Effects of On-Road Conditions on HVAC Noise 2020-01-1555

Noise inside the passenger cabin is made up of multiple sources. A significant reduction of the major sound sources such as the engine, wind and tire noise helped to improve comfort for passengers. Therefore, HVAC noise (heating, ventilation and air-conditioning) is unmasked as a primary noise source inside the passenger cabin and has to be taken into consideration when designing passenger cabin sound. While HVAC sound is often evaluated at stop, the most common situation of its use is while driving. In case of fresh air as mode of operation, the HVAC system connected to the environment through the air intake. Any change in the boundary conditions due to on-road driving events and gusts of wind affects the flow field in the HVAC system and in turn influences HVAC noise. This study investigates the effect of mass flow and pressure fluctuations on HVAC noise. In a first step, major influences on the HVAC system are identified in an on-road test. For further investigation, the HVAC system is analyzed in a simplified car model. The transient change of the inlet boundary condition is reproduced in a test rig that allows for adjustable flow modulation. The results of the on-road tests show that driving events and gusts of wind have an impact on pressure fluctuations in the HVAC system and cause a noticeable modulation of HVAC noise. Experiments in a simplified car model show that mass flow fluctuations are mainly made audible by the outlet slats and lead to a to modulated HVAC noise.