Hybrid trucks that blend electric motors with internal combustion engines promise
fuel efficiency, as well as plentiful, stealthy sources of electrical power
for battlefield sensors, weapons, and command and control systems.
The National Automotive Center, which reports to the Army Tank-Automotive and
Armaments Command, sponsored in recent years light, medium and heavy hybrid-electric
truck demonstrators. The upcoming Future Tactical Truck System (FTTS) Advanced
Concept Technology Demonstration will pursue motor, generator, energy storage
and power control technologies. According to NAC Deputy Director Paul Skalny,
“The beauty of doing it is we move from investment in components to full-up
systems in the hands of soldiers.”
The FTTS program will seek hybrid electric propulsion, intelligent load-handling,
diagnostics for two-level maintenance and other advanced truck technologies.
Phase I ACTD contracts cover modeling and simulation efforts for two versions—a
heavy (Class 7-8) maneuver sustainment truck and a lighter (Class 2B) utility
vehicle. The Humvee-like variant potentially could serve as a command and control
Phase II contracts, to be awarded in February or March 2004, are expected to
lead to vehicle deliveries in 2006. Program officials anticipate that multiple
contract winners will be asked to produce seven maneuver sustainment trucks
and 10 utility vehicles.
A Stryker brigade squad with seven maneuver sustainment and two utility demonstrators
will assess FTTS technologies in the field. “You focus on what you can
do with technologies to impact both the current force and the future force,”
According to the Defense Science Board, fuel takes up about 70 percent of the
logistical tonnage in a heavy armored division. The Department of Defense estimated
that a gallon of fuel, if flown into the theater, can cost up to $600. The Army
expects hybrid-electric trucks and the hybrid-electric Future Combat Systems
(FCS) to help the service attain its stated objective of 75 percent lower fuel
consumption by 2020.
One-off demonstrators show promise, contractors said. Oshkosh Truck Corp. expects
its ProPulse hybrid-electric HEMTT (Heavy Expanded Mobility Tactical Truck)
to burn up to 40 percent less fuel than a conventional HEMTT, depending on the
Under contract to Boeing and SAIC, BAE Systems demonstrated a hybrid drive
on an FMTV (Family of Medium Tactical Vehicles) truck. “If you don’t
see 30 to 35 percent [better] fuel efficiency, you probably don’t have
it adjusted properly,” said Cliff Plummer, manager for advanced military
systems at BAE.
While the pricetag of hybrid-electric propulsion is tough to justify in peacetime,
Skalny believes that “in wartime, there is a big payback.”
Fuel is a cost-driver for both the Army and the commercial truckers. NAC representatives
routinely meet with the trucking industry to keep pace with commercial hybrid,
electric developments. “We’ve always taken the approach that the
big bang for the buck will be how we leverage off industry,” says Skalny.
Hybrid-electric drives achieve greater efficiency in stop-and-go mission profiles
than they do in long-haul commercial duty cycles. The regenerative braking that
recovers and stores power as electrical energy stretches fuel farther, and electric
motors can generate instantaneous power for better off-road maneuvering.
Hybrid trucks can also generate “exportable” power to run other
equipment. The biggest generator typically towed by a Humvee provides 15 kW.
In contrast, the hybrid Humvee demonstrator—developed by PEI Electronics—has
a 75 kW generator resident in the vehicle. Common lead-acid batteries could
also supplement the generator and give the vehicle 500 to 600 kW. A hybrid-electric
Humvee exhibited at the Association of the U.S. Army annual convention carried
a mockup of a 100 kW laser.
With hot, noisy truck engines turned off, the batteries, ultracapacitors or fuel cells of hybrid-electric vehicles
provide “silent watch” power in stationary vehicles to avoid detection.
Another benefit is the stored energy. United Defense estimates its hybrid-electric FCS-W (Future Combat Systems—
Wheeled) demonstrator can travel 5 miles per hour for 30 minutes on level ground
using only stored electric power.
General Dynamics Land Systems integrated hub-mounted electric motors on an
8X8 combat vehicle and incorporated the technology in a 4X4 reconnaissance,
surveillance and targeting vehicle that the company is marketing to the military
While motor and generator technology are relatively well established, fuel
cells and other hybrid vehicle advances are farther from production. One goal
of the FTTS ACTD is to design an open drive architecture able to accommodate
advancing technologies. “I think it’s fair to say that the investments
we’ve made over time are what we’ll see in the Future Tactical Truck
System,” says Skalny.
The Army also is evaluating hybrid-electric commercially based tactical trucks
(COMBATT) or severe off road vehicle (SORV) demonstrators from General Motors
and Daimler Chrysler.
GM estimates its diesel-electric Chevrolet Silverado can improve fuel efficiency
25 to 40 percent. Driven by a 210 hp diesel engine or a 5 kW fuel cell, a split-power
continuously variable transmission with integral electric motors sends power
to the wheels. The regenerative fuel cell electrolyzes water and stores the
hydrogen in a metal hydride container. With the engine shut off, the fuel cell
serves as an auxiliary power unit. With the diesel running, the generator system
provides up to 30 kW exportable power.
Daimler Chrysler’s COMBATT C-11 hybrid-electric truck gets about 15 percent
better fuel efficiency than a conventional Dodge Ram 2500, the company says.
At rest, the C-11 powertrain generates 12.5kW continuous or up to 30kW peak
The modified heavy-duty pickups will be available commercially in 2004, and
the NAC is proposing a partnership to build up to 50 vehicles for an operational
assessment in 2005. While the Army has no requirement for a COMBATT or SORV
as of yet, the service and other government agencies may find such vehicles
on the GSA schedules attractive for administrative or non-tactical roles. COMBATT
hybrid electric technology may also be applicable to light, medium and heavy
Despite their clean-power potential, fuel cells still require long-term development
to cut their cost and improve their durability. They also fall short of chemical
batteries and ultracapacitors for quick bursts of power. Under contract to AM
General, PEI Electronics equipped four XM1124 Humvees with a hybrid-electric
drive with one 75 kW generator, two 75 kW propulsion motors and conventional
lead-acid batteries. “We have to be very sensitive to the initial cost
of the vehicle,” says Ken Winters, PEI vice president.
The cost of batteries rises with their performance. Nickel metal hydride batteries
would provide twice the energy storage capacity but half the power surge of
lead-acid batteries to drive the hybrid Humvee twice as far but not as fast.
More advanced but less available lithium-ion batteries would give the vehicle
four times the energy capacity with power density equal to lead acid. They could
power a command and control shelter for 12 hours.
The Army cancelled funding in fiscal years 2005 and 2006 for hybrid Humvee
production qualification testing, initial operational test and evaluation, and
logistics. The demonstrators nevertheless achieved impressive performance. With
their lead-acid batteries, they doubled the acceleration and attained higher
speeds than conventional Humvees.
Following two proof-of-concept vehicles, four hybrid-electric Humvee demonstrators
underwent testing at Aberdeen and Yuma Proving Grounds and Fort Greeley, Alaska.
Two remain at Fort Benning, Ga., for continuing tests, and two more are being
refurbished in Huntsville, Ala., pending future Army decisions.
Energy storage remains the principal challenge for integrators of hybrid electric
trucks. “The batteries are the long pole in the tent,” says Plummer,
of BAE Systems. “We don’t have batteries that could last the length
of time we’d like to see them last.”
The company drew upon its experience with aircraft control laws to maximize
the energy density in the lead-acid batteries of the Hybri-Drive already used
in New York City buses. A two-wheel drive hybrid FMTV truck was built under
contract to Stewart and Stevenson in 1999. The six-wheel-drive hybrid prototype
that BAE developed under the FCS Boeing contract recently completed 5,000 miles
of performance tests at Aberdeen Proving Ground with acceleration and fuel economy
better than conventional diesel FMTVs, Plummer said.
The two-motor series hybrid-electric drive in the truck is similar to the single-motor
Hybri-Drive used in buses. While the civilian bus uses an air-cooled generator,
the hardened truck uses a liquid-cooled generator that enables the FMTV to wade
through 30 inches of water.
The FMTV power module can provide 200 kW of continuous exportable power, but
future combat vehicles—packed with electronic systems—will require
smart power management. The sensors, radios, computers, active suspension systems,
electric gun turrets, nuclear/biological/chemical protective systems and other
mission equipment on future vehicle can double the power demands on a hybrid-electric
drive system. The ideal solution will automatically manage the load on available
resources, and draw power from generators, batteries and other sources.
Oshkosh Truck Corp. successfully used Maxwell Technologies ultracapacitors
in its HEMTT LAS proof-of-concept demonstrator to store the energy of regenerative
braking without batteries. In 2001, the National Automotive Center gave Oshkosh
a grant to integrate the company’s ProPulse hybrid-electric drive into
the so-called Transformation HEMTT. While the Army’s next-generation HEMTT
A3 is not yet definitely a hybrid-electric vehicle, Oshkosh officials say that
the ProPulse technology can help increase vehicle performance.
The first of six or seven hybrid-electric HEMTT pre-production test units will
be demonstrated during the next two years. Compared with the proof-of-concept
vehicle, the production hybrid HEMTT would have ruggedized components, to meet
military specifications. While the demonstrator has one electric motor per axle,
a productionized vehicle might use one motor per wheel end.
The proof-of-concept vehicle uses a 450 hp constant-speed diesel engine to
power a 335 kW electric generator. The generator in turn provides direct power
to the truck wheels without torque converters and other heavy transmission components.
Electrochemical ultracapacitors store energy as an electrostatic charge in
a polarized liquid layer between an electrolyte and an electrode. They can be
used with chemical batteries in hybrid electric vehicles. “The capacitors
are much better-suited to giving up and receiving large quantities of energy
in a short time,” says Gary Schmiedel, Oshkosh director of advanced products
Less vulnerable to extreme cold than batteries, ultracapacitors can last the
life of the vehicle. The ultracapacitors in the proof-of-concept vehicle are
expected to last 10 years, but the goal is 20 years. The technology in the Transformational
HEMTT improves acceleration and grade-climbing performance compared to the standard
truck, says Schmiedel.
The proof-of-concept vehicle has already powered hospital and airfield equipment,
and a production hybrid-electric truck would have an engine sized to Army requirements.
Unlike commercial hybrid vehicles that typically use smaller engines to maximize
fuel economy, the hybrid HEMTT uses the same size diesel as a conventional HEMTT
to preserve the original performance envelope. The 450 engine gives the demonstrator
335 kW of exportable power. A 505 hp engine could generate 400 kW. “We’re
engine-neutral,” says Schmiedel.
The hybrid-electric drive with ultracapacitors makes it possible to run the
engine at the most efficient speed, regardless of the road speed of the vehicle,
he adds. It also makes it possible to tune the engine exhaust system to minimize
noise signature when the engine is running. Engineers can bury hot mufflers
and manifolds deeper in the vehicle to reduce infrared signatures.
Fuel-efficient, low-polluting hybrids have special commercial appeal in the
stop-and-go duty cycles of municipal refuse trucks or “Wall-Mart Cycle”
distribution trucks. “We always invested or partnered with industry because
we knew where industry was moving,” says Skalny.