willyjp

which type of awd power distribution system does the R8 use? In your opinion or experience, is "torque steer" a POSSIBLE occurence in a normally functioning R8? How about a mal-functioning one?

GR8 Ghost

Never had torque steer, ever. Not sure with the power split that it is possible

floormat

some front tire scrubbing at low speed and full steering lock, but it's lessening everyday. Breaking the CV joints???

Fxhomie

from the Gallardo, although the Lambo is getting a new AWD system to debut in Geneva

Torque steer? Highly unlikely

willyjp

So, if it's viscous coupling, it is a Haldex type system. Does anyone know if it is actually sourced (or licensed) from Haldex, or does it have a different provenance?

VerrÜckt

It's nothing like the Haldex system and has nothing to do with Haldex.

RXBG

so why don't you tell him what it is like? he wants to know how it works.

willyjp

Yes, thank you! That's right, I'm just trying to understand the operation of the awd system a little better (while I spend a year or so waiting for an R8!).

In my simple mind, Audi's current awd systems so far can be classified as Torsen differential type or Haldex viscous electro-magnetic coupling type (or Borg-Warner v-e types now in the case of the Q7, I just learned). In the case of the TT, and perhaps some of the other, smaller cars, they've used a Haldex system for weight and space saving over the torsen box. I have NO idea what the basis for the R8 system is, other than many press comments say it is the Lamborghini Gallardo system. But Lambo was under Audi when they developed the Gallardo, and at that time they were already using a Haldex system in the TT (as also in the A3 & S3). The fellow above seems to confirm it is a "viscous coupling", so it's probably fair to say it's a least something like a Haldex!

The Haldex system is also used by Volvo and in the "R" model, Volvo went to some great lengths to integrate stability (yaw)and traction control toward the end of improving high speed over the road control. In the case of the Volvo "R" model, not only does esp act via individual wheel braking, but it also uses the electro-magnetic control of the traction system to shift power around according to the wheel angle, acceleration and yaw inputs.

Since everyone seems to characterize the R8 as "really a rear wheel drive car that just shifts power forward if the rear wheels slip", I am just wondering about the actual workings of the power distribution system and how much the esp/traction controls may be utilizing it.

These thought were just prompted by a post over on the "R8talk" forum where a guy is experiencing some directional instability when punching the throttle at speed. Since I have some experience with a Volvo "R", I'm just trying to understand a little better how the R8 system may be similar or different. If it's electro-mechanical, differences probably come down to control software (and torque capacity).

I threw this out in this forum because no one over there seems to be really in the know about the detailed mechanics of the R8. So far, no one over here seems to be either! Or maybe they're just not willing to tell!

Fxhomie

Haldex is an electrohydraulic system, utilizing clutch packs and software. Reaction is almost instantaneous. The only similarity to viscous coupling is that both apportion torque front/rear (and vice versa).

Viscous coupling uses plates with holes in them, (like a cheese grater) along with a fluid that changes consistency according to thermodynamic principles. One group of plates is attached to the front driveline and the other group to the rear. No electronics are involved. Further, reaction time is slow; slippage has to have already occurred for the torque transfer. The mechanism itself is heavier than Haldex - all that fluid and those plates. But it's cheaper than Haldex.

Bottom line: viscous coupling-old school, Haldex-school currently in session!<ul><li><a href="http://en.wikipedia.org/wiki/Viscous_coupling_unit">scoop on VC...</a></li></ul>

willyjp

Thanks! That explains a lot. I was confused because I have heard the Haldex system described as a fluid coupling that is locked by passing an electric current through a magnetic fluid causing it to solidify, thus allowing electric--and by extension, microprocessor--control of the amount of clutching/de-clutching of the link. So, then, if I'm understanding you correctly, the R8 system is entirely passive and not subject to electronic control?
The clarification is appreciated!