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Recently, vehicle owners have placed low wheel dust as a key component of customer satisfaction. To understand wheel dust, it is necessary to conduct a chemical analysis of influences on the accumulation of wheel dust and available countermeasures. The primary components of the brake wear debris chemical composition analysis are the amount of wear, the property of diffusion, the propensity of the debris to adhere on the wheel, and the granularity of the adhered debris. This study will aid in the design of new friction materials with a low propensity for wheel dust.

Rust accumulated on disk rotor surfaces causes brake judder. In this paper, the relation between the frictional properties of the rusted disk rotor and brake judder was examined by taking two approaches. First, the conditions reproducing the rusted disk rotor were considered. It was found that the rusted disk rotor equivalent to that collected from area where problems of rust judder are reported frequently could be reproduced by dipping in NaCl solution and the rust of this disk rotor formed two layers. Second, a hypothetical model and a theoretical formula of the torque variation caused by the rusted disk rotor were devised. Then, the influence of the coefficient of friction (hereinafter COF) differences between a disk pad and the rusted area / rust-free area with the disk rotor, half of which was covered with a rusted layer, for torque variation was verified. It was found that the COF of the rusted area / rust-free area of the disk rotor were greatly different.

It was reported that groan with a frequency synchronized with the rotation rate of a ventilated rotor is generated by contact of the friction pad with ripples on the vane/channel surface of the ventilated rotor. However, this groan-generation model does not account for the difference in groan sound pressure between friction pads differing in the composition even when the friction pads have the same shape and compressibility. In this study, the distribution of surface temperature of a rotating rotor, which was generating groan was examined. After the groan-generation test, elemental analysis of the rotor surface in the circumference direction was performed. As a result, the surface temperature in the vane area was about 50 °C higher than that in the channel area, and the adhesion of copper contained in the friction pad to the surface in the vane area was about 20% higher than that to the surface in the channel area.