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Hydraulic Hybrids

November 9, 2011

By way of Instapundit, a report on a new approach that combines internal combustion engines with hydraulic systems powered by pressurized air.  This hybrid recaptures braking energy otherwise lost as heat (nothing groundbreaking there) to pressurize the hydraulic fluid.  This design is perfect for buses, garbage trucks, etc. – large, heavy vehicles that make frequent stops thus maximizing the energy released from breaking. The vehicle is the work of Altair Product Design, as reported by Wired:

“Primarily it has to do with power density,” said Tim Smith, director of design engineering at Altair. “The best diesel-electric hybrid can only recover 25 percent of the braking energy. The limitations are that you just can’t charge the batteries fast enough to take all the potential energy that’s available in a braking event. You can charge them at maximum rate and the rest of the energy goes out as heat.”

In some applications, such as a city bus that is constantly slowing and accelerating, a hydraulic system allows for greater, and faster, accumulation of energy.

“With hydraulic, we’re able to recover 75 percent of the braking energy to be utilized for the next launch event,” Smith said.

HHV system diagram from EPA

UPS rolled out a number of early model versions of HHVs several years ago ( the illustration above is from the UPS design), but this is an upgraded technology.  Although it is ideal for large vehicles, Chrysler and other manufacturers are trying to find a way to utilize the technology, or parts of it, in passenger vehicles.   Another advantage of this system, not mentioned in the linked article, is that it does not require any exotic production materials or techniques.  Not only are hybrids and electrics dependent on rare earth metals for their fabrication, they are also relatively energy intensive in their construction, making their total lifetime energy use surprisingly high (although not, as once reported, greater than that of a Hummer).

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