Variable reluctance speed sensor of integral construction utilizing a shielded high coercive force rare earth magnet positioned directly adjacent the sensing rotating element

A variable reluctance speed sensing system including:

• a. a thin, disc shaped, rate earth permanent magnet of thickness L and diameter D for producing magnetic flux.
• b. a moving member having protuberances to vary the air gap relative to said magnet whereby the reluctance of the associated magnetic path and the magnetic induction in said path is varied,
• c. an integral housing for said magnet formed of a ferromagnetic material to provide a magnetic flux return path for the flux from said magnet and said moving member comprising:
• 1. wall means to provide a return flux path for the flux from said magnet after passage through said moving member;
• 2. a base member connecting said wall means,
• 3. a core member extending from said base and positioned re-entrantly within said wall means for supporting said magnet at its free end whereby said magnet is positioned directly adjacent to said moving member to establish a flux path from said magnet across an air gap to said moving member and back, the said air gap being varied as the member rotates and the protuberances move by said magnet, said re-entrant core member being positioned within said wall means to shield said core and said magnet from external magnetic effects.
• 4. a sensing coil supported on said core for producing a signal voltage therein due to flux variations produced by said moving member.