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Alternator Decoupler

Function

Why use an Isolator Decoupler Pulley?

The Overrunning Alternator Decoupler, or OAD, is a unique engine belt drive tuning device that can provide numerous significant benefits in a variety of engine and vehicle applications. These include:

extended belt life and increased drive system component durability by up to 2x.
extended tensioner life
quieter accessory drive system operation
smoother accessory drive system operation
reduced vibrations in passenger compartment

The OAD installs on the alternator and is a direct replacement for the standard alternator pulley.

Background:

The combustion cycle of engines inherently cause accelerations and decelerations of the crankshaft. The rotational speed of the crankshaft fluctuates with the ignition sequence in a sinusoidal pattern above and below the average RPM. The torsional vibrations that are transferred to the belt drive are caused by high rotational accelerations induced into the belt drive system via the crankshaft pulley. Because of these rotational accelerations, the especially heavy alternator rotor generates its own vibrations that can be felt throughout the vehicle. The Litens OAD absorbs, through the torsion spring, these vibrations and cancels out these high rotational accellerations. The dynamic forces within the system are therefore dramatically reduced and the belt tensioner as well as the entire system's durability is greatly increased.

Design

RotoRx Explosionszeichnung

1.CAP PLUG 2. BUSHING 3. SHAFT 4. SPRING 5. CARRIER 6. CLUTCH	7. THRUST WASHER 8. THRUST PLATE 9. BALL BEARING 10. PULLEY 11. SPACER

Technology

Not all Alternator Pulleys are created equal!

Solid Pulley

The Solid Alternator Pulley used to be the industry standard and has been around for many years. It has evolved from the V-type to the V-ribbed type (serpentine belt). Its only purpose is to drive the alternator via the belt.

If your alternator has a solid pulley, only replace if damaged, rusted or worn.

Overrunning Alternator Pulley

The Overrunning Alternator Pulley has a simple one-way-clutch inside the pulley. This internal clutch allows the rotor of the alternator to coast to a stop when the engine is shut down. This "overrunning" feature eliminates "chirp" sounds that happen when engine decelerates quickly causing the belt to slip at the alternator pulley (engine shut down or transmission shifting).

What to look for...

OAPs should spin freely in one direction and immediately lock in the other direction. Never replace an OAP with a solid pulley. The manufacture has designed the vehicle with it and damage to other components may occur if a solid pulley is substituted. Manufactures of simple OAPs include INA, NSK, Koyo etc.

Litens Overrunning Alternator Decoupler

The Overrunning Alternator Decoupler not only has a one-way clutch inside, it also incorporates a torsion spring to absorb energy. The effects of the internal clutch are the same as mentioned above; however, the patented internal torsion spring design is the key to the much higher level of function associated with the OAD. The internal spring is tuned (engine specific) to absorb base engine vibrations (cylinder firing pulses) before they reach the alternator rotor and therefore negatively affect the accessory drive. With the OAD installed you will see much less tensioner motion, reduced NVH and an all around more robust accessory drive. Many manufactures are now including OADs when designing their accessory belt drives. This allows them to use narrower belts with lower output tensioners. The lower system tension means the alternator, water pump, and other accessories bearings will last much longer.

What to look for...

OADs should rotate freely in one direction and have a "spring feel" in the other direction. Since duty cycle and/or mileage are usually unknown when rebuilding the alternator, you should always install a new OAD at this time. This will ensure a quality rebuilt alternator and help eliminate field failures.

Never substitute a solid alternator pulley or a simple OAP in place of an OAD. The vehicle manufacture has designed the vehicle with this higher level of function for a reason! Substituting a different alternator pulley may cause damage to accessory drive components. The only manufacturer of the OAD is Litens Automotive Group.