Patent ID: 7562432

Claim:
A method of manufacturing a magnetostrictive torque sensor, comprising: measuring a residual austenite content of a rotating shaft, including a portion of the rotating shaft on which a magnetostrictive plating part is to be formed, prior to the magnetostrictive plating part being formed on the portion of the rotating shaft, wherein the residual austenite content of the rotating shaft varies throughout the rotating shaft as a result of a manufacturing process of the rotating shaft; forming the magnetostrictive plating part on the portion of the rotating shaft; imparting magnetic anisotropy to the magnetostrictive plating part to form a magnetostrictive film by providing heat-treatment conditions to the rotating shaft and the magnetostrictive plating part that correspond to measurement information obtained while measuring the residual austenite content of the rotating shaft; wherein providing the heat-treatment conditions comprises: heat-treating the rotating shaft based upon a heat-treatment time that corresponds to the residual austenite content measured while measuring the residual austenite content, and heat-treating the rotating shaft in a state in which a prescribed twisting torque is applied to the rotating shaft; and wherein providing the heat-treatment conditions also comprises: heat-treating the magnetostrictive plating part of the rotating shaft with an induction heating coil, and controlling the heat-treatment time so that a value obtained by integrating a grid current over time is fixed, wherein the grid current is an electric current that is inversely proportional to an eddy current generated in the magnetostrictive plating part and the rotating shaft when a high-frequency current is supplied to the induction heating coil.