A two-degree-of-freedom vehicle model was used together with a non-linear leaf-spring model to study the ride behavior of heavy trucks, which often employ leaf springs as suspensions. Excitation was provided by a road model that is based on the power spectral densities (PSDs) of a large number of measured pavement profiles. The model agrees with measurements better than earlier models for low wave numbers. Periodic forcing from the rotating tire/wheel components, which can produce objectionable vibrations on smoother roads, was also used to excite the vehicle model. These models were used to generate data in the form of simulated time histories, which were then analyzed in the frequency domain to obtain PSDs, driving-point impedance, and transfer impedance functions.

Examples are shown of the interactions between road roughness and the leaf-spring nonlinearities, as they affect the transmissibility of the vehicle model. Two resonances, corresponding to bounce of the sprung and unsprung masses, appear at different frequencies and with different levels of modal damping, depending on the level of excitation. The effects of “friction level” and of a “friction distribution parameter” are also shown. Simulations with excitation from both the pavement and tire/wheel nonuniformities are used to show how the nonuniformities also interact with the leaf-spring nonlinearities to affect the vehicle response.