How AWD works (Includes Ford's 4A system)

[BigMeatsBronco]

Up to what you need it for, you can’t use Auto4wd off-road or you will burn up the transfer case from it switching on and off. I suppose it’s useful on the road on ice/snow but your really just revealing a poor set of tires for the conditions - it will get you moving with the wrong tires but won’t help ya stop with the wrong tires.

Fulltime AWD is infinitely more useful on road than Auto4wd. I would consider Auto4wd the system for the unknowledgeable. If you understand the conditions and inputs required then you’re not likely to miss the system.

If your desired setup includes Auto-4wd then by all means don’t avoid it. If your looking at a trim that does not include it then I wouldn’t spend more money to get it.

The only reason not to have a true AWD system with a locking center in this year in time is for the minuscule fuel economy decrease associated with keeping both sets of wheels driven. I feel Ford cheaped out on that.

That must be what they use the AWD in the race trucks? So the clutches can burn out? Do some research before you post BS...borg-warner has been using wet clutches in transfer cases for many years in many vehicles! They work fantastic and don't burn up as you described. I've put 350K miles on one with zero issues.

Ford definitely didn't cheap out on the transfer case!

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[BigMeatsBronco]

Yep, I pass people quite often, I'm sure they think I'm the idiot. But I really don't care, after I pass them their inabilities and fears are no longer my problem.

What really gets me is when you see a whole line of cars going slow with their flashers on. It reminds me of a group of kindergarteners holding hands out on a field trip.

Yep this is correct
I'm the same way.

 

[710-oil-614]

Up to what you need it for, you can’t use Auto4wd off-road or you will burn up the transfer case from it switching on and off. I suppose it’s useful on the road on ice/snow but your really just revealing a poor set of tires for the conditions - it will get you moving with the wrong tires but won’t help ya stop with the wrong tires.

Fulltime AWD is infinitely more useful on road than Auto4wd. I would consider Auto4wd the system for the unknowledgeable. If you understand the conditions and inputs required then you’re not likely to miss the system.

If your desired setup includes Auto-4wd then by all means don’t avoid it. If your looking at a trim that does not include it then I wouldn’t spend more money to get it.

The only reason not to have a true AWD system with a locking center in this year in time is for the minuscule fuel economy decrease associated with keeping both sets of wheels driven. I feel Ford cheaped out on that.

This is bad. Very bad.

4A in the Bronco receives input from AdvanceTrac 150x per second for things like throttle, steering, braking, wheel slippage and and adjusts power to the front wheels accordingly.

This guy doesn't understand Ford's 4A system or what goes into it at all.

 

[BigMeatsBronco]

If what you say is correct, " In a turn, they open the clutch. Or possibly feather it to allow some drive across while allowing slip." That would be differential action which is what I asked about. You DO NOT want the front end and rear end binding in the transfer case, that is not a good thing.

This system doesn't ”bind”

 

[BigMeatsBronco]

AWD is a proactive system, the Bronco does not have AWD. Auto 4WD(ie. Advanced 4wd) is over 20 years old now and is very much a Reactive system.

I really wish we wouldn’t mix terms, if Ford wanted to sell a true AWD system with a lockable center differential they could have. The two systems are entirely different and do not provide the same capability as one another.

Your version or idea of a ”true AWD” is a bit thwarted...for example if I pressed the accelerator down to the floor, the computer can and DOES apply voltage to the clutch pack, and engage the front axle, BEFORE the engine has a chance to respond...therefore the AWD is instantly engaged. It doesn’t wait until a rear tire slips to engage the front, it does it BEFORE it happens.

In a downhill, while deceleration, slippery turn, the traction controll knows the lean angle, G forces, speed, steering angle, individual tire speed and a ton of other information, and it can (and does) UN-LOCK the clutch to regain or improve steering traction and controll before you can blink.

Your favorite traditional center-diff-AWD can't do any of that, and the old system
will send power to the one axle and the one tire that has the least traction (essentially making it one-wheel-drive) and is antique in theory and design.
This clutch style system does send power to BOTH front and rear axles, even when one of the tires is off the ground or has ZERO traction. The old center diff system CANT do that.

 

[Oldhippie]

So from reading all this, no one actually knows how the “A” setting in the Bronco works or even if it has a differential in the transfer case? My original understanding from reading the little info Ford provided was it uses a clutch to lock and unlock the front axle. The ability for the clutch to “slip” in various degrees as needed makes much more sense and if true makes me glad to be getting it...but it would be nice to know what is actually in there and how it works...

 

[Rocketeer Rick]

Your favorite traditional center-diff-AWD can't do any of that, and the old system
will send power to the one axle and the one tire that has the least traction (essentially making it one-wheel-drive) and is antique in theory and design.
This clutch style system does send power to BOTH front and rear axles, even when one of the tires is off the ground or has ZERO traction. The old center diff system CANT do that.

I would debate this point at length - but it very much depends on the type of center diff in question. What you say was absolutely true on my Mazda 323GTX way back when. Three open diffs has distinct limitations.

But a lot of center diff systems aren't using open center diffs. With a VLSD center or helical gear center diff, you do have a system in place to proactively prevent axle/wheel spin, and it will favor more torque to the axle that can use more torque - ie not becoming "one-wheel drive". A helical gear diff will send torque to both axles, with more going to the one less likely to slip. Same is true of a viscous or other LSD function over a center diff (the old AWD Aerostar had an active clutch on the open center differential, for example). So in that context, I disagree with the above statement.

But it is also fair to say that such a differential will still need to be able to support a load on both outputs; if a tire is off the ground, they'd have to play off the traction control rather than rely on tire grip. An active clutch center has an advantage in that aspect. But they have to work a lot harder to provide the vehicle dynamics / handling benefits that a helical LSD provides naturally. Its all a matter of what is a better trade off for the vehicle in question.

Anyway, I digress, this is but a tangent on what's important in this overall discussion...

 

[Rocketeer Rick]

So from reading all this, no one actually knows how the “A” setting in the Bronco works or even if it has a differential in the transfer case? My original understanding from reading the little info Ford provided was it uses a clutch to lock and unlock the front axle. The ability for the clutch to “slip” in various degrees as needed makes much more sense and if true makes me glad to be getting it...but it would be nice to know what is actually in there and how it works...

What you described is how it works. As I noted previously, its basically the same as what is done in F-150 Raptor and Expedition. No real new ground broken here, but those systems are pretty well understood. There is a clutch to handle the AWD functionality, and I expect a dog clutch to positively lock up when in 4HI/4LO. Not novel today, but reliable.

 

[BigMeatsBronco]

What you described is how it works. As I noted previously, its basically the same as what is done in F-150 Raptor and Expedition. No real new ground broken here, but those systems are pretty well understood. There is a clutch to handle the AWD functionality, and I expect a dog clutch to positively lock up when in 4HI/4LO. Not novel today, but reliable.

Here ya go folkers....

This is what the internals have looked like on most ford (borg-warner) transfer cases for the past 20 years...just in case you guys have done any wrenching for a while...this system is called torque on-demand for those that are unaware.

Take a close look at the ball berrings and the ”ramps” the rest in...the slot changes as pressure changes...brilliant ultra reliable design that absorbs shock loads better than others....thats why they have been using this system in MOST of the race truck for many many years...this is old technology and people don't understand it.

 

[BigMeatsBronco]

I would debate this point at length - but it very much depends on the type of center diff in question. What you say was absolutely true on my Mazda 323GTX way back when. Three open diffs has distinct limitations.

But a lot of center diff systems aren't using open center diffs. With a VLSD center or helical gear center diff, you do have a system in place to proactively prevent axle/wheel spin, and it will favor more torque to the axle that can use more torque - ie not becoming "one-wheel drive". A helical gear diff will send torque to both axles, with more going to the one less likely to slip. Same is true of a viscous or other LSD function over a center diff (the old AWD Aerostar had an active clutch on the open center differential, for example). So in that context, I disagree with the above statement.

But it is also fair to say that such a differential will still need to be able to support a load on both outputs; if a tire is off the ground, they'd have to play off the traction control rather than rely on tire grip. An active clutch center has an advantage in that aspect. But they have to work a lot harder to provide the vehicle dynamics / handling benefits that a helical LSD provides naturally. Its all a matter of what is a better trade off for the vehicle in question.

Anyway, I digress, this is but a tangent on what's important in this overall discussion...

Maybe do some research on this so you have an idea what's inside your Bronco transfer case?

 

[BigMeatsBronco]

So from reading all this, no one actually knows how the “A” setting in the Bronco works or even if it has a differential in the transfer case? My original understanding from reading the little info Ford provided was it uses a clutch to lock and unlock the front axle. The ability for the clutch to “slip” in various degrees as needed makes much more sense and if true makes me glad to be getting it...but it would be nice to know what is actually in there and how it works...

I know exactly what's inside...

 

[BigMeatsBronco]

So this system uses the balls that roll in slots that are curved or change depth...so as the torque increases the balls are pushed farther in the trough, thereby applying pressure on the wet clutch plates. The harder you press the gas, or the more traction you get, the farther they roll, and the more pressure the clutch plates have...
Additionally, the balls are controlled by an electromechanical clutch. The computer can control where the balls go, and how far and how fast...regardless of the torque applied...

Now you know.

 

[BigMeatsBronco]

What you described is how it works. As I noted previously, its basically the same as what is done in F-150 Raptor and Expedition. No real new ground broken here, but those systems are pretty well understood. There is a clutch to handle the AWD functionality, and I expect a dog clutch to positively lock up when in 4HI/4LO. Not novel today, but reliable.

There is a spline connection in 4L and 4H...the clutch just unlocks the clutches in 2H and makes the clutches available in 4A

 

[Rocketeer Rick]

Maybe do some research on this so you have an idea what's inside your Bronco transfer case?

I know that, I said as much. The point of my post, though, was contesting your claim that center diffs can do none of things you outlined, not about what was in the Bronco t-case. That was why I said it was a tangent discussion.

There is a spline connection in 4L and 4H...the clutch just unlocks the clutches in 2H and makes the clutches available in 4A

Yes, the spline connection is the dog clutch I referred to. That just refers to a rigid, non-slipping connection. I was not talking about the plate clutch that provide the TOD function. Ball cam clutches are nothing new, as you noted. My employer has been making the electromagetic ball cam TOD couplings that went into many Ford AWD vehicles over the last 15 years, so I do actually know a little about it...

 

[JohnnyBronco]

So from reading all this, no one actually knows how the “A” setting in the Bronco works or even if it has a differential in the transfer case? My original understanding from reading the little info Ford provided was it uses a clutch to lock and unlock the front axle. The ability for the clutch to “slip” in various degrees as needed makes much more sense and if true makes me glad to be getting it...but it would be nice to know what is actually in there and how it works...

I would debate this point at length - but it very much depends on the type of center diff in question. What you say was absolutely true on my Mazda 323GTX way back when. Three open diffs has distinct limitations.

But a lot of center diff systems aren't using open center diffs.

Anyway, I digress, this is but a tangent on what's important in this overall discussion...

YES, because 3 OPEN different with zero limited slip capability only applies power to one wheel at a time. A single drive axle open diff only powers one wheel at a time.

Two axles, to supply power to one wheel front and one wheel rear requires a method of splitting torque(power) or independently driving the axles (electric or hydraulic motors)

To provide power to two wheels on the same axle demands a viscous coupling or clutch to essentially restrict power to one allowing the excess to go to the other.

Limited slip diffs between axles, maybe incorporated into transfer case, is what allows modern front axles on AWD to no longer sport locking hubs. An early Jeep or Scout had locking front hubs. If you don't get out and twist the knows up front ypu never get power to ftont wheels but to run with hubs locked while in 2wd mode causes excess diff and axle wear unnecessarily. These vehicles had solid gear or chain transfer cases.

I have, however, driven my Bronco enough miles in several modes to know that because of or in drive of what's inside it works very well......so far.

It does puzzle me why there is no snow/ice mode that would lock up everything. Slippery mode only allows 4A. Not 4H. So I have found best traction in 4A with center fiffvlock button emgaged

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