Investigations on the deposition behaviour of brake wear particles on the wheel surface.

The deposition behavior of brake wear particles on the surface of a rim and the mechanisms involved have not been fully researched. Similarly, it has not yet been answered how high the proportion of particles deposited on the wheel surface is compared with the particles emitted by the brake and what influences this. This information is a prerequisite for evaluating measurements of particle number and particle mass on the inertia dynamometer and comparing them with real emission behavior. The aim of this study is to verify the deposition behavior of brake particles on the surface of wheels. For this purpose, the real deposition behavior is first determined by on-road tests. For particle sampling, collection pads are adapted at different positions of a front and rear axle wheel. In addition to an RDE-compliant test cycle, urban, rural and motorway sections are used to evaluate speed-dependent influences. Microscopic analysis is used to determine the particle number concentration and particle size distribution of the collected samples. Another focus is the analysis of the deposition behavior on the inertia dynamometer under reproducible test conditions using ECE and NAO brake pads. For this purpose, a special setup is used which allows the simulation of realistic flow conditions. In addition to simulating the RDE-compliant test cycle, the WLTP brake cycle is used to ensure real world driving and braking conditions. Finally, simulative investigations on the basis of a transient CFD model allow the particle motion to be evaluated under consideration of the geometry and flow conditions. By implementing a physical deposition model, it is possible to quantify the deposition of particles as a function of particle size and material parameters. The investigations have shown that <15 % of the wear mass deposits on the surface of the rim. In addition, a correlation with the driving speed could be demonstrated. The highest relative proportions could be determined in the urban and motorway sections, the lowest in the city section. In addition, a clear correlation could be established between pad composition, particle size and deposition position.