7/30/2019 2008 Sport Differential Audi S4

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2008: The sport diferential

in the Audi S4

The sel-locking center diferential in the classic quattro power-

train does an excellent job o distributing the power between

the axles. To make driving even more dynamic, it needs an ad-

ditional component that actively splits the torque between the

wheels o the rear axle. Audi presented this solution in the newS4 in late 2008 the sport diferential.

The sport diferential is a state-o-the-art rear diferential.

A superposition gear comprising two sun gears and an internal

gear was mounted on the let and the right o a conventional rear

diferential. It turns 10 percent aster than the drive shat.

A multi-plate clutch in an oil bath and operated by an electro-

hydraulic actuator provides the power connection between the

shat and the superposition gear. When the clutch closes, it step-

lessly orces the higher speed o the superposition stage on the

gear. Being orced to turn aster results in the additional torque

required to do this being drawn of rom the opposing wheel onthe inside o the curve via the diferential. In this way nearly all o

the torque can be directed to one wheel. The maximum diference

between the wheels is 1,800 Nm (1,327.61 lb-t).

The sport diferential is just as efective while coasting as it is

under load. It is electronically controlled and reacts within a ew

hundredths o a second. Audi developed the sotware itsel. The

controller quickly and constantly recalculates the ideal distribu-

tion o the orces or each driving situation as a unction o the

steering angle, yaw angle, lateral acceleration, speed and other

inormation.

Vehicles with conventional axle drives tend to understeer in ast

corners. With the sport diferential, it is like riding on rails. When

turning into or accelerating in a curve, the majority o the torque

is directed to the outside wheel, pushing the car into the curve.

The system thus nips any tendency toward oversteer or under-

steer in the bud.

Source: DVD quattro Highlights 2010 | Status: 03/2010

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