Cars did not always have cabin filters. Those who in 1970 purchased a VW Beetle, Opel Ascona, BMW 2 series, Mercedes Stroke Eight or any other model did find a ventilation system, but the air itself was directed into the interior of the car without any filtration. In the following years this changed as traffic increased and more air pollution was the result. Therefore the cabin air filter was introduced in the 1990s and today almost all European cars are equipped with one. That’s understandable when considering that modern filters retain significantly more than 90% of the particulates and depending on the version are able to remove harmful gases such as NOx, SO2 or ozone, allergens, bacteria or mold spores sucked in with the air.
To make this happen, naturally a lot of development work had to be done. MANN+HUMMEL has carried out research and development in this field for many years and has always come up with new innovative products. And even today, where filter technology has reached a very sophisticated level, we are still on the look-out for ways to improve the product. In this process we are not afraid to challenge technical standards in order finding new approaches.
How does a modern cabin filter work? In simple terms, the air sucked in flows through a specially pleated high performance filter media and retains almost all of the dirt particles contained in the air. If this filter media is combined with activated carbon or other special coatings, it is also possible to retain harmful gases, allergens or bacteria. In this process the filters exploit some physical characteristics.
On the one hand purely mechanical forces are at work, whereby pollutants are separated in the filter because due to their inertia they are unable to follow the flow, because on their random path through the fiber structure they get in contact with a fiber, or because they are simply bigger than the gap between the fibers. Beside that the filtermedia gets an further source of particle attraction and therefore it is given an electric charge in the production process. These so-called electret media are able to achieve a particle separation efficiency of 99% for particles down to a size of 1 micrometer. What more could one want?
But the electrostatic charge of the filter media has certain disadvantages. Environmental influences such as high temperatures and high air humidity can reduce the positive effect of the charge. The result is that the filtration performance is slightly reduced. It may increase again when more particles are separated in the filter and as a result the fiber structure starts to clog. Nevertheless there may be a temporary reduction in the filter performance.
Why not simply increase the mechanical filter performance by making the fiber structure in the filter media more dense? Unfortunately this would reduce the air flow to such an extent that either the ventilation would no longer be effective or stronger blower would be needed leading to noise issues. Therefore neither of the two options offer a comprehensive solution. The basic problem, however, has occupied myself and my development team at the Marklkofen and Himmelkron locations for some time now.
We have looked for ways we can effectively address the problem and have begun to explore the possibilities of nanotechnology. Special fibers which are manufactured using a so-called electrospinning process are around 1000 times thinner than the fibers found in conventional nonwovens. This enables the creation of denser structures. At the same time, due to the fineness of the fibers, existing blowers would not be overburdened by the filter.
We are still working on the development of these filters which may possibly become the next generation of cabin filters. But a prototype has already been installed in our fine dust eater vehicle to test it under real driving conditions and confirm what has been established in the laboratory, namely that the increased filtration efficiency remains for the complete life of the filter.
And if you consider all of the developments at the recent Frankfurt motor show, you will see that in fact we have been able to address a subject which is currently very topical. It will not take long for the first premium models to be fitted with a sensor which measures the level of particulates in the interior of the vehicle in real time. In this situation a cabin filter with a better function will achieve better results. This is why we will continue to carry out research and development because then at the very latest good will not be good enough!