|02-03-2003, 12:46 PM||#1|
Join Date: Feb 2002
Location: Coconut Creek, Florida
Was home watching MotorWeek as I am to do on a Saturday morning and they reviewed the Nissan Murano SL AWD. I did not know it had a CVT so I was surprised to see how much MotorWeek gushed over the CVT in the Murano.
This morning I was looking at the Car and Driver site and saw they had a review of the Murano and this is the side bar on the CVT.
Behold the first belt-drive truck.
By now we're amply convinced that continuously variable transmissions (CVTs) can improve acceleration and fuel economy by optimally adjusting engine speeds and loads to driving conditions, permitting maximum acceleration at or near the power peak while cruising at higher load (lower rpm) for peak efficiency. But this is the first CVT with the torque capacity to work in a big SUV, at least in the U.S. Nissan does build a toroidal roller-type CVT in Japan called the Extroid, which can withstand 286 pound-feet. Unfortunately, this device can't tolerate the ultra-low temperatures encountered in America.
So how does the traditional Van Doorne-type push-belt Xtronic CVT, identical in concept to the tiny Subaru Justy's CVT that first arrived here in 1989, come by its newfound strength? The pulleys clamp the belt much more tightly, and they're hardened to withstand the added stress. A beefier belt uses individual steel plates that are 30 millimeters wide and are held together by twelve 0.2mm steel bands on each side instead of the nine used in Nissan's smaller CVT. The new belt's minimal running diameter is also increased, but the overall ratio spread is an impressive 5.40. That is considerably wider than the spreads offered by the Altima V-6's four-speed automatic and five-speed manual (4.04 and 4.09, respectively), although it trails the 6.04 ratio spread offered by the Audi CVT and the new ZF six-speed automatic.
A torque converter couples the CVT to the engine, but because of the high inertia of the belt and pulleys, it isn't needed to absorb drivetrain shock, so it can lock up at about 12 mph to further improve efficiency (most converters lock up at 30 mph), and its ultra-slim design is 23mm narrower than other Nissan converters of similar capacity.
Bottom line, the engineers at Jatco who developed Xtronic with Nissan claim a 14-percent improvement in acceleration and a 12-percent boost in EPA combined fuel economy relative to typical four- and five-speed automatics."
In the "Counterpoint" section it mentioned why Audi could not get a CVT for AWD on their V6. To that end, why not Saturn?
As for Audi, there is also a preview of the A4 3.0 Cabriolet with the CVT as well. Again. much praise for their CVT.
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