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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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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I'll be back in a minute. Going down to the garage to check the haldex controller on my Veyron.
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08-12-2013, 08:25 AM | #27 | |
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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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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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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:
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08-13-2013, 12:58 PM | #30 | |
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08-13-2013, 09:31 PM | #31 |
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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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08-13-2013, 11:50 PM | #33 | |
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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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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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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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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, 04:15 PM | #42 |
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05-12-2014, 05:18 PM | #44 |
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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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