TEG

For a mild hybrid that just captures braking energy and uses it to restart the gas motor and pull away from a stoplight (but with very little range from regen recapture), a hydraulic pressure hybrid system is an interesting alternative to an electric system.

Some links:


NextEnergy - Hydraulic Hybrids
A New Wrinkle in Hybrids Does Away With Batteries - New York Times
http://www.epa.gov/otaq/technology/420f04024.pdf
EPA Displays the First Advanced Hydraulic Hybrid Vehicle
Ford Invents Hybrid that is 300% more efficient than Toyota Prius
http://www.designnews.com/index.asp?layout=article&articleid=CA6451735
Hybrid-hydraulic powertrain generates worldwide interest - 06/29/05
Hybra-Drive.com

mt2

A Ford F-150 getting 60 mpg city? That's impressive. Of course it does squat for the highway mileage. The good news is that this can be easily incorporated into existing production lines and can greatly improve the efficiencies (and financial bottom line) of fleet vehicles. Think 'garbage truck'.

The bad news is that it will be used to justify buying a Canyonaro to haul the kids to Cub Scouts.

__________________
Mark Tomlinson
"I am not a trouble maker; I'm a catalyst for change."

JRP3

I'm very skeptical of most of the efficiency claims for hydraulics. Since hydraulic fluid is not compressible the hydraulics are not actually containing any energy, it has to be a pressurized gas system or something like that. It might be good for stop and go traffic in large vehicles but won't do much once you go any distance.

tonybelding

It could be either a compressible gas (like air, remember the Air Car?) or it could be the walls of the storage tank that are elastic. If you are stretching the walls of the tank, then the tank itself is the energy storage device and the hydraulic fluid merely transfers energy to and from it.

JRP3

Don't get me started on the ridiculousness of the "Air" car. The inefficiencies of using a power source to create electricity, to then compress air with an air pump that has the same frictional losses as an ICE, then decompress it in a motor with the same frictional losses as an ICE, etc. Then you have people running around all excited by a car that runs on "AIR".
Anyway, back on topic, I think the hydraulic systems I've seen use nitrogen as the compression gas.

mt2

From Wikipedia
The hydraulic fluid you buy at an auto parts store is designed not to compress. The fluids used in hydraulic regenerative braking are chosen to compress. The term hydraulic does not imply a particular type of fluid.

__________________
Mark Tomlinson
"I am not a trouble maker; I'm a catalyst for change."

tonybelding

I've never heard of a compressible liquid. It's hard for me to picture how that could work.

JRP3

I'm sorry but I'm pretty sure you're incorrect. Follow some of the links in this thread and you'll see they are specifically using nitrogen gas as the compressive medium, not the hydraulic fluid. Unless they are mixing the gas into the fluid, which doesn't make much sense, and still would be the gas that's compressing not the fluid.

mt2

Yeah, I knew that. But I edited the word "gasses" out of my post and put in "fluid" because it fit with the Wikipedia snippet better. The engineers in my family are always correcting me on such things. I can ruin an entire Thanksgiving dinner by saying something about "centrifugal force".

Point is that a hydraulic system doesn't mean they use hydraulic fluid from Auto Zone.

__________________
Mark Tomlinson
"I am not a trouble maker; I'm a catalyst for change."