By Matthew L. Wald, June 25, 2006
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 Washington last week was equipped with a prototype hybrid system using hydraulic fluid and a high-pressure pump instead of electrical current and a generator. In this design, energy is stored in a series of pressurized tanks, rather than in nickel-metal hydride or lithium-ion batteries; the energy moves not as high voltage current in copper wires but as hydraulic fluid pressurized to thousands of pounds per square inch.
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 Ark of oddball vehicles, began its experiments in the 1930’s with electric vans.
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.