# Viscous Coupling operating dynamics?

#### one_raven

I am looking for detailed information about the operating dynamics of viscous couplings.
When I search on the web, all I end up with is automotive sites that are selling them, telling you how to diagnose/repair them or explain what they do in a car.

I understand what they do.
I understand the basic mechanics of how they do it.

I am looking for more.
I want information regarding viscous couplings, but not necessarily automotive torque converters.

What aspects are they rated by?
Is RPM the only consideration when determining the amount (%) of Torque transfer that will take place?
Is there a Torque/RPM curve of some sort?
For example, if I wanted the turbine to begin to spin at 30 RPM, and lockup to occur at 120 RPM, how would the engine Torque come into play? Does the engine Torque only come into effect regarding the Torque load on the output? What I mean is: Is the coupling rated to transfer X% of engine Torque at Y RPM, with the RPM of the output simply being dependant upon the load on the output being less than Torque(in)*%Torque(transferred)+Torque(multiplication)?

What determines the curve between when the turbine starts to spin and effective lockup? (no lockup clutch)

Let's say the impeller RPM is 2000 and the turbine RPM is 1200. Now increase the impeller RPM to 3000 and the turbine reaches 2800 RPM. Now, if the impeller drops suddenly back to 2000 RPM, how do I determine how long will it take for the turbine RPM to drop back to 1200 RPM?

What if I wanted to use a viscous coupling as a fluid brake? If I fixed the output of the coupling and the coupling was rated to lockup at 500 RPM, would that brake the input shaft effectively as long as the Torque out does not exceed the max Torque rating of the coupling?

Can anyone help me find a source for all this information plus more?

Thanks a lot.

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#### one_raven

Here is one (of the many) specific things I was wondering about...

Are there any fluid couplings whose lockup RPM is independent of the rotation of the whole unit?

Let me explain...

Let's say I have two shafts that rotate at different speeds.
I don't want shaft B to rotate any more than 500 RPM greater than shaft A.
So, I attach them with the coupling I mentioned above.
The coupling lockup speed is 500 RPM (with a lockup clutch).
Since the whole unit is rotating lockup should occur at 500 RPM RELATIVE to the rotation of shaft A.
Hence Shaft B will never rotate any faster than Shaft A + <lockup speed> (which is 500 RPM).

Does this coupling exist?

Thanks again.

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