Step by step description of the function of a Torsen differential
Things to know before we start
1. Do a Google Images search for "Torsen". It is very educational.
2. Realize that there are two sides to the Torsen. The helical gear in the middel is actually two helical gears - one for each output shaft. The "pairs" of Invex (or "worm") gears aren't really pairs. There are three to one side and three to the other. Look at it as a two-sided unit.
3. The ring gear is attached to the housing and is not generally considered to be part of the differential. Sometimes the differential housing is spun via a chain, or in this case, a bevel gear meshing with a ring gear. The ring gear bolts on to the outer ring.
Now, let's begin:
Mesmerize yourself by staring at this diagram:
Ignore the arrows for the moment.
1) Rotate the shaft on the left counter-clockwise (CCW) - I like to pretend I'm turning it with my left hand.
2) The helical gear (splined directly to that shaft - just inside the housing) will now be rotating CCW.
3) The top Invex gear (or worm gear) is now rotating CCW about its journal pin (the pin through its axis).
4) Since that Invex gear is rotating CCW, the one right next to it is rotating clockwise (CW).
5) Since that Invex gear is rotating CW, so is the helical gear (on the other side) to which it is meshed. Thus, the other shaft is rotating CW.
Ta da! CCW on the left = CW on the right.
To take it one step further, see what happens when you rotate the housing and watch the gears inside. Pretend you are a little man sitting on the housing, rotating with it. As long as there is no applied torque to either shaft, both shafts and housing rotate in the same direction at the same speed. From your perspective as the little man, nothing is happening inside. All gears are stationary.
Now if one of the output shafts spins faster than the other (such as in wheel slip or turning) from your perspective as a little man on the housing, things will start to happen. You will see one shaft rotating CW and the other rotating CCW, with all the Invex gears rotating as described above. It actually isn't much different than an open differential, except the Torsen has a much greater sum of frictional forces between gears than an open diff, thus "limiting slip" between axles.
Other Torsen pics:
Careful... this pic is HUGE!
See how it sits inside the transmission?
A T1 Torsen diff as it comes from the factory. Note: No ring gear is attached! That's for you to do!
Sometimes the input shaft to the housing is hollow, sleeved over one of the output shafts. Makes the longitudinal transmission as compact as it can possibly be.
Not many moving parts, really.
Autozine is the best:
Here is what it would look like if it were chain-driven with a sprocket:
I thought this was hilarious. A LEGO interpretation of a Torsen diff.
Now, if you wanted to see a very literal interpretation of a limited slip differential, here it is. It's an open diff with essentially a viscous coupling on either output shaft. This is supposedly a differential made by Kaaz and it is used in Nissan vehicles, I think.
Modified by DHill at 3:11 PM 12-9-2005