Air-defense and missile-firing configurations of the Army’s
Humvee truck would be ideal candidates for a novel propulsion system
known as hybrid-electric drive, officials said.
Customized trucks that carry anti-ballistic missile interceptors,
such as the Army’s theater high-altitude area air defense
(THAAD), could benefit from this propulsion technology, which provides
a quiet ride and generates additional electrical power, said Army
and industry officials. Other specialty trucks where hybrid-electric
propulsion would make sense, for the same reasons, are the Striker
fire-support vehicle and the LOSAT (line-of-sight antitank) missile
platform.
The Striker surveillance and targeting vehicle, built on a Humvee
chassis, consists of advanced sensors, communications systems and
a machine gun. The LOSAT kinetic-energy missile is used by light
infantry units and also is mounted on a Humvee.
The Humvee is the Army’s high-mobility multipurpose tactical
wheeled vehicle.
All three special configurations of the Humvee are “possible
users” of hybrid-electric propulsion, said Randall Gaeremick,
deputy for systems acquisitions at the Army’s Tank-Automotive
and Armaments Command.
Although hybrid-electric designs for passenger cars and mass transit
buses have proved successful, officials noted that military vehicles
present a host of unique demands.
Having a large electric-power source onboard would help meet the
high energy demands of vehicles such as the THAAD, Striker or LOSAT
platforms, said Ken Winters, vice president of PEI Electronics,
in Huntsville, Ala. The company developed a hybrid-electric propulsion
system for the Humvee.
A hybrid propulsion unit includes a conventional engine, generator,
a battery pack and electric-drive motors.
The Army currently is testing two hybrid-electric Humvees at the
Aberdeen Proving Ground, in Maryland and at the Nevada Automotive
Test Center. The plan is to build eight to 10 more prototypes by
2002, Gaeremick said at an industry conference in Monterey, Calif.
A heavier truck, called the “extended-capacity” Humvee
also is being tested with a hybrid-electric drive and could be available
by 2004.
The new vehicles are funded under two separate programs. One is
managed by the Humvee original manufacturer, the AM General Corp.
PEI provides the power-train components that are needed to convert
Humvees to hybrid-electric drive, Winters said in an interview.
The other contract is with the Army’s Tank-Automotive and
Armament’s Command’s research and development center.
One of the two existing prototypes is a Humvee with a four-motor
drive. An individual motor drives each wheel. “That gives
it the highest possible performance we can get in that vehicle,”
said Winters. “It’s very efficient for operations in
sand, mud, because you get very good traction when the wheels are
controlled individually, rather than going through a mechanical
differential.”
The second prototype is a utility Humvee, with a two-motor design.
It has 30 percent less horsepower and uses a mechanical differential.
“It doesn’t have quite the mobility or the performance
of the four-motor drive,” said Winters. “But it is still
better than the standard Humvee.”
The next set of vehicles will be more sophisticated, he said. They
will incorporate advanced features that the Army is considering
for its next-generation Humvee, the A4 model. “We’ll
incorporate lessons learned from the testing from the first two
vehicles,” said Winters.
PEI officials hope to receive a production contract in mid-2004
or 2005.
Customized systems such as THAAD, Striker and LOSAT make fitting
candidates for hybrid-electric Humvees, which come with a 75-kilowatt
generator and large battery pack, he explained. “When you
are not driving the vehicle, you can use that electric power for
other applications.”
If the Army deployed a mobile tactical operations center, for example,
soldiers could draw power from the vehicle rather than bring a generator,
Winters said. “It’s a logistics savings. It allows you
to plan on the move. It reduces logistics footprint and saves weight.”
The unanswered question, however, is cost. “We really don’t
know yet,” said Winters. Companies often are reluctant to
divulge cost information about technologies that are still experimental.
Several industry sources said it would be reasonable to expect
that a hybrid-electric vehicle would come with a 20 percent cost
premium. Winters said that the savings from not needing an additional
electric-power generator will not be enough. “This vehicle
is too expensive to justify it only as a generator.”
“The product is becoming more mature,” Winters said.
But, “there is a lot of design work left to do.”
With a conventional engine, he said, a standard Humvee gets eight
miles per gallon (driving on hard roads at convoy speeds). A hybrid
vehicle would double the fuel economy to 16 miles per gallon.
For quiet operations, the vehicle can operate with electric power
only. It can run 20 to 25 miles on electric power before it has
to be recharged. The system can be recharged directly from the generator.
In addition to the 75-kilowatt engine generator, there is a 24 kilowatt-hour
lead-acid battery pack. “That’s sufficient reserve power
to drive the 20 to 25 mile range,” said Winters. “If
you are driving slower, you can get more range.”
Operating as a hybrid, with a 24-gallon tank, a truck could travel
375 miles without refueling. A conventionally-powered vehicle, he
said, will not make it past 275 miles.
The four-motor Humvee can accelerate from 0 to 50 miles per hour
in 7 seconds, Winters said. A standard vehicle does it in 15 to
16 seconds.
A conventional Humvee can achieve a 60-percent grade at a speed
of about 5.5 miles per hour, he noted. A hybrid vehicle can make
the 60-percent grade at about 17 miles per hour. “All this
reflects the increased horsepower,” said Winters.
“Mobility [in the hybrid] is much better than in the standard
Humvee,” he said. The drives on the wheels are electronically
controlled with software, “so we actually control the amount
of drive torque going to each wheel independently. If we see that
one of the wheels is starting to slip, we can reduce the torque
to that wheel, depending on the soil conditions.”
But hybrid-electric vehicles have been dismissed for not being
rugged enough. Critics, for example, have cautioned against the
hybrid drive’s lack of endurance in harsh weather conditions.
Winters conceded that batteries freeze and stop working in extremely
cold weather. “We designed this vehicle with an environmental
chamber built around the batteries, so we heat and cool the batteries
as necessary.” The system, he said, will work within the minus-40
to plus-65 degree temperature range.
The vehicle and the batteries are sealed, so Winters expects that
they will survive through 60 inches of water. “We haven’t
tested that yet. We don’t see a problem with that in the production
version.” There are still some technical problems that have
to be resolved, he said. “We have to go through the engineering
process and finish the design and testing.”
Winters hopes that, if the Army decides to fund a modernization
program to upgrade old Humvees, it will consider using the hybrid-electric
drive. “We design a kit, with all the parts necessary to convert
it from a standard drive to a hybrid vehicle. It’s an assembly
kit that can be inserted by the vehicle manufacturer or it can be
done as an after-market modification at [an Army] depot.”
Convincing military customers that they should adopt this technology
will take time and “education,” said Winters. “There
is an educational process to allow potential users to understand
how it’s used in the field. It takes a while to understand
the differences” between the performance of conventional vehicles
and hybrid-electric ones. “We have to go through that process
so [military officials] understand how to write requirements,”
he said.
Armored Vehicle
A hybrid-electric armored vehicle, meanwhile, is being developed
by the U.S. Army’s National Automotive Center and United Defense
LP (UDLP).
According to UDLP officials, the technology to make a hybrid armored
combat vehicle will be available for mass production in about two
years. The company built a hybrid-drive 15-ton prototype that was
on display at the Army’s winter convention in Ft. Lauderdale,
Fla. The demonstrator was based on an M113 armored personnel-carrier
chassis.
“The centerpiece technology of the demonstrator is the propulsion
system,” said Tim Balliett, from UDLP. In a published report,
Balliett and colleague Max Dodd explained that the propulsion system
consists of two 250 horsepower oil-cooled electric motors to drive
the sprockets, a battery pack for energy storage and a diesel-powered
engine-driven generator housed in the prime power unit (PPU).
“When the vehicle is being accelerated, power is provided
simultaneously from the battery pack and from the engine-driven
generator,” he said. “When the vehicle is operating
at normal speeds, the PPU is providing the average electric power
needed to drive the track sprockets and auxiliary equipment.”
The batteries provide transient power needs, such as accelerating,
steering and climbing, and store the energy produced when the brakes
are applied. “By using batteries to supply the transient peak
power demands, the engine can be made much smaller than that required
for a conventional combat vehicle,” Balliett said.
The demonstrator is capable of about 10 miles of silent all-electric
propulsion. If stationary, it could perform in an extended “silent-watch”
mode for 24 hours or more depending on the equipment installed,
he said. When stationary, the vehicle can generate about 200 kilowatts
of electricity and function as an auxiliary power unit.
“Relative to the M113A3, its closest conventional cousin,
this vehicle will produce nearly 500 horsepower in acceleration
versus 275 horsepower for the M113A3,” Dodd said. “This
500 burst horsepower is achieved by supplementing the conventional
engine’s generated power with the energy stored in the battery
pack.”
The hybrid-electric power train, he added, opens up more interior
space for payload. Since there is no power pack in the front of
the vehicle, the driver and commander sit roughly side by side,
Dodd said.
This prototype vehicle, unlike the conventional M113, has a one-piece
rubber “band” track, molded from rubber with bonded
steel reinforcement. UDLP officials said this track, compared to
conventional steel track, is more durable, weighs less, generates
less heat and noise and provides a one-piece assembly, for easier
maintenance.
“I think we will see something dramatic [in hybrid-electric
technology] during the next three to seven years,” said Robert
G. Bohn, chairman of the Oshkosh Truck Corp., in Wisconsin. “The
technology is working. ... Safety factors are starting to dissipate,”
he told the 2001 conference on tactical wheeled vehicles sponsored
by the National Defense Industrial Association.
The Army plans to continue to experiment with hybrid-electric vehicles.
Next fall, there are plans to introduce a hybrid-electric version
of the heavy expanded-mobility tactical truck (HEMTT) made by Oshkosh.
John Stoddart, the company’s vice president for government
programs, said the vehicle will be unveiled in October during the
Army’s annual convention in Washington. The Oshkosh- designed
drive, called ProPulse, will offer more “tactical mobility”
than other hybrid vehicles, Stoddard said.
Instead of batteries, he said, the system uses ultra-capacitors,
which are high-performance electric energy storage devices. “Batteries
are heavier, don’t last as long, require more maintenance,”
he said. The ProPulse drives will be introduced in the company’s
fire trucks during the next two years, he said.