This served as a reminder for how clutch based LSDs work.

The input pinion drives the ring gear. The carrier (aka “cage”) is attached to the ring gear. The carrier carries the pinion gears that drive the side gears (connected to the half shafts). As torque is applied, the carrier exerts force on the pinion gears’ shafts. They are moving with the carrier, so there has to be some force. In a clutch based LSD, these shafts are called cross pins.

Now suppose the carrier is in two halves, and the cross pins are in ramped slots. As torque is applied to the carrier, the cross pins, acting against the ramps, push the two halves apart. Now suppose that as the carriers are pushed apart they compress clutches that lock the output shafts to the carrier. Instead of moving at different rates, both output shafts will spin at the same speed as the carrier.

For deceleration, a different ramp (or no ramp) can be used at the cross pin/carrier interface. This allows different lockup behavior between acceleration and deceleration.

(I’m sure this would all make more sense with diagrams.)

I’m getting a little more clarity on the unloaded wheel thing. The planetary gears work together. When there’s a speed difference between wheels, they’re moving (as a set) towards the more slowly moving wheel. In doing so, they’re increasing the friction between the slow wheel’s planetary gears and the cage, thereby increasing the torque delivered to that wheel.

This effect works only when there is some resistance from the faster wheel. That resistance means there is force on the interface between the faster wheel’s sun gear and corresponding planetary gears. That drive force translates into lateral force (due to the helical cut), which is an essential element of the side-to-side movement of the planetary gears.