Patent ID: 7472004

Claim:
A steering angle sensor that detects a rotational angle of a steering system whose steering is assisted by driving of an electric motor via a reduction mechanism so as to calculate a steering angle of a steering wheel, comprising: a sensor wheel operating simultaneously with rotation of a steering shaft; and an absolute angle calculating means for calculating an absolute steering angle based on a steering angle signal from the sensor wheel; wherein the sensor wheel includes a GMR element and a magnetizing portion arranged around the GMR element, and wherein the rotational angle is detected by making two turns of the steering shaft as one cycle of the steering angle signal based on a change in resistance value of the GMR element obtained by changing a magnetic field direction according to a rotation of the magnetizing portion, and further detected based on the steering angle of the steering wheel by making two turns of the steering shaft as one cycle of the steering angle signal by adjusting a moderation ratio between the sensor wheel and the steering shaft.