Any of you guys know what the differences between this Haldex implementation and that in our Volvos? Here's what someone in the Audi forums has to say:
- the system is Haldex
- it sends about 5-10% of the torque to the rear on an ideal surface under straight driving
- when slip is detected (something like 15 degrees difference in rotation angle! - i.e., almost instantaneously), the clutch pack engages and can almost lock up fully (this was not the case with earlier, heavier Volvos and their units)
- although Gen. II is implemented, VW/Audi does not use the extra pump (Prex) that allows to pre-charge the system for yet faster available torque to the back
- the system relies on the differential rotation mechanically (the pump is driven by it), so it cannot engage via electronic impulses. A separate pump and reservoir could help with that --- then the system could be fully electronic, pro-actively engaging based on steering input, yaw angle, throttle, speed, rpm, etc. --- like some of Subaru's systems
- still, under most driving situations the system seems to be doing just fine, as per reviews. In particular, when not driving in a straight line, there is almost always sufficient differential rotation to engage the system
- the 50:50 vs. 0:100 number confusion stems from a misconception what constitutes transmitted torque. The only useful definition is the torque transmitted to the road via the wheels (or axles). Therefore, the Haldex system, since it can (almost) lock the differential, can transmit ~100% to the back although the front wheels are permanently driven (attached to the drive train). This can happen when there is virtually no traction up front, and good traction in the back. Both axles will turn at the same rate, but only the one with traction is actually transmitting torque to the road.
- marketing brochures of the R32, A3, or TT are not engineering specifications.