JP2004325105A - Liquid level sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid level sensor allowing reduction of influence of a change with the lapse of time to accurately measure levels over a long period. <P>SOLUTION: This liquid level sensor is provided with a plurality of Hall elements 17a-17d having equivalent performance in pairs. By respective magnetic flux densities detected by the Hall elements 17a-17d, two sine waves 17ab', 17cd' having the same periods and having a phase difference are generated. By dividing the other by one of the two sine waves, an amount corresponding to the change with the lapse of time of an amplitude value is removed. Accordingly, the influence of the change with the lapse of time of a magnet is removed to accurately measure levels over a long period. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a liquid level sensor, and more particularly, to a liquid level sensor using a magnet and a Hall element.
[0002]
[Prior art]
This type of liquid level sensor is used, for example, as a level sensor for monitoring the remaining amount of fuel in an automobile. In this type of liquid level sensor, a magnet connected to a float interlocked with the liquid level and a magnetic force generated by the magnet according to the liquid level are converted into an electric signal by a magnetoelectric conversion element such as a Hall element. Thus, the liquid level is detected.
[0003]
However, the conventional liquid level sensor has a problem that the magnetic flux density of the magnet changes due to a change over time such as high temperature demagnetization or low temperature demagnetization of the magnet, and the measured value of the liquid level is disturbed. This problem will be described with reference to FIGS. FIG. 9 is a plan view showing a conventional liquid level sensor. FIG. 10 is a diagram showing a state in which the liquid level sensor of FIG. 9 is mounted in the tank. FIG. 11 is a perspective view schematically showing a detection unit of the liquid level sensor of FIG. FIG. 12 is a graph showing a state where the detection level of the liquid level sensor of FIG. 9 has deteriorated with time.
[0004]
As shown in FIGS. 9 and 10, the liquid level sensor is fixed to the inner wall of the container TNK in order to detect the liquid level of the liquid LQ in the container TNK. The float 903 is connected to the magnet holder 911 via the arm 902. The float 903 has a cylindrical shape and is formed of a member having buoyancy with respect to the liquid LQ for measuring the liquid level. The arm 902 is formed of an elongated rod-shaped metal such as stainless steel. One end of the arm 902 passes through the center of the float 903 and is connected to the float 903.
[0005]
Further, the magnet holder 911 has an accommodation portion for accommodating the annular magnet 904 on the inside, and an arm holding portion 931 for holding the other end (arm 921) of the arm 902 having a T-shape on the outside, for example. have. The magnet holder 911 is formed of a non-magnetic material. The outer shape of the magnet holder 911 is such that the arm holding portion 931 is provided at the outer central portion of a cylindrical shape slightly larger than the outer shape of the magnet 904 housed therein. I have. The arm 902 connected to the float 903 via the arm holding portion 931 is also connected to the magnet holder 911.
[0006]
The magnet holder 911 is mounted on the sensor case 905 so as to be rotatable about a virtual rotation axis formed by the magnet holders 911 while being held by stopper flanges 961, 962, 963 as shown in FIG. Note that α shown in FIG. 9 is the rotation angle of the magnet 904 according to the liquid level.
[0007]
The accommodation portion of the magnet 904 of the magnet holder 911 described above has a cylindrical inner diameter in accordance with the outer shape of the magnet 904. The magnet 904 is fixed to the housing using an adhesive or the like. With such a structure, the magnet 904 rotates about the rotation axis in conjunction with the float 903 that moves according to the liquid level. The magnet 904 is a permanent magnet magnetized in two poles.
[0008]
At the center of the magnet 904, a Hall element 908 as a magnetoelectric conversion element is mounted on the wiring board 907 and fixedly arranged. The Hall element 908 detects the magnetic flux density by the magnet 904 rotating according to the liquid level, converts the detected magnetic flux into an electric signal, and outputs the electric signal. In the liquid level sensor, the Hall element 908 and the magnet 904 constitute a magnetic flux density detecting unit. As shown in FIG. 11, the Hall element 908 is fixedly arranged at the center of the annular magnet 904. Have been. Since the magnet 904 rotates in the direction indicated by the arrow in FIG. 11 according to the liquid level as described above, the magnetic flux density of the Hall element 908 that fluctuates with this rotation is used for liquid level measurement. .
[0009]
The wiring board 907 on which the Hall element 908 is mounted is fixed to a sensor case 905 constituting an outer shape of the housing of the present liquid level sensor by screws (not shown) or the like. A related electric circuit component necessary for liquid level measurement and a terminal 909 for outputting an electric signal corresponding to the liquid level converted from the magnetic flux density to the outside are also mounted. A case lid 910 is covered on the back side of the sensor case 905.
[0010]
In the above-described configuration, the float 903 moves according to a change in the liquid level. Since the magnet holder 911 rotates via the arm 902 in response to the movement of the float 903, the magnet 904 held and accommodated in the magnet holder 911 also rotates. Then, the Hall element 908 detects the magnetic flux density of the magnet 904 that rotates in accordance with the movement of the float 903 and converts the magnetic flux density into an electric signal, whereby the liquid level is measured based on the electric signal. become. Note that such a liquid level sensor is also disclosed in Patent Document 1 below.
[0011]
[Patent Document 1]
JP-A-2002-206959 (FIGS. 1 to 3)
[0012]
[Problems to be solved by the invention]
Incidentally, it is known that the magnetic flux density of a magnet changes with time due to high-temperature demagnetization, low-temperature demagnetization, and the like. Therefore, according to the conventional liquid level sensor having the above-described configuration, the magnetic flux density detected in accordance with the rotation angle of the magnet also changes from the initial characteristic shown by the solid line in FIG. Characteristic will be degraded. As a result, there has been a problem that the measured value of the liquid level gradually deteriorates.
[0013]
SUMMARY OF THE INVENTION In view of the above situation, it is an object of the present invention to provide a liquid level sensor capable of reducing the influence of the above-mentioned aging and enabling accurate level measurement over a long period of time.
[0014]
[Means for Solving the Problems]
The liquid level sensor according to claim 1, which has been made to solve the above-mentioned problem, is capable of moving a float formed of a member having buoyancy with respect to a liquid whose liquid level is to be measured, according to the liquid level. A liquid level sensor that detects a magnetic flux density of a rotating magnet and converts the magnetic flux density into an electric signal, and that measures the liquid level based on the electric signal; A plurality of conversion elements having the same performance are arranged so as to orbit around the rotation axis of the magnet, and the plurality of magnetoelectric conversion elements each have a predetermined phase difference at a rotation angle of the magnet. Is detected, and the magnetic flux density detected by one of the plurality of magnetoelectric conversion elements is divided by the magnetic flux density detected by the other magnetoelectric conversion element. There are, for measuring the liquid level, characterized in that.
[0015]
According to the first aspect of the invention, a plurality of magnetoelectric conversion elements having the same performance are arranged so as to orbit around the rotation axis of the magnet. Each of the plurality of magnetoelectric conversion elements detects a magnetic flux density with a predetermined phase difference at a rotation angle of the magnet. Then, the magnetic flux density detected by one of the plurality of magneto-electric conversion elements is divided by the magnetic flux density detected by the other magneto-electric conversion element, thereby removing a change with time.
[0016]
The liquid level sensor according to claim 2, which has been made to solve the above-described problem, is capable of moving a float formed of a member having a buoyancy with respect to a liquid whose liquid level is to be measured, in accordance with the liquid level. A liquid level sensor that detects a magnetic flux density of a rotating magnet and converts the magnetic flux density into an electric signal, and that measures the liquid level based on the electric signal; At least four conversion elements are arranged so as to orbit around the rotation axis of the magnet so as to detect the magnetic flux density with a phase difference of 90 degrees at a rotation angle of the magnet, and a phase difference of 180 degrees. A difference between the magnetic flux densities detected by the pair of magnetoelectric transducers arranged to detect the magnetic flux density, and another pair of magnetoelectric transducers arranged to detect the magnetic flux density with a phase difference of 180 degrees. Based on the result obtained by dividing the difference of the detected magnetic flux density by the child, measuring the fluid level, characterized in that.
[0017]
According to the second aspect of the present invention, at least four magneto-electric conversion elements are arranged so as to detect the magnetic flux density with a phase difference of 90 degrees at each rotation angle of the magnet, and the magnetic element is provided with a phase difference of 180 degrees. The difference between the magnetic flux densities detected by the pair of magnetoelectric transducers arranged to detect the density, which is detected by another pair of magnetoelectric transducers arranged to detect the magnetic flux density with a phase difference of 180 degrees. By subtracting the difference between the magnetic flux densities, the change with time is removed.
[0018]
The liquid level sensor according to claim 3, which has been made to solve the above problem, wherein the magnetoelectric conversion element is a Hall element in the liquid level sensor according to any one of claims 1 to 3. It is characterized by.
[0019]
According to the third aspect of the present invention, since the magnetoelectric conversion element is a Hall element, it is widely spread and easily available. Further, since the rotation angle of the magnet can be detected in a non-contact manner, the substrate on which the element is mounted can be sealed so as not to touch the liquid.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, an external structure of a liquid level sensor according to an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a perspective view showing one embodiment of a liquid level sensor of the present invention. FIG. 2 is an exploded perspective view of the liquid level sensor of FIG. FIG. 3 is a perspective view of the liquid level sensor of FIG. 1 viewed from the opposite direction.
[0021]
The liquid level sensor shown in FIGS. 1 to 3 is used fixedly on the inner wall of the container to detect the liquid level of the liquid in the container, similarly to the conventional liquid level sensor shown in FIG. Is done. As shown in FIG. 1, the present liquid level sensor basically includes a sensor main body 1, an arm 2, and a float 3. The float 3 has a cylindrical shape and is formed of a member having buoyancy with respect to the liquid whose liquid level is to be measured. The arm 2 is formed of an elongated rod-shaped metal such as stainless steel. One end of this arm 2 is bent, penetrates through the center of the float 3 and is connected to the float 3, and the other end also bends in the opposite direction and is inserted into the arm mounting hole 14 a 1 of the sensor body 1.
[0022]
The sensor main body 1 includes a sensor case 11, a substrate 12, a case lid 13, gears 14a and 14b, magnets 15, and a gear cover 16, as shown in FIGS. The sensor case 11 has an open box shape and accommodates the substrate 12, the gears 14a and 14b, and the magnet 15. Further, the sensor case 11 is also provided with a fixing arm for fixing to a predetermined portion in the container.
[0023]
In the sensor case 11, a substrate 12 is accommodated on the near side in FIG. The substrate 12 is provided with a plurality of holes 121 that are respectively fitted to the plurality of protrusions 111 provided on the sensor case 11 side. After the plurality of holes 121 are fitted into the plurality of protrusions 111 and the substrate 12 is accommodated in a predetermined position, the case lid 13 is covered thereon. Note that a plurality of Hall elements, a microcomputer (microcomputer), and the like are also provided on the substrate 12, and these will be described later with reference to FIGS.
[0024]
On the other hand, in the sensor case 11, gears 14a and 14b and a magnet 15 are accommodated on the other side in FIG. The gear 14a is a large-diameter gear directly connected to the arm 2, and the gear 14b is a small-diameter gear on which the magnet 15 is mounted. For example, the gear 14a has 36 teeth and the gear 14b has 10 teeth. With such a gear ratio, the rotation speed of the gear 14a directly connected to the arm 2 is converted to 3.6 times, and the gear 14b, that is, the magnet 15 rotates.
[0025]
The gear 14a has a cylindrical rotating shaft protruding therefrom, and an arm mounting hole 14a1 at the tip thereof. A part of the arm mounting hole 14a1 is formed with a notch so that the arm 2 does not rotate freely around the mounting hole 14a1. The gear 14b is provided with a magnet housing part having an inner diameter slightly larger than the outer diameter of the cylindrical magnet 15.
[0026]
The gear cover 16 is provided with a pair of protrusions 161, and the sensor case 11 side is provided with a pair of holes 113 respectively corresponding to these. After the gear 14a and the gear 14b in which the magnet 15 is housed are meshed and housed in a predetermined position of the sensor case 11, the pair of projections 163 are fitted in the corresponding holes 113, and the gear cover 16 is covered. Is done.
[0027]
In such a configuration, when the float 3 moves according to the fluctuation of the liquid level, as shown by the arrow in FIG. 1, the magnet 15 rotates with the movement of the float 3. Here, a plurality of Hall elements (not shown) each detect a magnetic flux density by the magnet 15 and convert the detected magnetic flux density into an electric signal, so that the liquid level is measured based on the electric signal. Note that the characteristic liquid level measuring method of the present invention will be described later with reference to graphs shown in FIGS.
[0028]
Next, an arrangement method of the Hall element and the magnet will be described with reference to FIGS. FIG. 4 is a schematic perspective view showing a method of arranging the Hall element and the magnet. FIG. 5 is a schematic perspective view showing an example using a multi-element hall IC. FIGS. 4 and 5 schematically show a substrate, a Hall element, a magnet, and the like in the liquid level sensor shown in FIGS.
[0029]
As shown in FIG. 4, as the float 3 moves in accordance with the fluctuation of the liquid level, the magnet 15 is rotatable in both directions about the rotation axis RX as indicated by the arrow. The magnet 15 is a cylindrical permanent magnet that is magnetized in two poles at the S pole and the N pole. The magnet 15 is arranged to rotate at a predetermined distance from the Hall elements 17a to 17d provided on the substrate 12.
[0030]
The four Hall elements 17a to 17d arranged on the substrate 12 are in two pairs. That is, the Hall elements 17a and 17b form one pair across the rotation axis RX, and the Hall elements 17c and 17d form the other pair across the rotation axis RX. Further, each of the four Hall elements 17a to 17d is arranged so as to detect a magnetic flux density with a phase difference of 90 degrees at a rotation angle of the magnet 15. The four Hall elements 17a to 17d all have the same performance. The Hall elements 17a to 17d correspond to the magneto-electric conversion elements in the claims. By using a Hall element as the magnetoelectric conversion element, the rotation angle of the magnet can be detected in a non-contact manner, so that the substrate on which this element is mounted can be sealed without touching the liquid.
[0031]
Although not shown, on the substrate 12, a microcomputer that calculates the rotation angle of the magnet 15 from the magnetic flux densities detected by the four Hall elements 17a to 17d and performs other processes related to the liquid level measurement is also provided. Are located.
[0032]
As the magnetoelectric conversion element, a plurality of independent Hall elements may be arranged as described above, but as shown in FIG. 5, a multi-element Hall IC 18 in which a plurality of Hall elements are mounted on one chip is used. Is also good. By using such a multi-element Hall IC 18, a liquid level sensor can be manufactured at lower cost. In the figure, a microcomputer 19 calculates a rotation angle and the like of the magnet 15 from magnetic flux densities in different phases detected by the Hall IC 18 and performs other processes related to liquid level measurement.
[0033]
Further, a method for measuring the rotation angle of the magnet 15, that is, the liquid level, using the magnetic flux density detected by the Hall elements 17a to 17d will be described with reference to FIGS. FIG. 6 is a graph showing the relationship between the magnetic flux density detected by the four Hall elements and the rotation angle of the magnet. FIG. 7 is a graph showing the relationship between the difference waveform of the magnetic flux density detected by the paired Hall elements and the rotation angle of the magnet. FIG. 8 is a graph showing the relationship between the arc tangent value obtained based on the two difference waveforms shown in FIG. 7 and the rotation angle of the magnet.
[0034]
In FIG. 6, 17a ', 17b', 17c 'and 17d' indicate the magnetic flux densities detected by the Hall elements 17a, 17b, 17c and 17d, respectively. It can be seen that each of the Hall elements 17a, 17b, 17c and 17d detects the magnetic flux density with a phase difference of 90 degrees at each rotation angle of the magnet 15.
[0035]
In FIG. 7, 17ab 'indicates the difference between the magnetic flux density 17a' and the magnetic flux density 17b 'shown in FIG. 6, and 17cd' indicates the difference between the magnetic flux density 17b 'and the magnetic flux density 17c' shown in FIG. Show. At this stage, both of the two sine waves indicating the difference 17ab 'and the difference 17cd' may still include a temporal change in the magnetic flux density of the magnet.
[0036]
However, since the Hall elements 17a, 17b, 17c, and 17d have the same performance, the change over time of the magnetic flux density of the magnet 15 is detected equally. Therefore, it can be seen that the two sine waves indicating the difference 17ab 'and the difference 17cd' are two equivalent sine waves (or may be called cosine waves) whose phases are shifted by 90 degrees. In this case, needless to say, the maximum amplitude values are also equal. Therefore, the value obtained by dividing one of the two sine waves by the other does not depend on the amplitude value. That is, by removing one of the two sine waves from the other, it is possible to remove a temporal change of the amplitude value, that is, a temporal change of the magnet.
[0037]
Since the relationship between the value obtained by dividing one of the two sine waves and the other and the rotation angle of the magnet 15 can be obtained in advance by experiments or the like, this is stored in the memory included in the microcomputer, and From time to time, the rotation angle of the magnet 15 corresponding to the divided value is read out, and the level of the liquid level can be detected based on the readout angle. Note that the two sine waves do not necessarily have to have a sine and cosine relationship, but the sine and cosine relationship has the following advantages.
[0038]
In FIG. 8, reference numeral 17 'denotes an arc tangent value corresponding to the rotation angle of the magnet 15, which is obtained based on the difference 17ab' and the difference 17cd '. As described above, since the difference 17ab 'and the difference 17cd' have a sine and cosine relationship, a tangent value can be obtained from these at the rotation angle of the magnet 15. Therefore, at the rotation angle of the magnet 15, θ satisfying this tangent value, that is, an arc tangent value can be obtained (vertical axis in FIG. 8).
[0039]
This arc tangent value θ has a linear relationship with the rotation angle of the magnet 15, as shown in FIG. Therefore, the change with time of the magnet is removed as described above, and the calculation process for measuring the liquid level is also facilitated. The relationship between the arc tangent value and the rotation angle of the magnet 15 can also be determined in advance by experiments or the like. This is stored in the memory included in the microcomputer, and the magnet tangent value corresponding to the arc tangent value is stored at any time. Fifteen rotation angles are read out, and based on this, the liquid level can be detected.
[0040]
The calculation of the difference, division, arc tangent value, rotation angle, and the like is performed by the microcomputer. Then, the calculated rotation angle of the magnet 15 is converted to the position of the float 3 and further to a liquid level, and transmitted to a display unit (not shown).
[0041]
As described above, according to the present embodiment, it is possible to provide a liquid level sensor capable of reducing the influence of a change over time due to high-temperature demagnetization, low-temperature demagnetization, or the like and performing accurate level measurement over a long period of time.
[0042]
Note that the present invention does not limit the number of Hall elements to four as described in the above embodiment. In order to improve measurement accuracy, four or more Hall elements may be mounted. Further, the present invention can be applied to uses other than monitoring of the remaining fuel amount of an automobile.
[0043]
【The invention's effect】
As described above, according to the first aspect of the present invention, a plurality of magnetoelectric conversion elements having the same performance are arranged so as to orbit around the rotation axis of the magnet. Each of the plurality of magnetoelectric conversion elements detects a magnetic flux density with a predetermined phase difference at a rotation angle of the magnet. Then, the magnetic flux density detected by one of the plurality of magneto-electric conversion elements is divided by the magnetic flux density detected by the other magneto-electric conversion element, thereby removing a change with time. Therefore, the influence of the aging of the magnet is removed, and the level can be accurately measured over a long period of time.
[0044]
According to the second aspect of the present invention, at least four magneto-electric conversion elements are arranged so as to detect the magnetic flux density with a phase difference of 90 degrees at each rotation angle of the magnet, and the magnetic element is provided with a phase difference of 180 degrees. The difference between the magnetic flux densities detected by the pair of magnetoelectric transducers arranged to detect the density, which is detected by another pair of magnetoelectric transducers arranged to detect the magnetic flux density with a phase difference of 180 degrees. By removing the difference between the magnetic flux densities, the change with time is removed. Therefore, the influence of the aging of the magnet is removed, and the level can be accurately measured over a long period of time. In particular, since the difference is obtained and then divided, the level can be measured more accurately over a long period of time.
[0045]
According to the third aspect of the present invention, since the rotation angle of the magnet is detected in a non-contact manner, the airtightness of the magnetoelectric conversion element is improved, and the level can be measured more accurately over a long period of time.
[Brief description of the drawings]
FIG. 1 is a perspective view showing one embodiment of a liquid level sensor of the present invention.
FIG. 2 is an exploded perspective view of the liquid level sensor of FIG.
FIG. 3 is a perspective view of the liquid level sensor of FIG. 1 as viewed from an opposite direction.
FIG. 4 is a schematic perspective view showing an arrangement method of a Hall element and a magnet.
FIG. 5 is a schematic perspective view showing an example using a multi-element hall IC.
FIG. 6 is a graph showing a relationship between a magnetic flux density detected by four Hall elements and a rotation angle of a magnet.
FIG. 7 is a graph showing a relationship between a difference waveform of a magnetic flux density detected by a pair of Hall elements and a rotation angle of a magnet.
8 is a graph showing a relationship between an arc tangent value obtained based on two difference waveforms shown in FIG. 7 and a rotation angle of a magnet.
FIG. 9 is a plan view showing a conventional liquid level sensor.
FIG. 10 is a diagram showing a state in which the liquid level sensor of FIG. 9 is mounted in a tank.
FIG. 11 is a perspective view schematically showing a detection unit of the liquid level sensor of FIG. 9;
12 is a graph showing a state where the detection level of the liquid level sensor of FIG. 9 has deteriorated with time.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Sensor main body 2 Arm 3 Float 11 Sensor case 12 Substrates 14a, 14b Gear 15 Magnet 16 Gear cover 17a-17d Hall element (magnetoelectric conversion element)

Claims (3)

The magnetic flux density of a magnet rotating with the movement according to the liquid level of a float formed of a member having a buoyancy with respect to the liquid whose liquid level is measured is detected and converted into an electric signal. A liquid level sensor having a magnetoelectric conversion element and measuring the liquid level based on the electric signal,
In the magnetoelectric conversion element, a plurality of elements having equivalent performance are arranged so as to orbit around the rotation axis of the magnet,
Each of the plurality of magnetoelectric conversion elements detects the magnetic flux density with a predetermined phase difference at a rotation angle of the magnet,
The liquid level is measured based on a result obtained by dividing a magnetic flux density detected by one of the plurality of magnetoelectric conversion elements by a magnetic flux density detected by the other magnetoelectric conversion element. ,
A liquid level sensor, comprising: The magnetic flux density of a magnet rotating with the movement according to the liquid level of a float formed of a member having a buoyancy with respect to the liquid whose liquid level is measured is detected and converted into an electric signal. A liquid level sensor having a magnetoelectric conversion element and measuring the liquid level based on the electric signal,
At least four magneto-electric conversion elements are arranged so as to orbit around the rotation axis of the magnet, so as to detect the magnetic flux density at a phase difference of 90 degrees at each rotation angle of the magnet,
A difference between the magnetic flux densities detected by a pair of magneto-electric transducers arranged to detect the magnetic flux density with a phase difference of 180 degrees, and the other arranged to detect the magnetic flux density with a phase difference of 180 degrees Based on the result of dividing the difference between the magnetic flux densities detected by the pair of magnetoelectric conversion elements, to measure the liquid level,
A liquid level sensor, comprising: The liquid level sensor according to claim 1 or 2,
The magnetoelectric element is a Hall element,
A liquid level sensor, comprising:

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