Suspension systems for motor vehicles are constantly evolving in order to ensure vehicle stability and traffic safety under all driving conditions. The present work aims to highlight the influence factors in the case of a quarter car model for semi-active suspensions. The functions that must be met by such suspension systems are first presented. Mathematical models for passive systems are first illustrated and then customized for the semi-active case. A simulation diagram was conceived for Matlab Simulink. The obtained simulation results allow conducting a frequency analysis of the passive and semi-active cases of the quarter car model. Various charts for Passive Suspension Transmissibility and for the Effect of Damping on Vertical Acceleration Response were obtained for both passive and semi-active situations. Analysis of obtained results allowed evaluating of the suspension systems behavior and their frequency dependence. Significant differences were found between the behaviors of passive and semi-active suspensions. It was found that semi-active suspensions ensure damping in accordance to the chosen control method, and are much more efficient than passive ones.
The present paper aims to investigate the impact of using magneto-rheologic fluids in semi-active suspension systems. For that purpose, the suspension system behavior will be analyzed in the case of dynamic control. It is verified whether a semi-active suspension system that uses magneto-rheologic fluids offers significant advantages by report to passive suspension systems. Two approaches were considered. The first one consisted of simulating both passive and semiactive suspension systems using Matlab Simulink. The conducted simulations yielded results for motion, speed, and accelerations of sprung and un-sprung masses. The second approach consisted of building an experimental set-up that uses a damper that is constructively contains a magneto-rheologic fluid, to which an adjustable variable magnetic field can be applied by means of a coil, in its turn controlled in current by a driver. The driver receives its excitation signals from sensors put in contact to the road surface model. The experimental set-up was conceived so that the un-sprung mass follows the road bumps. Simulation results were then compared to experimental ones.