Development of bearings and a damper based on magnetically controllable fluids

This paper presents two different kinds of magnetically controllable fluid bearings and a new magnetorheological fluid damper based upon open porous metallic foams. For the bearings, it will distinguish between a magnetohydrostatic bearing and a hydrostatic bearing with a magnetically controllable fluid. The magnetohydrostatic bearings get their load bearing capacity from the magnetohydrostatic pressure that is generated by the gradient of the magnetic field along a fluid surface. With such magnetohydrostatic bearings a specific load up to 1.6 N cm(2) can be reached. To support heavier loads hydrostatic bearings with magnetically controllable fluids can be used. This bearing concept makes it possible to achieve a constant bearing gap even if the load of the bearing changes. For this purpose the fluids are used as a hydraulic medium. Due to the magnetically controlled rheological behaviour of the fluid the bearing gap remains constant. The great advantage of this closed loop system compared to that of common hydrostatic bearings using valves is the quicker response to payload changes. The reason for that is that the active element ( i. e. the fluid) acts directly inside the bearing gap and not outside like in the case of valves. The foam damper developed uses the fluid to produce controllable damping forces. The open porous foam is directly placed in the active volume of the damper. By moving the foam piston the magnetically controllable fluid is pressed through the pores. The flow in the pores can be controlled by changing the fluid viscosity by applying a magnetic field. With this damper structure it is possible to reach higher damping forces whilst featuring a small design space.