How Chrysler's Hydraulic Hybrid Works: Energy From Pressure

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Chrysler's Sergio Marchionne & EPA Administrator Lisa Jackson announce hydraulic-hybrid program

Chrysler's Sergio Marchionne & EPA Administrator Lisa Jackson announce hydraulic-hybrid program

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Chrysler has come out of hibernation with a bang, as far as green and more fuel-efficient vehicles are concerned.

The company announced Wednesday that it would partner with the U.S. Environmental Protection Agency to build and test prototypes of a different kind of hybrid vehicle, one that accumulates energy not in a battery pack but by compressing a gas hydraulically.

CEO Sergio Marchionne joined U.S. EPA Administrator Lisa Jackson for the announcement, made at EPA laboratories in Ann Arbor, Michigan. They spoke in front of a silver 2011 Chrysler Town & Country minivan, representing one vehicle that would be tested with the new technology.

Chrysler's Sergio Marchionne & EPA Administrator Lisa Jackson announce hydraulic-hybrid program

Chrysler's Sergio Marchionne & EPA Administrator Lisa Jackson announce hydraulic-hybrid program

Enlarge Photo

Surfeit of hybrids

During the last 18 months, while the company restructured after its bankruptcy, integrated its product development with that of its new partner Fiat, and embarked on a crash program of refreshing its existing models, only a single "green" vehicle was known to be on the drawing board.

That's the low-volume electric conversion of the Fiat 500 minicar, which will be engineered in the U.S. for buyers here.

But in the space of only a week, Marchionne has said the company will launch a Chrysler 300 Hybrid by the end of next year and a hybrid minivan as well. The EPA announcement makes it a triple.

2011 Chrysler Town & Country

2011 Chrysler Town & Country

Enlarge Photo

Engine, but no battery

The system in question, originally developed at the EPA labs, uses engine overrun torque to capture otherwise wasted energy, as do conventional hybrid-electric vehicles. The engine is Chrysler's standard 2.4-liter four-cylinder, the base engine in its minivan line.

But rather than turning a generator, that torque powers a pump that uses hydraulic fluid to increase the pressure inside a 14.4-gallon tank of nitrogen gas, known as a high-pressure accumulator.

That compressed gas, stored at pressure as high as 5,000 pounds per square inch, represents energy waiting to be released. When the tank is sufficiently charged, that pressure is released to power a hydraulic axle motor that turns the wheels. The engine remains off as long as there's sufficient power to operate the motor.

Determining the possibility

Despite the hoopla around the announcement, though, any hydraulic hybrid minivan is still far from production. The partnership will simply "determine the possibility of adapting a hydraulic hybrid system" to certain vehicles.

Chrysler's Sergio Marchionne & EPA Administrator Lisa Jackson announce hydraulic-hybrid program

Chrysler's Sergio Marchionne & EPA Administrator Lisa Jackson announce hydraulic-hybrid program

Enlarge Photo

That translates to basic conceptual, design, laboratory, and prototyping work to reduce the system's size and complexity. Chrysler's projections say the system could raise fuel efficiency as much as 30 to 35 percent overall, and potentially more than double the city gas mileage. It would also be cheaper than a hybrid-electric system for the same vehicle.

The tests will be completed by July 2012, at which point Chrysler will decide whether the system is viable for production. If so, its next-generation minivans will be designed to accommodate the necessary tanks and pumps.

Garbage trucks, delivery vans

Presently, the few hydraulic hybrids on the road are found in large, heavy commercial vehicles where the cost of a suitable battery pack would be too steep. Garbage trucks, delivery vans, potentially even transit buses offer the best fit for the technology. The EPA is working with Eaton on such commercial-vehicle tests.

Hydraulic hybrids are not well suited to smaller vehicles--subcompacts to midsize--because the hydraulic equipment and storage tanks occupy too much space. For those vehicles, other technologies, from start-stop and smaller and more efficient engines to full electrification, make more sense to increase energy efficiency.

Chrysler's system, says the company, is destined for "large passenger cars and light-duty vehicles," meaning minivans and perhaps future delivery vans.

[EPA, Chrysler, Detroit News, Automotive News (subscription required)]

 
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