The Mechanism of Hissing Noise in the Automotive Cabin and Countermeasures for its Reduction 2019-01-1474

The popularity of environment friendly products such as electric vehicle (EV) and plug-in hybrid electric vehicle (PHEV) has been increasing. One of the major qualities of those vehicles is the quietness in the cabin with the help of the replacement of the drive power source and improvements of vibration reduction techniques. However, the reduction of the main noise can make the secondary noise like air-conditioning (A/C) noise to highly contribute to the automotive noise. A/C system induces some abnormal noise and its excessive noise level is unpleasant for customers. In this paper, the hissing noise generated from the refrigerant system is taken since it often occurs. In order to understand the mechanism, for the first step, the visualization method to capture the behavior of multi-phased refrigerant flow jet inside the pipe was proposed with high-speed camera, some light devices and acrylic test piece. In addition, image analysis to quantify the flow regime from a series of observed snapshots. Using proposed method, the correlation study between flow and noise was performed at A/C bench test. As a result, different flow features such as the velocity can be observed in the occurrence of the noise or not. It is also shown that the valve tends to open largely when it occurs. As another approach to clarify the mechanism, co-simulation method was developed with CFD and vibro-acoustic model. Pressure fluctuations on the inner wall of the pipe are calculated by CFD and they are imported to vibro-acoustic model as transient pressure load. Structural modes in the evaporator system and acoustic sensitivity in the HVAC are calculated and then the frequency characteristics are revealed. Lastly, from the perspective of both fluid and vibro-acoustic field, some counter-measures for its reduction are discussed.