| 06-11-2016, 09:54 PM | #1 |
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DCT partial throttle slippage question
So I'm still kinda new to the DCT F8x world as I've had my ZCP M4 DCT for just over a month and I've got a question in regards to normal DCT operation in S3 mode.
I've noticed, that when in S3 mode and up shifting to 3rd gear from 2nd gear at 50-70% throttle, the DCT slips the clutches a little too much and takes a long time to fully lock. When WOT the transmission will slam every gear, but moderate throttle causes the clutches to slip more than I'd prefer. For whatever reason, it is most prominant from 2nd to 3rd gear. Has anybody else experienced this? I love the way the DCT shifts at WOT and see zero issues with clutch slip in a full WOT scenario (it will chirp 4th gear), it is only during moderate to heavy partial throttle that I get this weird slippage. Maybe I need to reset adaptations? Also, this only happens in Sequential mode. Regular D modes don't cause this to happen and shifts are crisp and fast.
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| 06-12-2016, 01:29 PM | #2 |
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Anybody want to confirm if their DCT equipped F8x does this?
I will address this issue with my SA when I go in for my 1200 mile service. I might have them reset the DCT's adaptations and see what happens. |
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| 06-12-2016, 01:31 PM | #3 |
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I haven't experienced this with my DCT with 13000 miles.
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| 06-12-2016, 06:07 PM | #9 |
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never could compete with Lloyd Braun
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Mine does this in S3... At WOT, it shifts great but S3 feels actually less-crisp in my car at moderate part throttle than S2. S2 shifts are crisp no matter how much throttle I apply. This is my first DCT car, too, so I chalked it up to normal behavior but maybe it isn't?
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| 06-13-2016, 02:32 AM | #10 |
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Funny enough I much prefer the DCT in mode 2 not 3, since I feel like mode 3 gives it an uncomfortable shift. That was when I had my M5. Not sure how it is on an M4.
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| 06-13-2016, 03:53 AM | #11 | |
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never could compete with Lloyd Braun
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| 06-13-2016, 07:01 AM | #12 | |
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1. The adaptations probably need to be reset. I'm working on resetting those really soon as I don't have a OBDII cable here to use Rheingold. That is about to change. I will report back if this helped. It certainly won't hurt to try. 2. The ZCP targets more boost at part throttle than the non-ZCP and I've noticed the moderate boost/part throttle slippage happening when I'm on Map 1 on the JB4. When I'm running stock boost, the DCT doesn't slip during these conditions at all and shifts are nice and clean. Map 1 is an additive map of 4psi, but Map 1 is setup to be used in a "stage 1" configuration (I.e. Without a CANBus connection to the JB4). This means that the JB4 will increase boost 4 psi, regardless of condition (pedal input/RPM). Maps 2/3/5/7 are setup to be run with a CANBus connection and take pedal input and RPM into consideration when deciding the additive boost target over stock (a roaming additive boost target). When running map 3/7(or any other additive map that uses pedal input/RPM), I don't see this issue, because like stated above, the additive target doesn't ramp up boost over stock targets at these pedal inputs/RPMs. It was only happening on Map 1 (4psi increase across the board, regardless of the pedal input/RPM). Because the ZCP is already targeting boost pressures higher than the base S55 and with the addition of 4psi over the ZCP's stock boost target (map 1), the DCT doesn't have the clamping force programmed in it to be able to keep the clutches from slipping during moderate part-throttle. Basically, it looks like BMW didn't increase clamping forces over the base non-ZCP programming, at least for part throttle/moderate boost pressures. Now, I'm testing a few things with Terry @ BMS and I think we have a handle on the issue. We've switched Map 1 to use pedal input(for test purposes) to slowly ramp up the additive target at part throttle and I'm going to be testing Map 6 in additive mode with throttle input as well. Some tweaks will need to be made to the JB4 to run on the ZCP, but we're on it and Terry is VERY proactive (per usual). Don't let any of this alarm anybody. These are just growing pains as the ZCP is throwing us a few curve balls, but these issues are easy to work around. It takes testing and tuning to find these types of things. Also keep in mind, we're only talking about part throttle shifting slippage, once in gear and the clutches lock, there is zero slippage. WOT shifting is normal and violent (the way it's supposed to be). Here is a screenshot of the slippage event upon shifting into 4th. Notice how long and drawn-out the RPMs fall after the last gear change (3rd to 4th gear). Last edited by CaryTheLabelGuy; 06-13-2016 at 08:58 AM.. |
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| 06-13-2016, 08:59 AM | #13 |
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And another screenshot with the gear change highlighted with sensor info.
It slipped going from 2nd to 3rd gear, but slipped even worse going from 3rd to 4th gear. As you can see, the boost pressure is pretty high for such a small pedal input (44%). |
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| 06-13-2016, 02:15 PM | #14 |
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So does Map 2 slip as well?
my question: The M5 with a JB4 has alot more torque than the S55 with a map, yet the M5 does not have any clutch slippage. Why does the M4 have some? Especially since they are the exact same DCT. Something doesnt sound right. |
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| 06-13-2016, 02:20 PM | #15 | |
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First of all, I don't recommend Map 2 on pump gas for the ZCP. If you wanted to use Map 2, this problem wouldn't be there, because Map 2/3/5/7 uses pedal input and RPM to vary additive boost targets over the stock boost targets. Map 1 doesn't use pedal/RPM input and is commanding 4psi over stock boost pressure, regardless of pedal input/RPM, which is causing lazy shifts during moderate partial throttle due to the TCU expecting X-Amount of boost, but actually getting 4psi more. The TCU just isn't locking the clutches with enough force in these conditions. Second of all, the clutches aren't slipping under WOT. It's just a software tweak in the TCU , which controls the DCT and how hard the clutches clamp at a given load. Third, the M3/4/5/6 all use the same DCT with the same clutches. It is the software in the TCU that is different and has different clutch lock up parameters. |
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| 06-13-2016, 04:55 PM | #17 | |
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| 06-14-2016, 06:18 AM | #19 |
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I'm happy to report that the DCT clutch slippage issue at moderate part throttle has been solved.
My ENET cable will be here tomorrow and I will reset the adaptations just to be thorough and have the TCU/DME relearn adaptations. But the excessive boost during moderate part throttle causing lazy shifts has been mitigated. |
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| 06-14-2016, 07:10 AM | #20 | |
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