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isn't shudder a form of stick-slip of brakes or clutches? so anti-shudder components would be friction modifiers.
Right. One needs the right friction modification chemistry to allow something called, "dynamic friction."
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In an engine, we want to reduce kinetic friction, but in an Automatic Transmission, we want a specific type of static/kinetic friction.
http://en.wikipedia.org/wiki/Coefficient_of_friction
discusses static and kinetic friction. The frictional characteristics we are discussing here is dynamic friction, a special kind of 'static/kinetic' friction. Dynamic friction is a friction that changes its "coefficient of friction" as two surfaces come in contact and are in relative motion, such as in AT clutch plates.
Recall that clutch plates have alternating layers of clutch friction material and steel plates. The friction material is splined on the inside, where it locks to one of the gears. The steel plate is splined on the outside, where it locks to the clutch housing.
The pressure for the clutches is fed through passageways in the shafts. The hydraulic system controls which clutches are energized at any given moment.
In AT's we want the fluid to create a specific dynamic friction coefficient (dependent upon the clutch materials used) such that we have smooth engagement and disengagement, so we don't have shudder or slippage. Shudder and slippage cause increased frictional material wear and increased heat.
It is this complex package of frictional modifier chemical compounds found in ATF that is important for smooth operation.
Remember, a friction modifier can be a friction reducer, a friction increaser, or one that controls friction in a specified manner.
In an engine, we primarily want friction reduction. In an AT, we want controlled friction modification often called Mu(V) in the literature. The fluid must provide a specific friction versus velocity relationship.
There is a phenomenon commonly called "stick-slip" or "dynamic frictional vibration" and manifests itself as "shudder" or low speed vibration in the vehicle. Using friction modifiers in the ATF prevents this shudder.
http://www.bobistheoilguy.com/forums/ubb...ion#Post1111352