Damping effect on nonlinear drum brake squeal prediction

In the present study, Complex Eigenvalue Analysis (CEA) was used for predicting squeal noise generation in a commercial drum brake. By using a CEA model, Rayleigh damping properties were added to the computer simulation on ANSYS, and a discussion about its implications and proposed calculations are also shown. The Rayleigh damping coefficients (alpha and beta) were obtained through impact tests carried out in a commercial drum brake. Three different cases of damping levels were simulated: (a) Undamped condition, (b) Damped-0 bar, and (c) Damped-2 bar. Results of experimental tests showed that increasing brake pressure from 0 to 2 bar in the damped condition leads to a shift in the resonant frequencies towards higher values, as well as to increase the damping response of the drum brake system. Results of CEA showed a large number of vibration modes occurred within a narrow range of frequencies (0-4500 Hz). This means the drum brake is prone to modal coupling, which may lead to noise generation. The first model simulated by CEA (undamped case) showed five instabilities in the frequency range considered, from this point, the second model was built (damped-0 bar case) and only three instabilities were identified. Thus, the third model (damped-2 bar case) was analyzed and it showed only one unstable frequency, which means over-predictions could be avoided due to the addition of damping. Thus, it was noticed a significant negative offset caused by the damping effect, however, the system instabilities for all five modes remain. CEA models were validated by comparison of predicted and vehicle noise frequencies, which were very close.