Source: Applus IDIADA
Article by: Juan Jesús García, PhD, Product Manager, Braking Systems in Applus IDIADA
Previous parts of the article have revealed the actual velocity and displacement patterns of a drum brake shoe under squeal conditions and their variability along the lining material. In this last part, the proposed method is complemented with the running mode analysis, traditionally used within the brakes community.
Correlation of Results with Running Mode Analysis
Figures 9 to 11 show the running mode of the operational accelerations of the brake shoes and the back plate during squeal at 7.7 kHz. The results are consistent with the previous conclusions obtained in the previous part of the article, in the sense that we observe a high deformation in the leading edge of the lower shoe. The lower shoe exhibits a bending deformation which lacks symmetry, with the leading edge exhibiting a much higher deflection than the trailing edge. This suggests that the local friction condition at point 8 might tend to produce local sprag. We observe that the upper shoe has a lower and better distribution of vibration that the lower shoe.
Figure 12 also shows that the lower shoe suffers a noticeable torsion of the flange during squeal, which is higher than the one found for the lower shoe. This suggests that the friction tangential forces distribution must be quite irregular in a direction transversal to the surface of the shoe. The implications of a torsion on the shoe also introduces out-plane bending of the shoe, which is a highly undesirable condition in a drum brake.
Effective brake squeal investigation must be based on a global observation of the physical phenomena dominating noise generation in realistic situations. The information provided by the experimental methodology used here allows the definition of the experimental parameters and shoe brake dynamics that dominate squeal generation and, thus, it is very useful to create a well-correlated and robust simulation model. The exploitation of simulation models in combination with the definition of these experimental parameters can then be used to explore effective noise reduction countermeasures.
Some of these methods can be used to break down the observed movement of the brake shoes into two components: a rigid body contribution and a vibration contribution associated with the body deformation. This information can be very useful for understanding the noise generating mechanism and therefore, it is very important to create well correlated and robust simulation models.
The results presented in this article show and quantify the following points related to drum brake squeal:
- Brake shoe vibration during squeal is dominated by tangential and radial oscillations of local shoe points.
- During squeal, the leading edge of the primary shoe exhibits a high radial oscillation, normally not detected in the central point of the shoe. This radial and tangential oscillation can also be broken down into rigid and deformation components.
- The shape of the displacement pattern of the leading edge of the primary shoe shows that, under shoe resonance, this edge can locally sprag into the drum. The angle defined by the leading edge of the shoe and the rotating drum might affect the severity of the local spragging condition.
- The geometric deformation associated with rigid body vibration and the deformation mode is a useful tool for simulation correlation and squeal identification in FEM calculations
- As expected, the results obtained with the brake decomposition method presented here are consistent with those obtained carrying out conventional running mode analysis (operational deflection shapes) of brake shoe vibration.
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