07-10-2017, 02:13 PM | #155 | ||
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Regardless, the ZF6HP is a old transmission design and I find it much more relevant that BMW uses the ZF8HP45 in the M235i Racing for long distance competitions, apparently without any overheating issues. After all, it's not like they are going to use the ZF6HP in the M5... Here is ZF's introduction to the ZF8HP that also covers some of the advantages it has over the ZF6HP: https://www.zf.com/global/media/en_d...nsmissions.pdf As regards inertia (which is what I guess you are referring to) in the clutch/flywheel assembly compared to the inertia in a flexplate/torque converter you have to take into account the complete assemblies in both configurations. A DCT car has a flywheel (double mass for the S55 engine) and the twin clutch assembly. Which added together weighs roughly (weight of flywheel from Realoem.com):
An automatic transmission car with torque converter has the flexplate and torque converter assembly. Which added together weighs roughly (weight of flexplate from Realoem.com):
So, not a whole lot more of rotating mass and inertia between the two different systems. Yes, transmission fluid inside the converter also adds to the inertia of that system, I'll agree to that. But the systems aren't night and day apart in inertia, factor in all the other rotating masses and the percentage in weight difference becomes pretty small. I'm not sure I follow you in the use of heavier oil in MT cars with single mass flywheels. Tremec transmissions for instance use Dexron III ATF, which is a fairly thin oil... Even my old Sierra Cosworth with a single mass flywheel and a Borg Warner (now Tremec) T5 transmission use ATF transmission oil. So, I don't really see how much of an impact on vibrations that thin layer of oil between the cogs really can have, when Tremec for instance insists on using thin ATF oil. As regards my Google search examples. Try Googling "DSG overheating" and see if your theory about people driving sports cars are more "sensitive and caring"... DSG is the VAG workhorse transmission in cars like Skoda Octavia, VW Golf, Seat Leon, Audi A3 etc... VAG has had a lot of issues with their DSG transmissions, overheating being just one of them. And it seems even owners of lowly base models take to the internet and post in forums about these issues... So have to disagree with your "logic" about who posts online about issues with their car. It's not just the caring and sensitive sports car owners BTW, AMG's MCT transmission is an automatic transmission with a wet start up clutch assembly instead of a torque converter (just like the ZF HCC) and before that AMG's used to have pure automatic transmissions. Audi has the ZF 8-speed in the RS6/7, Jaguar has the ZF 8-speed in their R-models and the much lauded Alfa Romeo Giulia Quadrofoglio also has the ZF 8-speed, of which Top Gear said: Quote:
So in your opinion these cars aren't bought by people who loves driving and "drive like idiots"? I mean, since they have bough a car with an automatic... |
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07-10-2017, 02:44 PM | #156 | ||||
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I still stand on my two reasons I mentioned previously on why a transmission would overheat, and torque converter up until very recently has been the lesser being. I see that bumper aeros are also slightly different for M235i racing, and I assume that air duct path is also different. I wish I had the actual data to clarify the superiority of high end DCT vs high end torque converter other than the shifting speed and weight but I haven't digged in yet. Quote:
Where he mentions this about F12 M6. "Difference here is the powertrain. The powertrain is just absolutely extraordinary, because it is aggressive and you have to get up and use all of it; then this car comes alive, and it comes alive in a way that the others I'm afraid can't match." Which sums up the characteristics of DCT: sustainable at high rpm, rev happy, fast and aggressive.
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Last edited by kyrix1st; 07-10-2017 at 03:16 PM.. |
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07-11-2017, 11:57 AM | #158 | |
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I don't think that we have yet seen a ZF8HP that is as good as the DCT, even though the Alfa Romeo Giulia Quadrifoglio version seem to come pretty close, with fast and hard upshifts as well as aggressive rev matching on downshifting. I have just tried to clear up some of the obvious misconceptions about how shifting, the torque converter and lock up works in a modern automatic trans. I'm also worried about the apparent rpm limit in the ZF8HP. And if the rev counter video I shared is accurate, then it seems shift points have changed from roughly 7200rpm to between 6300-6700 rpm. That is a further deviation from the "high rpm M engine" philosophy if proven to be the case... BTW, you do know that VAG offer the DSG in Polo, Touran, Tiguan, Sharan, Transporter/Multivan cars and that the models I referred to was just a random selection of models. Also, I wouldn't consider a 1,6l diesel Golf a "hot hatch" just because it's a Golf... (even though it seems you do ). I have been to the Nürburgring quite a few times (once so far this year) and since no M-cars have had a automatic transmission it's not really a realistic proposition you make. However, a lot of AMG's, M235i's, Audi RS models, Jaguar F-type R's etc run around the Nürburgring with their 7- or 8-speed automatic transmissions without any problems. As well as a lot of ordinary BMW Gmbh models for instance. The last M-car I drove was the F80 M3 CP with DCT and I also love how hard it shifts and the near instant gear changes, that makes the driving experience that bit more "special". AFAIK there isn't any technical reasons they can't achieve the same with an automatic transmission, especially with the HCC wet start clutch system instead of the torque converter. And it seems that the ZF8HP in the Alfa allready comes pretty close to the DCT. Fingers crossed that the M5 will have a transmission that delivers! Last edited by Boss330; 07-11-2017 at 12:07 PM.. |
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07-17-2017, 09:47 PM | #159 | ||||||||||
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There are multiple versions of the ZF 8HP, and I asked specifically to see if you've driven the 2nd Generation (ZF 8HPTU) which incorporates many significant design and operating characteristic improvements. None of the cars you've listed have it. For BMW AG Products only certain vehicles with Sport Automatic Option have the GA8HP50, GA8HP75, GM8HP75 and GA8HP95 (one exception is Rolls Royce Ghost V Specification with the GA8HP90 which is a TU variant). That 3rd one is unique (note the M designation for M GmbH). It utilizes a different torque converter that does not unlock except when stationary, though comfort shifts have some slip included. The G12 Alpina B7 and G30 M550i share the same GA8HP75 with modified torque converter rated at 800nm but with RPM limitations on peak torque from below 3000rpm and above 5000rpm on the B7 and below 1800rpm on the M550ix. The M760LiX and Rolls Royce Ghost based Black Badge Variants use the GA8HP95 rated for the full 1000nm from 1200rpm to 6500rpm. Unfortunately with up to 900nm currently available at 1500rpm (this will be increased soon to 1000nm), launch control must occur with 2nd gear active to prevent damage to the Axle to body mounting points. The Max Speed on torque converters is an "issue" if a very high redline is needed. At 7200rpm input speed, the impeller vanes are near supersonic, causing bubbles to form in the fluid. At 7400rpm, these bubbles implode and vaporize at 7500rpm causing complete TC Stall and physical damage. I've personally gone head to head with engineers from ZF and multiple Auto Manufacturers over this issue (coined the term ZF Honk which earned me the nickname Keyser Söze of the Automotive World). My F90 will mark the 45th BMW Group vehicle I've acquired via personal means and additionally, it, along with equipment and features the F90 introduces, will be incorporated into BMW Security Vehicles and the Security Driver Training Program which I have been an instructor at for 2 decades. When the rumors first began about the F90 switching to the 8HP75, I answered a post in this forum that a TC was no-go unless the powerband was "neutered". Although this is one way of looking at it, compared to DCT, there is no calibrated torque reduction for the sake of the transmission or driving dynamics above 7km/h. It was the best choice for the F90. M DCT was a Getrag Manual Gearbox (it was to be the 7 Speed Manual that was patented) with Borg Warner Mechatronics and Clutch Pack just as ZF 7DT is also the basis of the ZF 7MT. Engine redline will be 7000rpm with fuel cutoff at 7200rpm to prevent possible TC Vane overspeed. Unlike the M550i, in certain operating modes it does not shift early. Overheating won't be an issue for the vast majority of track venues. ZF 8DT would be a handicap IMO (a DCT F90 Prototype I drove wasn't quite as good overall). In the ICE only version, Max torque is 750nm in AWD mode, Switchable 100% rear 2wd is not possible (and would have further torque restrictions), and it wastes space. Without the Electric Assist, the bell housing is essentially empty. Quote:
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Van Meel already confirmed the TC in the F90 (and GM8HP75) transmission. The TC is a combination between the ZF Active Launch Torque converter and HCC. My time behind the wheel recently has not produced any complaints worth mentioning. I go way back with him and the promises have been kept with the F90. Quote:
The Range Rover I'm using for DD is a test vehicle and has Drivetrain (except for the diesel power plant) more similar to the F90 than most current BMW's, but feels 100% Range Rover, easily copes with the daily torture tests, and only has shown one issue that can only be solved by the driver. It's about the programming now. It's what makes the F90 more special than its predecessors. Quote:
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There will be complaints, praises, and then those who actually get it. They'll be the ones out driving an amazing feat of engineering full of soul rather than googling DCT vs Slushbox and being internet experts. Last edited by lemetier; 07-18-2017 at 06:13 AM.. |
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07-18-2017, 12:55 AM | #160 | |
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Something you may know about, I've read mention of the 19" setup being a square 275/40r19 setup and the 20" setup being 275/35r20 up front with either 285/35r20 or 295/35r20 rear. Can you confirm? |
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07-18-2017, 11:58 AM | #161 | ||
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DIN weight and the distribution aren't an issue. Both are improved compared to the F10. The new Central Intelligence Module should also be reason not to balk over the transmission. Not only has the available data from ConnectedDrive been improved, data from PDC Radar, ACC Radar, 3D Pulse LIDAR, 3D Stereo Cameras, rear, side, and front Radar (depending on options installed) is fed into the system making it extremely difficult to put the car in a situation where the drivetrain cannot adapt. As for the tires, don't be surprised if there are several different combinations depending on equipment. The specs can be changed by the driver in iDrive (including out of range customer fitted combinations). |
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07-18-2017, 06:28 PM | #162 |
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an autobox does not in an M belong. dont care how "as good" it is. Porsche spent a boatload of money to develop a new pdk knowing the 8hp was around. ill enjoy my dct until I eventually get a car that has no transmission.
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07-19-2017, 12:37 AM | #163 | |||
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Thank you very much for your insight. Like I've mentioned previously, I was very unsure what to think of an automatic transmission. However, I'm convinced that M division has properly done their homework. I think the biggest storyline of this new M5 will be the Central Intelligence Module, and what it's capabilities are. I wonder if it employs fibre optics to ensure fast data transfer rates.
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07-19-2017, 06:50 AM | #164 | |
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How can a torque converter reproduce mechanical banging that is the result of engaging and disengaging pressure plates from dual clutches? If you are referring to exhaust "farts" apparently seen in F90 video, that is the same joke used in RS7. I do recognize that use of higher thermal capacity materials/layouts to dissipate heat could be well engineered to produce good results, but it seems rather than using higher thermal capacity materials ZF decided to direct oil flow so that higher thermal capacity is achieved. This is cost effective engineering, I'll give you that. My question is, why not make it so that less heat is produced so it doesn't work the cooler so hard in the first place? That's less weight for less heat (Q=mCdT.) If most of the DCT bellhousing is empty as you say and ZF8HP weighs 91kg compared to DCT of 78kg, advantage of DCT is or MT is in lighter rotating mass. Good info on ZF transmissions otherwise, efficient programming is always welcome regardless of its mechanical base; it's been a decade since Lexus focused on traction control programming rather than building a rigid chassis to cut down production cost and BMW seems to be following its predecessor albeit in different category.
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07-22-2017, 07:52 PM | #165 | |
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The "mechanical banging" isn't from the torque converter. It's from Transmission Brake Set B in gears 1-5 and only with the most aggressive settings active. The torque converter design and functions in this application produces the least heat and least mechanical wear while providing the widest range of shift types and shift quality. Might want to check the weight of 8DT75x vs 8HP75x (including the transfer box) WITH oil cooler and fluid included. The unit with the weight advantage isnt the one you suggest. |
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