Torque sensor and electric power steering system having same

A torque sensor for detecting torsion torque to be applied to a first shaft and a second shaft comprising:

• a resilient 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 torsion 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 rotatable 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 is varied when rotation displacement of the soft magnetic member relative to the ferromagnetic member is changed according to the twist of the resilient member;
• and
• 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,
• wherein
• the ferromagnetic member is a ring shaped magnet having N and S poles alternately arranged circumferentially,
• the soft magnetic member comprises first and second ring shaped magnetic yokes that are positioned around an outer circumference of the ferromagnetic member and axially opposed to each other with an axial gap therebetween,
• each of the magnetic yokes has multiple saw-tooth shaped claws which are circumferentially spaced at constant intervals and whose number is equal to that of the N and S poles,
• the claws of the first magnetic yokes axially extend toward and being positioned to alternate circumferentially with those of the second magnetic yoke,
• each axial center of the claws of both the magnetic yokes is positioned to substantially coincide with a boundary between immediately adjacent N and S poles of the magnet, when a twist angle of the resilient member shows a reference value, and
• the magnetic sensor is positioned in the axial gap between the pair of the magnetic yokes.

A torque sensor for detecting torsion torque to be applied to a first shaft and a second shaft comprising:

• a resilient 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 torsion 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 rotatable 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 is varied when rotation displacement of the soft magnetic member relative to the ferromagnetic member is changed according to the twist of the resilient member;
• and
• 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,
• wherein
• the ferromagnetic member is a ring shaped magnet having N and S poles alternately arranged circumferentially,
• the soft magnetic member comprises first and second ring shaped magnetic yokes that are positioned around an outer circumference of the ferromagnetic member and axially opposed to each other with an axial gap therebetween,
• each of the magnetic yokes has multiple claws which are circumferentially spaced at constant intervals and whose number is equal to that of the N and S poles,
• the claws of the first magnetic yokes axially extend toward and being positioned to alternate circumferentially with those of the second magnetic yoke,
• each of the claws has such a configuration that a circumferential width thereof is continuously decreased in a direction from its root, from which the claw axially extends toward the other magnetic yoke, to a forward end of the claw,
• each axial center of the claws of both the magnetic yokes is positioned to substantially coincide with a boundary between immediately adjacent N and S poles of the magnet, when a twist angle of the resilient member shows a reference value, and
• the magnetic sensor is positioned in the axial gap between the pair of the magnetic yokes.