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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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Comments (11)
  1. Again with the "Tronic" name? E- tron G- tron.just joking.
     
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  2. High number of gears is really needed due to the narrow power band curve of the ICE. With electric motor, you will only need 1 speed (or 2 speed for extreme high speed) gear box due to the broad torque and power curve of the electric motor with precise electronic control.
     
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  3. Diesels usually maintain decent torque even at lower RPMs; no doubt that such fine-grained gearbox can indeed help maximize the engine's output when one really steps on the gas, but I suspect that MB went this route also (mostly?) for fuel economy.

    I too remain impressed that such incredibly complex-looking gearboxes are apparently required to keep the ICEs vaguely efficient, especially compared to the EVs' straightforward single/fixed-speed gearing...
     
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  4. Actually, it is kind of amazing how "complex" the design is. Also, what is amazing is how "cheaply" an automaker can make that complex transmission.
     
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  5. What I find amazing is the recent spate of improvements the auto makers have quickly run to market with to improve mileage. With all the tech focus prior to 2008 being in huge gains in horsepower and little to no attention paid to efficiency. I know they are driven by profit and consumer trends but look how far we have come in essentially 3 years ( the first 2 years were dealing with the post 2008 panic/inventory glut). Imagine where would be if there was at least a modicum of conscience in our corporate psyche..Oh well, in this case, better to dwell on "what is" then "what could have been". Silver linings and all that.
     
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  6. @Lorne: I'd argue they're not being driven by "profit and consumer trends" in this case, but by stringent regulations in Europe, Asia, and the U.S. that require them to reduce carbon emissions / improve fuel efficiency substantially between now and 2025.
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  7. I imagine it wouldn't be bad as long as they make the shifts seamless. I rented a 2011 Malibu and the damn thing would shift 4 times by the time I hit 40mph. It was like driving a low-geared manual trans. I hated it.
     
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  8. heheh.. 4 times to 40mph b/c it still got 2 more gears left for the 40 mpg and above...

    Next time you floor it, it will stay in 2nd and 3rd until redline. It is a rental anyway... :)
     
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  9. All that and I still only managed 28mpg over the 200 miles I drove it. The Camry I rented got 36mpg on winter blend fuel and didn't have all the funky shifting. I couldn't wait to get back into my Volt! :p
     
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  10. CVT is where it is at…
     
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  11. Which type?

    The belt type or the two motor plantary gear type?
     
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