JP2007178243A - Liquid situation detecting sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To support both electrodes stably such that problems on increasing of the number of components and on assembly are not present, errors are absorbable by supporting of the electrodes, and, even when insulating film is formed on the surface of an internal electrode, damage is not caused to the film. <P>SOLUTION: In the liquid situation detecting sensor, which is equipped with a cylindrical outer casing electrode 10, an axial internal electrode 20 prepared on the inner side thereof, and an attaching section 40 supporting the both electrodes, keeping up insulation, at a proximal side of both electrodes, detecting liquid level and the like through measuring capacitance between the both electrodes, an edge of the internal electrode 20 is supported elastically at the internal side of rubber bushing 80 attached at inside of the outer casing electrode 10 through a holder 120 with a heater attached at the edge. For positioning of the apex of a rubber bushing 80, a positioning member 150 is attached to the inside of the outer casing electrode 10. Thus, the internal electrode 20 can be supported stably and elastically at the edge thereof through the holder 120 and additionally assembly also becomes easy. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a liquid state detection sensor (hereinafter also simply referred to as a sensor) that detects the state of a liquid stored in a liquid storage container (tank) by measuring a capacitance between electrodes.

Exhaust gas emitted from diesel vehicles contains nitrogen oxides (NOx) in addition to carbon monoxide (CO) and hydrocarbons (HC). Therefore, in recent years, this harmful nitrogen oxide (NOx) has been reduced to a harmless gas. For example, a NOx selective reduction catalyst (SCR) is installed in the middle of an exhaust gas exhaust muffler of a diesel vehicle, urea water is put as a reducing agent solution in a tank provided in a separate vehicle, and this urea water is injected onto the catalyst. Thus, a system for reducing NOx to a harmless gas such as N ₂ has been proposed. In this system, when the urea water is exhausted, the NOx reduction reaction cannot be promoted and a large amount of NOx is discharged. Therefore, the urea water is stored in a storage container (hereinafter also referred to as a tank) that stores urea water. A sensor for measuring the level of urea water (hereinafter also referred to as water level) is provided, and measures are taken such as issuing an alarm when the remaining amount of urea water falls below a specified amount.

  As an example of a sensor for measuring the water level, a capacitance type liquid state detection sensor is known. In this liquid state detection sensor, an elongated cylinder made of a conductor is used as an outer electrode (outer cylinder electrode), and between the elongated columnar or tubular inner electrode provided concentrically along the axial direction in the outer cylinder electrode. Is measured, and the water level is detected from the capacitance. For example, in a capacitive liquid state detection sensor used for measuring the level of a conductive liquid such as urea water, the surface of the inner electrode is used to prevent a short circuit between the outer cylinder electrode and the inner electrode. An insulating film is formed on the liquid crystal, and the liquid state detection sensor is set in a tank to be measured so that the axial direction of the outer cylinder electrode is the vertical direction of the water level. When measuring the water level of such a conductive liquid, the capacitance of the portion not immersed in the liquid depends on the thickness of the air layer between the gap between the inner and outer electrodes and the thickness of the insulating film of the inner electrode. . On the other hand, the capacitance of the portion immersed in the liquid depends on the thickness of the insulating film because the conductive liquid has the same potential as the outer cylinder electrode, and the capacitance is larger than the former. For this reason, as the portion immersed in the liquid increases, the measured capacitance increases and can be detected as a water level.

  Such a liquid state detection sensor is usually mounted in the tank so that the axial direction of the outer cylinder electrode is the vertical direction of the water level. For example, when the outer cylinder electrode (and the inner electrode) is attached in a hanging manner from the ceiling of the tank into the tank, the liquid state detection sensor positions the proximal end side of the outer cylinder electrode on the ceiling side, The base end (upper) of the outer cylinder electrode is fixed (or supported) to a base end support member having means for attaching to the tank. On the other hand, the internal electrode holds the insulation between the inner electrode and the inner electrode, and fixes the proximal end of the inner electrode itself to the proximal end in the outer tube electrode. However, if the electrodes are fixed or supported only at their base ends in this way, each electrode will be in a cantilevered state where the tip side is free, so the sensor is subject to vibration. When placed under (environmental) conditions or when an external force is applied from the lateral direction, each electrode swings in the radial direction of its axis or undergoes bending deformation. For this reason, an accurate electrostatic capacitance cannot be measured because the dimension between both electrodes becomes unstable or, in some cases, causes a contact between both electrodes. In addition, there is a risk that a large stress is generated in each electrode, particularly at the base of the internal electrode, and breaks due to the repetition of such deflection and deformation.

  For this reason, in such a sensor, a spacer or a supporting member may be interposed between both electrodes as a means for stabilizing the dimension between the two electrodes or a means for supporting the internal electrode for keeping the dimension between the two electrodes constant. Has been done. For example, a technique is known in which a plurality of spacers made of an insulating material are arranged in the longitudinal direction of an electrode along with its axis so that both the inner and outer electrodes are held concentrically (Patent Document 1). In addition, an insulating resin support member is placed between the electrodes at the tip of the inner and outer electrodes, and the distance (dimension) between the electrodes is constant while insulating the electrodes by the support member. There is also known a technique for maintaining the above (Patent Document 2).

However, the former means for supporting the internal electrode requires a plurality of spacers, which increases the number of parts. Moreover, after attaching each spacer to the outer peripheral surface of an internal electrode, it is necessary to press-fit (or insert) this into an outer cylinder electrode from the opening of the one end side, Therefore An assembly operation is troublesome. Further, in the latter technique of disposing a resin support member between the electrodes, since it is made of resin, vibration and external force are difficult to be absorbed between both electrodes, and there is the following problem. . First, when the support members are placed between both electrodes (tips) when the shafts of both electrodes are not correctly concentric due to manufacturing and assembly errors, residual stress is generated in each electrode in the lateral direction or uneven loads are applied. As a result, one of the electrodes may be broken at the base. On the other hand, in order to prevent this, it is necessary to extremely increase the dimensional accuracy of the parts including each electrode, resulting in an increase in manufacturing cost. In addition, since an ordinary resin support member is hard, vibration is directly transmitted between both electrodes through the support member. As a result, for example, an internal electrode in which an insulating film is formed on the surface Then, the insulating film is easily damaged, and there is a risk of breaking the insulation.
Japanese Utility Model Publication No. 01-151215 JP 09-152368 A

  In such a situation, the applicant of the present application solves the problem described in Patent Document 2, in the liquid state detection sensor as described above, outside the tip of the internal electrode or the portion near the tip and inside the outer cylinder electrode, An invention has been filed in which a tip support member made of an elastic body such as rubber is interposed by press-fitting or the like so that the tip of the internal electrode or a portion near the tip is elastically supported on the inner side of the outer cylindrical electrode. Application 2005-140071). In this case, since an elastic body that is not a hard resin is used for the support at the tip of the internal electrode, it is possible to absorb the above errors and accuracy problems, and an insulating film is formed on the surface of the internal electrode. Even in such a case, the internal electrode can be supported at the tip or a portion near the tip (hereinafter also simply referred to as the tip) without damaging the membrane.

  Such a tip support member made of an elastic body such as rubber (hereinafter referred to as an electrode support elastic member or simply a support elastic member) is disposed outside the tip of the internal electrode and inside the outer cylindrical electrode. Is a single part, for example, in the form of a bush, which usually has a through hole or a recess for passing the tip of the internal electrode in the center because of its manufacture and ease of mounting inside the outer cylindrical electrode. It becomes. Therefore, such an electrode supporting elastic member has an annular (ring shape) or a bottomed annular or cylindrical shape. On the other hand, it is necessary to stably interpose the electrode supporting elastic member without falling off, rotating, or moving inside the outer cylinder electrode. For this reason, the supporting elastic member is provided with a protruding portion (convex portion) protruding outward on the outer peripheral surface of the supporting elastic member, and the outer cylindrical electrode has an opening portion that penetrates in a radial direction at a portion closer to the tip thereof ( A through-hole) is provided, and the projection is fitted into the opening when it is interposed inside by press-fitting or the like.

  On the other hand, when using the electrode supporting elastic member made of such an elastic body to support the tip of the internal electrode inside the outer cylindrical electrode, the supporting elastic member is attached to the outer cylindrical electrode in the assembly of the sensor. Insert the inner electrode from the front end side by press-fitting, etc., fit the protrusion to the opening and attach it, then insert the inner electrode from the base end (rear end) side of the outer cylinder electrode to the inner side The tip of the internal electrode or a portion near the tip is inserted into the center (through hole) of the supporting elastic member so that the tip of the internal electrode is supported inside the outer cylinder electrode. However, in such insertion of the internal electrode, the tip of the internal electrode is always positioned straight in the axial center in the outer cylinder electrode due to the inclination of the internal electrode generated due to assembly work or accuracy. Is usually not possible. That is, in the insertion process, the internal electrode does not enter straight coaxially, or the tip is unevenly distributed from the axial center, so that it is not smoothly inserted into the central through hole of the supporting elastic member and is displaced from the center. It acts to push the part to the tip side. When such an effect is exerted, the supporting elastic member is pushed to the tip side, so that the protrusion fitted to the opening of the outer cylinder electrode receives a shearing force and has a crack or crack at its base. There is a risk of being damaged, and there is a possibility that the protruding portion may come off from the opening, and there is a problem in the stability or reliability of electrode support.

  In order to avoid such a problem, it is conceivable to round the tip of the internal electrode or round the outer side of the inlet of the central through hole of the supporting elastic member, but that is not sufficient. . Moreover, in order to stably support the internal electrode, there is a case where it is desired to support the internal electrode so that a compressive force acts in the axial direction. This is because, in such a case, even after the sensor is assembled (finished product) after the insertion, the supporting elastic member is always applied with a force pushed toward the tip side. For this reason, in the case of being used under vibration, such as when mounted on an automobile or the like, in the worst case, the protrusion is cut at the root and moved from the inside of the external electrode to the tip side. This is because there is a problem in the reliability of the support, for example, there is a problem of rotating around the axis or dropping off.

  The present invention has been made in view of these problems, and there is no increase in the number of parts or problems in assembling. In addition, an error can be absorbed in supporting the electrode, and an insulating film is formed on the surface of the internal electrode. It is an object of the present invention to provide a highly reliable support at the electrode tip without damaging the film even if it is formed.

The present invention according to claim 1 is a liquid state detection sensor for detecting the state of the liquid stored in the storage container,
It has a cylindrical outer cylinder electrode made of a conductor and an inner electrode made of a conductor provided along the axial direction in the outer cylinder electrode, and is accommodated in the receiving container between the electrodes. A level detector formed by forming a capacitor whose capacitance changes according to the level of the liquid;
An attachment portion for attaching a liquid state detection sensor to the storage container, located on the rear end side in the longitudinal direction of the level detection portion;
An elastic member for electrode support made of an elastic body having an annular portion that supports the outer peripheral surface of the inner electrode at a tip or a portion near the tip directly or indirectly, and is press-fitted inside the outer cylindrical electrode. An electrode supporting elastic member,
While the outer cylinder electrode is provided with an opening portion penetrating in the radial direction at a portion near the tip,
The electrode supporting elastic member has a protrusion that can be fitted into the opening on the outer peripheral surface thereof, and is press-fitted inside the outer cylindrical electrode to fit the protrusion into the opening. Installed in the
Furthermore, a positioning member for positioning the electrode supporting elastic member on the distal end side is attached to the distal end side of the electrode supporting elastic member and inside the outer cylindrical electrode,
The internal electrode is inserted into the outer cylinder electrode from the front end side, and the front end of the internal electrode or a portion closer to the front end is directly or via a separate member inside the annular portion of the electrode supporting elastic member. It is characterized by being inserted into and elastically supported.

  According to a second aspect of the present invention, the liquid is circulated between the inner side of the outer cylindrical electrode and the outer side of the inner electrode and between the distal end side of the positioning member and the inner side of the outer cylindrical electrode. 2. The liquid state detection sensor according to claim 1, wherein a flow passage is formed in communication with the electrode supporting elastic member and the positioning member.

  According to a third aspect of the present invention, the positioning member has a positioning plate portion whose outer diameter is smaller than the inner diameter of the outer cylinder electrode, and extends from the periphery of the positioning plate portion to the distal end side at a substantially right angle to the positioning plate portion. A leg portion and a hook projecting outward at the tip end of the leg portion, and the positioning plate portion is disposed inside the outer cylindrical electrode so as to support the tip end of the electrode supporting elastic member. The hook is engaged with the tip of the outer cylinder electrode, and at least a part of the leg is welded to the inner peripheral surface of the outer cylinder electrode. It is a liquid state detection sensor as described in above.

  According to the sensor of the present invention, the tip of the internal electrode or the portion near the tip is elastically supported on the inner side of the outer cylindrical electrode by the electrode supporting elastic member, so that the number of parts is also increased. In addition, the assembly for supporting is easy, and the internal electrode can be stably supported at the tip. In addition, since the electrode supporting elastic member made of an elastic body is used for supporting the internal electrode, it is possible to absorb dimensions and assembly errors of each electrode and the like. Further, even when an insulating film is formed on the surface of the internal electrode, the film is not damaged. That is, such a film is thin. Therefore, when it is used in an environment where the sensor is exposed to vibration, it is easily damaged by support by a conventional hard resin support member. Since the internal electrode is supported by the electrode supporting elastic member, such a risk is small. Moreover, the following specific effects can be obtained in the present invention.

  In the present invention, a positioning member for positioning the electrode supporting elastic member on the distal end side is attached to the distal end side of the electrode supporting elastic member and inside the outer cylindrical electrode. For this reason, the internal electrode is inserted into the outer cylinder electrode from the distal end side, and the distal end of the internal electrode or a portion closer to the distal end is inserted into the annular portion of the electrode supporting elastic member to be elastically supported. At this time, even if the internal electrode is inclined, for example, and the tip thereof is not positioned at the center of the electrode supporting elastic member, and this is pushed to the tip side, the electrode supporting elastic member becomes the positioning member. Therefore, the protrusion of the elastic member for electrode support is not sheared and is not detached from the opening. Therefore, the risk of the electrode support elastic member moving from the inner side of the external electrode to the tip side, rotating around the axis line, or dropping off even when mounted and used in an automobile or the like thereafter. As a result, the internal electrodes are supported extremely stably. In the present invention, “the tip of the internal electrode or a portion near the tip is directly or via another member” means that when a separate member such as a holder is attached to the tip or the portion near the tip. This is because the same effect can be obtained even through the separate member.

  According to the second aspect of the present invention, the measurement range can be expanded even if the total length (total height) of the electrodes is the same based on the configuration. Therefore, the total length of the sensor can be shortened as the measurement range is expanded, and therefore the size of the sensor can be reduced. That is, when the flow passage as in the present invention is not formed, a liquid inlet / outlet (such as a hole or a slit) through which liquid existing between the inner side of the outer cylinder electrode and the outer side of the inner electrode can enter and exit is provided. It is necessary to provide separately below the outer cylinder electrode. In this case, even if the liquid inlet / outlet is provided at the lower end of the outer cylinder electrode, there is a little liquid inside (accumulated) inside the outer cylinder electrode below the lower edge of the liquid inlet / outlet. The lower limit of the liquid level forming the range is the lower edge. Therefore, the part from the lower edge of the liquid inlet / outlet to the lower end of the outer cylinder electrode cannot contribute to the detection of the liquid level. On the other hand, in the present invention, since the flow passage is provided, a decrease (fluctuation) in the liquid level is secured even inside the electrode supporting elastic member regardless of the presence or absence of such a liquid inlet / outlet. Even if the total length (total height) of the two is the same, there is an effect that the measurement range can be expanded.

  Furthermore, according to the invention described in claim 3, since the hook of the positioning member is engaged with the tip of the outer cylinder electrode, the length of the leg portion is set to a desired size. The positioning member can be positioned in the axial direction of the outer cylinder electrode of the positioning member itself by inserting the positioning plate portion inside the outer cylinder electrode until the hook is engaged with the tip of the outer cylinder electrode. Positioning to the outer cylinder electrode can be easily performed. In addition, in the case where the positioning member is attached to the outer cylinder electrode by welding, it can be welded by resistance welding or the like at the leg portion located away from the positioning plate portion that supports the tip of the electrode supporting elastic member. Can also reduce the thermal influence on the elastic body.

  The electrode supporting elastic member only needs to elastically support the tip of the internal electrode or a portion close to the tip inside the outer cylindrical electrode. Therefore, the electrode supporting elastic member made of the elastic body according to the present invention. Are not limited to those made of rubber, and may have a structure including a non-elastic body, such as a cored bar. Note that, as described above, a representative example of the elastic body is rubber, and it may be appropriately selected from synthetic rubbers that are resistant to the liquid to be measured.

  The sensor according to the present invention is suitable for detection of various liquid states (liquid level, concentration, etc.), but is particularly suitable when the liquid to be measured is urea water. Since urea water has conductivity, it is necessary to form an insulating film made of fluorine resin or the like on the surface of the internal electrode. On the other hand, when the support at the tip of the internal electrode is elastically supported by the elastic member for electrode support made of an elastic body as in the present invention, even if vibration or external force acts on the sensor as described above, This is because the insulating film is effectively prevented from being damaged.

  Hereinafter, an embodiment of a liquid state detection sensor embodying the present invention will be described in detail with reference to FIGS. FIG. 1 is a longitudinal sectional front view showing an embodiment of a liquid state detection sensor. FIG. 2 is an enlarged view of the tip of the liquid state detection sensor of FIG. FIG. 3 is a schematic diagram showing a heater pattern of the ceramic heater. 4 is a perspective view of the rubber bush used in the sensor of FIG. 1 as viewed obliquely from below. FIG. 5 is a side view of a rubber bush used in the sensor of FIG. 6 is a plan view of a rubber bush used in the sensor of FIG. FIG. 7 is a cross-sectional view of the rubber bush viewed from the direction of the arrows along the one-dot chain line AA in FIG. 6. FIG. 8 is an exploded perspective view showing a portion near the tip of the external electrode, a rubber bush, and a positioning member. In the liquid state detection sensor 100 according to the present invention, the longitudinal direction of the level detection unit 70 (a capacitor composed of the outer cylinder electrode 10 and the internal electrode 20) is the axis O direction, and the side on which the liquid property detection unit 30 is provided. The front end side and the side on which the mounting portion 40 is provided are defined as the rear end side.

  The liquid state detection sensor 100 according to the present embodiment is a state of an aqueous urea solution used for reduction of nitrogen oxide (NOx) contained in exhaust gas of a diesel vehicle, that is, the level (liquid level) of the aqueous urea solution. However, the apparatus further includes a detecting means for detecting the concentration of urea as a specific component contained in the aqueous urea solution. First, the overall configuration of the sensor 100 will be described with reference to FIGS. As shown in FIGS. 1 and 2, a liquid state detection sensor (hereinafter, also simply referred to as a sensor) 100 includes an outer cylinder electrode 10 having a cylindrical shape, and the outer cylinder electrode 10 within the outer cylinder electrode 10. A level detection unit 70 composed of a cylindrical internal electrode 20 provided along the direction of the axis O, a liquid property detection unit 30 provided on the distal end side of the internal electrode 20, and a liquid state detection sensor 100 are combined with urea. An attachment portion 40 for attachment to a urea water tank (not shown) as an aqueous solution container is configured as described in detail below.

  The outer cylinder electrode 10 constituting the sensor 100 in this embodiment is made of a metal material and has a long and thin cylindrical shape extending in the axis O direction. A plurality of narrow slits 15 are intermittently opened along each bus bar on, for example, three bus bars that are equally spaced in the circumferential direction on the outer periphery of the outer cylindrical electrode 10. In addition, at the front end portion 11 of the outer cylinder electrode 10, a rubber electrode supporting elastic member (hereinafter referred to as a rubber bush) is interposed between each bus bar in which the slit 15 is formed and an internal electrode 20 described later. Each of the openings 16 is also provided so as to prevent the omission of 80. Furthermore, one air vent hole 19 is formed on a bus bar different from each bus bar in which the slits 15 are formed at a position close to the base end portion 12 on the rear end side of the outer cylinder electrode 10. Further, the distal end portion 11 of the outer cylinder electrode 10 is further covered with the axis O from the position of the opening portion 16 so as to surround the protector 130 that covers and protects the radial periphery of the ceramic heater 110 that forms the liquid property detection portion 30 described later. It is extended to the direction tip side. And the most advanced part is opened, The protector 130 which comprises the liquid property detection part 30 is in the state which can be visually recognized from the opening side (FIG. 1 lower side).

  The outer cylindrical electrode 10 is welded in a state in which the base end portion 12 is fitted (engaged) with the outer periphery of the electrode support portion 41 of a metal attachment portion (attachment member) 40. The attachment portion 40 functions as a base for fixing the liquid state detection sensor 100 to the urea water tank (not shown), and an attachment hole (not shown) for inserting the attachment bolt is formed in the flange portion 42. Further, on the opposite side of the electrode support portion 41 across the flange portion 42 of the mounting portion 40, a relay state provided for electrical connection between the liquid state detection sensor 100 and an external circuit (not shown). A housing portion 43 for housing the circuit board 60 and the like is formed.

  The circuit board 60 is placed on a board placement portion (not shown) protruding from the four corners of the inner wall surface of the housing portion 43. The accommodating portion 43 is covered and protected by a cover 45, and the cover 45 is fixed to the flange portion 42. Further, a connector 62 is fixed to the side surface of the cover 45, and a connection terminal (not shown) of the connector 62 and a pattern on the circuit board 60 are connected by a wiring cable 61. The circuit board 60 and an external circuit (not shown) are connected via the connector 62.

  A hole 46 penetrating into the accommodating portion 43 is opened in the electrode support portion 41 of the attachment portion 40, and the base end portion 22 of the internal electrode 20 is inserted into the hole 46. The internal electrode 20 of the present embodiment is made of a long and thin cylindrical metal material extending in the direction of the axis O. On the outer peripheral surface of the internal electrode 20, an insulating film 23 made of a fluorine resin such as PTFE, PFA, ETFE, an epoxy resin, a polyimide resin, or the like is formed. The insulating coating 23 is formed in the form of a resin coating layer by applying such a resin on the outer surface of the internal electrode 20 by dipping or electrostatic powder coating and heat-treating it. As will be described later, a level detector 70 is formed between the internal electrode 20 and the outer cylinder electrode 10 by forming a capacitor whose capacitance changes according to the level of the urea aqueous solution.

  A flange-shaped pipe guide 55 is fixed to the outer periphery of the base end portion 22 on the rear end side in the axis O direction of the internal electrode 20 to fix the internal electrode 20 to the mounting portion 40. 41 is disposed inside a cylindrical inner case 50 that is disposed with the upper end engaged in a hole 46 in 41, and is engaged via a pipe guide 55. That is, the pipe guide 55 is an annular guide member joined to the end edge of the base end portion 22 of the internal electrode 20. On the other hand, the inner case 50 is a flanged cylindrical resin member that positions and supports the internal electrode 20 so that the internal electrode 20 and the outer cylindrical electrode 10 are reliably insulated, and the tip side is an electrode support portion of the mounting portion 40. 41 is inserted into the hole 46. The inner case 50 is formed with a flange portion 51 that protrudes radially outward. When the inner case 50 is engaged with the electrode support portion 41, the electrode support portion is inserted from the housing portion 43 side. 41 is inserted through the hole 46. The flange 51 is brought into contact with the bottom surface of the housing 43 to prevent the inner case 50 from passing through the hole 46. Further, the internal electrode 20 is inserted into the inner case 50 from the accommodating portion 43 side, and the pipe guide 55 is brought into contact with the flange portion 51, so that the inner electrode 20 is prevented from falling off from the inner case 50.

  Further, an O-ring 53 and an O-ring 54 are provided on the outer periphery and the inner periphery of the inner case 50, respectively. The O-ring 53 seals a gap between the outer periphery of the inner case 50 and the hole 46 of the mounting portion 40, and the O-ring 54 is formed between the inner periphery of the inner case 50 and the outer periphery of the base end portion 22 of the internal electrode 20. The gap between them is sealed. Thereby, when the liquid state detection sensor 100 is attached to the top plate or the upper lid of the urea water tank (not shown), the water tightness is prevented so that the inside and the outside of the urea water tank do not communicate with each other through the accommodating portion 43. And airtightness is maintained. A plate-like seal member (not shown) is attached to the tip-side surface (lower surface in FIG. 1) of the flange portion 42 of the attachment portion 40, and the flange portion when the liquid state detection sensor 100 is attached to the urea water tank. The watertightness and airtightness between 42 and the urea water tank are maintained.

  As shown in FIG. 1, the pipe guide 55 is pressed against the flange 51 of the inner case 50 by the two pressing plates 56 and 57 as shown in FIG. It depends on. The holding plate 56 is fixed in the housing portion 43 by tightening with a screw 58 with an insulating holding plate 57 sandwiched between the pipe guide 55 and the pipe guide 55 being pressed. Thereby, the internal electrode 20 joined to the pipe guide 55 is fixed to the electrode support portion 41. A hole 59 is opened in the center of the holding plates 56 and 57 used for fixing, and two electrical connections are made between the electrode lead wire 52 of the internal electrode 20 and a ceramic heater 110 described later. A two-core cable 91 containing lead wires 90 (only one lead wire 90 is shown in FIG. 1) is inserted and electrically connected to the pattern on the circuit board 60, respectively. An electrode (not shown) on the ground side of the circuit board 60 is connected to the mounting portion 40, whereby the outer cylinder electrode 10 welded to the mounting portion 40 is configured to be electrically connected to the ground side. ing.

  Next, the liquid property detection unit 30 will be described. The liquid property detection unit 30 is connected to the distal end portion 21 of the internal electrode 20. As shown in an enlarged view in FIG. 2, the liquid property detection unit 30 in this example includes a ceramic heater 110 as a liquid property detection element for detecting the concentration of urea in the urea aqueous solution, and the ceramic heater 110 as a liquid property detection element. The tip is held in a protruding state, and the insulating resin holder 120 attached to the tip 21 of the internal electrode 20 and the periphery of the tip of the ceramic heater 110 exposed from the holder 120 are covered. And a protector 130 for protection.

  Among these, as shown in FIG. 3, in the ceramic heater 110, a heater pattern 115 mainly composed of Pt is formed on a plate-shaped ceramic base 111 made of an insulating ceramic, and a ceramic base (not shown) forming a pair. The heater pattern 115 is embedded in a state of being sandwiched between. Here, the cross-sectional area of the pattern constituting the heating resistor 114 is made smaller than the pattern of the lead portions 112 and 113 serving as both poles for voltage application, so that heat is generated mainly in the heating resistor 114 during energization. To be done. In addition, via conductors (not shown) penetrating the surface of the ceramic base 111 are provided at both ends of the lead portions 112 and 113, and two terminals 119 (relaying connections between the two lead wires 90) ( In FIG. 2, only one of them is displayed).

  Further, as shown in FIG. 2 and the like, the holder 120 made of an insulating resin for supporting the ceramic heater 110 is concentric and has a different diameter between the large-diameter cylindrical portion 122 having a large diameter and the small-diameter cylindrical portion 121 having a small diameter. The tip portion 21 of the internal electrode 20 is inserted inside the large-diameter cylindrical portion 122 so as to cover the outer periphery thereof. In this embodiment, the holder 120 is attached to the distal end portion 21 of the internal electrode 20 in this way. As will be described in detail later, the distal end portion is elastically attached to the inner side of the rubber bush 80 via the holder 120. I support it. Moreover, the outer peripheral surface of the part which connects the large diameter cylindrical part 122 and the small diameter cylindrical part 121 in this holder 120 is made into the taper-shaped step part (taper part) 123 which diameter-reduces toward a front-end | tip. Further, on the outer peripheral surface of the small-diameter cylindrical portion 121 that forms a portion closer to the tip of the holder 120, four concave portions 124 that are substantially rectangular in front view are formed (recessed) at a constant depth at equal angular intervals in the circumferential direction. ing. Further, a taper is attached to the outer peripheral portion of the tip (surface) 125 of the small diameter cylindrical portion 121 of the holder 120.

  On the other hand, the inner peripheral surface of the holder 120 is formed in a circular cross section that expands in a stepped shape toward the small diameter cylindrical portion 121, the step portion 123, and the large diameter cylindrical portion 122. However, an opening 126 having a rectangular shape (in the cross section) is formed at the tip 125 of the small-diameter cylindrical portion 121 so that the tip 110b of the ceramic heater 110 can protrude without a substantial gap. The short side and the long side of the rectangle in the cross section of the opening 126 are set so as to correspond to the dimensions of the thickness and width of the ceramic heater 110, respectively. Although not shown in detail, in the cross section, the center of each side of the opening 126 is formed so as to correspond to the centers of the four recesses 124 described above. In the ceramic heater 110, the lead portions 112 and 113 (see FIG. 3) in the longitudinal direction are inserted into the small-diameter cylindrical portion 121, and the tip portion 110b side in which the heating resistor 114 is embedded extends from the tip 125 of the holder 120. In this state, the ceramic heater 110 is fixed by holding a seal in the opening 126 of the holder 120 by filling and solidifying the adhesive or resin 129 in the inner peripheral surface 127 of the small-diameter cylindrical portion 121. ing.

  On the other hand, the inner diameter of the large-diameter cylindrical portion 122 is configured to be slightly larger than the outer diameter of the tip portion 21 of the internal electrode 20, and two concave grooves 128b are formed on the inner peripheral surface 128 in the circumferential direction in this embodiment. Has been. Thus, when such a holder 120 is externally fitted to the distal end portion 21 of the internal electrode 20 from the large-diameter cylindrical portion 122 side, two concave grooves on the inner peripheral surface 128 of the large-diameter cylindrical portion 122 are provided. A seal between the inner peripheral surface 128 and the outer peripheral surface of the internal electrode 20 is ensured via each seal ring (for example, rubber O-ring packing) 140 loaded in the 128b, and the internal electrode 20 has an internal seal. It is configured to prevent the liquid constituting the measurement object from entering through this interval. Further, an annular shelf step portion 128 c is formed on the inner peripheral surface of the step portion 123 of the holder 120, and when the holder 120 is mounted on the tip portion 21 of the internal electrode 20, The end surface 21b is in contact with the shelf step portion 128c so as to be positioned in the axis O direction. The insulating coating 23 is provided on the outer peripheral surface of the internal electrode 20 from the distal end side to the proximal end portion 22 on the rear end side from the position where the seal ring 140 is disposed at the distal end portion 21 on the distal end side of the internal electrode 20. Even if the level detector 70 is immersed in the urea aqueous solution in the urea water tank (not shown), the internal electrode 20 may be in direct contact with the urea aqueous solution. Not to be.

  Before the holder 120 is attached to the internal electrode 20, the core wires of the two lead wires 90 of the cable 91 are joined to the terminals 119 of the ceramic heater 110 by caulking or soldering, respectively. Furthermore, the insulating protection member 95 covers and protects the terminal 119 and the lead wire 90 together with the joint portion. The two lead wires 90 are inserted through the cylindrical internal electrode 20 and connected to the circuit board 60.

  A protector 130 that covers and protects the periphery of the tip of the ceramic heater 110 that is a liquid property detection element is attached to the tip of the holder 120. The protector 130 is formed into a bottomed cylindrical shape, for example, by deep drawing a metal plate. This is a protective member for the exposed portion of the heater 110, and the ridge angle portion between the bottom portion 132 and the body portion 133 is chamfered into a curved surface, and the rigidity is enhanced. In addition, on the outer periphery of the body portion 133 of the protector 130, in the present embodiment, two circulation holes 135 for forming a measurement object are formed on four bus bars that are equally spaced in the circumferential direction. Has been. The bottom portion 132 is formed with a flow hole 136 that is similarly opened at the center thereof. Such a protector 130 is set so that the inner diameter of the body part 133 is the same as or slightly larger than the outer diameter of the small-diameter cylindrical part 121 in the holder 120 described above. And the protector 130 is a proximal end (rear end) or a proximal end portion of the body portion 133 that is externally fitted to the holder 120, and is provided at four locations at equal angular intervals in the circumferential direction. By projecting inward and elastically deforming, a convex portion 137 that can be fitted into the concave portion 124 of the holder 120 is provided. The convex portion 137 is a protruding piece portion formed by cutting and raising the wall of the protector 130 so that its end portion is positioned on the tip side and protrudes obliquely inward, and the tongue-shaped claw is Presents. In addition, the convex part 137 is formed so that it may be located in the middle of each bus-line of the flow hole 135 provided in the trunk | drum 133, when the protector 130 is seen from the axis line O direction.

  The protector 130 elastically deforms the convex portion 137 outward by fitting the proximal end portion of the body portion 133 into the small-diameter cylindrical portion 121 on the distal end 125 side of the holder 120 and pushing it in. The protector 130 is configured to be fitted to the recess 124 so as to restore the deformation. In the fitted state, the protector 130 is configured to be attached to the holder 120 so as not to be detached and to be non-rotatable around the axis O. ing. By attaching the protector 130 to the holder 120 in this way, the ceramic heater 110 with the heating resistor 114 side exposed from the holder 120 is accommodated in the protector 130.

  As described above, the sensor of this embodiment includes the liquid property detection unit 30 having such a configuration. This is because the holder 120 is attached to the distal end portion 21 of the internal electrode 20, thereby the level detection unit 70. Insulated with each other. As shown in FIG. 2, the liquid property detection unit 30 is made of a rubber ring-shaped member interposed between the inner side of the outer cylindrical electrode 10 and the outer side of the inner electrode 20 together with the tip portion 21 of the inner electrode 20. The rubber bush 80, which is an electrode supporting elastic member, is positioned and supported in the outer cylindrical electrode 10 as follows.

  That is, in this embodiment, as shown in FIGS. 4 to 8, the rubber bush 80 is configured to have an annular shape as a whole, and the inner peripheral surface thereof is the outer peripheral surface of the body portion 133 of the protector 130. Among these, the body portion 133 and the large diameter cylinder are formed so as to straddle the front and rear in the direction of the axis O on the portion corresponding to the convex portion 137 and the outer peripheral surface of the large diameter cylindrical portion 122 of the holder 120 avoiding the protector 130. The inner peripheral surface 81 of the cylindrical portion on the front end side has a small diameter so that it can be attached to the outer peripheral surface of the portion 122 in an interference fit. The peripheral surface 82 has a large diameter. The inner diameter surface 81 of the small diameter is slightly smaller than the outer diameter of the body portion 133 of the protector 130, and the inner diameter surface 82 of the large diameter cylindrical portion is the large diameter cylinder of the holder 120. The taper is slightly smaller than the outer diameter of the portion 122, and the taper of the tapered inner peripheral surface 83 that connects them is a taper corresponding to the step portion 123 of the holder 120. And the formation part of the small diameter inner peripheral surface 81 of the rubber bush 80 is formed thicker than the formation part of the large inner peripheral surface 82.

  As described above, the inner peripheral surface of the rubber bush 80 includes two inner peripheral surfaces 81 and 82 having different inner diameters formed so that the outer peripheral surfaces of the holder 120 and the protector 130 are fitted in an interference fit. And a tapered inner peripheral surface 83 for connecting the two. However, on the inner peripheral surfaces 81 to 83, the positions corresponding to the buses on the outer peripheral surface 89 on which the protruding portions 87 are formed are extended from the small-diameter inner peripheral surface 81 side to the large-diameter inner peripheral surface 82 side. Groove portions 84 that are continuous on the inner peripheral surfaces 81, 83, and 82 are respectively provided (see FIGS. 6 and 7).

  Further, the rubber bush 80, which is an electrode supporting elastic member used in the present embodiment, is provided on each of the openings of the outer cylindrical electrode 10 on the three bus bars that are equally spaced in the circumferential direction on the outer peripheral surface 89. 16 are provided with protrusions 87 that are respectively fitted (engaged) to 16 and function as prevention of disengagement and rotation. In this embodiment, the projection 87 has a substantially circular front surface, but has a saw-tooth shape whose height decreases toward the rear end in a side view, and the outer cylinder electrode 10 of the rubber bush 80. In the press-fitting to the inner side, it is easy to fit into the opening 16 and has a retaining action. In the circumferential direction of the outer peripheral surface 89, a plurality of (five in this embodiment) groove portions 88 are provided along the axis O direction between the respective protrusions 87.

  Such a rubber bush 80 is formed on the inside of the outer cylinder electrode 10 from the portion where the inner peripheral surface 82 has a large diameter before the inner electrode 20 to which the holder 120 is attached is inserted into the outer cylinder electrode 10. It is press-fitted so as to be pushed in from the front end side, and the protrusion 87 on the outer peripheral surface is fitted into the opening 16 provided in the outer cylinder electrode 10 and attached. That is, the internal electrode 20 to which the holder 120 is attached is inserted after the rubber bush 80 is press-fitted inside the outer cylinder electrode 10 and attached. The process will be described later. As shown in FIG. 2, the rubber bush 80 attached to the inner side of the outer cylinder electrode 10, and on the inner side of the outer cylinder electrode 10, this rubber is provided. A positioning member 150 is attached to position the bush 80 so as to support the bush 80 on the tip 80a side.

  As shown in FIGS. 2, 8, and 9, in this embodiment, the positioning member 150 includes a positioning plate portion 152 formed of a circular plate portion having an annular shape and a substantially right angle from the outer peripheral edge of the positioning plate portion 152. The leg portion 154 extends toward the distal end side, and the hook 156 protrudes outward at the distal end of the leg portion 154. However, the tip of each leg 154 is vertically divided into three, and the hook 156 is provided at the tip of the center leg piece 154b. Here, the positioning plate portion 154 is an annular circular plate portion in order to insert the body portion 133 of the protector 130 together with the front end portion of the holder 120 into the inner side (inner peripheral surface) 153 in this embodiment. As shown in FIGS. 2 and 10, the flow of liquid between the inner side of the outer cylinder electrode 10 and the front end side of the positioning plate portion 152 is ensured through the groove portion 84 provided on the inner peripheral surface of the rubber bush 80. It is to do. In this embodiment, the inner diameter of the positioning plate portion 152 is matched with the diameter of a circle passing through the groove bottom of the groove portion 84. In this embodiment, the leg portion 154 and the hook 156 in the positioning member 150 are provided at three equiangular intervals in the circumferential direction of the positioning plate portion 152. Further, the positioning plate portion 152 has an outer diameter smaller than the inner diameter of the outer cylindrical electrode 10, and the leg portion 154 is set along the inner peripheral surface in the axial direction of the outer cylindrical electrode 10. In such a positioning member 150, after the rubber bush 80 is attached, the positioning plate portion 152 is disposed inside the outer cylindrical electrode 10 so as to support the tip 80a of the rubber bush 80, and the hook 156 is removed. In this state, at least a part W of each leg 154 is fixed to the outer cylinder electrode 10 by, for example, resistance welding.

  In the sensor 100 of this embodiment, as described above, the internal electrode 20 is pressed toward the front end side in the axis O direction by the two pressing plates 56 and 57 via the pipe guide 55. As shown in FIG. 2, the stepped portion 123 of the holder 120 attached to the distal end portion 21 of the internal electrode 20 is supported by the inner peripheral surface 83 of the rubber bush 80. Further, the internal electrode 20 is supported at the tip of the outer cylinder electrode 10 via the holder 120 and the protector 130. As described above, the inner periphery of the rubber bush 80 positioned and held by the positioning member 150 is used. The surface is elastically supported inside the outer cylinder electrode 10.

  According to the sensor 100 of this embodiment having such a configuration, as described above, the rubber bush 80 is used to elastically move the tip of the internal electrode 20 or a portion closer to the tip to the inside of the outer cylindrical electrode 10 via the holder 120 and the protector 130. Therefore, the internal electrode 20 can be stably supported at the tip thereof without any particular increase in the number of parts. In addition, since the rubber bush 80 is used, it is possible to absorb dimensions and assembly errors of each electrode and the like. Further, the insulating coating 23 formed on the surface of the internal electrode 20 is not damaged.

  Further, in the assembly of such a sensor 100, the internal electrode 20 to which the holder 120 or the like is attached is in an assembly stage as shown in FIGS. 11 and 12 from the holder 120 side of the tip. The base end portion 12 is inserted into the outer cylindrical electrode 10 welded to the electrode support portion 41 of the portion 40, and the body portion 133 of the protector 130 and the large-diameter cylindrical portion 122 of the holder 120 are attached in the outer cylindrical electrode 10. By inserting the rubber bush 80 into the inside, the tip or a portion near the tip can be elastically supported via the holder 120 or the like. Therefore, assembly can also be performed easily. Moreover, at the time of this insertion, as indicated by a two-dot chain line in FIGS. 11 and 12, the internal electrode 20 is inclined and the tip thereof (the holder 120 and the protector 130 in this embodiment) is attached to the rubber bush 80. In this embodiment, the rubber bush 80 is disposed on the distal end side of the outer cylinder electrode 10 on the distal end side of the rubber bush 80 even if it is pushed to the distal end side. A positioning member 150 for positioning so as to support is attached. Therefore, even in such a case, the rubber bush 80 is not pushed out toward the distal end side of the outer cylindrical electrode 10, and the protruding portion 87 is not sheared or detached from the opening 16.

  Thus, in the sensor 100 of the present embodiment, when the inner electrode 20 is inserted into the outer cylinder electrode 10, there is a problem even if the holder 120 at the tip thereof is pushed strongly into the rubber bush 80. Since it does not occur, the support of the internal electrode 20 with high reliability or high stability can be obtained. Furthermore, it is possible to prevent the holder 120 with the ceramic heater 110 from moving at the tip of the internal electrode 20, so that the sealing performance by the seal ring 140 that maintains the liquid tightness between the holder 120 and the internal electrode 20 can be obtained. It is possible to prevent the deterioration, and the reliability of the sensor can be remarkably enhanced.

  The operation of the liquid state detection sensor 100 itself will be described in detail below. When this sensor 100 is attached to a urea water tank (not shown) and used, as shown in FIG. 2, the outer cylinder electrode 10 has a B portion on the front end side in the axis O direction with respect to the rubber bush 80, and a rear part. The urea aqueous solution flows into the C portion on the end side through the opening and the slit 15 at the most distal end portion in the axis O direction of the outer cylinder electrode 10. In addition, the aqueous urea solution flows into part D in the protector 130 from part B via the liquid circulation holes 135 and 136. Then, the urea aqueous solution that has flowed into the B part and the C part passes through the flow path 85 formed by the groove part 88 of the rubber bush 80 and the inner peripheral surface of the outer cylinder electrode 10, and between the groove part 84 and the outer peripheral surface of the holder 120. It is circulated through the formed flow passage 86. Further, the flow passage 86 is continuous with the liquid circulation hole 135 of the protector 130. Accordingly, the urea aqueous solution is circulated between the B part and the C part and between the D part and the C part via the flow passages 85 and 86. In addition, when an empty urea water tank is filled with a urea aqueous solution, there is a possibility that air may remain in the B part and the D part, but this air can reach the C part through the flow passages 85 and 86.

  Next, the principle of detecting the level and concentration of the aqueous urea solution by the liquid state detection sensor 100 of the present embodiment will be described. First, the principle of detecting the level of the urea aqueous solution in the level detection unit 70 will be described with reference to FIG. FIG. 13 is an enlarged cross-sectional view of the vicinity of the water surface of the urea aqueous solution filled in the gap between the outer cylinder electrode 10 and the inner electrode 20.

  The liquid state detection sensor 100 is assembled in a urea water tank (not shown) containing a urea aqueous solution with the front end side of the outer cylinder electrode 10 and the internal electrode 20 facing the bottom wall side. That is, the level detection unit 70 of the liquid state detection sensor 100 sets the direction of displacement of the urea aqueous solution (the level of the urea aqueous solution level) in the urea water tank (not shown) as the axis O direction. In addition, the internal electrode 20 is assembled to a urea water tank (not shown) so that the tip side of the internal electrode 20 is a side (low level side) with a small capacity of the urea aqueous solution. And the electrostatic capacitance between the gaps of the outer cylinder electrode 10 and the inner electrode 20 is measured, and it is detected to what level the urea aqueous solution existing between the two is present in the axis O direction. As is well known, this is based on the fact that the capacitance increases as the difference in diameter between two points having different potentials in the radial direction decreases.

  That is, as shown in FIG. 13, in the portion not filled with the urea aqueous solution, the distance of the portion where the potential difference occurs between the gaps is interposed between the inner peripheral surface of the outer cylinder electrode 10 and the insulating coating 23. This is the total distance (indicated by distance E) of the distance corresponding to the thickness of the air layer (indicated by distance F) and the distance corresponding to the thickness of the insulating coating 23 (indicated by distance G). On the other hand, in the portion filled with the urea aqueous solution, the potential difference between the gaps is such that the potential of the outer cylinder electrode 10 and the urea aqueous solution is almost equal because the urea aqueous solution exhibits conductivity. The distance G corresponds to a thickness of 23.

  In other words, the capacitance between the gaps in the portion that is not filled with the urea aqueous solution is that the distance between the electrodes is F and the capacitance of the capacitor using air as a dielectric (non-conductor) is the distance between the electrodes. It can be said that this is the combined capacitance of a capacitor in which a capacitor having the insulating coating 23 as a dielectric is connected in series with G. The capacitance between the gaps in the portion filled with the urea aqueous solution can be said to be the capacitance of a capacitor in which the distance between the electrodes is G and the insulating coating 23 is a dielectric. And the electrostatic capacitance of the capacitor | condenser which connected both in parallel will be measured as an electrostatic capacitance of the level detection part 70 whole.

  Here, since the distance F between the electrodes sandwiching the air layer is larger than the distance G between the electrodes sandwiching the insulating coating 23, the capacitance per unit between the electrodes using air as a dielectric is The capacitance per unit between the electrodes using the insulating coating 23 as a dielectric is smaller. For this reason, the change in the capacitance of the portion filled with the urea aqueous solution is larger than the change in the capacitance of the portion not filled with the urea aqueous solution. Is proportional to the level of the aqueous urea solution. In this embodiment, the level detection of the aqueous urea solution is performed by a level detection circuit including a microcomputer mounted on the circuit board 60, and the level information signal obtained by the level detection circuit is sent via the connector 62. It outputs to an external circuit (for example, ECU). The external circuit determines whether or not the level of the urea aqueous solution is appropriate based on the input level information signal, and appropriately performs a process of notifying the driver when it is not appropriate.

  Next, the principle of detecting the concentration of urea as a specific component contained in the urea aqueous solution in the ceramic heater 110 constituting the liquid property detection unit 30 will be described. In general, it is known that the thermal conductivity of a liquid varies depending on the concentration of a specific component contained in the liquid. That is, when a heating resistor is used and the surrounding liquid is heated for a certain period of time, the temperature increase rate differs for liquids having different concentrations. It is also known that when a constant current is passed through the heating resistor, the resistance value of the heating resistor increases in proportion to an increase in the temperature around the heating resistor. From this, when a heating resistor is used and the surrounding liquid is heated for a certain period of time, if the degree of change in the resistance value of the heating resistor is obtained, the degree of temperature change in the surrounding liquid is obtained, and the concentration of the liquid is determined. Obtainable.

  In the liquid state detection sensor 100 of the present embodiment, a constant current is passed through the heating resistor 114, and a detection voltage Vd corresponding to the magnitude of its own resistance value is applied to both ends of the heating resistor 114. appear. When the potential at one end of the heating resistor 114 is Pin and the potential at the other end of the heating resistor 114 is Pout, the detection voltage Vd is obtained by the difference between the potential Pin and the potential Pout. Specifically, first, the detection voltage Vd immediately after the start of energization of the heating resistor 114 is measured, and the detection voltage Vd is measured again after a certain time (for example, after 700 ms). Then, the concentration of the urea aqueous solution is determined using a table (not shown) created in advance by experiments or the like, using the difference value between the two detection voltages Vd as a parameter. In this embodiment, similarly to the level detection of the urea aqueous solution, the concentration detection (calculation) of the urea aqueous solution is performed by the concentration detection circuit including the microcomputer mounted on the circuit board 60, and is obtained by the concentration detection circuit. The obtained concentration information signal is output to an external circuit (for example, ECU) via the connector 62. The external circuit determines whether or not the concentration of the urea aqueous solution is within an appropriate range based on the input concentration information signal, and appropriately performs a process of notifying the driver when it is not within the appropriate range.

  In the present embodiment, the heating resistor 114 of the ceramic heater 110 and the lead portions 112 and 113 are made of the same material and have different pattern cross-sectional areas, so that the heating resistor 114 mainly generates heat. Although it was made, each material may be made different. In this embodiment, the resistance value of the heating resistor 114 of the ceramic heater 110 is used and the urea concentration in the urea aqueous solution is obtained by referring to the table. The concentration of the urea aqueous solution may be calculated by substituting it into the calculation formula.

  In the embodiment described above, the support at the tip of the internal electrode 20 or the portion near the tip by the rubber bush 80 that is an electrode supporting elastic member is used as a liquid property detection element for the sensor 100 to detect the concentration of urea in the urea aqueous solution. Although what was performed via another member, such as the protector 130 and the holder 120, was illustrated based on the structure which has the liquid property detection part 30 containing the ceramic heater 110, in this invention, depending on a sensor, such a separate member is interposed. Instead, the tip of the internal electrode 20 or a portion near the tip may be directly and elastically supported by the electrode supporting elastic member. FIG. 14 shows an example thereof, which is embodied as a sensor that does not hold the liquid property detection unit 30 in the above-described embodiment, and is related to the configuration of the liquid property detection unit 30. Since only the points where the protector 130, the holder 120, etc. are omitted are different, the same parts are only given the same reference numerals, and detailed description thereof is omitted. In FIG. 14, the internal electrode 20 is embodied by a solid round bar instead of a cylindrical body. In this case, the tip of the internal electrode 20 or a portion close to the tip is formed into an interference fit with the large-diameter inner peripheral surface 82 of the rubber bush 80 so as to be elastically supported. The front end surface of the internal electrode 20 is set so as not to be pressed against the rubber bush 80.

  Further, in the above embodiment, the groove portions 84 and 88 of the rubber bush 80 which is an electrode supporting elastic member are used as the flow passages, and the inside of the positioning plate portion 152 of the positioning member 150, the outer peripheral edge thereof, and the inside of the external electrode 10. Using a gap S (see FIG. 10) with the peripheral surface, the liquid flows between the inner side of the outer cylindrical electrode 10 and the outer side of the inner electrode 20 and the tip side of the positioning member 152. Since the path is formed, as described above, the lowering (fluctuation) of the liquid level is secured even inside the rubber bush 80, so that the measurement range can be expanded even if the total length (total height) of the sensor is the same. it can. In addition, although the groove parts 84 and 88 of the rubber bush 80 which is an electrode supporting elastic member used in the above embodiment are provided in a groove shape on the inner peripheral side or the outer peripheral side of the rubber bush 80, a through hole penetrating the thick part You may form as. Further, the rubber bush 80 may be formed by omitting any of the groove portions 84 and 88. Moreover, although the outer cylinder electrode 10 and the inner electrode 20 are cylindrical, they may be rectangular.

  In the above description, the positioning member 150 has a shape in which the ring-shaped positioning plate portion 152 and the leg portion 154 are provided on the outer peripheral edge thereof. However, the positioning member 150 is located on the distal end side of the electrode supporting elastic member. As long as it is attached to the inside of the external electrode 10 in order to position it in such a way as to support it at its distal end side, its shape and attachment means are not limited. As a simple ring shape, it may be attached to the inside of the external electrode 10 by welding, or may be attached to the inside of the external electrode 10 by a screwing method. Further, the positioning member may be a simple disk or a cylindrical one. And in such a thing, when forming a flow path between the inner side of an outer cylinder electrode and the outer side of an internal electrode, and the front end side of a positioning member so that a liquid may distribute | circulate, a through-hole is in a proper place. May be provided.

  In addition, since the urea water is a measurement target in the above sensor, an insulating coating 23 is formed on the internal electrode 20, but the insulating coating 23 is adapted to the liquid characteristics (for example, oxidation / reduction properties). It is recommended to select a material that is not easily corroded. The insulating film was formed by dipping or electrostatic powder coating. However, if the air layer is not mixed with the internal electrodes, the insulating film can be formed using an insulating tube. Formation may be performed.

  The ceramic heater 110 as the liquid property detection element may be used to detect the detection of the temperature of the liquid and the lower limit level of the liquid in addition to the detection of the concentration of a specific component (for example, urea) contained in the liquid. . For example, when the temperature of the liquid is detected by the ceramic heater 110, the resistance value of the heating resistor 114 immediately after the constant current starts to flow through the heating resistor 114 (more specifically, the heating resistor 114), the temperature of the liquid can be detected. Since the resistance value immediately after the heating resistor 114 is energized shows a value corresponding to the temperature of the liquid, the temperature of the liquid can be detected by such a method. In addition, since the change behavior of the resistance value of the heating resistor 114 is greatly different between when the liquid exists around the ceramic heater 110 and when it does not exist, the lower limit level of the liquid is detected using this difference. You may do it.

The longitudinal section front view showing the embodiment of the liquid state detection sensor of the present invention. The enlarged view of the front-end | tip part of the liquid state detection sensor of FIG. The schematic diagram which shows the heater pattern of a ceramic heater. The perspective view which looked at the rubber bush used for the sensor of FIG. 1 from diagonally downward. The side view of the rubber bush used for the sensor of FIG. The top view of the rubber bush used for the sensor of FIG. Sectional drawing of the rubber bush seen from the arrow direction in the dashed-dotted line AA of FIG. The disassembled perspective view which shows the site | part near the front-end | tip of an external electrode, a rubber bush, and a positioning member. The expansion perspective view of a positioning member. The enlarged view which looked at the liquid state detection sensor shown in FIG. 1 in the axis line O direction from the front end side. The longitudinal cross-sectional front view explaining the assembly state of a sensor. The principal part enlarged view of FIG. The expanded sectional view of the water surface vicinity of the urea aqueous solution with which it filled between the gaps of a support outer cylinder electrode and an internal electrode. The principal part expanded sectional view of another example of the liquid state detection sensor of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Outer cylinder electrode 10a End of outer cylinder electrode 16 Opening part 16
20 Internal electrode 40 Mounting part 70 Level detection part 80 Bush (elastic member for electrode support)
80a Bush tip 85, 86 Flow path 87 Protrusion 100 Liquid state detection sensor 150 Positioning member 152 Positioning plate 154 Leg 156 Hook O Axis

Claims (3)

A liquid state detection sensor for detecting the state of the liquid stored in the storage container,
It has a cylindrical outer cylinder electrode made of a conductor and an inner electrode made of a conductor provided along the axial direction in the outer cylinder electrode, and is accommodated in the receiving container between the electrodes. A level detector formed by forming a capacitor whose capacitance changes according to the level of the liquid;
An attachment portion for attaching a liquid state detection sensor to the storage container, located on the rear end side in the longitudinal direction of the level detection portion;
An elastic member for electrode support made of an elastic body having an annular portion that supports the outer peripheral surface of the inner electrode at a tip or a portion near the tip directly or indirectly, and is press-fitted inside the outer cylindrical electrode. An electrode supporting elastic member,
While the outer cylinder electrode is provided with an opening portion penetrating in the radial direction at a portion near the tip,
The electrode supporting elastic member has a protrusion that can be fitted into the opening on the outer peripheral surface thereof, and is press-fitted inside the outer cylindrical electrode to fit the protrusion into the opening. Installed in the
Furthermore, a positioning member for positioning the electrode supporting elastic member on the distal end side is attached to the distal end side of the electrode supporting elastic member and inside the outer cylindrical electrode,
The internal electrode is inserted into the outer cylinder electrode from the front end side, and the front end of the internal electrode or a portion closer to the front end is directly or via a separate member inside the annular portion of the electrode supporting elastic member. A liquid state detection sensor, which is inserted into and elastically supported.   The electrode supporting elastic member and the positioning located inside the outer cylindrical electrode so that the liquid flows between the inner side of the outer cylindrical electrode and the outer side of the inner electrode and the distal end side of the positioning member. The liquid state detection sensor according to claim 1, wherein a flow passage connected to the member is formed. The positioning member includes a positioning plate portion having an outer diameter smaller than the inner diameter of the outer cylinder electrode, a leg portion extending from the peripheral edge of the positioning plate portion to the distal end side at a substantially right angle to the positioning plate portion, and a distal end of the leg portion. A hook projecting outward, and the positioning plate portion is disposed inside the outer cylinder electrode so as to support the tip of the electrode supporting elastic member, and the hook is disposed on the outer cylinder. 3. The liquid state detection sensor according to claim 1, wherein at least a part of the leg portion is welded to an inner peripheral surface of the outer cylinder electrode by engaging with a tip of the electrode.

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