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297x198_A6_S6_A6all_Fas09_Bild_54 54 17.02.12 13:08
54 quattro®/quattro® with sports differential
Why only use two wheels
when a car has four?
The quattro® permanent all-wheel drive.
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 centre differential. The basic
distribution is 40 : 60 – 40 % of the drive force
comes from to the front axle, 60 % to 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’re 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 sports differential
further reinforces this unmistakeable quattro
feeling. Vehicles tend to 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 sports differential on the
rear axle, this 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
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 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.
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