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EuroBrake 2022: Brake emission testing session overview

The Brake emission testing session will take place on Tuesday May 17th and will be chaired by Guido Perricone of Brembo S.p.A and co-chaired by Jens Wahlström of Lind University.

Topics and speakers for the session include:

Hard-metal-coated brake discs – impact of chemical and physical characteristics on fine dust emission behaviour

Manuel Wirth, Porsche AG

An upcoming fine dust regulation is recently the most challenging issue in the brake development of ICE vehicles. In regards of countermeasures to improve the fine dust behaviour the hard-metal-coated brake disc is one of the most promising ways to reduce the mass and number of brake fine dust particles.

According to the current publications of the PMP-group, todays foundation brake systems emit more the 10 mg per km fine dust in the size of PM10. Since an expected regulation reduces this amount significantly, the VW group is developing and monitoring the most promising approaches to fulfil the expected legislation. Our preferred idea is to prevent the production of fine dust.

To face this issue, high-speed laser gladded coatings on the brake disc friction surface is one of the mainstream technologies. Since we have a change in the tribology of the foundation brake system on the disc side, we are also developing with our partners adjusted brake pad materials.

This work focuses the influence of the mechanical and chemical properties of the brake disc coating on the fine dust emission behaviour. Therefore, we performed a test sequence with different tribological systems.

Application of regenerative braking using torque v. speed curves during inertia dynamometer tests for brake emissions

Carlos Agudelo, Link Engineering Co.

The automotive future is electric. And this future requires laboratory methods to characterize the particulate matter emitted by brakes fitted on vehicles with hybrid or fully electric propulsion systems.

Since adapting existing simulation technologies (like Hardware-in-the-Loop) may not apply to routine emissions testing, the industry needs a simplified method, which still yields relevant and useful results. Using functions that enable the emulation of the torque output of the electric machine during braking, provides an intermediate and practical platform to conduct testing. After explaining the key concepts and elements which comprise the torque v. speed and road load functionality, this paper presents results from three parts of the investigations.

The first part involves the use of Computer-Aided Engineering (CAE) tools to assess the regen torque v. speed curves relative to full vehicle simulation, the second part relates to the fidelity of the dynamometer torque v. speed curves replication close to the vehicle (validated) curves provided for the laboratory dynamometer tests. The third part of the paper presents results from applying the torque v. speed curves to the WLTP-Brake cycle developed by the UNECE/GRPE/PMP/IWG/TF1 and TF2 to present the effect of regenerative braking related to brake emissions.

When the three elements are understood and demonstrated (core concepts, validation to the vehicle, and application on the dynamometer), the automotive industry can pursue reliable and useful laboratory measurements for brake emissions from electrified vehicles. The work presented was a part of the development of the emission measurement procedure for electrified vehicles within Task Force 4 of PMP Group.

Investigations on the influence of pressure and velocity on the friction, wear, and emissions of different friction materials

Stefano Candeo, University of Trento

The design of new brake materials capable of reducing emissions is a very important and topical issue. A deep understanding of tribological mechanisms enables the design of friction materials with low emission characteristics. In addition to low emissions, the design of new friction materials must ensure excellent performance with stable coefficients of friction and low wear. Furthermore, the development and characterization of new materials take time and effort as there are many aspects to be considered and even small changes can generate substantial behavioural alterations.

In this study, to speed up procedures and provide a streamlined tool, a sub-scale dyno with a simplified cycle was used to investigate the correlations between the parameters of interest: friction, wear, and emissions. The sub-scale dyno was set up for the evaluation of emissions and it is embedded with an LVDT sensor for wear evaluations. Wear is expressed as the depth of wear (µm/brake) from LVDT measurement of different brake stops. Emissions were measured with an Optical Particle Sizer in the range of 0.3-10 µm and expressed in terms of mean concentration/brake. The brake cycle consists of a factorial design of experiment with brake blocks of repeated brake stops. Each brake block has fixed brake parameters of contact pressure and initial sliding velocity. The brake blocks were randomized in order to minimize the order effects.

Different friction materials (low-met, NAO, inorganic) were tested sliding against cast-iron discs. Initial sliding velocity was found a markedly more influencing parameter on the wear and emissions behaviours than contact pressure. In particular, the low-met friction material displayed an approx. cubic and monotonous dependence of the wear and emissions with initial sliding velocity. Whereas the NAO material showed a lower dependence with the initial sliding velocity. On the other hand, the inorganic material displayed a, not monotonous, behaviour regarding the wear and emissions at high velocity. Additionally, the characteristic relationships between the wear and emissions are proposed to describe the different tribological mechanisms.

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