Patent ID: 7447579

Claim:
A method for measuring an absolute steering angle φ of a steering shaft of a vehicle by using a first rotor and a second rotor respectively rotating at a determined RPM ratio according to the rotation of the steering shaft, the method comprising: obtaining a measured angle Ψ M ′ and a measured angle θ M ′ respectively by measuring a relative rotation angle Ψ′ of the first rotor and a relative rotation angle θ′ of the second rotor with an angle sensor having a measurement range of Ω; obtaining values of calculated angles θ C 's by calculating a plurality of relative rotation angles θ's which correspond to the Ψ M ′, wherein the calculations are based upon a functional relation defined by the relative rotation angle Ψ′ of the first rotor and the relative rotation angle θ′ of the second rotor; obtaining a periodic number i of the first rotor by comparing a plurality of the calculated angles θ C 's with the θ M ′; and obtaining the absolute steering angle of the steering shaft from a functional relation defined by Ψ and φ after gaining the absolute rotation angle Ψ of the first rotor by using the i.