F2006d187 Description of Broadband Structure-borne and Airborne Noise Transmission from the Powertrain

Binaural Transfer Path Analysis (BTPA) was originally developed for assessing the binaural contributions of individual vehicle noise paths. It is a powerful modeling tool enabling engineers to explore noise transfer mechanisms by distinguishing between excitation source strengths and the transfer behavior of individual elements. The method is well-known for powertrain noise analysis, including point-coupled structure-borne source paths and identified airborne source paths to a receiver location. Binaural Transfer Path Synthesis (BTPS) is the process of creating listenable vehicle interior noise data based on a BTPA model, also allowing for modifications. Modern methods of combustion (TDI, CDI, fuel direct injection etc.) in combination with new generations of valve trains and more light-weight materials in engine construction have produced changes in the temporal and spectral behavior of primary oscillation factors. As a consequence, the in-car noise produced by the engine is being determined more and more by higher frequency components. The methods used in Binaural Transfer Path Analysis and Synthesis are now more frequently confronted with limitations which can only be overcome by detailed observation of the various influencing variables. New, future-oriented methods for this purpose are described in the project at hand. Engine noise transmission fundamentally occurs in two ways, which have to be examined separately: a) the structure-borne path which is stimulated by the engine mountings and b) the airborne path which is fed by the direct sound radiation of the engine. For both paths, improved models which are traceable in signal and system theory are presented and their methodology is described. Starting by describing and measuring the source properties and transfer functions as exactly as possible, we arrived at an extremely simplified yet adequate model version of the complicated structure. An especially important improvement of the structure-borne transfer paths we introduce here is the description of the mechanical interfaces via complex four-pole parameters. Considering airborne sound transmission, we are reducing the in-car source measurement that was previously mandatory by describing the engine with an alternative source model which could be highly simplified through multi-pole source synthesis and which can be derived from testbench measurements. Using this simple model, the user receives a tool by means of which changes in transfer paths (e.g. the influence of the engine mounting) can be modeled in a theoretically correct way and the results can be made audible immediately. TECHNICAL PAPER