Four-Wheel Drive Systems

Four-Wheel Drive Systems

1-Speed Torque-On-Demand (TOD) Operation
The one-speed torque-on-demand (TOD) transfer case modes are controlled through the 4WD control module.

The modes are:
^ AWD auto - torque is supplied to the front and rear driveshafts only as needed during low traction situations. AWD auto can be switched to lock by pressing the message center SETUP button; the message "AWD AUTO" will be displayed, press RESET within 4 seconds, then the message "AWD LOCKED" will be displayed.
^ AWD locked - torque is supplied to the front and rear driveshafts constantly and the 4x4 indicator will stay illuminated in the instrument cluster. This mode is not recommended for use on dry pavement or hard surfaces. AWD locked can be cancelled by pressing RESET in the message center, the message center display "AWD LOCKED" will turn off and will return to "AWD AUTO" for 4 seconds when the transfer case clutch disengages.

If the transfer case begins to overheat, the system will default to the Autolock mode. The 4x4 indicator will illuminate in the instrument cluster. This condition may clear without any action being taken by the driver. The 4x4 indicator in the instrument cluster will turn off when the system cools down.

When a problem is detected in the AWD system, the powertrain malfunction indicator (wrench indicator) in the instrument cluster will illuminate.

2-Speed Torque-On-Demand (TOD) Operation
The automatic 4-wheel drive (A4WD) system is a 2-speed torque-on-demand (TOD) design that utilizes the following components:
^ Transfer case
^ Four-wheel drive (4WD) control module
^ Mode select switch (MSS)
^ Encoder assembly (part of the transfer case shift motor)
^ Transfer case shift motor
^ Shift motor sense plate (part of the encoder assembly)

Principles of Operation

Transfer Case Shift Motor
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 shift motor position information to the 4WD control module.

Mode Select Switch (MSS)
The push-button MSS, 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 4x4 Low range is selected.

Brake ON/OFF (BOO) Switch
The brake ON/OFF (BOO) switch is located on the brake pedal. The switch signals the 4WD control module when the operator presses on the brake pedal.

Digital Transmission Range (TR) Sensor (4.0L)
The digital transmission range (TR) sensor completes the start circuit in PARK and NEUTRAL, the back-up lamp circuit in REVERSE and the neutral sense circuit in NEUTRAL. The digital TR sensor also sends a digital output signal to the PCM indicating the manual lever position.

Controller Area Network (CAN) BUS (4.6L)
The CAN bus provides the signal indicating the manual lever position.

Throttle Position (TP) Sensor
The throttle position (TP) sensor is located on the throttle body. The sensor provides throttle position information to the powertrain control module (PCM). The PCM converts the throttle position signal to a pulse width modulated (PWM) signal, and sends it to the 4WD control module to control and adjust the transfer case clutch duty cycle.

Vehicle Speed Sensor (VSS)
The anti-lock brake system (ABS) provides the 4WD control module with the vehicle speed information to control and adjust the transfer case clutch duty cycle.

4WD Control Module
The 4WD control mod-ale controls the operation of the transfer case in response to the inputs from the shift motor, MSS, BOO switch, digital TR sensor (4.0L), neutral signal via CAN bus (4.6L), throttle position output from the PCM, anti-lock brake system (ABS) module 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 the front axle when electronically activated.

In 4x4 Auto mode, torque from the transmission is transferred to the input shaft. The input shaft output drives the rear output shaft which, in turn, drives the rear axle assembly. The electromechanical ball ramp clutch assembly drives the drive sprocket after the 4WD control module activates the clutch coil. The drive sprocket turns the chive chain and rotates the front output shaft and the front driveshaft. In the 4x4 High mode, the operation is the same as in the 4x4 Auto mode, except that the 4WD control mod-ale 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. The 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.

Control-Track Function
The Control-Track transfer case uses an electromechanical clutch assembly to control the torque to the front wheels. In Auto mode, while at rest and under cruising conditions, the 4WD control 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 corner on dry pavement. Under any of the following conditions, the 4WD control module will increase the torque sent through the clutch to the front wheels in order to prevent or control slip.

NOTE: At zero throttle, the duty cycle remains low.

Range Function
In 4x4 Low, 4x4 High and all wheel drive (AWD) modes, the 4WD control mod-ale uses throttle input and vehicle speed to determine control of the transfer case electromagnetic clutch. The transfer case shift motor rotates the shift cam to move the red-action shift fork to the 4x4 Low range position. This low range shift, accomplished through a planetary gear set, changes the torque to the drive shaft from 1: 1 to 2.48: 1 ratio.

In the 4x4 High range, with throttle input the 4WD control module signals the transfer case electromechanical clutch to lock the front and rear driveshafts for maximum 4-wheel drive traction. Never use the 4x4 High range or the 4x4 Low range when driving on dry or merely wet pavement. Use 4x4 High range or the 4x4 Low range only for driving off-road or in severe winter weather.

Neutral Tow
The neutral tow feature is a program embedded in the 4WD control mod-ale, which must be activated by a dealer technician. The neutral tow feature disengages the wheels from the powertrain by shifting the transfer case to the NEUTRAL position. This allows the vehicle to be towed with all 4 wheels on the ground. To activate the neutral tow feature, the dealer technician must access the 4WD control module through the diagnostic tool and data link connector. Once communication is achieved, the technician can request the neutral tow feature be enabled. The technician must also install the neutral tow indicator lamp in order for the feature to be activated.

Feature inputs:
^ Mode select switch (MSS)
^ Contact plate position inputs A, B, C, D
^ Vehicle speed signal (VSS)
^ Brake ON/OFF switch input (battery voltage when brake is pressed, open circuit otherwise)
^ 4.0L - digital transmission range (TR) sensor (ground when transmission is in NEUTRAL, open circuit otherwise)
^ 4.6L - selector lever assembly mounted neutral shifter position sensor provides NEUTRAL signal
^ Door ajar switch (battery voltage when door is closed, grounded circuit otherwise)

Feature outputs:
^ 4WD shift motor outputs
^ Neutral tow indicator lamp