Patent ID: 7424830
Filing Date: 2008-09-16
Classification: G01L

Abstract:
1. A torque sensor, comprising: a shaft member including two shafts; an elastic member for connecting the shafts coaxially with each other, a torsion angle of the elastic member being detected as a torque that affects the shaft member; a hard magnetic member fixed to one of the two shafts for generating a magnetic flux therearound, wherein an N pole is arranged at one end of the hard magnetic member and an S pole is arranged at an opposite end of the hard magnetic member in an axial direction; a pair of first soft magnetic members disposed in parallel with each other in the axial direction around the hard magnetic member, wherein the first soft magnetic members are fixed to the two shafts, respectively, wherein the pair of first soft magnetic members constitutes a first magnetic circuit together with the hard magnetic member, in which the first soft magnetic members are relatively displaced to each other in a circumferential direction by torsion of the elastic member to change a reluctance; a pair of second soft magnetic members disposed in parallel with each other in the axial direction around the pair of first soft magnetic members, wherein the pair of second soft magnetic members constitutes a second magnetic circuit together with the hard magnetic member to keep the reluctance constant; and a flux detection means disposed between the second soft magnetic members, for detecting a flux density of the second magnetic circuit that varies in accordance with the torsion angle of the elastic member.