Continous variable transmission???

Over the years I got used to think that such a transmission would be no more
than another incarnation of perpetuum mobile. But recently I learned that
some quite serious people got on the task, with interesting results.

The links below I copy from uk.rec.cycling

See:

http://www.fallbrooktech.com/NuVinci.asp

http://www.evworld.com/view.cfm?sect...le&storyid=841

http://www.californiabicycleracing.o...interbike.html

So, what do you think?

Jobst?

Cheers,

Tomek Li

Tomek Li Wrote:

So, what do you think?
It'll be interesting to see how efficient a CVT can be. From memory, the
current gear with derailer configuration is around 95-97% efficient, ie
only 3-5% of your power is lost. I read somewhere a while ago that a
CVT is around 80%. OK for cars which have endless power (????), but on
a bike, you need some pretty good payback through weight or price if
you're losing 20% of your power through the gears.
Only once this is addressed, will it become viable.
I'll try and dig up my source to check the figures, but I'm pretty sure
it's somewhere in that range.


--
peterlip

"peterlip" wrote in message
news

Tomek Li Wrote:

So, what do you think?
It'll be interesting to see how efficient a CVT can be. From memory, the
current gear with derailer configuration is around 95-97% efficient, ie
only 3-5% of your power is lost. I read somewhere a while ago that a
CVT is around 80%. OK for cars which have endless power (????), but on
a bike, you need some pretty good payback through weight or price if
you're losing 20% of your power through the gears.
Only once this is addressed, will it become viable.
I'll try and dig up my source to check the figures, but I'm pretty sure
it's somewhere in that range.

Agree, the video attached to the website shows, that the whole gizmo is
based on friction rather than positive gearing. Friction like friction,
can't be really efficient...

The other issue - why would one actually need infinite number of gears? What
would be the gain here?

I understand a need for fully enclosed transmission, but that problem has
been already addressed quite succesfully with epicyclic gears.

The thing which worries me is that the guys who've made it seem to know
their craft, so how comes they are not aware of poor viability of the whole
project?

Cheers,

Tomek Li

Tomek Li wrote:

http://www.fallbrooktech.com/NuVinci.asp

So, what do you think?

Looking at the diagram at that web site, I'm trying to visualize how a
bicycle application would actually work. I guess a freewheel with a
single sprocket would be attached to the Input Disk, hub flanges to the
Output Disk and a friction lever would be used to move the Idler body
sideways along the axle to alter the gear ratio.

I'm not an engineer, so I have some (possibly stupid) questions in mind.
What sort of torque could a device like this handle without slipping? It
looks as if the efficiency could actually be pretty good, but I don't
see any numbers on the web sites you mentioned.

It looks pretty simple so it could probably be made cheap.

-as

"Antti Salonen" wrote in message
...
Tomek Li wrote:

http://www.fallbrooktech.com/NuVinci.asp

So, what do you think?

Looking at the diagram at that web site, I'm trying to visualize how a
bicycle application would actually work. I guess a freewheel with a
single sprocket would be attached to the Input Disk, hub flanges to the
Output Disk and a friction lever would be used to move the Idler body
sideways along the axle to alter the gear ratio.


http://www.evworld.com/view.cfm?sect...le&storyid=841

needs road testing with "production models"
checking on wither said balls agree at 5000 miles
or disagree with a concomittant increase in log friction
ever drive the jeep viscous transfer case? eehhhayyyahhahaha!

Tomek Li writes:

Over the years I got used to think that such a transmission would be
no more than another incarnation of perpetuum mobile. But recently I
learned that some quite serious people got on the task, with
interesting results.

The links below I copy from uk.rec.cycling:
http://www.fallbrooktech.com/NuVinci.asp
http://www.evworld.com/view.cfm?sect...le&storyid=841
http://www.californiabicycleracing.o...interbike.html

So, what do you think?

NuVinci is nothing new in CVT's. It has been used in places where it
works bes, low torque smooth continuous motion at a large ange of
speeds. I see no way of making it work reliably on a bicycle both
because it is not suited for the high torque (aka low speed) and
maintenance requirement.

You don't see this type of CVT in motor vehicles for good reason.
Expensive sports cars would not be invensting in 7-speed automatic
transmissions if it were so simple to use a CVT.

It isn't only bicyclists who beleive more gears will make then arrive
faster at their goal, but 30-speed derailleur gears is more than the
automotive people desire.

No one has shown that all these gears and ready access to constaznt
shifting has the vague benefites alluded to them.

http://www.sheldonbrown.com/brandt/continuous.html

Jobst Brandt

Tomek Li wrote:

Over the years I got used to think that such a transmission would be no more
than another incarnation of perpetuum mobile. But recently I learned that
some quite serious people got on the task, with interesting results.

http://www.fallbrooktech.com/NuVinci.asp

I have this terrible feeling of Deja Nu.
See http://www.nupace.com/

I don't see much advantage to continuous variability.
If it's at all less efficient or less reliable, why bother.

Reasonably small jumps between gears are available
with either derailleur or internal hub gearing.

Tom Ace

but if it did work.....

On Fri, 21 Oct 2005 22:43:25 +1000, peterlip
wrote:

It'll be interesting to see how efficient a CVT can be. From memory, the
current gear with derailer configuration is around 95-97% efficient, ie
only 3-5% of your power is lost.

How do losses through hub gears compare with that?