Electromagnetic Clutches

[sharpie_matt]

Hi all,

I'm a bit confused about how electromagnetic clutches work. I understand there are many different designs for different purposes but I think this question applies to most designs. As far as I understand, you have an input shaft that is coupled to a rotor such that they always spin together when the shaft is driven by a motor. Then, there is a stator which contains the coils that engage the clutch when energized. The stator needs to remain stationary so it is often held in place by a pin or flange mounted to an external fixed structure and is also coupled to the input shaft with some mechanism (often ball bearings) that ensures that it doesn't spin with the input shaft. Please correct me if any of this is incorrect.

Then, there is the armature/armature hub. This is what I am confused about. I understand that you usually mount a pulley or sprocket or something onto the armature hub so that you can drive some other mechanism. But when the clutch is disengaged, do the armature and armature hub spin freely? How is the armature connected or not connected to the input shaft?

For example, in the design below, which I took from this link (Ball-bearing type mounting example with CYT), it looks like they attached a pulley (that contains its own ball bearings) to the armature hub with screws. I've circled in red what I am confused about. How does the armature hub rotate or not rotate when the clutch is disengaged?

See this thread to learn about my project. I need the armature hub to rotate freely with basically zero friction when the clutch is disengaged.

Any help is greatly appreciated.

Thanks,
Matt

 

[3DDave]

When the stator windings are energized it forms a magnetic field that is concentrated by the rotor laminations. The rotor has a key to the shaft. The field in the rotor laminations attracts the armature and the armature slides on the shaft to make contact with the rotor, causing the armature to rotate with the rotor.

The circled item looks like a spacer.

See this video which shows how they function:

https://www.youtube.com/watch?v=LfeQalzWmhQ

 

[BrianPetersen]

I think the key to understanding this which the original poster might have missed is that the "ring shaped metal disk spring" (black thing) is bolted to both the armature and the output pulley/sprocket. When the coil is energised, "air gap" becomes zero, and the "ring shaped metal disk spring" is pulled into a wavy pattern because the armature is pulled away from the output pulley/sprocket and in contact with the rotor.

 

[IRstuff]

Your picture shows the armature on ball bearings. Look inside your car for the air conditioning compressor, which typically has the same type of clutch, and the armature is being spun by the fanbelt. When the clutch is engaged, the armature is pulled against the compressor hub and the compressor is now spun up as well. When the clutch is disengaged, the only the armature is being spun by the fanbelt.

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