Stuttgart, Jul 18, 2011
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 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.
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, which covers an area 70 x 60 metres in size, 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; under overload conditions even 780 kW is possible for short periods. As a result, top speeds of up to 265 km/h 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 in one second; acceleration is thus 20 m/s2; as a comparison, gravitational acceleration in free fall is 9.81 m/s2.
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.
From a light breeze to a hurricane
As a general rule: whatever the route profile, the vehicle and its components are always tested under real-life conditions with a flow of air around them. This is provided in both new test facilities by a powerful wind tunnel. Its turbine can produce any form of airflow required, from a light breeze to a hurricane. As an extreme example, snowstorms with hurricane-force winds of up to 200 km/h would also be possible. Even at wind speeds of over 100 km/h, a human being cannot stand without something to hold on to.
Of course the wind speed can also be regulated as required. The airflow is controlled via a speed-regulated fan as well as by air jets with an adjustable airflow cross-section. As a rule of thumb: the smaller the cross-sectional area of the jet, the higher the speeds that can be achieved. For tests with passenger cars, the usual cross-section is eight square metres; for larger vehicles such as the Sprinter, it is increased to twelve square metres. For the Mercedes-Benz SLS AMG and other sports cars, on the other hand, the test engineers will choose a smaller opening, with an airflow cross-section of seven square metres.
As well as by adjustment of the wind speed, the sensitive regulation of climatic conditions is made possible by the ability to set the relative humidity in both the cold and the hot tunnel to a level between 5 and 95 percent. The two climatic wind tunnels do however differ in their further details, in order to be able to fulfil the wide-ranging requirements of the engineers.
Arctic cold and snowstorms in the cold tunnel
The temperature range in the cold tunnel stretches from minus 40 degrees to plus 40 degrees Celsius and thus accommodates most normal weather conditions with a generous margin. At temperatures above zero, it is possible to simulate an hourly rainfall level of up to 80 litres per square metre. At sub-zero temperatures, it is not a problem to produce even the heaviest sort of snowstorm, in which the snowflakes fly into the test vehicles at 200 km/h.
One important area of focus in the cold tunnel involves the de-icing process. Here, the heating system has to de-ice the windows of a previously deep-frozen vehicle as quickly as possible. A camera meticulously records this defrosting process.
The cold tunnel is also fitted with equipment used to simulate the build-up of dirt. In this case, the vehicle is sprayed during the test with a liquid that is visible under ultra-violet light and so can be reliably used as a means of revealing potential weak spots, which show up in the automatic photographic and video records of the test.
Simulating the desert sun in the hot tunnel
In the hot tunnel, it is possible to generate temperatures in the range from minus 10 to plus 60 degrees Celsius. The facility also includes a system for simulating the sun. Its 32 lamps radiate light with an intensity range equivalent to that of real sunlight. Over an area of 8 by 2.5 metres, it is possible to regulate this intensity to between 200 and 1200 watts per square metre. The higher figure here is comparable with the intensity of the real sun only as experienced in very few places in the world – such as Death Valley in the USA or in one or two remote desert locations. Even there it is only reached around midday when the sun is vertically overhead, corresponding as it does to a temperature of more than 50 degrees Celsius.
In the new Mercedes-Benz hot tunnel, the whole sun simulation system can be tilted sideways to as far as just five degrees above the horizon. This makes it possible to imitate very realistically the course of the sun through the day or to conduct meaningful tests in conditions involving strong sunlight from one side. Even rapid fluctuations of light and temperature, such as those experienced when clouds appear or when driving into a tunnel, can be included in the test programme. Fine mesh panels can be pushed over the front of the lamps to simulate the effect of clouds, while solid covers can be put over the lamps to imitate the abrupt change of light that comes when entering a tunnel.
A further development tool used in the new hot tunnel is the Hot Road, a simulated hot road surface, the temperature of which can be set on a continuously variable scale to between 50 and 70 degrees Celsius. This is used to simulate the heat radiated by a road in summer, as a means, once again, of creating conditions that are as realistic as possible.
In case of an unexpected incident, both hot and cold tunnels are equipped with a high-pressure water mist extinguishing system. Should, for example, a vehicle component catch fire, perhaps as a result of overheating brakes, jet nozzles will shoot up out of the floor in just fractions of a second to smother the fire in a fine mist of tiny water droplets. This mist has the effect of cutting off the supply of oxygen to the fire, while the large surface area of the water droplets also cools the vehicle down and prevents any further fire. Another positive effect: even if a test engineer is still inside the vehicle, the extinguishing system can nevertheless be immediately triggered.
Furthermore, by using this form of extinguisher, damage to the costly prototype is kept to a minimum.
Efficient preparation ensures good usage levels
The main objective for Mercedes-Benz in building the two new climatic wind tunnels was to use efficient methods to improve vehicle quality still further. This meant bringing nature, with all its extremes of weather, right into the test facility.
But efforts to achieve efficiency do not end at this point. The facility around the two climatic wind tunnels also includes six conditioning chambers in which the prototypes are prepared for testing. In these the vehicles can, for example, be pre-cooled before being taken by an ingenious new transport system, in less than ten minutes, to the large climatic wind tunnels. Once in the tunnel they can even be refuelled during endurance testing with preconditioned fuel.
Two of the six conditioning chambers also have acoustic insulation shielding them from external noise. These conditions provide the ideal environment for the engineers in which to track down those irritating switching or clicking sounds that only occur under certain climatic conditions.
A large workshop area with all the relevant machinery and workshop equipment facilitates this advance preparation of the vehicles. Changes to vehicles or further preparation work can thus be completed on-site within a very short space of time, without the need to transfer vehicles to outlying workshops.
Measures such as these ensure that the time actually spent in the costly climate tunnels is kept to a minimum and that each vehicle can be very quickly followed by another. The aim is to maximise the use made of the facility. This objective has already been met, for just a few weeks after the first trial run, the facility is currently operating with 20 members of staff working in two shifts.
More effective road tests, around the world
The results from the climatic wind tunnels are confirmed, as ever, in real-life testing in some of the most extreme climatic conditions on earth, such as the deserts of Dubai or Namibia, the heat of Death Valley, the cold and snow of northern Sweden or the heat and humidity of the tropical jungle. But this road testing now no longer needs to start quite so early, and is used essentially for verification purposes. This, in turn, has a further side effect: the engineers and prototypes no longer need to fly so often to those far-flung corners of the earth, while the total number of test kilometres driven is also much lower. The overall ecological impact of every vehicle is therefore very positively reduced.
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© 2011 Daimler AG. All rights reserved.