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"VCs operate because the engineers use a formulation that has a high degree, rate, of thermal expansion with a small change in temperature. It's the increasing PRESSURE of the fluid inside the SEALED chamber that raises the EFFECTIVE viscosity. That why many manufacturers that use an adequate fluid formulation can, and do, use a gas bubble inside the sealed case to delay the onset of coupling action."
First of all, you are talking about a mechanical device that, when spun rapidly, raises the temperature of a fluid in the case. In other words, you are using mechanical work to raise the thermal energy of the fluid. While this can happen, the amount of mechanical work needed to raise ANY fluids thermal energy level a significant amount is astronomical.
Assuming you stick by that logic, you must also consider that in order for the VC to release its "locking" of the two shafts together, you must lower the temperature of the fluid, which means giving off the same amount of energy as you put in, which is a long and slow process...which could mean that long after you leave your slipping wheel situation, your axle is still locked together, which is very unsafe and no manufacturer would ever be stupid enough to put that on a production car.
Also, according to you, the fluid only needs a small increase in temperature to provide enough pressure to lock up. Considering that you think that a mechanical device is being used to raise the temperature of the fluid, you must mean that this fluid has substancially altered its volume through thermal expansion, to couple the plates together, with only a few degrees of difference in temperature. But how do you account for climatic temperature changes? If this fluid expands significantly with only a few degrees of temperature change, then how does the unit not explode from pressure in 100 degree heat? How does it couple the shafts together in -40 degree weather?
The answer is simple. VC DOES NOT USE THERMAL EXPANSION TO COUPLE THE SHAFTS TOGETHER.
Summary: A bunch of VC discs spinning can only raise the temperature of a fluid by a few degrees in a few seconds. If that fluid has thermal expansion properties that allow a significant pressure change when the temperature changes by only a few degrees, then that little VC case would explode in summer, and not work at all in winter.
In reality, VCs use a very simple fluid. They do not need expensive special formulations to operate, like you suggest. If they did, all manufacturers would be using TORSEN instead. VCs actually operate on a very simple principle.
I am of the understanding that the hummer has a locking front diff'l. But what is more to the point is that your statement seems to imply that you are in agreement that the side to side Trac activity on the front cannot be too aggressive unless something is there to absorb the shocks resulting.
With reference to the VC:
http://www.mmae.ucf.edu/~jtt/differential.htm"...flat viscosity slope from -40F to +400F...."
My 68 Ford country squire station wagon had one of those.
says it ALL.
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