Design of Thermoelastic Friction Clutch using Numerical Analysis

Summary

A thermoelastic friction clutch for transferring mechanical torque is proposed and modeled. Friction clutches are devices used for transferring mechanical torque. They are widely used in numerous industrial, transport, and other applications. Their operation is mostly realized on the mechanical principle. The driving and driven parts are mechanically pressed to one another and the torque is transferred by the friction force acting between them. In other cases, they use the magnetic principle, where the force between the driving and driven parts is produced by magnetic field. The paper deals with a novel clutch based on forces produced by thermoelasticity. The initial design consist of two sets of static permanent magnets and the driving part of this axisymmetric device rotates these two rings. These magnets produce static magnetic field and their orientations change in an appropriate manner. The head of the driven part is placed between the rotating part and external ring with the outer permanent magnets. The end of the driving part is heated by eddy currents induced in it by its rotation in the magnetic field produced by permanent magnets and its external diameter grows. After reaching the dimensions of the external driven part it starts touching it with increasing pressure. In this way, the driven part begins to rotate together with the driving part. At this moment, the external part also starts to be heated not only due to eddy currents produced in it by rotation, but also due to heat transfer from already heated internal part. In order that the clutch continues functioning, the thermal dilatability of material of the driven part must be substantially lower than that of the driving part. The paper presents the complete mathematical model of the device that is solved numerically. The results provide a good idea about its behavior and operation parameters, which is illustrated on a typical example. The task represents a triply coupled problem characterized by the interaction of three physical fields: magnetic field produced by the permanent magnets (that produces eddy currents in the rotating ferromagnetic element), temperature field generated by the corresponding Joule losses and field of thermoelastic displacements produced by nonuniform distribution of temperature in the heated part of the device. The fields affect one another because the physical parameters of particular elements of the device are temperature-dependent quantities. The corresponding mathematical model is solved numerically by own code Agros and library Hermes based on a fully adaptive higher-order finite element method. Some results are verified by other professional code COMSOL Multiphysics. The methodology is illustrated by a typical example.