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The quietness of the interior of automobiles is perceived by consumers as a measure of quality and luxury. Great strides have been achieved in isolating interiors from noise sources. As noise is reduced, in particular wind and power train noise, other noise sources become evident. Noise reduction efforts are now focused on components like power steering pumps. To understand the contribution of power steering pumps a world-class noise and vibration test stand was developed. This paper describes the development of the test stand as well as it's objective to understand and improve the sound quality of power steering pumps.

A frequency domain substructure method is employed for deriving the motion transmissibility equation on a coupled structure. Various errors in its experimental implementation are investigated by numerical calculations in order to identify the most important source of errors so that future effort can be more focused. The interfaces with and without the tangential and rotational DOF's are taken into account when the DOF deficiency error is studied. By decomposing the DOF deficiency error into different components, it is shown that all six interfacial DOF's must be taken into account for general structures. The bias, noise, and underflow errors are investigated and their relative importance is compared with the DOF-deficiency error. It reveals that these three errors are moderate in nature and can be handled with traditional methods while there is no simple way to compensate for the DOF deficiency error.