The new Euro 7 standard is set to be in place by 2025, which will be the first legislation that will cap the emissions produced by a brake system. This has caused brake manufacturers to find alternative solutions to reduce the emissions generated from the conventional cast iron friction brake system. With electric vehicles (EVs) becoming the future of the modern vehicle, their regenerative braking system will cause the friction brakes not to be used as frequently as for an internal engine combustion vehicle. This may lead to a build-up of corrosion on the brake rotor that may not only affect the performance and service life of the brakes but also increase particle emission when braking. Aluminium metal matrix composite (Al-MMC) rotors could be an alternative solution to reduce the risk of corrosion failure, possibly produce lower brake emissions and also improve the efficiency of the EV by reducing its un-sprung mass. To understand the interrelation between brake rotor corrosion and particulate emission, this study concentrates on quantifying such emissions from an Al-MMC friction brake both before and after exposure to a corrosive environment. A ‘drag braking’ duty cycle was chosen for this dynamometer study, as this produces near steady-state conditions at the friction interface. Each test was run at a constant speed of 150 rpm and at three different brake hydraulic pressures, 5, 7.5 and 10 bars. The duration of each test was 90 minutes and each test was repeated three times. The brake pad material used was specifically designed to work on the Al MMC rotor which consisted of 30% silicon carbide reinforcement in an Al alloy matrix. Tests were conducted within an enclosed chamber on the Leeds brake dynamometer and airborne emissions were sampled using a Dekati electrical low-pressure cascade impactor (ELPI+). Tests were first conducted on the newly-machined uncorroded Al-MMC rotor surface The corrosion test consisted of exposing this brake rotor to a corrosive environment in a salt spray chamber for 96 hours. The salt spray conditions were based on the ASTM B117-11 standard. The corroded brake disc then underwent the same drag brake duty cycles repeated three times for each pressure condition. The brake wear particles were collected within the 14 stages of the ELPI+ and subjected to post-test analysis as described below. The post-test analysis consisted of using different microscopy techniques to investigate the topography and composition of the brake wear particles. Gravimetric wear measurement methods were also incorporated into the post-test protocol. Advanced characterisation techniques such as energy-dispersive X-ray spectroscopy (EDX) and secondary electron microscope (SEM) were used to characterise the surfaces of the brake pads and to characterise and identify the elements of the brake wear particles collected from the ELPI+ before and after the corrosion cycles. The results were compared with the corresponding emissions from a conventional grey cast iron rotor subjected to the identical corrosion and brake test cycles.
Mr. Ishmaeel Ghouri, PhD Student, University of Leeds; Prof. Richard Barker, Professor, Univeristy of Leeds; Prof. Peter Brooks, Associate Professor, Univeristy of Leeds; Prof. David Barton, Professor, Univeristy of Leeds