J. Patterson

We do not have a center differential that splits torque. We simply have a set of clutches that engage the rear axle when the sensors indicate slippage. Our front wheels will always slip first under power. When that occurs the clutches engage so that the front can't slip without turning the back too. (Like a 4 wheel drive pickup with the transfer case engaged) The Haldex controller decides when and how hard to engage the clutches. Our rear wheels can never spin faster than the fronts. Not possible. On a Torson Quattro car like an A4 they can. When the ratios in the Torson are split unequally with the rear axle being the one with greater mechanical advantage, the rear wheels will likely spin first. (reducing understeer) The best we can hope for is equal power to both axles when the Haldex clutches fully lock. Really not a bad thing with a front heavy car like ours.

JohnLZ7W

the main engagement mechanism for Haldex IS mechanical. The clutches engage based on oil pressure within the clutch pack. Pressure is built two ways, one with a mechanical pump that is driven based on differences in input and output shaft speeds, the other oil pump is driven by the controller. That second pump run by the controller is how the blue/orange controllers can start transferring torque before the front wheels actually start to slip.

mowog

if the front wheels were on say glare ice and the rears were on dry pavement, the front and rear wheels would turn at the same speed, but all the useful power would be at the back. So I guess you could say that more than 50% of the useful power could be transferred to the rear.

Back in the early list days there were figures like it only took a slippage of a sixth or eighth of a wheel revolution to fully engage the haldex. and if you could chirp the tires the haldex needed to be looked at. The new haldex site has less useful information than I remember, and they seem to have a couple of generations newer than our TTs.

The CW was that the TT was always FWD unless the front wheels lost some traction. During acceleration some bias was supposedly sent to the back, and I guess the expensive controllers were able to adjust this. I think during normal driving its basically FWD.

J. Patterson

"if the front wheels were on say glare ice and the rears were on dry pavement, the front and rear wheels would turn at the same speed, but all the useful power would be at the back. So I guess you could say that more than 50% of the useful power could be transferred to the rear"


I was getting frustrated that nobody (Well almost)seemed to understand that we don't send percentages of the torque to either axle. We simply lock the rear to the front when conditions warrant it.

bubba j

<center><img src="http://www.wak-tt.com/mods/haldexpp/graph.gif"></center><p>
The orange controller had the feature of not disengaging while under braking.

SMOOTTH DON

"August 30, 2004
Hi Don,

In normal driving (steady state) you will have a very low torque to the rear, close to nothing but the coupling is prepared for an immediate response to send it to the rear axle.

We do not have a max split since we are a fully adjustable system. In a theoretical situation when the front wheels have no grip at all (in the air or wet ice) you will send close to 100% to the rear.

Best Regards,

_________________________________________
Mats Johansson
Engineering &amp; Quality manager

HALDEX TRACTION AB
44708 Helm Street
Plymouth, MI 48170
U.S.A."

TTinCT

ahh....what John noted above.....thanks for posting Don