Ever wondered how a hydratrak diff works?

[billkara]

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.

[mik]

i`m guessing the waved washer tension and the size of the fluid holes decides how much spin is allowed between the two axles? hydraulic effect? i think the waved washers would lose a bit of tension after a while?
interesting bit of kit you have there.
my young brother has a torsen centre in his car, i think i would prefer the torsen to this type of unit unit.

[billkara]

Im guessing you think that the contoured part im talking about is a waved washer. Its actually solid metal. So they dont compress. I think the hydraulic effect alone is what determines the amount of spin.

Its a trick bit of gear, i think they were mainly used in the VS HSVs and so on. Did they continue using them in the early 2000's (if anyone can answer this)?

But yes, i think the torsen centres are much more effective and are a better design.

[smoo]

Some grand Cherokees are fitted with a New Process full time 4wd transfer case with a similar set up to send drive to the front under wheel spin, over time that fluid hardens and causes the diff to bind up, effectively acting like a full time locker. They are not a serviceable item.

[EF ECTIV]

the EL GT was fitted with a version of the hydratrak diff too... as billkara said
most the HSV from the mid nineties or so used them as well (VS GTS,
Senator etc)

[Spanrz]

The issues that you have to watch for these things, is the type of oil you use and change it regularly. These things would make lots of metal in diffs after a "hard" day. I don't see any seals ('o' rings), they must be sealed to a point (small gaps) to produce a slight sealing effect. Magnetic plugs are a must!

[Bossxr8]

Originally Posted by EF ECTIV

the EL GT was fitted with a version of the hydratrak diff too... as billkara said
most the HSV from the mid nineties or so used them as well (VS GTS,
Senator etc)

Falcon Outback or Longreach ? utes got it too.

They were usually removed for heavy duty track work as the fluid got too hot and stopped working properly, from memory.

[mik]

Originally Posted by billkara

Im guessing you think that the contoured part im talking about is a waved washer. Its actually solid metal. So they dont compress. I think the hydraulic effect alone is what determines the amount of spin.

Its a trick bit of gear, i think they were mainly used in the VS HSVs and so on. Did they continue using them in the early 2000's (if anyone can answer this)?

But yes, i think the torsen centres are much more effective and are a better design.

yep that was my thinking of that smaller bit, thanks for clarifying, 50+ year old eyes :(, it does`nt look like it would take a lot to make it lose hydraulic effect one way or the other, also as Spanrz has mentioned about filings and grit, but the idea is pretty clever anyway, thanks for posting pics.

[dogfish]

To me it looks like a combination of a Vane pump and Piston pump.
The vanes move in and out against the plate causing hydraulic pressure like a swash plate does in a Hydraulic Piston Pump.