Development of bearings and a damper based on magnetically controllable fluids

Abstract

This paper presents two different kinds of magnetically controllable fluid bearings and a newmagnetorheological fluid damper based upon open porous metallic foams. For the bearings,it will distinguish between a magnetohydrostatic bearing and a hydrostatic bearing with amagnetically controllable fluid. The magnetohydrostatic bearings get their load bearing capacityfrom the magnetohydrostatic pressure that is generated by the gradient of the magneticfield along a fluid surface. With such magnetohydrostatic bearings a specific load up to1.6 N cm2 can be reached. To support heavier loads hydrostatic bearings with magneticallycontrollable fluids can be used. This bearing concept makes it possible to achieve aconstant bearing gap even if the load of the bearing changes. For this purpose the fluidsare used as a hydraulic medium. Due to the magnetically controlled rheologicalbehaviour of the fluid the bearing gap remains constant. The great advantage ofthis closed loop system compared to that of common hydrostatic bearings usingvalves is the quicker response to payload changes. The reason for that is thatthe active element (i.e. the fluid) acts directly inside the bearing gap and notoutside like in the case of valves. The foam damper developed uses the fluid toproduce controllable damping forces. The open porous foam is directly placed inthe active volume of the damper. By moving the foam piston the magneticallycontrollable fluid is pressed through the pores. The flow in the pores can be controlledby changing the fluid viscosity by applying a magnetic field. With this damperstructure it is possible to reach higher damping forces whilst featuring a small designspace.