Talk:Viscous coupling unit

Energy loss

This page should have some discussion or reference to the amount of energy lost in a viscous coupling unit. --Nil0lab 17:23, 2 April 2006 (UTC)

Power transfer through the silicone fluid?

According to Popular Mechanics the silicone fluid becomes more viscous (thicker) when heated and that is what provides the power transfer accross the coupling, not friction directly between the plates. Which mechanism is correct? GrodenGlaive 14:26, 20 January 2007 (UTC)

== Silicone oil doesn't become thicker or solid when heated !!!! Transfers motion energy viscosity thermally stable high temps .Silicone Oils that range in viscosities from 5,000cSt to 100,000cSt (centistokes) @ 25°C. They are characterized by their low pour points, high flash points, wide service temperature range, low viscosity change at temperatures. The mechanism described in the article 'Viscous coupling unit' is completely wrong!

The visco coupling works because of the hydrodynamic resistance or friction, which is proportional to the velocity [[1]]. At low speeds the hydrodynamic resistance is low (when you move your hand very slowly in water you feel no resistance) but the resistance increases at higher speed (you feel a resistance when you move your hand in water quickly). The same principle makes the visco coupling possible. At low relative speeds between the plates submerged in the thick fluid there is no significant torque transfer between the plates, but at higher speeds the hydrodynamic resistance and torque transfer increase.

As a model you could imagine a pot with honey and a shaft with a kind of propeller (=equivalent of the plates in the visco coupling) submerged in the honey. Think the pot is the one side of the visco coupling and the shaft with the propeller is the other side of the coupling.

Now when you move (rotate) the propeller very slowly (that means, when both sides of the visco coupling rotates with almost the same speed) you can move the propeller with low resistance in the honey (= there is no torque transfer through the visco coupling) but when you start to move the propeller faster (e.g. with a drilling machine) you will feel that a significant amount of the torque of the propeller will be transfered through the honey to the pot (the coupling effect appears).

Could somebody change the article accordingly (my english is too bad for that) because it seems that the fable about the miraculous change of the thickness of the silicon oil in the visco coupling seems to disperse quickly? I found the same wrong explanation of the visco coupling principle in the polish Wikipedia (apparently translated from the english "original").

Jar —Preceding unsigned comment added by 217.5.182.66 (talk) 15:33, August 29, 2007 (UTC)

Viscous Clutch vs Torque Converter

The original article is good.

The guy that says he has it wrong seems to be describing a torque converter. —Preceding unsigned comment added by 165.173.34.238 (talk) 14:12, 6 March 2008 (UTC)

Not even selfconsistent

The article must be wrong. The dilatant fluid the article mentions works based on shear not heating. —Preceding unsigned comment added by 216.126.67.44 (talk) 19:39, 17 April 2009 (UTC)

Vibration dampers

I think viscous couplings are also used to damp crankshaft vibrations in large diesel engines. How does this work? Biscuittin (talk) 22:40, 13 November 2009 (UTC)

They put a viscus coupling between a flywheel and the crankshaft. Having essentially no friction or other loading, the flywheel will rotate at the same average speed that the crankshaft is spinning. When the crankshaft accelerates faster the coupling will provide drag and when the crankshaft slows the flywheel will return some angular momentum. A spring - flywheel combination can be used to perform the same function, but suffers from its own resonance problems. By using a lossy viscous coupling, damping is provided to the system and this prevents any resonance.206.192.249.5 (talk) 18:36, 14 January 2010 (UTC)

There is no coupling between the crankshaft and flywheel (i.e. it's not somewhere where it has to transmit the main driving torque). Instead it's between the crankshaft and a heavy flywheel-like mass that's not connected to anything else, usually at the opposite end to the main flywheel. There's also an older, non-viscous design, where a similar mass is connected through friction plates.

A two-stroke (not just a diesel) or a long multi-cylinder engine will tend to twist the crankshaft back and forth. This is a problem with two strokes in particular owing to their "torque reversal" effects, but it also happens with long multi-cylinder crankshafts just because of imbalances between cylinders. Andy Dingley (talk) 02:10, 10 March 2010 (UTC)

This article does not reference any scientific sources!

This article does not reference any scientific sources! Jar above is correct. I believe the confusion has come from this website: http://syncro.org/?page_id=2133 which seems to be based on some old VW manual where they appear to have measured the viscosity using the viscous coupling itself (!!!), and derived the 'viscosity' measurement from the increase in torque. Either that or they have just made up the viscosity plot to explain the operation of the device because they didn't understand it at the time. In fact it appears the fluid mechanics responsible is far more complicated than just a simple magic step in viscosity. One thing for certain is that THE VISCOSITY DOES NOT INCREASE WITH TEMPERATURE!

REFERENCES:

Peschke, W., 1986, ‘‘A Viscous Coupling in the Drive Train of an All-Wheel- Drive Vehicle,’’ SAE Technical Paper Series 860386. (Interestingly, also hosted on syncro.org!: http://www.syncro.org/sitephotos/Galleries/peschke_viscous_coupling_article/index.htm)

Mohan, S.K. and B.V. Ramarao, A comprehensive study of self-induced torque amplification in rotary viscous couplings. Journal of Tribology, 2003. 125(1): pp. 110-120.

Cheers,

dblube

Dblube (talk) 16:54, 4 February 2012 (UTC)