Typical Characteristics of Magnetorheological Grease and Its Application to a Controllable Damper

Abstract

This paper describes a successful application of Magnetorheological (MR) grease to controllable dampers for general use. MR fluid is known to have a great potential as intelligent material to be applied to many devices such as dampers, clutches and engine mounts. However, ferromagnetic particles in MR fluid settle out of the suspension over time due to the density difference between the particles and their carrier fluid. Consequently, devices using MR fluid is difficult to achieve the desired performance. We have solved the problem by developing MR grease using grease as the carrier fluid which holds the particles in its thickener networks. The typical characteristics of MR grease have been measured by using a rotational rheometer specially designed for MR suspensions. The relationship of shear stress to shear rate and magnetic flux density in the MR grease is as same as MR fluid. The performance of a prototype controllable damper using the MR grease has been verified to be a wide dynamic force range and high time response. The ratio of maximum damping force in on-state to that in off-state is approximately 13. The time constant of damping force is 45 ms in off to on-state and 33 ms in on to off-state.