limited slip gear design

[tomlab]

I'm looking for a design guide or any information on designing a fixed slip gear mechanism (ex the torque clutch in a drill). One side of the gear is fixed onto the end of a solenoid so it can be engaged and disengaged at will. The other end is cast into a magnesium housing. The trouble I’m having is being able to dial in the correct amount of break-away torque needed to allow the design to slip without causing damage to other components when not in use. Any information would be helpful.

 

[plasgears]

I designed a clutch limited output gear using a belleville spring and adjustment nut. At assy the nut was tightened until the required breakaway torque was achieved. Work closely with the manufacturing types to get the right tooling. Use a lubricant at assy so that your breakaway torque is representative of working conditions.

 

[tomlab]

Thanks for the reply, but I've been down those roads. Here's my dilemma. I'm relying on a wave spring to keep constant force on the gear faces, because there is 1. a shaft runs through the center of the clutch and 2. space is a premium so I can't put in an adjustment screw if I could find the space. I have thought about putting a lubricant on the surfaces but since this motor spin's in excess of 2000rpms and the temp will be over 125c I’m not to confident with the centrifugal forces that it will stay confined to the gear faces.

 

[MikeHalloran]

There exist some moly-like dry lubes that are intended to be baked on. They don't migrate. Their wear products do.

One way to dial in a slip torque by design is with ball detents.







Mike Halloran
Pembroke Pines, FL, USA

 

[tomlab]

Thanks i'll loook into the dry baked lubricants. Does anyone have any ideas were to start for the design?

 

[israelkk]

Wave spring doesn't give a constant force it gives a linear force vs deflection. Therefore, if you need to account for wear of the gear face the force exerted by the wave spring will decrease with wear. A belleville spring (not usually the one you get from a catalog) designed for a constant force over some distance can hold a constant force even with wear.

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