Abstract: The problem of magnetoelastic cirumferentially-magnetized torque transducers having a zero output magnetic field at zero torque is solved by pre-torqueing. This entails is circumferentially magnetizing the transducer element at a predetermined torque. The technique is advantageously applied to a pair of transducer elements (32, 34: 62, 64) whose outputs are combined (FIG. 6a: 76) to provide a range of measurement of torque (clockwise and counterclockwise) including zero torque. Various combinations of direction of pre-torque and direction of circumferential-magnetization are discussed. A circuit (FIG. 8) is disclosed for combining the signals to obtain a reference level (84) for gain control of the combined output signals V o from the two transducer elements (60, 62). Also disclosed is the application of the invention to other forms of torque transducer element in which a magnetic field is stored. One form is longitudinal magnetization (FIG. 10a). Another is radially spaced magnetization (FIG. 12a: FIG. 13).

Abstract: A power steering mechanism (10) for turning steerable wheels of a vehicle comprises a rotatable input member (22), a rotatable output member (26), and a torsion bar (28) connecting the input member and the output member. The torsion bar (28) is fixedly connected to the output member (26) and twists upon relative rotation between the input member (22) and the output member. The torsion bar (28) is made of a magnetoelastic material and has a defined surface area (90) which carries a magnetic field, which magnetic field varies upon twisting of the torsion bar, magnetic field detector (94) is located to sense variance in the magnetic field. The input member (22) is interposed between the torsion bar (28) and the magnetic field detector (94) and is made of a non-magnetic material.