Differential Technologies

[US Paul]

Hello everyone, I have a technical question, but not about engines. (please let me know if there is a more appropriate forum).

I have been trying to learn my way round the different differential technologies. I have found some really good information on Open (and derivative) types and TorSen types. Now I am looking for information on Viscous Coupling types. I understand the basic principle of operation, but I have not been able to find a company that sells high performance VCD's or information on the design criteria. If anyone has any good resources on VCD's I would really appreciate it if you could hook me up.

Also, for AWD cars, it seems like VCD's are used for at least 90% of the time. Anyone know of standout examples of using a TorSen or Open diff instead?

Thanks,
Paul

[kevinday]

Peugeot 405 Mi16 4x4 used Torsen diffs.

[deltaf]

Volkswagen Synchro used a viscous diff too.

[All Terrain]

RaRos and some disco's use vicous difs for thier center one.

[dannylt]

The BTR Hydratrak diff, as used in some TVR's? Should be plenty of info if you search on that. I think the idea is that it's speed sensitive rather than torque, and the viscous coupling starts to lock up as the speed differential increases. Supposedly helps traction on the limit, and for some driving styles, just spins the power away on the inside wheel.

danny

[GavinPearson]

Viscous couplings were developed by FF Developments which is now called Ricardo and is based in Leamington Spa, England. Ford Sierra XR4x4, Sierra Cosworth 4x4 and Escort Cosworth 4x4 used them in centre and rear. Very nice.

Torsen works by having gear inefficiencies limiting their ability to turn and hence slip is limited. Used in a lot of Audis. Very crude.

BTR Hydratrak works by having a cartridge that is geared to the diff output shafts and pumps fluid through orifices within the cartidge. So there comes a point where rpm between the wheels is limited and hence wheel slip is limited. They are used in a lot of Australian cars and having driven them like an animal on a split mu surface rate them very highly.

Plate diffs can be very good especially if you can control the preload actively.

If you are using a car for competition you can always just weld the diff gears in solid - not a disaster to drive either in my experience.

[All Terrain]

Erm transmission windup going round a corner? That can also lead to understeer if you weld up center or rear diff as it becomes like a rigid axle.

Or do I imagine that when I lock the diffs?

>> Edited by All Terrain on Friday 4th July 17:45

[GavinPearson]

I found the wheels 'chattered' when manoevring around a car park but when the car was pushed the tendency to experience wind up was not that high because the inside rear wheel was relatively unloaded under cornering. Certainly not a good idea on the road but very good on a circuit.