Collarless circularly magnetized torque transducer and method for measuring torque using same

A method of sensing a torque applied to a torqued member extending in an axial direction, comprising the steps of:

• (a) providing a first magnetoelastically active region in said member, said region being magnetically polarized in a single circumferential direction and possessing sufficient magnetic anisotropy to return the magnetization in said region, following the application of torque to said member, to said single cirumferential direction when the applied torque is reduced to zero, at least said magnetoelastically active region of said member being formed of a polycrystalline material wherein at least 50% of the distribution of local magnetizations lie within a 90.degree. quadrant symmetrically disposed around said single circular direction and having a coercivity sufficiently high that the field arising from said magnetoelastically active region does not magnetize regions of said member proximate to said magnetoelastically active region to give rise to parasitic magnetic fields which are of sufficient strength to destroy the usefulness, for torque sensing purposes, of the net magnetic field seen by said magnetic field sensing means;
• (b) producing a magnetic field as a consequence of the application of torque to said member;
• and
• (c) sensing the magnitude of the magnetic field at a position proximate to said magnetoelastically active region as an indication of the magnitude of the torque applied to said member.

A method of producing a magnetoelastic torque transducer from a member to which an axial torque is applied for producing a magnetic field varying with said torque, the magnitude of said magnetic field being sensed by magnetic field sensors for providing an output signal indicative of the applied torque, comprising the steps of:

• (a) providing a ferromagnetic, magnetostrictive member having a first magnetoelastically active region in said member;
• and
• (b) polarizing a finite axial extent of said region in a magnetizing field in a single circumferential direction, said region possessing sufficient magnetic anisotropy to return the magnetization in said region, following the application of torque to said member, to said single circumferential direction when the applied torque is reduced to zero;
• (c) said member being formed of a polycrystalline material wherein at least 50% of the distribution of local magnetizations lie within a 90.degree. quadrant symmetrically disposed around said single circumferential direction and having a coercivity sufficiently high that the field arising from said magnetoelastically active region does not magnetize regions of said member proximate to said magnetoelastically active region to give rise to parasitic magnetic fields which are of sufficient strength to destroy the usefullness, for torque sensing purposes, of the net magnetic field seen by said magnetic field sensors.