Patent ID: 6911798

Claim:
A rotation angle detecting apparatus for a multi-phase synchronous rotary electric machine which includes a stator having a plurality of phase-coils and a rotor having a prescribed number of salient poles thereby operating cyclically, said rotation angle detecting apparatus comprising: a ring-shaped magnetic flux supply member, fixed to said rotor, having a first number of first magnetic flux supply poles alternately disposed on a first circular zone at equal intervals and a second number of second magnetic flux supply poles disposed on a second circular zone at equal intervals; and a magnetic flux change detector, fixed to said stator, having a first detecting element disposed at a first position on said first circular zone to provide an A-phase signal when it detects flux of said first magnetic flux supply poles, a second detecting element disposed at a second position that corresponds to 90 degrees in phase difference from said A-phase signal on said first circular zone to provide a B-phase signal when it detects flux of said first magnetic flux supply poles, and a third detecting element disposed at a prescribed position on said second circular zone to provide an index pulse when it detects flux of said second magnetic flux supply poles; wherein said second number is equal to said prescribed number, thereby generating said index pulse each cycle period in which each of said phase-coils fully operates.