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Epicyclic gears and thrust washer rotation

Epicyclic gears and thrust washer rotation

Epicyclic gears and thrust washer rotation

(OP)
Hi All,

A quick question with respect to a gearbox with the following configuration. There will be some end play in the configuration shown below. The washer is bronze and lubricated so the friction should be minimal but it will exist. Both the thrust washer and retainer are free to spin. The carrier provides input to a secondary reduction.

I understand the function of a thrust washer, however do the thrust washer and retainer remain stationary or do they also rotate?

My initial thought was that the retainer and thrust washer would rotate but at different angular speeds to the motor shaft. I am trying to approach and explain the problem by referencing the static and kinetic friction elements at play during some scenarios.

The two scenarios I am looking at are when (1) the gearbox starts up i.e. motor shaft is initially zero, and (2) gear box operating at a constant speed.



Thank you

RE: Epicyclic gears and thrust washer rotation

My guess is that whether the thrust washer is rotating relative to the motorshaft and the retainer, will depend on the friction generated between the surfaces involved - friction depending on the material combination and whether lubrication takes place and a suitable the lubricant film can be formed. Thus, it will be very hard to foresee what exactly will happen - speed, material combination, roughness of the mating surfaces, lubricant viscosity and lubricity will all play a part in the final outcome. A fully floating thrust washer may not necessarily be the best solution because it can only be achieved at higher speeds - sufficiently high to get full fluid film lubrication between both shaft and washer and between washer and retainer. At lower speeds i guess the washer might be stationary relative to the retainer, and some form of mixed or boundary lubrication between shaft and washer will be available.

RE: Epicyclic gears and thrust washer rotation

With single helical gears the thrust forces at the sun and planet gear meshes will be in opposite directions, and so will the thrust forces at the planet and ring gear meshes. Calculate the net thrust force acting on each gear and size/locate your washers accordingly.

RE: Epicyclic gears and thrust washer rotation

Isn't this one of those situations where there are three places where sliding could take place, all subject to the same driving torque. One of those interfaces will break stiction first (the skill is in making sure it's the one you want) - after which the sliding load on the others disappears and they stay stuck together.

Or was that not the question.

A.

RE: Epicyclic gears and thrust washer rotation

(OP)
I think this was a difficult question to ask, it will depend upon material properties, lubrication and the thrust force etc. I think there would be scenarios where they would rotate together and when they would rotate relative to each other (sliding).

RE: Epicyclic gears and thrust washer rotation

Vibration could cause any or all surfaces to be in sliding friction condition.

Ted

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