Properties of a magnetorheological (MR) clutch have been investigated using newly developed MR fluids (suspensions)
which consist of the carbonyl iron particles and thixotropic carrier fluid. The carrier fluid is composed of a rapeseed ester
oil (vegetable oil) and synthetic smectite. The dependences of an output torque of the clutch on the applied magnetic
field were examined under a fixed input torque for different densities of particles, surfactant or smectite in the MR fluids.
The thixotropic behavior of the carrier fluids also was evaluated using a rheometer of the coaxial cylinder type. As for
the MR fluid of 81wt% particles with 7wt% smectite, the output torque of the clutch increased with increases of the
surfactant in the range of 0 to 5 wt%. On the other hand, the thixotropic effect was lost gradually with increase of the
surfactant over 5wt% at the smectite concentration of 7wt%, but the output torque increased with increasing the
surfactant accompanying by particles sedimentation. The sedimentation could be suppressed by the increase of the
smectite concentration without decreasing of the output torque. As a result, the output torque reached to 57Nm by
controlling the content of the surfactant and smectite in the MR fluids.