A belt pulley driven by an internal combustion engine is fitted with permanent magnets and serves as the rotor of a generator. The stator consists of a pack of laminations with copper windings.
The electric current induced in the windings is fed to the coil of an electromagnetic clutch. This switches automatically at a certain speed to connect the drive to a machine (in this case via a timing-belt pulley).
Where necessary, it is possible for the electromagnetic clutch to be switched on or off at any speed manually or by a control system.