JP2019053031A - Liquid level detector - Google Patents

Abstract

To provide a liquid level detector which can suppress reduction in the intensity of ultrasonic waves received by an ultrasonic sensor even if a route formation body is made of resin.SOLUTION: A liquid level detector 100 includes an ultrasonic sensor 111 and a route formation body 120. The ultrasonic sensor 111 emits ultrasonic waves and receives ultrasonic waves reflected by a liquid level 12. The route formation body 120 is a tube in which a propagation route 121 for propagating ultrasonic waves between the ultrasonic sensor 111 and the liquid level 12 is defined. The route formation body 120 has a horizontal pipe 130 and a vertical pipe 150. The horizontal pipe 130 and the vertical pipe 150 are made of resin and define a horizontal airtight chamber 131 and a vertical airtight chamber 151 holding gas in the inside of the wall of the route formation body 120.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to a liquid level detection device that detects the height of a liquid level in a tank using an ultrasonic sensor.

  Patent Document 1 discloses a liquid level detection device that detects the position of a liquid level based on a time difference between transmitting an ultrasonic wave toward a liquid level in a tank and receiving a reflected wave. The ultrasonic wave travels in the propagation path formed from the ultrasonic oscillation element to the liquid surface, reflects on the liquid surface, travels in the propagation path again, and is received by the ultrasonic oscillation element. The propagation path is formed of a metal or resin molded into a cylindrical shape.

JP 2005-201871 A

  A member (hereinafter referred to as a path forming body) that divides the propagation path on the inside can be formed of a resin for the purpose of weight reduction or the like. However, the reflectance of the ultrasonic wave at the boundary surface between the resin and the liquid tends to be lower than the reflectance of the ultrasonic wave at the boundary surface between the metal and the liquid due to the relationship between the acoustic impedances of the resin, the liquid, and the metal. Therefore, the path forming body formed of resin has a lower reflectance of the ultrasonic wave from the propagation path to the outside of the path forming body than the path forming body formed of metal. As a result, the ultrasonic wave easily leaks from the propagation path through the path forming body. Therefore, the intensity of the ultrasonic wave received by the ultrasonic sensor is lowered, and there is a possibility that accurate liquid level detection becomes difficult.

  An object of the present disclosure is to provide a liquid level detection device capable of suppressing a decrease in intensity of ultrasonic waves received by an ultrasonic sensor even when a path forming body is formed of a resin.

  The above object is achieved by a combination of features described in the independent claims, and the subclaims define further advantageous embodiments of the present disclosure. Reference numerals in parentheses described in the claims indicate a correspondence relationship with specific means described in the embodiments described later as one aspect, and do not limit the technical scope of the present disclosure. .

  This indication for achieving the above-mentioned object is a liquid level detection device (100) which detects the height (Lh) of the liquid level (12) of the liquid (11) accommodated in the tank (10) using ultrasonic waves. 200, 300, 400, 500) which emits ultrasonic waves and receives ultrasonic waves reflected by the liquid surface, and ultrasonic waves between the ultrasonic sensor and the liquid surface A pipe-shaped path forming body (120, 220) that divides a propagation path (121) for propagating the inside of the pipe, and the path forming body is formed of resin and gas is formed inside the wall of the path forming body. It has the hollow part (130, 150, 240, 260, 330, 350, 430) which divides the airtight chamber (131, 151, 241, 261, 331, 351) which hold | maintained.

  According to the above structure, the path | route formation body which divides a propagation path inside has a hollow part. The hollow part is formed of resin. The hollow part partitions the airtight chamber holding the gas inside the wall of the tube-shaped path forming body. Here, at the interface between the gas and the resin, the reflectance of the ultrasonic wave is substantially 100% due to the difference in acoustic impedance between the gas and the resin. Therefore, ultrasonic waves that pass from the propagation path to the outside through the inside of the wall of the path forming body are reflected at the interface between the resin forming the hollow portion and the gas held in the hermetic chamber. As a result, leakage of ultrasonic waves from the propagation path to the outside of the path forming body is suppressed in the hollow portion. Therefore, even when the path forming body is formed of resin, a decrease in the intensity of the ultrasonic wave received by the ultrasonic sensor is suppressed.

It is a figure which shows the whole structure of the liquid level detection apparatus in 1st embodiment. It is the arrow view seen from the II direction of FIG. It is a figure which shows reflection of the ultrasonic wave by a top plate and a liquid level. It is a functional block diagram which shows schematic structure of a control apparatus. It is a figure which shows the time fluctuation of various signals. It is a graph which shows the relationship between the detected liquid level height and the amplitude of an amplified signal. It is a figure which shows the structure of the horizontal pipe in 1st embodiment. It is a figure which shows the method of connecting a horizontal inner peripheral wall and a horizontal outer peripheral wall, and a horizontal cover part. It is the arrow view seen from the IX direction of FIG. FIG. 10 is a cross-sectional perspective view taken along line XX in FIG. 9. It is the XI-XI sectional view taken on the line of FIG. It is a graph which shows the relationship between the thickness of a horizontal inner peripheral wall and a vertical inner peripheral wall, and a reflectance. It is a figure which shows the whole structure of the liquid level detection apparatus in 2nd embodiment. It is a figure which shows the external appearance of the vertical pipe and hollow top plate in 2nd embodiment. It is a figure which shows the external appearance of the fixing member in 2nd embodiment. It is a figure which shows the whole structure of the liquid level detection apparatus in 3rd embodiment. It is a figure which shows the whole structure of the liquid level detection apparatus in 4th embodiment. It is a figure which shows the structure of the horizontal pipe in 4th embodiment. It is a figure which shows the whole structure of the liquid level detection apparatus in 5th embodiment. FIG. 20 is a cross-sectional perspective view taken along line XX-XX in FIG. 19. FIG. 10 is a sectional view taken along line XXI-XXI in FIG. 9.

  Hereinafter, a plurality of embodiments of the present disclosure will be described based on the drawings. In the description of each embodiment, corresponding constituent elements may be denoted by the same reference numerals and redundant description may be omitted. When only a part of the configuration is described, the embodiment described above can be applied to the other parts of the configuration. Further, not only the combination of configurations explicitly described in the description of each embodiment, but also the configuration can be partially combined even if it is not explicitly described if there is no problem in the combination.

<First embodiment>
The liquid level detection device 100 according to the first embodiment of the present disclosure is used in the liquid level detection system 1 as shown in FIGS. 1 and 2. The liquid level detection system 1 detects the height Lh (see FIG. 6 described later) of the liquid level 12 of the liquid 11 accommodated in the tank 10. The tank 10 is a fuel tank for a vehicle that contains fuel such as gasoline as the liquid 11, for example. In the following description, it is assumed that the posture of the liquid surface 12 is substantially parallel to the horizontal direction determined by the posture in which the tank 10 is disposed, and no inclination is generated. The liquid level detection system 1 includes a control device 20 in addition to the liquid level detection device 100.

  The liquid level detection device 100 is installed on the floor surface 13 of the tank 10. The liquid level detection device 100 is electrically connected to the control device 20 by a lead wire 15. The liquid level detection apparatus 100 includes a sensor unit 110 and a path forming body 120.

  The sensor unit 110 emits ultrasonic waves according to a drive signal input from the control device 20 via the lead wire 15. The sensor unit 110 receives the ultrasonic wave and outputs a reception signal indicating the reception state of the ultrasonic wave to the control device 20 via the lead wire 15. Ultrasonic emission and reception are performed by the ultrasonic sensor 111. The sensor unit 110 includes a case 112, a case lid 113, a lead wire 114, and an anti-vibration rubber 116 in addition to the ultrasonic sensor 111 described above.

  The ultrasonic sensor 111 is formed in a disc shape by a piezoelectric material such as lead zirconate titanate (PZT). A piezoelectric body is a substance that has the property of generating a voltage proportional to the received force when it receives a force from the outside while being deformed when a voltage is applied. The ultrasonic sensor 111 emits an ultrasonic wave of 1 MHz, for example, by applying a voltage. The ultrasonic sensor 111 is disposed in the tank 10 in a posture in which the thickness direction is substantially parallel to the liquid surface 12. Electrodes 115 are formed on both surfaces of the ultrasonic sensor 111.

  A voltage is applied between the electrodes 115 by a drive signal from the control device 20. The ultrasonic sensor 111 vibrates and emits ultrasonic waves in the thickness direction by the voltage applied between the electrodes 115. Therefore, the ultrasonic sensor 111 emits ultrasonic waves in the tank 10 in a direction substantially parallel to the liquid level 12. Further, due to the vibration of the ultrasonic sensor 111 accompanying reception of ultrasonic waves, the voltage between the electrodes 115 vibrates with an amplitude proportional to the amplitude of the vibration of the ultrasonic sensor 111. Therefore, the voltage between the electrodes 115 vibrates with an amplitude proportional to the intensity of the ultrasonic wave as the ultrasonic wave is received. The voltage between the electrodes 115 is output to the control device 20 as a reception signal.

  The case 112 is made of a resin that is unlikely to be deformed or deteriorated by the liquid 11 and is formed in a substantially cylindrical shape with a bottom that opens at one end. The case 112, together with the case lid 113, accommodates the ultrasonic sensor 111 and the like inside, and forms the external shape of the sensor unit 110. The central axis of the case 112 substantially coincides with the central axis of the ultrasonic sensor 111. The inner surface of the bottom plate of the case 112 is in contact with the entire surface of the ultrasonic sensor 111. Ultrasonic waves from the ultrasonic sensor 111 are emitted through the bottom plate of the case 112.

  The case lid 113 is formed in a plate shape from the same resin as the case 112. The case lid 113 covers the opening of the case 112 and accommodates the ultrasonic sensor 111 and the like inside.

  The lead wire 114 is a conducting wire arranged to penetrate the case lid 113. The lead wire 114 electrically connects each electrode 115 of the ultrasonic sensor 111 disposed inside the case 112 and the lead wire 15 disposed outside the case 112. A voltage input as a drive signal via the lead wire 15 is applied to each electrode 115 by the lead wire 114. A voltage generated between the electrodes 115 by the lead wire 114 is output as a reception signal through the lead wire 15.

  The anti-vibration rubber 116 is formed in a cylindrical shape by an elastomer such as synthetic rubber. The anti-vibration rubber 116 is disposed between the ultrasonic sensor 111 and the case lid 113 so as to extend along the thickness direction of the ultrasonic sensor 111. The anti-vibration rubber 116 suppresses transmission of vibration from the ultrasonic sensor 111 to the case lid 113.

  The path forming body 120 has a tube shape in which a propagation path 121 is formed inside. The propagation path 121 is a space defined by the horizontal pipe 130, the first metal cylinder 142, the reflecting plate 141, the second metal cylinder 143, and the vertical pipe 150. The propagation path 121 extends from a sensor end 1211 which is one end on the ultrasonic sensor 111 side to an upper end 1212 which is one end on the side away from the ultrasonic sensor 111. The propagation path 121 propagates ultrasonic waves between the ultrasonic sensor 111 and the liquid surface 12. The path forming body 120 includes a fixing member 140 and a top plate 160 in addition to the horizontal pipe 130, the first metal cylinder 142, the reflecting plate 141, the second metal cylinder 143, and the vertical pipe 150 described above.

  The horizontal pipe 130 is formed in a substantially cylindrical shape with both ends opened. The horizontal pipe 130 extends from the outside of the bottom surface of the case 112 along the central axis of the case 112. Therefore, inside the horizontal pipe 130, the ultrasonic wave emitted by the ultrasonic sensor 111 propagates in a direction substantially parallel to the liquid surface 12. A reference wall portion 1311 is formed on the horizontal pipe 130. The reference wall portion 1311 reflects a part of the ultrasonic waves from the ultrasonic sensor 111 toward the ultrasonic sensor 111 at a substantially constant distance from the ultrasonic sensor 111. Detailed configurations of the horizontal pipe 130 and the reference wall portion 1311 will be described later.

  The first metal cylinder 142 is formed in a cylindrical shape with both ends opened by a metal material such as a stainless steel material. The inner diameter of the first metal tube 142 is substantially the same as the inner diameter of one of the openings at both ends of the horizontal pipe 130 that is separated from the case 112. The first metal cylinder 142 extends in the axial direction of the case 112 from one of the openings at both ends of the horizontal pipe 130 that is separated from the case 112. Therefore, the ultrasonic wave that has passed through the inside of the horizontal pipe 130 from the ultrasonic sensor 111 continues to propagate in the direction substantially parallel to the liquid surface 12 through the inside of the first metal cylinder 142.

  The reflection plate 141 is formed in a plate shape from the same metal material as the first metal tube 142. The reflection plate 141 faces one of the openings at both ends of the first metal tube 142 that is separated from the ultrasonic sensor 111. The angle of the central axis of the first metal cylinder 142 with respect to the reflecting plate 141 is about 45 degrees. Due to the arrangement in the tank 10, one surface of the reflecting plate 141 facing the first metal tube 142 faces the liquid surface 12 in an attitude inclined about 45 degrees with respect to the liquid surface 12. Therefore, the reflecting plate 141 reflects the ultrasonic wave propagated in the direction parallel to the liquid surface 12 inside the first metal tube 142 in a direction substantially perpendicular to the liquid surface 12 and directed toward the liquid surface 12. Further, the reflecting plate 141 reflects the ultrasonic wave traveling in the downward direction perpendicular to the liquid surface 12 toward the inside of the horizontal pipe 130.

  The second metal cylinder 143 is formed in a cylindrical shape from the same metal material as the first metal cylinder 142. The inner diameter of the second metal cylinder 143 substantially matches the inner diameter of the first metal cylinder 142. The central axis of the second metal cylinder 143 is in a posture perpendicular to the central axis of the first metal cylinder 142. The opening at one end of the second metal tube 143 faces one surface of the reflecting plate 141 facing the first metal tube 142. The angle of the central axis of the second metal cylinder 143 with respect to the reflecting plate 141 is about 45 degrees. The second metal cylinder 143 is disposed in the tank 10 in such a posture that the central axis is perpendicular to the liquid surface 12 and one end facing the reflection plate 141 is on the lower side. Therefore, in the following description, the direction along the extending direction of the second metal cylinder 143 and from one end facing the reflection plate 141 toward the other end may be described as an upward direction. Moreover, it is a direction along the extending | stretching direction of the 2nd metal cylinder 143, Comprising: The direction toward one end from an other end may be demonstrated as a downward direction. Further, due to this posture, the ultrasonic wave propagates in a direction substantially perpendicular to the liquid surface 12 inside the second metal cylinder 143.

  The vertical pipe 150 is formed in a substantially cylindrical shape with both ends opened. The vertical pipe 150 extends from the other end side of the second metal cylinder 143 toward the liquid surface 12 along a direction perpendicular to the liquid surface 12. Therefore, inside the vertical pipe 150, the ultrasonic wave propagated in the direction substantially perpendicular to the liquid level 12 through the inside of the second metal cylinder 143 continues to propagate in the direction substantially perpendicular to the liquid level 12. The detailed configuration of the vertical pipe 150 will be described later.

  The fixing member 140 is formed in a bent tubular shape using the same resin as the case 112. The fixing member 140 holds the first metal cylinder 142, the reflecting plate 141, and the second metal cylinder 143 inside while maintaining the positional relationship therebetween. The fixing member 140 is connected to the horizontal pipe 130 while maintaining the positional relationship between the horizontal pipe 130 and the first metal cylinder 142. The fixing member 140 is connected to the horizontal pipe 130 by, for example, welding. The fixing member 140 is connected to the vertical pipe 150 while maintaining the positional relationship between the vertical pipe 150 and the second metal cylinder 143. The fixing member 140 is connected to the vertical pipe 150 by welding, for example. Accordingly, the fixing member 140 fixes the horizontal pipe 130 and the vertical pipe 150 in addition to the first metal cylinder 142, the reflecting plate 141, and the second metal cylinder 143 while maintaining the positional relationship therebetween.

  The top plate 160 is formed in a disk shape from the same metal material as the first metal tube 142. The outer diameter of the top plate 160 substantially matches the inner diameter of the vertical pipe 150. The top plate 160 is disposed at the upper end of the vertical pipe 150 in a posture perpendicular to the axial direction of the vertical pipe 150. The top plate 160 closes the opening on the upper end side among the openings of the vertical pipe 150.

  The reflectance of the ultrasonic wave on the surface of the top plate 160 is almost 100%. As shown in FIG. 3, the top plate 160 reflects substantially all of the ultrasonic waves in the extending direction of the vertical pipe 150. For this reason, the reflectance of the ultrasonic wave of the top plate 160 with respect to the extending direction of the vertical pipe 150 is approximately 100%. On the other hand, as shown in FIG. 3, the liquid level 12 inside the vertical pipe 150 is curved due to surface tension. For this reason, a part of the ultrasonic wave is reflected at the outer edge of the liquid surface 12 in a direction inclined with respect to the extending direction of the vertical pipe 150. Thereby, in the inside of the vertical pipe 150, the reflectance of the ultrasonic wave of the liquid surface 12 with respect to the extending direction of the vertical pipe 150 is lower than the reflectance of the liquid surface 12 that is not curved. For example, the reflectance of the liquid surface 12 inside the vertical pipe 150 is 80 to 90%. Therefore, the reflectance of the ultrasonic wave by the top plate 160 in the extending direction of the vertical pipe 150 is higher than the reflectance of the liquid surface 12 inside the vertical pipe 150.

  The control device 20 is an electronic control device having a function of controlling the liquid level detection device 100 and detecting the height Lh of the liquid level 12. The control device 20 is provided outside the tank 10. As illustrated in FIG. 4, the control device 20 has functions as a drive unit 21, an amplification unit 22, a detection unit 23, a comparison unit 24, a detection unit 25, and a top board determination unit 26.

  The drive unit 21 inputs the pulse voltage shown in FIG. 5 to the liquid level detection device 100 as a drive signal. The drive signal is applied to each electrode 115 via the lead wire 15 and the lead wire 114. By applying the drive signal, the ultrasonic sensor 111 emits an ultrasonic wave.

  The amplification unit 22 amplifies the reception signal output from the liquid level detection device 100 to obtain an amplification signal shown in FIG. The received signal vibrates with an amplitude proportional to the intensity of the ultrasonic wave when the ultrasonic sensor 111 receives the ultrasonic wave. Therefore, the amplified signal vibrates with an amplitude proportional to the intensity of the ultrasonic wave when the ultrasonic sensor 111 receives the ultrasonic wave.

  The detector 23 performs half-wave rectification on the amplified signal to obtain a detection signal shown in FIG. The detection signal becomes a voltage proportional to the intensity of the ultrasonic wave when the ultrasonic sensor 111 receives the ultrasonic wave.

  The comparison unit 24 compares the voltage of the detection signal with a preset threshold Th and outputs the comparison signal shown in FIG. The comparison signal represents the magnitude of the detection signal with respect to the threshold value Th as a binary value. The threshold value Th is a value for discriminating reception and noise of the ultrasonic wave reflected by the liquid surface 12 or the reference wall portion 1311. The comparison signal indicates whether or not the ultrasonic sensor 111 vibrates due to reception of the ultrasonic wave.

  The vibration state of the ultrasonic sensor 111 indicated by the comparison signal in FIG. 5 will be described. The comparison signal indicates the occurrence of vibration of the ultrasonic sensor 111 during the period from time t1 to time t2, from time t3 to time t4, and from time t5 to time t6. From time t1 to time t2, the ultrasonic sensor 111 vibrates and emits ultrasonic waves by the input of the drive signal. From time t3 to time t4, the ultrasonic sensor 111 is vibrated by the ultrasonic waves reflected by the reference wall portion 1311. From time t5 to time t6, the ultrasonic sensor 111 vibrates due to the ultrasonic wave reflected by the liquid surface 12. Therefore, the time from the time t1 to the time t3 indicates the reference round-trip time required for the round-trip of the ultrasonic reference distance. The reference distance is a distance between the ultrasonic sensor 111 and the reference wall portion 1311. The time from time t1 to time t5 indicates the liquid surface reciprocation time required for reciprocating the ultrasonic liquid surface distance. The liquid level distance is a distance between the ultrasonic sensor 111 and the liquid level 12.

  The detection unit 25 detects the height Lh of the liquid level 12 based on the comparison signal. Here, in the liquid 11, the speed of the ultrasonic wave is substantially constant. Therefore, the ratio between the reference distance and the liquid level distance substantially matches the ratio between the reference round trip time and the liquid level round trip time. The detection unit 25 first calculates the ratio of the liquid surface reciprocation time to the reference reciprocation time. Subsequently, the detection unit 25 obtains the liquid level distance by multiplying the calculated distance ratio by the reference distance. The detection unit 25 detects a value obtained by subtracting the distance between the ultrasonic sensor 111 and the reflecting plate 141 from the obtained liquid surface distance as the height Lh of the liquid surface 12.

  The top plate determination unit 26 determines the reflection of ultrasonic waves by the top plate 160. The operation of the top panel determination unit 26 will be described with reference to FIGS. 5 and 6. The intensity of ultrasonic waves decreases as the propagation distance increases. Therefore, the amplitude peak value Wh of the amplified signal from time t5 to time t6 shown in FIG. 5 tends to decrease as the height Lh of the liquid level 12 detected by the detection unit 25 increases. When the ultrasonic wave is reflected by the liquid surface 12, the peak value Wh with respect to the height Lh is shown by a graph G1 in FIG.

  Here, the top plate 160 reflects ultrasonic waves with a higher reflectance than the liquid surface 12 in the propagation path 121. For this reason, when the ultrasonic wave is reflected by the top plate 160, the intensity reduction of the ultrasonic wave reflected from the liquid surface 12 is suppressed. Thereby, when an ultrasonic wave is reflected by the top plate 160, the peak value Wh with respect to the height Lh is indicated by a graph G2 that tends to be higher than the graph G1.

  The top panel determination unit 26 determines the reflection of the ultrasonic wave by the top panel 160 based on the position of the point indicating the relationship between the peak value Wh and the height Lh. The top plate determination unit 26 determines that the ultrasonic wave is reflected by the top plate 160 when the point indicating the relationship of the peak value Wh to the height Lh is a position on the graph G2.

  For example, the point P1 indicating the correspondence relationship of the peak value Wh1 with respect to the predetermined height Lh1 in FIG. 6 in the height Lh of the liquid level 12 is located on the graph G2. In such a case, the top panel determination unit 26 determines that the ultrasonic wave is reflected by the top panel 160. The ultrasonic wave is reflected by the top plate 160 when the height Lh of the liquid surface 12 is higher than the height of the top plate 160. Therefore, the top plate determination unit 26 can determine that the liquid level 12 is located above the height Lh of the liquid level 12 that can be detected by the liquid level detection device 100.

  Next, the structure of the horizontal pipe 130 and the vertical pipe 150 which the path | route formation body 120 has is demonstrated in detail.

  The horizontal pipe 130 shown in FIG. 1 and FIG. 7 is formed of a hard resin that hardly changes in quality due to the liquid 11 and is difficult to deform. The horizontal pipe 130 is made of, for example, polyacetal resin (POM). The horizontal pipe 130 partitions a horizontal hermetic chamber 131 inside the cylindrical wall. The horizontal pipe 130 has a horizontal inner peripheral wall 132, a horizontal outer peripheral wall 133, a horizontal lid part 134, and a horizontal reinforcing wall 135 for partitioning the horizontal hermetic chamber 131.

  The horizontal airtight chamber 131 is a substantially cylindrical space extending along the direction in which the horizontal pipe 130 extends between the horizontal inner peripheral wall 132 and the horizontal outer peripheral wall 133. The horizontal hermetic chamber 131 is partitioned inside the wall of the horizontal pipe 130 that forms a part of the tube shape of the path forming body 120. A gas such as nitrogen, helium, argon, or air is held in the horizontal airtight chamber 131 of the horizontal pipe 130.

  The horizontal inner peripheral wall 132 is formed in a cylindrical shape having a circular cross section. The thickness dimension of the horizontal inner peripheral wall 132 is, for example, 1.2 mm. The horizontal inner peripheral wall 132 has a shape in which an inner diameter and an outer diameter are reduced from one end to the other end. The outer diameter of one end of the horizontal inner peripheral wall 132 is substantially equal to the outer diameter of the case 112. The horizontal inner peripheral wall 132 covers the outside of the bottom surface of the case 112 with an opening on one end side. Accordingly, the inner and outer diameters of the horizontal inner peripheral wall 132 become smaller as the distance from the case 112 increases. The central axis of the horizontal inner peripheral wall 132 substantially coincides with the central axis of the horizontal pipe 130. Therefore, the horizontal inner peripheral wall 132 extends in a direction substantially parallel to the liquid level 12 by installing the liquid level detection device 100. The inner peripheral surface of the horizontal inner peripheral wall 132 forms the inner peripheral surface of the horizontal pipe 130. A reference wall portion 1311 and an inner bead 1322 are formed on the horizontal inner peripheral wall 132.

  The reference wall portion 1311 is a step-like wall portion that is formed by gradually reducing the inner diameter and the outer diameter of the horizontal inner peripheral wall 132. The reference wall portion 1311 is formed in an annular plate shape. The central axis of the reference wall portion 1311 substantially coincides with the central axis of the case 112. The reference wall portion 1311 is located at a predetermined distance from the ultrasonic sensor 111. Therefore, the reference wall 1311 reflects a part of the ultrasonic wave toward the ultrasonic sensor 111 at a predetermined distance from the ultrasonic sensor 111.

  As shown in FIG. 8, the inner bead 1322 is formed by partially projecting end surfaces on the side away from the case 112 from both end surfaces of the horizontal inner peripheral wall 132. The inner bead 1322 is an annular protrusion formed over the entire circumference of the horizontal inner peripheral wall 132.

  The horizontal outer peripheral wall 133 is formed in a cylindrical shape. The inner diameter of the horizontal outer peripheral wall 133 is substantially equal to the outer diameter of one end of the horizontal inner peripheral wall 132 and the outer diameter of the case 112. The axial length of the horizontal outer peripheral wall 133 is substantially equal to the total length of the axial length of the horizontal inner peripheral wall 132 and the axial length of the case 112. The horizontal outer peripheral wall 133 extends along the axial direction of the case 112. The horizontal outer peripheral wall 133 extends from the opening of the case 112 toward the bottom surface of the case 112, and extends to the opening on the other end side of the horizontal inner peripheral wall 132. The horizontal outer peripheral wall 133 is arranged to cover the outer periphery of the case 112 and the horizontal inner peripheral wall 132. Therefore, the horizontal outer peripheral wall 133 is configured to extend along a direction horizontal to the liquid level 12 by installing the liquid level detection device 100. The inner diameter of the horizontal outer peripheral wall 133 is substantially constant even when it is away from the case 112. Therefore, the radial dimension of the gap between the outer peripheral surface of the horizontal inner peripheral wall 132 and the inner peripheral surface of the horizontal outer peripheral wall 133 increases as the distance from the case 112 increases. The horizontal outer peripheral wall 133 is connected to a part of one end side of the outer peripheral surface of the horizontal inner peripheral wall 132 by being molded integrally with the horizontal inner peripheral wall 132, for example. An outer bead 1331 is formed on the horizontal outer peripheral wall 133.

  As shown in FIG. 8, the outer bead 1331 is formed by partially projecting end surfaces on the side away from the case 112 out of both end surfaces of the horizontal outer peripheral wall 133. The outer bead 1331 is an annular protrusion formed over the entire circumference of the horizontal outer peripheral wall 133.

  The horizontal lid part 134 is formed in an annular plate shape. The inner diameter of the horizontal lid portion 134 is substantially equal to the inner diameter of the horizontal inner peripheral wall 132 on the side away from the case 112. The outer diameter of the horizontal lid part 134 is substantially equal to the outer diameter of the horizontal outer peripheral wall 133. The central axis of the horizontal lid part 134 substantially coincides with the central axis of the horizontal pipe 130. One end of the horizontal outer peripheral wall 133 and the horizontal inner peripheral wall 132 that are separated from the case 112 is connected to one surface of the horizontal lid portion 134 on the case 112 side. Specifically, the horizontal outer peripheral wall 133 and the horizontal inner peripheral wall 132 are connected to the horizontal lid portion 134 by welding an inner bead 1322 and an outer bead 1331 to one surface of the horizontal lid portion 134 on the case 112 side.

  The horizontal reinforcing wall 135 is formed in a plate shape. Both surfaces of the horizontal reinforcing wall 135 are oriented in the circumferential direction of the horizontal pipe 130. The horizontal reinforcing walls 135 are arranged at six positions that are substantially equidistant in the circumferential direction between the horizontal inner peripheral wall 132 and the horizontal outer peripheral wall 133. Each horizontal reinforcing wall 135 is connected to the outer peripheral surface of the horizontal inner peripheral wall 132 and the inner peripheral surface of the horizontal outer peripheral wall 133. Accordingly, each horizontal reinforcing wall 135 connects the horizontal inner peripheral wall 132 and the horizontal outer peripheral wall 133. Each horizontal reinforcing wall 135 is connected, for example, by being molded integrally with the horizontal inner peripheral wall 132 and the horizontal outer peripheral wall 133.

  The vertical pipe 150 shown in FIGS. 1, 9, 10, and 11 is formed of the same resin as the horizontal pipe 130. The vertical pipe 150 defines a vertical hermetic chamber 151 inside the cylindrical wall.

  The vertical hermetic chamber 151 is a space defined by a vertical inner peripheral wall 152, a vertical outer peripheral wall 153, an upper end cover part 154, a lower end cover part 155, and a vertical reinforcing wall 156. The vertical airtight chamber 151 has a substantially cylindrical shape extending along the direction in which the vertical pipe 150 extends between the vertical inner peripheral wall 152 and the vertical outer peripheral wall 153. The vertical hermetic chamber 151 is partitioned inside the wall of the vertical pipe 150 that forms a part of the tube shape of the path forming body 120. Therefore, the vertical hermetic chamber 151 is partitioned inside the tube-shaped wall of the path forming body 120. Similar to the horizontal airtight chamber 131, the vertical airtight chamber 151 holds a gas such as nitrogen, helium, argon, or air. The vertical pipe 150 includes the above-described vertical inner peripheral wall 152, vertical outer peripheral wall 153, upper end cover portion 154, lower end cover portion 155, and vertical reinforcing wall 156.

  The vertical inner peripheral wall 152 is formed in a cylindrical shape. The thickness dimension of the wall surface of the vertical inner peripheral wall 152 is, for example, 1.2 mm. The inner diameter of the vertical inner peripheral wall 152 substantially matches the inner diameter of the second metal cylinder 143. The central axis of the vertical inner peripheral wall 152 substantially coincides with the central axis of the second metal cylinder 143. Therefore, the vertical inner peripheral wall 152 extends in a direction substantially perpendicular to the liquid level 12 by installing the liquid level detection device 100. The inner peripheral surface of the vertical inner peripheral wall 152 forms the inner peripheral surface of the vertical pipe 150.

  The vertical outer peripheral wall 153 is formed in a cylindrical shape. The inner diameter of the vertical outer peripheral wall 153 is, for example, 2 to 4 mm larger than the outer diameter of the vertical inner peripheral wall 152. The length of the vertical outer peripheral wall 153 in the axial direction is substantially equal to the length of the vertical inner peripheral wall 152 in the axial direction. The vertical outer peripheral wall 153 is arranged to cover the outer periphery of the vertical inner peripheral wall 152. Accordingly, a gap of 1 to 2 mm is formed as the vertical hermetic chamber 151 between the vertical outer peripheral wall 153 and the vertical inner peripheral wall 152. Further, the vertical outer peripheral wall 153 is configured to extend along a direction perpendicular to the liquid level 12 by installing the liquid level detection device 100.

  The upper end lid 154 is formed in an annular plate shape. The inner diameter of the upper end lid 154 is substantially equal to the inner diameter of the vertical inner peripheral wall 152. The outer diameter of the upper end lid 154 is substantially equal to the outer diameter of the vertical outer peripheral wall 153. The center axis line of the upper end cover part 154 substantially coincides with the center axis line of the vertical inner peripheral wall 152. One end in the upward direction of the vertical outer peripheral wall 153 and the vertical inner peripheral wall 152 is connected to one lower surface of the upper end cover portion 154. The upper end lid 154 is connected by being molded integrally with the vertical inner peripheral wall 152 and the vertical outer peripheral wall 153, for example. The upper end lid 154 forms the upper end of the vertical pipe 150. Therefore, the top plate 160 is fitted inside the upper end lid portion 154. A communication groove 1541 is formed on an upper surface of the upper end lid 154.

  The communication groove 1541 extends in the radial direction. The communication groove 1541 is formed at two substantially equal intervals in the circumferential direction. The depth dimension of the communication groove 1541 is 1-2 mm larger than the thickness dimension of the top plate 160. Thereby, in the state in which the top plate 160 is fitted, a portion of the communication groove 1541 below the top plate 160 communicates the inside and the outside of the vertical pipe 150.

  The lower end cover part 155 is formed in an annular plate shape. The inner diameter of the lower end cover portion 155 is substantially equal to the inner diameter of the vertical inner peripheral wall 152. The outer diameter of the lower end cover portion 155 is substantially equal to the outer diameter of the vertical outer peripheral wall 153. The central axis of the lower end cover portion 155 substantially coincides with the central axis of the vertical inner peripheral wall 152. One end in the downward direction of the vertical outer peripheral wall 153 and the vertical inner peripheral wall 152 is connected to one upper surface of the lower end cover portion 155. For example, the lower end cover 155 is connected to the vertical outer peripheral wall 153 and the vertical inner peripheral wall 152 by welding or the like.

  The vertical reinforcing wall 156 is formed in a plate shape. Both surfaces of the vertical reinforcing wall 156 are oriented in the circumferential direction of the vertical pipe 150. The vertical reinforcing walls 156 are arranged at six substantially equal intervals in the circumferential direction between the vertical inner peripheral wall 152 and the vertical outer peripheral wall 153. Each vertical reinforcing wall 156 is connected to the outer peripheral surface of the vertical inner peripheral wall 152 and the inner peripheral surface of the vertical outer peripheral wall 153. Accordingly, each vertical reinforcing wall 156 connects the vertical inner peripheral wall 152 and the vertical outer peripheral wall 153. Each vertical reinforcing wall 156 is connected by being molded integrally with the vertical inner peripheral wall 152 and the vertical outer peripheral wall 153, for example.

[Summary of First Embodiment]
As described above, according to the first embodiment described above, the path forming body 120 that divides the propagation path 121 on the inside includes the horizontal pipe 130 and the vertical pipe 150. The horizontal pipe 130 and the vertical pipe 150 are each formed of resin. The horizontal pipe 130 and the vertical pipe 150 divide a horizontal hermetic chamber 131 and a vertical hermetic chamber 151 holding gas, respectively, inside a cylindrical wall.

Here, at the interface between the gas and the resin, the reflectance of the ultrasonic wave is substantially 100% due to the difference in acoustic impedance between the gas and the resin. Specifically, the reflectance Rp of the ultrasonic wave at the boundary surface between different media can be obtained by substituting the acoustic impedances Z1 and Z2 of each medium shown in Table 1 below into the following Equation 1.

  For example, the reflectance of the interface between the POM and air obtained by substituting the acoustic impedance Z of POM and air as Z1 and Z2 in Equation 1 is 99.95%. Therefore, ultrasonic waves that pass from the inside of the horizontal pipe 130 to the outside through the inside of the wall are reflected at the boundary surface between the resin forming the horizontal pipe 130 and the gas held in the horizontal hermetic chamber 131. Similarly, ultrasonic waves that pass from the inside of the vertical pipe 150 to the outside through the inside of the wall are reflected at the boundary surface between the resin forming the vertical pipe 150 and the gas held in the vertical hermetic chamber 151. As a result, in the horizontal pipe 130 and the vertical pipe 150, leakage of ultrasonic waves from the propagation path 121 to the outside of the path forming body 120 is suppressed. Therefore, even when the horizontal pipe 130 and the vertical pipe 150 are formed of resin, a decrease in the intensity of ultrasonic waves received by the ultrasonic sensor 111 is suppressed.

  In addition, in the first embodiment, since the horizontal hermetic chamber 131 is provided in a cylindrical shape between the horizontal inner peripheral wall 132 and the horizontal outer peripheral wall 133, the reflection direction of the ultrasonic waves by the inner peripheral surface of the horizontal hermetic chamber 131 is The reflection direction of the ultrasonic wave by the inner peripheral surface of the horizontal inner peripheral wall 132 substantially coincides. In addition, since the vertical hermetic chamber 151 is provided in a cylindrical shape between the vertical inner peripheral wall 152 and the vertical outer peripheral wall 153, the reflection direction of the ultrasonic wave by the inner peripheral surface of the vertical hermetic chamber 151 is different from that of the vertical inner peripheral wall 152. It substantially coincides with the reflection direction of the ultrasonic waves by the inner peripheral surface. As a result, diffusion of ultrasonic waves reflected by the horizontal pipe 130 and the vertical pipe 150 is suppressed. Therefore, the liquid level detection apparatus 100 can further suppress a decrease in the intensity of the ultrasonic wave received by the ultrasonic sensor 111.

  Furthermore, in the first embodiment, the connection between the horizontal inner peripheral wall 132 and the horizontal outer peripheral wall 133 by the horizontal reinforcing wall 135 increases the rigidity of the horizontal pipe 130. Further, according to the connection between the vertical inner peripheral wall 152 and the vertical outer peripheral wall 153 by the vertical reinforcing wall 156, the rigidity of the vertical pipe 150 is increased. As a result, the horizontal pipe 130 and the vertical pipe 150 are hardly elastically deformed with respect to the input from the liquid 11 or the like. Therefore, since the shape change of the propagation path 121 is suppressed, the accuracy of liquid level detection is maintained high.

In addition, in the first embodiment, the thickness of the horizontal inner peripheral wall 132 and the vertical inner peripheral wall 152 is 1.2 mm. Here, the reflectance Rp when ultrasonic waves are incident on the wall-shaped medium having the acoustic impedance Z2 and the thickness t from the medium having the acoustic impedance Z1 is obtained by substituting k = Z1 / Z2 into the following equation 2. It is obtained by.

  When the thickness t is an integral multiple of the half wavelength of the ultrasonic wave, the wall-shaped medium resonates and the reflectance Rp is substantially zero. For example, the reflectance Rp in the case of entering the POM from gasoline changes as shown by the graphs G3 and G4 in FIG. 12 depending on the thickness t of the POM wall. However, the graph G3 is a case of 20 ° C, and the graph G4 is a case of 60 ° C. The sound speed at 20 ° C. POM is approximately 2400 m / s as shown in Table 1. For this reason, the wavelength of 1 Mhz ultrasonic waves in POM is 2.4 mm. In the graph G3, the reflectance Rp is substantially 0 at t = 1.2 mm and T = 2.4 mm which are integral multiples of a half wavelength.

  As described above, since the horizontal inner peripheral wall 132 and the vertical inner peripheral wall 152 have a thickness that is an integral multiple of a half wavelength of the ultrasonic wave, they are resonated by the ultrasonic wave and the reflection on the inner peripheral surface is suppressed. As a result, the ultrasonic waves are mainly reflected on the inner peripheral surfaces of the cylindrical horizontal airtight chamber 131 and the vertical airtight chamber 151. Thereby, diffusion of ultrasonic waves reflected by the path forming body 120 is further suppressed. Accordingly, the liquid level detection apparatus 100 can further suppress a decrease in the intensity of the ultrasonic wave received by the ultrasonic sensor 111.

  In addition, a reference wall portion 1311 is formed in the horizontal pipe 130 of the first embodiment. The reference wall 1311 reflects a part of the ultrasonic wave at a substantially constant distance from the ultrasonic sensor 111 in the middle of the propagation path 121. Therefore, the detection unit 25 can detect the height Lh of the liquid surface 12 by correcting the change in the ultrasonic velocity based on the round-trip time of the ultrasonic wave reflected by the reference wall part 1311 and the distance to the reference wall part 1311. It is. Therefore, even when the horizontal pipe 130 is formed of resin, the liquid level detection system 1 using the liquid level detection device 100 can detect the height Lh of the liquid level 12 with high accuracy.

  In addition, a communication groove 1541 is formed in the upper end lid portion 154 of the first embodiment. Even if the top plate 160 blocks the upper end of the propagation path 121 due to the air flow through the communication groove 1541, the height Lh of the liquid level 12 in the propagation path 121 and the liquid level 12 outside the path forming body 120. A difference from the height Lh is suppressed. Further, since the communication groove 1541 is formed in the annular plate-shaped upper end cover part 154 that defines the upper end of the propagation path 121, the communication groove 1541 is in the direction in which the propagation path 121 extends in the part defined by the upper end cover part 154. Is inclined. Therefore, the ultrasonic wave propagating through the propagation path 121 hardly leaks from the propagation path 121 to the outside of the path forming body 120 through the communication groove 1541. Therefore, the liquid level detection apparatus 100 can suppress an error in the detected height Lh of the liquid level 12 while suppressing a decrease in the intensity of the ultrasonic wave received by the ultrasonic sensor 111 by providing the top plate 160.

  In the first embodiment, the horizontal pipe 130 and the vertical pipe 150 correspond to “hollow portions”. The horizontal hermetic chamber 131 and the vertical hermetic chamber 151 correspond to “airtight chambers”. The horizontal inner peripheral wall 132 and the vertical inner peripheral wall 152 correspond to the “inner peripheral wall”. The horizontal outer peripheral wall 133 and the vertical outer peripheral wall 153 correspond to the “outer peripheral wall”. The horizontal reinforcing wall 135 and the vertical reinforcing wall 156 correspond to “reinforcing walls”. The upper end lid 154 corresponds to the “upper end”. The communication groove 1541 corresponds to a “communication path”.

<Second embodiment>
The second embodiment shown in FIGS. 13 to 15 is a modification of the first embodiment. In the liquid level detection device 200 of the second embodiment, the path forming body 220 further includes a hollow top plate 260. Furthermore, in the liquid level detection apparatus 200, the configurations of the communication groove 1541 and the fixing member 240 are different from those of the first embodiment. Further, the path forming body 220 does not have the reflecting plate 141.

  The hollow top plate 260 shown in FIG. 13 and FIG. 14 is formed in a disc-like appearance by the same resin as the horizontal pipe 130. The outer diameter of the hollow top plate 260 substantially matches the outer diameter of the vertical pipe 150. The central axis of the hollow top plate 260 substantially coincides with the central axis of the vertical pipe 150. The lower surface of both surfaces of the hollow top plate 260 is connected to the upper end of the vertical pipe 150 by welding or the like. As a result, the hollow top plate 260 closes the opening at the upper end of the vertical pipe 150. The hollow top plate 260 divides the top plate hermetic chamber 261 inside a disk-shaped wall. The hollow top plate 260 has a top plate bottom 262 for partitioning the top plate hermetic chamber 261, a top plate outer peripheral wall 263, and a top plate upper lid 264.

  The top plate airtight chamber 261 is a disk-shaped space defined between the top plate bottom 262 and the top plate upper lid 264. The center axis of the top plate hermetic chamber 261 substantially matches the center axis of the hollow top plate 260. Therefore, the disk-shaped both surfaces of the top plate hermetic chamber 261 are substantially parallel to the liquid level 12 by the installation of the liquid level detection device 200. A gas such as nitrogen, helium, argon, or air is held in the top plate hermetic chamber 261 in the same manner as the horizontal pipe 130.

  The top plate bottom 262 is formed in a disc shape. The thickness dimension of the top plate bottom 262 is, for example, 1.2 mm. The outer diameter of the top plate bottom 262 is equal to the outer diameter of the hollow top plate 260. The central axis of the top plate bottom 262 substantially coincides with the central axis of the hollow top plate 260. The top plate bottom 262 is connected to the upper end of the vertical pipe 150 by welding or the like in a posture perpendicular to the extending direction of the vertical pipe 150. That is, the top plate bottom 262 forms the lower surface of the hollow top plate 260.

  The top plate outer peripheral wall 263 is formed in a cylindrical shape. The outer diameter of the top plate outer peripheral wall 263 matches the outer diameter of the vertical pipe 150. The thickness dimension in the radial direction of the wall surface of the top plate outer peripheral wall 263 is, for example, 1 to 2 mm. The length dimension of the top plate outer peripheral wall 263 in the axial direction is, for example, 1 to 2 mm. The center axis line of the top plate outer peripheral wall 263 substantially matches the center axis line of the hollow top plate 260. The top plate outer peripheral wall 263 is arranged to surround the outer periphery of the top plate hermetic chamber 261. Of the both end faces of the top plate outer peripheral wall 263, the lower end face is connected to the upper face of the top plate bottom 262. The top plate outer peripheral wall 263 is connected to the top plate bottom 262 by being molded integrally with the top plate bottom 262, for example.

  The top plate upper lid 264 is formed in a disc shape. The outer diameter of the top plate upper lid 264 substantially matches the outer diameter of the vertical pipe 150. The center axis of the top plate upper lid 264 substantially coincides with the center axis of the hollow top plate 260. The lower surface of the top plate upper lid 264 is connected to the upper end surface of the top plate outer peripheral wall 263 by welding or the like.

  The communication groove 2541 is formed with a depth of 1 to 2 mm. In a state where the hollow top plate 260 is connected to the vertical pipe 150, the communication groove 1541 communicates the inside and the outside of the vertical pipe 150 by forming a gap with the hollow top plate 260.

  The fixing member 240 shown in FIG. 15 is formed in a plate-like appearance by the same resin as that of the horizontal pipe 130. The fixing member 240 holds the first metal cylinder 142 and the second metal cylinder 143 inside while maintaining the mutual positional relationship. The fixing member 240 defines a reflection hermetic chamber 241 inside a tubular wall. The fixing member 240 includes a reflection inner wall 242 for partitioning the reflection hermetic chamber 241, an outer peripheral convex portion 243, and a reflection lid portion 244.

  The reflection hermetic chamber 241 is a plate-like space partitioned inside the tubular wall of the fixing member 240. The reflective hermetic chamber 241 is partitioned between the reflective inner wall 242 and the reflective lid 244. One surface of the plate shape of the reflection hermetic chamber 241 is opposed to the opening of the first metal cylinder 142 on the side separated from the horizontal pipe 130 and the opening of the second metal cylinder 143 on the side separated from the vertical pipe 150. The angles formed by the central axes of the first metal cylinder 142 and the second metal cylinder 143 with respect to both surfaces of the reflective hermetic chamber 241 are about 45 degrees, respectively.

  The reflection inner wall 242 is formed in a plate shape. The reflection inner wall 242 is formed between the first metal cylinder 142 and the second metal cylinder 143 and the reflection hermetic chamber 241. The angles formed by the central axes of the first metal cylinder 142 and the second metal cylinder 143 with respect to both surfaces of the reflection inner wall 242 are about 45 degrees, respectively. One surface of the reflection inner wall 242 facing the first metal tube 142 and the second metal tube 143 forms a part of the inner surface of the fixing member 240.

  The outer peripheral convex part 243 is formed in a substantially rectangular tube shape having a rectangular cross section. The outer peripheral convex portion 243 is arranged to extend so as to surround the outer periphery of the reflective hermetic chamber 241 from one surface of the reflective inner wall 242 that is separated from the first metal tube 142 and the second metal tube 143. The outer peripheral convex portion 243 protrudes, for example, 1 to 2 mm from one surface of the reflective inner wall 242 that is separated from the first metal tube 142 and the second metal tube 143.

  The reflective lid 244 is formed in a plate shape. The reflection lid 244 is disposed on the opposite side of the reflection inner wall 242 of the reflection hermetic chamber 241. One surface of the reflective lid portion 244 is connected to an end surface of the outer peripheral convex portion 243 that is separated from the reflective inner wall 242 by welding or the like.

[Summary of Second Embodiment]
As described above, also in the second embodiment described above, the horizontal airtight chamber 131 and the vertical airtight chamber 151 are defined inside the walls of the horizontal pipe 130 and the vertical pipe 150. Therefore, similarly to the first embodiment, even when the horizontal pipe 130 and the vertical pipe 150 are formed of resin, a decrease in the intensity of ultrasonic waves received by the ultrasonic sensor 111 is suppressed.

  In addition, in the second embodiment, the top plate hermetic chamber 261 and the reflection hermetic chamber 241 are defined inside the walls of the hollow top plate 260 and the fixing member 240, respectively. The ultrasonic wave that travels upward in the wall of the hollow top plate 260 is reflected by the boundary surface between the resin constituting the hollow top plate 260 and the gas held in the top plate hermetic chamber 261 and travels downward. As a result, the hollow top plate 260 replaces the top plate 160 of the first embodiment. In addition, the ultrasonic wave that has passed through the inside of the first metal tube 142 and entered the wall of the fixing member 240 is reflected at the boundary surface between the resin forming the fixing member 240 and the gas held in the reflective hermetic chamber 241. To the inside of the second metal cylinder 143. The ultrasonic waves that have passed through the inside of the second metal tube 143 and entered the wall of the fixing member 240 are reflected by the boundary surface between the resin forming the fixing member 240 and the gas held in the reflective hermetic chamber 241. It goes to the inside of one metal cylinder 142. As a result, the fixing member 240 replaces the reflector 141 of the first embodiment. Thus, even when the hollow top plate 260 that replaces the top plate 160 and the fixing member 240 that replaces the reflecting plate 141 are formed of resin, the ultrasonic sensor 111 receives ultrasonic waves. Strength reduction is suppressed.

  The vertical pipe 150 and the second metal cylinder 143 are connected via the fixing member 240 in a posture inclined at a substantially vertical angle with respect to the horizontal pipe 130 and the first metal cylinder 142. Therefore, when the vertical pipe 150 and the second metal cylinder 143 are arranged in a posture perpendicular to the liquid level 12, the horizontal pipe 130 and the first metal cylinder 142 are substantially perpendicular to the direction perpendicular to the liquid level 12. The posture is inclined at an angle. Since the reference wall portion 1311 is provided in such a horizontal pipe 130, an increase in the height dimension of the path forming body 120 due to the distance between the reference wall portion 1311 and the ultrasonic sensor 111 in the propagation path 121 is suppressed. The Accordingly, the liquid level detection device 200 can form the reference wall portion 1311 while suppressing an increase in the height dimension of the path forming body 120 even when the fixing member 240 replacing the reflecting plate 141 is formed of resin. It is.

  Also in the second embodiment, the upper end lid portion 154 is formed with a communication groove 2541. Even if the propagation path 121 is blocked by the hollow top plate 260 due to the air flow through the communication groove 2541, the height Lh of the liquid level 12 in the propagation path 121 and the height of the liquid level 12 outside the path forming body 120. The difference from the length Lh is suppressed. In addition, the communication groove 2541 is formed in the cylindrical upper end lid portion 154 that defines the upper end 1212 of the propagation path 121, and therefore is inclined with respect to the extending direction of the propagation path 121. Therefore, the ultrasonic wave propagating through the propagation path 121 is unlikely to leak out of the path forming body 120 from the propagation path 121 through the communication groove 2541. Therefore, the liquid level detection apparatus 200 can detect the height Lh of the liquid level 12 with high accuracy while suppressing a decrease in the intensity of the ultrasonic wave received by the ultrasonic sensor 111 as in the first embodiment.

  In the second embodiment, the fixing member 240 and the hollow top plate 260 correspond to “hollow portions”. The reflection hermetic chamber 241 and the top plate hermetic chamber 261 correspond to the “airtight chamber”. The fixing member 240 corresponds to the “reflection wall portion”. The hollow top plate 260 corresponds to the “top plate wall”. A portion of the propagation path 121 that is partitioned inside the horizontal pipe 130 and the first metal cylinder 142 corresponds to a “first section”. A portion of the propagation path 121 that is partitioned inside the second metal cylinder 143 and the vertical pipe 150 corresponds to a “second section”. The communication groove 2541 corresponds to a “communication path”.

<Third embodiment>
The third embodiment shown in FIG. 16 is another modification of the first embodiment. In the liquid level detection device 300 of the third embodiment, the configurations of the horizontal airtight chamber 331 and the vertical airtight chamber 351 partitioned inside the horizontal pipe 330 and the vertical pipe 350 are different from those of the first embodiment.

  The horizontal hermetic chamber 331 and the vertical hermetic chamber 351 are filled with foamed resin containing gas. For example, polypropylene, polyethylene, nylon or the like is filled in a foamed state.

[Summary of third embodiment]
As described above, according to the third embodiment described above, the horizontal airtight chamber 331 and the vertical airtight chamber 351 are filled with the foamed resin containing gas. Also in this aspect, ultrasonic waves that pass from the propagation path 121 through the inside of the wall of the path forming body 120 toward the outside are reflected at the boundary surface between the gas contained in the foamed resin and the resin. As a result, leakage of ultrasonic waves from the propagation path 121 to the outside of the path forming body 120 is suppressed in the horizontal hermetic chamber 331 and the vertical hermetic chamber 351. Accordingly, a decrease in the intensity of the ultrasonic wave received by the ultrasonic sensor 111 is suppressed. In the third embodiment, the horizontal pipe 330 and the vertical pipe 350 correspond to “hollow portions”, and the horizontal airtight chamber 331 and the vertical airtight chamber 351 correspond to “airtight chambers”.

<Fourth embodiment>
The fourth embodiment shown in FIGS. 17 and 18 is another modification of the first embodiment. In the liquid level detection device 400 of the fourth embodiment, the horizontal pipe 430 further includes a reference metal plate 4311.

  The reference metal plate 4311 is formed in an annular plate shape using the same metal material as that of the first metal cylinder 142. The inner diameter of the reference metal plate 4311 is equal to the inner diameter of the reference wall portion 1311. The outer diameter of the reference metal plate 4311 is equal to the outer diameter of the reference wall portion 1311. The central axis of the reference metal plate 4311 substantially coincides with the central axis of the reference wall portion 1311. The reference metal plate 4311 is fitted in the horizontal inner peripheral wall 132. One surface of the reference metal plate 4311 on the side away from the ultrasonic sensor 111 is in contact with the surface of the reference wall portion 1311 on the ultrasonic sensor 111 side.

[Summary of Fourth Embodiment]
As described above, also in the fourth embodiment described above, the horizontal airtight chamber 131 and the vertical airtight chamber 151 are defined inside the walls of the horizontal pipe 430 and the vertical pipe 150. Accordingly, similarly to the first embodiment, even when the horizontal pipe 430 and the vertical pipe 150 are formed of resin, a decrease in the intensity of ultrasonic waves received by the ultrasonic sensor 111 is suppressed.

  In the fourth embodiment, a reference metal plate 4311 is further provided. The reference metal plate 4311 reflects the ultrasonic wave emitted from the ultrasonic sensor 111 toward the ultrasonic sensor 111 at a predetermined distance from the ultrasonic sensor 111. Therefore, in the fourth embodiment, the reference metal plate 4311 replaces the reference wall portion 1311. In the fourth embodiment, the horizontal pipe 430 corresponds to a “hollow part”.

<Fifth embodiment>
The fifth embodiment shown in FIGS. 19 and 20 is another modification of the first embodiment. In the liquid level detection device 500 of the fifth embodiment, the metal cylinders 142 and 143 are not provided. Accordingly, the pipes 130 and 150 are directly connected to each other in a part of each circumferential direction, and are connected to each other via the reflecting plate 141 and the fixing member 140 in the remaining part of each circumferential direction. The horizontal inner peripheral wall 532 and the horizontal outer peripheral wall 533 sandwiching the horizontal airtight chamber 131 between the horizontal pipe 130 and the vertical inner peripheral wall 552 and the vertical outer peripheral wall 553 sandwiching the vertical airtight chamber 151 between the vertical pipe 150 are electromagnetic It is made of a resin having a shielding property. The resin forming these peripheral walls 532, 533, 552, and 553 is formed by dispersing and containing metal powder such as stainless steel in a resin base such as polyacetal. Thereby, especially each outer peripheral wall 533, 553 can electromagnetically shield the inside of the wall with respect to the outside of the wall, that is, can reduce or block electromagnetic noise.

  Further, in the liquid level detection apparatus 500, the lead wire 515 from which the reception signal indicating the reception state of the ultrasonic wave is output from the ultrasonic sensor 111 passes through the hermetic chambers 131 and 151 in this order from the horizontal pipe 130 side to the vertical pipe 150 side. It penetrates. Thus, the lead wire 515 that is electrically connected to the control device 20 outside the tank 10 is disposed across the hermetic chambers 131 and 151. The lead wire 515 passes through a portion of the upper end lid portion 154 of the vertical pipe 150 that bypasses the communication groove 1541, thereby exposing only the connection side portion 515 a to the control device 20 in the tank 10. A seal member is interposed at a portion where the lead wire 515 passes through the upper end lid portion 154. The seal member is formed of a rubber material or an adhesive, and seals the inside of the vertical hermetic chamber 151 from the outside.

[Summary of fifth embodiment]
As described above, according to the fifth embodiment described above, the lead wires 515 are arranged in the hermetic chambers 131 and 151 between the inner peripheral walls 532 and 552 and the outer peripheral walls 533 and 553. Therefore, in the lead wire 515 from which the reception signal indicating the reception state of the ultrasonic wave is output from the ultrasonic sensor 111, even if the reception signal corresponding to the height Lh of the liquid surface 12 is a low current signal, the hermetic chamber 131. 151, external electromagnetic noise can be blocked by the outer peripheral walls 533 and 553. Thereby, it is possible to ensure the accuracy of the liquid level detection.

  Furthermore, according to the fifth embodiment, the outer peripheral walls 533 and 553 formed of resin having electromagnetic shielding properties reduce electromagnetic noise outside the hermetic chambers 131 and 151 with respect to the lead wires 515 inside the hermetic chambers 131 and 151. Or can be blocked. According to this, it is possible to prevent the reception signal flowing through the lead wire 515 from superimposing electromagnetic noise on the low current signal, and to improve the accuracy of liquid level detection. In the fifth embodiment, the horizontal outer peripheral wall 533 and the vertical outer peripheral wall 553 correspond to the “outer peripheral wall”, and the lead wire 515 corresponds to the “sensor wiring”.

  As mentioned above, although embodiment of this indication was described, this indication is not limited to the above-mentioned embodiment, and the following modification is also included in the technical scope of this indication, and also a summary other than the following is given. Various modifications can be made without departing from the scope.

<Modification 1>
In the first modification relating to the first, second, fourth and fifth embodiments, the horizontal pipes 130, 430 and the vertical pipe 150 are formed of a soft elastomer or a soft resin. The horizontal pipes 130 and 430 and the vertical pipe 150 according to the first modification are given rigidity that does not easily cause deformation in the tank 10 depending on the pressure of the gas held in the horizontal airtight chamber 131 and the vertical airtight chamber 151.

<Modification 2>
In the modification 2 regarding 3rd embodiment, the horizontal pipe 330 and the vertical pipe 350 are formed with a foamed resin. In the foamed resin that forms the horizontal pipe 330 and the vertical pipe 350 of Modification 2, the ratio of the gas contained therein to the resin varies depending on the portion. Specifically, in the area corresponding to the horizontal inner peripheral wall 132, the horizontal outer peripheral wall 133, the horizontal lid portion 134, the vertical inner peripheral wall 152, the vertical outer peripheral wall 153, the upper end lid portion 154, and the lower end lid portion 155, a horizontal airtight chamber is provided. The ratio of the contained gas is made smaller than the region corresponding to 331 and the vertical hermetic chamber 351.

<Modification 3>
In the third modified example related to the fifth embodiment, only the outer peripheral walls 533 and 553 or only the inner peripheral walls 132 and 152 are formed of a resin having electromagnetic shielding properties.

<Modification 4>
In the fifth modification relating to the first to fourth embodiments and the first and second modifications, any one of the fifth embodiment and the third modification is combined.

10: Tank, 100, 200, 300, 400, 500: Liquid level detection device, 11: Liquid, 15, 515: Lead wire (lead wiring), 12: Liquid level, 111: Ultrasonic sensor, 120, 220: Path Formed body, 121: propagation path, 130, 330, 430: horizontal pipe (hollow part), 131, 331: horizontal airtight chamber (airtight room), 132, 532: horizontal inner peripheral wall (inner peripheral wall), 1311: reference wall part 133, 533: horizontal outer peripheral wall (outer peripheral wall), 135: horizontal reinforcing wall (reinforcing wall), 150, 350: vertical pipe (hollow part), 151, 351: vertical airtight chamber (airtight chamber), 152, 552: Vertical inner peripheral wall (inner peripheral wall), 153, 553: Vertical outer peripheral wall (outer peripheral wall), 154: Upper end lid (upper end), 156: Vertical reinforcing wall (reinforcing wall), 240: Fixing member ( Hollow part, reflection wall part), 241: reflection airtight chamber (airtight room), 260: hollow top plate (hollow part, top plate wall part), 261: top plate airtight room (airtight room), 1541, 2541: communication groove ( Communication route)

Claims (11)

A liquid level detection device (100, 200, 300, 400, 500) that detects the height (Lh) of the liquid level (12) of the liquid (11) contained in the tank (10) using ultrasonic waves. And
An ultrasonic sensor (111) for emitting the ultrasonic wave and receiving the ultrasonic wave reflected by the liquid surface;
A tube-shaped path forming body (120, 220) that divides a propagation path (121) for propagating the ultrasonic wave between the ultrasonic sensor and the liquid surface inside,
The path forming body is formed of a resin and has hollow portions (130, 150, 240) that define airtight chambers (131, 151, 241, 261, 331, 351) that hold gas inside the walls of the path forming body. 260, 330, 350, 430). The hollow portion defines a cylindrical inner peripheral wall (132, 152, 532, 552) that is formed of resin and defines the propagation path, and a cylindrical outer periphery that is formed of resin and located on the outer peripheral side of the inner peripheral wall. Walls (133, 153, 533, 553),
The liquid level detection device according to claim 1, wherein the airtight chamber is provided in a cylindrical shape between the inner peripheral wall and the outer peripheral wall.   The liquid level detection device according to claim 2, wherein the hollow portion further includes a reinforcing wall (135, 156) that connects the inner peripheral wall and the outer peripheral wall.   The liquid level detection device according to claim 2, wherein the inner peripheral wall is formed to have a thickness that is an integral multiple of a half wavelength of the inner peripheral wall of the ultrasonic wave. A sensor wiring (515) from which a reception signal indicating a reception state of the ultrasonic wave is output from the ultrasonic sensor;
The liquid level detection device according to any one of claims 2 to 4, wherein the sensor wiring is arranged in the airtight chamber between the inner peripheral wall (532, 552) and the outer peripheral wall (533, 553). .   The liquid level detection device according to claim 5, wherein the outer peripheral wall is formed of a resin having electromagnetic shielding properties.   The hollow portion forms a reference wall portion (1311) that reflects a part of the ultrasonic wave toward the ultrasonic sensor at a certain distance from the ultrasonic sensor in the middle of the propagation path. Item 7. The liquid level detection device according to any one of Items 1 to 6. The propagation path includes a first section including one end of the ultrasonic sensor side and the reference wall portion at both ends, a second section extending in a direction inclined with respect to a direction in which the first section extends, Including
The liquid level detection device according to claim 7, wherein the hollow portion forms a reflection wall portion (240) that reflects the ultrasonic wave propagated through the first section toward the second section. The path forming body has an annular upper end (154) that divides an upper end that is one of the two ends of the propagation path on the side away from the ultrasonic sensor inward,
The liquid level detection device according to any one of claims 1 to 8, wherein a communication path (1541, 2541) that communicates the inside and the outside of the upper end portion is formed at the upper end portion.   The liquid level detection device according to claim 9, wherein the hollow portion includes a top wall (260) that closes the upper end and reflects the ultrasonic wave toward the propagation path at the upper end.   The liquid level detection device according to claim 1, wherein the airtight chamber is filled with a foamed resin containing the gas.

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