Al: I'm not very familiar with hydraulic hybrids, but the EPA appears to be saying here that the series hybrid is the way to go. Why series instead of a parallel hybrid (where the pump/motor connects to the driveshaft)? Is that configuration being considered as well?
Those look like some pretty high barriers to use in smaller passenger vehicles: difficulty in shrinking everything into a smaller package, and especially the noise. No matter the frequency, some of us definitely don't want a lot of noise and find any highly irritating. And for others of us, we need to hear what kids or other people are saying inside the vehicle, so adding noise to the internal environment sounds like an even worse idea. I hope the auto makers considering the use of this technology in passenger cars are going to do some thorough pre-market user studies.
The technology started in heavy equipment, such as John Deere's hydrostatic drive. Anyone who has operated equipment with and without hydraulic drive will swear by it. While my experience has been off-road use, I am optimistic about how on-road use will work. This could very well cause a paradigm shift for, at least, heavy trucks.The auto market could be a little more resistant though; it tends to be more traditional.
This is one of those "V-8 moments," where you think to yourself that of course it makes sense that hybrid drive trains come to heavier trucks. In large fleets, even small fuel savings add up. Indeed, the economics probably make far more sense than they do for personal passenger cars, where you have trouble amortizing the cost of the vehicle versus the fuel savings. Not so in heavier trucks in large fleets, where the numbers work out much more quickly/easily.
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