Four-wheel Drive System
Selectable automatic Control Trac four-wheel drive designed by BorgWarner is standard on all 4WD Expeditions. There are four modes: Two High mode, Auto mode, Four High mode and Four Low mode. Each mode can be selected via a rotary control dial on the dash.
The Expedition's system uses a two-speed dual range BorgWarner transfer gearbox with a software controlled variable intelligent locking center multi-disc differential. The four-wheel drive system does not use a planetary or bevel geared center differential, which are typically found in permanent four-wheel drive systems where torque is permanently supplied to all four wheels.
Below is the operational behavior mode-by-mode for the current version of ControlTrac four-wheel drive used in the third generation (2007–present) Expedition.
Note that older versions still work in similar fashion, but will not be equipped with default off road program and may not be equipped with AdvanceTrac.
| Selectable Automatic ControlTrac Four-Wheel Drive | ||
|---|---|---|
| Mode | Drive type | Operation |
| Two High (2H) | Rear-wheel drive | Torque is routed to the rear-wheels only, with high range gearing. Imitates rear-wheel drive and is more economical for on road driving. |
| Auto (4A) | All-wheel drive (unlocked, variable) |
Software does all the work. All 100 percent of the engine’s torque is sent rearward until traction loss is anticipated or detected. The intelligent locking center multi-disc differential can "torque bias" redirecting any percentage of supplied torque to the front drive wheels while still allowing the front and rear drive shafts to turn at different rotational speeds. If severe traction loss is detected at the rear-wheels, up to 100 percent of the engine’s torque can be sent forward to the front-wheels. High range gearing is used. For use in all-weather on road (dry, wet or slippery pavement) conditions or light off road conditions. |
| Four High (4H) | All-wheel drive (locked) |
The intelligent locking center multi-disc differential is locked providing a permanent 50:50 torque distribution. The front and rear drive shafts are mechanically locked together forcing them to turn together with absolute zero rotational speed difference. Front drive wheels pull at the same rate the rear drive wheels push. High range gearing is used. Not for use on pavement, only for off road conditions. If Four High mode is used on pavement, torque windup and drivetrain binding can occur resulting in catastrophic driveline failure. |
| Four Low (4L) | All-wheel drive (locked) |
Similar to Four High mode in operation, the permanent 50:50 torque distribution is maintained; however, low range off road reduction gearing is engaged. A default off road program is automatically selected and remaps (reprograms) the electronic throttle control, traction control system (engine control), and turns off AdvanceTrac’s electronic stability control and roll stability control safety systems for off road use. Four-wheel electronic traction control (brake control) continues to function as normal. Not for use on pavement, only for off road conditions. If Four Low mode is used on pavement, torque windup and drivetrain binding can occur resulting in catastrophic driveline failure. |
4WD Expeditions come with standard dual front frame-mounted closed-loop recovery hooks and available off-road under body protection. Steel plates are placed over vital areas with a composite shield for the fuel tank. Expedition 4x4s are tested along side the F-150 and Super Duty trucks at Ford’s California and Arizona proving grounds. Expedition is put through the same durability tests and evaluations to meet the same durability standards as its pickup truck brethren.
Read more about this topic: Ford Expedition
Famous quotes containing the words drive and/or system:
“Expect no trivial truth from me, unless I am on the witness- stand. I will come as near to lying as you can drive a coach and four.”
—Henry David Thoreau (1817–1862)
“Justice in the hands of the powerful is merely a governing system like any other. Why call it justice? Let us rather call it injustice, but of a sly effective order, based entirely on cruel knowledge of the resistance of the weak, their capacity for pain, humiliation and misery. Injustice sustained at the exact degree of necessary tension to turn the cogs of the huge machine-for- the-making-of-rich-men, without bursting the boiler.”
—Georges Bernanos (1888–1948)