Design of a MR hydraulic power actuation system

Abstract

A magnetorheological (MR) fluid-based hydraulic power system is analyzed and experimentally validated by testing a prototype. A set of MR valves is proposed to implement within a Wheatstone bridge hydraulic power circuit to drive a hydraulic actuator using a pump. The MR valves are used in place of conventional mechanical servo valves. The proposed use of MR valves in hydraulic actuator systems has many advantages. First, MR valves have no moving parts, enhancing reliability. Second, the MR valves operate at the same speed as the actuation bandwidth (typically below twenty Hz in our applications). Third, the actuator relies on flow rates for a given pump speed, and avoids, to a large degree fluid compliance. Fourth, if a change in stroke direction is required, the flow through each of the MR valves can be controlled smoothly via changing the applied magnetic field. The performance of the Wheatstone bridge with MR valves is theoretically derived using three different models of the MR fluid behaviors: an idealized model, a Bingham-plastic model and a biviscous model. The analytical system efficiency in each case is compared, and departures from ideal behavior are recognized. The driving force and efficiency will be evaluated in the MR hydraulic power actuator system for both Bingham plastic and biviscous flows. An MR valve is designed using a magnetic finite element analysis. The magnetic flux density developed in the MR valve are verified by analytical and experimental methods. The yield stresses achieved in the MR valve due to the applied current are also measured to validate the design methodology. The overall performance of the MR fluid based hydraulic power system is described using the experimental MR valve performance data.