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Thu Nov 20 12:01:46 EST 2003

An interaxle center differential operates in the following 4 basic modes sho=
w in fig 10.&nbsp; In reverse, DRIVE becomes COAST and vise versa.<BR>
In DRIVE mode, a Torque Sensing differential will distribute the higher driv=
ing torque to the axle that tends to turn slower than the other one.<BR>
In COAST mode the higher braking torque will be distributed to the axle whic=
h tends to turn faster than the other one."<BR>
That indicates to me that in reverse, more torque goes to the axle spinning=20=
faster.&nbsp; The torque split (TBR) doesn't change, just the allocation pro=
perties of reversing the input torque.&nbsp; IOW, engine braking is the same=
 as driving in reverse.&nbsp; Under engine braking the effects of it in term=
s of tractive force is nil.&nbsp; Under engine torque (reverse), the effects=
 of the drive mode greatly affect tractive force.&nbsp; <BR>
Let's not confuse this with TBR in forward or reverse axle rotation.&nbsp; I=
t's still 75/25/75.&nbsp; <BR>
CONCLUSION:&nbsp; A torsen Center audi quatro will have better traction in f=
orward gears<BR>
&gt;Its difficult to use, because torsen, despite its cute name, IS sensitiv=
e to<BR>
&gt;axle speed difference. And not just alittle, but notoriously.<BR>
&gt;But yes, if you look for hint, then this hints indirectly that torsen te=
&gt;there was indeed indifferent to direction of torque..<BR>
ONLY in terms of TBR.&nbsp; Not in terms of which axle gets "more" torque.<B=
&gt;Engine has some finite rotational acceleration. Rotational acceleration=20=
&gt;wheel is called only to compensate for that rpm difference. When engine=20=
&gt;is limited, torque goes to 0. Torque=3DInertia*acceleration. Its quite e=
&gt;to derive max torque from rotational inertia if we know max rotational<B=
&gt;acceleration of engine, divided by final drive.<BR>
Keith is thinking oh no.&nbsp; I was here at one point too Andre.&nbsp; Torq=
ue at the ring gear doesn't change, hence torque at the torsen =3D engine to=
rque.&nbsp; Tractive torque (supported by wheels on ground) + inertial torqu=
e (slip) + frictional loss =3D torque at the torsen/engine torque.&nbsp; Add=
 more engine torque beyond what's supported by wheels on the ground, that to=
rque goes to slip.<BR>
&gt;but no, this is not the case. Reality is that if you engage full engine=20=
&gt;then 90% of it will go to accelerate low-mu wheel, 2% on traction from i=
&gt;and 8% to the gripping one. Or more correctly, you really can't engage a=
&gt;of the engine torque, only 10% of it. Too quick wheel acceleration will<=
&gt;prohibit any further torque increase.<BR>
Tractive force vs wheel spin.&nbsp; Add them up, you get Teng =3D Tring gear=
&gt;Take a look at it slightly differently. torsen has locking ability. Lock=
ing of<BR>
&gt;axles takes force. This force comes from jamming wormgears between engin=
e &gt;torque,<BR>
&gt;and traction forces. When there is traction, there is jamming force. Whe=
n there<BR>
&gt;is no traction, there is also no jamming force, no locking. Peculiarity=20=
&gt;torsen is in that it takes least tractive force, and multiplies it via w=
&gt;and uses that as locking force. It has linear dependance on least tracti=
&gt;force, and multiplier being ca bias ratio. When both axles have equal tr=
&gt;balance comes at 50/50, when different, after reaching 80/20, locking fo=
rce is<BR>
&gt;not enough to keep axles locked, and they start slipping. But ratio of l=
&gt;force stays same, 80/20. Thats why even when differentiating, spinning,=20=
&gt;there is more force on best axle. But not more than least tracking axle=20=
&gt;bias ratio.<BR>
Almost perfect.&nbsp; Except a torsen allocates based on turning ratio as we=
&gt;Take open diff. We could say it has bias ratio 1.0:1, 50/50 split at mos=
&gt;Could we say that with one axle in air, we can apply 50% of engine torqu=
&gt;onto gripping wheel?<BR>
An open diff allocates 50/50 ALWAYS T1=3DT2.&nbsp; If torque is 1 then .5 go=
es forward, .5 goes back.&nbsp; If one axle is in the air, T1 =3D 0, then T2=
=3D0.&nbsp; No engine torque can go to gripping wheel.<BR>
&gt;right, VERY small amounts of time. But there is another trick to make<BR=
&gt;poor-man EDL ;) Revv engine to good revs, letting slipping wheel spinnin=
&gt;and gaining rotational momentum. Then, pulsate brakes shortly and sharpl=
&gt;Rotational momentum will be partly grounded (slipping wheel), but partly=
&gt;also transferred to other axle (flywheel). After spinning wheel slows do=
&gt;it acts again as rotational inertia support force. Perfect job for abs.<=
No disagreement.&nbsp; In fact, that's what EDL systems do.&nbsp; A BETTER w=
ay would be to have EDL AND a rear torsen.&nbsp; Some of the S car boys are=20=
doing that.&nbsp; An even BETTER way would be the ability to reduce engine o=
utput as well.<BR>
&gt;&gt;So I'll restate it.. <BR>
&gt;&gt;"Torsen is AT MOST capable of transmitting 80% of current engine tor=
que output to the axle with most traction"<BR>
&gt;&gt;Does that work?<BR>
&gt;+ nope. ;) and yep ;) depends on what you want to "see" in that sentence=
&gt;OK.. this then..<BR>
&gt;"Torsen is AT MOST capable of transmitting 80% of current engine torque=20=
output to the<BR>
&gt;axle with most traction and current torque output is limited to 5 times=20=
&gt;capacity of the axle with the least traction or limited by the drivers d=
esire not to<BR>
&gt;spin the low traction wheels at very high speeds.." <BR>
&gt;Yes ;) thats correct. If one wants to nag further, it must be noted that=
&gt;5 times traction of worst axle cannot exceed sum of traction of worst an=
&gt;best axles. Or, in other words, this applies only after 80/20 max split<=
&gt;is reached, and does not apply to highgrip torque shifts due to turn rad=
Sure it does.&nbsp; Remember a Torsen isn't really sensing torque.&nbsp; A t=
orsen senses axle speed diferentiation at a very low angle, that's all.&nbsp=
; You could build more slop into it so that it's more like a VC, but then yo=
u'd have abrupt allocation and lose many of the straight line advantages.<BR=
The torsen doesn't change it's TBR based on drive or coast modes, nor does i=
t change it's TBR less or more so based on either actual traction or turning=
It's just too dumb to know the differences between these actual events.<BR>
Scott "torsen boy" Justusson<BR>

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