The overrunning clutch is one of the important components of automotive alternators designed to prevent the transmission of torque to the drive shaft when the drive shaft speed becomes too high. In addition, this clutch is included in the case when the torque needs to be transmitted in one direction.

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The principle of the HELLA brand Alternator Freewheel Clutch work

One of the weakest points of generators is precisely the belt drive. The problem is that the car's engine works unevenly - the torque through the shaft was transmitted by pulses, the sequence of which corresponded to the combustion of fuel in the cylinders. In turn, the rotor speed should be 2-3 times higher than the crankshaft speed. Add to this the fact that the car is constantly changing the speed mode (acceleration-deceleration), and imagine how over time the alternator belt stretches and then breaks. It was possible to neutralize this effect by introducing an overrunning clutch connected to the generator pulley.