JP5021528B2 - Liquid state detection sensor - Google Patents

Description

  The present invention relates to a liquid state detection sensor that detects the temperature of a liquid contained in a liquid container and the concentration of a specific component contained in the liquid.

  In recent years, for example, a NOx selective reduction catalyst (SCR) is sometimes used in an exhaust gas purifying apparatus that reduces nitrogen oxide (NOx) discharged from a diesel vehicle to a harmless gas, and a urea aqueous solution is used as the reducing agent. It is known that an aqueous urea solution having a urea concentration of 32.5 wt% may be used to efficiently perform this reduction reaction. However, urea aqueous solutions stored in urea water tanks mounted on automobiles are stored under severe environmental conditions, and the urea concentration may change due to changes over time. In addition, a different aqueous solution (for example, light oil) or water may be mistakenly mixed into the urea water tank. Therefore, a concentration sensor for detecting the urea concentration is attached to the urea water tank so that the urea concentration of the urea aqueous solution can be managed, and the concentration detection is performed.

  Conventionally, detection of such urea concentration utilizes the fact that the thermal conductivity varies depending on the urea concentration in the urea aqueous solution, so that the heating resistor and the temperature detecting element are immersed in the urea aqueous solution, This is performed by measuring the temperature rising tendency when the current is heated and the surrounding urea aqueous solution is heated by the temperature detecting element.

By the way, when the heating resistor is energized, the resistance value of the heating resistor changes depending on its own temperature. Since the heating resistor before energization is substantially the same as the temperature of the surrounding urea aqueous solution, the initial temperature of the urea aqueous solution can be measured by measuring the resistance value immediately after the energization is started. Further, the degree of temperature rise (that is, change in resistance value) when the heating resistor immersed in the urea aqueous solution is heated is affected by the thermal conductivity of the urea aqueous solution. Therefore, the heating resistor is energized for a predetermined time, the resistance value of the heating resistor is measured immediately after the energization and after the energization, and the temperature change of the heating resistor is obtained based on the measured resistance value. In light of the correlation between the urea concentration and the temperature change of the heating resistor, the concentration of urea contained in the urea aqueous solution can be detected without using a temperature detection element (see, for example, Patent Document 1).
JP 2007-114181 A

  However, when the present inventors conducted further studies to improve the performance of the concentration sensor, the urea concentration obtained from the correlation between the urea concentration and the temperature change of the heating resistor as in Patent Document 1 is the actual concentration. It was found that there was a slight deviation from the urea concentration. According to the examination results, the difference between the calculated urea concentration and the actual urea concentration increases as the difference between the reference temperature of the urea aqueous solution used as the reference in the calculation formula for calculating the urea concentration and the temperature of the urea aqueous solution to be detected is larger. There was a tendency for the value to increase (hereinafter referred to as “concentration distribution trend”). For example, as shown in FIG. 5, when the reference temperature of the calculation formula for obtaining the urea concentration is normal temperature (for example, around 25 ° C.), between the urea concentration obtained from the above correlation and the actual urea concentration at about normal temperature, Although no deviation occurs, the urea concentration higher than the actual urea concentration is calculated as the temperature of the urea aqueous solution shifts to the low temperature side or the high temperature side. Such a concentration distribution trend is expected to be influenced by the properties and thermal conductivity of the urea aqueous solution, but from the correlation between the urea concentration based on the physical properties and the temperature change of the heating resistor, It tends to be difficult to find. In order to improve the detection accuracy of the urea concentration, it is necessary to further correct the calculated urea concentration.

  The present invention has been made to solve the above-described problems, and corrects the concentration correspondence value obtained based on the temperature change when the heating resistor is energized to smooth the concentration distribution tendency indicated by the concentration correspondence value. An object of the present invention is to provide a liquid state detection sensor that can detect the concentration of a specific component contained in a liquid more accurately.

In order to achieve the above object, a liquid state detection sensor according to a first aspect of the present invention includes a liquid property detection element that includes a heating resistor that generates heat when energized and is disposed in a liquid storage container in which a liquid is stored. Energizing means for energizing the heating resistor for a predetermined detection time; first correspondence value acquiring means for acquiring a first corresponding value corresponding to the first resistance value of the heating resistor within the detection time; Temperature information acquisition means for obtaining temperature information of the liquid based on the first corresponding value, and after the first corresponding value is acquired within the detection time or after the detection time has elapsed, the heating resistor a second corresponding value acquisition means for acquiring a second corresponding value corresponding to the second resistance value, and the difference value calculating means for calculating a difference value of the second corresponding value and said first corresponding value, the difference value contained in the liquid correction to the basis of the temperature information That in the liquid state detecting sensor and a density corresponding value obtaining means for obtaining a density corresponding value corresponding to the concentration of a specific component, performing a secondary correction based on the temperature information to the concentration correspondence value, said liquid Correction density correspondence value acquisition means for obtaining a correction density correspondence value obtained by smoothing the density distribution tendency of the density correspondence value according to the temperature.

  According to a second aspect of the present invention, in addition to the configuration of the first aspect of the invention, the liquid property detecting element has a configuration in which the heating resistor is embedded in an insulating ceramic substrate. And it is arrange | positioned in the said liquid storage container so that the outer surface of the said insulating ceramic base | substrate may touch the said liquid.

  According to a third aspect of the present invention, in addition to the configuration of the first or second aspect of the invention, the liquid is a urea aqueous solution, and the specific component is urea. .

  In the liquid state detection sensor according to the first aspect of the present invention, the liquid property detection element has a heating resistor, but the heating resistor has a property that its resistance value changes as its temperature rises. Here, before energization of the heating resistor, the temperature of the heating resistor itself is substantially the same as the temperature of the surrounding liquid. That is, the resistance value of the heating resistor shortly after the start of energization to the heating resistor is still less influenced by its own heat generation and is correlated with the temperature of the surrounding liquid. Therefore, in the present invention, the temperature of the surrounding liquid is detected based on the first corresponding value corresponding to the first resistance value after the energization of the heating resistor is started.

  In addition, since the thermal conductivity of the liquid varies depending on the concentration of the specific component contained in the liquid, when the heating resistor is energized (heated) for a predetermined detection time, the heating resistor is different for each liquid having a different concentration of the specific component. The rate of temperature rise will be different. Therefore, in the present invention, the heating resistor is energized for a predetermined detection time, and the first corresponding value corresponding to the first resistance value of the heating resistor and the second corresponding value corresponding to the second resistance value are sequentially obtained. After that, a difference value between the two corresponding values is obtained, and based on the difference value, the degree of temperature rise of the heating resistor is captured, and a concentration correspondence value corresponding to the concentration of the specific component contained in the liquid is obtained.

  By the way, even if the concentration of the specific component contained in the liquid is the same, if the temperature of the liquid is different, the temperature rise rate of the heating resistor (that is, the difference value between the second corresponding value and the first corresponding value described above) The degree of change) will be different. That is, the temperature rise rate of the heating resistor has a dependency on the temperature of the liquid. Therefore, in the present invention, when detecting the concentration of the specific component contained in the liquid as described above, the temperature information of the liquid obtained based on the first corresponding value corresponding to the first resistance value of the heating resistor, The density correspondence value is obtained using the difference value between the second correspondence value and the first correspondence value.

  In correcting the difference value using the temperature information of the liquid, for example, the correlation of the difference value with respect to the temperature related to the reference liquid having a predetermined concentration is confirmed in advance, and a table created based on this correlation. This can be executed by storing (map) or an arithmetic expression in the density correspondence value acquisition means.

  Further, according to the study by the present inventors, as the deviation between the reference temperature of the urea aqueous solution used as a reference when creating the table and the arithmetic expression and the temperature of the urea aqueous solution as the concentration detection target increases, the concentration correspondence value and It has been found that there is a concentration distribution tendency in which the deviation from the actual urea concentration increases. Such a concentration distribution tendency tends to be difficult to find from the correlation of the difference value with respect to the temperature related to the reference liquid having a predetermined concentration based on the physical property values as described above. Therefore, in the invention according to claim 1, by further correcting the concentration correspondence value based on the temperature information and smoothing the concentration distribution tendency, the identification included in the liquid without depending on the temperature of the liquid The concentration of the component can be detected more accurately.

  When correcting the concentration correspondence value, similarly to the above, the concentration correspondence value to be originally acquired according to the concentration of the reference liquid at a predetermined temperature and the concentration correspondence value obtained by detection from the reference liquid. It can be executed by creating a table (map) or deriving an arithmetic expression based on the density distribution tendency obtained by confirming the deviation, and storing it in the correction density correspondence value acquisition means.

  Furthermore, in the present invention, the temperature of the liquid is measured using a liquid property detection element (a so-called direct heat type liquid property detection element) having a heating resistor that functions as both a heating element that generates heat and a temperature sensing element. Detection and density detection are performed. As a result, the liquid state detection sensor can be downsized, and the structure and detection circuit can be prevented from being complicated as compared with a sensor having an indirectly heated liquid property detection element.

  Further, according to the invention according to claim 2, since the liquid property detecting element is disposed in the liquid container such that the outer surface of the insulating ceramic substrate in which the heating resistor is embedded is in contact with the liquid, The sensitivity for detecting the temperature of the liquid and the concentration of the specific component contained in the liquid can be increased. Further, since the heating resistor is embedded in the insulating ceramic substrate, the liquid property detecting element can be directly immersed in the conductive liquid.

  According to the invention of claim 3, since the liquid whose state is detected by the liquid state detection sensor can be urea aqueous solution and the specific component can be urea, the temperature of the urea aqueous solution and the urea aqueous solution are included. The concentration of urea can be detected.

  Hereinafter, an embodiment of a liquid state detection sensor embodying the present invention will be described with reference to the drawings. First, the structure of a liquid state detection sensor 100 as an example will be described with reference to FIG. FIG. 1 is a partially cutaway longitudinal sectional view of the liquid state detection sensor 100. In the liquid state detection sensor 100, the longitudinal direction of the level detection unit 70 (capacitor constituted by 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 is the front end side and attached. The side where the portion 40 is provided is the rear end side.

  The liquid state detection sensor 100 of 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) and temperature of the aqueous urea solution. , And a sensor for detecting the concentration of urea as a specific component contained in the solution. As shown in FIG. 1, the liquid state detection sensor 100 includes a cylindrical outer cylinder electrode 10 and a cylindrical shape provided along the axis O direction of the outer cylinder electrode 10 inside the outer cylinder electrode 10. Mounting for attaching the level detection unit 70 constituted by the internal electrode 20, the liquid property detection unit 30 provided on the tip side of the internal electrode 20, and the liquid state detection sensor 100 to the urea water tank 98 (see FIG. 2). Unit 40.

  The outer cylinder electrode 10 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 three bus bars that are equally spaced in the circumferential direction on the outer periphery of the outer cylindrical electrode 10. Further, at the distal end portion 11 of the outer cylinder electrode 10, an opening portion 16 for preventing a rubber bushing 80 interposed between the inner electrode 20 (described later) from coming off is formed on each bus bar where the slit 15 is formed. Each is provided. Furthermore, one air vent hole 19 is formed on a bus bar different from each bus bar where 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 extended toward the distal end side in the axis O direction from the position of the opening 16, and the ceramic heater 110 of the liquid property detection unit 30 to be described later and the radial direction of the ceramic heater 110. It surrounds the protector 130 that covers the periphery and protects the ceramic heater 110. And the most advanced part (lowermost part in a figure) of the outer cylinder electrode 10 is opened, and the protector 130 which comprises the liquid property detection part 30 is in the state which can be visually recognized from the opening side. It should be noted that the leading end portion of the outer cylinder electrode 10 does not necessarily have to be opened, and a rectifying plate having a liquid inlet is provided at the distal end portion 11 of the outer cylinder electrode 10 so that the protector 130 cannot be visually recognized. Also good.

  Next, the outer cylindrical electrode 10 is welded to the electrode support portion 41 in a state where the base end portion 12 is engaged with the outer periphery of the electrode support portion 41 of the metal attachment portion 40. The attachment portion 40 functions as a base for fixing the liquid state detection sensor 100 to the urea water tank 98 (see FIG. 2), and attachment holes (not shown) for inserting attachment bolts are formed in the flange portion 42. Yes. A circuit for detecting the level, temperature, urea concentration, and the like of a urea aqueous solution 99 (see FIG. 2) described later, A housing portion 43 is formed for housing a circuit board 60 on which an input / output circuit for electrical connection with an external circuit (for example, an engine control unit (ECU) of an automobile) is mounted. Since the mounting portion 40 is connected to the circuit board 60 so as to have the same potential as a wiring portion (not shown) that forms the ground potential, the outer cylinder electrode 10 is grounded via the mounting portion 40. Has been.

  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. 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 (an input / output circuit unit 290 described later) on the circuit board 60 are connected by the wiring cable 61. Yes. The circuit board 60 and the ECU 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. Between the internal electrode 20 and the outer cylinder electrode 10, a level detection unit 70 is formed that forms a capacitor whose electrostatic capacity changes according to the level of the urea aqueous solution 99 (see FIG. 2).

  A pipe guide 55 and an inner case 50 for fixing the internal electrode 20 to the mounting portion 40 are engaged with the base end portion 22 on the rear end side in the axis O direction of the internal electrode 20. The pipe guide 55 is an annular guide member joined near the end edge of the base end portion 22 of the internal electrode 20. The inner case 50 is a 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. The inner case 50 has a cylindrical shape and is directed radially outward toward the rear end side. A protruding flange 51 is formed, and the tip end side engages with the hole 46 of the electrode support portion 41 of the attachment portion 40. When the inner case 50 is engaged with the electrode support portion 41, the inner case 50 is inserted into the hole 46 of the electrode support portion 41 from the housing portion 43 side, and the flange portion 51 abuts against the bottom surface in the housing portion 43, thereby The case 50 is prevented from passing through the hole 46. In addition, the internal electrode 20 is inserted into the inner case 50 from the accommodating portion 43 side, but the pipe guide 55 is brought into contact with the flange portion 51 so that the inner electrode 20 is prevented from falling off 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 urea water tank 98 (see FIG. 2), the water tightness and the inside of the urea water tank 98 are prevented from communicating with each other through the housing portion 43. Airtightness is maintained. Further, a plate-like seal member (not shown) is attached to the surface of the attachment portion 40 on the distal end side of the flange portion 42, and when the liquid state detection sensor 100 is attached to the urea water tank 98, the flange portion 42 and urea water are attached. Watertightness and airtightness are also maintained between the tank and the tank.

  When the internal electrode 20 is assembled to the mounting portion 40, the pipe guide 55 is pressed against the flange portion 51 of the inner case 50 by the two pressing plates 56 and 57. The insulating pressing plate 56 is fixed in the accommodating portion 43 with screws 58 in a state where the pressing plate 57 is sandwiched between the insulating guide plate 56 and the pipe guide 55. 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, and two lead wires 90 (in FIG. 1) for electrically connecting the electrode lead wire 52 of the internal electrode 20 and a ceramic heater 110 described later. Only one lead wire 90 is shown.) A two-core cable 91 containing the lead wire 90 is inserted, and is 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 electrically connected to the ground side.

  Next, the liquid property detection unit 30 provided at the distal end portion 21 of the internal electrode 20 detects the temperature of the urea aqueous solution 99 (see FIG. 2) and the concentration of the contained urea in the present embodiment. It has a ceramic heater 110 as an element. The ceramic heater 110 is fired by sandwiching a heater pattern mainly made of Pt between two plate-like insulating ceramic layers. Among the heater patterns, the cross-sectional area of the pattern constituting the heating resistor 114 (see FIG. 2) is made smaller than the cross-sectional area of the pair of output lead portions connected to the lead wire 90, During energization, heat is generated mainly in the heating resistor 114. The ceramic heater 110 corresponds to the “liquid property detecting element” in the present invention, and a laminate of two insulating ceramic layers corresponds to the “insulating ceramic substrate” in the present invention.

  The ceramic heater 110 is supported by a holder 120 made of an insulating resin that is attached to the distal end portion 21 of the internal electrode 20. The holder 120 has a cylindrical shape with two outer diameters, and the ceramic heater 110 is inserted into the inner peripheral side of the holder 120, and the heating resistor 114 (see FIG. 2) is exposed. In this state, the ceramic heater 110 is fixed to the inner periphery of the holder 120 by fixing members 125 and 126 made of an adhesive. The rear end side, which is the large diameter side of the holder 120, is attached to the front end portion 21 of the internal electrode 20 with an external fit, and a seal ring is provided between the outer peripheral surface of the internal electrode 20 and the inner peripheral surface of the holder 120. 121 is interposed, and watertightness and airtightness inside the cylindrical internal electrode 20 are ensured.

  By the way, before the holder 120 is mounted, an output extraction portion electrically connected to each lead portion formed on the outer surface of the ceramic heater 110 (the output extraction portion is formed by penetrating one insulating ceramic layer. Two relay terminals 119 (only one of the relay terminals 119 is shown in FIG. 1) are connected to the lead portion via the via conductor), and 2 of the cable 91 is connected to the relay terminal 119. The core wires of the two lead wires 90 are joined by caulking or soldering, respectively. Furthermore, the junction terminal 119 and the lead wire 90 are covered and protected by the insulating protective member 95 together with the joint portion. The two lead wires 90 are inserted through the internal electrode 20 and connected to the circuit board 60.

  Further, the portion of the ceramic heater 110 exposed from the holder 120 is covered and protected by a metal protector 130 formed in a bottomed cylindrical shape. The protector 130 is fitted on the outer periphery of the small diameter portion of the holder 120 on the opening side. A liquid circulation hole (not shown) is opened on the outer periphery of the protector 130, and the urea aqueous solution 99 (see FIG. 2) is exchanged inside and outside the protector 130 through the liquid circulation hole.

  The liquid property detection unit 30 having such a configuration is attached to the distal end portion 21 of the internal electrode 20 via the holder 120 and is elastically supported in the outer cylindrical electrode 10 by the rubber bush 80. The rubber bush 80 has a cylindrical shape, and a protrusion 87 formed on the outer peripheral surface thereof is engaged with and fixed to the opening 16 of the outer cylinder electrode 10 from the inner peripheral side. A plurality of grooves (not shown) along the axis O direction are provided in each of the outer peripheral surface and the inner peripheral surface of the rubber bush 80. When the liquid state detection sensor 100 is attached to the urea water tank 98 (see FIG. 2), the urea aqueous solution 99 flowing into the front end side of the rubber bush 80 and the urea aqueous solution 99 flowing into the rear end side through this groove. Liquid exchange and air removal are performed.

  Next, the electrical configuration of the liquid state detection sensor 100 will be described with reference to FIGS. FIG. 2 is a block diagram showing an electrical configuration of the liquid state detection sensor 100. FIG. 3 is a diagram showing the configuration of the storage area of the ROM 230.

  As shown in FIG. 2, the liquid state detection sensor 100 is attached to a urea water tank 98 as a liquid container, and includes a level detection unit 70 including a pair of electrodes (the outer cylinder electrode 10 and the internal electrode 20), and a heating resistance. The liquid property detection unit 30 including the ceramic heater 110 in which the body 114 is embedded is immersed in a urea aqueous solution 99 as a state detection target liquid contained in the urea water tank 98. The liquid state detection sensor 100 includes a microcomputer 210 mounted on a circuit board 60, and the microcomputer 210 includes a level detection circuit unit 280 that controls the level detection unit 70 and a liquid that controls the liquid property detection unit 30. The property detection circuit unit 250 is connected to an input / output circuit unit 290 that communicates with the ECU.

  The microcomputer 210 includes a CPU 220, a ROM 230, and a RAM 240 having a known configuration. The CPU 220 controls the liquid state detection sensor 100, and the ROM 230 is provided with a program storage area 231, a table storage area 232, a setting value storage area 233 and the like shown in FIG. 3. The program storage area 231 stores a property detection program (see FIG. 4), which will be described later, and is read and executed when the liquid state detection sensor 100 is driven. The table storage area 232 stores a density correction table that is referred to when the property detection program is executed. This table is a table that is referred to when performing secondary correction according to the temperature T of the aqueous urea solution 99 with respect to the urea concentration C obtained by the equation (1) described later, and is created in advance by experiments or the like. It is what is done. More specifically, the urea concentration is detected for each temperature T (or temperature range) of the specific urea aqueous solution 99, and a deviation between the urea concentration C obtained by the equation (1) and the actual urea concentration is obtained. Then, in order to bring the urea concentration C close to the actual urea concentration, a correction value Z (correction magnification) to be multiplied with the urea concentration C is calculated from the deviation, and is associated with the temperature T (or temperature range) of the urea aqueous solution 99. This may be stored in the table storage area 232 as a density correction table.

  In the setting value storage area 233, equations (1) to (3) (described later) used in the property detection program, initial values of various variables, threshold values, and the like are stored. The ROM 230 is also provided with other storage areas (not shown), and stores other programs (for example, a program for level detection) executed when the liquid state detection sensor 100 is driven, setting values, and the like. Similarly, the RAM 240 shown in FIG. 2 is also provided with various storage areas. When the property detection program or the like is executed, a part of the program, various variables, timer count values, etc. are temporarily stored in a predetermined storage area. Is remembered.

  The input / output circuit unit 290 controls the communication protocol in order to input and output signals between the liquid state detection sensor 100 and the ECU. Further, the level detection circuit unit 280 applied an AC voltage between the outer cylinder electrode 10 and the internal electrode 20 of the level detection unit 70 based on an instruction from the microcomputer 210, and flowed through a capacitor forming the level detection unit 70. The current is converted into a voltage, and the voltage signal is output to the microcomputer 210. In the present embodiment, when the urea aqueous solution 99 is introduced between the outer cylinder electrode 10 and the internal electrode 20, the insulating coating 23 formed on the outer peripheral surface of the internal electrode 20 is used as the main dielectric ( The level detection is performed by utilizing the fact that the capacitance of the capacitor (non-conductor) is greatly different between the portion where the conductive urea aqueous solution 99 is interposed and the portion where it is not interposed.

  Next, based on an instruction from the microcomputer 210, the liquid property detection circuit unit 250 supplies a constant current to the ceramic heater 110 of the liquid property detection unit 30, and outputs a detection voltage generated at both ends of the heating resistor 114 to the microcomputer 210. It is the circuit part which outputs. The liquid property detection circuit unit 250 includes a differential amplifier circuit unit 260, a constant current output unit 270, and a switch 255.

  The constant current output unit 270 outputs a constant current that flows through the heating resistor 114. The switch 255 is provided on the energization path to the heating resistor 114 and turns on / off the energization to the heating resistor 114 according to the control of the microcomputer 210. The differential amplifier circuit 260 outputs the difference between the potential Pin appearing at one end of the heating resistor 114 and the potential Pout appearing at the other end to the microcomputer 210 as a detection voltage.

  Next, the principle of detecting the temperature and urea concentration of the urea aqueous solution 99 using the ceramic heater 110 of the liquid state detection sensor 100 of the present embodiment will be briefly described.

  It is known that the heating resistor 114 formed mainly of Pt has a correlation between its own temperature and its resistance value. In addition, within a short period of time after the start of energization of the heating resistor 114, the heating resistor 114 has not yet generated a large amount of heat, so that the temperature of the heating resistor 114 itself is the urea aqueous solution 99 existing around itself. It is almost the same as the temperature. From this, the voltage value corresponding to the resistance value after the energization of the heating resistor 114 is started (however, it takes about 10 msec until the current value is stabilized after the energization is started), and the temperature of the urea aqueous solution 99 present in the surroundings. Can be measured in advance, the temperature of the urea aqueous solution 99 can be measured.

  Next, when energization to the heating resistor 114 is continued, the temperature of the heating resistor 114 itself is deprived by the urea aqueous solution 99 present in the surroundings, but the heat deprivation resistor 114 is deprived by the thermal conductivity of the urea aqueous solution 99. The amount of heat generated is different. That is, the rate of temperature rise of the heating resistor 114 varies depending on the thermal conductivity of the urea aqueous solution 99 existing around. In addition, it is known that the thermal conductivity of the urea aqueous solution 99 varies depending on the concentration of urea contained in the urea aqueous solution 99. Therefore, if the heating resistor 114 is immersed in the urea aqueous solution 99 and the heating resistor 114 is heated for a predetermined time to determine the degree of change in the resistance value of the heating resistor 114, the thermal conductivity of the surrounding urea aqueous solution 99 is obtained. The concentration of urea contained in the urea aqueous solution 99 can be obtained.

  Specifically, when the heating resistor 114 is immersed in a urea aqueous solution 99 at a reference temperature (for example, room temperature (25 ° C.)) and energized for 700 msec, the resistance value of the heating resistor 114 is set when the urea concentration of the urea aqueous solution 99 is 0 wt%. The voltage value change corresponding to the change is 1220 mV, and when it is 16.25 wt% and 32.5 wt%, they are 1262 mV and 1298 mV, respectively. That is, as the urea concentration in the urea aqueous solution 99 is increased, the thermal conductivity is decreased, and the heating resistor 114 is less likely to be deprived of heat, so that the rate of temperature increase is increased. As a result, the resistance value change of the heating resistor 114 becomes large, and the voltage value change corresponding to the resistance value change becomes large.

There is a proportional relationship between the urea concentration of the urea aqueous solution 99 and the resistance value change (voltage value change) of the heating resistor 114. Specifically, the relationship between the urea concentration of the urea aqueous solution 99 around the heating resistor 114 and the voltage value change (difference value ΔV) corresponding to the resistance value change of the heating resistor 114 is shown in the following equation.
ΔV = a _T · C + b _T (1)
ΔV is a difference value [mV] between a voltage value corresponding to a resistance value after the energization of the heating resistor 114 is started and a voltage value corresponding to a resistance value after a certain detection time (eg, 700 msec) has elapsed after the energization. Indicates. C represents the urea concentration [wt%] in the urea aqueous solution 99. a _T represents the slope of the ΔV-C straight line at the temperature T ° C. of the urea aqueous solution 99, and b _T represents the intercept of the ΔV-C straight line at the temperature T ° C. of the aqueous urea solution 99.

  On the other hand, even if the concentration of urea contained in the urea aqueous solution 99 is the same, if the temperature of the urea aqueous solution 99 is different, the temperature rise rate (that is, voltage value change) of the heating resistor 114 is different. That is, the temperature rise rate of the heating resistor 114 has a dependency on the temperature of the urea aqueous solution 99.

  For example, when the heating resistor 114 is energized for 700 msec and the urea aqueous solution 99 having a urea concentration of 32.5 wt% and a temperature of 25 ° C. is heated, the voltage value change (difference value ΔV) corresponding to the resistance value change of the heating resistor 114. ) Is 1298 mV. On the other hand, when the heating resistor 114 immersed in the urea aqueous solution 99 having the same concentration and the temperature of 80 ° C. is energized for 700 msec, the voltage value change is 1440 mV. That is, when the urea concentration of the urea aqueous solution 99 is constant, the resistance value change of the heating resistor 114 becomes smaller as the temperature of the urea aqueous solution 99 becomes lower, and the voltage value change corresponding to the resistance value change becomes smaller.

Thus, the relationship between the urea concentration of the urea aqueous solution 99 and the resistance value change (voltage value change) of the heating resistor 114 is dependent on the temperature of the urea aqueous solution 99. Therefore, the urea concentration can be accurately calculated by performing correction (calibration) according to the temperature of the urea aqueous solution 99 with respect to the expression (1). Specifically, an equation for performing correction based on the temperature of the urea aqueous solution 99 is shown below.
a _T = a ₂₅ + x (T−25) (2)
b _T = b ₂₅ + y (T−25) (3)
Here, a ₂₅ indicates the slope of the ΔV-C line when the temperature of the urea aqueous solution 99 is 25 ° C., and x is a temperature correction coefficient for the slope of the straight line. Similarly, b ₂₅ represents the intercept of the ΔV-C line when the temperature of the urea aqueous solution 99 is 25 ° C., and y is the temperature correction coefficient of the intercept of the straight line. When determining the urea concentration in the urea aqueous solution 99 using the above equations (1) to (3), if the calibration according to the temperature of the urea aqueous solution 99 is performed, the accurate urea concentration can be determined.

  By the way, the difference between the calculated urea concentration and the actual urea concentration tends to increase as the temperature of the urea aqueous solution 99 deviates from the calibration reference temperature (25 ° C. in the above formulas (2) and (3)). Concentration distribution trend). In the liquid state detection sensor 100 of the present embodiment, in order to smooth this concentration distribution tendency, a secondary correction corresponding to the temperature of the urea aqueous solution 99 is further made to the urea concentration C obtained by the equation (1). It is carried out. Specifically, the CPU 220 executes the property detection program stored in the ROM 230 of the microcomputer 210 to detect the temperature of the urea aqueous solution 99 and the urea concentration C, and the above-described urea concentration C Apply secondary correction. Hereinafter, the property detection program will be described with reference to FIGS. FIG. 4 is a flowchart of the property detection program. Each step in the flowchart in FIG. 4 is abbreviated as “S”. The liquid state detection sensor 100 also detects the level of the aqueous urea solution 99 according to the execution of another program, but the description of the level detection is omitted here.

  When the state of the urea aqueous solution 99 is detected based on an instruction from the ECU, the property detection program stored in the program storage area 231 of the ROM 230 shown in FIG. 3 is read into a predetermined storage area of the RAM 240 and executed. Is done.

  As shown in FIG. 4, when the switch 155 is closed based on a control signal from the microcomputer 210 (see FIG. 2), energization from the constant current output unit 270 to the heating resistor 114 is started (S1). Then, a count value of a timer program (not shown) that is separately executed is referred to, and a standby is performed until 10 msec elapses from the start of energization (S2: NO). As described above, in the present embodiment, 10 msec is set as the time until the current value is stabilized after the energization of the heating resistor 114 is started. By this process, the voltage value in S4 is set for 10 msec. No measurements are made.

  If 10 msec has elapsed (S2: YES), the process proceeds to S4, where the differential amplifier circuit 260 measures the detection voltage of the heating resistor 114, and the detection voltage is input to the microcomputer 210 (S4). The detection voltage value of the heating resistor 114 after the start of energization measured by the differential amplifier circuit unit 260 in S4 corresponds to the “first corresponding value” in the present invention, and the CPU 220 that acquires the voltage value This corresponds to the “first corresponding value acquisition unit” in the present invention.

  Subsequently, in the microcomputer 210, the temperature T of the urea aqueous solution 99 around the heating resistor 114 is obtained using an arithmetic expression set in advance based on the input voltage value of the heating resistor 114. The calculated temperature T is transmitted from the input / output circuit unit 290 to the ECU as a temperature information signal (S5). The CPU 220 that calculates the temperature T of the urea aqueous solution 99 in S5 corresponds to the “temperature information acquisition unit” in the present invention.

  Next, by referring to the count value of the timer program, a standby is performed until 700 msec elapses while energization to the heating resistor 114 is continued (S7: NO). When 700 msec has elapsed after the start of energization of the heating resistor 114 (S7: YES), the detection voltage of the heating resistor 114 measured by the differential amplifier circuit 260 is input to the microcomputer 210 as in S4 ( S8). When this voltage measurement is completed, a control signal for the switch 255 is output from the microcomputer 210, and energization to the heating resistor 114 is stopped (S10). In S8, the detected voltage value of the heating resistor 114 measured by the differential amplifier circuit 260 when 700 msec has passed after the energization of the heating resistor 114 has elapsed is the “second corresponding value” in the present invention. The CPU 220 that acquires the voltage value corresponds to the “second corresponding value acquisition unit” in the present invention. Further, in S1, the energization from the constant current output unit 270 to the heating resistor 114 is started, and in S7, after waiting for 700 msec corresponding to the “detection time” in the present invention, the switch is stopped so that the energization is stopped in S10. The CPU 220 that outputs a control signal of 255 corresponds to the “energizing means” in the present invention.

  Then, a difference value ΔV is calculated by subtracting the voltage value of the heating resistor 114 obtained in S4 from the voltage value of the heating resistor 114 obtained when 700 msec obtained in S8 has elapsed (S11). The calculated difference value ΔV is determined based on the maximum value (threshold value Q) of the voltage value change based on the possible value of the urea concentration of the aqueous urea solution 99, which is determined in advance by experiments or the like and stored in the setting value storage area 233 of the ROM 230. If it is also smaller (S13: YES), it is determined that the value of the difference value ΔV is within the normal value range, and the process proceeds to S19. Then, a calculation based on the equations (1) to (3) is performed, and the urea concentration C contained in the urea aqueous solution 99 is obtained (S19). The CPU 220 that calculates the difference value ΔV in S11 corresponds to the “difference value calculation means” in the present invention. In S19, the urea concentration C of the urea aqueous solution 99 corresponding to the “concentration corresponding value” in the present invention is calculated. The CPU 220 that performs the process corresponds to the “density corresponding value acquisition unit” in the present invention.

  Next, the density correction table stored in the table storage area 232 is referred to, and a correction value Z (correction magnification) corresponding to the temperature T (temporarily stored as a variable in the RAM 240) calculated in S5 is determined. The Then, the corrected urea concentration Cz is calculated by multiplying the urea concentration C obtained in S19 by this correction value Z (S20). The calculated corrected urea concentration Cz is transmitted as a concentration information signal from the input / output circuit unit 290 to the ECU (S22). In S20, the correction value Z corresponding to the temperature T is determined by referring to the concentration correction table and multiplied by the urea concentration C, thereby calculating the corrected urea concentration Cz corresponding to the “corrected concentration corresponding value” in the present invention. The CPU 220 that performs the process corresponds to the “corrected density corresponding value acquisition unit” in the present invention.

  Thereafter, by referring to the count value of the timer program, standby is performed until 60 seconds elapse (S23: NO). This waiting time is set as a time sufficient for the temperature of the heating resistor 114 itself energized for 700 msec to be equal to the temperature of the surrounding urea aqueous solution 99. After the elapse of 60 seconds, the process returns to S1 (S23: YES), and the temperature and urea concentration of the urea aqueous solution 99 are detected again.

  On the other hand, in S13, when the calculated difference value ΔV is equal to or greater than the threshold value Q (S13: NO), the periphery of the heating resistor 114, which is determined in advance through experiments or the like and stored in the setting value storage area 233, is determined. If it is larger than the minimum value (threshold R) of the voltage value change that can be taken in the case of air (S14: YES), it is determined that the vehicle is in an empty state. In this case, a notification signal for notification of airing is transmitted to the ECU via the input / output circuit unit 290 (S17).

  Even if the difference value ΔV is equal to or less than the threshold value R (S14: NO), it is determined that the liquid around the heating resistor 114 is not an aqueous urea solution (for example, light oil) because it is equal to or greater than the threshold value Q. Then, a notification signal for notifying the different liquid is transmitted to the ECU via the input / output circuit unit 290 (S16). In either case, the process proceeds to S23, returns to S1 after waiting for 60 seconds (S23: YES), and again detects the temperature of the urea aqueous solution 99 and the urea concentration.

  Needless to say, the present invention can be modified in various ways. For example, in the property detection program of the above embodiment, the temperature T of the urea aqueous solution 99 is calculated based on a predetermined arithmetic expression in S5. However, the present invention is not limited to this. And may be obtained by referring to the processing in S5. The urea concentration C in the urea aqueous solution 99 in S19 is also calculated based on the arithmetic expressions (1) to (3). However, the present invention is not limited to this, but by referring to a table created in advance through experiments or the like. You may ask for it. On the other hand, the corrected urea concentration Cz of the urea aqueous solution 99 obtained in S22 is obtained by multiplying the correction value Z determined by referring to the concentration correction table by the urea concentration C. However, the present invention is not limited to this. It may be calculated by substituting the density C, or may be calculated by adding or subtracting a plurality of correction values set in advance for each temperature.

  In addition, the respective standby times in S2, S7, and S23 are merely examples, and an optimal standby time may be obtained and set by experiments or the like. Furthermore, the standby time in S23 may be set in accordance with the temperature T of the urea aqueous solution 99 detected in S5.

  Further, the circuit board 60 is provided as a relay board for relaying outputs from the level detection unit 70 and the liquid property detection unit 30, and is connected to an external circuit on which the microcomputer 210 and the like are mounted, and the level detection is performed by controlling the external circuit. Alternatively, temperature / concentration detection may be performed.

  In the liquid state detection sensor 100 of the above embodiment, the outer cylinder electrode 10 and the inner electrode 20 are provided and the liquid level of the urea aqueous solution 99 is also detected. However, the outer cylinder electrode 10 and the inner electrode 20 are provided. Alternatively, the level detection may not be performed. Further, in the liquid state detection sensor 100 of the above embodiment, after waiting for 700 msec corresponding to “detection time” to elapse, the detection voltage value of the heating resistor 114 (corresponding to “second corresponding value”) is detected. However, the detection voltage value of the heating resistor 114 is detected at a timing after the start of energization to the heating resistor 114, after 10 msec has elapsed and before 700 msec has elapsed (for example, 680 msec), When 700 msec has elapsed, energization to the heating resistor 114 may be stopped.

  In the liquid state detection sensor 100 of the above embodiment, the constant current output unit 270 is provided in the liquid property detection circuit unit 250, a constant current is passed through the heating resistor 114, and a voltage corresponding to the resistance value of the heating resistor 114. The value was acquired. However, for example, a constant voltage output unit is provided in the liquid property detection circuit unit 250, a constant voltage is applied to the heating resistor 114, and a current value corresponding to the current flowing through the heating resistor 114 is output. Temperature / concentration detection may be performed.

  Moreover, in the liquid state detection sensor 100 of the present embodiment, an example of detecting the temperature, urea concentration, and level of the urea aqueous solution 99 is taken as an example, but the liquid to be detected is not limited to the urea aqueous solution. For example, it may be a sensor that uses ammonia as a specific component contained in a liquid and detects the properties of ammonia water (liquid level, temperature, concentration, etc.).

4 is a partially cutaway longitudinal sectional view of the liquid state detection sensor 100. FIG. 2 is a block diagram showing an electrical configuration of a liquid state detection sensor 100. FIG. 3 is a diagram illustrating a configuration of a storage area of a ROM 230. FIG. It is a flowchart of a property detection program. It is a graph which shows the tendency (concentration distribution tendency) of the deviation with respect to the temperature of urea aqueous solution of urea concentration in urea aqueous solution calculated by the conventional liquid state detection sensor, and actual urea concentration.

98 Urea water tank 99 Urea aqueous solution 100 Liquid state detection sensor 110 Ceramic heater 114 Heating resistor 210 Microcomputer 220 CPU

Claims (3)

A liquid property detecting element that has a heating resistor that generates heat when energized and is disposed in a liquid storage container in which a liquid is stored;
Energization means for energizing the heating resistor for a predetermined detection time;
First corresponding value acquisition means for acquiring a first corresponding value corresponding to the first resistance value of the heating resistor within the detection time;
Temperature information obtaining means for obtaining temperature information of the liquid based on the first corresponding value;
Second correspondence value acquisition means for acquiring a second correspondence value corresponding to the second resistance value of the heating resistor after obtaining the first correspondence value within the detection time or after the detection time has elapsed. When,
Difference value calculating means for obtaining a difference value between the second corresponding value and the first corresponding value;
In the liquid state detecting sensor and a density corresponding value obtaining means for obtaining a density corresponding value corresponding to the concentration of a specific component contained in the liquid correction to the basis of the difference value to the temperature information,
A corrected concentration correspondence value is obtained by performing a secondary correction based on the temperature information on the concentration correspondence value to obtain a corrected concentration correspondence value obtained by smoothing the concentration distribution tendency of the concentration correspondence value according to the temperature of the liquid. A liquid state detection sensor comprising means.   The liquid property detecting element has a structure in which the heating resistor is embedded in an insulating ceramic substrate, and is disposed in the liquid container so that an outer surface of the insulating ceramic substrate is in contact with the liquid. The liquid state detection sensor according to claim 1.   The liquid state detection sensor according to claim 1, wherein the liquid is an aqueous urea solution, and the specific component is urea.

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