Juratek highlights brake emissions issues
Braking components provider Juratek has outlined the impact that friction brakes exert on the levels of particulate matter (PM) emissions in the atmosphere.
“Studies show that the major concentration of emissions occur in areas of high vehicle density and a built-up environment,” said Juratek.
“Currently the bulk of emissions are from the vehicle exhaust, but as these are reduced through new technologies such as plug-in hybrid (PHEVs) and battery electric vehicles (BEVs), non-exhaust emissions from our roads, tyres and brakes assume a greater significance, in particular those from the passenger cars and vans which populate our towns and cities across the nation.”
In performing their function, friction brakes wear and, in so doing, contribute particulate matter to the environment, Juratek says, suggesting that brake wear generates approximately 25 per cent of the annual PM2.5 and PM10 produced by all forms of road transport in the UK.
“This comes about due to a combination of the abrasion of the two braking surfaces rubbing together and the thermal decomposition of the friction material, in particular its phenolic resin binder which starts to degrade at temperatures of around 200°C,” said the company.
“The braking ‘couple’ comprises two elements, the friction material (brake pad or lining) and its mating surface (brake disc or drum). In Europe, the composition of the majority of brake pads are classified as either ‘low steel’ or NAO (non-asbestos organic) – both families use a phenolic resin binder, with the low steel materials having a superior wear resistance at heavier duties and higher temperatures.”
The brake disc is produced from grey cast iron with carbon content of around 3.2 – 3.8 per cent, says Juratek, together with alloying elements like copper and chromium to help promote strength and hardness.
“The disc brake, being open to the atmosphere, would be expected to emit more particulate matter into the atmosphere during operation than the drum brake which in effect is a ‘closed’ system, the wear particles generated by braking being contained, to a large extent, within the drum,” the firm continued.
“A considerable amount of research work has already been undertaken across the world to try to quantify the volume and size of particulate matter emitted by brakes under different braking cycles with different levels of energy loading and temperature, with the ultimate aim in the next few years of introducing some form of regulation aimed at restricting the amount of particulate matter they are allowed to emit; this work is not yet complete and hitherto has been focused almost entirely on light vehicle disc brakes.
“Much remains to be done and agreed, not least the most appropriate ‘real world’ braking cycle that will be used to measure the volume and size of the particulate matter emitted; of course any emission legislation cannot be at the expense of braking safety…
“From the work that has been done so far the results are what might have been expected, low steel materials are better (relatively lower in emissions) at higher duty and NAO materials lower at lower speeds and temperatures.
“One can imagine that the focus on emissions could lead to the use of more wear resisting friction couples and we already see limited application of carbon-ceramic brake discs on some models albeit at a significant on cost and more recently the introduction of brake discs with a super hard coating. Another approach is to partially enclose the brake and fit special filters to capture the bulk of particulate emissions. A combined approach is perhaps most likely.”
Heavy vehicles are a rather different proposition, Juratek says.
“They are not frequent visitors to city centres. They fit engine brakes and retarders which help reduce the overall demand on their friction brakes, especially on downhill descents, and of course drum brakes have made something of a comeback on trailers and these would be expected to retain much of the product of wear within the drum.
“As yet there is no quantification of the amount of PM emitted by heavy vehicle axle brakes in the variety of roles that these vehicles undertake so a lot of work will need to be done to arrive at real world data under different conditions of operation to allow for the creation of appropriate test regimes and sensible legal rule making.”
It concluded: “Given the general trend in the data, Juratek would expect our longer life pad grades to have relatively lower levels of particulate emission but we will continue to assess, work and develop to ensure our braking product remains safe, secure and meets any future environmental requirements. “
