Schaeffler North America

FEAD – Front End Accessory Drive

Overrunning alternator pulley OAP

Alternators have the largest inertial torque in an accessory drive, greatly affecting belt drive behavior. An OAP decouples its inertial torque from the cyclic irregularities of the crankshaft in an internal combustion engine.

Since 1996 the OAP satifys our costumers by its outstanding cost-benefit ratio. Due to continuous development, we were able to accomplish the increased costumer requirements and to support their innovations perfectly.

Besides its reliable function and its contribution to CO2 reduction and therefore fuel saving, the OAP convinces of its solid construction, as well as with its technical support worldwide. Due to this general concept the INA OAP is the absolute world market leader of alternator uncouplers.


The positive effects on the accessory drive include:

  • Minimization of belt vibrations
  • Reduction of force peaks in belt drives
  • Reduction of tensioner movement
  • Increase in belt life
  • Improved noise behavior in the belt drive
  • Reduction of belt slip on the alternator pulley during upshift (particularly in fast shifting dualclutch and automatic transmissions)
  • Less strain on the overall system during engine start and stop-and-start function
  • Preload force reduction in the overall system, leading to reduced CO2 and frictional loss

Decoupling function

The large mass of the generator cannot follow the high irregularities of critical operating conditions. Thus it comes to differences of rotation angle speeds of crankshaft to alternator. Contrary to a rigid wheel the overrunning alternator pulley opens in overhauling direction. The alternator mass and their influences are decoupled from the accessory drive. In addition, the overrunning alternator pulley decouples the alternator’s inertial torque during a significant engine speed deceleration (shifting gears, upshifting).

Structural design

The overrunning alternator pulley consists of a pulley with an outside diameter suitable for using a poly-V belt, a one-way clutch unit with bearing supports, an inner ring and two seals. Following installation, an end cover is snapped onto the front of the alternator shaft to protect it from ambient media (e.g. penetration of contamination, salt water deposits). A modular system has been developed for overrunning alternator pulleys to provide an economical and flexible solution for customer inquiries. The one-way clutch unit and the seal components are standard parts. Unlike spring decouplers, an overrunning alternator pulley does not have its own resonant frequency and does not have to be adjusted to varying alternator sizes.


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