AzNRocKet

hey peeps,
i posted this thread to see what you people think
abut the CVT (continuously variable tranny).
Reviews about it say that it performs and saves fuel
better than the manual yet it shifts smoothlier than an
automatic. Do you think it ruins the fun of shifting???

Thanks for the comments.

Ray

Not really. I would love to have a CVT in a S2000. Imagine being able to keep the rev constant at 8500RPM from 15 MPH to 150 MPH. Plus a manual seven-step control with paddles behind the steering wheel should allow me to bring the rev instantly up or down.

It's an ideal transmission for small displacement car.

KrazyKarim

coud someone explain what a CVT is and how is works?

Karim

Clark

Hey Ray,

In reality, why would you need/want any sort of artificial stepped control of a CVT????? That would do you absolutely no good and just ruin the one thing that a CVT is good for; maximum efficiency.

AxNRocKet,

I personally think that from a technology point of view, CVT's are a great thing. As an Engineer myself, I like the idea of maximizing the efficiency of a system and the CVT does exactly that. However, I very much enjoy shifting for myself and (admittedly the only CVT I've driven was a Subaru Justy....eeewe) yes I feel it does take away from some of the joy of driving, at least in a road car. I feel the same about sequential gearboxes as well (never driven one of those), they are more efficient but they just don't have that same exhiliration as heel-toe downshifting and getting it all right and good all by yourself.

KrayzyKarim,

CVT is an acronym for Continuously Variable Transmission. It is a transmission that uses a belt (more like a chain than a rubber belt) to transmit power rather than gear-to-gear power transmission. With gears, the ratio if fixed. With this belt the ratio can be continously adjusted, typically by changing the distance the belt has to travel, so that there are not fixed gear ratios. This allows us to always keep an engine turning at the RPM where it makes maximum power, or fuel efficiency, whichever we choose.

The traditional weakness of the CVT is that they typically cannot handle alot of torque, and therefore have usually only been applied to very low torque/horespower engines (like the aforementiond Justy). Audi has a new CVT design out that is mated to a V6 making decent, though not earth-shattering, torque numbers. The other weakness is that without clever programming or some sort of manual control a CVT doesn't give very much engine braking, and it sometimes bothers the typical driver because it doesn't "feel right" (much like regenerative braking in an electric car).

Well, there's my little pamphlet on the whole topic.

Clark

Ray

Unless you have your brain hard wired to the transmission, you are going to want have some sort of control over the rpm and vehicle speed independent of the throttle position.

Audi's Multitronic for example, uses series of internal and external readings to choose the appropriate speed:rpm ratio program. It is an ingenius system, that makes the CVT ideal in almost all everyday world situations.

You can read more about it here:
http://www.audiworld.com/news/00/a6multitr...c/content.shtml

But on a places like Auto-X or race track, you are going to want to have more control over how the transmission reacts. Softwares have limits; you couldn't possibly expect them to react correctly 100% of the time.
By allowing partial manual mode at the push of a button, you can have higher degree of control independent of throttle and brake pedal positions, from which the tranny brain makes most of its decisions.

Audi actually have this feature included in their CVT. But since I've not driven one yet, I don't quite know how well the manual control and the software work together without trying to override each other. I gotta find an A4 in my area with CVT and try to get a test drive.

Clark

From everything I've read about Audi's Multitronic, pretty much the only reason they put the manual mode in is to alleviate the "creepiness" factor. That is to say that most people don't like stomping on the accelerator and having the engine race up to max power RPM and then stay there while they accrue speed (much in the same way that many drivers don't like regenerative braking in electric vehicles). They call and complain that the clutch is slipping when the CVT is actually working the way it is supposed to. So Audi builds in this manual mode, which is actually less efficient but it's a feel good for drivers that should really either know better or else should have bought the automatic.

As for having alternate control of engine RPM, even for track or appropriate, I'm not so sure that this is true though I'll say I think a sport or competition mode is necessary so that it always goes for max power/engine braking rather than looking for any sort of economy. Think about it, if the CVT always keeps the engine at max HP rpm, and holds it when you lift so that you have plenty of engine braking and weight transfer, of what value is having a means of appropriate your RPM? On the track you downshift upon entering a corner so that you are at the appropriate RPM to provide dynamic balance through the corner and have the appropriate power to exit the corner. If your CVT were to keep you at the engine's peak power RPM, this has been accomplished.

Clark

Ray

You are right. Manual mode would be just a gimmick. But I wouldn't mind having it.

AzNRocKet

I should've posted this link before. It precisely explains
what a CVT is.


link

josh3io

instead of having manual presets, like traditional gears, I imagine a racing CVT that has an infinitely variable control joystick for the CVT. That way you have precise control over your transmission ratio, anywhere between minimum and maximum setting. No more "You should be in 3rd gear for that corner," but you hear statements like "put your cvt at 50% to reduce throttle sensitivity in that corner"

Clark

josh3io,

You do make a good point there. Having a sort of rheostat type control would be particularly useful in inclement weather or bumpy corners. I really wonder though how much it might get used in any case other than to compensate for a poor track condition.

Clark