Patent ID: 7613559

Claim:
A method for controlling a central differential distributing the torque from an engine and transmission to front and rear wheels sets of a four wheel drive vehicle, the method comprising the steps of: determining only a vehicle speed and the transmission output torque wherein the transmission output torque is determined from only a current transmission gear ratio and a rotational speed differential across a hydraulic converter connected between the engine and the transmission, and when the vehicle speed is above a first speed threshold value and the transmission output torque is below a first torque threshold value, disengaging a longitudinal block, thereby allowing the transmission output torque to be differentially distributed between the front and the rear wheel sets, and when at least one of when the vehicle speed is below a second speed threshold value and the transmission output torque is above a second torque threshold value, engaging the longitudinal block, thereby allowing the front and the rear wheel sets to be directly driven by the transmission output torque.