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Passenger car customer expects both: low interior noise level and a sound quality, adapted to vehicle driving condition. The latter should be based upon a comfortable sound character without outstanding noise effects. One of the very unpleasant noise characteristics is roughness, also called rap noise or rumbling noise. Beside intake noise and powertrain structure bending, the dynamic crank train behaviour is one of the potential origins of a rough noise pattern. Material properties of the crankshaft and the layout of crankshaft damper can influence roughness as well as the crank train clearances. Subjects of this study, which was performed on a 4-cylinder spark-ignition (SI) engine, were the identification and objectivation of a specific noise concern which occurred during vehicle acceleration. Aim was to evaluate the noise concern sensitivity to the crank train clearances and to define optimum clearance ranges for noise quality improvement.

Distinguishing physical modes from mathematical modes in the modal analysis of complex systems, such as full vehicle structures, is a difficult and time-consuming process. The major tools frequently used are stabilization diagrams, mode indicator functions, or modal participation factors. When closely spaced modes are to be identified, the stabilization diagrams and mode indicator functions are no longer effective. Even the reciprocities of mode shapes and modal participation factors cannot be well satisfied to indicate whether a mode is a physical one, when measurement errors are large. To overcome these difficulties, an optimization procedure is developed, whereby physical modes can be sorted out in a given frequency range while the error between measured and synthesized frequency responses is minimized. An optimal subset selection algorithm is used in this procedure.

A series of system level experiments were conducted using 2 vehicles of identical design to measure, analyze and quantify crank rumble noise from the viewpoint of source strength and path dynamic response. One of the vehicles was known to produce relatively severe crank rumble response (noisy), while the second vehicle was almost free of the annoying response (quiet). Two specific operating conditions most susceptible to crank rumble noise were of interest: (1) no load snaps in neutral and (2) hard acceleration in second gear. For each condition, the vibration and sound pressure responses throughout the vehicle were obtained. The measured data was analyzed critically to determine frequency content and strength of rumble noise at each location. Calculations were also performed from the measured data to determine the modes of transmission and the relative contributions from air-borne and structure-borne paths.

In this paper, we discuss methods used to investigate a clearly audible gear whine problem in a modern automobile. Currently available PC-based computer software, coupled with more traditional engineering tools, such as spectrum analyzers, are employed to efficiently observe noise and vibration phenomena. Jury evaluations are conducted, using in-vehicle noise data, to rank actual gear whine levels. Additional jury studies using synthesized gear whine help us further understand listener preferences. Unloaded gear transmission error testing is explored as a means of predicting gear whine levels under light loads, such as those seen during highway cruising. We finally correlate many results to better understand the source and paths of the gear noise, and make recommendations for further exploration of this type of problem.

Torsional and lateral bending vibrations of cylinder block have a large effect on engine noise. Cylinder block vibration not only causes noise to radiate from the cylinder block itself but it is also the major exciting force to the oil pan and timing belt cover. In order to reduce engine noise, it is important to completely understand the mechanism of cylinder block vibrations. An analysis is conducted using FEM and BEM to compute the influence of crankshaft torsional vibrations on cylinder block vibrations. A crankshaft system for a four cylinder automobile engine was used for analysis. Finite Element model of crankshaft is created using parametric modelling software developed based on ANSYS FEA software. Finite Element model of cylinder block, bearing cap, oil sump is also created using another parametric software developed based on ANSYS FEA software.

By applying the dynamic stiffness matrix method, three-dimensional vibrations of the crankshaft system under firing conditions were investigated for an automobile engine, taking account of the vibration behavior of the torsional damper and the cylinder block. To simplify the analyses, the crankshaft was idealized by a set of jointed structures consisting of simple round rods and simple beam blocks of rectangular cross-section; the main journal bearings were idealized by a set of linear springs and dash-pots. For the flywheel of flexible structure, the dynamic stiffness matrix was derived from FEM. However, for the cylinder block, the dynamic stiffness matrix was constructed from the experimental values of the modal parameters obtained from the experimental modal analysis (EMA), because of the complicated structure.

The introduction of a thin fluid layer between two layers of sheet metal offers a highly effective and economical alternative to the use of constrained viscoelastic damping layers in sheet metal structures. A diesel engine gear cover, which is constructed of two sheet metal sections spot welded together, takes advantage of fluid layer damping to produce superior vibration and sound radiation performance. In this paper, the bending of a double layered plate coupled through a thin fluid layer is modeled using a traveling wave approach which results in a impedance function that can be used to assess the vibration and sound radiation performance of practical double layered plate structures. Guided by this model, the influence of fluid layer thickness and inside-to-outside sheet thickness is studied.

In diesel engines, combustion is found to be a significant noise excitation. However, the aim of the present study is to introduce a concept by which all the engine noise sources can be classified. A special test rig has been installed for this reason which enables simultaneous acoustic measurements, in addition to those related to thermodynamic measurements. The procedure for accurate determination of direct and indirect combustion noise is explained based on a 3D multi-zone steady-state interior-exterior acoustic problem. The predicted direct combustion noise is considered to be due to combustion noise point source within the engine cylinder enclosure, and according to boundary element method (BEM). Results indicate that the proposed combined experimental-prediction approach is a reasonable approximate technique for the separation of mechanical, direct combustion and indirect combustion noise from the total engine noise.

This paper will highlight the criteria and development efforts which have to be considered when planning to launch a SUV (Sports Utility Vehicle) or LDT (Light Duty Truck) equipped with a diesel engine. Basic engine design aspects as well as the choice and calibration of diesel fuel injection equipment will be discussed. Since the vibration excitation of the diesel engine is significantly higher than that of a comparable gasoline engine, the engine mounting arrangement is extremely important to guarantee good vibration isolation. Gear ratios have to be matched to the different torque and speed characteristics of the diesel engine. Finally, refinement of the complete vehicle with regard to interior and exterior noise is required.

This paper describes the rattle mechanisms that exist in seat belt retractors and the vehicle acceleration conditions that induce these responses. Three principal sources of rattle include: 1) the sensor, 2) the spool, and 3) the lock pawl. In-vehicle acceleration measurements are used to characterize retractor excitation and are subsequently employed for laboratory testing of retractor rattle. The merits and demerits of two testing methods, based on frequency domain and time domain shaker control, are discussed.

A practical approach for evaluating and validating global system designs for Squeak and Rattle performance is proposed. Using simple slip and rattle models, actual sound and vibration data, and the fundamentals of audiological perception, analysis tools adapted from Chaos Theory are used to establish threshold levels of performance and identify system characteristics which are significant contributors to Squeak and Rattle. Focus on system design is maintained by using a simple rattle noise indicator and relating rattle events to levels of dynamic motion (acceleration, velocity, etc.). The threshold level is defined as the level of acceleration at which the system moves from a non-rattling state to a rattling state. The approach is demonstrated with a simple analytical model applied to an experimental structure under dynamic load.

In recent years there has been much interest in problems involving the noise prediction and reduction inside and outside the vehicle. Tire/road exterior noise has been considered to be the major vehicle exterior noise source. However, this paper describes an investigation into the characteristics of the air pumping noise mechanism in terms of source locations and directionality. Some rubber tire/road air pumping noise measurements are presented, whereas some predicted results are computed based on the boundary element method (BEM) to display some parameters which are found to be difficult to be obtained experimentally.

One of the objectives in the European Research project TINO is to identify, in detail, the surfaces of a rotating tire which actually generate the radiated noise. The approach is completely experimental and is based upon the ASQ (Airborne Sound Quantification) technique. The quantification of the contribution of the different tire surfaces to the sound pressure measured under defined conditions is carried out through a process of near-field measurements during rotation of the tire and static acoustic transfer function measurements. The ASQ method is further developed and tested when focussing at the applications. In first instance, the procedure has been validated and fine-tuned under well-controlled boundary conditions at a tire chassis dynamometer. The results of this first investigation served also as a “reference” set of data which has been used for verification and validation of numerical tire models.

The authors participated in a task force that was required to develop a repeatable, dependable, and reliable test procedure to compare, rate, and evaluate the severity of rattles. The assemblies involved in the study are designed and manufactured by different companies and are tested by different people on test equipment and instrumentation from different suppliers. The challenges therefore, were considerable and involved both the vibration inputs and responses as well as the acoustic responses. At the beginning of this activity, it was observed that different test labs using the same Ford vibration specs were obtaining different sounds from the same test item! Clearly, this was unacceptable and the test methods had to be improved and standardized. This paper focuses on vibration related to rattle testing. The particular assemblies used in this study were seat belt retractors.

A method to create a CAE load by utilizing the vibration motions at structure attachments has been developed. This method employs the concept of enforced motion as the constraints of boundary conditions to create an equivalent input force/moment matrix for a sub-structure with multi-point attachments. The main assumption is that motions at the attachments of the sub-structure should be the same as the known motions of the main structure under the generated input load. The key concept of the developed methodology is the calculation of the input dynamic compliance matrix for sub-structure attachment locations. This method is developed to create a system level input load to be used for squeak and rattle CAE analysis on a component or sub-system. It can also be used for minor component design change evaluation using only the component CAE model, yet as if it is assembled in the vehicle.

Advancements in the area of noise and vibration control have succeeded in quieting the vehicle to the point that previously obscure squeak and rattles must now be addressed. One possible way to decrease the squeak levels is by judicious selection of the material friction pairs. The squeak levels produced by a given material friction pair are a function of a number of test conditions like interference, temperature, humidity and excitation frequency. This paper experimentally studies the dependence of squeak levels on these factors. Understanding the relationship between squeak and test conditions will guide the selection of materials and help us to carefully select the test conditions for squeak evaluations. It will also result in cost reductions to otherwise numerous and expensive squeak parameter testing.

Modern trends in noise control engineering have subjected the automobile to the “drained swamp” syndrome. Squeaks and rattles (S&R) have surfaced as major concerns. Customers increasingly perceive S&R as direct indicators of vehicle build quality and durability. The high profile nature of S&R has led manufacturers to formulate numerous specifications for assemblies and components. Even so, a large majority of buzz, squeak and rattle (BSR) issues are identified very late in the production cycle, some often after the vehicle is launched. Traditionally, the “find-and-fix” approach is widely adopted, leading to extensive BSR warranty bills. The “design-right-the-first-time” approach must replace the “find-and-fix” approach. Due to the vast breadth and depth of S&R issues, a comprehensive summary of the present state of the art is essential. This paper includes a literature survey of the current state of the art of S&R, and discusses the methods available to further advance it.

Squeak and rattle (S&R) noise is an important issue in the automobile industry because the presence of audible S&R in a vehicle can convey the impression of poor quality to the customer. Furthermore, addressing S&R problems can be a significant warranty cost issue. Overall-all level types of noise assessment, such as dB SPL and loudness, are not always suitable measures for S&R detection, characterization and scaling. This is primarily due to the highly dynamic temporal and localized spectral characteristics of most S&R events. In this report, Fourier and filterbank methods for the analysis of S&R events are considered, and several criteria for the detection and scaling of S&R noise are examined using data measured both in an ultra-quiet laboratory situation and in several realistic, on-road driving conditions. Recommendations are made for an analysis method that is robust across both laboratory and on-road measurement conditions.

Squeak & rattle issues for an automobile interior component design have rapidly increased due to customer's expectations for high quality vehicles. Also, due to advances in the reduction of vehicle interior and exterior noise, safety restraints have recently been brought to the forefront to meet the vehicle interior sound quality. When the retractor is subjected to a higher level of vibration input and is located close to the driver's or passenger's ears, the retractor is prone to rattle and the rattle noise is detectable subjectively. The objective of this paper is to experimentally analyze the seatbelt retractor rattle noise and to evaluate various rattle noise abatement methodologies through a design of experiment matrix. A test methodology specified in the vibration noise specification for the seatbelt retractor assembly demonstrates the promising attempt to correlate the in-vehicle noise evaluation.