A Study of the Effect of Brake Pad Scorching on Tribology and Airborne Particle Emissions

Mara Leonardi,Stefano Gialanella,Jens Wahlström,Guido Perricone,Minghui Tu,Ulf Olofsson,Yezhe Lyu

doi:10.3390/atmos11050488

Mara Leonardi, Stefano Gialanella + Show 5 more

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https://doi.org/10.3390/atmos11050488

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Abstract

Non-exhaust wear emissions from disc brakes affect the air quality in cities throughout the world. These emissions come from the wear of the contact surfaces of both the pads and disc. The tribological and emissions performance of disc brakes strongly depend on the contact surface characteristics of the pads and discs. The surfaces of conventional pads are scorched by heating it to several hundred degrees to make the resin carbonize down to a few millimetres deep into the pad. This is done to have a shorter run-in period for new pads. It is not known how scorching will affect the amount of airborne particle emissions. Therefore, the aim of the present study is to investigate how pad scorching influence the airborne particle emissions. This is done by comparing the pin-on-disc tribometer and inertia dyno bench emission results from a Cu-free friction material run against a grey cast iron disc. Three types of modified friction material surfaces have been tested: scorched, extra-scorched and rectified. The results show that the level of scorching strongly affects the airborne particle emissions in the initial phase of the tests. Even if the scorched layer is removed (rectified) before testing, it seems like it still has a measurable influence on the airborne particle emissions. The results from the tribometer tests are qualitatively in line with the inertia dyno bench test for about the first forty brake events; thereafter, the airborne particle emissions are higher for the scorched pads. It can be concluded that it seems that the level of scorching has an adverse influence on both the tribological performance and level of particle emissions.

Highlights

Emissions from the transport sector is one of the main contributors to the total airborne particle emission in urban areas [1]
It should be noted that electric vehicles are about 25% heavier than equivalent internal combustion engine vehicles [5,6], which means that the non-exhaust wear emissions are expected to increase in the future
It should be noticed that the coefficient of friction (CoF), air flow rate (Qair ), particle number concentration (PNC) and PM10 are only evaluated after running-in, while the mass losses of the pin and disc samples correspond to the whole test

Summary

Introduction

Emissions from the transport sector is one of the main contributors to the total airborne particle emission in urban areas [1]. Exhaust and non-exhaust emissions (airborne wear particles from tyres, roads, clutches and brakes) contribute to the total traffic generated emissions [2,3]. It has been reported [4] that wear emissions from brake systems contribute up to 55% of the non-exhaust airborne emissions. Some electric vehicles use regenerative brakes on the driving wheels, but they are still equipped with mechanical brakes on all axles. A major drawback with regenerative brakes is that the efficiency is very low at low vehicle speeds [7] and, the mechanical brakes are used

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