Automakers turn to gearless transmissions to improve gas mileage
By Chris Woodyard, USA TODAY
Sun Jun 11, 7:03 PM

Instead of slicker aerodynamics or reduced horsepower, automakers scrambling to increase mileage amid skyrocketing gas prices are going straight to an unexpected place — the transmission.

Nissan and DaimlerChrysler are hoping to raise gas mileage by up to 10% in models by equipping them with a type of computer-controlled transmission that never shifts gears. Called continuously variable transmissions or CVTs, these high-tech gearing systems let engines move seamlessly through the power range.

Auto enthusiasts aren't always fans of CVT. In some versions, it can sometimes create an odd driving experience as the car accelerates into mid-ranges. The engine might rev up to close to its maximum speed when the pedal is floored and stay there until the car picks up sufficient speed. Only then does the engine slow down.

General Motors' Saturn division tried CVT in the Vue SUV but changed back to a standard automatic transmission a couple years ago. "We felt the six-speed was a better place (for) our future," says Jerry Gillespie, the executive in charge of GM's compact crossover vehicles.

Chrysler Group engineers say they've overcome the problems. The computer detects when the car is revving up and adjusts the transmission to make the car feel as if it is running in a lower gear even as speed increases, says Frank Klegon, executive vice president of product development for Chrysler Group.

The new system, he says, is "pretty inventive."

Toyota has been using CVT in its hybrid vehicles, such as Toyota Prius and Lexus GS450h. Some drivers aren't accustomed to not being able to feel changing gears.

CVT "gives you a seamless range of gears, which some folks like and some don't," says Toyota engineer Dave Hermance.

How transmissions compare

The continuously variable transmission works differently than a standard automatic transmission.

Automatic transmission

The modern automatic transmission involves a series of gears — called planetary gears for the way they move around a central or sun gear. As a car goes faster, the low gear automatically shifts to a higher gear. The driver can hear or feel the change.

Continuously variable transmission

CVTs work on a system of belts and pulleys — kind of like the fan belt used to work in older cars. The difference is that the two spinning wheels, or pulleys, manipulate the belt to make it larger or smaller depending on the car's speed. The change is continuous, not gear-to-gear as in the regular automatic transmission. The driver may never sense the change.

The V-shaped belts are made of thin metal bands and small metal plates. They are more durable than rubber belts.

Who is using CVTs

Nissan. CVT already is in Nissan's Murano crossover SUV. Now it comes to its cars — Maxima, Altima and the new Versa subcompact. Jed Connelly, Nissan's U.S. marketing chief, says the CVT system can increase gas mileage up to 10%.

DaimlerChrysler. Patriot, Chrysler Group's new, most inexpensive Jeep, joins Dodge Caliber and Jeep Compass in offering an optional advanced second-generation CVT. The system is billed as delivering up to 8% better fuel economy than a traditional four-speed automatic.

Ford. The V-6 engine in Ford Freestyle crossover SUV is paired with a CVT for better fuel economy. CVT also is used in the Ford Five Hundred and Mercury Montego sedan models that have all-wheel drive.

Audi. The German automaker has CVT available on all its sedans — the A4, A6 and A8. It first showed up in the late 1990s. "It's very popular," says Audi spokesman Peter Thul.