Sensor cleaning :virtual tool for cleaning performance to maintain availability of AD sensor system

Active systems in cars are seen as crucial tool for mitigating accident on road and are getting wide-spread and more complex. Such systems include a variety of complementary sensors enabling a 360 degree view at all instants. These consists of cameras, LiDAR, radars and ultra-sound sensors, to cite a few. One major limitation to the benefits of active safety systems is the availability of the system in time. For instance, deposition of rain, snow or dirt impairs the performance of optical systems such as cameras, sensor and LiDAR. Cleaning systems are therefore vital for securing the benefits of active safety systems, especially in respect to autonomous vehicles. Cleaning systems are for now limited to maintain visibility for the driver which is subjectively assessed by the driver himself. With the increased importance of active safety and especially with the usage of autonomous drive systems it is crucial to maintain sufficient optical access for all sensors at all time. It is known that cameras, but also sensors like radar and LiDAR need a certain optical access and that their signal will be blocked due to i.e. rain, snow, heavy dirt or a water film. At harsh and potentially dangerous road conditions, such as snow, heavy rain or frost (salted roads), but also for everyday driving on rain, dirt or gravel active cleaning of sensors is needed to maintain the availability of the active safety and autonomous drive systems. With increasing need of sensor cleaning, the usage of cleaning liquid is expected to increase. Increased usage of cleaning liquid will emit more harmful substances into the environment, but also add significant to the total weight of the car, when the liquid storage has to be increased. Sensor can be located at different locations on the vehicle, one sensor cluster is behind the wind screen in the rear view mirror, and other sensors are located at bumper height, in the car centre or edges. The different locations are differently demanding concerning contamination and consequently their cleaning. On the wind screen, the complex interaction between wiper motion, water film and surface dirt is a multiphysics phenomenon. At locations which are exposed to the free air stream, the cleaning spray is heavily influenced by the air flow as a consequence of the driven speed. Therefore in this project a CFD computational fluid dynamic model of wiper cleaning system and a mathematical model for dirt dissolution is develop. This complex CFD model include; moving wipers on the car windscreen, wiper-fluid interaction, fine droplet sprays, detailed car and wipers geometry and the aerodynamic forces. The deposition and adhesion of solid particles on surfaces is usually an unfavourable phenomenon and is termed as fouling, incrustation or dusting, all of which happen on a daily basis in nature, industries and humans' life. The deposited particles in the latter phenomena are commonly referred to as “dirt”. These particles find a stable state because of the dissipation of free energy leading to formation of static patterns. Convection and evaporation, among others, are two energy dissipating mechanisms which build most of the patterns formed in nature. Such mechanisms are integrated within the process of convective drying of wet particulate systems. Through the latter process, while drying densifies the solid particles in the suspension, convection pushes the fluid to move faster than the congealed particles in the direction of the shear. Subsequently, due to the mechanical instabilities originated by the process, convective drying of suspensions can lead to complex and heterogeneous morphologies. A common form of dirt consists of wet or dry dust with salt or other minerals which dries and adheres to surfaces. The result of such deposition, is a strongly adhered crust over the surface. This can cause minor and major issues including hindering visibility through glass surfaces or even impeding optical and sensory systems. Recently, these problems have gained importance in the automotive industry, since many of the safety and autonomous driving systems are based on optical and sensory systems. Specifically, when driving in wet roads, suspensions of dirt are spread over the exterior surfaces of the vehicles and dried through the surrounding convective air flow caused by the relative velocity of the car compared to the surrounding air. Formation of such dirt crusts can either prevent the detection of a real hazard or lead to an incorrect detection of an approaching object. Nowadays, the active safety systems in cars are quickly developing and have significantly reduced the number of collisions and injuries on the roads. However, the failure of these systems, for instance via such dirt deposition, can lead to hazards since modern day drivers are becoming accustomed to having such safety features in place to protect them and as a result are becoming less alert when driving.

Language

  • English

Media Info

  • Pagination: 38p

Subject/Index Terms

Filing Info

  • Accession Number: 01739068
  • Record Type: Publication
  • Source Agency: Swedish National Road and Transport Research Institute (VTI)
  • Files: ITRD, VTI
  • Created Date: May 14 2020 9:41AM