Method for automatically actuating longitudinal blocks in four wheel drive vehicles, in particular in working machines and service vehicles

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.