In 2014 the United Nations Economic Commission for Europe (UNECE) / Working Party on Pollution and Energy (GRPE) commissioned the Particle Measurement Program Informal Working Group (PMP/IWG) to study non-exhaust particulate matter. The first objective of the PMP/IWG group was the development of a new test cycle that would represent the real working conditions of a braking system and the wear, particularly in light-duty vehicles. The driving cycle chosen is the recently developed WLTP (Worldwide harmonized Light Vehicles Test Procedure) (1). ITT Motion Technologies (headquarters in Barge, Italy), as a global leader in the production of automotive friction materials, has participated from the beginning in the activities of the PMP taking into account emissions from braking systems through the Materials and Process Innovation Team. In recent years, the growth of particulate matter emissions led to the application of new legislation regarding the issue: within 2025 the emission should drop to below 7 mg km-1. Now, the PMP works to reduce emissions from non-exhaust sources to stay under a limit threshold value of PN (Particle Number) and PM (Particulate Matter). In order to measure the effects of wear it has been historically used a chassis dynamometer system, which allows to simulate a brake system in a controlled environment.(2) To collect PM and measure PN, the dynamometer system is coupled with a Particle Counter and Impactor system. Wear analysis on friction materials with a tribometer represents a new direction taken in the research. This new approach allows to isolate the pad-disc interface from any source of interference and measure different parameters such as the coefficient of friction, the temperature of the system and the wear of the surfaces in real-time. ITT developed and validated the WLTP cycle on the tribometer system and build-up a new set-up instrumentation to collect PM emissions. The chemical characterisation of PM collected on filters was developed in collaboration with the University of Turin, focusing on the determination of the inorganic content. All samples were subjected to microwave-assisted acid mineralization and analyzed by Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS). The analytical procedure was optimized to determine major, minor, trace and ultra-trace concentrations of all the elements considered. From the comparison of the measurements in both approaches, a good correlation is found, showing the effectiveness of the procedure for the assessment of wear, the reproducibility of the WLTP cycle and the agreement of the chemical characterisation. In conclusion, the tribometer approach could be a valid screening test able to classify wear characteristics, particle emissions characterisation and a sensible time and cost reduction in comparison with the traditional approach. 1 https://unece.org/transport/vehicle-regulations/world-forum-harmonization-vehicle-regulations-wp29 2 Mathissen, M.; Grochowicz, J.; Schmidt, C.; Vogt, R.; Farwick zum Hagen, F. H.; Grabiec, T.; Steven, H.; Grigoratos, T. A Novel Real-World Braking Cycle for Studying Brake Wear Particle Emissions. Wear 2018, 414–415, 219–226. https://doi.org/10.1016/j.wear.2018.07.020.
Dr. Aleandro Diana, PhD Student, University of Turin; Dr. Andrea Lovera, Undergraduated, ITT Motion Technologies; Dr. Simone Balestra, PhD, ITT Motion Technologies; Dr. Riccardo Cecire, PhD, Università degli studi di Torino; Dr.-Ing. Agusti Sin, PhD, ITT Motion Technologies; Prof. Dr. Mery Malandrino, Professor, Università degli studi di Torino