lincoln

Two wheel drive standard, optional Ford's Control Trac selectable all wheel drive (2H - Auto4wd - 4H - 4L). In Auto4wd mode the behaviour is similar to the automatic all wheel drive - the vehicle is normally rear-wheel drive. Torque is transferred to the front axle via an electro-magnetic clutch when slipping occurs. In 4H mode the clutch is fully locked and the front and rear driveshafts turn at the same speed. The same system is used on Ford Expedition. Optional locking rear differential.

The automatic four-wheel drive (A4WD) system is an electronic-shift 4WD system that allows the operator to choose between 2WD and three different 4WD modes. The operator can switch between A4WD and 4WD HIGH modes at any speed. To engage or disengage 4WD LOW range, the vehicle speed must be less than 5 km/h (3.1 mph), the brake pedal must be pressed and the transmission must be in NEUTRAL.

Wheel slip is sensed using one axle shaft speed sensor on each axle. Based on throttle position and wheel slip, a pulse width modulated (PWM) signal is transmitted to the transfer case clutch when a predetermined slip-threshold is exceeded.

The 4WD control module will provide the IVD brake system with current clutch duty cycle and whether or not IVD may command the clutch duty cycle. The brake subsystem sends the following information signals to the 4WD system:

occurrences of brake events and failures

steering wheel angle status

average rear wheel speed

average front wheel speed

delta front wheel speeds

A concern with any of the above listed brake system signals will affect operation of the 4WD system.

The throttle position output signal is provided to the 4WD control module from the powertrain control module (PCM). This signal is used by the 4WD control module in controlling the 4WD clutch. The shift motor sense plate, an integral part of the gearmotor encoder assembly, informs the 4WD control module of the transfer case position.

The digital transmission range (TR) sensor is located on the LH side of the transmission. This sensor informs the 4WD control module when the transmission is in NEUTRAL.

The electric shift motor is mounted externally to the gearmotor encoder assembly at the rear of the transfer case. It drives a rotary cam which moves the mode fork and range fork within the transfer case between the HIGH range (A4WD, 4WD HIGH) and 4WD LOW range positions.

The 4WD shift motor is controlled by the 4WD control module which shifts the transfer case shift motor between HIGH range (A4WD, 4WD HIGH), and 4WD LOW modes.

The solid-state clutch is duty-cycled by the 4WD control module to activate the 4WD clutch within the transfer case. In the A4WD system, the 4WD control module varies the torque sent to the front driveline by controlling the transfer case clutch. At rest and under cruising conditions, the 4WD control module activates the transfer case clutch a minimum duty cycle (percentage of time the clutch is turned on), which allows for the slight difference between the front and rear driveshafts which normally occurs when negotiating a corner on dry pavement. Under any of the following conditions, the 4WD control module will increase the duty cycle in order to prevent or control slip:

slip is detected

heavy acceleration (throttle position)

Feature inputs:

brake ON/OFF switch

mode select switch (MSS)

digital TR sensor (automatic transmission only)

vehicle speed signal (transmitted from the ABS module)

front and rear driveshaft speed sensors

throttle position information (transmitted from the PCM)

gearmotor encoder contact plate position inputs A, B, C, D

Feature outputs:

solid state clutch (pulse width modulated signal)

4WD LOW indicator

4WD shift motor outputs

Shifts between A4WD and 4WD HIGH can be made at any speed.

Below are the inputs and outputs needed by the 4WD control module to execute a change between any

of these modes.

Feature inputs:

front and rear driveshaft speed sensors

vehicle speed signal

throttle position information

4WD Mode Select Switch (MSS)

Feature outputs:

4WD shift motor outputs

solid state clutch (pulse width modulated signal)

4WD HIGH switch indicator

When shifting into or out of LOW range, the 4WD control module requires that the vehicle speed is less than 5 km/h (3 mph), the brake is applied, and the transmission is in NEUTRAL.

Feature inputs:

throttle position information (transmitted from PCM)

MSS

gearmotor encoder contact plate position inputs A, B, C, D

vehicle speed signal (transmitted from ABS module)

brake ON/OFF (BOO) switch input (battery voltage when brake pedal is depressed,

open circuit when not activated)

digital TR sensor (ground when transmission is in NEUTRAL, open circuit otherwise)

Feature outputs:

4WD shift motor outputs

4WD LOW switch indicator

solid state clutch (pulse width modulated signal)

selectable all wheel drive (2H - Auto4wd - 4H), no low range. In the Auto4wd mode the behaviour is similar to the automatic all wheel drive - normally a rear-wheel drive vehicle, torque transfer to the front when needed.

"The Borg-Warner 1-speed torque-on-demand transfer case is a 2-piece magnesium design. The transfer case transfers engine power from the transmission to the front and rear axles. Under normal driving conditions, the unit is in All-Wheel Drive (AWD), but when desired, the operator may shift into 4x4 high (4H). The operator can switch between 2-Wheel Drive (2WD), AWD and Four-Wheel Drive (4WD) HIGH mode at any speed. The transfer case is equipped with an internal electromagnetic clutch and is shifted electronically. In AWD, the 4X4 control module varies the torque split between front and rear drivelines by controlling the transfer case clutch. Under most conditions, the 4X4 control module activates the transfer case clutch at a minimum duty cycle (percentage of time the clutch is turned on) which allows for a slight speed difference between the front and rear drivelines which normally occurs when negotiating a corner on dry pavement. When the rear wheels are overpowered, the 4X4 control module detects this slip condition and the duty cycle to the transfer case clutch is increased until the speed difference between front and rear drivelines is reduced. In this manner, the 4X4 control module can redirect engine torque to the front wheels when the rear wheels lose traction, yet still allow operation in the AWD mode on dry pavement. The unit is lubricated by a positive displacement fluid pump that channels fluid flow through holes in the rear output shaft."

Source: http://www.justanswer.com/questions/22909-2008-lincoln-navigator-4x4

See http://en.wikipedia.org/wiki/Control_Trac