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To reduce dependence on petroleum resources and pollution to the natural environment, electric vehicles as new energy vehicles have become the focus of various original equipment manufacturers and component companies. At the same time, the NVH performance of electric vehicles is the focus of attention of automobile companies, and higher requirements are placed on sound-proof packaging, which is an important part of reducing automobile noise. Compared with traditional internal combustion engine vehicles, the biggest difference between electric vehicles (EV) is their electric drive system. High-frequency noise is generated when the electric motor is used as a power device. When there is no engine noise, the problem of electric drive noise is more obvious. Generally, an sound package is used to block the transmission path of noise. Therefore, an sound package is selected to cover the electric motor to reduce the impact of noise on the interior of the vehicle.

SAE acoustics materials committee published updates of SAE J1400 Standard - Laboratory Measurement of the Airborne Sound Barrier Performance of Flat Materials and Assemblies in 2017. In the standard, a control sample is defined with a specific construction to determine the suitability of the test suite. A set of measured sound transmission loss data of the control sample are included in the published updated standard. Autoneum North America Acoustics Laboratory constructed a control sample based on the design in the standard. Sound transmission loss (STL) measurement of this control sample was performed and results are consistent with published data below 2000 Hz. Above 2000 Hz, STL results are above published limits. Sound intensity measurement and flanking noise paths measurements confirmed the measured STL values of the control sample.

OEMs are racing to develop lightweight vehicles as government regulations now mandate automakers to nearly double the average fuel economy of new cars and trucks by 2025. Lightweight materials such as aluminum, magnesium and carbon fiber composites are being used as structural members in vehicle body and suspension components. The reduction in weight in structural panels increases noise transmission into the passenger compartment. This poses a great challenge in vehicle sound package development since simply increasing weight in sound package components to reduce interior noise is no longer an option [1]. This paper discusses weight saving approaches to reduce noise level at the sources, noise transmission paths, and transmitted noise into the passenger compartment. Lightweight sound package materials are introduced to treat and reduce airborne noise transmission into multi-material lightweight body structure.

Lightweighting of vehicle panels enclosing vehicle cabin causes NVH degradation since engine, road, and wind noise acoustic sources propagate to the vehicle interior through these panels. In order to reduce this NVH degradation, there is a need to develop new NVH sound package materials and designs for use in lightweight vehicle design. Statistical Energy Analysis (SEA) model can be an effective CAE design tool to develop NVH sound packages for use in lightweight vehicle design. Using SEA can help engineers recover the NVH deficiency created due to sheet metal lightweighting actions. Full vehicle SEA model was developed to evaluate the high frequency NVH performance of “Vehicle A” in the frequency range from 200 Hz to 10 kHz. This correlated SEA model was used for the vehicle sound package optimization studies. Full vehicle level NVH laboratory tests for engine and tire patch noise reduction were also conducted to demonstrate the performance of sound package designs on “Vehicle A”.

The Multi Material Lightweight Vehicle (MMLV) developed by Magna International and Ford Motor Company is a result of a US Department of Energy project DE-EE0005574. The project demonstrates the lightweighting potential of a five passenger sedan, while maintaining vehicle performance and occupant safety. Prototype vehicles were manufactured and limited full vehicle testing was conducted. The Mach-1 vehicle design, comprised of commercially available materials and production processes, achieved a 364 kg (23.5%) full vehicle mass reduction, enabling the application of a 1-liter 3-cylinder engine resulting in a significant environmental benefit and fuel reduction. This paper includes details associated with the noise, vibration and harshness (NVH) sound package design and testing. Lightweight design actions on radiating panels enclosing the vehicle cabin typically cause vehicle interior acoustic degradation due to the reduction of panel surface mass.

This paper describes the work carried out to assess the structure-borne and airborne contributions in the Rieter APAMAT II testing machine. The APAMAT II system was designed to measure the effectiveness of various trim and barrier treatments in automotive interior applications. The individual structure-borne and airborne contributions from the ball impact on the treated panel cannot be obtained directly from the sound pressure level measurements in the receiver chamber of the system. A hybrid modeling technique is proposed that incorporates finite element (FE) and statistical energy analysis (SEA) methods to develop vibro-acoustic models across the entire frequency range for analyzing transmission characteristics of various trim configurations. This provides an analytical model that can adequately predict the vibro-acoustic response under structure-borne loads at low to mid frequencies.

Sound transmission loss and sound absorption measurements are conducted to characterize acoustical performance of noise control materials and components used in vehicles. These measured data are often used to select materials and define acoustical targets. It is imperative to have accurate and repeatable data. Process variability is often monitored using measurement data collected over time. A certain amount of variability due to random causes is always expected. Acoustical measurements have inherent variability from different operators, equipment, test setup, environment etc. When variation in the measurements is due to random causes the measurements are in-control and measured data are considered “good”. However, special cause variations in the measured data such as operator error or setup error must be identified and corrected. Control chart is a popular statistical tool for monitoring process variability and improving quality.

The paper discusses the development of a new SAE standard J2883 for measuring sound absorption performance of absorption materials in a small reverberation room. It discusses the need for such a standard particularly in the automotive industry. It also discusses the need for understanding the parameters such as the room volume, diffusion and cut-off frequency, and the sample size that affect the measurements and how to address these parameters in developing a robust test method. Finally, the paper discusses some of the findings of the round robin tests where measurements were conducted in various size rooms, task force activities, and the proposed repeatability and reproducibility values of the test method.

Biot's model of elastic porous materials is widely used to predict the acoustical performance of noise control materials in the automotive industry. Material properties of acoustical materials, often referred to as Biot parameters, such as porosity, airflow resistivity, tortuosity, viscous characteristic length and thermal characteristic length are required inputs in the Biot model. Various test methods have been developed to measure Biot parameters. This paper conducts a comprehensive review of the existing test methods, discusses accuracy and applicability of each test method, and provides recommendations to the SAE Acoustical Materials Committee regarding the need for the development of SAE test methods for Biot parameters.

Random incidence sound absorption measurements of automotive components such as floor carpets, seats, headliners and hoodliners are important during the design and development of noise control treatments in a vehicle. Small volume reverberation rooms [1]1 have been widely used in practice to determine the absorption properties of those components. The SAE Acoustical Materials Committee has organized a task force to develop a standard procedure for measuring random incidence sound absorption properties of flat samples, as well as automotive components in small reverberation rooms. Statistical analysis and correlation study between large reverberation rooms and small reverberation rooms of flat samples using data acquired from a recent round robin study were reported in SAE Paper 2005-01-2284 [2, 3].

System Engineering has increasingly been applied in the automotive industry to develop quality vehicles efficiently and effectively. It is particularly important to use System Engineering methods in the early stages of vehicle development when all requirements such as performance, package space, cost and weight are actively defined and balanced, and when decisions are made that have substantial downstream design consequences. To achieve effective balance, decisions have to be data driven to complement engineering experience and judgment. Analytical tools (CAE) have been developed in the industry to evaluate and synthesize designs. However, there are limited examples and discussions in the literature on how the “upfront” CAE can be implemented to integrate cross-functional requirements into the component design. Statistical Energy Analysis (SEA) method is the CAE tool used in sound package development.

Small reverberation rooms are used in common practice for determining random incidence sound absorption properties of flat materials and finished parts. Based on current small reverberation room usage in the automotive industry, there is a need for standardization that would bring about an appropriate level of consistency and repeatability. To respond to this need, a feasibility study is being pursued by an SAE task force, under the direction of the Acoustical Materials Committee, to develop a small volume reverberation room test method for conducting random incidence sound absorption tests. In addition to an accepted test method for small reverberation rooms, a data driven correlation that relates full size reverberation room absorption testing to small size reverberation room testing would be beneficial in understanding the usage of both. A Round Robin study has been underway for more than three years and will be completed in 2005.

In the early stages of a vehicle program, sound package design is significantly complicated by numerous competing requirements including cost, weight, acoustical targets and packaging space. The problem is further convoluted due to a limited definition of the vehicle at this time. In this article, a Statistical Energy Analysis (SEA) model of the vehicle is created based on a gross description of the vehicle architecture. A large material database of commonly used sound package configurations is then linked to the SEA model. Genetic Algorithms (GA) are finally applied to optimize the sound package design to satisfy cost, weight, acoustical targets and packaging requirements in the vehicle design.

For vehicle interior noise abatement and noise treatment, it is desirable to quantitatively determine sound power contribution from each vehicle component because: (1) Sound packages can be designed with maximized efficiency if sound power contribution into a vehicle is known; (2) Acoustic leakage inside a vehicle can be determined by comparing sound power contributions from adjacent vehicle components; and (3) Sound power flow information can be used to verify Statistical Energy Analysis (SEA) model. Simple sound pressure measurement does not produce any information about sound power flow and is unsuitable for these purposes. This paper describes an in-situ determination of sound power contribution inside a vehicle using sound intensity measurements. Sound power contribution from each vehicle component was determined for engine noise at idle speed. Acoustic leakage in the vehicle was also determined.

Statistical Energy Analysis (SEA) is being actively pursued in the automotive industry as a tool for vehicle high frequency noise and vibration analysis. A D-class passenger car SEA model has been developed for this purpose. This paper describes the development of load cases for the SEA model to simulate road noise on rumble road. Chassis roll test with rough shells was performed to simulate rumble road noise. Sound radiation from tire patch and vibration transmission through spindles were measured to construct the SEA load cases. Correlation between SEA model predictions and measured data was examined. Test and SEA result comparisons have shown that simulation of airborne road noise requires only a trimmed body SEA model, while simulation of structure-borne road noise may require SEA modeling of chassis components.

Statistical Energy Analysis (SEA) is a tool for estimating the response of complex dynamic systems at high modal density. This tool is seeing ever wider application in a range of industries, including aerospace industry, marine industry, and building trades. The automotive industry is beginning to explore the application of SEA to high frequency vehicle acoustic design. The SEA model of vibrational power transmission has a direct analogy to thermal power transmission (diffusion). As thermal power flow is proportional to temperature difference, vibrational power flow is proportional to modal energy difference. In this paper the thermal analogy is exploited to visualize the SEA results. This is accomplished by color coding a finite element representation of the structure. In this paper, the thermal analogy is used to correlate test data with SEA model results. This is accomplished by constructing a test based modal power thermogram.