The first two decades of the automobile were marked by permanent engine failures – in particular, due to the high dust concentration on the unpaved roads in those days. The dirt particles reached the combustion chambers, where they caused severe abrasions of the piston rings, pistons and cylinder walls. This resulted in reduced engine power or even the dreaded piston seizures. Only when the so-called air cleaners were invented in the mid-30s, repair and service intervals of up to 4,000 km could be reached. The success story of the internal combustion engine is therefore hard to imagine without air filters. However, it has been a long journey from the first oil bath air filter of the 30s to the modern air intake modules of today.
 | | The beginning: a mesh of wires
In the first air filters, the filter element was a wire mesh enclosed by a metal housing. The working principle of the so-called “oil bath air filter“ was based on physical flows. The deflection of the air stream in the metal mesh produced a sieving effect that was utilized to separate the dirt. In order to collect the dirt the steel mesh was covered with engine oil. These filter elements had to be dismantled regularly, cleaned with cleaner's solvent and finally covered in oil again. |
As engines became more and more efficient and fuel consumption decreased at the same time – the air requirement increased many times over. Filter elements made from wire mesh had now reached their limits, even when they were later combined with textile inserts.
In addition, filtration had to become finer and finer. There was also the demand to save weight and reduce size – and to cut back on servicing requirements in several respects. An oil filter needing extensive cleaning and problematic disposal did not meet the demands any longer: a new type of air filter system had to be developed.
An important innovation: Filters made of paper
When filter elements made of paper came on the market in 1953, they soon superseded the earlier metal mesh elements thanks to their far superior filter performance.
Only a short time later, in 1957, the Knecht Filterwerke (today: MAHLE Filtersysteme) developed a special kind of folding system for the filter paper and took out a patent under the trademark “MICRO-STAR“ for this system. This pleat system is still the standard in filter technology to this day.
The design of air filters has been adapted to meet the changing demands all the time. Initially, circular filter elements were used: a circular filter element is made from filter paper that is fixed with PUR foam. In order to separate dirt side and clean side at the pleat ends, these were sealed by a PUR end plate with sealing rib. This system of circular air filters is still used to this day.
The present time: Variable-length intake manifolds and complex intake systems
Already in the 90s, MAHLE developed so called variable-length intake manifolds in close cooperation with the automotive industry. On the one hand, this allows the engine to generate high torques even at low engine speeds and high peak power at high engine speeds on the other. A tumble flow that is generated deliberately in the combustion chamber (see text to the right) improves mixture formation and the combustion process. This results in reduced fuel consumption and exhaust emission.
Apart from air filtration, the complete intake systems used in modern engines with fuel injection systems have a number of additional tasks. Today's air filter housings often contain an airflow mass meter, a blow-by gas recirculation intake (see text to the right) as well as a service indicator and a heat shield that protects from direct thermal stress. Accordingly high are the demands on MAHLE as development partner and system supplier of the international automotive industry.
A glimpse ahead: The three-stage resonance system
Another milestone in air intake module technology is the threestage resonance system developed by MAHLE, which can be controlled via two flaps integrated into the intake manifold. Resonance charging is effective over a wide speed range in three engine speed stages up to 7,000 rpm. The resonance system, which has been optimized and virtually verified with the aid of charge calculations, has already been used successfully in practice. MAHLE offers a range of products and developments that goes also here far beyond air filtration and includes control units for the resonance system and a crankcase ventilation system with oil mist separator, pressure control and feed line into the air intake module.