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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.

This paper describes the procedures used to reduce the tonal noise of a class eight truck engine timing gear train that was initially found to be objectionable under idle operating conditions. Initial measurements showed that the objectionable sounds were related to the fundamental gear mesh frequency, and its second and third harmonics. Experimental and computational procedures used to study and trouble-shoot the problem include vibration and sound measurements, transmission error analysis of the gears under light load condition, and a dynamic analysis of the drive system. Detail applications of these techniques are described in this paper.

Rattling noise is regarded as an annoying feature. It usually draws quality concern and results in an increase of the warranty cost. For many cases the rattling is generated by the continuum-rigid type of contact, i.e., impacts of a plate-striker type systems. In some applications the rattling is due to the continuum-continuum type of contact, namely area contact. This type of contact may result in lower rattling noise level than that of the continuum rigid type. This paper will present the testing results of a plate-beam system which is of the continuum-continuum type and discuss the differences between the contact mechanisms of the plate-beam system and the plate-ball system. Results of this study may serve as a referable benchmark to the analytical estimation of the rattling sound.

Computer Aided Design and Optimization are two important directions of present research activity in spur gears. A review of literature indicates that the methods available, are iterative and rather tedious. In present work the non-linear optimization problem with the minimum centre distance as an objective function has been addressed. A new design space in terms of module and pinion number of teeth has been defined. Empirical relations to obtain Feasible Optimal Centre Distance based on input torque and gear ratio for 20° pressure angle for 20 gear materials, obtained by regression analysis, have been reported. A simple nomograph has been developed which gives pinion number of teeth and standard module.

A simulation methodology for dynamic modeling of geared rotor systems such as superchargers was used for determining the housing vibration response. The approach provides an ability to make quick parametric design modifications to the model for evaluation of relative noise response with the assumption that the averaged housing vibration level correlates approximately to the noise radiating from the surface. The housing in some cases was modeled as a lumped mass representation for efficiency, and when higher accuracy of housing modes was needed, a detailed flexible Finite Element Analysis (FEA) representation was used. The interesting features of the methodology were the use of constraint equations to model the gear mesh response per unit Transmission Error (TE) input, along with summarizing the component kinetic and strain energy for each mode and the mesh compliance for fast evaluation of opportunities for noise reduction.

Gear whine is a fundamental issue associated with the design of automotive transmission gears. The evaluation of gear whine has long been a subjective rating. The goal of this paper is a comparison of the objective data and the subjective rating system. Objective analysis can not always replace the subjective evaluation completely, but it can induce a consistency that subjective rating lacks. An objective analysis method of in-vehicle gear whine order tracked data subtracted from the overall noise level over a rpm range is compared to subjective rankings to establish an objective rating. A correlation and statistical analysis of the objective data has proven effective in evaluating the noise performance of gear whine in a vehicle. There is a concern for the acoustic performance of the gears in a transmission and a consistency in the evaluation, due to the ever increasing customer awareness of noises in automobiles

Fuel injection and cylinder pressures of diesel engines have increased substantially over the past decade, as have noise levels of many engines. Test results show that these two trends are linked: gear train impact, driven by fuel system and crankshaft torsional excitation, has become a dominant noise forcing function in heavy duty diesel engines. Fuel system torsional dampers, crank gear isolators, and rear gear trains can reduce gear impact noise. Empirical equations have been developed to predict the overall noise of heavy-duty diesel engines, based only on the size and location of the gear train. These simple equations can predict engine noise levels with surprising accuracy.

Powertrain radiated noise is an important design factor that must be evaluated during the concept phase of the design process. Unfortunately, the tools currently available to evaluate radiated noise, empirically derived relationships, detailed CAE models, or experimental data, are not useful during this critical phase of the design when many of the fundamental design aspects are determined. Empirical models are too general to capture the impact of many typical design decisions, and detailed CAE models or hardware tests are not practical due to the level of design detail necessary, the cost involved, and the timing. This paper lays out a simplified approach for the prediction of powertrain radiated noise that is useful for both quantitative and qualitative evaluation of design alternatives.