Design and prototype manufacturing of a semi-active shock absorber with magnetorheological (MR) fluids

Magnetorheological (MR) fluids are magnetic field dependent fluids used in the semi-active damping systems. MR fluids usually comprise magnetic particles dispersed in a carrier liquid. In this work, carbonyl iron and magnetite based five different MR fluids were prepared with iron concentration of 25 and 40 wt% in silicone oil. Furthermore, fumed silica as an additive was used to reduce sedimentation of the carbonyl iron particles. The sedimentation stability of MR fluids prepared was examined. Then, the density of MR fluids was measured by a picnometer. The effect of magnetic field on MR fluid was modelled using the finite element method in ANSYS/Electromagnetics software. Performance tests of the MR fluids were performed using the prototype of MR damper designed and manufactured according to the external dimensions of the OEM shock absorber for a passenger car. The influences of the magnetic particle type, concentration and usage of fumed silica on damping performance, sedimentation stability and dynamic force range of the MR fluids were studied. Increasing the current, the highest damping force 169,4N with an increment of 40% was obtained from the MRF-5 containing 40 wt% carbonyl iron and 2 wt% fumed silica. The equivalent damping coefficients of the MR fluids were calculated for different currents to compare the damping performance of the semi-active suspension system with the passive system. The mathematical model of the suspension system was obtained in state space form using a two degree of freedom quarter car model. Then, the simulations of the semi-active and the passive suspension system were performed in MATLAB/Simulink depending on this mathematical model. In these simulations, step, sinus and random sinus road excitations were used. The results were presented in time and frequency domain for the both suspension systems. It was concluded that the semi-active suspension system has a significant improvement for ride comfort and safety in comparison with the passive system.