Continuous Variable Transmission

Could someone explain, in small english words, what the heck a Continuous Variable Transmission IS, how it works, and whether there are any advantages to them?

A continuously variable transmission, or CVT, has a chain between two pulleys. the pulleys flanges are beveled and the width of the pulleys varies so that the chain is closer to or farther from the pulleys hubs. This gives an infinite number of ratios between the lowest and highest “gears”, which can make the most effective use of the engines power.

I think it was the Nissan Murano that I first read about as having a CVT, back in '04 or '05. I don’t know what other vehicles use this type of tranny, though.

There are CVT transmissions in many Fords.
My wife’s Escape hybrid has one .
You just push on the gas and go.
You’ll notice as you gain speed the engine rpm might drop some then gain some then drop as you get to your cruising speed .
– no shift points –
No gears of different ratios, just that aforementioned chain and pulleys of every and any ratio.
just an ever changing adaptaion between road speed and engine rpm.

My wife is so used to hers that the Expedition’s six speed shift points actually bother her now.

The easiest to see and explain CVT transmissions are in golf carts. It is a belt between two pulleys. Both pulleys can vary in size. At start up the motor pulley is small and the wheel pulley is large. As speed increases the motor pulley gets bigger and the wheel pulley gets smaller allowing the motor to maintain a constant rpm as vehicle speed increases. In golf carts the pulleys are controlled by simple spring action and centrifical forces.

In an automobile the transmission deals with more complicated situations and the pulley sizes and ratios is controlled by computors and physical actions to change the pulley sizes and ratios. The result is the same, but in a car a CVT can be much more complicated. Biggest issue with car CVT’s is they use differnent fluids than an normal automatic transmission and sometimes brainless techs put in the wrong fluid with castostrophic results. If you have car with a CVT trans you are best using only the brand name fluid for your transmission.

If you maintain them properly CVT’s seem to be doing OK in providing reliable power from the motor to the wheels.

The Escape, Prius, and other Ford and Toyota hybrids use a different type of CVT. While the typical CVT (Nissan and, a while ago, Subaru and Audi) is of the variable pulley type, the one Toyota and Ford hybrids used is created by clever manipulation of two electric motor/generators and the gas engine through a planetary gearbox. Google ‘hybrid synergy drive’ for more info.

If you search on youtube there are videos that show the transmission at work.

Snowmobiles have used them for years…The drive belt also must serve the function of the clutch. It must slip when starting off from a dead stop…

It was a pretty rocky start when they adapted them for use in cars…Remember the Subaru Justy? But today, they are able to build them with a reasonable life expectancy. In the past, if they failed, these transmissions were not rebuilt…They were replaced with a new factory transmission ($$$$$$) I don’t know if it’s still that way…

I think the first cars with CVT were Dutch DAFs

“I think it was the Nissan Murano that I first read about as having a CVT, back in '04 or '05”

“I think the first cars with CVT were Dutch DAFs”

Oldtimer is correct.
ClassicFan–Don’t feel too bad. The DAF Variomatic (CVT) transmission was introduced in 1958, so you are only “off” by a little over 4 decades.

For years, I thought that all CVTs worked like in doubleclutch’s anwswer, which is most analogous to the multiple speeds you can get out of a few gears on a bicycle. Then I found out about Nissan’s toroidal CVTs, which seems like a pretty brilliant idea. So I thought that the CVT in my Jeep Compass was like that, but it turns out that the Jeep just has the belt and variable-size pulleys.

That Jeep CVT transmission was just replaced under warranty after 43,000 miles. Not sure if it was an actual CVT component that went, or just a bearing in the final drive. The dealer couldn’t be bothered to figure it out, since they can’t service these things. Just a brand new transmission.

The whole point, of course, is to take better advantage of the optimum range of the engine’s powerband, instead of forcing it to run more inefficiently at lower revs and higher revs as it runs through conventional gears. Maximum power all of the time, or best efficiency, depending on what you want.

Round about 1993 the Williams Formula 1 team developed a CVT transmission. Their car immediately went something like 3 seconds a lap faster than anybody else during testing. It was banned before it got to race.

The Dynaflow transmission on the Buicks of the 1950s and the Powerglide transmission of the 1950-52 Chevrolets I always thought of as a continuously variable transmission. These transmissions depended on torque multiplication of the torque converter instead of having different gear ratios. These transmissions were not the same as today’s CVT–these early GM transmissions had considerable slippage. However, when one started off in “Drive”, the torque converter adjusted the drive ratio to meet conditions.

When the Ford 500 came out it was available with CVT.
Also I had a riding lawnmower with it, however you could lock the lever in whatever range you wanted to go.

Actually, VDC, I wasn’t saying I thought that the '04-'05 Nissan Murano was the first to have a CVT, just the first time I’d heard that terminology; I have heard of “belt-drive” transmissions in certain foreign cars like the Dutch-built DAF, but didn’t realize they were the same thing. I’m no authority on foreign cars, but I do know a good bit about American makes. I know in the late 1930s / early 1940s, Oldsmobile, then known as G.M.'s “experimental” division, first started succesfully using the Hydramatic transmission in their cars; G.M.'s other divisions were still using 3-speed manual gearboxes, and Buick had the Dynaflow as an option, which was slow off-the-line. Cadillac was the first division to use the Hydramatic after it was used in the Oldsmobiles for several years. I actually once owned a 1947 Olds Series-78 Dynamic Cruiser with a Hydramatic; this was a huge car with a short fastback tail, an enormous passenger compartment (rear seat was bigger than the front), and a hood long enough to launch an F-16 (to accomodate the Straight-8 engine). The transmission actally had 4 speeds, but only 2 positions on the selector lever. In “Lo” it had a really low granny gear and then 2nd, and in “Dr” it would go thru all 4 speeds. there was no “Park” available, you had to set the handbrake and put it in Neutral when parking. It also had a “cone” clutch for reverse, and you had to have it in gear and then move the lever really fast into reverse or else you’d grind the gears. Quite an interesting car.

I guess you could say motor boats have a continuously variable transmission. The prop gradually picks up more water as the boat increases speed. Fortunately, mother nature supplies the torque converter.

ClassicFan62–The GM Hydramatic, which was introduced on the 1940 Oldsmobile was a great transmission. During WW II, this tranmsission was adapted for use in military tanks. I think it was an option for the Cadillac in 1941. In 1948, it was an option in the Pontiac line. Ford Motor company bought Hydramatic transmissions from GM and offered them in the Lincoln starting in mid 1949. Nash used the GM Hydramatic in its 1950 models. Hudson and Kaiser used the GM Hydramatic in the 1951 models. The Hydramatic became available in the GMC pickup truck in 1953 and the Chevrolet pickup truck in 1954. This transmission utilized a fluid coupling as opposed to a torque converter. The fluid coupling provides no torque multiplication as the torque converter does. Therefore, the Hydramatic provided 4 forward speeds. There was a company that rebuilt and set up the Hydramatic transmission for drag racing. These transmissions were called the “B and W Hydrosticks”. Many claimed that with the same engine and rear axle gearing, the Hydrostick could beat a manual transmission off the line.