JP2007114051A - Liquid condition detection sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid condition detection sensor provided with a cylindrical electrode fixing structure fixed by welding at the end part of the base so as to project from the rear surface of the electrode fixing member wherein, the electrode fixing member is prevented from deforming caused by welding, and the sealing property at the fixing to a tank is improved. <P>SOLUTION: A cylindrical part 34 is provided on a rear surface 32a of the electrode fixing member 30. On the external perimeter of the cylindrical part 34, apart from the rear surface 32a by an interval K to the tip, a surface 34b of smaller diameter is formed, and a surface 34c facing to the tip direction is provided at the boundary of the end part of the large diameter and the small diameter part 34b. On the external perimeter of the small diameter part 34b the end part 12 of the cylindrical electrode 10 is fitted, and its end surface 13 is abutted to the surface 34c facing to the tip, and in the fitting state abutting surface is welded around the abutting surface. Because the position of the welding line is separated from the rear face 32a of the electrode fixing member 30 by interval K, the heat during welding is harder to be conducted to the rear surface 32a than the conventional case where there is no separation, therefore the deformation can be reduced. <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 (detects) a state such as a liquid level of a liquid stored in a liquid storage container 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 (SCR) catalyst is installed in the middle of an exhaust gas exhaust muffler of a diesel vehicle, and urea water is put as a reducing agent solution in a liquid container (hereinafter also referred to as a tank) provided in a separate vehicle. A system has been proposed in which NOx is reduced to a harmless gas such as N ₂ by injecting the urea water onto the catalyst. In this system, when the urea water is exhausted, the NOx reduction reaction cannot be promoted and a large amount of NOx is discharged. , Also called a water level), and measures such as issuing an alarm when the remaining amount of urea water falls below a specified amount are taken. As an example of a sensor for measuring the water level, a capacitive liquid state detection sensor is known (Patent Document 1).

  The liquid state detection sensor described in Patent Document 1 uses an elongated cylinder made of a conductor as an outer electrode (external electrode), and an elongated columnar shape provided concentrically along the axial direction inside the external electrode. Alternatively, the capacitance between the tubular internal electrode is measured, and the water level is detected from the capacitance. For example, in a capacitive liquid state detection sensor used to measure the level of a conductive liquid such as urea water, the surface of the internal electrode is used to prevent a short circuit between the external electrode and the internal electrode. An insulating film is formed, and then the liquid state detection sensor is attached to and set in a tank (casing) as a measurement target so that the axial direction of both electrodes is the vertical direction of the water level. When measuring the water level (liquid level) of such a conductive liquid, the capacitance of the portion not immersed in the liquid is the air layer between the gap between the inner and outer electrodes and the insulating film of the inner electrode. Depends on thickness. 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 external 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 the water level can be detected.

  Such a liquid state detection sensor is usually provided in the tank so that the axial direction of the external electrode is in the vertical direction of the water level. For example, the external electrode (and internal electrode) is the ceiling (top plate) of the tank. Alternatively, it is attached in a hanging manner from the lid into the tank. In this case, since the liquid state detection sensor positions the base end side (base side) of the external electrode on the ceiling side, the base end portion (upper end portion) of the external electrode is placed on the top plate of the tank (casing) ( It will be fixed to the top lid. And in this prior art, the fixing is provided with a recess or an opening on the back surface of the upper lid, the base end portion of the external electrode is fitted into the opening, the outer peripheral surface at the base end portion, and the back surface of the upper lid It was done by welding along the peripheral surface at the corner formed by

  As another sensor different from the prior art, as shown in FIG. 8, the electrodes 10 and 20 are suspended from the sensor mounting opening provided on the top plate (upper lid) of the tank T into the tank. Some are designed to be inserted. This is to fix the electrodes 10 and 20 to the top plate (lid) at the top of the tank T via an electrode fixing member (electrode support member) 30 that is fixed at the base end portion. is there. That is, in this device, the mounting flange 35 is provided on the outer peripheral surface along the bottom portion 32 of the electrode fixing member 30, while the opening 33 is provided in the bottom portion 32, and the cylindrical external electrode 10 is connected to the opening 33. The base end portion 12 of the electrode 10 is fixed to the inner periphery of the opening 33 by welding in the same manner as described above. In the sensor shown in the figure, an annular holder 50 made of an insulating material is inserted inside the base end portion 12 of the external electrode 10, and the internal electrode 20 is arranged inside the holder 50. That is, in this device, the base end portion 12 of the external electrode 10 is fitted into the opening 33, and the peripheral surface is formed at the corner angle formed by the outer peripheral surface of the base end portion 12 and the back surface of the electrode fixing member 30. It is fixed by welding along. Then, the mounting flange 35 provided on the outer peripheral surface of the electrode fixing member 30 is seated on the periphery of the mounting opening provided on the lid (or top plate) of the tank via, for example, the packing P, and the screw member The attachment is performed by tightening by screwing or the like (not shown).

As described above, in this type of conventional sensor, the cylindrical external electrode is fixed to the lid of the tank, or is fixed to the electrode fixing member as described above. The base end portion of the external electrode is inserted into the opening, and a corner portion formed by the outer peripheral surface of the inserted external electrode and the peripheral edge of the opening is welded along the outer peripheral surface of the external electrode. The sensor having such an electrode fixing structure has the following problems to be solved.
Japanese Utility Model Publication No. 01-151215

  That is, in a sensor having such an electrode fixing structure, the tank lid that forms the fixing member or the back surface of the mounting flange for the tank in the electrode fixing member is at the same level as the part to which the electrode to be fixed is welded. For this reason, deformation or distortion is caused by the influence of heat during welding performed along the circumferential direction. For this reason, when the sensor is mounted on the tank, the mounting stability of the mounting flange is impaired, and there is a problem that the sealing performance may be deteriorated even if it is mounted through packing. .

  The present invention has been made in view of the problem of such a sensor, and its purpose is to provide a structure in which a cylindrical electrode such as a cylindrical external electrode is fixed to an electrode fixing member by welding at its base end. In the sensor, the electrode fixing member (specifically, the mounting flange) is prevented from being deformed due to the welding.

In order to solve the above-mentioned problem, the invention according to claim 1 is a liquid state detection sensor that detects the state of the liquid stored in the liquid storage container based on the capacitance between the electrodes,
A cylindrical electrode for capacitance measurement that has a cylindrical shape, and an electrode fixing member that fixes the cylindrical electrode at its proximal end,
The electrode fixing member is provided with a mounting flange for mounting the sensor itself on the liquid container or its lid on the outside of the electrode fixing member, and on the inner side of the mounting flange on the back surface of the electrode fixing member. A cylindrical portion is provided so as to protrude from the back surface, and the back surface of the electrode fixing member and the tube are fitted in a state where the base end portion of the cylindrical electrode is fitted to the outer peripheral surface of the cylindrical portion. Characterized in that the base end portion of the cylindrical electrode and the outer peripheral surface of the cylindrical portion are welded along the circumferential direction while maintaining a predetermined interval between the end surface of the base end portion of the cylindrical electrode. To do.

  According to a second aspect of the present invention, a convex portion is provided so that the end surface of the proximal end portion of the cylindrical electrode is in contact with the outer peripheral surface of the cylindrical portion at a position separated from the back surface of the electrode fixing member. 2. The liquid state detection sensor according to claim 1, wherein the predetermined interval is maintained by bringing the end face of the base end portion of the cylindrical electrode into contact with the convex portion.

Invention of Claim 3 is a liquid state detection sensor which detects the state of the liquid accommodated in a liquid container based on the electrostatic capacitance between electrodes,
A cylindrical electrode for capacitance measurement that has a cylindrical shape, and an electrode fixing member that fixes the cylindrical electrode at its proximal end,
The electrode fixing member is provided with a mounting flange for mounting the sensor itself on the liquid container or its lid on the outside of the electrode fixing member, and on the inner side of the mounting flange on the back surface of the electrode fixing member. The cylindrical portion is provided so as to protrude from the back surface, and the outer diameter of the cylindrical portion is formed as a small diameter portion having a relatively small diameter from the distal end of the cylindrical portion, An end-facing surface having an annular shape is provided at the boundary of the different diameters, and the end surface of the base end portion of the cylindrical electrode is fitted to the outer peripheral surface of the small diameter portion with the base end portion of the cylindrical electrode being fitted. It is characterized in that it is formed in a butt shape on the tip-facing surface, and the end surface of the base end portion and the tip-facing surface are welded along the circumferential direction.

  The invention described in claim 4 is characterized in that a concave portion is provided along the circumferential direction on the outer peripheral surface at a corner angle formed by the tip-facing surface and the outer peripheral surface of the small-diameter portion. It is a liquid state detection sensor as described in above. The invention according to claim 5 is characterized in that the outer diameter of the cylindrical portion at the tip-facing surface and the outer diameter of the end surface of the proximal end portion of the cylindrical electrode are the same diameter. The liquid state detection sensor according to claim 3 or 4. Further, in the invention described in claim 6 according to any one of claims 1 to 5, chamfering is performed along the circumferential direction at the corner between the end surface of the proximal end portion of the cylindrical electrode and the inner peripheral surface thereof. It is a liquid state detection sensor characterized by being attached.

  In addition, like the liquid state detection sensor of the present invention, a device that detects the liquid state such as the liquid level in the liquid container (tank) by measuring the capacitance between the electrodes, a pair of positive and negative electrodes However, in the sensor of the present invention, the sensor itself is usually provided with a pair of electrodes, but is not necessarily limited to such a sensor. As provided with a pair of electrodes, as in the above-described prior art and prior art, provided in the axial direction in the cylindrical external electrode and the inside of the external electrode (inside the cylinder), Although the thing provided with the internal electrode which makes columnar shape (or cylinder shape) with a small diameter is illustrated, it is not limited to the thing of the form of such an electrode.

  Further, in order to measure the capacitance between the electrodes, when the liquid container itself is made of metal, the container (tank) itself can be used as an electrode. In such a case, the sensor itself may be provided with one electrode. Similarly, it is possible to provide one electrode independently from the sensor itself. In such a case, the sensor itself only needs to have one electrode. That is, the sensor of the present invention includes a sensor having only one of the paired electrodes, and the electrode in that case is the “cylindrical electrode” of the present invention.

  Furthermore, in the present invention, the electrode fixing member having a mounting flange for seating and mounting the sensor itself on the liquid container is a lid (top plate) of the container or other member constituting a part of the container. (For example, a bottom plate).

  According to the present invention, the welding part (position) for fixing the cylindrical electrode is separated from the back surface of the electrode fixing member seated on the liquid storage container or its lid by a predetermined distance. For this reason, the heat conduction efficiency during welding to the back surface of the electrode fixing member including the mounting flange can be reduced, so that the electrode fixing structure is welded on the same plane as the back surface as in the past. As compared with, deformation or distortion of the back surface including the mounting surface of the mounting flange can be reduced. Thus, the electrode fixing member is seated on the top plate (lid) of the liquid container (hereinafter also referred to as a tank) via the back surface, and the mounting flange is tightened with a screw member or the like, so that the sensor can be mounted. Even in the case of performing the above, the mounting can be stabilized. That is, as a result of less deformation and distortion of the back surface, the sealing property between the back surface and the tank can be enhanced. It should be noted that the interval K at which the end surface of the base end portion of the cylindrical electrode is separated from the back surface of the electrode fixing member is preferably large in order to prevent deformation due to heat conduction, but the deformation preventing effect, miniaturization of the electrode fixing member, etc. In view of the above requirement, the range of 3 to 10 mm is appropriate.

  In fitting the tubular electrode to the tubular portion during welding, in order to maintain a predetermined distance between the back surface of the electrode fixing member and the end surface of the tubular electrode, the assembly (fitting) A predetermined jig or the like may be used. However, in the invention according to claim 2 or 3, since the projecting portion provided on the outer peripheral surface of the cylindrical portion or the annular tip-facing surface forms a stopper in fitting, in the assembly and welding, As long as the end face of the base end portion of the cylindrical electrode is fitted so as to come into contact therewith, the interval is automatically maintained at a predetermined value. That is, in the invention according to claim 2 or 3, assembling and welding can be simplified. In particular, as described in claim 3, an annular tip-facing surface is provided, the end face of the base end portion of the cylindrical electrode is abutted against the tip-facing surface, and the end face of the base end portion and the tip end face In the case where the surface is welded along the circumferential direction, it is possible to perform welding in one circumferential direction, so that improvement in workability is also expected. According to a third aspect of the present invention, there is provided a tube with respect to the outer diameter of the small-diameter portion of the cylindrical portion by adopting a configuration in which the end face of the proximal end portion of the cylindrical electrode and the tip-facing surface of the cylindrical portion are butt welded. Tolerance management of the inner diameter of the electrode can be set relatively loose, making it easy to produce a cylindrical electrode and reducing the cost of the sensor.

  In Claim 3, as described in Claim 4, a concave portion is provided along the circumferential direction on the outer peripheral surface at a corner formed by the tip-facing surface and the outer peripheral surface of the small-diameter portion. It is preferable to do this. In the step of manufacturing the electrode fixing member, in the case of manufacturing this by cutting (machining), the corner angle formed by the tip-facing surface forming an annular shape in the cylindrical portion and the outer peripheral surface of the small diameter portion, A fillet (R) corresponding to a small radius at the tip of a cutting tool (for example, a cutting tool) is attached. In addition, even when forming by forging, it is inevitable that a fillet corresponding to a small radius of the corner of the mold (die) is attached. When the cylindrical electrode is fitted (externally fitted) to the outer peripheral surface of the small-diameter portion of the cylindrical portion with the fillet (R), even if it is a gap fit, the cylindrical electrode Even if the end surface is abutted against the annular tip-facing surface, the fillet R may hit and interfere with the inner peripheral edge angle of the end surface of the cylindrical electrode. For this reason, a gap is inevitably formed between the tip-facing surface of the cylindrical portion and the end surface of the cylindrical electrode, and the weldability deteriorates. On the other hand, if it makes it as described in Claim 4, since generation | occurrence | production of the clearance gap resulting from such interference can be prevented easily, weldability can be improved. Moreover, even if it makes it as described in Claim 5, there exists the same effect.

  An embodiment of a capacitive liquid state detection sensor embodying the present invention will be described with reference to the drawings. First, a liquid level sensor 1 as an example of a liquid state detection sensor will be described with reference to FIG. FIG. 1 is a longitudinally omitted cross-sectional view of the liquid level sensor 1. 2 is a cross-sectional view before fitting and fixing the cylindrical electrode to the electrode fixing member constituting the sensor of FIG. 1, FIG. 3 is a plan view of the electrode fixing member, and FIG. 4 is a cylinder in the cylindrical portion of the electrode fixing member. FIG. 2 is a partially enlarged view of FIG. 1 formed by fixing the electrode and a further enlarged view thereof. In this embodiment, the sensor is provided as a sensor having a pair of electrodes, a cylindrical electrode (external electrode) having a cylindrical shape and a columnar internal electrode arranged on the inside thereof. It demonstrates as what is made into an electrode.

  A liquid level sensor (hereinafter, also simply referred to as a sensor) 1 according to the present embodiment is attached to a tank containing urea water used for reduction of nitrogen oxide (NOx) contained in exhaust gas of a diesel vehicle, This is for detecting the state of the liquid inside (measuring the water level of urea water). In FIG. 1, a state in which the sensor 1 is attached in a hanging manner from the top plate (ceiling part) of the tank T is illustrated. As shown in FIG. 1, the sensor 1 of the present embodiment is provided with a cylindrical electrode 10 having a straight cylindrical shape with a certain thickness, and provided along the axis G direction inside the cylindrical electrode 10. The inner electrode 20 is formed in a columnar shape with a constant thickness, and is fixed (supported) at the base end portion (the upper end portion in the figure) of the inner electrode 20, and the electrode fixing member 30 is used as an attachment means to the tank T. Yes.

  The electrode fixing member 30 is for fixing (supporting) the cylindrical electrode 10 and the internal electrode 20 without contacting each other via an annular holder 50 made of an insulating material. In this embodiment, the electrode fixing member 30 opens upward. A cylindrical shape that protrudes downward on the back surface 32a of the case-shaped part 31 from a circular opening 33 in a plan view, which opens in the center of the flat bottom part 32, and the case-shaped part 31 formed in the shape of a rectangular parallelepiped case. A cylindrical portion 34 is provided. The cylindrical portion 34 has a predetermined length range from the distal end (lower end in FIG. 1) of the outer peripheral surface thereof, and a small diameter portion 34b having a smaller diameter than a portion (large diameter portion) 34a that is concentric and closer to the proximal end (upper end in FIG. 1). These two parts 34a and 34b are each a straight cylindrical part having a constant diameter in the vertical direction. An annular tip-facing surface 34c is formed at the boundary between the small-diameter portion 34b near the distal end and the large-diameter portion 34a near the proximal end, and will be described in detail later. When the proximal end portion 12 of the cylindrical electrode 10 is fitted to the outer peripheral surface, the end surface 13 is positioned so as to butt against the distal-facing surface 34c. The tip-facing surface 34c forms a plane perpendicular to the axis G of the cylindrical portion 34, and the interval (dimension) K from the back surface 32a is set in the range of 3 to 5 mm, for example. Further, the inner peripheral surface 34n of the cylindrical portion 34 is a straight having a constant diameter in the vertical direction, and the internal electrode 20 is inserted into the inner peripheral surface 34n via the holder 50, and at the base end portion 22 thereof. It is designed to be supported or fixed.

  On the other hand, a mounting flange 35 for mounting the sensor 1 to the top plate (or lid) of the tank T is provided on the outer periphery of the portion near the back surface of the case-shaped portion 31. A seating surface (mounting surface) 35 a of the mounting flange 35 with respect to the top plate (or lid) of the tank T is flush with the back surface 32 a of the case-shaped portion 31. The mounting flange 35 is generally rectangular in plan view, and its four corners are rounded into an arc shape (see FIG. 3). Further, a notch-shaped recess is provided at the center of the short side. Further, a plurality of through holes 36 for fixing the mounting flange 35 to the tank with screw members are provided at appropriate positions.

  On the other hand, inside the case-shaped part 31 surrounded by the side walls 37 and 41, an internal electrode 20 inserted and arranged in the holder 50 is inserted through an annular holder 50 made of the insulating material described later. Thus, a screw hole 39 is formed in the presser plate 57 to be fixed by tightening the screw member 58a. The screw hole 39 is formed at substantially the center of a shelf 38 that is provided in a raised shape in a rectangular shape along a side wall 37 that forms a short side in a plan view. Also, above the shelf 38, the case-like portion 31 is provided with support portions 46 for fixing the circuit board 60 for relay in the plan view of the case-like portion 31 in the plan view. The direction support portion 46 is provided with a screw hole 47, and is configured to fix the circuit board 60 by screwing the screw member 58b into the screw hole 47 (see FIG. 3). In this embodiment, the peripheral edge of the opening 33 of the bottom 32 of the case-like portion 31 is surrounded by the wall 40 of the shelf 38 and the side wall 41 having a long side in plan view, and a concave portion 43 having a rectangular shape in plan view. Thus, the flat bottom surface 44 is formed, and the holder 50 is engaged with the holder 50 in a suspended manner through a square flange 51 formed on the upper end thereof without rotating. The cylindrical portion 34 protruding toward the back surface 32 a side of the electrode fixing member 30 is configured such that the outer diameter of the base end portion 34 a substantially matches the dimension between the wall surfaces 40 of the shelf 38 in the recess 43. In this embodiment, a convex portion 42 having a sawtooth cross section is provided at an appropriate position on the outer surface of the side wall 41 having a long side in a plan view, and a cap-shaped protective cover 49 is fixed.

  In this embodiment, the cylindrical electrode 10 is fitted with a small gap on the outer peripheral surface of the small diameter portion 34b in the cylindrical portion 34 formed so that the inner diameter protrudes from the back surface 32a of the electrode fixing member 30. Thus, the diameter is slightly larger than the outer diameter of the small diameter portion 34b. The outer diameter of the cylindrical portion 34 is the same as the outer diameter of the large-diameter portion 34a. Thus, the cylindrical electrode 10 has its base end portion 12 fitted to the outer peripheral surface of the small diameter portion 34b of the cylindrical portion 34, and its end surface 13 is connected to the small diameter portion 34b and the large diameter portion 34a of the cylindrical portion 34. It is fixed by arc welding along the circumferential direction centering on the butting surfaces of both of them, in contact with the annular tip-facing surface 34c located at the boundary, that is, in a butting shape. Note that such a cylindrical electrode 10 is made of a conductive metal material (SUS 304 in this embodiment), and its intermediate portion is omitted in FIG. 1, but a long thin cylindrical tube (circular tube) is used as the material. It is said. Further, in this embodiment, narrow slits 14 and 16 are formed on the peripheral surface of the cylindrical electrode 10 along the generatrix, in order from the distal end portion 11 side to the base end portion 12 (the electrode fixing member 30 of the liquid level sensor 1). Are formed independently over the end side). These slits 14 and 16 are where liquid (urea water) or gas (air) can freely enter and exit. In this example, they are arranged intermittently along three buses that are substantially the same in shape and at equal intervals, and at equal angular intervals when viewed from the direction of the axis G. In addition, although not shown, an air vent hole is formed at an appropriate place (portion near the upper end in the figure) of the cylindrical electrode 10.

  In the present embodiment, a rectangular flange 51 in plan view is formed at the upper end of the cylindrical portion 52 with respect to the opening 33 of the electrode fixing member 30 to which the cylindrical electrode 10 is fixed in this way, that is, the inner peripheral surface of the cylindrical portion 34. The cylindrical portion 52 is inserted into the holder 50 made of an insulating material provided with the flange 51, and the flange 51 is non-rotatably engaged with the peripheral surface of the opening 33 on the bottom surface 44 of the recess 43. And the internal electrode 20 is inserted in the inner peripheral surface of the holder 50, the flange 23 provided in the outer periphery of the base end part 22 is engaged with the end surface 55 in the figure of the holder 50, and an insulating plate (resin plate) 56 is disposed on the flange 23, and a presser plate 57 is placed on the insulating plate 56, and the screw member 58 a is threaded through the through hole 57 a of the presser plate 57 and screwed in the shelf 38 in the case-like portion 31. The internal electrode 20 is fixed by screwing into the hole 39. Thus, the internal electrode 20 is supported in a suspended manner parallel to the inner side of the cylindrical electrode 10 by fitting the flange 23 of the base end portion 22 to the upper end surface 55 of the holder 50 in a mounting manner. ing. In addition, circumferential grooves are formed on the inner and outer peripheral surfaces of the holder 50, respectively, and ring packings 53 and 54 for liquid and airtightness are loaded, and the inner peripheral surface of the cylindrical portion 34 and the outer peripheral surface of the holder 50. And the seal | sticker of each clearance gap between the inner peripheral surface of the holder 50 and the outer peripheral surface of the internal electrode 20 is ensured, and the liquid which makes a measuring object inside the cylindrical electrode 10 is the inner and outer periphery of the cylindrical part 34 of the holder 50. Intrusion into the inside of the case-like portion 31 of the electrode fixing member 30 through the surface is prevented.

  In this embodiment, the terminal 28 is provided on the end surface 24 of the base end portion 22 of the internal electrode 20 so as to protrude toward the circuit board 60, and the terminal 28 is provided on the insulating plate 56 and the holding plate 57. It protrudes through each provided through hole. The terminal 28 is passed through a terminal (through hole terminal) (not shown) of the circuit board 60 for relay, which is arranged inside the case-like portion 31 and fixed by the screw member 58b, and is connected by soldering or the like. It is electrically connected to an external connector 62 via a wiring cable 61. Although not shown, an electrode on the ground side is connected to the electrode fixing member 30 from the circuit board 60, so that the cylindrical electrode 10 is electrically connected to the ground side. Note that a plurality of electronic components including a microcomputer are mounted on the circuit board 60, and the circuit board 60 is based on the capacitance information obtained from the detection unit composed of the cylindrical electrode 10 and the internal electrode 20, and urea water. The water level is detected, and the detection result is output via an external circuit (for example, ECU) connector 62.

  In the figure, reference numeral 49 denotes a protective cover, which is placed on the case-like portion (accommodating portion) 31 and is provided on the outer surface of the outer wall 41 of the case-like portion 31 in a through-hole provided on the outer side surface (not shown). The convex part 42 is fitted and attached. It should be noted that the internal electrode 20 is elastically applied at the tip 21 to the cylindrical wall in the vicinity of the tip portion 11 of the cylindrical electrode 10 (a portion closer to the tip) corresponding to the tip side (lower end side in FIG. 1) of the liquid level sensor 1. In order to support, a bush-like elastic body (in this example, a rubber elastic body) 25 is press-fitted. In addition, the elastic body 25 has a retaining protrusion 25 a provided on the outer peripheral surface thereof fitted in three through holes (openings) 15 provided at equal angular intervals on the peripheral surface of the cylindrical electrode 10. And it is supposed to be retaining. In this embodiment, the internal electrode 20 is a solid and cylindrical conductive metal bar (SUS 304 bar). In addition, an insulating film (not shown) made of, for example, a fluorine-based resin is formed on the surface of the internal electrode 20 by coating with a thickness of about 300 μm.

  Such a sensor 1 has a mounting flange 35 formed along the back surface 32a of the electrode fixing member (base member) 30 with a packing P made of rubber, for example, interposed between the top plate of the tank T or the surface of the lid. It is attached by screwing through a screw member into a through hole 36 provided in the flange 35 and used as a sensor. When the sensor 1 of this embodiment is assembled, that is, when the cylindrical electrode 10 is fixed to the cylindrical portion 34 of the electrode fixing member 30, the end surface 13 of the proximal end portion 12 of the cylindrical electrode 10 is the cylindrical portion 34. The small-diameter portion 34b is fitted to the tip-facing surface 34c located at the boundary with the large-diameter portion 34a to form a butt shape, and the butt surface is welded along the circumferential direction. The tip-facing surface 34c is spaced apart from the back surface 32a of the electrode fixing member 30 by a distance K (see FIGS. 1, 2, and 4). That is, conventionally, since the electrode fixing member 30 is fixed by welding the peripheral surface of the cylindrical electrode 10 at the level of the back surface 32a, the back surface 32a including the seating surface 35a of the mounting flange 35 by heat during welding. However, in this embodiment, the welded portion is separated from the back surface 32a of the electrode fixing member 30 by a distance K. Accordingly, heat conduction or transmission during welding to the back surface 32a can be reduced. For this reason, it is possible to prevent the back surface 32a including the seating surface 35a of the mounting flange 35 from being deformed or distorted by welding, and as a result, it is possible to improve the sealing performance with the tank.

  In the said form, it is near the front-end | tip of the cylindrical part 34 as a convex part which the end surface 13 of the cylindrical electrode 10 contact | abuts in the position which kept the space | interval K from the back surface 32a of the electrode fixing member 30 among the outer peripheral surfaces of the cylindrical part 34. A portion having a smaller diameter portion 34b having a smaller diameter than the portion closer to the proximal end and a larger diameter portion 34a having the portion closer to the proximal end formed to have a larger diameter, and a distal-facing surface 34c forming an annular shape at the boundary of the different diameters The base end portion 12 of the cylindrical electrode 10 is fitted to the outer peripheral surface of the small-diameter portion 34b, and the end surface 13 of the base end portion 12 is abutted against the tip-facing surface 34c. The end surface 13 of the portion 12 and the tip-facing surface 34c are welded along the circumferential direction. For this reason, the space | interval K which spaces apart the end surface 13 of the base end part 12 of the cylindrical electrode 10 from the back surface 32a of the electrode fixing member 30 can be kept constant easily. Moreover, since the butt surface is one circle, welding can be easily performed. Moreover, in this embodiment, since the outer diameter of the large diameter portion 34a of the cylindrical portion 34 and the outer diameter of the cylindrical electrode 10 are the same, the welded surface can be finished cleanly.

  That is, as shown in FIG. 5, in order to easily maintain a dimension for separating the end surface 13 of the base end portion 12 of the cylindrical electrode 10 from the back surface 32 a of the electrode fixing member 30, as shown in FIG. The outer diameter of the cylindrical portion 34 is the same from the base to the tip, and when the cylindrical electrode 10 is fitted to the cylindrical portion 34, the gap K is not abutted against the end face 13, but a gauge in assembly or the like. Or by welding along the circumferential direction the corner angle formed by the end surface 13 of the cylindrical electrode 10 and the outer peripheral surface of the cylindrical portion 34 under the fitted state. An effect of preventing deformation of the back surface of the electrode fixing member 30 is obtained. However, in the above embodiment, in fitting to the tubular portion 34, an annular tip-facing surface 34c is provided, and the end surface 13 of the tubular electrode 10 is abutted against this, so such a separate means is required. As a result, welding work is facilitated. In addition, about FIG. 5, since only the said point is different from the thing of FIG. 1, only the same code | symbol is attached | subjected to the same site | part.

  Further, in order to easily maintain a constant distance K at which the end surface 13 of the base end portion 12 of the cylindrical electrode 10 is separated from the back surface 32a of the electrode fixing member 30, it is not necessary to provide an annular tip-facing surface 34c. For example, as shown in FIG. 6, an appropriate number of convex portions 34 t that can contact the end surface 13 of the base end portion 12 of the cylindrical electrode 10 may be provided on the outer peripheral surface of the cylindrical portion 34. However, when the ring-shaped tip-facing surface 34c is formed as in the above embodiment, the formation thereof is easy, and as described above, welding is facilitated because the circumference is one circle. In FIG. 6, only the points described above are different from those in FIG. 1, and therefore the same parts are only given the same reference numerals.

  In the sensor of this embodiment shown in FIGS. 1 to 4, as shown in FIG. 7, the corner angle formed by the tip-facing surface 34 c forming the annular shape of the cylindrical portion 34 and the outer peripheral surface of the small diameter portion 34 b. In this case, a recess (concave groove) 34g may be provided on the outer peripheral surface of the small-diameter portion 34b along the circumferential direction. This is because, as described above, when the outer peripheral surface of the cylindrical portion 34 has the base end portion as the large diameter portion 34a and the distal end side as the small diameter portion 34b, the tip facing surface 34c of the boundary is formed. When forming the corner angle formed by the tip-facing surface 34c and the outer peripheral surface of the small-diameter portion 34b by machining, a tool that has a radius at the corner of the cutting edge tip of the cutting tool is used. Therefore, fillet R will be given. On the other hand, in the formation of the cylindrical electrode 10, when the end surface 13 is used with the material (tube material) cut into a predetermined length, the angle formed between the end surface 13 and the inner peripheral surface 10n is: A burr | flash will generate | occur | produce in any part of the circumferential direction, or the right angle | corner which has a sharp point will exist. In such a case, if the cylindrical electrode 10 is fitted and abutted against the small-diameter portion 34b of the cylindrical portion 34 from the end face 13, the risk of the corners interfering with the fillet radius increases, and therefore A minute gap is generated between the end surface 13 and the annular tip-facing surface 34c, resulting in poor weldability. On the other hand, as described above, a concave portion 34g can be provided along the circumferential direction on the outer peripheral surface at the corner angle formed by the annular front end facing surface 34c of the cylindrical portion 34 and the outer peripheral surface of the small diameter portion 34b. This is because such problems can be easily prevented.

  As understood from the foregoing, as shown in the enlarged view in FIG. 7, the corner between the end surface 13 of the base end portion 12 of the cylindrical electrode 10 and the inner peripheral surface 10n is along the circumferential direction. It is preferable to attach a chamfer 10c. This is because when the chamfering 10c is provided in this way, the end surface 13 of the cylindrical electrode 10 and the tip-facing surface 34c of the cylindrical portion 34 are not provided with the concave portion (concave groove) 34g. This is because it is possible to prevent interference with the fillet radius of the corner formed by the outer peripheral surface of the small diameter portion 34b. That is, if the size of the chamfer 10c is larger than the size of the fillet radius, the interference can be prevented. Therefore, the distal end surface 13 of the proximal end portion 12 of the cylindrical electrode 10 is not affected by the fillet radius and the gap in the fitting of the cylindrical electrode 10 to the small diameter portion 34b. What is necessary is just to set the magnitude | size of the chamfering 10c according to the fitting with respect to the cylindrical part 34 so that it can contact | abut to the front end surface 34c. Of course, the chamfering 10c may be provided after providing the recess (concave groove) 34g. In the above sensor, the electrode fixing member 30 has been described as being attached to the upper part (top plate or lid) of the tank via the mounting flange 35. However, in the present invention, the mounting flange 35 is included. The electrode fixing member 30 itself can also form a tank lid.

  In addition, the sensor of the above embodiment has been embodied as having a cylindrical electrode 10 and a pair of electrodes with the internal electrode 20, but the sensor of the present invention uses the tank itself as an electrode as described above. Therefore, in that case, the present invention can be embodied as only the cylindrical electrode 10 in the above embodiment as an electrode. In addition, in the sensor of the said form, although urea water was actualized as an example as a liquid which is the object which detects the state of a liquid, it is not limited to this. In addition, if the liquid to be measured is a non-conductive liquid (non-conductive liquid) such as urea water, in that case, an insulating film is provided on the outer peripheral surface like the internal electrode 20 in the above embodiment. There is no need to form. In such a case, as is well known, since there is a difference between the dielectric constant of air and the dielectric constant of the liquid that is the object of measurement, the capacitance between the inner and outer electrodes can be measured. This is because a change in capacitance can be detected.

  In addition, as the liquid state that is a detection target of the liquid state detection sensor, the liquid level is exemplified in the above, but in addition to this, the liquid concentration, the degree of deterioration, the quality, the degree of contamination of foreign matters, and the like can be used. That is, the sensor of the present invention can be widely applied to sensors that can detect each of these states of liquid by measuring the capacitance between two electrodes.

  Furthermore, in the above-described embodiment, the sensor is embodied in a hanging form from the top to the bottom. On the contrary, the sensor is also concretely arranged in a standing manner on the bottom of a liquid storage container such as a tank. Can be

BRIEF DESCRIPTION OF THE DRAWINGS The intermediate abbreviation longitudinal cross-sectional view and principal part enlarged view of embodiment which actualized the liquid state detection sensor (liquid level sensor) of this invention. The half sectional view and principal part enlarged view before fitting and fixing a cylindrical electrode to the electrode fixing member which makes the sensor of FIG. The top view of the electrode fixing member of FIG. The partial enlarged view of FIG. 1 formed by fixing a cylindrical electrode to the cylindrical part of an electrode fixing member, and the further enlarged view. The intermediate abbreviation longitudinal cross-sectional view of another embodiment of the liquid state detection sensor of this invention. It is another embodiment, Comprising: The fracture | rupture longitudinal cross-sectional view and partial enlarged view of the principal part which fixed the cylindrical electrode to the cylindrical part of the electrode fixing member. It is another embodiment, Comprising: The elements on larger scale which fixed the cylindrical electrode to the cylindrical part of the electrode fixing member, and the further enlarged view of the principal part. The longitudinal cross-sectional view explaining a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Liquid state detection sensor 10 Cylindrical electrode 10c Chamfering of the edge of the base end part of a cylindrical electrode, and the internal peripheral surface 12 Base end part 20 of a cylindrical electrode Internal electrode 30 Electrode fixing member 32a The back surface of an electrode fixing member 34 Cylindrical portion 34a of electrode fixing member Large diameter portion 34b of cylindrical portion Small diameter portion 34t of cylindrical portion Projection 34g on outer peripheral surface of cylindrical portion Recessed portion 34c on outer peripheral surface of small diameter portion of cylindrical portion Cylindrical portion Front-facing surface 35 Flange for mounting electrode fixing member K Distance between the back surface of the electrode fixing member and the end surface of the base end portion of the cylindrical electrode G axis T Liquid container (tank)

Claims (6)

A liquid state detection sensor for detecting the state of the liquid stored in the liquid storage container based on the capacitance between the electrodes,
A cylindrical electrode for capacitance measurement that has a cylindrical shape, and an electrode fixing member that fixes the cylindrical electrode at its proximal end,
The electrode fixing member is provided with a mounting flange for mounting the sensor itself on the liquid container or its lid on the outside of the electrode fixing member, and on the inner side of the mounting flange on the back surface of the electrode fixing member. A cylindrical portion is provided so as to protrude from the back surface, and the back surface of the electrode fixing member and the tube are fitted in a state where the base end portion of the cylindrical electrode is fitted to the outer peripheral surface of the cylindrical portion. Characterized in that the base end portion of the cylindrical electrode and the outer peripheral surface of the cylindrical portion are welded along the circumferential direction while maintaining a predetermined interval between the end surface of the base end portion of the cylindrical electrode. Liquid state detection sensor.   A convex portion is provided on the outer peripheral surface of the cylindrical portion at a position spaced from the back surface of the electrode fixing member so that the end surface of the proximal end portion of the cylindrical electrode is in contact with the cylindrical electrode. The liquid state detection sensor according to claim 1, wherein the predetermined interval is maintained by bringing an end face of the base end portion into contact with each other. A liquid state detection sensor for detecting the state of the liquid stored in the liquid storage container based on the capacitance between the electrodes,
A cylindrical electrode for capacitance measurement that has a cylindrical shape, and an electrode fixing member that fixes the cylindrical electrode at its proximal end,
The electrode fixing member is provided with a mounting flange for mounting the sensor itself on the liquid container or its lid on the outside of the electrode fixing member, and on the inner side of the mounting flange on the back surface of the electrode fixing member. The cylindrical portion is provided so as to protrude from the back surface, and the outer diameter of the cylindrical portion is formed as a small diameter portion having a relatively small diameter from the distal end of the cylindrical portion, An end-facing surface having an annular shape is provided at the boundary of the different diameters, and the end surface of the base end portion of the cylindrical electrode is fitted to the outer peripheral surface of the small diameter portion with the base end portion of the cylindrical electrode being fitted. A liquid state detection sensor characterized in that the end facing surface is abutted and the end surface of the base end and the distal facing surface are welded along the circumferential direction.   The liquid state detection sensor according to claim 3, wherein a concave portion is provided along the circumferential direction on the outer circumferential surface at a corner angle formed by the tip-facing surface and the outer circumferential surface of the small-diameter portion.   5. The liquid state according to claim 3, wherein an outer diameter of the cylindrical portion at the tip-facing surface and an outer diameter of the end surface of the proximal end portion of the cylindrical electrode are the same diameter. Detection sensor.   The liquid state according to any one of claims 1 to 5, wherein a chamfer is provided along a circumferential direction at an angle between an end surface of a proximal end portion of the cylindrical electrode and an inner peripheral surface thereof. Detection sensor.

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