DCT/ No Torque Converter

Nice Rumble · 09-03-2014, 06:45 AM

In a conventional automatic I tend to place the transmission in neutral at long stoplights to keep the vehicle from creeping forward and help with fuel economy.
Given the DCT does not have a torque converter is this no longer necessary? What is really going on inside a DCT transmission when stopped and in D? It feels like the vehicle does not want to creep forward until power is applied.

Helmsman · 09-03-2014, 07:35 AM

Yep, the clutch engage only when power is applied so doesn't have to worry about putting into N. Very nice once you get used to it...

EJT86 · 09-03-2014, 08:17 AM

Tap the accelerator and it will do the conventional "creep" like a regular auto also know that if you take you foot off the brake for more than three seconds it will roll in either direction like neutral if on a hill and you tap the accelerator without fully braking again hill start assist won't be active and you'll roll backward

jphughan · 09-04-2014, 10:53 AM

Being stopped with DCT in D is mechanically equivalent to holding the clutch pedal down in a 6MT while remaining in gear. A DCT literally disengages the clutch in that scenario, and as others have pointed out, tapping the throttle will engage creep mode by lightly slipping the clutch, just like letting the clutch pedal partway out on a 6MT.

As for which is preferable at a red light, I doubt it really matters. Driving 6MT, I put my car in Neutral to avoid unnecessary throwout bearing wear and give my left leg a break, so perhaps there's a bit less wear by doing that on a DCT as well, but I also have no doubt that BMW designed this trans to be able to remain in D at red lights.

crypticc · 09-04-2014, 02:27 PM

Dct neutral is effectively same as dct in drive with brake depressed fully. The two clutches are operated with hydraulic pressure and fully disengage until a gear is selected and throttle applied. Suggested google st813 dct drivelogic pdf

Shows neutral has two main clutches disengaged with sliding clutches also disengaged. 1st gear engages the sliding clutch for 1st but the main clutches won't be engaged at that point until you release brake and move away. Once moving there always a clutch engaged.

09-03-2014, 06:45 AM	#1
Nice Rumble Private First Class 28 Rep 173 Posts Drives: 2009 M3 DCT Coupe Join Date: Mar 2014 Location: New London, NH iTrader: (0)	DCT/ No Torque Converter In a conventional automatic I tend to place the transmission in neutral at long stoplights to keep the vehicle from creeping forward and help with fuel economy. Given the DCT does not have a torque converter is this no longer necessary? What is really going on inside a DCT transmission when stopped and in D? It feels like the vehicle does not want to creep forward until power is applied.
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09-03-2014, 07:35 AM	#2
Helmsman Major General 4465 Rep 7,109 Posts Drives: 2011 AW E90 M3 ZCP Join Date: Mar 2014 Location: Stockholm, Sweden iTrader: (0)	Yep, the clutch engage only when power is applied so doesn't have to worry about putting into N. Very nice once you get used to it...
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09-03-2014, 08:17 AM	#3
EJT86 Brigadier General 2383 Rep 3,726 Posts Drives: 2018 M2 Join Date: Mar 2014 Location: Boston, MA iTrader: (0) Garage List [0.00] 2018 BMW M2 [0.00]	Tap the accelerator and it will do the conventional "creep" like a regular auto also know that if you take you foot off the brake for more than three seconds it will roll in either direction like neutral if on a hill and you tap the accelerator without fully braking again hill start assist won't be active and you'll roll backward
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09-04-2014, 10:53 AM	#4
jphughan Brigadier General 594 Rep 4,488 Posts Drives: '16 Cayman GT4 Join Date: Mar 2011 Location: Austin, TX iTrader: (0)	Being stopped with DCT in D is mechanically equivalent to holding the clutch pedal down in a 6MT while remaining in gear. A DCT literally disengages the clutch in that scenario, and as others have pointed out, tapping the throttle will engage creep mode by lightly slipping the clutch, just like letting the clutch pedal partway out on a 6MT. As for which is preferable at a red light, I doubt it really matters. Driving 6MT, I put my car in Neutral to avoid unnecessary throwout bearing wear and give my left leg a break, so perhaps there's a bit less wear by doing that on a DCT as well, but I also have no doubt that BMW designed this trans to be able to remain in D at red lights. __________________ '16 Cayman GT4 (delivery pics, comparison to E92 M3 write-up) Gone but not forgotten: '11.75 M3 E92 Le Mans \| Black Nov w/ Alum \| 6MT (owned 5/2011 - 11/2015)
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09-04-2014, 02:27 PM	#5
crypticc Captain 73 Rep 963 Posts Drives: e92 M3 DCT + Comp Join Date: Dec 2011 Location: London, UK iTrader: (0)	Dct neutral is effectively same as dct in drive with brake depressed fully. The two clutches are operated with hydraulic pressure and fully disengage until a gear is selected and throttle applied. Suggested google st813 dct drivelogic pdf Shows neutral has two main clutches disengaged with sliding clutches also disengaged. 1st gear engages the sliding clutch for 1st but the main clutches won't be engaged at that point until you release brake and move away. Once moving there always a clutch engaged.
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