The importance of non-exhaust emissions is growing due to the optimisation of combustion engines with regard to exhaust emissions and the increased use of electric vehicles. The upcoming regulation of brake wear particle emissions by the legislator within the course of the Euro 7 standard brings coated brake discs into the focus of research and development. They are characterised by a low wear rate and reduced particle emissions. At the same time they offer protection against corrosion. This is particularly advantageous for the different operating behaviour of the friction brake in the course of electromobility. Given the trend towards increasing vehicle weights, there is an even greater need for robust friction pairings that can permanently handle the high energy conversion rates. To investigate the resistance to high loads, three different surface-coated brake discs are compared with each other. These differ in terms of the material composition of the coating as well as the coating technology. The brake discs are compared in regard to their emission behaviour and the coefficient of friction. The emission levels of the friction pairings are determined under WLTP Brake Cycle conditions. Between the emission measurements, high energy braking is performed, which can cause a change in the characteristics of particle emissions and friction coefficients. Possible physical damage to the disc surfaces is analysed and correlated with the tribological behaviour. For this purpose, ex-situ surface microscopy methods using laser scanning and digital microscopes are used, which are supplemented by in-situ thermography measurements to visualise the friction contact. Following the tribological investigations, the emissions are evaluated under WLTP Brake Cycle conditions again. The study shows a significant influence of high energy braking on the surface condition of coated brake discs. This results changes in the friction contact areas, which in turn have an effect on the friction coefficient and the emission level. The different coatings show various changes and damage patterns. These correspond to the wear characteristics.
Mr. Christopher Hamatschek, Research Engineer, Technical University Ilmenau; Mr. Lukas Storch, Research engineer, Technical University Ilmenau; Mr. Matti Wenke, student, Technical University Ilmenau; Mr. David Schobel, student, Technical University Ilmenau; Prof. Dr.-Ing. Thomas Bachmann, professor, Technical University Ilmenau; Dr.-Ing. Sebastian Gramstat, subject specialist, Audi AG