JP4594278B2 - 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, an aqueous urea solution stored in a urea water tank mounted on an automobile is 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.

By the way, since the thermal conductivity varies depending on the concentration of urea contained in the urea aqueous solution, the temperature of the heating element generated by energization is measured by the temperature sensing element, and the heat from the heating element to the temperature sensing element at that time is measured. If the conduction is affected by the liquid, the temperature of the heating element to be measured can be made to differ according to the concentration of the liquid. Therefore, if the heating element is energized for a predetermined time and the temperature of the heating element is measured before and after the energization to determine the temperature change of the heating element, the urea aqueous solution is obtained from the correlation between the urea concentration and the temperature change of the heating element. The concentration of urea contained in can be detected (see, for example, Patent Document 1). Since the correlation between the urea concentration and the temperature change of the heating element is dependent on the temperature of the liquid, in Patent Document 1, another temperature sensing element provided separately from the temperature sensing element is used. Then, the temperature of the urea aqueous solution is measured, and the urea concentration is detected based on the correlation between the concentration at each temperature and the temperature change. Patent Document 1 describes that a warning is issued when it is detected that the urea aqueous solution has dropped to a temperature at which the urea aqueous solution is frozen based on the output information from the other temperature sensing elements described above.
JP-A-2005-84026

  However, as disclosed in Patent Document 1, the concentration sensor becomes larger by providing another temperature sensing element separately from the temperature sensing element associated with the heating element to configure the density identification sensor unit, There has been a problem that the circuit configuration for performing the process becomes complicated.

  In cold districts, the urea aqueous solution stored in the urea water tank may freeze. In such a case, the urea aqueous solution cannot be sprayed onto the catalyst, so it is necessary to wait for the urea aqueous solution to thaw. . On the other hand, as described above, Patent Document 1 describes that the temperature of the urea aqueous solution is notified by using another temperature sensor provided separately from the temperature sensor associated with the heating element. There is no mention of processing on the heating element. However, when the urea aqueous solution is frozen, if the process of detecting the urea concentration by energizing the heating element for a predetermined time is repeatedly executed, the concentration identification sensor unit may be damaged. More specifically, when the heating element is energized for a predetermined time when the urea aqueous solution is frozen, a part of the urea aqueous solution around the concentration identification sensor part is thawed due to the heat generation. If the aqueous solution is in a state where most of the aqueous urea solution is still frozen, refreezing occurs, and the concentration identification sensor unit may be damaged by the freezing expansion pressure at that time.

  The present invention has been made to solve the above-described problems, and can detect the temperature and concentration of a liquid with a single element having a heating resistor, and prevent breakage of the element when the liquid is frozen. An object of the present invention is to provide a liquid state detection sensor that can perform the above-described operation.

Means and effects for solving the problems

  In order to achieve the above object, a liquid state detection sensor according to a first aspect of the present invention is a liquid state detection sensor for detecting the state of a liquid contained in a liquid container, and a heating resistor that generates heat when energized. A liquid property detection element disposed in the liquid container, energization means for energizing the heating resistor for a predetermined detection time, and a first resistance value of the heating resistor within the detection time. A first corresponding value acquiring means for acquiring a corresponding first corresponding value; a temperature information acquiring means for obtaining temperature information of the liquid based on the first corresponding value; and a second of the heating resistor after the detection time has elapsed. Second correspondence value acquisition means for obtaining a second correspondence value corresponding to the resistance value; difference value calculation means for obtaining a difference value between the second correspondence value and the first correspondence value; and the difference value and the temperature information. Based on the characteristics contained in the liquid And a concentration obtaining unit for obtaining the concentration of the component.

  In the liquid state detection sensor 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 surrounding liquid is heated for a certain period of time using a heating resistor, the temperature increase rate differs for liquids with different concentrations. become. 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 after energization of the heating resistor is started and the first value after the detection time has passed to the heating resistor. Based on the difference value with the second corresponding value corresponding to the two resistance values, the degree of the temperature rise of the heating resistor is detected and the concentration of the specific component contained in the liquid is detected.

  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 acquired after the energization of the heating resistor is started is used. The density detection is performed by correcting the difference value between the second corresponding value and the first corresponding value. By adopting such a configuration, it is possible to accurately detect the concentration of the specific component contained in the liquid without depending on the temperature of the liquid. 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. (Map) and calculation formula can be executed by storing them in the density acquisition means.

  Furthermore, in the present invention, a liquid property detection element (a so-called direct heat type liquid property detection element) having a heating resistor that also functions as a heating element that generates heat and a temperature sensing element is used to form a liquid. Temperature detection and concentration detection are performed. As a result, the liquid state detection sensor can be reduced in size, and the structure and detection circuit can be prevented from becoming complicated.

  A liquid state detection sensor according to a second aspect of the invention is a liquid state detection sensor for detecting the state of the liquid stored in the liquid storage container, and includes a heating resistor that generates heat when energized, and the liquid A liquid property detecting element disposed in the container, energizing means for energizing the heating resistor for a predetermined detection time, and a first corresponding value corresponding to a first resistance value of the heating resistor within the detection time. A first corresponding value acquiring means for acquiring temperature information acquiring means for obtaining temperature information of the liquid based on the first corresponding value, and a second corresponding to the second resistance value of the heating resistor after the detection time has elapsed. Second correspondence value acquisition means for obtaining two correspondence values, difference value calculation means for obtaining a difference value between the second correspondence value and the first correspondence value, and a specific component contained in the liquid based on the difference value Concentration acquisition means for determining the concentration of Within the detection time, based on the temperature information obtained by the temperature information acquisition means, a freeze determination means for determining whether or not the liquid is frozen, and the liquid is frozen by the freeze determination means And an energization stop unit that stops energization of the heating resistor by the energization unit when it is determined that the energization unit is present.

  Also in the liquid state detection sensor according to the second aspect of the present invention, one liquid property detecting element (so-called direct heat type liquid) having a heat generating resistor that also functions as a heat generating element that generates heat and a temperature sensing element. A configuration for performing temperature detection and concentration detection of a liquid using a property detection element) is employed. However, in the present invention, since the temperature detection and the concentration detection are performed by the liquid property detection element having such a configuration, the heating resistor is energized to detect whether or not the liquid is frozen. Need to get liquid temperature information. Then, following the temperature detection of the liquid, energization of the heating resistor is performed for a predetermined detection time, and the concentration detection is performed. However, if the liquid is frozen, Some liquid present around the liquid property detecting element causes partial thawing. However, the part of the liquid that has been thawed is refrozen if most of the liquid is still frozen, and the liquid property detecting element may be damaged by the freezing expansion pressure at that time.

  Therefore, in the present invention, first, before energization for a predetermined detection time is performed on the heating resistor, the liquid freezes based on the temperature information acquired by the temperature information acquisition means after the energization of the heating resistor is started. It is determined whether or not. When it is determined that the liquid is frozen, energization of the heating resistor by the energization means thereafter is forcibly stopped. In this way, even when the liquid is frozen, it is possible to avoid a situation in which the liquid property detecting element is damaged by the freezing expansion pressure at the time of refreezing, and a highly reliable liquid state detecting sensor and can do.

  The first corresponding value in the present invention may be a value corresponding to the first resistance value of the heating resistor, and specifically includes a voltage value, a current value, and a temperature converted value. Further, the second corresponding value of the present invention may be a value corresponding to the second resistance value of the heating resistor. However, in the present invention, since it is necessary to obtain a difference value between the second corresponding value and the first corresponding value, for example, when the first corresponding value is a voltage value, the second corresponding value is similarly a voltage value. There is a need to. Further, as described later, when obtaining the third corresponding value, it is necessary to obtain a difference value from the first corresponding value. For example, the voltage value is set in the same manner as when the first corresponding value is set as the voltage value. There is a need.

  Furthermore, in the present invention, the timing for acquiring the first corresponding value by the first corresponding value acquiring means is that the temperature of the heating resistor itself is substantially the same as the temperature of the surrounding liquid after the energization of the heating resistor is started. What is necessary is just to acquire within a certain period, and specifically, a 1st corresponding value should just be acquired within 100 msec after the energization start to a heating resistor. At the start of energization of the heating resistor, the current applied to the heating resistor tends to be difficult to stabilize. Therefore, after the energization of the heating resistor has started, 2 msec has elapsed and within 100 msec (more preferably It is preferable to acquire the first corresponding value within 50 msec).

  Further, in the liquid state detection sensor described above, in addition to the configuration of the invention according to claim 2, the freezing determination unit is configured to freeze the liquid when the temperature information is equal to or lower than the freezing temperature of the liquid. It is good to be comprised so that it may determine with having carried out.

  In the liquid state detection sensor of the present invention, it is determined whether or not the temperature information obtained by the temperature information acquisition means has become equal to or lower than the freezing temperature of the liquid, and whether or not the liquid is frozen is determined. Accordingly, it is possible to quickly determine whether or not the liquid is frozen, and when it is determined that the liquid is frozen, it is possible to quickly stop energization of the heating resistor. As a result, even when the liquid is frozen, it is possible to effectively avoid a situation where the liquid property detecting element is damaged by the freezing expansion pressure at the time of refreezing.

  Further, in the liquid state detection sensor described above, in addition to the configuration of the invention according to claim 2, a second resistance value corresponding to a third resistance value of the heating resistor within the detection time and after obtaining the first corresponding value is obtained. A third correspondence value obtaining unit for obtaining three correspondence values, wherein the freezing determination unit is configured such that the temperature information is equal to or lower than a preset temperature threshold value, and the third correspondence value and the first correspondence value are It is good to be comprised so that the said liquid may be determined to be frozen, when the intermediate | middle difference value which is a difference, and the freezing determination threshold value satisfy | fill predetermined | prescribed magnitude relationship.

  By the way, when the concentration of the specific component of the liquid changes, the freezing temperature of the liquid may change accordingly. For example, when the liquid is an aqueous urea solution, the freezing temperature increases as the concentration of urea decreases. Therefore, when determining whether or not the liquid is frozen, it is only necessary to compare the temperature information of the liquid with a preset freezing temperature, and when the concentration of the specific component contained in the liquid changes with time, it is accurate. There is a possibility that liquid freezing cannot be detected.

  Therefore, in the liquid state detection sensor of the present invention, the temperature information obtained by the temperature information acquisition means is compared with a preset temperature threshold value, and an intermediate value that is the difference between the third corresponding value and the first corresponding value. The difference value is compared with the freezing determination threshold value. Then, when the temperature information is equal to or lower than the temperature threshold value, and the intermediate difference value satisfies the freezing determination threshold value and a predetermined magnitude relationship, it is determined that the liquid is frozen. As the “predetermined magnitude relationship” here, [1] intermediate difference value <freezing determination threshold value, [2] intermediate difference value ≦ freezing determination threshold value can be exemplified. In this way, if the presence / absence of freezing in two stages, such as comparison between temperature information and a temperature threshold value and comparison between an intermediate difference value and a freezing determination threshold value, is determined, the specific component contained in the liquid is determined. Even when the concentration changes, it is possible to accurately determine whether or not the liquid is frozen.

  Further, in the liquid state detection sensor described above, in addition to the configuration of the invention according to any one of claims 2 to 4, the energization means may be configured to wait for a period of time after the energization of the heating resistor is stopped. The heating resistor is configured to start energization again, and when the energization means energizes the detection time as the waiting time, the first waiting time is selected, When energization to the heating resistor is stopped by the energization stopping unit, it is preferable to include a standby time selection unit that selects a second standby time shorter than the first standby time.

  In the liquid state detection sensor of the present invention, a standby time is provided to wait until the temperature of the heating resistor becomes substantially equal to the temperature of the surrounding liquid, thereby repeatedly performing accurate liquid temperature detection and specific component concentration detection. be able to. Here, if it is determined that the liquid is frozen, the heating resistor is forcibly stopped as described above, but the heating resistor is hardly energized for the detection time. Therefore, the heating resistor is not heated so much and is exposed to a temperature substantially equal to the surrounding liquid. Therefore, in the present invention, when it is determined that the liquid is frozen and the energization of the heating resistor is stopped, the standby time until the energization of the heating resistor is performed next is shortened. . Thereby, the re-detection of the liquid temperature can be repeated quickly, it can be quickly determined that the liquid has been thawed, and the concentration can be detected quickly after the liquid has been thawed.

  Further, in the liquid state detection sensor described above, in addition to the configuration of the invention according to any one of claims 1 to 5, the difference value obtained by the difference value calculation means is used, and the inside of the liquid container Abnormality determining means for determining the presence or absence of the abnormality, and the concentration acquisition means is adapted to the liquid by the concentration acquisition means only when the abnormality determination means determines that there is no abnormality among the difference values. It is good to comprise so that the density | concentration of the specific component contained may be calculated | required.

  Thus, by determining that an abnormality has occurred when the difference value acquired when detecting the concentration of the specific component contained in the liquid deviates from the normal range, for example, the liquid is stored in the liquid storage container. It is possible to notify the occurrence of an abnormality such as the liquid being a different kind of liquid such as light oil or the liquid container being empty, or to limit the operation of the device that uses the liquid. . Moreover, since the density | concentration of the specific component contained in a liquid is calculated | required based on the difference value of a normal range, the detection precision of a density | concentration can be improved.

  Further, in the liquid state detection sensor described above, in addition to the configuration of the invention according to any one of claims 1 to 6, the energization means is configured to energize the heating resistor with a constant current. The first corresponding value acquisition unit may acquire a first corresponding value that is a voltage value, and the second corresponding value acquisition unit may acquire a second corresponding value that is a voltage value.

  In this way, the energizing means is configured to energize the heating resistor with a constant current, the first corresponding value acquiring means acquires the first corresponding value that is a voltage value, and the second corresponding value acquiring means is the voltage value. By configuring so as to acquire a second corresponding value, it is possible to acquire an accurate difference value while simplifying the circuit configuration, and to provide a liquid state detection sensor at a low cost.

  Further, in the above liquid state detection sensor, in addition to the configuration of the invention according to any one of claims 1 to 7, the liquid property detection element includes a ceramic heater in which the heating resistor is embedded in a ceramic base. It is good to be. By configuring the liquid property detection element with a ceramic heater, it is excellent in durability and corrosion resistance, and can detect the temperature of the liquid and the concentration of the specific component contained in the liquid stably over a long period of time.

  Further, in the above liquid state detection sensor, in addition to the configuration of the invention according to any one of claims 1 to 8, the liquid is an aqueous urea solution, and the specific component can be urea. Thereby, the temperature of urea aqueous solution and the density | concentration of urea contained in urea aqueous solution are detectable.

  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 the liquid state detection sensor 100 as an example will be described with reference to FIGS. FIG. 1 is a partially cutaway longitudinal sectional view of the liquid state detection sensor 100. FIG. 2 is a schematic diagram showing the heater pattern 115 of the ceramic heater 110. 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. 3). 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 cylindrical electrode 10 is formed so as to surround the periphery of the ceramic heater 110 in the radial direction of the liquid property detection unit 30 described later together with the protector 130 that covers and protects the ceramic heater 110. It extends further to the front end side in the axis O direction than the position. And the most advanced part (the lowest part in the figure) is opened, and the protector 130 constituting the liquid property detecting unit 30 is visible from the opening side.

  Next, the outer cylinder electrode 10 is welded in a state in which the base end portion 12 is engaged with the outer periphery of the electrode support portion 41 of the metal attachment portion 40. The mounting portion 40 functions as a base for fixing the liquid state detection sensor 100 to the urea water tank 98, and a mounting hole (not shown) for inserting a mounting bolt is formed in the flange portion 42. In addition, on the opposite side of the electrode support portion 41 across the flange portion 42 of the mounting portion 40, a circuit for detecting the level, temperature, urea concentration, etc. of the urea aqueous solution, which will be described later, and an external circuit (not shown) such as an automobile A housing portion 43 for housing a circuit board 60 on which an input / output circuit for electrical connection with the engine control device (ECU) is mounted is formed. 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, in which a capacitor whose capacitance changes according to the level of the urea aqueous solution is formed.

  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 flanged cylindrical resin member that positions and supports the inner electrode 20 so that the inner electrode 20 and the outer cylinder electrode 10 are reliably insulated, and the tip side of the inner case 50 is the electrode support portion 41 of the mounting portion 40. Engage with hole 46. The inner case 50 is formed with a flange portion 51 that protrudes radially outward. When the inner case 50 is engaged with the electrode support portion 41, a hole in the electrode support portion 41 is formed from the housing portion 43 side. 46 is inserted. Then, the flange portion 51 abuts against the bottom surface in the housing portion 43, thereby preventing the inner case 50 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. 3), 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. A plate-like sealing member (not shown) is attached to the front end surface of the flange portion 42 of the attachment portion 40, 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 with the tank are maintained.

  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 of the lead wires 90 is shown.) A two-core cable 91 containing the lead wire 90 is inserted and electrically connected to the pattern on the circuit board 60, respectively. An electrode (not shown) on the ground side of the circuit board 60 is connected to the mounting portion 40, whereby the outer cylinder electrode 10 welded to the mounting portion 40 is electrically connected to the ground side.

  Next, the liquid property detection unit 30 provided at the tip portion 21 of the internal electrode 20 is a ceramic heater 110 as a liquid property detection element that detects the temperature of the urea aqueous solution and the concentration of urea contained in the present embodiment. A holder 120 made of an insulating resin that supports the ceramic heater 110 and is attached to the tip portion 21 of the internal electrode 20, and a protector 130 that covers and protects the periphery of the ceramic heater 110 exposed from the holder 120. It is prepared for.

  As shown in FIG. 2, the ceramic heater 110 is formed by forming a heater pattern 115 mainly composed of Pt on a plate-like ceramic base 111 made of an insulating ceramic, and sandwiching it between a pair of ceramic bases (not shown). The pattern 115 is formed in an embedded state. Heat generation is performed mainly in the heating resistor 114 during energization so that the cross-sectional area of the pattern constituting the heating resistor 114 is made smaller than the pattern of the lead portions 112 and 113 serving as both poles for voltage application. I am doing so. In addition, via conductors (not shown) connected to electrode pads provided on the surface of the ceramic substrate 111 are connected to both ends of the lead portions 112 and 113, respectively, and the connection with the two lead wires 90 is relayed. Each of the two connectors 119 (only one of them is shown in FIG. 1) is electrically connected. The ceramic heater 110 corresponds to the “liquid property detecting element” in the present invention.

  Next, as shown in FIG. 1, the holder 120 that supports the ceramic heater 110 has a cylindrical shape in which the outer diameter is configured to be two steps in a stepped shape, and the heating resistor 114 of the heating resistor 114 is formed on the distal end side having a small diameter. The ceramic heater 110 in a state where the embedded side (see FIG. 2) is exposed is fixed by fixing members 125 and 126 made of an adhesive. The rear end side, which is the large diameter side, is attached to the distal end portion 21 of the internal electrode 20, and a seal ring 140 is interposed between the outer peripheral surface of the internal electrode 20 and the inner peripheral surface of the holder 120. The water-tightness and air-tightness of the interior of the are secured.

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

  Next, the protector 130 is a metal protective member formed in a bottomed cylindrical shape. The opening side is fitted to the outer periphery of the small diameter portion of the holder 120. Further, a liquid circulation hole (not shown) is opened on the outer periphery of the protector 130, and the urea aqueous solution is exchanged inside and outside the protector 130.

  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. 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, liquid exchange and bubble removal between the urea aqueous solution flowing into the front end side of the rubber bush 80 and the urea aqueous solution flowing into the rear end side through this groove are performed. Is done.

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

  As shown in FIG. 3, 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 as a state detection target liquid stored in the urea water tank 98. The liquid state detection sensor 100 includes a microcomputer 220 mounted on the circuit board 60, a level detection circuit unit 250 that controls the level detection unit 70, and a liquid property detection circuit unit 280 that controls the liquid property detection unit 30. An input / output circuit unit 290 that communicates with the ECU is connected.

  The microcomputer 220 includes a CPU 221, a ROM 222, and a RAM 223 having a known configuration. The CPU 221 governs the control of the liquid state detection sensor 100, and the ROM 222 is provided with various storage areas (not shown). The property detection program to be described later, equations (1) to (5) to be described later, initial values of various variables, A threshold value and the like are stored in a predetermined storage area. Similarly, the RAM 223 is also provided with various storage areas. When the property detection program is executed, a part of the program, various variables, a timer count value, and the like are temporarily stored in a predetermined storage area.

  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 250 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 220, and flowed through a capacitor forming the level detection unit 70. The circuit unit converts the current into voltage and outputs the voltage signal to the microcomputer 220.

  Next, the liquid property detection circuit unit 280 applies a constant current to the ceramic heater 110 of the liquid property detection unit 30 based on an instruction from the microcomputer 220, and supplies the detection voltage generated at both ends of the heating resistor 114 to the microcomputer 220. It is the circuit part which outputs. The liquid property detection circuit unit 280 includes a differential amplifier circuit unit 230, a constant current output unit 240, and a switch 260.

  The constant current output unit 240 outputs a constant current that flows through the heating resistor 114. The switch 260 is provided on the energization path to the heating resistor 114 and opens / closes the switch according to the control of the microcomputer 220. The differential amplifier circuit unit 230 outputs a 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 220 as a detection voltage.

  Next, the principle of detecting the level, temperature, and urea concentration of the urea aqueous solution by the liquid state detection sensor 100 of the present embodiment will be described. First, the principle of detecting the level of the urea aqueous solution in the level detection unit 70 will be described with reference to FIG. FIG. 4 is an enlarged cross-sectional view of the vicinity of the water surface of the urea aqueous solution filled between the gap between the outer cylinder electrode 10 and the inner electrode 20.

  The liquid state detection sensor 100 (see FIG. 1) is assembled in a urea water tank 98 (see FIG. 3) containing a urea aqueous solution in a state where the front end side of the outer cylinder electrode 10 and the inner electrode 20 faces the bottom wall side. It is done. That is, the level detection unit 70 of the liquid state detection sensor 100 sets the direction of displacement of the urea aqueous solution whose capacity changes in the urea water tank 98 (the level of the urea aqueous solution level) as the axis O direction, and the outer cylinder electrode 10 and the internal electrode. 20 is assembled to the urea water tank 98 so that the tip side of 20 is the side (low level side) where the volume of the urea aqueous solution is small. And the electrostatic capacitance between the gaps of the outer cylinder electrode 10 and the inner electrode 20 is measured, and it is detected to what level the urea aqueous solution existing between the two is present in the axis O direction. As is well known, this is based on the fact that the capacitance increases as the difference in diameter between two points having different potentials in the radial direction decreases.

  That is, as shown in FIG. 4, in the portion not filled with the urea aqueous solution, the distance of the portion where the potential difference occurs between the gaps is interposed between the inner peripheral surface of the outer cylinder electrode 10 and the insulating coating 23. This is the total distance (indicated by distance X) of the distance corresponding to the thickness of the air layer (indicated by distance Y) and the distance corresponding to the thickness of the insulating coating 23 (indicated by distance Z). On the other hand, in the portion filled with the urea aqueous solution, the potential difference between the gaps is such that the potential of the outer cylinder electrode 10 and the urea aqueous solution is almost equal because the urea aqueous solution exhibits conductivity. The distance Z corresponds to a thickness of 23.

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

  Here, since the distance Y is larger than the distance Z, the capacitance per unit between the electrodes using air as a dielectric is the electrostatic capacity per unit between the electrodes using the insulating coating 23 as a dielectric. Smaller than capacity. For this reason, the change in the capacitance of the portion filled with the urea aqueous solution is larger than the change in the capacitance of the portion not filled with the urea aqueous solution. Is proportional to the level of the aqueous urea solution.

  The measurement of the level of the urea aqueous solution is performed by the microcomputer 220 via the level detection circuit unit 250, and the obtained level information signal is output from the input / output circuit unit 290 to an ECU (not shown). The

  Next, the principle of detecting the temperature of the urea aqueous solution and the concentration of urea as a specific component contained in the urea aqueous solution in the ceramic heater 110 constituting the liquid property detection unit 30 will be described with reference to FIGS. . FIG. 5 shows an example of an aqueous urea solution having a urea concentration of 32.5 wt% and a temperature of 25 ° C. As the temperature of the heating resistor itself increases with the passage of time since the start of constant current supply to the heating resistor. It is a graph which shows a mode that the voltage value corresponding to the resistance value rises. FIG. 6 is a graph showing that the voltage value change (difference value ΔV) of the heating resistor and the urea concentration of the urea aqueous solution are in a proportional relationship and have temperature dependence. FIG. 7 shows that when the relationship between the voltage value change (difference value ΔV) of the heating resistor and the urea concentration of the urea aqueous solution is corrected by the temperature of the urea aqueous solution, the corrected concentration (converted concentration) and the urea concentration are almost the same. It is a graph which shows that it corresponds.

  Within a short period of time after the start of energization, the heating resistor has not yet generated a large amount of heat, so the temperature of the heating resistor itself is substantially the same as the temperature of the liquid present around it. This is shown in the graph of FIG. The temperature of the heating resistor itself continuously increases with the passage of time after starting to flow a constant current to the heating resistor (however, it takes about 10 msec until the current value becomes stable after the start of energization). It is shown to go.

Therefore, if the correlation between the voltage value corresponding to the resistance value when 10 msec has elapsed from the start of energization of the heating resistor and the temperature of the urea aqueous solution existing in the surroundings is confirmed in advance, the temperature of the urea aqueous solution is determined. It is possible to measure. Below, the formula showing the relationship between the resistance value after the energization to the heating resistor and the temperature of the urea aqueous solution existing around the resistance value is shown.
R _T = R ₀ (1 + α ₀ T) (1)
Note that _RT represents the resistance value of the heating resistor at T ° C. When the energization of the heating resistor is started, the temperature of the liquid around the heating resistor is also T ° C. R ₀ represents the resistance value (Ω) of the heating resistor at 0 ° C. α ₀ indicates a temperature coefficient based on 0 ° C., but is determined by the material constituting the heating resistor. Therefore, it can be seen from the equation (1) that the resistance value of the heating resistor is proportional to the ambient temperature.

From Ohm's law,
R _T = V _T / I (2)
Although a constant current flows through the heating resistor, the current value I (A) is constant. That is, the voltage value V _T of the heating resistor (in this embodiment, the voltage value (V) output from the differential amplifier circuit unit 230) is proportional to the resistance value R _T (Ω) from the equation (2). From the equation (1), it can be seen that it is proportional to the ambient temperature.

  Next, when energization to the heating resistor is continued, the temperature of the heating resistor itself is taken away by the liquid present around, but the amount of heat taken away by the heating resistor varies depending on the thermal conductivity of the liquid. That is, the rate of temperature rise of the heating resistor varies depending on the thermal conductivity of the liquid present around. Further, it is known that the thermal conductivity of the liquid varies depending on the concentration of the specific component contained in the liquid. From this, when the heating resistor is immersed in the liquid and the liquid is heated for a certain period of time, if the degree of change in the resistance value of the heating resistor is obtained, the difference in the thermal conductivity of the surrounding liquid can be found, A liquid concentration can be obtained.

  This is shown in the graph of FIG. For example, when a heating resistor immersed in a urea aqueous solution at a temperature of 25 ° C. is energized for 700 msec, when the urea concentration of the urea aqueous solution is 0 wt%, the voltage value change corresponding to the resistance value change of the heating resistor is 1220 mV, which is 16.25 wt. % And 32.5 wt% are 1262 mV and 1298 mV, respectively. That is, as the urea concentration of the urea aqueous solution increases, the thermal conductivity decreases, and the heating resistor becomes difficult to take heat, so the rate of temperature rise increases, and as a result, the resistance value change of the heating resistor increases. It is shown that the voltage value change (indicated by ΔV in the figure) corresponding to the resistance value change increases.

Thus, it can be seen that there is a proportional relationship as shown in FIG. 6 between the urea concentration of the urea aqueous solution and the resistance value change (voltage value change) of the heating resistor. The following shows an expression representing the relationship between the urea concentration of the urea aqueous solution around the heating resistor and the voltage value change (difference value ΔV) corresponding to the resistance value change of the heating resistor.
ΔV = a _T C + b _T (3)
ΔV is a difference value (mV) between a voltage value corresponding to the resistance value after the energization start of the heating resistor and a voltage value corresponding to the resistance value after a certain detection time (for example, 700 msec) has elapsed after the energization. Show. C represents the urea concentration (wt%) in the urea aqueous solution. a _T represents the slope of the ΔV-C line at a temperature T ° C. of the urea aqueous solution, and b _T represents the intercept of the ΔV-C line at the temperature T ° C. of the urea aqueous solution.

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

  This is shown in the graph of FIG. For example, when a heating resistor is energized for 700 msec and a urea aqueous solution 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 is 1298 mV. On the other hand, when a heating resistor is energized for 700 msec to an aqueous urea solution having the same concentration and a temperature of 80 ° C., the voltage value change is 1440 mV. That is, when the urea concentration of the urea aqueous solution is constant, the resistance value change of the heating resistor is reduced as the temperature of the urea aqueous solution is lower, and the voltage value change corresponding to the resistance value change is reduced.

Thus, it can be seen that the relationship between the urea concentration of the urea aqueous solution and the resistance value change (voltage value change) of the heating resistor is dependent on the temperature of the urea aqueous solution. Therefore, by correcting (calibrating) the equation (3) according to the temperature of the urea aqueous solution obtained from the equations (1) and (2), it is possible to accurately calculate the urea concentration. The equation for performing correction according to the temperature of the urea aqueous solution is shown below.
a _T = a ₂₅ + x (T−25) (4)
b _T = b ₂₅ + y (T−25) (5)
Incidentally, a _25, the temperature of the urea aqueous solution shows the slope of [Delta] V-C lines in the case of 25 ° C., 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 is 25 ° C., and y is the temperature correction coefficient of the intercept of the straight line.

When correction values corresponding to the equations shown in the above (3), (4), and (5) were obtained by experiments and the like, a ₂₅ = 2.3, b ₂₅ = 1.223, x = 0.015 , Y = 2.45 was obtained. Using these values, FIG. 7 shows that the concentration (converted concentration) of the urea aqueous solution obtained by the correction substantially matches the actual urea concentration.

  In the liquid state detection sensor 100 of the present embodiment, the level, temperature, and urea concentration of the urea aqueous solution are detected based on such a principle. In particular, the temperature and urea concentration of the urea aqueous solution are detected by executing a property detection program stored in the ROM 222 of the microcomputer 220. Hereinafter, the property detection program will be described with reference to FIGS. 3, 8, and 9. FIG. 8 is a flowchart of the property detection program. FIG. 9 is a graph for explaining the thresholds Q and R for discriminating between the empty and different liquids. Each step of the flowchart in FIG. 8 is abbreviated as “S”.

  When the state of the urea aqueous solution is detected based on an instruction from the ECU, the property detection program stored in the ROM 222 is read into a predetermined storage area of the RAM 223 and executed. As shown in FIG. 8, when a control signal is transmitted from the microcomputer 220 (see FIG. 3) to the switch 260, the switch is closed and energization from the constant current output unit 240 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, 10 msec is set as the initial energization time, which is the time when the current value becomes stable after the energization of the heating resistor is started, and by this process, the voltage value is measured in S3 during the 10 msec. It will never be.

  When 10 msec has elapsed (S2: YES), the process proceeds to S3, where the differential amplifier circuit 230 measures the detection voltage of the heating resistor 114, and the detection voltage is input to the microcomputer 220 (S3). Note that the detected voltage value of the heating resistor 114 after the start of energization measured by the differential amplifier circuit unit 230 in S3 corresponds to the “first corresponding value” of the present invention, and the CPU 221 that acquires the voltage value This corresponds to the “first corresponding value acquisition unit” in the present invention.

In the microcomputer 220, the input voltage value of the heating resistor 114 is set to _VT, and calculation based on the equations (1) and (2) is performed to obtain the temperature T of the urea aqueous solution around the heating resistor 114. It is done. The calculated temperature T is transmitted from the input / output circuit unit 290 to the ECU as a temperature information signal (S6). The CPU 221 that calculates the temperature T of the urea aqueous solution in S6 corresponds to the “temperature information acquisition unit” in the present invention.

  On the other hand, the calculated temperature T of the urea aqueous solution is compared with the freezing temperature (−11 ° C.) of the urea aqueous solution stored in the ROM 222 in advance (S7). The control signal is transmitted to the switch 260 because it is determined that it is frozen, the switch is opened, and energization to the heating resistor 114 is stopped (S8). Then, a count value of a timer program (not shown) that is separately executed is referred to, and a standby is performed until 1 sec elapses after the power supply is stopped (S9: NO). This standby time is set as a time sufficient for the temperature of the heating resistor 114 itself energized for about 10 msec to be equal to the temperature of the surrounding urea aqueous solution. When 1 sec elapses, the process returns to S1, and the temperature detection of the heating resistor 114 that is equal to the temperature of the surrounding urea aqueous solution is started again. (S9: YES). Note that the CPU 221 that determines whether or not the temperature T of the urea aqueous solution is equal to or lower than the freezing temperature in S7 corresponds to the “freezing determination unit” in the present invention, and the switch 260 is set so as to stop energization of the heating resistor 114 in S8. The CPU 221 that outputs a control signal to “corresponds to the“ energization stopping means ”in the present invention. Further, by determining whether or not the temperature T of the urea aqueous solution is equal to or lower than the freezing temperature in S7, the CPU 221 that performs one of the waiting times in S9 and S22 performs the “waiting time selection” in the present invention. It corresponds to “means”.

  As long as the temperature T of the urea aqueous solution around the heating resistor 114 is below the freezing temperature, the urea aqueous solution once thawed by the heat of the heating resistor 114 may be frozen again, and the ceramic is generated by the freezing expansion pressure at that time. Since there is a possibility that the heater 110 is damaged, the processes of S1 to S9 are repeated, and the temperature T of the urea aqueous solution is monitored. When the temperature T of the urea aqueous solution becomes higher than the freezing temperature (S7: NO), the process waits until 700 msec elapses while the energization of the heating resistor 114 is continued by referring to the count value of the timer program. (S10: NO).

  When 700 msec has elapsed after the start of energization of the heating resistor 114 (S10: YES), the detection voltage of the heating resistor 114 measured by the differential amplifier circuit unit 230 is input to the microcomputer 220 as in S3 ( S11). When this voltage measurement is completed, a control signal for the switch 260 is output from the microcomputer 220, and energization to the heating resistor 114 is stopped (S12). In S11, the detected voltage value of the heating resistor 114 at the time when 700 msec has elapsed after energization of the heating resistor 114 measured by the differential amplifier circuit unit 230 becomes the “second corresponding value” of the present invention. The CPU 221 that acquires the voltage value corresponds to the “second corresponding value acquisition unit” in the present invention. In addition, the CPU 221 that outputs a control signal of the switch 260 starts the energization from the constant current output unit 240 to the heating resistor 114 in S1, waits for 700 msec in S10, and then stops energizing in S12. This corresponds to the “energization means” in the present invention.

  Then, a difference value ΔV is calculated by subtracting the voltage value of the heating resistor 114 obtained in S3 from the voltage value of the heating resistor 114 obtained after 700 msec obtained in S11 (S13). If the calculated difference value ΔV is smaller than the maximum value (threshold Q: see FIG. 9) of the voltage value change based on the possible value of the urea concentration of the urea aqueous solution, which is determined in advance by experiments or the like and stored in the ROM 222 ( (S14: YES), assuming that the value of the difference value ΔV is a normal difference value within the range of normal values, the process proceeds to S18 and the calculation based on the equations (3) to (5) is performed and included in the urea aqueous solution. The concentration C of urea to be obtained is determined. Note that the difference value (normal difference value) ΔV in this case takes a value smaller than the threshold value Q, for example, a magnitude E in FIG. The calculated urea concentration is transmitted from the input / output circuit unit 290 to the ECU as a concentration information signal (S18). The CPU 221 that calculates the difference value ΔV in S13 corresponds to the “difference value calculation unit” of the present invention, and the CPU 221 that calculates the urea concentration C of the urea aqueous solution in S18 is the “concentration acquisition unit” in the present invention. It corresponds to.

  Thereafter, by referring to the count value of the timer program, standby is performed until 60 seconds elapse (S22: NO). This standby 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. After 60 seconds, the process returns to S1 (S22: YES), and the temperature of the urea aqueous solution and the urea concentration are detected again.

  On the other hand, in S14, when the calculated difference value ΔV is equal to or greater than the threshold value Q (S14: NO), when the surroundings of the heating resistor 114, which is determined in advance by experiments or the like and stored in the ROM 222, is air. If it is greater than the minimum voltage value change that can be taken (threshold R: see FIG. 9) (S19: YES), it is determined that the vehicle is in an empty state, and an informing signal for informing of emptying is sent via the input / output circuit unit 290. Is transmitted to the ECU (S20). In this case, the difference value ΔV is larger than the threshold value R in FIG. The CPU 221 that determines that an abnormality has occurred by the determination processing in S14 and S19 and performs the processing in S20 or S21 corresponds to the “abnormality determination unit” in the present invention.

  Even if the difference value ΔV is equal to or less than the threshold value R (S19: 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. A notification signal for notifying the different liquid is transmitted to the ECU via the input / output circuit unit 290 (S21). In this case, the difference value ΔV takes a value of, for example, a magnitude F that is not less than the threshold value Q and not more than the threshold value R in FIG. In any case, the process proceeds to S22, returns to S1 after waiting for 60 seconds (S22: YES), and again detects the temperature and urea concentration of the urea aqueous solution.

  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 (S6) of the urea aqueous solution is calculated based on the expressions (1) and (2), and the urea concentration (S18) is calculated based on the expressions (3) to (5). However, it may be obtained by creating a table in advance by experiments or the like, storing the table in a predetermined storage area of the ROM 222, and referring to the processing in S6 and S18.

  In addition, the respective standby times in S2, S9, S10, and S22 are merely examples, and an optimal standby time may be obtained and set by experiments or the like. Furthermore, the standby times in S9 and S22 may be set in accordance with the temperature of the urea aqueous solution detected in S6. In the above embodiment, when the process of S8 is performed, the process proceeds to S9. However, the process of S9 may be omitted, and the process may be shifted to S22 after the process of S8 is completed. Furthermore, in S7, the temperature of the urea aqueous solution was calculated and then compared with the freezing temperature of the urea aqueous solution. However, the voltage value of the heating resistor 114 when 10 msec elapsed from the start of energization was obtained by a freezing temperature ( It may be compared with the voltage value of the heating resistor 114 corresponding to −11 ° C.).

  The circuit board 60 is provided as a circuit board for relaying the 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 220 or the like is mounted, and the level detection is performed by controlling the external circuit. Alternatively, temperature / concentration detection may be performed.

  Furthermore, in the liquid state detection sensor 100 of the above embodiment, the outer cylinder electrode 10 and the inner electrode 20 are provided to detect the liquid level of the urea aqueous solution, but the outer cylinder electrode 10 and the inner electrode 20 are not provided. Also good. In the liquid state detection sensor 100 of the above embodiment, the constant current output unit 240 is provided in the liquid property detection circuit unit 280, a constant current is passed through the heating resistor 114, and the 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 280, 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, so that the temperature of the urea aqueous solution is increased. -You may make it perform density | concentration detection.

  By the way, if the urea aqueous solution sometimes fluctuates violently due to the vibration of the vehicle or the like, the detected voltage value of the heating resistor 114 to be measured temporarily becomes a high value or a low value. Sometimes. In such a case, the obtained temperature information and concentration information may temporarily show an abnormal value.For example, the voltage measurement values for a plurality of times are stored, and the temperature information and concentration information are stored based on the average value. If acquired, more accurate temperature information and concentration information can be obtained. Hereinafter, a modified example of the property detection program that can further improve the accuracy of the temperature information and the concentration information will be described with reference to FIG. Moreover, the property detection program as a modified form shown in FIG. 10 is whether or not the liquid is frozen like the first property detection program (the property detection program shown in FIG. 8) of the above-described embodiment. The determination process is different, and the presence or absence of freezing of the liquid is determined through a two-stage determination as will be described later.

  In the second property detection program shown in FIG. 10, S4 and S5 are added between S3 and S6 of the property detection program of the present embodiment, and S15 to S17 are added between S14 and S18. The second property detection program is configured to execute the processes of S31 to S35 in place of the process of S7 described above. The other steps are the same as those in the present embodiment, are denoted by the same step numbers, and the description thereof is omitted or simplified.

  In the second property detection program, the value of the detection voltage of the heating resistor 114 after the start of energization measured in S3 and the value of the difference value ΔV calculated in S13 are obtained by a known memory management method. Five new ones are stored in a predetermined storage area of the RAM 223. In addition, counters that count the number of executions of the processes of S3 and S15 are stored in predetermined storage areas of the RAM 223, respectively. Values such as various variables and counters stored in the RAM 223 for use in the execution of the second property detection program are set to initial values (for example, 0) when the second property detection program is executed.

  As shown in FIG. 10, in the second property detection program, when energization to the heating resistor 114 is started and 10 msec elapses, the detection voltage of the heating resistor 114 is measured and input to the microcomputer 220 (S1 to S1). S3). At this time, the value of the detected voltage is stored in a predetermined storage area of the RAM 223, and the value of the counter that counts the number of executions of the process of S3 (that is, the number of samplings of the voltage value) is increased by one.

  In the next process of S4, the value of the execution frequency counter of the process of S3 is referred to, and after the execution of the second property detection program is started, it is confirmed whether or not the detection voltage measurement in S3 has been performed five times or more ( S4). If the sampling of the voltage value is less than 5 times (S4: NO), the process proceeds to S6, and the same voltage conversion as in the present embodiment is performed using the measured voltage value as it is.

  On the other hand, in the process of S3 after the fifth round, the value of the counter that counts the number of executions of the process of S3 is also 5 or more. For this reason, in the process of S4 after the fifth round, it is determined that sampling has been performed five times or more (S4: YES), and the process proceeds to S5. Note that since the detected voltage values measured as described above are stored in the RAM 223 up to the latest five voltage values, the oldest voltage value is determined in the processing of S3 after the sixth lap of the second property detection program. It will be overwritten.

  In S5, a process of calculating an average value of the three voltage values excluding the maximum value and the minimum value from the latest five voltage values stored in the predetermined storage area of the RAM 223 by the process of S3 that is repeatedly executed is performed (S5). S5). Then, using the average value of the calculated voltage values, the temperature T of the urea aqueous solution is calculated in the next S6.

  When the process of S6 is completed, the process proceeds to S31, and the temperature T of the urea aqueous solution calculated in S6 is compared with a temperature threshold value (here set to 0 ° C.) stored in the ROM 222 in advance, and is equal to or lower than the temperature threshold value. (S31: YES), it is determined that the urea aqueous solution is exposed to a cold atmosphere, and the process proceeds to S32. In S31, when the temperature T of the urea aqueous solution is equal to or higher than the temperature threshold value (S31: NO), it is determined that the urea aqueous solution is not frozen and the process proceeds to S10.

  Next, when an affirmative determination is made in S31 and the process proceeds to S32, by referring to the count value of the timer program, the energization of the heating resistor 114 is continued and a standby is performed until 300 msec elapses (S32: NO). When 300 msec has elapsed after the start of energization of the heating resistor 114 (S32: YES), the detected voltage of the heating resistor 114 measured by the differential amplifier circuit unit 230 (see FIG. 3) is similar to S3 described above. The data is input to the microcomputer 220 (S33). In S33, the detected voltage value of the heating resistor 114 at the time when 300 msec has passed after the energization of the heating resistor 114 measured by the differential amplifier circuit unit 230 becomes the “third corresponding value” of the present invention. The CPU 221 that acquires the voltage corresponds to the “third corresponding value acquisition unit” in the present invention.

  Next, in S34, the intermediate differential value ΔV1 obtained by subtracting the voltage value of the heating resistor 114 obtained in S3 from the voltage value of the heating resistor 114 obtained in S33 after 300 msec from the start of energization is obtained. Is done. Then, the process proceeds to S35, in which it is determined whether or not the intermediate difference value ΔV1 calculated in S34 is greater than the freezing determination threshold value TH that is determined in advance through experiments or the like and stored in the ROM 222. When it is determined that the intermediate difference value ΔV1 is larger than the freezing determination threshold value TH (S35: YES), the process proceeds to S10. If it is determined that the intermediate difference value ΔV1 is equal to or less than the freezing determination threshold value TH (S35: NO), it is determined that the urea aqueous solution is frozen and a control signal is transmitted to the switch 260, and the switch is turned on. It is opened and energization to the heating resistor 114 is stopped (S8). When the process of S8 is completed, the process proceeds to S9, and when 1 sec elapses, the process returns to S1 (S9: YES), and temperature detection of the heating resistor 114 is started again.

  On the other hand, if a negative determination is made in S31 (S31: NO) or an affirmative determination is made in S35 (S35: YES), the same processes of S10 to S12 as in the above-described embodiment are executed, and the process proceeds to S13. In the process of S13, the difference value ΔV obtained by subtracting the voltage value obtained in S3 (the latest voltage value stored in the RAM 223) from the voltage value obtained in S11 is calculated. When the difference value ΔV is smaller than the threshold value Q in the process (S14: YES), the difference value ΔV is stored in a predetermined storage area of the RAM 223, and is calculated based on the number of executions of the process of S15 (that is, based on sampling). The value of the counter that counts the number of times the difference value ΔV is a normal difference value is incremented by 1 (S15).

  Next, in the process of S16, the value of the counter that counts the number of executions of the process of S15 is referred to. If the difference value ΔV is determined to be normal and the number of times stored in the RAM 223 as a normal difference value is less than 5, that is, if the process of S15 is not executed more than 5 times (S16: NO), the process proceeds to S18. Concentration conversion similar to that in the present embodiment is performed using the calculated difference value ΔV as it is.

  On the other hand, after the fifth execution of the process of S15, the value of the counter that counts the execution of the process of S15 is 5 or more. For this reason, in the process of S16, it is determined that sampling of the difference value ΔV (but only when a normal value is taken) has been performed five times or more (S16: YES), and the process proceeds to S17. When the second property detection program is continuously executed and the process of S15 after the sixth time is performed, the oldest difference value ΔV is overwritten as described above, and the storage area of the RAM 223 is always the latest. These five difference values ΔV are stored.

  In S17, as in S6, the average value of the three difference values ΔV excluding the maximum value and the minimum value is calculated from the latest five difference values ΔV stored in the predetermined storage area of the RAM 223 by the repeatedly executed process of S13. Is performed (S17). Then, using the calculated average value of the difference values ΔV, density conversion is performed in the next S18.

  Other processes of the second property detection program are the same as those of the property detection program of the above-described embodiment. Thus, by detecting the temperature and concentration of the urea aqueous solution based on the average of three detection results among the latest five detection results, highly accurate temperature information and concentration information can be obtained. However, the number of times of performing the sampling is not limited to five. Further, the processing for excluding the maximum value and the minimum value of the detection result (detection voltage value or difference value ΔV) may be omitted.

  As described above, in the second property detection program, the intermediate difference value ΔV1 acquired in the process of comparing the temperature T of the urea aqueous solution with the temperature threshold (S31) and the process of energizing the heating resistor 114 and the freezing determination are performed. The presence or absence of freezing of the urea aqueous solution is determined through two steps such as a comparison process with the threshold value TH (S35). Therefore, even when the urea concentration of the urea aqueous solution has changed (becomes thin), the presence or absence of liquid freezing can be accurately determined by applying this property detection program. In this modified liquid state detection sensor, it is determined whether or not the temperature T of the urea aqueous solution is equal to or lower than the temperature threshold value in S7, and if the temperature T is equal to or lower than the temperature threshold value in S31, S35 The CPU 221 that determines whether or not the intermediate difference value ΔV1 satisfies a predetermined freezing relationship with the freezing determination threshold value (here, whether or not the intermediate difference value ΔV1 is larger than the freezing determination threshold value TH) is This corresponds to “freezing determination means” in claim 4 of the invention.

  The present invention can be applied to a liquid state detection sensor that can perform liquid temperature detection and concentration detection with a single sensor.

4 is a partially cutaway longitudinal sectional view of the liquid state detection sensor 100. FIG. It is a schematic diagram which shows the heater pattern 115 of the ceramic heater 110. FIG. 2 is a block diagram showing an electrical configuration of a liquid state detection sensor 100. FIG. FIG. 3 is an enlarged cross-sectional view of the vicinity of the water surface of a urea aqueous solution filled between the gap between the outer cylinder electrode 10 and the inner electrode 20. As an example of a urea aqueous solution having a urea concentration of 32.5 wt% and a temperature of 25 ° C., the resistance value of the heating resistor itself increases with the passage of time since the start of energization of a constant current to the heating resistor. It is a graph which shows a mode that the voltage value corresponding to is going up. It is a graph which shows that the voltage value change (difference value (DELTA) V) of a heating resistor and the urea density | concentration of urea aqueous solution have a proportional relationship, and have temperature dependence. When the relationship between the change in the voltage value of the heating resistor (difference value ΔV) and the urea concentration of the urea aqueous solution is corrected by the temperature of the urea aqueous solution, the corrected concentration (converted concentration) and the urea concentration almost coincide. It is a graph to show. It is a flowchart of the property detection program as an embodiment. It is a graph for demonstrating the threshold values Q and R for discriminating an airing and a different type liquid. It is a flowchart of the 2nd property detection program as a modification.

Explanation of symbols

98 Urea water tank 100 Liquid state detection sensor 110 Ceramic heater 114 Heating resistor 220 Microcomputer 221 CPU

Claims (9)

A liquid state detection sensor for detecting the state of the liquid stored in the liquid storage container,
A liquid property detecting element having a heating resistor that generates heat when energized, and disposed in the liquid container;
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 corresponding value acquisition means for acquiring a second corresponding value corresponding to the second resistance value of the heating resistor after the detection time has elapsed;
Difference value calculating means for obtaining a difference value between the second corresponding value and the first corresponding value;
A liquid state detection sensor comprising: a concentration acquisition unit that obtains the concentration of a specific component contained in the liquid based on the difference value and the temperature information. A liquid state detection sensor for detecting the state of the liquid stored in the liquid storage container,
A liquid property detecting element having a heating resistor that generates heat when energized, and disposed in the liquid container;
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 corresponding value acquisition means for acquiring a second corresponding value corresponding to the second resistance value of the heating resistor after the detection time has elapsed;
Difference value calculating means for obtaining a difference value between the second corresponding value and the first corresponding value;
Concentration acquisition means for determining the concentration of the specific component contained in the liquid based on the difference value;
Freezing determination means for determining whether or not the liquid is frozen based on the temperature information obtained by the temperature information acquisition means within the detection time;
A liquid state detection sensor comprising: an energization stop unit that stops energization of the heating resistor by the energization unit when the freeze determination unit determines that the liquid is frozen. .   The liquid state detection sensor according to claim 2, wherein the freezing determination unit determines that the liquid is frozen when the temperature information is equal to or lower than a freezing temperature of the liquid. A third corresponding value acquiring means for acquiring a third corresponding value corresponding to the third resistance value of the heating resistor within the detection time and after acquiring the first corresponding value;
The freezing determination means has a temperature difference equal to or lower than a preset temperature threshold value, and an intermediate difference value that is a difference between the third corresponding value and the first corresponding value and a freezing determination threshold value are predetermined. The liquid state detection sensor according to claim 2, wherein the liquid state detection sensor determines that the liquid is frozen when the magnitude relationship is satisfied. The energization means is configured to start energization to the heating resistor again after a lapse of a standby time after energization to the heating resistor is stopped,
As the standby time, a first standby time is selected when the energization means performs the detection time energization, and when the energization stop means energizes the heating resistor, the first wait time is selected. 5. The liquid state detection sensor according to claim 2, further comprising standby time selection means for selecting a second standby time shorter than one standby time. Using the difference value obtained by the difference value calculating means, comprising an abnormality determining means for determining the presence or absence of an abnormality in the liquid container,
The concentration acquisition unit obtains the concentration of a specific component contained in the liquid by the concentration acquisition unit only when the abnormality determination unit determines that there is no abnormality among the difference values. The liquid state detection sensor according to claim 1. The energizing means is configured to energize a constant current to the heating resistor,
The first corresponding value acquisition unit acquires a first corresponding value that is a voltage value, and the second corresponding value acquisition unit acquires a second corresponding value that is a voltage value. The liquid state detection sensor according to claim 6.   8. The liquid state detection sensor according to claim 1, wherein the liquid property detection element is a ceramic heater in which the heating resistor is embedded in a ceramic substrate. 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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