Speed sensor having a closed magnetic flux path for sensing speed from an axial face of a rotating member

Claim 1

A rotational speed sensor comprising: a stator having two portions; a first portion including two discrete elements which are circumferentially spaced along a circumference from one another and feature radially extending surfaces; each said surface having alternating circumferentially spaced regions offering first and second magnitudes of magnetic permeability; said stator having a second portion forming a high magnetic permeability structural interconnection between said surfaces of said discrete elements of said first portion; a magnet disposed between at least one of said discrete elements and said second portion of said stator and providing structural interconnection therebetween; a rotor arranged for rotation about a rotational axis and having alternating circumferentially spaced regions offering first and second magnitudes of magnetic permeability; said alternating circumferentially spaced regions of first and second magnitudes of magnetic permeability of said rotor and stator being axially opposed and arranged in close proximity to one another; said rotor, magnet and stator being arranged to form a magnetic flux path whereby a variation in magnetic flux indicative of the rotational speed of said rotor relative to said stator is produced in said magnetic flux path upon rotation of said rotor; and means for sensing variation in said flux disposed on said second portion of said stator.