A study of vehicle and measurement NVH variability

A range of nominally identical automotive vehicles have been tested for NVH variability by exciting the engine mount with an impact hammer and measuring the responses at different points on the vehicle. Normalised standard deviations were calculated from the mobility, which fell well within the boundaries of previous comparable measurements. The measurement variability was determined by taking repeat measurements on a single vehicle, which were found to be very repeatable, varying by up to 2.9%. A function that uses the coherence to determine the random error was applied to the data to determine the variability due to the measurement taking process. This was compared with repeat measurements taken on a single vehicle and was shown to agree well with one another. A design of experiments has also been created that determines the effect of each variable such as the temperature and angle of impact on the overall vehicle to vehicle variability

A survey on the variability of dynamic stiffness data of identical vehicles

The variation in material quality, production tolerances and joint conditions in nominally ‘identical’ vehicles means that the level of noise and vibration perceived in the cabin will vary from car to car. To assess the level of variability in the low and medium frequency range a series of measurement have been conducted on a small set of nominally identical sedan vehicles. Measurements are presented in the form of dynamic stiffness data for twenty three vehicle mounting and response points and for three different translational directions. In this paper, the methodology used to analyse the large data set is shown. The level of variability in the corresponding frequency response functions (FRFs) from all the vehicles are then presented and compared for different locations and the different loading measurement directions. The mean value is calculated for each data set and compared and the variability is also presented as a function of frequency for a selected set of the dynamic stiffness data. The intention is to demonstrate how the level of FRF variability changes depending upon the excitation/response location chosen and how this can be related to the frequency band characteristics