Climatic Wind Tunnels

Weather at the touch of a buttonMercedes-Benz Climatic Wind Tunnel

Mercedes-Benz has inaugurated two new climatic wind tunnels at its Sindelfingen site, designed to bring extreme weather conditions indoors. Temperatures ranging from minus 40 to plus 60 degrees Celsius, hurricanes with wind speeds of up to 265 km/h, tropical rainfall and heavy snowstorms are all part of the standard repertoire available here to the test engineers. If needs be, they can even provide a realistic simulation of a mercilessly hot sun. The new climatic wind tunnels make it possible for the engineers to optimise new vehicles or components for all possible weather conditions at a very early stage of the development process. So in future, real-life road tests, in arctic cold or the blazing heat of the desert, will only take place with prototypes that have already reached an advanced stage of development by being thoroughly tried and tested under the most extreme climatic influences. This enables Mercedes-Benz to achieve the highest possible quality. The clear ambition to do so has been a key element in the philosophy of the world’s oldest automotive manufacturer for the last 125 years.

Cars these days first take shape on the computer. The initial crash tests, aerodynamic studies or suspension testing, too, are undertaken as electronic simulations in a virtual world, long before the first prototype is built. Simulations like this can never, however, replace the use of test rigs or real-life tests.

In order to close further the gap between simulation and real-life testing, Mercedes-Benz has now taken two new state-of-the-art climatic wind tunnels at its Sindelfingen site into operation, following two years of construction work. This marks the completion to schedule of the next stage of expansion for the Mercedes-Benz Technology Centre. Research, development, design, planning and production teams work together at the Sindelfingen location in a close network that is unmatched by any other automotive manufacturer in the world.

Vehicle testing in its finest form

One of the two new climatic wind tunnels is designed as a cold tunnel, with a temperature range of minus 40 to plus 40 degrees Celsius. The new hot tunnel, on the other hand, offers a temperature range of minus 10 to plus 60 degrees. Each tunnel is equipped with an integrated twin-axle roller dynamometer that allows speeds of up to 265 km/h – and thus with sufficient reserves for even sports cars to be tested on the rig here.

The new climatic wind tunnels replace the cold tunnel that has been used until now, in which temperatures down to minus 20 degrees Celsius and speeds of up to 64 km/h (40 mph) are possible, as well as a hot tunnel in which the maximum limits are plus 40 degrees Celsius and a top speed of 100 km/h (62 mph).

Dr Thomas Weber, Member of the Board of Management of Daimler AG responsible for Group Research and Mercedes-Benz Cars Development: “Even in the arctic regions of Sweden, the temperatures in winter are not always as low as we would like them to be for our test drives. Likewise, nor can we always rely on getting the extreme high summer temperatures we need for testing, even in America’s infamous Death Valley. In our new climatic wind tunnels we can create whatever climate conditions we want at any time of year, whenever we need them. And we can do so with very tight tolerances, so the measurements can be reproduced at any time. That’s just not possible out in the open air.”

As Ulrich Mellinghoff, Head of Mercedes Safety Development adds: “We don’t want to use the new climatic wind tunnels as a substitute for road testing, but we can now do less of it and are also far better prepared when we do go out. For example, if we have 20 different engine heat shields, we can already eliminate many of them in the climatic wind tunnel because they don’t have the desired effect. We will then go on to do real-life testing with just the most promising two or three variants. We therefore spare ourselves a lot of very time-consuming road tests early on, and yet our prototypes are still at a much further advanced stage of development. And that means that we can meet our very challenging objectives much sooner.”

Realistic road tests in all weather conditions

The scope offered by the new tunnels is indeed enormous. They can be used to simulate virtually any environmental impact under a whole range of operating conditions. Driving under either full or partial load can be simulated, at top speed or at the crawling speed of a traffic jam, uphill or down, in order to test the brakes to their limits. And pretty well any sort of weather is possible. Extremes of heat and cold, dry desert air or the humidity of the jungle, drizzle or a heavy downpour, sleet or snowstorm, cloudy skies or blazing sunshine – the test engineers have a vast repertoire of weather conditions at their fingertips.

They take advantage of this in order to test a vast range of vehicle components and functions. They can test, for example, the engine cooling system under very different stresses. Or they can check whether the air conditioning and heating systems are capable of regulating the interior temperature in all circumstances, so ensuring that the occupants remain comfortable. The engineers will also take a detailed look at the windscreen wiper function to see if the side windows stay clear in filthy weather. In the new cold tunnel, they can even find out if snow swirled up by a truck driving ahead of the car is likely to block the air intakes. And of course they also subject the vehicle electronics to extreme climatic conditions, and test dozens of other vehicle components in the weather test station. From an engineer’s point of view, it is particularly important that the tests can all be repeated at any time under precisely the same conditions in order to verify the results – a luxury that nature does not always afford.

Fit for the future with alternative drive systems

A further advantage of the new climatic wind tunnels: they are designed to accommodate the use of hydrogen and therefore eminently suitable for all alternative drive systems of the future. Special sensors and an effective air extraction system mean that fuel-cell powered vehicles can also be subjected to exacting test programmes here.

Wind and weather tunnel plus roller dynamometer – all in one

There is a lot of complex engineering behind the exceptional capabilities delivered by the Mercedes-Benz’s new climatic wind tunnels. Around two thirds of the new 18-metre-high building (59 ft), which covers an area 70 x 60 metres in size (230 x 197 ft), is taken up by the two test rigs and their associated offices, including the control room. Vast and very well insulated windows enable the technicians to monitor every test extremely closely and to regulate temperature, humidity and wind speed as well as other settings. During a test, the sensors in the various measuring devices transmit their data to computers, where it is then displayed on monitors.

In order to simulate the road surface in each of the tunnels, powerful electric motors are used to drive four precision-built rollers, each almost two metres in diameter. As a result, even all-wheel drive vehicles can be tested under realistic conditions. The new climatic wind tunnels are furthermore so designed that they can be used by Mercedes-Benz to test a broad range of vehicle models – from the smart to the Sprinter.

The test rig is designed with an overall output of 600 kW (816 hp); under overload conditions even 780 kW (1061 hp) is possible for short periods. As a result, top speeds of up to 265 km/h (165 mph) are possible. The maximum tractive force of the dynamometer is 12,000 N per axle, under overload 20,000 N (to put it another way: a force of 20,000 N is sufficient to accelerate 1000 kilograms to 72 km/h (45 mph) in one second; acceleration is thus 20 m/s2; as a comparison, gravitational acceleration in free fall is 9.81 m/s.2

During braking tests, the rollers produce a similarly high negative force. This allows, for example, the simulation of long downhill stretches in high summer temperatures, so putting far more strain on the brakes than would be conceivable in real life.

If the test vehicle’s wheels are being turned by the power of its own engine, the dynamometer takes the output produced by the vehicle engine and acts as a generator to convert this into electrical power, which it feeds into the grid. The dynamometer then produces electricity as it measures, so reducing energy consumption.

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