Methodology for Sloshing Noise Measurement and Acoustic Target Definition for SCR Tanks to Improve Comfort

摘要

Within recent years, passenger comfort has become a main focus of the automotive industry. The topic is directly connected with acoustics, since sounds and noises have a major impact on the well-being of vehicle occupants. So-called “noise control” focuses on directly optimizing acoustic comfort by implementing innovative materials or geometries for automotive components and systems. One possibility to optimize the acoustics within a vehicle is connected to the phenomenon of sloshing in Selective Catalytic Reduction (SCR) tanks. Sloshing is a noise which is generated during normal driving situations by the motion of the Diesel Exhaust Fluid (DEF) in the tank. Until now, no procedure for measuring sloshing noise in SCR tanks has been defined, and neither a specific acoustic target which the SCR tanks need to fulfil. For this reason, it’s been developed a reproducible laboratory-based methodology to measure the sound generated by the tank and compare it with a defined sound pressure level target. As a first step the different phenomena of sloshing noise generation have been deeply analyzed (hit, splash, clonk, bubble-jet), each of which can be attributed to a specific movement of the liquid inside the tank. Aiming at a repeatable procedure which reflects the sound level occurring during realistic driving manoeuvres, the company designed and constructed a test bench able to reproduce real driving conditions of this kind and evaluated the results according to the identified target. Subsequently, an examination was conducted to assess the transmission paths of the noise from the tank to the vehicle cabin as well as the effects of the engine and driving manoeuvres on how the sounds are perceived by passengers. For this purpose, sloshing noises recorded for different tanks were modified in order to prepare psychoacoustic listening sessions and identify the most important parameters influencing the annoyance.