Development of a shear type controllable damper with magnetorheological grease

This paper describes a controllable damper with high reliability and wide dynamic range using magnetorheological (MR) grease and semi-active vibration control using the damper. Some types of cylindrical controllable dampers based on pressure difference between chambers in the dampers using "MR fluid", whose rheological properties can be varied by applying a magnetic field, have been reported as a semi-active device. However, there are some challenging issues of them. One is to improve dispersion stability. The particles dispersed in MR fluid would make sedimentation after a period due to density difference between the particles and the carrier fluid. Another is to expand dynamic range. Since cylindrical dampers require sealing elements because of pressure difference in the dampers, the dynamic range between the maximum and minimum damping force according to a magnetic field is reduced not making the best use of MR effect. In this study, a controllable damper using MR effect was proposed and its performance was experimentally verified to improve the dispersion stability by using "MR grease", which uses grease as the carrier of magnetic particles, and to expand the dynamic range by adopting a shear type structure not requiring sealing elements. As a result, it was confirmed that MR grease had the high dispersion stability and that the dynamic range of the present damper was seventy times, which was more than five times as high as the conventional dampers using MR effect. Furthermore, the MR grease damper was applied to a semi-active vibration control system of a one degree-of-freedom model structure using a simple on-off algorithm and its performance was experimentally verified. The results indicated that the vibration response was successfully reduced by using the on-off algorithm. It was shown that the MR grease damper effectively worked for the semi-active vibration control system.