CVT Transmission Questions

Hello,
Just trying to learn a bit.
Re the CVT type of transmissions that I guess the Altima and the Maxima have, what is the principle of their operation, basically ?
How different from the "regular" type of transmission ?
Pros and cons of ?
Why only Nissan, I think, has gone to it ?
Thanks, Bob
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Imagine two conical gears arranged side by side like this: |AV|, with a belt that moves up and down coupling them together. With the belt on the top, it has a ratio greater that one, as you move the belt down the ratio becomes less than one.

Substantially. It's actually simpler, and was invented by Leonardo da Vinci, but it has a belt (or a follower gear) that provides a single weak point. With a regular transmission, if you break the gear assembly on first gear, you can still start the car out in second... if you break synchronizers you can double-clutch it home. With a CVT there isn't as much to break, but if it does break you're dead in the water.

Well, it's continuous, so you can always have the transmission at the precise ratio that is optimal, you don't have to have it at the nearest gear. You don't need to use the clutch except for stopping, so the clutch wear is greatly reduced.

I believe there was a Dutch car manufacturer that used it in the 1950s. Subaru made one in the eighties too, as I recall. --scott
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On Aug 30, 1:30 pm, snipped-for-privacy@panix.com (Scott Dorsey) wrote:

Ford has had it in their 500 car for several years. It was designed by Volvo.
If you want to see a real simple design, hang out by the golf course and look at some of the older golf carts. Cushman also had this real simple design in a lot of their 3 and 4 wheel scooters that are used by a lot of zoos. Like already stated, the "V" in the drive pulley gets bigger and the "V" in the driven pulley gets smaller as you increase the speed. Continuously variable depending on the speed. Of course, the cars are computer controlled.
One disadvantage is that most applications do not allow you to do any towing.
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Kruse wrote:

Been in use a LONG time. Just look at 90% of the snowmobiles out there. They use the same system.
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Steve W. wrote:

John Deere lawn and garden tractors from the mid to early 60s, too. Actually they had a regular multi-speed gearbox COMBINED with a variable-speed belt drive system that allowed a broad range of speeds in each gear. Very cool, I wish modern L&G tractors were as well-designed and easy to use.
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Steve wrote:

Yep, the Vari-Speed drive. A mechanical version of hydrostatic drive.
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In article

Practically every snowmobile made (at least up through the late '80s, which was the last time I was in an area where a snowmobile could be found to look at) will provide you with an example, as well.
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In article

????
Towing the vehicle it's in, or towing something using the vehicle it's in?
If you mean to say a vehicle with a CVT can't tow, I'll beg to differ: We used to tow a 7-hole ice shanty out onto the lake using a snowmobile equipped with the typical-for-a-snowmobile CVT. The shanty took 7-8 strong men to hump it on or off the pickup, and likely weighed 1200 pounds, maybe more. So long as the sled could get enough traction on the ice to move itself, it towed the shanty without any noticeable difficulty.
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I agree. I have a Murano and have towed a rental trailer many times. It does not tow as much as a Suburban but it's also a lighter vehicle.
One disadvantage I have heard is that it's very expensive if there is something wrong with the transmission because nobody knows how to work on it, and the only option is to replace the whole thing at a dealer for $6-7k + labor. I'm seriously considering whether to buy extended warranty before the standard power train coverage expires.
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\ Right. DAF was the Dutch car. It featured a belt made with little metal stampings (for failure to be able to describe it more accurately)
Nissan did their homework and apparently came up with a CVT which is tough and reliable. It features steel belts.
I never knew Ford used any CVTs by Volvo, but if the poster says they did, it is fair enough with me.
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Wikipedia has an entry for CVT's...
http://en.wikipedia.org/wiki/Continuously_variable_transmission
As a side note, they've been using similar 'transmissions' on large jet aircraft for eons.
They're called 'constant speed drives' (CSD), and are used to drive engine driven alternators at a constant rpm regardless of engine speed.
They work a little differently than automotive CVT's though. CSD's internally have an engine driven variable output hydraulic pump powering a hydraulic motor that actually drives the alternator.
Large aircraft mostly use AC current, so their alternators are rectifier free, and output frequency is controlled by rotation speed. They're also synchronized to keep multiple alternators in phase with one another.
Aircraft constant speed drives cost mega bucks...
Erik
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The use of the CVTs goes back, I believe to the 1920s. Many companies have tried it through the years, none had a lot of success for very long. But then, the price of gas was never high enough. One obstacle in the past is that belt drive type CVT was limited in horsepower, which restricted it to lower powered cars. Nowadays there are supposed to be belts that can handle very high hp.
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Robert11 wrote:

Regular transmissions have a fixed number of predetermined ratios between the input and output shafts, so when the transmission shifts gears the engine speed has to drop suddenly (or slowly, but that wastes energy in slipping the transmission clutches.) A CVT gradually varies the input/output ratio so that the engine speed can remain constant or near-constant as the car speeds up.

Pros- the engine can spend more time at the RPM where it is most efficient. Cons: complexity, until recently fragility and limited to less powerful engines.

They're not the only ones. You can find CVTs in the Dodge Caliber, Jeep Compass/Patriot, and others.
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This one is interesting:
http://www.sapatransmission.com/binary_background.asp
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