Mercedes-Benz Launches Fuel-Saving Nine-Speed Auto

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Mercedes-Benz will slowly start rolling out a new nine-speed automatic across its range, starting with the E350 BlueTEC diesel-powered sedan and wagon. The new gearbox, dubbed the 9G-TRONIC, is yet to be announced for the U.S. market but Mercedes says it expects it to be offered as a standard feature on most of its models, including hybrids and plug-in hybrids, within the next couple of years.

Developed in-house, Mercedes’ 9G-TRONIC gearbox is said to improve not only the efficiency but the performance and ride of the automaker’s cars as well.

The key is the higher number of gears and broader gear ratio spread (9.15 for gears one to nine). This allows an engine to run at lower revs, meaning smoother operation and less fuel consumption.

For example, in the E350 BlueTEC, whose 3.0-liter turbodiesel develops 248 horsepower, cruising at 75 mph in ninth gear sees the engine ticking over at just 1,350 rpm.

Fuel economy, meanwhile, is a claimed 36.75 mpg in the city, up from 34 mpg with the previous 7G-TRONIC seven-speed automatic, while the highway figure remains unchanged at 50 mpg. Note, European figures are listed.

Mercedes also expects fuel savings from an engine stop-start system that is incorporated into the design and reduced overall weight compared to the seven-speed ‘box it replaces. Despite the extra gears and a torque rating of 737 pound-feet, the 9G-TRONIC requires as little installation space as its seven-speed predecessor and is lighter, too.

If that’s not enough, less frictional losses have been brought about by keeping the number of planetary gear sets and shift elements as low possible. Four simple planetary gear sets and six shift elements are used and work together with three speed sensors.

Mercedes, of course, is not alone in its quest to eke out fuel savings by adding more gears to its cars. Gearbox specialist ZF has already announced a nine-speed automatic that will appear in the Range Rover Evoque later this year and some Chrysler products, too. Ford and General Motors have also formed an alliance to develop nine-speed and even ten-speed automatics for use in their respective models.

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