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A clear signal

Using Flexline technology MANN+HUMMEL is able to offer solutions which take complex installation space into account. The latest application is also characterized by the small but important detail of using vortex generators to ensure an optimum air flow to the air mass sensor and a particularly stable signal of the air flow.

If the objective is to systematically reduce vehicle emissions, the combustion process has to be precisely controlled. In diesel engines, air mass measurement is the central reference variable for combustion. Among other things, it is used to control the exhaust gas recirculation rate (EGR rate), to calculate the optimum diesel injection quantity and for loader protection. The air mass sensor requires an optimal, uniform and stable inflow in order to deliver a stable and unaltered measuring signal to the engine control system. In today's confined space conditions for air intake, this places particularly high demands on the design.  MANN+HUMMEL has addressed this challenge: The design made it possible to generate a stable flow field so that the hot film air mass meter (HFM) precisely determines the air mass and thus enables optimum fuel injection.

 ‘We wanted to develop an air cleaner system which meets the high requirements for the accuracy of the air mass measurement and also only requires a small amount of space. To do this we had to find a way to maintain a seamless air flow, even though there is a deflection right in front of the air flow sensor.’ 

Michael Frank, Lead Product Engineer at MANN+HUMMEL

Vortex generators to ensure an optimum air flow to the air mass sensor Vortex generators to ensure an optimum air flow to the air mass sensor

Ideal use of installation space

The challenge in the development process was the limited amount of installation space found in modern vehicles. It has to be shared by numerous components in order to meet the requirements which are the result of modern driving standards. In fact, the filtration experts found a solution in this respect some time ago with the development of filter elements with curved external contours. Flexline filter elements live up to their name and allow extremely flexible design possibilities which can be adapted to even the most complex installation spaces. Every inch is exploited.

The installation space saved in this process serves to increase the filtration surface and inflow area. This has a positive effect on service life, filtration performance and acoustics. These are advantages which Mercedes-Benz has already exploited with two air cleaner variants in the A-Class and now also with its new 1.6 liter and 2.0 liter 4-cylinder diesel engines. The way there, however, was not straightforward.

Superior signal quality

MANN+HUMMEL was able to achieve its objective with a small but ingeniously effective measure: the use of vortex generators. These inconspicuous spikes which are also known from the wings of small aircrafts prevent uncontrolled flow separation inside the air cleaner. As a result, the air mass sensor is optimally flowed into, resulting in a considerably stabilized air mass signal. This forms an important basis for good exhaust gas values.

The innovation of the system is underlined by the fact that this is the first air cleaner using vortex generators. Besides, the system also has something to offer when it comes to acoustics. In order to dampen the intake noise, the developers inserted an overmolded synthetic fabric with a porous structure into the dirty air duct to suppress disruptive resonance.

The clean air duct with its injection molded bellows enables an ideal compensation of movement between the engine and vehicle. A special collapsing core is used to enable its manufacture from high‑temperature resistant polyamide. In contrast to blow molded bellows, the exactly defined wall thicknesses of injection molded bellows offer more flexibility without having to make compromises regarding collapse stability or acoustics. A contribution towards the acoustics was also made by the broadband silencer with antechamber which dampens the undesired high‑frequency noise of the turbocharger.

Flexibility uses installation space

When the application is complex, it‘s time for Flexline. The air filter solution from MANN+HUMMEL even fits into very tight installation spaces. Mercedes-Benz is now the first vehicle manufacturer to use the innovative solution in a series application.