Patent ID: 6707182
Filing Date: 2004-03-16
Classification: B62D,G01L

Abstract:
An electric power steering apparatus comprising:a first shaft; a second shaft; an elastic member having a first end and a second end, the first end of the elastic member connected to the first shaft and the second end of the elastic member connected to the second shaft; an electric motor for generating steering assistance power, the electric motor having an output shaft; a worm shaft connected to the output shaft of the electric motor; a worm wheel provided on the second shaft, the worm wheel meshing with the worm shaft so that steering assistance power is transmitted from the electric motor to the second shaft; a first detecting member provided on the second shaft, the first detecting member being made of magnetic material and having a plurality of radial notched portions defining first slots, the first slots provided on at least one side of the first detecting member so that the first slots are spaced around the first detecting member; a pair of second detecting members provided on both sides of the first detecting member so that the first detecting member is axially sandwiched between the second detecting members, the second detecting members being made of conductive and non-magnetic material and having a plurality of radial notched portions defining second slots so the second slots are spaced around the second detecting members, the second detecting members being coupled to the first shaft; a pair of detecting coils axially provided on both sides the first detecting member and the second detecting members so that the set of the first detecting member and the second detecting members are sandwiched between the detecting coils, the detecting coils capable of detecting a variation of torque generating between the first shaft and the second shaft based on a change in impedance of the detecting coils wherein the change in impedance is due to a variation of an over lap between the first slots and the second slots; a pair of yokes made of magnetic material, each of the yokes accommodating one of the detecting coils so that each yoke partially surrounds the one of the detecting coils; and a housing accommodating the first detecting member, the second detecting members, the detecting coils, and the yokes; wherein the yokes are fixed to the housing, and wherein the largest outer diameter of the first shaft is smaller than each of inner diameters of the first detecting member, the second detecting member and the yokes.