Petro-Hydraulic Vs. Petro-Electric Hybrids

[Punx0r]

I'd never even heard of petro-hydraulic hybrid passenger cars until I stumbled onto this today: http://en.wikipedia.org/wiki/Hybrid_vehicle#Petro-hydraulic_hybrid

I wouldn't have imagined a hydraulic drive in a passenger vehicle would ever be efficient, but it seems it can be.

Advantages appear to be:

Cheaper than an electric hybrid
75% efficient regenerative braking
Recovery of energy from suspension
No battery service-life worries
Unaffected by ambient temperature like a battery

The fuel economy figures quoted seem very good, at least comparable to something like a Prius, if not better. Does any one have better figures for comparison?

 

[nicobie]

Nice read. Thanks.

 

[Martin A]

Check this out:

http://www.gizmag.com/hydraulic-hybrid-transmission-artemis/11118/

 

[Ykick]

20-30 years ago I saw something like this intended for city busses. Hydrostatic wheel motors and high pressure storage tanks - the idea being to capture fuid pressure generated from stopping using the wheel motors and release the energy back into the motors to help get it rolling again.

The system I read about used a small diesel engine to maintain system pressure. For the right situation it could probably provide a service but there were shortcomings. What about back-up brakes? The expense or wheel motors, high pressure storage, pumps, etc?

 

[Punx0r]

Thanks for the link, Martin.

Ykick, seeing as hydraulic drive has been used on agricultural and earth-moving equipment for decades, I assume there's already any established fail-safe method of implementing hydraulic brakes. I guess they could be like air-brakes: loss of system pressure causes the brakes to automatically engage.

The petro-hydraulic system seems to have many of the same obstacles as petro-electric - namely that the layout of a traditional ICE car doesn't suit the hybrid technology. Instead of finding somewhere to put a large, heavy battery, you need somewhere to put a large, heavy hydraulic accumulator. In both cases the answer clearly seems to be to build it into the structure of the vehicle. That certainly sounds easier with a battery made of modular units than a carbon-fibre tank...