TRANSPORTATION /
Electrifying Transportation
Georgia Tech is helping design the electric and electric-hybrid vehicles of tomorrow
By Amy Stone
UNLIKE MEMORIES of the oil embargoes of the 1970s, the United States' reliance on foreign sources of fossil fuels has not faded, largely due to Americans' love affair with the car. This nationwide phenomenon causes an additional problem — pollution. In a project that will address both dependence on foreign oil and air pollution reduction, a group of researchers at the Georgia Institute of Technology is helping design vehicles of the future — electric and electric-hybrid vehicles.
courtesy of Solectria Corp.
Batteries and motors are hidden
beneath the standard-size bed of the Solectria electric pickup truck.
(Click on picture to see larger (58k) version.)
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Electric vehicles are quiet, generate no tailpipe pollution and would be the most efficient mechanism of transportation — but completely electric vehicles have some design hurdles that must be overcome before they can be mass produced. Hybrid-electric vehicles, a cross between electric vehicles and those that use internal combustion engines, run more cleanly than conventional internal combustion vehicles while maintaining the extended range that travelers have come to expect.
An added benefit of hybrid vehicles is that they could run on domestic fuels, such as ethanol, methanol, natural gas, propane or biodiesel. Therefore, pursuing the development of both types of vehicles simultaneously is wise, considering their differing strengths.
"Hybrid vehicles are more expensive because they have many redundant parts when compared to purely electric vehicles," says Robert Michelson, principal research engineer in the Georgia Tech Research Institute's (GTRI) Aerospace and Transportation Laboratory, and manager of the electric and hybrid vehicles program. "Therefore, the first users of this technology will be those who find tremendous advantage in tripling the fuel economy, such as public transportation or the military establishment."
Already, researchers at Georgia Tech have a prototype hybrid vehicle, a city bus in Augusta, Ga., which uses batteries and burns hydrogen to produce electricity. This bus will furnish data on real-world running conditions, allowing researchers to fine-tune its workings.
Electric and hybrid-electric vehicles would offer benefits for many users, ranging from consumers' desires for a non-polluting, economical form of transportation to the military's need for quiet, energy-saving tanks. In fact, the military, through the Defense Advanced Research Projects Agency (DARPA), funds much of Georgia Tech's electric vehicle program.
Georgia Tech is collaborating with the Southwest Research Institute, the University of Hawaii, and the University of Texas to identify current and needed technologies and to model these technologies into a complete vehicle. The collaborating team shares the task of modeling the hybrid-electric vehicle, and Georgia Tech is responsible for the following areas.
One of the problems with using batteries as a power source is the length of time required to recharge them after they have been depleted of energy. Current modes of recharging can take up to eight hours, which creates problems for consumers used to jumping in their cars whenever they need them, or for soldiers who depend on the readiness of their vehicles for mobility and survival.
photo courtesy Edison EV
Drivers can charge their electric vehicles
at stations provided by Edison EV.
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Conventional attempts to quick-charge batteries have used high currents, which resulted in excess amounts of heat and vented gas, which in turn, damaged the battery. By using a pulsed current, in which very high charges are given for short durations of time to charge the battery, Ding's design minimizes the production of heat and gas as byproducts, increases the cycle life, and prevents the premature loss of battery capacity — a significant consideration since some lead acid battery packs can cost $1,500 to $2,000 and generally last about three years.
Additionally, being able to quick charge the batteries helps address the problem of limited endurance of current batteries. Current batteries can only propel a vehicle for about 80 miles due to their low energy density. Until new battery technology solves this problem, the ability to quickly recharge current batteries will ease the strain of frequent chargings.
There is another benefit to being able to quickly recharge a battery: consumer acceptance. "If you make electric vehicles familiar to the user, consumers will accept the technology more easily," says Ding. "By charging the batteries quickly, it will be similar to filling a tank with gasoline."
New methods of charging batteries, such as Ding's, have been called "smart charging" because they will understand the state of the battery before charging and adjust accordingly.
From a theoretical point, one of the major limitations in the design of electric vehicles has been the lack of a model that would simulate battery use in real-world conditions. By collaborating with colleagues in the School of Electrical and Computer Engineering, Ding is helping to solve that problem by designing a model of battery power sources for electric and hybrid-electric vehicle designers and users (see "Modeling and Simulation," page 9). An additional problem is that there is no precise gauge to measure how much energy is left in the battery, as in the fuel gauge in a gasoline-powered automobile. Ding is also creating mathematical and real-time models of the average battery to develop a fuel gauge that takes into consideration temperature, speed, age of battery and driving conditions, allowing the user to know how much energy remains.
Another important component of designing an electric vehicle is the management of heat and cold. Dr. Krishan Ahuja, Regents researcher in GTRI's Aerospace and Transportation Laboratory and professor of aerospace engineering, along with graduate student Baha Suleiman, is developing a model that integrates heating, ventilation and air conditioning. The model does this by taking into consideration variables such as outside temperature, wind speed, location of the car (through the use of the Global Positioning System or by entering the latitude and longitude) and the number of passengers.
"Modern vehicles of the 21st century will be responsive to consumers' needs," says Ahuja. "For example, you park your car in the garage and it's -20 F outside. You want to get into a nice, cozy interior the next morning. Our model is capable of predicting how long it will take to reach a certain temperature. It will be possible to automatically turn the car heater on before you wake up, using the electric plug in the garage."
To develop the thermal load application, Ahuja and Suleiman divided the car body surfaces across which heat transfer takes place into many panels. They gathered information, such as wind speed and outside temperature, in order to calculate the energy balance — how much energy was coming into the car, in forms such as solar heat or radiation of body heat, and how much was leaving.
The calculations used in the approach will:
indicate how many watts of heat are needed to maintain a given temperature
in the vehicle's interior for certain conditions;
aid in decision-making about materials and insulation to be used when the
car is being designed;
allow future cars to automatically adjust to appropriate temperatures,
based on sensors and on-board computers.
"Additionally, this technology can be applied to military vehicles, such as tanks, helicopters, and submarines, and also to homes and large buildings," notes Ahuja.
Ahuja and Suleiman have just completed development of a theoretical model and computer code of their technique. The next step will be model testing in a wind tunnel, followed by similar testing using an actual electric vehicle, to validate their predictions.
Aiding all aspects of electric and hybrid vehicle creation is a simulator, created in collaboration with the Southwest Research Institute, the University of Hawaii and the University of Texas. Dr. Tom Habetler and his colleagues in Georgia Tech's School of Electrical and Computer Engineering have created the electrical components of the simulator, including the generator, motors and power electronics. The simulator allows people in the vehicle industry, such as engineers and manufacturers, to enter variables, such as weight of the proposed vehicle, the size of motors and their rated values, the voltage of batteries, and air and rolling resistance, among many others. The simulator then synthesizes the information and supplies predictions about the whole machine.
"You can even input how the driver positions the throttle, or gas pedal," says Habetler. "The simulator will help develop the battery, motor, controller, and integrated heating, ventilation and air conditioning models for the prototype vehicle."
The simulator is named PATHS, for Performance Assessment Toolbox for Hybrid Systems, and is programmed in Matlab/Simulink. Parts of PATHS have been uplinked to the national database in Hawaii and are already in use by certain military agencies.
Georgia Tech's electric and hybrid vehicle program has made great strides in a relatively short time. However, cautions Charles Stancil, chief of the Advanced Transportation Branch at GTRI, the bottom line is economic viability.
"This technology has to pass what we call the 'so what?' test, which means the models we develop have to be useable by consumers," says Stancil. "If not, people confronted with it will just say 'so what?'"
Additional activities on the electric and hybrid-electric vehicle scenes include the following:
Georgia Tech has been instrumental in fostering electric vehicle research
in the Southeast and has been an active member of the Southern Coalition for
Advanced Transportation since its inception.
Georgia Lottery funds totaling $170,000 were used to complete the new
"Advanced Vehicle Development and Integration Laboratory" located at GTRI's Cobb
County Research Facility. The money was used to buy test equipment and outfit
lab space into two reconfigurable bays for design, construction, and integration
of advanced air, land, and sea vehicles — especially unmanned systems.
The Georgia Department of Transportation has provided start-up funding to
Georgia Tech for a multi-disciplinary center called the Georgia Transportation
Institute, which will conduct research, development, education, and technology
transfer pertaining to all forms of transportation in the State of Georgia. The
Institute will coordinate and enhance the involvement of Georgia Tech and other
state universities doing research in transportation.
Further information is available from Robert Michelson, Aerospace and
Transportation Laboratory, Georgia Tech Research Institute, Georgia Institute of
Technology, Atlanta, GA 30332-0844.
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Last updated: Dec. 3, 1997