Avoidance of brake squeal by a separation of the brake ... - tuprints

4.2 Automotive brake disc with radial holes
Figure 4.10: Spectrum of the laser vibrometer’s velocity signal during squeal of
the full, symmetric disc.
always monofrequent with a frequency of 7.6 kHz, which exactly corresponds
to the 5/0 eigenmode of the disc without brake pads. The pads obviously
change the eigenfrequencies of the disc only marginally, which justifies the
modeling assumption to consider the terms originating from the brake pad as
perturbations.
The same squeal test procedure was applied to the optimized brake disc
with 18 holes. The measured surface velocity spectra for the same range
of rotational speed and brake pressure were analyzed. Still, no significant
amplitude in the spectra could be identified, the brake disc did not squeal
under any applied braking condition.
The three following points should be kept in mind concerning the interpretation
of these test results. First, the existing test rig at TU Darmstadt does
not allow to change the environmental conditions like air humidity or temperature
during the test, as is possible with more sophisticated test rigs used in
the automotive industry. Second, the tests were performed with constant rotational
speed, realistic stops with decreasing speed could not be performed.
And third, wear occuring over the lifetime of a brake disc and especially of the
pad could not be simulated. Despite these three facts, the test results strongly
indicate that the desired split of 50 Hz between the first 25 eigenfrequencies of
the brake disc indeed avoids brake squeal completely. This can be considered
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