Imidazole

Now correct me if I'm wrong... but wouldnt a CVT be much faster than a regular ol tranny?

Follow me here. If the CVT can keep the engine where it produces its MAXIMUM power, and continuously change the gear ratio keeping the engine right at it's sweet spot... Plus the fact there wont be any shifting... wouldnt that be insanely fast?

I mean, what if our RX8 could stay at 8000rpm (or wherever it had its max power) and continue churning out maximum super powerage while the tranny does the work?

Now, comes:

http://www.autoblog.com/2007/04/17/n...e-from-20-490/

Alright, I know its FWD. But 270hp + CVT could be magic. Amirite? Or is my logic flawed?

Rhawb

I have a feeling that the car companies, in their infinite wisdom, will not allow a CVT car to simply hold the revs in the powerband. They'll probably make it act like it's shifting to give it that "sports car" feeling or some equally frivolous and stupid "feature."

It would be very interesting if they ended up actually being able to hold on to the power band, though. Bet it would be all sorts of fast.

CarAndDriver

Current CVTs are pretty mediocre. Read the current review of the Sentra SE-R V. The CVT gets awful comments.

I remember how Subie touted the first CVT in a US production car in the Justy. That was a long time ago.

The technology would seem to suit many cars, but the implementation is not quite there yet.

scarroll

To add one to that how about a turbo system on a cvt, It wouldn't need to utilize a blowoff system nearly as much, keeping it spooooooled... and in the sweet spot.

I have driven several different CVT's and though I like them in terms of "commutabliltiy" the seem to absorb engine torque much more than a plain old auto. and obviously much more than a manual / clutch setup.

Of course, If I was in love with torque, I wouldn't be driving a ..., ok I'll shut up now...

Ajax

direct drive is the future.. screw transmissions. put all the power on the ground.

Renesis_8

Theoretically yes, but I dont think the technology is there for a CVT that can do that yet. Also it puts a lot of stresson the engine running at max power continously, even only at WOT. The OEM will not let that happen.
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scarroll

The first CVT I drove was a 1996 Civic HX, you could not feel that thing shift at all
and that was 11 year old technology. You would give it gas it would jump up to 4-5k rpm and just stay there while accelerating. 0-80 and as your speed leveled off, the rpm would slowly settle down to a cruising level.

It was very unsettling at first, but then you get use to it. If I'm driving an auto, I don't necessarily need to feel it shift.

Imidazole

Good info, Scarroll. So this might have good possibilities!

lone_wolf025

IIRC CVTs were orginally designed with gas mileage and power flow in mind. But according to the last article I read on them the technology isn't paying off as well as OEMs would like. One example is that there are 6spd trannys getting as good as if not better mileage than the CVT on the same vehicle.

It'll be interesting to see where things go but I suspect that we'll see 6-8spd trannys become more and more prevalent before CVTs really take off.

playdoh43

nissan seems to be making a big push with cvt including it on just about all their models now. it dosnt seem very performance oriented though.

MazdaMonkey

In the last Car and Driver the Editor-in-Chief pondered the same issue. He concluded that the reason that fewer and fewer manufacturers are using them is because they really are not more efficient when you taken into account the extra power that the auxiliary systems required for CVT sap up. I think he showed that the new Altima (or maybe Sentra)'s CVT didn't get any better gas mileage/acceleration than the other transmissions offered. Csaba Csere concluded that unless they can make the CVT more efficient, its future is questionable at best.

playdoh43

according to most reviews their CVT provide better and smoother accleration and better gas mileage.... its just not a performance oriented transmission, Nissan's paddle shift auto that has electronic rev matching is a better solution for their performance oriented cars

cquinn

CVTs right now are better, but not strong enough to transmit large amounts of power. The internals will not be able to withstand the large forces that a helical gearset will, at least for now

Rootski

iTrader: (1)

I agree. They've already made them so they "jerk" when you start to maintain the illusion of acceleration, which is a completely useless feature. Scaroll complained about the lack of torque in a CVT... it's there, it's just smoothed out, so you lose t hat "slammed in your seat" feeling.

scarroll

Agreed, It could also be the fact that every CVT that I have driven was economy minded... Civic HX doesn't make a helluva lot of torque to begin with, even when compaired against the EX or Si Civics much less than a push rod V8.

playdoh43

the CVT in the maxima (very torquey car) is really nice, dont know if you guys have seen that comerical that ran during march madness of the dude in the maxima accelerating hard but its real smooth in side, hes wife was putting on make up.

MikeW

Nissan had a longitudinal [full toroidal I believe] cvt, the extroid. The problem is that it only had a 4.4:1 ratio spread (GM's 4 speed auto, the 4L60 also has a 4.4:1). Then Nissan went back and added a planetary gear to improve the ratio spread, but doesn't that kind of defeat the purpose of a CVT.
Also the extroid operates at a two axis design, there is an extra set of gear meshes to return the power to the primary axis. Compare with 5th gear in the stick, 0 gear meshes.


The 6 speed auto in the Rx-8 has 6.1:1, the stick has 4.5:1. The automatic has way too tall gearing (the 4 speed automatic rx-8 top gear was ~24mph per 1000). I was hoping Mazda was going to use the ZF 6 speed auto, with top gear 25mph per 1000, so 5th gear (top speed gear, peak power on the 4 port was 7200rpm) would be 20mph per.
As is stands, 5th gear is ~24mph / 1K, 6th gear is almost 30mph per. Nutz.

The 6 speed manual is only ~20mph per 1000 in 6th. Aggressively short, but since the Renesis doesn't have any external exhaust gas recirculation, the mileage really sucks on the highway.

original extroid.
http://www.histomobile.com/histomob/tech/2/90.htm

As far as Csaba Csere article, something is way wrong there. The 6 speed stick has 4.6:1 ratio spread, and a top gear of ~22mph per 1K. The 4 speed auto has 4.1:1, with a top gear of ~25mph. The CVT has 6:1, with a top gear of ~30mph.

So either something was broken, or the programming is complete crap. The CVT has a low enough 1st gear, that the torque converter can stall up-then lockup, and stay that way. It should have blown away the 4 speed auto from 0-30mph.
The CVT can have a variable output pump necessary to develop the hydraulic pressure. Audi has had variable clamp load on the variators [it has torque sensors], so that only enough force to keep the chain from slipping is necessary.
The only issue with revving up to peak power, and changing from there is variator/chain wear. Audi/LUK said that if you drove that way, all the time the chain would only last 30,000 km. That could be the reason that Audi added a 'sport' mode to the Multitronic for the 2004 model year, that way the normal 'drive' can be economy oriented.