A four wheel drive powertrain control for an automotive vehicle is
disclosed. It includes a torque transfer case that distributes power from
an engine-powered transfer case mainshaft to a secondary driving axle
through a friction clutch as power is distributed directly from the
engine-powered mainshaft to a primary driving axle. The friction clutch
capacity is sufficient to mechanically lock the transfer case in a four
wheel drive mode. If the clutch torque capacity is exceeded, a control
algorithm will strategically ramp down engine torque requests by a
powertrain controller to eliminate clutch slip.