JP2004325104A - Liquid level sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid level sensor improved in measurement accuracy by improving resolution. <P>SOLUTION: Two sine waves having a 90-degree phase difference in a rotation angle of a magnet and having equivalent periods are generated by use of respective magnetic flux densities detected by a plurality of Hall elements 17a-17d, and an arc tangent value corresponding to the rotation angle of the magnet is found on the basis of the two sine waves. A liquid level is measured on the basis of the arc tangent value. Thereby, a rotation angle range of 360 degrees at the maximum can be assigned to the whole movement range of a float to drastically improve the resolution as compared to the conventional way. The resolution can be further improved by gears 14a, 14b as speed-increasing members. Accordingly, the level is measured with high accuracy. <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, in the conventional liquid level sensor, there is a problem that sufficient resolution cannot be obtained and measurement accuracy is not good because the rotation angle range of the magnet can be used only up to 180 degrees at the maximum. These problems 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 the relationship between the rotation angle of the magnet and the magnetic flux density by the liquid level sensor of FIG.
[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 with 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]
However, in the conventional liquid level sensor, as shown in FIG. 12, the detected magnetic flux density is symmetrical with respect to the rotation angle of the magnet of 180 degrees. Therefore, only a rotation angle range of 180 degrees (a range of 0 to 180 degrees ?? 'or a range of 180 to 360 degrees ?? ") can be assigned at most to the variation range ?? of the magnetic flux density. Even if the entire float movement range is assigned to the angle range, sufficient resolution cannot be obtained, and as a result, there is a problem that the measurement accuracy is not good.
[0013]
Accordingly, an object of the present invention is to provide a liquid level sensor that has improved resolution and improved measurement accuracy in view of the above-described current situation.
[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, each having the same performance as orbiting the rotation axis of the magnet, are arranged, and utilizing the respective magnetic flux densities detected by the plurality of magnetoelectric conversion elements, the rotation of the magnet is performed. Two sine waves having a phase difference of 90 degrees in angle and having the same period are generated, and an arc tangent value corresponding to the rotation angle of the magnet is obtained based on the two sine waves. , Based on the arc tangent value, measuring the fluid 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. Utilizing the respective magnetic flux densities detected by the plurality of magnetoelectric conversion elements, two sine waves having a phase difference of 90 degrees in the rotation angle of the magnet and having the same period are generated, and two An arc tangent value corresponding to the rotation angle of the magnet is obtained based on the sine wave. Then, the liquid level is measured based on the arc tangent value. Thereby, the rotation angle range of the magnet that can be used for level detection is extended to 360 degrees (see FIG. 8).
[0016]
According to a second aspect of the present invention, there is provided a liquid level sensor according to the first aspect, wherein the rotation speed of the magnet that rotates with the movement according to the liquid level is increased. And a speed increasing member.
[0017]
According to the second aspect of the present invention, since the speed increasing member that increases the rotation speed of the magnet that rotates with the movement according to the liquid level is provided, the resolution can be further improved.
[0018]
According to a third aspect of the present invention, there is provided a liquid level sensor according to the first or second aspect, wherein the magnetoelectric element is a Hall element.
[0019]
According to the third aspect of the invention, since the rotation angle of the magnet is detected in a non-contact manner, the airtightness of the magnetoelectric conversion element is improved.
[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. FIG. 4 is a plan view of both gears shown in FIG.
[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, as shown in FIG. 4, 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 fact that the magnet 15 rotates by 3.6 times means that, in other words, it is possible to allocate a 3.6 times change amount of the magnetic flux density to a predetermined rotation angle change amount of the magnet. Therefore, the resolution can be increased, and highly accurate level measurement can be performed. The gears 14a and 14b correspond to speed increasing members in the claims. It goes without saying that the gear ratios exemplified above can be appropriately changed.
[0026]
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.
[0027]
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.
[0028]
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. The characteristic liquid level measurement method of the present invention will be described later with reference to the graphs shown in FIGS.
[0029]
Next, an arrangement method of the Hall element and the magnet will be described with reference to FIGS. FIG. 5 is a schematic perspective view showing an arrangement method of the Hall elements and the magnets. FIG. 6 is a schematic perspective view showing an example using a multi-element hall IC. FIGS. 5 and 6 schematically show a substrate, a Hall element, a magnet, and the like in the liquid level sensor shown in FIGS.
[0030]
As shown in FIG. 5, as the float 3 moves in accordance with the fluctuation of the liquid level, the magnet 15 can rotate in both directions about the rotation axis RX as indicated by an 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.
[0031]
The four Hall elements 17a to 17d arranged on the substrate 12 are in two pairs. That is, the Hall elements 17a and 17c form one pair across the rotation axis RX, and the Hall elements 17b and 17d form the other pair across the rotation axis RX. Further, the four Hall elements 17a to 17d are arranged so as to detect the magnetic flux densities at phases different from each other by 90 degrees in the 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.
[0032]
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.
[0033]
As the magnetoelectric conversion element, a plurality of independent Hall elements may be arranged as described above, but as shown in FIG. 6, 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.
[0034]
Further, a method of measuring the rotation angle of the magnet 15, that is, the liquid level using the magnetic flux densities detected by the Hall elements 17a to 17d will be described with reference to FIGS. FIG. 7 is a graph showing the relationship between 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 sine waves shown in FIG. 7 and the rotation angle of the magnet.
[0035]
In FIG. 7, 17a 'and 17b' indicate the magnetic flux densities detected by the Hall elements 17a and 17b, respectively. It can be seen that each of the Hall elements 17a and 17b detects the magnetic flux density with a phase difference of 90 degrees at the rotation angle of the magnet 15. Although not shown, the same relationship applies to the magnetic flux densities detected by the Hall elements 17c and 17d. Supplementally, the Hall elements 17a, 17b, 17c and 17d detect the magnetic flux density with a phase difference of 90 degrees, respectively, at the rotation angle of the magnet 15. Since the Hall elements 17a to 17d have the same performance, the magnetic flux densities detected by the Hall elements 17a to 17d only have a phase difference as described above, and have a sine wave (also called a cosine wave) having the same period and amplitude value. Good).
[0036]
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 magnetic flux densities 17a' and 17b '. That is, since the magnetic flux densities 17a 'and 17b' have a cosine and sine relationship as described above, 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). The arc tangent value θ has a unique value corresponding to the rotation angle of the magnet 15 from 0 ° to 360 ° as shown in FIG. The arc tangent value θ changes linearly with the rotation angle of the magnet 15.
[0037]
As shown in FIG. 8, by using the arc tangent value θ, the rotation angle range of the magnet that can be used for level detection can be extended to 360 degrees (the range indicated by Δα in the figure). As a result, a rotation angle range of 360 degrees at the maximum can be allocated to the entire movement range of the float, and the resolution can be doubled as compared with the related art. Therefore, the resolution can be increased and the measurement accuracy can be improved.
[0038]
In the above-described example, the arc tangent value θ is obtained based on the magnetic flux density detected by the Hall elements 17a and 17b. However, the magnetic flux density detected by the Hall elements 17c and 17d or the Hall element 17b and The arc tangent value θ may be determined based on the magnetic flux density detected by the Hall element 17c or the Hall elements 17d and 17a. Further, the arc tangent value θ can be determined based on the difference between the magnetic flux densities detected by the Hall elements 17a and 17c and the difference between the magnetic flux densities detected by the Hall elements 17b and 17d. In short, if two sine waves have a phase difference of 90 degrees in the rotation angle of the magnet and have the same period, the arc tangent value corresponding to the rotation angle of the magnet based on these two sine waves Is required.
[0039]
The relationship between the arc tangent value and the rotation angle of the magnet 15 can be obtained in advance by an experiment or the like, and is stored in a memory included in the microcomputer. From this, the rotation angle of the magnet 15 corresponding to the arc tangent value is read at any time, and the level of the liquid level can be detected based on the readout angle. The arithmetic processing related to the level detection 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).
[0040]
As described above, according to the present embodiment, the arc tangent value is used to expand the rotation angle range of the magnet that can be used for level detection, and the gear ratio increases the rotation speed of the magnet to increase resolution and measure. A liquid level sensor with improved accuracy can be provided.
[0041]
The present invention does not limit the number of Hall elements to two or 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.
[0042]
【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. Utilizing the respective magnetic flux densities detected by the plurality of magnetoelectric conversion elements, two sine waves having a phase difference of 90 degrees in the rotation angle of the magnet and having the same period are generated, and two An arc tangent value corresponding to the rotation angle of the magnet is obtained based on the sine wave. Then, the liquid level is measured based on the arc tangent value. Thereby, the rotation angle range of the magnet that can be used for level detection is extended to 360 degrees (see FIG. 8). As a result, a rotation angle range of 360 degrees at the maximum can be allocated to the entire movement range of the float, and the resolution can be greatly improved as compared with the related art. Therefore, highly accurate level measurement can be performed.
[0043]
According to the second aspect of the present invention, since the speed increasing member that increases the rotation speed of the magnet that rotates with the movement according to the liquid level is provided, the resolution can be further improved. Therefore, more accurate level measurement can be performed.
[0044]
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 magneto-electric conversion element is improved, and more accurate level measurement can be performed.
[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 plan view of both gears shown in FIG. 3;
FIG. 5 is a schematic perspective view showing an arrangement method of a Hall element and a magnet.
FIG. 6 is a schematic perspective view showing an example using a multi-element hall IC.
FIG. 7 is a graph showing a relationship between 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 sine waves 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;
FIG. 12 is a graph showing a relationship between a rotation angle of a magnet and a magnetic flux density by the liquid level sensor of FIG. 9;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Sensor main body 2 Arm 3 Float 11 Sensor case 12 Substrates 14a and 14b Gear (member for speed increase)
15 Magnet 16 Gear cover 17a to 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,
Utilizing the respective magnetic flux densities detected by the plurality of magnetoelectric conversion elements, the two sine waves having a phase difference of 90 degrees at the rotation angle of the magnet, and having the same period, are generated.
Based on the two sine waves, determine an arc tangent value corresponding to the rotation angle of the magnet,
Measuring the liquid level based on the arc tangent value,
A liquid level sensor, comprising: The liquid level sensor according to claim 1,
A liquid level sensor further comprising a speed increasing member for increasing a rotation speed of a magnet that rotates with the movement according to the liquid level. 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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