BMW M dual-clutch transmission in detail

BMW M dual-clutch transmission in detail

BMW M dual-clutch transmission in detail

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Following the announcement of the new BMW M3 Convertible earlier this week comes news of the carmaker’s first dual-clutch transmission, which is set to make a simultaneous debut in the M3 Coupe and Sedan as well as the drop-top. BMW has raised the bar by introducing a seven-speed version of the increasingly popular gearbox design, promising to deliver optimum gearshifts and faster acceleration (than the conventional six-speed manual), while at the same time reducing fuel consumption.

The gearbox is linked with the M3’s Drivelogic system and its eleven electronically controlled driving programs. There are five shift programs for automatic mode and six shift programs for manual mode including the revered launch control system. When in manual mode, the driver can either shift gears using the gearstick or by flicking a set of paddles located on the steering wheel. Right paddle to shift up and left paddle to shift down.

The M double-clutch transmission with Drivelogic combines two gearbox components in a common housing but is no bigger than a conventional manual ‘box. 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.

First drives of the cars equipped with the new transmission aren’t scheduled until after the Geneva Motor launch next month, so we’ll have to wait until then to see the performance numbers of the new unit. But we think it’s safe to assume acceleration numbers will be a few tenths quicker than the current manual models.
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Comments (11)
  1. I've always wondered about one thing regarding these trannies; how fast can you double shift? i mean, if i wanna shift from 5th to 4th to 3rd, how fast can that be done? as fast as i can flick the paddle? think about it. 5th to 4th will be quick cause its just a matter of letting out one clutch and letting the other one in... but going from 4th to 3rd then means that the next gear has to be selected, and THEN the clutches can change again. how fast does that happen?

    also, if i switch from 5th to 4th, is there a program that looks at my driving style and decides whether to queue up 5th or 3rd? i mean, i could want to down shift from 5th all the way to 1st to do some engine breaking, or i could be driving through some twisty roads and be engine breaking in the corners to get the revs up and then punching it on the way out. just how does the car know which gear im going to want next; and does the gear selection happen so fast that theres no queuing or gears needed? it just selects the gear while doing the clutching and robert's your father's brother?

    I know the gear transitions are in the tenths and hundredths of a second (which is stellar btw) but just how fast can this thing go from queuing up the next gear it thinks im going to want and have to disengage that gear and go to the one that i actually selected??

  2. If you want to experience dual clutch gearbox just go to your next VW dealer and book a test drive in a Golf GTI DSG. These gearboxes are really smart and in my opionion they are the future. I can't tell you exactly how the technique is functioning but when you driving this thing it seems to always know which is the next gear you want to select. I can only explain this to myself in the way that both boxes (for the even and uneven gears) are operated like a sequential gearbox and the gearchanges and changes between the boxes are so fast that hardly notice any waiting time for a new gear. The most impressive thing is that on the upshifts you don't encounter any interruption of traction like you have it on manual, autos, or sequential gearboxes. The car just acclerates till its highspeed. One downside is that on the normale VW DSG gearboxes it changes up or down automactically when the revs are to high or to low like an automatic even in manual mode which I don't like so much for track use or sporty driving. But this is only a software issue which could be solved.

  3. Nothing beats the feel of a standart stick shift! How do you short shift a DSG? I often use the 1,3,5 patern in order to get to top gear as soon as possible.

  4. 7 gears seems like a lot of gears to keep track of if you're doing it yourself.
    With that short of gear ratios, it's better to let the car decide most of the time, and shift when you need to. I wonder if you can do that, sort of semi-automatic shifting?

  5. Do you short shift for better fuel economy? When the engine is warm you can also rev up in second and then change directly to the fifth gear.

  6. On most DSG systems if you press the downshift paddle twice quickly the system will move down 2 gears. However this will not be instant and usually take between 100-300ms.

  7. CK: i realize the shift times are incredible and theres no interuption of power.. i really get that. what i'm saying is.. if im in 4th.. theres two gears i can go to in a sequential box. 5 and 3. its a good assumption that im going to 5... but what if i wanna go to 3? if the thing is assuming 5... and its got it queued up.. ready to go.. just dump the clutch.. well i know how fast those shift times are.. theyre under 0.1 seconds on these things. what i wanna know is if you trip this thing up and go to the gear that it didnt think you'd want.. how long does it take for it to ACTUALLY SWITCH the gears. you kno?

    Ryanza; i agree, but even more so... I go 1-2-5. all the time. 1 gets me up to 30 kmph easily... 2nd will take me up to 80 or 90 even.. at which point 5th is my cruising gear. I'm not going to say i do that going onto highways.. i use the full range for sure... but 1-2-5 gets me going on city streets quite easily (and excitingly too. its nice to hear that elegant purr of a 4 cylinder.)

    Gus; in a sequential box, it doesnt matter how many gears you have.. just keep flipping that paddle up until it doesnt do anything. and from what CK is satying, they are semiautomatic, in the VW anyways. a lot of manumatics do that to prevent you from blowing the engine or the gear box. what i cant wait for is when ford puts this in their cars with a full auto mode. i think maserati is the only brand with that option thus far. I cant wait to be able to buy a ford focus with an either fully manual sequential DSG, or a fully automatic mode.

    CK: nice to know I'm not the only one. short shifting doesnt really give you better econ... ideally you'd short shift through every gear for better econ; try to keep the engine as close to the sweat spot as possible while keeping nothing more than a feather on the gas. skipping gears is just being lazy. And its a good way to get the engine up to temp quickly too. And its actually a good thing to give your engine the beans every once and a while. although, im sure you're better off doing that when its hot rather than when its cold.

    admin; thanks, this is pretty much what i was looking for. how fast are the total shift times... not the gear engaging times. 1/3rd of a second is plenty faster than i can do it. hell... even then.. going from 1-7th would take 2 seconds, with continuous power the entire time. thats slower than i could do it for sure.. but then again.. the continuous power is awesome. and you would never do that.. you'd go 1-2-4-7 or something like that on a 7 speed. but... on a sequential DSG, theres really no point in switching gears. UGH i'm over analysing. thanks for the info about the full gear shift cycle time.

  8. Gus - every dual-clutch system we've tried has an automatic mode and we have no reason to doubt there will be one without.

    Chris - interesting that you go from 1-2-5. I've never tried it but we should be getting a DSG equipped car again soon and I'll let you know how it goes.

  9. Maybe a stupid question but... How much km will these clutches make before needing a replacement ? And how much will the replacement cost ?

    Everything is nice on paper, but what about paper in my pocket ? :)

  10. DSG´s computer predicts gear changing. for example, if you´re accelerating in 2nd gear it will predict that after 2nd you´ll need 3rd gear to continue acceleration. also, if you decelerate on high rpm´s the system will set up for downshifting and you´ll get the gear changing in approx. 8 ms. it is possible that the shift time increases if you downshift while accelerating. I don´t see short shifting in formula one... so you don´t need it.

  11. How about BMW sends those DCT's into the 335 in North America soon,
    Australians have it already, why are we second class consumers?

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