Torque sensor and electric steering device using the same
A torque sensor is provided with a torsion bar, first and second elongate sleeves respectively secured to one and the other ends of the torsion bar, and a pair of resolvers respectively mounted on the first and second elongate sleeves. First and second stop portions are provided respectively at overlapping portions of the first and second elongate sleeves where the second elongate sleeve is fit partly on the external surface of the first elongate sleeve with a play. A rotary sleeve given to one of the resolvers is press-fit on the external surface of the stop portion provided on the second elongate sleeve for mounting one of the resolvers thereon as well as for reinforcing the mechanical strength of the stop portion provided on the second elongate sleeve. Further, the resolvers used therein are chosen as those respectively having n-poles and m-poles. Where the torsional angle of the torsion bar is represented by symbol “θ”, the first and second stop portions are constructed to satisfy an expression (θ<180°|1/n−1/m|). The torsional angle of the torsion bar is limited to being smaller than the angle determined by the expression, and hence, the resolvers are prevented from having the same values in their electrical angles, so that incorrect detection in torque can be obviated.
1. A torque sensor having a torsion bar rotatably provided inside a cylindrical body; a pair of resolvers different in the number of poles for detecting the torsional angle of said torsion bar in the form of electrical angles thereof; and means for measuring a load torque corresponding to the torsional angle of said torsion bar, based on the difference between the detected electrical angles, wherein:
a stop mechanism is provided for defining the maximum torsional angle of said torsion bar; and
where the numbers of poles of said resolvers are represented by symbols “n” and “m” and the torsional angle is represented by symbol “θ”, then said stop mechanism is constructed to satisfy the following expression
θ<180°|1/ n −1/ m|.
2. An electric steering device wherein the torque sensor as set forth in claim 1 is connected to a shaft which is rotated by the manipulation of a steering handle.