Not Fluid Coupling

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carvetia
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Joined: 22 Apr 2008, 10:51

Not Fluid Coupling

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I was wondering if any of you knew of any automotive (not marine & industrial) attempts, racing or otherwise, that used variable displacement axial pumps and hydraulic motors as a form of gearbox/transmission? That is, not hydraulics just as a clutch-like system. Would such a system ever be plausible with an ideal combination of fluids & motors? Or can the heat/friction issues not be overcome even with new materials, making them far too inefficient?

I don't have much knowledge on the topic so i was hoping someone could enlighten me or point me to some useful references ;) I assume there are good reasons for it's lack of practical implementations, but i'm struggling to find any reference at all to succesful hydraulic CVTs, bar Honda's HFT [warning .pdf!] and Hydro-Gear's system for lawnmowers! Obviously both companies are trying to sell their systems and thus aren't quick to shout about the limitations. By implication of their uses, obviously power transmission is a limitation, yet the devices seem very compact and thus surely have the potential to be scaled up.

People are always falsely claiming steps forwards with regard to CVTs as if it is some kind of holy grail, but the hydraulic principles are quite sound, hence my curiosity as to why it is not more actively developed?

Thank you for reading.

P.S. Found this other nice friendly page about the HFT.

riff_raff
132
Joined: 24 Dec 2004, 10:18

Re: Not Fluid Coupling

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carvetia,

There are many automotive CVT concepts that use variable displacement hydrostatic drives. Hydrostatic devices are used both in series and in parallel with conventional geared transmissions.

Parker Hannifin http://www.parker.com/portal/site/PARKE ... 021dac____ makes a series hydraulic hybrid drive for heavy trucks.

Steyer http://www.steyr-traktoren.com/Pages/en ... riebe.aspx makes a parallel (torque split) hydrostatic drive CVT for agricultural machinery.

Haven't seen anything for racing though.

riff_raff
"Q: How do you make a small fortune in racing?
A: Start with a large one!"

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mep
29
Joined: 11 Oct 2003, 15:48
Location: Germany

Re: Not Fluid Coupling

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