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First thing. You should not consider hydraulic versus electric hybrid. When battery technology gets to the point where you have the range and long life necessary then battery electric may end up as the primary means of transportation.
It's not an either or situation, but the best method or combination of methods that get us to energy independence. To ignore any means or method that would get us there is short sighted.
The issue then could be a combination of battery electric and hydraulic power train systems.
For a regeneration and power reapplication cycle hydraulic wins. Its important to consider the additional fact that a pure hydraulic power train, eliminates a lot of components in the power train itself.
The small hydraulic motors at each wheel would weigh the same as the brake components they would replace, leaving only the necessity for an emergency brake in the event of a total (quadruple redundant) system failure.
Consider the KERS systems used in the Formula 1 cars. It uses a torovec IVT and a small flywheel spinning at 60k RPM to store 60 KW of power for a few seconds. A race was won recently using that system, so that shows that systems can be made light enough to provide an advantage in the most lightweight and competitive racing situations.
Its easy to build a system for heavy trucks, but if you check the prior link you will see a direct comparison of two identical vehicles, one with a conventional power train, the other with a series hydraulic hybrid power train that replaces the conventional system. The fuel economy improvement is a 50% reduction in fuel consumption.
Parker Hannifin is trying to encourage development of ultra lightweight hydraulic hybrid power trains by sponsoring the "Chainless Challenge". This is an event where university students design bicycles with hydraulic power trains. If you can build a bicycle with a hydraulic power train, you can certainly build a car. In fact very light cars are in the near future with hydraulic power trains, and the performance will be exhilarating as well as very efficient.
regards
Mech
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