Quote:
Originally Posted by drob23
I suppose your definition of active is probably better, whereas mine is more in regards to how the torque split is optimized. In the case of xdrive you have an electronic control system, which filters sensor measurements in conjunction with driver inputs and uses a plant model to calculate actuator inputs, which in this case goes to the clutch pack. Thus, it is a combination of a feed-forward and feedback control system. The actuator input commands are limited with respect to dynamic response to reject noise from the sensors. You can generally sense this bandwidth limitation with xdrive/haldex, where the car powertrain seems to "change" once you start to hit a different surface.
On the other hand, a torque sensing differential, ie conventional limited slip differential, uses a mechanical gear set to optimize torque appropriation. There is no limitation on the actuator bandwidth other than the physics of the coupling mechanism (viscosity for example). These systems will provide optimum torque distribution in terms of maximum traction. On the other hand, one cannot enforce constraints such as: force all torque to the rear wheels, which might reduce understeer in certain instances.
Side - I don't think either the M5 nor C7 have active rear differentials. Only Audi, Lancer Evo, Acura SH-AWD, Nissan Nismo stuff and BMW x5m-x6m-x6 as far as I can tell
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I did not come up with the definition of active and passive differential. It's the industry standard and about as clear cut as the difference between an open diff and LSD.
The new M5 definitely has an active rear diff. Based on the press release available, the C7 will sport an active rear diff as well.
http://www.bimmerfile.com/2011/09/28...ial-in-detail/
Frankly, I don't know if you really know what you are talking about here. You don't know the fundamental difference between active and passive awd systems. Then you try to say that a Torsen based system is superior, how is that relevant to the rwd vs xdrive discussion here?
I will leave you this to ponder, if a passive Torsen diff is truly superior then why does Audi use an active rear diff today (namely the Sport Differential) instead of a Torsen rear diff like they did back in the late 80s?