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MRF actuators with reduced no-load losses

Magnetorheological fluids (MRF) are smart fluids with the particular characteristics of changing their apparent viscosity significantly under the influence of a magnetic field. This property allows the design of mechanical devices for torque transmission, such as brakes and clutches, with a continuously adjustable and smooth torque generation. A challenge that is opposed to a commercial use, are durable no-load losses, because a complete torque-free separation due to the permanent liquid intervention is inherently not yet possible. In this paper, the necessity of reducing these durable no-load losses will be shown by measurements performed with a MRF brake for high rotational speeds of 6000min-1 in a first step. The detrimental high viscous torque motivates the introduction of a novel concept that allows a controlled movement of the MR fluid from an active shear gap into an inactive shear gap and thus an almost separation of the fluid engaging surfaces. Simulation and measurement results show that the viscous induced drag torque can be reduced significantly. Based on this new approach, it is possible to realize MRF actuators for an energy-efficient use in the drive technology or power train, which avoid this inherent disadvantage and extend additionally the durability of the entire component.