Hybrid electric power trains may revolutionize today's ground
passenger vehicles by significantly improving fuel economy and
decreasing emissions. The NASA Lewis Research Center is working
with industry, universities, and Government to develop and demonstrate
a hybrid electric vehicle. Our partners include Bowling Green
State University, the Cleveland Regional Transit Authority, Lincoln
Electric Motor Division, the State of Ohio's Department of Development,
and Teledyne Ryan Aeronautical.
The vehicle will be a heavy class urban transit bus offering double
the fuel economy of today's buses and emissions that are reduced
to 1/10th of the Environmental Protection Agency's standards.
At the heart of the vehicle's drive train is a natural-gas-fueled
engine. Initially, a small automotive engine will be tested as
a baseline. This will be followed by the introduction of an advanced
gas turbine developed from an aircraft jet engine. The engine
turns a high-speed generator, producing electricity. Power from
both the generator and an onboard energy storage system is then
provided to a variable-speed electric motor attached to the rear
drive axle. An intelligent power-control system determines the
most efficient operation of the engine and energy storage system.
Hybrid electric power trains offer several advantages for vehicle
performance and emissions. First, the load seen by the engine
is decoupled from the short-term power requirements of the vehicle.
With constant load, the engine can be designed to operate nearly
continuously at its highest efficiency point. In addition, the
size of the engine can be reduced significantly in most vehicles
to the long-term average value of power. The electric drive train
provides additional benefits by eliminating losses in the fluid
couplings of conventional automatic transmissions. Finally, electric
drive trains can recover energy as the vehicle brakes, further
improving fuel economy. Gas turbines offer the additional benefits
of being lightweight, using multiple fuels, and having high reliability
and very low emissions.
In addition to initiating and coordinating the overall project,
the NASA Lewis Research Center is performing much of the system
engineering for the vehicle's electrical power system. A computer
program called Hybrid Electric Vehicle Analysis (HEVA) has been
developed to calculate vehicle performance and power requirements.
Lewis is also developing the power control software and integrating
an advanced capacitor system for energy storage. In addition,
Lewis combustion test facilities are being used to support the
gas turbine engine development. Initial operation of the prototype
vehicle is scheduled for the First Quarter of 1997.
Potential markets for this vehicle include regional transit authorities
in both the Northeast and California, who have already shown a
great interest in fuel-efficient, low-emission transit buses.
In addition to city transit buses, this technology has applications
for many other ground vehicles, including automobiles, delivery
vehicles, municipal waste trucks, school buses, and shuttle buses.
Manufacturing methods developed for these markets will also return
benefits to the aerospace industry through lower cost engines
for small aircraft.
Previous articleLast updated May 1, 1997
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