Design & SimulationMarch 9, 2021

Design for Effective Soiling and Water Management for Reliable Performance of Sensors in Vehicles

SIMULIA provides solutions to investigate a wide range of soiling and water management phenomena.
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Katie Corey

A study from INVENSITY, a technology and innovation consultancy, says that in the current environment 90% of the innovation in the automotive industry is driven by electronics and software, as the trend is moving towards higher levels of ADAS (Advanced Driver Assistance Systems) integration and autonomy. As ADAS systems are added to conventional vehicles to support the driver, they are designed to provide assistance in most normal scenarios.  However, these devices are designed only to assist the driver, who maintains the primary responsibility to operate the vehicle. On the other hand, for emerging autonomous vehicles (AV), these devices become the primary means of navigation and safety. The ADAS system then requires accurate real-time awareness and must demonstrate perfect performance under all conditions, both normal and extreme.

In the past few decades, demand for fuel-efficient vehicles has also gained more popularity.  As a result, cars are designed more aerodynamically to reduce drag. This is achieved, mainly, by managing the wake of the vehicle so that more air from the underbody impinges on the back of the vehicle. Unfortunately, the air from the underbody of the vehicle is often laced with dirt and water particles that impact the rear and side of the vehicle along with the air. In earlier days when ADAS systems were not that prevalent, soiling was a safety issue in terms of driver vision, but this was limited primarily to glass and mirror surfaces. Surface soiling on the rest of the vehicle was mainly about aesthetics. Now with the increasing number of ADAS systems, especially on AV vehicles, the surface soiling on the rest of the vehicle also becomes a passenger and traffic safety issue because it can interfere with the performance of cameras and sensors. Most of the automotive industries working on ADAS and AV are trying to find soiling problems in the early design stage. These studies and experiments are currently performed in climatic wind tunnels with controlled conditions for surface soiling and water management.  However, these wind tunnels are artificial environments and they don’t represent the real road and climatic conditions, as well as being very costly and time consuming to operate.

This leads to a few questions: are there any cost effective solutions to prevent soiling over the camera and sensors? Where should the sensors be placed for optimal performance? How do we make sure they all work correctly?  Given that one cannot avoid a situation when a splash of mud or other dirt hits the camera, can we control where and how vehicles interact with it?

Why sensors are needed, and how can they get soiled?

In the present era, an increasing number of sensors is a significant trend, as advanced technologies, autonomous driving, more electrification, and driver assistance systems are being implemented in modern vehicles. Autonomous vehicles are faced with a wide variety of operating situations, such as when the vehicle needs to be reversed, emerge from junctions, detect collision threats, etc. The cameras and sensors fitted on these vehicles thus become their eyes and ears, without which autonomous driving would be impossible. Both cameras and sensors must remain uncontaminated by any soiling to operate flawlessly – however, the environment in which they function rarely offers this luxury.

Now, contamination of such sensors and cameras can be due to direct soiling, third-party soiling, or self-soiling, depending on its source. Rain provides direct contamination. Third-party soiling on cars occurs due to spraying of mud/rock/soil/water ricocheted by both upstream and passing traffic. The spray of dirt caused by the vehicle’s own tires leads to self-soiling. Front-tire spray creates a “deposit zone” along the body side that extends from the front wheel to the rear wheel. Rear tires generate a spray that is the dominant source for contamination on rear surfaces.

Surround-view cameras (front, rear and blind spot detection cameras) are usually directly exposed to adverse environmental conditions. This is particularly worsened when the camera lenses are exposed to rain. This leads to both reduction in the vision of drivers and the performance of cameras, and results in a critical safety issue.

How to address this issue?

Dirt, water, and other contaminants are the reality of driving on roads. While we cannot prevent this, we can design vehicles to better interact with it. Some solutions exist for keeping sensors and cameras clean, such as automatic cleaning of lens by using a jet of water followed by a puff of air, or coatings over the lens. However, coatings don’t last long and are quite expensive, and the addition of cleaning solutions can increase weight leading reduced fuel efficiency as well as increased running costs. As an alternative to this, we can try to predict where rain, dirt, bugs, rocks, or other matter are going to hit the vehicle, and subsequently can optimize the sensor positions or recommend design changes to the vehicle to minimize the soiling over cameras. Then we can predict how any design change or the alteration of a camera position can affect the aerodynamic performance of the vehicle and hence the fuel economy.

The ultimate idea is to create vehicles where sensors are placed optimally for minimal dirt deposition and the least exposure to water. However, if any external cleaning devices are still needed, the position of such systems can be optimized.

“There will always be a balance between investing in an expensive coating on a surface, or just moving a sensor by a couple of inches. We can still help.”

Soiling and Water Management using SIMULIA Solutions

SIMULIA provides solutions to investigate a wide range of soiling and water management phenomena. Using PowerFLOW, one can perform detailed aerodynamics and particle flow simulations to assess vehicle design goals. The simulations are performed using PowerFLOW and by displaying the results in PowerVIZ, one can dynamically visualize the release of particles into the airflow and compute the particle trajectories until impingement on the surface. It allows the user to include dust, dirt, rock, and water in the simulation, which gives a clear understanding of how vehicles interact with the contaminant particles, hence giving OEMs the opportunity to better manage soiling over the vehicle surface. In addition, surface properties can be defined so particles can reflect off surfaces and create complex flow paths through the engine bay or on the vehicle surface.

For our study, we considered three scenarios, each with a different location of the camera in the car.

Scenario 1: Accumulation of dirt and mud over the rearview camera

In the first scenario, we simulate the accumulation of dirt and mud over the rearview camera, which is mainly due to the spray caused by the vehicle’s own tires, dominantly by the rear tires.

Scenario 2: Deposition of water over the BLIS (Blind Spot Information System) side mirror camera

In the second scenario, we simulate the deposition of water over the BLIS (Blind Spot Information System) side mirror camera in rainy conditions. One can simulate how the rainwater particles behave and interact with the camera lens for a specific door mirror design.

Scenario 3: Rock chips striking the front camera

In the third scenario, we have worked on understanding how the rock chips flying from passing traffic strikes at the front camera of a vehicle and affects its visibility and function.

Rear and side body soiling

A rear view camera, also known as a reversing camera, helps the vehicle or driver to see the area behind the car and improves the rear blind spot vision. The added visibility helps prevent a crash when backing up. For the baseline design of the car, the dirt particles emitted from the rear tires are deposited over the rear surface and obscure the view of the rear camera, ensuring an unsafe travel experience for the passengers. For this study, a design change in the underbody of the vehicle is proposed, with the goal to redistribute the contaminants away from the most sensitive locations, such as camera positions and license plate.


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