Patent ID: 7201070

Claim:
A rotational angle detecting apparatus for detecting a rotational angle of a rotor, comprising: one or a plurality of first targets provided at the rotor; second targets provided at the rotor or another rotor rotating coaxially with the rotor, the number of which is coprime with the number of the first targets; two sensors C, D, disposed opposite to the first targets, for outputting detection signals V C , V D having phases different from each other in accordance with each position of the first targets as the rotor provided with the first targets rotates; two sensors E, F, disposed opposite to the second targets, for outputting detection signals V E , V F having phases different from each other in accordance with each position of the second targets as the rotor provided with the second targets rotates; and a calculation processing circuit including: a table that stores predetermined data relating values of corrected detection signals V C ′, V C ′ and V E ′, V F ′ and detected signal phase zones Z CD , Z EF to electrical angles θ CD , θ EF , respectively; a sensor output correction section that calculates intermediate values V midC , V midD , V midE , V midF from peak-to-peak values for detection signals V C , V D , V E , V F respectively, and calculates corrected detection signals V C ′, V D ′, V E ′, V F ′ from V midC , V midD , V midE , V midF and point values of V C , V D , V E , V F , respectively; a steering angle calculating section that compares the magnitudes of the absolute values of corrected detection signals V C ′, V D ′, compares the magnitudes of the absolute values of corrected detection signals V E ′, V F ′, compares the magnitudes of corrected detection signals V C ′, V D ′, compares the magnitudes of corrected detection signals V E ′, V F ′, determines signal phase zones Z CD , Z EF for corrected detection signals V C ′, V D ′ and V E ′, V F ′, respectively, based on the results of the comparisons, and retrieves values for the electrical angles θ CD and θ EF from the table based on the determined signal phase zones Z CD , Z EF , and corrected detection signals V C ′, V D ′ and V E ′, V F ′, respectively; and an absolute steering angle calculating section that detects the rotational angle of the rotor on the basis of the obtained electrical angles θ CD , θ EF .