Banishing dirt

From distance measurement sensors to radar and lidar, the higher the degree of automation in advanced vehicles, the more important the sensors involved are. They have to work at all times, whatever the weather conditions – but it doesn’t take long for them to run into their limits if a film of dirt obscures the lens. IAV has developed a simulation method that identifies which parts of the vehicle will be least affected by spray, snow, or dirt even before the first prototype is built – making these areas perfect for sensor placement.

An autonomous vehicle glides soundlessly along the autobahn. All the occupants hear is the rain pattering against the windows. Suddenly, the car slows. The occupants look up from their tablets and toward the instrument cluster, which is blinking madly and displaying error messages – finally, the vehicle comes to a complete stop. The sensors are dirty. The car can no longer recognize its surroundings correctly, so it places an automatic emergency call to the nearest towing company. The vehicle’s occupants have nowhere to go but the shoulder of the road.

Admittedly, this is a worst-case scenario, but it isn’t unrealistic. Mud, snow, and spray can cover the sensors, disrupting the functioning of the driver assistance systems.

«If I’m on the road in a sleet shower, it doesn’t take long before my vehicle tells me adaptive cruise control (ACC) is unavailable. It’s annoying, but you can still continue to drive. But once vehicles are operating autonomously, the consequences are more bothersome.»

Rico Baumgart — Team manager of Simulation at IAV

Looking for the sweet spot

This is why Baumgart and his team of engineers have developed their own modeling approaches that identify areas of the vehicle at high and low risk of accumulating dirt – even before the first prototypes are built. The basis for this is the MeshFree base tool, an innovative algorithm used to calculate the flow of liquids by the Fraunhofer Institute for Industrial Mathematics (ITWM). The IAV approach eliminates the need for OEMs to conduct costly and laborious testing series, saving time and money – a crucial advantage in light of the fact that development cycles are growing ever shorter.

“With our simulation approaches, we identify exactly how much dirt there is in the various spots around the car after driving in the rain. We extrapolate from that for placement of the sensors later on,” Baumgart explains. Recommendations for minor geometric changes to the body to redirect flows of air – and water and dirt with them – are also possible. “Simulation tools are also used in body development to determine which areas of the vehicle could be affected by dirt. That’s why we are currently refining this mathematical and physical approach to be able to make statements in this regard as well,” explains Christopher Franzke, a development engineer on the simulation team at IAV.

Another advantage of IAV’s method is that sensor cleaning systems can be evaluated and optimized with an eye to effectiveness. This reduces the need for cleaning agents, which also reduces environmental impact while eliminating the need for frequent refills.

The customer determines the test case

In principle, the simulation model can be used for all vehicle types and component assemblies. To simulate a vehicle, all the engineers need is the relevant CAD data and detailed customer requests for the drive in the rain they are to simulate. “We can set test parameters like the vehicle’s speed at will and visualize different weather scenarios,” says Oliver Pettke of the simulation team at IAV. “The wind direction, the intensity of the rain, and the size of the raindrops can also be varied as desired.” Whichever test combination a manufacturer chooses, the complex physical processes involved can be analyzed with much greater detail and reproducibility than in practical tests. This also benefits the development process and the optimization of components.

With its new modeling approaches, IAV offers added value in manufacturers’ development process, but that isn’t all. This method can also make automated and autonomous vehicles significantly safer through targeted sensor placement – so the occupants of vehicles with well-placed sensors won’t be left standing out in the rain on their own.

The article appeared in automotion 03/2021, IAV’s automotive engineering trade magazine. Here you can order the automotion free of charge.

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