General purpose clutches are primarily made up of two major sub-assemblies. They are:
Field/rotor assembly This is the coil and backing plate. The coil provides the magnetic flux that allows the clutch to pull in. The rotor provides the input rotation as it is normally connected to an input shaft.
Pulley/armature assembly This includes the armature disk, springs, hub and pulley. This is normally the output of the clutch. In some instances, a mounting flange is used instead of a pulley.
In a general purpose clutch, either the pulley/hub or the bore (rotor) of the clutch can be the input. In most cases, the bore (rotor) is the input. This input is normally mounted directly on an engine shaft.
All general purpose clutches are bearing mounted. This means that the field is supported by a bearing on the shaft and does not have to be mounted separately. Some mobile clutches are one piece designs and some are two piece (the field/rotor is one part and armature/pulley is the other).
Engagement of the armature to the rotor is caused by the magnetic attraction between the rotor and the armature. The magnetic flux is transferred from the field into the rotor and then into the armature. The slots in the rotor and the armature are called banana slots. These slots allow the flux to contact the rotor and the armature in more than just two places. (A normal magnet only has a north and a south point of attraction.) By making multiple points of flux connection, the torque can be increased in this type of clutch.
The picture shows a standard clutch. It has three flux paths. This is called a triple flux or a six-pole design.
To disengage the clutch, the voltage going to the coil is simply turned off. Once the voltage is released, the springs between the armature and the hub pull the armature away from the rotor, creating an air gap so no contact is made when the clutch is turned off.