Patent ID: 8677835

Claim:
A torque sensor for detecting a torque generated on a first and second rotational shafts interconnected via a torsion bar, the torque sensor comprising: a sensor section including: at least one coil; a first magnetism-responsive member coupled with the first rotational shaft; and a second magnetism-responsive member coupled with the second rotational shaft, the first and second magnetism-responsive members being configured to cause an impedance change in the coil in response to a relative rotational position of the first and second rotational shafts; a coil driver circuit which supplies an excitation AC signal biased by a predetermined DC voltage to the coil; an offset voltage generating circuit which generates at least one of a DC voltage component contained in an output of the coil and a DC voltage corresponding to a peak amplitude value of the excitation AC signal as an offset voltage for a failure diagnosis; a differential amplifier circuit which obtains a difference between a detection output AC voltage component contained in the output of the coil and a reference AC voltage component according to the excitation AC signal and biases the obtained difference by the offset voltage to output an offset differential signal; a torque detection section which obtains detection data responsive to the impedance change in the coil as torque detection data by detecting an amplitude of an AC component in the offset differential signal output from the differential amplifier circuit; an offset voltage extraction section which extracts a voltage corresponding to a center of an oscillation of the AC component in the offset differential signal output from the differential amplifier circuit as the offset voltage; and a failure diagnostic section which determines that the torque is in a normal state if the extracted offset voltage falls within a predetermined range and that the torque is in an abnormal state if the offset voltage falls out of the predetermined range.