Hi,

oh I agree about the fill quantity affecting agressiveness of coupling.

but don't you wonder how overall pressure increase affects the plate
to plate contact in hump?

I mean, each side of the plate is exposed to the same pressure
increase, why would the plates move closer unless there is a
differential pressure? i believe, as illustrated by the diagrams i
just posted, that it is localised pressure differences that initiate
hump.

Back to fill quantity. The air left in the housing will not be one
"bubble" at the top, but it will dispersed throughout as tiny wee
bubbles. This, i believe, is the key. The amount of air left in the
vc will determine the amount of tiny wee bubbles throughout the vc.
Then you can see how localised pressure differences between plates
can be moderated by the air bubbles right in that region. (geez, not
comfortable with the term bubbles, its more like a air in silicone
emulsion, and emulsion is not the right term either).

  The more i read, the more I believe that the hump condition is
*the* torque transfer mechanism when the vc being called upon.

One more thing,I  like this discussion but sometimes it is hard to
convey ideas and concepts through email.

Alistair

On 2-Apr-10, at 11:42 AM, mark drillock wrote:

If you look at Table 2 in Dr. Mohan's SAE paper titled "Comprehensive
Theory of Viscous Coupling Operation" you can see that the initial
fill ratio of the special fluid inside plays a huge role in the onset
of the hump state with just a 1% or 2% change in fill having a large
effect. This implies to me that overall pressure in the unit is a
predominant factor in VC performance. In fact around the world
replacement VC offerings have included options for fill capacity to
tailor to specific needs.

IMHO, in the distant past there have been some false assertions on
the Syncro list that led to misunderstanding of the VC behavior.
Notably this involved an assertion that the torque level involved in
the hump phase was higher that the engine was capable of and thus
that hump phase was not important to VC operation. This error arose
from a failure to account for the torque multiplying effects of the
transmission in the lower gears.

Mark