inside the nuvinci hub

camlifter · #1 08-08-2010, 06:09 PM

heres some pics of the hub, don't know if this is the right section for it, but since we don't have a hub section and some morini guys are using it i'll put it here for now. crap, pics are small. hit view and zoom to 400%
i'll try and get some better pics up, but for now i'll try and explain what i've found, i posted before that my hub broke and quit working, well after taking it apart i found nothing wrong inside. this thing is made very heavy duty and there are few moving parts, it should be able to handle lots of power. there is no direct conection of any of the parts inside, it all runs from fluid pressure of which there is only about 2 oz. of fluid. whats happening in mine is the fluid has over heated and broken down and can no longer work the hub, like an auto trans that slips from burnt fluid, the piece in the 3rd pic is kind of like a clutch pack, when the fluid thins out that part can skip from lack of pressure holding it against the plate it drive and it makes a skipping sound and the hub no longer works, if i put new fluid in this thing it should work again but will most likely soon over heat and kill the fluid again. the fluid does all the work and i need to find a way to keep it from over heating.

Goat Herder · #2 08-09-2010, 08:22 PM

What kind of sediment was in the fluid. There is a point in time with a automatic transmission on cars that you don't service them or they will slip.[the only thing keeping it then going at that point would be the old clutches broke down in the fluid] When a said transmission needs rebuilt.

One of my prob's is keeping mine in the gear I chose under load.

camlifter · #3 08-10-2010, 06:20 AM

there was nothing in the fluid or hub to indicate wear but i'm sure the fluid has broken down. i'm working on getting some better pics, there is no clutch type material of any kind in the hub, all metal to metal, there is a one way sprag on each side of the balls. the ball unit is fixed to the axle and does not turn, the hub rotates around it. the shifter turns a shaft with a worm gear on the end which moves the spool in the center back and forth to tilt the balls, if it's changing gears without any input from the shifter the shaft must be loose or the worm gear worn.
i need to find out how much clearance they have built into the whole stack hight of parts. it seems to me that they have more than needed so that if you over power it the sprag unit will jump over it's ramps there by saving it from any damage, once the fluid breaks down theres enough clearance for it to jump and slip.
also the sprag unit has ramps and notch's that only have rollers in every other one, looks like adding the missing rollers and adding a shim to the clearance would make it stronger. all this will make more sense once i can show some better pics.

GearNut · #4 08-10-2010, 09:39 AM

Verry, verrrry interesting!!
I am watching this thread!

Goat Herder · #5 08-11-2010, 09:46 PM

Any more progress? I am posting these two links in hopes there may be another hub out there that has not been discovered?

Two speed motorcycle hub transmission - Patent 4083421
Sheldon Brown's Gunnar Street Dog Left Drive, 3-speed, Fixed-gear Bicycle

Kevlarr · #6 08-11-2010, 10:24 PM

From what I read and watching the Nuvinci video there isn't supposed to be actual metal to metal contact between the balls and the rings, the fluid actually becomes a solid when it goes between the balls and ring causing drag which makes the whole thing work.
So if that's the case maybe when the fluid breaks down it no longer provides the friction needed to transmit the power from one surface to the other.

camlifter · #7 08-12-2010, 06:01 AM

Quote:

Originally Posted by Kevlarr

From what I read and watching the Nuvinci video there isn't supposed to be actual metal to metal contact between the balls and the rings, the fluid actually becomes a solid when it goes between the balls and ring causing drag which makes the whole thing work.
So if that's the case maybe when the fluid breaks down it no longer provides the friction needed to transmit the power from one surface to the other.

thats correct, and since theres only about 2 oz of fluid it breaks down pretty fast in a high powered application, there also seems to be extra clearance built into it that lets the sprag unit skip when the fluid thins out, thats the noise i was hearing, the sprag skipping.
had a friend take some pics with his droid but theres some problem with emailing them, still working on more pics.

Pablo · #8 08-12-2010, 06:17 AM

What kind of fluid does Nuvinci recommend?

Goat Herder · #9 08-12-2010, 06:36 AM

Any distant pipe dream of reversing the NV you might see Cam? So's we can go left side drive? I am dieing to see some good close picts. Mine is still working don't have the heart to take it apart yet..

camlifter · #10 08-12-2010, 07:26 AM

if you were to lock out the freewheel in the hub and swap the sprag units it should work backwards, but then you would need to bolt a sprocket on the other side and use a freewheel pedal crank for normal bicycle mode. there are no gears of any kind in the hub, only the sprags drive it, there directional, only work one way, swaping them would let it drive the other direction.
they told me the fluid is made by valvoline just for them, they call it a traction fluid, it looks like B&M trick shift auto trans fluid.