great importance of aerodynamics can be illustrated by a number: in a modern
cab-over-engine truck in European long-distance operations, around one third of
the available mechanical energy is needed to overcome the air resistance. And
this is also reflected in the new Actros: the MirrorCam alone, which replaces
the traditional rear-view mirrors, contributes as much as 1.5 percent to the
overall fuel savings of the new Actros. New concave cab side deflectors on the
cab also make a contribution towards lowering the consumption.
improvements are due not least to intensive testing in the wind tunnel at
Daimler AG's Untertürkheim plant. There, the engineers simulated the flow
conditions around the truck with the aim of optimising the Cd value for wind
slip, and thus in turn also the fuel consumption. Especially with regard to the
MirrorCam, the tests in the plant provided valuable information.
the one hand for the aerodynamic design of the two camera arms and on the other
for the positioning of the camera arms on the right and left-hand sides of the
cab. Unlike conventional mirrors, these are fixed to the roof frame in the new
wind tunnel in Untertürkheim enables the developers to generate wind speeds of
up to 250 kilometres per hour.
The search for the optimum shape and position
how exactly has the team's work in the wind tunnel contributed to the further
improved aerodynamics of the new Actros? For example, by means of tests in
which the best position for the camera arms of the MirrorCam was determined.
Possible positions were the upper and lower sections of the A-pillar and the
upper part of the B-pillar. For these trials, a real Actros was used, on which
the exterior mirrors were replaced by prototypes of the camera arms – mounted
one after the other at the three test positions. The truck was placed on the
weighbridge in the wind tunnel and the fans were started. The use of a weighbridge
enabled the engineers to measure the air force acting on the vehicle as it
flowed around it. The result: the best position for the camera arms is on the
A-pillar in the area of the roof edge.
solution was also sought that would prevent stray light from above reducing the
performance of the cameras. In these tests, the small hood with which the
MirrorCam arms are now equipped prevailed. And the engineers were also
intensely involved in the development of the new, concave cab side deflectors.
The new cab side deflectors also contribute to the new Actros consuming less
fuel than any of its predecessors.
Considerable progress: a better view and greater safety
addition to keeping fuel consumption as low as possible, the engineers also
focused on keeping dirt out of the vehicle during their wind tunnel tests and
CFD analyses. Especially for safety-relevant areas such as the windscreen and
side windows, not to mention the lenses of the camera arms. The aerodynamics
influence how much dirt kicked up by your own vehicle and vehicles in front
actually remains stuck to the vehicle.
In operation for
decades: the wind tunnel in Untertürkheim
wind tunnel in Untertürkheim has been available to Mercedes-Benz developers for
eight decades. Through continued targeted modernisation, the system is kept at
the state-of-the-art. Two DC motors, each with an output of 250 kW, set the
nine-blade axial fan with its 8.5 metre diameter in motion – so powerful that
it can generate gusts of up to wind force 17. To do this, around 9,000 m3 of
air are blown horizontally through the 125-metre long, ring-shaped channel. In
the test area, the vehicle stands on a turntable with a diameter of twelve
metres, so that it can be exposed to the wind flow not only frontally, but also
laterally at any desired angle. Integrated into the turntable in addition to a
roller dynamometer is a six-component weighbridge. It is used for the highly
accurate determination of numerous forces, including the air force. The forces
are transmitted to load cells via levers and rods and can thus be evaluated.