JP2009300189A - Liquid level sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reliably detect continuous change of a liquid level, by using a magnetoelectric transducer, at a low cost. <P>SOLUTION: A liquid level sensor 1 has a constitution wherein a magnetic focusing member 11 having a prescribed length is provided on a support shaft 10 along the axial direction, and the magnetoelectric transducer 12 is used as a magnetic detection element. The magnetoelectric transducer 12 is provided at least on one end in the longitudinal direction of the magnetic focusing member 11. The magnetic focusing member 11 is provided, so that a range where a magnetic flux density is changed linearly can be taken widely. Consequently, a float 20 position, namely, a change of the liquid level can be detected continuously by detecting the change of the magnetic flux density by the magnetoelectric transducer 12. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a float type liquid level sensor.

  In a fuel tank of an automobile, a kerosene tank of an oil fan heater, a water storage tank of a humidifier, etc., a float type liquid level sensor is used to detect a change in the amount of liquid. In this liquid level sensor, a support shaft made of a cylindrical member is fixed to a liquid tank case or the like so as to be perpendicular to the liquid surface by a mounting flange provided so as to protrude outwardly. An annular float holding a ring-shaped magnet inside is arranged on the outer periphery of the cylinder, and the float moves up and down with the support shaft as a guide as the liquid level rises and falls. The support shaft incorporates a magnetic detection element such as a reed switch that detects the magnetic field of the magnet. When the float moves up and down as the liquid level changes, the magnetic detection element detects the magnetic field of the magnet built into the float. Then measure the liquid level.

However, the liquid level sensor having such a configuration detects a magnetic field generated by a ring-shaped magnet incorporated in the float with a reed switch incorporated at a predetermined position in the support shaft. It was only possible to detect the point only by turning OFF. For this reason, a continuous change in the liquid level could not be detected, and the liquid level could not be finely controlled. In view of this point, Patent Document 1 proposes a liquid level sensor in which a large number of reed switches are arranged in a direction perpendicular to a support shaft so as to detect a magnetic field at a number of points.
JP 2001-31654 A

  According to the liquid level sensor described in Patent Document 1, since a large number of reed switches are arranged, it is possible to detect liquid levels closer to each other as the float moves up and down. There is a problem that the cost is increased.

  It is also possible to use a magnetoelectric transducer that can detect a linear change in magnetic flux density, such as a Hall element or a magnetoresistive element, but it is practical because the linear range of the magnetic flux density change of the magnet built in the float is extremely narrow. It was not right.

  The present invention has been made in view of the above circumstances, and can detect a continuous change in liquid level reliably using a magnetoelectric conversion element, and compared with a configuration using a large number of reed switches. It is an object of the present invention to provide a float type liquid level sensor that can be realized at low cost.

In order to solve the above problems, a liquid level sensor of the present invention is arranged by inserting a support shaft that supports a magnetic detection element and a hole provided in a substantially central portion through the support shaft, and according to changes in the liquid level. A liquid level sensor comprising a float that is guided and displaced by the support shaft, and a magnet supported by the float, wherein the support shaft is formed of a cylindrical member, A magnetic convergence member having a predetermined length is provided along the direction, a magnetoelectric conversion element is used as the magnetic detection element, and the magnetoelectric conversion element is provided at at least one end in the longitudinal direction of the magnetic convergence member. It is characterized by.
It is preferable that the magnetoelectric conversion elements are provided at two locations, one end and the other end in the longitudinal direction of the magnetic converging member. Further, it is preferable that the magnet is formed in a ring shape, and the magnetic flux concentrating member is arranged in a vertical direction in the hollow portion of the support shaft so as to pass on a center line of the ring-shaped magnet. The magnet is magnetized so that the magnetization direction is the thickness direction.
The magnetic flux concentrator member is preferably made of a soft magnetic material formed in a length range of 20 to 100 mm, and the magnetic flux concentrator member further has a width of 1 to 2 mm and a thickness of 0.5 to 1.5 mm. It is preferable that it is formed in a flat plate shape. Moreover, it is preferable to use soft ferrite as the soft magnetic material.

  In the liquid level sensor of the present invention, a magnetic converging member having a predetermined length is provided on the support shaft along the axial direction, a magnetoelectric conversion element is used as the magnetic detection element, and the magnetoelectric conversion element is used in the longitudinal direction of the magnetic converging member. It is the structure provided in at least one end. Since the magnetic converging member is provided, the range in which the magnetic flux density changes linearly can be increased. Therefore, by detecting the change in the magnetic flux density with the magnetoelectric transducer, it is possible to continuously detect the float position, that is, the change in the liquid level, and finely control the liquid level.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of a liquid level sensor 1 of the present invention. As shown in this figure, the liquid level sensor 1 of the present embodiment includes a support shaft 10 and a float 20.

  The support shaft 10 is made of a cylindrical member having a predetermined length, and has a mounting flange 10a protruding outward. The support shaft 10 is attached so that the mounting flange 10a is fixed to an arbitrary part of a liquid tank case or the like, and the longitudinal direction thereof is perpendicular to the liquid surface.

  In the hollow portion 10b of the support shaft 10, a magnetic converging member 11 and a magnetoelectric conversion element 12 that is a magnetic detection element are arranged. The magnetic flux concentrator member 11 has a function of converging the magnetic flux from the ring-shaped magnet 21 incorporated in the float 20. By having the magnetic flux concentrator member 11, the magnetic flux concentrator member 11 has the magnetic flux concentrator member 11. Compared with the case where it does not, it can exert on the magnetoelectric conversion element 12 from a further distance. As a result, the range in which the magnetic flux density changes linearly can be increased. The magnetic flux concentrator member 11 is not limited as long as it performs such a function. For example, soft magnetic materials such as permalloy, electromagnetic soft iron, electromagnetic stainless steel, soft ferrite, and SPC are suitable. It is preferable to use soft ferrite.

  The size of the magnetic flux concentrator member 11 is in the range of 20 to 100 mm in length when applied to a relatively small liquid tank such as an automobile fuel tank, an oil fan heater kerosene tank, or a humidifier water storage tank. It is preferable. This is because the magnetic convergence effect described above is weakened when the thickness exceeds 100 mm. Further, as the width and thickness are increased, a problem of adsorption of the float 20 with the magnet 21 occurs, and the operation of the float 20 becomes less smooth. Therefore, both the width and thickness are preferably 2 mm or less. The shape may be circular, oval, etc., but considering the ease of processing, ease of attachment, etc., a thin flat plate is preferable. In that case, the width is in the range of 1 to 2 mm and the thickness is 0. It is preferable to set it as the range of 5-1.5 mm.

  As the magnetoelectric conversion element 12, it is preferable to use a magnetoresistive element, a Hall element or the like. The magnetoelectric conversion element 12 may be provided only at one end (upper end) of the magnetic converging member 11 or may be provided at both ends. The difference between the case where it is provided only at the upper end and the case where it is provided at both ends will be described later.

  The magnetic flux concentrator member 11 and the magnetoelectric transducer 12 are attached to an attachment member (not shown) along the axial direction of the support shaft 10 such that the longitudinal direction of the magnetic flux concentrator member 11 is the vertical direction in the hollow portion 10b. ) Or molded with synthetic resin and fixedly arranged.

  The float 20 has a hole 20a in the center, and is arranged so that the support shaft 10 is inserted through the hole 20a. The float 20 moves up and down with the outer periphery of the support shaft 10 as a guide as the liquid level changes. . A ring-shaped magnet 21 is incorporated in the float 20. The ring-shaped magnet 21 is magnetized in the thickness direction. In addition, the relative positional relationship between the ring-shaped magnet 21 and the magnetic focusing member 11 described above is arranged so that the magnetic focusing member 11 passes on the center line of the ring-shaped magnet 21.

(Test Example 1)
FIG. 2 shows the measurement results when the relationship between the magnetic flux density and the distance between the upper surface of the float 20 and the Gauss meter probe is measured by setting the Gauss meter probe on the upper end of the magnetic focusing member 11 as shown in the graph. It is the shown graph (Test Example 1). FIG. 2 also shows a case (Comparative Example 1) in which the same measurement is performed without arranging the magnetic flux concentrator member 11.

  As apparent from FIG. 2, in the case of Comparative Example 1, the linear range of the change in the magnetic flux density is slightly seen in an extremely narrow range of about 6 to 10 mm, but a clear linear range appears in other regions. Absent. On the other hand, in Test Example 1, a linear range appears at a long distance of about 20 to 40 mm, and it can be seen that it is easy to capture a linear change in magnetic flux density.

(Test Example 2)
A combination of a magnetoresistive element and a bias magnet is disposed as the magnetoelectric conversion element 12 at the position of the gauss meter probe illustrated in the graph of FIG. FIG. 3 shows the relationship between the output voltage and the distance (the distance between the upper surface of the float 20 and the magnetic detection element 12).

  FIG. 3 shows that a linear change in the output voltage is detected in the range of about 20 to 40 mm, and the continuous change in the liquid level can be detected in a wide range from the relationship between the output voltage and the distance.

(Test Example 3)
Magnetic detecting elements 12 were respectively arranged at the upper and lower ends of the magnetic flux concentrating member 11, and the relationship between the difference between the output voltages of the two magnetoelectric transducers 12 and the distance was measured. The result is shown in FIG. The magnetoelectric conversion element 12 is a combination of a magnetoresistive element and a bias magnet.

  Here, the distance on the horizontal axis in FIG. 4 is set to 0 mm when the magnetoelectric transducer 12 provided at the upper end of the magnetic flux concentrator member 11 and the upper surface of the float 20 reach the same position, as in FIG. As a result, the output voltage of the magnetoelectric conversion element 12 provided at the lower end of the magnetic flux concentrator member 11 decreases as the float 20 and the magnet 21 rise and approaches 0 mm. It becomes a graph to show. Then, the relationship between the output voltage difference between the magnetoelectric conversion element 12 provided at the upper end and the magnetoelectric conversion element 12 provided at the lower end and the distance is as shown in FIG.

  From FIG. 4, when the difference between the output voltages of the two is used, the range of about 15 to 65 mm appears as a linear range, and therefore, the continuous change in the liquid level is performed in a wider range than in the case of Test Example 2. Can be caught.

FIG. 1 is a longitudinal sectional view showing a schematic configuration of a liquid level sensor according to an embodiment of the present invention. FIG. 2 is a graph showing the relationship between magnetic flux density and distance in Test Example 1 and Comparative Example 1. FIG. 3 is a graph showing the relationship between the output voltage and the distance in Test Example 2. FIG. 4 is a graph showing the relationship between the output voltage difference and the distance in Test Example 3.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Liquid level sensor 10 Support shaft 11 Magnetic convergence member 12 Magnetoelectric conversion element 20 Float 21 Magnet

Claims (7)

A support shaft that supports the magnetic detection element, a float that is inserted through the hole provided in a substantially central portion, and is guided and displaced by the support shaft according to a change in liquid level, and a float A liquid level sensor comprising a supported magnet,
The support shaft is formed of a cylindrical member, and a magnetic converging member having a predetermined length is provided in the hollow direction in the hollow portion, and a magnetoelectric conversion element is used as the magnetic detection element, and the magnetoelectric conversion element Is provided at least at one end in the longitudinal direction of the magnetic flux concentrator member.   2. The liquid level sensor according to claim 1, wherein the magnetoelectric transducer is provided at two locations, one end and the other end in the longitudinal direction of the magnetic converging member.   The magnet is formed in a ring shape, and the magnetic flux concentrating member is arranged in a vertical direction in a hollow portion of the support shaft so as to pass on a center line of the ring-shaped magnet. Item 3. The liquid level sensor according to Item 1 or 2.   The liquid level sensor according to claim 1, wherein the magnet is magnetized so that a magnetization direction is a thickness direction.   The liquid level sensor according to any one of claims 1 to 4, wherein the magnetic converging member is made of a soft magnetic material formed in a length range of 20 to 100 mm.   6. The liquid level sensor according to claim 5, wherein the magnetic converging member is further formed in a flat plate shape having a width of 1 to 2 mm and a thickness of 0.5 to 1.5 mm.   7. The liquid level sensor according to claim 5, wherein the soft magnetic material is soft ferrite.

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