ca2kjet said:
I'd be curious to know if it's 50% when in 4WD.
Well, it can hit 47% in Auto. 4WD seems to do something else.
I played a bit with the Tech2 in Snapshot mode, uploaded the data to TIS, graphed it and grabbed some screen shots.
This first sample shows what typically happens while changing modes. The light red line is the 2WD light, green is Auto, dark blue is 4WD high, light blue is the front axle switch, dark red is the encoder gear position and yellow is the PWM duty cycle % applied to the transfer case slip clutch.
So, starting in 4WD and selecting 2WD, the 2WD light starts to flash, the slip clutch goes to 47%, the front axle disengages, slip clutch goes to 0, 4WD light goes out, encoder gear to 2WD, 2WD light on steady.
Selecting Auto is similar, Auto light flashes, 47% on the slip clutch, encoder gear changes to Auto position, front axle engages, lights change.
The last one, selecting 4WD, is most interesting in that it's the only time I see the slip clutch ever go to 100% -- but then it drops back to 0!
I think the 4WD position of the encoder gear must engage a mechanical lock of some sort, and the clutch is just used temporarily to ensure speeds are matched before it is engaged. Similarly, when coming out of 4WD, I think the clutch takes the torque while the mechanical lockup is disengaged -- but that's a guess, I don't know for certain.
The other graph I'll post shows what happens when the rear wheels start spinning in Auto mode. In this case, red is the rear prop shaft speed, green is the front prop shaft speed, dark blue is the slip speed (ie the difference between front and rear) and light blue is the PWM duty cycle % applied to the slip clutch.
Driving at low speed in Auto on snow, I goosed the throttle just enough to break the rear loose, then held it at a gentle acceleration.
There's a sharp spike in the slip speed as the rear prop shaft speed increases quickly. Slip speed peaks and starts falling as the slip clutch kicks in. PWM to the clutch hits 47% about the same time as the two shaft speeds equalize. (Front and rear tires are all actually spinning at this point). The system slowly eases off the slip clutch as it drops to 11%. Prop shaft speeds decrease until the tires stop spinning and then slowly start increasing again as the vehicle speed climbs. Interestingly, even though the prop shaft speeds have now equalized the system holds the clutch at 11% until I ease off the throttle.
So, I would think 100% duty cycle on the slip clutch = 50/50 torque distribution and therefore 47% = 25/75 (approximately)and that 11% after the event represents about 5/95 -- enough to discourage a second occurrence while still under acceleration without undue stress on the components.