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

4 Structural optimization of automotive and bicycle brake discs
mization result was rounded to one degree in the angular position and one
millimeter in drilling depth and the resulting distances were calculated again.
The chosen angular and radial precision was a worst case assumption on the
precision of the machine shop’s process of manufacturing the prototype and
is equivalent to a maximum change in the optimization parameters d h n and ϕ n
of 6%. The distances of the rounded configuration are shown in comparison
to the values resulting from the exact configuration in Fig. 4.6, b). The four
smallest distances between the eigenfrequencies do not change more than 4%
due to the rounding process, which reflects the robustness of the obtained solution
against manufacturing uncertainties. A consideration of uncertainties
in the parameters could be taken into account during the optimization, possibly
leading to an even increased robustness. However, the achieved result
was considered to be satisfying in this respect. Furthermore, the evaluation
of the objective function is considered to be too expensive to allow for an
optimization under uncertainties. For tests on the brake test bench at TU
Darmstadt, the optimized disc and a full disc without holes as a reference
were manufactured using S235JR steel.
4.2.2 Test results
Two types of tests were performed with the two prototype discs, originally
presented in the Bachelor thesis [57]. First, a modal analysis to check the
distances between the eigenfrequencies and therefore validate the optimization
results. Second, a squeal test to determine the achieved reduction in squeal
affinity of the optimized brake rotor. The test rig is shown in Fig. 4.7 with
the optimized brake rotor attached. In Fig. 4.7, a), a front view on the test
rig is shown. The bench contains an original car suspension, where fixation
of the brake disc is guaranteed by an adaptor instead of a rim. This allows
measurements with the laser vibrometer on the complete surface of the disc.
Also, it can be seen that the caliper is attached to the test rig. This allows for
the application of adjustable brake pressure during squeal tests; the caliper
is detached from the test rig during modal analysis tests. While during the
latter tests the disc is not rotating, it is driven by an electrical motor for squeal
76