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In the context of the upcoming reduction of Pass-By-Noise limits in the EU regulations, automotive manufacturers need to implement new concepts of shielding package. ECOBEX is a French funded research project aiming at reducing the powertrain noise contribution of the vehicle, whilst restricting additional mass and cost. Bringing together OEM, raw materials suppliers, shielding manufacturers, universities and specialized consultants in this research program enabled innovations in materials, design, tests and computational methods. This paper will focus on a new procedure for the optimization of the shielding package, based on a precise 3D localization and quantification of the acoustic sources of the powertrain and on their implementation in an Energy Boundary Element model, computing the acoustic propagation. Intensity maps emphasized the dominant acoustic paths and highlighted mitigation opportunities in terms of absorption and insulation.

Due to the increasing focus on noise and vibration for future vehicles, there is a need for a clear definition of the requirements between vehicle manufacturers and auxiliary suppliers. Auxiliary characterisations are also needed as input for structure-borne numerical prediction models. Strongly coupled systems are amongst the most difficult structure-borne noise issues, as the transmitted forces and powers are strongly dependent upon the mobilities of both the vibration source and receiver. The so-called “blocked forces” can be used as intrinsic source descriptions. The challenge is then to design auxiliary test benches perfectly rigid in the frequency range of interest. The current paper is based on the French research program MACOVAM dedicated to the vibro-acoustic characterisation of oil pumps for truck engines. An original test bench was designed to measure quasi-blocked forces over the [150 Hz-2800 Hz] frequency range.

In the context of more and more drastic noise regulation and increasing customers demand for lower noise annoyance, acoustic shields become essential for a wide range of vehicles. Due to reduced development time, acoustic design must start in the early stage of industrial projects, requiring precise and reactive prediction tools. The most widely used computation methods perform a numerical resolution of Helmholtz equation with a spatial discretization into Finite Elements or Boundary Elements. These methods are efficient in the low frequency range, but they reach their limits at higher frequencies, due to high computational cost, very precise mesh required, and high sensitivity to geometry and frequency. Then Ray Tracing techniques may be an alternative in some cases, but diffused reflection is generally ignored and convergence is not always reached, observation points receiving too few rays.