Specifications

297x198_A8_Integration_Fas09_Bild_054 54 18.02.13 12:27
quattro®/quattro® with sport differential54
Why only use two wheels when
a car has four?
The quattro® permanent all-wheel drive.
quattro is a permanent all-wheel drive. 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 centre
differential. 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 a better feel for the road – and thus more
safety. The quattro with sport differential further
reinforces this 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 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 electro-hydraulic
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 by
the drive force and follows the angle of the front
wheels. The variable left and right drive forces
also help stabilise the steering and the usual
steering corrections are hardly necessary.
The sport differential has a reaction time of less
than 100 milliseconds and is therefore faster
than the Electronic Stabilisation Control (ESC).
And while ESC can only take effect once there is a
certain difference between the steering angle
and the rotational movement of the vehicle, the
sport differential influences the dynamics of the
vehicle in advance.
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