Hmmm...well, that very nice gentleman might have a good point.
My thoughts are the design is such that the magnetic field generated by the coil, attracts the armature plate, which has tabs that engage the sprague, which has the rollers mounted in it.
So, if you have the diff fully assembled other than the front axles,
And you provide power to the coil,
That creates the magnetic field that slows the rotation of the sprague,
And that allows the rollers in the sprague to become wedged between the inside of the ring gear and the outside of the output hubs,
Which then would turn the front axles providing the machine with AWD.
I guess my question would be, can one spin the pinion gear fast enough to get the ring gear turning fast enough to wedge the sprague rollers between the ring gear and the output hubs? Perhaps so. I haven't actually tried it.
My thoughts up to now, were that the resistance provided through the axles, with the tires on the ground, would create the situation in which the diff would lock up and provide AWD.
Perhaps not, perhaps its the speed of rotation of the prop shaft and the magnetic field of the armature that creates the correct situation for lock up?
That would make sense in that the "transfer case" has the gearing to the rear output shaft and the front output shaft. Thus as long as the rear wheels have traction, the rear output shaft controls, limiting, the speed of the front prop shaft. And thus the front diff will not lock up until the rear wheels lose traction, and the rear output shaft speeds up, which speeds up the front prop shaft, and causes the front diff to lock up.
As soon as the rear wheels regain traction, the rear output shaft regains control of the speed of the front prop shaft, it slows down, and the front diff unlocks.
So that makes me think that its not just the speed of the front prop shaft that causes the front diff to lock, its the instantaneous acceleration of the front prop shaft that creates the situation in which the pinion gear rotation accelerates, the rotation of the ring gear accelerates, and the sprague rollers become wedged between the ring gear and the output hubs.
The locking of the front diff lasts only until the front prop shaft slows, just a bit, and the sprague rollers lose the wedging force that was created by the rapid acceleration of the font prop shaft when the rear output shaft accelerated due to the rear wheels losing traction.
So that leads me to think that if the rear wheels are spinning, and you let up on the gas, the two output shafts slow, and the sprague rollers lose their "wedge" between the ring gear and output hubs.
Would that not mean that if one is in snow or mud, or some other rotten situation in which the rear wheels have traction, lose traction, regain traction, lose traction...etc. The front diff is going to lock and unlock every time the rear wheels have or lose traction.
It would seem to me that the "wedging" of the sprague rollers does not occur 360 degrees around the sprague. Its the row of rollers closest to one of the slots in the interior diameter of the ring gear. I conclude that on the basis that the ring gear is a cast piece, and not a CNC machined piece. Thus the location of the slots is not perfect, but "close enough". When there is power to the coil, and the front prop shaft accelerates, which ever row or rows of rollers become wedged is all that keeps the front diff locked.
Might that be where the "flatness" of the armature plate comes into play? If the armature plate has a warped section, and that warped section happens to be at the location where "lock up" would occur, but instead the magnetic drag on the armature plate, and thus sprague, is not strong enough to slow the rotation of the sprague for the roller to become wedged?
Might then a warped armature plate only cause intermittent failure to lock up the diff?
Remembering that for most situations, the lack of traction at the rear wheels is not but for a few seconds. And thus, if the warped spot is where engagement should occur, and it doesn't...then one suspects the front diff of being "bad". On the other hand, if the warped section is not where engagement should occur, then one would not even be aware of the warped armature place.
WHEW...that put the mechanical engineer's brain through an exercise.
Does what I have written make sense?
Open to comments or suggestions!
Pirate
