A4 allroad quattro Audi S4 Saloon

quattro®
quattro is a permanent all-wheel drive system. If
the wheels on one axle of the vehicle lose grip on
the road and threaten to spin, then the drive force
is transferred to the other axle – automatically and
permanently distributed through the self-locking
centre differential with wheel- selective torque
control. The basic distribution is 40: 60 – 40% of
the drive force comes from the front axle, 60%
from the rear. The benefit is better traction during
acceleration and improved safety due to exceptional
grip. So much for the technology. But what makes
quattro unique is really the driving feel. “As if
you are stuck to the road,” some customers say.
We put it like this: quattro gives you more feel
for the road and thus increased safety.
The optional quattro with sport differential
further reinforces the unmistakeable quattro
feeling. Vehicles tend to experience understeer
when steering or driving into corners. This is a
normal physical process: a moving object opposes
a change in direction. The elastic tyres and the
suspension mounts tense up until the new
direction has been adopted. When accelerating
into a corner, the load on the front axle is reduced
and it therefore transfers less lateral force to
the tyres – the vehicle understeers. With the
sport differential on the rear axle, the tendency
to understeer is largely counteracted. This is
because the quattro rear axle differential has
been extended left and right by a clutch system
with two gear levels. They ensure that the
individual wheels on the rear axle receive different
levels of torque. The clutches are activated by an
electrohydraulic actuator. Depending, for example,
on the steering angle, lateral acceleration, yaw
angle and driving speed, the system calculates
the right distribution of wheel torque for any
driving situation. In this way the power is
specifically channelled to the outer rear wheel,
when steering or accelerating into a corner.
The effect: the vehicle is effectively pressed into
the corner and follows the angle of the front
wheels.
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Why only use two wheels
when a car has four?
The quattro® permanent all-wheel drive.
A4_Fas18_allroad_S_Modelle_2013_03.indd 54 19.04.13 11:15