[paul]

how i understand them. there is two pulleys, one is a fixed radius, the other is in a cone shape. the belt/chain between the pulleys moves up and down the cone shaped pulley, effectively changing its ratio.

one thing though,how does the belt move up and down the pulley? surely it would just slip to the smallest radius??

i been in a CVT car, and there is no gear changing going on, its just one long continous feed of power,no sudden changes of revs, nothing

anyone on here understand them better? or can give information for everyone? Nissan are developing a chain driven CVT arent they?

 

[Jodi_the_g]

CVT stands for continuously variable transmission.
It is basicly an automatic transmission that transmits a steady flow of power from the engine to the drive wheels without any shift points.
It makes a petrol engine work with the same smooth surge of power as an electric motor.
Instead of a manual transmission, with different gears chosen by the driver, or an automatic transmission, which does the shifting with gears and fluid couplings,
CVT used a simple set of pulleys connected by a belt.
Each pulley is split in half, like the bottoms of two saucers pressed together.
As they are pulled apart, the belt rides closer to the center; as they are squeezed together, the belt moves toward the outer edge of the pulley.
With pulleys on either end of the belt squeezing and moving apart between the engine and the drive wheels, the power transmission can vary in infinitesimal amounts, which is why it's called continuously variable.

Hope this answer your question it is not new technogoly it has been around since the 60's in a caer called the DAF City Car, its just until recently it has only been used in very small engines

 

[Jodi_the_g]

and nissian already have a CVT out for the Micra

 

[paul]

thanks, thats cleared up any problems i had with CVT's

 

[Jodi_the_g]

Audi/VW have got one that can with stand 170bhp by substituting a special chain for the belt and figuring out a way to make it ride reliably on the split pulleys, which Audi calls variators.
This could be similar to the one that you were on about nissian making.

 

[paul]

i read about the nissan one which was being developed for a higher powered car on a website a few months ago. it also mentioned Audi were developing/had developed a chain driven one to withstand 250bhp. if only i could remember the site

 

[Jodi_the_g]

I know audi are hoping to release 3- liter V-6, which spins out 220 horsepower with CVT on the quatuo but they are having difficults in getting in to 4-wheel drive

 

[somberg]

CVT was originally invented by DAF (at that time owned by the Van Doorne Family) as stated earlier in this thread. In 1995 (if I'm not mistaken) the CVT was successfully tested in a Williams F1 car. A Dutch company called VDT (Van Doorne Transmissies) continued to develop the CVT; somewhere in time they changed from a pull-type set up to a push type chain. Meanwhile they can cope with quite acceptable power. Advantage over a traditional automatic gearbox is that you can use the engine as a break, and it is more efficient since it doesn't use a torque converter. By using electronics, they can fix certain ratio's. That's what they do with the Audi Multitronic for instance. Drives quite nice, you can either drive it in auto mode or in the manual mode with the fixed ratio's. works like a sequential gearbox.
VDT is nowadays owned by Bosch. Located in Tilburg, NL.

 

[DCD]

Nissan actually uses a CVT transmission on the V35 Skyline 350GT-8. Same engine as the new Fairlady Z kicking out 280bhp. It has 8 pre programmed gear "ratios" ....which sounds all good...but in practice it's far from it. In fact the first word that comes to mind is ....well, shite!!

 

[somberg]

Dino

Have you driven it ? Why is it shite ?

Andre.

 

[DCD]

I haven't driven it yet but I've been out in a dealer car. Shifts are slow(very slow), and it makes the engine sounds like a vacum cleaner. Its a really strange experience as the engine just tends to stick to optimum revs for ages and once the "gear" is changed it drops down slowly a couple of 1000 rpm and the process repeats its self. Its definitely different, but not good at all in IMO! Thank God I've had no requests for a test drive yet!

 

[polarbearit]

My aunt has one of those DAF transmissions in her y reg Volvo 340, which quite amazingly has never had a problem in 20+ years

 

[somberg]

The CVT in the Audi I drove about a year ago wasn't that slow really. Must be due to different electronics.
I'm not in favour of an auto box personally, but if I had to choose I'd take a CVT and not a conventional one. I guess it's a bit unnatural "hovering" around; feels a bit strange indeed.

 

[ColinM]

This weeks Auto Express has a piece on the GTR replacement. It says the R35 concept car had the CVT but it cant handle a lot of power so it will not be used in the production car.

 

[somberg]

Hmmm interesting. What else does it say ? What kind of engine ?

 

[paul]

i have been in a CVT Fiesta, it is not particularly good. when its under a heavy load,or accelerating hard you can smell burning, and it also slips alot. i knbow its only a fiesta, but if it doesnt improve then i doubt it will catch on.

 

[polarbearit]

Have driven a CVT Punto and it really didn't add anything to the experience compared with the manual, but would probably be better than a std auto...

 

[ColinM]

@somberg
See my thread 'New details on R35 from Auto Express mag' in the R35 forum.