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

[John Cody Forbes]

Yes my break down was extremely simplified. I provided the in depth version for those that felt like reading 20 something pages and the at-the-most-basic-level version for those that didnt want to read the whole thing. There are many out there on this list that are not too technically inclined and adding more detail would only hurt understanding the basic function I described. Plus I'm on an iPhone and don't feel like typing too much ;-)

Tell me, please, how the rear diff is not completely engaged to the transmission output shaft when the Haldex clutches are fully engaged. There is no diff between the output shaft and the Haldex unit; the prop shaft is fully mechanically engaged to the transmission output shaft with no possibility of slippage until something breaks. 

-Cody (mobile)

On Jan 5, 2011, at 11:04 AM, qshipq at aol.com wrote:

> The pdf is good, your 'simple' description of operation can cause a tick to those nerds into AWD systems.  "Power is therefore variable between 100/0 and 50/50 front to rear" is not true of any locked set of front/rear axles.  If either axle is capable of supporting 100% of available engine torque, then "power" can be 100f/0r or 0f/100r.  In a straight line with locked axles, "power" (I prefer the proper term 'supported axle torque') will exactly follow weight transfer in acceleration and deceleration.  That said, a bit oversimplified in the Haldex, as under acceleration, the Haldex technically can never give 100% of power to the front axle, anymore than a VC.  If the Haldex is broken or decelerating that can be true (completely uncoupled), but under accelerative states, the Haldex is engaged/'preloaded'.  So it might be better to say the range is 95f/5r to 5f/95r.  Supporting the 'synchro' badge on the TT, and Haldex and Audis respective claims that Haldex is a 'full time awd' system.  I wince a bit that anyone can claim a vehicle without a center diff can be full time awd, but marketing is what it is.  A bit easier to understand these mis-claims than those made of the torsens....
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> Cody, the clutches can be partially engaged to the driveline as well, as that defines the torque split vs input voltage.  5v to the Haldex is not completely locked to anything, and the clutches are specifically engaged, so your explanation seems oversimplified.
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> The Touareg awd system is a electric clutchpack LSD to a full time awd with center differential.  It's more like the old Audi V8 electric clutch center diff, but the Touareg uses a stepper motor to only engage the plates enough to eliminate slippage between axles, the Audi v8 is an all or nothing electromagnetic lock over the center diff.  Both systems use ABS sensor input for lockup properties.
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> What makes the Haldex unique, is that it can have infinite inputs to uncoupling, specifically, it can have differentiating axle speeds and infinite axle supported torque splits, and still be uncoupled electronically (i.e. driving on ice, lift the handbrake on a Haldex equipped vehicle, rear is uncoupled instantly).  The VC on the other hand, needs equal axle speeds to uncouple, which can delay uncoupling, especially in turns/split mu (surface conditions) environments.
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> The key to current Haldex programming as I understand it, is that signals to uncouple, are immediate.  Some see that as a good thing.  I find going from fwd handling to awd handling without a differential, to be a lot less comforting, and much more noticeable intervention of it's two states.  Much more so than ANY full time awd with a center differential of any flavor.
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> Cheers and HTH
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> S 'torsen boy' J
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> -----Original Message-----
> From: John Cody Forbes <cody at 5000tq.com>
> To: Taka Mizutani <t44tqtro at gmail.com>
> Cc: qshipq at aol.com <qshipq at aol.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 8:27 am
> Subject: Re: [s-cars] Off topic - New Volvo S60 ? - Drat and double DRAT!
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> VW's Haldex self study manual, everything you want to know:
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> http://www.volkspage.net/technik/ssp/ssp/SSP_206.pdf
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> It's simple really. The Haldex is an electronically controlled clutch. There is 
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> no center diff at all. When the Haldex clutch is disengaged the rear wheels are 
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> not connected to the engine at all. When the clutch is engaged the rear wheels 
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> are completely locked to the engine. It can slip at any rate in between locked 
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> and unlocked. Power is therefore variable between 100/0 and 50/50 front to rear.
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> -Cody (mobile)
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> On Jan 5, 2011, at 9:04 AM, Taka Mizutani <t44tqtro at gmail.com> wrote:
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> > Scott-
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> > Does that mean that Haldex is either fully engaged at whatever the torque
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> > split is with it engaged or not at all?
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> > I guess I don't really understand the Haldex system and how it works.
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> > Now I have to find someone that makes a Haldex box for the Volvo, if I
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> > decide to keep the Volvo. Otherwise, I'll get a BMW 5 series xi with a stick
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> > or a diesel SUV.
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> > Your opinion on the Porsche Cayenne AWD or the VW Touraeg (which I think is
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> > the same setup)?
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> > Thanks,
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> > Taka
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