Patent ID: 6880411

Claim:
A torque sensor for detecting torison torque to be applied to a first shaft and a second shaft comprising: a resilent member disposed between and fixed to the first and second shafts so that the first shaft, the resilient member and the second shaft are coaxially in alignment with one another, the resilient member being resiliently twisted, when torison torque is applied to the first shaft and the second shaft; a ferromagnetic member connected to one of a given position of the first shaft and a given position of the resilient member on a side of the first shaft and rotable together therewith, the ferromagnetic member producing a magnetic field; a soft magnetic member connected to one of a given position of the second shaft and another given position of the resilient member on a side of the second shaft and rotatable together therewith, the soft magnetic member being positioned within the magnetic field and forming a magnetic circuit so that magnetic flux density generated in the magnetic circuit is varied when rotation displacement of the soft magnetic member relative to the ferromagnetic member is changed according to a twist of the resilient member; a magnetic sensor positioned in a vicinity of and without contacting the soft magnetic member for detecting the magnetic flux density generated in the magnetic circuit; a first rotation transmitting member through which the ring shaped magnet is connected to the one of the given position of the first shaft and the given position of the resilient member on a side of the shaft; and a second rotation transmitting member through which the soft magnetic member is connected to the other of the given position of the second shaft and the given position of the resilient member on a side of the second shaft, wherein: the ferromagnetic member includes a ring shaped magnet having N and S poles alternately arranged circumferentially, the soft magnetic member includes a pair of ring shaped magnetic yokes positioned around an outer circumference of the ring-shaped magnet and axially opposed to each other with an axial gap therebetween, each of the ring-shaped magnetic yokes having claws radially spaced at constant intervals, a number of the claws is equal to a number of the N and S poles, the claws of one of the pair of ring shaped magnetic yokes axially extending toward and being positioned to alternate circumferentially with the claws of the other of the pair of ring shaped magnetic yokes, the magnetic sensor is positioned in the axial gap between the pair of the magnetic yokes, and the ring shaped magnet and the pair of ring shaped magnetic yokes are positioned axially in parallel with the resilient member.