[mundo74]

Originally Posted by Boss330

Yes, the DCT clutches operate simultaneously as in one engaging as the other disengages. However there has to be a small window between engagement and disengagement of the two clutches as they can't be engaged simultaneously (such a situation would lock up the transmission). This is the big advantage for a DCT over a SMG type manual gearbox. On a SMG you need to disengage clutch, change gear, engage clutch again (just like on a regular manual gearbox, just managed by the TCU instead of by the driver).

But I think you have gotten how an automatic transmission works slightly wrong.

The torque converter has nothing to do with the gearshifts. The torque converter is simply the automatic transmissions equivalent to a clutch and transfers power from the engine to the transmission. On modern automatic transmissions (or since the '80ies) you have the lock up function in the torque converter which basically acts just like a clutch when engaged, ie no slippage allowed whatsoever. On the M5 lock up will be applied in every gear. This means that, when on the move, the torque converter will be locked up and no slip is allowed.

When changing gears in an automatic transmission the only delay between gears is down to how fast the clutches in the transmission (not the lock up clutch in the torque converter) that manipulates the planetary gears can be engaged/disengaged. Similar to how fast a DCT transmission can engage/disengage the two clutches. In an automatic transmission, unlike on a DCT/manual transmission, you don't mechanically move cogs/gearsets to engage a different gear. It's just engaging/disengaging band type clutches that operates the planetary gears. And if the lock up clutch in the torque converter is engaged, there is no slippage in the torque converter during the shifts. Which means, fast shift times and no slippage...

If you read the article on the new GM/Ford 10-speed auto, you saw that the shifts are ca 26-27% quicker than on a PDK (Porsche double clutch). This makes sense as the band type clutches are easier to operate in engagement/disengagement than the rather heavy/bulky clutches that is present on a DCT/manual transmission.

So, there is no mechanical design issues that should prevent a automatic transmission from having as fast shifts (or indeed faster as proven by the GM/Ford 10-speed) as a DCT/PDK type transmission. And with lock up available in every gear on the M5, no slippage in the torque converter either. This makes for a solution with the possibility of just as quick (or quicker) shifts as in a DCT. As well as the possibilty of no slip during shifts since the torque converter has lock up in every gear.

I suspect that the torque converter will only be unlocked when taking off from a standstill (just like on a DCT/manual when you have clutch slippage to avoid a jerky start) and during shifts when the car is in one of the comfort modes.

They might have to allow for some slip during WOT shifts to avoid breaking the drivetrain in AWD mode (just like you have a certain amount of slip on a DCT in the milliseconds it takes for the clutch to engage).

great technical summary.

[lemetier]

Originally Posted by dmboone25

It's interesting, because I had DCT on my 2010 135, and PDK on my 981 CS, and both cars would "creep" forward.

In my ZCP M3, it doesn't do anything until you press the throttle, which has taken some getting used to. I am not sure that aspect of the DCT going away would bother me too much...

That aspect isn't going away. Like M-DCT and PDK-S, brake release does not engage forward creep automatically.

Originally Posted by kyrix1st

Could be, but since the number is compared with other DCT equivalents, they are likely measuring time of o the identical mechanical process. Getrag isn't the fastest shifting DCT I've seen; I imagine it is due to some reliability compromise that comes with higher shifting speed.

DCT engages and disengages clutch simultaneously because the it has dual clutches(lol) where torque converter has to lock up gear each time; it is inherently slower, although I will point out that with the perfect balance of engine and powertrain, ZF also could be fast. I just do not like the less connected feel of torque converter since it moves on its own after releasing the brake.

PDK is not 7ms - 8ms for a gear change. I don't know of any Transmission capable of such and that's faster than any No-Interrupt Electrical Transfer Switch can achieve. Porsche publish "less than 100ms" for gear changes in the Lightning Shift mode on PDK-S, and "less than 200ms" on PDK in Sport with Chrono.

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?

[Boss330]

Originally Posted by lemetier

That aspect isn't going away. Like M-DCT and PDK-S, brake release does not engage forward creep automatically.



PDK is not 7ms - 8ms for a gear change. I don't know of any Transmission capable of such and that's faster than any No-Interrupt Electrical Transfer Switch can achieve. Porsche publish "less than 100ms" for gear changes in the Lightning Shift mode on PDK-S, and "less than 200ms" on PDK in Sport with Chrono.

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?

Agreed, and just wanted to add that the latest ZF 8-speed autos has a "Automatic Idle Shift" system that puts the transmission in a "pseudo-neutral state once the vehicle is close to stopping", when for instance waiting for a green light at a intersection (in order to save fuel). That way the engine can idle free, just like when in neutral or the clutch disengaged on a manual. To release AIS is usually done by throttle tip in or footbrake release.

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...

[Law]

Originally Posted by Mo@BMWofFairfax

They did for the e9x 328's...

Yup, and prior to that, the GM 5L40-E transmission basically powered an entire decade of BMW four & six-cylinder cars:
(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.

[Flying Ace]

why red?

[MParallel]

Ha, the Rewe supermarket in Adenau.

[kyrix1st]

Originally Posted by lemetier

That aspect isn't going away. Like M-DCT and PDK-S, brake release does not engage forward creep automatically.



PDK is not 7ms - 8ms for a gear change. I don't know of any Transmission capable of such and that's faster than any No-Interrupt Electrical Transfer Switch can achieve. Porsche publish "less than 100ms" for gear changes in the Lightning Shift mode on PDK-S, and "less than 200ms" on PDK in Sport with Chrono.

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?

6ms in a roughly 1cm travel distance of clutch engagement is very possible. Do the math and you get the horizontal velocity of 1.67 meters per second, which is 1/455th of a bullet travel speed (760m/s.) And electric transfer switch what? Speed of light is 3.72E5 times the speed of bullet.

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

[Boss330]

Originally Posted by kyrix1st

6ms in a roughly 1cm travel distance of clutch engagement is very possible. Do the math and you get the horizontal velocity of 1.67 meters per second, which is 1/455th of a bullet travel speed (760m/s.) And electric transfer switch what? Speed of light is 3.72E5 times the speed of bullet.

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

I think it's a bit unfair to compare a M DCT with a std car transmission. The std VAG DSG is miles apart in feel and shift speed to a PDK...

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

[kyrix1st]

Originally Posted by Boss330

I think it's a bit unfair to compare a M DCT with a std car transmission. The std VAG DSG is miles apart in feel and shift speed to a PDK...

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

It's funny because I mentioned VLN on my previous thread; they are likely using upgraded transmission cooler with bigger fans. Also, the car can't really be compared since it is less powered and much lighter than M5 so there is less strain.

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.

[Boss330]

Originally Posted by kyrix1st

It's funny because I mentioned VLN on my previous thread; they are likely using upgraded transmission cooler with bigger fans. Also, the car can't really be compared since it is less powered and much lighter than M5 so there is less strain.

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.

"Upgraded cooler with bigger fans", does that remind you of any current M-models as well?

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:

A further optimization of the system was achieved through an intelligent modular design of the lock-up clutches. It allows for 2, 4, or 6 friction surfaces with hydraulic circuit diameters of 235, 250, or 270 mm, which makes it easy to adapt the system to individual customer needs. In addition, more effective cooling of the lockup clutch, which ensures lower wear and higher heat losses, is achieved by implementing a three path system for these new generation torque converters. Despite the considerably enhanced performance density, the system requires less installation space. Very short high-performance axial solutions are available for applications with extremely limited installation space.

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

The low mass inertia torque and the compact design make the HCC® an ideal start-up element – not merely for sportive uses, but also for vehicles with a distinct start-up deficiency (due to i.e., turbo lag). The shifting of gears in an automatic transmission equipped with HCC® can be performed just as rapidly as in dual clutch transmissions.
The HCC® converts a conventional stepped automatic transmission to a sportive transmission.

And as is evident in the drawings of the ZF HCC system, it's pretty solid with multiple clutch disks and high thermal capacity. I think ZF know a little bit about designing transmissions and this has come along way from the good old GM TH350...

Will be interesting to see if the M5 has the torque converter with lock up, or if it has taken advantage of the HCC...

[kyrix1st]

Originally Posted by Boss330

"Upgraded cooler with bigger fans", does that remind you of any current M-models as well?

This is where it gets a little fuzzy: automatic transmissions traditionally overheat from prolonged high rpm usage where manuals or DCTs are quite robust in performance. Given that both transmissions have undergone regular fluid changes, I would assume that

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..

[Boss330]

Originally Posted by kyrix1st

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..

Did you bother to read the ZF document on double clutch, torque converter and the new HCC?

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.

[Boss330]

Originally Posted by kyrix1st

This is where it gets a little fuzzy: automatic transmissions traditionally overheat from prolonged high rpm usage where manuals or DCTs are quite robust in performance. Given that both transmissions have undergone regular fluid changes, I would assume that

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.

I assume you are now referring to old automatic transmissions without lock up converters? Because they are prone to overheat because of the heat generated in the torque converter since that relies on the fluid transferring power between stator and turbine. By introducing the latest generation of lock up converters with constant lock up you eliminate the heat build up in the torque converter.

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?

[DarthColin]

Informative videos:

HCC (Hydrodynamically Cooled Clutch):

TTD (Turbine Torsional Damper), which I assume is early version of TwinTD (Twin Torsional Damper):

[Boss330]

Originally Posted by DarthColin

Informative videos:

HCC (Hydrodynamically Cooled Clutch):

TTD (Turbine Torsional Damper), which I assume is early version of TwinTD (Twin Torsional Damper):

Thanks! Very illustrative videos.

The HCC wet clutch solution seems intriguing. Wonder if that is used in the M5...

[mundo74]

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.

[Boss330]

Originally Posted by mundo74

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.

Yeah, I agree that saying your M5 has an automatic transmission doesn't sound special. But to the rest of the world, any car with two pedals is a car with an automatic transmission anyway...

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...

[lemetier]

Originally Posted by Boss330

Thanks! Very illustrative videos.

The HCC wet clutch solution seems intriguing. Wonder if that is used in the M5...

ZF HCC units are what AMG use in the MCT transmissions. It is not what the F90 uses. The M235iR have two versions (2014 - 8HP45 with TC; 2015 - 8P45R with HCC)

[DarthColin]

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.

[mundo74]

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.

[kyrix1st]

Originally Posted by Boss330

I assume you are now referring to old automatic transmissions without lock up converters? Because they are......

Not the case with the ZF6HP on 3.0si z4 (e85). It has a lock up clutch and overheat like shit on track. It would be more time efficient for you to run both smg and zf versions of e85 on track than to give you shaky statistics behind my desk.
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."

[Boss330]

Originally Posted by lemetier

ZF HCC units are what AMG use in the MCT transmissions. It is not what the F90 uses. The M235iR have two versions (2014 - 8HP45 with TC; 2015 - 8P45R with HCC)

I didn't think AMG used the ZF HCC since AMG/MB makes their own transmissions, but that what they use is similar to the ZF HCC...

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?