Analysis of wear induced particle emissions from brake pads during the worldwide harmonized light vehicles test procedure (WLTP)

Brake emissions generated from brake systems were investigated to elucidate the mechanism of airborne particle generation using commercial brake pads. Brake emission tests were performed using a 1/5 scale brake dynamometer enclosed in a chamber, and the particles were counted using an electrical low-pressure impactor (ELPI+) as a particle counter. The results revealed that the emission factor of low-steel brake pads was approximately five times greater than that of non-steel brake pads on average. In comparison, brake emissions in the number concentration were about two times greater in the case of using low-steel pads. Considerable amounts of off-brake emissions were also found after brake applications. Although multiple concentration peaks were observed in the particle size distribution, there was no correlation among chemical composition, size distribution, and particle morphology. On the other hand, the amount of brake emissions and the size distribution were strongly influenced by the pad surface topography, which comprised contact plateaus and lowlands, regardless of the type of pad.