MAGNETIC TACHOMETER

• US 3,739,211 A
• Filed: 10/15/1971
• Issued: 06/12/1973
• Est. Priority Date: 10/15/1971
• Status: Expired due to Term

• Current Assignee: Alfred Hasler
• Original Assignee: Alfred Hasler
• Inventors: Hasler, Alfred
• Primary Examiner(s): Skudy, R.
• Application Number:
  US05/189,685
• Time in Patent Office: 606 Days
• Field of Search: 310/70,168,169,170,171,156
• US Class Current: 310/168
• CPC Class Codes: G01P 3/488 delivered by variable reluctance detectors

Abstract

A pair of toothed elements of magnetically permeable material are coaxially mounted for relative rotation with their teeth spaced opposed in rotational registration. The toothed elements are further mounted in magnetic circuit with magnets and a coil whereby magnetic flux provided by the magnets follows two separate magnetically parallel flux paths including the pair of toothed elements and the coil. As the toothed elements are relatively rotated, the net reluctance of the flux path through the tooth elements varies and causes a voltage to be induced in the coil which alternates at a frequency representative of the relative speed of rotation of the toothed elements. The other of the magnetically parallel flux paths is of a fixed reluctance and does not extend through the pair of toothed elements.

Claims

1. A magnetic tachometer comprising a first member of magnetically permeable material defining a surface extending circumaxially about an axis;

a second member of magnetically permeable material positioned relative to the first member defining a surface extending circumaxially about said axis;

means for supporting the first and second members for relative rotation about said axis with their said extending surfaces spaced opposed in rotational registration;

means for varying the reluctance in a first flux path extending through the members and between the spaced opposed surfaces at a plurality of angular intervals about the axis as the members are relatively rotated;

means for providing a second flux path of fixed reluctance separate from and magnetically parallel to the first flux path;

a source of magnetic flux supported relative to the members and magnetically parallel flux paths to establish magnetic flux in the first flux path and in the second separate flux path; and

a magnetic flux detector positioned to detect magnetic flux in one of the separate magnetically parallel paths.

2. The magnetic tachometer according to claim 1 wherein the magnetic flux detector is positioned to detect flux in the second flux path of fixed reluctance.

3. The magnetic tachometer according to claim 1 wherein the means for supporting the members for relative rotation includes a shaft of magnetically permeable material mounted for rotation about the axis and one of said members is fastened to the shaft for rotation therewith and is magnetically coupled to the shaft to form part of the second flux path of fixed reluctance.

4. The magnetic tachometer according to claim 3 wherein the magnetic flux detector includes an induction coil supported in a stationary position surrounding the shaft to permit said shaft to rotate relative to said coil.

5. The magnetic tachometer according to claim 4 wherein the first one of the members is a disc fastened at its center to the shaft for rotation about the axis, the disc is provided with serrations forming alternate projective and root segments along its surface extending circumaxially about the axis for varying the spacing between the members thereby establishing different reluctances, the second member includes an annular portion supported in a stationary position, the annular portion having serrations forming alternate projective and root segments along its surface extending circumaxially about the axis for varying the spacing between the members thereby establishing different reluctances, and the source of magnetic flux includes a permanent magnet supported in a stationary position at one side of the plane of the disc to couple magnetic flux from one of its poles to the disc while permitting the disc to rotate relative to the magnet.

6. The magnetic tachometer according to claim 5 wherein the disc has an axially extending surface about its circumferential perimeter defining its circumaxially extending surface, the serrations about the disc are located along the axially extending surface to form alternate projective and root segments about the axis with the projective segments spaced at regular angular intervals about the axis, the annular member is a cylindrical structure journally supported at its opposite ends to the shaft to permit the shaft to rotate relative thereto, the cylindrical structure is supported to surround the disc with a space therebetween, the cylindrical structure has a radial inwardly extending portion having an axially extending surface defining the circumaxially extending surface of the annular member, the serrations about the annular member are located along its axially extending surface to form alternate projective and root segments about the axis with the projective segments spaced the regular angular intervals about the axis, and the permanent magnet supported with its poles spaced from the disc and the cylinder and the shaft to form air gaps in the magnetic flux paths at its poles.

7. The magnetic tachometer according to claim 5 wherein the disc and the annular portion have the same number of alternate projective and root segments with the projective segments spaced the same regular angular intervals about the axis, and each of the projective segments has a tip of a finite width in the circumaxial direction with said tip width of each projective segment of one magnetically permeable member the same, the circumaxial width of the tips of the projective segments of the disc is smaller than the circumaxial width of the tips of the projective segments of the annular portion.