# Performance Development of Fluidic Oscillator Nozzle for Cleaning Autonomous-Driving Sensors
## 1 Introduction  
The performance of vehicles is improving by combining various technologies. In the past, driving performance was the most important factor when judging a vehicle; nowadays, driving convenience options are important to customers [1; 2; 3]. Accordingly, automakers are developing various convenience options and technologies to increase vehicle sales. Autonomous driving is one of the options offering convenience that reduces driver fatigue. Thus, automakers have applied autonomous-driving technology to various vehicles. However, consumer complaints regarding frequent malfunctions of autonomous-driving sensors are increasing; these malfunctions often result in accidents. Various factors cause autonomous-driving malfunctions and accidents with the pollution of autonomous-driving sensors (Lidar, radar, cameras, ultrasonic sensors, etc.) contributing the most. Since the autonomous-driving sensor is exposed to the external environment, various pollutants (snow, ice, dead insects, dust, mud, etc.) deposit on the sensor surface, causing autonomous-driving malfunctions. Various studies have focused on eliminating this pollution. [PERSON] and [PERSON] developed an algorithm that can determine the surface pollution of Lidar sensors in real time during vehicle operation and improve autonomous-driving accuracy by filtering pollution [4]. [PERSON] and [PERSON] installed a sound wave generator on the back of the sensor glass and studied self-cleaning by removing pollutants using sound waves and vibration [5]. [PERSON] et al. investigated the removal of fog, frost, snow, and water droplets by installing heating electrodes on autonomous-driving camera lenses [6]. [PERSON] et al. studied how various characteristics of pollutants such as blockage type, concentration, additives, and drynessaffect blockage [7]. Figure 1 shows patents related to the cleaning of the autonomous-driving sensor [8; 9; 10; 11; 12]. Figure 1a-d show vehicle Lidar sensor-cleaning devices of the sliding, folding, up-down, and ultrasonic vibration wiper types, respectively, whereas Figure 1e shows the Lidar sensor-cleaning device. The common operating mechanism sequence of Figure 1a-d is largely divided into three steps. In the first step, cleaning liquid is sprayed through a cleaning nozzle installed at the top or side to initially remove pollutants attached to the sensor surface. In the second step, the ultrasonic sensor slides or folds to cover the autonomous-driving sensor and then generates ultrasonic vibration to remove pollutants from the sensor surface. The differences in the operation of ultrasonic sensors in Figure 1a-d are as follows. Figure 1a operates the ultrasonic sensor cover in the up and down direction through a gear attached to the side. Figure 1b folds up or down the ultrasonic sensor using an electric motor. Figure 1c moves the ultrasonic sensor in the up and down direction using electric motors on both sides. In Figure 1d, the ultrasonic sensor moves up and down through the lever attached to the side. In the third step, air is sprayed from an air nozzle to blow away pollutants and cleaning liquid from the surface of the autonomous-driving sensor and dry it. In Figure 1e, the cleaning liquid and air nozzles are arranged sequentially, and the surface of the autonomous-driving sensor is cleaned using a cleaning liquid and then dried with air. When cleaning autonomous-driving sensors, nozzle performance is important because the sprayed cleaning solution physically cleans pollutants. In this study, the flow characteristics of the nozzle were studied to improve the cleaning performance of the nozzle in cleaning the autonomous-driving sensor. Currently, windshield-washer nozzles are used for cleaning autonomous-driving sensors, and few studies focused on nozzles for cleaning autonomous-driving sensors. Because the nozzle size is small, the error rate during precision machining is high, and the nozzle is sensitive to even minute changes  
Figure 1: Structures of patented autonomous-driving sensor-cleaning devices.