3 Series E91 330xi (N52) TOUR
The electric servomotor of the planetary gearbox is limited by an electric servomotor lock that blocks the worm
gear of the planetary gearbox.
The electric servomotor lock is spring-loaded, with the force of the spring countered by the power supply. Any
interruption of the power supply consequently locks the worm gear.
When the planetary gearbox is locked in this way, it ensures that the steering column enables the driver to steer
the vehicle. Under these circumstances, the steering reacts like a conventional, direct, steering gear system.
The purely mechanical steering linkage between the steering wheel and the front wheels is sustained even if the
Active Steering fails.
Yaw-rate control
If the vehicle tends to oversteer, for instance, when cornering, the yaw-rate control can correct the steering angle
on the front wheels. This stabilises the vehicle (with the emphasis on convenience and comfort). In this road
situation, therefore, the Active Steering supports Dynamic Stability Control (DSC).
DSC does not intervene unless the stabilising effect of the steering does not suffice to counteract the tendency
to yaw.
Yaw-moment compensation when braking on a road surface with non-uniform traction
> BMW 1 and 3-Series
Active Steering now has an additional function for driving stabilisation.
With conventional systems, the driver has to actively steer the vehicle in a straight line if the brakes are applied
on a road surface with non-uniform traction levels.
In such situations, the Active Steering performs this active steering intervention, so stabilising the vehicle.
Compared to pure ABS control, Active Steering with yaw moment compensation shortens the braking distance.
The driving stabilisation function of the Active Steering can be deactivated together with DSC with the DTC
button (when DSC is completely deactivated). Together with the hydraulic power steering, the variable steering-
gear ratio is always active.
> From X5 (3rd generation)
This function is completely integrated in the Active Steering control unit. Other model series will follow later.
Operation
Unlike DSC, which can be switched off by means of the DTC button, Active Steering cannot be deactivated.
Yaw-rate control and yaw-moment compensation are also deactivated when DSC is switched off. The variable
steering gear transmission ratio always remains active.
With the 3rd generation Active Steering, the yaw-rate control remains active when DSC is deactivated.
When DTC is activated, the DSC response thresholds have been widened. Active Steering increasingly assumes the
function of driving stabilisation if the vehicle is oversteered.
Preconditions for activation
Preconditions for activation for Active front Steering are:
-
Terminal 15 ON
-
Engine running
Steering-wheel position and the position of the steered wheels are synchronised as soon as the engine is running.
This ensures that the positions of the steering wheel and the road wheels match if, for example, the steering wheel
was moved while the vehicle was at a standstill with the ignition switched OFF.
Note: The synchronisation procedure can cause the steering wheel or the vehicle's front wheels to move.
Movements of the steering wheel or the vehicle's front wheels might be perceptible while synchronisation is
SBT Active Steering E60, E61, E63, E64, E70, E81, E87, E90, E91, E92, E93
BMW AG - TIS
22.02.2013 01:22
Issue status (12/2007) Valid only until next DVD is issued
Copyright
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