Guido Perricone

Towards a test stand for standardized measurements of the brake emissions

Brake-related particulate matter contributes considerably to the non-exhaust emissions of the transport sector in urban areas of the world. The airborne particle emissions from automotive brakes currently lack any proper regulations. Future regulations require test stands, test cycles and particle instruments to be suitable for measuring the brake emissions. This present work focuses on the design of a novel test stand for reliable measurements of the brake emissions with a high sampling efficiency. A test stand in the form of an inertial disc brake dynamometer was redesigned to allow control of the cleanness of the incoming air and to assure isokinetic sampling. The cleanness of the incoming air, together with an over-pressurized chamber around the brake assembly, ensures that all the particles measured originate from the brake materials. In order to evaluate the novel design, the number and size distributions of the brake emissions are measured online with and without control of the cleanness of the intake air. The results reveal that this test stand can be proposed as a standard test stand to assess objectively the emissions of airborne brake particles in future regulations.

Towards the ranking of airborne particle emissions from car brakes – a system approach

Airborne particulate matter emitted from motor vehicle brakes is a contributor to urban air quality. Therefore, a method to rank brake pairs (pads and rotors) with respect to their particle emission factors in a reliable way is needed to develop a low-emission disc brake. A novel inertial disc brake dynamometer designed for brake particle emission studies, a modified SAE J 2707 cycle, an electrical low-pressure cascade impactor and a filter are used to test five different pad materials against cast-iron rotors. By changing only the pad materials, it is shown that the differences between the mass emission factor and the number emission factor of the the worst brake pair and those of the best brake pair decreases by more than four times and 19 times respectively. Furthermore, the results show that the material combination ranked the best in terms of the mass emission factor is ranked the worst in terms of the number emission factor. The results reveal that this combination of a test stand, a test cycle and particle instruments can discriminate between different brake pair materials in a reliable way in the case of the mass emission factors while more research has to be carried out in the case of the number emission factors.

Sliding Behaviour of Friction Material Against Cermet Coatings: Pin-on-Disc Study of the Running-in Stage

Running-in is the initial stage during which a tribological system reaches a steady-state condition. In this study, the running-in behaviour of a commercial brake friction material, pin-on-disc tested under dry sliding conditions, has been investigated to understand the role of different surface finishing of hard coatings. These coatings were deposited onto cast iron counterface discs and then mechanically polished to achieve set values of average roughness, Ra, and roughness skewness, Rsk. The tribological data were modelled using an exponential relation for the wear rate, according to a literature approach. The model parameters were related to the above-mentioned disc surface roughness parameters. The results provided indications on the wear mechanisms acting during the sliding action. Furthermore, these mechanisms were correlated with the formation of the friction layers on the pins and on the disc wear tracks. Of particular relevance is the finding that a negatively skewed surface roughness is fundamental to achieve the best running-in performances. The beneficial effects, coming from this surface treatment, are derived from the reduction in abrasion and from the improved formation dynamics of the friction layer, with particular regard to those parts (secondary plateaus) made of compacted wear debris.

Scaling effects of measuring disc brake airborne particulate matter emissions – A comparison of a pin-on-disc tribometer and an inertia dynamometer bench under dragging conditions

An important contributor to non-exhaust emissions in urban areas is airborne particulate matter originating from brake systems. A well-established way to test such systems in industry is to use inertia dynamometer benches; although they are quite expensive to run. Pin-on-disc tribometers, on the other hand, are relatively cheap to run, but simplify the real system. The literature indicates promising correlations between these two test stands with regard to measured airborne number distribution. Recent studies also show a strong dependency between the airborne number concentration and the disc temperature. However, a direct comparison that also takes into account temperature effects is missing. The aim of this paper is, therefore, to investigate how the transition temperature is affected by the different test scales, under dragging conditions, and the effects on total concentration and size distribution. New and used low-steel pins/pads were tested against cast iron discs/rotors on both the aforementioned test stands, appositely designed for particulate emission studies. A constant normal load and constant rotational velocity were imposed in both test stands. Results show that a transition temperature can always be identified. However, it is influenced by the test scale and the frictional pair status. Nevertheless, emissions are assessed similarly when an equivalent frictional pair status is analysed (e.g. run-in). Further investigations for fully run-in samples on the pin-on-disc should be performed in order to finally assess the possibility of using the tribometers for the initial assessment of different friction materials.