Automotive Acoustics Conference 2015

Time Reversal (TR) concept has been proposed in the 1980s by Mathias Fink and colleagues, it is based on the symmetry of vibrations governing equations for positive and negative time, when damping effect is negligible. The main consequence of this property is the possibility of creating time reversed waves travelling back to the location where the primary waves were created. Several applications in bio mechanics, military purposes, room acoustics, structural vibrations and ultrasonics for SHM applications have been developed in literature. We just give here few papers for illustrating the different treated aspects [1, 2, 3, 4, 5, 6]

Meanwhile the concept of electric vehicles is well known, but still consumers have little personal experiences about driving electric vehicles. In order to improve the perceived quality of an electric vehicle, the optimization of the interior noise and vibration is highly relevant. But, how must an electric vehicle sound, what is the target sound of a certain electric vehicle, can NVH knowledge and experiences from the past be used for the optimization of modern electric vehicles as well? In order to find answers to such questions it seems necessary to clarify the notion of product sound quality first.

Electric vehicles with range extending internal combustion engines represent a particular noise and vibration challenge. The relatively quiet and smooth operation in electric mode is contrasted by the rather loud and harsh running range extender.

This situation is often exacerbated by the need for weight reduction throughout the vehicle to maximize the electric driving range. The omission of passive noise reduction measures like insulation material and engine balance shafts reduces weight but further increases perceived noise and vibration.

In this paper the application of an active vibration control system to such a vehicle with a gasoline range extender without balance shafts will be presented. The effects of error sensor choice and actuator inclination on interior noise and vibration levels will be addressed.

This article is a follow-up of companion articles published at the Automotive Acoustics Conference in 2011 and 2013 [1]-[2], documenting a numerical/experimental activity aimed at assessing the capabilities of deterministic numerical methods in relation to the simulation of powertrain exterior Acoustic Transfer Functions (ATFs).

In order to address the increased relevance of vehicle cabin acoustics as a constituent of the overall passenger’s comfort in automobiles, precise and predictive methodologies approaches are required to identify and reduce the relevant noise sources. In the present case this problem is addressed to the HVAC (Heating, Ventilation, Air Conditioning) systems, including blowers, mixing unit, ducts or registers

In the context of the development of lightweight and vehicle-NVH-refined sound package solutions, car manufacturers have identified that it is essential to promote new dedicated CAE design methods which can be applied at a very early stage, before body and trim designs are frozen.

In the case of body NVH design, simulation methods based on FE modelling are increasingly used in order to influence the weight reduction of damping products by finding their optimal layout on the body structure, while meeting panel vibration targets. Due to the availability of validated FE models even before the shape and stiffness of the different panels of the vehicle body are fixed, it is also becoming practically possible to perform optimizations of the damping pads simultaneously with smart panel local stiffening, thus offering further weight savings in the low and medium frequency range [1]. Some efforts are also spent in this context, to quantify the design performance with respect to panel radiated noise [2].

On the other hand in the case of trim NVH design, the parts are traditionally optimized with respect to airborne noise transmission in the medium and high frequency range, without systematically considering their side influence on the panel vibration. However, with the growing importance of rolling noise contribution to vehicle NVH, and with the introduction of light weight trim parts on body structures, it is shown that the vibroacoustic interaction of body structure and soft poro-elastic trim has increasing importance at medium frequencies, where structure borne noise propagation is dominant in vehicles. In this case, it becomes even more important to assess the design of the body NVH not only at the panel vibration level, but more at the panel radiated noise level.

This paper is bringing one major advancement in this CAE problematic, with the release and application at vehicle level of a methodology based on FE optimization for the design of the body NVH including damping and local stiffeners, while taking into account the influence of the trim, to be assessed on the SPL performance improvement, thus offering additionally the integration of the trim in a fully integrated optimization.

First of all, the FE representation of the trim can be included into the vehicle FE models that are traditionally used for structural optimization, so that the body vibration target can be substituted by a more realistic interior SPL target. Then the concept is extended to the inclusion of the trim variables (like poro-elastic materials) into the optimization variables, so that the body and trim designs can be accomplished simultaneously, taking into account the mutual influences. The technical aspects of this “integrated” simulation-based optimization have already been presented for a simple validation case [3]. In the present paper, the method is applied on an existing vehicle body in white, demonstrating the interactive influence of damping, stiffening and trim on the structure borne noise of a vehicle. The demonstration is completed by the execution of a simultaneous optimization, leading to an increased weight advantage, and by an interesting outlook towards future design strategies. Finally, the different intermediate optimization results, including the effect of both body and trim design changes, have been validated against test results on two different BIW and trim variants of the vehicle under consideration, using an experimental SPL contribution analysis based on the utilization of PU probes.

In automotive industry, the “diagnostics-ability” can be defined as “capacity to identify the defective part to be repaired or replaced on a vehicle using the customers’ complaints as input”. This is not an easy task when noise and vibrations are considered, due to the complexity of the excitation and transfer phenomena involved.

The NVH performance of conventional panels and structures is mainly driven by their mass. Vibro-acoustic metamaterials with stopband behaviour are looked upon as a possible solution for combing NVH and lightweight requirements for engineering structures. This contribution discusses a metamaterial concept based on sandwich structures with embedded resonant structures that exhibit vibro-acoustic stopband behaviour. This potential is shown through the design and measurement results of two demonstrators. First a metamaterial encapsulation is designed and produced to showcase the potential of this type of metamaterials to improve acoustic insulation performance in targeted frequency ranges. Second a graded metamaterial strip is designed; this strip is built as a combination of metamaterials with different design frequencies, opening up the potential for broadband vibration reduction in a low frequency zone. These metamaterials can be achieved through a variety of designs or production processes, depending on the application, and can offer technological benefits such as possible integration in structural parts, use in harsh environments and ease of design of the beneficial frequency ranges, paving the way for a new class of light and compact NVH solutions with ample applications in automotive for low and mid frequency NVH mitigation.

Sound field control involves the generation and manipulation of acoustic fields using electroacoustic transducers [1]. This encompasses spatial audio reproduction [2], zonal sound control [3], active absorption or reflection of sound [4], and active noise control [5]. In all of these technologies either loudspeakers or structural-acoustic actuators are used to produce a sound field with a controlled spatial and temporal distribution. For example, in the context of spatial audio an array of loudspeakers may be driven to reconstruct a pre-defined sound field, such as that experienced in a concert hall during an orchestral performance [6].

The design of automotive parts for the control of interior NVH involves the analysis of the noise contribution from interior carpet and dash insulator systems. The interior trim is usually designed with respect to insulation and absorption performance, for the control of air-borne noise that is commonly admitted to dominate the overall vehicle NVH for frequencies above approximately 800 Hz. Below this frequency range, it can be shown that the interior noise level is more dominated by structure borne phenomena that are transmitted through the vibration of the body structure, and for which the influence of the insulators is usually considered in a simplified way. In this low frequency range, it is preferred to exploit stiffness and damping countermeasures that act directly on the panel vibration, assuming that the vibration reduction will result in interior noise reduction. From this stand point, it sounds natural to privilege the selection of insulators, which on top of their air-borne primary function can also influence the panel vibration reduction at low and medium frequencies by means of added stiffness and/or damping. This is driving to favour stiffer, thus heavier porous decouplers. In this paper, we first of all show by means of FE simulations on simple flat samples the influence of decouplers on the panel vibration. Concurrently, it can be shown that the interior structure borne noise performance – that is the relevant customer annoyance – is also directly influenced by the insulator transmissibility. Due to the spring-mass nature of insulators, this may lead to the selection of softer and therefore lighter decouplers. Therefore, in the context of light weight insulator products, it is crucial to demonstrate the influence of material selection on the transmission of structure borne noise from the structural vibration to the interior acoustics. In this paper, the flat sample test case is extended to a vibro- acoustical plate-box case. By means of FEM simulation, we show the relation between the decoupler mechanical properties and the final structure borne noise performance. The results on flat samples offer an overview of different technical solutions, including felt, light foam or viscoelastic foam. The validation on a plate-box test rig confirms the simulated tendencies. At the same time, due to the manufacturing limitations of the decoupler materials, it is shown that the mechanical properties driving the final performance can come into conflict with other functional requirements, such as the density, or static compression. For light weight technologies, a proper analysis leads to comprehensive strategies for the design of 3D parts. In this article, we propose a particular focus on injected fibre technologies, where the simulation can be used to find the best material density selection versus thickness, with a final demonstration on a vehicle floor application.

The long lasting trend to minimize CO2 emissions leads to several changes in the powertrain. Besides downsizing, high ratio spreads, or hybrid technologies for example, the number of rolling bearings is increasing. Their benefit is the lower friction loss compared to plain bearings and they suit better to start-stop systems as well with reduced wear when starting from standstill. Furthermore rolling bearings need less oil pump power so that the fuel consumption decreases again.

Legislation drives the automotive megatrend to reduce fuel consumption and CO2 is resulting in small high output 3 and 4 cylinder engines. While customers have raised expectations on driving comfort, the smaller high output engines have inherent vibration noise, vibration and harshness (NVH) issues. Thus gear rattle in mass balance systems, cam gears, pump and accessory drives is an NVH issue. The most common approach is to use a split (scissor) gear assembly; the solution is complex, high in cost and heavy. High performance polymer injection molded net shape gears made from VICTREX® PEEK have gained growing attention and acceptance as cost effective, low mass and highly efficient solution to significantly reduce NVH in engine related application areas like mass balancer, cam and pumps. This paper presents test data done with validation customers and independent research institutes. It also references and discusses technical publications at SAE and VDI. With a successful case study it further it demonstrates the benefits of a net shape polymer gear solution offering a 3 dB (~50%) improvement in NVH, a 68% weight reduction resulting in 78% reduction of the moment of inertia and therefore 9% less torque required to operate compared to a cast iron gear set.

Reviewing the last 20 years of automotive development we realize a convincing progress in NVH behaviour with each model generation. Balancing shafts and reduction of engine speed make engine noise almost inaudible even with 4 cylinder engines and acoustic treatment of soft tops bring down wind noise of cabriolets to limousine level. Nevertheless there is one discipline with the least amount of progress, that’s road noise. It seems that a big part of the progress in sus-pension development has been invested into crisp handling and comfort improvements have almost been eaten up by the fashion trend to 20 inch rims and extreme low section tires. As a result road noise still is the dominant annoyance in long distance driving.

Near-field Acoustical Holography (NAH) is based on performing 2D spatial Discrete Fourier Transforms (DFT), and therefore the method requires a regular mesh of measurement positions. To avoid spatial aliasing problems, the mesh spacing must be somewhat less than half of the acoustic wavelength. In practice, this requirement sets a serious limitation on the upper frequency limit.

In the field of automotive engineering there is a lively international competition within each vehicle development sub-discipline. Depending on the vehicle segment, the requirements and customer profile, the development priorities differ for each competitor. In the premium segment, the part NVH, which covers all areas of the acoustic and vibration properties of an automobile has moved closer to the focus of the customers and therefore also the focus of the companies in recent years. Consequently, the effort of the developers is constantly increasing and they take advantage of new, improved analytical methods for practical application. It is the same with the beamforming, the localization and classification of sound sources.

Auch wenn der Einzug der elektrischen Antriebstechnik noch allmählich vonstattengeht, ist er nicht mehr aufzuhalten. Dementsprechend waren NVH-Aspekte von Hybrid- und Elektroautos ein neues Schwerpunktthema unter den 22 Vorträgen auf der 3. Internationalen ATZlive Automotive Acoustics Conference. Unter der wissenschaftlichen Leitung des Konferenzpartners Autoneum, dem führenden Automobilzulieferer für Akustik- und Wärmemanagement bei Fahrzeugen, fand sie am 23. und 24. Juni 2015 an der ETH Zürich statt.