kwikwi

New Porsche 911 Turbo S with "Porsche’s Torque Vectoring System with limited-slip differential".

Ref: http://www.eurocarblog.com/post/2797...cs-and-details

I don't really have details on the way it operates but this raises some questions.

On our B8S4, we have a Torque Vectoring System (SD) but we don't have LSD ? Am I accurate with this affirmation? If Yes, what would be the differences in the cars behaviour with our without the LSD?

Thank you for your input!

NWS4Guy

Ours is an LSD, it's just additionally an electronic one, which has clutches inside to suppliment what a normal LSD can do.

http://en.wikipedia.org/wiki/Limited_slip_differential

kwikwi

So, Audi B8S4 Sport Diff is equivalent to "Porsche’s Torque Vectoring System with limited-slip differential" in some sort of speaking ?

NWS4Guy

Different design and implementation but equivalent yes. We also have a LSD between the front and rear wheels as part of the standard quattro setup, with 60% power biased to the rear wheels. Audi doesn't call it a LSD, likely for marketing reasons, "Active Sport Diff with torque vectoring" sounds better than "Standard LSD with electronic clutches to redirect torque."

The Sport Diff name sounds like something totally new and revolutionary (which it is pretty new and revolutionary, though there are other implementations liek Porsche's and Acuras SH-AWD which do the same thing), rather than a spin on something old.

Speedy

I believe the Audi and Porsche systems are similar, in which rear diff. activley distributes torque to the outside wheel while at the same time braking is applied to the opposite wheel. (This is how the Audi EDL works - it is essentially an extention of the ABS/Stability system.)

NWS4Guy

Negative, the Audi system does not employ the brakes in any way on the Sport Diff. If the brakes come into play that is the skid control (nanny) kicking in. The Audi implementation takes up to 100% of all torque, whether under accel, decel, even in neutral, and points it to the outer wheel which has the weight load on the it, or the wheel which is NOT slipping in the case the cause is something like oil/ice/sand/water.

Speedy

I may not have stated this well, but I think I'm at least partially correct. From the write-up here on AudiWorld of how the sport differential works:

"Close to the car’s handling limits, the sport differential acts like ESP, but with the principle reversed: corrective movements are not initiated solely by altering the engine settings or applying the brakes, but also by controlled redistribution of tractive force."

This seems to imply the brakes (EDL) are still part of the equation - certainly not in how the sport differential itself works, but in how the whole thing works together, which is what I meant.

NWS4Guy

If you want to look at the entire system with ESP still on, then sure it will step in. If you want to just discuss how a Sport Diff versus non-Sport Diff car performs from this standpoint. it works like this in a high speed cornering maneuver:

- A non-Sport Diff car will use ABS to slow the inside wheel in order to help counter the understeer. This will slow the car in addition to fighting the understeer.

- A Sport Diff car will take the torque from the inside wheel losing grip and move it to the outside wheel. This wheel will then spin faster (and having more weight on it as the body shifts due to the inertial force from turning the car) causing the car to maintain or even speed up through the corner, while maintaining grip and rotating the rear of the car through the use of vectored torque to apply centripetal force to the car, rotating it around the curve.

The results are the same in that understeer is combated, but the methods and speed factors are completely opposite.

Speedy

^ As I should have stated earlier, you are absolutely correct. I apologize for not being more clear in my distinction between the sport differential itself and the entire system with regard to how quattro works with the EDL.

Your explanation is much more on target!

xtr3ma

Don't forget the 1st type of this system is Mitsubishi's AYC (or SAWC in today's EVO X), first debut on EVO IV 14 years ago.