The viscous losses at high rotational speeds in idle mode represent a major drawback for an energy-efficient operation of MRF brakes and clutches. In this paper, an innovative concept is presented that allows a complete torque-free idle mode of the mentioned actuators by the use of a MR-fluid control. Using magnetic forces, the MR-fluid control is capable to increase the efficiency and lifetime of MRF based actuators for torque transmission. An approach of designing actuators using the investigated MR-fluid control is applied which considers in detail the required magnetic excitation systems for enabling a MRF movement in the shear gaps. A clutch is presented and simulations of the transient switching behavior are performed. Measurements of a realized clutch underline the functionality and efficiency of those actuators. Additionally, further approaches for a shear gap design are introduced that increase the maximum torque capacity. By the use of a micro-grooved structure for the MR-fluid control, a torque-to-volume ratio can be achieved that is in the order of typical MRF actuators for torque-transmission with completely filled shear gaps.

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