Every time the engine decelerates, for example during gear changing or engine shutdown,
the alternator's inertia creates resistance against the belt. An overrunning alternator pulley
(OAP) allows the alternator to "free-wheel" or "overrun" when the belt suddenly slows down.
This prevents the belt from slipping and reduces vibration, wear and chirp noises.
- Pulley with appropriate multi-ribbed belt profile.
- Internal overrunning clutch unit with double bearing support,
allowing the alternator rotor to overrun when the engine
decelerates or is shut down.
- Protective cover.
- In addition to above features some pulley models incorporate a
patented internal application-specific torsion spring which isolates
torsional vibration. These pulleys with a higher level of functionality
are called overrunning alternator decouplers (OAD).