JP2006119046A - Liquid level detection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid level detection device capable of performing accurate liquid level detection by suppressing propagation of an ultrasonic wave emitted from an ultrasonic vibrator to the entity of a transmission pipe. <P>SOLUTION: A bracket 7 is in contact with a guide pipe 9 which is the transmission pipe and a body 12 at each tip of a plurality of circular cone-shaped projections 74 provided on the outer surface, namely, at the top of each circular cone. Hereby, since contact areas of the bracket 7 with the guide pipe 9 and the body 12 are extremely small, vibration energy transmitted from the bracket 7 to the guide pipe 9 and the body 12 at the oscillation time from an ultrasonic sensor 3 is extremely small or zero. Consequently, since propagation of the ultrasonic wave emitted from the ultrasonic sensor 3 to the entities of the guide pipe 9 and the body 12 can be suppressed surely, this fuel liquid level detection device 1 capable of performing accurate liquid level detection by suppressing a noise received by the ultrasonic sensor 3 can be realized. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a liquid level detecting device for detecting a liquid level position of a liquid in a tank, and is suitable for use for detecting a fuel level in a fuel tank installed in an automobile, for example.

  Conventionally, as a liquid level detecting device for detecting the level of liquid in a tank, for example, a thin tubular transmission tube is attached to the tank 1 in the depth direction, and ultrasonic vibration is applied to a watertight case at the bottom of the transmission tube. There is a type of measuring a liquid level accurately by mounting a child, emitting ultrasonic waves from an ultrasonic vibrator, and receiving reflected waves from the ultrasonic liquid surface by an ultrasonic vibrator. (For example, refer to Patent Document 1).

In the liquid level detection apparatus described above, a filler is provided between the ultrasonic transducer and the bottom surface of the watertight case to absorb ultrasonic pulses leaking from the ultrasonic transducer.
Japanese Unexamined Patent Publication No. 6-249697

  In the configuration of the conventional liquid level detection apparatus described above, the watertight case containing the ultrasonic transducer is provided integrally with the transmission tube.

  According to such a configuration, the ultrasonic wave emitted from the ultrasonic transducer propagates in the liquid filling the transmission tube, and is also transmitted from the watertight case to the transmission tube itself to propagate through the substance of the transmission tube. . The ultrasonic wave propagating through the transmission tube is reflected by the end of the transmission tube, etc., travels again through the transmission tube, and enters the ultrasonic transducer. That is, the ultrasonic transducer receives two types of reflected waves, a reflected wave from the liquid surface and a reflected wave from the end of the transmission tube. The reflected wave from the liquid surface is a signal necessary for detecting the liquid surface position, but the reflected wave from the end of the transmission tube is so-called noise, and there is a problem that accurate liquid level detection is hindered by this noise.

  The present invention has been made in view of the above points, and its purpose is to suppress the propagation of ultrasonic waves emitted from an ultrasonic transducer to the substance of a transmission tube and to detect liquid levels with high accuracy. It is to provide a liquid level detection device capable of performing the above.

  The present invention employs the following technical means to achieve the above object.

  According to a first aspect of the present invention, there is provided a liquid level detection apparatus comprising: an ultrasonic oscillation element disposed at a bottom of a tank that stores a liquid; and a reflected wave at a liquid level in the ultrasonic tank emitted from the ultrasonic oscillation element. Is a liquid level detection device that detects the position of the liquid level by receiving the ultrasonic oscillation element, and a case in which the ultrasonic oscillation element is hermetically stored and a case attached to one end side of the case and the internal space being super A substantially cylindrical transmission tube that forms a propagation path of ultrasonic waves emitted from the sound wave oscillating element, and a vibration isolating means for suppressing vibration propagation between the case and the transmission tube is interposed in the case and the mounting portion of the transmission tube. It is characterized by that.

  When the ultrasonic oscillation element vibrates and emits an ultrasonic wave, the vibration of the ultrasonic oscillation element is transmitted to the case and the case vibrates.

  According to the above-described configuration, the vibration of the case is attenuated by the vibration isolating means interposed between the case and the transmission tube, so that the vibration energy transmitted from the case to the transmission tube is negligible or zero.

  Thereby, it is possible to realize a liquid level detection device capable of accurately detecting the liquid level by reliably suppressing the ultrasonic wave emitted from the ultrasonic transducer from propagating to the substance of the transmission tube.

  In the liquid level detection device according to claim 2 of the present invention, the vibration isolating means is a protrusion provided on at least one of the case and the transmission tube, and the case and the transmission tube are in contact with each other at the tip of the protrusion. It is characterized by.

  In two members fixed to each other, when one member vibrates and the vibration is transmitted to the other member, the magnitude of vibration energy transmitted from one to the other varies depending on the contact area of both members. To do. That is, the greater the contact area between the two members, the greater the magnitude of vibration energy transmitted from one to the other.

  According to the above-described configuration, the contact area between the case and the transmission pipe is extremely small because the case and the transmission pipe are in contact with each other at the tip of the protrusion. Therefore, when the ultrasonic oscillating element oscillates, the vibration energy transmitted from the case to the transmission tube is negligible or zero.

  Thereby, it is possible to realize a liquid level detection device capable of accurately detecting the liquid level by reliably suppressing the ultrasonic wave emitted from the ultrasonic transducer from propagating to the substance of the transmission tube.

  The liquid level detection device according to claim 3 of the present invention is characterized in that the tip of the protrusion is dot-like or linear.

  Thereby, the contact area of a case and a transmission pipe can be made very small reliably.

  The liquid level detecting device according to claim 4 of the present invention is characterized in that the vibration isolating means is a flexible rubber material or resin material.

  In this case, when the ultrasonic oscillation element oscillates, the vibration of the case is transmitted to the transmission tube via the flexible vibration isolating means. At this time, the vibration of the case is attenuated by the damper action of the vibration isolating means while propagating through the vibration isolating means, and the vibration energy transmitted to the transmission pipe is negligible or zero.

  Thereby, it is possible to realize a liquid level detection device capable of accurately detecting the liquid level by reliably suppressing the ultrasonic wave emitted from the ultrasonic transducer from propagating to the substance of the transmission tube.

  Hereinafter, the liquid level detection apparatus according to the first embodiment of the present invention will be described with reference to the drawings, taking as an example a case where the liquid level detection apparatus is applied to a fuel liquid level detection apparatus 1 for detecting a fuel liquid level position in a fuel tank of an automobile. .

(First embodiment)
FIG. 1 is a partial sectional view of a fuel tank 2 in a fuel level detecting device 1 according to a first embodiment of the present invention. In FIG. 1, the vertical direction in the figure is the vertical direction of the automobile.

  2 is a cross-sectional view taken along line II-II in FIG.

  3 is a cross-sectional view taken along line III-III in FIG.

  4 is a cross-sectional view taken along line IV-IV in FIG.

  FIG. 5 is a schematic diagram for explaining an electric circuit configuration in the fuel level detecting device 1 according to the first embodiment of the present invention.

  As shown in FIG. 1, the fuel level detecting device 1 includes a fuel tank 2 as a tank that stores fuel 14 that is a liquid, an ultrasonic sensor 3 that is an ultrasonic oscillation element, and an ultrasonic wave emitted from the ultrasonic sensor 3. It is comprised from the body 12 as a transmission tube which forms the propagation path of a sound wave.

  That is, the fuel liquid level detection device 1 is largely composed of an ultrasonic transmission / reception functional element centered on the ultrasonic sensor 3 and an ultrasonic wave between the ultrasonic sensor 3 and the liquid level 14a of the fuel 14 from a functional viewpoint. It is composed of two functional elements of an ultrasonic wave propagation path functional element that forms a sound wave propagation path.

  Below, the structure of the fuel liquid level detection apparatus 1 by 1st Embodiment of this invention is demonstrated.

  First, ultrasonic transmission / reception functional elements centering on the ultrasonic sensor 3 will be described.

  The ultrasonic sensor 3 that is an ultrasonic oscillation element is a substance having a piezo effect (a property that changes in volume when a voltage is applied, but generates a voltage when receiving an external force), such as PZT (zirconate titanate). It is formed in a disk shape with lead. As shown in FIG. 2, electrodes 33 that are electrically connected to the outside are formed on the front surface 31 and the back surface 32 of the ultrasonic sensor 3. Both electrodes 33 are formed over substantially the entire surface 31 and the back surface 32 of the ultrasonic sensor 3, respectively. When a voltage is applied between the electrodes 33, the ultrasonic sensor 3 oscillates in the axial direction (the left-right direction in FIG. 2) which is the thickness direction due to the piezoelectric effect described above and emits ultrasonic waves. Connected to both electrodes 33 are lead wires 6 which are lead members for electrically connecting both electrodes 33 to the outside. Each lead wire 6 is soldered to the electrode 33. The ultrasonic sensor 3 is hermetically housed in a bracket 7 and a cover 8 that are cases.

  The bracket 7 as one side of the case is formed in a substantially bottomed cylindrical shape from, for example, a resin material, and the ultrasonic sensor 3 is disposed on the bottom 71 as shown in FIG. A cover 8 as the other side of the case is attached to the opening end 72 (the right end in FIG. 2) opposite to the bottom 71 of the bracket 7. The cover 8 is fixed in close contact with the open end 72 of the bracket 7, thereby sealing the ultrasonic sensor 3 in the bracket 7. Further, as shown in FIG. 2, a projection 74, which is a projection as a vibration isolating means, is provided on the outer surface of the bracket 7. The protrusion 74 is formed in a conical shape having the outer surface side of the bracket 7 as a bottom surface. A plurality of protrusions 74 are provided, and when the bracket 7 to which the cover 8 is attached is attached to the body 12, the protrusion 74 has an inner surface of the body 12 that is a transmission pipe and the guide pipe 9 at the apex of the cone as the tip. As shown in FIG. 2, it abuts on the end face. In addition, the shape of each protrusion 74 is formed in the same in the fuel liquid level detection apparatus 1 by 1st Embodiment of this invention. On the surface of the bracket 7, each projection 74 is set so that the posture of the bracket 7 in the body 12 is uniquely determined and the tips of all the projections 74 abut against the guide pipe 9 or 9 body 12. .

  That is, the bracket 7 is in contact with the guide pipe 9 by the three protrusions 74 as shown in FIG. In this case, as shown in FIG. 4, the three protrusions 74 that are in contact with the guide pipe 9 are arranged at intervals of 120 degrees on an arc that is substantially concentric with the guide pipe 9. The guide pipe 9 can be contacted stably. Further, as shown in FIG. 2, the bracket 7 is in contact with the body 12 by a protrusion 74. In this case, as shown in FIG. 4, the protrusions 74 that are in contact with the body 12 are arranged on the outer surface of the bracket 7 at intervals of 120 degrees, so that the bracket 7 is coaxial with the hole 12 b of the body 12. Can be maintained stably.

  The cover 8 is formed of, for example, a resin material, and is fixed to the bracket 7 with its locking claws 82 locked in the locking holes 73 of the bracket 7 as shown in FIG. The cover 8 is provided with a through hole 81 for extending the lead wire 6 connected to the ultrasonic sensor 3 to the outside of the cover 8. A connector portion 83 is formed on the surface of the cover 8 opposite to the bracket 7 (on the right side in FIG. 2), as shown in FIG. The connector portion 83 is provided with a terminal 84 made of a conductive material. The other end of the lead wire 6 whose one end is connected to the electrode 33 of the ultrasonic sensor 3 is connected to the terminal 84 by soldering or the like. The ultrasonic sensor 3 is electrically connected to the external electrical circuit by engaging the connector (not shown) extending from the external electrical circuit with the connector 83. A buffer member 4 is disposed between the cover 8 and the ultrasonic sensor 3.

  The buffer member 4 is made of a flexible resin material or rubber material. In the fuel level detecting device 1 according to the first embodiment of the present invention, the buffer member 4 is made of nitrile rubber. When the cover 8 is fixed to the bracket 7, the buffer member 4 is compressed and elastically deformed in the bracket 7. Since the ultrasonic sensor 3 is pressed against the bracket 7 by the elastic force of the buffer member 4, the ultrasonic sensor 3 is fixed at a predetermined position in the bracket 7. The buffer member 4 also serves to absorb an ultrasonic pulse that leaks from the ultrasonic sensor 3 to the back (right side in FIG. 2). Thereby, the ultrasonic pulse emitted from the ultrasonic sensor 3 advances only into the fuel 14 in the guide pipe 9 which is a transmission pipe (toward the left in FIG. 2).

  The body 12 which is a transmission pipe is formed of a resin material, for example, a resin material having excellent stability with respect to the fuel 14 in the fuel tank 2 in the fuel level detecting device 1 according to the first embodiment of the present invention. . The body 12 includes a locking claw 12a for holding and fixing the ultrasonic sensor 3, more specifically, for holding and fixing the bracket 7 housing the ultrasonic sensor 3. In the fuel liquid level detection device according to the first embodiment of the present invention, four locking claws 12a are provided. The locking claw 12a is elastically deformed when locked to the end of the cover 8 serving as a lid of the bracket 7, and the cover 8 is pressed toward the guide pipe 9 (left side in FIG. 2) by the elastic force. The body 12 includes a guide pipe 9, a reflecting plate 11, and a guide pipe 10 that are actually ultrasonic wave propagation paths. That is, the internal space of the guide pipe 9 and the guide pipe 10 is an ultrasonic wave propagation path. Further, as shown in FIG. 1, the guide pipe 9 and the guide pipe 10 are arranged with their axes A and B orthogonal to each other. However, the guide pipe 9 and the guide pipe 10 are superposed by a reflecting plate 11 arranged between the guide pipes 9 and 10. Ultrasonic waves are propagated between the guide pipes 9 and 10 by reflecting the sound waves.

  The guide pipe 9 is made of a metal material, and one end side (right side in FIG. 1) of the guide pipe 9 is in contact with the bracket 7 that holds and fixes the ultrasonic sensor 3. Specifically, as shown in FIG. 2, it abuts on the tip of the projection 74 provided on the bracket 7, that is, the apex of the cone. In the fuel level detecting device 1 according to the first embodiment of the present invention, the guide pipe 9 is made of an aluminum die casting alloy. Further, the guide pipe 9 has a cross-sectional shape in a direction orthogonal to the axis A, as shown in FIG. 3, and is formed in a circular shape, and an inner diameter dimension at an end portion on the ultrasonic sensor 3 side (right end in FIG. 1). Is d1, and the inner diameter dimension at the reflection plate 11 side end (left end in FIG. 1) described later is d2. Further, the guide pipe 9 is formed such that the cross-sectional area in the direction orthogonal to the axis A decreases as it moves away from the ultrasonic sensor 3, that is, as it goes from the right end to the left in FIG. . In other words, the guide pipe 9 is formed so that the diameter of the cross section in the direction orthogonal to the axis A decreases as the distance from the ultrasonic sensor 3 increases. That is, as shown in FIG. 1, the relationship d1> d2 is established. Further, as shown in FIG. 1, a step 91 is formed in the guide pipe 9. As shown in FIG. 3, the stepped portion 91 is formed in a ring shape and is formed as a surface facing the ultrasonic sensor 3. Therefore, a part of the ultrasonic wave emitted from the ultrasonic sensor 3 enters the stepped portion 91. This ultrasonic wave is reflected by the step portion 91, travels toward the ultrasonic sensor 3, and enters the ultrasonic sensor 3.

  Further, on the side opposite to the ultrasonic sensor 3 of the guide pipe 9 (left side in FIG. 1), a reflecting plate for reflecting the ultrasonic wave emitted from the ultrasonic sensor 3 toward the liquid surface 14a in the fuel tank 2. 11 are arranged as shown in FIG. The reflecting plate 11 is made of a metal material. In the fuel level detecting device 1 according to the first embodiment of the present invention, the reflecting plate 11 is formed of an iron-based metal, for example, a stainless steel plate. As shown in FIG. 1, the reflecting plate 11 is installed so as to reflect the ultrasonic wave emitted from the ultrasonic sensor 3 incident on the reflecting surface 11a toward the liquid surface 14a. Specifically, the ultrasonic wave traveling on the axis A of the guide pipe 9 is installed so as to be reflected toward the direction in which the incident angle to the liquid surface 14a becomes 0 °, that is, the direction orthogonal to the liquid surface 14a. That is, as shown in FIG. 1, the reflecting plate 11 is provided with an inclination of 45 ° with respect to the liquid surface.

  The guide pipe 10, which is a transmission pipe that forms an ultrasonic wave propagation path between the reflecting plate 11 and the liquid surface 14 a, is formed of a stainless steel pipe, like the guide pipe 9. Further, the guide pipe 10 has a circular cross-sectional shape in a direction orthogonal to the axis B, and the diameter of the guide pipe 10 is uniformly formed over the entire length to a diameter dimension d3. The diameter d3 of the guide pipe 10 is formed to be equal to the diameter d2 at the end of the guide pipe 9 on the reflecting plate 11 side. As shown in FIG. 1, the tip position of the guide pipe 10 on the liquid surface 14a side is a predetermined length above the liquid surface 14b when the amount of fuel 14 stored in the fuel tank 2 is maximum, that is, when the tank 14 is full. Is set to protrude.

  As described above, the guide pipe 9, the reflecting plate 11, and the guide pipe 10 are such that the axis A of the guide pipe 9 and the axis B of the guide pipe 10 intersect on the reflecting surface 11a of the reflecting plate 11, as shown in FIG. A positional relationship is formed.

  The body 12 holds and fixes the positional relationship among the guide pipe 9, the reflecting plate 11, and the guide pipe 10 as an ultrasonic propagation path with high accuracy.

  Next, the electric circuit configuration of the fuel level detecting device 1 according to the first embodiment of the present invention will be described with reference to FIG.

  As shown in the electric circuit configuration diagram of FIG. 5, the control circuit 15 is connected to the battery 18 via the ignition switch 17. The control circuit 15 is connected to the ultrasonic sensor 3. In addition, the display unit 16 is connected to the control circuit 15.

  The control circuit 15 is composed of, for example, a microcomputer or the like, and processes a reflected wave reception signal output from the pulse generation circuit 15a for applying a pulse voltage signal to the ultrasonic sensor 3 and the ultrasonic sensor 3, and based on it. The calculation circuit 15b calculates the liquid level position, and the drive circuit 15c outputs a drive signal for driving the display unit 16 based on the liquid level position signal calculated by the calculation circuit 15b. When the ignition switch 17 is turned on and electric power is supplied from the battery 18, the control circuit 15 starts the operation of the fuel liquid level detecting device 1.

  The display unit 16 includes, for example, a pointer instrument or a liquid crystal panel, and is installed in a combination meter (not shown) in front of the driver's seat of the automobile. The display unit 16 is driven by the drive circuit 15c of the control circuit 15 and displays the position of the liquid level 14a calculated by the arithmetic circuit 15b, that is, the remaining amount of fuel 14 in the fuel tank 2 so that the driver can visually recognize it.

  Next, the fuel level detection operation in the fuel level detection device 1 according to the first embodiment of the present invention will be described.

  When a pulse voltage signal is applied by the pulse generation circuit 15 a, the ultrasonic sensor 3 emits pulsed ultrasonic waves into the fuel 14 in the fuel tank 2. That is, the oscillation surface 31 of the ultrasonic sensor 3 vibrates, the vibration of the oscillation surface 31 is transmitted to the bottom of the bracket 7, and ultrasonic waves are emitted into the fuel 14 from the outer surface of the bracket 7. Part of this ultrasonic wave travels through the guide pipe 9 and enters the stepped portion 91. Then, the light is reflected and enters the oscillation surface 31 of the ultrasonic sensor 3 again. On the other hand, part of the pulsed ultrasonic waves emitted from the ultrasonic sensor 3 into the fuel 14 travels through the guide pipe 9 and enters the reflecting surface 11a. The light is reflected and travels through the guide pipe 10 toward the liquid level 14a. Further, it is reflected by the liquid surface 14 a and enters the ultrasonic sensor 3 through the same path as the forward path, that is, the guide pipe 10, the reflecting surface 11 a, and the guide pipe 9.

  That is, when the ultrasonic sensor 3 is driven by the pulse generation circuit 15a to emit one ultrasonic pulse, the two reflected pulses, that is, the reflected pulse from the step 91 and the liquid level are correspondingly generated as described above. The reflected pulse from 14a is received. As is clear from FIG. 1, the propagation path length from the ultrasonic sensor 3 to the step portion 91 is shorter than the propagation path length from the ultrasonic sensor 3 to the liquid surface 14a. A reflected pulse from the step 91 is received, and then a reflected pulse from the liquid surface 14a is received. The ultrasonic sensor 3 generates a voltage signal every time these reflected pulses are received, and this voltage signal is input to the arithmetic circuit 15b.

  The arithmetic circuit 15b calculates the time from when the pulse generation circuit 15a generates the pulse voltage signal to when the two reflected pulses described above are detected.

  Here, the step 91 is provided at a predetermined position with respect to the ultrasonic sensor 3. That is, the distance between the step 91 and the ultrasonic sensor 3 is known. Therefore, the arithmetic circuit 15b determines the fuel based on the time from when the pulse generation circuit 15a generates the pulse voltage signal until the reflected pulse from the step 91 is received and the distance between the step 91 and the ultrasonic sensor 3. 14 is calculated. Next, based on the propagation speed of the ultrasonic pulse in the fuel 14 calculated in this way and the time from when the pulse generation circuit 15a generates the pulse voltage signal until the reflection pulse from the liquid surface 14a is received. Then, the position of the liquid surface 14a, that is, the height H of the liquid surface 14a in FIG. 1, is calculated, and the remaining amount of fuel 14 in the fuel tank 2 is calculated based on the shape of the fuel tank 2 stored in advance.

  The drive circuit 15c displays a signal for displaying the liquid level 14a height H or the fuel 14 remaining amount calculated by the arithmetic circuit 15b on the display unit 16, for example, a pointer shaft (not shown). The drive signal for rotating to the angle corresponding to 14 remaining amount is output. Accordingly, the liquid level 14a height H or the fuel 14 remaining amount in the fuel tank 2 is displayed on the display unit 16.

  Next, the operation and effect of the protrusion 74 provided on the bracket 7 which is a feature of the fuel level detecting device 1 according to the first embodiment of the present invention will be described.

  When a pulse voltage signal is applied to the ultrasonic sensor 3, the oscillation surface 31 of the ultrasonic sensor 3 vibrates, the vibration of the oscillation surface 31 is transmitted to the bracket 7, and the bracket 7 vibrates. Ultrasonic waves are fired into the fuel 14 from the outer surface.

  Here, in the conventional liquid level detection device, since the watertight case as a bracket is tightly fixed to the transmission pipe, the vibration of the ultrasonic vibrator is also transmitted from the watertight case to the transmission pipe itself, so Propagate through. The ultrasonic wave propagating through the transmission tube is reflected by the end of the transmission tube, etc., travels again through the transmission tube, and enters the ultrasonic transducer. That is, the ultrasonic transducer receives two types of reflected waves, a reflected wave from the liquid surface and a reflected wave from the end of the transmission tube. The reflected wave from the liquid surface is a signal necessary for detecting the liquid surface position, but the reflected wave from the end of the transmission tube is so-called noise, and there is a problem that accurate liquid level detection is hindered by this noise.

  On the other hand, in the fuel level detecting device 1 according to the first embodiment of the present invention, the bracket 7 is transmitted at each tip of the plurality of conical protrusions 74 provided on the outer surface thereof, that is, at the apex of the cone. The pipe is in contact with the guide pipe 9 and the body 12. For this reason, since the contact area between the bracket 7 and the guide pipe 9 and the body 12 is extremely small, the vibration energy transmitted from the bracket 7 to the guide pipe 9 and the body 12 when the ultrasonic sensor 3 oscillates is extremely small. Slightly or 0.

  Thereby, since it can suppress reliably that the ultrasonic wave radiated | emitted from the ultrasonic sensor 3 propagates to the substance of the guide pipe 9 and the body 12, the noise which the ultrasonic sensor 3 receives is suppressed and an accurate liquid level The fuel level detecting device 1 capable of detection can be realized.

(Second Embodiment)
In FIG. 6, the fragmentary sectional view of the fuel level detection apparatus 1 by 2nd Embodiment of this invention is shown.

  In the fuel liquid level detection device 1 according to the second embodiment of the present invention, a part of the member on which the protruding portion which is the vibration isolating unit is formed is changed. That is, in the fuel level detecting device 1 according to the first embodiment of the present invention, all the projections 74 as the projections that are the vibration isolating means are formed on the bracket 7 that is the case, but the second embodiment of the present invention. In the fuel level detecting device 1 according to the above, a part of the fuel level detecting device 1 is provided on the body 12 side which is a transmission pipe. That is, as shown in FIG. 6, the protrusion 12 c is formed on the inner wall of the hole 12 b of the body 12.

  Also with this configuration, the vibration energy transmitted from the bracket 7 to the guide pipe 9 and the body 12 when the ultrasonic sensor 3 oscillates as in the case of the fuel level detecting device 1 according to the first embodiment of the present invention. Very little or zero. Therefore, the ultrasonic wave emitted from the ultrasonic sensor 3 is surely suppressed from propagating to the substance of the guide pipe 9 and the body 12, and the noise received by the ultrasonic sensor 3 is suppressed and the liquid level is detected with high accuracy. It is possible to realize the fuel level detecting device 1 capable of performing

  In this case, the protrusion 74 that contacts the guide pipe 9 may be eliminated, and instead, a protrusion may be provided on the end surface of the guide pipe 9 to contact the bracket 7.

(Third embodiment)
In FIG. 7, the fragmentary sectional view of the fuel liquid level detection apparatus 1 by 3rd Embodiment of this invention is shown.

  In the fuel level detecting device 1 according to the third embodiment of the present invention, the vibration isolating means is changed from a protrusion to a flexible rubber material. That is, as shown in FIG. 7, a vibration isolating member 19 made of a rubber material is disposed between the bracket 7 and the guide pipe 9 and the body 12, and the bracket 7 is connected to the guide pipe 9 and the body 12 via the vibration isolating member 19. Is pressed.

  As the vibration isolation member 19, a material that is highly stable with respect to the fuel 14 to be used, that is, a material that can maintain flexibility, that is, a damper action even when immersed in the fuel 14 for a long time, must be selected. It goes without saying that it must be done.

  According to this configuration, when the ultrasonic sensor 3 oscillates, the vibration of the bracket 7 is transmitted to the guide pipe 9 and the body 12 via the flexible vibration isolating member 19. At this time, the vibration of the bracket 7 is attenuated by the damper action of the vibration isolating member 19 while propagating through the vibration isolating member 19, and the vibration energy transmitted to the guide pipe 9 and the body 12 becomes very little or zero.

  Thereby, since it can suppress reliably that the ultrasonic wave radiated | emitted from the ultrasonic sensor 3 propagates to the substance of the guide pipe 9 and the body 12, the noise which the ultrasonic sensor 3 receives is suppressed and an accurate liquid level The fuel level detecting device 1 capable of detection can be realized.

  In the fuel level detecting device 1 according to the third embodiment of the present invention described above, the vibration isolating member 19 is disposed only between the bracket 7 and the body 12, and the protrusion 74 in the first embodiment is provided on the bracket 7. The projection 74 and the guide pipe 9 may be in contact with each other.

  Further, in the fuel level detecting device 1 according to the first and second embodiments of the present invention described above, the number of the protrusions 74 that abut on the guide pipe 9 is three, but it is necessary to limit the number to three. The predetermined posture of the bracket 7 is maintained in the hole 12b of the body 12, that is, the posture in which the surface 33 of the ultrasonic sensor 3 is orthogonal to the axis A of the guide pipe 9 can be stably maintained. Any number may be used.

  Further, in the fuel level detecting device 1 according to the first embodiment of the present invention described above, the number of the protrusions 74 contacting the body 12 is three on the same circumference, and the fuel liquid according to the second embodiment. In the surface detection device 1, the number of protrusions 12 c that abut on the bracket 7 is three on the same circumference, but it is not necessary to limit the number to three on the same circumference. As long as the predetermined posture is maintained, that is, the posture in which the surface 33 of the ultrasonic sensor 3 is orthogonal to the axis A of the guide pipe 9 can be stably maintained, the number may be any number.

  Further, the shape of the protrusion 74 in the fuel level detecting device 1 according to the first embodiment of the present invention and the shape of the protrusion 12c in the fuel level detecting device 1 according to the second embodiment described above are conical, The shape is not limited to a conical shape, and may be another shape, for example, a pyramid shape. Moreover, although the tips of the protrusions 74 and the protrusions 12c are point-like, it is not necessary to be limited to point-like shapes, and may be linear or minute surface shapes. In short, the shape may be such that the energy transmitted from the bracket 7 to the guide pipe 9 and the body 12 via the protrusion 74 or the protrusion 12c is extremely small.

  Moreover, in the fuel liquid level detecting device 1 according to the first to third embodiments of the present invention described above, the guide pipe 9 is formed from an aluminum die casting alloy, and the guide pipe 10 is formed from a stainless steel pipe. It is not necessary to limit to these metal materials, and other types of metal materials may be used. For example, the guide pipe 9 may be formed from a steel material, and the guide pipe 10 may be formed from an aluminum pipe. Further, the guide pipe 9 and the guide pipe 10 may be formed of a material other than a metal material, such as a resin material or a ceramic material. Any material can be used as long as the ultrasonic wave can be propagated into the liquid inside thereof with high efficiency.

  Further, in the fuel level detecting device 1 according to the first to third embodiments of the present invention, the step 91 is provided in the guide pipe 9, but the step 91 may not be provided. In this case, for example, the temperature of the fuel 14 in the fuel tank 2 is detected by a temperature sensor (not shown) or the like, thereby correcting the ultrasonic propagation velocity in the fuel 14 and calculating the liquid surface 14a height H. Thus, the liquid surface 14a height H can be calculated with high accuracy.

  Moreover, although each embodiment described above demonstrated the case where the liquid level detection apparatus by this invention was applied to the fuel liquid level detection apparatus 1 of a motor vehicle, you may apply other than the fuel liquid level detection apparatus 1 as an example. . That is, in order to detect the liquid level in other liquids installed in the vehicle, such as engine oil, brake fluid or window washer liquid, or in the liquid transport tank provided in the liquid transport vehicle You may apply. Furthermore, the present invention may be applied to the use of liquid level detection in liquid containers of various consumer devices other than automobiles and vehicles.

1 is a partial cross-sectional view of a fuel tank 2 in a fuel level detecting device 1 according to a first embodiment of the present invention. It is the II-II sectional view taken on the line in FIG. It is the III-III sectional view taken on the line in FIG. It is the IV-IV sectional view taken on the line in FIG. It is a schematic diagram explaining the electric circuit structure in the fuel liquid level detection apparatus 1 by 1st Embodiment of this invention. It is a fragmentary sectional view of the fuel liquid level detection apparatus 1 by 2nd Embodiment of this invention. It is a fragmentary sectional view of the fuel liquid level detection apparatus 1 by 3rd Embodiment of this invention.

Explanation of symbols

1 Fuel level detector (Liquid level detector)
2 Fuel tank (tank)
21 Bottom (bottom)
3 Ultrasonic sensor (Ultrasonic oscillator)
31 Front surface 32 Back surface 33 Electrode 4 Buffer member 41 Notch 5 Sleeve (cover)
6 Lead wire 7 Bracket (case)
71 Bottom 72 Open end 73 Locking hole 74 Protrusion (vibration isolation means, protrusion)
8 Cover (case)
81 Through-hole 82 Locking claw 83 Connector part 84 Terminal 9 Guide pipe 91 Step part 10 Guide pipe 11 Reflecting plate 11a Reflecting surface 12 Body 12a Locking claw 12b Hole part 12c Protrusion (vibration isolation means, protrusion part)
13 Electric wire 14 Fuel (liquid)
14a Liquid level 14b Liquid level 15 Control circuit 15a Pulse generation circuit 15b Arithmetic circuit 15c Drive circuit 16 Display unit 17 Ignition switch 18 Battery 19 Vibration isolation member (vibration isolation means, flexible rubber)
A Axis B B Axis H Liquid level

Claims (4)

An ultrasonic oscillator is placed at the bottom of the tank that stores the liquid,
A liquid level detection device for detecting the position of the liquid level by receiving a reflected wave of the ultrasonic wave emitted from the ultrasonic oscillation element on the liquid level in the tank by the ultrasonic oscillation element,
A case for hermetically housing the ultrasonic oscillation element;
The case is attached to one end side thereof, and the internal space includes a substantially cylindrical transmission tube that forms a propagation path of ultrasonic waves emitted from the ultrasonic oscillation element,
An apparatus for detecting a liquid level, characterized in that a vibration isolating means for suppressing vibration propagation between the case and the transmission pipe is interposed between the case and the transmission pipe mounting portion.   2. The vibration isolating means is a protrusion provided on at least one of the case and the transmission tube, and the case and the transmission tube are in contact with each other at the tip of the protrusion. Liquid level detection device.   The liquid level detection device according to claim 2, wherein the tip has a dot shape or a line shape.   The liquid level detection device according to claim 1, wherein the vibration isolating means is a flexible rubber material or a resin material.

Images