JP2012225788A - Liquid level sensor and liquid level detection apparatus with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid level sensor which is capable of measuring a liquid level of a liquid in a liquid tank in a detailed and accurate manner while ensuring airtightness of the liquid tank, and a liquid level detection apparatus comprising the liquid level sensor.SOLUTION: In a liquid level sensor 8, a second coil 21 of a second circuit 20 disposed in a fuel tank 6 is disposed while being opposed with a first coil 11 of a first circuit 10 disposed outside the fuel tank 6 with a flange 7 sealing an opening 6b of the fuel tank 6 interposed between the second coil and the first coil 11. An electrostatic capacitance body 22 connected to constitute a closed circuit with the second coil 21 in the second circuit 20 is composed of a pair of electrodes 32 which are disposed while being faced proximately with each other, and disposed within the fuel tank 6 in such a manner that a ratio of portions immersed in a fuel, in the pair of overall electrodes 32 is varied in accordance with a liquid level of the fuel F in the fuel tank 6.

Description

  The present invention relates to a liquid level sensor that measures the liquid level of a liquid contained in a liquid tank, and a liquid level detection device having the liquid level sensor.

  The fuel tank mounted on the vehicle is provided with a liquid level sensor for measuring the level of fuel inside the fuel tank (that is, the liquid level is also referred to as the liquid level). Based on the liquid level output measured by the sensor, the remaining amount of fuel in the fuel tank is detected. As such a liquid level sensor, there is a sliding resistance type sensor. The sliding resistance type liquid level sensor is, for example, a float (floating element) that is disposed inside the fuel tank and floats on the liquid level, a float arm that supports the float so as to be able to swing up and down, and a float arm. And a sender resistance as a sliding resistance whose resistance value changes in accordance with the rocking angle. A control device electrically connected to the liquid level sensor by a lead wire or the like is provided outside the fuel tank. The control device is based on a change in the resistance value of the liquid level sensor. Thus, the liquid level of the fuel in the fuel tank is detected, and the remaining amount of fuel in the fuel tank is obtained from the detected liquid level.

  However, for example, in a fuel tank that contains high-pressure fuel such as liquefied petroleum gas, it is important to ensure airtightness. Like the above-described sliding resistance type liquid level sensor, the fuel tank When connecting the liquid level sensor inside and the control device outside the fuel tank with a lead wire, it is necessary to provide a through hole for the lead wire to pass through the wall of the fuel tank. It was difficult to ensure sufficient airtightness. And the technique which solves such a problem is disclosed by patent document 1. FIG.

  As shown in FIGS. 9 and 10, an object detection apparatus 800 described in Patent Document 1 includes a sensor unit 801, an oscillation unit 802 that transmits a high-frequency signal to the sensor unit 801 via a transmission path 804, and a sensor. And a reflected wave sensor 803 that detects a reflected signal that is reflected by the sensor unit 801 and returned to the oscillating unit 802 side.

  In the object detection device 800, a high frequency signal is supplied from the oscillation unit 802 to the sensor unit 801 via the transmission path 804. The resonance frequency of the resonance circuit is set to match the frequency of the oscillation unit 802, and when there is no object in the vicinity of the sensor unit 801 (that is, only air), the impedance of the sensor unit 801 and the transmission path 804 It is adjusted so that the impedance matching can be taken.

  As a result, if there is no object in the vicinity of the sensor unit 801, the reflection of the high-frequency signal sent from the oscillation unit 802 becomes 0 and the output from the reflected wave sensor 803 becomes 0, so that “no object” is detected. it can. Further, when an object is present in the vicinity of the sensor unit 801, the impedance of the sensor unit 801 changes due to the magnetic influence due to the difference in permeability between air and the object, and the impedance of the sensor unit 801 greatly deviates from the matching impedance. Then, the reflected signal also becomes large, and this reflected signal is detected by the reflected wave sensor 803, and an analog signal corresponding to the change of the reflected wave, that is, the impedance is output, so that “object present” can be detected. By applying such an object detection device 800, the liquid level of the fuel inside the fuel tank can be detected from the outside of the fuel tank without providing a through hole in the fuel tank.

Japanese Patent Laid-Open No. 9-43007

  However, as can be seen from the configuration of FIG. 10, the object detection device 800 described above can detect whether or not the fuel level in the fuel tank is equal to or higher than a predetermined level, but the level of the fuel is detailed and accurate. There was a problem that it could not be detected.

  The present invention aims to solve the above problems. That is, the present invention provides a liquid level sensor capable of measuring the liquid level in the liquid tank in detail and accurately while ensuring airtightness of the liquid tank, and a liquid level detection having the liquid level sensor. The object is to provide a device.

  In order to achieve the above object, the invention described in claim 1 is a liquid level sensor that measures the liquid level of the liquid stored in the liquid tank, and is disposed outside the liquid tank. A first circuit having a first coil, a second coil disposed in the liquid tank, disposed so as to be magnetically coupled to the first coil, and the second coil constitute a closed circuit. A second circuit having a capacitance body connected in the manner described above, and the capacitance body is configured by a pair of electrodes disposed to face each other in close proximity to each other, and in the liquid tank The liquid level sensor is arranged in the liquid tank so that a ratio of a portion of the pair of electrodes immersed in the liquid changes according to a liquid level of the liquid.

  The invention described in claim 2 is the invention described in claim 1, wherein each of the pair of electrodes is covered with an insulating material.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, the pair of electrodes is configured by a wiring pattern formed in a comb-tooth shape that meshes with each other on an insulating base material. It is characterized by.

  The invention described in claim 4 is a liquid level detecting device for detecting the liquid level of the liquid stored in the liquid tank in order to achieve the above object. And an AC signal generator connected to one terminal of the first coil of the liquid level sensor, and an AC signal generator that outputs an AC signal, and the first coil of the liquid level sensor And a liquid level detecting unit that detects the liquid level based on a signal of the other terminal connected to the other terminal of the liquid level detecting device. .

  According to the first aspect of the present invention, the second coil of the second circuit disposed in the liquid tank is magnetically coupled to the first coil of the first circuit disposed outside the liquid tank. Are arranged as follows. In addition, the electrostatic capacity body connected to form a closed circuit with the second coil is composed of a pair of electrodes disposed in close proximity to each other and according to the liquid level of the liquid in the liquid tank. Since the ratio of the portion immersed in the liquid in the whole of the pair of electrodes is arranged in the liquid tank, the dielectric constant between the liquid in the liquid tank and the liquid is changed to the liquid level. Accordingly, the capacitance between the pair of electrodes changes, and therefore the resonance frequency of the second circuit changes. That is, since the first circuit outside the liquid tank and the second circuit inside the liquid tank are magnetically coupled, an AC signal is transmitted from the first circuit to the second circuit, and from the second circuit to the first circuit. The reflected signal of the AC signal is transmitted, so that the signal can be transmitted between the first circuit and the second circuit without providing a through hole in the liquid tank. Then, since the resonance frequency of the second circuit changes according to the liquid level of the liquid in the liquid tank, the magnitude of the reflected signal returning from the second circuit to the first circuit changes, and therefore, the resonance in the first circuit. Frequency shift occurs and impedance changes.

  According to the invention described in claim 2, since each of the pair of electrodes constituting the capacitance body is covered with the insulating material, when the liquid in the liquid tank has conductivity, the liquid It is possible to prevent a current from flowing between the electrodes.

  According to the invention described in claim 3, the pair of electrodes constituting the capacitance body is configured by the wiring pattern formed in a comb-tooth shape that meshes with each other on the insulating base material. The electrode length can be increased compared to the formed wiring pattern.

  According to the invention described in claim 4, the liquid level sensor according to any one of claims 1 to 3 is provided, an AC signal is input to the liquid level sensor, and the liquid level The liquid level is detected based on the signal output from the sensor.

  According to the first aspect of the present invention, since the signal can be transmitted between the first circuit and the second circuit without providing the through hole in the liquid tank, the airtightness of the liquid tank can be ensured. Further, since the impedance of the first circuit changes according to the liquid level of the liquid in the liquid tank, the liquid level can be measured in detail and accurately based on this impedance.

  According to the second aspect of the present invention, when the liquid in the liquid tank has conductivity, it is possible to prevent a current from flowing between the electrodes through the liquid. Can be measured.

  According to the invention described in claim 3, since the electrode length can be made longer than the wiring pattern formed in a straight line, the capacitance per liquid level in the capacitance body can be increased. The change in capacitance with respect to the change in liquid level can be increased, and the liquid level can be measured more accurately.

  According to the invention described in claim 4, the liquid level sensor according to any one of claims 1 to 3 is provided, an AC signal is input to the liquid level sensor, and the liquid level Since the liquid level is detected based on the signal output from the sensor, the liquid level can be measured in detail and accurately based on the impedance of the liquid level sensor.

It is a figure which shows the structure of one Embodiment of the liquid level detection apparatus of this invention. It is a figure which shows the circuit structure of the liquid level detection apparatus of FIG. (A) is a figure which shows an example of a structure of a pair of electrode of the electrostatic capacitance body of the liquid level sensor of FIG. 1, (b) is a figure which shows another example of a structure of the said pair of electrode. is there. It is a figure explaining the change of the impedance of the 1st circuit with respect to the electrostatic capacitance change of the electrostatic capacitance body of the liquid level sensor of FIG. It is a graph which shows an example of the alternating voltage signal which the alternating current signal generation part of FIG. 1 outputs. It is a graph which shows an example of the signal which the liquid level sensor of FIG. 1 outputs. It is a graph which shows an example of the DC voltage signal which the rectifier circuit of the liquid level detection part of FIG. 1 outputs. It is a graph which shows an example of the relationship between the electrostatic capacitance value of the capacitive body of a liquid level sensor, the frequency of the alternating voltage signal input into a liquid level sensor, and the passage characteristic of a 1st circuit. It is a figure which shows the circuit structure of the conventional object detection apparatus. It is a figure which shows an example of a structure which detects a liquid level by the object detection apparatus of FIG.

  Hereinafter, an embodiment of the liquid level detection device of the present invention will be described with reference to FIGS.

  A fuel tank 6 as a liquid tank as shown in FIG. 1 is mounted on the vehicle. The fuel tank 6 is made of, for example, a material having high rigidity and corrosion resistance, such as stainless steel. In this embodiment, the fuel tank 6 is formed in a substantially rectangular parallelepiped box shape, and the upper wall A circular opening 6b is provided in the portion 6a. The fuel tank 6 is provided with a disk-shaped flange 7 that closes the opening 6b so as to be hermetically sealed.

  The flange 7 is made of, for example, a non-conductive synthetic resin having excellent rigidity and chemical resistance such as polyphenylene sulfide resin (PPS resin). That is, the flange 7 constitutes a nonconductive wall portion of the fuel tank 6. A first coil 11 of the first circuit 10 and a second coil 21 of the second circuit 20, which will be described later, are arranged in parallel to face each other so as to be magnetically coupled to each other at the center portions of the upper surface 7a and the lower surface 7b of the flange 7. Is done. When the flange 7 is made of a resin material, it may be sandwiched between, for example, the first coil 11 and the second coil 21 because there is a possibility of a creep problem or a poor smoothness of the packing portion, which may cause a problem in airtightness. The flange 7 may be formed by combining a metal material and a resin material with only the portion being a resin material and the other portion being a metal material.

  The fuel tank 6 contains liquid fuel F. The vehicle is equipped with a liquid level detecting device 1 that detects the level of the fuel F together with the fuel tank 6.

  As shown in FIGS. 1 and 2, the liquid level detection device 1 includes a liquid level sensor 8, an AC signal generator 40, and a liquid level detector 50.

  The liquid level sensor 8 includes a first circuit 10 disposed outside the fuel tank 6 and a second circuit 20 disposed inside the fuel tank 6.

  The first circuit 10 includes a first coil 11 and an impedance matching capacitor 12 connected in parallel to the first coil 11. The first coil 11 is formed of a flat spiral wiring pattern formed on a printed circuit board (PCB), and is fixed on the upper surface 7a of the flange 7 so as to be densely stacked. The impedance matching capacitor 12 is composed of, for example, a surface mount type multilayer ceramic capacitor or the like, and is mounted on the PCB. The impedance matching capacitor 12, together with the first coil 11 and the second circuit 20 described later, is the liquid level sensor 8 when the output impedance of the AC signal generator 40 and the liquid level of the fuel F in the fuel tank 6 are zero. The input impedance is determined so that the input impedance matches. Further, by providing such an impedance matching capacitor 12, the impedances of the first circuit and the second circuit can be matched with respect to an arbitrary input frequency. Therefore, the first coil 11 and the second circuit 20 are matched. The transmission efficiency with the second coil 21 can be increased, and these coils can be reduced in size.

  The second circuit 20 includes a second coil 21 integrally formed by a wiring pattern laid on one support member 31 made of plastic having plasticity as an insulating base, and the second coil 21. The capacitance body 22 is connected so as to form a closed circuit, and the parallel resonance coil 23 is connected in parallel to the capacitance body 22. The second coil 21, the capacitance body 22, and the parallel resonance coil 23 are sandwiched between a support member 31 and a resin film 33 as an insulating material so as to be insulated from the fuel F.

  The second coil 21 is configured by a flat spiral wiring pattern formed on the support member 31, and is densely attached to the lower surface 7 b of the flange 7 described above so that the centers of the first coil 11 and each other coincide. It is fixed to overlap. Accordingly, the first coil 11 and the second coil 21 are disposed to face each other with the flange 7 interposed therebetween, and the second coil 21 is magnetically coupled to the first coil 11. In other words, by installing the first coil 11 and the second coil 21 on both surfaces of the non-conductive flange 7, the inside and outside of the fuel tank 6 are physically isolated while enabling signal transmission between each other. A complicated structure for taking out the lead wire is not required, and the airtightness of the fuel tank 6 is not impaired. Further, it is desirable to make the portion of the flange 7 sandwiched between the first coil 11 and the second coil 21 as thin as possible within a range in which a withstand voltage can be secured in order to increase the magnetic coupling efficiency.

  The electrostatic capacity body 22 is composed of a pair of electrodes 32 each having a comb-like wiring pattern formed on the support member 31 so as to store charges in close proximity to each other and to be engaged with each other. The capacitance body 22 is formed so that the total length of the pair of electrodes 32 is substantially the same as the height of the fuel tank 6, and the total length direction of the pair of electrodes 32 (the vertical direction in FIG. 3A) is the fuel tank. The distance between the pair of electrodes 32 so as not to be affected by the one side wall 6c of the fuel tank 6 (that is, the electric field does not change by the fuel tank 6) is set so as to be parallel to the height direction of the fuel tank 6. Open and fixed. Thus, for example, when the liquid level in the fuel tank 6 is 0% (no fuel F), the ratio of the portion immersed in the fuel F in the entire pair of electrodes 32 is 0%, and the liquid level is 30%. In this case, the ratio of the portion immersed in the fuel F in the entire pair of electrodes 32 is 30%, and the ratio of the portion immersed in the fuel F in the entire pair of electrodes 32 is 100% when the liquid level is 100%. That is, the amount of the fuel F that enters between the pair of electrodes 32 changes according to the liquid level, and the air in the fuel tank 6, the vaporized fuel F (hereinafter referred to as air), and the liquid fuel Since the dielectric constant is different from that of F, the capacitance value of the capacitance body 22 changes.

  An example of the configuration of the pair of electrodes 32 is shown in FIG. Of course, the pair of electrodes 32 is not limited to such a configuration. For example, as shown in FIG. 3B, linear wirings formed in parallel and close to each other on the support member 31. It may be a pattern. However, in the comb-like wiring pattern, the length of the electrode is substantially longer, and the change in the capacitance can be increased with respect to the change in the liquid level. In addition to these configurations, parallel plates and double cylinders arranged opposite to each other are arranged close to each other so as to be able to accumulate electric charges and according to the level of the fuel F in the fuel tank 6. What is necessary is just to be arrange | positioned in the fuel tank 6 so that the ratio of the part immersed in the fuel F among the whole pair of electrodes 32 may change.

  The parallel resonance coil 23 is configured by a flat spiral wiring pattern formed on the support member 31 similarly to the second coil 21, and the parallel resonance coil 23 is disposed between the lower wall portion 6 d of the fuel tank 6 and the parallel resonance coil 23. Is fixed at a distance that is not affected (that is, the characteristics are not changed by the fuel tank 6). The parallel resonance coil 23 needs to be arranged so as not to be magnetically coupled to the first coil 11 and the second coil 21 described above, and is arranged at a distance so as not to be magnetically coupled as in the present embodiment, or The first coil 11 and the second coil 21 are arranged so that their central axes are orthogonal to each other. Further, by arranging the parallel resonance coil 23 on the lower wall portion 6d of the fuel tank 6, the dielectric constant around the parallel resonance coil 23 does not change unless the fuel F in the fuel tank 6 is emptied. The influence of the inductance change due to the arrangement location can be reduced. Further, by forming a parallel resonance circuit in the second circuit 20 by the capacitance body 22 and the parallel resonance coil 23, a change in the capacitance value of the capacitance body 22, that is, the second circuit with respect to the liquid level. For example, a change in capacitance value, that is, a change in liquid level can be measured more broadly than a series resonant circuit having a sharp change in impedance. Further, the resonance frequency of the second circuit 20 can be adjusted by adjusting the inductance of the parallel resonance coil 23. The parallel resonance coil 23 may be constituted by, for example, a surface mount type micro inductor other than the wiring pattern described above. In addition, the structure which does not provide the parallel resonance coil 23 may be sufficient.

  The second coil 21, the capacitance body 22 (a pair of electrodes 32), and the parallel resonance coil 23 are patterned directly on the support member 31 by, for example, metal plating or sputtering, or patterned by punching or etching. Each is integrally formed by attaching a metal foil on the support member 31. By doing so, it is possible to reduce the number of parts, keep the cost low, and simplify the configuration. Of course, you may comprise the 2nd coil 21, the electrostatic capacitance body 22 (a pair of electrodes 32), and the parallel resonance coil 23 by a separate component, respectively.

  Even if the fuel tank 6 has a complicated shape, the second circuit 20 is formed along the shape by forming the second circuit 20 on the support member 31 or the flexible printed circuit board (FPC) made of the plastic having the above-described plasticity. it can. The plastic constituting the support member 31 may be made of a material having resistance to the fuel F (such as chemical resistance). Further, the second coil 21, the capacitance body 22 (a pair of electrodes 32), and the parallel resonance coil 23 are also configured so that the fuel F is directly in contact with the fuel F without providing the resin film 33. In addition to copper, a thin metal such as nickel or SUS can be used in addition to copper, so that it can be used even in highly corrosive fuel F.

  In the liquid level sensor 8 described above, the capacitance value (C2) of the capacitance body 22 included in the second circuit 20 constituting the LC resonance circuit disposed in the fuel tank 6 depends on the liquid level. This is a liquid level sensor that utilizes the change of the resonance frequency along with this change, and the change is detected by the first circuit 10 constituting the LC resonance circuit disposed outside the fuel tank 6. . Since the magnitude of the reflected wave from the second coil 21 to the first coil 11 in the fuel tank 6 changes as the resonance frequency of the second circuit 20 changes according to the liquid level, the magnitude of the reflected wave In response to this, a change in impedance due to a shift in resonance frequency occurs. The resonance frequency is represented by f = 1 / (2π√LC), and in the case of a parallel resonance circuit, the impedance becomes maximum at the resonance point.

  For example, the first circuit 10 outside the fuel tank 6 is supplied with an AC voltage signal having a constant input frequency that increases the impedance near the resonance frequency. Since the capacitance value (C2) of the capacitance body 22 of the second circuit 20 constituting the LC resonance circuit in the fuel tank 6 changes depending on the liquid level, the impedance of the second circuit 20 changes. Since the first coil 11 of the first circuit 10 and the second coil 21 of the second circuit 20 are magnetically coupled, the AC voltage signal supplied to the first circuit 10 is transmitted to the second circuit 20, Then, a reflected wave is generated from the second circuit 20 to the first circuit 10 due to the impedance matching shift of these circuits, and a resonance frequency shift is also generated in the first circuit 10 outside the fuel tank 6 to change the impedance. Since the magnitude of the reflected wave changes depending on the magnitude of the capacitance value (C2) of the capacitance body 22 of the second circuit 20, the level of the impedance change of the first circuit 10 is read as a voltage to obtain the liquid level. The level can be detected.

  FIG. 4 shows the impedance characteristics of the first circuit 10. Ca, Cb, and Cc are capacitance values (C2) of the capacitance body 22 of the second circuit 20, and impedances when the capacitance values (C2) fluctuate in a relationship of Ca <Cb <Cc, respectively. It is a change in characteristics. If the impedance of the first circuit 10 is maximized when the capacitance value (C2) in the fuel tank 6 is Ca at a certain frequency (f0), the matching with the second circuit 20 is Since it is good (impedance matching is achieved), the reflected wave is small and the impedance is Za. When the capacitance value (C2) changes to Cb, a reflected wave is generated and the impedance becomes Zb. When the capacitance value (C2) changes to Cc, the impedance becomes Zc and the impedance decreases continuously. Happens. Thus, by inputting an AC voltage signal having a constant frequency and a constant amplitude to the liquid level sensor 8, the impedance of the first circuit 10, that is, the AC voltage signal having an amplitude corresponding to the liquid level is changed to the liquid level. Since it is output from the sensor 8, the liquid level is detected based on the output voltage of the liquid level sensor 8.

  The AC signal generator 40 is configured to amplify a constant frequency AC voltage signal generated by, for example, an LC resonance circuit, a crystal oscillator, or a PLL circuit to a constant amplitude by an amplifier such as an operational amplifier, and output the amplified signal. Has been. The AC signal generator 40 is connected to one end of the first coil 11 included in the first circuit 10 of the liquid level sensor 8, and directs an AC voltage signal having a constant frequency and amplitude to the liquid level sensor 8. Output.

  The liquid level detector 50 includes, for example, a diode 51 and a capacitor 52, and includes a rectifier circuit 53 that rectifies a signal output from the liquid level sensor 8 into a DC voltage signal, and a microcomputer (MPU) 54. Have.

  The MPU 54 includes a central processing unit (CPU), a ROM, a RAM, a data memory, an external interface, and the like (not shown).

  The CPU performs various types of control in the liquid level detection apparatus 1 and executes various types of processing including control according to the present embodiment in accordance with various control programs stored in the ROM. The ROM stores various information such as the control program and parameters referred to by the control program. In particular, the ROM stores a control program for causing the CPU to function as various means such as a liquid level detecting means. And CPU functions as various means mentioned above by running this control program. The RAM appropriately stores data, programs and the like necessary for the CPU to execute various processes. The data memory is composed of a nonvolatile memory that can retain data even when the power is cut off, such as an EEPROM or a flash memory. The data memory stores various information such as parameters. In particular, this data memory stores a data table indicating the relationship between the DC voltage signal from the rectifier circuit 53 and the liquid level of the fuel F in the fuel tank 6. The external interface includes an analog-digital converter (A / D converter) to which a DC voltage signal from the rectifier circuit 53 is input, and a DC voltage converted from an analog value to a digital value by the analog-digital converter. A signal (ie, voltage value) is sent to the CPU. The external interface is connected to a vehicle network (not shown) so as to be able to communicate with other electronic equipment (ECU) such as a combination meter device equipped with a fuel gauge.

  The AC signal generator 40 generates an AC voltage signal having a constant frequency and a constant amplitude and outputs the AC voltage signal to the liquid level sensor 8. The liquid level sensor 8 has an impedance corresponding to the liquid level of the fuel F in the fuel tank 6, and a signal whose amplitude has changed from the AC voltage signal in accordance with this impedance is output from the liquid level sensor 8. The When the signal output from the liquid level sensor 8 is rectified into a DC voltage signal by the rectifier circuit 53 and this DC voltage signal is sent to the CPU through the A / D converter, the CPU detects the voltage of the DC voltage signal. The value is applied to the data table stored in the data memory, and the liquid level of the fuel tank 6 is acquired. Then, the CPU calculates the remaining amount of the fuel F in the fuel tank 6 from the liquid level, generates information indicating the remaining amount, and transmits the information to the meter device through the external interface. The meter device displays the remaining amount of fuel on the fuel gauge based on the information indicating the remaining amount.

  Next, an example of the operation (action) according to the present invention of the liquid level detection device 1 described above will be described with reference to FIGS. FIG. 5 shows an example of the waveform of the AC voltage signal output from the AC signal generator 40. FIG. 6 shows an example of a waveform of a signal output from the liquid level sensor 8. FIG. 7 shows an example of the waveform of the DC voltage signal output from the rectifier circuit 53 of the liquid level detector 50.

In the AC signal generator 40, an AC voltage signal having a constant frequency (15 MHz) and a constant amplitude of 5 V _PP (−2.5 V to +2.5 V) as shown in FIG. 5 is generated and input to the liquid level sensor 8. . In the liquid level sensor 8, the change range of the capacitance value (C2) due to the change of the liquid level in the capacitance body 22 of the second circuit 20 is 10 pF to 200 pF. When (fuel F is 0) and 200 pF, the pair of electrodes 32 is configured so that the liquid level is 100% (fuel F is full). At this time, when the adjustment is made so that the reflected wave from the second circuit 20 to the first circuit 10 is minimized at 10 pF, the liquid level is the lowest (capacitance value ( When C2) is 10 pF), the impedance of the first circuit 10 is maximized, the amplitude of the signal output from the liquid level sensor 8 is minimized, and the liquid level is increased to increase the capacitance value. When the amplitude of the signal output from the liquid level sensor 8 increases and the liquid level is the highest (the capacitance value (C2) is 200 pF), the impedance of the first circuit 10 is minimized and the liquid level sensor 8 The amplitude of the output signal is maximized. Then, when the signal output from the liquid level sensor 8 passes through the rectifier circuit 53 of the liquid level detector 50, it is rectified to a DC voltage signal as shown in FIG. 7, and this DC voltage signal is input to the MPU. Then, the liquid level according to the voltage value of the DC voltage signal is detected by the CPU.

  Note that the first coil 11 and the second coil 21 change the impedance of the first circuit 10 with respect to the change in the capacitance value of the capacitance body 22 (that is, the change in the signal output from the liquid level sensor 8). And the coupling coefficient of these coils and the inductance of the parallel resonance coil 23 can be arbitrarily changed.

  As described above, according to the present embodiment, the second coil 21 of the second circuit 20 disposed in the fuel tank 6 is in contact with the first coil 11 of the first circuit 10 disposed outside the fuel tank 6. The second coil 21 is disposed so as to be magnetically coupled to the first coil 11 because the flange 7 that seals the opening 6b of the fuel tank 6 is interposed between the first coil 11 and the first coil 11. Yes. In addition, the capacitance body 22 connected so as to form a closed circuit with the second coil 21 is constituted by a pair of electrodes 32 disposed in close proximity to each other and the liquid of the fuel F in the fuel tank 6. Since the ratio of the portion immersed in the fuel F in the whole of the pair of electrodes 32 changes according to the surface level, the dielectric between the air in the fuel tank 6 and the fuel F is arranged. By changing the rate, the capacitance value between the pair of electrodes 32 (that is, the capacitance body 22) changes according to the liquid level, and therefore the resonance frequency of the second circuit 20 changes.

  That is, since the first circuit 10 outside the fuel tank 6 and the second circuit 20 in the fuel tank 6 are magnetically coupled, an AC voltage signal is transmitted from the first circuit 10 to the second circuit 20, and The reflected signal of the AC voltage signal is transmitted from the two circuits 20 to the first circuit 10, so that the signal can be transmitted between the first circuit 10 and the second circuit 20 without providing a through hole in the liquid tank. The airtightness of the fuel tank 6 can be ensured. In addition, since the resonance frequency of the second circuit 20 changes according to the liquid level of the fuel F in the fuel tank 6, the magnitude of the reflected signal (reflected wave) returning from the second circuit 20 to the first circuit 10 changes. Therefore, the resonance frequency shifts in the first circuit 10 and the impedance changes. That is, since the impedance of the first circuit 10 changes according to the liquid level of the fuel F in the fuel tank 6, the liquid level can be measured in detail and accurately based on this impedance.

  Further, each of the pair of electrodes 32 constituting the capacitance body 22 is sandwiched and covered between the support member 31 and the resin film, which are insulating materials, so as to be insulated from the fuel F. When the fuel F in the fuel tank 6 has conductivity, it is possible to prevent a current from flowing between the electrodes 32 through the fuel F. Therefore, the liquid level of the fuel F having conductivity can be measured. it can.

  In addition, since the pair of electrodes 32 constituting the capacitance body 22 is composed of a wiring pattern formed in a comb-tooth shape that meshes with each other on the support member 31, compared to a wiring pattern formed in a linear shape. The electrode length can be increased, and therefore the capacitance per liquid level in the capacitance body 22 can be increased. Therefore, the change in the capacitance value with respect to the change in the liquid level can be increased. The surface level can be measured more accurately.

  In addition, since the first circuit 10 further includes an impedance matching capacitor 12 connected in parallel with the first coil 11, the first coil 11 and the second coil 21 can be connected to any input frequency. The transmission efficiency can be increased, so that it is not necessary to increase the magnetic coupling efficiency using a large coil, and the first coil 11 and the second coil 21 can be reduced in size. In order to increase the magnetic coupling efficiency, it is effective to shorten the distance between the coils. However, by reducing the size of the first coil 11 and the second coil 21, the area of the flange 7 of the fuel tank 6 or the flange 7 is provided. The area of the thin wall portion where the coils 11 and 21 are fixed can be reduced, the pressure resistance of the flange 7 can be increased, and the pressure resistance of the entire fuel tank 6 can be ensured.

  Further, since the second circuit 20 further includes a parallel resonance coil 23 connected in parallel with the capacitance body 22, the change in the capacitance value of the capacitance body 22, that is, against the liquid level. The change in impedance becomes gentle. For example, compared to a series resonance circuit in which the change in impedance is steep, a change in a wide capacitance value, that is, a change in liquid level can be measured.

  Further, the liquid level detecting device 1 has the liquid level sensor 8 described above, and inputs an AC voltage signal to the liquid level sensor 8 and also controls the liquid level based on the signal output from the liquid level sensor 8. Since the surface level is detected, the liquid level can be measured in detail and accurately based on the impedance of the liquid level sensor 8 while ensuring the airtightness of the fuel tank 6.

  In the above-described embodiment, the AC signal generator 40 generates an AC voltage signal having a constant frequency and amplitude and inputs the AC voltage signal to the liquid level sensor 8. However, the present invention is not limited to this. For example, in the AC signal generation unit 40, an AC voltage signal whose frequency gradually changes (frequency swept) is generated and input to the liquid level sensor 8, and the signal of the liquid level sensor 8 passes through the first circuit. Based on the frequency when the characteristic is minimized (that is, when the impedance of the first circuit 10 is maximized), the capacitance value of the capacitance body 22, that is, the liquid level is detected. May be.

  In the present embodiment, the first coil 11 and the second coil 21 described above are configured by a flat spiral wiring pattern, but are not limited thereto. For example, The configurations of the first coil 11 and the second coil 21 are arbitrary as long as they are magnetically coupled to each other, such as solenoid-type (cylindrical) coils arranged coaxially with each other. Moreover, although the 1st coil 11 and the 2nd coil 21 were each provided in the nonelectroconductive flange 7, it is not limited to this, For example, fuel tank 6 itself is comprised with a nonelectroconductive material. In such a case, the first coil 11 and the second coil 21 may be disposed so as to face each other with the wall portion of the fuel tank 6 interposed therebetween.

  The above-described embodiment describes the liquid level detecting device that detects the liquid level of the fuel F in the fuel tank that is mounted on the vehicle and stores the liquefied gas. However, the present invention is not limited to this. Absent. For example, it may be a liquid level detector that is installed in a factory or home, and contains various fuels or various chemicals and detects the liquid level thereof. The apparatus and system to which the liquid level sensor and the liquid level detector are applied are arbitrary. In addition, liquids that are subject to liquid level measurement include, for example, vehicle fuels such as petroleum liquefied gas, ethanol, gasoline, and light oil, liquefied gases for industrial use such as nitrogen, oxygen, and ammonia, and various chemical solutions. As long as the object of the invention is not violated, the type is arbitrary.

  In addition, embodiment mentioned above only showed the typical form of this invention, and this invention is not limited to embodiment. That is, various modifications can be made without departing from the scope of the present invention.

1 Liquid level detector 6 Fuel tank (liquid tank)
7 Flange 8 Liquid Level Sensor 10 First Circuit 11 First Coil 12 Impedance Matching Capacitor 20 Second Circuit 21 Second Coil 22 Capacitance Body 23 Parallel Resonant Coil 31 Support Member (Insulating Base Material)
32 Pair of electrodes 33 Resin film (insulating material)
40 AC signal generator 50 Liquid level detector 53 Rectifier circuit

Claims (4)

A liquid level sensor for measuring a liquid level of a liquid stored in a liquid tank,
A first circuit having a first coil disposed outside the liquid tank;
A second coil disposed in the liquid tank and disposed so as to be magnetically coupled to the first coil; a capacitance body connected to form a closed circuit with the second coil; A second circuit having
The electrostatic capacity body is composed of a pair of electrodes disposed in close proximity to each other, and a portion of the entire pair of electrodes that is immersed in the liquid according to the liquid level of the liquid in the liquid tank It is arrange | positioned in the said liquid tank so that the ratio may change, The liquid level sensor characterized by the above-mentioned.   The liquid level sensor according to claim 1, wherein each of the pair of electrodes is covered with an insulating material.   3. The liquid level sensor according to claim 1, wherein the pair of electrodes is formed of a wiring pattern formed in a comb-tooth shape that meshes with each other on an insulating base material. A liquid level detecting device for detecting a liquid level of a liquid stored in a liquid tank,
The liquid level sensor according to any one of claims 1 to 3,
An AC signal generator connected to one terminal of the first coil of the liquid level sensor and outputting an AC signal;
A liquid level detecting unit connected to the other terminal of the first coil of the liquid level sensor and detecting the liquid level based on a signal of the other terminal; Liquid level detection device.

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