Structural Dynamic Modelling of HVAC Systems 2024-01-2923

The structure-, fluid- and air-borne excitation generated by HVAC compressors can lead to annoying noise and low frequency vibrations in the passenger compartment. These noises and vibrations are of great interest in order to maintain high passenger comfort of EV vehicles. The main objective of this paper is to develop a numerical model of the HVAC system and to simulate the structure-borne sound transmission from the compressor through the HVAC hoses to the vehicle in a frequency range up to 1 kHz. An existing automotive HVAC system was fully replicated in the laboratory. Vibration levels were measured on the compressor and on the car body side of the hoses under different operational conditions. Additional measurements were carried out using external excitation of the compressor in order to distinguish between structure- and fluid-borne transmission. The hoses were experimentally characterised with regard to their structure-borne sound transmission characteristics. Strong temperature and pressure dependence were observed. A complete FEM model of the HVAC system was constructed. A rigid body compressor model was generated and the excitation vector assessed inversely such as to replicate the measured source levels. It will be shown that (i) in order to obtain sufficiently accurate results rotational degrees of freedom of the source (compressor flanges) must be included, (ii) that temperature effects cannot be omitted and (iii) that dynamic interaction between compressor and hoses must be accounted for in order to simulate low frequency vibration transmission. Furthermore, it could be concluded that fluid-borne excitation cannot be disregarded.