Edward R. Wendell IV
erwendell at mac.com
Wed Sep 1 23:32:59 EDT 2004
I finally got some time to chime in on this whole DSG thing. I can't
remember who it was but some one stated:
"But what I was expecting was a kick-in-tha-butt when upshifting."
As I recall, said quote was used as evidence of a problem with the DSG
system. I'd like to examine the physics of why I think that that action
is not possible due to the configuration of DSG and why it is also not
consistent with true performance driving with a conventional manual.
First off, a "kick-in-tha-butt" feel in an automobile can only mean a
large increase in acceleration and therefore a large increase in torque
at the driving axle. But where is that extra torque coming from? It's
certainly not the engine. Even if you factor in the fact that the
torque curve falls off at higher rpm it's not that dramatic, especially
when you consider that by shifting to a higher gear you have radically
reduced the torque multiplication provided by the gearbox. I contend
that the extra torque spike is due entirely to the energy that was
stored in the mass of the rotating flywheel. Following that line of
thought, the flywheel would therefor have to be spinning faster than it
should be when it is reconnected to the driveline via the clutch. So I
guess my point is, if the rpm isn't matched properly, than you will get
that "kick", which is impossible if the DSG is programmed correctly.
That also leads to the conclusion that people who are bragging that
their car has a powerful engine because they can bark the tires when
upshifting are really bragging about how heavy their flywheel is and
how much they can abuse their clutch, engine mounts, and drive axle
Concerning the design of the DSG gearbox, with two clutches competing
for the space that used to be occupied by one I would imagine that the
size and therefore mass of the flywheel is quite low. As one of the
factors that weighs in favor of a heavy flywheel is drivability, ie
resistance to stalling and smoother throttle response when shifting,
than the throttle by wire and fancy shifting and clutching algorithms
in the DSG controller would eliminate that need.
So I guess that my point is that DSG won't feel like a conventional
manual when shifted, especially when one is used to said conventional
manual being used somewhat incorrectly. I personally pride myself on
getting a shift so right that a person in the passenger seat with a
blindfold would be hard pressed to tell that a shift had taken place.
It sounds to me like the DSG is programmed to do the same.
Clarksburg WV USA
86, 87 5kcstq
87 MR2 times 2
Three turbos, two quattros, too much fun
More information about the quattro