Preliminary Comparisons of Particulate Emissions Generated from Different Disc Brake Rotors

Abstract

Lightweight disc brake rotors have become a popular alternative to conventional grey cast iron (GCI). The thermal and tribological response of these brake rotors will differ during a braking operation. This may result in the generation of particulate wear debris with different characteristics, which can affect the environment and human health to different degrees. Studies have shown a relationship between adverse health effects and the characteristics of airborne particulate matter such as particle size, concentration and chemical composition. In this study, the particulate matter released from a novel lightweight disc brake rotor is compared to that released from the conventional grey cast iron rotor. The lightweight brake rotor was made of aluminium alloy (Al6082) and its rubbing surfaces were treated using the Plasma Electrolytic Oxidation (PEO) process. The process produced hard, dense, wear-resistant and well-adhered alumina coatings of approximate thickness 50 microns. A novel test rig was developed based upon the existing Leeds full-scale disc brake dynamometer. An enclosure was constructed around the brake assembly and ducting was carefully designed to ensure the cleanliness of the intake air to the system. Both brake rotors were tested under drag-braking conditions of constant sliding speed and applied braking pressure. Three braking test conditions with hydraulic pressures of 5, 10 and 15 bar at a constant speed of 135 rpm were selected from initial brake dynamometer tests. Braking test parameters of rotor rubbing surface temperature and coefficient of friction were measured during the tests and their effect on the brake wear particle characteristics were investigated. To measure and collect airborne brake wear particles, the Dekati ELPI+ unit was utilised along with a custom-made probe. This probe was made of stainless steel and its geometry was tailored to comply with the isokinetic concept. A scanning electron microscope (SEM) equipped with an energy-dispersive X-ray spectroscopy (EDX) system was utilised to investigate the morphology and chemical composition of the airborne brake wear particles collected by the Dekati unit. The initial comparison results showed that the PEO-treated lightweight aluminium alloy (PEO-Al) rotor has the potential not only to significantly reduce the unsprung mass of the vehicle but also reduce particulate matter emissions compared with the standard GCI rotor. The results also revealed that the percentage of iron contained in the PEO-Al debris was about threefold lower than that from the GCI rotor under all steady-state drag braking conditions studied which may have important health implications

The Effects of Corrosion on Particle Emissions from a Grey Cast Iron Brake Disc

“…The present study shows that, as the brake pressure increases, the particle mass emissions decrease. A similar study carried out by Asmawi et al [30] found that the particle mass emissions in the PM10 category also decreased as the brake pressure increased. This decreasing particle mass with the increase of brake pressure could be attributed to the reduction in COF at higher brake pressures which was also reported by Asmawi et al [30].…”

“…A similar study carried out by Asmawi et al [30] found that the particle mass emissions in the PM10 category also decreased as the brake pressure increased. This decreasing particle mass with the increase of brake pressure could be attributed to the reduction in COF at higher brake pressures which was also reported by Asmawi et al [30]. The influences of the tribolayer not only affects the braking performance but also the formation of surface corrosion.…”

“…The results suggest that the brake wear particles damage tight junction cells and increased pro-inflammatory responses. Asmawi et al [30] investigated the particle emission from a conventional GCI rotor and a lightweight aluminium alloy with an alumina coating produced by the Plasma Electrolytic Oxidation (PEO) process. It was found that the GCI brake disc produced significantly more particle mass emissions compared to the PEO-coated disc.…”

“…A Dekati ELPI+ impactor is used to collect and measure the brake wear emission through an isokinetic probe inserted in the outlet ducting. The air sampling volume rate and the probe geometry have been tailored to provide isokinetic sampling conditions [30]. The Dekati ELPI+ is capable of measuring in real-time the particle number and mass distribution using a 14-stage impactor with particle size stages ranging from 10 µm down to 6 nm [35].…”