Magnetorheological Damper Utilizing an Inner Bypass for Ground Vehicle Suspensions

This study presents the design, fabrication, and test of a magnetorheological (MR) damper utilizing an inner bypass that can simultaneously produce large dynamic range (i.e., ratio of field-on to field-off stroking load) and low field-off stroking load at high piston velocity. These two damper properties, large dynamic range and low field-off stroking load, are critical to achieving high performance in ground vehicle suspensions. The MR damper is comprised of a pair of concentric tubes, a movable piston-shaft arrangement, and an annular MR fluid flow gap between the concentric tubes. The inner tube serves as the piston guide, the inner surface of the annular flow gap, and the bobbin for the five electromagnetic coils used in this design. The outer tube serves as the flux return and the outer surface of the annular flow gap. The annular flow gap is an inner bypass annular valve where the rheology of the MR fluids, and hence the stroking load of the damper, is controlled. The MR damper is analyzed using a Bingham-plastic nonlinear fluid mechanics model. To experimentally validate the analysis of the MR damper with the inner bypass, and to illustrate its advantages over the MR damper with the conventional annular orifice, the prototype damper is tested in terms of controllable damping force or stroking load, dynamic range, and equivalent damping as a function of shaft/piston velocity.