Arrangements for Magnetic Field Sensors That Act as Tooth Detectors

• US 20150022187A1
• Filed: 07/19/2013
• Published: 01/22/2015
• Est. Priority Date: 07/19/2013
• Status: Active Grant

• Current Assignee: Allegro Microsystems Incorporated (Sanken Electric Company Limited)
• Original Assignee: Allegro Microsystems Incorporated (Sanken Electric Company Limited)
• Inventors: Taylor, William P., Scheller, P. Karl, David, Paul
• Granted Patent: US 9,810,519 B2
• Time in Patent Office: Days
• US Class Current: 324/207.2
• CPC Class Codes: G01B 7/146 Measuring on gear teeth
• CPC Class Codes: G01D 5/147 influenced by the movement of a third element, the position of Hall device and the source of magnetic field being fixed in respect to each other
• CPC Class Codes: G01R 33/06 using galvano-magnetic devices
• CPC Class Codes: G01R 33/07 Hall effect devices
• CPC Class Codes: G01R 33/09 Magnetoresistive devices

Abstract

A variety of magnetic field sensor arrangements provide so-called “tooth detectors” using a simple low-cost magnet.

Claims

1. A magnetic field sensor for sensing motion of a ferromagnetic object, comprising:

a substrate, comprising;

a first major surface, wherein a first dimension across the first major surface of the substrate defines a width of the substrate and a second dimension across the first major surface of the substrate perpendicular to the first dimension defines a length of the substrate;

first and second substrate edges at ends of the width of the substrate;

a second major surface parallel to the first major surface, wherein the magnetic field sensor further comprises;

a magnet, comprising;

a first major surface proximate to the substrate, wherein a first dimension across the first major surface of the magnet defines a width of the magnet and a second dimension across the first major surface of the magnet perpendicular to the first dimension defines a length of the magnet;

a second major surface distal from the substrate and parallel to the first major surface of the magnet;

a center axis perpendicular to the first and second major surfaces of the magnet and centered within the width and length of the magnet, wherein the magnetic field sensor further comprises;

a first magnetic field sensing element disposed upon the first major surface or the second major surface of the substrate and configured to generate a magnetic field signal, wherein the first magnetic field sensing element comprises a center;

wherein the center of the first magnetic field sensing element is substantially closer to a first end of the width dimension of the magnet than to the center axis of the magnet.

2. The magnetic field sensor of claim 1, wherein a distance between the center axis of the magnet and the center of the first magnetic field sensing element is greater than a distance from the center axis of the magnet and the first end of the width dimension of the magnet.

3. The magnetic field sensor of claim 1, wherein the center of the first magnetic field sensing element is at or beyond the first end of the width dimension of the magnet.

4. The magnetic field sensor of claim 1, wherein the magnet has a north pole and a south pole, a line between which is parallel to the first major surface of the substrate.

5. The magnetic field sensor of claim 1, wherein the magnet has a north pole and a south pole, a line between which is perpendicular to the first major surface of the substrate.

6. The magnetic field sensor of claim 1, wherein the first magnetic field sensing element comprises a Hall element.

7. The magnetic field sensor of claim 1, wherein the first magnetic field sensing element comprises a magnetoresistance element.

8. The magnetic field sensor of claim 1, wherein the center axis of the substrate and the center axis of the magnet intersect the ferromagnetic object.

9. The magnetic field sensor of claim 1, wherein the magnet comprises a rectangular magnet.

10. The magnetic field sensor of claim 1, wherein the magnet consists of only one uniform material.

11. The magnetic field sensor of claim 10, wherein the magnet is comprised of a hard ferromagnetic material, and wherein the magnet does not have a core comprised of a different material.

12. The magnetic field sensor of claim 1, wherein the magnet is comprised of a hard ferromagnetic material, and wherein the magnet does not have a core comprised of a different material.

13. The magnetic field sensor of claim 1, wherein the magnet comprises magnetic particles molded within a mold compound.

14. The magnetic field sensor of claim 1, further comprising:

a leadframe over which the substrate is disposed, the leadframe comprising a plurality of leads;

a molded body encapsulating the substrate and selected parts of the leadframe; and

one or more passive electronic components disposed within the molded body and electrically coupled to at least two of the plurality of leads.

15. The magnetic field sensor of claim 1, wherein the first magnetic field sensing element is selected from a among a plurality of magnetic field sensing elements disposed upon the first major surface or the second major surface of the substrate.

16. The magnetic field sensor of claim 1, further comprising a second magnetic field sensing element disposed upon the first major surface or the second major surface of the substrate and configured to generate a second magnetic field signal, wherein the second magnetic field sensing element comprises a center, wherein the center of the second magnetic field sensing element is substantially closer to a second end of the width dimension of the magnet than to the center axis of the magnet.

17. The magnetic field sensor of claim 16, wherein a line passing through the first and second magnetic field sensing elements intersects the ferromagnetic object.

18. The magnetic field sensor of claim 17, wherein a distance between the center axis of the magnet and the center of the first magnetic field sensing element is greater than a distance from the center axis of the magnet and the first end of the width dimension of the magnet, and wherein a distance between the center axis of the magnet and the center of the second magnetic field sensing element is greater than a distance from the center axis of the magnet and the second end of the width dimension of the magnet.

19. The magnetic field sensor of claim 17, wherein the center of the first magnetic field sensing element is at or beyond the first end of the width dimension of the magnet, and wherein the center of the second magnetic field sensing element is at or beyond the second end of the width dimension of the magnet.

20. The magnetic field sensor of claim 17, wherein the magnet is comprised of a hard ferromagnetic material, and wherein the magnet does not have a core comprised of a different material.

21. The magnetic field sensor of claim 17, wherein the magnet comprises magnetic particles molded within a mold compound.

22. The magnetic field sensor of claim 17, further comprising an electronic circuit coupled to receive the first and second magnetic field signals and configured to sum the first and second magnetic field signals.

23. The magnetic field sensor of claim 17, further comprising:

a leadframe over which the substrate is disposed, the leadframe comprising a plurality of leads;

a molded body encapsulating the substrate and selected parts of the leadframe; and

one or more passive electronic components disposed within the molded body and electrically coupled to at least two of the plurality of leads.

24. The magnetic field sensor of claim 17, wherein the first magnetic field sensing element is selected from a among a first plurality of magnetic field sensing elements disposed upon the first major surface or the second major surface of the substrate and the second magnetic field sensing element is selected from a among a second plurality of magnetic field sensing elements disposed upon the first major surface or the second major surface of the substrate.

25. A magnetic field sensor for sensing motion of a ferromagnetic object, comprising:

a substrate, comprising;

a first major surface, wherein a first dimension across the first major surface of the substrate defines a width of the substrate and a second dimension across the first major surface of the substrate perpendicular to the first dimension defines a length of the substrate;

first and second substrate edges at ends of the width of the substrate;

a second major surface parallel to the first major surface, wherein the magnetic field sensor further comprises;

a magnet, comprising;

a first major surface proximate to the substrate, wherein a first dimension across the first major surface of the magnet defines a width of the magnet and a second dimension across the first major surface of the magnet perpendicular to the first dimension defines a length of the magnet;

a second major surface distal from the substrate and parallel to the first major surface of the magnet;

a center axis perpendicular to the first and second major surfaces of the magnet and centered within the width and length of the magnet, wherein the magnetic field sensor further comprises;

a first magnetic field sensing element disposed upon the first major surface or the second major surface of the substrate and configured to generate a first magnetic field signal;

a second magnetic field sensing element disposed upon the first major surface or the second major surface of the substrate and configured to generate a second magnetic field wherein a line passing through the first and second magnetic field sensing elements intersects the ferromagnetic object.

26. The magnetic field sensor of claim 25, wherein the first magnetic field sensing element is substantially closer to the ferromagnetic object than the second magnetic field sensing element.

27. The magnetic field sensor of claim 26, wherein the magnet is comprised of a hard ferromagnetic material, and wherein the magnet does not have a core comprised of a different material.

28. The magnetic field sensor of claim 26, wherein the magnet comprises magnetic particles molded within a mold compound.

29. The magnetic field sensor of claim 26, further comprising an electronic circuit coupled to receive the first and second magnetic field signals and configured to sum the first and second magnetic field signals.

30. The magnetic field sensor of claim 26, further comprising:

a leadframe over which the substrate is disposed, the leadframe comprising a plurality of leads;

a molded body encapsulating the substrate and selected parts of the leadframe; and

one or more passive electronic components disposed within the molded body and electrically coupled to at least two of the plurality of leads.

31. The magnetic field sensor of claim 26, wherein the first magnetic field sensing element is selected from a among a first plurality of magnetic field sensing elements disposed upon the first surface of the substrate and the second magnetic field sensing element is selected from a among a second plurality of magnetic field sensing elements disposed upon the first major surface or the second major surface of the substrate.