Comparative assessment of vertical vibrations of a vehicle on the road and during the EUSAMA test

The work was undertaken to assess the discrepancies between the vertical vibrations of a motor vehicle examined on an EUSAMA suspension tester and the vibrations that occur during rectilinear motion of the same vehicle with a constant speed on an uneven road. The road surface irregularities were of random type and have been described in accordance with recommendations of the International Organization for Standardization (ISO) specified in the document ISO/TC 108/253: "Reporting vertical road surface irregularities. Generalised vertical road inputs to vehicle". A largely nonlinear "quarter-car" model with two degrees of freedom (2DoF) was used, where the actual elasticity characteristics of vehicle suspension and tyres, sliding friction in the suspension system, and the phenomenon of tyre separation from the road ("bouncing") were taken into account. The smoothing properties of the tyres were also represented in the model. The description of these properties exactly corresponded to the results of measurements carried out on a test rig. The calculations were done for various values of the coefficient of viscous damping in the shock absorber. In total, 52 simulations of the EUSAMA test (with both nominal and zero sliding friction in the suspension system) and 26 numerical experiments for an average road (of class "C" according to IS08608) at a vehicle speed of 90 km/h were carried out. The values of the vertical tyre-road contact force, suspension deflection rate, and suspension damping force were analysed in detail. The results of the tests carried out have been chiefly presented in the form of graphs.