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In this paper, the vibro-acoustic transmission characteristics are investigated in the view point of the airborne noise in the interior cavity due to the tire wall vibrations. The analysis is carried out by categorizing the airborne noise transfer path into the two separate consecutive events. First, the noise transfer from the vibrating tire wall to the exterior car panels is modeled by using the direct boundary element method (BEM). To this end, after discretizing the whole geometry of exterior body panels, tires, and ground into BEM models, vibro-acoustic transfer characteristics are investigated at several frequency components associated with the cavity resonances of tire. Here, cavity resonance frequencies of tire are estimated by BEM and the distribution of tire wall vibrations excited by a special vibro-acoustic source is measured at those frequencies.

Perkins Technology has developed the technology for a Euro III compliant High Speed Direct Injection (HSDI) diesel engine. A prototype engine was built both to demonstrate this technology and the production feasibility for application to the executive car market where NVH performance was seen as the critical driver. This paper expands upon the approach used for the NVH aspects of the design, analysis and verification of the engine and its installation in a typical executive car. Results for both the powertrain and the vehicle installation are presented showing class leading NVH performance.

Simplified closed form equations are developed to predict the sound power radiated from a simply supported rectangular flat plate in an infinite rigid baffle. A modification is added to include the effect of periodic uniform ribs in either uni-directional or a cross hatch pattern. The equations are correlated to finite element/acoustic code analysis. The accuracy of the equations is presented for typical induction system components and an expression is developed to predict the error for other panel configurations.

Noise legislations and the increasing customer demands determine the NVH-development of modern commercial vehicles. In this paper suitable engineering approaches will be discussed. In order to meet the very stringent legislative requirements of the EEC and some other countries refinement of all vehicle noise sources is required. Cost-effective solutions, however, can only be found with low-noise powertrains, thus being able to avoid excessive noise packages on the vehicle. There is increasing demand, because modular systems should be ready to power a variety of different trucks and busses and allow for easy servicability. With this focus on powertrain noise, the paper discusses and outlines the technological developments required to achieve sufficient noise reduction which aims towards a 1m engine noise level of 93 dBA measured in an acoustic test cell under rated conditions.

In January 1996 Mercedes-Benz has introduced a new 4-cylinder engine OM 904 LA of the new engine family for light commercial vehicles. The power range of the OM 904 LA comprises ratings from 90 kW up to 125 kW at 2300 rpm. From the beginning of the design of this engine, a noise emission output as low as possible was strived for, aside from the high targets as far as durability, maintenace and fuel consumption are concerned. The basis is the development of noise regulations for commercial vehicles. The noise reduction measures have to be concentrated on the engine since up to now it still is one of the main noise emission sources at the vehicle. Already at the lay-out of the engine the prerequisits for a low-noise engine behaviour have been taken into consideration. The engine is equipped with a fuel injection system featuring particular unit injector pumps for each cylinder which is superior to the conventional in-line injection pump as far as acoustics are concerned.

Jaguar has developed a new V8 powertrain with the support of predictive design analysis techniques. This paper describes some of the work performed during this programme to ensure low frequency powertrain refinement. The concept of the engine was to produce a lightweight 4.0 litre engine with class leading specific torque and power, while satisfying customer aspirations for vehicle refinement. To meet the refinement objectives, an understanding of the structural dynamic performance of the powertrain was required. This understanding would be essential in developing the design from initial concept through to production intent. To support this requirement a programme of predictive work was included within the design plan. In the predictive work, low frequency modes of the powertrain and order tracked mount vibration were used to characterise the influence on in-vehicle refinement. Comparison with measured engine vibration confirmed the predicted effects of design changes.

An engine system finite-element model is developed and experimentally evaluated for predicting the structural vibration and radiated noise of the running engine. Combustion and inertial loads from a rigid-body dynamic analysis of the crank-piston motion are applied as operating loads in the model. Comparisons are made with measurements of the structural vibration and radiated noise of a running engine. The comparisons show that the accuracy of the model in predicting structural vibration and radiated noise is generally adequate.

Some years ago development, in the auto industry, of routine measurement of sound intensity in vector form, brought about major changes in determining sound power, particularly in improved accuracy and use in an indoor work area. However sound power is not yet being fully utilized. Accuracies within ± 10 % or ± 0.4 dB can be expected and narrow-band spectral data and intensity distributions on the integration surface can be used to identify and quantify component noise sources. In this paper new results are presented. In particular it is shown that sound power based on vector sound intensity can be determined accurately in a reverberation room.

In this paper, experimental evidence will be presented to demonstrate that unstiffened, low density fibrous materials are “limp”: i.e., their in vacuo bulk stiffness is very small compared to that of air with the result that the materials' solid phase motion becomes acoustically significant. Next, a new limp porous material model is presented. It is shown that this model may be used in conjunction with transfer matrices to predict the absorption or transmission loss of arbitrarily layered combinations of fibrous layers, permeable or impermeable membranes, and air spaces. The predictions of this model agree well with experimental measurements and so may be used to optimize sound absorption or transmission treatments.

The Scanning Laser Vibrometer can make full field, high resolution measurements of the normal surface velocity of automotive door glass and sheet metal vibrations. These properties make the vibrometer a very useful tool for locating compliant and noisy areas on the surface of a vehicle, generated by exterior wind noise. An advantage of the vibrometer is that it measures the vibration of the surface, capturing the transfer of noise through the surface, rather than simply measuring the exterior wind noise. Methods of experimental setup, testing, and problem analysis on outside rear view mirror/A-pillar/Sideglass configurations and body panel vibrations are discussed in the paper.

In an automotive engine impulsive sounds and vibration are induced by faults or design constraints which degrade the sound quality of the engine. Thus it is important for an NVH engineer to detect and analyse impulsive sound and vibration signals for both fault diagnosis and also for sound quality assessment. However it is often difficult to detect and identify impulsive signals because of interfering signals such as those due to engine firing, harmonics of crankshaft speed and broadband noise components. These interferences hinder the early detection of faults and improvement of sound quality. In order to overcome this difficulty we present a two-stage ALE (Adaptive Line Enhancer) which is capable of enhancing impulsive signals embedded in background noise. This method is used to pre-process signals prior to time-frequency analysis via a bilinear methods such as the Wigner-Ville distribution and the Choi-Williams distribution.

The characteristically good fuel economy of the high speed direct injection diesel engine has led to increased market share as the power unit of passenger cars. This trend is particularly true in Europe and, if not halted prematurely by emissions legislation, is likely to continue. However, another characteristic of the high speed DI engine is increased noise and vibration over its gasoline counterpart. This has meant that additional noise and vibration measures are required in order to approach the competitive refinement levels of gasoline engine installations. This paper considers some of the characteristic diesel engine noise and vibration problems associated with vehicle installation and passenger comfort. The paper also discusses subjective and objective assessment and considers approaches to engineering more desirable sound quality.

Two years after the start of production, some members in a family of power seat adjusters developed an intermittent loud squeal sound when operated in the vehicle. An exhaustive and comprehensive engineering analysis identified the noise source to be primarily a single component in the seat track which was excited under specific conditions to vibrate in its free - free natural resonant frequency mode. The component was identified as the horizontal lead screw which vibrated under stick-slip principles against mating hardware. The noise was not reproducible in any consistent way; therefore, it was not readily detectable with 100% serial testing. Several solutions were enacted for controlling the problem in the short term while an investigation to the root cause was completed. Three long term solutions which addressed the root cause were pursued in parallel up to the production release of the best solution.

Engineers doing squeak and rattle testing of instrument panels (IP's) have successfully used large electrodynamic vibration systems to identify sources of squeaks and rattles (S&R's). Their successes led to demands to test more IP's, i.e., to increase throughput of IP's to reflect the many design, material, and/or manufacturing process changes that occur, and to do so at any stage of the development, production, or QA process. What is needed is a radically different and portable way to find S&R's in a fraction of the time and at lower capital cost without compromising S&R detection results.

The problem being investigated involves a noise-quality issue on a power steering application, when a sudden change of steering wheel angle generates an unwanted steering system noise or “Squawk.” This phenomenon is mostly observed during parking maneuvers, especially at lock positions and when the hydraulic fluid reaches a critical temperature on the specific application. The objective of the work to solve this noise-quality issue was to first identify the cause and then eliminate the Squawk noise. There were several constraints: No change could be made in the properties or type of hydraulic fluid used due to specification requirements; Steering wheel valve torsion bar characteristic (torque vs. angle) needed to be maintained within specification for ride and handling purposes; and, In addition to the mentioned constraints, a high capability of noise elimination generated by the production tolerances and dispersion has been considered.

This paper presents the results of a combined theoretical and experimental study to find the relationship between a system's parameters and the sound generated when the system impacts against a rigid fixture. Although the particular physical structure investigated is a flexible cantilever beam, the approach adopted is such that the results are valid for a more general class of problem.

As automotive manufacturers continue to increase their use of thermoplastics for interior components (due to cost, weight, …), the potential for frictionally incompatible materials contacting each other, resulting in squeaks and rattles, will also increase. This will go counter to the increased customer demand for quieter interiors. To address this situation, Ford's Advanced Vehicle Technology Squeak and Rattle Prevention Engineering Department and Virginia Tech have developed a tester that can measure friction as a function of relative sliding velocity during frictional instabilities such as stick slip. The Ford/VT team is developing a polymeric material pairing database that will be used as a guide for current and future designs to eliminate potential squeak concerns. Based upon the database, along with a physical property analysis of the various plastic (viscoelastic) materials used in the interior, an analytical model will be developed as a tool to predict frictional behavior.

Squeak and rattle has become a primary source of undesired noise in automobiles due to the continual diminishment of engine, power train and tire noise levels. This article presents a finite-element-based methodology for the improvement of rattle performance of vehicle components. For implementation purposes, it has been applied to study the rattle of a glove compartment latch and corner rubber bumpers. Results from the glove compartment study are summarized herein. Extensions to other rattle problems are also highlighted.

The acceleration process on which the noise measuring method for the homologation test is based yields extremely high acceleration values associated with enhanced tyre-road noise contributions, which are not mirrored under real driving conditions. Measures taken by tyre manufacturers to reduce tyre-road noise in these atypical operating modes do not necessarily lead to a reduction of tyre-road noise in real traffic. The German Federal Environmental Agency (UBA) has commissioned extensive studies of driving behaviour in cars and commercial vehicles under real traffic conditions in order to evolve a concept for an improved noise measuring method, whose guiding principles and structure are presented

The sound quality of systems with electric motors has become increasingly important to customer perception of vehicle quality. This paper summarizes the results of a case study of the sound quality of twelve power window systems. Paired comparisons of preference and semantic differential subjective evaluations were performed with twenty-nine test subjects. The test subjects clearly perceived differences between the power window system sounds when asked to scale the sounds using the adjective pairs of ““no whine/whine”” and “steady/fluctuating”. A regression analysis related test subject preferences to a linear combination of IS0532B band passed loudness (300-2500 Hz) and motor speed dip (% of normalized motor speed).