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This paper discusses the use of experimental transfer path analysis (TPA) to find optimized solutions to NVH-problems remaining in late vehicle development stages. After a short review of the established TPA methods, a couple of practical cases are discussed to illustrate how TPA, FE-models and practical experiments can supplement each other efficiently for finding optimum and attribute-balanced solutions to remaining, complex NVH issues late in the development process. The first example discusses an interesting idle noise and vibration problem for a front-wheel drive car with a pendulum engine suspension and torque rods attached to a resiliently mounted subframe. The second example illustrates the somewhat different approach used for TPA at mid- and high frequencies. The third example illustrates analysis “shortcuts” that sometimes can save precious calendar time close to SOP, provided that the simplifications are based on qualified, expert judgments.

Some common assumptions used in simplifying vehicle NVH prediction and design, in conjunction with isolators and mounts, are examined with the aim of offering qualitative improvements. It is often assumed that only the translational degrees of freedom are sufficient for a detailed structural analysis. Errors introduced by this simplification are quantified for some illustrative and simple examples concerning isolators, coupled analyses and transfer path analyses. It is suggested that a complete measurement procedure can alleviate the need for assuming beforehand that the rotational degrees of freedom are not essential. Once obtained they can be disregarded if demonstrated unnecessary.

Many papers have been published on variation in noise and vibration as well as transfer function characteristics between individual vehicles with nominally identical design [1], [2] and [3]. However, prediction of Noise Vibration and Harshness (NVH) properties is mostly based on detailed, deterministic modelling with FE- and BE-methods. Time and computer resources for creation and experimental updating of these models need to be optimised with respect to achievable prediction accuracy, and in this context statistical, energy flow based methods (SEA, EFA etc.) should be considered as an efficient alternative for medium and high frequency NVH prediction. A basic study of variability for transfer function of multimodal systems, using ideal acoustic and structural components with parameters corresponding to vehicle body plates and cavities is performed. Well known theory on variability, originally developed for room acoustics, is demonstrated to apply also for simple plates.

The use of Statistical Energy Analysis (SEA) in the field of vehicle noise is discussed. Theoretical fundamentals and basic assumptions of the method are summarized. Examples of successful prediction of interior noise levels in vehicles using the “classical” formulation for SEA are reviewed. Recently methods have been presented for the in-situ experimental determination of coupling- and internal loss factors for vehicles, based on the power balance equations. The methods are a result of applying the SEA hypothesis to multi-subsystem models of complex structures. This approach is attractive for vibratory power flow models of very complex structures such as car bodies. Simple substructures or junctions can not easily be identified for such structures why models based on theoretical estimations for basic substructures or junctions become uncertain.

A state of the art brake noise dynamometer has been developed and installed at Rubore. The paper describes the features of the test apparatus, including the automated control and measurement system. The multi-channel noise and vibration measurement system is described as well as the measurement and analysis software. The environment around the brake system under test can be controlled (cooling air temperature, speed and humidity) and the dynamometer is enclosed in a separate chamber. Techniques for simulating typical road test cycles are implemented. Examples of test results from both regular brake pressure/pad temperature matrix tests as well as simulated road test cycles are given in the paper.

The use of the Power Injection method for measurement of loss factors of complex panels with different trim systems is described. The basic theory is reviewed including the use of frequency response function measurements instead of direct measurement of input power and mean square response. The fundamental errors are presented. Practical considerations for reliable results are discussed and examplified. Examples of loss factor measurements on trimmed automotive panels are included.

The process of analytic dynamic modelling of the new independent rear suspension is described. The necessary testing activities, including operational tests and careful modal analysis, to correlate the model are presented. The analytic modelling with Systan is summarised and some aspects such as modal reduction and some constraint equations are presented in more detail. It is concluded that dynamic system modelling of complex structures is most valuable not only during early system design phases but also in the fine tuning and optimization process later during development.