Power steering apparatus having failure detection device for rotation angle sensors

A power steering apparatus for a vehicle having a steering wheel to steer tire wheels, the apparatus comprising:

• a power assisting system including a torsion bar operatively coupled with the steering wheel, a first electric actuator operatively coupled with the output side of the torsion bar to provide steering assisting power to steer the tire wheels, a torsion bar sensor for detecting a rotation angle of an output side of the torsion bar, and a first actuator sensor for detecting a first rotation angle of the first actuator;
• and
• a variable gear transfer system including a second electric actuator provided between the steering wheel and the torsion bar for transferring rotation of the steering wheel to the torsion bar at a variable transfer ratio thereby to change an amount of steering angle of the tire wheels relative to an operation amount of the steering wheel, a steering sensor for detecting a steering rotation angle of the steering wheel, and a second actuator sensor for detecting a second rotation angle of an output side of the second actuator, characterized by further comprising:
• a failure detection device configured to calculate at least one of a first pinion angle and a second pinion angle based on the torsion bar rotation angle and the first actuator rotation angle detected by the torsion bar sensor and the first actuator sensor, respectively, calculate a third pinion angle by adding the steering rotation angle detected by the steering sensor and the first rotation angle detected by the first actuator sensor, compare the at least one of the first pinion angle and the second pinion angle with the third pinion angle, and determine rotation sensor failure if the compared pinion angles are in disagreement.