JP2010133851A - Rotation angle sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an accurate rotation angle sensor. <P>SOLUTION: The rotation angle sensor includes a pair of bias magnets 1 and 2 rotating together with a rotating body, a substrate 5 provided between the bias magnets 1 and 2, and a pair of magnetic members 3 and 4 provided on an internal end surface of the bias magnets 1 and 2, respectively. Grooves 3a and 4a extending in a direction parallel to a rotation center line are formed respectively on the internal end surface of the magnetic members 3 and 4. Therefore, a uniform magnetic field can be applied to the substrate 5. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a rotation angle sensor, and more particularly to a rotation angle sensor that detects a rotation angle of a rotating body. More specifically, the present invention relates to a rotation angle sensor that magnetically detects the rotation angle of a camshaft of an automobile engine and the rotation angle of motors of various machines such as machine tools and train cars.

  In recent years, a rotation angle sensor that magnetically detects the rotation angle of a camshaft has been used to monitor the open / closed state of a valve of an automobile engine. In this rotation angle sensor, a magnetic field that changes as the bias magnet fixed to the camshaft rotates is detected by a magnetoresistive element. A magnetoresistive element is an element whose resistance value changes with a change in magnetic field. Examples of the magnetoresistive element include a Hall element, an AMR (Anisotropic Magnetro Resistance) element, and a GMR (Giant Magnetro Resistance) element (see, for example, Patent Document 1).

The magnetoresistive element also includes an element that detects the direction of the magnetic field. For example, the GMR element that uses the spin valve structure described above can also detect the direction of the magnetic field. Further, there are TMR (Tunneling Magneto Resistance) elements and AMR (An-Isotropic Magneto Resistance) elements. In particular, the TMR element is a highly sensitive magnetoresistive element whose resistance change rate is one to two orders of magnitude greater than the resistance change rates of the Hall element, AMR element, and GMR element, and has a high tolerance for electrical noise.
Japanese Patent Laid-Open No. 2001-159542

  In order to detect the absolute angular position of the detected object using such a magnetoresistive element that detects the direction of the magnetic field, an attachment error occurs when the bias magnet is attached to the rotating body, or the magnetoresistive element is Even when the size of the chip to be configured is large, in order to suppress a detection error due to the distortion of the magnetic field, the direction of the magnetic field from the bias magnet fixed to the rotating body needs to be uniform over a wide range. Therefore, the development of a rotation angle sensor using a magnetoresistive element has a problem that a magnetic field having a uniform orientation must be formed in the space around the magnetoresistive element.

  A main object of the present invention is to provide a highly accurate rotation angle sensor.

  A rotation angle sensor according to the present invention is a rotation angle sensor that detects a rotation angle of a rotating body, and includes a pair of bias magnets, a magnetoresistive element, and a magnetic flux guide. The pair of bias magnets is provided on both sides of the rotation center line along a straight line orthogonal to the rotation center line of the rotating body, and rotates together with the rotating body. The magnetoresistive element is provided between the pair of bias magnets, and the resistance value changes according to the direction of the magnetic field between the pair of bias magnets. The magnetic flux guide equalizes the magnetic field between the pair of bias magnets. Each of the magnetic flux guides is provided corresponding to a pair of bias magnets, and includes a pair of magnetic members provided on end faces of the corresponding bias magnets on the magnetoresistive element side. A groove extending in a direction parallel to the rotation center line is formed on the end surface of each magnetic member on the magnetoresistive element side.

  In the rotation angle sensor according to the present invention, a magnetic flux guide for making the magnetic field between the pair of bias magnets uniform is provided. Each of the magnetic flux guides is provided corresponding to a pair of bias magnets, and includes a pair of magnetic members provided on end faces of the corresponding bias magnets on the magnetoresistive element side. A groove extending in a direction parallel to the rotation center line is formed on the end surface of each magnetic member on the magnetoresistive element side. Therefore, since a uniform magnetic field can be applied to the magnetoresistive element, a highly accurate rotation angle sensor can be realized.

  In the following embodiment, a case where a TMR element having the highest sensitivity is used as the magnetoresistive element for detecting the magnetic field direction will be described, but the same effect can be obtained even if other magnetoresistive elements are used. Is possible.

  FIG. 1 is a perspective view showing a configuration of a rotation angle sensor according to an embodiment of the present invention, and FIG. 2 is a top view thereof. 1 and 2, this rotation angle sensor includes a pair of bias magnets 1, 2, a pair of magnetic members 3, 4, a TMR element substrate 5, and a support base 6. For example, the rotation angle sensor magnetically detects the rotation angle of the camshaft in order to monitor the opening / closing state of a valve of an automobile engine.

  The bias magnets 1 and 2 are fixed to the camshaft and rotate together with the camshaft. The bias magnets 1 and 2 are arranged on one side and the other side of the Z axis along a straight line orthogonal to the rotation axis (Z axis) of the camshaft. The N poles and S poles of the bias magnets 1 and 2 are arranged along the length direction of a straight line orthogonal to the Z axis, and the N poles of the bias magnet 1 and the S pole of the bias magnet 2 are arranged to face each other.

  The magnetic members 3 and 4 are joined to the inner end faces of the bias magnets 1 and 2, respectively. The magnetic members 3 and 4 constitute a magnetic flux guide that makes the magnetic field between the bias magnets 1 and 2 uniform. Each of the magnetic members 3 and 4 has a shape like a fish tail when viewed from above.

  That is, when viewed from above, the magnetic member 3 is formed such that the inner side (bias magnet 2 side) width S2 is larger than the outer side (bias magnet 1 side) width S1, and Z on the inner end face thereof. A V-shaped groove 3a extending in a direction parallel to the axis is formed. The outer width S <b> 1 is formed larger than the width of the bias magnet 1. The width Ly of the groove 3 a is set to about half of the distance Lx between the magnetic members 3 and 4.

  Similarly, when viewed from above, the magnetic member 4 is formed such that the inner side (bias magnet 1 side) width S2 is larger than the outer side (bias magnet 2 side) width S1, and the inner end face thereof is formed. A V-shaped groove 4a extending in a direction parallel to the Z axis is formed. The outer width S <b> 1 is formed larger than the width of the bias magnet 2. The width Ly of the groove 4 a is set to about half of the distance Lx between the magnetic members 3 and 4.

  The TMR element substrate 5 is provided at an intermediate position between the bias magnets 1 and 2 and is fixed to the surface of the support base 6. The TMR element substrate 5 is fixed on the support base 6 so that its pin direction is located in a plane (XY plane) perpendicular to the rotation axis (Z axis). The direction of the magnetic field that changes with the detection is detected.

  FIG. 3 is a diagram showing the distribution of magnetic flux between the magnetic members 3 and 4. In FIG. 3, the magnetic field is emitted from the vicinity of both edges of the groove 3 a of the magnetic member 3 and absorbed near the edges of both sides of the groove 4 a of the opposite magnetic member 4. Near the rotation center axis on which the TMR element substrate 5 is installed, the direction of the magnetic field is uniformly directed in the X-axis direction in a wide region, and the magnetic flux density is made uniform in a wide region. Further, since the outer width S1 of the magnetic members 3 and 4 is made larger than the width of the bias magnets 1 and 2, the magnetic field strength near the TMR element substrate 5 can be increased.

  4A is a diagram showing the configuration of the TMR element substrate 5, and FIG. 4B is a circuit diagram showing the configuration. As shown in FIG. 4A, the TMR element substrate 5 includes a substrate 10 and four TMR elements 11 to 14 formed on the surface thereof. The TMR elements 11 and 12 are used to detect the direction of the magnetic field, and the TMR elements 13 and 14 are provided, for example, for correcting characteristic changes of the TMR elements 11 and 12 due to temperature changes in the engine room. It has been.

  A bridge circuit as shown in FIG. 4B is configured by these four TMR elements 11 to 14 and wired on the substrate 10. In addition to the TMR elements 11 to 14, a differential amplifier 15 for amplifying an electric signal from the bridge circuit, a signal processing circuit (not shown), and the like are formed on the surface of the substrate 10. Electric noise is reduced by this.

  More specifically, the TMR elements 11 and 14 are connected in series between the power supply voltage Vi line and the ground voltage GND line, and the TMR elements 13 and 12 are connected between the power supply voltage Vi line and the ground voltage GND line. They are connected in series. The node between the TMR elements 11 and 14 is connected to the inverting input terminal (− terminal) of the differential amplifier, and the node between the TMR elements 13 and 12 is connected to the non-inverting input terminal (+ terminal) of the differential amplifier. The Thereby, the change in the resistance value of the TMR elements 11 to 14 due to the change in the direction of the magnetic field is converted into the output voltage VO of the differential amplifier 15.

When the resistance value of each of the TMR elements 11 and 12 is Rs, the resistance value of each of the TMR elements 13 and 14 is Rr, and the amplification factor of the differential amplifier 15 is G, the output voltage VO of the differential amplifier 15 is It is represented by Formula (1).
VO = GVi (Rs−Rr) / (Rs + Rr) (1)
Each of the TMR elements 11 to 14 has a stacked structure of a pinned layer in which the direction of electron spin is fixed, a tunnel layer, and a free layer in which the direction of electron spin depends on the external magnetic field direction. The resistance value R (θ) of each of the TMR elements 11 to 14 is represented by the following equation (2) depending on the direction of the external magnetic field.
R (θ) ≈Rα−Rβcosθ (2)
Here, cos θ is a cosine of an angle formed between the direction of the electron spin (reference direction) of the pinned layer in each of the TMR elements 11 to 14 and the direction of the external magnetic field. Since Rα and Rβ do not depend on the magnitude of the external magnetic field, R (θ) is a value determined only by the direction of the external magnetic field. When the direction of the electron spin of the pinned layer and the direction of the electron spin of the free layer depending on the direction of the external magnetic field are parallel, R (θ) is the minimum value | Rα−Rβ |, and when it is antiparallel, (θ) Is the maximum value (Rα + Rβ).

  From the formulas (1) and (2), the relationship between the external magnetic field direction and the output voltage VO in the TMR elements 11 to 14 is determined. In this embodiment, the direction of the electron spin of the pinned layers of the TMR elements 11 and 12 and the direction of the electron spin of the pinned layers of the TMR elements 13 and 14 are directed in the direction reversed by 180 °. At this time, in the external magnetic field facing in one direction, the TMR elements 11 and 12 and the TMR elements 13 and 14 have different signs in the second term of the formula (2), and the denominator of the formula (1) is external. Since the constant does not depend on the magnetic field direction cos θ, the output voltage shows a waveform proportional to cos θ.

  As a result, for example, a sinusoidal output waveform as shown in FIG. 5 was obtained. However, TMR elements 11 to 14 having a magnetoresistance ratio of 20% were used, a bias voltage Vi was set to 2 V, and a differential amplifier 15 having a gain G of 5 was used. As can be seen from FIG. 5, an output waveform with extremely small waveform distortion could be obtained. As for the output amplitude, since the TMR element has a large magnetoresistance ratio, an output larger by one digit or more can be obtained as compared with the case where the AMR element is used. The absolute angle of rotation is obtained by converting such a sine wave output voltage VO into a digital signal.

  Next, the influence of an error in the mounting position of the TMR element substrate 5 with respect to the bias magnets 1 and 2 will be described. FIG. 6 is a diagram illustrating an example of an angular error estimated from the distortion of the output waveform when the distance between the central axis of rotation of the bias magnets 1 and 2 and the TMR element substrate 5 is changed. These data are obtained when the TMR elements 11 to 14 having a magnetoresistance ratio of 20% are used, the distance Lx between the two opposing magnetic members 3 and 4 is 7 mm, and the width Ly of the grooves 3a and 4a is changed. This is estimated from the waveform of the output voltage VO of the sensor.

  It can be seen from the data in FIG. 6 that the angular error increases uniformly as the TMR element substrate 5 moves away from the central axis of rotation of the bias magnets 1 and 2. It can also be seen that the angle error is small at a specific ratio (Ly / Lx = 0.63).

FIG. 7 shows data plotting the angle error when the ratio of Lx and Ly is changed when the TMR element substrate 5 is separated by 1 mm from the central axis of rotation of the bias magnets 1 and 2. FIG. 7 shows that the angle error has a minimum value at a specific ratio (Ly / Lx = 0.63), and the accuracy of the detected angle is improved. This data is a result when Lx = 7 mm. However, even when Lx has other values, when magnetic members 3 and 4 having the shape of the present embodiment are used, Ly / Lx = 0.63. Angle detection accuracy is optimal.
As described above, according to the present embodiment, the features of the TMR element are utilized to the maximum extent as a magnetoresistive element for detecting a change in the direction of magnetic flux, and the sensitivity is high and the output is high. It is possible to realize a rotation angle sensor that greatly improves the above.

  FIG. 8 is a diagram showing a modified example of this embodiment, and is a diagram to be compared with FIG. However, the illustration of the TMR element substrate 5 and the support base 6 is omitted. In FIG. 8, in this modified example, the magnetic members 3 and 4 are replaced with magnetic members 21 and 22, respectively. Each of the magnetic members 21 and 22 has a U-shaped cross section. Square grooves 21a and 22a extending in the direction parallel to the Z-axis are formed on the inner end faces of the magnetic members 21 and 22, respectively. Even in this modified example, the same effect as the embodiment can be obtained.

  In this modified example, the angle accuracy is improved when the ratio Ly / Lx between Lx and Ly is slightly smaller than the embodiment (about 0.5). Moreover, as shown in FIG. 9, you may cut off the angle | corner parallel to the Z axis | shaft of each outer side of the magnetic members 21 and 22 diagonally.

  FIG. 10 is a diagram showing another modification of this embodiment, and is a diagram contrasted with FIG. However, the illustration of the TMR element substrate 5 and the support base 6 is omitted. In FIG. 10, in this modified example, the magnetic members 3 and 4 are replaced with magnetic members 23 and 24, respectively. Each of the magnetic members 23 and 24 has a shape obtained by dividing an ellipse into two parts, and has a U-shaped cross section. U-shaped grooves 23a and 24a extending in a direction parallel to the Z-axis are formed on the inner end faces of the magnetic members 23 and 24, respectively. Even in this modified example, the same effect as the embodiment can be obtained.

  Even in this modified example, the angle accuracy is improved when the ratio Ly / Lx between Lx and Ly is slightly smaller than the embodiment (about 0.5). Moreover, as shown in FIG. 11, each of the magnetic members 23 and 24 may have a shape obtained by dividing a circle into two.

  In this embodiment, a TMR element is used as an element for detecting a magnetic field. However, the same effect can be obtained even when an AMR element or a GMR element is used as a magnetoresistive element.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

It is a perspective view which shows the structure of the rotation angle sensor by one Embodiment of this invention. It is a top view which shows the structure of the rotation angle sensor shown in FIG. It is a figure which shows distribution of the magnetic flux between a pair of magnetic members shown in FIG. It is a figure which shows the structure of the TMR element board | substrate shown in FIG. It is a figure which shows the relationship between the angle of the rotation angle sensor shown in FIG. 1, and output voltage. It is a figure which shows the relationship between the positional offset and angle accuracy of the rotating shaft of a pair of bias magnet shown in FIG. 1, and a TMR element board | substrate. It is a figure which shows the relationship between Ly / Lx shown in FIG. 2, and angle accuracy. It is a figure which shows the example of a change of embodiment. It is a figure which shows the other example of a change of embodiment. It is a figure which shows the further another example of a change of embodiment. It is a figure which shows the further another example of a change of embodiment.

Explanation of symbols

  1, 2 Bias magnet, 3, 4, 21-24 Magnetic member, 3a, 4a, 21a-24a Groove, 5 TMR element substrate, 6 Support base, 10 Substrate, 11-14 TMR element, 15 Differential amplifier.

Claims (3)

A rotation angle sensor for detecting a rotation angle of a rotating body,
A pair of bias magnets provided on both sides of the rotation center line along a straight line orthogonal to the rotation center line of the rotation body, and rotating together with the rotation body;
A magnetoresistive element provided between the pair of bias magnets, the resistance value of which varies according to the direction of the magnetic field between the pair of bias magnets;
A magnetic flux guide for uniformizing the magnetic field between the pair of bias magnets,
Each of the magnetic flux guides is provided corresponding to the pair of bias magnets, each including a pair of magnetic members provided on an end surface of the corresponding bias magnet on the magnetoresistive element side,
A rotation angle sensor, wherein a groove extending in a direction parallel to the rotation center line is formed on an end face of each magnetic member on the magnetoresistive element side.   The rotation angle sensor according to claim 1, wherein a width of the groove is set to 0.4 to 0.8 times a distance between the pair of magnetic members.   The rotation angle sensor according to claim 1 or 2, wherein a width of an end face of each magnetic member corresponding to the bias magnet is narrower than a width of the corresponding bias magnet.

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