Abstract
Electromagnetic clutches are widely used devices in industrial applications when a torque must be transmitted between two components without mechanical contact avoiding friction and so reducing wear and maintenance time. Hysteresis clutches are a particular variant of electromagnetic couplers used when a constant torque from zero to the synchronous speed needs to be transmitted. This paper deals with the analysis, design and optimization of hysteresis clutches. After a brief introduction on the operating principle, a new method of analysis is then introduced. The latter allows a fast prediction of the performance of hysteresis couplers without sacrificing the accuracy of the performance evaluation even when adopting anisotropic magnetic materials. The introduced method, based on a static finite element simulation followed by a post-processing of the evaluated magnetic field, is then used within an automatic design procedure in order to identify the inevitable trade-offs encountered when optimizing the geometry of any hysteresis clutches with a given outer envelope. The obtained results are commented in-depth and allow to draw general design guidelines with special regards to the selection of the number of poles and the magnetic materials. The effect of the high level of anisotropy of the most common magnetic materials showing the highest energy density is carefully taken into account allowing to deduce the optimal preferred direction of magnetization.
Highlights
I n many areas of engineering mechanical or electromagnetic clutches are used in order to separate parts in relative motion
The hysteresis motor is composed by a conventional slotted stator hosting a distributed winding and a rotor made of a ring of semi-hard or hard ferromagnetic material, such as AlNiCo, sustained by a shaft which can be either magnetic or non-magnetic
The low computational burden of the proposed method of analysis, consisting in a magnetostatic finite element analysis combined with a post-processing evaluation of the hysteresis torque, makes this method suitable to be implemented within an automatic design optimization procedure
Summary
I n many areas of engineering mechanical or electromagnetic clutches are used in order to separate parts in relative motion. The hysteresis motor is composed by a conventional slotted stator hosting a distributed winding and a rotor made of a ring of semi-hard or hard ferromagnetic material, such as AlNiCo, sustained by a shaft which can be either magnetic or non-magnetic. The drawbacks of this kind of electrical machines are the really poor power density and power factor and these are the reasons of their adoption only in niche applications [4]. Hysteresis clutch produces the same torque from zero to synchronous speed with a limited torque ripple [6]
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