• Jul 16, 2012

Before every car, SUV and truck sold in America gets turned into a gas-electric hybrid or all-electric vehicle to meet stiffer fuel economy standards imposed by the government, automakers are adding more and more technology that has been around for years to the internal combustion engine to reduce the amount of gas they burn.

One of those technologies is the continuously variable transmission, and every new car buyer should understand the basics of how it works before spending $20,000 and up on a new set of wheels that has the system under the hood.

What is it?

A continuously variable transmission, or CVT, is a type of transmission that doesn't have fixed gears. A conventional transmission, whether manual or automatic, has a defined set of gear ratios or "speeds," which is why we refer to it as a "5-speed manual transmission" or a "6-speed automatic." These types of transmissions move through their gears as the speed of the car increases, which results in the engine speed dropping every time a higher gear is selected. CVT's, however, allow an engine to operate at or near its optimal speed, with a varying gear ratio that can be adjusted in real time for maximum efficiency.

How does it work?

A CVT is actually quite simple, comprised of just two pulleys connected by a belt. One pulley is attached to the crankshaft of the engine – this one is called the drive pulley. The other pulley, the driven pulley, is attached to the output shaft of the transmission. This is connected to the drive-shaft, which in turn rotates the wheels. The belt that connects the pulleys is usually flexible but made of steel for strength. Both pulleys have a deep V groove that can have its width adjusted by the computer in the transmission. As the width in the pulley grooves change, the belt rides higher or lower in each, changing the gear ratio between the engine and the wheels.

When a car accelerates from a stop, the drive pulley has a wide groove and the driven pulley has a narrow groove, corresponding to a low gear. As the drive pulley's groove shrinks, the driven pulley's groove widens to keep the tension on the belt, changing the gear ratio as the belt slides up or down in the grooves. When the drive pulley has a narrow groove and the driven pulley's groove is wide, the CVT has reached its highest gear ratio.

Still with us?

Why would I want it?

One reason: Gas mileage. An engine coupled to a CVT can operate in its most efficient range for more of the time, meaning it uses less fuel to drive the same distance.

According to the United States Department of Energy, CVT's have a potential efficiency improvement of six percent. But just like every other automotive technology, CVT's are improving beyond that. Nissan has said that its newest CVT has a 10 percent improvement in efficiency over its older designs, a result of reduced friction, shrinking the size and weight of the transmission, and improving some of the basic design to increase the maximum spread of gear ratios available. The all-new 2013 Nissan Altima has the improved system.

Is there any downside?

CVT's take some getting used to. Most drivers are familiar with the sounds and sensations of a vehicle with a conventional transmission. The engine "revs" or runs faster and the accompanying sound of its intake and exhaust grows until the transmission shifts into the next highest gear and the process repeats itself. CVT's are different, allowing the engine to rev higher and much faster, usually leading to increased noise. Since the CVT does not "shift" to a higher gear, it can result in the engine sounding a bit like a vacuum cleaner.

Some manufacturers have had problems with the reliability of their CVT's, most notably General Motors and MINI, neither of which currently offer them. The technology is mature enough today that durability concerns should be a thing of the past.

What vehicles offer it?

Nissan has offered the most vehicles with CVT's in the North American market, from its smallest subcompact Versa to its large Maxima sedan and Murano SUV. Subaru has embraced the technology in it latest generation of vehicles, and Audi also uses CVT's in some of its models. Look for more vehicles to come equipped with CVTs, though, as many are adding technology like this to improve the fuel economy of their vehicles across the board to meet the higher government requirements.

Bottom line

In the quest for maximum mileage, there are plenty of new technologies. Continuously variable transmissions may not be as sexy as hybrids, but they are a key piece of the puzzle as manufacturers try to meet stringent fuel economy standards.



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    • 1 Second Ago
  • 21 Comments
      carlsonr
      • 2 Months Ago
      if you go with a CVT, know this..... someday, down the road, the belt will break... there is no warning..... you just drift to a stop. When it happens you have 3 options1. buy a new transmission, 2. buy a used (junkyard) transmission, 3 junk your car for what you are able to get...There are no parts available to repair it and if there were, the expert who tore mine down right in front of me to determine its failure mode said that " the labor to clean it up and find all the parts would be more that what he would reccoment as a reasonal repair price..
      wil2660
      • 2 Years Ago
      I have a 2007 Ford Five Hundred AWD with a CVT transmission, never had a problem with it and like the constant smooth ride when starting off.Reminds me of the old Buick Dyna-Flo.
      mikecalabrese
      • 2 Years Ago
      I had a Saturn Vue with a CVT. When it worked it was very smooth and I got very good gas mileage. The problem was that the tranny stopped working after about 63K. A bunch of other Saturn Vues and Ions did the same. So I'm not sold on the longevity of CVT's. They may be cheaper to make but will they hold up?
      rwilliamhoward
      • 2 Years Ago
      Seems like the experience would be much like the DyanFlow or PowerGlide trannys of old. I always liked the DynaFlow. It was smooth, and going up-hill in snow was a snap. You let the CAR pick out how fast it wanted to go up, and just held it there. No down shifting, which would spin the wheels, and no lugging of the engine, which made it downshift. The 'oldness' of the concept is not a problem. If it was sound 100 years ago, it's sound today. (The three-speed manual is still around. We still have the internal combustion engine) If they can make it reliable, it sounds good.
      • 2 Years Ago
      30 yr career tech here. this system is what is used in snowmobiles dirt bikes and lots of off road toys it is a very simple design as opposed to the traditional electronic automatic transmissions with hundreds of parts that can fail and are very costly due to the expertise required to repair one. durability can be worked out in a year or two of real world use. it will keep an entry level car cheap to repair. It will never be adaquite fo servere duty applications but has its place in commuter entry level cars.
      dreadcthulhu01
      • 2 Years Ago
      In the real world (and EPA tests, for that matter), current CVTs aren't more fuel efficient that a six-speed automatic - look at various comparisons of Nissan Altima vs other midsize sedans with similar size engines., for example. The friction losses of the pulley belts cancel out the benefit of keeping the engine in the optimum RPM range. And while Nissan is improving the efficiency of their CVTs, other car makers are improving their regular transmissions; 8-speed conventional autos & 6 gear dual-clutch autos are already available in mainstream vehicles, like the Dodge Charger & Ford Focus, respectively. And they still have reliability issues. Even Nissan, the largest maker of CVT vehicles, still has them fail at way too high of a rate. Nissan had to double the length of their warranty of CVTs to avoid a lawsuit on them.
        • 2 Years Ago
        @dreadcthulhu01
        I hate to sya your wrong, but you are wrong. Look at the 2012 Subaru Legacy, 2.5l (170 hp, 3248lb curb wieght .32 drag) with CVT vs the 2012 Dodge Avenger 2.4l (173 hp, 3400lb curb .38 drag) with a 6 speed automatic. The EPA says the Subaru gets 23/31 vs the Avengers 20/31. I admit everything there (hp, wieght, and drag) are a little in the Subarua's favor, but that is comparing an AWD vehicle to a FWD vehicle which is a lot more aof a disadvantage. For an apples to apples comparision, the Legacy 2.5l 6 speed manual gets 19/27, way less than the CVT. In fact if you look at AWD vehicles on the EPA's fuel website (fueleconomy_gov) the top car is a cvt (imprezza), followed by three hybrids. IF you remove the AWD all of the top cars are CVTs. Scroll through the hybrids with CVTs, and the top non-hybrid car is the Scion IQ, with a CVT. Just because Nissan's (and everyone else's) first generation of CVTs were lackluster, does not mean other auto companys are not getting it right. Even Nissan is getting better. As far as durability is concerned, once again, it is improving. This is the same as any new technology. Every manufacturer should go to titanium belts (like Subaru) instead of rubber. I will admit that using Subaru is a little unfair, since their first generation came and went in 1992 or so. This gives them the advantage of having further developed the technology than others. The 2013 Legacy has improved fuel economy over the 2012 even.
      Jack Holliday
      • 2 Years Ago
      just another version of the ancient centrifugal clutch thats been around for 100 years
      sjpxmas
      • 2 Years Ago
      I can shift if i want to,BUT IT'S JUST BOTHERSOME SO I JUST LEAVE IT IN DRIVE.....
      • 1 Year Ago
      If you're buying a brand new automobile, you will need to check drive one equipped with a unendingly Variable Transmission. The CVT is changing into additional and additional in style in today's vehicles. The CVT offers several blessings over the normal transmission. he CVT has no plates, no disc and extremely few elements. the overall plan is that the less elements the transmission has, the less elements that square measure probably to interrupt. The key components to a CVT are the input machine, the output machine and a metal or thick rubber belt. The CVT works during a} very simple manner. once driving a vehicle equipped with a CVT you may notice a continuing sleek increase in speed as you accelerate. This sleek and constant increase of speed is just outlined as a result of there are not any actual gears moving within the transmission. Sometimes, your car need repair and at this stage you can use rebuilt transmission service. Visit http://www.transmissionpartsdistributioninc.com/servlet/StoreFront for further automatic transmissions.
      BitRaptor Edyson Pav
      Take a look to this new transmission design by BitRaptor. Is a continuously variable transmission CVT gear only (the only one functional in the world), very compact and lightweight, and which could replace the current systems both for efficiency, simplicity and not least the costs. Because this CVT work only with pinions is better the all other systems by efficiency and high torque transmission. In the web page you will find more explanations, drawings and a short video of a basic prototype. http://www.bitraptor.com/en_edyson_CVT.html The first prototype will be ready for tests during this year.
      • 2 Years Ago
      A CVT is a great transmission alternative that not only increases fuel economy, but also often allows the computer to safeguard the transmission so a novice doesn't blow your transmission with the appropriate technology pairing like Mitsubishi's Sportronic 6sp CVT automatic transmission. It also ends up extending the life of the transmission because it helps protect the transmission from the misuse and abuse of the transmission that usually results in early failure. It is simply another tool to improve fuel economy for gas engines so we don't have to resort to ugly bricks like the Prius or the coffin that is the Smartfor2
        Leo
        • 2 Years Ago
        Most popular car with CVT = Prius. Yeah we might all have to resort to driving a prius. how awful. http://money.cnn.com/2012/10/23/autos/toyota-prius-sales-california/index.html
      • 2 Years Ago
      My 2005 Ford Freestyle with 138,000+ miles just got 30 mpg on a 1000 mile trip from Summit County,Colorado to Tucson, Arizona. It got 27 MPG on a 2000 mile RT from Tucson to Northern California a week later. It takes some getting used to, especially driving downhill where the car seems to freewheel and the transmission is useless for slowing the vehicle. Low gear does mostly nothing except make noise. It's towing and load capacity is also a joke for a car with as much room as the Freestyle has. Iusually overload by about 2000 lbs and still get high mileage. The trip from CO was in a totally overloaded car. However, if I have anything on the roof the gas mileage drops quickly. The same car on the same CO trip earlier in the year got 19 MPG with a loaded roof rack and 2 bicycles on the roof. The CVT didn't help with that kind of load and wind resistance.
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