Next in Line: Renault developing dual-clutch transmission
Dual-clutch transmissions are washing over the automotive industry like a wave, and Renault could be the next to hang ten. The French automaker intends to use more efficient transmissions – specifically DCTs and CVTs – to help meet its emissions-reducing targets.
Although Renault could easily borrow the continuously-variable transmission from its corporate cousin Nissan, the speculation is that it could also develop its own dual-clutch gearbox. Although Nissan uses one in the new GT-R, it's outsourced from Borg-Warner. If Renault did develop its own DCT, it would likely employ lighter-weight dry clutches, and would join the growing list of carmakers with DCTs that will soon include Fiat, Volvo, BMW and, of course, Volkswagen.
[Source: Automotive News Europe – Sub. Req.]
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Reader Comments (Page 1 of 1)
DDL 5:45PM (2/05/2008)
PLEASE put a DCT in the next Maxima, PLEASE!!!
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Tyo 5:48PM (2/05/2008)
I dont understand how CVT can Improve MPG.
Ive driven a CVT and it feels like theyre always in too low a gear, engine braking. too many revs.
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MikeW 7:11PM (2/05/2008)
http://www.caranddriver.com/reviews/1779/nissan-murano-sl-awd.html
Check page 3.
More torque converter lockup, less not more revs (when you are not on it).
and more ratio spread than 4 & 5 speed automatics.
Though the version used with lower power engines have a wider ratio spread.
I'd hope they would be working on a 7 speed double clutch now. CVTs are
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rgseidl 7:16PM (2/05/2008)
Like most auto makers in Europe, Renault doesn't develop any of its own transmissions from scratch. Rather, it leverages expertise and components from the supply chain to deliver the feature set, transmission ratios and form factor it needs for its vehicles.
@ Tyo -
engine developers can produce a map of specific fuel economy as a function of engine speed and average torque at the flywheel. In that map, the area of highest efficiency appears as an island surrounded by a set of isolines indicating worsening efficiency. The optimum is usually located at roughly 40-50% of maximum speed and 80-90% of maximum torque. You can also draw hyperbolae of constant power in the map. Each hyperbola is limited by the torque curve at either end and features a point or small extent in which that particular power level is delivered with the best available efficiency.
What a true CVT can do is adjust the transmission ratio such that the engine is always operated as efficiently as possible for a given power requirement. That usually implies lower RPM and higher torque than you may be used to. The downside is that when you do need extra power for a burst of acceleration, the engine has little reserve torque. Therefore, it has to speed up before the vehicle can.
This so-called rubber-band effect is a smooth slide-down of the transmission ratio (cp. jerky kick-down in an AT) and makes the whole car feel cheap - which it may well be, given that the setup enables the use of a small engine. This is probably the reason Japanese kei cars, which by law are limited to 660cc, now frequently feature CVTs rather than the heavier and more expensive conventional ATs.
Unfortunately, the CVT itself generates significant mechanical losses so a well-tuned automated transmission with a large number of discrete gears (e.g. 7-gear dual clutch type) will often deliver higher fuel economy overall. It also maintains the familiar aural sensation of engine revs rising linearly with vehicle speed, with step changes in pitch indicating gear changes.
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Bert 9:21PM (2/05/2008)
If the CVT is smart is can gear down to only require as much power from the engine to hold the current speed. My car (2000 Maxima, manual, yippee maybe a return to a manual Maxima!!!) turns 3000 RPM in 5th (top gear) @ 80 MPH (119 Km/H) I am sure (know) that there is tons more power on board at that gearing to accelerate.
It should not be hard to get the cruise-control and CVT to get the CVT to gear down to require minimum revs to keep the power up. (though minimum revs may not be the only consideration, as the fuel injection rate may reduce at higher RPMs)
Like the others have said.
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wushu 11:23PM (2/05/2008)
For a company which claims to have invented DSG, Porsche should be ashamed it still hasn't released its PDK yet. At this rate, they'll be last to the party. They're falling behind in technology all the time. CEO Wiedeking should consider giving back some of his multimillion dollar compensation package to help out with R&D, especially for the Cayman product line, which hasn't had any substantive upgrades since it came out years ago.
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Araemo 9:42AM (2/06/2008)
#1: All CVTs are different. I'm sure some do a much better job than others.
#2: I've read that the highest thermodynamic efficiency is achieved near WOT, so perhaps they accelerate like that to maximize efficiency? (Or perhaps the one you drove was too weak to really have any pick-up at low RPMs?)
Since they're completely computer-controlled, the thoughts of the engineers can make big differences in the end result.. the idea is to keep the engine working at its most efficient RPM as much as possible, and use the transmission to adjust the vehicle speed... but what is chosen as the 'most efficient' RPM may not agree with what you think it is..
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