1.2 The Road as the Source of Excitation
The unevenness of the road represents the most intensive source of excitation for the vibratory system of the motor vehicle in the frequency range up to approximately 30 Hz. The unevenness of the road induces vertical displacements of the vehicle body, and as a consequence, the road is in turn affected by the wheel load fluctuations.
Excitation as a result of road unevenness is generally characterized by differing amplitudes and wavelengths at irregular periods of time. This is called the stochastic excitation of the vehicle. In order to be able to examine the effects of road unevenness on the vibratory motor vehicle system, this unevenness has to be firstly described mathematically.
When a simple harmonic (sinusoidal) wave is considered, where the road unevenness excites an amplitude 'h' at equal distances L, an uneveness characteristic as shown in the figure results.