From: aas7@po.CWRU.Edu (Andrew A. Spencer)
Newsgroups: rec.autos
Subject: Re: Are there any Luxary AWD?
Date: 13 Nov 1992 02:05:29 GMT
Organization: Case Western Reserve University, Cleveland, OH (USA)
Reply-To: aas7@po.CWRU.Edu (Andrew A. Spencer)
NNTP-Posting-Host: slc5.ins.cwru.edu


In a previous article, eliot@lanmola.engr.washington.edu (eliot) says:

>In article <1dsuovINN7iu@usenet.INS.CWRU.Edu> aas7@po.CWRU.Edu (Andrew A. Spencer) writes:
>>...so Porsche designed
>>into their new AWD..whatever the call it.system so that it would 
>>reduce the understeer
>
>it would induce understeer to counter the oversteer.  i don't think it
>is because of one single lawsuit.  it has been a love/hate thing about
>911's since the very first one.  porsche decided to use high tech to
>deal with the lethal tail.  i've not driven the 964, so i can't say
>weather the result was good or bad.  one thing though: i detect a
>subtle preference among the rag-writers for the carrera 2. (rwd)
agreed..i was telling the story as the mag did..i think that the "person"
was more of an analogy for "the idiots who do not go through a driving 
school to learn thier tail-happy porsches' subtleties"..not necessarily
ONE specific case...
>>..the mag said that,even though it
>>cannot be turned off, that the system is incompatable with the 
>>braking system so that the differentials release completely upon
>>braking

>any tightly coupled AWD system is fundamentally incompatible with ABS,
>because ABS needs independently rotating wheels to sense lockup.  the
>release under braking is to allow ABS to work.  all the computer
>controlled systems do this, audi, subaru (yes, even the legacy),
>porsche, benz.  the wonderful torsen diff. does this mechanically.
>the crude viscous couplings that we see in the bmw 325iX, mitsubishis
>and a host of other cars, do not, and unpleasant compromises are
>necessary, which is why i'm not too great a fan of the 325iX.
agreed..sort of..but nothing to add with the porsche..agreed.
>>..so..they took it out, tossed it into the turns like a 
>>normal porsche, only they lightly touched the brakes, to turn off
>>the differentials,
>
>not to turn off the differentials, mind you, but to turn off the
>differential *locking*.. in effect you will have a "loosely coupled"
>4wd 911, i.e a 911 in which the four wheels can rotate independently
>under power.  the 4wd is permanent on the carrera 4.  you cannot 
>disconnect it without doing major surgery.
details details..geez..:-)..i assumed that it was known that you cannot
"turn off" differentials, as they (all of the automotive that i know of)
are mechanical couplings which do not have this capability....(except on
4wd(off road style)..i do not know exactly how they work)
>> and they said it drove like a REAL 911 improved..
> 
>since the differential locking is completely controlled by chips, it
>would be interesting to see if anybody will come out with a third
>party "handling" chip for the carrera 4.  the fact that there is no
>such thing at the present time is an indication of the immense
>complexity of the task.  (i have an interview of the porsche engineer
>who did the AWD system).  one bug in your program and you're going
>tail first into the tree!  :-)
agreed.
DREW
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