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This paper describes experimental methods for simulating and analyzing road noise using an artificial road surface mounted to a chassis dynamometer. The nature of the relationship of road noise to road surface is discussed, including the nature of sound produced by the artificial surface mounted to the dynamometer. A method is described for converting the harmonics usually produced in a chassis rolls test into a continuous spectrum. This method also smoothes statistical fluctuations which arise due to the short length of road simulated. Dynamometer techniques are shown to be particularly effective in separating sound contributions from the front and rear suspension, and in separating contributions due to road surface and the tire tread.

Road induced interior noise, vibration and harshness (NVH) of a vehicle are greatly influenced by the design of the vehicle chassis and body systems. The strategy of improving vehicle NVH performance is to reduce vehicle body sensitivities to suspension force inputs and to increase the isolation of the chassis system to road irregularities. The effectiveness of the isolation is evaluated by the magnitude of transmitted forces at all suspension-body attachments. Currently, no technique is available to directly measure the forces over a broad frequency range. Many efforts have been made to develop force estimation methods, such as Noise Path Analysis (NPA) techniques. NPA techniques have been used to estimate the transmitted forces for steady-state road and powertrain excitations. This paper presents an ongoing effort to extend the NPA techniques to transient excitations, such as impacts caused by tar strips and pot holes.