Automotive Acoustics Conference 2023

The EU noise policy has an objective to drastically reduce emissions from transportation by 2050 and promote electric vehicles. European Union lawmakers and member countries reached a deal to ban the sale of new gasoline and diesel cars and vans by 2035. From 2035, most of the personal vehicles sold in EU will be Battery Electric Vehicles – BEV (with probably some percentage of Fuel Cell Hydrogen vans and light commercial vehicles).

BEV are often referred to as quiet vehicles, comparatively to internal combustion engine (ICE) vehicles. For the public opinion, the BEV is a synonym to quiet urban traffic and a solution for urban noise pollution. The idea is that generalization of BEV will resolve urban noise issues. This assertion might be tempered in lot of cases. In the paper, the data available from the standard pass-by noise tests of BEV, has been analyzed and used to establish a model of exterior noise generated by BEV, for the urban driving conditions.

In course of architectural change from combustion engine to purely electric vehicles, the requirements of underbody paneling are also changing. Battery protection requires new concepts which cannot easily be solved in a common way with conventional textile, large-area sound-absorbing panels. At the same time, the tires dominate the road noise, why new measures of noise-reduction are getting even more necessary.

A possible alternative solution are absorbent bodies, which are attached to the transition area from the wheel arch lining to the underbody in front of and behind the wheels and which face to the sound source from the road surface and tires. The results of a current study on the exemplary implementation of such bodies and their effect on the exterior and interior noise of the vehicle will be presented.

A process for predicting road noise using virtual prototypes assembled from test-based and CAE-based component models is presented in response to automotive industry trends such as vehicle diversification and electrification, which drive the digitalization of NVH development methods and increased importance of road noise. First, a methodology for test-based component characterization for structureborne road noise is presented using a real-world case study. Then, a virtual prototype is assembled using test-based tire-wheel component models and CAE-based front and rear suspension, subframe and body component models. Finally, the road noise performance of the virtual prototype is predicted and decomposed into contributions from the structureborne paths, which are evaluated from objective and subjective point of view.

The recent race to electrification of passenger cars has changed the balance of noise sources inside the vehicle cabin, giving even higher importance – especially at low speeds, where the aerodynamic noise is low – to the tyre rolling noise (also called “road noise”). Tyre noise acts across a wide range of frequencies. Due to its prominent tonality, the noise associated with tyre cavity resonances – which usually acts in the range of 200 Hz due to the geometrical characteristics of the tyre – is probably the most annoying in customer’s perspective.

Concurrently, due to the importance of fuel economy and the increased cost of raw materials, there is a strong need for lightweight, high performance NVH solutions that provide an improvement compared to the “classical” damping materials or an alternative to structural modifications that might be hard to implement due to the trade-off with other performances, increased mass, and cost.

In this paper, a distribution of 3D printed resonant elements is used to dampen the vibration of a vehicle body panel that radiates tyre noise inside the cabin. Experiments are conducted on a full vehicle showing high potential for vibration reduction in the tuned “stopband” which is matched by an improvement in interior noise.

While several automotive Original Equipment Manufacturers (OEMs) develop vibration sources such as electric motors internally, many outsource the development and manufacturing of motors to suppliers. In both scenarios, having clear and well-defined vibration requirements for motors is critical during the development phase. This not only sets clear goals for motor development but also clarifies the division of responsibilities between the supplier and OEM, or among different development departments. However, determining the exact values for these vibration requirements is difficult and has not been addressed extensively.

This paper tries to improve the accuracy of defining these requirements by combining a) advanced vibration modeling and b) numerical methods for calculating target values. For vibration modeling, substructuring is used for coupling all structures in the vibration transfer path. The source excitation is modeled with component-based TPA, where the source excitation is represented by blocked forces, which are a property of the source component alone. This enables a decoupling between the source component (e.g. the motor) and the transfer path (e.g. the vehicle). The connection between the source component and the rest of the vehicle often has many degrees of freedom (DoFs), making it hard to analytically derive target values for source excitation. To address this issue, the paper employs numerical calculations to determine a solution space for each variable. Finally, the paper presents the proposed method through analytical examples. This research is currently in its early stages. Future work will focus on applying the method to industrial data of electric motors and steering gears. This research aims to improve the accuracy in defining vibration requirements. This is vital for the prevention of late phase trouble shooting and expensive redesigns.

When driving an electric vehicle, the interior sound experience is characterized by low overall levels. The frequency spectrum is dominated by tonal, high-frequency elements. The main source of this sound signature is the electric drive unit (EDU) powering the vehicle.

The challenge this poses to NVH development is twofold. On the one hand, tonality becomes the main criterion for evaluating the interior noise quality of electric vehicles. This means generating and applying metrics and methods that can robustly analyze and evaluate tonality is a must for electric vehicle NVH engineering. And on the other hand, the focus of powertrain NVH development shifts from achieving the lowest overall level possible to limiting the acoustic prominence of the electric drive unit’s tonal and high-frequency noise components.

To reconcile these challenges, AVL has developed a robust and flexible NVH development methodology for electric drive units. In this paper, AVL presents how this methodology can be applied throughout the development process.

Starting from vehicle benchmarking to generate reasonable NVH targets, these targets are detailed and broken down to system and component level where they support the conception and initial design of the electric drive unit and its components. In the concept and the design phase multiple subsystem models are combined to a Digital Twin accompanying the development of the physical electric drive unit. This Digital Twin ensures the continuous optimization of the system by using simulation and artificial intelligence techniques until the final vehicle integration. This allows robust virtual studies of different attributes like tolerances and temperatures and their influence on NVH behavior. From the first prototype onwards simulation and testing go hand in hand, refining the individual systems with each hardware generation resulting in an NVH-optimal electric drive unit. The method guarantees an efficient target achievement process and helps to avoid costly mistakes.

Numerical analysis plays a significant role in the development of passenger comfort in modern vehicles. Customer perception of quality and comfort is largely influenced by its vibro-acoustic properties.

To develop well engineered and robust vehicles that meet such customer requirements, many vibro-acoustic aspects and loading conditions need to be accounted for. This is only feasible when numerical analysis techniques, like the Finite Element Method, are applied over all design stages including the early concept phase.

As vibro-acoustic behaviour is typically of global nature, meaning vibrations of different components mutually interact throughout the whole system, complex full-vehicle analyses accounting for all components as well as the interior air cavity are required. Moreover, with the rise of electric vehicle development, the rotational motor speeds and hence the excitation frequencies of interest increase dramatically compared to conventional combustion engine based vehicles. Such large-scale simulations challenge even today’s high-performance computing hardware and software to its limits. For this reason, efficient numerical reduction schemes of the underlying systems of equations are essential to avoid excessive evaluation times and costs, which becomes especially relevant when optimization approaches are considered.

The presented paper illustrates the structure-borne acoustic analysis and optimization procedure of an electric full vehicle model subject to high frequency motor load cases. To reduce simulation times, the Frequency Response Function-Substructure reduction technique is applied to model components that are not modified in the successive optimization procedure enabling a very efficient reuse of precomputed data in each iteration cycle. As the focus in this work is on modifications in the powertrain, sub-systems like trimmed body and chassis are viable to be reduced.

A new machine learning based optimization approach is applied that combines the Nastran based fluid-structure coupled analyses with self- learning algorithms. A detailed/high-level description of this new easy-to-use and highly automated approach is provided along with a discussion of the obtained results. Besides the optimized acoustic response and design state, these results consist of relevant design parameter rankings and tolerance analysis to reveal the robustness of the optimized design state.

Modelling and simulation of aeroacoustic phenomena has progressed massively since the introduction of Lighthill’s analogy. New simulation methods and larger access to computational power allow large corporations in the automotive and aerospace sector to tackle problems such aircraft exhaust noise, side mirror noise, HVAC (Heating, Ventilation, and Air Conditioning) noise. On one side, the aeroacoustic community is very active on improving the accuracy and maturity level on these applications; on the other side, the community looks as well to new technologies which would be better suited to tackle markets which have a larger variety of products and combination of system which are not affordable at reasonable cost with combined unsteady flow and acoustic simulations. A representative important market for the last category is electronics where the combination of components and cooling fans are almost infinite. Challenges such as better fan noise prediction, complete system simulation including structures and acoustic treatments and high frequency accuracy will require new methods and workflows to be part of the design process of engineering companies. This paper will perform an overview of the aeroacoustic modeling techniques and methods, discuss the challenges that companies are facing when using aeroacoustic simulation, address the gaps in processes for making aeroacoustic simulation more accessible and examine the trends for the decades to come.

With the increased electric vehicle (EV) adoption and the reduced application of the traditional combustion engine, windnoise is becoming the major contributor to the interior noise level in the vehicle. The weakest point for the acoustical insulation of the car body remains the glazing due to its legal requirements of impact resistance and transparency. Moreover, in modern car design the relative glazing surface tends to increase contributing to the interior comfort and an enhanced viewing experience. Larger glass panels however show a larger transparency for environmental noise sources such as wind and passing-by noise. New polymeric interlayers have been developed to remediate this problem. In most cases the application of this PVB (polyvinylbutyral) films tends to be restricted to the laminated windscreen while other glazing surfaces are predominantly tempered glass.

In this study, aero-acoustical and vibro-acoustical modelling, using Actran^®, have been used as a tool to quantify the relative contribution of each glass panel to the interior noise level in the car. The local turbulence near the glazing positions was computed from a CFD simulation of the air flow over the car’s body. The respective noise sources were derived from the calculated kinetic energy and kinetic energy dissipation using Lighthill’s theorem and the Stochastic Noise Generation and Radiation (SNGR) methodology to determine the relative noise level up to a frequency of 10.000 Hz. The finite element (FE) technique, rather than the statistical energy approach, has permitted to simulate noise levels at specific locations in the cabin’s interior. These methods were used to evaluate the relative effect of different interlayer types in the respective glazing parts (windscreen, sunroof and sidelams) on the acoustical insulation. Specifically for the car model considered, the simulation results have indicated that the transfer path for aero-dynamically induced noise is strongly frequency dependent. In the lower frequency range, noise is predominantly transmitted through the side windows. At the higher frequencies a considerable fraction of the noise is also transferred through the sunroof. The outlined simulation strategy can be further applied to optimize noise insulation performance of the glass configurations.

This contribution describes a novel method for visualizing leakages in automotive structures using a rotating linear array of a few digital ultrasound microphones in combination with a multi-frequency ultrasound transmitter. The rotating array scans the incident sound field generated by the ultrasound transmitter on a circular area. In a typical measurement setup, the ultrasound transmitter is placed in a cavity (e.g. car interior, trunk or similar) and operates at distinct harmonic frequencies at around 40 kHz in an omnidirectional fashion. The rotating linear array is operated on the outside of the cavity and captures the sound field escaping through small leakages. While the reduced hardware complexity allows for the design of a lightweight, handheld sound imaging device, the algorithmic portion of the measurement system requires special attention. In fact, established methods of sound imaging like beamforming and nearfield holography cannot be applied to signals stemming from moving sensors. The proposed method of computing an acoustic image using the described measurement setup is based on compensating the moving microphone signals for Doppler distortions and evaluating the coherence of the resulting signals with a non-moving reference microphone for each point in the acoustic image. The setup and methodology is evaluated for leakage and tightness testing of actual automotive components and structures for production cars in a quality control context. The corresponding troubleshooting process from assessment and quantification of the situation to resolution of the root cause is described from a user perspective.

Carbon neutrality is one of the major task of recent vehicle development, and the CO₂ emission from acoustic package manufacturing process has relatively large contribution among the vehicle parts. In times of this new challenge, Lexus new RX which is TOYOTA flagship SUV and requires high NV performance as well as less CO₂ emission was released. In this paper, a new technique of acoustic package optimization and acoustic package development for carbon neutrality are introduced to achieve the high NV target and the CO₂ emission minimization.

Regarding the acoustic package optimization, TOYOTA adopted a newly developed process using Genetic Algorithm (GA) to optimize the thickness and weight of acoustic package.

For carbon neutrality, NIHON TOKUSHU TORYO(NITTOKU), TOYOTA, and TOYOTA MOTOR KYUSHU(TMK) with apparel manufacturers and Japanese local government are establishing the recycle scheme of clothing to produce felt material and made felt silencer like dash/floor silencer with mainly using post-consumer recycled felt. Finally, future vision of utilizing further use of recycle material for the car-to-car recycle of acoustic package will be explained.

New Model EV was realized segment above quietness especially low speed and takeoff driving scene. This quietness was designed by new BEV platform and E-powertrain. At once, large cabin roominess was realized by unique HVAC structure that is penetrated in dash panel. Therefore, new isolation design for dash area- was applied and quietness was realized. Key designed component is excitation motor, motor mounting system and isolation structure.

For the owner of a car, it is important that all quality scales are met, especially on a premium brand. One such scale is the acoustic situation inside the cabin: a new car should not have any squeak, rattle, or other unwanted noises perceptible by the passengers. The root causes of such acoustic anomalies are manifold.

Currently, the readily assembled cars are driven on an indoor roller dyno or an outdoor test track to have a human driver detect acoustic anomalies. To shift this subjective quality estimation to a reproducible and more objective level, the goal is to develop an automated test procedure for squeak & rattle integrated in the test facility of the production line. This is where the formerly proposed AI-based automated squeak & rattle detection comes into the play.

We explain the boundary conditions for such a procedure and describe a possible approach, before we take a closer look at a pre-test setup in a lab with a suitable excitation of the whole vehicle body, as well as the measurement setup of the microphones.

The initial results of a measurement campaign are discussed, highlighting the precision of the anomaly detection and – of course – the limits. The paper ends with an outlook on next steps.

Transmission loss (ATF or PPNR) is generally used as a method of evaluating vehicle sound insulation performance. But since transmission loss evaluation is conducted in a stopped state, it is difficult to reflect the characteristics of noise generated during driving, and it is difficult to determine how much each interior trim contributes to interior noise reduction.

In order to develop optimal vehicle sound insulation performance, it is necessary to identify major panels that contribute to interior noise under driving conditions (acceleration/constant speed) and to develop an integrated sound insulation performance index that quantifies the degree to which interior trims contribute to interior noise reduction. Using this integrated sound insulation performance index, it will be possible to develop an interior trim that can realize good sound insulation performance while considering cost/weight.

For developing an integrated sound insulation performance index for each driving condition in this study, Panel Contribution Analysis (PCA) was conducted on interior noise under actual vehicle conditions and bare conditions.

In the NVH development process, component or component changes are increasingly evaluated by simulation models only, as manufacturers are less and less able to realize real prototypes due to stricter time and cost targets. However, it is hardly possible to assess effects on noise and vibration behavior solely based on simulation results or, for example, test data determined on component test benches, because the perception of noise and vibrations in the vehicle cannot be reduced to diagrams and numerical values. The yardstick is and remains human experience. So how can manufacturers realistically evaluate NVH performance when they are conducting fewer and fewer physical testing?

An NVH simulator solves this problem. It makes measurement and simulation data audible in the earliest development phases via an interactive driving noise simulation, so that decision-makers do not have to judge only based on abstract figures. It also allows evaluation of the NVH performance or the active sound design of electric vehicles at very early design stages, when physical vehicles are not yet available or, for example, the installation of the components is not permitted for safety reasons. In virtual test drives, engineers can also modify different transfer paths without real prototypes or selectively suppress individual paths, then evaluate them and thus identify optimization potentials.

This paper also shows ways in which manufacturers can meaningfully integrate an NVH simulator at various stages in the development process. Thanks to several NVH simulator variants – from a simple desktop simulation to state-of-the-art application in the complete vehicle simulator – it can be optimally adapted to the respective requirements.

An NVH simulator makes simulated sound and vibration behavior a real experience and thus paves the way for the digital twin.

Stringent environmental and noise standards in the automotive sector, as well as customer expectations, are pushing the limits of classic noise and vibration mitigation solutions. In the search of novel vibro-acoustic solutions, locally resonant metamaterials come to the fore as they promise to combine a light weight with excellent vibro-acoustic properties, at least in dedicated target frequency regions. In this publication, a metamaterial solution is applied to a vehicle to reduce the interior structure-borne noise due to the acoustic tyre resonances around 220 Hz. This metal 3D printed novel solution is applied on the rear wheel arches of a vehicle and serves as an alternative for dynamic damper solutions that are typically installed in line with the suspension on the vehicle body. Numerical and experimental analyses show how 3D printed resonant metamaterials can be a performant lightweight alternative to the common noise and vibration solutions used in the automotive sector.

Particle dampers are passive devices for vibration control that dissipate the energy of a vibrating system by transferring it to a bed of particles, generally included in a container that is fixed to the vibrating system itself. For some time now, these devices have been used to control the vibrations of different types of vibrating systems, from buildings to spacecraft components to PCB boards. On the other hand, applications in the automotive field so far have been limited to mechanical components such as engine oil pans and gearboxes. This article presents a novel application of particle dampers in the automotive field, wherein particle dampers are integrated into sound package parts, with the purpose of conferring to sound-package parts a broadband damping function. In this way, thanks to particle dampers all three basic functions of noise and vibration control, i.e. sound absorption, sound insulation and vibration damping, may be integrated in a single sound package part. This may be advantageous in two respects. First of all it may help reducing, if not eliminating, the bituminous dampers traditionally distributed over the vehicle body. Secondly, it may also enable the weight reduction of sound package parts, by avoiding that such weight reduction compromises the low-frequency performance of the parts themselves.

The article presents an overview of the concept underlying this novel application of particle dampers to the automotive field, together with examples of in-vehicle tests that confirm its effectiveness. Some basic aspects of how the concept was industrialized will also be touched.

A repeatable objective means of specifying interior noise targets for EV whines is presented. It offers a solution to the reoccurring issue of defining defendable whine targets in electric vehicle programs

Electric vehicles tend to exhibit low level whines that have negligible effect on the overall level but can have a significant effect on the subjective perception

In a vehicle with an engine, the firing frequency and its harmonics tend to dominate the overall level during accelerations. With an EV, the most significant orders are typically magnetic, gear related or offset about the inverter frequency. They can occupy higher frequencies where there is less masking from road and wind noise and are, therefore, subjectively more prominent

Different cars will have different levels of masking. For instance, a car with a sporty bias may have higher levels of road noise than a luxury vehicle. The former can accept higher levels of whine noise without them being prominent. If stringent road noise targets are specified, stringent whine targets are also required

The method proposed here is suitable for low level whines, compensates for different levels of masking (road and wind noise) and provides a pressure target that can be cascaded to system level (EDU noise) using the principles of transfer path analysis.

The network effect has been one of the most powerful forces in the rise of Big Tech. All these companies have in common that they offer different kinds of networks, with services and products, which provide a huge benefit for the individual user. Adapting the network effect to NVH testing, especially in the development process of electric motors, offers a wide range of advantages. Various aspects, and hence different groups, are usually involved in the development process, e.g. structural testing, acoustics, electric power, and simulation. Alterations in any of these fields usually result in impacts on one of the other topics. Optimizing the NVH properties for example might have a negative impact on motor performance. In contrast the increase of performance also influences the NVH characteristics of the motor. Up to now each group involved in the process has been using specialized hard and software to focus on their own task, resulting in problems in the late development phase. Using a network-based approach enables a communication with specialized systems rather than trying to create an all-purpose system. A flexible NVH system can be used to acquire NVH data and analyze the data on the fly, providing feedback to the performance calibration system, so that performance and NVH can be optimized in parallel. Further the NVH data can be rapidly combined with blocked forces, simulating the integration of the motor into the full vehicle and its effect on the overall NVH characteristics.

In today’s automotive world EV segment is emerging continuously. EV major noise sources are tire, motor and aerodynamic noises etc. At high speeds wheel-road noise dominates as wheel-road noise level increases with vehicle speed. It is required to design acoustic wheel arch liners for tire noise reduction. Considering the criticality in overall EV noise reduction, optimization of acoustic performance of wheel arch liner is essential which requires precise evaluation in terms of sound absorption and mounting with air gap from body panel to reduce tire noise. This paper discusses about the extensive study done to develop the methodology for step by step evaluation of sound absorption of wheel arch liner at design stage (flat form), along with air gap and actual molded part in Autoneum make Alpha cabin. BIOT’s properties of flat and molded wheel arch materials evaluated using specialized test rigs in terms of AFR, Porosity, Tortuosity, VCL, TCL etc. Different types of wheel arch liners have been evaluated and effect of different parameters like sample construction, mounting, air gap behind with body panels, fiber structure of sample has been studied. Parametric study has been done using BIOT’s properties to tune the wheel arch liner absorption performance.