Hello,

I hope I'm not duplicating another topic.

CVT is not a new invention. I believe Subaru had one a while back for their JUSTY. Their CVT and their car didn't stay on the market very long.

I remember that some CVTs were using a drive belt that was held between 2 pulleys or cogs which changed diameter dynamically, how I can't remember.

The belt was either a metal chain (like a heavy duty timing chain), or a reinforced rubber drive belt.

Obviously this early technology had its problems.

Does anyone know how the CVT in the modern day Versa works?

Thanks for any information.

http://en.wikipedia.org/wiki/C...ssion

DOn't know what type the Versa has, but here is a good description of each of them work.

Same technology, better execution. CVTs have been used in Snowmobiles for ever. Improvements have come in the mechanics of the belt, in the servo controls for the pulleys, and lately in the software that's used to contol ratios.

You already have a basic concept, but if you want to know more, check out HowStuffWorks.com There's a great article on CVTs with some neat animations.

Ben

Nissan's Xtronic is what the Versa has. It's used for FWD configurations, and is a variable diameter belt/pulley type CVT.

Nissan's RWD CVT is the Extroid. It's a toroidal CVT

Xtronic:In the cutaway you can see how the pulleys pull apart or move together to adjust the diameter of the belt passing through them.

Extroid:

Thanks for posting the pics.

To replace the belt on the Xtronic someday, it looks like the back cover needs to be popped off and the pulleys disassembled. One would hope that this could be done from underneath the car without having to drop the motor.

I was surprised that the CVT beats out the 4AT only on the highway, as opposed to in the city. So that says to me that in the city, both transmissions accelerate the car with the same efficiency and whether you're cruising between stoplights at 35 mph with one transmission or the other, it does not make all that much difference.

Whereas on the highway at 65 mph, the CVT might be holding steady at 2300 rpm, but the 4AT might be at 2500, and it is that slight difference in rpms over many hours at highway speed that gives the CVT its only advantage in terms of fuel economy.

If you move the selector from drive (D) to low (L), how does that change the way the transmission applies compression to the engine?

With an ordinary automatic transmission, we use L1 or L2 to prevent the transmission from hunting for the right gear while going up a steep hill (with or without a trailer) and to force engine compression while going down a long steep hill. But with a CVT, there should never be any hunting, so the only reason I can see for having a L position in the Versa is to force compression while descending a hill.


Modified by montreal at 10:57 AM 10/1/2006

Engine-load braking for hill decent is one purpose. It is also probably nice for keeping the car in the torque band for passing--that's where I see it being the most useful.

So placing the CVT in Low forces a lower than usual gear ratio in order to keep the engine rpms higher during acceleration.

I would have thought that the throttle position sensor and the lower manifold pressure caused by opening the throttle plate would have tipped off the electronics in the CVT that you wanted to accelerate as quickly as possible, as is the case with ordinary automatic transmissions.

Perhaps choosing Low sets an upper limit on what the gear ratio can be and this can be forced seconds before you actually depress the gas pedal further.

Has anyone seen any 0-60mph testing for the CVT? I will be happy if it is under 10sec.

versabbo wrote:Has anyone seen any 0-60mph testing for the CVT? I will be happy if it is under 10sec.

I've read several comparison articles of the Versa vs. the competitors. Popular Mechanics said it was faster than all of its competitors, but that car was a 6MT. I seem to recall another test done with a CVT that ended up being slower than even a Yaris... but I can't for the life of me remember which article it was.