overmoment in yaw

[QSHIPQ@aol.com]

Dave E. writes:
>there's nothing "poor mans" about subaru's current awd system, although it's
>not state-of-the-art in pure technology terms, although no-one is
>complaining about the performance, just like the current audi system...

ALL exceptions so noted, including audis racing and rally programs

>yaw control is certainly now the state of the art, building on the advances
>made in coupling an awd system to tcs and abs systems.  for this to work you
>need your usual compliment of abs sensors, a yaw rate sensor (usually
>mounted behind the c of g, a steering angle sensor, and a lateral "g"
>sensor).  the system works by comparing yaw with the steering angle and
>figuring out if understeer or oversteer is happening. 

Can it make a mistake?  Like when sliding sideways?  What is it comparing 
there?  Or does it shut down.  My thinking is it's just fooled.  It can't 
"figure it out" all or most of the performance driving.  Most likely just 
raises the comfort limit a little higher than a torque sensing diff. 

 >the previous
>generation systems would then brake the left rear to correct understeer and
>the right front to correct oversteer (some systems apply all the brakes
>depending on the exact circumstances).  the major disadvantages with tcs are
>basically the lag in the system, the "cycle time" for the brakes, and the
>requirement for torque to make it all continue to happen.  with an active
>rear diff, the locking rate of the diff is changed to produce the right
>"moment" across the rear (fully locked rear = understeer, unlocked rear =
>oversteer).

Again, the system is designed to avoid the "next step".  Once that next step 
has "happened" the system has been fooled by definition.  Is it better than 
the torque sensing, or just different?  I argue the latter.  If you can use 
braking (which you already have) to accomplish the same thing (and probably 
better, see archives) without the hardware and obvious disadvantages, the 
numbers boys are happier.  Steamboat would be an interesting comparo of these 
compromised systems in a controlled "next" step environment.  Again, we are 
looking at active systems, designed to "help" you, that may be doing the 
exact opposite.  Hard to predict the nut behind the wheel.

>btw, mitsibushi have used electric control for their active diffs (clutches)
>due to concerns over the lag in hydraulic systems (and their serviceability
>and weight).

The boys in detroit are laughing their old tech butts off right now, the air 
and electric lockers have been around for a long time.  Considering mitsu 
pioneered the quick locking hydraulic (less than a .25 driveshaft 
revolution), and is a non servicable component, your weight idea seems to be 
the most valid.  That and an active system by definition needs to "control" 
locking.

Amazing what audi is phasing out in terms of diffs.

Scott Justusson