• Jul 19th 2010 at 4:31PM
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According to Autocar, an admission by a Mercedes-Benz engineer proves that the company is working on a nine-speed automatic transmission. That isn't exactly new, since talk of such a beast has been broached before. The difference this time is that Autocar's sources says the gearbox will be "introduced on large-capacity engines."

With no numbers for context we can't be sure what's meant by "large-capacity." However, Motor Trend reported that the baby SLS would get a nine-speed double-clutch transmission for it's twin-turbo-V6-hybrid engine, and Automobile said that all of the next generation S-Classes, arriving in 2012, would "have hybrid powertrains and a new nine-speed automatic transmission."

We don't expect any of those engines to be of particularly large displacement, especially now that the SSK AMG appears to have gone from a twin-turbo V8 to a V6 twin turbo with electric assistance. Still, we have no doubt we'll see a nine-speed transmission somewhere. And when the Mercedes engineers opine that "nine ratios is the maximum that is technically possible, as well as being the most that customers will be able to cope with," we believe they're wrong. A company is really going to leave double-digit transmission bragging rights on the table? Uh, no. Can I get a ten-speed... anyone...?

[Source: Autocar]

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    • 1 Second Ago
      • 5 Years Ago
      Does having so many speeds in a gearbox increase its size or weight significantly?

      I know only the basics of automatic transmission design, but I it seems the complexity is within the planetary gear set design, and hydraulic pumps. All the parts in an automatic are within each other it seems.

      A 9 speed DCT on the other hand i'm pretty sure would be a massive piece of engineering, since you need to provide separate space for all the gearsets, clutches and shafts.

      Anyone understand these principles more concretely?
      • 5 Years Ago
      Gud Lawd how many speeds to do ya need??? By the time you reach the 9th speed you'll be going 200 miles per hour.
      • 5 Years Ago
      A bicycle has lots of gears, because human legs have a very narrow power-band, in terms of applying torque to the pedals, compared to the speed at which the person is pedaling.

      Lots of gears mean than the bicyclist can maintain a pedaling pace, and the GEARS can adapt to the terrain, and allow various amounts of mechanical advantage.

      An engine, however, with a rev range as wide as 6000 rpms or more, needs fewer gears.

      Gears add weight, complexity, take up space, generate shearing in the oiling system, and add heat to the transmission. Lots of moving parts sharing the same space means each part has to be smaller, and more susceptible to breakage. more parts to break or get jammed by broken bits creates more damage if something goes wrong. It adds cost, both to build, and to repair or maintain.

      Frankly, some 7, 8, and 9 gear ratios in an automatic gearboxes are getting ridiculous. Automatic gearboxes used to be doing well to have FOUR ratios. Even autobahn german cars from a decade or two ago.

      Gears need to be properly chosen, and chosen systematically, in concert with engine power range from idle to redline, final drive ratio, wheel and tire rolling diameter, and vehicle road-speed consideration.

      Why should these companies that electronically limit every one of their vehicles to 155mph gear the transmission and final drive for 205mph? Or why do they continue to impose the electronic limit?

      Once you have the mathematical range that the transmission should be used for, engine range input, road-speed (factored for final drive and wheels) output range... you have your start and end points.

      Then you make determinations about how many intervals (gear ratios) between those two end points. Having 9 intervals is un-necessary, and overly complex. Depending on the range between the end-points, 5, 6, or barely maybe 7 should be plenty of intervals to accomplish the task of utilizing the engine's output to apply to road speed.

      The fewer parts in the same space, the more robust the parts can be, and the more efficient the machine can be, and the most cost-efficient the machine can be, as well.

      9 speed is just bragging rights to top BMW and Lexus. Nothing more, and it is futile. You don't have to be an automotive engineer to see that, and not everything auto engineers do is pure as the wind-driven snow. Sometimes the decision makers pass down the edicts to one-up the competition, or other non-technical orders that are expected to be met.
        • 5 Years Ago

        a range of 240rpm is not a wide power band at all, in a realm wider than physiology.

        A range of 90rpm is a very narrow power band.

        A car's engine has an effective power band thousands of rpms wide, and torquey MB V8s are on the generous side, rather than a narrow torque curve.
        • 5 Years Ago
        Total agree.
        The powerband of NA and turbo/supercharged engines is super wide these days. And the torque range is amazing too.

        This just adds complexity. And lots of odd powerless gaps and 'shift shock' while you're driving.

        Improvements could be made on the actual engines themselves. They are very low tech compared to Ford/Hyundai ...
        • 5 Years Ago
        The human legs have a wide power band. 0-240rpm.
        It is just not bio-mechanically efficient to pedal less than 90rpm or faster than 180rpm

        Hopefully MB gets a wide ratio spread, 9:1, a 50% improvement over the 7g-tronic.
        If they do, then the torque converter is going away, permanently.
        GM thought they had enough ratio spread with 'just' 6 speed automatics, they didn't.

        and they have to stay a half-step ahead of Hyundai.
        • 5 Years Ago
        Good points, but I would like to add to it:

        A point for more gears:
        I believe that what has opened up the door of more gears is the dual clutch. Suddenly, shifting is instaneous, so why not do it more often. Also when the shift happens between ratios that are closer together, it will happen more smoothly and cause less stress on the gears and clutches

        A point for fewer gears:
        Most companies are going toward the direction of direct injected, turbo charged lower displacement engines. These engines have much higher low end torque giving them an ideal, almost completely flat horsepower curve. If you can get the same hp regardless of what your tach reads, why shift so much? The low end torque does, however, argue for a higher top gear.
      • 5 Years Ago
      The engineers are working towards their holy grail of making it go to 11.
      • 5 Years Ago
      the more the merrier
        • 5 Years Ago
        Seven was one too many, nine is overkill.
      • 5 Years Ago
      Coming in the year 2020: A 185-speed automatic transmission; one gear for every mph!
      • 5 Years Ago
      Just drop a hi/low after a 6spd manual and you can have 12 shift points. And one leg much stronger than the other.
      • 5 Years Ago
      Mercedes TRucks have always been agead in the tranny sector... something like 16 gears in total, so the cars still have a long way to go lol...
      • 5 Years Ago
      If these transmissions are going to have super short gears, what's the point? Creates more gear hunting for the transmission. I'd take a 5 Speed Auto if it could keep the car at 1500 RPM at 70 MPH while returning decent fuel economy.
      • 5 Years Ago
      MB seems to thrive on the sport of one-upmanship...I remember about half a decade ago, when their AMG cars came out with superchargers and they systematically outpowered BMW and Audi's engines
      • 5 Years Ago
      This is getting to be like razor blades...
      • 5 Years Ago
      Erm, diesels should LOVE more gears.

      Also, for RWD applications, why not have multiple diff ratios? Instead of 9x1, have 4x3..
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