In a torque sensor, a first detection tube ( 13 ) made from magnetic material covers a cylindrical magnetic leak prevention member ( 12 ) that is made from nonmagnetic material and covers a first shaft ( 3 ) made from magnetic material. Magnetic resistance to magnetic flux, which passes through one end of the first detection tube ( 13 ) and one end of a second detection tube ( 14 ) that is made from magnetic material and rotates together with a second shaft ( 4 ), changes according to elastic relative rotation of the two shafts ( 3, 4 ) corresponding to transmitted torque, by providing a plurality of teeth ( 13 a , 14 a ) along the circumferential direction at the one end of each detection tube ( 13, 14 ). The first shaft ( 3 ) and the first detection tube ( 13 ) are integrated with the magnetic leak prevention member ( 12 ) so that they can rotate together, by being inserted in a mold for forming the magnetic leak prevention member ( 12 ) before the synthetic resin material is poured into the mold. The circumferential width of each resin holding space ( 13 A) between the teeth ( 13 a ) arranged along the circumferential direction at one end of the first detection tube ( 13 ) decreases gradually toward the other end of the first detection tube ( 13 ). The synthetic resin material solidified in the resin holding spaces ( 13 A) is pressed against the teeth ( 13 a ) due to shrinkage thereof.
1. A torque sensor comprising:
a first shaft made from magnetic material;
a second shaft connected to said first shaft so that they can rotate elastically with respect to each other;
a magnetic leak prevention member made from nonmagnetic material and covering the outer periphery of said first shaft;
a first detection tube made from magnetic material and covering the outer periphery of said magnetic leak prevention member;
a second detection tube made from magnetic material, integrated with said second shaft so that they can rotate together, and disposed so that one end thereof faces one end of said first detection tube via a gap; and
a coil constituting a magnetic circuit by generating magnetic flux passing through the one end of said first detection tube and the one end of said second detection tube; wherein
a plurality of teeth that are arranged along the circumferential direction are provided at the one end of said first detection tube and at the one end of the second detection tube so that magnetic resistance to magnetic flux in said magnetic circuit changes according to the amount of relative rotation of the two shafts;
said magnetic leak prevention member is molded from synthetic resin material poured into a mold;
said first shaft and said first detection tube are integrated with said molded magnetic leak prevention member so that they can rotate together, by being inserted in said mold before the synthetic resin material is poured thereinto;
each space between said adjacent teeth arranged along the circumferential direction at the one axial end of said first detection tube serves as a resin holding space;
said magnetic leak prevention member has a portion solidifying in said resin holding spaces; and
circumferential width of said resin holding space decreases gradually toward the other axial end of the first detection tube so that the synthetic resin material solidified in said resin holding spaces is pressed against said teeth due to shrinkage thereof.