1.5.1.1 Excitation by Real Road Unevenness
Unlike the single-wheel suspension model, the single-track suspension model is excited by every road irregularity twice: that is, first on the front axle and then once more on the rear axle. As a result, the body acceleration of the two-axle model not only depends on the excitation frequency but also on parameters such as the driving speed, the body natural frequency and the location of the measuring point in the vehicle.
In the following section, the irregularity profile of the road excites the vehicular vibratory system respectively on the front and rear axles over a time delay of Δt = l / v (l wheelbase, v driving speed). The equations of motion are solved with the aid of the MATLAB simulation tool.
Influence of Driving Speed
While the power spectral density of body acceleration and dynamic wheel load fluctuations permit a differentiated assessment of a vehicle suspension, it is possible to assess a trend also on the basis of the respective effective values.
This approach makes sense, for example, if those parameters which affect the entire power spectral density are used in the trend assessment, since then a value for suspension comfort or road grip can be stated as a function of the varied parameter.
The effective value of body acceleration can be determined on the basis of the time dependent curve of acceleration:
The effective value of body acceleration above the rear axle for an average load was determined this way in relation to the driving speed of a model vehicle, see figure.