Transfer Case: Description and Operation

Electronic Shift Description:

ELECTRONIC SHIFT OPERATION
The transfer case is equipped with a magnetic clutch, similar to an air conditioning compressor clutch, that is located inside the transfer case adjacent to the 2W-4W shift collar. The clutch is used to spin up the front drive system from zero to vehicle speed in milliseconds. This spin-up allows the shift between 2-High (2H) and 4-High (4H) to be made at any vehicle speed. When the transfer case rear and front output shafts reach synchronous speed, the spring loaded shift collar mechanically engages the mainshaft hub to the chain drive sprocket and the magnetic clutch is then deactivated. Shifts between 4-High and 4-Low can only occur with the clutch interlock or transmission safety switches closed. The vehicle's speed must also be within specified limits as determined by the transfer case speed sensor (3 mph or under). When the operator selects the drive combination through the push-button control, an electric motor turns a helical cam, that is linked to the high-low and 2W-4W shift forks through fork mounted roller bushing assemblies. As the electric motor turns the helical cam, the high-low fork bushing rides in a slotted lobe in the cam to make the low-high or high-low range change and the 2W-4W fork bushing rides on lobes at the end of the cam to make the 2W-4W shift.

ELECTRONIC SHIFT CONTROL
The Borg-Warner 13-56 electronic shift transfer case transfers power from the transmission to the front and rear axle assemblies when electrically actuated by either of the two switches mounted in the push-button control panel. The electronic control module will analyze information from the transfer case shift position sensor to verify its current position. The electronic control module also analyzes input information from the speed sensor and the clutch interlock switch (M/T) (or neutral safety switch (A/T) depending upon transmission application). When all conditions are met, the electronic control module will command the electronic shift motor to execute the desired function. After the shift occurs and the motor is turned off, the electronic control module resumes looking at the inputs from the shift position sensor to determine if the transfer case is in the position selected by the operator. The electronic control module illuminates the push-buttons in the control panel indicating that the desired function has been completed.