JP4795049B2 - Liquid level sensor - Google Patents

Description

  The present invention relates to a capacitive liquid level sensor that detects a liquid level based on a capacitance between a pair of electrodes immersed in a liquid.

  2. Description of the Related Art In recent years, a capacitive liquid level sensor that detects a liquid level by using a capacitance between a pair of electrodes immersed in a liquid has been used in a fuel tank of a vehicle such as an automobile. The capacitance between the pair of electrodes varies depending on the dielectric constant of the liquid, and the dielectric constant of the liquid varies depending on conditions such as the type of liquid and temperature. In view of this, a liquid level sensor that performs correction according to the dielectric constant of a liquid in a capacitance type liquid level sensor has been known (for example, see Patent Document 1).

  The sensor disclosed in Patent Document 1 includes a pair of flat plate-like measurement electrodes arranged so that the flat surface is vertical, and a pair of flat plate-like reference electrodes arranged opposite to each other. The water level is detected based on both the capacitance between the measurement electrodes and the capacitance between the pair of reference electrodes.

  The pair of reference electrodes are immersed in the liquid, and the dielectric constant of the liquid is obtained from the ratio of capacitance between the pair of reference electrodes in liquid and in the air. Then, the capacitance between the pair of measurement electrodes is corrected using the obtained dielectric constant of the liquid, and the water level is accurately detected.

Japanese Patent Laid-Open No. 11-108735

  However, in the sensor disclosed in Patent Document 1, if the pair of reference electrodes are exposed to the air even a little, an error occurs in the dielectric constant of the liquid required by the pair of reference electrodes, and the detection accuracy of the water level decreases. It becomes. Therefore, the pair of reference electrodes must always be arranged in the liquid, but this limits the water level detection range by the pair of measurement electrodes above the water level at which the pair of reference electrodes are completely immersed. Will be. When the pair of reference electrodes is downsized to expand the measurement range of the pair of measurement electrodes downward, the output of the pair of reference electrodes becomes unstable, and an error is generated in the dielectric constant of the liquid.

  As described above, in the sensor disclosed in Patent Document 1, it is difficult to measure the liquid level up to the bottom of the container containing the liquid, that is, to measure the liquid level when the liquid level is low. In recent automobiles where a thin fuel tank is required, the fact that the liquid level sensor cannot be measured at the bottom of the tank is a serious problem in terms of vehicle performance, and a liquid level sensor capable of measuring the bottom of the tank is required. It has been.

  The present invention has been made in view of the above-described circumstances, and an object thereof is to provide a liquid level sensor capable of accurately detecting the liquid level to the bottom of the liquid container regardless of the dielectric constant of the liquid. It is in.

The above object is achieved by the liquid level sensor according to the following (1) to ( 2 ) of the present invention.

(1) A first sensor element and a second sensor element in which a pair of electrodes are spirally wound in parallel with each other on the outer periphery of the insulating base,
The first sensor element and the second sensor element are respectively arranged such that the spiral axis of the pair of electrodes is vertical and the lower end of the first sensor element and the lower end of the second sensor element are at the same height. Has been
The pair of electrodes of the first sensor element and the pair of electrodes of the second sensor element have different helical pitches,
The spiral pitch of the pair of electrodes of the first sensor element is set to be gradually denser or sparse as it goes from the lower end to the upper end, and the spiral pitch of the pair of electrodes of the second sensor element is the first sensor element. Contrary to the spiral pitch of the pair of electrodes, it is set to gradually become sparse or dense from the lower end toward the upper end,
A liquid level sensor that measures the liquid level of the liquid based on capacitance between a pair of electrodes of the first sensor element and the second sensor element when immersed in the liquid.

( 2 ) The liquid according to ( 1 ), wherein the spiral pitch of the pair of electrodes of the first sensor element and the spiral pitch of the pair of electrodes of the second sensor element are vertically symmetrical. Surface level sensor.

According to the liquid level sensor having the above configuration (1), the first sensor element and the second sensor element have different spiral pitches of the pair of electrodes, and output characteristics when immersed in liquid, that is, a pair The capacitance changes between the electrodes are different from each other. Then, based on the ratio of the outputs of both sensor elements when the first sensor element and the second sensor element are both immersed in the liquid, the influence of the dielectric constant of the liquid is corrected and the liquid level is accurately detected. Can do.
Here, the liquid level can be detected as long as a part of each of the first sensor element and the second sensor element is immersed in the liquid, and the measurement range is horizontal between the first sensor element and the second sensor element. Overlapping direction. According to this, it is not necessary to always arrange the electrode pair in the liquid as in the prior art, and the liquid level can be measured up to the bottom of the liquid container or the vicinity thereof.

In addition , one of the first sensor element or the second sensor element, in which the spiral pitch of the pair of electrodes is made closer to the lower end, the rate of change in capacitance due to the liquid level displacement when the liquid level is at the lower end. On the other hand, the spiral pitch of the pair of electrodes is made sparser at the lower end, so that the rate of change of the capacitance accompanying the liquid level displacement when the liquid level is at the lower end is relatively small. Therefore, when the liquid level is at the lower ends of both sensor elements, the difference in the outputs of both sensor elements due to the liquid level displacement becomes significant, and the correction accuracy can be improved.

According to the liquid level sensor having the above configuration ( 2 ), the spiral pitch of the pair of electrodes of the first sensor element and the spiral pitch of the pair of electrodes of the second sensor element are symmetric in the vertical direction. Since the outputs of both sensor elements with respect to show reverse characteristics, correction becomes easy.

  According to the present invention, it is possible to provide a liquid level sensor that can accurately measure the liquid level regardless of the dielectric constant of the liquid and can measure up to the bottom of the liquid container.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the drawings.
1 is a front view of a first embodiment of a liquid level sensor according to the present invention, FIG. 2 is a bottom view of a first sensor element of the liquid level sensor of FIG. 1, and FIG. 3 is a liquid level sensor of FIG. It is a graph which shows the relationship between a liquid level displacement and the change of the electrostatic capacitance of a 1st sensor element and a 2nd sensor element. 4 is a front view of a second embodiment of the liquid level sensor according to the present invention, and FIG. 5 is a liquid level displacement and capacitances of the first sensor element and the second sensor element in the liquid level sensor of FIG. It is a graph which shows the relationship with a change of.

(First embodiment)
As shown in FIGS. 1 and 2, the liquid level sensor 10 of the present embodiment detects the level of the liquid level S of the liquid L by being immersed in the liquid L in the container 1. The liquid level sensor 10 includes a first sensor element 11 in which a pair of electrodes 13 and 14 are spirally wound in parallel with each other on an outer periphery of an insulating base 12, and a pair of electrodes 23 on an outer periphery of an insulating base 22. , 24 are spirally wound in parallel with each other, and the second sensor element 21 is provided.

  The insulating substrate 12 of the first sensor element 11 is formed in a substantially cross shape in a cross section perpendicular to the longitudinal direction, with ribs 15 projecting radially from the circumferential surface of the central part of the prismatic shape. The material of the insulating substrate 12 is not particularly limited, and it is preferable to use, for example, a synthetic resin such as a polyacetal resin in consideration of strength and resistance to liquid (vehicle fuel and the like). The insulating substrate 22 of the second sensor element 21 is formed of the same material and the same shape as the insulating substrate 12 of the first sensor element 11.

  The electrodes 13 and 14 of the first sensor element 11 are spirally wound around the outer periphery of the four ribs 15 of the insulating base 12 in parallel with each other, and the electrodes 13 and 14 are connected to the spiral pitch, respectively. The insulating base 12 provided with the terminals 16 and 17 is set so as to become denser gradually from one end in the longitudinal direction toward the other end.

  A plurality of holding grooves are formed on the outer edges of the ribs 15 in correspondence with the spiral pitches of the electrodes 13 and 14, and the electrodes 13 and 14 are inserted into these holding grooves while being outer edges of the ribs 15. It is wrapped around Note that it is preferable to use SUS, white or the like as the material of the electrodes 13 and 14 in consideration of resistance to liquid (vehicle fuel or the like).

  The electrodes 23 and 24 of the second sensor element 21 are spirally wound around the outer periphery of the four ribs of the insulating base 22 in parallel with each other, and the helical pitch is a terminal to which the electrodes 23 and 24 are connected, respectively. The insulating base 22 provided with 26 and 27 is gradually sparse from one end to the other end in the longitudinal direction, that is, set to be opposite to the pair of electrodes 13 and 14 of the first sensor element 11. Yes.

  Furthermore, the spiral of the pair of electrodes 13 and 14 of the first sensor element 11 assuming that the side on which the terminals 16 and 17 or the terminals 26 and 27 are provided is the upper side of the first sensor element 11 and the second sensor element 21. The pitch and the spiral pitch of the pair of electrodes 23 and 24 of the second sensor element 21 are set symmetrically.

  The first sensor element 11 and the second sensor element 21 are held by the case 2 so that the spiral axes of the pair of electrodes 13 and 14 or the electrodes 23 and 24 are vertical with the terminals 16 and 17 or the terminals 26 and 27 facing upward, respectively. It arrange | positions in the container 1 so that it may become. The lower ends of the first sensor element 11 and the second sensor element 21 are both near the bottom surface of the container 1 and located at the same height.

  As the liquid level S is displaced, the length of the portion of the pair of electrodes 13 and 14 of the first sensor element 11 where the liquid is interposed changes, and the capacitance between the pair of electrodes 13 and 14 changes. Changes. Similarly, with the displacement of the liquid level S, the capacitance between the pair of electrodes 23 and 24 of the second sensor element 21 also changes. The capacitance between the pair of electrodes 13 and 14 and the capacitance between the pair of electrodes 23 and 24 are measured by the drive circuit 3 connected to the terminals 16 and 17 and the terminals 26 and 27 and measured. A predetermined calculation is performed based on the two capacitances thus obtained, and the level of the liquid level S is thereby detected.

3, the capacitance C ₁ between the pair of electrodes 13 and 14 of the first sensor element 11 and the pair of electrodes 23 and 24 of the second sensor element 21 with respect to the height h of the liquid level S from the bottom surface of the container 1. It shows the relationship between the capacitance C ₂ between. In the figure, the one-dot difference line is a characteristic curve of the capacitance C ₁ of the first sensor element 11, and the two-dot chain line is a characteristic curve of the capacitance C ₂ of the second sensor element 21.

As shown in FIG. 3, the first sensor element 11 in which the spiral pitch of the pair of electrodes 13 and 14 is closer to the lower end has a capacitance associated with the displacement of the liquid level S when the liquid level S is at the lower end. The second sensor element 21 in which the change rate of C ₁ is relatively large and the spiral pitch of the pair of electrodes 23 and 24 is made sparser toward the lower end is accompanied by the displacement of the liquid level S when the liquid level S is at the lower end. the capacitance C ₂ of the change rate is relatively small. More specifically, since the spiral pitch of the pair of electrodes 13 and 14 of the first sensor element 11 and the spiral pitch of the pair of electrodes 23 and 24 of the second sensor element 21 are vertically symmetrical, The change in electrostatic capacitance exhibits reverse characteristics between the first sensor element 11 and the second sensor element 21.

ここで、ｋは定数であり、ε_ｒは液体の誘電率であり、ｇ_１（ｈ），ｇ_２（ｈ）はそれぞれ図３に示す第１センサエレメント１１の静電容量Ｃ_１又は第２センサエレメント２１の静電容量Ｃ_２の特性曲線を原点に平行移動したものであってｈの関数であり、Ｃ_０１，Ｃ_０２はそれぞれ第１センサエレメント１１又は第２センサエレメント２１の気中（ｈ＝０）における静電容量であり、本実施形態ではＣ_０１＝Ｃ_０２である。 The capacitance C ₂ of the capacitance C ₁ and the second sensor element 21 of the first sensor element 11 are indicated by the following formulas, respectively.

Here, k is a constant, ε _r is the dielectric constant of the liquid, and g _{1 (h)} and g _{2 (h)} are the capacitance C ₁ or second capacitance of the first sensor element 11 shown in FIG. The characteristic curve of the capacitance C ₂ of the sensor element 21 is translated from the origin and is a function of h, and C ₀₁ and C ₀₂ are the air in the first sensor element 11 or the second sensor element 21 ( h = 0), and in this embodiment, C ₀₁ = C ₀₂ .

Both sides divided by _{C 01} in formula (1), the following equation is obtained.

The following equation is obtained by rearranging equation (3).

Similarly both sides divided by C ₀₂ in formula (2), the following expression is obtained by organizing.

Dividing equation (5) side by side with equation (4), the following equation is obtained.

Equation (6) does not include the epsilon _r, that is, liquid level regardless the equation (6) the dielectric constant of the liquid is calculated.

Thus, according to the liquid level sensor of this embodiment, the spiral pitch of the pair of electrodes is different between the first sensor element and the second sensor element, and the output characteristics when immersed in the liquid, that is, Changes in capacitance between the pair of electrodes are different from each other. Then, based on the ratio of the outputs of both sensor elements when the first sensor element and the second sensor element are both immersed in the liquid, the influence of the dielectric constant of the liquid is corrected and the liquid level is accurately detected. Can do.
Here, the liquid level can be detected as long as a part of each of the first sensor element and the second sensor element is immersed in the liquid, and the measurement range is horizontal between the first sensor element and the second sensor element. Overlapping direction. According to this, it is not necessary to always arrange the electrode pair in the liquid as in the prior art, and the liquid level can be measured up to the bottom of the liquid container or the vicinity thereof.

  Moreover, according to the liquid level sensor of this embodiment, the liquid level of the first sensor element in which the spiral pitch of the pair of electrodes is closer to the lower end of the first sensor element or the second sensor element is lower end. The second sensor element has a relatively large change rate of capacitance due to the liquid level displacement, and the spiral pitch of the pair of electrodes is made sparser toward the lower end, so that the liquid level is lower when the liquid level is at the lower end. The rate of change of capacitance due to surface displacement is relatively small. Therefore, when the liquid level is at the lower ends of both sensor elements, the difference in the outputs of both sensor elements due to the liquid level displacement becomes significant, and the correction accuracy can be improved.

  Further, according to the liquid level sensor of the present embodiment, the spiral pitch of the pair of electrodes of the first sensor element and the spiral pitch of the pair of electrodes of the second sensor element are vertically symmetrical, Since the outputs of both sensor elements exhibit reverse characteristics, correction is easy.

  Further, according to the liquid level sensor of the present embodiment, the lower end of the first sensor element and the lower end of the second sensor element are at the same height, and the liquid level can be measured from the lower ends of both sensor elements. . Therefore, the liquid level can be measured up to the bottom of the liquid container.

(Second Embodiment)
Next, with reference to FIG.4 and FIG.5, 2nd Embodiment of the liquid level sensor which concerns on this invention is described.

  As shown in FIG. 4, the liquid level sensor 40 of the present embodiment is different from the liquid level sensor 10 of the first embodiment described above and the second sensor element, and a pair of outer surfaces of the insulating base 42 are arranged on the outer periphery. The electrodes 43 and 44 include a second sensor element 41 in which the electrodes 43 and 44 are spirally wound in parallel with each other, and other configurations are the same as those of the liquid level sensor 10 of the first embodiment. In addition, about the member which is common with the liquid level sensor 10 of 1st Embodiment, the same code | symbol is attached | subjected in a figure and description is abbreviate | omitted.

  The insulating base 42 of the second sensor element 41 is formed of the same material and the same shape as the insulating base 12 of the first sensor element 11. The electrodes 43 and 44 of the second sensor element 41 are spirally wound around the four ribs of the insulating base 42 in parallel with each other, and the helical pitch is set at equal intervals from the lower end to the upper end. Has been.

  Similar to the liquid level sensor 10 of the first embodiment, the first sensor element 11 and the second sensor element 41 are held by a case and are paired with terminals 16 and 17 or terminals 46 and 47, respectively. 13, 14 or the electrodes 43, 44 are arranged in the container 1 so that the spiral axes thereof are vertical. The lower ends of the first sensor element 11 and the second sensor element 41 are both near the bottom surface of the container and located at the same height.

  With the displacement of the liquid level, the length of the portion of the pair of electrodes 13 and 14 of the first sensor element 11 in which the liquid is interposed changes, and the capacitance between the pair of electrodes 13 and 14 is changed. Change. Similarly, with the displacement of the liquid level S, the capacitance between the pair of electrodes 43 and 44 of the second sensor element 41 also changes. The capacitance between the pair of electrodes 13 and 14 and the capacitance between the pair of electrodes 43 and 44 are measured and measured by a drive circuit connected to the terminals 16 and 17 and the terminals 46 and 47. The predetermined calculation is performed based on the two capacitances, thereby detecting the liquid level.

FIG. 5 shows the relationship between the capacitance C ₁ of the first sensor element 11 and the capacitance C ₂ of the second sensor element 41 with respect to the height h of the liquid level S from the bottom surface of the container 1. In the drawing, the one-dot difference line is a characteristic curve of the capacitance C ₁ of the first sensor element 11, and the two-dot chain line is a characteristic curve of the capacitance C ₂ of the second sensor element 41.

According to the liquid level sensor of the present embodiment, the spiral pitch of the pair of electrodes is different between the first sensor element and the second sensor element, and the output characteristics when immersed in the liquid, that is, between the pair of electrodes. The changes in the electrostatic capacitances are different from each other. Then, based on the ratio of the outputs of both sensor elements when the first sensor element and the second sensor element are both immersed in the liquid, the influence of the dielectric constant of the liquid is corrected and the liquid level is accurately detected. Can do.
Here, the liquid level can be detected as long as a part of each of the first sensor element and the second sensor element is immersed in the liquid, and the measurement range is horizontal between the first sensor element and the second sensor element. Overlapping direction. According to this, it is not necessary to always arrange the electrode pair in the liquid as in the prior art, and the liquid level can be measured up to the bottom of the liquid container or the vicinity thereof.

  Further, according to the liquid level sensor of the present embodiment, the second sensor element has a pair of electrodes with an equal pitch of the spiral, and the second sensor element is shared and the spiral pitch is variously changed. In combination with the sensor element, it can cope with various liquids having different dielectric constants, and is excellent in versatility.

  Further, according to the liquid level sensor of the present embodiment, the lower end of the first sensor element and the lower end of the second sensor element are at the same height, and the liquid level can be measured from the lower ends of both sensor elements. . Therefore, the liquid level can be measured up to the bottom of the liquid container.

  In addition, this invention is not limited to embodiment mentioned above, A deformation | transformation, improvement, etc. are possible suitably. In addition, the material, shape, dimension, numerical value, form, number, arrangement location, and the like of each component in the above-described embodiment are arbitrary and not limited as long as the present invention can be achieved.

It is a front view of 1st Embodiment of the liquid level sensor which concerns on this invention. It is a bottom view of the 1st sensor element of the liquid level sensor of FIG. 2 is a graph showing a relationship between a liquid level displacement and changes in electrostatic capacitances of a first sensor element and a second sensor element in the liquid level sensor of FIG. 1. It is a front view of 2nd Embodiment of the liquid level sensor which concerns on this invention. 5 is a graph showing the relationship between the liquid level displacement and the change in capacitance of the first sensor element and the second sensor element in the liquid level sensor of FIG. 4.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Container 10 Liquid level sensor 11 1st sensor element 12 Insulating base | substrate 13,14 Electrode 21 2nd sensor element 22 Insulating base | substrate 23,24 Electrode L Liquid S Liquid surface

Claims (2)

A first sensor element and a second sensor element in which a pair of electrodes are spirally wound in parallel to each other on the outer periphery of the insulating substrate;
The first sensor element and the second sensor element are respectively arranged such that the spiral axis of the pair of electrodes is vertical and the lower end of the first sensor element and the lower end of the second sensor element are at the same height. Has been
The pair of electrodes of the first sensor element and the pair of electrodes of the second sensor element have different helical pitches,
The spiral pitch of the pair of electrodes of the first sensor element is set to be gradually denser or sparse as it goes from the lower end to the upper end, and the spiral pitch of the pair of electrodes of the second sensor element is the first sensor element. Contrary to the spiral pitch of the pair of electrodes, it is set to gradually become sparse or dense from the lower end toward the upper end,
A liquid level sensor that measures the liquid level of the liquid based on capacitance between a pair of electrodes of the first sensor element and the second sensor element when immersed in the liquid. 2. The liquid level sensor according to claim 1 , wherein the spiral pitch of the pair of electrodes of the first sensor element and the spiral pitch of the pair of electrodes of the second sensor element are vertically symmetrical.

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