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1 In this study, we investigated a new type of groan noise that is different from other conventional types of groan noises during braking. This groan noise occurs immediately after stopping the vehicle. We investigated the behaviors of the pads and caliper on the vehicle with two types of pads. By comparing the data, we assumed that μ characteristics of those pads during the stopping event are different. Then we examined the friction surface of the pads in order to study the root cause. In conclusion, we determined that the shape of the contact plateaus of the brake pad surface contributed to this groan noise.

The disc brake pad is a part that is expected to exert the stable performance in a wide variety of working conditions, for example, in a wide speed range and in a wide temperature range. In addition to these working conditions, the stable performance in a variety of humid conditions has also been demanded. This is because most non-asbestos brake pads have the low friction coefficient μ in high humid conditions, which affects the performance of the disc brake pad. This study notes the film of the friction material on the disc rotor as the reason of a decrease in friction coefficient μ in the high humid environment and discusses the mechanism of the decrease in friction coefficient μ.