Hybrid Cars: Renewed Pressure for Fuel-Efficient Vehicles
Wu, Corinna, Science News
Renewed pressure for fuel-efficient vehicles
The moment automobiles rolled into people's lives, forward-thinking engineers began to dream about "the car of the future." For some, the phrase conjured up an image of a vehicle replete with all the comforts of home: a television, a refrigerator, a bed--maybe even the kitchen sink. For others, the car of the future resembled a sleek, aerodynamic egg zooming around in eerie silence.
The cars we actually end up driving by the turn of the century might not seem like anything special on the outside, but they'll have radical differences--as the salesmen say--under the hood.
In response to government mandates, auto companies are racing to manufacture cars that get markedly increased fuel efficiency and emit fewer pollutants than today's cars. To achieve these goals, researchers are assessing ways to power automobiles with electricity and alternative fuels. So far, though, all such systems have failed to meet drivers' needs.
Many engineers believe that the most promising, environmentally friendly car will be the hybrid electric vehicle (HEV), a car equipped with both a gas engine and an electric motor. Universities, federal and state governments, and automakers are already collaborating to build commercially acceptable HEVs by 1998.
Several years ago, the California legislature adopted a resolution requiring the seven automakers selling the most cars in the state to make 2 percent of those vehicles emissions-free by 1998. By 2003, that mandate will rise to 10 percent. Only electric cars are truly emissionsfree, but they carry the stigma of being practical only for short trips.
Alternative fuels such as methanol and natural gas produce fewer harmful emissions than gasoline, and researchers have built engines and cars that use them. Scientists are also looking seriously at fuel cells, which combine hydrogen and oxygen to produce energy, as a clean source of vehicle power. But even if automakers modify commercially produced cars to run on alternative fuels, the cars won't catch on in a big way until drivers can fill them up at the corner gas station. Currently, over 33,000 vehicles in the United States run on natural gas. By 1997, the Department of Energy plans to have 250,000 alternative fuel vehicles of all types in federal, state, and local fleets and--equally important--over 1,000 refueling stations.
For the near future, the combination of a gas engine and an electric motor may make the HEV the best of both worlds. For those family trips to Yellowstone National Park, an HEV's gas engine gives it the range of a regular car, but during the daily rush-hour commute, its clean electric motor keeps pollution to a minimum. And refueling is no problem; it simply means a visit to a gas pump and an electric outlet. Still, engineers must surmount many technical challenges before HEVs can find their way into the average garage.
HEVs come in two basic types, depending on whether their gas engine and electric motor work together in series or in parallel. In a series hybrid, the electric motor powers the vehicle and the gas engine runs mainly to charge the battery. In a parallel arrangement, both the engine and the electric motor can drive the car.
Each design has advantages and disadvantages. For a series hybrid, "the electric motor has to be big enough to achieve the kind of performance you want from your car," says Jeffrey W. Hodgson of the University of Tennessee in Knoxville. "In the parallel arrangement, the car can be driven by the electric motor and by the engine, so you don't need as large or as powerful an electric motor. . . as you would with the series arrangement."
The location of the components is a bit trickier in the parallel hybrid, since both the engine and the motor have to drive the car's wheels. And coordinating the switch between the two mechanisms requires more sophisticated computer controls. …