JP2014190860A - Liquid level detector - Google Patents

Abstract

An object of the present invention is to provide a liquid level detection device capable of accurately detecting a liquid level even when liquids having different capacitance characteristics are supplied.
A cylindrical casing;
A first electrode 36 that is provided in the housing and has a rectangular shape with a long side extending from the bottom surface of the fuel tank 14 along the upper surface direction, and is opposed to the first electrode. A second electrode 38 having a shape that spreads upward from the bottom surface side, and a float of a substance having a dielectric constant higher than that of the fuel so that a change in capacitance due to a change in fuel properties (change in alcohol concentration) can be ignored. 34.
[Selection] Figure 2

Description

  The present invention relates to a liquid level detection device, and more particularly to a liquid level detection device that detects the liquid level of a fuel tank in which a plurality of types of fuel are used.

  The liquid level is detected in order to detect the remaining amount of fuel stored in a fuel tank of an automobile. Generally, the liquid level is detected by a float type liquid level detection device. There is also a technique using this sensor.

  For example, in Patent Document 1, a main tank in which a liquid to be measured is stored and a pump for discharging the liquid are set, and the main tank communicates with the liquid in the tank. It is set to extend in the direction intersecting the liquid level of the liquid set in the sub tank, the reference electrode section set in the sub tank and immersed in the liquid in the sub tank, and the liquid set in the main tank. And a means for calculating the immersion depth of the measurement electrode portion with the liquid based on the capacitance measured at the reference electrode portion and the capacitance measured at the measurement electrode portion. An equipped liquid level measuring device has been proposed.

Japanese Patent Laid-Open No. 02-087022

  However, in the technique described in Patent Document 1, when different types of fuels having different alcohol concentrations or the like are supplied, the capacitance characteristics are different, so that the fuel level cannot be accurately measured.

  The present invention has been made in consideration of the above-described facts, and an object thereof is to provide a liquid level detection device capable of accurately detecting a liquid level even when liquids having different capacitance characteristics are supplied. To do.

  In order to achieve the above object, the liquid level detection device according to claim 1 is provided along a direction in which the liquid stored in the liquid tank is introduced and a direction intersecting the liquid level in the housing. And a pair of electrodes provided in the housing, having buoyancy with respect to the liquid, and having a dielectric constant higher than the dielectric constant of the liquid, and electrostatically interposed between the pair of electrodes. And a float for generating a capacity.

  According to the first aspect of the present invention, the liquid stored in the liquid tank is introduced into the casing. In addition, a pair of electrodes provided along the direction intersecting the liquid level is provided in the housing.

  That is, since the electrostatic capacity between the pair of electrodes changes depending on the liquid level of the liquid introduced into the housing, the liquid level can be detected from the electrostatic capacity between the pair of electrodes.

  However, if liquids having different capacitance characteristics are supplied, the liquid level cannot be detected accurately.

  Therefore, a float that is made of a substance having a dielectric constant higher than that of the liquid and generates a capacitance between the pair of electrodes is provided in the housing. By providing a float with a dielectric constant higher than the dielectric constant of the liquid, the detection value of the liquid level detection device is such that the capacitance between the pair of electrodes in the float portion and the electrostatic capacitance between the pair of electrodes in the liquid portion. The value is obtained by adding the capacitance, and the influence of the capacitance characteristics of the liquid is smaller when the liquid level is detected than when no float is provided.

  Therefore, if the float has a sufficiently large dielectric constant, the liquid level can be accurately detected even when liquids having different capacitance characteristics are supplied.

  For example, the float is made of a substance having a dielectric constant higher than the dielectric constant of the liquid to such an extent that the capacitance change between the pair of electrodes due to the change in liquid property can be ignored. Accordingly, the liquid level can be accurately detected even when liquids having different capacitance characteristics are supplied.

  As in the second aspect of the present invention, the pair of electrodes includes a first electrode having a rectangular shape and a second electrode having a shape extending from the bottom surface of the liquid tank toward the top surface. The electrode may be disposed between the first electrode and the second electrode, or the pair of electrodes may have two printed wirings in a comb-like shape and a liquid tank. The float may be arranged so as to be in contact with the print electrode. The print electrode is formed in a shape that spreads from the bottom surface toward the top surface. As a result, a wide dynamic range can be taken when the liquid level is detected, and the liquid level detection accuracy can be improved.

  As described above, according to the present invention, there is an effect that it is possible to provide a liquid level detection device capable of accurately detecting a liquid level even when liquids having different capacitance characteristics are supplied.

It is a figure which shows schematic structure of the fuel tank provided with the liquid level detection apparatus concerning embodiment of this invention. BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows schematic structure of the liquid level detection apparatus concerning 1st Embodiment of this invention, (A) is a perspective view which shows the external appearance of a liquid level detection apparatus, (B) is 3 directions of a liquid level detection apparatus. It is the top view seen from. (A) is a figure for demonstrating the equivalent circuit of the liquid level detection apparatus concerning 1st Embodiment, (B) is a figure which shows the equivalent circuit of the liquid level detection apparatus concerning 1st Embodiment. (A) is a figure which shows the relationship between the electrostatic capacitance of only a fuel liquid level, and a fuel liquid level, (B) is a figure which shows the relationship between the electrostatic capacitance by a float + liquid level, and a fuel liquid level. It is a figure which shows schematic structure of the liquid level detection apparatus concerning 2nd Embodiment of this invention, (A) is a perspective view which shows the external appearance of a liquid level detection apparatus, (B) is a top view, (C ) Is an enlarged view of a printed electrode. (A) is a figure for demonstrating the equivalent circuit of the liquid level detection apparatus concerning 2nd Embodiment, (B) is a figure which shows the equivalent circuit of the liquid level detection apparatus concerning 2nd Embodiment.

  Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of a fuel tank provided with a liquid level detection device according to an embodiment of the present invention.

  The fuel tank 14 stores a liquid fuel used in an automobile or the like that runs on an ethanol mixed fuel such as an FFV (flexible-fuel vehicle) car. The fuel stored in the fuel tank 14 is sucked up from a fuel pump 16 provided in the fuel tank 14 and supplied to an internal combustion engine such as an automobile engine.

  The fuel pump 16 is provided with a filter 18, and fuel is sucked up through the filter 18, so that clogging of the fuel pump 16 is suppressed.

  The fuel pump 16 is installed in a sub tank 20 provided in the fuel tank 14. A part of the fuel in the fuel tank 14 is stored in the sub tank 20. Therefore, even if a fuel bias occurs when the amount of fuel is reduced, a phenomenon in which a part of the fuel stored in the sub-tank 20 is separated from the fuel filter 18 (so-called fuel shortage) can be suppressed.

  A jet pump 22 is disposed below the peripheral wall of the sub tank 20. An introduction pipe 24 is connected to the jet pump 22, and a part of the fuel pumped up by the fuel pump 16 is introduced into the jet pump 22 from the introduction pipe 24 as return fuel without being sent to the outside. Fuel is fed into the sub tank 20.

  In the sub tank 20, a partition wall 20P is erected from the bottom wall 20B. The partition wall 20P is formed lower than the height of the peripheral wall 20S. And the temporary accommodating part 20T is comprised between a part of surrounding wall 20S and the partition 20P. The fuel introduced by the jet pump 22 is temporarily stored in the temporary storage unit 20T. The fuel overflowing from the temporary storage unit 20T passes through the partition wall 20P and is stored in the sub tank 20 (an area other than the temporary storage unit 20T).

  Further, a fuel inflow hole 26 is formed in the bottom wall 20B of the sub tank 20, and fuel movement from the fuel tank 14 to the sub tank 20 is allowed in the fuel inflow hole 26 and fuel movement in the reverse direction is prevented. A directional valve 28 is provided. For example, when initial fueling (fueling from a state in which no fuel is present in the fuel tank 14) is performed to the fuel tank 14, the fuel in the fuel tank 14 flows into the sub tank 20 from the fuel inflow hole 26. The fuel liquid level is equal between the fuel tank 14 and the sub tank 20. On the other hand, when the liquid level in the fuel tank 14 is lowered, the fuel in the sub tank 20 does not flow out into the fuel tank 14 through the fuel inflow hole 26. Since the fuel sent by driving the jet pump 22 is held in the sub tank 20, the fuel level is maintained at the upper end position of the sub tank 20.

  Further, the liquid level detection device 10 is disposed adjacent to the peripheral wall 20 </ b> S of the sub tank 20. The liquid level detection device has a cylindrical housing 10K. The housing 10K of the liquid level detection device 10 may be a housing separate from the sub tank 20, or may be integrally formed with the sub tank 20.

As shown in FIG. 1, the liquid level detection device 10 is provided with a fuel introduction path 32 at the lower end of a cylindrical housing 10 </ b> K, and the fuel introduction path 32 replaces the fuel in the liquid level detection apparatus. At the same time, part of the fuel pumped up by the fuel pump 16 is supplied to the liquid level detection device 10.
(First embodiment)
FIG. 2 is a diagram showing a schematic configuration of the liquid level detection device 10 according to the first embodiment of the present invention, and FIG. 2A is a perspective view showing an appearance of the liquid level detection device 10 according to the first embodiment. FIG. 2B is a plan view of the liquid level detection device 10 according to the first embodiment viewed from three directions.

The liquid level detection device 10 is provided with a float 34 having buoyancy with respect to the fuel. As the float 34, one containing a substance having a sufficiently high dielectric constant with respect to the fuel is applied. As a substance having a sufficiently high dielectric constant, a substance having a dielectric constant higher than that of the fuel is applied to such an extent that a change in capacitance due to a change in fuel properties (alcohol concentration change) can be ignored. For example, a substance having a dielectric constant of “water: 80” or more which is several times higher than the dielectric constant of ethanol: about 16 to 31 is desirable. As an example, the float 34 is made of a material such as titanium oxide (TiO ₂ ).

  Further, on the inner side wall of the casing 10K of the liquid level detection device 10, a first electrode 36 having a rectangular shape with a long side extending from the bottom surface of the fuel tank 14 in the upper surface direction, and the fuel tank 14 A second electrode 38 having a shape that spreads upward from the bottom surface side (in the present embodiment, the shape of an inverted triangle) is opposed to the second electrode 38. In this embodiment, as the second electrode 38, an inverted triangular shape is applied as shown in FIG. 2 (B), but the present invention is not limited to this. Any shape that expands toward the surface may be used.

  Next, liquid level detection by the liquid level detection apparatus 10 according to the first embodiment configured as described above will be described. FIG. 3A is a diagram for explaining an equivalent circuit of the liquid level detection device 10, and FIG. 3B is a diagram showing an equivalent circuit of the liquid level detection device 10.

  Between the first electrode 36 and the second electrode 38 of the liquid level detection device 10, it is divided into a portion where fuel is present, a portion where the float 34 is present, and a portion where nothing is present (air is present).

  Here, since the float 14 and the fuel have a predetermined dielectric constant, as shown in FIGS. 3A and 3B, the portion where the float 34 exists and the portion where the fuel exists are respectively the capacitance C1, Acts as a capacitor for C2. Therefore, the liquid level detection device 10 can be represented by an equivalent circuit in which the capacitor C1 and the capacitor C2 are connected in parallel as shown in FIG.

  In general, the capacity C of a capacitor is expressed by C = ε × S / L where the dielectric constant ε, the electrode area S, and the distance L between the electrodes, so if the liquid level rises, the fuel having the dielectric constant The area existing between the substrates increases and the capacitance also increases. Therefore, if the correspondence between the capacitance and the liquid level is obtained in advance, the liquid level can be detected by detecting the capacitance between the electrodes.

  However, in the present embodiment, since the ethanol mixed fuel is stored in the fuel tank 14, the dielectric constant changes depending on the stored ethanol concentration, and the liquid level is accurately detected simply by detecting the capacitor capacity. I can't.

  For example, when the ethanol concentration is E0 (ethanol 0%) and E100 (ethanol 100%), as shown in FIG. 4 (A), the capacitance is greatly different even if the liquid level is the same.

  Therefore, in this embodiment, the liquid level is detected in combination with the float 34. In the present embodiment, the material of the float 34 is a substance having a dielectric constant sufficiently higher than that of ethanol (for example, a dielectric constant of “water: 80” or more which is several times higher than the ethanol dielectric constant: about 16 to 31). Substance). As a result, the detection value of the liquid level detection device 10 is a value obtained by adding the capacitance C1 of the portion where the float 34 is present and the capacitance C2 of the portion where the fuel is present. As shown in FIG. 6, the capacitance change with respect to the ethanol concentration change can be made sufficiently smaller than the capacitance change with the liquid level change. Therefore, the capacitance change due to the ethanol concentration change can be made substantially negligible, and the influence of the ethanol concentration change when detecting the liquid level can be reduced.

In addition, since the shape of the second electrode 38 is a shape that expands upward from the bottom surface side of the fuel tank 14, the change in capacitance with respect to the change in the liquid level becomes larger than the use of a rectangular electrode for both poles. A wide dynamic range can be taken when detecting the liquid level, and the detection accuracy of the liquid level can be improved.
(Second Embodiment)
FIG. 5 is a diagram showing a schematic configuration of a liquid level detection device according to the second embodiment of the present invention, and FIG. 5 (A) is a perspective view showing an appearance of the liquid level detection device, and FIG. Is a plan view, and FIG. 5C is an enlarged view of a printed electrode.

Similarly to the first embodiment, the liquid level detection device 11 of the present embodiment is provided with a float 34 having buoyancy with respect to the fuel. As in the first embodiment, the float 34 that contains a substance having a sufficiently high dielectric constant relative to the fuel is applied. As a substance having a sufficiently high dielectric constant, a substance having a dielectric constant higher than that of the fuel is applied to such an extent that a change in capacitance due to a change in fuel properties (alcohol concentration change) can be ignored. For example, a substance having a dielectric constant of “water: 80” or more which is several times higher than the dielectric constant of ethanol: about 16 to 31 is desirable. As an example, the float 34 is made of a material such as titanium oxide (TiO ₂ ).

  Further, the float 34 is set to a size that moves according to the liquid level while being in contact with a print electrode 40 (described later) provided on the inner wall of the housing 10K of the liquid level detection device 11.

  In the first embodiment, the first electrode 36 and the second electrode 38 are arranged to face each other on the inner wall of the casing of the liquid level detection device 10. However, in the present embodiment, FIGS. ), A printed electrode 40 in which two printed wirings 40A and 40B are formed in a comb-teeth shape is provided on the inner wall of the liquid level detecting device 11. As shown in FIG. 5B, the printed electrode 40 has a shape that widens upward from the bottom surface side of the fuel tank 14. In this embodiment, as shown in FIG. 5 (B), the printed electrode 40 has an inverted triangular shape. However, the printed electrode 40 is not limited to this, and is upwardly directed from the bottom side of the fuel tank 14. Any shape that spreads out is acceptable.

  Next, the liquid level detection by the liquid level detection apparatus 11 according to the second embodiment configured as described above will be described. FIG. 6A is a view for explaining an equivalent circuit of the liquid level detection device 11 according to the second embodiment, and FIG. 6B is an equivalent circuit of the liquid level detection device 11 according to the second embodiment. FIG.

  In the printed electrode 40 of the liquid level detecting device 11 according to the second embodiment, two printed wirings 40A and 40B are formed in a comb shape, and each printed wiring 40A and 40B functions as a counter electrode of a capacitor. As shown in FIG. 6A, the printed electrode 40 is divided into a portion where the fuel is present, a portion where the float 34 is present, and a portion where nothing is present (air is present).

  Here, since the float 34 and the fuel have a predetermined dielectric constant, as shown in FIGS. 6A and 6B, the portion where the float 34 and the portion where the fuel exists of the printed electrode 40 are static. Acts as a capacitor of capacitances C1 and C2. Therefore, as shown in FIG. 6B, the liquid level detection device 11 of the present embodiment can also be represented by an equivalent circuit in which a capacitor C1 and a capacitor C2 are connected in parallel, as in the first embodiment.

  Also in the present embodiment, the liquid level is detected in combination with the float 34, and the float 34 is made of a material having a dielectric constant sufficiently higher than that of ethanol (for example, ethanol dielectric constant: about 16 to 31). A substance having a dielectric constant of “water: 80” or more that is twice as high. As a result, the detection value of the liquid level detection device 11 is a value obtained by adding the capacitance C1 of the portion where the float 34 is present and the capacitance C2 of the portion where the fuel is present. As can be seen, the capacitance change with respect to the ethanol concentration change can be made sufficiently smaller than the capacitance change with the liquid level change. Therefore, as in the first embodiment, it is possible to reduce the influence of the ethanol concentration change when the liquid level is detected.

  Also in this embodiment, since the shape of the printed electrode 40 is a shape that expands upward from the bottom surface side of the fuel tank 14, the capacitance change with respect to the liquid surface is larger than when the rectangular printed electrode 40 is used. Therefore, a wide dynamic range for detecting the liquid level can be taken, and the detection accuracy of the liquid level can be improved.

  The second electrode 38 according to the first embodiment and the printed electrode 40 according to the second embodiment have a shape that spreads upward from the bottom surface side of the fuel tank 14, but the shape is not limited thereto. is not. Although the liquid level detection accuracy is lower than in each of the above embodiments, for example, a rectangular one may be applied.

  In the above embodiment, the case of a mixed fuel mixed with ethanol has been described as an example. However, the fuel is not limited to ethanol, and a fuel mixed with another alcohol may be applied. You may apply when using the mixed fuel which mixes a fuel.

10, 11 Liquid level detection device 10K Housing 34 Float 36 First electrode 38 Second electrode 40 Print electrode 40A, 40B Print wiring

Claims (4)

A cylindrical housing into which the liquid stored in the liquid tank is introduced;
A pair of electrodes provided along the direction intersecting the liquid level in the housing;
A float that is provided in the housing and has a buoyancy with respect to the liquid, and is made of a substance having a dielectric constant higher than a dielectric constant of the liquid, and generates a capacitance between the pair of electrodes;
A liquid level detection device. The pair of electrodes includes a first electrode having a rectangular shape and a second electrode having a shape extending from the bottom surface of the liquid tank toward the top surface,
The liquid level detection device according to claim 1, wherein the float is disposed between the first electrode and the second electrode. The pair of electrodes is a printed electrode in which two printed wirings are comb-like and formed in a shape that extends from the bottom surface of the liquid tank toward the top surface,
The liquid level detection device according to claim 1, wherein the float is disposed so as to contact the printed electrode.   The said float consists of a substance of a dielectric constant higher than the dielectric constant of the said liquid to such an extent that the electrostatic capacitance change between the said pair of electrodes by the change of a liquid property can be disregarded. Liquid level detection device.