Torque sensor

Abstract

A plural number of grooves, circumferentially spaced, are formed in a surrounded portion of a first rotary shaft made of magnetic material. A thin tubular member made of conductive and nonmagnetic material, is integrally coupled with a second rotary shaft in the rotation direction, while surrounding the surrounded portion of the first rotary shaft. A plural number of windows are formed in the tubular member. The windows are arrayed so as to partially overlap with the grooves, respectively. An overlapping area of the window and the groove associated therewith is varied in accordance with a relative turn of the tubular member to the surrounded portion. The portions of the tubular member having the windows formed therein are surrounded by coils. The self-induction electromotive force of each of the coils is measured. A torque is detected on the basis of the self-induction electromotive forces measured. An axial length of each of the windows is longer than an axial length of each of the coils but shorter than an axial length of each of yokes for holding the coils. A circumferential width of each of the grooves of the surrounded portion is wider than that of a raised part of the surrounded portion between adjacent ones of the grooves. A side wall of each of the grooves is raised in a radial direction of the first rotary shaft.