So i have acquired a prototype hydratrak differential. It is an unfinished product, which allows me to pull it apart and see how it works. These diffs were unserviceable as they are a fully sealed item. They are filled with a silicon based fluid that apparently changes viscosity as it heats up. Here are some photos of it...
The gold coloured centre component is free to rotate. As it rotates, the 10 pins follow the contour that’s machined on the top component (part on the right). The top component and the case are fully welded together to form a completely sealed part.
This picture shows that there is also a machined contour shape on the inside of the case, so the pins also follow this as the centre component rotates. You can also see how the pins sit in the centre component. The gold coloured component is attached to one axle of the car, and the case/top component to the other axle.
This photo shows how the pins follow the contour. You can imagine as one tyre achieves wheel spin, the gaps between the pins, the contour and the gold component increase and decrease. This provides forces on the fluid as it is being forced through the gaps of the diff. Essentially this creates an lsd effect as the forces on the fluid try to equal out the rotating speeds of the components in the diff.
I am not 100% sure if they do use a varying viscosity fluid, but i can imagine if this was true, then the lsd effect would be multiplied.
I think it is a great engineering design, but could have been improved by making it a serviceable item as the fluid will lose its characteristics over time.