Building space is precious. In architecture as well as in automobile manufacturing. However, for design reasons an air filter requires a certain amount of space – depending on the engine even a significant amount – in order to allow the required air volume to pass through. This means that an air filter element for commercial vehicles can be of considerable size, depending on the size of the vehicle or engine.
As turbo charged engines allow higher power density and reduced exhaust emissions they are used more and more. Due to their particular design, the demand on combustion air and therefore space for the air filter is even higher. In other words, the engine compartment becomes more and more crowded.
The MAHLE air filter designers are faced with the challenge to achieve maximum functional density. In other words, to increase dirt collection capacity, reduce size and increase the time between servicing at the same time.
This has been achieved with a unique solution: away from the widely used star-shaped filter elements – and towards a main filter element in “wound design” with axial flow-through that offers exceptionally favourable aerodynamic characteristics.
This wound filter with the name SYMMETRIX® consists of a large number of filter channels that are closed alternately. The air flows into one channel, moves through the filter media, which cleans it from dirt, and leaves the filter element through the adjacent channel in the other direction.
Working principle of the wound filter:
(1) The contaminated air flows into the channels at the dirty side of the filter.
(2) The air flows through the filter medium and is cleaned from dirt.
(3) The cleaned air leaves the filter element.
An additional advantage: in contrast to conventional star-shaped air filter elements, the housing of the SYMMETRIX® filter element does not require additional volume for in-flowing and out-flowing air thanks to the in-line flow-through principle. The dirt collection capacity can therefore be increased by more than 2.5 times at the same physical size. The diagrams illustrate the increase in dirt collection capacity and reduction in required volume for the same dirt collection.
Comparison of dirt collection at the same housing volume.
Required filter volume at same dirt collection capacity.
Thanks to its metal-free design, the filter element can be incinerated completely, allowing environmentally friendly disposal.
FILTER MEDIUM: INNOVATION WITH NANO TECHNOLOGY
However, the performance increase of the new SYMMETRIX® wound filter is not only due to its special configuration – also in the filter medium no “fibre was left unturned”. In order to satisfy the high demands, a very thin filter medium has been developed with extremely high overall collection efficiency. This was achieved with a lining of nano-fibres. This increases the free flow area and reduces therefore the pressure loss in the filter. Depending on demands and applications in commercial vehicles, this medium can also be applied with a flame retardant impregnation.
ALL IN ONE (MODULAR) SYSTEM
The wound filter is also part of a complete-filter modular system for relevant applications such as agricultural machines, commercial vehicles or passenger cars. Matched to specific applications, various modifications are available. This includes a safety element that is fitted between the actual filter element and the engine – useful for combine-harvesters at harvest for example. The filter element ensures that no damaging dirt reaches the engine directly via the intake passage when a filter is replaced in the field.
An additional feature of this complete-filter is the so called pre-cleaner at the dirty side. Several cyclones (in this example 26, see picture) pre-clean here the intake air – in a simple but ingenious process: due to small wings, the air is made to swirl – and the resulting centrifugal forces move the coarser dirt particles from the air flow towards the outside. The accumulated dirt is continuously moved to the outside through an opening. The pre-cleaner can be washed out during an inspection or filter change.
As development partner of the automobile and engine industry, MAHLE is currently in dialog with renowned vehicle manufacturers to prepare the employment of the SYMMETRIX® in series production.
Integrated cyclones for effective pre-cleaning in the new SYMMETRIX®.
The three-part design of the pre-cleaner.