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NVH targets for future vehicles are often defined by utilizing a competitive benchmarking vehicle in conjunction with an existing production and/or reference vehicle. Mode management of full vehicle modes is one of the most effective and significant NVH strategies to achieve such targets. NVH dynamic characteristics of a full vehicle can be assessed and quantified through experimental modal testing for determination of global body mode resonance frequency, damping property, and mode shape. Major body modes identified from full vehicle modal testing are primarily dominated by the vehicle's body-in-white structure. Therefore, an estimate of BIW modes from full vehicle modes becomes essential, when only full vehicle modes from experimental modal testing exist. Establishing BIW targets for future vehicles confines the fundamental NVH behavior of the full vehicle.

A variety of expandable sealants are used to fill vehicle body cavities to impede noise, water, air, and dust from entering (and exiting) the passenger compartment. This paper compares three sealant technologies used for filling body cavities. The technologies are rubber-based elastomeric preformed parts; thermoplastic elastomeric preformed parts, and two-component polyurethane that is foamed-in-place directly in the vehicle body cavity. The following comparisons are made between the three technologies: application methods and issues, cost, material properties and acoustical performance.

Once the design of a door sheetmetal and accessories is confirmed, the acoustics of the door system depends on the sound package assembly. This essentially consists of a watershield which acts as a barrier and a porous material which acts as an absorber. The acoustical performance of the watershield and the reverberant sound build-up in the door cavity control the performance. This paper discusses the findings of a design study that was developed based on design of experiments (DOE) concepts to determine which parameters of the door sound package assembly are important to the door acoustics. The study was based on conducting a minimum number of tests on a five factor - two level design that covered over 16 different design configurations. In addition, other measurements were made that aided in developing a SEA model which is also compared with the findings of the results of the design study.

Vehicles are faced with a variety of airborne and structure-borne noise sources, such as wind, road, tire, engine and powertrain. To minimize the noise intrusion into the passenger compartment, a system level approach must be taken. This system level approach requires a focused effort to minimize noise at the primary sources, and an engineering initiative to desensitize the transfer paths through proper body design, sealing, and the implementation of noise control materials. This paper looks at different innovative materials applied to the body structure, their design and placement of them to support a quiet interior. A series of vehicle case studies details the in-vehicle performance and benefits of both preformed and bulk material solutions that are applied to the body structure: baffles, sealers, barriers, dampers and structural reinforcements. An emphasis is placed on low cost, low mass and high performance optimized solutions.

Typical automotive sound package components are usually characterized by their absorption coefficients and their acoustic power-based insertion loss. This insertion loss (IL) is usually obtained by subtracting the transmission loss (TL) of a bare flat steel plate from the TL of the same plate covered with the trim material. While providing useful information regarding the performance of the component, air-borne insertion loss is based solely on acoustic excitations and thus provides very little information about the structure-borne performance of the component. This paper presents an attempt to introduce a standard procedure to define the power-based structure-borne insertion loss of sound package components. A flat steel plate is excited mechanically using a shaker. Different carpet constructions are applied on the plate and tested. Based on velocity measurements, a force transducer and intensity probe, the mechanical input and the acoustic radiated power are obtained.

With the ever increasing popularity of SUV automobiles, studies involving driveline specific problems have grown. One prevalent NVH problem is axle whine associated with the assembled motion transmission error (MTE) of an axle system and the corresponding vibration/acoustic transfer paths into the vehicle. This phenomenon can result in objectionable noise levels in the passenger compartment, ensuing in customer complaints. This work explores the methodology and test methods used to diagnose and solve a field axle whine problem, including the use of cab mount motion transmissibility path analysis, running modes and a detailed MTE best-of-the-best (BOB)/worst-of-the-worst (WOW) study. The in-vehicle axle whine baseline measurements including both vehicle dynamometer and on-road test conditions, along with the countermeasures of axle whine fixes are identified and presented in this paper.

Maintaining or improving acoustic and vibration quality of vehicles, the automotive industry continually faces design goals to reduce weight and manufacturing cost. In light of these objectives, advanced material design techniques facilitate the development of a high performance bulk applied constrained layer vibration damper aimed at improved automotive acoustics. The overall vehicle acoustic and vibration quality relies heavily on floor pan vibration dampers. A review of current industry damping technologies is addressed. Industry migration to bulk applied extensional dampers from the once ubiquitous asphalt sheet damper is discussed. Furthermore, this paper addresses the development of a new bulk applied constrained layer damper technology that delivers superior acoustical performance. The paper presents the chemistry formulation, the prediction of analytical results, and experimental validation.

Liquid spray applied damping materials have potential advantages over conventional sheet damping materials in automotive body panel vibration applications. In order to understand the acoustical impact, a laboratory based NVH study was conducted to compare the damping and stiffness performance characteristics of various sprayable damping materials versus the production damping treatment. Based on this comparison, a criteria was developed to select potentially viable sprayable damping materials for vehicle testing. In-vehicle tests were also performed and compared to the laboratory findings to understand how well the results correlate. This paper discusses a criteria for selecting sprayable damping materials based on bench-top tests for vehicle applications, and the potential benefits of sprayable materials.

A new semi-active damping approach for the reduction of transmitted acoustic noise is investigated. It involves the controlled variation of the system's spring constant in response to the system's motion in such a way as to maximize the energy lost in the damping elements. A Discrete Mechanics simulation of a prototypical spring-mass-damper system is used to compare the performance of this approach with the semi-active viscous damping approach being applied to this problem today. It is found that: (1) Parametric damping does not require precise phase matching between the noise signal and the response of the system. (2) “Runaway” catastrophes associated with the nonlinear response of the spring constant are avoided by saturating the response of the spring. (3) An algorithm that controls the response of the element by recognizing when it is storing undesired energy suffices to attenuate harmonic and transient noise below 1:1 transmissibility for all frequencies at and below resonance.

Chemically and heat reactive, expandable sealants are used as “acoustical baffles” in the automotive industry. These acoustic baffles are used to impede noise, water and dust propagation inside of structural components and body cavities. Use of these sealant materials has grown significantly as the demands to improve vehicle acoustic performance has increased. Various test methods have been developed to quantify the performance of these materials through direct comparison of material samples. These investigations use standardized testing procedures to characterize the acoustic performance of a material sample on the basis of controlled laboratory test conditions. This paper presents a step in the progression of evaluating acoustic baffle performance in the vehicle. Standard experimental techniques are used to investigate the influence of the baffles on the vehicle acoustic performance.