Liquid Spring Shock Absorber with Controllable Magnetorheological Damping

An automotive suspension strut is investigated that utilizes compressible magnetorheological (CMR) fluid. A CMR strut consists of a double-ended rod in a hydraulic cylinder and a bypass comprising tubing and an MR valve. The diameter of the rods on either side of the piston are set to be different in order to develop spring force by compressing the MR fluid hydrostatically as a result of varying shaft volume in the hydraulic cylinder. The MR bypass valve is adopted to develop a controllable damping force. A hydromechanical model of the CMR strut is derived by considering lumped hydraulic parameters such as compliances of chambers inside the cylinder and flow resistances through the MR bypass valve. The spring force and nominal spring rate owing to fluid compressibility and the controllable flow resistance and pressure drop in the bypass were analytically investigated on the basis of the model. Finally, a CMR strut, filled with silicone oil-based MR fluid, is fabricated and tested. The spring force and variable damping force of the CMR strut are clearly observed in the measured data, and compare favourably with the analytical model. Additionally, characteristics of a double-rod strut whose rod diameters are the same, so that the shaft volume in the hydraulic cylinder is constant, are analysed and compared with a CMR strut whose rod diameters are different.