Quote:
Originally Posted by Old Mechanic
Ken, this discussion has me thinking. Best efficiency for a hydraulic accumulator is quoted (EPA) at 99%. Best efficiency for a hydraulic pump at 0-800 RPM is supposedly around 95%. Does this sound correct to you?
regards
Mech
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I think that 99% is high even for considering the accumulator from only from the "pure" physics (without flow losses in and out). I'd think that compressing the gas would cause a temperature rise that would (unless the tank is very well insulated) go off as waste heat (then the pressure would drop).
The 95% for an efficient pump sounds about right. (Most vendors will provide efficiency curves, etc. which show that the peak efficiency does not always hold up well for off-peak loads.)
I think that the UPS and Fed X trials with hybrids showed the electric versions to be more efficient. For garbage trucks, where the cycles are really short, hydraulics could work. Electrics (especially now with good batteries and controllers) are hard to beat, however. Hydraulic control tends to be lossy -- thus those heat exchangers.
But if you are thinking of experimenting it would be interesting to hear what you come up with. All sorts of interesting infinitely variable speed transmission possibilities, etc. Storage of a lot of energy is hard, but a hybrid in which the engine was smallish and the hydraulics did regen and acceleration could be interesting.
many years ago... many many years ago... A friend built a dragster powered by a VW 40 hp engine, driving a hydraulic pump. The pump charged an accumulator that was so big it was effectively the car's chassis. Four wheel motors made it go down the strip really quickly for a "VW". Simple control: "Open the big valve."
Cheers,
Ken