The sound quality problem inside the car cabin is important in the automotive field, especially in the case of upmarket vehicles. The reductions of the noise produced by internal combustion engines and the emergence of hybrid and electric solutions have transformed the perception of sound by the user. The acoustic contribution of equipment such as the HVAC has become paramount and must be studied from the design stage.
The main purpose of Cevas project is the development of a virtual and acoustic prototyping computer tool on the air conditioners and cooling batteries for electric and hybrid vehicles. The tool should allow to predict the noise generated by ventilation systems and design solutions at less cost and with less delay to reduce noise and improve sound quality of these embedded systems.
The project results will be integrated into a calculation software that will interface with an "acoustic synthesis module" allowing to quantify through listening the influence of each component of the internal circuit on the overall acoustic performance and on the sound quality of the ventilation system.
The integrated tool should allow the assessment following psychoacoustic sound quality ventilation systems criteria for different conditions of use and if vehicle integration.
In order to treat acoustic problems and provide virtual prototyping tools, a thesis work was conducted within the framework of the Cevas project to study and characterize the components of an automotive HVAC.
An acoustic synthesis approach is used to identify the components responsible for the noise generated and transmitted. Their active and passive properties, translated by a source term and a transmission loss, have been studied and represented by thin strips spectra. This definition allows sound synthesis of the noise produced and the study of sound quality using acceptance laws. The source term of the fan is predicted by an original law, based on experimental data and inspired by ASHRAE law. The source term of the flap is characterized by using the Nelson and Morphey empirical method. The source term of the heat exchanger is determined from measurements. The transmission losses of the flap and the heat exchanger are obtained using the scattering matrix. The transposition of the source terms from a standardized test environment to an acoustic medium representative of the HVAC has been studied.
The developed method is based on modelling the source term by acoustic excitation whose amplitude and location are independent of the environment. The application of this method has required analytical and numerical models to characterize the acoustic excitation. In the case of the fan, its propagation in a simplified HVAC is studied. A virtual prototyping tool has been implemented in the case of the simplified HVAC. The noise prediction is confronted with sound power measurements. The use of the prototyping tool allows studying the contribution of each component considering various cases of ventilation.
The thesis can be downloaded from the following weblink: https://tel.archives-ouvertes.fr/tel-01555908v1
Maxime Legros. Synthèse acoustique d'un module de ventilation automobile. Mécanique [physics.med-ph]. Université de Technologie de Compiègne, 2016. Français.