Magnetostrictive torque sensor and electric power steering apparatus

Abstract

This magnetostrictive torque sensorincludes a rotating shaftused to rotate according to an input torque and provided with magnetostrictive filmsA andB, an excitation coilconfigured to apply an alternating magnetic fieldto the magnetostrictive film, and detection coilsA andB each of which detects a change in the magnetic characteristic of an associated one of the magnetostrictive films. The magnetostrictive torque sensor is configured so that a bias magnetic field is added to the alternating magnetic field from a bias power supplyso as to satisfy the following conditions:H<H<H; and−where H(>0) is an applied magnetic field corresponding to a maximum magnetic permeability obtained according to a magnetic hysteresis curveof the magnetostrictive film, which shows magnetization caused by the alternating magnetic field, H(>0) is an applied magnetic field corresponding to an end of a range in which a discontinuous magnetization is performed, and H(>0) is an applied magnetic field that determines a sensitivity range to be set on a magnetostrictive sensitivity curve representing a magnetostrictive sensitivity exhibited by the magnetostrictive film.