Detection of relative position between magnetic pole and drive coil in brushless DC motor

Claim 1

A brushless direct-current motor which is equipped with a rotor having a plurality of magnetic poles and multi-phase coils which are wound around a magnetic core to form magnetic paths and whose first terminals are connected in common to each other, said rotor being rotationally driven by selectively supplying bidirectional currents to the other terminals of said multi-phase coils, said brushless direct-current motor comprising: energization means for successively performing energizations of said multi-phase coils with energization patterns respectively predetermined for all combinations of two of said multi-phase coils when said rotor is in a stopping state; comparison means for comparing a reference voltage with a voltage developed at the other terminal of the coil which is in a non-energized state, in correspondence with a variation of an inductance generated in the coils due to a vector sum of a magnetic flux passing through the magnetic paths in response to the energization to the coils and a magnetic flux passing through the magnetic paths by the magnetic poles of said rotor; time-measuring means for measuring a time taken until the output value of said comparison means varies after the energization with one of said energization patterns is performed with respect to the coil whose voltage is compared therewith by the comparison means; and position detecting means for detecting a relative position of said rotor with respect to said multi-phase coils on the basis of the time value measured by said time-measuring means.