Continous variable transmission???

Tomek Li said:

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" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Tomek Li said:

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 said:

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" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Tomek Li said:

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?section=article&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 said:

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.

Quoted message said:

The links below I copy from uk.rec.cycling:

http://www.fallbrooktech.com/NuVinci.asp
http://www.evworld.com/view.cfm?section=article&storyid=841
http://www.californiabicycleracing.org/news-archive/041031a_interbike.html

Quoted message said:

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 said:

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.

Quoted message said:

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.....

peterlip said:

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?

I don't know that it would work on a bike, but I love to floor my Saturn Vue and watch the tach jump up to 5500 rpm and stay there until I am going as fast as I care to...

The CVT is a significant part of why I bought my Vue. Since I read about automotive CVT's in Popular Mechanics back in the 70's I always thought they were neat. Of course there seem to have been issues with their implementation since they discontinued them.

dgregory57 said:

I don't know that it would work on a bike, but I love to floor my Saturn
Vue and watch the tach jump up to 5500 rpm and stay there until I am
going as fast as I care to...

The CVT is a significant part of why I bought my Vue. Since I read
about automotive CVT's in Popular Mechanics back in the 70's I always
thought they were neat. Of course there seem to have been issues with
their implementation since they discontinued them.

DAF couldn't manage to make them sturdy enough to be used with serious
engines, so they became known for bad performance, although it was more
the crappy engines and tiny cramped cars than particularly the fault of
the CVT. Also were mofos to maintain, originally. Plus DAF was just too
small a manufacturer.

Materials science has improved, and now they're extremely useful.

Jasper

Andrew Price said:

How do losses through hub gears compare with that?

See http://www.ihpva.org/pubs/HP52.pdf
for results of efficiency tests of several drivetrains,
some with derailleurs and some with internal hub gearing.

Tom Ace

Tom Ace said:

See http://www.ihpva.org/pubs/HP52.pdf
for results of efficiency tests of several drivetrains,
some with derailleurs and some with internal hub gearing.

Thanks.

quote='Tom Ace'Tomek Li said:

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.

Quoted message said:

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[/QUOTE]

There may be rare niches where the CVT has some advantages.
If a driveshaft bike were used, some CVT designs could used with the drivetrain direction changes, giving you the option of not having to suffer a cascading of both inefficiencies on top of one another-the drive shaft inefficiencies would not be added to those from the CVT.

Anyone noticed that NuPace has a greater overdrive than any Internal Gear Hub presently on the market (their direct drive is low, and the Sturmey 8 will have the same range and overdrive as the NuPace when and if it becomes available). Could be the market is too small for such a high overdrive for the bigger internal gear hub makers- NuPace may be situtated to catch such a market and a CVT may fit the bill, particularly in the small wheeled commuter-folder arena where efficiency is not necessarily that big of a priority anyway.

BTW- is NuVinci somehow affiliated with NuPace?

meb said:

There may be rare niches where the CVT has some advantages.
If a driveshaft bike were used, some CVT designs could used with the drivetrain direction changes, giving you the option of not having to suffer a cascading of both inefficiencies on top of one another-the drive shaft inefficiencies would not be added to those from the CVT.

Anyone noticed that NuPace has a greater overdrive than any Internal Gear Hub presently on the market (their direct drive is low, and the Sturmey 8 will have the same range and overdrive as the NuPace when and if it becomes available). Could be the market is too small for such a high overdrive for the bigger internal gear hub makers- NuPace may be situtated to catch such a market and a CVT may fit the bill, particularly in the small wheeled commuter-folder arena where efficiency is not necessarily that big of a priority anyway.

BTW- is NuVinci somehow affiliated with NuPace?

The Sturmy Archer 8 speed is already on the market. At least one OEM that I know of (Cadillac) is using them.
Dan

For Gawd sakes man! Don't let Shimano hear you, they'll go and force us
all to buy a complete new groupo again!

- -

Chris Zacho ~ "Your Friendly Neighborhood Wheelman"

"May you have the winds at your back,
And a really low gear for the hills!"

Chris'Z Corner
http://www.geocities.com/czcorner

Quoted message said:

Tomek Li said:

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.

Quoted message said:

The links below I copy from uk.rec.cycling:

http://www.fallbrooktech.com/NuVinci.asp
http://www.evworld.com/view.cfm?section=article&storyid=841
http://www.californiabicycleracing.org/news-archive/041031a_interbike.html

Quoted message said:

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.

er, like /these/ "7-speed" cvt's from honda?

http://world.honda.com/news/2002/4020912.html

toyota have them too.

Quoted message said:

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 said:

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?section=article&storyid=841

http://www.californiabicycleracing.org/news-archive/041031a_interbike.html

So, what do you think?

Jobst?

Cheers,

Tomek Li

Not a true CVT as they assert since the blades would span integral quantities of links, but an interesting approach to hyper selection ratios:

andersoncvt.comandersoncvt.comOpen ↗

Not sure it gains a lot over a wide ratio deraileur system either other than some more marketting muscle through a sophisticated solution to a simple problem.

meb said:

Tomek Li Wrote:

Quoted message said:

Not a true CVT as they assert since the blades would span integral
quantities of links, but an interesting approach to hyper selection
ratios:
http://www.andersoncvt.com/

It is a true CVT. There is no mechanism that forces the chain links and
the cones into any sort of engagement with the chain. It is, in fact,
pretty close to how automotive CVTs are constructed. The first DAF CVTs
used a belt of some kind on the cones, and torque and power was limited by
the belt. Modern automotive CVTs on the DAF principle use chains like this
one does.

Jasper