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Substantial activity in the field of recycling has made industry increasingly aware of the need to find novel ways of reusing post industrial and post consumer waste to produce useful products for our markets. The traditional approaches have been to use the scrap material as is into the original markets targeted for virgin materials, and finding areas that can accept the resultant downgraded properties. This approach has created difficulties in the recycling of automotive painted thermoplastic polyolefin (TPO) fascia and trim products. The presence of the paint contaminant has substantially degraded the physical properties of the plastic. This paper reviews the use of painted TPO scrap as a raw material for automotive sound barrier applications whereby the inherent material characteristics of TPO are capitalized on. The material modifications and functional characteristics as they relate to this application are described.

The influence of manifold geometry on exhaust noise is studied. First, a linear description of the problem is presented, so that potential relevant factors may be identified. Then a full non-linear simulation is performed, for a simple geometry, in order to check, in more realistic conditions, the ideas obtained from the linear theory. The results indicate that, although some qualitative trends may be obtained from the linear analysis, the role of back-reaction of the manifold on the engine (a non-linear coupling effect) may be determinant.

Flow noise from exhaust systems is a noise source that contributes to drive-by noise measurements. A prediction tool that allows us to choose the right duct dimensions would be very helpful. Therefore we integrated a flow noise module in a given linear acoustic prediction software. A flow noise source is modelized as an acoustic source. The source spectra is a function of the Strouhal number. The noise level depends on flow speed. A flow noise measurement with cold flow gives a set of source describing parameters. Using these parameters and the flow noise source model, a prediction of flow noise for mufflers is possible.

This paper describes a method to determine an objective measure of disturbing sounds of automotive exhaust noise (e.g. booming noise, whistle, flow noise,…). First, a disturbing sound catalogue is established. Then the approach used to make the different disturbing sounds measurable is presented. By making the perception of the disturbing sounds objective, it becomes easy to determine when they appear and to what extent. Finally, the contribution of this research in the framework of the global integration of sound quality in the design process of exhaust systems will be discussed.

This paper presents an integrated design/simulation/test approach for evaluating the sound quality of exhaust noise as early as possible in the exhaust system design and development process. A time domain engine/exhaust simulation program is used to calculate the engine order content of the tailpipe radiated noise from an odd fire V-10 exhaust system. Both steady state and transient conditions are simulated and sound files generated for exhaust sound quality evaluation. To increase the realism of played back sounds, the predicted engine orders are mixed with synthesized or recorded background noise for both steady state and transient conditions. These alternative approaches will be described and evaluated for technical feasibility and sound quality.

The research of pulsation wave propagation inside exhaust pipe installed in V8 engine shows that pulsation from engine was changed by joining two front pipes in entire exhaust pipe. In short, frequency of pulsation inside the pipe is not always equal to engine explosion first order frequency or its harmonics. Accordingly, structure of junction has been studied, which indicated that having volume at junction add engine revolution first order component pressure fluctuation to blow-down wave component and makes exhaust sound worse. This phenomena is caused by irregular explosion interval on each bank of V8 engine and phase delay of propagation at junction.

There are growing demands for condition monitoring of IC engines, and therefore any method in order to improve the performance of the engines ought to be evaluated. This paper proposes a new approach for the prediction and optimisation of noise and exhaust emissions in IC engines. The idea is to reconstruct the cylinder pressure from vibration measurements on the engine surface by using the complex cepstrum method [3, 4]. The reconstructed cylinder pressure is further used as input in Multivariate models, based on cylinder pressure, for estimating noise and exhaust emissions. This paper demonstrates the applicability of the method for modelling of noise and exhaust emissions

Vibration of an exhaust tube with a non-linear fixing construction is analyzed. Numerical and laser holography investigation methods are used for the determination of vibration processes happening nearby the cylinder fixing areas. Obviously, the analyzed non-linear system can produce complex reactions even to harmonic excitations. The knowledge about such zones of “wrong” dynamic behavior may help to eliminate and reduce higher noise levels and extend the lifetime of the construction.

This paper covers the application of hybrid vibro-acoustic simulation methods to shorten the design cycle of power-plant components. A comparison is made between Frequency Response Function based and Modal based algorithms for the generation of a predictive powerplant assembly model. The effectiveness of design modifications is evaluated by loading the original and modified predictive models with experimentally identified excitation forces. The procedure is validated by correlation with experimental data.

The air induction system of an automobile engine contributes to the noise level generated by a passenger car. The contribution is significant in the perception of vehicle noise quality. There is a great value in reducing and controlling passenger car air induction noise. Helmholtz resonators are widely used for noise reduction in vehicle induction and exhaust system. These resonators are usually mounted as side branch volumes to the main induction system, occupying larger space. The design presented here describes the use of compact inline Helmholtz resonator (Patent application no. 190/Bombay/98) for elimination of low frequency noise character in passenger car. Finite element model of the acoustic cavity of induction system along with the inline resonator is made. The transmission loss characteristics computed analytically correlates very well with the experimental transmission loss characteristics.

Silencers are very often filled with absorbent fibers to optimize the acoustic performance, particularly when the volume is limited. The fibers have to meet several specifications concerning (1) acoustic damping as a function of frequency, (2) temperature stability, (3) processing, and (4) blow-out resistance. This paper will review the characteristic properties for continuous fibers including Advantex™ versus standard E Glass as well as discontinuous fibers such as basalt wool. The failure mechanism of the various fibers will be explored in detail. Thermal shock testing, single filament tensile strengths, and weight loss measurements will be used to contrast the failure mechanism of these fibers. Additionally, the acoustic performance of silencers filled with different fibers will be analyzed and compared. The selection of different filling materials is closely linked to the production process utilized.

Typical automotive muffler designs contain complex internal components such as extended inlet/outlet tubes, thin baffles with eccentric holes, internal connecting tubes, perforated tubes, perforated baffles, flow plugs and sound-absorbing materials. An accurate performance prediction for highly complicated muffler designs would greatly reduce the effort in fabricating and testing of multiple design iterations for engineers. This paper discusses the use of a component-based computer simulation tool for design and analysis of exhaust mufflers. A comprehensive computer program based on the Direct Mixed-Body Boundary Element Method was developed to predict the transmission loss characteristics of muffler systems. The transmission loss is calculated by an improved four-pole method that does not require solving the boundary element matrix twice at each frequency, and hence, it is a significantly faster approach when compared to the conventional four-pole method.

Design optimisation with respect to interior noise is currently a topic of great concern for the automotive industry. An essential element in this process is to obtain a correct understanding of the various noise sources which are present, and the ways in which these sources propagate to the critical receiver. An experimental source-transfer-receiver methodology is presented, that allows quantifying the structure borne and airborne source strength of the intake system components and its contribution to the interior noise. The method allows interior noise optimisation after identification of the dominant contributors. The methodology is applied to identify the noise contribution of the air intake system to the interior noise of an 8-cylinder upper class vehicle. Correlation of the Structure Borne Transfer Path Analysis and Airborne Source Quantification models with physical decoupling experiments demonstrates a high correspondence.

The study employed the rig test method for the intake/exhaust noise investigation by using shaker. This article describes two case studies including 1.2 liter minivan and a 250 c.c. motorcycle. For the minivan case, it was verified that along with the reduction of 5∼8 dB(A) of intake noise the interior noise was also improved using the rig test optimization result. For the motorcycle case, It was found that there was very good correlation of the exhaust noise measured among the engine dynamometer, road test and rig test after the temperature effect was compensated. Hence, the study chose the rig test as a development tool to get prompt NVH evaluation results on the different exhaust pipe lengths and keep the development time schedule. From the results, it is concluded that the simple and cheap rig test evaluation technique is vital and a very effective tool to achieve the vehicle NVH development goal.

Current progress and concepts of the IEEE P1451 Draft Standards for Smart Transducer Interfacing of Sensors and Actuators will be reviewed. Topics include the Network Capable Application Processor Information Model (P1451.1), Smart Transducer Independent Interface (1451.2), Distributed Multidrop Systems (P1451.3), and Mixed-mode Communication Protocols (P1451.4).

Large channel count data acquisition systems have seen increasing use in the acquisition and analysis of rotating machinery, these systems have the ability to generate very large amounts of data for analysis. The most common operating measurement made on powertrains or automobiles on the road or on dynamometers has become the order track measurement. Order tracking analysis can generate a very large amount of information that must be analyzed, both due to the number of channels and orders tracked. Analysis methods to efficiently analyze large numbers of Frequency Response Function (FRF) measurements have been developed and used over the last 20 years in many troubleshooting applications. This paper develops applications for several FRF based analysis methods as applied for efficient analysis of large amounts of order track data.

The component response synthesis approach utilizing frequency response function (FRF) has been used to analyze the dynamic interaction of two or more vehicle components coupled at discrete interface points. This method is somewhat suitable for computing higher frequency response because experimental component FRFs can be incorporated into the formulation directly. However its calculations are quite sensitive to measurement errors in the FRFs due to the several matrix inversion steps involved. In the past, researchers have essentially used a combined direct inverse and truncated singular valued decomposition (TSVD) technique to ensure a stable calculation, which is typically applied semi-empirically due to the lack of understanding of the influence of measurement error.

In the analysis of automotive vibration signals, it is often desirable to precisely track individual tonal components of a signal over time. This kind of analysis is useful in defining root cause of cyclic vibrations, allowing the engineer to localize a vibration problem to a specific subsystem. The most commonplace analysis methods are block-oriented Fourier Transform (FT) approaches. However, these methods invariably lead to time localization uncertainty and imprecise frequency resolution. Other analysis methods are available that can estimate the precise frequency of content of a signal at every time step, given certain signal assumptions. This paper studies several of these analysis methods. Narrow Band filters, Kalman filtering, Auto-Regressive signal modeling and the Phase Locked Loop are examined as methods of signal decomposition and order extraction.

Recent trends in signal processing have led to the discovery and implementation of wavelets as tools of many different applications. This paper focuses on their use as a tool for transient extraction. From the Discrete Wavelet Transform (DWT), specific coefficients are picked using a coherence-based criterion. These coefficients are then taken back to the time domain as the extracted transient. If the extracted transient is a response from a measured input, then a frequency response function can be formulated.

The following document is a set of guidelines intended to be used as a reference for the practicing automotive sound quality (SQ) engineer with the potential for application to the field of general consumer product sound quality. Practicing automotive sound quality engineers are those individuals responsible for understanding and/or conducting the physical and perceptual measurement of automotive sound. This document draws upon the experience of the four authors and thus contains many “rules-of-thumb” which the authors have found to work well in their many automotive related sound quality projects over the past years. When necessary, more detailed publications are referenced. The intent of publication of this document is to provide a reference to assist in automotive sound quality work efforts and to solicit feedback from the general sound quality community as to the completeness of the material presented.