The Euro 7 proposal mandates limiting brake emissions to be not more than 7 mg/km/vehicle for particles with an aerodynamic diameter of approximately 10 µm or less. This limit has multiple factors influencing the result, with the test being a source of variation in addition to formulation and manufacturing effects. This presentation aims to answer the question using the ISO 5725 series of standards to estimate the standard deviations and critical differences for test control parameters and outputs. Estimates of variability can guide manufacturers, authorities, and testing facilities better prepare for Euro 7 and understand results as part of future homologation processes. The presentation uses the second Interlaboratory Study (ILS-2) results from Task Force 3 of the Informal Working Group within the Particulate Measurement Programme of the UN Working Party on Pollution and Energy (UNECE GRPE/PMP/IWG/TF3). The methodology follows the main steps outlined in ISO 5725 related to a) data preparation and validation, b) calculation of statistical parameters depending upon the datasets for each parameter, c) estimation of averages, d) application of robust algorithms for means and standard deviations, estimation of standard deviations for repeatability, sample effect, laboratory effect, and total reproducibility, e) analysis of stragglers and outliners, and f) estimation of the uncertainty for repeatability and reproducibility. For specific parameters (e.g., kinetic energy dissipation, climatic controls, brake temperatures, emissions factors), the statistical analysis enables the estimation of critical differences. Due to the nature of the analysis, the work emphasizes data visualization tools to make the results easier to convey to the audience. The numerical results illustrate (using well-established statistical tools and processes applied in many industries) the components of variability among the testing facilities that were part of the Interlaboratory Study (ILS). The results focus on critical dynamometer factors that influence brake emissions (particle mass and particle number) and any meaningful correlations between the measurand level (e.g., speed, torque, temperature) and the level of variations. The ILS results provide different friction materials, vehicle applications, braking systems, and loading conditions. Some facilities could conduct a repeat test on a reference brake (used during the development of the WLTP-Brake cycle and the ILS for the dynamometer test cycle several years ago). In this dataset (repeat test), the ISO 5725 statistical methods yield values for the standard deviation for sample contribution. Some limitations related to this presentation include the following: a) the limited number of test facilities with two complete sets of results to enable the assessment of sample contribution to variability, b) incomplete datasets from some labs, with the corresponding increase in the uncertainty of the estimates of variability, and c) adaptation of the statistical methods to test that are destructive in the statistical sense (with the behavior of the brake under testing changing its response during the test). This presentation extends the results already published within the PMP, provides a systematic assessment of variability using actual test results, and enables the stakeholders to compare test results to the performance and control limits established on the GRPE-87-40 method. Lastly, the results enable test facilities and their (first-, second-, or third-party) customers to find opportunities to improve their test setup and execution during future screening, benchmarking, validation, and homologation phases for a vehicle, braking system, or component programs. Results from this presentation can provide valuable input for future interlaboratory studies using testing facilities and setups complying with the technical and operational requirements of the GTR/GRPE-87-40 document.
Mr. Carlos Agudelo, Director Applications Engineering, Link Engineering Co.; Dr. Barouch Giechaskiel, Directorate C - Energy, Transport, and Climate, Joint Research Centre (JRC); Dr. Theodoros Grigoratos, Consultant, Freelancer; Dipl.-Ing. Hartmut Niemann, Research Application Engineer, Link Engineering Co. GmbH; Dipl.-Ing. Jaroslaw Grochowicz, Technical Specialist Foundation Brakes and Friction Materials, Ford-Werke GmbH; Dipl.-Ing. Marcel Mathissen, Research Scientist, Ford-Werke GmbH