The stated window for time to market of 3..5 years has not quite expired yet, so maybe they're having, uh, development problems.

... which would not be surprising. I recall seeing section drawings of at least a hundred similar tilting-ball CVTs, few of which got very far past the first prototype. I'd guess that durability issues associated with contact stresses did them in.

Contrast that with the (VW?) steel belt CVT, the first one good for more than a few miles of use, and AFAIK the basis for most/all current production CVTs.

Mike Halloran
Pembroke Pines, FL, USA

"It will be late in this decade before the product is introduced to the heavy-duty truck market"

Previous versions of this have failed at the contact point between the rotors and the ball or wheel. If you can solve that then they work quite well - low power ones are used in some electric motor transmissions for industrial installations.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

Looks like it may have made it to production for bicycles.
Fallbrook calls its bicycle system NuVinci.
https://www.amazon.com/NuVinci-N360-rear-hole-silv...

Primemovers are actually a good market for novel transmissions, since historically they have been plug and play so far as engines and transmissions go. So if this unit doesn't work out it is no great trauma for the owner to replace it with a standard unit.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

I will never understand how anyone with any understanding of torque transfer would even try to design something to transfer many hundreds ft/lbs of torque on such an infinitesimal small contact point that also has close to zero friction ie no teeth to engage and bathed in a lubricant. The pressures involved would have to be in the thousands of tons range for it to even come close to working a little bit. This is one of those typical designed on a computer cad system deals that looks real cute and that is about it. And gee didn't we already have a cvt of sorts the day the torque converter was designed? Lose the belts and the balls, minds well have the slush its simpler.


Edit I remove "and" after Gee.

Well, I drove the Perbury box in 1981, long before CAD became commonplace. That was a very similar concept.

It's like the wankel engine, it seems to have some significant benefits but has one major point of difficulty. Solve that and you are quids in.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

I think the reason Allison was interested in this CVT design is for use as a variable speed drive for automotive superchargers or engine driven accessories. It's compact and efficient, but it does not have the capability to scale up well to the torque levels required for most auto/truck transmission applications.

there are some more of these types of transmission around and none has actually it made to the market yet in big numbers. the great idea behind it all is to have a large range of transmission rations within a small space and with very little slip or frictional losses. in practice that yet is still very difficult if not impossible to achieve.

durability is the main problem, and also lack of suitable lubricants for this specific purpose. the power transmitting balls need to be lubricated to prevent excessive friction and at the same time when torque needs to be transferred the lubricant more or less needs to freeze in place stopping momentarily when the lubricated mating parts need not move relatively to each other. that calls for a socalled traction fluid where the viscosity temporarily can go very high if enough pressure is applied.

various oil companies work on developing suitable fluids, with only limited success so far. for the Nuvinci bicycle drive a naphthenic oil is used - the viscosity rises quite a bit more then with the paraffinic or synthetic baseoils used in most modern lubricants when pressure is applied.

I think Fallbrook has done a fairly decent job with their CVT for engine driven accessories. For these applications it has satisfactory ratio range, efficiency and durability. The only issues that have not been fully resolved are cost vs. benefit, and added complexity.

Valvoline partnered with Fallbrook to develop a traction fluid (Invaritorc 638) specifically for their small CVT drives.

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