BMW E61 Sports Wagon 530xiT, Руководство пользователя

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opening and closing operation so as to determine the beginning and end of the clutch
closing procedure. The angle setting is determined by means of a Hall sensor integrated
in the actuator motor.
A clutch and oil wear model is additionally calculated in the transfer case control unit.
Where necessary, this model limits the lockup torque in order to reduce friction.
In the event of DSC failure, an emergency strategy for driving the transfer case clutch is
integrated as a fall-back level in the transfer case control unit in order to maintain all-
wheel drive also in this case.
Transfer Case Control
Control of the lockup torque of the multi-disc clutch in the transfer case facilitates infinite-
ly variable coupling of the front axle to the drive train.
As a result, the drive torque at the front axle can be increased or reduced corresponding
to the driving situation and the condition of the road. When the torque at the front axle is
increased, the drive torque at the rear axle is, of course, reduced by this torque.
The advantages of variable distribution of the drive torque at the front and rear axles are:
• Optimum utilization of the lateral cornering and wheel peripheral forces applied at
the front and rear axles.
• Brake interventions by the DSC are required considerably later, thus increasing over-
all comfort.
• Compared to a transfer case with fixed transmission ratio (open longitudinal differen-
tial) and DSC, with xDrive the drive torque distribution is considerably improved in
connection with greatly differing friction values at the front and rear axles.
Even when DSC is turned off, TCC is still active to ensure maximum traction and vehicle
dynamics.
Permanent all-wheel drive is cancelled to a large extent or completely in only three control
situations:
• When negotiating extremely tight corners with little engine torque in order to allow
speed equalization between the front and rear axle (e.g. parking)
• At speeds in excess of 180 km/h
• In extreme understeer driving situations
The control algorithm of the transfer case clutch control can be described in three main
modules:
• Tire tolerance logic
• Pilot control
• Traction control/vehicle dynamics control
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E61 Sports Wagon