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EPA invents battery-less hybrid system
Hybrid drivetrain uses compressed fluid instead of electricity. To be tested on UPS trucks.
December 22, 2005: 10:31 AM EST
By Peter Valdes-Dapena, CNNMoney.com staff writer
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NEW YORK (CNN/Money) - The Environmental Protection Agency says it can help drivers save fuel. It has said that for a long time, of course, but this time it's not talking about providing fuel mileage data for car shoppers. It's talking about a new invention created in its own Ann Arbor, Mich. research laboratories

Called hydraulic hybrid technology, the system uses energy stored up during braking to help propel a vehicle during acceleration. The energy is stored in pressurized hydraulic fluid, the same sort of fluid used in brake lines and for power steering.

Ordinarily, when a driver applies the brakes in a car the energy removed from the vehicle's forward motion is simply lost as heat through the car's brake pads and rotors.

In gasoline-electric hybrids, like the Toyota Prius, some of that energy is recaptured through generators that charge batteries that, in turn, can help provide supplementary power to the vehicle.

In the EPA's hydraulic hybrid system, braking pressure is used to power pumps that compress hydraulic fluid. This stores energy in the same way you would if you squeezed a spring with your hands. When needed, the pressure is released and the expanding hydraulic fluid is used to power gears that help turn the vehicle's wheels.

Also, just as a gasoline-electric hybrid's gas engine can charge the batteries directly during highway cruising, the hydraulic hybrid's engine can also pump up the pressurized fluid tanks as the vehicle drives.

The EPA holds about 20 patents for technology used in the new system, said Margo Oge, director of the EPA's office of transportation and air quality.

While the EPA labs in Ann Arbor, Mich., are better known for creating new fuel mileage and emissions tests and standards, in recent years the labs have also begun working on creating new technologies for cleaner and more fuel-efficient vehicles.

The EPA began working on the system about 10 years ago, said Oge, under a Clinton administration program to research clean energy technology.

Pros and cons

There is a major advantage to the EPA's new system and one major disadvantage, the agency said. The advantage is its simplicity and relatively low cost. The system would cost an estimated $600 to install on a mass-production basis, the agency estimates, compared to $3,000 to $6,000 for an electric hybrid system.

The disadvantage is the system's weight, the EPA says. According to a 2004 EPA report, a hydraulic hybrid SUV would weigh about 190 pounds more than a conventional SUV. That means the EPA's system is most applicable to trucks where the added weight would make a smaller overall difference, the agency said.

The added weight of the system is similar to the weight of an electric hybrid system, although the EPA itself cites weight as a disadvantage.

Like gasoline-electric hybrids, hydraulic hybrid vehicles would see greater fuel savings in stop-and-go city driving than in steady highway cruising.

While the system could pay for itself in as little as a year in a heavier vehicle like big four-wheel-drive SUV, it would take at least four years to pay for itself in a midsized car, according to the EPA's report.

Still, the EPA says, that's a shorter payback time than drivers of gasoline-electric hybrids will see.

The EPA's system was demonstrated at an engineering conference last year on a prototype Ford Expedition SUV and will be used next year in at least one UPS delivery truck next year.

The UPS truck could get as much a 70 percent increase in fuel efficiency in city routes, the EPA estimates, and the added cost of the trucks should be paid off in fuel savings in about 2.5 years.

All these vehicles are diesel powered. Diesel engines are inherently more fuel efficient, to begin with, than gasoline engines. The use of diesel also allows the EPA to show off "clean diesel" technology it has also developed in its laboratories.

The system is currently being developed in partnership with International Truck and Engine Corp., Eaton Hydraulics, Parker Hannifin Corp., which specializes in making hydraulic controls, and the U.S. Army.

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