07-05-2017, 04:42 PM | #133 | ||
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07-06-2017, 02:35 AM | #134 | ||
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The torque converter does not "lock up gear each time". It goes to 100% lock from a standstill before 1000rpm in Sport+. It does not unlock again while in motion, even during a shift. Only the shifting elements after the TC manipulate shifts and they are sequential, overlap, clutch-to-clutch through the full range. What vehicles with this same transmission have you driven? |
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07-06-2017, 09:35 AM | #135 | |
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Quite possibly this function can be incorporated on the M cars so you don't have forward creep automatically when releasing the brake, but have to apply "throttle tip in" to activate forward motion. By the way, the ZF 8-speed also has the possibility to perform multiple downshift strategies and can be downshifted from 8th to 2nd in one gearchange. It will be interesting to see how they implement the ZF 8-speed and which functionalities they implement. And also how it's perceived by the press and owners when the cars start to arrive... |
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07-06-2017, 01:45 PM | #136 | ||
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(includes all touring "t", sport "s", coupe "c" variants, where applicable) E34 525i E36 318i E36 325i E36 323i E36 328i E39 528i E39 530i E46 323i E46 328i E46 330xi E53 (3.0i) E36/7/8 Z3 (1.9i, 2.3i, 2.5i, 2.8i) Even though BMW never went that route for any M-cars, they've had an extensive history of using GM transmissions as demonstrated above.
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07-06-2017, 03:43 PM | #137 |
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why red?
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07-07-2017, 01:58 PM | #138 |
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07-08-2017, 07:23 AM | #139 | |
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By this transmission, do you mean ZF8HP? I've never owned one with it, but I've driven 120d, M135i, Audi RS7 (pre-facelift). I didn't say I dislike it, I just think it doesn't quite fit the M character. ZF could be fast, but you can't argue you don't feel as connected as that of SMG or DCT. Downshifts never feel as firm. Other ones I've driven (haven't owned them all except E60 for brief period) E60 M5, F82 M4, F10 M5, Cayenne (tiptronic) and Panamera S. PDK feels faster than the current Getrag DCT in the M. Thinking of getting a low mileage E63 coupe/F87 (two very different cars I know) in the coming months but torque converter is unlikely to be on my priority list for the enthusiastic driving. Overheats way too quickly and goes into limp mode; sucks for prolonged high rpm (>7000) driving. Ever noticed how ZF doesn't like you shifting at the redline? Their limit is 7500rpm before shit starts breaking down
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07-08-2017, 05:59 PM | #140 | ||
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Not sure where you have the overheating claims from, but the ZF 8-speed works pretty well in long distance racing on the Nurburgring in the M235i Racing... The only modifications to the transmission is electronics, no mechanical changes over the std version in the M235i. I would suspect that any overheating problems that you imply this transmission has should be evident during the 4 and 6 hour long races in the VLN cup at the Nurburgring. Not to mention the 24 hour race at the same track... The shifts seem pretty quick in this onboard at Spa Francorchamps BTW... And this video teaser from BMW indicates pretty quick shifts and aggressive downshifts |
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07-09-2017, 03:25 AM | #141 | |
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I think it would depend on which ZF tranny they are running; the one with 1000Nm torque limit should have much higher threshold whereas 750Nm one will run very close. If you like the floating carpet feel, ZF is the right choice. I don't think it's right for M, it should be more dynamic. There will never be half the aggressiveness of mechanical "banging" in torque converters since it absorbs all that shock by tranny fluid.
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07-09-2017, 04:46 AM | #142 | |||
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ZF claims it's the exact same transmission mechanically as in the std M235i, apart from software tweaks and one drive mode only available (Super Sport). It might have more cooling than the M235i, but so do a M3/M4 over a 335i as well. Higher output and sportier driving capabilities means the need for better cooling. The M235i has the ZF 8HP45 model, which is listed at 450Nm so it should run at "it's limit" in this configuration as well. But it seems to cope pretty well... As has been mentioned before, the torque converter has lock up in every gear. So there is no "absorbing by tranny fluid" in the torque converter when it's locked up. Soft shifts that you experience in these transmissions are down to how hard/aggressive the shift clutches for the planetary gears operate. ZF claims that for the std model of the ZF 8-speed,the lock up clutches only allow for a maximum of 40rpm rev drop during shifts. None of us has driven the new M5, so we don't know how it will behave. Perhaps it won't be as brutal as a DCT or perhaps it will be similar or better than the DCT... Torque converters have moved on and the lock up function is exactly what it says, it locks up the torque converter! http://articles.sae.org/4166/ Notice the ruggedness of the clutch part of the torque converter here: ZF explains their lock up clutch system as foolows: Quote:
From ZF's technical brochure on their double clutch and automatic transmissions, they explain their new "start up clutch system" that also can be applied to the automatic transmission instead of the std torque converter with lock up: https://www.zf.com/global/media/prod...steme_2015.pdf Quote:
Will be interesting to see if the M5 has the torque converter with lock up, or if it has taken advantage of the HCC... Last edited by Boss330; 07-09-2017 at 04:58 AM.. |
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07-09-2017, 07:38 AM | #143 | |
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1. materials used in auto/mt/dct transmissions are thermal conductors of different nature. 2. cooling system is not up to the task. If you are into cars, you have probably encountered countless cases where one of the two has been the culprit for overheat->tow aftermath for those with tiptronic/auto at the track where MTs or DCTs rarely if never have these problems. For a mechanical reason I assume, torque converters are heavier than DCT and much heavier than manuals. This current M5 has less weight most likely due to carbon fiber roof+ some aluminum chassis parts that they should have used long time ago. + the new DCT would have been the ideal package. As for the vibration, it is a fluid coupling nonetheless, and much of drivetrain vibration is absorbed by 6-10 quarts of tranny fluid that is used to spin the turbine to connect the flywheel to the transmission, resulting in much smoother ride than any of DCT or MT (which does so with the use of spring damped pressure plate or flywheel) which is good for daily driving I suppose, but it doesn't feel lively enough for me. Characteristic is one very important factor in these cars you see..
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07-09-2017, 08:34 AM | #144 | |
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Again, the lock up in a torque converter is a mechanical coupling just like the clutch on a DCT or single clutch manual transmission! The "fluid coupling" part of the torque converter is only used for start and stop. After that the lock up clutches mechanically locks the connection between the crank and the input shaft of the transmission. Again, if you had read the ZF document you would have seen that the lock up system also employs a "twin torsional damper", to create the same effect a dual mass flywheel does, since gearshifts are done with the torque converter locked up! So to repeat once again, the fluid coupling is only used for takeoff, after that lock up is employed and vibrations are taken up by the torsional damping system (since the torque converter now is in a mechanically locked state). A 270mm dual clutch pack weighs 13kg A 270mm torque converter weighs between 17,4 and 18,8kg So, yes a torque converter is roughly 5kg heavier than a DCT clutch pack I'm not sure if you don't want to understand how the lock up system works or if you just want to argue Look at these drawings that explains how the torque converter and lock up clutch works. Notice that the torsional damper is connected to the lock up clutch, not the torque converter. That is because the power transfer during driving goes through the lock up clutch and the damper takes up vibrations during shifting and on/off throttle situations etc. Last edited by Boss330; 07-09-2017 at 08:51 AM.. |
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07-09-2017, 08:51 AM | #145 | |
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Do you have any verification that modern automatic lock up transmissions are prone to overheating? Try Googling "DCT overheat" and "ZF 8 speed overheat"... Guess which search gets the most hits Just one example: http://f80.bimmerpost.com/forums/sho....php?t=1326527 Cars with DCT even has a warning of risk of transmission overheating in the owners manual, do BMW's with the ZF 8-speed have that as well? |
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07-09-2017, 09:57 AM | #146 |
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Informative videos:
HCC (Hydrodynamically Cooled Clutch): TTD (Turbine Torsional Damper), which I assume is early version of TwinTD (Twin Torsional Damper):
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07-09-2017, 11:20 AM | #147 | |
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The HCC wet clutch solution seems intriguing. Wonder if that is used in the M5... |
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07-09-2017, 01:04 PM | #148 |
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dont care how sophisticated the ZF is, it just sounds bad to say your m5 has an automatic transmission. doesn't sounds special one bit. after all buying these types of cars are mostly emotional and not rational.
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07-09-2017, 01:55 PM | #149 | |
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But I haven't really heard people say that the AMG MCT 7-speed (or 9-speed in the latest AMG E63) is an "automatic transmission" in the same way they talk about a traditional automatic transmission... As I guess we all know, the MCT from AMG is a traditional automatic transmission but with wet start up clutches instead of the torque converter (just like the ZF HCC as excplained above). Do people think of the AMG E63, or the other MCT equipped AMG's, as having an automatic transmission? No, I think people just think of it as a MCT transmission, "whatever that is"... I guess what I'm saying is that it's all in how you market the technology and how you can create an aura of emotion around it. If the M5 still employs the torque converter ZF, they will have more of a struggle to get past that "automatic transmission" perception among the enthusiasts than if they opt for the HCC wet clutch similar to what AMG does. And if shift times and driving experience are a match, or better, than the DCT then why not... |
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07-09-2017, 05:20 PM | #150 | ||
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07-09-2017, 07:55 PM | #151 |
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DCT is considered automatic in Car and Driver, as well as Road and Track I believe. Jeremy Clarkson labels them as flappy paddles. Let's hope they're good and fast when you want them to be, and smooth all the time.
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07-09-2017, 08:56 PM | #152 |
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automated manual to us gearheads but I understand the magazines need to dumb down content to its readers. I want some edginess and visceral feel to an M car and not a smooth shifting "steptronic" (like my old 328).
after all there are a lot of smooth capable cars (M550i) in the lineup before you get to the M cars.
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07-09-2017, 09:38 PM | #153 | |
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As for the article, if you can direct me the mechanical difference between zf 6 speed and 8 speed other than the obvious I will bother to read that. I was not implying that lock up clutch does not act similar or identical to clutch packed manuals or dct; anything with centripetal acceleration will have centrifugal force outwards the rotating mass, in this case damped flywheel by dampers and turbine (as it seems to be in alignment with shaft rotation from your picture) in torque converter which will also be damped by tranny fluids inside the turbine. I do admit the way I said it is solely thanks to tranny fluid, which obviously isn't. In MT cars however, we do adjust gear rattle in SM flywheel with heavier oil so you can't say drivetrain vibration has nothing to do with fluid; it lubricates the rotating components afterall. I have to point out the fallacy in your google logic of DCT vs torque converter is that people who drive sports cars with DCT tend to be more sensitive and caring while people with traditional automatics just go to service shop rather than discuss online because forum chatting is more time consuming so google doesn't do justice in showing demographics. People with automatics don't drive like complete idiots as sports car owners do. Thats why they buy an automatic! Launch control in addition is peformed from standstill, and while thermal capacity may favor zf torque convs, you launch once off the start line and sustain the momentum at high speeds both to cool the car and drive fast. Why would you launch the car several times except for drag race? This car isn't built for that. Buy a challenger for that stuff. I have said repeatedly that primary disappointment is lack of connection between the car and the driver in torque converters, not just the creep(which can be adjusted seen in X6M) but each gear change which lacks the "bang." Last edited by kyrix1st; 07-09-2017 at 10:59 PM.. |
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07-10-2017, 12:40 PM | #154 | |
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And thanks for the info on the newer M235i Racing using the HCC instead of the torque converter. Do you have a source that verifies that the F90 M5 won't use the HCC? |
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