JP2011080881A - Liquid-level detection apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately detect a liquid level of a liquid in a container, if the properties of the liquid to be housed in the container change. <P>SOLUTION: A liquid level detector includes a detecting section 26 having light-propagation agents 32, 34 and 36; and a determining section determining the liquid level of the liquid based on detection results detected by the detecting section. The light-propagation agents 32, 34 and 36 change an intensity of light to be propagated, depending on a type of a substance coming into contact with a sensing section, and a contact area of the substance and the sensing section. The detecting section detects the intensity of first light to be propagated by the light-propagation agents, when the contact area of the sensing section and the liquid responds to the liquid level; the intensity of second light to be propagated by the light-propagating agents, when the liquid comes into an entire surface of the sensing section; and the intensity of third light to be propagated by the light-propagating agents when a reference substance comes into contact with the entire surface of the sensing section. The determining section determines the liquid level of the liquid in the container based on the first light intensity, the second light intensity, and the third light intensity to be detected by the detecting section. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a liquid level detection device that detects a liquid level of a liquid stored in a container.

  Patent Document 1 discloses a liquid level detection device that detects the liquid level of a liquid stored in a container. This liquid level detection device has a light source, an optical fiber on which light from the light source is incident, and a photodetector that detects the intensity of light propagated through the optical fiber. A sensing unit is provided in a part of the optical fiber. The sensing unit is disposed in the container and extends in the vertical direction (that is, the direction perpendicular to the liquid level in the container when the container is horizontally disposed). For this reason, when the liquid level of the liquid in the container changes, the area of the sensing unit in contact with the liquid changes, and the intensity of light propagating through the optical fiber changes. The level of the liquid in the container is detected by detecting the change in the intensity of the light with a photodetector.

JP 2008-170327 A

  In this type of liquid level detection device, the intensity of light propagating through the optical fiber also changes depending on the properties of the liquid stored in the container. In general, since the influence of the liquid property is small, the liquid level can be detected at a level with no practical problem. However, in recent years, the types of liquid stored in containers have diversified, and depending on the stored liquid, there are cases where the influence of liquid properties cannot be ignored. For example, in recent years, the use of a fuel containing alcohol (such as bioethanol) as a fuel for an internal combustion engine has been studied. In such fuels, the ratio of gasoline and alcohol is often not constant, and as a result, it is considered that the properties of the fuel stored in the tank change greatly each time fuel is supplied. In such a case, when a conventional liquid level detection device is used, the liquid level of the liquid in the container may not be detected accurately.

  The present application has been made in view of the above circumstances, and can accurately detect the liquid level in the container even when the properties of the liquid contained in the container change. An object is to provide a liquid level detection device.

The liquid level detection device of the present application detects the liquid level of the liquid stored in the container. This liquid level detection device uses a detection unit having at least one light propagating body provided with a sensing unit, and a detection result detected by the detection unit to detect the liquid level of the liquid stored in the container. It has the determination part which determines. The light propagating body changes the intensity of light propagating in accordance with the type of substance that contacts the sensing unit and the contact area between the substance and the sensing unit. (1) The intensity of the first light propagated by the light propagating body when the contact area between the sensing unit and the liquid in the container corresponds to the liquid level of the liquid in the container; 2) Intensity of the second light propagated by the light propagating body when the liquid in the container contacts the entire surface of the sensing unit, and (3) Propagated by the light propagating unit when the reference substance contacts the entire surface of the sensing unit. Detecting the intensity of the third light. The determination unit determines the liquid level in the container from the intensity of the first light, the intensity of the second light, and the intensity of the third light detected by the detection unit.
The liquid level detection device includes a first light intensity (light intensity when the contact area between the sensing unit and the liquid corresponds to the liquid level) and a second light intensity (the liquid is present on the entire surface of the sensing unit). Based on the light intensity at the time of contact) and the third light intensity (light intensity at the time when the reference substance contacts the entire surface of the sensing unit), the liquid level of the liquid in the container is determined. Since the characteristics (properties) of the reference substance are known, the properties of the liquid in the container can be specified from the relationship between the second light intensity and the third light intensity. For this reason, the liquid level of the liquid in the container is corrected by correcting the first light intensity according to the liquid level from the relationship between the second light intensity and the third light intensity according to the property of the liquid. It can be determined with high accuracy.

  In the liquid level detection device, the determination unit preferably further determines the property of the liquid in the container from the intensity of the second light and the intensity of the third light detected by the detection unit. Thereby, the liquid level and properties of the liquid in the container can be detected by the same device.

  The liquid level detection device described above can take the following aspects. That is, the detection unit includes a first light propagating body, a second light propagating body, a third light propagating body, a first housing that houses the second light propagating body, and a third light. It has the 2nd container which accommodates a propagation body. In the first light propagating body, the contact area between the sensing unit and the liquid in the container changes according to the liquid level of the liquid in the container. The first container can be filled with the liquid in the container, and the second container can be filled with the reference substance. According to such a configuration, the first light intensity can be detected from the light propagated by the first light propagating body, the second light intensity can be detected from the light propagated by the second light propagating body, The third light intensity can be detected from the light propagated by the three light propagating bodies.

  Further, the liquid level detection device described above may take the following mode. That is, the detection unit includes a first light propagating body, a second light propagating body, and a housing that houses the second light propagating body. In the first light propagating body, the contact area between the sensing unit and the liquid in the container changes according to the liquid level of the liquid in the container. The container can be switched between a first state filled with the reference substance and a second state filled with the liquid in the container. According to such a configuration, the first light intensity can be detected from the light propagated by the first light propagating body, and the second light propagating body can be switched by switching between the first state and the second state. It is possible to detect the second light intensity and the third light intensity from the light propagated in the above.

  In the liquid level detection device described above, a water repellent layer may be formed on at least a part of the surface of the first light propagating body. According to such a configuration, when the liquid level of the liquid in the container changes and a part of the first light propagating body is exposed from the liquid to the outside of the liquid, the liquid adhering to the exposed part Is repelled by the water repellent layer and flows down from the surface of the first light propagating body. Therefore, a decrease in the liquid level detection accuracy due to the liquid adhering to the surface of the first light propagating body due to surface tension or the like is prevented.

  In the liquid level detection device described above, when the container is installed on a horizontal plane, at least a part of the first light propagating body extends in the vertical direction and a sensing unit is formed. A plurality of water-repellent layers extending in the vertical direction are formed, and the plurality of water-repellent layers can be spaced apart from each other. By adopting such a configuration, the liquid is removed from the surface of the light propagating body when exposed to the outside of the liquid while ensuring the contact between the surface of the light propagating body (part other than the water-repellent layer) and the liquid. Can be suitably performed.

  Note that a metal film that generates a surface plasmon phenomenon may be formed on the sensing portion of the light propagating body. By comprising in this way, the detection sensitivity of a sensing part improves and a detection accuracy can be improved.

The figure which shows the whole structure of the liquid level detection apparatus which concerns on one Embodiment of this invention. The figure which shows the structure of a detection part. The figure which shows the other structure of a detection part. The figure which shows the other structure of a detection part. The figure which shows the other structure of a detection part. The figure which shows the other structure of a detection part. The figure which shows the detailed structure of the detection part shown to FIG. 6 (B). The figure which shows the example which formed the water-repellent layer in the optical fiber. The figure which shows the other example which formed the water-repellent layer in the optical fiber.

  A liquid level detection device 20 according to an embodiment embodying the present invention will be described with reference to the drawings. As shown in FIG. 1, the liquid level detection device 20 detects the liquid level and fuel properties of the fuel 18 stored in the fuel tank 10. The fuel tank 10 is mounted on a vehicle such as an automobile and stores fuel 18 used in an internal combustion engine such as an automobile. The fuel property of the fuel 18 varies depending on the heavy / light ratio (ratio of heavy fuel to light fuel), the alcohol content, and the like. A fuel supply device 12 is accommodated in the fuel tank 10. The fuel supply device 12 includes a fuel pump 14, a fuel filter 15, and a pressure regulator 17. The fuel pump 14 boosts the fuel in the fuel tank 10 and discharges the boosted fuel to the outside of the fuel pump 14. Foreign matter is removed from the fuel discharged from the fuel pump 14 by the fuel filter 15. The pressure of the fuel from which the foreign matter has been removed is adjusted by the pressure regulator 17. The fuel whose pressure is adjusted by the pressure regulator 17 is supplied to an injector disposed outside the fuel tank 10 through a fuel supply path 19. The return fuel from the pressure regulator 17 is supplied to the liquid level detection device 20 through the fuel supply path 16.

  The liquid level detection device 20 includes a detection unit 26 disposed in the fuel tank 10, a relay circuit 24 that relays a signal output from the detection unit 26, and an output from the detection unit 26 that inputs via the relay circuit 24. ECU (control device) 22 for determining the liquid level and fuel properties of the fuel 18 based on the above.

  The detector 26 detects the light intensity that changes in accordance with the liquid level and fuel properties of the fuel 18 stored in the fuel tank 10. As shown in FIG. 2, the detection unit 26 includes a light source 30, optical fibers 32, 34, 36, photodetectors 46, 48, 50, and a temperature sensor 54. The light source 30 is accommodated in a casing 28 that supports one end of the optical fibers 32, 34, and 36. The light source 30 is connected to the ECU 22 via a relay circuit 24 by wiring not shown. The ECU 22 controls ON / OFF of the light source 30. When the light source 30 is turned on, light is emitted from the light source 30. Light emitted from the light source 30 enters one end face of the optical fibers 32, 34, and 36. In the present embodiment, since light from one light source 30 is incident on each of the optical fibers 32, 34, and 36, a decrease in detection accuracy due to the use of different light sources 30 is prevented. In the present embodiment, an LED (light emitting diode) is used as the light source 30, but various light sources (for example, a laser light source) other than the LED can be used as the light source 30.

  The optical fibers 32, 34, and 36 are installed in the fuel tank 10 so that when the fuel tank 10 is installed horizontally, the axis thereof extends in the vertical direction. Each of the optical fibers 32, 34, and 36 has the same configuration, and propagates light incident on one end face to the other end face. The optical fibers 32, 34, and 36 are provided with sensing units 32a, 34a, and 36a. The optical fibers 32, 34, and 36 change the intensity of light propagating to the other end surface according to the type of substance that contacts the sensing units 32 a, 34 a, and 36 a and the contact area between the substance and the sensing units 32 a, 34 a, and 36 a It is supposed to be. The sensing units 32a, 34a, and 36a of the present embodiment employ a configuration that utilizes a surface plasmon resonance phenomenon. Specifically, the optical fibers 32, 34, and 36 have a core and a clad provided on the outer peripheral surface of the core. The core and the clad are made of quartz glass or plastic having a high transmittance for light. The refractive index of the core is larger than the refractive index of the cladding. As a result, most of the light incident on the optical fibers 32, 34, and 36 propagates through the core. A portion of the cladding has been removed. The core is exposed on the surface where the cladding is removed. In a portion where the core is exposed on the surface, a gold thin film (hereinafter referred to as a gold thin film) is formed on the surface of the core. The gold thin film can be formed by a vacuum evaporation method. The thickness of the gold thin film is 1 to 200 nm, and is formed to a thickness at which surface plasmon resonance phenomenon easily occurs.

  The optical fiber 32 is exposed in the fuel tank 10, and the fuel 18 in the fuel tank 10 is in contact with the sensing portion 32a. Since the optical fiber 32 is installed so as to extend in the vertical direction when the fuel tank 10 is installed horizontally, the contact area between the sensing unit 32a and the fuel 18 is that of the fuel 18 stored in the fuel tank 10. It depends on the liquid level.

  The optical fiber 34 is accommodated in a sealed container 38. The sealed container 38 is filled with air. For this reason, the entire surface of the sensing unit 34a of the optical fiber 34 is always in contact with air. The sealed container 38 may be filled with a substance other than air (a substance having a known refractive index).

  The optical fiber 36 is accommodated in the fuel pipe 40. An inlet 42 is provided at one end of the fuel pipe 40, and an outlet 44 is provided at the other end of the fuel pipe 40. The fuel supply path 16 is connected to the inlet 42. For this reason, when the fuel pump 14 is operated, fuel is supplied from the fuel supply path 16 into the fuel pipe 40. When fuel is supplied from the fuel supply path 16 into the fuel pipe 40, the fuel pipe 40 is filled with fuel. As a result, the entire surface of the sensing portion 36a of the optical fiber 36 comes into contact with the fuel. The fuel supplied into the fuel pipe 40 flows through the fuel pipe 40 and returns to the fuel tank 10 from the outlet 44.

In the present embodiment, a gold thin film is formed on the surfaces of the optical fibers 32, 34, and 36 as a thin film for causing the surface plasmon resonance phenomenon. (For example, silver, copper, aluminum, etc.) can be used. A thin film in which gold and these metals are stacked can also be used.
In addition, the configuration of the sensing units 32a, 34a, and 36a is not limited to that using the surface plasmon resonance phenomenon, and various known configurations (for example, Patent Document 1, Japanese Patent Application Laid-Open No. 54-118865, Japanese Patent Application Laid-Open No. 2003-337103). Issue).

  The photodetectors 46, 48, 50 are disposed at the other ends of the optical fibers 32, 34, 36 and are accommodated in a casing 52 that supports the other ends of the optical fibers 32, 34, 36. Each of the photodetectors 46, 48, and 50 receives the light propagated through the optical fibers 32, 34, and 36, and outputs a signal corresponding to the intensity of the received light. The photodetectors 46, 48, and 50 are connected to the relay circuit 24 by wiring (not shown). Signals output from the photodetectors 46, 48 and 50 are input to the ECU 22 via the relay circuit 24. For the photodetectors 46, 48, and 50, a known sensor that detects the intensity of light can be used. For example, a photodiode can be used.

  The temperature sensor 54 is attached to the outer surface of the casing 52 and is immersed in the fuel 18 of the fuel tank 10. The temperature sensor 54 detects the temperature of the fuel 18 in the fuel tank 10. The temperature sensor 54 is connected to the relay circuit 24 by wiring (not shown). A signal output from the temperature sensor 54 is input to the ECU 22 via the relay circuit 24. The temperature sensor 54 may be a known sensor that detects temperature, for example, a thermistor.

  The relay circuit 24 relays signals transmitted and received between the detection unit 26 and the ECU 22. Specifically, signals output from the photodetectors 46, 48, 50 and the temperature sensor 54 of the detection unit 26 are input to the ECU 22 via the relay circuit 24. Further, the ECU 22 outputs a signal for turning on / off the light source 30 of the detection unit 26 to the light source 30 via the relay circuit 24. The signal output from the relay circuit 24 to the ECU 22 may be an analog method or a digital method. Further, the relay circuit 24 may convert the detection result detected by the detection unit 26 into a voltage, output it, or convert it into a frequency and output it, or convert it into a pulse width. And may be output after being converted into the number of pulses. Further, the relay circuit 24 and the ECU 22 may be connected by a single signal line, and the signals output from the photodetectors 46, 48, 50 and the temperature sensor 54 may be output by time division processing.

  The ECU 22 determines the liquid level and fuel properties of the fuel 18 stored in the fuel tank 10 based on signals output from the photodetectors 46, 48, 50 and the temperature sensor 54. Specifically, with reference to the light intensity detected by the light detector 48 (the intensity of light propagated by the optical fiber 34), the light intensity detected by the light detector 46 (the intensity of light propagated by the optical fiber 36). ) To determine the fuel properties. That is, the optical fiber 34 is housed in a sealed container 38 filled with air, while the optical fiber 36 is housed in a fuel tube 40 filled with fuel. The intensity of light propagating through the optical fibers 34 and 36 varies depending on the refractive index of the substance that the sensing units 34a and 36a are in contact with. Since the refractive index of air is known, the refractive index of the fuel 18 is specified by comparing the intensity of light propagated through the optical fiber 34 (reference light intensity) and the intensity of light propagated through the optical fiber 36. be able to. The refractive index of the fuel 18 varies depending on the fuel properties (for example, heavy / light ratio, alcohol content (alcohol concentration), density, etc.) and the temperature of the fuel 18. The temperature of the fuel 18 is measured by the temperature sensor 54. For this reason, if the refractive index of the fuel 18 is known, the ECU 22 can specify the fuel properties (for example, the heavy / light ratio, alcohol concentration, density, etc.) of the fuel 18 from the refractive index and temperature of the fuel 18.

  Further, the ECU 22 determines the level of the fuel 18 in the fuel tank 10 based on signals output from the photodetectors 46, 48, 50. That is, the optical fiber 34 is accommodated in a sealed container 38 filled with air, and the optical fiber 36 is accommodated in a fuel tube 40 filled with fuel. Therefore, the light intensity detected by the photodetector 48 (the intensity of light propagated through the optical fiber 34) corresponds to the light intensity when the liquid level is “0%”. The light intensity detected by the photodetector 46 (the intensity of light propagated through the optical fiber 36) corresponds to the light intensity when the liquid level is “100%”. If the light intensity when the liquid level is “0%” and “100%” is known, the liquid level of the fuel 18 is determined from the light intensity detected by the photodetector 50 (the intensity of the light propagated through the optical fiber 32). Can be identified. When the sealed container 38 is filled with a substance other than air (however, the refractive index is known), the refractive index of the liquid is specified from the light intensity detected by the photodetectors 46 and 48, and the refraction is performed. Based on the rate, the light intensity when the liquid level becomes “0%” and “100%” is calculated. Next, the liquid level of the fuel 18 may be specified from the light intensity detected by the photodetector 50.

  As is clear from the above description, in the liquid level detection device 20 of the present embodiment, the optical fiber 34 in which the reference substance contacts the entire surface of the sensing unit, the optical fiber 36 in which the fuel 18 contacts the entire surface of the sensing unit, and the fuel 18. By using the optical fiber 32 in which the contact area of the sensing unit corresponds to the liquid level, the fuel property and liquid level of the fuel 18 can be accurately detected. In particular, since the liquid level is detected in consideration of the fuel properties, the liquid level of the fuel 18 can be detected with high accuracy.

  Further, the liquid level detection device 20 of the present embodiment includes three optical fibers 32, 34, and 36 and photodetectors 46, 48, and 50 that detect light propagating through the three optical fibers 32, 34, and 36. And comparing the three light intensities detected by the photodetectors 46, 48 and 50 to determine the liquid level and fuel properties of the fuel 18. For this reason, when one of these fails, the detected value detected by the optical fiber and / or the photodetector related to the failure becomes an abnormal value. Therefore, the abnormality can be detected. For example, when the light intensity detected by the photodetector 46 (the intensity of light propagated through the optical fiber 36) does not become a value corresponding to the fuel, it is determined that the optical fiber 36 and / or the photodetector 46 is out of order. can do. Further, when the light intensity detected by the photodetector 48 (the intensity of light propagated through the optical fiber 34) does not become a value corresponding to air, it is determined that the optical fiber 34 and / or the photodetector 48 are out of order. can do. Further, the light intensity detected by the photodetector 50 (the intensity of light propagated through the optical fiber 32) is a value between the light intensity detected by the photodetector 46 and the light intensity detected by the photodetector 48. If not, it can be determined that the optical fiber 32 and / or the photodetector 50 are out of order.

  In the present embodiment, a common light source 30 is used for the three optical fibers 32, 34, and 36. For this reason, even if the light quantity of the light source 30 is reduced due to the aging of the light source 30, the effect is similarly generated in each of the three optical fibers 32, 34, and 36. Therefore, the liquid level and fuel properties of the fuel 18 can be accurately detected over a long period of time.

  Furthermore, in this embodiment, a gold thin film is formed on the surfaces of the optical fibers 32, 34, and 36, and a part of the light propagating through the core is absorbed by the surface plasmon resonance phenomenon. For this reason, the intensity of light received by the photodetectors 46, 48, 50 greatly changes with respect to the change in the refractive index of the fuel 18. Thereby, the detection accuracy of the liquid level and fuel property of the fuel 18 is enhanced.

  In the above-described embodiment, the photodetectors 46, 48, and 50 are provided for the three optical fibers 32, 34, and 36, respectively, and one light source 30 is provided for the three optical fibers 32, 34, and 36. Used in common. However, the present invention is not limited to such a form, and can be implemented in various forms. For example, as in the detection unit 55 shown in FIG. 3, light sources 56, 58, and 60 are provided for the optical fibers 32, 34, and 36, and a common photodetector 62 is provided for the optical fibers 32, 34, and 36. You may do it. In this case, only the light source 56 is turned on, and the light intensity propagated through the optical fiber 32 is detected by the photodetector 62. Similarly, only the light source 58 is turned on to detect the intensity of light propagated through the optical fiber 34, and only the light source 60 is turned on to detect the intensity of light propagated through the optical fiber 36. By controlling on / off of the light sources 56, 58, 60 by the ECU 22, the intensity of light propagating through each of the optical fibers 32, 34, 36 can be detected by a single photodetector 62. By sharing the photodetector 62 in this way, it is possible to prevent a decrease in detection accuracy due to variations in the photodetector 62.

  Furthermore, unlike the configuration shown in FIG. 3, a light source and a photodetector may be provided for each of the three optical fibers. By providing each with a light source and a photodetector, each can be operated independently. Alternatively, the light source and the photodetector of three optical fibers may be shared. In this case, a shutter that shields light from the light source may be provided on each optical fiber so that the light enters only one optical fiber. According to such a configuration, since the light source and the photodetector are shared, it is possible to prevent a decrease in detection accuracy due to variations in these characteristics.

  In the above-described embodiment, the optical fiber 34 for detecting the light intensity (the reference light intensity) when the reference substance is in contact with the entire surface of the sensing unit, and the fuel is in contact with the entire surface of the sensing unit. Although the optical fiber 36 for detecting the light intensity at the time and the optical fiber 32 for detecting the light intensity when the fuel has a contact area corresponding to the liquid level are provided, the present invention is not limited to such a form. For example, as shown in FIG. 4, the detection unit 64 can be configured by two optical fibers 32 and 66. Specifically, the optical fiber 32 is exposed in the fuel tank 10 as in the above-described embodiment, and a part of the optical fiber 32 is submerged in the fuel 18. The contact area between the sensing portion of the optical fiber 32 and the fuel 18 is in accordance with the liquid level of the fuel 18 stored in the fuel tank 10. On the other hand, the optical fiber 66 is accommodated in a fuel / air introduction pipe 68. The fuel / air introduction pipe 68 is switched between a state filled with fuel 18 and a state filled with air by a switching valve (not shown). Switching of this state is performed by the ECU 22. According to such a configuration, the light intensity serving as a reference can be detected by reading the output of the photodetector 70 in a state where the fuel / air introduction pipe 68 is filled with air, and the fuel / air introduction can be detected. By reading the output of the photodetector 70 with the tube 68 filled with fuel, it is possible to detect the light intensity when the fuel comes into contact with the entire surface of the sensing unit. By sharing the optical fiber, the manufacturing cost can be reduced. In addition, it is possible to prevent a decrease in detection accuracy due to variations in the characteristics of the optical fiber.

  Furthermore, as shown in FIG. 5, the reference light intensity, the light intensity when the fuel comes into contact with the entire surface of the sensing unit, and the fuel contact according to the liquid level by one optical fiber 106 The light intensity when the area is reached can be detected. That is, one optical fiber 106 is accommodated in one conduit 104. Then, by controlling the switching valve 112, the state in which the inside of the conduit 104 is filled with air, the state in which the conduit 104 is filled with fuel, and the contact area corresponding to the liquid level of the fuel 18 in the fuel tank 10 are obtained. Let it be filled with air. In each state, the light intensity of the light output from the light source 102 is detected by the photodetector 114, so that the three light intensities can be detected by the single optical fiber 104.

  In the above-described embodiment, the optical fiber is disposed so as to extend in the vertical direction, the light source is disposed at the upper end of the optical fiber, and the photodetector is disposed at the lower end of the optical fiber. However, the present invention is limited to such a form. Absent. For example, as shown in FIG. 6A, the optical fibers 76a, 76b, and 76c can be bent and arranged in a U shape. In such a configuration, the light source 72 and the photodetector 74 are not submerged in the fuel 18, so that the light source 72 and the photodetector 74 are not required to have high sealing performance and fuel resistance. In the case of adopting this configuration, a sensing unit may be provided in a portion extending in the vertical direction among the optical fibers 76a, 76b, and 76c.

  Further, as shown in FIG. 6B, the optical fibers 80, 82, 84 are arranged to extend in the vertical direction, and the light source and the photodetector are installed in the casing 78 that supports the upper ends of the optical fibers 80, 82, 84. It may be arranged. Even with such a configuration, the light source and the photodetector can be prevented from being immersed in the fuel 18. In the case of adopting such a configuration, for example, as shown in FIG. 7, a light source 86, an optical fiber 80 (82, 84), and a photodetector 88 can be arranged. That is, a reflecting plate that reflects light is disposed at the lower end of the optical fiber 80. A beam splitter 90 is disposed between the light source 86 and the optical fiber 80. In such a configuration, the light emitted from the light source 86 passes through the beam splitter 90 and enters the upper end surface of the optical fiber 80. The light incident on the optical fiber 80 propagates in the optical fiber 80 and is reflected at the lower end of the optical fiber 80. The light reflected by the lower end of the optical fiber 80 propagates through the optical fiber 80 and exits from the upper end surface of the optical fiber 80. The light emitted from the upper end surface of the optical fiber 80 is reflected by the beam splitter 90 and guided to the photodetector 88. By adopting such a configuration, the light source and the photodetector can be disposed at the same end of the optical fiber, and the detection unit can be made compact.

In addition, it is preferable that a water-repellent layer is formed on at least a part of the surface of the optical fiber used in each embodiment described above. For example, as shown in FIG. 8, a water-repellent film 92b is formed on the surface of the main body 92a of the optical fiber 90. By forming the water repellent film 92 b, the fuel 18 is prevented from coming into contact with the portion of the optical fiber 90 that is not submerged by the surface tension of the fuel 18. Thereby, the liquid level can be detected with high accuracy.
9A and 9B, the water-repellent layers (water-repellent films) 96 and 98 are formed so as to be continuous in the vertical direction, while being spaced apart in the horizontal direction. Preferably it is formed. By forming the water-repellent layers 96 and 98 in this way, it is possible to prevent a decrease in sensor sensitivity due to the water-repellent layers 96 and 98.

Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.
The technical elements described in this specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology illustrated in the present specification or the drawings achieves a plurality of objects at the same time, and has technical utility by achieving one of the objects.

10: Fuel tank 12: Fuel supply device 14: Fuel pump 20: Liquid level detection device 22: ECU
24: Relay circuit 26: Detection unit 30: Light sources 32, 34, 36: Optical fibers 46, 48, 50: Photo detector 54: Temperature sensor

Claims (7)

It is a liquid level detection device that detects the liquid level of the liquid stored in the container,
A detection unit having at least one light propagating body provided with a sensing unit;
A determination unit that determines the liquid level of the liquid stored in the container using the detection result detected by the detection unit;
The light propagating body is designed such that the intensity of light propagating changes according to the type of substance that contacts the sensing unit and the contact area between the substance and the sensing unit,
(1) The intensity of the first light propagated by the light propagating body when the contact area between the sensing unit and the liquid in the container corresponds to the liquid level of the liquid in the container; 2) Intensity of the second light propagated by the light propagating body when the liquid in the container contacts the entire surface of the sensing unit, and (3) Propagated by the light propagating unit when the reference substance contacts the entire surface of the sensing unit. Detecting the intensity of the third light,
The determination unit determines a liquid level of the liquid in the container from the intensity of the first light, the intensity of the second light, and the intensity of the third light detected by the detection unit. apparatus.   The liquid level detection according to claim 1, wherein the determination unit further determines the property of the liquid in the container from the intensity of the second light and the intensity of the third light detected by the detection unit. apparatus. The detection unit includes a first light propagating body, a second light propagating body, a third light propagating body, a first housing that houses the second light propagating body, and a third light propagating body. A second container for housing
The first light propagating body is configured such that the contact area between the sensing unit and the liquid in the container changes according to the liquid level of the liquid in the container,
The first container can be filled with a liquid in a container, and the second container can be filled with a reference material. Liquid level detection device. The detection unit has a first light propagating body, a second light propagating body, and a housing that houses the second light propagating body,
The first light propagating body is configured such that the contact area between the sensing unit and the liquid in the container changes according to the liquid level of the liquid in the container,
The liquid according to claim 1 or 2, wherein the container is switchable between a first state filled with the reference substance and a second state filled with the liquid in the container. Position detector.   The liquid level detection device according to any one of claims 1 to 4, wherein a water repellent layer is formed on at least a part of the surface of the first light propagating body.   When the container is installed on a horizontal plane, at least a part of the first light propagating body extends in the vertical direction and is formed with a sensing unit, and the sensing unit includes a plurality of water repellency extending in the vertical direction. The liquid level detection device according to claim 5, wherein a plurality of water repellent layers are formed and spaced apart from each other.   The liquid level detection device according to claim 1, wherein a metal film that generates a surface plasmon phenomenon is formed in the sensing unit of the light propagating body.

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