1. Geartrains

1.2. Pendulum Vibration Absorbers

LO 9-07: Identify and describe the purpose, types, construction, and operation of the engine geartrain.

 

Pendulum Vibration Absorbers

In addition to scissor gears and viscous dampers, which are used to provide torsional vibration damping for the geartrain and camshaft, pendulum dampers are a unique torsional damper Figure 59. Unlike regular balancers, pendulum vibration absorbers provide torsional control by producing forces that directly cancel the forces producing torsional vibration. Steel rollers called centrifugal pendulums fit loosely into a specific number of holes in either a harmonic balancer or an overhead cam drive gear. The rollers store and release energy back into the drive gear rather than converting the mechanical energy into heat energy as dampers do. A patented mathematical algorithm is used to calculate roller size, hole size, and gear size to determine how the rollers will move forward during the compression strokes when the crank slows and rolls backward during the power stroke. Movement of the rollers back and forth minimizes engine speed changes to the camshaft, keeping torsional vibration low. Manufacturers claim that the pendulum damper provides a smoother-running engine and increases valve train stability while offering more accurate injection timing. Pendulum dampers have the added advantage of being lighter than conventional dampers.

  Technicians Tip  
  Unusual geartrain noise usually indicates problems with excessive gear lash; chipped, pitted, broken, or damaged gear teeth; or excessive bearing wear. Whenever unusual noise develops in a geartrain, the geartrain should be removed to inspect the geartrain and bearings supporting the gears. A rattling noise usually indicates excessive gear backlash in contrast to a high-pitched whining noise that indicates too little gear lash.  
  Fig09_59

FIGURE 09-59: A pendulum torsional vibration damper installed on the cam gear for an overhead camshaft engine.

 

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