Patent ID: 6909290

Claim:
A rotor angle detecting apparatus for a DC brushless motor, the apparatus comprising: a voltage applying unit for applying a drive voltage to three phase armatures of the DC brushless motor; an inspection voltage imposing unit for imposing an inspection voltage on the drive voltage, the inspection voltage being generated by multiplying fundamental voltage string data in which a certain voltage output pattern in a predetermined period is set by a modulation coefficient whose value changes on every predetermined period; a current detecting unit for detecting a current which flows to the armatures of the motor; a reference value calculating unit for making reference to a detected current of the current detecting unit in a predetermined control cycle within the predetermined period when the inspection voltage is imposed on the drive voltage by the inspection voltage imposing unit and then calculating a sine reference value corresponding to a sine value of an angle which is twice a rotor angle of the motor and a cosine reference value corresponding to a cosine value of the angle which is twice the rotor angle of the motor based on a variation of the detected current detected by the current detecting unit in each control cycle, the fundamental current string data and the modulation coefficient; and a rotor angle detecting unit for detecting the rotor angle of the motor based on the sine reference value and the cosine reference value which are so calculated.