Pilot Control
The pilot control algorithm reflects the driver's choice and calculates the necessary lock-
up torque as a function of:
• accelerator pedal value,
• engine torque,
• engine speed,
• vehicle speed,
• gear and
• steering angle
while taking into account the maximum load on the clutch, transfer case and axle drive.
The clutch is operated with minimum slip during normal vehicle operation, making avail-
able permanent all-wheel drive with a drive torque distribution of 40 % at the front axle
and 60 % at the rear axle.
Even in the case of greatly differing frictional values at the front and rear axle, e.g. when
the rear axle is on a sheet of ice, the pilot control ensures extremely rapid system
response as illustrated in the graphic below.
In addition, as opposed to a transfer case with fixed gear ratio (open longitudinal differen-
tial), with xDrive no brake intervention is required at the rear axle in this case as no slip
can occur.
In the open longitudinal differential system, the brake is applied on detecting slip at the
rear axle. Consequently, 62%of the drive torque is applied at the two rear brake discs so
that only 38%of the drive force is available at the front axle for the purpose of driving off
the sheet of ice. This takes significantly less time (approx. one/tenth of a second).
24
E61 Sports Wagon
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