Just_me

Since the trends in auto industry are heading towards gasoline turbocharged engines combined with direct injection (more power, less gas consumption), and dual clutch transmissions (smoother shifting, less torque loss, better emission & consumption control), BMW are going straight with this trends.

We have already seen the introduction of first (of many) BMW gasoline turbo engines: the N54 bi-turbo HPI, 3.0L I6, 225kW, 400Nm.

And we all known the rumours of upcoming "ZSG" gearbox - a VW/Audi DSG (BorgWarner's DualTronic) fighter. The German automotive media have spaculated about "ZSG" for a while.

But - is it real?

IMO: it is not - not in a form German media were describing it: as Centrally Synchronized Gearbox ("ZSG").

I have no info that any of transmission specialists (ZF, Getrag, BorgWarner, etc) are developing "ZSG" type of gearbox.

So there are two options: either BMW are developing & producing the gearbox by themselves - which is very unlikely since they have no production capacities - , or they will use the DCT solution developed (I guess in cooperation with BMW) & produced by ZF Sachs AG - which is more likely.

ZF Sachs AG (a very involved BMW development partner: DynamicDrive, ActiveSteering, 6-speed automatic gearbox, etc) has recently developed (prototype was presented at IAA 2005) a 7-speed wet dual clutch transmission named 7 DCT 50 - a BorgWarner's DualTronic fighter.

7 DCT 50 specs:
7 speeds, up to 520Nm, up to 9000rpm, dual-mass flywheel, 3 driving modes (comfort, sport, manual) etc. ( I hope this is something for the new M3)

Looks like a perfect match for N54 engine.

Here is the 7 DCT 50 presentation (click on "Animations"):
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PS (added later): latest hint is that this specific model by Sahcs: "7 DCT 50" will not be used in 335(s)i but in some other BMW products further down the line. But 335 is to get even more advanced gearbox.

True - this DCT / "ZSG" gearbox will be used in non-M cars only. /M/ will still stick with SMG. Why? Here is the answer by Gerd Richter, technical director of the M GmbH:

"The dual-clutch system has a smoother automatic mode, and it performs seamless upshifts. For a 7-series, this may be the way to go. But an M car should always combine efficiency with emotion. That's why there are six shift speeds to choose from, from velvet glove to iron fist. That's why we cut the torque into seven slices. That's why we added special features like a hill holder, a designated drive program for steep climbs and descents, and a downshift assistant, which briefly dips the clutch to avoid destabilizing wheel spin."

Btw, MB has a 7-speed automatic gearbox (Lexus even 8-speed one in new LS), not a dual clutch transmission.

BMW is also heading to 7-speed gearboxes: SMG is a 7-speed gearbox, DCT will have 7 speeds , and I guess sometimes in the near feature BMW will use a 7-speed automatic gearbox (already developed by ZF Fridricshaften AG - just like 6-speed auto gearbox BMW are using now) - if it will not be completely dropped in favor of DCT.

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As I said earlier:

335 will get something else - not 7 DCT 50 dual clutch gearbox by ZF Sachs. This gearbox will be used in some other BMW product down the line.

335 could get a 7-speed dual clutch transmission by Getrag "DCT 436":
hydraulic actuation
2 contrentic wet clutches
7-speeds
up to 600Nm

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Latest info:

Not only DCT is to be featured in 335si (coming to German market in 2007), but BMW are also testing new DCT gearbox in the new M3. And SMG III as well.

Tests results will determine which gearbox will be featured in the new M3: DCT or SMG III. First tests shows very impressive DCT performance. But that's only the begining.

PS: DCT is of course a superior solution to SMG, so BMW want to use it in M cars as well. Therefore they are testing it. The first indications are M3 will get the DCT, and then also new M's will get it when they come out.

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vabboud

could we eventually see it in the MZ4 coupe/roadtser for example?

Harry Plopper

Getrag has developed a series of DCT transmissions:

DCT 477 - transaxle longitudinal, 7-speed, 700Nm, wet concentric clutches, hydraulic actuation
DCT 436 - inline, 7-speed, 600Nm, wet concentric clutches, hydraulic actuation
DCT 250 - front transversal, 6-speed, 250Nm, dry clutches, 3-shaft design, electromechanical actuation
DCT MPS6 PowerShift(tm) - front transversal, 6-speed, 450Nm, wet parallel clutches, 3-shaft design, hydraulic actuation
DCT SPS6 PowerShift(tm) - front transversal, 6-speed, 450Nm, wet parallel clutches, 2x2-shaft design, hydraulic actuation

I only got a confirmation 7-speed DCT 436 (600Nm max) will be used in BMW vehicles (335si first). A variant of this gearbox is tested in a new M3. Same mechanics, different sowtware settings.

Not sure about DCT 477 & DCT 250. While DCT MPS6 & SPS6 are exclusivelly for Ford Group.

Some say DCT 477 will be combined with BMW diesel engines, but I doubt it. Getrag makes transaxles for Audi & Porsche only. So DCT 477 could be either for Porsche or new top-end Audis.

DCT 436:

Just_me

I wonder what this is: wet concentric clutches

vabboud

my (educated) guess is 2 clutches one inside the other, the bigger being hollow, and lubrificated with oil (hence wet) to allow smooth activation

the outer clucth is the engaged one, the inner one is the one ready for engaging (or vice versa)

Harry Plopper

You've posted a link!

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Read the articles & watch animation.

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