Quote:
Originally Posted by Serious
Here is my impression of DCT vs ZF8:
At lower RPM's (under ~4500 or so) both gearboxes feel pretty similar in shift speed and feel.
The difference I perceived is noticeable at high RPM where the G80 feels like it ramps down engine torque prior to and after the shift to save the gearbox. The DCT has no torque ramp at the shift so it feels faster and more dramatic.
The actual shift time change between gears is probably very close between the two gearboxes if you just measure the time at 0 torque but the entire shift process the ZF executes (where it ramps down torque, shifts, ramps up torque) is longer than DCT.
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Quote:
Originally Posted by Serious
Yes but there is still a small amount of time where you have 0 torque. It's milliseconds but it is there.
I think bmw quoted shift times are like 80ms DCt and 120ms ZF but either way it's very very small amount of time for both transmissions.
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This graph/interpretation is flawed, as neither the DCT nor the ZF8 have a complete interruption of torque transmission during the upshift. Both transmissions slip one clutch pack against the other to permit continuous transmission of torque during the shift. The "shift time" is not a time where there is zero torque transmitted, it is the time laps for the first clutch pack to completely disengage while the second one simultaneously engages.
The difference lies in the fact that the DCT can make a WOT powershift and recuperate the inertia of the engine rpm drop to provide a momentary surge in acceleration. The ZF8 needs to briefly reduce engine torque during the shift to allow the planetary clutch pack to grab.