Power steering apparatus and control circuit for power steering apparatus

A control circuit for a power steering apparatus, the power steering apparatus including

• a steering mechanism including a steering shaft configured to rotate along with a rotation of a steering wheel, and a rack bar configured to be axially displaced according to the rotation of the steering shaft and made from a ferrous metallic material,
• an electric motor configured to provide a steering force to the steering mechanism,
• a speed reducer provided between the steering mechanism and the electric motor and configured to transmit a rotational force of the electric motor to the steering mechanism, the speed reducer including a ball screw mechanism,
• the ball screw mechanism including
• a wheel turning shaft-side ball screw groove provided on an outer peripheral side of the rack bar and having a helical groove shape,
• a nut formed annularly so as to surround the rack bar and made from a ferrous metallic material, the nut being provided rotatably relative to the rack bar,
• a nut-side ball screw groove provided on an inner peripheral side of the nut and having a helical groove shape, the nut-side ball screw groove forming a ball circulation groove together with the wheel turning shaft-side ball screw groove,
• a plurality of balls made from a ferrous metallic material and loaded in the ball circulation groove, and
• a circulation member provided on an outer side of the nut in a radial direction with respect to a rotational axis of the nut and connecting one end side and an opposite end side of the ball circulation groove so as to allow the plurality of balls to be circulated from the one end side to the opposite end side of the ball circulation groove,
• the power steering apparatus further including a torque sensor configured to detect a steering torque generated at the steering mechanism,
• the control circuit comprising:
• a motor control circuit configured to calculate, based on the steering torque, an instruction current value for controlling driving of the electric motor, and output the calculated instruction current value to the electric motor;
• and
• an abnormality detection circuit configured to detect an abnormality in the power steering apparatus based on whether there is a periodic change within a predetermined frequency range with respect to the number of rotations of the electric motor, a steering velocity, which is the number of rotations of the steering shaft, or the steering torque,
• wherein the steering mechanism includes a torsion bar provided at the steering shaft,
• wherein the torque sensor is configured to detect the steering torque based on a torsional amount of the torsion bar, and
• wherein the predetermined frequency in the abnormality detection circuit is set to a frequency lower than a resonant frequency of the torsion bar.

A power steering apparatus comprising:

• a steering mechanism including a steering shaft configured to rotate along with a rotation of a steering wheel, and a rack bar configured to be axially displaced according to the rotation of the steering shaft and made from a ferrous metallic material;
• an electric motor configured to provide a steering force to the steering mechanism;
• a speed reducer provided between the steering mechanism and the electric motor and configured to transmit a rotational force of the electric motor to the steering mechanism, the speed reducer including a ball screw mechanism,
• the ball screw mechanism including
• a wheel turning shaft-side ball screw groove provided on an outer peripheral side of the rack bar and having a helical groove shape,
• a nut formed annularly so as to surround the rack bar and made from a ferrous metallic material, the nut being provided rotatably relative to the rack bar,
• a nut-side ball screw groove provided on an inner peripheral side of the nut and having a helical groove shape, the nut-side ball screw groove forming a ball circulation groove together with the wheel turning shaft-side ball screw groove,
• a plurality of balls made from a ferrous metallic material and loaded in the ball circulation groove, and
• a circulation member provided on an outer side of the nut in a radial direction with respect to a rotational axis of the nut and connecting one end side and an opposite end side of the ball circulation groove so as to allow the plurality of balls to be circulated from the one end side to the opposite end side of the ball circulation groove,
• the power steering apparatus further comprising:
• a torque sensor configured to detect a steering torque generated at the steering mechanism;
• a control unit configured to calculate, based on the steering torque, an instruction current value for controlling driving of the electric motor, and output the calculated instruction current value to the electric motor;
• an abnormality detection circuit provided in the control unit and configured to detect an abnormality in the power steering apparatus based on whether there is a periodic change within a predetermined frequency range with respect to the number of rotations of the electric motor, a steering velocity, which is the number of rotations of the steering shaft, or the steering torque;
• and
• a low-pass filter provided in the control unit,
• wherein the abnormality detection circuit is configured to detect the abnormality in the power steering apparatus based on a signal indicating the number of rotations of the electric motor, the steering velocity, or the steering torque that is subjected to filter processing by the low-pass filter.