While the commercial hybrid vehicle market is geared toward fuel efficiency,
reducing fuel consumption is not a driving factor in the military’s pursuit
of alternatively fueled tactical vehicles.
The benefit of military hybrid vehicles, officials say, is the ability to generate
power and reduce heat and sound signatures, rather than fuel economy.
The Army, Navy and Marine Corps are interested in acquiring a hybrid-electric
version of the High Mobility Multipurpose Wheeled Vehicle, or Humvee. In these
vehicles, pneumatic and hydraulic systems are replaced by cleaner and more efficient
electric devices, said Mike Gallagher, program manager for Marine Corps expeditionary
power systems.
The Army wanted to know “how much of [a] conventional Humvee could [it]
keep and still make it a hybrid,” said Scott Doudna, of the Army Tank
- Automotive and Armaments Command.
The Army has invested $4.5 million in the development of four hybrid Humvee
test vehicles. The service has identified a potential of 20,000 trucks that
could be converted to hybrid electric, said Doudna at an industry conference
in Norfolk, Va.
If tests continue to go well, the Army could award a contract to Humvee manufacturer
AM General this summer, said Doudna.
The Office of Naval Research and the Defense Advanced Research Projects Agency,
meanwhile, are jointly funding the RST-V program, a hybrid electric vehicle
designed by General Dynamics for reconnaissance, surveillance and targeting
missions. DARPA is funding 60 percent, said ONR’s Mike Byerly.
“Even though we started way earlier than the HE-Humvee program we are
a little bit behind,” said Byerly.
Early analysis showed that even if every Humvee and Medium Vehicle Tactical
Replacement (MTVR) truck were converted to hybrid, it would only save about
2 to 4 percent of the fuel requirement of a Marine expeditionary force going
ashore, Gallagher said.
Even though fuel savings may be negligible, Gallagher said the Marine Corps
wants to move away from the “diesel river”—or long fuel supply
lines.
The Army’s version of the hybrid Humvee showed an increase in fuel economy
over a standard version during mission profile testing, Doudna said. However,
he agreed with Gallagher that fuel economy is “not a driver for the hybrid
in the military.”
The Army’s hybrid-electric Humvee and the Navy’s RST-V both have
been undergoing testing at Aberdeen Proving Grounds, as well as Yuma Proving
Ground and other test sites, to examine acceleration, speed, and ability to
be transported on aircraft. The HE-Humvee must be able to demonstrate power
generation capability, fuel consumption reduction and that it can fit on a C-130
transport aircraft.
With a special kit, the vehicle did fit inside a C-130, Doudna said.
The RST-V faced a more daunting challenge. Not only did it have to be able
to haul around enough equipment for a 10-day mission, but it also had to fit
inside the V-22 Osprey, without slowing down the tilt-rotor craft, said Byerly.
“It’s difficult to get on the V-22,” he said. “Unfortunately,
a V-22 is very narrow.”
To work around this problem, the RST-V was fitted with an innovative suspension
that can shrink the width of the vehicle from 70 inches to 62 inches, Byerly
said.
The payoff for military hybrids is their ability to generate power for on and
off board uses and to reduce the vehicle’s thermal and acoustic signature,
Doudna said.
In earlier tests, the HE-Humvee was able to generate 35 kilowatts of DC power,
he said.
“It was purposely designed for that,” Doudna said. “It can
get up to 75 kW.”
In one test, the vehicle produced 15 kW of power for eight hours. In a second
test, it generated 30 kW for another eight hours, Doudna said.
The RST-V was able to run on batteries only, or silent mode (no engine noise),
for 23 miles, Byerly said.
Later this year, the RST-V will undergo testing to convert the vehicle into
a 60-kilowatt mobile generator, Byerly said.
But a hybrid RST-V may not be in the Navy or Marine Corps’ future, Byerly
noted. The cost of the vehicles’ battery system “would add a tremendous
amount to [the] production cost,” he said.
“The only benefit is the silent mode,” he added.
Both the HE-Humvee and the RST-V did come close to meeting performance predictions.
Doudna said testers had predicted the Army’s hybrid would be able to
accelerate from 0 to 30 miles per hour in 7 seconds. It actually took the hybrid
almost 10 seconds to reach 30 mph. The vehicle fared worse when going from 0
to 50 mph. Testers had predicted the hybrid would be able to hit 50 mph in 22
seconds, but it actually took almost 31 seconds.
Doudna acknowledged that the actual numbers were a bit higher than what was
predicted. “In an effort to spare the battery pack and get a longer life
out of it, we sacrificed acceleration,” he said.
The HE-Humvee reached a top speed of almost 58 mph, better than predicted,
but still slightly slower than a standard Humvee, Doudna said. It was able to
fully ascend and descend a 40 percent grade, but failed to climb a 50 percent
grade, Doudna added.
The vehicle encountered difficulties with its Auxiliary Power Distribution
System (APDS). The system uses DC power from the vehicle and converts it to
standards similar to that of the Tactical Quiet Generator. Doudna said there
was a lack of communication between the vehicle and the APDS.
The lack of communication was attributed to the absence of a link between the
HE-Humvee’s power train and APDS.
A second-generation APDS now being tested at Aberdeen does have a communication
link so that the vehicle can better respond to the power demands of APDS.
In speed tests, the RST-V topped out at 70 mph on a dry, level surface for
20 minutes with no malfunctions, Byerly said. It reached a top speed of 57 mph
on batteries alone, he added.
The RST-V also out accelerated a standard Humvee. It took the RST-V almost
four seconds to go from 0 to 30 (6 seconds faster than a Humvee) and 12 seconds
to go from 0 to 60 (14 seconds faster than a Humvee), Byerly said.
In April, at the Bosch Automotive Proving Ground in New Carlyle, Ind., the
RST-V ascended a 60 percent grade in all three modes—diesel electric (where
the engine powers the generator), battery only and then hybrid electric, Byerly
said.
One lesson learned by the RST-V team was that the vehicle suffered airflow
disturbance at high speeds that prevented the lower portion of the radiator
from getting air. That is because of the flat-nose design of the vehicle, Byerly
said.
The front of the RST-V may be redesigned to fix the problem, he said.
In the fall the vehicle will go through heat tests as well as operational evaluation
at Yuma Proving Grounds.
Two of the Army’s HE-Humvees have been delivered to Fort Benning, Ga.
One test vehicle, the HE-2, will continue testing at Aberdeen Proving Ground
and HE-3 is being refurbished.