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      03-27-2008, 12:45 PM   #111
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Quote:
Originally Posted by swamp2 View Post
Footie, there is another effect here. This engine under WOT at redline produces about 250 ft lb. Shifting when getting on it drops the rpm to something like 6000 (of course this varies gear by gear and on gas pedal depression as well). Around that 6k rpm the engine is producing very close it its peak torque, 300 ft lb. Aren't you going to feel a jerk when you try to apply 20 more ft lb over a very short time interval? Unless you make a careful effort to hide it you are going to feel it. You can play tricks with DCT and all sort of parameters as I have mentioned many times in the past like spark, timing, fuel flow, automated throttle control, clutch times and clutch phasing, etc. to control the jerkiness. As long as the jerk is not fake, which I highly doubt it is, I suspect that even with DCT more performance requires more jerk. But in all cases the jerk is less than SMG because there is almost no deceleration. My innacuracy in the past may have been believing that BMW could provide the most performance with little to no jerk. I do think I was wrong about the subtlety myself.

The jerk is not just from the torque differences at different rpm. Acutally this is only a small part of it. If you shift very fast at 8,300 rpm into the next gear, which needs 6,000 rpm at the current road speed, then there is 2,300 rpm of engien speed which must disappear. This is kinetic engergy from the rotating mass of the engine components and is converted to a surge or jerk or what ever you want to call it if the shift happens quickly.

If you slow the shift down, like I think happens in D1 or D2, then that kinetic energy can dissipate as heat through internal friction of the engine slowing the rpm.
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      03-27-2008, 01:02 PM   #112
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ABSOLUTELY. Don't forget one of my favorite videos of the M6 getting a bit of "scratch" all the way into 5th. Play this mutha loud!

This is simply heavenly! I wonder if the M3 will "chirp" into 4th, I'd say 3rd for sure.

Does this M6 have SMG??? Forgive me for the retarded question.... When I drove an M5 w/ SMG is shifted NO WHERE nearly as fast and hard as that...my buddy said it was in the sportiest mode, but maybe he was wrong? That is one major reason I am shying away from the M5, because I though the SMG was too slow shifting. If that phucker shifts like that M6, I may have to reconsider. Somebody fill me in!

edit: Isn't the M6 only available in SMG? I am tripping out here...because if that M5 shifts like that, omfg, I may have to buy one.
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      03-27-2008, 01:57 PM   #113
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Quote:
Originally Posted by footie View Post
Enigma and Swamp,

You guys are still think of DCT like you would SMG, eg. one clutch controlling all of the gears. The jerk is engineered, please go and get a bit of advice on DCT and dual clutch technology before ranting.



Correct in your comments on why you don't what jerk but to think that the Veyron would suffer from traction issues, the Veyron can put all of it's 1160hp (yes that's right) to the road even in the rain. The reason jerk is unwanted is because it will cause unbalance the chassis during cornering.



ICT is the future, not CVT and BMW are a big player (among other car and gearbox manufacturers) in this technology as they are co-testing this technology with http://www.torotrak.com/, the company which invented it. Unlike CVT IVT can cope with more torque than is currently produced by any production vehicle and unlike CVT it uses special oil which increases friction, specially developed by Shell. The advantage of IVT is that it will optimise the engine's power and torque by acceleration at the optimum rev point unlike either a manual or automatic which has fixed ratios.

P.S.

And not a jerk in sight.
Well you have some OK points here but to insult either me or enigma in saying we do not understand how a DCT works is utter nonsense. Perhaps you should read my dozens of posts on the topic and the explanations I have provided to others before spouting such drivel. I think you have but maybe your memory just sucks as well.

You have continued to exhibit a clear lack of technical knowledge and grasp here on the forum. You do offer many valuable comments and opinions but your weakness is clear. I have my weaknesses as well, but generally technical understanding and ability isn't one of them.

It is a very interesting idea this whole jerk thing. Could BMW have possibly engineered the jerk back into the system when by its fundamental design there is no jerk? I just do not think it is possible. But in the future it may be. We have discussed extensively here on this forum the differences between speed (i.e. acceleration) and the perception of acceleration. It is a foregone conclusion that jerk is a more important factor in the perception of acceleration, but not actually in the measured acceleration and hence actual performance. Folks LOVE the SMG S6 smack, the jerk, it simply feels fast. But IT IS NOT AS FAST as it can be. It is not because it wastes time and bleeds speed by decelerating. The deceleration while the throttle is lifted and clutch is engaged with any MT or SMG system slows you down and produces less acceleration compared to an equivalent DCT design. We have explained why without some careful management even a DCT transmission will produce a spike/jerk. It is flywheel intertia and engine torque vs rpm.

Do you even have any idea what an accelerometer trace for a shift in a MT/SMG/DCT/AT will even look like and what they mean? Let me try help as much as possible. Below are some quick sketches of acceleration vs. time. There are not position vs. time, not velocity vs. time, but acceleration vs. time. Qaulitatively the height of each curve represent how much push you feel on your back in the seat at any instant. These curves are not exact by any means, but do get all the main points across. Before clutching you are in a mode of acceleration dropping as engine torque does. When throttle is reduced and clutching the acceleration drops very sharply. If or how far you get below the x axis of zero accelertation depends on how fast you are going and how much air resistance there is. Here since you actually go to negative acceleration these shifts are likely above 50 mph or so. When you clutch out the accleration builds and you get the positive jerk as the flywheels momentum is conserved and the engine is transitioned to a lower rpm at a point it produces more torque. SMG exhibits both the dip and rise but they are very short. The AT smoothes everything over and generally lengthens the total shift time. Now with DCT you almost entirely eliminate the negative jerk via simultaneous clutching and are just left with the positive jerk (surge as BWM is calling it) from the flywheel effects and from the engine simply producing more torque at lower rpm.

Now much like an automatic transmission, but accomplished by very different means the Veyron and VW DSGs very much reduce the positive spike/jerk shown in my approximated DCT graph. As well lower A modes in DCT will similarly reduce the spike shown (and very likely stretch the time out, like the automatic but more on the time scale of a very good automatic, say the IS-F).

I think I am in part to blame for your misunderstanding here. I have talked much about how the BMW system will be very smooth yet still offer great performance. I was likely incorrect on their ability to have the ultimate performance with almost no jerk. My predictions here were based on both the Veyron and GTI DSG units as well.

It really seems like BMW has obtained the best of both worlds. There is less jerk than a MT or SMG, however there still is jerk but it is a surge rather than containing any deceleration. I would be very willing to live with little to no jerk myself if it meant more performance, but most would not. Almost no one can separate their perception of speed with obtaining true speed, hence everyone really wants the jerk. I guess that is why the forum seems to appreciate me and enigma!

Footie, please take some serious time and think this through. We are realyl trying to help you. Others: Correct my mistakes and predictions and let's keep the discussion going.



P.S. Thanks for the info on IVT, I am always keen on the emerging technologies. Some reading and research needed here for sure.
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      03-27-2008, 02:00 PM   #114
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Quote:
Originally Posted by GT3 Tim View Post
Does this M6 have SMG??? Forgive me for the retarded question.... When I drove an M5 w/ SMG is shifted NO WHERE nearly as fast and hard as that...my buddy said it was in the sportiest mode, but maybe he was wrong? That is one major reason I am shying away from the M5, because I though the SMG was too slow shifting. If that phucker shifts like that M6, I may have to reconsider. Somebody fill me in!

edit: Isn't the M6 only available in SMG? I am tripping out here...because if that M5 shifts like that, omfg, I may have to buy one.
I agree .

This is a M6 in drivelogic mode S6 with launch control used. You got a bum ride from someone! M5 and M6 only come with SMG (SMG III, is the exact variant) everywhere in the world except in the US (maybe NA as well as US, not quite sure). Here our stubborn enthusiasts demanded a MT. M3 with DCT and LC will be quite similar!
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      03-27-2008, 02:22 PM   #115
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swamp,

I apologize for my remarks but when someone talks down to you on something that they have neither sampled or are 100% knowledgeable with the technology it's hard not to get a little angry and upset.

The graphs are interesting but according to what I have been told by someone which should know better that the jerk/surge has been engineered into the system for not other reason than to appeal to the present following of SMG customers. There is no doubt that such an experience will give the feeling of more speed ever if the reality is not the case.

P.S.
I was also told that the shift time of both the new DCT and DSG gearboxes are 30ms, no more, no less.
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      03-27-2008, 02:23 PM   #116
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Quote:
Originally Posted by swamp2 View Post
Let me try help as much as possible. Below are some quick sketches of acceleration vs. time. There are not position vs. time, not velocity vs. time, but acceleration vs. time. Qaulitatively the height of each curve represent how much push you feel on your back in the seat at any instant. These curves are not exact by any means, but do get all the main points across.
These are a very good rough draft. I think for the M3 the in gear acceleration for the previous and next gear will be much closer in level.
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      03-27-2008, 02:26 PM   #117
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Originally Posted by footie View Post
swamp,

I apologize for my remarks but when someone talks down to you on something that they have neither sampled or are 100% knowledgeable with the technology it's hard not to get a little angry and upset.
What makes you think I don't have experience with the Audi system? Just because I don't agree doesn't mean its because I have not tried it.

Footie, tell me, where does that stored energy go if not to the rear wheels?
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      03-27-2008, 02:37 PM   #118
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Nice graphs swamp. However, I would say that the "jerk" is not the acceleration but the rate of change of acceleration. That being the case, jerk would be identified in the graphs as the slope of the curve at any point in time. The way you have drawn the curves shows the top three (6MT, SMG and DCT) have "jerks". You can also see much greater range in 6MT and SMG as compared to the DCT. The bottom graph does not have large slopes, hence not much jerk, i.e. much smoother.

Assuming you're right with these curves, I find this a very good graphic way of conveying the concept. Great idea swamp. It's posts like this that make this forum useful. Thanks.
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      03-27-2008, 02:41 PM   #119
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Originally Posted by ersin View Post
Assuming you're right with these curves, I find this a very good graphic way of conveying the concept. Great idea swamp. It's posts like this that make this forum useful. Thanks.
I am pretty sure he is. This is real logged data from my 6mt car going 3->4 at laguna seca.



I'll try to log the same thing for my SMG car this weekend.

EDIT: Log was from this driving session
http://video.google.com/videoplay?do...40764726878137
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      03-27-2008, 02:43 PM   #120
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Enigma,

What hardware did you use to produce that graph?
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      03-27-2008, 02:46 PM   #121
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Quote:
Originally Posted by ersin View Post
Enigma,

What hardware did you use to produce that graph?
Race Technology DL-1. Its from one of my better laps at laguna seca in the Elise.
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      03-27-2008, 02:51 PM   #122
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Originally Posted by swamp2 View Post
I agree .

This is a M6 in drivelogic mode S6 with launch control used. You got a bum ride from someone! M5 and M6 only come with SMG (SMG III, is the exact variant) everywhere in the world except in the US (maybe NA as well as US, not quite sure). Here our stubborn enthusiasts demanded a MT. M3 with DCT and LC will be quite similar!
Thanks bro. I didn't mean to step on this thread as there is some great info/ideas coming forth...but I was just blown away by that video. I definately got a bum ride (to his defense, he just got the car so maybe didn't quite understand it yet..plus, he is not a gearhead either). Thanks again.
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      03-27-2008, 02:56 PM   #123
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Based on enigma's graph I would reckon that the SMG in S6 will has a shorter drop on the graph but the rising slope between the lowest point and the highest point will be more extreme and will happen is less than the half the duration. If I am right this might explain why it's effect is more felt and extreme.

swamp,

I haven't an answer to your question, but all I know is what I have been told and knowing the person and his position I reckon he should know what his talking about. And according to him it's there for no other reason than the appeal to SMG customer. I will be interesting to see a graph from all the respective modes to see what is happening during the shifts to see if there is any adjustment to the shift time. I think is here were we will finally understand what is happening.
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      03-27-2008, 02:59 PM   #124
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Quote:
Originally Posted by footie View Post
...
The graphs are interesting but according to what I have been told by someone which should know better that the jerk/surge has been engineered into the system for not other reason than to appeal to the present following of SMG customers. There is no doubt that such an experience will give the feeling of more speed ever if the reality is not the case.

P.S.
I was also told that the shift time of both the new DCT and DSG gearboxes are 30ms, no more, no less.
Great info, what is your source? Again, I seriously doubt the first point, the principal one of immediate debate but am glad to hear about the second. Confirms my estimates right on the money. To be clear on that I would say depending on mode minimum shift time would be ~ 30 ms.
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      03-27-2008, 03:04 PM   #125
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Originally Posted by ersin View Post
Nice graphs swamp. However, I would say that the "jerk" is not the acceleration but the rate of change of acceleration. That being the case, jerk would be identified in the graphs as the slope of the curve at any point in time. The way you have drawn the curves shows the top three (6MT, SMG and DCT) have "jerks". You can also see much greater range in 6MT and SMG as compared to the DCT. The bottom graph does not have large slopes, hence not much jerk, i.e. much smoother.

Assuming you're right with these curves, I find this a very good graphic way of conveying the concept. Great idea swamp. It's posts like this that make this forum useful. Thanks.
Right, jerk is the derivative of acceleration. My curves were not supposed to be perfect matched vs. data. As you can see enigmas data shows things a bit more piecewise linear and less smooth than my curvy graphs. But essentially they are right on the money. The DCT curve does definitely show jerk, it just does not exhibit much deceleration. So MT and SMG have both large negative jerk and large positive jerk. DCT will have almost no negative jerk and probably less positive jerk, again depending on the drivelogic mode.
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      03-27-2008, 03:06 PM   #126
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Quote:
Originally Posted by footie View Post
Based on enigma's graph I would reckon that the SMG in S6 will has a shorter drop on the graph but the rising slope between the lowest point and the highest point will be more extreme and will happen is less than the half the duration. If I am right this might explain why it's effect is more felt and extreme.
That is absolutely correct. I think you are getting it.
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      03-27-2008, 03:12 PM   #127
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Race Technology DL-1. Its from one of my better laps at laguna seca in the Elise.
Cool. I have an AP-22 which I believe is made by the same company but is older and uses accelerometers only. The DL-1 also has GPS, right? I could get the same data (a vs. t) but I don't believe it will be anywhere near the time resolution you get with the DL-1. It's been a while since I've played with this toy. I'll have to break it out again.
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      03-27-2008, 03:16 PM   #128
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One additional point to all:

In the acceleration vs. time curves, the area under the curve is proportional to the speed. And when the curve dips below zero, you're losing speed. See how the DCT stays above zero? The area under the curve is greater for the DCT than the rest over the same duration. This is the speed advantage of the DCT. And note that the little jump that the DCT curve takes adds a bit to the speed but not as much as if it were of longer duration. However, because of it's slope, it feels like you're getting a "jerk" and feels faster.
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      03-27-2008, 03:18 PM   #129
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Quote:
Originally Posted by swamp2 View Post
Great info, what is your source? Again, I seriously doubt the first point, the principal one of immediate debate but am glad to hear about the second. Confirms my estimates right on the money. To be clear on that I would say depending on mode minimum shift time would be ~ 30 ms.
My info is coming from a competitor with a similar system and that's all I am saying.

Regarding the 30ms, of course this depends of mode but shouldn't really as the longer the time the less smooth it should be. I would reckon the time will vary being more to do with what you are trying to do with the gearbox, ie. change down more than one gear or decide to change down after changing up for more than two shifts, in this the gearbox software would assume you would want to shift up and thus have the higher gear already preselected. In this scenario I reckon the shift time will be greater than the 30ms being quoted.
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      03-27-2008, 03:40 PM   #130
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I wonder if there is an idea that the manual mode will be as good as the better SMGs out there such as the newer Ferrari F1 tranny or the Lambo e-gear.

I understand they are different the SMG is one clutch and the DCT (in theory) should be better (especially in the auto mode).

it's two things to wonder about...

1) how does it behave as a autobox? Which is secondary to me.

2) how does it behave as a Manual tranny mode up and down (with throttle blips I suppose?).

If the DCT is likely better than the SMG do you think mainly in the auto mode or do you think it's better in both auto and manual modes?

I have driven one DSG (GTi)
I have driven two SMGs (F430 and Gallardo)

I was very pleased with all three trannies. I suspect I would be very happy with the DCT but I have to order without a test drive.

I liked the M3 6MT, but I was not in LOVE with it. I sit far back and the 4-5 shift is a long throw. I don't think it's a deal breaker but I could go either way..

Thanks if anyone has any advice.
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      03-27-2008, 03:43 PM   #131
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Quote:
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My info is coming from a competitor with a similar system and that's all I am saying.
Let me translate that.

Being a competitor of course they think their decision is right and anyone else makign a different one is wrong. They have to say that.

So by "Engineered in" they really mean "Didn't hide from driver the transfer of energy". They think this was the wrong decision, and for people looking for a status symbol they would be right. If it were going into the 550 or 335 I might even agree.

Remember Audi has a different target market. They are more after the "it just works" crowd and less after the entusiast crowd.
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      03-27-2008, 03:44 PM   #132
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Quote:
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I am pretty sure he is. This is real logged data from my 6mt car going 3->4 at laguna seca.



I'll try to log the same thing for my SMG car this weekend.

EDIT: Log was from this driving session
http://video.google.com/videoplay?do...40764726878137
Thanks for the graph, at which speed do you have to shift to 4th? The deceleration (of the car) swamp mentioned means mighty 0.3kph slower here...


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