Patent ID: 7227353

Claim:
An angular position determining apparatus comprising: a hard magnetic member joined to a rotary member, said hard magnetic member having a circumference and magnetized in a circumferential direction thereof to have a first and a second magnetic pole which produce a magnetic field therearound; a soft magnetic member disposed outside the circumference of said hard magnetic member within the magnetic field produced by said hard magnetic member, said soft magnetic member having a circumference and being made up of a plurality of magnetic sections array along the circumference of said soft magnetic member through gaps, rotation of the rotary member to change a relative angular position between the said hard magnetic member and said soft magnetic member causes a magnetic flux density within each of the gaps to change; a plurality of magnetic flux density measuring sensors each of which works to measure the magnetic flux density within one of the gaps to produce an electric signal as a function of the magnetic flux density as indicating an angular position of the rotary member; an angular position determining circuit woricing to determine an angular position of the rotary shaft using the electric signals outputted from the magnetic flux density measuring sensors; and a malfunction detecting circuit working to detect occurrence of a malfunction of each of the magnetic flux density measuring sensors based on the eleciric signals outputted from the magnetic flux density measuring sensors and outputting a signal indicative thereof wherein said malfunction detecting circuit works to measure changes in the electric signals outputted from two of the magnetic flux density measuring sensors in a given period of time, when an absolute value of a difference between the changes is greater than a given value, said malfunction determining circuit determining that either of the two of the magnetic flux density measuring sensors has failed.