Electromagnetic power generating type rotation sensor

Claim 1

An electromagnetic power generating type rotation sensor comprising a housing, a magnetic rotator mounted on an object the rotation of which is to be detected, said magnetic rotator having an irregular surface on at least one of its outer peripheral part and its side part; a magnetic pole means arranged in proximity to said irregular surface of said magnetic rotator for alternately cooperating with projections and recesses of said irregular surface to change the amount of magnetic flux; and a coil (4, 14) for generating an AC output voltage responsive to said change in the amount of magnetic flux of said magnetic pole means for determining the rotational speed of said object from said AC output voltage, said magnetic pole means being divided into an outer magnetic pole piece (3a, 13a) made of a magnetic yet corrosion resistant material and located in a position close to said irregular surface of said magnetic rotator, and an inner magnetic pole piece (3b, 13b) made of a magnetic material having a lower corrosion resistance than said outer magnetic pole piece, said inner magnetic pole piece of lower corrosion resistance being located adjacent to said outer magnetic pole piece but inside said housing and inwardly of said outer magnetic pole piece to protect said inner magnetic pole piece from the external environment.