Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
  • G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
  • G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
  • G01N27/14—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of an electrically-heated body in dependence upon change of temperature
  • G01N27/18—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of an electrically-heated body in dependence upon change of temperature caused by changes in the thermal conductivity of a surrounding material to be tested
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/34—Chemical or biological purification of waste gases
  • B01D53/46—Removing components of defined structure
  • B01D53/54—Nitrogen compounds
  • B01D53/56—Nitrogen oxides
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
  • G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
  • G01F1/68—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using thermal effects
  • G01F1/684—Structural arrangements; Mounting of elements, e.g. in relation to fluid flow
  • G01F1/6842—Structural arrangements; Mounting of elements, e.g. in relation to fluid flow with means for influencing the fluid flow
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
  • G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
  • G01F1/68—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using thermal effects
  • G01F1/684—Structural arrangements; Mounting of elements, e.g. in relation to fluid flow
  • G01F1/688—Structural arrangements; Mounting of elements, e.g. in relation to fluid flow using a particular type of heating, cooling or sensing element
  • G01F1/69—Structural arrangements; Mounting of elements, e.g. in relation to fluid flow using a particular type of heating, cooling or sensing element of resistive type
  • G01F1/692—Thin-film arrangements
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
  • G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
  • G01F1/68—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using thermal effects
  • G01F1/696—Circuits therefor, e.g. constant-current flow meters
  • G01F1/698—Feedback or rebalancing circuits, e.g. self heated constant temperature flowmeters
  • G01F1/699—Feedback or rebalancing circuits, e.g. self heated constant temperature flowmeters by control of a separate heating or cooling element
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N25/00—Investigating or analyzing materials by the use of thermal means
  • G01N25/18—Investigating or analyzing materials by the use of thermal means by investigating thermal conductivity
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2251/00—Reactants
  • B01D2251/20—Reductants
  • B01D2251/206—Ammonium compounds
  • B01D2251/2067—Urea
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2257/00—Components to be removed
  • B01D2257/40—Nitrogen compounds
  • B01D2257/404—Nitrogen oxides other than dinitrogen oxide
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL-COMBUSTION ENGINES
  • F01N2610/00—Adding substances to exhaust gases
  • F01N2610/02—Adding substances to exhaust gases the substance being ammonia or urea

Definitions

• the present invention relates to a thermal sensor used to measure the concentration and other characteristic values of an aqueous liquid using the thermal properties of an aqueous liquid, and a measuring apparatus using the thermal sensor. Is.
• the thermal sensor and measuring device of the present invention is an exhaust gas purification catalyst for decomposing nitrogen oxides (NOx) in a system for purifying exhaust gas exhausted by power, such as an internal combustion engine of an automobile. Can be used to measure the urea concentration of aqueous urea solution sprayed on
• Fossil fuels such as gasoline and light oil are burned in an internal combustion engine of an automobile.
• water, carbon dioxide, etc. as well as unburned carbon monoxide (CO) and hydrocarbons (HC), sulfur oxide (SOx), nitrogen oxide (NOx), etc.
• CO carbon monoxide
• HC hydrocarbons
• SOx sulfur oxide
• NOx nitrogen oxide
• various measures have been taken to purify the exhaust gas from automobiles, particularly in order to protect the environment and prevent pollution of the living environment.
• One such measure is the use of an exhaust gas purification catalyst device.
• a three-way catalyst for exhaust gas purification is placed in the middle of the exhaust system, where CO, HC, NOx, etc. are decomposed by oxidation reduction to make them harmless.
• an aqueous urea solution is sprayed onto the force catalyst immediately upstream of the exhaust catalytic device.
• This urea aqueous solution needs to be in a specific urea concentration range in order to enhance the NOx decomposition effect, and the urea concentration of 32.5% is considered to be optimal.
• the concentration of urea aqueous solution that is contained in a urea aqueous solution tank mounted on an automobile may change with time, and the concentration distribution may be locally uneven in the tank.
• the urea aqueous solution supplied to the spray nozzle by the pump through the supply pipe is generally collected by the outlet force close to the bottom of the tank, the catalyst device must have a predetermined urea concentration in this region. Is important to increase the efficiency of The
• Patent Document 1 Japanese Patent Application Laid-Open No. 11-153561
• a heating element is heated by energization, the temperature sensing element is heated by this heating, and heat is transferred from the heating element to the temperature sensing element.
• a fluid identification method that determines the type of fluid to be identified based on the electrical output corresponding to the electrical resistance of the temperature sensing element, which is thermally affected by the fluid to be identified. The method to do is disclosed. That is, here, a thermal sensor is used.
• fluid identification can be performed by using representative values for substances having substantially different properties such as water, air, and oil. It is difficult to perform accurate and quick identification by applying to the identification of whether the liquid to be measured is a urea aqueous solution having a predetermined urea concentration.
• Patent Document 1 Japanese Patent Application Laid-Open No. 11 153561 (in particular, paragraphs [0042] to [0049])
• Patent Document 2 Japanese Patent Application Laid-Open No. 11-153465
• Patent Document 3 Japanese Patent Laid-Open No. 11-153466
• Patent Document 4 Japanese Patent Laid-Open No. 2002 202166
• Patent Document 5 Japanese Patent Laid-Open No. 2003-279395
• Patent Document 6 Japanese Patent Laid-Open No. 2003-302271
• the present invention is a thermal type that can reduce the adhesion of bubbles to the outer surface of the sensor and improve the measurement accuracy, particularly when the object to be measured is an aqueous liquid.
• the object is to provide a sensor and a measuring device using the sensor.
• a heat provided with a sensing element including a temperature sensing element, a resin mold that seals the sensing element, and a heat transfer member that conducts heat between the sensing element and an aqueous liquid to be measured.
• a sensing element including a temperature sensing element, a resin mold that seals the sensing element, and a heat transfer member that conducts heat between the sensing element and an aqueous liquid to be measured.
• a part of the heat transfer member is exposed from the resin mold to form an exposed surface portion.
• a thermal sensor characterized in that a hydrophilic film is attached to the exposed surface portion.
• the hydrophilic film is an oxide silicon film. In one aspect of the present invention, the hydrophilic film is also applied to the surface portion of the resin mold located around the exposed surface portion of the heat transfer member. In one embodiment of the present invention, the sensing element also includes a heating element.
• a thermal sensor as described above, and an arithmetic unit that calculates a characteristic value of the liquid to be measured based on an output of the thermal sensor are provided.
• a measuring device characterized by comprising.
• a flow path for the liquid to be measured that passes in the vicinity of the exposed surface portion of the heat transfer member is formed around the thermal sensor, and the flow path is formed.
• a hydrophilic film is also attached to the surface portion of the member facing the exposed surface portion of the heat transfer member.
• the liquid to be measured is an aqueous urea solution, and the calculation unit is configured to calculate the urea concentration of the liquid to be measured.
• the surface force of the resin mold that seals the sensing element is exposed to the exposed surface portion of the heat transfer member.
• the wettability can be improved, and the gas such as the dissolved air in the aqueous liquid to be measured, and the air that is in contact with the aqueous liquid to be measured through its free surface are contained in the aqueous liquid to be measured. Even if the air bubbles are formed, the air bubbles are less likely to adhere to the exposed surface portion of the heat transfer member, so that heat transfer between the detection element and the aqueous liquid to be measured is improved and measurement accuracy is improved.
• FIG. 1 is an exploded perspective view showing an embodiment of a urea concentration measuring apparatus according to the present invention.
• FIG. 2 is a partially omitted cross-sectional view of the urea concentration measuring device in FIG.
• FIG. 3 is a view showing a state where the urea concentration measuring device of FIG. 1 is attached to a tank.
• FIG. 4 is an enlarged view of the indirectly heated concentration detector and the liquid temperature detector.
• FIG. 5 is a cross-sectional view of the indirectly heated concentration detector in FIG.
• FIG. 6 is an exploded perspective view of a thin film chip of an indirectly heated concentration detector.
• FIG. 7 is a configuration diagram of a circuit for density discrimination.
• FIG. 8 is a diagram showing a relationship between a single pulse voltage P applied to a heating element and a sensor output Q.
• FIG. 9 is a diagram showing an example of a calibration curve.
• FIG. 10 is a diagram showing an example of an output value T corresponding to a liquid temperature.
• FIG. 11 is a diagram showing an example of a relationship between a density-corresponding voltage value V0 and an actual density.
• FIG. 12 is a diagram showing an example of the relationship between the analog output voltage value V0 ′ corresponding to concentration and the actual concentration.
• FIG. 13 is a diagram showing an example of a relationship between an analog output voltage value T ′ corresponding to a liquid temperature and an actual temperature.
• FIG. 14 is a perspective view showing an embodiment of a thermal sensor according to the present invention.
• FIG. 15 is a cross-sectional view of the thermal sensor in FIG.
• FIG. 16 is a diagram showing an example of the relationship between actual concentrations and sensor display concentration values for various types of liquids to be measured.
• Urea concentration identification device 110 Urea aqueous solution supply pump
• FIG. 1 is an exploded perspective view showing an embodiment of a thermal sensor and a measuring device using the same according to the present invention
• FIG. 2 is a partially omitted sectional view
• FIG. It is a figure which shows the attachment state of.
• the liquid to be measured is an aqueous urea solution
• the urea concentration as a characteristic value thereof is measured.
• the measuring apparatus of this embodiment also identifies whether or not the detected urea concentration is within a predetermined range (may be identified as urea aqueous solution by urea concentration or simply identified as urea concentration). For this reason, in the following description, the urea concentration measuring device or the urea concentration measuring device is sometimes referred to as a urea concentration identifying device or a urea concentration identifying device.
• an opening 102 is provided in the upper part of the urea solution tank 100 for NOx decomposition constituting an exhaust gas purification system mounted on an automobile.
• a urea concentration discriminating device 104 according to the present invention is attached to the part.
• the tank 100 is provided with an inlet pipe 106 through which urea solution is injected and an outlet pipe 108 through which the urea solution is taken out.
• the outlet pipe 108 is connected to the tank at a height close to the bottom of the tank 100 and is connected to a urea solution sprayer (not shown) via the urea solution supply pump 110! RU
• the urea solution is sprayed onto the catalyst device by the urea solution sprayer disposed immediately before the exhaust gas purifying catalyst device.
• the urea concentration identification device includes a concentration identification sensor unit 2 and a support unit 4.
• the density identification sensor unit 2 is attached to one end (lower end) of the support 4, and the attachment 4 a for attaching to the tank opening 102 is provided to the other end (upper end) of the support 4. It is provided.
• the concentration identification sensor unit 2 includes an indirectly heated concentration detection unit 21 including a heating element and a temperature sensing body, and a liquid temperature detection unit 22 that measures the temperature of the urea solution.
• the indirectly heated concentration detection unit 21 and the liquid temperature detection unit 22 are arranged at a certain distance in the vertical direction.
• Fig. 4 shows an enlarged view of the indirectly heated concentration detector 21 and the liquid temperature detector 22, and
• Fig. 5 shows a cross-sectional view thereof.
• the indirectly heated concentration detector 21 and the liquid temperature detector 22 are made of a resin mold (for example, made of silica and Z or carbon-containing epoxy resin) 23. It is integrated.
• the indirectly heated concentration detection unit 21 includes a thin film chip 21a including a heating element and a temperature sensing element, and heat for the concentration detection unit bonded to the thin film chip by a bonding material 21b. It has metal fins 21c as transmission members, and external electrode terminals 21e electrically connected to the electrodes of the heating elements of the thin film chip and the electrodes of the temperature sensing elements by bonding wires 21d.
• the thin film chip 21a corresponds to the sensing element in the present invention.
• the liquid temperature detection unit 22 has the same configuration, that is, has a metal fin 22c and an external electrode terminal 22e as heat transfer members for the liquid temperature detection unit, and the detection element is sealed with a resin mold 23. Has been.
• FIG. 6 shows an exploded perspective view of the thin film chip 21a of the indirectly heated concentration detector 21.
• the thin film chip 2 la has, for example, a substrate 21al made of Al 2 O, a temperature sensing element 21a2 made of Pt, and an SiO force.
• a protective film 21a6 that also has SiO force and an electrode pad 21a7 made of TiZAu are sequentially stacked as appropriate.
• the temperature sensing element 21a2 is formed in a meandering pattern.
• the thin film chip 22a of the liquid temperature detection unit 22 has the same structure, but only the temperature sensing element 22a2 is activated without the heating element acting. However, use a liquid temperature detector 22 without a heating element.
• the density identification sensor unit 2 has a base 2a attached to the lower end of the support part 4, and the O-ring 2b is attached when the base is attached. Intervened.
• the resin mold 23 for the indirectly heated concentration detecting unit 21 and the liquid temperature detecting unit 22 is attached via an O-ring 2c.
• a cover member 2d is attached to the base body 2a so as to surround the concentration detecting portion fin 21c and the liquid temperature detecting portion fin 22c.
• This cover member forms a urea solution flow passage 24 open at both the upper and lower ends and extending vertically through the concentration detecting portion fin 21c and the liquid temperature detecting portion fin 22c. Is done.
• a part of the metal fins 21c, 22c is exposed from the resin mold 23 to form an exposed surface portion, and the exposed surface portion is hydrophilic.
• the membrane 50 is attached. More preferably, a hydrophilic film 50 is also provided on the surface portion of the resin mold 23 located around the exposed surface portions of the metal fins 21c and 22c. That is, the hydrophilic film 50 is formed over the exposed surface portions of the metal fins 21c and 22c and the surface portion of the resin mold 23 around the exposed surface portions. In FIGS. 1 and 2, the hydrophilic film 50 is not shown.
• the hydrophilic film 50 is, for example, an oxide silicon film.
• the thickness of the oxide silicon film 50 is, for example, 0.01 / ⁇ ⁇ to 1 / ⁇ ⁇ .
• the silicon oxide film 50 has good adhesion to both the metal fins 21c and 22c and the resin mold 23, and has high film strength.
• the surface of the oxide silicon film 50 is more hydrophilic than the surfaces of the metal fins 21c, 22c and the resin mold 23.
• the degree of hydrophilicity can be expressed by the contact angle with water. Generally, the contact angle with water is about 40 ° or less.
• the water contact angle of the oxide silicon film 50 can be 40 ° or less, and the oxide silicon film 50 exhibits hydrophilicity.
• the water contact angle of the hydrophilic membrane 50 is preferably 35 ° or less, more preferably 30 ° or less, still more preferably 25 ° or less, and particularly preferably 20 ° or less. .
• the oxide silicon film 50 can be formed, for example, by sputtering, CVD (chemical vapor deposition), or coating with a coating material.
• sputtering and CVD require a long actual processing time, and it is difficult to form a large-thickness film, which increases the size of the apparatus for film formation.
• application of the coating agent has many practical advantages such as simple processing and a relatively short actual processing time if it is left alone.
• the coating agent one containing an organic silicon compound and forming an oxide silicon film by a reaction after coating can be used.
• Such coating agents include polysilazanes such as perhydropolysilazane, a silane coupling agent added as necessary, an organic solvent, and a noradium catalyst or amine catalyst used as necessary (for example, a key available from Clariant Japan Co., Ltd. Comica (registered trademark)) is exemplified.
• An example of the specific steps of application and related pre- and post-treatment is as follows:
• Coating agent coating process (performed by spray coating, brush or waste coating, flow coating, dip coating, etc.)
• Heating process for solvent removal and acid-silicon transfer: 125-200 ° C, about 1 hour
• Heating and humidifying process for acid-silicon transfer: 50 to 90 ° C, 80 to 95%, about 3 hours
• Examples of the cleaning step include those using an organic solvent such as acetone, isopropyl alcohol, or hexane as the cleaning solvent in addition to the above-mentioned ethanol or xylene as the cleaning solvent.
• an organic solvent such as acetone, isopropyl alcohol, or hexane
• the heating temperature of the heating process can be lowered.
• the heating temperature in the heating process is about 250 ° C.
• the thickness of the formed silicon oxide film is, for example, 0.01 ⁇ m to 1 ⁇ m. If the thickness is too thick, peeling tends to occur, while if too thin, the hydrophilicity is maintained for a long time. Is more preferably 0.05 / ⁇ ⁇ ⁇ 0.
• a circuit board 6 constituting a density detection circuit described later is arranged at the upper end of the support part 4, and a lid member 8 is attached to cover the circuit board. It is.
• the support unit 4 accommodates the indirectly heated concentration detection unit 21 and the liquid temperature detection unit 22 of the concentration identification sensor unit 2 and the wiring 10 that electrically connects the circuit board 6.
• Circuit board 6 A microcomputer (microcomputer) that constitutes the identification calculation unit to be described is installed. Wiring 14 for communication between the circuit board 6 and the outside is provided through a connector 12 provided on the lid member 8.
• the identification calculation unit can be arranged outside the circuit board 6, and in this case, the circuit board 6 and the identification calculation unit are connected via the wiring 14.
• the base 2a and the cover member 2d, the support member 4 and the lid member 8 of the concentration identification sensor unit 2 described above are both made of a corrosion-resistant material such as stainless steel.
• FIG. 7 shows a configuration of a circuit for density identification in the present embodiment.
• a bridge circuit 68 is formed by the temperature sensor 21a2 of the indirectly heated concentration detection unit 21, the temperature sensor 22a2 of the liquid temperature detection unit 22, and the two resistors 64 and 66.
• the output of the bridge circuit 68 is input to the differential amplifier 70, and the output of the differential amplifier (also referred to as concentration detection circuit output or sensor output) constitutes an identification calculation unit via an AZD converter (not shown).
• the microcomputer 72 receives a liquid temperature corresponding output value corresponding to the liquid temperature of the urea aqueous solution from the temperature sensing element 22a2 of the liquid temperature detecting unit 22 via the liquid temperature detecting amplifier 71.
• the microcomputer 72 outputs a heater control signal for controlling opening and closing of the switch 74 located in the energization path to the heating element 21a4 of the indirectly heated concentration detection unit 21.
• the urea aqueous solution US When the urea aqueous solution US is accommodated in the tank 100, the urea aqueous solution US is also filled in the urea aqueous solution introduction path 24 formed by the cover member 2d of the concentration identification sensor unit 2. Urea aqueous solution introduction path 24 The urea aqueous solution US in the tank 100 including the inside 24 does not substantially flow.
• the heating element 21a4 By closing the switch 74 for a predetermined time (for example, 4 seconds) by the heater control signal output from the microcomputer 72 to the switch 74, the heating element 21a4 has a single height (for example, 10V). One pulse voltage P is applied to cause the heating element to generate heat.
• the output voltage (sensor output) Q of the differential amplifier 70 at this time gradually increases during voltage application to the heating element 21a4 as shown in FIG. 8, and gradually after the voltage application to the heating element 21a4 ends. Decrease.
• the sensor output is sampled a predetermined number of times (for example, 256 times) for a predetermined time (for example, 0.1 second) before the voltage application to the heating element 21a4 is started.
• the average initial voltage value VI is obtained by calculating the average value.
• This average initial voltage value VI corresponds to the initial temperature of the temperature sensing element 21a2.
• the sensor output is sampled a predetermined number of times (for example, 256 times) for a predetermined time (for example, 0.1 second) before the voltage application to the heating element 21a4 is stopped, and the average value is obtained.
• This average peak voltage value V2 corresponds to the peak temperature of the temperature sensing element 21a2.
• a calibration curve showing the relationship between the temperature and the concentration-corresponding voltage value VO is obtained in advance for some urea aqueous solutions (reference urea aqueous solutions) with known urea concentrations by such a method.
• the line is stored in the storage means of the microcomputer 72.
• Figure 9 shows an example of a calibration curve. In this example, calibration curves are created for reference urea aqueous solutions with urea concentrations of 0%, 20%, and 40%.
• the concentration-corresponding voltage value VO depends on the temperature
• the liquid temperature detector 22 The liquid temperature corresponding output value T input from the temperature sensor 22a2 via the liquid temperature detection amplifier 71 is also used.
• An example of the liquid temperature corresponding output value T is shown in Fig. 10.
• Such a calibration curve is also stored in the storage means of the microcomputer 72.
• FIG. 11 shows an example of the relationship between the concentration-corresponding voltage value V0 obtained with urea solutions having different temperatures and urea concentrations and the actual concentration.
• the concentration-corresponding voltage value V0 (X; t) obtained for the urea aqueous solution to be measured corresponds to what percentage of the urea concentration the concentration-corresponding voltage values V0 (0%; t), V0 ( 20%; t) and VO (40%; t) are determined by performing a proportional operation using at least two (for example, V0 (20%; t) and VO (40%; t)).
• V0 (20%; t) and VO (40%; t) the concentration-corresponding voltage values
• a signal indicating the concentration value obtained in this way is transmitted through a DZA modification (not shown) to The power is output to an output buffer circuit 76 shown in FIG. 5 and is also output as an analog output to a main computer (ECU) that performs combustion control of an automobile engine (not shown).
• Figure 12 shows an example of the relationship between the analog output voltage value VO 'corresponding to this concentration and the actual concentration. It can be seen that the temperature difference in this relationship is small and practical enough.
• Fig. 13 shows an example of the relationship between the analog output voltage value T 'corresponding to the liquid temperature and the actual temperature. This analog output voltage value T corresponding to the liquid temperature is also output to the main computer (ECU).
• the signal indicating the concentration value and the liquid temperature value can be taken out as a digital output if necessary and input to a device that performs display, alarm, and other operations.
• the urea concentration identification of the urea aqueous solution described above is based on the principle that t has a correlation between the kinematic viscosity of the urea aqueous solution and the sensor output using natural convection.
• the cover member 2d also functions as a protective member that prevents contact of foreign matter.
• the surface portion (ie, the inner surface portion) of the cover member 2d facing the exposed surface portion of the concentration detecting portion fin 21c and the liquid temperature detecting portion fin 22c is hydrophilic.
• a membrane 50 is attached.
• the hydrophilic film 50 ′ is the same as the hydrophilic film 50 described above.
• the optimum urea concentration of the aqueous urea solution used in the exhaust gas purification system is 32.5%. For example, 25% to 40% or 30% to 35% is an appropriate range. If an identification result outside this appropriate range is obtained, a warning can be issued. Also, if the urea aqueous solution in the tank is reduced and no urea aqueous solution is left in the urea aqueous solution passage 24, the above-mentioned case where the concentration of urea aqueous solution is within the appropriate range is determined at the time of concentration discrimination as described above. It is possible to obtain a concentration-corresponding voltage value that is remarkably far away, and in this case, the required warning can be issued.
• the hydrophilic surface 50 is attached to the exposed surface portions of the metal fins 21c, 22c and the surface portion of the peripheral resin mold 23, and the cover member 2d. Since the hydrophilic film 50 'is also attached to the inner surface portion of the surface, the wettability of these surface portion, surface portion and inner surface portion with respect to the urea aqueous solution can be improved. Therefore, even if bubbles are generated in the urea aqueous solution, the bubbles are unlikely to adhere to the hydrophilic membranes 50 and 50 ′, and even if bubbles are attached, the bubbles are formed based on the wettability of the hydrophilic membranes 50 and 50 ′. Drop off quickly and easily. For this reason, heat transfer between the sensing element and the urea aqueous solution is excellent, and high measurement accuracy is obtained.
• FIG. 14 is a perspective view showing still another embodiment of the thermal sensor according to the present invention
• FIG. 15 is a sectional view thereof.
• members or parts having the same functions as those of the embodiment described with reference to FIGS. 1 to 13 are denoted by the same reference numerals.
• the heat transfer member 21c ' for the concentration detector and the heat transfer member 22c' for the liquid temperature detector, only one surface is exposed from the resin mold 23 without protruding outward. What is being used. Similar to the above embodiment, the hydrophilic film 50 is attached to the exposed surface portion of the heat transfer members 21c ′ and 22c ′ and the surface portion of the resin mold 23 around the heat transfer members 21c ′ and 22c ′. In FIG. 14, the hydrophilic film 50 is not shown.
• an aqueous urea solution is used as the liquid to be measured !, but other aqueous liquids may be used in the present invention.
• a saline solution or a sugar solution if the salt concentration or sugar concentration is different, as with the urea solution, the concentration changes accordingly.
• Sensor output value can be obtained.
• FIG. 16 shows a sensor output value using a calibration curve for measuring the urea concentration of an aqueous urea solution.
• an accurate salt concentration value and sugar concentration value can be obtained by using a calibration curve prepared in advance for each of the salt solution and the sugar solution, as in the case of the urea solution.
• the concentration of the aqueous solution is adopted as the measured characteristic value of the liquid to be measured.
• the characteristic value measured in the present invention for example, the kinematic viscosity and the specific gravity other than the concentration are used. Etc.
• a calibration curve prepared in advance in the same manner as in the case of clear concentration may be used for each characteristic item.
• temperature measured by the liquid temperature detector 22
• the characteristic value measured by the thermal sensor is also adopted as the characteristic value measured by the thermal sensor.
• a urea concentration measuring device (urea concentration identifying device) as in the embodiment described with reference to FIGS. 1 to 13 was produced.
• the heat transfer member 21c 'for the concentration detector and the heat transfer member 22c' for the liquid temperature detector of the thermal sensor are 0.3 mm thick with a stainless steel (SUS316L) force.
• the exposed surface was also 5mm wide and 3mm high.
• the resin mold 23 was composed of silica and carbon-containing epoxy resin.
• the heat transfer member 21c ′ for the concentration detection unit, the heat transfer member 22c ′ for the liquid temperature detection unit, and the oxide silicon film 50 formed on the surface portion of the resin mold 23 around them have a thickness of 0.
• the water contact angle was 28 °.
• the formation of the silicon oxide film 50 was carried out using Aquamica [registered trademark] NL1 50A using (1) ethanol cleaning step, (2) xylene cleaning step, (3) drying step (100 C, 1 hour), ( 4) Aquamica application process (spray application), (5) Heating process (175 ° C, 1 hour), (6) Heat humidification process (70 ° C, 90%, 3 hours) and (7) Cooling process went.
• the concentration identification sensor part of the urea concentration measuring device was placed in a urea aqueous solution having a urea concentration of 32.5%, and the urea aqueous solution was heated to 35 ° C. One hour after the start of heating, the urea concentration value was obtained as the output of the measuring device.
• the measurement cycle as described above was executed 10 times, and the average value for 10 measurements of the absolute value of the deviation from the true value (32.5%) of the urea concentration value obtained in each measurement was calculated. As a result, it was 1%. The measurement accuracy is high enough.
• a thermal sensor and a urea concentration measuring device were produced in the same manner as in the example except that the silicon oxide film 50 was not attached to the thermal sensor.

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