Haldex torque split level on the DIS? (A3/S3 quattro)

[martinlop]

Under normal operating conditions the Haldex clutch operates a rate of 5% torque transmission. Under adverse conditions where the car's road wheel speed sensors have determined that both front wheels have lost traction, the Haldex clutch can lock at 100% clamping force, meaning all torque is transferred to the rear axle. The torque split between left and right wheels is achieved with a conventional open differential. If one side of the driven axle loses grip, then the Electronic Differential Lock (EDL) component of the ESP controls this.
Is there Any coding where actual % of torque split level is shown on the dis?
Or only way would be via OBD2 dongle and some app reading this parameter from th canbus?

 

[GSB]

Where does this "normal" 5% figure come from?

 

[A3SBQ]

The torque reading would be a great thing to have but sadly not possible to display as what I know.

Only way would be via a MFA XP unit if it was to be programmed to read this channel.

 

[GSB]

Under adverse conditions where the car's road wheel speed sensors have determined that both front wheels have lost traction, the Haldex clutch can lock at 100% clamping force, meaning all torque is transferred to the rear axle.

Martin, this often quoted factoid about Haldex traction only applies to the first and second generation systems which were rendered obsolete in 2004 when the third gen Haldex coupling appeared. Since then all Haldex couplings have been entirely proactive, and can drive with whatever degree of torque transmission the cars designers want, at any time. 100% locking can be applied at standstill if needed, and high levels of torque transmission can be continually applied without reference to front wheel slip.

In the clip below is a third gen AWD coupling being monitored on a 2006 Mazda MPS6, showing that in almost all conditions some degree of torque transmission takes place. The coupling on this car was electrically actuated rather than hydraulically as in the Audi which makes direct measurement very easy, but the fundamentals and principles involved are exactly the same. For reference on the video, 0 volts equals coupling disengaged, anything greater than about 4.5v = fully locked. 2.25 v would equal about 50% engagement. Still providing significant drive, but allowing slip at higher torque inputs to avoid transmission wind up and undue noise and efficiency losses.


I'm not sure if Audi uses EDL on the rear axle, although it is certainly fitted to the front. The mazda above is equipped with a mechanical limited slip rear differential, and Haldex have also provided active control of the rear diff as an additional function for certain car makers with the additional XWD coupling fitted behind the main coupling. This coupling is able to variably control the locking of thereardifferential from fully open to full locked. Neither is fitted to the 8V

For reference, the 8V system is fifth generation.

If you wanted to have a visible indication of the rear driveline status, then it would be possible to fit a current monitor to the pump circuit the rear coupling and fit a separate gauge. The current consumption of the variable speed pump would provide an approximation of the amount of torque transmission being applied.