Page 223 - Gear Technology Solutions

Figure 2 shows how in three steps first the gear runout, then the pinion runout
and finally the tooth mesh is filtered out. In the example, no residual ampli-
tudes are left. It can be assumed that a listener can clearly hear all three sepa-
rate frequencies. At the bottom in Figure 2 the FFT result contains bars for the
gear runout, the pinion runout and the tooth mesh frequency. The side bands
of the tooth mesh frequency originate from the gear and pinion runout. The
side bands are spaced away from the tooth mesh frequency by their respective
runout frequencies. Although the gear and pinion runout and even the generat-
ing flats commonly have a dominating sinusoidal shape, the tooth mesh in
most real cases is parabolic resulting in many additional frequency amplitudes
which are attributed to the transformation algorithm which is used in Fourier
analysis and does not exactly represent the audible frequencies.

Figure 3: Separation of parabolic and harmonic motion transmission elements

Also, in Figure 3 the motion transmission error is separated from the elements
gear runout, pinion runout and tooth mesh. The difference to Figure 2 is the

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