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      08-11-2013, 08:31 PM   #23
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Yeah, the Bugatti Veyron has a dual clutch tranny so high TQ and HP should not be an issue for this technology. They are not cheap though, the M3's will run you a cool $14k to replace which is a bargain compared to the Veyron's Ricardo box at $120k...
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      08-11-2013, 08:48 PM   #24
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Quote:
Originally Posted by solstice View Post
Yeah, the Bugatti Veyron has a dual clutch tranny so high TQ and HP should not be an issue for this technology. They are not cheap though, the M3's will run you a cool $14k to replace which is a bargain compared to the Veyron's Ricardo box at $120k...
Not sure mentioning anything on a Veyron in the context of a regular production vehicle means too much It probably has the same haldex controller as a Ford Taurus, right?
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      08-11-2013, 09:07 PM   #25
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Quote:
Originally Posted by drob23 View Post
Not sure mentioning anything on a Veyron in the context of a regular production vehicle means too much It probably has the same haldex controller as a Ford Taurus, right?
I'll be back in a minute. Going down to the garage to check the haldex controller on my Veyron.
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      08-11-2013, 11:35 PM   #26
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wow, are we really talking about wanting a torque converter in the new one? Holey snarkies...officially jumped the shark.
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      08-12-2013, 08:25 AM   #27
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Quote:
Originally Posted by drob23 View Post
One thing that hasn't been pointed out is that DCT's tend to have lower torque/HP ratings. Audi (who are pretty anti manual) use the ZF slushboxes on their top of the line models like S7, S8, RS6, RS7 (I could be wrong on some of those).

Edit - just realized the M5 uses a DCT, so torque limits of Audi S-tronic is probably more that their DCT's aren't as capable as the M-DCT.
Yeah, and as a follow-on to your edit regarding the M5, Audi does offer the DSG transmission for the RS6 and RS7 - just not in the US. The lower output engines in the S6 and S7 obviously can be mated to the DCT no problem then (and it is offered in the US in those cases I believe). I'm sure the A8 V8 and S8 could be offered that way too given they have basically the same engine output as those others respectively, but I don't know if Audi sells them in that configuration anywhere or not.

By the way, to the guy who asked about the ZF, keep in mind that the transmission technologies being compared really boil down to torque converter vs dual hydraulic wet clutch (dry clutch setup is used in non-performance applications, however), and planetary gear sets with torque bands and integral clutch packs vs. step down helical gear trains with dog gears and synchros.
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      08-13-2013, 08:20 AM   #28
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Quote:
Originally Posted by mkoesel View Post
By the way, to the guy who asked about the ZF, keep in mind that the transmission technologies being compared really boil down to torque converter vs dual hydraulic wet clutch (dry clutch setup is used in non-performance applications, however), and planetary gear sets with torque bands and integral clutch packs vs. step down helical gear trains with dog gears and synchros.
So in your opinion, what would be the advantages/disadvantages between these transmissions aside from the actual coupling between flywheel and transmission (i.e. torque converter vs dual clutch)? I know this isn't the most well defined question, but it seems everyone has a pretty good handle on drivability differences between torque converters and "manual" style clutch based transmissions.

One issue I see is reliability of the DCT mechatronic unit, which must physically perform the same function as the shift lever. I feel fine about the clutchpack wear/tear, but the mechatronic unit is worrisome...although could be because I have an Audi which can have this problem
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      08-13-2013, 12:47 PM   #29
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Quote:
Originally Posted by drob23 View Post
So in your opinion, what would be the advantages/disadvantages between these transmissions aside from the actual coupling between flywheel and transmission...
Well, a compound planetary gearset as employed in an autmatic transmission requires several clutches and brake bands to engage the desired drive gear and disengage the current one. The process is somewhat complex, hence why you don't see planetary gearsets used in a purely manual transmission. It could be done but the mechanical linkage required to do so would be involved. Also, traditionally these mechanics were slow to activate, but that has been addressed in recent years.

A DCT on the other hand works much like a manual transmission except that it has two lay shafts and two concentric clutches. So the shift action is simple by comparison. This is especially the case if the computer correctly guesses the next gear (which is usually the case because gears typically get selected in order) since it will already be engaged on the other shaft. All the computer needs to do is open one clutch and close the other which happens very quickly and simultaneously via hydraulic pressure.

The DCT has the disadvantage of not scaling as well. Adding more gears requires adding more length to the transmission. This is somewhat true in a planetary box too but you can add by using more compound carriers or by adding an additional compound gearset. So you can pack more ratios into a smaller space.

An ideal transmission might use the pest parts of each - multiple concentric clutches driving multiple planet carriers in a massively compound planetary gear assembly. I suppose it would face durability and packaging issues as well as high internal friction. But it would be able to select any gear almost instantly, at least in theory. I guess that would require a very sophisticated set of hydraulic clutches to achieve too.

Quote:
One issue I see is reliability of the DCT mechatronic unit, which must physically perform the same function as the shift lever. I feel fine about the clutchpack wear/tear, but the mechatronic unit is worrisome...although could be because I have an Audi which can have this problem
The Getrag in my M3 has been reliable do far (80k miles). I do sometimes worry about this supposed lifetime fluid though. I guess VAG uses BorgWarner design and components. I think BMW actually uses their control module too but probably the mechanical parts are all Getrag.
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      08-13-2013, 12:58 PM   #30
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Quote:
Originally Posted by Boss330
Quote:
Originally Posted by Thurman Murch View Post
I thought the new M3/M4 would have an 8 speed M-DCT. And down the road offer a 7-gear manual.
Let's hope not a 7-speed manual... Porsche's attempt at a 7-speed manual has been voted one of the worst transmission ideas in auto history...
How so? I mean is it the 7th gear that makes it bad somehow or is it that the whole box is crap?
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      08-13-2013, 09:31 PM   #31
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Quote:
Originally Posted by mkoesel View Post
Yeah, and as a follow-on to your edit regarding the M5, Audi does offer the DSG transmission for the RS6 and RS7 - just not in the US.
Are you sure about this? I don't see the RS6 or RS7 available with the DCT, looks like slushbox only. Which specific market are you talking about?
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      08-13-2013, 09:32 PM   #32
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Quote:
Originally Posted by mkoesel View Post
Well, a compound planetary gearset as employed in an autmatic transmission requires several clutches and brake bands to engage the desired drive gear and disengage the current one. The process is somewhat complex, hence why you don't see planetary gearsets used in a purely manual transmission. It could be done but the mechanical linkage required to do so would be involved. Also, traditionally these mechanics were slow to activate, but that has been addressed in recent years.

A DCT on the other hand works much like a manual transmission except that it has two lay shafts and two concentric clutches. So the shift action is simple by comparison. This is especially the case if the computer correctly guesses the next gear (which is usually the case because gears typically get selected in order) since it will already be engaged on the other shaft. All the computer needs to do is open one clutch and close the other which happens very quickly and simultaneously via hydraulic pressure.

The DCT has the disadvantage of not scaling as well. Adding more gears requires adding more length to the transmission. This is somewhat true in a planetary box too but you can add by using more compound carriers or by adding an additional compound gearset. So you can pack more ratios into a smaller space.

An ideal transmission might use the pest parts of each - multiple concentric clutches driving multiple planet carriers in a massively compound planetary gear assembly. I suppose it would face durability and packaging issues as well as high internal friction. But it would be able to select any gear almost instantly, at least in theory. I guess that would require a very sophisticated set of hydraulic clutches to achieve too.



The Getrag in my M3 has been reliable do far (80k miles). I do sometimes worry about this supposed lifetime fluid though. I guess VAG uses BorgWarner design and components. I think BMW actually uses their control module too but probably the mechanical parts are all Getrag.
Thanks for the response, was very interesting and looks like lots of stuff a non-ME like myself needs to read up on
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      08-13-2013, 11:50 PM   #33
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Quote:
Originally Posted by bimmerjph View Post
How so? I mean is it the 7th gear that makes it bad somehow or is it that the whole box is crap?
From what I have read the reviewers seem to hate the added complexity for no additional benefit.
They did the 7 speed box to help meet/beat fuel consumption regulations, that's all. Ultra long 7th gear for the bulk of the consumption test.
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      08-14-2013, 06:18 AM   #34
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Quote:
Originally Posted by drob23 View Post
Are you sure about this? I don't see the RS6 or RS7 available with the DCT, looks like slushbox only. Which specific market are you talking about?
You know what, I thought that I had read that in a review but I can't find a trace of it anywhere so It was either edited or I just got confused. My apologies.
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      08-14-2013, 09:33 AM   #35
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Quote:
Originally Posted by drob23 View Post
So in your opinion, what would be the advantages/disadvantages between these transmissions aside from the actual coupling between flywheel and transmission (i.e. torque converter vs dual clutch)? I know this isn't the most well defined question, but it seems everyone has a pretty good handle on drivability differences between torque converters and "manual" style clutch based transmissions.

One issue I see is reliability of the DCT mechatronic unit, which must physically perform the same function as the shift lever. I feel fine about the clutchpack wear/tear, but the mechatronic unit is worrisome...although could be because I have an Audi which can have this problem
Don't forget, the ZF8HP has a clutch that disengages the TC, so is not a true slush box. In the past max RPM has been limited by the TC, now with clutch bypass, this is not as big an issue.

I can see auto's coming out in the future with no TC at all. All it is doing now is controlling torque transfer during pull off, and slight slip during gear changes (however when in manual Sport+ mode a ZF kicks almost like a DCT in mode 3). These functions can be carried out by better clutch mechatronics.
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      05-12-2014, 03:46 PM   #36
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DCT vs. ZF8?

I posted here because I don't know how the DCT is improved in the E80/E82. There seems to be a consensus that the 7 speed DCT is better than the ZF 8 speed. Well, it's certainly a lot more exclusive in the BMW lineup, but what makes it objectively better? I'm looking for measurable like shift times, power loss, etc..
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      05-12-2014, 04:00 PM   #37
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Could be anything. More heft with another gear, packaging, smaller gears can't take the torque etc. Imo 7 gears is plenty.
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      05-12-2014, 04:02 PM   #38
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Quote:
Originally Posted by BimmerBoomer View Post
I posted here because I don't know how the DCT is improved in the E80/E82. There seems to be a consensus that the 7 speed DCT is better than the ZF 8 speed. Well, it's certainly a lot more exclusive in the BMW lineup, but what makes it objectively better? I'm looking for measurable like shift times, power loss, etc..
Dual clutch versus single. I'd say the biggest advantage is the speed of shifting the dct has over the regular auto. The DCT is one of the best out there.

No knock on the ZF8 though, that is a fantastic transmission in it's own right, but a dct it isn't.
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      05-12-2014, 04:03 PM   #39
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I am not sure about shift time as both are extremely quick.
However, you can feel clutch engaging to selected gear with DCT when you do manual up/downshift.
With ZF, there is some disconnected feeling when it comes to this.
ZF feels somewhat artificial in this area.
This is the primary reason why I only buy cars with DCT.
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      05-12-2014, 04:09 PM   #40
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No torque converter!
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      05-12-2014, 04:14 PM   #41
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Originally Posted by Johnmd View Post
No torque converter!
/thread

we can all go home now!
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      05-12-2014, 04:15 PM   #42
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Quote:
Originally Posted by Johnmd View Post
No torque converter!
^This

The direct connection between engine and drive wheels is the main benefit. A regular automatic can be programmed to shift extremely fast, but the power still needs to be transmitted through the torque converter.
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      05-12-2014, 05:15 PM   #43
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Good grief...

That's the sum of the objective knowledge here?
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      05-12-2014, 05:18 PM   #44
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Quote:
Originally Posted by tdizzle View Post
/thread

we can all go home now!
Yea Torque converter is a no go, thing create heavy rotating mass as well. ZF 8 is not as fast as DCT when shifting at high RPMs from my experience
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