Text version of the page

Geislinger Damper

Selection Criterion: Moment of Inertia

First select a damper with the damper’s outer part inertia in realistic proportion to the engine’s total inertia: For 2 stroke engines: 5 to 25%. For 4 stroke engines: 10 to 50%.

Selection Criterion: Stiffness

With the Geislinger Damper, assuming infinite damper stiffness (C
D = ), one calculates the first natural frequency of the engine. From the resonance speeds one can already judge which harmonic orders are of importance within the engine speed range. It is on those orders one has to concentrate when tuning the damper. Knowing which one is the most important order, assuming infinite damper stiffness (C
D = , black curve) a forced torsional vibration calculation is carried out for this order. As a result the angular amplitudes at the crankshaft free end are known. Their values are plotted as a diagram (Dia. 1) The next step is to select a suitable damper stiffness. It is known, that with most installations the damper’s natural frequency should be less than the engine’s natural frequency ( ). This formula will give a good first approximation for C
D .
2

IC

sD I
s moment of inertia of damper outer part kgm
2 C
D torsional stiffness of damper Nm/rad phase velocity of the engine rad/s With C
D fixed as mentioned above a new forced torsional vibration calculation is carried out. As expected, an additional mass and stiffness C
D result in an additional natural frequency and split the original single resonance into two separate resonances (Dia. 2) If the crankshaft free end amplitudes (red curve) are plotted one can find two characteristic points: the fixed points FP1 and FP2. Characteristic for them is, that they are common for both vibratory systems (C
D = and C
D ). The same results as for C
D = and = 0 will be achieved for C
D and = . The conclusion is that, whatever rate of damping is defined the curve of any damped vibrations have to pass through these two fixed points. Dampened vibrations pass below the two fixed points if additional system damping is considered. Taking this into account, one can already judge an optimum tuning, without having calculated a damped vibration yet. One is trying to arrange the fixed points at equal amplitudes (Dia. 4) In Dia. 2 it can be seen that a correct tuning has not yet been achieved. The calculation is repeated with lower damper stiffness. The results are shown in Dia. 3. Now the stiffness is obviously
Geislinger GmbH, 5300 Hallwang, Austria Damper Catalog: Version 15.1 8 / 37