[s-cars] Haldex fun

[Keith Maddock]

Paulie Canopened:

2nd, since joining the list, my layman's understanding of AWD speak has
grown (Thank You Torsen Boy, et al...  seriously) past just reading
AutoWeek.  I now get Torsen, EDL, Viscous, etc., but does Haldex work in
comparison? (Paul asks as can of worms is opened...)

-Paulie Handbraker


OK, I've gotta make this quick, I can wax on more later though if you have more questions.

This description is specifically about the Haldex BRAND Limited Slip Coupling.

A Haldex LSC is a coupling device, which basically allows the rear axle to be progressively connected or disconnected from the front axle.   The Haldex LSC is designed to add AWD to vehicles which have a transverse front engine.

It is NOT a differential.  When this puppy is OFF, you have FWD.

(as opposed to a Torsen Differential, when it is "off" (defined as no torque difference Front/Rear), you have 50/50 AWD)

The haldex basically has a hydraulic pump that connected to both the front and rear driveshafts.  As soon as there is a difference in speed between the driveshafts, the pump starts pumping.  This generates hydraulic pressure, which actuates a wet clutch-pack, which progressively connects the rear axle to the front axle.

This hydraulic pressure can be controlled by the Haldex ECU by means of a pressure relief valve.  This allows the Haldex ECU, by talking to a lot of other vehicle sensors including the ABS/TC/EDL/DSC module (hey , that's me!!), to partially or completely de-couple (revert to FWD) in certain circumstances such as turning, excessive yaw, ABS activity, DSC activity, etc.  There's also a very small electric pump that allows them to maintain a VERY small amount of hydraulic pressure on the clutch when there is no speed difference front/rear.

OK that's a very basic discussion on it.  Pro's and con's of the haldex unit can be found by searching the recent [Torsen] list archives.  Torsenboy (now aka Haldexboy), I and some other guy just had a "fun" discussion about it.

For more details, feel free to ask a specific question, but only after you spend at least 10 minutes surfing the following site:
http://www.haldex-traction.com/
Click on Technical Information in the blue bar at the top
Click on Design Info on the bar on the right
Enjoy

Ok back to work on the Haldex-Golf  (a pretty sweet car actually, VR6, Haldex, Leather Recaros, mmmm :)  )  Can't wait for our R32 to get instrumented, and then I get to use that!


Keith "HaldexBoyJunior" Maddock



****************************************************************
Keith Maddock, TRW Automotive,  Koblenz, Germany
Slip Control Systems, Systems Design, Traction Control
+49 (0)261/ 895 2474     -    -    keith.maddock at trw.com
** In Arvidsjaur, Sweden,  02-13 December 2003 **
** Direct line: +46 960 /  57 869    Reception  x800  **