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Throughout The Car Industry

CVT Transmissions

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On: Fri, Sep 30, 2011 at 1:11PM | By: Peter C Sessler

CVT Transmissions

The carmakers are always concerned with gas mileage, considering how America is infatuated with pickup trucks and —which aren’t known for getting good gas mileage. Still, the carmakers have federal gas mileage standards to meet and they aren’t going down. That is why we’re seeing hybrid drivetrains, lightweight construction, and the feasibility of using alternative fuels. The thinking is that eventually another gas crisis may come, but, also, the more economical cars that are sold, the more gas hogs they are allowed to sell. The high mileage of the econo-cars is averaged with that of the SUVs and trucks, and so a corporate “average” is attained.

So anything that can be used to allow cars to get better mileage is under scrutiny. One of these is the CVT (continuously variable transmission). Actually, this technology is not new by any means as it was originally introduced in 1886. Honda was the first manufacturer to introduce a CVT in U.S.A. in their 1996 Civic HX, which got 35/41 mpg city/highway. Typically, a CVT is about 20% more fuel efficient than a regular automatic.

Instead of using a combination of gears, clutches, hydraulic fluid, and a torque converter, the CVTs use a simple belt and pulley design. The pulleys are cone-shaped and there’s a belt that runs between the narrow and wide end of each pulley and, thus, a variable ratio is achieved. For example, in the Honda, as the belt moves between the wide and narrow sections of the pulleys, an equivalent gear ratio of 0.45 to 2.45 is attained.

Because there are no gears changing, a CVT is smoother, but its real advantage is that it allows an engine to stay in its power band without having to shift if a hill or a situation requiring acceleration is encountered.

Sounds great, so why don’t all cars use them? The problem is they haven’t quite figured out how to make these transmissions live with high torque/horsepower engines. Belts and pulleys aren’t as strong as gears, which is why CVTs are limited to small engines. GM introduced its version of CVT known as VTi in 2002. It was used in the Saturn Vue and Saturn Ion models. This transmission was quickly withdrawn in 2005 models due to high failure rates.

Even so, more than one million CVT-equipped cars are sold yearly—most of them in Japan. Still, as more car companies—such as Chrysler, Audi, BMW, Mitsubishi, and others—refine the design, improvements are bound to be made and we’ll see more and more CVTs in American cars.


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