Dynamic Modelling and Validation of Hoses in an HVAC Circuit

The structure-, fluid- and air-borne excitation generated by heating, ventilation and air conditioning (HVAC) compressors can lead to annoying noise and low frequency vibrations in the passenger compartment. These noise and vibration phenomena are of great interest to ensure a high passenger comfort of electric vehicles (EV). This publication describes the development of a numerical finite element (FE) model of the HVAC system and the simulation results of structure-borne sound transmission from the compressor via the HVAC hoses to the vehicle body in a frequency range up to 1 kHz. The simulation results were validated with measurements. 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 finite element models of the hoses were characterised with regard to their structure-borne sound transmission properties using the results of experimental tests. Strong temperature and pressure dependence were observed and taken into account in the numerical models. A complete FE 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 neglected.