Transfer case shift control system using automatic shutdown relay circuit

Abstract

A transfer case includes an input shaft driven by the output of an engine and transmission, a first output shaft connected to a first driveline, a second output shaft connected to a second driveline, and a power transfer mechanism for transferring drive torque from the input shaft to at least one of the output shafts. The power transfer mechanism includes a gear reduction unit driven by the input shaft and a range clutch operable for engaging the gear reduction unit to establish high-range and low-range drive modes between the input shaft and the first output shaft. A transfer case shift control system controls actuation of the range clutch during motive operation of the motor vehicle, thereby permitting on-the-move shifting of the transfer case between its high-range and low-range drive modes. The transfer case shift control system includes a mode selector for generating a mode signal, a relay circuit interconnected between the engine's fuel and ignition systems and a powertrain control module of the motor vehicle, and a transfer case control module receiving the mode signal and vehicle input signals from the powertrain control module. The transfer case module generates a control signal based on the mode signal and the input signals and, if necessary, sends the control signal to the relay circuit for varying characteristics of the vehicle's fuel and ignition systems to reduce the amount of engine torque delivered to the input shaft independent of the powertrain control module. Thereafter, the transfer case control module generates a shift signal for actuating the range clutch to establish the selected one of the high-range and low-range drive modes.