Hydraulic hybrid engines: better than electric hybrids? [View All]

Does anyone know more about this system, and why it isn't in use more? Basically it works like a conventional electric hybrid, but instead of electricity stored in a battery, it stores pressurized fluids in a tank during breaking. During acceleration, the pressurized fluids are used for acceleration and reduce gas consumption.


The local newspaper was discussing work college students at the U of MN were doing on engines, trying to convert smaller car and truck engines to hydraulic hybrid drives, and stated you could see a 30% increase in fuel efficiency. They mentioned a 55% increase in the fuel economy of a converted Ford Explorer SUV, to 33 mpg. It seems that hydraulic systems would be more easily implemented than the electric systems currently used in hybrids today, not relying on a battery pack and such. What are the potential cons that are holding hydraulic hybrids back?