The effect of dilution oil in the torque performance of magnetorheological grease

Abstract

Magnetorheological (MR) brake is a device that uses MR material to produce braking torque according to induced current. Even though MR Fluid (MRF) is widely used in MR brake as it has high response and is easy to fabricate, the sedimentation issue has degraded the performance of M R brake. Therefore, MR grease (MRG) is introduced to overcome the drawbacks of MRF. Another important benefit of MRG is its self-sealing property which can solve the leaking problem in MRF. Despite the advantageous of no sedimentation of MRG, high viscosity of MRG lower the MR response to the current induced. Thus, the high viscosity of MRG can be reduced by adding dilution oil. Furthermore, the effect of the oil in diluted MRG in MR brake has not been investigated. Several samples of MRGs with different types of dilution oil were prepared by mixing grease and spherical carbonyl iron particles (CIP) using mechanical stirrers. The rheological properties in rotational mode were tested by using rheometer meanwhile the torque performance of MRGs in MR brake were evaluated by changing the current of 0A, 0.4A, 0.8A and 1.2A and fixed the angular speed. The result shows that MRG 3 has the lowest viscosity which is almost 93% reduction while the reduction of viscosity of MRG 2 was 25%. Yet, the torque performances generated by MRG 3 was the highest, 1.44 Nm, followed by MRG 2 and MRG 1. This phenomenon indicated that the improvement of torque performance was dependent on the viscosity of MRGs without the occurrence of sedimentation. Thus, the use of MRG with dilution oil as a substitution of MRF could reduce the sedimentation in MR device and improve the torque performance of MRGs in MR brake.