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Green
Tech A
New Wrinkle in Hybrids Does Away With Batteries By MATTHEW L. WALD Published: BY now, hybrid
vehicles are familiar enough that buyers find nothing peculiar about
a car's gasoline engine getting help from an electric motor. But just as
drivers have grown comfortable with concepts like regenerative
braking and issues like battery life expectancy, new types of
hybrids are emerging — including one that uses no electricity at
all. For instance, a
United Parcel Service delivery truck the government rolled out in
Standing next to
the truck painted with U.P.S.'s signature color, Stephen L. Johnson,
administrator of the Environmental
Protection Agency, said: "Brown is the new green." The Army is
testing a truck with similar technology and FedEx is watching with
interest. The E.P.A., which holds some patents on the technology,
has visions of full-size sedans that will go 80 miles on a gallon of
gasoline, with better acceleration and lower emissions, at a cost
premium so small that fuel savings will quickly pay for the hybrid
hardware. A hydraulic
hybrid is more specialized than the gasoline-electric hybrids sold
today. It works better on heavier vehicles, and in stop-and-go
traffic; backers say the ideal vehicle for this system is a garbage
truck, but that it could work well in vehicles as small as S.U.V.'s.
"We've
always said there's a lot of flavors of hybrid," said Bill Van
Amberg, executive vice president of WestStart, a government-industry
research consortium. The hydraulic
hybrid is conceptually similar to battery-electric hybrids like the Toyota
Prius or the Honda
Civic. It has an internal combustion engine, and its design
makes it possible to store power for a while before sending it to
the wheels. When the driver
presses the brake pedal, the storage system may engage, slowing the
vehicle by capturing the energy of its forward motion rather than
using the brakes. This design, known as regenerative braking, is
more efficient than conventional friction brakes which simply
convert the vehicle's momentum into wasted heat. The captured energy
can be stored and returned to the wheels when the traffic light
turns green. A hydraulic
hybrid has several advantages. One is that it can accept and deliver
huge amounts of energy quickly, which batteries cannot. And its
storage ability does not degrade over time, which is a fact of life
with batteries available today. Generally speaking, though,
hydraulic systems do not store as much total energy as an electrical
battery does, because the storage tanks are bulky. The U.P.S. van
has four "accumulator tanks" of 22 gallons each which can
be pressurized as high as 5,000 pounds. When fully charged, the
system holds 2,000 horsepower-seconds of energy, according to
Benjamin M. Hoxie, engineering manager for hydraulic hybrids at
Eaton, an automotive supplier that built the prototype, using
technology developed by the E.P.A.. Stated
differently, it could deliver 100 horsepower for about 20 seconds.
In electrical terms, that is less than half a kilowatt hour — but
no electric battery could absorb and deliver energy so quickly. When the truck
is in operation, its diesel engine runs a pump to fill the storage
tanks with fluid. The tanks contain nitrogen gas to When the driver
presses on the accelerator, pressurized fluid is released from the
high pressure tank and routed to the pump. The pressurized fluid
pushes a piston down in its cylinder, recycling some of the energy
to turn the vehicle's wheels. The company says
that because the diesel engine runs at constant speed, it will have
a head start in meeting the stricter pollution standards that take
effect in 2010. The prototype
truck has a 6-liter V-8 diesel engine but Eaton engineers say that
with the hybrid system it could use a much smaller engine and still
get the same performance; soon they will try a 4.5-liter V-6. But
even using the existing engine, the truck is expected save about
1,000 gallons of diesel fuel a year, the company says. Hydraulic
hybrids use technology that has been in service for decades, and
unlike a computer-controlled Prius, they might not require a
mechanic with an engineering degree to do repairs. "Mine can
be fixed by a 19-year-old," said James A. O'Brien, president of
Hybra-Drive Systems of Deerfield, Mich., who has converted a 1965
Volkswagen Beetle to a hydraulic hybrid as a test project. "It
can work with no electronics at all," he said. In fact, the
E.P.A. truck has no battery beyond the conventional one that turns
the starter motor and lights the headlamps. Simplicity
impresses Robert K. Hall, the fleet environmental manager for U.P.S.
His company, a veritable Noah's U.P.S., which
operates nearly 92,000 vehicles worldwide that cover two billion
miles a year runs about 1,500 alternative vehicles, most using
compressed natural gas or propane, but it also has tractor-trailer
trucks running on liquefied natural gas, delivery vans running on
fuel cells and conventional gasoline-electric hybrid vehicles. The
company calculated recently that its alternative fuel trucks had
driven 108 million miles since 2000. "Every one
we're running is working O.K.," Mr. Hall said. The hydraulic
hybrid, unlike the electric one, has "fittings and high
pressure hoses you can easily inspect to ensure they are functioning
properly," he said. FedEx is a bit
behind, but not much. Mitch Jackson, managing director of
environmental programs, said that hydraulic hybrids "have the
potential to play a very significant role." He said that the
systems had an advantage over alternatives in heavy stop-and-go
traffic. The Army, always
interested in technologies that would cut fuel needs on the
battlefield, has tested a heavy truck with hydraulic drive built in
part by Permo-Drive Inc., the American subsidiary of a company with
the same name in New South Wales, Australia. Jim Borovac, the
president of the subsidiary, said it allowed the use of a relatively
small engine, while the truck still had the power to accelerate up
steep grades. At the
introduction of the U.P.S. truck, Eaton announced that by next year
it would commercialize a related technology, a "hybrid launch
assist," which could be retrofitted on existing vehicles. It
would capture braking energy and deliver it to the wheels again when
it was time to accelerate.
©2006 Hybra-Drive Systems, LLC All Rights Reserved |