Electromagnetic clutches use a magnetic force to engage and disengage the clutch in a vehicle or other machine. Both manual and automatic transmission automobiles use a clutch to convert the power created by the car's engine into a force that turns the car's wheels. Electromagnetic is the most frequently used type of clutch in automobiles. Both magnetic force and friction play a role in helping the car's wheels spin at the proper speed.
A car's engine is constantly spinning while the car is running, but the car's wheels are not. The clutch in a car allows the transmission and the engine to connect and spin together, then disconnect when the car needs to shift gears or brake. If the transmission remained connected to the engine and the driver tried to brake, it would cause the engine to die, or turn off.
When the clutch is engaged, a magnetic force field is created in the rotor. The rotor is the part of the clutch attached to the engine. As the magnetic field grows stronger, a part known as the armature is drawn toward the rotor. The armature connects with the rotor and begins to spin at the same speed as the already spinning rotor. Once this connection is made, the spinning motion begins to turn the wheels of the car and the car drives forward.
At some point or another, the driver will need to stop the car. To do this, the electromagnetic clutch needs to disengage so the wheels can stop spinning while the engine continues to spin freely. To do this, the magnetic field is slowly reduced until the armature disconnects from the router and the wheels slow to a stop.
Friction also plays a role in turning the clutch. Once the electromagnetic clutch is engaged, the friction between the router and the armature allows them to lock together and rotate at the same speed. The friction does cause the materials to wear down over time, however, and the materials used in the electromagnetic clutch determine how well it stands up to the friction.
The electromagnetic clutch works both to create power and act as a break. In a car, the clutch helps transfer power from the engine to the tires when the driver presses the gas pedal. Other machines may use an electromagnetic clutch as a brake. The magnetic force attracts the brake pads toward it and the friction from the brake pads slows and stops the machine.