[s-cars] Fwd: Off topic - New Volvo S60 ? - Drat and double DRAT!

[Mark Strangways]

Begin forwarded message:

> From: Mark Strangways <MarkS1234 at spamarrest.com>
> Date: January 5, 2011 7:05:21 PM EST
> To: qshipq at aol.com
> Subject: Re: [s-cars] Off topic - New Volvo S60 ? - Drat and double DRAT!
> 
> ohh goody, a thread about differentials and wheels again... Cool ;-)
> 
> Been a while 
> 
> Carry on
> On 2011-01-05, at 7:03 PM, qshipq at aol.com wrote:
> 
>> 
>> 
>> They aka'd me 'Torsen Boy' for a reason, I'm pretty nerdy about how differentials and locking axle 4wd systems work, it's my thing I guess, has been for many years.  I get really picky when incorrect terms are used for a relatively simple concept.  It's just plain incorrect to state that power is 50f/50r on ANY center differential or locked axles with a single, sole and only exception:  An open differential will ALWAYS distribute power 50/50 to two axles, regardless of variables, period.    Which means specifically, no other differential or locked axles can, other than in theory.  If all the variables are just right, a locked Haldex can pass thru a 50f/50r power split state in theory.  Any other moment in time or input variable, it's not.
>> 
>> By theory it can I mean you go back to how a Haldex works, specifically what's making it 'lock up'?  It's a combination of variables that makes the 50/50 nary impossible in that locked up state.  What you state in your 50f/50r is the commonly accepted way to define an open differential, it's not really a property or description of a Haldex.  
>> 
>> Technically, your description of a gen 1 quattro is not correct either.  To the Haldex locked in a straight line (simple example):  If torque follows weight transfer in a locked f/r axle quattro in a straight line on a hi cf track, how exactly can you ever be 'roughly equal to all wheels with infinite traction"?  There is no such thing Cody, torque will only be equal if you are coasting where Trg (torque ring gear) = 0.  As soon as you speed up or slow down, torque follows weight transfer again.  Add Hap 670hp foot to the floor or jam a set of Big Reds, torque to the axles is not roughly equal, not even close.
>> 
>> Cheers
>> 
>> S 'torsen boy' J
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>> 
>> -----Original Message-----
>> From: John Cody Forbes <cody at 5000tq.com>
>> To: qshipq at aol.com <qshipq at aol.com>
>> Cc: t44tqtro at gmail.com <t44tqtro at gmail.com>; mtgadbois at aol.com <mtgadbois at aol.com>; pkrasusky at ups.com <pkrasusky at ups.com>; s-car-list at audifans.com <s-car-list at audifans.com>
>> Sent: Wed, Jan 5, 2011 1:07 pm
>> Subject: Re: [s-cars] Off topic - New Volvo S60 ? - Drat and double DRAT!
>> 
>> 
>> Talking about power/torque splits is always going to be confusing because it depends on so many factors. In theory a gen1 quattro with all the locks on CAN put 100% power to any single rear wheel, the rears as a pair, the fronts as a pair, or 3 wheels as long as two of them are in the rear. I fully understand what you are saying and agree, but I chose to go with the commonly accepted way of conveying the point. With infinite tire traction the power is going to be roughly equally distributed between all of the wheels when the Haldex is engaged. When disengaged the Haldex is basically as if you removed the prop shaft. Except for oil friction there is zero force being transmitted from the transmission to the rear diff. Thus is why it is completely safe to tow a Haldex car with the rear axle on the ground and the front lifted. According to VW you can even dyno a Haldex car as if it was front wheel drive.
>> 
>> 
>> My initial statement may have left out that when I said "clutch is engaged" I meant the Haldex clutch pack, yes. The point stands that when the Haldex clutches are fully engaged with no slip (slipping the Haldex is a possibility, but pretty remote except for extreme circumstances) the rear diff is tied solidly to the transmission output shaft, and most lay persons will see that as being tied to the engine.
>> 
>> -Cody (mobile)
>> 
>> On Jan 5, 2011, at 12:12 PM, qshipq at aol.com wrote:
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>> Cody
>> "50/50 power split"  is the most common mis-statement about locked axles, not oversimplified, just not correct on any level or description of locked axles.  Not sure your question if you reread your statement below.  The rear prop shaft is ALWAYS connected to the transmission and is always spinning at the input of the Haldex in the rear diff.  When the coupler is engaged there absolutely can be slippage, my point to your simple exact statement "when the clutch is engaged the rear wheels are completely locked to the engine".  That's just not correct as written.  I suspect what you meant to write was "When the Haldex is fully locked, the rear differential is completely locked to the prop shaft (transmission/input axle)".  To exactly what you wrote on the other hand, when the clutch is engaged the rear wheels are not 'locked' to anything. Specifically the rear axles can slip in relation to the input shaft speed up to fully locked = any state less than a fully locked up Haldex coupler.
>> 
>> HTH 
>> 
>> SJ
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