Our man Bruno, at the University of Michigan's Automotive Research Center, hipped us to the fact that the EPA has been playing around with hydraulic drive systems for a while. He notes, "They work especially well for larger vehicles, where batteries are becoming very expensive. Also, the large mass of SUVs & delivery trucks requires a very high rate of energy charge & discharge, which is where hydraulic accumulators excel in comparison to batteries." We still wonder why this system hasn't been adapted to cars, as it seems to us that while hydraulic fluid can be made recyclable, batteries inherently cause lots of waste. Not to mention that the electrocution factor's a lot lower when hydraulics are involved.
-Davey G. Johnson
Hydraulic Hybrid SUV [EPA]
Using Fluid to Save Fuel: The Intertial Storage Transmission [Internal]