In the context of the Green Deal and the objectives of “carbon neutrality” and “zero pollution”, the European Commission has committed to reducing current emission limits, from all sources. Brake wear is a significant contributor to respirable particulate matter (PM10 and PM2.5), particularly in areas with high traffic density and frequent braking, and up to an 80% of these particles may come from the wear of the rotor (Grey Cast Iron), and are mainly formed by Iron Oxide. In electric vehicles, the lack of use of the mechanical brake due to the existence of regenerative braking means the appearance of new problems with the use of gray cast iron discs, such as corrosion, which generates noise and safety problems. So this is a holistic matter, with many variables involved in the final output.
From a legislation point of view, what the emission limit should/will be is still unclear. CLOVE’s (Consortium for ultra Low Vehicle Emissions) proposals to regulate brake wear particle emissions for the first time as part of the Euro 7 EU vehicle emission standards. CLOVE proposed limits would result in a reduction of brake emissions of between 40-60% compared to current cars (Table 8). But other entities, like some EU cities as well as organizations like T&E (Transport&Environment) and its NGO network, considers the proposed limits insufficien, and do not come close to the reduction achievable by the best available technology for brake emissions reduction.
Table: Current brake emissions of cars and suggested CLOVE limit options.
From a homologation point of view, how to measure the emissions is also a key factor. Although there is no definitive standard yet, there’s a huge effort on developing the testing methods and standards for this. The IWG (Informal Working Group) of the WP29 GRPE PMP (Particle Measurement Procedure) of The United Nations, established the GRPE-81-12 specification, as a conference document. The work of the IWG focuses on the development of the WLTP braking cycle and the measurement of braking emissions at the dynamometer level. The WLTP braking cycle has high requirements when performing the test, especially for the speed parameters, and, unlike the main wear standard used traditionally brake/rotor assessment, focus on the low service temperature range.
Both factors may drive some technological changes in the friction industry. One of the main factors that has been driving the development of friction materials is the wear resistance at high temperature. Changing the focus to the low temperature, due to the future homologation standards, may bring changes in formulation styles and row/materials. But also, new technologies that are being developed to reduce the brakes emissions may see a commercial future. Vacuum aspiration technology focus to capturing the particles, and has been shown to be effective in reducing brake particle mass (PM) emission by 85% and particle number emission by up to 90%. With current average brake PM emissions of 11 mg/km, this equates to emissions of 1.67 mg/km, a third of the most ambitious 5 mg/km limit proposed by CLOVE. Other technologies, like the hard-coated rotors, focus on eliminating the source of the problem, the particles itself, through the introduction of a wear resistant coating on top of the grey cast iron of the rotor. This technology is mainly related to the development of the Extra High Speed Laser Cladding coating technology.
How far emission regulation may transform friction industry is still to see. But there’s no doubt that after 35 years creating innovative, reliable, adaptable and sustainable solutions for friction industry, and making Innovation and growth-spirit attitude the axes of our success, at rimsa we are excited to see how far we are able to contribute in the solution to those challenges, also with our sister company Innovamat. More than ever, we have the opportunity to be People Rethinking Solutions.
