Application of magnetorheological dampers in motorcycle rear swing arm suspension

Magnetorheological (MR) fluid is a smart fluid containing ferrous particles that allow it to change its apparent viscosity in the presence of a magnetic field. Dampers consisting of MR fluids provide a means of active damping by using a current input to an electromagnet to control the damping properties. A swing arm suspension system is unique to two-wheeled vehicles, and links the rear wheel to the frame of the vehicle through a pivot. The swing arm also connects the rear suspension system to the frame. The goal of this study is to experimentally analyze the vibration mitigation capabilities of MR dampers in a (rear) swing arm suspension system in a motorcycle. A set of commercially available MR dampers is used in a fixture that has been developed to represent the rear swing arm system. The dampers are characterized and preliminary mathematical models have been developed to investigate the capability of the damping system. Multiple iterations of testing are performed on the shaker table to evaluate the performance of the damping system at different locations of the frame. Accelerometers are used for this evaluation, and the analysis of the acceleration data is performed in time domain as well as frequency domain. Results indicate that the mitigation in root mean square (RMS) acceleration ranges from 50 to 80% at varying levels of damping. Significant mitigation is observed at different locations of the fixture that correspond to the rider seat and the position of the foot pegs on a motorcycle. The semi-active behavior of the damper is a critical property that can be used to overcome the constraints of a traditional passive suspension system, where the stiffness and damping is tuned to provide enhanced ride comfort or improved handling. In a passive system, some compromise is necessary between the two competing requirements of ride comfort and handling. The MR damping system could be used to overcome this constraint by exercising direct control over the input current of the electromagnet. The results from this study indicate that an MR damping system would allow the swing arm suspension to adapt so as to provide improved ride comfort as well as enhanced handling.