Magnetoresistive type position detecting device

• US 6,452,381 B1
• Filed: 11/23/1998
• Issued: 09/17/2002
• Est. Priority Date: 11/28/1997
• Status: Expired due to Term

• Current Assignee: DENSO Corporation
• Original Assignee: DENSO Corporation
• Inventors: Uenoyama, Hirofumi, Nakatani, Shinji, Kinpara, Takamasa
• Primary Examiner(s): Snow, Walter E.
• Application Number:
  US09/198,567
• Time in Patent Office: 1,394 Days
• Field of Search: 324/207.21, 324/207.24, 324/207.25, 324/174, 324/235, 324/207.12, 338/32.R
• US Class Current: 324/207.21
• 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

Abstract

In a position detecting device for a moving object, such as a camshaft gear, having ridges and valleys, magnetoresistive elements are disposed in positions offset in the rotation direction of the moving object from the magnetic center of a bias magnetic field projected by a bias magnet. The direction of the bias magnetic field is different when the moving object is in a ridge position from when it is in a valley position. A mid-point potential of the MREs is taken as the output of an MRE bridge to obtain an output value which is different when the moving object is in the ridge position from when it is in the valley position. It is thus possible to distinguish between the ridge position and the valley position of the moving object.

Claims

1. A position detecting device comprising:

a moving object having a ridge and a valley arranged alternately thereon;

a bias magnet for projecting a bias magnetic field toward the ridge and the valley of the moving object; and

a resistive element group including at least one magnetoresistive element disposed between the moving object and the bias magnet, and responsive to a change in direction of the bias magnetic field caused by movement of the moving object,

wherein the resistive group including at least one magnetoresistive element is disposed in a position offset in a moving direction of the moving object from a magnetic center of the bias magnetic field corresponding to a center axis of the bias magnet in order that an output signal of the resistive element group produced when the ridge of the moving object faces the bias magnet is different in signal level from an output signal of the resistive element group produced when the valley of the moving object faces the bias magnet in a stationary state of the moving object,

wherein the resistive element group including at least one magnetoresistive element includes a first magnetoresistive element and a second magnetoresistive element, and the first and second magnetoresistive elements are formed on a surface of a substrate that is arranged substantially in parallel with the moving direction of the moving object, and

wherein the first and second magnetoresistive elements are connected in series and arranged so that a center axis therebetween is laterally offset from and parallel to the magnetic center of the bias magnetic field.

2. A position detecting device as in claim 1, wherein the moving object is a rotary gear, and the first and second magnetoresistive elements are both disposed in a position offset from the magnetic center of the bias magnetic field in the moving direction of the rotary gear.

3. A position detecting device as in claim 1, wherein:

the first magnetoresistive element and the second magnetoresistive element are disposed so as to make angles of about 45°

to the magnetic center of the bias magnetic field and form the shape of the non-parallel sides of a regular trapezium, and

the center axis of the regular trapezium the shape of whose non-parallel sides is formed by the first magnetoresistive element and the second magnetoresistive element is disposed in a position offset from the magnetic center of the bias magnetic field in the moving direction of the moving object.

4. A position detecting device as in claim 1, wherein:

the first magnetoresistive element and the second magnetoresistive element are connected in series to form a first magnetoresistive element bridge, and

a potential between the first magnetoresistive element and the second magnetoresistive element is taken as an output signal of the first magnetoresistive element bridge.

5. A position detecting device as in claim 1, further comprising:

another resistive element group including at least one magnetoresistive element disposed between the moving body and the bias magnet and having third and fourth magnetoresistive elements, and responsive to a change in the bias magnetic field caused by movement of the moving body,

wherein the another resistive element group including at least one magnetoresistive element is disposed in a position offset from the magnetic center of the bias magnetic field in the moving direction of the moving object in the opposite direction from the first resistive element group including at least one magnetoresistive element.

6. A position detecting device as in claim 5, wherein:

the third magnetoresistive element and the fourth magnetoresistive element are connected in series a potential between the third magnetoresistive element and the fourth magnetoresistive element is taken out, and

two outputs of the resistive element groups are applied to a circuit for comparison therebetween.

7. A position detecting device as in claim 6, wherein the circuit includes:

means for amplifying a difference between the two outputs; and

means for comparing the amplified difference with a predetermined threshold value.

8. A position detecting device as in claim 1, wherein:

the output produced from the resistive element group when the valley of the rotating member reaches a position facing the bias magnet and the output produced from the resistive element group when the ridge reaches the position facing the bias magnet are different in signal level.

9. A position detecting device as in claim 8, wherein:

the bias magnet is in a hollow shape, and

the resistive element group is formed on a substrate held in the bias magnet.

10. A position detecting device as in claim 5, wherein the width of the valley is wider than the spacing between the two resistive element groups.

11. A position detecting device as in claim 1 wherein:

the output signal of the resistive element group including at least one magnetoresistive element produced when the ridge of the moving object faces the bias magnet and the output signal of the magnetoresistive element group produced when the valley of the moving object faces the bias magnet have substantially zero slope.

12. A position detecting device as in claim 1 wherein:

the output signal of the resistive element group produced when the ridge of the moving object faces the bias magnet and the output signal of the resistive element group produced when the valley of the moving object faces the bias magnet are different from an output signal produced when an edge between the ridge and the valley of the moving object faces the bias magnet.

13. A position detecting device as in claim 1, wherein:

the first and the second magnetoresistive elements are disposed on a plane substantially parallel with a planar surface of the moving object.

14. A position detecting device as in claim 5 wherein:

the third and the fourth magnetoresistive elements are disposed on a plane substantially parallel with a planar surface of the moving object.

17. A position detecting device according to claim 5, wherein the moving object is a rotary gear, and the planar surface is parallel to a surface of the rotary gear perpendicular to rotational axis of the rotary gear.

18. A position detecting device according to claim 13, wherein the moving object is a rotary gear, and the planar surface is parallel to a side surface of the rotary gear perpendicular to rotational axis of the rotary gear.

19. A position detecting device according to claim 5, wherein the plurality of magnetoresistive elements are disposed on a surface of a substrate that is substantially arranged in parallel with a side surface of the rotatable member perpendicular to rotational axis of the rotatable member.

15. A position sensing device for detecting the stationary position of a rotatable member having alternating ridges and valleys thereabout, said device comprising:

a biasing magnetic field generator disposed to provide a biasing magnetic field directed toward said rotatable member about a biasing magnetic field axis;

at least one MRE unit disposed within said biasing magnetic field and comprising a plurality of magnetoresistive elements symmetrically disposed with respect to each other in said unit about an MRE unit axis that is offset from said biasing magnetic field axis; and

a bridge circuit connection of said magnetoresistive elements with at least one electrical signal amplifier which produces discernibly different output signals when the rotatable member is stationary corresponding respectively to the positions of a ridge or a valley thereof with respect to the sensing device.

21. A position sensing device according to claim 15, wherein an output signal produced when an edge between the ridge and the valley of the rotatable member is substantially changed in comparison with an output signal produced when the ridge or valley of the rotatable member faces the biasing magnet.

16. A method for detecting the stationary position of a rotatable member having alternating ridges and valleys thereabout, said method comprising:

generating a biasing magnetic field disposed to provide a biasing magnetic field directed toward said rotatable member about a biasing magnetic field axis;

disposing at least one MRE unit within said biasing magnetic field, said unit comprising a plurality of magnetoresistive elements symmetrically disposed with respect to each other in said unit about an MRE unit axis that is offset from said biasing magnetic field axis; and

sensing a signal from a bridge circuit connection of said magnetoresistive elements with at least one electrical signal amplifier which produces discernibly different output signals when the rotatable member is stationary corresponding respectively to the positions of a ridge or a valley thereof with respect to the sensing device.

20. A method for detecting the stationary position of a rotatable member according to claim 16, wherein the plurality of magnetoresistive elements are disposed on a side surface of a substrate that is substantially arranged in parallel with a surface of the rotatable member perpendicular to rotational axis of the rotatable member.

22. A position sensing device according to claim 16, wherein an output signal produced when an edge between the ridge and the valley of the rotatable member is substantially changed in comparison with an output signal produced when the ridge or valley of the rotatable member faces the biasing magnet.

23. A position detecting device comprising:

a moving object having a ridge and a valley arranged alternately thereon;

a bias magnet for projecting a bias magnetic field toward the ridge and the valley of the moving object; and

a resistive element group including at least one magnetoresistive element disposed between the moving object and the bias magnet, and responsive to a change in direction of the bias magnetic field caused by movement of the moving object,

wherein the resistive group including at least one magnetoresistive element is disposed in a position offset in a moving direction of the moving object from a magnetic center of the bias magnetic field corresponding to a center axis of the bias magnet in order that an output signal of the resistive element group produced when the ridge of the moving object faces the bias magnet is different in signal level from an output signal of the resistive element group produced when the valley of the moving object faces the bias magnet in a stationary state of the moving object, and

wherein the resistive element group including at least one magnetoresistive element includes a first magnetoresistive element and a second magnetoresistive element, the first and second magnetoresistive elements being connected in series and arranged so that a center axis therebetween is laterally offset from and parallel to the magnetic center of the bias magnetic field, and further comprising;

another resistive element group including at least one magnetoresistive element disposed between the moving body and the bias magnet and having third and fourth magnetoresistive elements, and responsive to a change in the bias magnetic field caused by movement of the moving body,

wherein the another resistive element group including at least one magnetoresistive element is disposed in a position offset, in the moving direction of the moving object from the magnetic center of the bias magnetic field, in the opposite direction from the first resistive element group including at least one magnetoresistive element.

24. A position detecting device as in claim 23, wherein said third and fourth magnetoresistive elements are connected in series and arranged so that a center axis therebetween is laterally offset from and parallel to the magnetic center of the bias magnetic field, said center axis of said third and fourth magnetoresistive elements being offset in said opposite direction from the center axis of the first and second magnetoresistive elements.