A quote from WIKIPEDIA:
"CVTs have been used in aircraft electrical power generating systems since the 1950s and in Sports Car Club of America (SCCA) Formula 500 race cars since the early 1970s(Interesting factoid: CVT's were banned from Formula 1 in 1994 because they were making the cars too fast).More recently, CVT systems have been developed for go-karts and have proven to increase performance and engine life expectancy. The Tomcar range of off-road vehicles also utilizes the CVT system"
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Variable-diameter pulley (VDP) or Reeves drive
In this most common CVT system,[1] there are two V-belt pulleys that are split perpendicular to their axes of rotation, with a V-belt running between them. The gear ratio is changed by moving the two sections of one pulley closer together and the two sections of the other pulley farther apart. Due to the V-shaped cross section of the belt, this causes the belt to ride higher on one pulley and lower on the other. Doing this changes the effective diameters of the pulleys, which in turn changes the overall gear ratio. The distance between the pulleys does not change, and neither does the length of the belt, so changing the gear ratio means both pulleys must be adjusted (one bigger, the other smaller) simultaneously in order to maintain the proper amount of tension on the belt.
The V-belt needs to be very stiff in the pulley's axial direction in order to make only short radial movements while sliding in and out of the pulleys. This can be achieved by a chain and not by homogeneous rubber. To dive out of the pulleys one side of the belt must push. This again can be done only with a chain. Each element of the chain has conical sides, which perfectly fit to the pulley if the belt is running on the outermost radius. As the belt moves into the pulleys the contact area gets smaller. The contact area is proportional to the number of elements, thus the chain has lots of very small elements. The shape of the elements is governed by the static of a column. The pulley-radial thickness of the belt is a compromise between maximum gear ratio and torque. For the same reason the axis between the pulleys is as thin as possible. A film of lubricant is applied to the pulleys. It needs to be thick enough so that the pulley and the belt never touch and it must be thin in order not to waste power when each element dives into the lubrication film. Additionally, the chain elements stabilize about 12 steel bands. Each band is thin enough so that it bends easily. If bending, it has a perfect conical surface on its side. In the stack of bands each band corresponds to a slightly different gear ratio, and thus they slide over each other and need oil between them. Also the outer bands slide through the stabilizing chain, while the center band can be used as the chain linkage
FROM EDMONDS AUTOMOTIVE:
"CVT Enters the Mainstream
By Scott Memmer
Email
Our staff, as well as other automotive enthusiasts, has noticed an ever-increasing level of interest about a new/old technology called CVT (continuously variable transmission) and its burgeoning rise in the automotive world.
We say "new/old" because CVT has actually been around since 1886, but has only recently begun to find its way into production automobiles.
CVT's promise, both as a boon to fuel economy and as a low-cost alternative to conventional transmissions, has prompted us to revisit the topic.
Since our article CVT For You and Me appeared, a number of automakers have brought new CVT-equipped vehicles to market, and more are on the way. We felt now was a good time to take a closer look at this innovative — and time-tested — technology.
As we mentioned above, CVT has been around for more than a hundred years. However, until recently, it was reserved for industrial applications — running lathes or light-duty drill presses, for instance. With the introduction of improved materials, such as high-density rubber belts, advanced hydraulics and, more recently, high-speed sensors and microprocessors, the stage was set for CVT's rise in the automobile.
CVT's design advantages lie not only in its efficiency but in its simplicity. It consists of very few components. A continuously variable transmission typically includes the following major component groups:
•a high-power/density rubber belt
•a hydraulically operated driving pulley
•a mechanical torque-sensing driving pulley
•microprocessors and sensors
That's it.
Because of this simplicity in design, CVT offers some advantages over traditional transmissions, although it also has certain drawbacks. For instance, its belt-driven orientation limits its application; until recently, cars with engines larger than 1.2 liters were considered incompatible with CVT. More and more, however, CVTs are becoming available that can handle more powerful engines, such as the V6 power plants found in some Nissan and Audi vehicles.
Other disadvantages include its larger size and weight.
Still, in the right situation, CVT's advantages outweigh its disadvantages. Less complexity and moving parts theoretically mean fewer things to go wrong and maintain.
The first U.S.-sold production automobile in the world to offer a CVT transmission was the Subaru Justy GL, from 1989 through 1993. The engine in that car was 1.2 liters.
How it Works
Although there are different variations on the CVT theme, most passenger cars use a similar setup. Essentially, a CVT transmission operates by varying the working diameters of the two main pulleys in the transmission.
The pulleys have V-shaped grooves in which the connecting belt rides. One side of the pulley is fixed; the other side is moveable, actuated by a hydraulic cylinder. When actuated, the cylinder can increase or reduce the amount of space between the two sides of the pulley. This allows the belt to ride lower or higher along the walls of the pulley, depending on driving conditions, thereby changing the gear ratio. If you think about it, the action is similar to the way a mountain bike shifts gears, by "derailing" the chain from one sprocket to the next — except that, in the case of CVT, this action is infinitely variable, with no "steps" between.
The "stepless" nature of its design is CVT's biggest draw for automotive engineers. Because of this, a CVT can work to keep the engine in its optimum power range, thereby increasing efficiency and gas mileage. This translates to a gain of about 1-2 mpg, but as with any car, your mileage will vary based on your driving habits. A CVT can convert every point on the engine's operating curve to a corresponding point on its own operating curve.
With these advantages, it's easy to understand why manufacturers of high-mileage vehicles often incorporate CVT technology into their drivetrains.
Look for more CVTs in the coming years as the battle for improved gas mileage accelerates and technological advances further widen their functionality."
I KNOW IT'S VERY LONG ...BUT WORTH THE READ!
Ken
