Continuously Variable Transmissions ( CVT )

Continuously Variable Transmissions Are Gaining Popularity
CVTs are the hot ticket right now in the automotive industry. While you were busy understanding and repairing two-speed Powerglide and Fordomatic transmissions and then the three-, four-, and now five-speed trannies, some manufacturers were already toying with the CVT principle. One of them was the small Dutch manufacturer van Doorne Automobiel Fabriek, who launched a very small car, the DAF 600, in 1958. It was probably the very first mass produced car with a CVT transmission, but it was not a success. Motorists would have to wait until 1987 to get another small car with a CVT transmission in North America, the Subaru Justy. But once again, the mechanical part was not very popular with car buyers.

A new era
Actually, one of the most important manufacturers to really get involved in the development of the CVT was Japanese automaker Nissan when it launched its new Murano crossover available only with a CVT. That was in 2003. Today, Nissan offers the CVT transmission on many of its new products, including the redesigned Murano, the Altima, the Maxima, the Rogue, the Sentra, and the Versa.

CVT transmissions can also be found on some Audi A4 models, on Chrysler’s Dodge Caliber, Jeep Compass and Patriot, on Ford’s Hybrid Escape (and, in the past, on its Five-Hundred and Freestyle), on BMW Minis, on Mercedes-Benz Class Bs, on certain Honda Civic Hybrids, on Mitsubishi Lancers, and even on some Hybrid Toyota Camrys and Highlanders.

What’s a CVT?
But what is a CVT transmission? As most regular automatic transmissions rely upon standard gears to operate, the Continuously Variable Transmission has very few parts to operate. Basically, the actual CVT transmission now in production uses a system of variable pulleys connected by a belt to work. The first pulley is made of two variable “cups” connected to the engine. The second pulley is also made of two variable “cups” that are connected to the transmission shaft. Both pulleys are connected by a “belt” made of very small chain links all connected together or thin, high strength metal slices riding on steel bands (some manufacturers like GM tried rubber components on its Saturn cars and SUVs but that was a failure that obligated GM to withdraw from that technology). When the “drive pulley” (connected to the engine) increases its radius, the “output pulley” (the one connected to the driveshaft) decreases its radius to keep the belt tight. As the engine accelerates its speed, the drive pulley sees its cups parting and the radius increase. At the other end, the output pulley sees its cups closing in on each other. At the beginning, when the drive pulley has closed its cups and the output pulley has spaced its cups, the transmission is considered in “low” gear. With increasing engine speed and the drive pulley cups spacing out while the output pulley cups are closing in, the transmission is going into “high gear.” But since we are talking about cups closing in and spacing out, there are no actual gears.

Consequently, the CVT is more or less like an automatic transmission that would have 60 to 80 “gears.” As far are the movement of the pulleys is concerned, their “cups” might space up or close in by hydraulic pressure, centrifugal force or spring tension. And before you ask, yes, it is the same principle found on press drills, some tractors, motor scooters, snowmobiles, and ATVs. But these vehicles or tools rely upon a rubber belt. It is not so for cars, as we explained earlier.

What are the advantages?
So, if traditional automatic transmissions worked so well for the past fifty years or so, why change to the CVT? Actually, it has been proven that CVTs save a lot of fuel compared to the traditional automatic transmission. They do so by using the engine’s best torque band at its max with as less friction as possible. The CVT produces less friction because it has less working parts. And it has infinite gear ratios so it makes it more economical. Also, since it does not actually “change gears,” it will not produce jerky movements. Acceleration is constant and linear. Obviously, some drivers might feel a little uncomfortable without those movements. So some manufacturers will “add” a shift pattern to their CVT transmission to make it feel like a more conventional automatic transmission.

Driving a CVT equipped car
Driving a CVT equipped car requires a little getting used to. For most drivers accustomed to more regular automatic transmissions, driving a CVT equipped car or SUV will be a new experience. The sound of the engine might increase but it will not decrease like it does when shifting gears with an automatic. When passing, a driver who puts his foot to the floor will hear the engine roaring and keeping its revs pretty high until he releases the accelerator. If he doesn’t, the car will pick up speed until it reaches its electronically set maximum.

How reliable is it?
Obviously, like any mechanical parts, some CVT transmissions have failed. But most reports show that CVT transmissions are fairly reliable. But it seems that their application is better on smaller cars than bigger vehicles, which might explain why Ford has not continued the use of CVTs when their bigger Five Hundreds and Freestyles with a 3.0-litre V6 engine were modified into Tauruses and Taurus Xs with a more powerful 3.5-litre V6. Heat is the CVT’s biggest enemy so there are specific oils for these transmissions. One of the most important CVT manufacturers is Japanese builder JATCO, who provides CVTs for such automakers as Chrysler, Nissan, and Mitsubishi. Ford relied upon the ZF-Batavia CVT product. Consequently, expect to see more and more CVT trannies coming up on cars, especially the small ones.

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