Lincoln Aviator: Four-Wheel Drive Systems / Description and Operation - Four-Wheel Drive Systems - System Operation and Component Description

System Operation

Principles of Operation

The 4WD system is active all the time and requires no input from the driver. The 4WD system continuously monitors vehicle conditions and automatically applies torque to the front wheels when conditions or a drive mode selection commands it. During normal operation, torque is always applied to the rear drive axle. If wheel slip is detected the vehicle is under heavy acceleration or if the vehicle is in a handling event, the 4WD system commands the transfer case actuator motor to apply torque to the ball ramp and clutch, and provide 4WD torque distribution to both the front and rear axles.

The 4WD system uses a single speed automatically activating transfer case. When torque is required at the front axle, the transfer case motor applies torque to a ball ramp activated high capacity clutch pack, allowing torque from the input shaft to be provided to both the rear driveshaft output flange, and the front axle output shaft via a chain drive. Torque is always provided to the rear wheels via the rear driveshaft, rear differential and driveshafts. Torque (when commanded) is provided to the front wheels via the front driveshaft, front differential side gear and the front axle disconnect actuator (FADA).

Drive Mode Control

NOTE: Drive mode changes may not be available when the ignition is off or when the engine is not running.

The system delivers a driving experience through a suite of sophisticated electronic vehicle systems. These systems optimize steering, handling and powertrain response. This provides a single location to control the performance settings of multiple systems.

Drive Mode Control (if equipped)

Changing the drive mode automatically changes the functionality of the following systems:

• EPAS system adjusts steering effort and feel based on the mode you select.

• ESC and traction control maintain your vehicle control in adverse conditions or high performance driving.

• Electronic throttle control enhances the powertrain response to your driving inputs.

• Transmission controls become optimized with shift cycles tuned to each mode.

• 4WD settings are optimized and tuned to each mode.

Drive mode selection is made through the drive mode switch. For center console mounted drive mode switch, the switch is integral to the ATCM. For column shift stalk mounted drive mode switch, the mode selection is made using the drive mode button underneath the information display.

System Diagram

4WD system consists of the following components:

• Transfer case

• AWD module

• Front axle disconnect actuator (FADA)

• Front half shaft speed sensor
• Front driveshaft
• Rear driveshaft
• Rear half shafts
• Front half shafts
• Front differential
• Rear differential

Spare Tire And Mismatched Tire Sizes

A circumference difference up to 0.5” inch or more between any driven wheel may cause drivability concerns with the 4WD system. Major dissimilar tire sizes between the front and rear axles (for example, 17 inch low profile tires on the front axle and 22 inch high profile tires on the rear axle) could cause the 4WD system to stop functioning and default to rear-wheel drive or damage the 4WD system.

For optimum AWD performance, it is recommended to follow the tire rotation maintenance schedule. To avoid potential 4WD malfunction or 4WD system damage, it is recommended to replace all four tires rather than mixing significantly worn tires with new tires.

AWD Control And Fault Indicators

Faults are indicated by wrench lamp indicator in the IPC and 4WD messages in the message center.

Component Description

AWD Module

The 4WD module is the logic module for the four-wheel drive system. Multiple modules/system inputs are used for the four-wheel drive system to determine the percentage of torque to be transferred to the front driveshafts.

ATCM

The ATCM is the logic module for the drive modes function.

Transfer Case

The transfer case is a supplementary gearbox attached to the transmission and is used to direct power to the front drive axle via the front driveshaft.
Refer to: Transfer Case - Overview (307-07B Transfer Case, Description and Operation).

The transfer case consists of the following components:

• Transfer case clutch actuator with integral position sensors A and B

• Transfer case actuator motor

• Actuator motor reduction gearset

• Clutch ramp and ball ramp

• Input shaft

• Front output shaft

• Rear output shaft

• Chain drive from input shaft to front output shaft

Refer to: Transfer Case - Overview (307-07B Transfer Case, Description and Operation).

Transfer case clutch actuator

The transfer case uses a brushless reversible DC motor (transfer case clutch actuator ) to provide torque to the transfer case clutch mechanism, when commanded. The motor is commanded by the 4WD module and is used to actuate the multi-plate clutch pack within the transfer case assembly.

Front Drive Axle

Refer to: Front Drive Axle and Differential (205-03 Front Drive Axle/Differential, Description and Operation).

Rear Drive Axle

Refer to: Rear Drive Axle and Differential (205-02 Rear Drive Axle/Differential, Description and Operation).