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Strategies for weight reduction have driven the noise treatment advanced developments with a great success considering the already mastered weight decreases observed in the last years in the automotive industry. This is typically the case for all soft trims parts. In the early 2010's a typical european B-segment car soft trims weights indeed 30 to 40% less than in the early 2000's years. The main driver behind such a gap has been to combine insulation and absorption properties on a single part while increasing the number of layers. This product-process evolution was conducted using a significant improvement in the simulation capacities. In that sense, several studies presenting very good correlation results between Transmission Loss measurements and finite elements simulations on dashboard or floor insulators were presented. One may consider that those kinds of parts have already achieved a considerable improvement in performance.

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.

The purpose of the SONVERT project is to create a link between the acoustical sources of a car and the environment in terms of traffic and architecture. Based on well validated approaches, it introduces the notion of a “macro-source” which integrates the major acoustic sources: engine, tires and exhaust, taking into account the low and high frequency aspects, from measurements made on real vehicles. The macro-source is then integrated into an original approach dealing with outdoor propagation. The proposed method can consequently be seen as a first step toward a global approach for the study of traffic noise in real conditions.

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).

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.

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.