Keywords: rotational stiffness, vehicle bushings, FRF coupling, underestimation, natural frequencies, vehicle body structures, front axle, frequency response function, vehicle noise, vehicle vibration
Effects of rotational stiffness of bushings on natural frequency estimation for vehicles by substructure coupling based on frequency response functions
In this study, a frequency response function (FRF) coupling analysis is presented for a vehicle body and a front axle with four pair of bushings between the two substructures. In order to investigate effects of the rotational stiffness of bushings on the natural frequency estimation, basic formulas are derived and confirmed by using simple beamlike structures. It is illustrated that the natural frequencies of the coupled structure are underestimated in general and the order of modes can be interchanged when the rotational stiffness of the coupling elements is neglected. The results from the analysis on a real vehicle structure reveal that neglect of the rotational stiffness of bushings causes downshift of the natural frequencies by 11 Hz at maximum around a natural frequency of about 100 Hz. This indicates that the effects of the rotational stiffness of bushings can be most responsible for the possible large errors in the mid frequency range.