Torque detection device and electric power steering system including the same

A torque detection device, comprising:

• a torsion bar that couples a first shaft and a second shaft to each other;
• a permanent magnet that is fixed to the first shaft, and that forms a magnetic field around the permanent magnet;
• a magnetic yoke that is fixed to the second shaft, that is arranged within the magnetic field formed by the permanent magnet, and that forms a magnetic circuit in which a magnetic flux density changes in accordance with a change in a relative position between the magnetic yoke and the permanent magnet due to torsion of the torsion bar;
• an annular magnetic flux collecting unit that includes an annular holder made of resin, having a holding protrusion on an inner periphery of the holder, and having a through-hole that extends through the holder and that is formed at a position next to the holding protrusion, a magnetic flux collecting ring that is fitted to the inner periphery of the holder by being held by the holding protrusion and that collects magnetic fluxes from the magnetic yoke, and a magnetic shield that is fitted to an outer periphery of the holder so as to cover the through-hole and that reduces influence of an external magnetic field on the magnetic circuit, the magnetic flux collecting unit being arranged so as to surround the magnetic yoke;
• a magnetic sensor that detects magnetic fluxes that are generated in the magnetic circuit via the magnetic flux collecting ring;
• and
• a sensor housing that is formed integrally with the magnetic flux collecting unit by supplying resin onto an outer periphery of the magnetic flux collecting unit, wherein
• a resin flow passage is formed in the outer periphery of the holder, the resin that is supplied at the time of forming the sensor housing flowing into the through-hole through the resin flow passage.