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Under the constraints of improved vehicle refinement, automotive OEMs are challenged to improve vehicle noise, vibration and harshness (NVH) characteristics, reduce vehicle weight, and streamline manufacturing and assembly processes. In support of these objectives, alternate methods of vehicle noise control are being investigated. This paper will address one area where alternate material strategies are being investigated to meet these requirements. Floorpan damping treatments are a primary component of the overall vehicle noise package. This paper will investigate three floorpan damping treatments. Comparisons will be made between asphaltic melt sheets, constrained layer dampers, and spray-on dampers. Performance of these treatments will be measured using laboratory methods and will feature a case study using a Body-In-White (BIW) to demonstrate performance of the different materials.

Recently, many authors have attempted to represent an automobile body in terms of experimentally derived frequency response functions (FRFs), and to couple the FRFs with a FEA model of chassis for performing a total system dynamic analysis. This method is called Hybrid FEA-Experimental FRF method, or briefly HYFEX. However, in cases where the chassis model does not include the bushing models, one can not directly connect the FRFs of the auto body to the chassis model for performing a total system dynamic analysis. In other cases when the chassis model includes the bushings, the bushing dynamic rates are modeled as constant stiffness rather than frequency dependent stiffness, the direct use of the HYFEX method will yield unsatisfactory results. This paper describes how the FRF's of the auto body and the frequency dependent stiffness data of the bushings can be combined with an appropriate mathematical formulation to better represent the dynamic characteristics of a full vehicle.

The popularity of AWD passenger vehicles presents a challenge to provide car-like drive-train NVH within a relatively small package space. This paper describes a drive-train NVH case study in which analysis and test were used, in conjunction, to solve an NVH problem. Also, it details a systematic process of using the analytical model to identify and resolve similar problems. The particular problem for this case study is a noise and vibration issue occurring at 75 MPH primarily in the middle seat of an all-wheel drive vehicle. Tests indicated that it may be due to propeller shaft imbalance. Analysis results showed good correlation with the tests for that loading condition. Several solutions were identified, which were confirmed by both test and analysis. The most cost-effective of these solutions was implemented.

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.

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.

A 50 Hz Solid-State Relay (SSR) was used to provide pulse-width-modulated power to engine cooling fans for continuous speed control, to reduce airflow noise and improve efficiency. However, this caused the cooling fans to vibrate at the switching frequency and harmonics, thus degrading vehicle NVH performance. This paper describes the problem associated with SSR- powered cooling fans, including root-cause analysis, and identification of areas sensitive to vibration affected by the switching power supply. Based on our analysis, we found several solutions to the problem. Our production solution and some generic recommendations for shroud design are presented in the paper.

Improving vehicle crash, NVH and metal fatigue performance using expanding polymeric foams can be achieved with a systematic approach. By employing a systematic approach with expandable epoxy foams and alternative carriers, the product development process can be significantly reduced. As a result, high strength and lightweight solutions can be designed to improve the structural performance of today's vehicles. This technical paper will examine the key steps in utilizing a systematic approach to selecting, designing and modeling structural expandable epoxy foam solutions used in conjunction with metallic and non-metallic carriers. A review of material properties, alternative designs and finite element modeling methods will allow for a thorough understanding of how expandable epoxy foams can meet the demanding challenges for improved occupant safety, reduced interior noise levels and increased durability at a reduced vehicle weight.

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.

Low frequency torsional vibrations can be a significant source of objectionable vehicle vibrations and in-vehicle boom, especially with changes in engine operation required for improved fuel economy. These changes include lower torque converter lock-up speeds and cylinder deactivation. This paper has two objectives: 1) Examine the effect of increased torsional vibrations on vehicle NVH performance and ways to improve this performance early in the program using test and simulation techniques. The important design parameters affecting vehicle NVH performance will be identified, and the trade-offs required to produce an optimized design will be examined. Also, the relationship between torsional vibrations and mount excursions, will be examined. 2) Investigate the ability of simulation techniques to predict and improve torsional vibration NVH performance. Evaluate the accuracy of the analytical models by comparison to test results.

In the development of several outside mirror designs for vehicles, a high frequency noise (whistling) phenomenon was experienced. First impression was that this might be due to another source on the vehicle (such as water management channels) or a cavity noise; however, upon further investigation the source was found to be the mirror housing. This “laminar whistle” is related to the separation of a laminar boundary layer near the trailing edges of the mirror housing. When there is a free stream impingement on the mirror housing, the boundary layer starts out as laminar, but as the boundary layer travels from the impingement point, distance, speed, and roughness combine to trigger the transition turbulent. However, when the transition is not complete, pressure fluctuations can cause rapidly changing flow patterns that sound like a whistle to the observer. Because the laminar boundary layer has very little energy, it does not allow the flow to stay attached on curved surfaces.

NVH refinement of passenger vehicles is crucial to customer acceptance of contemporary vehicles. This paper describes the vehicle NVH development process, with specific examples from a Diesel sedan application that was derived from gasoline engine-based vehicle architecture. Using an early prototype Diesel vehicle as a starting point, this paper examines the application of a Vehicle Interior Noise Simulation (VINS) technique in the development process. Accordingly, structureborne and airborne noise shares are analyzed in the time-domain under both steady-state and transient test conditions. The results are used to drive countermeasure development to address structureborne and airborne noise refinement. Examples are provided to highlight the refinement process for “Diesel knocking” under idle as well as transient test conditions. Specifically, the application of VINS to understanding the influence of high frequency dynamic stiffness of hydro-mounts on Diesel clatter noise is examined.

In noise and vibration control, damping treatments are applied on panel surfaces to dissipate the energy of flexural vibrations. Presence of damping treatment on the surface of a panel also plays an important role in the resulting vibro-acoustic characteristics of the composite system. The focus of this study is to explore possibilities of reducing the weight of damping treatments by means of perforation without sacrificing performance. The power injection concept from Statistical Energy Analysis (SEA) is used in conjunction with Finite Element Analysis (FEA) to predict the effect of perforated unconstrained layer treatments on flat rectangular panels. Normalized radiated sound power of the treated panels are calculated to assess the effect of varying percentage of perforation on structural-acoustic coupling.

Buffeting is a wind noise of high intensity and low frequency in a moving vehicle when a window or sunroof is open and this noise makes people in the passenger compartment very uncomfortable. In this paper, side window buffeting was simulated for a typical SUV using the commercial CFD software Fluent 6.0. Buffeting frequency and intensity were predicted in the simulations and compared with the corresponding experimental wind tunnel measurement. Furthermore, the effects of several parameters on buffeting frequency and intensity were also studied. These parameters include vehicle speed, yaw angle, sensor location and volume of the passenger compartment. Various configurations of side window opening were considered. The effects of mesh size and air compressibility on buffeting were also evaluated. The simulation results for some baseline configurations match the corresponding experimental data fairly well.

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.

Advances in the design and manufacturing of Expandable Epoxy Foam Inserts have resulted in a dramatic rise in the use of these technologies for the treatment of structureborne noise and vibration control. The evolution of these technologies has resulted in light weight and cost competitive solutions when compared to changes in primary body structure and surrounding sheet metal. These advances are discussed in detail. A structured, methodical approach to the identification of requirements for vehicle treatments is discussed. Based on these requirements, a process for the evaluation of application designs and the design optimization process are discussed. Validation of both the material technology and the engineering approach are presented through demonstration on actual vehicle applications.

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.