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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.

It is well known that customer perception of the annoyance of steady-state wind noise can be fairly well characterized by calculating the loudness of such sounds. Commonly used is the ISO532B or Zwicker method [1]. What is not known, however, is how a customer would react to time-varying wind noise. Such situations can occur when a vehicle experiences cross-wind conditions on the highway. Turbulent air flow generated by either a passing vehicle or when traveling in the wake of another vehicle can cause the wind noise to take on time-varying characteristics. The time-varying wind noise created by such situations is commonly referred to as “buffeting.” Customer complaint field data indicates that wind buffeting is a source of annoyance, but the level of the effect has never been quantified. In this study, binaural sounds were recorded inside an aeroacoustic wind tunnel. Varying degrees of buffeting were simulated using a “blocker” vehicle situated in front of the test vehicle.

Over recent years MIRA has conducted a large number of vehicle noise appraisals and listening experiments. Their results have highlighted significant differences in people's perception of vehicle noise which can partially be attributed to the age of the participating individuals. Initial investigations suggest that this is primarily due to natural loss in hearing sensitivity especially at high frequencies, resulting from the physiological changes that occur with age (presbycusis). Its effect on subjects' vehicle noise assessments can be highly significant, potentially causing total disagreement between individuals of different ages. This is particularly pertinent in the case of vehicle NVH development, where young NVH engineers may be developing vehicles targeted at the luxury vehicle sector with a relatively older customer base.

Sound data were recorded from a series of trucks that were operated in various powertrain conditions. The acquired sounds from both the steady state engine speed and second gear wide open throttle operation were then presented to a group of subjects as paired comparisons. Correlation between these subjective ratings to the objective measures of the engine sound were then done and a linear relationship developed.

Research interest in vehicle NVH to improve riding comfort has increased significantly in the recent years. The air- and structure- born noise generated by the automotive shock absorber become a key factor to evaluate quality of vehicles. The ultimate goal of this study is to create a vibro-acoustic model of a shock absorber which can be used as a predictive tool by design engineers in the early stage of shock absorber design process. The efficiency of CAE tools developed in this study may also allow for more design iterations and alternatives within a relatively shorter design time, which may lead to a higher level of refinement and better-optimized design

An All Wheel Drive Spin-Torsional Dynamometer facility has been constructed at the Advanced Engineering Center of Ford Motor Company, adding unique capability for powertrain NVH testing. This state-of-the-art facility is designed to concurrently deliver controlled rotational and torsional engine inputs to the drivetrain. While the facility supports the use of a live engine for input, it is also equipped with an engine simulator to allow detailed examination of the NVH characteristics of new powertrain configurations before prototype powerplants are available, without the need for a live engine. This will reduce development timing for new powertrains significantly. The virtual engine consists of a driving dynamometer coupled with a high frequency servo-hydraulic torsional actuator.

Noise from vehicles is a major contributor to community noise. While at high speed often the pavement-tire interaction may be the predominant source, engine noise may also be significant, especially at low speeds. In some European countries most trucks, autos, and motorcycles must be tested at regular intervals per ISO 5130 (1982) “Acoustics- measurement of noise emitted by stationary vehicles- Survey method.” The standard requires a measure of the maximum emitted exhaust Fast, A-weighted sound level between a given engine RPM and an idle condition. In the past, the RPM has required a significant time to measure since it requires connecting a transducer somewhere in the engine compartment. This paper discusses an instrument that extracts the engine RPM from the acoustic signal at the exhaust, based on different engine types. This eliminates the need for a direct connection and considerably speeds vehicle tests.

The objective of this paper is to present the complex analysis method for the free vibration of general anisotropic rotors. The approach developed in this work represents the natural mode of the rotor as the sum of two sub-modes, one that rotates in the forward direction and the other in the backward direction. It is shown that the natural mode has to be described as such to satisfy the complex equation of motion of general rotor systems. Physical interpretation of results from the analysis of a model of the anti-symmetric motion of the rigid rotor shows that the complex mode contains modal directivity information as well as the conventional modal information. Proposed representation of the natural mode enables one to make clear definition of the forward mode and the backward mode, and more importantly enables one to complete the complex rotor analysis procedure.

Acoustical laboratories for vehicle testing have specialized requirements which differ from those for most conventional buildings and facilities. As a result, the normal design and building process takes on added dimensions which need to be carefully considered and addressed. This paper presents an overview of the process that starts with conceptualization of the laboratory and ends with the validation and qualification of the laboratory, and includes particular emphasis on the inherent peculiarities. Case studies are provided of several potential perils and pitfalls that may be encountered in the process which can adversely affect the usability of the laboratory as well as the validity and repeatability of test results obtained by that laboratory. The paper concludes with suggested courses of action which will help either to avoid or minimize the compromises that imperil the functional effectiveness of a laboratory.

There are a number of factors that dictate the size, type, and resultant over all cost of a controlled acoustical environment in which measurements can be made accurately and reliably. The type of acoustical environment is generally specified in the appropriate SAE, ISO, ANSI or ASTM standards. The purpose of this paper is to concentrate upon the design considerations of a properly engineered anechoic chamber. Anechoic is defined as “free from echoes or reverberations”. An ideal chamber would contain no reflections of sound from its walls, ceiling, or floor and an acoustical free-field condition would exist. Probably the best testing environment is outside with no boundaries to cause reflections. However, temperature, pressure, humidity, and wind can significantly and unpredictably disturb the uniform radiation of sound waves. In an ideal free-field environment, the inverse square law would function perfectly.

A frequency domain order tracking method is developed that is able to separate both close and crossing orders. This method is based upon the multiple input H1 FRF estimator. The method can use either the actual tachometer pulse train or a simulated chirp function as an assumed input to formulate the FRFs which are actually order tracks. The advantages and disadvantages of using each type of assumed input are discussed. The performance of this method in both simple and complex order tracking cases is evaluated. Analytical datasets are used to evaluate the performance of these order tracking methods under a variety of operating conditions which include close orders. Finally, this paper will develop the necessary derivation to show the analytical relationship between the Time Variant Discrete Fourier Transform (TVDFT) and the FRF based techniques, one being an order domain method and one being a frequency domain method.

Practical issues to consider when making measurements for Nearfield Acoustical Holography (NAH) analysis are addressed. These include microphone spacing and placement from the test surface, number of microphones and array size, reference microphone number and placement, and filtering of the data. NAH has become an accepted analysis tool so that several commercial packages are available. Its application is limited to test surfaces that are fairly planar, lending itself well to tire testing, front of dash testing, engine face testing, etc. In order to achieve accurate NAH results, the measurement and analysis process must be clearly understood on a practical level. Understanding the advantages and limitations of NAH and the measurement parameters required of it will allow the user to determine if NAH is applicable to a particular test object and environment.

We propose the use of an active element in conjunction with a passive, reasonably-damped Suspension to make an engine mount capable of satisfyingBoth damping and isolation requirements while avoiding 1) the loss of performance due to detuning of tunable (such as hydraulic) engine mounts and 2) the undesirable on/off switching associated with the decoupler in hydraulic mounts. In the proposed scheme, the damping will be provided by the proper choice of damped elastomeric material and isolation will be achieved by controlling the active element using a novel kalman-estimator based algorithm developed by the authors. To demonstrate the effectiveness of the proposed mounting scheme the distributed parameter models of a typical engine/chassis system was developed. Finite element analysis of the chassis was performed to find its natural frequencies and mode shapes which in turn were used to construct the state space control model.

Engine noise is still one of the dominating sources to vehicle interior noise. Among the engine components, engine covers are often the significant contributors to overall engine noise, requiring in-depth acoustic investigation to achieve substantial reduction. Ford Motor Company has acquired a 150 channel Nearfield Acoustic Holography (NAH) system for powertrain NVH development. This system provides new acoustic information with various metrics and visualization of non-stationary sound field in time domain to facilitate better understanding of noise generation/propagation mechanism. This paper focus on investigating the design of engine covers which radiate chain whine, fully utilizing the capability of this system including spatial transformation. Based on reconstruction of noise sources, effective design change to achieve significant reduction of chain whine is derived and then verified in very short time compared to previous methods.

Interior noise in motor vehicles is essentially influenced by the engine which may contribute via both, structural and acoustic transmission paths. This engine related interior noise components may be controlled deliberately by active control measures without changing any source or transfer paths characteristics. Besides attenuating dominant noise components, the approach may equally be used to optimise interior sounds with respect to sound quality. Based on general considerations how active noise and vibration control measures may effect subjective criteria, the paper gives examples how different, sometimes extremely contrasting noise characteristics may be realised in a given car.

This paper deals with the results of an investigation of moulded cases such as acoustic deflectors housing noisy equipment of the vehicle. The main advantage of the deflector is to decrease the level of noise, but the phenomenon of self-excitation is important, too, because it becomes a new source of noise. Readjustment of the vibration modes spectrum is possible by creating special structural variations, which increase the internal dissipation of energy of the vibrations in the deflector material. This approach is related to the introduction of design variables, the kind of material or to the choice of the points of fixation. The principal indication of a vibration mode of such a structure as a deflector is the number of nodal points. This characteristic gives the possibility to select several groups of modes, which are effective from the viewpoint of decreasing vibration amplitudes. Other possibilities are related to the means of active vibroinsulation.

A silencer to attenuate engine exhaust noise using active control methods has been developed. The device consists of an electrically driven valve, combined with a buffer volume, which is connected to the exhaust outlet. Using the mean flow through the valve and the pressure fluctuations in the volume, the valve regulates the flow in such a way that only the mean flow passes through the exhaust outlet. The fluctuations of the flow are temporally buffered in the volume. To carry out optimization and validation experiments, a cold engine simulator has been developed. This device generates realistic exhaust noise as well as the matching gas flow using compressed air. The simulator allows quick and reliable acoustic and fluid dynamic experiments on exhaust prototypes. The silencer is developed using electrical equivalent circuits, wherein at first instance a feedforward control is applied.