Patent ID: 7366636

Claim:
A device for detecting rotational angle of a rotor, the device comprising: a main gear rotated integrally with the rotor and including an n number of teeth; a first detection gear including an m number of teeth engageable with the main gear and rotated together with the main gear; a second detection gear including an L number of teeth engageable with the main gear and rotated together with the main gear, wherein L is greater than m; a first detection means for detecting rotational angle α of the first detection gear within a cycle set in accordance with a predetermined angle; a second detection means for detecting rotational angle β of the second detection gear within the cycle; and a rotational angle calculating means for calculating a rotational angle θ of the rotor using the rotational angle α of the first detection gear within the cycle detected by the first detection means and the rotational angle β of the second detection gear within the cycle detected by the second detection means; wherein the rotational angle calculating means calculates a first rotational angle θ 1 based on θ 1 =mL/{n(L−m)}×[(α−β)+(i−j)Ω], where Ω is an angle corresponding to the cycles of α and β, i is an integer indicating the number of cycles completed by the first detection gear in relation with the rotational angle α, j is an integer indicating the number of cycles completed by the second detection gear in relation with the rotational angle β, i=j is satisfied in the case of α≧β, and i=j+1 is satisfied in the case of α<β; the rotational angle calculating means calculates a second rotational angle θ 2 based on θ 2 =m/n×α; the rotational angle calculating means calculates the integer i indicating the number of cycles completed by the first detection gear in relation with the rotational angle α based on i=(θ 1 −θ 2 )n/(mΩ) using the calculated first rotational angle θ 1 and the second rotational angle θ 2 ; and the rotational angle calculating means calculates the rotational angle θ of the rotor based on θ=m/n×(α+iΩ) using the calculated integer i.