JPH0933548A - Rotation sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rotation sensor which holds high sensitivity and high accuracy and is reliable even in the case when magnetic noise for the sensor is generated much by a magnet for a liquid crystal display operation used for some of flowmeters or when noise is much and a signal is weak as in measurement of low-speed rotation of ABS in an automobile, and which is economical, in addition. SOLUTION: A rotation sensor which comprises a magnetic sensor 1 having a core constituted of a magnetic material having a bistable magnetic characteristic and one or two or more magnetic flux sources 3 provided in a rotating body 2 and detects a change in a magnetic flux induced from the magnetic flux sources 3 by the rotation of the rotating body 2, and which is featured by that a shield tube 4 constituted of the magnetic material and being longer than the core is provided around the magnetic sensor 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rotation sensor which detects magnetic flux fluctuations induced by rotation of an object with high sensitivity and accuracy, is resistant to magnetic noise, and is economical. More specifically, the present invention is used in a detector of a flow meter used for measuring the flow rate of liquid or gas, or an antilock brake system (AB) of an automobile.
The present invention relates to a rotation sensor used as a vehicle speed detection sensor in S) and the like.

[0002]

2. Description of the Related Art Conventionally, a magnetic sensor such as an electromagnetic power generation type sensor or a reed switch, or an optical sensor such as a phototransistor has often been used as a rotation sensor for measuring the number of rotations and a rotation angle of an object. In the magnetic sensor, in the radial direction from the center of the rotating body (radial direction in the case of a circular rotating body), a magnetic flux source in which the central axis directions of the magnetic poles are matched, for example, a permanent magnet or an electromagnetic flux source is arranged in the rotating body, The magnetic flux generated by the magnetic flux source is rotated and changed by the rotation of the object, and the fluctuation of the magnetic flux is detected by a magnetic sensor in which a copper wire is wound around a magnetic material and converted into a voltage signal for use.

When a magnetic material having a bistable magnetic characteristic is used as the magnetic core of this magnetic sensor, a sharp pulse voltage signal can be obtained, and a rotation sensor having excellent rotation angle accuracy and high sensitivity can be obtained. it can. That is, in the AC magnetic hysteresis curve of the magnetic core, a pulse-shaped voltage signal is generated in the detection coil due to a sudden magnetization reversal at the point of the magnetization reversal critical magnetic field. However, in this rotation sensor, when the strength of the magnetic field entering from the outside is larger than the magnetization reversal critical magnetic field of the magnetic sensor, the sensor reacts to the external magnetic field, which makes it difficult to perform accurate measurement. There was a problem.

Further, the electromagnetic power generation type sensor also has a problem that it is weak against noise entering from the outside. That is, in the above-mentioned sensor, since the output level changes depending on the moving speed and distance of the detection target, there is a lot of noise, the excitation speed is slow, and in a situation where the rotation signal is weak, sufficient output cannot be obtained and noise is generated. More, S
In some cases, the / N ratio was reduced, and it was not suitable as a rotation sensor. Further, when trying to make the output and S / N ratio sufficient when detecting low speed rotation, the shape of the sensor becomes too large and complicated machining is required, resulting in high cost. There was also a problem. On the other hand, it is necessary to miniaturize the sensors installed on the drive shaft of automobiles and sensor installation parts of flowmeters as much as possible and to reduce machining as much as possible. It was an important issue in the automotive field.

Further, a magnetic sensor using a reed switch has a problem that it cannot be used for a long period of time because the contact deteriorates due to repeated on / off operations each time a magnetic pole passes. On the other hand, the optical sensor is strong against magnetic noise, but the detection part is weak against dirt, so it needs to be used in an environment that does not easily get dirty, and it must be regularly cleaned. There was a problem that it was expensive.

Further, in Japanese Unexamined Patent Publication No. 62-239020, a magnetic material having bistable magnetic characteristics is used as a magnetic core, and a plurality of magnetic sensors wound with a copper wire are connected in series, so that a low speed is achieved. It is disclosed that a rotation sensor with high sensitivity and high accuracy and a good S / N ratio can be obtained even when there is a lot of noise and a weak signal, such as when measuring the rotation of a wheel. However, this rotation sensor detects with a plurality of magnetic sensors connected in series and superimposes the pulse-shaped rotation signals of the respective magnetic sensors to increase the sensor output signal, thereby increasing the signal-to-noise ratio, that is, S / N. The characteristic is that the ratio is sufficient.In this case, the magnetization reversal critical magnetic field of each sensor is constant, so a signal is generated when there is magnetic noise whose magnetic intensity is greater than the magnetization reversal critical magnetic field. I had to do it. Further, since a plurality of sensors are used, it is not economically efficient.

Further, Japanese Laid-Open Patent Publication No. 4-155222 discloses a magnetic sensor which shields magnetic flux entering from the outside by a shield plate made of an amorphous metal surrounding only an amorphous powerless magnetic sensor. Since the magnetization reversal critical magnetic field of is small, if an external magnetic field with a large saturation amount of the amorphous metal shield plate enters, magnetic flux will be added to the sensor magnetic core and a pulse will be generated, making accurate measurement impossible. There was a problem that occurred.

[0008]

SUMMARY OF THE INVENTION The present invention is applicable to a case where there is a large amount of magnetic noise to a sensor due to a liquid crystal display operating magnet used in a part of a flow meter, or a low speed rotation measurement of an ABS in an automobile. High sensitivity, high accuracy and reliability, even when there is a lot of noise and the signal is weak.
Moreover, it is an object to provide an economical rotation sensor.

[0009]

DISCLOSURE OF THE INVENTION The inventors of the present invention solve these problems, and the gist of the present invention is to provide a magnetic sensor using a magnetic material having bistable magnetic characteristics as a magnetic core. In a rotation sensor that is composed of one or more magnetic flux sources mounted on a rotating body, and that detects magnetic flux fluctuations induced from the magnetic flux source by the rotation of the rotating body, is composed of a magnetic material,
In addition, the rotation sensor is characterized in that a shield tube longer than the length of the magnetic core is provided around the magnetic sensor.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic perspective view showing an example of the rotation sensor of the present invention. In FIG. 1, the rotation sensor of the present invention comprises a magnetic sensor 1 having a magnetic material having a magnetic material having bistable magnetic characteristics as a magnetic core, and one or more magnetic flux sources 3 mounted on a rotating body 2. is necessary. As the magnetic core of the magnetic sensor 1, for example, when an Fe-based amorphous magnetic material is used, the coercive force is smaller and the saturation magnetic flux density is higher than the conventional material, and the rectangular BH characteristic is maintained, so that the output is high. It is preferable because a highly sensitive and highly accurate rotation pulse signal can be obtained. The diameter of the magnetic core is 20 to
150 μmφ is particularly preferable and 25 to 30 μmφ is preferable, and the length of the magnetic core is 5 to 100.
In particular, it is preferably 7 mm to 13 mm.

The magnetic sensor 1 according to the present invention can be manufactured by inserting the magnetic core into a bobbin and winding a copper wire around the bobbin. Here, it is particularly preferable that the bobbin has a diameter of 1 to 5 mm.
mmφ is preferable, and the length of the bobbin is
It is preferably from 7 to 110 mm, particularly preferably from 10 to 15 mm. As the copper wire to be wound, for example, an insulation-coated copper wire (polyurethane, polyester, polyimide, etc.) having a diameter of 10 to 50 μm can be used on a bobbin.
It is preferable to use it by winding 0 to 10,000 turns.

Further, in the rotation sensor of the present invention, as the magnetic flux source 3 mounted on the rotating body 2, for example, a rare earth magnet having a surface magnetic flux density of 1 to 2 kG is used. Place it on the circumference of the disk so that it is perpendicular to the direction of emission from the central axis of the disk, or
Alternatively, it is preferable to equip the disk with a ferrite ring magnet magnetized so that the magnetic poles alternate with a surface magnetic flux density of 0.6 to 2 kG. Further, the number of magnetic flux sources 3 mounted on the rotating body 2 is preferably 2 to 10.

The magnetic sensor 1 used in the rotation sensor of the present invention detects a magnetic field change by the rotating magnetic flux source 3 and generates a pulse signal. This phenomenon is called the large Barkhausen effect because the magnetization reversal instantly occurs at a certain value of the applied magnetic field (magnetization reversal critical magnetic field). The causes of rapid magnetization reversal include internal stress due to flow in the nozzle during the manufacturing process of the magnetic core, rapid solidification without strain relaxation, and significant increase in domain wall energy density in relation to high magnetostriction. It is conceivable that bistable magnetic characteristics with stable saturation level are exhibited and high electromotive force is obtained.

Further, in the rotation sensor of the present invention, the shield tube 4 made of a magnetic material and longer than the length of the magnetic core is used.
Must be provided around the magnetic sensor. By providing the shield tube 4 made of a magnetic material around the magnetic core, the shield tube 4 absorbs the magnetic flux up to the saturation level, preventing magnetic noise from reaching the magnetic core, and effectively exciting the magnetic field. It can act on the sensor 1. Moreover, the apparent magnetization reversal critical magnetic field of the sensor can be changed by the shield of the magnetic material,
This apparent magnetization reversal critical magnetic field can be changed to about 0.5 to 15 Oe depending on the positions and lengths of the magnetic sensor 1 and the shield tube 4.

In the rotation sensor of the present invention, the apparent magnetization reversal critical magnetic field of the rotation sensor is made larger than the magnetization reversal critical magnetic field of the magnetic core alone by making the shield tube 4 longer than the length of the magnetic core. By doing so, the disturbance magnetic field can be effectively shielded.

FIG. 2 shows a magnetic sensor 1 used in the present invention.
FIG. 3 is a schematic perspective view showing an example of a shield tube 4 provided around it and around it. The shield tube 4 made of a magnetic material is arranged longer than the length of the magnetic core so as to cover the magnetic sensor in order to make the apparent magnetization reversal critical magnetic field of the rotation sensor larger than the magnetization reversal critical magnetic field of the magnetic core alone. If done,
Any shape may be used, but in order to obtain a good magnetic shielding effect while reducing the shape, the shield tube 4 is provided so as to be perpendicular to the magnet for excitation mounted on the rotating body,
An opening 5 that has a cylindrical shape with both ends open and that penetrates in the axial direction.
Is preferably formed. A magnetic sensor is arranged in the center of the shield tube 4 along the axial direction.

Regarding the size of the shield tube 4, the optimum size varies depending on the size of the magnet for excitation and the facing distance between the magnet and the magnetic sensor 1, but the length L is the total length 1 (L) of the magnetic core. It is necessary to make the length longer, preferably 1.1 times or more of the total length 1 (L) of the magnetic core, and more preferably 1.1 times or more and 1.5 times or less of the total length 1 (L) of the magnetic core. is there. The diameter D of the shield tube 4 is preferably about 1.1 to 2 times the diameter d of the magnetic sensor.
Further, the width A of the opening 5 of the shield tube 4 is preferably about 1/10 of the diameter D of the shield tube 4. In addition, as the distance (gap) between the shield tube 4 and the magnetic core,
It is preferably 0.5 to 3.0 mm.

The size of the shield tube 4 in the present invention is, for example, 10 to 20 mm in length and 25 to 3 in diameter.
When the magnetic core of 0 μmφ is used, the length L of the shield tube 4 is 11 to 22 mm and the diameter D of the shield tube 4 is 3 to 7 m.
mφ, the width A of the opening of the shield tube 4 is 0.5 to 1.0 m
m is preferable. In addition, as the magnetic material used for the shield tube 4 in the present invention, a general 45
An example is a PB grade iron-nickel magnetic alloy plate containing nickel by weight, but the material is not limited to this as long as it is a magnetic material.

[0019]

Next, the present invention will be described specifically with reference to examples and comparative examples. Example 1 As a magnetic core of a magnetic sensor, length 10 mm, diameter 30 μm
Using one φ Fe amorphous metal fiber (manufactured by Unitika Ltd.), a magnetic core was inserted into a bobbin having a length of 13 mm and a diameter of 2.75 mm, and a polyurethane coated copper wire having a diameter of 50 μm was wound on the bobbin for 1450 turns. . As an exciting magnetic field for inducing magnetization reversal in the magnetic core, a 70 mm aluminum circular disk is used as a rotating body, and 10 rare earth magnets having a surface magnetic flux density of 1.9 kG are arranged on the outer edge of the disk so that the magnetic poles alternate. They were installed at symmetrical positions with a positional relationship of 36 °. The magnet has a diameter of 4 mm and a thickness of 2 m.
m, and the direction of the magnetic pole was set to be perpendicular to the direction of radiation from the central axis of the circular disk. This excitation circular disk is designed to rotate with an axis installed in the center.

A shield tube made of a magnetic material and having a length (L) of 13 mm and a diameter (D) of 5 mm was installed around the magnetic sensor. Here, in order to obtain a good magnetic shielding effect while making the shape small, the shield tube is provided so as to be perpendicular to the exciting magnet mounted on the rotating body, and the shield tube has a cylindrical shape with both ends open. And an opening portion was provided to penetrate in the axial direction. And the magnetic sensor was arrange | positioned along the axial direction in the center part of this shield tube. The width (A) of the opening was 0.5 mm.

With this shield tube made of a magnetic material, the apparent magnetization reversal critical magnetic field of the rotation sensor can be changed, and the magnetization reversal critical magnetic field of the magnetic core alone is 1 Oe. The magnetization reversal critical magnetic field was 8.0 Oe. FIG. 3 shows an AC magnetic hysteresis curve of the rotation sensor. As a disturbance magnetic field, even when a liquid crystal display operating magnet having a surface magnetic flux density of 1.6 kG was brought close to 35 mm, measurement could be performed without counting errors of output pulses of the rotation sensor.

Comparative Example 1 As shown in FIG. 4, the shield tube is shorter than the length of the magnetic core, and the length of the magnetic core is 10 mm and the length of the shield tube is 9 m.
The same as Example 1 except that m was set. As a result, even when the shield tube was installed, the magnetization reversal critical magnetic field of the rotation sensor was 1 Oe as in the case where the shield tube was not installed. FIG. 5 shows an AC magnetic hysteresis curve of the rotation sensor. When the liquid crystal display magnet was brought close to it as in Example 1, occurrence of a measurement error of 30 counts was observed during 1000 counts of the output pulse of the rotation sensor.

[0023]

In the rotation sensor of the present invention, the apparent magnetization reversal critical magnetic field of the sensor can be made larger than the magnetization reversal critical magnetic field of the magnetic core alone, and therefore, the liquid crystal used in a part of the flowmeter. Even when there is a lot of magnetic noise to the sensor due to the display operation magnet, or when there is a lot of noise and the signal is weak, such as when measuring the rotation of an ABS at a low speed in a car, the disturbance magnetic field is shielded, and high sensitivity, high accuracy and reliability are achieved. It is possible to measure with certainty.

[Brief description of drawings]

FIG. 1 is a schematic perspective view showing an example of a rotation sensor of the present invention.

FIG. 2 is a schematic perspective view showing an example of a magnetic sensor and a shield tube used in the present invention.

FIG. 3 is a diagram showing an AC magnetic hysteresis curve of the rotation sensor according to the first embodiment.

4 is a schematic perspective view showing a magnetic sensor and a shield tube used in Comparative Example 1. FIG.

5 is a diagram showing an AC magnetic hysteresis curve of the rotation sensor in Comparative Example 1. FIG.

[Explanation of symbols]

 1 magnetic sensor 2 rotating body 3 magnetic flux source 4 shield tube 5 opening

Claims (1)

[Claims] 1. A magnetic sensor including a magnetic material having a bistable magnetic property as a magnetic core, and one or more magnetic flux sources mounted on a rotating body, which are induced from the magnetic flux source by rotation of the rotating body. A rotation sensor for detecting magnetic flux fluctuations, characterized in that a shield tube made of a magnetic material and having a length longer than the length of the magnetic core is provided around the magnetic sensor.