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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.

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.

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.

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.

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.

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.

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.

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.