continuously variable transmission (CVT)

[Dawn Light]

this is so cool


i like gear shifting...

are there any bikes with CVT?

here is how it works: http://auto.howstuffworks.com/cvt.htm

[Chris_B]

There are some bikes out there with a CVT tranny. I forget the name of the newer one but some of the old CB750's had them. I think they were the belt type though, like in a snowmobile.

[Codger]

Rokon ran a V-Belt type.

I think there were automatic Guzzis and Hondas with torque converters. I don't know about a belt type honda.

Husquavarna had a 4 speed auto that was a conventional constant mesh with 4 centrifugal clutches and 3 sprag overrrunning clutches.

Of course the new clutchless yamaha is only a couple of lines of code from being a fully automatic bike.  I bet that they will see the reception and debugging of the current bike and possibly release a full automatic in a couple of years.

[Kasumi]

Yamaha FJR1300 comes in an automatic 6 speed transmission i believe.

[sledge]

Despite achieving similar results, Auto and CVT are totaly different systems and should not be confused with each other. CVT will provide an infinate number of ratios dependent on engine speed and load. Auto boxes have a certain number of fixed ratios and the change between these is made automaticaly, again dependent on engine speed and load.

[ducati_nolan]

Most scooters have a belt type CVT. The drive pully is tapered and as the speed increases it squezes together, essentialy making the pully bigger. Thats why when a scooter takes off it will rev up pretty quick and then stay at that RPM more or less constantly while it accelerates.

[Egaeus]

I drove a Ford Freestyle with a CVT.  I didn't like it.  Felt like it had a clutch that was always slipping.  However, it seems to be popular with the new hybrids for fuel economy or something.  Damn you future!

[Caffeine]

http://world.honda.com/news/2005/2051019.html

Honda is playing around with the idea.   

Just as a side note, I think the first CVT to hit the market was the Subaru Justy in 1987 or 88. 

CVT's usually offer a very different driving experience.  When you first hit the gas from a stop, the engine goes from idle to 3 or 4,000 RPM's (depending on what its most efficient range is) and once the car starts moving, the engine speed stays the same and the car "catches up" to the RPM's.   It's a weird feeling, nothing like either a manual shift or automatic transmission.    It puts many people off the idea of a CVT when they test drive one for the first time.

[Codger]

Ditto on the Subaru Justy.

An issue to note on CVT between major systems and scooters is that the scooter is a basic centrifugal drive to the pulley.  It is simply rpm related.

The Maxima apparently has one out.  I'm sure that the computer shuffles all of the data and directs the drive.  I should give a far more reasonable drive.

I think the current Yamaha has a pushbutton shift and is not fully automatic.  But there is so much computer control of the system that all that prevents it from being fully automatic has to be activating the code.

Agreed, There is a distinct difference between CVT and a shifting automatic.  The beauty of a proper CVT is that it could allow you to keep the engine at a designated criteria, whether it is max efficiency or max horsepower. 

One of the problems with most CVT systems is a specifically limited turndown ratio.  A discrete gear set may not allow the same engine control, but it allows access to a wider speed output range from the range of input speeds.

[sledge]

CVT was first used in automotive applications almost 50 years . DAF pioneered it way back in the late 50`s. I doubt you guys in the USA will have ever seen one of these cars
http://dafcars.members.beeb.net/DAF2beeb2/Brief_Historyx.html
and they have been used in industry since way before then
http://www.renold.com/Renold/web/site/Products/VariableSpeed/CarterBeltVariator.asp
I have lost count of the number of times I have serviced units like these.

[Codger]

Sledge, I don't recall a US equivalent.
Some of us off the farm grew up with hydraulic controlled v-belt drives on older combines and cotton strippers/pickers.  These have been predominately replaced by variable volume pump and motor hydrostatic drives.  A current agricultural trend is toward a hydrostatic unit as a power splitter on a planetary gear set, so the hydraulic losses are restricted to a portion of the total horsepower.  The slick part of the planetary splitter is that you can get a larger ratio rangeability.