JP2004333283A - Liquid level sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid level sensor capable of raising the accuracy of liquid level detection, suppressing increase in its size and cost. <P>SOLUTION: This liquid level sensor is constituted so that the periphery of a magnet 6 is covered with a cover 8 made of ferromagnetic material. Consequently, the level of the output signal of a Hall device 7 can be made higher by suppressing leakage magnetic flux from the magnet 6, and an influence of an external magnetic field on magnetic flux passing through the Hall device 7 can be excluded by causing magnetic flux by magnetism from outside to pass through the cover 8 selectively. Accordingly, the accuracy of liquid level detection by the fuel level gauge 1 can be raised, without increasing the size of the magnet, or without using a more-expensive magnet having stronger magnetism. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a liquid level sensor for measuring a liquid level of a liquid stored in a container, and more particularly to a non-contact type liquid level sensor using a magnetoelectric conversion element.
[0002]
[Prior art]
This type of liquid level sensor is used, for example, as a liquid level sensor for monitoring the amount of fuel stored in a fuel tank of an automobile.
[0003]
In this type of liquid level sensor, a float that moves up and down in conjunction with the liquid level, an annular magnet that is connected to the float and rotates by the up and down movement of the float, and intersects the magnetic flux generated by the magnet A magneto-electric conversion element arranged to convert the magnetic flux density of the magnet into an electric signal.The magneto-electric conversion element detects a change in the magnetic flux density passing through the magneto-electric conversion element due to rotation of the magnet in conjunction with the vertical movement of the float, and The liquid level is measured based on an electric signal from the conversion element (for example, see Patent Document 1).
[0004]
In this liquid level sensor, the output of the magnetoelectric conversion element, for example, the output voltage increases as the magnetic flux density of the magnet passing through the magnetoelectric conversion element increases. Therefore, by increasing the magnetic flux density of the magnet, the influence of noise or the like is reduced and the liquid level detection can be performed with higher accuracy.
[0005]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 2002-206959
[Problems to be solved by the invention]
In the conventional liquid level sensor described above, the magnet is used as a single unit, and therefore, there is a problem that a large amount of magnetic flux leaking from the magnet is generated and the magnetic force of the magnet cannot be used effectively for liquid level detection. .
[0007]
In addition, there is a problem in that the magnetic flux density passing through the magnetoelectric conversion element fluctuates due to the influence of magnetism from an external electromagnetic machine, for example, an electric motor, a transformer, or the like, thereby lowering the liquid level detection accuracy.
[0008]
2. Description of the Related Art In recent years, in automobiles, a liquid level sensor and an electric fuel pump, which are various components disposed in a fuel tank, are integrally modularized to reduce the number of steps required for mounting the fuel tank. In this case, since the liquid level sensor and the electric fuel pump are arranged close to each other, the magnetoelectric conversion element is easily affected by the magnetism of the electric fuel pump.
[0009]
As a solution to these problems, there is a method of increasing the magnetic force of the magnet. That is, the size of the magnet is increased, or a magnet having a high magnetic flux density is used.
[0010]
However, the former method has a problem that the size of the liquid level sensor becomes large. On the other hand, the latter method has a problem that the physical size does not change but the cost increases.
[0011]
The present invention has been made in view of the above points, and an object of the present invention is to provide a liquid level sensor capable of increasing the accuracy of liquid level detection while suppressing an increase in the size and cost of the liquid level sensor. It is to be.
[0012]
[Means for Solving the Problems]
The present invention employs the following technical means to achieve the above object.
[0013]
A liquid level sensor according to a first aspect of the present invention includes a float floating on a liquid whose liquid level is to be measured, a magnet holder rotatably held by a main body, and rotation of the magnet holder by the magnet holder. A two-pole magnetized cylindrical magnet fixed coaxially to the axis, an arm that connects the float and the magnet holder and converts the vertical movement of the float into a rotational movement of the magnet holder, and a substantially center of the magnet holder And a magnetic-electric conversion element that detects the magnetic flux density of the magnet and converts the magnetic flux density into an electric signal, and detects the magnetic flux density of the magnet and intersects with the magnetic flux of the magnet. A liquid level sensor that measures the liquid level based on the magnet, wherein the outer periphery of the magnet is covered with a cover made of a ferromagnetic material.
[0014]
In general, when a ferromagnetic material is brought into close contact with a magnet, the ferromagnetic material forms a magnetic path to reduce magnetic flux leakage from the magnet.
[0015]
Accordingly, in the configuration according to the first aspect of the present invention, even if a magnet having the same magnetic force as the conventional liquid level sensor is used, by providing the cover, the gap between the opposed magnetic poles on the inner circumferential side of the cylindrical magnet is provided. The magnetic flux density can be increased. In other words, compared to the conventional liquid level sensor without a cover, the magnetic flux density passing through the magnetoelectric transducer is increased, and the fluctuation of the magnetic flux density passing through the magnetoelectric transducer due to the influence of magnetism from an external electromagnetic machine is suppressed. As a result, the liquid level detection accuracy can be maintained satisfactorily.
[0016]
Therefore, it is possible to realize a liquid level sensor capable of increasing the accuracy of liquid level detection while suppressing an increase in the size and cost of the liquid level sensor.
[0017]
Further, in the configuration according to claim 1 of the present invention, almost no magnetic flux flows outside the cover. In other words, since the cover also functions as a magnetic shield for the magnet, foreign substances made of a magnetic material can reduce the magnetic force of the magnet. It is possible to prevent a drawback that the magnet holder is attracted to and adheres to the magnet or the magnet holder and hinders the rotation of the magnet holder in conjunction with the vertical movement of the float.
[0018]
A liquid level sensor according to a second aspect of the present invention includes a float floating on a liquid whose liquid level is to be measured, a magnet holder rotatably held by a main body, and rotation of the magnet holder by the magnet holder. Two float-magnetized magnets, which are arranged 180 degrees opposite to each other on the circumference of the same axis as the axis and opposite magnetic poles, are connected to the float and the magnet holder, and the float is moved up and down by the magnet holder. An arm that converts to rotational motion, and a magneto-electric converter that is fixed to the main body so as to be located at the approximate center of the magnet holder and intersects the magnetic flux of the magnet, detects the magnetic flux density of the magnet, and converts this to an electric signal And a liquid level sensor for measuring a liquid level based on an electric signal from the magnetoelectric conversion element. The liquid level sensor includes a cover made of a ferromagnetic material. The outer periphery of the magnet has a configuration covering the extrapolate.
[0019]
Also in this case, as in the case of the liquid level sensor according to the first aspect of the present invention, the magnetic flux density between the opposed magnetic poles of the two magnets can be increased. In other words, compared to the conventional liquid level sensor without a cover, the magnetic flux density passing through the magnetoelectric transducer is increased, and the fluctuation of the magnetic flux density passing through the magnetoelectric transducer due to the influence of magnetism from an external electromagnetic machine is suppressed. As a result, the liquid level detection accuracy can be maintained satisfactorily.
[0020]
Therefore, it is possible to realize a liquid level sensor capable of increasing the accuracy of liquid level detection while suppressing an increase in the size and cost of the liquid level sensor.
[0021]
The liquid level sensor according to the third aspect of the present invention is configured such that the ferromagnetic material is an iron-based metal.
[0022]
Iron-based metals as ferromagnetic materials have a wide variety of magnetic properties and high market availability. Further, since the workability is good, a cover having desired characteristics and shape can be easily formed.
[0023]
In the liquid level sensor according to a fourth aspect of the present invention, the cover is formed in a cylindrical shape.
[0024]
Thereby, the attachment of the cover to the magnet can be improved.
[0025]
In the liquid level sensor according to a fifth aspect of the present invention, the cylindrical cover is formed by rolling a plate material.
[0026]
Thereby, the cover can be formed easily and at low cost.
[0027]
BEST MODE FOR CARRYING OUT THE INVENTION
A liquid level sensor according to an embodiment of the present invention will be described below with reference to the drawings, taking as an example a case where the liquid level sensor is mounted in a fuel tank of an automobile and is applied to a fuel level gauge that detects a liquid level position of fuel. In each drawing, the same components are denoted by the same reference numerals.
[0028]
FIG. 1 is a sectional view of a fuel level gauge 1 which is a liquid level sensor according to an embodiment of the present invention, and is a sectional view taken along line II of FIG.
[0029]
FIG. 2 is a front view of the fuel level gauge 1 and shows a state where the liquid level 11 of the fuel is at the lowest level.
[0030]
1 and 2, the upper part of the figure is the upper part in a state where the fuel level gauge 1 is attached to the automobile.
[0031]
FIG. 3 is a schematic diagram showing a magnetized state of the magnet 6 in the liquid level sensor 1 according to one embodiment of the present invention.
[0032]
FIG. 4A is a schematic diagram illustrating a magnetic flux distribution state of the magnet 6 in the liquid level sensor 1 according to one embodiment of the present invention, and FIG. It is a schematic diagram explaining a magnetic flux distribution state.
[0033]
FIG. 5A is a schematic diagram illustrating a magnetic flux distribution state of the magnet 6 when an external magnetic field acts on the liquid level sensor 1 according to the embodiment of the present invention, and FIG. FIG. 3 is a schematic diagram illustrating a magnetic flux distribution state of a magnet when an external magnetic field acts on a surface level sensor.
[0034]
The fuel level gauge 1 is mounted on a fuel tank (not shown) of an automobile. That is, as shown in FIGS. 1 and 2, the body 5 as a main body is fixed to a bracket 12 that hangs from an inner surface (not shown) of a top plate of a fuel tank (not shown) of an automobile. 1 and 2 show a state in which the liquid level 11 of the fuel is at the lowest level. When the liquid level 11 of the fuel is at the highest level, that is, when the fuel tank is full, most of the body 5 Are immersed in the fuel.
[0035]
The float 2 is made of resin or the like, and has an apparent specific gravity set so as to float on the liquid surface 11 of the fuel.
[0036]
The magnet holder 4 is made of resin or the like, and is rotatably held by a body 5 which is a main body described later. That is, the hole 41 of the magnet holder 4 and the shaft 51 of the body 5 are rotatably fitted. When the fuel level gauge 1 is assembled, the movement of the magnet holder 4 in the left direction in FIG. Further, as shown in FIG. 2, the magnet holder 4 is provided with a holding portion 42 coaxially with the hole portion 41. A magnet 6 and a cover 8, which will be described later, are held and fixed in the holding section 42. Further, the magnet holder 4 is provided with a through hole 43 for fixing the arm 3 described later.
[0037]
The arm 3 is formed of, for example, a metal rod, and connects the float 2 and the magnet holder 4. That is, as shown in FIG. 1, the float 2 is fixed to one end of the arm 3, and the other end of the arm 3 is press-fitted and fixed to the through hole 43 of the magnet holder 4. A snap ring 10 is attached to the end of the arm 3 on the float 2 side to prevent the float 2 from falling off. When the float 2 moves up and down due to fluctuations in the level of the liquid surface 11, this movement is transmitted to the magnet holder 4 by the arm 3 and converted into rotational movement of the magnet holder 4.
[0038]
The magnet 6 is formed, for example, from a ferrite magnet or the like into a cylindrical shape, that is, a ring shape as shown in FIG. As shown in FIG. 3, the magnet 6 is magnetized in two poles on its inner peripheral surface. The magnet 6 is fixed in the holding portion 42 of the magnet holder 4 coaxially with the hole 41 of the magnet holder 4, in other words, coaxially with the shaft portion 51 of the body 5. Further, a cover 8 made of a ferromagnetic material is tightly fixed to the outer periphery of the magnet 6.
[0039]
The cover 8 is formed in a cylindrical shape from a ferromagnetic material, for example, iron or the like. For example, it is formed by cutting a seamless drawn steel pipe to a predetermined length.
[0040]
When the magnet 6 and the cover 8 are inserted and fixed in the holding portion 42 of the magnet holder 4, the three members of the magnet holder 4, the magnet 6, and the cover 8 are firmly fixed to each other to be integrated.
[0041]
The body 5, which is a main body, is formed of, for example, resin. As shown in FIG. 1, the magnet holder 4 is rotatably held on the body 5. The body 5 is provided with an accommodation room 52. In the accommodation room 52, a Hall element 7 as a magnetoelectric conversion element described later is arranged. Further, the body 5 is provided with a terminal 9 for electrically connecting the Hall element 7 to the outside. As shown in FIG. 1, one end of the terminal 9 extends into the accommodation chamber 52 and is connected to a lead 71 of the Hall element 7. On the other hand, the other end of the terminal 9 extends into the connector portion 54 of the body 5 and is connected to external wiring via the connector portion 54.
[0042]
As shown in FIG. 1, the Hall element 7 is disposed substantially at the center of the magnet holder 4, that is, at the substantially rotation center of the magnet holder 4 and at the inner periphery of the magnet 6. Thus, the Hall element 7 always crosses the magnetic flux of the magnet 6.
[0043]
Here, the operation of the Hall element 7 will be briefly described.
[0044]
The Hall element 7 is made of a semiconductor, and generates a Hall voltage proportional to the magnetic flux density passing through the Hall element 7 when a magnetic field is applied from the outside while a voltage is applied from the outside.
[0045]
In the fuel level gauge 1 according to one embodiment of the present invention, the positional relationship between the Hall element 7 and the magnet 6 is set as described above. In this case, the Hall voltage becomes maximum when the magnetic flux of the magnet 6 is orthogonal to the Hall element 7, and the magnet 6 rotates from this state, that is, as the magnet holder 4 rotates due to the fluctuation of the liquid level 11, the Hall voltage increases. Decreases. That is, the level of the liquid surface 11 can be measured by detecting this Hall voltage.
[0046]
Next, the operation and effect of the cover 8 which is a feature of the fuel level gauge 1 according to one embodiment of the present invention will be described.
[0047]
When there is no conventional fuel level gauge, that is, when there is no cover 8, the magnetic flux distribution of the magnet 6 is as shown by a solid line in FIG. In other words, the magnetic flux is distributed between the N pole and the S pole on the inner circumference of the magnet 6 and also distributed outside the magnet 6 to be a leakage magnetic flux. Therefore, the magnetic flux density of the magnetic flux distributed on the inner periphery of the magnet 6, that is, the magnetic flux crossing the Hall element 7 and used for liquid level detection is small.
[0048]
On the other hand, in the fuel level gauge 1 according to the embodiment of the present invention, the iron cover 8 is attached to the outer periphery of the magnet 6 in close contact. In this case, the magnetic flux distribution of the magnet 6 is distributed between the N pole and the S pole on the inner circumference of the magnet 6 as shown by a solid line in FIG. There is no leakage flux passing outside of 8. Therefore, the magnetic flux distributed on the inner periphery of the magnet 6, that is, the magnetic flux density of the magnetic flux crossing the Hall element 7 and used for liquid level detection becomes larger than that of the conventional fuel level gauge shown in FIG. ing.
[0049]
As a result, the magnetic flux density passing through the Hall element 7 is increased, the Hall voltage, that is, the output signal level of the Hall element 7 is increased, and the liquid level detection accuracy by the fuel level gauge 1 can be improved.
[0050]
Next, the effect of a magnetic force from an electric fuel pump (not shown) disposed near the fuel level gauge 1 on the fuel level gauge 1 will be described.
[0051]
When the conventional fuel level gauge, that is, the cover 8 is not provided, the magnetic flux around the magnet of the fuel level gauge is distributed as shown in FIG. That is, in FIG. 5B, the solid line shows the magnetic flux of the magnet, and the broken line shows the magnetic flux from the electric fuel pump (not shown). In this case, the magnetic flux of the magnet is distorted by the action of the magnetic flux from the electric fuel pump (not shown) as shown in FIG. For this reason, even at the same liquid level, the magnetic flux density passing through the Hall element 7 fluctuates. As a result, the Hall voltage, that is, the output signal level of the Hall element 7 fluctuates, and the accuracy of liquid level detection decreases. I do.
[0052]
On the other hand, in the fuel level gauge 1 according to the embodiment of the present invention, the magnetic flux around the magnet 6 of the fuel level gauge 1 is distributed as shown in FIG. That is, in FIG. 5A, the solid line shows the magnetic flux of the magnet, and the broken line shows the magnetic flux from the electric fuel pump (not shown). In this case, a part of the magnetic flux from the electric fuel pump selectively passes through the inside of the cover 8 made of a ferromagnetic material having a high relative permeability, and passes through the inner peripheral side of the cover 8, in other words, the inner peripheral side of the magnet 6. I do not pass. Therefore, the magnetic flux of the magnet 6 is not affected by the magnetic flux from the electric fuel pump (not shown).
[0053]
Therefore, in the fuel level gauge 1 according to the embodiment of the present invention, even if a magnetic force acts from the outside, the accuracy of the liquid level detection does not decrease as in the conventional fuel level gauge, and the good liquid level Detection accuracy can be maintained.
[0054]
Furthermore, in the fuel level gauge 1 according to one embodiment of the present invention, the cover 8 suppresses the magnetic flux of the magnet 6 from leaking outside the cover 8. For this reason, the foreign matter of the magnetic substance of the fuel tank (not shown), for example, a small iron piece or iron sand is attracted by the magnetic force of the magnet 6 and is prevented from adhering to the magnet 6 and the magnet holder 4. Therefore, it is possible to prevent a problem that the rotation of the magnet holder 4 interlocked with the vertical movement of the float 2 is hindered by the adhesion of various foreign substances, in other words, the liquid level detection function is hindered.
[0055]
In the fuel level gauge 1 according to one embodiment of the present invention, in order to ensure that the cover 8 exerts the function of suppressing the leakage magnetic flux from the magnet 6 and the function of shielding the external magnetic field, the cover 8 is It is a necessary condition that no magnetic saturation occurs due to the magnetic flux from the outside and the external magnetic field. Therefore, it is necessary to appropriately select the thickness t of the cover 8 shown in FIG. 1 and the ferromagnetic material forming the cover 8.
[0056]
In the fuel level gauge 1 according to the embodiment of the present invention described above, the cover 8 is formed from a seamless drawn steel pipe, but may be formed from another material such as silicon steel, permalloy, or the like. . Further, it may be formed by a method other than the method of cutting the tubular material. For example, the plate material may be formed into a cylindrical shape by press working, or the plate material may be rolled into a cylindrical shape. In the case where the plate material is rolled into a cylindrical shape, a gap may be provided at the joint.
[0057]
Further, in the fuel level gauge 1 according to the embodiment of the present invention described above, the magnet 6 is formed in a ring shape. However, the magnet 6 is not limited to a ring shape. For example, as shown in FIG. It may be formed in an arc shape and two pieces may be arranged facing each other.
[0058]
Further, in the fuel level gauge 1 according to the embodiment of the present invention described above, the material of the magnet 6 is a ferrite magnet, but another material such as a rare earth magnet or a bond-based magnet may be used.
[0059]
Further, in the fuel level gauge 1 according to the embodiment of the present invention described above, the Hall element 7 is used as the magnetic detection element, but other magnetic detection elements, for example, a magnetoresistive element or a magnetic diode are used. May be used.
[0060]
Further, in the embodiment of the present invention described above, the case where the liquid level sensor is applied to the fuel level gauge 1 for an automobile has been described as an example, but the application is not limited to the fuel level gauge 1 for an automobile. It may be applied to other liquid level sensors. Further, the liquid as the liquid level detection target is not limited to the fuel, but may be water, lubricating oil, various chemicals, or the like.
[Brief description of the drawings]
FIG. 1 is a sectional view of a fuel level gauge 1 according to an embodiment of the present invention, which is a sectional view taken along line II in FIG.
FIG. 2 is a front view of the fuel level gauge 1 according to the embodiment of the present invention, showing a state where the liquid level 11 is at the lowest level.
FIG. 3 is a schematic diagram showing a magnetized state of a magnet 6 of the fuel level gauge 1 according to one embodiment of the present invention.
FIG. 4A is a schematic diagram illustrating a magnetic flux distribution state of a magnet 6 in a liquid level sensor 1 according to an embodiment of the present invention, and FIG. It is a schematic diagram explaining the magnetic flux distribution state of a magnet.
FIG. 5A is a schematic diagram illustrating a magnetic flux distribution state of a magnet 6 when an external magnetic field acts on the liquid level sensor 1 according to one embodiment of the present invention, and FIG. FIG. 5 is a schematic diagram illustrating a magnetic flux distribution state of a magnet when an external magnetic field acts on the liquid level sensor of FIG.
FIG. 6 is a schematic diagram showing a modification of the fuel level gauge 1 according to one embodiment of the present invention.
[Explanation of symbols]
1 Fuel level gauge (liquid level sensor)
2 Float 3 Arm 4 Magnet holder 41 Hole 42 Holder 5 Body (main body)
Reference numeral 51 Shaft part 52 Housing chamber 53 Locking part 54 Connector part 6 Magnet 7 Hall element (magnetoelectric conversion element)
71 Lead 8 Cover 9 Terminal 10 Snap ring 11 Liquid surface N Magnetic pole S Magnetic pole

Claims (5)

A float floating on the liquid whose liquid level is to be measured,
A magnet holder rotatably held by the main body,
A two-pole magnetized cylindrical magnet fixed to the magnet holder coaxially with the rotation axis of the magnet holder;
An arm that connects the float and the magnet holder and converts the vertical movement of the float into a rotational movement of the magnet holder;
A magneto-electric conversion element that is fixed to the main body so as to be located substantially at the center of the magnet holder and crosses the magnetic flux of the magnet, detects a magnetic flux density of the magnet, and converts the magnetic flux density into an electric signal. A liquid level sensor that measures the liquid level based on an electric signal from the magnetoelectric conversion element,
A liquid level sensor, wherein an outer periphery of the magnet is covered with a cover made of a ferromagnetic material. A float floating on the liquid whose liquid level is to be measured,
A magnet holder rotatably held by the main body,
Two two-pole magnetized magnets arranged on the magnet holder so as to face 180 degrees on the same axis as the rotation axis of the magnet holder and to face different magnetic poles;
An arm that connects the float and the magnet holder and converts the vertical movement of the float into a rotational movement of the magnet holder;
A magneto-electric conversion element that is fixed to the main body so as to be located substantially at the center of the magnet holder and crosses the magnetic flux of the magnet, detects a magnetic flux density of the magnet, and converts the magnetic flux density into an electric signal. A liquid level sensor that measures the liquid level based on an electric signal from the magnetoelectric conversion element,
A liquid level sensor, wherein the outer circumferences of the two magnets are extrapolated by a cover made of a ferromagnetic material. The liquid level sensor according to claim 1, wherein the ferromagnetic material is an iron-based metal. The liquid level sensor according to any one of claims 1 to 3, wherein the cover is formed in a cylindrical shape. The liquid level sensor according to claim 4, wherein the cylindrical cover is formed by rolling a plate material.

Images