Under the skin: we need to stick together on Audi’s new drift technology Car News

The upcoming new Audi RS3 is equipped with a new torque vectoring system on the rear axle Torque Splitter which does away with the rear differential gears and replaces them with two “wet” clutch packs.

The downside of a conventional differential is that it allows a wheel to spin if it loses traction, and in powerful cars that becomes a problem. The traditional solution is a Limited Slip Differential (LSD), which does just that: reacts if a wheel begins to slip by limiting the difference in rotational speed between the left and right wheels. These can be controlled mechanically or electronically.

Audi’s new Torque Splitter is a complete change from its earlier systems in that it places no differential gears in the rear axle. Instead, a pair of bevel gears transmits the drive at 90 degrees, and these are flanked by two electronically controlled clutches operating in oil. Each pack has its own controller, and both are overseen by a Modular Vehicle Dynamics Controller (MVDC), which is like a conductor overseeing an entire group of chassis systems.

In the case of the RS3, the MVDC not only synchronizes the two Torque Splitter control units, but also the adaptive dampers and individual torque control at the wheels. Sensors measure longitudinal and lateral acceleration, steering angle, throttle position and yaw angle (the angle of rotation of the car), the latter being crucial for the torque vectoring system. Many of these sensors already exist for engine and stability control systems, and all of the data is used to control the torque splitter.

You may have already noticed that this system supplied by Magna looks suspiciously similar to GKN’s Twinster system (as used by the most recent Ford Focus RS and others). What the two have in common is the basic dual clutch layout and a lack of “spider” differential gears, but there is one crucial difference. The Ford system has a slightly higher final transmission ratio on the rear axle to create the “overspeed” needed to send more torque to the rear than to the front for drifting. When not needed, torque is reduced rearward by sliding both clutches.

Audi has taken a different approach. Unperturbed, its system has a 50:50 front-to-rear torque distribution; and when more torque is needed at the rear for the drift, the torque at the front is reduced. In the RS Torque Rear mode used for drifting, it continuously varies the torque forward to keep the car balanced and can send 100% of the torque to the outer rear wheel, if only for a moment. fleeting. At the other extreme, the Comfort / Efficiency mode, it favors the front by sliding the rear clutches.

In other driving modes, increasing the amount of torque to the outside wheel in a turn can have the effect of reducing understeer and increasing agility. By allocating more torque to the inner wheel, it can also reduce oversteer.

Ford uses torture