JP2831375B2 - Position detection device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a position detection device that detects a position of a detection target by using a magnetoresistive element whose electric resistance is determined by a magnetic state.

[Conventional technology]

Conventionally, position detection devices have been used as control devices in a wide range of fields, such as position sensors or rotational speed sensors.However, there are strong demands for high detection accuracy, a wide range of ambient temperature, a small and simple structure, and magnetic detection. Formulas came to be used. This is because the magnetoresistive element has high sensitivity, is relatively stable to temperature changes, and is easy to manufacture. Furthermore, in an electronic circuit that converts a magnetic state into an electric signal, the magnetic state directly determines the resistance value, so that the design of the detection circuit is easy. The above features are effective for building a magneto-resistive element and a detection circuit in one chip. FIG. 7 shows a resistance bridge circuit used as a resistance value detection circuit.
FIG. 7 is a detection circuit diagram including a voltage amplification circuit 72 for detecting and amplifying an output voltage V with an output voltage 71.

Here, the magnetoresistive element is an element whose resistance value changes depending on the direction and intensity of the applied magnetic field. When a position detecting device is configured using this feature, as shown in FIG. 8, a bias magnet for applying a magnetic field to a magnetoresistive element and a detection target (a gear in FIG. 8) made of a magnetic material are used. A magnetoresistive element is arranged between the two.

[Problems to be solved by the invention]

However, the present inventors have confirmed that the relative positional accuracy between the bias magnet and the magnetoresistive element greatly affects the sensitivity and accuracy of the position detecting device. This will be described with reference to FIGS. 4 to 8.

As shown in FIGS. 4 and 5, FIG. 6 shows a bias in a plane parallel and perpendicular to the longitudinal direction of the magnetoresistive element under a magnetic field strength at which the resistance change is saturated. FIG. 6 shows how the resistance changes when the magnetic field angle is changed. As shown in FIG. 4, the resistance change when the bias magnetic field angle is changed in a plane parallel to the longitudinal direction of the magnetoresistive element is as shown by a curve A in FIG.
Also, as shown in FIG. 5, the resistance when the bias magnetic field angle is changed in a plane perpendicular to the longitudinal direction of the magnetoresistive element is as shown by a curve B in FIG.

The position detecting device detects the movement of the detection target using a change in resistance of the magnetoresistive element due to a change in the angle of the magnetic field applied to the magnetoresistive element (see FIG. 6).
Therefore, it can be seen that the sensitivity and accuracy are sensitive to the applied magnetic field angle.

Generally, when a magnet is placed in the air, the magnetic field angle diverges as shown in FIG. 8 (hereinafter, this kind of magnet is called a straight magnet). Therefore, there is a problem that the bias magnetic field angle greatly differs depending on the position of the magnetoresistive element. In FIG. 8, 1 is a magnet, 2a, 2b and 2c are magnetoresistive elements,
Assuming that the respective magnetic field angles are θa, θb, θc, θa <θ
b <θc. Therefore, even if the magnetoresistive elements 2a, 2b, and 2c have exactly the same resistance value and other characteristics, their resistance values will differ if their relative positions with respect to the magnets are different, and the detection circuit (see FIG. 7) connected to the magnetoresistive element will have a problem. Occurs. That is, in FIG. 8, the resistance change of the magnetoresistive element reaches a region where the resistance change of the magnetoresistive element is saturated in FIG. 6 with a slight offset amount in the X direction on the installation surface of the magnetoresistive element. When the resistance change of the magnetoresistive element due to rotation is small and a bridge circuit for detecting the resistance value is configured, the bridge does not satisfy the equilibrium condition, and the voltage across the two orthogonal ends of the bridge circuit depends on the rotation of the detection target. Does not intersect, that is, the rotation of the detection target cannot be detected.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described circumstances, and has as its object to provide a position detecting device which is hardly affected by the sensitivity and accuracy even if the magnetic field generating means and the magnetoresistive element are slightly misaligned.

[Means for solving the problem]

In order to achieve the above object, the present invention is a position detecting device that detects a position of a detection target having a magnetic material, wherein the magnetic field generation unit generates a bias magnetic field toward the detection target, A magnetoresistive element that is installed on a predetermined installation surface in a magnetic field and that changes resistance according to a change in the state of the bias magnetic field in accordance with the position of the detection target; In a position detecting device provided with a detecting circuit for detecting a position, the magnetic field generating means has a magnetic field generating surface for generating a bias magnetic field toward the magnetoresistive element, and the magnetic field generating surface faces the magnetoresistive element. Compensates for the divergent bias magnetic field generated on the installation surface of the magnetoresistive element,
Technical means is employed in which the bias magnetic field is formed in a concave shape that is substantially perpendicular to the installation surface.

[Action]

In the above configuration, the bias magnetic field generated from the magnetic field generating surface is compensated for diverging on the mounting surface of the magnetoresistive element by the concave shape of the magnetic field generating surface of the magnetic field generating means, and the bias magnetic field is substantially applied to the mounting surface. Orthogonal.

〔Example〕

FIG. 1 is a sectional view showing an embodiment of the position detecting device according to the present invention. In FIG. 1, the inner plate 3 of low thermal expansion metal (for example, Kovar, stainless steel 430, etc.)
The housing 8 made of a non-magnetic metal material is fixed by brazing, welding or press fitting. Output pins 4 are sealed to the inner plate 3 with sealing glass 5. A varistor 6, a magnetoresistive element, and a Si chip 7 on which a detection circuit shown in FIG. 7 is formed are adhered to the inner plate 3 with a low-melting glass or an adhesive (not shown). The electrical connection between the output pin 4 and the Si chip 7 is made by a bonding wire 9. To protect the Si chip 7 and the bonding wire 9, a junction coating agent 10 is applied and cured by heating. An outer case 11 made of a nonmagnetic material is press-fitted into the housing 8 and has an outer peripheral portion at the tip.
The Si chip 7 is completely sealed by using the housing 11a as a housing 8 and closely contacting each other by means such as laser welding. Outer case 11
The bracket 12 for fixing the position detecting device is fixed in advance by means such as brazing. A magnet 15 having a concave surface facing the Si chip 7 on which the magnetoresistive element is formed is fixed from outside the housing 8 with an adhesive (not shown). 13 is a ferrite bead for preventing malfunction due to electromagnetic noise. After the concave magnet 15 and the ferrite beads 13 are fixed, the mold resin material 14 is poured and heated and hardened to form the position detecting device shown in FIG.

In the position detecting device using the concave magnet of the present embodiment,
FIG. 3 shows the result of measuring the magnetic field angle at the position of the magnetoresistive element using a Hall probe. FIG. 9 shows the magnetic field angle when a straight magnet according to the prior art is used. The concave magnet and the straight magnet used in the experiment both had a magnetic flux density of 12 at the position of the magnetoresistive element.
00 Gauss. The distance between the position of the magnetoresistive element and the gear to be detected is the same for both.

3 and 9, the horizontal axis represents the rotation angle of the gear to be detected, and the gear pitch is 7 degrees. When comparing FIG. 3 and FIG. 9, there is no difference in the amplitude of the magnetic field angle between the concave magnet and the straight magnet, but the change in the offset amount Δx in the X direction in FIG. 8 or FIG. A large difference occurs in the center values. Here, the offset amount Δ
The position of x = 0 indicates that the line connecting the center of the gear and the center of the magnet is orthogonal to the offset direction. In the case of the straight magnet, the magnetic field diverges when the offset amount Δx increases. Therefore, the change in the center value of the magnetic field angle is large, and when the Δx changes by 1 mm, the magnetic field angle changes by 8 degrees. This means that if the center value of the magnetic field angle deviates by more than 90 degrees in FIG. 6, the resistance change is saturated even if the amplitude of the magnetic field angle is present. Therefore, the resistance detecting bridge shown in FIG. This is because the voltage at both ends in the case of configuring 71 is reduced.

On the other hand, in the concave magnet, since the magnetic field receives a slight convergence at the center and corrects the divergence, the change in the center value of the magnetic field angle is small even if the offset amount Δx increases. This indicates that the change in the center value of the magnetic field angle is small even if an offset occurs, and thus the magnetoresistive element can be used in a region where the resistance change of the magnetoresistive element is steep in FIG.

In the above embodiment, the varistor 6 is used so that the detection circuit on the Si chip is not destroyed by the application of the overvoltage. However, when only the magnetoresistive element is formed on the Si chip, the varistor 6 is omitted. Is also good.

Further, in the above embodiment, the magnetic field generating surface of the magnet 15 is formed as a concave surface, but as shown in FIG. 10, a magnet having a straight pole end surface such as a conventional bias magnet is used. A yoke 15a made of a concave magnetic material may be connected. In addition, multiple small magnets
By arranging as shown in FIG. 11, a concave magnetic field generating surface may be formed. 10 and 11, the magnetoresistive element 2 has an upper side in FIG.
That is, it is provided on the concave side.

In addition, in order to form the magnet in a concave shape, a plastic magnet may be used, and the magnet may be formed by a mold, so that the magnet can be easily formed.

〔The invention's effect〕

As described above, according to the present invention, the concave shape of the magnetic field generating surface of the magnetic field generating means compensates for the bias magnetic field generated from the magnetic field generating surface to diverge on the magnetoresistive element mounting surface, and Since the magnetic field is made to be substantially perpendicular to the surface on which the magnetoresistive element is provided, there is an excellent effect that a position detecting device having little influence on sensitivity and accuracy by positioning the magnetic field generating means and the magnetoresistive element can be provided.

[Brief description of the drawings]

FIG. 1 is a sectional configuration view of a position detecting device according to an embodiment of the present invention,
FIG. 2 is an explanatory view showing the convergence of the magnetic field of the concave magnet, FIG. 3 is an experimental result showing the change of the magnetic field angle with respect to the rotation angle of the gear to be detected by the concave magnet of one embodiment, and FIG. FIG. 5 is a diagram showing a magnetic field angle applied in a direction parallel to the longitudinal direction of the resistance element, FIG. 5 is a diagram showing a magnetic field angle applied in a direction perpendicular to the longitudinal direction of the magnetoresistive element, and FIG. Characteristic diagram showing resistance change,
FIG. 7 is a detection circuit diagram, FIG. 8 is an explanatory diagram showing the divergence of the magnetic field of the straight magnet, and FIG. FIG. 10 and FIG. 11 are schematic configuration diagrams of magnetic field generating means showing another embodiment. 1 ... Bias magnet, 2 ... Magneto-resistive element, 7 ... Si chip formed with magneto-resistive element and detection circuit, 15 ... Bias magnet, 15a ... Recessed yoke, 16 ... Target object.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Tadashi Hattori 14 Iwatani, Shimowasumi-cho, Nishio-shi, Aichi Pref. Japan Automobile Parts Research Institute Co., Ltd. Surveyed field (Int.Cl. ⁶ , DB name) G01P 3/00-3/80 G01D 5/00-5/249

Claims (1)

(57) [Claims] 1. A position detecting device for detecting a position of a detection target having a magnetic material, wherein: a magnetic field generating means for generating a bias magnetic field toward the detection target; and a predetermined installation surface in the bias magnetic field. A magnetoresistive element that is installed in the device and generates a resistance change due to a change in the state of the bias magnetic field according to the position of the detection target; and a detection circuit that detects the position of the detection target based on a change in the resistance value of the magnetoresistance element. In the position detecting device provided, the magnetic field generating means has a magnetic field generating surface for generating a bias magnetic field toward the magnetoresistive element, and the magnetic field generating surface has a bias magnetic field generated toward the magnetoresistive element. A position detecting device which compensates for divergence on a setting surface of the magnetoresistive element and is formed in a concave shape which makes the bias magnetic field substantially perpendicular to the installation surface. .