JP3128930B2 - Liquid level detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid level detector for detecting a liquid level in a fuel tank or the like.

[0002]

2. Description of the Related Art Conventionally, as a detecting device for detecting a liquid level in a tank, there is a capacitance type detecting device. This capacitance type liquid level detector can detect the liquid level with high accuracy, and is therefore installed in a fuel tank, for example. In this type of detection device, measurement electrodes are arranged on the assumption that the bottom surface of the tank and the liquid surface are parallel (horizontal) to each other.

However, when this liquid level detecting device is mounted on a fuel tank of an automobile, for example, the vehicle often leans in the front-rear direction and the left-right direction while the vehicle is running or stopped. Then, in this case, the measurement electrode is also inclined with the vehicle. Therefore, the measurement electrode is inclined relatively to the liquid level. As a result, an error occurs in the measurement of the capacitance, and an accurate liquid level cannot be detected. Therefore, in order to prevent the above error, conventionally, for example, a liquid surface level detecting device configured to measure three liquid surface levels at a front position and at both left and right positions in a tank and detect an accurate liquid surface level is provided. Used. In addition, this capacitance type detection device requires a correction electrode for correcting the dielectric constant of the liquid in order to compensate for its own disadvantage.

[0004] Further, this capacitance type liquid level detecting device comprises a sensor section comprising the three measuring electrodes and one correction electrode, and a liquid level calculating section connected to the sensor section via an oscillator. And The oscillator is provided for each of the three measurement electrodes and one correction electrode, and oscillates at an oscillating frequency according to the capacitance detected at each electrode. The liquid level calculator calculates a liquid level based on the oscillation cycle of the oscillator.

[0005]

However, in the conventional detecting device, the sensor portion is composed of three measuring electrode rods and one measuring electrode.
And two correction electrode rods. Further, since each electrode is provided so as to face the ground electrode, each of the four electrodes has a size of about 3 cm in diameter. Therefore, the size of the entire sensor unit is large, and the mounting window must be enlarged in order to mount the sensor unit in the fuel tank.

[0006] Further, since the weight is large in accordance with the physique, a high-strength fixture is required to fix the sensor portion so as not to swing in the fuel tank. Therefore, the fixture of the sensor part also becomes large. SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a small-sized, light-weight, and easy-to-install electrostatic capacitance type liquid level detecting device.

[0007]

According to the present invention, there is provided an electrostatic sensor comprising: a sensor unit for detecting a liquid level of a liquid in a tank based on a capacitance; and a liquid level calculating unit connected to the sensor unit via an oscillator. In the capacitive type liquid level detecting device, the sensor section includes a long cylindrical common ground electrode, a long insulating base provided inside the common ground electrode, and a 90-degree angle with respect to each other on the insulating base. The three measurement electrodes and the correction electrode are provided at the positions which form the following three lines, and the lower ends of the three measurement electrodes are all arranged at the same height, while the lower end of the correction electrode has the lower end of the measurement electrode. Liquid level detecting device, which is located above the liquid level detecting device.

The most remarkable point of the present invention is that the insulating base having the three measurement electrodes and the correction electrode provided at 90 degrees from each other is inserted into a cylindrical common ground electrode. The two measuring electrodes have their lower ends at the same height, while the lower ends of the correction electrodes are located above the lower ends of the measuring electrodes.

The common ground electrode is a long tubular body such as a square tube or a cylinder, and is made of a conductive material such as an aluminum alloy or stainless steel. The insulating base is a long body in which three measuring electrodes and correction electrodes are positioned at an angle of 90 degrees along the length direction. The insulating base is formed of a cylindrical or columnar body such as a square or a circle. In the case of a cylindrical body, the weight can be further reduced. The insulating base is made of a plastic such as polyacetal or PBT, or an electrically insulating material such as glass epoxy or ceramic.

The measurement electrode and the correction electrode are formed of a conductive material such as copper, nickel or the like which can detect the capacitance. Both electrodes are formed on the surface of the insulating substrate by sticking, sputtering, vapor deposition and the like. Alternatively, it is formed by plating the above conductive material on the surface of the insulating base by chemical plating or the like, and then etching it into an arbitrary electrode pattern shape.
There are three measuring electrodes, which are of the same length and whose lower ends are at the same height and extend below one other correction electrode.

The insulating substrate on which the measurement electrode and the correction electrode are formed as described above is inserted and arranged in the common ground electrode.
Each electrode faces the common ground electrode. In the liquid tank, the liquid is located between the two, and the capacitance is detected. The measurement electrode and the correction electrode are electrically paired with a common ground electrode, respectively, and connected to an oscillator (see FIG. 4).

The above three measuring electrodes are located in the front and both left and right directions, for example, in a fuel tank of an automobile, and the correction electrodes are located behind. The liquid level detecting device of the present invention is particularly effective as a liquid level detecting device for liquids such as fuel in automobiles, industrial vehicles, ships, and the like in which the liquid level is inclined with respect to the electrodes.

[0013]

In the liquid level detecting device according to the present invention, the capacitance of the liquid level at each electrode position is detected by the three measurement electrodes and the correction electrode and transmitted to each oscillator. Then, in each oscillator, the capacitance at each liquid level is converted into a frequency and transmitted to the liquid level calculation unit.

The liquid level calculator calculates the dielectric constant based on the oscillation period signal of each frequency, calculates the liquid level at the three measurement electrode positions, and further corrects the inclination to calculate the true liquid level. Calculate the levels and display them. The above-mentioned permittivity can be measured by providing the height difference at each lower end of the measurement electrode and the correction electrode. Further, since the lower end of the correction electrode is above the lower end of the measurement electrode, the liquid level at the position of the correction electrode cannot be directly detected, but can be calculated from the liquid level of the three measurement electrodes. These details are given in the examples.

In the sensor section of the liquid level detecting device according to the present invention, the three measuring electrodes and the correction electrode are provided on a long insulating base, and these are inserted into a cylindrical common ground electrode. I have. Liquid is interposed in the gap between each electrode and the common ground electrode. Therefore, the true liquid level can be detected as described above by detecting the capacitance accompanying the vertical fluctuation of the liquid level.

Since the sensor section has the above-described structure, the common ground electrode and the insulating base can be formed as a single cylindrical assembly, and the size can be extremely reduced. That is,
Compared to a conventional sensor unit composed of four independent electrode bodies consisting of three measurement electrodes and one correction electrode, the size is significantly reduced. Therefore, the size and weight of the sensor can be reduced. Therefore, the sensor unit can be easily mounted in the liquid tank. Therefore, according to the present invention, it is possible to provide a capacitance-type liquid level detecting device that is small, lightweight, and easy to mount.

[0017]

【Example】

Embodiment 1 A liquid level detecting device according to an embodiment of the present invention will be described with reference to FIGS. In this example, the detection device is mounted on a fuel tank of an automobile. As shown in FIGS. 1 and 4, the detection device of this embodiment includes a sensor unit 10 for detecting a liquid level of a liquid (fuel) in a fuel tank (not shown) by capacitance, and a sensor unit 10 for detecting the liquid level. And a liquid level calculating section 500 connected to the liquid crystal panel via oscillators 531 to 533 and 540.

The sensor section 10 includes a long cylindrical common ground electrode 1, a long insulating base 2 disposed inside the common ground electrode 1, and 9
It comprises three measurement electrodes 31 to 33 and a correction electrode 4 provided at a position forming 0 degree. The above three measurement electrodes 31 to 33
Are the same length, and their lower ends 316, 326, 3
36 are all arranged at the same height. The lower end 46 of the correction electrode 4 is connected to the lower ends 316, 3 of the measurement electrodes 31 to 33.
26, 336, the height ΔL. As shown in FIG. 1, the common ground electrode 1 is a square tube having no bottom and made of an aluminum alloy. On the other hand, the insulating base 2 is a rectangular tube having a cavity 21 having substantially the same length as the common ground electrode 1 and made of glass epoxy. On four surfaces of the insulating base 2, measurement electrodes 31, 32 and 33 are provided on the front side, left side and right side. A correction electrode 4 is provided on the rear side. Further, the common ground electrode 1 and the insulating base 2 are fixed to a support plate above them (not shown).

These four electrodes are copper films formed by a vapor deposition method. The upper end of each electrode has a terminal (for example, the terminal 325 of the measurement electrode 32 and the terminal 45 of the correction electrode 4). As shown in the circuit diagram of FIG. 4, the measurement electrodes 31 to 33 and the correction electrode 4 are connected to the respective oscillators 531, 532, 53 via lead wires 37, respectively.
3 and 540. The common ground electrode 1
It is connected to each oscillator. Each oscillator is a liquid level calculation unit 50
Connected to 0.

The insulating base 2 is suspended inside the common ground electrode 1, and a gap 11 is provided between the two.
Is provided. The fuel 65 in the fuel tank freely enters and leaves the gap 11 from the bottom of the common ground electrode 1. For this reason, the liquid level changes with the change in the amount of fuel in the fuel tank. Further, the common ground electrode 1 and the insulating base 2 are arranged perpendicular to the bottom surface 61 of the tank (FIG. 3). This arrangement is not necessarily required to be vertical, and it is sufficient that the common ground electrode 1 and the insulating base 2 have a fixed positional relationship with respect to the bottom surface of the tank, and may be inclined.

Next, the operation and effect will be described. First, in FIG. 4, the measurement electrodes 31, 32, 33 and the correction electrode 4
The detection result according to the liquid level of the fuel 65 is input to the oscillation circuits of the oscillators 531 to 533 and 540. Then, here, the frequencies corresponding to the liquid level are oscillated and input to the liquid level calculating section 500. The liquid level calculator 500 calculates a true liquid level based on the oscillation cycle corresponding to each of the above frequencies, and displays this (FIG. 5 described later).

Next, as shown in FIG. 4, when the vehicle is in a horizontal position and the liquid surface 60 of the fuel 65 in the fuel tank is parallel (horizontal) to the bottom surface 61 of the fuel tank, the measuring electrodes 31 and 32 are used. , 33, the correction electrode 46 and the liquid level 60 are in a vertical relationship. Therefore, the detection values of the capacitance based on the liquid level of the fuel 65 are all the same in the measurement electrodes 31, 32, and 33. Therefore, as will be understood from the description regarding the tilting time described below, the liquid level calculating section 500 includes:
If the dielectric constant according to the type of fuel is corrected by a signal from the correction electrode 4, the true liquid level can be measured.

Next, the measurement of the true liquid level when the vehicle tilts and the fuel tank tilts will be described with reference to FIGS.
5 will be described. When the fuel tank is tilted, as shown in FIG.
0 is relatively inclined. Therefore, each of the measurement electrodes 31 to 3
3. The liquid level at each position in the correction electrode 4 is different.

In this case, it is assumed that the inclination is made in the left-right direction (measuring electrodes 32 and 33) as well as in the front-back direction (measuring electrode 31 and correction electrode 4). The angle of inclination in the front-rear direction is α, and the angle of inclination in the left-right direction is β. And each electrode 3
As shown in FIGS. 1 and 2, 9 to 33 and 4
It is located at 0 degree, and the same distance d 'from the center of the sensor part
Let's say The liquid levels that can be actually detected in the front, rear, left, and right directions are intermediate points between the electrodes 31 to 33 and 4 and the common ground electrode 1. When the gap between the electrodes is G, detection can be performed at the same distance d = d ′ + (G / 2) from the center of the sensor unit.
These are shown in FIG. 3 as F, B, HL, and H, respectively.
Let it be R.

Here, the liquid levels F, HL, and HR on the front and both left and right sides can be measured by the measuring electrodes 31 to 33, but the liquid level on the rear is such that the lower end of the correction electrode is located above the measuring electrode. Cannot be measured directly.
However, the liquid level at this rear position can be obtained as follows.

That is, as shown in FIG. 3, first, the center liquid level C at the center point of the sensor section is C = (HL +
HR) / 2, while the rear liquid level B at the correction electrode position is B = C + [CF]. Therefore, when this equation is expanded, B = (HL + HR) / 2 + [(HL + H
R) / 2-F] = HL + HR-F. Thus, the liquid level B of the correction electrode can be calculated.

Next, the measurement of the true liquid level will be described with reference to FIG.
This will be described with reference to the flowchart of FIG. First, in step (hereinafter abbreviated) 101, as described above, the capacitance according to the liquid level is detected by the measurement electrodes 31 to 33 and 33 on the front side, the left side and the right side, and the correction electrode 4 on the rear side.
Then, the detection results are output to the oscillators 531 to 533 and 540.
The oscillation periods T _{1 to} T ₄ are measured and input to the liquid level calculator 500. These vary depending on the liquid level and the dielectric constant of the liquid fuel.

Next, at 102, the dielectric constant ε is determined based on the oscillation periods T _{1 to} T ₄ by ε = [(T ₂ + T ₃ −T
₁ ) -T ₄ ] / AΔL. Here, A is the oscillation circuit constant, and ΔL is the difference in height between the lower ends of the measurement electrodes 31 to 34 and the correction electrode 4 (FIGS. 1 and 4). Next, in step 103, each liquid level is estimated. That is, each estimated liquid level L ₁ ~ ₃ = [(T ₁ ~ ₃
−AL ₀ ) / A (ε−1)] + h. Here, L ₀ is the total length from the lower end of the measuring electrode to the upper terminal, the distance between the lower end and the fuel tank bottom 61 for h measuring electrode (FIG. 3). In addition, about this distance of h,
The signal of the measuring electrode does not change.

Next, at 104, the liquid level is corrected for the fuel tank inclination to calculate the true liquid level. That is, first, the liquid level at the center position of the sensor unit 10 is calculated as described above. Next, the inclination angle α in the front-rear direction and the inclination angle β in the left-right direction are obtained by the following equations. Each symbol is as described above. α = tan ⁻¹ {[F− (HL + HR) / 2] / d} β = tan ⁻¹ [(HL−HR) / 2d]

After that, a correction value is obtained from a table in the microcomputer prepared in advance for each of the center height and each inclination angle. This correction value is determined based on the shape of the fuel tank and the position of the sensor unit in the fuel tank. Then, the correction value is subtracted from the center height to estimate the liquid level in the horizontal state, that is, the true liquid level L. Next, at 105, in order to reduce the error due to the fluctuation of the liquid level while the vehicle is running, for example, an average value for 30 seconds is obtained, and the true liquid level is averaged. 10
In step 6, the display of the true liquid level is performed. The above steps 101 to 106 are repeated.

In measuring the dielectric constant, it is necessary to use two types of electrodes having the same liquid level and different heights at the lower end (ΔL). However, if two electrodes are simply arranged side by side, the liquid level of each electrode differs due to the inclination of the fuel tank, and an accurate dielectric constant cannot be measured. In this example, as described above,
This point is solved by signals from the two measurement electrodes 31 to 33 and the correction electrode 4.

In the liquid level detecting device of this embodiment, the sensor unit 10 includes a long cylindrical common ground electrode 1, an insulating base 2 disposed therein, and measurement electrodes 31 provided on four surfaces of the insulating base 2. 33 and the correction electrode 4. Therefore, the sensor unit 10 can be configured as a single cylindrical assembly, and can be extremely reduced in size and weight as compared with the conventional example. In particular, in this embodiment, the insulating base 2 is also a cylindrical body, so that the weight can be further reduced.

The sensor unit 10 is small and lightweight.
Can be easily installed in the fuel tank. The liquid level is measured by three measurement electrodes 31 to 33, and the correction electrode 4 is measured.
As a result, the liquid level can be accurately measured even when the fuel tank is tilted.

Embodiment 2 In this embodiment, as shown in FIG. 6, the sensor section 100 is constituted by a cylindrical common ground electrode 1 and a cylindrical insulating base 20. As in the first embodiment, the measurement electrodes 31, 32, and 33 are provided on the insulating base 20 at intervals of 90 degrees.
And a correction electrode 4 are provided. Others are the same as the first embodiment. In this embodiment, the same effect as in the first embodiment can be obtained.

[Brief description of the drawings]

FIG. 1 is a perspective view of a sensor unit according to a first embodiment.

FIG. 2 is a sectional view taken along the line AA of FIG. 1;

FIG. 3 is an explanatory diagram of a liquid level when the fuel tank is tilted in the first embodiment.

FIG. 4 is a circuit diagram of a liquid level detection device according to the first embodiment.

FIG. 5 is a flowchart of liquid level measurement in the first embodiment.

FIG. 6 is a sectional view of a sensor unit according to the second embodiment.

[Explanation of symbols]

 1. . . Common earth electrode, 10,100. . . Sensor part, 2, 20. . . Insulating base, 21. . . Hollow, 31-33. . . Measuring electrode, 316, 326, 336, 46. . . Lower end, 4. . . Correction electrode, 500. . . Liquid level calculator, 531 to 533, 540. . . Oscillator, 61. . . Bottom of fuel tank, 65. . . fuel,

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01F 23/26

Claims (1)

(57) [Claims] 1. An electrostatic capacitance type liquid level comprising a sensor unit for detecting the liquid level of a liquid in a tank based on capacitance and a liquid level calculating unit connected to the sensor unit via an oscillator. In the detection device, the sensor section is provided with a long cylindrical common ground electrode, a long insulating base provided inside the common ground electrode, and a position at 90 degrees to each other on the insulating base. Three measurement electrodes and a correction electrode, the three measurement electrodes having their lower ends all arranged at the same height, while the correction electrode has its lower end positioned above the lower end of the measurement electrode. A liquid level detection device, comprising: