Collarless circularly magnetized torque transducer having two phase shaft 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 member which is unitary and of generally homogeneous chemical composition throughout, said member comprising separate magnetically active and magnetically substantially passive regions, 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 to prevent irreversible loss of the magnitude of the circumferential polarization;
• (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 unitary member which is of generally homogeneous chemical composition throughout;
• (b) inducing phase transformations in said member by processes selected from the group consisting of thermal processes, mechanical processes and combinations thereof for defining in said member separate magnetically active and magnetically substantially passive regions;
• and
• (c) polarizing a finite axial extent of a first magnetoelastically active 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;
• (d) 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 circmferential direction and having a coercivity sufficiently high to prevent irreversible loss of the magnitude of the circumferential polarization.