https://www.ford-trucks.com/forums/8...-equipped.html


This thread is prompted by the above questions from the linked thread, for those who are curious and/or want to know how the Expedition’s 4-wheel-drive system works. (note that those who are already well educated on the 4-wheel-drive system will find this information redundant)


History:
Firstly the 4-wheel-drive system in all 4x4 equipped Expedition’s are unusually sophisticated for a vehicle of its price range. It is also very underrated by those who do not understand how it works.

The system was designed by the people at BorgWarner in the late ‘80s. BorgWarner called it Torque-On-Demand (Ford calls it the ControlTrac 4-wheel-drive system) and it originally called for a 2-speed transfer case with a heavy geared conventional center differential and multi plate clutch pack. The purpose of a center differential is to allow different rotational speeds between the front driveshaft and rear primary driveshaft, such that the 4-wheel-drive system can be used full-time, even on dry pavement, without suffering drivetrain binding and/or torque windup.

The engineers at BorgWarner discovered that they could use clever programming of the system’s microprocessor to control the clutch pack to virtually eliminate drivetrain binding and torque windup, thus effectively turning the clutch pack itself into a center differential and allowing the 4-wheel-drive system to be engaged on dry pavement. As a result the system no longer needed a geared conventional center differential.

The Locking Center Differential

The ControlTrac 4-wheel-drive system’s center "differential" is a electronically-controlled electromagnetic multi-disc (multi-plate) clutch pack. Through use of sophisticated control software, the multi-disc clutch imitates a traditional geared center differential. Under normal on-road conditions, it sends 100% of torque rearward, but can send 100% of torque forward if needed. While adjusting torque between the front and rear wheels the software watches for any drivetrain binding or torque windup, and controls the center multi-plate clutch "differential" accordingly to eliminate it.

Originally the system included four selectable settings 2H, 4A, 4H and 4L from 1997-1998 model years. From 1999-2002 model years the 2H mode was dropped and the system was only 4A, 4H and 4L. From 2003-onward model years the system regained its 2H mode.

What are the modes, and how do they differ?
(note this is the operational behavior of a 2008 Ford Expedition. Newer and older Expeditions will vary only slightly)

• 2H 2-wheel-drive with high range gearing (1.00:1) Rear-wheel-drive capability,
2-wheel electronic traction control system is enabled

• 4A 4-wheel-drive Auto with high range gearing (1.00:1) Full-time all-wheel-drive capability,
Electronically adjusted torque split to front & rear wheels, Electronically variable center differential,
Front driveshaft & rear primary driveshaft allowed rotational speed difference,
4-wheel electronic traction control system is enabled

• 4H 4-wheel-drive with high range gearing (1.00:1) Part-time 4-wheel-drive capability,
Continuous 50/50 torque split to front & rear wheels, Electronically locked center differential,
Front driveshaft & rear primary driveshaft mechanically locked with no rotational speed difference,
4-wheel electronic traction control system is enabled

• 4L 4-wheel-drive with low range gearing (2.64:1) Part-time 4-wheel-drive capability,
Continuous 50/50 torque split to front & rear wheels, Electronically locked center differential,
Front driveshaft & rear primary driveshaft mechanically locked with no rotational speed difference,
4-wheel electronic traction control system is enabled, ESC and RSC are disabled

In 4A mode the center differential is electronically-controlled and rear drive wheel bias. The on-board computer monitors for any sign of rear drive wheel slip (loss of traction)
If loss of traction is detected, the center differential is told to send a share of the engine’s torque to the front drive wheels. It will not let the front driveshaft turn at the same speed as the rear driveshaft.

What about traction management?
1997-2002 model Ford Expeditions offered an optional limited-slip rear differential (LSD). A conventional open rear differential was standard along with the conventional open front differential and the electronic locking center differential.

2003-2006 model Ford Expeditions offered an optional limited-slip rear differential (LSD). A conventional open rear differential was standard along with the conventional open front differential and the electronic locking center differential.

2007-onward model Ford Expeditions do not offer a optional limited-slip rear differential (LSD) for civilian buyers. A conventional open rear differential, conventional open front differential and electronic locking center differential are standard.

2003-2006 model Ford Expeditions offered AdvanceTrac as an optional and it was later made standard on all 2007-onward Ford Expeditions.

What is AdvanceTrac?
AdvanceTrac is an electronic mitigation suite that included electronic traction control system (TCS) and electronic stability control (ESC). Newer versions of it have expanded to include roll stability control (RSC) and trailer sway control (TSC).


TCS is a 2-wheel electronic traction control system on Expedition 2-wheel-drives and Expedition 4-wheel-drives (that are in 2H, 2-wheel-drive mode).

In 4A, 4H and 4L modes the system becomes a 4-wheel electronic traction control system. Armed at all four wheels, it guards against drive wheel traction loss.

TCS uses two methods of controlling drive wheel slip. One it reduces engine power via engine management and two, initiating an ABS brake apply & release cycle on the wheel (or wheels) which have lost traction. The brakes will rapidly clamp down and then release on any wheel which has lost traction, the differentials will respond by transferring more torque to the opposing wheel which still has traction.

In 4A, 4H or 4L modes the AdvanceTrac system performs like having front & rear limited-slip differentials.

The engine management portion of the traction control system can be deactivated to restore full engine power for off road situations (deactivation of this system varies slightly depending on the year model of the Expedition). Electronic stability control is also deactivated so it does not interfere while off road. In newer versions roll stability control (RSC) is also deactivated.

AdvanceTrac is programmed to work in unison with the ControlTrac 4-wheel-drive system. In the right situations the Expedition can keep moving even if only one wheel has traction, no matter which wheel it is, front, rear, left or right.

Have any questions? Feel free to ask ...

 

Ahh ha! That solves the mystery!

Very, very cool! Thanks for the post, lots of great information and a good timeline of the Expedition 4WD system.

 

Do you know if this description, aside from the 4-Lo part, applies to Navigators as well?

Interestingly, I have an '07 Navigator brochure that says the Navigator has 4-Lo... does anybody know if that was ever true on the current series?

Thanks for a great post... nice to know how impressive the system is!

 

On older Navigators the ControlTrac 4-wheel-drive system is virtually the same as the Expedition.

However, the 2007 model year saw the departing of the Navigator from the Expedition’s 4-wheel-drive system.

The Expedition still has a proper 4-wheel-drive system with a center differential that can be locked in high or low range gearing. 4A and 4H modes can be shifted on the move (below a certain speed) from 2H mode. To access 4L mode, the Expedition must be brought to a halt and the 6-seed automatic transmission shifted into neutral. Only then can you bump the dial to 4L. "4x4 Shift In Progress" will display in the message center, then the appropriate mode will display letting you know the shift was successful and what mode your in.

To access the Expedition’s off road crawl, make sure 4L mode is selected, this locks the center differential and engages 2.64:1 low range gearing. Simply shift the 6-speed automatic transmission into manual 1st gear. If the Expedition has the optional 3.73:1 rear axle ratio (code 16), the off road crawl ratio will be 41.06:1.

For 2007-2008 Expedition AdvanceTrac operation:
To disable engine management, electronic stability control (ESC) and roll stability control (RSC) for off road use, simply depress the AdvanceTrac deactivation button (sliding car icon) on the dash. 4-wheel electronic traction control will continue to function. Engine management, ESC and RSC will stay deactivated, but will reactivate if the vehicle goes over 25 mph. The system is designed for traditional low speed off roading. ESC and RSC are automatically disabled when 4L mode is selected.

2009 Expeditions do not disable ESC and RSC in 4L mode. Engine management, electronic stability control (ESC) and roll stability control (RSC) can still be deactivated by depressing the AdvanceTrac deactivation button. Again the systems will stay off below 25 mph.

2010 Expeditions will only disable engine management, ESC and RSC in 4L mode.

2007-onward Navigators do not have low range gearing, but can disable engine management, ESC and RSC like the Expedition up to the 2009 model year.

2010 Navigators cannot disable engine management, ESC or RSC. These systems are always-on.

 

Thanks for very complete run down on the system and its history. My question about Posi's was abit tongue n cheek as many know what open diffs can and can't do. BTW where did you find such a complete explaination of the system and have it be easy to follow both in on the tech/funtcionwise and model historywise? Thats good stuff to point folks to.

 

For everyone...please note I am not flaming anyone just wanted to explain my question and/or reason behind posing one.

 

I'm curious if there is a difference in gas mileage between 4X4 auto as opposed to 4X4 Hi? Or are both just as abysmal or the same as 2WD?

 

I would think that 4x4 Auto would be better as it only "kicks" in when needed. I don't find the gas milage that great on these no matter what really .

BTW, I never knew how the whole system worked until reading your post GL&W. Ford could do everyone a favor and put that in the manual or their website.

Thanks!

 

In 4-wheel-drive Auto mode the software does all the work. Geeks, computer programmers and general technology fanatics would fall in love with the Expedition’s 4-wheel-drive system.

It has its own dedicated microprocessor (a fast one at that), with advanced software and programming. Said to be able to learn terrain and driver habits, it can sometimes engage before wheel slip is detected. The software is so advanced its said to be almost predictive.

BorgWarner has tinkered with the system over the years, improving it, but never straying too far from its core design.

Ford may claim to have designed the system, I do not know if they do or ever have. Though if Ford does or did, they may have had some marketing agreement with BorgWarner. If Ford did have anything to do with the system, they, at the very least played a small role it. I know they did pick the name "ControlTrac". The ControlTrac 4-wheel-drive system is the brainchild of the 4-wheel-drive engineers at BorgWarner.

 

So if in 4 wheel auto the software does all the work, what is the advantage of 4 wheel high? Or is it just for off roading? The manual makes it sound like 4-hi is for when their is less traction and 4-auto is for basically wet conditions.

 

4 Hi is good for heavy active precip on the road, say 6 inches of snow

4 auto is good for slick roads, mild precip (say 1-3 inches).

The big difference is the ability to spin at different speeds in the 4 auto vs the 4 high which has the same rotational speed. That will make a difference plowing through heavy crap.

 

Auto mode adjusts the torque split between the front and rear wheels when needed, it is not constant, and the torque split is normally something similar to 40/60 or so. It does this by giving full control of the center differential to the on-board computer.

It can be used for dry pavement, wet pavement or applicable to any slippery on-road condition. It can also be used for "light" off road use.

4-high mode simply locks the center differential, giving a continuous 50/50 torque split thus increasing overall grip, for off road use.

4-low mode is for conditions considered to be severe off road. In 2007-2008 model Expeditions, ESC and RSC are disabled, the throttle is recalibrated via the default off road torque program and the transmission does a 2nd gear start.


Ford doesn’t recommend using 4-high or 4-low on pavement. You can use them if you’re going to be driving straight (such as pulling a large boat up a slick boat ramp) but making tight turns will cause torque windup and drivetrain binding, as the front driveshaft and rear driveshaft can’t turn at different speeds.




The Ford Explorer used ControlTrac 4-wheel-drive also, similar to the Expedition’s setup but less robust, from 1995-2010 (model years)

The 2011 Ford Explorer seems not to be getting the ControlTrac system. It appears Ford is going to give the new Explorer a single-speed transfer gearbox with all-wheel-drive. No locking center differential or low range gearing.

The Expedition will be the only SUV to get the ControlTrac system.

 

Thanks for all the info. Very informative. As someone else suggested, you should write the manual for Ford.

 

From what I have read and seen underneath the vehicle, there is no center differential on the expedition. If it had one that it would be AWD not 4wd. The computer uses the transfer case to engage/disengage the front axle. I don't know where you came up wit this but if you give me a good reference than I might believe it but trucks do not have center differentials.

Mark

Here is the definition of ControlTrac 4 wheel drive.

The "Auto" mode normally routes all engine torque to the rear differential until wheel slippage is detected by electronic sensors. When slippage is detected, an electromagnetic clutch activates in the transfer case, progressively transferring torque to the front differential. This mode should be used all the time on the road and in nearly all weather conditions. The "4H" mode locks the center clutch, forcing the front and rear drive shafts to turn at the same speed. This mode should only be used in relatively extreme situations such as off-roading or deep snow or sand. Since the center clutch is locked, turning can cause binding in the drivetrain which can cause damage. "4L" is similar to 4H, but additional low gearing is utilized to maximize torque, such as towing a boat out of water. Due to the low gearing, the fastest one can go in 4L is roughly 20 miles per hour (32 km/h). Since 2007, the Expedition's Control Track system has had a fourth position on the rotary ****, 2H (2 high) for more economical driving.

 

It does not have a heavy conventional geared center differential. If you look for one, you’ll be disappointed.

Instead the center differential is an electronically-controlled electromagnetic multi disc (multi plate) wet clutch pack. Its location is inside the 2-speed transfer case where a geared center differential would go.

In Auto mode the vehicle is all-wheel-drive, when needed. The system can and will engage on dry pavement if needed.

They are also sometimes called "active differentials" or "clutch pack differentials" depending on the manufacturer. Mitsubishi calls theirs a Active Differential. The all-wheel-drive Porsche Cayenne also uses a multi disc wet clutch pack center differential.

Several 4-wheel-drive systems use this design instead of conventional differentials.

Some of that information you gave looks like it came from Wikipedia, unfortunately, which is not entirely correct.

The 4-wheel-drive system regained its 2H mode for the 2003 model year, not 2007. 1997-1998 models had 2H mode, 1999-2002 models did not.