@katekebo
Serious question for you though if the Ring and Planetary gears are locked (Center diff locked) then they are rotating fixed at the same rotation rate as the sun gear (output of the torsion portion). How can you achieve variable torque split when locked when all three are turning together as one, and thus there is no lateral motion on the planetary gears due to different rotation rates to engage the friction plates?
Once they are locked, there is no variable torque distribution. Torsen is essentially a type of limited slip differential (LSD). What makes it different from a conventional LSD is that it can distribute the torque in a specific ratio. In a conventional LSD, left- and right- side gears are symmetrical, so it splits torque evenly between both outputs (when not slipping, of course). Because Torsen is based on a planetary gearset, by default in splits torque unevenly between the two outputs. The amount of friction and consequently torque bias toward the axle with more traction is achieved by the angle of the helical gears, which produce axial thrust and hence friction between the gear and the axial bearing (friction plate).
I don't think that is correct, think of doing a burnout in a dragster just because the tires are lit up doesn't mean all the available torque output of the engine isn't going to them, it's just the torque overtook the tractive force. The torque applied is going to be whatever the engine is capable of multiplied by the final gear ratio. Concur on the lifting a wheel, but I don't call that torque distribution, there is still x amount lb/ft. on the spinning tire just no traction to make use of it.
If the t-case is locked 50% is only available to either axle, it's not possible for either the front or rear drive shaft to not rotate at the same rate unless something breaks or unless there is some unknown operation of the torsen diff that I'm missing?
When locked its really no different than a part-time system while in 4WD, you can feel the tires binding on both when turning on too high of a traction surface even with open diffs front and rear because the front isn't allowed to turn at a different rate than the rear.
The advantage of the torsen center diff is only when its unlocked as it can safely provide 4WD and torque distribution front and rear. A torsen diff on the other hand especially a locking one vs a clutch LSD. electronic LSD or open diff is far superior as it can prevent getting stuck in the first place due to its instantaneous torque transfer ability.
I don't know maybe it's semantics but something doesn't jive with me in this thread???
As a real world example my 80 series was Full-time and has been converted to part-time. To get into 4WD and to use this conversion kit two things are required. Conversion from full float axles to manual hubs and the new axles to go with them (to lock the axles to the hubs) and a center locking diff to connect the front to the t-case output shaft.
OK. So let's look first at the case when the central Torsen differential is unlocked. By design, it has 1:1 reduction ratio, so both input and output shafts rotate at the same speed, and the sum of the torque of both output shafts (front and rear) is equal to the torque of input shaft. For simplicity, let's assume that the input shaft torque is 100 (units don't matter). Because the planetary gearset is asymmetrical, the torque is not distributed evenly between the two output shafts. Toyota sized the gearset so that under normal circumstances 60% the torque goes to the rear output shaft and 40% to the front (the percentages are approximate but close enough for the purpose of this explanation). So when input shaft torque is 100, rear propeller shoft torque is 60 and front propeller shaft is 40 (60+40=100). Now let's assume that the front axle hits an icy patch and looses traction. With less traction, it will slip and rotate slightly faster than the rear axle (Torsen is a differential, so it allows the output shafts to turn at different speeds, for example when making a turn, in which front axle has to cover more distance than rear axle). This will cause the planet gears in the Torsen to turn, while pushing against the friction plates. This internal friction will cause more torque to go to the non-slipping axle, just like any LSD would do. The LC Torsen is designed to shift up to 10% of the available torque to the axle that has more traction. So when front axle slips (and turns faster than rear axle), the 100 units of torque will be distributed 30 to the front and 70 to the rear. Ideally this will be sufficient to prevent further slipping of the front axle and the "balance" will be re-established. If the axle with less friction is the rear one, the torque will be distributed 50/50. All this works nicely as long as there is at least some traction (resistance) on one of the axles. If one axle has zero traction, the torque absorbed by this axle will be zero, and consequently there will be no resistance against the input torque, so the load on the input shaft will be zero, and the axle with no traction will spin, the engine will race, and we won't move. Now, because there is always some internal friction on the powertrain, this "zero torque" situation never occurs and at least some torque will be available at the other axle. But because the torque distribution between the axles in uneven, if the axle with no traction is the the front one, it's more likely that there will be enough torque at the rear to make the car move. But if the spinning axle is the rear one, there torque at the front is minimal. This is very nicely illustrated in this video. If you don't want to watch the entire video, skip to approx. 1 minutes to see what happens when front axle has no traction, and then to approx. 3:30 minutes, where the axle with no traction is the rear one. It shows perfectly how the front-rear torque distribution is uneven. Then at 4:30 it shows how A-TRAC artificially creates some resistance at the spinning axle and hence allows some torque to go to the other axle.
Now let's consider when the central differential is locked (so basically the differential functionality is disabled and all three shafts - input and both outputs - are rigidly connected to each other). Again let's assume that input torque is 100. You're driving straight and the torque is distributed 50/50 between front and rear output shafts. Now let's assume that one axle looses traction completely, hence the resistance it offers is 0. The 100 units of torque have to go somewhere, so all this torque will now go to the only axles that offers (more) resistance.
Hopes this long explanation helps.
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