June 9, 2005 Bionics, the combination of biology and technology is a recent field of research which has nonetheless already made remarkable progress possible in different areas. Nature has provided ideas for high-strength materials, dirt-repellent coatings and even Velcro fastenings and this has lead to an interdisciplinary project combining biologists and engineers the Mercedes-Benz Technology Center (MTC) to develop the Mercedes-Benz bionic car - a concept vehicle based on examples in nature. Engineers looked for specific example in nature whose shape and structure approximated to their ideas for an aerodynamic, safe, spacious and environmentally compatible car. Using these examples, the team designed and constructed a vehicle with intelligent lightweight construction and extraordinary aerodynamics.
Leaving familiar paths and giving new ideas a chance is one of the core philosophies of DaimlerChrysler that has enabled it to remain a technological leader among automobile manufacturers for a century. The company was founded on the creativity of its engineers and on their enthusiasm for visions and little has changed to the present day - Daimler Chrysler specialists take up the challenge to shape the future of the automobile on a daily basis.
It was upon these principals that the unique bionic car research project was founded - in order to create trailblazing innovations for even more safety, environmental compatibility and comfort, interdisciplinary thinking was employed to consider all the possibilities offered by technology and science.
This was not a matter of detailed solutions but of a complete transfer from nature to technology – a first. This required teamwork: biologists, bionics scientists and automotive researchers from various disciplines embarked on an extraordinary expedition into the animal kingdom which soon led them into the depths of the underwater world where they found a surporising technological role-model.
The boxfish – angular streamlined
It was not the fast, sleek swimmers such as the shark or dolphin that came closest to the ideals of the research engineers, but a creature that looks anything but streamlined and agile at first sight: the boxfish.
The boxfish has its home in the coral reefs, lagoons and seaweed of the tropics, where researchers found it had a great deal in common with automobiles.
Firstly, it is designed by nature to be frugal – to move with the least possible consumption of energy - which requires powerful muscles and a streamlined shape.
Secondly, it must withstand high pressures and protect its body during collisions, which requires a rigid outer skin.
And finally, it must also be highly manoeuvrable as it needs to move in the confined spaces of coral reefs in its search for food. Accordingly, researchers soon began to view the boxfish quite differently, and realise there was far more to its raw-boned design than initially meets the eye: despite its angular body, it is an excellent swimmer whose cube-shaped structure is by no means a hindrance.
On the contrary, the boxfish possesses unique characteristics and is a prime example of the ingenious inventions developed by nature over millions of years of evolution.
The basic principle of this evolution is that nothing is superfluous and each part of the body has a purpose – sometimes several purposes.
The outer skin of the boxfish consists of numerous bony, hexagonal plates that are interlinked to form a rigid “suit of armour”. This bony, armour-plated structure gives the body of the fish great rigidity, protects it from injury and is also the secret of its outstanding manoeuvrability, as tiny vortices form along the edges on the upper and lower parts of the body to stabilise the fish in any position and ensure that it remains safely on course even in areas of great turbulence.
It does not need to move its fins in the process, and can therefore conserve its strength. Applied to automotive engineering, the boxfish is therefore an ideal example of rigidity and aerodynamics.
Moreover, its rectangular anatomy is practically identical to the cross-section of a car body. And so the boxfish became the modelfor a so far unique automotive development project.
The aerodynamic boxfish
The first sub-project tackled by the engineers at the Mercedes-Benz Technology Centre and DaimlerChrysler Research concerned aerodynamics.
In wind tunnels and water channels they examined how the attributes of the living model could be transferred to an automobile. The results are impressive.
Despite its angular structure, the boxfish had similar aerodynamic qualities to the teardrop – a shape which streamlining specialists consider to be the ideal aerodynamic form. When exposed to an open flow, this streamlined shape has a Cd value of 0.04. Using computer calculations and wind tunnel tests with an accurate model of the boxfish, the Mercedes engineers achieved a value which came very close to this ideal, namely 0.06 – an outstanding result. It explains why the boxfish is such a good swimmer and is so manoeuvrable with minimal effort.
To make use of the aerodynamic potential the specialists in Stuttgart first created a 1:4 scale model car whose shape substantially corresponded to the boxfish.
The angular outside contours of the living model were adapted in the area of the roof and side skirts, as was the prominent, descending rear end with its heavily scalloped sides and pronounced wedge shape.
In doing this they were disobeying important principles in automotive aerodynamics, and were all the more surprised at the results: the Cd value for the car was 0.095. In aerodynamic terms it was just as good as the shape – as measured on the ground - considered ideal by aerodynamics specialists (Cd 0.09).
The research model in the shape of a boxfish betters the drag coefficient of today’s compact cars by more than 65 percent.
Building the full-size car
Once the theory had been established, the second phase of the bionic car project got underway - to develop a full-size, roadworthy automobile on the basis of the boxfish contours – a fully equipped model for four occupants, with typical Mercedes attributes in terms of safety, comfort, design and day-to-day practicality, and equipped with all the technology necessary for minimal fuel consumption and the best possible environmental compatibility.
The result of this unique vehicle project is a compact car with two doors, four comfortable single seats, a panoramic windscreen, a glass roof and a large tailgate – 4.24 metres long, 1.82 metres wide and 1.59 metres high.
Naturally the exacting requirements with respect to practicality, everyday suitability and design made compromises compared with the 1:4 model necessary, but the concept car still retains outstanding aerodynamic characteristics: with a Cd value of 0.19 the fully-functioning and driveable Mercedes-Benz bionic car is among the aerodynamically most efficient in this size category.
In addition to the boxfish-like basic shape, this result is made possible by a number of other aerodynamic features, e.g.rear wheels which are almost completely shrouded with sheets of plastic, flush-fitted door handles and the use of cameras instead of exterior mirrors.
In the Mercedes study, the optimal aerodynamic properties derived from the boxfish and a new lightweight construction concept taken from nature create the conditions for excellent performance and fuel consumption.
Equipped with a 103 kW/140-hp direct-injection diesel engine, the concept car consumes 4.3 litres of fuel per 100 kilometres (combined), making it 20 percent more economical than a comparable standard-production model.
In accordance with the US measuring method (FTP 75) the range is around 70 miles per US gallon (combined), which is about 30 percent more than for a standard-production car.
At a constant speed of 90 km/h the EU fuel consumption falls to a mere 2.8 litres per 100 kilometres – corresponding to 84 mpg in the US test programme.
Nature’s construction principles
Biology not only provides ideas for aerodynamic efficiency, but also gives impulses for innovative lightweight construction methods.
Both the external armour-plating of the boxfish and the bone structures of other creatures show how nature achieves maximum strength with the minimum use of materials.
Bone structures are always in accordance with the actual loads encountered. In the case of the human thigh bone, for example, the position and strength of the bone matter is precisely right for the tensile and pressure loads which the limb must withstand.
It is not only bone structures but also tree branches and roots that grow according to biological laws – a perfect lightweight construction strategy on the part of nature.
In consultation with bionics experts, DaimlerChrysler researchers have developed a computer-assisted process for transferring the growth principle used by nature to automobile engineering. It is based on the SKO method (Soft Kill Option).
Computer simulation is used to configure body and suspension components in such a way that the material in areas subject to lower loads can be made less resistant, and can perhaps even be eliminated ("killed") completely, while highly stressed areas are specifically reinforced.
This bionic SKO process enables an optimal component geometry to be identified which meets the requirements of lightweight construction, safety and durability in equal measure. The hexagonal scales of the boxfish likewise obey the principle of maximum strength for the least weight. Transferred to the external panelling of a car door, this natural construction principle produces a honeycomb pattern with up to 40 percent more rigidity.
If the entire bodyshell structure is configured according to the SKO method, its weight is reduced by around 30 percent – while retaining its exemplary stability, crash safety and handling dynamics.
In this area too, bionics can therefore make a further major contribution to greater fuel economy.
Key data at a glance
Length/width/height - 4243/1815/1594 mm Wheelbase - 2568 mm Engine output - 103 kW/140 hp Max. torque - 300 Nm at 1600-3000 rpm Fuel consumption (combined) - 4.3 l/100 km; 70 mpg (US gallons) Acceleration 0-100 km/h - 8.2 s Max. speed - 190 km/h
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