Liquid Level Detection Device

Abstract

A liquid level detecting device (21) is provided with a venting cylinder (27) provided penetrating through a side surface portion (22A) of a case (22) in a position further toward an upper side (other side) of the case (22) than a water flow-through hole (25) and an ultrasonic sensor (23). In addition, an external venting hole (28) that opens outside the case (22) and an internal venting hole (29) that opens inside the case (22) on the upper side (other side) of the case (22) and that communicates with the external venting hole (28) are formed in the venting cylinder (27).

Description

[Technical Field]

[0001] The present invention relates to a liquid level detection device provided in a liquid tank that stores a liquid such as urea water used to purify exhaust gas. [Background technology]

[0002] Generally, construction machinery and the like are equipped with diesel engines as their prime movers. Recently, in order to remove nitrogen oxides (NOx) from the exhaust gas emitted by diesel engines, construction machinery and the like have been equipped with exhaust gas purification devices that use urea water (urea solution) as a reducing agent. Therefore, construction machinery is provided with a urea water tank for storing urea water.

[0003] The urea water tank is provided with a liquid level detection device for detecting the remaining amount of urea water, i.e., the liquid level of the urea water. A known liquid level detection device includes a cylindrical case extending vertically inside the urea water tank, an ultrasonic sensor provided at the bottom of the case that detects the liquid level by reflecting ultrasonic waves oscillated upward from the liquid level of the urea water, a water passage provided at the bottom of the case for introducing and discharging urea water between the inside and outside of the case, and an air vent provided in the case above the liquid level of the urea water for introducing and discharging air between the inside and outside of the case (Patent Document 1).

[0004] When the construction machine is traveling or working, the urea water ripples in the urea water tank, generating air bubbles. If air bubbles are contained in the urea water, they reflect the ultrasonic waves emitted from the ultrasonic sensor, which may make it impossible to detect the correct liquid level. Therefore, in Patent Document 1, the water passage hole is covered with a porous membrane to prevent air bubbles from entering the case. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2020 / 036648 Summary of the Invention

[0006] As described above, in Patent Document 1, the water vent hole is covered with a porous membrane to prevent air bubbles from entering the case. However, construction machinery may operate on rough, uneven, or sloping ground, and at such sites, the urea water may ripple and reach the upper vent hole. When the urea water containing air bubbles enters through the vent hole, the air bubbles affect the detection of the liquid level of the urea water, reducing reliability.

[0007] In this case, it is conceivable to cover the air vent with a porous membrane, just like the water vent, to prevent air bubbles from entering the case. However, the porous membrane not only creates resistance to airflow, but also becomes blocked even with a splash of urea water, reducing breathability and making it impossible to maintain equal pressure.

[0008] The present invention has been made in consideration of the problems of the prior art described above, and an object of the present invention is to provide a liquid level detection device that can improve the reliability of detecting the liquid level position by preventing liquid containing bubbles from entering the case through the air vent.

[0009] The liquid level detection device of the present invention comprises a cylindrical case having a water passage hole for allowing liquid to flow inside, and an ultrasonic sensor provided on one side of the case for emitting and receiving ultrasonic waves, and further comprises an air vent tube provided through the side portion of the case at a position on the other side of the case relative to the water passage hole and the ultrasonic sensor, and the air vent tube is formed with an external air vent opening to the outside of the case, and an internal air vent hole opening to the other side of the case inside the case and communicating with the external air vent hole.

[0010] According to the present invention, it is possible to prevent liquid containing bubbles from entering the case through the air vent, and it is possible to improve the reliability of detection of the liquid level position. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a left side view showing a wheel loader equipped with a liquid level detection device according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view showing a urea water tank, a liquid level detection device, etc. [Figure 3] FIG. 3 is a perspective view showing the liquid level detection device in FIG. 2. [Figure 4] FIG. 10 is a perspective view showing a liquid level detection device according to a second embodiment. [Figure 5] FIG. 10 is a perspective view showing a liquid level detection device according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A liquid level detection device according to an embodiment of the present invention will be described in detail below with reference to the accompanying drawings, taking as an example a case where the liquid level detection device is provided in a urea water tank of a wheel loader as a construction machine.

[0013] Figures 1 to 3 show a first embodiment. In Figure 1, a wheel loader 1 as a construction machine is configured to include a rear vehicle body 2, a front vehicle body 3 connected to the front side of the rear vehicle body 2 so as to be able to swing left and right, rear wheels 4 provided on both left and right sides of the rear vehicle body 2, front wheels 5 provided on both left and right sides of the front vehicle body 3 (only the left side of each is shown), and a working device 6 provided on the front side of the front vehicle body 3 so as to be able to be raised and lowered.

[0014] The rear body 2 is equipped with an engine 7, which serves as a drive source, a torque converter 8, a transmission 9, a hydraulic pump (not shown), etc. The engine 7 is configured as a diesel engine. An exhaust gas purification device 13, which will be described later, is provided on the exhaust side of the engine 7.

[0015] A cab 10 for an operator is provided above the rear body 2. The transmission 9 is connected to a rear axle device 11 via a propeller shaft 9A extending in the front-to-rear direction. The transmission 9 is also connected to a front axle device 12 via a propeller shaft 9B.

[0016] The exhaust gas purification device 13 is provided on the exhaust side of the engine 7 and purifies the exhaust gas emitted by the engine 7. The exhaust gas purification device 13 is formed as a NOx purification device that purifies nitrogen oxides (NOx) in the exhaust gas using urea water (urea aqueous solution) 15, which will be described later. The exhaust gas purification device 13 has a housing cylinder 13A connected to the exhaust side of the engine 7, and the housing cylinder 13A is provided with a urea selective reduction catalyst, an oxidation catalyst, and a urea water injection valve (none of which are shown). The urea water injection valve is supplied with urea water 15 from a urea water tank 14, which will be described later, via a urea water pipe (not shown).

[0017] As a result, the exhaust gas purification device 13 injects urea water 15 into the exhaust gas using a urea water injector, and reduces NOx in the exhaust gas using ammonia generated from the urea water 15 by a urea selective reduction catalyst, decomposing it into water and nitrogen. Then, the ammonia in the exhaust gas is reduced by an oxidation catalyst.

[0018] The urea water tank 14 as a liquid tank is provided, for example, on the rear side of the rear vehicle body 2. As shown in Fig. 2, the urea water tank 14 stores urea water 15 as a reducing agent to be supplied to a urea water injector of the exhaust gas purification device 13. The urea water tank 14 is provided with a liquid level detection device 21, which will be described later. The urea water tank 14 is also provided with a pipe connecting the urea water tank 14 to the urea water injector, a quality sensor for detecting the quality of the urea water 15, and the like (none of which are shown).

[0019] Here, the urea water tank 14 may shake significantly when the wheel loader 1 is traveling or working. In this case, the urea water 15 ripples, generating bubbles (including microbubbles) 15A inside the urea water tank 14.

[0020] Next, the configuration of the liquid level detection device 21, which is a characteristic feature of the first embodiment, will be described in detail with reference to FIGS.

[0021] 2, the liquid level detection device 21 is provided in the urea water tank 14. The liquid level detection device 21 detects the liquid level position, i.e., the remaining amount, of the urea water 15 stored in the urea water tank 14. The liquid level detection device 21 includes a case 22, an ultrasonic sensor 23, a water vent hole 25, an air vent cylinder 27, an external air vent hole 28, and an internal air vent hole 29, which will be described later.

[0022] The case 22 is disposed inside the urea tank 14 and extends vertically. For example, the other upper side of the case 22 protrudes upward from the top surface 14A, and one lower side of the case 22 is located near the bottom surface 14B of the urea tank 14. As shown in FIG. 3 , the case 22 is formed, for example, in the shape of a rectangular tube with a closed upper side. Specifically, the case 22 includes four side surfaces 22A arranged to form a rectangle and a top surface 22B that closes the upper sides of the four side surfaces 22A. The lower side of the case 22 is closed by an ultrasonic sensor 23, which will be described later. Note that the lower side of the case may be closed by a bottom surface, and the ultrasonic sensor may be built into this bottom surface. The case may also be formed as a polygonal tube other than a cylindrical or rectangular tube.

[0023] Furthermore, cylinder mounting holes 22C are formed on the upper sides of the side portions 22A facing each other in the case 22. The two cylinder mounting holes 22C are positioned higher than the liquid level of the urea water 15 when the tank is full. Ventilation cylinders 27, which will be described later, are inserted into the two cylinder mounting holes 22C.

[0024] The ultrasonic sensor 23 is provided on the lower side, which is one side of the case 22. The ultrasonic sensor 23 has an oscillation / reception unit 23A with an ultrasonic vibrator (piezoelectric element) on the upper surface. The ultrasonic sensor 23 can receive sound waves oscillated from the oscillation / reception unit 23A by reflecting them on the liquid surface of the urea water 15. The ultrasonic sensor 23 is also connected to the controller 24.

[0025] Then, the ultrasonic sensor 23 transmits the time from when the sound waves are emitted from the oscillator / receiver 23A until when they are received by the oscillator / receiver 23A to the controller 24. As a result, the controller 24 detects (calculates) the liquid level position of the urea water 15 from the time from when the sound waves are emitted until when they are received.

[0026] The water passage hole 25 is provided on the lower side of the side surface portion 22A of the case 22 near the ultrasonic sensor 23. The water passage hole 25 forms a passage for introducing and discharging the urea water 15 between the inside and outside of the case 22.

[0027] The membrane 26 is provided to cover the water passage hole 25. The membrane 26 is formed of a porous membrane having a large number of micropores. When the urea water 15 in the urea water tank 14 flows into the case 22 through the water passage hole 25, the membrane 26 prevents the intrusion of air bubbles (microbubbles) 15A and allows only the urea water 15 to flow in. In this way, the membrane 26 prevents erroneous detection caused by the sound waves of the ultrasonic sensor 23 hitting the air bubbles 15A.

[0028] The vent tube 27 is provided at an upper position of the case 22 that is higher than the liquid level of the urea water 15 when the tank is full. Specifically, the vent tube 27 is inserted into the tube mounting hole 22C and extends horizontally so as to penetrate the opposing side surfaces 22A of the case 22. The vent tube 27 is formed as a circular tube that extends in a straight line and is open at both ends. In other words, the vent tube 27 is provided so that the two connected ends are located outside the case 22. In addition, the vent tube 27 protrudes from the side surface 22A of the case 22 to the outside of the case 22, so that an external vent hole 28 (described later) opens at a position spaced apart from the side surface 22A. The vent tube may be an elliptical or rectangular tube other than a circular tube.

[0029] The external vent holes 28 are provided so as to open at both ends of the vent tube 27, which are located outside the case 22. The external vent holes 28 are located above the liquid level of the urea water 15 and constitute one of the vent holes that allow air to enter and exit between the inside and outside of the case 22. The external vent holes 28 are located at a position spaced apart from the side surface portion 22A of the case 22 toward the outside. This allows the external vent holes 28 to be spaced apart from the internal vent holes 29, which will be described later, to be spaced apart from each other. Therefore, even if the urea water 15 enters the vent tube 27, the urea water 15 can settle at a lower position within the vent tube 27 before reaching the vicinity of the internal vent hole 29. In other words, the urea water 15 can be kept away from the internal vent hole 29 within the vent tube 27. Furthermore, the external ventilation hole can prevent the urea water 15 from entering the external ventilation hole even if the urea water 15 adhering to the side surface portion 22A flows down.

[0030] The internal vent hole 29 is provided inside the case 22 and opens above the vent cylinder 27. The internal vent hole 29 constitutes the other of the vent holes that allows air to flow in and out between the inside and outside of the case 22. By opening the internal vent hole 29 above the vent cylinder 27, even if the urea water 15 enters the vent cylinder 27 from the external vent hole 28, it is possible to prevent the urea water 15 from flowing out into the case 22.

[0031] The liquid level detection device 21 according to the first embodiment has the above-described configuration, and next, an operation when detecting the liquid level of the urea water 15 in the urea water tank 14 will be described.

[0032] First, the urea water 15 in the urea water tank 14 flows in and out of the case 22 through the water passage hole 25, so the liquid level of the urea water 15 in the case 22 is the same as the liquid level of the urea water 15 outside the case 22 (inside the urea water tank 14). In this case, the case 22 is provided with a membrane body 26 made of a porous membrane so as to cover the water passage hole 25, so that when the urea water 15 in the urea water tank 14 flows into the case 22, it is possible to prevent the intrusion of air bubbles (microbubbles) 15A.

[0033] Furthermore, when the amount of urea water 15 inside the case 22 increases or decreases (the liquid level position displaces vertically), it is necessary to let in or release the air that has accumulated in the upper part of the case 22 in order to maintain equal pressure inside and outside the case 22. In this case, since the upper space inside the case 22 communicates with the inside of the urea water tank 14 through the external vent hole 28 and the internal vent hole 29 provided in the vent cylinder 27, almost no ventilation resistance occurs, and air can be freely let in or released in accordance with the increase or decrease in the amount of urea water 15. In other words, equal pressure can be maintained inside and outside the case 22.

[0034] The ultrasonic sensor 23 then emits sound waves upward from the oscillator / receiver 23A. At this time, since the urea water 15 in the case 22 does not contain any air bubbles 15A, the sound waves emitted from the oscillator / receiver 23A are reflected by the surface of the urea water 15 and received by the oscillator / receiver 23A. By transmitting this detection data to the controller 24, the controller 24 detects (calculates) the liquid surface position of the urea water 15 from the time from emission to reception, and displays the remaining amount of urea water 15 on a monitor (not shown) inside the cab 10.

[0035] Incidentally, the wheel loader 1 not only repeatedly runs and stops, but also may operate on rough, uneven, or sloping ground. In such a working environment, as shown in FIG. 2 , the urea water 15 in the urea water tank 14 may become wavy, and the urea water 15 containing the air bubbles 15A may reach the external air vent 28.

[0036] According to the first embodiment, the liquid level detection device 21 includes a vent tube 27 that penetrates the side surface 22A of the case 22 at a position above (on the other side of) the case 22 relative to the water passage 25 and the ultrasonic sensor 23. The vent tube 27 is formed with an external vent hole 28 that opens to the outside of the case 22, and an internal vent hole 29 that opens to the upper side (on the other side) of the case 22 inside the case 22 and communicates with the external vent hole 28.

[0037] Therefore, even if the urea water 15 containing the air bubbles 15A enters the vent cylinder 27 through the external vent hole 28, the internal vent hole 29 opens at an upper position of the vent cylinder 27, and the urea water 15 containing the air bubbles 15A flows through the vent cylinder 27 and flows out into the urea water tank 14 (outside the case 22). This prevents the urea water 15 containing the air bubbles 15A from entering the case 22 through the external vent hole 28 and the internal vent hole 29. In other words, it is possible to prevent the air bubbles 15A from mixing into the urea water 15 in the case 22. As a result, the ultrasonic sensor 23 can function properly, and the reliability of detection of the liquid level position of the urea water 15 can be improved.

[0038] The vent cylinder 27 is provided so that its two ends, which are in communication with each other, are located outside the case 22. In addition, external vent holes 28 are provided at the two ends of the vent cylinder 27. As a result, if the vehicle body tilts while the wheel loader 1 is working on rough ground, uneven ground, sloped ground, or the like, the urea water 15 containing the air bubbles 15A can be reliably discharged from the external vent hole 28 provided at the lower of the two ends.

[0039] The vent tube 27 protrudes from the side surface 22A of the case 22, and the external vent hole 28 is disposed at a position spaced apart from the side surface 22A of the case 22 to the outside. Therefore, the external vent hole 28 is far away from the internal vent hole 29. As a result, even if the urea water 15 enters the vent tube 27 from the external vent hole 28, the vent tube 27 can allow the urea water 15 to settle at a lower position within the vent tube 27 before it reaches the vicinity of the internal vent hole 29. Furthermore, even if the urea water 15 adhering to the side surface 22A flows downward, the vent tube 27 can prevent the urea water 15 from entering the external vent hole 28.

[0040] The vent tube 27 is formed of a cylindrical pipe member with both ends serving as external vent holes 28. The vent tube 27 is provided so as to penetrate through the opposing side surface portions 22A of the case 22. This allows the vent tube 27 to be easily formed using a straight pipe member.

[0041] Next, Fig. 4 shows a second embodiment of the present invention. The second embodiment is characterized in that the vent tube that penetrates the side of the case is formed as a cylinder with an open end on the outside of the case and a closed end on the inside of the case. In the second embodiment, the same components as those in the first embodiment are designated by the same reference numerals, and their description will be omitted.

[0042] 4, a liquid level detection device 31 according to the second embodiment includes a case 32. The case 32 has four side surfaces 32A and a top surface 32B, and one of the side surfaces 32A is provided with a tube mounting hole 32C at a position higher than the liquid level of the urea water 15 in a full tank. The case may be formed as a polygonal tube other than a cylindrical or rectangular tube.

[0043] The vent tube 33 extends horizontally and is inserted into the tube mounting hole 32C so as to penetrate through the side surface 32A of the case 32. The vent tube 33 is formed as a covered circular tube that extends in a straight line and has an open end outside the case 32 and a closed end inside the case 32 with a lid 33A. Similar to the vent tube 27 of the first embodiment, the end outside the case 32 protrudes from the side surface 32A.

[0044] The external vent hole 34 opens to the end of the vent tube 33 outside the case 32. The internal vent hole 35 communicates with the external vent hole 34 through the vent tube 33 and opens to an upper position of the vent tube 33 inside the case 32.

[0045] Thus, the liquid level detection device 31 according to the second embodiment configured as described above can also achieve the same functions and effects as those of the first embodiment. In particular, the liquid level detection device 31 according to the second embodiment only requires the vent tube 33 to be inserted into one side surface portion 32A, thereby simplifying the configuration.

[0046] Next, Fig. 5 shows a third embodiment of the present invention. The third embodiment is characterized in that a curved vent tube is provided so as to penetrate adjacent side surfaces of the case. In the third embodiment, the same components as those in the first embodiment are designated by the same reference numerals, and their description will be omitted.

[0047] 5, a liquid level detection device 41 according to the third embodiment includes a case 42. The case 42 has four side surfaces 42A and a top surface 42B, and two adjacent side surfaces 42A are provided with tube mounting holes 42C at positions higher than the liquid level of the urea water 15 in a full tank. The case may be formed as a polygonal tube other than a cylindrical or rectangular tube.

[0048] The vent tube 43 is formed as an L-shaped cylinder bent at a bent portion 43A at the middle portion in the longitudinal direction. The L-shaped vent tube 43 extends horizontally and is inserted into the tube mounting hole 42C so as to penetrate adjacent side surfaces 42A of the case 42. Similar to the vent tube 27 of the first embodiment, the end of the vent tube 43 outside the case 42 protrudes from the side surface 42A.

[0049] The external vent holes 44 are arranged at two ends of the vent tube 43 outside the case 42. The internal vent hole 45 communicates with the external vent hole 44 through the vent tube 43, and is arranged inside the case 42 above the bent portion 43A of the vent tube 43.

[0050] Thus, the liquid level detection device 41 according to the third embodiment configured as described above can also achieve the same functions and effects as those of the first embodiment.

[0051] In the first embodiment, the vent tube 27 penetrates two side surfaces 22A of the case 22, and in the second embodiment, the vent tube 33 penetrates one side surface 32A of the case 32. However, the present invention is not limited to this, and the vent tube may be configured to have a trifurcated T-shape or Y-shape and penetrate three side surfaces. Also, the vent tube may be configured to have a cross shape and penetrate four side surfaces.

[0052] In the first embodiment, an example has been described in which the liquid level detection device 21 is provided in the urea water tank 14 of a wheel loader 1 as a construction machine. However, the present invention is not limited to this, and the liquid level detection device may be configured to be provided in the urea water tank of other construction machines such as a hydraulic excavator. The liquid level detection device can also be used to detect the liquid level of liquids other than urea water (fuel, water, etc.). These configurations can be similarly applied to the other embodiments. [Explanation of symbols]

[0053] 15 Urea water (liquid) 15A Air bubbles 21, 31, 41 Liquid level detection device 22, 32, 42 cases 22A, 32A, 42A side part 23 Ultrasonic Sensor 25 Water vent 27, 33, 43 Ventilators 28, 34, 44 External ventilation holes 29,35,45 Internal ventilation holes

Claims

1. a cylindrical case having a water passage hole for allowing liquid to flow therein; an ultrasonic sensor provided on one side of the case for emitting and receiving ultrasonic waves, a ventilation tube provided through a side surface of the case at a position on the other side of the case relative to the water passage hole and the ultrasonic sensor, A liquid level detection device characterized in that the ventilation cylinder is formed with an external ventilation hole that opens to the outside of the case, and an internal ventilation hole that opens to the other side of the case inside the case and communicates with the external ventilation hole.

2. 2. The liquid level detection device according to claim 1, the ventilation tube is provided so that a plurality of communicating ends are located outside the case, The liquid level detection device is characterized in that the external vent holes are formed at the plurality of ends.

3. 2. The liquid level detection device according to claim 1, The ventilation tube protrudes from the side surface of the case to the outside, The liquid level detection device is characterized in that the external air vent is formed at a position spaced from the side surface of the case to the outside.

4. 2. The liquid level detection device according to claim 1, The liquid level detection device is characterized in that the ventilation tube is formed of a cylindrical pipe member having both ends serving as the external ventilation holes.

5. 4. The liquid level detection device according to claim 3, The liquid level detection device is characterized in that the vent pipe is provided so as to penetrate the side surfaces of the case facing each other.

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