Radially anisotropic ring r-tm-b magnet, its production method, die for producing it, and rotor for brushless motor

Abstract

A method for producing a radially anisotropic ring magnet having at least one axial groove on the inner surface comprises using a die comprising a cylindrical, magnetic core, a magnetic sleeve having an axial ridge in alignment with the groove on the outer surface and disposed on an outer peripheral surface of the core, and an outer, cylindrical die member defining a cavity for forming the ring magnet with the magnetic sleeve, and compression-molding magnet powder charged into the cavity while applying a magnetic field in a radial direction, and a radially anisotropic ring magnet substantially having a composition of R-TM-B, wherein R is at least one of rare earth elements including Y, TM is at least one of transition metals, and B is boron, having at least one axial groove on the inner surface, and magnetized such that centerlines between magnetic poles do not overlap grooves.

What is claimed is: 
     
         1 . A radially anisotropic ring magnet substantially having a composition of R-TM-B, wherein R is at least one of rare earth elements including Y, TM is at least one of transition metals, and B is boron, said ring magnet having at least one axial groove on the inner surface, and being magnetized such that said groove does not overlap centerlines between magnetic poles. 
     
     
         2 . A rotor for a brushless motor comprising the radially anisotropic ring magnet recited in  claim 1 , and a rotor yoke having an axial ridge in alignment with at least one groove of said radially anisotropic ring magnet, both concentrically fixed to each other.