Question about ADD

I was watching some videos about how our Toyota part time 4 WD systems work. I understand when in 2 WD the front drive shaft does not spin but the CV half axles spin freely with the wheels. When we engage the transfer case to 4WD, there is a signal sent to the ADD, when essentially locks the 2 front half axles together thru the differential.It locks the passenger side axle going to the wheel, to the flange exiting that side of the diff which looks to be spinning in the opposite direction. Before that ADD action, the spider gears in the differential and the flanges they are connected to (flanged to CV shafts) are spinning in opposite directions. This is the action you see on a car on a lift when you spin one wheel and observe the other wheel spins opposite direction. What causes the spider gears and their interfacing flanges to stop moving so the ADD can connect the 2 front shafts together? It seems to me you could not lock the 2 CV axles together if the diff flange on that side is rotating backwards. But being able to shift to 4 Hi kinda defies that logic. Does anyone know how you lock the 2 CV axles together thru the diff while moving?

 

It shifts the transfer case first which gets the driveshaft moving. The front diff carrier spinning from the front driveshaft moves the spider gears in the forward direction which applies to both the left and intermediate shafts via their side gears, which then gets the intermediate shaft spinning in the right direction.

It shifts the transfer case, once it has confirmation that was successful, it moves onto the ADD and starts to move the fork over, applying pressure until the collar eventually slides over once the splines line up.

 

Magic.

 

Thanks! I failed to consider what effect the front driveshaft would have on the spider gear and associated flange rotations. I just knew something had to happen. It really is a neat system. Heck, the guy who created the differential was very clever.

 

It is for sure a pretty neat setup and works well. My only wish is that the transfer case was manually shifted, or at least if we could get that as an option. But oh well.

 

Here you go,

https://youtu.be/47m7QAPrpsI?si=ZwWarS3CKqxksb_O

 

Your logic is correct and so is @BLtheP.

The transfer case shifts firsts using a synchro to spin up the front output and driveshaft to match the rear output and complete the tcase shift. Once this is done the front ring gear/carrier is matching the ground speed because it's driven by the front driveshaft and the left side gear of the diff matches ground speed because it's mated to the rolling LF wheel. Since these two items match ground speed then by definition the right side gear of the diff must also match ground speed. This means it's synchronized to the shaft mated to the RF wheel and the ADD actuator can shift to lock the last disconnect in the front drive system.

On the 4HI to 2HI shift the items are reversed with the ADD disconnecting first followed by the transfer case.

 

Magic!