15,000 kilometers in tests without any “major” failures. He adds that the RST-V could be ready for production in just a few years.

Despite that, Khalil says, vehicles associated with the Army’s future combat systems could be the first military hybrids to enter mass production — sometime around 2010.

Even if that were the case, and today’s demonstrators remain just demonstrators, manufacturers’ efforts haven’t been wasted, Khalil contends.

Prototypes developed in 1992 and in 2005 are two different vehicles in terms of performance, he says. “The whole community knows a lot more about how to integrate hybrid-electric technology into military platforms than it did 15 years ago. And acceptance has grown based on the experimentation.”

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