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The challenge of a NVH development is to define a link between the target of the OEMs expressed in terms of acoustic performance, weight and cost and the design of the optimized acoustic package reaching this target. The “Vehicle Acoustic Synthesis Method” (VASM) has been developed in order to create this link. The VASM method, which is an energy based hybrid simulation technique, calculates the Sound Pressure Level at ear location from the combination of sound power measurements and acoustic frequency response functions (FRF) panel/ear, either measured or simulated with Ray-Tracing Methods.

The weight reduction challenge has taken a new shape in the past two years due to high pressure on CO2 emissions in the automotive industry. The new question is: what level of acoustic performance can you get with an insulator weighting less than 2500 g/m2? The existing solutions at this weight being mainly dissipative (absorption) concepts give a satisfactory performance only if the pass-throughs are poor and present critical leakages. Respecting the less than 2500 g/m2 weight target, we have developed a wide range of new or optimized concepts switching from extremely absorbing to highly insulating noise treatments playing with multi-layers insulators (typically three to four layers), in combination or not with tunable absorbers on the other side of the metal sheet (in the engine compartment for example).

Due to increasing attention paid to the optimization of leakages and passthroughs in general, measurements on cut out modules in large coupled reverberant rooms are often carried out in the middle and high frequency range, in order to optimize the insulation performance of trims installed in their actual environment (Transmission Loss). Using optimal controlled mounting conditions, we have been able to extend the frequency range to the low frequencies in order to validate trim FEM models of a headliner cut out module with structureborne and airborne excitations.

In order to reach the new 2020 CO2 emissions regulations, we have developed a wide range of lightweight noise treatment technologies going from pure absorbing to highly insulating ones, depending on the pass-through quality situation. This Generalized Light-Weight Concepts family was first optimized using the 2D Transfer Matrix Method (TMM) combined with quick SEA approaches. Taking into account thickness 3D maps with TMM is an efficient and quick intermediate “2,5D” optimization method, but it is not a real 3D approach. This work presents a new 3D optimization procedure based on poroelastic finite elements including intermediate cavities (like Instrument Panels) for designing these Generalized Light-Weight Concepts. A parallel reflection deals with products and processes in order to check the feasibility of the resulting 3D optimized insulator designs.

In order to reach OEMs acoustic treatment targets (improving performance while minimizing the weight and cost impact), we have developed an original hybrid approach called “Vehicle Acoustic synthesis method”[1] to simulate - and therefore to optimize - noise treatments for both insulation and absorption, and to calculate the resulting Sound Pressure Level (SPL) at ear points for the middle and high frequency range. To calculate the SPL, we identify equivalent volume velocity sources from intensity measurements, and combine them to acoustic transfer functions (panel/ear) measured or computed with ray tracing codes using the reciprocity principle. Compared to our first approach [1], this paper shows a new measurement technique using pressure-particle velocity probes [2]. This technique allows to reduce acquisition time by a factor four, and makes therefore possible a synthesis method on a complete car within two weeks.

With the increasing importance of electrified powertrains, electric motors and gear boxes become an important NVH source especially regarding whining noises in the high frequency range. Engine encapsulation noise treatments become often necessary and present some implementation, modeling as well as optimization issues due to complex environments with contact uncertainties, pass-throughs and critical uncovered areas. Relying purely on mass spring systems is often a too massive and relatively unefficient solution whenever the uncovered areas are dominant. Coverage is key and often a combination of hybrid backfoamed porous stiff shells with integral foams for highly complex shapes offer an optimized trade-off between acoustic performance, weight and costs.