LO 8-10 Identify and describe the types of crankshaft vibration
1. Vibration Dampers
1.2. Viscous Dampers
LO 8-10: Identify and describe the types of crankshaft vibration. |
|
Viscous Dampers Silicone fluid is used in viscous dampers to tune out harmonic and torsional vibrations. Higher horsepower (hp) engines, those over 300 hp (224 kilowatts [kW]), possess higher vibrational energy, which can lead to fatigue from overheating and shorten an elastomer damper’s life. In a viscous damper, the inertia ring rotates inside a sealed case connected to the crankshaft Figure 69. A thin film of highly viscous silicone fluid fills the small gap between the inner inertia ring and the outer case. During changes in crankshaft speed, the silicone fluid drags the inertia ring, permitting it to rotate at approximately the same rpm as the crankshaft. If no torsional vibration is present, the inertia ring and outer casing rotate at identical speeds; however, changes to crankshaft speed (due to harmonic and torsional vibrations) cause the inertia ring and outer case to shear the silicone fluid. This converts the relative motion between the inertia ring and the outer case into heat energy, which effectively dampens torsional and harmonic vibrations. The oscillating movement between the ring and the case allows the viscous damper to dissipate more energy than the same size elastomeric damper, permitting more effective damping of torsional vibrations. To determine whether this type of damper is defective, it should be visually inspected for leaks, excessive runout, or dents that could prevent movement of the inner ring. If an engine is operated for about half an hour, the viscous damper will be warm or even hot to the touch. This can be measured with an infrared thermometer. The increased temperature is due to silicone fluid shearing and is one of several quick test methods that indicate that the damper is operating correctly. |
FIGURE 08-69: A viscous damper uses a heavy inertia ring that moves and shears silicone fluid inside a steel case. |
| Technicians Tip | ||
| Dampers should never be removed with a puller applied to the outer inertia ring. Most dampers are designed to be removed with hand force only. Pulling on the outer ring or the case of a viscous damper destroys the component because distortion of the case or bending of the inner inertia ring will prevent proper mechanical functioning of the damper. |
Combination Dampers
As the name suggests, combination dampers combine the damping advantages of both viscous and elastomeric dampers. Elastomeric dampers provide good low-speed harmonic damping in comparison to viscous dampers. The reverse is true at higher engine speeds, and viscous dampers provide better damping of harmonic vibrations.
2026 - CDX |