BMW DCT Information

aus335iguy

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Most interestingly the DKG doesnt actually have a sensor on the output shaft. That means that errors relating to final drive changes must be “derived” from other information such as the ABS sensors on each wheel or otherwise.
 
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Blue335is

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Most interestingly the DKG doesnt actually have a sensor on the output shaft. That means that errors relating to final drive changes must be “derived” from other information such as the ABS sensors on each wheel or otherwise.
Now thats a fascinating discovery
 

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Most interestingly the DKG doesnt actually have a sensor on the output shaft. That means that errors relating to final drive changes must be “derived” from other information such as the ABS sensors on each wheel or otherwise.

It gets wheel speed via PT-CAN from the DSC unit, RPM from DME. That's all the info it needs to internally do the plausibility calcs and checks. I am sure it has it's own internal values for final drive ratio and tire height.
 

aus335iguy

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It gets wheel speed via PT-CAN from the DSC unit, RPM from DME. That's all the info it needs to internally do the plausibility calcs and checks. I am sure it has it's own internal values for final drive ratio and tire height.
It does have 3 input shaft speed sensors. One engine speed, and two post clutch input speed sensors.... yet no output shaft sensors. Can’t think why they would double down on engine speed and yet have no output sensing?? They trust the DSC and not the DME? Why does it get its tits in a twist from a shorter ratio and not a longer one(@dyezak is using stock diff with m3 calibration)?
 

aus335iguy

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It must be deriving output shaft speed from input speed and gear selector position. That might explain how it might “know” output shaft speed. It still doesn’t explain why an M3 TCU tolerates a 335 diff and not the other way around....? The things I ponder at 3 am when I can’t sleep....
 

doublespaces

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You’re right. It would also explain why @dyezak’s car thumps into gear really hard going up the gears and fumbles the downshift.

I thought this was taken care of by the GTS flash, or does he still have the 335is diff?
 

RSL

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Hope he gets some logs of what torque output, limiters, load, etc are doing on up/down shifts before/after he swaps to 3.15.
 
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dzid_

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It does have 3 input shaft speed sensors. One engine speed, and two post clutch input speed sensors.... yet no output shaft sensors. Can’t think why they would double down on engine speed and yet have no output sensing?? They trust the DSC and not the DME? Why does it get its tits in a twist from a shorter ratio and not a longer one(@dyezak is using stock diff with m3 calibration)?
The output shaft speed sensor is not required for shifting if there are sensor on the transmission side of the clutch.
To control the shift control SW is looking only at engine and transmission side of the clutch speeds.
Output shaft has very little to do with performing the shift and it would be too inaccurate because flexing of the drive shafts, backlashes, etc.

Output shaft has to do with shift scheduling though, because industry practise is to set shiftpoints based on pedal position and output shaft speed (in this case calculated from gear ratios or less likely ABS). But changing differential wouldn't help (unless for scheduling they actually use ABS sensors). But most likely those M3 GTS shiftpoints are just low - this car has V8, so they can be low. Someone could confirm how really are they in M3 GTS.

I imagine this is because switching from a longer to a shorter ratio mimics clutch slip (higher rpm relative to expected rpm for a given engine speed)
I don't believe that would be the reason. In-gear is the time when plausibility checks would happen (to asses the sensors are working correctly). I don't know why putting 335i soft to M3 doesn't work. Maybe it is just luck that we don't hit diagnostic bands from one side, but we do from another. Or 335i has tighter diagnostic bands because they never consider people would swap differentials on 335i's.

You’re right. It would also explain why @dyezak’s car thumps into gear really hard going up the gears and fumbles the downshift.
Again, I don't think FDR has anything to do with shift quality. I would think more that different dynamic of engine control/engine inertia have more to do with it.

Still there is a chance that his problems are mainly due to reset clutch adaptations.
 
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