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While the electrical and mechanical components of
hybrid vehicles are reasonably mature, the main obstacle for full Hybrid Electric Drive
(HED)
maturation with the military are the batteries. The main drawbacks
of current batteries are their sensitivity to extreme environmental
conditions (heat, freeze, humidity). To prevent freezing the batteries
are contained in an environmental chamber, which maintains the
temperature at operational conditions. This method enables the vehicle
to operate from -40C to +65C degree temperature range.
Battery cost is another aspect causing slow adaptation
of HED. Current designs are using lead-acid, which are widely
available and lower-cost batteries. Nickel Metal Hydride (NiMH)
batteries provide twice the energy storage of lead-acid, but only half
the power surge, therefore, they can drive a vehicle twice as far but
not as fast. Lithium-Ion cells are delivering the highest performance
but their cost is still prohibitive for mass-production. Fuel cells
are also considered, but such technology is still far from maturation
for large scale applications.
Lithium-ion batteries would give a vehicle four times
the energy capacity with power density equal to lead acid. They could
also power a command and control shelter for 12 hours. The cost of
such batteries is still too high and current battery research is
examining issues such as the cost of raw materials, materials
processing, cell packaging, and module packaging in an effort to make
the process more economical. R&D is also addressing lithium-based
battery performance limitations, which include the reduction in
discharge pulse power at low temperatures and the loss of power over
time. Lithium Technology Corporation and T/J Technologies are
developing such large format rechargeable Lithium batteries, under a
$5.1M U.S. Army TACOM Life Cycle Management Command contract.
Another aspect of the new hybrid and electrically
powered vehicles will be the power management. Although these vehicles
will pack significantly more power than current vehicles, they will
also consume more power – by employing more sensors, radios,
computers, active suspension systems, electric gun turrets,
nuclear/biological/chemical protective systems and other mission
equipment. Future vehicles could also mount electrical armor
protection, which will significantly increase power demands. These
future vehicles will require an automatic load management, matching
power demands with resources, drawing available power from generators,
batteries and other sources.
HED Providing Mobile Power
The use of HED powered vehicles in power generation
role is evaluated by the ONR under a 3 year program focusing on 20,
30, and 60 kW power generation provided by modified Humvee and MTVR
vehicles. The biggest generator typically towed by a Humvee provides
15 kW. In contrast, the hybrid Humvee demonstrator can produce 75 kW.
When supplemented by common lead-acid batteries the vehicle can
provide 500 to 600 kW. This capacity opens new opportunities for the
employment of power-hungry weapon systems – such as a mobile
solid-state 100 kW laser currently under development. Another program
will evaluate the RST-V capability to convert as a 60 kW mobile power
generator, thus reducing battlefield logistical tail.
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