A fellow I used to work with at a tractor repair shop used to experiment with hydraulics, including using hydro drive on a pickup truck.
He approached several folks about this sort of use, but was turned away, even by the EPA (so he claimed... I wasn't there).
Now, the EPA has patented (fortunately, into the public domain) a hybrid hydraulic drive almost identical to what my old friend showed me, using
two tanks and a pump, with a small diesel engine driving the pump at its most efficient/clean rpms, storing the pressure in a nitrogen/5606 combination in a high pressure tank. When it was needed, the pressure would be released, through a hydro motor for propulsion, into a low pressure tank.
He was going to set it up for regenerative braking as well, though I didn't have all the details before moving to 'Bama.
So.... to the topic at hand... I'm wondering about trying a homebuilt version of this in my '86. Or... even building a 4x4 from the ground up (well... using one of our chassis, that is). I'd imagine such a system would make a great offroad machine, and once the kinks were worked out, a fabulously efficient overlander/offroad camper.
Anybody know anything about this stuff? It's about as far as you can get from my airplane wrenching experience, but I do have a little bit of hydraulics experience... just with aircraft landing gear and brakes. Simple, light duty stuff on the planes I'm used to.
I also considered using a smaller pump and a couple hub motors to provide some front drive to a stock 2wd truck. As a supplemental system, it could maybe be charged solely with regen braking. I'm not planning on this being a super-duper end-all solution right away. It'd be experimental, and would be more for education than for actual fuel savings, etc. Though... I'd hope to make a decent machine out of it eventually.