ARTICLE

January 2003

Hybrid-Electric Vehicles Not Yet Ready for the Battlefield

by Sandra I. Erwin

More than 20 years after the Army first experimented with hybrid-electric vehicles, none has been fielded yet. But as the Army increasingly is compelled to lower fuel consumption and improve the overall performance of its tactical trucks, a consensus is emerging that hybrid engines may be the way to go.

The Army’s National Automotive Center already has been testing a hodgepodge of hybrid-electric military vehicles, including armored personnel carriers and heavy-duty trucks.

But the Army’s position is that it does not want to be a proverbial guinea pig for unproven technologies and is hesitant to commit to a production contract until the commercial industry begins mass-producing hybrid-electric vehicles. Auto giants Toyota and Honda only recently have introduced hybrid-electric cars into the commercial market.

Most of the hybrid power drives the Army is testing today involve some combination of a diesel engine and an energy-storage device such as batteries or capacitors. Experts said that the poor performance of the current generation of batteries poses a considerable technical roadblock. For the most part, batteries available today don’t last long enough nor can they endure the extreme weather conditions specified for military equipment. One industry source noted that, every time he talks to military commanders about propulsion and power, inevitably the comment heard is that “batteries are the number-one problem.”

In the meantime, the Army plans to continue research and development efforts, and will spend several million dollars to expand ongoing experiments and assess the state of the technology.

Richard E. McClelland, the director of the U.S. Army’s Tank-Automotive Armaments Research, Development and Engineering Center, said his agency will spend about $5 million this year to buy several hybrid-electric vehicles and get them “in the hands of troops” as quickly as possible.

It is important for soldiers to be given an opportunity to try out the vehicles and determine whether they in fact deliver what they promise, before the Army decides on long-term buys, McClelland explained.

The $5 million will cover an array of light, medium and heavy trucks, as well as combat vehicles, all of which would be shipped to field units by late 2003, he said.

Skepticism abounds when it comes to hybrid-electric vehicles, McClelland said. Military commanders don’t want to take untested technologies to war. The experimentation that TARDEC is funding, he said, “should break the ice,” particularly if the Army plans to install a hybrid-electric engine in the Future Combat System. The service does not want the FCS to be the first hybrid-electric fielded vehicle that the troops ever operated.

Many of the hybrid power drives the Army is testing claim about 10-25 percent more fuel efficiency than conventional diesel power packs, particularly in frequent start-and-stop scenarios.

To lower the fuel consumption more drastically, the Army will have to consider using fuel cells, experts noted.

Hydrogen fuel cells are a tough sell, however, said McClelland, because the Army wants to be able to power them with existing fuels, rather than hydrogen. “We are not even close to having a fuel cell that can burn Army tactical fuels,” he said. Altogether, the Army is spending $10 million this fiscal year on fuel-cell research, development and testing.

The commander of TACOM, Army Maj. Gen. N. Ross Thompson III, estimated that fuel cells are about five to six years away from achieving the maturity needed for military tactical applications. “But fuel cells are the way of the future,” he said.

Fuel cell technology also is being funded under the 21st Century Truck program, co-sponsored by the National Automotive Center, along with the U.S. Departments of Energy and Transportation, the Environmental Protection Agency and the U.S. trucking industry. The project seeks to develop commercial technologies that will cut the fuel consumption and emissions of heavy-duty commercial trucks and buses.

Under this program, General Dynamics C4 Systems recently installed a 5-kilowatt fuel cell—made by Acumentrics Corp.—on an experimental truck. The fuel cell will act as a battery charger to electrify the air conditioning and other utilities when the vehicle is parked.

Fuel-cell technology is expected to mature further under the Army’s Objective Force Warrior program, a modernization project to equip infantry soldiers with advanced lightweight weapons and sensors. Among the more promising technologies is a methanol fuel cell currently in development. The fuel cell would help eliminate at least 6-10 pounds of batteries that each soldier must carry for a 72-hour mission, said an industry source.

Many Choices Available
Incorporating hybrid-electric platforms in the Army’s vehicle mix will not be a simple yes-or-no decision. There are multiple variants of hybrid vehicles, each possibly suited better for specific applications, said experts. More than likely, the Army will need a combination of vehicle types to be able to accomplish its diverse combat missions.

A case in point is the Army’s medium truck, the FMTV. There are now three different hybrid-propulsion designs being tested.

Two are called “series hybrid electric,” and one is a “parallel hybrid electric,” which has a mechanical link from the engine to the wheels. The third type is a “hybrid hydraulic.”

The series hybrid, which does not have a mechanical link to the power train, is viewed as more suitable for launcher applications, such as the HIMARS artillery launcher and the MEADS air-defense system, said Regis Luther, vice president of technology at Stewart & Stevenson, the manufacturer of FMTV.

Series hybrids tend to be lighter, Luther said, because they don’t have a mechanical drive train—only an electric power train. This technology offers better performance for operating the vehicle with the engine off, in a “stealth mode,” which is desirable for a weapons launcher, he said. “The vehicle would generate all the power required to run the launcher.”

The series drive also offers more flexibility in the vehicle design, Luther said. “You can locate the wheel motors toward the end of the axles. Depending on the suspension, it can free up additional space for parts of the launcher system or electronics for the radar.” From a “packaging” perspective, he said, “the series system would be most amenable to the launcher,” which has to be C-130 transportable. Two types of series drives are now being tested: one was developed by Allison Transmission Co. and the other by BAE Systems.

The parallel hybrid is heavier, but offers some advantages, Luther said. The mechanical link operates more efficiently in line-haul cargo trucks. “Weight is less critical in a cargo application than a launcher,” he said. Theoretically, the parallel drive offers “higher reliability,” said Luther, because “you have two ways of powering the vehicle—if one failed, the other one would work.”

This month, the Army will begin testing the BAE Systems series hybrid-electric on a 5-ton FMTV. “As of now, there are no commitments for production orders,” said Larry Stone, a BAE Systems spokesman. “If they materialize, it probably will be around 2005.”

The hybrid hydraulic drive also has a mechanical link in the power train. The primary difference between this vehicle and the hybrid-electric is in the media used to store energy. Hybrid electric drives store the energy electrically, in a battery or capacitor. In the hybrid hydraulic, the energy is stored in a hydraulic recuperator.

The system being demonstrated on an FMTV truck is called “hybrid regenerative drive system,” designed by Permo-Drive Technologies. During a line-haul operation, a hybrid-hydraulic system can increase the acceleration and regenerative braking capability, which reduces fuel consumption, said Luther. “One of the things you notice is a dramatic improvement in acceleration over a conventional power train. That pairs nicely with the requirements in a launcher, where a high performance vehicle may be more desirable.”

In anticipation of future business opportunities, Stewart & Stevenson is working with other companies to develop a “fourth generation” hybrid electric drive, which would be lighter than current systems, he said.

For the time being, Luther noted, it makes sense for the FMTV program to test a variety of technologies, because the Army may not be able to meet all its needs with one type of truck. “What we are finding is that there may not be one simple answer that fits all applications.”

The Army still has a few years to ponder its choices. “It is possible that hybrid technology could be introduced during the next six years ... as a variant of the FMTV for specific applications,” he said. So far, “it looks as if different drives can be optimized for different uses.”

Even if the Army wanted to operate a fleet of mixed parallel and series hybrid-electric vehicles, some components could be standardized. Both could use the same energy storage media—batteries or capacitors—if they improve enough, said Luther. Portions of the control system also could be standardized. “There would be slight differences, not unlike those found between manual and automatic transmissions, coupled with a specific type of engine.”

Another consideration is cost, he added. In the absence of mass commercial production, the Army can expect to pay big money for hybrid trucks. “Based on penetration in the commercial market, one system may become less expensive.”

Oshkosh Truck Corp., meanwhile, has introduced its own hybrid-electric vehicle design. The company is competing against Stewart & Stevenson for a four-year new production FMTV contract.

The Oshkosh technology, called ProPulse, uses a modular series-hybrid drive. A diesel engine powers a large electric generator, which provides direct power to the wheels, eliminating the torque converter, automatic transmission, transfer case, and drive shafts. The company claims that ProPulse technology can increase fuel economy by up to 40 percent over conventional power trains. When traction drives are disconnected, the alternator can generate up to 500 kW of electricity.

On the light-truck front, the Army is testing four Humvees equipped with a hybrid-electric drive made by PEI Electronics. AM General Corp., the manufacturer of the Humvee, expects that there will be a competition later this year for the design and development of eight hybrid-electric trucks, said a company official. A production decision is not anticipated until at least 2005, he said. If the technology works as promised, the Army could end up buying between 5,000 to 20,000 hybrid-electric Humvees, to be used in tactical applications such as air-defense and artillery.

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