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Modal analysis and operating vibration analysis are well established techniques which require the presentation of deflected shapes of the test structure's geometry. Computer animation of these results and enhancement of measured geometry has made interpretation of data easier. Dedicated software has been written for this animation using solid fill surfaces, which has proven a significant improvement over wire frame images. This software enables easy assimilation of the most complex data sets, and a direct video recording capability allows effective presentations to be generated quickly. The application of these methods to vehicle NVH problems is illustrated by a number of case studies for operating vibration analysis.

The objectives of this work were to establish a method to diagnose the source of gear rattle and to evaluate the rattle objectively. The methods are described in detail, applied to two passenger cars as an example. Investigations were conducted into transmission rattle under transient conditions. By analysing the transmission casing vibration with respect to the engine flywheel angle, and presenting the data in the form of contour maps, it was shown that the two vehicles had different characteristics of gear impacts. Further measurements of the angular motion of each gear revealed the impact conditions at the input mesh in the transmission largely controlled the character of the rattle and were fundamentally different between the two vehicles. A rattle index was developed, based on the casing vibration under transient driving conditions.