Rotational speed indication signal generator having a plurality of generating coils

Claim 1

A rotational speed indication signal generator, comprising: (a) a base plate; (b) a rotary shaft mounted rotatably with respect to said base plate, said rotary shaft being arranged to be driven by an external rotational force applied thereto; (c) an outer disk made of a magnetic material and coaxially arranged with respect to said rotary shaft, said outer disk having gear teeth along its inner periphery; (d) an inner disk made of a magnetic material, said inner disk having gear teeth at its outer periphery so that said gear teeth of said outer disk surround and face said gear teeth of said inner disk with an annular gap between said outer and inner disks, said inner disk having a plurality of slots radially extending for defining a plurality of equiangularly spaced apart integral radial projections, angles between successive projections being less than 180°, one of said outer and inner disks being stationary with respect to said base plate, the other of said outer and inner disks being stationary with respect to said rotary shaft; (e) a permanent magnet attached to said outer or inner disk for constituting a magnetic circuit together with said outer and inner disks; and (f) a plurality of generating coils wound respectively around said radial projections in such a manner that the axis of each of said generating coils is normal to said rotary shaft so that said generating coils are radially arranged and lie along axes in a common plane angles between successive axes being less than 180° said generating coils being electrically connected in series so that resultant sum voltage caused from a component of ambient magnetic flux at any angle parallel to the plane of said inner disk equals zero.