Transfer Case-Automatic Shift
Transfer CaseMotor, Electric Shift
The externally mounted transfer case shift motor, located at the rear of the transfer case, turns the shift cam assembly. As the shift cam assembly turns, it positions the reduction shift fork for desired transfer case operation. An integral position sensor in the shift motor provides motor position information to the 4x4 electronic module.
Switch, Push Button U4 Mode
The push button 4x4 mode switch, mounted on the instrument panel, allows the operator to select the 4x4 Auto, 4x4 High, and 4x4 Low transfer case operating modes. The indicator light, on the instrument cluster push button, will illuminate only when the 4x4 Low position is engaged.
Switch, Brake Pedal Position (BPP)
The Brake Pedal Position (BPP) switch is located on the brake pedal. The switch signals the 4x4 electronic module when the operator activates the brake pedal.
Switch, Clutch Pedal Position (CPP)
The Clutch Pedal Position (CPP) switch is located on the clutch pedal bracket. On vehicles equipped with a manual transmission and an electronic shift transfer case, the clutch pedal must be fully depressed and vehicle stopped in order to make a range shift from HIGH to LOW, or from LOW to HIGH.
Sensor, Digital Transmission Range (DTR)
The DTR sensor is located on the outside of the transmission near the transmission shift cable attachment. The DTR sensor completes the start circuit in PARK and NEUTRAL, the back-up lamp circuit in REVERSE and the neutral sense circuit (4WD) in NEUTRAL. The DTR sensor also sends a digital output signal to the Powertrain Control Module (PCM) indicating the manual lever position (P, R, N, D, 2, 1).
Sensor, Throttle Position (TP)
The TP sensor is located on the throttle body. The sensor provides throttle position information to the PCM. The PCM converts the throttle position signal to a Pulse Width Modulated (PWM) signal, and sends it to the 4x4 electronic module to control and adjust the transfer case clutch duty cycle.
Sensor, Front and Rear Output Shaft Speed (OSS)
The externally mounted OSS sensors are located at the rear of the transfer case. The sensors provide the 4x4 electronic module with front and rear driveshaft speeds to control and adjust the transfer case clutch duty cycle.
Sensor, Vehicle Speed Sensor (VSS)
The Anti-Lock Brake System (ABS) provides the 4x4 electronic module with vehicle speed information to control and adjust the transfer case clutch duty cycle.
4X4 Electronic Module
The electronic module (located behind the glove compartment) controls the operation of the transfer case in response to inputs from the electric shift motor, 40 mode switch, CPP switch, BPP switch, DTR sensor, throttle position output from the PCM, front and rear OSS sensors, and the VSS.
Mechanical Operation
The Borg-Warner 44-11 transfer case is available in the Explorer (A4WD) vehicle. The transfer case transfers power from the transmission to the rear axle, and also to the front axle when electronically activated.
In the Auto mode, torque from the transmission is transferred to the input shaft which, in turn, drives the rear output shaft that drives the rear axle assembly. The electromechanical ball ramp clutch assembly drives the drive sprocket after the 4x4 electronic module activates the clutch coil. The drive sprocket turns the drive chain that rotates the front output shaft and the front driveshaft. In the 4x4 High mode, the operation is the same as in the Auto mode, except that the 4x4 electronic module consistently activates the electromechanical ball ramp clutch assembly.
The high-low shift occurs when the reduction shift fork moves the high-low collar to lock the planetary gear set to the output shaft. Then, torque, transmitted through the sun gear, from the input shaft, turns the front planetary gear set assembly. The front planetary gear set assembly, which is now engaged, provides transfer case speed reduction.
Transfer Case Functions
There are three transfer case modes, Auto, 4x4 Low, and 4x4 High. Neutral is only available as a dealer installed option.
Control-Trac Function
The Control-Trac transfer case uses an electromechanical clutch assembly to control torque to the front wheels. In the Auto mode, while at rest and under cruising conditions, the 4x4 electronic module activates the transfer case clutch at a minimum level. This allows for the slight difference between the front and rear driveshafts which occurs normally when negotiating a comer on dry pavement. Under any of the following conditions, the 4x4 electronic module will increase the torque sent through the clutch to the front wheels in order to prevent or control slip.
^ Slip is detected (by monitoring the front and rear OSS sensors in the transfer case)
^ Throttle position (by using the throttle position signal from the PCM)
Range Function
NOTE: At zero throttle, the duty cycle remains low.
In the 4x4 Low Range, with throttle input, the transfer case electromechanical clutch locks the front and rear driveshafts for maximum 4x4 traction. The transfer case shift motor rotates the shift cam to move the reduction shift fork to the 4x4 Low range position. This low range shift, accomplished through a planetary gear set, changes the torque to the driveshaft from 1: 1 to 2.48:1 ratio.
In the 4x4 High Range, with throttle input, the 4x4 electronic module signals the transfer case electromechanical clutch to lock the front and the rear driveshafts for maximum 4x4 traction. Never use the 4x4 High range or the 4x4 Low range when driving on dry or merely wet pavement. Use the 4x4 High range or the 4x4 Low range only for driving off-road or in severe winter weather.