Zexel pixels - and F1 key for spin (LONG!)

[QSHIPQ@aol.com]

Dave E. writes:
> 
>[snip]
>scott, you've said that the torsen doesn't understand relative slip
>angles for months.  the engineers who wrote the paper disagree with you.
>wherever the text discusses increased front or rear slip ratios, this
>is, of course, always in relation to the other axle.

Well, the statement:
"Furthermore, the sudden variation from positive torque (DRIVE) to negative
torque (COAST) causes a critical transitory phase, as it generates a variation
of several dynamic parameters." 

Doesn't really tell you all that much in regards to slip angle.  We certainly
can see a lot of F1 discussions in relations to what happens in scenarios 1-4.
I suppose we could argue they talk of relative slip the same as they do
'spin'.  

>exercise for the reader.  count the number of times the words 'side
>slip', 'lateral slip', and 'longitudional slip'  occur in this section
>of the paper.  the number of times *changing* slip angles are discussed.
>the torsen doesn't understand slip? errrr....

I look at all the effects of those references in terms of counting the number
of times we see SPIN that is never said either.  This whole paper is the
funniest and most exciting verbiage on this subject.  Still, lateral slip and
and longitudinal slip are in relation to the end of the car losing it's
traction ability (or specifically spinning or u-off's).  The relation in terms
of the device is NOT discussed, Dave.  Specifically, how it can be fooled.
And it can be, you admitted it, Chocholek did, and it's the design of the
device.  Zexel doesn't address it.  

>with regard to the chocholek paper, there is *nothing* in that paper of
>the behaviour of the torsen in varied cornering manoeuvres, or details
>about the characteristics of that diff.  most of these things are left
>unstated.  what the paper does a good job off, is developing a
>mathematical model of the diff.

Wonder how Chocholek would describe a SPIN?  If he meant spin and said spin,
would the paper have been published?  I'm still laughing at the thought of
these boys and their chassis dynamics thesaurus.  

>this paper also doesn't deal exhaustively with the application of the
>torsen as a centre diff, but at least it gives pages more information on
>the diff in a centre and an axle application, than does the chocholek
>paper which accords the centre torsen 1 paragraph.

Neither paper addresses the main problem with fooling the center torsen, which
is relative slip angle.  I find both incomplete, but Chocholek wasn't trying
to address center torsen applications.  I don't think Zexel did much better of
a job frankly (but then I didn't see all those graphs).  Why?  Cuz there is no
reference to relative slip angle, only it's effects (spin).  I do hope that
you did see cf instead of cof in that paper as well tho.

>i fail to see where you get this understanding of the diff from?  it
>*does* understand relative slip angle differences between the axles.  in
>as much as slip angles influence torque reaction (grip), it has to.
>longitudinal and lateral slip are a *function* of each other (the
>friction circle).  for example, as the side slip angle increases, so the
>torque reaction (i.e.. available grip) at the axle decreases, and so the
>longitudinal slip [must] also increase.   you seem to have some problem
>with this.  it's simple physics.

WHOA Dave.  Stop. NO. The center torsen doesn't understand relative slip
angles, it CAN'T.  You admitted this earlier, Chocholek discussed this with
Jeff, and now it "*does*"?!?!?!!?.  It IS simple physics, and out of the
ability of the device.  You are now fogging settled issues.  I have a problem
with a dumb device being smart.  By definition it's NOT.  You are trying to
make it so now.  It's still dumb.  Just cuz it 'anticipates' doesn't make it
any smarter.  Given what the device does do, not sure I wouldn't have used a
different thesaurus for that word.   

>the diff detects this.  on both axles.  all the time.  by design.
>anticipation?  in as much as the torsen responds to changing slip, yes,
>it is anticipating.

NO.  All inputs to the device are interpreted as TRACTION.  Anticipating
Traction in a slip world can give the wrong division of torque.  It's in THIS
paper too Dave.  "Changing engine torque characteristics and given cf" means
that compromises to traction were accepted, reread the Zexel conclusions on
how BR is chosen.  

>1) switching of braking torque to the front is *not* [necessarily]
>understeer, as much as it is removal of oversteer.  no grip at the rear,
>so torque to the front.  sounds like the best of a bad deal to me.
 
In an audi chassis with a front weight distribution a 50/50 weight
distribution is UNDERSTEER in a quattro dave.  Best of a bad deal?  Depends on
how much load that distribution puts on the front.  Best of a bad deal drives
you right into the ditch. (er, ah that would be a large loading of the front
wheels could cause undesireable overloading of the front tires, causing them
to increase their slip into the ditch:)

>2) any car that has power oversteer and then the operator lifts throttle
>has a [big] problem.  would you rather be in a bmw m3 or a porker 911?
>doubt it, for anyone who's btdt.

NOT with you here dave.  Lift throttle oversteer is a lot different to control
than lift throttle understeer OR oversteer depending on your relative slip
angles, torque characteristics and cf.  As described in the Zexel paper.

>3) in this situation, the torsen is helping you.  by definition.  the
>paper makes clear that torque is only sent to the rear in low-speed
>manoeuvres. 
...  Remember, as cf lowers and or engine torque increases, things change.
How bout some snow? Or Ice?

> at high speed power-lift, torque is sent to the front.
>this is caused by the increased *relative* slip angle between the front
>and the rear (there is greater slip at the rear, so torque is sent to
>the front).  so the paper states that the diff is removing braking
>torque from the rear and sending it to the front.  this leaves more
>lateral grip at the rear and decreases the drop throttle oversteer.
>i'll take that, thanks very much.

So you go from U to power up O to lift throttle U, or lift throttle O (spin),
as defined in the Zexel paper.  U-O-U or U-O-O depending...  You can have
it...


> 
>lets keep our feet on the ground here, scott.
>we know that at the end of the day, 4x0 = 0 and, awd or not, you're
>going to visit the scenery if you're going fast enough, and given enough
>provocation.

At the cause of this F1, is it the device that's helping me that a) is the
reason for the scenery, and/or b) once it starts helping me, it keeps
'helping' me in the same objective, potentially fooled and 'anticipating'
kinda way.  My btdt says you can have that. I tend to not provocate dumb gear
jamming frictional devices anymore.  They are too dumb to 'anticipate' that.

>their point is quite right.  understeer is a much safer condition to
>oversteer, which is why all manufacturers seem to make their cars
>exhibit this characteristic in all but the most extreme cases.  the
>solution to understeer *is* easy.  power off. if that doesn't help,
>you've got to do some driving to get out.

They are right in the description of O spin, lift throttle O spin, and U.
Predicting and anticipating those are not within the design of the device.  If
a rear slip angle is high enough, transfering that to the front is a nice
understeer right off the road.  Understand WHY we are lifting.  Run the
scenarios thru Dave, they are very clear when you map them in terms of audi
chassis dynamics.

>scott, the way you throw "u"s and "o"s around, you'd think this was
>playschool.

When grownups say SPIN, they understand what is being said in terms of U and
O.

>  fact:  with the torsen, corner entry is not "u" as you
>describe, certainly wrt the locked centre, because more torque is being
>sent to the rear.  so your "u-o-u" is simply disengenious.  it's
>actually "n-o" in the scenario that paper is discussing, as the torque
>originally sent to the rear, is now being split equally.  "steady state"
>as the paper says.  with the locker it is "u".

Once again Dave, you don't understand Audi chassis dynamics.  With no power
applied in a turn, what does an audi do?  U.  Add poer it goes to O.  You get
"steady state" that's the same as a locker 50f/50r that's U.  There is no N in
an audi quattro chassis.  

>ok, playschool again.  here the torsen is reacting to the changing
>relative slip angles (front to rear), and releaving the front axle
>understeer condition by sending more torque to the rear.  a good thing?
>sure, i'll take it.

Playschool is a 3 year and up concept.  Dave, you don't get it, by definition
flunking playschool.  Are you sure you want to continue playschool analogies?
The torsen doesn't react to relative slip angles, it reacts to driveshaft
torque.  

> 
>this is just stupid scott.  do you seriously think that audi's with the
>torsen react like this going around a high-speed corner?  or that, if
>they did, drivers wouldn't notice?   seriously????

Hey, I'm an idiot.  Damn, so's the Torsen center.  The torsen reacts EXACTLY
like this, cuz it's DESIGNED to.  Whether the driver 'notices' it or not,
reality sucks.

>right, they don't. 

...  From a playschool student that has never been bitten, I would say you
answered your own question.

>the paper states that during a high speed cornering manoeuvre, the car
>will enter a steady-state, neutral condition.  

NO.  Steady state has to do with equalizing of driveshaft torque.  Driveshafts
that spin 50/50 make an audi understeer.  Don't bring neutral into the
equation, there is no such thing Dave.  You don't understand what you are
reading here.

>good.  after this, you
>will either get understeer or oversteer.  why?  because there are a
>number of *dynamic* conditions in operation which are dependent upon
>speed, corner radius, cf, steering input, throttle position, weight
>transfer and torque available (among others).

EXACTLY, and not a mention of relative slip angle.  A dynamic condition of
it's own, not identified.

>the paper states this, and that if understeer results, then torque is
>sent to the rear.  result: less understeer.  which is good.
>or that, if oversteer results, torque is sent to the front.  result:
>less oversteer, which is also good.

No.  Less understeer is what exactly dave?  More oversteer?  Where is Neutral?
At what slip angle?  You can't predict it, THAT's the problem.  And yet, in
this paper, the Torsen is predicting *something*.  That's ALL based on
driveshaft torque.  Well, less understeer means something, I'm not with you
that that is good.  

>it's called throttle sensitivity and, with a good chassis (ur-q or
>similar), it makes the car delightful in low-cf, or high torque
>situations.  balanced on the throttle.  a little bit more throttle, and
>you get push, button off, and the car returns to neutral.  or you get
>oversteer, so lift slightly, and the rear tucks back in.  just as the
>paper says.  and many road testers with the torsen ur-q have described.
>just as anyone with a torsen ur-q knows.

OR, the torsen predicts that the throttle input means that the rears lost
traction, when they actually just lost slip angle.  It's NOT that smart Dave.
IT's specifically a dumb gear jamming frictional device.  And the paper says
it's predicting.  Dumb things predicting all the right things.  With the same
device in ALL audi chassis.  I'm not buying this.

>but, don't take my word for it, try a torsen ur-q yourself.
>u-o-u-o-u-o-u-o-u?  nope.

I look at the above, and see the inference that a torsen is smart in an Urq,
but maybe dumb in a 44 chassis.  Not (read the Zexel conclusion) if the cf
changes.  

>the paper says consistent (not "constant", jeff) assistance is required
>...just
>as the paper says.

But the paper DOESN'T say this Dave.  If the consistent assistance is wrong, I
suppose we could argue, at least it's consistent (specifically consistently
inconsistent).  I think you haven't read the paper with your chassis dynamics
thesaurus.


> 
> Hey let's just say SPIN next time boys.
>actually they are trying to tell us what the torsen is doing to
>*prevent* the natural consequences of these manoeuvres.... (high speed
>cornering throttle lift).  care to try that in a 911?  an m3?
BTDT.  Very consistently too (tho a major difference between your two
comparos).  The problem is the <OR> in the torsen which is lift throttle
understeer possibilities.  You get one OR the other, and if time is on your
side, you get one OR the other a couple times in the same turn.  

> 
>huh?  to countersteer on oversteer is one of the most normal, natural
>and fastest reactions.  are you trying to tell me that on high speed
>cornering oversteer you *don't* correct with the steering wheel?

Are you telling me you do?  Towards the apex or away from?  Countersteer on
oversteer may be instinctual.  The problem is that changes relative slip
angle, which changes torque distribution.  This can lead to sudden unloading
of the rear tires, causing the rear tires to exceed their traction ability,
leading to an undesireable swapping of the rear with the front of the car.  I
find the issue of steering counter or otherwise at the limit of adhesion,
somewhat of an oxymoron.

[snip]
Me>> It might also directly conflict with the
>>statement
>>> that the Torsen is:  "Anicipating loss of directional stability..."
>>That's just not something the device can do consistently in a turn.

>if the paper agrees with you, you'd think it was ok? mmmmm....
The point is Dave, the paper doesn't DISAGREE with me.  It is fine as written.
Just not complete.

>so the zexel engineers  just kind of over-looked the bite?  
They didn't overlook it, reread what the effects of powerup oversteeer and
lift throttle oversteer/understeer are.  They are EXACTLY the bite.  They just
used a lot of thesaurus words to describe what happens.  It's clearer when you
use my playschool U-O.  It's what they are saying

>these are the same engineers who talk about the consequences of panic
>throttle lift whilst cornering at high speed?  of high speed cornering
>oversteer?  of high speed cornering understeer?  who talk of manouevers
>at the limit of adhesion?

The best engineer is one who can say spin the most times in a paper without
using the word spin...  :)  They put some interesting disclaimers in the
conclusion section you need to study Dave.  The compromise in chosing BR to
ALL the 1-4 statements, are the chassis dynamics of the automobile AND the BR,
and the engine torque, and the cf.  That would indicate to this Toyz R Us
manager, that change any of these variables, the paper changes too.  

>these are the same engineers who, it is apparent in the rest of the
>paper, actually went out onto skid pans and took measurements of torque
>splits?  who describe traction control systems hunting.  with
>measurements to show this.  just plain overlooked it?
>nope, don't think so.  however, i will say that it is clear that the
>paper is not an exhaustive treatment of the torsen centre.  it is a
>discussion of the application of traction control systems to torsen
>cars.
I missed the part about the application of traction control systems.  Is that
in a later section.  The part you posted ONLY has to do with a center torsen
in a center torsen car.  There is no traction control here.  Or did I miss
something.


>other points:
>1) it is good to see that we no longer have this bite @70% bullsh*t.
This is one of the reasons you flunked playschool dave.  Now go stand in the
corner. They say bite, just the same way they do spin.  You seemed to have
missed both.

>2) it is good to see that there are no more comments about "the torsen
>wasn't designed for a centre application".

Well it wasn't.  The paper deals with what was done, not whether appropriate
or sound in reasoning.  Don't read too much here, you haven't read enough yet.

>3) it is good to see that we have a clear description of the importance
>of the chassis dynamics to the effective operation of the torsen.  as
>well as just the bias ratio.

And engine torque characteristics and cf (no cof, thanks).  Reread the
conclusions about the importance of that BR, and the 'compromises'.  What
would those be exactly?  I wonder....

>4) it is good to see that the paper deals with the centre torsen's
>reaction to varying (front/rear) slip angles.
No, it talks of O-U.  It doesn't deal with relative slip angles much at all.
We could infer that you have O, or U, with different relative slip angles, but
that would be a paper hard to write given the differing "given engine torque
characteristics and varying cf".  

>scott, you time and again make statements about "u-o-u"-type cornering.
>as though this is an intrinsic part of just the torsen.  it's not, and i
>can't believe that you think that it is.

Hold on a second Dave.  I'm an idiot.  The torsen sends torque to the front or
the rear driveshaft.  We know that (and you admit) any quattro can power up
oversteer (lower cf even the 90q can).  We also know that a quattro is a
statically understeering chassis.  We also know that a quattro at a rigid
connection (50f/50r) is an understeering chassis.  So anything above 50f/50r
is more understeer (up to the limits of the available traction) and 78r/22f is
oversteer (up to the limits of the available traction).  It doesn't matter
what happens the rest of the time.  And the paper says EXACTLY what Jeff,
myself and Chocholek have been regarding O and U.  I just translated the paper
into plain english.  I'm saving the spin definitions for later use, thanks.
You are right that N has to happen, but it's not measureable yet.  We do have
measureable and agreed knowns.  That's really all we need to translate quattro
to U and O.


>for instance, lets look at the locker accelerating through a turn.
>using your own hypothesis:
>slow corner entry:
>front axle wants to be "faster" than the rear.  result: fixed axle
>speeds causes slip difference and wind-up torque between front and rear
>axles. causing major understeer.  the tighter the corner, the more
>understeer. result:"u".  torsen is "n" at this point with torque going
>to the rear.
You say the torsen is N.  In actuality it is somewhere between U and O.
Depends on corner tightness.  Really tight corner, BR maxes, torsen U.  Not
with you here.

>mid-corner (medium speed):
>axles at the same "speed", so no slip difference. result:"n" for
>neutral.  torsen is also "n"
I'll give this to you, but if the slip angles are different how can you say
either is N?  Remember the basics, we are TURNING here.

>corner exit (high speed): rear axle wants to be "faster" than the front,
>causing another slip difference between the axles, except this time the
>opposite (from the slow speed corner).  so now, the wind-up torque in
>the system produces an oversteering moment.  result: "o".  at high
>speed, this causes loss of torque reaction at the rear (i.e. more slip),
>meaning more torque at the front (less slip).  result: back to "u",
>until the rear slip angles recover.  this will cause increased slip at
>the front, resulting in less torque reaction etc....
>so we have: "u-n-o-u-o-u" in the same turn.  with the locker.  the
>torsen is "n-n-o-n".

NO (sure wish you started with this).  There is no N 'state' in a torsen, nor
is there in a locker.  I think you read steady state to mean N, it's not.
Steady state refers to the Torsens design to resist differing driveshaft
rotation.  Steady state then, is 50f/50r, translated is U.

You only have given N if you are in a straight line.  If you turn, you can
ONLY claim to be between U and O.  Somewhere you passed N, you have to, I
suppose.  But there is no <stop> there.  There is a stop for O which we know
is 78/22, max BR.  There is a stop for U, which is a range 50f/50r to 78f/33r.
I see what you are arguing here Dave.  The problem is that hanging N takes
throttle, steering, cf, and relative slip angle (let's talk of modulating
turbo throttle in terms of engine torque characteristics shall we?).   And
anticipating the torsens' anticipation of what all that is in relation to
driveshaft torque.  Put too much of throttle you get O, too little of
throttle you get U, lift throttle you get O (spin) or U (braking torque to
50/50).  That's a line that dancing consistently is impossible.  Why?  Cuz the
dumb gear jamming frictional device doesn't know or care what N is.  It only
"knows" Max BR and "steady state".  That's 78f/22r (U) or 50/50 (U) or 78r/22f
(O).  It reacts to differences in driveshaft torque, and returns to 50/50.
That's all it can do.  It can't consistently give you 65r/35front for N
(assuming that to be N), it only passes thru that torque split on it's way to
Max BR.  Relative Slip angles would dictate that pass is not a controllable
stop in all the above turning and chassis variables.  Not even in a straight
line.  

I don't buy that you or any other driver can reverse drive a torsen (fooling a
fooled device, by definition).  Are you sure you can anticipate a dumb gear
jamming frictional devices anticipation of driveshaft torque split?

I'm spinning again.  And firmly believe you don't get it Dave.  This Zexel
paper, despite my playschool simplicity attempts, only confuses you more.
Your understanding of the device is clear.   Despite what is written before
you.

So be it.

Scott Justusson
Playskool Graduate 1998