When the German emissions sticker was introduced for cars in 2007 it wasn’t easy for a diesel driver to obtain one of the desired green stickers. In those days only roughly 20% of all diesel cars met the requirements necessary for the emissions class Euro 4. Today the situation has changed and one has to actually look around to even find a vehicle with a yellow or red sticker. The reason is that in the meantime more than 90% of all diesel cars are so clean that they are classified as Euro 4, 5 or 6.

Naturally, independent of the sticker, while the diesel engine has been modernized the subject of particulates has lost its intensity. In 2016, breaches of the limit values set by the EU of over 50 micrograms per cubic meter of particulate matter of the particle size PM10 on more than 35 days per year could only be observed in Stuttgart. In fact, ten years earlier across Germany there were 33 cities and local authorities which were partly many times above the limit value. Nevertheless, the particulates still exist. If the limit value today was only slightly tightened in accordance with proposals currently being discussed in the EU, a further 25 cities would join Stuttgart and have a serious problem. Given this scenario, is it advisable to further tighten the emission controls for cars?

dusty problem

Yes and no. As in the past, the traffic is only a part of the problem. It is responsible for half of the particulate matter load. Private heating systems, industry and agriculture share the other half of the load. Therefore it is a good idea to look for new solutions to reduce the particulates caused by traffic, even when on their own these measures can only solve a part of the problem.

MANN+HUMMEL has been doing research in this area for some years. We naturally know that only around 10% of the particulate matter from cars comes out of the exhaust pipe. The majority of the particulate matter comes from the abrasion of tires and brakes, road wear and dispersion of road dust. Even if we were all to drive through Stuttgart tomorrow with electric cars, the load would not really be much lower.

brake caliper

At this year’s Frankfurt motor show we will present a prototype which focuses on an area which few people anticipated, namely the brakes. A survey carried out by Swiss Federal Laboratories for Materials Testing and Research (EMPA) established that just the dust produced by brakes accounts for roughly a fifth of the particulates produced by traffic. If one considers that four new brake pads weigh approximately half a kilo which during the lifetime of the brake will be transformed into dust, the dimension becomes clear. Here we are not only talking about diesel engines, but also about all drive concepts, which includes 60 million cars alone in Germany.

brake dust particulate filter

It would be a good idea to filter the abrasive particles before they enter the ambient air. Therefore we have conducted research and developed a solution. In this process we have found a method which is currently able to collect about 80% of all of the particles resulting from the wear of the brakes directly at the place where the particles are created. We achieve this with a robust housing which is fitted close to the brake caliper. The housing contains a filter which is made of a temperature and corrosion-resistant material. It is designed to efficiently filter different particle sizes. That is necessary because 90% of brake dust consists of particularly small particles which can deeply penetrate the lungs. In addition, the geometry of the filter is designed to ensure that the air flow generated by the braking action exactly guides the particles into the filter but at the same time does not significantly hinder the cooling of the brake discs. The idea is for the filter change to only take place when the brake pads are changed, whereby development work in this respect is still ongoing.

dusty problem

In order to learn more about its application, our brake dust particulate filter is currently being tested under real driving conditions. For this purpose it has been fitted to our specially equipped fine dust eater vehicles. These vehicles have a filter installed on the roof which separates particulates from the ambient air. The vehicle occupants are also protected by an innovative cabin filter which as well as retaining dust is also particularly good at binding nitrogen oxides. The test is taking place in the region of Stuttgart. This is surely a good choice because as already mentioned the fine dust pollution remains a real issue in that place. At the present time, however, the driving of the fine dust eater has been interrupted due to the fact that the vehicle will exhibited until the end of September at the Frankfurt motor show. At the trade fair interested visitors can learn about the special technological solutions offered by the vehicle and also how MANN+HUMMEL is solving existing problems with new ideas.