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In the design of an automobile, an important consideration is to minimize the amount of “boom” noise that the vehicle occupant could experience. Vehicles equipped with four cylinder engines can experience powertrain boom noise in the 40 to 200 Hz frequency range. Boom noise can also be generated by road input, and it is just as annoying. In this paper, a CAE methodology for predicting boom noise is demonstrated for a vehicle in the early design stage in which only 3-D CAD geometry exists. From the CAD geometry, a detailed finite element (FE) model is constructed. This FE model is then coupled with an acoustic model of the interior cavity. The coupled structural-acoustic model is used to predict acoustic response due to powertrain inputs. As a part of the detailed design process, various design modifications were considered and implemented in the vehicle system model. Many of these modifications proved successful at reducing the boom levels in the vehicle.

A truck cab latch assembly is presented as an example to illustrate the usefulness of computer based geometrical and statistical modeling. An economic analysis is conducted to show a typical cost benefit of the approach. Further applications of the approach relative to existing computer design tools is discussed as a topic for presentation in a later paper. Various packages currently available from SDRC are referenced as typical examples of these tools. Product cost is shown to be significantly reduced using this method. Correlation of the manufacturing scenerio to a “real world” situation is discussed.

This paper describes techniques for dynamic evaluation of complex mechanical systems, particularly construction equipment. By coupling experimental and analytical techniques, a thorough understanding of system performance can be obtained, and improved predictions of dynamic failures can be made. In particular, the ability to obtain reliable predictions of system stress and/or vibration response to adverse loading conditions is presented. It is not necessary or advisable to restrict the testing of earthmoving and agricultural equipment to static loading conditions only. Dynamic studies, using combined automatic transfer function analysis (TFA) equipment and related computer capabilities, are practical and beneficial. The object of this paper is to point out advantages of dynamic investigations and to present another tool for construction and agricultural machinery engineers in their continuing endeavor to improve their products.

The design of complex products such as automobiles and aircraft often requires performing repeated dynamic analyses using detailed finite element models. The high computational costs and long turnaround times associated with the use of these models can impede the design process. In this paper, a practical method for performing efficient design parameter studies using Eigensolution Reanalysis is discussed. Special purpose software has been developed which interfaces with commercial finite element analysis codes. The special purpose software uses the baseline modes to calculate new modes for each design change. The software can also compute forced response of the modified designs given user specified dynamic load cases. This method provides dramatic savings in CPU time compared to the traditional method of re-solving the full eigenproblem for the modified design modes. Typically, the reanalysis calculations use less than five percent of the CPU time required for the baseline analysis.

Structural connections involving a T-stub arrangement often result in fasteners loaded in tension. The working load developed in the fastener is dependent upon the stiffness and deformation of the T-stub itself. Tests have shown that this “prying action” phenomenon can influence fastener performance. A number of analytical and experimental models has been developed to predict the relationship between applied forces and subsequent bolt forces. It is felt that the detailed analysis provided by finite element theory could add additional insight into this phenomenon by more rigorously defining the load distribution between connected members. Finite element analyses could then be utilized to efficiently evaluate the effects of alternative support and fastener stiffnesses and variations in fastener pre-load.

The design of automotive components for low structure-borne interior noise and vibration requires the ability to reliably simulate total vehicle system response over a wide operating frequency range. This implies that the car body, its interior acoustic cavity, and critical structural components must be included in this overall dynamic model. Unfortunately, most noise and vibration problems occur in the 200-1000 Hz frequency range where existing finite element and experimental modal methods have limited applicability. This is due to the high modal density, high damping levels, and sensitivity to fine geometric detail. Moreover, it is highly doubtful that these methods will ever be practical tools for the study of the total body dynamics over the frequency range of 200-1000Hz. In this paper, a practical hybrid experimental-analytical approach is proposed in response to the need to simulate high frequencies structure-borne noise and vibration in automotive systems.

An overview of the analytical noise, vibration, and harshness (NVH) simulations performed to support the design and development of the Nissan Quest mini-van is presented. The use of analytical techniques on this project was unique in that analytical results were used to drive the pre-prototype design efforts, as well as to assist in the prototype development phase. Analytical models were developed, and simulations performed, prior to the release of prototype drawings. The simulation results identified necessary changes which were incorporated into the design. Once prototype vehicles became available, analytical simulations and development testing were used hand-in-hand to minimize development time as well as to optimize the cost, weight, and performance of NVH countermeasures. The extensive use of analytical simulations in the design and development process was critical in achieving the aggressive NVH performance objectives set for the vehicle.

In rear wheel drive vehicles, passenger perceived tonal noise is often generated by high frequency rotational vibrations of the transmission output shaft. This rotational vibration is excited by the transmission and couples with the dynamic and inertial properties of the driveline and suspension to generate forces through the suspension attachment locations. This paper demonstrates an approach which uses experimental techniques to measure the rotational dynamics of the output shaft and noise path analysis procedures to predict the vehicle system interaction and resulting vehicle noise contribution from this path. An evaluation of three rotational data acquisition techniques, a measurement technique used to characterize a vehicle's torsional acoustic sensitivity, and an application of mobility coupling to the torsional noise path is presented.

The design of automotive components for low structure-borne interior noise and vibration is facilitated by the ability to reliably simulate total vehicle system response over a wide operating frequency range. This requires that the car body, its interior acoustic cavity, and critical chassis components must be included in the overall dynamic model. Unfortunately, most noise and vibration problems occur in the 200-1000 Hz frequency range where finite element and experimental modal methods have limited applicability. This is due to the high modal density, high damping levels, and sensitivity to fine geometric detail. A simulation method has been proposed earlier which uses component finite element models and component experimental transfer functions to predict combined system response [1]. This method has allowed for a practical approach to automotive system noise and vibration simulation.

Powertrain noise is often dominated by the radiation from individual panels or covers. A structural side cover for a front wheel drive transmission represents a complex noise and vibration design problem. Amongst the NVH concerns are the radiation of structural borne sound and the sound transmission loss characteristics. This paper addresses the use of acoustic boundary elements and structural finite elements to predict the radiation of noise from a structural side cover. A comparison is made to experimental measurements, and discussion provided for practical application of these modeling methods to total side cover design.

With the extensive improvements achieved in vehicle driveline and road noise quality manufacturers are turning their attention to component and ancillary noise sources and expecting their suppliers to include sound quality in the assessment of their designs. This paper describes an investigative project into the principal components contributing to the perceived sound quality of powered seat adjusters in passenger vehicles and the statistical methods of analyzing jury preference data.

Body acoustic sensitivity, defined as the interior sound pressure due to a unit force applied to the body, has a major influence on the powertrain and road noise of a vehicle. Body acoustic sensitivity can be predicted analytically in the design stage of a vehicle program using structural-acoustic analysis. Recognition and correction of potential problems at this stage is a cost effective approach to improving a vehicle’s NVH performance. This paper describes the structural-acoustic analysis procedure. Techniques for developing the structural and acoustic models and coupling them to form a structural-acoustic system model are discussed. An application of the procedure for prediction and improvement of body acoustic sensitivity is given for a passenger vehicle.

Much attention has been devoted to the importance of vehicle dynamics relative to human response ride criteria. The present work extends this effort by providing a practical computerized design approach in which the vehicle designer selects a representative terrain input, either sinusoidal or power spectral density, to excite a vehicle model constructed by the modal Building Block method. To evaluate vehicle ride the resulting system response, accounting for human dynamic characteristics, is compared to accepted ride criteria, such as ISO spectra and absorbed power. An example involving an agricultural tractor is presented to illustrate the approach.

The widespread use of finite element models in assessing system dynamics for NVH evaluation has led to a recognition of the need for improved procedures for correlating models to experimental results. With the greater occurrence of finite element models preceding the first prototype hardware, it is now practical to employ pre-test analysis procedures to guide the execution of the tests in the correlation process. This aids in the efficiency of the test process, ensuring that the test article is neither under nor over instrumented. The test-analysis model (TAM) that results from the pre-test simulation provides a means to compare the test and model both during the test and during the model updating process. This paper discusses procedures for pre-test analyses and demonstrates their application to the correlation of a transmission side cover.

This paper discusses the nature of noise production of automotive transmissions and the various measures which may be taken to reduce operating noise. The measures discussed include investigation and modification of the gear-shaft system dynamics in both bending and torsion. Also discussed are determination of dynamic characteristics of the transmission housing and ways of reducing the levels of vibration of housing areas and of decreasing the radiation efficiency of those areas.