NuVinci CVT hub

[Miles]

Thanks for that link, flecc - much more useful than the video.....

 

[Flying Kiwi]

I think the blue arrow path shows it better on this link, as the two diameter points of drive transfer can be seen better than in the video, which I also found poor.

Thanks flecc, that does make it clearer. My email to the company has been sent. Certainly it has the capacity to be very efficient due to its extremely small, inflexible contact area and consequently low friction. Miles, just as a train wheel on a rail wastes much less energy than a truck tyre on a bumpy road, thats the key to its efficiency.

My concern would be over its robustness given the extremely precise tolerances that would be needed in manufacturing and the high stresses it would need to be preloaded with. Just as trains rely on their weight for traction, those disks would have to be squashing the balls considerably if they're not to slip. The bit about the solidification of the fluid inside was also unclear. If its a lubricant then it will encourage the balls to slip on the disk, if its not, the rotating balls will wear through their axles/bearings. I have the general gist at least but I still prefer the idea of the Swizzbee arrangement (other than the fact it contains derailleur gears).

 

[flecc]

I agree on the pressures involved Flying Kiwi. While I also agree about the rail analogy, I'm far from convinced about the efficiency with that fluid pressure system. The fluid compression forces involved on all those contact points of the balls would add up to a considerable total and the pressures would generate heat, itself an indication of lost efficiency. On a bicycle that would be unwelcome, and on the larger vehicles they project it for, the pressures and heat generation would be very high. All in all, I don't think we'll be seeing that much of it in practical applications.

 

[Flying Kiwi]

I'm far from convinced about the efficiency with that fluid pressure system. The fluid compression forces involved on all those contact points of the balls would add up to a considerable total and the pressures would generate heat, itself an indication of lost efficiency. On a bicycle that would be unwelcome, and on the larger vehicles they project it for, the pressures and heat generation would be very high. All in all, I don't think we'll be seeing that much of it in practical applications.

I just think of it operating without the fluid having any significant effect - after all what happens when there's fluid on a rail line (such as leaf juice)... It would depend on the viscosity and other properties of the fluid as to how much energy is taken up, just as its easier to use an egg beater in water than in treacle. I see an increase in efficiency compared to a standard bevel or helical gear train (particularly one with plastic or nylon gears). The contact area looks to be smaller than where gears mesh and I suspect it's more rolling contact and less sliding. It would certainly be alot more efficient than belt CVTs (which have been used in fairly recent low power cars).

 

[Miles]

Miles, just as a train wheel on a rail wastes much less energy than a truck tyre on a bumpy road, thats the key to its efficiency.

Maybe, but 97%.... I'm sorry, that figure doesn't seem credible, even at 1:1.

 

[flecc]

Yes, I'm certainly no fan of belt CVTs.

I still have many question marks on that point contact transmission though. If I eventually see it successfully in long term production applications I'll have to concede, but I'm not holding my breath.