JP2009002718A - Liquid state detection sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid state detection sensor capable of determining precisely whether liquid has frozen or not by detecting an abnormality of a current carrying path including a resistor. <P>SOLUTION: When a current is made to flow through the current carrying path including the resistor provided in a liquid property detection element, the liquid state detection sensor for detecting the state of liquid stored in a liquid storage container acquires the first corresponding value corresponding to the first resistance value of the resistor, and then determines the temperature of the liquid on the periphery of the liquid state detection sensor based on the first corresponding value. Thereafter, the sensor compares the temperature of the peripheral liquid with the first temperature, to thereby determine whether the liquid has frozen or not (S52), and further compares the temperature of the peripheral liquid with the second temperature which is lower than the first temperature, to thereby determined whether the current carrying path is in an abnormal state or not (S60). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a liquid state detection sensor that detects the state of a liquid contained in a liquid container, for example, the temperature of the liquid 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, the urea aqueous solution stored in the urea water tank mounted on the automobile is stored under severe environmental conditions, and the urea concentration may change due to changes with time. In addition, a different aqueous solution (for example, light oil) or water may be mistakenly mixed into the urea water tank. For this reason, a urea concentration detection concentration sensor having a liquid state detection element having a heating element is attached to the urea water tank.

By the way, the urea aqueous solution stored in the urea water tank may freeze in cold districts and the like, and 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. . 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 unit is thawed due to the heat generation. If the aqueous solution is in a state in which most of the aqueous urea solution is still frozen, it will freeze again, and the concentration identification sensor unit may be damaged by the freezing expansion pressure at that time. Therefore, a liquid state detection sensor has been proposed that can perform temperature detection and concentration detection of a liquid with a single element having a heating resistor, and can prevent breakage of the element when the liquid is frozen (Patent Document). 1). In the liquid state detection sensor of Patent Document 1, when it is determined that the liquid is frozen, energization of the heating resistor by the energization means thereafter is forcibly stopped.
JP 2007-114181 A

  However, when the liquid temperature information is obtained based on the first corresponding value of the heating resistor as in the conventional liquid state detection sensor, it is necessary to consider the abnormality of the energization path including the resistor such as the heating resistor. is there. Specifically, when the energization path is short (ground short), when the current of the energization path is abnormally low, or when the resistance value of the energization path is abnormally low, etc., regardless of the temperature of the liquid Temperature information corresponding to a temperature lower than the freezing temperature of the liquid is obtained. In addition, when the energization path including the resistor is disconnected, when the current of the energization path is abnormally large, or when the resistance value of the energization path is abnormally large, etc. Temperature information corresponding to a temperature higher than the boiling point is obtained. When it is determined whether or not the liquid is frozen in a state where there is an abnormality in the energization path in this way, it is not possible to distinguish between the abnormality in the energization path and the freezing of the liquid, and there is a possibility of overlooking the abnormality in the energization path. there were.

  The present invention has been made to solve the above-described problems, and provides a liquid state detection sensor that can detect an abnormality in a current-carrying path including a resistor and accurately determine whether or not the liquid is frozen. The purpose is to provide.

  In order to solve the above problems, a liquid state detection sensor according to a first aspect of the present invention is a liquid state detection sensor that detects a state of a liquid stored in a liquid storage container, and the liquid state detection sensor detects its own state according to the temperature of the surrounding liquid. A liquid property detecting element having a resistor whose resistance value varies, disposed in the liquid container, energizing means for energizing an energizing path including the resistor, and energizing the energizing path by the energizing means A first corresponding value acquiring means for acquiring a first corresponding value corresponding to the first resistance value of the resistor, and a temperature acquiring means for determining the temperature of the liquid based on the first corresponding value. And a freezing determination means for determining whether or not the liquid is frozen by comparing the temperature obtained by the temperature obtaining means with the first temperature, and the temperature obtained by the temperature obtaining means From the first temperature It compares the low second temperature, and a first current path abnormality determination means for determining whether the current path is in an abnormal state.

  According to a second aspect of the invention, in addition to the configuration of the first aspect of the invention, the liquid state detection sensor includes the temperature obtained by the temperature acquisition means and a third temperature higher than the first temperature. In comparison, there is provided second energization path abnormality determining means for determining whether or not the energization path is in an abnormal state.

  According to a third aspect of the present invention, in addition to the configuration of the first or second aspect of the invention, the resistor is a heating resistor that generates heat when energized. The first corresponding value acquisition means is configured to acquire the first corresponding value within the detection time, while the freezing determination means is configured to energize the energization path for a predetermined detection time. A second response is configured to determine whether or not the liquid is frozen within the detection time, and acquires a second corresponding value corresponding to the second resistance value of the resistor after the detection time has elapsed. When the liquid is frozen by the value acquisition means, the concentration acquisition means for obtaining the concentration of the specific component contained in the liquid based on the second corresponding value and the first corresponding value, and the freezing determination means If determined, before the detection time elapses And a power supply stopping means for stopping the current supply to the resistor by the energization means.

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

  According to the liquid state detection sensor of the first aspect of the present invention, the resistor included in the liquid state detection sensor of the present invention has a property that the resistance value of which the resistance value changes according to the temperature of the surrounding liquid changes. 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 resistor is started. Based on the temperature, it is determined whether or not an abnormality has occurred in the energization path in addition to whether or not the liquid is frozen. The second temperature used for determining whether or not there is an abnormality in the energization path is lower than the first temperature used for determining whether or not the liquid is frozen, and when there is no abnormality in the energization path A temperature that is not assumed in a normal use environment is set as appropriate. Therefore, the abnormality of the energization path that can be detected in the present invention is when the energization path is short-circuited, when the current of the energization path is abnormally small, or when the resistance value of the energization path is abnormally low (hereinafter referred to as these An abnormality in the energization path is simply referred to as “energization path short-circuit abnormality”). For this reason, by detecting the abnormality of the energization path, it is possible to avoid erroneously determining that the liquid is frozen regardless of the actual temperature of the liquid by overlooking the abnormality of the energization path. It is possible to appropriately determine whether or not the liquid is frozen.

  The first corresponding value in the present invention may be a value corresponding to the first resistance value of the resistor, and specifically includes a voltage value, a current value, and a temperature converted value. Further, as described above, the “resistor” constituting the liquid state detecting element may be a resistor whose resistance value changes in accordance with the temperature of the surrounding liquid, and generates heat when energized, and at the liquid temperature. It also includes a self-heating resistor whose resistance value changes accordingly.

  According to the liquid state detection sensor of the second aspect of the invention, as the third temperature used for determining whether or not an abnormality has occurred in the energization path, the first temperature used for determining whether or not the liquid is frozen. A higher temperature is set, and the third temperature is compared with the temperature obtained by the temperature acquisition means. Thereby, when the energization path including the resistor is disconnected, when the current of the energization path is abnormally large, or when the resistance value of the energization path is abnormally large, etc. It is also possible to detect an abnormality in the energization path (referred to as “energization path open abnormality”).

  According to the liquid state detection sensor of the invention of claim 3, in addition to the configuration of the invention of claim 1 or 2, a heating resistor (so-called so-called heating element) having both functions of a heating element that generates heat and a temperature sensing element. The liquid property detection element having a self-heating resistor) is used to detect the temperature and concentration of the liquid. 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. Similar to the first corresponding value, 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 the concentration of the specific component contained in the liquid based on the second corresponding value and the first corresponding value, for example, when the first corresponding value is a voltage value, the second value Similarly, the corresponding value needs to be a voltage value.

  As in the liquid state detection sensor according to claim 3, when the determination result of the freezing determination unit is used to stop energization to the heating resistor, the determination by the freezing determination unit is determined by the first energization path. It is preferable to carry out priority over determination by the abnormality determination means. This is because damage to the liquid property detecting element can be more reliably prevented when the liquid is frozen.

  According to the liquid state detection sensor of the invention of claim 4, in addition to the configuration of the invention of claim 3, the temperature of the urea aqueous solution and the concentration of urea contained in the urea aqueous solution 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, with reference to FIG. 1 and FIG. 2, the structure of the liquid state detection sensor 100 as an example is demonstrated. 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. In the present embodiment, the most distal portion (the lowermost portion in the figure) of the outer cylinder electrode 10 is opened. However, in order to make it less susceptible to the influence of the flow of urea aqueous solution around the ceramic heater 110, the outer cylindrical electrode 10 is You may make it provide a lower cover in the form which ensured the liquid inlet in the opening part of the cylinder electrode 10. FIG.

  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 attachment portion 40 functions as a base for fixing the liquid state detection sensor 100 to the urea water tank 98 (see FIG. 3), and attachment holes (not shown) for inserting attachment bolts are formed in the flange portion 42. Yes. 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 and the like of a urea aqueous solution described later, and an external circuit (not shown) such as an automobile A housing part 43 for housing a circuit board 60 and the like on which an input / output circuit and the like for electrical connection with the engine control unit (ECU) are mounted is formed.

  The circuit board 60 is placed on a board placement portion (not shown) protruding from the four corners of the inner wall surface of the housing portion 43. The accommodating portion 43 is covered and protected by a cover 45, and the cover 45 is fixed to the flange portion 42. 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 coating 23 made of a fluorine resin such as PTFE, PFA, ETFE, an epoxy resin, a polyimide resin or the like is formed. Between the internal electrode 20 and the outer cylinder electrode 10, a level detection unit 70 is formed, in which a capacitor whose electrostatic capacity 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.

  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 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 the contained urea in the present embodiment. And a holder 120 made of an insulating resin that supports the ceramic heater 110 and is attached to the tip 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 relay terminals 119 (only one of them is shown in FIG. 1) is electrically connected. The ceramic heater 110 of the present embodiment corresponds to a “liquid property detection element” in the present invention. In addition, the heating resistor 114, and the lead parts 112 and 113, the via conductor, the relay terminal 119, the lead wire 90, and the switch 260, which are conductive members on the path connecting the heating resistor 114 and the constant current output unit 240, are provided. Corresponds to the “energization path” in the present invention. The member constituting the energization path only needs to include at least the heating resistor 114, and can be changed as appropriate.

  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 relay terminal 119 of the ceramic heater 110 by caulking or soldering, respectively. Further, the relay terminal 119 and the lead wire 90 are covered and protected by the insulating protection member 95 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.

  Further, the rubber bush 80 that supports the holder 120 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.

  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 in the figure, and property detection programs to be described later, initial values of various variables, threshold values, and the like are stored in a predetermined storage area. . Similarly, the RAM 223 is provided with various storage areas, and various flags, various variables, timer count values, and the like are temporarily stored in a predetermined storage area when the property detection program is executed.

  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 300 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 cylindrical electrode 10 and the insulating coating 23. 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 301 filled with the urea aqueous solution, the distance between the portions where the potential difference occurs between the gaps is insulative because the urea aqueous solution shows conductivity, and the potentials of the outer cylinder electrode 10 and the urea aqueous solution are almost equal. The distance Z corresponds to the thickness of the coating 23.

  In other words, the capacitance between the gaps in the portion 300 that is not filled with the urea aqueous solution is the capacitance of the capacitor in which the distance between the electrodes is Y and air is a dielectric (non-conductor), and the distance between the electrodes. It can be said that this is the combined capacitance of a capacitor in which Z is a capacitor and the capacitor having the insulating coating 23 as a dielectric is connected in series. Further, the capacitance between the gaps in the portion 301 filled with the aqueous urea 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 301 filled with the urea aqueous solution is larger than the change in the capacitance of the portion 300 not filled with the urea aqueous solution, and the capacitor comprising the outer cylinder electrode 10 and the inner electrode 20 The overall capacitance 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.

  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. The temperature of the heating resistor itself continuously increases over time after a constant current starts to flow through the heating resistor (however, it takes about 10 msec until the current value becomes stable after the start of energization). I will do it.

  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.

  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.

  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 is less likely to take heat, so the temperature rise rate increases, and as a result, the resistance value change of the heating resistor increases. 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 and the resistance value change (voltage value change) of the heating resistor.

  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. 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 aqueous urea solution is constant, the lower the temperature of the aqueous urea solution, the smaller the resistance value change of the heating resistor, and the smaller the voltage value change corresponding to the resistance value change. Thus, 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.

  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. Hereinafter, the property detection process executed in the liquid state detection sensor 100 will be described with reference to FIGS. 3, 5, and 6. FIG. 5 is a flowchart of the property detection process. FIG. 6 is a flowchart showing the flow of the freeze determination / energization path abnormality determination process executed in the property detection process of FIG. Each step of the flowcharts in FIGS. 5 and 6 is abbreviated as “S”. 5 and 6 is stored in the ROM 222, and is executed by the CPU 221 shown in FIG. Also, it is assumed that various information necessary for executing the program is read from the ROM 222 and stored in a predetermined storage area of the RAM 223.

  As shown in the flowchart of FIG. 5, first, the switch 260 is closed based on a control signal from the microcomputer 220 (see FIG. 3), 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, in the liquid state detection sensor 100 of the present embodiment, 10 msec is set as the initial energization time, which is the time when the current value becomes stable, after energization of the heating resistor 114 is started. The measurement of the voltage value in S3 is not performed during 10 msec.

  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 It functions as the “first corresponding value acquisition unit” in the present invention.

  Subsequently, in the microcomputer 220, the temperature T of the urea aqueous solution 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 (S4). The CPU 221 that calculates the temperature T of the urea aqueous solution in S4 functions as the “temperature acquisition means” in the present invention.

  Subsequently, based on the temperature T calculated in S4, it is determined whether or not the liquid around the liquid state detection sensor 100 is frozen, and whether or not there is an abnormality in the energization path including the heating resistor 114. Freezing determination / energization path abnormality determination processing for determination is executed (S5). Details of the freeze determination / energization path abnormality determination process will be described later with reference to the flowchart of FIG. In S5, when it is determined that the liquid around the liquid state detection sensor 100 is frozen, the freezing determination flag is set to 1. When it is determined that the liquid is not frozen, the freezing determination is performed. The flag is set to 0 and is stored in a predetermined storage area of the RAM 223. Subsequently, a predetermined storage area of the RAM 223 is referred to, and it is determined in S5 whether or not the freezing determination flag is set to 1 (S7).

  When 1 is set in the freezing determination flag (S7: YES), the processing of S22 to be described later is performed without performing the processing of S10 to S21. On the other hand, when 1 is not set in the freezing determination flag (S7: No), by referring to the count value of the timer program, the energization to the heating resistor 114 is continued until 700 msec elapses. Performed (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. Correspondingly, the CPU 221 that acquires the voltage value functions as the “second corresponding value acquisition means” in the present invention. Further, in step S1, the energization of the heating resistor 114 from the constant current output unit 240 is started, and in step S10, after waiting for 700 msec corresponding to the detection time of the present invention, the energization is stopped in step S12. The CPU 221 that outputs the control signal functions as 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 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 value Q) 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). Then, a predetermined calculation is performed on the assumption that the difference value ΔV is a normal difference value within the range of normal values, and the concentration C of urea contained in the urea aqueous solution is obtained. 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 and calculates the urea concentration C of the urea aqueous solution in S18 functions as the “concentration acquisition unit” in the present invention.

  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 larger than the minimum value (threshold value R) of the voltage value change that can be taken (S19: YES), it is determined that the vehicle is in an empty state, and a notification signal for notifying of emptying is transmitted to the ECU via the input / output circuit unit 290. (S20).

  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 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.

  Next, the freezing determination / energization path abnormality determination process executed in the property detection process of FIG. 5 will be described with reference to the flowchart of FIG. As shown in FIG. 6, in the freezing determination / energization path abnormality determination processing, first, a predetermined freezing in which the temperature T calculated in S4 of FIG. 5 is determined that the liquid around the heating resistor 114 is frozen. It is determined whether or not the temperature is lower than the determination temperature (S52). The freezing determination temperature used as the threshold value in S52 corresponds to the “first temperature” of the present invention. This freezing judgment temperature is appropriately determined according to the type of liquid, the concentration of the solute, the freezing temperature of the liquid, etc., and in this embodiment, the freezing temperature of the liquid is assumed to be surely frozen. Slightly lower -15 ° C.

  If the temperature T calculated in S4 of FIG. 5 is lower than a predetermined freezing determination temperature at which it is determined that the liquid around the heating resistor 114 is frozen (S52: YES), then The freezing determination flag is set to 1 and stored in a predetermined storage area of the RAM 223 (S54). This freezing determination flag is referred to in S7 of FIG. 5 as described above. Subsequently, as a process in a case where it is determined that the liquid is frozen, the switch 260 is opened based on a control signal from the microcomputer 220, and energization to the heating resistor 114 is stopped (S56). In S56, the CPU 221 shown in FIG. 3 that transmits a control signal to open the switch 260 and stops energization of the heating resistor 114 functions as the “energization stopping means” of the present invention.

  On the other hand, if the temperature T calculated in S4 of FIG. 5 is not lower than the freezing determination temperature (S52: NO), then the freezing determination flag is set to 0 and stored in a predetermined storage area of the RAM 223. (S58). Note that the freezing determination flag is set to 1 or 0 based on whether or not the temperature T calculated in S4 of FIG. 5 is lower than the freezing determination temperature (S52, S54, S58). The CPU 221 shown functions as “freezing determination means” of the present invention.

  Subsequent to S56 or S58, when the temperature T calculated in S4 of FIG. 5 is equal to or lower than the lower temperature limit (S60: YES), it is determined that the energization path is in an abnormal state (S62). This lower temperature limit corresponds to the “second temperature” of the present invention. The lower temperature limit of this embodiment is a temperature lower than the freezing determination temperature (−15 ° C.) used in S52, and is a temperature −50 ° C. that is not assumed in a normal use environment when there is no abnormality in the energization path. Examples of the abnormality in the energization path detected in S62 include an energization path short-circuit abnormality. 5 is compared with the temperature lower limit calculated in S4 (S60) to determine whether the energization path is in an abnormal state (S62, S74), the CPU 221 shown in FIG. It functions as the “first energization path abnormality determining means” of the present invention.

  On the other hand, when the temperature T calculated in S4 of FIG. 5 is not lower than the temperature lower limit (S60: NO), but is higher than the temperature upper limit (S64: YES), it is determined that the energization path is in an abnormal state. (S66). This upper temperature limit corresponds to the “third temperature” of the present invention. The upper temperature limit of the present embodiment is a temperature higher than the freezing determination temperature (−15 ° C.) used in S52, and is 150 ° C. which is not assumed in a normal use environment when there is no abnormality in the energization path. The upper temperature limit of the present embodiment is set to a temperature that is higher than the boiling point of the liquid as a temperature that is not assumed in a normal use environment. The abnormality in the energization path detected in S66 includes, for example, an energization path open abnormality including a resistor. 5 is compared with the temperature upper limit calculated in S4 (S64) to determine whether the energization path is in an abnormal state (S66, S74). The CPU 221 shown in FIG. It functions as the “second energization path abnormality determining means” of the present invention.

  If the temperature T calculated in S4 of FIG. 5 is not lower than the lower temperature limit (S60: NO) and not higher than the upper temperature limit (S64: NO), then it is stored in a predetermined storage area of the RAM 223. The current energization path abnormality detection count is cleared (S74). This process is a process when it is determined that the energization path is not in an abnormal state. By this process, when an abnormality of the energization path is detected continuously a predetermined number of times (for example, 5 times), it can be determined that the energization path is abnormal. Subsequently, the freeze determination / energization path abnormality determination process is terminated, and the process returns to the process of FIG.

  Subsequent to S62 or S66, the energization path abnormality detection count is incremented by 1 (incremented) and stored in a predetermined storage area of the RAM 223 (S68). The initial value of the energization path abnormality detection count is 0, and is initialized when the property detection process is activated. Further, when an upper limit value (for example, 5 times) is provided for the number of times of energization path abnormality detection, and when the number of energization path abnormality detection has already reached the upper limit value, this process is omitted. Subsequently, when the RAM 223 is referred to and the energization path abnormality detection count is greater than or equal to the specified number (S70: YES), a determination result that the energization path is in an abnormal state is confirmed, and the determination result is a predetermined value in the RAM 223. It is stored in the storage area (S72). The specified number of times is appropriately determined according to the application of the liquid state detection sensor 100, the installation location, the accuracy of detecting an abnormality in the energization path, and the like, and is 5 times in the present embodiment. Subsequently, the freeze determination / energization path abnormality determination process is terminated, and the process returns to the property detection process of FIG. On the other hand, when the RAM 223 is subsequently referred to and the energization path abnormality detection count is not equal to or greater than the prescribed count (S70: NO), the freezing determination / energization path abnormality determination process is terminated and the process returns to the property detection process of FIG. .

  As described above, the CPU 221 shown in FIG. 3 executes the freezing determination / energization path abnormality determination process. Part or all of the determination result in the above-described freezing determination / energization path abnormality determination process is output to an external device such as an ECU via the input / output circuit unit 290, and is illustrated by a program separately executed in the external device. You may make it alert | report to a user by display means, such as a non-display display, audio | voice alerting means, such as an alarm device and a speaker, an alarm lamp.

  The liquid state detection sensor 100 of the present embodiment described in detail above uses a single ceramic heater 110 having a heating resistor 114 that functions as both a heating element and a temperature sensing element that generate heat when energized, and the temperature of the urea aqueous solution. (S4 in FIG. 5), a configuration is employed in which the concentration of urea contained in the urea aqueous solution is detected and (S18 in FIG. 5) is performed. Thereby, the liquid state detection sensor 100 can be reduced in size, and the structure and detection circuit can be prevented from becoming complicated.

  Further, 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 114 is started (S4 in FIG. 5). Then, before energization of the heating resistor 114 is performed for a predetermined detection time, it is determined whether or not the liquid is frozen based on the temperature T calculated in S4 after the energization of the heating resistor 114 is started. (S52 in FIG. 6). When it is determined that the liquid is frozen (S52: YES), the switch 260 is opened to forcibly stop energization to the heating resistor 114 thereafter (S56). By doing so, even when the liquid is frozen, it is possible to avoid a situation in which the ceramic heater 110 is damaged by the freezing expansion pressure at the time of refreezing, and the highly reliable liquid state detection sensor 100 and can do.

  After freezing determination (S52), it is determined whether or not the energization path is in an abnormal state (S60, S64). First, the second temperature (−50 ° C.) which is lower than the first temperature (−15 ° C.) used for determining whether or not the liquid is frozen and is not assumed in a normal use environment when there is no abnormality in the energization path. Is compared with the temperature T calculated in S4 of FIG. 5 to determine whether or not the energization path is in an abnormal state (S60). An abnormality of the energization path that can be detected in S60 includes an energization path short-circuit abnormality. Subsequently, it is higher than the first temperature (−15 ° C.) used for determining whether or not the liquid is frozen, and is not assumed in a normal use environment when there is no abnormality in the energization path, that is, higher than the boiling point of the liquid. The high third temperature (150 ° C.) is compared with the temperature T calculated in S4 of FIG. 5 to determine whether or not the energization path is in an abnormal state (S64). The energization path abnormality that can be detected in S64 includes an energization path open abnormality.

  In this embodiment, when it is determined that the energization path is in an abnormal state continuously for a specified number of times (for example, 5 times) (S70: YES), it is determined that the energization path is in an abnormal state. For this reason, although the energization path itself is normal, there is a risk of erroneously determining that the energization path is in an abnormal state when the temperature of the liquid converted in S4 of FIG. 5 accidentally shows an abnormal value. Thus, a more reliable determination result can be obtained. By determining whether or not there is an abnormality in the energization path in this way, it is possible to appropriately determine whether or not the liquid is frozen while accurately detecting the abnormality in the energization path.

  In the present embodiment, the determination as to whether or not the heating resistor 114 is frozen before stopping the energization is performed prior to the determination as to whether or not the energization path is in an abnormal state. For this reason, when the liquid is frozen (S54: YES), the energization to the heating resistor 114 can be stopped earlier. For this reason, damage to the ceramic heater 110 can be prevented more reliably.

  The present invention is not limited to the embodiment described in detail above, and various modifications may be made without departing from the scope of the present invention. For example, you may add the change shown to the following (A)-(I).

  (A) In the property detection process of the above embodiment, the temperature (S6) of the urea aqueous solution is calculated based on a predetermined arithmetic expression, but is not limited to this. For example, a table may be created in advance by experiments or the like, stored in a predetermined storage area of the ROM 222, and obtained by referring to the processing in S4 of FIG.

  (B) Each waiting time in S2, S10, and S22 in FIG. 5 is merely an example, and an optimum waiting time may be obtained and set by experiments or the like. Furthermore, the standby time in S22 may be set in accordance with the temperature of the urea aqueous solution detected in S4.

  (C) The circuit board 60 is provided as a circuit board that relays 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 is controlled by the control of the external circuit. Detection and temperature / concentration detection may be performed.

  (D) In the liquid state detection sensor 100 of the above embodiment, the outer cylinder electrode 10 and the internal electrode 20 are provided to detect the liquid level of the urea aqueous solution. A size, a member, etc. can be changed suitably. For example, in the liquid state detection sensor 100, the outer cylinder electrode 10 and the inner electrode 20 need not be provided. For example, the present invention may be applied to a so-called indirectly heated liquid state detection sensor that performs temperature detection and concentration detection using separate elements. In this case, the element that performs temperature detection is provided with a resistor whose resistance value changes according to the temperature of the liquid. This resistor also corresponds to the “resistor” of the present invention. The energization path including the resistor corresponds to the “energization path” of the present invention.

  (E) 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, and a constant current is passed through the heating resistor 114 to correspond to the resistance value of the heating resistor 114. The voltage 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.

  (F) In the liquid state detection sensor 100 of the above embodiment, the freezing determination / energization path abnormality determination process is performed during the detection time. However, based on the acquired first corresponding value, the liquid state detection sensor 100 What is necessary is just to obtain the temperature of the surrounding liquid, and is not limited to this.

  (G) In the freezing determination / energization path abnormality determination process shown in the flowchart of FIG. 6 of the above embodiment, a process of determining whether or not the liquid temperature T converted in S4 of FIG. Both S60) and the process of determining whether or not the temperature T is equal to or higher than the temperature upper limit (S64) may be performed, but only the process of S60 may be performed. Even when only S60 is performed, it is possible to avoid erroneously determining that the liquid is frozen regardless of the actual temperature of the liquid by overlooking the abnormality of the energization path. It is possible to appropriately determine whether or not it is frozen.

  (H) In the freezing determination / energization path abnormality determination process shown in the flowchart of FIG. 6 of the above embodiment, the freezing determination and the energization path abnormality determination are performed separately, but the present invention is not limited to this. For example, freezing determination and energization path abnormality determination may be performed in combination as follows. When the temperature T calculated in S4 of FIG. 5 is equal to or lower than the temperature lower limit, it is determined that the energization path is abnormal, and when it is higher than the temperature lower limit and lower than the freezing determination temperature, it is determined that the liquid is frozen. To do. Further, when the temperature T calculated in S4 of FIG. 5 is equal to or higher than the freezing determination temperature and lower than the upper temperature limit, it is determined that the liquid is not frozen, and when the temperature T is higher than the upper temperature limit, the energization path is abnormal. Is determined. In this case, it is possible to clearly distinguish between a liquid abnormality and an energization path abnormality.

  Further, in the freezing determination / energization path abnormality determination process shown in the flowchart of FIG. 6 of the above embodiment, when the liquid temperature T converted in S4 of FIG. 5 is equal to or lower than the temperature lower limit, the conduction path short circuit abnormality is suspected (S60). : YES, S62), or when the temperature T is equal to or higher than the temperature upper limit and the energization path open abnormality is suspected (S64: YES, S66), the energization path abnormality detection count is increased by 1. It is not limited to. For example, two types of energization path abnormality detection times may be provided and counted separately according to the assumed energization path abnormality type. In this case, the specified number of times compared with the number of times of detection of the energization path abnormality may be changed according to the assumed type of abnormality of the energization path, or the same value may be used. In such a case, for example, by outputting the type of abnormality of the energized path assumed to the ECU or the like, in addition to whether or not the energized path is in an abnormal state, the cause of the expected energized path abnormality Can be grasped.

  Furthermore, in S52 of FIG. 6, the temperature T of the urea aqueous solution was calculated and then compared with the freezing determination temperature of the urea aqueous solution, but the voltage value VT of the heating resistor 114 when 10 msec elapsed from the start of energization was previously tested. The voltage value of the heating resistor 114 corresponding to the freezing determination temperature obtained by the above may be compared.

  (I) In the liquid state detection sensor 100 of the above embodiment, as an example, the liquid state detection sensor that detects the temperature and concentration of the urea aqueous solution is illustrated, but the present invention is not limited thereto. For example, the present invention may be applied to a liquid state detection sensor that detects the state of ammonia water (water level, temperature, concentration, etc.) using ammonia as a specific component.

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. It is a flowchart which shows the flow of a property detection process. It is a flowchart which shows the flow of the freezing determination / energization path | route abnormality determination process performed in the property detection process shown in the flowchart of FIG.

Explanation of symbols

90 Lead wire 98 Urea water tank 100 Liquid state detection sensor 110 Ceramic heater 111 Ceramic base body 112, 113 Lead portion 114 Heating resistor 119 Relay terminal 220 Microcomputer 221 CPU
222 ROM
223 RAM
260 switches

Claims (4)

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 resistor whose resistance value changes depending on the temperature of the surrounding liquid, and disposed in the liquid container;
Energization means for energizing the energization path including the resistor;
First corresponding value acquisition means for acquiring a first corresponding value corresponding to the first resistance value of the resistor when the energization means is energizing the energization path;
Temperature acquisition means for determining the temperature of the liquid based on the first corresponding value;
Freezing determination means for comparing the temperature obtained by the temperature acquisition means with the first temperature to determine whether or not the liquid is frozen;
Comparing the temperature obtained by the temperature acquisition means with a second temperature lower than the first temperature to determine whether or not the energization path is in an abnormal state; A liquid state detection sensor comprising:   Comparing the temperature obtained by the temperature acquisition means with a third temperature that is higher than the first temperature, there is provided second energization path abnormality determining means for determining whether or not the energization path is in an abnormal state. The liquid state detection sensor according to claim 1. The resistor is a heating resistor that generates heat when energized,
The energization means is configured to energize the energization path for a predetermined detection time,
The first corresponding value acquisition means is configured to acquire the first corresponding value within the detection time, while the freezing determination means determines whether or not the liquid is frozen within the detection time. Configured to determine,
Second corresponding value acquisition means for acquiring a second corresponding value corresponding to the second resistance value of the resistor after the detection time has elapsed;
Concentration acquisition means for determining the concentration of a specific component contained in the liquid based on the second corresponding value and the first corresponding value;
And an energization stop unit that stops energization of the resistor by the energization unit before the detection time elapses when the freezing determination unit determines that the liquid is frozen. The liquid state detection sensor according to claim 1 or 2.   The liquid state detection sensor according to claim 3, wherein the liquid is an aqueous urea solution, and the specific component is urea.

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