Gear Housing Tooth Clearance question

[mrpi]

Hello, this question is related to my other post regarding idler gear mounting.

Design Background:
I have designed a pinion-idler train housing that mounts to a customer-supplied driven gear housing. My idler gear sticks part way out of my housing in order to accomplish this. All the gears in the gear train (pinion, idler, driven) are in a "row" so to speak (centers of rotation line along a line).

I had assumed that the customer would address the grease requirement of the gears when mating the two housings. However, they have requested that my pinion-idler housing include provisions for the addition of grease (I'm assuming the customer will add grease as needed as part of regular maintenance schedule). SO, I added a "Zerk" type fitting to my pinion-idler housing.
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Question:
This is where I have some questions regarding the lubrication requirement of gears.

Are there general guidelines or requirements for radial clearance over the tooth of the gears (max or min) to allow for the distribution and movement of grease within the housing???

Will any movement of the grease occur?

I currently have the Zerk fitting feeding into the pinion pocket pointing towards the idler pocket. My reasoning being that as grease is pumped into the pinion pocket, it will fill and extrude into the idler pocket etc.

Any comments or suggestions are appreciated.

Thanks.



Beat to fit, paint to match.

 

[TVP]

Any chance you could upload a drawing, sketch, etc.? Regarding "movement" of the grease, do you intend for this to circulate within the housing, over multiple gears or shaft, or something else? Is there already some provision for basic oil lubrication within the housing?

 

[mrpi]

Let me see what I can get together for a CAD screen-shot or something of the parts.

These are straight spur gears.

There is no provision for oil lubrication, grease is the intended lubricant (I'm assuming because speeds are low).

I apologize, Im not very familiar with gear design.

The grease would be intended to lubricate the gear teeth only, all bearings etc withing the housings are sealed ball bearings lubricated for the life of the unit.

I wasn't sure if circulation of the grease would be a requirement driving the radial clearance around the gears.

Grease requested by our customer is "Aeroshell Grease 22".

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[mrpi]

I'll have to wait till Monday for those screenshots.

Beat to fit, paint to match.

 

[mrpi]

Ok, here are a few screen shots of the gears.

One image shows the gears mounted in the housing. The pinion gear is mounted to the output shaft of a purchased gearbox. The "cross-over" gear is protruding out of the side of the gear housing.

The other two images show cross-sections of the gears to show the radial clearance around the gears. This is what I was wondering about.

If grease is pumped into the gear housing near the pinion gear until it comes out near the "cross-over" gear, do I need to provide certain geometry around the gears as a 'path' of sorts for the grease to flow?

Duty cycles are very low and backlash is not critical. This is part of a lifting mechanism, so perhaps periodic lubrication through the Zerk fitting is all that is needed?

That's the direction I'm leaning.



Beat to fit, paint to match.

 

[mrpi]

Cross section image

Beat to fit, paint to match.

 

[plasgears]

A tighter envelope around the gears will minimize grease reqd and allow all grease to enter into lubing the gears. Metal gears are relatively rigid, and some clearance will account for tolerances, etc. A mistake in plastic gear systems is allowing too much clearance. Plastics are flexible and could create too much clearance under load resulting in noise and wear. Extra clearance should not be provided for lube clearance.