Vibration Modes of an Automobile Driveline

A theoretical and experimental study of the vibrations of the conventional driveline of a car with a rear-wheel drive has identified at least 11 modes of vibration in the range 10-200 Hz. There are indications that a simple theoretical model, which ignores coupling with the vibration modes of the body, is adequate to predict the most important modes. It is found that the model can be improved by the inclusion of the dynamic characteristics of the rubber insulators in the system and the gyroscopic effects of the rotating wheel.

A significant increase of the noise level in the interior of the vehicle was attributed to the first bending mode of the rear axle. Random excitation by force inputs at the road surface, and forces and couples at twice the frequency of rotation of the driveshaft and engine crankshaft, cause the major resonance. When the noise cannot be attenuated by attention to the rear axle design or the path of the vibration, then recourse to a simple absorber or detuner may be necessary.