Design And Research Of Carbon Fiber Rotor Sheath For High-speed Permanent Magnet Machine

High-speed permanent magnet machine has the advantages of high efficiency,big power factor and small volume.It has been one of the major research fields in high-speed motor.The surface-mounted magnets cannot support the ultra-high centrifugal force due to high-speed rotation of the steel shaft of the rotor.Thus the overwrap is used as a protective sheath for providing the radial compressive stress resultant over the outer surface of magnets.At present,the main sheath materials are alloys and carbon fiber composites.Due to lightweight,high strength,and decrease in eddy-current losses,carbon fiber sheath has broad prospects in application.This paper will take two different volume rotors into consideration,and different ways of formation of the radial compressive stress,that is,wound by ultra-high fiber tension and produced by interference fit,are offered,and analyze the mechanical stress in different states of the rotor parts.First,based on the characteristics of carbon fiber filament winding technology,the basic mechanical properties of T800 CF/epoxy NOL rings and unidirectional plates wound by different fiber tension are tested.Considering the tension influence on the performance of filament wound products,the ultimate fiber tension is determined.And the basic material parameters are provided for design and analysis of carbon fiber sheath.Secondly,for small size of high-speed permanent magnet rotors,an ultra-high fiber tension winding sheath is proposed to provide the radial compressive stress during the manufacture process.Considering the stress relaxation caused by deformations of internal cone,the analytical algorithm applies to calculate the residual stress distribution and radial compressive stress resultant with different tension models according to superposition principle of elastic theory.On this basis,using the confined condition that permanent magnets are always pressed in radial direction the sheath thickness is designed according to the material strength criterion.Then,using finite element software ABAQUS to simulate the stress relaxation and winding process for the composite sheath wound by ultra-high fiber tension.The mechanical stress distribution of rotor in static state and high speed rotation under the constant tension model and constant stress model are obtained.And the analytical solution is compared with the finite-element results to verify the consistency of these two computational methods.The static test at radial compressive stress of permanent magnets was conducted to prove the feasibility of ultra-high tension filament winding sheath and the correctness of analytical algorithm and finite element model.Finally,for large size of high-speed permanent magnet rotors,the composite overwrap wound by ultra-high tension cannot counteract the big centrifugal force,therefore the scheme of interference fit is considered.An approach of calculating the stress deformation in static state and high speed rotation according to superposition principle of elastic theory is advanced.Based on analytical analysis,the thickness of the sheath and the interference can be more reasonable chosen.Then the finite element method is used to verify the correctness of analytic equations.At last,a rotor product using carbon fiber interference sheath was manufactured.Filament wound high speed permanent magnet rotors using ultra-high fiber tension not only presents a novel application of filament winding,but also may offer a new strategy for the preparation of carbon fiber sheath.With the development of carbon fiber materials and winding tension technology,the range of rotors can be applied more and more widely.