JP2009008650A - Liquid level detecting apparatus and design method of same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid level detecting apparatus capable of highly accurately detecting liquid levels over a long period even in the case of exposure to electrolytic solutions. <P>SOLUTION: The liquid level detecting apparatus 1 includes both a sensor 2 arranged in a container which stores a liquid and an electric power circuit 4 for intermittently applying a voltage to the sensor 2 at a prescribed period. The sensor 2 has a variable resistor 3 for changing a resistance value by moving a contact in conjunction with displacements of a liquid level and outputs a voltage signal according to a resistance value of a variable resistor 3 when a prescribed voltage is applied. An energization time period during which the electric power circuit 4 applies a voltage to the sensor 2 is ≤40 ms for one period. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to a liquid level detection device, for example, a liquid level suitable for detecting the remaining fuel level of a vehicle such as an automobile using an electrolytic fuel such as alcohol itself such as ethanol or methanol or an alcohol fuel containing them. The present invention relates to a design method for a level detection device and a liquid level detection device.

  An example of a conventional liquid level detecting device is shown in FIG. The liquid level detecting device 101 shown in FIG. 9 includes a sensor 102 disposed in a container that stores liquid. The sensor 102 has a variable resistor 103 that changes the resistance value by moving the contact in conjunction with the displacement of the liquid level, and a voltage corresponding to the resistance value of the variable resistor 103 when a predetermined voltage is applied. Output a signal. Further, the liquid level detection device 101 includes a power supply circuit 104 that applies a voltage to the sensor 102 (see, for example, Patent Document 1).

  An example of the configuration of the sensor 102 is shown in FIG. A sensor 102 shown in FIG. 10 includes an arm 111 with a float 110 that floats on a liquid attached to the tip, a frame 112 that rotatably supports the base end of the arm 111, a substrate 113 attached to the frame 112, And a contact 114 provided at the proximal end portion of the arm 111. A resistor (not shown) is formed on the surface of the substrate 113, and a predetermined voltage is applied to the resistor by the power supply circuit 104. As the arm 111 rotates, the contact 114 turns around the rotation axis of the arm 111 and slides on the resistor of the substrate 113 (see, for example, Patent Document 4).

  One end of the resistor of the substrate 113 and the contact 114 are electrically connected to the output terminals 115 and 116 of the sensor 102, respectively. The float 110 moves up and down in conjunction with the displacement of the liquid level, and the arm 111 is rotated accordingly, and the contact 114 slides on the resistor. As a result, the resistance value between one end of the resistor connected to the output terminal 115 and the contact 114 (hereinafter referred to as the first region of the resistor) changes. That is, the variable resistor 103 is constituted by these resistors and the contact 114. The voltage applied to the resistor is divided according to the resistance value of the first region of the resistor, and the voltage applied to the first region is detected between the output terminals 115 and 116 as an output signal of the sensor 102. .

  Referring to FIG. 9 again, the liquid level detecting device 101 acquires the output signal of the sensor 102 by the processing circuit 105, and drives the meter 106 that displays the remaining amount of liquid based on the acquired signal.

By the way, when detecting the remaining amount of fuel in a vehicle such as an automobile, the sensor 102 of the liquid level detecting device 101 is disposed in the fuel tank. Recently, bioethanol or the like has begun to be used as a vehicle fuel. Alcohol-based fuels such as bioethanol are electrolytes, and when the resistor of the sensor 102 and the sliding contact surface of the contactor 114 are exposed to the electrolytic solution, electrolysis such as electrolytic corrosion occurs on the sliding contact surface with energization. The reaction occurs and deteriorates, and the contact resistance of the contact point rises, preventing accurate measurement. In order to avoid such problems, it has been proposed to intermittently apply a voltage to the sensor 102 at a predetermined cycle (see, for example, Patent Documents 1 to 3).
Japanese Patent Laid-Open No. 2002-214023 JP-A-63-138215 JP 2006-214828 A Japanese Patent No. 3898913

  Here, the energization time is an important factor in electrochemical reactions such as electrolytic corrosion. However, in Patent Documents 1 to 3 mentioned above, no suitable energization time per cycle is mentioned, which is a sufficient measure. There wasn't.

  The present invention has been made in view of the above-described circumstances, and an object thereof is a liquid level detecting device capable of detecting a liquid level with high accuracy over a long period of time even when exposed to an electrolytic solution, and An object of the present invention is to provide a method for designing a liquid level detecting device.

The above object is achieved by the following (1) to (5) liquid level detecting device and the following (6) designing method of the liquid level detecting device according to the present invention.
(1) It has a variable resistor which is arranged in a container storing liquid and moves a contact point in conjunction with displacement of the liquid level to change the resistance value, and a predetermined voltage is applied to the variable resistor. A sensor that outputs a voltage signal in accordance with a resistance value; and a power supply circuit that intermittently applies the voltage to the sensor at a predetermined cycle; and an energization time during which the power supply circuit applies a voltage to the sensor. A liquid level detection apparatus characterized by being 40 ms or less per cycle.
(2) The liquid level detecting device according to (1), wherein an energization time during which the power supply circuit applies the voltage to the sensor is 15 ms or less per cycle.
(3) The liquid level detecting device according to (2), wherein an energization time during which the power supply circuit applies the voltage to the sensor is longer than 1 ms per cycle.
(4) The liquid level detecting device according to (1), wherein an energization time during which the power supply circuit applies the voltage to the sensor is approximately 5 ms per cycle.
(5) The liquid level detecting device according to any one of (1) to (4), wherein a ratio of the energization time in one cycle is 50% or less.
(6) A variable resistor that is arranged in a container that stores liquid and changes a resistance value in conjunction with a displacement of the liquid level, and that is applied with a predetermined voltage according to the resistance value of the variable resistor. In a liquid level detecting device comprising: a sensor that outputs a voltage signal; and a power supply circuit that intermittently applies the voltage to the sensor at a predetermined cycle, the variable resistors are first and second extending in parallel with each other. A second conductive pattern; and a contactor bridged by the first and second conductive patterns and sliding on the first and second conductive patterns in conjunction with displacement of a liquid level. In addition, when the voltage is applied to the sensor in a state where the contact portion between the first and second conductive patterns and the contactor is insulated, the current flowing through the first and second conductive patterns tends to increase. The time to become over 60s Design method described above, liquid level detection device, wherein the power supply circuit selects the energization time per cycle for applying the voltage to the sensor.

  According to the liquid level detecting apparatus having the above configuration, electrochemical reaction such as electrolytic corrosion at the contact portion of the variable resistor is suppressed even when exposed to the electrolytic solution. The reason is considered as follows. A molecule involved in a chemical reaction needs to overcome the energy barrier before it can move into the product state. In the electrolytic corrosion of the contact portion, as shown in FIG. 4, it is necessary to overcome the potential energy barrier on the metal surface of the contact portion. Release, ionize and elute. When the energization time per cycle is 40 ms or less, the metal molecules in the contact portion return to the ground state S1 again without being excited from the ground state S1 to the activated state S2. The energization time per cycle is preferably 15 ms or less, more preferably more than 1 ms and 15 ms or less, and particularly preferably about 5 ms. If the energization time per cycle is 1 ms or less, the sampling time may be insufficient when the output signal of the sensor is sampled. This is because a capacitor may be interposed between the sensor and the A / D converter to prevent direct current from flowing into the A / D converter. This is because the rise of the output signal of the sensor is dull. Further, since the time for returning to the ground state S1 is longer than the time required for excitation, it is preferable that the ratio of the energization time in one cycle is 50% or less.

  In addition, when a voltage is applied to the sensor with the contact portion between the first and second conductive patterns of the variable resistor and the contacts insulated, a capacitor is formed between the first and second conductive patterns. The When the applied voltage is higher than the withstand voltage, electrolysis occurs in the first and second conductive patterns serving as both electrodes of the capacitor, and a current flows. In the design method of the liquid level detecting device having the above configuration, if the time until the current value rise start point is long, the metal of the first and second conductive patterns is difficult to elute, and the eluted metal ions also move. From the idea that it is difficult to conduct, a more appropriate energization time is selected according to the energization time and the time characteristics up to the current value rise start point. The eluted metal ions move mainly from the anode to the cathode by migration when energized, but move by diffusion and convection when not energized. According to diffusion and convection, metal ions move (disperse) in various directions between the first and second conductive patterns, so that the moving speed toward either one of the two conductive patterns toward the cathode side is slow. That is, the electrochemical reaction is suppressed. When the energization time per cycle is 15 ms or less, the time until the current value starts to rise is 60 s or more, and the tendency to suppress elution of metal ions is remarkably increased.

  According to the present invention, even when exposed to an electrolytic solution, it is possible to suppress an electrochemical reaction such as electrolytic corrosion at the contact portion of the variable resistor of the sensor. Can be detected.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

  1 is a diagram illustrating a schematic configuration of an embodiment of a liquid level detecting device according to the present invention, FIG. 2 is a diagram illustrating a sensor used in the liquid level detecting device of FIG. 1, and FIG. It is a figure explaining the principal part of the sensor shown.

  As shown in FIG. 1, the liquid level detection device 1 of the present embodiment includes a sensor 2 arranged in a container that stores a liquid. The sensor 2 has a variable resistor 3 that changes the resistance value by moving the contact in conjunction with the displacement of the liquid level, and a signal corresponding to the resistance value of the variable resistor 3 when a predetermined voltage is applied. Is output. Further, the liquid level detection device 1 includes a power supply circuit 4 that applies a predetermined voltage to the sensor 2 (see, for example, Patent Document 1).

  Referring to FIG. 2, sensor 2 includes an arm 11 having a float 10 that floats on a liquid attached to the tip, a frame 12 that rotatably supports a base end of arm 11, and a substrate attached to frame 12. 13 and a contact 14 provided at the base end of the arm 11.

  As shown in FIG. 3, a first conductive pattern 15 and a second conductive pattern 16 are provided on the surface of the substrate 13, and the first conductive pattern 15 and the second conductive pattern 16 rotate the arm 11. The axes O (see FIG. 2) extend in parallel with each other in a circular arc shape. An input / output conductive portion 17 is connected to one end of the first conductive pattern 15, and an input / output conductive portion 18 is connected to one end of the second conductive pattern 16.

  The first conductive pattern 15 located on the outer diameter side includes a plurality of conductive segments 15a arranged at predetermined intervals in the circumferential direction, and a resistor that electrically connects the plurality of conductive segments 15a to each other. 15b. The second conductive pattern 16 includes a plurality of conductive segments 16a arranged at predetermined intervals in the circumferential direction, and a connecting body 16b that electrically connects the plurality of conductive segments 16a to each other. Has been.

  The conductive segment 15a of the first conductive pattern 15 and the conductive segment 16a of the second conductive pattern 16 are made of, for example, silver palladium having excellent corrosion resistance, and the resistor 15b is made of, for example, ruthenium oxide having excellent corrosion resistance.

  The contact 14 is provided with two contacts 19 and 20 that are electrically connected to each other. The contact 14 rotates around the rotation axis O of the arm 11 as the arm 11 rotates, and slides on the conductive segment 15 a of the first conductive pattern 15 at the contact point 19, and moves to any one of the conductive segments 15 a. Connecting. At the same time, the contact 14 slides on the conductive segment 16a of the second conductive pattern 16 at the contact point 20 and is connected to one of the conductive segments 16a. Thereby, the length of the resistor 15b interposed in the circuit between the input / output conductive portion 17 and the input / output conductive portion 18 changes, and the resistance value of the circuit changes. That is, the variable resistor 3 is configured by the first conductive pattern 15, the second conductive pattern 16, and the contact 14.

  The sensor 2 further includes a fixed resistor 7 having one end connected to the input / output conductive portion 17 and connected in series to the variable resistor 3. A predetermined voltage is applied to the variable resistor 3 and the fixed resistor 7 by the power supply circuit 4.

  The float 10 moves up and down in conjunction with the displacement of the liquid level, and the arm 11 rotates accordingly. As the arm 11 rotates, the contact 14 rotates, whereby the resistance value of the variable resistor 3 changes. The voltage applied to the variable resistor 3 and the fixed resistor 7 is divided according to the ratio between the resistance value of the variable resistor 3 and the resistance value of the fixed resistor 7, and the voltage applied to the variable resistor 3 is An output signal of the sensor 2 is detected between the input / output conductive portions 17 and 18.

  Here, when the slidable contact surfaces of the conductive segments 15a of the first conductive pattern 15 and the conductive segments 16a of the second conductive pattern 16 and the contacts 19, 20 of the contactor 14, that is, the contact portions, are exposed to the electrolyte, the sensor 2 When the voltage is continuously applied to the first conductive pattern 15, for example, the conductor of the first conductive pattern 15 on the anode side deteriorates due to electrolytic corrosion, while the second conductive pattern 16 on the negative electrode side has the first conductive pattern 15. Metal ions eluted from the precipitate. The deposited metal tends to be an inactive insulator, and when the slidable contact surface of the conductive segment 16a of the second conductive pattern 16 is covered with an insulator, the contact resistance of the contact portion increases, which hinders accurate measurement.

  Therefore, in the liquid level detection device 1 of the present embodiment, the power supply circuit 4 is configured to intermittently apply a voltage to the sensor 2 at a predetermined cycle, and the energization time for applying the voltage to the sensor 2 is: It is set to 40 ms or less per cycle. Thereby, even when the contact portion is exposed to the electrolytic solution, electrochemical reaction such as electrolytic corrosion at the contact portion is suppressed. Preferably, the ratio of energization time in one cycle, that is, the duty ratio is 50% or less.

  Referring to FIG. 1 again, the liquid level detection device 1 acquires the voltage between the input / output conductive portions 17 and 18 of the sensor 2 by the processing circuit 5 as an output signal of the sensor 2. The processing circuit 5 acquires the output signal of the sensor 2 in synchronization with the cycle in which the power supply circuit 4 applies a voltage to the sensor 2. Then, the processing circuit 5 drives a meter 6 as display means for displaying the remaining amount of liquid based on the acquired output signal of the sensor 2.

In order to confirm the effect of the present invention, the liquid level detection device 1 described above was prepared by changing the energization time to the sensor 2 per cycle in various ways, and was immersed in ethanol-mixed gasoline for 500 hours. The output of each subsequent sensor 2 was measured. The measurement conditions are shown below. Note that the contactor 14 is fixed at a position where the contactor 14 is rotated when the displacement of the liquid in the container is at the lowest position, and measurement is performed. Moreover, the measurement is performed in a state where the entire substrate 13 is immersed in the liquid.
[Measurement condition]
Material of conductive segments 15a and 16a: Silver palladium Material of resistor 15b: Ruthenium oxide Applied voltage to sensor 2: 16V
Ethanol concentration of ethanol mixed gasoline 30%
Ethanol mixed gasoline temperature: 60 ℃
1 cycle: 100 ms

  The measurement results are shown in FIG. In the graph shown in FIG. 5, the output of each sensor is shown at a ratio relative to the output of the sensor before immersion. From the measurement results shown in FIG. 5, when the energization time to the sensor 2 is 40 ms or less, the sensor output increase rate is 0.4% or less, which is within the range that does not hinder the liquid level detection. This is because the contact resistance at the contact portion is not increased, that is, it is understood that an electrochemical reaction such as electrolytic corrosion at the contact portion is suppressed.

  Moreover, the energization time per cycle to the sensor 2 was 10 ms, 20 ms, 40 ms, 60 ms, and constant energization under the above measurement conditions, and the results of measuring the amount of change in the resistance value of each variable resistor 3 on the time axis Is shown in FIG. Further, FIG. 7 shows the result of measuring the amount of change of the resistance value of the variable resistor 3 on the time axis under the above measurement conditions, with the energization time per cycle of the sensor 2 being 5 ms.

  From the measurement results shown in FIG. 6, when the energization time to the sensor 2 is 40 ms or less, the amount of change (increase) in the resistance value of the variable resistor 3 is less than 2Ω, and does not hinder the liquid level detection. It is in range. Furthermore, from the measurement results shown in FIG. 7, when the energization time per cycle to the sensor 2 is 5 ms, there is almost no change in the resistance value of the variable resistor 3, and 5 ms is particularly preferable as the energization time per cycle. I understand.

Next, the first conductive pattern 15 and the second conductive pattern 16 of the sensor 2 of the liquid level detection device 1 described above are maintained in the positional relationship in the sensor 2, and they are immersed in ethanol-mixed gasoline alone to assemble the capacitor. Formed. Then, a voltage was applied to the first conductive pattern 15 and the second conductive pattern 16 with various energization times per cycle varied, and currents flowing through the patterns 15 and 16 were measured. The measurement conditions are shown below.
[Measurement condition]
Material of conductive segments 15a and 16a: Silver palladium Material of resistor 15b: Ruthenium oxide Applied voltage to sensor 2: 16V
Ethanol concentration of ethanol mixed gasoline 30%
Temperature of ethanol mixed gasoline: 18 ℃
1 cycle: 100 ms

  The measurement results for each energization time and the time during which the current value tends to increase are shown in FIG. From the measurement results shown in FIG. 8, it can be seen that when the energization time per cycle is 15 ms or less, the time to the current value rise start point is 60 s or more, and the elution suppression tendency of metal ions is remarkably increased.

  As described above, when a voltage is applied to the sensor 2 intermittently at a predetermined cycle, and the energization time for applying the voltage to the sensor 2 is set to 40 ms or less per cycle, when exposed to the electrolyte, In addition, an electrochemical reaction such as electrolytic corrosion at the contact portion of the variable resistor of the sensor 2 can be suppressed, and thereby the liquid level can be detected with high accuracy over a long period of time.

  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 are not limited as long as the present invention can be achieved.

It is a figure explaining the schematic structure of one Embodiment of the liquid level detection apparatus which concerns on this invention. It is a figure explaining the sensor used for the liquid level detection apparatus of FIG. It is a figure explaining the principal part of the sensor shown in FIG. It is a figure explaining the energy state in the reaction process of electrolytic corrosion. It is a graph which shows the measurement result of a sensor output about an example and a comparative example. It is a graph which shows the measurement result of a sensor resistance value about an example and a comparative example. It is a graph which shows the measurement result of a sensor resistance value about an example. It is a graph which shows the measurement result of an electric current value about an example and a comparative example. It is a figure explaining an example of the conventional liquid level detection apparatus. It is a figure explaining an example of the sensor used for the conventional liquid level detection apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Liquid level detection apparatus 2 Sensor 3 Variable resistor 4 Power supply circuit 5 Processing circuit 6 Meter 10 Float 11 Arm 12 Frame 13 Substrate 14 Contact 15 First conductive pattern 15a Conductive segment 15b Resistor 16 Second conductive pattern 16a Conductive segment 16b Linkage 17 Conductive part for input / output 18 Conductive part for input / output 19 Contact 20 Contact O Rotating shaft of arm

Claims (6)

A variable resistor that is disposed in a container that stores liquid and that changes the resistance value by moving the contact point in conjunction with the displacement of the liquid level, and a predetermined voltage is applied to the resistance value of the variable resistor. A sensor that outputs a voltage signal according to the
A power supply circuit that intermittently applies the voltage to the sensor at a predetermined period;
With
An energization time for applying a voltage to the sensor by the power supply circuit is set to 40 ms or less per cycle.   2. The liquid level detection apparatus according to claim 1, wherein an energization time during which the power supply circuit applies the voltage to the sensor is 15 ms or less per cycle.   3. The liquid level detection device according to claim 2, wherein an energization time during which the power supply circuit applies the voltage to the sensor is more than 1 ms per cycle. 4.   2. The liquid level detection apparatus according to claim 1, wherein an energization time during which the power supply circuit applies the voltage to the sensor is approximately 5 ms per cycle.   The liquid level detecting device according to any one of claims 1 to 4, wherein a ratio of the energization time in one cycle is 50% or less. A variable resistor is disposed in a container storing liquid and changes a resistance value in conjunction with the displacement of the liquid level, and a voltage signal corresponding to the resistance value of the variable resistor is applied by applying a predetermined voltage. In a liquid level detection apparatus comprising: a sensor for outputting; and a power supply circuit that intermittently applies the voltage to the sensor at a predetermined cycle.
The variable resistor is bridged by the first and second conductive patterns extending in parallel with each other and the first and second conductive patterns, and the first and second conductive patterns are interlocked with the displacement of the liquid level. A contact that slides on the pattern, and
When the voltage is applied to the sensor in a state where the contact portion between the first and second conductive patterns and the contactor is insulated, the current flowing through the first and second conductive patterns tends to increase. A design method of a liquid level detecting device, wherein the power supply circuit selects a current-carrying time per cycle during which the power supply circuit applies the voltage to the sensor so that the time until the time is 60 seconds or more.

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