BMW’s Dual-Clutch 7-speed manumatic transmission is about to make waves

Discussion in 'BMW' started by xcel, Jan 27, 2008.

  1. xcel

    xcel PZEV, there's nothing like it :) Staff Member

    First dual-clutch auto tranny to handle the output of a consumer based performance automobile.

    [xfloat=right]http://www.cleanmpg.com/photos/data/501/2008_European_BMW_M3.jpg[/xfloat]Wayne Gerdes - CleanMPG - Jan. 26, 2008

    2008 BMW M3 Convertible -- 400 + HP and almost 300 Ft-lb’s of torque through an automatic transmission that allows superior performance, better FE and weighs just 40 pounds more than the manual it replaces.

    BMW debuts the world’s first Double Clutch Gearbox with Drivelogic developed for higher speed, higher power output consumer based engines. Unfortunately, it is currently only available on the new European M3 Coupe, M3 Sedan, and M3 Convertible.

    The M’s double-clutch transmission is a seven-speed gearbox designed for high power throughput. Compared with a conventional automatic or manual transmission, the new gearbox ensures optimum shifts and better acceleration while at the same time reducing fuel consumption. The transmission does this by seamlessly shifting gears without power interruption from a stop to any speed with or without driver input. The standard automatic mode is available with the gearshift in D (drive). Two manual modes are also available while in S (Sport) mode which allows shifting via either the paddle shifters on the steering wheel or with the gearshift in a straight and sequential manner.

    Racing sets the stage for the consumer

    The double clutch gearbox was first developed for motor sports where every tenth of a second is crucial. Over the years, this unique transmission concept has proven its worth in the same way as the sequential gearshift used in Formula 1. The ability to shift up at WOT without the slightest interruption in the application of torque allows even professional drivers to shave a few fractions of a second off their best times at the track.

    Until now, consumer based double clutch manumatic gearboxes could only be used with lower revving and relatively low torque engines. For the first time, the benefits of a double clutch gearbox are now available to the consumer regardless of the size or power of the engine.

    How does a double clutch manumatic transmission operate?

    Double-clutch transmissions combine two gearbox components in a common housing with the same compact dimensions as a conventional manual gearbox. The “heart” of the new M double-clutch transmission in technical terms is formed by the two oil-cooled wet clutches. One of the two clutches is for the even (2, 4, 6), the other for the uneven (1, 3, 5, 7) gears and, in addition, for the reverse gear.

    While driving, one of the two clutches is always closed, the other is open. When accelerating – and when shifting down – the clutches are activated in an alternating process, one after the other. When shifting gears, therefore, the first clutch opens just as the second clutch is closing. This ensures an absolutely smooth, comfortable and at the same time incomparably fast gearshift without the slightest interruption in the flow of power. This interaction of two clutches ensures an unparalleled rate of gear change in particular because the transmission control unit pre-selects the next gear. The transmission ratio is matched ideally to engine and road speed and the gear is held in waiting for immediate operation.

    The key to the entire process is that it takes only a few milliseconds, meaning that in the time even a skilled driver takes to press down the clutch pedal the M double-clutch transmission with Drivelogic has easily completed the entire process of shifting gears, continuing to accelerate in the next gear higher up.

    With the process of engaging and disengaging the gears continuing in a smooth flow, the positive engagement of the engine to the transmission is not interrupted, allowing the driver to set off smoothly, comfortably and, in particular, to shift up at an incomparably fast speed.

    When down shifting, a double-clutch transmission works exactly the same. The only difference is that the electronic transmission control makes the process of engaging the clutch smoother and softer to prevent the rear wheels from being slowed down too suddenly.

    Negatives?

    Special cooling requirements are required to handle the M’s double-clutch transmission under extreme conditions. Due to the possibility of high thermal loads during high power output, the M’s transmission fluid is kept within an optimal temperature range by using both a standard engine coolant based transmission cooler and an additional air/oil cooler to avoid excessively high temperatures.

    A positive to the design is that the transmission fluid is also heated by the engines coolant system during initial start-up allowing the transmission to reach normal operating temperature faster in colder climates. This helps to reduce frictional losses in the warm-up phase and saves fuel in the process.

    More gears allowing higher efficiency

    Compared with a conventional automatic or manual transmission, the M’s double-clutch transmission allows greater fuel economy and cleaner emissions using the same engine with the same power. This is primarily attributable to the more direct connection between the engine and the transmission, the lack of RPM cycling between shifts during accelerations and the ability to run taller gears without a standard automatic's power robbing frictional losses.

    With the advent of track tested dual clutch transmissions for the masses offering superior performance and higher fuel economy over and above either a standard manual or automatic transmissions today, it should only be a matter of time before we see these advanced but lightweight drivetrains in far less expensive and more main stream vehicles in the near future.
     
    Last edited: Jan 27, 2008
  2. Tochatihu

    Tochatihu Well-Known Member

    Sounds complicated, with a lot of little whirly things in there. It is amazing the lengths that engineers will go, to avoid an eCVT with a couple of electric motors. Ah but variety is the spice of life.

    Short ATF change intervals ("Special cooling requirements...") might eat into those fuel economy saving. What a whiner I am!

    DAS
     
  3. xcel

    xcel PZEV, there's nothing like it :) Staff Member

    Hi Doug:

    ___The cool thing is when looking at the sedan, the Dual clutch unit was lighter than the manual by 10 pounds! The only reason for the extreme cooling on the M3’s is BMW expects the darn things to actually spend some of their time on the track! For the average DSG in a non-racing performance environment, I suspect a std. cooling solution would suffice just as it does in a std. automatic.

    ___If you have ever seen the inside of a modern day automatic, the smaller, smoother shifting and lower weight dual-clutch units are far less complicated imho.

    ___Then you have HSD :p

    ___Good Luck

    ___Wayne
     
  4. antrey

    antrey Well-Known Member

    The dual clutch transmission in the new Mitsubishi Evolution X also counts as a high torque capable dual clutch tranny and slightly beat BMW to the punch.
     
  5. koreberg

    koreberg Junior Member

    @antrey

    I think they said high speed/power because vw has had a dsg for sometime now that does the same thing but in cars making about 70% of the power.

    Hopefully this will work better than the smg, that was good on full throttle and light throttle but not good anywhere in the middle.
     
  6. WriConsult

    WriConsult Super Moderator

    Tochatihu, as I understand it eCVTs are not exactly the most efficient transmissions on the market. I think I remember hearing they're on the order of ~70%, which is why GM/DaimerChrysler chose a slushbox based system for the 2Mode system, still several percent less efficient than a dual clutch/DSG system.
     
  7. brick

    brick Answers to "that guy."

    Tell them to wake me up when it goes into a 330d Touring for the US market. (Umm...and wake me up if I'm ever making enough money to afford that.)
     
  8. psyshack

    psyshack He who posts articles

    Im waiting on the 1 series as my next evil set of wheels.....

    Ive been very impressed with the 3 and z4 over the last few years. As spirited driving machines. And they seem to hold up well too. And with BMW's free four year maint. program. Im looking forward to a garage queen BMW.

    6MT :ip:
     
  9. xcel

    xcel PZEV, there's nothing like it :) Staff Member

    Hi Antrey:

    ___The last time I did one of these write-ups on the dual-clutch units was Audi’s a few weeks ago but what impressed me was the Mitsu display at the 2008 NAIAS with their own Dual-clutch attached to an upcoming diesel IIRC. I could have picked it up myself given the compactness. There is some good news wrt VW as well. Their current 6-speed DSG is being converted over to the new 7-speed and from the press site, anything under 250 Nm of torque will get it for their own automatic solution. There was no information if their own will make it to the US but everything in Europe below the torque limit will be sticks or the new 7-speed DSG’s! Somebody asked about VW and their own DSG in another thread around here a few days ago but I could not find it and I did not want to write-up yet another Dual-clutch News item so soon … It might make us sound like a bunch of geeks or something ;)

    ___These new dual-clutchers are light, compact, less complicated, as fuel efficient then a stick (more in some respects) and absolutely seamless from 0 to whatever speed you are headed up to. Knocks the hell out of a std. Auto we have been driving and stuck with the past 50 years imho. FAS’ing is still an unknown with some of these units however … The good old flat tow in the manual will give us the answer to that question wrt to BMW’s solution ;)

    ___Jeff, that 1-series with the new 2.0 Turbo-diesel, a dual-clutch auto (or 6-speed stick ;)) and all the handling BMW is known from any of their vehicles would be a very nice ride indeed!

    ___Good Luck

    ___Wayne
     
  10. shifty35

    shifty35 Well-Known Member

    My comments roughly mirror my comments on the previous twin-clutch setup. Seems like maintenance hell, as I like to do my own maintenance. A standard clutch is easily doable with a decent set of tools, but I'd be scared out of my mind to rip apart a BMW trans.

    FE-wise, I'd venture the benefit doesn't have anything to do with the twin-clutch, but the 7 gears available.
     

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