JP4947657B2 - Urea water sensor - Google Patents

Description

  The present invention relates to a urea water sensor.

For example, in an exhaust gas purification device that reduces nitrogen oxide (NOx) discharged from a diesel vehicle, a NOx selective reduction (SCR) catalyst may be used, and an aqueous urea solution is used as the reducing agent. In order to efficiently perform this reduction reaction, it is known to use a urea aqueous solution having a urea concentration of 32.5 wt%. However, in a urea aqueous solution stored in a urea water tank mounted on a diesel vehicle, the urea concentration may change due to a change with time. In addition, there is a possibility that a different kind of solution (such as light oil) or water may be mistakenly mixed in the urea water tank. In view of such a current situation, a urea water sensor (urea concentration identification device) has been proposed to manage the urea concentration of the urea aqueous solution in the urea water tank (see, for example, Patent Document 1).
JP-A-2005-84026

  The urea concentration identification device disclosed in Patent Document 1 provides a urea solution identification device capable of accurately and quickly identifying the urea concentration of a urea solution even while the automobile is running. That is, the concentration identification sensor unit includes an indirectly heated concentration detection unit and a liquid temperature detection unit (detection unit) provided with metal fins. Furthermore, a cover member that forms a urea solution introduction path so as to surround the metal fin, and an enclosure in which flow holes are formed in the upper and lower end face plates are attached to the concentration identification sensor portion (liquid concentration detection element). .

  In general, the entire urea solution stored in a tank or the like is disposed around the detection unit (side heat type concentration detection unit and liquid temperature detection unit) of the concentration detection element (concentration identification sensor unit). Since it is necessary to locate a urea solution that appropriately reflects the state of the concentration, temperature, etc., the urea solution is appropriately disposed outside the urea water sensor (urea concentration identification device) around this detection unit. When the urea solution around the detector moves violently, the influence of the urea solution state such as concentration and temperature is appropriate. This is because it may be difficult to detect the density and the error of the density measurement value may increase.

  By the way, there is a possibility that a driver or an operator at the filling station mistakes the urea water tank as a light oil tank and mistakenly injects the light oil into the urea water tank. Since the light oil has a smaller specific gravity than the urea aqueous solution, when the light oil is mixed in the urea water tank, the urea aqueous solution is located on the lower side in the vertical direction and the light oil is located on the upper side in the vertical direction. In this case, if the urea aqueous solution decreases due to use and the liquid level is lowered below the urea water sensor, and the liquid (urea aqueous solution and light oil) in the urea water tank moves vigorously due to vibrations, In some cases, a droplet of the urea aqueous solution enters the enclosure member (enclosure).

  However, as a result of studies by the present inventor, the urea aqueous solution that has entered the enclosure member can be appropriately discharged to the outside of the enclosure member even if a through hole for liquid circulation is provided in the lower part of the enclosure member. However, although the light oil is located outside (around) the surrounding member, the urea aqueous solution may accumulate only inside the surrounding member, and the detection unit may be surrounded by the urea aqueous solution. Then, the level of the urea aqueous solution is lowered below the detection unit, and the urea water sensor is installed in the urea water tank in spite of an abnormal situation in which light oil mistakenly injected into the urea water tank may be supplied to the catalyst. There is a risk of erroneously detecting that a proper urea aqueous solution is contained in. In addition, even when liquid fuel having a specific gravity smaller than that of an aqueous urea solution such as gasoline is accidentally injected into the urea water tank, the same problem as in the case of injecting light oil as described above may occur. .

  The present invention has been made in view of such a situation, and a liquid fuel having a specific gravity smaller than that of a urea aqueous solution such as light oil is erroneously accommodated in a urea water tank, and the liquid level of the urea aqueous solution is below the urea water sensor. It is an object of the present invention to provide a urea water sensor that can prevent a malfunction that erroneously detects that an appropriate aqueous urea solution is contained in a urea water tank when the amount of the aqueous urea solution is lowered.

The solution is whether the liquid immersed in the urea aqueous solution stored in the urea water tank and stored in the urea water tank is the urea aqueous solution or a different liquid having a different thermal conductivity. And a surrounding member that surrounds the periphery of the detection unit so that the liquid comes into contact with the detection unit and has a plurality of through-holes that penetrate the detection unit. When the urea water sensor is attached to the plurality of through-holes of the surrounding member, the plurality of through-holes are vertically lower than the lower through-holes positioned on the lower side in the vertical direction than the detection unit and the lower end of the detection unit. An upper through hole located on the upper side in the direction, and the maximum diameter of the virtual first virtual disk that can be arranged inside the lower through hole is the inner side of the upper through hole. Can be placed in a virtual A urea sensor is greater than the maximum diameter of the second hypothetical circle.

In the urea water sensor of the present invention, as the plurality of through holes provided in the surrounding member, a lower side through hole located on the lower side in the vertical direction than the detection unit, and a position above the lower end in the vertical direction than the lower end of the detection unit The upper through hole is provided, and the lower through hole is set to a size that satisfies a specific relationship with the upper through hole. Specifically, the maximum diameter of the first virtual disk that can be arranged inside the lower through hole is the maximum diameter of the second virtual disk that can be arranged inside the upper through hole. The mutual through-holes are set so as to satisfy a larger relationship.

When the urea water sensor is installed, the upper side through hole mainly functions to introduce a droplet of urea aqueous solution from the positional relationship. By setting the size to satisfy the specific relationship, even if the urea water tank accidentally enters the enclosure member with the liquid fuel having a specific gravity smaller than that of the urea aqueous solution such as light oil contained in the urea water tank. The urea aqueous solution can be discharged to the outside of the surrounding member through the lower through hole.
Therefore, in the urea water sensor of the present invention, when the liquid fuel having a specific gravity smaller than the urea aqueous solution such as light oil is mistakenly stored in the urea water tank, and the liquid level of the urea aqueous solution is lowered below the detection unit, It is possible to prevent a malfunction that erroneously detects that a proper urea aqueous solution is accommodated in the urea water tank.

Since the urea water sensor of the present invention is often used by being mounted on a urea water tank mounted on a diesel vehicle, the urea water tank is mistaken for a light oil tank. There is a high risk of being injected. On the other hand, in the urea water sensor of the present invention, as described above, it is possible to appropriately detect that the different liquid (light oil) is erroneously stored in the urea water tank. It is possible to prevent a problem that light oil erroneously injected into the tank is supplied to the catalyst.

  The maximum diameter of the first virtual disk is preferably not more than twice the maximum diameter of the second virtual disk. When the maximum diameter of the first virtual disk is excessively increased with respect to the maximum diameter of the second virtual disk, the urea aqueous solution stored in the urea water tank is vibrated (for example, during operation of a diesel vehicle). When the liquid flow is generated from the lower side in the vertical direction to the upper side, the influence of the liquid flow may reach the detection unit through the lower through hole, and the detection accuracy of the detection unit may be lowered. Accordingly, the first virtual disk contained in the lower through hole is based on the maximum diameter of the second virtual disk contained in the upper through hole mainly functioning to introduce a droplet of urea aqueous solution. By making the maximum diameter less than twice, it is possible to make the influence of the liquid flow difficult to reach the detection unit.

In the urea water sensor, the first virtual disk may be a urea water sensor having a maximum diameter of 3.5 mm or more.
By setting the maximum diameter of the first virtual disk to be 3.5 mm or more, the urea aqueous solution droplet is accidentally stored in the urea water tank with a liquid fuel having a specific gravity smaller than that of the urea aqueous solution such as light oil. Even if it enters into the surrounding member, the urea aqueous solution can be discharged to the outside of the surrounding member through the lower through hole.

Note that the lower through-hole may have a configuration in which the first virtual disk having a maximum diameter of 3.5 mm or more is disposed on the inner side, but the urea water tank is in a stationary state (in other words, the urea water sensor is in a stationary state). Even if the liquid of the urea aqueous solution enters the enclosure member in a state where liquid fuel having a specific gravity smaller than that of the urea aqueous solution such as light oil is mistakenly stored in the urea water tank, the urea through the lower through-hole It is preferable that the aqueous solution can be discharged. From this viewpoint, the first virtual disk preferably has a maximum diameter of 5.0 mm or more.
In addition, as a form of the lower through hole, for example, a circular through hole having a diameter of 3.5 mm or more, an oval through hole having a short diameter of 3.5 mm or more, and a plurality of slits having a width of 3.5 mm or more are mutually connected. Examples include a through hole that intersects and a circular through hole that has a diameter of 3.5 mm or more and a slit that extends radially from the through hole.

  Furthermore, in the urea water sensor, the lower through-hole of the surrounding member is a urea in which the first virtual disk faces downward in the vertical direction when the urea water sensor is in the posture. A water sensor is recommended.

  In the urea water sensor of the present invention, the lower through hole of the surrounding member is configured such that the first virtual disk faces downward in the vertical direction when the urea water sensor is attached to the urea water tank. This is preferable because the urea aqueous solution that has entered the surrounding member as described above can be easily discharged to the outside of the surrounding member.

  Further, in the urea water sensor, the surrounding member has a bottomed cylindrical shape having a bottom portion facing downward in the vertical direction when the urea water sensor is in the posture, and the lower through-hole is A urea water sensor arranged at the bottom may be used.

  In the urea water sensor of the present invention, the surrounding member has a bottom portion facing downward in the vertical direction, and a lower through-hole is disposed in the bottom portion. As a result, even when the urea aqueous solution stored in the urea water tank is subjected to vibration (for example, vibration generated during operation of the diesel vehicle) and a liquid flow directed upward from the lower side in the vertical direction is generated, The urea aqueous solution can be discharged to the outside through the lower flow hole while reducing the liquid flow from reaching the detection portion at the bottom.

  Further, in the urea water sensor, when the urea water sensor is in the posture, the rectifying counter is opposed to the first virtual disk in the vertical direction below the first virtual disk of the lower through hole. A rectifying member having a surface, wherein the rectifying counter surface is projected toward the first virtual disk vertically above, and the entire first virtual disk is projected on the rectifying counter surface. It is preferable that the urea water sensor includes a rectifying member having a distance between the rectifying facing surface and the first virtual disk of 3.0 mm or more.

  The urea aqueous solution accommodated in the urea water tank may generate a liquid flow upward from the lower side in the vertical direction due to the influence of vibration (for example, vibration generated during operation of the diesel vehicle). On the other hand, as described above, when the first virtual disk is provided with the lower through hole in the vertical direction facing downward in the vertical direction, such a liquid flow is surrounded through the lower through hole without weakening its momentum. Enter the member. As a result, the urea aqueous solution around the detection unit may move violently. As a result, in the detection unit, the liquid contained in the urea water tank is a urea aqueous solution or a different type of liquid having a different thermal conductivity. It may not be possible to properly detect whether or not.

  On the other hand, in the urea water sensor of the present invention, when the urea water sensor is mounted on the urea water tank, the first virtual disk is opposed to the first through-hole in the vertical direction below the first virtual disk. A rectifying member having a rectifying facing surface is provided. The rectifying facing surface of the rectifying member is configured to include the entire first virtual disk in the projection region of the rectifying facing surface when projected toward the first virtual disk vertically above. That is, when the urea water sensor according to the present invention is attached to the urea water tank and the vertical upper side is viewed from the vertical lower side of the urea water sensor, the first virtual disk contained in the lower through hole is rectified. It is in a state in which it cannot be seen by being blocked by a portion of the member that forms the rectifying facing surface.

  Therefore, even when a liquid flow is generated in the urea water tank from the lower side in the vertical direction to the upper side in the vertical direction, the liquid flow is directly It is possible to prevent entry into the enclosure member through the lower through-hole. As a result, the influence of such a liquid flow on detection of whether the liquid contained in the urea water tank is a urea aqueous solution or a different type of liquid having a different thermal conductivity from the detection unit is appropriately Can be suppressed.

  In addition, in the urea water sensor of the present invention, the distance between the rectifying facing surface and the first imaginary disk is set to 3.0 mm or more. By doing so, the flow of urea aqueous solution that has entered the enclosure member as described above is prevented from being discharged to the outside of the enclosure member through the lower through-hole by the rectification member (rectification facing surface). Absent. That is, the aqueous urea solution droplets that have entered the surrounding member as described above can be appropriately discharged to the outside of the surrounding member through the lower through hole.

  Furthermore, in any one of the urea water sensors described above, the detection unit includes a heating unit in which a heating resistor whose resistance value changes according to its own temperature is sealed in a liquid-tight manner in a ceramic insulating base. A urea water sensor having

  If a different kind of liquid with different thermal conductivity from the urea aqueous solution is stored in the urea water tank by mistake, if this different type of solution is heated by a heating resistor, the aqueous urea solution will be stored due to the difference in thermal conductivity. The rate of temperature rise will be different from when it is done. For example, a different liquid having a lower thermal conductivity than a urea aqueous solution, such as light oil, has a lower temperature increase rate than a urea aqueous solution.

  The urea water sensor of the present invention has a temperature raising part in which a heating resistor is liquid-tightly sealed in a ceramic insulating base. For this reason, when the temperature raising part having the heating resistor is immersed in the liquid stored in the urea water tank and the heating resistor is energized, the temperature increase rate of the liquid (that is, the liquid type, etc.) It will affect the temperature rise of the body. Since this heating resistor has a resistance value corresponding to its own temperature, it generates heat after a predetermined energization time due to the difference in thermal conductivity (difference in liquid type, etc.) of the liquid contained in the urea water tank. A difference will arise in the resistance value of a resistor. Accordingly, based on the output value output corresponding to the resistance value of the heating resistor, the liquid stored in the urea water tank is appropriately a urea aqueous solution or a different liquid having a different thermal conductivity ( Light oil etc.) can be detected.

By the way, the urea concentration discriminating apparatus of the above-mentioned Patent Document 1 (Japanese Patent Laid-Open No. 2005-84026) has side heat having an element in which a substrate, a temperature sensing element, an insulating layer, a heating element, and a protective layer are sequentially laminated. A mold concentration detector is provided. In this urea concentration identification device, the heating element is energized for a predetermined time, and the urea concentration is detected based on the temperature change of the heating element measured by the temperature sensing element before and after the energization.
On the other hand, as described above, the urea water sensor of the present invention uses a heating resistor having a resistance value corresponding to its own temperature as the detection unit, and therefore outputs in accordance with the resistance value of the heating resistor. Based on the output value, it is possible to detect whether the liquid stored in the urea water tank is a urea aqueous solution or a different liquid having a different thermal conductivity. Therefore, unlike the urea concentration discriminating apparatus of Patent Document 1, it is not necessary to provide a temperature sensing element for detecting the temperature of the heating resistor. For this reason, the urea water sensor of the present invention is preferable because the configuration of the detection unit can be simplified and downsized as compared with the urea concentration identification device of Patent Document 1.

  Further, in the urea water sensor, the temperature raising portion has a flat plate shape, and has a temperature rising portion main surface having the largest heat generation area and a temperature raising portion rear surface located on the opposite side thereof. When the urea water sensor is provided with the rectifying member, at least all of the through-holes except for the lower through-hole are in direct contact with the temperature rising part main surface and the temperature rising part back surface. When the urea water sensor is not provided with the rectifying member, the surrounding member includes any of the through-holes including the lower through-hole, The urea water sensor is preferably arranged at a position that does not face the back surface of the temperature raising unit.

  The urea aqueous solution stored in the urea water tank may generate a liquid flow due to the influence of vibration (for example, vibration generated during operation of a diesel vehicle). On the other hand, as described above, a through hole is formed in the surrounding member surrounding the detection unit. For this reason, when a liquid flow is generated in the urea water tank, the liquid flow may enter the enclosure member through the through hole without weakening the momentum. At this time, when the through-hole of the surrounding member is disposed at a position facing the temperature rising portion main surface and the temperature rising portion back surface, the urea aqueous solution adjacent to the temperature rising portion main surface and the temperature rising portion back surface As a result, the detection unit appropriately detects whether the liquid contained in the urea water tank is an aqueous urea solution or a different type of liquid having a different thermal conductivity. There is a risk that it will not be possible.

  On the other hand, in the urea water sensor according to the present invention, when the urea water sensor includes the rectifying member, the surrounding member includes at least the through hole excluding the lower through hole, the temperature rising portion main surface and the temperature rising portion. It is arranged at a position that does not face the back surface. Alternatively, when the urea water sensor does not include the rectifying member, the surrounding member is arranged such that none of the through holes including the lower through hole are directly opposed to the temperature rising part main surface and the temperature rising part back surface. . As a result, even if the liquid flow enters the enclosure member through the through hole, the liquid flow does not directly hit the temperature rising portion main surface and the temperature rising portion back surface, and the temperature rising portion main surface and the temperature increasing portion described above. It is possible to prevent the urea aqueous solution adjacent to the back surface from moving vigorously. Therefore, in the urea water sensor of the present invention, even when a liquid flow is generated in the urea water tank, the liquid stored in the urea water tank is a urea aqueous solution or has a thermal conductivity different from that in the detection unit. It is possible to appropriately detect whether the liquid is a different kind of liquid.

(Embodiment)
An embodiment of a urea water sensor embodying the present invention will be described below. The urea water sensor 1 according to the present embodiment shown in FIG. 1 is an exhaust gas purification that reduces nitrogen oxide (NOx) contained in the exhaust gas of an automobile equipped with a diesel engine or the like with an aqueous urea solution and renders it harmless. The apparatus is used as an apparatus for detecting the urea concentration of the urea aqueous solution LQ1 accommodated in the urea water tank 10 and the liquid level LQH of the urea aqueous solution LQ1.

  The urea water sensor 1 (hereinafter, also simply referred to as sensor 1) includes a base 2 and a sensor unit 3 that extends downward from the base 2 in FIG. The urea water sensor 1 has a base 2 attached around an opening 11 of a urea water tank 10 containing a urea aqueous solution LQ1 indicated by a broken line, and the sensor unit 3 extends in the vertical direction Y (vertical direction in FIG. 1). The sensor unit 3 is used by being immersed in the urea aqueous solution LQ1 as an extended posture.

  In the present specification, unless otherwise specified, the sensor 1 and each component will be described in the posture in which the sensor 1 is attached to the urea water tank 10 (the posture shown in FIG. 1). Therefore, when the sensor 1 is mounted in the urea water tank 10, as shown in FIG. 1, the direction (axis direction) along the axis AX of the sensor 1 is the vertical direction Y (vertical direction in FIG. 1). Of the directions along AX, the lower side is the lower vertical direction Y1, and the upper side is the upper vertical direction Y2.

  Of the urea water sensor 1, the base portion 2 includes a mounting flange portion 21, a lid body 25, a wiring board 22 surrounded by them, an external connection cable 24, and a bush 23 that holds this. The sensor unit 3 includes a double cylindrical liquid level sensor unit 4 and a urea concentration sensor unit 5. As shown in FIG. 1, the urea concentration sensor unit 5 is configured to be positioned vertically below the liquid level sensor unit Y1 in the posture in which the urea water sensor 1 is attached to the urea water tank 10. Yes.

  First, the base 2 will be described in detail. The mounting flange 21 is made of metal and used as a pedestal for mounting the urea water sensor 1 to the opening 11 of the urea water tank 10. The mounting flange 21 is formed with a bolt insertion hole (not shown) so that the urea water sensor 1 (base 2) can be fixed to the urea water tank 10 with a bolt.

  On the other hand, the wiring board 22 indicated by a broken line in FIG. 1 is arranged in the vertical direction Y <b> 2 above the mounting flange 21. The wiring board 22 is formed with a control circuit (not shown) including a CPU, an electric circuit, and the like, and this control circuit is electrically connected to the liquid level sensor unit 4 and the urea concentration sensor unit 5. In addition, it can be connected to an external electric circuit via the external connection cable 24. Further, the wiring board 22 is covered with a lid body 25 attached to the attachment flange portion 21, and is protected liquid-tightly.

  The control circuit formed on the wiring board 22 is based on an output signal corresponding to the resistance value of the internal heater wiring 518 by energizing the concentration sensor element 51 shown in FIG. Specifically, the urea concentration of the urea aqueous solution LQ1 is detected based on a potential difference (voltage value) generated at both ends of the internal heater wiring 518 by passing a predetermined current through the concentration sensor element 51.

Next, the sensor unit 3 will be described. As described above, the sensor unit 3 includes the liquid level sensor unit 4 and the urea concentration sensor unit 5. Among these, first, the liquid level sensor unit 4 will be described, and then the urea concentration sensor unit 5 will be described.
As shown in FIG. 1, the liquid level sensor unit 4 is disposed in a cylindrical outer cylinder 41 extending in the vertical direction Y (vertical direction in FIG. 1), and the outer cylinder 41 is coaxial. An inner cylinder 42 having a relatively small diameter and a cylindrical shape. The inner peripheral surface of the outer cylinder 41 and the outer peripheral surface of the inner cylinder 42 are separated from each other at a predetermined interval.

  Out of these, the outer cylinder 41 is made of metal and serves as one electrode for detecting the liquid level LQH. Further, as shown in FIG. 1, the outer cylinder 41 has a narrow ellipsoidal slit 415 whose longitudinal direction is the vertical direction Y (vertical direction in FIG. 1), and between the inner cylinder 42. The urea aqueous solution LQ1 can be accommodated as shown by a broken line in a state of communication with the outside. The lower end 41T of the outer cylinder 41 is opened to form a lower end opening OP, while the upper end 41B is fixed to the mounting flange 21 by welding or the like.

  In the sensor 1 of the present embodiment, the outer cylinder 41 is welded to the mounting flange 21. Further, the mounting flange 21 is connected to a ground potential in a control circuit (not shown) formed on the wiring board 22. As a result, the outer cylinder 41 is set to the ground potential. Further, as shown in FIG. 2 in an enlarged manner, between the holding portion 412 located slightly above the lower end 41T of the outer cylinder 41 and the lower end portion 421 located on the lower side of the inner cylinder 42, A rubber bush 56 described later is interposed. The holding portion 412 of the outer cylinder 41 is engaged with an engaging protrusion 562 formed on the outer periphery of the rubber bush 56, and a holding hole 41H for holding the rubber bush 56 (urea concentration sensor portion 5). However, it is formed at a plurality of predetermined positions in the circumferential direction (three places in the present embodiment). Further, a flow hole 41R for allowing the urea aqueous solution LQ1 to flow between the inside of the outer cylinder 41 is formed below the holding hole 41H.

  The inner cylinder 42 is also made of metal, and is electrically insulated from the outer cylinder 41 as the other electrode for measuring the liquid level LQH. It is electrically connected to the circuit. The outer peripheral surface 42G of the inner cylinder 42 is covered with an insulating coating 43 made of, for example, fluorine resin such as PTFE, PFA, ETFE, epoxy resin, polyimide resin, or the like, and between the inner cylinder 42 and the outer cylinder 41. Even if the urea aqueous solution LQ1 is interposed in the outer cylinder 41, the outer cylinder 41 is electrically insulated.

In order to detect the liquid level LQH of the urea aqueous solution LQ1 by the liquid level sensor unit 4, as shown in FIG. 1, the liquid level sensor unit 4 is immersed in the urea aqueous solution LQ1, and the urea aqueous solution LQ1 is Then, it flows through the slit 415 between the outer cylinder 41 and the inner cylinder 42 (insulating coating 43).
Then, in this liquid level sensor unit 4, between the outer cylinder 41 and the inner cylinder 42, a portion where the urea aqueous solution LQ1 is present and a portion where the urea aqueous solution LQ1 is present are formed according to the liquid level LQH. The capacitance of the capacitor formed between the inner cylinder 42 changes according to the liquid level LQH. Therefore, when an AC voltage is applied between the outer cylinder 41 and the inner cylinder 42, a current corresponding to the magnitude of this capacitance flows. Therefore, by knowing the magnitude of the current, the liquid level LQH of the urea aqueous solution LQ1 Can be detected.

Next, the urea concentration sensor unit 5 will be described.
As shown in FIG. 1, the urea concentration sensor unit 5 is arranged in the vertical lower portion Y1 of the liquid level sensor unit 4 and includes a concentration sensor element 51, a holder member 55, a surrounding member 58, a rubber bush 56, and the like. Yes.

  Among these, the density sensor element 51 is held by the holder member 55 in a form in which the lower end portion thereof protrudes. The concentration sensor element 51 is electrically connected to a control circuit formed on the wiring board 22 via a connection terminal 52 and a connection cable 53 that are fixed to the density sensor element 51 by soldering (see FIGS. 2 and 3). Has been. On the other hand, the holder member 55 is held by the holding portion 412 of the outer cylinder 41 by a rubber bush 56 interposed between the holder member 55 and the outer cylinder 41 surrounding the holder member 55. Further, the surrounding member 58 is engaged with and held by the lower end portion (small diameter portion 553) of the holder member 55 so as to surround the lower end portion 511 protruding from the holder member 55 of the density sensor element 51. Yes.

  First, the concentration sensor element 51 (see FIG. 3) in the urea concentration sensor unit 5 will be described. The concentration sensor element 51 has a rectangular plate shape in plan view, and includes two flat ceramic layers 519 (519A and 519B) made of alumina ceramics, and an internal liquid-tightly disposed therebetween. Wiring 516 is provided. The internal wiring 516 includes a pair of wide internal lead wirings 517 and an internal heater wiring 518 disposed between them and folded in a bellows shape.

  2 and 3, the density sensor element 51 is inserted through the holder member 55 adjacent to the lower end portion 511 protruding from the holder member 55 and the upper portion Y2 in the vertical direction of the lower end portion 511. The portion 512 is further divided into a resin holding portion 513 positioned in the vertical direction Y2 above the insertion portion 512, and an upper end portion 514 formed by soldering and connecting the pair of connection terminals 52.

  As shown in FIG. 3A, an internal heater wiring 518 is arranged inside the lower end portion 511. Therefore, in this embodiment, the lower end portion 511 is heated by energization to detect the concentration of urea in the urea aqueous solution LQ1, and whether the liquid stored in the urea water tank 10 is the urea aqueous solution LQ1. A temperature rise detection unit 510 that detects whether the liquid is a different type of liquid having different thermal conductivity is included. As shown in FIG. 3B, the lower end portion 511 has a main surface 511A composed of the ceramic layer 519A and a back surface 511B composed of the ceramic layer 519B in parallel with the main surface 511A. Yes. Further, regarding the temperature increase detection unit 510, the temperature increase detection unit 510 has a temperature increase unit main surface 511AS included in the main surface 511A and a temperature increase unit back surface 511BS included in the back surface 511B.

  By the way, among the ceramic layers 519, one ceramic layer 519A is thinner than the other ceramic layer 519B. For this reason, the heat generated by the temperature rise detection unit 510 due to energization, specifically, the heat generated in the internal heater wiring 518 is more easily transferred to the ceramic layer 519A side than the ceramic layer 519B, and is externally transmitted. The temperature is also easily transmitted from the relatively thin ceramic layer 519A to the internal heater wiring 518.

  The connection terminal 52 is formed by bending a metal plate having a predetermined shape into a U shape. The lower end 521 of the connection terminal 52 has a shape extending downward, and is connected to a pad (not shown) formed on the upper end 514 of the density sensor element 51 by soldering. It is fixed to the element 51. As a result, the connection terminal 52 (lower end 521) is connected to the internal lead wiring 517 via a via conductor (not shown) penetrating the one ceramic layer 519A. Therefore, when a voltage is applied between the pair of connection terminals 52, the internal heater wiring 518 mainly generates heat through the internal lead wiring 517. The resistance value of the internal heater wiring 518 changes according to its own temperature.

  On the other hand, the core wire 533 of the lead wire 532 of the connection cable 53 is electrically and mechanically connected to the upper end portion 522 of the connection terminal 52 by soldering. As shown in FIG. 1, the connection cable 53 is inserted into the inner cylinder 42, extends in the vertical upper direction Y2, and is connected to the wiring board 22 (control circuit).

  Further, the holder member 55 is made of an insulating resin material as a whole, and as shown in FIG. 2, is a hollow member having a holder through hole 55H penetrating itself in the vertical direction Y (vertical direction in FIG. 2). is there. The holder through-hole 55H has a three-stage circular hole portion of the inner cylinder holding hole 55H1, the second step hole 55H2, and the third step hole 55H3 that gradually becomes smaller in diameter from the top to the bottom, and the most distal side. It consists of a substantially square hole-shaped element holding hole 55H4 (downward in the figure).

  The holder member 55 holds the density sensor element 51. Specifically, the insertion portion 512 of the concentration sensor element 51 is inserted into the element holding hole 55H4 of the holder member 55, and the resin holding portion 513 of the concentration sensor element 51 arranged in the third step hole 55H3 is the third holding hole 55H4. It is fixed by a sealing resin 59 filled in the step hole 55H3. The gap between the concentration sensor element 51 and the holder member 55 is liquid-tightly sealed by the sealing resin 59. As a result, the lower end portion 511 of the concentration sensor element 51 in which the internal heater wiring 518 is disposed is disposed so as to protrude from the element holding hole 55H4 of the holder member 55 in the downward vertical direction Y1.

Further, as shown in FIG. 2, the holder member 55 holds the lower end portion 421 of the inner cylinder 42 inside the inner cylinder holding hole 55H1 of the holder through hole 55H, and the inner cylinder holding hole 55H1 The stepped inner cylinder contact surface 55D positioned between the second step hole 55H2 contacts the lower end 422 of the inner cylinder 42, and the axial direction (vertical direction Y) between the inner cylinder 42 and the holder member 55 Positioning is performed.
Two O-ring insertion grooves 55G1 and 55G2 are recessed in the inner cylinder holding hole 55H1 of the holder through-hole 55H, and the holder member 55 and the inner cylinder 52 are formed by O-rings 571 and 572 arranged inside these. The space between (insulating coating 43) is sealed in a liquid-tight manner, and the inner cylinder 42 is held.

  Since the holder member 55 holding the density sensor element 51 and the inner cylinder 42 are connected as described above, most of the upper end portion 514 of the density sensor element 51 and the entire connection terminal 52 are The inner cylinder 42 is disposed. The lower end portion 421 of the inner cylinder 42 is made of an insulating resin having rubber-like elasticity, and the concentration inside the inner cylinder 42 while insulating between the density sensor element 51 and the connection terminal 52 and the inner cylinder 42. A separator 54 that elastically holds the sensor element 51 and the connection terminal 52 is disposed.

Next, the surrounding member 58 in the urea concentration sensor unit 5 will be described.
As shown in FIG. 2, the surrounding member 58 has a bottomed cylindrical shape, and includes a cylindrical side portion 581 and a lower end portion (bottom portion) 582 that closes the lower end side of the side portion 581. Among these, in order to allow the urea aqueous solution LQ1 to flow inside and outside of the surrounding member 58, the side portion 581 has three circular liquid circulation holes 58H1, 58H2, 58H3, as shown in FIGS. And the keyhole-shaped liquid circulation hole 58H4 which consists of the circular hole part 58H41 and the long slit part 58H42 extended from this to the front end side is equally arranged and formed in the circumferential direction. The liquid circulation holes 58H1, 58H2, 58H3 and the circular hole portion 58H41 of the liquid circulation holes 58H4 are provided with the urea water sensor 1 attached to the urea water tank 10 as shown in FIGS. In this case, all of them have an upper through-hole positioned vertically above the lower end of the temperature rise detection unit 510 of the concentration sensor element 51. In the present embodiment, the diameter of the circular holes 58H41 of the liquid circulation holes 58H1, 58H2, 58H3 and the liquid circulation holes 58H4 which are the upper side through holes is set to 3.0 mm. In other words, these upper side through-holes have a form in which a virtual disk having a diameter (maximum diameter) of 3.0 mm can be arranged inside.

Also, at the lower end (bottom) 582, in order to allow the urea aqueous solution LQ1 to flow in and out of the surrounding member 58, one circular lower through hole 58H6 is formed at the center thereof. As shown in FIG. 2, the lower through-hole 58 </ b> H <b> 6 is configured to face downward in the vertical direction when the urea water sensor 1 is attached to the urea water tank 10.
In the present embodiment, the diameter of the lower through hole 58H6 is 5.0 mm. That is, the lower through hole 58H6 has a virtual disk K having a diameter (maximum diameter) of 3.5 mm or more (5.0 mm in the present embodiment) disposed on the inner side, as shown by hatching in FIG. Is in a possible form. Further, as can be seen from these descriptions, in this embodiment, the diameter (maximum diameter) of the virtual disk K included in the lower through hole 58H6 is the liquid through holes 58H1, 58H2, 58H3, which are the upper through holes, and The diameter of the virtual disk included in each of the circular hole portions 58H41 of the liquid circulation hole 58H4 (maximum diameter) is set larger than the maximum of the virtual disk included in the upper through hole. The size is set to be twice or less the diameter.

  By the way, at a gas station, a driver or an operator of a diesel vehicle mistakes the urea water tank 10 as a light oil tank, and as shown in FIG. 9, the oil oil LQ2 (heterogeneous liquid) is mistakenly placed in the urea water tank 10. May be injected. Since the specific gravity of the light oil LQ2 is smaller than that of the urea aqueous solution LQ1, when the light oil LQ2 is injected into the urea water tank 10, the urea aqueous solution LQ1 is positioned on the lower side in the vertical direction and the light oil LQ2 is positioned on the upper side in the vertical direction. Become. In this case, the urea aqueous solution LQ1 is reduced by use, and the liquid level LQH is lowered below the lower end of the temperature rise detection unit 510. When the LQ1 and the light oil LQ2) move vigorously, the droplets of the urea aqueous solution LQ1 may enter the surrounding member 58 through the liquid circulation holes 58H1 to 58H4 as indicated by arrows in FIG.

  However, as a result of investigation by the present inventor, the urea aqueous solution that has entered the surrounding member can be appropriately discharged to the outside of the surrounding member even if a through hole for liquid circulation is provided in the lower portion of the surrounding member. First, the light oil is located in the outer periphery of the surrounding member, but the urea aqueous solution is accumulated only inside the surrounding member, and the detection unit (temperature rise detection unit) is surrounded by the urea aqueous solution. was there. As a result, the level of the urea aqueous solution is lowered below the detection unit (temperature rise detection unit), and the urea water is supplied in spite of an abnormal situation in which the light oil erroneously injected into the urea water tank may be supplied to the catalyst. There is a possibility that the sensor may erroneously detect that a proper urea aqueous solution is contained in the urea water tank.

(Liquid removal test 1)
Therefore, the diameter of the lower through-hole 58H6 provided at the lower end (bottom) of the surrounding member 58 is varied, and the urea aqueous solution LQ1 droplet that has entered the surrounding member 58 as described above is appropriately discharged to the outside. It was investigated whether or not. Specifically, the holder 55 and the concentration sensor are respectively provided in four types of surrounding members that differ only in that the diameter of the lower through hole 58H6 is changed to 3.0 mm, 3.5 mm, 4.0 mm, and 5.0 mm. Four types of samples (samples 1, 2, 3, and 4 in order) equipped with the element 51 and the like were prepared. The diameters of the circular holes 58H41 of the liquid circulation holes 58H1, 58H2, 58H3 and the liquid circulation holes 58H4, which are upper through holes, were set to 3.0 mm.

  Next, these samples are light oil contained in a tank, which is immersed in light oil that is in a stationary state, and the urea aqueous solution is slowly introduced into the surrounding member 58 through the liquid flow holes 58H1 to 58H4 of the surrounding member 58. Injected. Then, in the samples 1, 2, and 3 in which the diameter of the lower through hole 58H6 is 3.0 mm, 3.5 mm, and 4.0 mm, the urea aqueous solution gradually accumulates in the surrounding member 58, and the temperature rise detection unit 510 The aqueous urea solution has accumulated to the surroundings. On the other hand, in the sample 4 in which the diameter of the lower through hole 58H6 is 5.0 mm, the urea aqueous solution smoothly flows out from the lower through hole 58H6, and the urea aqueous solution does not accumulate around the temperature increase detection unit 510.

(Liquid removal test 2)
Next, the four types of samples prepared in the above-described liquid leakage test 1 were subjected to the conditions in which vibrations assumed at the time of idling of the vehicle (in this test, vibrations of 20 Hz) were applied to a tank containing light oil. Then, it was immersed in light oil in the tank and slowly poured an aqueous urea solution. Then, in the sample 1 in which the diameter of the lower through hole 58H6 is 3.0 mm, the urea aqueous solution gradually accumulates inside the surrounding member 58, and the urea aqueous solution accumulates around the temperature increase detection unit 510. On the other hand, in the samples 2, 3, and 4 in which the diameter of the lower through hole 58H6 is 3.5 mm, 4.0 mm, and 5.0 mm, the urea aqueous solution smoothly flows out from the lower through hole 58H6, and The urea aqueous solution did not collect up to the periphery.

  From these results, by setting the diameter of the lower through hole to 5.0 mm or more, when the tank is in a stationary state, as described above, even if the urea aqueous solution droplet enters the enclosure member, the lower through hole penetrates downward. It can be said that the oil can be discharged to the outside of the surrounding member through the hole, and the light oil can be positioned around the temperature rise detection unit 510, similarly to the outside (around) of the surrounding member. In addition, by setting the diameter of the lower through hole to 3.5 mm or more, during normal use of the sensor, if the vibration of the urea water tank is frequently applied, the urea aqueous solution droplets will enter the enclosure member. However, it can be discharged to the outside of the surrounding member through the lower through-hole, and it can be said that the light oil can be positioned around the temperature rise detection unit 510 in the same manner as the outside (around) of the surrounding member.

  In the urea water sensor 1 of this embodiment, the lower through hole 58H6 having a diameter of 5.0 mm is provided in the surrounding member 58 as described above. Therefore, in the urea water sensor 1 of the present embodiment, the light oil LQ2 is mistakenly stored in the urea water tank 10, and the liquid level LQH of the urea aqueous solution LQ1 is lowered below the temperature rise detection unit 510 (FIG. 9). (See FIG. 4), it is possible to prevent a malfunction that the correct urea aqueous solution LQ1 is erroneously detected as being contained in the urea water tank 10. That is, it is possible to appropriately detect that the different type liquid (light oil LQ2) is erroneously stored in the urea water tank 10.

  In the liquid drop test, the shape of the lower through-hole is circular, but the shape of the lower through-hole is not limited to a circle, and any form may be used. Therefore, from the result of this test, it is considered that the lower through-hole should be configured so that a virtual disk K having a diameter of 3.5 mm or more (preferably 5.0 mm or more) can be disposed inside. For example, like a surrounding member 158 shown in FIG. 12, a circular through hole 158H61 having a diameter of 3.5 mm or more (a virtual disk K can be arranged inside), and four slits 158H62 extending radially from the through hole 158H61. It is good also as the downward through-hole 158H6 which consists of these. Moreover, as shown in the surrounding member 258 of FIG. 14, it is good also as the oval lower through-hole 258H6 whose short diameter (dimension of the left-right direction in FIG. 13) is 3.5 mm or more.

  Further, in the liquid drop test, the lower through hole is provided at the lower end (bottom) of the surrounding member, but the position of the lower through hole is not limited to the lower end (bottom) of the surrounding member. In other words, it may be a position where the urea aqueous solution droplets that have entered the surrounding member can be discharged to the outside so as not to accumulate around the temperature rise detection unit 510. Therefore, the lower through hole only needs to be disposed such that at least a part of the virtual disk K is positioned vertically below the temperature rise detection unit 510 when the urea water sensor is attached to the urea water tank 10. it is conceivable that.

  In addition, in the vicinity of the upper end of the side portion 581 of the surrounding member 58, four locking tongue portions 583 formed with U-shaped cuts and bent inward are formed uniformly in the circumferential direction. Therefore, as shown in FIG. 10, the locking tongue portion 583 of the surrounding member 58 can be locked to the surrounding member locking recess 55G3 formed on the outer periphery of the small diameter portion 553 of the holder member 55. Thereby, the surrounding portion 580 of the surrounding member 58 is disposed so as to surround the temperature rise detecting portion 510 of the concentration sensor element 51.

  4 to 7, liquid flow holes 58H1, 58H2, 58H3, and 58H4 are equally formed in the circumferential direction on the side portion 581 of the surrounding member 58 that surrounds the temperature rise detection portion 510. Has been. Further, as shown in FIG. 8, a lower through hole 58 </ b> H <b> 6 is formed in the lower end portion (bottom portion) 582 of the surrounding member 58. For this reason, when a liquid flow is generated in the urea water tank 10, the liquid flow enters the enclosure member 58 through one of the liquid circulation holes 58H1 to 58H4 and the lower through-hole 58H6 without reducing the momentum. There are things to do.

  At this time, when any one of the liquid circulation holes 58H1 to 58H4 and the lower through hole 58H6 is disposed at a position facing the temperature rising portion main surface 511AS and the temperature rising portion back surface 511BS of the concentration sensor element 51, The liquid adjacent to the warm part main surface 511AS and the warm part back surface 511BS may move violently. As a result, the temperature rise detection unit 510 detects whether the liquid stored in the urea water tank 10 is the urea aqueous solution LQ1 or a different kind of liquid (light oil or the like) having a different thermal conductivity, and urea. Therefore, there is a possibility that the density detection cannot be performed properly.

  On the other hand, in the urea water sensor 1 of this embodiment, as shown in FIGS. 4 to 8, the surrounding member 58 includes the liquid circulation holes 58H1 to 58H4 and the lower through-hole 58H6. 511AS (part indicated by broken line hatching in FIG. 5) and temperature rising portion back surface 511BS (part indicated by broken line hatching in FIG. 7) are arranged at positions that do not face each other. Thereby, even if the liquid flow enters the surrounding member 58 through the liquid circulation holes 58H1 to 58H4 and the lower through hole 58H6, the liquid flow directly strikes the temperature rising part main surface 511AS and the temperature rising part back surface 511BS. The liquid adjacent to the temperature riser main surface 511AS and the temperature riser rear surface 511BS can be prevented from moving violently.

  Therefore, in the urea water sensor 1 of the present embodiment, even when a liquid flow is generated in the urea water tank 10, in the temperature rise detection unit 510, is the liquid stored in the urea water tank 10 the urea aqueous solution LQ1? Therefore, it is possible to appropriately detect whether the liquid is a different kind of liquid (light oil or the like) having a different thermal conductivity and detect the urea concentration. 4 to 8, the concentration sensor element 51 is indicated by a broken line as a reference so that the position of the temperature rise detection unit 510 in the urea water sensor 1 equipped with the surrounding member 58 can be seen.

Further, the holder member 55 holding the concentration sensor element 51 and the enclosing member 58 is held by the insulating rubber bush 56 provided with a holder holding hole 56H compatible form on the outer peripheral surface thereof. As shown in FIG. 2, the rubber bush 56 is formed with the above-described holder holding hole 56H at the center thereof, and has a cylindrical bush main body 561 having an outer diameter that can be fitted to the outer cylinder 41, and the bush main body. There are locking projections 562 that are evenly arranged at three locations on the outer periphery of the portion 561 and project radially outward from the bush body 561. The holder holding hole 56 </ b> H of the bush main body 561 is in contact with the holder member 55 and the surrounding member 58 and has a shape capable of holding them.

  The rubber bush 56 is held by the outer cylinder 41 by inserting and locking the locking projections 562 into the holding holes 41H of the outer cylinder 41. Thus, the holder member 55 that holds the concentration sensor element 51 and the surrounding member 58 is held by the rubber bushing 56, and the rubber bushing 56 is held by the outer cylinder 51, so that the urea concentration sensor unit 5 as a whole is the outer cylinder 41. The holding portion 412 and the lower end portion 421 of the inner cylinder 42 are held.

  Further, a number of outer peripheral slits 561G extending in the vertical direction Y (vertical direction in FIG. 2) are provided in the outer peripheral surface between the locking projections 562 of the bush main body 561. As shown in FIG. 2, the outer circumferential slit 561 </ b> G allows the urea aqueous solution LQ <b> 1 to flow in the vertical direction Y between the bush main body 561 and the outer cylinder 41 by fitting the rubber bush 56 into the outer cylinder 41. , And a flow path that allows air to be removed.

  Further, a rectifying member 61 is fitted into the distal end portion 411 of the outer cylinder 41. As shown in FIGS. 2 and 11, the rectifying member 61 includes a disk-shaped shielding portion 611 having an outer diameter smaller than the inner diameter of the outer cylinder 41 and larger than the outer diameter of the surrounding member 58, From the periphery of this shielding part 611, it has the three bridge parts 612 which extend diagonally upward in FIG. 2 and reach the front-end | tip part 411 of the outer cylinder 41. As shown in FIG. At the end of the bridge portion 612, a curved plate-like plate-like portion 613 is provided that is further inverted along the lower Y1 in the vertical direction and is disposed along the inner peripheral surface 41N of the distal end portion 411 of the outer cylinder 41. It has been. The tip of the plate-like portion 613 is bent toward the radially outer side of the outer cylinder 41 to form an engaging claw portion 614.

  In the sensor 1 of the present embodiment, as shown in FIG. 2, the rectifying member 61 is in a state in which the engaging claw portion 614 at the tip of the plate-like portion 613 is engaged with the lower end 41 </ b> T of the outer cylinder 41. The welded portion 613 </ b> W of the shaped portion 613 is spot welded to the distal end portion 411 of the outer cylinder 41. Thereby, the shielding portion 611 of the rectifying member 61 is in a state of closing a part (center portion) of the lower end opening OP of the outer cylinder 41.

The shielding part 611 of the rectifying member 61 has a virtual disk K of the lower through hole 58H6 on the lower side Y1 of the lower through hole 58H6 formed in the lower end part 582 of the surrounding member 58.
Has a rectifying facing surface 611B. Further, as shown in FIG. 2, the rectifying facing surface 611B rectifies the entire lower through hole 58H6 (virtual disk K) when projected onto the upper vertical direction Y2 (toward the lower through hole 58H6). It is set as the form included in the projection area | region TR of the opposing surface 611B. That is, when the urea water sensor 1 is attached to the urea water tank 10 and the vertical upper side Y2 is viewed from the vertical lower side (lower side in FIG. 2) of the urea water sensor 1, the lower through hole 58H6 (virtual circle) The plate K) is blocked by the shielding portion 611 of the rectifying member 61 (the portion of the rectifying member 61 that forms the rectifying facing surface 611B) and cannot be seen.

  By doing in this way, even when a liquid flow is generated in the urea water tank 10 from the lower side in the vertical direction of the urea water sensor 1 toward the upper direction Y2 in the vertical direction, the shielding portion 611 of the rectifying member 61 (of the rectifying member 61). The presence of the rectifying facing surface 611B) can prevent this liquid flow from directly entering the surrounding member 58 through the lower through hole 58H6. Thereby, in such a liquid flow, the liquid stored in the urea water tank 10 in the temperature increase detection unit 510 is the urea aqueous solution LQ1 or a different kind of liquid (such as light oil) having a thermal conductivity different from that. And the influence of the temperature rise detection unit 510 on the urea concentration detection can be appropriately suppressed. In other words, it is possible to prevent the urea aqueous solution around the temperature rise detection unit 510 from vigorously moving due to the influence of such a liquid flow, and thereby, the temperature rise detection unit 510 accommodates the urea water tank 10. It is possible to appropriately detect whether the liquid is the urea aqueous solution LQ1 or a different liquid (light oil or the like) having a different thermal conductivity from that of the urea aqueous solution LQ1, and the urea concentration.

  By the way, the closer the distance L between the shielding portion 611 (rectification facing surface 611B) of the rectifying member 61 and the lower through hole 58H6 (virtual disk K) is, the lower the vertical direction of the urea water sensor 1 is, the higher the vertical direction Y2 is. It is preferable because the liquid flow can be prevented from directly entering the surrounding member 58 through the lower through hole 58H6. However, if the distance L is too close, as described above, when the droplet of the urea aqueous solution LQ1 enters the surrounding member 58 with the light oil LQ2 contained in the urea water tank 10, the solution of the urea aqueous solution LQ1 There is a possibility that the droplets are prevented from being discharged to the outside of the surrounding member 58 through the lower through-hole 58H6 by the shielding portion 611 (rectification facing surface 611B).

(Liquid removal test 3)
Therefore, the distance L between the shielding portion 611 (rectifying facing surface 611B) of the rectifying member 61 and the lower through hole 58H6 (virtual disk K) is changed to be within the surrounding member 58 in the same manner as in the liquid leakage test 1. It was investigated whether or not the droplets of the urea aqueous solution LQ1 that entered could be appropriately discharged to the outside. Specifically, as the surrounding member, the surrounding member 58 in which the diameter of the lower through hole 58H6 is unified to 5.0 mm was used, and the distance L was changed to three types of 2.0 mm, 3.0 mm, and 4.0 mm. Three types of urea water sensors (samples 5, 6, and 7 in this order) were prepared.

  Next, these samples were immersed in stationary light oil, and the urea aqueous solution was slowly injected into the surrounding member 58 through the liquid flow holes 58H1 to 58H4 of the surrounding member 58. Then, in the sample 5 in which the distance L is 2.0 mm, the urea aqueous solution gradually accumulates in the surrounding member 58 and the urea aqueous solution has accumulated around the temperature increase detection unit 510. On the other hand, in the samples 6 and 7 in which the distance L is set to 3.0 mm and 4.0 mm, the urea aqueous solution smoothly flows out from the lower through hole 58H6, and the urea aqueous solution does not accumulate around the temperature increase detection unit 510. It was.

  From this result, the distance L between the shielding portion 611 (rectifying facing surface 611B) of the rectifying member 61 and the lower through hole 58H6 (virtual disc K) is set to 3.0 mm or more, so that the inside of the surrounding member 58 as described above. It can be said that the shielding part 611 (rectification facing surface 611B) does not hinder the droplet of the urea aqueous solution LQ1 that has entered the outside from being discharged to the outside of the surrounding member 58 through the lower through hole 58H6. That is, by setting the distance L to 3.0 mm or more, the aqueous solution LQ1 droplet that has entered the surrounding member 58 as described above is appropriately discharged to the outside of the surrounding member 58 through the lower through hole 58H6. It can also be said.

Next, the operation of the urea concentration sensor unit 5 of the sensor 1 in detecting the urea concentration of the urea aqueous solution LQ1 will be described.
In the urea water sensor 1 of the present embodiment, a current having a predetermined magnitude is supplied from the control circuit configured on the wiring board 22 to the concentration sensor element 51 of the urea concentration sensor unit 5 for a predetermined time (for example, 700 ms). The internal heater wiring 518 generates heat. Then, a detection voltage corresponding to the magnitude of its own resistance value is generated in the internal heater wiring 518. Therefore, the change in the detection voltage is detected by the control circuit, and the concentration of the urea aqueous solution is detected.

  Specifically, the detection voltage immediately after the start of energization of the concentration sensor element 51 and the detection voltage after the elapse of a predetermined time from the start of energization are measured. Then, using the change amount of the detected voltage during this period, the concentration of the urea aqueous solution corresponding to the change amount is obtained from the relationship between the concentration of the urea aqueous solution and the change amount obtained in advance.

Incidentally, since the light oil LQ2 has a smaller thermal conductivity than the urea aqueous solution LQ1, the amount of change in the detection voltage is larger than that of the urea aqueous solution LQ1, regardless of the urea concentration. Therefore, the change amount of the detection voltage is obtained in advance for the urea aqueous solution LQ1 having various concentrations, the maximum value is obtained as the battle value Q, and the actual change amount of the detection voltage is larger than the battle value Q. In this case, it can be determined that the light oil LQ2 is stored in the urea water tank 10. On the other hand, when the actual change amount of the detected voltage is below the threshold value Q, it can be determined that the urea aqueous solution LQ1 is stored in the urea water tank 10, and the urea concentration is set as described above. Obtainable.

In the present embodiment, the concentration of the urea aqueous solution LQ1 is detected by using a CPU or the like in the control circuit, and the concentration notification signal obtained by the control circuit passes through the external connection cable 24 to the external circuit. (For example, ECU). In this external circuit, it is determined whether or not the concentration of the urea aqueous solution LQ1 is within an appropriate range based on the input concentration notification signal. Processing such as notification is appropriately performed. In addition, the light oil LQ2 is contained in the urea water tank 10.
If it is determined that the battery is contained, the driver is notified of this, and processing such as prompting for replacement with an aqueous urea solution is appropriately performed.

In the above, the present invention has been described with reference to the embodiment. However, the present invention is not limited to the above-described embodiment, and it is needless to say that the present invention can be appropriately modified and applied without departing from the gist thereof. Absent.
For example, in the above-described embodiment, as the urea water sensor 1, a sensor of a type in which the liquid level sensor unit 4 and the urea concentration sensor unit 5 are combined is illustrated. However, the present invention can also be applied to a device that does not have a function as a liquid level sensor and that does not include an outer cylinder.

In the above-described embodiment, the urea concentration sensor unit 5 has been described with respect to the method of detecting the concentration of the urea aqueous solution. From the resistance value immediately after the concentration sensor element 51 (internal heater wiring 518) is energized, The liquid temperature can also be measured. Accordingly, it can be used as a liquid temperature sensor for measuring the liquid temperature in addition to the concentration of the urea aqueous solution.
Moreover, in above-mentioned embodiment, what has the wiring board 22 which mounted the control circuit as the urea water sensor 1 was illustrated. However, the urea water sensor of the present invention only needs to include a liquid concentration detection element, a holder member that holds the liquid concentration detection element, a surrounding member, and the like, and includes a urea water sensor that does not include a control circuit.

It is a partial broken sectional view of the urea water sensor concerning an embodiment. It is a longitudinal cross-sectional view of a urea concentration sensor part among the urea water sensors concerning embodiment. (A) is explanatory drawing which shows each form and connection form of a density sensor element, a connection terminal, and a lead wire, (b) is a side view of the front-end | tip part of a density sensor element. It is a front view of an enclosing member. It is a left view of an enclosing member. It is a rear view of an enclosing member. It is a right view of an enclosing member. It is a bottom view of an enclosing member. It is explanatory drawing when urea aqueous solution LQ1 and light oil LQ2 are accommodated in the urea water tank. It is explanatory drawing which shows the mode of a coupling | bonding of a holder member and a surrounding member. It is a perspective view which shows the shape of a baffle member. It is a figure which shows the lower through-hole 158H6 of another form, and is a bottom view of the surrounding member 158. It is a figure which shows the lower through-hole 258H6 of another form, and is a bottom view of the surrounding member 258.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Urea water sensor 10 Urea water tank 51 Concentration sensor element 58 Enclosing member 58H1, 58H2, 58H3, 58H4 Liquid circulation hole (Upper through-hole, through-hole)
58H6 Lower through hole (through hole)
61 Rectifying member 510 Temperature rise detection unit (detection unit, temperature rise unit)
511 Lower end portion 511AS Temperature rising portion main surface 511BS Temperature rising portion back surface 518 Internal heater wiring (heating resistor)
519 Ceramic layer (ceramic insulating substrate)
611B Rectification facing surface K Virtual disk (first virtual disk)
LQ1 Urea aqueous solution LQ2 Light oil

Claims (8)

A detection unit that detects whether the liquid stored in the urea water tank is immersed in the urea aqueous solution stored in the urea water tank and whether the liquid is the urea aqueous solution or a different liquid having a thermal conductivity different from that. When,
An enclosing member that surrounds the periphery of the detection unit so that the liquid contacts the detection unit, the enclosing member having a plurality of through holes penetrating the detection unit;
A urea water sensor comprising:
The plurality of through-holes of the surrounding member are vertically above the lower through-hole located on the lower side in the vertical direction than the detection unit and the lower end of the detection unit when the urea water sensor is mounted. An upper through hole located on the side,
The maximum diameter of the virtual first virtual disk that can be arranged inside the lower through hole is that of the virtual second virtual disk that can be arranged inside the upper through hole. A urea water sensor larger than the maximum diameter . The urea water sensor according to claim 1,
The urea water sensor , wherein the maximum diameter of the first virtual disk is not more than twice the maximum diameter of the second virtual disk . The urea water sensor according to claim 1 or 2 ,
The urea water sensor , wherein the first virtual disk has a maximum diameter of 3.5 mm or more . The urea water sensor according to any one of claims 1 to 3 ,
The lower through hole of the surrounding member is
The urea water sensor configured such that when the urea water sensor is in the posture, the first virtual disk faces downward in the vertical direction . The urea water sensor according to any one of claims 1 to 4 ,
The surrounding member has a bottomed cylindrical shape having a bottom portion facing downward in the vertical direction when the urea water sensor is in the posture.
The urea water sensor , wherein the lower through hole is arranged at the bottom . The urea water sensor according to claim 4 or 5 ,
When the urea water sensor is in the posture,
A rectifying member having a rectifying facing surface opposed to the first virtual disk below the first virtual disk in the lower through-hole,
The rectifying facing surface is configured to include the entire first virtual disk in the projection region of the rectifying facing surface when projected toward the first virtual disk in the upper vertical direction.
The distance between the rectifying facing surface and the first virtual disk is 3.0 mm or more.
A urea water sensor provided with a flow regulating member . The urea water sensor according to any one of claims 1 to 6 ,
The detector is
A urea water sensor , wherein a heating resistor whose resistance value changes in accordance with its own temperature has a temperature raising portion formed by liquid-tightly sealing in a ceramic insulating substrate . The urea water sensor according to claim 7 ,
The temperature raising part is
It has a flat plate shape, and has a heating part main surface with the largest heat generation area and a heating part back surface located on the opposite side thereof,
When the urea water sensor includes the rectifying member,
The surrounding member is arranged at a position where at least all of the through holes excluding the lower through hole are not directly opposed to the temperature rising part main surface and the temperature rising part back surface,
When the urea water sensor does not include the rectifying member,
The urea water sensor , wherein the surrounding member is arranged such that none of the through holes including the lower through hole are opposed to the temperature rising part main surface and the temperature rising part back surface .