Community Research and Development Information Service - CORDIS

Final Report Summary - REBRAKE (50% Reduction of Brake Wear Particulate Matter)

Particulates, also known as Particulate Matter (PM), are fine particles that can stand in the air. Particulate matter is frequently classified according to its size: PM10, PM2.5 and PM0.1 are particulates with an aerodynamic diameter smaller than, respectively, 10 μm, 2.5 μm and 0.1 μm. Very coarse particles (D > 10 μm) are generally filtered in the nose and throat via cilia and mucus meanwhile coarse particles (2.5 μm < D < 10 μm) can settle in the bronchi and lungs, and fine particles (0.1 μm < D < 2,5 μm) can easily penetrate into the lungs gas exchange regions. Ultrafine particles (D < 0.1 μm) or nanoparticles can reach intimate structure of tissues.
Whilst exhaust gases in the road transport are monitored and object of the European directives, less is known about the particulates originating from the wear of e.g. brakes and tyres.
In order to better understand brake wear emissions and aiming to improve the air quality, the REBRAKE ultimate and tangible objectives will consist in:
- At least 50% particulate matter (PM10) mass reduction from brake wear, in compliance with the EU2020 thematic strategy of 47% reduction of particulate matter by 2020;
- Deeper comprehension of the physical and chemical phenomena underlying the brake wear process, including higher comprehension and analysis of characteristics coarse, fine and UFP particles.

The REBRAKE project has been articulated in four phases. In the first phase of the project, the experimental brake tests consists in setting up experimental tests and elaborating PM collection methodologies. In the second phase, the collected particles, from conventional and, newly developed materials, are chemically and morphologically characterized and compared with literature results regarding human health impacts. In the third phase of the project, wear mechanisms are modelled and correlated to the actual brake system parameters and to the ingredients of the linings under investigation. In the fourth phase, novel brake systems will be engineered, in order to cut down the PM emissions by 50%. In this process inputs from different phases will be iteratively taken into account.

Work carried out to achieve the project's objectives:
The REBRAKE project chose as a reference a car representative of an average European car and defined several wear test cycles – the last of which represented real driving that happens on public roads –to be executed on an industrial dynamometric inertia bench. This latter test stand was engineering updated in order to be able to sample particles in an unbiased manner at the system level. Pin-on-disc test stand was also used. In both these test stands particles are sampled with a cascade impactor: this instrument enables measurements in real-time of particle size distributions in 14 size stages (from 6 nm up to 10 mm). The impactor technology makes it possible to collect particulates on filters in the different size stages and to conduct size divided chemical analysis of the particulates sampled. Both these test stand were used to screen and rank different pad and disc material, and to investigate which variables influence more the PM emissions, such as the temperature.
Numerical models to simulate the contact conditions at the pad to rotor interface on both microscopic level (CA) and macroscopic level (FE) were also developed. Both approaches were validated by comparison with results from the dynamometric bench tests. The CA can be used to study the local contact situation and the build-up and destruction of the contact plateaus, whereas the FE-approach can be used to study the influence of the calliper design on the macroscopic contact conditions and forecast the wear of the surfaces at the pad to rotor interface.
An experimental protocol for a streamline characterization of wear products was set. The experimental methodologies identified are X-Ray diffraction (XRD) and Energy Dispersive X-Ray Spectroscopy (EDXS) for bulk analysis, and Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and EDXS for single particle analysis. Wear tracks were observed to identify the main wear mechanisms.
The ultimate objective "At least 50% particulate matter (PM10) mass reduction from brake wear, in compliance with the EU2020 thematic strategy of 47% reduction of particulate matter by 2020" was targeted with modification of formulation of brake pads and different kind of modification of cast iron discs: in particular the focus was on the formulation of brake pads without copper because the utilization of copper in formulation of brake linings will be banned in close future. Moreover, the substitution of phenolic resin by cement binder was tested as the first environment friendly oriented formulation strategy. In the case of cast iron discs several modifications were discussed and tested: surface thermal treatment; coatings and brake discs with tuned chemical composition.
The results achieved in the REBRAKE project show that it is possible to reduce 50% the PM emissions with a specific material design of the tribo-couple, using as a reference modern pads without copper.

Potential impact and use:
The technical results obtained in the REBRAKE project are potentially useful from two different perspectives. First, the project boosted particle emissions knowledge. Indeed, the brake emission research is young. Since the beginning, the research focus has been to describe and characterize particles from different braking systems. However, few studies investigated the relations with brake system parameters, which has been done in the REBRAKE project constituting basic knowledge to start implementing particle emission into the brake system design phase. In addition a methodology for particle characterization has been developed, which could be used for future standards. Such knowledge has been disseminated, both in conferences familiar to the brake system community and in scientific journals. That already increased the public awareness, and boosted industrial research. The latter is taking a special advantage from the inertia dynamometric bench test design developed into the REBRAKE project. Indeed most of the relevant industrial player are proposing different design, clearly connected to the REBRAKE one.

Socio-economic impact of the project:
In urban areas, one of the major particulate matter emissions contributor is the road transport sector. The continuous improvements in exhausts technologies have led non-exhaust emissions to equal exhaust ones nowadays. Among the latter, particles generated by the braking systems are a primary emission source.
Thanks to REBRAKE , it is possible to claim that substituting all vehicles frictional couples with the less emission one indicated in the project results, the brake system contribution would be reduced by more than half, reducing its overall contribution to the exhaust sources, and maintaining a challenge on exhaust ones.
Since 2014, the REBRAKE researchers started to attend the Particle Measurement Program (PMP), managed by UNECE, where experts in particle emissions discuss on the ongoing research and try to develop a harmonized test cycle, and test stand to address particle emissions. The product of the PMP group would be of use for future regulations.
The REBRAKE project laid the foundations in terms of state of the art and test stands design, which is still considered from the experts the best configuration available. Most of the work is about to possibly improve it, and make the measurement system repeatable.
The huge quantity of instruments and actions adopted during the project execution, were able to guarantee during the professional development of the REBRAKE researchers. Furthermore, three of the researchers coming from Brembo, followed a PhD program as students within the University of Trento and Royal Technical Institute of Stockholm and currently are – or are going to be – fresh PhD.

More information about REBRAKE project is available at:

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