Magnetoresistive gear tooth sensor

• US 10,060,941 B2
• Filed: 06/04/2013
• Issued: 08/28/2018
• Est. Priority Date: 06/04/2012
• Status: Active Grant

• Current Assignee: Multidimension Technology Co., Ltd
• Original Assignee: Multidimension Technology Co., Ltd
• Inventors: Bai, Jianmin, Deak, James Geza, Iv, Hua, Shen, Weifeng
• Primary Examiner(s): LE, SON T
• Application Number:
  US14/405,736
• Publication Number:
  US 20150145504A1
• Time in Patent Office: 1,911 Days
• CPC Class Codes: G01D 5/142 using Hall-effect devices measuring magnetic variables using Hall-effect or other galvanomagnetic devices G01R33/06
• CPC Class Codes: G01P 13/045 with speed indication
• CPC Class Codes: G01P 3/488 delivered by variable reluctance detectors
• CPC Class Codes: G01P 3/54 by measuring frequency of generated current or voltage
• CPC Class Codes: G01R 33/093 using multilayer structures, e.g. giant magnetoresistance sensors thin magnetic films H01F10/00
• CPC Class Codes: G01R 33/098 comprising tunnel junctions, e.g. tunnel magnetoresistance sensors

Abstract

The present invention discloses a magnetoresistive gear tooth sensor, which includes a magnetoresistive sensor chip and a permanent magnet. The magnetic sensor chip is comprised of at least one magnetoresistive sensor bridge, and each arm of the sensor bridge has at least one MTJ element group. The magnetoresistive gear tooth sensor has good temperature stability, high sensitivity, low power consumption, good linearity, wide linear range, and a simple structure. Additionally, the magnetoresistive gear tooth sensor has a concave soft ferromagnetic flux concentrator, which can be used to reduce the component of the magnetic field generated by the permanent magnet along the sensing direction of the MTJ sensor elements, enabling a wide linear range. Because it is arranged as a gradiometer, the magnetoresistive gear tooth sensor bridge is not affected by stray magnetic field; it is only affected by the gradient magnetic field generated by gear teeth in response to the permanent magnet bias. The magnetoresistive gear tooth sensor of the present invention is able to detect the position of a specific tooth or a missing tooth of a gear. This magnetoresistive gear tooth sensor is also capable of determining the speed and direction of motion of a gear.

Claims

1. A magnetoresistive gear tooth sensor, comprising:

a first permanent magnet and a sensor chip that includes at least one sensor bridge, wherein each arm of the sensor bridge is comprised of at least one magnetic tunnel junction (MTJ) element group, wherein each MTJ element group is comprised of at least one magnetoresistive MTJ element having a sensitive direction; and

a soft ferromagnetic flux concentrator with a U-shaped slot placed between the first permanent magnet and the sensor chip such that the slot is located on the side of the soft ferromagnetic flux concentrator facing the sensor chip, wherein the soft ferromagnetic flux concentrator is configured to reduce a magnetic field parallel to the sensitive direction to ensure the MTJ element operates in a linear region,

wherein the magnetoresistive gear tooth sensor is configured to generate a bias magnetic field (H_mag) across each MTJ element group in an oblique direction with respect to the sensitive direction such that, for each MTJ element group, the oblique direction of H_mag provides a first component perpendicular to the sensitive direction of the MTJ element group to set a sensitivity of the MTJ element group, and provides a second component parallel to the sensitive direction to cancel a Neel coupling field H₀ of the MTJ element group to also ensure the MTJ element operates in a linear region.

2. The magnetoresistive gear tooth sensor of claim 1, wherein each arm of the sensor bridge comprises a multiplicity of MTJ element groups interconnected in series, parallel, or a combination of series and parallel.

3. The magnetoresistive gear tooth sensor of claim 2, wherein the multiplicity of interconnected MTJ element groups has the same sensing direction.

4. The magnetoresistive gear tooth sensor of claim 1, wherein the MTJ element groups within each arm of the sensor bridge have the same sensing direction.

5. The magnetoresistive gear tooth sensor of claim 1, wherein the sensor chip comprises a full bridge, a half bridge, or two full bridges wired as a gradiometer.

6. The magnetoresistive gear tooth sensor of claim 1, wherein more than one magnetoresistive MTJ elements is interconnected in series, parallel, or a combination of series and parallel.

7. The magnetoresistive gear tooth sensor of claim 1, wherein a plurality of magnetoresistive MTJ elements with the same sensing direction connected in series, parallel or a combination of series and parallel.

8. The magnetoresistive gear tooth sensor of claim 1, wherein the magnetoresistive MTJ element is comprised of a multilayered structure with the following sequence:

a pinning layer, a ferromagnetic pinned layer, a tunnel barrier, and a ferromagnetic free layer.

9. The magnetoresistive gear tooth sensor of claim 1, wherein the magnetoresistive gear tooth sensor includes a pair of second permanent magnets positioned around each MTJ element group to provide the bias magnetic field for each MTJ element group.

10. The magnetoresistive gear tooth sensor of claim 9, wherein the pair of second permanent magnets is positioned on both sides of each MTJ element group obliquely with respect to the sensing direction of the corresponding MTJ element group.

11. The magnetoresistive gear tooth sensor of claim 9, wherein the pair of the second permanent magnets have a magnetization set at an angle to provide the first and second components.

12. The magnetoresistive gear tooth sensor of claim 1, wherein the magnetoresistive MTJ element is comprised of a multilayered structure with the following sequence:

a pinning layer, a ferromagnetic pinned layer, a tunnel barrier, a ferromagnetic free layer, and a magnetic bias layer.

13. The magnetoresistive gear tooth sensor of claim 12, wherein the magnetoresistive MTJ elements further include an isolation layer deposited between the magnetic free layer and the magnetic bias layer.

14. The magnetoresistive gear tooth sensor of claim 1, further comprising a microcontroller electrically interconnected with the sensor bridge.

15. The magnetoresistive gear tooth sensor of claim 14, wherein the microcontroller is used to determine the position of a gear tooth according to a relationship between the position of the gear tooth and the voltage signals of the magnetoresistive gear tooth sensor.

16. The magnetoresistive gear tooth sensor of claim 14, comprising two full sensor bridges, wherein each arm of the two full sensor bridges includes a MTJ element group, and the microcontroller is used to determine the movement direction of a gear using the voltage output of the magnetoresistive gear tooth sensor.

17. The magnetoresistive gear tooth sensor of claim 1, further comprising an outer casing.

18. A magnetoresistive gear tooth sensor, comprising:

a first permanent magnet and a sensor chip that includes at least one sensor bridge, wherein each arm of the sensor bridge is comprised of at least one magnetic tunnel junction (MTJ) element group, wherein each MTJ element group is comprised of at least one magnetoresistive MTJ element having a sensitive direction;

a soft ferromagnetic flux concentrator with a U-shaped slot placed between the first permanent magnet and the sensor chip such that the slot is located on the side of the soft ferromagnetic flux concentrator facing the sensor chip, wherein the soft ferromagnetic flux concentrator is configured to reduce a magnetic field parallel to the sensitive direction to ensure the MTJ element operates in a linear region; and

a pair of second permanent magnets positioned around each MTJ element group in order to provide a bias magnetic field for each MTJ element group, wherein the pair of the second permanent magnets have a magnetization set at an oblique angle with respect to the sensitive direction to provide a parallel bias field component that is parallel to the sensitive direction to cancel Neel coupling generated by the corresponding MTJ element group to also provide a perpendicular bias field component that is perpendicular to the sensitive direction to ensure the MTJ element operates in a linear region.

19. The magnetoresistive gear tooth sensor of claim 18, further comprising a microcontroller electrically interconnected with the at least one sensor bridge, wherein the microcontroller is used to determine the position of a gear tooth according to a relationship between the position of the gear tooth and the voltage signals of the magnetoresistive gear tooth sensor.

20. The magnetoresistive gear tooth sensor of claim 18, wherein the at least one sensor bridge comprises two full sensor bridges, the sensor further comprising further comprising a microcontroller, wherein each arm of the two full sensor bridges includes a MTJ element group, and the microcontroller is used to determine the movement direction of a gear using the voltage output of the magnetoresistive gear tooth sensor.