A Study on the Sound Transmission Loss of Split HVAC for Electric Vehicles 2022-01-0981

Generally, the HVAC system of a vehicle is composed of Blower unit assembly and Heater unit assembly, and is located on the driver’s side of the dash panel. However, electric vehicles have far fewer parts than conventional internal combustion engine vehicles, so electric vehicles have large space in the engine room. This allows HVAC, which occupies large volume in the interior side, to be pushed in the direction of the engine room altogether, or by placing a part inside the engine room to make a slim cockpit and expand the interior space. However, this new structure, called the Split HVAC System, is mounted through the dash, allowing noise to pass through relatively easily. Since this adversely affects the NVH of an electric vehicle, it needs to be developed in terms of noise transmission. Therefore, in this paper, a study was conducted to predict the sound transmission loss of Split HVAC through an analytical method. Hybrid (FEM+SEA) analysis was performed using VA One, an acoustic analysis software, in order to analyze up to the high frequency range (~4 kHz) by reflecting the structural characteristics of the split HVAC. In addition, a buck test for the sound transmission loss of Split HVAC was performed, and the analysis accuracy was confirmed by comparing the test-analysis results. After that, a contribution analysis was performed to derive an improvement plan and an improvement analysis was performed. Finally, it could be predicted that the contribution of sound transmission through the HVAC was greatly reduced by changing the HVAC outer cover structure and applying vibration isolation to the connection part.