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08-23-2008, 05:36 AM | #1 |
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PRELIMINARY M-DCT shift times - results and data
I have done some preliminary measurements of the M-DCT shift times. The numbers are not too much of a surprise and are quite consistent with my previous estimates and rumored and quoted values for other DC vehicles. However, the differences between modes with and without surge are quite surprising.
For those that don't want to read the remaining details nor actually look at the data the shift times likely vary from about 30 to 200 ms. Thanks again to the members who helped fund the purchase of the equipment to accomplish these measurements, T-Bone, lucid, TLud and OC Kid. The thread that proposed this is located here. The equipment used is listed here as well. We would still like to test many more cars listed on that thread, if you or someone you know would volunteer their car (preferably in the Southern California or Boston area) please PM me. Of course the process to get better, cleaner and more accurate data will be refined before moving forward with a lot more testing. Since these measurements involve ONLY the time for the actuation of the clutches they DO NOT include the delay which has already been noted in S modes between the actuation of the paddle/stick and the beginning of the clutch actuation (and hence any measureable changes in acceleration). So until that can be better instrumented and tested these are shift times in D modes or partial shift time NOT INCLUDING any shift lag. We know already that not all gears, all modes and all rpms produce equal shift times and these are the approximate measured range. When including the 1->2 shift in LC mode and the 6->7 shift I would expect that range to widen (just an educated guess here to about 20 to 400 ms. The former figure being maybe D2 6-7th at low throttle and the latter for 1-2 under LC as it really slurs this shift, while not sacrificing acceleration. Caveats:
Data and results: First graph Mode: D3 Power: Normal Throttle (qualitative): medium to high, close to WOT Shift: 3->4 Data sampling rate: 300 Hz Vertical axis: acceleration in g's Shift time: 32 +/- 5 ms Second graph Mode: S4 (recall this means the transmission will exhibit surge or more precisely stated a noticeable jerk) Power: Normal Throttle (qualitative): medium to high, close to WOT Shift 2->3 Data sampling rate: 500 Hz Vertical axis: acceleration in g's Shift time: 200 +/- 50 ms Discussion: The 30 or so ms observed in D modes is consistent with figures discussed for VAG DSG. Many sources quoted 8 ms but a more credible source provided a very similar figure. 8 ms has always seemed way too low given it is still a mechnical and hydraulic system. There are about 10 individual sample points across the duration of the shift in the first graph. The acceleration profile shows the steady state acceleration drop as the first clutch is disengaged very quickly followed by an equal duration surge of a higher magnitude as the second clutch engages. The S4 shift time is a big surprise. They certainly feel faster than the S3 shifts but it is psychological. The mathematical surge/jerk in S3 is actually much greater (a large jump in g force over a shorter duration) compared to the more plateau like positive and lengthy acceleration profile in S4. I think what is happening is that the jerk in S3 is simply so short we just don't feel it, whereas the much more lengthy profile, all at an increased acceleration compared the the steady state, both before and after the shift provides this jerk/surge/"clunk" that we know so well from modes S4->S6. A quick calculation of the extra speed that this surge provides compared to the wash in D3 is given by: ΔV = a x t = 3/8 g x .15 s ≈ 0.6 m/s ≈ 1.2 mph This is the relative gain comparing the mph after the 2->3 shift in S4 vs. D3. So again footie, my friend, S4->S6 with surge does not shift faster than D modes but it is faster. The former result I believe is quite novel but the later one was what I and others have been saying all along. |
08-23-2008, 07:10 AM | #2 |
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No problems in admitting that the surge is proving to provide an additional increase in forward momentum, so we are roughly looking at a 1 mph surge over D3, but D3 is completing it's shift 6 times quicker, is that about right or have I misunderstood what you were saying.
Next we need to compare the acceleration times between 20~120mph between D3 and S4, that will determine how much of a true benefit the surge is providing other than the feeling of sportiness which is the most noticeable benefit. |
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08-23-2008, 11:22 AM | #3 |
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Even though the shift can be 200ms, is the car still providing power to the tires during the shift?
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08-23-2008, 11:45 AM | #4 |
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Thanks Swamp. This is rather interesting preliminary data. I am looking forward to seeing more measurements taken at a higher sampling rate (300 Hz on the first graph seems to be just the bare minimum for capturing anything meaningful), and a comparison of the same shift, say 2->3, in D and S modes under WOT so that we can isolate any effects of your throttle input during the shift, which might not be constant (I assume that's why we are not seeing a significant drop in acceleration after the 2->3 shift, which should happen due to the change in gearing, or is it just the scale of the y-axis combined with the noise that makes it difficult to observe this?). I realize that is not easy to do on public roads though. Is there any reason why you are not using the 1kHz sampling rate? I believe the accelerometer will do that, right? And, yes mounting the accelerometer rigidly should decrease noise significantly.
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08-23-2008, 12:13 PM | #5 | |
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08-23-2008, 02:23 PM | #6 |
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Thanks Swamp...good initial set. It would be good if you can compile statistics on the shift programs.
I.e. get shift times for all shifts in S and D mode. Then we can do figure out mean times for each gear shift by program.
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08-23-2008, 02:30 PM | #7 |
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Swamp - please see http://www.m3post.com/forums/showthread.php?p=3213213
I would love to see some SMG3 data once you sort out the methodology.
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08-23-2008, 04:00 PM | #8 |
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The car is not only accelerating during the entire S4 shift, it is accelerating MORE than the background, steady state acceleration (i.e. that due to the car pretty much being pegged!). In D3 the car actually very briefly (~15 ms) decelerates, but again one can't feel it.
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08-23-2008, 04:11 PM | #9 | |
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08-23-2008, 04:35 PM | #10 | |
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I dug around a bit and thought the seat rails would be the best location for easy access and very rigid mounting, while remaining on the interior of the car. However, the attachment of the bracket to the rails is not 100% straight forward and it should be as rigid as possible. Do note you can easily pop the protective plastic cover right off the front of the seat rails. I am certainly open to other ideas. The accel dimensions and mounting dimensions are given in the attached pdf. The mounting screws are M2 x 12 FHCS. I could make it slightly easier for you by dropping the actual accel off, that way there could be no uncertainty. You should make an attempt to get the accel as normal to both the ground and direction of travel as possible. Definitely not a huge deal, nor does it need to be perfect, but this would be a goal. Last but not least, I strongly believe the braket should be made of bar instead of sheet. You probably meant that. I use "sheet" for any material measured in gages and "bar" for the stuff in inches beginning around 1/8". Based on the screws and accel thickness my suggestion would be 3/16" thick minimum. Thanks again! |
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08-23-2008, 04:36 PM | #11 | |
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08-23-2008, 05:28 PM | #12 |
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I will check Sunday to see what material I have
(near 3/16") and use the PDF sensor dimensions to layout a design. I don't think I will need the sensor to do the layout. I also read through the Dytran technical material on mounting and will follow their recommendations. The attached PDF was in their tech education link at the bottom of thier web page. http://www.dytran.com/go.cfm/en-us/c...ucation/x?SID= There is also additional info there that might help with the testing. |
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08-23-2008, 06:14 PM | #13 | |
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DSG seems to performs like s3 by the sound of it, i.e. ultra quick shifts with the surge which isn't noticeable, why BMW and Porsche are choosing to increase the shift duration to make the surge felt is unknown, I agree that it feels good when you are 'ON IT' and as Swamp has found it does generate a kick of approx >1mph. The next thing needed to be ascertained is whether this longer duration shift with felt surge over the ultra quick shift with the greater surge that isn't felt actually benefits the overall acceleration times over a set discipline (20~120mph). This will be very interesting to see how that one plays out. |
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08-23-2008, 06:16 PM | #14 | |
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Here is the right URL http://www.m5board.com/vbulletin/e60...ml#post1397994
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08-23-2008, 06:41 PM | #15 | |
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I saw your earlier comment about 10 data points within the interval. Visually, it seems less, but I guess some of the points line up well with the lines. Regardless, it would be good to have more.
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08-23-2008, 06:56 PM | #17 | |
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so if the shift is 30 ms, 3.3 is 9x's... 3.3 is theoretically enough to capture 8 ms... Nyquist-Shannon If a function f(t) contains no frequencies higher than W cps, it is completely determined by giving its ordinates at a series of points spaced 1/(2W) seconds apart. |
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08-23-2008, 07:23 PM | #18 | |
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08-23-2008, 07:40 PM | #19 | |
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I'm thinking it's the shift, not the noise... and as swamp stated, he got good transitons and reversal of direction... obviously more is better...but the Nyquist theorem is valid...it's how they cram so much signal on the net, phones, TV, etc. and not lose any information... it would be better, as he stated, if filtering was applied...but that has risk too, filtering out signal along with noise...but if you only filter stuff outside 2x's the bandwidth you should not lose any information... it's one reason 44.1khz was used for cd's, basically 2x's the range of human hearing of 20khz... signal theory is manipulated in the f domain, not t....that way you can see the f's where the energy (information) lies... I'd like to see the raw data transformed into the frequency domain with matlab I bet the first one would have a spike at say 3f and f, discard the 3f...filter result in t; flat line with an asymetric sine wave at the shift the second one would have a spike at say 10f and f, discard the 10f...filter resul in t; flat line with a pulse at the shift Last edited by ArtPE; 08-23-2008 at 07:55 PM.. |
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08-23-2008, 08:11 PM | #20 | |
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This is also what I'm getting from their test. I've also bolded what I'd really like to know. What is going to get you the best performance Awesome stuff guys, this is the kind of stuff that really impresses me about the M family. Just wanted to give a thanks to you guys for doing something like this and getting some great info. |
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08-23-2008, 08:17 PM | #21 | |
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How the hell is a D mode shifting faster than S4, is BMW truly slowing down the shift so that the "surge" is not "slurred" through a quick and smooth shift? With the extra 1.2mph in speed you get from the "surge" if they could take that and the shift times of the D3 mode, isn't that the idea situation? How is S4 so much slower in the shift and how can that be good for performance? Sorry if I sound ignorant......
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08-23-2008, 08:40 PM | #22 | |
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