Escape full-time 4WD system-Can someone explain it??

[coral191]

Because I've heard several explanations, none of which I trust.

It is a 2005 Escape XLT 3.0 V-6 4WD. There are no controls, switches, levers, locking hubs, etc for the 4WD system. It's workings seem seamless & smooth.

The layout is a typical front wheel drive transverse mount V-6 with automatic transmission with the PTU (power transfer unit, gear box, differential, final drive-whatever you want to call it) on the back side of the transmission.

The transmission & PTU are separate (not a transaxle) with ATF in the transmission and synthetic 75W-140 gear lub in the PTU. The 2 front axles come out of the PTU like on a front drive vehicle, but there is a third shaft that comes out of the rear of the PTU. It drives a shaft to the rear that connects to a typical looking rear right angle drive differential. It is full independent suspension, so there are 2 CV Joint axles coming out each side in the rear.

Soooo.... after that long explanation, before I get stuck in the snow this winter-can somebody who actually knows explain how the power is distributed on this thing??? I'm thinking it is probably basically an open differential on the front axles and an open differential on the rear axles????
And-does the rear get driven all the time, or just when it senses slipping in front?? It seems to be in 4WD when taking off because its hard to spin the tires loose. Anyway, somebody tell me what I've got, please.

 

[adsm08]

From the Ford shop manual's D&O on the 4x4 system:

The All-Wheel Drive (AWD) system consists of the following:

Power Transfer Unit (PTU)
Rear driveshaft
AWD relay module
Rear axle with coupling device
Torque from the engine is transferred through the transaxle to the PTU . This torque is transferred from the driveshaft to the rear axle, which drives the rear halfshafts. The AWD system, also referred to as an Active Torque Coupling (ATC) system, is always active and requires no driver input.

The AWD system continuously monitors vehicle conditions and automatically adjusts the torque distribution between the front and rear wheels. During normal operation, most of the torque is delivered to the front wheels. If wheel slip between the front and rear wheels is detected, or if the vehicle is under heavy acceleration, the AWD system increases torque to the rear wheels to prevent or control wheel slip. When the AWD system is functioning properly, there should be no perceived speed difference between the front and rear axles when launching or driving the vehicle on any uniform surface. Traction should be similar to a part time Four-Wheel Drive (4WD) system in 4H (4X4 HIGH), but have no binding in turns.

Serviceable components of the PTU are limited to the output shaft seal and flange, intermediate shaft seal and deflector, and the PTU transaxle compression seal. No internal components are serviced. There should be no need to remove the PTU cover. If any of the internal geared components, bearings, case cover or shafts are worn or damaged, a new PTU must be installed.

The control of rear axle engagement that they mention is achieved with a unit called an "active torque coupling" that is part of the Rear Drive Unit or RDU (the diff). If I remember correctly (been a while since I did that web course) the active torque coupling is similar to the viscous couplers used in Explorer/Mountaineer AWD systems, but there is a PCM controlled solenoid that allows for partial selective engagement and total disengagement so that they don't wear out as fast.

 

[coral191]

Was gone yesterday and just getting back to this-Thanks for the info-it makes sense. The front would be more efficient than the rear drive due to no right angle transference of power up front (like a front drive vehicle). So I can see most of the torque going to the front. Also explains why it doesn't slip or spin on hard acceleration.

What about the distribution of torque between left & right axles on front and L&R axles on the rear?? Is it basically 2 open type differentials?? Is either end limited slip?

Thinking about practical operation & real world situations. I guess if all 4 tires have fairly equal traction, the torque would be fairly evenly distributed between L&R at both ends. (with more at the front than the rear)

But what about a situation where one side of the vehicle had traction, but the other side was on ice or in a ditch, etc. Say the right side of the vehicle is on ice, in mud, off in a ditch, etc with RF & RR wheels having no traction, but the left side F&R wheels had traction....is it going to act like an open diff at F&R with the torque going to the wheels that spin the easiest-leaving me stuck???

I've never had a 4WD vehicle and I can't wait for some snow this winter to go play with it. I'm just trying to figure out how capable of a 4WD system it is........
Thanks again for explaining all this.

 

[Earl43P]

It will pulse the ABS brakes on the slipping side effectively stopping the wheel spin, regaining traction to provide propulsion.

A feature that Ford has used for years on RWD platforms is an open rear diff that gets the slipping side's ABS pulsed to eliminate the slippage. If that proves insufficient (typical driver keeps on pressing the gas pedal increasing rpm and slippage), the PCM will retard the timing to the point that you can only get so much engine rpm (1500-ish). Pressing the gas pedal further will not rev up the engine.

I was driving a 2000 Mercury Grand Marquis up a snow and ice covered cemetery road. Both rear wheels would alternately ABS pulse, slow their slippage rotation, grab traction and propel the car mere inches at a time up that steep hill. The engine sounded like it had a misfire (sort of) regardless of how hard I floored the go pedal. It was quite an eye-opening experience to a stick-shift guy.

I drove that same car, on a dry road, while turning a sharp city street corner. I had just replaced all the spark plugs and one coil (4.6 V8 with COP). Earl was hot-rodding it, squawling the rear tires around the corner doing your basic rear wheel fishtail. Not so fast there, Skippy! That bad boy pulsed the ABS to the squawling outside tire, extreme traction took hold (no timing retard on this event!) and launched that car back under full power in a direction that shook Earlie up pretty good.

I would expect that your more modern Escape would have both of those features working to provide traction (ABS based traction control and Timing retard), plus another Stability Control System in the case of steep angles and sharp steering wheel movements.

I think you will be quite surprised how well it does in the snow and ice, and all you have to do is steer and press the gas. Women LOVE those cars (including Explorers with similar systems) for that very reason. They just GO.

I doubt you'll ever find a limited slip rear differential on any new RWD passenger vehicle again. Cheaper to do efficient traction control with ABS, plus it saves weight. Trucks might still offer it as an option, I haven't checked.

 

[wildbill23c]

Sounds like the system works based on wheel speed differences possibly, which when a difference in wheel speed occurs it sends the message to the 4WD (AWD) system to engage the rear wheels. During normal operation I believe it reverts to 100% front wheel drive and the rear drive train is just along for the ride at that point.

The differentials are open, just like a typical vehicle, nothing special there. Just remember its front wheel drive, don't rely on it for anything major as the system may not be able to handle it.

 

[coral191]

I don't know about it having Traction Control

I've read all through the owners manual and it says nothing anywhere in the manual or on the vehicle saying it has Traction Control. It has no Traction Control light on the dash that has ever come on.

It does have 4 wheel (disc) antilock brakes for sure, with the usual ABS light on the dash.

I guess I've have to wait until it snows, but I don't get the impression that it has any traction control to help control wheel slip, so I'm thinking willbill is probably correct in his statement as far as L-to-R torque distribution.

Now watch it NOT snow any here for the next 3-4 years or something

 

[wildbill23c]

I've read all through the owners manual and it says nothing anywhere in the manual or on the vehicle saying it has Traction Control. It has no Traction Control light on the dash that has ever come on.

It does have 4 wheel (disc) antilock brakes for sure, with the usual ABS light on the dash.

I guess I've have to wait until it snows, but I don't get the impression that it has any traction control to help control wheel slip, so I'm thinking willbill is probably correct in his statement as far as L-to-R torque distribution.

Now watch it NOT snow any here for the next 3-4 years or something

Since I bought my first 4WD truck 8 years ago, we haven't had a good snow here in Idaho where I live to even use the 4WD in any of my vehicles.

 

[adsm08]

The 1st gen Escapes don't have the traction control system. It was a pretty basic ABS.

Bear in mind that the Escape is primarily a FWD vehicle. It has a traditional transaxle with a final drive unit that is the equivalent of an open diff. The only difference in the AWD unit is that the passenger side has the splines on the outside of the shaft, not the inside. The PTU goes over that and has a pass-through tube that the RH axle shaft splines into.

The guts of the PTU are a bunch of pinion gears that ultimately turn the output pinion, which looks a lot like the one if a diff.

The RDU, after the coupler, is basically an open diff.


As for the vehicle's capability in mud, snow, and ice, I have found the tires to be the limiting factor. In 3 years we have gotten our "stuck" (I was able to rock and walk it out) after she went and plowed up a nice burm of snow with the front valence and got the treads on the ContiProContacts packed with snow.

I do not bother to shovel our driveway in the winter because it is so long and I don't have a plow or blower. The Escape runs right up the pack-snow as well as the Ranger or the BII do in 4-hi. We have only kicked the traction control on a few times running into the drive way, and a few of those I did it on purpose. You will have fun with her when bad weather hits if you get some good AT tires on it.

 

[coral191]

I agree totally that good tires are a big key to vehicle performance. I need/want to get some new tires for the Escape, even though the cheap-ass Chinese Primewell tires on it now look brand new, just not very sticky and squeal like a pig around corners.

I use the Escape for a lot of around town driving, taking the dogs out, and general running around. It snows/ices maybe 1 or 2 times a year around here, but I have to get to work when it does..

I want to get as good of gas mileage as possible, but also want a tire that will perform adequately in light snow, but not such an aggressive tread pattern that it cost mileage. So I wonder if the trade off in gas mileage by going with an AT type tread would be worth it for the few times it snows.....

I'm thinking of going with a regular All-Season light truck highway tread-specifically-Firestone Destination LE2s.....unless you guys talk me into something else???

 

[kryptonitecb]

Goodyear AT's a not a good tire to go with. They perform well in the rain until the sipes wear out. Offroad they become mud slicks in any type of damp soil.

Sent from the road while ignoring traffic

 

[bigmark303]

Im going to throw out Cooper HTs. Best highway tire ive had that also performs very well in off road situations. Had three sets to date and all were great.

Also just summing up the Full time 4wd (AWD). It is a system as on any AWD equiped vehicle (whatever the manufacturer calls it) that operated two different differentials at the same time. The driveline is not locked together as a true 4wd is. There is always a center differential which is open that connects the two sets of drive wheel differentials. Thats how you can be in AWD and not bind. In optimal conditions where traction is plentyfull both front and rear will work together just like both left and right tire would work together on a RWD or FWD with an open differential. This is nice but you can be stuck just as easy as a regular FWD or RWD if you dont watch out. If you try to say climb over a snow drift on an unplowed road you could easily end up spinning one set of drive wheels while the other set does nothing at all because it has traction.

 

[adsm08]

You know, bang for the buck I can't really say anything is going to beat the ContiProContacts.

They are primarily a street tread, but they do the job. Like I said, we have not had any issues through the first half of the tread on ours, except in a spot where almost anything is going to get stuck.

Also, in my experience these are one of the better wearing tires on Escapes. Particularly given the AWD Escape's propensity to chew up tires if they aren't rotated regularly.

 

[coral191]

Continental tires??

I was looking at Continental Tires on Tire Rack, and about half of their tires are called ContiProContacts something or other. Are you speaking of the "Grand Touring" class general auto tire called just ContiProContacts, with no numbers or other letters in the name?