This paper deals with low-frequency squeal phenomena generated in floating type of car disc brake units. First, the vibration characteristics of low-frequency squeal (about 2 kHz) were investigated. Here, in order to reproduce the squeal, a bench-test apparatus consisting of an actual automotive disc brake unit was utilized, itself comprising a disc, pad, and caliper. With this, the associated frequency characteristics were experimentally determined. It was found that the squeal is caused by coupled out-of-plane vibration modes among the disc and caliper due to Coulomb friction. As an experimental countermeasure, a dynamic absorber was applied to the leading side or the trailing side of the inner caliper. It was found that squeal can be suppressed when the natural frequency of the dynamic absorber is tuned so as to be near the frequency of the squeal, and that squeal can be suppressed even without viscous damping of the dynamic absorber. Also, using linear characteristic value analysis, a simple analytical model of an automotive disc brake system composed of a disc, pad and caliper was set up. As obtained from the analytical model, the unstable vibration modes of the disc and caliper, and its generation mechanism, qualitatively agree with experimental results. In our analysis, a dynamic absorber was applied to the leading and trailing sides of the inner caliper, and it was found that unstable vibration can be stabilized only when the natural frequency of the dynamic absorber is tuned to be near the frequency of the unstable vibration. It was also found that within the range of the natural frequency of the dynamic absorber, unstable vibration can be stabilized even if the damping value of the dynamic absorber is zero. These results also agree well with experimental results.
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