Patent ID: 8818636

Claim:
An electric power steering apparatus, comprising: a first rotary shaft connected to a steering wheel; a rack shaft configured to effect turning of a wheel to be turned, by a rectilinear motion; a second rotary shaft configured to effect the rectilinear motion of the rack shaft; a torsion bar configured to provide a connection between the first rotary shaft and the second rotary shaft, and configured to be twisted by operation of the steering wheel; an electric motor configured to apply assist force for the operation of the steering wheel; a steering torque detector configured to detect steering torque of the steering wheel; and a target current setting unit configured to set a target current to be supplied to the electric motor, on the basis of the steering torque detected by the steering torque detector, a feedback controller configured to perform feedback control on the target current set by the target current setting unit, the target current setting unit comprising: a target current determination unit configured to determine the target current; and a resonance compensator provided on an output side of the steering torque detector that is also an input side of the target, current determination unit, the resonance compensator being configured to suppress a resonance frequency component of a control system including the torsion bar as a spring element, and the electric motor, the second rotary shaft, and the rack shaft as inertial elements, and the target current setting unit being further configured to set the target current in accordance with the steering torque subjected to the suppression of the resonance frequency component by the resonance compensator, wherein a transfer function H(s) of the resonance compensator is defined as: H ( s )= a ·((2π f c1 )·(2π f c2 ))/(( s+ 2π f c1 )·( s+ 2π f c2 )); wherein: a = ( 4 ⁢ ⁢ π 2 · γ 1 2 · J 1 + 4 ⁢ ⁢ π 2 · J 2 + m · γ 2 2 ) · s 2 + 4 ⁢ ⁢ π 2 · k tb 4 ⁢ ⁢ π 2 · γ 1 , ⁢ or a = ( 4 ⁢ ⁢ π 2 · γ 1 2 · J 1 + 4 ⁢ ⁢ π 2 · γ 1 2 · J 2 + m · γ 1 2 · γ 2 2 ) · s 2 + 4 ⁢ ⁢ π 2 · γ 1 2 · k tb 4 ⁢ ⁢ π 2 · γ 1 · γ 2 ; ⁢ and wherein: s donates an operator for the Laplace transform, f c12 and f c2 represent cut-off frequencies of low-pass filters, γ 1 =θ 1 /θ 2 , where θ 1 represents an angle of rotation of the electric motor, and θ 2 represents an angle of rotation of the second rotary shaft, γ 2 =2·π·r, where r represents a radius of rotation of the second rotary shaft, J 1 represents inertia of a motor shaft of the electric motor, J 2 represents inertia of the second rotary shaft, m represents mass of the rack shaft, and k tb represents a spring constant of the torsion bar.