RXBG

just heard about it. sounds better than the R8 system. please discuss. kind of bummed about that.

Silver Stealth

I'm curious too...any details on Torque Vectoring Quattro??

John J Szobocsan

<ul><li><a href="http://www.motorage.com/motorage/article/articleDetail.jsp?id=396900">Torque Vectoring</a></li></ul>

Silver Stealth

Thanks!!

Alan(NJ)

what's new about that? I wonder if the packaging and flexibility is new and thus cars that could use this, but don't already have it, can be easily adapted.

Please explain how this is different than current awd drivetrains that proportionate torque as needed?

Alan(NJ)

"An engine's twisting power is of limited use unless it can be turned into forward motion. This is no small challenge in the new 911 Turbo. To apply the engine's 460 lb.-ft. of torque to the road, Porsche engineers have developed a new traction control system for the car's full-time all-wheel drive. In the previous 911 Turbo (Type 996), a viscous multi-disk clutch responded to relative front/rear speed differences to determine how much torque to apply at either axle. The new 911 Turbo, by contrast, employs an electronically controlled multidisk clutch that responds to traction changes almost instantaneously. Onboard sensors measure a range of values, including the rotational speed of all four wheels, the car's lateral and longitudinal acceleration, and the current steering angle. The sensor data is analyzed in real time, enabling immediate adjustments in the torque split between the front and rear axles.

The benefits are wide-ranging. For example, if the rear wheels lose traction under acceleration, more drive torque is instantly transmitted to the front axle. The integral Anti-Slip Regulation (ASR) function also minimizes wheelspin. When cornering, Porsche Traction Management (PTM) adjusts drive to the front wheels in order to maintain optimum lateral grip. On variable-grip surfaces, traction is enhanced using the Automatic Brake Differential (ABD) function. For optimum traction, manual transmission cars can also be equipped with an optional mechanical limited-slip rear differential."

John J Szobocsan

Audi uses a Torsen, torque sensing, differential between the front and rear axles while Porsche uses a viscous coupling to accomplish virtually the same function. The Torsen differential is mechanical and transfers torque across the front and rear axles based on immediate need. The viscous coupling requires a signal sent from a controller to lock a series of clutch plates in the coupling. Viscous couplings could, and do, overheat if driven over slippery surfaces for a period of time. Most Porsche owners spend very little time driving on extremely slippery surfaces.

The Torque Vectoring system is similar to what is found in the Honda SH-AWD, in terms of routing torque between the two rear wheels. It is best to think of it as a dynamic differential, transmitting torque, to alter the drive characteristics of the vehicle. Audi, as far as I can tell, utilizes the torsen-based center differential, with the torque vectoring system. Honda does not employ a center differential.

-J

Alan(NJ)

The 997tt does not use a viscous coupling (read the passage I posted more carefully) - the 996tt did as does the current 997 C4S.

RXBG

audi uses both torsen and haldex, depending on the car.

John J Szobocsan

The function between the current 997TT and the previous generation Porsche AWD system is functionally similar; however the current generation has a faster response time to apportion torque fore and aft.

The idea of torque vectoring is to dynamically send torque to a wheel or wheels to affect the dynamics of a vehicle. Previous generation AWD systems "passively" allocated torque based on the criteria of what wheel(s) could generate as a tractive force. With torque sensing, torque may be withheld-or sent-to a wheel regardless of the wheel(s) need for tractive force.

Consider a typical nose-heavy Audi entering into a turn. As the Audi begins to understeer, the front of the car ascribes a larger radius than the rear of the car. Now consider what would happen if the car was also made to "oversteer." The rear of the car would begin, in isolation of the understeer condition, to ascribe a larger radius turn than the front of the vehicle. Add the two together with both the front and rear of the car now following similar trajectories or turn radii. The understeer characteristics is effectively neutralized and the car, to the driver, would exhibit neutral handling characteristics.

I hope this explanation is easier to follow. The lack of graphics is hindering my abilities to effective disseminate the concept of torque vectoring and vehicle dynamics.